Method for generating cylindrical vector beams through a scattering medium

Abstract

The present invention discloses a method for generating a cylindrical vector beam through a scattering medium, comprising the following steps: S1. Select the polarization state of the incident light by rotating a polarizer and measure the transmission matrices in two polarization directions; S2. Use a mask to construct a new operator and obtain a transmission matrix for encoding the cylindrical vector beam; S3. Combine the output light fields in two polarization states, perform a binary polarization approximation to obtain a polarization transmission matrix; S4. Load the conjugate polarization light field onto a spatial light modulator, and through optical path playback, realize the generation of a cylindrical vector beam through the scattering medium. The present invention combines the polarization characteristics of the cylindrical vector beam, combines it with the polarization transmission matrix, and successfully realizes the research on generating a cylindrical vector beam through a scattering medium, opening up prospects for super-resolution imaging through a scattering medium.

Description

Technical Field

[0001] The present invention relates to the generation of various structured light beams through a scattering medium, belonging to the field of wavefront shaping methods, and particularly relates to a method for generating cylindrical vector beams through a scattering medium. Background Art

[0002] There are many scattering media in daily life, such as biological tissues, turbid liquids, rain and fog, etc. When light passes through a scattering medium, a scattering effect occurs and the wavefront will be damaged. Usually, some special optical means can be used to deal with the scattering problem of the scattering medium. Researchers have proposed the optical transmission matrix technology. Through the transmission matrix, the connection between the input light field and the output light field is established, and wavefront shaping can be achieved.

[0003] Flexible beam shaping through a scattering medium is of great significance in biological tissue imaging and high-resolution imaging. So far, it has been experimentally confirmed that traditional OAM beams, Bessel beams, spiral beams, needle beams and perfect vortex beams can be generated using a scattering medium.

[0004] Cylindrical vector beams refer to a class of optical wave modes with a spatially non-uniform polarization state. The intensity and polarization of a cylindrical vector beam have axial symmetry on the beam cross-section. Among them, the radially polarized beam with the electric field direction along the radial direction and the azimuthally polarized beam along the azimuthal direction have attracted extensive attention. These two polarized beams play an important role in material processing, particle capture, increasing storage density, and high-resolution microscope measurement, etc.

[0005] However, when most special beams are generated using a scattering medium, the influence of the scattering medium on the polarization characteristics of light is not considered, and a large amount of research has been concentrated on the amplitude or phase. The present invention combines the polarization characteristics of cylindrical vector beams and combines them with the polarization transmission matrix to realize the generation of cylindrical vector beams through a scattering medium. Summary of the Invention

[0006] The purpose of the present invention is to propose a method for generating cylindrical vector beams through a scattering medium.

[0007] To achieve the above purpose, this method measures the transmission matrices in the horizontal polarization direction and the vertical polarization direction, multiplies them by a specific phase mask to obtain two virtual transmission matrices for encoding the cylindrical vector beam. After cross-correlation operation, the polarization transmission matrix is calculated, its polarization angle is subjected to binary polarization approximation, and finally conjugate inversion is performed to obtain the cylindrical vector beam.

[0008] This method includes the following four steps: S1, measuring two transmission matrices; S2, obtaining two virtual transmission matrices; S3, synthesizing the polarization transmission matrix; S4, generating the cylindrical vector beam.

[0009] S1: Measuring two transmission matrices. By loading different phase maps in the spatial light modulator, the incident light wave can be adjusted. Rotate the second polarizer and measure the transmission matrices T obtained when the light is incident in the horizontal polarization direction and the vertical polarization direction respectively. H and T V ;

[0010] S2: Obtaining two virtual transmission matrices. Perform two-dimensional Fourier transforms on the transmission matrices T for the two polarization directions respectively to generate x In the formula,

[0011]

[0012]

[0013] where is a column of , c represents the horizontal polarization direction H or the vertical polarization direction V, k is the wave vector, and t mn is the incident light field of the m-th output mode connected to the n-th input mode.

[0014] Cylindrical vector beams include a radially polarized beam and an azimuthally polarized beam respectively. The radially polarized beam is formed by the superposition of HG in the vertical polarization direction 10 and HG in the horizontal polarization direction 01 ; The azimuthally polarized beam is formed by the superposition of HG in the vertical polarization direction 01 and HG in the horizontal polarization direction 10 . If you want to generate the radially polarized beam, multiply each column of by the phase mask P to obtain new numerical filtering elements in the Fourier domain:

[0015]

[0016]

[0017] where k x is the wave vector in the x direction, and k y is the wave vector in the y direction.

