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Photonics
Volume 11
Issue 9
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Photonics, Volume 11, Issue 9 (September 2024) – 113 articles

Cover Story (view full-size image): SU-8 is an emerging polymer material for integrated optical circuits working in cryogenic environments. We investigated the thermo-optical properties of SU-8 at the wavelength λ = 850 nm, from room temperature down to 14 K. To measure the material properties, we designed and fabricated SU-8 racetrack resonators via electron beam lithography. We measured the resonance spectrum as a function of the temperature, from which we determined the temperature-induced variations in the effective and group indexes of the waveguide. With the aid of eigenmode simulations, we derived the temperature dependence of the SU-8 refractive index. At T~295 K, the thermo-optic coefficient is dnSU−8/dT = −5.3 ± 0.2 × 10−5 K−1. At T~14 K, dnSU−8/dT = −1.27 ± 0.05 × 10−4 K−1. Our research shows the potential of using SU-8 photonics within cryogenic environments. View this paper
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15 pages, 2894 KiB  
Article
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 - 23 Sep 2024
Viewed by 956
Abstract
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)
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18 pages, 24192 KiB  
Article
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 - 23 Sep 2024
Viewed by 838
Abstract
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  
Article
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 - 22 Sep 2024
Viewed by 908
Abstract
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  
Article
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 - 21 Sep 2024
Cited by 1 | Viewed by 4878
Abstract
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  
Article
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 - 21 Sep 2024
Viewed by 841
Abstract
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  
Article
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 - 20 Sep 2024
Cited by 1 | Viewed by 688
Abstract
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 Mx2 = 1.00, My2 = 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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12 pages, 4334 KiB  
Article
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 - 20 Sep 2024
Cited by 1 | Viewed by 740
Abstract
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  
Article
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 - 20 Sep 2024
Viewed by 1183
Abstract
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  
Article
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 - 20 Sep 2024
Cited by 1 | Viewed by 802
Abstract
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  
Article
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 - 20 Sep 2024
Viewed by 862
Abstract
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  
Communication
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 - 20 Sep 2024
Viewed by 770
Abstract
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  
Article
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 - 20 Sep 2024
Cited by 1 | Viewed by 1264
Abstract
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  
Article
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
Viewed by 913
Abstract
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  
Article
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
Viewed by 985
Abstract
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  
Communication
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
Cited by 1 | Viewed by 1091
Abstract
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  
Communication
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
Viewed by 741
Abstract
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  
Article
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
Cited by 1 | Viewed by 1040
Abstract
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  
Article
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
Cited by 1 | Viewed by 1020
Abstract
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  
Article
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
Cited by 1 | Viewed by 890
Abstract
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  
Article
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
Viewed by 1062
Abstract
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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20 pages, 11342 KiB  
Article
Accurate Inspection and Super-Resolution Reconstruction for Additive Manufactured Defects Based on Stokes Vector Method and Deep Learning
by Shangrongxi Sun, Xing Peng and Hongbing Cao
Photonics 2024, 11(9), 874; https://doi.org/10.3390/photonics11090874 - 18 Sep 2024
Cited by 1 | Viewed by 1144
Abstract
Defects in additive manufacturing processes are closely related to the mechanical and physical properties of the components. However, the extreme conditions of high temperatures, intense light, and powder during the manufacturing process present significant challenges for defect detection. Additionally, the high reflectivity of [...] Read more.
