JP2017146189A - Transmission wavefront measuring method, device and system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmission wavefront measuring method, a device and a system that can acquire images before and after defocusing to be used for wavefront estimation with compact constitution, and can perform wavefront estimation of desired precision.SOLUTION: A wavefront measuring method of measuring a transmission wavefront based upon at least a first image before defocusing and a second image after defocusing comprises: acquiring the images before and after defocusing as point image responses (PSF_r, PSFd_r) by picking up a point image; calculating point image responses (PSF, PSFd) corresponding to at least a first wavefront (WF) before defocusing and a second wavefront (WFd) after defocusing generated using the estimated wavefronts, respectively; and changing the estimated wavefront WF based upon errors between the calculated point image responses (PSF, PSFd) and the acquired point image responses (PSF_r, PSFd_r).SELECTED DRAWING: Figure 4

Description

  The present invention relates to a technique for measuring distortion of a transmitted wavefront with a compact configuration.

  A technology (wavefront sensor) that measures aberrations of a transmitted wavefront caused by medium disturbance such as atmospheric fluctuations is indispensable for an adaptive optical system. In particular, when mounted on a space vehicle such as a satellite, it is necessary to install the wavefront sensor in a limited space. Therefore, a configuration that is as compact as possible and has a high degree of design freedom is desirable.

  As wavefront measurement methods, the Shack-Hartmann method and the Curvature method are known. The Shack-Hartmann method requires a two-dimensional array of small lenses and the arrangement of sensors corresponding to each lens, so the dynamic range is wide, but the device configuration is complicated, and processing is performed to determine wavefront aberration. The amount of data to be calculated and the amount of calculation are also increased.

  In contrast, in the Curvature method, it is possible to derive a wavefront in an analog manner by giving a boundary condition to an ITE (Intensity Transport Equation) that is a second-order partial differential equation shown in the following equation (1). It is.

ここで、Ｉ_Ｚ(r)は強度（画像の輝度値に反映）、φ_Ｚ(r)は波面のＺ方向の位相、ｒ＝（ｘ，ｙ）、ｋ＝２π／λ、∇＝（∂／∂ｘ）＋（∂／∂ｙ）、右辺の第１項は法曲(Curvature)、第２項は傾斜(Slope)を表す。この方程式は適切な境界条件が与えられれば、解が一意に決まることが知られている。

Here, I _Z (r) is the intensity (reflected in the luminance value of the image), φ _Z (r) is the phase of the wavefront in the Z direction, r = (x, y), k = 2π / λ, ∇ = (∂ / ∂x) + (∂ / ∂y), the first term on the right side represents the Curvature, and the second term represents the slope. It is known that the solution is uniquely determined if appropriate boundary conditions are given.

  As described in Non-Patent Document 1, the boundary condition is acquired by measuring intensity values at two different points in the optical axis direction by the Phase Diversity method. For example, in the method using the beam splitter in the Phase Diversity method, the wavefront is separated into two by the beam splitter, an image is acquired on the surface that focuses one, and the optical axis direction (z By acquiring an image with a defocus plane shifted by a known amount in the direction corresponding to the axis), two different images in the optical axis direction can be acquired. In addition, in the method of scanning two optical sensors whose positions are shifted in the optical axis direction, two optical sensors are arranged in the scanning direction, and one of them is “float” attached by a known amount in the optical axis direction. By scanning the optical sensor, two different images in the optical axis direction can be acquired.

What is important when obtaining the boundary conditions for solving the above-mentioned ITE is that the original images that are the basis of two different images in the optical axis direction are exactly the same, that is, the images at the same time. is there. Briefly, g (x) is the acquired image, f (x) is the original image, and s (x) is the point spread response or point spread function (PSF) of the optical system. The image g (x) to be displayed is expressed by the following equation (2).
g (x) = f (x) * s (x) (2)
Here, the operation * indicates convolution.

When the equation (2) is Fourier transformed, the convolution is a product of the corresponding components, and the following equation (3) is obtained.
G (u) = F (u) S (u) (3)
Here, S (u) is an optical transfer function (OTF) of the optical system.

An image obtained by removing the focal plane by a predetermined distance is set as gd (x) = f (x) * sd (x), and when Fourier transform is performed in the same manner, the following expression (4) is obtained.
Gd (u) = F (u) Sd (u) (4)

  As a result, two formulas of formula (3) and formula (4) and three unknowns: S (u), Sd (u), and F (u), but S (u) and Sd (u) Since there is a relationship that differs only in the defocus component, the number of expressions increases by one to three. Therefore, if the original images f (x) that are the basis of two images g (x) and gd (x) that are different in the optical axis direction are exactly the same, the above equation can be solved. In the method using the beam splitter described above, the focused image g (x) and the out-of-focus image gd (x) can be acquired from the original image at exactly the same time, but in the method of scanning two optical sensors, Although the images acquired by the respective optical sensors are not at the same time in a strict sense, the difference is extremely small, so that the images can be handled substantially as images at the same time.

