Proceedings Volume 5280

Materials, Active Devices, and Optical Amplifiers

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Proceedings Volume 5280

Materials, Active Devices, and Optical Amplifiers

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Volume Details

Date Published: 12 May 2004
Contents: 22 Sessions, 137 Papers, 0 Presentations
Conference: Asia-Pacific Optical and Wireless Communications 2003
Volume Number: 5280

Table of Contents

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Table of Contents

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  • Semiconductor Lasers I
  • Fiber Lasers I
  • Quantum Dots and Nanostructures
  • Semiconductor Optical Amplifiers
  • Photonic Crystal I
  • Fiber Amplifiers I
  • WDM Lasers
  • Fiber Lasers II
  • Semiconductor Lasers II
  • Organic Optoelectronics
  • Device Requirements for WDM Networks
  • Fiber Amplifiers II
  • WDM Devices
  • Optoelectronic Packaging
  • Photonic Crystal II
  • LED
  • VCSEL
  • Optical Detectors
  • Novel Devices I
  • Solid State Devices
  • Novel Devices II
  • Poster Session
Semiconductor Lasers I
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Experimental research and analyze on grating external-cavity laser
Jie Jin, Yuanchao Wang, Yi Zhang, et al.
In this paper, Fiber Bragg Grating external cavity semiconductor laser and Blazed grating external cavity semiconductor laser are analyzed in theory. Some experiments on two types of Blazed Grating external cavity laser (Littrow and Littman set-up) are done, and some conclusions are also obtained. Two set-ups are compared in detail; at last the intending application of the laser is prospected.
Design and calculation characteristics of a novel diode-pumped long-wavelength vertical-external-cavity surface-emitting semiconductor laser
Changling Yan, Li Qin, Shumin Zhang, et al.
A novel design of diode-pumped long wavelength vertical-external-cavity surface-emitting semiconductor laser with GaInNAs/GaAs multiple quantum wells at 1.3μm as an active region optically pumped by 980nm diode laser is proposed in this paper. The device design realizes the integrating diode-pumped lasers with long wavelength vertical-cavity surface-emitting laser structure, drawing on the advantages of both. The characteristics such as threshold condition and output power are calculated theoretically. An optimum number of quantum wells is obtained from the calculation results, and the calculation results also predict high output power (>500mW) in this kind of device structure. Finally the thermal characteristic is also considered.
Thermal property of tunnel cascaded and coupled multiactive-region laser diodes
Pengcheng Lu, Jianjun Li, Bifeng Cui, et al.
Tunnel cascaded and coupled multi-active regions laser diodes are novel high power laser diodes. This kind of laser diodes can achieve high output power at relatively low current density and overcome the main hindrance of the normal high power semiconductor lasers: catastrophic optical damage (COD) by increase the size of facula. Transient thermal property of these laser diodes has been calculated by using finite element method (FEM). Three kinds of laser diode structures, one active region, two active regions with one tunnel junction and three active regions with two tunnel junctions, are simulated. The calculated results are in agreement with the measured data. The result indicates that for tunnel cascaded and coupled multi-active regins laser diodes, temperature rising of the active region near the substrate is a little higher than that near heat sink. With active region number increasing, the temerature of the laser diodes rises but multi-active regions were fabricated on the uniform substrate, its thermal resistance is still smaller than that of series with the same number normal laser diodes.
Optical analysis of AlGaInP laser diodes with real refractive index guided self-aligned structure
Yun Xu, Xiaopeng Zhu, Xiaojun Ye, et al.
Optical modes of AlGaInP laser diodes with real refractive index guided self-aligned (RISA) structure were analyzed theoretically on the basis of two-dimension semivectorial finite-difference methods (SV-FDMs) and the computed simulation results were presented. The eigenvalue and eigenfunction of this two-dimension waveguide were obtained and the dependence of the confinement factor and beam divergence angles in the direction of parallel and perpendicular to the pn junction on the structure parameters such as the number of quantum wells, the Al composition of the cladding layers, the ridge width, the waveguide thickness and the residual thickness of the upper P-cladding layer were investigated. The results can provide optimized structure parameters and help us design and fabricate high performance AlGaInP laser diodes with a low beam aspect ratio required for optical storage applications.
Fiber Lasers I
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Multiwavelength fiber source using a reflection Mach-Zehnder filter and double-pass backward configuration
A new spectrum sliced multi-wavelength fiber source (MWFS) with no power loss is presented in this paper. The source is composed by a reflection Mach-Zehnder filter (RMZF) with double-pass backward superfluorescent fiber source (DPB SFS) configuration. The RMZF not only provides spectrum filtering but also provides the double-pass function. Multi-wavelength source with extinction ratios larger than 15 dB can easily be obtained over the total conventional band gain region with appropriate erbium-doped fiber (EDF) length and pump power. There is no power loss with the MWFS as compared to the original DPB SFS owning to the RMZF also provides the double-pass function. More than 50 channels of 0.57nm wavelength spacing between 1530nm-1560nm are obtained.
Efficient tunable multiwavelength Yb3+-doped double-clad fiber laser
Shenggui Fu, Wande Fan, Zhi Wang, et al.
We present a tunable multi-wavelength Yb3+-doped double-clad fiber laser based on a Fabry-Perot filter (FPF). By adjusting the FPF, the number of lasing wavelength and their spaces are controlled which is in agreement well with the numerical analysis. The laser can oscillate at different number of wavelengths from one to ten while the oscillation is quite stable. In ten-wavelength laser, the system allows us to extract more than 1.5 W with a slope efficiency of 67%.
Experimental research of doubled-clad fiber laser
Jie Jin, Qiang Jiao, Yan Chang, et al.
The double-clad fiber laser is a novel one with high-efficiency. It has many advantages such as narrow line width and tunable, good beam quality and compact configuration. It can be widely used in optic communications, optic sensor, optic measurement, etc. In this paper, the principle and experimental results of double-clad Yb3+-doped fiber laser are reported. This kind of laser is pumped by a high power semiconductor laser array and coupled by a set of lens. The laser output of 209mW at 1.0872μm is obtained with a pump threshold of 192mW. The slope efficiency is 49%.
Novel design of widely tunable Ytterbium doped double-clad fiber laser by using polarization effects
A novel design of widely tunable Ytterbium-doped double-clad fiber laser is realized in this paper. The tunable wavelength output can be achieved by using a polarizer and polarization controller into the Frabry-Perot Ytterbium doped double-clad fiber laser. Wide wavelength tunability (1054-1080nm) is achieved either by rotating the polarizer or by varying the fiber birefringence with an in-line polarization controller (PC).
Observation of noise-like solitons
Yandong Gong, Ping Shum, M. Tang, et al.
Noise-like ultra-short soliton pulses train of 72fs without CW components are observed from Figure-8 passively mode locked fiber laser; noise-like bound states of asymmetrical solitons train with pulse width of 103fs and separation of 585.5fs are also observed. The bound soliton separation and pulsewidth keep unchanged even after 1.2Km Single Mode Fiber transmission.
Quantum Dots and Nanostructures
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Self-assembled vertically stacked InAs quantum dots
Shuwei Li, Kazuto Koike
In quantum dots (QDs) three-dimensional confinement of carriers lead to energy level discreteness to exhibit a rich spectrum of phenomena including quantum confinement, exchange splittings, Coulomb blockade, and multiexciton transitions. The 5-period vertically stacked samples with the size-controlled growth were grown by molecular-beam epitaxy (MBE) with solid sources of Al, Ga, In, and As in non-cracking K-cell. Measurements by reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM), and photoluminescence (PL) showed that the vertically stacked QDs was well-distributed, which can make the vertically stacked InAs QDs to exhibit the effects of the strong quantum confinement and coupling. The quantum dot, the behavior of which is to capture and emit carriers like a giant trap, is studied using a deep level transient spectroscopy (DLTS) technique, too. The electrons and holes in the QDs are respectively emitted from the relevant energy levels to the conduction and valence bands of the barrier layer with increasing measurement temperature, and the thermal emission energies from the QDs are related to their discrete energy levels. One of the attractive features of vertically stacked InAs/AlGaAs quantum dots, which were buried in AlGaAs high potential barrier and spacer epilayer, exhibits an unknown macroscopic quantum phenomenon (i.e., phase-change splitting of the ground state). In the vertically aligned QDs, due to many-body effect and quantum-mechanical renormalization, the electron ground state splits into series of peaks of which the intensity gradually, systematically decreases to redshift direction with a wavelength constant.
Visible electroluminescence from p-n junction porous Si diode with a polyaniline film contact
Hongjian Li, Hao-Yang Cui, Baiyun Huang, et al.
The interface formed between a p-type conducting polyaniline layer and a n-type porous silicon wafer was studied. The contact has rectifying behavior demonstrated clearly by the IV curves. The series resistance Rs in the p-type conducting polyaniline/n-porous Si diode is reduced greatly and has a lower onset voltage compared with. ITO/n-porous Si diode. The porous silicon has an orange photoluminescence band after coating with polyaniline. Visible electroluminescence has been obtained from this junction when a forward bias is applied. The emission band is very broad extending from 600-803 nm with a peak at 690nm.
Formation process of Si nanoparticles deposited by pulse laser ablation
Yinglong Wang, Rongmei Zhang, Guangsheng Fu, et al.
The deposited dynamic process of Si nanoparticles prepared by pulsed laser ablation is numerically simulated by using the direct simulation Monte Carlo method. It is found that there is a mixed region where the high-density Si vapor peak and the gas peak are overlapped. The Si nanoparticles are formed by Si vapor condensation in the region and their sizes depend on the properties of the region such as density and range. The properties of the mixed region are changed constantly when its position are oscillated with time is increased, and get to stable state at certain a time, i.e., oscillating time. The oscillating time determines the distribution of nanoparticles in size. The influence of the experimental parameters on oscillating time of the mixed region is analyzed theoretically. The results show that the Si-based nanostructure materials with more uniform nanoparticles in size can be obtained by using appropriate proportion of He and Ar as ambient gas.
Semiconductor Optical Amplifiers
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Additional spectral broadening of ultrashort optical pulse due to birefringence in semiconductor optical amplifiers
Birefringence in semiconductor optical amplifier (SOA) has begun to receive increasing attentions in recent years, in this paper we investigate the effect of birefringence on spectral broadening of ultrashort optical pulse, based on Jones Matrix method, Fourier transform method and a multi-section model, which takes into account the polarization dependency of phase modulation. The time-dependent carrier distribution, pulse amplification process and pulse spectrum evolution along SOA is simulated. It is found that a considerable part of spectral broadening comes from birefringence, this kind of additional spectral broadening depends on bias current, optical power and pulse shape of input pulse.
The influence of series resistance on the longitudinal spatial hole burning in semiconductor optical amplifier
The longitudinal spatial hole burning (LSHB) in semiconductor optical amplifiers (SOA) is investigated using an improved wideband numerical model. The main new feature of the model is that it takes into account the current self-distribution effect, which induced by the axial variations of the separation between quise-Fermi levels in active region. The current self-distribution effect leads to the nonuniform current injection, and it tends to smoothen the carrier density distribution over the active region and reduces the strength of LSHB. It is found that the internal series resistance of SOA, which comes from mental-semiconductor Ohmic contacts, heterointerface and semiconductor bulk resist, significantly influences the strength of current self-distribution effect. The assumption of current injected uniformly gives rise to an overestimation of the strength of LSHB in SOA. The simulation results also show that the series resistance influences the gain and noise figure of SOA greatly. It is proposed that reducing the series resistance can enhance the small signal gain and reduced the noise figure of SOA efficiently.
Simultaneous 16-channel wavelength conversion at 10 Gb/s based on cross-gain modulation of ASE spectrum in SOA
A simple scheme for multi-channel wavelength conversion based on cross-gain modulation of Amplified Spontaneous Emission (ASE) spectrum in Semiconductor Optical Amplifier (SOA) is described. Simultaneous 16-channel wavelength conversion at 10Gb/s is first demonstrated without any additional probe lights, the modulation information carried by one pump light could be converted into arbitrary many channels if only the demultiplexer with enough channels is exploited.
Experimental investigation on all-optical wavelength conversion in a fiber SOA-Sagnac interferometer
The theory and experimental system of an all-optical wavelength conversion in a SOA-Sagnac interferometer are put forward. The wavelength conversion with RZ light pulse at 622 Mbit/s was obtained, and the wavelength conversion range of about 43nm with the extinction ratio of larger than 10 dB was achieved.
