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Asymmetrical Three-Dimensional Conformal Imaging Lens
$Period-Doubling Route to Chaos in Photorefractive Two-Wave Mixing$
Period-Doubling Route to Chaos in Photorefractive Two-Wave Mixing

Journal Description

Photonics

Photonics is an international, scientific, peer-reviewed, open access journal on the science and technology of optics and photonics, published monthly online by MDPI.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, CAPlus / SciFinder, and other databases.
Journal Rank: JCR - Q2 (Optics)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 14.8 days after submission; acceptance to publication is undertaken in 2.6 days (median values for papers published in this journal in the first half of 2024).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Companion journal: Lights.

Impact Factor: 2.1 (2023); 5-Year Impact Factor: 2.1 (2023)

Imprint Information Journal Flyer Open Access ISSN: 2304-6732

Latest Articles

15 pages, 814 KiB

Open AccessArticle

The Application of Digital Holographic Speckle Pattern Interferometry to the Structural Condition Study of a Plaster Sample

by Kyriaki Kosma and Vivi Tornari

Photonics 2024, 11(9), 894; https://doi.org/10.3390/photonics11090894 (registering DOI) - 23 Sep 2024

We use non-destructive Digital Holographic Speckle Pattern Interferometry (DHSPI), post-processing image analysis and one-dimensional exponential analysis to visualize, map and describe the structural condition of a plaster-based material. The body is heated by infrared radiation for two different time windows and the cooling [...] Read more.

We use non-destructive Digital Holographic Speckle Pattern Interferometry (DHSPI), post-processing image analysis and one-dimensional exponential analysis to visualize, map and describe the structural condition of a plaster-based material. The body is heated by infrared radiation for two different time windows and the cooling process that follows is monitored in time by the so-called interferograms that are developed and are the result of the superposition of the holographic recordings of the sample prior to the thermal load and at variable time intervals during the cooling process. The fringe patterns in the interferometric images reveal features and characteristics of the interior of the material, with the experimental method and the post-process analysis adopted in this work offering accuracy, sensitivity and full-field diagnosis, in a completely non-destructive manner, without the need of sampling. Full article

(This article belongs to the Special Issue Advances in Holography and Its Applications)

18 pages, 24192 KiB

Open AccessArticle

Attenuation Characteristics of a 905-nm Pulsed Laser for Short-Range Transmission in Snowfall Environments

by Miaomiao Chen, Lin Gan, He Zhang and Changkun Ke

Photonics 2024, 11(9), 893; https://doi.org/10.3390/photonics11090893 (registering DOI) - 23 Sep 2024

Aiming at the problems of power attenuation and spot expansion of pulsed laser transmission in snowfall environments, based on ray scattering and Fraunhofer diffraction theories, a model of laser transmission attenuation in snowfall environments is established. The model considers the influence of multiple [...] Read more.

Aiming at the problems of power attenuation and spot expansion of pulsed laser transmission in snowfall environments, based on ray scattering and Fraunhofer diffraction theories, a model of laser transmission attenuation in snowfall environments is established. The model considers the influence of multiple scattering effects by introducing a forward correction coefficient. The Monte Carlo multiple scattering model was used to numerically simulate the attenuation characteristics of a 905-nm pulsed laser in snowfall environments, and an experimental platform for the attenuation characteristics was constructed. The experimental, simulation, and theoretical results show that, in three snowfall environments of 0 < SR < 1, 1 < SR < 2, and 2 < SR < 3, the laser transmittance decreases with the increase of transmission distance, and when the transmission distance is the same, the laser transmittance decreases with the increase in snowfall rate. The influence of transmission distance, simulated photon number, and asymmetry factor on spot extension was studied. The simulation results show that the spot radius increases with the increase in transmission distance, remains almost constant with the increase in the simulated photon number, and decreases with the increase in the asymmetry factor in three snowfall environments. Full article

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

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23 pages, 7922 KiB

Open AccessArticle

Development of Miniaturised Fibre-Optic Laser Doppler Velocimetry for Opaque Liquid: Measurement of the Velocity Profile in the Engine Oil Flow of a Lubrication System

by Tsutomu Tajikawa, Shimpei Kohri, Taiki Mouri, Takaichi Fujimi, Hiromasa Yamaguchi and Kenkichi Ohba

Photonics 2024, 11(9), 892; https://doi.org/10.3390/photonics11090892 (registering DOI) - 22 Sep 2024

This study developed a fibre-optic laser Doppler velocimetry sensor for use in opaque, high-temperature, and high-pressure fluid flows by inserting the fibre perpendicular to the main flow. The tip of the optical fibre was obliquely polished and chemically etched using a buffered hydrofluoric [...] Read more.

