Photonics

9 pages, 2950 KiB

Open AccessArticle

Singular Warped Beams Controlled by Tangent Phase Modulation

by Gustavo Funes, Eduardo Peters and Jaime Anguita

Photonics 2021, 8(8), 343; https://doi.org/10.3390/photonics8080343 - 23 Aug 2021

Cited by 1 | Viewed by 2391

We analyze the effect of spatial phase modulation using non-linear functions applied to singular warped beams to control their topological states and intensity distribution. Such beams are candidates for optical trapping and particle manipulation for their controllable pattern of intensities and singularities. We [...] Read more.

We analyze the effect of spatial phase modulation using non-linear functions applied to singular warped beams to control their topological states and intensity distribution. Such beams are candidates for optical trapping and particle manipulation for their controllable pattern of intensities and singularities. We first simulate several kinds of warped beams to analyze their intensity profiles and propagation characteristics. Secondly, we experimentally validate the simulations and investigate the far-field profiles. By calculating the intensity gradients, we describe how these beams are qualified candidates for optical manipulation and trapping. Full article

(This article belongs to the Special Issue Singular Optics)

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24 pages, 4300 KiB

Open AccessReview

Roadmap on Universal Photonic Biosensors for Real-Time Detection of Emerging Pathogens

by Morgan G. Blevins, Alvaro Fernandez-Galiana, Milo J. Hooper and Svetlana V. Boriskina

Photonics 2021, 8(8), 342; https://doi.org/10.3390/photonics8080342 - 20 Aug 2021

Cited by 9 | Viewed by 5035

Abstract

The COVID-19 pandemic has made it abundantly clear that the state-of-the-art biosensors may not be adequate for providing a tool for rapid mass testing and population screening in response to newly emerging pathogens. The main limitations of the conventional techniques are their dependency [...] Read more.

The COVID-19 pandemic has made it abundantly clear that the state-of-the-art biosensors may not be adequate for providing a tool for rapid mass testing and population screening in response to newly emerging pathogens. The main limitations of the conventional techniques are their dependency on virus-specific receptors and reagents that need to be custom-developed for each recently-emerged pathogen, the time required for this development as well as for sample preparation and detection, the need for biological amplification, which can increase false positive outcomes, and the cost and size of the necessary equipment. Thus, new platform technologies that can be readily modified as soon as new pathogens are detected, sequenced, and characterized are needed to enable rapid deployment and mass distribution of biosensors. This need can be addressed by the development of adaptive, multiplexed, and affordable sensing technologies that can avoid the conventional biological amplification step, make use of the optical and/or electrical signal amplification, and shorten both the preliminary development and the point-of-care testing time frames. We provide a comparative review of the existing and emergent photonic biosensing techniques by matching them to the above criteria and capabilities of preventing the spread of the next global pandemic. Full article

(This article belongs to the Special Issue Integrated Optics and Devices)

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11 pages, 2065 KiB

Open AccessArticle

Recovery from Idiopathic Facial Paralysis (Bell’s Palsy) Using Photobiomodulation in Patients Non-Responsive to Standard Treatment: A Case Series Study

by Claudio Pasquale, Anatoliy Utyuzh, Maria Vladimirovna Mikhailova, Esteban Colombo and Andrea Amaroli

Photonics 2021, 8(8), 341; https://doi.org/10.3390/photonics8080341 - 20 Aug 2021

Cited by 16 | Viewed by 8102

Abstract

Diminished facial movement and marked facial asymmetry can lead to a consistent psychological burden. Bell′s palsy (BP) is one of the most common causes of facial nerve illness, which comes with unilateral acute facial paresis. Nowadays, no clear guidelines for treating BP are [...] Read more.

Diminished facial movement and marked facial asymmetry can lead to a consistent psychological burden. Bell′s palsy (BP) is one of the most common causes of facial nerve illness, which comes with unilateral acute facial paresis. Nowadays, no clear guidelines for treating BP are available. We carried out a case series study to test the efficacy of photobiomodulation (PBM) therapy in patients with BP non-responsive to standard treatment. The study was experimentally performed at the Department of Surgical and Diagnostic Sciences, University of Genoa (Genoa, Italy), in accordance with case report guidelines. Patients were referred to our department by colleagues for evaluation to be included in the case series because no consistent improvement was observed at least 3 months from the diagnosis of BP. All the patients interrupted their pharmacological therapy before the initiation of PBM therapy. PBM therapy (808 nm, 1 W irradiated in continuous-wave for 60 s on spot-size 1 cm²; 1 W/cm²; 60 J/cm²; and 60 J) was administered every 2 days until complete resolution. Evaluation of the House-Brackmann scale was performed before and after treatments. Fourteen patients were screened as eligible for the study. Patients were Caucasians (36% females and 64% males) with a mean age ± standard deviation of 56.07 ± 15.21 years. Eleven patients out of 14, who experienced BP a maximum of 6 months, completely recovered through PBM. The three patients that did not show improvement were those who had experienced BP for years. PBM could be a supportive therapy for the management of BP in patients non-responsive to standard treatment. However, randomized controlled trials are necessary to sustain our encouraging results, exclude bias, and better explain the boundary between the time from diagnosis and the recovery of BP through PBM therapy. Full article

(This article belongs to the Special Issue Light as a Cure: Photobiomodulation, from the Cell to the Clinical Application)

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Graphical abstract

20 pages, 382 KiB

Open AccessReview

Spectral Output of Homogeneously Broadened Semiconductor Lasers

by Daniel T. Cassidy

Photonics 2021, 8(8), 340; https://doi.org/10.3390/photonics8080340 - 19 Aug 2021

Cited by 1 | Viewed by 2268

Abstract

Gain, spontaneous emission, and reflectance play important roles in setting the spectral output of homogeneously broadened lasers, such as semiconductor diode lasers. This paper provides a restricted-in-scope review of the steady-state spectral properties of semiconductor diode lasers. Analytic but transcendental solutions for a [...] Read more.

