Photonics

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14 pages, 4169 KB

Open AccessArticle

Cost-Effective, Contactless Optical Vibration Sensor for Rotating Machinery Based on Fiber-Optic Telecommunication Components and a Cross-Correlation Method

by Nino Rozić, Petar Bašić, Zvonimir Šipuš and Elis Sutlović

Photonics 2026, 13(7), 683; https://doi.org/10.3390/photonics13070683 - 17 Jul 2026

Viewed by 447

Abstract

Vibration measurements are essential for the early detection of faults in rotating machinery and are particularly important for hydrogenerators in hydro power plants. Industrial applications of vibration measurements typically rely on displacement, velocity, and acceleration sensors, each offering distinct advantages and limitations. This [...] Read more.

Vibration measurements are essential for the early detection of faults in rotating machinery and are particularly important for hydrogenerators in hydro power plants. Industrial applications of vibration measurements typically rely on displacement, velocity, and acceleration sensors, each offering distinct advantages and limitations. This paper discusses and proposes a cost-effective, contactless optical vibration sensing system based on standard fiber-optic telecommunication components, enabling its integration into existing fiber-optic networks. The proposed system utilizes interferometric sensing principles, providing inherent immunity to electromagnetic interference and galvanic effects while achieving micrometer-scale resolution. The key advancement of the proposed sensor lies in the relatively simple and cost-effective configuration—the realization of the Michelson interferometer. It facilitates a combination of standard optical communication hardware, including a 3 × 3 fiber-optic coupler and two photodetectors for reliable discrimination of vibration displacement directions. The associated signal processing platform is based on a cross-correlation algorithm by which both the direction and the magnitude of displacement are determined. The optical sensor was experimentally validated using a realistic-scenario laboratory setup, which demonstrates the feasibility and performance of the proposed approach. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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26 pages, 1873 KB

Open AccessArticle

Energy-Efficient Autoencoder-Based Compact Image Payload Transmission over Noisy Indoor Industrial VLC Links

by Alejandro Arratia Pavat, Pablo Palacios Játiva, María Camila Reyes, Muhammad Ijaz, Cesar Azurdia Meza, David Zabala-Blanco and Iván Sanchez

Photonics 2026, 13(7), 660; https://doi.org/10.3390/photonics13070660 - 10 Jul 2026

Viewed by 403

Abstract

Visible light communication (VLC) can reduce radio-frequency (RF) congestion in indoor industrial monitoring, but a short transmitted payload does not by itself prove that visual or task-relevant information has been preserved. This study therefore frames the proposed method as an autoencoder-based compact latent-payload [...] Read more.

Visible light communication (VLC) can reduce radio-frequency (RF) congestion in indoor industrial monitoring, but a short transmitted payload does not by itself prove that visual or task-relevant information has been preserved. This study therefore frames the proposed method as an autoencoder-based compact latent-payload transmission scheme and explicitly distinguishes it from channel-aware joint source-channel coding (JSCC). Raw red–green–blue (RGB), lossless Huffman, and autoencoder latent payloads are first compared under the same VLC model using bit error rate (BER), calculated/model-derived VLC transmission energy, reconstruction quality, and task utility. The 128-component latent representation contains 4096 bits, corresponding to a 294-fold payload-size reduction relative to an uncompressed

224 \times 224

, 24-bit RGB image; this ratio is used only as a raw-payload reference and not as a general codec-compression claim. An independent industrial-domain audit is conducted on 30 Northeastern University (NEU) steel-surface images using four-fold out-of-fold evaluation, peak signal-to-noise ratio (PSNR), structural similarity index measure (SSIM), and a fixed defect-class proxy. An NEU architecture-and-resolution comparison shows that changing from Compact-NEU to the full

