Photonics

14 pages, 905 KB

Open AccessArticle

IQ-Modulation Using Phase and Amplitude Modulators and Multimode Interference

by Frank H. Peters

Photonics 2026, 13(1), 44; https://doi.org/10.3390/photonics13010044 - 31 Dec 2025

Optical amplitude and phase modulators are an integral part of modern optical communications systems. As optical data formats transitioned from encoding amplitude exclusively to both amplitude and phase, several different methods for creating the quadrature amplitude modulation (QAM) have been proposed, demonstrated and [...] Read more.

Optical amplitude and phase modulators are an integral part of modern optical communications systems. As optical data formats transitioned from encoding amplitude exclusively to both amplitude and phase, several different methods for creating the quadrature amplitude modulation (QAM) have been proposed, demonstrated and employed. This paper will provide an overview and analysis of current techniques for creating these signals and will then show how a more elegant and efficient design is possible by taking advantage of the phase properties of multimode interference devices (MMIs). Using two 2 × 2 MMIs in a Mach Zehnder configuration is a well-known technique for creating a BPSK signal using phase modulators and has also been shown to work with amplitude modulators. This paper will also show how two 4 × 4 MMIs can be used to create QAM signals using either phase or amplitude modulation. Full article

(This article belongs to the Special Issue Advances in Photonic–Electronic Integration)

14 pages, 3782 KB

Open AccessArticle

Strategies for Managing Charge in Electron-Beam Lithography on Glass

by Zhongyang Liu, Yue Chen, Leyang Dang, Wenwu Zhang, Luwei Wang and Junle Qu

Photonics 2026, 13(1), 43; https://doi.org/10.3390/photonics13010043 - 31 Dec 2025

Abstract

Optical metasurfaces fabricated via electron beam lithography (EBL) are increasingly pivotal for biosensing and bioimaging applications. However, charge accumulation on insulating glass substrates persists as a critical barrier, causing distortion of the incident electron beam and degradation of patterning fidelity manifested as pattern [...] Read more.

Optical metasurfaces fabricated via electron beam lithography (EBL) are increasingly pivotal for biosensing and bioimaging applications. However, charge accumulation on insulating glass substrates persists as a critical barrier, causing distortion of the incident electron beam and degradation of patterning fidelity manifested as pattern deflection, increased line-edge roughness (LER), and overlay inaccuracy. Here, we evaluate three charge-mitigation strategies: optimization of electron-beam resist (EBR) thickness, spin-coated conductive polymer layers, and thin metal capping layers. A reduction in EBR thickness from 800 nm to 150 nm led to a significant improvement in LER attributed to a shortened charge dissipation path. The introduction of a conductive polymer further enhanced pattern integrity, whereas the most substantial improvement was attained by depositing a 20 nm Au layer, which offers a highly conductive pathway for rapid charge dissipation and resulted in the lowest LER of 0.24. Our comparison establishes a clear hierarchy of effectiveness and identifies metal capping as the most reliable approach for high-fidelity nanofabrication on insulating substrates, thereby offering practical solutions for advancing glass-based photonic and meta-optical devices. Full article

(This article belongs to the Section Optoelectronics and Optical Materials)

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29 pages, 3965 KB

Open AccessReview

Physical Layer Security Techniques for Terahertz Communications Above 100 GHz: A Review

by Shenghong Ye, Ming Che, Yuya Mikami and Kazutoshi Kato

Photonics 2026, 13(1), 42; https://doi.org/10.3390/photonics13010042 - 31 Dec 2025

Abstract

Terahertz (THz) communication above 100 GHz is widely recognized as a key enabler for sixth-generation (6G) networks because of its ultra-broad bandwidth and strong directionality. Meanwhile, the rapid evolution of artificial intelligence has considerably weakened conventional cryptographic methods at the network layer, making [...] Read more.

