Photonics

16 pages, 4959 KiB

Open AccessArticle

Parameter Study on Ultraviolet Rayleigh–Brillouin Doppler Lidar with Dual-Pass Dual Fabry–Perot Interferometer for Accurately Measuring Near-Surface to Lower Stratospheric Wind Field

by Fahua Shen, Zhifeng Shu, Jihui Dong, Guohua Jin, Liangliang Yang, Zhou Hui and Hua Xu

Photonics 2025, 12(1), 92; https://doi.org/10.3390/photonics12010092 - 20 Jan 2025

Viewed by 411

Abstract

To suppress the influence of aerosols scattering on the double-edge detection technique and achieve high-accuracy measurement of the wind field throughout the troposphere to the lower stratosphere, an ultraviolet 355 nm Rayleigh–Brillouin Doppler lidar technology based on a dual-pass dual Fabry–Perot interferometer (FPI) [...] Read more.

To suppress the influence of aerosols scattering on the double-edge detection technique and achieve high-accuracy measurement of the wind field throughout the troposphere to the lower stratosphere, an ultraviolet 355 nm Rayleigh–Brillouin Doppler lidar technology based on a dual-pass dual Fabry–Perot interferometer (FPI) is proposed. The wind speed detection principle of this technology is analyzed, and the formulas for radial wind speed measurement error caused by random noise and wind speed measurement bias caused by Mie scattering signal contamination are derived. Based on the detection principle, the structure of the lidar system is designed. Combining the wind speed measurement error and measurement bias on both sides, the parameters of the dual-pass dual-FPI are optimized. The free spectral range (FSR) of the dual-pass dual-FPI is selected as 12 GHz, the bandwidth as 1.8 GHz, and the peak-to-peak spacing as 6 GHz. Further, the detection performance of this new type of Rayleigh–Brillouin Doppler lidar with the designed system parameters is simulated and analyzed. The simulation results show that at an altitude of 0–20 km, within the radial wind speed dynamic range of ±50 m/s, the radial wind speed measurement bias caused by aerosol scattering signal is less than 0.17 m/s in the cloudless region; within the radial wind speed dynamic range of ±30 m/s, the bias is less than 0.44 m/s and 0.91 m/s in the simulated cumulus cloud at 4 km where aerosol backscatter ratio R_β = 3.8 and cirrus cloud at 9 km where R_β = 2.9, respectively; using a laser with a pulse energy of 350 mJ and a repetition frequency of 50 Hz, a 450 mm aperture telescope, setting the detection zenith angle of 30°, vertical resolution of 26 m@0–10 km, 78 m@10–20 km, and 260 m@20–30 km, and a time resolution of 1 min, with the daytime sky background brightness taking 0.3 WSr⁻¹m⁻²nm⁻¹@355 nm, the radial wind speed measurement errors of the system during the day and night are below 2.9 m/s and 1.6 m/s, respectively, up to 30 km altitude, below 0.28 m/s at 10 km altitude, and below 0.91 m/s at 20 km altitude all day. Full article

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9 pages, 1632 KiB

Open AccessCommunication

Bifunctional Electromagnetic Manipulation of Surface Waves Using Metasurfaces Under One Circularly Polarized Incidence

by Min Kang, Lixing Chen, Shuaipeng Qin, Liang Ma, Aoxiang Rui and Shiqing Li

Photonics 2025, 12(1), 91; https://doi.org/10.3390/photonics12010091 - 20 Jan 2025

Viewed by 531

Abstract

The ability to freely manipulate the wavefronts of surface plasmon polaritons (SPPs) or surface waves (SWs), particularly with multifunctional integration, is of great importance in near-field photonics. However, conventional SPP control devices typically suffer from low efficiency and single-function limitations. Although recent works [...] Read more.

The ability to freely manipulate the wavefronts of surface plasmon polaritons (SPPs) or surface waves (SWs), particularly with multifunctional integration, is of great importance in near-field photonics. However, conventional SPP control devices typically suffer from low efficiency and single-function limitations. Although recent works have proposed metasurfaces that achieve bifunctional SPP manipulation, their implementation relies on the excitations of circularly polarized (CP) light with different helicities. Here, we propose a generic approach to designing bifunctional SPP meta-devices under single-helicity circularly polarized incidence. Constructed using carefully selected and arranged meta-atoms that possess both structural resonance and a geometric phase, this kind of meta-device can exhibit two distinct SPP manipulation functionalities in both co- and cross-polarized output channels under one CP incidence. As proof of this concept, we designed a bifunctional meta-device in the microwave regime and numerically demonstrated that it can convert a normally incident left circularly polarized (LCP) beam into SWs, exhibiting both a focused wavefront in the co-polarized output channel and a deflected wavefront in the cross-polarized output channel. Our findings substantially enrich the capabilities of metasurfaces to manipulate near-field electromagnetic waves, which can find many applications in practice. Full article

(This article belongs to the Special Issue New Perspectives in Optical Design)

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15 pages, 3375 KiB

Open AccessReview

Review of the Fundamental Measurement Modalities in Photoacoustic Mechanical Imaging

by Xiaohan Shi, Jianqin Sun, Hua Yuan, Liming Li, Haiyang Zhang and Yue Zhao

Photonics 2025, 12(1), 90; https://doi.org/10.3390/photonics12010090 - 20 Jan 2025

Viewed by 490

Abstract

Photoacoustic (PA) imaging is a non-invasive imaging technique with high optical resolution and acoustic penetration depth, which has been widely used in medical and clinical researches. As an important part in functional PA imaging, photoacoustic mechanical imaging (PAMI) has great potential in visualizing [...] Read more.

Photoacoustic (PA) imaging is a non-invasive imaging technique with high optical resolution and acoustic penetration depth, which has been widely used in medical and clinical researches. As an important part in functional PA imaging, photoacoustic mechanical imaging (PAMI) has great potential in visualizing and understanding the local development of pathological process. This review provides lots of PA breakthroughs which have been made in elasticity detection, viscosity detection, and viscoelasticity detection through PAMI techniques. The current research problems, challenges and future development directions were discussed. Full article

(This article belongs to the Special Issue Advanced Technologies in Biophotonics and Medical Physics)

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15 pages, 9536 KiB

Open AccessArticle

Propagation Properties of Partially Coherent Flat-Topped Beam Rectangular Arrays in Plasma and Atmospheric Turbulence

by Xinkai Ma, Hui Zhang, Yuanhao Zhao, LinXuan Yao, Changchun Yu, Yaru Gao, Yangsheng Yuan, Yangjian Cai and Bohan Guo

Photonics 2025, 12(1), 89; https://doi.org/10.3390/photonics12010089 - 19 Jan 2025

Viewed by 631

Abstract

Propagation properties represent a critical aspect of laser beams utilized in free space optical (FSO) communications. We examined the evolution characteristics of the electric field associated with partially coherent flat-topped beam rectangular arrays propagating bidirectionally through the turbulent atmosphere and plasma links. Utilizing [...] Read more.

