Fig. 1. Structure of OPLL. PFD, phase frequency detector; MCU, microcontroller unit; Fast PD, fast photodiode.

Fig. 2. Schematic configuration of homemade RF generator.

Fig. 3. (a) A typical spectrum of the closed-loop beat note signal (resolution bandwidth is 10 kHz). (b) Expanded view of the beat note signal (resolution bandwidth is 1 Hz)

Fig. 4. (a) Phase noise spectrum of the reference signal. (b) Phase noise spectrum of the OPLL.

Fig. 5. Dynamic performance of the OPLL. Transition time between t1 and t2 is approximately 50 μs.