All-optical wavelength conversion using amplified spontaneous emission of SOA and a delayed interference configuration
All-optical wavelength conversion is demonstrated by using a spectrum-sliced amplified spontaneous emission (ASE) in the semiconductor optical amplifier (SOA) as the probe light and a delay interference configuration. Characteristics of the ASE output in terms of its spectral dependences under the co-propagating injection by a signal light are analyzed theoretically. Analytical expressions for the ASE output in terms of power and phase changes in the wavelength conversion are deduced. An experimental system based on this scheme is built and its operation principles are introduced. System's performances are investigated and several experimental results on measurements of bit error ratios, extinction ratios under different wavelengths and time waveforms as well as eye diagrams are presented.
Rising and falling time of the amplified pulse after a optical pulse passing through a semiconductor light amplifier
After presenting an improved theoretical model that describes the dynamic process of optical pulse amplification by the semiconductor light amplifiers (SLAs), both the rising and falling time of amplified picosecond optical pulses by the SLAs have been investigated numerically. The results show that with the increase of the bias current of SLAs, the rising time will decrease and the falling time increase; the input pulse with a large peak power will accelerate the rising time shortening and the falling time lengthening; the gain compression has an obvious influence on the rising and falling time for several picosecond width input pulses; the gain asymmetry and shift violently affects the rising and falling time.
Semiconductor optical amplifier for amplification and switching applications
Martin Hai Hu, Catherine G. Caneau, Herve P. LeBlanc, et al.
This paper presents recent progress on SOAs with dilute optical mode. The SOA optical mode is designed to be large to achieve high saturation power and low coupling losses of 1.16 and 0.89 dB for TE and TM polarizations with a lens fiber. A 2-mm long SOA has high saturation power (16.3 dBm), low PDG (<1 dB), low noise figure (<7.2 dB) and medium gain (>19.5 dB) across C-band. A 1.5mm-long SOA was successfully used as a 10 Gbit/s booster amplifier for 100km transmission. The dynamic properties of the SOA were characterized to support application as optical gate switch in sub GHz speed.
Photonic Crystal I
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Mechanically or optically switchable photonic crystal structures
Photonic crystal structures open new possibility for the construction of novel optical switch structures that are highly compact and functional. In this paper, we introduce two novel examples of photonic crystal switches: a mechanically switchable photonic crystal filter structure, and a low-power and high-speed all-optical transistor based upon cross waveguide geometry in photonic crystals.
Experiment verification of photonic bandgap extension of one-dimensional photonic crystal based on incident angle domain
Biqin Huang, Peifu Gu
Existence of photonic band gap is the key to the application of one-dimensional photonic crystals. Some methods have been proposed to extend the photonic band gap, which are normally based on frequency domain. In this paper, experiment has been carried out to verify one new extension method, which is based on the incident angle domain. In experiment the relative band width of hybrid structure composed of four one dimensional photonic crystals is up to 37%. This indicates that this new method can extend the photonic band gap of one dimensional photonic crystals greatly.
Bistability of photonic crystals with detects of nonlinear dielectric materials
We report on the properties of light transmission in one-dimension photonic crystals with defects of nonlinear dielectric material, photonic crystals have simple and complex period dielectric structure with multi-unit layer. In particular, we are interested in the transmittance of defect mode and the intensity enhancement factor of localized light. By the transfer-matrix method, we can calculate the electromagnetic waves transmission through a photonic crystal, the intensity enhancement factor of localized light can be obtained. The method calculated the transmission properties normal incident on a finite thickness slab of material. The numerical calculation shows that the transmission with defect layer of nonlinear dielectric material can induced to bring about change by the input intensity of light, and the change of the transmission shows the bistability. For simple and complex period dielectric in PC, if the threshold of input intensity be satisfied, the properties should be emerged easier. For complex period dielectric in PC, the transmission can show the property of complex results. When the total transmission is big, the bistability is also displayed. In addition, the character is seen to determine by the saturation absorption coefficient of the defect medium, the refractive index ratio and the number of layers.
Fiber Amplifiers I
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Study on a polarization-insensitive and high-pump-efficiency EDFA employing a fiber Bragg grating and a Faraday rotator mirror
Qinlian Bu, Tao Deng, Yong Luo, et al.
A novel structure of EDFA employing an FBG and an FRM is presented in the paper. Experiments are conducted to verify the theoretical model. And the result shows that the novel structure has strong points than conventional structure in PMD,PDG and pump efficiency.
Characterization of gain spectral variation of erbium-doped fibers codoped with aluminum
Baishi Wang, Gabe Pub, Rich Osnato, et al.
Characteristics of gain spectral variation of EDFs and its dependence on aluminum doping level and fiber mode design are quantitatively studied. Based on experimental data and manufactured fibers with different aluminum levels, the correlation between aluminum concentration and both absorption spectrum and gain flatness is revealed. Gain spectral variation for over a million meters of EDFs manufactured in last several years is presented. The result shows that peak-to- peak spectral shape variation for all these fibers are within 0.8% in a 36nm C-band window.
An intelligent EDFA design for metro application
Wen Liu, Keyu Wu
A new intelligent EDFA design for metropolitan optical networks is proposed. It integrates a post-amplifier and a pre-amplifier function within one module. Only one pump laser, the gain resource could be tunable deployed between the forward and backward directions. In other word, all pump power will be used high efficiently. To demonstrate the super-flexibility of this EDFA, there are a few application cases are described, including the ring and mesh networks situation.
WDM Lasers
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Tunable laser sources for (D)WDM
For several years tunable lasers and other WDM sources has been as one of the hottest components topics in photonics, but like other areas the downturn has hit hard. In this paper we will describe the latest developments in the area of optical sources for DWDM systems, including tunable lasers and multiwavelength sources, and we will look at the companies (still) competing in this area. We will start by introducing the basic technologies used for DWDM sources. After that we will give an overview of the source options, and discuss tuning methods and wavelength control issues. The source options under discussion will include monolithic tunable lasers, hybrid structures and external cavity lasers, wavelength selectable laser arrays, tunable VCSELs, and non-semiconductor alternatives. Numerous examples will be shown, and the characteristics and performance of the various devices will be discussed. The key performance parameters, such as tuning range, power and switching speed will be related to the expected areas of application. These areas include sparing, fixed wavelength transmitter replacement, and use in wavelength switched networks.
Novel external-cavity laser using interference filter as wavelength-selecting component for DWDM applications
In this paper a novel external cavity laser with interference filter as wavelength selective component is introduced. Effective reflection coefficient for compound cavity and static operation characteristics of the laser are analyzed theoretically. Experimental results show that precise wavelength lasing with side mode suppression ratio more than 40dB and spectral linewidth nearly 0.2 nm at -20dB is realized. And the wavelength stability of the laser is also dramatically improved.
Novel athermal WDM laser with polymer grating
Gefan Huang, Siyuan Yu, Aeneas Massara, et al.
In this work we propose and fabricate a novel low cost wavelength stable single mode laser for uncooled WDM applications using hybrid semiconductor-polymer diode structures. A ridge waveguide Fabry-Perot laser with an integrated spot size convertor on the output is modified for athermal single frequency operation. The prototype device consists of an active section and an athermalized polymer grating structure. The latter is etched by focused ion beam (FIB) and filled with a negative temperature coefficient polymer material to compensate thermal wavelength drift. The active region thermal drift is thereby partially compensated by the polymer grating without requiring active wavelength or temperature control. This potentially facilitates low-cost, low-footprint, low-power-consumption packaging.
Fiber Lasers II
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Researches on the CW Tm:Ho codoped silica fiber lasers operating at 2-um spectral region
Shufu Dong, Guofu Chen, Xianhua Wang, et al.
The properties of a Ti:sapphire pumped CW operation Tm-Ho co-doped silica fiber lasers are presented. The lasing wavelength, output power, slope efficiency, and threshold are measured under different conditions. The measured maximum output power from the fiber laser of 240 mW at about 1870 nm was generated for a fiber length of 52 cm with an absorbed pumped power of 1.05 Watt at 796 nm. The slope efficiency of approximately 31% is similar to the singly Tm-doped fiber lasers. The longest output wavelength of 1970 nm was also generated from the Tm-Ho co-doped fiber laser when the fiber length was extended to 3.03 m, which shows the energy transfer process of the Tm-Ho co-doped system. A simplified numerical model is also constructed for the Tm-Ho co-doped silica system for 3F4 ground state absorption (GSA) pumping, which can be used to analyze the performance theoretically of the Tm-Ho co-doped silica fiber lasers.
Synchronously pumped mode-locked Yb3+-doped fiber laser
Xinhuan Feng, Wande Fan, Shenggui Fu, et al.
A synchronously pumped mode-locked Yetterbium-doped Fiber Laser which has the advantages of simple design and broad applications is obtained when the pump semiconductor laser current is modulated sinusoidally at the appropriate frequency. Steady pulses were obtained on harmonic mode-locked status. At the repetition rate of 623kHz,the pulse width is about 50ns,the average output power is 2.34 mW.
Study on the polarization characteristics of fiber grating ring lasers
Based on the theory of Jones Matrix, a model for the analysis of non-PM fiber ring lasers polarization characteristics was developed. The model was further tested by experiments. From the numerically and experimentally analysis results, it was found that lasers composed by non-PM fiber can achieve stable output but its polarization varied with external perturbation. If a polarizer was inserted into the laser cavity, though the polarization state was more stable, the instability of output was even more serious. So special polarization control must be performed to obtain single polarization laser output using non-PM fiber.
Research on all-fiber Q-switched fiber laser based on the hi-bi fiber Sagnac loop filter
Chen Yong, Xiaopeng Dong, Lin Jun
The Sagnac loop filter composed of the highly birefringent (Hi-Bi) fiber and a 3-dB coupler has been employed in the novel structure of Q-switched fiber laser in this paper. We use square-wave-driven PZT to modulate the filter, whose period is changed according to that of the wave. Therefore, the Hi-Bi fiber Sagnac loop filter will not only fulfill the function of choosing the wavelength of the laser but also serve as a Q-switching that changes the transmission ratio of the whole resonator. In the experiment of Q-switched fiber laser based on the ring resonator, the output laser pulse remains stable at an external frequency of 3 kHz-8 kHz. When the frequency is 3.2 KHz and the pump power is 19mw, the FWHM (Full Width at Half Maximum) of the pulse is approximately 10.5μs, and the average output power is 685.3μW, and the peak power is 41.1mW. Meanwhile, another novel structure of Q-switched fiber with linear resonator has also been studied in the paper.
Experiments and analysis of double-cladding erbium-ytterbium-codoped optical fiber lasers
Shufu Dong, Shanghong Zhao, Maolu Zhuang, et al.
The experimental results of erbium-ytterbium co-doped double-cladding fiber lasers (EYDCFLs) are reported. The output powers as functions of the input pump power, and the reflectivity of the cavity mirror are described. The maximum output power is about 733 mW, with a slope efficiency of about 30% and optical to optical conversion efficiency of 25.3 %. Numerical analysis of this EYDCFL was also performed based on the rate and propagation equations. The calculated output powers of 1.492 W and conversion efficiency of 51.4 % are doubled than the experimental results. That means further improvements could be made by optimum design of the laser, such as well cutting the fiber-end, adding dichroic mirror at the output end, or making fiber Bragg gratings directly in the fiber core.
High-efficiency and -stability L-band erbium-doped superfluorescent fiber source
A novel one-stage configuration for high stability L-band (1565-1605nm) erbium-doped superfluorescent fiber source (SFS) is designed and investigated. The superfluorescent source is realized in a 19m erbium-doped fiber with double-pass bi-directional pumping configuration. High pumping conversion efficiency and pump power insensitive mean wavelength characteristic due to the bi-directional pumping configuration. Pumping conversion efficiency about 60% and flat spectral linewidth over 30 nm is obtained by the proposed SFS.
High-power broadband superfluorescent source with a Yb-doped double-cladding fiber
Wande Fan, Shenggui Fu, Xiang Yang, et al.
A high-power and broadband super-fluorescent source (SFS) based on an Yb-doped double-cladding fiber is described. The source is pumped at 976 nm from a laser diode by end-pumping system. The SFS generated a maximum 100 mW of broadband emission centered at 1066nm, with an about 40nm FWHM spectrum. The basic characteristics of the superfluorescent source, such as the output power and output linewidth, have been analyzed and studied.
Semiconductor Lasers II
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Correlation between the g-r noise in semiconductor lasers and device reliability
Guijun Hu, Yadong Sun, Hongmei Zhang, et al.
The g-r noise in semiconductor lasers and its relation with device quality and reliability are studied. The results indicated that g-r noise has close relation with semiconductor defects, the devices with g-r noise degrade rapidly during electric aging, the P-I characteristics of the devices evidently become bad, or the devices have failed after aging. By measuring g-r noise in semiconductor lasers, the devices quality and reliability can be estimated, which is an effective and non-destructive method.
