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.