阅读说明：本技术 基于傅里叶频谱消除的扩展物体波前传感装置及方法 (Fourier spectrum elimination-based spreading object wavefront sensing device and method ) 是由 张思炯 李常伟 陆彦婷 于 2021-07-26 设计创作，主要内容包括：本发明公开了一种基于傅里叶频谱消除的扩展物体波前传感装置及方法。该装置包括场镜、准直透镜、微透镜阵列和CCD相机,微透镜阵列由多个呈阵列式排布的微透镜组成,场镜位于准直透镜的前焦面上,微透镜阵列位于准直透镜之后并紧贴准直透镜,CCD相机位于微透镜阵列的后焦面上。本发明通过使用场镜确保每一个微透镜收集到的物体的信息完全一致,进而使CCD相机记录的每一个子像包含的扩展物体的傅里叶频谱都完全相同,在频域中,通过消除扩展物体的傅里叶频谱操作,完全消除扩展物体,从而重构出每个微透镜的光学传递函数和点扩散函数,进而计算重构点扩散函数的重心偏移,最后通过点光源夏克-哈特曼波前重构算法重构出入射畸变波前。(The invention discloses a Fourier spectrum elimination-based device and method for sensing the wavefront of an extended object. The device comprises a field lens, a collimating lens, a micro-lens array and a CCD camera, wherein the micro-lens array is composed of a plurality of micro-lenses which are arranged in an array manner, the field lens is positioned on the front focal plane of the collimating lens, the micro-lens array is positioned behind the collimating lens and clings to the collimating lens, and the CCD camera is positioned on the rear focal plane of the micro-lens array. The method ensures that the information of the object collected by each micro lens is completely consistent by using the field lens, further ensures that the Fourier frequency spectrum of the extended object contained in each sub image recorded by the CCD camera is completely the same, completely eliminates the extended object by eliminating the Fourier frequency spectrum operation of the extended object in a frequency domain, thereby reconstructing the optical transfer function and the point spread function of each micro lens, further calculating the gravity center offset of the reconstructed point spread function, and finally reconstructing the incident and emergent distorted wavefront through a point light source shack-Hartmann wavefront reconstruction algorithm.)

1. Expanded object wavefront sensing device based on Fourier spectrum eliminates, its characterized in that, including field lens (1), collimating lens (2), microlens array (3) and CCD camera (4), microlens array (3) are a plurality of microlens that are the array and arrange, field lens (1) be located collimating lens (2) the preceding focal plane on, microlens array (3) are located collimating lens (2) after and hug closely collimating lens (2), CCD camera (4) are located the back focal plane of microlens array (3).

2. The fourier spectrum cancellation based spreading object wavefront sensing device of claim 1, wherein the sensing device performs wavefront sensing directly on a spreading object.

3. The spread object wavefront sensing device based on fourier spectrum elimination as claimed in claim 1, wherein the information of the object collected by each microlens is consistent, and each sub-image recorded by the CCD camera (4) contains exactly the same fourier spectrum of the spread object.

4. The device for sensing the wavefront of an extended object based on fourier spectrum elimination as claimed in claim 2, wherein the wavefront sensing can be performed on the extended object by eliminating fourier spectrum information of the extended object in a frequency domain and reconstructing a point spread function of each microlens.

5. The wavefront reconstruction method of the extended object wavefront sensing device based on fourier spectrum elimination of any one of claims 1 to 4, wherein the field lens is used to ensure that the information of the object collected by each microlens is completely consistent, so that the fourier spectrum of the extended object contained in each subimage recorded by the CCD camera is completely the same, and in the frequency domain, the extended object is completely eliminated by eliminating the fourier spectrum operation of the extended object, so as to reconstruct the optical transfer function and the point spread function of each microlens, further calculate the gravity center shift of the reconstructed point spread function, and finally reconstruct the incident and exiting distorted wavefront through the point light source shack-hartmann wavefront reconstruction algorithm.

6. The method of Fourier spectrum cancellation-based wavefront reconstruction of claim 5, wherein Fourier spectrum operation of the cancellation spreading object is to:

the sub-image is represented in the frequency domain as:

I_m,n(f_x,f_y)＝O(f_x,f_y)H_m,n(f_x,f_y)

where m and n denote the serial numbers of the rows and columns in which the microlenses are located, I_m,n(f_x,f_y) Representing the Fourier transform, O (f), of the corresponding micro-mirror image_x,f_y) Fourier spectrum, H, representing an object_m,n(f_x,f_y) Representing an optical transfer function of the corresponding microlens; the optical transfer function of the corresponding microlens is reconstructed as:

wherein, H'_m,n(f_x,f_y) Representing the reconstructed optical transfer function, P the aperture function of the corresponding microlens,the associated operation is shown to be performed,representing the optical transfer function of the microlens in the ideal case, arg the phase-taking operation, I_rThe delta is a constant between 0.01 and 0.0001 for Fourier transform of the corresponding sub-image of the central microlens.

