Photonics

16 pages, 1519 KB

Open AccessArticle

Single-Path Spatial Polarization Modulation for Vector Transmission Matrix Measurement and Polarization Control in Scattering Media

by Edvard Grigoryan, Aram Sargsyan, Tatevik Sarukhanyan and Mushegh Rafayelyan

Photonics 2025, 12(11), 1145; https://doi.org/10.3390/photonics12111145 - 20 Nov 2025

Viewed by 827

Abstract

Controlling light’s polarization through disordered media is crucial for advanced optical applications but remains challenging due to scattering and depolarization. Most existing approaches either require interferometric or multi-path measurements, or they recover only part of the polarization response. We present a comprehensive approach [...] Read more.

Controlling light’s polarization through disordered media is crucial for advanced optical applications but remains challenging due to scattering and depolarization. Most existing approaches either require interferometric or multi-path measurements, or they recover only part of the polarization response. We present a comprehensive approach for spatially resolved polarization control by accurately retrieving the vector transmission matrix (VTM) of a scattering system from intensity-only, full-Stokes polarimetric measurements. Using a simple single-path setup comprising a liquid-crystal spatial light modulator (SLM) with a tunable retarder after it, we achieve spatial polarization modulation at the input, thereby enabling probing of the medium’s polarization–scattering characteristics. The VTM is retrieved with an adapted Gerchberg–Saxton procedure that enforces not only the measured output amplitudes but also the relative phase between the two orthogonal output polarization components obtained from the Stokes parameters. We show that a single retarder setting results in inter-block correlations in the retrieved VTM due to input coupling, while two linearly independent retarder settings decouple the intrinsic blocks and recover the full VTM. In our experiment, for a

16 \times 16

set of input–output spatial modes, the VTM is retrieved with about

90 %

accuracy, enabling polarization-resolved focusing with up to

10 \times

enhancement for horizontal, vertical, arbitrary linear, and circular states. This work offers a compact framework for active polarization shaping and for polarimetric characterization of complex media, advancing our understanding of vectorial light–matter interactions. Full article

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8 pages, 419 KB

Open AccessCommunication

Parallel DNA Molecular Analysis Platform Based on a Plano-Concave Fabry–Pérot Microcavity Laser Array

by Chan Seok Jun and Wonsuk Lee

Photonics 2025, 12(11), 1144; https://doi.org/10.3390/photonics12111144 - 20 Nov 2025

Viewed by 328

Abstract

We present a parallel DNA molecular analysis platform based on an array of plano-concave Fabry–Pérot (PC-FP) microcavity lasers that enables the simultaneous, sequence-specific detection of multiple DNA targets. Each PC-FP cavity is functionalized with a distinct probe DNA and integrated within a microfluidic [...] Read more.

We present a parallel DNA molecular analysis platform based on an array of plano-concave Fabry–Pérot (PC-FP) microcavity lasers that enables the simultaneous, sequence-specific detection of multiple DNA targets. Each PC-FP cavity is functionalized with a distinct probe DNA and integrated within a microfluidic channel, allowing localized hybridization and lasing emission upon optical pumping. When Cy3-labeled complementary targets were introduced, distinct lasing peaks emerged from corresponding cavities at ~607 nm, whereas single-base-mismatched sequences produced no measurable signal. The lasing threshold was approximately 0.6 µJ/mm², confirming highly efficient optical feedback and cavity-enhanced signal amplification. The parallel operation of three PC-FP cavities demonstrated independent, multiplexed detection without optical crosstalk. The plano-concave geometry provides mode stability, compact alignment tolerance, and a tenfold reduction in threshold compared to flat FP mirrors. These results highlight the potential of PC-FP microcavity laser arrays as a scalable alternative to fluorescence-based assays, offering rapid, high-throughput DNA hybridization and melting analysis within a miniaturized solid-state architecture. Full article

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10 pages, 5047 KB

Open AccessArticle

Topological Phase Transition by Tuning Central Unit in C₃ Symmetric Lattice of Terahertz Photonic Crystals

by Zhigang Yan, Kangrong Deng, Shuangjie Song, Tingting Liu, Jinhui Cai, Le Zhang and Bo Fang

Photonics 2025, 12(11), 1143; https://doi.org/10.3390/photonics12111143 - 19 Nov 2025

Viewed by 393

Abstract

A terahertz band-switchable photonic topological insulator (PTI) composed of a C₃-symmetric rod-type photonic crystal is designed. By tuning the size of the central cylinder in the lattice, a topological phase transition can occur in the PTI, and the topological nontrivial bandgap [...] Read more.

A terahertz band-switchable photonic topological insulator (PTI) composed of a C₃-symmetric rod-type photonic crystal is designed. By tuning the size of the central cylinder in the lattice, a topological phase transition can occur in the PTI, and the topological nontrivial bandgap can be switched from the first to the second bandgap. In both cases, before and after switching, topological edge-state transport of terahertz waves along zigzag topological domain walls, as well as terahertz corner-state localization in constructed resonant cavities, are numerically demonstrated. In addition, an existence of the topological phase transition is also confirmed when tuning the central unit in the lattice of another C₃-symmetric hole-type photonic crystal. This work provides a new approach for flexible terahertz waveguiding and lasing applications. Full article

(This article belongs to the Special Issue Emerging Terahertz Devices and Applications)

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10 pages, 2738 KB

Open AccessCommunication

Power Domain Hybrid Modulation-Based Coherent Optical Transmission with Successive Interference Cancelation

by Xiaoling Zhang and Yong Geng

Photonics 2025, 12(11), 1142; https://doi.org/10.3390/photonics12111142 - 19 Nov 2025

Viewed by 404

Abstract

The 6G era necessitates advanced multiplexing techniques that fully utilize various physical dimensions, including time, frequency, polarization, and space to enhance the achievable bitrate per wavelength and satisfy growing demands for capacity and spectral efficiency. Power domain hybrid modulation (PDHM) emerges as a [...] Read more.

The 6G era necessitates advanced multiplexing techniques that fully utilize various physical dimensions, including time, frequency, polarization, and space to enhance the achievable bitrate per wavelength and satisfy growing demands for capacity and spectral efficiency. Power domain hybrid modulation (PDHM) emerges as a viable technology to overcome the orthogonal limitations inherent in existing multiplexing schemes. In this paper, we introduce an iterative successive interference cancelation (SIC) algorithm for coherent optical transmission systems employing PDHM. The proposed system multiplexes a 16-ary quadrature amplitude modulation (16-QAM) signal with a quadrature phase shift keying (QPSK) signal at distinct power ratios. With the proposed iterative SIC, the system performance is improved by about one order of magnitude. Full article

(This article belongs to the Special Issue Advancements in Optical Information Processing and Communication Technologies)

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21 pages, 3110 KB

Open AccessArticle

High-Precision Construction of Off-Axis Multi-Reflective Systems for a Single Field of View Based on a Stable Initialization Seed Curve Extension Algorithm

by Yuan Hu and Jiaqi Huo

Photonics 2025, 12(11), 1141; https://doi.org/10.3390/photonics12111141 - 18 Nov 2025

Viewed by 280

Abstract

Freeform optical design is regarded as a key approach to overcoming the performance limits of traditional imaging systems. However, the existing Seed Curve Expansion (SCE) algorithm has two major limitations. First, the initial and ideal image points are selected randomly, causing unstable optical [...] Read more.

