Polarization correlation imaging scheme for extracting target from objects with same material and different roughness

Abstract

The invention relates to a polarization correlation imaging scheme for extracting a target from objects which are made of the same material and have different roughness. The laser generates a Gaussian beam, and random speckles are generated through the rotary ground glass. A polarizer is placed behind the ground glass to control the polarization direction, and a beam splitter divides speckles into a test beam and a reference beam. The reference light beam is received by the CCD, and the test light beam is reflected after irradiating an object and is separated by the beam splitter. One beam of light is received by the barrel detector after passing through the + 45-degree polarizer, and the other beam of light is collected by the other two barrel detectors after passing through the polarization beam splitter. And the computer performs correlated imaging on the signals acquired by the barrel detector and the preset speckles. By modulating the polarization state of the light field and designing the receiving end, additional object surface polarization information is introduced, so that the system can extract a target from objects which are made of the same material and have different roughness, and the system has application value in a complex confrontation environment.

Description

Technical Field

[0001] The present invention relates to a polarization correlation imaging technology for extracting a target from objects of the same material but different roughness, and in particular to a scheme for modulating the polarization state of a light beam to enrich the object information acquired by the system, which can be applied to target detection and other fields. Background Art

[0002] Correlation imaging is an indirect imaging technology based on the correlation measurement of light field intensity. In the traditional correlation imaging system, the illumination light field is divided into two beams by a non-polarizing beam splitter. One beam is irradiated onto the object and is received by a bucket detector after reflection or transmission. The other beam does not interact with the object and is received by a detector with spatial resolution. The two beams can be reconstructed into a high-resolution image through correlation operation. In order to improve image quality or reduce imaging requirements, many scholars have conducted further research on this basis. In 2009, Ori Katz et al. proposed a compressed sensing algorithm (Reference 1: X. Zhang, H. Zhong, and L. Cao, "Robust compressed ghost imaging against environmental influence factors," Opt. Express 32 (2), 1669-1676 (2024).), which can obtain higher quality images with a small number of samples. Zhou Yang et al. proposed an adaptive threshold method to achieve iterative denoising (Reference 2: XRYao, WKYu, XFLiu, LZLi, MFLi, LAWu and GJZhai, "Iterative denoising of ghostimaging," Opt. Express 22 (20), 24268-24275 (2014).), which can significantly improve the visual effect and peak signal-to-noise ratio of imaging. In addition, there are differential correlation imaging, subtraction correlation imaging, etc. However, traditional correlation imaging cannot effectively distinguish the target from the background when the reflectivity or transmittance is similar or the surface structure of the object is complex. Therefore, some scholars proposed polarization correlation imaging technology (Reference 3: 9. DFShi, SXHu, and YJWang, "Polarmetric ghostimaging," Org. Lett 39 (5), 1231-1234 (2014).). This technology adds polarization information to traditional correlation imaging and obtains more information about the target object through the polarization characteristics of light. In addition, since polarization characteristics are less sensitive to background light, polarization correlation imaging can effectively break through the limitations of traditional correlation imaging that is difficult to distinguish under complex backgrounds, thereby achieving clearer imaging.

[0003] Traditional polarization correlation imaging is performed by obtaining light intensities obtained by horizontal and vertical polarization in the object arm. The only target information obtained is the component related to linear polarization in the main diagonal of the object Mueller matrix. It is impossible to study the difference of other target information when polarized light is incident. Moreover, when the target and the background are made of the same material and the difference in the linear polarization-related components between the two is very small, the target cannot be separated from the background. To address this problem, we propose a new method to obtain more object information, change the polarization state of the illumination speckle at the incident end, and add the modulated polarization direction in the signal extraction at the receiving end, thereby adding another element related to the circular polarization component in the main diagonal of the Mueller matrix, which can relatively improve the image quality. When the target and the background are made of the same material and only the roughness is different, the two can also be well distinguished. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a polarization correlation imaging scheme for extracting targets from objects of the same material with different roughness. The scheme is detailed, simple in principle, easy to implement, and can extract targets from objects of the same material with different roughness, especially under the condition of high background roughness, it still shows good imaging effect, which makes it have important practical application value in complex confrontation environments.

