All-Optical Phase Control of a Square-Wave Photonic Clock

We propose and demonstrate an all-optical technique to control the phase of a class of square-wave photonic clocks. The particular photonic clock used for our demonstration is comprised of a traveling-wave semiconductor optical amplifier (SOA) connected to a resonant-type SOA exhibiting hysteresis. Phase control is achieved by cross-gain modulation within the travelling-wave (TW)-SOA, which suspends clock generation over a controlled time interval to achieve the desired phase. We used 1576-nm control pulses with 62- μW peak power and arbitrary polarization states, features that are telecommunications compatible. A useful feature of our scheme is that phase control is independent of the synchronization between the initial clock phase and arrival time of the control pulse.