Photonics

11 pages, 880 KiB

Open AccessCommunication

Prediction of Power Fluctuations of Gaussian Beams After Transmission Through Turbulent Atmosphere

by Zhihao Wan, Jiayi Zhu, Cheng Huang, Zhimin He, Jun Zeng, Fuchang Chen, Chaoqun Yu, Yan Li, Huanting Chen, Yongtao Zhang, Jixiong Pu and Huichuan Lin

Photonics 2024, 11(12), 1108; https://doi.org/10.3390/photonics11121108 - 22 Nov 2024

Abstract

As laser beams propagate through free space, power fluctuation occurs due to atmospheric turbulence, which significantly increases the bit error rate of free-space optical communication. If the precise prediction of power fluctuations can be achieved, it will be of great benefit for improving [...] Read more.

As laser beams propagate through free space, power fluctuation occurs due to atmospheric turbulence, which significantly increases the bit error rate of free-space optical communication. If the precise prediction of power fluctuations can be achieved, it will be of great benefit for improving communication efficiency. To achieve this goal, this paper proposes a novel Time Series Long Short-Term Memory Fully Connected Processing Network (TSLSTMFCPN), which consists of two long short-term memory (LSTM) network layers and a fully connected layer, for predicting the power fluctuations of laser beams caused by atmospheric turbulence. The experimental results show that the mean absolute percentage error of the TSLSTMFCPN in predicting laser power fluctuations is only 1.2%. This result indicates that this model can accurately predict the laser power fluctuations caused by atmospheric turbulence. Our results are expected to be applied in free-space optical communication systems and imaging laser radar system. Full article

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

15 pages, 2612 KiB

Open AccessArticle

Modeling of Complex Integrated Photonic Resonators Using the Scattering Matrix Method

by Di Jin, Sian Ren, Junkai Hu, Duan Huang, David J. Moss and Jiayang Wu

Photonics 2024, 11(12), 1107; https://doi.org/10.3390/photonics11121107 - 22 Nov 2024

Abstract

We propose a universal approach for modeling complex integrated photonic resonators based on the scattering matrix method. By dividing devices into basic elements including directional couplers and connecting waveguides, our approach can be used to model integrated photonic resonators with both unidirectional and [...] Read more.

We propose a universal approach for modeling complex integrated photonic resonators based on the scattering matrix method. By dividing devices into basic elements including directional couplers and connecting waveguides, our approach can be used to model integrated photonic resonators with both unidirectional and bidirectional light propagation, with the simulated spectral response showing good agreement with experimental results. A simplified form of our approach, which divides devices into several independent submodules such as microring resonators and Sagnac interferometers, is also introduced to streamline the calculation of spectral transfer functions. Finally, we discuss the deviations introduced by approximations in our modeling, along with strategies for improving modeling accuracy. Our approach is universal across different integrated platforms, providing a useful tool for designing and optimizing integrated photonic devices with complex configurations. Full article

4 pages, 141 KiB

Open AccessEditorial

Advancing the Frontier of Photonics: Exploring Micro–Nano Optical Devices—An Overview of the Special Issue on Micro–Nano Optical Devices

by Yanfeng Zhang and Yan Shen

Photonics 2024, 11(12), 1106; https://doi.org/10.3390/photonics11121106 - 22 Nov 2024

Abstract

The relentless pursuit of miniaturization in the field of photonics has led to the emergence of micro–nano optical devices as a cornerstone of modern technology [...] Full article

(This article belongs to the Special Issue Micro-Nano Optical Devices)

15 pages, 8416 KiB

Open AccessArticle

Interference Measurements Across Vacuum and Atmospheric Environments for Characterization of Space-Borne Telescope

by Yi-Kai Huang and Cheng-Huan Chen

Photonics 2024, 11(12), 1105; https://doi.org/10.3390/photonics11121105 - 22 Nov 2024

Abstract

A space-borne telescope is used for Earth observation at about 500 km above sea level in the thermosphere where the air density is very low and the temperature increases significantly during daytime. If the telescopes are aligned and characterized on the ground with [...] Read more.