High-speed directly modulated and uncooled long-wavelength DFB semiconductor lasers
Dingli Wang, Jun Zhang, Tao Liu, et al.
This paper summarizes the recent advances and results of uncooled, high-speed directly modulated long-wavelength DFB laser diodes. It discusses ways of obtaining high temperature operation of laser diodes. By assessing the effect of carrier transport, doping and strain in active region, as well as the non-active region factor, such as laser waveguide properties and microwave parasitic parameters, various methods are discussed to improve the direct modulation bandwidth.
High-speed injection-locked lasers
Injection locking has been actively researched for its possibility to improve laser performance for both digital and analog applications. When a modulated follower laser (also termed "slave" laser) is locked to the master laser, its nonlinear distortion and frequency chirp may be reduced. As well, the resonance frequency can increase to several times higher than its free running case. In this paper, we show that the frequency response (S21) of an injection-locked laser is similar to a parasitic-limited laser with a high resonance frequency. The S21 was studied experimentally and the condition to achieve a flat, enhanced frequency response was identified. For analog applications, a record 112 dB-Hz2/3, single-tone third harmonic spur-free dynamic range of a 1.55 μm VCSEL was demonstrated. An improvement was attained for a wide injection parameter space. Furthermore, the RIN of the VCSEL was found to be 10 dB lower at 2 GHz for certain injection condition. In a 50 km 2.5 Gb/s digital link, a 2 dB power penalty reduction at 10-9 bit-error-rate was also demonstrated. As a novel application, an injection-locked uncooled tunable VCSEL was shown to have a reasonable modulation performance in a wide ambient temperature range. The VCSEL was locked to a designated wavelength and the injection compensated the temperature-induced performance degradation. This concept can be extremely attractive for low-cost DWDM transmitters.
Organic Optoelectronics
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Block copolymers for optoelectronics
Sam-Shajing Sun, Zhen Fan, Yiqing Wang, et al.
A D(donor)-B(bridge)-A(acceptor)-B(bridge)-type block copolymer system has been developed and preliminarily examined for potential opto-electronic photovoltaic functions. The unique feature of the device includes a primary DBAB-type block copolymer backbone, where D and A are conjugated donor and acceptor polymer blocks, and B is a non-conjugated and flexible chain, a π orbital stacked and conjugated chain self-assembled and ordered "secondary structure", and a donor/acceptor asymmetric layers sandwiched D/A columnar "tertiary structure". This structure is expected to improve photovoltaic power conversion efficiency significantly in comparison to most existing organic or polymeric donor/acceptor binary photovoltaic systems due to the reduction of "exciton loss", the "carrier loss", as well as the "photon loss" via three-dimensional space and energy level optimizations. Preliminary experimental results revealed better morphology and opto-electronic properties of DBAB vs. D/A blends.
The spectral sensitivity of long-period gratings and its application in electro-optic polymer modulator
Xiaowei Dong, Li Pei, Wei Jian, et al.
LPG's sensitivities in the spectral shift and the strength change of the attenuation band to the surrounding medium are analyzed and the results are in close agreement with our experiments. According to the characteristics of LPG, we will introduce, for the first time to our knowledge, a novel all-fiber electro-optic (EO) polymer modulator that is based on the LPG. The materials used in the modulator are chosen and the processing is also given. The purpose of this analysis is to provide design insight and the feasibility of making such a device. Using the theory of multi-claddings optical wave-guide, we achieved the relationship between LPG’s resonant wavelength and the drive voltage.
Characteristics of LCoS phase-only spatial light modulator and its application
Optimize the working model of LCoS (Liquid Crystal on Silicon) in parameter space by simulation. Two models are selected, which is suitable for phase modulating. One is the RTN-52° model, the other is parallel alignment ECB model. Phase changing is measured when various voltage are applied to Lcos. Show some results when the Lcos is used as a Fresnel lens.
Design and application of reflective LCoS-based amplitude spatial light modulators
Several modes are simulated in parameter space to find profitable mode for amp SLM design and RTN52° with high reflectance, high dDn and low phase shift is used for experiment. The reflectance and contrast are measured on a RTN52° LCOS device.
Device Requirements for WDM Networks
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Practical techniques in commercial Tbps WDM optical fiber transmission equipment
Jia Ying Wang, Huijun Xu
Key techniques in practical Tbps WDM optical transmission equipments are summarized in this talk, regarding optical transmission issues and the relative engineering solutions in the wide spectrum range and long distances, for example, the issues and solutions of Raman amplification and enhanced forward error correction. Moreover, new challenges in the manufacturing of this equipment include the controlling and managing aspects, to meet the practical requirements of Tbps WDM transmission. New devices and systems should be highly automatic, to ensure characteristics of automatic auxiliary maintenance or adjusting. Hence, intelligence solutions of spectral controlling, bit error rate optimizing, security ensuring, protection switching etc. are also referred in this talk. These are new characteristics of commercial Tbps WDM equipments in the future.
Will rapid advances in optical integration have a disruptive impact on carriers' optical networks?
James Pan, Ian M. White, David L. Harris, et al.
While many system vendors are concerned about losing a generation of well-developed product because of the prolonged slow market, many optical component and subsystem vendors continue to pursue various avenues towards dramatic reduction of total cost of ownership for next generation optical transmission equipment. This paper is intended to provide a carrier's perspective on the potential disruptive impact of the optical integration based new devices to next generation optical transmission equipment. The emphasis is put on emerging applications of these new devices and related technical requirements. By providing the carriers' perspective, this paper may help promote a new line of thinking about what new technologies vendors should focus on in order to make next-generation optical transmission systems much lower in cost, smaller in footprint, and lower in power consumption.
Recent progress in parametric amplification and signal processing
Stojan Radic, Colin J. McKinstrie, Yikai Su
Recent advances in fiber parametric amplifiers are reviewed. The physics, operation and applications of two-pump parametric fiber amplifiers are described. Methods for broadband, equalized parametric gain exceeding that of conventional EDFAs are discussed. The inherent nonlinear nature of parametric amplifiers forms a basis for all-optical signal processing. Optical regeneration in high-order, two-pump parametric amplifiers is described and demonstrated. All-optical penalty reversal using polarization-invariant signal conjugation is discussed and described over multiple SMF spans
WDM and optical devices: new evolution and new requirements
Dejiang Zhang, Weishi Li
Based on introduction of WDM evolution and technology trend, the requirements to the optical devices of next generation WDM systems are analyzed. The requirements are focused on intelligence and low cost. Moreover, the evolution of several important optical devices is discussed. The low cost dynamic optical devices will play a important role in the next generation WDM system. It will be a main developing direction for optical devices applied in WDM systems.
Fiber Amplifiers II
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Gain spectrum self-control device and algorithm for mutiply pumped Raman amplifiers
For both forward- and backward-pumped Raman amplifiers, devices to perform gain-spectrum self-control of multi-laser pumps are depicted in this paper. The algorithm supporting the devices is presented also. The function of automatic control is suitable for on-line maintenance of WDM equipment.
Research of dispersion compensation hybrid fiber Raman amplifier in S band
Shangzhong Jin, Wen Zhou, Zaixuan Zhang, et al.
Hybrid FRA consisting of general fiber G652 and dispersion compensation fiber DCF includes DCF +G652, G652 +DCF and G652+DCF +G652. The operation principle is discussed and configurations have been researched in S band. The gain and noise characteristic of 5km DCF+50km G652 fibers configuration FRA is better than 50km G652+5km DCF FRA and 25km G652+5km DCF+25km G652 FRA in experiment. The gain and noise spectrum characteristic of 5km DCF+50km G652 FRA were measured. In the DWDM fiber transmission system, the transmitted characteristic of two channels that spectral interval is 0.262nm(34.1GHz)in the dispersion compensation FRA is better than those of 50km G652 positive dispersion FRA and 5km DCF negative dispersion FRA in S band .
Optimal design scheme for multiwavelength backward-pumped Raman amplifiers
Chengxia Li, Dawei Fang, Zaixuan Zhang, et al.
A new and practically applicable scheme of optimally configuring backward multiple pumps in optical fiber Raman amplifiers is presented based on the characteristics of Raman gain spectra and the fact that different pump powers and wavelengths have different impact on the gain slope by using Optiamplifier 4.0 simulating software, which is made in Optiwave Corporation, Canada. We use the idea to optimize a distributed Raman amplifier pumped by 2-walvelength sources. The optimized design contained signal channels between 1490 and 1530 nm with 4-nm separations. The fiber used as the gain medium was a 50-km single-mode fiber (SMF) with 9.9e-14m/W peak Raman-gain coefficient. After calculating 11 times optimum pump wavelengths 1390nm, 1427nm are obtained. The achieved gain flatness is 1.46dB and the maximum forward on/off gain is 10.43 dB, which is much better than initial un-optimized gain flatness 5 dB. Then after 24 calculations we get the optimum pump powers. The final optimized pump sources are 1390nm 300mW, 1427nm 290mw. Gain ripple less than 1.2 dB in 40nm and maximum Raman on/off gain about 10.1 dB are obtained. Finally the factors of the noise figure are analyzed and ASE is found to be the main noise source.
Effects of stimulated Brillouin scattering on gain saturation in discrete Raman fiber amplifiers
Ronghua Chi, Qingning Li, Xianqin Li, et al.
The generation of SBS in discrete Raman gain must be considered along with the problem of limited gain per unit pump power when developing a practical Raman amplifier. In this paper, we focus on discrete Raman amplifier with 15 km dispersion compensating fibers (DCFs). The gain saturation of both forward and backward pumping schemes have been considered and compared. As the pump power increased, the SBS threshold decreased and the reflected power increased dramatically. The 7th SBS stokes have been observed when the pump power is 490mW. The experimental results clearly indicate that the SBS effects produced a saturation of the Raman gain.
Novel design of Raman amplifier pump module
Xinda Yin, Wanhui He, Chengpeng Fu
Raman amplifier is one of enabler technologies for next generation optic communication system, especially for 40Gbit/s based system. To get wide commercial application, however, there are several obstacles that should be overcome. Main problems of distributed Raman amplifier include reliable and low cost design, safety operation, automatic gain control, signal power monitoring and so on. For Raman gain is relevant to relative polarization state between pump light and signal light over fiber, two pumps with same wavelength and same power but perpendicular polarization state are often required. In general, this will lead to more components, high cost, complexity and big size. On the other hand, this will limit the number of pump wavelength that can be used, and limit Raman amplifier's performance. For the first time, we invented two kind of key component to solve the problem thoroughly, one component is micro optic depolarizer, and another is depolarizer-isolated PBC hybrid component. Based on these two key component, we demonstrated a novel flexible and low cost structure design of Raman pump module. We also test new Raman pump module, which show low DOP and very low PDG gain in backward or forward pumping scheme.
FWM in distributed Raman fiber amplifier
Wanhui He, Xinda Yin, Chengpeng Fu, et al.
We observed the FWM (Four Wave Mixing) phenomenon in broadband distributed Raman fiber amplifier (DRFA). This is one of the nonlinear effects which limits the performance of Raman amplified systems. We analyze the FWM effects for different fiber types. Finally we reduced the FWM influence successfully by choosing proper wavelengths in experiment.
Pump wavelength and power distribution algorithm in Raman amplifier
An algorithm is discussed to achieve target gain and gain flatness in Raman amplifier through adjusting the pump wavelength and power distribution. It is convenient for Raman amplifier designer to decide the pump wavelength accounting of the trade-off between the gain flattening and gain efficiency. The algorithm based on both the effective interaction lengths and propagation equation, as well as its application in all-Raman Wavelength Division Multiplexing (WDM) system to dynamically adjust the gain and gain flatness are discussed. In this paper, we also give a fast numerical method to realize the simulation of the algorithm.
Simulation and analysis of gain characteristics of multipumped fiber Raman amplifier
Power propagation equations of multi-pumped fiber Raman amplifier (FRA) is reasonably simplified, multistep average power method is applied to compute composite Raman gain of multi-signals in dense wavelength division multiplexed system (DWDM) amplified by multi-pumped FRA. Based on such a simple and effective model, the influence of the number, input power and wavelength distribution of multi-pumps on Raman gain is researched, the rules to decide their values are reached and the ultra broad and flat Raman gain bandwidth is implemented. All the simulation and analyses supply helpful references for the application of multi-pumped FRA in DWDM system.
WDM Devices
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Analysis of dynamic channel power equalization by using nonlinear amplifying Sagnac interferometer for ASK-WDM transmission
Feng Qu, Xiaoming Liu, Jianhui Zhao
A power equalization using an asymmetric nonlinear amplifying Sagnac interferometer (NASI) for ASK modulation is studied numerically. A nonreciprocal phase bias was proposed to be introduced into the structure. The nonreciprocal phase bias reduces not only the demanding for amplifier power or fiber non-linearity, but also increase the dynamic input power range. The power equalization is demonstrated for RZ modulation by nonlinear phase analysis and eye diagram simulation.
