Photonics

Research

Jump to: Review

13 pages, 11936 KiB

Open AccessArticle

Performance of Adaptive Bit-Interleaved Polar Coded Modulation in FSOC System

by Qingfang Jiang, Zhi Liu, Haifeng Yao, Zhonglin Luo, Xin Zhang, Shutong Liu, Chenming Cao, Gang Jing, Hao Li and Peng Lin

Photonics 2024, 11(1), 34; https://doi.org/10.3390/photonics11010034 - 29 Dec 2023

Viewed by 817

Abstract

This paper proposes an adaptive bit-interleaved polar coded modulation (A-BIPCM) method based on minimum logarithmic upper bound weight (MLUW). It is designed to reduce the fading effects and long string of bit error interference caused by atmospheric turbulence in free-space optical communications (FSOC). [...] Read more.

This paper proposes an adaptive bit-interleaved polar coded modulation (A-BIPCM) method based on minimum logarithmic upper bound weight (MLUW). It is designed to reduce the fading effects and long string of bit error interference caused by atmospheric turbulence in free-space optical communications (FSOC). To assess the effectiveness of this method across turbulent channels of varying intensities, we conducted an evaluation of the bit error rate (BER) performance of polar codes in turbulent channels. The results demonstrate significant performance improvements provided by the A-BIPCM method compared to conventional polar code encoding and decoding. Specifically, under weak, moderate, and strong turbulence conditions, the A-BIPCM method achieves performance gains of 0.96 dB, 1.66 dB, and 1.35 dB, respectively. Additionally, an experimental verification platform for FSOC employing intensity modulation direct detection (IM/DD) with an atmospheric turbulence simulation channel, is established in this work. When the optical power of the detector is −16 dBm, the traditional polar code encoding and decoding performance at BER = 2.36 × 10⁻⁵, whereas the A-BIPCM scheme exhibits a significantly higher performance at BER = 2.11 × 10⁻⁶. The BER has been improved by representing an order of magnitude. Full article

(This article belongs to the Special Issue Space Laser Communication and Networking Technology)

► Show Figures

Figure 1

22 pages, 2683 KiB

Open AccessArticle

Performance Analysis of Multi-Hop FSOC over Gamma-Gamma Turbulence and Random Fog with Generalized Pointing Errors

by Yidi Chang, Zhi Liu, Haifeng Yao, Shiming Gao, Keyan Dong and Shutong Liu

Photonics 2023, 10(11), 1240; https://doi.org/10.3390/photonics10111240 - 8 Nov 2023

Cited by 2 | Viewed by 869

Abstract

The multi-hop amplify-and-forward free-space optical communication (FSOC) system is studied in random fog using the I-function, considering Gamma-Gamma atmospheric turbulence and Beckmann pointing error. Outage probability, average bit error rate and average ergodic channel capacity are obtained. Channel-state-information assisted relay performs better [...] Read more.

The multi-hop amplify-and-forward free-space optical communication (FSOC) system is studied in random fog using the I-function, considering Gamma-Gamma atmospheric turbulence and Beckmann pointing error. Outage probability, average bit error rate and average ergodic channel capacity are obtained. Channel-state-information assisted relay performs better than fixed-gain relay under high transmitted power. Increasing the hop number significantly improves the performance. More hops are needed in medium fog than in light fog to achieve the same performance. In addition, on a single-hop link, the influence of fog channel on system performance is dominant, while atmospheric turbulence intensity, normalized jitter standard deviation and normalized boresight error have little effect on the system performance. However, on a multi-hop link, atmospheric turbulence intensity, normalized jitter standard deviation and normalized boresight error have serious effects on system performance. Compared with correcting the normalized boresight error, compensating the normalized jitter standard deviation greatly improves the multi-hop FSOC system performance. Furthermore, optimizing beam width can further improves the performance. To ensure good communication, the system should select a low-order modulation scheme. Full article

(This article belongs to the Special Issue Space Laser Communication and Networking Technology)

► Show Figures

Figure 1

10 pages, 1868 KiB

Open AccessArticle

Channel Performance Analysis of Visible Light Communication Technology in the Internet of Vehicles

by Xinyi Liu, Hao Zhang, Qiqi Ma, Xin Zhao and Chenqi Di

Photonics 2023, 10(11), 1197; https://doi.org/10.3390/photonics10111197 - 27 Oct 2023

Viewed by 803

Abstract

The emergence of visible light communication technology has alleviated the pressure of wireless network communication and provided new ways for vehicle networking technology. Therefore, it is necessary to analyze the performance changes in visible light communication in vehicle networking communication. This article mainly [...] Read more.

