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

Deadline for manuscript submissions: closed (15 December 2024) | Viewed by 27345

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Special Issue Editors

Dr. Tianxu Xu

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Guest Editor

National Center for International Joint Research of Electronic Materials and Systems, School of Electrical and Information Engineering, Zhengzhou University, Zhengzhou 450001, China
Interests: optical imaging; optical sensing; computer vision

Dr. Kaiheng Zou

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Guest Editor

Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA
Interests: optical communications

Dr. Cong Liu

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Guest Editor

Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA
Interests: optical communication; quantum optics; nonlinear optics

Prof. Dr. Yang Yue

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Guest Editor

School of Information and Communications Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Interests: intelligent photonics; optical communications; optical perception; optical chip
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

With the iterative upgrade and popular application of new information technologies such as 5G, cloud computing, big data, and artificial intelligence, the global data traffic and the demand for computing power has ushered in explosive growth. Traditional data transmission speed, information capacity and chip computing performance can no longer meet the processing needs of big data. Recent progress in optical technologies has highlighted a feasible development route for these contradictions. In particular, optical communication, optical perception, and optical chips are considered to be the most promising research directions in the future. At present, optical communication focuses on core technical issues, including larger bandwidth, lower latency, and smaller packet loss rate, to ensure that high-quality networks meet and support the development of new industries, such as 4K/8K live broadcast, VR/AR, and free-view video; optical perception technology has the advantages of convenient acquisition, low cost, and a large amount of information. With the continuous innovation of basic theory and analysis technology, researchers are devoted to developing the perception system, constructing a multi-dimensional image knowledge system, and promoting the development of image theory and application to a deeper level. As a design that closely matches the optical computing architecture and the artificial intelligence algorithm, optical chip has the advantages of high-speed parallelism and low power consumption and can solve many problems in the application fields such as long processing time and high power consumption. The above-mentioned research cover the core technologies in key fields to provide high speed, wide bandwidth, large volume and low power consumption.

This Special Issue focuses on the state-of-the-art advancements in optical technologies for communication, perception, and chips. Digital, electrical, and optical signal processing theories, artificial intelligence, integrated chips, devices, subsystems/systems, as well as future perspectives are all within the scope. Topics of interest include, but are not limited to, the following areas:

Active and passive optical devices;
Digital signal processing for sensing and communication;
Fiber optics;
Integrated optics;
Nonlinear photonics;
Optical AI: optical neural networking, neuromorphic;
Optical communications and networking;
Optical for 5G/6G;
Optical imaging and display;
Optical sensing and perception;
Optical signal processing;
Optoelectronic signal processing devices;
Semiconductor optical chips;
Signal processing for 3D/AR/VR.

Dr. Tianxu Xu
Dr. Kaiheng Zou
Dr. Cong Liu
Prof. Dr. Yang Yue
Guest Editors

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Keywords

optical communications
optical computing
optical sensing
optical perception
optical chip
optical device
optical waveguide

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Published Papers (11 papers)

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Research

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15 pages, 4019 KiB

Open AccessArticle

Demodulation of Fibre Bragg Grating Sensors by Using Cumulative Sum as a Preprocessing Method

by Sławomir Cięszczyk, Marek Kida and Patryk Panas

Sensors 2025, 25(3), 634; https://doi.org/10.3390/s25030634 - 22 Jan 2025

Viewed by 740

Abstract

Fibre Bragg gratings are one of the most popular sensors with a huge number of applications. Their most important advantage is signal modulation consisting in shifting the spectrum in the wavelength domain. Determining the wavelength shift is the most important issue in precise measurements of various quantities. New demodulation methods are constantly being developed. Many of them have good properties, but they do not gain much polarity. This is partly due to their high complexity and partly to a small improvement in the accuracy of determining the wavelength shift in relation to classical methods. Cumulative preprocessing is a very simple method of spectrum processing with the property of reducing the influence of noise on the result. The method can be used directly or with additional algorithms. In this article, we demonstrate the advantages of this method and the possibilities of combining it with other signal processing methods. We show that this method is much simpler than the spectrum denoising methods and additionally simplifies the next stage of the algorithm, i.e., determining the wavelength shift itself. Full article

