Photonics

11 pages, 3517 KiB

Open AccessArticle

Optimized Dual-Stokes Raman Laser for 1.1 µm Emission and Temperature Sensing

by Jesus Alberto Coba-Ramos, Lelio de la Cruz May, Angeles Yolanda Pages-Pacheco, Efrain Mejia-Beltran, Daniel Jauregui-Vazquez, Manuel May-Alarcon, Rafael Sanchez-Lara and Jose Alfredo Alvarez Chavez

Photonics 2025, 12(5), 470; https://doi.org/10.3390/photonics12050470 (registering DOI) - 10 May 2025

Abstract

This work experimentally validates an improved Raman fiber laser, developed through cascade core variation splicing of optical fibers and the integration of fiber Bragg gratings. A continuous-wave Yb-doped fiber laser was used as the pump source, delivering up to 10 W at 1064 [...] Read more.

This work experimentally validates an improved Raman fiber laser, developed through cascade core variation splicing of optical fibers and the integration of fiber Bragg gratings. A continuous-wave Yb-doped fiber laser was used as the pump source, delivering up to 10 W at 1064 nm. The first Stokes emission generates laser output centered at 1119 nm, while the second Stokes emission produces a lasing mode at 1179 nm. Fiber Bragg gratings control these emissions. Furthermore, both Stokes laser emissions can be tuned by applying temperature changes, achieving a 15.07 pm/°C sensitivity. The proposed laser presents a compact and practical solution for remote temperature sensing applications using fiber lasers. Full article

(This article belongs to the Special Issue High-Power Fiber Lasers)

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13 pages, 5808 KiB

Open AccessArticle

A Point Cloud Registration Method Based on Point-to-Triangulation Estimation for Optical Window Free-Form Surfaces Testing by Coordinate Measuring Machine

by Chuanchao Wu, Junjie Shi, Taorui Li, Haijiao Huang, Fudong Chu, Siyuan Jiang, Longyue Li and Chiben Zhang

Photonics 2025, 12(5), 469; https://doi.org/10.3390/photonics12050469 (registering DOI) - 10 May 2025

Abstract

Optical window freeform surfaces have emerged as a critical research focus in advanced optical engineering owing to their extensive surface degrees of freedom. These surfaces enable the simultaneous correction of on-axis and off-axis aberrations while satisfying stringent requirements for high-performance, lightweight, and compact [...] Read more.

Optical window freeform surfaces have emerged as a critical research focus in advanced optical engineering owing to their extensive surface degrees of freedom. These surfaces enable the simultaneous correction of on-axis and off-axis aberrations while satisfying stringent requirements for high-performance, lightweight, and compact optical systems. In the initial metrological characterization of these surfaces, coordinate measuring machines (CMMs) are conventionally employed for target point cloud acquisition. However, the achievable measurement accuracy (>2 μm) inherently constrained by CMM precision imposes fundamental limitations for subsequent optical inspections requiring sub-micron to nanometer-level resolution. Meanwhile, although optical measurement methods can result in higher measurement accuracy, they also lead to an increase in costs and testing difficulties. To overcome these limitations, we propose an accelerated point cloud registration methodology based on point-to-triangulation distance estimation. In simulation, using optimal coordinate transformation enabled good capabilities for exceptional surface characterization: peak-to-valley (PV) surface error of 10⁻⁶ nm, residual error of 5 nm, and registration accuracy of log₁₀ (mm/°). Further, in the experiment, the PV surface error was reduced from 27.3 μm to 6.9 μm, equivalent to a reduction of 3.95 times. These results confirm that the point-to-triangulation distance approximation maintains sufficient fidelity to the nominal point-to-surface distance, thereby empirically validating the efficacy of our proposed methodology. Notably, compared with conventional 3D alignment methods, our novel 2D estimation registration approach with point-to-triangulation surface normal vectors demonstrates significant advantages in computational complexity, which achieved a 78% reduction from O(n³) to O(n) while maintaining sub-millisecond alignment times. We believe that the method has potential for use as a low-cost optical precision measurement in manufacturing technology. Full article

