Photonics

14 pages, 4193 KiB

Open AccessArticle

Guided-Wave Properties of Slow-Wave Substrate-Integrated Waveguide Patterned with Non-Uniform Metasurface Unit Cells with Various Degrees of Rotation

by Hailu Jin, Xiaorong Jing and Ping Wang

Photonics 2023, 10(4), 482; https://doi.org/10.3390/photonics10040482 - 21 Apr 2023

Viewed by 1310

Abstract

A novel slow-wave waveguide structure is proposed, the guided-wave properties of which can be controlled by the rotation of nonuniform metasurface elements loaded on the surface of the substrate-integrated waveguide. The proposed nonuniform metasurface unit cell can exhibit anisotropic guided-wave parameters of interest, [...] Read more.

A novel slow-wave waveguide structure is proposed, the guided-wave properties of which can be controlled by the rotation of nonuniform metasurface elements loaded on the surface of the substrate-integrated waveguide. The proposed nonuniform metasurface unit cell can exhibit anisotropic guided-wave parameters of interest, i.e., equivalent permittivity and permeability along the transverse direction that are different from those along the longitudinal direction. Such characteristics suggest different propagation behaviors along different directions. Therefore, the equivalent permittivity and permeability change as the proposed nonuniform cross-unit cell rotates through various angles, which would modify the guided-wave properties as well. In this way, the cutoff frequency and phase constant of the proposed anisotropic SW-SIW can be controlled flexibly by rotating the patterned metasurface unit cells over different angles. Several SW-SIW experimental prototypes with different rotation angles are implemented, and their respective measured results are in good agreement with their simulated counterparts. Thereby, the proposed method can provide more flexibility for designing and controlling an anisotropic SW-SIW. Full article

(This article belongs to the Special Issue Metasurfaces and Applications of Communication/Imaging/Signal Processing)

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10 pages, 1604 KiB

Open AccessArticle

Classification of Healthy and Cancer Colon Cells Grown on Glass Coverslip by Means of Fourier Transform Infrared Spectroscopy and Multivariate Methods

by Giuseppe Perna, Vito Capozzi and Maria Lasalvia

Photonics 2023, 10(4), 481; https://doi.org/10.3390/photonics10040481 - 21 Apr 2023

Cited by 4 | Viewed by 1537

Abstract

For several years, Fourier transform infrared (FTIR) microspectroscopy has been proving to be very promising for use in cytological diagnostics because of its capability of providing rapid and label-free biochemical information about cell samples. The adoption of FTIR as a clinical tool has [...] Read more.

For several years, Fourier transform infrared (FTIR) microspectroscopy has been proving to be very promising for use in cytological diagnostics because of its capability of providing rapid and label-free biochemical information about cell samples. The adoption of FTIR as a clinical tool has been slowed because of the poor compatibility with cells deposited on glass slides, commonly used in clinical practice, because of the absorption of IR radiation by glassy materials in the 1000–1800 cm⁻¹ spectral range. However, the possibility of also obtaining diagnostic information from the IR absorption spectra in the 2700–3700 cm⁻¹ range (including few peaks related to vibrational modes in cell lipids and proteins) has recently emerged. In this work, we investigate the use of the FTIR technique in the 2700–3700 cm⁻¹ range for diagnostic purposes about human colon cells grown on glass coverslips. In fact, using the principal components analysis (PCA) technique, we are able to discriminate FTIR spectra of healthy cells from those of cancerous ones, mainly due to the larger relative lipid content in the former compared to the latter. In addition, principal component analysis-linear discriminate analysis (PCA-LDA) and partial least square-discriminant analysis (PLS-DA) were used to build classification models for unknown FTIR spectra with optimal accuracy. These results support the promotion of the translation of the FTIR technique as a complementary diagnostic tool in cytological routine practice. Full article

(This article belongs to the Special Issue Women’s Special Issue Series: Photonics)

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11 pages, 1987 KiB

Open AccessEditor’s ChoiceCommunication

All-Fiber Laser Feedback Interferometry for Sequential Sensing of In-Plane and Out-of-Plane Displacements

by Zhanwu Xie, Meng Zhang, Jie Li, Wei Xia and Dongmei Guo

Photonics 2023, 10(4), 480; https://doi.org/10.3390/photonics10040480 - 21 Apr 2023

Viewed by 1533

Abstract

In this paper, an all-fiber laser feedback interferometer (LFI) with a diffraction grating was developed for sequential measurement of in-plane and out-of-plane displacements without changing the optical arrangement. When the light emitted from an erbium-doped fiber ring laser is incident on a reflection [...] Read more.

In this paper, an all-fiber laser feedback interferometer (LFI) with a diffraction grating was developed for sequential measurement of in-plane and out-of-plane displacements without changing the optical arrangement. When the light emitted from an erbium-doped fiber ring laser is incident on a reflection grating at the Littrow angle, the diffracted light will return into the laser cavity along the original path, thus generating laser feedback interference. Experimental results reveal that the all-fiber system could achieve a precision of 40 nm in both in-plane and out-of-plane displacements sensing. Compared with the traditional all-fiber LFI, the proposed sensing system transfers the measuring scale from laser wavelength to grating period, and it has the advantages of good anti-interference performance and reliability. Full article

(This article belongs to the Special Issue Advanced Photonic Sensing and Measurement)

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10 pages, 8377 KiB

Open AccessCommunication

Preparation of Antireflection Microstructures on ZnSe Crystal by Femtosecond Burst Bessel Direct Laser Writing

by Sikun Zhou, Junjie Yang, Sha Wang, Shutong Wang, Guoliang Deng and Shouhuan Zhou

Photonics 2023, 10(4), 479; https://doi.org/10.3390/photonics10040479 - 21 Apr 2023

Cited by 2 | Viewed by 1862

Abstract

In this work, we fabricated the antireflection microstructures (ARMs) on ZnSe surfaces using a femtosecond Bessel direct laser writing in burst mode. The morphology and transmittance performance of ARMs with different single-pulse energies (from 200 nJ to 500 nJ), different burst modes (burst [...] Read more.

