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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Optical Sensors".

Deadline for manuscript submissions: closed (20 April 2025) | Viewed by 7489

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Special Issue Editor

Dr. Alain Richard Ndjiongue

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Guest Editor

School of Science and Environment, Grenfell Campus, Memorial University of Newfoundland, 20 University Drive, Corner Brook, NL A2H 5G4, Canada
Interests: beyond 5G and 6G enabling technologies; optical wireless communications; hybrid optical wireless and radio frequency communications; reconfigurable intelligent surfaces and smart environments; physical layer security in wireless networks; visible light communications; power line communications

Special Issue Information

Dear Colleagues,

With the deployment of fifth-generation mobile systems and preparations ongoing for the sixth generation, optical communications technology is presented as a key concept. Such advances provide unprecedented communication capacity and cost-effective interconnections to support high-bandwidth applications.

This Special Issue, entitled “Challenges and Future Trends in Optical Communications”, explores this exciting field. It presents original and unpublished papers on all aspects of optical communication and networking. It focuses on optical systems research, development, and applications. Authors are invited to submit manuscripts for the Special Issue, including, but not limited to, the following topics (keywords).

Manuscripts must be submitted through the Sensors website; authors will need to register and proceed to the author center. Please then follow the links for the Special Issue on Challenges and Future Trends in Optical Communications.

Dr. Alain Richard Ndjiongue
Guest Editor

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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. Sensors is an international peer-reviewed open access semimonthly 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 2600 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

optical network protocols and architectures
physical layer security in optical networks
next-generation optical transport systems
performance analysis of optical communications and networks
optical devices and system architectures
optical networking for data center applications
digital signal processing for optical communications and systems
optical flexible networks and systems
cost-effective and green optical communications, networks, and systems
hybrid RF–optical systems and networks
testbeds for optical systems and network
free space optical communications systems
visible light communications
RIS-assisted optical systems
RIS-assisted hybrid RF-optical wireless communication systems and networks

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Published Papers (6 papers)

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Research

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13 pages, 4339 KiB

Open AccessArticle

FPGA Implementation for 24.576-Gbit/s Optical PAM4 Signal Transmission with MLP-Based Digital Pre-Distortion

by Sheng Hu, Tianqi Zheng, Chengzhen Bian, Xiongwei Yang, Xinda Sun, Zonghui Zhu, Yumeng Gou, Yuanxiao Meng, Jie Zhang, Jingtao Ge, Yichen Li and Kaihui Wang

Sensors 2024, 24(23), 7872; https://doi.org/10.3390/s24237872 - 9 Dec 2024

Cited by 1 | Viewed by 895

Abstract

In this work, we implemented a short-reach real-time optical communication system using MLP for pre-distortion. Lookup table (LUT) algorithms are commonly employed for pre-distortion in intensity modulation and direct detection (IM/DD) systems. However, storage limitations typically restrict the LUT pattern length to 9, limiting its effectiveness in compensating for nonlinear effects. A multilayer perceptron (MLP) can overcome this limitation by predicting errors and generating pre-distorted signals, thus replacing the extensive storage requirements of LUTs with minimal computational resources. The MLP-based digital pre-distortion (MLP-DPD) technique enables the creation of long-pattern LUTs for improved nonlinear compensation. In this work, an MLP-DPD scheme was implemented on a field-programmable gate array (FPGA). The FPGA was used to generate a 14.7456 GBaud pre-distorted pulse amplitude modulation 4-level (PAM4) signal. This signal was then transmitted over 20 km of standard single-mode fiber (SSMF). At the receiver, the parallel constant modulus algorithm (PCMA) was applied for signal processing. The bit error rate (BER) achieved met the 2.4 × 10⁻² threshold for soft-decision forward error correction (SD-FEC), enabling a net transmission bit rate of 24.576 Gbit/s. This approach demonstrates the feasibility of using MLP-DPD for effective nonlinear compensation in high-speed optical communication systems with limited resources. Full article

(This article belongs to the Special Issue Challenges and Future Trends in Optical Communications)

