Mid-infrared type-II interband cascade lasers

Interband cascade (IC) lasers that utilize optical transitions between the conduction and valence bands in a staircase of Sb-based type-II quantum wells (QWs) represent a new class of mid-IR diode lasers. By combining the advantages of quantum cascade lasers and type-II QW interband lasers, type-II IC lasers show promise of operating in continuous-wave (CW) mode up to room temperature with high output powers. Significant advances toward such high performance have been reported in terms of record-high differential external quantum efficiency (DEQE>600%), peak output power (~6 W/facet at 80 K), CW power conversion efficiency (>16% at 80 K), and room-temperature operation under pulsed conditions. Here, we will review the progress made in the past few years and discuss the issues encountered during the development. Also, the current status of type-II IC lasers and the remaining challenges will be discussed     

Power efficiency and quantum efficiencies of electron-beam pumped lasers

The object is to identify and assess factors and mechanisms that control the conversion of electron-beam power into coherent light through excitation of a semiconductor laser cavity. First, we examine the question of pump power losses associated with electron backscattering and pair creation. It is shown that power retention and ionization yield reflect target characteristics (atomic number and bandgap energy) only. The external quantum efficiency, which is best expressed as a product of quantum yield, coherence ratio, and escape probability, involves two parameters: pumping ratio and output coupling. This leads to a straightforward optimization procedure. Heating effects are analyzed in terms of a differential quantum efficiency and are shown to degrade the saturation value of the efficiency by a factor roughly proportional to the pulse rise time, if adiabatic conditions hold. These considerations are illustrated using power-efficiency figures reported for CdS, CdTe, and GaAs lasers; it is demonstrated that the photon-loss coefficient of excited "perfect" CdS must be less than 1.5 cm^-1, at 4.2°K.     

Investigation of mid-infrared type-II “W” diode lasers

We report an experimental investigation of 16 different mid-infrared diode laser samples with type-II “W” active regions. A number of design modifications were employed to study effects on the I–V characteristics, lasing threshold, and wallplug efficiency. Contrary to expectations, the threshold current density at low temperatures did not vary significantly with the number of active quantum-well periods, nor was there any clear correlation between lasing threshold and photoluminescence intensity. A shorter-wavelength device (3.2–3.6 μm) produced >500 mW of cw power at 80 K, and a second device displayed a wallplug efficiency >10%. The maximum lasing temperature was 317 K for pulsed operation and 218 K for cw operation. At T=100 K, cavity-length studies indicated an internal loss of 7 cm⁻¹ and nominal internal efficiency of 96%. Hakki-Paoli measurements of the gain spectrum implied an intrinsic linewidth enhancement factor of ∼1.3, which slightly exceeds the theoretical prediction. Longer-wavelength devices (λ ≈ 3.8–4.5 μm) showed similarly low threshold current densities at T=80 K but degraded more rapidly with increasing temperature.     

Power conversion efficiency of semiconductor injection lasers and laser arrays in CW operation

In many applications it is important to optimize the power conversion efficiency of semiconductor lasers and laser arrays. A method for calculating this efficiency which takes into account temperature effects is described, and some calculated results are presented and discussed. It is found that under certain conditions, a small increase in the thermal resistance of the device can result in a large reduction of its efficiency. Temperature effects are important in high-power semiconductor lasers, and in particular in laser arrays, where low thermal resistance heat sinking may be crucial to the device operation.     

键合界面对面发射激光器的光、热性质影响

分析了采用双面键合长波长面发射激光器时,键合界面光吸收系数和电、热导率的变化对器件的光、热性质的影响。对于1λ光学腔的面发射激光器,键合界面吸收系数对器件光学性能影响较大,而对于1.5λ光学腔的面发射激光器,其光学性能基本不受键合界面吸收系数的影响。由有限元方法对面发射激光器的温度分布计算结果可知,当键合界面电、热导率小于GaAs电、热导率的1%时,激光器有源层的温度会有较大的上升。     

高量子效率中波InAs/GaSb II类超晶格探测器分子束外延生长及特性

基于分子束外延（MBE）生长技术获得了高量子效率的InAs/GaSb T2SLs中波红外（MWIR）光电探测器结构材料,表现出了层状结构生长的光滑表面和出色的晶体结构均匀性。此超晶格中波红外探测器的50%截止波长约为5.5 μm,峰值响应率为2.6 A/W,77 K下量子效率超过了80%,与碲镉汞的量子效率相当。在77 K,-50 mV偏压下的暗电流密度为1.8×10^-6 A/cm²,最大电阻面积乘积（RA）（-50 mV偏压）为3.8×10⁵Ω·cm²,峰值探测率达到了6.1×10¹² cm Hz^{1 / 2}/W。     

High slope efficiency and low noise characteristics intapered-active-stripe DFB lasers with narrow beam divergence

We report high slope efficiency and low noise characteristics in a distributed feedback (DFB) laser lasing at 1.3 μm with narrow beam divergence by employment of a laterally tapered active stripe over the whole cavity. This tapered structure is designed to realize narrow beam divergence, low threshold current, and high longitudinal mode selectivity. The fabricated tapered-active-stripe DFB lasers demonstrated of 9.20×13.40 and a record slope efficiency, for a narrow beam DFB laser, of 0.59 mW/mA. The temperature characteristics from -10°C to 85°C shows high output power at high temperature, stable single longitudinal mode oscillation and stable far-field patterns. Furthermore, for the first time ever, a low relative intensity noise characteristic of under -155 dB/Hz has been realized when butt-coupling into a single-mode fiber     

Nearly room-temperature type-II quantum-well lasers at 3–4 μm

We report optically pumped four-constituent InAs/InGaSb/InAs/AlSb type-II quantum-well lasers emitting at 3.2–4.1 μm. Lasing was observed up to 350K under pulsed operation, with a characteristic temperature T₀ up to 68K at temperatures above ambient.     

