Photonics

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Open AccessArticle

Long-Haul Microwave-Photonic Optical Fiber Transfer Delay Measurement via Microwave Signal Interferometry

by Yiguang Yang, Hengrui Liu, Ziyi Wang, Hanwen Zhang, Hongyu Li, Yibo Yuan and Xujin Li

Photonics 2025, 12(10), 949; https://doi.org/10.3390/photonics12100949 - 23 Sep 2025

Optical-carried microwave interferometry (OCMI) has attracted increasing attention in recent years, as it combines the ease of phase extraction and manipulation of microwave techniques with the low-loss transfer of optical fibers. Conventional OCMI implementations typically employ broadband light sources and coherent photodetection, which inevitably suffer from dispersion, polarization fading, and phase drift, severely limiting the achievable sensing distance. In this work, we proposed an optimized OCMI architecture that adopts incoherent photodetection combined with electric-domain microwave interferometry. Comprehensive theoretical analysis and systematic experiments demonstrate that the proposed system enables robust, dynamic, and long-haul fiber transfer delay (FTD) measurements, no less than in 15 km length, with improved resolution and stability. It provides new insight for building long-haul FTD sensor networks. Full article

(This article belongs to the Special Issue Emerging Trends in Fiber Optic Sensing)

3133 KB

Open AccessArticle

Random Phase Screen in Scattering Media with Multi-Parameter Coupling

by Pengfei Wu, Yixiao Li, Sichen Lei, Jiao Wang, Zhenkun Tan, Tong Zhang and Xiaofan Wang

Photonics 2025, 12(10), 948; https://doi.org/10.3390/photonics12100948 - 23 Sep 2025

Abstract

The modeling of light propagation in scattering media is an important topic that has attracted considerable attention in recent decades. Coupling microscopic parameters such as particle concentration, particle size, and the refractive index of the medium can broaden the applicability of the model and improve simulation accuracy. In this work, these parameters are used to regulate the anisotropy factor and the mean free path. They are then integrated into a random phase screen model constructed using the Monte Carlo and the Gerchberg–Saxton algorithm. An optical experimental setup was established, in which a Laguerre–Gaussian beam was employed as the incident light source and diffusers with mesh numbers of 1500, 600, and 220 were used as the scattering media. The model was validated through comparative analysis between simulated and experimental results. Correlation coefficients between the simulated and experimental beam profiles exceeded 0.73, and the maximum relative error in power-in-the-bucket was only 4.9%, confirming the model’s accuracy and reliability. Numerical simulations were performed based on the established model to investigate beam propagation behavior. The results indicate that increasing particle concentration and particle size both lead to enhanced beam centroid shift and beam broadening. This modeling method provides a useful tool for analyzing beam propagation in complex scattering media and holds potential applications in wavefront correction and structured beam recognition. Full article

(This article belongs to the Section Optical Interaction Science)

7356 KB

Open AccessReview

Advances in Deep Learning-Driven Metasurface Design and Application in Holographic Imaging

by Manxu Lv, Huizhen Feng, Yongxing Jin and Ying Tian

Photonics 2025, 12(10), 947; https://doi.org/10.3390/photonics12100947 - 23 Sep 2025

Abstract

Currently, the integration of deep learning technology with metasurface holographic imaging technology has propelled the development of optical imaging. Owing to the precise control of metasurfaces over the characteristics of light waves, holographic imaging technology can produce corresponding three-dimensional images after processing. Therefore, their integration enables the acquisition of high-quality images. The number of articles on metasurface design using neural network-based deep learning methods is increasing day by day; however, reviews on this topic remain scarce. This review introduces the development of neural networks and the relevant content on metasurface design using the four types of networks and the applications of deep learning-designed metasurface holographic imaging technology, thereby enhancing readers’ systematic understanding of such technologies. Full article

(This article belongs to the Special Issue Novel Developments in Optoelectronic Materials and Devices)

1202 KB

Open AccessArticle

Microwave Frequency Comb Optimization for FMCW Generation Using Period-One Dynamics in Semiconductor Lasers Subject to Dual-Loop Optical Feedback

by Haomiao He, Zhuqiang Zhong, Xingyu Huang, Yipeng Zhu, Lingxiao Li, Chuanyi Tao, Daming Wang and Yanhua Hong

Photonics 2025, 12(10), 946; https://doi.org/10.3390/photonics12100946 - 23 Sep 2025

Abstract

Microwave frequency comb (MFC) optimization for frequency-modulated continuous-wave (FMCW) generation by period-one (P1) dynamics with dual-loop optical feedback are numerically investigated. The linewidth, the side peak suppression (SPS) ratio, and the comb contrast are adopted to quantitatively evaluate the optimization performance, which directly influence the phase stability, spectral purity and repeatability of the MFC. The results show that intensity modulation of the optical injection can generate a sweepable FMCW signal after photodetection via the optical beat effect. When optical feedback loops are introduced, the single-loop configuration can reduce the phase noise of the FMCW signal whereas a dual-loop configuration exploits the Vernier effect to achieve further linewidth reduction and wide tolerance to the feedback strength. Finally, for both the SPS ratio and comb contrast, the dual-loop configuration achieves a higher SPS ratio and maintains high contrast across a wide range of optical feedback loop delays, which outperforms the loop time tolerance of the single-loop configuration. Full article

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

835 KB

Open AccessArticle

Enhanced Nanoparticle Detection Using Momentum-Space Filtering for Interferometric Scattering Microscopy (iSCAT)

by Xiang Zhang and Yatao Yang

Photonics 2025, 12(10), 945; https://doi.org/10.3390/photonics12100945 - 23 Sep 2025

Abstract

Interferometric scattering microscopy (iSCAT) is a powerful tool for single-particle detection. However, the detection sensitivity is significantly limited by high-frequency noise. In this paper, we have proposed a novel method leveraging frequency component analysis in the Fourier domain to enhance interference patterns, thus efficiently improving the detection accuracy. The bright–dark rings momentum feather has been effectively restored by a combined filter for high-frequency noise and aperture attenuation. The value of the structural similarity index measure has been improved from 0.73 to 0.98. We validate this method on gold nanoparticle samples. The results demonstrate its great potential to advance single-particle tracking by enhancing background suppression in iSCAT applications. Full article

(This article belongs to the Special Issue Research, Development and Application of Raman Scattering Technology)

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Photonics, Volume 12, Issue 10 (October 2025) – 5 articles

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