A polarization tomography apparatus and imaging method based on a single-pixel detector

Abstract

This invention belongs to the field of polarization imaging technology, specifically relating to a polarization tomography device and method based on a single-pixel detector. A polarization tomography device based on a single-pixel detector includes, from front to back, a light source module, a first modulation module, a second modulation module, an acquisition module, and an image processing module. The object to be measured is placed inside the first modulation module. The light source module emits a one-dimensional parallel beam. The one-dimensional parallel beam enters the first modulation module, is modulated by the first modulation module into beams carrying different polarization states representing information of the object to be measured, and then exits, before entering the second modulation module. The acquisition module acquires the beam signal emitted after modulation and encoding by the second modulation module, converts the beam signal into an electrical signal, and transmits it to the image processing module to reconstruct the image. The imaging device of this invention has a simple structure, low requirements for ambient light intensity, and high imaging quality.

Description

Technical Field

[0001] This invention belongs to the field of polarization imaging technology, specifically relating to a polarization tomography imaging device and imaging method based on a single-pixel detector. Background Technology

[0002] With the development of imaging detection technology, the increasingly better imaging effects have further improved the research and development efficiency of scientific researchers.

[0003] Existing imaging devices mostly detect targets based on the difference in intensity between the reflected or radiated light waves between the target and the background, and reconstruct images using parameters such as amplitude or phase. However, such imaging devices have poor resolution in low-light environments, and useful information is easily mixed with background noise, making it difficult to obtain high-quality reconstructed images. Furthermore, most of these imaging devices acquire images through mechanical scanning, which inevitably introduces more noise into the acquisition process due to the vibration of the mechanical device, further reducing the quality of the reconstructed image.

[0004] Many scientific research projects do not allow strong light to be present in order to protect the site, which makes it urgent to have an imaging device with high imaging quality under low light conditions. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a polarization tomography imaging device based on a single-pixel detector, which has low requirements for ambient light intensity and high imaging quality.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A polarization tomography device based on a single-pixel detector includes, from front to back, a light source module, a first modulation module, a second modulation module, an acquisition module, and an image processing module. The object under test is placed inside the first modulation module. The light source module emits a one-dimensional parallel beam. The one-dimensional parallel beam enters the first modulation module, is modulated by the first modulation module into beams of different polarization states carrying characteristic information of the object under test, and then exits, before entering the second modulation module. The acquisition module acquires the beam signal emitted after modulation and encoding by the second modulation module, converts the beam signal into an electrical signal, and transmits it to the image processing module to reconstruct an image.

[0008] Preferably, the light source module includes a light source generator and a collimating lens. The light source generator is disposed in front of the collimating lens, and the center of the collimating lens is coaxially arranged with the center of the light source emitted by the light source generator.

[0009] Preferably, the first modulation module includes a first polarization section, which includes a first polarizer and a first waveplate. The first polarizer is disposed behind the collimating lens, and the first waveplate is disposed behind the first polarizer and in front of the object under test. The center of the first polarizer, the center of the first waveplate, and the geometric center of the object under test are all coaxially arranged with the center of the collimating lens.

[0010] Preferably, the first modulation module further includes a second polarization section, which includes a second polarizer and a second waveplate. The second polarizer is disposed behind the object under test, and the second waveplate is disposed behind the second polarizer. The center of the second polarizer and the center of the second waveplate are both coaxially arranged with the center of the collimating lens.

[0011] Preferably, both the first polarizer and the second polarizer are linear polarizers, and both the first waveplate and the second waveplate are quarter-wave plates.

[0012] Preferably, the second modulation module includes, from front to back, a cylindrical mirror and a modulation disk, with the cylindrical mirror positioned behind the second waveplate; the modulation disk includes a non-modulation center area near the center and a modulation area away from the center; the non-modulation center area includes a fixing hole at the center and several positioning holes surrounding the fixing hole, the fixing hole being fitted and fixed to the motor shaft, and the modulation disk being driven to rotate by the motor shaft; the center of the second waveplate, the cylindrical mirror, and the center of the modulation area are coaxially arranged.

[0013] Preferably, the modulation area is an annular shape with an inner diameter of r1 and an outer diameter of r2. The modulation area is divided into several concentric sub-rings according to the same ring width Δr from the inner radial direction to the outer diameter. The sub-rings are divided by the same central angle Δθ to form several fan-shaped modulation grids. A portion of the modulation grid is made of a light-transmitting material or is set to be hollow.

[0014] Preferably, the acquisition module includes a reverse beam expander and a single-pixel detector arranged sequentially from front to back. The reverse beam expander is located behind the modulation disk, and the center of the reverse beam expander is coaxially arranged with the center of the modulation area and the center of the photosensitive surface area of ​​the single-pixel detector.

