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FEATURE: PHOTONIC INTEGRATION


GRAPHENE DREAMS


GRAPHENE COULD TRANSFORM NETWORKS IF ITS REMARKABLE PROPERTIES CAN SUSTAIN A VIABLE SUPPLY CHAIN


ANDY EXTANCE D


aniel Schall’s experiments in 2009 quickly demonstrated to him and his colleagues ‘that the optical properties of graphene were absolutely unique’.


Together with results from Heinrich Kurz’s team at RWTH Aachen, Germany, Schall’s PhD findings at the nearby company that Kurz founded, AMO, promised great things. ‘Te question was: can we build an


electro-optic device like a photodetector or modulator?’ Schall recalls. By 2011, the team had waveguide-integrated devices ready, some based on large-scale CVD graphene, some based on graphene flaked from graphite. When, in 2014, AMO published several results on detectors and modulators ‘it became clear that the process steps involved should be possible on wafers’, Schall said. He and his colleagues demonstrated the first wafer-based results in 2015. ‘Today we have a graphene photonics platorm and we fabricate more than a thousand devices on a wafer,’ Schall continued, including prototype photodetectors and modulators. AMO is not doing this in isolation. It’s part


of the Graphene Flagship project in Europe that started in 2013. Te project aims to establish a supply chain intending to exploit


10 FiBRE SYSTEMS n Issue 26 n Winter 2020


the wonder material’s well-known properties, such as electron mobility over a hundred times greater than silicon. Tere remain practical and commercialisation hurdles to overcome, but progress so far has been promising. ‘Bandwidth is absolutely important in optical


communication and graphene devices are naturally fast,’ explained Schall. ‘Graphene has this unique set of properties that do not require any alteration or manipulation for high performance electro-optic devices. Our next step is to come from research-level devices demonstrating certain performance, to real products. We expect graphene photodetectors to be marketable in the near future.’


Performance indicators Nokia is also involved in the Graphene Flagship project. Wolfgang Templ, manager of the wireless transceiver research department at Nokia Bell Labs in Stutgart, said that the company is interested in ‘future communication systems beyond 5G which need to deal with bitrates over 1Tb/s per optical channel.’ With its project partners, Nokia has started investigating graphene electro-optical and opto-electrical converters. ‘We integrate the components


provided by our research partners into our communication systems and analyse and assess their performance,’ Templ said. Such applications benefit from graphene’s


high charge carrier mobility. ‘Graphene might get into an enabling role with a unique selling point if we succeed in maintaining its inherent properties during the device integration process,’ he said. ‘Moreover, based on the material’s electronic properties, graphene-based photonic components feature a wide spectral tuning range. Tis feature perfectly serves the needs of future dynamically reconfigurable networks.’ Yet Templ believes that delivering on


theoretical predictions about the superior performance of graphene is the biggest challenge faced by the Graphene Flagship. ‘Te properties of the pristine material predicted by theory degrade substantially when it comes to physical component realisation,’ he said. ‘Te crystallographic quality of graphene layers is still not sufficient for achieving the required high carrier mobilities, and the contacts still feature too-high sheet resistance.’ As such, today’s graphene-based optical modulators are still behind the overall performance of equivalent


www.fibre-systems.com @fibresystemsmag


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