A space-borne telescope is used for Earth observation at about 500 km above sea level in the thermosphere where the air density is very low and the temperature increases significantly during daytime. If the telescopes are aligned and characterized on the ground with standard temperature and pressure (STP) conditions, different from that of the thermosphere, their performance could drift during their mission. Therefore, they are usually placed in a thermal vacuum chamber during ground testing in order to verify the system can perform well and withstand the harsh environment such as a high vacuum level and large temperature variations before being launched. Nevertheless, it remains a challenge to build up an in situ optical measurement system for a large aperture telescope in a thermal vacuum chamber due to the finite internal space of the chamber, limited aperture size of the vacuum view port and thermal dissipation problem of the measuring instruments. In this paper, a novel architecture of an interferometer whose light path travels across a vacuum chamber and an atmospheric environment has been proposed to resolve all of these technical issues. The major feature of the architecture is the diverger lens being located within the vacuum chamber, leaving the rest of the interferometer outside. The variation of the interference fringe due to the relocation of the diverger lens has been investigated with optical simulations and the solutions for compensation have also been proposed. Together with a specific alignment procedure for the proposed architecture, the interferogram has been successfully acquired from a prototype testbed. Full article

(This article belongs to the Special Issue Optical Systems for Astronomy)

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11 pages, 3542 KiB

Open AccessArticle

Bend Distortion and Thermal Lensing Effect on Transverse Mode Instability

by Dan Cheng, Qing Zhong, Yujun Feng, Kun Zhang, Zhaochen Cheng, Dayong Zhang and Hong Zhao

Photonics 2024, 11(12), 1104; https://doi.org/10.3390/photonics11121104 - 22 Nov 2024

Abstract

In this work, we conducted a numerical analysis to investigate the combined effect of thermal lensing and bending-induced mode distortion on transverse mode instability in conventional large-mode-area (LMA) step-index fibers. Utilizing the finite element method, conformal mapping, and thermal conduction equations, we simulated [...] Read more.

In this work, we conducted a numerical analysis to investigate the combined effect of thermal lensing and bending-induced mode distortion on transverse mode instability in conventional large-mode-area (LMA) step-index fibers. Utilizing the finite element method, conformal mapping, and thermal conduction equations, we simulated the mode profiles in LMA 20/400 and 25/400 fibers subjected to both bending and thermal lensing effects; the corresponding evolution of mode loss and effective area were explored as well. Additionally, by introducing the derived mode profiles to the TMI coefficient calculations, we analyzed the influence of bending and thermal lensing (TL) on TMI; the simulation results indicate that the mode distortion caused by bending and the TL effect, under the bending conditions commonly encountered in practice, do not have pronounced impacts on TMI coefficient and TMI threshold. Full article

(This article belongs to the Special Issue The Emerging Science and Applications of Fiber Laser Technology)

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16 pages, 1242 KiB

Open AccessArticle

Logic Gate Generation in a Monostable Optical System: Improving the Erbium-Doped Fiber Laser Reconfigurable Logic Operation

by Samuel Mardoqueo Afanador-Delgado, José Luis Echenausía-Monroy, Guillermo Huerta-Cuellar, Juan Hugo García-López, Erick Emiliano Lopez-Muñoz and Rider Jaimes-Reátegui

Photonics 2024, 11(12), 1103; https://doi.org/10.3390/photonics11121103 - 22 Nov 2024

Abstract

A logic gate is typically an electronic device with a Boolean or other type of function, e.g., adding or subtracting, including or excluding according to its logical properties. They can be used in electronic, electrical, mechanical, hydraulic, and pneumatic technology. This paper presents [...] Read more.