Gain, spontaneous emission, and reflectance play important roles in setting the spectral output of homogeneously broadened lasers, such as semiconductor diode lasers. This paper provides a restricted-in-scope review of the steady-state spectral properties of semiconductor diode lasers. Analytic but transcendental solutions for a simplified set of equations for propagation of modes through a homogeneously broadened gain section are used to create a Fabry–Pérot model of a diode laser. This homogeneously broadened Fabry–Pérot model is used to explain the spectral output of diode lasers without the need for guiding-enhanced capture of spontaneous emission, population beating, or non-linear interactions. It is shown that the amount of spontaneous emission and resonant enhancement of the reflectance-gain (RG) product as embodied in the presented model explains the observed spectral output. The resonant enhancement is caused by intentional and unintentional internal scattering and external feedback. Full article

(This article belongs to the Special Issue Optical Gain in Semiconductors)

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8 pages, 2361 KiB

Open AccessArticle

Spectral Hump Formation in Visible Region of Supercontinuum from Shaped Femtosecond Laser Filamentation in Fused Silica

by Junwei Chang, Dongwei Li, Tingting Xi, Lanzhi Zhang and Zuoqiang Hao

Photonics 2021, 8(8), 339; https://doi.org/10.3390/photonics8080339 - 19 Aug 2021

Cited by 2 | Viewed by 2471

Abstract

We investigate experimentally the local intensity control in the visible region of the supercontinuum (SC) generated from femtosecond laser filamentation in fused silica by using pulse shaping technology. Based on the genetic algorithm, we show that a distinct spectral hump at any preset [...] Read more.

We investigate experimentally the local intensity control in the visible region of the supercontinuum (SC) generated from femtosecond laser filamentation in fused silica by using pulse shaping technology. Based on the genetic algorithm, we show that a distinct spectral hump at any preset wavelength can be formed in the blue-side extension. The local intensity control in the SC could improve the abilities of the SC applications. Full article

(This article belongs to the Special Issue Recent Advances in Nonlinear Optics and Nonlinear Optical Materials)

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9 pages, 2514 KiB

Open AccessCommunication

Nondestructive Structural Investigation of Yttria-Stabilized Zirconia Fiber Insulation Tile by Synchrotron X-ray In-Line Phase-Contrast Microtomography

by Shengkun Yao, Benxue Liu, Jing Ren, Jingwen Liu, Meili Qi and Yangjian Cai

Photonics 2021, 8(8), 338; https://doi.org/10.3390/photonics8080338 - 17 Aug 2021

Viewed by 2249

Abstract

Zirconia (ZrO₂) aerogels show excellent insulating performance and have been widely applied as a thermal protector in furnaces, nuclear reactors, and spacecraft. The nondestructive determination of their interior microstructure is significant for evaluating their mechanical and insulating performance. In this study, [...] Read more.

Zirconia (ZrO₂) aerogels show excellent insulating performance and have been widely applied as a thermal protector in furnaces, nuclear reactors, and spacecraft. The nondestructive determination of their interior microstructure is significant for evaluating their mechanical and insulating performance. In this study, we performed nondestructive structural investigation of an yttria-stabilized ZrO₂ fiber insulation tile using synchrotron X-ray in-line phase-contrast microtomography at a pixel resolution of 6.5 µm. Taking advantage of the edge enhancement of phase-contrast imaging, single yttria-stabilized ZrO₂ fibers were clearly distinguished; furthermore, interior aggregates were nondestructively observed at this spatial resolution. This work demonstrates the advantages and potential of synchrotron X-ray microtomography for the structural analysis of porous ceramic materials. By combining higher-brilliance synchrotron radiation sources and CCD detectors with higher spatial and temporal resolutions, we anticipate that we can further understand the relationship between aerogel microstructure and function, especially under in-service conditions at high temperatures. Full article

(This article belongs to the Special Issue Advances in X-ray Optics)

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8 pages, 3166 KiB

Open AccessCommunication

Augmented Reality Vector Light Field Display with Large Viewing Distance Based on Pixelated Multilevel Blazed Gratings

by Jiacheng Shi, Jianyu Hua, Fengbin Zhou, Min Yang and Wen Qiao

Photonics 2021, 8(8), 337; https://doi.org/10.3390/photonics8080337 - 16 Aug 2021

Cited by 16 | Viewed by 3542

Abstract

Glasses-free augmented reality (AR) 3D display has attracted great interest in its ability to merge virtual 3D objects with real scenes naturally, without the aid of any wearable devices. Here we propose an AR vector light field display based on a view combiner [...] Read more.

Glasses-free augmented reality (AR) 3D display has attracted great interest in its ability to merge virtual 3D objects with real scenes naturally, without the aid of any wearable devices. Here we propose an AR vector light field display based on a view combiner and an off-the-shelf purchased projector. The view combiner is sparsely covered with pixelated multilevel blazed gratings (MBG) for the projection of perspective virtual images. Multi-order diffraction of the MBG is designed to increase the viewing distance and vertical viewing angle. In a 20-inch prototype, multiple sets of 16 horizontal views form a smooth parallax. The viewing distance of the 3D scene is larger than 5 m. The vertical viewing angle is 15.6°. The light efficiencies of all views are larger than 53%. We demonstrate that the displayed virtual 3D scene retains natural motion parallax and high brightness while having a consistent occlusion effect with natural objects. This research can be extended to applications in areas such as human–computer interaction, entertainment, education, and medical care. Full article

(This article belongs to the Special Issue Smart Pixels and Imaging)

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14 pages, 2894 KiB

Open AccessCommunication

Optical Fiber Fabry–Perot Interferometer Based Spirometer: Design and Performance Evaluation

by Ana Catarina Nepomuceno, Tiago Paixão, Nélia Alberto, Paulo Sérgio de Brito André, Paulo Antunes and M. Fátima Domingues

Photonics 2021, 8(8), 336; https://doi.org/10.3390/photonics8080336 - 15 Aug 2021

Cited by 5 | Viewed by 2969

Abstract

Spirometry enables the diagnosis and monitoring of multiple respiratory diseases, such as asthma and chronic obstructive pulmonary disease (COPD). In this paper, we present an optical fiber-based device to evaluate the pulmonary capacity of individuals through spirometry. The proposed system consists of an [...] Read more.

