GRINSCH—SQW激光器波导特性的数值分析

采用折射率台阶近似法将梯度折射率分别限制异质结单量子阱(GRINSCH—SQW)激光器波导结构中的缓变折射率层离散成折射率近似为常数的亚层,从而推导出此波导的近似本征方程,并用数值计算求解出波导对于基模的等效折射率。在此基础上,通过计算波导中垂直于激光器结平面方向上的光强近场分布,计算出与激光器的阈值电流有密切关系的光学常数——激光器有源层的光限制因子P以及各种波导结构参数对P的影响,同时计算了激光器的远场图形。计算结果可用于GRINSCH-SQW激光器波导结构参数的优化设计。     

Role of localized excitons in the stimulated emission in ultra-thin CdSe/ZnSe/ZnSSe single quantum-well structures

Photo-pumped lasing properties have been investigated in a CdSe/ZnSe/ZnSSE single quantum wells (SQWs) with the well-layer thickness (L_W) of 1, 2 and 3 monolayer (ML). At 20 K, the laser threshold for the SQW withL_W = 1 ML was the lowest in spite of the smallest active layer thickness. The carrier (exciton) sheet density at the threshold (n)_thwas estimated to be as low as 7 × 10¹⁰cm⁻², which is well below Mott's screening density. Time-resolved photoluminescence has revealed that the localized biexciton band, whose peak energy agrees with the lasing peak, appeared on the low-energy side of the main PL peak at this level of carrier concentrations. Theoretical calculation has also shown that the localized biexciton recombination has to be taken into account for the lasing process. On the contrary, then_thvalues of the SQWs with 2 and 3 ML are 1 order of magnitude larger than that of the SQW with 1 ML. This may be due to the smaller oscillator strength of both localized excitons and localized biexcitons because of the larger inhomogeneous broadening, resulting in an increased carrier density for achieving optical gain sufficient to overcome the reflection losses.     

InGaAs/GaAs应变量子阱激光器线宽展宽因子的理论研究

详细地介绍了计算线宽展宽因子(α因子)的理论基础及推导过程, 建立了α因子的简便模型. 该模型分别考虑了带间跃迁、带隙收缩和自由载流子效应对α因子的影响, 利用不同载流子浓度下的增益曲线得到光子能量随载流子浓度的变化速率以及微分增益, 进而对α因子进行近似计算. 模拟计算了InGaAs/GaAs量子阱激光器的增益曲线及α 因子的大小, 计算结果与文献报道的实验值相符. 进一步讨论了InGaAs/GaAs量子阱阱宽及In组分对α 因子的影响. 结果表明, α 因子随In组分和阱宽的增加而增加.     

InGaAsSb/AlGaAsSb长波长多量子阱激光器有源区的优化设计

系统地研究了波长为2.7μm的InGaAsSb/AlGaAsSb多量子阱激光器中有源区的优化设计.分别用含应变势的6带KP模型和抛物带模型计算价带和导带的能带结构，并得到薛定谔方程和泊松方程的自洽解，由此计算量子阱在载流子注入时的增益谱.研究表明制约量子阱增益的主要因素不是跃迁矩阵元，而是粒子数反转程度，尤其是空穴填充HH1子带的概率.增加压应变或减小阱宽都会提高量子阱增益.前者降低了价带HH1子带空穴的平面内有效质量；后者拉大了价带子带间距，尽管它同时略微增加了空穴有效质量.这两种因素都导致价带顶空穴态     

Band structures and characteristics of InGaAs/InGaAsP strain-compensated quantum well lasers

Analysis is performed for valence band structures and some characteristics of InGaAs/InGaAsP strain-compensated quantum well lasers lattice-matched to InP substrate. The computed results show that band offsets are functions of strain compensation instead of constants; strain compensation changes the band structures and the density of states, and hence affects the optical gain and the threshold current density. Under the condition of zero net strain, the values of the well width, cavity length and relative threshold carrier density and threshold current density are determined for realization of 1.55 m wavelength emission.     