The emergence of visible light communication technology has alleviated the pressure of wireless network communication and provided new ways for vehicle networking technology. Therefore, it is necessary to analyze the performance changes in visible light communication in vehicle networking communication. This article mainly considers the impact of vehicle speed on the quality of visible light communication technology services during the driving duration. Firstly, the impact of vehicle speed on signal-to-noise ratio changes was analyzed. Secondly, the channel states in different V2I/V2V scenarios were analyzed. Finally, the transformation in signal-to-noise ratio in V2I/V2V scenarios was analyzed through simulation. Full article

(This article belongs to the Special Issue Space Laser Communication and Networking Technology)

► Show Figures

Figure 1

16 pages, 11996 KiB

Open AccessArticle

Research on Bandwidth Improvement of Fine Tracking Control System in Space Laser Communication

by Furui Lv, Yongkai Liu, Shijie Gao, Hao Wu and Feng Guo

Photonics 2023, 10(11), 1179; https://doi.org/10.3390/photonics10111179 - 24 Oct 2023

Viewed by 986

Abstract

Piezoelectric fast steering mirror (PZT FSM) is the core component of the fine tracking system for space laser communication, and its actuator is a piezoelectric ceramic. Consequently, there is a hysteretic nonlinear disturbance throughout the entire range of the FSM’s steering. To enhance [...] Read more.

Piezoelectric fast steering mirror (PZT FSM) is the core component of the fine tracking system for space laser communication, and its actuator is a piezoelectric ceramic. Consequently, there is a hysteretic nonlinear disturbance throughout the entire range of the FSM’s steering. To enhance the fine tracking system’s performance, this paper innovatively analyzes and verifies the effect of the PZT FSM hysteresis characteristics on the error suppression bandwidth of the fine tracking system. Firstly, the rate-dependent hysteresis model is established by serially connecting the Prandtl–Ishlinskii (P-I) model with the dynamic linear mode. The inverse model is designed as a feedforward controller, followed by the conduction of open-loop feedforward compensation experiments. Subsequently, we propose a compound control method based on the rate-dependent hysteresis mode and conduct a simulation analysis. Finally, the experimental platform for the fine tracking system is set up, and the optimization effect of compensating for hysteresis nonlinearity on the fine tracking system is verified. The experimental results show that the nonlinearity of the PZT FSM is improved by 30% in the middle- and high-frequency ranges, and the error suppression bandwidth of the fine tracking system is improved by 41.7%. This effectively enhances the fine tracking system’s error suppression capability. Full article

(This article belongs to the Special Issue Space Laser Communication and Networking Technology)

► Show Figures

Figure 1

19 pages, 20594 KiB

Open AccessArticle

Fresnel Lens Array-Based Phase Mask Location Method for Adjustable Multi-Pass Cavity

by Ximing Wang, Xichang Yu, Tianyu Yang, Cheng Ruan, Shijie Gao and Lie Ma

Photonics 2023, 10(9), 1059; https://doi.org/10.3390/photonics10091059 - 19 Sep 2023

Cited by 1 | Viewed by 936

Abstract

The modulation accuracy of Multi-Plane Light Conversion (MPLC) mainly depends on the positioning accuracy of the phase mask on the Spatial Light Modulator (SLM). To improve positioning accuracy, the impact of phase mask shift on modulation accuracy is investigated, and a position method [...] Read more.

