Low-noise speckle interference system and method based on polarization camera

Abstract

The invention provides a low-noise speckle interference system and method based on a polarization camera, and relates to the technical field of speckle interference. According to the low-noise speckle interference system, a polarization camera and a speckle interference system are combined, so that a single speckle interference pattern comprises four different polarization state channels, in the image processing process, the complex amplitude difference before and after deformation is averaged, information fusion of the four channels is achieved, and the speckle interference pattern is obtained. The standard deviation of the speckle interference noise can be reduced to the original # imgabs0 #, so that the suppression effect of the speckle interference noise is greatly improved; in the aspect of data processing, only one-step averaging operation is added compared with a traditional speckle interference technology, the influence on the overall measurement speed is small, and the flexibility is excellent; in addition, by reducing the speckle noise standard deviation, the requirement of the speckle interference technology for a filtering algorithm is reduced, and the practicability of the speckle interference technology is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of speckle interferometry, and particularly relates to a low-noise speckle interferometry system and method based on a polarization camera. Background Art

[0002] Speckle interferometry originated from digital holography. By observing the speckles generated when coherent light irradiates the surface of an object and comparing the speckle phase changes under different object states, the deformation occurring on the object surface can be equivalently obtained. Due to the advantages of full-field non-contact and real-time detection of speckle interferometry, it is now widely used in the measurement of material mechanical properties.

[0003] Since the phase obtained by speckle interferometry is wrapped in (-π, π], the phase is presented in the form of a phase fringe pattern. When calculating the deformation of the object surface, a phase unwrapping algorithm needs to be used to expand the phase to obtain the phase directly corresponding to the deformation, and then the deformation information is calculated in combination with the displacement sensitivity factor. However, like other coherent light illumination technologies, the phase map obtained by speckle interferometry contains significant speckle noise. Speckle noise will seriously interfere with the stability of the unwrapping algorithm, affect the accuracy of the unwrapped phase, and thus damage the measurement of object deformation.

[0004] Common speckle noise suppression methods are to use image filtering algorithms in computer vision to filter out speckle noise. Considering that the edges of the phase fringe pattern are relatively sharp, the filtering algorithm needs to be improved to protect the edges. The cosine transform combined with the spatial domain filtering algorithm is the most common filtering algorithm, which has good filtering effect and fast filtering speed. However, when facing high-density fringes, spatial domain filtering will inevitably cause aliasing between fringes, affecting the phase distribution. The window Fourier transform, as a representative of frequency domain filtering, is a filtering algorithm with recognized good filtering effect, and has good filtering performance for high-density fringes or high-intensity noise. However, on the one hand, its filtering speed is slow, and the filtering time can reach several minutes for the pixel resolution of tens of millions of modern industrial cameras. On the other hand, it has many parameters, and in order to obtain better filtering quality, it must be tried many times. The superposition of these two factors results in very poor flexibility of window Fourier filtering and is difficult to be applied to actual dynamic measurements.

[0005] Reducing the distribution of speckle noise through optical path design and then combining with a simple filtering algorithm may achieve a better overall effect. However, the current optical path design focuses on destroying the temporal coherence of the illumination beam. For example, the beam is transmitted through a rotating ground glass and irradiated on the object to be measured, and the optical path and control are relatively complex. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the present invention provides a low-noise speckle interferometry system and method based on a polarization camera, which solves the problems of poor speckle interference noise suppression effect and poor flexibility.

[0007] To achieve the above object, the present invention is realized by the following technical solutions:

[0008] A low-noise speckle interference system based on a polarization camera, the low-noise speckle interference system comprising: a laser source, a beam expander, a first plane mirror, a first beam splitter, a test object, a second plane mirror, a quarter-wave plate, a second beam splitter, a third plane mirror and an imaging system;

[0009] The laser beam emitted by the laser source is reflected by the first plane mirror to the first beam splitter after passing through the beam expander, and the laser beam is split into a first light beam and a second light beam by the first beam splitter;

[0010] The first light beam irradiates the surface of the test object and undergoes diffuse reflection, and the scattered light of the diffuse reflection enters the imaging system as object light;

[0011] The second light beam is reflected by the second plane mirror, modulated by the quarter-wave plate, reflected by the second beam splitter, and reflected by the third plane mirror and then enters the imaging system as reference light;