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26 pages, 20655 KiB

Open AccessArticle

CEEMDAN-MRAL Transformer Vibration Signal Fault Diagnosis Method Based on FBG

by Hong Jiang, Zhichao Wang, Lina Cui and Yihan Zhao

Photonics 2025, 12(5), 468; https://doi.org/10.3390/photonics12050468 (registering DOI) - 10 May 2025

Abstract

In order to solve the problem that the vibration signal of transformer is affected by noise and electromagnetic interference, resulting in low accuracy of fault diagnosis mode recognition, a CEEMDAN-MRAL fault diagnosis method based on Fiber Bragg Grating (FBG) was proposed to quickly [...] Read more.

In order to solve the problem that the vibration signal of transformer is affected by noise and electromagnetic interference, resulting in low accuracy of fault diagnosis mode recognition, a CEEMDAN-MRAL fault diagnosis method based on Fiber Bragg Grating (FBG) was proposed to quickly and accurately evaluate the vibration fault state of transformer.The FBG sends the wavelength change in the optical signal center caused by the vibration of the transformer to the demodulation system, which obtains the vibration signal and effectively avoids the noise influence caused by strong electromagnetic interference inside the transformer. The vibration signal is decomposed into several intrinsic mode functions (IMFs) by complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN), and the wavelet threshold denoising algorithm improves the signal-to-noise ratio (SNR) to 1.6 times. The Markov transition field (MTF) is used to construct a training and test set. The unique MRAL-Net is proposed to extract the spatial features of the signal and analyze the time series dependence of the features to improve the richness of the signal feature scale. This proposed method effectively removes the noise interference. The average accuracy of fault diagnosis of the transformer winding core reaches 97.9375%, and the time taken on the large-scale complex training set is only 1705 s, which has higher diagnostic accuracy and shorter training time than other models. Full article

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21 pages, 6467 KiB

Open AccessArticle

Research on High-Precision Time–Frequency Phase-Synchronization Transmission Technology for Free-Space Optical Communication Systems on Mobile Platforms

by Fengrui Liu, Ning Sun, Jia Wei, Yingkai Zhao, Xingfa Wang, Weijie Zhang and Jianguo Liu

Photonics 2025, 12(5), 467; https://doi.org/10.3390/photonics12050467 (registering DOI) - 10 May 2025

Abstract

This paper proposes a free-space time–frequency phase (TFP)-synchronization transmission architecture based on optoelectronic hybrid technology, addressing the high-precision TFP synchronization and high-speed communication requirements between mobile platforms in distributed collaborative positioning and other applications. The proposed scheme utilizes symmetric free-space optical (FSO) links [...] Read more.

This paper proposes a free-space time–frequency phase (TFP)-synchronization transmission architecture based on optoelectronic hybrid technology, addressing the high-precision TFP synchronization and high-speed communication requirements between mobile platforms in distributed collaborative positioning and other applications. The proposed scheme utilizes symmetric free-space optical (FSO) links to effectively suppress drift errors, integrating the high bandwidth of optical links and the high stability of microwave links, enabling one-to-many networking synchronization between mobile platforms. The system adopts optical wireless transmission technology based on pseudo-code regenerative ranging, integrating 1.5 Gbps high-speed data transmission with high-precision TFP-synchronization functionality. An experimental system consisting of a main station and two auxiliary stations was established in an outdoor mobile platform scenario. Experimental results show that while achieving high-speed communication, the frequency synchronization precision is 0.0131 ppb, frequency stability is in the order of 10⁻¹⁰@1 s, and phase synchronization precision is approximately 3.56°. The system achieves time synchronization precision at the picosecond level. The proposed technology is highly suitable for high-precision synchronization communication in scenarios lacking fiber-optic infrastructure, effectively fulfilling rigorous requirements in mobile platform applications such as distributed collaborative positioning. Full article