In this work, we fabricated the antireflection microstructures (ARMs) on ZnSe surfaces using a femtosecond Bessel direct laser writing in burst mode. The morphology and transmittance performance of ARMs with different single-pulse energies (from 200 nJ to 500 nJ), different burst modes (burst 1, 3, and 5 modes), different periods (from 3 μm to 6 μm), and different arrangements were investigated. The results revealed that tetragonally arranged ARMs fabricated by 500 nJ of single-pulse energy, the burst 3 mode, and a period of 3 μm show the best transmittance performance. The average transmittance of the ARMs was about 17.13% higher than that of bulk ZnSe in the range of 8–12 μm, and the highest transmittance of 81.75% (an improvement of 18.63% on one side of the ZnSe) was achieved at 12.36 μm. This process makes it possible to enhance ARMs’ transmittance in the infrared wavelength range by using direct laser writing in burst mode. Full article

(This article belongs to the Special Issue Femtosecond Laser-Induced Microfabrication)

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19 pages, 5594 KiB

Open AccessArticle

A Theoretical Study on Mid-Infrared Difference Frequency Generation Based on Periodically Poled Thin-Film LiNbO₃

by Runze Jia, Meihong Liu, Jiamin Liu, Pingrang Hua and Delong Zhang

Photonics 2023, 10(4), 478; https://doi.org/10.3390/photonics10040478 - 21 Apr 2023

Cited by 2 | Viewed by 1900

Abstract

A mid-infrared difference frequency generator (DFG) based on a periodically poled thin-film lithium niobate rib waveguide on a sapphire substrate is theoretically studied. A mode analysis is carried out at the mid-infrared region, and the analysis focuses on the effects of waveguide geometry [...] Read more.

A mid-infrared difference frequency generator (DFG) based on a periodically poled thin-film lithium niobate rib waveguide on a sapphire substrate is theoretically studied. A mode analysis is carried out at the mid-infrared region, and the analysis focuses on the effects of waveguide geometry on effective refractive indices of a few lower-order modes. A complete theory suitable for modeling a DFG based on a waveguide structure is described. Its validity is confirmed by comparing the theoretical results with previously reported experimental data. Explicit expressions are presented for nonlinear conversion efficiency, thermal tunability and quasi-phase matching (QPM) bandwidth. The effects of waveguide geometry and mode hybridization on the effective mode field area and mode overlap factor, which are either inversely or linearly proportional to nonlinear conversion efficiency, are studied in detail. In this article, an optimized mid-infrared DFG with improved geometry that exhibits excellent performance, including a higher nonlinear conversion efficiency of 230–273% W⁻¹cm⁻² in the temperature range of 20–120 °C; a larger temperature tunability of 2.2 nm/°C; a larger QPM bandwidth of ~130 nm; and a higher idler wave output power, as much as −2 dBm when P_p = 20 dBm and P_s = 11.5 dBm, is suggested. Full article

(This article belongs to the Special Issue Integrated Waveguide-Based Photonic Devices)

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19 pages, 12721 KiB

Open AccessArticle

Beam Properties of a Partially Coherent Beam Propagating Horizontally in Atmospheric Turbulence

by Zengyan Wu, Zhejun Feng, Shubing Ye, Baoming Song, Runxi Wei and Chaoran Yu

Photonics 2023, 10(4), 477; https://doi.org/10.3390/photonics10040477 - 21 Apr 2023

Cited by 5 | Viewed by 1759

Abstract

This study explored the impact of atmospheric turbulence on partially coherent light propagation. Atmospheric turbulence causes random modulation of the intensity and phase of light, resulting in a speckle pattern in the far field. This study focused on partially coherent Gaussian Schell model [...] Read more.

This study explored the impact of atmospheric turbulence on partially coherent light propagation. Atmospheric turbulence causes random modulation of the intensity and phase of light, resulting in a speckle pattern in the far field. This study focused on partially coherent Gaussian Schell model beams and derived an analytical expression of the cross-spectral density function for their transmission through atmospheric turbulence, based on the generalized Huygens–Fresnel principle and the Tatarski spectrum model. Numerical simulations were used to investigate the effects of the source parameters and turbulence strength on the intensity distribution, beam width, and coherence length of partially coherent light in horizontal atmospheric transmission. The results demonstrate that diffraction-induced broadening primarily affects the intensity distribution of light in free-space transmission. Short transmission distances in atmospheric turbulence have comparable characteristics to those in a vacuum; however, as the turbulence intensity and transmission distance increase, the beam broadening effect amplifies, and the coherence length is reduced. The findings are relevant to the design of acquisition, pointing, and tracking systems for wireless laser communication systems and offer insights into the optimization of optical systems for atmospheric conditions. Full article

(This article belongs to the Special Issue Novel Laser Technologies and Their Applications)

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14 pages, 3805 KiB

Open AccessArticle

Significant Substrate Effects on Electromagnetic Scattering by Particles in the Infrared Atmospheric Window

by Feifei Gao, Shangyu Zhang, Wenjie Zhang, Lanxin Ma and Linhua Liu

Photonics 2023, 10(4), 476; https://doi.org/10.3390/photonics10040476 - 21 Apr 2023

Viewed by 1734

Abstract

Particle-dispersed coatings emerged as a promising approach to regulate the apparent radiative properties of underlying substrates in various applications, including but not limited to radiative cooling, thermal management, and infrared stealth. However, most research efforts in this field overlooked the dependent scattering mechanisms [...] Read more.

Particle-dispersed coatings emerged as a promising approach to regulate the apparent radiative properties of underlying substrates in various applications, including but not limited to radiative cooling, thermal management, and infrared stealth. However, most research efforts in this field overlooked the dependent scattering mechanisms between the particles and the substrate, which can impact the optical properties of the particles. In this study, we explored the particle-substrate interactions within the atmospheric radiative window of 8–14 µm. Using the T-matrix method, we calculated the scattering and absorption efficiencies of a dielectric/metallic particle situated above a metallic/dielectric substrate, considering the different gap sizes. Near the small gaps (<0.5a with a the sphere radius), we found that the strong local fields induced by the interaction between the induced and image charges largely enhanced the absorption and scattering efficiencies of the particles. With the increasing gap sizes, the absorption and scattering efficiencies presented a significant oscillation with a period of about 4.5a, which was attributed to the interference (standing wave) between the scattered fields from the sphere and the reflected fields from the substrate. Our findings identify a crucial role of the particle–substrate interactions in the infrared properties of particles, which may guide a comprehensive insight on the apparent radiative properties of the particle composite coatings. Full article

(This article belongs to the Section Optical Interaction Science)

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14 pages, 6582 KiB

Open AccessArticle

The Effect of Spectral Resolution on the Quantification of OP-FTIR Spectroscopy

by Yusheng Qin, Jingjing Tong, Xiangxian Li, Xin Han and Minguang Gao

Photonics 2023, 10(4), 475; https://doi.org/10.3390/photonics10040475 - 21 Apr 2023

Cited by 1 | Viewed by 1936

Abstract

Open-path Fourier Transform infrared spectroscopy (OP-FTIR) is widely used in polluted gas monitoring. The spectral resolution, as a key parameter of FTIR detection technology, affects the quantitative analysis of gas concentration. In OP-FTIR, the nonlinear least square (NLLS) method based on a synthetic [...] Read more.