  In this way, the Curvature method uses an image directly acquired by an optical sensor, so that an optical sensor of an imaging optical system can be used, and the dynamic range is small, but a new one like the Shack-Hartmann method is used. It is not necessary to add a device, and the device configuration is simplified. Furthermore, since the ITE is solved using the image acquired by the optical sensor, in principle, the wavefront at an arbitrary position within the angle of view can be measured, and there is an advantage that the amount of data to be processed and the amount of calculation are reduced.

R. L. Kendrick, D. S. Acton and A.L. Duncan, “Phase-diversity wave-front sensor for imaging systems”, APPLIED OPTICS, Vol. 33, No. 27, Sept., 1994.

  However, in the method using the beam splitter described above, a focused image and a defocused image can be acquired from the same original image. However, since it is necessary to arrange the beam splitter in front of the imaging surface, the beam splitter (glass) The aberration due to cannot be ignored. In order to avoid this aberration, in reality, it is necessary to provide a mechanism for bringing the beam splitter out of the light beam during normal imaging, and it is necessary to secure a space for arranging two optical sensors. It becomes difficult and the configuration becomes complicated.

  Further, the above-described method of scanning the two optical sensors is not based on the same original image in a strict sense, and requires a space for juxtaposing the two optical sensors in the scanning direction, so that it is difficult to reduce the size. is there. Furthermore, it may be difficult to realize a configuration in which two optical sensors are juxtaposed. For example, there are a case where optical sensors are staggered in order to secure a necessary observation width on the light detection surface, and a case where a plurality of optical sensors are arranged in the scanning direction in order to observe a plurality of wavelengths.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a wavefront measuring method, apparatus, and system that can acquire images before and after defocusing used for wavefront estimation with a compact configuration and that can perform wavefront estimation with desired accuracy.

A wavefront measuring method according to the present invention is a wavefront measuring method for measuring a transmitted wavefront based on at least a first image before defocusing and a second image after defocusing, and a) imaging a point image to First and second images are acquired as point image responses, respectively, and b) point images corresponding to at least the first wavefront before defocusing and the second wavefront after defocusing generated using the estimated wavefront, respectively. A response is calculated, and c) changing the estimated wavefront based on an error between the calculated point image response and the acquired point image response.
A wavefront measuring apparatus according to the present invention is a wavefront measuring apparatus that measures a transmitted wavefront based on at least a first image before defocusing and a second image after defocusing, and captures the first image by capturing a point image. And point image response acquisition means for acquiring the second image as a point image response, respectively, and at least the first wavefront before defocusing and the second wavefront after defocusing generated using the estimated wavefront, respectively. Computation means for calculating a point image response; and evaluation means for changing the estimated wavefront based on an error between the calculated point image response and the acquired point image response. .
A wavefront measurement system according to the present invention is a wavefront measurement system that measures a transmitted wavefront based on at least a first image before defocusing and a second image after defocusing, the imaging optical system, and the imaging optical An optical device having a focus adjusting unit of the system and an optical sensor provided on a focal plane of the imaging optical system, and performing the defocusing by controlling the focus adjusting unit. Point image response acquisition means for acquiring the first and second images as point image responses by capturing images, and at least the first wavefront before defocusing and after defocusing generated using the estimated wavefront Calculating means for calculating a point image response corresponding to each of the second wavefront, and evaluating means for changing the estimated wavefront based on an error between the calculated point image response and the acquired point image response , Characterized by having a.

  According to the present invention, images before and after defocusing used for wavefront estimation can be acquired with a compact configuration, and wavefront estimation with desired accuracy can be performed.