[0005] To achieve the above object, the technical solution adopted by the present invention is to provide a polarization correlation imaging solution for extracting targets from objects of the same material with different roughness. The device used in the solution includes: a signal source 1, polarizers 2a, 2b, beam splitters 3a, 3b, CCD 4, an object 5, a polarization beam splitter 6, bucket detectors 7, 8, 9 without resolution capability, and a computer 10; the solution includes the following steps:

[0006] (1) The laser emits a Gaussian beam, which passes through a rotating frosted glass to generate random speckles. A linear polarizer is placed behind the frosted glass to control the polarization direction of the light, and a beam splitter is used to split the speckles into a test beam and a reference beam.

[0007] (2) In the reference arm, the light beam is received by the CCD after propagating a certain distance; in the test arm, the light beam is incident on the object after propagating the same distance.

[0008] (3) The light beam reflected by the imaging object is focused by a convex lens and then separated into two beams by a beam splitter. One beam passes through a +45° polarizer and is received by a barrel detector, and the other beam passes through a polarization beam splitter and is collected by the other two barrel detectors.

[0009] (4) The computer correlates the signal collected by the bucket detector with the preset speckle pattern.

[0010] In the above technical solution, the signal source is composed of a laser and a rotating frosted glass in order to generate a signal light beam.

[0011] In the above technical solution, the linear polarizer is used to control the polarization state of the illumination speckle, thereby introducing additional polarization information on the surface of the object.

[0012] In the above technical solution, the CCD is a detector with spatial resolution capability, the purpose of which is to obtain the reference light intensity distribution to facilitate subsequent correlation calculations.

[0013] In the above technical solution, the purpose of the +45° linear polarizer is to modulate the reflected light so that the system has the ability to receive additional polarization information on the surface of the object.

[0014] In the above technical solution, the bucket detector is a single-pixel detector without spatial resolution capability, which is used to receive the light beam reflected by the object and record the total intensity of the reflected light beam.

[0015] In the above technical solution, the computer is used to perform a second-order correlation operation on the light intensity distribution from the CCD and the bucket detector to reconstruct a high-resolution image, wherein the second-order correlation operation adopts a public correlation imaging formula:

[0016] GI= r (x r )I t (x t )>- r (x r )> t (x t )>;

[0017] Where GI is the correlation imaging result, I t (x t ) and I r (x r ) are the reference light and object light signals respectively, and < > represents the ensemble average.

[0018] In the above technical solution, the linear polarizer 2a is placed behind the frosted glass to control the polarization direction of the light. This is a new incident light field modulation method proposed by the present invention. The incident light with changed polarization direction interacts with the imaging object, and the reflected light carries the circular polarization information of the object surface. The Stokes vector of the incident light can be described as: S i =[1cos(2β) sin(2β) 0] T , where β is the polarization direction of the incident light. The process of reflected light carrying the polarization information of the object can be expressed by the Stokes-Mueller matrix: S r (x,y)=M(x,y)·S i ​​​(x,y), where S i and S r Representing the polarization state of incident and reflected light, the 4×4 Mueller matrix M shows the ability of different objects to change the polarization of light. M can be described as:

[0019]

[0020] Where R(x,y) is the reflectivity of the corresponding position, and the element m on the main diagonal is 11 ,m 22 and m 33 represent linear polarization, circular polarization and elliptical polarization respectively. Then the reflected light can be described as:

[0021] S r (x,y)=M(x,y)S i (x,y)=R(x,y)[1 m 11 (x,y)cos(2β) m 22 (x,y)sin(2β) 0] T ,

[0022] Therefore, when β≠N·180° and N is any non-zero integer, the system can introduce the circular polarization information of the object.

