Large modulation depth, single-moded quantum well waveguide modulator operating around 1.57 mu m

The performance of long wavelength single-mode waveguide modulators suitable for monolithic integration with a quantum well laser is reported. The device operated between 1.560 mu m and 1.570 mu m. The guiding layer was formed by a 0.27 mu m quaternary layer at the centre of which were four 50 AA In/sub 0.53/Ga/sub 0.47/As quantum wells separated by 100 AA InP barrier layers. Lateral confinement was obtained by etching ridges in the top InP contact layer. For devices of 500 mu m length, a modulation depth of 19 dB was obtained at a wavelength of 1.568 mu m with a reverse bias voltage of only 3 V and an internal loss of 2.5 dB.<>     

Quantum well interferometric modulator monolithically integrated with 1.55 mu m tunable distributed Bragg reflector laser

The first monolithically integrated laser/interferometric modulator is reported. The total chip length of 2.5 mm includes a 970 mu m-long strained InGaAs-InGaAsP quantum well gain section, a 230 mu m-long wavelength tuning section containing a distributed Bragg reflector grating, and an 800 mu m-long active length Mach-Zehnder modulator based on electrorefractive InGaAsP-InP quantum wells. 4 V push-pull drive voltage produces 12.5 dB modulation depth with -9 dBm optical power coupled into a cleaved fibre.<>     

Low-drive voltage intersectional waveguide optical switch usingGaInAs/InP MQW structure

A low-drive voltage intersectional waveguide optical switch using 1.6 μm GaInAs/InP MQW (multiple quantum well) structure, which was fabricated by only one-step epitaxial growth of MQW structure followed by a one-step pattern etching of the waveguide is demonstrated. Extinction ratio at the straight port of 9.9 dB and that at the reflection port of 4.4 dB were obtained at an applied voltage of -4 V     

基于直接调制和外调制的高速半导体激光光源

直接调制和外调制的半导体激光光源在现代光纤通信系统中有着重要的应用。首先介绍了应用于10 Gb/s接入网系统的直接调制AlGaInAs多量子阱DFB激光器。由于AlGaInAs量子阱的导带不连续性较大,因此基于该材料的半导体激光器具有良好的温度特性,其特征温度达到了88 K。同时,该直接调制激光器的3 dB小信号调制响应带宽超过15 GHz。随后介绍面向40 Gb/s干线传输系统的高速DFB激光器/EA调制器集成光源。该集成光源采用同一外延层集成方案,并采用Al2O3高速微波热沉进行了管芯级封装,在3 V反向偏压下获得大于13 dB的静态消光比,3 dB小信号调制带宽超过40 GHz。     

Monolithic Integration DFB Laser Array by Angling Active Stripe and Using Thin-Film Stripe Heater

Multi-wavelength quantum well DFB laser array has been fabricated on an InP substrate by angling the active stripe at an oblique angle to the axis of the grating lines and coating a Pt/Ti thin-film heater to change the laser temperature. Owing to the oblique angle,four sin-gle-mode lasing wavelengths around 1.55μm were obtained simultaneously. By changing the working of the thin-film heater,the DFB laser can be tuned continuously beyond a range of 2.2nm with 3. 8nm/W of tuning efficiency while maintaining a side-mode suppression ratio (SMSR) more than 30dB.     

Laser diode pumped Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped fluoride fiber amplifiers operating at 1.3 mu m

Both Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped singlemode fibres with high numerical apertures are pumped by laser diodes with InGaAs/GaAs strained quantum well structures. A net gain of 5.2 dB is obtained from Pr/sup 3+/-doped fluoride fibre pumped by laser diodes operating at 1.1017 mu m and a net gain of 3.2 dB is obtained from Pr/sup 3+/-Yb/sup 3+/-codoped fibre pumped by laser diodes operating at 0.98 mu m. The pumping efficiency difference between Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped fibre is discussed.<>     

Symmetric self-electro-optic effect device using symmetric-cavityquantum well electroabsorption modulators

We report results obtained from a symmetric-cavity Fabry-Perot quantum well modulator in GaAs/AlGaAs. A reflection-change of ≈46% with an insertion loss of 1.3 dB are obtained in the normally-off mode under a reverse bias voltage of 7.5 V. Bistable operation is demonstrated, for the first time using such devices, by connecting two modulators in the symmetric self-electro-optic effect device configuration     

Reduced intermodulation distortion in 1300 nm gain-clamped MQWlaser amplifiers

A 1300 nm gain-clamped DFB multiple quantum well laser amplifier with negligible pass band ripple, 20 dB fiber to fiber gain, and 10 dB reduction in gain saturation is demonstrated. The remaining gain saturation is attributed to longitudinal hole burning. After some modifications the reduction in gain saturation is improved to more than 30 dB for an input signal having the same polarization state as the lasing mode. From these experiments and a theoretical analysis it is concluded that there is a potential for realizing highly linear 1300 nm CATV semiconductor laser amplifiers using gain-clamping with less intermodulation distortion than today's directly modulated linear semiconductor lasers     