This study developed a fibre-optic laser Doppler velocimetry sensor for use in opaque, high-temperature, and high-pressure fluid flows by inserting the fibre perpendicular to the main flow. The tip of the optical fibre was obliquely polished and chemically etched using a buffered hydrofluoric acid solution, and a reflective mirror was deposited on the surface of the oblique fibre tip. Based on the results of the verification test using the rotating annular open channel, the fabrication conditions of the fibre tip were optimized for measuring the lubricating oil flow. The flow velocity profiles in the engine’s oil flow of the lubrication system during engine bench testing were measured. These velocity profiles were influenced by variations in the measurement position, oil temperature, and engine speed. The measurement accuracy of this sensor was compared with the volumetric flow rate obtained by cross-sectional area integration of the flow velocity profile, as measured using a Coriolis flowmeter, and the difference was within 1%. By combining computational simulation for flow and optical attenuation and particle scattering in light transmission through a working fluid, this fibre-optic sensor achieved a measurement volume of 200 microns in length and 200 microns in width at a distance of 900–1000 microns from the sensor. Full article

(This article belongs to the Special Issue Science and Applications of Optical Fiber Sensors: Recent Advances and Future Trends)

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18 pages, 18137 KiB

Open AccessArticle

Characterizing Normal and Tumour Blood Microcirculatory Systems Using Optical Coherence Tomography

by Héctor A. Contreras-Sánchez, William Jeffrey Zabel, Costel Flueraru, Lothar Lilge, Edward Taylor and Alex Vitkin

Photonics 2024, 11(9), 891; https://doi.org/10.3390/photonics11090891 (registering DOI) - 21 Sep 2024

Blood vessels transport blood and deliver essential molecules to cells. In cancer, the tumour vasculature evolves very differently from healthy tissue, not only in morphology but also in functionality. Comprehensive 3D in vivo imaging of the tumour microcirculatory system thus might lead to [...] Read more.

Blood vessels transport blood and deliver essential molecules to cells. In cancer, the tumour vasculature evolves very differently from healthy tissue, not only in morphology but also in functionality. Comprehensive 3D in vivo imaging of the tumour microcirculatory system thus might lead to a clearer understanding of the vascular role in tumour growth and response to cancer therapy. Here, we employed two optical coherence tomography (OCT) extensions, speckle-variance and Doppler, to study the microvascular architecture and blood flow in normal murine and xenograft tumour tissue. We explored the biophysics of blood flow in microcirculation and extracted relevant quantification features such as vessel diameters and velocity histograms, and combined diameter–velocity plots. It was demonstrated that tumour microcirculation evolves in time and differs from healthy tissue, impacting tumour growth kinetics. This proof-of-principle study demonstrates the potential of OCT to provide an understanding of the temporal evolution of the tumour vasculature and its relationship with tumour development. Full article

(This article belongs to the Special Issue OCT Technology Advances and Their Applications in Disease Studies)

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10 pages, 4214 KiB

Open AccessArticle

SBS Mitigation by Manipulating the Injecting Polarization Direction in a High-Power Monolithic PM Amplifier

by Yu Wen, Chun Zhang, Chenxu Liu, Qiuhui Chu, Lingli Huang, Yuan Zhu, Haoyu Zhang, Rumao Tao, Honghuan Lin and Jianjun Wang

Photonics 2024, 11(9), 890; https://doi.org/10.3390/photonics11090890 (registering DOI) - 21 Sep 2024

The polarization direction-dependent SBS threshold was investigated, and the terminal polarization control technique was demonstrated to restore the linear polarization state. By increasing the relative angle of the injecting polarization direction from 0° to 90°, the measured SBS threshold increased until reaching a [...] Read more.