Propagation properties represent a critical aspect of laser beams utilized in free space optical (FSO) communications. We examined the evolution characteristics of the electric field associated with partially coherent flat-topped beam rectangular arrays propagating bidirectionally through the turbulent atmosphere and plasma links. Utilizing the optical transmission matrix, alongside the second moment theory and Wigner distribution functions, we derived analytical expressions for both the intensity distribution and propagation factors of the partially coherent flat-topped beam rectangular arrays affected by the atmospheric turbulence and plasma disturbances. The numerical results indicate that appropriately selecting parameters such as beam order, transverse spatial coherence width, and beam width can effectively mitigate the adverse effects on propagation properties caused by the turbulent atmosphere and plasma. Our results have significant implications for FSO communications within specific environmental contexts. Full article

(This article belongs to the Special Issue Laser Beam Propagation and Control)

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17 pages, 5879 KiB

Open AccessArticle

Melanopsin Contribution to Pupillary Light Reflex and Brightness Perception Based on a 65-Inch Four-Primary Projected Display

by Nianfang Zhu, Yan Tu, Lili Wang and Yunyang Shi

Photonics 2025, 12(1), 88; https://doi.org/10.3390/photonics12010088 - 19 Jan 2025

Viewed by 426

Abstract

Melanopsin contribution to visual and non-visual effect has drawn widespread concern. However, research about whether this contribution can be applied to display system design is limited. Here, a four-primary display system was designed and constructed based on three projectors with filters to realize [...] Read more.

Melanopsin contribution to visual and non-visual effect has drawn widespread concern. However, research about whether this contribution can be applied to display system design is limited. Here, a four-primary display system was designed and constructed based on three projectors with filters to realize isolation control of melanopsin and cones, and a 65-inch uniform display area was achieved. The melanopic luminance metamers (higher and lower) of different colours have been modulated thusly. The effect of melanopic luminance on pupillary light reflex (PLR) and brightness perception was explored under a luminous environment of 300 lx to ensure the saturation of rod. The results showed that the higher melanopic luminance level contributed to delayed contraction maintenance. Moreover, a log relationship was found between melanopic equivalent daylight luminance and pupillary contraction maintenance parameters with coefficient of determination more than 0.85. Furthermore, stimuli of higher melanopic luminance level appeared brighter, indicating that melanopsin contributed to brightness perception. Full article

(This article belongs to the Special Issue New Technologies for Human Visual Function Assessment)

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13 pages, 7492 KiB

Open AccessArticle

Design and Fabrication of Orthokeratology Lens with Multi-Linear and Spherical Aberration Corrected for Myopia Control

by Zhengwang Li, Ruijin Hong and Dawei Zhang

Photonics 2025, 12(1), 87; https://doi.org/10.3390/photonics12010087 - 19 Jan 2025

Viewed by 515

Abstract

Myopia, an increasingly grave public health concern, necessitates the implementation of various techniques for its management. These techniques predominantly comprise the employment of spectacles correction, orthokeratology (ortho-k), and soft bifocal and multifocal lenses. In the present study, a pioneering polish-free ortho-k lens was [...] Read more.

Myopia, an increasingly grave public health concern, necessitates the implementation of various techniques for its management. These techniques predominantly comprise the employment of spectacles correction, orthokeratology (ortho-k), and soft bifocal and multifocal lenses. In the present study, a pioneering polish-free ortho-k lens was devised, featuring two reverse lines and three alignment lines, which, respectively, expedite the shaping process and enhance centration. The structural blueprint of the ortho-k lens, along with the simulation of fluorescence staining, was executed employing the FocalPoints software V7.0 (Advance Medical, Milan, Italy). Subsequently, lens aberration elimination was accomplished through ray tracing utilizing ZEMAX software V13.0 (Focus Software, Wixom, MI, USA). The fabrication of the lens was carried out via high-precision lathe turning using the UPC 100 Vision instrument (SCHNEIDER, Ratingen, Germany). The power profile of the ortho-k lens was measured using the CONTEST 2 apparatus (ROTLEX, Omer, Israel). The surface quality was observed under a 200× microscope (ZEISS, Oberkochen, Germany). The fitting of the lens was assessed through the utilization of both Slit-lamp microscopy (MediWorks, Shanghai, China) and Corneal topographer (Medmont E300, Melbourne, VIC, Australia) Full article

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8 pages, 2791 KiB

Open AccessCommunication

Laser Radar System Based on Lightweight Diffractive Lens Receiver System

by Jiajia Yin, Mengxia Hou, Bin Fan, Jiang Bian and Junfeng Du

Photonics 2025, 12(1), 86; https://doi.org/10.3390/photonics12010086 - 17 Jan 2025

Viewed by 462

Abstract

Diffractive lens has advantages over traditional reflective lens, such as light weight, high folding compression ratio, high tolerance for surface figure error and low manufacturing costs. It provides a new technical approach for a lightweight LiDAR ranging system. In this work, a laser [...] Read more.

Diffractive lens has advantages over traditional reflective lens, such as light weight, high folding compression ratio, high tolerance for surface figure error and low manufacturing costs. It provides a new technical approach for a lightweight LiDAR ranging system. In this work, a laser radar system based on a diffractive lens receiver system has been designed. The receiver system is a hybrid structure consisting of an eight-level diffractive lens, a collimation set and a convergence set. Combined with the single photodetector, the designed laser radar system can simultaneously achieve measurements at near-field distances of 6.0 m, 9.9 m, and 16.1 m and far-field distances of 851.2 m. Full article

(This article belongs to the Special Issue Diffractive Optics and Its Emerging Applications)

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14 pages, 4800 KiB

Open AccessArticle

Design and Analysis of Compact High–Performance Lithium–Niobate Electro–Optic Modulator Based on a Racetrack Resonator

by Zixin Chen, Jianping Li, Weiqin Zheng, Hongkang Liu, Quandong Huang, Ya Han and Yuwen Qin

Photonics 2025, 12(1), 85; https://doi.org/10.3390/photonics12010085 - 17 Jan 2025

Viewed by 546

Abstract

With the ever-growing demand for high-speed optical communications, microwave photonics, and quantum key distribution systems, compact electro-optic (EO) modulators with high extinction ratios, large bandwidth, and high tuning efficiency are urgently pursued. However, most integrated lithium–niobate (LN) modulators cannot achieve these high performances [...] Read more.

