PhD defence of Jose Garcia-Echeverria – Stabilized Optical Microrings for Analog and Digital Computing
Abstract
The increasing demand for computational performance and speed in data-intensive applications has driven the exploration of new computing paradigms that leverage photonic technologies for analog and digital operations. This thesis presents several key research contributions toward the realization of a microring-based system for optical analog and digital computing. First, it introduces the theoretical foundations of silicon photonics, optical neural networks, and optical digital computing. Building on this background, a self-referenced thermal feedback stabilization circuit is proposed and experimentally validated. The circuit maintains microring operation at a stable point where the through and drop port average powers are equal, ensuring self-calibration and immunity to temperature and fabrication variations over a wavelength range of 5.88 nm. The thesis then explores the use of this stabilization technique for optical analog computing by implementing a microring-based weight function for neuromorphic photonic systems. The system demonstrates state-of-the-art precision of 11.3 bits and accuracy of 9.3 bits for 2 Gbps optical payload signals and shows potential to maintain reliable operation across temperature fluctuations up to 60 °C.
In the context of digital computing, a microring-modulator optical logic gate (OLG) was designed, fabricated, and fully characterized. Its measured power transfer characteristic (PTC) exhibits a peak optical gain of approximately −171 W/W , far exceeding the slope of −1 W/W threshold generally accepted for reliable signal regeneration. The proposed logic gate offers a reasonable noise margin of 12.5 % when driven with -6 dBm (250 μW ) continuous-wave laser enabling robust cascadable OLG-based systems. The designed logic gate delivers a 64 μWpp differential output swing while remaining functional with inputs as low as 8 μWpp, translating into a practical fan-out of four to eight subsequent gates. A 2 × 2 optical switch assembled from seven interoperating OLGs validated system-level scalability: toggling the differential select line between 46 μW (logic 0) and 78 μW (logic 1) correctly routed 250 μW input signals into the desired bar or cross outputs without logic errors.
The optical computing device stabilizer presented in this thesis further advance the silicon-on-insulator platform toward scalable and manufacturable solutions. While CMOS-compatible silicon photonics has long been viewed as a promising path, its adoption has been limited by scalability and integration challenges. By enabling robust analog and digital computing with microrings, this work supports a unified approach to computation and communication using fully integrated silicon photonics.