Metasurface structures for on-chip focusing column vector beams and on-chip detection devices

Abstract

A metasurface structure for on-chip focusing of a column vector beam includes: a plurality of first spin-response structural units, each of which includes: an elongated first nanoslit; and an elongated second nanoslit, wherein the major axis of the second nanoslit is perpendicular to the major axis of the first nanoslit. The center points of the plurality of first nanoslits are arranged at uniform intervals along a semi-circular trajectory. The plurality of second nanoslits are located radially outside the semi-circular trajectory. For the same first spin-response structural unit, the angle bisector between the major axes of the first and second nanoslits is in the same direction as the tangent of the semi-circular trajectory at the center point of the first nanoslit, so that when the column vector beam is perpendicularly irradiated onto the metasurface structure, it is focused at a point on the metasurface structure. An on-chip detection device for detecting the order of a column vector beam, including the above metasurface structure, is also proposed.

Description

Technical Field

[0001] This application belongs to the field of optical technology, and in particular relates to a metasurface structure for on-chip focusing of a cylindrical vector beam and an on-chip detection device for detecting the order of the cylindrical vector beam. Background Technology

[0002] Cylindrical vector beams (CVBs) are a novel type of vortex beam that can be decomposed into two orthogonal vortex beams with opposite topological charges. Compared to traditional vortex beams, CVBs, in addition to being orthogonal to each other at different orders, are also orthogonal to each other at the same order with a 90° phase difference. Due to this dual orthogonality, CVBs are widely used in fields such as high-capacity optical communication.

[0003] In current applications of cylindrical vector beams, to maximize their performance, it is typically necessary to focus the beam and detect its order by detecting the focal point. However, this usually requires multiple optical components, a large optical system, a complex detection process, and low diffraction efficiency, which limits the application range of cylindrical vector beams. Therefore, how to achieve on-chip integration and detection of cylindrical vector beams using a simple mechanism remains a challenge. Summary of the Invention

[0004] In view of the above, this application proposes a metasurface structure for on-chip focusing of cylindrical vector beams and an on-chip detection device for detecting the order of cylindrical vector beams, so as to solve the problems of difficult on-chip integration and detection of cylindrical vector beams in the current industry.

[0005] The technical solution adopted in this application is as follows.

[0006] According to a first aspect of this application, a metasurface structure for on-chip focusing column vector beams is provided, comprising: a plurality of first spin-responsive structural units, wherein each first spin-responsive structural unit comprises:

[0007] The first nano-slit is elongated; and

[0008] The elongated second nano-slit has its major axis perpendicular to the major axis of the first nano-slit.

[0009] In this configuration, the center points of multiple first nano-slits are arranged at uniform intervals along a semi-circular trajectory, and multiple second nano-slits are located radially outside the semi-circular trajectory.

[0010] For the same first spin response structural unit, the angle bisector between the major axis of the first nanoslit and the major axis of the second nanoslit is in the same direction as the tangent of the semi-circular trajectory at the center point of the first nanoslit, so that when the cylindrical vector beam is perpendicularly irradiated onto the metasurface structure, it is focused at a point on the metasurface structure.

[0011] According to a second aspect of this application, an on-chip detection device is provided for detecting the order of a cylindrical vector beam, comprising:

[0012] A cylindrical vector beam generator is used to generate cylindrical vector beams.

[0013] According to the metasurface structure of the first aspect of this application, the optical axis of the cylindrical vector beam generated by the cylindrical vector beam generator is perpendicular to the metasurface structure to excite surface plasmons on the metasurface structure.

[0014] A near-field acquisition device for acquiring the electric field distribution of excited surface plasmons; and

[0015] The processor is configured to: receive the electric field distribution acquired by the near-field acquisition device, calculate the focal point of the surface plasmon on the metasurface structure based on the electric field distribution, calculate the distance x between the focal point and the origin of the semi-circular trajectory, and calculate the order m of the cylindrical vector beam based on the distance x.

[0016] The above is only a brief overview of the technical solution proposed in this application. The technical solution proposed in this application may have various further embodiments or implementation methods, which will be described in more detail below. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of a metasurface structure provided according to an embodiment of the first aspect of this application.

[0019] Figure 2 This is a partial schematic diagram of a metasurface structure provided according to an embodiment of the first aspect of this application.