Freeform optical design is regarded as a key approach to overcoming the performance limits of traditional imaging systems. However, the existing Seed Curve Expansion (SCE) algorithm has two major limitations. First, the initial and ideal image points are selected randomly, causing unstable optical performance and low construction accuracy, especially under finite object distance and non-paraxial incidence. Multiple trials are often needed, reducing efficiency and repeatability. Second, the algorithm cannot constrain aperture, focal length, or geometry; thus, despite good imaging quality, the final system parameters often deviate from design requirements, limiting engineering applicability. To address these issues, this work proposes a Stable Initialization Seed Curve Expansion (SI-SCE) algorithm based on ray tracing and Fermat’s principle. The method accurately calibrates the initial point and the ideal image point, eliminating uncertainties caused by randomness. A virtual auxiliary surface strategy is introduced to achieve high-precision freeform construction under finite object distance. In addition, a parameter constraint mechanism is embedded in the algorithm, enabling the designed off-axis multi-reflective freeform system to directly meet specified requirements on pupil diameter, focal length, and geometric size. The feasibility of the SI-SCE algorithm was demonstrated by designing a freeform off-axis three-mirror imaging system with a rectangular

6 ° \times 6 °

field of view and a moderate F-number. The final system features an F-number of 3.4 and an entrance pupil diameter of 60 mm. It achieves diffraction-limited performance across the Visible–NIR

(0.38 - 2 μ m)

wavelength range. Full article

(This article belongs to the Special Issue Emerging Topics in Freeform Optics)

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17 pages, 4405 KB

Open AccessArticle

A Pre-Measurement Device for Contour Measurement Path Planning of Complex Small Workpieces

by Lei Liu, Zexiao Li and Xiaodong Zhang

Photonics 2025, 12(11), 1140; https://doi.org/10.3390/photonics12111140 - 18 Nov 2025

Viewed by 281

Abstract

Small overall dimensions, intricate geometries, and discontinuous local surface normals characterize complex small workpieces. These features impose stringent requirements on the alignment accuracy of the workpieces when using a profilometer for three-dimensional surface measurement. This paper presents a pre-measurement method based on a [...] Read more.

Small overall dimensions, intricate geometries, and discontinuous local surface normals characterize complex small workpieces. These features impose stringent requirements on the alignment accuracy of the workpieces when using a profilometer for three-dimensional surface measurement. This paper presents a pre-measurement method based on a reverse projection algorithm. By capturing shadow contours from multiple viewing angles, the three-dimensional pointcloud of the workpiece can be reconstructed. The reconstructed pointcloud is then used to analyze the workpiece pose and guide the path planning of a point-scanning profilometer. Experimental results show that, for a standard sphere with a radius of 12,703 mm, the measured results of the proposed measurement device achieve a fitted radius deviation of 1.8 μm when measuring 70% of the area of the spherical surface. This accuracy meets the precision requirement for guiding the path planning of the profilometer. Furthermore, the measured results from the device are employed to correct the scanning path of a five-axis profilometer for complex workpieces, such as cross-cylinder workpieces, without the need for manual pose adjustment or high-precision fixtures. Full article

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19 pages, 4316 KB

Open AccessArticle

Development of a Spindle-Type FBG Pressure Sensor for Pressure Monitoring at the Wind Turbine Foundation Ring–Concrete Interface

by Xinxing Chen, Wenjing Wu, Zhenpeng Yang, Shijie Zheng and Heming Wei

Photonics 2025, 12(11), 1139; https://doi.org/10.3390/photonics12111139 - 18 Nov 2025

Viewed by 385

Abstract

This study presents a fiber Bragg grating (FBG) pressure sensor with a spindle-type protective structure, optimized using the NSGA-II algorithm, for monitoring pressure variations at the contact interface between wind turbine foundation rings and concrete. To optimize the sensor sensitivity and measurement range, [...] Read more.

This study presents a fiber Bragg grating (FBG) pressure sensor with a spindle-type protective structure, optimized using the NSGA-II algorithm, for monitoring pressure variations at the contact interface between wind turbine foundation rings and concrete. To optimize the sensor sensitivity and measurement range, the NSGA-II algorithm was employed to determine the optimal structural dimensions and material properties of the spindle-type sensor. This approach addresses two critical challenges: firstly, enhancing the survivability of FBG pressure sensors in harsh service environments, and secondly, enabling accurate monitoring of weak pressure signals at the foundation ring–concrete interface. Linearity verification tests demonstrate a sensor sensitivity of 55.01 pm/MPa within a 10 MPa measurement range, accompanied by a linear correlation coefficient of 0.999, confirming high stability of the fabricated sensors. Furthermore, wind turbine foundation model experiments validate the practical service performance of the proposed sensor. Results indicate that the spindle-type FBG pressure sensor not only withstands severe operating conditions but also achieves real-time monitoring of interfacial pressure changes in foundation ring–concrete systems. Full article

(This article belongs to the Special Issue Optical Fibers Beyond Communication: Advances in Sensing, Imaging, and Energy Applications)

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13 pages, 2871 KB

Open AccessArticle

Genetic-Algorithm-Driven Intelligent Spatiotemporal Mode-Locking in All-Fiber Laser with Hysteresis

by Yangbing Lin, Yongguo Zheng and Xinhai Zhang

Photonics 2025, 12(11), 1138; https://doi.org/10.3390/photonics12111138 - 18 Nov 2025

Viewed by 577

Abstract

We demonstrate a robust intelligent spatiotemporal mode-locked fiber laser with large modal dispersion, based on the nonlinear polarization rotation mechanism and an electric polarization controller (EPC). The hysteresis phenomenon induced by the polarization controller poses a substantial challenge to achieving stable intelligent spatiotemporal [...] Read more.

