Broadband light skyrmion generator

Abstract

The invention provides a broadband light skyrmion generator, which belongs to the technical field of light field regulation and control, and comprises a spin-orbit coupling function unit which has optical anisotropy in rotational symmetry distribution and is used for modulating the polarization state of incident light so as to generate a light field covering all polarization states of a Poincare sphere; the focusing effect function unit has lens type transmission phase distribution and is used for performing spatial reconstruction on the polarization state of the modulated light field; under the combined action of the spin-orbit coupling function unit and the focusing effect function unit, optical Stokes vector distribution of a focusing light field on a focus cross section forms an optical Skyrmion topological structure. According to the optical skyrmion generator, the optical skyrmion generator with a large available bandwidth is realized, and the application of the optical skyrmion in the field of information transmission is promoted.

Description

Technical Field

[0001] This invention relates to the field of optical field manipulation technology, and in particular to a broadband optical skyrmion generator. Background Technology

[0002] Skyrmons are topological states widely found in various condensed matter physics systems and fields. For example, skyrmons with diverse topological forms can be generated in ferroelectric and ferromagnetic materials. Utilizing the topological protection properties and the rich variety of skyrmons' topological states, it is hoped that skyrmons can be used in information storage and transmission to achieve high-density information storage and robust information transmission. Although significant progress has been made with skyrmons in ferroelectric and ferromagnetic materials, in these condensed matter systems, skyrmons are localized to specific spatial locations within the material, making them difficult to use for long-distance information transmission.

[0003] As electromagnetic waves, light fields possess advantages such as multiple physical degrees of freedom and high transmission speed, making them ideal carriers for high-speed, high-capacity information transmission. Therefore, constructing optical skyrmions and achieving robust transmission of them in free space is a crucial path to promoting their application in information transmission. Currently, the optical components used in series in the optical path for generating optical skyrmions have specific operating bandwidths, limiting their generation to a narrow usable bandwidth and lacking an effective scheme for generating broadband optical skyrmions. Summary of the Invention

[0004] This invention provides a broadband optical skyrmion generator, which realizes an optical skyrmion generator with a large available bandwidth, and is conducive to promoting the application of optical skyrmions in the field of information transmission.

[0005] In a first aspect, the present invention provides a broadband optical skyrmion generator, comprising: The spin-orbit coupling functional unit, with rotationally symmetric optical anisotropy, is used to modulate the polarization state of incident light to generate an optical field covering all polarization states of the Poincaré sphere. The focusing effect functional unit has a lens-type transmission phase distribution and is used to spatially reconstruct the polarization state of the modulated optical field. Under the combined action of the spin-orbit coupling functional unit and the focusing effect functional unit, the optical Stokes vector distribution of the focused light field on the focal section constitutes the optical skyrmion topology.

[0006] According to the broadband optical skyrmion generator provided by the present invention, the orientation angle θ of the optical anisotropy principal axis of the spin-orbit coupling functional unit and the spatial azimuth angle of the optical anisotropy principal axis of the spin-orbit coupling functional unit are respectively... satisfy: θ= + 0; in, 0 is a fixed offset angle.

[0007] According to the present invention, in a broadband optical skyrmion generator, the optical anisotropic principal axes of the spin-orbit coupling functional unit are arranged tangentially, radially, or in a torsional manner.

[0008] According to the broadband optical skyrmion generator provided by the present invention, the center thickness d of the spin-orbit coupling functional unit along the light propagation direction satisfies the following non-half-wave and non-full-wave conditions: 2(n e -n o )d / λ≠m; Where λ is the center operating wavelength, m is any integer, and n e and n o , respectively, are the refractive indices of the optical anisotropic materials constituting the spin-orbit coupling functional unit in the two orthogonal principal axis directions, and n e ≠n o .

[0009] According to the present invention, a broadband optical skyrmion generator is provided, wherein the spin-orbit coupling functional unit is composed of a medium with birefringence characteristics, and the optical axis direction of the medium continuously changes with the spatial azimuth angle in a plane perpendicular to the light propagation direction.

[0010] According to the present invention, a broadband optical skyrmion generator is provided, wherein the medium is a solid crystal, a liquid crystal functional device, or a subwavelength structure metasurface.

[0011] According to the present invention, a broadband optical skyrmion generator is provided, wherein the focusing effect functional unit is a transmission optical focusing structure, including a plano-convex lens, a biconvex lens, a conical lens, a spherical lens, an aspherical lens, or a Fresnel lens.

[0012] According to the present invention, a broadband optical skyrmion generator is provided in which the spin-orbit coupling functional unit and the focusing effect functional unit are integrated into a single optical element.

[0013] According to the present invention, a broadband light skyrmion generator is provided, wherein the incident light is circularly polarized light, elliptically polarized light, or linearly polarized light; when the incident light is circularly polarized light, the focused light field forms Stokes skyrmions; when the incident light is linearly polarized light, the focused light field forms quadrature skyrmions; and when the incident light is elliptically polarized light, the focused light field forms biskyrmions.

[0014] According to a broadband optical skyrmion generator provided by the present invention, the spin-orbit coupling functional unit and the focusing effect functional unit are configured as multiple units and arranged on a substrate to form an optical functional structure array.

