Abstract

Free-space optical (FSO) communication links can benefit from recovering both amplitude- and phase-encoded data (e.g., quadrature-amplitude-modulation, QAM) by mixing a local oscillator (LO) with a received data beam in a coherent detector. However, atmospheric turbulence can cause power coupling from a fundamental Gaussian mode of the data beam to higher-order modes, resulting in a significantly degraded mixing efficiency between the data and a fundamental Gaussian LO. Previously, a turbulence-resilient pilot-assisted self-coherent FSO QAM link has been demonstrated by transmitting a frequency-offset Gaussian pilot beam along with the Gaussian data beam. The pilot and data beams experienced similar modal coupling and thus can efficiently mix in a self-heterodyne detector. However, a frequency guard band was used to avoid signal-signal beating interference, thereby reducing the utilization efficiency of the detector's bandwidth. To increase the detector's bandwidth utilization, we experimentally demonstrate in this article a turbulence-resilient 12-Gbit/s 16-QAM FSO link using pilot-assisted self-homodyne detection. The pilot beam is located at the same center optical frequency as the data channel but on an orthogonal polarization. At the receiver, we utilize self-homodyne detection to achieve the efficient mixing of the data and pilot. Compared to self-heterodyne, our approach has ∼2X the utilization efficiency of the detector's bandwidth. Compared to conventional LO-based coherent (homodyne or intradyne) detection, the pilot-assisted self-homodyne link shows up to ∼20-dB improvement of optical-to-electrical mixing efficiency under a turbulence strength of $2{{\boldsymbol{w}}}_0/ \ {{\boldsymbol{r}}}_0 = \ \sim\! {\boldsymbol{7}}.{\boldsymbol{5}}$ . The turbulence resilience of the link is demonstrated with a bit-error rate below the 7% forward error correction limit for 400 different turbulence realizations.

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)

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)

Automatic turbulence mitigation for coherent free-space optical links using crystal-based phase conjugation and fiber-coupled data modulation

Huibin Zhou, Yuxiang Duan, Hao Song, Xinzhou Su, Zhe Zhao, Kaiheng Zou, Haoqian Song, Runzhou Zhang, Robert W. Boyd, Moshe Tur, and Alan E. Willner
Opt. Lett. 48(8) 2194-2197 (2023)

16-QAM optical packet switching and real-time self-homodyne detection using polarization-multiplexed pilot-carrier

Satoshi Shinada, Moriya Nakamura, Yukiyoshi Kamio, and Naoya Wada
Opt. Express 20(26) B535-B542 (2012)

Demonstration of 120 Gbit/s turbulence-resilient coherent optical communication employing cylindrical vector beam multiplexing

Yong Yu, Mingfeng Xu, Mingbo Pu, Jiazheng Ding, Shuangcheng Chen, Yiqun Zhang, Mengjie Zhou, Yinghui Guo, Xiong Li, Xiaoliang Ma, and Xiangang Luo
Opt. Express 31(25) 42165-42175 (2023)