224 \times 224

model increases PSNR from 14.12 dB to 15.61 dB at the same 4096-bit bottleneck, while a regularized full model gives the highest SSIM of 0.471. Because input resolution and network capacity both change in this comparison, the result is interpreted as evidence that the architecture/resolution setting contributes to the industrial-domain gap, not as a strict isolation of capacity alone. Finally, an end-to-end JSCC-VLC baseline with 4096 nonnegative optical channel uses is trained through a differentiable intensity channel. It obtains 23.82 dB/0.568 SSIM in the clean case and 22.18 dB/0.519 SSIM at 5 dB SNR, showing more channel-aware behavior and more graceful degradation than the separated serialized-latent pipeline. Overall, the results support the modeled energy and active-time benefits of compact latent payloads while showing that robust industrial visual transmission requires architecture/resolution controls, practical codec baselines, and channel-aware JSCC comparisons. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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15 pages, 2506 KB

Open AccessArticle

Brillouin Optical Time Domain Reflectometry for Distributed Temperature Monitoring of Battery Energy Storage Systems

by Tjorven Hilbert, Florian Azendorf, Hamzeh Beiranvand, Johannes Diers, Marco Liserre, Annika Dochhan and Stephan Pachnicke

Photonics 2026, 13(6), 564; https://doi.org/10.3390/photonics13060564 - 8 Jun 2026

Viewed by 559

Abstract

The concept of Brillouin optical time domain reflectometry as a means of distributed temperature monitoring for battery systems is investigated and deemed feasible. The concept has been investigated regarding measurement speed, temperature accuracy, measurement range, and responsivity of the fiber material. The experiments [...] Read more.

The concept of Brillouin optical time domain reflectometry as a means of distributed temperature monitoring for battery systems is investigated and deemed feasible. The concept has been investigated regarding measurement speed, temperature accuracy, measurement range, and responsivity of the fiber material. The experiments show fast and accurate measurement results for surfaces with a uniformly distributed temperature, with an average absolute error of 0.51 K, a largest absolute error of 2.07 K, and a measurement time of approximately 60 s for a sampling point after 5 km. Additionally, hotspots only impacting 25% of the sensor fiber have been detected. Furthermore, the established concept provides a reliable and scalable solution for simultaneous temperature monitoring of spatially distributed sampling points without the need for individual cabling of every measurement sensor, like in commonly deployed electrical temperature detectors. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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18 pages, 13804 KB

Open AccessArticle

Automated Inverse Design Framework for Traveling-Wave Electrode Electro-Optic Modulators with Discrete Fabrication Constraints

by Qi You, Pingrang Hua, Yifei Chen, Xingshan Chen and Tong Ye

Photonics 2026, 13(5), 500; https://doi.org/10.3390/photonics13050500 - 18 May 2026

Viewed by 476

Abstract

The utilization of electro-optic modulators in engineering is progressively expanding. In this paper, an automated inverse design framework is proposed for traveling-wave electrode electro-optic modulators (EOM). It addresses key challenges in modulator design, such as multi-parameter coupling and discrete fabrication constraints. Applied to [...] Read more.

The utilization of electro-optic modulators in engineering is progressively expanding. In this paper, an automated inverse design framework is proposed for traveling-wave electrode electro-optic modulators (EOM). It addresses key challenges in modulator design, such as multi-parameter coupling and discrete fabrication constraints. Applied to a segmented electrode lithium niobate modulator, the framework achieves a 100 GHz electro-optic (EO) bandwidth and a half-wave voltage-length product of

V π \cdot L = 1 V \cdot c m

at 5 mm length, with all 20 independent runs converging successfully under the tested conditions. The framework is further validated on four modulator structures and six engineering conditions, consistently yielding EO bandwidth > 40 GHz and

V π \cdot L < 5 V \cdot c m

. This work offers a practical and adaptable solution for the automated design of high-performance electro-optic modulators under realistic fabrication constraints. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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19 pages, 10695 KB