[0023] After the reflected light passes through the linear polarizer 2b with a polarization direction of +45°, the barrel detector 7 can receive the circular polarization information of the object surface. Then the Stokes vector of the reflected light in the horizontal, vertical and +45° directions can be described as:

[0024]

[0025] The light intensity collected by the bucket detectors 7, 8, and 9 corresponds to the first term of the Stokes vector of the reflected light, so the system can obtain the circular polarization information of the object. The computer 10 performs a second-order correlation operation with the preset speckle to obtain a high-resolution reconstructed image.

[0026] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0027] (1) Compared with the traditional polarization correlation imaging device, the polarization correlation imaging device can adjust the polarization state of the incident light so that the reflected light after interacting with the object has circular polarization information. In addition, the reflected light can be modulated at the receiving end, so that the device has the ability to obtain circular polarization information;

[0028] (2) Since the polarization correlation imaging device can obtain more polarization information on the surface of an object, its anti-interference ability is enhanced.

[0029] (3) It breaks through the limitations of traditional polarization correlation imaging and can extract targets from objects of the same material with similar reflectivity but different roughness. Especially when the background roughness is large, the imaging effect is better.

[0030] (4) The device has a simple structure and is easy to operate; BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic structural diagram of a polarization correlation imaging solution for extracting targets from objects of the same material but different roughnesses provided by an embodiment of the present invention.

[0032] In the figure, 1: signal source; 2a, 2b: linear polarizer; 3a, 3b: beam splitter; 4: CCD; 5: imaging object; 6: polarization beam splitter; 7, 8, 9: bucket detectors; 10: computer. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0034] See attached Figure 1 , this embodiment proposes a polarization correlation imaging scheme for extracting targets from objects of the same material but different roughness, including a signal source 1, linear polarizers 2a, 2b, beam splitters 3a, 3b, CCD 4, imaging object 5, polarization beam splitter 6, bucket detectors 7, 8, 9, and a computer 10.

[0035] The functions of the above parts are described as follows:

[0036] Signal source 1: It consists of a laser and a rotating frosted glass, used to generate a Gaussian signal beam;

[0037] Linear polarizers 2a, 2b: used to adjust the polarization state of incident light and reflected light;

[0038] Beam splitters 3a, 3b: split the incident light field into two beams of equal intensity;

[0039] CCD 4: obtain reference light intensity distribution;

[0040] Imaging object 5: After interacting with the incident light field, it reflects reflected light with the polarization information of the object surface;

[0041] Polarization beam splitter 6: separates the reflected light with polarization information into polarized light in horizontal and vertical directions;

[0042] Bucket detectors 7, 8, 9: receive the light beam reflected by the object and record the total intensity of the reflected light beam;

[0043] Computer 10: Performs a second-order correlation operation on the light intensity distribution from the CCD and the bucket detector to reconstruct a high-resolution image.

[0044] A polarization correlation imaging scheme for extracting targets from objects of the same material with different roughness is designed for the above experimental device. The specific operation steps are as follows:

[0045] (1) The laser emits a Gaussian beam, which generates random speckles through a rotating frosted glass. A linear polarizer 2a is placed behind the frosted glass to control the polarization direction of the light, and a beam splitter 3 is used to split the speckles into a test beam and a reference beam.

[0046] (2) In the reference arm, the light beam is received by the CCD 4 after propagating a certain distance, and in the test arm, the light beam is incident on the imaging object 5 after propagating the same distance.

[0047] (3) The reflected light beam is separated into two beams by the beam splitter 3. One beam passes through the +45° polarizer 2b and is received by the barrel detector 7. The other beam passes through the polarization beam splitter 6 and is collected by the other two barrel detectors 8 and 9.

[0048] (4) The computer correlates the signal collected by the bucket detector with the preset speckle pattern.