[0015] This invention achieves both spin-orbit coupling and focusing functions simultaneously through a spin-orbit coupling functional unit and a focusing effect functional unit. Utilizing the combined effect of these two optical responses, the polarization state of the light field completely covers the Poincaré sphere on the cross-section of the focal light field, and the optical Stokes vector exhibits skyrmion topological state characteristics. This structure does not rely on micro / nano structures with specific wavelength resonance, but rather on the combined effect of geometric phase and transmission phase. Its skyrmion generation effect is insensitive to wavelength changes, thus naturally possessing broadband characteristics. This overcomes the narrow operating bandwidth limitation of existing technologies and has significant potential application value in the field of optical communication. Furthermore, the broadband optical skyrmion generator is not only applicable to the visible light band but can also be extended to infrared, terahertz, and other bands, exhibiting broad applicability. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of a broadband optical skyrmion generator provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the focal field characteristics of an independent spin-orbit coupling functional unit and a focusing effect functional unit provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of another broadband optical skyrmion generator provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the distribution of Stokes vectors in optical skyrmions generated by a broadband optical skyrmion generator under different incident wavelength conditions according to an embodiment of the present invention; Figure 5 This is a schematic diagram showing the distribution of the Stokes vector in optical skyrmions generated by a broadband optical skyrmion generator under three polarization incident conditions, according to an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0019] Figure 1 This is a schematic diagram of a broadband optical skyrmion generator provided in an embodiment of the present invention. Figure 1 As shown, the broadband optical skyrmion generator includes a spin-orbit coupling functional unit 100 and a focusing effect functional unit 200. The spin-orbit coupling functional unit 100 has rotationally symmetric optical anisotropy and is used to modulate the polarization state of the incident light to generate an optical field covering all polarization states of the Poincaré sphere. The focusing effect functional unit 200 has a lens-type transmission phase distribution and is used to spatially reconstruct the polarization state of the modulated optical field. Under the combined action of the spin-orbit coupling functional unit 100 and the focusing effect functional unit 200, the optical Stokes vector distribution of the focused optical field on the focal section constitutes the optical skyrmion topology.

[0020] Specifically, a broadband optical skyrmion generator refers to a device capable of stably generating optical skyrmion topologies over a relatively wide wavelength range. The spin-orbit coupling functional unit 100 refers to an optical functional structure with rotationally symmetric optical anisotropy, capable of modulating the spatial distribution of the polarization state of incident light, thereby generating rich spatially varying polarization states in the outgoing light field. This unit achieves modulation of the light field through a geometric phase mechanism, its core feature being the rotationally symmetric distribution of the principal axes of optical anisotropy in a plane perpendicular to the optical axis. Rotationally symmetric optical anisotropy refers to the principal axis directions of the optically anisotropic material being arranged in a regular rotationally symmetric manner around a central axis in a plane perpendicular to the direction of light propagation. This distribution results in different optical axis orientations of the material at different azimuth angles, thus applying azimuth-dependent phase modulation to the incident light.

[0021] The focusing effect functional unit 200 refers to an optical structure with a lens-type transmission phase distribution, capable of applying spherical or parabolic phase modulation to transmitted light, thereby converging parallel incident light to the focal position. The lens-type transmission phase distribution refers to the phase distribution characteristic where the phase changes proportionally to the square of the radial distance; it is the physical essence of a lens's focusing function. The Poincaré sphere is a three-dimensional unit spherical representation used to completely describe the polarization state of light. Each point on the sphere corresponds to a polarization state; the north and south poles represent left-handed and right-handed circular polarization, respectively, points on the equator represent linear polarization, and other positions represent elliptical polarization. The Stokes vector is a vector composed of four parameters used to describe the polarization state of light waves: S0, S1, S2, and S3. S0 represents light intensity, and S1, S2, and S3 describe the polarization state. At the focal section, the light field at each point has a corresponding Stokes vector. The optical skyrmion topology refers to the vortex-like distribution pattern with topological protection properties formed by the Stokes vectors of the light field in space. This structure consists of continuous, smooth vector field entanglement, has a definite topological charge number, i.e., skymin number, and is robust to external disturbances.

[0022] The generation of optical skyrmions is achieved through the synergistic effect of the spin-orbit coupling functional unit 100 and the focusing effect functional unit 200. First, incident light illuminates the spin-orbit coupling functional unit 100. Due to the rotationally symmetric optical anisotropy of this unit, a spin-orbit coupling effect occurs when light passes through. Specifically, the rotationally symmetric optical anisotropy medium applies geometric phase modulation related to the azimuth angle to light at different spatial positions. For circularly polarized basis vectors, this modulation can be equivalent to: the circularly polarized component with the same rotation direction as the incident light does not carry an additional spatial phase, while the circularly polarized component with the opposite rotation direction carries a helical phase proportional to the spatial azimuth angle. The physical essence of this process is that the rotationally symmetric optical anisotropy medium disrupts the translational symmetry of the system, causing the polarization degree of freedom of light to couple with the spatial mode degree of freedom. As a result, the outgoing light field is no longer uniformly polarized, but contains rich spatially varying polarization states, specifically manifested as the coherent superposition of two circularly polarized components with different rotation directions, one of which carries a helical phase.

[0023] Subsequently, the modulated light field is incident on the focusing effect functional unit 200. This unit has a lens-type transmission phase distribution, applying phase modulation proportional to the square of the radial distance to the transmitted light, thereby converging the light field to the focal plane. Since the two circularly polarized components have different phase distributions—that is, the co-rotating component does not carry a helical phase, while the anti-rotating component does—their intensity distributions on the focal plane are also different. The co-rotating component forms an Airy disk-like distribution with the highest central intensity, while the anti-rotating component forms a donut-shaped distribution with zero central intensity.

[0024] These two intensity distributions coherently superimpose on the focal plane to form the total optical field. In the central region of the light spot, the same-rotation component dominates, resulting in circular polarization with the same rotation as the incident light. In the peripheral region, the opposite-rotation component dominates, resulting in circular polarization with the opposite rotation as the incident light. In the intermediate transition region, the two components have comparable intensities, resulting in elliptical or linear polarization. Along the radial direction, the polarization state smoothly transitions from circular polarization at the center to circular polarization with the opposite rotation at the periphery, completely covering all polarization states on the Poincaré sphere. This spatial distribution characteristic of polarization states is the optical skyrmion topology. This topology can be fully characterized by measuring the Stokes vector at every point on the focal section.