Spirometry enables the diagnosis and monitoring of multiple respiratory diseases, such as asthma and chronic obstructive pulmonary disease (COPD). In this paper, we present an optical fiber-based device to evaluate the pulmonary capacity of individuals through spirometry. The proposed system consists of an optical fiber containing an intrinsic Fabry–Perot interferometer (FPI) micro-cavity attached to a 3D printed structure that converts the air flow into strain variations to the optical fiber, modulating the FPI spectral response. Besides providing the value of the flow, its direction is also determined, which enables a differentiation between inhale and exhale cycles of breathing. A simulation study was conducted to predict the system behavior with the air flow. The preliminary tests, performed with the FPI-based spirometer led to average values of forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) parameters of 4.40 L and 6.46 L, respectively, with an FEV1/FVC index (used as an airway function index) of 68.5%. An average value of 5.35 L/s was found for the peak expiratory flow (PEF). A comparison between the spirometry tests using the presented FPI system and a commercial electronic device showed that the proposed system is suitable to act as a reliable spirometer. Full article

(This article belongs to the Special Issue Optical Fiber Interferometric Sensors: New Production Methodologies and Novel Applications)

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14 pages, 3773 KiB

Open AccessReview

Recent Advancement in Power-over-Fiber Technologies

by Motoharu Matsuura

Photonics 2021, 8(8), 335; https://doi.org/10.3390/photonics8080335 - 15 Aug 2021

Cited by 48 | Viewed by 10837

Abstract

Power-over-fiber is a power transmission technology using optical fibers that offers various features not available in conventional power lines, such as copper wires. The basic configuration of power-over-fiber comprises three key components: light sources, optical fibers, and photovoltaic power converters. This review article [...] Read more.

Power-over-fiber is a power transmission technology using optical fibers that offers various features not available in conventional power lines, such as copper wires. The basic configuration of power-over-fiber comprises three key components: light sources, optical fibers, and photovoltaic power converters. This review article presents the features of power-over-fiber and its key components. Moreover, recent advancement in power-over-fiber technologies based on their latest results is introduced, focusing primarily on papers presented at the Optical Wireless and Fiber Transmission Conferences (OWPT) from 2019 to 2021. Full article

(This article belongs to the Special Issue Latest Papers Related to OWPT 2019-22 on the Topics of Photovoltaic Components, Devices and Systems)

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10 pages, 5461 KiB

Open AccessCommunication

Photonic Nanojet Modulation Achieved by a Spider-Silk-Based Metal–Dielectric Dome Microlens

by Ching-Bin Lin, Yu-Hsiang Lin, Wei-Yu Chen and Cheng-Yang Liu

Photonics 2021, 8(8), 334; https://doi.org/10.3390/photonics8080334 - 14 Aug 2021

Cited by 8 | Viewed by 2781

Abstract

The photonic nanojet is a non-resonance focusing phenomenon with high intensity and narrow spot that can serve as a powerful biosensor for in vivo detection of red blood cells, micro-organisms, and tumor cells in blood. In this study, we first demonstrated photonic nanojet [...] Read more.

The photonic nanojet is a non-resonance focusing phenomenon with high intensity and narrow spot that can serve as a powerful biosensor for in vivo detection of red blood cells, micro-organisms, and tumor cells in blood. In this study, we first demonstrated photonic nanojet modulation by utilizing a spider-silk-based metal–dielectric dome microlens. A cellar spider was employed in extracting the silk fiber, which possesses a liquid-collecting ability to form a dielectric dome microlens. The metal casing on the surface of the dielectric dome was coated by using a glancing angle deposition technique. Due to the nature of surface plasmon polaritons, the characteristics of photonic nanojets are strongly modulated by different metal casings. Numerical and experimental results showed that the intensity of the photonic nanojet was increased by a factor of three for the gold-coated dome microlens due to surface plasmon resonance. The spider-silk-based metal-dielectric dome microlens could be used to scan a biological target for large-area imaging with a conventional optical microscope. Full article

(This article belongs to the Special Issue Photonic Jet: Science and Application)

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18 pages, 13159 KiB

Open AccessArticle

Spectroscopic Approach to Correction and Visualisation of Bright-Field Light Transmission Microscopy Biological Data

by Ganna Platonova, Dalibor Štys, Pavel Souček, Kirill Lonhus, Jan Valenta and Renata Rychtáriková

Photonics 2021, 8(8), 333; https://doi.org/10.3390/photonics8080333 - 13 Aug 2021

Cited by 5 | Viewed by 2207

Abstract

The most realistic information about a transparent sample such as a live cell can be obtained using bright-field light microscopy. Under high-intensity pulsing LED illumination, we captured a primary 12-bit-per-channel (bpc) response from an observed sample using a bright-field microscope equipped with a [...] Read more.

The most realistic information about a transparent sample such as a live cell can be obtained using bright-field light microscopy. Under high-intensity pulsing LED illumination, we captured a primary 12-bit-per-channel (bpc) response from an observed sample using a bright-field microscope equipped with a high-resolution (4872 × 3248) image sensor. In order to suppress data distortions originating from the light interactions with elements in the optical path, poor sensor reproduction (geometrical defects of the camera sensor and some peculiarities of sensor sensitivity), we propose a spectroscopic approach for the correction of these uncompressed 12 bpc data by simultaneous calibration of all parts of the experimental arrangement. Moreover, the final intensities of the corrected images are proportional to the photon fluxes detected by a camera sensor. It can be visualized in 8 bpc intensity depth after the Least Information Loss compression. Full article

(This article belongs to the Special Issue Tissue Optics)

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47 pages, 11067 KiB

Open AccessReview

Miniaturized Interferometric Sensors with Spectral Tunability for Optical Fiber Technology—A Comparison of Size Requirements, Performance, and New Concepts

by Hartmut Hillmer, Carsten Woidt, Aliaksei Kobylinskiy, Matthias Kraus, André Istock, Mustaqim S. Q. Iskhandar, Robert Brunner and Thomas Kusserow

Photonics 2021, 8(8), 332; https://doi.org/10.3390/photonics8080332 - 13 Aug 2021

Cited by 10 | Viewed by 3973

Abstract

Optical interferometric sensors have acquired significant importance in metrology and information technology, especially in terms of their potential application in launching size, selectivity, sensitivity, resolution, spectral tuning ranges, efficiency, and cost. However, these demands are often contradictory and counteract one another, and are [...] Read more.