[0012] A piezoelectric ceramic is installed behind the third plane mirror, and the piezoelectric ceramic drives the third plane mirror to perform regular reciprocating motion;

[0013] The imaging system includes: a first Fourier lens, a second Fourier lens, a polarization camera and a third beam splitter;

[0014] The first Fourier lens and the second Fourier lens have the same focal length, both being f; the distance between the first Fourier lens and the second Fourier lens is 2f, the distance between the first Fourier lens and the test object is f, the distance between the second Fourier lens and the polarization camera is f, and the third beam splitter is arranged between the second Fourier lens and the polarization camera;

[0015] The object light enters the imaging system and then passes through the first beam splitter, the first Fourier lens, the second Fourier lens and the third beam splitter in sequence and then irradiates the polarization camera;

[0016] The reference light enters the imaging system and passes through the second beam splitter, and is reflected by the third beam splitter and then irradiates the polarization camera;

[0017] The object light and the reference light are combined at the third beam splitter and interfere on the polarization camera.

[0018] Preferably, the laser beam emitted by the laser source is a linearly polarized light beam.

[0019] Preferably, the beam expander is used to expand the beam diameter while maintaining beam collimation.

[0020] Preferably, the quarter-wave plate is used to convert linearly polarized light into circularly polarized light.

[0021] Preferably, the imaging system is a 4f system with a magnification of 1:1, and a diaphragm is provided on the spectral plane of the imaging system.

[0022] Preferably, each pixel of the polarization camera is equipped with a corresponding polarizer, and all the polarizers are arranged in the same 2×2 matrix array and cover the entire polarization camera.

[0023] Preferably, a coordinate system is established with the upper left corner of the polarization camera as the origin, a superpixel is defined as a 2×2 matrix, and each pixel of the polarization camera has its corresponding superpixel and serves as the upper left corner element in the superpixel.

[0024] A low-noise speckle interferometry method based on a polarization camera, the low-noise speckle interferometry method comprising:

[0025] The linearly polarized laser beam emitted by the laser source is expanded in beam diameter by a beam expander and then split into a first beam and a second beam by a first beam splitter; the laser beam emitted by the laser source and the first beam and the second beam split therefrom are reflected by a plurality of plane mirrors to plan the path;

[0026] The first beam irradiates the surface of the test object on its path, undergoes diffuse reflection to generate speckles, and the scattered light of the diffuse reflection, as the object light, passes through the first Fourier lens, the diaphragm and the second Fourier lens and then is directed to the polarization camera through a third beam splitter;

[0027] The second beam passes through a quarter-wave plate modulation and a third plane mirror reflection on its path and then serves as the reference light and is directed to the polarization camera through a third beam splitter;

[0028] A piezoelectric ceramic is installed behind the third plane mirror, and the piezoelectric ceramic drives the third plane mirror to perform regular reciprocating motion, introducing a periodic phase change to the third plane mirror;

[0029] The first Fourier lens and the second Fourier lens have the same focal length, both being f; the distance between the first Fourier lens and the second Fourier lens is 2f, the distance between the first Fourier lens and the test object is f, the distance between the second Fourier lens and the polarization camera is f, and the third beam splitter is arranged between the second Fourier lens and the polarization camera;

[0030] The object light and the reference light are combined at the third beam splitter and interfere on the polarization camera.

[0031] Preferably, the light intensity expression of the interference pattern obtained on the target surface of the polarization camera (13) is:

[0032] I(x,y) = I0(x,y) + I m (x,y)cos(φ(x,y) + φ p (x,y));

[0033] Among them, I0(x, y) is the intensity of the background light;

[0034] I m (x, y) is the intensity of the modulated light;

[0035] φ(x, y) is the phase difference between the object light and the reference light;

[0036] φ p (x, y) is the phase introduced by the polarizer on the polarization camera (13);

[0037] Deriving with four-step phase shift, the intensities of the four speckle interferograms obtained are:

[0038]

[0039] Among them, And it can be calculated by the following formula:

[0040]

[0041] Using the four-step phase shift technique, four speckle interferograms are collected before deformation to calculate the phase Four speckle interferograms are collected before deformation to calculate the phase The phase difference before and after deformation is:

