Wideband optical polarizing films using oblique metal island (OMI) films composed of prolate metal nanoclusters (i.e., islands) inclining to one side has been investigated theoretically. The OMI films exhibit resonance-type absorption in visible region and large optical anisotropy as the resonance wavelengths for the polarization along the shorter and longer axes of the prolate metal nanoclusters are different from each other. In the previous work (OPTO 2006), we proposed an optical polarizing film consisting of the multilayer of the OMI layers and thin glass layers. The proposed optical polarizing films have high heat resistivity in comparison with commercially available polarizing films consisting of dichromatic polymer film as those are made of glass and metal. In this work, we have theoretically investigated wideband optical polarizing films for visible region useful for liquid crystal displays and projectors. Aluminum (Al) is chosen as metal since the Al OMI films have shorter resonance wavelengths from larger plasma frequency of Al. As the resonance wavelength depends not only on the choice of metal but also on the aspect ratio of the prolate islands, the resonance wavelength region of the multilayer consisting of different types of OMI layers with various aspect ratios of islands could be expanded. We have successfully designed the optical polarizing films for shorter wavelength region of 350 - 550 nm by using 7 types of Al OMI layer. The extinction ratio of designed optical polarizing films is greater than 20 dB and insertion loss is less than 0.5 dB. We have also designed the polarizing films for longer wavelength rerion of 600 - 730 nm by using Ag as metal.

In this article, optical switching effect of a thermochromic thin film is reported. The transmittance of the film increased from 0.64 at 120°C to 0.96 at 200°C indicating strong temperature dependence for its optical properties. The temperature dependence of the optical properties was found to be reversible during the heating and cooling processes. The possibility to reduce the size of the laser beam with the nonlinear optical switching effect of the thermochromic film is discussed.

Recently, optical thin films have been increasingly needed in optical components. SiO₂ is most frequently used as a low- refractive-index material of optical thin films. The stress of the film is an important parameter that relates to the adhesion of the film. However, the long-term time dependence of the stress has not been thoroughly discussed for SiO₂ optical thin films. In this report, the time dependence of the stress of SiO₂ optical thin film is discussed in terms of optical characteristics in the infrared region. The optical properties and the structure of SiO₂ optical thin films deposited by vacuum deposition (using an EB) and ion-assisted deposition (IAD) were observed by FT-IR, XRD and SEM. The stress of SiO₂ optical thin films was measured using an interferometer to determine the change in the substrate shape. The SiO₂ thin films prepared by both vacuum deposition and IAD exhibited compression stress. Decreases in the stress of the films deposited by vacuum deposition were observed to continue for more than 1000 hours. This result is different from that of the conventional stress model in which the stress changes stop after about one week. The stresses of the films prepared by IAD were observed to change little. Optical absorption by Si-O bonds was observed at 1100cm^-1. The change in bonds from Si-O to Si-OH was observed in the film deposited by vacuum deposition. It is thought that this result of the change in bonds was related to the decrease in the stress of the films.

We present the design and initial fabrication for a wavelength-agile, high-speed modulator that enables a long-term vision for the THz Scannerless Range Imaging (SRI) sensor. This modulator takes the place of the currently utilized SRI micro-channel plate which is limited to photocathode sensitive wavelengths (primarily in the visible and near-IR regimes). The new component is an active Resonant Subwavelength Grating (RSG). An RSG functions as an extremely narrow wavelength and angular band reflector, or mode selector. Theoretical studies predict that the infinite, laterally-extended RSG can reflect 100% of the resonant light while transmitting the balance of the other wavelengths. Previous experimental realization of these remarkable predictions has been impacted primarily by fabrication challenges. Even so, we have demonstrated large-area (1.0mm) passive RSG reflectivity as high as 100.2%, normalized to deposited gold. In this work, we transform the passive RSG design into an active laser-line modulator.

