A perfect vortex beam control method and system for eliminating zero-order light spot interference

Abstract

The application discloses a perfect vortex beam regulation method and system for eliminating zero-order light spot interference, and relates to the technical field of light field regulation. The method comprises the following steps: acquiring the planar position coordinates of each pixel point of a spatial light modulator and a preset topological charge, and generating a spiral phase distribution; generating a radial compensation phase distribution based on a preset far-field annular light spot radius, a working wavelength of an incident light beam and a focal length of a Fourier lens; generating a transverse off-axis grating phase distribution based on a preset grating period parameter; superimposing the three phase distributions to obtain a composite phase distribution, and performing numerical normalization processing; generating a calculated hologram based on the normalized composite phase distribution and loading the calculated hologram to the spatial light modulator to perform phase modulation on the incident light beam of the spatial light modulator, so as to obtain a perfect vortex beam without zero-order light spot interference. The application realizes complete spatial separation of zero-order stray light and signal light, and improves the generation quality of the perfect vortex beam.

Description

Technical Field

[0001] This application relates to the field of light field manipulation technology, and in particular to a perfect vortex beam manipulation method and system for eliminating zero-order beam interference. Background Technology

[0002] Perfect vortex beams, due to their singular property that the radius of their annular optical field is independent of topological charge, have become a core light source type in fields such as orbital angular momentum optical communication, particle manipulation, and structured light processing. Currently, schemes for generating perfect vortex beams based on phase-type spatial light modulators are quite common. However, limited by the finite phase modulation efficiency of the spatial light modulator itself, an unmodulated zero-order diffraction stray light always remains at the center of the modulated optical path. This stray light fills the inherent phase singularity region of the vortex beam, destroying its hollow dark core structure, leading to a significant decrease in beam mode purity, and causing problems such as intermodal crosstalk and wavefront distortion, severely restricting the performance of vortex beams in high-precision applications.

[0003] Therefore, it is necessary to provide a perfect vortex beam manipulation method to eliminate zero-order beam interference in order to solve the above problems. Summary of the Invention

[0004] The purpose of this application is to provide a method and system for perfect vortex beam control that eliminates zero-order spot interference, aiming to achieve complete spatial separation of zero-order stray light and signal light from a physical mechanism level, thereby improving the generation quality of perfect vortex beams.

[0005] To achieve the above objectives, this application provides the following solution: In a first aspect, this application provides a method for perfect vortex beam manipulation to eliminate zero-order beam interference, the method comprising: Obtain the planar position coordinates of each pixel in the spatial light modulator, and generate a spiral phase distribution based on the planar position coordinates and a preset topological charge; A radially compensated phase distribution is generated based on the preset far-field annular spot radius of the perfect vortex beam, the working wavelength of the incident beam, and the focal length of the Fourier lens. Based on preset grating period parameters, a transverse off-axis grating phase distribution is generated; A composite phase distribution is obtained by linearly superimposing the spiral phase distribution, the radial compensation phase distribution, and the transverse off-axis grating phase distribution. The composite phase distribution is numerically normalized to obtain a normalized composite phase distribution; the phase value of the normalized composite phase distribution is within the preset modulation phase range of the spatial light modulator. Based on the normalized composite phase distribution, a computational hologram is generated and loaded onto the spatial light modulator to perform phase modulation on the incident beam of the spatial light modulator, thereby obtaining a perfect vortex beam with no zero-order spot interference at the center.

[0006] In one embodiment, a spiral phase distribution is generated based on the planar position coordinates and a preset topological charge, specifically including: Using formula Based on the plane position coordinates, calculate the azimuth angle; Using formula Based on the azimuth angle and the preset topological load, a spiral phase distribution is generated; in, for The azimuth at that location, To find the included angle function, These are the discrete pixel coordinates of the plane where the spatial light modulator's LCD screen is located. for Spiral phase distribution at the location; This is the preset topology load.