(This article belongs to the Special Issue Advanced Optical Technologies for Communications, Perception, and Chips)

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7 pages, 2998 KiB

Open AccessCommunication

Speed of Light in Hollow-Core Photonic Bandgap Fiber Approaching That in Vacuum

by Xiaolu Cao, Mingming Luo, Jianfei Liu, Jie Ma, Yundong Hao and Yange Liu

Sensors 2024, 24(21), 6954; https://doi.org/10.3390/s24216954 - 30 Oct 2024

Viewed by 1069

Abstract

A Fresnel mirror is introduced at a hollow-core photonic bandgap fiber end by fusion splicing a short single-mode fiber segment, to reflect the light backward to an optical frequency domain reflectometry. The backward Fresnel reflection is used as a probe light to achieve light speed measurement with a high resolution and a high signal-to-noise ratio. Thus, its group velocity is obtained with the round-trip time delay as well as the beat frequency at the reflection peak. Multiple Fresnel peaks are observed from 2180.00 Hz to 13,988.75 Hz, corresponding to fusion-spliced hollow-core fiber segments with different lengths from 0.2595 m to 1.6678 m, respectively. The speed of light in the air guidance is calculated at 2.9753 × 10⁸ m/s, approaching that in vacuum, which is also in good agreement with 2.9672 × 10⁸ m/s given by the numerical analysis with an uncertainty of 10⁻³. Our demonstration promises a key to hollow-core waveguide characterization for future wide-bandwidth and low-latency optical communication. Full article

(This article belongs to the Special Issue Advanced Optical Technologies for Communications, Perception, and Chips)

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15 pages, 3517 KiB

Open AccessArticle

Scenarios for Optical Encryption Using Quantum Keys

by Luis Velasco, Morteza Ahmadian, Laura Ortiz, Juan P. Brito, Antonio Pastor, Jose M. Rivas, Sima Barzegar, Jaume Comellas, Vicente Martin and Marc Ruiz

Sensors 2024, 24(20), 6631; https://doi.org/10.3390/s24206631 - 15 Oct 2024

Cited by 2 | Viewed by 1219

Abstract

Optical communications providing huge capacity and low latency remain vulnerable to a range of attacks. In consequence, encryption at the optical layer is needed to ensure secure data transmission. In our previous work, we proposed LightPath SECurity (LPSec), a secure cryptographic solution for optical transmission that leverages stream ciphers and Diffie–Hellman (DH) key exchange for high-speed optical encryption. Still, LPSec faces limitations related to key generation and key distribution. To address these limitations, in this paper, we rely on Quantum Random Number Generators (QRNG) and Quantum Key Distribution (QKD) networks. Specifically, we focus on three meaningful scenarios: In Scenario A, the two optical transponders (Tp) involved in the optical transmission are within the security perimeter of the QKD network. In Scenario B, only one Tp is within the QKD network, so keys are retrieved from a QRNG and distributed using LPSec. Finally, Scenario C extends Scenario B by employing Post-Quantum Cryptography (PQC) by implementing a Key Encapsulation Mechanism (KEM) to secure key exchanges. The scenarios are analyzed based on their security, efficiency, and applicability, demonstrating the potential of quantum-enhanced LPSec to provide secure, low-latency encryption for current optical communications. The experimental assessment, conducted on the Madrid Quantum Infrastructure, validates the feasibility of the proposed solutions. Full article

(This article belongs to the Special Issue Advanced Optical Technologies for Communications, Perception, and Chips)

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12 pages, 3116 KiB

Open AccessArticle

Compact Silicon-Arrayed Waveguide Gratings with Low Nonuniformity

by Chengkun Yang, Zhonghao Zhou, Xudong Gao, Zhengzhu Xu, Shoubao Han, Yuhua Chong, Rui Min, Yang Yue and Zongming Duan

