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The development of optical interconnect techniques greatly expands the communication bandwidth and decreases the power consumption at the same time. It provides a prospective solution for both intra-chip and inter-chip links. Herein reported is an integrated wavelength-division multiplexing (WDM)-compatible multimode optical switching system-on-chip (SoC) for large-capacity optical switching among processors. The interfaces for the input and output of the processor signals are electrical, and the on-chip data transmission and switching process are optical. It includes silicon-based microring optical modulator arrays, mode multiplexers/de-multiplexers, optical switches, microring wavelength de-multiplexers and germanium-silicon high-speed photodetectors. By introducing external multi-wavelength laser sources, the SoC achieved the function of on-chip WDM and mode-division multiplexing (MDM) hybrid-signal data transmission and switching on a standard silicon photonics platform. As a proof of concept, signals with a 25 Gbps data rate are implemented on each microring modulator of the fabricated SoC. We illustrated 25 × 3 × 2 Gbps on-chip data throughput with two-by-two multimode switching functionality through implementing three wavelength-channels and two mode-channel hybrid-multiplexed signals for each multimode transmission waveguide. The architecture of the SoC is flexible to scale, both for the number of supported processors and the data throughput. The demonstration paves the way to a large-capacity multimode optical switching SoC.

We present a polarization-independent tunable optical filter with variable bandwidth based on silicon-on-insulator (SOI) waveguides. The polarization-independent operation is achieved through the use of a polarization splitter-rotator and a polarization rotator-combiner, which are based on a bilevel adiabatic taper and an asymmetric directional coupler. Two stages of second-order microring resonators (MRRs) with different radii are used to achieve wavelength filtering with variable bandwidth and large free spectral range (FSR). Each stage of the second-order MRRs has a flat-top spectrum. The central wavelength of the filter is tuned by synchronous tuning of the two stages. The 3 dB bandwidth is adjusted via intentional misalignment of the passbands of the two stages. We demonstrate a prototype of such an optical filter on the SOI platform. The FSR of the fabricated device is about 90 nm. We show the tuning of the central wavelength from 1460 to 1550 nm. We adjust the 3 dB bandwidth from 37.5 to 100 GHz with a step of 12.5 GHz, with the overall insertion loss varying from −5.4 to −7.9 dB.