Wavefront Sensorless Adaptive Optics Research Articles

无波前探测自适应光学对光通信性能影响分析

无波前探测自适应光学对光通信性能影响分析

Optimization-based wavefront sensorless adaptive optics for multiphoton microscopy.

Optical aberrations have detrimental effects in multiphoton microscopy. These effects can be curtailed by implementing model-based wavefront sensorless adaptive optics, which only requires the addition of a wavefront shaping device, such as a deformable mirror (DM) to an existing microscope. The aberration correction is achieved by maximizing a suitable image quality metric. We implement a model-based aberration correction algorithm in a second-harmonic microscope. The tip, tilt, and defocus aberrations are removed from the basis functions used for the control of the DM, as these aberrations induce distortions in the acquired images. We compute the parameters of a quadratic polynomial that is used to model the image quality metric directly from experimental input-output measurements. Finally, we apply the aberration correction by maximizing the image quality metric using the least-squares estimate of the unknown aberration.

Wavefront sensorless adaptive optics temporal focusing-based multiphoton microscopy.

Temporal profile distortions reduce excitation efficiency and image quality in temporal focusing-based multiphoton microscopy. In order to compensate the distortions, a wavefront sensorless adaptive optics system (AOS) was integrated into the microscope. The feedback control signal of the AOS was acquired from local image intensity maximization via a hill-climbing algorithm. The control signal was then utilized to drive a deformable mirror in such a way as to eliminate the distortions. With the AOS correction, not only is the axial excitation symmetrically refocused, but the axial resolution with full two-photon excited fluorescence (TPEF) intensity is also maintained. Hence, the contrast of the TPEF image of a R6G-doped PMMA thin film is enhanced along with a 3.7-fold increase in intensity. Furthermore, the TPEF image quality of 1μm fluorescent beads sealed in agarose gel at different depths is improved.

Estimating the atmospheric correlation length with stochastic parallel gradient descent algorithm

The atmospheric turbulence measurement has received much attention in various fields due to its effects on wave propagation. One of the interesting parameters for characterization of the atmospheric turbulence is the Fried parameter or the atmospheric correlation length. We numerically investigate the feasibility of estimating the Fried parameter using a simple and low-cost system based on the stochastic parallel gradient descent (SPGD) algorithm without the need for wavefront sensing. We simulate the atmospheric turbulence using Zernike polynomials and employ a wavefront sensor-less adaptive optics system based on the SPGD algorithm and report the estimated Fried parameter after compensating for atmospheric-turbulence-induced phase distortions. Several simulations for different atmospheric turbulence strengths are presented to validate the proposed method.

Wavefront sensorless adaptive optics optical coherence tomography for in vivo retinal imaging in mice

We present wavefront sensorless adaptive optics (WSAO) Fourier domain optical coherence tomography (FD-OCT) for in vivo small animal retinal imaging. WSAO is attractive especially for mouse retinal imaging because it simplifies optical design and eliminates the need for wavefront sensing, which is difficult in the small animal eye. GPU accelerated processing of the OCT data permitted real-time extraction of image quality metrics (intensity) for arbitrarily selected retinal layers to be optimized. Modal control of a commercially available segmented deformable mirror (IrisAO Inc.) provided rapid convergence using a sequential search algorithm. Image quality improvements with WSAO OCT are presented for both pigmented and albino mouse retinal data, acquired in vivo.

Wavefront sensorless modal deformable mirror correction in adaptive optics: optical coherence tomography

We present a method for optimization of optical coherence tomography images using wavefront sensorless adaptive optics. The method consists of systematic adjustment of the coefficients of a subset of the orthogonal Zernike bases and application of the resulting shapes to a deformable mirror, while optimizing using image sharpness as a merit function. We demonstrate that this technique can compensate for aberrations induced by trial lenses. Measurements of the point spread function before and after compensation demonstrate near diffraction limit imaging.

A parallel system for adaptive optics based on parallel mutation PSO algorithm

Wavefront sensor-less adaptive optics technology has a much higher requirement for the processing speed than ever before. To improve the efficiency of particle swarm optimization (PSO), this paper proposes a novel parallel mutation particle swarm optimization (PMPSO) algorithm based on a master-slave model. The parallel system based on PMPSO algorithm is applied in a 61-element adaptive optics system to control the deformable mirror. The experimental results show that the parallel system based on PMPSO algorithm has a rapid convergence speed, which can effectively correct the wavefront aberration.

