Generalized Kramers-Kronig Receiver for Coherent THz Communications

TL;DR

This paper extends the Kramers-Kronig receiver concept to high-speed THz wireless communications, simplifying receiver hardware and achieving 115 Gbit/s data rate over 110 meters using 16QAM modulation.

Contribution

It introduces a generalized KK processing method for THz signals using Schottky diodes, enabling high-speed data transmission with simplified receiver architecture.

Findings

Achieved 115 Gbit/s data rate with 16QAM at 0.3 THz

Successfully transmitted over 110 meters

Generalized KK theory for nonlinear THz devices

Abstract

High-speed communication systems rely on spectrally efficient modulation formats that encode information both on the amplitude and on the phase of an electromagnetic carrier. Coherent detection of such signals typically uses rather complex receiver schemes, requiring a continuous-wave (c.w.) local oscillator (LO) as a phase reference and a mixer circuit for spectral down-conversion. In optical communications, the so-called Kramers-Kronig (KK) scheme has been demonstrated to greatly simplify the receiver, reducing the hardware to a single photodiode. In this approach, an LO tone is transmitted along with the signal, and the amplitude and phase of the complex signal envelope are reconstructed from the photocurrent by digital signal processing. This reconstruction exploits the fact that the real and the imaginary part, or, equivalently, the amplitude and the phase of an analytic signal are connected by a KK-type relation. Here, we transfer the KK scheme to high-speed wireless communications at THz carrier frequencies. We use a Schottky-barrier diode (SBD) as a nonlinear element and generalize the theory of KK processing to account for the non-quadratic characteristics of this device. Using 16-state quadrature amplitude modulation (16QAM), we transmit a net data rate of 115 Gbit/s at a carrier frequency of 0.3 THz over a distance of 110 m.