A method for generating a special correlation twisted vector beam

Abstract

The application discloses a method for generating special correlation twist vector light beams. Firstly, an expression of a partially coherent twist light beam with angular correlation and radial correlation is designed and constructed, then a set of holograms is prepared by using a computer and loaded to a spatial light modulator. Each hologram is played repeatedly dynamically on a liquid crystal screen at the same time interval; a laser passes through two beam splitters and the spatial light modulator to generate special correlation twist vector light beams and reflect, forming a "Sagnac interferometer loop" to form vector light. Finally, a spot image of the special correlation twist vector light beams is obtained on a CCD camera. The special correlation twist vector light beams provided by the application can be applied to the fields of optical imaging, optical information regulation and the like. The method provided by the application can generate special correlation twist vector light beams by controlling digital holograms, so as to construct vector light in the "Sagnac interferometer loop". Moreover, the device has only one laser and one spatial light modulator, and the optical path is simple and easy to operate.

Description

Technical Field

[0001] This invention provides a method for generating a specially correlated twisted vector beam. The specially correlated twisted vector beam generated by this method can achieve angular and radial control of light, and also has the characteristics of twisted beams and vector beams, belonging to the field of optical information control. Background Technology

[0002] A specially correlated twisted vector beam is a partially coherent beam with a correlated structure and non-uniform polarization. It possesses three important characteristics: partial coherence, vector polarization, and twisted phase. The beam's spatial coherence lies between complete coherence and incoherence, thus exhibiting strong resistance to turbulence disturbances. The beam's specially correlated structure, with its twisted phase, imparts orbital angular momentum, resulting in beam rotation during propagation in astigmatic systems. The beam's non-uniform polarization distribution enables tight focusing and super-resolution imaging. These novel propagation and imaging properties make this new type of structured light play a crucial role in optical imaging, optical communication, and particle trapping, demonstrating immense application potential.

[0003] While some theoretical models of twisted vector beams have been reported, experimental methods for generating them remain scarce. Methods for controlling the correlation structure of twisted vector beams are limited. In particular, there is a lack of beam generation schemes that can simultaneously control the spatial coherence of the beam in both angular and radial dimensions, and achieve twisted phase and non-local polarization loading. This deficiency in experimental methods severely restricts the application of this novel vector structure beam. This invention can generate a special correlated twisted vector beam whose coherence in both angular and radial dimensions can be controlled separately, achieving both control of the coherent structure and successful loading of a twisted phase onto the vector beam.

[0004] Prior art [Chinese Patent CN114815282A, entitled "A Device for Achieving Super-Resolution with an Angular-Radial Correlated Light Source"] discloses an angular-radial correlated light source. This light beam can achieve two-dimensional control of the light source in both angular and radial directions, but it is limited to scalars and cannot load a distorted phase. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing technologies and provide a method for generating a twisted vector light source. The method provided by this invention can generate a special correlation function while maintaining the twisted phase and vector polarization characteristics of the light beam, and the optical path is simple and easy to operate.

