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Photonics
Volume 12
Issue 4
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Photonics, Volume 12, Issue 4 (April 2025) – 110 articles

Cover Story (view full-size image): In the field of short-reach optical communications, self-coherent detection (SCD) systems, which can achieve low-complexity optical field recovery at a low cost, have garnered significant research attention. However, a guard band is required between the carrier and the signal in SCD systems due to the limitations of non-ideal receiver transfer function. In this paper, we propose a spectrum inversion-based double-sideband (SI-DSB) modulation scheme. Through the shifting of the signal to the high-frequency region by means of spectrum inversion, a guard band is created around zero frequency. The results show that the proposed SI-DSB modulation scheme not only achieves comparable performance to the conventional twin-SSB modulation scheme but also significantly reduces DSP complexity. View this paper
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35 pages, 3588 KiB  
Article
Metasurface-Refractive Hybrid Lens Modeling with Vector Field Physical Optics
by Ko-Han Shih and C. Kyle Renshaw
Photonics 2025, 12(4), 401; https://doi.org/10.3390/photonics12040401 - 21 Apr 2025
Abstract
Metasurfaces (MSs) have emerged as a promising technology for optical system design. When combined with traditional refractive optics, MS-refractive hybrid lenses can enhance imaging performance, reduce optical aberrations, and introduce new functionalities such as polarization control. However, modeling these hybrid lenses requires advanced [...] Read more.
Metasurfaces (MSs) have emerged as a promising technology for optical system design. When combined with traditional refractive optics, MS-refractive hybrid lenses can enhance imaging performance, reduce optical aberrations, and introduce new functionalities such as polarization control. However, modeling these hybrid lenses requires advanced simulation techniques that usually go beyond conventional raytracing tools. This work presents a physical optics framework for modeling MS-refractive hybrid lenses. We introduce a ray-wave hybrid method that integrates multiple propagation techniques to account for vector wave propagation through various optical elements. At the center of the proposed framework is the Gaussian decomposition method for modeling beam propagation through refractive optics. Ray-path diffraction is automatically considered in this method, and complex input wavefront can be modeled as well. Several techniques are integrated to ensure accuracy in decomposing an incoming vector wave into Gaussian beamlets, such as adaptive consideration of local wavefront principal curvatures and best-fit beam width estimation from the local covariance matrix. To demonstrate the effectiveness of our method, we apply it to several hybrid lens designs, including polarization-sensitive MSs and aberration-correcting MSs integrated into complex optical systems. Full article
(This article belongs to the Special Issue Advancements in Optical Metamaterials)
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20 pages, 2107 KiB  
Article
Exact Solutions to Cancer Laser Ablation Modeling
by Luisa Consiglieri
Photonics 2025, 12(4), 400; https://doi.org/10.3390/photonics12040400 - 21 Apr 2025
Abstract
The present paper deals with the study of the fluence rate over both healthy and tumor tissues in the presence of focal laser ablation (FLA). We propose new analytical solutions for a coupled partial differential equation (PDE) system, which includes the transport equation [...] Read more.
The present paper deals with the study of the fluence rate over both healthy and tumor tissues in the presence of focal laser ablation (FLA). We propose new analytical solutions for a coupled partial differential equation (PDE) system, which includes the transport equation modeling of light penetration into biological tissue, the bioheat equation modeling the heat transfer, and its respective damage. The present work could be the first step toward knowledge of the mathematical framework for biothermophysical problems, as well as the main key to simplify the numerical calculations due to its zero cost. We derive exact solutions and simulate results from them. We discuss the potential physical contributions and present respective conclusions about the following: (1) the validity of the diffusion approximation of the radiative transfer equation; (2) the local behavior of the source of scattered photons; (3) the unsteady state of the fluence rate; and (4) the boundedness of the critical time of the thermal damage to the cancerous tissue. We also discuss some controversial and diverging hypotheses. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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18 pages, 8067 KiB  
Article
Microstructured Waveguide Sensors for Point-of-Care Health Screening
by Svetlana S. Konnova, Pavel A. Lepilin, Anastasia A. Zanishevskaya, Alexey Y. Gryaznov, Natalia A. Kosheleva, Victoria P. Ilinskaya, Julia S. Skibina and Valery V. Tuchin
Photonics 2025, 12(4), 399; https://doi.org/10.3390/photonics12040399 - 20 Apr 2025
Abstract
Biosensor technologies in medicine, as in many other areas, are replacing labor-intensive methods of monitoring human health. This paper presents the results of experimental studies on label-free sensors based on a hollow core microstructured optical waveguide (HC-MOW) for human blood serum analysis. The [...] Read more.
Biosensor technologies in medicine, as in many other areas, are replacing labor-intensive methods of monitoring human health. This paper presents the results of experimental studies on label-free sensors based on a hollow core microstructured optical waveguide (HC-MOW) for human blood serum analysis. The MOWs with a hollow core of 247.5 µm in diameter were manufactured and used in our work. These parameters allow the hollow core to be filled with high-viscosity solutions due to the capillary properties of the fiber. Calculations of the spectral properties of the HC-MOW fiber were carried out and experimentally confirmed. Twenty-one blood serum samples from volunteers were analyzed using standard photometry (commercial kits) and an experimental biosensor. The obtained transmission spectra were processed by the principal component analysis method and conclusions were drawn about the possibility of using this biosensor in point-of-care medicine. A significant difference was shown between the blood serum of healthy patients and patients with confirmed diagnoses and a long history of cardiovascular system abnormalities. Algorithms for spectra processing using the Origin program are presented. Full article
(This article belongs to the Special Issue Optical Sensors for Advanced Biomedical Applications)
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15 pages, 3015 KiB  
Article
Noise Reduction in LED-Based Photoacoustic Imaging
by Takahiro Kono, Kazuma Hashimoto, Keisuke Fukuda, Uma Maheswari Rajagopalan, Kae Nakamura and Jun Yamada
Photonics 2025, 12(4), 398; https://doi.org/10.3390/photonics12040398 - 18 Apr 2025
Viewed by 68
Abstract
Photoacoustic tomography (PAT), also known as optoacoustic tomography, has been emerging as a biomedical imaging modality that can provide cross-sectional or three-dimensional (3D) visualization of biological tissues such as blood vessels and lymphatic vessels in vivo at high resolution. The principle behind the [...] Read more.
