Regulation and control method of multilayer petal-shaped light field

Abstract

The invention discloses a regulation and control method of a multilayer petal-shaped light field, which is specifically applied to the field of optical polarization phase modulation and micro-nano operation, and the specific regulation and control method comprises the following steps: realizing the conversion of the layer number of the multilayer petal-shaped light field between one layer and three layers by using the amplitude modulation of a transmission-type liquid crystal spatial light modulator, a reflective metasurface polarization generator is used for carrying out hybrid polarization modulation, a hybrid polarization order is modulated, the number of petals of a multi-layer petal-shaped light field is adjusted, a hybrid polarization rotation angle is modulated, rotation of the multi-layer petal-shaped light field is achieved, and a pure-phase spatial light modulator is used for carrying out phase modulation. The conversion of the number of layers of the multi-layer petal-shaped light field between one layer and two layers is realized, and the modulated light beam is focused on the focusing plane of the complementary metal oxide semiconductor detector to generate adjustable and controllable multi-layer petal-shaped light spots. Compared with other methods of the petal-shaped light field, the method has the advantages that the light path of the petal-shaped light field is more simplified and compact, the petal-shaped light field has higher regulation and control degree of freedom, the number of layers of the petal-shaped light field is increased to three, capturing of various particles is achieved, and the optical micro-control efficiency is improved.

Description

Technical Field

[0001] The invention relates to the fields of optical polarization phase modulation and optical micromanipulation, and in particular to a method for regulating a multi-layer petal-shaped light field. Background Art

[0002] In recent years, the generation and control of structured light fields have been a hot topic in the fields of light manipulation, optical imaging, and optical communications. This is a light field that can be arbitrarily adjusted in all degrees of freedom from space to time. Petal-shaped light fields are a special type of structured light generated by the superposition of multiple Laguerre-Gaussian mode beams with opposite topological charges. This light field can capture multiple particles and is widely used in the field of optical micromanipulation.

[0003] In 2014, the patent document "Composite Dammann Vortex Grating" (publication number CN104280802A) uses two Dammann vortex gratings carrying basic topological charges of equal size and opposite sign to generate multiple petal-shaped light spots, and by adjusting the lateral relative displacement between the two Dammann vortex gratings, the controllable rotation of the petal-shaped light spots along the circumferential direction can be achieved; in 2022, the patent document "Method and system for simultaneous measurement of displacement distance and direction based on orbital angular momentum" (publication number CN115079197A) uses a light beam carrying orbital angular momentum to be divided into a reference beam and a measurement beam, and the measurement beam irradiates the target object. The reflected measurement beam and the reference beam coaxially interfere through a beam combiner, and a petal-shaped light spot is generated after interference. However, the generated petal-shaped light spot has only one layer, and the generation method relies on the superposition of positive and negative topological vortex light. The use of multiple spectroscopic devices for beam splitting and coaxial superposition will lead to a complex optical path system, and there are also deficiencies such as the petal-shaped light field can only be controlled by phase, resulting in a low degree of control freedom. Summary of the invention

[0004] The present invention aims to solve the problems that the petal-shaped light spot generated by the current method has only one layer, and the generation method relies on the superposition of positive and negative topological vortex light. The use of multiple splitting devices to split the light beam and coaxially superpose it will lead to a complex optical path system, and the petal-shaped light field has only a single layer and can only be controlled by phase, resulting in a low degree of control freedom. The present invention proposes a method for using mixed polarization to generate an adjustable multi-layer petal-shaped light field, and modulates the amplitude, phase and polarization to adjust the number of layers, the number of petals and the rotation of the light field, thereby increasing the degree of control freedom, realizing the capture of multiple particles, improving the efficiency of optical micromanipulation, and simplifying the optical path to make the system simpler.