基于模糊控制的自适应激光功率稳定系统研究

研究了一种基于模糊控制的嵌入式激光功率稳定系统,用声光调制器作为功率稳定的外部环路反馈器件,采用模数转换器和数模转换器以及数字信号处理芯片组成数控功率稳定电路。用模糊控制方案解决了传统比例-积分-微分(PID)的超调问题,反馈环路的稳定时间为1.8 ms。有效抑制了激光功率在低频部分的相对强度噪声,在1 Hz处从-88 dBc/Hz改善至-110 dBc/Hz。激光功率的相对起伏由0.29%降低至0.035%。相比于传统PID,模糊PID可以根据系统所处状态实时调整参数,从而达到自适应的效果。     

Uncooled performance of 10-Gb/s laser modules with InGaAlAs-InP and InGaAsP-InP MQW electroabsorption Modulators integrated with semiconductor amplifiers

Uncooled operation of long-reach high performance C-band 10 Gb/s of optical modulator modules is presented. Modules consisting of a distributed feedback laser and a chip with a monolithically integrated electroabsorption modulator and semiconductor optical amplifier based on multiquantum-well structures of both InGaAsP-InP and InGaAlAs-InP material systems are presented. Dispersion penalty of 1 dB over 94-km transmission, output power above 0 dBm, and low extinction ratio variation are demonstrated over an 80/spl deg/C temperature range. A simple analysis of the quantum confined Stark effect is employed to explain the temperature-dc bias voltage dependence.     

Room-temperature singlemode continuous-wave operation of distributed feedback GaInNAs laser diodes at 1.5 μm

Room-temperature continuous-wave operation of distributed feedback GalnNAs quantum well laser diodes on GaAs in the 1.5 mum wavelength range is demonstrated for the first time. Singlemode emission with a sidemode suppression ratio of more than 45 dB is obtained at 1486 nm with a threshold current of 44 mA and an external efficiency of 0.06 W/A.     

MQW tuned semiconductor lasers with uniform frequency response

A tunable semiconductor laser with an intrinsically wideband uniform frequency response has been developed, using the quantum confined Stark effect in quantum well material as the tuning mechanism. A frequency response uniform within 3 dB from 20 kHz to 1.2 GHz was achieved, limited by the measuring system at low frequencies and by device capacitance at high frequencies. Analysis shows that with optimised tuning elements a uniform frequency response to over 50 GHz should be achievable with this technique     

Low-switching-voltage InGaAsP/InP waveguide interferometricmodulator for integrated optics

An InGaAsP/InP electrooptic Mach-Zehnder modulator consisting of two 3-dB Y-branch couplers and phase modulation arms is fabricated by the metal-organic vapor-phase epitaxy growth method. A schematic illustration and cross section of the interferometric modulator as well as the current-voltage characteristics of the arms are shown. The modulator is formed by a waveguide having almost the same cross-sectional configuration as a double-heterostructure laser diode. The switching voltage of 4.5 V applied to one arm of the modulator results in an excitation of about 7 dB     

Automatic frequency control in a semiconductor laser and an optical amplifier

Automatic frequency control (AFC) in an injection locked or resonant type amplifier in an AlGaAs semiconductor laser was achieved through using the terminal voltage change induced by light injection. Signal-to-noise ratio in the control signal of 10 dB was obtained when the input optical power was -47 dBm and the optical gain Was 51 dB. The AFC was maintained for 3 h with an 0.3-percent output power fluctuation for 2°C ambient temperature change and 65-MHz frequency stability. Step response showed that the system response time was 1.5 s. Sensitivity to input optical power deteriorates at -49 dBm, with a 53-dB locking gain, because of frequency deviation caused by temperature modulation. The second derivative of the induced voltage and it's relation to the optical frequency is constant at5 times 10^{-10}[V/(MHz)²] for all input power levels in a buried-heterostructure (BH)-AlGaAs laser. Terminal voltage change induced by light injection is calculated by simple rate equations with a Gaussian-Halperin-Lax (GHL) bandtail model. Good agreement with experimental results was seen.     

Polarization-independent electroabsorption modulators using strain-compensated InGaAs-InAlAs MQW structures

The improved modulation properties of strain compensated InGaAs-InAlAs multiple quantum well (MQW) electroabsorption modulators and their modules have been demonstrated. Introduction of a 0.5% tensile strain in wells and a 0.5% compression in barriers provides highly efficient operation such as a low driving voltage (V/sub 20/ dB=1.6 V) and a large modulation bandwidth (f/sub 3/ dB>20 GHz). This is in addition to low polarization-dependence with an extinction ratio difference between TE and TM and polarization of less than 1 dB.     

