An all optical coherent receiver for self-homodyne detection of digitally phase modulated optical signals

A novel optical phase-locked loop (OPLL) system for the self-homodyne detection of digitally phase modulated optical signals is introduced. A Mach-Zehnder type interferometer is used to self-homodyne binary phase-modulated optical signals with an external phase modulator inserted in the control arm of the interferometer. In the absence of thermal noise, this arrangement is 3 dB less sensitive than a homodyne receiver for a background noise limited operation. For a negligible background noise level and when the receiver thermal noise is ignored, a power penalty of 6 dB is incurred,