Terahertz (THz) communication above 100 GHz is widely recognized as a key enabler for sixth-generation (6G) networks because of its ultra-broad bandwidth and strong directionality. Meanwhile, the rapid evolution of artificial intelligence has considerably weakened conventional cryptographic methods at the network layer, making THz physical layer security increasingly critical. THz links are inherently susceptible to jamming and eavesdropping, which calls for dedicated security mechanisms that integrate physical structures with advanced signal processing. This review summarizes recent advances in two complementary directions. The first addresses signal domain strategies, including frequency hopping spread spectrum techniques, channel modeling, and artificial noise injection, to strengthen confidentiality and robustness against intentional interference. The second focuses on spatial domain strategies, where intelligent reflecting surfaces and beam steering architectures leverage topological diversity to reduce interception risks. This review also discusses the practical challenges these techniques may face in future 6G scenarios and identifies potential directions for further research. Full article

(This article belongs to the Special Issue Signal Processing and System Integration for Next-Generation Optical Communication)

10 pages, 3995 KB

Open AccessCommunication

Broadband Trilayer Adiabatic Edge Coupler on Thin-Film Lithium Tantalate for NIR Light

by Shiqing Gao, Xinke Xing, Shuai Chen and Kaixuan Chen

Photonics 2026, 13(1), 41; https://doi.org/10.3390/photonics13010041 - 31 Dec 2025

Abstract

This work addresses the challenge of realizing broadband, low-loss fiber-to-waveguide coupling in the short-wavelength near-infrared range (700–1050 nm), where the required fine structural dimensions and taper tips approach or even exceed current fabrication limits, resulting in tight fabrication tolerances and degraded coupling efficiency. [...] Read more.

This work addresses the challenge of realizing broadband, low-loss fiber-to-waveguide coupling in the short-wavelength near-infrared range (700–1050 nm), where the required fine structural dimensions and taper tips approach or even exceed current fabrication limits, resulting in tight fabrication tolerances and degraded coupling efficiency. We propose a broadband trilayer adiabatic edge coupler on a thin-film lithium tantalate platform that requires only two standard lithography and etching steps. The design integrates a crossed bilayer taper and a dual-core mode converter to achieve adiabatic mode transformation from a ridge to a thin strip waveguide, ensuring excellent fabrication tolerance and process simplicity. Simulations predict a minimum coupling loss of 0.57 dB at 850 nm, which includes the transmission through the complete edge-coupler structure, along with a 0.5-dB bandwidth exceeding 140 nm. The proposed structure provides a broadband, low-loss, and fabrication-tolerant interface for short-wavelength photonic systems such as quantum photonics, biosensing, and visible-light communications. Full article

(This article belongs to the Special Issue Advanced Photonic Integration Technology and Devices)

51 pages, 4796 KB

Open AccessReview

Review of Optical Fiber Sensors: Principles, Classifications and Applications in Emerging Technologies

by Denzel A. Rodriguez-Ramirez, Jose R. Martinez-Angulo, Jose D. Filoteo-Razo, Juan C. Elizondo-Leal, Alan Diaz-Manriquez, Daniel Jauregui-Vazquez, Jesus P. Lauterio-Cruz and Vicente P. Saldivar-Alonso

Photonics 2026, 13(1), 40; https://doi.org/10.3390/photonics13010040 - 31 Dec 2025

Abstract

Optical fiber sensors (OFSs) have emerged as essential tools in the monitoring of physical, chemical, and bio-medical parameters in harsh situations due to their high sensitivity, electromagnetic interference (EMI) immunity, and long-term stability. However, the current literature contains scattered information in most reviews [...] Read more.

