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Acceleration of Heavy Ions by Ultrafast High-Peak-Power Lasers: Advances, Challenges, and Perspectives
Ag-Grid and Ag-Nanowires Hybrid Transparent Electrodes to Improve Performance of Flexible Organic Light-Emitting Devices
Sub-Nanosecond, Room-Temperature, Mid-IR Fe:ZnSe Gain-Switched Laser: Experimental Characterization and Modeling
$Impact of Sn Particle-Induced Mask Diffraction on EUV Lithography Performance Across Different Pattern Types$
Impact of Sn Particle-Induced Mask Diffraction on EUV Lithography Performance Across Different Pattern Types

Journal Description

Photonics

Photonics is an international, scientific, peer-reviewed, open access journal on the science and technology of optics and photonics, published monthly online by MDPI.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, Ei Compendex, CAPlus / SciFinder, and other databases.
Journal Rank: CiteScore - Q2 (Instrumentation)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 14.8 days after submission; acceptance to publication is undertaken in 1.9 days (median values for papers published in this journal in the first half of 2025).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Companion journal: Lights.

Impact Factor: 1.9 (2024); 5-Year Impact Factor: 2.0 (2024)

Imprint Information Journal Flyer Open Access ISSN: 2304-6732

Latest Articles

23 pages, 7721 KiB

Open AccessArticle

Strengthening-Effect Assessment of Smart CFRP-Reinforced Steel Beams Based on Optical Fiber Sensing Technology

by Bao-Rui Peng, Fu-Kang Shen, Zi-Yi Luo, Chao Zhang, Yung William Sasy Chan, Hua-Ping Wang and Ping Xiang

Photonics 2025, 12(7), 735; https://doi.org/10.3390/photonics12070735 - 18 Jul 2025

Carbon fiber-reinforced polymer (CFRP) laminates have been widely coated on aged and damaged structures for recovering or enhancing their structural performance. The health conditions of the coated composite structures have been given high attention, as they are critically important for assessing operational safety [...] Read more.

Carbon fiber-reinforced polymer (CFRP) laminates have been widely coated on aged and damaged structures for recovering or enhancing their structural performance. The health conditions of the coated composite structures have been given high attention, as they are critically important for assessing operational safety and residual service life. However, the current problem is the lack of an efficient, long-term, and stable monitoring technique to characterize the structural behavior of coated composite structures in the whole life cycle. For this reason, bare and packaged fiber Bragg grating (FBG) sensors have been specially developed and designed in sensing networks to monitor the structural performance of CFRP-coated composite beams under different loads. Some optical fibers have also been inserted in the CFRP laminates to configure the smart CFRP component. Detailed data interpretation has been conducted to declare the strengthening process and effect. Finite element simulation and simplified theoretical analysis have been conducted to validate the experimental testing results and the deformation profiles of steel beams before and after the CFRP coating has been carefully checked. Results indicate that the proposed FBG sensors and sensing layout can accurately reflect the structural performance of the composite beam structure, and the CFRP coating can share partial loads, which finally leads to the downward shift in the centroidal axis, with a value of about 10 mm. The externally bonded sensors generally show good stability and high sensitivity to the applied load and temperature-induced inner stress variation. The study provides a straightforward instruction for the establishment of a structural health monitoring system for CFRP-coated composite structures in the whole life cycle. Full article

(This article belongs to the Special Issue Science and Applications of Optical Fiber Sensors: Recent Advances and Future Trends)

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10 pages, 3012 KiB

Open AccessArticle

A Perovskite-Based Photoelectric Synaptic Transistor with Dynamic Nonlinear Response

by Jiahui Liu, Zunxian Yang, Yujie Zheng and Wenkun Su

Photonics 2025, 12(7), 734; https://doi.org/10.3390/photonics12070734 - 18 Jul 2025

Nonlinear characteristics are essential for neuromorphic devices to process high-dimensional and unstructured data. However, enabling a device to realize a nonlinear response under the same stimulation condition is challenging as this involves two opposing processes: simultaneous charge accumulation and recombination. In this study, [...] Read more.