We demonstrate a robust intelligent spatiotemporal mode-locked fiber laser with large modal dispersion, based on the nonlinear polarization rotation mechanism and an electric polarization controller (EPC). The hysteresis phenomenon induced by the polarization controller poses a substantial challenge to achieving stable intelligent spatiotemporal mode-locking (STML). To address this, we propose and implement a memory-diffusion genetic algorithm to achieve stable STML operation with a single-pulse energy of 8.6 nJ via automatic EPC optimization. Thus, understanding and coping with hysteresis is crucial for realizing robust intelligent STML fiber lasers. To the best of our knowledge, this is the first demonstration of an intelligent all-fiber STML laser operating under large modal dispersion. This work provides a new pathway toward achieving stable and intelligent spatiotemporal mode locking in fiber lasers. Full article

(This article belongs to the Special Issue The Interaction between Photonics and Machine Learning)

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12 pages, 6151 KB

Open AccessArticle

Watt-Level Tunable Mid-Infrared Laser Emission at 2.8 μm Generated by Stimulated Raman Scattering of Methane Molecules in Hollow-Core Fibers

by Peicong Liu, Wenxi Pei, Luohao Lei, Tianyu Li, Guorui Lv, Qi Chen, Guangrong Sun, Shuyi Wang, Zhiyue Zhou and Zefeng Wang

Photonics 2025, 12(11), 1137; https://doi.org/10.3390/photonics12111137 - 18 Nov 2025

Viewed by 490

Abstract

Fiber lasers operating at 2.8 μm have important applications in fields such as polymer material processing and medical surgery. Fiber gas lasers (FGLs) based on stimulated Raman scattering (SRS) in hollow-core fibers (HCFs) provide a superior approach to generating tunable, high-power laser at [...] Read more.

Fiber lasers operating at 2.8 μm have important applications in fields such as polymer material processing and medical surgery. Fiber gas lasers (FGLs) based on stimulated Raman scattering (SRS) in hollow-core fibers (HCFs) provide a superior approach to generating tunable, high-power laser at 2.8 μm. Here, we demonstrated a watt-level mid-infrared FGL with a tuning range from 2812 nm to 2862 nm by the SRS of methane molecules in a 26.7 m long HCF. By pumping with a tunable pulsed fiber amplifier at 1.5 μm, an average output power of approximately 1 W was obtained, with a low Raman threshold peak power of 1.7 kW. Additionally, we observed transverse mode instability (TMI) in the HCFs, which has rarely been reported previously, and propose that the TMI was caused by the thermal effect generated when methane molecules absorbed the pump laser. This work achieved both the wavelength flexibility and watt-level power of FGLs based on methane-filled HCFs in the 2.8 μm waveband. It also found that the TMI was a key factor limiting further improvement in output power. This work provides important experimental basis and optimization directions for the future realization of higher-power tunable fiber lasers in the 2.8 μm waveband. Full article

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22 pages, 5389 KB

Open AccessArticle

Design and Analysis of a Photonic Crystal Fiber Sensor for Identifying the Terahertz Fingerprints of Water Pollutants

by Sajjad Mortazavi, Somayeh Makouei, Karim Abbasian and Sebelan Danishvar

Photonics 2025, 12(11), 1136; https://doi.org/10.3390/photonics12111136 - 18 Nov 2025

Cited by 1 | Viewed by 534

Abstract

Ensuring the purity of water sources is a paramount global challenge, necessitating the development of highly sensitive and rapid detection technologies. In this work, a novel Zeonex-based photonic crystal fiber (PCF) sensor is designed and numerically analyzed for the effective differentiation of pure [...] Read more.

Ensuring the purity of water sources is a paramount global challenge, necessitating the development of highly sensitive and rapid detection technologies. In this work, a novel Zeonex-based photonic crystal fiber (PCF) sensor is designed and numerically analyzed for the effective differentiation of pure and polluted water by identifying their unique fingerprints in the terahertz (THz) spectrum. The proposed structure features a rectangular core for analyte infiltration, surrounded by a unique hybrid cladding, meticulously engineered with four inner “mode-shaping” rectangular air holes and an outer “confinement” ring of elliptical air holes. This complex topology is strategically designed to maximize the core-power fraction while ensuring robust mode confinement, enabling the exceptional performance metrics observed. The guiding properties and sensing performance of the sensor are rigorously scrutinized using the Finite Element Method (FEM) over a broad frequency range of 0.5 to 3 THz, accommodating analytes with refractive indices from 1.33 to 1.46. This range is specifically chosen to cover the refractive index of pure water (≈1.33) and a broad spectrum of common chemical and biological pollutants. The simulation results demonstrate the exceptional performance of the sensor. For polluted water, the sensor achieves an ultra-high relative sensitivity of 99.6% with a negligible confinement loss of 1.4 × 10⁻¹¹ dB/m at an operating frequency of 3 THz. In contrast, pure water exhibits a high sensitivity of 96% and a confinement loss 9.4 × 10⁻⁶ of dB/m at the same frequency, showcasing a remarkable capability to distinguish between different water qualities. The superior sensitivity, extremely low loss, and structurally feasible design make the proposed PCF sensor an up-and-coming candidate for real-time water quality monitoring within the THz domain. Full article

(This article belongs to the Special Issue Emerging Technologies and Applications in Fiber Optic Sensing)

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11 pages, 1020 KB

Open AccessArticle

Coherent Perfect Absorption in a Parametric Cavity-Ensemble System

by Zi-Wei Li, Yan-Xue Cheng, Ying-Xia Wu, Jiaojiao Chen and Wei Xiong

Photonics 2025, 12(11), 1135; https://doi.org/10.3390/photonics12111135 - 17 Nov 2025

Viewed by 416

Abstract

We propose a scheme to achieve CPA not only in the strong-coupling regime but also in the weak-coupling regime. The system under consideration consists of an atomic ensemble coupled to an optical cavity containing an optical parametric amplifier (OPA). We show that when [...] Read more.

We propose a scheme to achieve CPA not only in the strong-coupling regime but also in the weak-coupling regime. The system under consideration consists of an atomic ensemble coupled to an optical cavity containing an optical parametric amplifier (OPA). We show that when the OPA introduces an effective loss, CPA can occur only in the strong-coupling regime. In contrast, when the OPA provides an effective gain, CPA can emerge in both the weak- and strong-coupling regimes. We further demonstrate that in the weak-coupling regime, CPA cannot occur within the bistable region, whereas in the strong-coupling regime, CPA can indeed appear in the bistable region. Moreover, the output intensity can be flexibly controlled by tuning the effective strength and the phase of the OPA. Our work opens a potential way to design a coherent perfect absorber based on weak coupling mechanism. Full article

(This article belongs to the Special Issue Quantum Optics: Communication, Sensing, Computing, and Simulation)

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22 pages, 690 KB

Open AccessArticle

Liouvillian Superoperator and Maxwell–Bloch Dynamics Under Optical Feedback via the Self-Mixing Effect in Terahertz Quantum Cascade Lasers

by Aleksandar Demić, Zoran Ikonić, Paul Dean, Xiaoqiong Qi, Thomas Taimre, Karl Bertling, Aleksandar D. Rakić and Dragan Indjin

Photonics 2025, 12(11), 1134; https://doi.org/10.3390/photonics12111134 - 17 Nov 2025

Viewed by 464

Abstract

We present a Maxwell–Bloch dynamics model for Terahertz Quantum Cascade Lasers (THz QCLs) that integrates a density matrix transport model, independent of the number of states per QCL period, with the Maxwell wave equation under the slow-varying envelope approximation. This model is extended [...] Read more.