A logic gate is typically an electronic device with a Boolean or other type of function, e.g., adding or subtracting, including or excluding according to its logical properties. They can be used in electronic, electrical, mechanical, hydraulic, and pneumatic technology. This paper presents a new method for generating logic gates based on optical systems with an emission frequency equal to that used in current telecommunications systems. It uses an erbium-doped fiber laser in its monostable operating region, in contrast to most results published in the literature, where multistable behavior is required to induce dynamic changes, and where a DC voltage signal in the laser pump current provides the control between obtaining the different logic operations. The proposed methodology facilitates the generation of the gates, since it does not require taking the optical system to critical power levels that could damage the components. It is based on using the same elements that the EDFL requires to operate. The result is a system capable of generating up to five stable and robust logic gates to disturbances validated in numerical simulation and experimental setup. This eliminates the sensitivity to the initial conditions affecting the possible logic gates generated by the system and the need to add noise to the system (as is performed in works based on stochastic logic resonance). The experimental observations confirm the numerical results and open up new aspects of using chaotic systems to generate optical logic gates without bistable states. Full article

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12 pages, 4480 KiB

Open AccessArticle

He-Kr Gas-Discharge Laser Based on Hollow-Core Fiber

by Igor Bufetov, Dmitry Komissarov, Sergey Nefedov, Alexey Kosolapov, Vladimir Velmiskin, Alexander Mineev and Alexey Gladyshev

Photonics 2024, 11(12), 1102; https://doi.org/10.3390/photonics11121102 - 22 Nov 2024

Viewed by 75

Abstract

Recently, two completely different types of lasers—a fiber laser and a gas-discharge laser—were combined into a single device by demonstrating 2.03 µm laser generation in He-Xe plasma that was produced by a microwave discharge directly inside a hollow-core fiber. This new type of [...] Read more.

Recently, two completely different types of lasers—a fiber laser and a gas-discharge laser—were combined into a single device by demonstrating 2.03 µm laser generation in He-Xe plasma that was produced by a microwave discharge directly inside a hollow-core fiber. This new type of laser—a gas-discharge fiber laser—provides excellent opportunities to greatly enrich the wavelength range of the operation of fiber lasers. In this work, we investigate a He-Kr gas mixture as an active medium of this new type of laser. As a result, a He-Kr gas-discharge fiber laser is demonstrated for the first time. The laser was pumped by a microwave discharge in a He:Kr (40:1) mixture that was filled into a revolver fiber with the hollow-core diameter of 130 µm. The total gas pressure was about 100 torr. With broadband mirrors of the laser resonator, generation was observed simultaneously at wavelengths of 2190 and 2523 nm. The output power of the He-Kr gas-discharge fiber laser was about 1 mW. Full article

(This article belongs to the Special Issue Advanced Solid-State and Fiber Mid-IR Lasers: Novel Materils, Components, Systems and Applications)

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9 pages, 5150 KiB

Open AccessArticle

Reliability Study of Fiber Coupling Efficiency of 980 nm Semiconductor Laser

by Gang Liu, Shuhao Pang, Xin Zhang, Mingzhi Tang, Lei Liang, Rui Li and Rui Huang

Photonics 2024, 11(12), 1101; https://doi.org/10.3390/photonics11121101 - 21 Nov 2024

Viewed by 206

Abstract

In order to improve the stability of semiconductor laser fiber coupling efficiency, based on the coupling principle, the optimal parameters for semiconductor laser fiber coupling were simulated to be θ = 45°, r = 3.25 μm, and z = 5.65 μm. By optimizing [...] Read more.