Monolithically integrated InGaAs-AlGaInAs Mach-Zehnder Interferometer optical switch using quantum-well intermixing

A highly efficient monolithically integrated Mach-Zehnder interferometer (MZI) optical switch based on a 1.5-/spl mu/m InGaAs-AlGaInAs multiple-quantum-well structure is reported. The device was fabricated by integrating phase shifter sections with bandgap-shifted low-loss waveguides obtained by a single step sputtered SiO/sub 2/-annealing quantum-well intermixing technique. Evaluation of the refractive index change induced by current injection (plasma, band-filling, band-shrinkage effects) and applied electric field (quantum confined Stark effect) based on the MZI was investigated. A device with an active length of 400 /spl mu/m in one of the MZI arms had an extinction ratio /spl ges/20 dB with a half-wavelength current (I/sub /spl pi//) and half-wavelength voltage V/sub /spl pi// as low as 3.2 mA and 3.5 V (1.9 V in push-pull configuration), respectively.     

Theoretical design optimization of multiple-quantum-wellelectroabsorption waveguide modulators

Optical on-off modulators require low insertion loss, high contrast ratio (CR), small drive power and large bandwidth or bit-rate. A systematic approach to optimize the total performance of these modulators based on the quantum-confined Stark effect is presented here. The approach consists of minimizing the power/bandwidth ratio while satisfying a given CR and insertion loss. Our design consists of a large-core multimode passive waveguide with a thin buried active layer. The passive waveguide is designed to yield a high coupling efficiency to conventional single-mode fibers. The quantum well material structure is designed to maximize Δα/ΔF², while maintaining a sufficiently large Δα/α₀, where Δα is the absorption change, α₀ is the residual absorption at zero bias, and ΔF is the swing of the applied electric field. Our theoretical model shows that i) wider quantum wells give larger Δα/ΔF², and ii) the bandwidth/power ratio as high as 4 GHz/mW can be achieved simultaneously with small insertion loss, For example, with a drive voltage of 3 V, an RC limited bandwidth as high as 60 GHz is predicted, while a contrast ratio of 20 dB and a total insertion loss of 4.5 dB may also be obtained     

Design and realization of InGaAs/GaAs strained layer DFB quantumwell lasers

Optical waveguiding in an InGaAs/GaAs strained-layer distributed feedback (DFB) quantum well laser is investigated using the one-dimensional shooting method presented. The numerical approach is used to optimize the waveguide geometry and to calculate the corrugation period and the coupling factor for the integrated Bragg grating. The quantum well DFB structure designed according to the numerical calculations for an emission wavelength of 982 nm was realized for the first time entirely by molecular beam epitaxy (MBE) growth. Thus, side-mode suppression ratios of 49 dB, threshold currents of 7 mA and quantum efficiencies of 0.4 mW/mA were achieved     

Analog characterization of low-voltage MQW traveling-wave electroabsorption modulators

In this paper, high-speed traveling-wave electroabsorption modulators (TW-EAMs) with strain-compensated InGaAsP multiple quantum wells as the absorption region for analog optical links have been developed. A record-high slope efficiency of 4/V, which is equivalent to a Mach-Zehnder modulator with a V/sub /spl pi// of 0.37 V and a high extinction ratio of > 30 dB/V have been measured. A detailed study of the nonlinearity and the spurious-free dynamic range (SFDR) is presented. By optimizing the bias voltage and the input optical power, the SFDR can be improved by 10-30 dB. After minimizing the third-order distortion, an SFDR as high as 128 dB-Hz/sup 4/5/ is achieved at 10 GHz. A simple link measurement was made using this EAM and an erbium-doped fiber amplifier and a 50-/spl Omega/ terminated photodetector. At 10 GHz, a link gain of 1 dB is achieved at a detected photocurrent of 7.6 mA with higher gains at lower frequencies. The dependence of link gains on bias voltage, input optical, and radio frequency powers are investigated in detail.     

Asymmetric quantum well broadband thyristor laser

A broadband thyristor laser based on InGaAs/GaAs asymmetric quantum well (AQW) is fabricated by metal organic chemical vapor deposition (MOCVD). The 3-μm-wide Fabry-Perot (FP) ridge-waveguide laser shows an S-shape I-V characteristic and exhibits a flat-topped broadband optical spectrum coverage of ~27 nm (Δ_-10 dB) at a center wavelength of~1090 nm with a total output power of 137 mW under pulsed operation. The AQW structure was carefully designed to establish multiple energy states within, in order to broaden the gain spectrum. An obvious blue shift emission, which is not generally acquired in QW laser diodes, is observed in the broadening process of the optical spectrum as the injection current increases. This blue shift spectrum broadening is considered to result from the prominent band-filling effect enhanced by the multiple energy states of the AQW structure, as well as the optical feedback effect contributed by the thyristor laser structure.