Optical phase-locked loop for coherent detection optical receiver

A novel subcarrier-based optical phase-locked loop (SC-OPLL^®), with off-the-shelf optical components, is presented and demonstrated. The method, based on a continuous-wave laser and optical subcarrier modulation using a standard LiNbO₃ Mach-Zehnder modulator, allows easier practical implementation than the previously proposed OPLL circuits based on laser direct modulation.