Method for overcoming beam breakage to generate skyrmion topology

Abstract

The invention discloses a method for generating Skyrmion topology by overcoming beam breakage, which comprises the following steps of: S1, performing coherent superposition on left-handed Gaussian light and high-order right-handed Laguerre Gaussian light to generate a Skyrmion beam with a specific topological structure; s2, shielding templates of different shapes are constructed, the shielding templates are used for shielding the skyrmion light beam, and therefore fractures of different shapes are introduced in the light beam propagation process; and S3, focusing the broken skyrmion beam through an objective lens, analyzing a focal field, observing the distribution of the intensity and the topological state of the skyrmion beam, and evaluating the robustness of the skyrmion beam under different breaking conditions and the reconstruction effect of focusing on the broken skyrmion beam. According to the method and the device, the shielding mask plates with different shapes are constructed and the broken light beams are focused, so that the robustness of the skyrmion light beams under different fractures can be comprehensively evaluated, and the problem that the skyrmion light beams in a free space are damaged during propagation is solved.

Description

Technical Field

[0001] The present invention relates to the field of vector light field control, and in particular to a method for overcoming light beam breaking to generate skyrmion topology. Background Art

[0002] Skyrmions were first proposed by British physicist Tony Skyrme in 1962 to describe the stability of hadrons in high-energy physics. Skyrmions have an integer topological invariant, called the skyrmion number. The skyrmion number measures the degree of distortion of the field and has topological protection properties, which makes skyrmions a stable field. The concept of skyrmions has been widely promoted and can be applied to a variety of physical systems, such as condensed matter physics, spin electronics, magnetism, acoustics, optics, etc. In 2018, S. Tsesses et al. used circularly polarized light to excite surface plasmons in a hexagonal grating structure on a gold film, controlled the surface plasmons to interfere, and formed standing waves on the surface of the gold film to produce a stable optical skyrmion lattice composed of an electric field. This was the first time that optical skyrmions were generated. Subsequently, S. Gao et al. constructed a skyrmion beam by coherently superposing two Laguerre-Gaussian modes with orthogonal polarization states and different topological charges. The skyrmion topology can be constructed by using its Stokes parameter as the skyrmion vector. On this basis, Y. Shen further proposed that the coherent superposition of two Laguerre-Gaussian lights with non-orthogonal polarizations but orthogonal spatial modes can generate a vector beam carrying the bimeron topology. Controlling the relative phase difference between the two modes involved in the superposition can regulate the topological state of the bimeron. D. Marco et al. constructed an optical Meron lattice that is propagated invariantly in space based on the Stokes parameters of the beam, and the lattice shape is adjustable. J. Ma et al. constructed Y-shaped and L-shaped optical skyrmion arrays based on the Stokes parameters in a strongly focused light field. In addition, some scholars have also carried out the generation of Stokes skyrmions in an integrated manner. W.Lin et al. fabricated a silicon ring resonator on a silicon substrate on an insulator, and designed two angular diffraction gratings consisting of half-etched holes on the ring of the resonator to diffract different polarization states and orbital angular momentum orders. The integrated device can generate Stokes skyrmions with specific topological invariants. T.He et al. designed some metasurface structures on optical fibers to generate high-quality Stokes skyrmions, demonstrating the topological switchability and topological stability of skyrmion beams. A.Wang et al. studied the robustness of Stokes skyrmion beams in complex media and demonstrated that the topological stability of optical skyrmions comes from its boundary structure.

