Photonics

8 pages, 3412 KB

Open AccessCommunication

Fano Resonances in Location-Dependent Terahertz Stub Waveguide

by Yanrui Li, Shuxiang Ma, Hongguang Li, Yuanbo Wang, Deng Zhang, Lin Chen and Yiming Zhu

Photonics 2025, 12(11), 1088; https://doi.org/10.3390/photonics12111088 - 4 Nov 2025

The quest for simpler structures that do not require the use of nanofabrication techniques and exhibit high Q Fano resonances has attracted growing interest in the past decade. Here, we study an arrangement of coupled resonator waveguides that can excite Fano resonances. The [...] Read more.

The quest for simpler structures that do not require the use of nanofabrication techniques and exhibit high Q Fano resonances has attracted growing interest in the past decade. Here, we study an arrangement of coupled resonator waveguides that can excite Fano resonances. The results show that an odd mode, except for the usual even mode, is excited due to the symmetry breaking of the position stub intersection. The superposition of the even and odd modes generates a Fano-shaped spectrum with a very narrow linewidth. Coupled mode theory is used to analyze these waveguide-based Fano resonances. Experimental results obtained using VNA and VDI show good agreement with theory and simulations. Such waveguide-based Fano resonances can be tailored and are simple in structure and have potential applications in narrowband filtering, sensing, lasing, and nonlinearity enhancement. Full article

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

► Show Figures

Figure 1

17 pages, 4854 KB

Open AccessArticle

Second-Order Topological States in Non-Hermitian Square Photonic Crystals

by Wenchen Ding and Yaru Feng

Photonics 2025, 12(11), 1087; https://doi.org/10.3390/photonics12111087 - 4 Nov 2025

Abstract

Non-Hermitian photonic crystals offer a versatile platform for observing exotic phenomena, including the non-Hermitian skin effect and higher-order topological phases. In this work, we construct non-Hermitian photonic crystals by embedding balanced gain and loss into a magneto-optical photonic medium. Within the associated supercell, [...] Read more.

Non-Hermitian photonic crystals offer a versatile platform for observing exotic phenomena, including the non-Hermitian skin effect and higher-order topological phases. In this work, we construct non-Hermitian photonic crystals by embedding balanced gain and loss into a magneto-optical photonic medium. Within the associated supercell, we demonstrate the emergence of second-order topological corner states whose degeneracies are selectively lifted by non-Hermitian effects, while others remain protected. Remarkably, the bulk states exhibit strong unidirectional localization toward a single corner, providing unambiguous evidence of the non-Hermitian skin effect. The coexistence of higher-order corner states and the NHSE within the same photonic platform reveals an intricate interplay between crystalline symmetry and non-Hermitian topology. Beyond its fundamental intrigue, our approach offers a versatile means of engineering and controlling the non-Hermitian skin effect in realistic photonic architectures, paving the way for applications in topological nanolasers, robust light localization, and quantum photonic emulators. Full article

(This article belongs to the Special Issue Advanced Research in Topological Photonics)

► Show Figures

Figure 1

15 pages, 2783 KB

Open AccessArticle

Tunable Filtering via Lossy Mode Resonance in Integrated Photonics

by Edvins Letko

Photonics 2025, 12(11), 1086; https://doi.org/10.3390/photonics12111086 - 3 Nov 2025

Abstract

This study explores an integrated tunable filter based on lossy mode resonance (LMR) in TiO_x thin films, modeled in COMSOL Multiphysics using the Wave Optics and Semiconductor modules. By exploiting the electro-optic (EO) modulation of free carrier concentration in TiO_x, [...] Read more.

This study explores an integrated tunable filter based on lossy mode resonance (LMR) in TiO_x thin films, modeled in COMSOL Multiphysics using the Wave Optics and Semiconductor modules. By exploiting the electro-optic (EO) modulation of free carrier concentration in TiO_x, the LMR wavelength can be actively tuned under an applied electric field. The results demonstrate a tuning efficiency of

4.0 nm / V

, which surpasses many reported EO tunable filters. Optimization studies reveal that thinner ITO electrodes and TiO_x layers enhance tuning efficiency, while the initial bulk free carrier concentration has limited influence due to the compensating effect of the Debye length. These findings extend the applicability of LMR beyond sensing, highlighting its potential for active photonic components in integrated optics. Full article

