Self routing all-optical switch for WDM applications
Author(s):
Franco Chiaraluce;
Ennio Gambi;
Paola Pierleoni
Show Abstract
We present the theory and modeling of an all-optical device which realizes self-routing of waves at different wavelengths. The device exploits spatial soliton interaction in the Kerr-like nonlinear medium and can be used in WDM networks. Interaction is governed by four-wave mixing that produces the desired effects under suitable excitation conditions. We give the example of a device able to route ten wavelengths, with good spatial separation at the output and practically no loss.
All-fiber optical wavelength converter
Author(s):
Juan Diao;
Pak Lim Chu
Show Abstract
We report that an optical wavelength converter can be constructed by combining a figure-8 laser and a nonlinear loop mirror (NOLM), all in fiber form. This forms a hybrid passively and actively mode-locked laser. The input signal pulse train is fed into the NOLM and the output wavelength- converted pulse train is obtained through a fiber coupler in the figure-8 laser.
Effective traffic-balanced routing scheme in WDM lightwave networks
Author(s):
Juan Diao;
Pak Lim Chu
Show Abstract
In this paper, we propose a new traffic-balanced routing scheme for WDM networks based on the de Bruijn graphs. This scheme has the combined advantages of small number of hops, lower queuing delay and high throughput in packet-switched networks. We also analyze its blocking probability in circuit-switched all-optical networks and find that this probability is consistently lower than the Longest Path scheme.
Femtosecond optical Kerr shutter switching in glass containing high concentration of Bi2O3
Author(s):
Naoki Sugimoto;
Setsuro Ito;
Seiji Fujiwara;
Toshio Suzuki;
Hirohisa Kanbara;
Kazuyuki Hirao
Show Abstract
Nonresonant-type Bi2O3-B2O3-SiO2 glass containing high concentration of Bi2O3 was prepared by a melting method. Optical Kerr shutter switching and degenerated four wave mixing experiments for this glass were performed using femtosecond laser. This glass exhibited ultrafast response below 150 femtosecond in optical Kerr switching operation. Moreover, THz optical switching was successfully performed with this glass using 1.5 THz pulse train as the gate beam. Ultrafast response and high threshold for optical damage were also confirmed with this glass at the communication wavelength of 1.5 micrometers . These results indicate that high speed switching beyond THz can be realized using Bi2O3-glass.
4-channel optoelectronic switch for use in WDM networks
Author(s):
Alan J. P. Hnatiw;
Dave W. Boertjes;
Ray G. DeCorby;
James N. McMullin;
Dino J. Corazza;
R. Ian MacDonald;
E. Johnson
Show Abstract
We report a 4 X 4 hybrid-integrated optoelectronic switch that is capable of switching digital signals with bit rates up to 9.95 Gb/s (OC-192). The inherent analogue design of the switch, along with its high bandwidth, allows it to operate independently of the format and bit rate of the input signals. In addition, the modular design of the switch allows it to be connected in either an electrical- in/electrical-out or an optical-in/optical-out configuration.
Polarization independent multi-channel wavelength conversion by difference-frequency generation in AlGaAs waveguides
Author(s):
S. J. Ben Yoo
Show Abstract
Wavelength conversion in multi-wavelength networks offers resolution of wavelength contentions and distribution of network management. It is desired in such a network that wavelength converters can simultaneously convert multiple channels at the same time so that the resulting cross- connect can scale 'the degree of wavelength conversion' as the network evolution demands such as upgrade. In addition to the multi-channel conversion capability, the wavelength converters must offer polarization independent conversion efficiency and transparency to most of the signal formats and protocols. While numerous wavelength conversion techniques have been demonstrated to date, only difference- frequency-generation offers polarization independent, strictly transparent, and multi-channel wavelength conversion without significant crosstalk. The recent experimental results obtained in AlGaAs waveguides show 17 channel wavelength conversion with no measurable cross-talk and polarization-independent conversion efficiency. The linearity to signal power levels and the spectral inversion demonstrated by experiments also imply strict transparency of the conversion process. Successful bit-error-rate measurements were obtained at both 2.5 Gb/s and 10 Gb/s, and simultaneous conversion of both 2.5 Gb/s and 10 Gb/s showed extremely low bit-error-rate with negligible cross-talk. The impact of strictly transparent wavelength converting cross- connect in multi-wavelength networks will also be discussed.
Fused-tapered fiber coupler all-optical switch using femtosecond optical pulses
Author(s):
Masaaki M. Imai;
Masahito Kajinuma;
Jun Nakai
Show Abstract
A fused-tapered fiber coupler, which is fabricated by fusing and elongating two single-mode fibers, exhibits a nonlinear coupling characteristics when it is excited with an intense light, since an intensity-dependent index of refraction is induced in fiber couplers due to optical Kerr effect. An abrupt change of power transmission at coupled and through ports in the coupler can be observed at certain wavelength of incident light and it was found that the critical wavelength is shifted into a longer wavelength as the incident power increases. The experimental verification using a mode-locked Ti:sapphire laser that produces 50 femtosecond pulses at wavelengths of 800 - 850 nm with a repetition rate of 80 MHz is followed by the theory.
Dynamically refreshable optical fiber loop memory
Author(s):
Yanjie Chai;
Jye-Hong Chen;
Xiangjun Zhao;
Jun Ping Zhang;
Jem Yu Fan;
Fow-Sen Choa;
Wei-Jyh Lin
Show Abstract
An optical fiber loop memory can be used in a packet switched optical network to resolve the contention problems and increase the system flexibility. We report a multi- wavelength optical fiber loop memory with in-loop waveguide grating router. Bit error rate of stored packets is analyzed both experimentally and theoretically. A new refreshable multi-wavelength loop memory configuration is proposed and experimentally demonstrated. With this refreshable optical memory, which works like a DRAM (dynamic random access memory), optical signal can be stored as long as system required.
Impact of crosstalk on the performance of an optical cross-connect considering finite extinction ratio
Author(s):
David Remondo;
Rajan Srinivasan;
Victor F. Nicola;
Wim C. van Etten;
Henk E. P. Tattje
Show Abstract
In this paper we investigate the performance degradation in a wavelength division multiplexing network due to crosstalk in optical cross-connects. Worst-case analysis is carried out including in-band crosstalk components. In contrast with the approximate methods in the literature, all beat-noise terms are included, and both input signal hypotheses are considered. The results are obtained by using appropriate importance sampling strategies. The optimization of importance sampling parameters was done with new adaptive techniques based on stochastic Newton recursions, combined with a novel technique called the g-method. Accurate performance measures for practical system parameter values are obtained in short simulation run-times. Infinite and finite extinction ratios are considered. The results indicate that the detection threshold has a strong impact on the system performance. The importance sampling techniques are also useful for the optimization of this system parameter.
High speed 4x4 optoelectronic switch with on-chip optical signal distribution
Author(s):
Carlos Almeida;
Francois L. Gouin;
Lucie Robitaille;
Claire L. Callender;
Julian P. Noad
Show Abstract
In this paper, a high-speed 4 X 4 optoelectronic switch with on-chip optical signal distribution is presented. The switching matrix integrates both metal-semiconductor-metal photodetectors and polyimide waveguides onto a monolithic structure. The bias-switched photodetectors are used to select which incident optical signals are to be detected and converted to electrical signals for distribution. The polyimide waveguides provide on-wafer distribution of the input optical signals to the detectors. This switch had an isolation of less than 48 dB at 1.0 GHz, a crosstalk of greater than -26 dB at 0.8 GHz, and a bandwidth between 4.3 to 6.5 GHz depending on the particular crosspoint being measured. This optoelectronic switch shows improved performance over a wider bandwidth compared to the 3 X 3 optoelectronic switch presented earlier. The current switching implementation is also easier to package because it does not require the precise alignment to discrete fibers over the photodetectors for optical distribution. Fabrication details, circuit configuration, and performance for the 4 X 4 optoelectronic switch will be discussed in greater detail in these proceedings.
Neural network experiment demonstrating all optical data switching
Author(s):
Evert C. Mos;
H. de Waardt;
J. J. H. B. Schleipen
Show Abstract
In our laser neural network (LNN), previously reported, a laser diode with an extended cavity is used to provide all- optical neural action. The neurons of the network are the longitudinal cavity modes of the laser. Weighted inputs are provided to these neurons via an optical matrix vector multiplier placed in the external cavity. A setup that uses a fast liquid crystal display and a loop mirror is used to expand the capabilities of the LNN to data switching applications. Up to 32 neurons can be defined having up to 12 inputs. As an example a 1:16 data decoder is demonstrated.
Scheme of all-optical on/off gate based on nonlinear channel waveguide grating
Author(s):
Bing Li;
Peida Ye
Show Abstract
A novel all-optical On/Off gate structure base on nonlinear channel waveguide grating is investigated in theory. The reflectivity of the grating to the signal, and thus the ON/OFF state of the device, is modified optically by the control light which has different wavelength with the signal. The simulation result of the performance of the device is given.
Photonic integrated circuits for multiwavelength networks
Author(s):
Y. Siang Oei;
Meint K. Smit
Show Abstract
In this paper we present a scheme for integration of a number of key devices for WDM-networks based on three components. The elementary components, such as phased array demultiplexers, multi mode interference (MMI)-couplers and Mach-Zehnder Interferometer optical switches, are explained and experimental results are presented on integrated Multiwavelength (MW) add-drop multiplexers, MW-optical crossconnects. The integration of optical amplifiers and detectors to MW-sources and MW-receivers is briefly discussed.
Passband-flattened arrayed-waveguide grating design using an aspheric output star coupler
Author(s):
Michael C. Parker;
Farsheed Farjady;
Stuart D. Walker
Show Abstract
We describe a novel technique for passband control and shaping of an arrayed-waveguide grating (AWG) by designing the output star coupler to exhibit a parabolic deviation from the standard Rowland circle geometry. Passband broadening from 1 nm to 12 nm is possible using this approach. In principle, the phase-apodization function is equivalent to incorporating a synthetic aperture within the AWG, so that the same effect can be achieved by positioning a suitable aspheric-shaped anomalous refractive-index region within the arrayed-waveguide section of the device.
Effect of optical confinement factor and gain constant on the distortion levels in InGaAsP semiconductor laser diodes
Author(s):
Fatih V. Celebi;
Remzi Yildirim;
Kenan Danisman;
Ahmet Ozek
Show Abstract
The effect of optical confinement factor and gain constant (optical gain coefficient) on harmonic distortion in 1.55 micrometers semiconductor laser diodes are investigated by using a mathematical model based on multi-mode rate equations. The model can be extended and used to simulate the output of any direct modulated Fabry-Perot semiconductor laser in long wavelength by changing some of the parameters. Gain and spontaneous emission are included as spectrums, since each mode experiences different gain and spontaneous emission coupled to each mode is different. The important parameters such as Auger recombination, nonradiative recombination, spontaneous emission life time and gain saturation are included in the model. The second harmonic distortion levels are examined and computed graphically for different threshold levels.
Experimental analysis of microwave loss due to substrate carrier concentration in traveling-wave electro-optic modulators
Author(s):
H. R. Khazaei;
O. Berolo;
Wei Jian Wang;
P. Maigne;
M. Young;
K. Ozard;
M. Reeves;
Fadhel M. Ghannouchi
Show Abstract
Planar electrodes such as coplanar waveguides and coplanar strips are used in high-speed GaAs/AlGaAs traveling-wave electro-optic modulators. The modulation bandwidth of these modulators strongly depends on the microwave and optical velocity match and also on the microwave loss of the electrodes. The effect of substrate carrier concentration on the microwave loss of planar electrodes is experimentally investigated. Microwave losses were measured up to 40 GHz as a function of substrate carrier concentration over the range of 1 X 108 cm-3 to 2 X 1018 cm-3 using both epitaxially grown and ion-implanted GaAs/AlGaAs substrates. It was found that a critical residual carrier density limit of 5 X 1014 cm-3 exists, above which the microwave loss increases rapidly. These results were verified by growing a heterostructure optical waveguide with a carrier density of less than 5 X 1014 cm-3 and measuring the microwave loss. A modulation bandwidth in excess of 22 GHz and a half-wave voltage of 30 V were measured for this structure.
Key to OC-192 deployment dispersion compensation using fiber Bragg grating
Author(s):
C. Su;
Peter Kung;
W. H. Loh
Show Abstract
The effects and characteristics of group delay ripple of chirped fiber gratings on the performance of a 10 Gb/s NRZ transmission system has been experimentally investigated. For the power penalty less than 1 dB at bit-error-rate of 10-9, our experiment results show that the ripple magnitude of dispersion compensating gratings should be less than +/- 20 ps within its pass-band for 10 Gb/s systems.
Demultiplexing 120 optical channels with an integrated concave grating with total internal reflection facets
Author(s):
Kenneth A. McGreer;
Z. J. Sun;
James N. Broughton;
M. S. D. Smith
Show Abstract
The shape of the grooves of a diffraction grating can be designed to take advantage of total internal reflection. We demonstrated the effectiveness of the total internal reflection (TIR) grating numerically for the bulk optic case and experimentally for the integrated optic case. The results indicated that the efficiency of the retro- diffracted order is enhanced by about 10 dB when the TIR grating design is used in place of an echelle grating with no facet metalization. We demonstrate that a TIR grating can be integrated on a chip to demultiplex 120 optical channels that are transmitted in a dense wavelength division multiplexing (DWDM) application. The wavelengths of the channels had a 0.29 nm spacing and were within the 1550 nm wavelength band for DWDM applications.
Performance of 10 Gb/s transmission systems using MQW Mach-Zehnder modulators and electroabsorption modulators
Author(s):
John C. Cartledge
Show Abstract
The chirp and optical extinction ratio of multiple quantum well Mach-Zehnder modulators and electroabsorption modulators depend on the device design and the modulating voltage waveform. For transmission over non-dispersion shifted fiber, 10 Gb/s system performance is reviewed by considering joint optimization of the bias and modulation voltages. The implications of modulator design are examined taking into consideration group velocity dispersion and self-phase modulation arising from the Kerr nonlinearity. The results demonstrate that optimization of the bias and modulation voltages is effective for increasing the transmission distance, reducing the variation in performance obtained when Mach-Zehnder modulators of different designs are operated with maximum optical extinction ratio, and reducing the variation in performance obtained with different transmitted powers when electroabsorption modulators are operated with maximum optical extinction ratio.
Role of optical feedback for controlling chaotic cases in semiconductor laser diodes
Author(s):
Remzi Yildirim;
Kenan Danisman;
Fatih V. Celebi;
Ahmet Ozek
Show Abstract
In this study the effect of optical feedback in semiconductor laser diodes (LD) has been examined using small signal analysis. The transfer function of LD is given as H (j(omega) m)D and transfer function of external cavity LD is given as TF (j(omega) m)HD respectively. The investigated parameters of these transfer functions are external cavity length (Lext), line-width enhancement factor ((alpha) ) and mirror power reflection coefficient (R). The gain change occurring due to optical feedback noise is shown by broadening the bandwidth and narrowing the frequency spectra and the state of chaos (coherence collapse) is determined in each case. By varying the level of reflected optical feedback power (fext) the optical feedback system of LD has been improved. In addition to that the system is driven out of chaos by finding reasonable levels for these variables.
Sidelobes suppression in fiber gratings: a new design
Author(s):
Alejandro Carballar;
Miguel A. Muriel;
Jose Azana
Show Abstract
We propose a new design to remove the undesirable sidelobes prevalent in fiber grating spectra. This method is based on the grating period variation according to the apodization function in order to maintain constant the Bragg condition along the structure.
Analysis and demonstration of adjustable correlator
Author(s):
Shun-Chen Yang;
Shyh-Lin Tsao
Show Abstract
A new optical encoder/decoder structure, named adjustable correlator, in optical CDMA networks is proposed. This adjustable correlator uses fiber-optical recirculating delay lines as programmable configuration and adapts only two electro-optical switches. Experiments were set up to measure the characteristics of a dynamic correlator and the experimental results show good agreements with theoretical model.
Continuously tunable optical mm-waves for fiber radio applications and ultra high bit-rate communications
Author(s):
Herbert Burkhard;
H. Schoell
Show Abstract
For the generation of optical mm-waves many schemes have been investigated19 because of its increasing technical interest for the wireless local ioop. Simple beating of two different laser lines yields high flexibility, the excessive phase noise, however, is a drawback. Nearly all methods for pulse generation are based on RF injection into single or two mode DFB lasers or Fabry Perot lasers. The tunability ofthese mm-sources is rather limited. The RF power in some cases exceeds 25 dBm, so that the generation of the optical mm-waves becomes quite costly. Our method relies on two dc-biased DFB lasers. The output of one of them (master laser) is injected via an isolator into a second DFB laser (slave laser): Under these conditions output power oscillations ofthe slave laser can be created of nearly arbitrary repetition frequency up to the THz range with high modulation index, high output power and very low phase noise. The additional continuous tunability makes this method attractive for a very flexible and low cost optical mm-wave generation.
