A phase selection based system and method for suppressing the side lobes of a Bessel beam

Abstract

The application relates to the technical field of optical beam shaping, and particularly provides a Bessel beam sidelobe suppression system and method based on phase selection, which comprises a light source, an axicon phase map library and a spatial light modulator. The axicon phase map library stores pre-optimized multi-layer axicon phase maps for different working distances. The spatial light modulator is used for loading the multi-layer axicon phase maps to perform phase modulation on a Gaussian beam provided by the light source, so that a Bessel beam with suppressed sidelobe energy is generated. The method comprises the following steps: according to an actual working distance, calling a corresponding multi-layer axicon phase map in the axicon phase map library, and loading the selected multi-layer axicon phase map to the spatial light modulator to realize sidelobe energy suppression in the Bessel beam generation process. The application solves the problems of large filtering energy loss and poor flexibility of the diffraction element in sidelobe suppression in the conventional scheme.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical beam shaping, and particularly relates to a Bessel beam side lobe suppression system and method based on phase selection. BACKGROUND

[0002] As a kind of non-diffracting beam, Bessel beam has the characteristic of keeping the spot shape unchanged during propagation, and has great application potential in the fields of laser precision machining, optical microscopic imaging, optical trapping and manipulation, laser communication, etc. Phase modulation of Gaussian beam by an axicon lens is one of the most classic and direct technical means to generate Bessel beam. However, the traditional axicon-generated Bessel beam has inherent defects in precision machining, and the generated beam is accompanied by significant side lobes. These side lobe structures seriously affect the performance upper limit of Bessel beam in practical application, and the side lobe energy will reduce the machining precision.

[0003] The existing schemes for suppressing side lobe energy have many deficiencies. For example, the scheme of using spatial filtering method to suppress side lobe energy has the problem of excessive energy loss, which will significantly reduce the optical power. The scheme of using fixed parameter diffractive optical element to modulate the incident wavefront to obtain the required beam at one time. This scheme can only work for specific wavelength, specific propagation distance and specific side lobe suppression requirement because the phase function, periodic structure and order of the diffractive optical element cannot be changed after processing. Therefore, it lacks flexibility and cannot meet the actual application requirements. Therefore, there is currently a lack of systematic solution to dynamically achieve effective side lobe suppression in a wide range from near field to far field.

[0004] Therefore, it is urgent to develop a Bessel beam generation method that can dynamically optimize and effectively suppress side lobes in a long working distance. SUMMARY

[0005] Therefore, the present application aims to provide a Bessel beam side lobe suppression system and method based on phase selection, which pre-optimizes a library of axicon phase patterns. In actual application, the optimal phase pattern is called from the library of axicon phase patterns according to the actual working distance, and is loaded by a spatial light modulator. This solves the problems of large filtering energy loss in traditional schemes and poor flexibility of diffractive element in suppressing side lobes.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] The present application provides a Bessel beam side lobe suppression system based on phase selection, which comprises:

[0008] a light source for providing a Gaussian beam;

[0009] an axicon phase mask library storing a plurality of multi-layer axicon phase masks for different working distances;

[0010] a spatial light modulator for loading a corresponding multi-layer axicon phase mask in the axicon phase mask library according to an actual working distance; the spatial light modulator is arranged in the light path of a Gaussian beam provided by a light source to perform phase modulation on the Gaussian beam and generate a Bessel beam with suppressed side lobe energy.

[0011] Preferably, the multi-layer axicon phase mask comprises a plurality of concentric rings, each ring corresponding to a different equivalent axicon cone angle, and the plurality of axicon phase structures are superimposed to form destructive interference on the beam propagation path to suppress the side lobe energy.

[0012] Preferably, the phase distribution model of the multi-layer axicon phase mask is :

[0013] ;

[0014] wherein, is a smooth transition mask function of the nth ring, is a wave number, is an equivalent cone angle parameter of the nth ring, , is a base cone angle, is a cone angle change rate, is a radial coordinate, is a topological charge number, is an azimuthal angle.

