  Future wireless communication networks have to handle data rates of tens or
even hundreds of Gbit/s per link, requiring carrier frequencies in the
unallocated terahertz (THz) spectrum. In this context, seamless integration of
THz links into existing fiber-optic infrastructures is of great importance to
complement the inherent portability and flexibility advantages of wireless
networks by the reliable and virtually unlimited capacity of optical
transmission systems. On the technological level, this requires novel device
and signal processing concepts for direct conversion of data streams between
the THz and the optical domains. Here, we report on the first demonstration of
a THz link that is seamlessly integrated into a fiber-optic network using
direct terahertz-to-optical (T/O) conversion at the wireless receiver. We
exploit an ultra-broadband silicon-plasmonic modulator having a 3 dB bandwidth
in excess of 0.36 THz for T/O conversion of a 50 Gbit/s data stream that is
transmitted on a 0.2885 THz carrier over a 16 m-long wireless link.
Optical-to-terahertz (O/T) conversion at the wireless transmitter relies on
photomixing in a uni-travelling-carrier photodiode.