7. The wavefront reconstruction method based on fourier spectrum cancellation according to claim 5, specifically comprising the steps of:

firstly, acquiring an extended object image array through a CCD camera, and performing preprocessing operation;

secondly, segmenting the image array according to the preprocessing result to obtain the image distribution of the extended object corresponding to each micro lens;

performing Fourier transform on each divided image, dividing the Fourier transform by the image corresponding to the central microlens, and reconstructing an optical transfer function of each microlens;

fourthly, performing inverse Fourier transform on the reconstructed optical transfer function of each micro lens, and reconstructing a point spread function of each micro lens;

and fifthly, extracting the centroid offset of the centroid of each microlens point spread function relative to an ideal reference point, and reconstructing the incident distorted wavefront by adopting a point light source shack-Hartmann sensor wavefront reconstruction algorithm.

Technical Field

The invention belongs to the technical field of optics, relates to a novel wavefront sensor, and particularly relates to a method for realizing wavefront sensing and wavefront reconstruction aiming at an extended object by eliminating the Fourier spectrum of the extended object in a frequency domain.

Background

The wavefront sensing technology is a very important research direction in the field of optical technology, and is also a core key technology in the field of adaptive optics. In an adaptive optical system, a wavefront sensor needs to accurately measure the wavefront information of an incident light field in real time, and based on the wavefront information, a wavefront corrector corrects the distorted wavefront of the incident light field in real time to realize high-resolution imaging. Therefore, the wave front sensing technology has important application value in the fields of astronomical observation, microscopic imaging, real-time monitoring and the like.

Currently, wavefront sensors commonly used in adaptive optics include shack-hartmann wavefront sensors, curvature sensors, and shearing interferometers. All three wavefront sensors are basically only suitable for wavefront sensing in the case of a point source, such as the natural director in the sky. However, in most cases, the object to be observed by imaging belongs to an extended object, not a point light source. Aiming at the problem that a point light source is lacked in wavefront sensing, most of the existing solutions adopt an artificial point light source for wavefront sensing. For example, in night astronomical observation, the problem of low sky coverage of a natural guide star is solved by emitting laser to the sky to generate an artificial laser guide star as a point light source for wave front sensing. The disadvantage of the laser guide is that it requires the addition of a laser emitting system, making the entire optical system complex and costly. In microscopic imaging, there is usually no structure that can be used as a point light source in a biological sample, and the existing solution is to implant a fluorescent bead in a sample, and to generate a point light source by exciting the fluorescent bead to emit light, thereby performing wavefront sensing. The fluorescent bead as a point light source for wavefront sensing has the disadvantages that an optical system for exciting the fluorescent bead to emit light and an optical system for imaging need to work in different wave bands, so that the complexity of the system is greatly increased, and the sample is complex to manufacture and cannot be applied to living sample observation. Human retina does not have a structure suitable for serving as a point light source, and only a point light source can be formed on the retina by focusing a narrow laser beam to realize wavefront sensing. Although the artificial point light source solves the difficulty in wavefront sensing to a certain extent, the artificial point light source cannot be introduced in many application occasions, and the problems greatly limit the wide application of adaptive optics.

The difficulty of directly carrying out wavefront sensing on an extended object is that the wavefront sensor cannot distinguish the wavefront caused by the structure of the extended object from the wavefront actually required to be measured by a system. At present, although a shack-hartmann sensor adopting a correlation or phase correlation algorithm can obtain local inclination of an incident wavefront through image correlation operation to realize wavefront sensing, the method is only applied to certain specific places, such as a solar particle structure, and has no universality and limited sensing precision. Therefore, a wavefront sensor with good versatility and high measurement accuracy is a wavefront sensing technology that is urgently needed in the field of adaptive optics in the case of an extended object.

Disclosure of Invention

In order to break through the bottleneck existing in the wave front sensing of the extended object, the invention aims to provide a novel universal wave front sensor of the extended object. The wavefront sensor has the characteristics of convenience in use, good real-time performance, high precision and strong universality, and can expand the application range of adaptive optics, such as the fields of microscopic imaging, remote monitoring and the like which need to overcome wavefront distortion to realize high-resolution imaging. The invention also provides a wave-front reconstruction method of the novel extended object wave-front sensor.

In order to achieve the purpose, the invention adopts the technical scheme that:

the device comprises a field lens, a collimating lens, a micro-lens array and a CCD (charge coupled device) camera, wherein the micro-lens array is composed of a plurality of micro-lenses arranged in an array manner, the field lens is positioned on the front focal plane of the collimating lens, the micro-lens array is positioned behind the collimating lens and clings to the collimating lens, and the CCD camera is positioned on the rear focal plane of the micro-lens array.