[0042]

[0043] Among them, represents the phase difference caused by deformation; for speckle interferometry, the phase after deformation needs to be subtracted from the phase before deformation, and the deformation is calculated based on the phase difference. Therefore, φ p (x, y) is eliminated during subtraction and does not affect the measurement, so it can be ignored;

[0044] Taking the interference light waves corresponding to the pixels at the coordinate positions (1, 1) and (2, 2) as the reference, before deformation, the complex amplitudes of the light waves corresponding to these two pixels are:

[0045]

[0046] Among them, φ 1,1 and φ 2,2 are the specific values at the pixels with coordinate positions (1, 1) and (2, 2);

[0047] According to the Jones matrix or the principle of vector superposition, the complex amplitudes of the other two pixels in this superpixel are expressed as:

[0048]

[0049] Assume that remaining unchanged within a superpixel, after deformation, the complex amplitudes of the two reference light waves are as follows:

[0050]

[0051] The complex amplitudes of the other two pixels in this superpixel are expressed as:

[0052]

[0053] where ε1 and ε2 are the speckle noises introduced by the deformation in the pixels at the coordinate positions (1,1) and (2,2). The polarization states corresponding to these two speckle noises are perpendicular to each other, so they have the characteristics of independent and identical distribution; in order to ensure remaining unchanged within a superpixel, the average size d of the speckles must be greater than 4 pixels; the average size of the speckles is affected by the diameter D of the system aperture diaphragm, and its rule is expressed as Performing conjugate multiplication on the complex optical fields before and after deformation, we get:

[0054]

[0055] where * is the conjugate operation. Averaging the four complex amplitude differences in this superpixel, we can obtain the averaged complex amplitude difference:

[0056]

[0057]

[0058] Taking the argument of the above averaged complex amplitude difference, the phase introduced by the deformation can be obtained Adding the averaged speckle noise; let the averaged speckle noise be ε, then:

[0059]

[0060] where angle represents taking the argument of a complex number;

[0061] The speckle noise ε is a random variable; considering that the speckle noises ε1 and ε2 are independent and identically distributed, defining their standard deviation as σ(ε n ), the standard deviation of the averaged speckle noise can be obtained:

[0062]

[0063] Finally, the speckle noise is suppressed.

[0064] The present invention provides a low-noise speckle interference system and method based on a polarization camera. Compared with the prior art, it has the following beneficial effects:

[0065] In the present invention, the low-noise speckle interference system combines a polarization camera with a speckle interference system, so that a single speckle interference pattern contains four different polarization state channels. During the image processing, the mean value processing is performed on the complex amplitude difference before and after deformation to realize the information fusion of the four channels, and the standard deviation of the speckle interference noise can be reduced to a large extent, which greatly improves the suppression effect of the speckle interference noise; and in terms of data processing, compared with the traditional speckle interference technology, only one additional averaging operation is added, which has little impact on the overall measurement speed and has excellent flexibility; in addition, by reducing the standard deviation of the speckle noise, the requirements for the filtering algorithm of the speckle interference technology are reduced, and the practicability of the speckle interference technology is improved. Brief Description of the Drawings

[0066] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0067] Figure 1 It is a schematic structural diagram of the low-noise speckle interference system in the embodiment of the present invention.

[0068] The reference numerals in the figure are set as follows: laser source 1, beam expander 2, first plane mirror 3, first beam splitter 4, test object 5, second plane mirror 6, quarter-wave plate 7, second beam splitter 8, third plane mirror 9, piezoelectric ceramic 10, first Fourier lens 11, second Fourier lens 12, polarization camera 13, third beam splitter 14, aperture 15. Detailed Embodiments

[0069] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0070] The embodiments of the present application provide a low-noise speckle interference system and method based on a polarization camera, which solve the problems of poor suppression effect and poor flexibility of speckle interference noise.

[0071] To better understand the above technical solutions, the above technical solutions will be described in detail below in conjunction with the accompanying drawings of the specification and specific embodiments.

