亚波长光栅调制的偏振稳定垂直腔面发射激光器研究

基于微光学技术设计得到了偏振稳定垂直腔面发射激光器结构, 将亚波长光栅结构集成在上分布布拉格反射镜表面, 光栅周期小于材料中光波长, 透射波和反射波中仅包含零级衍射, 避免了高级次衍射造成 的损耗. 集成光栅后不同偏振方向光阈值增益不同, 从而实现偏振控制. 实验结 果显示, 集成亚波长光栅结构后, 整个激射过程中偏振方向被固定在平行于光栅槽方向上, 获得偏振稳定激光输出, 正交偏振抑制比大于12 dB, 且阈值电流仅增大7.14%.     

N-DBR和双氧化限制层对VCSEL电、光、热特性的影响

根据增益波导垂直腔面发射激光器直接耦合的准三维理论模型,通过有限差分法对注入电流密度、载流子浓度、光场和热场分布方程求自洽解.研究了垂直腔面发射激光器的电、热和光波导特性,同时提出了一种具有双氧化限制层的增益波导垂直腔面发射激光器结构,并通过对比研究了N-型分布布喇格反射镜和双氧化限制层对增益波导垂直腔面发射激光器特性的影响.计算结果表明,如果忽略N-型分布布喇格反射镜的影响将与实际的垂直腔面发射激光器有较大偏差;双氧化限制层结构对激光器特性有较大的改善,它为增益波导垂直腔面发射激光器提供了一种降低阈值,抑制高阶横模的方法.     

A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well vertical-cavity surface-emitting laser

A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well (QW) vertical-cavity surface-emitting laser (VCSEL) based on an intra-cavity contacted structure is fabricated. A threshold current of 1.5 mA for a 22 μm oxide aperture device is achieved, which corresponds to a threshold current density of 0.395 kA/cm². The peak output optical power reaches 17.5 mW at an injection current of 30 mA at room temperature under pulsed operation. While under continuous-wave (CW) operation, the maximum power attains 10.5 mW. Such a device demonstrates a high characteristic temperature of 327 K within a temperature range from -12℃ to 96℃ and good reliability under a lifetime test. There is almost no decrease of the optical power when the device operates at a current of 5 mA at room temperature under the CW injection current.     

Analysis of anticipated performance of 650-nm GaInP/AlGaInP quantum-well GaAs-based VCSELs at elevated temperatures

The possibility of application of the 650-nm oxide-confined GaInP/AlGaInP quantum-well vertical-cavity surface-emitting diode lasers (VCSELs) at elevated temperatures as sources of the carrier 650-nm wave in the fibre optical communication using POFs has been investigated with the aid of the comprehensive self-consistent model. An increase in the VCSEL threshold current at higher temperatures has been found to be mostly associated with both the carrier leakage from the valley of the Ga_0.43In_0.57P quantum-well material to the X-valley of the (Al_0.67Ga_0.33)_0.52In_0.48P barriers and the band-to-band absorption within the Ga_0.52In_0.48P layer of the band-gap comparable with the energy of emitted radiation. Nevertheless, the AlGaInP VCSELs exhibit encouraging thermal behaviour with the characteristic temperature T₀ equal to as much as 134 K for the active-region temperatures up to 357 K. For the 5-μm devices, the maximal achievable output has been determined to decrease from a quite high value of 1.0 mW for 293 K to 0.6 mW for 320 K and to still high 0.33 mW for 340 K. However, an efficient operation of the above VCSEL at elevated temperatures requires still some structure modifications leading to a reduction of both the above effects, the electron leakage from the valley and the band-to-band absorption within GaInP layers.     

Thermal properties and wavelength analysis of telecom oriented photonic-crystal VCSELs

Results of the self-consistent comprehensive analysis of a room-temperature operation of InP-based 1300-nm AlInGaAs photonic-crystal (PhC) VCSELs are presented. In particular, an influence of PhC parameters on thermal effects within VCSEL volume and its emission wavelength are analysed. The PhC has been found to introduce a number of opposite effects including a possible light leakage through PhC holes. From one side, PhC holes make more difficult heat-flux extraction from VCSEL volume leading to higher temperature increases within it. But, from the other side, a properly manufactured PhC creates an efficient radial confinement mechanism for VCSEL radiation field. It enhances an interaction between the field and the active-region carriers leading to a decrease in both the VCSEL lasing threshold and temperature increases. Seemingly both effects may similarly affect VCSEL operation, but our analysis revealed, that thermal properties of the PhC VCSEL are mainly dependent on an efficient confinement of its radiation field within the active region impeding a mode leakage through PhC holes, whereas an importance of deterioration of heat-flux extraction from VCSEL volume is much less essential. The wavelength shift induced by a change of PhC parameters has been found not to exceed 4×10⁻³ μm.     

