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.
Terahertz isolators, one of the typical nonreciprocal devices that can break Lorentz reciprocity, are indispensable building blocks in terahertz systems for their critical functionality of manipulating the terahertz flow. Here, we report an integrated terahertz isolator based on the magneto-optical effect of a nonreciprocal resonator. By optimizing the magneto-optical property and the loss of the resonator, we experimentally observe unidirectional propagation with an ultrahigh isolation ratio reaching up to 52 dB and an insertion loss around 7.5 dB at ~0.47 THz. With a thermal tuning method and periodic resonances, the isolator can operate at different central frequencies in the range of 0.405–0.495 THz. This on-chip terahertz isolator will not only inspire more solutions for integrated terahertz nonreciprocal devices, but also have the feasibility for practical applications such as terahertz sensing and reducing unnecessary reflections in terahertz systems.
Polarization multiplexing technology is widely adopted for increasing the capacity in optical communication systems. Especially, silicon‐based integrated polarization division multiplexing (PDM) optical receivers with large bandwidth therein play an important role, which are crucial for on‐chip large‐capacity optical interconnection. Here, a silicon‐based PDM optical receiving chip is enabled by two‐dimensional grating couplers and graphene‐on‐plasmonic slot waveguide photodetectors. Utilizing the advantages of the designed focusing two‐dimensional grating couplers and plasmonic‐slot‐waveguide‐enhanced graphene–light interaction, the optical receiving chip is achieved with an ultra‐small footprint, a bandwidth exceeding 70 GHz and a reception of PDM signals in a line rate of 128 Gbit s−1 non‐return‐to‐zero and 224 Gbit s−1 four‐level pulse‐amplitude‐modulation at 1550 nm, accompanied by the bit error rates lower than the KP4 forward error correction threshold and 15% soft‐decision forward error correction threshold, respectively. Comparing with receiving the single‐polarization state, simultaneous receiving dual‐polarization state introduces about 1 dB additional power penalty because of inter‐polarization crosstalk. The graphene‐plasmonic PDM optical receiving chip can greatly improve the line rate of the system, showing its unique advantages of small footprint, high speed, large bandwidth, low crosstalk and complementary metal–oxide–semiconductor compatibility, which can be potentially used in the next generation silicon‐based high‐speed optical communication.
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