A method and device for recovering quantum orbital angular momentum array beam scattering medium imaging based on median filtering algorithm

Abstract

A method and device for recovering the imaging of a scattering medium using a quantum orbital angular momentum array beam based on a median filter algorithm belongs to the field of laser radar technology. The present invention addresses the problem of reduced signal-to-noise ratio in target imaging under foggy conditions. The method of the present invention includes the following steps: S1. An M×N array of vortex beams modulated and output by a spatial light modulator is projected onto a target in a foggy environment, generating an echo signal; a diffraction grating is obtained by adjusting the grating constant, the amplitude at each diffraction order, the initial phase, and the topological charge, and loaded into the spatial light modulator, which outputs an array of vortex beams with different topological charges at different positions; S2. The echo signal is received and an intensity image is generated; S3. The intensity image is filtered using a median filter algorithm to generate a target image. The device for implementing the above method includes a laser, a polarization controller, a first collimator, a polarizer, a spatial light modulator, a second collimator, a fog particle screen, a receiving optical system, a CCD camera, and a computer.

Description

Technical Field

[0001] The present invention relates to a solution for further improving imaging recovery in scattering media based on the combination of a median filtering algorithm and a vortex beam array controlled emission method, belonging to the technical field of laser radar. Background Art

[0002] Vortex beam array imaging is a new type of imaging system. Because vortex beams carry orbital angular momentum, the information dimension they carry is increased compared to traditional Gaussian beams, making them more resistant to influences in complex environments. Compared to single beams, array-shaped beams can obtain information at multiple locations of the target in a single detection during imaging, which can greatly improve the imaging rate. When transmitting in a foggy environment, the random scattering of fog particles causes the light field to scatter and diffuse in space, generating noise, which reduces the signal-to-noise ratio when imaging the target. This requires the use of certain noise filtering algorithms and the adjustment of the topological charge of sub-beams at different positions to reduce the crosstalk between the sub-beams of the vortex beam array in foggy environments and improve the signal-to-noise ratio of imaging. Summary of the Invention

[0003] To address the problem of reduced signal-to-noise ratio of target imaging in foggy environments, the present invention provides a method and device for restoring quantum orbital angular momentum array beam scattering medium imaging based on a median filtering algorithm.

[0004] In one aspect, the present invention provides a method for recovering quantum orbital angular momentum array beam scattering medium imaging based on a median filtering algorithm, the method comprising the following steps:

[0005] S1, the M×N array vortex beam modulated by the spatial light modulator hits the target in the foggy environment and generates an echo signal;

[0006] The phase function exp(iφ(x,y)) of the spatial light modulator loaded onto the M×N array vortex beam is:

[0007]

[0008] Where i is an imaginary number, φ(x,y) represents the phase loaded into the beam after grating modulation,

[0009] c a,b is the complex amplitude of the light beam at the diffraction order (a, b), where a and b are the diffraction orders in the x and y directions, respectively. where |c a,b |、τ a,b and l a,b are the amplitude, initial phase and topological charge at the diffraction order (a, b), respectively; is the angular coordinate in the cylindrical coordinate system;

[0010] γx , γ y are the spatial angular frequencies in the x and y directions, γ x =2π / T x , γ y =2π / T y , T x 、T y are the grating constants in the x and y directions respectively;

[0011] By adjusting the grating constant T x 、T y , the amplitude of each diffraction order |c a,b |, initial phase τ a,b and topological charge l a,b A diffraction grating can be obtained, and when the diffraction grating is loaded into a spatial light modulator, the spatial light modulator outputs a rectangular array of vortex beams with different topological charges at different positions.

[0012] S2, receiving echo signals and generating intensity images;

[0013] S3. Use the median filter algorithm to filter the noise of the intensity image and generate the target image.

[0014] Preferably, the expression of the M×N array vortex beam in the rectangular coordinate system is:

[0015]

[0016] Where x, y, z are the coordinates in the rectangular coordinate system, l is the topological charge of the beam, ω(z) is the waist radius of the beam at the transmission distance z, and z R is the Rayleigh distance, k is the wave number of the light wave, M and N are the number of rows and columns in the array, and m and n are the mth row and nth column.

[0017] Preferably, the process of filtering the intensity image using the median filter algorithm in step S3 is as follows:

[0018] Sort the pixel values ​​in the neighborhood of the intensity image and select the median value after sorting to replace the pixel at that location, specifically:

[0019] First, select a window of length L, where L = 2Q + 1, and Q is a positive integer. The median of the sorted pixels is:

[0020] Y(j)=Med[X(jQ),...,X(j),...,X(j+Q)]

[0021] Where X(j) is the different pixel values ​​in the neighborhood of the position to be processed.