Enhanced single-fundamental LP01 mode operation of 650-nm GaAs-based GaInP/AlGaInP quantum-well VCSELs

Minimal optical attenuation of plastic (polymer) optical fibres (POFs) corresponds to the 650-nm wavelength. Currently the GaInP/AlGaInP quantum-well (QW) oxide-confined (OC) vertical-cavity surface-emitting diode lasers (VCSELs) are undoubtedly the laser devices most suited to be used in 650-nm POF optical communication, for which the stable single-fundamental-mode LP₀₁ emission (SFM) is definitely the one most desired. In the present paper, the comprehensive fully self-consistent VCSEL model is used to examine mode selectivity of the above VCSELs. An increase in the VCSEL active-region diameter leads to a gradual modification of the current injection into this region and subsequent carrier radial diffusion within it before their recombination, which is followed by an essential transformation of active-region optical-gain profiles deciding upon an excitation of successive transverse modes. In standard arsenide OC VCSELs, SFM operation is usually limited to relatively small active regions. But for a room-temperature continuous-wave operation of the GaInP/AlGaInP VCSELs, the fundamental LP₀₁ mode remains surprisingly the lowest-threshold one up to relatively large active regions of 9-μm diameters. Nevertheless, in such VCSELs, thresholds of many LP modes become very similar to one another, which leads to their relatively poor mode selectivity and an unwanted multi-mode operation for higher output powers.     

Low threshold current density, low resistance oxide-confined VCSEL fabricated by a dielectric-free approach

We present the fabrication process and experimental results of 850-nm oxide-confined vertical cavity surface emitting lasers (VCSELs) fabricated by using dielectric-free approach. The threshold current of 0.4 mA, which corresponds to the threshold current density of 0.5 kA/cm², differential resistance of 76 Ω, and maximum output power of more than 5 mW are achieved for the dielectric-free VCSEL with a square oxide aperture size of 9 μm at room temperature (RT). L–I–V characteristics of the dielectric-free VCSEL are compared with those of conventional VCSEL with the similar aperture size, which indicates the way to realize low-cost, low-power consumption VCSELs with extremely simple process. Preliminary study of the temperature-dependent L–I characteristics and modulation response of the dielectric-free VCSEL are also presented.     

载流子输运和寄生参数对隧道再生双有源区垂直腔面发射激光器调制特性的影响

建立了一种适用于多量子阱和多有源区的多层速率方程模型. 通过小信号分析,得到了光子密度、载流子俘获、逃逸和隧穿时间等关键参数对单有源区和隧道再生双有源区垂直腔面发射激光器频率响应特性的影响,并分析了在相同驱动电流下隧道再生双有源区器件调制带宽大于单有源区器件的原因. 进一步研究了隧道再生双有源区内腔接触氧化限制型垂直腔面发射激光器的寄生电参数及其寄生电路,对其频率响应进行了模拟分析. 关键词： 垂直腔面发射激光器 速率方程 调制特性 隧道再生     

Design of a monolithic piezoelectrically actuated microelectromechanical tunable vertical-cavity surface-emitting laser

We report the design of a monolithic piezoelectrically actuated microelectromechanical tunable vertical-cavity surface-emitting laser (VCSEL). The main advantages of piezoelectric actuation compared with conventional capacitive techniques are improved wavelength control, reduced external and tilt losses, and lower power supply voltages. The details of the piezoelectric actuation scheme for a 980-nm VCSEL with a variable air gap are described. A tuning range of approximately 35 nm can theoretically be achieved with a 3-V power supply (2 x reduction from that of electrostatic actuation) by use of a 250-microm-long cantilever beam. The proposed actuation mechanism is insensitive to the pull-in phenomenon, therefore improving wavelength control and reducing threshold current. Drastic improvements in power efficiency make it ideal for low-power applications such as all-optical communication, chip-scale atomic clocks, and biological studies.     

Improved thermal property of strained InGaAlAs/AlGaAs quantum wells for 808-nm vertical cavity surface emitting lasers

The 808-nm vertical cavity surface emitting laser (VCSEL) with strained In_0.13Ga_0.75Al_0.12As/Al_0.3Ga_0.7As quantum wells is designed and fabricated. Compared with the VCSELs with Al_0.05Ga_0.95As/Al_0.3Ga_0.7As quantum wells, the VCSEL with strained In_0.13Ga_0.75Al_0.12As/Al_0.3Ga_0.7As quantum wells is demonstrated to possess higher power conversion efficiency (PCE) and better temperature stability. The maximum PCE of 43.8% for 10-μm VCSEL is achieved at an ambient temperature of 30 ℃. The size-dependent thermal characteristics are also analyzed by characterizing the spectral power and output power. It demonstrates that small oxide-aperture VCSELs are advantageous for temperature-stable performance.     

