An apparatus and method for generating symmetric speckle based on a modified transmission matrix

Abstract

The present invention discloses an apparatus and method for generating symmetric speckles based on a modified transmission matrix. The method specifically includes: first, using a spatial light modulator to modulate a laser to measure the transmission matrix of a scattering system; then generating a modification factor to perform a transformation on the transmission matrix to obtain a modified transmission matrix; the conjugate transpose of the initial transmission matrix and the modified transmission matrix form a new matrix; performing eigenvalue decomposition on this matrix to obtain eigen output modes, and using numerical phase conjugation inversion of the modified transmission matrix to obtain input modes, taking its phase and loading it onto the spatial light modulator, and a symmetrically distributed speckle pattern can be obtained on the detection plane. The present invention can control the speckle distribution and generate a symmetric speckle pattern; the optical path of the present invention adopts a double optical arm to maximize the number of adjustable input modes, and the effect of measuring the transmission matrix is good.

Description

Technical Field

[0001] The present invention belongs to the field of speckle engineering, and specifically relates to a device and method for generating symmetric speckles based on modifying a transmission matrix. Background Art

[0002] When light propagates in a medium with an uneven refractive index distribution, its amplitude and phase will be perturbed and deviate from a plane wave to become a complex spatial distribution of "speckle patterns". The relationship between the input field and the output field of an optical system including a scattering medium can be described by an optical transmission matrix, and by controlling this transmission matrix, the control of the output speckle pattern can be achieved.

[0003] Currently, the research on methods for controlling the output speckle distribution by using the transmission matrix includes: A. Boniface et al. based on the transmission matrix measured in the experiment, calculated a "customized" operator in the Fourier domain by adding an arbitrary mask to modify the matrix, and used the modified matrix to achieve focused vortex spots, etc.; Louisiane Devaud et al. based on the transmission matrix measured in the experiment, filtered it by adding a mask in its Fourier domain to achieve the control of the output speckle distribution, and finally achieved speckle distributions such as x-direction elongated speckles and short-range periodic speckles. The above methods all require filtering operations on the frequency domain output of each column of the transmission matrix, and the process is complex. And the above methods all achieve the control of speckles by controlling the output frequency, and the control of speckles is limited. Summary of the Invention

[0004] In order to solve the above technical defects in the prior art, the present invention proposes a device for generating symmetric speckles based on modifying a transmission matrix.

[0005] The technical solution for achieving the object of the present invention is: A device for generating symmetric speckles based on modifying a transmission matrix, comprising a laser light source, a first polarizer, a beam expander, a first beam splitter, an attenuator, a second polarizer, a reflector, a second beam splitter, a third beam splitter, a spatial light modulator, a first lens, a diaphragm, a second lens, a first objective lens, a scattering medium, a second objective lens, a third lens, a third polarizer, a photodetector; the laser light source, the first polarizer, the beam expander, the first beam splitter, the attenuator, the second polarizer, the reflector, the second beam splitter, the third beam splitter, the spatial light modulator, the first lens, the diaphragm, the second lens, the first objective lens, the scattering medium, the second objective lens, the third lens, the third polarizer, the photodetector are arranged as follows:

[0006] The laser emitted by the laser light source has its polarization state selected by a first polarizer to meet the polarization modulation requirements of the spatial light modulator; the obtained laser is collimated and expanded by a beam expander; the collimated and expanded laser is split into two parallel light beams by a first beam splitter, and one of the parallel light beams is attenuated in intensity by passing through an attenuator and the polarized light in a specific direction is emitted by a second polarizer; the light beam continues to propagate as a reference light, is reflected by a mirror and propagates to the second beam splitter; the other parallel light beam is further split into two parallel light beams by a third beam splitter, and one of the parallel light beams is irradiated onto the spatial light modulator for modulation; the modulated light beam is split into two light beams again after passing through the third beam splitter; one light beam is reflected out of the optical path, and the other light beam continues to propagate forward and is reduced in beam size and filtered through a first lens, a diaphragm and a second lens; the obtained reduced beam is focused onto a scattering medium (15) by a first objective lens to obtain scattered light; the obtained scattered light is collected by a second objective lens; it propagates through a third lens, and at the second beam splitter, the scattered light interferes with the reference light; the interference light is emitted by selecting the light in a specific polarization direction by a third polarizer and is finally detected by a photodetector.

