高效率量子级联激光器

由于宽带宽光通信和光记录应用的需求,二极管激光器的商业用途在过去十年中极大地提高。电子和空穴被电力射入激活区,以发射光子复合,激光波长基本由激活区的带隙决定。这些激光器在光谱的近红外(08～16μｍ)和可见光区(包括蓝光)达到高效率。但由于缺乏合适的高质量小带隙半导体,它在中红外光谱带(2～20μｍ)有严重缺陷。与现在广泛用于通信和消费电子器件的短波长材料(ＡｌＧａＡｓ/ＧａＡｓ,ＩｎＰ/ＧａＩｎＡｓＰ)相比,这些材料(如铅盐)一般不够耐用,难于处理,可靠性较低。中红外光谱(图1)称作“分子足迹区”,该区气体有与分子振动相关…     

基于室温脉冲量子级联激光器的脉内光谱技术研究

介绍了基于量子级联激光器的脉内光谱技术,一个长激发脉冲应用在中心波长为7.85 μm脉冲量子级联激光器上,用于快速波长扫描,通过分析比较不同工作参数下的激光光谱信号,寻求最佳的激光器工作参数,并且在选定的工作参数下对目标气体的吸收谱线进行测量,得到了中心在1273.7 cm-1的N2O 吸收谱线.     

应变补偿InGaAs/InAlAs量子级联激光器

利用应变补偿的方法研制出激射波长 λ≈ 3.5— 3.7μm的量子级联激光器 .条宽 2 0 μm,腔长 1 .6mm的 Inx Ga1- x As/Iny Al1- y As量子级联激光器已实现室温准连续激射 .在最大输出功率处的准连续激射可持续 30 min以上 .     

应变补偿InGaAs/InAlAs量子级联激光器

利用应变补偿的方法研制出激射波长λ≈3.5—3.7μm的量子级联激光器.条宽20μm,腔长1.6mm的InxGa1-xAs/InyAl1-yAs量子级联激光器已实现室温准连续激射.在最大输出功率处的准连续激射可持续30min以上.     

纳秒级红外量子级联激光器驱动电源的设计

为了使量子级联激光器(QCL)应用于中红外气体检测,设计了一种纳秒级脉冲型的QCL驱动电源。本系统基于压控恒流源的原理,以S3C2410A芯片为主处理器,实现周期、占空比、幅值均可调的驱动电流。硬件电路主要包括控制电路、脉冲调节电路和恒流源电路。同时具备延时软启动电路、过流保护电路、过压保护电路、静电防护电路等,以确保激光器的长期稳定工作。利用该驱动电源对中心波长为7.71μm的QCL进行驱动实验。结果表明,脉冲上升时间小于8ns,脉冲下降时间小于12ns,最大电流幅值3.3A,为QCL在红外气体检测应用中提供保证。     

基于FPGA脉宽可调的窄脉冲激光器驱动电路设计

针对激光驱动电路纳秒脉冲宽度无法调节的问题,设计了一种新型的脉宽可调的窄脉冲激光驱动电路。利用FPGA和激光二极管的工作原理,设计并搭建半导体激光器驱动电路。电路采用高速MOSFET作为开关器件驱动激光二极管SPLPL90-3,并利用LTspice仿真软件分析激光驱动电路中电源电压、储能电容和阻尼电阻对驱动脉冲的影响,最终选择最佳的电路参数。当电源电压为150 V,储能电容为1 nF,阻尼电阻为2Ω时,最终输出激光二极管的电流为39.7 A,脉冲宽度6 ns,上升沿3 ns,满足了大电流纳秒脉冲半导体激光器驱动电路的设计要求。     

基于量子级联激光器光腔衰荡光谱技术的痕量氨气检测

采用基于红外脉冲量子级联激光器的高灵敏光腔衰荡光谱(Cavity ring-down spectroscopy)技术建立了氨气在1027 cm-1(9.7 μm)附近的吸收光谱痕量检测实验装置.使用该装置对人体口腔呼出气体以及超净实验室环境中氨气成份进行了测量和分析,氨气的检测灵敏度达到10 ppb.模拟分析了激光器光谱线宽对测量结果和系统检测灵敏度的影响,随着激光器光谱线宽的增加,测量结果偏低,系统检测灵敏度下降.为了减小光源线宽对测量结果的影响,通过修正曲线对测量数据进行修正,得到了较好的结果.     

半导体激光器的大电流窄脉冲驱动电路的研究

介绍利用高频小功率晶体管的雪崩效应设计激光器的大电流窄脉冲驱动电路,对该电路建立了数学模型,并对电路参数进行了仿真。实验制作了产生宽度约为１０ｎｓ,峰值约２０Ａ的脉冲电路,仿真结果与实验相吻合,因此,对实际应用有一定的指导意义。     

量子级联激光器的电路模型分析

通过分析量子级联激光器(QCL)中的电子在量子阱输运的单极行为,得到它的速率方程,以此为基础建立起它的等效电路模型,利用PSPICE进行电路模拟,得到了它的频率响应特性,并对可能影响它的调制特性的一些因素进行了分析.     

量子级联激光器的一种新的等效电路模型

采用电路建模方法,通过分析量子级联激光器（QCL,quantum cascade laser）中电子在子能带间跃迁机理和量子阱间的输运特性得到其二层级电子速率方程和光子速率方程,以此建立QCL的等效电路模型。电路模型的建立使得对QCL特性可以用通用电路仿真工具进行模拟仿真,克服了数值分析方法计算复杂,模拟时间长的缺点。...     