[0015] Preferably, the image processing module includes a lock-in amplifier, a data acquisition card, and a computer connected in series, and the single-pixel detector is electrically connected to the lock-in amplifier.

[0016] The present invention also provides an imaging method for a polarization tomography device based on a single-pixel detector, employing the polarization tomography device based on a single-pixel detector as described above, comprising the following steps:

[0017] S1, the object to be measured is placed between the first wave plate and the second polarizer, the light source generator is turned on, and the light source signal emitted by the light source generator forms a one-dimensional parallel beam after passing through the collimating lens.

[0018] S2, the computer sends a drive signal to drive the first polarizer, the first waveplate, the second polarizer, and the second waveplate to rotate respectively. The first polarizer and the first waveplate cooperate with each other to modulate the incident one-dimensional parallel beam into a first-order modulated beam containing different polarization states, which then illuminates the object to be measured.

[0019] S3, after the first-order modulated beam is reflected and / or transmitted through the surface of the object under test to form a second-order modulated beam carrying characterization information, it is then modulated by a second polarizer and a second waveplate that work together to form a third-order modulated beam.

[0020] S4, the third-order modulated beam becomes a compressed beam after passing through the cylindrical mirror, which illuminates the modulation area on the front of the modulation disk. The computer drives the signal modulation disk to rotate to modulate and encode the compressed beam.

[0021] S5, the emitted light from the modulation disk, i.e. the modulated and coded beam, is converged by the reverse beam expander to the photosensitive area of ​​the single-pixel detector. The photosensitive area of ​​the single-pixel detector collects the beam signal for at least one modulation cycle, converts the beam signal into an analog electrical signal, and then transmits it to the lock-in amplifier.

[0022] S6, after the analog electrical signal is suppressed by the lock-in amplifier and the signal is amplified, it is sent to the data acquisition card to be converted into a digital signal. The digital signal is transmitted to the computer. The computer calculates and generates an encoding matrix based on the digital signal within one modulation cycle. Then, it generates a polarization state image of the object under test based on the various matrix elements in the encoding matrix. Finally, it reconstructs the image of the object under test based on the various polarization state images.

[0023] The beneficial effects of this invention are as follows:

[0024] (1) In this invention, a polarized beam is introduced into the traditional tomographic imaging technology. Multiple polarized beams are obtained through the first modulation module. The polarized beams are then used to form a modulated beam carrying the characterization information of the object under test after reflection or transmission on the object under test. The modulated beam is then modulated and encoded by the second modulation module and enters the acquisition module. The polarized beam signal is converted into an electrical signal. The electrical signal is then processed by the image processing module and restored into images of various polarization states. The reconstructed image can restore and reflect the detailed features of the surface morphology, texture, and tissue structure of the object under test, thereby improving the quality of the reconstructed image.

[0025] (2) In the first modulation module of the present invention, two sets of polarization sections are set before and after the object to be tested, so that the light beam finally emitted from the first modulation module contains image information under 16 polarization states carrying the characterization information of the object to be tested. That is, the process of image acquisition of the object to be tested is a comprehensive characterization information acquisition process, which greatly reduces the information omission in the image acquisition process and provides sufficient characterization information for subsequent high-quality image reconstruction.

[0026] (3) The present invention further modulates and encodes the emitted beam of the first modulation module by rotating the modulation disk; under the condition that the ambient light intensity is constant, the modulation effect of the modulation disk on the incident compressed beam can be increased by increasing the number of modulation grids on the modulation disk and making full use of the modulation area space of the modulation disk, thereby improving the accuracy of the modulation encoding process. This is also reflected in the increase of the order of the encoding matrix formed by the light intensity of the compressed beam transmitted through the modulation disk received by the detection photosensitive surface area of ​​the subsequent single pixel detector within one modulation cycle, that is, to present the characterization information of the object under test as comprehensively and completely as possible, so as to restore the image under different polarization states as much as possible and reconstruct a high-quality image.

[0027] (4) The light source generator uses a white light source, so that the object under test will not be damaged during the process of image acquisition of the object under test by the imaging device of the present invention.

[0028] (5) The collimating lens collimates the light beam emitted by the light source generator, reducing the energy loss of the light beam in a low-light environment. This enables the imaging device of the present invention to successfully complete the acquisition of the characterization information of the object under test and the subsequent modulation of the light beam in a low-light environment, and reconstruct a high-quality image.