Open-path Fourier Transform infrared spectroscopy (OP-FTIR) is widely used in polluted gas monitoring. The spectral resolution, as a key parameter of FTIR detection technology, affects the quantitative analysis of gas concentration. In OP-FTIR, the nonlinear least square (NLLS) method based on a synthetic background spectrum is used to quantitatively analyze the gas concentration, and the influence of the spectral resolution is studied. It is found that the influence of the spectral resolution on quantitative gas analysis is related to the full width at half maximum (FWHM) of the gas spectrum. The concentration of gases with different spectral FWHMs were quantitatively analyzed using infrared spectra with different resolutions (1, 2, 4, 8, 16 cm⁻¹). The experimental results show that the relatively optimal spectral resolution for propane (C₃H₈) with a broad FWHM is 16 cm⁻¹, where the standard deviation is 0.661 and the Allan deviation is only 0.015; the relatively optimal spectral resolution for ethylene (C₂H₄) with a narrow FWHM is 1 cm⁻¹, where the standard deviation is 0.492 and the Allan deviation is only 0.256. Therefore, for the NLLS quantitative analysis method based on the synthetic background spectrum, which is used in OP-FTIR, gas with a narrow FWHM at high resolutions or gas with a broad FWHM at low resolutions is most effective for performing quantitative analyses. Full article

(This article belongs to the Special Issue Environmental Optical Detection)

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13 pages, 1055 KiB

Open AccessCommunication

Measurement of the Temperature Dependence of Polarization Switching in Gain-Switched VCSELs for Quantum Random Number Generation

by Iván Rivero, Alfonso Lázaro del Pozo, Marcos Valle-Miñón, Ana Quirce and Angel Valle

Photonics 2023, 10(4), 474; https://doi.org/10.3390/photonics10040474 - 20 Apr 2023

Cited by 3 | Viewed by 2777

Abstract

We report an experimental study of the effect of the temperature of the VCSEL on the probability of excitation of a linearly polarized mode when gain-switching the device. We consider different modulation frequencies and amplitudes. We show that the probability of excitation of [...] Read more.

We report an experimental study of the effect of the temperature of the VCSEL on the probability of excitation of a linearly polarized mode when gain-switching the device. We consider different modulation frequencies and amplitudes. We show that the probability of excitation of a linearly polarized mode significantly changes with the value of the temperature of the device. We also show that for low values of the temperature the probability of excitation saturates to a constant value as the amplitude of the modulation increases. This extends our previous results obtained at larger temperatures for which that saturation was not observed. We identify situations in which the distributions of the linearly polarized signals at a sampling time are approximately uniform. For these cases we evaluate the quality of the random numbers by using statistical test. Full article

(This article belongs to the Special Issue Advancements in Semiconductor Lasers)

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12 pages, 4356 KiB

Open AccessCommunication

High Performance Dual-Core D-Shaped PCF Refractive Index Sensor Coated with Gold Grating

by Yu Ying, You Xia, Siyu Cheng, Dan Shan, Zhijun Gao, Guangyuan Si and Xiaoxi Tian

Photonics 2023, 10(4), 473; https://doi.org/10.3390/photonics10040473 - 20 Apr 2023

Cited by 3 | Viewed by 2476

Abstract

In this study, a dual−core D-shaped photonic crystal fiber (PCF) surface plasmon resonance sensor coated with gold grating is designed and analyzed using the finite-element method (FEM). The surface plasmon resonance (SPR) effect between the fiber core modes and surface plasmon polariton (Spp) [...] Read more.

In this study, a dual−core D-shaped photonic crystal fiber (PCF) surface plasmon resonance sensor coated with gold grating is designed and analyzed using the finite-element method (FEM). The surface plasmon resonance (SPR) effect between the fiber core modes and surface plasmon polariton (Spp) modes is used to measure the analyte refractive index. The effects of the PCF structure parameters (polishing depths, large holes, and small holes) and grating parameters (grating heights, grating periods, and grating duty) are discussed, and a two-feature interrogation method that combines wavelength and intensity interrogations is introduced to enhance the resolution. The results show that the grating and dual-core play important roles in enhancing the sensor properties. The proposed sensor achieves an average wavelength sensitivity of 994.5 nm/RIU when the analyte refractive index increases from 1.33 to 1.37. Furthermore, a maximum amplitude sensitivity of 181.049 RIU⁻¹ is obtained. The two-feature interrogation is determined to have a resolution of 2.03 × 10⁻⁶ RIU, which is better than the wavelength and amplitude interrogations. The proposed sensor has a good sensing performance and is highly suitable for practical applications. Full article

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21 pages, 8421 KiB

Open AccessArticle

Low-Complexity Modulation Format Identification Based on Amplitude Histogram Distributions for Digital Coherent Receivers

by Ming Hao, Xuedong Jiang, Xingzhong Xiong, Roger Giddings, Wei He and Jianming Tang

Photonics 2023, 10(4), 472; https://doi.org/10.3390/photonics10040472 - 20 Apr 2023

Cited by 2 | Viewed by 1741

Abstract

In this work, a prior-training-free and low-complexity modulation format identification (MFI) scheme, based on amplitude histogram distributions, was proposed and demonstrated, both numerically and experimentally, for autonomous digital coherent receivers. In the proposed scheme, after having performed power normalization, incoming polarization division multiplexed [...] Read more.

In this work, a prior-training-free and low-complexity modulation format identification (MFI) scheme, based on amplitude histogram distributions, was proposed and demonstrated, both numerically and experimentally, for autonomous digital coherent receivers. In the proposed scheme, after having performed power normalization, incoming polarization division multiplexed (PDM) signals were classified into QPSK, 8QAM, 16QAM, 32QAM and 64QAM signals, according to their ratios. Ratios were defined according to specific features of their amplitude histograms. The proposed MFI scheme used only amplitude information. As such, it was insensitive to carrier phase noise. Furthermore, the proposed scheme did not require any prior information, such as optical signal-to-noise ratio (OSNR). The performance of the proposed MFI scheme was numerically verified using 28GBaud PDM-QPSK/-8QAM/-16QAM/-32QAM/-64QAM signals. The numerical simulation results showed that the proposed scheme was able achieve a 100% correct identification rate for all five modulation formats when their OSNR values were higher than the thresholds corresponding to the 20% FEC correcting bit error rate (BER) of 2.4 × 10⁻². To further explore the effectiveness of the proposed MFI scheme, proof-of-concept experiments in 28GBaud PDM-QPSK/-8QAM/-16QAM, and 21.5GBaud PDM-32QAM transmission systems were also undertaken, which showed that the proposed scheme as robust against fiber nonlinearities. To explore the scheme’s feasibility for use in practical transmission systems, the computational complexity analysis of the proposed scheme was conducted. It showed that, compared with relevant MFI schemes, the proposed MFI scheme was able to significantly reduce the computational complexity. Full article

(This article belongs to the Special Issue Optical Performance Monitoring)

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10 pages, 17681 KiB

Open AccessArticle

Systematic Analysis of a Modified Uni-Traveling-Carrier Photodiode under High-Power Operating Conditions

by Wanshu Xiong, Zhangwan Peng, Ruoyun Yao, Qianwen Guo, Chaodan Chi and Chen Ji

Photonics 2023, 10(4), 471; https://doi.org/10.3390/photonics10040471 - 20 Apr 2023

Cited by 4 | Viewed by 1958

Abstract

We theoretically analyzed the detailed carrier transport process based on the drift-diffusion model in the InGaAs/InP modified Uni-Traveling-Carrier Photodiode (MUTC-PD) under high optical input power conditions. A high-speed MUTC-PD design was simulated in depth using the commercial simulation software APSYS. The complex interplay [...] Read more.