[0022] In another aspect of the present invention, a device for imaging and restoring a scattering medium of a quantum orbital angular momentum array beam based on a median filtering algorithm is provided, the device comprising a laser 1, a polarization controller 2, a first collimator 3, a polarizer 4, a spatial light modulator 5, a second collimator 6, a cloud particle screen 7, a receiving optical system 8, a CCD camera 9, and a computer 10;

[0023] First, a single Gaussian beam is generated by a laser 1. The polarization state of the incident light field is adjusted by a polarization controller 2. The beam is collimated by a first collimator 3 and then regulated by a polarizer 4. A grating is loaded into a spatial light modulator 5, which modulates the incident Gaussian beam to obtain a vortex beam array arranged in a rectangular space. The topological charge of the sub-beams at different positions is changed by adjusting the grating. The modulated vortex beam array is collimated by a second collimator 6 and transmitted to a target 11 in a foggy environment. A fog particle screen 7 is set on the beam incident path and reflection path of the target 11 to simulate a foggy environment. The echo signal reflected by the target 11 is scattered by the foggy environment and transmitted to a receiving optical system 8. The receiving optical system 8 focuses and receives the light beam scattered by the foggy environment and converges it into a CCD camera 9 to obtain an intensity image of the target reflected in the foggy environment. The intensity image is processed by a computer 10 to generate a target image. The median filtering algorithm is used to filter the noise in the target image after the foggy scattering.

[0024] Beneficial effects of the present invention:

[0025] The present invention achieves a diffraction grating by adjusting the grating constant, the amplitude, phase, and topological charge at each diffraction order. Loading this into a corresponding spatial light modulator, a rectangular array of vortex beams with varying topological charges at different locations can be generated. Separately adjusting the topological charges of the sub-beams at different locations within the vortex beam array effectively reduces crosstalk between sub-beams in a foggy scattering medium. Combined with a median filtering algorithm, this algorithm denoises the target image after fog interference, reducing diffuse crosstalk between sub-beams and improving the signal-to-noise ratio of target imaging in foggy environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a block diagram of a device for imaging and restoring a scattering medium of a quantum orbital angular momentum array beam based on a median filtering algorithm according to the present invention;

[0027] Figure 2 is a schematic diagram of the intensity distribution of a vortex beam array with the same topological charge;

[0028] Figure 3 Schematic diagram of the intensity distribution of vortex beam arrays with different topological charges. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0030] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0032] Specific implementation method 1: Figures 1 to 3 This embodiment describes a method for imaging and restoring scattering media of a quantum orbital angular momentum array beam based on a median filtering algorithm. According to the information of the orbital angular momentum carried by the vortex beam, the method can improve the ability to resist influence in complex environments. By utilizing the orthogonality between vortex beams with different topological charges and adjusting the topological charges of sub-beams at different positions in the vortex beam array, the diffuse crosstalk between each sub-beam can be reduced. The median filtering algorithm is then used to denoise the image, reduce the random fluctuations caused by uneven clouds and fog, and improve the signal-to-noise ratio of the imaging.

[0033] The method comprises the following steps:

[0034] S1, the M×N array vortex beam modulated by the spatial light modulator hits the target in the foggy environment and generates an echo signal;

[0035] The phase function exp(iφ(x,y)) of the spatial light modulator loaded onto the M×N array vortex beam is:

[0036]

[0037] Where i is an imaginary number, φ(x,y) represents the phase loaded into the beam after grating modulation,

[0038] c a,b is the complex amplitude of the light beam at the diffraction order (a, b), where a and b are the diffraction orders in the x and y directions, respectively. where |c a,b |、τ a,b and l a,b are the amplitude, initial phase and topological charge at the diffraction order (a, b), respectively; is the angular coordinate in the cylindrical coordinate system;

[0039] γ x, γ y are the spatial angular frequencies in the x and y directions, γ x =2π / T x , γ y =2π / T y , T x 、T y are the grating constants in the x and y directions respectively;

[0040] By adjusting the grating constant T x 、T y , the amplitude of each diffraction order |c a,b |, initial phase τ a,b and topological charge l a,b A diffraction grating can be obtained. The diffraction grating is a phase function. When loaded onto a spatial light modulator, the phase of the light beam can be adjusted. When the diffraction grating is loaded into the spatial light modulator, the spatial light modulator outputs a rectangular array of vortex beams with different topological charges at different positions.