Our status of glass-based photonics materials research for practical functional devices in future optical networks is presented in this paper. New candidates for metal-doped broadband gain media and fiber Raman gain media are presented. Bi-doped lithium alumino silicate glasses have been comprehensively investigated as a candidate of new broadband band gain medium. It was found that the peak wavelength and width of the emission from Bi-doped lithium alumino silicate glasses can be controlled by the excitation wavelength. The emission spectrum had the broadest full width of half maximum (FWHM) of more than 500 nm under the 900 nm excitation. The emission covered a spectral range from 920 to wavelengths over 2000 nm. The bandwidth exceeded 1000 nm. The lifetime was almost independent of temperature up to 350 K, indicating that the emission from the Bi-doped lithium alumino silicate glass has strong resistance to the thermal quenching. The quantum efficiency of the emission was obtained as 11 % when the glass was excited at 974 nm. As new fiber Raman gain media, TeO₂-BaO-SrO-Nb₂O₅ (TBSN) glass system containing WO₃ and P₂O₅ was systematically studied. The TBSN glass doped with WO₃ and P₂O₅ showed high stability against crystallization. New Raman bands due to WO₄ and PO₄ tetrahedra occurred and broadened the Raman spectrum of the glass system. The Raman gain coefficient and bandwidth of the TBSN tellurite glass have been tailored by systematically adding WO₃ and P₂O₅. The glass system showed the broadest gain bandwidth so far achieved in tellurite glasses while maintaining higher gain coefficients. The gain bandwidths of these glasses were more than twice that of a conventional tellurite-based glass and 70% larger than that of the silica glass. These glasses developed are promising candidates for photonics devices in future photonic systems.

Silica-hafnia glass-ceramics waveguides activated by Er³⁺ ions were fabricated by the bottom up technique. Hafnia nanocrystals were first prepared by colloidal route and then mixed in a silica-hafnia:Er³⁺ sol. The resulting sol was deposited by dip coating on a silica substrate. Optical spectroscopy showed that after incorporation of the nanocrystal in a glassy waveguide and an adapted heat treatment, erbium ions tends to migrate toward hafnia nanocrystals. Analysis of the luminescence properties has demonstrated that erbium ions are, at least partially, trapped in a crystalline phase. Losses measurements at different wavelengths highlight a very low attenuation coefficient indicating that this nanostructured material is suitable for a single band waveguide amplifier in the C band of telecommunication.

Y₂O₃ nanocrystals doped with rare-earth ions have attracted considerable interest because of their chemical and thermal stability and their possible application in the light emitting devices and three-dimensional displays. Trivalent-rare-earth ion-doped Y₂O₃ nanoparticles have been synthesized, and their spectroscopic studies have been carried out using visible laser excitation. The size of the nanoparticles has been estimated using atomic force microscope and scanning electron microscope.

Organic-inorganic hybrid sol-gel materials have been widely used for the fabrication of optoelectronic devices due to advantages such as low cost, low loss, low temperature fabrication, ease of processing, good thermal and mechanical stability, and large refractive index tunability. However, the residual OH-like groups remaining after low temperature treatment have hindered the development of the erbium doped waveguide amplifiers working at ~1550 nm. A variety of means have been adopted to overcome this problem: (1) low vibration energy deuterated or fluorinated polymers have been applied as matrix materials; (2) erbium ions have been incorporated into organic or inorganic complexes for protection and the ligands of the complexes have been further modified to reduce the vibrational energy or increase the pump energy transfer efficiency; and (3) the erbium ions have been shielded in inorganic nanoparticles or other micro-structures. Doping erbium ions along with ytterbium ions to increase the pumping efficiency in lanthanum phosphate nanoparticles appears to be a very promising approach since (i) the emission lifetime is fairly long; (ii) at ~1550 nm the nanoparticles are transparent and have a refractive index very close to that of standard optical fiber; and (iii) the nanoparticles are highly dispersible in most organic media. Here we demonstrate how Er³⁺/Yb³⁺ containing lanthanum phosphate nanoparticles dispersed in an organically modified sol-gel can be used in a reverse mesa waveguide to achieve optical signal enhancement. Er³⁺/Yb³⁺ containing lanthanum phosphate nanoparticles have been synthesized with a molar ratio of La:Yb:Er = 76:21:3 and dispersed in cyclopentanone with 30wt% hydrolyzed MAPTMS. The composite has been incorporated into a 4mm reverse mesa waveguide prepared using an organic-inorganic hybrid sol-gel material based on MAPTMS and zirconium n-propoxide. An optical signal enhancement of ~2 dB/cm at 1527 nm has been obtained using a 200 mW 980 nm pump laser. Modeling analyses have shown that the overall performance can be further improved. The results indicate that such hybrid sol-gel reverse mesa waveguides using Er³⁺/Yb³⁺ containing lanthanum phosphate nanoparticles are very promising for optical amplifiers in integrated optical systems.