We theoretically analyzed the detailed carrier transport process based on the drift-diffusion model in the InGaAs/InP modified Uni-Traveling-Carrier Photodiode (MUTC-PD) under high optical input power conditions. A high-speed MUTC-PD design was simulated in depth using the commercial simulation software APSYS. The complex interplay between photo-electron and hole transport processes was quantitatively analyzed. The slowdown of hole transit time due to E field reduction in the undoped InGaAs absorber layer dominated the response speed of MUTC-PDs at a high optical power level. The optimized MUTC-PD design has a relatively strong dependence on optical power level. Based on an optimized design, an O–E conversion responsivity around 0.15 A/W and the intrinsic 3 dB bandwidth of 172 GHz were demonstrated when the input optical power density reached 20 mW/μm². Our simulation analysis results presented here can be utilized for designing broadband MUTC-PDs in future sub-Terahertz free-space data link applications. Full article

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15 pages, 5576 KiB

Open AccessEditor’s ChoiceReview

GaN-Based VCSELs with A Monolithic Curved Mirror: Challenges and Prospects

by Tatsushi Hamaguchi

Photonics 2023, 10(4), 470; https://doi.org/10.3390/photonics10040470 - 20 Apr 2023

Cited by 8 | Viewed by 3805

Abstract

In this paper, we introduce how gallium nitride-based (GaN-based) VCSELs with curved mirrors have evolved. The discussion starts with reviewing the fundamentals of VCSELs and GaN-based materials and then introducing the curved-mirror cavity’s principle and history and the latest research where the structure [...] Read more.

In this paper, we introduce how gallium nitride-based (GaN-based) VCSELs with curved mirrors have evolved. The discussion starts with reviewing the fundamentals of VCSELs and GaN-based materials and then introducing the curved-mirror cavity’s principle and history and the latest research where the structure is applied to GaN-based materials to form VCSELs. We prepared these parts so that readers understand how VCSELs with this cavity work and provide excellent characteristics such as efficiency, life, stabilized mode behavior, etc. Finally, we discussed the challenges and prospects of these devices by touching on their potential applications. Full article

(This article belongs to the Special Issue Nanophotonics Pioneer: Prof. Dr. Dieter Bimberg ‘Green Photonics Networks: From VCSELs to Nanophotonics’)

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7 pages, 10525 KiB

Open AccessCommunication

Near-Field Evolution of Optical Vortices and Their Spatial Ordering behind a Fork-Shaped Grating

by Denis A. Ikonnikov, Sergey A. Myslivets, Vasily G. Arkhipkin and Andrey M. Vyunishev

Photonics 2023, 10(4), 469; https://doi.org/10.3390/photonics10040469 - 20 Apr 2023

Cited by 4 | Viewed by 1454

Abstract

Fork-shaped gratings are periodic structures containing a spatial dislocation known to be used for the production of optical vortices in a far field. Spatial overlapping of diffraction orders in a near field results in complex spatial evolution of optical vortices. In this paper, [...] Read more.

Fork-shaped gratings are periodic structures containing a spatial dislocation known to be used for the production of optical vortices in a far field. Spatial overlapping of diffraction orders in a near field results in complex spatial evolution of optical vortices. In this paper, we report the results of near-field diffraction on fork-shaped gratings with different topological charges and analyze the evolution of specific optical vortices during propagation. Optical vortices have been shown to form two-dimensional well-ordered spatial configurations in specific transverse planes. The locus of points of optical singularities has been shown to form two helical lines twisted around the

\pm 1

diffraction order directions. Our results demonstrate that the spatial behaviour of optical vortices is in close connection with the spatial ordering arising from the Talbot effect. The quantity of optical vortices demonstrates complex spatial dynamics, which includes spatial oscillations and decreasing along the propagation direction. These results provide a foundation towards a deeper understanding of near-field singular optics phenomena. Full article

(This article belongs to the Special Issue Light Focusing and Optical Vortices)

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18 pages, 7233 KiB

Open AccessArticle

A Lightweight Swin Transformer-Based Pipeline for Optical Coherence Tomography Image Denoising in Skin Application

by Jinpeng Liao, Chunhui Li and Zhihong Huang

Photonics 2023, 10(4), 468; https://doi.org/10.3390/photonics10040468 - 19 Apr 2023

Cited by 7 | Viewed by 2164

Abstract

Optical coherence tomography (OCT) has attracted attention in dermatology applications for skin disease characterization and diagnosis because it provides high-resolution (<10 μm) of tissue non-invasively with high imaging speed (2–8 s). However, the quality of OCT images can be significantly degraded by speckle [...] Read more.

Optical coherence tomography (OCT) has attracted attention in dermatology applications for skin disease characterization and diagnosis because it provides high-resolution (<10 μm) of tissue non-invasively with high imaging speed (2–8 s). However, the quality of OCT images can be significantly degraded by speckle noise, which results from light waves scattering in multiple directions. This noise can hinder the accuracy of disease diagnosis, and the conventional frame averaging method requires multiple repeated (e.g., four to six) scans, which is time consuming and introduces motion artifacts. To overcome these limitations, we proposed a lightweight U-shape Swin (LUSwin) transformer-based denoising pipeline to recover high-quality OCT images from the noisy OCT images by utilizing a fast one-repeated OCT scan. In terms of the peak signal-to-noise-ratio (PSNR) performance, the results reveal that the denoised images from the LUSwin transformer (26.92) are of a higher quality than the four-repeated frame-averaging method (26.19). Compared to the state-of-the-art networks in image denoising, the proposed LUSwin transformer has the smallest floating points operation (3.9299 G) and has the second highest PSNR results, only 0.02 lower than the Swin-UNet, which has the highest PSNR results (26.94). This study demonstrates that the transformer model has the capacity to denoise the noisy OCT image from a fast one-repeated OCT scan. Full article

(This article belongs to the Special Issue High-Performance Optical Coherence Tomography)

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10 pages, 1657 KiB

Open AccessArticle

Corneal Densitometry with Galilei Dual Scheimpflug Analyzer

by Alejandra Consejo, Silvia Basabilbaso and Laura Remon

Photonics 2023, 10(4), 467; https://doi.org/10.3390/photonics10040467 - 19 Apr 2023

Cited by 2 | Viewed by 1611

Abstract

This study aims to apply the densitometry distribution analysis (DDA) method to study corneal densitometry depending on age and corneal region from Galilei Dual Scheimpflug Analyzer tomography. A total of 83 healthy participants aged 39.02 ± 18.34 years (range 9–81 years) were screened [...] Read more.

