Carrier transport effects in quantum well lasers: an overview

Early theoretical predictions and later experimental work have shown that lasers with quantum well active areas have enhanced differential gain over bulk lasers. The resonance frequency in a semiconductor laser is proportional to the square root of the differential gain. The resonance frequency is directly related to the modulation bandwidth, and the enhancement in the intrinsic differential gain led to theoretical predictions of increased modulation bandwidth in quantum well lasers. This enhancement in the modulation bandwidth proved to be elusive initially, and later it was realized that other factors, namely carrier transport effects, played a more dominant role in the high-speed properties of quantum well lasers. Carrier transport effects, in addition to bandfilling, affect a wide range of static and dynamic properties of the quantum well lasers. This paper will present an overview of our present understanding of the carrier transport processes and their effects in quantum well lasers.     

增益非线性对超短腔激光器速率方程的影响

用量子阱激光器增益与载流子浓度的对数关系（增益饱和效应）取代了体材料的线性关系，得到了适用于量子阱结构的速率方程。详细分析和计算了这一修正的影响。计算表明，对长腔（低损耗）器件线性关系是较好的近似；对短腔（高损耗）、线性关系则有较大的误差，必须考虑增益饱和的影响，否则将过高估算自发辐射因子的测量值，过高估计弛豫振荡频率和最大调制频率。这一结果对微腔激光器的研究具有重要的意义。     

马赫-陈德尔型全光波长变换器的动态特性分析

利用高频饱和滤波效应和动态载波子恢复时间概念分析了基于半导体光放大器中交叉相位调制的马赫－陈德尔型全光波长变换器的频率啁啾和码间干扰。当采用反禹波长变换时,对于不同的探测光功率在维持消光比不变的情况下,变换信号性能较差的原因是较长的载了恢复时间和较强的码间干扰。但是对于同向波长变换,大的探测光的载流子恢复时间的情况下变换信号的工不一定好于探测光功率较小时达的变换信号的性能。     

Effect of stimulated Brillouin scattering on the gain saturation of distributed fiber Raman amplifier and its suppression by phase modulation

For distributed fiber Raman amplifiers(DFRAs), stimulated Brillouin scattering(SBS) can deplete the pump once occurring and consequently generate gain saturation. On the basis of such a theory, theoretical gain saturation powers in DFRAs with various pump schemes are obtained by calculating SBS thresholds in them, and the experimental results show that they are in excellent agreement with the calculation results. The saturation power of the DFRA with a 300 m W forward pump is as low as 0 d Bm, which needs to be enhanced by phase modulation, and the effect is quantitatively studied. A simple model taking both modulation frequency and index into consideration is presented by introducing a correction factor to evaluate the effect of phase modulation on the enhancement of saturation power. Experimentally, it is shown that such a correction factor decreases as the modulation frequency increases and approaches zero when the modulation frequency becomes high enough. In particular, a phase modulation with a modulation frequency of 100 MHz and a modulation index of 1.380 can enhance the saturation power by 4.44 d B, and the correction factor is 0.25 d B, in which the modulation frequency is high enough. Additionally, the factor is 1.767 d B for the modulation frequency of 25 MHz. On this basis,phase modulations with various indexes and a fixed frequency of 25 MHz are adopted to verify the modified model, and the results are positive. To obtain the highest gain saturation power, the model is referable. The research results provide a guide for the design of practical DFRAs.     

基于饱和滤波效应的半导体光放大器高速调制特性分析

本文分析了半导体光放大器的高频滤波效应,给出了具有高速响应的半导体光放大器各参量的优化设计方法,提出了动态载流子恢复时间的概念,为分析基于半导体光放大器的各种器件的高频动态特性提供了一种简单的近似方法.     

调制自由载流子吸收测量半导体载流子输运参数的三维理论

推导出用于测量半导体载流子输运特性(载流子寿命、载流子扩散系数和前表面复合速度)的调制自由载流子吸收(modulated free carrier absorption, MFCA)检测技术的三维理论模型,给出了调制自由载流子吸收检测信号与调制频率和抽运-探测光相对距离的关系.定性分析了在不同调制频率时各个载流子输运参数对径向位置扫描曲线(信号与两束光相对距离的关系)的影响,结果表明调制自由载流子吸收检测信号对各个参数的灵敏度随抽运-探测光相对距离的增加而增加.仿真和实验结果表明,通过拟合不同调制频率时调 关键词： 调制自由载流子吸收 载流子输运特性 径向位置扫描     