[0005] The light beam output by the laser is expanded by a half-wave plate and an optical 4F system to output a horizontally polarized light beam. The horizontally polarized light beam is amplitude modulated by a transmissive liquid crystal spatial light modulator. The amplitude-modulated light beam is incident on a reflective metasurface polarization generator for hybrid polarization modulation. The modulated light beam is reflected to a pure phase spatial light modulator for phase modulation. After the phase-modulated light beam is reflected, it is collimated and focused by a tube lens on the focal plane of a complementary metal oxide semiconductor detector to generate an adjustable multi-layer petal-shaped light spot. The focused light field expression of the multi-layer petal-shaped light spot is:

[0006]

[0007] in is the polar coordinate on the focal plane of the complementary metal oxide semiconductor detector, Amp is the amplitude function, plr is the Jones matrix of polarization, is the phase distribution function, The conversion matrix from the object field to the image field polarization and the divergence angle θ between the ray direction and the optical axis are parameters in the reference "Richards, B., and E.Wolf. "Electromagnetic Diffraction in Optical Systems. II. Structure of the Image Field in an Aplanatic System." Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, vol. 253, no. 1274, 1959, pp. 358-79.";

[0008] The laser is a 532nm solid-state laser, emitting continuous laser light with a wavelength of 532nm;

[0009] The half-wave plate can rotate around the optical axis, and by rotating the half-wave plate, the polarization direction of the outgoing light is adjusted to the sensitive direction of the transmissive liquid crystal spatial light modulator;

[0010] The optical 4F system includes two lenses with a distance of twice the focal length and the same focal length. After beam expansion, the diameter of the beam becomes larger and the far-field divergence angle decreases, which is conducive to focusing the beam.

[0011] The transmissive liquid crystal spatial light modulator is a transmissive liquid crystal spatial light modulator loaded with an amplitude function Amp, and is used for amplitude modulation of a light beam;

[0012] The amplitude modulation is performed by using the amplitude function Amp loaded by the transmissive liquid crystal spatial light modulator. The expression of the amplitude function Amp is:

[0013]

[0014] where r A is the polar coordinate at the transmissive liquid crystal spatial light modulator, the initial radius r 0 =0.72, J 1 is the Bessel function of the first kind, β 0 is the amplitude modulation factor, ranging from 0 to 2. The amplitude factor β is modulated by a transmissive liquid crystal spatial light modulator. 0 When modulation is performed, β 0 Changing from 0 to 2, the number of layers of the multi-layer petal-shaped light field can be changed from 2 to 1;

[0015] The reflective metasurface polarization generator is a polarization device that can generate a light beam of any polarization, and can generate a mixed polarization and perform mixed polarization modulation on an amplitude modulated light beam;

[0016] The hybrid polarization modulation is modulated by using a hybrid polarization Jones matrix plr loaded by a reflective metasurface polarization generator. The hybrid polarization Jones matrix plr is:

[0017]

[0018] where r p and is the polar coordinate at the reflective metasurface polarization generator, α is the rotation angle of the mixed polarization, l is the order of the mixed polarization, the mixed polarization order l is modulated to achieve the petal number adjustment of the multi-layer petal-shaped light field, the number of petals in each layer of the light field is 2l, the mixed polarization angle α is modulated to achieve the rotation of the multi-layer petal-shaped light field, and the rotation angle of the entire light field is

[0019] The pure phase spatial light modulator is a polarization-independent pure phase spatial light modulator, which is a spatial light modulator that can modulate all polarization states;

[0020] The phase modulation is to modulate the loaded phase distribution function Phase using a pure phase spatial light modulator, and the phase distribution function expression Phase is:

[0021]

[0022] where r phs is the polar coordinate at the pure phase spatial light modulator, μ is the phase modulation factor, the value range is 1 to 3, the phase difference δ of the non-zero phase in the phase distribution is (μ-1)*π, when μ changes, the phase difference δ changes between 0 and 2π, when the phase difference δ=0.5π and 1.5π, the number of layers increases to 3, and then the amplitude modulation is performed, the number of layers of the multi-layer petal-shaped light field can be transformed from 1 layer to 3 layers;

[0023] The tube lens is used for focusing and collimating the light beam, so that the light beam is finally focused on the focal plane of the complementary metal oxide semiconductor detector;

[0024] Compared with the prior art, the present invention has the following beneficial technical effects:

[0025] 1. The present invention proposes a method for generating a petal-shaped light field, which avoids the use of a splitter device by using a petal-shaped light field generated by mixed polarization, simplifies the optical path, and compresses the optical path by using a reflective modulation device;

[0026] 2. The present invention has a higher degree of control freedom. By modulating the polarization order l of the mixed polarization, the number of lobes can be modulated. By the rotation angle α of the mixed polarization, the rotation of the light field can be achieved. By adjusting the phase factor μ and the amplitude factor β 0 The modulation of the multi-layer petal-shaped light field can realize the conversion of the number of layers, which is beneficial to the capture of various particles and improves the efficiency of optical micromanipulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the optical path of a method for controlling a multi-layer petal-shaped light field according to the present invention;