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

► Show Figures

Figure 1

8 pages, 1179 KB

Open AccessCommunication

Numerical Investigation of Idler Pulse Generation by Four-Wave Mixing in Nonlinear Optical Ring Resonator

by José L. S. Lima and Carlos H. A. Ferraz

Photonics 2025, 12(11), 1085; https://doi.org/10.3390/photonics12111085 - 3 Nov 2025

Abstract

Generation of idler pulses via the four-wave mixing (FWM) effect in a nonlinear optical ring resonator (NORR) was investigated numerically. It was found that the relative delay

τ

between input pump pulses significantly affects both the energy and temporal–spectral characteristics of generated idler [...] Read more.

Generation of idler pulses via the four-wave mixing (FWM) effect in a nonlinear optical ring resonator (NORR) was investigated numerically. It was found that the relative delay

τ

between input pump pulses significantly affects both the energy and temporal–spectral characteristics of generated idler pulses. Specifically, idler pulse energy decreases with increasing

τ

due to phase-matching conditions in FWM. Maximum energy transfer occurs for

τ

= 0, where optimal phase alignment among pump, signal, and idler waves is achieved. Temporal and spectral analysis at different relative delays reveals a change from a symmetric, multi-subpulse structure with a comb-like spectrum (for

τ

= 0) to a near-single-pulse form with a single-comb-line spectrum (for

τ

= 9 ps). These findings demonstrate the critical dependence of FWM efficiency on pump pulse synchronization. Therefore, precise control of the relative delay is essential for optimizing idler pulse generation in NORRs. Full article

(This article belongs to the Special Issue Nonlinear Optics and Hyperspectral Polarization Imaging)

► Show Figures

Figure 1

19 pages, 60374 KB

Open AccessArticle

Lobster Eye (LE) X-Ray Optics Demonstrator for CubeSats Applications

by Veronika Marsikova, Adolf Inneman, Peter Oberta, Ladislav Pina and Rene Hudec

Photonics 2025, 12(11), 1084; https://doi.org/10.3390/photonics12111084 - 3 Nov 2025

Abstract

We present a Lobster Eye (LE) X-ray optics module utilizing Multi-Foil Optics (MFO) technology. Designed for CubeSat-class missions, the system is based on the Schmidt arrangement and consists of two orthogonally oriented submodules composed of smooth, gold-coated glass foils. This configuration enables wide-field [...] Read more.

We present a Lobster Eye (LE) X-ray optics module utilizing Multi-Foil Optics (MFO) technology. Designed for CubeSat-class missions, the system is based on the Schmidt arrangement and consists of two orthogonally oriented submodules composed of smooth, gold-coated glass foils. This configuration enables wide-field X-ray imaging with a short focal length of 400 mm and a characteristic cross-shaped focal spot. Key optical parameters, including focal length, full width at half maximum (FWHM), angular resolution, field of view (FOV), and effective area, have been experimentally verified in a vacuum setup using various X-ray sources and detectors. The Lobster Eye (LE) X-ray optics is ready for integration into a CubeSat demonstrator. Full article

(This article belongs to the Special Issue Advances in EUV/X-Ray Optics: Science and Applications)

► Show Figures

Figure 1

9 pages, 1165 KB

Open AccessArticle

Nonparaxial Exploding Cylindrical Vector Beams

by Marcos G. Barriopedro, Manuel Holguín and Miguel A. Porras

Photonics 2025, 12(11), 1083; https://doi.org/10.3390/photonics12111083 - 2 Nov 2025

Abstract

Exploding or concentrating beams, vortex beams, and cylindrical vector beams have a precisely shaped transversal amplitude profile such that they produce a continuously concentrating and intensifying focal spot upon focusing as the lens aperture is opened. This effect is the physical manifestation of [...] Read more.