We present a Maxwell–Bloch dynamics model for Terahertz Quantum Cascade Lasers (THz QCLs) that integrates a density matrix transport model, independent of the number of states per QCL period, with the Maxwell wave equation under the slow-varying envelope approximation. This model is extended to include external homodyne feedback, generalizing the Lang–Kobayashi model typically used for diode lasers. Unlike previous approaches, our model allows for the simulation of the self-mixing (SM) effect in THz QCLs without the need for effective parameters, commonly used in diode laser models. We demonstrate the model’s ability to capture laser dynamics and analyze the SM effect through numerical simulations. The model enables us to evaluate the quality of THz QCL designs for SM applications, which is not possible with effective two-level treatment via the Lang–Kobayashi approach. Full article

(This article belongs to the Special Issue Quantum Cascade Lasers: Recent Progress and Novel Applications)

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10 pages, 2176 KB

Open AccessArticle

Trace Gas Monitoring by Hollow-Core Anti-Resonant Fiber-Enhanced Raman Spectroscopy with Sub-ppm Sensitivity

by Xuran Zhu, Hanwen Yu, Xiao Wang, Yanzong Meng, Huixin Liu, Hongsong Lian and Qingwen Lian

Photonics 2025, 12(11), 1133; https://doi.org/10.3390/photonics12111133 - 17 Nov 2025

Viewed by 488

Abstract

The demand for accurate and sensitive trace gas detection in environmental monitoring and industrial diagnostics has driven the development of compact, high-performance Raman-based sensing systems. In this study, a hollow-core anti-resonant fiber (HC-ARF)-enhanced Raman spectroscopy system was developed to improve detection sensitivity. A [...] Read more.

The demand for accurate and sensitive trace gas detection in environmental monitoring and industrial diagnostics has driven the development of compact, high-performance Raman-based sensing systems. In this study, a hollow-core anti-resonant fiber (HC-ARF)-enhanced Raman spectroscopy system was developed to improve detection sensitivity. A double-lens signal collection module coupled with a small-core multimode fiber (MMF) was designed to improve Raman signal collection efficiency while mitigating background interference. Together with the CCD row-selective integration strategy, this configuration effectively minimized spatially nonuniform noise and enhanced the overall signal-to-noise ratio of the system. The system performance was systematically evaluated under varying integration times, demonstrating linearity, repeatability, and long-term stability. Under optimized conditions, sub-ppm detection limits were achieved for CO₂ isotopic species (¹²CO₂: 5.13 ppm, ¹³CO₂: 0.82 ppm) and multiple hydrocarbons including CH₄ (2.5 ppm), C₂H₂ (2.7 ppm), C₂H₄ (2.84 ppm), and C₂H₆ (0.57 ppm). These results confirm the performance of the proposed configuration for multi-component gas detection. Overall, this work provides an effective strategy for noise suppression in HC-ARF-based fiber-enhanced Raman systems and demonstrates their potential for real-time, high-precision environmental and industrial gas analysis. Full article

(This article belongs to the Special Issue Advanced Optical Fiber Sensors for Harsh Environment Applications)

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13 pages, 1739 KB

Open AccessArticle

The Diffusion of Triplet Excitons in Perylenediimide Derivative Crystals

by Changyu Gao, Hongyan Shi, Jiafan Qu, Bo Gao and Chunfeng Hou

Photonics 2025, 12(11), 1132; https://doi.org/10.3390/photonics12111132 - 16 Nov 2025

Viewed by 358

Abstract

Perylenediimide derivatives are materials that exhibit singlet fission (SF), capable of absorbing a single photon to generate multiple triplet excitons. This exciton multiplication process holds the potential to surpass the Shockley-Queisser limit. To effectively harness the energy of triplet excitons, they must possess [...] Read more.

Perylenediimide derivatives are materials that exhibit singlet fission (SF), capable of absorbing a single photon to generate multiple triplet excitons. This exciton multiplication process holds the potential to surpass the Shockley-Queisser limit. To effectively harness the energy of triplet excitons, they must possess sufficient diffusion capability. However, the diffusion of triplet excitons in perylenediimide derivatives has rarely been studied. In this work, we synthesized perylenediimide derivative crystals (C5) and fabricated composites (C5-Pe-QDs) by incorporating surface-ligand-functionalized quantum dots (Pe-QDs) at varying concentrations. The Pe-QDs act as traps within the C5 crystals, capturing triplet excitons when they diffuse into their capture range. The experimental and computational results indicate that the diffusion coefficient of triplet excitons in C5 crystals is approximately 3.58 × 10⁻⁵ cm² s⁻¹, with a diffusion length of about 50.9 nm. Using Monte Carlo simulations, we estimated the triplet exciton capture probability by Pe-QDs under ideal distribution conditions to be around 79.5%. The above findings indicate that, in the C5-Pe-QDs composites, triplet excitons can efficiently diffuse to the quantum dots, providing a novel and viable pathway for the effective utilization of triplet exciton energy in silicon-based photovoltaic systems. Full article

(This article belongs to the Section Optical Interaction Science)

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10 pages, 3281 KB

Open AccessArticle

Multi-Peak Narrowband Perfect Absorber Based on the Strong Coupling Between Fabry–Perot Mode and SPP Waveguide Mode

by Yusheng Zhai, Weiji He and Qian Chen

Photonics 2025, 12(11), 1131; https://doi.org/10.3390/photonics12111131 - 15 Nov 2025

Viewed by 417

Abstract

Plasmonic- or metamaterial-based multi-narrowband perfect absorbers hold significant potential applications in filtering, photodetection, and spectroscopic sensing. However, it is rather challenging to realize multi-peak and narrowband absorption simultaneously only using plasmonic metallic materials due to the single or dual resonance and large optical [...] Read more.

Plasmonic- or metamaterial-based multi-narrowband perfect absorbers hold significant potential applications in filtering, photodetection, and spectroscopic sensing. However, it is rather challenging to realize multi-peak and narrowband absorption simultaneously only using plasmonic metallic materials due to the single or dual resonance and large optical losses in the metallic nanostructure. Here, we numerically demonstrate a new multi-narrowband perfect absorber based on the strong coupling between the Fabry–Perot cavity modes and the surface plasmon polariton waveguide modes in a nanostructure consisting of periodic Ag grating and Ag film separated by a SiO₂ waveguide layer. Six absorption peaks, an ultranarrow absorption resonance with FWHM as narrow as 8 nm, and an absorption peak amplitude surpassing 95% have been achieved. Furthermore, the optical properties of the designed nanostructures can be precisely tuned by modulating the grating period, slit width, height, as well as the thickness and refractive index of the waveguide layer. This approach establishes a versatile platform for designing high performance multi-narrowband absorbers, with promising applications in optical filters, nonlinear optics, and biosensors. Full article

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13 pages, 1248 KB

Open AccessArticle

Structure-Optimized Photonic Phase-Change Memory Achieving High Storage Density and Endurance Towards Reconfigurable Telecommunication Systems

by Chen Gao, Zhou Han, Gaofei Wang and Wentao Huang

Photonics 2025, 12(11), 1130; https://doi.org/10.3390/photonics12111130 - 15 Nov 2025

Viewed by 1142

Abstract

Next-generation photonic memory, leveraging broad spectral operability and electromagnetic immunity, enables ultrafast data storage with high density, overcoming the physical limitations of silicon-based electronic memory in the post-Moore era. Phase-change materials (PCMs) are particularly promising for photonic memory due to their exceptional optical [...] Read more.

