Photonics

Research

11 pages, 4986 KiB

Open AccessArticle

Improved Optical Signal Processing with On-Chip Programmable Filter

by Tiantian Li, Yumeng Liu, Luwen Xing, Shuo Lang, Zhangfeng Ge, Dongdong Han, Zhanqiang Hui, Huimin Du and Haowen Shu

Photonics 2025, 12(5), 416; https://doi.org/10.3390/photonics12050416 - 25 Apr 2025

Viewed by 80

Abstract

Bandwidth-limited transmitters have become a severe issue with the rapid growth of bandwidth-hungry services. We investigate the impact of an on-chip optical pre-emphasizer on a bandwidth-limited transmitter and quantitatively analyze the results of bandwidth extension. Improvements in eye diagram performance are discussed. The [...] Read more.

Bandwidth-limited transmitters have become a severe issue with the rapid growth of bandwidth-hungry services. We investigate the impact of an on-chip optical pre-emphasizer on a bandwidth-limited transmitter and quantitatively analyze the results of bandwidth extension. Improvements in eye diagram performance are discussed. The 3 dB electro-optical bandwidth of the transmission system is effectively extended from 18 GHz to 40 GHz. The extinction ratio of the on–off keying (OOK) signal at data rates of 20 to 50 Gbps is improved by 0.64–3.2 dB. Additionally, the Q factor of the eye diagram increases by 0.78–4.36 at data rates ranging from 20 to 50 Gbps. Full article

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

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13 pages, 12023 KiB

Open AccessArticle

Wideband Dual-Polarized Filtering Antennas Using Short-Circuited Coupling Structure for 4G/5G Multi-Input-Multi-Output (MIMO) Antenna Decoupling Design

by Haitao Song, Feifei Zhang and Baoxing Duan

Photonics 2025, 12(3), 259; https://doi.org/10.3390/photonics12030259 - 13 Mar 2025

Viewed by 306

Abstract

A short-circuited coupling structure (SCCS) is proposed to obtain a gain-filtering response for dual-polarized antennas. A conventional dipole is designed with two intrinsic radiation nulls. By introducing an SCCS, an additional radiation null is obtained, and the impedance bandwidth of an antenna can [...] Read more.

A short-circuited coupling structure (SCCS) is proposed to obtain a gain-filtering response for dual-polarized antennas. A conventional dipole is designed with two intrinsic radiation nulls. By introducing an SCCS, an additional radiation null is obtained, and the impedance bandwidth of an antenna can be further improved. Based on this design principle, two dual-polarized filtering antennas are designed for 4G and 5G wireless communication devices. The impedance bandwidth of the proposed 4G filtering antenna is 1.63–2.97 GHz (|S11| < −15 dB), with four radiation nulls at 1.1 GHz, 3.25 GHz, 3.5 GHz, and 4.0 GHz. The impedance bandwidth of the proposed 5G filtering antenna is 3.23–4.21 GHz (|S33| < −15 dB), with four radiation nulls at 1.7 GHz, 2.5 GHz, 3 GHz, and 4.6 GHz. Further, the decoupling function of the SCCS on 4G/5G MIMO antenna designs is also discussed. When introducing an SCCS, the port isolation levels of two elements between the 4G and 5G antennas, as well as the adjacent 5G antennas, can be improved by 14 dB and 6 dB, respectively. The port isolation levels of five elements between the 4G and 5G antennas, as well as the adjacent 5G antennas, can be improved by 15.2 dB and 9.5 dB, respectively. This technique could also be a potential candidate for optical antenna designs in optical front-ends and other multi-wavelength fiber lasers with microstructures. Full article

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

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11 pages, 7727 KiB

Open AccessCommunication

Differentially Fed, Wideband Dual-Polarized Filtering Dielectric Resonator Patch Antenna Using a Sequentially Rotated Shorting Coupling Structure

by Haitao Song, Baoxing Duan and Feifei Zhang

Photonics 2025, 12(3), 239; https://doi.org/10.3390/photonics12030239 - 6 Mar 2025

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Abstract

A wideband dual-polarized dielectric resonator antenna (DRA) with gain-filtering response was proposed in this paper. First, a differentially fed, low-profile crossed-DRA was used to obtain orthogonal polarizations with two resonant modes. A radiation null at upper band edge was also generalized. Second, with [...] Read more.