[0029] (6) The imaging device of the present invention does not acquire images through mechanical scanning, but generates polarized light and modulates and encodes the polarized beam carrying the characterization information of the object under test to restore images under different polarization states, and finally reconstructs the image of the object under test. Therefore, it avoids the introduction of a large amount of noise into the acquisition of images due to the jitter of the mechanical device, and improves the quality of the final reconstructed image.

[0030] (7) The polarization tomography device based on a single-pixel detector of the present invention has low cost, simple operation method, low requirements for ambient light intensity, and high versatility. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a polarization tomography device based on a single-pixel detector according to the present invention;

[0032] Figure 2 for Figure 1 A first schematic diagram of the modulation disk in the image;

[0033] Figure 3 for Figure 1 A second schematic diagram of the modulation disk in the diagram;

[0034] Figure 4 This is a flowchart of an imaging method for a polarization tomography device based on a single-pixel detector.

[0035] The actual correspondence between the reference numerals and component names in this invention is as follows:

[0036] 1. Light source module; 11. Light source generator; 12. Collimating lens;

[0037] 2. Acquisition module; 21. Reverse beam expander; 22. Single pixel detector;

[0038] 3. First modulation module; 31. First polarization section; 311. First polarizer; 312. First waveplate;

[0039] 32. Second polarizing section; 321. Second polarizer; 322. Second waveplate;

[0040] 4. Second modulation module; 42. Cylindrical mirror; 43. Modulation disk; 431. Modulation area; 431a. Modulation grid; 432. Non-modulation center area; 432a. Fixing hole; 432b. Positioning hole;

[0041] 5. Image processing module; 51. Lock-in amplifier; 52. Data acquisition card; 53. Computer;

[0042] 6. The object to be tested. Detailed Implementation

[0043] To make the technical solution of the present invention clearer and more explicit, the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Solutions derived by those skilled in the art through equivalent substitution and conventional reasoning of the technical features of the present invention without creative effort all fall within the protection scope of the present invention.

[0044] Example 1

[0045] like Figure 1The polarization tomography device based on a single-pixel detector shown includes, from left to right, a light source module 1, a first modulation module 3, a second modulation module 4, an acquisition module 2, and an image processing module 5; the object under test 6 is placed in the first modulation module 3. The light source module 1 emits a one-dimensional parallel beam, which is modulated by the first modulation module 3 to become a one-dimensional beam containing different polarization states, and then illuminates the object under test 6. The emitted beam from the object under test 6 carries the image information of the object under test 6 into the second modulation module 4, and after being modulated by the second modulation module 4, it enters the acquisition module 2; the acquisition module 2 converges and acquires the polarization beam carrying the image information of the object under test 6, and then inputs the image signal into the image processing module 5. The image processing module 5 performs noise reduction and amplification on the image signal and then reconstructs the image.

[0046] The light source module 1 includes a light source generator 11 and a collimating lens 12. The light source generator 11 is positioned in front of the collimating lens 12, and the center of the light source emitted by the light source generator 11 is coaxial with the center of the lens of the collimating lens 12. The light source generator 11 generates a light source, and the light from the light source enters the collimating lens 12 as an incident light ray from the front side. After being refracted into a one-dimensional parallel beam by the collimating lens 12, it exits from the back side of the collimating lens 12.

[0047] In this embodiment, the light source generator 11 is positioned five centimeters away from the collimating lens 12.

[0048] Preferably, the light source generator 11 emits a white light source.

[0049] The first modulation module 3 includes a first polarizing section 31 disposed in front of the object under test 6 and a second polarizing section 32 disposed behind the object under test 6. The first polarizing section 31 includes a first polarizer 311 and a first waveplate 312, and the second polarizing section 32 includes a second polarizer 321 and a second waveplate 322. The centers of the first polarizer 311, the first waveplate 312, the second polarizer 321, and the second waveplate 322, as well as the geometric center of the object under test 6, are all on the beam emitted from the collimating lens 12. The one-dimensional parallel beam emitted from the collimating lens 12 passes through the first polarizer 311 and the first waveplate 312 in sequence, and is modulated into a first-order modulated beam containing different polarization states before illuminating the object under test 6. Affected by the polarization sensitivity of the object under test 6, the polarization state of the first-order modulated beam illuminating the object under test 6 changes, becoming a second-order modulated beam before leaving the object under test 6. It then passes through the second polarizer 321 and the second waveplate 322 in sequence, and is modulated into a third-order modulated beam before entering the second modulation module. The second-order modulated beam carries characterization information of the object under test 6, including surface texture characteristics, size parameters, and light transmission performance of the object under test 6.

