Coherent wireless THz transmission and reception with a Kramers-Kronig receiver

Previously, frequencies in the range f = (0.1…10)THz found mostly applications in molecular biology, medical imaging, security screening, and particle accelerators. Meanwhile, also terrestrial wireless THz communications has gained interest. The non-regulated frequency spectrum beyond 0.275THz has atmospheric transmission windows with a power attenuation of 2dB/km @ 0.2THz, 5dB/km @ 0.3THz, 20dB/km @ 0.4THz, and 70dB/km @ 0.9THz. The unity-gain free-space propagation loss over a distance of L = 100m amounts to adB = 120dB at λ = 1mm (f = 0.3THz). In this case, and with a point-to-point link having an antenna gain of about 100dBi, atmospheric losses are of secondary importance. To generate 16QAM signals at carrier frequencies f = 0.3THz, we use optical-to-terahertz conversion by photomixing in a unitravelling- carrier photodiode (UTC). At the receiver side, a simple Schottky-barrier diode (SBD) directly detects the signal’s intensity, from which the optical phase can be retrieved according to the Kramers-Kronig scheme. We demonstrate data transmission at a rate of 115 Gbit/s over a distance of 110m, and we discuss the complexity of the Kramers-Kronig receiver. ... mehrIn a lecture-hall point-to-multipoint demonstration, we use a frequency-steered leaky-wave antenna, and transmit with 16QAM signaling a total of 80 Gbit/s over 16m to a maximum number of four simultaneous users. For two users spaced 3.4m apart, we transmit 40Gbit/s per user. A monolithic microwave integrated circuit (MMIC) serves as the IQ receiver.