[0028] Figure 2 (a) is the amplitude distribution when the present invention generates a double-layer petal-shaped light field, (b) is the phase distribution when the present invention generates a double-layer petal-shaped light field, (c) is the polarization distribution when the present invention generates a double-layer petal-shaped light field, (d) is the intensity distribution of the double-layer petal-shaped light field at the focal plane of the present invention;

[0029] Figure 3 The normalized multi-layer petal-shaped light field intensity distribution when the mixed polarization order l of the present invention is 4, 5, 6, and 9;

[0030] Figure 4 The intensity distribution of the multi-layer petal-shaped light field under the rotation angle α of different mixed polarizations of the present invention;

[0031] Figure 5 The different phase differences δ and amplitude factors β of the present invention are 0 The intensity distribution of multi-layer petal-shaped light fields with different numbers of layers; DETAILED DESCRIPTION

[0032] The present invention is described below in conjunction with the accompanying drawings, but the present invention is not limited thereto.

[0033] A method for controlling a multi-layer petal-shaped light field, the optical path schematic diagram of the present invention is as follows Figure 1As shown, the following are arranged in sequence according to the optical path: 1, laser 2, half-wave plate 3, optical 4F system 4, transmissive liquid crystal spatial light modulator 5, reflective metasurface polarization generator 6, pure phase spatial light modulator 7, tube lens 8, complementary metal oxide semiconductor detector.

[0034] The light beam output by the laser 1 is expanded by the half-wave plate 2 and the optical 4F system 3 to output a horizontally polarized light beam. The horizontally polarized light beam is amplitude modulated by the transmissive liquid crystal spatial light modulator 4. The amplitude-modulated light beam is incident on the reflective metasurface polarization generator 5 for hybrid polarization modulation. The modulated light beam is reflected to the pure phase spatial light modulator 6 for phase modulation. After the phase-modulated light beam is reflected, it is collimated and focused by the tube lens 7 on the focusing plane of the complementary metal oxide semiconductor detector 8 to generate an adjustable multi-layer petal-shaped light spot.

[0035] The laser 1 emits continuous laser light with a wavelength of 532 nm.

[0036] The half-wave plate 2 is rotated to adjust the polarization direction of the outgoing light to the sensitive horizontal direction of the transmissive liquid crystal spatial light modulator.

[0037] As the preferred optical 4F system 3, two plano-convex lenses with a focal length of 150 mm are selected and are twice the focal length apart, so that the diameter of the laser beam after beam expansion becomes larger and the far-field divergence angle is reduced, which is conducive to focusing the beam;

[0038] The transmissive liquid crystal spatial light modulator 4 is a transmissive liquid crystal spatial light modulator from Meadowlark, USA, which is used for amplitude modulation of the light beam; the reflective metasurface polarization generator 5 is a polarization device that can generate a light beam of any polarization, and performs mixed polarization modulation on the amplitude modulated light beam; the pure phase spatial light modulator 6 is a polarization-independent pure phase spatial light modulator from BNS, USA, which is a spatial light modulator that can modulate all polarization states.

[0039] This embodiment generates a double-layer eight-petal flower-shaped light field, taking the amplitude factor β 0 =1, the mixed polarization order l=4, the rotation angle of the mixed polarization α=0°, the phase factor μ=3, that is, the phase difference δ=(μ-1)*π=2π, the amplitude, phase and mixed polarization distribution are as follows Figure 2 As shown in (a), (b), and (c), the light is finally focused on the focal plane of the complementary metal oxide semiconductor detector 8 to generate a double-layer eight-petal petal-shaped light field, as shown in FIG. Figure 2 (d) shows the normalized light field intensity distribution.

[0040] The reflective metasurface polarization generator 5 is used to modulate the mixed polarization order l. In this example, the normalized double-layer petal-shaped light field intensity distribution when l=4, 5, 6, and 9 is as follows: Figure 3 As shown, the total number of light petals is: number of layers*2l, realizing the petal number adjustment of the multi-layer petal-shaped light field.

[0041] Using the reflective metasurface polarization generator 5, the mixed polarization angle α is modulated, and the light field rotation angle is like Figure 4 As shown, when α is 0-180°, the mixed polarization order of this example is l=4, then every time α changes by 30°, the overall light field rotates by 7.5°, realizing the rotation of the multi-layer petal-shaped light field.

