Automatic Optical Heterodyne Phase Lock by Microcomputer-assisted Loop Filter

Abstract

This paper demonstrates signal light carrier automatic pull-in and phase-lock to an optical frequency comb reference by our newly developed microcomputer-assisted phase-lock loop circuit. The microcomputer utilizes a binary-search algorithm to alter the oscillation frequency of the slave laser and achieve rapid pull-in to the master laser. It achieves automatic phase-locking time of 0.45msec when the laser-diode frequency lies within the pull-in range of ±100MHz. The single side band phase noise is just 1.8°at offset frequencies from 10Hz to 5MHz. This phase noise value is not expected to cause any power penalty with QPSK modulation.