金刚石复合热沉面发射激光器面阵热特性研究

通过设计基于金刚石微槽结构的复合热沉,利用不同材料的热导率差异改变热流传导方向,以优化垂直腔面发射半导体激光器(VCSEL)面阵由于温度分布不均匀导致的中心热量堆积的问题,从而改善激光器面阵整体的输出功率,提高可靠性。基于有限元分析法建立三维热电耦合模型,研究了VCSEL面阵单元排布方式对激光器热串扰效应的影响,同时还研究分析了金刚石复合热沉中微槽形状和位置的变化对半导体激光器内部温度的影响,设计最优结构对激光器的出光性能做进一步优化。采用金刚石复合热沉后的垂直腔面发射激光器面阵,与传统金刚石热沉的封装结构相比,激光器发光单元的温度差值降低了29%,为大面积半导体激光器面阵的输出功率优化提供了新思路。     

Thermal and Stark-Effect Roll-Over of Quantum-Cascade Lasers

A computational and experimental analysis of rollover in high-performance lambda ~ 8 mum quantum-cascade (QC) lasers is presented. In addition to conventional, thermal rollover, which is also a common cause of power rollover in diode lasers, ";Stark-effect"; rollover is observed. While both effects can occur in the same QC laser design, thermal and Stark-effect rollover are shown to be the dominating factor for high-temperature continuous wave operated, and pulsed low-temperature operated and low-doped lasers, respectively. Additionally, the role of the continuum above the wells and barriers is discussed for both effects.     

Integrated output power detection for AlGaAs laser array

A linear array of closely spaced AlGaAs lasers is mounted on an Si heat sink. Schottky diode detectors formed on the same Si chip provide optical sensing and electrical feedback signals for output power stabilization of the individual laser elements. The performance of a typical pair of adjacent devices is tested showing that electrical and optical crosstalk between lasers is virtually eliminated.     

Substrate and Device Pattern Dependence of the Thermal Crosstalk in Y Ba2Cu 3O7−δ Transition Edge Bolometer Arrays

Using YBa₂Cu₃O_7-delta (YBCO) thin films, pulsed laser deposited on 1-mm-thick LaAlO₃ or SrTiO₃ substrates, we made 4times1 pixel arrays of transition edge bolometers with separations between neighboring pixels ranging from 40 mum to 170 mum for testing purposes. We investigated the effects of the YBCO film thickness (200 and 400 nm), substrate material, and back-etching of the substrate, on the crosstalk between the pixels of the arrays. The investigation was based on the analysis of the voltage response of the dc current biased bolometers versus the modulation frequency of a near-infrared laser source. We observed that the bolometer arrays made of 400-nm-thick films had less interpixel thermal crosstalk than the 200-nm-thick films. The effect of substrate thickness on the response of the pixels was investigated by up to 500 mum back-etching of the substrates. The bolometers made on back-etched LaAlO₃ substrates had anomalous crosstalk response behavior, which was effective at higher modulation frequencies. In addition, we present an analytical thermal model for explaining the observed effects of the thermal crosstalk on the response characteristics of the pixels of the arrays. We report the measured response and the anticipated thermal crosstalk of the characterized bolometers'. We describe the responses based on the thermal models and discrepancies from the model's predictions     

Thermal crosstalk in 4/spl times/4 vertical-cavity surface-emitting laser arrays

We measured thermal crosstalk in 4/spl times/4 VCSEL arrays with a 30-/spl mu/m pitch between devices. The effective thermal resistance of laser diodes in two-dimensional (2-D) arrays is about 50% higher than that of single elements. The output power of the lasers is fairly temperature insensitive under constant voltage operation. From experiments we inferred values for the average thermal conductivity of AlAs-GaAs Bragg reflectors. We found anisotropy in the effective thermal conductivity with numbers of 0.28 W/(cmK) and 0.35 W/(cmK) for the transverse and lateral direction, respectively.     