Optical interferometric sensors have acquired significant importance in metrology and information technology, especially in terms of their potential application in launching size, selectivity, sensitivity, resolution, spectral tuning ranges, efficiency, and cost. However, these demands are often contradictory and counteract one another, and are thus difficult to simultaneously fulfill during their interaction. This review focuses on a detailed comparison of seven different strongly miniaturized sensor concepts investigating the limits of these demands. For the visible and near-infrared spectral range, seven optical sensors were reviewed based on the following methodologies: classical optical transmission and reflection gratings, arrayed waveguide gratings, static Fabry–Pérot (FP) filter arrays, MEMS tunable FP interferometers, MEMS tunable photonic crystals, plasmonic filters, and fiber tip sensors. The comparison between the selected concepts concentrates on (i) the minimum space required for a particular spectral range, (ii) resolution, (iii) the integration in optical fiber technology, (iv) tunability to save space, (v) efficiency in using available light, (vi) multiplexing, (vii) miniaturization limits, and (viii) the potential of nanoimprint for cost reduction. Technologies for enhancing efficiency to obtain more available light and their applicability to the different methodologies were studied. Full article

(This article belongs to the Special Issue Optical Fiber Interferometric Sensors: New Production Methodologies and Novel Applications)

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14 pages, 10078 KiB

Open AccessArticle

Multi-View 3D Integral Imaging Systems Using Projectors and Mobile Devices

by Nikolai Petrov, Maksim Khromov and Yuri Sokolov

Photonics 2021, 8(8), 331; https://doi.org/10.3390/photonics8080331 - 13 Aug 2021

Cited by 2 | Viewed by 3577

Abstract

Glassless 3D displays using projectors and mobile phones based on integral imaging technology have been developed. Three-dimensional image files are created from the 2D images captured by a conventional camera. Large size 3D images using four HD and Ultra HD 4K projectors are [...] Read more.

Glassless 3D displays using projectors and mobile phones based on integral imaging technology have been developed. Three-dimensional image files are created from the 2D images captured by a conventional camera. Large size 3D images using four HD and Ultra HD 4K projectors are created with a viewing angle of 35 degrees and a large depth. Three-dimensional images are demonstrated using optimized lenticular lenses and mobile smartphones, such as LG and Samsung with resolution 2560 × 1440, and 4K Sony with resolution 3840 × 2160. Full article

(This article belongs to the Special Issue Holography)

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12 pages, 6090 KiB

Open AccessArticle

Three-Dimensional Stitching of Binocular Endoscopic Images Based on Feature Points

by Changjiang Zhou, Hao Yu, Bo Yuan, Liqiang Wang and Qing Yang

Photonics 2021, 8(8), 330; https://doi.org/10.3390/photonics8080330 - 12 Aug 2021

Cited by 4 | Viewed by 2863

Abstract

There are shortcomings of binocular endoscope three-dimensional (3D) reconstruction in the conventional algorithm, such as low accuracy, small field of view, and loss of scale information. To address these problems, aiming at the specific scenes of stomach organs, a method of 3D endoscopic [...] Read more.

There are shortcomings of binocular endoscope three-dimensional (3D) reconstruction in the conventional algorithm, such as low accuracy, small field of view, and loss of scale information. To address these problems, aiming at the specific scenes of stomach organs, a method of 3D endoscopic image stitching based on feature points is proposed. The left and right images are acquired by moving the endoscope and converting them into point clouds by binocular matching. They are then preprocessed to compensate for the errors caused by the scene characteristics such as uneven illumination and weak texture. The camera pose changes are estimated by detecting and matching the feature points of adjacent left images. Finally, based on the calculated transformation matrix, point cloud registration is carried out by the iterative closest point (ICP) algorithm, and the 3D dense reconstruction of the whole gastric organ is realized. The results show that the root mean square error is 2.07 mm, and the endoscopic field of view is expanded by 2.20 times, increasing the observation range. Compared with the conventional methods, it does not only preserve the organ scale information but also makes the scene much denser, which is convenient for doctors to measure the target areas, such as lesions, in 3D. These improvements will help improve the accuracy and efficiency of diagnosis. Full article

(This article belongs to the Special Issue Smart Pixels and Imaging)

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15 pages, 4084 KiB

Open AccessFeature PaperArticle

Water Resistant Cellulose Acetate Based Photopolymer for Recording of Volume Phase Holograms

by Sabad-e- Gul, John Cassidy and Izabela Naydenova

Photonics 2021, 8(8), 329; https://doi.org/10.3390/photonics8080329 - 12 Aug 2021

Cited by 5 | Viewed by 3026

Abstract

The development of environmentally robust photosensitive materials for holographic recording is crucial for applications such as outdoor LED light redirection, holographic displays and holographic sensors. Despite the progress in holographic recording materials development, their sensitivity to humidity remains a challenge and protection from [...] Read more.

The development of environmentally robust photosensitive materials for holographic recording is crucial for applications such as outdoor LED light redirection, holographic displays and holographic sensors. Despite the progress in holographic recording materials development, their sensitivity to humidity remains a challenge and protection from the environment is required. One approach to solving this challenge is to select substrate such as cellulose acetate, which is water resistant. This work reports the development of a cellulose-based photopolymer with sensitivity of 3.5 cm²/mJ and refractive index modulation of 2.5 × 10⁻³ achieved in the transmission mode of recording. The suitability for holographic recording was demonstrated by recording gratings with the spatial frequency of 800 linepairs/mm. The intensity dependence of the diffraction efficiency of gratings recorded in 70 μm thick layers was studied and it was observed that the optimum recording intensity was 10 mW/cm². The robustness of the structures was studied after immersing the layer in water for one hour. It was observed that the diffraction efficiency and the surface characteristics measured before and after exposure to water remain unchanged. Finally, the surface hardness was characterized and was shown to be comparable to that of glass and significantly higher than the one of PVA-based acrylamide photopolymer. Full article

(This article belongs to the Special Issue Holography)

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13 pages, 3182 KiB

Open AccessCommunication

Experimental Study on 25 Gbps C-Band PON over up to 25 km SMF Using a 10G-Class DML + APD IM-DD System

by Haoyi Wang, Pablo Torres-Ferrera, Valter Ferrero and Roberto Gaudino

Photonics 2021, 8(8), 328; https://doi.org/10.3390/photonics8080328 - 11 Aug 2021

Cited by 5 | Viewed by 2699

Abstract

In this paper we present an experimental analysis of several modulation formats (pulse amplitude modulation (PAM-2), quaternary pulse amplitude modulation (PAM-4) and electrical duobinary (EDB)) for passive optical network (PON) applications at 25 Gbps bit rate in a C-band 10G-class directly modulated lasers [...] Read more.