高功率980nm垂直腔面发射激光器的亮度特性

在循环水冷却(工作环境温度控制在15℃)和连续注入电流条件下,从垂直腔面发射激光器(VCSEL)亮度基本定义出发,实验测量了不同注入电流时口径为400μm的高功率980nm InGaAs/GaAs应变量子阱垂直腔面发射激光器(VCSEL)的亮度特性。结果表明:在注入电流4 A时,随着注入电流的增加,亮度也跟着增加;当注入电流4A时,尽管输出功率在增加,但是器件的光束质量变差,M2因子升高,表明此时影响器件亮度的主导因素是M2因子,所以亮度减小;在注入电流为4A,输出功率为1.2W时,亮度达到最大值2.43kW/cm2.sr,此时的光束质量最好,M2因子为207。最后,分析了影响高功率VCSEL器件亮度特性的主要因素,提出了提高器件亮度特性的解决方法。     

径向桥电极高功率垂直腔面发射激光器

为改善高功率垂直腔面发射半导体激光器的热特性,提高它的输出功率,研制了新型径向桥电极高功率垂直腔面发射半导体激光器器件,对新型半导体激光器的结构模型进行理论分析表明,采用径向桥式电极可以降低器件P型DBR电阻,减小焦耳热;降低热阻,提高器件的散热能力。实验制备了出光孔径同为200μm的径向桥电极与常规电极的高功率垂直腔面发射半导体激光器,并对器件的性能进行了实验对比测试。结果表明径向桥电极高功率垂直腔面发射半导体激光器器件的微分电阻为0.43Ω;室温下最大输出功率可达340 mW,是常规电极垂直腔面发射半导体激光器的1.7倍;器件的热阻为0.095℃/mW,在80℃时,仍能正常激射,具有良好的热特性,径向桥电极高功率垂直腔面发射半导体激光器的光电特性与温度特性要远好于常规电极的高功率垂直腔面发射半导体激光器器件。     

注入电流引起质子轰击VCSEL中的模式竞争

为了分析质子轰击垂直腔面发射激光器(VCSEL)中注入电流引起的激光模式竞争过程,在三维空间中对VCSEL激射后光电热进行了研究。给出仿真光电热的方程之后,在室温连续工作条件下,对电流孔半径r为4μm、阈值电流Ith为4.5 m A的VCSEL进行自洽求解。当注入电流Iin分别为5.0,5.5,6.0 m A时,得到了对应的外加电压和输出光功率,并绘制了VCSEL的电势、注入电流、载流子、光场和热场的空间分布,给出了连续工作下输出光功率随注入电流变化的曲线。仿真结果表明:随着注入VCSEL中的电流增加,电流密度增大,激光的横向基模和横向一阶模式同时增强。横向一阶模式增加的强度及扩展的范围大于横向基模,激光输出能量逐渐向横向一阶模式过渡,横向模式竞争的同时产生载流子空间烧孔,因此在电流孔半径r≥4μm的VCSEL中,连续工作激光模式不稳定。     

表面液晶-垂直腔面发射激光器温度特性的研究

本文利用向列相液晶层作为激光偏振调控单元,涂覆于垂直腔面发射激光器（VCSEL）表面,测量并分析了不同温度下VCSEL正交线偏振光的阈值电流、峰值光功率和I-P特性. 实验结果表明：温度为293 K时,涂覆液晶后激光偏振第一跳变点和第二跳变点之间的电流值ΔI增大了2.2 mA,比无液晶时增大1倍. 温度为313 K、注入电流为3 mA时,两种正交线偏振光的光功率差ΔP由133.6 μW增大到248.8 μW,进一步增加了线偏振光的各向异性. 表面液晶层的引入有效地扩大了VCSEL的正交线偏振态稳定范围和光功率差,为实现液晶VCSEL高温单偏振稳定的设计和器件制备提供了理论和实验基础. 关键词： 垂直腔面发射激光器 向列相液晶 偏振态     

808nm半导体激光芯片电光转换效率的温度特性机理研究

提高808 nm大功率半导体激光器电光转换效率具有重要的学术意义和商业价值,是实现器件小型化、轻量化、高可靠性的必要前提.本文以腔长1.5 mm的传导冷却封装808 nm半导体激光阵列为研究对象,在热沉温度-40—25?C范围内对其进行光电特性测试,对不同温度下电光转换效率的影响因子进行了实验研究和理论分析.结果表明:在-40?C环境温度下,最高电光转换效率从室温25?C时的56.7%提高至66.8%,内量子效率高达96.3%,载流子泄漏损耗的占比贡献由16.6%下降至3.1%.该研究对实现808 nm高效率半导体激光芯片的自主研发具有重要意义.     

