ASYMMETRIC LAMBDA/4-SHIFTED INGAASP/INP DFB LASERS

1. 5- mu m asymmetric lambda /4-shifted InGaAsP/InP DFB (distributed feedback) lasers in which the lambda /4-shift position was moved from the center of the DFB region toward the front side were made in order to obtain higher output power with high single-longitudinal-mode (SLM) yield. Statistical measurements showed that for an increase of the differential quantum efficiency from the front facet without a noticeable decrease of the SLM yield, the lambda /4-shift position should be moved toward the front facet by 10-15% of the total DFB length. The output efficiencies of diodes with AR coatings on the window structure were almost coincident to those expected from theoretical calculations. The main-to-submode ratio P//0/P//1 in the rear spectra of the asymmetric devices noticeably decreased with increasing asymmetry. From an experimental point of view, a criterion for stable SLM operation, for example, P//0/P//1 greater than equivalent to 1. 5 in the rear spectrum at I equals 0. 9I//t//h for the lambda /4-shift position l//f:l//r equals 35:65, is presented.