The impact of nonequilibrium gain in a spectral laser diode model

We describe the inclusion of nonequilibrium gain into a self-consistent 2.5D CW spectral laser diode model and report on the use of this model to investigate the origin of gain compression in a 975 nm high-brightness tapered QW laser diode. Nonequilibrium gain is calculated using a dynamic gain model, which simulates the dynamic relaxation of the quantum well carrier energy distributions under the influence of steady-state electrical and optical excitation. Calculated gain and spontaneous emission spectra are included in the laser model via parameterised look up tables. Both simulated and experimentally measured intracavity spontaneous emission spectra show an increased carrier density and a blue-shift of the gain maximum with increasing bias caused by carrier heating and spectral hole burning. The accurate incorporation of nonequilibrium gain compression is therefore vital for the accurate prediction of the operating characteristics of these devices and for the experimental determination of the active region temperature.     

Analysis and minimization of cross phase modulation in semiconductor optical amplifiers for multichannel WDM optical communication systems

A theoretical model for crosstalk in multichannel wavelength division multiplexing communication systems due to cross phase saturation in semiconductor optical amplifier structure is developed. This theoretical model is used to analyze the impact of the cross phase noise on the performance of semiconductor optical amplifiers in saturation region for WDM communication system by using differential phase shift modulation format. It is shown that by increasing the carrier life time, width and thickness while reducing the confinement factor, differential gain and bias current in the SOA structure mitigates the cross talk due to cross phase saturation. The impact of penalty and cross phase noise imposed on multichannel WDM links have been investigated for different parameters of the SOA with the variation in transmission distance. With the slight increase in differential gain of 200.2 × 10⁻¹⁸ cm² and confinement factor 0.41, the maximum transmission distance observed is 5220 km with good quality and nil power penalty for 10 × 40 Gb/s soliton RZ-DPSK WDM signals for the first time.     

Modulation bandwidth of planar waveguide laser with 1D photonic crystal mirrors

An analysis of the 3-dB modulation bandwidth in planar waveguide laser based on 1D photonic crystal structures is presented. The theoretical model takes into account the gain saturation effect, transverse and longitudinal field distribution. A small-signal perturbation solution of the coupled laser rate equation is used to obtain relations describing the dynamic operation. In paper, the distributed Bragg resonator DBR created as 1D photonic crystal is considered. The active waveguide is surrounded by 1D photonic crystal mirrors consisting of alternately placed stripes with different refractive indices. In particular, the influence of the photonic crystal parameters on the 3-dB modulation bandwidth is investigated.     

THEORETICAL STUDY OF SELF-STARTING MODE-LOCKED ALL-FIBER LASERS

In this paper, the self-startlng mode-locking characteristics of all-fiber lasers are in-vestigated theoretically. The mechanism of self-starting mode-locking is analyzed and the experimental phenomena are explained successfully by introducing effective energy gain. The modulation characteristics of all-fiber lasers and the effect of gain saturation on modulation characteristics are discussed by analyzing the transmissivity of Er-doped fiber loop. Finally, the dynamic processes of all-fiber self-starting mode-locked lasers are simulated numerically.     

半导体特性的调制自由载流子吸收变距频率扫描方法研究

根据调制自由载流子吸收（modulated free carrier absorption,MFCA）检测技术的三维理论模型,采用变间距频率扫描方式测量单晶硅样品的电子输运参数,进行了仿真与实验,对结果进行了分析;通过多参数拟合,获取了测试样品的载流子扩散系数、少数载流子寿命和前表面复合速度.仿真与实验都表明,变间距频率扫描结合多参数拟合,可以提高输运参数的测量精度. 关键词： 调制自由载流子吸收 电子输运参数 变间距频率扫描 多参数拟合     

A dynamic model to predict modulation sidebands of a planetary gear set having manufacturing errors

In this study, a nonlinear time-varying dynamic model is proposed to predict modulation sidebands of planetary gear sets. This discrete dynamic model includes periodically time-varying gear mesh stiffnesses and the nonlinearities associated with tooth separations. The model uses forms of gear mesh interface excitations that are amplitude and frequency modulated due to a class of gear manufacturing errors to predict dynamic forces at all sun-planet and ring-planet gear meshes. The predicted gear mesh force spectra are shown to exhibit well-defined modulation sidebands at frequencies associated with the rotational speeds of gears relative to the planet carrier. This model is further combined with a previously developed model that accounts for amplitude modulations due to rotation of the carrier to predict acceleration spectra at a fixed position in the planetary transmission housing. Individual contributions of each gear error in the form of amplitude and frequency modulations are illustrated through an example analysis. Comparisons are made to measured spectra to demonstrate the capability of the model in predicting the sidebands of a planetary gear set with gear manufacturing errors and a rotating carrier.     