The modulation accuracy of Multi-Plane Light Conversion (MPLC) mainly depends on the positioning accuracy of the phase mask on the Spatial Light Modulator (SLM). To improve positioning accuracy, the impact of phase mask shift on modulation accuracy is investigated, and a position method is proposed. In order to investigate the influence of phase mask offset on the input light conversion effect, a convolution transmission model for the adjustable multi-pass cavity is established. Then, the positioning process for the phase masks is analyzed and simulated, and a method of positioning the phase masks is presented. This method reduces the positioning time and increases the positioning accuracy to 8 μm. Finally, experiments are performed to verify the feasibility of the method. Experimental results show that the similarity of the adjustable multi-pass cavity positioned by this method can reach 93.44%. Full article

(This article belongs to the Special Issue Space Laser Communication and Networking Technology)

► Show Figures

Figure 1

14 pages, 4548 KiB

Open AccessArticle

Study on the Difference of Wavefront Distortion on Beams Caused by Wavelength Differences in Weak Turbulence Region

by Jiali Wu, Xizheng Ke, Weilong Kang, Jingyuan Liang and Chenghu Ke

Photonics 2023, 10(7), 725; https://doi.org/10.3390/photonics10070725 - 25 Jun 2023

Cited by 3 | Viewed by 858

Abstract

In dual-wavelength free-space optical communication systems, the wavefront distortion differences caused by the wavelength difference of the signal and beacon lights cannot be completely corrected. In this study, according to the method of geometric optics, the relationship between the wavefront phases of the [...] Read more.

In dual-wavelength free-space optical communication systems, the wavefront distortion differences caused by the wavelength difference of the signal and beacon lights cannot be completely corrected. In this study, according to the method of geometric optics, the relationship between the wavefront phases of the signal and beacon lights is analyzed by establishing a mathematical model of the cross-correlation ratio of the arrival-angle fluctuation and phase relationship of different Gaussian-beam wavelengths under weak turbulence near the surface. The numerical results show that after Gaussian beams of different wavelengths propagate through the same atmospheric channel, the cross-correlation number of the arrival-angle fluctuation decreases with an increase in the wavelength difference, waist radius, and turbulence intensity, and increases with an increase in propagation distance. The beam-wavefront phase difference increases with an increasing wavelength difference. Finally, a wavefront distortion correction experiment of a dual-wavelength adaptive optical system verified the correctness of the wavefront phase-difference relationship between the signal light and beacon light established in this study. Full article

(This article belongs to the Special Issue Space Laser Communication and Networking Technology)

► Show Figures

Figure 1

17 pages, 5058 KiB

Open AccessArticle

Effect of Wavefront Distortion in Non-Kolmogorov Turbulence on the Performance of Multi-Beam Transmission Coherent Detection

by Chenghu Ke, Tian Xing and Xizheng Ke

Photonics 2023, 10(7), 718; https://doi.org/10.3390/photonics10070718 - 23 Jun 2023

Viewed by 1075

Abstract

This study aims to address the multi-beam transmission problem of optical wireless coherent communication systems under the influence of non-Kolmogorov turbulence. This paper establishes the mathematical model for mixing efficiency and BER of non-Kolmogorov turbulence wavefront distortion and multi-beam transmission coherent detection systems. [...] Read more.

This study aims to address the multi-beam transmission problem of optical wireless coherent communication systems under the influence of non-Kolmogorov turbulence. This paper establishes the mathematical model for mixing efficiency and BER of non-Kolmogorov turbulence wavefront distortion and multi-beam transmission coherent detection systems. The influence of factors such as spectral power-law index, zenith angle, and transmission distance on the communication performance of the system is analyzed, and an experimental system is built using adaptive optics equipment to test the proposed theory. Numerical analyses show that in a non-Kolmogorov turbulence environment, as the spectral power-law index, zenith angle, transmission distance, Fresnel zone, and pointing error attenuation increase, the mixing efficiency of the coherent detection system decreases and the BER increases; under the same conditions, the mixing efficiency and BER of the system are improved after increasing the number of transmission beams at the transmitting end. Experimental research shows that, for the coherent detection system after wavefront correction using adaptive optics, the wavefront PV and RMS variances are 1.68 μm² and 0.05 μm² when a single beam of light is transmitted at the transmitting end, and the wavefront PV and RMS variances are 0.23 μm² and 0.01 μm² when two beams are transmitted. It is verified that using multi-beam transmission wavefront superposition to suppress wavefront distortion and wavefront jitter can effectively improve the mixing efficiency and BER of the coherent detection system at the receiving end. Full article

