半导体光放大器增益饱和特性的研究

在理论上研究了行波半导体光放大器的增益饱和特性，并从半导体的单模速率方程出发，应用半导体光放大器的传输波动方程，推导了放大器的增益特性表达式。从中得出：当放大器的输出功率为饱和输出功率时，信号增益相对于不饱和增益降低４．３４ｄＢ。     

半导体光放大器增益饱和及其开关特性的研究

从理论上研究了行波半导体光放大器的增益饱和特性。由半导体的单模速率方程出发，应用半导体光放大器的传输波动方程，推导了放大器的增益特性表达式。根据半导体光放大器增益饱和特性，研究了开关特性。     

影响VCSOAs增益饱和特性因素分析

为了改善垂直腔半导体光放大器增益饱和特性,基于其结构上的特点,引入了增益增强因子,修正了边界条件,采用建立腔内光子数与输入信号光功率关系的研究方法,分析了影响垂直腔半导体光放大器增益饱和特性因素。并进行了理论分析和实验论证,取得了影响增益饱和特性的4个关键数据。结果表明,有源区截面积、顶层镜面反射率、抽运功率、自发辐射因子影响着增益饱和特性,优化相关参数,可以将输入饱和功率提高到-2dBm。这一结果对如何改善垂直腔半导体光放大器增益饱和特性是有帮助的。     

行波半导体光放大器的增益饱和及其在解复用技术中的应用

本文通过对行波半导体光放大器增益饱和及其瞬态增益特性的分析，指出了利用半导体光放大器增益饱和快的特点，可使半导体光放大器环路镜实现超高速的解复用功能。     

半导体光放大器的增益特性和偏振特性

介绍了半导体光放大器的两个重要特性:增益特性和偏振特性。增益特性中,描述了放大器中增益调制现象和增益饱和现象,并介绍了提高半导体光放大器增益的方法。偏振特性中,分析了半导体光放大器增益偏振敏感产生的原因,并列举了低偏振敏感度放大器的实现方法。最后报道了近几年才被注意的半导体光放大器相位偏振敏感特性。     

半导体光放大器的超快动态增益特性

提出了一种包括载流子密度脉动(CDP)、载流子加热(CH)和光谱烧孔(SHB)效应在内的半导体光放大器(SOA)的时域动态模型。利用该模型分析了半导体光放大器中的增益饱和、超快增益动态以及光脉冲在增益饱和半导体光放大器中的波形畸变,其中重点考虑了超短脉冲的情况。模拟计算表明,对于10ps量级以下的短脉冲,分析半导体光放大器的动态增益特性时,不能忽略载流子加热和光谱烧孔等带内超快非线性效应的影响。     

增益饱和的半导体激光放大器响应特性研究

详细讨论了行波半导体激光放大器工作在饱和状态时，入射脉冲的脉宽和放大器工作状态对放大脉冲的形状和频谱的影响，有利于更好地利用增益饱和的光放大器的非线性特性对光信号进行相位补偿。     

半导体光放大器的快速饱和效应及其长度对TOAD解复用器性能的影响

分析了半导体光放大器 (SOA)的快速饱和效应及其长度对 TOAD解复用器性能的影响 ,对小开关窗口和大开关窗口两种工作模式进行了研究。经分析发现 ,半导体光放大器的快速增益饱和效应对开关窗口的形状和开关能量都有很大的影响 ,而且开关能量随控制脉冲宽度的变化关系对两种工作模式是完全不同的。研究表明考虑 SOA长度效应后 ,第二个开关窗口的幅度可大大减小 ,这说明适当地增加半导体光放大器的长度可以进一步降低 TOAD的开关窗口 ,提高 TOAD的速率。     

半导体光放大器相位补偿特性的研究

本文详细分析了饱和工作状态下的行波半导体光放大器（ＴＷ－ＳＯＡ）的啁啾特性，从理论上证实了利用其增益饱和所引起的自相位调制来对光源啁啾进行相位补偿的可行性，并且发现，对于不同脉宽的入射脉冲，光放大器均能发挥相位补偿的作用，这一特性可用来补偿光源啁啾．     

