Terahertz Quantum Cascade Laser at 3.39THz

We demonstrate the growth of terahertz quantum cascade laser （THz QCL） by gas source molecular beam epitaxy. X-ray diffraction and cross-sectional transmission electron microscopic measurements show the high crystalline quality of the THz QCL active region, From the cross-sectional transmission electron microscopy image, sharp interfaces are observed and the deduced cascade period thickness is consistent with the result of x-ray diffraction. The test device is lasing at 3.39THz and operating up to lOOK in pulsed mode. At IOK, the maximum output power is greater than 1 mW with a threshold current density of 738 A/cm^2.     

太赫兹量子级联激光器光束特性分析

用有限元法计算太赫兹量子级联激光器激光模式的阈值增益.结果表明:接触层厚度和掺杂浓度对阈值增益的影响远远大于波导宽度和激射波长;接触层厚度较小(大)和掺杂浓度较低(高)时,TM₁(TM₀)模的阈值增益较小.在此基础上,用矢量衍射理论分析岀射光束的远场特性,得到光束的远场光斑基本是椭圆;x方向的远场散射角随波导宽度或激射波长的增加分别线性减小或增加,尽管对应的接触层厚度和掺杂浓度不同,但TM₀和TM₁模x方向的远场散射角相同;另外,还得到y方向远场散射角不受波导宽度或少受激射波长的影响.在阈值增益和光束质量方面,TM₁模都优于TM₀模.     

Simulation of Confined and Interface Phonons Scattering in Terahertz Quantum Cascade Laser

We have performed the calculation of resonant-phonon transition in a terahertz quantum cascade laser. The electron wavefunctions and energy levels are obtained by solving the Schroedinger and Poisson equations selfconsistently. The scattering rates of the confined, interface, and bulk phonons are calculated by using the Fermi golden rule. It has been shown that the confined phonon scattering is comparable to the interface phonon scattering and should be taken into consideration in the calculation.     

基于掩埋光栅一级分布反馈结构的太赫兹量子级联激光器

结合理论和实验研究了掩埋光栅一级分布反馈太赫兹量子级联激光器中的模式竞争和功率特性。理论计算得到掩埋光栅腐蚀深度与两个带边模式的波导损耗、光学限制因子、辐射损耗以及辐射效率的关系。理论计算表明,掩埋光栅分布反馈结构可以通过改变腐蚀深度,保证激光器稳定单模工作在高频带边模式的同时,调节激光器的阈值增益以及辐射效率。实验和测试结果表明,激光器辐射波长和掩埋光栅的周期成正比,激光器可以在整个动力学范围内稳定单模工作。单模激光器的波长范围可覆盖86.2~91.7μm的范围,边模抑制比可达25 dB,最大输出功率为9.1 mW。该工作有助于高性能单模太赫兹激光器及锁相耦合激光器阵列的研制。     

Microcavity‐Stabilized Quantum Cascade Laser

Narrow‐linewidth lasers are key elements in optical metrology and spectroscopy. Spectral purity of these lasers determines accuracy of the measurements and quality of collected data. Solid state and fiber lasers are stabilized to relatively large and complex external optical cavities or narrow atomic and molecular transitions to improve their spectral purity. While this stabilization technique is rather generic, its complexity increases tremendously moving to longer wavelenghts, to the infrared (IR) range. Inherent increase of losses of optical materials at longer wavelengths hinders realization of compact, room temperature, high finesse IR cavities suitable for laser stabilization. In this paper, we report on demonstration of quantum cascade lasers stabilized to high‐Q crystalline mid‐IR microcavities. The lasers operating at room temperature in the 4.3‐4.6 μm region have a linewidth approaching 10 kHz and are promising for on‐chip mid‐IR and IR spectrometers.