Open AccessArticle

Probabilistic Shaping-Assisted Bases Precoding in QAM Quantum Noise Stream Cipher

by Shuang Wei, Sheng Liu, Wei Wang, Chao Lei, Kongni Zhu, Mingrui Zhang, Yuang Li, Yunbo Li, Dong Wang, Dechao Zhang, Han Li, Yajie Li, Yongli Zhao and Jie Zhang

Photonics 2026, 13(3), 307; https://doi.org/10.3390/photonics13030307 - 23 Mar 2026

Viewed by 718

Abstract

We propose a probabilistic shaping-assisted base precoding quantum noise stream cipher (PSABP QNSC) scheme to effectively alleviate the encryption penalty in QAM QNSC systems. In contrast to the uniformly distributed bases adopted in traditional QNSC, Gaussian distributed bases can provide shaping gain. We [...] Read more.

We propose a probabilistic shaping-assisted base precoding quantum noise stream cipher (PSABP QNSC) scheme to effectively alleviate the encryption penalty in QAM QNSC systems. In contrast to the uniformly distributed bases adopted in traditional QNSC, Gaussian distributed bases can provide shaping gain. We theoretically analyze the underlying gain mechanism of Gaussian distributed bases in the PSABP QNSC scheme. Experimental results of 160 km reveal that the encryption penalties of QPSK and 16QAM are reduced by 0.44 dB and 0.27 dB, in terms of OSNR. Moreover, the security is quantified through the number of masked signals as a primary key metric. To mitigate the impact of base precoding, we propose the effective bases and effective ciphertext symbol points to refine the security evaluation. Moreover, the security is estimated in terms of mutual information leakage, with

2.2 \times 10^{- 4}

bits of QPSK and

1.85 \times 10^{- 4}

bits of 16QAM. The results indicate that the PSABP QNSC scheme provides effective protection against eavesdropping. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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14 pages, 2941 KB

Open AccessArticle

High-Sensitivity Optical Sensor Driven by the High-Q Quasi-Bound States in the Continuum of an Asymmetric Bow-Tie Metasurface

by Zanhui Chen, Jiandao Huang, Qinghao Tan, Gongli Xiao, Tangyou Sun, Fabi Zhang, Ahmad Syahrin Idris, Qiping Zou, Haiou Li and Guo-Wei Lu

Photonics 2026, 13(1), 77; https://doi.org/10.3390/photonics13010077 - 16 Jan 2026

Viewed by 1110

Abstract

All-dielectric metasurfaces based on quasi-bound states in the continuum (quasi-BICs) have emerged as a powerful platform for nanophotonic sensing, as they support high-Q resonances and strong near-field enhancements. Herein, we propose and numerically investigate an asymmetric bow-tie metasurface composed of two silicon semi-cylinders [...] Read more.

All-dielectric metasurfaces based on quasi-bound states in the continuum (quasi-BICs) have emerged as a powerful platform for nanophotonic sensing, as they support high-Q resonances and strong near-field enhancements. Herein, we propose and numerically investigate an asymmetric bow-tie metasurface composed of two silicon semi-cylinders with unequal radii and a central bar to achieve a quasi-BIC resonance with a Q-factor of 11,000. The transition mechanism of the BIC modes in the asymmetric bow-tie metasurface is analyzed. Additionally, the spectral features of the asymmetric bow-tie metasurface as a function of the refractive index and temperature of the local environment are also investigated. The proposed structure exhibits a refractive index sensitivity of 454 nm/RIU and a temperature sensitivity of 134 pm/°C. Furthermore, a high figure of merit (FOM) of 3159 RIU⁻¹ is achieved, and the nearly 100% modulation depth maintained across three distinct resonance dips. Our study suggests that the proposed asymmetric bow-tie metasurface offers a promising approach for the development of high-sensitivity biosensing platforms. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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20 pages, 2430 KB

Open AccessArticle

Tunable Band-Pass Filters with Long Periodicity Using Cascaded Mach-Zehnder Interferometer Networks

by Sergio Rivera, Jessica César-Cuello, Daniel Gallego and Guillermo Carpintero

Photonics 2025, 12(12), 1154; https://doi.org/10.3390/photonics12121154 - 24 Nov 2025

Cited by 1 | Viewed by 879

Abstract

This paper introduces a theoretical framework for designing and tuning band-pass filters with a highly extended periodicity using cascaded Mach-Zehnder Interferometer (MZI) networks. We show that a filter centered at frequency f₀ with a bandwidth of FSR₀ and an arbitrarily large [...] Read more.