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10 pages, 4552 KiB

Open AccessArticle

High Precision Range Extracting Method for FMCW LiDAR Using Semiconductor Laser Based on EO-PLL and NUDFT

by Tao Xue, Jingyang Liu, Cheng Lu and Guodong Liu

Photonics 2025, 12(5), 466; https://doi.org/10.3390/photonics12050466 (registering DOI) - 10 May 2025

Abstract

Frequency tuning nonlinearities in semiconductor lasers constitute a critical factor that degrades measurement precision and spectral resolution in frequency-modulated continuous-wave (FMCW) LiDAR systems. This study systematically investigates the influence of nonlinear beat signal phase distortions on spectral peak broadening and develops a phase-fitting-based [...] Read more.

Frequency tuning nonlinearities in semiconductor lasers constitute a critical factor that degrades measurement precision and spectral resolution in frequency-modulated continuous-wave (FMCW) LiDAR systems. This study systematically investigates the influence of nonlinear beat signal phase distortions on spectral peak broadening and develops a phase-fitting-based pre-correction algorithm. To further enhance system performance, an electro-optic phase-locked loop architecture combined with non-uniform discrete Fourier transform signal processing is implemented, establishing a comprehensive solution for tuning nonlinearity suppression. Experimental validation demonstrates a sub-18 µm standard deviation in absolute distance measurements at a 19 m target range. This integrated approach represents a significant advancement in coherent frequency-sweep detection methodologies, offering considerable potential for high-precision photonic radar applications. Full article

(This article belongs to the Special Issue High-Precision Laser Interferometry: Instruments and Techniques)

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11 pages, 1898 KiB

Open AccessCommunication

Dynamic Observation of Ultrashort Pulses with Chaotic Features in a Tm-Doped Fiber Laser with a Single Mode Fiber–Grade Index Multimode Fiber–Single Mode Fiber Structure

by Zhenhong Wang, Zexin Zhou, Yubo Ji, Qiong Zeng, Yufeng Song, Geguo Du and Hongye Li

Photonics 2025, 12(5), 465; https://doi.org/10.3390/photonics12050465 (registering DOI) - 9 May 2025

Abstract

In this study, we have demonstrated an ultrafast Tm-doped fiber laser utilizing the nonlinear multimode interference (NL-MMI) effect, with a single mode fiber–grade index multimode fiber–single mode fiber (SMF-GIMF-SMF) structure serving as the saturable absorber (SA). In addition to stable pulses, mode-locked pulses [...] Read more.

In this study, we have demonstrated an ultrafast Tm-doped fiber laser utilizing the nonlinear multimode interference (NL-MMI) effect, with a single mode fiber–grade index multimode fiber–single mode fiber (SMF-GIMF-SMF) structure serving as the saturable absorber (SA). In addition to stable pulses, mode-locked pulses with chaotic features can be obtained in this fiber laser, characterized by a high average output power and pulse energy, resembling noise-like pulses. By employing the time-stretch dispersive Fourier transform (TS-DFT) technology, it can be seen that the sub-pulses constituting these pulses exhibit noisy characteristics with random intensities and energies. Furthermore, the numerical simulations elucidate the corresponding generation mechanism and dynamic evolution. These findings significantly enhance the comprehension of pulse dynamics and offer novel insights into the technological development and application prospects of ultrafast fiber lasers. Full article

(This article belongs to the Special Issue Advances in Nonlinear Optics: From Fundamentals to Applications)

5 pages, 161 KiB

Open AccessEditorial

High-Power Lasers and Light–Matter Interactions

by Zhaohong Liu, Sensen Li and Jiawei Sun

Photonics 2025, 12(5), 464; https://doi.org/10.3390/photonics12050464 - 9 May 2025

Abstract

High-power laser systems and the study of light–matter interactions at high intensities
are crucial for numerous scientific and technological fields, ranging from industrial materials
processing [..] Full article

(This article belongs to the Special Issue Emerging Topics in High-Power Laser and Light–Matter Interactions)