941nm大功率应变单量子阱激光器的波长设计

从薛定谔方程出发推导了阶梯形有限深应变单量子阱中的特征值方程，研究了台阶宽度对激射波长、电子第一子能级、空穴第一子能级的影响以及空穴第一子能级对激射波长的影响，计算结果表明当有源区In组分较大时，不能忽略空穴第一子能级对激射波长的影响.该模型计算结果与实验值相吻合. 关键词： 薛定谔方程 有限深势阱 应变量子阱 特征值方程     

非线性增益对外部注入半导体激光器动态行为的影响

研究了非线性增益对外部注入半导体激光器动态行为的影响。研究结果表明:非线性增益对外部注入半导体激光器的动力学行为影响极大;随着非线性增益系数的增加,激光器达到锁定时的注入系数减小,产生混沌的注入系数的范围缩小;当非线性增益系数过大时,外部注入激光器表现为混沌;非线性增益还影响外部注入半导体激光器混沌同步系统的性能,非线性增益系数越大,参数失配引起的混沌同步误差越小。     

Control of gain and thermal carrier loss profiles for mode optimization in 980-nm broad-area vertical-cavity surface-emitting lasers

Optical gain and thermal carrier loss distributions regarding current diffusion and various electric contact areas are investigated to improve the near-field modes from the ring-shape to a Gaussian-like configuration for extra-broad-area and oxide-confined vertical-cavity surface-emitting lasers. In this work an equivalent circuit network model is used. The resistance of the continuously-graded distributed Bragg reflectors （DBRs）, the current diffusion and the temperature effect due to different electric-contact areas are calculated and analyzed at first, as these parameters affect one another and are the key factors in determining the gain and thermal carrier loss. Finally, the gain and thermal carrier loss distributions are calculated and discussed.     

基于两端自发荧光辐射的808nm半导体激光器增益偏振特性实验表征和能带分析

通过半导体激光器两端的放大自发荧光辐射可以获取器件的光学增益信息. 本文利用这一新的增益实验测量方法, 开展了对连续运行的808nm GaAs/AlGaAs量子阱激光器横向电场 (TE)与磁场(TM)偏振增益特性的实验研究. 通过将实验结果与理论增益曲线对比, 分析了非应变GaAs量子阱TE和TM极化偏振对应的空穴子能带随注入电流的变化规律, 以及激光器在连续运行状态下的实际增益状态和影响因素. 关键词： 半导体激光器 增益测量 偏振 量子阱和能带     

SCH量子阱激光器的光学限制特性

通过对描述半导体激光器基本光波导方程的数值求解，分析了ＡｌＧａＡｓ／ＧａＡｓ分别限制量子阱激光器的光学限制特性，比较了不同缓变结构及多量子阱结构的光学限制因子。     

Influence of the Depolarization Effect on Optical Rectification in Electric-Field-Biased Quantum Well

The effect of the depolarization field on the optical rectification due to resonant intersubband transition in electric-field-biased quantum well is studied. Calculations are performed using a compact density-matrix approach. The obtained results show that the depolarization effect shifts the peak of the optical rectification coefficient, and the shift increases with increasing of the bias field.     

Effect of Quantum Well Width Reduction for GaInNAs/GaAs Lasers

We investigated the function of the quantum well (QW) width for laser characteristics especially for reduction of the well width. We pointed out that such reduction has almost no influence on the optical gain or the carrier overflow for a large conduction band offset system, such as GaInNAs QWs. A thin QW is advantageous for suppression of the carrier overflow to the higher quantized energy levels which results in good temperature and gain characteristics. Thin GaInNAs QWs is a good candidate for an active layer structure of the lasers utilized in the next optical communication systems.     

高功率垂直外腔面发射半导体激光器增益设计及制备

垂直外腔面发射半导体激光器(vertical external cavity surface emitting laser, VECSEL)兼具高功率与良好的光束质量,是半导体激光器领域的持续研究热点之一.本文开展了光抽运VECSEL最核心的多量子阱增益区设计,对量子阱增益光谱及其峰值增益与载流子浓度及温度等关系进行系统的理论优化,并对5种不同势垒构型的量子阱增益特性进行对比,证实采用双侧GaAsP应变补偿的发光区具有更理想的增益特性.对MOCVD生长的VECSEL进行器件制备,实现了VECSEL在抽运功率为35 W时输出功率达到9.82 W,并且功率曲线仍然没有饱和;通过变化外腔镜的反射率, VECSEL的激光波长随抽运功率的漂移系数由0.216 nm/W降低至0.16 nm/W,证实外腔镜反射率会影响VECSEL增益芯片内部热效应,从而影响VECSEL激光输出功率.所制备VECSEL在两正交方向上的发散角分别为9.2°和9.0°,激光光斑呈现良好的圆形对称性.     