[0050] Preferably, the first polarizer 311 and the second polarizer 321 are both linear polarizers, and the first waveplate 312 and the second waveplate 322 are both quarter-glass plates. In this case, in the first polarizing section 31, the first waveplate 312 has two orthogonal axes, one is the fast axis and the other is the slow axis. The light beam emitted from the collimating lens 12 becomes linearly polarized light after passing through the first polarizer 311. When the linearly polarized light is incident perpendicularly on the first waveplate 312 and the amplitude vector of the linearly polarized light is incident at 45° with the fast axis, the linearly polarized light is initially decomposed into two equal components along the fast axis and along the slow axis. The component emitted along the fast axis is one-quarter of the wavelength ahead of the component emitted along the slow axis. Thus, the light emitted from the first waveplate 312 is circularly polarized light. When the linearly polarized light is incident perpendicularly on the first waveplate 312 and the amplitude vector of the linearly polarized light is incident at 0° and 90° with the fast axis, the light emitted from the first waveplate 312 is linearly polarized light. When the amplitude vector of the linearly polarized light is at an angle to the fast axis that is neither circularly polarized nor linearly polarized, it is elliptically polarized light. Therefore, by simply rotating and adjusting the first polarizer 311 and the first waveplate 312, the one-dimensional beam illuminating the object under test 6 can be made to contain different polarization states through the first polarization section 31, that is, the one-dimensional parallel beam emitted from the collimating lens 12 can be modulated into a first-order modulated beam. Similarly, in the second polarization section 32, the second-order modulated beam is modulated into a third-order modulated beam in the same way, which will not be described in detail here. In this invention, the third-order modulated beam contains 16 polarization states, corresponding to the fourth-order Mueller matrix M. The values ​​of each matrix element in the fourth-order Mueller matrix M represent the image of the object under test 6 under 16 different polarization states. Different Mueller matrices M uniquely correspond to the characterization information of one object under test 6.

[0051] The process by which the first-order modulated beam, after illuminating the object under test 6, is transformed into the second-order modulated beam can be expressed by formula S. o =M×S l It indicates that S o S is the vector representation of the second-order modulated beam. l Let M be the Stokes vector of the first-order modulated beam, and M denote the Mueller matrix.

[0052] In this invention, The elements of the Mueller matrix M represent images under various polarization states, totaling 16 polarization states; the vector representation S of the second-order modulated beam... o Each matrix element in the matrix represents an image of the object under test 6 under various polarization states.

[0053] The first modulation module 3 may also include only a first polarization section 31 disposed in front of the object under test 6. That is, the one-dimensional parallel beam emitted from the collimating lens 12 sequentially passes through the first polarizer 311 and the first waveplate 312, and is modulated into a first-order modulated beam containing different polarization states. This first-order modulated beam then illuminates the object under test 6. Influenced by the polarization sensitivity of the object under test 6, the polarization state of the first-order modulated beam illuminating the object under test 6 changes, becoming a second-order modulated beam before leaving the object under test 6 and directly entering the second modulation module. At this point, the second-order modulated beam contains fewer than 16 polarization states, meaning the beam carries less characterization information about the object under test 6. Consequently, the final imaging quality of the polarization tomography device is lower than that of a polarization tomography device containing both the first polarization section 31 and the second polarization section 32, but still higher than that of existing imaging devices.

[0054] The second modulation module 4 includes, from front to back, a cylindrical mirror 42 and a modulation disk 43. The center of the cylindrical mirror 42 and the center of the modulation disk 43 are both on the beam emitted from the first modulation module 3. The second modulation module 4 encodes and modulates the third-level modulation beam carrying the characterization information of the object under test 6, facilitating subsequent image processing and reconstruction. After the third-level modulation beam enters the cylindrical mirror 42, the cylindrical mirror 42 compresses the incident light into a compressed beam and projects it onto one side of the center of the front surface of the modulation disk 43. The compressed beam projected onto the front surface of the modulation disk 43 is linear, and its extension passes through the center of the modulation disk 43; the compressed beam passing through the modulation disk 43 enters the acquisition module 2.

[0055] like Figure 2 As shown, the modulation disk 43 is divided into two parts: a non-modulation center area 432 near the center and a modulation area 431 away from the center. The compressed beam is projected onto the modulation area 431 on the front side of the modulation disk 43. The non-modulation center area 432 includes a fixing hole 432a at the center and several positioning holes 432b surrounding the fixing hole 432a. The fixing hole 432a of the modulation disk 43 is fitted and fixed on the motor shaft, so that the modulation disk 43 can rotate with the rotation of the motor shaft. The positioning holes 432b are used for position marking and positioning during the rotation of the modulation disk 43. For example, one positioning hole 432b is marked as the "rotation starting point", and another positioning hole 432b located 180° counterclockwise from the "rotation starting point" is marked as the "rotation midpoint". Then, the number of rotations of the modulation disk 43 can be accurately controlled during the rotation of the modulation disk 43.

