40GHz clock recovery from 640Gbit/s OTDM signal using SOA-based phase comparator

A 40GHz clock with low jitter is recovered from a 640Gbit/s optical time-division multiplexed (OTDM), single-polarised, return-to-zero PRBS data signal. The clock recovery circuit is an injection-locked loop which contains a 40GHz Gunn oscillator, a 40GHz pulse source, and a semiconductor optical amplifier (SOA) assisted by a filtered chirp as optical phase comparator.