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Photonics
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Free-Space Optical Communication and Networking Technology
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Free-Space Optical Communication and Networking Technology

A special issue of Photonics (ISSN 2304-6732). This special issue belongs to the section "Optoelectronics and Optical Materials".

Deadline for manuscript submissions: 20 June 2025 | Viewed by 6545

Special Issue Editor

Prof. Dr. Zhi Liu

E-Mail Website
Guest Editor
National and Local Joint Engineering Research Center of Space Optoelectronics Technology, Changchun University of Science and Technology, Changchun 130022, China
Interests: space laser communication and networking technology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The focus of researchers in the field of free-space optical communication (FSOC) lies in improving communication performance in various channels, including free space, the Earth's atmosphere, seawater, and interstellar space. This Special Issue aims to explore different aspects that contribute to enhancing FSOC performance in these channels.

The topics to be covered include the networking mechanism of many-to-many simultaneous laser communication optical routing, modeling and simulation of multi-hop laser communication links, multi-link simultaneous bidirectional transmission and reception between different nodes in dynamic networks, optical routing technology, all-optical switching and wavelength conversion, as well as the technology of a communication network’s main node and the efficient coupling technology of space beams to optical fiber.

The current research on FSOC technology encompasses various areas. This includes advanced optical terminal and photoelectric system fusion designs to improve the signal-to-noise ratio of light; the utilization of efficient pointing, acquiring, and tracking (APT) units to enhance beam pointing accuracy; investigating the impact of atmospheric turbulence and seawater channels on light wave performance to determine optimal design parameters; employing advanced modulation, demodulation, and error correction coding technology to achieve higher transmission rates and lower bit error rates (BERs); studying FSOC ad hoc network protocols and advanced network topology structures to facilitate networking applications; and more.

In light of these research areas, this Special Issue aims to foster discussions on the related technologies of FSOCs, enabling researchers to gain a better understanding of the objectives that promote the advancement of FSOC technology. We welcome high-quality submissions related, but not limited, to the following topics:

  • Present and future optical wireless communication terminals, systems and links;
  • Atmospheric propagation, transmission effects and compensation techniques;
  • Adaptive optics, modulation, demodulation, coding and decoding technologies;
  • Advanced optical signal processing technologies;
  • Optical communication ad hoc networks and network topologies;
  • Visible-light and underwater optical communication technologies.

Researchers are encouraged to submit complete unpublished papers with their contributions, exploring emerging technologies toward optical wireless communication.

Prof. Dr. Zhi Liu
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Photonics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • free-space optical communications
  • optical signal processing
  • optical communication network
  • optical propagation
  • adaptive optics

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Published Papers (5 papers)