Optical fiber sensors (OFSs) have emerged as essential tools in the monitoring of physical, chemical, and bio-medical parameters in harsh situations due to their high sensitivity, electromagnetic interference (EMI) immunity, and long-term stability. However, the current literature contains scattered information in most reviews regarding individual sensing technologies or domains. This study provides a structured exploratory review in a novel inter-family analysis of both intrinsic and extrinsic configurations by analyzing more than 23,000 publications between 2019 and 2025 in five key domains: industry, medicine and biomedicine, environmental chemistry, civil/structural engineering, and aerospace. The analysis aims to critically discuss how functional principles/parameters and methods of interrogation affect the applicability of different OFS categories. The results reveal leading trends in the use of techniques like the use of fiber Bragg gratings (FBG) and distributed sensing in high-accuracy conditions or the rising role of extrinsic sensors in selective chemical situations and point out new approaches in areas like Artificial Intelligence (AI)- or Internet of Things (IoT)-integrated sensors. Further, this synthesis not only connects pieces of knowledge but also defines the technological barriers in terms of calibration cost and standardization: this provides strategic insight regarding future research and the scalability of industry deployment. Full article

(This article belongs to the Special Issue Advancements in Mode-Locked Lasers)

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26 pages, 2659 KB

Open AccessReview

Dispersion Compensation Scheme with a Simple Structure in Ultra-High-Speed Optical Fiber Transmission Systems

by Ying Wu, Ying Wang, Luhan Jiang and Jianjun Yu

Photonics 2026, 13(1), 39; https://doi.org/10.3390/photonics13010039 - 31 Dec 2025

Abstract

With the explosive growth of global data traffic, long-distance fiber optic transmission systems are continuously evolving towards higher capacity and longer distances. However, to overcome the high complexity of fiber dispersion compensation algorithms, various dispersion compensation techniques have emerged. This paper aims to [...] Read more.

With the explosive growth of global data traffic, long-distance fiber optic transmission systems are continuously evolving towards higher capacity and longer distances. However, to overcome the high complexity of fiber dispersion compensation algorithms, various dispersion compensation techniques have emerged. This paper aims to systematically review and summarize dispersion compensation algorithms in long-distance fiber optic transmission. First, we briefly introduce the physical mechanism of fiber dispersion. Then, this paper focuses on digital domain compensation algorithms, dividing them into two major categories: compensation algorithms without penalty and with penalty. For compensation algorithms without penalty, we elaborate on traditional block processing strategies such as Overlap-Save (OLS), and various enhanced strategies combining intelligent filter segmentation and optimized frequency domain workflows. For compensation algorithms with penalty, we focus on analyzing a scheme that redesigns chromatic dispersion compensation (CDC) algorithm into a hardware-friendly structure using geometric clustering of taps, and finite-impulse-response (FIR) filters based on frequency response approximating the ideal inverse chromatic dispersion (CD) transfer function. By numerical simulation, we analyze the core principles, computational complexity, and compensation performance of each type of algorithm. Finally, this paper summarizes the limitations and development trends of existing dispersion compensation algorithms, pointing out that low-complexity and small-scale deployment algorithm structures will be an important research direction in the future. Full article

(This article belongs to the Special Issue Machine Learning and Artificial Intelligence for Optical Networks)

9 pages, 1045 KB

Open AccessBrief Report

Kerr-Lens Mode-Locked Tm,Ho:Ca(Gd,Y)AlO₄ Laser

by Zhang-Lang Lin, Peixiong Zhang, Pavel Loiko, Xavier Mateos, Ge Zhang, Zhen Li, Zhenqiang Chen, Uwe Griebner, Weidong Chen and Valentin Petrov

Photonics 2026, 13(1), 38; https://doi.org/10.3390/photonics13010038 - 31 Dec 2025

Abstract

We demonstrate Kerr-lens mode-locked operation of a Tm,Ho:Ca(Gd,Y)AlO₄ laser pumped by a narrow-linewidth, continuous-wave Ti:sapphire laser at 797 nm. Soliton pulses as short as 145 fs are generated at 2087.8 nm in σ-polarization via soft-aperture Kerr-lens mode-locking, with an average output power [...] Read more.