[0018] Then, perform two-dimensional inverse Fourier transforms on the above two equations to return to the spatial domain:

[0019]

[0020]

[0021] Thus, two virtual transmission matrices for encoding the radially polarized beam are obtained and

[0022] S3: In the process of synthesizing the polarization transfer matrix, perform cross-correlation between the combined virtual transfer matrix and the polarization transfer matrix containing the polarization angle, and perform binary polarization approximation on the obtained linear polarization angle to determine the polarization transfer matrix;

[0023] S4: In the process of generating the cylindrical vector beam, conjugate-invert the processed polarization transfer matrix through the algorithm, and through optical path playback, realize the generation of a radially polarized beam in the cylindrical vector beam at the output plane behind the scattering medium.

[0024] Compared with the prior art, the beneficial effect of the technical solution provided by the present invention is: This method realizes the generation of a cylindrical vector beam through a scattering medium for the first time. Compared with the generation of a vortex beam through a scattering medium, the cylindrical vector beam is widely used in various fields due to its special polarization distribution and focusing characteristics. Description of the Drawings

[0025] Figure 1 System schematic diagram of the method for generating a cylindrical vector beam through a scattering medium provided by the present invention.

[0026] Figure 2 Flowchart of the method for generating a cylindrical vector beam based on passing through a scattering medium.

[0027] Figure 3 Results of generating a cylindrical vector beam through a scattering medium in the specific implementation manner, (a) radially polarized beam generated by the present invention, (b) azimuthally polarized beam generated by the present invention.

[0028] Description of the reference numerals:

[0029] 1. Laser, 2. Attenuator, 3. Microscope objective, 4. Pinhole, 5. First convex lens, 6. Second convex lens, 7. First mirror, 8. Second mirror, 9. First 1 / 2 wave plate, 10. First polarizer, 11. Aperture, 12. Beam splitter prism, 13. Spatial light modulator, 14. Second polarizer, 15. Third convex lens, 16. Scattering medium, 17. Fourth convex lens, 18. Third polarizer, 19. Image sensor. Specific Embodiments

[0030] The following gives the implementation process of the present invention in combination with the drawings to illustrate the technical solution of the present invention in detail.

[0031] Example

[0032] As Figure 1As shown, the laser light emitted by the laser (1) is adjusted in light intensity by the attenuation sheet (2) to be adjusted to an appropriate light intensity value for the entire optical path; subsequently, the laser light passes through the microscope objective lens (3), the pinhole (4), the first convex lens (5), and the second convex lens (6) to achieve collimation and beam expansion; the expanded light is adjusted to an appropriate light height by the first mirror (7) and the second mirror (8); the numerical aperture NA of the microscope objective lens (3) is 0.3, the diameter of the pinhole (4) is 15 mm, and the central wavelength of the laser (1) is 532 nm.

[0033] After that, the polarization state is corrected by the first 1 / 2 wave plate (9) and the first polarizer (10) to meet the requirements of the spatial light modulator (13). The spatial light modulator (13) uses a nematic silicon-based liquid crystal panel and has the best modulation effect on vertically polarized light; the aperture stop (11) adjusts the diameter of the light beam to an appropriate size; the adjusted light passes through the beam splitter prism (12) and is split into two parallel light beams. One of them is not used in the optical path, and the other parallel light beam irradiates the spatial light modulator (13).

[0034] The aperture stop (11) adjusts the diameter of the light beam to an appropriate size so that after the light beam irradiates the spatial light modulator (13), the area ratio of the modulated central part to the non-central reference part is 65%:35%.

[0035] When the spatial light modulator (13) is not modulated, it is used as a mirror. The reflected light passes through the beam splitter prism (12) and the second polarizer (14), and the third convex lens (15) and the fourth convex lens (17) form a 4f system. The scattering medium (16) is located behind the spectral plane of the 4f system, and after passing through the third polarizer (18) for polarization analysis, the speckle image generated is collected by the image sensor (19).

[0036] In the process of measuring the transmission matrix, different phase maps can be loaded in the spatial light modulator to adjust the incident light wave. The second polarizer is rotated to the horizontal polarization direction and the vertical polarization direction respectively, and the transmission matrices T H and T V ;

[0037] In the process of obtaining the transmission matrix for encoding the cylindrical vector beam, the two-dimensional Fourier transform is performed on the transmission matrices T c in the two polarization directions to generate

[0038]

[0039]

[0040] In the formula, is a column of, c represents the horizontal H or vertical V polarization direction, k is the wave vector, and t mn connects the incident light field of the m-th output mode to the n-th input mode.

[0041] The cylindrical vector beam respectively includes a radially polarized beam and an azimuthally polarized beam. The radially polarized beam is formed by the superposition of HG with a vertical polarization direction 10 and HG with a horizontal polarization direction 01 ; The azimuthally polarized beam is formed by the superposition of HG with a vertical polarization direction 01 and HG with a horizontal polarization direction 10 .