A wideband dual-polarized dielectric resonator antenna (DRA) with gain-filtering response was proposed in this paper. First, a differentially fed, low-profile crossed-DRA was used to obtain orthogonal polarizations with two resonant modes. A radiation null at upper band edge was also generalized. Second, with the introduction of four parasitic patches at the top of the crossed DRA, another resonant mode at lower band was excited, and the bandwidth was greatly expanded. Moreover, the introduction of parasitic patches could also help improve the selectivity of realized gain with another radiation null at the upper band edge. Furthermore, four sequentially rotated shorting coupling structures (SRSCSs) were proposed for the first time to generalize two additional radiation nulls. Finally, a wideband bandpass filtering response of the realized gain with four radiation nulls was obtained. Prototypes of the proposed antennas were fabricated, and the testing results showed that the antenna had a wide operation band of 57.1% from 2.75 GHz to 4.95 GHz with sharp roll-off at the band edge. This technique could also be used in wireless communication devices at millimeter/optical front ends and other multi-wavelength fiber lasers with micro structures. Full article

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

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11 pages, 2029 KiB

Open AccessCommunication

Efficient Frequency-Domain Block Equalization for Mode-Division Multiplexing Systems

by Yifan Shen, Jianyong Zhang, Shuchao Mi, Guofang Fan and Muguang Wang

Photonics 2025, 12(2), 161; https://doi.org/10.3390/photonics12020161 - 17 Feb 2025

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Abstract

In this paper, an adaptive frequency-domain block equalizer (FDBE) implementing the adaptive moment estimation (Adam) algorithm is proposed for mode-division multiplexing (MDM) optical fiber communication systems. By packing all frequency components into frequency-dependent blocks of a specified size

B

, we define an [...] Read more.

In this paper, an adaptive frequency-domain block equalizer (FDBE) implementing the adaptive moment estimation (Adam) algorithm is proposed for mode-division multiplexing (MDM) optical fiber communication systems. By packing all frequency components into frequency-dependent blocks of a specified size

B

, we define an adaptive equalization matrix to simultaneously compensate for multiple frequency components at each block, which is computed iteratively using the Adam, recursive least squares (RLS) and least mean squares (LMS) algorithms. Simulations show that the proposed FDBE using the Adam algorithm outperforms those using the LMS and RLS algorithms in terms of adaptation speed and symbol error rate (SER) performance. The FDBE using the Adam algorithm with

B = 1

has the fastest adaption time, requiring about

n_{t r} = 100

and

n_{t r} = 900

less training blocks than the RLS algorithm at the SER of

3.8 \times 10^{- 3}

for the accumulated mode-dependent loss (MDL) of

ξ = 1 d

B and

ξ = 5 d

B, respectively. The Adam algorithm with

B = 16

and

B = 8

has

0.4 d

B and

0.3 d

B SNR better than the RLS algorithm with

B = 4

for MDL and

ξ = 1 d

B and

ξ = 55 d

B, respectively. Full article

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

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18 pages, 1807 KiB

Open AccessArticle

3DVT: Hyperspectral Image Classification Using 3D Dilated Convolution and Mean Transformer

by Xinling Su and Jingbo Shao

Photonics 2025, 12(2), 146; https://doi.org/10.3390/photonics12020146 - 11 Feb 2025

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Abstract

Hyperspectral imaging and laser technology both rely on different wavelengths of light to analyze the characteristics of materials, revealing their composition, state, or structure through precise spectral data. In hyperspectral image (HSI) classification tasks, the limited number of labeled samples and the lack [...] Read more.