FIG. 1 is a block diagram showing a schematic configuration of a wavefront measuring system according to a first embodiment of the present invention. FIG. 2 is a schematic configuration diagram of an optical system for explaining a method for acquiring images having two different focal planes in the first embodiment. FIG. 3 is a block diagram showing an example of the configuration of the wavefront measuring apparatus according to the first embodiment. FIG. 4 is a diagram showing a functional configuration of the wavefront measuring method according to the first embodiment. FIG. 5 is a flowchart showing an actual point image response data acquisition procedure in the wavefront measuring method according to the first embodiment. FIG. 6 is a flowchart showing a procedure for searching for an optimum solution in the wavefront measuring method according to the first embodiment. FIG. 7 is a block diagram showing a schematic configuration of a wavefront measuring system according to the second embodiment of the present invention. FIG. 8 is a configuration diagram showing an imaging optical system which is a first application example of the wavefront measuring apparatus according to each embodiment of the present invention. FIG. 9 is a block diagram showing an example of an optical telescope which is a second application example of the wavefront measuring apparatus according to each embodiment of the present invention. FIG. 10 is a block diagram showing another example of an optical telescope as a third application example of the wavefront measuring apparatus according to each embodiment of the present invention. FIG. 11 is a side sectional view showing a configuration example of the focus adjustment mechanism used in the embodiment.

<Outline of Embodiment>
According to the embodiment of the present invention, a focused image and a defocused image used for wavefront estimation are acquired as point image responses, and the estimated wavefront is calculated by comparing the estimated point image response with the actually measured point image response. adjust. Since the original image is a “point”, it is possible to ignore the difference in image due to the difference in image acquisition time. In addition, since the focus adjustment mechanism and optical sensor of the imaging optical system can be used, it is possible to obtain a focused image and a defocused point image using a single optical sensor without adding a special device. Can be realized.

  In the following, embodiments of the present invention will be described in detail. However, a Zernike polynomial expansion (hereinafter referred to as Zernike expansion), which is a wavefront expression method used in the following embodiments, will be briefly described.

<Zernike deployment>
Since the ITE represented by the above-described equation (1) is a second-order partial differential equation, an analytical solution cannot be simply obtained, and several methods for calculating a wavefront as an approximate solution have been proposed. Among them, a method of expressing an ITE solution by a Zernike polynomial that is an orthogonal system is often used. The reason is that the terms of each dimension in the Zernike polynomial reflect physical characteristics such as distortion and defocus, and are easy to handle in application.

  When the coordinates (x, y) through which the light beam passes are converted into polar coordinates (ρ, θ) by polar coordinate conversion (x, y) = (ρcosθ, ρsinθ), the wavefront aberration W (ρ, θ) of the optical system is expressed as a Zernike polynomial. Is expressed by the following equation (5).

Here, ρ is a radial dimension (0 ≦ ρ ≦ 1), θ is a declination, n is a dimension related to radial direction ρ, and is an integer greater than or equal to 0, and m is a dimension related to azimuthal direction θ. An integer greater than or equal to 0 (where n ≧ m), A _{n, m} is a Zernike coefficient, R ^m _n (ρ) cos | m | θ and R ^m _n (ρ) sin | m | θ are Zernike basis functions. R ^m _n (ρ) is a two-dimensional notation of n and m, but this is replaced with a Noll index j, and (n, m) = (0, 0) is replaced by j = 1, (n, m) = ( 1, 1) is j = 2, (n, m) = (1, -1) is j = 3, (n, m) = (2, 0) is j = 4, etc. Use the notation. Hereinafter, for simplicity, when the index of the Zernike coefficient is represented by the Noll index, each low-dimensional term of the Zernike polynomial reflects the following physical characteristics.

j = 1 Constant term (piston)
j = 2 x-tilt
j = 3 y-tilt
j = 4 Defocus
j = 5 astigmatism in ± 45 degrees direction (oblique astigmatism)
j = 6 90 degree astigmatism (vertical astigmatism)
j = 7 y-direction frame (vertical coma)
j = 8 x coma (horizontal coma)

  As will be described later, in the embodiment of the present invention, the fourth term (j = 4) representing defocus is used. In the Phase Diversity method, it is assumed that all conditions except for the focus are the same, and it can be seen that the Zernike polynomial expansion of the focused wavefront aberration and the defocused wavefront aberration differs only in the Zernike coefficient of j = 4. That is, the difference between S (u) in equation (3) and Sd (u) in equation (4) is the difference in the fourth term of the Zernike coefficient. As described above, when the wavefront is represented by a Zernike polynomial, mathematical processing is simplified. In the embodiment described below, the wavefront aberration is represented by a Zernike polynomial using a Noll index.

1. First Embodiment A wavefront measuring apparatus according to a first embodiment of the present invention uses an imaging optical system and an optical sensor that constitute an optical apparatus, and a point image in a focused state and a defocused state acquired by the optical sensor. By adjusting the Zernike coefficient of the estimated wavefront using the data, it is possible to perform wavefront measurement with desired accuracy with a compact configuration.