The simulation of thermal characteristics of 980 nm vertical cavity surface emitting lasers

In order to design a single mode 980 nm vertical cavity surface emitting laser (VCSEL),a 2μm output aperture is designed to guarantee the single mode output.The effects of different mesa sizes on the lattice temperature,the output power and the voltage are simulated under the condition of continuous working at room temperature,to obtain the optimum process parameters of mesa.It is obtained by results of the crosslight simulation software that the sizes of mesa radius are between 9.5 to 12.5μm,which cannot only obtain the maximum output power,but also improve the heat dissipation of the device.     

热助推泵浦Nd∶YAG激光器热性能研究

采用热助推泵浦技术,实现了885 nm LD热助推泵浦的板条Nd∶YAG脉冲激光器运转。从粒子跃迁机理上对热助推泵浦方式做了理论分析,并通过实验验证了885 nm热助推泵浦相对于802 nm泵浦的优势。885 nm热助推泵浦的光光效率比802 nm泵浦方式提高了26%,废热产生则减少了约23%,结果表明热助推泵浦方案在热性能相对传统泵浦有明显的优势。     

Room-temperature low-threshold type-II quantum-well lasers at 4.5 /spl mu/m

We report optically pumped InAs-InGaSb-InAs-AlSb type-II quantum-well lasers at 3.84-4.48 /spl mu/m. Lasing was observed at temperatures up to 300 K with a characteristic temperature T/sub 0/ of 61.6 K. The average absorbed threshold power was only 0.7 mW at 220 K, and 2.7 mW at 300 K with a pulselength of 650 ns and a repetition rate of 2 kHz. At 49 K, the continuous-wave (CW) output power was 4.2 mW/facet with an absorbed threshold pump power of 31.5 mW and an absorbed pump power of 62 mW, indicating a differential quantum efficiency of 54% for two facets.     

Enhanced tuning efficiency in tunable laser diodes using type-II superlattices

We propose a type-II AlGaAsSb-AlGaInAs heterostructure superlattice for improved electronically tunable laser diodes exploiting the free-carrier plasma effect. In electronically tunable laser diodes, commonly type-I heterostructure diodes (e.g., GaInAsP-InP) are used as tuning region; however, at equal tuning, the type-II heterostructure superlattices provide the advantage of significantly smaller recombination rates due to the spatial separation of electrons and holes. As a consequence, the required tuning currents can be reduced and the maximum achievable carrier density in an optimized type-II diode can be enhanced by about a factor of two.     

Fiber DFB lasers with ultimate efficiency

A novel method for designing distributed feedback (DFB) lasers with ultimate efficiency is presented. The method is based on the calculation of the optimum signal distribution for a given pumping scheme and derivation of the grating profile that sustains this distribution so that at every point in the cavity pump-to-signal conversion efficiency is maximum. Theory applied experimentally in Er-Yb co-doped fiber resulting in a 57% increase in the efficiency with 10% shorter device length compared with standard optimized co-pumped designs.     

Quantum efficiency of electron-beam pumped GaAs lasers

Measurements of differential external quantum efficiency as high as 66 percent have been observed at 77°K in an electron-beam pumped GaAs laser doped at2 times 10^{18}/cm³with Sn. Peak-power output of the order of 20 watts has been obtained at both 4.2° and 77°K.     

固体激光器的发热效率

在分析板条激光器发热效率基础上,提出了发热效率的测量新方法,给出了板条器件和圆棒器件的测量结果。     

Impedance characteristics of quantum-well lasers

We derive theoretical expressions for the impedance of quantum-well lasers below and above threshold based on a simple rate equation model. These electrical laser characteristics are shown to be dominated by purely electrical parameters related to carrier capture/transport and carrier re-emission. The results of on-wafer measurements of the impedance of high-speed In_0.35Ga_0.65 As/GaAs multiple-quantum-well lasers are shown to be in good agreement with this simple model, allowing us to extract the effective carrier escape time and the effective carrier lifetime, and to estimate the effective carrier capture/transport time     

XeCl激光器的放电特性研究

本文介绍了利用放电电压和电流的测量结果,对XeGl准分子激光器的耦合功率与等离子体特性阻抗的研究。分析了特性阻抗的函数形式对放电过程的影响以及放电稳定性的分类等,对存在的问题也进行了讨论。     

High single-mode power conversion efficiency vertical-cavitytop-surface-emitting lasers

We report advances in the power conversion (wall-plug) efficiency of vertical-cavity top-surface-emitting lasers. The devices were fabricated from molecular beam epitaxial layers using deep proton implants to define gain-guided lasers. The epitaxial structure included low resistance, piecewise linearly graded n-type and p-type mirrors, a triple In_0.2Ga_0.8As quantum-well active region, and a delta-doped contact layer. Power conversion efficiencies as high as 12.7% for continuous-wave single-mode operation were measured after several hours of device operation