Characteristics measurement of multiple output laser with arrayed-waveguide grating
Author(s):
Shyh-Lin Tsao;
Shu-Tsung Kuo;
Tang-Yuan Chang
Show Abstract
In this paper, we develop a multiple output laser with 14 outputs. The multiple output laser composes of an 8 X 8 arrayed waveguide grating (AWG) and a semiconductor optical amplifier. We combine these two elements to achieve a ring configuration in this experiment. The multiple output laser with AWG can provide multichannel of light sources simultaneously. The characteristics of all unconnected fiber arms of the 8 X 8 AWG multiplexer are measured.
Assessment of laser intensity noise spectrum from rigorous numerical simulation of singlemode laser rate equations
Author(s):
Jose A. P. Morgado;
Adolfo V. T. Cartaxo
Show Abstract
A rigorous numerical method of solving the stochastic laser rate equations is investigated. Using this method, statistically correct numerical simulations of the relative intensity noise (RIN) spectrum at laser output are performed. The method is validated by comparison of the simulation results with analytical theoretical predictions. To estimate the RIN spectrum the periodogram technique is used. The impact of the number of periodograms, number of points, and time interval width on the RIN spectrum estimation is discussed. It is shown also that the usual methods of solving deterministic nonlinear differential equations should not be used to obtain by simulation the RIN at the laser output.
Static and dynamic behavior of the three cavity semiconductor laser diodes and oscillation frequency shift suppression
Author(s):
Kenan Danisman;
Ahmet Ozek;
Remzi Yildirim;
Fatih V. Celebi
Show Abstract
In this study, static and dynamic behavior of a three cavity laser diode model have been analyzed and oscillation frequency shift under the dynamic structure is explained theoretically. In the analysis, the effect of both the laser facet and the external cavity reflectivities as well as the lengths on the threshold conditions are investigated theoretically. The results have shown that when the optical feedback is increased depending upon the phase of the reflected field, the threshold gain of the laser is decreased. The results indicate that strong optical feedback, AR coating of the laser facet and large external cavity lengths are effect for the frequency shift suppression.
Effects of multiple quantum well nonlinearities on coupling coefficient and wavelength detuning in distributed-feedback laser structures
Author(s):
Glenn D. Isenor;
Jingyi Wang;
Toshihiko Makino;
Michael Cada
Show Abstract
Using a finite element formalism, the effects of an intensity dependent refractive index nonlinearity on the coupling coefficient and wavelength detuning of an index coupled multiple quantum well distributed-feedback laser structure are modeled. The associated nonlinear 1D guided wave equation is numerically solved for the effective index (eigenvalue) and the transverse field profile (eigenvector). Results are obtained for varying numbers of quantum wells and grating thickness. Changes in wavelength detuning and coupling coefficient for a given laser structure are shown to change linearly with increasing optical power.
Wide-range tunable semiconductor lasers using multiple quantum wells of different widths
Author(s):
Bor-Lin Lee;
Ching-Fuh Lin;
Miin-Jang Chen
Show Abstract
In this paper, we present wide range tunable semiconductor lasers using multiple quantum wells of different widths. Conventional semiconductor-laser gain medium using the quantum-well structure for the wavelength near 0.8 micrometers has only 50 meV bandwidth. Using quantum wells of different widths could significantly broaden the gain bandwidth, so broadband tuning of the laser could be easily achieved. Two types of samples designed for broad bandwidth operation have been used in this experiment. In addition, unlike the past tuning experiments that suffer from serious ASE noise, this experiment demonstrates very high ASE suppression ratio (> 40 dB) over the entire tuning range by using a triangular ring cavity.
Large optical parametric amplification and efficient difference-frequency generation in transverse-pumping geometry
Author(s):
Yujie J. Ding;
Jacob B. Khurgin
Show Abstract
We have investigated optical parametric amplification and difference-frequency generation in the transverse-pumping geometry. For the amplification, when the pump power is set to the threshold, a very large gain is predicted if the input power for the signal is much lower than the threshold. However, as the input power increases, the gain decreases rapidly. On the other hand, for the difference-frequency generation, for each value of the pump power, there is an optimal input power at which the output power at the difference frequency reaches a maximum.
Light emission from silicon nanometer-scale diode-antifuses
Author(s):
V. E. Houtsma;
J. Holleman;
V. Zieren;
P. H. Woerlee
Show Abstract
Results are presented of the spectrally resolved absolute measurements of the electroluminescence of reverse-biased silicon nanometer-scale diode-antifuses brought into breakdown. The emission spectrum of the diode-antifuses is measured in the energy range of 1.4 - 2.8 eV at different reverse currents. The dependence of the emission intensity on the current was evaluated to study the dominant emission processes. Also the stability of the diode-antifuses has been tested. Results indicate that the diode-antifuse is basically a high quality device. Furthermore due to the nanometer-scale dimensions of the diode-antifuse, very high electrical fields and current densities are possible at low power consumption. This makes the diode-antifuse an excellent candidate to be utilized as a light source in Si- based sensors and actuator applications.
Up-conversion devices for 1.5 um imaging
Author(s):
Hui Chun Liu;
Ming Gao;
Margaret Buchanan;
Zbigniew R. Wasilewski;
Philip J. Poole
Show Abstract
This paper present a novel idea of integrating a photodetector and a light emitting diode (LED) for wavelength conversion. The detector of interest here responds in the 1.5 micrometers wavelength region and LED emits in the near infrared (e.g., 800 - 900 nm). A proof-of-the- concept experiment has been conducted and presented here. The eventual application is to use this device in a focal plane imaging format for up-converting a 1.5 micrometers image to the near infrared then captured by a Si CCD camera.
Generation of blue light by frequency-doubling in periodically-poled bulk and waveguide KTP
Author(s):
Yu Wang;
Valentin T. Petrov;
Yujie J. Ding;
Jacob B. Khurgin;
William P. Risk
Show Abstract
We have investigated second-harmonic generation in short- period periodically-poled bulk and waveguide potassium titanyl phosphate crystals to generate blue light using subpicosecond laser pulses. For the bulk, the maximum conversion efficiency is approximately equals 5.5%, which is about two orders of magnitude larger than that achieved previously. For the waveguide, the maximum conversion efficiency is approximately equals 32%, which is about a factor of 4 higher than that obtained before. These measured values are in good agreement with our theoretical results. We have observed saturation of conversion efficiency, which sets a limit to the maximum conversion efficiency that can be obtained.
Lasing characteristics of a thulium-doped ZBLAN fiber laser at 481 nm
Author(s):
Real Vallee;
Pierre Laperle;
Alain Chandonnet
Show Abstract
The main features of a thulium-doped ZBLAN fiber laser are presented and compared to the results of a numerical analysis. Particularly, the problem of the photoinduced absorption arising from the formation of color-centers is addressed with special attention to its detrimental effects on laser operation. Practical solutions to this problem are also explored.
Lateral band gap engineering by focused ion beam implantation for optoelectronic devices
Author(s):
Johann-Peter Reithmaier;
N. Mais;
H. Koenig;
Alfred W. B. Forchel
Show Abstract
For the integration of optoelectronic components, like lasers, modulators, detectors or waveguides, materials with different band gaps are necessary, e.g. to avoid absorption in waveguides or to get optimal intensity contrast in modulators. By implantation induced thermal intermixing of semiconductor quantum film structures the band gap can be selectively changed and the band gap shift can be controlled by the implantation parameters. Focused ion beam technology additionally allows maskless patterning, which simplifies epitaxial overgrowth and makes in-situ processing possible. The paper gives an overview about highly spatially resolved quantum well intermixing by focused ion beam technology and how this technique can be applied for the definition of optoelectronic devices and components. By the high spatial resolution of the currently used focused ion beam systems the definition of first order gratings for wavelengths from the infrared to the visible spectrum were achieved. New approaches for the fabrication of gain coupled distributed feedback lasers based on implanted first order gratings for 1.0 and 1.55 micrometers emission wavelength are discussed and device results will be presented.
Modeling of the electrical derivative characteristic of InGaAsP multiple-quantum-well lasers
Author(s):
Alain Champagne;
Romain Maciejko;
Toshihiko Makino
Show Abstract
A comprehensive semiconductor laser model is used to analyze the first electrical derivative characteristic of long wavelength MQW semiconductor lasers. It is found that the charge neutrality condition and the continuity of the quasi- Fermi levels, usually assumed in the rate equation approach, need not be respected. The first electrical derivative characteristics of abrupt and GRINSCH MQW structures are presented. The effects of doping in the active region on the optical gain and on the first electrical derivative characteristic are also studied.
Polarization insensitivity of AlGaAs/GaAs interdiffused quantum wells
Author(s):
Wallace C. H. Choy;
E. Herbert Li;
Bernard L. Weiss
Show Abstract
Modeling is used to show that interdiffusion can generate a polarization independent parabolic-like quantum well. Criteria to achieve the parabolic-like quantum wells by interdiffusion are discussed. The results indicated that interdiffused quantum wells can produce equal eigen-state spacing, polarization insensitive Stark shift and modulation characteristics similar to an ideal parabolic quantum well. The design process to obtain polarization insensitive ON- and OFF-states in the parabolic-like interdiffused quantum wells is discussed. The predicted modulation depth is comparable to those measured using parabolic quantum wells. The diffused quantum wells have the advantage of using an as-grown rectangular quantum well with post-growth annealing to tailor its confinement profile. These features suggest that the interdiffused quantum well structure can be used to product polarization insensitive electro-absorptive modulation.
Enhanced stimulated emission in a two-dimensional photonic crystal
Author(s):
Kazuaki Sakoda
Show Abstract
An analytical expression is presented for light amplification by stimulated emission in arbitrary photonic crystals, which shows an enhancement due to small group velocity. This enhancement was evaluated quantitatively for a 2D crystal with a finite thickness composed of a square array of circular air-rods formed in a dielectric material. In addition to the enhancement at photonic band edges where the group velocity is equal to zero, an extremely large enhancement due to the group-velocity anomaly peculiar to 2- and 3-D crystals was found even for quite a thin structure.
Hollow-cathode He-Cd+ multi-color laser: a spectroscopic investigation on the laser emission
Author(s):
P. Ramalingam;
C. Grey Morgan;
Helmut H. Telle
Show Abstract
A single gun He-Cd+ laser utilizes a He-Cd mixture as a laser medium and oscillates at seven spectral lines of three primary colors emitted from excited Cd+ simultaneously. Because the powers at the three primary colors are balanced, the composite output beam appears white. Hence the name `white light laser'. White light lasers have various applicability in the fields of science and technology such as medical diagnostics and surgery, photochemistry and isotope separation as an energy source, and for color display, color holography, color printers as a light source. In this report, we present conclusive evidence about the population mechanisms to produce excited Cd ions, especially for the green laser lines.
Visible quantum dots under reversed bias
Author(s):
Fang Yang;
Geof C. Aers;
Karin Hinzer;
Yan Feng;
Simon Fafard;
John P. McCaffrey;
N. Sylvain Charbonneau;
Anthony J. SpringThorpe
Show Abstract
Time-resolved photoluminescence (PL), steady-state PL, and electro-luminescence techniques have been used to characterize the carrier relaxation processes and carrier escape mechanisms in a self-assembled AlInAs quantum dots (SAQD) p-i-n laser structure under reversed bias. The measurements were performed between 5 K and room temperature on a ring mesa sample as a function of bias. At 100 K, the PL decay time originating from the SAQD decreases with increasing reversed bias from approximately 450 ps under flat band condition to approximately 150 ps for biases of -4 V. The data can be explained by a simple model based on electron recombination in the quantum dots or escape our of the dots. The escape can occur by one of three possible routes: direct tunneling out of the distribution of electron excited state level, thermally assisted tunneling of ground state electrons through the upper electron excited states or thermionic emission to the wetting layer.
Photorefractive spatial solutions: a route towards optical switching
Author(s):
Nicolas Fressengeas;
Delphine Wolfersberger;
Jean Maufoy;
Godefroy Kugel
Show Abstract
All optical logic and switching is one of the key issues of optical computing and addressing. This paper proposes a low power switching technology with which switching can be achieved with optical powers on the scale of a few mW/cm2. This can be achieved by using a sensitive optical nonlinearity: the photorefractive effect. The drawback of the photorefractive effect sensitivity being its slow time response, this paper shows that this can be worked around by founding the switching technology on the transient photorefractive state rather than on its slow steady state.
Towards quantum dot laser diodes emitting at 1.5 microns
Author(s):
Simon Fafard;
John P. McCaffrey;
Yan Feng;
C. Ni. Allen;
Hugues Marchand;
L. Isnard;
Patrick Desjardins;
S. Guillon;
Remo A. Masut
Show Abstract
Quantum Dot laser diodes have been made using InAs self- assembled quantum dots (QDs) in the active region of separate confinement heterostructures. The lasers grown by Molecular Beam Epitaxy (MBE) with stacked InAs QDs grown on GaAs gave record low thresholds of 13 A/cm2 at 77 K and 82 A/cm2 at 15 degree(s)C. On InP substrates, InAs QDs have been grown by Metal-Organic Chemical Vapor Deposition (MOCVD) with InP claddings, and by MBE in InGaAlAs separate confinement heterostructures. For the InAs/InP by MOCVD, the QD photoluminescence (PL) peaks between 1.51 micrometers and 1.57 micrometers at 77 K and close to 1.6 micrometers at 300 K. Transmission Electron Microscope analysis correlated with the PL results reveal that the QD density depends on the growth interrupt time which follows the InAs deposition. For the InAs/InGaAlAs by MBE, the QD electroluminescence peaks at approximately 1.42 micrometers at 300 K.
Transmission spectra of two-dimensional InGaAsP-InP photonic crystals
Author(s):
Kim Ryel;
Romain Maciejko
Show Abstract
We present a study of a 2D photonic crystals composed of circular InGaAsP rods in air on an InP substrate for frequencies that span from the near-infrared to the far- ultraviolet. The crystal forms a square lattice and consists of infinitely long cylindrical rods. We use the transfer- matrix method and the multiple scattering formalism to calculate the transmission spectra as a function of the filling fraction, the incident angle of the wave, the compositions of Ga and As, the temperature and the impurity concentrations.
Static and dynamic response of a novel optical decision circuit
Author(s):
Jinying Sun;
Geert Morthier;
Roel G. Baets
Show Abstract
A novel Optical Decision Circuit (ODC) based on a Mach- Zehnder Interferometer with a Gain Clamped Semiconductor Optical Amplifier in each arm is proposed. Both its static and dynamic response from simulation results demonstrate that the ODC exhibits excellent reshaping capabilities. Also the high speed response of the ODC has been investigated.
Mid-IR light emitting diodes using InAs, InAs1-yPxSby epilayers on InAs (100)
Author(s):
Nelson L. Rowell;
Tomuo Yamaguchi;
X. Y. Gong;
Hirofumi Kan
Show Abstract
The development of mid-infrared optoelectronic emitters and detectors is important for long-wave photonic applications. We report mid-IR emission spectra for three types of narrow- gap III-V light emitting diodes consisting of n-/p-InAs homojunctions and of n-InAs1-ySby/p-InAs1-ySby, and n-InAs/p-InAs1-x-yPxSby heterojunctions all grown by liquid phase epitaxy on InAs (100) substrates. Spectra were obtained under forward bias for photon energies between 300 and 425 meV (4.1 - 2.9 micrometers ), temperatures from 5 to 292 K, and bias currents from 20 (mu) A to 12 mA. Comparison are made with photoluminescence spectra from similar material.
Optical chips interconnects: economically viable
Author(s):
Roger A. Vounckx;
Paul L. Heremans;
Daniel Coppee;
Reiner Windisch;
Gustaaf Borghs;
Maarten Kuijk
Show Abstract
We propose a simple, low cost, parallel optical data bus for CMOS to CMOS optical interconnects. At the light emission side, NRC-LEDs are chosen for their high external quantum efficiency at low currents (10 - 20% at sub-mA level), their expected high yield and temperature insensitive operation. Image Fiber Bundles (IFBs) are the medium of choice for conducting the high number of parallel light channels. IFBs are a mature product of glass technology, being at the same time flexible, low cost, low risk and highly efficient. Light is received directly in CMOS, using the concept of Spatially Modulated Light detection in combination with a Sense-Amplifier receiver at a bitrate of 180 Mbit/s.
Effective fabrication of long period gratings by the use of microlens array
Author(s):
Michael S. Y. Liu;
Hwa-Yaw Tam;
Weichong Du
Show Abstract
A new method for fabricating Long Period Grating (LPG) using a microlens array is introduced. Instead of blocking the excimer laser beam, this new method convergences the UV laser beam into an intensity modulated profile and the writing efficiency is improved. This method enables shorter grating writing time and also suitable for batch production of LPGs, thus providing an efficient method with potential in the mass production of LPGs.
Polarization holographic gratings in azopolymers for detecting and producing circularly polarized light
Author(s):
Paul L. Rochon;
V. Drnoyan;
Almeria Natansohn
Show Abstract
Polarization holographic gratings were inscribed in azobenzene side chain polymer films. The polarization gratings were produced using two orthogonally circularly polarized beams and the resulting stable transmission gratings were studied using a low power HeNe laser. The gratings were observed to efficiently separate left and right circularly polarized light from the probe beam and two generate two elliptically polarized beams in the first order diffraction direction.