Sensors 2024, 24(16), 5303; https://doi.org/10.3390/s24165303 - 16 Aug 2024

Cited by 1 | Viewed by 1649

Abstract

Array waveguide gratings (AWGs) have been widely used in multi-purpose and multi-functional integrated photonic devices for Microwave photonics (MWP) systems. In this paper, we compare the effect of output waveguide configurations on the performance of AWGs. The AWG with an output waveguide converging on the grating circle had larger crosstalk and lower nonuniformity. We also fabricated a 1 × 8 AWG with an output waveguide converging onto the SOI’s grating circle, whose central operation wavelength was around 1550 nm. The fabricated AWG has a chip size of 500 μm × 450 μm. Experimental results show that the adjacent channel crosstalk is −12.68 dB. The center channel insertion loss, as well as 3 dB bandwidth, are 4.18 dB and 1.22 nm at 1550 nm, respectively. The nonuniformity is about 0.494 dB, and the free spectral range is 19.4 nm. The proposed AWG is expected to play an important role in future MWP systems given its good nonuniformity and insertion loss level. Full article

(This article belongs to the Special Issue Advanced Optical Technologies for Communications, Perception, and Chips)

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14 pages, 927 KiB

Open AccessArticle

Enhancing Security in Visible Light Communication: A Tabu-Search-Based Method for Transmitter Selection

by Ge Shi, Wei Cheng, Xiang Gao, Fupeng Wei, Heng Zhang and Qingzheng Wang

Sensors 2024, 24(6), 1906; https://doi.org/10.3390/s24061906 - 16 Mar 2024

Viewed by 1127

Abstract

In this paper, we explore the secrecy performance of a visible light communication (VLC) system consisting of distributed light-emitting diodes (LEDs) and multiple users (UEs) randomly positioned within an indoor environment while considering the presence of an eavesdropper. To enhance the confidentiality of the system, we formulate a problem of maximizing the sum secrecy rate for UEs by searching for an optimal LED for each UE. Due to the non-convex and non-continuous nature of this security maximization problem, we propose an LED selection algorithm based on tabu search to avoid getting trapped in local optima and expedite the search process by managing trial vectors from previous iterations. Moreover, we introduce three LED selection strategies with a low computational complexity. The simulation results demonstrate that the proposed algorithm achieves a secrecy performance very close to the global optimal value, with a gap of less than 1%. Additionally, the proposed strategies exhibit a performance gap of 28% compared to the global optimal. Full article

(This article belongs to the Special Issue Advanced Optical Technologies for Communications, Perception, and Chips)

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14 pages, 3074 KiB

Open AccessArticle

A High-Capacity Optical Metro Access Network: Efficiently Recovering Fiber Failures with Robust Switching and Centralized Optical Line Terminal

by Rahat Ullah, Sibghat Ullah, Ahmad Almadhor, Hathal Salamah Alwageed, Abdullah A. Al-Atawi, Jianxin Ren and Shuaidong Chen

Sensors 2024, 24(4), 1074; https://doi.org/10.3390/s24041074 - 7 Feb 2024

Cited by 8 | Viewed by 1659

Abstract

This study proposes and presents a new central office (CO) for the optical metro access network (OMAN) with an affordable and distinctive switching system. The CO’s foundation is built upon a novel optical multicarrier (OMC) generation technique. This technique provides numerous frequency carriers that are characterized by a high tone-to-noise ratio (TNR) of 40 dB and minimal amplitude excursions. The purpose is to accommodate multiple users at the optical network unit side in the optical metropolitan area network (OMAN). The OMC generation is achieved through a cascaded configuration involving a single phase and two Mach Zehnder modulators without incorporating optical or electrical amplifiers or filters. The proposed OMC is installed in the CO of the OMAN to support the 1.2 Tbps downlink and 600 Gbps uplink transmission, with practical bit error rate (BER) ranges from 10⁻³ to 10⁻¹³ for the downlink and 10⁻⁶ to 10⁻¹⁴ for the uplink transmission. Furthermore, in the OMAN’s context, optical fiber failure is a main issue. Therefore, we have proposed a possible solution for ensuring uninterrupted communication without any disturbance in various scenarios of main optical fiber failures. This demonstrates how this novel CO can rapidly recover transmission failures through robust switching a and centralized OLT. The proposed system is intended to provide users with a reliable and affordable service while maintaining high-quality transmission rates. Full article

(This article belongs to the Special Issue Advanced Optical Technologies for Communications, Perception, and Chips)