Defects in additive manufacturing processes are closely related to the mechanical and physical properties of the components. However, the extreme conditions of high temperatures, intense light, and powder during the manufacturing process present significant challenges for defect detection. Additionally, the high reflectivity of metallic components can cause pixels in image sensors to become overexposed, resulting in the loss of many defect signals. Thus, this paper mainly focuses on proposing an accurate inspection and super-resolution reconstruction method for additive manufactured defects based on Stokes vector and deep learning, where the Stokes vectors, polarization degree, and polarization angles of the inspected defects are effectively utilized to suppress the high reflectivity of metallic surfaces, enhance the contrast of defect regions, and highlight the boundaries of defects. Furthermore, a modified SRGAN model designated SRGAN-H is presented by employing an additional convolutional layer and activation functions, including Harswish and Tanh, to accelerate the convergence of the SRGAN-H network and improve the reconstruction of the additive manufactured defect region. The experiment results demonstrated that the SRGAN-H model outperformed SRGAN and traditional SR reconstruction algorithms in terms of the images of Stokes vectors, polarization degree, and polarization angles. For the scratch and hole test sets, the PSNR values were 33.405 and 31.159, respectively, and the SSIM values were 0.890 and 0.896, respectively. These results reflect the effectiveness of the SRGAN-H model in super-resolution reconstruction of scratch and hole images. For the scratch and hole images chosen in this study, the PSNR values of SRGAN-H for single image super-resolution reconstruction ranged from 31.86786 to 43.82374, higher than the results obtained by the pre-improvement SRGAN algorithm. Full article
(This article belongs to the Special Issue New Perspectives in Optical Design)
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32 pages, 6923 KiB  
Review
A Comprehensive Exploration of Contemporary Photonic Devices in Space Exploration: A Review
by Muhammad A. Butt
Photonics 2024, 11(9), 873; https://doi.org/10.3390/photonics11090873 - 18 Sep 2024
Cited by 1 | Viewed by 2972
Abstract
Photonics plays a pivotal role in propelling space exploration forward, providing innovative solutions to address the challenges presented by the unforgiving and expansive realm of outer space. Photonic-based devices, encompassing technologies such as lasers, optical fibers, and photodetectors, are instrumental in various aspects [...] Read more.
Photonics plays a pivotal role in propelling space exploration forward, providing innovative solutions to address the challenges presented by the unforgiving and expansive realm of outer space. Photonic-based devices, encompassing technologies such as lasers, optical fibers, and photodetectors, are instrumental in various aspects of space missions. A notable application is in communication systems, where optical communication facilitates high-speed data transfer, ensuring efficient transmission of information across vast interplanetary distances. This comprehensive review unveils a selection of the most extensively employed photonic devices within the realm of space exploration. Full article
(This article belongs to the Special Issue Innovations in Optical Wireless Communications: Challenges and Opportunities)
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17 pages, 3138 KiB  
Review
Advances in Photoacoustic Endoscopic Imaging Technology for Prostate Cancer Detection
by Ningning Wei, Huiting Chen, Bin Li, Xiaojun Dong and Bo Wang
Photonics 2024, 11(9), 872; https://doi.org/10.3390/photonics11090872 - 18 Sep 2024
Viewed by 1509
Abstract
The rapid progress in biomedical imaging technology has generated considerable interest in new non-invasive photoacoustic endoscopy imaging techniques. This emerging technology offers significant benefits, including high spectral specificity, strong tissue penetration, and real-time multidimensional high-resolution imaging capabilities, which enhance clinical diagnosis and treatment [...] Read more.
The rapid progress in biomedical imaging technology has generated considerable interest in new non-invasive photoacoustic endoscopy imaging techniques. This emerging technology offers significant benefits, including high spectral specificity, strong tissue penetration, and real-time multidimensional high-resolution imaging capabilities, which enhance clinical diagnosis and treatment of prostate cancer. This paper delivers a thorough review of current prostate cancer screening techniques, the core principles of photoacoustic endoscopy imaging, and the latest research on its use in detecting prostate cancer. Additionally, the limitations of this technology in prostate cancer detection are discussed, and future development trends are anticipated. Full article
(This article belongs to the Special Issue New Perspectives in Biomedical Optics and Optical Imaging)
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44 pages, 4819 KiB  
Review
Photonic Angular Momentum in Intense Light–Matter Interactions
by Alex Schimmoller, Spencer Walker and Alexandra S. Landsman
Photonics 2024, 11(9), 871; https://doi.org/10.3390/photonics11090871 - 17 Sep 2024
Cited by 2 | Viewed by 1661
Abstract
Light contains both spin and orbital angular momentum. Despite contributing equally to the total photonic angular momentum, these components derive from quite different parts of the electromagnetic field profile, namely its polarization and spatial variation, respectively, and therefore do not always share equal [...] Read more.