13 pages, 3079 KiB

Open AccessArticle

A Dual-Band Tunable Electromagnetically Induced Transparency (EIT) Metamaterial Based on Vanadium Dioxide

by Lei Zhu, Shujie Wang, Yun Wang, Liang Dong, Hailong Li, Yiya Wang and Xumin Ding

Photonics 2025, 12(5), 463; https://doi.org/10.3390/photonics12050463 - 9 May 2025

Abstract

A dual-band tunable terahertz electromagnetically induced transparency (EIT) metamaterial is introduced. The EIT metamaterial consists of two rectangular split rings, two metal strips, and a patterned vanadium dioxide (VO₂) located at the back. The rectangular split rings serve as the bright [...] Read more.

A dual-band tunable terahertz electromagnetically induced transparency (EIT) metamaterial is introduced. The EIT metamaterial consists of two rectangular split rings, two metal strips, and a patterned vanadium dioxide (VO₂) located at the back. The rectangular split rings serve as the bright resonator to generate two resonance valleys at distinct frequencies. The metal strips act as the dark resonator and are indirectly activated via the coupling influence of the bright resonator. The EIT metamaterial’s response mechanism is analyzed via the field effect and the two-particle model, with theoretical fitting results showing strong agreement with the simulation results. Moreover, VO₂’s conductivity is altered to dynamically control the EIT effect in both frequency bands. Two transparency windows, with modulation depths of 70% and 75%, are observed as the conductivity of VO₂ decreases. Simultaneously, the simulation results reveal a favorable slow light effect, with group delays reaching 51 ps and 74 ps at the transparency windows. The proposed metamaterial holds considerable promise for future modulator, filter, and slow light device applications. Full article

(This article belongs to the Special Issue Photonics Metamaterials: Processing and Applications)

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13 pages, 2864 KiB

Open AccessArticle

Ultrafast Laser Beam Profile Characterization in the Front-End of the ELI-NP Laser System Using Image Features and Machine Learning

by Tayyab Imran

Photonics 2025, 12(5), 462; https://doi.org/10.3390/photonics12050462 - 9 May 2025

Abstract

Ultrafast laser systems, implemented at the ELI-NP, require exceptional beam quality and spatial stability due to their femtosecond pulse durations and extremely high peak powers. This work presents a diagnostic and computational framework for analyzing the ELI-NP Front-End beam characteristics, where spatial coherence [...] Read more.

Ultrafast laser systems, implemented at the ELI-NP, require exceptional beam quality and spatial stability due to their femtosecond pulse durations and extremely high peak powers. This work presents a diagnostic and computational framework for analyzing the ELI-NP Front-End beam characteristics, where spatial coherence and precise pulse shaping are essential for reliable amplification and experimental consistency. The methodology integrates classical beam diagnostics with image processing and machine learning tools to evaluate anomalies based on high-resolution beam profile images. We use centroid tracking to monitor pointing fluctuations, statistical intensity analysis to detect energy instabilities, and Sobel-based edge detection to evaluate beam sharpness and extract structural features from the beam image. Geometric parameters such as ellipticity, roundness, and symmetry indicators are extracted and examined over time. The system applies an unsupervised Isolation Forest algorithm to detect subtle or short-lived anomalies, identifying irregularities without relying on predefined thresholds. These diagnostics are supported by visual plots and statistical summaries, offering a clear picture of the beam’s behavior under real operating conditions. Results confirm that this integrated approach effectively captures major and minor beam instabilities, making it a practical tool for continuous monitoring and performance optimization in ultrafast laser systems. Full article

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

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13 pages, 5736 KiB

Open AccessArticle

Chitosan/Polyacrylic Acid Functionalized Side-Polish Polymer Optical Fiber-Based SPR Sensor for Cu²⁺ Ion Detection

by Chuanxin Teng, Rongping Yang, Shiyuan Ying, Hongyun Xia, Yuting Zhang, Liying Shi, Shijie Deng, Zining Chen, Hanli Qiao and Libo Yuan

Photonics 2025, 12(5), 461; https://doi.org/10.3390/photonics12050461 - 9 May 2025

Abstract

A polymer optical fiber SPR sensor for detecting Cu²⁺ ion concentration in water is proposed. The sensor employs a simple side-polish structure and realizes the detection of Cu²⁺ ion concentration by employing the chitosan (CS)/polyacrylic acid (PAA) bilayer film on the [...] Read more.