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12 pages, 5109 KiB

Open AccessArticle

Optimizations of Double Titanium Nitride Thermo-Optic Phase-Shifter Heaters Using SOI Technology

by Eylon Eliyahu Krause and Dror Malka

Sensors 2023, 23(20), 8587; https://doi.org/10.3390/s23208587 - 19 Oct 2023

Cited by 5 | Viewed by 2352

Abstract

A commercial thermo-optic phase shifter (TOPS) is an efficient solution to the imbalance problem in the fabrication process of Mach–Zehnder modulator (MZM) arms. The TOPS consumes electrical power and transforms it into thermal energy, which changes the real part of the effective refractive index at the waveguide and adjusts the MZM transfer function to work in the linear region. The common model being used today is constructed with only one heater; however, this solution requires more electrical power, which can increase the transmitter system cost. To reduce the system energy cost, we propose a pioneering optimal double titanium nitride heater model under forward biasing at 1550 nm wavelength using the standard silicon-on-insulator technology. Numerical investigations were carried out on the key relative geometrical parameters, heat distribution at the silicon layer, thermal crosstalk, and laser wavelength drift. Results show that the optimal TOPS design can function with a low electrical power of 19.1 mW to achieve a π-phase shift, with a low thermal crosstalk of 0.404 and very low optical losses over 1 mm length. Thus, the proposed device can be used for improving the imbalance problem in MZMs with low electrical power consumption and low losses. This functionality can be utilized to obtain better performances in transmitter systems for data centers and long-range optical communication system applications. Full article

(This article belongs to the Special Issue Advanced Optical Technologies for Communications, Perception, and Chips)

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11 pages, 8655 KiB

Open AccessArticle

Parabolic-Index Ring-Core Fiber Supporting High-Purity Orbital Angular Momentum Modes

by Yuanpeng Liu, Yingning Wang, Wenpu Geng, Wenqian Zhao, Hao Zhang, Weigang Zhang, Zhongqi Pan and Yang Yue

Sensors 2023, 23(7), 3641; https://doi.org/10.3390/s23073641 - 31 Mar 2023

Cited by 10 | Viewed by 2437

Abstract

We design a graded-index ring-core fiber with a GeO₂-doped silica ring core and SiO₂ cladding. This fiber structure can inhibit the effect of spin-orbit coupling to mitigate the power transfer among different modes and eventually enhance the orbital angular momentum (OAM) mode purity. By changing the high-index ring core from the step-index to parabolic graded-index profile, the purity of the OAM_1,1 mode can be improved from 86.48% to 94.43%, up by 7.95%. The proposed fiber features a flexible structure, which can meet different requirements for mode order, effective mode area, etc. Simulation results illustrate that the parabolic-index ring-core fiber is promising in enhancing the OAM mode purity, which could potentially reduce the channel crosstalk in mode-division-multiplexed optical communication systems. Full article

(This article belongs to the Special Issue Advanced Optical Technologies for Communications, Perception, and Chips)

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15 pages, 5688 KiB

Open AccessFeature PaperArticle

Face Mask Identification Using Spatial and Frequency Features in Depth Image from Time-of-Flight Camera

by Xiaoyan Wang, Tianxu Xu, Dong An, Lei Sun, Qiang Wang, Zhongqi Pan and Yang Yue

Sensors 2023, 23(3), 1596; https://doi.org/10.3390/s23031596 - 1 Feb 2023

Cited by 4 | Viewed by 2501

Abstract

Face masks can effectively prevent the spread of viruses. It is necessary to determine the wearing condition of masks in various locations, such as traffic stations, hospitals, and other places with a risk of infection. Therefore, achieving fast and accurate identification in different application scenarios is an urgent problem to be solved. Contactless mask recognition can avoid the waste of human resources and the risk of exposure. We propose a novel method for face mask recognition, which is demonstrated using the spatial and frequency features from the 3D information. A ToF camera with a simple system and robust data are used to capture the depth images. The facial contour of the depth image is extracted accurately by the designed method, which can reduce the dimension of the depth data to improve the recognition speed. Additionally, the classification process is further divided into two parts. The wearing condition of the mask is first identified by features extracted from the facial contour. The types of masks are then classified by new features extracted from the spatial and frequency curves. With appropriate thresholds and a voting method, the total recall accuracy of the proposed algorithm can achieve 96.21%. Especially, the recall accuracy for images without mask can reach 99.21%. Full article