(This article belongs to the Special Issue Space Laser Communication and Networking Technology)

► Show Figures

Figure 1

23 pages, 7176 KiB

Open AccessArticle

Effect of Wavefront Distortion on the Performance of Coherent Detection Systems: Theoretical Analysis and Experimental Research

by Shangjun Yang, Tian Xing, Chenghu Ke, Jingyuan Liang and Xizheng Ke

Photonics 2023, 10(5), 493; https://doi.org/10.3390/photonics10050493 - 24 Apr 2023

Viewed by 1019

Abstract

Atmospheric turbulence causes signal beam wavefront distortion at the receiving end of a coherent detection system, which decreases the system mixing efficiency. Based on the coherent detection theory, this study establishes a mathematical model of wavefront distortion with mixing efficiency and mixing gain. [...] Read more.

Atmospheric turbulence causes signal beam wavefront distortion at the receiving end of a coherent detection system, which decreases the system mixing efficiency. Based on the coherent detection theory, this study establishes a mathematical model of wavefront distortion with mixing efficiency and mixing gain. It also analyzes the improvement limits of wavefront correction on mixing efficiency and mixing gain under different atmospheric turbulence intensities and experimentally measures them. Simulation results show that the mixing efficiency can be improved to 51%, 55%, and 60% after correcting for tilt, defocus, and astigmatism terms, respectively, when turbulence intensity D/r₀ is 2. The mixing gain with homodyne detection is 3 dB higher than heterodyne detection. Meanwhile, the wavefront correction orders required for optimal mixing efficiency are higher than the heterodyne correction order. In the experiment, Haso4 NIR + DM 40 was used, and the turbulence intensity D/r₀ was 2. After the closed-loop control algorithm corrects the tilt, defocus, and astigmatism terms, the indoor experimental results showed that the mixing efficiency is improved to 36%, 47%, and 62%, respectively. The outdoor experimental results showed that the mixing efficiency improved to 36%, 51%, and 68%, respectively. Full article

(This article belongs to the Special Issue Space Laser Communication and Networking Technology)

► Show Figures

Figure 1

Review

Jump to: Research

25 pages, 11921 KiB

Open AccessReview

A Review of Variable-Beam Divergence Angle FSO Communication Systems

by Guoqiang Zhang, Jiabin Wu, Yatian Li, Ximing Wang, Xichang Yu, Shijie Gao and Lie Ma

Photonics 2023, 10(7), 756; https://doi.org/10.3390/photonics10070756 - 30 Jun 2023

Cited by 3 | Viewed by 2328

Abstract

Free-space optical (FSO) communication is widely used in satellites, ships, aircraft, and ground stations due to its advantages of high speed, large capacity, good confidentiality, and strong anti-interference ability. Variable-beam divergence angle (VBDA) technology makes FSO systems more flexible; this has the benefits [...] Read more.

Free-space optical (FSO) communication is widely used in satellites, ships, aircraft, and ground stations due to its advantages of high speed, large capacity, good confidentiality, and strong anti-interference ability. Variable-beam divergence angle (VBDA) technology makes FSO systems more flexible; this has the benefits of higher acquisition probability, stronger tracking ability, wider communication link range, and lower energy consumption. In other words, the study of VBDA has both theoretical significance and practical relevance. This paper conducts a comprehensive search of relevant scientific databases, journals, conference proceedings, patents, and books to identify publications related to VBDA technology. We analyze these publications, classify and organize various VBDA techniques based on their respective methods. To the best of our knowledge, this is the first review of VBDA technology. In this paper, we first explain the basic principle of changing the beam divergence angle by employing the ABCD matrix, and further furnish a detailed overview of the methods used for VBDA along with their corresponding advantages and disadvantages. In addition, we provide a comprehensive summary of the research conducted using VBDA technology across different link types. Lastly, we identify the challenges and potential future research directions for VBDA technology. Full article

(This article belongs to the Special Issue Space Laser Communication and Networking Technology)

► Show Figures