The polarization direction-dependent SBS threshold was investigated, and the terminal polarization control technique was demonstrated to restore the linear polarization state. By increasing the relative angle of the injecting polarization direction from 0° to 90°, the measured SBS threshold increased until reaching a maximum value, beyond which it decreased in a nearly symmetrical trend. The highest SBS threshold was achieved with the relative polarization angle being 45°, delivering a 67% threshold enhancement compared with that at 0°. A quarter-wave-plate was used to restore the polarization state of the output laser manually from an elliptic to a linearly polarized state, and temperature-dependent polarization fluctuation was observed, which intensified as the laser power was scaled. By reducing the cooling temperature, a 1 kW laser with a linearly polarized state was demonstrated using a 45° polarization direction-injected monolithic PM amplifier. Full article

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

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13 pages, 2967 KiB

Open AccessArticle

Multi-Fresnel-Lens Pumping Approach for Simultaneous Emission of Seven TEM₀₀-Mode Beams with 3.73% Conversion Efficiency

by Hugo Costa, Dawei Liang, Ana Matos and Joana Almeida

Photonics 2024, 11(9), 889; https://doi.org/10.3390/photonics11090889 (registering DOI) - 20 Sep 2024

TEM₀₀-mode operation is a requirement in many laser-based applications due to the small divergence and high-power density of the emitted laser beam. A solar laser scheme was designed and numerically studied with the goal of increasing the solar-to-laser power conversion efficiency [...] Read more.

TEM₀₀-mode operation is a requirement in many laser-based applications due to the small divergence and high-power density of the emitted laser beam. A solar laser scheme was designed and numerically studied with the goal of increasing the solar-to-laser power conversion efficiency in the TEM₀₀-mode operation. The collection and primary concentration of sunlight was performed via twelve sets of folding mirrors and Fresnel lenses, toward a laser head composed of a fused silica torus volume and seven Ce:Nd:YAG rods, in a side-pump configuration. With this scheme, TEM₀₀-mode laser power totaling 212.39 W could potentially be produced from seven beams, with six of them being 32.60 W each and with

M_{x}^{2}

= 1.00,

M_{y}^{2}

= 1.01 quality factors. Notably, 35.40 W/m² collection efficiency and, most importantly, 3.73% solar-to-laser power conversion efficiency were numerically achieved. The latter efficiency value represents a 1.81-time improvement over the experimental record, established with a prototype that had a single Ce:Nd:YAG rod in an end-side pump configuration. Full article

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

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13 pages, 4334 KiB

Open AccessArticle

Iron-Modified Nano-TiO₂: Comprehensive Characterization for Enhanced Photocatalytic Properties

by Élida M. Margalho, Orlando Lima, Jr., Cátia Afonso, Iran Rocha Segundo, Salmon Landi, Jr., Elisabete Freitas, Manuel F. M. Costa and Joaquim Carneiro

Photonics 2024, 11(9), 888; https://doi.org/10.3390/photonics11090888 (registering DOI) - 20 Sep 2024

This study investigates the effect of iron-modified nano-TiO₂, using the co-precipitation method with different concentrations of FeCl₃ (0.1, 1, and 10%), to improve its photocatalytic properties for outdoor applications. To this end, modified and unmodified nano-TiO₂ were characterized using [...] Read more.

This study investigates the effect of iron-modified nano-TiO₂, using the co-precipitation method with different concentrations of FeCl₃ (0.1, 1, and 10%), to improve its photocatalytic properties for outdoor applications. To this end, modified and unmodified nano-TiO₂ were characterized using different techniques. The optical properties were characterized by diffuse reflectance spectroscopy (DRS) followed by band gap calculation. X-ray diffraction (XRD) was used to analyze the crystalline structure. Chemical and morphological characterization were carried out using energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). The photocatalytic activity was investigated by decolorizing Rhodamine B aqueous solutions under similar sunlight irradiation. The results indicate that the modification improved light absorption in the UV range for all iron concentrations; however, only the concentration of TiO₂: FeCl₃ (10%) shifted the absorption to the visible region. Also, including Fe³⁺ in TiO₂ decreased the band gap energy from 3.14 to up to 2.80 eV. There were variations in crystallite size from 21.13 to up to 40.07 nm. The nano-TiO₂ morphology analysis showed that it did not change after iron modification. EDS showed an FeCl₃ peak only at higher concentrations (10%). In addition, the 0.1% Fe-modified TiO₂ exhibited the highest activity in the photocatalytic process, with an efficiency of 95.23% after 3 h of irradiation. Full article