[0006] The technical solution to achieve the objective of this invention is to provide a method for generating a special correlated twisted vector beam, comprising the following steps: (1) A partially coherent twisted beam with angular and radial correlation is generated, and its cross spectral density function is: Where r = (r, θ), δ0 is the transverse coherence width of the beam, θ and r are the angular and radial coordinates, and τ(r) = exp(-αr) 2 +iL·θ) is the complex amplitude, L is the topological charge, and α is a real number; r1=(x1,y2) and r2=(x2,y2) represent two spatial positions in the source plane in rectangular coordinates, μ is the torsion factor, and the condition is satisfied. "*" indicates conjugation, and Sinc(·) represents the sigma function; the steps to generate the above beam are as follows: A. Define a complex function H(r,v) as follows: H(r,v)=τ(r)exp[-iv·g(r)]exp(-iμ(x1y2-x2y1)) (2) Define a real function p(v) as follows: v = (v x ,v y Then ) represents the position coordinates of the incoherent light, and rect(·) is a rectangular function; B. A computer-generated digital hologram capable of producing a superposition-state light field of the following form: In the above expression, Represents an N-dimensional random phase. It is the nth random phase; v n Then it is a real variable; according to p(v)=δ0 2 rect(δ0 2 From v), we can obtain the specific expression for the light field required to generate this digital hologram: C. A set of pre-prepared digital holograms is loaded onto the spatial light modulator. Each hologram is dynamically and repeatedly played on the LCD screen with the same duration. The spatial light modulator continuously loads the above holograms. There is a random phase between each frame of holograms to ensure the realization of incoherent superposition. The first-order diffracted light emitted from the spatial light modulator is a partially distorted coherent beam with angular and radial correlation. (2) The partially coherent twisted beam is injected into a Sagnac interferometer loop, and the light exiting from the loop passes through a quarter-wave plate. This exiting beam is the specially correlated twisted vector beam. The propagation process of the partially coherent twisted beam in the Sagnac interferometer is as follows: A. The beam enters the beam splitter BS, and its transmitted light continues to enter the polarization beam splitter PBS. At this time, PBS simultaneously emits a transmitted polarized light (horizontally polarized) and a reflected polarized light (vertically polarized). The transmitted polarized light is first reflected once on the mirror surface and passes through a half-wave plate and a Dowell prism, and then enters the spatial light modulator through the pinhole aperture. The reflected polarized light enters the pinhole aperture, takes the first-order diffraction light, and then directly enters the spatial light modulator. B. Once the above optical path is constructed, place a quarter-wave plate and a CCD camera at the loop entrance of the Sagnac interferometer, i.e., in the direction of the reflected light from the beam splitter BS, and connect them to a computer to obtain the corresponding vector light image.

[0007] The beneficial effects of this invention are:

[0008] 1. This invention proposes a method for generating a specially correlated twisted vector beam. The beam generated by the method proposed in this invention can achieve angular and radial control of light, and also has the characteristics of a twisted beam and a vector beam.

[0009] 2. The device used in this invention has a simple optical path, is easy to operate, and has a fast imaging speed. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the optical path of a method for generating a special correlated twisted vector beam provided in an embodiment of the present invention.

[0011] Figure 2 This is an experimental result diagram of the cross spectral density function of a special correlated twisted beam prepared in an embodiment of the present invention, with topological charges L = 1, 2, 3, and the fixed point located at the origin and the non-origin. Detailed Implementation

[0012] The present invention will be further described in detail below with reference to the embodiments. The following embodiments are explanations of the present invention and are also preferred application forms of the present invention, but the present invention is not limited to the following embodiments.

[0013] like Figure 1 As shown, this is a schematic diagram of the optical path for a method of preparing a special correlated twisted vector beam provided in this embodiment: it includes a laser 1; a half-wave plate 2; a beam splitter 3; a polarizing beam splitter 4; a reflecting mirror 5; a half-wave plate 6; a Dowell prism 7; a first pinhole aperture 8; a spatial light modulator 9; a second pinhole aperture 10; a first computer 11; a quarter-wave plate 12; a second polarizing beam splitter 13; a CCD camera 14; and a second computer 15.