[0007] In one embodiment, a radially compensated phase distribution is generated based on the preset far-field annular spot radius of the perfect vortex beam, the operating wavelength of the incident beam, and the focal length of the Fourier lens, specifically including: Using formula Based on the preset far-field annular spot radius of the perfect vortex beam, the working wavelength of the incident beam, and the focal length of the Fourier lens, a radially compensated phase distribution is generated. in, for Radial compensation phase at the location; These are the discrete pixel coordinates of the plane in which the spatial light modulator's LCD screen is located; The preset far-field ring radius; The operating wavelength of the incident light beam; The focal length of the Fourier lens; Let be the radial coordinate on the plane where the spatial light modulator's LCD screen is located. .

[0008] In one embodiment, a transverse off-axis grating phase distribution is generated based on preset grating period parameters, specifically including: Using formula Based on preset grating period parameters, a transverse off-axis grating phase distribution is generated; in, for Lateral off-axis grating phase at the location; These are the discrete pixel coordinates of the plane in which the spatial light modulator's LCD screen is located; These are the preset grating period parameters.

[0009] In one embodiment, the expression for the composite phase distribution is: ; in, for The composite phase at the location; For the preset topology load; for Azimuth at the location; These are the discrete pixel coordinates of the plane in which the spatial light modulator's LCD screen is located; The preset far-field ring radius; The operating wavelength of the incident light beam; The focal length of the Fourier lens; The radial coordinates on the plane where the spatial light modulator's LCD screen is located; These are the preset grating period parameters.

[0010] In one embodiment, the expression for the normalized composite phase distribution is: ; in, for The normalized composite phase distribution at the location; For the modulo operation; for Composite phase distribution at the location; These are the discrete pixel coordinates of the plane where the spatial light modulator's LCD screen is located.

[0011] Secondly, this application provides a perfect vortex beam control system for eliminating zero-order spot interference. This system is used to implement the aforementioned perfect vortex beam control method for eliminating zero-order spot interference. The perfect vortex beam control system for eliminating zero-order spot interference includes: A computer is used to generate a computational hologram based on the perfect vortex beam modulation method for eliminating zero-order spot interference, and to send the computational hologram to a spatial light modulator. Laser, used to emit a fundamental Gaussian beam; The beam preprocessing module is located in the output optical path of the laser and is used to perform intensity attenuation, beam expansion and collimation, aperture truncation and polarization state adjustment on the fundamental mode Gaussian beam, and output a collimated beam with polarization state matching. A spatial light modulator is disposed on the outgoing light path of the beam preprocessing module. It is used to load the computational hologram and apply phase modulation to the collimated beam with polarization matching using the computational hologram to generate first-order diffracted light carrying vortex information and propagating with a preset angle deflection, as well as zero-order unmodulated light propagating along the original optical axis. The second aperture is set in the output light path of the spatial light modulator to select the first-order diffracted light and block the zero-order unmodulated light, so as to obtain a perfect vortex beam without zero-order light spot interference in the center. A camera, positioned on the outgoing light path of the second aperture, is used to acquire and record the diffraction spot morphology of the perfect vortex beam.

[0012] In one embodiment, the beam preprocessing module includes: An attenuator is placed in the output optical path of a laser to reduce the intensity of the fundamental mode Gaussian beam, thus obtaining an attenuated beam. A beam expander is placed in the output light path of the attenuator to broaden the cross-sectional size of the attenuated beam and filter out stray light interference to obtain an expanded beam. The first aperture is set in the output light path of the beam expander to intercept the preset aperture area of ​​the expanded beam and obtain the beam intercepted by the first aperture. A polarizer is placed on the outgoing light path of the first aperture to adjust the polarization state of the beam after it is cut off by the aperture, so as to obtain a collimated beam with matching polarization state.