(This article belongs to the Special Issue Current Advances on Applications of Optics and Photonics – Selected Papers from the 6th International Conference on Applications of Optics and Photonics, AOP2024)

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12 pages, 3246 KiB

Open AccessArticle

Long-Range Imaging through Scattering Media Using Deep Learning

by Ying Jin, Cangtao Zhou and Wanjun Dai

Photonics 2024, 11(9), 887; https://doi.org/10.3390/photonics11090887 (registering DOI) - 20 Sep 2024

Imaging through scattering media is an important and challenging problem, and the technology has been used in many fields, such as autonomous driving, industrial inspections, remote sensing imaging, and biomedical imaging. However, most of the previous experiments used numbers or letters for close-range [...] Read more.

Imaging through scattering media is an important and challenging problem, and the technology has been used in many fields, such as autonomous driving, industrial inspections, remote sensing imaging, and biomedical imaging. However, most of the previous experiments used numbers or letters for close-range imaging, while objects in life are colorful. In this study, a new deep learning network, DesUNet, was constructed to image realistic objects at medium and long distances under sunlight through scattering media, and to realize object recognition. In addition, this study also compares the imaging results of different neural networks, and the results show that the DesUNet network improves the feature information storage ability and enhances the image reconstruction. It not only clearly restores the original appearance of the object, but also extracts the physical information about the object. In order to further verify the power of the DesUNet network, this study also conducted indoor near distance and outdoor medium distance imaging experiments. For indoor reconstructed objects, the appearance of the objects could be clearly identified. For outdoor reconstructed objects, the confidence level could reach above 0.9 through YOLO. The experiments show that the DesUNet network has good robustness and generalization. Full article

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11 pages, 3871 KiB

Open AccessArticle

A Bidirectional Mode-Locked Fiber Laser for Asynchronous Noise-like Pulse Generation

by Yongguo Zheng, Anshuang Wang, Yue Cai, Fan Zhang and Xinhai Zhang

Photonics 2024, 11(9), 886; https://doi.org/10.3390/photonics11090886 (registering DOI) - 20 Sep 2024

We demonstrate a bidirectional fiber laser with an artificial saturable absorber of a step-index multimode fiber sandwiched by single-mode fibers. Two asynchronous noise-like pulse sequences with a repetition frequency difference of 3.16 kHz are obtained. The average power of the bidirectional asynchronous noise-like [...] Read more.

We demonstrate a bidirectional fiber laser with an artificial saturable absorber of a step-index multimode fiber sandwiched by single-mode fibers. Two asynchronous noise-like pulse sequences with a repetition frequency difference of 3.16 kHz are obtained. The average power of the bidirectional asynchronous noise-like pulses is greater than 36 mW, and the pulse energy is greater than 3 nJ. The laser we demonstrate has potential applications in micromachining, supercontinuum spectrum generation, and signal processing. Full article

(This article belongs to the Special Issue Nonlinear Optics and Hyperspectral Polarization Imaging)

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14 pages, 3284 KiB

Open AccessArticle

Low Complexity Parallel Carrier Frequency Offset Estimation Based on Time-Tagged QPSK Partitioning for Coherent Free-Space Optical Communication

by Siqi Zhang, Liqian Wang, Kunfeng Liu and Shuang Ding

Photonics 2024, 11(9), 885; https://doi.org/10.3390/photonics11090885 (registering DOI) - 20 Sep 2024

To effectively mitigate the effects of atmospheric turbulence in free space optical (FSO) communication, we propose a parallel carrier frequency offset estimation (FOE) scheme based on time-tagged QPSK partitioning (TTQP). This scheme can be applied to spatial diversity polarization multiplexing (PM) coherent FSO [...] Read more.