[0025] Therefore, this embodiment of the invention simultaneously achieves both spin-orbit coupling and focusing functions through the spin-orbit coupling functional unit 100 and the focusing effect functional unit 200. Utilizing the combined effect of these two optical responses, the polarization state of the light field completely covers the Poincaré sphere on the cross-section of the focal light field, and the optical Stokes vector exhibits skyrmion topological state characteristics. This structure does not rely on micro / nano structures with specific wavelength resonance, but rather on the combined effect of geometric phase and transmission phase. Its skyrmion generation effect is insensitive to wavelength changes, thus naturally possessing broadband characteristics. This overcomes the narrow operating bandwidth limitation of existing technologies and has significant potential application value in the field of optical communication. Furthermore, the broadband optical skyrmion generator is not only applicable to the visible light band but can also be extended to infrared, terahertz, and other bands, exhibiting wide applicability.

[0026] In some embodiments, the orientation angle θ of the optical anisotropic principal axis of the spin-orbit coupling functional unit 100 and the spatial azimuth angle of the optical anisotropic principal axis of the spin-orbit coupling functional unit 100 are... satisfy: θ= + 0; in, 0 is a fixed offset angle.

[0027] Specifically, the optical anisotropic principal axis refers to the direction with the higher refractive index in an optically anisotropic material. The orientation angle θ refers to the pointing angle of the optical anisotropic principal axis in a plane perpendicular to the direction of light propagation. This angle is a function of spatial position and determines the magnitude of the geometric phase modulation exerted on the incident light at that position. Spatial azimuth angle. It refers to the azimuth angle of a certain position relative to a reference direction, with the center of the structure as the origin, within a plane perpendicular to the optical axis. The value ranges from 0 to 2π. Fixed offset angle. 0 is a constant angle independent of spatial position, determining the initial offset between the principal axis orientation of optical anisotropy and the spatial azimuth. By selecting different... A value of 0 can achieve different molecular arrangement patterns, such as the corresponding Tangential arrangement of 0=0, corresponding A radial arrangement with 0 = π / 2 or a torsional arrangement between the two.

[0028] The above calculation formula describes the variation of the principal axis orientation of optical anisotropy with spatial position. When circularly polarized light is incident, a tiny region at each spatial position can be considered as a waveplate with a specific optical axis orientation. After the light passes through this region, its polarization state evolution follows the geometric phase principle. Specifically, for the circularly polarized component e in the incident light... σ Where left-handed circular polarization σ=1, right-handed circular polarization σ=-1, and the component of the outgoing light with the same rotational direction as the incident light e σ Without obtaining additional phase modulation, the component e in the opposite direction to the incident light... -σ This yields a geometric phase equal to ±2σθ, where the sign depends on the incident spin.

[0029] Since θ= + 0, therefore the geometric phase obtained by the anti-rotation component is 2σ( + 0)=2σ +2σ 0. Where 2σ Item follows azimuth angle A linear change corresponds to a spiral phase with a topological charge of 2σ; 2σ A constant phase bias of 0 does not affect the topological characteristics of the helical phase. Therefore, the effect of the entire spin-orbit coupling functional unit 100 on the incident circularly polarized light can be described as: generating a component with the same helical direction as the incident light and without a helical phase, and a component with a helical phase and a topological charge of 2σ with the opposite helical direction to the incident light. The relative intensity of these two components is determined by the birefringence phase difference Δ. It is determined that the complex amplitude of the emitted light satisfies the calculation formula E. out =cos(Δφ / 2)e σ +isin(Δφ / 2)e 2iσθ e -σ Where i is a complex number representing the complex amplitude form of the electric field.

[0030] Therefore, the embodiments of the present invention limit θ= + The relationship of 0 enables precise design of the optical response of the spin-orbit coupling functional unit 100, ensuring that the helical phase generated by the spin-orbit coupling effect has a definite topological charge 2σ and changes continuously and smoothly throughout the entire structure, avoiding phase singularities or abrupt changes. Simultaneously, by selecting different... A value of 0 allows for flexible control over the specific shape of the optical field topology, providing design freedom for generating different types of optical topologies.

[0031] Furthermore, according to the aforementioned formula, the polarization state of the outgoing light can be decomposed into a superposition of two circularly polarized light beams with the same rotation direction. For the portion whose rotation direction is consistent with the incident circularly polarized state, i.e., for the circularly polarized component e... σ It does not carry a helical phase, and its intensity distribution at the focal point is an Airy disk. For the portion whose helical direction is opposite to the incident circularly polarized state, i.e., the circularly polarized component e... -σ Because it carries the spiral phase term e 2iσθ The intensity distribution at its focal point is in the shape of a donut.

[0032] For the total optical field, the circular polarization state at the center of the light spot is e σ The outer edge of the light field is a circularly polarized state e with opposite rotation carrying a spiral phase factor. -σ In the radial direction, the polarization state of the light field evolves continuously between the two poles along the meridian of the Poincaré sphere. Therefore, the polarization state of the light field at the focal point can completely cover both Poincaré spheres, thus forming a Stokes-skyrmion topology with a topological charge of ±2, where the incident light is left-handed circularly polarized (positive sign) and right-handed circularly polarized (negative sign). Furthermore, the focal field intensity distribution characteristics of the two circularly polarized components are insensitive to the incident wavelength; that is, changing the wavelength of the incident light over a wide bandwidth does not significantly affect the distribution characteristics of the focal field polarization state, and the spatial distribution characteristics of the light field polarization state are wavelength robust. Therefore, by utilizing the combined effects of optical spin-orbit coupling and focusing, broadband generation of optical skyrmions can be achieved.