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Research

11 pages, 3271 KiB  
Article
Focal Plane Array Based on Silicon Nitride for Optical Beam Steering at 2 Microns
by Qing Gao, Jiaqi Li, Jincheng Wei, Jinjie Zeng, Dong Yang, Xiaoqun Yu, Mingshen Peng, Hongwen Xuan, Ruijun Wang and Yanfeng Zhang
Photonics 2025, 12(5), 448; https://doi.org/10.3390/photonics12050448 - 5 May 2025
Viewed by 351
Abstract
The 2 μm wavelength is ideal for light detection and ranging and gas sensing due to its eye-safe operation, strong molecular absorption targeting, and low atmospheric scattering—critical for environmental monitoring and free-space communications. The existing 2 μm systems rely on mechanical beam steering, [...] Read more.
The 2 μm wavelength is ideal for light detection and ranging and gas sensing due to its eye-safe operation, strong molecular absorption targeting, and low atmospheric scattering—critical for environmental monitoring and free-space communications. The existing 2 μm systems rely on mechanical beam steering, which limits speed and reliability. Integrated photonic solutions have not yet been demonstrated in this wavelength. We propose a focal plane array design to address these challenges. Compared to optical phased arrays requiring complex phase control for each antenna, FPAs have a simple switch-based control and high suppression of background noise. Although FPAs need an external lens for beam collimation, they significantly reduce system complexity. This study introduces a compact, low-loss 1 × 8 focal plane array operating in the 2 μm range, employing a cascaded Mach–Zehnder interferometer switch array on a silicon nitride platform. The device demonstrates a field of view of 16.8°, background suppression better than 17 dB, and excess loss of −1.4 dB. This integrated photonic beam steering solution offers a highly promising, cost-effective approach for rapid beam switching. This integrated photonic beam steering solution offers a highly promising, cost-effective approach for rapid beam switching. Full article
(This article belongs to the Special Issue Free-Space Optical Communication and Networking Technology)
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12 pages, 2134 KiB  
Article
A Self-Healing WDM Access Network with Protected Fiber and FSO Link Paths Effective Against Fiber Breaks
by Tsu-Hsin Wu, Chien-Yu Liao, Chien-Hung Yeh, Yuan-Wen Chen, Yu-Hsin Kao, Sung-Yi Lin, Yu-Heng Lin and Shien-Kuei Liaw
Photonics 2025, 12(4), 323; https://doi.org/10.3390/photonics12040323 - 30 Mar 2025
Viewed by 232
Abstract
In this article, an additional protected fiber and free-space optical (FSO) link path is proposed, to provide self-healing capabilities for protection against fiber faults in wavelength division multiplexed passive optical network (WDM-PON) systems. The new optical line terminal (OLT), remote node (RN), and [...] Read more.
In this article, an additional protected fiber and free-space optical (FSO) link path is proposed, to provide self-healing capabilities for protection against fiber faults in wavelength division multiplexed passive optical network (WDM-PON) systems. The new optical line terminal (OLT), remote node (RN), and optical network unit (ONU) in the presented PON architecture result in self-protective function against fiber breakpoints. In the measurement, 25 Gbit/s on-off keying (OOK) modulation was applied on each WDM channel to assess the downstream and upstream signals after 25 km single-mode fiber (SMF) and 25 km SMF + 2 m FSO connections, respectively. In addition to using protected fiber paths for self-healing operations. This PON system can also apply the FSO link method. The measured bit error rate (BER) for all downstream and upstream traffic was maintained below 3.8 × 10−3 with forward error correction (FEC). The detected optical power sensitivity of the proposed self-restorative fiber- and FSO-based WDM-PON for downstream and upstream WDM signals ranged from −33.5 to −28.5 dBm and from −33 to −28.5 dBm, respectively, and the corresponding power budgets of the downstream and upstream WDM signals were between 29.5 and 30.5 dB and 33 and 38 dB, respectively. Full article
(This article belongs to the Special Issue Free-Space Optical Communication and Networking Technology)
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9 pages, 6017 KiB  
Article
Manchester Return-to-Zero On–Off Keying Modulation for Free-Space Optical Communication
by Wenhao Zong, Qianwen Jing, Minfang Liu, Yan Gao and Yanqing Hong
Photonics 2024, 11(6), 496; https://doi.org/10.3390/photonics11060496 - 24 May 2024
Cited by 2 | Viewed by 1136
Abstract
This paper proposes a Manchester return-to-zero on–off keying (M-RZ-OOK) modulation for free-space optical (FSO) communication. M-RZ-OOK modulation is achieved by introducing Manchester coding into the RZ-OOK format. M-RZ-OOK has the features of phase-flipped impulse series in the spectrum. Therefore, normal and inversed channel [...] Read more.