A novel all-optical switch based on Fabry-Perot cavity
A novel configuration of semiconductor all-optical switch based on Fabry-Perot cavity is proposed. The principle and structure of this kind of all-optical switch are presented. We also analyze the performance of the all-optical switch. The wavelength selectivity of the all-optical switch changed with the power of the control light is given. We discuss its viable application in the future optical switching.
Optical device technology for packet-based optical networks
This paper summarises recent progress in realising rapidly re-configurable optical devices in Bristol. These include a monolithically integrated optical crosspoint switch matrix based on an active vertical coupler (AVC) structure, a monolithically integrated wavelength converter array based on similar structures, and a new concept for a rapidly tunable laser device. Operational principles, computer simulation results, and where appropriate, optical characterisation data, and transmission measurement results are presented.
Transparent ITO electrode in the polymer network liquid crystal variable optical attenuator
Xindong Zhang, Wei Dong, Caixia Liu, et al.
Indium tin oxide (ITO) films as transparent conductors have caused a great deal of interest due to their prominent electro-optical behavior. This paper describes a study of the properties of ITO thin films that are used for a new type variable optical attenuator using polymer network liquid crystal (PNLC). The mechanism of PNLC optical attenuator operation is that the light from the input fiber is scattered when no voltage is applied, and the light passes through the attenuator when sufficient voltage is applied. So the ITO thin films can provide transparent electrodes for PNLC. They were deposited under various preparation conditions using the radio-frequency (rf) magnetron sputtering technique. Here discuss the results of the structural, electrical and optical properties of the ITO films. The paper presents some experimental results obtained in laboratory.
Different effects on bandwidth for traveling-wave quantum well electro-absorption modulator and bulk Mach-Zehnder electric-opto modulator
Jianying Zhou, Xiaoping Zhou, Xiaoqing Jiang, et al.
For high-speed traveling-wave modulator, impedance match, velocity match and low microwave attenuation are important. But they have different effects on bandwidth for different structure and scheme for quantum well electroabsorption modulator and bulk Mach-Zehnder electrooptic modulator. For bulk Mach-Zehnder electrooptic modulator, the longer active waveguide is needed, and at such situation, according to the normalized gain (or modulation reduction factor) the velocity match and impedance match and low microwave attenuation should be well satisfied to achieve good performance. While for the quantum well electroabsorption modulator, limited by the optical loss, short active waveguide must be used. When the device length is largely reduced match requirement is not so strict and it is also difficult to achieve good match. Low terminator electroabsorption modulator is reported recently. Its concept could be inferred from the normalized gain formula. And some technology tendency in traveling-wave electroabsorption and Mach-Zehnder modulator could be also obtained and could explain series of experiment. From calculation and experiment the low impedance and low terminator could expand the bandwidth by slight mismatch. The relation of modulator characteristic impedance, microwave phase velocity and microwave attenuation is not much considered for simplification. The results are useful to design and optimize modulator.
Tunable optical filter based on liquid crystal Fabry-Perot etalon
The tunable optical filter used for WDM system was fabricated by employed the birefringence of liquid crystal. When the driver voltage changed, the refractive index of the liquid crystal was altered, which inverted to change the effective thickness of the cavity of the filter based on the Fabry-Perot etalon, so the peak of the transmittance was shifted and the filter achieved the tunable performance. The experiment result of the device was achieved to the tunable range from 1534.5nm to 1562.5nm and the full width of the half maximum is nearly 0.8nm and was in agreement with the design one.
Optoelectronic Packaging
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Design and development of optical coatings on laser bar facets
Dale E. Morton, Ian Stevenson, Michel Garcia
There are a variety of optical coatings needed on laser bar facets to make them functional. There are also several different types of laser bar facet materials to be coated which complicates the problem a little bit. These coatings fall into three types; antireflection coatings, high reflectors and partial reflectors. A wide range of coating designs and materials to be used in the coatings has been studied. The anti reflection coating (AR) typically used is either a single layer coating, obviously consisting of one material, or dual layer coatings consisting of two materials. There are a limited number of applications that may involve larger number of layers if more than one wavelength or a wavelength band of more than 40 nm needs to be covered. The single layer coatings usually do not provide very low reflectance. Dual layer coatings provide the ability to design coatings with very low reflectance. Manufacturing process limitatins allow for producing AR coatings with a residual reflection in the 0.1%-0.2% range. Although lower reflecting coatings can be designed, process control parameters and optical measurement problems limit the coating manufacturer to this range with R ≤ 0.2% being a standard specification. This paper will discuss the various coating designs for achieving low reflectance on InP and GaAs laser facets and the optical measurements problems.
Automated packaging platform for low-cost high-performance optical components manufacturing
Delivering high performance integrated optical components at low cost is critical to the continuing recovery and growth of the optical communications industry. In today's market, network equipment vendors need to provide their customers with new solutions that reduce operating expenses and enable new revenue generating IP services. They must depend on the availability of highly integrated optical modules exhibiting high performance, small package size, low power consumption, and most importantly, low cost. The cost of typical optical system hardware is dominated by linecards that are in turn cost-dominated by transmitters and receivers or transceivers and transponders. Cost effective packaging of optical components in these small size modules is becoming the biggest challenge to be addressed. For many traditional component suppliers in our industry, the combination of small size, high performance, and low cost appears to be in conflict and not feasible with conventional product design concepts and labor intensive manual assembly and test. With the advent of photonic integration, there are a variety of materials, optics, substrates, active/passive devices, and mechanical/RF piece parts to manage in manufacturing to achieve high performance at low cost. The use of automation has been demonstrated to surpass manual operation in cost (even with very low labor cost) as well as product uniformity and quality. In this paper, we will discuss the value of using an automated packaging platform.for the assembly and test of high performance active components, such as 2.5Gb/s and 10 Gb/s sources and receivers. Low cost, high performance manufacturing can best be achieved by leveraging a flexible packaging platform to address a multitude of laser and detector devices, integration of electronics and handle various package bodies and fiber configurations. This paper describes the operation and results of working robotic assemblers in the manufacture of a Laser Optical Subassembly (LOS), its subsequent automated testing and burn/in process; and the placement of the LOS into a package body and hermetically sealing the package. The LOS and Package automated assembler robots have achieved a metrics of less than 1 um accuracy and 0.1 um resolution. The paper also discusses a method for the critical alignment of a single-mode fiber as the last step of the manufacturing process. This approach is in contrast to the conventional manual assembly where sub-micron fiber alignment and fixation steps are performed much earlier during the assembly process. Finally the paper discusses the value of this automated platform manufacturing approach as a key enabler for low cost small form factor optical components for the new XFP MSA class of transceiver modules.
Novel efficient compact package of high-power laser diode arrays with single-piece copper microchannel heat sink cooling
Yun Liu, Xinsheng Liao, Yuxia Tang, et al.
Novel efficient and compact package of high power laser diode arrays with single piece microchannel heatsink cooling was designed. The width of microchannel was optimized by theoretic analysis. Using single piece microchannel heatsink we manufactured 5 bars high power laser diode stack and obtained 40W CW output, the lifetime of laser diode stack was more than 5000 hours.
980-nm broad-area diode laser coupled to a cylindrical lensed multimode fiber
Shizhe Shen, Quan J. Zhang, Yuanxiang Wang
A theoretical model is presented to calculate the fiber coupling efficiency and alignment tolerances for the case of a 980nm 100μm broad-area diode laser directly coupled to a 100μm round-shaped cylindrical lensed multimode fiber. Both radius and wedge angle of the round-shaped cylindrical lens are optimized for maximum coupling efficiency. It is found that with proper design, a coupling efficiency of up to 98% may be obtained theoretically. The alignment tolerances for all three directions (vertical, horizontal, and axial offsets) are also calculated. It is found that the vertical offset (X-offset) tolerance is the most critical one among three, but is still acceptable (~2μm) for low-cost practical packaging. It is also found that the distance between the diode and the fiber, and the lens shape on the fiber can be further varied to improve this tolerance.
XFP optical engines: design considerations for low cost, high performance and small form factor
Richard B. Bylsma, Robert L. Hartman, Padman Parayanthal
The recent activity in transceiver and transponder multi-source agreements has led to smaller, cost efficient modules to enable telecom and datacom systems in many different applications. At data rates of 10Gb/sec these applications can be include transmission distances < 100m or greater than 80km. The transmitter optical engines which go into these products must meet many constraints in terms of performance, cost, size and manufacturability. This paper will identify some of the key design issues engineers must address and potential solutions for those issues.
Photonic Crystal II
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Magneto-optical Kerr effect and photonic bandgap in cobalt nanodisc array
Kin Man Tsia, Chi Lok Cheng, Silas T. Hung, et al.
In this paper, we report our experimental investigation on two-dimensional (2-D) magneto-photonic crystals (MPCs) by using high-precision magneto-optical Kerr effect (MOKE) measurement. Our 2-D MPC is in the form of a periodic triangular array of cobalt (Co) circular nano-discs on a silicon (Si) substrate. Preliminary longitudinal MOKE measurement reveals a hysteresis loop that suggests a saturated Kerr rotation of ≈ 0.05°. We numerically investigate the potential photonic band gap (PBG) phenomenon of a triangular nano-disc array with the Co real refractive index = 2.26 by using 2-D finite-different time-domain (FDTD) method. We observe relatively wide TM-polarization (E-field⊥substrate) band gaps in the 1550-nm telecommunication wavelengths: 500 nm in the -M Γ direction whereas 400 nm in the -K Γ direction.
Spontaneous emission of a two-level atom in photonic crystals
Lingjiang Yao, Jingcui Peng, Hongjian Li, et al.
We investigate spontaneous emission from a two-level atom embedded in photonic crystals. Due to the photon localization and the quantum interference between the two dressed states, some changes of the radiation field happen, and the energy is transferred among the excited atom, the localized field, the propagating field and the diffusion field. If there is a localized field, it appears quasi-oscillation behaves of the population evolution in the excited level. If there isn't a localized field, it appears no quasi-oscillation. Moreover, there have some steady-state trapped atom populations in the excited level, and the spontaneous emission spectrum near the forbidden gap edge is different from that in the vacuum. All these characteristics depend not only on the relative position of the excited level from the band-edge but also on the photon density of states (or the band-edge smoothing parameter) near the band edge.
High-directivity photonic bandgap antenna
Yuan Li, Huancai Li, Yuanchao Wang, et al.
The microstrip patch antenna is a low-profile low cost robust planar structure. A wide practical range of can be obtain with this type of antenna and, due to the ease of manufacture, is inexpensive compared with other types of operation, low gain, and a potential decrease in radiation efficiency due do surface-wave losses. In this paper, a new type of high directivity PBG patch antenna is proposed. It has been demonstrated that take advantages of both the suppression of surface waves and high directivity.
One-dimensional chiral photonic bandgap structure analyzed by nonsymmetric transmission-line method
In this paper, the formula of reflection coefficient of multi-layer chiral media is derived by non-symmetric transmission-line method. Then, it is applied to 1-D chiral photonic crystal structure, which is composed of thin chiral layers sandwiched by air. The results show that it is difficult to obtain photonic band gap for general dielectric when the difference of two media refractive indices isn't large, and the reflection coefficient is small. With the increasing of the refractive index of the medium, reflection coefficient becomes gradually large, and reflection bandwidth basically keeps unchanged. These characteristics are agreed with results of theoretical analysis of photonic crystal. However, for chiral photonic crystal, although the refractive index of chiral layer is small, the wave spectrum obtained contains forbidden zones and the reflection coefficient from such a structure is found to be almost equal to 1, i.e., the wave is almost totally reflected through adjusting chiral parameter. Therefore it is easier to obtain an ideal photonic band gap.
LED
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Angled stripe InGaAsP/InP SLED fabricated by low- damage inductively coupled plasma dry etching
Jun Zhang, Xiaodong Huang, Jin Chang, et al.
We successfully fabricated the angled strip DC-PBH style SLED devices by using low damage ICP dry etching technology. The mesa of DC-PBH SLED was formed by Cl2/N2 ICP dry etching process. The low DC bias (<100 eV) of ICP etching technology can reduce the damage caused by ordinary RIE technique and Cl2/N2 based process can get rid of chemical damage caused by CH4/H2. High out-put power SLED device was obtained by using low damage ICP dry etching, the out-put power is 2 mW at 100 mA inject current (CW) at 25°C. Through optimized the angle of the active strip and AR optical film design, the full width of the half maximum (FWHM) of the spectrum at 2 mW out-put power can reach 46.4nm and the ripple of the SLED spectrum is low down to 0.4 dB.