[0033] In some embodiments, the optical anisotropic principal axes of the spin-orbit coupling functional unit 100 are arranged tangentially, radially, or torsionally.

[0034] Specifically, tangential alignment refers to an arrangement in which the orientation of the optical anisotropic principal axes is always perpendicular to the line connecting that point and the center of the structure. When a fixed offset angle is used... When θ = 0, the orientation angle θ is equal to the spatial azimuth angle. At any position, the principal axis is perpendicular to the radial direction, that is, along the tangent direction of the circumference. Radial alignment refers to the arrangement in which the orientation of the optical anisotropic principal axes is always along the line connecting that point and the center of the structure. When the offset angle is fixed... When 0 = π / 2, the principal axis points radially at any position. Torsional alignment refers to an arrangement where the orientation of the optical anisotropic principal axes lies between tangential and radial. When a fixed offset angle is used... When 0 takes other values ​​between 0 and π / 2, the principal axis direction and the radial direction maintain a constant non-right angle, forming a spiral arrangement.

[0035] In the corresponding In a 0=0 tangential arrangement, the principal axes of optical anisotropy are everywhere perpendicular to the radial direction. The geometric phase modulation produced by this arrangement results in the spiral phase acquired by the anti-rotational circular polarization component being... This corresponds to a pure vortex phase. In the corresponding... In a radial arrangement where 0 = π / 2, the principal axes of optical anisotropy point radially everywhere. This is equivalent to adding a constant phase offset to the vortex phase, without affecting the topological characteristics of the vortex. In the case of 0 < In the torsional arrangement where 0 < π / 2, the principal axis maintains a constant angle with the radial direction, which is also based on the vortex phase with an additional constant phase offset. Therefore, regardless of the arrangement mode, a spiral phase with a topological charge of 2σ can be generated, only the additional constant phase offset is different.

[0036] Therefore, this invention provides three typical arrangement schemes, all of which can achieve spin-orbit coupling. Tangential and radial arrangements are the two most common and easiest to fabricate, while torsional arrangements offer greater design flexibility. By selecting different arrangement schemes, details of the final skyrmion topology can be fine-tuned, such as rotation direction and symmetry, thereby meeting the needs of different application scenarios.

[0037] In some embodiments, the center thickness d of the spin-orbit coupling functional unit 100 along the light propagation direction satisfies the following non-half-wave condition and non-full-wave condition: 2(n e -n o )d / λ≠m; Where λ is the center operating wavelength, m is any integer, and n e and n o are the refractive indices of the optical anisotropic material constituting the spin-orbit coupling functional unit 100 in the two orthogonal principal axis directions, and n e ≠n o .

[0038] Specifically, the center thickness d refers to the maximum thickness of the spin-orbit coupling functional unit 100 along the direction of light propagation, which can be located, for example, at the geometric center of the spin-orbit coupling functional unit 100. The non-half-wave condition and non-full-wave condition refer to the condition that the birefringent phase difference introduced by the spin-orbit coupling functional unit 100 is not an integer multiple of π. The mathematical expression is 2(n e -n o d / λ≠m, where m is any integer. When m is odd, it corresponds to the half-wave condition; when m is even, it corresponds to the full-wave condition. The center operating wavelength λ refers to the primary operating wavelength targeted by the device design. e Let n be the refractive index of the optically anisotropic material along the principal optical axis. oThe refractive index of the material is in the direction orthogonal to the optical principal axis. The fact that the two are not equal is a sign that the material has birefringence.

[0039] The above formula E out =cos(Δφ / 2)e σ +isin(Δφ / 2)e 2iσθ e -σ The physical meaning lies in controlling the relative weights of the two circularly polarized components. According to the Jones matrix analysis of spin-orbit coupling, the co-rotational component e in the outgoing light field... σ The amplitude coefficient is cos(Δ / 2), anti-rotational component e -σ The amplitude coefficient is sin(Δ / 2), where Δ =2π(n e -n o )d / λ is the birefringence phase difference. When 2(n e -n o When d / λ equals an integer m: if m is even, then Δ =2kπ,cos(Δ / 2)=±1,sin(Δ / 2)=0, the emitted light field contains only the same-rotational component e σ No anti-rotation component is produced, and interference cannot be formed; if m is odd, then Δ =(2k+1)π,cos(Δ / 2)=0, sin(Δ / 2)=±1, the emitted light field contains only the anti-rotation component e -σ Similarly, interference between the two components cannot be formed. Only when 2(n) e -n o When d / λ is not equal to an integer, the amplitude coefficients of both components are not zero, and only then can they coherently superimpose on the focal plane to form a skyrmion topology.

[0040] Therefore, by defining non-half-wave and non-full-wave conditions, this embodiment of the invention ensures that two circularly polarized components simultaneously exist in the output optical field of the spin-orbit coupling functional unit 100, which is a prerequisite for the subsequent formation of the skyrmion topology. More importantly, this condition gives the invention broadband characteristics. Because even if the incident wavelength deviates from the central operating wavelength, 2(n e -n o The value of d / λ will change, but as long as it is not exactly equal to an integer, the two components will still coexist and the skymin substructure will not disappear.

[0041] In some embodiments, the spin-orbit coupling functional unit 100 is composed of a medium with birefringence properties, wherein the optical axis direction of the medium changes continuously with the spatial azimuth angle in a plane perpendicular to the direction of light propagation.