Exploding or concentrating beams, vortex beams, and cylindrical vector beams have a precisely shaped transversal amplitude profile such that they produce a continuously concentrating and intensifying focal spot upon focusing as the lens aperture is opened. This effect is the physical manifestation of the mathematical fact that Fresnel diffraction integral predicts an infinite intensity at the focus when the aperture effects are ignored. Here, using a full electromagnetic, nonparaxial focusing model, we show that the singularity in exploding cylindrical vector beams is an artifact of the paraxial approximation. Nevertheless, the exploding or concentrating effect, alien to any other light beam with finite power, keeps going up to unit numerical aperture, equivalent to infinite aperture radius. This unique feature enables a dynamic control of the focal intensity and spot size down to the sub-wavelength scale using a single light beam, imitating similar control when focusing an ideal plane wave, but requiring a finite amount of power. Full article

► Show Figures

Figure 1

12 pages, 3906 KB

Open AccessCommunication

Utilizing Optical Coherence Tomography to Estimate Ablation Depth on Intraocular Lenses (IOLs) Under Femtosecond Laser Ablation

by Georgios Ninos, Constantinos Bacharis, Virgilijus Vaičaitis, Ona Balachninaitė and Nikolaos Merlemis

Photonics 2025, 12(11), 1082; https://doi.org/10.3390/photonics12111082 - 2 Nov 2025

Abstract

Intraocular lens (IOL) implantation is currently the most effective method for restoring vision following cataract surgery and is also used in cases of high myopia or hyperopia. However, IOL implantation eliminates accommodation, forcing patients to choose between corrected distance vision, requiring reading glasses [...] Read more.

Intraocular lens (IOL) implantation is currently the most effective method for restoring vision following cataract surgery and is also used in cases of high myopia or hyperopia. However, IOL implantation eliminates accommodation, forcing patients to choose between corrected distance vision, requiring reading glasses for near tasks, or near vision supplemented by distance correction with spectacles. This limitation underscores the need for fully customized, patient-specific IOLs. To address this challenge, we performed femtosecond laser ablation experiments on polymethyl methacrylate (PMMA) IOLs using 200 fs pulses at 513 nm to investigate controlled surface modification. Laser-induced surface structuring offers a pathway to inscribe micron-scale patterns, including apodized features, in transparent polymers. To our knowledge, this is the first demonstration of femtosecond laser irradiation at 513 nm applied to IOL surfaces. Furthermore, this study is the first to combine scanning electron microscopy (SEM) and optical coherence tomography (OCT) as detection technologies to analyze and quantify ablation morphology and depth. The formation of smooth craters with minimal surrounding thermal damage highlights the potential of femtosecond laser processing as a promising tool for the development of customized, patient-tailored intraocular lenses. Full article

► Show Figures

Figure 1

26 pages, 3689 KB

Open AccessReview

Optical Sensor Technologies for Enhanced Food Safety Monitoring: Advances in Detection of Chemical and Biological Contaminants

by Furong Fan, Zeyu Liao, Zhixiang He, Yaoyao Sun, Kuiguo Han and Yanqun Tong

Photonics 2025, 12(11), 1081; https://doi.org/10.3390/photonics12111081 - 1 Nov 2025

Abstract

Optical sensing technologies are revolutionizing global food safety surveillance through exceptional sensitivity, rapid response, and high portability. This review systematically evaluates five major platforms, revealing unprecedented detection capabilities from sub-picomolar to single-cell resolution. Surface plasmon resonance achieves

0.021 ng / mL

detection [...] Read more.

Optical sensing technologies are revolutionizing global food safety surveillance through exceptional sensitivity, rapid response, and high portability. This review systematically evaluates five major platforms, revealing unprecedented detection capabilities from sub-picomolar to single-cell resolution. Surface plasmon resonance achieves

0.021 ng / mL

detection limits for veterinary drugs with superior molecular recognition. Quantum dot fluorescence sensors reach

0.17 nM

sensitivity for pesticides, enabling rapid on-site screening. Surface-enhanced Raman scattering attains

0.2 pM

sensitivity for heavy metals, ideal for trace contaminants. Laser-induced breakdown spectroscopy delivers multi-elemental analysis within seconds at

0.0011 mg / L

detection limits. Colorimetric assays provide cost-effective preliminary screening in resource-limited settings. We propose a stratified detection framework that strategically allocates differentiated sensing technologies across food supply chain nodes, addressing heterogeneous demands while eliminating resource inefficiencies from deploying high-precision instruments for routine screening. Integration of microfluidics, artificial intelligence, and mobile platforms accelerates evolution toward multimodal fusion and decentralized deployment. Despite advances, critical challenges persist: matrix interference, environmental robustness, and standardized protocols. Future breakthroughs require interdisciplinary innovation in materials science, intelligent data processing, and system integration, transforming laboratory prototypes into intelligent early warning networks spanning the entire food supply chain. Full article