We demonstrate Kerr-lens mode-locked operation of a Tm,Ho:Ca(Gd,Y)AlO₄ laser pumped by a narrow-linewidth, continuous-wave Ti:sapphire laser at 797 nm. Soliton pulses as short as 145 fs are generated at 2087.8 nm in σ-polarization via soft-aperture Kerr-lens mode-locking, with an average output power of 203 mW (0.5% output coupler) at ~80.5 MHz. To the best of our knowledge, this result represents the first demonstration of a Kerr-lens mode-locked laser based on a Tm,Ho:Ca(Gd,Y)AlO₄ crystal exhibiting both structural and compositional disorder. Full article

(This article belongs to the Special Issue Emerging Trends in Rare-Earth Doped Material for Photonics)

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12 pages, 3382 KB

Open AccessArticle

Passively Mode-Locked Fiber Laser Based on a TiO₂/SiO₂-Assisted Microsphere Resonator

by Tianjiao Wu, Tianshu Wang and Baoqun Li

Photonics 2026, 13(1), 37; https://doi.org/10.3390/photonics13010037 - 31 Dec 2025

Abstract

A composite dual-cavity passively mode-locked fiber laser based on a functionalized microsphere resonator is proposed and experimentally demonstrated. The nonlinear response of the resonator is enhanced by depositing TiO₂ film on a SiO₂ microsphere, which leads to improved mode-locking performance. The [...] Read more.

A composite dual-cavity passively mode-locked fiber laser based on a functionalized microsphere resonator is proposed and experimentally demonstrated. The nonlinear response of the resonator is enhanced by depositing TiO₂ film on a SiO₂ microsphere, which leads to improved mode-locking performance. The wavelength selectivity and optical field confinement of the microsphere resonator are exploited, allowing it to simultaneously serve as an intracavity narrowband filter and a nonlinear modulation element. The threshold of the mode-locked laser was measured to be as low as 34 mW, and stable mode-locked operation was achieved at a pump power of 105.7 mW, with a pulse duration of 2.8 ns, a repetition rate of 13.88 MHz, and a signal-to-noise ratio of 74.86 dB. The output spectrum exhibited a central wavelength of 1560.12 nm, a 3 dB linewidth of 0.06 nm, and a side-mode suppression ratio of 55.13 dB. This straightforward design provides an effective approach for the miniaturization of passively mode-locked fiber lasers. Full article

(This article belongs to the Special Issue Advanced Fiber Laser Technology and Its Application: 2nd Edition)

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21 pages, 3893 KB

Open AccessReview

Progress in Spectral Information Processing Technology for Brillouin Microscopy

by Zhaohong Liu, Xiaoxuan Li, Xiaorui Sun, Zihan Yu, Yunjun Gao, Yun Zhang, Yu Zhou, Qiang Su, Yuanqing Xia, Yulei Wang and Zhiwei Lv

Photonics 2026, 13(1), 36; https://doi.org/10.3390/photonics13010036 - 31 Dec 2025

Abstract

This paper systematically reviews the key spectral information extraction methods in Brillouin microscopy, aiming to address the core challenge of accurately extracting material mechanical parameters from raw spectra. Based on technical principles, the methods are categorized into three types for elaboration: Spontaneous Brillouin [...] Read more.

This paper systematically reviews the key spectral information extraction methods in Brillouin microscopy, aiming to address the core challenge of accurately extracting material mechanical parameters from raw spectra. Based on technical principles, the methods are categorized into three types for elaboration: Spontaneous Brillouin Scattering (SpBS) is characterized by low signal-to-noise ratio (SNR) and strong background interference, and its processing relies on high-precision spectrometers and complex preprocessing procedures to mitigate noise and background effects; Stimulated Brillouin Scattering (SBS) operates on the mechanism of optical gain/loss, which achieves significantly improved data SNR and thereby enables more robust and accurate Lorentzian fitting for spectral analysis; Impulsive Stimulated Brillouin Scattering (ISBS) retrieves the frequency spectrum by inverting time-domain oscillating signals, and the core of its processing lies in super-resolution algorithms such as Fast Fourier Transform (FFT) and the Matrix Pencil Method, which are tailored to match its high-speed data acquisition capability. The paper further compares the advantages and disadvantages of various methods, outlines future development trends of intelligent processing technologies such as deep learning and multi-modal data fusion, and provides a clear guide for selecting the optimal data processing strategy in different application scenarios. Full article