[0042] Specifically, a birefringent medium refers to a material with optical anisotropy, whose refractive index varies with the angle between the polarization direction of the light wave and the principal axis of the material. This type of material has two mutually orthogonal principal axis directions, corresponding to the maximum refractive index n. e and minimum refractive index n o The optical axis direction refers to the direction of the principal axis of optical anisotropy, corresponding to n. e The direction of the optical axis. For liquid crystal materials, the optical axis direction is the direction of the long axis of the molecules; for birefringent crystals, the optical axis direction depends on the crystal cutting method; for metasurfaces, the optical axis direction is determined by the geometric orientation of the anisotropic nanostructure units. A plane perpendicular to the optical axis refers to a cross-sectional plane perpendicular to the direction of light propagation. In this invention, for the spin-orbit coupling functional unit 100, the plane perpendicular to the direction of light propagation is the cross-section of the device. Continuous variation with spatial azimuth means that within the cross-sectional plane, the optical axis direction rotates smoothly and continuously around the center of the structure in a circular direction, without abrupt changes or discontinuities. This is a prerequisite for achieving continuous geometric phase modulation.

[0043] First, the spin-orbit coupling functional unit 100 must be constructed of a birefringent medium, which is the material basis for generating the spin-orbit coupling effect. A birefringent medium has different refractive indices for light with different polarization directions, thus enabling modulation of the polarization state of the incident light. Second, the optical axis of this medium continuously varies with the spatial azimuth angle in a plane perpendicular to the light propagation direction. This characteristic makes the geometric phase modulation applied by the medium to light at different spatial positions related to the azimuth angle. Specifically, when the optical axis changes linearly with the azimuth angle, the geometric phase generated for circularly polarized light is also linearly related to the azimuth angle, thus forming a spiral phase distribution. This continuous variation ensures the smoothness and integrity of the phase modulation, avoiding phase singularities or dislocations.

[0044] Therefore, this embodiment of the invention defines the essential characteristics of the spin-orbit coupling functional unit 100 from both material and structural perspectives. The birefringent medium ensures that the unit has polarization modulation capability; the continuous change of the optical axis direction with the spatial azimuth angle ensures that this modulation has rotational symmetry and can generate a complete helical phase.

[0045] In some embodiments, the medium is a solid crystal, a liquid crystal functional device, or a subwavelength structure metasurface.

[0046] Specifically, solid-state crystals refer to crystalline materials with natural birefringence properties, such as calcite, quartz, and lithium niobate. Through specific cutting and processing methods, the optical axis of the crystal can be made to exhibit rotational symmetry within the cross-section. Liquid crystal functional devices refer to functional devices made of inductive liquid crystal materials, such as commercially available q-wave plates based on fluid dynamic liquid crystals. Through alignment layer processing, liquid crystal molecules can be arranged in a rotationally symmetric manner within the cross-section to achieve the desired optical axis distribution. Liquid crystal devices have advantages such as simple fabrication, low cost, and the ability to be controlled by an electric field. Subwavelength metasurfaces refer to artificial two-dimensional materials composed of an array of anisotropic structural units at the subwavelength scale. By designing the structural orientation of each unit, the desired rotationally symmetric birefringence distribution can be equivalently achieved. Metasurfaces have advantages such as flexible design, high integration, and the ability to simultaneously realize multiple functions.

[0047] For solid-state crystals, a special cutting technique is used to make the optical axis of the crystal rotate within the cross-section, changing its spatial orientation. This method offers advantages such as stable material properties, a wide operating wavelength, and a high damage threshold. For liquid crystal functional devices, an alignment layer is coated on a substrate. Optically or triboelectrically aligned molecules in the alignment layer are then distributed in a rotationally symmetrical manner within the cross-section. Liquid crystal material is then filled in, aligning the molecules along the alignment layer direction to form the desired optical axis distribution. This method is simple to fabricate, low-cost, and allows for dynamic control of the liquid crystal molecule orientation via an applied electric field, enabling tunable functionality. For subwavelength metasurfaces, an array of anisotropic nanostructure units is fabricated on a substrate. Each unit acts as a miniature waveplate, with its optical axis direction determined by the unit's geometric orientation. By designing the orientation of each unit to continuously change with spatial position, the desired rotationally symmetrical birefringent distribution can be achieved. This method offers design flexibility, can simultaneously encode multiple functions, and is easily integrated with other optical components.

[0048] Therefore, the solid-state crystal method in the embodiments of the present invention is suitable for scenarios requiring high stability and high power tolerance; the liquid crystal method is suitable for scenarios requiring low cost, large-area fabrication or dynamic tunability; and the metasurface method is suitable for scenarios requiring high integration, multifunctional composite or special band operation.

[0049] In some embodiments, the focusing effect functional unit 200 is a transmissive optical focusing structure, including a plano-convex lens, a biconvex lens, a conical lens, a spherical lens, an aspherical lens, or a Fresnel lens.

[0050] Specifically, a transmissive optical focusing structure refers to an optical element that allows light to pass through and applies focusing phase modulation to the transmitted light. Compared to a reflective focusing structure, a transmissive structure is easier to integrate with other components and has a simpler optical path design. A plano-convex lens is a lens with one flat surface and the other convex. A biconvex lens is a lens with both convex spherical surfaces, offering stronger focusing capabilities. A conical lens is a lens with a conical surface that can focus parallel light into a linear focal field distributed along the optical axis, rather than a point focal point. A spherical lens is a lens with a spherical surface. An aspherical lens is a lens with an aspherical surface that can correct spherical aberration and obtain a more ideal focused spot. A Fresnel lens is a thin lens that simulates the phase distribution of a lens through a concentric ring-shaped stepped structure, offering advantages such as light weight and thinness.