Nonlinear characteristics are essential for neuromorphic devices to process high-dimensional and unstructured data. However, enabling a device to realize a nonlinear response under the same stimulation condition is challenging as this involves two opposing processes: simultaneous charge accumulation and recombination. In this study, a hybrid transistor based on a mixed-halide perovskite was fabricated to achieve dynamic nonlinear changes in synaptic plasticity. The utilization of a light-induced mixed-bandgap structure within the mixed perovskite film has been demonstrated to increase the recombination paths of photogenerated carriers of the hybrid film, thereby promoting the formation of nonlinear signals in the device. The constructed heterojunction optoelectronic synaptic transistor, formed by combining a mixed-halide perovskite with a p-type semiconductor, generates dynamic nonlinear decay responses under 400 nm light pulses with an intensity as low as 0.02 mW/cm². Furthermore, it has been demonstrated that nonlinear photocurrent growth can be achieved under 650 nm light pulses. It is important to note that this novel nonlinear response is characterized by its dynamism. These improvements provide a novel method for expanding the modulation capability of optoelectronic synaptic devices for synaptic plasticity. Full article

(This article belongs to the Special Issue Polaritons Nanophotonics: Physics, Materials and Applications)

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19 pages, 2875 KiB

Open AccessReview

Streamlining ICI Transformed as a Nonnegative System

by David Hyland

Photonics 2025, 12(7), 733; https://doi.org/10.3390/photonics12070733 - 18 Jul 2025

More than seventy-five years ago, R. Hanbury Brown and R. Q. Twiss performed the first experiments in quantum optics. At the outset, their results showed great promise for the field of astronomical science, featuring inexpensive hardware, immunity to atmospheric turbulence, and enormous interferometry [...] Read more.

More than seventy-five years ago, R. Hanbury Brown and R. Q. Twiss performed the first experiments in quantum optics. At the outset, their results showed great promise for the field of astronomical science, featuring inexpensive hardware, immunity to atmospheric turbulence, and enormous interferometry baselines. This was put to good use for the determination of stellar diameters up to the present time. However, for two-dimensional imaging with faint objects, the integration times are prohibitive. Recently, in a sequence of papers, the present author developed a stochastic search algorithm to remove this roadblock, reducing millions of hours to minutes or seconds. Also, the author’s paper entitled “The Rise of the Brown-Twiss Effect” summarized the search algorithm and emphasized the mathematical proofs of the algorithm. The current algorithm is a sequence of six lines of code. The goal of the present article is to streamline the algorithm in the form of a discrete-time dynamic system and to reduce the size of the state space. The previous algorithm used initial conditions that were randomly assorted pixel intensities. The intensities were mutually statistically independent and uniformly distributed over the range

[0, δ)

, where

δ

is a (very small) positive constant. The present formulation employs a transformation requiring the uniformly distributed phase of the fast Fourier transform of the cross correlations of the data as initial conditions. We shall see that this strategy results in the simplest discrete-time dynamic system capable for exploring the alternate features and benefits of compartmental nonnegative dynamic systems. Full article

(This article belongs to the Special Issue Optical Imaging and Measurements: 2nd Edition)

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28 pages, 5787 KiB

Open AccessReview

Silicon-Based On-Chip Light Sources: A Review

by Yongqi Yang, Jiaqi Yang, Zhouyang Cheng, Shuyan Zhang, Zhen Yang, Shengchuang Bai and Rongping Wang

Photonics 2025, 12(7), 732; https://doi.org/10.3390/photonics12070732 - 18 Jul 2025

Silicon-based on-chip light sources are important since they can provide a compact solution for various applications in the field of high-speed optical communications, high-precision sensing, quantum information processing, and so on. We review the progress of silicon-based on-chip light sources in various materials. [...] Read more.

Silicon-based on-chip light sources are important since they can provide a compact solution for various applications in the field of high-speed optical communications, high-precision sensing, quantum information processing, and so on. We review the progress of silicon-based on-chip light sources in various materials. We provide some key parameters like pump thresholds, output powers, and pump schemes of on-chip lasers based on various materials. Finally, we point out the existing issues in the current investigations and possible solutions in the future. Full article

(This article belongs to the Special Issue Recent Progress in Integrated Photonics)

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38 pages, 2401 KiB

Open AccessReview

Mie Coefficients

by Henk F. Arnoldus

Photonics 2025, 12(7), 731; https://doi.org/10.3390/photonics12070731 - 18 Jul 2025

We consider the scattering of electromagnetic radiation by a spherical particle, known as Mie scattering. The electric and magnetic fields are represented by multipole fields, and the amplitudes are the Mie scattering coefficients. Properties of the particle are mainly contained in these coefficients. [...] Read more.