(This article belongs to the Special Issue AI for Photonics: Intelligent Imaging, Learning-Driven Optics, and Photonic Computing)

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3 pages, 144 KB

Open AccessEditorial

Editorial for the Special Issue “Advances in Holography and Its Applications” in Photonics

by Julia Marín-Sáez and Jesús Atencia

Photonics 2026, 13(1), 35; https://doi.org/10.3390/photonics13010035 - 31 Dec 2025

Abstract

Holography was first introduced by Dennis Gabor as a method to improve microscopic imaging [...] Full article

(This article belongs to the Special Issue Advances in Holography and Its Applications)

17 pages, 9023 KB

Open AccessArticle

Plasmonic Sensor Based on an MIM Waveguide Coupled with a Ring–Bridge–Rounded Square Resonator

by Weixin Liu, Shubin Yan, Zhenyang Xu, Yang Cui, Biyi Huang, Guang Liu, Di Zheng and Taiquan Wu

Photonics 2026, 13(1), 34; https://doi.org/10.3390/photonics13010034 - 30 Dec 2025

Abstract

Fano resonance sensors based on metal–insulator–metal (MIM) waveguides often face the challenge of balancing high sensitivity (S) and a high figure of merit (FOM). In this work, a high-performance refractive index sensor is proposed, consisting of a straight MIM waveguide side-coupled to a [...] Read more.

Fano resonance sensors based on metal–insulator–metal (MIM) waveguides often face the challenge of balancing high sensitivity (S) and a high figure of merit (FOM). In this work, a high-performance refractive index sensor is proposed, consisting of a straight MIM waveguide side-coupled to a novel ring–bridge–rounded square (RBS) resonator. The transmission characteristics and the formation mechanism of Fano resonance are systematically analyzed using the finite element method (FEM). The results demonstrate that the synergistic introduction of rounded square units and an internal bridge structure significantly enhances electromagnetic field localization and optimizes the coupling strength. The optimized device achieves a remarkable refractive index sensitivity of 3268 nm/RIU (refractive index unit, RIU) and a high FOM of 55.4. Furthermore, by employing ethanol as the filling medium, the proposed configuration functions as a temperature sensor, exhibiting a high linear sensitivity of 1.644 nm/°C over the range of −70 °C to 70 °C. The proposed RBS resonator holds promise for compact and high-precision nanophotonic sensing applications. Full article

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13 pages, 8549 KB

Open AccessArticle

Mach–Zehnder Interferometer Electro-Optic Modulator Based on Thin-Film Lithium Niobate Valley Photonic Crystal

by Ying Yao, Hongming Fei, Xin Liu, Mingda Zhang, Pengqi Dong, Junjun Ren and Han Lin

Photonics 2026, 13(1), 33; https://doi.org/10.3390/photonics13010033 - 30 Dec 2025

Abstract

Thin-film lithium niobate (TFLN) electro-optic modulators (EOMs) offer distinct advantages, including high speed, broad bandwidth, and low power consumption. However, their large size hinders the density of integration, which trades off with the half-wave voltage. Photonic crystal (PC) structures can effectively reduce the [...] Read more.

Thin-film lithium niobate (TFLN) electro-optic modulators (EOMs) offer distinct advantages, including high speed, broad bandwidth, and low power consumption. However, their large size hinders the density of integration, which trades off with the half-wave voltage. Photonic crystal (PC) structures can effectively reduce the device footprint via the slow-light effect; however, they experience significant losses due to fabrication defects and sharp corners. Here, we theoretically demonstrate an ultracompact Mach–Zehnder interferometer (MZI) EOM based on a TFLN valley photonic crystal (VPC) structure. The design can achieve a high forward transmittance (>0.8) due to defect-immune unidirectional propagation in the VPC, enabled by the unique spin-valley locking effect. The EOM, with a small footprint of 21 μm × 17 μm, achieves an extinction ratio of 16.13 dB and a modulation depth of 80%. The design can be experimentally fabricated using current nanofabrication techniques, making it suitable for broad applications in optical communications. Full article