This paper introduces a theoretical framework for designing and tuning band-pass filters with a highly extended periodicity using cascaded Mach-Zehnder Interferometer (MZI) networks. We show that a filter centered at frequency f₀ with a bandwidth of FSR₀ and an arbitrarily large free spectral range (FSR) can be built with a minimal number of MZIs by using stages with FSRs that are prime multiples of FSR₀. Due to the inherent multi-spectral transparency of materials, this design ensures that only a single narrow passband is transparent. We derive the total power transmission for such a cascaded system and show that the filter’s overall periodicity is the product of the individual MZI transfer functions. Furthermore, we deduce the linear relationship between the applied differential voltage and the resulting frequency shift, offering a precise method for continuous spectral tuning without altering the filter’s intrinsic FSR. We propose a new, simplified electronic circuit that uses a single input current and series impedances for continuous resonant peak tuning and analyze the feasibility of such a design. This circuit improves practical implementation and allows for compensation of fabrication errors. This work offers crucial analytical tools and insights for developing advanced reconfigurable photonic integrated filters, essential for future optical communication and sensing systems. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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15 pages, 4045 KB

Open AccessArticle

A Low-Complexity Receiver-Side Lookup Table Equalization Method for High-Speed Short-Reach IM/DD Transmission Systems

by Junde Lu, Yu Sun, Jun Qin, Changhao Han, Jie Shi, Lanling Chen, Jianyu Shi, Jiaxin Zheng, Shuo Jiang, Chi Zhang, Yang Yang, Yueqin Li, Jian Sun and Guo-Wei Lu

Photonics 2025, 12(11), 1091; https://doi.org/10.3390/photonics12111091 - 6 Nov 2025

Cited by 1 | Viewed by 1148

Abstract

In this paper, we demonstrate a receiver-side lookup table (Rx-side LUT) equalization method for high-speed short-reach intensity modulation and direct detection (IM/DD) transmission systems, which alleviates the computational complexity of neural network-based equalization algorithms. Compared to conventional pre-equalization techniques applied at the transmitter [...] Read more.

In this paper, we demonstrate a receiver-side lookup table (Rx-side LUT) equalization method for high-speed short-reach intensity modulation and direct detection (IM/DD) transmission systems, which alleviates the computational complexity of neural network-based equalization algorithms. Compared to conventional pre-equalization techniques applied at the transmitter side, which utilize distortion correction values stored in LUTs derived from the transmitted symbols and their corresponding recovered counterparts, the Rx-side LUT relies solely on receiver-side data. The received data to be equalized serves as the index of the LUT, with a nearest-neighbor algorithm employed to find the element closest to the index and then return the corresponding equalization result from the table. With a lightweight lookup process, the proposed method releases the computation complexity of neural network-based equalization algorithms by replacing the computationally intensive operations performed during the inference phase. Experimental results indicate that compared to baseline fully connected neural network (FCNN) and gated recurrent unit (GRU) equalization, the Rx-side LUT could decrease the algorithm execution time by 25.5% and 34.6% for 100 GBaud and 22.8% and 36.9% for 112 GBaud PAM4 signals, respectively, while maintaining comparable system performance. The proposed scheme provides a low-complexity solution for high-speed, low-cost IM/DD optical interconnects. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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8 pages, 2243 KB

Open AccessCommunication

The Sensing Attack: Mechanism and Deployment in Submarine Cable Systems

by Haokun Song, Xiaoming Chen, Junshi Gao, Tianpu Yang, Jianhua Xi, Xiaoqing Zhu, Shuo Sun, Wenjing Yu, Xinyu Bai, Chao Wu and Chen Wei