High-performance quantum cascade lasers with electric-field-freeundoped superlattice

An optimized design of quantum cascade lasers with electric field free undoped superlattice active regions is presented. In these structures the superlattice is engineered so that: (1) the first two extended states of the upper miniband are separated by an optical phonon to avoid phonon bottleneck effects and concentrate the injected electron density in the lower state and (2) the oscillator strength of the laser transition is maximized. The injectors' doping profile is also optimized by concentrating the doping in a single quantum well to reduce the electron density in the active material. These design changes result in major improvements of the pulse/continuous-wave performance such as a weak temperature dependence of threshold (T₀=167 K), high peak powers (100-200 mW at 300 K) and higher CW operating temperatures for devices emitting around at λ~8.5 μm     

Mid-infrared tunable quantum cascade lasers for gas-sensingapplications

The quantum cascade (QC) laser does not involve the material bandgap for the generation of light. Therefore, InP- and GaAs-based III-V semiconductor materials can now be used for the generation of long-wavelength, mid-infrared light. These materials are also straightforward to process and pattern. This is essential for the more sophisticated device geometries such as distributed feedback (DFB) lasers. DFB lasers provide a very elegant and reliable method to achieve a well-defined single-wavelength emission (called single-mode operation) as opposed to the usually multiple-mode emission of free-running Fabry-Perot resonators. QC-DFB lasers were first demonstrated in 1996. They have evolved very rapidly and have already shown great promise in many different gas-sensing applications     

Horn antennas for terahertz quantum cascade lasers

Far-field pattern and extraction efficiency of double metal 1.8 THz quantum cascade lasers (QCL) are controlled using miniaturised horn antennas. Enhancement of the optical output power of ten times and quasi-circular beam pattern are obtained     

Photonic-crystal distributed-feedback quantum cascade lasers

Because of an intrinsically low linewidth-enhancement factor, the quantum cascade laser (QCL) is especially favorable for patterning with a recently proposed 2-D photonic crystal (PC) lattice that substantially increases the device area over which optical coherence can be maintained. In this work, we use an original time-domain Fourier-transform (TDFT) algorithm to theoretically investigate the beam quality and spectral purity of gain-guided PC distributed-feedback (DFB) quantum cascade lasers. The conventional 1-D DFB laser and also the angled-grating DFB (α-DFB) laser are special cases of the PCDFB geometry. By searching the parameter space consisting of tilt angle, coupling coefficients, stripe width, and cavity length, we have theoretically optimized the PCDFB gratings for QCL gain regions. At a wavelength of 4.6 μm, the simulations project single-mode emission from stripes as wide as 1.2 mm, and etendues of no more than three times the diffraction limit for 2-mm stripes. We also examine the tolerances required for single-mode and high-brightness operation. Comparisons are made to analogous simulations of a-DFB QCL lasers     

High-power continuous-wave quantum cascade lasers

High-power continuous-wave (CW) laser action is reported for a GaInAs-AlInAs quantum cascade structure operating in the mid-infrared (λ≃5 μm). Gain optimization and reduced heating effects have been achieved by employing a modulation-doped funnel injector with a three-well vertical-transition active region and by adopting InP as the waveguide cladding material to improve thermal dissipation and lateral conductance. A CW optical power as high as 0.7 W per facet has been obtained at 20 K with a slope efficiency of 582 mW/A, which corresponds to a value of the differential quantum efficiency η_d=4.78 much larger than unity, proving that each electron injected above threshold contributes to the optical field a number of photons equal to the number of periods in the structure. The lasers have been operated CW up to 110 K and more than 200 mW per facet have still been measured at liquid nitrogen temperature. The high overall performance of the lasers is also attested by the large “wall plug” efficiency, which, for the best device, has been computed to be more than 8.5% at 20 K. The spectral analysis has shown finally that the emission is single-mode for some devices up to more than 300 mW at low temperature     

Gain measurements on GaAs-based quantum cascade lasers using atwo-section cavity technique

A two-section cavity device has been used to measure gain spectra and waveguide losses of a GaAs-based quantum cascade laser. The device operates at 8.9 μm and optical confinement is obtained by means of Al-free cladding layers. We investigated the gain characteristics in a spectral window of ~60 meV and up to 200 K. For current densities ranging from 1 to 8 kA/cm², we report a constant gain coefficient of 13 cm/kA at 4 K and 6 cm/kA at 200 K. At low temperatures and for current densities above 8 kA/cm², we observe gain saturation which we attribute to a reduced electron injection in the active region caused by space charge effects. We report a value of 22 cm ^-1 for the waveguide losses in good agreement with previous measurements     

GaAs-based quantum cascade lasers with native oxide-defined currentconfinement

The development of broad area (width ≈100 μm) GaAs-based quantum cascade lasers (QCLs) with 20 μm-wide current apertures defined by selective oxidation of the Al_0.9Ga_0.1As optical cladding layers is reported. Processing the lasers in this way enhances heat removal from the active region of the structure, allowing improved pulsed performance at higher duty cycles compared with conventional ridge waveguide structures     

InAs-based distributed feedback quantum cascade lasers

InAs/AlSb distributed feedback quantum cascade lasers are presented. The lasers can operate in the single frequency regime at 3.34-3.38 mum in the 0-100degC temperature range in pulse mode. The wavelength tuning rate of the lasers is 0.27 nm/K and continuous tuning range up to 10 nm can be achieved.