[0072] Embodiment:

[0073] As Figure 1 shown, the present invention provides a low-noise speckle interference system based on a polarization camera. The low-noise speckle interference system includes: a laser source 1, a beam expander 2, a first plane mirror 3, a first beam splitter 4, a test object 5, a second plane mirror 6, a quarter-wave plate 7, a second beam splitter 8, a third plane mirror 9, and an imaging system;

[0074] The laser beam emitted by the laser source 1 is reflected by the first plane mirror 3 after passing through the beam expander 2 and then reaches the first beam splitter 4. The laser beam is split into a first light beam and a second light beam by the first beam splitter 4 through reflection and transmission;

[0075] The first light beam irradiates the surface of the test object 5, undergoes diffuse reflection to generate speckles, and the scattered light of the diffuse reflection enters the imaging system as object light;

[0076] The second light beam is reflected by the second plane mirror 6, modulated by the quarter-wave plate 7, reflected by the second beam splitter 8, and reflected by the third plane mirror 9, and then enters the imaging system as reference light;

[0077] A piezoelectric ceramic 10 is installed behind the third plane mirror 9. The piezoelectric ceramic 10 drives the third plane mirror 9 to perform regular reciprocating motion, introducing a periodic phase change to the third plane mirror 9;

[0078] The imaging system includes: a first Fourier lens 11, a second Fourier lens 12, a polarization camera 13, and a third beam splitter 14;

[0079] The first Fourier lens 11 and the second Fourier lens 12 have the same focal length, both being f; the distance between the first Fourier lens 11 and the second Fourier lens 12 is 2f, the distance between the first Fourier lens 11 and the test object 5 is f, the distance between the second Fourier lens 12 and the polarization camera 13 is f, and the third beam splitter 14 is arranged between the second Fourier lens 12 and the polarization camera 13;

[0080] The object light enters the imaging system and then passes through the first beam splitter 4, the first Fourier lens 11, the second Fourier lens 12, and the third beam splitter 14 in sequence and then shoots towards the polarization camera 13;

[0081] The reference light enters the imaging system and passes through the second beam splitter 8, and is reflected by the third beam splitter 14 and then shoots towards the polarization camera 13;

[0082] The object light and the reference light are combined at the third beam splitter 14 and interfere on the polarization camera 13.

[0083] The laser beam emitted by the laser source 1 is a linearly polarized light beam.

[0084] The beam expander 2 is used to expand the beam diameter and at the same time keep the beam collimated.

[0085] The quarter-wave plate 7 is used to convert linearly polarized light into circularly polarized light to prevent extinction in a specific polarization state of the polarization camera 13.

[0086] As Figure 1 shown, the imaging system is a 4f system with a magnification of 1:1. A diaphragm 15 is provided on the spectral plane of the imaging system to adjust the size of the speckles.

[0087] As Figure 1 shown, each pixel of the polarization camera 13 is equipped with a corresponding polarizer. All the polarizers are arranged in the same 2×2 matrix array and cover the entire polarization camera 13.

[0088] Taking the upper left corner of the polarization camera 13 as the origin, a coordinate system (i, j) is established. A superpixel is defined as a 2×2 matrix. Each pixel of the polarization camera 13 has its corresponding superpixel and is used as the upper left corner element in the superpixel.

[0089] The present invention provides a low-noise speckle interferometry method based on a polarization camera. The low-noise speckle interferometry method includes:

[0090] The linearly polarized laser beam emitted by the laser source 1 is expanded in beam diameter by the beam expander 2 and then split into a first beam and a second beam by the first beam splitter 4; the laser beam emitted by the laser source 1 and the first beam and the second beam split therefrom are reflected by a number of plane mirrors to plan the path;

[0091] The first beam irradiates the surface of the test object 5 in its path, undergoes diffuse reflection to generate speckles, and the scattered light of the diffuse reflection is used as object light to pass through the first Fourier lens 11, the diaphragm 15, and the second Fourier lens 12 and then is directed to the polarization camera 13 through the third beam splitter 14;

[0092] The second beam is modulated by the quarter-wave plate 7 and reflected by the third plane mirror 9 in its path and then used as reference light to be directed to the polarization camera 13 through the third beam splitter 14;

[0093] A piezoelectric ceramic 10 is installed behind the third plane mirror 9. The piezoelectric ceramic 10 drives the third plane mirror 9 to perform regular reciprocating motion, introducing a periodic phase change to the third plane mirror 9;

[0094] The first Fourier lens 11 and the second Fourier lens 12 have the same focal length, both being f; the distance between the first Fourier lens 11 and the second Fourier lens 12 is 2f, the distance between the first Fourier lens 11 and the test object 5 is f, the distance between the second Fourier lens 12 and the polarization camera 13 is f, and the third beam splitter 14 is arranged between the second Fourier lens 12 and the polarization camera 13;

[0095] The object light and the reference light are combined by transmission and reflection at the third beam splitter 14 and interfere on the polarization camera 13.