In order to improve the stability of semiconductor laser fiber coupling efficiency, based on the coupling principle, the optimal parameters for semiconductor laser fiber coupling were simulated to be θ = 45°, r = 3.25 μm, and z = 5.65 μm. By optimizing the structure and position of the lens fiber, it has been experimentally proven that the maximum fiber coupling efficiency of the 980 nm semiconductor laser can reach 87.1%, and the average coupling efficiency can also reach 84%. After temperature cycling and aging experiments, the average coupling efficiency of the device was 81.7%, indicating a decrease in coupling efficiency. At the same time, the effect of fiber stress on the reliability of coupling efficiency was analyzed, and the stability and consistency of the device before and after temperature cycling were explored. In future work, it will be necessary to further optimize the thermal stress caused by UV glue curing and tail pipe soldering, find suitable process parameters, and obtain stable and reliable coupling modules. Full article

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

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11 pages, 1995 KiB

Open AccessArticle

Angle-Tunable Method for Optimizing Rear Reflectance in Fabry–Perot Interferometers and Its Application in Fiber-Optic Ultrasound Sensing

by Yufei Chu, Mohammed Alshammari, Xiaoli Wang and Ming Han

Photonics 2024, 11(12), 1100; https://doi.org/10.3390/photonics11121100 - 21 Nov 2024

Viewed by 218

Abstract

With the introduction of advanced Fiber Bragg Grating (FBG) technology, Fabry–Pérot (FP) interferometers have become widely used in fiber-optic ultrasound detection. In these applications, the slope of the reflectance is a critical factor influencing detection results. Due to the intensity limitations of the [...] Read more.

With the introduction of advanced Fiber Bragg Grating (FBG) technology, Fabry–Pérot (FP) interferometers have become widely used in fiber-optic ultrasound detection. In these applications, the slope of the reflectance is a critical factor influencing detection results. Due to the intensity limitations of the laser source in fiber-optic ultrasound detection, the reflectance of the FBG is generally increased to enhance the signal-to-noise ratio (SNR). However, increasing reflectance can cause the reflectance curve to deviate from a sinusoidal shape, which in turn affects the slope of the reflectance and introduces greater errors. This paper first investigates the relationship between the transmission curve of the FP interferometer and reflectance, with a focus on the errors introduced by simplified assumptions. Further research shows that in sensors with asymmetric reflectance slopes, their transmittance curves deviate significantly from sinusoidal signals. This discrepancy highlights the importance of achieving symmetrical slopes to ensure consistent and accurate detection. To address this issue, this paper proposes an innovative method to adjust the rear-end reflectance of the FP interferometer by combining stress modulation, UV adhesive, and a high-reflectivity metal disk. Additionally, by adjusting the rear-end reflectance to ensure that the transmittance curve approximates a sinusoidal signal, the symmetry of the slope is maintained. Finally, through practical ultrasound testing, by adjusting the incident wavelength to the positions of slope extrema (or zero) at equal intervals, the expected ultrasound signals at extrema (or zero) can be detected. This method converts the problem of approximating a sinusoidal signal into a problem of the slope adjustment of the transmittance curve, making it easier and more direct to determine its impact on detection results. The proposed method not only improves the performance of fiber-optic ultrasound sensors but also reduces costs, paving the way for broader applications in medical diagnostics and structural health monitoring. Full article

(This article belongs to the Special Issue Optical Sensing Technologies, Devices and Their Data Applications)

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18 pages, 12480 KiB

Open AccessArticle

Bionic Compass Method Based on Atmospheric Polarization Optimization in Non-Ideal Clear Condition

by Yuyang Li, Xia Wang, Min Zhang, Ruiqiang Li and Qiyang Sun

Photonics 2024, 11(12), 1099; https://doi.org/10.3390/photonics11121099 - 21 Nov 2024

Viewed by 203

Abstract

The bionic polarization compass is a fascinating subject in the navigation domain. Existing polarization navigation models are primarily based on Rayleigh scattering theory, which is applicable to high-altitude, dry, and clear weather conditions. In most scenarios, it is difficult to meet such ideal [...] Read more.