Independently addressable VCSEL arrays on 3-μm pitch

We present an exceedingly dense linear vertical-cavity surface-emitting laser (VCSEL) array with independently addressable elements on a staggered 3-μm pitch. Our devices utilize an all-epitaxial structure and operate at a wavelength of 813 mm with threshold currents below 400 μA. The high-packing density is enabled by combining transparent contact technology with a planar laterally oxidized device architecture. The array exhibits low interelement thermal crosstalk and has electrical resistances of 3 MΩ between adjacent array elements     

Crosstalk Analysis of a Fiber Laser Sensor Array System Based on Digital Phase-Generated Carrier Scheme

A detailed study on analyzing the crosstalk in a wavelength division multiplexed fiber laser sensor array system based on a digital phase generated carrier interferometric interrogation scheme is reported. The crosstalk effects induced by the limited optical channel isolation of a dense wavelength division demultiplexer (DWDM) are presented, and the necessary channel isolation to keep the crosstalk negligible to the output signal was calculated via Bessel function expansion and demonstrated by a two serial fiber laser sensors system. Finally, a three-element fiber laser sensor array system with a 50-dB channel-isolation DWDM was built up. Experimental results demonstrated that there was no measurable crosstalk between the output channels.     

光纤激光阵列自组织相干合成的性能研究

研究了基于倏逝波耦合的自组织相干合成激光阵列。应用静态本征模/超模理论推导阵列模式;通过数值方法考察阵列激光系统的动态特性进而分析输出功率的稳定性、阵列的扩展能力和阵列模式;并对两种方法得到的阵列模式进行了比较分析。结果表明:输出功率的稳定性以及输出功率的大小受阵列的锁相性能和阵元间的相位差影响;随着激光单元数目的增加,阵列总输出功率会非线性增大。通过跟踪各个阵元的相位变化并考察阵列模式的近场和远场特性,初步验证了37单元阵列的相干合成,随着阵元数目的增加,中心阵元与其邻近层阵元的振幅差会逐渐减小。     

A Compact SOI-Integrated Multiwavelength Laser Source Based on Cascaded InP Microdisks

We report on the performance of a compact multi- wavelength laser (MWL) source heterogeneously integrated with and coupled to a silicon-on-insulator (SOI) waveguide circuit. The MWL consists of four InP-based microdisk lasers, coupled to a common SOI wire waveguide. The microdisk lasers operate in continuous-wave regime at room temperature, with a threshold current around 0.9 mA and a waveguide-coupled slope efficiency of up to 8 muW/mA, for a microdisk diameter of 7.5 mum. The output spectrum contains four laser peaks uniformly distributed within the free-spectral range of a single microdisk. While thermal crosstalk is negligible, laser peak output powers vary up to 8 dB for equal microdisk drive currents, as a result of loss due to coupling with higher order modes supported by the 1-mum-thick microdisks. This nonuniformity could be eliminated by reducing the microdisk thickness.     

Experimental investigation of thermal crosstalk in a distributed feedback laser array

Thermal crosstalk between lasers in a distributed feedback laser array has been investigated by measuring the oscillating-wavelength shift. Between closely situated lasers, thermal crosstalk due to lateral heat spreading decreases proportionally to the inverse of the laser distance. Thermal crosstalk due to heating in the heat sink and stem becomes dominant between relatively distant ( approximately 300 mu m) lasers. A diamond heat sink reduces thermal crosstalk to about 1/3 compared to a silicon heat sink.<>     

Integrated four-wavelength DFB laser array with 10 Gb/s speed and 5nm continuous tuning range

A 1.5 μm, four-wavelength DFB (distributed feedback) laser array operating at a speed of 10 Gb/s and with a continuous tuning range of 5 nm for each laser has been demonstrated. An adjacent channel electrical crosstalk penalty of 0.6 dB was measured, and the thermal tuning limitation was identified. Each laser could be modulated at a speed of 10 Gb/s with moderate electrical crosstalk penalty (~0.6 dB) from the adjacent laser. The high-speed performance was not degraded by thermal tuning up to 3.2 nm     

