Liquid lens wavefront detection device and method based on background schlieren method

Abstract

The invention discloses a liquid lens wavefront detection device and method based on a background schlieren method. The detection device comprises a first reference wavefront beam generation assembly, a double-side telecentric lens and a camera, and a reference wavefront beam emitted from the first reference wavefront beam generation assembly enters a liquid lens to be detected, enters the double-side telecentric lens after being transmitted by the liquid lens to be detected, and is collected by the camera after being transmitted by the double-side telecentric lens. The detection device is used for collecting a reference image and a dynamic image of the to-be-detected liquid lens, so that background displacement is obtained, wavefront slope distribution is further obtained, and finally wavefront distribution and wave aberration of the to-be-detected liquid lens are obtained after integral reconstruction is conducted on the wavefront slope distribution. The telecentric background schlieren method is adopted for liquid lens wave aberration detection, and the problems that in a traditional Shack-Hartmann wavefront detection technology, a microlens array needs to be used for dividing wavefront to be detected into a plurality of wavelets, and the spatial resolution is limited by the microlens size and the duty ratio are solved.

Description

Technical Field

[0001] The present invention relates to a lens wavefront detection device and method in the field of optical measurement, and particularly to a liquid lens wavefront detection device and method based on the background schlieren method. Background Art

[0002] A liquid lens is an optical element without a solid mechanical structure composed of a liquid, and has been widely used in imaging systems such as immersion lithography, microscopic imaging, and machine vision. Since the refractive index distribution of the fluid inside the liquid lens is affected by various factors such as density, temperature, pressure, and flow, it is easy to cause dynamic changes in the wavefront, thereby reducing the imaging quality of the optical system. Therefore, accurately and real-time detecting the wave aberration of the liquid lens is crucial for ensuring its performance under various working conditions.

[0003] Existing wavefront detection techniques include traditional interferometry, Hartmann method, shear interferometry, and point diffraction method. Although these methods have achieved good results in the detection of objective wave aberration, they still face some challenges. Interferometry usually requires a reference optical path and is suitable for off-line detection; the Hartmann method and shear interferometry can perform on-line detection, but only the wavefront slope can be measured, and complex calculation processes are required to reconstruct the wavefront; the point diffraction method faces the problems of reduced light flux and decreased accuracy. For high-resolution lithography or microscopic imaging systems, the current mainstream detection method is the Phase Measuring Interferometer (PMI), for example: the P-PMI technology proposed by Nikon based on the Shack-Hartmann sensor, the wave aberration in-situ detection interferometer based on the line diffraction principle by Canon, and the ILIAS lateral shear interferometry technology based on the shear interferometry principle by ASML. However, as the last objective lens, the liquid lens directly contacts the photoresist and cannot perform wave aberration compensation like a solid lens, so a detection method for the wave aberration of the liquid lens is needed.

[0004] The Background Oriented Schlieren Technique (BOS) is a relatively novel flow detection technique proposed by Meier et al. around 2000. The BOS technique can overcome the difficulties brought by self-luminescence to the illuminance change of the traditional schlieren technique, and at the same time use the PIV or optical flow algorithm, eliminating the complex and expensive experimental device of the traditional schlieren technique. The BOS technique was first applied to quantitatively measure the density field in aerodynamic optics, and then extended to fields such as fluid temperature measurement, free surface measurement, and aerodynamic optical wavefront measurement. The BOS technique device has a simple composition, and the measurement sensitivity and accuracy mainly depend on the optical path design, camera resolution, background pattern design, and background displacement algorithm.

[0005] The existing wavefront aberration detection methods for optical systems include lateral shearing interference technology (CN102368139A, CN104111161A) and Shack-Hartmann technology (US9574967B2, US7391497B2). Different from solid lens systems, the refractive index distribution of liquid lenses has spatio-temporal inhomogeneity. Therefore, it is necessary to propose a wavefront detection device and method for liquid lenses. Summary of the Invention

[0006] In order to overcome the deficiencies in the background technology, the present invention provides a liquid lens wavefront detection device and method based on the background schlieren method.

[0007] The first object of the present invention is to provide a liquid lens wavefront detection device based on the background schlieren method. This device can measure the refractive index inhomogeneity caused by temperature in an incompressible flow field, reduce the system complexity, without using traditional interference methods or microlens arrays, and avoid introducing system errors due to the use of multiple gratings or microlens arrays. Using bilateral telecentric background schlieren to overcome the contradiction between the spatial resolution and sensitivity of the traditional BOS system, and using a high-speed camera as the image receiving device to ensure the time resolution.