[0007] The present invention also proposes a method for generating symmetric speckles based on modifying the transfer matrix, and the specific steps are as follows:

[0008] Step 1: Use a spatial light modulator to load the column vectors of the Hadamard matrix, and a photodetector receives the speckle pattern formed by the detection beam after passing through the scattering medium, and use the five-step phase-shifting method to measure the transfer matrix of the scattering system;

[0009] Step 2: Generate a modification factor, perform a transformation operation on the transfer matrix to obtain a modified transfer matrix;

[0010] Step 3: Use the conjugate transpose of the initial transfer matrix and the modified transfer matrix to form a new matrix;

[0011] Step 4: Perform eigenvalue decomposition on the new matrix to obtain the eigen output mode, use the numerical phase conjugation inversion of the modified transfer matrix to obtain the input mode, take the phase of the input mode and load it onto the spatial light modulator, and the modulated light is scattered by the scattering medium to obtain a symmetric speckle pattern on the photodetector.

[0012] Preferably, a frequency is loaded in the modulation region of the spatial light modulator, so as to obtain a target light beam at the positive first diffraction order.

[0013] Preferably, the modified transfer matrix specifically obtained by performing a transformation on the initial transfer matrix by the modification factor is:

[0014] K new = G × K obs

[0015] In the formula, K new represents the modified transfer matrix, G represents the modification factor, K obsRepresents the initial transmission matrix.

[0016] Preferably, the new matrix formed by the conjugate transpose of the initial transmission matrix and the modified transmission matrix is specifically:

[0017]

[0018] In the formula, W represents the new matrix, and K new represents the modified transmission matrix, and K obs represents the initial transmission matrix.

[0019] Preferably, the specific formula for performing eigenvalue decomposition on the new matrix is:

[0020] WE N =α N E N

[0021] In the formula, E N represents the eigenvector, and α N represents the eigenvalue, and WE N is the eigenoutput modulus.

[0022] Preferably, select the eigenvector corresponding to the largest eigenvalue of the new matrix, that is, the first eigenvector as the output, and the specific input pattern obtained by numerically phase conjugate inversion using the modified transmission matrix is:

[0023]

[0024] In the formula, represents the input modulus corresponding to the first eigenoutput, represents the first eigenoutput modulus, and K new represents the modified transmission matrix.

[0025] Preferably, load the phase of the input pattern onto the spatial light modulator, and the symmetric speckle pattern obtained on the photodetector after the modulated light is scattered by the scattering medium is specifically:

[0026]

[0027] In the formula, represents the output symmetric speckle, K represents the true transmission matrix of the scattering system, represents the phase of the input modulus corresponding to the first eigenoutput.

[0028] Compared with the prior art, the significant advantages of the present invention are:

[0029] 1) The optical path of the present invention is rigorous. By introducing a reference arm and loading a carrier frequency in the modulation region, the uniform distribution of the reference light intensity is ensured and the influence of the zero-order light on the signal light is eliminated, improving the measurement accuracy of the transmission matrix;

[0030] 2) The present invention does not need to filter the output frequency domain of the transfer matrix, and can directly apply a transformation operation to the transfer matrix.

[0031] 3) The present invention realizes a symmetrically distributed speckle pattern.

[0032] Other features and advantages of the present invention will be described in the following specification, and some of them will become obvious from the specification, or can be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures specifically pointed out in the written specification, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings are only for the purpose of showing specific embodiments, and are not considered as a limitation to the present invention. Throughout the drawings, the same reference signs represent the same components.

[0034] Figure 1 is a schematic diagram of a device for generating symmetric speckles based on a modified transfer matrix.

[0035] Figure 2 is the symmetric speckle pattern realized by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] It is easy to understand that according to the technical solution of the present invention, without changing the essence of the present invention, those of ordinary skill in the art can imagine various embodiments of the present invention. Therefore, the following detailed embodiments and drawings are only exemplary descriptions of the technical solution of the present invention, and should not be regarded as all of the present invention or as a limitation or definition of the technical solution of the present invention. On the contrary, the purpose of providing these embodiments is to enable those skilled in the art to understand the present invention more thoroughly. The preferred embodiments of the present invention will be specifically described below with reference to the drawings, where the drawings form a part of this application and are used together with the embodiments of the present invention to illustrate the innovative concept of the present invention.