1.1) System Configuration As shown in FIG. 1, the optical apparatus 10 used in the system according to the present embodiment includes an imaging optical system 11, an optical sensor 12, and a focus adjustment mechanism 13 of the imaging optical system 11. . The focus adjusting mechanism 13 may be any mechanism that drives the imaging optical system 11 so that a predetermined defocusing distance df is obtained with the light receiving surface of the optical sensor 12 as the focal plane 12a, and the driving method is not limited. The focus adjustment mechanism 13 is controlled by the focus control system 20 and the control unit 30.

  The wavefront measuring unit 100 acquires imaging data from the optical sensor 12, and executes a defocusing operation and wavefront calculation for wavefront measurement described later based on the acquired data. The wavefront measurement unit 100 may control the focus adjustment mechanism 13 through the control unit 30 and the focus control system 20, but directly controls the focus adjustment mechanism 13 through the focus control system 20 for defocusing operation of the wavefront measurement. Also good.

  In the present embodiment, the image formed on the focal plane 12a by the imaging optical system 11 is a point image, and the wavefront measuring unit 100 performs wavefront measurement using the point image data. A point image can be easily obtained by using a star, a night city, or the like as a subject, or using reflected light from a convex mirror. However, as described above, the transmitted wavefront is distorted due to the disturbance of the medium such as atmospheric fluctuation. The wavefront measuring unit 100 according to the present embodiment verifies the transmission wavefront estimated by calculation using the point image data of the in-focus state and the defocused state acquired by the optical sensor 12 according to the above-described Phase Diversity method. The coefficient is adjusted so as to reduce the error between the point image response and the measured point image response. An example of a method for forming a defocus point image is shown in FIG.

  In FIG. 2, when the reflecting mirror 11 b in the imaging optical system 11 is at the initial position, the transmitted wavefront 14 is reflected by the reflecting mirror 11 b to form a focused image 12 f on the focal plane 12 a of the optical sensor 12. The focused image 12f is picked up by the optical sensor 12. Subsequently, when the reflecting mirror 11b is moved in the Z direction along the optical axis, the transmitted wavefront 14 is reflected by the moving reflecting mirror 11b and forms a defocus point image 12df on the focal plane 12a of the optical sensor 12. This defocus point image 12 df is picked up by the optical sensor 12. Thus, the focused image 12f and the defocused point image 12df for estimating the wavefront can be acquired.

  As shown in FIG. 3, the wavefront measuring unit 100 includes an estimating unit that estimates a wavefront by calculation, and an actual measuring unit that acquires a focused image and a defocused point image. The estimating unit includes a transmitted wavefront calculating unit 101, a point The image response analysis unit 102, the error evaluation unit 103, and the Zernike coefficient correction unit 104 are included. The actual measurement unit includes an optical sensor point image data memory 105 and a point image response generation unit 106.

  The transmitted wavefront calculation unit 101 executes Zernike expansion according to the initial value or the changed Zernike coefficient. The initial value is an estimated transmitted wavefront on the orbit using, for example, a transmitted wavefront measured on the ground. The transmitted wavefront calculation unit 101 calculates an estimated wavefront WF before defocusing (in-focus state) and an estimated wavefront WFd after defocusing. The defocusing is performed by using the fourth term (j = j = Zernike polynomial) as described above. 4; Zernike coefficient representing defocus can be changed by a predetermined value and can be realized by calculation. The change amount of the fourth term coefficient corresponds to the defocus distance df shown in FIGS. The point image response analysis unit 102 outputs the point image response and the defocused point image response at the in-focus position respectively corresponding to the estimated wavefront WF and the defocused estimated wavefront WFd to the error evaluation unit 103.

  As described with reference to FIGS. 1 and 2, the optical sensor point image data memory 105 stores point image data corresponding to the focused image 12f and the defocused point image 12df, respectively. By re-sampling each point image data, the measured focused image response and defocused point image response are output to the error evaluation unit 103.

  The error evaluation unit 103 evaluates an error between the estimated focus and defocus point image response and the actually measured focus and defocus point image response, and outputs the evaluation result to the Zernike coefficient correction unit 104. The Zernike coefficient correction unit 104 instructs the transmitted wavefront calculation unit 101 to change the Zernike coefficient so that the error is reduced according to the evaluation result. When the evaluation result reaches a predetermined accuracy by repeating the change of the Zernike coefficient and its evaluation, the result of the Zernike expansion (Zernike coefficient) of the transmitted wavefront calculation unit 101 at that time is output as the final transmitted wavefront.

