表面液晶-垂直腔面发射激光器阵列的热特性

液晶与垂直腔面发射半导体激光器(VCSELs)阵列结合可实现波长可调谐、偏振精确控制等,同时液晶的引入也会改变垂直腔面发射半导体激光器阵列的热特性,本文设计了表面液晶-垂直腔面发射激光器阵列结构,并开展了阵列的热特性实验研究.对比分析了向列相液晶层对VCSEL阵列热特性的影响,实验结果表明,1×1,2×2,3×3三种表面液晶-VCSEL阵列的阈值电流温度变化率最高可降低23.6%,热阻降低26.75%;同时,激光器阵列各发光单元之间的温度均匀性显著提高,出光孔与周围温差小于0.5℃.综上所述,VCSEL阵列中液晶层的引入不仅大大加速激光器阵列单元热量扩散,而且降低了有源区结温,提高了VCSELs激光器阵列热特性,为实现高光束质量的单偏振波长可控VCSEL激光器阵列打下了良好的理论和实验基础.     

新型垂直腔面发射半导体激光器阵列

设计出四次质子注入工艺制备垂直腔面发射激光器(VCSEL)阵列的方法,实现了对阵列中单元器件间的隔离以及对单元器件注入电流限制的分别作用。一方面通过对VCSEL外延片上分布布拉格反射镜(DBR)两次较浅的质子注入形成高电阻区域实现对阵列中单元器件间的隔离,另一方面通过再次的两次较深度的可以达到有源区上表面的质子注入形成高电阻区域实现对单元器件注入电流的限制。由瞬态热传导方程对阵列中单元器件间的热相互作用进行了理论分析。采用四次质子注入工艺实现了2×2、3×3简单的二维GaAs/AlGaAs量子阱VCSEL阵列,并对器件的激射近场、光谱特性及功率等进行了测量。     

Thermal analysis of high-index-contrast grating (HCG)-based VCSEL

A 3-D thermal analysis of 870 nm high-index-contrast grating (HCG)-based vertical cavity surface emitting laser (VCSEL) by using finite volume method (FVM) is presented in this paper. The HCG-based VCSEL is modeled by applying a steady-state 3-D heat dissipation model. Temperature distribution profile and thermal resistance (R_th) of the device are investigated by inserting the heat source value into the thermal simulation. Also, this analysis is performed for a conventional VCSEL operating at the same wavelength and under the same injected current as well as the same geometric sizes. The analysis shows that the maximum temperature inside the HCG-based VCSEL is lower than that inside the conventional VCSEL.     

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。     

Characteristics of selective oxidation during the fabrication of vertical cavity surface emitting laser

Taking into account oxidation temperature, N₂ carrier gas flow, and the geometry of the mesa structures this paper investigates the characteristics of selective oxidation during the fabrication of the vertical cavity surface emitting laser (VCSEL) in detail. Results show that the selective oxidation follows a law which differs from any reported in the literature. Below 435℃ selective oxidation of Al_0.98Ga_0.02As follows a linear growth law for the two mesa structures employed in VCSEL. Above 435℃ approximately increasing parabolic growth is found, which is influenced by the geometry of the mesa structures. Theoretical analysis on the difference between the two structures for the initial oxidation has been performed, which demonstrates that the geometry of the mesa structures does influence on the growth rate of oxide at higher temperatures.     

Power dissipation in oxide-confined 980-nm vertical-cavity surface-emitting lasers

We presented 980-nm oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with a 16-μm oxide aperture. Optical power, voltage, and emission wavelength are measured in an ambient temperature range of 5℃ C-80℃. Measurements combined with an empirical model are used to analyse the power dissipation in the device and the physical mechanism contributing to the thermal rollover phenomenon in VCSEL. It is found that the carrier leakage induced selfheating in the active region and the Joule heating caused by the series resistance are the main sources of power dissipation. In addition, carrier leakage induced selfheating increases as the injection current increases, resulting in a rapid decrease of the internal quantum efficiency, which is a dominant contribution to the thermal rollover of the VCSEL at a larger current. Our study provides useful guidelines to design a 980-nm oxide-confined VCSEL for thermal performance enhancement.     