The bionic polarization compass is a fascinating subject in the navigation domain. Existing polarization navigation models are primarily based on Rayleigh scattering theory, which is applicable to high-altitude, dry, and clear weather conditions. In most scenarios, it is difficult to meet such ideal clear conditions. This paper proposes a bionic navigation method based on atmospheric polarization optimization to improve heading accuracy under non-ideal clear conditions. A signal model under non-ideal clear conditions was firstly established to introduce disturbances of aerosols and other particles into the raw signal function acquired by a camera. Then, an energy functional optimization model was constructed to eliminate the disturbances caused by large particle scattering and restore the original sky polarization pattern. Subsequently, the heading angle was calculated using astronomical data, enhancing accuracy under non-ideal conditions. Finally, we constructed a polarization compass system and conducted field experiments. The results demonstrate that the proposed algorithm effectively mitigates the impact of scattering from aerosols and other particles, reducing the heading angle error to within 2° under sunny, cloudy, overcast and sandy conditions. Full article

(This article belongs to the Special Issue Polarization Optics)

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10 pages, 2370 KiB

Open AccessCommunication

Extra-Cavity Modulating a Soliton Molecule with Chirped Gaussian Pulse Shape

by Daqian Tang, Junxiao Zhan, Dayu Wang, Haoming Wang, Yangyang Peng, Zian Cheak Tiu and Yan Zhou

Photonics 2024, 11(12), 1098; https://doi.org/10.3390/photonics11121098 - 21 Nov 2024

Viewed by 172

Abstract

In this work, we theoretically simulate the modulation of a soliton molecule that has an initial chirped Gaussian pulse shape in a 1 μm extra-cavity optical fiber modulation system. Different soliton parameters in orthogonal polarizations are applied to achieve controllable optical solitons’ output [...] Read more.

In this work, we theoretically simulate the modulation of a soliton molecule that has an initial chirped Gaussian pulse shape in a 1 μm extra-cavity optical fiber modulation system. Different soliton parameters in orthogonal polarizations are applied to achieve controllable optical solitons’ output with specific properties in the time/frequency domain. For instance, when the phase difference is changed, both pulse shapes’ and corresponding optical spectra’s peak intensities will have a sudden change when the orthogonal phase difference is π/2. These simulation results provide a beneficial reference value for extra-cavity shaping of different solitons that come from nonlinear optical systems. Optimally, the reported results could pave the groundwork for industrial growth in ultrafast laser design. Full article

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

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12 pages, 1342 KiB

Open AccessArticle

Diffraction Losses in a Stack of Diamond X-Ray Lenses

by Nataliya Klimova and Anatoly Snigirev

Photonics 2024, 11(12), 1097; https://doi.org/10.3390/photonics11121097 - 21 Nov 2024

Viewed by 253

Abstract

Compound refractive lenses, crafted from single-crystal materials like diamond and silicon, are increasingly favored, particularly in cutting-edge facilities, such as free electron lasers and fourth-generation synchrotrons. These lenses are prized for their low parasitic scattering and resistance to significant radiation doses over extended [...] Read more.

Compound refractive lenses, crafted from single-crystal materials like diamond and silicon, are increasingly favored, particularly in cutting-edge facilities, such as free electron lasers and fourth-generation synchrotrons. These lenses are prized for their low parasitic scattering and resistance to significant radiation doses over extended periods. However, they do encounter a notable drawback known as the “glitch effect”, wherein undesired diffraction can occur across various X-ray energies. This phenomenon leads to a decrease in transmitted intensity, impacting experiments, particularly in spectroscopy. Typically, a series of lenses is employed to achieve optimal beam parameters, and each lens has its own spectrum of glitches. This paper presents experimentally measured glitches in stacks of 1, 4, 8, and 16 diamond compound refractive lenses, elucidating the theory behind glitch formation and offering strategies to predict and mitigate glitches in diverse focusing systems employing lenses made from single-crystal materials. Full article

(This article belongs to the Special Issue Advances in X-ray Optics for High-Resolution Imaging)

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Photonics, Volume 11, Issue 12 (December 2024) – 12 articles

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