Photoacoustic tomography (PAT), also known as optoacoustic tomography, has been emerging as a biomedical imaging modality that can provide cross-sectional or three-dimensional (3D) visualization of biological tissues such as blood vessels and lymphatic vessels in vivo at high resolution. The principle behind the visualization involves the light being absorbed by the tissues which results in the generation of ultrasound. Depending on the strength of ultrasound and its decay rate, it could be used to visualize the absorber location. In general, pulsed lasers such as the Q-switched Nd-YAG and OPO lasers that provide high-energy widths in the range of a few nanoseconds operating at low repetition rates are commonly used as a light source in photoacoustic imaging. However, such lasers are expensive and occupy ample space. Therefore, PAT systems that use LED as the source instead of lasers, which have the advantage of being obtainable at low cost and portable, are gaining attention. However, LED light sources have significantly low energy, and the photoacoustic signals generated have a low signal-to-noise ratio (SNR). Therefore, in LED-based systems, one way to strengthen the signal and improve the SNR is to significantly increase the repetition rate of LED pulses and use signal processing, which can be achieved using a high-power LED along M-sequence signal decoding. M-sequence signal decoding is effective, especially under high repetition rates, thus improving the SNR. However, power supplies for high-power LEDs have a circuit jitter, resulting in random temporal fluctuations in the emitted light. Such jitters, in turn, would affect the M-sequence-based signal decoding. Therefore, we propose a new decoding algorithm which compensates for LED jitter in the M-sequence signal processing. We show that the proposed new signal processing method can significantly improve the SNR of the photoacoustic signals. Full article
(This article belongs to the Special Issue Emerging Trends in Biomedical Optical Imaging)
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12 pages, 3644 KiB  
Communication
A Plasmonic Modulator with High Modulation Depth Based on the Dual-Control Mechanism
by Zesheng Chen, Sisi Yang, Xuefang Hu, Changgui Lu and Mengjia Lu
Photonics 2025, 12(4), 397; https://doi.org/10.3390/photonics12040397 - 18 Apr 2025
Viewed by 121
Abstract
The dispersion relationship of plasmons can be modulated by changing the carrier density of the propagating medium, which provides a new degree of freedom for optical modulation. Traditional graphene plasmonic modulators based on carrier control mainly revolve around chemical doping or voltage control [...] Read more.
The dispersion relationship of plasmons can be modulated by changing the carrier density of the propagating medium, which provides a new degree of freedom for optical modulation. Traditional graphene plasmonic modulators based on carrier control mainly revolve around chemical doping or voltage control methods, but using a single method of modulation limits the optimization of modulation depth. Herein, we propose a hybrid substrate–dielectric–silicon–graphene structure, which can achieve periodic control of the carrier density in graphene through chemical doping of silicon gratings and overall control of the carrier density by applying an external voltage between the substrate and graphene. The numerical results show that the optical transmission can reach 54.6 dB when the grating length, width, period, and working wavelength are 54 nm, 30 nm, 60 nm, and 8 μm, respectively. The modulation depth of the modulator is significantly optimized by combining the above control mechanisms. This structure will have potential applications in optoelectronic sensing, optoelectronic detection, and optical modulation. Full article
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18 pages, 4553 KiB  
Article
Improving Temperature Prediction Precision for Aerial Cameras by Correcting Structure and Parameters of Thermal Network Models
by Yue Fan, Wei Feng, Zhenxing Ren, Bingqi Liu and Jinying Li
Photonics 2025, 12(4), 396; https://doi.org/10.3390/photonics12040396 - 18 Apr 2025
Viewed by 124
Abstract
Accurate temperature prediction is a prerequisite for precise thermal control of an aerial camera, which is crucial for capturing high-resolution images. This paper introduces a methodology for improving the precision of temperature predictions generated by thermal network models for aerial cameras, which involves [...] Read more.
Accurate temperature prediction is a prerequisite for precise thermal control of an aerial camera, which is crucial for capturing high-resolution images. This paper introduces a methodology for improving the precision of temperature predictions generated by thermal network models for aerial cameras, which involves correcting the structure and parameters of the thermal network. The passive thermal control optimization design of the frame insulation structure and convective heat transfer coefficients ensures that key thermal parameter values are maintained within optimum ranges. Following an analysis of the change trend consistency between the predicted temperatures and the transient thermal experimental data, the thermal network structure is modified to reduce the discrepancy between the thermal network and physical models. Using the Monte Carlo algorithm, parameter spaces for key thermal parameters are explored using different sampling numbers. The optimal parameter values are then derived by satisfying the tolerance limit condition and minimizing the objective function. As the sampling number increases, the RMSE between the predicted and experimental results decreases from 1.82 °C to 1.44 °C, and the R-squared value increases from 0.78 to 0.91. The proposed correction method demonstrates its efficiency and validity in refining the accuracy of thermal network models for aerial cameras. Full article
(This article belongs to the Special Issue Optoelectronic Detection Technologies and Applications)
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32 pages, 2964 KiB  
Article
Enhancement of Optical Wireless Discrete Multitone Channel Capacity Based on Li-Fi Using Sparse Coded Mask Modeling
by Yong-Yuk Won, Heetae Han, Dongmin Choi and Sang Min Yoon
Photonics 2025, 12(4), 395; https://doi.org/10.3390/photonics12040395 - 18 Apr 2025
Viewed by 59
Abstract
A sparse coded mask modeling technique is proposed to increase the transmission capacity of an optical wireless link based on Li-Fi. The learning model for the discrete multitone (DMT) signal waveform is implemented using the proposed technique, which is designed based on a [...] Read more.
A sparse coded mask modeling technique is proposed to increase the transmission capacity of an optical wireless link based on Li-Fi. The learning model for the discrete multitone (DMT) signal waveform is implemented using the proposed technique, which is designed based on a masked auto-encoder. The entire length of the DMT signal waveform, encoded using quadrature phase shift keying (QPSK) or 16-quadrature amplitude modulation (16-QAM) symbols, is divided into equal intervals to generate DMT patches, which are subsequently compressed based on the specified masking ratio. After 1-m optical wireless transmission, the DMT signal waveform is reconstructed from the received DMT patch through a decoding process and then QPSK or 16-QAM symbols are recovered. Using the proposed technique, we demonstrate that we can increase the transmission capacity by up to 1.85 times for a 10 MHz physical bandwidth. Additionally, we verify that the proposed technique is feasible in Li-Fi networks with illumination environments above 240 lux. Full article
(This article belongs to the Special Issue Optical Signal Processing for Advanced Communication Systems)
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15 pages, 7045 KiB  
Article
Reconstruction Algorithm of Absorption Spectral Field Distribution Based on a Priori Constrained Bivariate Polynomial Model
by Chuge Chen, Dingfeng Shi, An Huang, Suman Ai, Rantong Niu, Ting Jiao and Zhenyu Xu
Photonics 2025, 12(4), 394; https://doi.org/10.3390/photonics12040394 - 18 Apr 2025
Viewed by 128
Abstract
Computed Tomography–Tunable Diode Laser Absorption Spectroscopy (CT-TDLAS) is an effective diagnostic method for analyzing combustion flow fields within engines. This study proposes an adaptive reconstruction algorithm utilizing constrained polynomial fitting within the CT-TDLAS framework. Based on existing polynomial fitting models, the proposed algorithm [...] Read more.
