Nonlinear gain effects on spectral dynamics in quantum well lasers

A theoretical analysis is presented to show how nonlinear gain affects the spectral dynamics of quantum well (QW) lasers. The results indicate that the nonlinear gain, which is enhanced by the quantum confinement of carriers, causes an increase in the linewidth enhancement factor alpha . This enhancement of alpha results in spectral rebroadening: under high power output conditions. These properties should be taken into account when quantum well lasers are designed for highly coherent lasers.<>     

Threshold currents for AlGaAs quantum well lasers

The threshold currents for AlGaAs quantum well lasers are studied theoretically. The structure dependent gain coefficient is obtained by taking into account the electron distribution inLvalleys. Theoretical threshold current densities calculated using the gain coefficient agree well with reported experimental results for separate-confinement heterostructure lasers. A design procedure for low threshold current laser is elucidated. The lowest threshold currents are 570 and 53 μA per 1 μm stripe width for modified multiple quantum well lasers with 32 percent and 90 percent reflectivity facet mirrors, respectively.     

Measurement of spectral linewidth of AlGaAs/GaAs distributed feedback lasers

The spectral linewidth of AlGaAs/GaAs distributed feedback (DFB) lasers was measured for the first time. The linewidth-power product decreased with temperature, which indicates that the relative position of the oscillation wavelength and the gain peak strongly affects the linewidth of DFB lasers.     

单模AlGaAs／GaAs脊形波导量子阱半导体激光器

本文报道用分子束外延设备研制梯度折射率分别限制式单量子阱AlGaAs/GaAs脊形波导半导体激光器。该激光器具有良好的性能,条宽5μm器件室温阈值电流23mA,线性连续输出单模激光功率大于15mW。     

Theory for the spectral linewidth of passive-coupled-cavitysemiconductor lasers

A simple expression for the spectral linewidth of passive-coupled-cavity (PCC) semiconductor lasers is presented. Experimentally observed linewidth narrowing and periodic variation of the linewidth as functions of the injection current and the gap between the active cavity (laser) and the passive cavity (graded index, or GRIN rod) can be satisfactorily explained by this formula     

量子阱半导体激光器调制特性和噪声的电路模拟

给出一种量子阱半导体激光器（QWLD）小信号等效电路模型,可以作为含有QWLD系统计算机辅助设计的模型。模型包括QWLD的高速调制特性和噪声,对QWLD的调制特性和噪声进行了模拟,并对比了已发表的模拟和实验结果。     

Differential gain in bulk and quantum well diode lasers

Differential gain (g^') of bulk and single-quantum-well (SQW) lasers was determined from threshold current density and differential quantum efficiency measurements. The threshold measurement technique was used to show that g^' is a function of cavity length (L) in SQW lasers and independent of L in bulk lasers. It was found that g^' of long SQW lasers (1000 μm) is about 7×10^-16 cm² , approximately two times that of bulk lasers. At short cavity lengths (250 μm), g^' is about the same for both laser types     

Theory of spectral linewidth of external cavity semiconductor lasers

A new formula of the spectral linewidth of external cavity semiconductor lasers is proposed, with which linewidth narrowing with the optical feedback is discussed. It is shown that in the limit of large external cavity length, the linewidth caused by the phase diffusion due to spontaneously emitted photons becomes dominant and the linewidth decreases proportionally to the inverse of the external cavity length.     

Gain and carrier lifetime measurements in AlGaAs single quantum well lasers

We have measured the optical gain and carrier lifetime (τ) at threshold in AlGaAs single quantum well lasers in the temperature range10-70degC. The small shift of the spectral position of the gain peak with increasing injection is evidence for the two-dimensional-like density of states in a quantum well. The net gainGis found to vary linearly with the currentI. The observed slow decrease ofdG/dIand τ with increasing temperature suggests the absence of a large temperature-dependent nonradiative carrier loss or optical absorbtion loss in these lasers. This is also supported by the observed low temperature dependence of the external differential quantum efficiency.     