In this paper we present an experimental analysis of several modulation formats (pulse amplitude modulation (PAM-2), quaternary pulse amplitude modulation (PAM-4) and electrical duobinary (EDB)) for passive optical network (PON) applications at 25 Gbps bit rate in a C-band 10G-class directly modulated lasers (DML) and avalanche photodiode (APD) intensity modulation and direct detection (IM-DD) system over a single mode fiber (SMF) of up to 25 km, optimizing DML operations and demonstrating that PAM-2 is a promising choice. We also theoretically and experimentally analyzed the channel frequency response of DML and SMF affected by DML chirp and SMF chromatic dispersion. Full article

(This article belongs to the Special Issue Directly-Modulated Lasers)

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7 pages, 1712 KiB

Open AccessCommunication

Highly Efficient Double-Layer Diffraction Microstructures Based on New Plastics and Molded Glasses

by Grigoriy I. Greisukh, Viktor A. Danilov, Evgeniy G. Ezhov, Sergey V. Kazin and Boris A. Usievich

Photonics 2021, 8(8), 327; https://doi.org/10.3390/photonics8080327 - 11 Aug 2021

Cited by 5 | Viewed by 1881

Abstract

Within the framework of rigorous diffraction theory, the maximum possible incidence angles of radiation on two-layer sawtooth relief-phase microstructures in the visible (0.4 ≤ λ ≤ 0.7 μm) spectral range are compared. Optical materials for the layers of these microstructures are selected from [...] Read more.

Within the framework of rigorous diffraction theory, the maximum possible incidence angles of radiation on two-layer sawtooth relief-phase microstructures in the visible (0.4 ≤ λ ≤ 0.7 μm) spectral range are compared. Optical materials for the layers of these microstructures are selected from a database of 47 plastics and 165 molded glasses. It is shown that when the ratio of the spatial period of the microstructure to the effective depth of the relief is greater than 20, the achievable angles within which the diffraction efficiency exceeds 0.95 lie in a wide range from 18.5° to 40.5° for single-relief structures and 7.5° to 22.3° for structures with two internal reliefs. The best results for purely plastic microstructures are obtained when the plastic CMT and the indium tin oxide nanocomposite in polymethylmethacrylate are used. Full article

(This article belongs to the Special Issue Polarized Light and Optical Systems)

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11 pages, 443 KiB

Open AccessCommunication

Quantum Chaos in Time Series of Single Photons as a Superposition of Wave and Particle States

by Benjamín David Mendoza, Diego Alberto Lara, Jehú López-Aparicio, Gustavo Armendáriz, Leonardo López-Hernández, Víctor Velázquez, Edna Magdalena Hernández, Marcela Grether, Enrique López-Moreno and Alejandro Frank

Photonics 2021, 8(8), 326; https://doi.org/10.3390/photonics8080326 - 11 Aug 2021

Cited by 2 | Viewed by 2826

Abstract

We build a time series of single photons with quantum chaos statistics, using a version of the Grangier anti-correlation experiment. The criteria utilized to determine the presence of quantum chaos is the frame of the Fano factor and the power spectrum. We also [...] Read more.

We build a time series of single photons with quantum chaos statistics, using a version of the Grangier anti-correlation experiment. The criteria utilized to determine the presence of quantum chaos is the frame of the Fano factor and the power spectrum. We also show that photons with chaotic statistics are in a balanced superposition of photons with both wave-like and particle like behaviors. To support the presence of quantum chaos, we study both Shannon’s entropy, and the complexity of single photons time series. Full article

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12 pages, 6826 KiB

Open AccessArticle

High-Precision Time-Frequency Signal Simultaneous Transfer System via a WDM-Based Fiber Link

by Qi Zang, Honglei Quan, Kan Zhao, Xiang Zhang, Xue Deng, Wenxiang Xue, Faxi Chen, Tao Liu, Ruifang Dong and Shougang Zhang

Photonics 2021, 8(8), 325; https://doi.org/10.3390/photonics8080325 - 10 Aug 2021

Cited by 13 | Viewed by 3085

Abstract

In this paper, we demonstrate a wavelength division multiplexing (WDM)-based system for simultaneously delivering ultra-stable optical frequency reference, 10 GHz microwave frequency reference, and a one pulse per second (1 PPS) time signal via a 50 km fiber network. For each signal, a [...] Read more.

In this paper, we demonstrate a wavelength division multiplexing (WDM)-based system for simultaneously delivering ultra-stable optical frequency reference, 10 GHz microwave frequency reference, and a one pulse per second (1 PPS) time signal via a 50 km fiber network. For each signal, a unique noise cancellation technique is used to maintain their precision. After being compensated, the transfer frequency instability in terms of the overlapping Allan deviation (OADEV) for the optical frequency achieves 2 × 10

^{- 17}

/s and scales down to 2 × 10

^{- 20}

/10,000 s, which for the 10 GHz microwave reference, approaches 4 × 10

^{- 15}

/s and decreases to 1.4 × 10

^{- 17}

/10,000 s, and the time uncertainty of the 1 PPS time signal along the system is 2.08 ps. In this scheme, specific channels of WDM are, respectively, occupied for different signals to avoid the possible crosstalk interference effect between the transmitted reference signals. To estimate the performance of the above scheme, which is also demonstrated in this 50 km link independent of these signals, the results are similar to that in the case of simultaneous delivery. This work shows that the WDM-based system is a promising method for building a nationwide time and frequency fiber transfer system with a communication optical network. Full article

(This article belongs to the Special Issue Optical Network and Access Technologies)

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19 pages, 33495 KiB

Open AccessReview

A Review of Transparent Sensors for Photoacoustic Imaging Applications

by Danyang Ren, Yizhe Sun, Junhui Shi and Ruimin Chen

Photonics 2021, 8(8), 324; https://doi.org/10.3390/photonics8080324 - 10 Aug 2021

Cited by 36 | Viewed by 6054

Abstract

Photoacoustic imaging is a new type of noninvasive, nonradiation imaging modality that combines the deep penetration of ultrasonic imaging and high specificity of optical imaging. Photoacoustic imaging systems employing conventional ultrasonic sensors impose certain constraints such as obstructions in the optical path, bulky [...] Read more.