HOLONS--a new facility for the development of optically recorded diffraction elements for neutron scattering
Author(s):
Romano A. Rupp;
F. Havermeyer;
J. Vollbrandt;
R. Kampmann;
Eckhard E. Kraetzig
Show Abstract
A description of a new research facility for HOLOgraphy and Neutron Scattering (HOLONS) at the Geesthacht Neutron Facility, is given. It essentially consists of a light- optical holographic set-up inserted into a small-angle neutron scattering instrument of a beamline for cold neutrons. Among other possibilities, this facility permits to follow the buildup of holographic gratings during recording (i.e., in real time) by simultaneous light and neutron diffraction experiments. Thus it is especially suitable for the development of optically recorded diffraction elements for neutron scattering. The main features of this new facility will be described below and first results will be presented. In particular, we point out some interesting perspectives which became now open for investigation.
Hybrid integration of microoptic and optoelectronic elements by replication in polymers
Author(s):
Andreas H. Braeuer;
Peter Dannberg;
Lars Erdmann
Show Abstract
After demonstration of a large variety of microoptic and optoelectronic components in many institutions world-wide, the main interest is focused on their hybrid integration into miniaturized systems. This concerns modules comprising lightsources, detectors, conventional and microoptical elements, like lenses, prisms, filters, and, for some applications, miniaturized actuators. A solution is described for replication of polymer microoptical elements on arbitrary substrates (semiconductor, glass). The replication is done on wafer scale level and includes the adjustment step between the optical elements and the substrate. Demonstrators are 90 degree(s) deflection prisms for the efficient coupling between monomode waveguides and photodiodes and various microlens-arrays. From the many different replication techniques, UV-reaction molding is chosen for this application. This technique has advantages against hot embossing and injection molding. Network polymers which are stable against temperature changes can be used. The replication is made in thin layers on a solid substrate resulting in high mechanical stability and very good flatness of the samples. There is neither mechanical stress nor thermal load on the substrate which can be a fully processed semiconductor wafer containing elements like diodes or VCSELs.
Thin metal island plasmon sensor
Author(s):
Fabrice Meriaudeau;
Todd R. Downey;
A. Passian;
Patrick Ian Oden;
A. G. Wig;
P. B. Crilly;
S. Mangeant;
Trinidad L. Ferrell
Show Abstract
The effects of the local dielectric environment on the surface-plasmon resonances of annealed gold-island films are studied experimentally and modeled theoretically. Gold- island films were annealed at 600 degree(s)C to produce spheroidal shape particles which exhibit well-resolved resonances in polarized, angle-resolved, absorption spectra. These resonances are shifted in different amounts by the depolarization effect of the surrounding medium (liquids with various refraction indices). Cross-section calculations based upon non-retarded, single-particle, dielectric interaction for these various configurations are presented and found to be in good agreement with the experimental observations.
Real time THz imaging system based on electro-optic crystals
Author(s):
Z. G. Lu;
Xi-Cheng Zhang
Show Abstract
We present a focal plane terahertz (THz) ray imaging system through use of a big-size <100> oriented ZnTe electro- optic crystal plate. Some concealed living insects and moving objects have been directly imaged and the dynamic processes of the THz field distributions are clearly displayed, both in real-time model. We also discuss the maximum and minimum sizes of the available imaging objects in this THz imaging system, and give ways to improve them.
Chaos synchronization in optically programmable logic cells
Author(s):
Ana P. Gonzalez-Marcos;
Jose Antonio Martin-Pereda
Show Abstract
A possible approach to the synchronization of chaotic circuits is reported. It is based on an Optically Programmable Logic Cell and the signals are fully digital. A method to study the characteristics of the obtained chaos is reported as well as a new technique to compare the obtained chaos from an emitter and a receiver. This technique allows the synchronization of chaotic signals. The signals received at the receiver, composed by the addition of information and chaotic signals, are compared with the chaos generated there and a pure information signal can be detected. Its application to cryptography in Optical Communications comes directly from these properties. The model here presented is based on a computer simulation.
Broadband impedance-matched metal-semiconductor-metal photodetector arrays
Author(s):
Ray G. DeCorby;
Alan J. P. Hnatiw;
Dave W. Boertjes;
James N. McMullin;
R. Ian MacDonald
Show Abstract
An electrically interconnected, linear array of photodetectors is a useful component for several optoelectronic systems applications. Traveling-wave concepts were employed in matching arrays of metal-semiconductor- metal photodetectors to a 50 (Omega) load, over a broad bandwidth. The photodetectors are embedded in a microstrip transmission line, to form a periodically loaded structure. The bias of each detector is independently controllable. Such periodic structures can be designed to exhibit specified characteristic impedance, and to be non-dispersive up to very high frequencies. With proper matching, each photodetector exhibits broadband response into an external load. Experimentally, a monolithic array of eight metal- semiconductor-metal photodetectors, attached to a microstrip bus, is shown to have uniform 12 GHz bandwidth. A model for the array is discussed, and theoretical and experimental results are in good agreement. Applications of broadband photodetector arrays are also discussed.
1.55 um mode expanders using single epitaxial growth
Author(s):
Mario Dagenais;
Simarjeet S. Saini;
Vijayanand Vusirikala;
Robert E. Bartolo;
Ralph D. Whaley Jr.;
F. G. Johnson;
Dennis Stone
Show Abstract
We report on two techniques developed at the University of Maryland, College Park for fabricating expanded mode laser arrays. Both of these techniques use single epitaxial growth and conventional fabrication techniques. The first of these techniques is based on adiabatic mode transformation from a tightly confined active waveguide to a loosely confined large underlying passive waveguide over a mode transmission region 500 micrometers long. The devices butt couple to a standard single mode fiber with a coupling loss of 3.6 dB and reduced farfield divergence angles of 22 degree(s) and 9 degree(s) in the transverse and lateral directions respectively. The excess mode transformation loss is 1.3 dB. The second device is based on a novel resonant coupling scheme between two waveguides of different dimensions and refractive indices. The mode is transformed over a taper length of 200 micrometers with excess mode transformation loss of 0.6 dB. Butt coupling efficiencies of 41% (3.8 dB coupling loss) is achieved to a standard single mode fiber. The farfield divergence angles achieved are 24 degree(s) and 13 degree(s) in the transverse and lateral directions respectively.
Method of proton exchange in lithium niobate
Author(s):
Wiley K. Smith
Show Abstract
This report is on a new method of proton exchange that is much easier to use than current methods, is of equal optical quality, less substrate stress, and lends itself to large scale manufacturing. This process relates to annealed proton-exchanged guided wave devices in lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) used in integrated optic circuits (IOC's). IOC's are useful in fiber optic gyros, photonic switching devices, and intensity/phase modulation systems. They have low optical loss, low voltage drive, high frequency bandwidth, and small size and weight.
Fabrication of rare-earth doped sol-gel based composite planar optical waveguides on glass
Author(s):
S. R. Natarajan;
Talabuttala Srinivas;
M. J. Joseph;
Ananth Selvarajan
Show Abstract
Incorporation of active materials, such as Neodymium (Nd3+) and Erbium (Er3+) in suitable host media has potential applications in lasers and amplifiers. We have fabricated composite planar waveguides on glass substrates doped with Nd3+ and Er3+ ions using the sol-gel process. The composite sol-gel was prepared using polyvinylpyrrolidone as the organic part, while Tetraethyl orthosilicate and Titanium isopropoxide formed the inorganic part. The samples were prism coupled and it was found that they supported single mode at (lambda) equals 633 nm. Gain measurement of the Nd3+ samples have also been carried out.
Physical surface effects of Ti:LiNbO3 diffusion
Author(s):
Wiley K. Smith
Show Abstract
Titanium (Ti) diffusion into lithium niobate (LiNbO3) is often used to define waveguides for integrated optics devices which are now of considerable commercial importance. I report here on changes in the surface shape caused by titanium diffusion for fabricating (LiNbO3) integrated optical devices. I found that the processing leaves surface ridges whose height and shape depend on mass flow of lithium niobate, thickness of titanium, hydrogen content of diffusion atmosphere, and time at temperature. I also describe the surface effects of a reaction between LiNbO3 and quartz (silicon). To my knowledge the effects reported here have never before been reported in the open literature.
Silica-based rib waveguides for integrated optics using multimode interference
Author(s):
N. S. Lagali;
R. Ian MacDonald;
M. Reza Paiam;
Kerstin Woerhoff;
Alfred Driessen
Show Abstract
Integrated optical waveguides, as well as splitters and switches utilizing the principle of multimode interference have been realized in PECVD SiON/SiO2 technology. The waveguide design has been optimized to meet a number of requirements, such as small device size, polarization- independent operation, and low-power active operation. The design, fabrication, and initial experimental results for these devices are discussed.
Accessing guides first order mode influence and optimize tolerances in multimode interference couplers
Author(s):
C. Vazquez;
Candido Aramburu;
Jose M. Sanchez-Pena;
Manuel Lopez-Amo
Show Abstract
Influence of first order mode excitation in input/output waveguides of multimode interference couplers is analyzed. Emphasis in common mode rejection ratio penalty in 3-dB couplers as part of balance coherent detection receivers is encountered. Design analysis is carried out in InGaAsP/InP buried waveguides. Coupler behavior is modified basically when first order mode is excited at input waveguides. A drastically reduction of 25% couplers width tolerance is derived from first order mode partial presence (10% of full input optical power) in accessing waveguides. Some guidelines about width tolerance improvement in restricted interference couplers against general interference couplers is also reported. Couplers dependence on fabrication tolerance was described as a function of power distribution between different modes in multimode section.
Modal analysis of rectangular MQW waveguide: a novel approach using scanning angle method
Author(s):
Youn Sub Lim;
Young-Wan Choi
Show Abstract
We present a novel method for the analysis of the rectangular MQW waveguide. Preferentially 2D structure is transformed into 1D structure by using the effective index method. Then, the characteristic matrix of the resultant planar MQW waveguide is analyzed by the scanning angle method proposed in this paper. The effective index, modal field intensity, and confinement factor of rectangular MQW waveguide can be effectively obtained by this method. Our simulation results show excellent agreement with the accurate solutions based on the finite element method. We also introduce the approximation methods for the analysis of rectangular MQW waveguide and investigate their validity.
Optical confinement via quantum well intermixing on a buried InGaAs/InGaAsP heterostructure
Author(s):
Joan E. Haysom;
Andre Delage;
Philip J. Poole;
Yan Feng;
Jian Jun He;
Emil S. Koteles;
N. Sylvain Charbonneau;
Richard D. Goldberg;
Ian V. Mitchell
Show Abstract
Selective area quantum well intermixing is used to create buried heterostructure narrow waveguides, which are shown to be effective waveguides for a narrow range of wavelengths near the lasing wavelength of the structure. Measurements on as-grown and uniformly intermixed slab waveguide are used to determine the refractive index of the two regions, and the net refractive index difference is used to predict modal behavior of the buried waveguides.
Waveguided, non-linear contradirectional couplers based on multiple quantum wells
Author(s):
Domenico Campi;
Claudio Coriasso;
C. Cacciatore;
Cesare F. Rigo;
Alessandro Stano;
L. Faustini;
L. Gastaldi;
S. Mautino
Show Abstract
This work describes the implementation of all-optical switching in distributed-feedback single-mode waveguides having a non-linear multiple-quantum well core. The optical nonlinearity is due to variations of the excitonic optical properties induced by the presence of a carrier plasma, that is photogenerated using a pump beam. We summarize the theory and present results of both static and dynamic experiments, documenting pJ switching energies, bistability and pulse compression, at wavelength of interest to telecommunication applications.
Polarization controllable and monolithically integrable optical waveguide devices
Author(s):
Weimin Zhou;
Jagadeesh Pamulapati;
Hongen Shen
Show Abstract
Polarization controllable semiconductor optical waveguide material/devices have been design and studied using different type of strained quantum well heterostructures in the active region of the waveguide. A phase modulator devices has demonstrated a linear relative phase shift between the TE and TM polarizations with a V(pi ) of approximately 4 V. Another electro-absorption waveguide modulator structure has shown a bias tunable polarization mode so that the polarization properties can be actively controlled. We are also developing a monolithic integration techniques using selective epitaxial growth to achieve band gap variation within the same wafer and therefore, fabric integrated passive and active waveguide systems without high cost regrowth or device coupling.
Improved variable transformed Fourier method to analyze nonlinear dielectric waveguides
Author(s):
Juan Gonzalo Wanguemert Perez;
I. Molina-Fernandez
Show Abstract
An improved variable transformed Fourier decomposition method to analyze nonlinear dielectric waveguides is presented in which, to increase the efficiency for nonsymmetrical and nonlinear situations, a new degree of freedom (the offset) is allowed in the tangent type variable transformation. Soundness of the method is provided by means of a new self-consistent algorithm to automatically find the numerical parameters of the variable transformation which allows blind detection of quasi-optimum values. This algorithm lies upon the fact that the optimum numerical parameters are those which minimize the variance of the spectrum of the functions to be approximated. The proposed method has been tested in a linear and nonlinear (Kerr type) graded-index waveguide of exponential profile for a great variety of situations showing excellent results.
Design and fabrication of 16x16 ion-exchanged glass waveguide star couplers
Author(s):
Wei Jian Wang;
Ezio Berolo;
H. R. Khazaei
Show Abstract
16 X 16 integrated optical star couplers were designed and fabricated using an ion exchange technique in glass substrates. The devices demonstrated a very good optical power distribution uniformity, low excess loss, low polarization sensitivity and excellent reproducibility.
Quantum well intermixing for photonic IC applications
Author(s):
E. Herbert Li
Show Abstract
Photonic IC is an attractive information processing means to fully utilize the enormous bandwidth carried by the optical signals. The full integration of photonics devices, such as tunable lasers, modulators and photodetectors have to be developed and which can be obtain by using the Quantum Well Intermixing technology. This paper will explore on the wavelength tunability using different Quantum Well Intermixing techniques, such as impurity induced diffusion and impurity-free vacancy diffusion. Emphasis will be put on the development of very recent innovations and applications.
Trends in integrated optics for fiber networks
Author(s):
Alain Carenco
Show Abstract
The extensive efforts being devoted to integrated optics to enhance fiber system capabilities and to develop all-optical architectures will be addressed. The talk will highlight current research, mostly on InP-based components, to face the demand for new functions needed in high-bit-rate systems, wavelength-division-multiplexing and networking.
Tapered waveguide for broad-band WDM optical dispersion compensation
Author(s):
Francois Baribeau;
Dominique Brichard;
B. Dareys;
Vincent Delisle;
Michel A. Duguay;
U. Langbein;
J.-F. Leclerc;
Udo E. Trutschel
Show Abstract
Mode conversion is used in a large refractive index difference tapered planar waveguide structure in order to obtain high negative dispersion (-1.5 to -200 ps/nm- cm) over 0.5 to 100 nm bandwidths. Light injected into a top silica core as a fast ARROW mode adiabatically converts into a slow conventional high-order mode of an underlying tapered silicon layer. The large differential velocity between the `redder' and the `bluer' spectral components of a pulse leads to dispersion compensation. Tailoring the profile of the silicon taper can compensate for higher-order dispersion in fibers.
Novel Si structures for photonic applications
Author(s):
Z. H. Lu;
J.-M. Barubeau;
David J. Lockwood;
Margaret Buchanan;
Nacir Tit;
C. Dharma-Wardana;
Geof C. Aers
Show Abstract
Although silicon is the paramount material for the microelectronic industry, bulk Si is of little use for photonic devices owing to its indirect band-gap, which prevents the all-important direct optical transitions. However, a new type of luminescent Si has opened up its future for photonic applications. This new material is light-emitting SiO2/Si superlattices, fabricated in our laboratory. Our theoretical calculations showed that the energy band within the silicon layer has direct bandgap character, a result of strong quantum-confinement caused by the large band-offset at the SiO2/Si interface, so that the direct optical transition is not only possible but also vigorous. For a quantum-confined amorphous silicon, the breakdown of angular momentum will naturally make all optical transition possible. Our experiments have shown that SiO2/Si superlattices can indeed emit bright light. Moreover, the band-gap or the wavelength can be tuned over the visible range by changing the Si layer thickness, in good agreement with quantum confinement theory. The luminescence intensity as a function of Si layer thickness is found to increase, reach a maximum, and then decrease. Theoretical studies show that this phenomena is caused by competition between an increased overlap of electron-hole wave functions in the normal direction to the quantum well and an increased exciton radius in the plane of the quantum well.