Light contains both spin and orbital angular momentum. Despite contributing equally to the total photonic angular momentum, these components derive from quite different parts of the electromagnetic field profile, namely its polarization and spatial variation, respectively, and therefore do not always share equal influence in light–matter interactions. With the growing interest in utilizing light’s orbital angular momentum to practice added control in the study of atomic systems, it becomes increasingly important for students and researchers to understand the subtlety involved in these interactions. In this article, we present a review of the fundamental concepts and recent experiments related to the interaction of beams containing orbital angular momentum with atoms. An emphasis is placed on understanding light’s angular momentum from the perspective of both classical waves and individual photons. We then review the application of these beams in recent experiments, namely single- and few-photon transitions, strong-field ionization, and high-harmonic generation, highlighting the role of light’s orbital angular momentum and the atom’s location within the beam profile within each case. Full article
(This article belongs to the Special Issue Optical Vortex: Fundamentals and Applications)
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11 pages, 4746 KiB  
Article
Second-Order Microring Filter with Large Free-Spectral-Range and Wavelength-Tunable-Range over 50 nm
by Jiamei Gu, Shuojian Zhang, Qiongchan Shao, Mingyu Li, Xiao Ma and Jian-Jun He
Photonics 2024, 11(9), 870; https://doi.org/10.3390/photonics11090870 - 16 Sep 2024
Viewed by 894
Abstract
The high-order microring filter has been proposed for a larger free spectral range (FSR) compared with the single microring filter; therefore, it has great potential to be used in wavelength division multiplexing (WDM) systems. In this article, we have designed and fabricated a [...] Read more.
The high-order microring filter has been proposed for a larger free spectral range (FSR) compared with the single microring filter; therefore, it has great potential to be used in wavelength division multiplexing (WDM) systems. In this article, we have designed and fabricated a second-order microring filter made up of two rings connected in series with two Ti thermal heaters deposited above them. The large FSR of 56.8 nm is obtained by decreasing the difference of the radii between the two series rings, achieving similar FSRs to that of higher-order filters but with a simpler and more compact design. The average electrical tuning efficiencies of the two heaters are 0.186 nm/mW and 0.207 nm/mW, and the center wavelength of the filter can be tuned over the entire FSR with an applied electrical power of less than 40 mW. Full article
(This article belongs to the Special Issue Silicon-Based Integrated Optics: From Design to Applications)
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19 pages, 6503 KiB  
Article
Analysis of the Temperature Field Characteristics and Thermal-Induced Errors of Miniature Interferometric Fiber Optic Gyroscopes in a Vacuum Environment
by Zicheng Wang, Xiuwei Xia, Wei Gao and Xiangjun Zhang
Photonics 2024, 11(9), 869; https://doi.org/10.3390/photonics11090869 - 16 Sep 2024
Cited by 1 | Viewed by 3629
Abstract
This paper investigates the mechanism of thermal-induced errors in interferometric fiber optic gyroscopes (IFOGs) caused by temperature changes in a vacuum environment, proposing a method for calculating thermal-induced errors in small fiber coils. Firstly, based on the Shupe effect and the thermal stress [...] Read more.
