Low threshold current and high efficiency of 1.3-mum MQW lasers with tapered active stripe for butt-coupling to single-mode fiber

摘要

Semiconductor lasers with narrow beam divergence are strongly required for low-cost laser modules, from the view point of high coupling efficiency for butt-coupling to single-mode fiber. In order to reduce the beam divergence, several types of lasers with spot-size transformers have been proposed. Most of the reported spot-size transformers were mainly composed of a tapered waveguide monlithically integrated to an active layer.~(1-4) However, such transformers require not only a long cavity but also complicated fabrication processes.