To effectively mitigate the effects of atmospheric turbulence in free space optical (FSO) communication, we propose a parallel carrier frequency offset estimation (FOE) scheme based on time-tagged QPSK partitioning (TTQP). This scheme can be applied to spatial diversity polarization multiplexing (PM) coherent FSO communication systems. Specifically, the TTQP scheme performs QPSK partitioning by time-tagging signal points, accurately recording the time intervals between signals, and significantly reducing implementation complexity through a modified Mth power algorithm. The simulation results for the PM 16-quadrature amplitude modulation (QAM) validate the effectiveness of the proposed scheme. Compared to traditional QPSK partitioning algorithms, the TTQP algorithm achieves high accuracy, low complexity, and multi-format versatility in high-speed coherent FSO communication. Full article

(This article belongs to the Special Issue Challenges and Opportunities in Free Space Optical Communication)

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9 pages, 2402 KiB

Open AccessCommunication

Study on the Influence of Atmospheric Light Intensity Scintillation Effect on Optical Fiber Coupling Efficiency

by Xiaoying Ding and Xin Zhao

Photonics 2024, 11(9), 884; https://doi.org/10.3390/photonics11090884 (registering DOI) - 20 Sep 2024

Light intensity flicker is the most basic and important effect of turbulence. Fiber coupling efficiency is the primary parameter that ensures the system’s communication quality. The light intensity flicker effect caused by atmospheric turbulence significantly affects the coupling efficiency of space light in [...] Read more.

Light intensity flicker is the most basic and important effect of turbulence. Fiber coupling efficiency is the primary parameter that ensures the system’s communication quality. The light intensity flicker effect caused by atmospheric turbulence significantly affects the coupling efficiency of space light in a single-mode optical fiber. Based on the principle of fiber coupling efficiency, this paper first establishes the relationship between light intensity flicker and spatial coherence radius, then analyzes the influence of light intensity flicker on fiber coupling efficiency through the spatial coherence radius. A laser communication system was built, and real-time measurement experiments on atmospheric light intensity flicker and optical fiber coupling efficiency at different transmission distances and altitudes above the ground were completed. The experimental results show that the constructed experimental system can simultaneously measure the scintillation index and fiber coupling efficiency. When the communication distance is 12,000 m and the height is 600 m above the ground, the scintillation index is measured to be 0.63, and the coupling efficiency is 0.05. The results of the study provide an experimental and theoretical basis and data support to promote the development of atmospheric laser communications. Full article

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

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14 pages, 841 KiB

Open AccessArticle

A Closed-Form Analytical Conversion between Zernike and Gatinel–Malet Basis Polynomials to Present Relevant Aberrations in Ophthalmology and Refractive Surgery

by Masoud Mehrjoo, Damien Gatinel, Jacques Malet and Samuel Arba Mosquera

Photonics 2024, 11(9), 883; https://doi.org/10.3390/photonics11090883 (registering DOI) - 20 Sep 2024

The Zernike representation of wavefronts interlinks low- and high-order aberrations, which may result in imprecise clinical estimates. Recently, the Gatinel–Malet wavefront representation has been introduced to resolve this problem by deriving a new, unlinked basis originating from Zernike polynomials. This new basis preserves [...] Read more.

The Zernike representation of wavefronts interlinks low- and high-order aberrations, which may result in imprecise clinical estimates. Recently, the Gatinel–Malet wavefront representation has been introduced to resolve this problem by deriving a new, unlinked basis originating from Zernike polynomials. This new basis preserves the classical low and high aberration subgroups’ structure, as well as the orthogonality within each subgroup, but not the orthogonality between low and high aberrations. This feature has led to conversions relying on separate wavefront reconstructions for each subgroup, which may increase the associated numerical errors. This study proposes a robust, minimised-error (lossless) analytical approach for conversion between the Zernike and Gatinel–Malet spaces. This method analytically reformulates the conversion as a nonhomogeneous system of linear equations and computationally solves it using matrix factorisation and decomposition techniques with high-level accuracy. This work fundamentally demonstrates the lossless expression of complex wavefronts in a format that is more clinically interpretable, with potential applications in various areas of ophthalmology, such as refractive surgery. Full article

(This article belongs to the Special Issue Visual Optics)

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10 pages, 6069 KiB

Open AccessArticle

Robust Sensing Based on Exceptional Points in Detuned Non-Hermitian Scattering System

by Jipeng Xu, Yuanhao Mao, Ken Liu and Zhihong Zhu

Photonics 2024, 11(9), 882; https://doi.org/10.3390/photonics11090882 - 20 Sep 2024

Non-Hermitian optics has revealed a series of counterintuitive phenomena with profound implications for sensing, lasing, and light manipulation. While the non-Hermiticity of Hamiltonians has been intensively investigated, recent advancements in the non-Hermitian scattering matrix have given birth to a lot of unique phenomena, [...] Read more.

