OREANDA-NEWS. In the effort to develop a DFB laser with high-speed response suited to 25Gbps operation, a current-blocking structure with semi-insulating semiconductors that have high electrical resistance by doping impurity showed promise, but high output power was not possible because of poor current injection efficiency in the active region. In response, Mitsubishi Electric developed the new current-blocking structure with semi-insulating semiconductors that realize efficient current injection in the active region.