[0020] Figure 3 This is a schematic diagram of two metasurface structures provided according to an embodiment of the first aspect of this application, and a schematic diagram of the electric field distribution of the surface plasmons excited therefrom.

[0021] Figure 4 This is a schematic diagram of two metasurface structures provided according to another embodiment of the first aspect of this application, and a schematic diagram of the electric field distribution of the surface plasmons excited therefrom.

[0022] Figure 5 This is a schematic diagram of two metasurface structures provided according to another embodiment of the first aspect of this application, and a schematic diagram of the electric field distribution of the surface plasmons excited therefrom.

[0023] Figure 6 This is a schematic diagram of a metasurface structure provided according to yet another embodiment of the first aspect of this application.

[0024] Figure 7 This is a schematic diagram of a metasurface structure provided according to yet another embodiment of the first aspect of this application.

[0025] Figure 8 This is a schematic diagram of a metasurface structure provided according to another embodiment of the first aspect of this application.

[0026] Figure 9 This is a schematic diagram of an on-chip detection device according to an embodiment of the second aspect of this application.

[0027] Figure 10 This is a schematic diagram of an on-chip detection device according to another embodiment of the second aspect of this application.

[0028] Figure 11 The relationship between the order m of the cylindrical vector beam and the distance x from the focal point to the origin is illustrated schematically. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0030] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0031] It should be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. It is worth noting that the sizes of the various structures shown in the accompanying drawings of this application are merely exemplary and not a limitation on the actual application of the technical solution of this application.

[0032] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified. The terms "comprising," "including," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0033] Before describing the specific embodiments of this application, a brief introduction to cylindrical vector beams will be given to facilitate a deeper understanding of the technical solutions of this application. For a cylindrical vector beam J of order m... m It can be expressed as follows:

[0034]

[0035] Where m is the polarization order of the cylindrical vector beam, ψ is the angular angle of the cylindrical vector beam, and φ0 is the initial phase angle of the cylindrical vector beam. From the above expression, it can be seen that a cylindrical vector beam J of order m... m The beam can be viewed as a superposition of a left-handed circularly polarized beam E1 with a topological charge of -m and a right-handed circularly polarized beam E2 with a topological charge of m. Therefore, achieving on-chip focusing of the cylindrical vector beam only requires achieving on-chip focusing of the left-handed and / or right-handed circularly polarized beams of the cylindrical vector beam. Then, by detecting the on-chip focusing position of the left-handed and / or right-handed circularly polarized beams, the order m of the cylindrical vector beam can be detected.

[0036] According to an embodiment of the first aspect of this application, a metasurface structure 100 for on-chip focusing column vector beams is provided, such as... Figure 1As shown in (a) and (b), it may include: a plurality of first spin-response structural units 110, wherein each first spin-response structural unit 110 includes: an elongated first nanoslit 111; and an elongated second nanoslit 112, wherein the major axis of the second nanoslit 112 is perpendicular to the major axis of the first nanoslit 111, the center points of the plurality of first nanoslits 111 are arranged at uniform intervals along a semi-circular trajectory, the plurality of second nanoslits 112 are located radially outside the semi-circular trajectory, and for the same first spin-response structural unit 110, the angle bisector between the major axis of the first nanoslit 111 and the major axis of the second nanoslit 112 is in the same direction as the tangent of the semi-circular trajectory at the center point of the first nanoslit 111, so that when the cylindrical vector beam is perpendicularly irradiated onto the metasurface structure 100, it is focused on a point on the metasurface structure 100.

[0037] In this embodiment, since the major axis of the first nanoslit 111 is perpendicular to the major axis of the second nanoslit 112, the center points of the plurality of first nanoslits 111 are arranged at uniform intervals along a semi-circular trajectory, and the plurality of second nanoslits 112 are located radially outside the semi-circular trajectory. Furthermore, the angle bisector between the major axes of the first nanoslits 111 and the second nanoslits 112 has the same direction as the tangent to the semi-circular trajectory at the center point of the first nanoslit 111. This essentially determines the position and arrangement of all slits in the entire metasurface structure 100. As a preferred embodiment, the dimensions of the first nanoslits 111 and the second nanoslits 112 can be the same.