Claims

1. A polarization correlation imaging scheme for extracting a target from objects of the same material with different roughness, the device used comprising: Signal source 1, polarizer 2a, 2b, beam splitter 3a, 3b, CCD 4, object 5, polarization beam splitter 6, bucket detector without resolution capability 7, 8, 9, computer 10; The specific process of the polarization correlation imaging scheme for extracting targets from objects of the same material with different roughness is as follows: (1) The laser emits a Gaussian beam, which generates random speckles through a rotating frosted glass. A linear polarizer is placed behind the frosted glass to control the polarization direction of the light, and a beam splitter is used to divide the speckles into a test beam and a reference beam. (2) In the reference arm, the light beam is received by the CCD after propagating a certain distance, and in the test arm, the light beam is incident on the object after propagating the same distance; (3) The light beam reflected by the imaging object is separated into two beams by a beam splitter. One beam is received by a barrel detector after passing through a +45° polarizer, and the other beam is collected by the other two barrel detectors after passing through a polarization beam splitter. (4) The computer correlates the signal collected by the bucket detector with the preset speckle pattern.

2. A polarization correlation imaging scheme for extracting targets from objects of the same material with different roughness, characterized by: The laser emits a Gaussian beam, which generates random speckles through the rotating frosted glass. A linear polarizer is placed behind the frosted glass to control the polarization direction of the light, and a beam splitter is used to divide the speckles into a test beam and a reference beam. In the reference arm, the beam is received by the CCD after propagating a certain distance, and in the test arm, the beam is incident on the object after propagating the same distance. The reflected beam is separated into two beams by the beam splitter. One beam is received by the barrel detector after passing through a +45° polarizer, and the other beam is collected by the other two barrel detectors after passing through a polarization beam splitter. The computer uses the second-order correlation calculation to image the signal collected by the barrel detector and the preset random speckle. The second-order correlation operation adopts the public correlation imaging formula: GI= r (x r )I t (x t )>- r (x r )> t (x t )>;​​​ Where GI is the correlation imaging result, I t (x t ) and I r (x r ) are the reference light and object light signals respectively, and <> represents the ensemble average.

3. The polarization correlation imaging scheme for extracting targets from objects of the same material but different roughnesses according to claim 2, characterized in that: The detection object is a target and a background made of the same material with different roughness, and the background has a greater roughness.

4. The polarization correlation imaging scheme for extracting targets from objects of the same material but different roughnesses according to claim 2, characterized in that: The polarization correlation imaging device adjusts the polarization direction of the incident light at the incident end, thereby introducing the circular polarization information of the object. The Stokes vector of the incident light can be described as: S i =[1 cos(2β) sin(2β) 0] T , where β is the polarization direction of the incident light. The process of reflected light carrying the polarization information of the object can be expressed by the Stokes-Mueller matrix: S r (x,y)=M(x,y)·S i (x,y), where S i and S r Representing the polarization state of incident and reflected light, the 4×4 Mueller matrix M shows the ability of different objects to change the polarization state of light. M can be described as: Where R(x,y) is the reflectivity of the corresponding position, and the element m on the main diagonal is 11 ,m 22 and m 33 represent linear polarization, circular polarization and elliptical polarization respectively; then the reflected light can be described as: S r (x,y)=M(x,y)S i (x,y)=R(x,y)[1 m 11 (x,y)cos(2β) m 22 (x,y)sin(2β) 0] T , Therefore, when β≠N·180° and N is an arbitrary integer, the system can introduce the circular polarization information of the object.

5. The polarization correlation imaging scheme for extracting targets from objects of the same material but different roughnesses according to claim 2, characterized in that: The polarization-correlated imaging device described above is to add a +45° polarizer at the receiving end, so the Stokes vector of the reflected light in the horizontal, vertical and +45° directions can be described as: The light intensity collected by the bucket detector corresponds to the first term of the Stokes vector of the reflected light, so the system can obtain the circular polarization information of the object and use it for correlation imaging.

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