Next-generation photonic memory, leveraging broad spectral operability and electromagnetic immunity, enables ultrafast data storage with high density, overcoming the physical limitations of silicon-based electronic memory in the post-Moore era. Phase-change materials (PCMs) are particularly promising for photonic memory due to their exceptional optical contrast between amorphous and crystalline states. Furthermore, photonic phase-change memory can be deployed as tunable components (such as optical attenuators and delay lines) within reconfigurable integrated photonic systems for telecommunications and computing. Here, we optimize the thickness of PCM cells to maximize crystalline-state light absorption and enhance transmission contrast. The resulting photonic memory achieves outstanding performance: ultralow-energy programming (0.96 pJ/operation), 9 fJ detection sensitivity, >10⁵ s retention, 6000-cycle endurance, and multi-level storage capacity (209 distinct states). Furthermore, by structuring the PCM into a micro-cylinder array atop a PCM film, we achieve stable transmission contrast through 2 × 10⁶ cycles—far exceeding the durability of single-cell structures—and an 8.69 dB improvement in contrast over film-free micro-cylinder arrays. These advances highlight the critical role of microstructural optimization in enabling high-performance, on-chip photonic memory for future integrated photonic telecommunication and computing systems. Full article

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9 pages, 2194 KB

Open AccessCommunication

High-Modulation-Efficiency Lithium Niobate Electro-Optic Modulator Based on Sunken Dual-Layer Electrode

by Yicheng Huang, Qing Liao, Yihui Yin, Zanhui Chen, Fabi Zhang, Tangyou Sun, Haiou Li and Meihua Shou

Photonics 2025, 12(11), 1129; https://doi.org/10.3390/photonics12111129 - 14 Nov 2025

Viewed by 775

Abstract

Electro-optic modulators with high bandwidth, high modulation efficiency, and low loss play a crucial role in many fields, such as artificial intelligence, analog communications, and satellite data links. The modulation efficiency and loss, which are related to the chip size and integration, are [...] Read more.

Electro-optic modulators with high bandwidth, high modulation efficiency, and low loss play a crucial role in many fields, such as artificial intelligence, analog communications, and satellite data links. The modulation efficiency and loss, which are related to the chip size and integration, are important parameters for modulators. However, the modulation efficiency and optical loss of electro-optic modulators are interrelated in general. In this study, an improved scheme combining sunken electrodes and dual-layer capacitance-loaded electrodes is exhibited, improving the constraint between the modulation efficiency and optical loss of thin-film lithium niobate electro-optic modulators by enhancing the electric field effect. An electro-optic modulator with a high bandwidth (>60 GHz), low optical loss (0.14 dB/cm), and low half-wave voltage–length product (1.52 V·cm) has been realized using finite element analysis software. Full article

(This article belongs to the Section Optical Communication and Network)

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12 pages, 4662 KB

Open AccessArticle

High-Sensitivity Broadband Acoustic Wave Detection Using High-Q, Undercoupled Optical Waveguide Resonators

by Xiaoxia Chu, Zhongqiang Zhao, Jiangong Cui and Junbin Zang

Photonics 2025, 12(11), 1128; https://doi.org/10.3390/photonics12111128 - 14 Nov 2025

Viewed by 2072

Abstract

In the field of acoustic wave detection, optical sensors have significant potential applications in numerous civilian and military fields due to their high sensitivity and immunity to electromagnetic interference. This study designed an undercoupled silica optical waveguide resonator (OWR) with a 2% refractive [...] Read more.

In the field of acoustic wave detection, optical sensors have significant potential applications in numerous civilian and military fields due to their high sensitivity and immunity to electromagnetic interference. This study designed an undercoupled silica optical waveguide resonator (OWR) with a 2% refractive index contrast. Mode spot converters were introduced at both ends of the straight waveguide to achieve efficient optical transmission between the fiber and the waveguide. The resonator was fabricated using plasma-enhanced chemical vapor deposition (PECVD) and inductively coupled plasma (ICP) etching technologies. The results show that the quality factor (Q-factor) of the resonator reached 2.75 × 10⁶. Compared with a resonator with a refractive index difference of 0.75%, the Q-factor remained at the same order of magnitude while the sensor size was significantly reduced. To achieve high-sensitivity acoustic wave detection, this study employed an intensity demodulation method to realize acoustic wave detection with the resonator. Test results demonstrate that the OWR can detect acoustic signals in the frequency range of 25 Hz to 20 kHz, with a minimum detectable sound pressure of 1.58 μPa/Hz^1/2 @20 kHz and a sensitivity of 1.492 V/Pa @20 kHz. The sensor exhibits a good signal-to-noise ratio and stability. The proposed method shows broad application prospects in the field of acoustic sensing and is expected to enable large-scale applications in scenarios such as communication, biomedical monitoring, and precision industrial sensing. Full article

(This article belongs to the Special Issue Recent Advances and Applications in Optical Fiber Sensing)

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13 pages, 1390 KB

Open AccessArticle

Angle-Scanning and Size-Scaling Pixelated Quasi-BIC Metasurface Array for Broadband Terahertz Fingerprint Biosensing

by Mengya Pan, Haotian Ling, Dongjin Xin, Xijian Zhang, Yanpeng Shi and Yifei Zhang

Photonics 2025, 12(11), 1127; https://doi.org/10.3390/photonics12111127 - 14 Nov 2025

Viewed by 433

Abstract

Metasurface biosensing confronts a significant challenge in simultaneously achieving broadband response, high quality-factor (Q-factor), and ultrahigh sensitivity for specific trace-analyte detection at terahertz (THz) frequencies. Recently, quasi-bound states in the continuum (QBICs) metasurfaces provided enhanced light–matter interactions and ultrahigh sensitivity in narrow resonant [...] Read more.