[0038] In this embodiment, when a cylindrical vector beam of order m perpendicularly illuminates the metasurface structure 100, the left-hand circularly polarized light E1 and the right-hand circularly polarized light E2 of the cylindrical vector beam interact with the first nanoslit 111 and the second nanoslit 112, respectively, to excite surface plasmons (SPPs) on the metasurface structure 100. Since the phase difference between the left-hand circularly polarized light E1 and the right-hand circularly polarized light E2 of the cylindrical vector beam is 90° or -90°, the first nanoslit 111 is always perpendicular to the corresponding second nanoslit 112, and the multiple first spin-response structural units 110 composed of multiple first nanoslits 111 and multiple second nanoslits 112 are generally arranged in a semi-circular shape. Therefore, the surface plasmons excited by the multiple first nanoslits and the surface plasmons excited by the multiple second nanoslits will interfere with each other, thereby ultimately achieving focusing of the left-hand circularly polarized light E1 or the right-hand circularly polarized light E2 of the cylindrical vector beam on the metasurface structure. In a preferred embodiment of this invention, the axis of the cylindrical vector beam coincides with the origin of the semi-circular trajectory, thereby achieving a better focusing effect for the cylindrical vector beam.

[0039] It is worth noting that, since the left-hand circularly polarized light E1 and the right-hand circularly polarized light E2 of the cylindrical vector beam have a phase difference of 90° or -90°, the metasurface structure of this embodiment is used to excite surface plasmons: when the left-hand circularly polarized light E1 of the cylindrical vector beam excites an inwardly focused surface plasmon on the metasurface structure 100, the right-hand circularly polarized light E2 of the cylindrical vector beam will excite an outwardly divergent surface plasmon on the metasurface structure 100; when the right-hand circularly polarized light E2 of the cylindrical vector beam excites an inwardly focused surface plasmon on the metasurface structure 100, the left-hand circularly polarized light E1 of the cylindrical vector beam will excite an outwardly divergent surface plasmon on the metasurface structure 100. However, this does not affect the detection of the order m of the cylindrical vector beam, because once the metasurface structure 100 in this embodiment is adopted, although the focal points of the surface plasmons excited by the left-hand circularly polarized light E1 and the right-hand circularly polarized light E2 of the same cylindrical vector beam on the metasurface structure 100 are in opposite directions from the origin of the semi-circular trajectory, the distances of the focal points from the origin of the semi-circular trajectory will be the same. Therefore, as long as the left-hand circularly polarized light E1 or the right-hand circularly polarized light E2 of the cylindrical vector beam is focused on the metasurface structure and the position of the focal point is detected by a suitable method, the detection of the order m of the cylindrical vector beam can be indirectly promoted.

[0040] Based on the above embodiments, a metasurface structure according to another embodiment of the first aspect of this application has the basic technical features of the above embodiments, and, based on the above embodiments, such as... Figure 2 As shown (only a portion of the first spin-response structural unit 110 is shown for structural detail), for the same first spin-response structural unit 110, the distance S is the perpendicular segment from the center point of the second nanoslit 112 to the tangent of the semi-circular trajectory at the center point of the first nanoslit 111, and the arc distance d between the intersection of the extension of the perpendicular segment and the semi-circular trajectory and the center point of the first nanoslit 111 is the arc distance on the semi-circular trajectory. S and d satisfy the following relationships:

[0041]

[0042] Where λ0 is the incident wavelength of the cylindrical vector beam, ∈1 is the dielectric constant of air, ∈2 is the dielectric constant of the metasurface structure 100, and λ SPP Let be the propagation wavelength of the surface plasmons excited by the cylindrical vector beam on the metasurface structure 100. Furthermore, the arc distance between the center points of two adjacent first nanoslits on the semi-circular trajectory is D, and D = 2d.

[0043] In this embodiment, the positions of the first nanoslit 111 and the second nanoslit 112 in each first spin-response structural unit 110 are further defined relative to the transmission wavelength λ of the surface plasmons excited on the metasurface structure 100.SPP The relationship between the two adjacent first nanoslits 111 and the transmission wavelength λ of the surface plasmons excited on the metasurface structure 100 is defined. SPP The relationship between these factors is as follows: According to the calculation formula above, once the material of the metasurface structure 100 is determined, the dielectric constant of the metasurface structure 100 is determined to be 2; once the medium in which the metasurface material is located (e.g., air) is determined, the dielectric constant of the medium is determined to be 1; and once the wavelength λ0 of the cylindrical vector beam is determined, the propagation wavelength λ of the surface plasmons excited by the cylindrical vector beam on the metasurface structure 100 is determined. SPP The three parameters ∈1, ∈2, and λ0 uniquely determine the relative positional relationship of the first nanoslit 111 and the second nanoslit 112 in the multiple first spin response structural units 110 of the approximately semi-circular structure, as well as the relative positional relationship of two adjacent first nanoslits 111.