[0051] These optical focusing structures share a common feature: a lens-type transmission phase distribution, which applies phase modulation to the transmitted light that is proportional to the square of the radial distance. (r)=-kr 2 / (2f), where k is the wavenumber and f is the focal length. This phase distribution causes the plane wavefront to bend into a spherical wavefront, thereby converging parallel light to the focal point. Regardless of the specific form used, the core function of the focusing effect functional unit 200 is to apply the same transmission phase modulation to the two circularly polarized components, converging them to the focal plane. Since the initial phase distributions of the two components are different—one is unspiraled and the other is helical—they form different intensity distributions on the focal plane, ultimately forming a skyrmion topology through interference.

[0052] Therefore, the different lens types in the embodiments of the present invention have different characteristics: plano-convex lenses and biconvex lenses have simple structures; conical lenses can produce special linear focal fields; aspherical lenses can correct aberrations and obtain higher quality skyrmion patterns; Fresnel lenses can achieve thin and lightweight designs. Those skilled in the art can select the appropriate lens type according to specific application requirements.

[0053] For example, in the embodiments of the present invention, the wavelength can be 532nm, the radial and tangential phase delays in the spin-orbit coupling functional unit 100 are 0.8π, and the NA of the focusing effect functional unit 200 is 0.47. Figure 2 This is a schematic diagram of the focal field characteristics of an independent spin-orbit coupling functional unit and a focusing effect functional unit provided in an embodiment of the present invention. The Stokes parameter distribution on the focal field cross section corresponding to the aforementioned specific numerical settings is as follows: Figure 2 It exhibits characteristics of light skyrmions. Among them, Figure 2 The upper diagram corresponds to the Stokes parameter distribution of the focal field when left-handed circularly polarized light is incident; the lower diagram corresponds to the Stokes parameter distribution of the focal field when right-handed circularly polarized light is incident.

[0054] Figure 3 This is a schematic diagram of another broadband optical skyrmion generator provided in an embodiment of the present invention. Figure 1 The structure shown differs from the focusing effect functional unit, which is a discrete component, in that the spin-orbit coupling functional unit is a discrete component. Figure 3 In the broadband optical skyrmion generator with the structure shown, the spin-orbit coupling functional unit and the focusing effect functional unit are integrated into a single optical element 300.

[0055] Specifically, the integration of a single optical element 300 refers to the simultaneous realization of spin-orbit coupling and focusing effects on a single physical entity, rather than a combination of discrete optical elements. This single optical element simultaneously possesses rotationally symmetric optical anisotropy and a lens-like geometry or phase distribution, enabling it to simultaneously generate spin-orbit coupling and focusing effects on incident light. Such integrated elements can be implemented in various ways. For example, a lens surface can be directly fabricated on a liquid crystal device with a rotationally symmetric birefringence distribution, giving the element both a rotationally symmetric molecular arrangement and a plano-convex lens geometry. The rotationally symmetric molecular arrangement is used to achieve spin-orbit coupling, while the plano-convex lens geometry is used for focusing. Another example is in metasurface design, where each nanostructure unit simultaneously encodes two functions: geometric phase is achieved through unit orientation, and transmission phase is achieved through unit size or shape. The geometric phase is used for spin-orbit coupling, and the transmission phase is used for focusing. In this way, a single metasurface layer can simultaneously achieve both functions. When incident light shines on such an integrated element, the light undergoes both spin-orbit coupling modulation and focusing phase modulation simultaneously during its passage through the element. The two effects do not occur in separate steps, but rather act simultaneously and synergistically on the light field. The resulting Stokes vector distribution on the focal plane is consistent with the discrete element scheme, thus forming the optical skyrmion topology.

[0056] Therefore, by integrating two functional units into a single optical element 300, this embodiment of the invention achieves further miniaturization and integration of the device. Compared to discrete component solutions, the integrated solution reduces the number of components, simplifies optical path design and assembly; eliminates alignment errors between components, improving system stability and reliability; further reduces device size, making it more suitable for integrated optical systems; and lowers overall cost.

[0057] In some embodiments, the incident light is circularly polarized, elliptically polarized, or linearly polarized; when the incident light is circularly polarized, the focused light field forms a Stokes skyrmion; when the incident light is linearly polarized, the focused light field forms a tetrad; and when the incident light is elliptically polarized, the focused light field forms a biskyrmion.

[0058] Specifically, the endpoint of the electric vector of circularly polarized light traces a circle over time, representing the most uniform polarization state. The electric vector of linearly polarized light vibrates in a fixed direction. The endpoint of the electric vector of elliptically polarized light traces an ellipse, representing a general form between linear and circular polarization. Stokes skyrmions, tetrads, and biskyrmions are three different types of optical Stokes vector topologies that describe different patterns of the spatial distribution of polarization states within the focal plane.

[0059] When the incident light is circularly polarized, the system exhibits the highest symmetry. When the incident light is left-handedly circularly polarized, the number of skyrmions produced is 2; when the incident light is right-handedly circularly polarized, the number of skyrmions produced is -2. Ultimately, at the focal plane, a rotationally symmetric pattern of polarization states smoothly transitions from a central point (e.g., left-handed circular polarization) to another peripheral point (e.g., right-handed circular polarization) is formed, which is the standard Stokes skyrmion, with a topological charge of ±2. When the incident light is linearly polarized, it can be decomposed into a superposition of equal amplitude left-handed and right-handed circularly polarized light. These two circularly polarized components interact with the structure, each producing a set of helical phase modulations with opposite phases. At the focal plane, these two sets of patterns coherently superimpose, resulting in four characteristic regions in the polarization state distribution, forming a topological structure with four lobes, i.e., a tetrad. When the incident light is elliptically polarized, it can be decomposed into two left-handed and right-handed circularly polarized light with unequal amplitudes. Their interaction lies between the two cases mentioned above, forming a complex pattern in the focal plane composed of nested or combined two skyrmions, namely, double skyrmions.

