Development of a Control System for Photonic Integrated Circuits

Abstract

Silicon photonics is at the helm of the data communication technologies used for densely- integrated wavelength-based optical communication. Its CMOS compatibility allows the increasing demand for high-bandwidth and low-power demands to be easily met. Micro-ring resonators have garnered a lot of attention as a versatile optical device that can be used as optical modulators, switches and filters. However, the high thermo-optic coefficient of silicon (1.8 × 10−4K−1 at 300K) and frequency sensitivity to fabrication tolerances (∼100GHz/nm) are reportedly deleterious to their use in dense wavelength division multiplexing applications where the channel wavelength spacings are tight and temperatures can vary as much as 15 C. Numerous potent solutions for addressing this challenge have been proposed such as athermalization and thermal stabilization by control based methods. However, there is scant literature on the application of control-based methods on higher-order ring resonator based optical devices.

In this work, we show experimentally how wavelength-locking and tracking of a higher order coupled-resonator optical waveguide (CROW) optical add-drop multiplexer (OADM) with integrated heaters can be carried out using low-speed electronics, a feedback signal via photodiodes and a LabVIEW-based control algorithm. We discuss about the standard methods used to actively compensate the local thermal variations and track the resonant frequency of the OADMs, the concept and architecture of the control algorithm that we developed and how we tested it on a silicon photonic based integrated optical system. We also discuss the factors that make it challenging to implement such a control system. The algorithm is fairly simple to integrate for multiple CROW based optical filters and can carry out the wavelength tracking of several CROW filters in parallel. It is able to recover the wavelength from a ±1 C deviation in chip temperature during tracking within 30 s. The modular structure and parameter-based operation makes it versatile for applications with a range of optical devices that modulate the optical intensity. Additionally, for future development, our algorithm is well suited to carry out controlled increase of bandwidth at the cost of some optical intensity.

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