Non-Hermitian optics has revealed a series of counterintuitive phenomena with profound implications for sensing, lasing, and light manipulation. While the non-Hermiticity of Hamiltonians has been intensively investigated, recent advancements in the non-Hermitian scattering matrix have given birth to a lot of unique phenomena, such as simultaneous lasing and anti-lasing, reflectionless scattering modes (RSMs), and coherent chaos control. Despite these developments, the investigation has predominantly focused on static and symmetric configurations, leaving the dynamic properties of non-Hermitian scattering in detuned systems, which is essential for applications in sensing and beyond, largely unexplored. Here, we extend the stationary behaviors associated with the RSMs to resonant detuned systems. Contrary to the common belief of exceptional point (EP) sensors as being susceptible to parametric disturbances, we induce an RSM EP in a one-dimensional optical cavity and demonstrate its robustness in displacement sensing against laser frequency drifts up to 10 MHz. Our findings not only contribute to the broader understanding of non-Hermitian scattering phenomena but also pave the way for the next generation of non-Hermitian sensors. Full article

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

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13 pages, 3642 KiB

Open AccessArticle

A Fast Solution of the Dynamic Rate Equation for a High-Power Fiber Laser

by Lei Duan, Runqin Xu, Shudan Tan, Xiongxin Tang and Fanjiang Xu

Photonics 2024, 11(9), 881; https://doi.org/10.3390/photonics11090881 - 19 Sep 2024

In the study of dynamic behaviors, such as nonlinear effects, power evolution, and pulse evolution of light in fiber gain media, solving dynamic rate equations in fiber laser systems is involved, which is computationally intensive and directly affects overall computational efficiency. A modified [...] Read more.

In the study of dynamic behaviors, such as nonlinear effects, power evolution, and pulse evolution of light in fiber gain media, solving dynamic rate equations in fiber laser systems is involved, which is computationally intensive and directly affects overall computational efficiency. A modified difference scheme is proposed to solve fiber dynamic rate equations efficiently. The advantages of the improved scheme and its convergence rate are analyzed. By incorporating a correction coefficient into the finite difference, the approximations of spatial and temporal derivatives are improved, greatly enhancing the performance of the numerical method. The computational results of the proposed method are compared with those of the conventional upwind difference scheme, demonstrating that the improved method is more stable and requires fewer sampling points to maintain a certain level of precision, thereby saving significant computation time and computational resources. The power and spectral evolutions of the fiber laser oscillator under different pump conditions are simulated and compared with experimental data, validating the applicability and reliability of the rapid solving method. Full article

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

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8 pages, 956 KiB

Open AccessCommunication

Quality Assessment of Perovskite Solar Cells: An Industrial Point of View

by Nicolò Lago, Francesco Moretti, Noah Tormena, Alessandro Caria, Matteo Buffolo, Carlo De Santi, Nicola Trivellin, Andrea Cester, Gaudenzio Meneghesso, Enrico Zanoni, Matteo Meneghini, Fabio Matteocci, Jessica Barichello, Luigi Vesce, Aldo Di Carlo and Federico Quartiani

Photonics 2024, 11(9), 880; https://doi.org/10.3390/photonics11090880 - 19 Sep 2024

The mass production of photovoltaic (PV) devices requires fast and reliable characterization methods and equipment. PV manufacturers produce a complete module roughly every 20 s, and the electrical performance assessment is typically completed in less than 1 s. Times are even more stringent [...] Read more.

The mass production of photovoltaic (PV) devices requires fast and reliable characterization methods and equipment. PV manufacturers produce a complete module roughly every 20 s, and the electrical performance assessment is typically completed in less than 1 s. Times are even more stringent during cell manufacturing. To be competitive in the PV market, perovskite solar cells and modules aim to the same target, i.e., fast and reliable quality assessment. This communication report discusses the limit of characterizing the current perovskite technology. Standard current vs voltage measurements are compared to maximum power point tracking (MPPT), and a fast MPPT procedure is developed to meet the highly demand standard for quality control in the industry of PV production. Full article

(This article belongs to the Special Issue Advances in Perovskite Solar Cells)

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7 pages, 2081 KiB

Open AccessCommunication

Improving the Performance of Bidirectional Communication System Using Second-Order Raman Amplifiers

by Zhongshuai Feng, Peili He, Wei Li, Kaijing Hu, Fei Tong and Xingrui Su

Photonics 2024, 11(9), 879; https://doi.org/10.3390/photonics11090879 - 19 Sep 2024

In order to achieve low-cost scalability, the same-wavelength bidirectional (SWB) fiber communication system is a better solution. We present a detailed investigation of the performance of the different orders Raman amplifiers in same-wavelength bidirectional fiber communication systems. We discuss how to suppress the [...] Read more.