Surface acoustic wave controlled charge dynamics in a thin InGaAs quantum well

We experimentally study the optical emission of a thin quantum well and its dynamic modulation by a surface acoustic wave (SAW). We observe a characteristic transition of the modulation from one maximum to two maxima per SAW cycle as the acoustic power is increased which we find in good agreement with numerical calculations of the SAW controlled carrier dynamics. At low acoustic powers the carrier mobilities limit electron-hole pair dissociation, whereas at high power levels the induced electric fields give rise to efficient acousto-electric carrier transport. The direct comparison between the experimental data and the numerical simulations provide an absolute calibration of the local SAW phase.     

探测光功率对半导体全光波长变换器性能的影响分析

根据半导体光放大器的高频滤波效应,利用动态载流子恢复时间的概念,分析了基于半导体光放大器交叉增益调制的全光波长变换器中变换信号的波形、啁啾与探测光功率的关系。理论计算表明,在保持变换信号消光比相同的情况下,在大的探测光功率下,变换信号的波形将变好,并且啁啾对变换信号码间干扰的影响会减小,理论很好地解释了文献中的实验结果。     

半导体激光放大器用于啁啾补偿的研究

详细分析了饱和工作状态下的行波半导体激光放大器的啁啾特性，从理论上证了实了利用其增益饱和所引起的自相位调制来对光源啁啾和光纤色散进行啁啾补偿的可行性，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，这一特性可用来在长距离光纤传输系统中，对微弱啁光脉冲同时进行能量和相位的补偿。     

适用于量子阱激光器的速率方程

首次在理论上用量子阱激光器增益与载流子密度的对数关系替代了原有速率方程中的线性关系，得到了改进了速率方程，分析了稳态和调制特性，从理论上得到了获得最低阈值的最佳阱数和最大调制带宽的最佳腔长。     

Performance of analog optical links employing fiber Raman amplifiers

We present the characterization of an analog optical link employing external modulation and optical carrier in the C-band using a fiber Raman amplifier (FRA). The figures of merit gain and noise figure were characterized from 1 to 9 GHz, whereas the spurious-free dynamic range was measured and compared for both setups for frequencies from 2 to 9 GHz, all with and without the Raman amplifier. Experimental results demonstrate that FRA can simultaneously increase the spurious-free dynamic range, the analog gain and decrease the analog noise figure when compared to the same configuration without optical amplifier.     

The effect of carrier level on tuning in amplitude-modulation masking

The effect of carrier level on tuning in modulation masking was investigated for noise and tonal carriers. Bandwidths of the modulation filters, estimated from the masked detection thresholds using an envelope power spectrum model, were independent of level for the noise carrier but seemed to decrease with increasing level for the tonal carrier. However, the apparently sharper tuning could be explained by increased modulation sensitivity and modulation dynamic range with increasing level rather than improved modulation-frequency selectivity. Consistent with this interpretation, the addition of a high-pass noise with a level adjusted to maintain the same threshold for the detection of the signal modulation for each carrier level used eliminated the effect of level on tuning. Overall, modulation filters estimated from psychophysical data do not depend on level in contrast to the modulation transfer functions obtained from neural recordings in the inferior colliculus in physiological studies. The results highlight differences between the characteristics of modulation processing obtained from neural data and perception. The discrepancies indicate the need for further investigation into physiological correlates of tuning in modulation processing.     

啁啾脉冲激光放大中的自相位调制效应

利用光与物质相互作用的半经典理论建立了啁啾脉冲激光放大的输运方程,数值分析了多程放大过程中自相位调制对啁啾脉冲时域特性和频域特性的影响研究结果表明,由于自相位调制引起附加频率啁啾产生,啁啾脉冲瞬时频率发生变化,放大特性受到影响.通过对增益饱和状态下自相位调制效应的研究,提出利用入射脉冲的线性频率啁啾抑制自相位调制的影响. 关键词：