[0056] The center of the modulation disk 43 is also the center area of ​​the modulation zone 431.

[0057] The modulation disk 43 has a radius of r. An inner diameter r1 and an outer diameter r2, both at a distance from the center, are pre-defined on the modulation disk 43. The annular portion between the inner and outer diameters r1 and r2 is the modulation area 431. The modulation area 431 is then divided into several concentric sub-rings of equal width Δr from the inside out. These concentric sub-rings are further divided into several sectors with the same central angle Δθ. These sectors are the modulation grids 431a. Some of the modulation grids 431a are set to be hollow or made of a translucent material. The modulation grids 431a within the modulation area 431 are set according to the technician's requirements for image quality. This setting of the modulation grids 431a ensures that the modulation disk 43 can stably modulate and encode the incident compressed beam. Where r1 < r2 ≤ r, Δr < r2, and Δθ < 180°.

[0058] The modulation scheme matrix C is obtained based on the lowest imaging quality in computer 53. Then, the modulation grids 431a are set according to the elements in the modulation scheme matrix C, such as setting the number of modulation grids 431a and which modulation grids 431a are hollow or transparent materials. The modulation scheme matrix C is described in detail later.

[0059] The number of modulation grids 431a in modulation region 431 corresponds to the matrix elements of modulation matrix C. A sub-ring within modulation region 431 represents a row in modulation matrix C, and the sub-ring covered by the same central angle within modulation region 431 represents a column in modulation matrix C. In modulation matrix C, if the modulation grid 431a corresponding to each matrix element is a transparent modulation grid 431a, the current matrix element is recorded as 1; otherwise, it is recorded as 0. As the number of modulation grids 431a increases, rotating modulation disk 43 causes the compressed beam to sweep across more modulation grids 431a within one rotation cycle. The compressed beam exits from the transparent modulation grids 431a and enters acquisition module 2, meaning the acquisition module can acquire more transparent information from the modulation grids 431a. Therefore, the number of matrix elements in modulation matrix C also increases synchronously. The second modulation module 4 also encodes and modulates the third-level modulation beam into more detailed and multi-dimensional representation information, resulting in higher quality reconstructed images. Figure 3 As shown.

[0060] However, due to the limited size of the linearly compressed beam, if the modulation area 431 is too large, the modulation grids 431a that the linearly compressed beam cannot sweep across during the rotation of the modulation disk 43 will become invalid matrix elements in the encoding matrix formed in the computer 53 as the beam signal received in the acquisition module 2. If the modulation area 431 is too small, a section of the compressed beam will always remain outside the modulation area 431 during the rotation of the modulation disk 43, causing a portion of the representation of the object under test 16 to be unacquired by the acquisition module 2, making it impossible to reconstruct the image and thus impossible to improve the quality of the reconstructed image. Therefore, the size of the modulation disk 43 is fixed, and the area of ​​the modulation area 43 is also fixed. If the number of modulation grids 431a is too large, although it will encode and modulate the third-level modulation beam into more detailed and multi-dimensional representation information, if the area of ​​the modulation grids 431a is too small, the beam emitted to the acquisition module 2 when the translucent modulation grids 431a are swept by the compressed beam may be too dim and blurry, resulting in errors in some representation information of the acquisition module 2 during the acquisition process. Therefore, after multiple experiments, the modulation area 431 and modulation grid 431a on the modulation disk 43 can be set to increase the number of modulation grids 431a as much as possible while ensuring that the reconstructed image is still usable at the lowest quality. This will improve the utilization rate of the modulation disk 43, achieve precise control of beam modulation, and further improve the quality of the reconstructed image.

[0061] One rotation of the modulation disk 43 is recorded as one modulation cycle, and the modulation disk 43 must rotate at least one revolution. As the number of modulation cycles increases, the intensity of the beam information acquired by the acquisition module 2 is continuously superimposed, which improves the accuracy of information acquisition by the acquisition module 2 and ensures that the subsequent image processing module 5 can reconstruct a high-quality image.

[0062] The acquisition module 2 includes a reverse beam expander 21 and a single-pixel detector 22 arranged sequentially from front to back. A compressed beam passes through the modulation disk 43 and enters the reverse beam expander 21. The reverse beam expander 21 reduces the incident beam size and projects it onto the photosensitive surface area of ​​the single-pixel detector 22. The presence of the reverse beam expander 21 ensures that the compressed beam is completely converged within the photosensitive surface area of ​​the single-pixel detector 22, preventing the loss of characterization information due to beam diffusion. The single-pixel detector 22 converts the beam signal received by the photosensitive surface area through the modulation disk 43 into an analog electrical signal and transmits it to the image processing module 5.