A polymer optical fiber SPR sensor for detecting Cu²⁺ ion concentration in water is proposed. The sensor employs a simple side-polish structure and realizes the detection of Cu²⁺ ion concentration by employing the chitosan (CS)/polyacrylic acid (PAA) bilayer film on the gold film of the optical fiber surface. The structure of the fiber probe is optimized, and the sensing performances for the Cu²⁺ ion detection are analyzed experimentally. The experimental results demonstrate that the sensor exhibits a high sensitivity of 465.539 nm/ppm for the Cu²⁺ ion detection in the concentration range of 0–0.04 ppm. And it has a fast response speed and good selectivity for Cu²⁺ ions. The sensor has the advantages of simple structure and low cost, and has potential applications in the field of heavy metal detection. Full article

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

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19 pages, 5298 KiB

Open AccessArticle

Efficient Generation of Transversely and Longitudinally Truncated Chirped Gaussian Laser Pulses for Application in High-Brightness Photoinjectors

by Andreas Hoffmann, Sumaira Zeeshan, James Good, Matthias Gross, Mikhail Krasilnikov and Frank Stephan

Photonics 2025, 12(5), 460; https://doi.org/10.3390/photonics12050460 - 9 May 2025

Abstract

The optimization of photoinjector brightness is crucial for achieving the highest performance at X-ray free-electron lasers. To this end, photocathode laser pulse shaping has been identified as a key technology for enhancing photon flux and lasing efficiency at short wavelengths. Supported by beam [...] Read more.

The optimization of photoinjector brightness is crucial for achieving the highest performance at X-ray free-electron lasers. To this end, photocathode laser pulse shaping has been identified as a key technology for enhancing photon flux and lasing efficiency at short wavelengths. Supported by beam dynamics simulations, we identify transversely and longitudinally truncated Gaussian electron bunches as a beneficial bunch shape in terms of the projected emittance and 5D brightness. The realization of such pulses from chirped Gaussian pulses is studied for 514 nm and 257 nm wavelengths by inserting an amplitude mask in the symmetry plane of the pulse stretcher to achieve longitudinal shaping and an aperture for transverse beam shaping. Using this scheme, transversely and longitudinally truncated Gaussian pulses can be generated and later used for the production of up to 3 nC electron bunches in the photoinjector. The 3D pulse shape at a wavelength of 514 nm is characterized via imaging spectroscopy, and second-harmonic generation frequency-resolved optical gating (SHG FROG) measurements are also performed to analyze the shaping scheme’s efficacy. Furthermore, this pulse-shaping scheme is transferred to a UV stretcher, allowing for direct application of the shaped pulses to cesium telluride photocathodes. Full article

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

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10 pages, 3648 KiB

Open AccessArticle

Compact Optical 90° Hybrid on a Thin-Film Lithium Niobate Platform Used for Integrated Coherent Transceivers

by Haolei Feng, Yuqiong Chen, Zheyuan Shen, Man Chen, Hanyu Wang, Jianguo Liu, Suo Wang and Zeping Zhao

Photonics 2025, 12(5), 459; https://doi.org/10.3390/photonics12050459 - 9 May 2025

Abstract

A 90° optical hybrid employing an MMI coupler was fabricated on a thin-film lithium niobate (TFLN) platform that can be used for integrated coherent transceivers. The fabricated 90° optical hybrid exhibited a CMRR greater than 20 dB, a phase error below ±7.5°, and [...] Read more.