With the ever-growing demand for high-speed optical communications, microwave photonics, and quantum key distribution systems, compact electro-optic (EO) modulators with high extinction ratios, large bandwidth, and high tuning efficiency are urgently pursued. However, most integrated lithium–niobate (LN) modulators cannot achieve these high performances simultaneously. In this paper, we propose an improved theoretical model of a chip-scale electro-optic (EO) microring modulator (EO-MRM) based on X-cut lithium–niobate-on-insulator (LNOI) with a hybrid architecture consisting of a 180-degree Euler bend in the coupling region, double-layer metal electrode structure, and ground–signal–signal–ground (G-S-S-G) electrode configuration, which can realize highly comprehensive performance and a compact footprint. After parameter optimization, the designed EO-MRM exhibited an extinction ratio of 38 dB. Compared to the structure without Euler bends, the increase was 35 dB. It also had a modulation bandwidth of 29 GHz and a tunability of 8.24 pm/V when the straight waveguide length was 100 μm. At the same time, the proposed device footprint was 1.92 × 10⁴ μm². The proposed MRM model provides an efficient solution to high-speed optical communication systems and microwave photonics, which is helpful for the fabrication of high-performance and multifunctional photonic integrated devices. Full article

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12 pages, 4456 KiB

Open AccessArticle

A Detailed Study of a Resonant-Assisted Segmented Cladding Fiber for Large Mode Area Applications

by Minmin Xue, Hao Qin, Suwen Li, Yuqi Hao and Libo Yuan

Photonics 2025, 12(1), 84; https://doi.org/10.3390/photonics12010084 - 17 Jan 2025

Viewed by 364

Abstract

In this work, we have proposed and optimized a large mode area segmented cladding fiber (SCF) with an unconventional low-index segment cladding. The low-refractive-index cladding proposed in this paper consists of three parts. There three geometric parameters chosen as design variables were the [...] Read more.

In this work, we have proposed and optimized a large mode area segmented cladding fiber (SCF) with an unconventional low-index segment cladding. The low-refractive-index cladding proposed in this paper consists of three parts. There three geometric parameters chosen as design variables were the length and width of the first part and the leg length of the isosceles trapezoid in the second part. To investigate the properties of the proposed SCF, numerical modeling based on the finite element method (FEM) was performed. A high leakage loss ratio (>9000) between the high-order modes (HOMs) and the fundamental mode was achieved at a wavelength of 1310 nm, which is significantly higher than that of conventional SCFs. Additionally, the mode area of the proposed fiber reaches 890 µm² at a core radius of 20 µm. The bending effects on the SCF were also studied. When the bending radius is greater than 0.3 m, the mode area greater than 880 µm² and remains stable, and the leakage loss of the least high-order mode (LP11h) exceeds 30 dB/m. The new fiber design demonstrates significant potential for high-power fiber lasers Full article

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17 pages, 5934 KiB

Open AccessArticle

Investigation of an Ultra-Wideband Optical Absorber with the Bandwidth from Ultraviolet C to Middle Infrared

by Chih-Ching Hung, Xin-Yu Lin, Tung-Lung Wu, Shu-Han Liao, Ho-Sheng Chen and Cheng-Fu Yang

Photonics 2025, 12(1), 83; https://doi.org/10.3390/photonics12010083 - 17 Jan 2025

Viewed by 510

Abstract

In the development of optical absorption technology, achieving ultra-wideband high absorption structures that span from the 200 nm ultraviolet C region to the 5800 nm mid-infrared range has been a significant challenge in materials science. Previous studies have shown that few optical absorbers [...] Read more.

In the development of optical absorption technology, achieving ultra-wideband high absorption structures that span from the 200 nm ultraviolet C region to the 5800 nm mid-infrared range has been a significant challenge in materials science. Previous studies have shown that few optical absorbers can simultaneously achieve an absorption rate above 0.900 and cover such a vast spectral range. This study presents an innovative seven-layer composite structure that successfully addresses this long-standing technical issue. Through a carefully designed layered architecture, the researchers employed COMSOL Multiphysics (version 6.0) for detailed numerical simulations to verify the optical performance of the structure. The structural design features two key innovations. In the layered composition, the bottom (h1), h3, and h5 layers are made of metallic Fe, while the layers above them (h2, h4, and h6) use SiO₂. The top layer is composed of a discontinuous cylinder Ti matrix. The first innovation involves the use of an inwardly recessed square design on the metallic Fe planes of the h4 and h6 layers, achieving high absorption across the 600–5800 nm range. The second innovation involves the use of the discontinuous cylinder Ti matrix for the top layer, which successfully enhances absorption performance in the 200–600 nm wavelength range. This structure not only employs relatively low-cost metals and oxide materials but also demonstrates significant optical absorption potential. Through numerical simulations and precise structural design, this study provides new ideas and technological pathways for the development of ultra-wideband optical absorbers. Full article

(This article belongs to the Special Issue Optical Metamaterials for Advanced Optoelectronic Devices)

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8 pages, 1932 KiB

Open AccessArticle

High-Harmonic Generation in an Optical Fiber Functionalized with Zinc Oxide Thin Films

by Idris Tiliouine, Yann Leventoux, Jean-Christophe Orlianges, Aurelian Crunteanu, Marie Froidevaux, Hamed Merdji and Sébastien Février

Photonics 2025, 12(1), 82; https://doi.org/10.3390/photonics12010082 - 17 Jan 2025

Viewed by 407

Abstract

High-order harmonic generation (HHG) in semiconductor thin films from ultrashort mid-infrared laser drivers holds the potential for the realization of integrated sources of extreme ultraviolet light. Here, we demonstrate solid-state HHG in zinc oxide thin films synthesized by the radiofrequency reactive magnetron sputtering [...] Read more.

