Silicon photonics for high-speed communications and photonic signal processing

Leveraging on the mature processing infrastructure of silicon microelectronics, silicon photonic integrated circuits may be readily scaled to large volume production for low-cost high-volume applications such as optical transceivers for data centers. Driven by the rapid growth of generative artificial intelligence and the resultant rapid increase in data traffic in data centers, new integrated optical transceivers will be needed to support multichannel high-capacity communications beyond 1.6Tb/s. In this paper, we review some of the recent advances in high performance optical waveguide grating couplers (WGC) as a key enabling technology for future high capacity communications. We describe the novel use of shifted-polysilicon overlay gratings on top of the silicon grating that enabled foundry manufactured chips to have fiber-chip coupling losses of under 1 dB. The use of mirror symmetry and resonant cavity enhancement in the design of gratings can increase the 1-dB optical bandwidths of grating couplers to over 100 nm. Multimode waveguide grating couplers (MWGC) may be designed for the selective launch of different modes channels in multimode fibers for mode-division-multiplexing (MDM) communications. The use of different modes or polarizations in optical fibers for high capacity communications requires the unscrambling of data lanes which are mixed together during the optical fiber transmission. We describe how silicon photonic circuits can be used to perform unitary matrix operations and unscramble the different data lanes in multichannel optical communication systems. We also describe recent advances on high-speed silicon modulators for enabling data rates of individual data lanes in an integrated optical transceiver beyond 300 Gb/s.