Metasurface biosensing confronts a significant challenge in simultaneously achieving broadband response, high quality-factor (Q-factor), and ultrahigh sensitivity for specific trace-analyte detection at terahertz (THz) frequencies. Recently, quasi-bound states in the continuum (QBICs) metasurfaces provided enhanced light–matter interactions and ultrahigh sensitivity in narrow resonant bands. In this work, an angle-scanning QBIC metasurface array pixelated with just 5 × 5 scaling units is proposed to achieve an ultra-broad spectrum from 1 to 2.8 THz for fingerprint bio-detection. The symmetry-protected QBIC is excited by breaking the symmetry of copper block dimer resonator structures, achieving a Q-factor of 20 and a sensitivity of 500 GHz/RIU. A spectral step of approximately 10 GHz is demonstrated in this approach, and glutamic acid and glutamine are specifically detected, with detection limits reaching 15.4 μg/cm² and 14.7 μg/cm². This design provides a novel approach for achieving ultra-wideband, specific, and highly sensitive detection. This capability offers an efficient strategy for monitoring tumor metabolic biomarkers and paves the way for applications in early diagnosis and advanced broadband THz detection. Full article

(This article belongs to the Special Issue Technologies and Applications of Terahertz Metamaterials)

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12 pages, 1820 KB

Open AccessArticle

A High-Extinction-Ratio Resonator for Suppressing Polarization Noise in Hollow-Core Photonic-Crystal Fiber Optic Gyro

by Weiqi Miao, Huachuan Zhao, Fei Yu and Lingyu Li

Photonics 2025, 12(11), 1126; https://doi.org/10.3390/photonics12111126 - 14 Nov 2025

Viewed by 372

Abstract

Polarization-induced noise remains a primary source of bias drift, fundamentally limiting the performance of hollow-core photonic-crystal fiber optic gyroscopes (HC-RFOGs). To overcome this limitation, we propose and demonstrate a novel resonator design with an intrinsically high polarization extinction ratio (PER). The resonator’s core [...] Read more.

Polarization-induced noise remains a primary source of bias drift, fundamentally limiting the performance of hollow-core photonic-crystal fiber optic gyroscopes (HC-RFOGs). To overcome this limitation, we propose and demonstrate a novel resonator design with an intrinsically high polarization extinction ratio (PER). The resonator’s core innovation is a four-port coupler architecture that strategically integrates a pair of polarization beam splitters (PBSs) with conventional beam splitters (BSs). This configuration functions as a high-fidelity polarization filter, suppressing undesired polarization states for both clockwise and counter-clockwise propagating light within the hollow-core fiber loop. Our theoretical model predicts that the effective in-resonator PER can exceed 48 dB, which is sufficient to mitigate polarization-related errors for tactical-grade applications. Experimental validation of a prototype HC-RFOG incorporating this resonator yields a bias instability of 1.34°/h and an angle random walk (ARW) of

0.078 ° / \sqrt{h}

(with a 200 s averaging time). These results confirm that engineering a high-polarization-extinction-ratio resonator (HPERR) is a potent and direct pathway to substantially reducing polarization noise and advancing the performance of HC-RFOGs. Full article

(This article belongs to the Special Issue Optical Fiber Sensors: Design and Application)

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8 pages, 1708 KB

Open AccessArticle

Solar-Blind Mobile Deep Ultraviolet Optical Communication Utilizing Photomultiplier Tubes

by Lei Zhang, Tianle Li and Yongjin Wang

Photonics 2025, 12(11), 1125; https://doi.org/10.3390/photonics12111125 - 14 Nov 2025

Viewed by 449

Abstract

Ozone in the atmosphere strongly absorbs deep ultraviolet light with wavelengths between 200 and 280 nm. Therefore, this characteristic is advantageous and promising for unperturbed, non-disturbed information transmission in fields such as secure communications when deep ultraviolet light is employed. However, existing optical [...] Read more.

Ozone in the atmosphere strongly absorbs deep ultraviolet light with wavelengths between 200 and 280 nm. Therefore, this characteristic is advantageous and promising for unperturbed, non-disturbed information transmission in fields such as secure communications when deep ultraviolet light is employed. However, existing optical communication systems utilizing deep ultraviolet light are characterized by substantial size, which presents significant challenges in terms of local transferability. This paper employs an array of 275 nm deep ultraviolet light-emitting diodes (LEDs) connected in series, paired with photomultiplier tubes (PMTs) as transmitters and receivers. The system is encapsulated with a visual tracking module and mounted on drones and vehicles, achieving mobile duplex real-time communication under sunlight. The communication distance reaches 30 m with a packet loss rate of 1.36%. This work enables rapid and flexible deployment of deep ultraviolet optical communication systems, offering broad application prospects. Full article

(This article belongs to the Special Issue Emerging Trends in Photodetector Technologies)

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13 pages, 6067 KB

Open AccessArticle

Experimental Study on the Scintillation Index of Vortex Beam Superposition States Perturbed by Linear Array Acoustic Sources in Atmospheric Environments

by Jialin Zhang, Mingjun Wang, Luxin Diao, Yafei Wei and Pengchao Zhu

Photonics 2025, 12(11), 1124; https://doi.org/10.3390/photonics12111124 - 14 Nov 2025

Viewed by 320

Abstract

Acoustic waves, as mechanical waves, can perturb atmospheric pressure during propagation, altering the refractive index and turbulence distribution. This study explores a method to mitigate the impact of atmospheric turbulence on optical wave transmission using a linear array acoustic source. We investigated the [...] Read more.

Acoustic waves, as mechanical waves, can perturb atmospheric pressure during propagation, altering the refractive index and turbulence distribution. This study explores a method to mitigate the impact of atmospheric turbulence on optical wave transmission using a linear array acoustic source. We investigated the transmission characteristics of vortex beam superposition states under acoustic perturbation, examining the effects of different wave frequencies and propagation distances on the acoustic field distribution, scintillation index, and atmospheric refractive index structure constant. The results show that acoustic field distributions vary with frequency, and a stable acoustic field is achievable with proper configuration. The scintillation index and refractive index structure constant are influenced by both the acoustic wave propagation distance and sound pressure level. Furthermore, a higher sound pressure level of the source enhances the impact of the linear array acoustic waves on both the scintillation index and the atmospheric refractive index structure constant. This research presents a novel approach to improving optical wave transmission by mitigating atmospheric turbulence. Full article

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12 pages, 2580 KB

Open AccessArticle

Analysis of Thermal Effects in Yb:YAG Laser Amplifiers with Active-Mirror Structure

by Xiaojin Cheng, Hanguo Zhang, Jianhua Shang, Hui Bai, Chenhui Lu and Yunpeng Guo

Photonics 2025, 12(11), 1123; https://doi.org/10.3390/photonics12111123 - 14 Nov 2025

Cited by 1 | Viewed by 465

Abstract

To address the challenge of laser beam distortion induced by thermal effects in high-power slab laser amplifiers, a coupled thermal–mechanical–optical model for a face-pumped Yb:YAG multi-pass amplifier was developed. The thermal effects under different thermal management strategies were systematically investigated using the finite [...] Read more.