High-power pulse-emitting lasers in the 1.5–1.6 μm spectral region

The metalorganic chemical vapor deposition (MOCVD) method is used for growing heterostructures in the system of AlGaInAs/InP materials with different versions of the configuration of the active region. Laser diodes are fabricated from the grown heterostructures; with the purpose of increasing the output optical power, the laser diodes are integrated into bars and arrays. Single laser diodes exhibit a high output power of ～6 W in the pulse mode. The laser bars exhibit an output power of 20 W in the pulse mode. The highest achieved pulse output optical power for an array of 30 elements amounts to ～110 W.     

Single-Shot, High-Speed, Thermal-Interface Characterization of Semiconductor Laser Arrays

Through a detailed characterization of thermally induced output power degradation it is possible to use junction heating as a tool to resolve thermal interfaces on mus timescales using a single-shot characterization technique. In this work, the deleterious effect junction heating has on the optical output power of a laser array is characterized and then used to infer the time-dependent junction temperature in response to current pulses of varying widths. The extracted parameters are also used numerically to model the laser as a temperature-dependent heat source for thermal simulations. This treatment allows realistic packaging and emitter-placement studies to be parametrically performed by incorporating the relationship between temperature and output power/efficiency for each emitter. In this respect, once the temperature behavior of a single emitter is quantified, the operating temperature and output power performance can be accurately predicted for any realistic physical arrangement of laser array and packaging. The experimental method presented in this work is also compared to other techniques and numerical simulations using the nonlinear heat source; this demonstrates the utility of this approach and the convenience of using easily measured parameters in thermal simulations.     

1.5 μm InP/GaInAsP linear laser array with twelve individuallyaddressable elements

Linear arrays of twelve individually addressable InP/GaInAsP channelled-substrate buried-heterostructure lasers emitting at λ=1.5 μm were fabricated. Spacing between active elements (250 μm) was made to match the fibre spacing in a 12-fibre ribbon. Individual arrays were epoxy bonded, p-side up to metallised BeO carriers. Best case uniformity of laser characteristics within an array is indicated by tight distributions of lasing threshold (9.8±0.9 mA at 30°C) and output powers of (8.6±0.4 mW at 100 mA). While no significant optical crosstalk could be detected, small increases (≃10%) in device lasing thresholds were observed when two adjacent elements were operated CW simultaneously, probably due to the thermal impedance of the epoxy-bond employed and the resultant heating of operating nearest-neighbour devices. Such arrays offer the potential for reduced fibre alignment time per element thus reducing packaging costs per source. In addition, reduced space requirement per source is realised     

千瓦级传导冷却半导体激光器阵列热特性

随着半导体激光器输出功率的进一步提高,热管理已经成为制约其性能和可靠性的关键瓶颈之一。利用有限元方法对千瓦级高功率传导冷却型（G-Stack）半导体激光器阵列的热特性进行数值模拟与分析。结果表明工作脉宽大于250 μs时器件各发光单元之间会发生严重的热串扰现象。在横向及垂直方向的热量分别为64.7%与35.3%,横向方向热阻的74.9%及垂直方向热阻的66.5%来自CuW,表明CuW对于激光器的散热性能有着决定性的影响。实验测试了器件在不同占空比条件下的光谱特性,得到工作频率分别为20、30、40 Hz相对50 Hz的温差分别为2.33、1.56、0.78℃,根据累积平均温度法计算得到的温差分别为2.13,1.47,0.75℃,理论模拟结果相对于实验结果的平均误差小于6.85%,结果表明理论模拟结果和实验瞬态热阻基本吻合。     