High-order harmonic generation (HHG) in semiconductor thin films from ultrashort mid-infrared laser drivers holds the potential for the realization of integrated sources of extreme ultraviolet light. Here, we demonstrate solid-state HHG in zinc oxide thin films synthesized by the radiofrequency reactive magnetron sputtering process directly on the cleaved facets of optical fibers. Harmonics 3 to 13 of the radiation from a fiber-based laser system delivering 500 kW, 96 fs pulses at 3130 nm are produced in the thin film and guided along the fiber. A proper choice of the laser wavelength and fiber material allows for filtering out the mid-IR pump laser and achieving the HHG mode selection. The possibility to nanostructure the fiber exit by, e.g., focused ion beam milling paves the way to an increased control over the HHG spatial mode. Full article

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

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10 pages, 10681 KiB

Open AccessCommunication

Losses and Energy Backflows of the Fundamental Core Mode in Solid Core Micro Structured Optical Fibers

by Andrey Pryamikov

Photonics 2025, 12(1), 81; https://doi.org/10.3390/photonics12010081 - 17 Jan 2025

Viewed by 341

Abstract

This work discusses the behavior of transverse energy fluxes of the fundamental core mode of a holey fibers and a photonic band gap fibers when the polarization state of this mode changes. The behavior of the transverse component of the Poynting vector of [...] Read more.

This work discusses the behavior of transverse energy fluxes of the fundamental core mode of a holey fibers and a photonic band gap fibers when the polarization state of this mode changes. The behavior of the transverse component of the Poynting vector of the fundamental core mode is considered for both linear and elliptical polarization. It is demonstrated that despite the difference in the distribution of the Poynting vector stream lines in the cross section of the fibers for the two polarizations, the leakage loss level is maintained constant due to the forward and reverse energy flows in the radial direction. Differences in the level of leakage losses in different micro structured fibers arise from the vortex structure of the Poynting vector of the fundamental core mode. Full article

(This article belongs to the Special Issue Recent Advances in Diffractive Optics)

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12 pages, 1119 KiB

Open AccessArticle

Photodynamic Therapy Effects with Curcuma longa L. Active Ingredients in Gel and Blue LED on Acne: A Randomized, Controlled, and Double-Blind Clinical Study

by Jaqueline de Souza Crusca, Luis Henrique Oliveira de Moraes, Thiago Gomes Figueira, Nivaldo Antonio Parizotto and Gerson Jhonatan Rodrigues

Photonics 2025, 12(1), 80; https://doi.org/10.3390/photonics12010080 - 17 Jan 2025

Viewed by 447

Abstract

Photodynamic therapy (PDT) using the photosensitizer curcumin and blue light has a relevant effect on bacteriological decontamination caused by C. acne. The aim is to verify PDT’s effectiveness with curcumin in individuals diagnosed with moderate to severe acne. This study was carried out [...] Read more.

Photodynamic therapy (PDT) using the photosensitizer curcumin and blue light has a relevant effect on bacteriological decontamination caused by C. acne. The aim is to verify PDT’s effectiveness with curcumin in individuals diagnosed with moderate to severe acne. This study was carried out on a total of 35 volunteers of both genders (12–32 years old), with moderate to severe acne vulgaris. The volunteers were randomized into five groups: L (LED), V (Vehicle), C (Curcumin), L + V (LED + Vehicle), and L + C (LED + Curcumin). The curcumin gel and LED with blue wavelength (450 nm ± 10 nm) were used. Qualitative and quantitative evaluations were used to verify the efficacy of the treatment by counting inflamed and non-inflamed lesions. The L + C group until day 30 showed a lower percentage of inflammatory lesions than the Vehicle group for the same period. On day 60, the L + C group showed lower inflammatory lesion values compared to the other groups. Intragroup analysis of hydration in the Vehicle group (V) showed a difference on days 30 and 60 compared to day zero. In an intragroup analysis, the L + C group showed a decrease in the mean scores on day 30, and day 60 compared to day zero, showing an improvement in the psychosocial status of these volunteers. Taken together, our results showed that the combination of blue LED therapy and curcumin proved to be an effective and safe treatment for reducing inflamed acne lesions in individuals with moderate to severe acne, while also enhancing their quality of life from a psychosocial perspective. Full article

(This article belongs to the Special Issue Biomedical Optics：Imaging, Sensing and Therapy)

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14 pages, 3383 KiB

Open AccessReview

Room Temperature Terahertz and Frequency Combs Based on Intersubband Quantum Cascade Laser Diodes: History and Future

by Manijeh Razeghi and Quanyong Lu

Photonics 2025, 12(1), 79; https://doi.org/10.3390/photonics12010079 - 17 Jan 2025

Viewed by 531

Abstract

The year 2024 marks the 30-year anniversary of the quantum cascade laser (QCL), which is becoming the leading laser source in the mid-infrared (mid-IR) range. Since the first demonstration, QCL has undergone tremendous development in terms of the output power, wall plug efficiency, [...] Read more.

The year 2024 marks the 30-year anniversary of the quantum cascade laser (QCL), which is becoming the leading laser source in the mid-infrared (mid-IR) range. Since the first demonstration, QCL has undergone tremendous development in terms of the output power, wall plug efficiency, spectral coverage, wavelength tunability, and beam quality. Owing to its unique intersubband transition and fast gain features, QCL possesses strong nonlinearities that makes it an ideal platform for nonlinear photonics like terahertz (THz) difference frequency generation and direct frequency comb generation via four-wave mixing when group velocity dispersion is engineered. The feature of broadband, high-power, and low-phase noise of QCL combs is revolutionizing mid-IR spectroscopy and sensing by offering a new tool measuring multi-channel molecules simultaneously in the μs time scale. While THz QCL difference frequency generation is becoming the only semiconductor light source covering 1–5 THz at room temperature. In this paper, we will introduce the latest research from the Center for Quantum Devices at Northwestern University and briefly discuss the history of QCL, recent progress, and future perspective of QCL research, especially for QCL frequency combs, room temperature THz QCL difference frequency generation, and major challenges facing QCL in the future. Full article

(This article belongs to the Special Issue The Three-Decade Journey of Quantum Cascade Lasers)

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19 pages, 4735 KiB

Open AccessArticle

Study of Point Scanning Detection Mechanisms for Vibration Signals with Wavefront Sensors

by Quan Luo, Hongsheng Luo, Yiyou Fan, Guihan Wu, Haoming Chen, Yun Pan, Wei Jiang and Jinshan Su

Photonics 2025, 12(1), 78; https://doi.org/10.3390/photonics12010078 - 16 Jan 2025

Viewed by 534

Abstract

Seismic wave laser remote sensing is extensively employed in seismic monitoring and resource exploitation. This work establishes a vibration signal point scanning detection system utilizing wavefront sensors, leveraging their high resolution, array detection capabilities, and the independent detection of each microlens based on [...] Read more.

