We review our recent progress on graphene integrated photonics for next generation optical communications. We present the design principles of graphene photodetectors and optical modulators as well as recent results on Si and SiN photonic platforms. We show optical modulators at communication wavelengths with electro-optical bandwidth up to 30GHz and operation at 50Gb/s on-off keying (OOK). We report on very recent progress about graphene photodetectors with ultra-high bandwidth (>67GHz) based on the photo-thermo-electric (PTE) effect. The last is of particular interest as it enables a zero dark-current direct conversion of the optical signal into a voltage which can be amplified by a voltage pre-amplifier rather than a transimpedance amplifier (TIA). This is a potential breakthrough in scaling the bandwidth of photoreceiver towards increasing bandwidths, as the TIA imposes strict trade-offs between gain and bandwidth. With the proposed device we show direct detection of optical signals exceeding 100Gb/s in a voltage detection scheme without dark current bias.
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.
Within the European Project TERABOARD, a photonic integration platforms including electronic-photonic integration is developed to demonstrate high bandwidth high-density modules and to demonstrate cost and energy cost target objectives. Large count high bandwidth density EO interfaces for onboard and intra-data center interconnection are reported. For onboard large count interconnections a novel concept based on optical-TSV interconnection platform with no intersections and no WDM multiplexing is reported. All input/output coupler arrays based on a pluggable silica platform are reported as well.