Full metal organic microcavity emitting device
Chunyu Zhang, Fengying Ma, Yongqiang Ning, et al.
A red emitting microcavity device with a multiple layer of Glass/DBR/Ag/NPB/DCM:Alq3/ Alq3/LiF/Al was fabricated. Comparing with device of Glass/ITO/NPB/DCM: Alq3/ Alq3/LiF/Al, the spectrum of the microcavity device was narrowed from 67nm to 27nm and the peak intensity was increased by a factor of 2.5, while the current density was one eighth of that of non-cavity device at the same bias voltage. By inserting an Ag layer between ITO and NPB the current intensity was sharply enhanced about three times and because of weak cavity effects the spectrum changed largely.
The influences of injection and recombination on the EL efficiency in organic single-layer EL devices
Chu-jun Zhao, Hongjian Li, Hao-yang Cui, et al.
We have developed an analytical model to calculate the EL profile at high electric field in single layer structure, taking into account the charge injection process at each electrode, fission and recombination of polaron-excitons. By simulation, the influences of injection barriers on EL efficiency and fission distance on recombination efficiency are thoroughly studied. Using either both ohmic contacts or using an ohmic contact to inject the low mobility carrier and a contact limited contact to inject the high mobility carrier can obtain efficient devices. By comparison of the theoretical results with the experimental data reported in the literature, we found this model can reasonably elucidates the influences of some factors on injection and recombination.
Using a mixed emitting layer of hole and electron transporting molecules to improve the performance of MOLED
Fengying Ma, Chunyu Zhang, Yun Liu, et al.
Performance of the devices is significantly influenced by the charge balance between holes and electrons since the excess of one type over the other would lead to an increase in current but no emission contribution. The device performances were dramatically enhanced by using a mixed emitting layer of NPB and Alq3 molecules, placed between pure NPB and Alq3 layer. Comparing with the conventional heterostructure the turn-on voltage was reduced from 7v to 4v and the V--L characteristics was also improved by mixing hole and electron transporting layers. By changing the weight ratio of NPB and Alq3 the spectrum have 33nm shift and the CIE coordinates have relevant change.
Color-tunable organic thin film light-emitting devices based on heterostructure
Organic light emitting devices (OLEDs) have attracted great interest because of their bright future as a competitive flat-panel display technique of LCD. OLEDs based on PDDOPV [poly (2,5-bis (dodecyloxy)-phenylenevinylene)]/Alq3 (8-hydroxyquinoline aluminum) heterostructure were fabricated. The emission spectrum of the device base on heterostructure PDDOPV(70nm)/Alq3(20nm) is similar to that of single layer device of PDDOPV except the emission intensity is enhanced by several magnitude order. But the emission spectrum of the device based on heterostructure PDDOPV(70nm)/Alq3(32nm) is composed of two parts, one is originated from PDDOPV , the other is from Alq3. The emission from PDDOPV dominates at low drive voltage but the contribution from alq3 emission increases with the increase of applied voltage. Finally ,Alq3 emission dominates at high applied voltage.
Alternating-current polymer light-emitting devices
Xuejun Hu, Haishu Tan
Alternating current polymer light emitting devices (PLEDs) have attracted much attention because ac operation can partially reverse electrochemical reaction at interfaces and a longer lifetime is expected over dc operation. Most ac PLEDs to date are based on symmetrical structure. Here novel alternating current EL devices with asymmetric structure are successfully fabricated by using a hole type polymer PDDOPV [poly (2,5-bis (dodecyloxy)-phenylenevinylene)] and an electron type polymer PPQ [poly (phenyl quinoxaline)]. Two devices with following structure were made, Device 1: ITO/PDDOPV(70nm)/PPQ(40nm)/Al, Device 2: ITO/PDDOPV(100nm)/PPQ(70nm)/Al. Both devices can be operated at forward and reverse dc bias and ac modes but the performance of Device 1 is much better than that of Device 2. Emitting intensity of both devices at forward dc bias was several magnitude orders stronger than that at reverse dc bias. Both the highest luminescent intensity and efficiency of Device 1 at ac operation were the same magnitude order as those at dc operation, but those of Device 2 at ac operation were about 1 magnitude order higher than those at dc operation. Contribution from PPQ increases with the increase of applied voltage.
VCSEL
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Commercialization of VCSELs and VCSEL arrays
Karlheinz Gulden, Yu Gao, Paul Royo, et al.
Various aspects relevant for the commerzialization of VCSELs used in data communications and sensor applications are discussed. In particular, reliability results obtained on selective oxide VCSELs and production reliability assurance procedures are discussed. For typical operating conditions of 50°C and 6 mA we obtain a time to 1% failure of 1.7 Million hours.
Advances in the spectroscopic characterization of vertical-cavity optoelectronic devices and structures using modulated reflectance
The vertical-emitting devices, resonant-cavity LEDs (RCLEDs) and vertical-cavity surface-emitting lasers (VCSELs) are key components in a broad range of applications including optical communications. However, the complexity of these multi-layer structures causes significant difficulties in their non-destructive characterisation at the pre-fabrication stage, and they have defied analysis by conventional optical techniques, such as photo-luminescence (PL). Fortunately, a complementary spectroscopy, modulated reflectance (MR), provides a viable alternative. MR is a simple technique in which the reflection spectrum of a semiconductor is periodically externally perturbed - most usefully using a mechanically-chopped laser beam, i.e. photo-modulated reflectance (PR). This yields sharp derivative-like spectra which are replete with features from ground-state, and, in contrast to PL, many other possible higher-energy optical transitions. This detailed information enables the deduction of material parameters crucial to efficient device operation, such as compositions, layer thicknesses, in-built electric fields and band line-ups. PR is truly non-destructive because samples need no special mounting, can be studied in air at room-temperature, and can be full-sized pre-fabrication wafers. At Surrey we have pioneered the application and interpretation of MR to the assessment of VCSELs and RCLEDs, and here we discuss the advances that we have made, which have attracted interest from the growth industry.
Design and analysis of VCSEL-based two-dimensional wavelength converter by using developed TLLM
Hairong Liu, Ping Shum, Ming-Seng Kao
We develop a complete two-dimension transmission line laser model (TLLM) to analyze the proposed twodimension vertical cavity surface emission laser (VCSEL) based wavelength converter. Modified connecting matrices are used to model the Bragg reflectors. The longitudinal variations of carrier density, photon density and the amplified spontaneous emission noise are taken into account. Therefore, extinction ratio, frequency chirping, optical pulse patterns and dynamic characteristics can be accurately estimated. In this paper, extinction ratio and frequency chirp of the output signal have been calculated for various parameters such as wavelength, input signal power, cavity diameter and facet reflectivity.
Controlling chaos of vertical-cavity surface-emitting lasers with optical feedback
Wei Pan, Xiaoxia Zhang, Bin Luo, et al.
The authors propose a new compound cavity model with optical feedback for study the nonlinear dynamic behavior of VCSEL. The results show that system can be controlled to its fixed point, periodic orbits by using modulation parameters. In addition, the stable range be obtained and indicate the introduction of external reflectivity enhances chaotic characteristics. As increase of the external mirror reflectivity the CW state become unstable and the output power exhibit single period oscillation, higher order bifurcation, eventually leading to chaos.
Long-wavelength oxide-confined VCSEL using InGaAsN quantum wells
Characteristics of oxide-confined vertical-cavity surface emitting laser emitting at 1289nm will be presented in this paper. The wafer is monolithically grown using InGaAsN/GaAs QWs as active layer and GaAs/AlGaAs conventional DBRs. In the structure, the laser employs 39 pairs N-GaAs/Al0.9GaAs and 23 pairs P-GaAs/Al0.9GaAs with a selectively oxide layer located at first DBR close to active region, providing the current and optical confinement. The device processing is similar to the fabrication for current 850nm oxVCSELs. Mesa etching is used to expose the Al-rich AlGaAs layer and followed by oxidation to form the current confinement. The maximum light output power is around 950uW at room temperature under CW operation with a threshold current around 6mA for 10um aperture size devices. The device can still lase at 1000C with a maximum power of 0.14mW. Slope efficiency is 0.133(W/A) and side mode suppression ratio (SMSR) is around 20dB at 10mA operation. The aging data and speed transmission experimental data will also be presented.
Optical Detectors
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High-coupling efficiency and high-speed InP/InGaAs resonant-cavity-enhanced photodetector with micropectinated carrier collected layer
Hui Huang, Lei Lei, Yanjun Li, et al.
High efficiency, long wavelengths InP/InGaAs resonant-cavity enhanced (RCE) Photodetector was fabricated. To circumvent the difficulty in achieving high reflective InP-based DBR, the Si/SiO2 DBR was evaporated as the bottom mirror of the cavity by using back illumination from the substrate. A quantum efficiency of 80% at 1.583um was achieved with an absorption layer thickness of only 0.2um. In addition, the Micro-pectinated Carrier-Collected Layer (MCCL) was fabricated by proton implantations, thus device capacitance can be reduced without decreasing of the illuminating area. The bandwidth was increased from 600MHz to 800MHz experimentally by formation of MCCL, without decreasing of the quantum efficiency.
A robust 40-Gb/s evanescently coupled waveguide photodiode with high efficiency for use in dual wavelengths: 1310 and 1550-nm
Kazuhiro Shiba, Takeshi Takeuchi, Takeshi Nakata, et al.
An evanescently coupled waveguide photodiode (EC-WG-PD) for both 1310-nm and 1550-nm wavelength bands has been developed for use in long-haul and high capacity very-short-reach (VSR) transmission systems. The EC-WG-PD is much more robust than a conventional waveguide photodiode (WG-PD) under high optical input operation because its absorbed optical power density is distributed along the light propagation in the waveguide. High external quantum efficiency of 65% for 1310 nm and 74% for 1550 nm, and a high 3-dB-down bandwidth of 41 GHz were demonstrated. No significant degradation of the frequency response was observed up to an average photocurrent of 10 mA. Moreover, a clear receiving eye-waveform was obtained at 40 Gb/s for an implemented single-output receiver module.
Evolution beyond resonant-cavity-enhanced photodetectors
The RCE photodetectors have evolved rapidly and been succeeded by a new variety of devices, i.e. the integrated OWDM tunable demultiplexing and detection unit. The concepts, device structure and operation principles differ to some extent from the original RCE photodetectors. As a good example, One-Mirror-Inclined Three-Mirror-Cavity (OMITMiC) photodetector, which combines a Fabry-Perot filtering-cavity with a taper absorption-cavity, features high-speed, high quantum efficiency and ultra-narrow spectral linewidth simultaneously and allows wide range tuning when proper tuning mechanism is introduced. First fabrication and demonstration of this kind of device on GaAs substrate had been done in our laboratory. A quantum efficiency of 75% and a spectral linewidth of 0.8nm (FWHM) were achieved with an absorption layer as thin as 0.119μm. Relevant micromechanical tunable Fabry-Perot filter with a tuning range about 30nm had been achieved. Research works on the key technologies to transfer our success to InP based long wavelength device are also presented.
Test of 1.06-µm photo detector of PIN photodiode
The paper introduces the principle and structure of the PIN diode detector, and then describes the researching background and the responding characteristic of the detector. The high responsibility of photodiode response characteristic is important. The paper designs a set of testing device to measure the responsibility. The optical part can produce a laser pulse of 1.06μm with a certain frequency and energy, with the aid of white light source and CCD camera, the laser beam can focus on the surface of the photon detector of PIN diode. The signal-testing instruments can measure the responding characteristic of the photon detector, and the average noise power. The paper gives the waveforms of the laser pulse and the responding signals.
The design on a coplanar waveguide used in 40-Gb/s PIN/TIA and the investigation on its matching problems
Ding-Guo Qing, Xing-Yao Liu
The structure of some waveguide types of PIN photodetector and the brief circuit diagram of transimpedance amplifier (TIA) are introduced. Some coplanar waveguide designs used in the connection between 40Gb/s PIN and 40Gb/s TIA are described. The terminal impedance matching of the coplanar waveguide are discussed further.
Monolithic integration of 1x2 digital photonic switching with photodetectors
A digital photonic switching through the use of monolithically grown thin-film photodetectors based on SiGe materials is proposed for optical communication at the wavelengths of 1.3- and 1.55- mm. Experimental analysis has been investigated and shows that the heterostructure can be monolithically integrated with other devices made from similar materials. The device performances are measured. The crosstalks of the digital photonic switching at a forward modulation bias of 1.2 V are -25 and -18 dB at 1.3- and 1.55- mm, respectively. The insertion losses are 2.01 and 2.64 dB for 1.3- and 1.55- mm, respectively. At -5 V reverse bias, the dark currents of the detectors at the 1.3- and 1.55- mm output branches are 45 and 64 nA, respectively. The photocurrent responsivities of 0.08 and 0.07 A/W for the two detectors at the 1.3- and 1.55- mm output branches have been achieved. The quantum efficiencies of the whole switching and detector integration system are estimated to be about 19 and 18.2% for the 1.3- and 1.55- mm output branches, respectively.
