Graphene has been proposed to be integrated with Si Photonics because of its very high mobility, fast carrier dynamics and ultra-broadband optical properties. High speed graphene photodetectors have been demonstrated so far, however the most are based on the photo-bolometric or photo-conductive effect. These devices are characterized by large dark current, in the order of milli-Amperes. Photothermal effect (PTE) photodetectors can be used in voltage detection mode with no dark current, it is ultra fast and it operates near zero-bias. Graphene PTE-based photodetectors have been reported so far but high-speed optical telecommunication signal detection has not been shown yet. Here, we report on a graphene PTE-based photodetector on SOI waveguide. Thanks to the optimized design we show a direct detection of 105Gb/s non-return to zero (NRZ) and 120Gb/s 4-level pulse amplitude modulation (PAM) optical signals.
The future global-scale quantum communication network will require free-space and satellite links able to work in daylight conditions and compatible with the telecom fiber infrastructure. Here we present a full prototype for daylight quantum key distribution at 1550 nm exploiting an integrated silicon-photonics chip as state encoder. We tested our prototype in the urban area of Padua (Italy) over a 145m-long free-space link, obtaining a quantum bit error rate around 0.5% and an averaged secret key rate of 30 kbps. The developed chip represents a cost-effective solution for portable free-space transmitters and a promising resource for future satellite missions.
Due to its remarkable properties, graphene-based devices are particularly promising for optoelectronic applications. Thanks to its compatibility with standard silicon technology, graphene could compete III-V compounds for the development of low cost and high-frequency optoelectronic devices. We present a new optoelectronic device that consists in a coplanar waveguide integrating a commercially-available CVD graphene active channel. With this structure, we demonstrate high-frequency (30 GHz) broadband optoelectronic mixing in graphene, by measuring the response of the device to an optical intensity-modulated excitation and an electrical excitation at the same time. These features are particularly promising for RADAR and LIDAR applications, as well as for low-cost high-speed communication systems.
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