We consider the scattering of electromagnetic radiation by a spherical particle, known as Mie scattering. The electric and magnetic fields are represented by multipole fields, and the amplitudes are the Mie scattering coefficients. Properties of the particle are mainly contained in these coefficients. We have studied the dependence of these coefficients on the various parameters, with an emphasis on the dependence on the particle radius. Central to this discussion is what is known as the ‘Mie circle’. Without absorption in the particle or the embedding medium, the Mie scattering coefficients lie on this universal circle in the complex plane. We have studied the location of the Mie scattering coefficients on this circle as a function of the particle radius. The Mie circle also serves as a reference for the case when there is absorption in the particle or the medium. In the limit of a small particle, a peculiar divergence appears in the expression for the Mie coefficients, known as the Fröhlich resonance. We show that this apparent singularity is a consequence of the fact that the limit of a small particle fails in the neighborhood of this resonance, and we derive an expression for the correct small-particle limit in the neighborhood of this resonance. Full article

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28 pages, 6374 KiB

Open AccessReview

Recent Progress in GaN-Based High-Bandwidth Micro-LEDs and Photodetectors for High-Speed Visible Light Communication

by Handan Xu, Jiakang Ai, Tianlin Deng, Yuandong Ruan, Di Sun, Yue Liao, Xugao Cui and Pengfei Tian

Photonics 2025, 12(7), 730; https://doi.org/10.3390/photonics12070730 - 18 Jul 2025

Visible light communication (VLC) is an emerging communication technology that integrates lighting and communication, offering significant advantages in terms of data transmission rates and broad application prospects. With advancements in semiconductor technology, micro-light-emitting diodes (micro-LEDs) have emerged as one of the most promising [...] Read more.

Visible light communication (VLC) is an emerging communication technology that integrates lighting and communication, offering significant advantages in terms of data transmission rates and broad application prospects. With advancements in semiconductor technology, micro-light-emitting diodes (micro-LEDs) have emerged as one of the most promising light sources for high-speed VLC systems, owing to their high brightness, low power consumption, and high modulation bandwidth. Recent developments have also seen substantial progress in high-bandwidth GaN-based visible light detectors, which complement the transmission capabilities of micro-LEDs. This paper reviews the latest advancements in micro-LEDs as high-speed transmitters for VLC, detailing their capabilities in terms of bandwidth, data rates, modulation techniques, and diverse applications, including structured lighting systems that combine positioning, communication, and illumination. Additionally, the advantages of using micro-LEDs in GaN-based photodetectors (PDs) are discussed, highlighting their potential in enhancing bandwidth and data rates and facilitating high-speed communications across multifunctional applications. Therefore, this review will benefit the further development of micro-LEDs and their application in 6G communication and global interconnect. Full article

(This article belongs to the Special Issue New Advances in Optical Wireless Communication)

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12 pages, 2993 KiB

Open AccessArticle

Integrated Multiband-Mode Multiplexing Photonic Lantern for Selective Mode Excitation and Preservation

by Li Zhao, Ting Yu, Yunhao Chen and Jianing Tang

Photonics 2025, 12(7), 729; https://doi.org/10.3390/photonics12070729 - 17 Jul 2025

We propose and experimentally demonstrate an Integrated Multiband-Mode Multiplexing Photonic Lantern (IM3PL) that enables the selective excitation of high-order modes and stable modal preservation across multiple wavelength bands. As a proof-of-concept configuration, the IM3PL integrates a custom-designed input fiber array composed of three [...] Read more.

We propose and experimentally demonstrate an Integrated Multiband-Mode Multiplexing Photonic Lantern (IM3PL) that enables the selective excitation of high-order modes and stable modal preservation across multiple wavelength bands. As a proof-of-concept configuration, the IM3PL integrates a custom-designed input fiber array composed of three 980 nm single-mode fibers (SMFs) and two few-mode fibers (FMFs) operating at 1310 nm and 1550 nm, respectively. Simulations verify that 980 nm input signals can selectively excite

L P_{01}

,

L P_{11 a}

, and

L P_{11 b}

modes at the FMF output, while the modal integrity of high-order linear polarized modes is preserved at 1310 nm and 1550 nm. The fabricated IM3PL device is experimentally validated via near-field pattern measurements, confirming the selective excitation at 980 nm and low-loss, mode-preserving transmission at the signal bands. This work offers a scalable and reconfigurable solution for multiband high-order-mode multiplexing, with promising applications in mode-division multiplexed fiber communication systems and multiband high-mode fiber lasers. Full article

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14 pages, 2681 KiB

Open AccessArticle

Waveguide-Assisted Magneto-Optical Effects in 1D Garnet/Co/Au Plasmonic Crystals

by Tatiana Murzina, Andrey Dotsenko, Irina Kolmychek, Vladimir Novikov, Nikita Gusev, Ilya Fedotov and Sergei Gusev

Photonics 2025, 12(7), 728; https://doi.org/10.3390/photonics12070728 - 17 Jul 2025

Magneto-plasmonic structures have been a subject of tremendous attention of researchers in recent decades as they provide unique approaches regarding the efficient control of optical, magneto-optical, and nonlinear-optical effects. Among others, magneto-plasmonic crystals (MPCs) have become one of the most studied structures, known [...] Read more.