► Show Figures

Figure 1

11 pages, 2734 KB

Open AccessArticle

Coaxial LiDAR System Utilizing a Double-Clad Fiber Receiver

by Hao Chen, Zhenquan Su, Zhuolun Li, Hanfeng Ding and Jun Zhang

Photonics 2025, 12(11), 1080; https://doi.org/10.3390/photonics12111080 - 1 Nov 2025

Abstract

LiDAR technology has undergone significant advancement in recent years, establishing itself as a technique for long-range, high-precision detection. As its use expands into more intricate scenarios, the need to overcome blind spots in the scanning field and enhance system stability has become increasingly [...] Read more.

LiDAR technology has undergone significant advancement in recent years, establishing itself as a technique for long-range, high-precision detection. As its use expands into more intricate scenarios, the need to overcome blind spots in the scanning field and enhance system stability has become increasingly critical. This paper introduces a novel coaxial LiDAR system featuring a double-clad optical fiber-based receiver which consists of a single-mode fiber core for the emission of the laser beam and a multimode inner cladding for the collection and transmission of the back-reflected beam. The real-time system is specifically engineered to measure distances in both near and far fields, eliminating blind spots. Experimental evaluations demonstrate that our system achieves a detection range of 0.2–70.7 m, with a distance accuracy of 3.4 cm and an angular resolution of 0.018°. Compared with conventional LiDAR systems, our approach eliminates the need for complex optical pathway designs and algorithmic compensation. It offers a simplified structure, enhanced stability, and high accuracy. Full article

► Show Figures

Figure 1

14 pages, 4674 KB

Open AccessArticle

PN Junction Optimization for High-Speed Silicon Photonic Modulators

by Mahmoud Hamouda, Carine Mankarious, Aser El-Dahshan, Alaa Fathy, Eslam El-Fiky and Diaa Khalil

Photonics 2025, 12(11), 1079; https://doi.org/10.3390/photonics12111079 - 31 Oct 2025

Abstract

PN-junction-based modulators are widely used in silicon photonic transceivers for different applications. Different junction shapes have been proposed in the literature. This work studies the optimization of the PN junction by tailoring the doping profile to achieve a high-efficiency modulator with sufficient bandwidth. [...] Read more.

PN-junction-based modulators are widely used in silicon photonic transceivers for different applications. Different junction shapes have been proposed in the literature. This work studies the optimization of the PN junction by tailoring the doping profile to achieve a high-efficiency modulator with sufficient bandwidth. For this purpose, a new N-shaped junction is proposed, which achieves superior performance compared to other junction shapes. The proposed junction has an efficiency that is 60% better than that of the lateral PN junction for the same doping condition, while maintaining a high bandwidth similar to other junctions such as the L-shaped and S-shaped designs. A junction design with an estimated RC bandwidth between 70 GHz and 94 GHz is also proposed. The impact of using the proposed junction in micro-ring modulators (MRMs) is also studied. N-shaped junctions in MRM demonstrated a 112% increase in electro-optic bandwidth over the vertical PN junction, with 60% and 140% improvements in extinction ratio (ER) and optical modulation amplitude (OMA), respectively, compared to the lateral PN junction. Full article

(This article belongs to the Special Issue Recent Advancement in Microwave Photonics)

► Show Figures

Figure 1

21 pages, 4096 KB

Open AccessArticle

Highly Sensitive Dual-Polished Dual-Core PCF-Based SPR Sensor for Hemoglobin Detection Using FEM and Machine Learning

by Abrar Adib, Anik Chowdhury, Aditta Chowdhury, Md Abu Huraiya, Abu Farzan Mitul and Mohammad Istiaque Reja

Photonics 2025, 12(11), 1078; https://doi.org/10.3390/photonics12111078 - 31 Oct 2025

Abstract

This research investigates a dual-polished surface plasmon resonance sensor based on dual-core photonic crystal fiber, featuring an innovative design aimed at enhancing hemoglobin concentration detection in blood, providing a valuable tool for diagnosing numerous health issues, such as chronic obstructive pulmonary disease. The [...] Read more.