[0015] Preferably, the method for generating a plurality of multi-layer axicon phase masks for different working distances in the axicon phase mask library comprises:

[0016] setting a target transmission distance range, and dividing the target transmission distance range into n subintervals;

[0017] setting a phase distribution model wherein the number of ring layers n, the base cone angle and the cone angle change rate are variables, and the optimal parameter combination corresponding to each subinterval is found by an optimization algorithm with the side lobe energy suppression effect in each subinterval as the optimization target; ;

[0018] generating a multi-layer axicon phase mask for each subinterval according to the optimal parameter combination of the subinterval;

[0019] the multi-layer axicon phase masks of all subintervals constitute the axicon phase mask library.

[0020] Preferably, the actual working distance is determined, a sub-interval in which the actual working distance is located is determined, a multi-layered axicon phase pattern corresponding to the sub-interval in which the actual working distance is located is called, and the spatial light modulator is loaded with the multi-layered axicon phase pattern corresponding to the sub-interval in which the actual working distance is located to perform phase modulation on the Gaussian light beam to generate the Bessel light beam with suppressed sidelobe energy.

[0021] Preferably, the light source is a laser.

[0022] Preferably, the optical path between the light source and the spatial light modulator is further provided with a beam expander collimator lens group and a polarization beam splitter.

[0023] Preferably, the spatial light modulator is a reflective liquid crystal phase modulator.

[0024] The application further provides another aspect of a Bessel light beam sidelobe suppression method based on phase selection, which adopts a Bessel light beam sidelobe suppression system based on phase selection and comprises the following steps:

[0025] The actual working distance is determined according to the spatial position of the target plane;

[0026] A multi-layered axicon phase pattern corresponding to the actual working distance is called from a library of axicon phase patterns;

[0027] The selected multi-layered axicon phase pattern is loaded to the spatial light modulator;

[0028] The spatial light modulator loaded with the selected multi-layered axicon phase pattern is used to perform phase modulation on the Gaussian light beam incident from the light source, so as to generate the Bessel light beam with suppressed sidelobe energy at the target plane.

[0029] Compared with the prior art, the application can achieve the following beneficial effects:

[0030] Traditional methods for generating Bessel beams using axial pyramids and for wavefront modulation to suppress sidelobes using diffraction elements can only achieve optimal performance at a specific distance. Since the modulation parameters of the axial pyramids and diffraction elements are fixed, they cannot be applied to different working distances. Generating Bessel beams at different working distances requires the design and customization of the axial pyramids and diffraction elements, resulting in high costs, extremely low flexibility, and limitations in manufacturing processes that prevent the fabricated axial pyramids and diffraction elements from meeting theoretical requirements, further leading to poor modulation effects and accuracy. This invention, however, utilizes a spatial light modulator instead of optical elements, freeing it from the constraints of fixed-parameter diffraction optical elements. Through a pre-generated phase pattern library covering the entire target working range, combined with a real-time dynamic selection mechanism, the system can automatically call upon the current optimal phase pattern across continuous propagation distances from near field to far field. This achieves stable and efficient sidelobe suppression across the entire working domain, offering advantages such as reusability and dynamic phase pattern loading, completely solving the problem of drastic performance degradation caused by changes in working distance in traditional methods.

[0031] Furthermore, this invention designs a phase distribution model for a multi-layer axial pyramid phase map and transforms the phase distribution problem at different distances into an optimal solution problem. By using an optimization algorithm, the optimal parameter combination for each sub-interval is obtained, generating a multi-layer axial pyramid phase map for each sub-interval. This allows for the supplementation, modification, and reconstruction of the axial pyramid phase map library according to actual needs, offering high flexibility and effectively solving the long-standing problem of sidelobe suppression that has constrained the practical application of Bessel beams. Attached Figure Description

[0032] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0033] Figure 1 This is a schematic diagram of the optical path of a phase-selective Bessel beam sidelobe suppression system provided in an embodiment of the present invention;

[0034] Figure 2 This is a flowchart illustrating the construction process of the axial pyramid phase map library provided in an embodiment of the present invention;

[0035] Figure 3 This is a comparison diagram of the multi-axis pyramid phase of the present invention and the single-axis pyramid phase of a conventional Bessel beam generation system, according to an embodiment of the present invention.

[0036] Figure 4 This is a comparison diagram of the two-dimensional light intensity distribution of Bessel light obtained by multi-axis pyramidal phase modulation and single-axis pyramidal phase modulation according to an embodiment of the present invention;

[0037] Figure 5is a global intensity distribution diagram of the Bessel light generated by the application and the traditional scheme under logarithmic coordinates according to an embodiment of the application;

[0038] Figure 6 is an enlarged view of the central region of the Bessel light generated by the application and the traditional scheme under linear coordinates according to an embodiment of the application.