Thin films of LiNbO3 prepared on SiO2/Si by sol-gel processing for active SOS device applications
Author(s):
Shi De Cheng;
Chan Hin Kam;
Yan Zhou;
Yee Loy Lam;
Yuen Chuen Chan;
X. Z. Wang;
Zhuo Sun
Show Abstract
Thin films of lithium niobate are derived on SiO2/Si substrate by the sol-gel method. The solution is prepared by mixing LiOC2H5 and Nb(OC2H5)5. The films are deposited by spin coating and are annealed at different temperatures of 400 degree(s)C, 500 degree(s)C, 600 degree(s)C and 700 degree(s)C. The films are characterized by means of X-ray diffraction, atomic force microscopy and variable angle spectroscopic ellipsometry. The experimental results show that when the heat treatment temperature is about 500 degree(s)C, the films starts to crystallize and the desirable ferroelectric phase dominates. The crystalline size of the 500 degree(s)C annealed film ranges from 39 nm to 86 nm and the film is microscopically continuous and uniform. The refractive index of the film is found to be 1.83 at the wavelength of 633 nm. The nanocrystalline nature, the ferroelectric phase and the refractive index of the films make them potential candidates for active integrated optical component applications.
Characteristics of fiber-optic systolic arrays and resonant circuits
Author(s):
Otto Schwelb
Show Abstract
We report on simulated performance results obtained for resonant and lattice circuits, comprised of 2 X 2 couplers, waveguides, Bragg gratings and wavelength independent reflective elements. The range of operating wavelength depends on the type of components used and on the adequacy of the circuit model. A unified analysis allows the investigation of a large variety of network configurations by the same computer code. The method of analysis and the numerical results should be useful for the wavelength engineering of spectral filters, add/drop combiners, sensors, etc.
Measurement of pump-induced thermal effect in Er/Yb codoped fiber
Author(s):
Hwa-Yaw Tam;
Yuanzhong Xu;
M. Suleyman Demokan
Show Abstract
We report here the experimental results of pump-induced thermal effect in Er/Yb fibers. A 10-mm long fiber Bragg grating, written directly in a highly photosensitive B/Ge/Si annulus of a 12-mm long Er/Yb-P/Al/Si fiber, was employed for determining the temperature rise caused by nonradiative transitions in the Er/Yb fiber by measuring its Bragg wavelength shift. A temperature rise of 0.85 degree(s)C per mW of pump power was measured for the Er/Yb fiber. A fiber laser constructed with a FBG written directly in one end of the fiber and a mirror butt joined to the other end was investigated for the pump-induced thermal effect. Its lasing wavelength was shifted by 0.25 nm when the pump power was varying from 4 mW to 56 mW.
Thermal modeling and temperature measurements in optoelectronic waveguide devices
Author(s):
M. Allard;
Marcel G. Boudreau;
Remo A. Masut
Show Abstract
Optoelectronic devices are particularly sensitive to temperature changes induced by light absorption and current flow. In order to study the thermal issues arising in the Mach-Zehnder optical modulator manufactured by Nortel, a non-linear finite-element thermal model of the device was constructed, which computes the internal temperature as a function of the applied voltage and optical power in the waveguide. An experimental technique was also developed, in which liquid crystals are used to measure the temperature on the device surface. The model predictions and the experimental results were found to agree well over wide ranges of optical power and voltage. The model and the technique have produced evidence of a thermal cross-talk between an integrated laser and the modulator: the peak internal temperature inside the modulator is higher in integrated devices than in the stand-alone configuration for identical voltage and optical power. Because of the desire to integrate multiple devices on a common substrate and the continuous increase of the optical powers in optical fiber systems, thermal issues will only become more important in future systems.
Ultrafast time division multi-access networks
Author(s):
Katie L. Hall;
Kristin A. Rauschenbach;
Steven G. Finn
Show Abstract
Ultra-high speed optical time division multi-access networks, operating at single-stream data rates of 100 Gb/s, may offer unique advantages over wavelength division multiplexed systems. These advantages include providing integrated services, including packet service to high-end users, multiple quality of service levels and truly flexible bandwidth-on-demand. In this paper, we discuss architectures and technologies for implementing ultrafast TDMA networks. In addition, we discuss novel applications for the ultrafast technologies that have been developed.
Evolutionary multi-dimensional access architecture featuring cost-reduced components
Author(s):
Farsheed Farjady;
Michael C. Parker;
Stuart D. Walker
Show Abstract
We describe a three-stage wavelength-routed optical access network, utilizing coarse passband-flattened arrayed- waveguide grating routers. An N-dimensional addressing strategy enables 6912 customers to be bi-directionally addressed with multi-Gb/s data using only 24 wavelengths spaced by 1.6 nm. Coarse wavelength separation allows use of increased tolerance WDM components at the exchange and customer premises. The architecture is designed to map onto standard access network topologies, allowing elegant upgradability from legacy PON infrastructures at low cost. Passband-flattening of the routers is achieved through phase apodization.
New multichannel optical local area network based on an original star topology with an adapted multi-Ethernet protocol
Author(s):
Caroline Brisson;
Alain Kueng;
P.-A. Nicati;
Philippe A. Robert;
Daniel Rodellar;
Cristian Bungarzeanu
Show Abstract
We propose a new optical physical layer and protocol for optical Load Area Networks (LANs), which allow a large number of hosts to be connected while offering a large capacity and exhibiting a high degree of modularity and scalability. The physical layer of the optical LAN is first presented. It is based on a passive star topology and exploits the benefits of combining multichannel techniques together with coherent detection. It shows very simple emission and detection schemes requiring only one laser and one photodetector per node. The experimental setup of this physical layer has been implemented and is described. A new multichannel Ethernet protocol, tailored to the physical layer is also proposed and is presented in the second part of this paper. It results in a considerable improvement of the performance (transmission delay and packet loss), when compared to a single Fast Ethernet channel protocol with the same total capacity.
New architecture and codes for optical frequency-hopping multiple access
Author(s):
Louis-Patri Boulianne;
Leslie Ann Rusch
Show Abstract
We propose a new architecture for an optical fast frequency- hop code division multiple access system using tunable Bragg gratings. Previously proposed architectures called for a series of in-fiber Bragg gratings, each independently tunable with a piezo-electric device. We propose a system where the entire fiber of multiple Bragg gratings uses one piezo-electric device to tune to a particular code. We introduce a new set of codes to take advantage of the new architecture and increase the bit rate of each user, as well as the total number of users and hence aggregate bit rate.
Terabit single-hop TDMA network with the spectrum-domain modulation
Author(s):
Aleksandra Smiljanic;
Hisashi Kobayashi;
June-Koo Rhee
Show Abstract
In this paper, we propose a single-hop TDMA optical network with throughput of several Tb/s. This high throughput is achieved by combining spectrum encoding and fast demultiplexing. Fast packet switching is accomplished by using a rapidly tunable delay line. The frequency domain DPSK modulation is adopted, which provides 3 dB improvement over FD-OOK. Finally, we discuss a scalable protocol that can be employed in a network with a large number of channels and users.
Performance of fiber optic CDMA LANs with less-than-ideal components
Author(s):
Subrat Kar;
G. Ramakrishnaiah;
Swades K. De
Show Abstract
We investigate the performance of CDMA. systems with laser chirping effects, single mode fiber dispersion effect and by assuming a Poisson shot noise model for an APD receiver. We develop the time-domain simulation models for the functional blocks in CDMA LANs and evaluate the end-to-end system performance using these models. The use of direct sequence CDMA LANs attracts attention due to the improved usage of the bandwidth of the optical fiber [1] [2] . We investigate the effect of using non-ideal components (sources, medium, detectors) on the performance of such a CDMA fiber-optic LAN. In our simulation the system comprises of the following signal processing blocks—Data source (NRZ) , Electrically programmable encoder, Laser, Optical encoder and decoder, Single mode fiber and Receiver.
Progress in high speed 1300 nm optical communication
Author(s):
H. de Waardt;
J. G.L. Jennen;
R. C. J. Smets;
J. J. E. Reid
Show Abstract
The current status of high speed 1300 nm optical transmission will be reviewed in this paper. In particular the activities within the collaborative ACTS Upgrade project will be presented comprising 10 Gbit/s field trials, an experimental 40 Gbit/s OTDM laboratory test bed and initial work on 40 Gbit/s WDM transmission.
Relative intensity noise induced by fiber dispersion near zero-dispersion wavelength in linear singlemode fibers
Author(s):
Adolfo V. T. Cartaxo;
Jose A. P. Morgado
Show Abstract
Transmission of intensity noise along linear single-mode fiber taking into account the first- and second-order fiber dispersion is investigated theoretically and numerically. Excellent agreement between our theoretical predictions and accurate numerical simulations of intensity noise spectra after single-mode fiber transmission is obtained for different laser bias currents and fiber dispersion parameters. Our theoretical and simulation results show that the intensity noise spectrum at the fiber output is not dependent on the second-order fiber dispersion, and therefore it is determined solely by the first-order fiber dispersion. Accordingly, second-order dispersion effects on the intensity noise spectrum are proved to be irrelevant even for very long broadband optical communication systems operating near zero-dispersion wavelength.
Performance of QAM fiber optic links under the influence of RF phase noise
Author(s):
Apurva N. Mody;
Mehdi Shadaram;
Stephen A. Pappert;
Pritam Kabe
Show Abstract
The effect of RF phase noise and phase delay fluctuations on the performance of a Quadrature Amplitude Modulated fiber optic link is investigated. Plots showing the bit error rate against the phase noise for 16, 64 and 256 QAM systems are presented. Two techniques are used for evaluating the average error probability performance namely, numerical integration and Taylor series approximation. To alleviate the difficulties in the simulations, phase noise is assumed to have a zero mean Gaussian probability distribution function.
Research on a practical Telecom and CATV co-network transmission system
Author(s):
Youju Mao
Show Abstract
A practical co-network transmission system of Telecom and CATV over installed Telecom network is designed. The system, making use of WDM and other technologies, has undergone experiments and performance tests on the Public Switched Telephone Network, which illustrate that optical fiber telecommunication network could be thereby transformed into a unified broadband network integrating VOICE, DATA, and VEDIO expeditiously and conveniently.
From duobinary coding to phase-shaped binary transmission (PSBT)
Author(s):
Denis Penninckx
Show Abstract
Optical duobinary coding is an attractive technique to increase the chromatic dispersion limit, to increase the spectral efficiency and even both. This topic has recently drawn considerable attention from various companies and universities.
Validation of small-signal analysis for nonlinear dispersive fiber systems with multiple in-line amplifiers using numerical simulation
Author(s):
Adolfo V. T. Cartaxo;
Jose A. P. Morgado
Show Abstract
A general small-signal theory for nonlinear dispersive optical fiber systems with in-line amplification is investigated and validated through numerical simulation for different dispersion propagation regimes, optical powers, and number of fiber segments. This theory allows for any arbitrary phase and intensity modulation at the transmission system input from which phase and intensity at the transmission system output are derived. It is shown that in case of anomalous dispersion regime the conversion factors between power and phase can be remarkably enhanced and their dips move towards higher frequencies as the number of fiber sections increases, even for moderate powers. In case of normal dispersion regime, all conversion factors can be significantly reduced and their dips move towards lower frequencies as the number of fiber sections increases.
Submicrosecond transient time responses in cascades of EDFAs
Author(s):
Ljubisa Tancevski;
Leslie Ann Rusch
Show Abstract
Simple analytical expressions for determining the characteristic time of a single EDFA and evaluating the 1 dB time response of a cascade of EDFA are given in a form of a difference equation. It is shown that the expressions are in remarkable agreement with the results obtained through solving numerically the differential equations for chains of EDFAs. Simulations of the transient time response to channel drop/add are also included.
Role of standards in building the worldwide optical telecommunications network
Author(s):
Jack Dupre;
Lorenzo Freschet
Show Abstract
The unprecedented growth in demand for network capacity, driven by the internet and data services in general, has motivated equipment manufacturers and service providers to fully exploit the bandwidth potential of single-mode optical fiber. In addition to the optical fiber itself, erbium-doped fiber amplifiers and dense wavelength division multiplexing components have enabled capacities approaching 1 Tb/s on a single fiber. Optical networking, in which signal routing and switching are at the optical layer, is currently a subject of active research and debate. This presentation summarizes many of the current activities working on the physical layer aspects of the optical network including system and component issues.
Separation of noise from distortion for amplified optical fiber system link budgeting
Author(s):
Rongqing Hui;
Masoud Vaziri;
J. Zhou;
Maurice S. O'Sullivan
Show Abstract
In optical transmission systems with in-line optical amplifiers, system performance degradation caused by random noise and optical path distortions are usually thought to be inseparable, which makes system performance evaluation complicated. We proposed to use an optical system eye-mask parameterization technique to separate noise from distortion in the system budgeting. The basic idea of this approach is to find the worst-case path distortion factor which is independent of the noise characteristics and system implementations. Both theoretical development and experimental verification are discussed.
View of next generation optical communication systems--possible future high-capacity transport implementations
Author(s):
Richard Cowper
Show Abstract
Possible implementations of next generation high-capacity transport are presented and associated technical challenges are discussed. From the expected spectral efficiency of conventional modulation formats and based on substantial practical system integration experience, it is estimated that a practical transmission capacity for a single 1000 km fiber is between 2 and 5 Tb/s, assuming a 10 THz transmission window.
Modulating retroreflector architecture using multiple quantum wells for free space optical communications
Author(s):
G. Charmaine Gilbreath;
William S. Rabinovich;
Rita Mahon;
Michael R. Corson;
John F. Kline;
Joshua H. Resnick;
H. Charles Merk;
Michael J. Vilcheck
Show Abstract
In this paper, we describe a demonstration using a Multiple Quantum Well modulator combined with an optical retroreflector which supported a high speed free space optical data link. Video images were transmitted over an 859 nanometer link at a rate of 460 kilo bits per second, where rate of modulation was limited by demonstration hardware, not the modulator. Reflection architectures for the modulator were used although transmission architectures have also been investigated but are not discussed in this paper. The modulator was a GaAs/Al0.3Ga0.7As quantum well which was designed and fabricated for use as a shutter at the Naval Research Laboratory. We believe these are the first results reported demonstrating a high speed free space optical data link using multiple quantum well shutters combined with retroreflectors for viable free space optical communications.
Contributions to composite second-order distortion for 80 channel analog systems from chromatic dispersion, PMD, and PDL
Author(s):
M. Ajaaz Zainul
Show Abstract
Composite second-order distortion (CSO) can significantly impair system performance of analog systems. Of the three mechanisms that contribute to the CSO level, namely, chromatic dispersion, PMD, and polarization-dependent loss (PDL), modeling and experimental results show that chromatic dispersion may be the main contributor if PMD from typical currently manufactured fibers are used. Because of this and due to the low variability of the chromatic dispersion values, levels higher than -70 dB of CSO can be accommodated. Using chirp values from current directly modulated lasers at 1310 nm, system lengths as long as 40 km are predicted to be achievable. Sixteen picoseconds of instantaneous PMD can be tolerated provided chromatic dispersion and PDL are reasonably controlled.
Interchannel interference effects in spectrum-sliced WDM systems
Author(s):
Vivek Arya;
Ira Jacobs
Show Abstract
In spectrum-sliced WDM systems with an optical preamplifier receiver there is an optimum m equals BoT (Bo equals optical channel bandwidth, T equals bit duration) to minimize the average number of photons-per-bit (Np) required at the receiver for a given error probability (Pe). These results, previously obtained for the case of rectangular filters and no interchannel interference, are extended to the case of practical filters. It is shown that interchannel interference increases the optimum m and the minimum Np. Operating at this optimum, the total system throughput with first-order filters is maximized at a channel spacing-to- bandwidth ratio of 3.3, and this throughput is 31 Gbit/s when the total system bandwidth is 4.4 THz (35 nm).
Design and investigation of an all-optical WDM ring-network
Author(s):
Doutje T. van Veen;
Erwin Rikkers;
Federiko N. Krommendijk;
B. H. Sikken;
G. J. M. Krijnen;
P. W. C. Linders;
A. F. Bakker;
J. L. Joppe;
Mart B. J. Diemeer;
Alfred Driessen;
Antonius M. J. Koonen;
Meint K. Smit
Show Abstract
This paper describes the implementation and investigation of an all-optical amplified ring network with Phased Array based optical add/drop multiplexers (OADMs). From crosstalk analysis follows that an OADM with a foldback-structure and 1 X 2-switches has an outstanding crosstalk performance. From the investigation of the dynamic behavior of Erbium doped fiber amplifiers (EDFAs) in a ring configuration we found that EDFAs in a ring-configuration require a faster gain-control when compared to a cascade-configuration.
High-performance optical amplifier for WDM communication systems
Author(s):
Martin Rochette;
Martin Guy;
Jocelyn Lauzon;
Sophie LaRochelle;
Francois Trepanier
Show Abstract
Gain equalization of an EDFA is performed by introducing spectrally designed all-fiber filters in the mid-stage of a dual-stage fiber amplifier. Two types of filters are studied: a cascade of narrow-band Bragg gratings for discrete equalization of a finite number of channels and a wide-band Bragg grating performing equalization over the whole 1539 nm to 1557 nm range. In future work, it is planned to use the discrete Bragg grating configuration to simultaneously perform Dispersion compensation (D), Equalization (E) and Stabilization of gain (S) and Channel dropping (C) in a dual-stage EDFA. Integration of these functions will result in a high performance amplifier called the DESC-EDFA.
