A Monolithic Microring Modulator-Based Transmitter With a Multiobjective Thermal Controller

This article presents a multiobjective thermal controller that stabilizes the resonance wavelength of silicon photonic microring modulators (MRMs) under varying temperature conditions and fluctuations in laser power. The controller operates in the background while live data is flowing, adjusting the MRM resonance wavelength to achieve optimal application-specific performance metrics, including any one of extinction ratio (ER), optical modulation amplitude (OMA), or level separation mismatch ratio (RLM). This universal bias-assisted photocurrent-based controller is capable of selectively tuning for any of these transmitter metrics without the need for broadband circuits. Notably, this is the first controller proposed to tune the MRM for optimizing RLM, which is particularly important as MRMs are now increasingly adopted for 4-PAM modulation. The controller functionality is verified on an MRM monolithically integrated in a silicon photonic 45-nm CMOS SOI process with a high-swing $4.7~{V}_{\text {pp}}$ digital-to-analog converter (DAC)-based 5.5-bit resolution driver, dissipating $1.7~\text {pJ/b}$ at $40~\text {Gb/s}$ . With the controller optimizing for different objectives, an ER of 10.3 dB, OMA of $540~\mu \text {W}$ (normallized OMA of −3.2 dB), transmitter dispersion eye closure quaternary (TDECQ) of 0.67 dB, and RLM of 0.96 are achieved without employing a nonlinear feed-forward equalizer (FFE) or predistortion.