Computed Tomography–Tunable Diode Laser Absorption Spectroscopy (CT-TDLAS) is an effective diagnostic method for analyzing combustion flow fields within engines. This study proposes an adaptive reconstruction algorithm utilizing constrained polynomial fitting within the CT-TDLAS framework. Based on existing polynomial fitting models, the proposed algorithm integrates physical boundary constraints on temperature and concentration fields, optimizing integrated absorbance errors. This method significantly enhances reconstruction accuracy and computational efficiency, while also lowering computational complexity. The adaptive strategy dynamically adjusts the polynomial order, effectively mitigating issues of overfitting or underdetermination typically associated with fixed polynomial orders. Numerical simulations demonstrate reduced temperature reconstruction errors of 2%, 1.6%, and 2% for single-peak, dual-peak, and mixed distribution flow fields, respectively. Corresponding concentration errors were 2%, 1.8%, and 2.6%, which are all improvements over those achieved by the Algebraic Reconstruction Technique (ART). Experimental results using a McKenna flat-flame burner revealed an average reconstruction error of only 0.3% compared to thermocouple measurements for high-temperature regions (>1000 K), with a minimal central temperature difference of 6 K. For lower-temperature peripheral regions, the average error was 188 K, illustrating the practical applicability of the proposed algorithm. Full article
(This article belongs to the Special Issue Laser as a Detection: From Spectral Imaging to LiDAR for Remote Sensing Applications)
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13 pages, 3398 KiB  
Article
Orthogonally Polarized Dual-Wavelength Pr:LLF Green Laser at 546 nm and 550 nm with the Balanced Output Powers at All Pump Power Level
by Haotian Huang, Jing Xia, Nguyentuan Anh, Yuzhao Li, Yuanxian Zhang, Qian Zhang, Zhexian Zhao and Yanfei Lü
Photonics 2025, 12(4), 393; https://doi.org/10.3390/photonics12040393 - 18 Apr 2025
Viewed by 156
Abstract
A continuous-wave (CW) orthogonally polarized dual-wavelength (OPDW) Pr3+:LiLuF4 (Pr:LLF) green laser with a balanced output power on the 3P0→3H5 transition was demonstrated for the first time. We theoretically analyzed the conditions for achieving equal [...] Read more.
A continuous-wave (CW) orthogonally polarized dual-wavelength (OPDW) Pr3+:LiLuF4 (Pr:LLF) green laser with a balanced output power on the 3P0→3H5 transition was demonstrated for the first time. We theoretically analyzed the conditions for achieving equal output power in the OPDW laser operation using two intracavity etalons and experimentally realized the OPDW green laser in a Pr:LLF crystal. Under pumping with a frequency-doubled optically pumped semiconductor laser (2ω-OPSL) generating 10 W at 479 nm, an OPDW green laser at 546 nm in π-polarization and 550 nm in σ-polarization was obtained with a total output power of 1.68 W. The output powers of the two wavelengths were equal for all the pump power levels. Further, a CW ultraviolet (UV) laser at 274 nm by intracavity sum-frequency mixing was also achieved with a maximum output power of 386 mW. The OPDW Pr:LLF green lasers with the balanced output power were desirable for medical detection and the generation of UV lasers. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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18 pages, 1429 KiB  
Article
Comprehensive Optical Inter-Satellite Communication Model for Low Earth Orbit Constellations: Analyzing Transmission Power Requirements
by Michail Gioulis, Thomas Kamalakis and Dimitris Alexandropoulos
Photonics 2025, 12(4), 392; https://doi.org/10.3390/photonics12040392 - 17 Apr 2025
Viewed by 181
Abstract
Free-space optical communications have emerged as a powerful solution for inter-satellite links, playing a crucial role in next-generation satellite networks. This paper introduces a comprehensive model that enables the dynamic evaluation of optical power requirements for realistic low Earth orbit satellite constellations throughout [...] Read more.
Free-space optical communications have emerged as a powerful solution for inter-satellite links, playing a crucial role in next-generation satellite networks. This paper introduces a comprehensive model that enables the dynamic evaluation of optical power requirements for realistic low Earth orbit satellite constellations throughout the orbital period. Our approach incorporates the constellation architecture, link budget analysis, and optical transceiver design to accurately estimate the power required for sustaining connectivity for both intra- and inter-orbit links. We apply the model considering Walker delta-type constellations of varying densities. We show that in dense constellations, even at high data rates, the required transmission power can be low enough to mitigate the need for optical amplification. Dynamically estimating the power requirements is vital when evaluating energy savings in adaptive scenarios where terminals adaptively change the emitted power depending on the link status. Our model is implemented in Python and is openly available under an open-source license. It can be easily adapted to various alternative constellation configurations. Full article
(This article belongs to the Special Issue Advanced Technologies in Optical Wireless Communications)
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14 pages, 1074 KiB  
Article
WDM-PON Free Space Optical (FSO) System Utilizing LDPC Decoding for Enhanced Cellular C-RAN Fronthaul Networks
by Dokhyl AlQahtani and Fady El-Nahal
Photonics 2025, 12(4), 391; https://doi.org/10.3390/photonics12040391 - 17 Apr 2025
Viewed by 300
Abstract
Modern cellular systems rely on high-capacity and low-latency optical networks to meet ever-increasing data demands. Centralized Radio Access Network (C-RAN) architectures offer a cost-effective approach for deploying mobile infrastructures. In this work, we propose a flexible and cost-efficient fronthaul topology that combines Wavelength [...] Read more.