[0008] The second object of the present invention is to provide a liquid lens wavefront detection method based on the background schlieren method. This method can obtain the wavefront slope through the measured background displacement, and then reconstruct the wavefront distribution of the dynamic flow field to achieve real-time wavefront detection.

[0009] The technical solution adopted by the present invention is as follows: I. A liquid lens wavefront detection device based on the background schlieren method The liquid lens wavefront detection device includes a first reference wavefront beam generating component, a bilateral telecentric lens, and a camera. The first reference wavefront beam generating component, the bilateral telecentric lens, and the camera are sequentially arranged at intervals along the optical axis. The liquid lens to be measured is placed between the first reference wavefront beam generating component and the bilateral telecentric lens. The reference wavefront beam emitted from the first reference wavefront beam generating component is incident on the liquid lens to be measured, and after passing through the liquid lens to be measured, it is incident on the bilateral telecentric lens, and then after passing through the bilateral telecentric lens, it is collected by the camera.

[0010] The liquid lens to be measured includes a fluid, a transparent glass cover plate, and a lens housing. A through groove is provided in the lens housing along the optical axis direction. Corresponding transparent glass cover plates are respectively installed in the lens housing at both ends of the through groove, so that the lens housing is a sealed structure; a fluid cavity is formed in the lens housing between the two transparent glass cover plates. The lens housing is also provided with a water injection port and a drainage port, and the water injection port and the drainage port are communicated with the fluid cavity, and the fluid cavity is filled with a fluid.

[0011] The device further includes a disturbance correction component, which includes a second reference wavefront beam generation component, a disturbance correction liquid lens, a mirror, and a beam splitter prism; the wavelength of the reference wavefront beam emitted from the second reference wavefront beam generation component is different from that of the reference wavefront beam emitted from the first reference wavefront beam generation component; the second reference wavefront beam generation component is arranged on the side of the first reference wavefront beam generation component, and the reference wavefront beam emitted from the second reference wavefront beam generation component is incident on the disturbance correction liquid lens. The structure and fluid type of the disturbance correction liquid lens are the same as those of the liquid lens to be measured. The fluid in the disturbance correction liquid lens is in a static state. The beam transmitted through the disturbance correction liquid lens is incident on the mirror. The beam splitter prism is arranged between the liquid lens to be measured and the double-sided telecentric lens. The beam transmitted through the liquid lens to be measured is incident on the beam splitter prism and undergoes transmission. The beam reflected by the mirror is incident on the beam splitter prism and undergoes reflection. The beams transmitted and reflected by the beam splitter prism are both incident on the double-sided telecentric lens; a first optical path is formed among the first reference wavefront beam generation component, the liquid lens to be measured, and the beam splitter prism, and a second optical path is formed among the second reference wavefront beam generation component, the disturbance correction liquid lens, the mirror, and the beam splitter prism. The optical paths of the first optical path and the second optical path are the same.

[0012] The first reference wavefront beam generation component includes a background pattern board and an LED illumination system. The background pattern board is a transparent screen scattered with random dot arrays; the LED illumination system is used to generate parallel beams.

[0013] The double-sided telecentric lens includes a first positive lens and a second positive lens arranged at intervals along the optical axis in sequence. The aperture stop is located between the first positive lens and the second positive lens, and the aperture stop is located at the focal point of the first positive lens and the focal point of the second positive lens.

[0014] II. A method for detecting the wavefront of a liquid lens based on the background schlieren method Step 1: Install the liquid lens to be measured in the liquid lens wavefront detection device described above; Step 2: Use the camera to sequentially collect the reference image I of the liquid lens to be measured in the undisturbed state ref and the dynamic image I generated under the action of a temperature gradient and having disturbances disturbed ; Step 3: After processing the obtained reference image I ref and the dynamic image I disturbed , obtain the background displacement (△x’, △y’); Step 4: Based on the background displacement (△x’, △y’), use Fermat's principle and Malus' law in geometric optics to establish the relationship between the background displacement (△x’, △y’), the ray deflection angles (ε x , ε y ) and the wavefront slope, so as to calculate the wavefront slope distribution; Step 5: After performing integral reconstruction on the wavefront slope distribution, obtain the wavefront distribution and wave aberration of the liquid lens to be measured.

[0015] In the said Step 3, use the cross-correlation or optical flow algorithm to process the acquired reference image I ref and the dynamic image I disturbed for processing.

[0016] In the said Step 5, use the trapezoidal integral algorithm or iterative reconstruction algorithm to perform integral reconstruction on the wavefront slope distribution.