Performance analysis of multichannel coherent optical CPFSK system in the presence of fiber chromatic dispersion
Author(s):
Mohammed Nazrul Islam;
Masaaki M. Imai
Show Abstract
The effect of fiber chromatic dispersion on the performance of a multichannel optical coherent CPFSK system is analyzed including also the effects of shot and thermal noises and crosstalk interference. The sensitivity penalty is found to increase due to waveform distortion caused by chromatic dispersion. The channel frequency separation is, therefore, required to increase to overcome the dispersion effect. The channel spacing requirements become worse with increase in intermediate frequency (IF) and IF bandwidth.
Application of variable length spreading sequence in fiber-optic WDMA/CDMA networks
Author(s):
Che-Li Lin;
Yang-Han Lee;
Jingshown Wu
Show Abstract
A novel and simple design of all-optical encoder/decoder utilizing variable length orthogonal spreading sequences is proposed. The proposed encoder/decoder is applicable to fiber-optic WDMA/CDMA networks which combine wavelength division multiple access (WDMA) and code division multiple access (CDMA) techniques to provide large system capacity. Because when traffic is light, the subscriber can shorten the spreading sequence, and the utilization of network can be further increased.
Wavelength-division-multiplexed (WDM) data-block switching for parallel computing and interconnects
Author(s):
Jem Yu Fan;
Xiangjun Zhao;
Jun Ping Zhang;
Fow-Sen Choa;
Yanjie Chai;
Jye-Hong Chen;
E. Miller;
Howard E. Motteler;
Pao-Lo Liu;
Tawee Tanbun-Ek;
Patrick W. Wisk;
Won-Tien Tsang;
George J. Zydzik;
Charles A. Burrus
Show Abstract
We report a new generation switch, the data-block switch, which can greatly increase the capacity and reduce the complexity of the interconnect network of a parallel computing system. By using WDM techniques, parallel data can be multiplexed and transmitted through a single fiber. By using photonic switching techniques, we can switch a block of parallel data in one switch operation to any site desired. In this work, we demonstrate such an operation with our fabricated 1 X 2 semiconductor optical amplifier (SOA) switch. This integrated device is an active/passive Y- junction waveguide device with a passive waveguide region in the middle and 3 active waveguide regions at each end. The amplified spontaneous emission spectrum of the SOA shows that this broadband switch can easily cover a wavelength range of more than 64 ITU wavelength grids (100 GHz). The switch operation of multiple wavelengths and the switching speed of the device were studied. A switching time of around 400 ps was achieved.
Numerical simulation models of soliton systems
Author(s):
Tony T. Yuk;
Siu Fung Yu;
Po Ching Chui;
Ping Shum
Show Abstract
This paper describes the development of numerical simulation models of soliton systems using a newly developed Fourier Series Analysis Technique to analyze the nonlinear Schrodinger equation of soliton propagation. Generation of sub-picosecond solitons in an active mode-locked fiber ring laser with amplitude and phase modulators and soliton pulse compression mechanisms using dispersion decreasing fiber are investigated.
Light emission in silicon nanostructures
Author(s):
David J. Lockwood
Show Abstract
Interest in obtaining useful light emission from silicon- based materials has never been greater. This is because there is a strong demand for optoelectronic devices based on silicon and also because there has recently been significant progress in materials engineering methods. Here we review the latest developments in this work, which is aimed at overcoming the indirect band gap limitations in light emission from silicon. One promising new approach, based on thin-layer Si/SiO2 superlattices, is reviewed in detail. The incorporation of these different materials into devices is described and future device prospects are assessed.
Optical characterization of light-emitting porous silicon covered by transparent a-C:H coating
Author(s):
Alexander Dorofeev;
Franco Gaspari;
Dammika Manage;
Emmanuel Sagnes;
Tome Kosteski;
Stefan Zukotynski
Show Abstract
Porous silicon (PS) is a promising but rather unstable photonic material. Plasma deposition of a protective amorphous hydrogenated carbon (a-C:H) coating was used to improve the stability of porous silicon's compositional and optical properties. a-C:H films, 0.2 - 0.5 micrometers thickness, were deposited on porous silicon at room temperature from a methane plasma generated in a five-electrode saddle-field glow-discharge chamber. Plasma-deposited films exhibited good adhesion, nano-scale smoothness, and excellent mechanical integrity. Photoluminescence, UV/VIS reflectance, SEM, and FTIR adsorption spectra of a-C:H/PS structures were measured. The a-C:H films were over 80% transparent in the 0.5 - 5 micrometers range and enhanced the stability of the luminescence of the light-emitting PS.
Optical and structural characterization of nc-Si/a-SiO2 superlattices
Author(s):
G. Grom;
Leonid Tsybeskov;
Karl D. Hirschman;
Philippe M. Fauchet;
Mario Zacharias;
Thomas N. Blanton;
John P. McCaffrey;
Jean-Marc Baribeau;
G. I. Sproule;
H. J. Labbe;
David J. Lockwood
Show Abstract
Nanocrystalline (nc)-Si/amorphous (a)-SiO2 superlattices (SLs) have been studied by transmission electron microscopy, Auger elemental microanalysis (AEM), Raman spectroscopy and optical reflection spectroscopy. Recrystallized Si/SiO2 SL is extremely stable under high temperature annealing (up to 1100 degree(s)C) and aggressive wet thermal oxidation: AEM and Raman spectroscopy of folded acoustic phonons show no changes in periodicity in the growth direction and the abruptness of the nc-Si/a-SiO2 interfaces. Furthermore, Raman spectroscopy in the optical phonon range indicates that the annealing decreases the defect density in the Si nanocrystals, possibly due to Si-Si bond rearrangement accompanied by surface reconstruction and surface defect passivation by oxygen.
Optimization of reflectivity, rise time and fidelity of a self-pumped phase conjugate BaTiO3:Rh ring mirror at 1.06 um
Author(s):
Nicolas Huot;
Jean-Michel C. Jonathan;
Gilles Pauliat;
Daniel Rytz;
Gerald Roosen
Show Abstract
It is now well known that rhodium doped barium titanate (BaTiO3:Rh) exhibits a significant photorefractive response at near infrared wavelengths .We studied and characterized this crystal at 1 .06 jtm by two-wave mixing experiments. In a 45°-cut crystal with a low absorption (0.1 cm1), we measured a photorefractive gain F of 23 cm1 with cw illumination and 16.6 cm1 with nanosecond illumination. Using spectroscopic determinations of the photorefractive sites 2(Rh3+, Rh4+, RhS+), we demonstrated that the photorefractive properties of BaTiO3:Rh are well described by a three charge state model '. Internal parameters of the material were derived using these experimental characterizations which allowed to accurately predict its performances at 1 .06 tm. Comparative characterizations of several BaTiO3 :Rh samples proved that this material is now well reproducible. Reproducibility, high photorefractive gain, low absorption and accurate theoretical description make BaTiO3:Rh a good candidate for realization and optimization of non linear functions like optical phase conjugation. The application we are interested in, is the dynamic wavefront correction of nanosecond Nd:YAG master-oscillator power amplifier (MOPA) laser sources. We implemented a ring self-pumped phase conjugate mirror using a BaTiO3:Rh crystal . This geometry brings several advantages. The threshold in terms of "gain X interaction length" product, is low (F1=2) 6 This phase conjugate mirror does not require a source of long coherence length 7and the gratings involved in the four wave mixing process can be well controled. Moreover the phase conjugate beam can be efficiently selected among the backscattered light by inserting optical elements in the ring 8,9• Such a self-pumped mirror is self-starting and the four-wave mixing process is initiated by the beam-fanning. To avoid spurious internal oscillations in total reflection on the crystal faces that initially developed in several of our experiments and prevented phase conjugation we optimized the geometry of the crystal. Roof-cut, 45° orientation of the c axis and antireflection coatings of the crystal suppressed these internal oscillations and efficient phase conjugation was demonstrated.
Pockels and Kerr cells fabricated with thin organic crystal films
Author(s):
Javier Wu;
Yulong Cui;
Alexander Leyderman
Show Abstract
Pockels and Kerr cells were fabricated by growing N-(4- nitrophenyl)-L-prolinol crystal films between two transparent fused quartz plates on which indium-tin-oxide layers were deposited. Both linear and quadratic electro- optic effects of the crystals with thickness of 5 and 10 micrometers were examined by an ac modulation method. Large modulation signals were observed with a low driving voltage, the figure of merit of the electro-optic phase retardation were estimated to be 8.0 X 10-11 m/V. It is suggested that the electro-optic cells are promising for application because of their durability, relative easy manipulation during crystal growth and high figure of merit.
Azo-dye-doped cellulose acetate for optical data storage and processing
Author(s):
Rouslan Birabassov;
Tigran V. Galstian;
F. Dechamplain;
Anna-Marie R. Ritcey
Show Abstract
Dynamic holography and cross modulation techniques are used to study a new photosensitive polymeric material, cellulose acetate doped with the azo-dye DR1. This allowed the identification of the principal photophysical mechanisms involved in the resonant photoexcitation processes. Angular hole burning and reorientation mechanisms are used to write intensity and polarization holograms of comparable diffraction efficiency. Application of the material for the creation of polarization manipulation holographic elements is demonstrated.
Photofabrication of multiple beam splitters in a self-developing polymer system
Author(s):
Rene M. Beaulieu;
Roger A. Lessard;
Michel Bolte;
Tigran V. Galstian
Show Abstract
Diffraction properties of phase relief gratings which can be photofabricated in dichromated poly(acrylic acid) films have been analyzed. The formation of these gratings which produce multiple diffracted waves takes place in darkness subsequent to the holographic illumination at a wavelength of 442 nm. The holographic surface relief gratings are obtained by self-development and without any chemical treatment or wet processing. Theoretical calculations of diffraction efficiencies and experimental results at a wavelength of 543.5 nm for a seven beam splitter are presented.
New PVK-based photorefractive polymers
Author(s):
Ryszard Burzynski;
Saswati Ghosal;
Martin K. Casstevens;
Deepak N. Kumar;
John F. Weibel
Show Abstract
This work describes the development, characterization and optimization of materials for optical memory storage applications. The photorefractive polymers are designed to contain second-order nonlinear optical (NLO) chromophores and charge transporting (CT) molecules embedded in a polymer matrix. The necessary electrooptic response is achieved by subjecting samples to a strong dc electric fields in order to induce a non-centrosymmetric arrangement of the NLO chromophores. This paper presents work performed on the design of a new multifunctional NLO-CT polymer.
Self-focusing and soliton propagation of light pulses in photorefractive media
Author(s):
Delphine Wolfersberger;
Nicolas Fressengeas;
Jean Maufoy;
Godefroy Kugel
Show Abstract
The paper presents a theoretical and experimental investigation of the self-focusing of a laser pulse in a photorefractive medium on a nanosecond time-scale. For times shorter than the dielectric recombination time, we analyze the space-charge field build-up with time and space and provide strong hints on the short time self-focusing of a narrow powerful beam. In order to validate our theoretical and numerical analysis, systematic investigations were performed on a Bi12TiO20 crystal, which show that under the influence of an applied electric field, a beam can be self-focused in a very short time.
Rare earth doped tellurite glasses
Author(s):
S. Q. Man;
H. W. Liu;
Edwin Y. B. Pun;
Po Sheun Chung
Show Abstract
Glasses based on TeO2-BaO-MgO-ZnO-Na2O have been made successfully. The Raman scattering and the transmission properties were measured, and the photoluminescence properties of Pr3+ doped tellurite glasses were studied. Tellurite glasses exhibit an IR transmission cut- off beyond approximately 6 micrometers . The maximum-phonon band is at 745 cm-1. The emission from the Pr3+:1G4 yields 3H5 transition is at 1.295 micrometers wavelength with a spectral bandwidth of 30 nm. Pr3+ doped tellurite glasses appear to be a promising candidate for waveguide amplifiers in the 1.3 micrometers telecommunication window.
Interaction of 10 fs to 15 ns KrF laser pulses with metals
Author(s):
Ying Y. Tsui;
Robert Fedosejevs;
Clarence E. Capjack
Show Abstract
Numerical studies of the interaction of KrF laser pulses with pulselengths ranging from 10 fs to 15 ns with aluminum have been carried out at intensities around the threshold for damage. These results are compared with experimental measurements of interactions with pulse lengths of picosecond to nanosecond duration. The calculated damage thresholds and ablation depths agree reasonably well with those from experiments. For a material irradiated by femtosecond and picosecond pulses the damage threshold is sensitive to the material's electron-phonon coupling constant. The value of electron-phonon coupling constant which gives good agreement is close to that calculated based on free electron theory.
Laser formation of titanium nitride films as a result of Ti coating modification in a nitrogen atmosphere
Author(s):
Sergei Eskin
Show Abstract
Laser treatment of the 303 and 416 stainless steels with Ti precoating was studied. CW CO2 and UV ArF excimer lasers were used. The TiN films were formed at a treatment velocity of 0.5 to 3 - 5 cm/sec and a power density of CO2 laser at (3 - 5) 104 W/cm2. X-ray diffractometry, x-ray mapping and Auger electron spectroscopy techniques indicated a TiN phase on the surface with oxygen content 12 - 25 at%. The thickness of the TiN film was 0.3 - 0.4 micrometers after treatment of the 5 micrometers Ti coating and about 900 angstroms for the 0.3 micrometers coating. Some characteristics of TiN films were examined and features of the nitriding process are discussed.
Modulation of the nonlinear optical response by KNbO3 thin films deposited on a KTaO3 substrate
Author(s):
Huimin Liu;
Weiyi Jia;
Yanyung Wang;
Y. Fu;
Lynn A. Boatner
Show Abstract
Fluorescence and time-resolved degenerate-four-wave-mixing (DFWM) techniques have been used to characterize the optical properties of KNbO3/KTaO3 superlattice grown by pulsed laser deposition on a KTaO3 substrate. The superlattice consisted of 8 layers with thicknesses of 40 nm (KTaO3) and 30 nm (KNbO3). In the fluorescence measurement a significant change of emission profile with the KNbO3 thin films deposited on the substrate has been observed. In DFWM measurements the time-resolved spectrum is characterized by a sharp coherent response signal peaked at the time of zero delay followed by a build-up of a longer- lived signal. The third-order susceptibility (chi) (3) was estimated to be dramatically increased by 2 orders of magnitude.
Crosslinkable polyimides for electrooptic applications
Author(s):
Ryszard Burzynski;
Saswati Ghosal;
John F. Weibel;
Paul M. Kurtz;
Martin K. Casstevens
Show Abstract
The development of second order nonlinear optical (NLO) polymers involves several important steps. The first step is the design, synthesis and characterization of second-order NLO chromophores followed by the identification of a suitable polymer matrix into which the chromophore can be incorporated either as a guest, as a side-chain or a main- chain group. Thin films of candidate polymers are then fabricated and studied by a number of spectroscopic and thermal analyses techniques in order to characterize their NLO properties such as EO coefficient (or (chi) (2)), optical losses, and temporal stabilities of poling-induced chromophore alignment. This work describes the development, characterization and optimization of materials for second- order nonlinear optical applications. The second-order nonlinear optical materials are designed to possess large second-order nonlinearity by embedding 2nd order NLO active chromophores in high glass transition temperature polyimide structures.
Photorefractive grating formation with very short pulses: the bulk photovoltaic effect
Author(s):
Hideki Okamura;
Kazuo Takeuchi
Show Abstract
We investigated the role of the photovoltaic effect on the photorefractive grating formation under illumination of weak ultrashort light pulses whose duration is much shorter than the time constants of the carrier and compared it with the cw case. In our experiments using mode-locked picosecond and cw Nd:YAG lasers, the bulk photovoltaic current in an iron- doped lithium niobate crystal were confirmed to be in the same order of magnitude for both light sources. The evolution of photorefractive gratings was also essentially the same. The Glass expression for the bulk photovoltaic effect is not compatible with the scheme of the band transport model for a very fast response. Therefore we developed a model in which the bulk photovoltaic current was implemented as a spatial shift in the initial carrier distribution. The resultant expression agreed with that of the quasi-cw approximation in the limit of a small spatial shift.
Effective stimulated emission and excited-state absorption cross-section spectra of luminescent polymers
Author(s):
Alfons Penzkofer;
Wolfgang Holzer;
S.-H. Gong;
Donal D. C. Bradley;
Xiao Long;
Andreas Bleyer;
Werner J. Blau;
A. P. Davey
Show Abstract
The effective stimulated emission cross-section spectra of a para-phenylene-vinylene polymer and of two paraphenylene- ethynylene polymers are determined by a fluorescence amplification technique. For these luminescent polymers laser action has been achieved in solution. The effective stimulated emission cross-section spectra are found to be small compared to the stimulated emission cross-section spectra calculated from fluorescence quantum distribution and fluorescence lifetime measurements. The laser excitation of the polymer solutions seems to form lattice relaxed exciton conformations extending over a few monomer units which are thought to be responsible for upper-to-lower-state stimulated emission and lower-to-upper-state (excited-state) absorption.