Modern cellular systems rely on high-capacity and low-latency optical networks to meet ever-increasing data demands. Centralized Radio Access Network (C-RAN) architectures offer a cost-effective approach for deploying mobile infrastructures. In this work, we propose a flexible and cost-efficient fronthaul topology that combines Wavelength Division Multiplexing (WDM) passive optical networks (PONs) with free-space optical (FSO) links. To enhance overall system performance, we introduce Low-Density Parity Check (LDPC) decoding, which provides robust error-correction capabilities against atmospheric turbulence and noise. Our system transmits 20 Gbps, 16-QAM intensity-modulated orthogonal frequency-division multiplexing (OFDM) signals, achieving a substantial reduction in bit error rate (BER). Numerical results show that the proposed WDM-PON-FSO architecture, augmented with LDPC decoding, maintains reliable transmission over 2 km under strong turbulence conditions. Full article
(This article belongs to the Special Issue Recent Advances in Optical Wireless Communication Systems and Networks)
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18 pages, 6501 KiB  
Article
Airborne Constant Ground Resolution Imaging Optical System Design
by Zhiqiang Yang, Shizhen Gao, Qianxi Chen, Bohan Wu, Qiang Xu, Lei Gong and Lihong Yang
Photonics 2025, 12(4), 390; https://doi.org/10.3390/photonics12040390 - 16 Apr 2025
Viewed by 131
Abstract
When an unmanned aerial vehicle (UAV) tilts to capture an image of a ground target, variations in object distance may lead to uneven resolution distribution, with the focal length ranging from zero to the full field of view. The field-of-view focal length (FFL), [...] Read more.
When an unmanned aerial vehicle (UAV) tilts to capture an image of a ground target, variations in object distance may lead to uneven resolution distribution, with the focal length ranging from zero to the full field of view. The field-of-view focal length (FFL), which is a function of the field of view, characterizes the optical properties of the system for each viewing angle. The field-of-view focal length (FFL) quantifies the incremental change in image height resulting from marginal rays exiting the optical system, with infinitesimal angular variations at the field boundary. The optical aberration manifests as an effective focal length variation that exhibits field-dependent characteristics. Through systematic calculation and optimization of the field-of-view focal lengths (FFLs) for ground resolution (GR) control, a mid-wave infrared (MWIR) optical system has been successfully designed, featuring a 10° × 8° field of view (FOV) with an F-number of 3. The optical system implements field-adapted focal length adjustment across distinct viewing angles to ensure consistent ground resolution preservation throughout the full field of view. The designed optical system achieves near-diffraction-limited modulation transfer function (MTF) performance across the full field of view, with all dispersion spots consistently confined within the Airy disk at every viewing angle. The optical system demonstrates superior imaging performance with all dispersion spots confined within the Airy disk radius, fully complying with stringent image quality specifications. Featuring a compact structural configuration, the system exhibits optimal suitability for airborne ground-target reconnaissance applications. Full article
(This article belongs to the Special Issue Advances in Optical System Design)
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15 pages, 2859 KiB  
Article
Constructing a Micro-Raman Spectrometer with Industrial-Grade CMOS Camera—High Resolution and Sensitivity at Low Cost
by Goran Zgrablić, Davor Čapeta, Ana Senkić and Mario Rakić
Photonics 2025, 12(4), 389; https://doi.org/10.3390/photonics12040389 - 16 Apr 2025
Viewed by 154
Abstract
Until now, achieving both a high spectral resolution on the order of a few wavenumbers and the highest sensitivity in Raman scattering spectroscopy has required reliance on high-end laboratory instruments. Here, we introduce an innovative yet design-wise simple alternative: a cost-effective and compact [...] Read more.
Until now, achieving both a high spectral resolution on the order of a few wavenumbers and the highest sensitivity in Raman scattering spectroscopy has required reliance on high-end laboratory instruments. Here, we introduce an innovative yet design-wise simple alternative: a cost-effective and compact micro-Raman spectrometer (µRS) that combines exceptional spectral resolution and sensitivity. Leveraging industrial-grade CMOS cameras and high-quality photographic objectives, our µRS maintains a footprint at least five times smaller than traditional lab-based spectrometers. Through detailed characterization and direct experimental comparison, which includes the use of calcite as a Raman standard, we demonstrate that our µRS achieves a spectral resolution of down to 2.5 cm−1. Using a single-layer MoS2 sample, we found that the sensitivity of our system, while somewhat lower, remains within a useful range compared to commercial research-grade confocal Raman microscopy systems. This study presents a compelling solution for researchers seeking efficient and high-resolution Raman spectroscopy tools across diverse applications, particularly in resource-limited or field-based settings. Full article
(This article belongs to the Special Issue Research, Development and Application of Raman Scattering Technology)
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22 pages, 11551 KiB  
Article
Adaptive Freeform Optics Design and Multi-Objective Genetic Optimization for Energy-Efficient Automotive LED Headlights
by Shaohui Xu, Xing Peng and Ci Song
Photonics 2025, 12(4), 388; https://doi.org/10.3390/photonics12040388 - 16 Apr 2025
Viewed by 201
Abstract
In addressing the design imperatives of automotive headlight miniaturization and energy conservation, this paper puts forth a design methodology for vehicle lighting systems that is predicated on free surface optics and an intelligent optimization algorithm. The establishment of the energy mapping relationship between [...] Read more.
In addressing the design imperatives of automotive headlight miniaturization and energy conservation, this paper puts forth a design methodology for vehicle lighting systems that is predicated on free surface optics and an intelligent optimization algorithm. The establishment of the energy mapping relationship between the light source surface and the target surface is predicated on relevant performance standards. The numerical calculation is then integrated with MATLAB R2022a to obtain the free-form surface coordinate points and establish a three-dimensional model. To optimize the parameter design, a genetic algorithm is employed to fine-tune the design parameter θmax, thereby attaining the optimal θmax that strikes a balance between volume and luminous efficiency. The experimental results demonstrate that by integrating the optimal incidence angle into the design of the high beam and low beam, the final simulation results show that the optical efficiency of the low beam is 88.89%, and the optical efficiency of the high beam is 89.40%. This enables the automotive headlamp system to achieve a balance between volume and luminous efficiency. The free-form lamp design framework proposed in this study provides a reference for the compact design and intelligent optimization of the lamp system. Full article
(This article belongs to the Special Issue New Perspectives in Micro-Nano Optical Design and Manufacturing)
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10 pages, 2124 KiB  
Article
Multifunctional Hierarchical Metamaterials: Synergizing Visible-Laser-Infrared Camouflage with Thermal Management
by Shenglan Wu, Hao Huang, Zhenyong Huang, Chunhui Tian, Lina Guo, Yong Liu and Shuang Liu
Photonics 2025, 12(4), 387; https://doi.org/10.3390/photonics12040387 - 16 Apr 2025
Viewed by 158
Abstract
With the rapid development of multispectral detection technology, realizing the synergistic camouflage and thermal management of materials in multi-band has become a major challenge. In this paper, a multifunctional radiation-selective hierarchical metamaterial (RSHM) is designed to realize the modulation of optical properties in [...] Read more.