[0017] III. A method for detecting the wavefront of a liquid lens based on the background schlieren method Step 1: Install the liquid lens to be measured in the said liquid lens wavefront detection device; Step 2: The camera sequentially records the reference image I of the liquid lens to be measured in the undisturbed state in the double-frame mode ref and the first corrected reference image of the disturbed correction liquid lens; then, the camera sequentially records the dynamic image I of the liquid lens to be measured under the action of a temperature gradient in the double-frame mode disturbed and the second corrected reference image of the disturbed correction liquid lens; Step 3: After processing the acquired reference image I ref and the dynamic image I disturbed , obtain the original background displacement (△x’, △y’); and after processing the first corrected reference image and the second corrected reference image, obtain the disturbance displacement; after subtracting the original background displacement (△x’, △y’) from the disturbance displacement, obtain the corrected background displacement; Step 4: Based on the corrected background displacement, use Fermat's principle and Malus's law in geometric optics to establish the relationship between the background displacement (△x’, △y’), the ray deflection angle (ε x , ε y ) and the wavefront slope, so as to calculate the wavefront slope distribution; Step 5: After performing integral reconstruction on the wavefront slope distribution, obtain the wavefront distribution and wave aberration of the liquid lens to be measured.

[0018] The present invention applies the background schlieren method to quantitatively measure the wavefront gradient of an incompressible liquid lens, and then reconstructs the wave aberration, which is particularly suitable for real-time quantitative measurement of the dynamic changes of wave aberration caused by factors such as temperature and density inside the liquid lens.

[0019] The beneficial effects of the present invention are: The present invention provides a liquid lens wavefront detection device based on the background schlieren method. The device uses the background schlieren method instead of the microlens array measurement method to obtain the wavefront slope of the parallel light wave after passing through the liquid lens to be measured, and then reconstruct the entire wavefront distribution, overcoming the shortcomings of the microlens array itself, such as insufficient spatial resolution and high duty cycle.

[0020] The present invention uses the background schlieren method to reduce system complexity and alleviate the disadvantage of introducing more system errors by using multiple gratings or microlens arrays.

[0021] The device and method proposed in the present invention can not only measure the wave aberration of the liquid lens, but also simultaneously obtain the flow information of the internal flow field of the liquid lens, thereby enhancing the understanding and control of the optical quality of the liquid lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the liquid lens wavefront detection device in the present invention.

[0023] Figure 2 Schematic diagram of the structure of the liquid lens in the present invention, wherein (a) is a side sectional view of the liquid lens, and (b) is an end sectional view of the liquid lens.

[0024] Figure 3 Schematic diagram of the displacement of the background schlieren pattern in the present invention.

[0025] Figure 4 Schematic diagram of the structure of the liquid lens wavefront detection device in Example 1.

[0026] Figure 5 Schematic diagram of the structure of the liquid lens wavefront detection device in Example 2.

[0027] Figure 6 This is a flow chart of the liquid lens wavefront detection method in Example 1.

[0028] In the figure, 1: background pattern plate; 2: liquid lens; 21: fluid; 22: transparent glass cover; 23: lens shell; 3: double-sided telecentric lens; 31: first positive lens; 32: aperture; 33: second positive lens; 4: LED lighting system; 41: blue light LED with a wavelength of 450nm; 42: red light LED with a wavelength of 660nm; 5: camera; 6: data processor; 7: reflector; 8: dichroic prism. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the accompanying drawings and implementation modes.

[0030] Example 1

[0031] like Figure 1 and Figure 4As shown in the figure, the liquid lens wavefront detection device includes a first reference wavefront beam generating component, a bilateral telecentric lens 3, and a high-speed camera 5. The first reference wavefront beam generating component, the bilateral telecentric lens 3, and the high-speed camera 5 are sequentially arranged at intervals along the optical axis. The liquid lens 2 to be measured is placed between the first reference wavefront beam generating component and the bilateral telecentric lens 3. The reference wavefront beam emitted from the first reference wavefront beam generating component is incident on the liquid lens 2 to be measured. After passing through the liquid lens 2 to be measured, it is incident on the bilateral telecentric lens 3, and then after passing through the bilateral telecentric lens 3, it is collected by the high-speed camera 5. The high-speed camera 5 is connected to a data processor 6. The bilateral telecentric lens 3 and the camera 5 are arranged on the same optical axis, and the beam incident on the bilateral telecentric lens 3 can have an angle with the optical axis.

[0032] The bilateral telecentric lens 3 includes a first positive lens 31 and a second positive lens 33 that are sequentially arranged at intervals along the optical axis. The aperture stop 32 is located between the first positive lens 31 and the second positive lens 33, and the aperture stop 32 is located at the focal point of the first positive lens 31 and the focal point of the second positive lens 33. The first positive lens 31 and the second positive lens 33 are positive thin lenses, and their focal lengths are f1 and f2 respectively.