Photoacoustic imaging is a new type of noninvasive, nonradiation imaging modality that combines the deep penetration of ultrasonic imaging and high specificity of optical imaging. Photoacoustic imaging systems employing conventional ultrasonic sensors impose certain constraints such as obstructions in the optical path, bulky sensor size, complex system configurations, difficult optical and acoustic alignment, and degradation of signal-to-noise ratio. To overcome these drawbacks, an ultrasonic sensor in the optically transparent form has been introduced, as it enables direct delivery of excitation light through the sensors. In recent years, various types of optically transparent ultrasonic sensors have been developed for photoacoustic imaging applications, including optics-based ultrasonic sensors, piezoelectric-based ultrasonic sensors, and microelectromechanical system-based capacitive micromachined ultrasonic transducers. In this paper, the authors review representative transparent sensors for photoacoustic imaging applications. In addition, the potential challenges and future directions of the development of transparent sensors are discussed. Full article

(This article belongs to the Special Issue Photoacoustic Imaging and Systems)

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9 pages, 2006 KiB

Open AccessArticle

Photonic Crystal Surface Emitting Laser Operating in Pulse-Periodic Regime with Ultralow Divergence Angle

by Ziye Wang, Cunzhu Tong, Lijie Wang, Huanyu Lu, Sicong Tian and Lijun Wang

Photonics 2021, 8(8), 323; https://doi.org/10.3390/photonics8080323 - 10 Aug 2021

Cited by 4 | Viewed by 3490

Abstract

The nanosecond-level pulse-operation characteristics of photonic-crystal surface-emitting lasers (PCSELs) with ultralow divergence were investigated in detail. We demonstrate a maximum peak output power of 14 W for a current pulse width of 9 ns, which is about 28 times the saturated power under [...] Read more.

The nanosecond-level pulse-operation characteristics of photonic-crystal surface-emitting lasers (PCSELs) with ultralow divergence were investigated in detail. We demonstrate a maximum peak output power of 14 W for a current pulse width of 9 ns, which is about 28 times the saturated power under continuous wave (CW) operation. The full width at half maximum (FWHM) of the optical response pulse is about 3 ns wider than the current pulse. The maximum repetition frequency reaches 400 kHz at 10 A without significant degradation of output power while the value is 100 kHz at 40 A. Moreover, the multimode behavior of the PCSEL at a high peak current was analyzed. Full article

(This article belongs to the Special Issue Semiconductor Lasers)

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2 pages, 834 KiB

Open AccessCorrection

Correction: Zia, H. Enhanced Pulse Compression within Sign-Alternating Dispersion Waveguides. Photonics 2021, 8, 50

by Haider Zia

Photonics 2021, 8(8), 322; https://doi.org/10.3390/photonics8080322 - 10 Aug 2021

Viewed by 1775

Abstract

Error in Figure 2 [...] Full article

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15 pages, 3783 KiB

Open AccessArticle

Low-Light-Level Image Super-Resolution Reconstruction Based on a Multi-Scale Features Extraction Network

by Bowen Wang, Yan Zou, Linfei Zhang, Yan Hu, Hao Yan, Chao Zuo and Qian Chen

Photonics 2021, 8(8), 321; https://doi.org/10.3390/photonics8080321 - 10 Aug 2021

Cited by 18 | Viewed by 3847

Abstract

Wide field-of-view (FOV) and high-resolution (HR) imaging are essential to many applications where high-content image acquisition is necessary. However, due to the insufficient spatial sampling of the image detector and the trade-off between pixel size and photosensitivity, the ability of current imaging sensors [...] Read more.

Wide field-of-view (FOV) and high-resolution (HR) imaging are essential to many applications where high-content image acquisition is necessary. However, due to the insufficient spatial sampling of the image detector and the trade-off between pixel size and photosensitivity, the ability of current imaging sensors to obtain high spatial resolution is limited, especially under low-light-level (LLL) imaging conditions. To solve these problems, we propose a multi-scale feature extraction (MSFE) network to realize pixel-super-resolved LLL imaging. In order to perform data fusion and information extraction for low resolution (LR) images, the network extracts high-frequency detail information from different dimensions by combining the channel attention mechanism module and skip connection module. In this way, the calculation of the high-frequency components can receive greater attention. Compared with other networks, the peak signal-to-noise ratio of the reconstructed image was increased by 1.67 dB. Extensions of the MSFE network are investigated for scene-based color mapping of the gray image. Most of the color information could be recovered, and the similarity with the real image reached 0.728. The qualitative and quantitative experimental results show that the proposed method achieved superior performance in image fidelity and detail enhancement over the state-of-the-art. Full article

(This article belongs to the Special Issue Smart Pixels and Imaging)

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13 pages, 2492 KiB

Open AccessArticle

Thermal, Optical, and IR-Emission Properties of Extremely Low Hydroxyl TeO₂-WO₃-Bi₂O₃-La₂O₃-xEr₂O₃ Glasses for Mid-Infrared Photonics

by Vitaly V. Dorofeev, Vasily V. Koltashev, Sergei E. Motorin, Alexander D. Plekhovich and Arkady V. Kim

Photonics 2021, 8(8), 320; https://doi.org/10.3390/photonics8080320 - 9 Aug 2021

Cited by 10 | Viewed by 2892

Abstract

A series of glass samples of the tungsten–tellurite system TeO₂-WO₃-Bi₂O₃-(4-x) La₂O₃-xEr₂O₃, x = 0; 0.4; 0.5; 0.7; 1.2; 2; 4 mol%, C_Er = 0 - 15 [...] Read more.