We report a 1.2 at. % Nd:YAG ceramic pumped with an 808-nm laser diode, placed in a 1.92-m cavity, and passively mode-locked at 1064-nm with a 1% modulation depth SESAM. At a pump power of 11.1 W, this laser produced 2.6 W of average power with a slope efficiency of 27%. The pulse length was 26 ps at a repetition rate of 78 MHz. The ceramic exhibited no peak power degradation during a 20-hour test of doubling efficiency with periodically-poled, near-stoichiometric lithium tantalate.

In this paper we present the fluorescence decay profiles of vanadium and titanium doped gallium lanthanum sulphide (GLS) glass at various doping concentrations between 0.01 and 1% (molar). We demonstrate that below a critical doping concentration the fluorescence decay profile can be fitted with the stretched exponential function: exp[-(t/&tgr;)^&bgr;], where &tgr; is the fluorescence lifetime and &bgr; is the stretch factor. At low concentrations the lifetime for vanadium and titanium doped GLS was 30 &mgr;s and 67 &mgr;s respectively. We validate the use of the stretched exponential model and discuss the possible microscopic phenomenon it arises from. We also demonstrate that above a critical doping concentration of around 0.1% (molar) the fluorescence decay profile can be fitted with the double exponential function: a*exp-(t/&tgr;₁)+ b*exp-(t/&tgr;₂), where &tgr;₁ and &tgr;₂ are characteristic fast and slow components of the fluorescence decay profile, for vanadium the fast and slow components are 5 &mgr;s and 30 &mgr;s respectively and for titanium they are 15 &mgr;s and 67 &mgr;s respectively. We also show that the fluorescence lifetime of vanadium and titanium at low concentrations in the oxide rich host gallium lanthanum oxy-sulphide (GLSO) is 43 &mgr;s and 97 &mgr;s respectively, which is longer than that in GLS. From this we deduce that vanadium and titanium fluorescing ions preferentially substitute into high efficiency oxide sites until at a critical concentration they become saturated and low efficiency sulphide sites start to be filled.

Mid-infrared (IR) lasers are of interest for a variety of applications including environmental sensing, LIDAR and military counter measures. However, this wavelength range lacks powerful, coherent, robust and compact sources. A solution can lie in chalcogenide glasses as host materials for rare earth ions. With an extended infrared transparency, low phonon energy limiting the non radiative multiphonon relaxation rates and suitable rare earth solubility, sulfide glasses based on Ge-Ga-Sb-S system make available radiative transitions in the mid-IR range. The glasses with nominal composition of Ge₂₀Ga₅Sb₁₀S₆₅ doped with Er³⁺ (500 to 10000 ppm) were prepared by means of conventional melting and quenching method. The Er³⁺, widely studied in glass fibers for near-IR amplification, was initially selected for the transition ⁴I_9/2 to ⁴I_11/2 emitting at around 4.5 &mgr;m in order to demonstrate the ability of this sulfide composition for midinfrared fiber lasers application. In these objectives, absorption and emission spectra have been recorded and the radiative decay lifetime of excited levels (⁴I_9/2, ⁴I_11/2 and ⁴I_13/2) has been determined. These last experimental results were compared with those obtained by Judd-Ofelt model from absorption cross-sections of all observable transitions. Therefore, the ⁴I_9/2 radiative quantum efficiency was estimated at 67 %. The emission cross-section was 2.6x10^-21 cm² at 4.6 &mgr;m obtained by Fütchbauer-Ladenburg theory. The product of measured lifetime and emission cross-section for ⁴I_9/2 -> ⁴I_11/2 transition is about 1.87x10^-24 cm².s is comparable with that for GaLaS glasses. The fiber drawing of the Er³⁺ doped Ge₂₀Ga₅Sb₁₀S₆₅ glasses and measurements of optical losses in mid-IR are currently in progress and first results were presented.

The recent finding of new low phonon materials (both glasses and crystals) as rare-earth (RE) hosts that may significantly decrease the nonradiative emissions from excited state levels has renewed the interest in investigating new RE anti-Stokes emission channels. In this work we present, together with recent findings on cooling processes in Yb³⁺- doped low phonon materials, the first experimental demonstration of anti-Stokes laser-induced cooling in the same matrices doped with Er³⁺: a low phonon KPb₂Cl₅ crystal and a fluorochloride glass. In order to assess the presence of internal cooling in these systems we used the photothermal deflection and conventional excitation spectroscopy techniques whereas the bulk cooling in the Er³⁺ -doped samples was detected by means of a calibrated thermal sensitive camera. The experimental results are in good agreement.