[0033] As Figure 4 shown, the liquid lens wavefront detection device is vertically arranged, and the liquid lens 2 to be measured is horizontally arranged. The reference wavefront beam generating component is arranged on the same optical axis as the bilateral telecentric lens 3 and the high-speed camera 5. The light rays emitted by the illumination system are incident on the background pattern board 1 approximately parallelly. The bilateral telecentric lens 3 and the high-speed camera 5 ensure that the background image is incident on the imaging plane approximately parallelly. The magnification of the component composed of the bilateral telecentric lens 3 and the high-speed camera 5 is related to the focal lengths of the two thin lenses in the bilateral telecentric lens and is independent of the relative distances between the schlieren object, the background, and the camera.

[0034] Figure 1 Among them, Z_D represents the distance between the flow field to be measured and the background pattern board; Z_A represents the distance between the flow field to be measured and the first positive lens; Z_i represents the distance between the second positive lens and the camera imaging plane; Δy’ represents the displacement in the y direction of the background pattern at the background pattern board due to the deflection of the light rays; Δy represents the displacement corresponding to the displacement of the pattern in the y direction at the background pattern board on the camera imaging plane.

[0035] As Figure 2 in (a) and Figure 2As shown in (b), the liquid lens 2 to be measured includes a fluid 21, a transparent glass cover plate 22, and a lens housing 23. The lens housing 23 is made of an opaque material. A through groove is provided in the lens housing 23 along the optical axis direction. Corresponding transparent glass cover plates 22 are respectively installed in the lens housing 23 at both ends of the through groove, so that the lens housing 23 is a sealed structure; a fluid cavity is formed in the lens housing 23 between the two transparent glass cover plates 22. The lens housing 23 is also provided with a water injection port and a drainage port, and the water injection port and the drainage port are communicated with the fluid cavity. The fluid cavity is filled with a fluid, and the fluid 21 is continuously updated through the water injection port and the water outlet. A temperature gradient flow field can be formed through the two water injection ports. The fluid is ultrapure water.

[0036] The first reference wavefront beam generation component includes a background pattern plate 1 and an LED illumination system 4. The background pattern plate 1 is a transparent screen scattered with random dot matrices. As Figure 3 shown, the displacement information available for wavefront reconstruction is generated after the dot matrix characteristics pass through the liquid lens. The imaging size of the background pattern speckles on the photosensitive element of the camera 5 should be 3 to 5 pixel sizes. The speckle spacing should be greater than the speckle diameter without aliasing, and the gray level gradient at the speckle edge is clear. After passing through the liquid lens 2, the background pattern 1 is distorted, and the background pattern generates displacements (△x’, △y’). All the background displacement vectors form a displacement vector field.

[0037] The LED illumination system 4 is used to generate parallel beams. The LED illumination system 4 includes a light source and a collimator. The beam with a specific wavelength emitted from the light source becomes a plane wave after passing through the collimator, and a plane wave containing the background pattern image is obtained after passing through the background pattern plate 1. Due to the spatio-temporal non-uniform refractive index distribution of the internal flow field of the liquid lens, after the plane wave containing the background pattern image passes through the liquid lens, the wavefront is distorted. After being screened by the bilateral telecentric lens 3, the perturbed wavefront is parallel to the principal optical axis again and converges on the photosensitive element of the camera 5. After the camera takes pictures, continuous images are obtained and output to the data processor 6 for post-processing.

[0038] The data processor 6 is used to receive and store the background pattern output by the high-speed camera and perform post-processing calculations, including: background displacement estimation, ray deflection angle calculation, wavefront slope calculation, and wavefront reconstruction.