This research investigates a dual-polished surface plasmon resonance sensor based on dual-core photonic crystal fiber, featuring an innovative design aimed at enhancing hemoglobin concentration detection in blood, providing a valuable tool for diagnosing numerous health issues, such as chronic obstructive pulmonary disease. The sensor makes use of an external sensing mechanism and utilizes gold (Au) coating as the plasmonic material, chosen for its strong plasmonic response and excellent chemical stability, ensuring robust performance across the 1.31–1.42 refractive index range. The electromagnetic characteristics and efficacy of the designed sensor were thoroughly investigated using the finite element method. Our proposed sensor demonstrates outstanding performance metrics, attaining peak amplitude sensitivity of about 734 RIU⁻¹, and wavelength sensitivity of 74,000 nm/RIU along with 1.35 × 10⁻⁶ RIU wavelength resolution. It also exhibits a notable Figure of Merit value of 667 for a corresponding Full width at Half Maximum value of 111 nm. Finally, a machine learning model based on linear regression was employed that enables the prediction of any hemoglobin concentration levels corresponding to analyte RI values. These exceptional performance metrics highlight the potential of our sensor as a reliable, cost-effective and highly sensitive solution for real-time biosensing applications. Full article

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

► Show Figures

Figure 1

17 pages, 5143 KB

Open AccessArticle

Hybrid Physical-Data Modeling Approach for Surface Scattering Characteristics of Low-Gloss Black Paint

by Zhen Mao, Zhaohui Li, Wei Liu, Yunfei Yin, Limin Gao and Jianke Zhao

Photonics 2025, 12(11), 1077; https://doi.org/10.3390/photonics12111077 - 31 Oct 2025

Abstract

This study presents a hybrid BRDF modeling framework combining a five-parameter physical model with a (20,20,20) Multilayer Perceptron (MLP) model network to address the critical challenge of accurate grazing-angle prediction for low-gloss black coatings (SB-3A, Z306, PNC). While the baseline parametric model achieves [...] Read more.

This study presents a hybrid BRDF modeling framework combining a five-parameter physical model with a (20,20,20) Multilayer Perceptron (MLP) model network to address the critical challenge of accurate grazing-angle prediction for low-gloss black coatings (SB-3A, Z306, PNC). While the baseline parametric model achieves <5% RMSE at θ_i ≤ 60°, its inability to capture shadowing effects leads to >1.2 RMSE at 80° incidence. The proposed MLP model-enhanced solution reduces these high-angle errors to <0.012 RMSE while maintaining <5-min computational efficiency. Comprehensive validation shows the framework’s universality across materials with apparent anisotropy indices (ASI) of 0.465–30.26. The work demonstrates that neural networks can optimally compensate for missing physics in traditional models without sacrificing interpretability, offering immediate industrial value for aerospace coating analysis. Full article

► Show Figures

Figure 1

12 pages, 4256 KB

Open AccessArticle

Tunable-Charge Optical Vortices Through Edge Diffraction of a High-Order Hermit-Gaussian Mode Laser

by Shuaichen Li, Yiyang Zhang, Ying Li, Linge Mao, Pengfan Zhao and Zhen Qiao

Photonics 2025, 12(11), 1076; https://doi.org/10.3390/photonics12111076 - 30 Oct 2025

Abstract

An optical vortex is a typical structured light field characterized by a helical wavefront and a central phase singularity. With its expanding applications in modern information technology, the demand for generating vortex beams with diverse topological charges continues to grow. Existing methods for [...] Read more.

An optical vortex is a typical structured light field characterized by a helical wavefront and a central phase singularity. With its expanding applications in modern information technology, the demand for generating vortex beams with diverse topological charges continues to grow. Existing methods for modulating the topological charges of vortex beams involve complex operations and high costs. This study proposes a novel approach to modulate the topological charges of optical vortices through edge diffraction of a high-order Hermit–Gaussian (HG) mode laser. First, a high-order HG mode laser is built using off-axis pumping configuration. By selectively obscuring specific lobes of the high-order HG beam, various optical vortices are generated using a cylindrical lens mode converter. The topological charge can be continuously tuned by controlling the number of obscured lobes. This method substantially improves the efficiency of topological charge modulation, while also enabling the generation of fractional vortex states. These advancements show potential in mode-division-multiplexed optical communications and encryption. Full article