Seismic wave laser remote sensing is extensively employed in seismic monitoring and resource exploitation. This work establishes a vibration signal point scanning detection system utilizing wavefront sensors, leveraging their high resolution, array detection capabilities, and the independent detection of each microlens based on research into seismic wave laser remote sensing detection. The experiments validate that each microlens of the wavefront sensor possesses autonomous detecting capabilities, enabling the sensor to scan and identify points of vibrational signals. This work also significantly improved the scanning efficiency by increasing the diameter of the scanning spot. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Photonics Sensors)

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13 pages, 5328 KiB

Open AccessArticle

InP/Si₃N₄ Hybrid Integrated Lasers for RF Local Oscillator Signal Generation in Satellite Payloads

by Jessica César-Cuello, Alberto Zarzuelo, Robinson C. Guzmán, Charoula Mitsolidou, Ilka Visscher, Roelof B. Timens, Paulus W. L. Van Dijk, Chris G. H. Roeloffzen, Luis González, José Manuel Delgado Mendinueta and Guillermo Carpintero

Photonics 2025, 12(1), 77; https://doi.org/10.3390/photonics12010077 - 16 Jan 2025

Viewed by 507

Abstract

This paper presents an integrated tunable hybrid multi-laser module designed to simultaneously generate multiple radiofrequency (RF) local oscillator (LO) signals through optical heterodyning. The device consists of five hybrid InP/Si₃N₄ integrated lasers, each incorporating an intracavity wavelength-selective optical filter formed [...] Read more.

This paper presents an integrated tunable hybrid multi-laser module designed to simultaneously generate multiple radiofrequency (RF) local oscillator (LO) signals through optical heterodyning. The device consists of five hybrid InP/Si₃N₄ integrated lasers, each incorporating an intracavity wavelength-selective optical filter formed by two micro-ring resonators. Through beating the wavelengths generated from three of these lasers, we demonstrate the simultaneous generation of two LO signals within bands crucial for satellite communications (SatCom): one in the Ka-band and the other in the V-band. The device provides an extensive wavelength tuning range across the entire C-band and exhibits exceptionally narrow optical linewidths, below 40 kHz in free-running mode. This results in ultra-wideband tunable RF signals with narrow electrical linewidths below 100 kHz. The system is compact and highly scalable, with the potential to generate up to 10 simultaneous LO signals, being a promising solution for advanced RF signal generation in high throughput satellite payloads. Full article

(This article belongs to the Special Issue Photonics: 10th Anniversary)

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13 pages, 5015 KiB

Open AccessArticle

Cost-Effective and Energy-Efficient Photonics-Based Frequency Hopping by Single Wavelength-Tunable Laser for Secure THz Communication

by Naoto Masutomi, Shenghong Ye, Bo Li, Ryota Kaide, Ming Che, Yuya Mikami, Yuta Ueda and Kazutoshi Kato

Photonics 2025, 12(1), 76; https://doi.org/10.3390/photonics12010076 - 16 Jan 2025

Viewed by 416

Abstract

A photomixing-based frequency-hopping spread spectrum (FHSS) system is effective for future secure terahertz (THz) wireless communications. Conventional photomixing systems are typically composed of two lasers, which result in an increased system size and power consumption. To address this issue, we applied our proposed [...] Read more.

A photomixing-based frequency-hopping spread spectrum (FHSS) system is effective for future secure terahertz (THz) wireless communications. Conventional photomixing systems are typically composed of two lasers, which result in an increased system size and power consumption. To address this issue, we applied our proposed THz wave generation method, using a single wavelength-tunable laser, to the FHSS system. In the experiments, we successfully demonstrated a J-band (220–330 GHz) FHSS system with a frequency-hopped interval of 400 ns. Full article

(This article belongs to the Special Issue Recent Advancements in Tunable Laser Technology)

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26 pages, 15021 KiB

Open AccessReview

Research Progress on Applications of Metasurface-Based Optical Image Edge Detection Technology

by Yuying Jiang, Qingcheng Sun, Tauseef Abbas, Hongyi Ge, Guangming Li, Keke Jia, Yuwei Bu and Huifang Zheng

Photonics 2025, 12(1), 75; https://doi.org/10.3390/photonics12010075 - 16 Jan 2025

Viewed by 551

Abstract

With the rapid development of metasurface technology, metasurfaces have gained significant attention in optical edge detection. Owing to their precise control over the phase, amplitude, and polarization state of electromagnetic waves, metasurfaces offer a novel approach to edge detection that not only overcomes [...] Read more.

With the rapid development of metasurface technology, metasurfaces have gained significant attention in optical edge detection. Owing to their precise control over the phase, amplitude, and polarization state of electromagnetic waves, metasurfaces offer a novel approach to edge detection that not only overcomes the size limitations of traditional optical devices but also significantly enhances the flexibility and efficiency of image processing. This paper reviews recent research advances in metasurfaces for optical edge detection. Firstly, the principles of phase-controlled metasurfaces in edge detection are discussed, along with an analysis of their features in different applications. Then, methods for edge detection based on polarization and dispersion modulation of metasurfaces are elaborated, highlighting the potential of these technologies for efficient image processing. In addition, the progress in multifunctional metasurfaces is presented, offering new perspectives and application prospects for future optical edge detection, along with a discussion on the limitations of metasurface-based edge detection technologies and an outlook on their future development. Full article

(This article belongs to the Special Issue Photonics: 10th Anniversary)

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17 pages, 11992 KiB

Open AccessArticle

Multi-Color Channel Gamma Correction in Fringe Projection Profilometry

by Xiang Sun, Yunpeng Zhang, Lingbao Kong, Xing Peng, Zhenjun Luo, Jie Shi and Liping Tian

Photonics 2025, 12(1), 74; https://doi.org/10.3390/photonics12010074 - 16 Jan 2025

Viewed by 414

Abstract

Three-dimensional shape measurement plays an important role in various fields. As a way of three-dimensional measurement, fringe projection profilometry (FPP) is widely used because of its non-contact, simple structure, and high stability. One of the key challenges affecting measurement accuracy is the gamma [...] Read more.

