The strength of graphene's optical absorption can be tuned by controlling its charge carrier density, which makes it promising for use as a miniature broadband optical modulator. Ming Liu and co-workers from the University of California in Berkeley and Lawrence Berkeley National Lab in the USA have now presented a device design that comprises a 400-nm-wide, 40-μm-long silicon wire waveguide covered by a graphene–Al2O3–graphene sandwich, which functions as a p–oxide–n junction. Grating couplers with a period of 780 nm are used to couple 1,537 nm light in and out of the device. The researchers report a modulation depth of up to 6.5 dB and a peak transmission of −25 dB, with most of the loss being due to the grating couplers. Their measurements also indicate that the modulator has a 3 dB bandwidth of 1 GHz and a modulation depth of around 0.16 dB μm−1 per unit length at a drive voltage of approximately 5 V. The researchers say that using multiple pairs of double-layer graphene could further reduce the footprint and energy consumption of the device.
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Won, R. Double-layer graphene boost. Nature Photon 6, 268 (2012). https://doi.org/10.1038/nphoton.2012.95
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DOI: https://doi.org/10.1038/nphoton.2012.95