Measurement of reflectivity of butt-joint active-passive interfaces in integrated extended cavity lasers

A method and measurement results are presented for the determination of the reflectivity of butt-joint active-passive interfaces in a series of extended cavity Fabry-Pe/spl acute/rot lasers. The method is based on the analysis of subthreshold laser spectra. The small reflections at the two intracavity active-passive interfaces modify the mode structure of the laser. By fitting the calculated subthreshold mode structure to the recorded data, values of the reflectivities are extracted. An average value of 9.10/sup -5/ has been determined. The value of the reflectivity of those interfaces is relevant for photonic integrated circuits and particularly integrated mode-locked lasers.