[0063] The elements in the beam signal S received by the single-pixel detector 2 on the photosensitive surface area are also the light intensity values ​​of the compressed beam emitted through each modulation grid 431a to the photosensitive surface area detected by the single-pixel detector 2. The beam signal S contains information of the modulation mode matrix C, so the beam signal S can also be represented by S = D × C, where D represents the vector representation of the incident compressed beam on the front of the modulation disk 43, and each matrix element in the modulation mode matrix C represents the setting mode of the modulation grid on the modulation disk 43. Each matrix element in the matrix corresponds to the light intensity value emitted by the compressed beam through each modulation grid 431a. Transparent modulation grids 431a are marked as 1, and otherwise marked as 0.

[0064] The image processing module 5 includes a lock-in amplifier 51, a data acquisition card 52, and a computer 53, which are connected in sequence. Analog electrical signals are transmitted to the lock-in amplifier 51, where noise is suppressed and the useful signal is amplified. The signal is then converted into a digital signal by the data acquisition card 52 and transmitted to the computer 53. The computer 53 processes the digital signal within one modulation cycle to generate an encoding matrix. Different matrix elements in the encoding matrix correspond to different polarization state images. The computer 53 then reconstructs the image based on these different polarization state images.

[0065] Therefore, we can pre-set the vector D of the incident compressed beam according to the low-light environment required for image acquisition, and then let the computer 53 set the encoding matrix according to the minimum imaging quality. The modulation mode matrix C is derived from the encoding matrix. Based on the modulation mode matrix C, we can determine whether the current modulation grid 431a setting on the modulation disk 43 meets the minimum imaging quality. If it does not meet the minimum imaging quality, we can increase the number of modulation grids 431a according to the currently calculated modulation mode matrix C to increase the order of the modulation mode matrix C, thereby enhancing the modulation effect of the modulation disk 43 on the incident compressed beam, or appropriately supplementing the light intensity at the image acquisition site.

[0066] The image processing module 5 includes a lock-in amplifier 51, a data acquisition card 52, and a computer 53, which are connected in sequence. The analog electrical signal is transmitted to the lock-in amplifier 51. After the lock-in amplifier 51 suppresses noise and amplifies the useful signal, it is converted into a digital signal by the data acquisition card 52 and then transmitted to the computer 53. The computer 53 converts the received digital signal into images of various polarization states of the object under test 6, and then reconstructs the image based on the images of various polarization states.

[0067] The present invention provides a polarization tomography imaging device based on a single-pixel detector:

[0068] 1. In traditional tomographic imaging technology, polarized light beams are introduced. Multiple polarized lights are obtained through the first modulation module. The polarized light is reflected or transmitted on the object under test to form a modulated light beam carrying the characterization information of the object under test. The modulated light beam is then modulated and encoded by the second modulation module and enters the acquisition module. The polarized light beam signal is converted into an electrical signal. The electrical signal is then processed by the image processing module to restore the image to various polarized images. The reconstructed image can restore and reflect the detailed features of the surface morphology, texture, and tissue structure of the object under test, thus improving the quality of the reconstructed image.

[0069] 2. Two sets of polarization sections are set in front of and behind the object under test in the first modulation module, so that the beam emitted from the first modulation module contains images in 16 polarization states carrying the characterization information of the object under test. That is, the process of image acquisition of the object under test is a comprehensive characterization information acquisition process, which greatly reduces the information loss in the image acquisition process and provides sufficient characterization information for subsequent high-quality image reconstruction.

[0070] 3. The emitted beam from the first modulation module is further modulated and encoded by a rotating modulation disk. Under the condition of constant ambient light intensity, the modulation effect of the modulation disk on the incident compressed beam can be increased by increasing the number of modulation grids on the modulation disk and making full use of the modulation area space of the modulation disk. This improves the accuracy of the modulation encoding process and is also reflected in the increased order of the encoding matrix formed by the light intensity of the compressed beam transmitted through the modulation disk received by the photosensitive surface area of ​​the subsequent single-pixel detector within one modulation cycle. That is, the characterization information of the object under test is presented as comprehensively and completely as possible to restore the image under different polarization states and reconstruct a high-quality image.

[0071] 4. The light source generator uses a white light source, so that the object under test will not be damaged during the image acquisition process of the imaging device of the present invention.