To address the challenge of laser beam distortion induced by thermal effects in high-power slab laser amplifiers, a coupled thermal–mechanical–optical model for a face-pumped Yb:YAG multi-pass amplifier was developed. The thermal effects under different thermal management strategies were systematically investigated using the finite element method. Firstly, the temperature distribution, thermal stress, and deformation within the Yb:YAG crystal were analyzed and compared under both room-temperature (293 K) and cryogenic (150 K) cooling conditions using a microchannel cooling structure. The results demonstrate that under a pump power of 100 W and room-temperature cooling, the peak temperature of the gain medium reaches 363 K, with a peak thermal stress of 1.04 MPa and a maximum thermal deformation of 1.44 μm. In contrast, under cryogenic cooling at 150 K, the maximum temperature is reduced to 188 K, and both thermal stress and deformation exhibit a more uniform distribution within the pumped region. Subsequently, the thermal lensing of bonded and non-bonded Yb:YAG crystals was compared and analyzed by ray-tracing. It was found that under a pump power of 100 W, the thermal focal lengths of non-bonded Yb:YAG are 1112 mm and 2559 mm at cooling temperatures of 293 K and 150 K, respectively. For bonded crystals with a 3 mm undoped YAG thickness under identical pumping and cooling conditions, the corresponding thermal focal lengths measure 1508 mm and 3044 mm. When the undoped YAG thickness increases to 6 mm, the thermal focal lengths further extend to 1789 mm and 4206 mm, respectively. Full article

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12 pages, 3277 KB

Open AccessArticle

Screening Effect Suppression and Radiation Performance Improvement in Photoconductive Terahertz Emitters with Metallic Nanoarray Structure

by Shihang Xu and Xiaolong Hu

Photonics 2025, 12(11), 1122; https://doi.org/10.3390/photonics12111122 - 14 Nov 2025

Viewed by 370

Abstract

As core components of terahertz (THz) radiation sources, photoconductive antennas (PCAs) suffer from performance limitations due to inefficient carrier generation/transport and space-charge shielding effects. This study first introduced cylindrical Au nanoarray structures within the electrode gaps of photoconductive antennas to enhance radiation performance. [...] Read more.

As core components of terahertz (THz) radiation sources, photoconductive antennas (PCAs) suffer from performance limitations due to inefficient carrier generation/transport and space-charge shielding effects. This study first introduced cylindrical Au nanoarray structures within the electrode gaps of photoconductive antennas to enhance radiation performance. A combination of the finite element method solver and COMSOL Multiphysics was implemented to refine the model by accounting for the shielding field, which is often neglected in the calculations. Guided by the theoretical and simulation model, the generated current, THz radiation power and the shielding field were comparatively studied in the plasmonic nanoarray PCA and traditional PCA without the plasmonic nanoarray structure. The results demonstrate that emitters with the cylindrical nanoarray structures achieve a radiation power 3.81 times higher than that of the traditional structure, along with a 50% broader bandwidth. Further optimization of photogenerated carrier distribution through engineered metallic nanoarray structures reveals that plasmonic photoconductive THz emitters with triangular nanoarrays reduce the space-charge shielding field by 28.7% compared to the cylindrical structures while enhancing the radiation field intensity by a factor of 1.21. This work presents an effective approach to designing high-performance photoconductive THz emitters, holding significant theoretical and practical significance. Full article

(This article belongs to the Special Issue Photonics & Optical Fiber Sensors: Recent Advancements, Emerging Trends, and Future Prospects)

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12 pages, 4901 KB

Open AccessArticle

Tunable Unidirectional Guided Resonances in Momentum Space via a Si-Ge₂Sb₂Te₅ Metasurface

by Zhi-Yuan Zheng and Ying Yu

Photonics 2025, 12(11), 1121; https://doi.org/10.3390/photonics12111121 - 13 Nov 2025

Viewed by 589

Abstract

Unidirectional guided resonances (UGRs) in periodic metasurfaces have recently attracted research interest because of their ability to achieve unidirectional radiation in all-dielectric structures without metal reflectors, which offers new possibilities for efficient grating couplers and unidirectional lasers. Here, we propose a hybrid metasurface [...] Read more.

Unidirectional guided resonances (UGRs) in periodic metasurfaces have recently attracted research interest because of their ability to achieve unidirectional radiation in all-dielectric structures without metal reflectors, which offers new possibilities for efficient grating couplers and unidirectional lasers. Here, we propose a hybrid metasurface consisting of silicon and

{Ge}_{2} {Sb}_{2} {Te}_{5}

(GST) phase change material for controlled UGR generation in the mid-infrared region. Leveraging GST’s phase-change properties to modulate the optical response of the metasurface, we achieve tunable generation of the UGR, which is demonstrated to carry a topological charge of +1. Moreover, by adjusting the degree of GST phase transition, continuous tuning of the radiation asymmetry ratio from

10^{4}

to 1 is achieved for a specific in-plane momentum and operating wavelength. These findings offer a promising avenue for dynamically controllable UGRs, with potential applications in tunable on-chip optical couplers and light sources. Full article

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14 pages, 3077 KB

Open AccessArticle

Theoretical and Experimental Investigation of Differential Modulation and Detection in FSO Systems

by Hao Zhou, Zhenning Yi, Jingyuan Wang, Jianhua Li, Zhiyong Xu, Jiyong Zhao and Yang Su

Photonics 2025, 12(11), 1120; https://doi.org/10.3390/photonics12111120 - 13 Nov 2025

Viewed by 352

Abstract

In free-space optical (FSO) communication systems, on–off keying (OOK) modulation is widely used due to its simplicity. However, systems applying OOK suffer from the BER floor in atmospheric turbulence channels, leading to persistently high BER even at high SNR. To mitigate this limitation [...] Read more.

In free-space optical (FSO) communication systems, on–off keying (OOK) modulation is widely used due to its simplicity. However, systems applying OOK suffer from the BER floor in atmospheric turbulence channels, leading to persistently high BER even at high SNR. To mitigate this limitation in atmospheric turbulence channels, differential modulation and detection (DMD) can be adopted. An in-depth theoretical and experimental investigation of DMD in FSO systems is conducted in this paper, considering the effects of turbulence. A comprehensive derivation of the system performance for DMD under atmospheric turbulence channels is also provided, with the results of research revealing that DMD outperforms OOK in high-SNR regions. To validate the theoretical analysis, an experimental platform is set up to sample the fluctuation of light intensity. Furthermore, the system performance of DMD is analyzed under varying scintillation indices, modulation depths, and transmission rates in this paper. Based on the data acquired from experiments, the results corroborate the analytical findings, confirming the great advantages of DMD in turbulent environments. The insights provided in this study establish a foundation for practical FSO system design, enabling the development of simpler and more reliable communication systems. Full article

(This article belongs to the Special Issue Advances in Free-Space Optical Communications)

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10 pages, 1974 KB

Open AccessArticle

Demonstration of Multiple Access FSO Communication System Based on Silicon Optical Phased Array

by Siwen Fan and Anpeng Song

Photonics 2025, 12(11), 1119; https://doi.org/10.3390/photonics12111119 - 13 Nov 2025

Viewed by 564

Abstract

The silicon photonic optical phased array (OPA) has attracted enormous interest in free-space optical communication (FSO) owing to its high integration and agile beam steering. However, existing studies have only used its ability for fast beam switching to achieve point-to-multipoint communication, which results [...] Read more.