With the rapid development of multispectral detection technology, realizing the synergistic camouflage and thermal management of materials in multi-band has become a major challenge. In this paper, a multifunctional radiation-selective hierarchical metamaterial (RSHM) is designed to realize the modulation of optical properties in a wide spectral range through the delicate design of microstructures and nanostructures. In the atmospheric windows of 3–5 μm and 8–14 μm, the emissivity of the material is as low as 0.14 and 0.25, which can effectively suppress the radiation characteristics of the target in the infrared band, thus realizing efficient infrared stealth. Simultaneously, it exhibits high emissivity in the 2.5–3 μm (up to 0.80) and 5–8 μm (up to 0.98) bands, significantly improving thermal radiation efficiency and enabling active thermal management. Notably, RSHM achieves low reflectivity at 1.06 μm (0.13) and 1.55 μm (0.005) laser wavelengths, as well as in the 8–14 μm (0.06) band, substantially improving laser stealth performances. Additionally, it maintains high transmittance in the visible light range, ensuring excellent visual camouflage effects. Furthermore, the RSHM demonstrates exceptional incident angle and polarization stability, maintaining robust performances even under complex detection conditions. This design is easy to expand relative to other frequency bands of the electromagnetic spectrum and holds significant potential for applications in military camouflage, energy-efficient buildings, and optical devices. Full article
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22 pages, 9562 KiB  
Article
Design of a Polarization-Insensitive and Wide-Angle Triple-Band Metamaterial Absorber
by Shaoxin Zheng, Manna Gu, Guilan Feng, Mingfeng Zheng, Tianqi Zhao and Xufeng Jing
Photonics 2025, 12(4), 386; https://doi.org/10.3390/photonics12040386 - 16 Apr 2025
Viewed by 200
Abstract
This paper proposes a tri-band wide-angle polarization-insensitive absorber operating in the C-band and Ku-band, based on the design concept of metal–dielectric–metal. The absorber achieves absorption efficiencies of 99.05%, 99.3%, and 97.9% at 4.23 GHz, 7.403 GHz, and 14.813 GHz, respectively. The first two [...] Read more.
This paper proposes a tri-band wide-angle polarization-insensitive absorber operating in the C-band and Ku-band, based on the design concept of metal–dielectric–metal. The absorber achieves absorption efficiencies of 99.05%, 99.3%, and 97.9% at 4.23 GHz, 7.403 GHz, and 14.813 GHz, respectively. The first two absorption frequencies are in the C-band, while the third absorption frequency is in the Ku-band, both of which are commonly used in satellite communication. The designed absorber consists of three differently sized regular hexagonal rings. To analyze the interaction mechanism between the electromagnetic wave and the absorber, we applied the theory of impedance matching and equivalent media to analyze the metamaterial properties of the absorber. In addition, the equivalent circuit model of the absorber has been analyzed. We then determined the existence of coupled electromagnetic resonances between the top and bottom surfaces by analyzing the distribution of the electric field, magnetic field, and surface currents on the absorber. By varying the polarization angle and incident angle of the incoming wave, we found that the absorber exhibits polarization insensitivity and wide-angle absorption characteristics. The TE and TM waves maintain more than 90% absorption efficiency up to incident angles of 50° and 60°, respectively. The absorber’s thickness is 1.07 mm, which is 0.0154 times the wavelength corresponding to the lowest resonant frequency (λ0), and the edge length of the subunit’s regular hexagon is 7.5 mm (0.108λ0), making the absorber sub-wavelength in scale while maintaining its compactness. The proposed absorber operates in the C-band and Ku-band, and can be applied in the field of satellite communications, achieving functions such as electromagnetic shielding and stealth. Full article
(This article belongs to the Special Issue Novel Developments in Optoelectronic Materials and Devices)
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10 pages, 8810 KiB  
Communication
Utility of Low-Cost Multichannel Data Acquisition System for Photoacoustic Computed Tomography
by Mohsin Zafar, Rayyan Manwar, Seyed Mohsen Ranjbaran and Kamran Avanaki
Photonics 2025, 12(4), 385; https://doi.org/10.3390/photonics12040385 - 16 Apr 2025
Viewed by 181
Abstract
Typically, multi-single-element photoacoustic computed tomography (PACT) systems utilize numerous ultrasound transducers arranged in cylindrical or hemispherical configurations for detection, combined with a single diffuse light source or multiple sparse light sources to illuminate the imaging target. While these systems produce high-quality 3D PA [...] Read more.
Typically, multi-single-element photoacoustic computed tomography (PACT) systems utilize numerous ultrasound transducers arranged in cylindrical or hemispherical configurations for detection, combined with a single diffuse light source or multiple sparse light sources to illuminate the imaging target. While these systems produce high-quality 3D PA images, they require complex, multi-channel data acquisition (DAQ) systems to acquire data from all transducers. These DAQ systems are often bulky and expensive, significantly limiting the clinical translation of PACT systems for patient care. In this study, we evaluated the feasibility of using a compact and cost-effective Texas Instruments analog front-end DAQ module for multi-single-element PACT systems. By imaging a simple 3D phantom, we demonstrated the capability of this affordable DAQ board, with reconstructed images showing promise for practical and economical solutions in PACT systems. This advancement paves the way for broader applications of PACT in both research and clinical settings. Full article
(This article belongs to the Special Issue Recent Advances in 3D Optical Measurement)
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14 pages, 4597 KiB  
Article
An Optically Transparent Metasurface for Microwave Amplitude–Phase Manipulation
by Hanyu Xue, Jiahao Ge, Yaqiang Zhang, Xianwu Jiang, Cheng Zhang, Hongxing Dong and Long Zhang
Photonics 2025, 12(4), 384; https://doi.org/10.3390/photonics12040384 - 16 Apr 2025
Viewed by 167
Abstract
Current microwave metasurfaces predominantly suffer from the disadvantages of optically opaque and phase-only modulation, which inevitably hinder their application potential. Herein, we have proposed a simple but efficient strategy for designing a multifunctional metasurface that is capable of simultaneously achieving visible transparency and [...] Read more.