Novel Devices I
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Accelerating tomorrow's optoelectronic technologies: a comprehensive introduction to advanced optoelectronic materials and devices in the National Hi-Tech R&D Program (863-Program)
Shan Jiang, Haoming Chen, Xiaomin Ren, et al.
The National Hi-Tech R&D Program (the 863-Program) is to enhance China's international competitiveness and improve China's overall capability of R&D in high technology and to bridge the gap between the laboratory and the marketplace. Advanced Optoelectronic Materials and Devices are one of the technology areas strategically important to China's information industry. It has been one of the major priority research fields funded by the 863 Program even since 1987 when the plan was first initiated. From the viewpoint of Priority Expert Group (PEG), this paper will give a comprehensive introduction to advanced optoelectronic materials and devices in the national 863-Program during the current five years period (up to 2005) which includes the main aims and goals and especially the main content of each subject.
Effect of SiO2 encapsulation on the nitrogen reorganization in GaNAs/GaAs single quantum well
Ying-Qiang Xu, Wei Zhang, Zichuang Niu, et al.
Effects of SiO2 encapsulation and rapid thermal annealing (RTA) on the optical properties of GaNAs/GaAs single quantum well (SQW) were studied by low temperature photoluminescence (PL). A blueshift of the PL peak energy for both the SiO2-capped region and the bare region was observed. The results were attributed to the nitrogen reorganization in the GaNAs/GaAs SQW. It was also shown that the nitrogen reorganization was obviously enhanced by SiO2 cap-layer. A simple model [1] was used to describe the SiO2-enhanced blueshift of the low temperature PL peak energy.
Preparation and characterization of ZnS thin films by chemical bath deposition and electron beam evaporation
K. V. Murali, Antony Aldrin, Manoj Ramachanrdan, et al.
Zinc sulphide thin films were prepared by chemical bath deposition (CBD) and the properties of these films are compared with those deposited by Physical vapour deposition (PVD). The variation in the optical and electrical properties of the CBD grown ZnS films with the pH of the reaction mixture was investigated. The chemically deposited ZnS films showed a wide band gap of 3.93eV and a transparency of more than 80% in the visible region. The lowest resistivity of ~104 Ωcm was obtained for the films prepared from a chemical bath of pH 10.6. The refractive index, extinction coefficient and the dielectric constants of CBD ZnS films are also reported.
Simulation and experimental study of high-power fiber lasers
Yuzhai Pan, Jun Zhang, Guijun Hu, et al.
High power fiber laser was demonstrated by using Yb-doped double-clad fiber based on laser cavity consisted of both fiber Bragg gratings spliced onto fiber ends, which pumped by a fiber-coupled multimode laser diode (FMLD) with 970nm central wavelength. In our experiment star-shape double clad Ytterbium-doped fiber was used, the MAX output power and center wavelength is 6W cw and central wavelength of 1100nm respectively, FWHM is about 0.66nm, the slope efficiency is about 51%.
Spectroscopic properties of Er3+/Yb3+-codoped niobate-phosphate glasses
Tong-Zhao Gu, Maohua Zhu, Wanghe Cao
The niobate-phosphate glasses with high Er3+/Yb3+ concentration were prepared. The absorption and fluorescence emission spectra were measured. The effect of Er3+/Yb3+ ion concentrations on the spectroscopic properties was researched. The emission cross sections for 4I13/2 4I15/2 transition of Er3+ was calculated by McCumber theory. It was found that the emission cross sections around 1534nm increase and then decrease with the increase of rare earth ion concentrations. The maximum intensity of fluorescence occurs at the concentration of 6wt%. The effective emission cross section bandwidth was also discussed.
Fiber optic evanescent wave sensor for ammonia gas
P. Suresh Kumar, V. S. Abraham, C. P. G. Vallabhan, et al.
This article describes the design, development and characterization of an evanescent wave fiber optic sensor (EWFS) for the detection of toxic ammonia gas. Sol-gel technology is employed for immobilizing a reversible ammonia sensitive dye on the middle unclad region of a multimode fiber. Ammonia gas permeating into the immobilized dye, the color of the dye changes reversibly from yellow to blue with increasing concentration of ammonia gas. The concentration of ammonia gas can be determined by measuring the absorption at a given wavelength. The response of the sensor to different concentrations of ammonia, recovery time, reusability, etc of the developed sensor is also discussed. The techniques described here is also relevant to the detection of a wide range of other gases.
Solid State Devices
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Investigation of electro-optic wavelength tuning in lithium niobate optical parametric oscillator
Chun Li, Yuying An, Xiaodong Zeng
An OPO with lithium niobate used as nonlinear material and frequency agility accomplished by the electro-optic effect is presented in this letter. The proposed LiNbO3 electro-optic wavelength tuning OPO is based on phase-matching equations controlled by changing values of applied DC voltages. The wavelength tuning range we acquired is about 139.6nm for idler wave and 22.8nm for signal wave with the applied DC voltages changing from -4.5kV to 4.5kV.
Temperature, angle, and grating period simultaneously tuned QPM optical parametric oscillator based on PPLN
Baigang Zhang, Degang Xu, Xin Ding, et al.
We report a temperature, angle and grating period simultaneously tuned all-solid-state optical parametric oscillator with periodically poled lithium niobate (PPLN) pumped by a 1064nm acousto-optically Q-switched cw-diode-end-pumped Nd: YVO4 laser. Continuously tunable signal output from 1441.2nm to 1532.6nm is obtained by changing the temperature, the angle and the position of the multi-grating PPLN crystal. The PPLN crystal contained three gratings, equally spaced in period from 28 to 29μm (at room-temperature).
Thermal effect in diode-side-pumped solid state laser
The thermal effect in the laser diode (LD)-side-pumped solid-state laser is studied. The pump power, the temperature distribution figures and the laser beam parameters are obtained. The thermal effects under different cooling conditions are numerically calculated, as well as those in diode-end-pumped solid-state laser. The calculation results are compared with those in diode-side-pumped solid-state laser.
Research on glass ceramics with negative coefficient of thermal expansion used as fiber Bragg grating substrate
The β-eucryptite glass ceramics with negative coefficient of thermal expansion (CTE) is studied in this paper. And the coefficient of thermal expansion, the crystal phases and the structure are researched by XRD and SEM. The β-eucryptite glass ceramics with negative CTE is produced by glass crystallization method, and whose negative CTE of -103.7×10-7/°C (from room temperature to 200°C) is obtained, which can be used as fiber Bragg grating (FBG) substrate. The substrate shrinks with a rise in temperature which compensates for the Bragg wavelength shift with temperature. It can be confirmed that β-eucryptite glass ceramics have suitable thermal expansion characteristics for FBG.
Study on rate equations and numerical analyzing for phosphate glass waveguide laser
We have developed a rigorous phenomenological model for analyzing Yb3+/Er3+-codoped phosphate waveguide lasers. The model is based on time-dependent laser rate equations for an Yb3+/Er3+-codoped laser host with multiple energy levels. We have used the model to predict the characteristics of waveguide lasers pumped by a 980-nm source. We also define and discuss the waveguide laser intensity distributions, host parameters, doping profiles, and the laser cavity design parameters. Solutions for the laser signal power, pump power, and populations of ion energy levels as functions of space and time are obtained for waveguide lasers.
Writing waveguides in fused silica using a femtosecond laser
Lin Ma, Shunxiang Shi, Guanghua Cheng, et al.
A new and more-flexible and directly femtosecond laser writing technique for the fabrication of waveguides has been demonstrated. By using this avenue, waveguides of 5mm are produced, and their characters are discussed. At the same time, the two writing manners are compared and the related physical mechanisms are summarized in detail.
Novel Devices II
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Comparison and research for several bi-directional reflectance distribution function (BRDF) measurements
Jingmin Dai, Chao Qi, Xiaogang Sun
The characteristics of spatial light scattered from optical material surfaces are effectively described by BRDF. There are two forms for measuring BRDF: they are absolute measuring and relative measuring. The absolute measuring includes the definition method and introducing bi-directional reflectance factor method. The relative measuring includes the substitution method and single reference measuring method. The measuring methods based on vary principles are comprised and the features of each method are analyzed, a set of system based on personal computer for BRDF measuring has been developed, it is made of optical path, electronic path, and mechanical path. With He-Ne laser and YVO4 solid laser, the measurements on 1500 CCR/RC.S.G Silicon carbide abrasive paper have been made within the -55°-55° of reflectance zenith angle, the experimental results show that it has better Lambertian diffusion characteristic.
Enhancement of thermal lens signal intensity from molecules of rhodamine 6G dispersed in colloidal silver
A. Santhi, V. S. Abraham, P. Radhakrishnan, et al.
We report a novel technique to enhance the thermal lens signal intensity by the use of silver nanosol. Thermal lens signal measurements of the laser dye rhodamine 6G dissolved in double distilled water has been carried out using the 532 nm excitation from a Diode pumped solid state (DPSS) laser, both in the presence and absence of silver sol for various concentrations. It has been observed that there is a very noticeable increase in signal intensity when silver nanosol is added to the dye solution. Though the enhancement varies with concentration, it is generally greater than 56 percent. The results presented in this work are of great importance to configuration and optimization of extremely sensitive thermal lens instruments, which is the trend in the development of analytical instruments. We have also carried out the fluorescence quantum yield (Qf) measurements of the dye using the dual beam thermal lens technique for two different pump powers and observed that at higher pump power there is only about 10% reduction in the quantum yield at low concentration in comparison with about 50% reduction at low pump power. At higher concentrations, the percentage reductions are almost identical in both cases.
Beta-In2S3 thin films prepared by the sulpherization of evaporated indium films
Yoosuf Rahana, Kalloor Cheekku Jerome, Antony Aldrin, et al.
β-In2S3 films were grown on glass and quartz substrates by the rapid heating of metallic indium films in H2S atmosphere. The effect of sulphurisation temperature and time on the growth of single phase In2S3 and its electrical and optical properties have been investigated. The influences of processing parameters on the electrical and optical properties have been studied. The band gaps of In2S3 films were in the range 1.9 eV to 2.3eV. All the films exhibit n-type conductivity. The studies on temperature dependence of conductivity indicate a variable range hopping mechanism.
Poster Session
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Propagation of optical soliton in a fiber Raman amplifier
In this paper we present a numerical analysis of soliton propagation in fiber Raman amplifier. By employing the concept of distributed Raman amplification, which utilizes the transmission medium as the amplification medium, we obtain the equivalent fiber loss which later be incorporated into the soliton propagation analysis.
Photoinduced molecular orientation in bulk azodye-doped polymer by nonresonant femtosecond laser pulses
Jinhai Si, Jianrong Qiu, Kazuyuki Hirao
We show two kinds of photoinduced molecular orientations in bulk azodye-doped polymers: photoinduced molecular orientation with centrosymmetry and photoinduced molecular orientation with noncentrosymmetry. For the photoinduced molecular orientation with centrosymmetry, the samples were irradiated with a linearly polarized femtosecond laser whose wavelength (800 nm) was out of the absorption range of the azodye molecules. This photoinduced molecular orientation with centrosymmetry resulted in a birefringence in the sample, based on which an optical image storage was demonstrated. The probe transmittance for the induced birefringence was estimated to be 92%. For the photoinduced molecular orientation with noncentrosymmetry, the sample was irradiated simultaneously by coherent superposition of the 1500-nm fundamental and 750-nm second-harmonic light of a femtosecond laser. The second-harmonic generation (SHG) conversion efficiency of a 105-μm thick film was estimated to be about 2%.
The effect of the CsCl buffer layer on the performances of the organic electro-luminescent devices
Wenfa Xie, Jingying Hou, Yi Zhao, et al.
We studied electron injection form Al cathode into the tris(8-hydroxyquinoline)aluminum (Alq3). When a thin CsCl layer is inserted between Alq3 and Al, a substantial enhancement in electron injection is observed. The results show that the device with the cathode containing the ultrathin CsCl layer has a higher brightness and electroluminescent efficiency than the device without this layer. Further, organic light-emitting devices (OLEDs) based on tris-(8-hydroxyquinoline)aluminum using a trilayer of CsCl/LiF/Al as cathodes have been fabricated. The results show that the device with the cathode containing 0.5 nm CsCl layer and 1.0 nm LiF layer has a higher brightness and electroluminescent efficiency than that of the device with LiF/Al or CsCl/Al cathodes. The maximum EL efficiency of the CsCl/LiF/Al cathode device is 3.41 cd/A, which is higher than the 2.74 cd/A of the LiF/Al device and 2.49 cd/A of the CsCl/Al device.