[0072] 5. The collimating lens collimates the light beam emitted by the light source generator, reducing the energy loss of the light beam in low-light environments. This allows the imaging device of the present invention to successfully complete the acquisition of the characterization information of the object under test and the subsequent modulation of the light beam in low-light environments, thereby reconstructing a high-quality image.

[0073] 6. The imaging device of the present invention does not acquire images through mechanical scanning, but generates polarized light and modulates and encodes the polarized beam carrying the characterization information of the object under test to restore images under different polarization states, and finally reconstructs the image of the object under test. Therefore, it avoids the introduction of a large amount of noise into the acquisition of images due to the jitter of the mechanical device, and improves the quality of the final reconstructed image.

[0074] 7. The polarization tomography device based on a single-pixel detector of the present invention has low cost, simple operation method, low requirements for ambient light intensity, and high versatility.

[0075] Example 2

[0076] The present invention also provides an imaging method for a polarization tomography device based on a single-pixel detector, such as... Figure 4 This includes the following steps:

[0077] S1, the object to be tested 6 is placed between the first wave plate 312 and the second polarizer 321, and the light source generator 11 is turned on. The light source signal emitted by the light source generator 11 forms a one-dimensional parallel beam after passing through the collimating lens 12.

[0078] S2, computer 53 sends a drive signal to drive the first polarizer 311, the first waveplate 312, the second polarizer 321, and the second waveplate 322 to rotate respectively. The first polarizer 311 and the first waveplate 312 cooperate with each other to modulate the incident one-dimensional parallel beam into a first-order modulated beam containing different polarization states, and then illuminate the object to be tested 6.

[0079] S3, after the first-level modulated beam is reflected and / or transmitted through the surface of the object under test 6 to form a second-level modulated beam carrying characterization information, it is then modulated by the second polarizer 321 and the second waveplate 322 in cooperation to form a third-level modulated beam.

[0080] If the object under test 6 is opaque, the first-level modulated beam is reflected by the surface of the object under test 6 to form a second-level modulated beam carrying characterization information; if the object under test 6 is transparent, the first-level modulated beam is transmitted and reflected by the object under test 6 to form a second-level modulated beam carrying characterization information.

[0081] S4, the third-order modulated beam forms a compressed beam after passing through the cylindrical mirror 42, which illuminates the modulation area 431 on the front of the modulation disk 43. The computer 53 drives the signal modulation disk 43 to rotate to modulate and encode the compressed beam.

[0082] S5, the emitted light from the modulation disk 43, i.e. the modulated and encoded beam, is converged by the reverse beam expander 21 to the photosensitive surface area of ​​the single pixel detector 22. The photosensitive surface area of ​​the single pixel detector 22 collects the beam signal for at least one modulation cycle, converts the beam signal into an analog electrical signal, and then transmits it to the lock-in amplifier 51.

[0083] S6, after the analog electrical signal is suppressed by the lock-in amplifier 51 and the signal is amplified, it is sent to the data acquisition card 52 and converted into a digital signal. The digital signal is transmitted to the computer 53. The computer 53 calculates and generates an encoding matrix based on the digital signal within a modulation cycle, and then generates a polarization state image of the object under test 6 based on the various matrix elements in the encoding matrix. Finally, it reconstructs the image of the object under test 6 based on the various polarization state images.

[0084] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the invention. All techniques, shapes, and structural elements not described in detail herein are well-known technologies.

Claims

1. A polarization tomography imaging device based on a single-pixel detector, characterized in that: The system includes, from front to back, a light source module (1), a first modulation module (3), a second modulation module (4), an acquisition module (2), and an image processing module (5). The object to be tested (6) is placed inside the first modulation module (3). The light source module (1) emits a one-dimensional parallel beam. The one-dimensional parallel beam enters the first modulation module (3), is modulated by the first modulation module (3) into beams of different polarization states carrying the characterization information of the object to be tested (6), and then exits and enters the second modulation module (4). The acquisition module (2) acquires the beam signal emitted after modulation and encoding by the second modulation module (4), and converts the beam signal into an electrical signal and transmits it to the image processing module (5) to reconstruct the image. The light source module (1) includes a light source generator (11) and a collimating lens (12). The first modulation module (3) further includes a second polarization section (32), which includes a second polarizer (321) and a second waveplate (322). The first modulation module (3) includes a first polarization section (31), which includes a first polarizer (311) and a first waveplate (312). The first polarizer (311) is disposed behind the collimating lens (12), and the first waveplate (312) is disposed behind the first polarizer (311) and in front of the object to be tested (6). The center of the first polarizer (311), the center of the first waveplate (312), and the geometric center of the object to be tested (6) are all coaxially disposed with the center of the mirror surface of the collimating lens (12). The second modulation module (4) includes, from front to back, a cylindrical mirror (42) and a modulation disk (43). The cylindrical mirror (42) is located behind the second waveplate (322). The modulation disk (43) includes a non-modulation center area (432) near the center and a modulation area (431) away from the center. The non-modulation center area (432) includes a fixing hole (432a) at the center and several positioning holes (432b) surrounding the fixing hole (432a). The fixing hole (432a) is fitted and fixed on the motor shaft. The modulation disk (43) is driven by the motor shaft to rotate. The center of the second waveplate (322), the cylindrical mirror (42), and the center of the modulation area (431) are coaxially arranged. The modulation area (431) is an annular shape with an inner diameter of r1 and an outer diameter of r2. The modulation area (431) is divided into several concentric sub-rings according to the same ring width Δr from the inner radial direction and the outer diameter. The sub-rings are divided by the same central angle Δθ to form several fan-shaped modulation grids (431a). A part of the modulation grid (431a) is made of light-transmitting material or is set to be hollow.