Current microwave metasurfaces predominantly suffer from the disadvantages of optically opaque and phase-only modulation, which inevitably hinder their application potential. Herein, we have proposed a simple but efficient strategy for designing a multifunctional metasurface that is capable of simultaneously achieving visible transparency and microwave amplitude–phase manipulation. The designed meta-atom consists of a metal-frame-based H-shaped resonator and a metallic mesh layer separated by a transparent dielectric substrate, enabling eight-level phase modulation with a π/4 interval and continuous amplitude modulation covering the range of 0–0.9 at 16 GHz. As a proof-of-concept demonstration, a spatially multiplexed complex-amplitude hologram utilizing the designed meta-atom is simulated and experimentally validated. The results show that two distinct holographic images can be reconstructed in different imaging planes, and the measured average optical transmittance attains 63.7% at a wavelength range of 400–800 nm. Our proposed design strategy paves the way to an optically transparent microwave metasurface which is expected to have great potential in application scenarios requiring both visible transparency and microwave wavefront control. Full article
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10 pages, 5579 KiB  
Article
Frequency Stabilization of Wideband-Tunable Low-Phase-Noise Optoelectronic Oscillator Based on Fundamental and Subharmonic RF Injection Locking
by Zhihao Zhang, Dan Lu, Hao Song, Fei Guo and Lingjuan Zhao
Photonics 2025, 12(4), 383; https://doi.org/10.3390/photonics12040383 - 16 Apr 2025
Viewed by 132
Abstract
A frequency stabilization scheme for a wideband-tunable optoelectronic oscillator (OEO) based on fundamental and subharmonic RF injection locking is proposed, achieving a tuning range of 2–22 GHz with low phase noise. The injection-locked performance of the OEO using the fundamental RF signal and [...] Read more.
A frequency stabilization scheme for a wideband-tunable optoelectronic oscillator (OEO) based on fundamental and subharmonic RF injection locking is proposed, achieving a tuning range of 2–22 GHz with low phase noise. The injection-locked performance of the OEO using the fundamental RF signal and its 1/n subharmonic is investigated. The fundamental injection locking achieves a phase noise of <−130 dBc/Hz @ 10 kHz offset across the entire tuning range. An examination of phase noise behavior at different subharmonic orders reveals that fundamental and subharmonic injection locking achieve a five-order-of-magnitude improvement in Allan variance (0.1 s) and approximately 40 dB phase noise reduction at a 10 Hz offset from the carrier. This approach leverages the low-phase-noise advantage of the OEO while benefiting from the high stability of low-frequency external RF sources, enabling multi-frequency point frequency stabilization optimization. Full article
(This article belongs to the Special Issue Recent Advancement in Microwave Photonics)
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15 pages, 3973 KiB  
Article
Modeling and Configuration Optimization of Spatial Angle Diversity Reception for Underwater Multi-Faceted Optical Base Station
by Junjie Shi, Jun Ao, Chunbo Ma, Xu Tian and Hanjun Guo
Photonics 2025, 12(4), 382; https://doi.org/10.3390/photonics12040382 - 15 Apr 2025
Viewed by 148
Abstract
Compared with point-to-point underwater wireless optical communication (UWOC) systems with a single direction, the underwater multi-faceted optical base station (OBS) offers independent fields of view and directions for each receiving detector, supporting multiple user access and mobile communication. This study aims at the [...] Read more.
Compared with point-to-point underwater wireless optical communication (UWOC) systems with a single direction, the underwater multi-faceted optical base station (OBS) offers independent fields of view and directions for each receiving detector, supporting multiple user access and mobile communication. This study aims at the issue of link interruptions and a limited communication area caused by restricted OBS receiver fields of view when underwater devices move. A field-of-view model and spatial angle diversity reception framework for the multi-faceted OBS in underwater channels have been developed, visualizing the effective reception field of the OBS. This model helps analyze the impact of multi-faceted OBS detector layouts on link performance in underwater environments. Furthermore, under constraints on the number of detectors, configuration adjustments are made to the field-of-view angles and deflection angles of detectors. Simulation results show that, under the same typical underwater environmental conditions, the optimized configuration reduces the blind area compared to the typical configuration, enhancing the effective spatial field of view of the OBS receiver by over 10%. The OBS’s effective communication coverage for mobile devices on different planes is also improved. This research provides a theoretical model and parameter configuration guidelines for the design of the underwater multi-faceted OBS. Full article
(This article belongs to the Special Issue Underwater Optical Communications Channel Models: Trends and Challenges)
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11 pages, 3520 KiB  
Article
Enhancing Atmospheric Turbulence Phase Screen Generation with an Improved Diffusion Model and U-Net Noise Generation Network
by Hangning Kou, Min Wan and Jingliang Gu
Photonics 2025, 12(4), 381; https://doi.org/10.3390/photonics12040381 - 15 Apr 2025
Viewed by 147
Abstract
Simulating atmospheric turbulence phase screens is essential for optical system research and turbulence compensation. Traditional methods, such as multi-harmonic power spectrum inversion and Zernike polynomial fitting, often suffer from sampling errors and limited diversity. To overcome these challenges, this paper proposes an improved [...] Read more.
Simulating atmospheric turbulence phase screens is essential for optical system research and turbulence compensation. Traditional methods, such as multi-harmonic power spectrum inversion and Zernike polynomial fitting, often suffer from sampling errors and limited diversity. To overcome these challenges, this paper proposes an improved denoising diffusion probabilistic model (DDPM) for generating high-fidelity atmospheric turbulence phase screens. The model effectively captures the statistical distribution of turbulence phase screens using small training datasets. A refined loss function incorporating the structure function enhances accuracy. Additionally, a self-attention module strengthens the model’s ability to learn phase screen features. The experimental results demonstrate that the proposed approach significantly reduces the Fréchet Inception Distance (FID) from 154.45 to 59.80, with the mean loss stabilizing around 0.1 after 50,000 iterations. The generated phase screens exhibit high precision and diversity, providing an efficient and adaptable solution for atmospheric turbulence simulation. Full article
(This article belongs to the Section Data-Science Based Techniques in Photonics)
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9 pages, 4301 KiB  
Article
Rotational Doppler Signal Classification Based on Support Vector Machine
by Song Qiu, Jin Zheng and Minghui Xiong
Photonics 2025, 12(4), 380; https://doi.org/10.3390/photonics12040380 - 14 Apr 2025
Viewed by 154
Abstract
The rotational Doppler effect (RDE) has been playing a vital role in the detection of rotational motion in recent years. However, the results obtained from this detection method are easily influenced by the detection conditions. It means that the characteristic of the frequency [...] Read more.