This paper investigates the mechanism of thermal-induced errors in interferometric fiber optic gyroscopes (IFOGs) caused by temperature changes in a vacuum environment, proposing a method for calculating thermal-induced errors in small fiber coils. Firstly, based on the Shupe effect and the thermal stress caused by temperature changes around the fiber coil, a three-dimensional thermal-induced error model for small fiber coils is established. Secondly, a spatial fiber optic inertial measurement unit (IMU) model is designed using the Creo 3D modeling software (creo 7.0.0). The model is then imported into the Ansys finite element simulation software (ANSYS Workbench 15.0), where a temperature field is applied to the IMU based on actual temperature profiles to obtain the temperature distribution of the fiber coil at different times in a vacuum state. These data are then used in the three-dimensional thermal-induced error model to calculate the thermal-induced error of the FOG. Finally, a thermal vacuum experimental platform is set up to collect temperature variation data from the inertial measurement components. The experimental data are compared with the three-dimensional error model proposed in this paper as well as traditional error models. The root mean square error is approximately 33% lower than that of traditional error calculation methods, which also proves the theoretical accuracy. Full article
(This article belongs to the Special Issue Advances in Optical Fiber Sensing Technology)
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12 pages, 7899 KiB  
Article
A Modified Current-Mode VCSEL Driver for Short-Range LiDAR Sensor Applications in 180 nm CMOS
by Juntong Li, Yeojin Chon, Shinhae Choi and Sung-Min Park
Photonics 2024, 11(9), 868; https://doi.org/10.3390/photonics11090868 - 16 Sep 2024
Viewed by 918
Abstract
This paper presents a modified current-mode vertical-cavity surface-emitting laser (VCSEL) driver as a transmitter for short-range light detection and ranging (LiDAR) sensors, where a stable bias generator is suggested with a regulated cascode current mirror circuit to provide the bias current of 1 [...] Read more.
This paper presents a modified current-mode vertical-cavity surface-emitting laser (VCSEL) driver as a transmitter for short-range light detection and ranging (LiDAR) sensors, where a stable bias generator is suggested with a regulated cascode current mirror circuit to provide the bias current of 1 mA with a trivial deviation of 5.4%, even at the worst-case process–voltage–temperature (PVT) variations. Also, a modified current-steering logic circuit is exploited with N-type MOSFET (NMOS) switches to deliver the modulation currents of 0.1~10 mApp to the VCSEL diode simultaneously, with no overshoot distortions. Post-layout simulations of the modified current-mode VCSEL driver (m-CMVD), using 180 nm CMOS technology, demonstrate very large and clean output pulses with significantly reduced signal distortions. Hereby, the VCSEL diode is transformed into an equivalent circuit with a 1.6 V DC voltage and a 50 Ω resistor for circuit simulations. The proposed m-CMVD consumes a maximum of 11 mW from a 3.3 V supply voltage and the chip core occupies an area of 0.196 mm2. Full article
(This article belongs to the Special Issue Semiconductor Lasers: Innovations, Challenges, and Future Perspectives)
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22 pages, 2851 KiB  
Article
Enhanced Three-Axis Frame and Wand-Based Multi-Camera Calibration Method Using Adaptive Iteratively Reweighted Least Squares and Comprehensive Error Integration
by Oleksandr Yuhai, Yubin Cho, Ahnryul Choi and Joung Hwan Mun
Photonics 2024, 11(9), 867; https://doi.org/10.3390/photonics11090867 - 15 Sep 2024
Viewed by 1035
Abstract
The accurate transformation of multi-camera 2D coordinates into 3D coordinates is critical for applications like animation, gaming, and medical rehabilitation. This study unveils an enhanced multi-camera calibration method that alleviates the shortcomings of existing approaches by incorporating a comprehensive cost function and Adaptive [...] Read more.
The accurate transformation of multi-camera 2D coordinates into 3D coordinates is critical for applications like animation, gaming, and medical rehabilitation. This study unveils an enhanced multi-camera calibration method that alleviates the shortcomings of existing approaches by incorporating a comprehensive cost function and Adaptive Iteratively Reweighted Least Squares (AIRLS) optimization. By integrating static error components (3D coordinate, distance, angle, and reprojection errors) with dynamic wand distance errors, the proposed comprehensive cost function facilitates precise multi-camera parameter calculations. The AIRLS optimization effectively balances the optimization of both static and dynamic error elements, enhancing the calibration’s robustness and efficiency. Comparative validation against advanced multi-camera calibration methods shows this method’s superior accuracy (average error 0.27 ± 0.22 mm) and robustness. Evaluation metrics including average distance error, standard deviation, and range (minimum and maximum) of errors, complemented by statistical analysis using ANOVA and post-hoc tests, underscore its efficacy. The method markedly enhances the accuracy of calculating intrinsic, extrinsic, and distortion parameters, proving highly effective for precise 3D reconstruction in diverse applications. This study represents substantial progression in multi-camera calibration, offering a dependable and efficient solution for intricate calibration challenges. Full article
(This article belongs to the Special Issue Recent Advances in 3D Optical Measurement)
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10 pages, 4066 KiB  
Article
Hunting for Monolayer Black Phosphorus with Photoluminescence Microscopy
by Chenghao Pan, Yixuan Ma, Quan Wan, Boyang Yu, Shenyang Huang and Hugen Yan
Photonics 2024, 11(9), 866; https://doi.org/10.3390/photonics11090866 - 14 Sep 2024
Viewed by 1093
Abstract
Monolayer black phosphorus (BP) holds great promise for naturally hyperbolic polaritons and correlated states in rectangular moiré superlattices. However, preparing and identifying high-quality monolayer BP are challenging due to its instability and high transparency, which limits extensive studies. In this study, we developed [...] Read more.
