Optical communication formed the backbone of the internet age and is expected to be equally pivotal for the developing 5G networks. Modern communications rely on optical links that fly information at the speed of light, and on circuitry such as photodetectors and modulators which is able to encode a wealth of information onto these light beams. Although silicon is the material of choice for photonic waveguides on optical chips, photodetectors are made from other semiconductors such as GaAs, InP, or GaN, because silicon is transparent at standard telecomm wavelengths. Integrating these other semiconductors with silicon is difficult, complicating fabrication processes and raising expenses. Also, thermal management is becoming a problem as photonic devices keep shrinking while using more power.
Graphene is a promising material for telecomm photodetectors, because it absorbs light over a large bandwidth, including standard telecomm wavelengths. It is also compatible with CMOS technology, which means it can be technologically integrated with silicon photonics. Furthermore, graphene is an excellent heat conductor, promising a reduction in heat consumption of graphene-based photonic devices. For these reasons, graphene for optical communications has been an intense field of research, which is now gaining fruition in full working prototypes.
The first graphene photodetectors were developed in a research lab at IBM already in 2009. These transistor-based photodetectors had bandwidths exceeding 25 GHz and were subsequently used to transfer data over a 10 Gbit s-1 optical data link. The efficiency of detection in those devices was improved by employing an asymmetric metal-graphene-metal transistor configuration. Analysis suggests that the bandwidth of such graphene photodetectors may ultimately exceed 500 GHz.
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