On carrier injection and gain dynamics in quantum well lasers

A detailed carrier dynamics model for quantum well lasers is presented. The model describes the transport of carriers using full continuity equations and the gain by rate equations for each well separately, and it also takes into account electron-hole interactions which modify the energy band structure. To this end, the model includes Poisson and Schrodinger equations. The model is solved in steady state where it yields nonuniform carrier distributions along the crystal growth axis. Dynamically, the model is solved in the time domain, yielding the evolution of carriers in time and space and highlighting a new effect, photon-assisted carrier transport. The model is also solved in the small-signal regime where the phase lag in gain between wells is determined     

Low-voltage phase modulation in GaAs/AlGaAs quantum well opticalwaveguides

Reports GaAs/AlGaAs quantum well waveguide phase modulators with high phase shift coefficients, as large as 520 degrees per V mm. By operating at wavelengths far below the bandedge and applying DC bias the authors achieve large electro-optic modulation with low absorption loss in device lengths on the order of 100 μm and drive voltages on the order of 1 V     

Experimental evidence for hole transport limited intensity modulation response in quantum well lasers

Direct experimental evidence is presented to show that it is the hole transport across wide separate confinement heterostructures and not the electron quantum capture that leads to the low-frequency rolloff in the intensity modulation response of quantum well lasers.<>     

GaAs/AlGaAs环形激光器的量子阱结构优化

为了研究量子阱结构对半导体环形激光器阈值电流的影响,从F-P腔激光器的振荡条件出发,分析了半导体环形激光器的阈值电流密度与量子阱结构参量的函数关系,并推导出最佳量子阱数的表达式。利用器件仿真软件ATLAS建立环形激光器的等效模型,仿真、分析了不同工作温度下,量子阱数、阱厚及势垒厚度对阈值电流的影响。结果表明,阈值电流随量子阱数和阱厚的增加先减小后增大,存在一组最佳值;在确定合适的量子阱数和阱厚后,相对较窄的势垒厚度有助于进一步降低阈值电流;采用GaAs/AlGaAs材料体系和器件结构,其最佳量子阱结构参量为M=3,dw=20nm及db=10nm。     

Dependence of linewidth enhancement factor on crystal orientationin strained quantum well lasers

The linewidth enhancement factor a in strained quantum well (QW) lasers is estimated theoretically for various crystallographic directions. It is found that the a factor in a strained In_0.7Ga_0.3As-InP QW laser on a (111) substrate is less than 1.4, much lower than for conventional strained QW lasers on (001) substrates     

High power and low optical feedback noise AlGaAs single quantum well lasers

GaAs-AlGaAs single quantum well self-aligned lasers have been developed for optical disc recording. The lasers emitting at 834 nm have realised low optical feedback noise as well as high output power. The lasers have shown less than -130 dB/Hz relative intensity noise at 3 mW, and stable 50 mW operation (over 500 hours at 50 degrees C ambient).<>     

Laser gain and current density in a disordered AlGaAs/GaAs quantum well

The laser gain and current density at room temperature are analysed for disordered (interdiffusion induced) Al/sub 0.3/Ga/sub 0.7/As/GaAs single quantum well structures at a carrier injection level of 4*10/sup 12/ cm/sup -2/. The results show that both the peak gain and current density remain about the same strength during the initial stages of disordering, and provide a bandwidth of 55 nm.<>     

Frequency modulation locking in 980 nm strained quantum well lasers

The fundamental and second-harmonic spectral characteristics of frequency modulation locking have been observed in strained-layer InGaAs quantum well Fabry-Perot ridge-waveguide lasers emitting at 980 nm.<>     

Anomalous length dependence of threshold for thin quantum well AlGaAs diode lasers

The threshold current in conventional semiconductor diode lasers decreases linearly with decreasing cavity length. We have found that for AlGaAs diode lasers fabricated from very thin active layer material, the threshold current can be essentially constant over a wide range of cavity lengths. At short cavity lengths, threshold increases dramatically. This anaomalous behaviour is attributed to physical mechanisms which become important when active layer threshold gain requirements become unusually high.     

Evidence of no k-selection in gain spectra of quantum well AlGaAs laser diodes

It is suggested, contrary to present views, that the processes giving rise to radiation in undoped or lightly doped quantum well laser diodes can be described by using a nok-selection model. The reason is contained in the good fit of experimental gain spectra which we obtain on the basis of this assumption. This does not rule out the possibility that spectra can, in principle, be obtained in the future which are subject to the strictk-selection rule.     

半导体激光器谱宽的测量研究

本文从范德玻尔(van der Pol)方程出发,导出了描述延迟自差拍法谱宽测量的公式。讨论了各结构参数对测量的影响。报道了用该法对单频半导体激光器测量的一些结果。