[0013] According to the specific embodiments provided in this application, this application has the following technical effects: This application discloses a perfect vortex beam control method and system for eliminating zero-order spot interference. By constructing a triple composite phase collaborative modulation framework of "spiral phase - radial compensation phase - lateral off-axis grating phase", the zero-order stray light interference problem is systematically solved from the physical mechanism level. First, addressing the physical limitation inherent in zero-order unmodulated light due to the limited modulation efficiency of spatial light modulators, a transverse off-axis grating phase is used to apply transverse diffraction shift to the first-order diffracted light carrying vortex information. This causes the signal light to deviate from its original optical axis, while the zero-order unmodulated light, lacking wavefront modulation, continues to propagate along its original optical axis. This achieves complete spatial separation, physically eliminating the possibility of zero-order stray light coinciding with the vortex dark core and improving the generation quality of the perfect vortex beam. Simultaneously, addressing the shortcomings of conventional grating stacking schemes, which lack phase coupling constraints, disrupt radial compensation matching conditions, leading to annular distortion and loss of topological charge independence, the three phases are linearly superimposed and coupled to the same spatial light modulator. This ensures that the transverse grating phase only changes the beam propagation angle without altering the radial phase distribution and vortex structure, guaranteeing that the radial compensation phase independently locks the far-field annular radius and is topological charge independent. This maintains the "perfect" characteristics of the perfect vortex while completely eliminating the interference and damage to the annular structure caused by the zero-order bright spot, ultimately yielding a high-purity perfect vortex beam with a naturally pure dark core at its center. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 A flowchart illustrating a perfect vortex beam manipulation method for eliminating zero-order spot interference provided in an embodiment of this application; Figure 2 As provided in one embodiment of this application, when only a spiral phase distribution is applied, the topological load... , The corresponding phase hologram and diffraction spot schematic diagram; Figure 3 When applying a helical phase distribution and a radial compensation phase distribution according to an embodiment of this application, the topological load... The corresponding phase hologram and diffraction spot schematic diagram; Figure 4 A schematic diagram of a perfect vortex beam control system for eliminating zero-order spot interference provided in an embodiment of this application; Figure 5 An embodiment of this application provides an applied composite phase distribution and phase period parameter. At that time, topological load The corresponding phase hologram and diffraction spot schematic diagram; Figure 6 An embodiment of this application provides an applied composite phase distribution and phase period parameter. At that time, topological load The corresponding phase hologram and diffraction spot diagram.

[0016] Figure label: Laser-1, beam preprocessing module 2, attenuator 21, beam expander 22, first aperture 23, polarizer 24, spatial light modulator 3, second aperture 4, camera 5. Detailed Implementation

[0017] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] Even the most advanced spatial light modulators cannot be ideal modulation devices, thus failing to achieve 100% phase modulation of the incident light field. The fundamental Gaussian light emitted from the laser can be decomposed into two components: a phase-modulated signal light and an unmodulated direct zero-order light. The zero-order diffracted light propagates along the original optical axis without wavefront modulation or angular deflection, ultimately focusing at the geometric center of the optical path. This zero-order light at the center completely coincides with the dark nucleus of the vortex beam, causing two major physical defects: First, the zero-order stray light fills the phase singularity, disrupting the hollow structure of the vortex beam, annihilating the dark nucleus characteristics, and significantly reducing the purity of the beam mode and orbital angular momentum. Second, conventional zero-order suppression methods use simple superposition of grating phases, which only achieves beam shifting without establishing phase coupling constraints. The transverse grating phase disrupts the matching conditions of the radial focusing phase, leading to a ring distortion in the shifted vortex field and completely losing the core characteristic of a perfectly topologically independent vortex beam.

