An in situ monitoring technique for optimizing anti-reflection coatings using a monolithic integrated photodetector
A very low reflectivity of the order of 10−4 is demonstrated for dual-layer anti-reflection coatings on normal facet semiconductor lasers, by integrated in situ monitoring. The method has been tested on three and eight quantum-well InGaAsP ridge lasers that consist of a gain section and an integrated absorber section. The principle is to monitor the change in the photocurrent generated in the absorber that is proportional to the output optical intensity from the laser, which changes as the coating progresses.