Three-dimensional shape measurement plays an important role in various fields. As a way of three-dimensional measurement, fringe projection profilometry (FPP) is widely used because of its non-contact, simple structure, and high stability. One of the key challenges affecting measurement accuracy is the gamma effect. With the development of FPP technology, multi-color channels are gradually applied to the measurement, and the response of different colors in the projector-camera system (pro-cam system) is not exactly the same. Therefore, more accurate gamma correction for different color channels is required. To solve this problem, a model of joint gamma correction for different color channels is proposed. In this model, the light is subdivided into three channels: red; green; and blue (RGB). In the pro-cam system, the different responses of different colors and the influence of background light intensity on gamma correction are comprehensively considered, and some error compensation is made for color crosstalk. Compared with the traditional gamma correction methods, the gamma correction method proposed in this paper is more accurate and has a larger effective working range after correction. This method is particularly beneficial in scenarios where multiple color channels are used for measurement, as it more accurately reflects the true measurement results for each channel. The effectiveness and accuracy of the method are validated through experiments. Full article

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26 pages, 3630 KiB

Open AccessArticle

Tailoring Spectral Response of Grating-Assisted Co-Directional Couplers with Weighting Techniques and Rational Transfer Functions: Theory and Experiment

by Anatole Lupu

Photonics 2025, 12(1), 73; https://doi.org/10.3390/photonics12010073 - 15 Jan 2025

Viewed by 413

Abstract

This work addresses the tailoring spectral response of grating-assisted co-directional couplers (GADCs) in the context of wavelength filtering for fiber-to-the-home (FTTH) applications. Design methods for spectral response engineering by means of coupling profile apodization-type weighting techniques and also more advanced rational transfer functions [...] Read more.

This work addresses the tailoring spectral response of grating-assisted co-directional couplers (GADCs) in the context of wavelength filtering for fiber-to-the-home (FTTH) applications. Design methods for spectral response engineering by means of coupling profile apodization-type weighting techniques and also more advanced rational transfer functions fitting a predefined spectral window template are presented. Modeling results based on coupled mode theory are then applied for the design and experimental fabrication of InGaAsP/InP GADCs targeting 1.3+/1.3− µm diplexer application in FTTH access networks. The experimental results are found to be in good agreement with the modeling predictions. The design tools presented are quite general and can be easily adapted to other technology platforms, such as silicon photonics for the use of GADCs as add-drop wavelength division multiplexers. The field of parity–time symmetry is another avenue where these types of gain–loss-assisted GADCs as active components are of interest for switching applications, and the design methods presented here may find utility. Full article

(This article belongs to the Special Issue Silicon-Based Integrated Optics: From Design to Applications)

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7 pages, 2734 KiB

Open AccessCommunication

High-Energy Burst-Mode 3.5 μm MIR KTA-OPO

by Haowen Guo, Chunyan Jia, Shuai Ye, Yongping Yao, Tiejun Ma, Jiayu Zhang, Meng Bai, Jinbao Xia, Hongkun Nie, Bo Yao, Jingliang He and Baitao Zhang

Photonics 2025, 12(1), 72; https://doi.org/10.3390/photonics12010072 - 15 Jan 2025

Viewed by 498

Abstract

In this paper, a high energy 3.5 μm mid-infrared (MIR) burst-mode KTA optical parametric oscillator (OPO) was demonstrated. Utilizing a quasi-continuous wave (QCW) laser diode (LD) side-pump module and electro-optic (EO) Q-switching technique, a high beam quality 1064 nm burst-mode laser was achieved [...] Read more.

In this paper, a high energy 3.5 μm mid-infrared (MIR) burst-mode KTA optical parametric oscillator (OPO) was demonstrated. Utilizing a quasi-continuous wave (QCW) laser diode (LD) side-pump module and electro-optic (EO) Q-switching technique, a high beam quality 1064 nm burst-mode laser was achieved as the fundamental source, generating 30 mJ high-energy pulses at burst repetition rates of 100 Hz and 200 Hz with sub-burst repetition rates of 20 kHz, 40 kHz, and 50 kHz. The KTA-OPO produced a 3.5 μm MIR burst-mode laser output with 4 to 11 sub-pulses per pulse envelope. The output energies were 2.9 mJ, 2.81 mJ, and 2.79 mJ at 100 Hz, as well as 2.8 mJ, 2.75 mJ, and 2.72 mJ at 200 Hz, with corresponding conversion efficiencies of 9.6%, 9.3%, and 9.3% at 100 Hz, as well as 9.3%, 9.2%, and 9.1% at 200 Hz, respectively. Our results pave a new way for generating burst-mode MIR lasers. Full article

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16 pages, 861 KiB

Open AccessArticle

Theoretical Study of the Pre-Plasma Density Scale Length’s Influence on the Absorption Efficiency in Laser–Solid Interaction at Relativistic Laser Intensities for PW-Class Lasers

by Iuliana-Mariana Vladisavlevici, Michael Ehret, Evgeny Filippov, Enrique García-García, Cruz Mendez, Marta Olivar Ruíz, Óscar Varela, Luca Volpe and Jose Antonio Pérez-Hernández

Photonics 2025, 12(1), 71; https://doi.org/10.3390/photonics12010071 - 15 Jan 2025

Viewed by 535

Abstract

This work studied the pre-plasma that builds up in interactions of focused high-power PW-class lasers with solid targets at the target surface facing the laser beam, and its impact on the global laser absorption efficiency as well as on the spectral cut-off energy [...] Read more.

This work studied the pre-plasma that builds up in interactions of focused high-power PW-class lasers with solid targets at the target surface facing the laser beam, and its impact on the global laser absorption efficiency as well as on the spectral cut-off energy of laser-generated proton beams. Our practical heuristic estimates were derived from the example of the VEGA-3 laser at CLPU. Our modeling results for the pre-plasma expansion due to the laser pedestal of VEGA-3 were benchmarked by hydrodynamic simulations, revealing good agreement for the evolution before the arrival of the main Gaussian laser intensity peak. Our detailed numerical two-dimensional Particle-in-Cell simulations showed the impact of different pre-plasma scale lengths on the absorption efficiency of laser energy into electrons, relevant for the seeding of other types of radiation. It was shown that the absorption can increase manyfold when increasing the pre-plasma scale length. This effect can be beneficial for the spectral cut-off energy of accelerated protons, where a trade-off between absorption and electron dynamics yields an optimum pre-plasma scale length. The findings can be applied to other PW-class laser facilities. Full article

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12 pages, 4233 KiB

Open AccessArticle

Theoretical Investigation of Terahertz Spoof Surface-Plasmon-Polariton Devices Based on Ring Resonators

by Can Liu, Shenghao Gu, Mingming Sun, Ya Liu, Ying Zhang and Jiaguang Han

Photonics 2025, 12(1), 70; https://doi.org/10.3390/photonics12010070 - 15 Jan 2025

Viewed by 509

Abstract

Terahertz is one of the most promising technologies for high-speed communication and large-scale data transmission. As a classical optical component, ring resonators are extensively utilized in the design of band-pass and frequency-selective devices across various wavebands, owing to their unique characteristics, including optical [...] Read more.