Further, the sensing device directly performs wavefront sensing on the extended object.

Further, the information of the object collected by each microlens is consistent, and the fourier spectrum of the extended object contained in each sub-image recorded by the CCD camera is identical.

Further, the Fourier spectrum information of the expansion object is eliminated in the frequency domain, the point spread function of each micro lens is reconstructed, and the wavefront sensing can be carried out on the expansion object.

According to the wave front reconstruction method of the extended object wave front sensing device based on Fourier spectrum elimination, the field lens is used for ensuring that the information of the object collected by each micro lens is completely consistent, the Fourier spectrum of the extended object contained in each sub image recorded by the CCD camera is completely the same, in a frequency domain, the extended object is completely eliminated through Fourier spectrum elimination operation of the extended object, so that the optical transfer function and the point spread function of each micro lens are reconstructed, the gravity center offset of the reconstructed point spread function is calculated, and finally the incident and emergent distorted wave front is reconstructed through a point light source shack-Hartmann wave front reconstruction algorithm.

Further, the fourier spectrum operation of the cancellation spreading object is:

the sub-image is represented in the frequency domain as:

I_m,n(f_x,f_y)＝O(f_x,f_y)H_m,n(f_x,f_y)

where m and n denote the serial numbers of the rows and columns in which the microlenses are located, I_m,n(f_x,f_y) Representing the Fourier transform, O (f), of the corresponding micro-mirror image_x,f_y) Fourier spectrum, H, representing an object_m,n(f_x,f_y) Representing an optical transfer function of the corresponding microlens; the optical transfer function of the corresponding microlens is reconstructed as:

wherein, H'_m,n(fx, fy) denotes an optical transfer function of the reconstruction, P denotes an aperture function of the corresponding microlens,the associated operation is shown to be performed,representing the optical transfer function of the microlens in the ideal case, arg the phase-taking operation, I_rThe delta is a constant between 0.01 and 0.0001 for Fourier transform of the corresponding sub-image of the central microlens.

Further, the method specifically comprises the following steps:

firstly, acquiring an extended object image array through a CCD camera, and performing preprocessing operation;

secondly, segmenting the image array according to the preprocessing result to obtain the image distribution of the extended object corresponding to each micro lens;

performing Fourier transform on each divided image, dividing the Fourier transform by the image corresponding to the central microlens, and reconstructing an optical transfer function of each microlens;

fourthly, performing inverse Fourier transform on the reconstructed optical transfer function of each micro lens, and reconstructing a point spread function of each micro lens;

and fifthly, extracting the centroid offset of the centroid of each microlens point spread function relative to an ideal reference point, and reconstructing the incident distorted wavefront by adopting a point light source shack-Hartmann sensor wavefront reconstruction algorithm.

Compared with the existing wave-front sensing technology of the extended object, the invention mainly has the following advantages:

(1) the invention has high wave front sensing precision. According to the invention, the Fourier spectrum of the expansion object is eliminated in the frequency domain, and the point spread function of the micro lens is reconstructed, so that the wavefront sensing of the expansion object is converted into the wavefront sensing of a point light source. Therefore, the wavefront sensing precision of the invention is equivalent to the wavefront sensing precision of a point light source, and is higher than the precision of a shack-Hartmann sensor based on a correlation algorithm and a phase correlation algorithm.

(2) The wavefront sensing of the invention has good real-time performance. The invention aims at the sub-images corresponding to each micro lens to carry out fast Fourier transform, but because the number of pixels of each sub-image is not large and a fast Fourier transform algorithm can be adopted, the invention can meet the real-time requirement.

(3) The invention has good universality and wide application range. The theoretical basis of the invention is to eliminate Fourier spectrum information of the extension object in the frequency domain, so that the invention has no special requirements on the structure of the extension object, has good universality and can be widely applied to the wavefront sensing link aiming at various extension objects in the adaptive optics.

Drawings

Fig. 1 is a schematic diagram of a principle structure of an extended object wavefront sensor based on fourier spectrum elimination.

FIG. 2 is an example of a theoretical simulation of a spread object wavefront sensor based on Fourier spectral cancellation.

The labels in the figure are: 1 is a field lens, 2 is a collimating lens, 3 is a micro-lens array, and 4 is a CCD camera.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

The invention relates to a novel wavefront sensor, which realizes wavefront sensing and wavefront reconstruction aiming at an extended object by eliminating a Fourier spectrum of the extended object in a frequency domain.

In this embodiment, the wavefront sensor of an extended object based on fourier spectrum cancellation, referring to fig. 1, includes a field lens 1, a collimating lens 2, a micro-lens array 3, and a CCD camera 4, where the field lens 1 is located on a front focal plane of the collimating lens 2, the micro-lens array 3 is located behind the collimating lens 2 and clings to the collimating lens, and the CCD camera 4 is located on a rear focal plane of the micro-lens array 3.