This study aims to apply the densitometry distribution analysis (DDA) method to study corneal densitometry depending on age and corneal region from Galilei Dual Scheimpflug Analyzer tomography. A total of 83 healthy participants aged 39.02 ± 18.34 years (range 9–81 years) were screened using a Ziemer Galilei G2. Images were analysed using the DDA, and two parameters, α (corneal transparency) and β (corneal homogeneity), were estimated. A two-way ANOVA analysis was performed to investigate whether α and β are influenced by age, corneal región (four concentric areas were considered), and their interaction. The parameters α and β statistically change with age and corneal region. A statistically significant interaction effect of 13% (α) and 11% (β) exists between age and corneal region. However, the corneal region plays a more significant role than aging in corneal densitometry; 31% (α) and 51% (β) of the variance can be attributed to the corneal region, while 28% (α) and 5% (β) can be attributed solely to aging. Corneal densitometry can be objectively assessed from Galilei G2 images using the DDA method. The corneal region plays a more significant role than aging in corneal densitometry. Consequently, general results on corneal densitometry and aging should be taken cautiously. Full article

(This article belongs to the Special Issue Visual Optics)

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7 pages, 1022 KiB

Open AccessCommunication

Two-Photon Absorption in Ca₃(VO₄)₂ and Ca_2.7Sr_0.3(VO₄)₂ Crystals

by Igor O. Kinyaevskiy, Valery I. Kovalev, Nikita S. Semin, Pavel A. Danilov, Sergey I. Kudryashov, Andrey V. Koribut and Elizaveta E. Dunaeva

Photonics 2023, 10(4), 466; https://doi.org/10.3390/photonics10040466 - 19 Apr 2023

Cited by 1 | Viewed by 1165

Abstract

Two-photon absorption has been systematically studied in Ca₃(VO₄)₂ and Ca_2.7Sr_0.3(VO₄)₂ crystals, both of which are prospective nonlinear optical and laser host materials. A strong dependence of the two-photon absorption coefficients on [...] Read more.

Two-photon absorption has been systematically studied in Ca₃(VO₄)₂ and Ca_2.7Sr_0.3(VO₄)₂ crystals, both of which are prospective nonlinear optical and laser host materials. A strong dependence of the two-photon absorption coefficients on the orientation of the laser beam polarization with respect to the optical c-axis of the crystals is revealed. The measured coefficients for perpendicular and parallel orientations were 50 ± 10 cm/TW and 19 ± 4 cm/TW in Ca₃(VO₄)₂, and 18 ± 3 cm/TW and 10 ± 2 cm/TW in Ca_2.7Sr_0.3(VO₄)₂, respectively. Thus, to minimize optical losses caused by two-photon absorption, an orientation of Ca_2.7Sr_0.3(VO₄)₂ crystals with the laser beam polarization parallel to the crystal optical c-axis is preferred. Full article

(This article belongs to the Topic Optical and Optoelectronic Properties of Materials and Their Applications)

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19 pages, 12339 KiB

Open AccessArticle

All-Glass Single-Mode Leakage Channel Microstructured Optical Fibers with Large Mode Area and Low Bending Loss

by Alexander Denisov, Vladislav Dvoyrin, Alexey Kosolapov, Mikhail Likhachev, Vladimir Velmiskin, Sergey Zhuravlev and Sergey Semjonov

Photonics 2023, 10(4), 465; https://doi.org/10.3390/photonics10040465 - 19 Apr 2023

Cited by 2 | Viewed by 1410

Abstract

The paper presents the results of theoretical and experimental studies of all-glass leakage channel microstructured optical fibers (MOFs) with a large mode area and low bending losses. These MOFs contain two layers of fluorine-doped silica glass elements with a reduced refractive index, different [...] Read more.

The paper presents the results of theoretical and experimental studies of all-glass leakage channel microstructured optical fibers (MOFs) with a large mode area and low bending losses. These MOFs contain two layers of fluorine-doped silica glass elements with a reduced refractive index, different diameters, and different distances between them. A numerical analysis of the properties of these MOFs was performed using the finite element method. The leakage losses for the fundamental and higher-order modes were calculated in the spectral range from 0.65 μm to 1.65 μm. Simulation results show that the proposed MOF design allows for single-mode guidance in the spectral range from 0.92 μm to 1.21 μm with a bending radius of down to 0.08 m. The measured losses of the fabricated MOF with a core diameter of 22.5 μm and a bending radius of 0.1 m were less than 0.1 dB/m in the spectral range from 0.9 μm to 1.5 μm. It is demonstrated that the segments of this MOF longer than 5 m are single-mode. Full article

(This article belongs to the Special Issue Fiber Optics and Mainstream Areas of Photonics)

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22 pages, 14854 KiB

Open AccessArticle

In Vitro Assessment of the Impact of Ultraviolet B Radiation on Oral Healthy and Tumor Cells

by Otilia Gag, Ioana Macasoi, Iulia Pinzaru, Stefania Dinu, Ramona Popovici, Mioara-Raluca Cosoroaba, Roxana Buzatu, Madalina Cabuta and Sorin Dan Chiriac

Photonics 2023, 10(4), 464; https://doi.org/10.3390/photonics10040464 - 18 Apr 2023

Cited by 6 | Viewed by 1911

Abstract

Ultraviolet radiation (UVR) is generally considered a primary tumorigenic agent. While UVR exposure has been studied, especially at the skin level, the impact of UV exposure on internal tissues and its effect on the appearance and the development of tumors has not yet [...] Read more.