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11 pages, 12766 KiB

Open AccessCommunication

Few-Mode Fiber with Low Spontaneous Raman Scattering for Quantum Key Distribution and Classical Optical Communication Coexistence Systems

by Qi Zhao, Jianjun Tang, Weiwen Kong, Zhenyu Zhao, Jingjing Zheng and Yang Liu

Sensors 2024, 24(23), 7645; https://doi.org/10.3390/s24237645 - 29 Nov 2024

Viewed by 678

Abstract

In this paper, the theoretical model of spontaneous Raman scattering (SpRS) in few-mode fiber (FMF) is discussed. The influence of SpRS on quantum key distribution (QKD) in FMF is evaluated by combining wavelength division multiplexing (WDM) and space division multiplexing (SDM) techniques. On this basis, an improved ring-assisted FMF is designed and characterized; the transmission distance can be increased by up to 54.5% when choosing different multi-channels. The effects of forward and backward SpRS on QKD are also discussed. Full article

(This article belongs to the Special Issue Challenges and Future Trends in Optical Communications)

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27 pages, 5309 KiB

Open AccessArticle

A Case Study on the Integration of Powerline Communications and Visible Light Communications from a Power Electronics Perspective

by Felipe Loose, Juan Ramón Garcia-Meré, Adrion Andrei Rosanelli, Carlos Henrique Barriquello, José Antonio Fernandez Alvárez, Juan Rodríguez and Diego González Lamar

Sensors 2024, 24(20), 6627; https://doi.org/10.3390/s24206627 - 14 Oct 2024

Viewed by 1431

Abstract

This paper presents a dual-purpose LED driver system that functions as both a lighting source and a Visible Light Communication (VLC) transmitter integrated with a Powerline Communication (PLC) network under the PRIME G3 standard. The system decodes PLC messages from the powerline grid and transmits the information via LED light to an optical receiver under a binary phase shift keying (BPSK) modulation. The load design targets a light flux of 800 lumens, suitable for LED light bulb applications up to 10 watts, ensuring practicality and energy efficiency. The Universal Asynchronous Receiver-Transmitter (UART) module enables communication between the PLC and VLC systems, allowing for an LED driver with dynamic control and real-time operation. Key signal processing stages are commented and developed, including a hybrid buck converter with modulation capabilities and a nonlinear optical receiver to regenerate the BPSK reference signal for VLC. Results show a successful prototype working under a laboratory environment. Experimental validation shows successful transmission of bit streams from the PLC grid to the VLC setup. A design guideline is presented in order to dictate the design of the electronic devices involved in the experiment. Finally, this research highlights the feasibility of integrating PLC and VLC technologies, offering an efficient and cost-effective solution for data transmission over existing infrastructure. Full article

(This article belongs to the Special Issue Challenges and Future Trends in Optical Communications)

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14 pages, 3833 KiB

Open AccessArticle

Real-Time Indoor Visible Light Positioning (VLP) Using Long Short Term Memory Neural Network (LSTM-NN) with Principal Component Analysis (PCA)

by Yueh-Han Shu, Yun-Han Chang, Yuan-Zeng Lin and Chi-Wai Chow

Sensors 2024, 24(16), 5424; https://doi.org/10.3390/s24165424 - 22 Aug 2024

Cited by 3 | Viewed by 1312

Abstract

New applications such as augmented reality/virtual reality (AR/VR), Internet-of-Things (IOT), autonomous mobile robot (AMR) services, etc., require high reliability and high accuracy real-time positioning and tracking of persons and devices in indoor areas. Among the different visible-light-positioning (VLP) schemes, such as proximity, time-of-arrival (TOA), time-difference-of-arrival (TDOA), angle-of-arrival (AOA), and received-signal-strength (RSS), the RSS scheme is relatively easy to implement. Among these VLP methods, the RSS method is simple and efficient. As the received optical power has an inverse relationship with the distance between the LED transmitter (Tx) and the photodiode (PD) receiver (Rx), position information can be estimated by studying the received optical power from different Txs. In this work, we propose and experimentally demonstrate a real-time VLP system utilizing long short-term memory neural network (LSTM-NN) with principal component analysis (PCA) to mitigate high positioning error, particularly at the positioning unit cell boundaries. Experimental results show that in a positioning unit cell of 100 × 100 × 250 cm³, the average positioning error is 5.912 cm when using LSTM-NN only. By utilizing the PCA, we can observe that the positioning accuracy can be significantly enhanced to 1.806 cm, particularly at the unit cell boundaries and cell corners, showing a positioning error reduction of 69.45%. In the cumulative distribution function (CDF) measurements, when using only the LSTM-NN model, the positioning error of 95% of the experimental data is >15 cm; while using the LSTM-NN with PCA model, the error is reduced to <5 cm. In addition, we also experimentally demonstrate that the proposed real-time VLP system can also be used to predict the direction and the trajectory of the moving Rx. Full article