[0039] The detection method relies on the background displacement information collected by the liquid lens wavefront detection device based on the background schlieren method. According to Malus' law, after the light rays perpendicular to the wave surface pass through any number of refractions or reflections, the emerging wave surface of the light rays must be perpendicular to the emerging light rays, and the optical paths of all the light rays between the corresponding points of the incident wave surface and the emerging wave surface are equal. As Figure 1 shown, the angle between the perturbed wavefront and the y-axis is equal to the deflection angle ε of the light ray after passing through the liquid lens. y, the trapezoidal integration algorithm or the iterative algorithm is used to obtain the wavefront distribution information of the liquid lens. The present invention proposes a method for detecting the wavefront of a liquid lens based on the background schlieren method. As Figure 6 shown, the detection method includes the following steps: Step 1: Install the liquid lens 2 to be measured in the liquid lens wavefront detection device, that is, build the liquid lens wavefront detection device; Step 2: Use the high-speed camera 5 to sequentially collect the reference image I of the liquid lens 2 to be measured in the undisturbed state ref (that is, the fluid in the liquid lens 2 to be measured is in a static state, and the liquid lens 2 to be measured is a static flow field) and the dynamic image I generated under the action of the temperature gradient disturbed (that is, the fluid in the liquid lens 2 to be measured is in a flowing state with a temperature gradient, and the liquid lens 2 to be measured is a flow field with a temperature gradient); Step 3: Use the cross-correlation method to process the obtained reference image I ref and the dynamic image I disturbed After processing, the background displacement (Δx’, Δy’) is obtained; specifically: select an appropriate window size, perform cross-correlation processing on the processed reference image and a series of dynamic images to obtain the background displacement. Or select an appropriate optical flow algorithm for displacement estimation to obtain the background displacement.

[0040] Step 4: Based on the background displacement (Δx’, Δy’), use Fermat's principle and Malus' law in geometric optics to establish the relationship between the background displacement (Δx’, Δy’), the ray deflection angle (ε x , ε y ) and the wavefront slope, so as to calculate the wavefront slope distribution; specifically, use the relationship formula between the background displacement and the ray deflection angle, and the relationship formula between the ray deflection angle and the wavefront slope to obtain the wavefront slope at each point of the liquid lens, so as to obtain the wavefront slope distribution.

[0041] According to Figure 1 the geometric relationship and the small angle assumption, the relationship between the background displacement (Δx’, Δy’) and the ray deflection angle (ε x , ε y ) can be obtained: ε x ≈tanε x =Δx’ / Z_D ε y ≈tanε y =Δy’ / Z_D and the relationship between the ray deflection angle (ε x , ε y ) and the wavefront slope: where, Δx’ is the displacement of the background pattern in the x direction, Δy’ is the displacement of the background pattern in the y direction, ε x is the deflection angle of the light in the x direction, ε y is the deflection angle of the light in the y direction, OPL(x,y) refers to the optical path length, OPL = ∫ s nds, n is the refractive index, and s is the distance along the optical path. Therefore, the optical path difference OPD can be defined as: OPD = OPL - OPL’ where, OPL represents the optical path length, OPL’ refers to the average optical path length. Therefore, the phase aberration ΔΦ of the light wave is: ΔΦ = 2π·OPD / λ where, λ represents the wavelength of the light.

[0042] Step 5: After integrating and reconstructing the wavefront slope distribution using the trapezoidal integration algorithm, the wavefront distribution and wave aberration of the liquid lens 2 to be measured are obtained. Specifically, according to the currently obtained light deflection angles (ε x , ε y ), a two-dimensional wavefront reconstruction is performed using the trapezoidal integration algorithm or an iterative algorithm, so as to obtain the wavefront distribution and wave aberration information of the liquid lens. Among them, the iterative algorithm can discretize the wavefront to be measured, perform a finite difference fitting on the optical path length OPL of each node, and then use singular value decomposition to solve the entire matrix. This method has an increasing demand for computing power as the matrix size increases. Another iterative algorithm is the Southwell integration algorithm. For the optical path length OPL of each node, it is represented by its surrounding four nodes, and finally, a weighted average is performed on the obtained four values to obtain the wavefront distribution of the current liquid lens.

[0043] Embodiment 2

[0044] As Figure 5 shown, the liquid lens wavefront detection device includes a first reference wavefront beam generation component, a perturbation correction component, a bilateral telecentric lens 3, and a high-speed camera 5. The first reference wavefront beam generation component, the bilateral telecentric lens 3, and the high-speed camera 5 are sequentially arranged at intervals along the optical axis. The liquid lens 2 to be measured is placed between the first reference wavefront beam generation component and the bilateral telecentric lens 3. The reference wavefront beam emitted from the first reference wavefront beam generation component is incident on the liquid lens 2 to be measured. After passing through the liquid lens 2 to be measured, it is incident on the bilateral telecentric lens 3, and after passing through the bilateral telecentric lens 3, it is collected by the high-speed camera 5. The high-speed camera 5 is connected to a data processor 6. The bilateral telecentric lens 3 includes a first positive lens 31 and a second positive lens 33 that are sequentially arranged at intervals along the optical axis. The aperture stop 32 is located between the first positive lens 31 and the second positive lens 33, and the aperture stop 32 is located at the focal point of the first positive lens 31 and the focal point of the second positive lens 33.