量子点半导体光放大器的速率方程和增益特性

为了深入研究量子点半导体光放大器(QD-SOA)的特性,建立了量子点半导体光放大器子带导带的三能级系统模型.把系统载流子的速率方程与其他文献采用的速率方程进行了对比优化.通过数值计算得到了瞬态解,并得到载流子在放大器各能级态的浓度分布,验证了量子点中能级分立特性.利用电子和空穴各自的占有几率在基态成一定的线性关系,在稳态下对速率方程求解,得出了量子点半导体光放大器相关的增益特性,以及增益特性与基态电子的占有几率之间的关系.结果表明量子点半导体光放大器具有很高的饱和增益和微分增益,较低的阈值电流等特性.说明量子点半导体光放大器具有比其他体材料和量子阱光放大器更加优异的特性.为光放大器的设计提供了有力的理论指导.     

A novel analytical expression of saturation intensity of InGaAsPtapered traveling-wave semiconductor laser amplifier structures

We have proposed a novel approximate analytical expression for saturation intensity for tapered traveling-wave semiconductor laser amplifier structures. The application of this analytical expression of saturation intensity has been demonstrated by considering the effect of gain saturation on polarization sensitivity of two tapered amplifier structures, linear and exponential tapered amplifier structures. It is found that polarization sensitivity of the tapered amplifier structure is several decibels higher than that of passive tapered waveguides in unsaturated condition. Polarization sensitivity of the two tapered amplifier structures has also been investigated in a highly saturated condition. The combined effects of mode conversion and gain saturation on fundamental TE gain have also been investigated using the proposed analytical expression for saturation intensity     

Multiple-quantum-well GaInAs/GaInAsP tapered broad-area amplifierswith monolithically integrated waveguide lens for high-powerapplications

A 1.48-μm tapered broad-area semiconductor laser amplifier with a monolithically integrated waveguide lens as demonstrated. The gain saturation characteristics of the tapered amplifier were examined. A maximum output power of 300 mW and a 3-dB saturation power of 200 mW under quasi-CW conditions were obtained from the amplifier without the waveguide lens. Output power of 200 mW was obtained with a broad emission spectrum of ~30 nm when the device was used as a superluminescent diode. The amplified output was focused to a single lobe by the monolithically integrated aspheric waveguide lens, which may be useful for efficient coupling of the output into a single-mode fiber     

Mode-locked operation of a master oscillator power amplifier

We report the first mode-locked operation of a tapered amplifier MOPA to generate short optical pulses with record high average powers and pulse energies. The MOPA is constructed using a discrete semiconductor oscillator and amplifier operating at 940 mm wavelength. Pulses of 4.2 ps duration are generated with average powers of 296 mW and peak powers of 28.1 W. The energy of these pulses was 118 pJ, corresponding to energies more than an order magnitude greater than the gain saturation energy in the mode-locked laser itself, and also corresponds to energies internal in the amplifier in excess of the gain saturation energy. Although the amplifier saturation energy limits the pulse energy obtainable in a mode-locked laser, the MOPA configuration demonstrates that generation of pulses with energies in excess of the amplifier saturation energy is feasible in a post-amplification stage     

A scheme of picosecond pulse shaping using gain saturationcharacteristics of semiconductor laser amplifiers

To obtain high power, well shaped picosecond pulses from gain-switched semiconductor lasers, the use of dynamic gain saturation characteristics of semiconductor laser amplifiers was investigated theoretically and experimentally. A configuration of a reflected-wave amplifier (RWA) with single-side external coupling is introduced for pulse shaping, which is found to be suitable for enhancing dynamic gain saturation. By a combination of a distributed feedback laser oscillator at 1.3 μm in wavelength and a reflected-wave amplifier of 400 μm cavity length with asymmetric facet reflectivities of 0.01% and 30%, single-mode optical pulses with almost no tailing, full width at half maximum of 15 ps, and peak power exceeding 50 mW were obtained without pulse broadening, despite the considerable tail structure of the incident pulse     

GaInAsP semiconductor laser amplifiers for single-mode fiber communications

Gain, polarization sensitivity, saturation power, and noise characteristics of quaternary semiconductor laser amplifiers of the Fabry-Perot (FP) and traveling-wave (TW) types are reviewed. The status of antireflection coatings for TW amplifiers is presented. New results concerning the polarization sensitivity and output saturation power of a 1.5-μm buried-heterostructure (BH) amplifier are reported. A theoretical model is presented concerning the influence of the waveguide structure on the maximum internal gain of a CW-operating 1.5- μm BH amplifier, including thermal effects, and a comparison of this model with recent experimental results is reported. The influence of nonresonant losses on the noise factor of 1.5-μm amplifiers is discussed.     