[0003] The formation of Stokes parameter skyrmion beams is based on special polarization modulation. Different polarization states of the light field correspond to different Stokes parameters. By mapping the Stokes parameters to the Poincare sphere space, a vector arrow can be synthesized from three parameters. The arrow can clearly present the state of the polarization of light in space. By customizing the polarization distribution at different positions in the vector field, a unique structure that conforms to the skyrmion topology is obtained from the vector field. Beam breaking refers to the breaking of the integrity and symmetry of the beam, which causes the distribution of the light field to change. Although researchers have conducted a lot of research on optical skyrmions, research on skyrmion beam breaking is still scarce, and there is a lack of in-depth and systematic exploration methods. The present invention proposes a method to overcome beam breaking to generate skyrmion topology, and describes an innovative solution, which injects new vitality and depth into the research in this field, has an important inspiration and driving role, and also provides a new way for the research and application of skyrmions, and provides ideas and references for subsequent scientific research. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for overcoming beam breakage to generate skyrmion topology. By constructing a shielding mask with different breakage shapes and sizes and focusing the broken beam, the robustness of the skyrmion beam under different breakages can be comprehensively evaluated, thereby solving the problem of skyrmion beams being destroyed during propagation in free space. In order to achieve the above-mentioned purpose and other advantages according to the present invention, a method for overcoming beam breakage to generate skyrmion topology is provided, comprising:

[0005] S1. The left-handed Gaussian light is coherently superimposed with the high-order right-handed Laguerre-Gaussian light to generate a skyrmion beam with a specific topological structure; the Laguerre-Gaussian beam expression is

[0006]

[0007] The fundamental mode expression of Laguerre-Gaussian beam is:

[0008]

[0009] is the Laguerre polynomial, Describes the change of beam radius with propagation distance z, w0 is the beam waist radius, is the Rayleigh distance, p is the radial index, R(z)=z[1+(z R / z) 2 ] is the wavefront curvature radius, l is the orbital angular momentum topological charge, k = 2π / λ is the wave number, λ is the wavelength of the incident light, ψ(z) = tan -1 (z / z R) is the Gouy phase;

[0010] S2. constructing shielding masks with different shapes to shield the skyrmion beam, thereby introducing different shapes of breaks during beam propagation; wherein the shapes of the shielding masks include but are not limited to fan-shaped, rectangular, cross-shaped and irregular shapes;

[0011] S3. Use an objective lens to focus the broken skyrmion beam, analyze the focal field, observe its intensity and topological state distribution, evaluate the robustness of the skyrmion beam under different breaking conditions and the effect of focusing on the reconstruction of the broken skyrmion beam.

[0012] Preferably, in step S1, the superposition of left-handed Gaussian light and high-order right-handed Laguerre-Gaussian light is a key step in generating a skyrmion beam. Skyrmion beams of different orders are generated by controlling the topological charge of the orbital angular momentum carried by the high-order Laguerre-Gaussian light.

[0013] Preferably, in step S2, when analyzing the skyrmion topological state of the light beam, the Stokes parameter is measured to characterize the polarization distribution of the light beam and to construct the skyrmion vector of the light beam, so as to observe the influence of the breaking on the skyrmion beam.

[0014] Preferably, in step S3, an objective lens is used to focus the broken skyrmion beam, the beam is focused on a focal plane, the field distribution of the focal field is obtained by the Richard Wolf vector diffraction formula, the Stokes parameter of the focal field is calculated, and the skyrmion topological state is regenerated.

[0015] Preferably, in step S3, the simulation results are analyzed in depth, and the shape of the break is adjusted to perform multiple numerical simulations to evaluate the performance of the skyrmion beam under different conditions. The reconstruction of the skyrmion beam under various breaks is relatively ideal, which shows that the focusing process can effectively overcome the adverse effects of the break on the skyrmion beam and regenerate the skyrmion topology in the focal field.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The present invention can deeply study the influence of beam breaking on the generation of skyrmions in the focal field by comparing the changes in light field intensity distribution, polarization distribution and topological state under different occlusion conditions. This is a direction that the prior art has not involved in or explored in depth, which helps to fill the gap in the research on the generation of skyrmion topology under beam breaking and provides ideas and references for subsequent scientific research.