[0060] Therefore, by simply changing the polarization state of the external incident light without altering the device itself, this invention can generate various optical topologies such as skyrmions, tetradions, and double skyrmions at the output, greatly expanding the device's application scenarios and enabling it to adapt to different optical coding, information processing, or particle manipulation needs. More importantly, this ability to generate different topologies is also wavelength-insensitive, demonstrating its broadband characteristics.

[0061] In some embodiments, a plurality of spin-orbit coupling functional units 100 and focusing effect functional units 200 are configured and arranged on a substrate to form an optical functional structure array.

[0062] Specifically, the substrate is the substrate material used to support and carry the functional units, and can be transparent or opaque materials such as glass, silicon wafers, and polymer films. An optical functional structure array refers to a combination of multiple functional units arranged in a certain pattern on the same substrate. Each array unit can be a combination of discrete spin-orbit coupling functional units 100 and focusing effect functional units 200, or it can be a single optical element integrating both functions.

[0063] Multiple spin-orbit coupling functional units 100 and focusing effect functional units 200, or a single optical element integrating both functions, are fabricated on a substrate and arranged in a specific pattern to form an array. During fabrication, multiple functional units can be simultaneously formed on the substrate using various methods such as spin coating-heat treatment, inkjet printing, and template-assisted fabrication. By controlling process parameters, the position, size, and spacing of each unit can be precisely controlled to form the desired array arrangement. During operation, when incident light simultaneously covers the entire array area, each array unit independently modulates the optical field of its corresponding region, generating its own optical skyrmion topology at the corresponding position on the focal plane. Therefore, multiple skyrmion patterns appear simultaneously on the focal plane, forming a skyrmion array. The size of each array unit determines the spatial scale of a single skyrmion, while the spacing between units determines the array density.

[0064] Therefore, this invention, by expanding a single functional unit into an array structure, achieves the parallel generation of multiple optical skyrmions. This improves information processing capabilities, allowing for the simultaneous generation, transmission, or processing of multiple optical skyrmions, which is crucial for high-capacity optical information encoding and parallel optical computing. It also meets the development needs of integrated photonics for high-density, multifunctional devices. The position and size of each unit in the array can be designed as needed, providing great design flexibility. Furthermore, the fabrication process is compatible with that of a single unit, without adding additional complexity.

[0065] The working principle of a broadband optical skyrmion generator is explained in detail below with a specific embodiment: First, the rotational anisotropy of the spin-orbit coupling functional unit 100 generates optical spin-orbit coupling. Under the influence of spin-orbit coupling, abundant polarization states are generated in the outgoing light, which can then be used to further construct optical skyrmions. For example, the circularly polarized component e in the incident light... σ After being coupled by the spin-orbit coupling function unit 100, it will be converted into circularly polarized e with opposite rotation direction. -σ It also carries the spiral phase factor e 2iσθ Under the focusing effect of the focusing unit 200, the circularly polarized component e, which does not contain a spiral phase factor, is focused. σ It will form an Airy spot-like focused intensity distribution, containing circularly polarized components with opposite spiral directions of the spiral phase factor e. -σ This will result in a donut-shaped intensity distribution. After coherent superposition, the polarization state of the total light field exhibits the following characteristics: the center of the light field is in a circularly polarized state e. σ The outer edge of the light field is circularly polarized with opposite rotation e -σ In the radial direction, the polarization state of the light field evolves between the two poles along the meridian of the Poincaré sphere, i.e., from e σ Circular polarization evolves into e -σCircular polarization, with a rotationally symmetric spatial distribution of polarization states. These characteristics indicate that the light field generated at the focal point is composed of Stokes-skyrmions, with a skyrmion number of ±2.

[0066] Although the above-described optical spin-orbit coupling process is sensitive to the wavelength of the incident light, the two circularly polarized states of the outgoing light always exhibit a specific phase relationship, which satisfies the following calculation formula: E out =cos(Δφ / 2)e σ +isin(Δφ / 2)e 2iσθ e -σ Utilizing this characteristic, an optical focusing effect is introduced, resulting in a specific intensity distribution in the focused fields of the two circularly polarized lights, e σ For the intensity distribution of Airy disks, e -σ The specific focusing field, denoted as a donut-shaped intensity distribution, is a Stokes-skyrmion and is insensitive to the wavelength of incident light over a wide bandwidth. Therefore, broadband optical skyrmions can be generated using the spin-orbit coupling functional unit 100 and the focusing effect functional unit 200.

[0067] The above analysis is based on the case where the incident light is circularly polarized. Building upon this, changing the polarization state of the incident light yields a wider variety of optical topologies. When the incident light is linearly polarized, a tetrad-type optical Stokes topology is generated due to the rotational symmetry of the structure. When the incident light is elliptically polarized, a biskymonic optical Stokes topology is generated.

[0068] Figure 4 This is a schematic diagram illustrating the distribution of the Stokes vector in optical skyrmions generated by a broadband optical skyrmion generator under different incident wavelengths, according to an embodiment of the present invention. Figure 4 The incident wavelength corresponding to the top attached image is 450 nanometers. Figure 4 The incident wavelength corresponding to the middle figure is 610 nanometers. Figure 4 The bottom attached diagram corresponds to an incident wavelength of 750 nanometers, and the Stokes vectors include mutually perpendicular vectors S1, S2, and S3. Figure 4 It is known that when the incident light is circularly polarized, the broadband optical skyrmion generator can generate optical Stokes skyrmions in a broadband range of 450 nm to 750 nm, indicating that the broadband optical skyrmion generator proposed in this invention can generate optical skyrmions and has the significant characteristics and advantages of a large usable broadband.