[0039] The reference signs in the drawings include:

[0040] Light source 1, beam expander collimator lens group 2, polarizing beam splitter 3, spatial light modulator 4, control device 5, 4f system lens group 6, CCD 7. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not constitute a limitation on the present application. In different embodiments, similar elements are associated with similar element numbers. In the following embodiments, many details are described in order to make the present application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different cases, or can be replaced by other elements, materials or methods. In some cases, some operations related to the present application are not shown or described in the specification in order to avoid the core part of the present application being overwhelmed by too much description, and it is not necessary for those skilled in the art to describe these related operations in detail according to the description in the specification and the general technical knowledge in the art.

[0042] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other to form various embodiments without conflict. Meanwhile, the steps or actions in the method description can also be sequentially adjusted or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of clearly describing a certain embodiment, and do not mean that the sequence is necessary, unless otherwise stated that a certain sequence must be followed.

[0043] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" and the like can be explicitly or implicitly included one or more. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0044] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0045] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0046] Please refer to Figure 1 In an embodiment of the present application, a phase selection based Bessel beam sidelobe suppression system is provided, comprising:

[0047] A light source 1 for providing a Gaussian beam;

[0048] An axicon phase map library storing a plurality of axicon phase maps for different working distances;

[0049] A spatial light modulator 4 for loading the corresponding plurality of axicon phase maps in the axicon phase map library according to the actual working distance; the spatial light modulator 4 is arranged on the light path of the Gaussian beam provided by the light source 1, and modulates the phase of the Gaussian beam to generate a Bessel beam with suppressed sidelobe energy.

[0050] Wherein, the light source 1 is a helium-neon laser, which is used to provide a Gaussian beam with a wavelength of 632.8nm, which is used for subsequent modulation to generate a Bessel beam.

[0051] The spatial light modulator 4 is selected as a reflective liquid crystal phase type modulator, the resolution is 1920*1200, the phase modulation range is 0~2pi, and the response time is less than 20ms. The embodiment of the application adopts the spatial light modulator 4 to modulate the Gaussian light beam to generate the Bessel light beam. The scheme of modulating the Gaussian light beam by using the traditional axial prism is replaced, the optical parameters of the axial prism are fixed, so the characteristics and inherent side lobes of the Bessel light beam generated by the axial prism are also fixed. It cannot be flexibly adjusted according to the requirements, and a new axial prism can only be redesigned and processed. The embodiment of the application adopts the spatial light modulator 4 to load the phase diagram to create a virtual axial prism, the spatial light modulator 4 can switch and load different phase diagrams according to actual needs, when the target working distance changes, another axial prism phase diagram is called from the axial prism phase diagram library, so that the modulation of the Gaussian light beam can be realized, and the Bessel light beam meeting the requirements can be generated. The application can generate Bessel light beams with different core sizes by simply changing the multi-layer axial prism phase diagram loaded by the spatial light modulator 4, and can also adapt to different laser wavelengths, and can be seamlessly switched in the working distance range (such as 160-260mm), and the whole process of side lobe suppression can be realized.

[0052] The core innovation of the application is that an axial prism phase diagram library is pre-optimized and constructed, a plurality of multi-layer axial prism phase diagrams optimized for different propagation distance intervals are stored in the axial prism phase diagram library, in actual application, the system dynamically calls the most suitable phase diagram from the axial prism phase diagram library according to the target working distance and loads the spatial light modulator 4, so that the effective suppression of the side lobe of the Bessel light beam can be realized in a continuous and expanded working range.

[0053] As an optional embodiment, the multi-layer axial prism phase diagram in the axial prism phase diagram library is composed of a non-continuous composite phase structure including a plurality of concentric rings, each ring is given an equivalent axial prism cone angle different from other rings. The ring phase structure with different equivalent cone angles superimposes a plurality of axial prism phase structures when the light beam propagates, and the generated light field in the side lobe area is subjected to destructive interference, and the side lobe energy distribution is suppressed. The design is:

[0054] ;

[0055] Wherein, The smooth transition mask function of the nth ring is used to realize the smooth transition between layers, The wave number is, The equivalent cone angle parameter of the nth ring is, , The basic cone angle is, The cone angle change rate is used to control the steepness of the gradient change, Radial coordinates, The topological charge number is used to generate the vortex phase. It is the azimuth angle.