[0037] The inventive concept of the present invention is as Figure 1As shown, a device and method for generating symmetric speckles based on a modified transmission matrix, characterized in that it includes a laser light source 1, a first polarizer 2, a beam expander 3, a first beam splitter 4, an attenuator 5, a second polarizer 6, a reflector 7, a second beam splitter 8, a third beam splitter 9, a spatial light modulator 10, a first lens 11, a diaphragm 12, a second lens 13, a first objective lens 14, a scattering medium 15, a second objective lens 16, a third lens 17, a third polarizer 18, and a photodetector 19; the laser light source 1, the first polarizer 2, the beam expander 3, the first beam splitter 4, the attenuator 5, the second polarizer 6, the reflector 7, the second beam splitter 8, the third beam splitter 9, the spatial light modulator 10, the first lens 11, the diaphragm 12, the second lens 13, the first objective lens 14, the scattering medium 15, the second objective lens 16, the third lens 17, the third polarizer 18, and the photodetector 19 are arranged as follows:

[0038] The laser emitted by the laser light source 1 has its polarization state selected by the first polarizer 2 to meet the polarization modulation requirements of the spatial light modulator; the subsequent laser is collimated and expanded by the beam expander 3; then it is split into two parallel beams by the first beam splitter 4, and one of the parallel beams is attenuated in intensity by passing through the attenuator; then the second polarizer 6 selects the polarized light in a specific direction to be emitted; the beam continues to propagate as the reference light and is reflected by the reflector 7 and propagates to the second beam splitter 8; the other parallel beam is further split into two parallel beams by the third beam splitter 9, and one of the parallel beams is irradiated onto the spatial light modulator 10 for modulation; the modulated beam is split into two beams again after passing through the third beam splitter 9; one beam is reflected out of the optical path, and the other beam continues to propagate forward and is subjected to beam reduction and filtering by the first lens 11, the diaphragm 12, and the second lens 13; the obtained reduced beam is focused onto the scattering medium 15 by the first objective lens 14 to obtain scattered light; the obtained scattered light is collected by the second objective lens 16; it propagates through the third lens 17, and at the second beam splitter 8, the reference light and the scattered light interfere; the interference light is selected by the third polarizer 18 to emit light in a specific polarization direction and is finally detected by the photodetector 19.

[0039] In a further embodiment, the laser light source 1 is a continuous laser, and the emitted light is continuous visible laser light.

[0040] In a further embodiment, the second polarizer 6 and the third polarizer 18 select the light beam with a polarization direction perpendicular to the optical axis to be emitted.

[0041] In a further embodiment, the diaphragm 12 is placed at the rear focal plane of the first lens 11 to select specific light to be emitted and achieve filtering.

[0042] The working process of the present invention is as follows:

[0043] Use a spatial light modulator 10 to load the column vectors of the Hadamard matrix. The photodetector 12 is used to receive the speckle pattern formed after the detection beam passes through the scattering medium 15. The five-step phase-shifting method is used to measure the transmission matrix of the scattering system. Then, a transformation factor is generated to perform a transformation operation on the transmission matrix to obtain a transformed transmission matrix. Then, a new matrix is formed by using the initial transmission matrix and the transformed transmission matrix. The eigenvalue decomposition is performed on this matrix to obtain the eigen output mode. The input mode is obtained by numerically phase-conjugate inversion of the transformed transmission matrix, and its phase is loaded onto the spatial light modulator 10. The modulated light is scattered by the scattering medium 15, and a symmetric speckle pattern is obtained on the photodetector 19.

[0044] In the present invention, a reference arm is introduced and a carrier frequency is loaded in the modulation region, which ensures the uniform distribution of the reference light intensity and eliminates the influence of the zero-order light on the signal light, and improves the measurement accuracy of the transmission matrix.