1.2) Wavefront Estimation Operation Hereinafter, the operation of the wavefront measurement unit 100 will be described with reference to FIGS. It is assumed that the wavefront measuring unit 100 stores in advance an assumed transmitted wavefront on an orbit using a measured transmitted wavefront on the ground as an initial value.

  In FIG. 4, the transmitted wavefront calculation unit 101 first uses the initial value, and thereafter uses the previous estimated wavefront to calculate the wavefront WF (Zernike coefficient set) before defocusing (focus position) by Zernike expansion. (Operation S201). Further, the transmitted wavefront calculation unit 101 calculates a wavefront WFd after defocusing by changing only a fourth term (focus shift term) in the Zernike coefficient set of the estimated wavefront WF by a predetermined amount (operations S202 and S203). The point image response analysis unit 102 performs a point image response analysis by Fourier-transforming the defocused estimated wavefront WFd and taking out the square of its amplitude component, and generates a defocused point image response PSFd (operation) S204). Similarly, the point image response analysis unit 102 performs a point image response analysis by Fourier-transforming the estimated wavefront WF before defocusing and taking out the square of its amplitude component, and generates a point image response PSF before defocusing (Operation S205).

  On the other hand, as described above, for example, when the point image data before and after defocusing actually acquired on the orbit is stored in the memory 105, the point image response generation unit 106 resamples from the point image data before defocusing. Then, the optical sensor point image response PSF_r is generated (operation S206), and similarly, the optical sensor point image response PSFd_r is generated by resampling from the defocused point image data (operation S207). Note that resampling is generally performed by sampling an acquired image at a constant interval (sampling interval, which is called a sampling position in two dimensions), and then changing the sampling interval. Sampling has the following two meanings. One is that since the centroids of a plurality of acquired point images are usually shifted, the centroids are matched to obtain a point image response with a sampling interval smaller than the pixel size by interpolation from the plurality of point images. Another is to resample at intervals with the center of gravity as a reference for comparison of point image responses before and after focus adjustment.

  The error evaluation unit 103 inputs the point image response PSF before defocusing from the point image response analysis unit 102, and the measured point image response PSF_r before defocusing from the optical sensor point image response generation unit 106, respectively. The least square error e1 is calculated (operation S208). Similarly, the error evaluation unit 103 inputs the point image response PSFd after defocusing from the point image response analysis unit 102, and the measured point image response PSFd_r after defocusing from the optical sensor point image response generation unit 106, respectively. Then, the least square error e2 is calculated (operation S209). Subsequently, the error evaluation unit 103 determines whether the larger one of the least square errors e1 and e2 is less than a predetermined threshold E (operation S210).

  If the larger one of the least square errors e1 and e2 is smaller than the predetermined threshold E (YES in operation S210), the current Zernike expansion (the wavefront WF estimated in operation S201) appropriately represents the actual wavefront. The process is terminated. Conversely, if the larger one of the least square errors e1 and e2 is equal to or greater than the predetermined threshold E (NO in operation S210), the current Zernike expansion (the wavefront WF estimated in operation S201) appropriately sets the actual wavefront. A search routine for an appropriate Zernike coefficient is executed (operation S211). For example, at least one Zernike coefficient is changed in a direction in which the larger one of the least square errors e1 and e2 becomes smaller by the steepest gradient method or the like, and the optical part transmitted wavefront by Zernike expansion is calculated again with the changed Zernike coefficient ( Operation S201). By repeating the above estimation operations S201 to S205 and S208 to S211, a Zernike coefficient (that is, an estimated wavefront WF) that is equal to or less than the threshold value E can be acquired.

  The wavefront calculation method described above results in an optimization problem that derives a parameter set that minimizes the evaluation function calculated using a certain parameter group by iteration. Whether or not to reach the overall minimum value (optimum value) so as not to fall into the local minimum solution (minimal solution) depends on the initial value, but the initial value is in the vicinity of the optimal solution, and the initial value dependency Since there are various numerical calculation methods to reduce, it is possible to derive the optimum value by this method. The reason why the Zernike coefficient must be estimated at two positions of the in-focus position and the out-of-focus position by this method is that the Zernike expansion needs to satisfy Expression (1), and the left side of Expression (1) is z This is because it is a differential of the direction, and at least two measurements in the optical axis direction are required.

1.3) Control Operation The wavefront measurement unit 100 and the focus control system 20 described above can realize the same function by executing software stored in a memory (not shown). Hereinafter, a case where the control unit 30 as a computer executes a wavefront measurement program will be described. However, description of operations similar to the wavefront estimation operation described above will be simplified.