A model is presented that successfully predicts electro-optical properties of Lanthanide materials, irrespective whether these materials are inorganic or organic, diluted or concentrated, metallic, semi-conducting or insulating. The model is firmly based on recent experimental data revealing that the variation in 4f and 5d energies relative to the valence band over the Ln series (La, Ce, Pr,.. ,Lu) is universal. Application to LnS and the oxides LnO, Ln₂O₃ and LnO₂ demonstrates its potential by correctly predicting the ground state electron configuration, metallic, insulating or semi-conducting behavior, Ln ion valence state and band-gap of these model Ln systems.

This paper reviews different fiber design approaches for high power lasers. First, we discuss the conventional step index profile design and methods for achieving single mode operation in high power lasers such as bending, helical core fibers and Yb dopant profile designs. Then we present new design approaches for reducing the SBS through profile and glass composition designs. Finally, we describe fiber designs to achieve single polarization and at the same time to mitigate the SRS effect.

Recently, great effort has been devoted to waveguide lasers, because of their inherent simplicity with respect to fiber lasers. Actually, due to their compactness, such lasers are expected to achieve a higher temporal coherence, making them attracting for fiber optical reflectometry, distribute sensing, and range finding applications. Furthermore, the availablity of fast saturable absorbers based on carbon nanotubes allows for a cheap and reliable implementation of the passive mode-locking technique with the potential for generating high repetition rate pulse trains. Such lasers will provide low-noise and inexpensive pulsed sources for applications in optical communications, optically sampled analog-to-digital converters, and spectral line-by-line pulse shaping. We report here on advanced waveguide lasers, operating both in continuous wave and pulsed regimes, based on active waveguides fabricated by femtosecond laser writing in a phosphate glass substrate. A single longitudinal mode waveguide laser providing more than 50 mW with 21% slope efficiency was demonstrated. Furthermore, by combining a high gain waveguide and an innovated fiber-pigtailed saturable absorber based on carbon nanotubes, a mode-locked ring laser providing transform limited 1.6-ps pulses was also demonstrated.

A study was initiated to understand requirements to widen and flatten the gain coefficient spectra of tellurite-based glasses for their application as new gain media for photonic devices. Rationale of broadening was found to be generating Raman active structural elements such as WO₄, MoO₄ and PO₄ tetrahedra in appropriate concentrations in suitable base glasses. Suitable base glass with best compromise between glass formations, optical and thermal properties were determined. Raman active WO₄ and PO₄ tetrahedra were generated either separately or jointly in a TeO₂-Nb₂O₅-BaO (TNB) glass system. The Raman spectral response to this addition was studied by exciting the samples at four wavelengths, 488, 532, 633, and 785 nm. The Raman intensity and bandwidth increased when WO₃ and P₂O₅ were jointly added in TNB. Pure non-resonant Raman gain coefficient spectra of the new glasses were derived by comparing with the gain spectrum of fused silica. The bandwidth of the gain spectra of the present tellurite glasses were more than twice that of a conventional TeO₂-Bi₂O₃-ZnO-Na₂O glass and 70% larger than silica glass. However, gain coefficient of glasses with broader bandwidths was not impressive. This made us to use transition metal oxides as a network modifier in place of the alkaline earth oxide and use them as base glasses. By doing so, higher gain coefficients and broader bandwidths were achieved in a single glass.

We report the first measurement of the stimulated Brillouin scattering (SBS) gain coefficient of a phosphate fiber. Using single-pass amplification of spontaneous Brillouin scattering noise, we measured an SBS gain coefficient of 2.1 × 10^-11 m/W in a 124.5-cm single-mode Yb³⁺-doped phosphate fiber. This is a factor of two less than the SBS gain coefficient of silica fiber, which puts phosphate glass fiber at an advantage for high-power applications.

