Abstract

We experimentally demonstrate turbulence-resilient free-space optical (FSO) coherent communications with multiple multiplexed data channels in different orthogonal domains, including mode, polarization, and wavelength. The turbulence resiliency is enabled by utilizing pilot-assisted optoelectronic mixing of the received beams, wherein one pilot is being mixed with its corresponding beam. By transmitting additional continuous-wave (CW) pilot tones, whose frequencies are offset from the data-carrying beams, and mixing all pilot tones and beams in a single free-space-coupled photodetector (PD) at the receiver, the turbulence-induced modal coupling could be efficiently suppressed. The paper first discusses an experimental demonstration of a turbulence-resilient mode-division-multiplexed (MDM) FSO communication link using two orbital angular momentum (OAM) beams. Each OAM beam carries an independent 2-Gbit/s quadrature-phase-shift-keying (QPSK) data channel. Experimental results indicate that (i) the channel crosstalk under both the weaker and stronger turbulence distortions are measured to be lower than ∼−25.7 dB, (ii) the turbulence-induced OAM modal coupling could be effectively suppressed for the emulated 15 random turbulence realizations, and (iii) the error-vector magnitudes (EVM) of the multiplexed QPSK data channels are measured to be lower than by 17.4% and 19.8% under the relatively weaker and stronger turbulence effects, respectively. The paper subsequently describes an experimental demonstration of a turbulence-resilient FSO link with eight 0.5-Gbit/s QPSK data channels multiplexing two OAM beams (l = +1 & l = −2), two polarizations, and two wavelengths. The measured bit-error rates (BERs) of all data channels under turbulence effects are below the 7% forward-error-correction (FEC) limit, with power penalties less than ∼3.7 dB.

Turbulence mitigation of four mode-division-multiplexed QPSK channels in a pilot-assisted self-coherent free-space optical link using a photodetector array and DSP-based channel demultiplexing

Huibin Zhou, Hao Song, Xinzhou Su, Yuxiang Duan, Kaiheng Zou, Runzhou Zhang, Moshe Tur, and Alan E. Willner
Opt. Lett. 49(5) 1209-1212 (2024)

Turbulence-resilient pilot-assisted self-coherent free-space optical communications using a photodetector array for bandwidth enhancement

Hao Song, Runzhou Zhang, Huibin Zhou, Xinzhou Su, Kaiheng Zou, Yuxiang Duan, Narek Karapetyan, Haoqian Song, Kai Pang, Nanzhe Hu, Amir Minoofar, Moshe Tur, and Alan E. Willner
Opt. Lett. 47(21) 5723-5726 (2022)

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)

Turbulence-resistant high-capacity free-space optical communications using OAM mode group multiplexing

Long Zhu, Mingliang Deng, Bing Lu, Xiaojin Guo, and Andong Wang
Opt. Express 31(9) 14454-14463 (2023)

Crosstalk mitigation using pilot assisted least square algorithm in OFDM-carrying orbital angular momentum multiplexed free-space-optical communication links

Tengfen Sun, Minwen Liu, Yingchun Li, and Min Wang
Opt. Express 25(21) 25707-25718 (2017)