GaN基LED电流扩展的有限元模型及电极结构优化

针对目前蓝宝石衬底上外延生长制备的GaN基半导体发光二极管(LED)器件存在电流分布不均匀的问题,建立了LED的电流扩展模型,提出了定量评价其特性的参数和标准。通过用有限元方法计算LED中电流的三维空间分布,对不同的电极结构进行了定量的比较,给出了优化的电极结构。计算结果显示,在相同工艺参数下,采用插指型电极结构的LED与采用传统型电极结构和扩展正极型电极结构的LED相比,电流扩展更均匀,串联电阻更小。在此基础上,对插指型电极结构作了进一步的参数优化,得出了使LED的串联电阻取最小值时的插指型电极的结构参数。根据优化得到的参数制作了相应的LED样品,并与采用扩展正极型电极结构的LED做了对比实验。实验结果表明,计算得出的结果与实验结果符合得很好。采用了优化后的插指型电极结构的LED与采用扩展正极型电极结构的LED相比,前者的串联电阻仅为后者的44.4%。     

894nm高温垂直腔面发射激光器及其芯片级铯原子钟系统的应用

报道了自行研制的894 nm高温垂直腔面发射激光器(VCSEL)以及基于此类器件的芯片级铯原子钟系统的应用实验结果.根据芯片级铯原子钟对VCSEL在特定高温环境下产生894.6 nm线偏振激光的要求,对器件的量子阱增益及腔模位置等材料结构参数进行了优化,确定增益-腔模失谐量为-15 nm,使器件的基本性能在高温环境下保持稳定.研制的VCSEL器件指标为:20—90?C温度范围内阈值电流保持在0.20—0.23 m A,0.5 m A工作电流下输出功率0.1 mW;85.6?C温度环境下激光波长894.6 nm,偏振选择比59.8:1;采用所研制的VCSEL与铯原子作用,获得了芯片级铯原子钟实施激光频率稳频的吸收谱线和实施微波频率稳频的相干布居囚禁谱线.     

百瓦级近衍射极限VCSEL泵浦激光器

报道了高功率、高光束质量的垂直腔面发射半导体激光器(VCSEL)侧泵的Nd:YAG激光振荡器。从VCSEL泵浦源的主动冷却的热沉结构出发,设计了5个227 W的VCSEL线阵,并且通过优化侧面泵浦大口径激光棒的结构,研制成了具备480 W输出能力的棒状激光模块,相应的光-光效率为49.7%。在此基础上,设计了一种高功率、高光束质量的VCSEL侧面泵浦棒状Nd:YAG激光振荡器。腔内插入望远镜光学元件,并通过优化各光学元件的参数使其工作在热近非稳区域,以达到增大基横模体积和抑制高阶横模目的。最终,获得114 W的输出功率,相应的平均光束质量因子M2为1.42。由于VCSEL具备优秀的波长-温度稳定性,这种高功率、高光束质量的VCSEL泵浦的固体激光器在工业、空间等领域,具有极为广阔的应用前景。     

Operation performance characteristics of vertical-cavity surface-emitting lasers (VCSELs) under high thermal neutron irradiated fields

To operate and read out even the innermost detectors under any particular conditions, electronics and optical components must be developed accordingly. For semiconductor lasers, on which we will concentrate here, it has been found that an inner temperature increase has a direct impact on the light power emitted by the device. It was found that the effects of radiation on the behavior of semiconductor lasers are convolved with those of temperature. An optimized coupling to the cooling of the laser device reduces the thermal effects in the material. Therefore, a test stand to qualify the effect of heat in the device and the adoption of the heat sink is realized. In this paper, we create a model describing the degradation of the light power and voltage characteristic of a semiconductor-laser undergoing irradiation where the high temperature effects are taken into account. This VCSEL-device model can be used to predict the behavior and operation-performance characteristics (rise time, 3 dB bandwidth, light power, resonance frequency, and transmission bit rate) of a laser being irradiated with different neutron doses. We check the robustness of the model against the high fluence (in excess of 10¹⁵ neutrons/cm²). We take into account the study of different semiconductor- and polymeric material-based VCSEL devices such as aluminum gallium arsenide (AlGaAs), indium gallium arsenide phosphors (InGaAsP), and polymeric polymethylmethacrylate (PMMA) under the same operating conditions.     