[0042] Multiply each column of the transmission matrix in the frequency domain by the Hermite-Gaussian mode corresponding to the polarization direction to obtain new numerical filtering elements. Multiply each column of by the phase mask P to obtain new numerical filtering elements in the Fourier domain:

[0043]

[0044]

[0045] Then, return to the spatial domain by performing an inverse two-dimensional Fourier transform on the above two equations:

[0046]

[0047]

[0048] Thus, two virtual transmission matrices for encoding the radially polarized beam are obtained and

[0049] In the process of synthesizing the polarization transmission matrix, assume that the virtual transmission matrix combination performs cross-correlation with the polarization transmission matrix containing the polarization angle, and perform a binary polarization approximation on the obtained linear polarization angle to determine the polarization transmission matrix.

[0050] In the process of generating the cylindrical vector beam, use the spatial light modulator (13) for modulation. The modulated light is focused on the scattering medium (16) through the third convex lens (15). The outgoing scattered light passes through the fourth convex lens (17), and after polarization analysis by the third polarizer (16), the radially polarized light is collected by the image sensor (17), as Figure 3 (a) shows.

[0051] The present invention can also generate an azimuthally polarized beam in the cylindrical vector beam by multiplying each column of the transmission matrix by the Hermite-Gaussian mode corresponding to the azimuthally polarized light in the frequency domain, as Figure 3 shown in (b).

[0052] The embodiments in the specific implementation manners only represent one implementation manner of the present invention. Embodiment 1 is an implementation device and process designed according to the method proposed by the present invention, and does not represent the protection scope of the present invention. All those skilled in the relevant technical fields can design various different embodiments according to the method proposed by the present invention. As long as the implementation manner conforms to the claims of the present invention, it is within the protection scope of this patent.

Claims

1. Method for generating a cylindrical vector beam through a scattering medium, characterized in that, It includes the following four steps: S1, measuring two transmission matrices; S2, obtaining two virtual transmission matrices; S3, synthesizing a polarization transmission matrix; S4, generating a cylindrical vector beam; S1: Measure the two transmission matrix processes. Loading different phase maps in the spatial light modulator can adjust the incident light wave, and the transmission matrices T incident with the horizontal polarization direction and the vertical polarization direction are measured respectively by rotating the polarization angle. H and T V ; S2: Obtain two virtual transmission matrices, perform two-dimensional Fourier transform on the transmission matrices of the two polarization directions, and the cylindrical vector beam is the Hermite-Gaussian mode HG with two polarization directions perpendicular to each other. 10 and HG 01 The new numerical filter element is obtained by multiplying each column of the transmission matrix by the Hermite-Gaussian modulus of the corresponding polarization direction, and the inverse Fourier transform is performed on it to return to the spatial domain to obtain the virtual transmission matrix of the two polarization directions; S3: In the process of synthesizing the polarization transmission matrix, perform cross-correlation between the combined virtual transmission matrix and the polarization transmission matrix containing the polarization angle, and perform binary polarization approximation on the obtained linear polarization angle to determine the polarization transmission matrix; S4: In the process of generating a cylindrical vector beam, conjugate-invert the polarization transmission matrix processed by the algorithm, and through optical path playback, realize the generation of a cylindrical vector beam on the output plane after the scattering medium.

2. The method for generating a cylindrical vector beam through a scattering medium according to claim 1, characterized in that: In S2, the cylindrical vector beams respectively include a radially polarized beam and an azimuthally polarized beam. The radially polarized beam is formed by superimposing the HG in the vertical polarization direction 10 and the HG in the horizontal polarization direction 01 ; The azimuthally polarized beam is formed by superimposing the HG in the vertical polarization direction 01 and the HG in the horizontal polarization direction 10 .

3. The method for generating a cylindrical vector beam through a scattering medium according to claim 1, wherein: In S2, the transfer matrix T c is subjected to two-dimensional Fourier transform to generate In the formula, is a column of, c represents the horizontal polarization direction H or the vertical polarization direction V, k is the wave vector, and t mn of the incident optical field of the m-th output mode is connected to the n-th input mode.

4. The method for generating a cylindrical vector beam through a scattering medium according to claim 3, wherein: In S2, the numerical filtering process is to multiply each column of by the phase mask P to obtain new numerically filtered elements in the Fourier domain: where k x is the wave vector in the x direction, and k y is the wave vector in the y direction; then, by performing an inverse two-dimensional Fourier transform on the above two equations, it returns to the spatial domain: Thus, two virtual transmission matrices for encoding a radially polarized beam are obtained and

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