[0044] In this embodiment, through further definition by the above formula, the relative positional relationship between the slits 111 and 112 in the metasurface structure 100 is related to the transmission wavelength λ of the surface plasmons excited on the metasurface structure 100. SPP A close connection was formed due to a transmission wavelength λ of the surface plasmon polariton. SPP The transmission angle is 2π. Since the left-handed circularly polarized light E1 and the right-handed circularly polarized light E2 of the cylindrical vector beam have different chirities and a phase difference of 90° or -90°, both S and d are constrained to the transmission wavelength of a quarter of a surface plasmon polariton, i.e., λ. SPP / 4, which enables the surface plasmons excited by the left-hand circularly polarized light E1 and the right-hand circularly polarized light E2 of the cylindrical vector beam along the angular direction of the semi-circular trajectory on the metasurface structure 100 to interfere destructively, thus retaining only the surface plasmons excited along the radial direction of the semi-circular trajectory. Furthermore, the relative positional relationship between two adjacent first nanoslits 111 is defined as half the transmission wavelength of one surface plasmon, i.e., λ. SPP / 2, which enables the surface plasmons that focus the cylindrical vector beam into the semi-circular trajectory through each of the first spin response structural units 110 to enhance the beam. It is worth noting that, due to the different chirality of the left-handed circularly polarized light E1 and the right-handed circularly polarized light E2 of the cylindrical vector beam, when the left-handed circularly polarized light E1 is focused into the semi-circular trajectory on the metasurface structure 100, the right-handed circularly polarized light E2 will diverge outwards from the semi-circular trajectory; conversely, when the right-handed circularly polarized light E2 is focused into the semi-circular trajectory on the metasurface structure 100, the left-handed circularly polarized light E1 will diverge outwards from the semi-circular trajectory. However, only one of the left-handed circularly polarized light E1 and the right-handed circularly polarized light E2 needs to be focused into the semi-circular trajectory on the metasurface structure 100 to achieve our goal of on-sheet focusing of the cylindrical vector beam, and this also prepares for subsequent order detection of the cylindrical vector beam.

[0045] It is worth noting that since S and d are uniquely determined by parameters ∈1, ∈2, and λ0, i.e. by the transmission wavelength λ of the surface plasmon polariton... SPP Once the radius of the semi-circular trajectory to be designed is determined, the number of first spin structure response units is also uniquely determined. It is worth noting that the radius of the semi-circular trajectory does not affect the focal point of the inwardly focusing surface plasmons. However, for a metasurface structure of a selected material, the propagation depth of the surface plasmons excited on the metasurface structure is constant. Therefore, the radius of the semi-circular trajectory needs to be considered in conjunction with the propagation depth of the surface plasmons; it cannot be too large or too small. If the radius of the semi-circular trajectory is designed to be too large, since the propagation depth of the surface plasmons is constant, the focusing effect may not be achieved.

[0046] Based on the above embodiments, a metasurface structure according to another embodiment of the first aspect of this application has the basic technical features of the above embodiments, and, based on the above embodiments, such as... Figure 3 As shown in (a) and (d), the semi-circular trajectory can be an upper semi-circular trajectory. Exemplarily, and not limitingly, it is assumed that the incident wavelength of the cylindrical vector beam is 633 nm, and the propagation wavelength of the surface plasmons excited on the metasurface structure is... The radial distance S and angular distance d between the first and second nanoslits of the same first spin-response structural unit are both λ. SPP / 4≈150nm, and the angular distance D between two adjacent first nanoslits is λ. SPP / 2≈300nm. Exemplarily, and not limitingly, the thickness of the metasurface structure can be 200nm. Exemplarily, and not limitingly, the length and width of the first and second nanoslits can be 200nm and 40nm, respectively. The above data examples are only for illustrating specific experimental results and are not intended to impose a specific limitation on the size of the metasurface structure of this application. Undoubtedly, the size of the metasurface structure of this application, as well as the size and number of slits therein, can be determined according to actual needs.

