Modal coupling and crosstalk due to turbulence and divergence on free space THz links using multiple orbital angular momentum beams

Zhe Zhao*, Runzhou Zhang, Hao Song, Kai Pang, Ahmed Almaiman, Huibin Zhou, Haoqian Song, Cong Liu, Nanzhe Hu, Xinzhou Su, Amir Minoofar, Hirofumi Sasaki, Doohwan Lee, Moshe Tur, Andreas F. Molisch, Alan E. Willner

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

26 Scopus citations

Abstract

Orbital-angular-momentum (OAM) multiplexing has been utilized to increase the channel capacity in both millimeter-wave and optical domains. Terahertz (THz) wireless communication is attracting increasing attention due to its broadband spectral resources. Thus, it might be valuable to explore the system performance of THz OAM links to further increase the channel capacity. In this paper, we study through simulations the fundamental system-degrading effects when using multiple OAM beams in THz communications links under atmospheric turbulence. We simulate and analyze the effects of divergence, turbulence, limited-size aperture, and misalignment on the signal power and crosstalk of THz OAM links. We find through simulations that the system-degrading effects are different in two scenarios with atmosphere turbulence: (a) when we consider the same strength of phasefront distortion, faster divergence (i.e., lower frequency; smaller beam waist) leads to higher power leakage from the transmitted mode to neighbouring modes; and (b) however, when we consider the same atmospheric turbulence, the divergence effect tends to affect the power leakage much less, and the power leakage increases as the frequency, beam waist, or OAM order increases. Simulation results show that: (i) the crosstalk to the neighbouring mode remains < − 15 dB for a 1-km link under calm weather, when we transmit OAM + 4 at 0.5 THz with a beam waist of 1 m; (ii) for the 3-OAM-multiplexed THz links, the signal-to-interference ratio (SIR) increases by ~ 5–7 dB if the mode spacing increases by 1, and SIR decreases with the multiplexed mode number; and (iii) limited aperture size and misalignment lead to power leakage to other modes under calm weather, while it tends to be unobtrusive under bad weather.

Original languageEnglish
Article number2110
JournalScientific Reports
Volume11
Issue number1
DOIs
StatePublished - Dec 2021

Funding

FundersFunder number
Airbus Institute for Engineering Research
Defense Security Cooperation AgencyDSCA 4440646262
National Science FoundationECCS-1509965
National Science Foundation
Office of Naval ResearchN00014-16-1-2813
Office of Naval Research
Qualcomm
Astrophysics Science Division
Office of the Assistant Secretary for Research and Technology
Nippon Telegraph and Telephone

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