Magneto-plasmonic structures have been a subject of tremendous attention of researchers in recent decades as they provide unique approaches regarding the efficient control of optical, magneto-optical, and nonlinear-optical effects. Among others, magneto-plasmonic crystals (MPCs) have become one of the most studied structures, known for their high-quality tunable resonant optical properties. Here, we present the results of experimental and numerical studies on the functional magneto-optical (MO) response of planar 1D plasmonic crystals composed of Co/Au stripes of submicron period on the surface of a 3 μm thick rare-earth garnet layer. The experimental and numerical studies confirm that the wavelength–angular spectra of such structures contain a set of tunable resonant features in their optical and magneto-optical response, associated with the excitation of (i) surface plasmon polaritons at the Co/Au grating–garnet interface, as well as (ii) waveguide (WG) modes propagating in the garnet slab. A comparison of the MO effects in the transversal and longitudinal magnetization of the plasmonic structures is presented. We show that the most efficient Fano-type MPC magneto-optical response is realized for the WG modes of the first order for the longitudinal magnetization of the structure. Further perspectives regarding the optimization of this type of plasmonic crystal are discussed. Full article

(This article belongs to the Section Lasers, Light Sources and Sensors)

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16 pages, 9618 KiB

Open AccessArticle

Scattering of Radiation by a Periodic Structure of Circular and Elliptical Microcavities in a Multimode Optical Waveguide

by Alexandra Yu. Petukhova, Anatolii V. Perminov, Mikhail A. Naparin and Victor V. Krishtop

Photonics 2025, 12(7), 727; https://doi.org/10.3390/photonics12070727 - 17 Jul 2025

We developed a mathematical model to examine the scattering of radiation by a periodic structure of circular and elliptical microcavities formed in a planar optical waveguide. The waveguide simulates the behaviour of a 62.5/125 µm multimode optical fibre. The calculations focused on the [...] Read more.

We developed a mathematical model to examine the scattering of radiation by a periodic structure of circular and elliptical microcavities formed in a planar optical waveguide. The waveguide simulates the behaviour of a 62.5/125 µm multimode optical fibre. The calculations focused on the intensity distribution of scattered light with a wavelength of 1310 nm along the periodic structure, i.e., along the side surface of the waveguide, as a function of the microcavity dimensions and their spatial arrangement within the waveguide core. The optimal geometrical parameters of the microstructure, ensuring the most uniform light scattering, were identified. The model is valid for multimode optical fibres containing strictly periodic structures of microcavities with spherical or elliptical cross-sections that scatter laser radiation in all directions. One potential application of such fibres is as light sources in medical probes for surgical procedures requiring additional illumination and uniform irradiation of affected tissues. Furthermore, the findings of this study offer significant potential for the development of sensing elements for fibre-optic sensors. The findings of this study will facilitate the design of scattering structures with microcavities that ensure a highly uniform scattering pattern. Full article

(This article belongs to the Section Optical Interaction Science)

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16 pages, 2133 KiB

Open AccessArticle

Effects of Chromatic Dispersion on BOTDA Sensor

by Qingwen Hou, Mingjun Kuang, Jindong Wang, Jianping Guo and Zhengjun Wei

Photonics 2025, 12(7), 726; https://doi.org/10.3390/photonics12070726 - 17 Jul 2025

This study investigates the influence of chromatic dispersion on the performance of Brillouin optical time-domain analysis (BOTDA) sensors, particularly under high-pump-power conditions, where nonlinear effects become significant. By incorporating dispersion terms into the coupled amplitude equations of stimulated Brillouin scattering (SBS), we theoretically [...] Read more.