Hybrid point/ring-defect photonic crystal VCSEL with high spectral purity and high output power

A hybrid point/ring-defect photonic crystal vertical-cavity surface-emitting laser (VCSEL) is presented. To analyze the possible lasing supermodes, the device is simplified to a 3 × 1 VCSEL array along any direction in plane due to the hybrid point/ring defects with approximately radial symmetry. Three supermodes are predicted based on the coupled-mode theory. In the experiment, only three supermodes appear at most over the entire current range, consistent with the theoretical predictions. The full width at half maximum of the lasing spectrum at rollover is less than 0.1 nm, and the maximum output power of the device reaches 4.3 mW.     

大功率半导体激光器阵列热串扰行为

以硬焊料传导制冷,30%填充因子半导体激光器阵列为例,建立了三维有限元模型,对阵列内部各发光单元之间的热串扰行为进行了分析研究。结果表明,当其连续波工作时间大于1.2 ms后,阵列内发光单元之间出现热串扰现象;当次热沉由CuW合金改为铜金刚石复合材料时,阵列内发光单元自热阻和相邻发光单元的串扰热阻降低,有效地降低了各发光单元之间的热串扰行为。保持阵列宽度、发光单元数目及发光单元周期不变,发现随阵列填充因子的增加,器件热阻以指数衰减趋势逐渐降低,而发光单元间的热串扰特性对此变化并不敏感;保持阵列单个发光单元输出功率,发光单元尺寸及阵列宽度不变,增加发光单元个数后,阵列内各发光单元之间热串扰加剧,填充因子越高阵列升温速率越快;但在最初约70 s内,包含不同数目发光单元的阵列最高温度差异仅约0.5 ℃,有利于多发光单元高填充因子器件高功率输出。     

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.     

Improved efficiency of GaAs-based VCSEL by utilizing fan-pad metallization and trench patterning

Emphasizing the Vertical-Cavity Surface-Emitting Laser (VCSEL) device packaging, fan-pad metallization and trench patterning are demonstrated for VCSEL operating at 850 nm of the electromagnetic spectrum. The fabricated devices are observed to exhibit low threshold current and series resistance, contributing thereby to higher VCSEL efficiency. It is also observed that the output spectral characteristics of the fabricated device show stable multimode operation. The results indicate that the proposed VCSEL packaging exhibits superior device performance as compared to the VCSEL device packaged with square-pad metal.     

Thermal focusing effect in solid-state microchip lasers connected directly with vertical-cavity surface-emitting laser diodes

In this paper, we model and analyze thermal focusing effect in the microchip lasers pumped by vertical-cavity surface-emitting lasers (VCSELs) for a special pump scheme, in which the microchip is axially connected with the VCSEL pump source without a gap between them to form a sort of ultra-compact monolithic micro-lasers. Thus, the thermal effects are related to twofold heating processes in the microchip. One is the common pump beam heating. The other is the heat flux diffusion from VCSEL to microchip through the contact interface between both, the latter leads to different thermo-optic characteristics from that generated only by the pump beam heating in the microchip. The temperature-, the stress- and the expansion-related phase variations and thus the thermal focusing properties of the microchip regarding the twofold heating processes are calculated and discussed for various pump power densities and temperatures of the VCSEL using analytical models. The results show that both heating processes in such a pump configuration can produce comparable thermal effects to each other. The influence of the heat transfer from the VCSEL to the microchip laser performance is discussed as well.     