(This article belongs to the Special Issue Challenges and Future Trends in Optical Communications)

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14 pages, 4452 KiB

Open AccessArticle

A New Internet of Things Hybrid VLC/RF System for m-Health in an Underground Mining Industry

by Daniel Iturralde, Javier Guaña-Moya, Pablo Palacios Játiva, Iván Sánchez, Muhammad Ijaz, Ali Dehghan Firoozabadi and David Zabala-Blanco

Sensors 2024, 24(1), 31; https://doi.org/10.3390/s24010031 - 20 Dec 2023

Cited by 5 | Viewed by 1785

Abstract

This paper proposes a new system based on the Industrial Internet of Things (IIoT) for the monitoring of Mobile Health (m-Health) of workers in the underground mining industry. The proposed architecture uses a hybrid model in data transmission. Visible Light Communication (VLC) is used for downlink because of its narrow coverage, which aids in worker positioning. Radio frequency (RF) communication technology is used to send data for primary vital signs in the uplink, which is more efficient in transmission and is a viable solution according to the problem raised. The results obtained in terms of coverage and transmission for the downlink and uplink links show the feasibility of implementing the proposed system. Full article

(This article belongs to the Special Issue Challenges and Future Trends in Optical Communications)

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Review

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34 pages, 3195 KiB

Open AccessReview

Beyond Fiber: Toward Terahertz Bandwidth in Free-Space Optical Communication

by Rahat Ullah, Sibghat Ullah, Jianxin Ren, Hathal Salamah Alwageed, Yaya Mao, Zhipeng Qi, Feng Wang, Suhail Ayoub Khan and Umar Farooq

Sensors 2025, 25(7), 2109; https://doi.org/10.3390/s25072109 - 27 Mar 2025

Viewed by 475

Abstract

The rapid advancement of terahertz (THz) communication systems has positioned this technology as a key enabler for next-generation telecommunication networks, including 6G, secure communications, and hybrid wireless-optical systems. This review comprehensively analyzes THz communication, emphasizing its integration with free-space optical (FSO) systems to overcome conventional bandwidth limitations. While THz-FSO technology promises ultra-high data rates, it is significantly affected by atmospheric absorption, particularly absorption beyond 500 GHz, where the attenuation exceeds 100 dB/km, which severely limits its transmission range. However, the presence of a lower-loss transmission window at 680 GHz provides an opportunity for optimized THz-FSO communication. This paper explores recent developments in high-power THz sources, such as quantum cascade lasers, photonic mixers, and free-electron lasers, which facilitate the attainment of ultra-high data rates. Additionally, adaptive optics, machine learning-based beam alignment, and low-loss materials are examined as potential solutions to mitigating signal degradation due to atmospheric absorption. The integration of THz-FSO systems with optical and radio frequency (RF) technologies is assessed within the framework of software-defined networking (SDN) and multi-band adaptive communication, enhancing their reliability and range. Furthermore, this review discusses emerging applications such as self-driving systems in 6G networks, ultra-low latency communication, holographic telepresence, and inter-satellite links. Future research directions include the use of artificial intelligence for network optimization, creating energy-efficient system designs, and quantum encryption to obtain secure THz communications. Despite the severe constraints imposed by atmospheric attenuation, the technology’s power efficiency, and the materials that are used, THz-FSO technology is promising for the field of ultra-fast and secure next-generation networks. Addressing these limitations through hybrid optical-THz architectures, AI-driven adaptation, and advanced waveguides will be critical for the full realization of THz-FSO communication in modern telecommunication infrastructures. Full article

(This article belongs to the Special Issue Challenges and Future Trends in Optical Communications)

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