The microring resonator is critical for dense wavelength division multiplexed (DWDM) chip-to-chip optical I/O, enabling modulation and channel selection at the μm-scale suitable for a VLSI chip. Microring-based links, however, require active tuning to counteract process and thermo-optic variations. Here, we present a bit-statistical tuner that decouples tracking of optical one and zero-levels to realize non-dc-balanced data transmission, an “eye-max”-locking controller, and self-heating cancellation without need for a high-speed sensing frontend. We implement the tuner on a 45 nm CMOS-SOI process with monolithically integrated photonic devices and circuits. The tuner consumes 0.74 mW in the logic while achieving a record 524 GHz (> 50 K temperature) tuning range at 3.8 μW/GHz heater efficiency. To our knowledge, this is the highest range and heater efficiency reported by an on-chip closed-loop thermal tuner to date. The tuner integrates with a 5 Gb/s 30 fJ/bit monolithic microring transmitter, achieving wavelength-lock and immunity to both tracking failures and self-heating events caused by arbitrary, nondc-balanced bitstreams. In addition, the tuner provides critical functionality for an 11-λ DWDM transmitter macro capable of 11 × 8 Gb/s bandwidth on a fiber. Together with the transmitter, a 10 Gb/s on-chip monolithic optical receiver with 10-12 BER sensitivity of 9 μA at 10 Gb/s enables a sub-pJ/bit 5 Gb/s optical chip-to-chip link, with the bit-statistical tuner providing thermally robust microring operation.
Chen Sun, Mark Wade, Michael Georgas, Sen Lin, Luca Alloatti, Benjamin Moss, Rajesh Kumar, Amir H. Atabaki, Fabio Pavanello, Jeffrey M. Shainline, Jason S. Orcutt, Rajeev J. Ram, Milos Popovic, and Vladimir Stojanovic