Ultraviolet radiation (UVR) is generally considered a primary tumorigenic agent. While UVR exposure has been studied, especially at the skin level, the impact of UV exposure on internal tissues and its effect on the appearance and the development of tumors has not yet been fully examined. Although there are maximum limits for UVR exposure on external tissues, other internal tissues, such as oral tissue, can be exposed to UVR as well. Over the course of diagnosis and treatment, oral cells may be exposed to ultraviolet radiation; however, there has not been an established limit for UV radiation exposure. Therefore, the aim of the current study was to examine the effects of ultraviolet-B (UVB) radiation at two doses (2.5 and 5 J/cm²) on tumor cells (pharyngeal carcinoma and tongue carcinoma) and healthy cells (gingival fibroblasts). The viability of the cells and their morphology, actin filaments, and nuclei structures; the expression of anti-apoptotic (Bcl-2) and pro-apoptotic (Bax) genes; and the roles of caspases-3/7, 8, and 9 were determined after the cells had been exposed to UVB. The experiments revealed that both types of cell lines showed reductions in viability, especially at a dose of 5 J/cm². Additionally, apoptotic-like changes (rounding of the cells, the condensation of the nuclei, the re-organization of the actin filaments) were observed in all analyzed cells. The expression of anti-apoptotic (Bcl-2) and pro-apoptotic (Bax) genes revealed that UVB (5 J/cm²) may induce apoptosis in both oral tumor and healthy cells. Moreover, an analysis of caspases-3/7, 8, and 9 showed that UVB exposure enhanced their activity, suggesting that cell death could be caused by both intrinsic and extrinsic apoptosis. Accordingly, UVB exposure at the maximum doses used in dental practices (5 J/cm²) induced nonselective apoptotic changes, thereby reducing both tumor and healthy cell viability. Full article

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15 pages, 6551 KiB

Open AccessArticle

Research on Very-Low-Frequency Hydroacoustic Acoustic Velocity Sensor Based on DFB Fiber Laser

by Chenxia Ruan, Mo Chen, Yang Yu, Yichi Zhang, Jianfei Wang, Zhenrong Zhang, Junbo Yang, Shuolong Zhu and Boyuan Qu

Photonics 2023, 10(4), 463; https://doi.org/10.3390/photonics10040463 - 18 Apr 2023

Cited by 1 | Viewed by 1415

Abstract

We have conducted a study on a very-low-frequency acoustic-velocity sensor which is based on a cantilever of distributed-feedback (DFB) fiber laser immersed in castor oil. A mathematical model of the frequency dependent response of the proposed sensor to the acoustic pressure signal influenced [...] Read more.

We have conducted a study on a very-low-frequency acoustic-velocity sensor which is based on a cantilever of distributed-feedback (DFB) fiber laser immersed in castor oil. A mathematical model of the frequency dependent response of the proposed sensor to the acoustic pressure signal influenced by the fluid viscosity is established. We have fabricated the proposed sensor and conducted experimental measurements in the standing wave tube. The results show that the sensor has an average phase sensitivity of −179.5 dB (0 dB = 1 rad/μPa) with ±1.45 dB fluctuation over the frequency range of 20–38 Hz. It has good cosine directivity with a directivity index of 32.5 dB and axial maximum asymmetry of 0.4 dB. The sensor presents promising applications for detecting very-low-frequency underwater acoustic signals. Full article

(This article belongs to the Special Issue Fiber Laser Systems: Novel Concepts, Designs, Capabilities, and Applications)

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14 pages, 4011 KiB

Open AccessArticle

Polar-Coded Transmission over 7.8-km Terrestrial Free-Space Optical Links

by Shingo Fujita, Eiji Okamoto, Hideki Takenaka, Hiroyuki Endo, Mikio Fujiwara, Mitsuo Kitamura, Ryosuke Shimizu, Masahide Sasaki and Morio Toyoshima

Photonics 2023, 10(4), 462; https://doi.org/10.3390/photonics10040462 - 17 Apr 2023

Viewed by 1809

Abstract

Free-space optical (FSO) communications can offer high-capacity transmission owing to the properties of the laser beams. However, performance degradation caused by atmospheric turbulence is an urgent issue. Recently, the application of polar codes, which can provide capacity-achieving error-correcting performance with low computational cost [...] Read more.

Free-space optical (FSO) communications can offer high-capacity transmission owing to the properties of the laser beams. However, performance degradation caused by atmospheric turbulence is an urgent issue. Recently, the application of polar codes, which can provide capacity-achieving error-correcting performance with low computational cost for decoding, to FSO communications has been studied. However, long-distance and real-field experiments have not been conducted in these studies. To the best of our knowledge, this study is the first to present the experimental results of polar-coded transmission over 7.8-km FSO links. Using experimental data, we investigated the performance of polar codes over atmospheric channels, including their superiority to regular low-density parity-check codes. We expect that our results will offer a path toward the application of polar codes in high-speed optical communication networks including satellites. Full article

(This article belongs to the Special Issue Advances in Free Space Optical Communications and Optical Turbulence Modeling)

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13 pages, 25808 KiB

Open AccessCommunication

Statistical Properties of Partially Coherent Higher-Order Laguerre-Gaussian Power-Exponent Phase Vortex Beams

by Zhiyuan Ma, Yuqi Pan, Jiantai Dou, Jiang Zhao, Bo Li and Youyou Hu

Photonics 2023, 10(4), 461; https://doi.org/10.3390/photonics10040461 - 17 Apr 2023

Cited by 2 | Viewed by 1652

Abstract

In this paper, partially coherent radially polarized (RP) Laguerre-Gaussian (LG) rotationally symmetrical power-exponent phase vortex (RSPEPV) beams with the LG-correlated Schell-model (LGSM) were introduced. The statistical properties of the tightly focused beams, including intensity distribution, degrees of polarization and coherence, and Stokes vector, [...] Read more.

In this paper, partially coherent radially polarized (RP) Laguerre-Gaussian (LG) rotationally symmetrical power-exponent phase vortex (RSPEPV) beams with the LG-correlated Schell-model (LGSM) were introduced. The statistical properties of the tightly focused beams, including intensity distribution, degrees of polarization and coherence, and Stokes vector, were studied based on vectorial Richards-Wolf diffraction integral theory. Moreover, when the distance between focal plane and the observation plane z = 0, the relationships between the tight-focusing properties of RP-LG-RSPEPV beams with LGSM and the order of LGSM p’, topological charges l, power exponent n, spatial correlation δ, and radial index p were investigated. The results show that by changing the order of LGSM, topological charge, power exponent, spatial correlation length, and radial index, the focal spot distribution of various shapes can be obtained. This work provides ideas for the application of partially coherent beams in particle capture and optical tweezers. Full article

(This article belongs to the Special Issue Coherent and Polarization Optics)

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15 pages, 4713 KiB

Open AccessArticle

Optical Attenuation Coefficient Optimization Algorithm for Deep Tissue Signals in Optical Coherence Tomography Based on Kalman Filter

by Jian Liu, Yanyu Chen, Yang He, Nan Lu, Dongni Yang, Yu Tian, Yao Yu, Yuqian Zhao, Yi Wang and Zhenhe Ma

Photonics 2023, 10(4), 460; https://doi.org/10.3390/photonics10040460 - 16 Apr 2023

Viewed by 2040

Abstract

Optical coherence tomography (OCT) attenuation imaging is a technique that uses the optical attenuation coefficient (OAC) to distinguish the types or pathological states of tissues and has been increasingly used in basic research and clinical diagnosis. With the increasing application of swept-source OCT, [...] Read more.