[0045] A method for generating a symmetric speckle based on a transformed transmission matrix, the specific steps are as follows:

[0046] Step 1, Set up an experimental device as Figure 1 . The laser emitted from the laser light source 1 has its polarization state corrected by the first polarizer 2, and then the obtained laser is collimated and expanded by the beam expander 3. Subsequently, the laser is split into two parallel beams by the first beam splitter 4, and one of the beams is attenuated in intensity by passing through an attenuator. Then, the light of a specific polarization direction is selected and emitted by the second polarizer 6. The light continues to propagate and is reflected by a mirror 7 onto the second beam splitter 8. The other parallel beam is further split into two parallel beams by the third beam splitter 9, and one of the parallel beams is irradiated onto the spatial light modulator 10 for modulation. The modulated beam is split into two beams again after passing through the third beam splitter 9. One beam is reflected out of the optical path, and the other beam continues to propagate forward and is subjected to beam reduction and filtering through the first lens 11, the aperture 12, and the second lens 13. The obtained beam with reduced intensity is focused onto the scattering medium 15 by the first objective lens 14 to obtain scattered light. The obtained scattered light is collected by the second objective lens 16. After passing through the third lens 17, at the second beam splitter 8, the reference light and the scattered light interfere. The interfering light selects and emits light of a specific polarization direction through the third polarizer 18, and finally is detected by the photodetector 19.

[0047] Step 2, Load a frequency in the modulation region of the spatial light modulator (10), so as to obtain a target beam at the positive first diffraction order.

[0048] Step 3, The transformed transmission matrix obtained by performing a transformation on the initial transmission matrix by the transformation factor is specifically:

[0049] K new = G × K obs

[0050] where K newLet the modified transmission matrix be denoted as, the modification factor be denoted as G, and K obs denote the initial transmission matrix.

[0051] Step 4: The new matrix formed by the conjugate transpose of the initial transmission matrix and the modified transmission matrix is specifically:

[0052]

[0053] In the formula, W represents the new matrix.

[0054] Step 5: The calculation formula for the eigen-decomposition of the new matrix is:

[0055] WE N = α N E N

[0056] In the formula, E N represents the eigenvector, and α N represents the eigenvalue.

[0057] Step 6: Select the eigenvector corresponding to the largest eigenvalue of the new matrix, that is, the first eigenvector as the output. The corresponding input mode obtained by numerically phase-conjugate inversion of the modified transmission matrix is specifically:

[0058]

[0059] In the formula, represents the input mode corresponding to the first eigen-output, represents the first eigen-output mode.

[0060] Step 7: Load the phase of the input mode onto the spatial light modulator. The modulated light is scattered by the scattering medium, and the symmetric speckle pattern finally obtained on the photodetector is specifically:

[0061]

[0062] In the formula, represents the output symmetric speckle, K represents the true transmission matrix of the scattering system, represents the phase of the input mode corresponding to the first eigen-output.

[0063] The present invention realizes a symmetrically distributed speckle image, and the actual photographed image is as Figure 2 shown.

[0064] The above is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto.

[0065] Any change or replacement that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

[0066] It should be understood that, in order to streamline the present invention and assist those skilled in the art in understanding various aspects of the present invention, in the above description of the exemplary embodiments of the present invention, various features of the present invention are sometimes described in a single embodiment or with reference to a single figure. However, the present invention should not be construed as meaning that the features included in the exemplary embodiments are all essential technical features of the patent claims.

[0067] It should be understood that the modules, units, components, etc. included in the device of an embodiment of the present invention can be adaptively changed to be arranged in a device different from that of this embodiment. Different modules, units or components included in the device of the embodiment can be combined into one module, unit or component, or they can be divided into multiple sub-modules, sub-units or sub-components.

Claims

1. An apparatus for generating symmetric speckles based on a modified transmission matrix, characterized in that, It includes a laser light source (1), a first polarizer (2), a beam expander (3), a first beam splitter (4), an attenuator (5), a second polarizer (6), a reflector (7), a second beam splitter (8), a third beam splitter (9), a spatial light modulator (10), a first lens (11), a diaphragm (12), a second lens (13), a first objective lens (14), a scattering medium (15), a second objective lens (16), a third lens (17), a third polarizer (18), and a photodetector (19); the laser light source (1), the first polarizer (2), the beam expander (3), the first beam splitter (4), the attenuator (5), the second polarizer (6), the reflector (7), the second beam splitter (8), the third beam splitter (9), the spatial light modulator (10), the first lens (11), the diaphragm (12), the second lens (13), the first objective lens (14), the scattering medium (15), the second objective lens (16), the third lens (17), the third polarizer (18), and the photodetector (19) are arranged as follows: The laser emitted by the laser light source (1) has its polarization state selected by the first polarizer (2) to meet the polarization modulation requirements of the spatial light modulator (10); the obtained laser is collimated and expanded by the beam expander (3); the collimated and expanded laser is split into two parallel beams by the first beam splitter (4), and one of the parallel beams is attenuated in light intensity through the propagation of the attenuator (5), and the polarized light in a specific direction is emitted by the second polarizer (6); the light beam continues to propagate as a reference light, is reflected by the reflector (7) and propagates to the second beam splitter (8); the other parallel beam is further split into two parallel beams by the third beam splitter (9), and one of the parallel beams irradiates the spatial light modulator (10) for modulation; the modulated light beam is split into two light beams again after passing through the third beam splitter (9); one light beam is reflected out of the optical path, and the other light beam continues to propagate forward and is reduced in beam size and filtered through the first lens (11), the diaphragm (12), and the second lens (13); the obtained reduced beam is focused on the scattering medium (15) by the first objective lens (14) to obtain scattered light; the obtained scattered light is collected by the second objective lens (16); It propagates through the third lens (17) and, at the second beam splitter (8), the scattered light interferes with the reference light; The interfering light selects the light with a specific polarization direction and is emitted by the third polarizer (18), and finally is detected by the photodetector (19).