In order to achieve low-cost scalability, the same-wavelength bidirectional (SWB) fiber communication system is a better solution. We present a detailed investigation of the performance of the different orders Raman amplifiers in same-wavelength bidirectional fiber communication systems. We discuss how to suppress the main factor affecting system performance which is Rayleigh scattering noise (RSN). By using different Raman amplifiers to construct different quasi-lossless transmission, the performance changes in the same-wavelength bidirectional fiber optic communication system were studied. On this basis, multi-channel and same-wavelength single fiber bidirectional system experiments were conducted to compare the performance of second-order Raman systems and first-order Raman systems. The results indicate that the Rayleigh scattering suppression effect of second-order Raman systems is better, and compared to first-order Raman systems, the average signal-to-noise ratio (SNR) can be increased by 2.88 dB. Full article

(This article belongs to the Special Issue Advancements in Optical Sensing and Communication Technologies)

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16 pages, 7263 KiB

Open AccessArticle

Asymmetric Optical Scanning Holography Encryption with Elgamal Algorithm

by Chunying Wu, Yinggang Ding, Aimin Yan, Ting-Chung Poon and Peter Wai Ming Tsang

Photonics 2024, 11(9), 878; https://doi.org/10.3390/photonics11090878 - 19 Sep 2024

This paper proposes an asymmetric scanning holography cryptosystem based on the Elgamal algorithm. The method encodes images with sine and cosine holograms. Subsequently, each hologram is divided into a signed bit matrix and an unsigned hologram matrix, both encrypted using the sender’s private [...] Read more.

This paper proposes an asymmetric scanning holography cryptosystem based on the Elgamal algorithm. The method encodes images with sine and cosine holograms. Subsequently, each hologram is divided into a signed bit matrix and an unsigned hologram matrix, both encrypted using the sender’s private key and the receiver’s public key. The resulting ciphertext matrices are then transmitted to the receiver. Upon receipt, the receiver decrypts the ciphertext matrices using their private key and the sender’s public key. We employ an asymmetric single-image encryption method for key management and dispatch for securing imaging and transmission. Furthermore, we conducted a sensitivity analysis of the encryption system. The image encryption metrics, including histograms of holograms, adjacent pixel correlation, image correlation, the peak signal-to-noise ratio, and the structural similarity index, were also examined. The results demonstrate the security and stability of the proposed method. Full article

(This article belongs to the Special Issue Holographic Information Processing)

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9 pages, 3631 KiB

Open AccessArticle

Kilowatt-Level High-Efficiency Narrow-Linewidth All-Fiber Tm³⁺-Doped Laser

by Hongyu Wang, Qilai Zhao, Hang Liu, Yuxin Sun, Jialong Li, Junjie Zheng, Ye Yuan, Qianwen Zhang, Changsheng Yang, Yujun Feng, Yinhong Sun, Zhongmin Yang and Shanhui Xu

Photonics 2024, 11(9), 877; https://doi.org/10.3390/photonics11090877 - 19 Sep 2024

In this study, a kilowatt-level high-efficiency narrow-linewidth all-fiber Tm³⁺-doped continuous-wave laser operating at 1.95 μm is demonstrated. Benefitting from an advanced boost design of a two-stage main amplifier, it not only effectively manages heat dissipation resulting from the high pump-induced quantum [...] Read more.

