Experimental Demonstration of sub-THz Wireless Communications Using Multiplexing of Laguerre-Gaussian Beams When Varying Two Different Modal Indices

Amir Minoofar, Xinzhou Su, Huibin Zhou, Runzhou Zhang, Fatemeh Alishahi, Kaiheng Zou, Hao Song, Kai Pang, Shlomo Zach, Moshe Tur, Andreas Molisch, Hirofumi Sasaki, Doohwan Lee, Alan E. Willner

Research output: Contribution to journalArticlepeer-review

Abstract

The ability to multiplex multiple structured beams for sub-terahertz (sub-THz) wireless communications has been recently explored. The spatial orthogonality of structured beams enables mode-division multiplexing (MDM). In an MDM system, multiple data-carrying beams are transmitted and received simultaneously through a single aperture pair with low inherent crosstalk. This can increase data capacity and spectral efficiency of the system. Here, we experimentally demonstrate multiplexing orthogonal sub-THz Laguerre-Gaussian (LG_(l,p)) beams when varying two different modal indices (i.e., both l and p); this contrasts with prior reports when varying only one index (i.e., l) and could potentially provide a larger set of channels and beams in an MDM system. In our demonstration, specially designed phase patterns are used: (1) at the transmitter, to convert two THz Gaussian beams to two different LG beams, each carrying an independent data channel; and (2) at the receiver, to separate and convert the LG beams back to Gaussian-like THz beams. An 8-Gbit/s quadrature-phase-shift-keying (QPSK) link containing two multiplexed LG modes over 40 cm is experimentally demonstrated. For the above link, three different LG modal sets are chosen (i.e., {LG_(-2,0) and LG_(1,1)} or {LG_(3,0) and LG_(0,1)} or {LG_(2,1) and LG_(0,1)}). All channels are recovered with bit error rates (BERs) below the 7% forward error correction (FEC) limit. The experimental results indicate that: (a) higher-order LG modes experience more divergence, larger size, and lower conversion efficiency, contributing to higher power loss; and (b) the modal coupling and crosstalk for different LG modes is < -12 dB, which could be due to the transmitter/receiver misalignments as well as beam truncation by the limited-sized receiver aperture.

Original languageEnglish
JournalJournal of Lightwave Technology
DOIs
StateAccepted/In press - 2022

Keywords

  • Apertures
  • Diffraction
  • Diffraction gratings
  • Frequency division multiplexing
  • Laguerre-Gaussian modes
  • Laser beams
  • Multiplexing
  • Optical transmitters
  • mode-division multiplexing (MDM)
  • terahertz communication
  • terahertz photonics

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