[0045] The disturbance correction component is used to correct the system error composed of low-frequency disturbances introduced by disturbances along the optical path, the cooling fan of the high-speed camera 5, and other factors in the system. It includes a second reference wavefront beam generation component, a disturbance correction liquid lens, a mirror 7, and a beam splitter prism 8; the wavelength of the reference wavefront beam emitted from the second reference wavefront beam generation component is different from that of the reference wavefront beam emitted from the first reference wavefront beam generation component, and the others are the same; the second reference wavefront beam generation component is arranged on the side of the first reference wavefront beam generation component, and the reference wavefront beam emitted from the second reference wavefront beam generation component is incident on the disturbance correction liquid lens. The structure and fluid type of the disturbance correction liquid lens are the same as those of the liquid lens 2 to be measured, and the fluid in the disturbance correction liquid lens is in a static state (i.e., not updated, and the reference beam generated in the second optical path remains undistorted after passing through the liquid lens). The beam emitted after passing through the disturbance correction liquid lens is incident on the mirror 7. The beam splitter prism 8 is arranged between the liquid lens 2 to be measured and the double-sided telecentric lens 3 and is coaxially arranged with the liquid lens 2 to be measured and the double-sided telecentric lens 3. The beam transmitted through the liquid lens 2 to be measured is incident on the beam splitter prism 8 and undergoes transmission, and the beam reflected by the mirror 7 is incident on the beam splitter prism 8 and undergoes reflection. The beams transmitted and reflected by the beam splitter prism 8 are both incident on the double-sided telecentric lens 3; a first optical path is formed among the first reference wavefront beam generation component, the liquid lens 2 to be measured, and the beam splitter prism 8, and a second optical path is formed among the second reference wavefront beam generation component, the disturbance correction liquid lens, the mirror 7, and the beam splitter prism 8. The optical paths of the first optical path and the second optical path are the same. Therefore, the generated background displacement can be regarded as the system error composed of low-frequency disturbances introduced by disturbances along the optical path, the cooling fan of the high-speed camera 5, and other factors. The background displacements in the two optical paths are quickly recorded through the double-frame mode of the high-speed camera 5, and the false displacements caused by the system error in the first optical path are removed, improving the wavefront detection accuracy of the liquid lens.

[0046] As Figure 2 shown in (a) of Figure 2 and (b) of

[0047] The background pattern plates 1 in the first reference wavefront beam generation component and the second reference wavefront beam generation component are the same, but the wavelengths of the light emitted by the LED illumination system 4 are different. The light source of the first reference wavefront beam generation component is a blue LED 41 with a wavelength of 450 nm; the light source of the second reference wavefront beam generation component is a red LED 42 with a wavelength of 660 nm. To better reflect the false displacement caused by systematic errors, the background pattern shooting for the two optical paths needs to ensure an extremely short time interval. The dual-frame mode of the high-speed camera 5 is used for recording. First, an exposure is carried out on the first optical path, with an exposure time of approximately 20 μs. After the first optical path ends, an exposure is carried out on the second optical path after an interval of approximately 10 μs, and the exposure time is also approximately 20 μs.

[0048] The present invention proposes a method for detecting the wavefront of a liquid lens based on the background schlieren method. The method includes the following steps: Step 1: Install the liquid lens 2 to be measured in the liquid lens wavefront detection device. Step 2: The high-speed camera 5 sequentially records the reference image I of the liquid lens 2 to be measured in the undisturbed state ref (that is, the fluid in the liquid lens 2 to be measured is in a static state, and the liquid lens 2 to be measured is a static flow field) and the first corrected reference image of the disturbance-corrected liquid lens; then, the high-speed camera 5 sequentially records the dynamic image I of the liquid lens 2 to be measured under the action of a temperature gradient disturbed (that is, the fluid in the liquid lens 2 to be measured is in a flowing state with a temperature gradient, and the liquid lens 2 to be measured is a flow field with a temperature gradient) and the second corrected reference image of the disturbance-corrected liquid lens; Step 3: Use the optical flow algorithm to process the obtained reference image I ref and the dynamic image I disturbed After processing, the original background displacement (△x’, △y’) is obtained; and after processing the first corrected reference image and the second corrected reference image, the disturbance displacement is obtained; after subtracting the original background displacement (△x’, △y’) from the disturbance displacement, the corrected background displacement is obtained; in the cross-correlation or optical flow algorithm, by selecting an appropriate observation window size, the processed reference image is convolved with a series of dynamic images to obtain the continuous background displacement.