A series of glass samples of the tungsten–tellurite system TeO₂-WO₃-Bi₂O₃-(4-x) La₂O₃-xEr₂O₃, x = 0; 0.4; 0.5; 0.7; 1.2; 2; 4 mol%, C_Er = 0 - 15 × 10²⁰ cm⁻³ were synthesized from high-purity oxides in an oxygen flow inside a specialized sealed reactor. In all samples of the series, an extremely low content of hydroxyl groups was achieved (~n × 10¹⁶ cm⁻³, more than 4 orders of magnitude lower than the concentration of erbium ions), which guarantees minimal effects on the luminescence properties of Er³⁺. The glasses are resistant to crystallization up to 4 mol% Er₂O₃, and the glass transition temperatures do not depend on the concentration of erbium oxide when introduced by replacing lanthanum oxide. Thin 0.2 mm plates have high transmittance at a level of 20% in the 4.7–5.3 µm range, and the absorption bands of hydroxyl groups at about 2.3, 3, and 4.4 µm, which are typical for ordinary tellurite glass samples, are indistinguishable. The introduction of erbium oxide led to an insignificant change in the refractive index. Er₂O₃-concentration dependences of the luminescence intensities and lifetimes near the wavelengths of 1.53 and 2.75 μm were found for the ⁴I₁₃_/₂–⁴I₁₅_/₂ and ⁴I₁₁_/2–⁴I₁₃_/_{2 /}transitions of the Er³⁺ ion. The data obtained are necessary for the development of mid-infrared photonics; in particular, for the design of Er³⁺-doped fiber lasers. Full article

(This article belongs to the Special Issue Advances in Modern Photonics)

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12 pages, 6794 KiB

Open AccessArticle

Efficient Fourier Single-Pixel Imaging with Gaussian Random Sampling

by Ziheng Qiu, Xinyi Guo, Tian’ao Lu, Pan Qi, Zibang Zhang and Jingang Zhong

Photonics 2021, 8(8), 319; https://doi.org/10.3390/photonics8080319 - 9 Aug 2021

Cited by 17 | Viewed by 3813

Abstract

Fourier single-pixel imaging (FSI) is a branch of single-pixel imaging techniques. It allows any image to be reconstructed by acquiring its Fourier spectrum by using a single-pixel detector. FSI uses Fourier basis patterns for structured illumination or structured detection to acquire the Fourier [...] Read more.

Fourier single-pixel imaging (FSI) is a branch of single-pixel imaging techniques. It allows any image to be reconstructed by acquiring its Fourier spectrum by using a single-pixel detector. FSI uses Fourier basis patterns for structured illumination or structured detection to acquire the Fourier spectrum of image. However, the spatial resolution of the reconstructed image mainly depends on the number of Fourier coefficients sampled. The reconstruction of a high-resolution image typically requires a number of Fourier coefficients to be sampled. Consequently, a large number of single-pixel measurements lead to a long data acquisition time, resulting in imaging of a dynamic scene challenging. Here we propose a new sampling strategy for FSI. It allows FSI to reconstruct a clear and sharp image with a reduced number of measurements. The key to the proposed sampling strategy is to perform a density-varying sampling in the Fourier space and, more importantly, the density with respect to the importance of Fourier coefficients is subject to a one-dimensional Gaussian function. The final image is reconstructed from the undersampled Fourier spectrum through compressive sensing. We experimentally demonstrate the proposed method is able to reconstruct a sharp and clear image of 256 × 256 pixels with a sampling ratio of 10%. The proposed method enables fast single-pixel imaging and provides a new approach for efficient spatial information acquisition. Full article

(This article belongs to the Special Issue Smart Pixels and Imaging)

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14 pages, 27459 KiB

Open AccessArticle

Time and Spatial Jitter Influence on the Performance of FSO Links with DF Relays and OC Diversity Over Turbulence Channels

by Panagiotis J. Gripeos, Hector E. Nistazakis, Andreas D. Tsigopoulos, Vasilis Christofilakis and Evgenia Roditi

Photonics 2021, 8(8), 318; https://doi.org/10.3390/photonics8080318 - 7 Aug 2021

Cited by 1 | Viewed by 2787

Abstract

FSO communication is a viral technology among optical wireless communications, gathering the interest of both researchers and manufacturers. This is because of the many advantages associated with FSO communication, including high data rates, reliability, safety, and economy. However, there are several unavoidable drawbacks [...] Read more.

FSO communication is a viral technology among optical wireless communications, gathering the interest of both researchers and manufacturers. This is because of the many advantages associated with FSO communication, including high data rates, reliability, safety, and economy. However, there are several unavoidable drawbacks that shadow the performance of FSO systems. For example, atmospheric turbulence is a well-known problem related to the weather conditions of the channel, which causes the scintillation effect. Also, spatial jitter due to pointing errors is a critical factor of the link’s performance, caused by occasional misalignments between the transmitter and the receiver. Moreover, time jitter is another limiting agent that deteriorates the total throughput, inducing bit stream misdetections, caused by the arrival of out-of-sync pulses. All three effects have been exhaustively studied and many statistical models and interesting solutions have been proposed in the literature to estimate their magnitude and compensate for their impact. In this work, the turbulence effect was treated by Málaga distribution, the spatial jitter effect was regulated by the non-zero boresight model, and the time jitter effect was modeled by the generalized Gaussian distribution. Various modulation schemes were studied, along with DF multi-hop and optimal combining diversity techniques at the receiver’s end. New, accurate mathematical expressions of average BER performance have been obtained, and valuable conclusions were drawn thanks to the presented numerical results. Full article

(This article belongs to the Special Issue Optical Wireless Communications Systems)

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12 pages, 5783 KiB

Open AccessArticle

Multispectral Photonic Jet Shaping and Steering by Control of Tangential Electric Field Component on Cuboid Particle

by Cheng-Yang Liu, Wei-Yu Chen, Oleg V. Minin and Igor V. Minin

Photonics 2021, 8(8), 317; https://doi.org/10.3390/photonics8080317 - 6 Aug 2021

Cited by 4 | Viewed by 2221

Abstract

In this study, we present the simulations and experimental observations of photonic jet (PJ) shaping by control of tangential electric field components at illuminating wavelengths of 405 nm, 532 nm, and 671 nm. The PJs are generated by a single dielectric 4-micrometer cube [...] Read more.