Hill-climbing algorithm based on Zernike modes for wavefront sensorless adaptive optics

To solve the local optimum problem, a modified hill-climbing algorithm based on Zernike modes is presented for wavefront sensorless adaptive optics. This algorithm adopts the Zernike mode coefficients, instead of the actuators' voltages in a traditional hill-climbing algorithm, as the adjustable variables to optimize the object function. First, the prin- ciple of the algorithm is described. Then the efficiency of the modified and traditional hill-climbing algorithms are analyzed numerically and experi- mentally using a He-Ne laser beam shaping system with a 37-element unimorph deformable mirror. The results of both simulations and experi- ments demonstrate that the modified hill-climbing algorithm can eliminate the local optimum problem with a fast speed of about 100 iterations. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10.1117/1.OE.52.1.016601) Subject terms: wavefront sensorless; adaptive optics; hill-climbing algorithm; Zernike modes; deformable mirror.

Semidefinite programming for model-based sensorless adaptive optics

Wavefront sensorless adaptive optics methodologies are widely considered in scanning fluorescence microscopy where direct wavefront sensing is challenging. In these methodologies, aberration correction is performed by sequentially changing the settings of the adaptive element until a predetermined image quality metric is optimized. An efficient aberration correction can be achieved by modeling the image quality metric with a quadratic polynomial. We propose a new method to compute the parameters of the polynomial from experimental data. This method guarantees that the quadratic form in the polynomial is semidefinite, resulting in a more robust computation of the parameters with respect to existing methods. In addition, we propose an algorithm to perform aberration correction requiring a minimum of N+1 measurements, where N is the number of considered aberration modes. This algorithm is based on a closed-form expression for the exact optimization of the quadratic polynomial. Our arguments are corroborated by experimental validation in a laboratory environment.

A simplified free-space adaptive optics system against atmospheric turbulence

Optical free-space communications have the distinct advantages over conventional radio frequency and microwave systems in terms of information capacity and increased security. However, optical carrier frequencies drastically suffer due to atmospheric turbulence. This effect is a random process and time-varying process; therefore, it is very difficult to overcome the effect. Adaptive optics is the technology used to mitigate chaotic optical wave-front distortions in real time by measuring the wave-front distortion with the help of a sensor and then adapting the wave-front corrector to lessen the phase distortions and ultimately to recover a closely approximated signal to its original counterpart. But these systems are too expensive and large. This study employs the various aspects of Adaptive Optics system, such as wave-front corrector, wave-front sensors and analytical analysis of open and closed-loop systems using loop equations, in order to make free-space optics communication links more vulnerable against atmospheric turbulence and wave-front phase distributions. The purpose of this study is to investigate a wave-front sensorless adaptive optics system, which would provide reduced complexity, size and cost.

Beam cleanup of a 532-nm pulsed solid-state laser using a bimorph mirror

A successful beam cleanup of a 5-mJ/200-mu s pulsed solid-state laser system operating at 532-nm wavelength is demonstrated. In this beam cleanup system, a wave-front sensor-less adaptive optics (AO) system is set up with a 20-element bimorph mirror (BM), a high-voltage amplifier, a charge-coupled device camera, and a control software implementing the stochastic parallel gradient descent (SPGD) algorithm. The brightness of the laser focal spot is improved because the wave-front distortions have been compensated. The performance of this system is presented and the experimental results are analyzed.

Correction of static and thermal aberrations of a zigzag slab amplif ier employing a wave-front sensor-less adaptive optics system

We present a wave-front sensor-less adaptive optics (AO) system for a Nd:YAG Zigzag slab amplifier. A 39-element rectangular piezoelectric deformable mirror in combination with a stochastic parallel gradient descent (SPGD) algorithm is introduced for both static and thermal aberrations correction. Preliminary experiments demonstrate that the output beam quality can be enhanced greatly at different power levels.

A Study of an Improved PSO Algorithm Used in an Adaptive Optics System

Wavefront sensor-less adaptive optics is an important method for correcting wavefront aberration. An appropriate optimization algorithm is crucial to aberration correction. An improved particle swarm optimization (IPSO) is presented which well addresses slow convergence rate and low calculation precision in the standard PSO. In IPSO, mutation strategies are adopted to keep the diversity of population and make particles explore the solution space efficiently. Based on these two algorithms, an adaptive optics system with a 37-element deformable mirror is established. The experimental results show that IPSO is better than SPSO in convergence rate, reconstruction performance and correction effect.

Wavefront sensorless adaptive optics ophthalmoscopy in the human eye

Wavefront sensor noise and fidelity place a fundamental limit on achievable image quality in current adaptive optics ophthalmoscopes. Additionally, the wavefront sensor ‘beacon’ can interfere with visual experiments. We demonstrate real-time (25 Hz), wavefront sensorless adaptive optics imaging in the living human eye with image quality rivaling that of wavefront sensor based control in the same system. A stochastic parallel gradient descent algorithm directly optimized the mean intensity in retinal image frames acquired with a confocal adaptive optics scanning laser ophthalmoscope (AOSLO). When imaging through natural, undilated pupils, both control methods resulted in comparable mean image intensities. However, when imaging through dilated pupils, image intensity was generally higher following wavefront sensor-based control. Despite the typically reduced intensity, image contrast was higher, on average, with sensorless control. Wavefront sensorless control is a viable option for imaging the living human eye and future refinements of this technique may result in even greater optical gains.