The rotational Doppler effect (RDE) has been playing a vital role in the detection of rotational motion in recent years. However, the results obtained from this detection method are easily influenced by the detection conditions. It means that the characteristic of the frequency signals varies greatly under different detection conditions. How to efficiently and automatically classify and recognize different signal features is of great significance for the accurate extraction of rotating speed information in the future. Based on the well-known support vector machine (SVM) model, we built an SVM learn model to automatically classify and recognize RDE signals under different detection conditions. The results show that the SVM learn model can effectively recognize the category of detection signals with high accuracy. By accurately identifying signal categories, it can provide a great foundation for extracting target speed and other information in the future, and has broad application prospects in engineering practice. Full article
(This article belongs to the Section Data-Science Based Techniques in Photonics)
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17 pages, 11490 KiB  
Article
A Transceiver-Shared Photonic Integrated Broadband Multi-Beamformer Based on an Extended Blass Matrix
by Ruixuan Wang, Weichao Ma and Wangzhe Li
Photonics 2025, 12(4), 379; https://doi.org/10.3390/photonics12040379 - 14 Apr 2025
Viewed by 120
Abstract
Multi-beam phased array antennas have become essential in modern radar and communication systems, offering high gain, superior directivity, and exceptional agility. However, traditional multi-beam phased array antennas face significant challenges in meeting the growing demand for large, instantaneous bandwidth and compatibility with transmit-and-receive [...] Read more.
Multi-beam phased array antennas have become essential in modern radar and communication systems, offering high gain, superior directivity, and exceptional agility. However, traditional multi-beam phased array antennas face significant challenges in meeting the growing demand for large, instantaneous bandwidth and compatibility with transmit-and-receive multi-beamforming. To achieve these requirements, we propose a novel transceiver-shared photonic integrated broadband multi-beamforming network architecture based on an extended Blass matrix framework. Combined with wavelength division multiplexing, the architecture enables the separation and decoupling of transmit and receive channels, ensuring the independent synthesis of multiple beams for transmission and receiving. Furthermore, we design and implement a 3 × 3 transceiver-shared photonic integrated broadband multi-beamformer on a standard silicon-on-insulator platform. The proposed multi-beamformer successfully demonstrates broadband multi-beamforming across six independent directions, with transmitted beams at 15°, 30°, and 45° and received beams at 20°, 40°, and 60°, covering both the whole X and Ku bands. Full article
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14 pages, 5826 KiB  
Communication
Research on the Superposition Evolution of Double Laguerre–Gaussian Modes Based on Astigmatic Mode Conversion
by Lingmin Zhao, Jingliang Liu, Jiaxin Yuan, Yongji Yu, Guangyong Jin and Xinyu Chen
Photonics 2025, 12(4), 378; https://doi.org/10.3390/photonics12040378 - 14 Apr 2025
Viewed by 147
Abstract
In this paper, the evolution of the beam from the double Hermite–Gaussian beam superposition state to the double Laguerre–Gaussian beam superposition state is realized based on the astigmatism conversion. Firstly, the tunable output of the double Hermite–Gaussian mode superposition state is realized by [...] Read more.
In this paper, the evolution of the beam from the double Hermite–Gaussian beam superposition state to the double Laguerre–Gaussian beam superposition state is realized based on the astigmatism conversion. Firstly, the tunable output of the double Hermite–Gaussian mode superposition state is realized by adjusting the off-axis pumping distance of the crystal. On this basis, an astigmatic mode converter is added to the back end of the resonant cavity output mirror. By utilizing it, the evolution from the double Hermite–Gaussian mode superposition state to the specific double Laguerre–Gaussian mode superposition state is realized. The evolution process of the double mode superposition state based on the astigmatic mode is analyzed theoretically. The light field change of the evolution process is demonstrated experimentally. Full article
(This article belongs to the Special Issue Realization and Application of Vortex Laser)
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21 pages, 4256 KiB  
Article
Detection of Vibration Signal by Plane Scanning Utilizing Wavefront Sensors
by Yun Pan, Quan Luo, Yiyou Fan, Haoming Chen, Hongsheng Luo and Jinshan Su
Photonics 2025, 12(4), 377; https://doi.org/10.3390/photonics12040377 - 14 Apr 2025
Viewed by 165
Abstract
Laser remote sensing of seismic waves is extensively utilized in earthquake monitoring and resource exploitation. This article leverages wavefront sensors’ high resolution and array detection capabilities to effectively conduct planar scanning of target areas in seismic wave laser remote sensing research, thereby properly [...] Read more.
Laser remote sensing of seismic waves is extensively utilized in earthquake monitoring and resource exploitation. This article leverages wavefront sensors’ high resolution and array detection capabilities to effectively conduct planar scanning of target areas in seismic wave laser remote sensing research, thereby properly acquiring regional vibration data. The error margin is between 1% and 2% relative to the source information. Full article
(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Photonics Sensors)
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18 pages, 6306 KiB  
Article
Spectral Envelope Analysis of Subwavelength Grating Waveguide Micro Racetrack Ring Resonator for Cancer Sensing Using Integrated Photonics
by Shalini Vardhan, Devansh Srivastava, Naveen Kumar Gupta, Ritu Raj Singh and Santosh Kumar
Photonics 2025, 12(4), 376; https://doi.org/10.3390/photonics12040376 - 14 Apr 2025
Viewed by 151
Abstract
Silicon-on-Insulator (SOI) technology and optical resonators have significantly influenced the field of photonics for malignancy sensing. Cancer, a malignant disease, necessitates the precise and advanced diagnostic technique. This study introduces a novel approach for cancer detection utilizing a micro racetrack ring resonator (MRTRR) [...] Read more.