     

Strain-Compensated InGaAs/InAlAs Quantum Cascade Detector of 4.5 μm Operating at Room Temperature

We present a strain-compensated InP-based InGaAs/InAlAs photovoltaic quantum cascade detector grown by solid source molecular beam epitaxy. The detector is based on a vertical intersubband transition and electron transfer on a cascade of quantum levels which is designed to provide longitudinal optical phonon extraction stairs. By careful structure design and growth, the whole epilayer has a residual strain toward InP substrate of only -2.8× 10^-4. A clear narrow band detection spectrum centered at 4.5 μm has been observed above room temperature for a device with 200／times 200 ×μm^2 square mesa.     

分布反馈量子级联激光器脉冲驱动电源的研制

为了满足中红外一氧化碳检测中分布反馈量子级联激光器的驱动要求,设计并实现了一种专用型脉冲驱动电源.首先,研制了高稳定的供电系统和完善的保护系统,显著提高了驱动脉冲的质量并保证了电源工作的可靠性;其次,依据"多级隔离"的思想设计了电源各功能电路,很大程度上提高了驱动电源的抗干扰能力;同时,将深度电压负反馈与比例-积分-微分控制算法相结合,有效提高了输出电流的稳定度.利用该驱动电源对中科院半导体所研制的波长为4.76μm的分布反馈量子级联激光器做了驱动测试.实验结果表明,在长时间(200h)运行中,系统驱动电流的稳定度为2.5×10-5,线性度为0.004%,满足分布反馈量子级联激光器的驱动要求,为中红外一氧化碳的可靠检测提供了保障.     

量子级联激光器调制特性的电路模拟

量子级联激光器(QCL)是波长范围在中远红外的一类新型激光器,到目前为此,对于它的脉冲响应及调制响应等动态特性了解并不是很深入,为此以贝尔实验室在1994年发明的量子级联激光器器件模型为基础,通过分析量子级联激光器中的电子在多量子阱间输运及跃迁的单极行为,得到它的速率方程。以此为基础,通过用电路元素对方程进行改造,建立起其相应的等效电路模型,利用PSPICE电路模拟软件进行模拟仿真,得到了它的调制响应特性,对可能影响其调制特性的一些因素如各阱之间的弛豫时间进行了讨论,并与其它类型激光器作了比较,发现量子级联激光器的动态性能并不优良,而这一点应缘于其独特的激射能级结构。     

室温连续中红外量子级联激光器驱动电源的研制

为了满足中红外波长调制光谱技术中室温连续中红外量子级联激光器的驱动要求,设计并研制了一种量子级联激光器驱动电源系统.首先,设计了直接数字合成模块来产生直流、锯齿波和正弦波的叠加驱动信号以调谐激光器的电流,进而调制其输出波长;其次,设计了高速(约40ns)过流保护电路,配合电压深度负反馈原理,保证激光器工作的可靠性,提高激光器电流的稳定度;再次,将比例-积分-微分软件算法与温度模拟控制电路相结合,在简化电路结构的同时,有效地控制和稳定激光器的温度,防止因温度变化造成激光器输出波长的漂移和发光功率的波动.利用该驱动电源系统对中科院半导体所研制的中心波长为4.76μm的量子级联激光器做驱动测试,结果表明:驱动电源系统电流调节的线性度为0.0068%,驱动电源的长期(240h)电流稳定度为4.99×10-5,量子级联激光器的光强稳定度为5.07×10-4,控温稳定性为0.01℃,温度稳定时间为17s;当量子级联激光器的驱动电流为330mA,温度为21℃时,在240h内峰值波长的漂移为±0.02nm.     

Low Threshold Current Density Operation of Strain-Compensated Quantum Cascade Laser

We report the low threshold current density operation of strain-compensated In0.64 Ga0.36As/In0.3sAl0.62As quantum cascade lasers emitting near 4.94 μm. By employing an enlarged strain-compensated structure and optimizing the injector doping density, a rather low threshold current density of 0.57kA/cm^2 at 80 K is achieved/or an uncoated 20-μm-wide and 2.5-mm-long laser.     

