Resonant Wavelength Tuning and CMOS Circuits for Silicon Photonic Transmitters with Microring Modulators

Microring modulators (MRMs) have emerged as a promising solution for silicon photonic optical transmitters, offering compact size, high bandwidth density, and energy-efficient operation compared to traditional Mach-Zehnder modulators (MZMs). MRMs are particularly advantageous for wavelength-division multiplexing (WDM) transceivers, where their wavelength-selective nature enables dense spectral utilization. However, their widespread adoption is hindered by electro-optic (EO) nonlinearity and sensitivity to process and thermal variations, which can cause the resonance wavelength to deviate significantly from the laser wavelength, impacting critical metrics such as optical modulation amplitude (OMA), extinction ratio (ER), and level separation mismatch ratio (RLM). This thesis comprehensively investigates the design, optimization, and control of MRM-based optical transmitters. First, the impact of MRM resonance detuning on OMA, ER, and RLM is analyzed, uncovering key trade-offs and providing insights for optimizing transmitter performance. Second, a self-optimizing 4-PAM bit-statistical controller is introduced, which autonomously tunes the MRM for maximum OMA while compensating for EO nonlinearity. This is the first design to leverage a thermal controller for MRM EO nonlinearity compensation. Third, a multi-objective thermal controller is proposed to stabilize the resonance wavelength of MRMs under varying temperature conditions and laser power fluctuations. Operating in real-time during live data transmission, this universal bias-assisted photocurrent-based controller selectively tunes MRMs for any of the target metrics—OMA, ER, or RLM—without requiring broadband circuits. Notably, this is the first controller designed to optimize RLM, a critical metric as MRMs gain prominence in 4-PAM modulation systems. Fourth, the design considerations of high-swing segmented cascode drivers, commonly used with MRMs, are explored, with a focus on trade-offs between voltage swing, power consumption, linearity, and bandwidth. Finally, the proposed multi-objective controller is validated on an MRM monolithically integrated into a silicon photonic 45nm CMOS SOI process with our high-swing 4.7Vpp digital-to-analog converter (DAC)-based 5.5-bit resolution driver, dissipating 1.7pJ/b at 40Gb/s. With the controller optimizing for different objectives, an ER of 10.3dB, OMA of 540µW (normallized OMA of −3.2dB), Transmitter and Dispersion Eye Closure Quaternary (TDECQ) of 0.67dB, and RLM of 0.96 are achieved without employing a nonlinear feed-forward equalizer (FFE) or predistortion.

Department dc:contributor.department

Electrical and Computer Engineering

Year dc:date.issued

2025

Author dc:creator

• Sadr, Ali

Advisor dc:contributor.advisor

• Carusone, Anthony Chan

Handle dc:identifier.uri

https://hdl.handle.net/1807/150691

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/150691