This study investigates the influence of chromatic dispersion on the performance of Brillouin optical time-domain analysis (BOTDA) sensors, particularly under high-pump-power conditions, where nonlinear effects become significant. By incorporating dispersion terms into the coupled amplitude equations of stimulated Brillouin scattering (SBS), we theoretically analyzed the dispersion-induced pulse broadening effect and its impact on the Brillouin gain spectrum (BGS). Numerical simulations revealed that dispersion leads to a moderate broadening of pump pulses, resulting in slight changes to BGS characteristics, including increased peak power and reduced linewidth. To explore the interplay between dispersion and nonlinearity, we built a gain-based BOTDA experimental system and tested two types of fibers, namely standard single-mode fiber (SMF) with anomalous dispersion and dispersion-compensating fiber (DCF) with normal dispersion. Experimental results show that SMF is more prone to modulation instability (MI), which significantly degrades the signal-to-noise ratio (SNR) of the BGS. In contrast, DCF effectively suppresses MI and provides a more stable Brillouin signal. Despite SMF exhibiting narrower BGS linewidths, DCF achieves a higher SNR, aligning with theoretical predictions. These findings highlight the importance of fiber dispersion properties in BOTDA design and suggest that using normally dispersive fibers like DCF can improve sensing performance in long-range, high-power applications. Full article

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11 pages, 1461 KiB

Open AccessArticle

Global–Local Cooperative Optimization in Photonic Inverse Design Algorithms

by Mingzhe Li, Tong Wang, Yi Zhang, Yulin Shen, Jie Yang, Ke Zhang, Dehui Pan and Ming Xin

Photonics 2025, 12(7), 725; https://doi.org/10.3390/photonics12070725 - 17 Jul 2025

We developed the Global–Local Integrated Topology inverse design algorithm (denoted as the GLINT algorithm), which employs a trajectory-based optimization strategy with waveguide–substrate material-flipping structural modifications, enabling the direct optimization of discrete waveguide–substrate binary structures. Compared to the conventional Direct Binary Search (DBS), the [...] Read more.

We developed the Global–Local Integrated Topology inverse design algorithm (denoted as the GLINT algorithm), which employs a trajectory-based optimization strategy with waveguide–substrate material-flipping structural modifications, enabling the direct optimization of discrete waveguide–substrate binary structures. Compared to the conventional Direct Binary Search (DBS), the GLINT algorithm not only significantly enhances computational efficiency through its global search–local refinement framework but also achieves a superior 20 nm × 20 nm optimization resolution while maintaining its optimization speed—substantially advancing the design capability. Utilizing this algorithm, we designed and experimentally demonstrated a 3.5 µm × 3.5 µm dual-port wavelength division multiplexer (WDM), achieving a minimum crosstalk of −11.3 dB and a 2 µm × 2 µm 90-degree bending waveguide exhibiting a 0.31–0.52 dB insertion loss over the 1528–1600 nm wavelength range, both fabricated on silicon-on-insulator (SOI) wafers. Additionally, a 4.5 µm × 4.5 µm three-port WDM structure was also designed and simulated, demonstrating crosstalk as low as −36.5 dB. Full article

(This article belongs to the Special Issue Recent Progress in Integrated Photonics)

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9 pages, 902 KiB

Open AccessArticle

Flat Top Non-Polarizing Optical Bandpass Filtering in Form of Planar Optical Waveguide

by Jianhua Liu and Ping Jiang

Photonics 2025, 12(7), 724; https://doi.org/10.3390/photonics12070724 - 17 Jul 2025

To obtain a flat top shaped passband in a conventional thin-film-based optical bandpass filter (OBF), it needs a large number of constitutional layers of thin films, which makes the film deposition systems more complicated and accumulates errors in film growth. A flat top [...] Read more.

To obtain a flat top shaped passband in a conventional thin-film-based optical bandpass filter (OBF), it needs a large number of constitutional layers of thin films, which makes the film deposition systems more complicated and accumulates errors in film growth. A flat top and polarization-independent optical bandpass filter structure is proposed based on experimentally verified polarization independency in the form of a prism-pair coupled planar optical waveguide (POW). The POW is composed of two waveguide stacks, which consists of nine planar thin-film layers. Theoretical simulations show that the flat band top spans about 5 nm with transmittance over 97.8%. The passband is designed to be centered at 632.8 nm, the He-Ne laser wavelength, and the FWHM (full width at half maximum) bandwidth is about 35 nm. Within 0.5° tuning for the incident angle of the light, the passband could be shifted within 50 nm, while its transmittance fluctuates only less than 1% and the passband shape distorts only slightly. This type of OBF is potentially applicable in various fields of optical and laser spectroscopies. Full article

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11 pages, 7216 KiB

Open AccessArticle

Low-Finesse Fabry–Perot Cavity Design Based on a Reflective Sphere

by Ju Wang, Ye Gao, Jinlong Yu, Hao Luo, Xuemin Su, Xu Han, Yang Gao, Ben Cai and Chuang Ma

Photonics 2025, 12(7), 723; https://doi.org/10.3390/photonics12070723 - 17 Jul 2025

Low-finesse Fabry–Perot (F–P) cavities, widely applied in the field of micro-displacement measurement, offer significant advantages in reducing the influence of higher-order reflections and improving the accuracy of measurement systems. Generally, an F–P cavity finesse of 0.5 is required to achieve high-precision micro-displacement measurements. [...] Read more.

