Karlsruhe Series in Photonics & Communications, Vol. 24 Tobias Harter Wireless THz Communications: Optoelectronic Devices and Signal Processing Tobias Harter Wireless Terahertz Communications: Optoelectronic Devices and Signal Processing Karlsruhe Series in Photonics & Communications, Vol. 24 Edited by Profs. C. Koos, W. Freude and S. Randel Karlsruhe Institute of Technology (KIT) Institute of Photonics and Quantum Electronics (IPQ) Germany Wireless Terahertz Communications: Optoelectronic Devices and Signal Processing by Tobias Harter Karlsruher Institut für Technologie Institut für Photonik und Quantenelektronik Wireless Terahertz Communications: Optoelectronic Devices and Signal Processing Zur Erlangung des akademischen Grades eines Doktor-Ingenieurs von der KIT-Fakultät für Elektrotechnik und Informationstechnik des Karlsruher Instituts für Technologie (KIT) genehmigte Dissertation von Tobias Harter, M.Sc. Mündliche Prüfung: 28. November 2019 Hauptreferent: Prof. Dr. Christian Koos Korreferenten: Prof. Dr. Dr. h. c. Wolfgang Freude Prof. Dr. Guillermo Carpintero-del-Barrio Impressum Karlsruher Institut für Technologie (KIT) KIT Scientific Publishing Straße am Forum 2 D-76131 Karlsruhe KIT Scientific Publishing is a registered trademark of Karlsruhe Institute of Technology. Reprint using the book cover is not allowed. www.ksp.kit.edu This document – excluding the chapters 3 to 5, C to E, the cover, pictures and graphs – is licensed under a Creative Commons Attribution-Share Alike 4.0 International License (CC BY-SA 4.0): https://creativecommons.org/licenses/by-sa/4.0/deed.en The cover page is licensed under a Creative Commons Attribution-No Derivatives 4.0 International License (CC BY-ND 4.0): https://creativecommons.org/licenses/by-nd/4.0/deed.en Print on Demand 2021 – Gedruckt auf FSC-zertifiziertem Papier ISSN 1865-1100 ISBN 978-3-7315-1083-3 DOI 10.5445/KSP/1000128941 Table of Contents Kurzfassung ....................................................................................................... v Preface ..............................................................................................................ix Achievements of the present work .................................................................xi 1 Introduction ................................................................................................. 1 2 THz communications and devices ............................................................. 5 2.1 Fundamentals of T-wave communications ........................................ 6 2.1.1 Baseband and bandpass signals .............................................. 6 2.1.2 Mixer and balanced mixer ...................................................... 8 2.1.3 Digital communications ....................................................... 10 2.1.4 T-wave communication channel .......................................... 12 2.2 T-wave transmitters: State of the art ................................................ 15 2.2.1 Electronic transmitters ......................................................... 15 2.2.2 Optoelectronic transmitters .................................................. 17 2.3 T-wave receivers: State of the art ..................................................... 18 2.3.1 Electronic receivers .............................................................. 19 2.3.2 Optoelectronic receivers....................................................... 19 2.4 T-wave communications: State of the art ......................................... 20 3 Kramers-Kronig receiver for coherent THz communications ............. 23 3.1 Introduction ...................................................................................... 24 3.2 Future wireless backbone networks ................................................. 25 3.3 Generalized Kramers-Kronig processing ......................................... 26 3.4 Experimental setup and results ......................................................... 30 3.5 Summary........................................................................................... 36 4 Wireless THz link with optoelectronic transmitter and receiver ......... 39 4.1 Introduction and background ........................................................... 40 4.2 Implementation of optoelectronic receiver ...................................... 43 4.3 Demonstration of wireless T-wave links .......................................... 45 4.3.1 Single-channel transmission and wideband tunability ......... 46 4.3.2 Multi-channel transmission .................................................. 50 i Table of Contents 4.3.3 Potential for further improvements ..................................... 52 4.4 Summary .......................................................................................... 54 5 Silicon-plasmonic integrated circuits for THz signal generation and coherent detection ............................................................................. 55 5.1 Introduction ..................................................................................... 56 5.2 Silicon-plasmonic T-wave systems ................................................. 58 5.3 PIPED for optoelectronic T-wave processing ................................. 60 5.4 Demonstration of T-wave generation and detection ....................... 65 5.5 Monolithically integrated T-wave system ....................................... 72 5.6 Summary and outlook ...................................................................... 74 6 Summary and Outlook ............................................................................ 77 6.1 Summary .......................................................................................... 77 6.2 Outlook and future work ................................................................. 78 Appendices ...................................................................................................... 81 A. Important antenna parameters .............................................................. 83 A.1 Aperture of an isotropic antenna ..................................................... 84 A.2 Free-space path loss ......................................................................... 85 B. Photodiode implementations ................................................................... 87 C. Kramers-Kronig receiver ........................................................................ 91 C.1 Methods ........................................................................................... 91 C.2 Experimental setup .......................................................................... 97 C.3 Model of the Schottky-barrier diode receiver ................................. 99 C.4 Characterization of SBD receiver .................................................. 102 C.5 THz link budget and noise analysis ............................................... 106 C.6 Spectral broadening by non-quadratic SBD characteristics .......... 110 C.7 Oversampling requirements in the DSP ........................................ 111 C.8 32QAM measurements .................................................................. 114 C.9 Comparison of generalized Kramers-Kronig processing and heterodyne detection with guard band ........................................... 115 C.10 Comparison of EVM for QPSK and 16QAM ............................... 117 C.11 Outdoor performance ..................................................................... 118 C.12 Comparison of phase retrieval algorithms .................................... 119 ii Table of Contents D. Optoelectronic THz receiver .................................................................. 123 D.1 Mathematical model ....................................................................... 123 D.2 T-wave receiver .............................................................................. 125 D.3 Wireless T-wave communication link............................................ 131 D.4 T-wave amplifiers and UTC-PD .................................................... 136 D.5 Link budget and noise analysis ...................................................... 140 E. Silicon-plasmonic integrated circuits .................................................... 145 E.1 Methods .......................................................................................... 145 E.2 Detailed derivation of formulae ..................................................... 151 E.3 Calibration of T-wave Tx and Rx reference .................................. 154 E.4 Antenna-coupled Tx and Rx .......................................................... 155 E.5 T-wave Rx ...................................................................................... 156 E.6 Damage threshold ........................................................................... 158 E.7 Operating conditions of Rx ............................................................ 159 E.8 Equivalent-circuit of T-wave systems ............................................ 160 E.9 Frequency roll-off ........................................................................... 168 E.10 Simulation of frequency-dependent radiated Tx power ................. 170 E.11 Electric field distribution of integrated T-wave system ................. 172 E.12 Conversion from S-parameters to Z-parameters ............................ 173 E.13 Performance improvement ............................................................. 174 F. 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