[0019] To overcome the defect of zero-order stray light interference, this application proposes a method and system for perfect vortex beam manipulation to eliminate zero-order spot interference. This method is based on the triple-composite phase-coordinated modulation theory, coupling a spiral phase, a radially compensated phase, and a transverse off-axis grating phase onto a single spatial light modulator. The spatial separation of the zero-order direct light and the perfect vortex light is achieved using the spatial beam splitting characteristics of grating diffraction, ensuring that the dark, hollow ring structure of the diffracted perfect vortex beam is not disrupted by interference. Simultaneously, an optical experimental platform is constructed with a simple optical path structure, high optical field stability, and good beam fidelity, completely solving the stray light pollution problem in the perfect vortex beam manipulation system from a physical mechanism perspective.

[0020] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] In one exemplary embodiment, such as Figure 1 As shown, a perfect vortex beam manipulation method for eliminating zero-order beam interference is provided, comprising the following steps: Wherein: Step S1: Obtain the planar position coordinates of each pixel of the spatial light modulator, and generate a spiral phase distribution based on the planar position coordinates and a preset topological charge.

[0022] In one embodiment, step S1 specifically includes: Step S11, using the formula Based on the plane position coordinates, calculate the azimuth angle; Step S12, using the formula Based on the azimuth angle and the preset topological load, a spiral phase distribution is generated; in, for The azimuth at that location, To find the included angle function, These are the discrete pixel coordinates of the plane where the spatial light modulator's LCD screen is located. for Spiral phase distribution at the location; The preset topological charge determines the beam's orbital angular momentum quantum number and wavefront spiral structure.

[0023] Specifically, based on the mathematical expression for the spiral phase distribution, the corresponding phase hologram is obtained through MATLAB programming, as shown below. Figure 2 As shown, Figure 2 In the figure, (a) to (c) represent the topological loads, respectively. , The hologram obtained at that time will Figure 2 The mid-phase hologram is loaded onto the spatial light modulator, and the diffracted light spot is captured by the camera. The corresponding diffracted light spot morphology is as follows: Figure 2 As shown in (d) to (f).

[0024] observe Figure 2 As can be seen, the size of the dark hollow structure shown in the dashed box gradually increases with the increase of the topological charge value, indicating that the topological charge value directly affects the size of the light spot. Therefore, it is necessary to further constrain the size of the light spot.

[0025] Step S2: Based on the preset far-field annular spot radius of the perfect vortex beam, the operating wavelength of the incident beam, and the focal length of the Fourier lens, a radially compensated phase distribution is generated.

[0026] In one embodiment, step S2 specifically includes: Using formula Based on the preset far-field annular spot radius of the perfect vortex beam, the working wavelength of the incident beam, and the focal length of the Fourier lens, a radially compensated phase distribution is generated. in, for Radial compensation phase at the location; These are the discrete pixel coordinates of the plane in which the spatial light modulator's LCD screen is located; The preset far-field ring radius; The operating wavelength of the incident light beam; The focal length of the Fourier lens; Let be the radial coordinate on the plane where the spatial light modulator's LCD screen is located. .

[0027] Specifically, to offset the topological load Variation in spot size caused by changes in light intensity; radial compensation phase is set. Constrain the spot size and spiral phase With radial compensation phase The superposition results in the following change in the phase transfer function: ; The corresponding parameters , Substituting into the superimposed phase transfer function, and setting the topological charges as follows: , , , to obtain Figure 3 The phase hologram shown, Figure 3 In the figure, (a) to (c) represent the topological loads, respectively. , The phase hologram obtained at that time, and then Figure 3 The phase holograms corresponding to (a) to (c) are loaded into the spatial light modulator, and the camera captures the morphology of the modulated light spot as follows: Figure 3 As shown in (d) to (f).

[0028] from Figure 3 As can be seen, the modulated spot morphology corresponding to the superimposed phase distribution not only produces a ring-shaped spot, but also maintains the same spot size regardless of the topological charge value, thus generating a perfect vortex. However, there is a very obvious bright spot at the center of the ring-shaped spot. Therefore, it is necessary to further eliminate the bright spot at the center.

[0029] Step S3: Generate a transverse off-axis grating phase distribution based on preset grating period parameters.