[0018] 2. The present invention has powerful performance. By focusing the broken skyrmion beam, the skyrmion topology can be reconstructed in the focal field, and its topological structure is complete, ensuring its stable existence in the physical system. The method provided by the present invention can regenerate the skyrmion topology in a variety of broken scenarios, and has a certain universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The schematic diagram of the principle of the method for overcoming beam breakage and generating skyrmion topology in the present invention, wherein the shape of the mask used to block the skyrmion beam includes but is not limited to a fan shape, a rectangle and a cross shape, etc., and the skyrmion topology can be regenerated in the focal field by focusing the broken skyrmion beam;

[0020] Figure 2 The intensity and polarization distribution of the incident light beam under the cross-shaped mask in the present invention (a), and the topological distribution constructed by its Stokes vector (b); the figure also shows the intensity and polarization distribution of the corresponding focal field (c), and the topological distribution constructed by the Stokes vector of the focal field (d);

[0021] Figure 3 The intensity and polarization distribution of the incident light beam under the rectangular mask in the present invention (a), and the topological distribution constructed by its Stokes vector (b); the figure also shows the intensity and polarization distribution of the corresponding focal field (c), and the topological distribution constructed by the Stokes vector of the focal field (d);

[0022] Figure 4 The intensity and polarization distribution of the incident light beam under a 60° fan-shaped mask in the invention (a), and the topological distribution constructed by its Stokes vector (b); the figure also gives the intensity and polarization distribution of the corresponding focal field (c), and the topological distribution constructed by the Stokes vector of the focal field (d). DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Reference Figure 1 , a method for overcoming beam breaking to generate skyrmion topology, comprising the following steps:

[0025] S1. The left-handed Gaussian light is coherently superimposed with the high-order right-handed Laguerre-Gaussian light to generate a skyrmion beam with a specific topological structure; the Laguerre-Gaussian beam expression is

[0026]

[0027] The fundamental mode expression of Laguerre-Gaussian beam is:

[0028]

[0029] is the Laguerre polynomial, Describes the change of beam radius with propagation distance z, w0 is the beam waist radius, is the Rayleigh distance, p is the radial index, R(z)=z[1+(z R / z) 2 ] is the wavefront curvature radius, l is the orbital angular momentum topological charge, k = 2π / λ is the wave number, λ is the wavelength of the incident light, ψ(z) = tan -1 (z / z R ) is the Gouy phase;

[0030] S2. constructing shielding masks with different shapes to shield the skyrmion beam, thereby introducing different shapes of breaks during beam propagation; wherein the shapes of the shielding masks include but are not limited to fan-shaped, rectangular, cross-shaped and irregular shapes;

[0031] S3. Use an objective lens to focus the broken skyrmion beam, analyze the focal field, observe its intensity and topological state distribution, evaluate the robustness of the skyrmion beam under different breaking conditions and the effect of focusing on the reconstruction of the broken skyrmion beam.

[0032] Furthermore, in step S1, the superposition of left-handed Gaussian light and high-order right-handed Laguerre-Gaussian light is a key step in generating skyrmion beams. Skyrmion beams of different orders can be generated by controlling the topological charge of the orbital angular momentum carried by the high-order Laguerre-Gaussian light.

[0033] Furthermore, in step S2, when analyzing the skyrmion topological state of the light beam, the Stokes parameter is measured to characterize the polarization distribution of the light beam and to construct the skyrmion vector of the light beam, so as to observe the influence of the breaking on the skyrmion beam.

[0034] Furthermore, in step S3, an objective lens is used to focus the broken skyrmion beam, the beam is focused on a focal plane, the field distribution of the focal field is obtained by the Richard Wolf vector diffraction formula, the Stokes parameters of the focal field are calculated, and the skyrmion topological state is regenerated.

[0035] Furthermore, in step S3, the simulation results are analyzed in depth, and the shape of the broken part is adjusted to perform multiple numerical simulations to evaluate the performance of the skyrmion beam under different conditions. The reconstruction of the skyrmion beam under various broken parts is relatively ideal, which shows that the focusing process can effectively overcome the adverse effects of the broken part on the skyrmion beam and regenerate the skyrmion topology in the focal field.

