Wavelength Locking of a Si Ring Modulator Using an Integrated Drop-Port OMA Monitoring Circuit

Abstract

Silicon micro-ring modulators have the potential to enable energy efficient, high-bandwidth-density optical interconnects in CMOS compatible silicon technologies. However, their operation is highly susceptible to any thermal, laser wavelength or process variations and, as such, require a feedback control system for guaranteeing stable modulation. This paper demonstrates wavelength locking of a hybrid CMOS-silicon photonics ring-based transmitter using a 40 nm CMOS circuit to directly monitor the optical modulation amplitude (OMA) at the drop port of the ring modulator. OMA stabilization with an accuracy of $\sim {0.125}\,\,\,^{\circ }\text {C}$ or within $\sim $ 2% of the maximum OMA), a tracking speed of 5 nm/s ( $\sim {62.5}\,\,^{\circ }\text {C}$ /s), and a tuning range of 5 nm ( $\sim {62.5}\,\,^{\circ }\text {C}$ ) is demonstrated by subjecting the photonic transmitter both to thermal and laser wavelength variations under dynamic modulation at 2 Gbps. The demonstrated wavelength locking concept is also robust to the variations in the input laser power and can be implemented with low power.