This paper proposes a Manchester return-to-zero on–off keying (M-RZ-OOK) modulation for free-space optical (FSO) communication. M-RZ-OOK modulation is achieved by introducing Manchester coding into the RZ-OOK format. M-RZ-OOK has the features of phase-flipped impulse series in the spectrum. Therefore, normal and inversed channel state information (CSI) can be extracted by applying a local oscillator (LO) with the frequencies of impulses, respectively. These extracted CSIs can be applied to realize adaptive threshold decision (ATD) and adaptive power transmission (APT) in the forward and backward links simultaneously. The proposed M-RZ-OOK modulation was verified in simulations using various turbulence channels. The simulation results demonstrated that ATD and APT were effectively accomplished in the forward and backward links with the estimated normal and inversed CSIs. Full article
(This article belongs to the Special Issue Free-Space Optical Communication and Networking Technology)
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14 pages, 7186 KiB  
Article
The Application of a Fisheye Lens in the Automatic Alignment of Wireless Optical Communication
by Haoyu Xu and Xizheng Ke
Photonics 2024, 11(4), 344; https://doi.org/10.3390/photonics11040344 - 9 Apr 2024
Viewed by 1681
Abstract
To achieve a lightweight design and wide field of view for the automatic alignment system in wireless optical communication, in the receiving antenna—a fisheye lens is incorporated as the receiving optical system. This feature enables the detection and tracking of lasers. The system [...] Read more.
To achieve a lightweight design and wide field of view for the automatic alignment system in wireless optical communication, in the receiving antenna—a fisheye lens is incorporated as the receiving optical system. This feature enables the detection and tracking of lasers. The system utilizes a micro motor as the control servo system and a four-quadrant detector as the detection unit. Sequential and non-sequential ray tracing techniques were used to simulate the analysis of the fish-eye lens. Point array diagrams, ray trace diagrams, and encircled energy analysis were utilized to evaluate the spot’s quality. The simulation results demonstrate that the fish-eye lens has a field of view of 120°, and the spot with 80% energy has a diameter smaller than 30 μm. The experimental results indicate that the fish-eye lens effectively captures the light beam within the range of ±30°. The simulated and experimental results for the sum and difference frequency amplitudes show good agreement. The outdoor experiments have demonstrated a tracking error of 22.757 μrad in this system. After alignment, the average output optical power of the detector is 3.23 μW, and the detected waveform amplitude is 12.48 mV. These findings demonstrate the system’s potential for automatic alignment in wireless optical communication. Additionally, the system is relatively simple and practical. Full article
(This article belongs to the Special Issue Free-Space Optical Communication and Networking Technology)
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12 pages, 7946 KiB  
Article
All-in-One BPSK/QPSK Switchable Transmission and Reception for Adaptive Free-Space Optical Communication Links
by Yaling Chen, Chengze Ming, Ke Xie, Shiming Gao, Qingfang Jiang, Zhi Liu, Haifeng Yao and Keyan Dong
Photonics 2024, 11(4), 326; https://doi.org/10.3390/photonics11040326 - 30 Mar 2024
Cited by 2 | Viewed by 2020
Abstract
Adaptive free-space optical (FSO) communication links have been extensively studied in order to adapt to variable atmospheric channel environments due to factors such as atmospheric turbulence. As a supporting technology, an all-in-one BPSK/QPSK switchable transmission and reception method is proposed and experimentally demonstrated [...] Read more.
Adaptive free-space optical (FSO) communication links have been extensively studied in order to adapt to variable atmospheric channel environments due to factors such as atmospheric turbulence. As a supporting technology, an all-in-one BPSK/QPSK switchable transmission and reception method is proposed and experimentally demonstrated for adaptive modulation format switching in FSO links. The transmission and reception of both modulation formats are realized based on the same IQ modulator and single-photodetector coherent receiver. Simulation and experimental results show that the QPSK signal has a power penalty of about 3–4 dB compared to the BPSK signal with a BER of about 1 × 10−3. The basis for format switching is given according to the various atmospheric channel conditions. The proposed method provides a flexible and efficient solution for variable FSO communication environments to improve their performance. Full article
(This article belongs to the Special Issue Free-Space Optical Communication and Networking Technology)
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