980 nm 垂直腔面发射激光器低欧姆接触电阻制备

研究了980 nm的垂直腔面发射激光器(VCSEL)欧姆接触技术.降低VCSEL的欧姆接触电阻,可有效地提高VCSEL的输出功率和延长其可靠性.P面采用高掺杂的P-GaAs/Ti/Pt/Au系统,N面采用N-GaAs/Ge/Au/Ni/Au系统,通过优化合金温度,得到了最佳优化合金温度为440 ℃,最低欧姆接触电阻值为0.04 Ω,同时对比了440 ℃和450 ℃器件的输出功率和转换效率之间的对比关系.测试结果表明,440 ℃器件的欧姆接触电阻0.04 Ω,峰值波长980.1 nm,光谱的半高宽0.8 nm,平行发散角θ_‖ 15.2°,垂直发散角θ_⊥ 13.5°,输出功率1.4 W,转换效率最大值为14.4%,而450℃的器件欧姆接触电阻为0.049 Ω,输出功率为1.3 W,转换效率为12.8%.通过优化合金温度能有效地降低980 nm的VCSEL欧姆接触电阻.     

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.     

Power-induced polarization switching and bistability characteristics in 1550-nm VCSELs subjected to orthogonal optical injection

The polarization switching(PS) and polarization bistability(PB) characteristics of a 1550-nm vertical-cavity surfaceemitting laser(VCSEL) subjected to orthogonal optical injection are systematically investigated.The simulated results show that the PS and polarization-resolved nonlinear dynamical states of the VCSEL are critically dependent on the changing paths of the injected power.The polarization dynamics for different scanning directions of the injected power is presented to explain the polarization evolution during the formation of PS.In the case of forward scanning injected power,with the increase of frequency detuning level between the VCSEL and the injected light,the injected power required for PS gradually increases for negative frequency detuning but exhibits fluctuations for positive frequency detuning.In the case of reversely scanning injected power,the injected power required for PS displays fluctuant changes within the whole frequency detuning range.Specifically,PS may disappear under certain negative frequency detuning and large bias current.Furthermore,the hysteresis width as a function of the frequency detuning is calculated,and the regions for the appearance and disappearance of PB have been determined in the parameter space of the bias current and frequency detuning.     

An efficient approach to characterizing and calculating carrier loss due to heating and barrier height variation invertical-cavity surface-emitting lasers

It is important to determine quantitatively the internal carrier loss arising from heating and barrier height variation in a vertical-cavity surface-emitting quantum well laser (VCSEL). However, it is generally difficult to realize this goal using purely theoretical formulas due to difficulty in deriving the parameters relating to the quantum well structure. In this paper, we describe an efficient approach to characterizing and calculating the carrier loss due to the heating and the barrier height change in the VCSEL. In the method, the thermal carrier loss mechanism is combined with gain measurement and calculation. The carrier loss is re-characterized in a calculable form by constructing the threshold current and gain detuning-related loss current using the measured gain data and then substituting them for the quantum well-related parameters in the formula. The result can be expressed as a product of an exponential weight factor linked to the barrier height change and the difference between the threshold current and gain detuning-related loss current. The gain variation at cavity frequency due to thermal carrier loss and gain detuning processes is measured by using an AlInGaAs--AlGaAs VCSEL structure. This work provides a useful approach to analysing threshold and loss properties of the VCSEL, particularly, gain offset design for high temperature operation of VCSELs.     

Analysis of thermal and electrical properties of ZnO arrester block

Voltage–current characteristics of ZnO surge arresters are highly dependent on temperature in the low-conduction region. ZnO surge arresters experience thermal runaway when the temperature exceeds the acceptable limit. This phenomenon is associated with the increase of resistive leakage current due to degradation. This paper presents the thermal and electrical characteristics of ZnO arrester blocks under the power frequency AC operating voltages. The leakage currents of ZnO arrester blocks were measured over a period of the time. The temperature profiles of ZnO arrester blocks were observed by the infrared camera. The degradation and the thermal runaway of the ZnO arrester blocks are closely related to the temperature limit which determines the heat generation and dissipation. As the leakage current was 0.5 mA, the amount of heat generation is lower than that of heat dissipation. So temperature of the ZnO arrester blocks was rarely changed. On the other hand, as the leakage current was 0.7 and 1 mA, the amount of heat generation was greater than that of the heat dissipation. The temperature of ZnO arrester blocks gradually increases and the test specimen experiences thermal runaway. At that time the temperature located at the center of ZnO arrester blocks string was higher compared to that of ZnO block at both edges.