Terahertz is one of the most promising technologies for high-speed communication and large-scale data transmission. As a classical optical component, ring resonators are extensively utilized in the design of band-pass and frequency-selective devices across various wavebands, owing to their unique characteristics, including optical comb generation, compactness, and low manufacturing cost. While substantial progress has been made in the study of ring resonators, their application in terahertz surface wave systems remains less than fully optimized. This paper presents several spoof surface plasmon polariton-based devices, which were realized using ring resonators at terahertz frequencies. The influence of both the radius of the ring resonator and the width of the waveguide coupling gap on the coupling coefficient are investigated. The band-stop filters based on the cascaded ring resonator exhibit a 0.005 THz broader frequency bandwidth compared to the single-ring resonator filter and achieve a minimum stopband attenuation of 28 dB. The add–drop multiplexers based on the asymmetric ring resonator enable selective surface wave outputs at different ports by rotating the ring resonator. The devices designed in this study offer valuable insights for the development of on-chip terahertz components. Full article

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19 pages, 1014 KiB

Open AccessArticle

A Novel Flip-Filtered Orthagonal Frequency Division Multiplexing-Based Visible Light Communication System: Peak-to-Average-Power Ratio Assessment and System Performance Improvement

by Hayder S. R. Hujijo and Muhammad Ilyas

Photonics 2025, 12(1), 69; https://doi.org/10.3390/photonics12010069 - 15 Jan 2025

Viewed by 572

Abstract

Filtered orthogonal frequency division multiplexing (F-OFDM), employed in visible light communication (VLC) systems, has been considered a promising technique for overcoming OFDM’s large out-of-band emissions and thus reducing bandwidth efficiency. However, due to Hermitian symmetry (HS) imposition, a challenge in VLC involves increasing [...] Read more.

Filtered orthogonal frequency division multiplexing (F-OFDM), employed in visible light communication (VLC) systems, has been considered a promising technique for overcoming OFDM’s large out-of-band emissions and thus reducing bandwidth efficiency. However, due to Hermitian symmetry (HS) imposition, a challenge in VLC involves increasing power consumption and doubling inverse fast Fourier transform IFFT/FFT length. This paper introduces the non-Hermitian symmetry (NHS) Flip-F-OFDM technique to enhance bandwidth efficiency, reduce the peak–average-power ratio (PAPR), and lower system complexity. Compared to the traditional HS-based Flip-F-OFDM method, the proposed method achieves around 50% reduced system complexity and prevents the PAPR from increasing. Therefore, the proposed method offers more resource-saving and power efficiency than traditional Flip-F-OFDM. Then, the proposed scheme is assessed with HS-free Flip-OFDM, asymmetrically clipped optical (ACO)-OFDM, and direct-current bias optical (DCO)-OFDM. Concerning bandwidth efficiency, the proposed method shows better spectral efficiency than HS-free Flip-OFDM, ACO-OFDM, and DCO-OFDM. Full article

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

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21 pages, 3250 KiB

Open AccessReview

Coherent Optics for Passive Optical Networks: Flexible Access, Rapid Burst Detection, and Simplified Structure

by Guangying Yang, Yixiao Zhu, Ziheng Zhang, Lina Man, Xiatao Huang, Xingang Huang and Weisheng Hu

Photonics 2025, 12(1), 68; https://doi.org/10.3390/photonics12010068 - 14 Jan 2025

Viewed by 537

Abstract

With the development of the Internet of Things, cloud networking, and 4K/8K high-definition video, global internet traffic has seen a dramatic increase. This surge in traffic has placed higher demands on the performance of optical networks, featuring higher data rates, lower latency, and [...] Read more.

With the development of the Internet of Things, cloud networking, and 4K/8K high-definition video, global internet traffic has seen a dramatic increase. This surge in traffic has placed higher demands on the performance of optical networks, featuring higher data rates, lower latency, and lower cost. The passive optical network (PON) is a representative scenario of optical access networks. Issues such as burst-mode detection in upstream PON scenarios, flexible rate allocation in downstream scenarios, and the simplification of hardware complexity at the optical network unit (ONU) side have attracted considerable attention. Compared to intensity modulation/direct detection (IM/DD), a recently proposed coherent PON incorporates a local oscillator laser at the receiver, enabling superior receiver sensitivity, spectrally efficient modulation, linear optical field recovery, and flexible channel selection. These features significantly enhance the flexibility and data rates of PON systems. This paper provides a comprehensive review of the development of coherent PONs, particularly in aspects of preamble design for burst-mode detection in upstream scenarios, the design of flexible rate PONs in downstream scenarios, and solutions for reducing hardware complexity at the ONU side. Full article

(This article belongs to the Special Issue Optical Networking Technologies for High-Speed Data Transmission)

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17 pages, 23090 KiB

Open AccessArticle

Design Method of Infrared Stealth Film Based on Deep Reinforcement Learning

by Kunyuan Zhang, Delian Liu and Shuo Yang

Photonics 2025, 12(1), 67; https://doi.org/10.3390/photonics12010067 - 14 Jan 2025

Viewed by 462

Abstract

With the rapid advancement of infrared detection technology, the development of infrared stealth materials has become a pressing need. The study of optical micro/nano infrared stealth materials, which possess selective infrared radiation properties and precise structural features, is of significant importance. By integrating [...] Read more.