The silicon photonic optical phased array (OPA) has attracted enormous interest in free-space optical communication (FSO) owing to its high integration and agile beam steering. However, existing studies have only used its ability for fast beam switching to achieve point-to-multipoint communication, which results in link disconnection and time waste during the switching process. To address this problem, we make full use of the light field manipulation capabilities of Si-OPA to generate beams with multiple main lobes pointing to different targets at the same time, and combine code division multiple access (CDMA) to achieve uninterrupted point-to-multipoint communication. Through detailed data analysis, it is experimentally demonstrated that the proposed method has improved the communication efficiency by 24.576% compared with the previous beam-switching solution. This method provides a new application idea for Si-OPA in FSO communication. Full article

(This article belongs to the Special Issue Advances in Free-Space Optical Communications)

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19 pages, 17086 KB

Open AccessArticle

Recovering the Reduced Scattering and Absorption Coefficients of Turbid Media from a Single Image

by Philipp Nguyen, David Hevisov, Florian Foschum and Alwin Kienle

Photonics 2025, 12(11), 1118; https://doi.org/10.3390/photonics12111118 - 13 Nov 2025

Viewed by 431

Abstract

This study introduces a physics-based inverse rendering method for determining the reduced scattering and absorption coefficients of turbid materials with arbitrary shapes, using a single image as input. The approach enables fully spectrally-resolved reconstruction of the wavelength-dependent behaviour of the optical properties while [...] Read more.

This study introduces a physics-based inverse rendering method for determining the reduced scattering and absorption coefficients of turbid materials with arbitrary shapes, using a single image as input. The approach enables fully spectrally-resolved reconstruction of the wavelength-dependent behaviour of the optical properties while also circumventing the specialised sample preparation required by established measurement techniques. Our approach employs a numerical solution of the Radiative Transfer Equation based on an inverse Monte Carlo framework, utilising an improved Levenberg–Marquardt algorithm. By rendering the edge effects accurately, particularly translucency, it becomes possible to differentiate between scattering and absorption from just one image. Importantly, the errors induced by only approximate prior knowledge of the phase function and refractive index of the material were quantified. The method was validated through theoretical studies on three materials spanning a range of optical parameters, initially using a simple cube geometry and later extended to more complex shapes. Evaluated via the CIE

Δ E_{2000}

colour difference, forward renderings based on the recovered properties were indistinguishable from those preset, which were obtained from integrating sphere measurements on real materials. The recovered optical properties showed less than 4% difference relative to these measurements. This work demonstrates a versatile approach for optical material characterisation, with significant potential for digital twin creation and soft-proofing in manufacturing. Full article

(This article belongs to the Special Issue Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology, 2nd Edition)

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10 pages, 1110 KB

Open AccessArticle

Far-Infrared Imaging Lens Based on Dual-Plane Diffractive Optics

by Chao Yan, Zhongzhou Tian, Xiaoli Gao, Xuezhou Yang, Qingshan Xu, Ligang Tan, Kai Li, Xiuzheng Wang and Yi Zhou

Photonics 2025, 12(11), 1117; https://doi.org/10.3390/photonics12111117 - 13 Nov 2025

Viewed by 447

Abstract

Far-infrared imaging is a powerful tool in night vision and temperature measurement, with broad applications in military, astronomy, meteorology, industrial, and medical fields. However, conventional imaging lenses face challenges such as large size, heavy weight, and difficulties in miniaturization, which hinder their integration [...] Read more.

Far-infrared imaging is a powerful tool in night vision and temperature measurement, with broad applications in military, astronomy, meteorology, industrial, and medical fields. However, conventional imaging lenses face challenges such as large size, heavy weight, and difficulties in miniaturization, which hinder their integration and use in applications with strict requirements for mass and volume, such as drone-based observation and imaging. To address these limitations, we designed a dual-plane diffractive optical lens optimized for the 10.9–11.1 μm wavelength band with a 0.2 μm bandwidth. By optimizing parameters including focal length, spot size, and field of view, we derived the phase distribution of the lens and converted it into the surface sag. To enhance diffraction efficiency and minimize energy loss, the lens was fabricated using a continuous phase surface on single-crystal Germanium. Finally, an imaging system was constructed to achieve clear imaging of various samples, demonstrating the feasibility of both the device and the system. This approach shows great potential for applications requiring lightweight and miniaturized solutions, such as infrared imaging, machine vision, remote sensing, biological imaging, and materials science. Full article

(This article belongs to the Special Issue Advancements in Optical Metrology and Imaging)

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15 pages, 4772 KB

Open AccessArticle

High-Efficiency Terahertz Generation Using a Photoconductive Antenna with Vertically Distributed Ring-Disc Electrodes

by Hao Du, Guipeng Liu, Xingpeng Liu, Zhuofeng Li, Shuxiang Song and Linsheng Liu

Photonics 2025, 12(11), 1116; https://doi.org/10.3390/photonics12111116 - 12 Nov 2025

Viewed by 623

Abstract

Current photoconductive antennas (PCAs) fail to maximize the use of photogenerated carriers at the electrode edges. To address this limitation, we designed a novel PCA structure featuring a ring electrode and a disc electrode. The positive and negative electrodes are positioned on opposite [...] Read more.

Current photoconductive antennas (PCAs) fail to maximize the use of photogenerated carriers at the electrode edges. To address this limitation, we designed a novel PCA structure featuring a ring electrode and a disc electrode. The positive and negative electrodes are positioned on opposite sides of the substrate, and eight metal tips are incorporated into the ring electrode to enhance performance. The PCA-1 photoconductive antenna with both positive and negative electrodes on the same side of the substrate generates a peak current of about 18 μA, whereas under the same simulation parameters, the peak current generated by the PCA-1 and the conventional interdigitated photoconductive antenna are equal, and the PCA-2 photoconductive antenna with positive and negative electrodes on the top and bottom sides of the substrate generates a current nearly 1.45 times higher than that generated by the PCA-1. The PCA-3 photoconductive antenna with positive and negative electrodes on the top and bottom of the substrate and eight additional metal tips on the circular electrodes is nearly twice the peak current generated by the PCA-1, and the terahertz radiated power of the designed PCA-3 is four times that of the PCA-1, which suggests that the designed THz-PCA can improve the optical-terahertz conversion efficiency, and it has a great prospect of popularizing terahertz technology based on the THz-PCA. Full article

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