A novel type of filters based on a combination of a Fabry-Perot etalon and a volume Bragg grating is demonstrated. The proposed solid-spaced Fabry-Perot etalon consists of a high quality fused silica window with both faces having identical dielectric mirrors coatings. The transmission of this Fabry-Perot etalon is a discrete channel spectrum consisting of narrow lines (typically a few tens of picometers) which are separated by gaps with constant width defined as the free spectral range (typically between 0.1 and 10 nm). These discrete resonances define the addressable wavelengths. The second element of this complex filter is a volume Bragg grating. This component is obtained by recording of a sinusoidal refractive index modulation into the volume of a photo-thermo-refractive glass plate. Central wavelength of such element can be tuned over several tens of nanometers by rotating the Bragg grating and therefore changing the incidence angle. This element is thus used to select one of the Fabry-Perot resonances and switch between them. We present the features of this filter and two experimental demonstrations of different configurations of Fabry-Perot-Bragg filters combining different Fabry-Perot etalons and volume Bragg gratings. That way, the flexibility of such kind of filters is demonstrated.

A simple focusing device is proposed for de Broglie matter-waves - a diffractive lens, based on the optical effect of diffractive multifocal focusing of radiation. This matter-wave lens consists of two co-axial circular apertures in which the second aperture of smaller diameter is located where the Fresnel number of the first aperture is unity. It is shown that diffraction of a de Broglie matter wave by a system of two pinholes on an optical axis exhibits the multifocal focusing effect of matter waves in the near-field (Fresnel) zone. The focusing, defocusing and refocusing phenomenon is explained as resulting from periodic phase changes at singular points, which are points where the intensity is zero and the phase is undefined. It is shown that the proposed matter-wave lens could create a very intense, spatially-localized beam of atoms. Theoretical predictions for the focusing efficiency of a neutral atomic beam by the diffractive lens are: the spot diameter is ~ 0.1 &mgr;m, the ratio of focal and incident intensities is ~ 15, the focal length of the diffractive lens is in the range ~ 0.13.6 cm, the focusing depth is in the range ~ 15.30 cm, and the energy transmitting efficiency is ~ 30%. For the relatively-large diameters of the pinholes, ⩾ 5.0 &mgr;m, the proposed configuration acts as a matter-wave lens with a large focal length and a long focusing depth.

We present theoretical and experimental data and possible applications of a photo-elastic-modulator (PEM) made of LiTaO₃. The device with dimensions 13.2x7.1x5.5 mm in x-, y- and z-direction and electrodes on the zx-surfaces offers basic modulation frequencies at 199, 348 and 377 kHz corresponding to the longitudinal oscillations in x- and y-direction and to a yz-shear oscillation mode. The light travels along the optical axis. At the main resonance at 199 kHz the voltage amplitude to achieve a quarter wave retardation amplitude is only ~2.5 V, a very low value due to the strong piezo-electric response and the low loss of LiTaO₃. Hence when compared to a conventional photo-elastic modulator, which is made out of at least two components, the device is extremely compact, cheap and easy to operate, especially when placed in a feedback loop of an amplifier such that it operates on one fixed frequency.

We propose and demonstrate a new method to reduce the absorption recovery time of semiconductor saturable absorber mirrors operating at the 1060-nm wavelength range. The method is based on controlling the amount of nonradiative recombination centers within the absorbing region by incorporating an InGaP epitaxial layer with a relative large lattice mismatch to GaAs (~2.2 %). The defect density within the absorbing region can be controlled by the thickness of a GaAs buffer layer grown between the InGaP lattice mismatched layer and the InGaAs/GaAs quantum-wells. For thickness of the GaAs buffer of ~110 nm and ~570 nm the absorption recovery time was ~5 ps and ~10 ps, respectively. It is important to note that the fast recovery time was achieved without degrading the nonlinear optical properties of the saturable absorber mirror. The practicality of the structures was proved by demonstrating a reliable self-starting operation of a mode-locked Yb-doped fiber laser.

Carrier-injection-type high-speed semiconductor optical switches have been of interest in recent years due to their nanosecond switching times, their immunity to variations in temperature, wavelength, polarization, etc, and the ease with which they can be monolithically integrated with other optoelectronic components and electronic circuitry. Their drawbacks, however, have been high insertion loss and excessive power dissipation. To overcome these limits, a novel, large cross-section, single-mode AlGaAs/GaAs optical switch has been designed and fabricated. The switch's strip-loaded waveguide uses a five-layer W-shaped heterostructure and a 1.7&mgr;m-thick core layer, which provides high fiber-coupling efficiency. Since the constituent heterojunction band discontinuities can impede the current across the junction, the addition of 20nm-40nm thick, compositionally graded interfaces significantly reduces the switching voltage. In addition, using a lightly doped core layer can reduce the series resistance of the switch, which is important in heat reduction. The core doping needs to be low otherwise it will cause increased free-carrier absorption, which contributes to high insertion loss. We have fabricated switches with different core doping levels using both abrupt and graded heterojunctions. The measured on-chip optical propagation losses are 0.3dB/cm for unintentionally doped core, 1.5dB/cm for n = 1x10¹⁶cm^-3 doped core, and 2.7dB/cm for n = 5x10¹⁶cm^-3 doped core. The measured I-V curves show that the switching voltage can be reduced by changing abrupt heterojunctions to graded ones. The calculated theoretical band structure for switches with abrupt/graded heterojunctions based on thermionic emission clearly demonstrated the advantages of applying grading in semiconductor optical switches.