[0056] For different working distances, the phase distribution model The optimal parameters differ from those in the model; therefore, a phase distribution model can be used. Based on this, phase distribution models for different working distances are developed. Parameter optimization is performed to generate multi-layered axisymmetric phase maps at different working distances, constructing an axisymmetric phase map library covering the entire target working range. Specifically, such as... Figure 2 As shown, the method for generating multi-layer axial pyramid phase maps with different working distances includes the following steps:

[0057] First, define the target transmission distance range for this system. Based on the requirements for sidelobe energy suppression of Bessel beams, the target transmission distance range is... Divide into n sub-intervals The preferred method is to divide the sub-intervals at equal intervals.

[0058] According to the study, changes in working distance mainly affect the phase distribution model. The number of annular layers n and the basic cone angle and cone angle change rate Therefore, the number of ring layers n and the basic cone angle are set. and cone angle change rate Using the sidelobe energy suppression effect within each sub-interval as the variable, the optimization objective is set to ensure that the sidelobe energy of the generated Bessel beam after suppression is below a certain threshold. This applies to the phase distribution model. The number of annular layers n, the base cone angle and cone angle change rate Random sampling is performed to generate different multi-layer axial pyramid phase maps. Based on the suppression effect of each multi-layer axial pyramid phase map on sidelobe energy, variable parameters are selected to optimize the phase distribution model. Determine the optimal distribution model for each sub-interval. Specific distribution model The variable-solving problem is transformed into an optimization problem. Using existing optimization algorithms, the optimal parameter combination for each subinterval can be obtained through a process of deliberation. This allows you to determine each sub-interval. Optimal distribution model . Each sub-interval and the corresponding optimal distribution model The binding is carried out, and the axis pyramid phase map library is formed. In the actual Bessel beam generation process, it is judged which sub-interval the working distance is in, the optimal distribution model of the multi-layer axis pyramid phase map corresponding to the sub-interval is called, and the selected multi-layer axis pyramid phase map optimal distribution model is loaded by using the spatial light modulator 4. Thus, the Bessel beam generation and sidelobe energy suppression at different working distances can be realized.

[0059] As an optional embodiment, a beam expansion collimation lens group 2 and a polarization beam splitter 3 are further arranged on the light path between the light source 1 and the spatial light modulator 4. The Gaussian beam provided by the light source 1 first passes through the beam expansion collimation lens group 2. The beam expansion collimation lens group 2 performs beam shaping on the Gaussian beam and adjusts the diameter of the Gaussian beam. The beam expansion collimation lens group 2 expands the small Gaussian beam, so that the diameter of the expanded Gaussian beam completely covers the entire effective aperture of the spatial light modulator 4, thereby fully utilizing each pixel of the spatial light modulator 4 for phase modulation and avoiding energy waste and effective aperture loss. In addition, the beam expansion collimation lens group 2 also performs collimation processing on the Gaussian beam provided by the light source 1. After the Gaussian beam is expanded and collimated, it is incident on the polarization beam splitter 3. Since the spatial light modulator 4 modulates the phase by changing the orientation of liquid crystal molecules, the modulation effect is extremely sensitive to the polarization direction of light. Therefore, the polarization beam splitter 3 is used to perform polarization filtering on the Gaussian beam, so as to ensure that the polarization state of the light beam transmitted through the polarization beam splitter 3 meets the requirements of the spatial light modulator 4 for the incident light.

[0060] The Gaussian beam that has undergone expansion, collimation and polarization state processing is incident on the spatial light modulator 4. The spatial light modulator 4 loads the corresponding multi-layer axis pyramid phase map according to the actual working distance, and performs phase modulation on the incident Gaussian beam, thereby effectively suppressing the sidelobe energy of the Bessel beam and generating a Bessel beam with suppressed sidelobe energy.

[0061] A 4f system lens group 6 is further arranged on the subsequent light path of the Bessel beam. The 4f system lens group 6 is composed of a Fourier lens and an imaging lens, and its function is to accurately perform Fourier transform and imaging on the light field modulated by the spatial light modulator 4, and finally perform imaging on the CCD 7 to obtain the Bessel beam pattern.