In this study, we present the simulations and experimental observations of photonic jet (PJ) shaping by control of tangential electric field components at illuminating wavelengths of 405 nm, 532 nm, and 671 nm. The PJs are generated by a single dielectric 4-micrometer cube that was fabricated from polydimethylsiloxane (PDMS). The dielectric cube is deposited on a silicon substrate and placed on two aluminum masks with a width equal to the side length of the cube. Due to the appearance of the metal masks, the focal length and decay length of the generated PJs decreased almost twice, while the PJ resolution increased 1.2 times. Thus, PJ shaping can be controlled by the presence of the metal mask along the lateral surface of the cube without changing the external shape or internal structure of the cube. This effect is based on the control of the tangential components of the electric field along the lateral surface of the cube. In the case of a one-sided metal mask, the effect of optical deflection and bending is predicted to form a photonic hook. Due to the low cost of these dielectric cubes, they have potential in far-field systems to better meet the requirements of modern optical integration circuits and switches. Full article

(This article belongs to the Special Issue Photonic Devices and Systems)

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10 pages, 4106 KiB

Open AccessCommunication

Development of a 1 TW/35 fs Ti:sapphire Laser Amplifier and Generation of Intense THz Waves Using Two-Color Laser Filamentation

by Vanessa Ling Jen Phung, Keekon Kang, Seongjin Jeon, Jinju Kim, Kyungmin Roh and Hyyong Suk

Photonics 2021, 8(8), 316; https://doi.org/10.3390/photonics8080316 - 5 Aug 2021

Cited by 2 | Viewed by 2967

Abstract

We developed a compact Ti:sapphire laser amplifier system in our laboratory, generating intense laser pulses with a peak power of >1 TW (terawatt), a pulse duration of 34 fs (femtosecond), a central wavelength of 800 nm, and a repetition rate of 10 Hz. [...] Read more.

We developed a compact Ti:sapphire laser amplifier system in our laboratory, generating intense laser pulses with a peak power of >1 TW (terawatt), a pulse duration of 34 fs (femtosecond), a central wavelength of 800 nm, and a repetition rate of 10 Hz. The laser amplifier system consists of a mode-locked Ti:sapphire oscillator, a regenerative amplifier, and a single-side-pumped 4-pass amplifier. The chirped-pulse amplification (CPA)-based laser amplifier was found to provide an energy of 49.6 mJ after compression by gratings in air, where the pumping fluence of 1.88 J/cm² was used. The amplified spontaneous emission (ASE) level was measured to be lower than 10⁻⁷, and ps-prepulses were in 10⁻⁴ or lower level. The developed laser amplifier system was used for the generation of intense THz (terahertz) waves by focusing the original (800 nm) and second harmonic (400 nm) laser pulses in air. The THz pulse energy was shown to be saturated in the high laser energy regime, and this phenomenon was confirmed by fully electromagnetic, relativistic, and self-consistent particle-in-cell (PIC) simulations. Full article

(This article belongs to the Special Issue Laser Amplifiers)

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14 pages, 4959 KiB

Open AccessCommunication

Geometric Interpretation and General Classification of Three-Dimensional Polarization States through the Intrinsic Stokes Parameters

by José J. Gil

Photonics 2021, 8(8), 315; https://doi.org/10.3390/photonics8080315 - 4 Aug 2021

Cited by 8 | Viewed by 2441

Abstract

In contrast with what happens for two-dimensional polarization states, defined as those whose electric field fluctuates in a fixed plane, which can readily be represented by means of the Poincaré sphere, the complete description of general three-dimensional polarization states involves nine measurable parameters, [...] Read more.

In contrast with what happens for two-dimensional polarization states, defined as those whose electric field fluctuates in a fixed plane, which can readily be represented by means of the Poincaré sphere, the complete description of general three-dimensional polarization states involves nine measurable parameters, called the generalized Stokes parameters, so that the generalized Poincaré object takes the complicated form of an eight-dimensional quadric hypersurface. In this work, the geometric representation of general polarization states, described by means of a simple polarization object constituted by the combination of an ellipsoid and a vector, is interpreted in terms of the intrinsic Stokes parameters, which allows for a complete and systematic classification of polarization states in terms of meaningful rotationally invariant descriptors. Full article

(This article belongs to the Special Issue Polarized Light and Optical Systems)

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13 pages, 2988 KiB

Open AccessArticle

Controlled Excitation of Supermodes in a Multicore Fiber with a 5 × 5 Square Array of Strongly Coupled Cores

by Nikolay A. Kalinin, Elena A. Anashkina, Olga N. Egorova, Sergey G. Zhuravlev, Sergei L. Semjonov, Arkady V. Kim, Alexander G. Litvak and Alexey V. Andrianov

Photonics 2021, 8(8), 314; https://doi.org/10.3390/photonics8080314 - 4 Aug 2021

Cited by 11 | Viewed by 2570

Abstract

Coherent propagation of supermodes in a multicore fiber is promising for power scaling of fiber laser systems, eliminating the need for the active feedback system to maintain the phases between the channels. We studied the propagation of broadband pulsed radiation at a central [...] Read more.

Coherent propagation of supermodes in a multicore fiber is promising for power scaling of fiber laser systems, eliminating the need for the active feedback system to maintain the phases between the channels. We studied the propagation of broadband pulsed radiation at a central wavelength of 1030 nm in a multicore fiber with coupled cores arranged in a square array. We designed and fabricated a silica multicore fiber with a 5 × 5 array of cores. For controllable excitation of a desired supermode, we developed a beam-forming system based on a spatial light modulator. We experimentally measured intensity and phase distributions of the supermodes, in particular, the in-phase and out-of-phase supermodes, which matched well the numerically calculated profiles. We obtained selective excitation and coherent propagation of broadband radiation with the content of the out-of-phase supermode of up to 90% maintained without active feedback. Using three-dimensional numerical modeling with allowance for a refractive index profile similar to those of the developed fiber, we demonstrated stable propagation of the out-of-phase supermode and collapse of the in-phase supermode at a high signal power. Full article

(This article belongs to the Special Issue Integrated Optics and Devices)

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