Phase-locked timing extraction from 40 Gbps optical signal using harmonically mode-locked Er-doped fiber ring laser

A prescaled 10 GHz clock recovery from a 40 Gbps time-division-multiplexed (TDM) optical signal has been demonstrated with a low-frequency-oscillator- free phase-locked loop (PLL) circuit based on four-wave-mixing in a semicon ductor optical amplifier, 40 GHz optical PLL using a 10 GHz mode-locked fib er ring laser as a clock pulse was stable over 5 h within 10 KHz lock-in fr equency detuning of 40 GHz TDM optical signal.