[0069] Figure 5 This is a schematic diagram illustrating the distribution of the Stokes vector in optical skyrmions generated by a broadband optical skyrmion generator under three polarization incident conditions, according to an embodiment of the present invention. Figure 5 The topmost attached image corresponds to the incident conditions for circularly polarized light. Figure 5 The middle diagram corresponds to the incident conditions of elliptically polarized light. Figure 5 The bottom diagram corresponds to the incident conditions of linearly polarized light. The Stokes vectors include mutually perpendicular vectors S1, S2, and S3. Figure 5 The distribution of the Stokes vector on the cross section of the focal field is given for incident light in circularly polarized, elliptically polarized, and linearly polarized states. When the incident light is circularly polarized, the topological state of the generated optical Stokes vector is a skyrmion; when the incident light is elliptically polarized, the topological state of the generated optical Stokes vector is a biskyrmion; and when the incident light is linearly polarized, the topological state of the generated optical Stokes vector is a tetradion. It is evident that by changing the polarization state of the incident light, a rich variety of optical topological states can be generated using a broadband optical skyrmion generator.

[0070] It should be noted that, under existing conditions, the embodiments of the present invention demonstrate that a light skyrmion generator can be realized using the spin-orbit coupling functional unit 100 and the focusing effect functional unit 200, with an usable bandwidth covering the visible light range, and capable of generating various optical topological states, including skyrmions, biskyrmions, and tetrads. Further analysis based on this is also feasible; that is, by adjusting the size parameters and optical anisotropy parameters of the spin-orbit coupling functional unit 100 and the focusing effect functional unit 200, the generation of optical skyrmions in other wavelength bands, such as in the infrared and even terahertz bands, is entirely feasible. Therefore, the present invention not only exhibits excellent performance in the field of light skyrmion generation but also has significant multi-band applicability value.

[0071] In summary, this invention has the following advantages: First, by utilizing the combined effects of optical spin-orbit coupling and focusing, this invention can generate broadband optical skyrmions, effectively overcoming the shortcomings of existing technologies that can only operate within a single wavelength or narrow band. Second, it can realize micrometer-scale optical skyrmion generators, meeting the requirements of integrated development of photonic devices. Third, the broadband optical skyrmion generator can not only generate typical skyrmion topologies, but also tetrads and biskyrmion topologies. These multi-topologies are expected to broaden the application of optical skyrmions in high-capacity information transmission. Fourth, the broadband optical skyrmion generator has wide applicability, not only applicable to the optical band, but also extending to the infrared and even terahertz bands, possessing significant application value. Fifth, the spin-orbit coupling functional unit 100 and the focusing effect functional unit 200 can be flexibly arrayed as needed, thereby obtaining arrayed optical skyrmions. This results in a compact broadband optical skyrmion generator, which has advantages such as broadband availability, compact size, ability to generate multiple topologies, wide applicability, high processing efficiency, and low cost. It has broad application and development prospects in the field of optical skyrmion generation and control.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A broadband optical skyrmion generator, characterized in that, include: The spin-orbit coupling functional unit, with rotationally symmetric optical anisotropy, is used to modulate the polarization state of incident light to generate an optical field covering all polarization states of the Poincaré sphere. The focusing effect functional unit has a lens-type transmission phase distribution and is used to spatially reconstruct the polarization state of the modulated optical field. Under the combined action of the spin-orbit coupling functional unit and the focusing effect functional unit, the optical Stokes vector distribution of the focused light field on the focal section constitutes the optical skyrmion topology.

2. The broadband optical skyrmion generator according to claim 1, characterized in that, The orientation angle θ of the optical anisotropic principal axis of the spin-orbit coupling functional unit and the spatial azimuth angle of the optical anisotropic principal axis of the spin-orbit coupling functional unit. satisfy: θ= + 0; in, 0 is a fixed offset angle.

3. The broadband optical skyrmion generator according to claim 2, characterized in that, The optical anisotropic principal axes of the spin-orbit coupling functional unit are arranged tangentially, radially, or torsionally.

4. The broadband optical skyrmion generator according to claim 1, characterized in that, The center thickness d of the spin-orbit coupling functional unit along the light propagation direction satisfies the non-half-wave condition and the non-full-wave condition: 2(n e -n o )d / λ≠m; Where λ is the center operating wavelength, m is any integer, and n e and n o , respectively, are the refractive indices of the optical anisotropic materials constituting the spin-orbit coupling functional unit in the two orthogonal principal axis directions, and n e ≠n o .

5. The broadband optical skyrmion generator according to claim 1, characterized in that, The spin-orbit coupling functional unit is composed of a medium with birefringence properties, and the optical axis of the medium changes continuously with the spatial azimuth angle in a plane perpendicular to the direction of light propagation.

6. The broadband optical skyrmion generator according to claim 5, characterized in that, The medium is a solid crystal, a liquid crystal functional device, or a subwavelength structure metasurface.

7. The broadband optical skyrmion generator according to claim 1, characterized in that, The focusing effect functional unit is a transmission optical focusing structure, including a plano-convex lens, a biconvex lens, a conical lens, a spherical lens, an aspherical lens, or a Fresnel lens.

8. The broadband optical skyrmion generator according to claim 1, characterized in that, The spin-orbit coupling functional unit and the focusing effect functional unit are integrated into a single optical element.

9. The broadband optical skyrmion generator according to any one of claims 1-8, characterized in that, The incident light is circularly polarized, elliptically polarized, or linearly polarized; when the incident light is circularly polarized, the focused light field forms a Stokes skyrmion; when the incident light is linearly polarized, the focused light field forms a tetrad; when the incident light is elliptically polarized, the focused light field forms a biskyrmion.

10. The broadband optical skyrmion generator according to any one of claims 1-8, characterized in that, The spin-orbit coupling functional unit and the focusing effect functional unit are configured as multiple units and arranged on the substrate to form an optical functional structure array.

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