The bandwidth of electrical interconnects is reaching a bottleneck, leading to a surge of interest in silicon photonic interconnects. Microring modulators (MRM) are particularly attractive because of their high bandwidth, energy efficiency, and small size. However, implementing MRMs in commercial products is challenging due to their high thermal sensitivity caused by their high thermo-optic coefficient. Control systems that actively stabilize MRM have demonstrated the ability to compensate for thermal fluctuations, but none have addressed all system requirements for large-scale commercial applications. This work presents a simple and calibration-free method to stabilize MRM that can potentially fulfill all system prerequisites.

The proposed thermal controller requires a double-bus microring resonator (MRR) to monitor the through and drop averages and lock the operation where the through and drop power outputs are identical. This operating point has been shown to be within 3 \% of the optimal optical modulation amplitude (OMA), making it an excellent operating point. Furthermore, this controller is proven to be immune to any external perturbations and requires only analog components. After designing and building a printed circuit board (PCB) that incorporated the proposed thermal tuner, experimental tests were conducted on the controller using an MRM. The obtained results served to validate the functionality of the controller.

Finally, in applications where MRMs have unbalanced input data, the original proposed design is demonstrated to suffer from a region of locking instead of a single operating wavelength. A modified design was then developed and validated to extend that approach to unbalanced data.