模态信息非完备采样对水下声源检测的影响及改进方法

给出了海洋波导中位置未知简谐声源的广义似然比检测器及其理论检测性能.通过对检测器中模态相关矩阵进行特征值分解,将该检测器分解为与各阶特征值相对应的谱成分.推导了各阶谱成分的统计特性并以此获得了谱成分对输入信号的空间处理增益,该增益与谱成分对应的特征值成正比.当模态信息采样不完备时,模态相关矩阵存在部分接近于0的小特征值,相应的谱成分对输入信号的空间处理增益与其余谱成分相比非常小.通过舍去这部分谱成分,提出了有效谱检测器.该检测器在保持其输出中目标信号成分与广义似然比检测器相同的基础上,有效减少了其中的噪声成分,因此,具有比广义似然比检测器更好的检测性能.在典型的浅海环境下进行仿真实验,仿真结果验证了理论分析、推导以及有效谱检测器的有效性,并且表明非完备采样程度越严重,有效谱检测器相对于广义似然比检测器的检测性能提高越显著.此外,有效谱检测器具有比广义似然比检测器更好的数值计算稳健性.     

基于复合结构的气体电子倍增器增益模拟和实验研究

气体电子倍增器(GEM)作为高性能的微结构气体探测器在高能物理相关领域内得到了广泛的研究和应用.其中增益是GEM探测器基本性能研究中的一个重要参数,该值的精确测量至关重要.增益的测量一般采用电流测量或者能谱测量方法,但均存在精度较低或者过程繁琐的问题,且无法精确测量低增益值.针对GEM探测器增益的精确测量,本文提出了一种由GEM探测器与微网结构气体探测器(MM)级联构成的复合结构探测器(GEM-MM).利用GEM-MM结构以相对方法实现GEM增益的精确测量.该方法既可以省去传统方法中复杂的电子学标定过程,同时不需要进行原初电离电子数的估算,保证了增益的精确测量,并且可以实现GEM低增益的测量.基于GEM-MM测量GEM增益的原理,本文首先对GEM-MM电荷输运过程进行了模拟研究,优化了合适的工作电压.比较了三种不同类型和配比工作气体下GEM增益模拟结果,并在Ar/iC_4H_(10)(95/5)气体中测量了单层GEM在3—24范围内的有效增益.不同Penning系数下GEM增益的模拟结果表明,Penning系数为0.32时GEM增益的模拟结果与实验测量结果符合得很好.由此可以确定一个大气压下的Ar/iC_4H_(10)(95/5)气体中,Penning系数为0.32±0.01.     

系统增益对光混沌通信系统性能影响的研究

针对强注入开环结构的外腔反馈半导体激光器混沌通信系统,数值计算得到系统增益与注入系数的定量关系曲线.对比是否使用系统增益对接收系统输出进行校正两种情况下系统的解调性能,表明使用增益校正的相减解调法获得的信息更接近原始信息.通过采用不同频率的正弦信号进行调制,表明信息频率对系统增益没有影响;用不同调制方法对0.2?Gbit/s数字信号加密,结果表明系统增益与信号类型及调制方法无关. 关键词： 光混沌通信 强注入 系统增益 同步     

MgXI等离子体软X射线自发辐射放大增益的数值模拟

本文采用碰撞辐射模型,考虑MgX,MgXII,MgXIII的基态及MgXI主量子数n≤6到光谱项层次的21个能级,假定等离子体电子温度按高斯函数随时间下降,用初始温度下定态能级占据数速率方程的解作初值,求解瞬态能级占据数速率方程,根据各能级粒子数的时间分布分析了MgXI1s3p—1s4d,1s3d—1s4f跃迁的自发辐射放大增益系数的时间特性。     

铒纤长度对EDFA增益斜率影响的实验研究和数值模拟

基于掺铒光纤放大器(EDFA)的增益斜率随着铒纤(EDF)长度变化的实验现象,对EDFA的增益斜率进行了分析,研究了不同EDF长度对EDFA的增益斜率的影响,从理论上对实验现象进行了解释。然后用OptiSystem模拟不同EDF长度下的EDFA增益谱,与实验室增益斜率数据相一致,得出了用EDF的长度来控制EDFA增益斜率的方法。     

Effects of transverse mode coupling and optical confinement factor on gallium-nitride based laser diode

We have investigated the transverse mode pattern and the optical field confinement factor of gallium nitride （GaN） laser diodes （LDs） theoretically. For the particular LD structure, composed of approximate 4 μm thick n-GaN substrate layer, the maximum optical confinement factor was found to be corresponding to the 5^th order transverse mode, the so-called lasing mode. Moreover, the value of the maximum confinement factor varies periodically when increasing the n-side GaN layer thickness, which simultaneously changes and increases the oscillation mode order of the GaN LD caused by the effects of mode coupling. The effects of the thickness and the average composition of Al in the AlGaN/GaN superlat.tice on the optical confinement factor are also presented. Finally, the mode coupling and optimization of the layers in the GaN-based LD are discussed.