Terahertz Communication: A Story of Bandwidth and Silicon Photonic Integration

The need for faster wireless data is ever-increasing. This puts pressure on the radio spectrum as most sub-6 GHz bands are already congested. Moving to higher bands, in the mmWave and Terahertz (THz) spectrum, unlocks large ranges of bandwidth. At these THz frequencies, however, high-gain directive beams are needed to compensate the higher path loss. Phased Antenna Arrays (PAA) provide this gain but need efficient beamforming feeding networks. In contrast to all-electrical approaches, an optical beamforming network (OBFN) is able to scale to large planar arrays. This is thanks to its small-footprint – as the radio signals are modulated on an optical carrier with a much smaller waveguide - and low-loss waveguides in Silicon Photonic (SiPh) platforms - feeding every individual antenna element. Generating THz signals is then only limited by the efficiency of the photomixer, i.e. a photodetector that converts the beat note of two optical signals to a THz signal. To this end, we have integrated a photodiode with a bandwidth of 155 GHz on a Silicon Nitride (SiN) waveguide and demonstrated its capabilities in a back-to-back THz link at 280 GHz. Doing so, we achieved data rates beyond 100 Gbit/s