Microwave plasmonic mixer in a transparent fibre-wireless link.

To cope with the high bandwidth requirements of wireless applications1, carrier frequencies are shifting towards the millimetre-wave and terahertz bands2-5. Conversely, data is normally transported to remote wireless antennas by optical fibres. Therefore, full transparency and flexibility to switch between optical and wireless domains would be desirable6,7. Here, we demonstrate for the first time a direct wireless-to-optical receiver in a transparent optical link. We successfully transmit 20 and 10 Gbit/s over wireless distances of 1 and 5 m at a carrier frequency of 60 GHz, respectively. Key to the breakthrough was a plasmonic mixer directly mapping the wireless information onto optical signals. The plasmonic scheme with its subwavelength feature and pronounced field confinement provides a built-in field enhancement of up to 90'000 over the incident field in an ultra-compact and CMOS compatible structure. The plasmonic mixer is not limited by electronic speed and thus compatible with future terahertz technologies.