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 semiconductor optical amplifier. 40 GHz optical PLL using a 10 GHz mode-locked fiber ring laser as a clock pulse was stable over 5 h within 10 KHz lock-in frequency detuning of 40 GHz TDM optical signal.