[0047] As one implementation method of this embodiment, such as Figure 3 As shown in (a), the leftmost first spin response structural unit among multiple first spin response structural units can be in an inverted V-shape, so that when a cylindrical vector beam is perpendicularly irradiated onto the metasurface structure, as shown in (a). Figure 3 As shown in (c), the right-hand circularly polarized light of the cylindrical vector beam can be focused onto a single point on the metasurface structure, while simultaneously... Figure 3 As shown in (b), the left-handed circularly polarized light of the cylindrical vector beam diverges outward.

[0048] As one implementation method of this embodiment, such as Figure 3 As shown in (d), the leftmost first spin response structural unit among multiple first spin response structural units can be shaped like a herringbone, so that when a cylindrical vector beam is perpendicularly irradiated onto the metasurface structure, as shown in (d), the first spin response structural unit can be shaped like a herringbone, so that when the beam perpendicularly irradiates the metasurface structure, the first spin response structural unit can be shaped like a herringbone, as shown in (d). Figure 3 As shown in (e), the left-handed circularly polarized beam of the cylindrical vector beam is focused at a point on the metasurface structure, while simultaneously... Figure 3 As shown in (f), the right-hand circularly polarized light of the cylindrical vector beam diverges outward.

[0049] In this embodiment, by designing the leftmost first spin response structure unit among a plurality of first spin response structure units that are basically in the upper semi-circular structure to be in the shape of an inverted V-shape or V-shape, the right-hand circularly polarized light or left-hand circularly polarized light of the cylindrical vector beam can be focused at a point inside the upper semi-circular trajectory when the cylindrical vector beam is perpendicularly irradiated by the metasurface structure, thereby achieving on-chip focusing of the cylindrical vector beam.

[0050] It is worth noting that, from Figure 3As can be seen, although the orientation of multiple first spin response structural units, which are essentially in the shape of an upper semi-circular ring, can focus either the right-handed or left-handed circularly polarized light of a cylindrical vector beam onto a single point within the upper semi-circular trajectory, the left-handed and right-handed circularly polarized light, due to their different chirality, focus in the opposite direction from the origin of the upper semi-circular trajectory. Based on this, it is conceivable that by rotating the multiple first spin response structural units, which are essentially in the shape of an upper semi-circular ring, by 180° and then constructing them together with the multiple first spin response structural units, which are also essentially in the shape of an upper semi-circular ring, both the left-handed and right-handed circularly polarized light of the cylindrical vector beam can be simultaneously focused onto the metasurface structure, thereby achieving complete on-chip focusing of the cylindrical vector beam.

[0051] like Figure 4 As shown, by way of example and not limitation, Figure 4 Figure (a) shows the leftmost first spin response structure unit among multiple first spin response structure units, which is an inverted herringbone shape and generally has an upper semi-ring shape. Figure 4 Figure (b) shows a generally lower-ring-shaped response structure obtained by rotating the plurality of first spin response structural units as a whole by 180°. This is illustrative and not limiting. Figure 4 Figure (c) shows a right-handed circularly polarized light with a topological charge of 2 incident perpendicularly on a... Figure 4 The focusing electric field distribution of surface plasmons excited on the response structure, which is generally in the shape of an upper ring, in (a) Figure 4 Image (d) shows a left-handed circularly polarized light with a topological charge of -2 incident perpendicularly on a... Figure 4 The focusing electric field distribution of surface plasmons excited on the response structure, which is generally in the shape of a lower half-ring, in (b).

[0052] like Figure 5 As shown, by way of example and not limitation, Figure 5 Figure (a) shows the leftmost first spin response structure unit among multiple first spin response structure units, which is a herringbone-shaped response structure with a generally upper semi-ring shape. Figure 5 Figure (b) shows a generally lower-ring-shaped response structure obtained by rotating the plurality of first spin response structural units as a whole by 180°. This is illustrative and not limiting. Figure 5 Figure (c) shows a left-handed circularly polarized light with a topological charge of -2 incident perpendicularly on a... Figure 5 The focusing electric field distribution of surface plasmons excited on the response structure, which is generally in the shape of an upper ring, in (a) Figure 5 Figure (d) shows a right-handed circularly polarized light with a topological charge of 2 incident perpendicularly on a... Figure 5The focusing electric field distribution of surface plasmons excited on the response structure, which is generally in the shape of a lower half-ring, in (b).