2. The polarimetric tomography apparatus of claim 1, wherein: The light source generator (11) is positioned in front of the collimating lens (12), and the center of the mirror surface of the collimating lens (12) is coaxially arranged with the center of the light source emitted by the light source generator (11).

3. The polarimetric tomography apparatus of claim 2, wherein: The second polarizer (321) is positioned behind the object to be tested (6), and the second waveplate (322) is positioned behind the second polarizer (321); the center of the second polarizer (321) and the center of the second waveplate (322) are both coaxially positioned with the center of the collimating lens (12).

4. The polarimetric tomography apparatus of claim 3, wherein: The first polarizer (311) and the second polarizer (321) are both linear polarizers, and the first waveplate (312) and the second waveplate (322) are both quarter-wave plates.

5. The polarimetric tomography apparatus of claim 4, wherein: The acquisition module (2) includes a reverse beam expander (21) and a single-pixel detector (22) arranged sequentially from front to back. The reverse beam expander (21) is located behind the modulation disk (43), and the center of the reverse beam expander (21) is coaxially arranged with the center of the modulation area (431) and the center of the photosensitive surface area of ​​the single-pixel detector (22).

6. The polarimetric tomography apparatus of claim 5, wherein: The image processing module (5) includes a lock-in amplifier (51), a data acquisition card (52), and a computer (53) connected in series, and the single-pixel detector (22) is electrically connected to the lock-in amplifier (51).

7. An imaging method for a polarization tomography device based on a single-pixel detector, employing the polarization tomography device based on a single-pixel detector as described in claim 6, characterized in that, Includes the following steps: S1, the object to be tested (6) is placed between the first wave plate (312) and the second polarizer (321), and the light source generator (11) is turned on. The light source signal emitted by the light source generator (11) forms a one-dimensional parallel beam after passing through the collimating lens (12). S2, the computer (53) sends a drive signal to drive the first polarizer (311), the first waveplate (312), the second polarizer (321), and the second waveplate (322) to rotate respectively. The first polarizer (311) and the first waveplate (312) cooperate with each other to modulate the incident one-dimensional parallel beam into a first-order modulated beam containing different polarization states, and then irradiate the object to be tested (6). S3, after the first-order modulated beam is reflected and / or transmitted through the surface of the object under test (6) to form a second-order modulated beam carrying characterization information, it is modulated by the second polarizer (321) and the second waveplate (322) that cooperate with each other to form a third-order modulated beam; S4, the third-order modulated beam passes through the cylindrical mirror (42) to form a compressed beam, which illuminates the modulation area (431) on the front of the modulation disk (43). The computer (53) drives the signal modulation disk (43) to rotate to modulate and encode the compressed beam. S5, the emitted light from the modulation disk (43), i.e. the modulated and encoded beam, is converged by the reverse beam expander (21) to the photosensitive area of ​​the single pixel detector (22). The photosensitive area of ​​the single pixel detector (22) collects the beam signal for at least one modulation cycle, and after converting the beam signal into an analog electrical signal, it is transmitted to the lock-in amplifier (51). S6, after the analog electrical signal is suppressed by the lock-in amplifier (51) and the signal is amplified, it is sent to the data acquisition card (52) and converted into a digital signal. The digital signal is transmitted to the computer (53). The computer (53) calculates and generates an encoding matrix based on the digital signal within a modulation cycle, and then generates a polarization state image of the object under test (6) based on various matrix elements in the encoding matrix. Finally, the object under test (6) is reconstructed based on various polarization state images.

Images