(This article belongs to the Special Issue Advances in Solid-State Laser Technology and Applications)

► Show Figures

Figure 1

19 pages, 2671 KB

Open AccessReview

The Transition of Luminescent Materials and Conductive Electrodes in Upconversion Devices to Flexible Architectures

by Huijuan Chen, Weibo Feng and Tianling Qin

Photonics 2025, 12(11), 1075; https://doi.org/10.3390/photonics12111075 - 30 Oct 2025

Abstract

Flexible upconversion (UC) devices, owing to their unique combination of high–efficiency optical energy conversion and mechanical flexibility, have attracted increasing attention in the fields of optoelectronics, wearable devices, flexible displays, and biomedical applications. However, significant challenges remain in balancing optical performance, mechanical adaptability, [...] Read more.

Flexible upconversion (UC) devices, owing to their unique combination of high–efficiency optical energy conversion and mechanical flexibility, have attracted increasing attention in the fields of optoelectronics, wearable devices, flexible displays, and biomedical applications. However, significant challenges remain in balancing optical performance, mechanical adaptability, long–term stability, and scalable fabrication, which limit their practical deployment. This review systematically introduces five representative upconversion mechanisms—excited–state absorption (ESA), energy transfer upconversion (ETU), energy migration upconversion (EMU), triplet–triplet annihilation upconversion (TTA–UC), and photon avalanche (PA)—highlighting their energy conversion principles, performance characteristics, and applicable scenarios. The article further delves into the flexible transition of upconversion devices, detailing not only the evolution of the luminescent layer from bulk crystals and nanoparticles to polymer composites and hybrid systems, but also the optimization of electrodes from rigid metal films to metal grids, carbon–based materials, and stretchable polymers. These developments significantly enhance the stability and reliability of flexible upconversion devices under bending, stretching, and complex mechanical deformation. Finally, emerging research directions are outlined, including multi–mechanism synergistic design, precise nanostructure engineering, interface optimization, and the construction of high–performance composite systems, emphasizing the broad potential of flexible UC devices in flexible displays, wearable health monitoring, solar energy harvesting, flexible optical communications, and biomedical photonic applications. This work provides critical insights for the design and application of high–performance flexible optoelectronic devices. Full article

(This article belongs to the Special Issue Organic Photodetectors, Displays, and Upconverters)

► Show Figures

Figure 1

14 pages, 2622 KB

Open AccessArticle

Enhancing the Solar-Blind UV Detection Performance of β-Ga₂O₃ Films Through Oxygen Plasma Treatment

by Rongxin Duan, Guodong Wang, Lanlan Guo, Yuechao Wang, Yumeng Zhai, Xiaolian Liu, Junjun Wang, Yingli Yang and Xiaojie Yang

Photonics 2025, 12(11), 1074; https://doi.org/10.3390/photonics12111074 - 30 Oct 2025

Abstract

This study systematically investigated the effects of oxygen plasma treatment on oxygen vacancy defects in sputtered β-gallium oxide (β-Ga₂O₃) films and their corresponding ultraviolet (UV) detection performance. The sputtered β-Ga₂O₃ film subjected [...] Read more.

This study systematically investigated the effects of oxygen plasma treatment on oxygen vacancy defects in sputtered β-gallium oxide (β-Ga₂O₃) films and their corresponding ultraviolet (UV) detection performance. The sputtered β-Ga₂O₃ film subjected to 1 min of oxygen plasma treatment exhibited optimal photodetection properties. Compared to the untreated sample, the dark current was reduced by approximately one order of magnitude to 0.378 pA at 10 V bias. It exhibited an 86% (from 2.92 s to 0.41 s) decrease in response time, a 41.6% increase in photocurrent, a very high photo-to-dark current ratio of 9.18 × 10⁵, and a specific detectivity of 2.62 × 10¹⁰ cm·Hz^1/2W⁻¹ under 254 nm UV illumination intensity of 799 μW/cm² at 10 V bias. Notably, appropriate oxygen plasma treatment minimizes electron capture, enhances the separation and collection of photogenerated carriers, and suppresses the persistent photoconductivity (PPC) effect, thus ultimately shortening the response time. Oxygen plasma processing thus provides an effective approach to fabricating high-performance β-Ga₂O₃ solar-blind photodetectors (SBPDs). Full article