A fiber acousto-optic tunable filter (FAOTF) is developed for near infrared (NIR) spectroscopy applications. The FAOTF is built on a 7-cm long cladding etched high numerical aperture (NA) single mode fiber. By tailoring the dispersion of the fiber, the core mode to higher order cladding mode coupling of the FAOTF is completely suppressed, leaving only LP₀₁ mode (the core mode) to LP₁₁ mode (the first order cladding mode) coupling enabled. This technique enables the FAOTF to operate with a record large free spectral range (FSR) of >700nm, which is required by NIR spectroscopy applications. Other features of the fiber AOTF include a large wavelength tuning range of >500nm (from 1700nm to 2200nm), a narrow bandwidth of <5.5nm, a low insertion loss of <0.2dB, and a small electrical power consumption of <100mW. For test purposes, the fiber AOTF spectrometer is utilized to measure the output spectrum of a super-luminescence diode (SLD) light source emitting at around 2100nm. In comparison with the same spectrum measured with a PbS array spectrometer, the spectrum acquired with the AOTF spectrometer shows much better resolution and reveals fine spectral features of the SLD light source.

A novel optical tuning technology based on new non-resonant interferometer (Optune interferometer) is described. This interferometer has a totally reflective layer either parallel with a partially reflective layer or tilted with a small angle, with an adjustable air gap between them. An input fiber optic collimator delivers a free space collimated beam that is incident first on the totally reflective layer at a small incidence angle. This beam bounces many times between the two reflective layers. An output fiber optic collimator collects all the beams going through the partially reflective layer making them to interfere at the entrance aperture of the output fiber. The optical configuration has no resonant frequencies. A broadband signal at the input is available at the output as a comb with even spacing. Any arbitrary wavelength can be selected by adjusting accurately the gap size. Tuning across 90 nm range could require less than 10 &mgr;m change of the gap size. Some properties of Optune interferometer are: 240 nm tuning range, no tuning holes, 0.2 ms / 100 nm tuning speed, 1 pm tuning accuracy, 0.15 nm bandwidth, 1 dB insertion loss, 45 dB contrast, 0.2 dB flatness, 0.15 dB polarization dependent loss. Optune interferometer can be used either for filtering or for generating optical wavelengths in a broad range of applications such as optical monitoring of structures (FBG and Brillouin technologies), and in optical communications. U.S. Patent No. 7,002,696 covers Optune interferometer and also optical tuning technology based on it.

We have been able to produce soft glass conventional core-clad and micro-structured fibers using rod-and-tube and stack-and-draw method respectively. The stack-and-draw technique shows several difficulties when used with soft glasses, that we managed to avoid using two different lead and alkaline glasses. Non commercial glasses and fibers were thermo-mechanically and optically characterized.

A new polymeric open optical fiber with a star cross section from extruded PMMA grains was developed. We have painted the external surface of this fiber with the Europium chelate or Antracene. We have observed the typical luminescence of these compounds when excited with nanosecond 355 nm pulsed laser. These results show that the developed fiber presents potentialities for optical sensing.

In this article, photosensitivity of optical fibers is discussed. The comparison on the influence of pulse width and wavelength of different trimming lasers on the fiber Bragg gratings shows significant effects on the performance of the gratings. The characteristics of the fiber Bragg gratings have been investigated under different environmental conditions and their dependences can serve as the basis for applications as sensors.