[0014] In this embodiment, the first computer 11 is used to generate superimposed light fields. Connect the first computer 11 to the spatial light modulator 9; load the digital hologram used to generate the specially correlated twisted beam into the spatial light modulator 9; turn on the laser 1 to generate wavelength-stable linearly polarized light, adjust the half-wave plate 2 to match the polarization direction of the laser light emitted from the laser 1 with the spatial light modulator 9; direct the laser beam emitted from the laser 1 into the beam splitter prism 3; after passing through the beam splitter prism, the transmitted light of the laser beam propagates to the polarization beam splitter prism 4, the transmitted polarized light emitted from the polarization beam splitter prism is reflected by the reflecting mirror 5 and propagates to the Dowell prism 7 after the polarization direction is adjusted by the half-wave plate 6, the beam undergoes multiple reflections in the prism, and the pinhole aperture... Stray light is filtered out, and the resulting first-order diffracted light propagates to the spatial light modulator 9. The reflected polarized light emitted from the polarization beam splitter 4 enters the spatial light modulator 9 through the second aperture stop 10. The laser beam in the propagation path is split into two directions, clockwise and counterclockwise, and enters the spatial light modulator to form a "Sagnac interference circuit". The beam is reflected along the optical path by the spatial light modulator, and after propagating a certain distance, it is reflected by the beam splitter 3. After passing through the quarter-wave plate 12 and the polarization beam splitter 13, it is detected by the CCD camera 14. The spot image of the special correlated twisted vector beam captured by the CCD camera 14 is observed on the second computer 15.

[0015] In this embodiment, the angular and radial parameters in the expression of the specially associated twisted beam can be changed to obtain a new hologram, which is loaded onto the spatial light modulator 9 by the first computer 11 for dynamic playback; the spot images of the specially associated twisted vector beam with different angular and radial parameters captured by the CCD camera 14 after changing the digital hologram are observed on the second computer 15.

Claims

1. The technical solution to achieve the objective of this invention is to provide a method for generating a special correlated twisted vector beam, comprising the following steps: (1) A partially coherent twisted beam with angular and radial correlation is generated, and its cross spectral density function is: Where r = (r, θ), δ0 is the transverse coherence width of the beam, θ and r are the angular and radial coordinates, and τ(r) = exp(-αr) 2 +iL·θ) is the complex amplitude, L is the topological charge, and α is a real number; r1=(x1,y2) and r2=(x2,y2) represent two spatial positions in the source plane in rectangular coordinates, μ is the torsion factor, and the condition is satisfied. "*" indicates conjugation, and Sinc(·) represents the sigma function; the steps to generate the above beam are as follows: A. Define a complex function H(r,v) as follows: H(r,v)=τ(r)exp[-iv·g(r)]exp(-iμ(x1y2-x2y1)) (2) Define a real function p(v) as follows: v = (v x ,v y Then ) represents the position coordinates of the incoherent light, and rect(·) is a rectangular function; B. A computer-generated digital hologram capable of producing a superposition-state light field of the following form: In the above expression, Represents an N-dimensional random phase. It is the nth random phase; v n Then it is a real variable; according to p(v)=δ0 2 rect(δ0 2 From v), we can obtain the specific expression for the light field required to generate this digital hologram: C. A set of pre-prepared digital holograms is loaded onto the spatial light modulator. Each hologram is dynamically and repeatedly played on the LCD screen with the same duration. The spatial light modulator continuously loads the above holograms. There is a random phase between each frame of holograms to ensure the realization of incoherent superposition. The first-order diffracted light emitted from the spatial light modulator is a partially distorted coherent beam with angular and radial correlation. (2) The partially coherent twisted beam is injected into a Sagnac interferometer loop, and the light exiting from the loop passes through a quarter-wave plate. This exiting beam is the specially correlated twisted vector beam. The propagation process of the partially coherent twisted beam in the Sagnac interferometer is as follows: A. The beam enters the beam splitter BS, and its transmitted light continues to enter the polarization beam splitter PBS. At this time, PBS simultaneously emits a transmitted polarized light (horizontally polarized) and a reflected polarized light (vertically polarized). The transmitted polarized light is first reflected once on the mirror surface and passes through a half-wave plate and a Dowell prism, and then enters the spatial light modulator through the pinhole aperture. The reflected polarized light enters the pinhole aperture, takes the first-order diffraction light, and then directly enters the spatial light modulator. B. Once the above optical path is constructed, place a quarter-wave plate and a CCD camera at the loop entrance of the Sagnac interferometer, i.e., in the direction of the reflected light from the beam splitter BS, and connect them to a computer to obtain the corresponding vector light image.

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