Low-finesse Fabry–Perot (F–P) cavities, widely applied in the field of micro-displacement measurement, offer significant advantages in reducing the influence of higher-order reflections and improving the accuracy of measurement systems. Generally, an F–P cavity finesse of 0.5 is required to achieve high-precision micro-displacement measurements. However, in optical design, low-finesse cavities impose strict requirements on reflectivity, and maintaining fine stability during cavity movement is challenging. Achieving ideal orthogonal interference with a finesse of 0.5 thus presents considerable difficulties. This study proposes a novel low-finesse F–P cavity design that employs a high-reflectivity spherical reflector and the end face of a fiber collimator as the reflective surfaces of the cavity. By utilizing beam divergence characteristics and geometric parameters, a structure with a finesse of approximately 0.5 is quantitatively designed, enabling a simplified implementation without the need for angular alignment. Compared with conventional approaches, this method eliminates the need for precise angular alignment of the reflective surfaces, significantly simplifying implementation. The experimental results show that, under fixed receiving field angles and beam radii of the fiber collimators, ideal orthogonal interference can be achieved by selecting the radius of the reflective sphere. Under varying working distances, the average finesse values of the interference spectra measured by Collimators 1 and 2 are 0.496 and 0.502, respectively, both close to the theoretical design value of 0.5, thereby meeting the design requirements. Full article

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

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17 pages, 4685 KiB

Open AccessArticle

Development of an Automated Phase-Shifting Interferometer Using a Homemade Liquid-Crystal Phase Shifter

by Zhenghao Song, Lin Xu, Jing Wang, Xitong Liang and Jun Dai

Photonics 2025, 12(7), 722; https://doi.org/10.3390/photonics12070722 - 16 Jul 2025

In this paper, an automatic phase-shifting interferometer has been developed using a homemade liquid-crystal phase shifter, which demonstrates a low-cost, fully automated technical solution for measuring the phase information of optical waves in devices. Conventional phase-shifting interferometers usually rely on PZT piezoelectric phase [...] Read more.

In this paper, an automatic phase-shifting interferometer has been developed using a homemade liquid-crystal phase shifter, which demonstrates a low-cost, fully automated technical solution for measuring the phase information of optical waves in devices. Conventional phase-shifting interferometers usually rely on PZT piezoelectric phase shifters, which are complex, require additional half-inverse and half-transparent optics to build the optical path, and are expensive. To overcome these limitations, we used a laboratory-made liquid-crystal waveplate as a phase shifter and integrated it into a Mach–Zehnder phase-shifting interferometer. The system is controlled by an STM32 microcontroller and self-developed measurement software, and it utilizes a four-step phase-shift interferometry algorithm and the CPULSI phase-unwrapping algorithm to achieve automatic phase measurements. Phase test experiments using a standard plano-convex lens and a homemade liquid-crystal grating as test objects demonstrate the feasibility and accuracy of the device by the fact that the measured focal lengths are in good agreement with the nominal values, and the phase distributions of the gratings are also in good agreement with the predefined values. This study validates the potential of liquid-crystal-based phase shifters for low-cost, fully automated optical phase measurements, providing a simpler and cheaper alternative to conventional methods. Full article

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9 pages, 2042 KiB

Open AccessCommunication

A 1 × 4 Silica-Based GMZI Thermo-Optic Switch with a Wide Bandwidth and Low Crosstalk

by Yanshuang Wang

Photonics 2025, 12(7), 721; https://doi.org/10.3390/photonics12070721 - 16 Jul 2025

The growing demand for communication capacity has driven advancements in optical switches. However, measurement procedures for large-scale switching arrays become more complex as the number of units increases. Multi-port optical switches can reduce the measurement complexity. In this work, we demonstrate a 1 [...] Read more.