[0049] Step 4: Based on the corrected background displacement, use Fermat's principle and Malus's law in geometric optics to establish the relationship between the background displacement (△x’, △y’), the ray deflection angle (ε x , ε y ) and the wavefront slope, so as to calculate the wavefront slope distribution; Step 5: After integrating and reconstructing the wavefront slope distribution using the iterative reconstruction algorithm, the wavefront distribution and wave aberration of the liquid lens 2 to be measured are obtained.

[0050] The optical system part layout method of Example 2 is the same as that of Example 1, and some devices are the same. The difference lies in the different wavelengths of the illumination systems. The wavelength of the illumination system in the first reference wavefront beam generation component is 450 nm, and the wavelength of the illumination system in the second reference wavefront beam generation component is 660 nm. In order to better reflect the false displacement caused by system errors, the background pattern shooting of the two optical paths needs to ensure a very short interval time and is recorded using the dual-frame mode of the high-speed camera 5. First, exposure is performed on the first optical path, and the exposure time is approximately 20 μs. After the first optical path ends, the second optical path is exposed after an interval of about 10 μs, and the exposure time is also about 20 μs. It is applicable to situations that require high-precision measurement.

[0051] In Example 2, the background displacement (△1x’, △1y’) obtained from the first optical path is composed of the background displacement (△x’ disturb , △y’ disturb ) caused by the flow field disturbance and the false displacement (△x’ system , △y’ system ) caused by system errors. The background displacement (△2x’, △2y’) obtained from the second optical path only contains the false displacement (△x’ system , △y’ system ) caused by system errors. Therefore △x’ = △1x’ - △2x’ = (△x’ disturb + △x’ system ) - △x’ system △y’ = △1y’ - △2y’ = (△y’ disturb + △y’ system ) - △y’ system Because the exposure time interval between the two optical paths is very short, the false displacements caused by low-frequency disturbances such as the vibration of the high-speed camera fan and the fluctuation of the ambient temperature can be regarded as the same in the two optical paths. Therefore, Example II is applicable to situations that require high-precision measurement.

[0052] In the description of the positional relationship of the present invention, terms indicating orientation or positional relationship such as "inner", "outer", "upper", "lower", "left", "right", etc. are based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the embodiments and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the present invention. In addition, terms such as "parallel" and "perpendicular" do not mean that the components are required to be absolutely parallel or perpendicular, but allow a slight inclination. At the same time, although the steps shown in the flowchart of the drawings show a logical order, in some cases, the steps shown or described can be executed in a different order than here.

[0053] The above content and structure describe the basic principles, main features and advantages of the product of the present invention, which should be understood by those skilled in the art. What is described in the above examples and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A liquid lens wavefront detection device based on background schlieren method, characterized in that The liquid lens wavefront detection device includes a first reference wavefront beam generating component, a bilateral telecentric lens (3), and a camera (5). The first reference wavefront beam generating component, the bilateral telecentric lens (3), and the camera (5) are sequentially arranged at intervals along the optical axis. The liquid lens to be measured (2) is placed between the first reference wavefront beam generating component and the bilateral telecentric lens (3). The reference wavefront beam emitted from the first reference wavefront beam generating component is incident on the liquid lens to be measured (2), and after passing through the liquid lens to be measured (2), it is incident on the bilateral telecentric lens (3), and then after passing through the bilateral telecentric lens (3), it is collected by the camera (5).

2. The liquid lens wavefront detection device based on background schlieren method according to claim 1, wherein, The liquid lens to be measured (2) includes a fluid (21), a transparent glass cover plate (22), and a lens housing (23). A through groove is provided in the lens housing (23) along the optical axis direction. Corresponding transparent glass cover plates (22) are respectively installed in the lens housing (23) at both ends of the through groove, so that the lens housing (23) is a sealed structure; a fluid cavity is formed in the lens housing (23) between the two transparent glass cover plates (22). The lens housing (23) is also provided with a water injection port and a drainage port, and the water injection port and the drainage port are communicated with the fluid cavity, and the fluid cavity is filled with a fluid.