2. The device for generating symmetric speckles based on a modified transmission matrix according to claim 1, characterized in that, The laser light source (1) is a continuous laser, and the emitted light is continuous visible laser light.

3. The device for generating symmetric speckles based on the transformed transmission matrix according to claim 1, wherein The second polarizer (6) and the third polarizer (18) select the light beam with a polarization direction perpendicular to the optical axis and emit it.

4. A method based on the device according to any one of claims 1-3, characterized in that The specific steps are as follows: Step 1: Use the spatial light modulator (10) to load the column vector of the Hadamard matrix, and the photodetector (19) receives and detects the speckle pattern formed by the light beam after passing through the scattering medium (15), and use the five-step phase-shifting method to measure the transmission matrix of the scattering system; Step 2: Generate a transformation factor and perform a transformation operation on the transmission matrix to obtain a transformed transmission matrix; Step 3: Use the conjugate transpose of the initial transmission matrix and the transformed transmission matrix to form a new matrix; Step 4: Perform eigen - decomposition on the new matrix to obtain the eigen - output modulus, use the numerical phase - conjugate inversion of the modified transmission matrix to obtain the input mode, take the phase of the input mode and load it onto the spatial light modulator (10), the modulated light is scattered by the scattering medium (15), and a symmetric speckle pattern is obtained on the photodetector (19).

5. The method for generating symmetric speckles based on the transformed transfer matrix according to claim 4, characterized in that Load the frequency in the modulation region of the spatial light modulator (10), so as to obtain the target beam at the positive first diffraction order.

6. The method for generating symmetric speckles based on the transformed transmission matrix according to claim 4, wherein, The modified transmission matrix obtained by transforming the initial transmission matrix by the modification factor is specifically:[[]] K new = G × K obs where, K new represents the modified transfer matrix, G represents the modification factor, and K obs represents the initial transfer matrix.

7. The method for generating symmetric speckles based on a modified transmission matrix according to claim 4, wherein The new matrix formed by the initial transmission matrix and the conjugate transpose of the modified transmission matrix is specifically:[[]] Wherein, W represents the new matrix, and K new represents the modified transmission matrix, and K obs represents the initial transmission matrix.

8. The method for generating symmetric speckles based on a modified transmission matrix according to claim 4, characterized in that, The specific formula for performing eigen - decomposition on the new matrix is:[[]] WE N = α N E N where E N represents the eigenvector, α N represents the eigenvalue, and WE N is the eigen-output modulus.

9. The method for generating symmetric speckles based on a modified transmission matrix according to claim 4, characterized in that, Select the eigen - vector corresponding to the largest eigenvalue of the new matrix, that is, the first eigen - vector as the output. The input mode obtained by the numerical phase - conjugate inversion using the modified transmission matrix is specifically:[[]] Wherein, represents the input module corresponding to the first feature output, represents the first feature output module, K new represents the modified transmission matrix.

10. The method for generating symmetric speckles based on a modified transmission matrix according to claim 4, wherein Take the phase of the input mode and load it onto the spatial light modulator (10), the modulated light is scattered by the scattering medium (15), and the symmetric speckle pattern obtained on the photodetector (19) is specifically:[[]] In the formula, represents the output symmetric speckle, and K represents the true transmission matrix of the scattering system. represents the phase of the input mode corresponding to the first eigen output.

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