Self calibration of sensorless adaptive optical microscopes

We present a self-calibrating scheme for microscopes using model-based wavefront sensorless adaptive optics. Unlike previous methods, this scheme permits the calibration of system aberration modes without the need for a separate wavefront sensor or interferometer. Basis modes are derived from the deformable mirror influence functions and an image cross-correlation method is used to remove image displacement effects from these modes. Image based measurements are used to derive an optimum modal representation from the displacement-free basis modes. These new modes are insensitive to system misalignments and the shape of the illumination profile. We demonstrate the effectiveness and robustness of these optimal modes in a third harmonic generation (THG) microscope.

Wavefront sensorless adaptive optics: a general model-based approach

Wavefront sensorless adaptive optics (AO) systems have been widely studied in recent years. To reach optimum results, such systems require an efficient correction method. In this paper, a general model-based correction method for a wavefront sensorless AO system is presented. The general model-based approach is set up based on a relationship wherein the second moments (SM) of the wavefront gradients are approximately proportionate to the FWHM of the far-field intensity distribution. The general model-based method is capable of taking various common sets of functions as predetermined bias functions and correcting the aberrations by using fewer photodetector measurements. Numerical simulations of AO corrections of various random aberrations are performed. The results show that the Strehl ratio is improved from 0.07 to about 0.90, with only N + 1 photodetector measurement for the AO correction system using N aberration modes as the predetermined bias functions.

Optimum deformable mirror modes for sensorless adaptive optics

Wavefront sensorless adaptive optics schemes rely upon the accurate generation of aberration modes by the adaptive element, usually a deformable mirror. Analytic functions are often used for representation of the aberrations in these systems. Such functions cannot be perfectly reproduced by deformable mirrors and the approximation errors can affect the aberration correction procedure. We derive alternative modal basis sets directly from the actuator influence functions, thus avoiding the approximation errors. We investigate how the choice of aberration modes affects the performance of a sensorless adaptive imaging system. The new modes are found to be most advantageous for deformable mirrors with a small number of actuators.

Extracting hysteresis from nonlinear measurement of wavefront-sensorless adaptive optics system

In many scientific and medical applications wavefront-sensorless adaptive optics (AO) systems are used to correct the wavefront aberration by optimizing a certain target parameter, which is nonlinear with respect to the control signal to the deformable mirror (DM). Hysteresis is the most common nonlinearity of DMs, which can be corrected if the information about the hysteresis behavior is present. We report a general approach to extract hysteresis from the nonlinear behavior of the adaptive optical system, with the illustration of a Foucault knife test, where the voltage-intensity relationship consists of both hysteresis and some memoryless nonlinearity. The hysteresis extracted here can be used for modeling and linearization of the AO system.

Adaptive optics for structured illumination microscopy

We implement wave front sensor-less adaptive optics in a structured illumination microscope. We investigate how the image formation process in this type of microscope is affected by aberrations. It is found that aberrations can be classified into two groups, those that affect imaging of the illumination pattern and those that have no influence on this pattern. We derive a set of aberration modes ideally suited to this application and use these modes as the basis for an efficient aberration correction scheme. Each mode is corrected independently through the sequential optimisation of an image quality metric. Aberration corrected imaging is demonstrated using fixed fluorescent specimens. Images are further improved using differential aberration imaging for reduction of background fluorescence.

No wavefront sensor adaptive optics system for compensation of primary aberrations by software analysis of a point source image 1 Methods

Adaptive optics (AO) has been recently used for the development of ophthalmic devices. Its main objective has been to obtain high-resolution images for diagnostic purposes or to estimate high-order eye aberrations. The core of every AO system is an optical device that is able to modify the wavefront shape of the light entering the system; if you know the shape of the incoming wavefront, it is possible to correct the aberrations introduced in the optical path from the source to the image. The aim of this paper is to demonstrate the feasibility, although in a simulated system, of estimating and correcting an aberrated wavefront shape by means of an iterative gradient-descent-like software procedure, acting on a point source image, without expensive wavefront sensors or the burdensome computation of the point-spread-function (PSF) of the optical system. In such a way, it is possible to obtain a speed and repeatability advantage over classical stochastic algorithms. A hierarchy in the aberrations is introduced, in order to reduce the dimensionality of the state space to be searched. The proposed algorithm is tested on a simple optical system that has been simulated with ray-tracing software, with randomly generated aberrations, and compared with a recently proposed algorithm for wavefront sensorless adaptive optics.