[0042] Under the condition that the mixed polarization order is l = 4 and α = 0°, the amplitude factor β is 4 pairs of the transmissive liquid crystal spatial light modulator. 0 Modulation, such as Figure 5 As shown, in β 0 = 0.1 and β 0 = 1.0, the number of layers of the multi-layer petal-shaped light field is 2, and in β 0 = 2.0, the number of layers is 1; if in β 0 = 0.1 and β 0 =1.0, the phase factor μ is modulated by the pure phase spatial light modulator 6 to make the phase difference δ=(1.5-1)*π=π / 2, and the number of layers of the multi-layer petal-shaped light field changes from 2 to 3, thereby realizing the regulation of the number of layers of the multi-layer petal-shaped light field.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention, and should be included in the spirit and scope of the present invention, and should be included in the scope of the claims of the present invention.

Claims

1. A method for controlling a multi-layer petal-shaped light field, characterized in that: include: The light beam output by the laser is expanded by a half-wave plate and an optical 4F system to output a horizontally polarized light beam. The horizontally polarized light beam is amplitude modulated by a transmissive liquid crystal spatial light modulator. The amplitude-modulated light beam is incident on a reflective metasurface polarization generator for hybrid polarization modulation. The modulated light beam is reflected to a pure phase spatial light modulator for phase modulation. After the phase-modulated light beam is reflected, it is collimated and focused by a tube lens on the focal plane of a complementary metal oxide semiconductor detector to generate an adjustable multi-layer petal-shaped light spot. The focused light field expression of the multi-layer petal-shaped light spot is: in is the polar coordinate on the focal plane of the complementary metal oxide semiconductor detector, Amp is the amplitude function, plr is the mixed polarization Jones matrix, is the phase distribution function, The transformation matrix from object field to image field polarization and the divergence angle θ between the ray direction and the optical axis.

2. The method for controlling a multi-layer petal-shaped light field according to claim 1, characterized in that: The half-wave plate can rotate around the optical axis. By rotating the half-wave plate, the polarization direction of the outgoing light is adjusted to the sensitive direction of the transmissive liquid crystal spatial light modulator.

3. The method for controlling a multi-layer petal-shaped light field according to claim 1, characterized in that: The optical 4F system includes two lenses with a distance of twice the focal length and the same focal length, which are used for beam expansion to reduce the far-field divergence angle, which is beneficial to the focusing of the beam.

4. The method for controlling a multi-layer petal-shaped light field according to claim 1, characterized in that: The amplitude modulation is performed by using the amplitude function Amp loaded by the transmissive liquid crystal spatial light modulator. The expression of the amplitude function Amp is: where r A is the polar coordinate at the transmissive liquid crystal spatial light modulator, the initial radius r0=0.72, J1 is the first kind Bessel function, β0 is the amplitude modulation factor, and its value range is 0-2. When the amplitude factor β0 is modulated by the transmissive liquid crystal spatial light modulator, β0 varies within the range of 0-2, and the number of layers of the multi-layer petal-shaped light field can be changed from 2 to 1.

5. The method for controlling a multi-layer petal-shaped light field according to claim 1, characterized in that: The hybrid polarization modulation is modulated by using a hybrid polarization Jones matrix plr loaded by a reflective metasurface polarization generator. The hybrid polarization Jones matrix plr is: where r p and is the polar coordinate at the reflective metasurface polarization generator, α is the rotation angle of the mixed polarization, l is the order of the mixed polarization, the mixed polarization order l is modulated to achieve the petal number adjustment of the multi-layer petal-shaped light field, the number of petals in each layer of the light field is 2l, the mixed polarization angle α is modulated to achieve the rotation of the multi-layer petal-shaped light field, and the rotation angle of the entire light field is 6. The method for controlling a multi-layer petal-shaped light field according to claim 1, characterized in that: The phase modulation is to modulate the loaded phase distribution function Phase using a pure phase spatial light modulator, and the phase distribution function expression Phase is: where r phs is the polar coordinate at the pure phase spatial light modulator, μ is the phase modulation factor, and its value range is 1 to 3. The phase difference of the non-zero phase in the phase distribution is (μ-1)*π. When μ changes, its phase difference varies between 0 and 2π. When the phase difference is 0.5π and 1.5π, the number of layers increases to 3. By performing the amplitude modulation, the number of layers of the multi-layer petal-shaped light field can be transformed from 1 to 3.

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