(This article belongs to the Special Issue Photonics Metamaterials: Processing and Applications)

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15 pages, 3029 KB

Open AccessArticle

Simulation Analysis of Microwave Metasurface Sensing Based on Bound States in the Continuum

by Fanghao Li, Zhibao Huang and Tingting Lang

Photonics 2026, 13(1), 32; https://doi.org/10.3390/photonics13010032 - 30 Dec 2025

Abstract

High-sensitivity microwave sensing plays a vital role in material characterization and nondestructive testing, with its performance being largely determined by the quality factor (Q factor) of the sensing structure. In this work, a high-Q microwave metasurface sensor based on the mechanism of bound [...] Read more.

High-sensitivity microwave sensing plays a vital role in material characterization and nondestructive testing, with its performance being largely determined by the quality factor (Q factor) of the sensing structure. In this work, a high-Q microwave metasurface sensor based on the mechanism of bound states in the continuum (BIC) is designed and realized to overcome the intrinsic Q-factor limitations of conventional microwave resonators. By introducing a controlled asymmetric perturbation into the meta-atom, a quasi-BIC mode is successfully excited, and its sensing performance is systematically investigated through frequency-domain simulations. The results indicate that the proposed metasurface achieves an exceptionally high radiation Q factor of up to 4599.7 in the microwave band, along with a refractive index sensitivity of 31.267 GHz/RIU. These findings not only demonstrate the significant potential of the BIC mechanism for achieving ultra-high-Q microwave resonators but also provide an effective and promising approach for the development of high-performance microwave sensing systems. Full article

(This article belongs to the Special Issue Advances in Optical Sensors and Applications)

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14 pages, 1968 KB

Open AccessArticle

Multispectral Camouflage Photonic Structure for Visible–IR–LiDAR Bands with Radiative Cooling

by Lehong Huang, Yuting Gao, Bo Peng and Caiwen Ma

Photonics 2026, 13(1), 31; https://doi.org/10.3390/photonics13010031 - 30 Dec 2025

Abstract

The rapid development of detection technologies has increased the demand for multispectral camouflage materials capable of broadband concealment and effective thermal management. To address the conflicting optical requirements between infrared camouflage and LiDAR camouflage, we propose a composite design combining a germanium–ytterbium fluoride [...] Read more.

The rapid development of detection technologies has increased the demand for multispectral camouflage materials capable of broadband concealment and effective thermal management. To address the conflicting optical requirements between infrared camouflage and LiDAR camouflage, we propose a composite design combining a germanium–ytterbium fluoride (Ge/YbF₃) selective emitter with an amorphous silicon (a-Si) two-dimensional periodic microstructure. The multilayer film, optimized using the transfer-matrix method and a particle swarm optimisation algorithm, achieves low emissivity in the 3–5 μm and 8–14 μm infrared atmospheric windows and high emissivity within 5–8 μm for radiative cooling, while introducing a narrowband absorption peak at 1.55 μm. Additionally, the a-Si microstructure provides strong narrowband absorption at 10.6 μm via a grating-resonance mechanism. FDTD simulations confirm low emissivity in the infrared windows, high absorptance at LiDAR wavelengths, and good angular and polarization robustness. This work demonstrates a multifunctional photonic structure capable of integrating infrared camouflage, laser camouflage, and thermal-radiation control. Full article

(This article belongs to the Section Optoelectronics and Optical Materials)

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10 pages, 2281 KB

Open AccessCommunication

Photonic Nyquist Pulse Generation Based on Phase-Modulated Fiber Bragg Gratings in Transmission

by Xin Liu, Xuewen Shu and Lin Zhang

Photonics 2026, 13(1), 30; https://doi.org/10.3390/photonics13010030 - 30 Dec 2025

Abstract

Nyquist pulses are critical in optical communication networks and signal processing systems. We present, to our best knowledge, the first demonstration of all-optical Nyquist pulse generation using phase-modulated fiber Bragg gratings (PM-FBGs) in transmission. PM-FBGs are a class of fiber gratings that have [...] Read more.