In this study, a kilowatt-level high-efficiency narrow-linewidth all-fiber Tm³⁺-doped continuous-wave laser operating at 1.95 μm is demonstrated. Benefitting from an advanced boost design of a two-stage main amplifier, it not only effectively manages heat dissipation resulting from the high pump-induced quantum defect but also realizes the controlled extraction of optical gain and improves the optical conversion efficiency. Finally, this laser system has realized an output power of 1018 W, a linewidth of 3.8 GHz, and a slope efficiency of 60.0% simultaneously. Moreover, a high optical signal-to-noise ratio of over 45 dB and excellent beam quality of M² factors 1.19 are obtained. To the best of our knowledge, this represents the narrowest linewidth and highest slope efficiency achieved in a kilowatt-level Tm³⁺-doped fiber laser. Such a high-performance laser is ideally suited for mid-infrared generation and remote sensing applications. Full article

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

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11 pages, 4907 KiB

Open AccessArticle

The Correction Method for Wavefront Aberration Caused by Spectrum-Splitting Filters in Multi-Modal Optical Imaging System

by Xiaolin Liu, Ying Huang, Xu Yan, Li Wang, Qiang Li, Tingcheng Zhang, Bin Hu, Wenping Lei, Shengbo Mu and Xiaohong Zhang

Photonics 2024, 11(9), 876; https://doi.org/10.3390/photonics11090876 - 19 Sep 2024

In current biomedical and environmental detection, multi-modal optical imaging technology is playing an increasingly important role. By utilizing information from dimensions such as spectra and polarization, it reflects the detailed characteristics and material properties of the targets. However, as detection system performance becomes [...] Read more.

In current biomedical and environmental detection, multi-modal optical imaging technology is playing an increasingly important role. By utilizing information from dimensions such as spectra and polarization, it reflects the detailed characteristics and material properties of the targets. However, as detection system performance becomes more complex, issues such as aberrations introduced by multilayered lenses, signal attenuation, decreased polarization sensitivity, and latency can no longer be ignored. These factors directly affect the assessment of image details, influencing subsequent analyses. In this paper, we propose a method for designing and optimizing spectrum-splitting filters that considers the wavefront aberration and transmittance of the multi-modal optical imaging system. The method of optimizing coating phases to minimize scalar phase aberrations while maximizing system transmission leads to substantially improved imaging performance. Simulation and experimental results demonstrate that the method can improve the imaging performance. The proposed approach has potential applications in fields such as biomedical field, multi-spectral, remote sensing and microscopy. Full article

(This article belongs to the Special Issue Optical Technologies for Biomedical Science)

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13 pages, 5982 KiB

Open AccessArticle

Comparative Study on the Interest in Non-Uniform Rational B-Splines Representation versus Polynomial Surface Description in a Freeform Three-Mirror Anastigmat

by Clément Freslier, Guillaume Druart, Alice Fontbonne, Thierry Lépine, Christophe Buisset, Tibor Agocs, Arnaud Heliere, Fanny Keller, Jean-Baptiste Volatier, Stéphane Beaussier and Paul Jougla

Photonics 2024, 11(9), 875; https://doi.org/10.3390/photonics11090875 - 18 Sep 2024

Novel freeform optical design methods can be classified in two categories, depending on whether they focus on the generation of a starting point or the development of new optimization tools. In this paper, we design a freeform three-mirror anastigmat (TMA) and compare different [...] Read more.

Novel freeform optical design methods can be classified in two categories, depending on whether they focus on the generation of a starting point or the development of new optimization tools. In this paper, we design a freeform three-mirror anastigmat (TMA) and compare different surface representations using either a differential ray tracer as a new optimization tool or a commercial ray tracer (ANSYS-ZEMAX OpticStudio). For differential ray tracing, we used FORMIDABLE (Freeform Optics Raytracer with Manufacturable Imaging Design cApaBiLitiEs), an optical design library with differential ray tracing and Non-Uniform Rational B-Splines (NURBS) optimization capabilities, available under the European Software Community License (ESCL). NURBS allow a freeform surface to be represented without needing any prior knowledge of the surface, such as the polynomial degree in polynomial descriptions. OpticStudio and other commercial optical design software are designed to optimize polynomial surfaces but are not well-suited to optimize NURBS surfaces, requiring a custom optical design library. In order to demonstrate the interest in using NURBS representation, we designed and independently optimized two freeform telescopes over different iteration cycles; with NURBS using FORMIDABLE or with XY polynomials using OpticStudio. We then compared the resulting systems using their root mean square field maps to assess the optimization quality of each surface representation. We also provided a full-system comparison, including mirror freeform departures. This study shows that NURBS can be a relevant alternative to XY polynomials for the freeform optimization of reflective three-mirror telescopes as it achieves more a uniform imaging quality in the field of view. Full article

(This article belongs to the Special Issue New Advances in Freeform Optics Design)

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