[0041] S2, receiving echo signals and generating intensity images;

[0042] S3. Use the median filter algorithm to filter the noise of the intensity image and generate the target image.

[0043] The derivation process of the expression of the M×N array vortex beam in step S1 is:

[0044] The expression of a single vortex beam propagating along the z direction in the cylindrical coordinate system is:

[0045]

[0046] Where l is the topological charge of the beam, p is the radial index, ω(z) is the waist radius of the beam at the transmission distance z, is a cylindrical coordinate system, where are radial coordinates, angular coordinates, and axial coordinates respectively. is the associated Laguerre polynomial, i is the imaginary unit, z R is the Rayleigh distance, and k is the wave number of the light wave.

[0047] Let the radial index p = 0, and use Euler's formula to expand to obtain the expression in the rectangular coordinate system (x, y, z):

[0048]

[0049] Where x and y are coordinates in the rectangular coordinate system, and the expression of the vortex beam array with M rows and N columns in a rectangular arrangement is:

[0050]

[0051] Where dx and dy are the spacing between sub-beams in the x and y directions respectively, M and N are the number of rows and columns in the array, and m and n are the mth row and nth column respectively.

[0052] The grating of the spatial light modulator is represented by the transmittance function of the phase diffraction grating in the rectangular coordinate system as exp(iφ(x,y)). The characteristic wave function of the vortex beam is The phase function loaded into the beam after grating modulation is exp(iφ(x,y)), and the Fourier expansion is:

[0053]

[0054] The phase function of the grating loading contains two parts. The first part is This part imposes the initial phase and characteristic wave function of the vortex beam on the beam, c a,b is the complex amplitude of the light beam at the diffraction order (a, b), where a and b are the diffraction orders in the x and y directions, respectively. where |c a,b |、τ a,b and l a,b are the amplitude, initial phase and topological charge at the diffraction order (a, b), respectively; is the azimuth. The second part is exp(i(aγ x x+bγ y y)), the position of the characteristic wave function in the x and y directions can be controlled, so that sub-beams with different topological charges are obtained at different positions after diffraction. x , γ y are the spatial angular frequencies in the x and y directions, γ x =2π / T x , γ y =2π / T y , T x 、T y are the grating constants in the x and y directions respectively;

[0055] By adjusting the grating constant T x 、T y , the amplitude of each diffraction order |c a,b |, initial phase τ a,b and topological charge l a,b A diffraction grating can be obtained and loaded into a spatial light modulator. The spatial light modulator then outputs a rectangularly arranged vortex beam array with different topological charges at different positions, and the orbital angular momentum distribution of the vortex beam array at different spatial positions is obtained.

[0056] In this step, the topological charges of the sub-beams at different positions in the vortex beam array are adjusted separately to reduce the crosstalk between the sub-beams in the cloud scattering medium. By adjusting the distribution of different topological charges, the best distribution that is resistant to the influence of the scattering medium can be obtained. Then, the median filtering algorithm is combined to denoise the target image after cloud interference to improve the imaging performance.

[0057] The intensity distribution diagrams of vortex beam arrays with the same topological charge and the intensity distribution diagrams of vortex beam arrays with different topological charges are shown in Figure 2. Figure 2 and Figure 3 shown.

[0058] The process of using the median filter algorithm to filter the intensity image noise in step S3 is as follows:

[0059] Sort the pixel values ​​in the neighborhood of the intensity image and select the median value after sorting to replace the pixel at that location, specifically:

[0060] First, select a window of length L, where L = 2Q + 1, and Q is a positive integer. The median of the sorted pixels is:

[0061] Y(j)=Med[X(jQ),...,X(j),...,X(j+Q)]

[0062] Where X(j) is the different pixel values ​​in the neighborhood of the position to be processed.

[0063] Specific implementation method 2: The following is combined Figure 1 This embodiment describes a device for recovering a scattering medium image of a quantum orbital angular momentum array beam based on a median filtering algorithm, which is used to implement the method described in Embodiment 1. The device includes a laser 1, a polarization controller 2, a first collimator 3, a polarizer 4, a spatial light modulator 5, a second collimator 6, a cloud particle screen 7, a receiving optical system 8, a CCD camera 9, and a computer 10.