A 90° optical hybrid employing an MMI coupler was fabricated on a thin-film lithium niobate (TFLN) platform that can be used for integrated coherent transceivers. The fabricated 90° optical hybrid exhibited a CMRR greater than 20 dB, a phase error below ±7.5°, and an excess loss less than 1.8 dB (including contributions from the 90° hybrid, a 1 × 2 MMI coupler, and an optical delay line, after subtracting the losses from the coupler and delay line, the 90° optical hybrid introduced less than 0.9 dB of loss) over the C-band with a compact footprint of 13.8 × 250 μm², facilitating the future development of high-bandwidth optical coherent transceivers heterogeneously integrated on TFLN. Full article

(This article belongs to the Special Issue Microwave Photonics: Science and Applications)

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6 pages, 173 KiB

Open AccessEditorial

Machine Learning Applied to Optical Communication Systems

by Zhaopeng Xu and Jinlong Wei

Photonics 2025, 12(5), 458; https://doi.org/10.3390/photonics12050458 - 9 May 2025

Abstract

As the global demand for high-speed and high-capacity communication continues to surge, driven by cloud computing, artificial intelligence, 5G, virtual reality, and the Internet of Things (IoT), optical communication systems have emerged as the backbone of modern digital infrastructure [...] Full article

(This article belongs to the Special Issue Machine Learning Applied to Optical Communication Systems)

10 pages, 3552 KiB

Open AccessArticle

Generation of Tunable Coherent Tri-Frequency Microwave Signals Based on Optoelectronic Oscillator

by Nan Zhang, Zexuan Kong, Huiyun Tang, Chao Luo, Yumo Lei, Ming Li, Ninghua Zhu and Wei Li

Photonics 2025, 12(5), 457; https://doi.org/10.3390/photonics12050457 - 8 May 2025

Abstract

We report a coherent tri-frequency microwave signal generation approach using an optoelectronic oscillator (OEO). In the previous literature, the OEO-based schemes can only generate coherent microwave signals with dual frequencies. In this work, we demonstrate that the generation of coherent tri-frequency microwave signals [...] Read more.

We report a coherent tri-frequency microwave signal generation approach using an optoelectronic oscillator (OEO). In the previous literature, the OEO-based schemes can only generate coherent microwave signals with dual frequencies. In this work, we demonstrate that the generation of coherent tri-frequency microwave signals is also possible using an OEO loop. The key component in our scheme is a tri-passband electrical filter, which has a narrow passband in the middle and two wide passbands on both sides. The OEO loop initially oscillates at the central frequency of the narrow passband with a single-tone f₁. By injecting a microwave signal, f_inj, into the OEO loop, down- and up-converted microwave signals at frequencies of f₂ = f₁ − f_inj and f₃ = f₁ + f_inj, respectively, are generated by frequency mixing in a microwave mixer. The two wide passbands of the electrical filter allow the oscillation of the converted signals at a wide frequency bandwidth by simply tuning the frequency of the injected signal. Moreover, the tri-frequency microwave signals are phase-locked through frequency mixing and mutual injection locking. The proposed scheme is theoretically analyzed and experimentally validated. In the experiments, coherent tri-frequency microwave signals with low phase noise are successfully generated at a fixed frequency of 14 GHz and two tunable frequency ranges from 9 to 12 GHz and from 16 to 19 GHz, respectively. Full article

(This article belongs to the Special Issue Microwave Photonics: Science and Applications)

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25 pages, 1882 KiB

Open AccessArticle

Boundary Integral Equations Approach for a Scattering Problem of a TE-Wave on a Graphene-Coated Slab

by Yury Smirnov and Stanislav Tikhov

Photonics 2025, 12(5), 456; https://doi.org/10.3390/photonics12050456 - 8 May 2025

Abstract

This paper focuses on a transmission problem describing the scattering of a TE-wave on a slab having an absolutely conducting wall at the bottom and covered with graphene at the top, accounting for the optical nonlinearity of graphene. This problem is reduced to [...] Read more.