[0096] The light intensity expression of the interference pattern obtained on the target surface of the polarization camera 13 is:

[0097] I(x,y) = I0(x,y) + I m (x,y)cos(φ(x,y) + φ p (x,y)); (1)

[0098] where, I0(x,y) is the background light intensity;

[0099] I m (x,y) is the modulated light intensity;

[0100] φ(x,y) is the phase difference between the object light and the reference light;

[0101] φ p (x,y) is the phase introduced by the polarizer on the polarization camera 13;

[0102] Taking four-step phase shifting as an example for derivation, the intensities of the four speckle interference patterns obtained are:

[0103]

[0104] where, and can be calculated by the following formula:

[0105]

[0106] Using the four-step phase shifting technique, four speckle interference patterns are collected before deformation to calculate the phase Four speckle interference patterns are collected before deformation to calculate the phase The phase difference before and after deformation is:

[0107]

[0108] where, represents the phase difference caused by deformation; for speckle interference, the phase after deformation needs to be subtracted from the phase before deformation, and the deformation is calculated based on the phase difference. Therefore, φ p (x,y) is eliminated during subtraction and does not affect the measurement, so it can be ignored;

[0109] The phase φ p (x,y) introduced by the polarization camera 13 remains unchanged at any time, so it is eliminated during the subtraction process and thus does not affect the overall phase distribution; for the sake of simple and general discussion of the principle of speckle noise suppression based on polarization diversity, hereFigure 1 Analyze the first superpixel shown in the figure; for the pixels with coordinate positions (1, 1) and (2, 2), the polarization states of the corresponding interfering lights are perpendicular to each other; since the speckles with perpendicular polarization states are not correlated in statistical distribution, the interfering light waves corresponding to these two pixels are used as a reference for discussion. Before deformation, the complex amplitudes of the light waves corresponding to these two pixels are:

[0110]

[0111] where φ 1,1 and φ 2,2 are the specific values at the pixels with coordinate positions (1, 1) and (2, 2) in the coordinate system;

[0112] Considering that the phase has been directly solved by formula (3), the amplitude of the complex amplitude is set to 1 at this time to simplify the discussion; according to the Jones matrix or the principle of vector superposition, the complex amplitudes of the other two pixels in this superpixel are expressed as:

[0113]

[0114] Assume that remains unchanged within a superpixel range. After deformation, the complex amplitudes of the two reference light waves are:

[0115]

[0116] The complex amplitudes of the other two pixels in this superpixel are expressed as:

[0117]

[0118] where ε1 and ε2 are the speckle noises introduced by the deformation at the pixels with coordinate positions (1, 1) and (2, 2) in the coordinate system. The polarization states corresponding to these two speckle noises are perpendicular to each other, so they have the characteristics of independent and identical distribution; to ensure that remains unchanged within a superpixel range, the average size d of the speckles must be greater than 4 pixels; the average size of the speckles is affected by the diameter D of the system aperture diaphragm, and its law is expressed as Perform conjugate multiplication on the complex light fields before and after deformation to obtain:

[0119]

[0120] where * is the conjugate operation. By averaging the four complex amplitude differences in this superpixel, the averaged complex amplitude difference can be obtained:

[0121]

[0122] ​By calculating the argument of the averaged complex amplitude difference, the phase introduced by deformation can be obtained. Add the averaged speckle noise; let the averaged speckle noise be ε, then:

[0123]

[0124] where angle represents calculating the argument of a complex number;

[0125] The speckle noise ε is a random variable; considering that the speckle noises ε1 and ε2 are independent and identically distributed, and defining their standard deviation as σ(ε n ), the standard deviation of the averaged speckle noise can be obtained:

[0126]

[0127] Finally, the speckle noise is suppressed.