[0036] like Figure 1 As shown, a customized incident light beam carrying a specific skyrmion topology can be regenerated into a stable skyrmion topology in the focal field after being focused by an objective lens under the shielding of constructed masks of different shapes (such as fan-shaped, cross-shaped, and rectangular). The field distribution of the focused light field can be calculated using the Richard Wolf vector diffraction formula. Here, the specific implementation of the technical solution is illustrated by taking the constructed cross-shaped, rectangular, and fan-shaped masks as examples, including the following steps:

[0037] Step 1: For the first-order skyrmion, we can determine p = 0, l = -1, and substitute into formula (1), ignoring the constant term, to obtain

[0038]

[0039] To simplify the expression of the incident beam, we can take z = 0, and then determine the incident field as

[0040]

[0041] Where L = [e x ie y ] T Represents left-handed circularly polarized light, R = [e x -ie y ] T Represents right-handed circularly polarized light.

[0042] Step 2: Construct rectangular, fan-shaped and cross-shaped masks. The expression of the cross-shaped mask is

[0043]

[0044] Wherein, d0 is half of the width of the light blocking portion in the cross-shaped mask plate, and in this embodiment, d0 is 0.3 mm.

[0045] The expression of the rectangular mask is

[0046]

[0047] Wherein, D0 is half of the width of the light-blocking portion in the rectangular mask plate, and in this embodiment, D0 is 0.3 mm.

[0048] The expression of the sector mask is

[0049]

[0050] Wherein, φ0 is the central angle of the light-blocking part of the sector-shaped mask, and in this embodiment, φ0 is set to π / 3. The three types of masks are used to block the incident field to generate a broken vector beam E·mask ε (x, y), ε = cross, rect, sector.

[0051] Step 3: Use the objective lens to focus the broken vector beam. According to Richard Wolf's vector diffraction formula, the focal field can be obtained as

[0052]

[0053] Where E Ω (θ, φ) is the refraction field of the rear surface of the objective lens, expressed as follows

[0054]

[0055] represents the radial coordinate on the focal plane, represents the azimuth on the focal plane, is the apodization function of the objective lens. max =sin -1 (NA) is the angle between the focused light and the optical axis, and NA is the numerical aperture of the objective lens. In this embodiment, NA is 0.9, and the focal length of the objective lens is 2 mm.

[0056] Under the action of the cross-shaped mask, the intensity and polarization distribution of the incident light beam are as follows: Figure 2 As shown in (a), a cross-shaped break appears in the incident field, making the incident beam incomplete. The topological structure constructed based on the Stokes parameters of the incident beam after the break is shown in Figure 2 As shown in (b), the topological structure of the incident beam is no longer complete, and its skyrmion number is only -0.28, indicating that the incident beam no longer has skyrmion topology. The incident field is focused by an objective lens, and the intensity and polarization distribution of the focal field are shown in Figure 2 As shown in (c), the focal field is restored to a complete light spot, and its polarization distribution is non-uniform. The topological structure constructed based on the Stokes parameters of the focal field is shown in Figure 2 As shown in (d), it can be seen that the focal field has a complete topological structure and its skyrmion number is -1.00, indicating that there is skyrmion topology in the focal field.

[0057] Under the action of the rectangular mask, the intensity and polarization distribution of the incident light beam are as follows: Figure 3 As shown in (a), a rectangular break appears in the incident field. The topological structure constructed based on the Stokes parameters of the incident beam after the break is as follows: Figure 3 As shown in (b), the topological structure of the incident beam is no longer complete, and its skyrmion number is only -0.39, indicating that the incident beam no longer has skyrmion topology. The incident field is focused by an objective lens, and the intensity and polarization distribution of the focal field are shown in Figure 3 As shown in (c), the focal field is restored to a complete light spot, and its polarization distribution is non-uniform. The topological structure constructed based on the Stokes parameters of the focal field is shown in Figure 3 As shown in (d), it can be seen that the focal field has a complete topological structure and its skyrmion number is -0.96, indicating that there is skyrmion topology in the focal field.