Hyperspectral imaging and laser technology both rely on different wavelengths of light to analyze the characteristics of materials, revealing their composition, state, or structure through precise spectral data. In hyperspectral image (HSI) classification tasks, the limited number of labeled samples and the lack of feature extraction diversity often lead to suboptimal classification performance. Furthermore, traditional convolutional neural networks (CNNs) primarily focus on local features in hyperspectral data, neglecting long-range dependencies and global context. To address these challenges, this paper proposes a novel model that combines CNNs with an average pooling Vision Transformer (ViT) for hyperspectral image classification. The model utilizes three-dimensional dilated convolution and two-dimensional convolution to extract multi-scale spatial–spectral features, while ViT was employed to capture global features and long-range dependencies in the hyperspectral data. Unlike the traditional ViT encoder, which uses linear projection, our model replaces it with average pooling projection. This change enhances the extraction of local features and compensates for the ViT encoder’s limitations in local feature extraction. This hybrid approach effectively combines the local feature extraction strengths of CNNs with the long-range dependency handling capabilities of Transformers, significantly improving overall performance in hyperspectral image classification tasks. Additionally, the proposed method holds promise for the classification of fiber laser spectra, where high precision and spectral analysis are crucial for distinguishing between different fiber laser characteristics. Experimental results demonstrate that the CNN-Transformer model substantially improves classification accuracy on three benchmark hyperspectral datasets. The overall accuracies achieved on the three public datasets—IP, PU, and SV—were 99.35%, 99.31%, and 99.66%, respectively. These advancements offer potential benefits for a wide range of applications, including high-performance optical fiber sensing, laser medicine, and environmental monitoring, where accurate spectral classification is essential for the development of advanced systems in fields such as laser medicine and optical fiber technology. Full article

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

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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

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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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10 pages, 3849 KiB

Open AccessCommunication

Tunable Single-Longitudinal-Mode Thulium–Holmium Co-Doped Fiber Laser with an Ultra-Narrow Linewidth by Utilizing a Triple-Ring Passive Sub-Ring Resonator

by Pengfei Wang, Fengping Yan, Qi Qin, Dandan Yang, Ting Feng, Peng Liu, Ting Li, Chenhao Yu, Xiangdong Wang, Hao Guo, Yuezhi Cai, Wenjie Ji and Youchao Jiang

Photonics 2025, 12(1), 19; https://doi.org/10.3390/photonics12010019 - 28 Dec 2024

Viewed by 747

Abstract

A low-cost, wavelength-tunable single-longitudinal-mode (SLM) thulium–holmium co-doped fiber laser (THDFL) in a 2 μm band with a simple structure is described in the present paper. To obtain a stable SLM and narrow laser linewidth, a five-coupler-based three-ring (FCTR) filter is utilized in the [...] Read more.

A low-cost, wavelength-tunable single-longitudinal-mode (SLM) thulium–holmium co-doped fiber laser (THDFL) in a 2 μm band with a simple structure is described in the present paper. To obtain a stable SLM and narrow laser linewidth, a five-coupler-based three-ring (FCTR) filter is utilized in the ring cavity of the fiber laser. Tunable SLM wavelength output from THDFLs with kHz linewidths can be achieved by designing the FCTR filter with an effective free-spectral range and a 3 dB bandwidth at the main resonant peak. The measurement results show that the laser is in the SLM lasing state, with a highly stabilized optical spectrum, a linewidth of approximately 9.45 kHz, an optical signal-to-noise ratio as high as 73.6 dB, and a relative intensity noise of less than −142.66 dB/Hz. Furthermore, the wavelength can be tuned in the range of 2.6 nm. The proposed fiber laser has a wide range of applications, including coherence optical communication, optical fiber sensing, and dense wavelength-division-multiplexing. Full article

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

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8 pages, 3202 KiB

Open AccessCommunication

Optimization Design and Simulation of Coin-Slot-Type Anti-Resonant Fiber Structure for 2 μm Transmission

by Boyue Zhang, Zhaoyang Tian, Yu Li, Xinyang Su, Hongxiang Chi, Zikun Nie, Xiaoyu Luo, Bohan Li, Tianran Sun, Sergey Sarkisov and Sergey Kobtsev

Photonics 2024, 11(12), 1109; https://doi.org/10.3390/photonics11121109 - 23 Nov 2024

Viewed by 963

Abstract

In this work, we propose a new type of hollow-core anti-resonant fiber (HC-ARF) structure called a coin-slot structure. In this type of structure, two more layers of glass walls are added into the outer cladding capillary, which can effectively prevent light from leaking [...] Read more.

In this work, we propose a new type of hollow-core anti-resonant fiber (HC-ARF) structure called a coin-slot structure. In this type of structure, two more layers of glass walls are added into the outer cladding capillary, which can effectively prevent light from leaking out of the fiber. In aiming to explore the influence of the outer resonant tube on loss at a wavelength of 2 μm, the fundamental mode loss, high-order mode loss, and higher-order mode extinction ratio (HOMER) under different geometric parameters are studied. Full article

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

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