Long-Period Fiber Gratings (LPFGs) were fabricated in single mode fibers (SMF28) by using electric arc discharges produced from a commercial fiber splicer. In our experimental set-up, we noticed that, during each arc, the fiber becomes slightly tapered due to the presence of the longitudinal tension: the quantitative effect depends on the time length and arc power. We have experimentally studied how the LPFG performance may be affected by the arc discharge process, and we found that, with periods typically of few hundreds microns, the spectral response of the grating depends on the period &Lgr;, the intensity of the perturbation, the grating length and the type of mode-coupling induced. The reproducibility of the grating is very important, in particular for applications like a gain equalizer for an erbium-doped optical amplifier. In the modelling of the process, the mode coupling induced by the LPFG cannot be estimated directly from the transmission spectra; therefore, we propose a method to determine the mode-coupling occurring in the fiber and to assess the index modulation induced by the electric arcs. This method combines experimental and simulated data, and its use is not limited to the case of electric-arc-induced LPFGs.

In this work, properties of Ag thin-film ion exchange in Schott IOG-1 phosphate glass has been studied. Emphasis has been put on finding the proper diffusion parameters (self-diffusion coefficient for Ag⁺ ions and the mobility ratio between the participating ions) at process temperatures of 90°C and 230°C. In order to extract the diffusion parameters a following procedure was utilized: An ion-exchanged slab waveguide was fabricated using the same process conditions as in the case of a two-dimensional waveguide fabrication. After slab waveguide fabrication, the effective refractive indices of the propagating modes were measured by prism coupling. Thereafter, a smooth refractive index profile was constructed by improved inverse Wentzel-Kramers-Brillouin method. This refractive index profile was compared with the Ag⁺ ion concentration profile calculated from the diffusion equation by Crank-Nicolson method. The self-diffusion coefficient for Ag⁺ ions and the ratio of the self-diffusion coefficients of Ag⁺ and Na⁺ ions were varied until convergence between the refractive index profile and the concentration profile was found. Using the diffusion parameters obtained from these experiments, two-dimensional waveguide mode profiles were calculated by finite difference method. These theoretically obtained mode profiles were compared with the measured mode profiles with different mask opening widths.

The design of quarter-wave retarders for the Dense Wave Division Multiplexing using parallel mirrors coated with a single layer is presented. The output light from the device is parallel to the input light and it is displaced by a distance d. The quarter wave retarder overall reflection was in the range of 83%. Error analysis on the design is conducted. The error analysis shows how changes on the angle of incident and the thin film thicknesses effect the design of the retarders.

The structure of optical thin films changes depending on various parameters. Typical these parameters are materials, coating methods and coating parameters (for example, assisted ion beam power etc.). For example, titanium dioxide thin films prepared by IAD (Ion Assisted Deposition) method take the column structure. Foggy levels of the deposited film depend on the film structure. Recently, the foggy levels are measured using a haze meter. But weak foggy sample with small haze value does not correspond to visual inspection. In this work, optical thin films were characterized by not only the intensity of the scattered light but also wavelength parameter. As a result, it was found that the estimation of the structure of optical thin films was possible by using the wavelength dependence of the scattered light.

We present a novel chromatic dispersion measurement method using a spectral domain interferometer for single mode optical fiber over a wide spectral range (200 nm). This technique is based on the Mach-Zehnder interferometer using a white light source and spectrometer. A phase was directly retrieved from a measured spectral interferogram to obtain relative group velocity, chromatic dispersion and dispersion slope. The measured results with the proposed method were compared with those obtained using a conventional measurement method. Those results have good agreement with each other. Our proposed method can simply, accurately, and quickly (< 500 ms) measure chromatic information for a short length of optical fiber as well as optical devices.

Optical fibers for high power lasers and amplifiers are fabricated on the basis of quartz glass which has outstanding properties concerning high fiber strength, high power hardness and low optical losses compared with other glasses such as heavy metal fluoride or oxide glasses. It is well known, however, that the host properties of pure silica regarding the active rare earth ions are insufficient and the laser medium has to be improved by the incorporation of codopants. Here we present new investigations of material and fiber properties for phosphorus/aluminium codoping, with regard to the realization of efficient rare earth doped cw and pulsed high power fiber devices. The diffusion behaviour in the complex systems shows characteristic interaction effects, which influence the dopant concentration and their spatial distribution. The refractive index in the codoped systems and the basic attenuation deviate remarkably from additivity relations. The absorption spectrum in the VIS/NIR region depends on codopant concentration and on preparation conditions, with influence on the fluorescence properties of the rare earths and the laser efficiency.