Optical coherence tomography (OCT) attenuation imaging is a technique that uses the optical attenuation coefficient (OAC) to distinguish the types or pathological states of tissues and has been increasingly used in basic research and clinical diagnosis. With the increasing application of swept-source OCT, scholars are increasingly inclined to explore deep tissues. Unfortunately, the accuracy of OAC calculation when exploring deep tissues has yet to be improved. Existing methods generally have the following problems: overestimation error, underestimation error, severe fluctuation, or stripe artifacts in the OAC calculation of the OCT tail signal. The main reason for this is that the influence of the noise floor on the OCT weak signal at the tail-end is not paid enough attention. The noise floor can change the attenuation pattern of the OCT tail signal, which can lead to severe errors in the OAC. In this paper, we proposed a Kalman filter-based OAC optimal algorithm to solve this problem. This algorithm can not only eliminate the influence of the noise floor, but can also effectively protect the weak signal at the tail-end from being lost. The OAC of deep tissues can be calculated accurately and stably. Numerical simulation, phantom, and in vivo experiments were tested to verify the algorithm’s effectiveness in this paper. This technology is expected to play an essential role in disease diagnosis and in the evaluation of the effectiveness of treatment methods. Full article

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17 pages, 4609 KiB

Open AccessArticle

Inference-Optimized High-Performance Photoelectric Target Detection Based on GPU Framework

by Shicheng Zhang, Laixian Zhang, Huichao Guo, Yonghui Zheng, Song Ma and Ying Chen

Photonics 2023, 10(4), 459; https://doi.org/10.3390/photonics10040459 - 16 Apr 2023

Cited by 2 | Viewed by 1550

Abstract

Deep learning has better detection efficiency than typical methods in photoelectric target detection. However, classical CNNs on GPU frameworks consume too much computing power and memory resources. We propose a multi-stream inference-optimized TensorRT (MSIOT) method to solve this problem effectively. MSIOT uses knowledge [...] Read more.

Deep learning has better detection efficiency than typical methods in photoelectric target detection. However, classical CNNs on GPU frameworks consume too much computing power and memory resources. We propose a multi-stream inference-optimized TensorRT (MSIOT) method to solve this problem effectively. MSIOT uses knowledge distillation to effectively reduce the number of model parameters by layer guidance between CNNs and lightweight networks. Moreover, we use the TensorRT and multi-stream mode to reduce the number of model computations. MSIOT again increases inference speed by 9.3% based on the 4.3–7.2× acceleration of TensorRT. The experimental results show that the model’s mean average accuracy, precision, recall, and F1 score after distillation can reach up to 94.20%, 93.16%, 95.4%, and 94.27%, respectively. It is of great significance for designing a real-time photoelectric target detection system. Full article

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11 pages, 6109 KiB

Open AccessCommunication

Nonzero-Order Resonances in Single-Beam Spin-Exchange Relaxation-Free Magnetometers

by Kun Wang, Kaixuan Zhang, Nuozhou Xu, Yifan Yan, Xiaoyu Li and Binquan Zhou

Photonics 2023, 10(4), 458; https://doi.org/10.3390/photonics10040458 - 15 Apr 2023

Cited by 1 | Viewed by 1881

Abstract

Zero-field optically pumped magnetometers operating in the spin-exchange relaxation-free (SERF) regime have been extensively studied, and usually depend on zeroth-order parametric resonance to measure the magnetic field. However, the studies conducted on this topic lack thorough analyses and in-depth discussion of nonzero-order magnetic [...] Read more.

Zero-field optically pumped magnetometers operating in the spin-exchange relaxation-free (SERF) regime have been extensively studied, and usually depend on zeroth-order parametric resonance to measure the magnetic field. However, the studies conducted on this topic lack thorough analyses and in-depth discussion of nonzero-order magnetic resonances in single-beam SERF magnetometers. In this paper, we analyzed the nonzero-order resonance, especially the first-order resonance, based on a single-beam SERF magnetometer, and discussed its various applications. A comprehensive theoretical analysis and experiments were conducted with respect to multiple functions, including nonzero finite magnetic field measurements, spin polarization measurement, and in situ coil constant calibration. The results showed that first-order resonance can be utilized for nonzerofinite magnetic field measurements, and the spin polarization of alkali-metal atoms can be determined by measuring the slowing-down factor using the resonance condition. Furthermore, acquiring the first-order resonance point at an equivalent zero pump light power through fitting offers an approach for quick and precise in situ coil constant calibration. This study contributes to the applications of SERF magnetometers in nonzero finite magnetic fields. Full article

(This article belongs to the Special Issue Optically Pumped Magnetometer and Its Application)

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12 pages, 2985 KiB

Open AccessArticle

Time Coding-Based Single-Photon-Counting Lidar for Obtaining Spatial Location

by Hanfu Zhang, Jie Liu, Qichang An and Jianli Wang

Photonics 2023, 10(4), 457; https://doi.org/10.3390/photonics10040457 - 15 Apr 2023

Cited by 1 | Viewed by 1811

Abstract

This paper proposes a single-photon-counting lidar based on time coding that can obtain the target’s spatial location and measure the distance and azimuth angle in real time without needing a scanning device. Multiple optical fibers were used to introduce laser echo photons into [...] Read more.

This paper proposes a single-photon-counting lidar based on time coding that can obtain the target’s spatial location and measure the distance and azimuth angle in real time without needing a scanning device. Multiple optical fibers were used to introduce laser echo photons into a single-pixel single-photon detector. According to the deviation in the detection time of the echo photons passing through different optical fibers, multiple distances can be obtained simultaneously. Combining the measured distances with the fiber spacing allows the calculation of the distance, azimuth angle, and spatial coordinates of the target. This lidar has the advantages of high photon detection efficiency, short signal acquisition time, and low cost compared to array detectors. Full article

(This article belongs to the Special Issue Advanced Photonic Sensing and Measurement)

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9 pages, 3024 KiB

Open AccessCommunication

Highly Efficient Solution-Processed Bluish-Green Thermally Activated Delayed Fluorescence Compounds Using Di(pyridin-3-yl)methanone as Acceptor

by Yuting He, Cheng Zhang, Hao Yan, Yongshuai Chai and Deyun Zhou

Photonics 2023, 10(4), 456; https://doi.org/10.3390/photonics10040456 - 14 Apr 2023

Viewed by 1424

Abstract

Solution-processed devices with thermally activated delayed fluorescence (TADF) compounds have gained great attention due to their low cost and high performance. Here, two solution-processable TADF emitters named ACCz-DPyM and POxCz-DPyM were synthesized by coupled 9,10-dihydro-9,9-dimethylacridine or phenoxazine modified carbazole as donor with di(pyridin-3-yl)methanone [...] Read more.

