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

点击翻译按钮获取中文摘要

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