Influences of material performance parameters of GaAs/AlGaAs photoemission
Xiaoqing Du, Benkang Chang
Photocathode based on GaAs/AlGaAs heterojunction has been applied broadly for its broad spectral response wavelength, high quantum efficiency and low dark current. To obtain more effective photoemission, reasonable selection of material parameters of GaAs/AlGaAs heterojunction is required. In this paper on basis of three step photoemission model, the dependence of adsorption coefficient of GaAs, electron diffusion length and surface escape probability on p-type doping concentration are made analysis, and theoretic quantum efficiency of GaAs/AlGaAs heterojunction photocathodes for different doping concentrations are deduced. From the calculated results the optimum doping concentration for p-type GaAs is between 3.0×1018cm-3 and 6.0×1018cm-3 and response threshold wavelength moves towards long-wave with doping concentration increases.
Optical fiber sensing and communication systems using fiber and microchip laser sources
Junewen Chen, Pie-Yau Chien, Jun-Ting Lin
Fiber optic strain sensor systems using fiber Bragg grating have been developed in our Section with time demultiplexing phase stabilized feed back Fabry-Perot tunable filter and signal processing technologies. The system can resolve < 1 μ strain, with measuring range of 4000 μ strain; and can monitor 20 points simultaneously. It has been used in real time long term hazard investigation and warning system on the bridges and traffic high-pass ways. The data from these smart fiber optic distributed stress and strain sensing systems had constantly been observed with satisfactory results. Our fiber optic communication system is a bi-directional audio-video and data signal transmission system. The source laser diodes are TE cooled with temperature control circuits. The system is dual audio bi-directional transmission and receiving channel with bandwidth 4.8 KHz. Video one direction transmission and receiving, meets NTSC specification with bandwidth 6 MHz. Dual data signals bi-directional transmission adn receiving channel, meets RS-232C specification and the Buad rate are 9.6 Kbps. The sstems are carefully designed and fabricated to meet the environmental wide temperature range conditions as well as high vibration and shock mobile transportation.
Blue and white organic light-emitting devices based on 2,5,2',5'-tetrakis (4'-biphenylenevinyl)-biphenyl
Gang Cheng, Feng He, Yi Zhao, et al.
Blue and white organic light-emitting devices using a novel dimeric trimeric phenylenvinylene (TPV) derivative , 2,5,2',5'-tetrakis(4'-biphenylenevinyl)-biphenyl (TBVB) containing a biphenyl center are fabricated. Structures of these devices are simple, where tris (8-hydroxyquinoline) aluminum (Alq) and N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) are used as electron-transporting and hole-transporting layers, respectively. In blue device, TBVB is used as light-emitting layer. The peak of electroluminescent (EL) spectra of the device with TBVB is at 468 nm, and its maximum efficiency is greatly higher than that of the reported oligomer poly(phenylenvinylene) (PPV) devices. By inserting an ultra thin layer of rubrene between TBVB and Alq layers, a fairy pure white OLED with CIE coordinates of (0.33, 0.34) is realized. Its maximum luminances and efficiencies are 4025 cd/m2 and 3.2 cd/A, respectively.
White organic light-emitting devices using a thin layer of tris (8-hydroxyquinoline) aluminum doped with 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl) as chromaticity-tuning layer
Yi Zhao, Gang Cheng, Jingying Hou, et al.
Efficient white organic light-emitting devices are demonstrated by inserting a thin layer of tris (8-hydroxyquinoline) aluminum (Alq) doped with 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl) (DCJTB) into N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) layer. Alq without doping is used as an electron-transporting layer and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine or BCP) as an exciton-blocking layer. NPB layers are separated by the doped Alq layer, the layer that sandwiched between BCP and doped Alq layers acts as a blue-emitting layer, and the other as a hole-transporting layer. The doped Alq layer acts as a red and green-emitting as well as chromaticity-tuning layer, whose thickness and position as well as the concentration of DCJTB in Alq permit the tuning of the device spectrum to achieve a balanced white emission with Commission Internationale De L'Eclairage coordinates of (0.33, 0.33), which are largely insensitive to the applied voltages, especially at high brightness (>1000cd/m2). The device have maximum luminance and efficiency of 6745 cd/m2 and 2.56 cd/A, respectively.
Analysis of Raman gain in various optical fibers
Jiping Ning, Zhiqiang Chen, Wen Xu, et al.
Raman gain in various optical fibers G652, G653, G655 and DCF (dispersion compensating fiber) and the selection of fibers in discrete broadband Raman fiber amplifiers (RFA) are studied. Using the experimental results from references, we have obtained a polynomial formula of the SRS (stimulated Raman scattering) Stokes spectrum and the effective area of the fibers by sampling and digital fitting. The effective Raman gain coefficients are calculated using the formula. Based on the formula, Raman gains of multi-wave pump RFA in different fibers are obtained with the consideration of arbitrary interaction between pump waves and signal waves. Comparing the pump power distributions and the lengths in the four optical fibers, we propose appropriate selections of optical fibers in Raman fiber amplifiers.
Gain variations in bi-directionally pumped fiber Raman amplifier due to PMD
Sheng Cui, Xiaoming Ma, Jinsong Liu
Due to the polarization sensitivity of Raman gain and the random nature of PMD in the fiber the gain of fiber Raman amplifier not only depends on the polarization states of the input signal and pump but also fluctuates over a wide range during a relative long time. The fluctuations are related to the PMD parameter of the fiber and the pumping scheme. In this paper the statistics of the gain fluctuations in an amplifier employing bi-directionally pumping schemes is studied. The ratio of forward to total pumping power is optimized to achieve best trade-off between the OSNR and nonlinear distortions beforehand. The results obtained are useful for the further optimization of bi-directionally pumped amplifiers.
Improved AC pixel electrode circuit for active matrix of organic light-emitting display
Yujuan Si, Liuqi Lang, Wanzhong Chen, et al.
In this paper, a modified four-transistor pixel circuit for active-matrix organic light-emitting displays (AMOLED) was developed to improve the performance of OLED device. This modified pixel circuit can provide an AC driving mode to make the OLED working in a reversed-biased voltage during the certain cycle. The optimized values of the reversed-biased voltage and the characteristics of the pixel circuit were investigated using AIM-SPICE. The simulated results reveal that this circuit can provide a suitable output current and voltage characteristic, and little change was made in luminance current.
Analytical expressions for saturated signal gain and output power of fiber optical parametric amplifiers
Cao Hui, Junqiang Sun, Guojie Chen, et al.
With the increasing availability of high output power EDFA as well as the development of highly nonlinear fibers, more and more fiber optical parametric amplifiers are operated near or in the saturated-gain region rather than small-signal gain region, where the signal gain characteristics are expected to be different from those in the linear-gain region. For the first time, two very pithy and powerful analytical expressions for saturated signal gain and signal output power of fiber optical parametric amplifiers are educed with numerical analysis. Those are realized in three steps, first, a series of numerical values are worked out by numerically solving the couple NLS equations that governed the fiber parameter process. Then the function form for saturated signal gain is figured out by control variates method. At last, adopting least square method, three coefficients are finely obtained with the maximum relative error (in terms of calculated saturated signal gain with numerical integration) no more than 0.46%. At the same time, we worked out the analytical expression for saturated signal output power. From those expressions, we can safely come to a conclusion that saturated signal gain of fiber optical parametric amplifiers is related to pump and signal power while saturated signal output power only rely on pump power, but both have nothing to do with nonlinear coefficient and fiber length, which is quite different from small-signal gain but accord well with law of conservation of energy. Two expressions presented in this paper are very useful in designing and analyzing fiber optical parametric amplifiers. Results of this work agree well with existing experiment results.
Design of optical fiber type travelling-wave modulator
Jiusheng Li, Zhenwu Bao, Hongjuan Zhou
In this paper, a novel electro-optic modulator-optical fiber type traveling wave modulator was proposed and analyzed. Its modulation bandwidth, half-wave driving voltage and characteristic impedance have been analyzed and calculated. Furthermore, considering these factors, we could get an optimized modulator. The result shows that the novel fiber type traveling wave modulator has the advantages of wide bandwidth, low driving voltage and impedance match. It meets the need of high speed and broadband optical communication.
Limiting the transient response of intelligent EDFA by pump controlling in DWDM network
Liming Zheng, Hongbin Huang, Xiaofeng Chen, et al.
The excursion mechanism of transient in the EDFA is analyzed and the corresponding impairments to the DWDM are discussed. Based on the analysis and the discussion, an experiment is designed to reduce the transient by pump controlling and the method is demonstrated to be feasible by the experimental results.
Design and fabrication of PIN photodiode used in PET photon detection
Bingruo Chen, Mu Wu, Dong-Qing Wei, et al.
The silicon PIN photodiode is small size and cheap cost, so we hope that it can replace PMT as detector used in PET photon detection. The Si PIN photodiode that is satisfied with detecting PET photon must enhance responsibility for short-wave light, respond to weak signal and operate in high speed. The characteristics of PIN device with single crystal silicon substrate are analyzed, and a PIN photodiode made of epitaxial wafer with high resistivity is presented. By choosing proper configuration and material parameters, the performance of PIN photodiode is improved, and the main photoelectic characteristics of samples have achieved the requirement of design.
The feature of color comparator with double Si p-n junction
Bingruo Chen, Song Wang
The current ratio of color comparator is presented to characterize the color difference which results from variation in spectral power of color source. For actual application, spectral power distribution of color source is fitted by one or more Lorentzian function. The relation between the variation in color source and current ratio of color comparator is analyzed numerically. The results show that the variation in the peak wavelength of spectral power distribution of color source will result in the considerable color difference and can be effectively discriminated by color comparator. An experiment to confirm resolution of color comparator is designed. The experimental observation confirms the theoretical analysis.
Optimization of the peak power of Q-switched diode-pumped lasers
Yan Ye, Shiyu Wang, Zhen Guo, et al.
The Q-switching technique of LD pumped Nd:YAG laser with high repetition and short pulse-width was studied. According to the theoretical and experimental research, the way to obtain the optimal pulse parameters was presented, which is the theoretical and experimental base for increasing peak power and decreasing pulse width of a Q-Switched laser output pulse. It is of great value for the research of light source of the laser space communication and laser imaging. Q-switching technique is the key technique of the output pulse of DPL. By using the rate equations, the numerical solution for the trace of a giant pulse and simple expression for the peak power are derived. Therefore the crucial factors of the peak power and the pulse width are the ratio of the initial to the final population inversion ni/nt and the photon decay time tc. As ni/nt increases and the tc decreases, the peak power goes up and the pulse width goes down. From which the optimal parameters of an output pulse can be obtained. According to the analysis above, the way to obtain the optimal pulse parameters was put forward as follows. The power of pumping LD should be as high as possible, while the resonator length as small as possible, and the corresponding optimum reflector should also be selected.
On the modal performance of VCSELs with oxidized aperture
Yinglong Wang, Yunlong Zheng, Zheng Yan, et al.
In this paper, vertical-cavity surface-emitting laser (VCSEL) with pillar structure which has potential applications in optical communication and optical interconnect is theoretically analyzed, the calculation model that used to discuss the modal performance of cylinder VCSEL with oxidized aperture is established by using vector field model. The numerical simulations show oscillating wavelength and threshold gain against inner and outer radius of laser, the layer refractive index and pair number of Bragg mirror, thickness, position and oxidized material’s refractive index of oxidized aperture, in detail. According to the standard that oscillating wavelength should approach to the designed one and threshold gain should be as low as possible, we give the appropriate range of parameters discussed in the paper.
Photorefractive edge-enhancement and its application to pattern recognition
Huayong Ge, Baohua Wang, Weiming Ji, et al.
Coupling theory is employed to analyze the coupling gain and a novel optical system is presented for image edge-enhancement by employing photorefractive two-wave coupling in BaTiO3 crystal, in which the ordinarily discarded background light is recycled as the pump source to amplify the signal light. Further, we demonstrate the principle of optical correlation and compare the discrimination capability of two kinds of correlators by computer simulation, in one of which input images are edge-enhanced and in the other the ones do not experience edge-enhancement. At last, we draw a conclusion that edge-enhancement preprocessing can improve discrimination capability effectively.