In use, a wavefront sensor is composed as follows: on the same optical axis, a field lens, a collimating lens, a micro-lens array and a CCD camera are sequentially arranged. The field lens is positioned on the front focal plane of the collimating lens, the micro lens array is positioned behind the collimating lens and clings to the collimating lens, and the CCD camera is positioned on the rear focal plane of the micro lens array.

The wavefront reconstruction method based on the wavefront sensor is mainly based on fourier optics. Fourier optics is a method for describing optical system characteristics by using spatial frequency, and is a common method for characterizing the optical system characteristics and realizing high-resolution imaging at present. The field lens is used for ensuring that the information of the object collected by each micro lens is completely consistent, so that the Fourier spectrum of the extended object contained in each sub image recorded by the CCD camera is completely the same, in a frequency domain, the extended object can be completely eliminated by eliminating the Fourier spectrum operation of the extended object, the optical transfer function and the point spread function of each micro lens are reconstructed, the gravity center offset of the reconstructed point spread function is further calculated, and finally the incident and emergent distorted wavefront is reconstructed through a point light source shack-Hartmann wavefront reconstruction algorithm.

In the wavefront reconstruction algorithm, the principle of eliminating the fourier spectrum of the spread object is as follows.

Due to the use of the field lens, Fourier spectrum information of the extended object contained in each sub-image recorded by the CCD camera is completely consistent, and the sub-images can be represented in a frequency domain

I_m,n(f_x,f_y)＝O(f_x,f_y)H_m,n(f_x,f_y)

Where m and n denote the serial numbers of the rows and columns in which the microlenses are located, I_m,n(f_x,f_y) Representing the Fourier transform, O (f), of the corresponding micro-mirror image_x,f_y) Fourier spectrum, H, representing an object_m,n(f_x,f_y) Representing the optical transfer function of the corresponding microlens. Since the frequency spectrum of the object contained by each microlens is identical, the optical transfer function of the corresponding microlens can be reconstructed as

Wherein, H'_m,n(fx, fy) denotes the reconstructed optical transfer function, P denotes the corresponding microlensThe function of the aperture is,the associated operation is shown to be performed,representing the optical transfer function of the microlens in the ideal case, arg the phase-taking operation, I_rThe delta is a small constant (between 0.01 and 0.0001) for Fourier transform of the corresponding sub-image of the central microlens. It can be seen that the reconstructed optical transfer function eliminates the fourier spectrum of the extended object. And performing inverse Fourier transform on the reconstructed optical transfer function to obtain a point spread function corresponding to the micro lens, so that the wavefront sensing of the expanded object is converted into the wavefront sensing of a point light source, and the incident wavefront can be reconstructed by adopting a common wavefront reconstruction algorithm of the point light source shack-Hartmann sensor.

The wavefront reconstruction method based on the wavefront sensor specifically comprises the following steps:

firstly, acquiring an extended object image array through a CCD camera, and carrying out preprocessing such as background noise removal, image center positioning, spot reconstruction radius determination and the like; secondly, segmenting the image array according to the preprocessing result to obtain the image distribution of the extended object corresponding to each micro lens; performing Fourier transform on each divided image, dividing the Fourier transform by the image corresponding to the central microlens, and reconstructing an optical transfer function of each microlens; fourthly, performing inverse Fourier transform on the reconstructed optical transfer function of each micro lens, and reconstructing a point spread function of each micro lens; and fifthly, extracting the centroid offset of the centroid of each microlens point spread function relative to an ideal reference point, and reconstructing the incident distorted wavefront by adopting a point light source shack-Hartmann sensor wavefront reconstruction algorithm.

FIG. 2 is an example of a theoretical simulation of a spread object wavefront sensor based on Fourier spectral cancellation. The incident wavefront represents a distorted wavefront incident on the sensor, the reconstructed wavefront represents a wavefront sensed by the sensor, and the residual represents a difference between the reconstructed wavefront and the incident distorted wavefront.

At present, wavefront sensors for extended objects are primarily shack-hartmann sensors based on correlation and phase correlation algorithms. Although the correlation algorithm based on the shack-Hartmann sensor can realize the wavefront sensor aiming at a specific extended object to a certain extent, such as a solar particle structure, the correlation algorithm has the problems of low precision and small application range. According to the invention, the Fourier spectrum information of the extended object is eliminated in the frequency domain, the point spread function of each micro lens is reconstructed, and the wave front sensing aiming at the extended object is realized. The invention breaks through the bottleneck existing in the expanded object wavefront sensing and realizes a rapid, universal and efficient expanded object wavefront sensing technology.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.