[0062] As an optional embodiment, a control device 5 is further arranged. The axis pyramid phase map library is stored in the control device 5, and the control device 5 is also used for human-computer interaction. In the actual Bessel beam generation process, the actual working distance is input into the control device 5. The control device 5 determines the distance sub-interval to which the actual working distance belongs, calls the multi-layer axis pyramid phase map corresponding to the sub-interval in which the actual working distance is located, and controls the spatial light modulator 4 to load the selected multi-layer axis pyramid phase map to perform phase modulation on the Gaussian beam, thereby generating a Bessel beam with suppressed sidelobe energy.

[0063] In another embodiment of the present application, a phase selection based Bessel beam side lobe suppression method is provided, and a Bessel beam is generated by using the aforementioned phase selection based Bessel beam side lobe suppression system, specifically comprising the following steps:

[0064] determining the actual working distance according to the spatial position of the target plane;

[0065] calling a multi-layer axicon phase pattern corresponding to the actual working distance from an axicon phase pattern library;

[0066] loading the selected multi-layer axicon phase pattern to a spatial light modulator;

[0067] phase modulating the Gaussian beam incident by the light source by using the spatial light modulator loaded with the selected multi-layer axicon phase pattern, so as to generate a Bessel beam with suppressed side lobe energy at the target plane.

[0068] In order to verify the effectiveness and superiority of the present application, under certain parameter settings, a multi-layer axicon phase pattern is constructed, and the multi-layer axicon phase of the present application is compared with the single axicon phase of the conventional Bessel beam generation system as shown in Figure 3 , wherein Figure 3 a is the conventional single axicon phase, Figure 3 b is the multi-layer axicon phase of the present application. The multi-layer axicon phase distribution of the present application is composed of a plurality of superimposed concentric ring structures, each ring corresponds to a different equivalent axicon cone angle, and by superimposing a plurality of axicon phase structures, destructive interference is formed on the beam propagation path, thereby reducing the side lobe energy distribution. The comparison of the two-dimensional light intensity distribution of the Bessel light obtained by the multi-layer axicon phase and the single axicon phase modulation is shown in Figure 4 , wherein Figure 4 a is the two-dimensional light intensity distribution of the Bessel light obtained by using the conventional single axicon phase modulation, and there is still obvious side lobe. Figure 4 b is the two-dimensional light intensity distribution of the Bessel light obtained by using the multi-layer axicon phase of the present application, and the side lobe energy has been significantly suppressed.

[0069] It is verified by numerical simulation that the side lobe suppression can be achieved within the range of 160-260mm, Figure 5 is the global light intensity distribution diagram of the Bessel light generated by the present application and the conventional scheme under logarithmic coordinates, and the multi-layer axicon phase pattern of the present application is 16 layers of ring bands. Figure 5 In the conventional scheme, the light intensity distribution of the Bessel beam generated by the ordinary axicon has obvious curve protrusions on both sides of the main lobe, and the corresponding side lobes. In the entire radial range, all the side lobes of the red optimization curve are completely below the blue conventional curve. It is explained that after the optimization of the system of the present application, the intensity of the side lobe at any position is much lower than that of the conventional method.

[0070] Figure 6 Figure 8 is a zoomed-in view of a central region of a Bessel beam generated by the present application and a conventional scheme in a linear coordinate according to an embodiment of the present application. The two curves coincide completely in the central main lobe region, which shows that the present application method completely suppresses the side lobe energy without damaging the brightness, shape and size of the central main lobe. For the side lobes on both sides of the central main lobe, the side lobes of the conventional method are very obvious, while the side lobes of the optimized curve are almost flattened, which proves that the optimized core main lobe is perfect and the side lobes are almost eliminated. The side lobe intensity is reduced by more than 30% compared with the conventional single-axis prism structure.

[0071] By using the system and method of the present application, the long-distance effective suppression of the Bessel beam side lobe is achieved through the dynamic adjustable multi-layer axial prism phase structure, which solves the problem of side lobe enhancement outside the fixed distance of the conventional single-axis prism system, and has the advantages of fast response and strong adaptability.