Silicon-on-Insulator (SOI) technology and optical resonators have significantly influenced the field of photonics for malignancy sensing. Cancer, a malignant disease, necessitates the precise and advanced diagnostic technique. This study introduces a novel approach for cancer detection utilizing a micro racetrack ring resonator (MRTRR) integrated with Subwavelength Gratings (SWGs). The grating pitch size (Λ) is 300 nm. The findings demonstrate that the SWG MRTRR achieves high Sensitivity (S) due to enhanced light matter interaction and weak mode confinement. The SWG MRTRR produces a spectral envelope as the transmission output, which eliminates the limitation of free spectral range (FSR). The ‘S’ values obtained for cervical cancer, breast cancer type-1, and breast cancer type-2 are 1825 nm/RIU, 1705.14 nm/RIU, and 1004.71 nm/RIU. The Q-factor and the intrinsic Limit of Detection (iLoD) values are 269.68, 280.78, 315.76, 3.28 × 10−3, 3.37 × 10−3, and 5.09 × 10−3, respectively. 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, 5862 KiB  
Article
Digitalized Polarization Fading Suppression and Phase Demodulation Scheme of Phase-Sensitive Optical Time-Domain Reflectometry Based on Polarization Diversity Virtual Coherence
by Xiatong Wu, An Sun, Yanming Liu and Wei Ji
Photonics 2025, 12(4), 375; https://doi.org/10.3390/photonics12040375 - 14 Apr 2025
Viewed by 187
Abstract
In this paper, a digitalized polarization fading suppression and phase demodulation technique for a phase-sensitive optical time-domain reflectometry (φ-OTDR) sensing system utilizing polarization diversity virtual coherence is proposed, in which virtual cross-coherence between the polarization diversity digital signals is employed for simultaneous fading [...] Read more.
In this paper, a digitalized polarization fading suppression and phase demodulation technique for a phase-sensitive optical time-domain reflectometry (φ-OTDR) sensing system utilizing polarization diversity virtual coherence is proposed, in which virtual cross-coherence between the polarization diversity digital signals is employed for simultaneous fading noise suppression and phase demodulation. The principle of the proposed demodulation algorithm is presented and analyzed. Based on this, the practicability and validity of the proposed demodulation method for fading noise suppression and distributed vibration sensing are confirmed through experiments. The experimental results indicate that the proposed demodulation scheme can effectively reduce the polarization fading noise caused by the polarization mismatch between the probe light and the reference light, and the phase changes induced by external interference can also be accurately recovered with a signal-to-noise ratio (SNR) of vibration signal localization of 27.14 dB and an SNR of vibration signal phase demodulation of 47.88 dB, which provides a simplified method for simultaneous polarization fading suppression and the phase demodulation of the φ-OTDR system. Full article
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11 pages, 3159 KiB  
Article
Stability Assessment of Rydberg Electromagnetically Induced Transparency Locking via Optical Heterodyne Spectroscopy
by Qiuyu Yin, Yanzhao Liang, Haitao Lin, Ning Ji and Thibault Vogt
Photonics 2025, 12(4), 374; https://doi.org/10.3390/photonics12040374 - 13 Apr 2025
Viewed by 196
Abstract
Frequency locking to reference atomic lines using Rydberg electromagnetically induced transparency (EIT) has been recently introduced as an inexpensive and reliable technique for laser frequency stabilization. In this work, we carry out a systematic study of this technique using heterodyne beat spectroscopy. Two [...] Read more.
Frequency locking to reference atomic lines using Rydberg electromagnetically induced transparency (EIT) has been recently introduced as an inexpensive and reliable technique for laser frequency stabilization. In this work, we carry out a systematic study of this technique using heterodyne beat spectroscopy. Two different commercial semi-conductor lasers are locked to the same reference frequency using EIT locking, and their relative frequency stability is analyzed and continuously monitored in real time. A substantial improvement in the laser frequency stability is achieved through searching for the optimal proportional–integral settings and EIT probe laser powers. The results show that the cutoff frequency of the beat signal can be lowered to less than 500 kHz. We also compare the frequencies of free running lasers with that of a locked laser and characterize their frequency drifts. This study is important in assessing the use of Rydberg EIT locking in atomic electrometers. Full article
(This article belongs to the Special Issue Recent Advances in Nonlinear Optics: From Fundamentals to Applications)
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15 pages, 12373 KiB  
Article
Vibration Deformation Measurement and Defect Identification Based on Time-Averaged Digital Holography
by Dongyang Hu, Chen Wang, Di Li, Weiyu Xu and Xiangchao Zhang
Photonics 2025, 12(4), 373; https://doi.org/10.3390/photonics12040373 - 13 Apr 2025
Viewed by 200
Abstract
Based on time-averaged digital holography, a vibration deformation measurement system was designed and a full process reconstruction and identification strategy was developed for detecting the micro-defects in optical materials. Through the double beam expansion setting and off-axis imaging adjustments, it is suitable for [...] Read more.
Based on time-averaged digital holography, a vibration deformation measurement system was designed and a full process reconstruction and identification strategy was developed for detecting the micro-defects in optical materials. Through the double beam expansion setting and off-axis imaging adjustments, it is suitable for measuring optical materials with non-specular surfaces by double exposure shots. The scheme was applied to optical sandwich composites and 3D printed glass. Abnormal amplitudes occur at the defects due to different resonance frequencies, resulting in anomalous vibrations under excitation, and the differences in the amplitudes and phases before and after vibration can effectively characterize vibration amplitude and subsurface defects, proving that this method has a high detecting sensitivity. Full article
(This article belongs to the Special Issue Advancements in Optical Metrology and Imaging)
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12 pages, 2383 KiB  
Article
Novel Focusing Performances of High-Numerical-Aperture Micro-Fresnel Zone Plates with Selective Occlusion
by Qiang Liu, Yunpeng Wu, Yuanhao Deng, Junli Wang, Wenshuai Liu and Xiaomin Yao
Photonics 2025, 12(4), 372; https://doi.org/10.3390/photonics12040372 - 13 Apr 2025
Viewed by 208
Abstract
In this study, novel focusing performances of high-numerical-aperture (NA) micro-Fresnel zone plates (FZPs) with selective occlusion are identified and investigated through numerical calculations based on vectorial angular spectrum (VAS) theory, and further rigorously validated using the finite-difference time-domain (FDTD) method. The central occlusion [...] Read more.
In this study, novel focusing performances of high-numerical-aperture (NA) micro-Fresnel zone plates (FZPs) with selective occlusion are identified and investigated through numerical calculations based on vectorial angular spectrum (VAS) theory, and further rigorously validated using the finite-difference time-domain (FDTD) method. The central occlusion of a standard micro-FZP can significantly extend the depth of focus while keeping the lateral size of the focusing spot essentially unchanged. When a standard micro-FZP only retains two separated transparent rings and all other rings are obstructed, it will result in multi-focus phenomena; at the same time, the number of focal points is equal to the difference in number between the two separated transparent rings. Furthermore, a focusing light needle can be generated by combining the central occlusion and wavelength shift of a standard micro-FZP. This study not only provides new ideas for the design and optimization of micro-FZPs but also provides reference for the expansion of practical applications of FZPs. Full article
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