[0030] In one embodiment, step S3 specifically includes: Using formula Based on preset grating period parameters, a transverse off-axis grating phase distribution is generated; in, for Lateral off-axis grating phase at the location; These are the preset grating period parameters.

[0031] Specifically, to achieve spatial separation between the zero-order light and the modulation signal light, a transverse one-dimensional linear grating phase is introduced to apply transverse diffraction shift to the modulation light field, thus designing a transverse off-axis grating phase. This phase, by constructing a spatially periodic phase structure, causes the modulation light field carrying vortex information to undergo diffraction shift, while the unmodulated zero-order spot remains at the optical axis center. According to the grating diffraction equation, the beam diffraction deflection angle under the small-angle approximation satisfies... By adjusting the phase period parameter It can precisely control the spatial separation distance between signal light and zero-order light, achieving complete physical isolation.

[0032] Step S4: The spiral phase distribution, the radial compensation phase distribution, and the transverse off-axis grating phase distribution are linearly superimposed to obtain a composite phase distribution.

[0033] In one embodiment, in step S4, the expression for the composite phase distribution is: ; in, for The composite phase at that point.

[0034] Specifically, the spiral phase distribution, radial compensation phase distribution, and transverse off-axis grating phase distribution are linearly superimposed to construct a unified composite phase function. The resulting phase is not a simple superposition of the three phases. The spiral phase independently controls the beam trajectory angular momentum, determining the topological characteristics and spiral wavefront structure of the vortex beam. The radial compensation phase locks the far-field spot radius, and its coefficient is determined by the focal length, wavelength, and spot radius. The transverse grating phase introduces linear wavefront tilting, changing the beam propagation angle without altering the radial phase distribution and vortex structure of the optical field.

[0035] Step S5: Perform numerical normalization on the composite phase distribution to obtain a normalized composite phase distribution. The phase value of the normalized composite phase distribution is within the preset modulation phase range of the spatial light modulator.

[0036] In one embodiment, in step S5, the expression for the normalized composite phase distribution is: ; in, for The normalized composite phase distribution at the location; For the remainder operation.

[0037] Specifically, the composite phase distribution is numerically normalized to fit the modulation range of the spatial light modulator. The effective modulation phase range of the phase-type spatial light modulator used in this application is... To adapt to the physical characteristics of the spatial light modulator, the superimposed composite phase is numerically normalized to obtain a phase structure that conforms to the modulation range of the modulator.

[0038] From the perspective of diffraction optics, the DC component of the light field corresponding to the zero-order diffracted light is not subject to phase holographic modulation, and its propagation direction is always along the center of the optical axis. The first-order diffracted signal light carrying the triple composite phase is shifted to the side space by the transverse grating phase. The two achieve complete spatial separation at the Fourier back focal plane, with no vortex light field energy distribution at the center of the optical path, forming a naturally pure dark nucleus. This completely eliminates the interference of the zero-order diffracted light spot on the vortex dark nucleus from a physical mechanism perspective.

[0039] Step S6: Based on the normalized composite phase distribution, a computational hologram is generated and loaded onto the spatial light modulator to perform phase modulation on the incident beam of the spatial light modulator, thereby obtaining a perfect vortex beam with no zero-order spot interference at the center.

[0040] Specifically, based on the normalized composite phase distribution, the corresponding computational hologram can be obtained through MATLAB programming.

[0041] Based on the same inventive concept, this application also provides a perfect vortex beam control system for implementing the above-described method for eliminating zero-order spot interference. The solution provided by this system is similar to the solution described in the above method. Therefore, the specific limitations of one or more embodiments of the perfect vortex beam control system for eliminating zero-order spot interference provided below can be found in the limitations of the perfect vortex beam control method for eliminating zero-order spot interference described above, and will not be repeated here.

