Photonics

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18 pages, 44237 KiB

Open AccessArticle

The Lattice Geometry of Walsh-Function-Based Adaptive Optics

by Qi Hu, Yuyao Xiao, Jiahe Cui, Raphaël Turcotte and Martin J. Booth

Photonics 2022, 9(8), 547; https://doi.org/10.3390/photonics9080547 - 4 Aug 2022

Cited by 1 | Viewed by 2331

We show that there is an intrinsic link between the use of Walsh aberration modes in adaptive optics (AO) and the mathematics of lattices. The discrete and binary nature of these modes means that there are infinite combinations of Walsh mode coefficients that [...] Read more.

We show that there is an intrinsic link between the use of Walsh aberration modes in adaptive optics (AO) and the mathematics of lattices. The discrete and binary nature of these modes means that there are infinite combinations of Walsh mode coefficients that can optimally correct the same aberration. Finding such a correction is hence a poorly conditioned optimisation problem that can be difficult to solve. This can be mitigated by confining the AO correction space defined in Walsh mode coefficients to the fundamental Voronoi cell of a lattice. By restricting the correction space in this way, one can ensure there is only one set of Walsh coefficients that corresponds to the optimum correction aberration. This property is used to enable the design of efficient estimation algorithms to solve the inverse problem of finding correction aberrations from a sequence of measurements in a wavefront sensorless AO system. The benefit of this approach is illustrated using a neural-network-based estimator. Full article

(This article belongs to the Special Issue Various Applications of Methods and Elements of Adaptive Optics)

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13 pages, 5183 KiB

Open AccessArticle

Real-Time Correction of a Laser Beam Wavefront Distorted by an Artificial Turbulent Heated Airflow

by Alexey Rukosuev, Alexander Nikitin, Vladimir Toporovsky, Julia Sheldakova and Alexis Kudryashov

Photonics 2022, 9(5), 351; https://doi.org/10.3390/photonics9050351 - 17 May 2022

Cited by 14 | Viewed by 2150

Abstract

This paper presents a FPGA-based closed-loop adaptive optical system with a bimorph deformable mirror for correction of the phase perturbation caused by artificial turbulence. The system’s operating frequency of about 2000 Hz is, in many cases, sufficient to provide the real-time mode. The [...] Read more.

This paper presents a FPGA-based closed-loop adaptive optical system with a bimorph deformable mirror for correction of the phase perturbation caused by artificial turbulence. The system’s operating frequency of about 2000 Hz is, in many cases, sufficient to provide the real-time mode. The results of the correction of the wavefront of laser radiation distorted by the airflow formed in the laboratory conditions with the help of a fan heater are presented. For detailed consideration, the expansion of the wavefront by Zernike polynomials is used with further statistical analysis based on the discrete Fourier transform. The result of the work is an estimation of the correction efficiency of the wavefront distorted by the turbulent phase fluctuations. The ability of the bimorph adaptive mirror to correct for certain aberrations is also determined. As a result, it was concluded that the adaptive bimorph mirrors, together with a fast adaptive optical system based on FPGA, can be used to compensate wavefront distortions caused by atmospheric turbulence in the real-time mode. Full article

(This article belongs to the Special Issue Various Applications of Methods and Elements of Adaptive Optics)

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11 pages, 3929 KiB

Open AccessArticle

Local Correction of the Light Position Implemented on an FPGA Platform for a 6 Meter Telescope

by Valentina Klochkova, Julia Sheldakova, Ilya Galaktionov, Alexander Nikitin, Alexis Kudryashov, Vadim Belousov and Alexey Rukosuev

Photonics 2022, 9(5), 322; https://doi.org/10.3390/photonics9050322 - 8 May 2022

Cited by 1 | Viewed by 1698

Abstract

The low-frequency component of the distortions caused by both the atmospheric turbulence and the behavior of the telescope itself has been studied. A corrector for the position of the center of the star image has been developed and is being used in front [...] Read more.

