Graphene-based photodetectors have attracted significant attention for high-speed optical communication due to their large bandwidth, compact footprint, and compatibility with silicon-based photonics platform. Large-bandwidth silicon-based optical coherent receivers are crucial elements for large-capacity optical communication networks with advanced modulation formats. Here, we propose and experimentally demonstrate an integrated optical coherent receiver based on a 90-degree optical hybrid and graphene-on-plasmonic slot waveguide photodetectors, featuring a compact footprint and a large bandwidth far exceeding 67 GHz. Combined with the balanced detection, 90 Gbit/s binary phase-shift keying signal is received with a promoted signal-to-noise ratio. Moreover, receptions of 200 Gbit/s quadrature phase-shift keying and 240 Gbit/s 16 quadrature amplitude modulation signals on a single-polarization carrier are realized with a low additional power consumption below 14 fJ/bit. This graphene-based optical coherent receiver will promise potential applications in 400-Gigabit Ethernet and 800-Gigabit Ethernet technology, paving another route for future high-speed coherent optical communication networks.

Metasurfaces consisted of subwavelength nanostructures can extremely interact with light and manipulate the characteristics of amplitude, phase, and polarization. In particular, on-chip dielectric metasurfaces have attracted significant attention for optical communication and computing, due to its compact footprint, low loss, and broad bandwidth. Herein, an ultradensely integrated multidimensional optical system with a footprint of only 20 × 30 µm 2 based on inverse-designed dielectric metasurface network, incorporating mode-division multiplexing, and coherent optical communication technologies that can multiply the system capacity is demonstrated. It is assembled by the ultracompact multifunction on-chip metasurface devices, including four-mode demultiplexer, optical hybrid, crossing, and bending, which all have a size of only several micrometers. The inverse-designed work can significantly broaden the integrated device applications of on-chip metasurfaces and pave an alternative way for large-scale high-capacity optical communication system.

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