  In FIG. 5, the control unit 30 sets the focus adjustment mechanism 13 to a default state (in-focus state), acquires the image data of the focused image 12f from the optical sensor 12, and stores it in the memory 105 (operation S301). Subsequently, the control unit 30 controls the focus adjustment mechanism 13 to shift the focus by a predetermined distance (operation S302), acquires image data of the defocus point image 12df from the optical sensor 12 in the defocus state, and stores the memory 105. (Operation S303). The control unit 30 resamples the focused image data and defocused point image data obtained in this way, respectively, and generates and stores point image responses PSF_r and PSFd_r, respectively (operation S304).

  Subsequently, in FIG. 6, the control unit 30 reads the initial value, which is the transmitted wavefront on the orbit estimated using the measured transmitted wavefront on the ground (Operation S <b> 305), and Zernike of the initial wavefront (estimated wavefront). An optical system point image response PSF is calculated from the expansion by Fourier transform (operation S306). Subsequently, the control unit 30 changes only the fourth Zernike coefficient term (focus shift term) of the estimated wavefront WF by an amount corresponding to the predetermined defocus distance df (operation S307). Subsequently, the control unit 30 calculates the optical system point image response PSFd by Fourier transform from the Zernike expansion of the estimated wavefront after defocusing (operation S308).

  Subsequently, the control unit 30 reads the point image responses PSF_r and PSFd_r obtained from the measured data from the memory 105 (operation S309), and calculates the calculated point image response PSF before defocusing and the measured point image response PSF_r. The least square error e1 is calculated from the calculated point image response PSFd after defocusing and the actually measured point image response PSFd_r (operation S310). Subsequently, the control unit 30 determines whether or not the larger one of the least square errors e1 and e2 is below a predetermined threshold E (operation S311), and the larger one of the least square errors e1 and e2 is a predetermined threshold. If it is smaller than E (YES in operation S311), the process is terminated. Conversely, if it is equal to or greater than a predetermined threshold E (NO in operation S311), the larger one of the least square errors e1 and e2 by the steepest gradient method or the like. The Zernike coefficient is changed in the direction in which becomes smaller than the threshold value E, and the operation S306 is executed with the changed Zernike coefficient. The above estimation operations S306 to S312 are repeated, and the Zernike coefficient (that is, the estimated wavefront WF) when the threshold value E is equal to or less than the threshold E in operation S311 is determined as the final estimated wavefront.

1.4) Effect According to the first embodiment of the present invention, a compact configuration is obtained by adjusting the Zernike coefficient of the estimated wavefront using the point image data of the focused state and the defocused state acquired by the optical sensor. Thus, wavefront measurement with desired accuracy can be performed. In addition, by using an imaging optical system and an optical sensor provided in an optical device such as an optical telescope, the device configuration can be made compact, and when mounted on a satellite, the arrangement space in the satellite can be reduced. Savings are possible. Furthermore, by using the focus adjustment mechanism of the optical system, wavefront measurement can be performed with a simple optical system.

2. Second Embodiment A wavefront measuring apparatus according to a second embodiment of the present invention can acquire point images of different wavelengths and perform the same wavefront measurement as in the first embodiment described above for each wavelength. In the following, the same functional units as those in the first embodiment shown in FIG.

  As shown in FIG. 7, the optical sensor 12 of the optical device 10 used in the present embodiment is assumed to include light receiving elements that respectively detect a plurality of wavelengths (here, three wavelengths λ1 to λ3). As in the first embodiment, the image formed on the focal plane 12a by the imaging optical system 11 is a point image, and the light receiving element converts each point image data of the wavelengths λ1 to λ3 to the wavefront measuring unit 100a for each wavelength. Output to. Since the point image data of each wavelength is processed in the same manner as in the first embodiment and wavefront measurement is performed, details are omitted.

  The optical sensor 12 that acquires point image data for each wavelength λ1-λ3 may have a configuration in which each pixel is provided with three light receiving elements (CCD sensor, CMOS sensor, etc.) corresponding to the wavelengths λ1-λ3. A configuration may be employed in which line sensors each having a light receiving element that receives the light in a line are arranged in parallel at a predetermined interval corresponding to the number of wavelengths, or a configuration in which a two-dimensional sensor is provided for each wavelength. As a method for receiving light of each wavelength, a configuration in which a filter that transmits only the wavelengths λ1 to λ3 is provided in a light receiving element having the same characteristics can be employed.

3. Application Examples The wavelength measuring devices according to the above-described embodiments can be mounted on optical devices having various imaging optical systems. Some examples are given below.