[0072] In summary, the above only describes the preferred embodiments of the present application, and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0073] The system, device, module or unit illustrated by one or more embodiments described above can be specifically implemented by a computer chip or entity, or by a product with certain functions. A typical implementation device is a computer. Specifically, the computer may, for example, be a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0074] It should also be noted that the terms "comprising", "including", or any other variant thereof are intended to cover non-exclusive inclusion, so that processes, methods, articles or devices including a series of elements not only include those elements, but also include other elements not explicitly listed, or other elements inherent to such processes, methods, articles or devices. Without more limitations, the element defined by the statement "including a" does not exclude the presence of additional identical elements in the process, method, article or device including the element.

[0075] The various embodiments described in this specification are presented by way of example, and each embodiment is not inherently more important than any other embodiment. The same can hold true for the various implementations of the systems and methods within each embodiment.

Claims

1. A phase-selective Bessel beam sidelobe suppression system, characterized in that, include: A light source used to provide a Gaussian beam; The axial pyramid phase diagram library stores multi-layer axial pyramid phase diagrams for different working distances. The multi-layer axial pyramid phase diagrams include multiple concentric rings, each ring corresponding to a different equivalent axial pyramid cone angle. By superimposing multiple axial pyramid phase structures, destructive interference is formed on the beam propagation path to suppress sidelobe energy. A spatial light modulator is used to load the corresponding multi-layer axial pyramid phase map from the axial pyramid phase map library according to the actual working distance; the spatial light modulator is placed in the optical path of the Gaussian beam provided by the light source to perform phase modulation on the Gaussian beam and generate a Bessel beam with suppressed sidelobe energy.

2. The phase-selective Bessel beam sidelobe suppression system according to claim 1, characterized in that, Phase distribution model of multi-layer axial pyramid phase diagram for: ； in, Let n be the smooth transition mask function for the nth ring band. For wave number, Let be the equivalent cone angle parameter of the nth ring. , Based on the cone angle, The rate of change of the cone angle, Radial coordinates, For topological load number, This is the azimuth angle.

3. The phase-selective Bessel beam sidelobe suppression system according to claim 2, characterized in that, The method for generating multi-layer axial pyramid phase maps for different working distances in the axial pyramid phase map library includes: Define a target transmission distance range and divide the target transmission distance range into n sub-intervals; Define the phase distribution model Number of middle ring layers n, base cone angle and cone angle change rate Using the sidelobe energy suppression effect within each sub-interval as the variable, and taking the optimization objective as the sidelobe energy suppression effect within each sub-interval, the optimal parameter combination for each sub-interval is found through an optimization algorithm. ; Based on the optimal parameter combination for each sub-interval Generate a multi-layered axial pyramid phase diagram for this sub-interval; The multi-layered axial pyramid phase diagrams of all sub-intervals constitute the axial pyramid phase diagram library.

4. The phase-selective Bessel beam sidelobe suppression system according to claim 3, characterized in that, The actual working distance is determined, and the sub-interval in which the actual working distance is located is determined. The multi-layer axial pyramid phase diagram corresponding to the sub-interval in which the actual working distance is located is called. The spatial light modulator adds the multi-layer axial pyramid phase diagram corresponding to the sub-interval in which the actual working distance is located to perform phase modulation on the Gaussian beam, thereby generating a Bessel beam with suppressed sidelobe energy.

5. The phase-selective Bessel beam sidelobe suppression system according to claim 1, characterized in that, The light source is a laser.

6. The phase-selective Bessel beam sidelobe suppression system according to claim 1, characterized in that, The optical path between the light source and the spatial light modulator is further provided with: a beam expander collimating lens group and a polarizing beam splitter.

7. The phase-selective Bessel beam sidelobe suppression system according to claim 1, characterized in that, The spatial light modulator is a reflective liquid crystal phase modulator.

8. A method for suppressing Bessel beam sidelobes based on phase selection, characterized in that, The system employs a phase-selective Bessel beam sidelobe suppression system as described in any one of claims 1 to 7, and includes the following steps: The actual working distance is determined based on the spatial location of the target plane; Retrieve the multi-layer axial pyramid phase diagram corresponding to the actual working distance from the axial pyramid phase diagram library; The selected multi-layer axial pyramid phase map is loaded into the spatial light modulator; A Gaussian beam incident from a light source is phase-modulated using a spatial light modulator loaded with a selected multi-layer axial pyramid phase map, thereby generating a Bessel beam with suppressed sidelobe energy at the target plane.

Images