Nyquist pulses are critical in optical communication networks and signal processing systems. We present, to our best knowledge, the first demonstration of all-optical Nyquist pulse generation using phase-modulated fiber Bragg gratings (PM-FBGs) in transmission. PM-FBGs are a class of fiber gratings that have a nearly uniform coupling strength and a spatially varying grating period. As examples, we have designed and numerically simulated photonic Nyquist pulses with roll-off factors of 0.9, 0.5, and 0.1, respectively. The grating profiles are obtained employing numerical optimization algorithms. Numerical simulations confirm that the generated pulses are in good agreement with ideal Nyquist pulses over a 500 GHz bandwidth and have a good tolerance to the variations in the input pulse width. Full article

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30 pages, 3773 KB

Open AccessReview

Thermoluminescence, a Critical Reappraisal of Successes, Uncertainties, and a Look to the Future

by Peter D. Townsend, Yafang Wang and Stephen W. S. McKeever

Photonics 2026, 13(1), 29; https://doi.org/10.3390/photonics13010029 - 29 Dec 2025

Abstract

Thermoluminescence has a long and successful history in applied radiation dosimetry, as well as in a wide range of other applications and basic research. However, there is a dichotomy that, despite the many commercial successes, there continue to be entrenched systematic errors in [...] Read more.

Thermoluminescence has a long and successful history in applied radiation dosimetry, as well as in a wide range of other applications and basic research. However, there is a dichotomy that, despite the many commercial successes, there continue to be entrenched systematic errors in data collection, signal processing, and models. This overview offers suggestions to address these issues. Improving initial data collection is certainly feasible and may offer deeper insights into the potential mechanisms of thermoluminescence. There is an extremely complex challenge in suggesting and confirming models for lattice sites that generate luminescence signals. Currently, such models are highly speculative and simplistic. In reality, they should involve not only immediate lattice sites but also extremely long-range interactions. Weaknesses in data collection and models impact and generate errors in the extraction of activation energies and frequency factors that are routinely ascribed to data analysis. Overall, it is possible to suggest ways to improve data collection and slightly improve modelling of relevant lattice sites and parameters such as their activation energies, but in reality, these factors will always be speculative and imprecise. Fortunately, this does not inhibit the extension of the technique into other areas of application, but the suggested improvements will enable greater diversity. Full article

(This article belongs to the Section Optoelectronics and Optical Materials)

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18 pages, 6167 KB

Open AccessArticle

Reconfigurable Millimeter-Wave Generation via Mutually Injected Spin-VCSELs

by Yichuan Xiong, Yu Huang, Pei Zhou, Kuenyao Lau and Nianqiang Li

Photonics 2026, 13(1), 28; https://doi.org/10.3390/photonics13010028 - 29 Dec 2025

Abstract

We propose a novel scheme for generating high-frequency millimeter-wave signals by exploiting period-one (P1) dynamics in a mutual injection configuration of two spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs). The frequency of the generated millimeter-wave signal is jointly determined by the birefringence rate of the [...] Read more.