(This article belongs to the Special Issue New Advances in Semiconductor Optoelectronic Materials and Devices)

► Show Figures

Figure 1

9 pages, 2178 KB

Open AccessArticle

High-Bandwidth Intensity-Difference Squeezed State at 895 nm Based on Four-Wave Mixing

by Rong Ma, Wen Zhang, Xiaowei Wu, Xiaoqin Qu and Xiaolong Su

Photonics 2025, 12(11), 1073; https://doi.org/10.3390/photonics12111073 - 30 Oct 2025

Abstract

As an essential quantum resource, the intensity-difference squeezed state based on four-wave mixing (FWM) in atomic vapor is widely applied in quantum information processing. In particular, a high intensity-difference squeezing bandwidth is vital for the realization of high-speed information processing. However, limited by [...] Read more.

As an essential quantum resource, the intensity-difference squeezed state based on four-wave mixing (FWM) in atomic vapor is widely applied in quantum information processing. In particular, a high intensity-difference squeezing bandwidth is vital for the realization of high-speed information processing. However, limited by the bandwidth of photodetectors, broadband intensity-difference squeezed state based on this system has not yet been reported. Here, we developed a transimpedance broadband balanced homodyne detector at 895 nm, achieving a bandwidth greater than 100 MHz and a maximum signal-to-noise ratio of 15 dB with 4 mW optical power. Utilizing this detector in a nondegenerate FWM process based on cesium vapor, we experimentally achieved broadband intensity-difference squeezing with a bandwidth of 100 MHz, which yielded a maximum squeezing of −7.17 ± 0.8 dB between 20 and 40 MHz. Meanwhile, using this detector, we experimentally investigated the cavity-enhanced FWM process, achieving a squeezing level of −6.07 ± 0.5 dB within a 4 MHz frequency range, which is limited by the cavity bandwidth. This work provides a reliable detection tool and experimental foundation for the research and application of broadband squeezed light sources based on FWM. Full article

(This article belongs to the Special Issue Advanced Research in Quantum Optics)

► Show Figures

Figure 1

15 pages, 2261 KB

Open AccessArticle

Compact Six-Degree-of-Freedom Displacement Sensing Based on Laser Reflection and Position-Sensitive Detectors

by Jingyu Chen, Junjie Li, Yuan Diao, Ke Wang, Wenbo Dong, Mengxi Yu and Zongfeng Li

Photonics 2025, 12(11), 1072; https://doi.org/10.3390/photonics12111072 - 29 Oct 2025

Abstract

To meet pose-control and vibration-suppression requirements in confined spaces, a compact, noncontact six-degree-of-freedom (6-DoF) displacement-sensing method is proposed. The method is based on laser reflection and a position-sensitive detector (PSD) and features an adjustable incidence angle. An adjustable-incidence-angle PSD–corner-cube retro-reflector (CCR) configuration is [...] Read more.

To meet pose-control and vibration-suppression requirements in confined spaces, a compact, noncontact six-degree-of-freedom (6-DoF) displacement-sensing method is proposed. The method is based on laser reflection and a position-sensitive detector (PSD) and features an adjustable incidence angle. An adjustable-incidence-angle PSD–corner-cube retro-reflector (CCR) configuration is devised, which reduces the PSD’s spatial footprint to 10.4% of that of a conventional layout. Building on this configuration, an analytical model is derived that maps the target’s 6-DoF displacement to the PSD spot motion as a function of the fixed relative pose between the PSD and the CCR mounted on the target. The model is linearized under the small-angle assumption. Experiments show an accuracy of 5.89 μm for translation within ±1.5 mm and 0.0027° for rotation within ±0.5°. The method couples a compact architecture with high precision and provides both a theoretical basis and an engineering-ready pathway for high-bandwidth pose sensing in confined spaces. Full article

(This article belongs to the Special Issue New Progress in Optical Precision Measurement in the Field of Space Technology)

► Show Figures

Figure 1

21 pages, 8124 KB

Open AccessArticle

Design of Miniaturized Cooled Medium-Wave Infrared Curved Bionic Compound-Eye Optical System

by Fu Wang, Yinghao Chi, Linhan Li, Nengbin Cai, Yimin Zhang, Yang Yu, Sili Gao and Kaijun Ma

Photonics 2025, 12(11), 1071; https://doi.org/10.3390/photonics12111071 - 29 Oct 2025

Abstract

To address the issues of insufficient detector target size and high system complexity in infrared bionic compound-eye systems, this paper designs a miniaturized cooled medium-wave infrared curved bionic compound-eye optical system specifically for large target surface detectors and develops a proof-of-concept prototype for [...] Read more.

