Efficient Wavelength Tuning Techniques for Integrated Silicon Photonics

Abstract

The past decade has seen a significant amount of academic and industrial research into interconnect topologies that employ optical channels for next generation high speed communication systems. Integrated optical interconnects have taken center stage in tackling channel loss limitations of traditional electrical links and bandwidth requirements for inter-chip and intra-chip signal processing for multi-core processors. Wavelength-division multiplexing (WDM) optical interconnect architectures based on microring resonator devices offer a low-area and energy-efficient approach to realize both high-speed modulation and WDM with high-speed transmit-side ring modulators and high-Q receive-side drop filters.

At the heart of silicon photonics is the silicon microring resonator. These high-Q refractive devices can achieve high contrast ratios with their small footprint and enable distance independent communication. A major challenge to the use of microring resonators is the sensitivity of their resonance wavelength to process and fabrication imperfections and temperature perturbations. To curtail the effects of resonance wavelength drifts, stabilization schemes are implemented to properly align the resonance wavelength of the microring device with the input laser wavelength.

This thesis work focuses on three main issues. Firstly, the sources and effects of mismatch in silicon microring resonators are identified. Secondly, a review of literature is done to examine existing resonance wavelength stabilization techniques. Based on the reference search tuning algorithm, a new dual-loop tuning method which combines the benefits of bias-based and thermal-based tuning schemes is proposed. Furthermore, we evaluate the tuning efficiency of some existing and the proposed tuning schemes using a statistical model to determine optimal power and speed efficiency. Modeling results of carrier injection ring resonator devices with common thermal tuning and the new dual-bias/thermal scheme reveals that the latter scheme offers ~ 50% improvement in power with small variations and close to 16X speed improvement.

Finally, the tuning control loop is fabricated in GP 65nm CMOS process. Transmit-side and receive-side are independently implemented for a 5-channel WDM system. Measurement results are presented in both cases. The transmitter IC achieved both static and dynamic tuning, stabilizing ring resonance wavelength in the midst of temperature fluctuations from an adjacent ring. The total power consumed was 5.17mW while covering a wavelength tuning range of ~ 0:8nm. Static tuning was successfully demonstrated for the receiver IC. A tuning range of 0:7nm was achieved over a 2mA dynamic range of current.