  In FIG. 8, the imaging optical system 400 includes three mirrors, a primary mirror 401, a secondary mirror 402, and a tertiary mirror 403, and a folded plane mirror 404. Here, the plane mirror 404 can be moved in the optical axis direction by the focus adjustment mechanism 13, and by moving the plane mirror 404 by a predetermined distance, the focal plane can be changed by the predetermined defocusing distance df as described above.

  In FIG. 9, an optical telescope 500 has an imaging optical system including a primary mirror 501, a secondary mirror 502, a first folding mirror 503, a tertiary mirror 504, and a second folding mirror 505, and further includes a second optical mirror. A focus adjustment mechanism 13 for moving the folding mirror 505 is provided.

  The primary mirror 501 and the secondary mirror 502 are provided on the same optical axis, and the incident light beam condensed by the primary mirror 501 is reflected by the secondary mirror 502 and provided at the center of the primary mirror 501. It passes through the opening 501a. The light beam that has passed through the opening 501 a is bent by the first folding mirror 503 to the tertiary mirror 504, collected by the tertiary mirror 504, reflected by the second folding mirror 505, and then coupled onto the optical sensor 12. Image. The focus adjustment mechanism 13 can change the focal plane by a predetermined defocus distance df as described above by moving the second folding mirror 503 along the optical axis direction by a predetermined distance.

  In FIG. 10, an optical telescope 600 has an imaging optical system including a primary mirror 601, a secondary mirror 602, a tertiary mirror 603, a first folding mirror 604, and a second folding mirror 605. A focus adjusting mechanism 13 for moving the one folding mirror 604 is provided.

  The primary mirror 601 and the secondary mirror 602 are provided on the same optical axis, and the incident light beam condensed by the primary mirror 601 is reflected by the secondary mirror 602 and provided at the center of the primary mirror 601. It passes through the opening 601a. The light beam that has passed through the opening 601 a is collected by the tertiary mirror 603 and then reflected by the first and second folding mirrors 604 and 605 to form an image on the optical sensor 12. The focus adjustment mechanism 13 can change the focal plane by a predetermined defocusing distance df as described above by moving the first folding mirror 604 by a predetermined distance along the optical axis direction.

  The focus adjustment mechanism 13 used in each of the above-described embodiments and application examples is a linear motion that can obtain a predetermined defocus distance df by moving a predetermined optical element of the imaging optical system 11 in the optical axis direction. Any mechanism may be used. As the predetermined optical element to be moved, a plane mirror constituting the imaging optical system 11 is desirable. For example, the reflecting mirror 11b shown in FIG. 2, the plane mirror 404 shown in FIG. 8, the second folding mirror 505 shown in FIG. A first folding mirror 604 shown. As an example of the focus adjustment mechanism 13 for accurately moving such a plane mirror by a predetermined distance, FIG. 11 shows a focus adjustment mechanism 13a.

  As illustrated in FIG. 11, the focus adjustment mechanism 13 a includes a linear motion mechanism 1303 for moving a mounting surface 1301 to which a reflecting mirror for focus adjustment is attached along the linear guide 1302. The linear motion mechanism 1303 can linearly move the attachment surface 1301 fixed to the nut by a predetermined distance df by rotating a screw mechanism by an actuator 1304, for example. The actuator 1304 is controlled by the focus control system 20. The focus adjustment mechanism 13 used in each of the above embodiments and application examples is not limited to the configuration of the focus adjustment mechanism 13a shown in FIG.

  The present invention can be used for a wavefront sensor mounted on a satellite and used for wavefront estimation in orbit.

DESCRIPTION OF SYMBOLS 10 Optical apparatus 11 Imaging optical system 11b Reflector 12 Optical sensor 12a Focal plane 12f In-focus image 12df Out-of-focus point image 13, 13a Focus adjustment mechanism 14 Transmitted wave surface 20 Focus control system 30 Control unit 100 Wavefront measuring unit 100a For every wavelength Wavefront measurement unit 101 Transmission wavefront calculation unit 102 Point image response analysis unit 103 Error evaluation unit 104 Zernike coefficient correction unit 105 Memory 106 Optical sensor point image response generation unit

Claims (18)