The growing demand for communication capacity has driven advancements in optical switches. However, measurement procedures for large-scale switching arrays become more complex as the number of units increases. Multi-port optical switches can reduce the measurement complexity. In this work, we demonstrate a 1 × 4 thermo-optic switch fabricated on a silica platform, based on a Generalized Mach–Zehnder Interferometer (GMZI) structure with a wide bandwidth and low crosstalk. The device enables flexible switching among four output channels, achieving a crosstalk below −15 dB over the 1500–1580 nm wavelength range and an insertion loss of −6.51 dB at 1550 nm. Full article

(This article belongs to the Special Issue Advances in Integrated Photonics)

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22 pages, 5418 KiB

Open AccessArticle

TickRS: A High-Speed Gapless Signal Sampling Method for Rolling-Shutter Optical Camera Communication

by Yongfeng Hong, Xiangting Xie and Xingfa Shen

Photonics 2025, 12(7), 720; https://doi.org/10.3390/photonics12070720 - 16 Jul 2025

Using the rolling-shutter mechanism to enhance the signal sampling frequency of Optical Camera Communication (OCC) is a low-cost solution, but its periodic sampling interruptions may cause signal loss, and existing solutions often compromise communication rate and distance. To address this, this paper proposes [...] Read more.

Using the rolling-shutter mechanism to enhance the signal sampling frequency of Optical Camera Communication (OCC) is a low-cost solution, but its periodic sampling interruptions may cause signal loss, and existing solutions often compromise communication rate and distance. To address this, this paper proposes NoGap-RS, a no-gap sampling method, theoretically addressing the signal loss issue at longer distances from a perspective of CMOS exposure timing. Experiments show that NoGap-OOK, a OCC system based on NoGap-RS and On-Off key modulation, can achieve a communication rate of 6.41 Kbps at a distance of 3 m, with a BER of

10^{- 5}

under indoor artificial light. This paper further proposes TickRS, a time slot division method, innovatively addressing the overlap that occurs during consecutive-row exposures to further enhance communication rate. Experiments show that TickRS-CSK, a OCC system based on TickRS and Color-Shift Key, can achieve a communication rate of 20.09 Kbps at a distance of 3.6 m, with a BER of

10^{- 2}

under indoor natural light. Full article

(This article belongs to the Special Issue Innovations in Optical Wireless Communications: Challenges and Opportunities)

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11 pages, 3627 KiB

Open AccessArticle

The Influence of Traps on the Self-Heating Effect and THz Response of GaN HEMTs

by Huichuan Fan, Xiaoyun Wang, Xiaofang Wang and Lin Wang

Photonics 2025, 12(7), 719; https://doi.org/10.3390/photonics12070719 - 16 Jul 2025

This study systematically investigates the effects of trap concentration on self-heating and terahertz (THz) responses in GaN HEMTs using Sentaurus TCAD. Traps, inherently unavoidable in semiconductors, can be strategically introduced to engineer specific energy levels that establish competitive dynamics between the electron momentum [...] Read more.

This study systematically investigates the effects of trap concentration on self-heating and terahertz (THz) responses in GaN HEMTs using Sentaurus TCAD. Traps, inherently unavoidable in semiconductors, can be strategically introduced to engineer specific energy levels that establish competitive dynamics between the electron momentum relaxation time and the carrier lifetime. A simulation-based exploration of this mechanism provides significant scientific value for enhancing device performance through self-heating mitigation and THz response optimization. An AlGaN/GaN heterojunction HEMT model was established, with trap concentrations ranging from 0 to

5 \times 10^{17} {c m}^{- 3}

. The analysis reveals that traps significantly enhance channel current (achieving 3× gain at

1 \times 1 0^{17} {c m}^{- 3}

) via new energy levels that prolong carrier lifetime. However, elevated trap concentrations (>

1 \times 10^{16} {c m}^{- 3}

) exacerbate self-heating-induced current collapse, reducing the min-to-max current ratio to 0.9158. In THz response characterization, devices exhibit a distinct DC component (

U_{d c}

) under non-resonant detection (

ω τ ≪ 1

). At a trap concentration of

1 \times 10^{15} {c m}^{- 3}

,

U_{d c}

peaks at

0.12 V

when

V_{g} D C = - 7.8 V

. Compared to trap-free devices, a maximum response attenuation of 64.89% occurs at

V_{g} D C = - 4.9 V

. Furthermore,

U_{d c}

demonstrates non-monotonic behavior with concentration, showing local maxima at

4 \times 10^{15} {c m}^{- 3}

and

7 \times 10^{15} {c m}^{- 3}

, attributed to plasma wave damping and temperature-gradient-induced electric field variations. This research establishes trap engineering guidelines for GaN HEMTs: a concentration of

4 \times 10^{15} {c m}^{- 3}

optimally enhances conductivity while minimizing adverse impacts on both self-heating and the THz response, making it particularly suitable for high-sensitivity terahertz detectors. Full article

(This article belongs to the Special Issue Development and Optimization of High-Power Semiconductor Laser Diodes and Photodetectors)