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     

Theory of signal degradation in semiconductor laser amplifiers indirect detection systems

Theoretical studies are carried out on long haul direct detection optical fiber communication systems, with inline optical semiconductor amplifier repeaters. Calculations are made of the noise, eye diagrams, and bit-error-rate characteristics of lightwave systems with optical amplifiers. Indications are given of the effect of amplifier characteristics such as spontaneous noise and signal distortion due to gain saturation on the system performance. The nonlinear process within semiconductor laser amplifiers leads generally to pulse amplitude-temporal distortions due to gain saturation. This theoretical study demonstrates that the system penalty caused by these nonlinear effects appears progressively as the optical input power at each amplifier is increased. For example, nonregenerated fiber transmission using traveling wave semiconductor laser amplifiers was simulated, and results obtained at 0.5 and 2.5 Gb/s are presented. In order to improve the system performance, the influence of structure and bulk dimensions of the amplifier cavity is also considered     

Gain saturation properties of a semiconductor gain medium withtensile and compressive strain quantum wells

Gain saturation properties of a multiple-quantum-well structure with both tensile and compressively strained quantum wells are investigated analytically. This type of structure has recently been experimentally demonstrated to serve as a basis for the implementation of a two-polarization/two-frequency laser and polarization insensitive travelling wave(TW) amplifier. The performance of these devices strongly depends on the interaction between the TE and TM gains of the structure. The gain medium model appropriate for this type of structure is developed and the rate equation approach is used to describe the saturation properties of TE/TM gains and the coupling between the TE and TM gains due to gain saturation. The minimum amount of coupling between the two is governed by the basic symmetry of the light-hole wavefunction which interacts with photons of both polarization: photon cross-coupling. The finite rate of carrier escape from the quantum wells provides for carrier induced coupling between the populations of the two well types and therefore also couples TE and TM gains: carrier cross-coupling. The performance of a polarization insensitive amplifier, laser, and polarization control element is evaluated as a function of the amount of carrier cross-coupling, which is a structure dependent parameter. A structure with high degree of cross-coupling is desirable for polarization insensitive TW amplifier, while two-polarization lasers and polarization control elements require minimum cross-coupling     

Gain saturation properties of a polarization insensitivesemiconductor amplifier implemented with tensile and compressive strainquantum wells

The gain saturation properties of a 1.3 μm polarization insensitive semiconductor amplifier implemented with tensile and compressive strain quantum well active region are experimentally investigated in order to determine how well the amplifier maintains its polarization insensitivity in the saturation regime. The amplifier has unsaturated gain of 12 dB and in the saturation regime the maximum observed gain imbalance between TE and TM gains is 0.9 dB. The measured 3 dB saturation output power is 5 mW     

Analysis of gain and saturation characteristics of a semiconductorlaser optical amplifier using transfer matrices

The transfer matrix method (TMM) has been applied to analyze the gain and saturation characteristics of semiconductor laser optical amplifiers. This method approximates the amplifier cavity by dividing it into M discrete subsections, and TMM has been applied to analyze the stepwise longitudinal field distribution at each subsection along the amplifier cavity. By incorporating also the carrier rate equations into the analysis, it has been shown that the approximation can accurately describe the carrier density and longitudinal field distribution along the amplifier cavity if M is sufficiently large (i.e., the size of each subsection is about an order of magnitude of one wavelength of the input signal). By assuming that the amplifier is biased below oscillation threshold such that the contribution of spontaneous emissions to the gain characteristics can be neglected, we have shown that our proposed method yields a fast and efficient algorithm in analyzing the gain and saturation characteristics of laser amplifiers. We have compared the results produced by our method to those analyzed using the average photon density (AVPD) approximation technique, as well as to experimental results on a 1.5-μm buried heterostructure semiconductor laser amplifier