Using a fiber-type confocal scanning optical microscope system, we have obtained a stable refractive index profile measurement system of good performance. We could acquire excellent index precision and good spatial resolution by using a fiber-optic system for the majority part instead of a bulk-optic system and a single mode fiber at visible region with a 4 &mgr;m core diameter instead of a pinhole structure. Also, using a power detection system that is synchronous with fiber-coupled detector, we have improved system stability by reducing noise generated by the roughness of a sample surface because of using the optical fiber as a pinhole system. The light reflected by the sample surface was divided by a beam splitter; one ray passed back through the optical fiber in order to detect a confocal point and another ray entered the synchronous power detector in order to detect reflected power. The power detected by the synchronous power detector without a pinhole is less sensitive to the surface roughness than the power detected by the fiber-coupled detector. We could implement the simple and robust index measurement system by using a fiber-optic system and a synchronous detection system, and a single mode fiber was measured to demonstrate the effectiveness of our proposed measurement system.

Tellurite glasses are important as a host of Er³⁺ ions because of their great solubility and because they present broader gain bandwidths than Er³⁺-doped silica, with promise to increase the bandwidth of communication systems. However, the small glass stability range (GSR) of tellurite glasses compromises the quality of the optical fibers. We show that the addition of CsCl to tellurite glasses can increase their GSR, making it easier to draw good quality optical fibers. CsCl acts as a network modifier in glass systems, weakening the network by forming Te-Cl bonds. We show that the thermal expansion coefficient mismatch is in the right direction for optical fiber fabrication purposes and that the Bi₂O₃ content can be used to control the refractive index of clad and core glasses. Single-mode and multi-mode Er³⁺-doped optical fibers were produced by the rod-in-tube method using highly homogeneous TeO₂-ZnO-Li₂O-Bi₂O₃-CsCl glasses. Far infrared spectra of the glass samples exhibit absorption bands of the Te-Cl bond.

Optical realization of nonlinear dynamical systems such as one-dimensional maps requires nonlinear optical devices whose degree of nonlinearity is more than saturation. It is shown that the equilibrium-state emission of the electron-trapping material (ETM) under simultaneous blue light and near-infrared (NIR) illumination has highly nonlinear behavior. By controlling the two exposures, the luminescence of this stimulable storage phosphor can produce a variety of nonlinear behaviors. This nonlinear behavior is utilized in nonlinear optical signal processing.

Wavelength interleaver is an important component of dense wavelength division multiplexing systems. Various techniques are proposed to implement the wavelength interleaver. Among these approaches, the one based on the birefringent crystal might be the first ever been proposed and manufactured. The birefringent wavelength interleaver has a de facto standard structure consisting of n pieces of birefringent crystal with designed rotation angles. One important yet often overlooked issue regarding this structure is worthy of discussion. It is well known that the lossless finite impulse response (FIR) filter pair can be used to model the "standard" birefringent interleaver without material loss, and a "standard" interleaver consisting of n pieces of birefringent crystals implements nth-order Z-transform transfer functions. However, it is seldom mentioned that, this popular birefringent interleaver diagram can not represent arbitrary nth-order Z-transform functions of a lossless FIR filter pair. In other words, for an nth-order lossless FIR filter whose transfer function is derived from signal processing theory, it might not be feasible with the standard birefringent wavelength interleaver diagram. This fact makes it difficult to apply signal processing techniques to birefringent wavelength interleaver design. In this article, we present an alternative birefringent wavelength interleaver diagram to solve this problem.

In this paper Tm-doped tellurite glasses (75TeO₂-20ZnO-5 Na₂O, mol%) were prepared and characterized, and codoping with Yb was investigated in order to improve pump efficiency and wavelength emission range. Emission spectra and lifetime measurements were obtained by pumping Tm-doped tellurite glasses at 800 nm and Yb-Tm co-doped tellurite glasses at 980 nm, thus exploiting the Yb-Tm energy transfer mechanism. Highly Yb-doped Tm-tellurite glasses were investigated (Yb₂O₃ concentrations up to 5 wt%) and an increase in ³F₄ lifetime with Yb₂O₃ concentrations higher than 3% was observed. This showed that high amounts of Yb do not affect lifetime of the metastable state, thus allowing investigation of lasers in this range of doping concentrations.

We present a new miniature electro-optic (EO) switch array structure. The input signal can be effectively switched to the output waveguide with a low insertion loss of < 0.2dB. A high extinction ratio of > 30dB can be achieved at a low switching voltage of 0.6V. The innovative device structure enables easy scale-up to NxN array with a size of only a few millimeter square. The EO optical switch array provides a promising EO switches technology for high-speed optical networks.