The low-frequency component of the distortions caused by both the atmospheric turbulence and the behavior of the telescope itself has been studied. A corrector for the position of the center of the star image has been developed and is being used in front of the high-resolution Echelle spectrograph on the 6 m telescope of the Special Astrophysical Observatory, Russian Academy of Sciences. To speed up the calculations and to increase the bandwidth, a laser beam angular stabilization system based on an FPGA platform is considered. The system consists of two tip-tilt mirrors and two quadrant photodiodes. The FPGA analyzes the signals from the photodiodes, calculates and then applies the voltages to the piezo-driven tip-tilt mirrors to minimize the displacement of the beam on the photodiodes. The stabilization system was developed as a part of the adaptive optical system to improve the efficiency of the high-resolution Echelle spectrograph. Full article

(This article belongs to the Special Issue Various Applications of Methods and Elements of Adaptive Optics)

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10 pages, 5937 KiB

Open AccessCommunication

State-of-the-Art Technologies in Piezoelectric Deformable Mirror Design

by Vladimir Toporovsky, Alexis Kudryashov, Arkadiy Skvortsov, Alexey Rukosuev, Vadim Samarkin and Ilya Galaktionov

Photonics 2022, 9(5), 321; https://doi.org/10.3390/photonics9050321 - 8 May 2022

Cited by 22 | Viewed by 2803

Abstract

In this work, two advanced technologies were applied for manufacturing a bimorph wavefront corrector: laser ablation, to vaporize conductive silver coating from piezoceramic surface, and parallel-gap resistance microwelding, to provide a reliable electrical contact between the piezodisk surface silver electrodes and copper wires. [...] Read more.

In this work, two advanced technologies were applied for manufacturing a bimorph wavefront corrector: laser ablation, to vaporize conductive silver coating from piezoceramic surface, and parallel-gap resistance microwelding, to provide a reliable electrical contact between the piezodisk surface silver electrodes and copper wires. A step-by-step guide for bimorph mirror production is presented, together with the ‘bottlenecks’. Optimization of the laser ablation technique was carried out using an Nd:YAG laser with an output power of 4 W and a frequency of 20 kHz. A comparison of the ultrasonic welding and parallel-gap resistance microwelding methods was performed. The tensile strength in the first case was in the range of 0.2…0.25 N for the system ‘copper wire–silver coating’. The use of resistance welding made it possible to increase the value of this parameter for the same contact pair by almost two times (0.45…0.5 N). Full article

(This article belongs to the Special Issue Various Applications of Methods and Elements of Adaptive Optics)

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10 pages, 2940 KiB

Open AccessArticle

Focusing of a Laser Beam Passed through a Moderately Scattering Medium Using Phase-Only Spatial Light Modulator

by Ilya Galaktionov, Alexander Nikitin, Julia Sheldakova, Vladimir Toporovsky and Alexis Kudryashov

Photonics 2022, 9(5), 296; https://doi.org/10.3390/photonics9050296 - 27 Apr 2022

Cited by 14 | Viewed by 2700

Abstract

The rarely considered case of laser beam propagation and focusaing through the moderately scattering medium was researched. A phase-only spatial light modulator (SLM) with 1920×1080 pixel resolution was used to increase the efficiency of focusing of laser radiation propagated through the 5 mm [...] Read more.

The rarely considered case of laser beam propagation and focusaing through the moderately scattering medium was researched. A phase-only spatial light modulator (SLM) with 1920×1080 pixel resolution was used to increase the efficiency of focusing of laser radiation propagated through the 5 mm layer of the scattering suspension of 1 µm polystyrene microbeads in distilled water with the concentration values ranging from 10⁵ to 10⁶ mm⁻³. A CCD camera with micro-objective was used to estimate the intensity distribution of the far-field focal spot. A Shack-Hartmann sensor was used to measure wavefront distortions. The conducted experimental research demonstrated the 8% increase in integral intensity and 16% decrease in diameter of the far-field focal spot due to the use of the SLM for laser beam focusing. Full article

