A novel frequency discriminated phase controller for high-speed optical clocks generated from laser diodes

We demonstrate the in-situ frequency discrimination and continuous phase tuning of high-speed optical clocks generated from a directly modulated/encoded laser diode with respect to a free-running microwave clock. This is performed by using a dc-voltage controlled, frequency-discriminated optoelectronic phase shifter (OEPS). The transfer function of the phase shifter versus controlled voltage is linear with a maximum phase-tuning range of up to 1 95 (340 ). The tuning responsivity of the OEPS can be adjusted from 50 to 90 V. The fluctuation and drift in phase of the controlled signal are about 0.05 and 0.003 min. The tuning resolution of 0.2 at a 3-mV increment of controlling voltage is achieved by using a high-precision voltage regulator. Relative timing jitter of the controlled optical microwave clock is less than 5 ps.