Winter 2018 Optical Connections Magazine




2018 was definitely the year that applications for optical communications using the remarkable properties of graphene came closer to reality. Peter Dykes looks at how the potential for new applications of this seemingly miraculous material have been developed over the last 12 months.

A s long ago as January Belgian nano-electronics centre imec demonstrated a graphene-based optical modulator working at up to 10 Gbps, as part of its silicon photonics research programme investigating next- generation optical interconnect. Interest in graphene stems from the material’s ability to change its light-absorbing characteristics over a wide spectral range. “Graphene has a high potential for a wide-band modulator solution and also for an athermal design,” said Joris Van Campenhout, programme director for optical I/O at imec. He added, “The key achievement is that we have been able to show that you can operate at 10 Gigabit with very clean modulation eye diagrams.” Van Campenhout, believed that with design improvements, the modulator’s speed can reach 25 Gigabit. Jump forward to April 2018 and Japan’s Science and Technology Agency, based in Tokyo, had deployed high-speed, highly-integrated graphene-based on-silicon-chip blackbody emitters in the near-infrared (NIR) region including telecommunication wavelength. High- 2015, it was mooted there was a strong possibility that graphene might have applications in the optical communications industry.

speed light emitters integrated on silicon chips can support new architectures for silicon-based optoelectronics. However, compound-semiconductor-based light emitters faced major challenges for their integration with a silicon-based platform because of their difficulty of direct fabrication on a silicon substrate. Researchers found however that graphene-based blackbody emitters are also promising light emitters on silicon chip in NIR and mid-infrared region. But, although graphene-based blackbody emitters had been demonstrated under steady-state conditions or relatively slow modulation (100 kHz), the transient properties of these emitters under high-speed modulation had not been reported at the time. Also, the optical communications with graphene-based emitters had never been demonstrated. However, a highly integrated, high-speed and on-chip blackbody emitter based on graphene in NIR region including telecommunication wavelength was demonstrated. A fast response time of ~ 100 ps, which is ~ 105 higher than the previous graphene emitters, had been experimentally demonstrated for single and few-layer graphene, the emission responses could be controlled by the graphene contact with the substrate depending on the number of graphene

layers. Most importantly however, first real-time optical communication with graphene-based light emitters was experimentally demonstrated, indicating that graphene emitters are novel light sources for optical communication. The researchers reported, “We fabricated integrated, two-dimensional array emitters with large-scale graphene grown by chemical vapour deposition method and capped emitters operable in air, and carried out the direct coupling of optical fibres to the emitters owing to their small footprint and planar device structure.” Researchers found that graphene light emitters offer great advantageous over conventional compound semiconductor emitters because they can be highly integrated on silicon chip due to simple fabrication processes of graphene emitters and direct coupling with silicon waveguide through an evanescent field. Because graphene can realise high- speed, small footprint and on-Si-chip light emitters, which are still challenges for compound semiconductors, the graphene-based light emitters can open new routes to highly integrated optoelectronics and silicon photonics. ULTRA-BROAD BANDWIDTH In May 2018, the Graphene Flagship project in Cambridge, UK, Milan, and


| ISSUE 15 | Q4 2018

Made with FlippingBook - Online catalogs