We propose a novel scheme for generating high-frequency millimeter-wave signals by exploiting period-one (P1) dynamics in a mutual injection configuration of two spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs). The frequency of the generated millimeter-wave signal is jointly determined by the birefringence rate of the spin-VCSEL and the frequency detuning between the two lasers. By leveraging the complex dynamics of free-running spin-VCSELs, we explore the coupling of three distinct dynamic states: continuous-wave (CW) injected into CW, CW injected into P1 oscillation, and P1 oscillation injected into P1 oscillation. Our results reveal that these interactions not only enhance the tunability and frequency of the millimeter-wave output but also significantly reduce the linewidth, offering substantial advantages for reconfigurable photonic systems. This study demonstrates the remarkable potential of mutually injected spin-VCSELs for generating high-performance, tunable photonic millimeter waves and highlights their promising applications in advanced communication and radar systems. Full article

(This article belongs to the Special Issue Vertical-Cavity Surface-Emitting Laser Technology: Innovations and Future Trends)

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13 pages, 4519 KB

Open AccessArticle

Systematic Analyses of the Ideal Selective Spectrum and the Practical Design Strategies for the Solar Thermophotovoltaic System

by Yuanlin Chen, Zhiwei Zhang, Yulian Li, Qiulong Chen, Bowen An and Jiajia Jiao

Photonics 2026, 13(1), 27; https://doi.org/10.3390/photonics13010027 - 29 Dec 2025

Abstract

Solar thermophotovoltaic (STPV) systems can break the Shockley–Queisser (SQ) limit through selective absorbers and emitters, whose ideal emissivity is crucial as a design target. In this paper, we systematically analyze the ideal selective spectrum and solve the conflict between energy and efficiency in [...] Read more.

Solar thermophotovoltaic (STPV) systems can break the Shockley–Queisser (SQ) limit through selective absorbers and emitters, whose ideal emissivity is crucial as a design target. In this paper, we systematically analyze the ideal selective spectrum and solve the conflict between energy and efficiency in photothermal conversion efficiency by modifying the corresponding equation. The ideal emissivity of the absorber is one in [

E_{c}

, ∞] and zero out of this range. For actual design, if spectra deviation cannot be avoided,

E_{c}

is preferable to redshifting. The ideal emissivity of the emitter is one in

[E_{g}, E_{\max}]

and the decrease in

E_{\min}

should be suppressed relative to

E_{\max}

. Besides, the optimal bandwidth of the emitter is about 0.08 eV for different photovoltaic cells and working conditions, which gives a rough and valuable guide in practical design. The analytical progress and design strategies will give a reference and direction for the future design of STPV. Full article

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19 pages, 2443 KB

Open AccessArticle

Wide-Range All-Fiber Optical Current Transformer Based on Spatial Non-Reciprocal Phase Modulation

by Tianxiao Zhang, Weibin Feng, Haosong Yang, Yanyan Liu and Yuefeng Qi

Photonics 2026, 13(1), 26; https://doi.org/10.3390/photonics13010026 - 29 Dec 2025

Abstract

A reflective all-fiber optical current transformer based on a spatial non-reciprocal phase modulation technique is investigated by theoretical analysis and experimental measurement. The modulation unit, composed of a phase delay wave plate (LiNbO₃) and two Faraday rotators, achieves flexible frequency adjustment [...] Read more.

A reflective all-fiber optical current transformer based on a spatial non-reciprocal phase modulation technique is investigated by theoretical analysis and experimental measurement. The modulation unit, composed of a phase delay wave plate (LiNbO₃) and two Faraday rotators, achieves flexible frequency adjustment by converting modulation from the time domain to the spatial domain. Therefore, the avoidance of the impact caused by delay coils is achieved in principle. The absence of intrinsic frequency limitations eliminates the demand for precise timing control in demodulation, thereby simplifying the demodulation circuit and reducing the cost and size of the transformer. In previous studies, redundancies were identified in the optical path coupling devices. The half-wave voltage of the modulator is excessively high, and its size is considerable due to constraints inherent in the manufacturing process. The measurement range is within 1800 A. The scheme simplifies some optical path components. By optimizing the phase delay wave plate, the half-wave voltage of the modulator is significantly reduced by a factor of 150. Experimental results demonstrate that the current transformer exhibits excellent detection consistency within the rated current range of 30–3600 A (1–120%), the response time is within 3 ms, and the measurement error and peak error reach 0.052% and 0.127%. This configuration provides a novel option for the design and practical application of all-fiber optical current transformers. Full article

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