[0042] In one exemplary embodiment, such as Figure 4 As shown, a perfect vortex beam control system for eliminating zero-order beam interference is provided, comprising: a computer (not shown in the figure), a laser 1, a beam preprocessing module 2, a spatial light modulator 3, a second aperture 4, and a camera 5.

[0043] The computer is used to generate a computational hologram based on the perfect vortex beam modulation method for eliminating zero-order spot interference, and sends the computational hologram to the spatial light modulator 3; Laser 1 is used to output a fundamental mode Gaussian beam; The beam preprocessing module 2 is set in the output optical path of the laser 1 and is used to perform intensity attenuation, beam expansion and collimation, aperture truncation and polarization state adjustment on the fundamental mode Gaussian beam, and output a collimated beam with polarization state matching. The spatial light modulator 3 is disposed on the outgoing light path of the beam preprocessing module 2. It is used to load the computational hologram and apply phase modulation to the collimated beam with polarization state matching using the computational hologram to generate first-order diffracted light carrying vortex information and propagating with a preset angle deflection, as well as zero-order unmodulated light propagating along the original optical axis. The second aperture 4 is set in the output light path of the spatial light modulator 3 to select the first-order diffracted light and block the zero-order unmodulated light, so as to obtain a perfect vortex beam without zero-order light spot interference in the center. Camera 5 is positioned on the outgoing light path of the second aperture 4 to collect and record the diffraction spot morphology of the perfect vortex beam.

[0044] In one embodiment, the beam preprocessing module 2 includes: an attenuator 21, a beam expander 22, a first aperture 23, and a polarizer 24.

[0045] Attenuator 21 is disposed in the output optical path of laser 1 to reduce the intensity of the fundamental mode Gaussian beam and obtain an attenuated beam; The beam expander 22 is disposed on the output optical path of the attenuator 21 to broaden the cross-sectional size of the attenuated beam and filter out stray light interference to obtain the expanded beam. The first aperture 23 is set on the output light path of the beam expander 22 to intercept the preset aperture area of ​​the expanded beam and obtain the beam intercepted by the first aperture. Polarizer 24 is disposed on the outgoing light path of first aperture 23 to adjust the polarization state of the beam after the aperture is cut off, so as to obtain a collimated beam with polarization state matching.

[0046] The spatial light modulator used is model FSLM-2K70-P02, the LCD screen size is 1920×1080 pixels, and each pixel size is 8μm; the laser is used as the light source, and a solid-state laser with a wavelength of 532 nm is used here.

[0047] The Gaussian beam emitted from the laser passes through an attenuator, which reduces the laser intensity to protect the spatial light modulator from excessive light energy. After energy attenuation, the laser beam is widened by a beam expander, then passes through a first aperture to cut off a suitable spot size and filter out some external stray light interference. After passing through a polarizer, the beam incident on the spatial light modulator meets the modulator's polarization requirements, improving modulation efficiency. The spatial light modulator is loaded with a computational hologram designed in this invention to generate a perfect vortex beam. The modulated beam then passes through a second aperture to filter out some environmental interference light. The modulated spot area can be freely selected by adjusting the aperture position and the aperture size. Finally, the modulated spot shape is captured by a camera.

[0048] To verify the effect of the computational hologram corresponding to the designed composite phase distribution in generating a perfect vortex beam, the following experiment was conducted: Discussion of spiral phase distribution and radial compensation phase The modulation effect after linear coupling and superposition with the phase distribution of the transverse off-axis grating maintains , The parameter values ​​remain unchanged, and the settings are changed. The topological loads are obtained by taking... , , Holograms of time Figure 5 As shown, where, Figure 5 In the figure, (a) to (c) represent the topological loads, respectively. , The holograms obtained at that time are also sequentially loaded onto the spatial light modulator 3 to obtain diffraction spots as shown. Figure 5 As shown in (d) to (f).

[0049] Depend on Figure 5 It can be seen that the bright spot at the center of the controlled spot shifts relatively, and the resulting perfect annular vortex begins to separate from the central interfering bright spot, but some overlap still occurs.