Suitability of AlAs/GaAs (001) superlattices for photonic applications
Author(s):
Nacir Tit
Show Abstract
The effects of (Gamma) X-valley mixing in (AlAs)n(GaAs)n (001) superlattices (SLs) on the electronic and optical properties are theoretically investigated versus the SL period (n equals 1.25) and the band offsets. The calculations are based on both the empirical sp3s* tight-binding model and the surface Green-function-matching method. The results show that the top state of the valence band is always confined to the GaAs slabs, whereas the bottom state of the conduction band (CB) shows different behaviors as it is sensitive to band mixing and, therefore, can control the optical properties of the superlattice. For large values of n (n >= 9) the SL is found to have a direct bandgap at (Gamma) -point and, thus, forms of type-I heterostructure consisting of multiple quantum wells. Whereas for the ultrathin-layer SLs (n <EQ 8), the interaction between the wells becomes considerable and band mixing effects are important. The X-valley, attributed to the AlAs slabs, becomes the lowest state in the CB and therefore the SL forms a type-II heterostructure with an indirect bandgap. These valley-mixing effects are shown to be efficient only for small conduction band offsets (CBO <EQ 190 meV). As the SL bandgap energy varies from 2.1 to 1.6 eV when n changes from 1 to 25 respectively, and these former values do, indeed, lie within the energy spectrum of the visible light, we concluded that the studied SLs are suitable for photonic device applications when the layer thicknesses are LGaAs >= LAlAs >= 26 angstroms.
Chemically sensitive surface plasmon devices employing a self-assembled monolayer composite film
Author(s):
J. C. DePriest;
Fabrice Meriaudeau;
Patrick Ian Oden;
Todd R. Downey;
A. Passian;
A. G. Wig;
Trinidad L. Ferrell
Show Abstract
In this paper the results of detecting volatile organic compounds (VOC) employing surface plasmon-based sensors are presented. The initial step in preparing the sensing elements herein requires depositing Au degree(s) on a quartz slide. The sensing elements are based on either (1) freshly deposited Au degree(s) or (2) growth of a self assembled monolayer composite film (SAM) on to a freshly deposited Au degree(s) surface. The desired SAM is either (1) acid terminated using (omega) -mercaptoundecanoic acid (MUA-COOH) or (2) Cu2+ metal ion terminated yielding (omega) - mercaptoundecanoic acid-Cu2+ (MUA-Cu2+). The experimental apparatus shown here measures the reflectivity of the Au degree(s) surface as a function of time at a given angle. The response of this surface plasmon device to various VOC's is correlated to the composition of the SAM film.
Dynamic and polychromatic SPR-leaky mode spectroscopy with Teflon AF films on silver for chemo-sensing
Author(s):
R. P. Podgorsek;
Hilmar Franke;
Serge Caron;
Pierre Galarneau
Show Abstract
The reflectivity of a polymer film on top of a thin metal layer is usually recorded for a fixed wavelength and the TM polarization as a function of the angle of incidence. This angular spectrum contains the surface plasmon resonance due to the metal layer and the leaky modes caused by the waveguide resonances of the polymer film. Here we investigated the reflectivity spectrum of such a multilayer for a white light source as a function of the wavelength at a constant angle of incidence. The leaky mode resonances on the wavelength scale have been detected. Dynamic measurements of the reflectivity of such a multilayer at constant angle and constant wavelength have been demonstrated for vapors of Toluene as an example. The realization of compact and simple devices using this technique is possible.
Gas concentration measurements with DFB lasers to monitor volcanic activity
Author(s):
Paolo De Natale;
Livio Gianfrani;
G. De Natale;
R. Cioni
Show Abstract
We report construction and operation of a multiplexed laser spectrometer, based on fiber coupled Distributed Feed-Back semiconductor diode lasers, for monitoring concentration of gases emitted from volcanoes. The main problems related to this particular application, as well as the way of operation of the apparatus are discussed. The first experimental data, recorded at the test site of Solfatara volcano, Naples, Italy are reported. To our knowledge, this is the first design of a small, low power consuming laser spectrometer for geochemical applications.
Theoretical assessment of optical reflectometry for film chemical-sensors
Author(s):
Augusto Garcia-Valenzuela;
J. M. Saniger-Blesa;
C. Garcia-Segundo
Show Abstract
We investigate theoretically the limits to the resolution imposed by the fundamental optical noises in film-based chemical sensors interrogated by optical reflectometry. We suggest a dynamic reflectometry approach as a possible technique to achieve the ultimate resolution. We find that a theoretical resolution around 1010 absorbed analyte molecules/cm2 is possible in different cases. In the case of conducting films appreciably lower values may be possible.
Wine spectrocolorimetry
Author(s):
Oliverio D.D. Soares;
Paulo Barros
Show Abstract
Spectrocolorimetry in wines is analyzed within the context of the CIE recommendations and applicable standards in measurements and quality control (ISO 9 000). A methodology is presented for wine color measurements with traceability to the spectrocolorimetric scale. The concept of uncertainty in color measurements is emphasized as necessary to the intercomparison of measurements performed by different operators, at different times, different locations and with diverse instruments so that color communication is possible without misunderstanding. The layout of a norm is described involving all phases from concept to details on sample preparation. Applications on color of wine measurements in Port Wine are presented for model validation and to show the possibility of the study of the effects on influential parameters such as temperature, pH, sugar contend and aging. Reference to the application of the procedure to the control of wine color in blends is also described.
Measuring Raman time constant (TR) for subpicosecond soliton pulses in standard single mode fiber
Author(s):
Ahmad K. Atieh;
Piotr Myslinski;
Jacek Chrostowski;
P. Galko
Show Abstract
The Raman time constant (TR) used in the generalized nonlinear Schrodinger equation is determined experimentally to be around 1550 nm, based on the Raman self-frequency shift in standard single mode fiber. The measured effective value of the TR is found to be 3.0 fs. Detailed error analysis shows that the uncertainty in the measurement is less than +/- 1.0 fs. Accurate knowledge of the value of the TR is essential in modeling subpicosecond pulse propagation in optical fibers.
New measurement technique of optical fiber nonlinearity using the first dip frequency of fiber transfer function
Author(s):
Jose A. P. Morgado;
Adolfo V. T. Cartaxo
Show Abstract
A new measurement technique of optical fiber nonlinearity coefficient is proposed. This technique is settled numerically utilizing the general small-signal analysis for nonlinear dispersive optical fiber. It is shown that for moderate power the first dip frequency of intensity modulation fiber transfer function scales linearly with optical power at the fiber input, and a linear scaling between the rate of dip frequency increase with the optical power and the fiber nonlinearity coefficient is observed. Using these properties, measurements of the frequency of the first dip at low and moderate optical power at the fiber input allow us to calculate the rate of dip frequency increase with the optical power and, from this, the fiber nonlinearity coefficient.
Spectrocolorimetric scale harmonization
Author(s):
Oliverio D.D. Soares;
Jose Luis C. Costa
Show Abstract
A three phase procedure is described for insuring spectrocolorimetric scale harmonization. The first phase includes the intercomparison of spectrophotometer scales of wavelength, spectral bandwidth and spectral transmittance (involving 23 laboratories). This comprehends a set of three neutral density glass filter standards and a crystal with sharp absorption bands as wavelength and spectral bandwidth standard. The second phase relates to the intercomparison of measuring procedures using product standards. The third phase addresses a real testing by the measurement of wine samples and intercomparison of results. The implementation of the procedure, results and conclusions will be described.
Experimental evaluation of the modulation transfer function of an infrared focal plane array using the Talbot effect
Author(s):
Nicolas Guerineau;
Jerome Primot;
Marcel Caes;
Michel Tauvy;
Joel Deschamps
Show Abstract
A test bench for measuring the Modulation Transfer Function of an InfraRed Focal Plane Array (IRFPA) is described. The system is based on the use of the self-imaging property of a periodic target made of thin slits for a direct projection of a high-resolution pattern directly on to the tested sensor. The test bench has furnished two different types of experimental results on a specific IRFPA. On one hand, a global method called Canted Periodic Target Test has been developed and applied leading to MTF evaluation up to five times the Nyquist frequency. On the other hand, a local line scanning of every pixel has been made.
Individual mode's bending loss measurement for multimode channel waveguides using phase modulator and prism-coupler
Author(s):
Ching-Ting M. Lee
Show Abstract
We present a method which applies a combination of the phase modulator, butt-couple and prism coupler to the measurement of individual mode's bending loss in multimode waveguides. By tuning the effective length of a channel waveguide with a phase modulator, the contrast in the transmitted intensity of Fabry-Perot resonance for individual guided mode separated by a prism coupler can be measured. The associated bending loss is obtained from these experimental results.
Experimental investigations of wavelength and angular errors in holographic gratings
Author(s):
Monish R. Chatterjee;
Vivek Ray
Show Abstract
Perfect Bragg matching is generally desirable for accurate optical interconnections with holographic gratings. In reality, however, gratings may be illuminated by READ beams with non-Bragg-matched angles, or wavelengths, or both. In such cases, the scattered beams are generally misdirected, and may suffer loss of efficiency and possibly more serious errors such as crosstalk noise or missed connections. A conventional wavevector triad method of analyzing the scattered beam errors leads readily to near-Bragg estimates of the output angular misalignment. However, the READ wavevector triads appear to indicate a possible wavelength shift in the output beam even with a Bragg-matched READ wavelength, which is counter-intuitive. This paper presents some of the theoretical findings for output beam characteristics under READ misalignments, and the results of a series of experiments aimed at verifying both the output angular error as well as whether or not any unexpected wavelength shift occurs in the output beam. Based on the experimental findings, the interpretation of the misaligned READ wavevector triad is appropriately modified.
Whole film inspection using extended source
Author(s):
Arun A. Aiyer;
Henry K. Chau
Show Abstract
Traditionally in the semiconductor industry, thin film measurements are done by sampling a pre-determined number of points on the film. This is true whether the wafer is patterned or not. Point measurements do not provide correct information on trend in thickness variation across the wafer surface. Such information is quite effective while developing new coating, deposition, etching or polishing processes. Hence, a system that can map film thickness across the whole wafer or a large area of the wafer will be very useful to process developers. In this paper, we will discuss a technique that can map film thickness across a large area in a relatively short amount of time. The approach has been breadboarded and its applicability demonstrated. Using a single wavelength, this technique makes it possible to characterize film thickness without having to know optical constants of the substrate material.
Spectral bandwidth standard based on symmetrical absorption bands of a crystal standard
Author(s):
Oliverio D.D. Soares;
Jose Luis C. Costa
Show Abstract
A calibration procedure of spectral bandwidth of high- resolution spectrophotometers recurring to the symmetrical absorption bands of a crystal standard is described. The method involves spectral line shape fitting followed by convolution with the slit function of the spectrophotometer. A calibration curve on transmittance versus spectral bandwidth is provided for practical and accurate metrological verification of the actual spectral bandwidth of the spectrophotometer. Results will be provided on the testing of the method on an intercomparison of spectral bandwidth calibration involving twenty laboratories.
Multi-wavelength characterization of a traveling-wave photodetector including electrode effects
Author(s):
Pierre Berini
Show Abstract
A novel Schottky-contact traveling-wave photodetector has been rigorously characterized at two optical wavelengths using the Method of Lines. This method is an accurate numerical technique used to model the electromagnetic performance of optical and microwave devices. Attention has been paid to the proper modeling of the nearby overlying electrode in order to determine its influence on the optical performance of the photodetector. It has been found that the electrode has an important impact, reducing power confinement in the active region of the device and increasing its polarization sensitivity. The wavelength dependency of these effects has been determined for the first time in such a device. The results illustrate the importance of rigorous modeling as an essential step in the design of high-speed optoelectronic components.
Remote optical sensor system for E-field measurements
Author(s):
Robert Heinzelmann;
Andreas Stoehr;
Thomas Alder;
D. Kalinowski;
Manuel Schmidt;
Matthias Gross;
Dieter Jaeger
Show Abstract
The concept of a remote optical sensor system for frequency selective electric field measurements will be presented. The system will be applicable to field measurement problems up to frequencies in the microwave regime. Additionally, it will provide minimum interference with the measured field, due to the optical fiber coupled sensor head. The electrooptic key components within the head of this sensor system are an array of photovoltaic cells and an electroabsorption waveguide modulator. Based on experimental results these components will be discussed and evaluated for the application within the sensor system. Furthermore, a novel fiber modulator coupling technique employing the monolithic integration of the device with InP V-grooves will be presented.
High-speed 12-layer two-dimensional bar-code detection system with wide-band photo-detection amplifier and balanced raster scanner
Author(s):
Hiroo Wakaumi;
Hiroshi Ajiki
Show Abstract
A high-speed 12-layer 2D bar-code detection system (BCDS) consisting of a photodetection amplifier with an amplification-type current-voltage converter and a balanced raster scanner combined with the complementary light emission drive method for laser diodes, has been developed in order to provide both a high effective scanning speed and multi-layer bar-code detection. This BCDS performs 1,250 scan/s, which is two and a half times the scanning speed of a conventional bar-code detection system. A new theoretical modulation model that gives an accurate model for laser scanning beam traces obtained by the balanced raster scanner is proposed. This model allows an optimum BCDS to be designed easily.
Extremely high resolution fiber temperature sensor
Author(s):
Shyh-Lin Tsao;
Bih-Chyun Yeh
Show Abstract
A novel medical temperature sensor using two fiber Bragg gratings is presented. The experimental results demonstrate this sensor can employ as high as 0.01 degree(s)C resolution. It is expected that with interpolation, this sensor can achieve the resolution as high as 0.001 degree(s)C.
Distributed temperature sensing using the Landau-Placzek ratio
Author(s):
Gareth P. Lees;
Peter C. Waite;
Trevor P. Newson
Show Abstract
We report a commercially viable high spatial resolution, long range optical fiber distributed temperature sensor based on Brillouin scattering exploiting a low cost detection system. A spatial resolution of 3.0 meters with a Brillouin temperature resolution of 0.9 degree(s)C at a range of 16 km has been achieved.
Cell effects on high resolution transmission spectroscopy
Author(s):
Oliverio D.D. Soares
Show Abstract
Liquids molecular transmission spectrophotometry has a broad area of applications including spectrophotometry. The measurement of the spectral transmission factor could require levels of accuracy in the order of 10-3 to 10-4. This implies the need for detailed analysis of the corrections to compensate measuring cell unpairing, differences in refractive index between reference liquid (water or solvent) and corresponding spectral non-flatness as well as the multiple inter-reflection at the various dielectric interfaces. Procedures for self-correction of optical measuring cells unpairing and compensation of further effects are presented.
Multiplexing of white-light and polarimetric fiber-optic sensors for application in engineering mechanics
Author(s):
Wojtek J. Bock;
Waclaw Urbanczyk;
Andrzej Barwicz
Show Abstract
We present an interferometric and a polarimetric fiber-optic sensor systems employing highly birefringent fibers for stress monitoring in civil engineering applications. Both systems are designed to be used with concrete-embeddable pressure cells optimized for stress measurement inside a concrete or soil medium. The concept of coherence multiplexing was applied in the interferometric system. Serial and serial-parallel configurations of this system were built and tested. In the serial configuration, four sensors were multiplexed, two for pressure and two for temperature measurement. In the serial-parallel configuration, eight sensors were multiplexed, four for pressure measurements and four for temperature measurements. In its present form, the polarimetric system employs a space-division multiplexing concept and it contains up to four pressure sensors. The overall accuracy of white-light and polarimetric systems, including temperature drift in a wide range of temperatures, is better than 1% at pressures up to 40 MPa.
Mode switching oscillation of an external cavity laser diode and its application to length measurement
Author(s):
Seiichi Kakuma;
Jun Hoshii;
Ryoji Ohba
Show Abstract
An external cavity laser diode system is proposed for a double mode light source, in which the oscillation mode can also alternately switch between TE- and TM-modes. An external cavity laser diode system is implemented to oscillate periodically switching between a TE- and a TM-mode in the identical frequency. The system is applied to length measurement. Accuracy of the measurement is quite excellent with the relative error of +/- 0.0100%, and proves that the present method is one of highly accurate practical non- contact length measuring means. In the present paper, we present both its principle and results of the experiments.
Principle and the application of an etched fiber-optic sensor
Author(s):
Yan Jiang;
Shuming Pang;
Yiping Cui
Show Abstract
In this work a kind of etched optical fiber sensors are introduced. By the method of combing thermal carving technique with chemical etching, some periodically etched sections were formed directly onto the fiber cladding and the structure to sense strain can be made into an inherent part of the fiber. The etched fiber sensing elements have been fabricated and tested as temperature and liquid level sensors to investigate the performance of this kind of sensors. The results of the experiments show that the designed sensors possess the linear and repeatable responses without any measurable hysteresis. The sensors, which are superior to other kinds of sensors, have the high sensitivity and is easy to integrate.