[0128] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0129] In the embodiment of the present invention, the low-noise speckle interference system combines a polarization camera with a speckle interference system, so that a single speckle interference pattern contains four channels with different polarization states. During the image processing, the complex amplitude differences before and after deformation are averaged to realize the information fusion of the four channels, and the standard deviation of the speckle interference noise can be reduced to greatly improving the suppression effect of the speckle interference noise; and in terms of data processing, only one additional averaging operation is added compared with the traditional speckle interference technology, which has little impact on the overall measurement speed and excellent flexibility; in addition, by reducing the standard deviation of the speckle noise, the requirements for the filtering algorithm of the speckle interference technology are reduced, and the practicality of the speckle interference technology is improved.

[0130] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0131] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A low-noise speckle interferometry system based on a polarization camera, characterized in that: The low-noise speckle interferometry system comprises: a laser source (1), a beam expander (2), a first plane mirror (3), a first beam splitter (4), a test object (5), a second plane mirror (6), a quarter-wave plate (7), a second beam splitter (8), a third plane mirror (9) and an imaging system; The laser beam emitted by the laser source (1) passes through a beam expander (2) and is then reflected by a first plane mirror (3) to a first beam splitter (4), where the laser beam is split into a first beam and a second beam by the first beam splitter (4); The first light beam is irradiated onto the surface of the test object (5) to generate diffuse reflection, and the diffusely reflected scattered light enters the imaging system as object light; The second light beam is sequentially reflected by a second plane mirror (6), modulated by a quarter wave plate (7), reflected by a second beam splitter (8), and reflected by a third plane mirror (9), and then enters an imaging system as a reference light; A piezoelectric ceramic (10) is installed behind the third plane mirror (9), and the piezoelectric ceramic (10) drives the third plane mirror (9) to perform regular reciprocating motion; The imaging system comprises: a first Fourier lens (11), a second Fourier lens (12), a polarization camera (13) and a third beam splitter (14); The first Fourier lens (11) and the second Fourier lens (12) have the same focal length, both being f; the distance between the first Fourier lens (11) and the second Fourier lens (12) is 2f, the distance between the first Fourier lens (11) and the test object (5) is f, the distance between the second Fourier lens (12) and the polarization camera (13) is f, and the third beam splitter (14) is arranged between the second Fourier lens (12) and the polarization camera (13); After entering the imaging system, the object light sequentially passes through the first beam splitter (4), the first Fourier lens (11), the second Fourier lens (12) and the third beam splitter (14) and then is emitted to the polarization camera (13); After entering the imaging system, the reference light passes through the second beam splitter (8), is reflected by the third beam splitter (14), and then is directed toward the polarization camera (13); The object light and the reference light are combined at a third beam splitter (14) and interfere on a polarization camera (13).

2. The low-noise speckle interferometry system based on a polarization camera according to claim 1, characterized in that: The laser beam emitted by the laser source (1) is a linearly polarized beam.

3. The low-noise speckle interferometry system based on a polarization camera according to claim 1, characterized in that: The beam expander (2) is used to expand the diameter of the light beam while keeping the light beam collimated.

4. The low-noise speckle interferometry system based on a polarization camera according to claim 1, characterized in that: The quarter wave plate (7) is used to convert linearly polarized light into circularly polarized light.

5. The low-noise speckle interferometry system based on a polarization camera according to claim 1, characterized in that: The imaging system is a 4f system with a magnification of 1:1, and a diaphragm (15) is arranged on the spectrum plane of the imaging system.

6. The low-noise speckle interferometry system based on a polarization camera according to claim 1, characterized in that: Each pixel of the polarization camera (13) is equipped with a corresponding polarizer, and all polarizers are arranged in the same 2×2 matrix array and spread throughout the entire polarization camera (13).

7. The low-noise speckle interferometry system based on a polarization camera according to claim 6, characterized in that: A coordinate system is established with the upper left corner of the polarization camera (13) as the origin, and a superpixel is defined as a 2×2 matrix. Each pixel of the polarization camera (13) has its corresponding superpixel and serves as the upper left corner element in the superpixel.