This paper focuses on a transmission problem describing the scattering of a TE-wave on a slab having an absolutely conducting wall at the bottom and covered with graphene at the top, accounting for the optical nonlinearity of graphene. This problem is reduced to a nonlinear hypersingular boundary integral equation defined on

R

. To find an approximate solution to this equation, we develop a novel mathematical approach that combines the collocation method using Chebyshev series to represent a solution (it allows to calculate hypersingular integrals analytically) with an iterative scheme (it allows to account for the nonlinearity of graphene). Using this approach, we numerically simulate the scattering of TE-wave at 3 THz by a ten-micron graphene-coated slab filled with silica. It is shown that by tuning the chemical potential of graphene, one can modulate both the phase and amplitude of the reflected wave. The presented simulation results also demonstrate the effect of the nonlinearity of graphene on the reflected wave. Full article

(This article belongs to the Special Issue Optical Waveguides: Numerical Methods, Mathematical Modeling, and AI Techniques)

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13 pages, 3316 KiB

Open AccessArticle

Time Parameter Optimization for the Semiconductor Laser-Based Time-Delay Reservoir Computing System

by Qiudi Li, Yushuang Hou, Keqiang Li, Xiaoyu Guo, Chunxia Hu and Dianzuo Yue

Photonics 2025, 12(5), 455; https://doi.org/10.3390/photonics12050455 - 8 May 2025

Abstract

Time-delay reservoir computing (RC) systems, particularly those based on semiconductor lasers (SLs), have gained attention due to their low energy consumption, high response rates, and rich nonlinear dynamics. This work investigates the influence of key time parameters—virtual node interval (θ), delay [...] Read more.

Time-delay reservoir computing (RC) systems, particularly those based on semiconductor lasers (SLs), have gained attention due to their low energy consumption, high response rates, and rich nonlinear dynamics. This work investigates the influence of key time parameters—virtual node interval (θ), delay feedback (τ), and data injection period (T) on the performance of SL-based time-delay RC systems. Using the Santa Fe time series prediction task and memory capacity evaluation task, we analyze how these parameters affect prediction accuracy and memory capability. The results reveal that θ = 0.2T_ro (where T_ro is the relaxation oscillation period of the SLs) optimizes prediction performance, while θ = 0.5T_ro maximizes memory capacity. Additionally, feedback delay τ significantly impacts system performance. Shorter τ values (e.g., τ = 0.54T) enhance prediction accuracy, whereas longer τ values (e.g., τ = 1.74T) improve memory capacity. These findings provide valuable insights for optimizing time-delay RC systems, enabling better task-specific performance and stability. Full article

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36 pages, 5120 KiB

Open AccessReview

Enhancing Optoelectronic Performance Through Rare-Earth-Doped ZnO: Insights and Applications

by Shagun Sood, Pawan Kumar, Isha Raina, Mrinmoy Misra, Sandeep Kaushal, Jyoti Gaur, Sanjeev Kumar and Gurjinder Singh

Photonics 2025, 12(5), 454; https://doi.org/10.3390/photonics12050454 - 8 May 2025

Abstract

Rare-earth (RE) doping has been found to be a potent method to improve the structural, optical, electronic, and magnetic properties of ZnO, positioning it as a versatile material for future optoelectronic devices. This review herein thoroughly discusses the latest developments in RE-doped ZnO [...] Read more.

Rare-earth (RE) doping has been found to be a potent method to improve the structural, optical, electronic, and magnetic properties of ZnO, positioning it as a versatile material for future optoelectronic devices. This review herein thoroughly discusses the latest developments in RE-doped ZnO based on the role of the dopant type, concentration, synthesis method, and consequences of property modifications. The 4f electronic states of rare-earth elements create strong visible emissions, control charge carriers, and design defects. These structural changes lead to tunable bandgap energies and increased light absorption. Also, RE doping considerably enhances ZnO’s performance in electronic devices, like UV photodetectors, LEDs, TCOs, and gas sensors. Though, challenges like solubility constraints and lattice distortions at higher doping concentrations are still key challenges. Co-doping methodologies and new synthesis techniques to further optimize the incorporation of RE into ZnO matrices are also reviewed in this article. By showing a systematic comparison of different RE-doped ZnO systems, this paper sheds light on their future optoelectronic applications. The results are useful for the design of advanced ZnO-based materials with customized functionalities, which will lead to enhanced device efficiency and new photonic applications. Full article

