Demonstration and optimization of an optoelectronic phase-locked phase shifter for optical microwave signals

We demonstrate the tracking and continuous tuning of the relative phase difference between the free-running microwave clock and the optically distributed microwave signals from laser diode by using a modified optoelectronic phase shifter (OEPS). This is implemented by using a voltage-controlled optoelectronic digital phase-locked loop. The maximum phase deviation is up to 340/spl deg/ under the change in controlling voltage of 4.8 V, which is completely independent of operating frequency. A linear transferred function of the OEPS with responsivity of 69/spl deg//V was measured. The resolution and phase fluctuation of the OEPS can he as small as 0.2/spl deg/ and 0.05/spl deg/, respectively.