Abstract-Generalized Kramers–Kronig receiver for coherent terahertz communications

T. Harter, C. Füllner, J. N. Kemal, S. Ummethala, J. L. Steinmann, M. Brosi, J. L. Hesler, E. Bründermann, A.-S. Müller, W. Freude, S. Randel, C. Koos

https://www.nature.com/articles/s41566-020-0675-0

Modern communication systems rely on efficient quadrature amplitude modulation formats that encode information on both the amplitude and phase of an electromagnetic carrier. Coherent detection of such signals typically requires complex receivers that contain a continuous-wave local oscillator as a phase reference and a mixer circuit for spectral down-conversion. In optical communications, the so-called Kramers–Kronig scheme has been demonstrated to simplify the receiver, reducing the hardware to a single photodiode1,2,3. In this approach, a local-oscillator tone is transmitted along with the signal, and the amplitude and phase of the complex signal envelope are digitally reconstructed from the photocurrent by exploiting their Kramers–Kronig-type relation4,5,6. Here, we transfer the Kramers–Kronig scheme to high-speed wireless communications at terahertz carrier frequencies. To this end, we generalize the approach to account for non-quadratic receiver characteristics and employ a Schottky-barrier diode as a nonlinear receiver element. Using 16-state quadrature amplitude modulation, we transmit a net data rate of 115 Gbit s−1 at a carrier frequency of 0.3 THz over a distance of 110 m.

Abstract-Silicon–plasmonic integrated circuits for terahertz signal generation and coherent detection

T. Harter, S. Muehlbrandt, S. Ummethala, A. Schmid, S. Nellen, L. Hahn, W. Freude,  C. Koos,

https://www.nature.com/articles/s41566-018-0237-x

Optoelectronic signal processing offers great potential for generation and detection of ultra-broadband waveforms in the terahertz range (so-called T-waves). However, fabrication of the underlying devices still relies on complex processes using dedicated III–V semiconductor substrates. This severely restricts the application potential of current T-wave transmitters and receivers and impedes co-integration of these devices with advanced photonic signal processing circuits. Here, we demonstrate that these limitations can be overcome by plasmonic internal-photoemission detectors (PIPEDs). PIPEDs can be realized on the silicon photonic platform, which allows exploiting the enormous opportunities of the associated device portfolio. In our experiments, we demonstrate both T-wave signal generation and coherent detection at frequencies up to 1 THz. To prove the viability of our concept, we monolithically integrate PIPED transmitters and receivers on a common silicon chip and use them to measure the complex transfer impedance of an integrated T-wave device.

Abstract-Wireless sub-THz communication system with high data rate

Prospective application scenario for a long-range, high-capacity wireless communication link at terahertz frequencies. (Here, the wireless link bridges a broad river in difficult-to-access terrain to provide high-speed internet access in remote and rural areas. The figure shows key elements of our 100 Gbit s⁻¹ SISO wireless link at 237.5 GHz carrier frequencies).

• S. Koenig,
• D. Lopez-Diaz,
• J. Antes,
• F. Boes,
• R. Henneberger,
• A. Leuther,
• A. Tessmann,
• R. Schmogrow,
• D. Hillerkuss,
• R. Palmer,
• T. Zwick,
• C. Koos,
• W. Freude,
• O. Ambacher,
• J. Leuthold
• & I. Kallfass

In communications, the frequency range 0.1–30 THz is essentially terra incognita. Recently, research has focused on this terahertz gap, because the high carrier frequencies promise unprecedented channel capacities¹. Indeed, data rates of 100 Gbit s⁻¹ were predicted² for 2015. Here, we present, for the first time, a single-input and single-output wireless communication system at 237.5 GHz for transmitting data over 20 m at a data rate of 100 Gbit s⁻¹. This breakthrough results from combining terahertz photonics and electronics, whereby a narrow-band terahertz carrier is photonically generated by mixing comb lines of a mode-locked laser in a uni-travelling-carrier photodiode. The uni-travelling-carrier photodiode output is then radiated over a beam-focusing antenna. The signal is received by a millimetre-wave monolithic integrated circuit comprising novel terahertz mixers and amplifiers. We believe that this approach provides a path to scale wireless communications to Tbit s⁻¹ rates over distances of >1 km.