Photonics 2025, 12(10), 976; https://doi.org/10.3390/photonics12100976 - 30 Sep 2025

Viewed by 1033

Abstract

Submarine cable systems, serving as the critical backbone of global communications, face evolving resilience threats. This work proposes a novel sensing attack that utilizes ultra-narrow-linewidth lasers to surveil these infrastructures. First, the Narrowband Jamming Attack (NJA) is introduced as an evolution of conventional [...] Read more.

Submarine cable systems, serving as the critical backbone of global communications, face evolving resilience threats. This work proposes a novel sensing attack that utilizes ultra-narrow-linewidth lasers to surveil these infrastructures. First, the Narrowband Jamming Attack (NJA) is introduced as an evolution of conventional physical-layer jamming. NJA is divided into three categories according to the spectral position, and the non-overlapping class represents the proposed sensing attack. Its operational principles and the key parameters determining its efficacy are analyzed, along with its deployment strategy in submarine cable systems. Finally, the sensing capability is validated via OptiSystem simulations. Results demonstrate successful localization of vibrations within the 50–200 Hz range on a 1 km fiber, achieving a spatial resolution of 1 m, and confirm the influence of vibration parameters on sensing performance. This work reveals that the proposed sensing attack has the potential to covertly monitor environmental data, thereby posing a threat to information security in submarine cable systems. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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17 pages, 3315 KB

Open AccessArticle

Fiber Eavesdropping Detection and Location in Optical Communication System

by Yuang Li, Yuyuan Liang, Mingrui Zhang, Shuang Wei, Huatao Zhu, Yajie Li, Yongli Zhao and Jie Zhang

Photonics 2025, 12(5), 501; https://doi.org/10.3390/photonics12050501 - 16 May 2025

Cited by 7 | Viewed by 2682

Abstract

Fiber eavesdropping severely endangers the confidentiality of data transmitted in optical networks. Therefore, it is necessary to explore how to detect and locate fiber eavesdropping in an effective approach. To leverage the advantages of the state of polarization (SOP) in detecting various abnormal [...] Read more.

Fiber eavesdropping severely endangers the confidentiality of data transmitted in optical networks. Therefore, it is necessary to explore how to detect and locate fiber eavesdropping in an effective approach. To leverage the advantages of the state of polarization (SOP) in detecting various abnormal events while addressing its challenges in acquiring the SOP of different fiber links, we propose a multi-channel joint SOP estimation scheme to estimate the SOP of different fiber spans. Based on the proposed scheme, we provide a comprehensive solution for fiber eavesdropping location and detection in optical communication systems. In this solution, the estimated SOP and optical performance monitoring (OPM) data are utilized for rapid fiber eavesdropping detection and coarse location at the span level. The effectiveness of the solution is validated by experiments. In the aspect of detection, we achieve the detection of the start or end of fiber eavesdropping, the overlapping of fiber eavesdropping and abnormal events, and other abnormal events. The overall accuracy is 99.77%. In the aspect of location, we can locate the fiber span that has been eavesdropped. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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11 pages, 2679 KB

Open AccessArticle

Analysis of Randomization Capacity in Quantum Noise Randomized Cipher System

by Mingrui Zhang, Shuang Wei, Yuang Li, Yajie Li, Yongli Zhao and Jie Zhang

Photonics 2024, 11(11), 1093; https://doi.org/10.3390/photonics11111093 - 20 Nov 2024

Viewed by 1438

Abstract

We propose and verify a method for analyzing the randomization capacity in a 160 km quantum noise randomized cipher system with different data modulation formats. The randomization capacity is defined as the difference in mutual information between Alice and Bob while the randomization [...] Read more.