Investigation of the mode splitting induced by electro-optic birefringence in a vertical-cavity surface-emitting laser by polarized electroluminescence

The mode splitting induced by electro-optic birefringence in a P-I-N InGaAs/GaAs/A1GaAs vertical-cavity surface- emitting laser （VCSEL） has been studied by polarized electroluminescence （EL） at room temperature. The polarized EL spectra with E｜｜[110] and E ｜｜ [150] directions, are extracted for different injected currents. The mode splitting of the two orthogonal polarized modes for a VCSEL device is determined, and its value increases linearly with the increasing injected current due to electro-optic birefringence; This article demonstrates that the polarized EL is a powerful tool to study the mode splitting and polarization anisotropy of a VCSEL device.     

Transverse-mode selectivity in possible nitride vertical-cavity surface-emitting lasers

Excitation of various transverse modes in possible nitride vertical-cavity surface-emitting lasers (VCSELs) is investigated and compared using the effective frequency optical model. In the comparative analysis of laser mode selectivity, two distinctly different configurations of possible nitride VCSELs are considered: the traditional VCSEL design with both (n-side and p-side) ring contacts as well as the uniform-current-injection (UCI) VCSEL design. Our simulation reveals that, during the continuous-wave device operation at room temperature, a multi-mode operation dominated by higher-order transverse modes is typical for traditional nitride VCSEL configurations whereas a desirable single-mode (based on the fundamental LP₀₁ mode) operation turns out to be characteristic for the wide current range in UCI ones. The above different threshold device behaviours are an immediate consequence of essentially different current-spreading phenomena in both VCSEL designs, resulting in completely different not only gain profiles but also temperature distributions within the laser active regions of both VCSELs. Seemingly similar behaviour has been also reported in arsenide VCSELs but it is expected to be much more severe in the case of nitride ones as a result of much higher both electrical resistivities of p-type nitrides and their temperature derivatives of refractive indices.     

High-power vertical-cavity surface-emitting lasers bonded with efficient packaging

<正>High-power vertical-cavity surface-emitting lasers(VCSELs) are processed using a wet thermal-selective oxidation technique.The VCSEL chips are packaged by employing three different bonding methods of silver solder,In-Sn solder,and metalized diamond heat spreader.After packaging,optical output power, wavelength shift,and thermal resistance of the devices are measured and compared in an experiment.The device packaged with a metalized diamond heat spreader shows the best operation characteristics among the three methods.The 200-μm-diameter device bonded with a metalized diamond heat spreader produces a continuous wave optical output power of 0.51 W and a corresponding power density of 1.6 kW/cm~2 at room temperature.The thermal resistance is as low as 10 K/W.The accelerated aging test is also carried out at high temperature under constant current mode.The device operates for more than 1000 h at 70℃,and the total degradation is only about 10%.     

Room temperature continuous wave low threshold current 850 nm ion implanted vertical cavity surface emitting laser using tungsten wires as mask

Vertical cavity surface emitting laser (VCSEL) emitting at 850 nm plays more important role in local fiber communication. Most of the VCSEL products emitting at 850 nm are fabricated by ion implanting. Their threshold current is about 4–6 mA. Using tungsten wires as mask, we developed the parameter of implantation and fabricated 850 nm VCSEL under room temperature CW (continuous wave) operation. The threshold current was 1.4 mA, which was lower than that of most similar devices reported before. The resistance of the device was 206 Ω. The light power was 0.92 mW at 6.74 mA under room temperature CW operation, while the light power did not achieve obvious saturation. The most remarkable advantage was that the fabrication method was simple and the optimization was available to implanting parameter.     

Optimization of electro-optical characteristics of GaAs-based oxide confinement VCSEL

An experimental study has been presented of the oxide-confined vertical-cavity surface-emitting lasers (VCSEL) operating in the 850 nm region of the electromagnetic spectrum. In this regard, various relevant VCSEL samples with numerous oxide aperture sizes have been fabricated and characterized. Thorough investigations of the electrical as well as optical characteristics of the fabricated samples have been performed which includes the overall device performance as a function of the oxidize aperture sizes. It is reported that the VCSEL with oxide aperture size <10 μm require low threshold currents (<1 mA). Further, the differential quantum efficiencies up to 28% were measured for a number of these devices. It is found that devices employing oxide aperture of 10 to 15 μm shows promising electro-optical characteristics for 850 nm oxide VCSEL optimization.