[0050] Furthermore, set The corresponding computational hologram and the modulated diffraction spot are as follows: Figure 6 As shown. Among them, Figure 6 In the figure, (a) to (c) represent the topological loads, respectively. , The hologram obtained at that time Figure 6 In the diagram, (d) to (f) are the diffraction spots after adjustment.

[0051] Compare Figure 5 and Figure 6 It is clearly observed that when the period parameter As the numerical value decreases, the fringes of the computational hologram become denser, which increases the relative offset between the zero-order bright spot and the perfect vortex. This achieves complete spatial separation between the central bright spot and the perfect vortex ring structure, eliminating the interference and damage of the central bright spot to the perfect vortex ring structure.

[0052] Beneficial effects: 1) This application designs a hologram with triple-reinforced phase-coordinated modulation to eliminate zero-order bright spot interference, and builds a corresponding optical experimental platform for perfect vortex control generation. It realizes complete spatial decoupling and separation of zero-order stray light and perfect vortex light, completely eliminates central bright spot interference, and greatly improves the mode purity of perfect vortex beam, providing a new approach for the control generation of perfect vortex beam.

[0053] 2) The method proposed in this application for achieving spatial separation of interference light through spatial translation can be widely applied in the field of optical field manipulation, providing a useful reference for the efficient manipulation of structured light fields.

[0054] 3) This application can generate computational holograms that are compatible with different optical systems and laser bands simply by adjusting different combinations of wavelength, focal length and grating period. It has strong engineering versatility and the optical path system structure is simple with few components, which is conducive to meeting the development needs of miniaturization and integration in practical engineering applications.

[0055] 4) The perfect vortex beam generation method and system proposed in this application can be used to realize stable mode multiplexing of multiple topological loads after spatial separation, and is expected to be widely used in the field of orbital angular momentum optical communication.

[0056] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0057] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods, systems, and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for perfect vortex beam manipulation to eliminate zero-order beam interference, characterized in that, The method includes: Obtain the planar position coordinates of each pixel in the spatial light modulator, and generate a spiral phase distribution based on the planar position coordinates and a preset topological charge; A radially compensated phase distribution is generated based on the preset far-field annular spot radius of the perfect vortex beam, the working wavelength of the incident beam, and the focal length of the Fourier lens. Based on preset grating period parameters, a transverse off-axis grating phase distribution is generated; A composite phase distribution is obtained by linearly superimposing the spiral phase distribution, the radial compensation phase distribution, and the transverse off-axis grating phase distribution. The composite phase distribution is numerically normalized to obtain a normalized composite phase distribution; the phase value of the normalized composite phase distribution is within the preset modulation phase range of the spatial light modulator. Based on the normalized composite phase distribution, a computational hologram is generated and loaded onto the spatial light modulator to perform phase modulation on the incident beam of the spatial light modulator, thereby obtaining a perfect vortex beam with no zero-order spot interference at the center.

2. The perfect vortex beam manipulation method for eliminating zero-order beam interference according to claim 1, characterized in that, Based on the planar position coordinates and the preset topological load, a spiral phase distribution is generated, specifically including: Using formula Based on the plane position coordinates, calculate the azimuth angle; Using formula Based on the azimuth angle and the preset topological load, a spiral phase distribution is generated; in, for The azimuth at that location, To find the included angle function, These are the discrete pixel coordinates of the plane where the spatial light modulator's LCD screen is located. for Spiral phase distribution at the location; This is the preset topology load.