Solution-processed devices with thermally activated delayed fluorescence (TADF) compounds have gained great attention due to their low cost and high performance. Here, two solution-processable TADF emitters named ACCz-DPyM and POxCz-DPyM were synthesized by coupled 9,10-dihydro-9,9-dimethylacridine or phenoxazine modified carbazole as donor with di(pyridin-3-yl)methanone as acceptor. Both TADF compounds show same small ΔΕ_ST of 0.04 eV and high PLQY of 66.2% and 58.2%. The devices fabricated by ACCz-DPyM and POxCz-DPyM as emitters show excellent performance as solution-processed with low turn-on voltage of 4.0 and 3.4 V, high luminance of 6209 and 3248 cd m⁻² at 8 V, the maximum current efficiency of 9.9 and 15.9 cd A⁻¹, the maximum external quantum efficiency of 6.6% and 6.5% and low efficiency roll-off. The solution-processed device based on ACCz-DPyM shows bluish-green emission. These results show that ACCz-DPyM and POxCz-DPyM are suitable for solution processing devices. Full article

(This article belongs to the Special Issue Organic and Hybrid Optoelectronic Materials and Devices)

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12 pages, 8178 KiB

Open AccessCommunication

Research on Germanium Photodetector with Multi-Mode Waveguide Input

by Longsheng Wu, Dongsheng Lv, Nengyang Zhao, Ruxue Wang and Aimin Wu

Photonics 2023, 10(4), 455; https://doi.org/10.3390/photonics10040455 - 14 Apr 2023

Cited by 3 | Viewed by 2419

Abstract

In this work, a vertical N-I-P germanium (Ge) photodetector (PD) with a multi-mode waveguide input is presented. The fabricated devices exhibit a low dark current of 10 nA at bias of −1 V, and a high responsivity of exceeding 0.75 A/W over the [...] Read more.

In this work, a vertical N-I-P germanium (Ge) photodetector (PD) with a multi-mode waveguide input is presented. The fabricated devices exhibit a low dark current of 10 nA at bias of −1 V, and a high responsivity of exceeding 0.75 A/W over the wavelength range from 1270 to 1350 nm. High-frequency characteristics measurements show that the photodetector has a 3 dB opto-electrical (OE) bandwidth of 23 GHz under −3 V bias, which can be further improved by optimization of the photodetector configuration. A 50 Gb/s clear eye diagram with a non-return-to-zero (NRZ) modulation format is demonstrated. By using a single-mode excitation source, which is used to simulate light coming from the wavelength division multiplexing (WDM) devices, and sweeping its position, it is shown that the multi-mode input photodetector can be utilized in a WDM receiver to achieve both high responsivity and a flat-top passband. Full article

(This article belongs to the Section Optical Communication and Network)

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14 pages, 2037 KiB

Open AccessArticle

High Efficiency and High Stability for SHG in an Nd:YVO₄ Laser with a KTP Intracavity and Q-Switching through Harmonic Modulation

by Samuel Mardoqueo Afanador Delgado, Juan Hugo García López, Rider Jaimes Reátegui, Vicente Aboites, José Luis Echenausía Monroy and Guillermo Huerta Cuellar

Photonics 2023, 10(4), 454; https://doi.org/10.3390/photonics10040454 - 14 Apr 2023

Cited by 2 | Viewed by 2183

Abstract

In this paper, the stabilization and high efficiency of an unstable Second Harmonic Generation (SHG) of an

N d : Y V O_{4}

laser with a KTP intracavity is demonstrated. By using a passive Q-switching crystal ( [...] Read more.

In this paper, the stabilization and high efficiency of an unstable Second Harmonic Generation (SHG) of an

N d : Y V O_{4}

laser with a KTP intracavity is demonstrated. By using a passive Q-switching crystal (

C r^{4 +} : Y A G

) and a parametric modulation method (harmonic modulation), the stabilization of the laser is reached. An harmonic modulation was applied to the pumping of the

N d : Y V O_{4}

-KTP laser to control the amplitude and frequency of the laser emission. The results were characterized by using power spectra analysis, optical spectrum, bifurcation diagrams, and temporal series of the laser intensity. The promising application of this green light source is materialized when such light is necessary for high-density optics, such as in the treatment materials industry or in some aesthetic applications. Full article

(This article belongs to the Special Issue Lasers and Dynamic of Systems)

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17 pages, 5171 KiB

Open AccessArticle

An Ultra-Low-Loss Waveguide Based on BIC Used for an On-Chip Integrated Optical Gyroscope

by Zhenkun Yuan, Jian Chen, Dingbo Chen, Shuolong Zhu, Junbo Yang and Zhenrong Zhang

Photonics 2023, 10(4), 453; https://doi.org/10.3390/photonics10040453 - 14 Apr 2023

Viewed by 3401

Abstract

The development of integrated optical technology and the continuous emergence of various low-loss optical waveguide materials have promoted the development of low-cost, size, weight, and power optical gyroscopes. However, the losses in conventional optical waveguide materials are much greater than those in optical [...] Read more.

The development of integrated optical technology and the continuous emergence of various low-loss optical waveguide materials have promoted the development of low-cost, size, weight, and power optical gyroscopes. However, the losses in conventional optical waveguide materials are much greater than those in optical fibers, and different waveguide materials often require completely different etching processes, resulting in severely limited gyroscope performance, which is not conducive to the monolithic integration of gyroscope systems. In this paper, an ultra-low-loss Archimedean spiral waveguide structure is designed for an on-chip integrated optical gyroscope by using the high Q value and low-loss optical characteristics of the bound state in the continuum (BIC). The structure does not require the etching of high-refractive-index optical functional materials, avoiding the etching problem that has been difficult to solve for a long time. In addition, the optical properties of the BIC straight and the BIC bent waveguide are simulated using the finite element method (FEM) to find the waveguide structural parameters corresponding to the BIC mode, which is used to design the integrated sensing coil and analyze the gyroscope performance. The simulation results show that the gyroscope’s sensitivity can reach 0.6699°/s. This research is the first time a BIC optical waveguide has been used for an integrated optical gyroscope, providing a novel idea for the monolithic integration of optical gyroscopes. Full article

(This article belongs to the Special Issue Recent Advances in Micro-Nano Optics)

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