Monolithically integrated laser/photodetector

The fabrication and performance characteristics of a laser structure with monolithically integrated monitoring photodiode are described. The structure utilises semi-insulating Fe doped InP layers for confinement of the current to the active region of the laser and for the separation of the laser and the photodetector sections. The lasers have threshold currents in the range 30–40 mA and emit in a single frequency by virtue of frequency selective feedback, provided by a grating etched on the substrate. The photodetector provides ⋍300/μA of photocurrent per mW of laser power which is comparable to the value for a large area Ge photodiode generally used to monitor laser power. The new structure also minimises the unwanted reflection effects on laser performance caused by light reflected from the photodiode interface.