Optical measurements on overhead optical fiber cables for stresses and damage identification
Author(s):
Fabien L. Ravet;
Bernard Heens;
D. Daniaux;
Jean-Christophe Froidure;
Michel Blondel;
M. Dascotte;
P. Lots
Show Abstract
This paper concerns the characterization of various trunks of an OPGW based network. No strong fiber aging has been observed but combined OTDR and PMD measurements have pointed out strong cable clamping at suspension pylon. Large local losses have been measured at both 1.55 micrometers and 1.6 micrometers and stress induced birefringent behavior have been experienced. PMD temporal evolution has also been studied. A correlation between temperature variation and PMD evolution has been observed.
Toroidal surface profilometries through Ronchi deflectrometry: constancy under rotation of the sample
Author(s):
Josep Arasa;
Santiago Royo;
Carlos Pizarro
Show Abstract
Toroidal surface profilometries have been obtained using the well-known Ronchi deflectometry arrangement. From the intensity pattern formed when sampling the wavefront with a Ronchi ruling, the direction of the normal vectors to the toroidal surface at a set of positions is obtained, allowing the measurement of the radius of curvature along the surface's principal meridians. Results are presented for a toroidal surface with its principal meridian of minimum radius oriented at 0 degree(s), 30 degree(s), 60 degree(s) and 90 degree(s) from X axis, keeping the lines on the Ronchi ruling along X and Y axes. The results obtained at different orientations are highly coincident, showing the stability of deflectrometric measurements under rotation of the sample in the case the surface doesn't have rotational symmetry. Influence of little angular errors in the placement of the principal meridians on the quality of the measurements is also studied, yielding that if angular errors in the placement of the principal meridians are up to 5 degree(s), the error introduced is the 0.1% of the measured value.
Fiber ring laser gyroscope based on Er-doped fiber pumped at 1480 nm
Author(s):
J. Li;
Yee Loy Lam;
Yan Zhou
Show Abstract
We describe the experimental results of a fiber ring laser gyroscope based on erbium-doped fiber pumped with a semiconductor laser at 1480 nm. The gyroscope was constructed from a bidirectional lasing erbium-doped ring laser. Distinct response of the gyroscope to rotation was successfully demonstrated by the fiber ring laser gyroscope.
High-g accelerometer based on in-fiber Bragg grating: a novel detection scheme
Author(s):
S. Theriault;
Kenneth O. Hill;
Derwyn C. Johnson;
Jacques Albert;
Francois Bilodeau;
Guymont Drouin;
A. Beliveau
Show Abstract
A simple accelerometer detection technique based on the measurement of the optical convolution between two identical fiber Bragg gratings, one used as a reference and the other used as a sensor, is presented. Theoretical calculations on sensitivity and for different tolerances on linearity are considered for uniform and apodized gratings at different reflectivity levels. Experimental measurements made with a Hopkinson bar setup where one grating is used as an acceleration sensor are presented.
Wavelength measurement system for Bragg fiber optic sensors using a quantum well electroabsorption photodetector
Author(s):
Trenton G. Coroy;
Raymond M. Measures
Show Abstract
A wavelength measurement system based on a quantum well electroabsorption photodetector is demonstrated and used to monitor a Bragg fiber optic sensor. A bandwidth limited wavelength resolution of +/- 3.62 pm/(root)Hz was achieved, corresponding to a strain resolution of +/- 3.02 (mu) (epsilon) /(root)Hz for a 1553.5 nm BFOS. A total accessible wavelength range of 90 nm was demonstrated for the system, making the system well suited for wavelength multiplexing applications.
Ultrasonic probe using short in-fiber Bragg gratings
Author(s):
Norman E. Fisher;
David J. Webb;
Christopher N. Pannell;
David A. Jackson;
L. R. Gavrilov;
J. W. Hand;
Lin Zhang;
Ian Bennion
Show Abstract
We demonstrate that short in-fiber Bragg gratings (with a length less than the acoustic wavelength in fused quartz) coupled with an appropriate desensitization of the fiber, may be successfully used to measure MHz ultrasonic fields.
Moving object trajectory estimation using an optical Fourier processor
Author(s):
Pierre Mark Lane;
K. Steven Knudsen;
Michael Cada
Show Abstract
A vision system that estimates the trajectory (velocity and direction) of moving targets in a 2D field at video frame rates has been developed and constructed. The system uses an optical Fourier processor to calculate the frequency domain representation of moving objects from which their trajectory is estimated using conventional electronic processing techniques. In a series of experiments, target velocities were estimated to within 4 percent of their actual value and direction was estimated to within 3 degrees.
High precision remote sensing of microsphere distortion
Author(s):
Moses Fayngold
Show Abstract
A theoretical model is presented for detecting very small (less than size of an atom) distortions of a dielectric microsphere at distances beyond the resolution limit of an imaging optical system. The method described involves illumination of the object with the circularly polarized light and the ellipsometry of the backscattered light. Comparing the results for right and left polarizations of the incident light gives also information of the spatial attitude (orientation) of the deformed sphere.
Beacon produced by stimulated Brillouin-scattering effect in laser propagation in atmosphere
Author(s):
Xiaojun Du;
Yuezhu Wang;
Zuguang Ma
Show Abstract
The wavefront aberration of laser beam produced in the process of laser propagation in the atmosphere can be compensated with the stimulated Brillouin-scattering (SBS) effect. However, in case of an uncooperative extensive target, the beacon is remained as a problem. Based on the method of active beacon, and making use of threshold effect of SBS, we present a method to obtain a beacon of small area on an uncooperative target, and with it, the laser beam can be focused on the small area.
Development of a compact experimental apparatus for the evaluation of the effects of laser dazzling on second and third generation image intensifier tubes
Author(s):
Trevor R.K. Kraus;
Andre Cantin;
A. Fernet
Show Abstract
Recently low light level intensifier systems have come into widespread use by law enforcement agencies for drug and border control. At the same time that image tube technology has advanced, laser technology has seen similar improvements. As a result, due to the potentially damaging effects that lasers have on image intensifier (I2) tubes an evaluation procedure and test equipment needed to be developed in order to characterize the laser-to-I2 interaction. The evaluation test apparatus developed in- house allows complete independent control on the four critical variables: background intensity, laser intensity/power, lasing angle of incidence, and target spatial frequency content. The uniqueness of the developed apparatus is that it is able to quantify the dazzling effects, both quantitatively and qualitatively. The apparatus was primarily designed to evaluate I2 tube performance in the presence of a laser source by analyzing the loss of resolution by contrast reduction and image degradation of the image tube's output image. This document presents the compact experimental apparatus developed in- house necessary to study the effects of laser dazzling on second and third generation I2 tubes.
Status of the development of the miniaturized digital high angular resolution laser irradiation detectors (HARLIDtm) technology
Author(s):
Andre Cantin;
G. Pelletier;
Paul P. Webb;
M. Cordray;
Daniel Pomerleau;
Jack H. Parker Jr.;
Mark L. DeLong;
S. A. Milligan
Show Abstract
Miniaturized digital HARLID modules integrating linear silicon and indium gallium arsenide arrays have been developed by the Defence Research Establishment Valcartier in collaboration with EG&G Optoelectronics Canada. These modules are designed to locate a laser source within +/- 1 degree(s) over a 90 degree(s) field of view either in azimuth or elevation. The principle of operation of these modules is based on the use of a Gray code mask to encode the angle of arrival of a laser beam. The performance of the 1-band HARLID has been recently investigated by the Laser Sensor Technology Laboratory, Wright-Patterson AFB, Dayton OH. The performance of a Laser Warning Receiver (LWR) integrating two 1-band modules has been successfully demonstrated in the laboratory and in the field. More recently the performance of this LWR has been evaluated at White Sands NM in desert conditions. Two-band HARLID modules have been recently fabricated by EG&G that makes use of a sandwich of Si and InGaAs detector arrays. The use of this configuration extends the spectral band from 400 to 1700 nm. Their E-O performance has been measured in the laboratory. The integration of HARLID modules with other sensors and through a Defensive Aids Suite is underway. Future plans of HARLID development have been established to enhance their E-O performance.
Parameter estimation of clutter pdf models
Author(s):
George A. Lampropoulos;
George Gigli;
Anastasios Drosopoulos
Show Abstract
In this paper we present a method to obtain a maximum likelihood estimation of the parameters of the Generalized Gamma and K probability density functions. Explicit closed form expressions are derived between the model parameters and the experimental data. Due to their nonlinear nature global optimization techniques are used for solving the derive expressions with respect to clutter model parameters. Experimental results show in all attempted cases that the resulting expressions are convex functions of the parameters. In addition to the maximum likelihood solution we present two other solutions. One is based on moment and the other on histogram matching.
Model based calculation on the dynamic point spread function of a radiometer: a case study ScaRaB FM1
Author(s):
Steven Dewitte;
Piet Boekaerts;
Jan P.H. Cornelis
Show Abstract
For the correct quantitative usage of a remote sensing imaging instrument, a complete characterization of the instrument is necessary. Besides the standardly used calibration factor and spectral sensitivity curve, one also needs the knowledge of the function which describes the spatial sensitivity of the instrument: the Point Spread Function (PSF). Ideally this function should be measured prior to launch. Alternatively, a model based approximation for the PSF can be calculated. This is illustrated for the Scanning Radiometer for radiation Budget studies (ScaRaB) instrument broadband channels.
Comparison of probability statistics for automated ship detection in SAR imagery
Author(s):
Michael D. Henschel;
Maria T. Rey;
J. W. M. Campbell;
D. Petrovic
Show Abstract
This paper discuses the initial results of a recent operational trial of the Ocean Monitoring Workstation's (OMW) ship detection algorithm which is essentially a Constant False Alarm Rate filter applied to Synthetic Aperture Radar data. The choice of probability distribution and methodologies for calculating scene specific statistics are discussed in some detail. An empirical basis for the choice of probability distribution used is discussed. We compare the results using a l-look, k-distribution function with various parameter choices and methods of estimation. As a special case of sea clutter statistics the application of a (chi) 2-distribution is also discussed. Comparisons are made with reference to RADARSAT data collected during the Maritime Command Operation Training exercise conducted in Atlantic Canadian Waters in June 1998. Reference is also made to previously collected statistics. The OMW is a commercial software suite that provides modules for automated vessel detection, oil spill monitoring, and environmental monitoring. This work has been undertaken to fine tune the OMW algorithm's, with special emphasis on the false alarm rate of each algorithm.
R&D activities in airborne SAR image processing/analysis at Lockheed Martin Canada
Author(s):
Langis Gagnon;
H. Oppenheim;
Pierre Valin
Show Abstract
We give an overview of some R&D projects in SAR imagery at Lockheed Martin Canada. These projects are motivated by airborne surveillance applications such as the landmass and coastal surveillance missions of the Canadian CP-140 (Aurora) aircraft. The activities reviewed here are: (1) R&D supports to CP-140 Spotlight SAR upgrade, (2) fast multiresolution prescreening filter for CFAR detection, (3) comparison of traditional and wavelet-based speckle filters and (4) high-level ship classification in high-resolution SAR imagery.
Multiple layer reflectance and spectroscopic calibration for remote sensing spectral imagers
Author(s):
William F. Seng;
Bruce Rafert;
Leonard John Otten III;
Andrew D. Meigs
Show Abstract
UV-VIS-NIR ratiometric reflectance data was obtained for several commonly utilized remote sensing calibration standards used in Fourier Transform Hyperspectral Imaging. We found that single layer reflectance depends on the degree of translucency and hence on the particular choice of background material, from which multiple layer reflectance and extracted absorption and scattering curves logically follow. These data are given as a function of incident wavelength for each calibration standard. Because optical properties are determined by the combination of scattering and absorption, we deconvolved their effects on each material's spectrum.
New adaptive coherent CFAR wavelet detector
Author(s):
George A. Lampropoulos;
George Gigli;
A. Damini;
Maria T. Rey
Show Abstract
The objective of this paper is to present a new coherent adaptive Constant False Alarm Rate (CFAR) wavelet detector which can be used as an additional independent detector for effective CFAR detection of point targets. It is shown through examples that this detector may provide a reliable estimate of the clutter mean which in turn is used, when multiplied by a constant, to determine the CFAR detector cutoff point for the target detection process. The detector is coherent and furthermore, the real and imaginary parts of the clutter and target are processed independently and their results are combined. As shown through an experimental example, coherent detectors offer better performance over amplitude detectors at high Signal to Noise Ratios (SNRs). At low SNRs their performance approximates that of amplitude detectors due to the fact that phase information is very sensitive to noise at low SNRs and its contribution becomes insignificant.
Estimation of optimal error diffusion for computer-generated holograms
Author(s):
Ken-ichi Tanaka;
Teruo Shimomura
Show Abstract
The computer-generated hologram (CGH) is made because of 3D image reconstruction, the pattern recognition and so on. In the synthesis of CGH, quantization causes the adverse effect on image quality. This paper describes the selection of diffusion coefficient about the error diffusion method to reduce a bad influence in quantization. SA is applied to search for diffusion coefficient with the best image quality of the reconstructed image. In this simulation, diffusion coefficient obtained by the search with SA reduces MSE in the reconstructed image to 34% compared with it obtained by a stochastic analysis. The search for diffusion coefficient with SA is effective to obtain the reconstructed image of high image quality.
Lossless multiresolution uniform representation of remote sensing satellite data on a sphere
Author(s):
Steven Dewitte;
Dominique A.H. Crommelynck;
Jan P.H. Cornelis
Show Abstract
Remote sensing data are collected by different instruments with different time and space sampling characteristics, producing a large amount of data. For easy treatment, a compact representation over multi-resolution grids is needed. Multi-resolution spherical grids exist and wavelet transforms have been defined over those grids. As an extension of the lossless wavelet transform for cartesian images defined, a lossless wavelet transform for spherically sampled data is presented.
Automatic recognition of targets from hyperspectra images
Author(s):
George A. Lampropoulos;
Yifeng Li;
James F. Boulter
Show Abstract
In this paper, we present the formulation of the problem for recognition of targets from hyperspectra images. It is shown that conventional recognition techniques may be extended to hyperspectra images for the distribution process. It is also shown that the recognition process is directly proportional to the number of multispectra frames that represent each target. For the discrimination process we propose a parametric and a nonparametric process in which both are extensions to Fisher and Fukunaga-Mantock methods respectively. Examples that show the composition of hyperspectra features are presented.
Red AlGaInP-lasers: tunable and powerful
Author(s):
Heinz Schweizer;
N. Lichtenstein;
H. P. Gauggel;
Justus Kuhn;
R. Hofmann;
R. Winterhoff;
Christian Geng;
A. Mortiz;
Andreas Hangleiter;
Ferdinand Scholz
Show Abstract
In this article fabrication techniques and the analysis of AlGaInP semiconductor lasers for single mode emission and high power emission will be reported. Special emphasis will be spent on the appropriate vertical and longitudinal device structures. Furthermore we discuss low damage dry etching and epitaxial regrowth of DFB laser structures. The devices investigated are DBR- DFB- and MOPA-lasers.
Photo-degradation in II-VI heterostructures using n-i-n photoconductors
Author(s):
Alexander N. Cartwright;
Sundari Nagarathnam;
E. H. Lee;
H. Luo
Show Abstract
In this work, photo-degradation in ZnSe/Zn0.67Cd0.33Se multiple quantum well (MQW) structures was studied using photoluminescence of undoped structures and photocurrent of n-i-n photoconductors. The photoluminescence measurements were performed with respect to sample temperature, pump power and pump wavelength. The dependence of the measured photo-degradation from optical pumping on each of these parameters was quantified. To further understand this problem, n-i-n photoconductors were fabricated from these materials. Using these photoconductors, the formation of non-radiative recombination sites was monitored using standard photocurrent experiments. Moreover, the photocurrent generated was investigated as a function of applied voltage and excitation wavelength. The magnitude of the photocurrent decayed in a similar fashion to the photoluminescence measurements. Furthermore, n-i-n photoconductors fabricated from bulk material, as opposed to MQW structures, showed no evidence of photo-degradation. This implies that the photo- degradation is due to the interaction of the two constituent material systems.
Carrier dynamics in InGaAsP MQW laser structures
Author(s):
C. Rejeb;
Romain Maciejko;
D. Morris;
Toshihiko Makino
Show Abstract
We investigate vertical carrier transport, carrier relaxation and capture in three In1-xGaxAsyP1-y multiple-quantum-well lasers structures emitting at 1.3 and 1.55 micrometers at room temperature using time resolved photoluminescence. In the initial regime following the excitation, high effective carrier temperatures Tc different from the lattice temperature TL equals 77 K are reported. A significant signature of transport and capture is observed with characteristic times of approximately 10 ps and approximately 12 ps respectively.
Adaptive wavelength hopping in compound-cavity laser diodes
Author(s):
Yun Liu;
Peter Davis
Show Abstract
An experimental system is proposed for a compound-cavity laser diode which can adaptively select a dominant lasing mode. Chaotic mode-hoppings and multistability of dominant mode are verified in the system. An chaotic search algorithm is used to adaptively select a dominant lasing mode by switching a control parameter between multistability and chaotic mode-hopping states. Chaotic dynamics of mode- hoppings are also analyzed in both experiments and numerical simulations and the results show that the distribution of dominant mode residence time differs significantly from that of noise-induced mode-hoppings.