High-Quality Continuous-Wave Imaging with a 2.53THz Optical Pumped Terahertz Laser and a Pyroelectric Detector

A cw terahertz （THz） transmission imaging system is demonstrated and a high-quality THz image can be obtained using a pyroelectric detector. The factors that affect the imaging quality, such as the THz wavelength, spot size on the sample surface, step length of the motor, and frequency of the chopper, are theoretically and experimentally investigated. The experimental results show that the maximum resolution of the THz image can reach 0.4mm with the THz wavelength of 118.8μm, the spot size of 1.8mm and the step length of 0.25mm.     

Optical Switching of a Quantum Cascade Laser in Continuous Wave Operation

We demonstrate an optical switching in a middle infrared continuous-wave quantum cascade laser operated in single mode by illuminating its front facet with a near infrared laser. A decrease in the laser net gain is observed in the amplified spontaneous emission spectrum. This is attributed to an increase of the carrier concentration caused by the near infrared excitation. The net gain reduction allows the quantum cascade laser to be completely switched off from single mode lasing. This optical switching can be used to convert near infrared signals into middle infrared signals for free space communication.     

光场驱动下退化的级联三能级原子中的量子相干效应

研究了退化的级联三能级原子在施加静磁场后的量子相干效应,系统既可出现单光子电磁诱导透明,也可出现双光子电磁诱导透明以及双光子电磁诱导吸收,这取决于两个驱动场的拉比频率和塞曼分裂的相干性。 Quantum coherence effects in degenerate cascade three-level atom subject to magnetic field are investigated. One-photon EIT, two-photon EIT and two-photon EIA are obtained, due to the coherence between the drive Rabi frequency and Zeeman splitting.     

纤锌矿型量子级联激光器的界面与受限声子比较(英文)

利用传输矩阵方法对纤锌矿型量子级联激光器有源区的界面与受限声子进行了研究.计算结果显示:在纵光学频域有一组界面声子与二组受限声子存在,而且最低频率的两个界面声子在一定条件下能转变为受限模式.通过比较界面声子与受限声子的色散及声子势发现两者有很大不同,且计算电声散射速率可以发现由这两种声子引起的散射率是可比拟的.     

Al组分对AlGaN/GaN量子级联激光器性能的影响

通过对激光器一个周期单元的一维薛定谔方程与泊松方程进行自洽求解,得到了能带与电子波函数的分布情况,并且计算了在近共振条件下偶极跃迁元与垒层Al组分的关系,得到了Al组分的优化结果。结果表明,垒层材料的Al组分大约等于0.15时激光器的偶极跃迁元最大,此时激光器处于垂直跃迁工作状态。     

自发辐射对量子级联激光器发光噪声的影响

为得到量子级联激光器特有的光噪声特性,通过在速率方程中引入Langevin噪声源以及自发辐射因子的方法,在单模与线性增益的情况下讨论了自发辐射因子及与偏置电流等参数与光噪声的强度及带宽等特性之间的关系,计算结果表明,增大自发辐射因子能降低光噪声的强度,增宽光噪声的3-dB截止频率,进一步的研究也表明,自发辐射因子对光噪声的影响与激光器的偏置电流有密切关系,这种影响在偏置电流较小时比较明显,但当偏置电流很大时自发辐射因子对光噪声的影响将变得很弱。     

High-Duty-Cycle Operation of GaAs/AlGaAs Quantum Cascade Laser above Liquid Nitrogen Temperature

We present a detailed study of λ- 9.75 μm GaAs/AlGaAs quantum cascade lasers. For a coated 2-rmm-long and 40-μm-wide laser, an optical power of 85 μ W is observed at 95% duty cycle at 80K. At a moderate driving pulse （1 kHz and 1% duty cycle）,the device presents a peak power more than 20mW even at 120K. At 80K, the fitted result of threshold current densities shows evidence of potential cw operation.     

基于量子级联激光器照明的高对比度红外内窥成像

对单丝直径为20μm,12×9阵列方形面阵的Ge-As-Te-Se组分光纤束进行了测试,并开展红外成像研究.利用5～11μm连续可调谐红外量子级联激光器作为光源,对光纤束损耗进行检测,传输损耗平均为1 dB/cm.设计并加工了基于像方远心成像的紧凑型物镜,总长13.6 mm,直径6 mm,最终实现了2 mm×2 mm视...