Research of Low Threshold Current and High Efficiency Distributed-Reflector Lasers with Wirelike Active Regions

本文研究了一种与量子线激光器和具有线状有源区的分布反馈激光器相同的新型分布反射器激光器。研究结果如下：(1)采用电子束光刻、CH_4/ h_2反应离子刻蚀和有机金属气相外延再生制备了1.55 μm波长GaInAsP/InP强指数耦合和增益匹配的周期性线状有源区分布反馈激光器。这种具有线状有源区的DFB激光器由于其强的折射率耦合和减少了有源介质体积，可以在很低的阈值下工作。然而，与传统的DFB激光器相比，这种类型的DFB激光器由更大的蚀刻/再生界面组成。因此，激光特性的可靠性测试是非常重要的。进行了连续波寿命试验。在大约10倍阈值的偏置电流下，老化8200小时后，激光特性没有下降。(2)利用横向量子约束效应，首次展示了一种由线状有源段和无源DBR段组成的新型分布式反射器激光器，具有量子线状结构。理论分析表明，与无有源层相比，DBR结构的波导损耗仅增加1 cm^<-1>。采用该波导结构作为无源DBR截面，当线宽为40 nm， DBR截面长度为200 μm时，反射率可达97%。当有效截面长度为240 μm时，得到阈值电流为15.4 mA，对应的阈值电流密度为320 A/cm^2。无源DBR截面长度为440 μm，条纹宽度为20 μm，两切面均有劈裂。前面板的差分量子效率为16.2%，后面板的差分量子效率为0.57%，实现了28的非对称输出比。这种强不对称输出特性是DR激光器的一个特殊特性。为了实现低阈值和单模工作，还制备了窄条纹DR激光器。结果表明，在RT-CW条件下，当主动式截面长度为310μm，被动式截面长度为270 μm，条纹宽度为3 μm时，获得的阈值电流为7.6 mA，前端差分量子效率为5.1%。在相对较低的偏置电平（I=1.2I_<th>）下实现了40 dB的子模抑制比（SMSR）单模工作。少

A new type of DR (distributed reflector) lasers fabricated by the same fabrication process as that of quantum-wire lasers and distributed feedback (DFB) lasters with wirelike active regions have been studied.Results obtained in this research are as follows :(1) High-performance 1.55 μm wavelength GaInAsP/InP strongly index-coupled and gain-matched distributed feedback lasers with periodic wirelike active regions were fabricated by electron beam lithography, CH_4/H_2-reactive ion etching, and organometallic vapor-phase epitaxial regrowth. This type of DFB laser with wirelike active regions can operate at very low threshold because of its strong index coupling and the reduction of the active medium volume. However, this type of DFB laser consists of a larger portion of etched/regrowth interfaces than conventional DFB laser. Therefore the reliability test of lasing characteristics is very important. A CW life test was carried out. No degradations in lasing characteristics were observed af … More ter an aging time of 8200 hours at a bias current of around 10 times the threshold.(2) By using a lateral quantum confinement effect, a new type of distributed reflector laser consisting of a wirelike active section and a passive DBR section with quantum-wire structure was demonstrated for the first time. In theoretical analysis, a waveguide loss of a DBR structure increases by only l cm^<-1> compared with the value in case of no active layers. Using this waveguide structure as a passive DBR section, a maximum reflectivity of 97 % would be obtained for the wire width of 40 nm and DBR section length of 200 μm. Threshold current of 15.4 mA, which corresponds to the threshold current density of 320 A/cm^2, was obtained for the active section length of 240 μm. The passive DBR section length of 440 μm and the stripe width of 20 μm with both facets cleaved. The differential quantum efficiency form the front facet was 16.2% and the rear facet was 0.57 %, hence an asymmetric output ratio of 28 was realized. This strong asymmetric output characteristic is a specific property of the DR laser. For a lower threshold and a single-mode operation, narrow stripe DR laser was also fabricated. As a result, Threshold current of 7.6 mA and differential quantum efficiency from the front facet of 5.1 % were obtained under RT-CW condition for the active section length of 310μm, the passive section length of 270 μm and the stripe width of 3 μm. A single-mode operation with sub-mode suppression ratio (SMSR) of 40 dB was achieved at relatively low bias level (I=1.2I_<th>). Less