Mr. Jiancang Liu Profile

Jiancang Liu

at National Univ of Defense Technology

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Proceedings Article | 4 December 2024 Paper

Study on the propagation performance of OAM-hopping in atmospheric turbulence channel

Yadi Chen, Jiancang Liu, Bing Lei

Proceedings Volume 13283, 132830C (2024) https://doi.org/10.1117/12.3033048

KEYWORDS: Turbulence, Atmospheric turbulence, Free space optics, Telecommunications, Optical transmission, Atmospheric propagation, Resistance, Signal intensity, Signal detection, Optical simulations

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Free space optical communication (FSO) is susceptible to atmospheric turbulence, which greatly affects the practical application of atmospheric laser communication. In this paper, we explore a simple and effective anti-atmospheric turbulence technique based on the feasibility study of orbital angular momentum beam (OAM) hopping. Different modes of OAM beams with distinct topological charges are sequentially transmitted within a symbol period to achieve diversity gains by ensuring orthogonality among them and varying spatial paths. The transmission characteristics of OAM beams in atmospheric turbulence are analyzed, and an intensity modulation/direct detection (IM/DD) FSO model is established under the Gamma-Gamma atmospheric turbulence channel. By comparing the power fluctuation and bit error rate (BER) of the communication system employing OAM-hopping with single-mode beams system, the effects of mode spacing and the number of mode hopping on the turbulence resistance capability of the OAM-hopping mechanism are investigated. Simulation results demonstrate that, under moderate turbulence conditions (𝐶_n² = 1 × 10⁻¹³), using the mode set {+1, +3, +5} for OAM-hopping transmission reduces the power fluctuations and BER by approximately 10.6% and 20.1%, respectively, compared to the system using only a single-mode beam for transmission. The research findings validate the feasibility and effectiveness of OAM mode-hopping technology for turbulence-resistant applications in FSO, providing an important technical approach to enhance the performance of FSO systems in atmospheric turbulence.

Proceedings Article | 1 November 2021 Paper

Improving the stability of turbulent FSO links by utilizing OAM-hopping

Jiancang Liu, Bing Lei

Proceedings Volume 12057, 120574W (2021) https://doi.org/10.1117/12.2607082

KEYWORDS: Free space optics, Turbulence, Atmospheric turbulence, Gaussian beams, Scintillation, Telecommunications, Spiral phase plates, Signal detection, Adaptive optics, Receivers

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Free-Space optical (FSO) communication is severely affected by atmospheric turbulence, causing the decrease of link stability and even link outage. We explore a new scheme to reduce the effects of atmospheric turbulence by introducing the OAM (orbital angular momentum) Hopping into FSO communication systems. In this approach, the Gaussian optical carrier is switched randomly to different spiral phase plates (SPPs) via a high-speed optical switch and is converted into the OAM beam. The switch rate is up to serval times of symbol rate, and the distribution of turbulence can be regarded as static in a symbol period. The OAM beam whose topologic charge changes randomly will experience different fading in atmospheric turbulence due to different size of waist and phase distribution, and the diversity gain is achieved during this process without additional optical antenna. The possibility of all OAM modes falling into deep fade at the same symbol period is much less than a single mode or a single Gaussian beam transmitting system, which helps to improve the link performance. According to the numerical simulation results, OAM-hopping can effectively reduce the received power fluctuations under moderate atmospheric turbulence, and the degree of improvement will become more obvious with the increase of turbulence intensity. The OAM-hopping can also be combined with traditional mitigation technologies of turbulence effects such as adaptive optics (AO) and multiple input multiple output (MIMO) to obtain further improvement.

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