Fully Integrated Optical Injection Locking With Schottky Photodiodes in 65-nm CMOS

Abstract

This article presents an optical injection-locked oscillator implemented in a standard 65-nm CMOS process with integrated Schottky photodiodes (PDs). This optoelectronic integration aims to facilitate synchronization and clock transmission in long-distance communication systems. The locking performance of N-well, P-well, and P-substrate Schottky PDs is compared using a CMOS cross-coupled LC oscillator for 1310- and 1550-nm light. The P-substrate diode demonstrated superior performance, reducing the free-running rms jitter from 38.7 to 1.02 ps at 1310 nm with 3.5-mW optical power or to 2.51 ps at 1550 nm with 1.0-mW optical power. Across three samples, the oscillator exhibited a tuning range from 2.9 to 3.3 GHz, with a maximum variance of 37 MHz and a power consumption of 4.41 mW. These findings underscore the potential of fully integrated optical systems in standard CMOS to enhance long-distance communication networks.