Multiple-quantum-well laser simulation: a comparison between the Monte Carlo method and the drift-diffusion approximation
Author(s):
A. D. Gueclue;
Romain Maciejko;
Alain Champagne;
M. Abou-Khalil;
Toshihiko Makino
Show Abstract
A self-consistent ensemble Monte Carlo calculation of steady state carrier distribution functions in InGaAsP-based multiple-quantum-well lasers is performed. The results are compared to those obtained with a drift-diffusion classical simulator. The outcome of the two methods is found to be similar. Still, the Monte Carlo approach offers much more insight into several issues such as the energy distribution of carriers and the effects of particle-particle interactions.
New design of four-pass dye laser amplifier and suppression of amplified spontaneous emission
Author(s):
Jae Won Hahn;
Yong Shim Yoo;
Eun Seong Lee
Show Abstract
We have demonstrated a new design of a four-pass dye laser amplifier that can suppress parasitic oscillation in a multi-pass amplifier. Amplified spontaneous emission (ASE) in the output beam of the amplifier is reduced with a diffraction grating. A high-peak power pulsed dye laser beam is obtained by amplifying a continuous-wave narrow-bandwidth dye laser with power gain greater than 2 X 106. The eventual bandwidth of the pulses is measured to be approximately 130 MHz. The obtained ASE ratio of the four- pass amplifier system is < 1.5%. Also, we have obtained a high-resolution coherent anti-Stoke Raman spectrum of oxygen in air using the laser system.
Three-dimensional imaging using a femtosecond amplifying optical Kerr gate
Author(s):
Kaoru Minoshima;
Takeshi Yasui;
Emmanuel Abraham;
Hirokazu Matsumoto;
Gediminas Jonusauskas;
Claude Rulliere
Show Abstract
Optical Kerr gate with a function of light amplification and a femtosecond opening time in a special fast setup is applied to time-resolved imaging. Transient induced anisotropy created by a first pump pulse is canceled by the perpendicular-induced anisotropy which is created by a delayed pump. The transverse resolution of the image is better than 90 micrometers without degradation originated from optical Kerr effect or optical amplification process. Moreover, rather wide spectral band of the gate offers the possibility of spectroscopic imaging. 3D imaging of small- signal objects using the femtosecond amplifying optic al Kerr gate are demonstrated for several types of transmittance objects hidden behind light diffusers.
Generalized model of passive Q-switching: influence of nonlinear absorption anisotropy in crystalline switch on laser output parameters
Author(s):
N. N. Il'ichev;
Alexander V. Kir'yanov;
Pavel P. Pashinin
Show Abstract
A model is proposed of passive Q-switching in a laser by a crystalline switch with phototropic centers. Expressions for the output energy and duration of a giant pulse are derived taking account of the geometric factor representing the distribution of the orientations of these centers relative to the crystal lattice of the passive switch. The calculated results are in agreement with those obtained in an experimental investigation of passive Q-switching in a neodymium laser with a switch based on a doped LiF:F2- or Cr4+:YAG crystal.
Further development of a diode-pumped Nd:YVO4/Nd:YAG hybrid oscillator
Author(s):
John A. Alcock;
Denis Julien Gendron;
Suwas K. Nikumb
Show Abstract
A hybrid diode-pumped laser, incorporating an end-pumped Nd:YAG rod and a side-pumped slab of Nd:YVO4 used at grazing incidence, has been operated at a repetition rate of 1000 pps. With an average power of 5 W deposited in the Nd:YAG, the output power of 1.8 W was twice that obtained when only the Nd:YVO4 was pumped. With a pulse duration of 4.5 ns, this system provides a peak power of 400 kW in a near diffraction limited beam.
Tuning characteristics of semiconductor optical amplifier fiber rings
Author(s):
Hongchang Lu;
Bin Luo;
Zheng Chen;
Wei Pan
Show Abstract
The tunable output power characteristics of a semiconductor optical amplifier fiber ring have been studied using rate equations. An expression for the tunable output power is deduced. The analysis presents first that there is an optimum coupler splitting ratio to trade off between wavelength tuning range and output power.
Coded imaging of fusion neutrons in inertial confinement fusion experiments
Author(s):
Olivier Delage;
B. Savale;
Henri H. Arsenault
Show Abstract
In Inertial Confinement Fusion (ICF) experiments, radiation from the compressed core is increasingly reabsorbed. For the largest experiments, the only radiation to escape is the 14 MeV fusion neutrons in which we must turn to learn of the physical processes taking place. The most important parameters are the shape and the size of the compressed core and this involves imaging the neutrons produced by the fusion reactions. The penumbral technique is ideally suited to neutron imaging and the feasibility of this technique has been demonstrated at the Lawrence Livermore National Laboratory in the United States. At the Phebus laser facility in France, this method has been used in image compressed ICF cores with diameters of 150 micrometers yielding approximately 109 neutrons, and the overall spatial resolution obtained in the reconstructed source was approximately 100 micrometers . On the Laser Megajoule project which is the equivalent of the National Ignition Facility in the United States, the spatial resolution required to diagnose high-convergence targets is 10 micrometers . We wish first to obtain a spatial resolution of 30 micrometers to image source with a diameter <EQ 100 micrometers at a neutron yield in the range of 1011 - 1014 neutrons/4(pi) . A collaborative experimental program with the Laboratory for Laser Energetics at the University of Rochester in this perspective is planned. At the same time, there is a research program in collaboration with Laval University (Quebec) concerning coded aperture designs and the associated reconstruction techniques. In this article we first review the basic requirements of such imagery and the concept of the penumbral imaging technique. Then we concentrate on the parameters that condition the spatial resolution and the description of our imaging system. Finally, we survey the reconstruction techniques used followed by results and comparative evaluation of those methods.
Application of a liquid crystal display as a multi-level quantized phase-mostly filter in a 4-f optical correlator
Author(s):
Mark Starzomski;
Michael Cada
Show Abstract
A twisted nematic liquid crystal display (TN-LCD) from a video projector was characterized for phase modulation. It was found to have a phase modulation of approximately 1.5 to 2(pi) with consistently flat amplitude. Using this knowledge a fast Fourier transformed complex 2D frequency domain image was encoded with 2, 4, 8, and 16 levels of phase modulation. The LCD was then used to display the phase-mostly computer generated (CG) matched filter, known as a kinoform, in the Fourier plane of a 4-f correlator. An intensity modulated LCD was used to display input information to the correlator. Results showed that a CG multi-level phase filter had similar correlation peaks to a CG binary phase filter, but there was a less likely chance of detecting a character or image that was similar to the inverted image used to generate the matched filter. Further study was done with the autocorrelation of images as well as detecting an image amongst other images using an 8 level phase-mostly matched filter.
Fractal in laser lithographic digital hologram
Author(s):
Tianji Wang;
Yaotang Li;
Shining Yang;
Shaowu Fan;
Shichao Zhang;
Huanrong Wen
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Authors design and manufacture a laser lithographic digital hologram using chaos theory and fractal images. The feature of the fractal image is presented. Fractals are a mathematical graph-object that is self-similar and chaotic. They have a special shapes, which show similar features at any different size. The another characteristic of the fractal images is divisible property infinitely besides their self-similar property. Authors introduce the fractal patterns to laser lithographic digital hologram for improvement and increase anti-counterfeiting function of the hologram. A laser lithographic digital hologram system is equipped with the fractal images at author's laboratory. The fractal digital embossing holograms are used to security and anticounterfeiting with success in the China.
LiF:F2+ color center laser oscillation under F2-F2+ conversion
Author(s):
Taiju Tsuboi
Show Abstract
A reliable pulsed LiF:F2+ color center laser with a two-mirror cavity has been constructed. A near-infrared laser has shown a stable operation at room temperature and remarkable amplitude by pumping with the second harmonic of pulsed Nd3+-doped YAG laser. The 532 nm radiation gives rise to create the F2+ centers by ionization of the F2 centers in a process of two-photon excitation. The LiF:F2+ laser has a broadband with peak at 930 nm and half width of 40 nm. The slope efficiency is 8% and the pump threshold is 10 mW.
Diode-laser-array-pumped Nd:YAG thin slab laser
Author(s):
Dalwoo Kim;
Wentao Hu;
Xinglong Yan
Show Abstract
We set up a Nd:YAG slab laser and side-pumped with a 2D diode-laser array. The Nd:YAG slab is designed to oscillate with seven internal reflections per pass, and the entrance angle is adjusted to Brewster's angle to minimize the loss. The laser resonator consists of a 2 m radius-of-curvature concave high reflector and a flat output coupler. The diode- array is pulsed for 200 microsecond(s) ec at power of 300 W, and the pump energy of 48 mJ is coupled into the slab. By using an output coupler with transmission of 15.5%, maximum output energy of 8 mJ is obtained with a slope efficiency of 20.2%.
Continuous-wave and self-starting passively mode-locked broadband Cr4+:YAG laser system
Author(s):
Yongmao Chang;
Romain Maciejko;
Richard Leonelli;
Anthony Spring Thorpe
Show Abstract
We have developed a continuous-wave and self-starting passively mode-locked broadband laser system based on Cr4+:YAG crystal. The laser wavelength in the cw mode is tunable in the 1.34 - 1.56 micrometers region with one mirror set. For pulsed operation, the technique relies on the passive mode-locking that arise from the saturable Bragg reflector. The cavity design incorporates the one intracavity prism configuration. We demonstrate self- starting and stable subpicosecond pulses of about 400 fs widely tunable from 1420 to 1510 nm with an output power as high as 230 mW.
Adjustable depth resolution OCT imaging
Author(s):
Adrian Gh. Podoleanu;
Mauritius Seeger;
David J. Webb;
David A. Jackson;
Fred W. Fitzke;
Alex R. Wade
Show Abstract
Using an in house low coherence reflectometry system, a large number of en-face images of the retina for different depths are collected. These images are then processed to produce an aggregated intensity image by the superposition of a number of individual transversal images. Varying the number of transversal OCT images superposed, the effective depth sectioning interval of the superposed image is altered. In this way, the sectioning interval width can be varied from the minimum given by the coherence length, to a maximum given by the range covered by the data collection.
Step-etched prism coupling for optical waveguide biosensors
Author(s):
Yan Zhou;
Yee Loy Lam;
Shi De Cheng;
Chan Hin Kam
Show Abstract
We report a light input coupling method into a buried planar waveguide that is very promising for applications in disposable optical waveguide biosensors. The superstrate of the waveguide is step-etched and a prism made from polystyrene is permanently bonded onto the etched step using optical glue. The plastic prism and the waveguide form a `plug-in' assembly of the disposable part of a biosensor system. For light input coupling, no other pressure sensitive contact of optical components is required and a laser beam simply needs to be directed at the right position. Our experimental results show that the coupling has a highly reproducible efficiency of more than 20% and the coupling efficiency is reasonably tolerant of misalignment. Since the waveguide is fabricated using the ion-exchange process and the prism can be made using injection molding, we believe that our method is very suitable for planar-waveguide-based disposable biosensors.
Integrated optical devices with liquid crystal overlays for the sensing of volatile organic compounds
Author(s):
Bernd Drapp;
D. Pauluth;
Albrecht Brandenburg;
Guenter Gauglitz
Show Abstract
We report the application of nematic liquid crystals for the optical sensing of organic solvents using two different evanescent field probes. Liquid crystals with different nematic ranges are used as sensitive coating materials on integrated optical reflection grating couplers and on integrated optical Mach-Zehnder interferometers as well. A non-linear behavior was observed when the liquid crystal coated IO transducers were exposed to various concentrations of toluene, meta-xylene and para-xylene. The calibration over a wide range pointed out a phase transition of the liquid crystal due to the penetration by the analyte. The birefringend liquid crystal and an isotropic polymer coating are compared by their responses to the xylene isomeres. The data indicate that the liquid crystal's response is mainly given by a decrease of the order parameter S. Furthermore, we take advantage from the non-linearity and the clearing point in order to improve the performance of the sensor system.
Laser induced fluorescence imaging of bacteria
Author(s):
Peter J. Hilton
Show Abstract
This paper outlines a method for optically detecting bacteria on various backgrounds, such as meat, by imaging their laser induced auto-fluorescence response. This method can potentially operate in real-time, which is many times faster than current bacterial detection methods, which require culturing of bacterial samples. This paper describes the imaging technique employed whereby a laser spot is scanned across an object while capturing, filtering, and digitizing the returned light. Preliminary results of the bacterial auto-fluorescence are reported and plans for future research are discussed. The results to date are encouraging with six of the eight bacterial strains investigated exhibiting auto-fluorescence when excited at 488 nm. Discrimination of these bacterial strains against red meat is shown and techniques for reducing background fluorescence discussed.
Development of a fiber optic sensor based on gold island plasmon resonance
Author(s):
Fabrice Meriaudeau;
Todd R. Downey;
A. Passian;
A. G. Wig;
S. Mangeant;
P. B. Crilly;
Trinidad L. Ferrell
Show Abstract
We present an optical fiber chemical sensor based on gold- island surface plasmon excitation. The sensing part of the fiber is a one inch portion on which cladding has been removed and onto which a thin layer of gold (40 angstroms) has been deposited to form a particulate surface. Annealing the gold reshapes the particles and produces an absorbance near 535 nm when the only medium residing outside the surface is air. A range of wavelengths provided by a white light source and monochromator is launched through the optical fiber. The transmitted spectra display shifts in the resonance absorption due to any changes in the medium surrounding, or adsorbed onto the fiber. Experimental results for the sensitivity and dynamic range in the measurement of liquid solutions are in agreement with a basic theoretical model which characterizes the surface plasmon using nonretarded electrodynamics. Furthermore, the model assumes the particles are isolated oblate spheroids with a distribution of eccentricities.
Image processing based on a model of the mammalian retina
Author(s):
Jose Antonio Martin-Pereda;
Ana P. Gonzalez-Marcos
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A first study in order to construct a simple model of the mammalian retina is reported. The basic elements for this model are Optical Programmable Logic Cells, OPLCs, previously employed as a functional element for Optical Computing. The same type of circuit simulates the five types of neurons present in the retina. Different responses are obtained by modifying either internal or external connections. Two types of behaviors are reported: symmetrical and non-symmetrical with respect to light position. Some other higher functions, as the possibility to differentiate between symmetric and non-symmetric light images, are performed by another simulation of the first layers of the visual cortex. The possibility to apply these models to image processing is reported.
Numerical simulation and experimental study of time-resolved optical tomographic imaging
Author(s):
H. J. Zhao;
Feng Gao;
Hanben Niu;
Ji Li;
Hai Zhang
Show Abstract
Near infra-red optical computerized tomographic imaging through a turbid tissue by using time-resolved measurement has been gaining widespread attentions from the field of biomedical research for its non-invasiveness and ability of disclosing the functional information of tissue. A variety of techniques, aimed at implementing a clinically-useful system, have been proposed for eliminating the obstacles arising from multiple light scattering of biological tissue. Among these scheme, one of the primary goals has been to seek for a fast, effective and mathematically rigorous algorithm for the reconstruction tasks. In this paper we first present the basic principle of time-resolved optical tomography. The diffusion approximation-based photon transport model in a highly scattering tissue, which offers an advantage in computational speed in comparison with other stochastic models, and the procedure for solving this forward model by using the finite-element method are then accessed. Theoretically, an iterative Newton-Raphson algorithm for solving the inverse problem is introduced based on the implicit calculation of Jacobian of the forward operator. Numerically simulated images of absorbers embedded in a homogeneous tissue sample are reconstructed from either mean-time-of-flight or integrated intensity data for the verification of the approach. Finally, the experiment setup which are under construction in our Lab is described in detail.
Ultraviolet photorefraction in alpha-LiIO3
Author(s):
Romano A. Rupp;
Jingjun Xu;
H. Kabelka;
Franco Laeri;
U. Vietze
Show Abstract
Experimental results on ultraviolet photorefraction in nominally pure and iron doped (alpha) -LiIO3 crystals are presented. At room temperature two time constants and a characteristic minimum are observed in holographic erasure experiments. With decreasing temperature the maximum diffraction efficiency rises by two orders of magnitude. These features of the erasure kinetics and temperature dependence are explained by a theoretical model taking into account only electronic photoconductivity and ionic conductivity.
Towards a practical technology for ultrafast optical switching
Author(s):
Peter W. E. Smith
Show Abstract
There is increasing interest in developing ultrafast optical switching and signal-processing capabilities for tomorrow's information system. To find significant application, an ultrafast switching technology should utilize components that are small, have low power consumption, and are integrable with other optoelectronic components such as lasers and detectors. In this paper we describe recent progress in the development of semiconductor materials with ultrafast optical response, and in the design of devices using these materials with useful ultrafast switching characteristics. We show that these devices should be able to satisfy all of the criteria for a practical ultrafast switching technology.