3. The perfect vortex beam manipulation method for eliminating zero-order beam interference according to claim 1, characterized in that, Based on the preset far-field annular spot radius of the perfect vortex beam, the operating wavelength of the incident beam, and the focal length of the Fourier lens, a radially compensated phase distribution is generated, specifically including: Using formula Based on the preset far-field annular spot radius of the perfect vortex beam, the working wavelength of the incident beam, and the focal length of the Fourier lens, a radially compensated phase distribution is generated. in, for Radial compensation phase at the location; These are the discrete pixel coordinates of the plane in which the spatial light modulator's LCD screen is located; The preset far-field ring radius; The operating wavelength of the incident light beam; The focal length of the Fourier lens; Let be the radial coordinates on the plane where the spatial light modulator's LCD screen is located. .

4. The perfect vortex beam manipulation method for eliminating zero-order beam interference according to claim 1, characterized in that, Based on preset grating period parameters, a transverse off-axis grating phase distribution is generated, specifically including: Using formula Based on preset grating period parameters, a transverse off-axis grating phase distribution is generated; in, for Lateral off-axis grating phase at the location; These are the discrete pixel coordinates of the plane in which the spatial light modulator's LCD screen is located; These are the preset grating period parameters.

5. The perfect vortex beam manipulation method for eliminating zero-order beam interference according to claim 1, characterized in that, The expression for the composite phase distribution is: ； in, for The composite phase at the location; The preset topology load; for Azimuth at the location; These are the discrete pixel coordinates of the plane in which the spatial light modulator's LCD screen is located; The preset far-field ring radius; The operating wavelength of the incident light beam; The focal length of the Fourier lens; The radial coordinates on the plane where the spatial light modulator's LCD screen is located; These are the preset grating period parameters.

6. The perfect vortex beam manipulation method for eliminating zero-order beam interference according to claim 1, characterized in that, The expression for the normalized composite phase distribution is: ； in, for The normalized composite phase distribution at the location; For the modulo operation; for Composite phase distribution at the location; These are the discrete pixel coordinates of the plane on which the spatial light modulator's LCD screen is located.

7. A perfect vortex beam control system for eliminating zero-order beam interference, characterized in that, The perfect vortex beam manipulation system for eliminating zero-order spot interference is used to implement the perfect vortex beam manipulation method for eliminating zero-order spot interference as described in any one of claims 1-6. The perfect vortex beam manipulation system for eliminating zero-order spot interference includes: A computer is used to generate a computational hologram based on the perfect vortex beam modulation method for eliminating zero-order spot interference as described in any one of claims 1-6, and to send the computational hologram to a spatial light modulator; Laser, used to emit a fundamental Gaussian beam; The beam preprocessing module is located in the output optical path of the laser and is used to perform intensity attenuation, beam expansion and collimation, aperture truncation and polarization state adjustment on the fundamental mode Gaussian beam, and output a collimated beam with polarization state matching. A spatial light modulator is disposed on the outgoing light path of the beam preprocessing module. It is used to load the computational hologram and apply phase modulation to the collimated beam with polarization state matching using the computational hologram to generate first-order diffracted light carrying vortex information and propagating with a preset angle deflection, as well as zero-order unmodulated light propagating along the original optical axis. The second aperture is set in the output light path of the spatial light modulator to select the first-order diffracted light and block the zero-order unmodulated light, so as to obtain a perfect vortex beam without zero-order light spot interference in the center. A camera, positioned on the outgoing light path of the second aperture, is used to acquire and record the diffraction spot morphology of the perfect vortex beam.

8. The perfect vortex beam control system for eliminating zero-order beam interference according to claim 7, characterized in that, The beam preprocessing module includes: An attenuator is placed in the output optical path of a laser to reduce the intensity of the fundamental mode Gaussian beam, thus obtaining an attenuated beam. A beam expander is placed in the output light path of the attenuator to broaden the cross-sectional size of the attenuated beam and filter out stray light interference to obtain an expanded beam. The first aperture is set in the output light path of the beam expander to intercept the preset aperture area of ​​the expanded beam and obtain the beam intercepted by the first aperture. A polarizer is placed on the outgoing light path of the first aperture to adjust the polarization state of the beam after it is cut off by the aperture, so as to obtain a collimated beam with matching polarization state.

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