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 1.957π (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