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14 pages, 2149 KiB

Open AccessArticle

Gain Characteristics of Hybrid Waveguide Amplifiers in SiN Photonics Integration with Er-Yb:Al₂O₃ Thin Film

by Ziming Dong, Guoqing Sun, Yuqing Zhao, Yaxin Wang, Lei Ding, Liqin Tang and Yigang Li

Photonics 2025, 12(7), 718; https://doi.org/10.3390/photonics12070718 - 16 Jul 2025

Integrated optical waveguide amplifiers, with their compact footprint, low power consumption, and scalability, are the basis for optical communications. The realization of high gain in such integrated devices is made more challenging by the tight optical constraints. In this work, we present efficient [...] Read more.

Integrated optical waveguide amplifiers, with their compact footprint, low power consumption, and scalability, are the basis for optical communications. The realization of high gain in such integrated devices is made more challenging by the tight optical constraints. In this work, we present efficient amplification in an erbium–ytterbium-based hybrid slot waveguide consisting of a silicon nitride waveguide and a thin-film active layer/electron-beam resist. The electron-beam resist as the upper cladding layer not only possesses the role of protecting the waveguide but also has tighter optical confinement in the vertical cross-section direction. On this basis, an accurate and comprehensive dynamic model of an erbium–ytterbium co-doped amplifier is realized by introducing quenched ions. A modal gain of above 20 dB is achieved at the signal wavelength of 1530 nm in a 1.4 cm long hybrid slot waveguide, with fractions of quenched ions f_q = 30%. In addition, the proposed hybrid waveguide amplifiers exhibit higher modal gain than conventional air-clad amplifiers under the same conditions. Endowing silicon nitride photonic integrated circuits with efficient amplification enriches the integration of various active functionalities on silicon. Full article

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12 pages, 5633 KiB

Open AccessArticle

Study on Joint Intensity in Real-Space and k-Space of SFS Super-Resolution Imaging via Multiplex Illumination Modulation

by Xiaoyu Yang, Haonan Zhang, Feihong Lin, Xu Liu and Qing Yang

Photonics 2025, 12(7), 717; https://doi.org/10.3390/photonics12070717 - 16 Jul 2025

This paper studied the general mechanism of spatial-frequency-shift (SFS) super-resolution imaging based on multiplex illumination modulation. The theory of SFS joint intensity was first proposed. Experiments on parallel slots with discrete spatial frequency (SF) distribution and V-shape slots with continuous SF distribution were [...] Read more.

This paper studied the general mechanism of spatial-frequency-shift (SFS) super-resolution imaging based on multiplex illumination modulation. The theory of SFS joint intensity was first proposed. Experiments on parallel slots with discrete spatial frequency (SF) distribution and V-shape slots with continuous SF distribution were carried out, and their real-space images and k-space images were obtained. The influence of single illumination with different SFS and mixed illumination with various combinations on SFS super-resolution imaging was analyzed. The phenomena of sample SF coverage were discussed. The SFS super-resolution imaging characteristics based on low-coherence illumination and highly localized light fields were discovered. The phenomenon of image magnification during SFS super-resolution imaging process was discussed. The differences and connections between the SF spectrum of objects and the k-space images obtained in SFS super-resolution imaging process were explained. This provides certain support for optimization of high-throughput SFS super-resolution imaging. Full article

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12 pages, 3406 KiB

Open AccessArticle

Singular Value Decomposition-Assisted Holographic Generation of High-Quality Cylindrical Vector Beams Through Few-Mode Fibers

by Angel Cifuentes, Miguel Varga and Gabriel Molina-Terriza

Photonics 2025, 12(7), 716; https://doi.org/10.3390/photonics12070716 - 16 Jul 2025

Full control of the light field at the tip of the fiber holds the possibility of producing structured illumination patterns such as LG-beams or vector light fields, which have important applications in different fields such as imaging and quantum technologies. In this work, [...] Read more.

Full control of the light field at the tip of the fiber holds the possibility of producing structured illumination patterns such as LG-beams or vector light fields, which have important applications in different fields such as imaging and quantum technologies. In this work, we show how, by measuring the transmission matrix (TM) and shaping the input of a few-mode fiber, we are able to produce cylindrical vector beams at the fiber output. We use singular value decomposition (SVD) to analyze the TM and use the singular vectors as the basis for beam shaping. We demonstrate the method in three different commercially available fibers supporting 6, 12 and 16 modes each. Full article

(This article belongs to the Special Issue Vortex Beams: Transmission, Scattering and Application)

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