Compact Integrated Phase Locked Loop for Optical Frequency Difference Locking

In this paper, a compact integrated CMOS phase locked loop (PLL) is proposed to lock the drifting beatnote generated by heterodyning two optical lasers/comb tones. The integrated PLL is fabricated in TSMC 65nm CMOS process. It takes dc power of 9.8 mW and occupies an area of 0.67 mm2. When heterogeneously integrated with photonic chips, stable and high-power millimeter wave (mm-wave) could be generated in a compact packaging for radio-over-fiber communication systems and antenna remoting. A prototype of the integrated PLL is demonstrated and measured with the beatnote locked at 1.12 GHz.