(This article belongs to the Special Issue Advances in Micro and Nano-Photonics: Emerging Materials and Applications)

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14 pages, 4750 KiB

Open AccessArticle

Ultra-Wide-Field Long-Wave Infrared System via Hybrid Refractive–Reflective Structure and Field of View Stitching

by Yiruo Wang, Shan Mao and Jianlin Zhao

Photonics 2025, 12(5), 453; https://doi.org/10.3390/photonics12050453 - 7 May 2025

Abstract

To address the application demands of ultra-wide-field optical systems, we developed a compact, long-infrared waveband optical system using a field-of-view (FoV) stitching method. This system features a refractive–reflective hybrid structure, with the reflective pathway expanding the FoV and the refractive pathway employing germanium [...] Read more.

To address the application demands of ultra-wide-field optical systems, we developed a compact, long-infrared waveband optical system using a field-of-view (FoV) stitching method. This system features a refractive–reflective hybrid structure, with the reflective pathway expanding the FoV and the refractive pathway employing germanium to correct field defects and aberrations. By stitching the FoVs of the two structures, we achieved an ultra-wide-field long-infrared-waveband imaging system over a range of 0°~190°, with an operational wavelength range of 8.7~11.5 μm. The system exhibits excellent imaging performance, with a modulation transfer function (MTF) exceeding 0.5 at 17 lp/mm, the blur spot remaining within the airy disk limit, and the energy concentration exceeding 60% at 15 μm: the tolerance design meets the imaging requirements. Additionally, the system maintains stable image quality within the temperature range of −20 °C~60 °C. The design offers excellent imaging quality, high design flexibility, good real-time performance, compact size, and low economic cost, providing an effective optical structure and realization strategy for ultra-wide-field imaging systems. Full article

(This article belongs to the Special Issue Optical Systems and Design)

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11 pages, 2910 KiB

Open AccessCommunication

A Broadband Thin-Film Lithium Niobate Modulator Using an Electrode with Dual Slow-Wave Structures

by Peng Wang, Dechen Li, Tian Zhang, Jinming Tao, Xinwei Wang, Jianguo Liu and Jinye Li

Photonics 2025, 12(5), 452; https://doi.org/10.3390/photonics12050452 - 7 May 2025

Abstract

With the rapid development of information technology, the global data volume has been continuously expanding, placing unprecedented demands on communication networks to accommodate precipitously increasing throughput. Thin-film lithium niobate (TFLN) modulators, characterized by their large theoretical bandwidth, low half-wave voltage, and suitability for [...] Read more.

With the rapid development of information technology, the global data volume has been continuously expanding, placing unprecedented demands on communication networks to accommodate precipitously increasing throughput. Thin-film lithium niobate (TFLN) modulators, characterized by their large theoretical bandwidth, low half-wave voltage, and suitability for high-density integration, show great application potential in high-speed optical modules and optical interconnection networks. However, the persistent issue of velocity mismatch between radio frequency (RF) signals and optical carriers invariably hinders the utilization of higher-frequency bands, which restricts the modulation speed of the fabricated devices. In this paper, an electrode co-loaded with square serrations and T-shaped stubs was utilized to achieve precise velocity matching and excellent impedance matching. Leveraging this approach, a TFLN modulator chip with an electro-optic bandwidth far exceeding 67 GHz and a return loss of greater than 12 dB was successfully fabricated on a silicon substrate. The velocity of RF signals can be tuned by altering the lengths of the slow-wave structures, which provides guidance for the design and optimization of broadband modulators. Full article

(This article belongs to the Special Issue Microwave Photonics: Science and Applications)

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