Monolayer black phosphorus (BP) holds great promise for naturally hyperbolic polaritons and correlated states in rectangular moiré superlattices. However, preparing and identifying high-quality monolayer BP are challenging due to its instability and high transparency, which limits extensive studies. In this study, we developed a method for rapidly and nondestructively identifying monolayer BP and its crystal orientation simultaneously using modified photoluminescence (PL) microscopy. The optical contrast of monolayer BP has been significantly increased by at least twenty times compared to previous reports, making it visible even on a transparent substrate. The polarization dependence of optical contrast also allows for the in situ determination of crystal orientation. Our study facilitates the identification of monolayer BP, expediting more extensive research on and potential industrial applications of this material. Full article
(This article belongs to the Special Issue Recent Advances in Infrared Photodetection and Imaging)
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20 pages, 26165 KiB  
Article
In-Vivo Dosimetry for Ultra-High Dose Rate (UHDR) Electron Beam FLASH Radiotherapy Using an Organic (Plastic), an Organic–Inorganic Hybrid and an Inorganic Point Scintillator System
by Verdi Vanreusel, Hugo Vallet, Jordi Wijnen, Benjamin Côté, Paul Leblans, Paul Sterckx, Dirk Vandenbroucke, Dirk Verellen and Luana de Freitas Nascimento
Photonics 2024, 11(9), 865; https://doi.org/10.3390/photonics11090865 - 13 Sep 2024
Viewed by 1032
Abstract
Dosimetry is crucial in radiotherapy to warrant safe and correct treatment. In FLASH radiotherapy, where ultra-high dose rates (UHDRs) are used, the dosimetric demands are more stringent, requiring the development and investigation of new dosemeters. In this study, three prototype fiber-optic dosemeters (FODs)—an [...] Read more.
Dosimetry is crucial in radiotherapy to warrant safe and correct treatment. In FLASH radiotherapy, where ultra-high dose rates (UHDRs) are used, the dosimetric demands are more stringent, requiring the development and investigation of new dosemeters. In this study, three prototype fiber-optic dosemeters (FODs)—an inorganic, an organic–inorganic hybrid metal halide, and an organic (plastic) scintillator are optimized and investigated for UHDR electron irradiations. The plastic FOD is developed by Medscint, whereas the others are in-house made. The stem signal is minimized by spectral decomposition for the plastic scintillator, and by band-pass wavelength filters for the inorganic and organic–inorganic hybrid metal halide FOD. All prototypes are tested for the dose rate defining parameters. The optimal band-pass wavelength filters are found to be centered around 500 nm and 425 nm for the inorganic and organic–inorganic hybrid metal halide FODs, respectively. A sampling frequency of 1000 Hz is chosen for the inorganic and organic–inorganic hybrid metal halide FODs. The plastic FOD shows to be the least dose rate dependent with maximum deviations of 3% from the reference for the relevant beam settings. The inorganic and organic–inorganic hybrid metal halide FODs, in contrast, show large deviations of >10% from the reference and require more investigation. The current FOD prototypes are insufficient for application in UHDR electron beams, and require further development and investigation. Full article
(This article belongs to the Special Issue Optical Fibre Sensing: Recent Advances and Future Perspectives)
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