Low-power 7-bit hybrid volatile/ nonvolatile tuning of ring resonators

Programmable photonic integrated circuits are expected to play an increasingly important role to enable high-bandwidth optical interconnects, and large-scale in-memory computing as needed to support the rise of artificial intelligence and machine learning technology. To that end, chalcogenide-based non-volatile phase-change materials (PCMs) present a promising solution due to zero static power. However, high switching voltage and small number of operating levels present serious roadblocks to widespread adoption of PCM-programmble units. Here, we demonstrate electrically programmable wide bandgap Sb2S3-clad silicon ring resonator using silicon microheater at CMOS compatible voltage of < 3V. Our device shows low switching energy of 35.33 nJ (0.48 mJ) for amorphization (crystallization) and reversible phase transitions with high endurance (> 2000 switching events) near 1550 nm. Combining volatile thermo-optic effect with non-volatile PCMs, we demonstrate 7-bit (127 levels) operation with excellent repeatability and reduced power consumption. Our demonstration of low-voltage and low-energy operation, combined with the hybrid volatilenonvolatile approach, marks a significant step towards integrating PCM-based programmable units in large-scale optical interconnects.