Modeling and analysis of strain effects on optical gain property of interband quantum cascade lasers
Ligong Yang, Peifu Gu
In this paper a complete model and theoretical analysis based on model-solid theory and the envelop-function approach are presented to investigate the strain effects in the interband quantum cascade lasers. The electronic properties and the optical gain of two different type-II quantum well configurations are calculated under different strain conditions and two kinds of active region configuration. Through the comparison and analysis between these example structures, the detailed quantitative results of the strain effects are given.
Optimization design and fabrication of photonic crystal waveguides based on SOI using 248-nm deep-UV lithography
In this work, methods of design and fabrication of photonic bandgap structures (PBG) and photonic crystal waveguides based on SOI (silicon on insulator) are presented. In theory, a method that incorporates the plane wave expansion (PWE) method based on supercell with the finite-difference time-domain (FDTD) method with a perfectly matched layer (PML) boundary condition has been investigated. At first, PWE simulation will present a band structure. Then according to the band structure, FDTD tool can simulate a light propagation and can obtain optimized parameters easily. With the method, several photonic crystal devices suitable for 248nm Deep UV lithography and 0.18um ion-beam etching are designed and fabricated.
Numerical computation of heat conductivity with surface photothermal data
In this paper, a local marching numerical method is developed to solve the one-dimensional inverse nonlinear heat conductivity problem (INHCP). Numerical analysis shows that the method has absolute stability. It can be more efficiently applied to efficiently determine the heat conductivity distribution by some measured surface temperature signal of some materials, such as semiconductor, steel, and so on.
Single-photon detector at 1550 nm with gate-mode quenched InGaAs/InP avalanche photodiode
In our recent experiment, we have designed a novel single-photon detecting module for quantum key distribution using an InGaAs/InP avalanche photodiode with gate-mode quenched photo-detection. At a repetition rate of 100 kHz and the working temperature of -60°C, we obtained the detection efficiency η higher than 10% and 20% at the dark probability Pd about 1.3×10-5 and 1.6×10-5 per nanosecond, respectively. Also at 100 kHz, we got the best ratio of Pd/η as 1.7×10-3 per pulse (20 ns). And at a lower repetition such as 10 kHz, we obtained Pd/η as 8.9×10-4 per pulse.
Study on structural and optical properties of TiO2 thin films prepared by sol-gel process
Shuang Zhang, Caixia Liu, Zhiyong Zhao, et al.
TiO2 thin films were prepared at various calcinations temperatures by sol-gel process and their structural and optical properties were examined. The influence of calcinations temperature on the structural properties of the prepared TiO2 thin films was investigated by the X-ray diffraction (XRD) and atomic force microscope (AFM). The XRD results showed that TiO2 thin film was transformed into the anatase phase at 350°C, and further into rutile phase at 850°C. The AFM results show quite a smooth surface and are in reasonably well agreement with the crystallite sizes estimated by XRD peak broadening. The influence of calcinations temperature on the optical properties of the prepared TiO2 thin films was investigated by UV-Vis spectrum and variable angle incidence spectroscopic ellipsometer (VASE). The results showed the both anatase phase and rutile phase of the TiO2 thin films prepared have good optical properties in UV region.
Low-cost high-manufacturability and thermal stability optical front-end for 10 Gb ethernet applications
Shin-Ge Lee, Chun-Hsing Lee, Li-Chun Liao, et al.
With the drastic expansion of internet usage, the demand of 10Gb/s transmission optoelectronic devices for local-area-network (LAN) and storage-area-network (SAN) are increasing. The key issues of these applications are to improve cost, manufacturability and reliability of optoelectronic devices in high speed transmission. The authors have demonstrated extremely low cost, high manufacturability and thermal stability optical fron-end for 10Gb/s Ethernet applications in this paper. High performance and high sensitivity of 10Gb/s transmitter optical sub-assembly (TOSA) and receiver optical sub-assembly (ROSA) with TO-Can packages are discussed and demonstrated to overcome the critical points in high speed applications, respectively. Moreover, 10km interconnection of 10Gb/s optical front-end without isolated elements inside are also proved to be error free at 10.3125Gb/s. In order to improve the signal integrity and manufacturability of 10Gb/s OSA in small form factor transceiver modules assembly, the authors also integrate high speed flex board and OSA package to extend the signal path, and to minimize the effect of crosstalk in modules. Furthermore, the integration of flex board and OSA package more release the difficulties in conjuunction OSA and electrical sub-assembly (ESA) in module to fulfill the request of 10Gb/s transeivers' Multi-Source Agreement (MSA). The performance of temperature stabilized TOSA over wide case temperature range is also experimented. The optical eye diagram of 10Gb/s TOSA developed in this study showing excellent eye quality passing 10Gb/s Ethernet mask test between 0°C to 85°C.
Tunable and self-probed wavelength conversion in SOA-based fiber ring laser
Xinliang Zhang, Fan Xu, Junqiang Sun, et al.
Tunable all-optical wavelength converters have been regarded as key optoelectronic devices in intelligent next generation optical networks. Novel scheme for tunable wavelength conversion based on semiconductor optical amplifier (SOA)-based fiber ring laser is proposed out firstly. Theoretical model for this novel scheme is established. Conversion output characteristics are calculated theoretically and measured experimentally in different conditions. Experimental results are coincidence with theoretical results. Tunable wavelength conversion at 2.5Gb/s with 40nm tuning range is demonstrated experimentally. Experimental and theoretical studies show that this novel scheme is worthy of further investigation.
ICP etching of InP and related materials using photoresist as mask
New processes using HBr chemistry have been developed for etching InP and related materials using photoresist as a mask in a high ion density inductively coupled plasma system. An etch rate of above 1 micron/min, a selectivity of 14:1 with vertical profile, and smooth etched surface have been achieved. The effects of ICP power, table temperature, chamber pressure and DC bias on etching rate, selectivity, etched profile and surface morphology will be discussed in this paper.
Direct radiography (DR) for conventional x-ray medical imaging application
Xiaoyu Jiang, Ping Lee, Quan Yee
This paper introduces a new medical X-ray diagnostic imaging method: direct radiography (DR), which will resolve digitalization problem of conventional X-ray medical imaging, and may replace film imaging in the future. In our developed DR system, a high resolution amorphous Silicon (a-Si) image sensor is used which can acquire 1920*1536*12bits image in 1.6 seconds in its fastest imaging speed. The software of the system including DR image acquisition workstation and DR image post-process workstation can not only acquire, correct and store the images, but also can manage the DR images in network database. In the paper, the mechanism of DR imaging, the composition of the developed DR system, the advantages of DR imaging over traditional X-ray medical imaging are described, and DR imaging results of the developed system are shown at last.
Discretely tunable all-fiber Fabry-Perot laser based on birefringence fiber loop mirror and fiber Bragg grating
Hao Zhang, Ling Yu, Yange Liu, et al.
In this paper, we present a novel structure discretely tunable linear cavity fiber laser. A fiber Bragg grating (FBG) and a high birefringence fiber loop mirror are used as cavity reflectors. By changing the deflection of an equivalent-strength beam, the reflective wavelength of the FBG can be tuned accordingly. Since the reflectivity of the HiBi fiber loop mirror varies periodically, the output laser of this Fabry-Perot laser based on HiBi fiber loop mirror and FBG can be tuned discretely. From 1543.8nm to 1555.2nm, 15-wavelength lasers (SMSR>54dB) with approximately 0.8nm spacing have been obtained and the output laser intensity reaches about 2.5dBm in average. Nevertheless, some 0.8nm spacing lasers much weaker than the above lasers have also been observed. And they are expected to be eliminated by using narrower linewidth FBG as reflective mirror.
The design of CY-1R night vision helmet
In this paper, the research intention and design principle of CY-1R night vision helmet are explained which fills the gaps in active-passive combined night vision field in our country. The structure, composition, mechanism and overall performance of the goggle are analyzed. It is a new type device consisting of laser illuminator system, special optical system and high performance low-level-light intensifier. Based on these characteristics, the sensitivity of the system is high and the image observed is very clear. Taking advantage of it, we can complete the military operation under any atrocious weather conditions.
Experimental research on the stability and the multilongitudinal mode interference of bidirectional outputs of LD-pumped solid state ring laser
Shunping Wan, Qian Tian, Liqun Sun, et al.
This paper reports an experimental research on the stability of bidirectional outputs and multi-longitudinal mode interference of laser diode end-pumped Nd:YVO4 solid-state ring laser (DPSSL). The bidirectional, multi-longitudinal and TEM00 mode continuous wave outputs are obtained and the output powers are measured and their stabilities are analyzed respectively. The spectral characteristic of the outputs is measured. The interfering pattern of the bidirectional longitudinal mode outputs is obtained and analyzed in the condition of the ring cavity with rotation velocity. The movement of the interfering fringe of the multi-longitudinal modes is very sensitive to the deformation of the setup base and the fluctuation of the intracavity air, but is stationary or randomly dithers when the stage is rotating.
Generation of highly directional ultrasonic waves in sea
Bing Han, Xinzhi P. Sheng, Yongping Teng, et al.
A theoretically and experimentally analysis was presented of ultrasonic wave generation in water by intensity modulated elliptical Gaussian laser beams. It was found that generated acoustic radiation is highly directional both in polar and azimuthally directions. Experimental results showed that over the frequency range of 5 to 20 kHz, there was an almost flat response with an average normalized phase sensitivity of -300 dB re 1/μPa and an average pressure sensitivity of -150.0 dB re rad/μPa. These results indicate that the present design offers the possibility of getting highly directional sound beams in a simple configuration.
The ion-exchange temperature matching technology in GRIN glass containing silver ion
For making Gradient index (GRIN) glass with silver ion, it is difficult to get glass with high silver content by normal glass moltening process because silver ion will be extruded from molten glass at the high temperature. For solving this hard problem, the two-step ion-exchange process based on sodium rich glass is applied to get GRIN glass containing silver ion. In this process, the matching between the temperature of glass soft point and the highest working point of silver molten salt is one of key technologies. In this paper, the sodium-rich glass was made as the glass substrate for silver ion-exchange. Then the glass composition was adjusted to get transparent sodium-rich glass with low soft point and high chemical stability. On the other hand, the silver salt with high dissociation temperature for ion exchange was studied. At last the glass substrate with low soft point and the salt source with high dissociation temperature were matched at the suitable temperature in order to improve ion-exchange process.
A measurement technique of the tiny rotatory angle
Bing Han, Xinzhi P. Sheng, Xiaoqiu Zheng, et al.
A new and simple method was developed for accurate measurement of Faraday rotation in materials with low rotation using Faraday magneto-optical modulator. A rode of glass with a large Verdet constant is used for this measurement. The rotatory angle can take values in the magnitude of sub-millidegree (10-4 degrees). Detailed theoretical and experimental analysis was given.
Research on the 20-W double-cladding fiber laser pumped by 915-nm and 975-nm diode lasers
Jun Zhou, Qihong Lou, Zhijiang Wang
The output characteristics of double cladding fiber laser are investigated pumped by 915nm and 975nm diode lasers. The average effective absorption coefficients for two kinds pump wavelengths are given. A 20W Ytterbium - doped fiber laser in 1110nm region with near diffraction limited beam spread angle are reported.
Optical filter in two-dimensional photonic crystal waveguide
Xiyao Chen, Peijun Yao, Bo Chen, et al.
The factors that affect the properties of the filters in a two-dimensional photonic crystal (2-D PC) waveguide are investigated quantitatively. The waveguide is constructed by omitting one line rods in a perfect 2-D PhC composed of circular dielectric rods located at a square lattice. The 2-D PC filters (2-D PCF) are formed by adding some defect rods in the waveguide. The numerical calculation results show that the reflectivity and transmission of the filter are dependent on the size, dielectric constant and number of defect rods. Moreover, the transmission spectrum of a PCF is also obtained by using fast fourier transform (FFT) method and comb-like curve shape similar to that in the transmission spectrum of Fabry-Perot etalons is found in it .
Accurately nonselective and selective etching of GaAs/Al0.8Ga0.2As/AlAs structure for making air-gap cavity
Zhou Zhen, Yun Du, Yongqing Huang, et al.
We have demonstrated a wet etching technique capable of fabricating air-gap cavity. The process utilizes nonselective and selective etchants respectively to form air-gap cavity. The etching characteristics of GaAs/Al0.8Ga0.2As/AlAs structure in different nonselective and selective etchants are investigated. The volumetric 3:2:20 ratios of H3PO4/H2O2/H2O solution and volumetric 600:1 ratio of DI water/buffered oxide [mixture of 7:1 NH4F(36%)-HF(6.4%)] solution are better nonselective and selective etchants respectively. We have used this process technique to form a tunable air-gap cavity optical filter. The measure results of the transmission spectral show that the air-gap cavity has high optical quality. These simple etching processes can be applied to fabricate the air-gap cavity devices.