窄线宽可调谐外腔半导体激光器阵列

介绍一种半导体激光器(LDs)阵列的外腔可调谐系统。腔体是Littrow结构,2个透镜将光栅选取的锁模光信号形成颠倒阵列像反馈回各个LD中。系统容易调整,对中心波长810nm、输出功率20W的单排24管LDs阵列,在光学元件参数均非最佳的情况下,获得线宽0．5nm(230GHz)、可调范围近30nm和输出功率为LDs阵列自由运行时的60％。实验结果表明,阵列中单个LD接收到的锁模信号并不必是自己发出的光,而可以来自阵列中其它LDs;此外,只要阵列中部分LDs获得锁模信号,即可达到全阵列锁模的目的。     

Quantum cascade superluminescent light emitters with high power and compact structure

Quantum cascade(QC)superluminescent light emitters(SLEs)have emerged as desirable broadband mid-infrared(MIR)light sources for growing number of applications in areas like medical imaging,gas sensing and national defense.However,it is challenging to obtain a practical high-power device due to the very low efficiency of spontaneous emission in the intersubband transitions in QC structures.Herein a design of^5μm SLEs is demonstrated with a two-phonon resonancebased QC active structure coupled with a compact combinatorial waveguide structure which comprises a short straight part adjacent to a tilted stripe and to a J-shaped waveguide.The as-fabricated SLEs achieve a high output power of 1.8 mW,exhibiting the potential to be integrated into array devices without taking up too much chip space.These results may facilitate the realization of SLE arrays to attain larger output power and pave the pathway towards the practical applications of broadband MIR light sources.     

910 nm高峰值功率垂直腔面发射激光光源

报道了910 nm高峰值功率垂直腔面发射半导体激光器列阵(Vertical Cavity Surface Emitting Laser,VCSEL)的设计方法及测试结果.所制备的910 nm VCSEL列阵在准连续工作时激光功率达到2 W;在重复频率10 kHz,脉冲宽度30 ns,工作电流60 A的电脉冲驱动条件下,VCSEL列阵峰值输出功率达到25.5 W.随着工作电流的增加,VCSEL列阵输出的激光光谱呈现明显办展宽现象,证实VCSEL列阵即使在窄脉冲工作时大的电流驱动仍然会产生严重的内部热效应;VCSEL列阵输出激光的光脉冲波形在驱动电流增大至60 A时脉宽仅展宽了6 ns左右,证实VCSEL阵列具有非常优越的脉冲响应特性.对VCSEL列阵进行光束准直处理后,在1 m距离处得到了近圆形的均匀光斑.我们相信这种高功率的910 nm面阵光源在未来汽车光探测测距(LiDAR)等智能驾驶领域具有很大的应用潜力.     

热畸变对单板条热容激光器输出的影响

开展了激光二极管(LD)抽运的全固态热容激光器的理论与实验研究,数值模拟了在热容工作条件下侧面抽运的Nd∶YAG板条激光器的热透镜效应,分析了热透镜效应对激光输出的影响,并进行了相应的实验论证。实验中采用的晶体尺寸为57mm×40mm×4mm,激光二极管阵列的抽运峰值功率为12kW,重复频率为1kHz,占空比为20%,为了获得较高的增益,将抽运光通过光学系统进行聚焦,抽运光在晶体侧面的光斑大小为15mm×57mm.实验中观察了1s内的脉冲能量输出的波动情况,在开始工作的时候单脉冲能量输出为1J,在1s后单脉冲能量输出下降到开始的50%。     

阵列波导光栅复用/解复用器光栅孔径对器件性能影响的数值分析

阵列波导光栅复用 /解复用器中波导光栅孔径是器件重要的结构参数 .波导光栅孔径数值有限 ,部分光场将因未被耦合进而损失掉 .同时引起输出波导接收端焦场变形 ,增加了器件串扰 .本文详细分析和计算了由于波导光栅孔径有限引起的光场损耗和信号串扰 ,选择适当孔径参数可使其引入的信号损耗和串扰降到足够低 ,以优化设计器件