To address the issues of insufficient detector target size and high system complexity in infrared bionic compound-eye systems, this paper designs a miniaturized cooled medium-wave infrared curved bionic compound-eye optical system specifically for large target surface detectors and develops a proof-of-concept prototype for verification. The system comprises three components: (1) a curved multi-aperture array, which consists of 61 sub-apertures with an entrance pupil diameter of 5 mm and a focal length of 10 mm; (2) a cooled planar detector; and (3) a relay imaging system, which adopts secondary imaging technology and achieves the matching between the array and detector with only six infrared lenses. The fill factor is introduced to analyze light energy utilization efficiency, providing a theoretical basis for improving the system’s signal-to-noise ratio and spatial information collection capability; meanwhile, the focal length distribution and pupil matching are analyzed to ensure the system’s optical performance. The system operates within the 3.7–4.8 μm wavelength band, with a total focal length of 3.08 mm, F-number of 2, and field of view reaching 108°. Simulations demonstrate that all sub-aperture imaging channels have MTF values greater than 0.47 at 33.3 lp/mm, with distortion less than 3%. Imaging test results verify that the system possesses excellent imaging performance. Full article

► Show Figures

Figure 1

21 pages, 4970 KB

Open AccessArticle

Measuring Phase–Amplitude Coupling Effect with OPM-MEG

by Yong Li, Hao Lu, Chunhui Wang, Fuzhi Cao, Jianzhi Yang, Binyi Su, Ying Liu and Xiaolin Ning

Photonics 2025, 12(11), 1070; https://doi.org/10.3390/photonics12111070 - 29 Oct 2025

Abstract

Optically pumped magnetometers (OPMs) present a promising opportunity to advance magnetoencephalography (MEG), enhancing the accuracy of neuronal activity recordings due to their high spatiotemporal resolution. However, to fully realize the potential of OPM-MEG as an emerging brain functional imaging technology, it is essential [...] Read more.

Optically pumped magnetometers (OPMs) present a promising opportunity to advance magnetoencephalography (MEG), enhancing the accuracy of neuronal activity recordings due to their high spatiotemporal resolution. However, to fully realize the potential of OPM-MEG as an emerging brain functional imaging technology, it is essential to measure key indicators of neural dynamics, particularly phase–amplitude coupling (PAC). PAC is a fundamental mechanism for integrating information across different frequency bands and plays an important role in various cognitive functions and neurological disorders. Therefore, measuring PAC with OPM-MEG is a crucial step toward expanding its applications. In this study, brain signals under pitch sequence stimulation were recorded using OPM-MEG to analyze the PAC effect in the primary auditory cortex (Aud) and the inferior frontal gyrus (IFG), as well as the functional connectivity between brain regions. The findings were validated through EEG control experiments. The results indicated that the PAC effect measured by OPM-MEG was largely consistent with that measured by EEG, with OPM-MEG appearing to detect PAC more prominently under the current experimental conditions. The PAC of Aud exhibited a trend of initially increasing and then decreasing centered on the target pitch, showing hemispheric symmetry. The PAC of IFG showed variations under different pitch conditions and displayed right hemisphere lateralization. Functional connectivity analysis provided convergent evidence for the mechanisms underlying the PAC effect and suggested the reliability of the OPM-MEG system in capturing cross-frequency neural dynamics. To our knowledge, this study provides the first task-based evidence that OPM-MEG can measure PAC effects in cortical regions, offering an initial foundation for future investigations of brain dynamics using this technology. Full article

(This article belongs to the Section Quantum Photonics and Technologies)

► Show Figures

Figure 1

Journal Description

Photonics

Latest Articles

Journal Menu

Journal Browser

Highly Accessed Articles

Latest Books

E-Mail Alert

News

Topics

Conferences

Special Issues

Further Information

Guidelines

MDPI Initiatives

Follow MDPI