3. The liquid lens wavefront detection device based on the background schlieren method according to claim 1, wherein The liquid lens wavefront detection device further includes a perturbation correction component. The perturbation correction component includes a second reference wavefront beam generating component, a perturbation correction liquid lens, a mirror (7), and a beam splitter prism (8); the wavelength of the reference wavefront beam emitted from the second reference wavefront beam generating component is different from the wavelength of the reference wavefront beam emitted from the first reference wavefront beam generating component; The second reference wavefront beam generating component is arranged on the side of the first reference wavefront beam generating component. The reference wavefront beam emitted from the second reference wavefront beam generating component is incident on the perturbation correction liquid lens. The structure and fluid type of the perturbation correction liquid lens are the same as those of the liquid lens to be measured (2). The fluid in the perturbation correction liquid lens is in a static state. The beam emitted after passing through the perturbation correction liquid lens is incident on the mirror (7). The beam splitter prism (8) is arranged between the liquid lens to be measured (2) and the bilateral telecentric lens (3). The beam transmitted through the liquid lens to be measured (2) is incident on the beam splitter prism (8) and undergoes transmission. The beam reflected by the mirror (7) is incident on the beam splitter prism (8) and undergoes reflection. The beams transmitted and reflected by the beam splitter prism (8) are both incident on the bilateral telecentric lens (3); a first optical path is formed among the first reference wavefront beam generating component, the liquid lens to be measured (2), and the beam splitter prism (8), and a second optical path is formed among the second reference wavefront beam generating component, the perturbation correction liquid lens, the mirror (7), and the beam splitter prism (8). The optical paths of the first optical path and the second optical path are the same.

4. The liquid lens wavefront detection device based on background schlieren method according to claim 1, wherein The first reference wavefront beam generating component includes a background pattern plate (1) and an LED illumination system (4). The background pattern plate (1) is a transparent screen scattered with random dot matrices; the LED illumination system (4) is used to generate parallel beams.

5. A liquid lens wavefront detection device based on background schlieren method according to claim 1, characterized in that The bilateral telecentric lens (3) includes a first positive lens (31) and a second positive lens (33) which are arranged at intervals along the optical axis in sequence. The aperture stop (32) is located between the first positive lens (31) and the second positive lens (33), and the aperture stop (32) is located at the focal point of the first positive lens (31) and the focal point of the second positive lens (33).

6. A method for detecting the wavefront of a liquid lens based on background schlieren method, characterized in that, It includes the following steps: Step 1: Install the liquid lens to be measured (2) in the liquid lens wavefront detection device described in Claim 1; Step 2: Use the camera (5) to sequentially collect the reference image I of the liquid lens to be measured (2) in a non-disturbed state ref and the dynamic image I generated under the action of the temperature gradient with disturbances disturbed ; Step 3: Process the obtained reference image I ref and the dynamic image I disturbed to obtain the background displacement (△x’, △y’); Step 4: Based on the background displacement (△x’, △y’), establish the relationship between the background displacement (△x’, △y’), the ray deflection angle (ε x , ε y ) and the wavefront slope by using Fermat's principle and Malus' law in geometric optics, so as to calculate the wavefront slope distribution; Step 5: After performing integral reconstruction on the wavefront slope distribution, obtain the wavefront distribution and wave aberration of the liquid lens to be measured (2).

7. A method for detecting the wavefront of a liquid lens based on the background schlieren method according to claim 6, characterized in that, In the said step 3, the obtained reference image I ref and the dynamic image I disturbed are processed.

8. A method for detecting the wavefront of a liquid lens based on background schlieren method according to claim 6, characterized in that, In the said Step 5, the trapezoidal integral algorithm or the iterative reconstruction algorithm is used to perform integral reconstruction on the wavefront slope distribution.

9. A method for detecting the wavefront of a liquid lens based on background schlieren method, characterized in that, It includes the following steps: Step 1: Install the liquid lens to be measured (2) in the liquid lens wavefront detection device described in Claim 3; Step 2: The camera (5) sequentially records the reference image I of the liquid lens to be measured (2) in an undisturbed state in the double-frame mode ref and the first corrected reference image of the perturbed and corrected liquid lens; then, the camera (5) sequentially records the dynamic image I of the liquid lens to be measured (2) perturbed under the action of a temperature gradient in the double-frame mode disturbed and the second corrected reference image of the perturbed and corrected liquid lens; Step 3: For the obtained reference image I ref and the dynamic image I disturbed After processing, the original background displacement (Δx’, Δy’) is obtained; and after processing the first corrected reference image and the second corrected reference image, the perturbation displacement is obtained; after subtracting the original background displacement (Δx’, Δy’) from the perturbation displacement, the corrected background displacement is obtained. Step 4: Based on the corrected background displacement, establish the relationship between the background displacement (△x’, △y’), the ray deflection angle (ε x , ε y ) and the wavefront slope by using Fermat's principle and Malus' law in geometric optics, so as to calculate the wavefront slope distribution; Step 5: After performing integral reconstruction on the wavefront slope distribution, obtain the wavefront distribution and wave aberration of the liquid lens to be measured (2).

10. A method for detecting the wavefront of a liquid lens based on the background schlieren method according to claim 9, characterized in that In the said step 3, the obtained reference image I ref and the dynamic image I disturbed are processed by using the cross-correlation or optical flow algorithm.

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