(This article belongs to the Special Issue Various Applications of Methods and Elements of Adaptive Optics)

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14 pages, 5622 KiB

Open AccessArticle

Development of Singular Points in a Beam Passed Phase Screen Simulating Atmospheric Turbulence and Precision of Such a Screen Approximation by Zernike Polynomials

by Feodor Kanev, Nailya Makenova and Igor Veretekhin

Photonics 2022, 9(5), 285; https://doi.org/10.3390/photonics9050285 - 21 Apr 2022

Cited by 1 | Viewed by 1820

Abstract

This article addresses two issues. Firstly, it was shown that if the initial phase of a Gaussian beam is specified by the sum of Zernike polynomials or by a screen simulating atmospheric turbulence, in the process of propagation, singular points appear in the [...] Read more.

This article addresses two issues. Firstly, it was shown that if the initial phase of a Gaussian beam is specified by the sum of Zernike polynomials or by a screen simulating atmospheric turbulence, in the process of propagation, singular points appear in the wavefront of such a beam. With the use of numerical simulation, the dependence of the vortices number on the distortion characteristics and on the distance traveled by the beam was determined. The second problem analyzed in the article is the problem of a phase screen approximation by a series formed by Zernike polynomials. The carried out numerical experiments made it possible to determine the dependence of approximation accuracy on the screen parameters and on the number of polynomials entering the basis of approximation. Full article

(This article belongs to the Special Issue Various Applications of Methods and Elements of Adaptive Optics)

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12 pages, 2927 KiB

Open AccessArticle

On-Demand Phase Control of a 7-Fiber Amplifiers Array with Neural Network and Quasi-Reinforcement Learning

by Maksym Shpakovych, Geoffrey Maulion, Alexandre Boju, Paul Armand, Alain Barthélémy, Agnès Desfarges-Berthelemot and Vincent Kermene

Photonics 2022, 9(4), 243; https://doi.org/10.3390/photonics9040243 - 6 Apr 2022

Cited by 8 | Viewed by 2454

Abstract

We report a coherent beam combining technique using a specific quasi-reinforcement learning scheme. A neural network learned by this method enables the tailoring and locking of a tiled beam array on any phase map. We present the experimental implementation of on-demand phase control [...] Read more.

We report a coherent beam combining technique using a specific quasi-reinforcement learning scheme. A neural network learned by this method enables the tailoring and locking of a tiled beam array on any phase map. We present the experimental implementation of on-demand phase control by a neural network in a seven-fiber laser array. This servo loop needs only six phase corrections to converge to the desired phase set at any profile, with a bandwidth higher than 1 kHz. Moreover, we demonstrate the dynamical feature of adaptive phase control, performing sequences of controlled phase sets. It is the first time, to the best of our knowledge, that an actual array of seven-fiber amplifiers has been successfully phase-locked and controlled by machine learning. Full article

(This article belongs to the Special Issue Various Applications of Methods and Elements of Adaptive Optics)

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20 pages, 18820 KiB

Open AccessArticle

Adaptive Detection of Wave Aberrations Based on the Multichannel Filter

by Pavel A. Khorin, Alexey P. Porfirev and Svetlana N. Khonina

Photonics 2022, 9(3), 204; https://doi.org/10.3390/photonics9030204 - 21 Mar 2022

Cited by 12 | Viewed by 2651

Abstract

An adaptive method for determining the type and magnitude of aberration in a wide range is proposed on the basis of an optical processing of the analyzed wavefront using a multichannel filter matched to the adjustable Zernike phase functions. The approach is based [...] Read more.