[0064] First, a single Gaussian beam is generated by a laser 1. The polarization state of the incident light field is adjusted by a polarization controller 2. The beam is collimated by a first collimator 3 and then regulated by a polarizer 4. A grating is loaded into a spatial light modulator 5, which modulates the incident Gaussian beam to obtain a vortex beam array arranged in a rectangular space. The topological charge of the sub-beams at different positions is changed by adjusting the grating. The modulated vortex beam array is collimated by a second collimator 6 and transmitted to a target 11 in a foggy environment. A fog particle screen 7 is set on the beam incident path and reflection path of the target 11 to simulate a foggy environment. The echo signal reflected by the target 11 is scattered by the foggy environment and transmitted to a receiving optical system 8. The receiving optical system 8 focuses and receives the light beam scattered by the foggy environment and converges it into a CCD camera 9 to obtain an intensity image of the target reflected in the foggy environment. The intensity image is processed by a computer 10 to generate a target image. The median filtering algorithm is used to filter the noise in the target image after the foggy scattering.

[0065] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in conjunction with other described embodiments.

Claims

1. A method for restoring the image of a scattering medium using a quantum orbital angular momentum array beam based on a median filter algorithm, characterized in that: The method comprises the following steps: S1, the M×N array vortex beam modulated by the spatial light modulator hits the target in the foggy environment and generates an echo signal; Phase function of the spatial light modulator loaded into the M×N array vortex beam for: Where, is an imaginary number, represents the phase loaded into the beam after grating modulation, Diffraction order The complex amplitude of the beam at 、 They are 、 The diffraction order in the direction, ,in 、 and Diffraction orders The amplitude, initial phase and topological charge at ; is the angular coordinate in the cylindrical coordinate system; 、 They are 、 The spatial angular frequency in the direction, 、 , 、 They are and grating constant of the direction; By adjusting the grating constant 、 , the amplitude at each diffraction order , initial phase and topological charge A diffraction grating can be obtained, and when the diffraction grating is loaded into a spatial light modulator, the spatial light modulator outputs a rectangular array of vortex beams with different topological charges at different positions. S2, receiving echo signals and generating intensity images; S3, using the median filter algorithm to filter the noise of the intensity image to generate the target image; The expression of the M×N array vortex beam in the rectangular coordinate system is: Where, are coordinates in the rectangular coordinate system, is the beam topological charge, The transmission distance is The beam waist radius at is the Rayleigh distance, is the wave number of the light wave, M and N are the number of rows and columns in the array, and m and n are the mth row and nth column.

2. The method for restoring the image of a scattering medium of a quantum orbital angular momentum array beam based on a median filter algorithm according to claim 1, characterized in that: The process of using the median filter algorithm to filter the noise of the intensity image in step S3 is as follows: Sort the pixel values ​​in the neighborhood of the intensity image and select the median value after sorting to replace the pixel at that location, specifically: First, select the length Window, , is a positive integer, and the median of the sorted pixels is: in are the different pixel values ​​in the neighborhood of the position to be processed.

3. A device for imaging and restoring a scattering medium of a quantum orbital angular momentum array beam based on a median filtering algorithm, for implementing the method described in any one of claims 1-2, characterized in that: The device includes a laser (1), a polarization controller (2), a first collimator (3), a polarizer (4), a spatial light modulator (5), a second collimator (6), a cloud particle screen (7), a receiving optical system (8), a CCD camera (9) and a computer (10); First, a single Gaussian beam is generated by a laser (1), and the polarization state of the incident light field is adjusted by a polarization controller (2). The beam is collimated by a collimator (3), and then the beam is regulated by a polarizer (4). A grating is loaded in a spatial light modulator (5). The spatial light modulator modulates the incident Gaussian beam to obtain a vortex beam array arranged in a rectangular shape in space. The topological charge of the sub-beams at different positions is changed by adjusting the grating. The vortex beam array generated by the modulation is collimated by a collimator (6) and transmitted to the target in a foggy environment ( 11), a cloud particle screen (7) is set on the incident path and reflection path of the light beam of the target (11) to simulate the cloud environment; the echo signal generated by the reflection of the target (11) is scattered by the cloud environment and transmitted to the receiving optical system (8), and the receiving optical system (8) focuses and receives the light beam scattered by the cloud environment and converges it into the CCD camera (9), thereby obtaining an intensity image of the target after reflection in the cloud environment. The intensity image is processed by the computer (10) to generate the target image, and the median filtering algorithm is used to filter the noise of the target image after the cloud scattering.

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