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 ( ${{\bf L}}{{{\bf G}}_{\ell,{{\bf p}}}}$ ) beams when varying two different modal indices (i.e., both $\ell $ and ${{\bf p}}$ ); this contrasts with prior reports when varying only one index (i.e., $\ell $ ) 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., { ${{\bf L}}{{{\bf G}}_{ - 2,0}}$ and ${{\bf L}}{{{\bf G}}_{1,1}}$ } or { ${{\bf L}}{{{\bf G}}_{3,0}}$ and ${{\bf L}}{{{\bf G}}_{0,1}}$ } or { ${{\bf L}}{{{\bf G}}_{2,1}}$ and ${{\bf L}}{{{\bf G}}_{0,1}}$ }). All channels are recovered with bit errorrates (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.

Experimental demonstration of a 200-Gbit/s free-space optical link by multiplexing Laguerre–Gaussian beams with different radial indices

Guodong Xie, Yongxiong Ren, Yan Yan, Hao Huang, Nisar Ahmed, Long Li, Zhe Zhao, Changjing Bao, Moshe Tur, Solyman Ashrafi, and Alan E. Willner
Opt. Lett. 41(15) 3447-3450 (2016)

400-Gbit/s QPSK free-space optical communication link based on four-fold multiplexing of Hermite–Gaussian or Laguerre–Gaussian modes by varying both modal indices

Kai Pang, Haoqian Song, Zhe Zhao, Runzhou Zhang, Hao Song, Guodong Xie, Long Li, Cong Liu, Jing Du, Andreas F. Molisch, Moshe Tur, and Alan E. Willner
Opt. Lett. 43(16) 3889-3892 (2018)

Demonstration of a 10  Mbit/s quantum communication link by encoding data on two Laguerre–Gaussian modes with different radial indices

Kai Pang, Cong Liu, Guodong Xie, Yongxiong Ren, Zhe Zhao, Runzhou Zhang, Yinwen Cao, Jiapeng Zhao, Haoqian Song, Hao Song, Long Li, Ari N. Willner, Moshe Tur, Robert W. Boyd, and Alan E. Willner
Opt. Lett. 43(22) 5639-5642 (2018)

Adaptive-optics-based turbulence mitigation in a 400 Gbit/s free-space optical link by multiplexing Laguerre–Gaussian modes varying both radial and azimuthal spatial indices

Xinzhou Su, Zile Jiang, Yuxiang Duan, Huibin Zhou, Hao Song, Kai Pang, Cong Liu, Kaiheng Zou, Runzhou Zhang, Haoqian Song, Nanzhe Hu, Moshe Tur, and Alan E. Willner
Opt. Lett. 48(24) 6452-6455 (2023)

Demonstration of turbulence mitigation in a 200-Gbit/s orbital-angular-momentum multiplexed free-space optical link using simple power measurements for determining the modal crosstalk matrix

Nanzhe Hu, Haoqian Song, Runzhou Zhang, Huibin Zhou, Cong Liu, Xinzhou Su, Hao Song, Kai Pang, Kaiheng Zou, Brittany Lynn, Moshe Tur, and Alan E. Willner
Opt. Lett. 47(14) 3539-3542 (2022)