8. A low-noise speckle interferometry method based on a polarization camera, characterized in that: The low-noise speckle interferometry method comprises: A linearly polarized laser beam emitted by a laser source (1) is expanded in diameter by a beam expander (2) and then split into a first beam and a second beam by a first beam splitter (4); the laser beam emitted by the laser source (1) and the first beam and the second beam split into the first beam and the second beam are reflected by a plurality of plane mirrors to plan paths; The first light beam is irradiated onto the surface of the test object (5) on its path, and diffuse reflection occurs to generate speckles. The diffusely reflected scattered light is transmitted as object light through the first Fourier lens (11), the aperture (15) and the second Fourier lens (12), and then passes through the third beam splitter (14) to the polarization camera (13); The second light beam is modulated by a quarter wave plate (7) and reflected by a third plane mirror (9) on its path, and then emitted as reference light through a third beam splitter (14) toward a polarization camera (13); A piezoelectric ceramic (10) is installed behind the third plane mirror (9), and the piezoelectric ceramic (10) drives the third plane mirror (9) to perform regular reciprocating motion, thereby introducing a periodic phase change into the third plane mirror (9); The first Fourier lens (11) and the second Fourier lens (12) have the same focal length, both of which are f; the distance between the first Fourier lens (11) and the second Fourier lens (12) is 2f, the distance between the first Fourier lens (11) and the test object (5) is f, the distance between the second Fourier lens (12) and the polarization camera (13) is f, and the third beam splitter (14) is arranged between the second Fourier lens (12) and the polarization camera (13); The object light and the reference light are combined at the third beam splitter (14) and interfere with each other on the polarization camera (13).

9. The low-noise speckle interferometry method based on a polarization camera as claimed in claim 8, characterized in that: The interference pattern light intensity expression obtained on the target surface of the polarization camera (13) is: I(x,y)=I0(x,y)+I m (x,y)cos(φ(x,y)+φ p (x,y)); Among them, I0(x,y) is the background light intensity; I m (x,y) is the modulated light intensity; φ(x,y) is the phase difference between the object light and the reference light; φ p (x, y) is the phase introduced by the polarizer on the polarization camera (13); Deduced with four-step phase shift, the intensity of the four speckle interferograms is: in, And can be calculated by the following formula: Using the four-step phase shifting technique, four speckle interferograms are collected before deformation to calculate the phase Collect four speckle interferograms before deformation to calculate phase The phase difference before and after deformation is: in, Indicates the phase difference caused by deformation; speckle interferometry requires subtracting the phase before deformation from the phase after deformation, and calculating the deformation based on the phase difference, so φ p (x,y) is eliminated during subtraction and does not affect the measurement and can be ignored; Taking the interference light waves corresponding to the pixels at coordinate positions (1,1) and (2,2) as the reference, before deformation, the complex amplitudes of the light waves corresponding to these two pixels are: Among them, φ 1,1 and φ 2,2 for The specific values ​​at the pixels at coordinate positions (1,1) and (2,2); According to the Jones matrix or vector superposition principle, the complex amplitudes of the other two pixels in the superpixel are expressed as: assumed If it remains unchanged within a super-pixel range, then after deformation, the complex amplitudes of the two reference light waves are: The complex amplitudes of the other two pixels in this superpixel are expressed as: Among them, ε1 and ε2 are the speckle noise introduced by the pixels whose positions in the coordinate system are (1,1) and (2,2). The polarization states corresponding to these two speckle noises are perpendicular to each other, so they have the characteristics of independent and identical distribution. In order to ensure To keep the same within a superpixel range, the average size d of the speckle must be greater than 4 pixels; the average size of the speckle is affected by the aperture diameter D of the system, and its rule is expressed as By conjugating and multiplying the complex light field before and after deformation, we get: Among them, * is a conjugate operation. The four complex amplitude differences in the superpixel are averaged to obtain the averaged complex amplitude difference: The phase angle introduced by the deformation can be obtained by calculating the phase angle of the complex amplitude difference after the above average. Add the averaged speckle noise; let the averaged speckle noise be ε, then: Among them, angle means to find the angle of the complex number; The speckle noise ε is a random variable. Considering that the speckle noise ε1 and ε2 are independent and identically distributed, their standard deviation is defined as σ(ε n ), the averaged speckle noise standard deviation can be obtained: Finally, the speckle noise is suppressed.

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