We propose and verify a method for analyzing the randomization capacity in a 160 km quantum noise randomized cipher system with different data modulation formats. The randomization capacity is defined as the difference in mutual information between Alice and Bob while the randomization level is at 0 and at its maximum, under the condition of error-free transmission. Our experimental analysis examines the capacity of quantum noise randomized cipher systems under different optical signal-to-noise ratios for each modulation format. Additionally, we analyze the noise masking values while the randomization reaches its capacity. The experimental results indicate that the binary phase shift-keying-based quantum noise randomized cipher system achieves the highest randomization capacity and highest noise masking value. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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10 pages, 1117 KB

Open AccessCommunication

Efficient Direct Detection of Twin Single-Sideband Quadrature-Phase Shift Keying Using a Single Detector with Hierarchical Blind-Phase Search

by Hongbo Zhang, Jiao Liu, Guo-Wei Lu, Min Zhang, Feng Wan, Ju Cai, Weiwei Ling and Liming Hu

Photonics 2024, 11(7), 624; https://doi.org/10.3390/photonics11070624 - 29 Jun 2024

Cited by 1 | Viewed by 2165

Abstract

We propose a novel reception scheme for twin single-sideband (twin-SSB) signals using just a single photodetector (PD), significantly reducing the system complexity and cost. To detect a twin-SSB with power-unbalanced quadrature-phase shift keying (QPSK) sidebands upon detection via a single PD at the [...] Read more.

We propose a novel reception scheme for twin single-sideband (twin-SSB) signals using just a single photodetector (PD), significantly reducing the system complexity and cost. To detect a twin-SSB with power-unbalanced quadrature-phase shift keying (QPSK) sidebands upon detection via a single PD at the receiver side, two QPSKs carried in two sidebands are coherently superposed and detected in a 16-ary quadrature amplitude modulation (16-QAM) format. This technique notably diminishes the linearity and effective number of bits required for the transmitter components in high-speed optical transmission systems. Moreover, a hierarchical blind-phase search (HBPS) algorithm is proposed to compensate for the imperfect phase rotation of QPSK signals during transmission. To demonstrate the effectiveness of our proposed method, we successfully conducted simulations of 112 Gb/s 16-QAM signal transmission over a 10 km standard single-mode fiber (SSMF), achieving bit error ratios (BERs) of

7.84 \times 10^{- 4}

, well below the 7% hard-decision forward error correction (HD-FEC) threshold of

3.8 \times 10^{- 3}

. In addition, the synthetic transmission scheme proposed in this paper is compared with the traditional 16-QAM signal transmission scheme, and the results show that the proposed scheme does not introduce a performance cost with the same received optical power (ROP) and transmission distance. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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15 pages, 6095 KB

Open AccessArticle

Fabrication Tolerances’ Impact on an ODAC-Based PAM-4 Transmitter

by Adebayo E. Abejide, João Santos, Tanay Chattopadhyay, Francisco Rodrigues, Mario Lima and António Teixeira

Photonics 2024, 11(7), 589; https://doi.org/10.3390/photonics11070589 - 24 Jun 2024

Viewed by 2261

Abstract

Photonic integrated circuits (PIC) devices are impacted by fabrication tolerances and therefore, prior knowledge of such variations could improve the PIC fabrication process and overall yield. This paper presents a method for predicting the fabrication impacts on a telecommunication optical digital to analog [...] Read more.

Photonic integrated circuits (PIC) devices are impacted by fabrication tolerances and therefore, prior knowledge of such variations could improve the PIC fabrication process and overall yield. This paper presents a method for predicting the fabrication impacts on a telecommunication optical digital to analog converter (oDAC)-based pulse amplitude modulator level four (PAM-4) transmitter as a case study where the certainty of this passive device is subjected to random variation. Our findings allow us to estimate the production yield in a fabrication scenario using the symbol error rate (SER) benchmark and this contributes to the study of the viability of oDAC PAM-4 transmitters to replace conventional electrical digital to analog converter (eDAC) PAM-4 transmitters. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing, 2nd Edition)

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