High-sensitivity measurements of return loss by self-heterodyne in a laser diode

Summary form only given. Return loss measurements in excess of 60 dB require high-sensitivity detectors and special care to avoid spurious contributions from the optics. We present a new method with an unprecedented sensitivity yet easy to implement, using a self-heterodyne sensing mechanism. Single-mode laser power is launched into the pigtail of a PZT phase modulator and gets into the device under test (DUT) through an angled joint. Light coupled back into the laser cavity generates a modulation of laser power, that can be picked by a photodetector placed on the rear mirror of the laser