[0058] Under the action of the 60° sector mask, the intensity and polarization distribution of the incident beam are as follows: Figure 4 As shown in (a), a fan-shaped break appears in the incident field. The topological structure constructed based on the Stokes parameters of the incident beam after the break is as follows: Figure 4 As shown in (b), the topological structure of the incident beam is no longer complete, and its skyrmion number is only -0.74, indicating that the incident beam no longer has skyrmion topology. The incident field is focused by an objective lens, and the intensity and polarization distribution of the focal field are shown in Figure 4 As shown in (c), the focal field is restored to a complete light spot, and its polarization distribution is non-uniform. The topological structure constructed based on the Stokes parameters of the focal field is shown in Figure 4 As shown in (d), it can be seen that the focal field has a complete topological structure and its skyrmion number is -0.95, indicating that there is skyrmion topology in the focal field.

[0059] In summary, for skyrmion beams with cross-shaped, rectangular and fan-shaped breaks, the skyrmion topology can be regenerated in the focal field after being focused by the objective lens, which shows the effectiveness of the method proposed in the present invention to overcome beam breaking and generate skyrmion topology.

[0060] The number of devices and processing scales described here are used to simplify the description of the present invention, and the application, modification and variation of the present invention will be obvious to those skilled in the art.

[0061] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A method for overcoming beam breaking to generate skyrmion topology, characterized in that: include: S1. The left-handed Gaussian light is coherently superimposed with the high-order right-handed Laguerre-Gaussian light to generate a skyrmion beam with a specific topological structure; the Laguerre-Gaussian beam expression is The fundamental mode expression of Laguerre-Gaussian beam is: is the Laguerre polynomial, Describes the change of beam radius with propagation distance z, w0 is the beam waist radius, is the Rayleigh distance, p is the radial index, R(z)=z[1+(z R / z) 2 ] is the wavefront curvature radius, l is the orbital angular momentum topological charge, k = 2π / λ is the wave number, λ is the wavelength of the incident light, ψ(z)=tan-1(z / zR) is the Gouy phase; S2. constructing shielding masks with different shapes to shield the skyrmion beam, thereby introducing different shapes of breaks during beam propagation; wherein the shapes of the shielding masks include but are not limited to fan-shaped, rectangular, cross-shaped and irregular shapes; S3. Use an objective lens to focus the broken skyrmion beam, analyze the focal field, observe its intensity and topological state distribution, evaluate the robustness of the skyrmion beam under different breaking conditions and the effect of focusing on the reconstruction of the broken skyrmion beam.

2. According to claim 1, a method for overcoming beam breaking to generate skyrmion topology is characterized in that: In step S1, the superposition of left-handed Gaussian light and high-order right-handed Laguerre-Gaussian light is a key step in generating skyrmion beams. Skyrmion beams of different orders can be generated by controlling the topological charge of the orbital angular momentum carried by the high-order Laguerre-Gaussian light.

3. A method for overcoming beam breaking to generate skyrmion topology according to claim 1, characterized in that: In step S2, when analyzing the skyrmion topological state of the light beam, the Stokes parameter is measured to characterize the polarization distribution of the light beam and to construct the skyrmion vector of the light beam to observe the influence of the breaking on the skyrmion beam.

4. A method for overcoming beam breaking to generate skyrmion topology according to claim 1, characterized in that: In step S3, an objective lens is used to focus the broken skyrmion beam, and the beam is focused on the focal plane. The field distribution of the focal field is obtained by the Richard Wolf vector diffraction formula, and the Stokes parameters of the focal field are calculated to regenerate the skyrmion topological state.

5. A method for overcoming beam breaking to generate skyrmion topology according to claim 1, characterized in that: In step S3, the simulation results are analyzed in depth, and the performance of the skyrmion beam under different conditions is evaluated by performing multiple numerical simulations by adjusting the shape of the broken beam. The reconstruction of the skyrmion beam under various broken beams is relatively ideal, which shows that the focusing process can effectively overcome the adverse effects of the broken beam on the skyrmion beam and regenerate the skyrmion topology in the focal field.

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