A wavefront measurement method for measuring a transmitted wavefront based on at least a first image before defocusing and a second image after defocusing,
a) By capturing a point image, the first and second images are respectively acquired as point image responses;
b) calculating point image responses respectively corresponding to at least the first wavefront before defocusing and the second wavefront after defocusing generated using the estimated wavefront;
c) changing the estimated wavefront based on an error between the calculated point image response and the acquired point image response;
A wavefront measuring method characterized by the above.   2. The wavefront measurement according to claim 1, wherein the first image and the second image are picked up by an optical sensor by moving a focal plane by a predetermined defocusing distance by adjusting a focus of the imaging optical system. Method.   The wavefront measurement method according to claim 1, wherein the defocused wavefront is generated by changing a coefficient indicating a focal shift of a polynomial expressing the estimated wavefront.   If the error between the calculated point image response and the acquired point image response is greater than or equal to a predetermined level, the estimated wavefront so that the calculated point image response approaches the acquired point image response The wavefront measuring method according to claim 1, wherein the wavefront measuring method is changed.   5. The wavefront measurement according to claim 4, wherein at least one coefficient of a polynomial representing the estimated wavefront is changed so that the calculated point spread response approaches the acquired point spread response. Method.   If the error between the calculated point image response and the acquired point image response is greater than or equal to a predetermined level, the estimated wavefront so that the calculated point image response approaches the acquired point image response 6. The wavefront measuring method according to claim 4 or 5, wherein b) and c) are repeated until the error becomes smaller than the predetermined level.   The error between the calculated point image response and the acquired point image response is the error between the point image response corresponding to the first wavefront and the point image response corresponding to the first image, and the second wavefront. The wavefront measurement method according to claim 1, wherein an error between a point image response corresponding to the second image and a point image response corresponding to the second image is a larger one. A wavefront measuring device for measuring a transmitted wavefront based on at least a first image before defocusing and a second image after defocusing,
Point image response acquisition means for acquiring the first and second images as point image responses by capturing point images; and
Calculating means for calculating point image responses respectively corresponding to at least the first wavefront before defocusing and the second wavefront after defocusing generated using the estimated wavefront;
Evaluation means for changing the estimated wavefront based on an error between the calculated point image response and the acquired point image response;
A wavefront measuring apparatus comprising:   9. The apparatus according to claim 8, further comprising control means for moving the focal plane by a predetermined defocus distance by adjusting the focus of the imaging optical system, and imaging the first image and the second image with an optical sensor. Wavefront measuring device.   10. The wavefront measuring apparatus according to claim 8, wherein the calculation unit generates the wavefront after the defocusing by changing a coefficient indicating a focal shift of a polynomial expressing the estimated wavefront. .   If the error between the calculated point image response and the acquired point image response is greater than or equal to a predetermined level, the evaluation means causes the calculated point image response to approach the acquired point image response. The wavefront measuring apparatus according to claim 8, wherein the estimated wavefront is changed.   12. The evaluation means changes at least one coefficient of a polynomial representing the estimated wavefront so that the calculated point spread response approaches the acquired point spread response. The wavefront measuring apparatus described in 1.   If the error between the calculated point image response and the acquired point image response is greater than or equal to a predetermined level, the evaluation means causes the calculated point image response to approach the acquired point image response. 13. The wavefront measuring apparatus according to claim 11 or 12, wherein the wavefront measuring apparatus is configured to change the estimated wavefront and to control the calculation means so as to repeat the calculation until the error becomes smaller than the predetermined level.   The error between the calculated point image response and the acquired point image response is the error between the point image response corresponding to the first wavefront and the point image response corresponding to the first image, and the second wavefront. The wavefront measuring apparatus according to claim 8, which is a larger one of an error between a point image response corresponding to the point image response and a point image response corresponding to the second image. A wavefront measurement system for measuring a transmitted wavefront based on at least a first image before defocusing and a second image after defocusing,
An optical apparatus comprising: an imaging optical system; a focus adjusting unit of the imaging optical system; and an optical sensor provided on a focal plane of the imaging optical system;
Point image response acquisition means for executing the defocusing by controlling the focus adjustment means, and acquiring the first and second images as point image responses by capturing point images by the optical sensor;
Calculating means for calculating point image responses respectively corresponding to at least the first wavefront before defocusing and the second wavefront after defocusing generated using the estimated wavefront;
Evaluation means for changing the estimated wavefront based on an error between the calculated point image response and the acquired point image response;
A wavefront measuring system comprising: A program that causes a computer to function as a wavefront measuring device that measures a transmitted wavefront based on at least a first image before defocusing and a second image after defocusing,
a) a function of acquiring the first and second images as point image responses by capturing a point image;
b) a function for calculating point image responses respectively corresponding to at least the first wavefront before defocusing and the second wavefront after defocusing generated using the estimated wavefront;
c) a function of changing the estimated wavefront based on an error between the calculated point image response and the acquired point image response;
A program characterized by realizing the above in a computer in the previous term.   A system including a computer that executes the program according to claim 16.   A spacecraft provided with the wavefront measuring apparatus according to any one of claims 8-13.

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