Silicon Photonic Integrated Circuits for Wavelength-Division Multiplexing Applications

Silicon photonics is perceived to provide low-cost, high-bandwidth and compact optical components for a wide range of applications in optical communications and interconnects. One of the cited key advantages is the capability of wavelength-division multiplexing (WDM). However, the nature of high-index contrast of silicon photonic devices leads to significant challenges for WDM filters, one of the key components in WDM circuits. In this paper, we review our demonstrated WDM circuits based on two methods, namely, monolithically integrated silicon nitride arrayed-waveguide gratings (AWGs) and thermally tunable silicon microring filters. The use of silicon nitride waveguides with lower index contrast than silicon leads to high performance AWGs. Meanwhile, they can evanescently couple to silicon waveguides with high efficiency. In the second method, thermally tunable rings are used to implement versatile WDM circuits, such as functioning as modulators and wavelength (de)multiplexing filters. Reconfigurability of channel spacing and central wavelengths can be achieved by individual tuning of the rings. The reviewed high-capacity monolithic optical circuits here include multiple-channel modulators, polarization insensitive receiver, and variable optical attenuation with multiplexer. The remaining challenges to implement these circuits in products are also discussed.