Monolithic optical PAM-4 transmitter with autonomous carrier tracking

We present two single channel optical PAM-4 transmitters, one based on a novel 3-section PN-capacitive micro-ring modulator with on-chip low-power driver and a near-zero power capacitive wavelength locking system and another one based on a 2-section thermally tuned PN micro-ring modulator of the similar size with the same modulator driver. The maximum error-free data-rate of 16 Gb/s and 22 Gb/s at the energy efficiency of 200 fJ/b and 430 fJ/b for the former and the latter transmitters are measured, respectively, and the design trade-offs are discussed. The chips are fabricated in the GlobalFoundries 90 nm CMOS SOI process.