With the rapid advancement of infrared detection technology, the development of infrared stealth materials has become a pressing need. The study of optical micro/nano infrared stealth materials, which possess selective infrared radiation properties and precise structural features, is of significant importance. By integrating deep reinforcement learning with a multilayer perceptron, we have framed the design of radiation-selective films as a reinforcement learning problem. This approach led to the creation of a Ge/Ag/Ge/Ag multilayer micro/nano optical film that exhibits infrared stealth characteristics. During the design process, the agent continuously adjusts the thickness parameters of the optical film, exploring and learning within the defined design space. Upon completion of the training, the agent outputs the optimized thickness parameters. The results demonstrate that the film structure, optimized by the agent, exhibits a low average emissivities of 0.086 and 0.147 in the 3∼5 µm and 8∼14 µm atmospheric windows, respectively, meeting the infrared stealth requirements in terms of radiation characteristics. Additionally, the film demonstrates a high average emissivity of 0.75 in the 5∼8 µm range, making it effective for thermal radiation management. Furthermore, we coated the Si surface with the designed thin film and conducted experimental validation. The results show that the coated material exhibits excellent infrared stealth properties. Full article

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10 pages, 613 KiB

Open AccessCommunication

Block-Based Mode Decomposition in Few-Mode Fibers

by Chenyu Wang, Jianyong Zhang, Baorui Yan, Shuchao Mi, Guofang Fan, Muguang Wang and Peiying Zhang

Photonics 2025, 12(1), 66; https://doi.org/10.3390/photonics12010066 - 14 Jan 2025

Viewed by 394

Abstract

A block-based mode decomposition (BMD) algorithm is proposed in this paper, which reduces computational complexity and enhances noise resistance. The BMD uses randomly selected sample blocks of the beam images to restore mode coefficients instead of all pixels in the beam images. It [...] Read more.

A block-based mode decomposition (BMD) algorithm is proposed in this paper, which reduces computational complexity and enhances noise resistance. The BMD uses randomly selected sample blocks of the beam images to restore mode coefficients instead of all pixels in the beam images. It allows for blocks of any shape, such as triangles. In noise-free simulations, compared to the spatially degenerated mode decomposition (SPMD) algorithm, the BMD algorithm requires only 1% of the multiplication operations, thereby significantly increasing the computational efficiency while maintaining a high mode decomposition accuracy. In simulations with noise, increasing the signal-to-noise ratio (SNR) reduces decomposition errors across all configurations. The amplitude error of BMD can outperform SPMD by 15 dB. The experimental results show that BMD has a better performance than SPMD. Full article

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

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13 pages, 3629 KiB

Open AccessArticle

Modeling Femtosecond Beam Propagation in Dielectric Hollow-Core Waveguides

by Valer Tosa, Ana Maria Mihaela Gherman, Katalin Kovacs and István Tóth

Photonics 2025, 12(1), 65; https://doi.org/10.3390/photonics12010065 - 13 Jan 2025

Viewed by 574

Abstract

The propagation of femtosecond pulses in guided structures is a matter of both fundamental and practical interest in nonlinear optics. In particular, hollow-core waveguides (HCWs) filled with a gas medium are fabricated and used as devices for the generation of attosecond pulses from [...] Read more.

The propagation of femtosecond pulses in guided structures is a matter of both fundamental and practical interest in nonlinear optics. In particular, hollow-core waveguides (HCWs) filled with a gas medium are fabricated and used as devices for the generation of attosecond pulses from high-order harmonics. In this process, the configuration of the laser field (intensity and phase) inside the waveguide is of crucial importance for enhancing the (well-known, low) efficiency of high-order harmonic generation (HHG). Here, we present numerical calculations which demonstrate the main features of the propagation process in fabricated HCWs. We consider a variety of experimental parameters like gas pressure, waveguide size, laser wavelength, and pulse energy and duration. In particular, the beam profile at the fiber input is found to be a sensitive parameter which influences the whole evolution of the laser field along the propagation. Our model is based on a split-step method modified to account for propagation in ionized media and is validated against experimental and theoretical data from the literature. Our results contribute to the description of the main features of beam propagation in HCWs and provide guiding directions for designing efficient configurations for HHG. Full article

(This article belongs to the Special Issue Advances in Ultrafast Laser Science and Applications)

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11 pages, 5416 KiB

Open AccessArticle

Design, Analysis, and Implementation of the Subdivision Interpolation Technique for the Grating Interferometric Micro-Displacement Sensor

by Jiuhui Tang, Haifeng Peng, Peng Yang, Shangzhou Guo, Wenqiang Sun, Li Jin, Kunyang Xie and Mengwei Li

Photonics 2025, 12(1), 64; https://doi.org/10.3390/photonics12010064 - 13 Jan 2025

Viewed by 389

Abstract

A high-resolution grating interferometric micro-displacement sensor utilizing the subdivision interpolation technique is proposed and experimentally demonstrated. As the interference laser intensity varies sinusoidally with displacement, subdivision interpolation is a promising technique to achieve micro-displacement detection with a high resolution and linearity. However, interpolation [...] Read more.

A high-resolution grating interferometric micro-displacement sensor utilizing the subdivision interpolation technique is proposed and experimentally demonstrated. As the interference laser intensity varies sinusoidally with displacement, subdivision interpolation is a promising technique to achieve micro-displacement detection with a high resolution and linearity. However, interpolation errors occur due to the phase imbalance, offset error, and amplitude mismatch between the orthogonal signals. To address these issues, a subdivision interpolation circuit, along with 90-degree phase-shifter and high-precision DC bias-voltage techniques, converts an analog sinusoidal signal into standard incremental digital signals. This novel methodology ensures that its performance is least affected by the nonidealities induced by fabrication and assembly errors. Detailed design, analysis, and experimentation studies have been conducted to validate the proposed methodology. The experimental results demonstrate that the micro-displacement sensor based on grating interferometry achieved a displacement resolution of less than 1.9 nm, an accuracy of 99.8%, and a subdivision interpolation factor of 208. This research provides a significant guide for achieving high-precision grating interferometric displacement measurements. Full article

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

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22 pages, 1909 KiB

Open AccessArticle

Focusing Hemispherical Waves

by Colin J. R. Sheppard

Photonics 2025, 12(1), 63; https://doi.org/10.3390/photonics12010063 - 13 Jan 2025

Viewed by 458

Abstract

The field in the focal plane of a hemispherically focused wave in an aplanatic optical system can be expressed in an analytical form. In fact, many different cases of hemispherically focused scalar and vectorial waves can be analytically expressed. We consider focusing with [...] Read more.

The field in the focal plane of a hemispherically focused wave in an aplanatic optical system can be expressed in an analytical form. In fact, many different cases of hemispherically focused scalar and vectorial waves can be analytically expressed. We consider focusing with linear or circular polarized illumination as well as other cases such as electric dipole, transverse electric, and radial polarizations. We also investigate 4Pi focusing and the focusing of vortex waves. These results can be applied to focusing with microscope objectives of high numerical aperture. Full article

(This article belongs to the Special Issue Laser Beam Propagation and Control)

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Photonics, Volume 12, Issue 1 (January 2025) – 92 articles

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