(This article belongs to the Special Issue Advanced Optical Technologies for Communications, Perception, and Chips)

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Review

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110 pages, 4916 KiB

Open AccessReview

Revolutionizing Free-Space Optics: A Survey of Enabling Technologies, Challenges, Trends, and Prospects of Beyond 5G Free-Space Optical (FSO) Communication Systems

by Isiaka A. Alimi and Paulo P. Monteiro

Sensors 2024, 24(24), 8036; https://doi.org/10.3390/s24248036 - 16 Dec 2024

Cited by 2 | Viewed by 6623

Abstract

As the demand for high-speed, low-latency communication continues to grow, free-space optical (FSO) communication has gained prominence as a promising solution for supporting the next generation of wireless networks, especially in the context of the 5G and beyond era. It offers high-speed, low-latency data transmission over long distances without the need for a physical infrastructure. However, the deployment of FSO systems faces significant challenges, such as atmospheric turbulence, weather-induced signal degradation, and alignment issues, all of which can impair performance. This paper offers a comprehensive survey of the enabling technologies, challenges, trends, and future prospects for FSO communication in next-generation networks, while also providing insights into the current mitigation strategies. The survey explores the critical enabling technologies such as adaptive optics, modulation schemes, and error correction codes that are revolutionizing FSO communication and addressing the unique challenges of FSO links. Also, the integration of FSO with radio frequency, millimeter-wave, and Terahertz technologies is explored, emphasizing hybrid solutions that enhance reliability and coverage. Additionally, the paper highlights emerging trends, such as the integration of FSO with artificial intelligence-driven optimization techniques and the growing role of machine learning in enhancing FSO system performance for dynamic environments. By analyzing the current trends and identifying key challenges, this paper emphasizes the prospects of FSO communication in the evolving landscape of 5G and future networks. In this regard, it assesses the potential of FSO to meet the demands for high-speed, low-latency communication and offers insights into its scalability, reliability, and deployment strategies for 5G and beyond. The paper concludes by identifying the open challenges and future research directions critical to realizing the full potential of FSO in next-generation communication systems. Full article

(This article belongs to the Special Issue Advanced Optical Technologies for Communications, Perception, and Chips)

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30 pages, 4848 KiB

Open AccessReview

A Review of Hybrid VLC/RF Networks: Features, Applications, and Future Directions

by Lisandra Bravo Alvarez, Samuel Montejo-Sánchez, Lien Rodríguez-López, Cesar Azurdia-Meza and Gabriel Saavedra

Sensors 2023, 23(17), 7545; https://doi.org/10.3390/s23177545 - 30 Aug 2023

Cited by 26 | Viewed by 4334

Abstract

The expectation for communication systems beyond 5G/6G is to provide high reliability, high throughput, low latency, and high energy efficiency services. The integration between systems based on radio frequency (RF) and visible light communication (VLC) promises the design of hybrid systems capable of addressing and largely satisfying these requirements. Hybrid network design enables complementary cooperation without interference between the two technologies, thereby increasing the overall system data rate, improving load balancing, and reducing non-coverage areas. VLC/RF hybrid networks can offer reliable and efficient communication solutions for Internet of Things (IoT) applications such as smart lighting, location-based services, home automation, smart healthcare, and industrial IoT. Therefore, hybrid VLC/RF networks are key technologies for next-generation communication systems. In this paper, a comprehensive state-of-the-art study of hybrid VLC/RF networks is carried out, divided into four areas. First, indoor scenarios are studied considering lighting requirements, hybrid channel models, load balancing, resource allocation, and hybrid network topologies. Second, the characteristics and implementation of these hybrid networks in outdoor scenarios with adverse conditions are analyzed. Third, we address the main applications of hybrid VLC/RF networks in technological, economic, and socio-environmental domains. Finally, we outline the main challenges and future research lines of hybrid VLC/RF networks. Full article

(This article belongs to the Special Issue Advanced Optical Technologies for Communications, Perception, and Chips)

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