An adaptive method for determining the type and magnitude of aberration in a wide range is proposed on the basis of an optical processing of the analyzed wavefront using a multichannel filter matched to the adjustable Zernike phase functions. The approach is based on an adaptive (or step-by-step) compensation of wavefront aberrations based on a dynamically tunable multichannel filter implemented on a spatial light modulator. For adaptive filter adjustment, a set of criteria is proposed that takes into account not only the magnitude of the correlation peak, but also the maximum intensity, compactness, and orientation of the distribution in each diffraction order. The experimental results have shown the efficiency of the proposed approach for detecting wavefront aberrations in a wide range (from 0.1λ to λ). Full article

(This article belongs to the Special Issue Various Applications of Methods and Elements of Adaptive Optics)

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10 pages, 9086 KiB

Open AccessCommunication

Design, Fabrication and Characterization of an Adaptive Retroreflector (AR)

by Freddie Santiago, Carlos O. Font, Sergio R. Restaino, Syed N. Qadri and Brett E. Bagwell

Photonics 2022, 9(3), 124; https://doi.org/10.3390/photonics9030124 - 22 Feb 2022

Cited by 3 | Viewed by 2926

Abstract

Recent work at the U.S. Naval Research Laboratory studied atmospheric turbulence on dynamic links with the goal of developing an optical anemometer and turbulence characterization system for unmanned aerial vehicle (UAV) applications. Providing information on the degree of atmospheric turbulence, as well as [...] Read more.

Recent work at the U.S. Naval Research Laboratory studied atmospheric turbulence on dynamic links with the goal of developing an optical anemometer and turbulence characterization system for unmanned aerial vehicle (UAV) applications. Providing information on the degree of atmospheric turbulence, as well as wind information and scintillation, in a low size, weight and power (SWaP) system is key for the design of a system that is also capable of adapting quickly to changes in atmospheric conditions. The envisioned system consists of a bi-static dynamic link between a transmitter (Tx) and a receiver (Rx), relying on a small UAV. In a dynamic link, the propagation distance between the Tx/Rx changes rapidly. Due to SWaP constraints, a monostatic system is challenging for such configurations, so we explored a system in which the Tx/Rx is co-located on a mobile platform (UAV), which has a mounted retroreflector. Beam divergence control is key in such a system, both for finding the UAV (increased beam divergence at the Tx) and for signal optimization at the Rx. This led us to the concept of using adaptive/active elements to control the divergence at the Tx but also to the implementation of an adaptive/active retroreflector in which the return beam divergence can be controlled in order to optimize the signal at the Rx. This paper presents the design, fabrication and characterization of a low SWaP adaptive retroreflector. Full article

(This article belongs to the Special Issue Various Applications of Methods and Elements of Adaptive Optics)

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16 pages, 8965 KiB

Open AccessArticle

Filtered Influence Function of Deformable Mirror for Wavefront Correction in Laser Systems

by Yamin Zheng, Ming Lei, Shibing Lin, Deen Wang, Qiao Xue and Lei Huang

Photonics 2021, 8(10), 410; https://doi.org/10.3390/photonics8100410 - 23 Sep 2021

Cited by 2 | Viewed by 2167

Abstract

An influence function filtering method (IFFM) is presented to improve the wavefront correction capability in laser systems by curbing the correction performance degradation resulted from the IF measurement noise. The IFFM is applied to the original measured IF. The resulting filtered IF is [...] Read more.

An influence function filtering method (IFFM) is presented to improve the wavefront correction capability in laser systems by curbing the correction performance degradation resulted from the IF measurement noise. The IFFM is applied to the original measured IF. The resulting filtered IF is then used to calculate the wavefront control signal in each iteration of the closed-loop correction. A theoretical wavefront correction analysis model (CAM) is built. The impact of the IF measurement noise as well as the improvement of the IFFM on the wavefront correction capability are analyzed. A simulation is set up to analyze the wavefront correction capability of the filtered IF using Zernike mode aberrations. An experiment is carried out to study the effectiveness of the IFFM under practical conditions. Simulation and experimental results indicate that the IFFM could effectively reduce the negative effect of the measurement noise and improve the wavefront correction capability in laser systems. The IFFM requires no additional hardware and does not affect the correction speed. Full article

(This article belongs to the Special Issue Various Applications of Methods and Elements of Adaptive Optics)

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