[0053] In view of the above, based on the above embodiments, as follows Figure 6 As shown, a metasurface structure 200 according to another embodiment of the first aspect of this application has the basic technical features of the above embodiments. Based on the above embodiments, in addition to including multiple first spin-response structures 210 having first nano-slits 211 and second nano-slits 212, the metasurface structure 200 may also include multiple second spin-response structure units 220. Each second spin-response structure unit 220 may include: an elongated third nano-slit 221; and an elongated fourth nano-slit 222, wherein the major axis of the fourth nano-slit 222 is perpendicular to the major axis of the third nano-slit 221. The center points of the multiple third nano-slits 221 are arranged at uniform intervals along the lower half-ring trajectory. The multiple fourth nano-slits 222 are located radially outside the lower half-ring trajectory, which is separated from the upper half-ring trajectory by a transmission wavelength λ. SPP For the same second spin response structural unit, the angle bisector formed by the major axis of the third nano-slit 221 and the major axis of the fourth nano-slit 222 of the concentric semi-circular trajectory has the same direction as the tangent of the lower semi-circular trajectory at the center point of the third nano-slit.

[0054] In this embodiment, since the leftmost and rightmost ends of the lower and upper half-loop tracks cannot overlap, the lower and upper half-loop tracks can be connected at a transmission wavelength λ. SPP The interval is set to an integer multiple, but this does not affect the focusing position of surface plasmons on the metasurface structure. Based on this, the radius of the lower half-loop trajectory can be larger than the radius of the upper half-loop trajectory, which carries the transmission wavelength λ. SPP An integer multiple of the radius of the upper half-circle trajectory, or smaller than the transmission wavelength λ. SPP The radius of the lower half-loop trajectory is an integer multiple of the upper half-loop trajectory. In a preferred embodiment of this invention, the radius of the lower half-loop trajectory is either larger or smaller than the radius of the upper half-loop trajectory by a transmission wavelength λ. SPP .

[0055] As one implementation method of this embodiment, Figure 6 and Figure 7 The diagram schematically illustrates two types of metasurface structures 200 when the radius of the lower half-ring trajectory is smaller than the radius of the upper half-ring trajectory by one transmission wavelength λSPP. As can be seen from the diagram, when the leftmost first spin response structural unit 210 among the multiple first spin response structural units 210 is as follows... Figure 6When the shape is inverted (V-shape), the leftmost second spin response structural unit among the multiple second spin response structural units 220 is V-shaped; when the leftmost first spin response structural unit among the multiple first spin response structural units 210 is as shown... Figure 7 When the shape is V-shaped, the leftmost second spin response structure unit among the multiple second spin response structure units 220 is inverted V-shape, so that when the cylindrical vector beam is perpendicularly irradiated by the metasurface structure, the left-hand circularly polarized light and the right-hand circularly polarized light of the cylindrical vector beam can be simultaneously focused at the same point on the metasurface structure, thereby achieving complete on-chip focusing of the cylindrical vector beam.

[0056] According to an embodiment of the first aspect of this application, for the same second spin-response structural unit, the distance S is the perpendicular segment from the center point of the fourth nano-slit to the tangent line of the lower semi-circular trajectory at the center point of the third nano-slit; the arc distance d is the distance between the intersection of the extension of the perpendicular segment and the lower semi-circular trajectory and the center point of the third nano-slit on the lower semi-circular trajectory; and the arc distance D is the distance between the center points of two adjacent third nano-slits on the lower semi-circular trajectory. The definitions of parameters S, d, and D in this embodiment can be found in the relevant description of the first spin-response structural unit in the above embodiments, and will not be repeated here.

[0057] Based on the above embodiments, a metasurface structure 200 according to another embodiment of the first aspect of this application has the basic technical features of the above embodiments. Furthermore, the metasurface structure may include multiple layers of first spin response structure units and multiple layers of second spin response structure units positioned according to multiple upper semi-circular trajectories and multiple lower semi-circular trajectories, wherein the multiple layers of first spin response structure units and multiple layers of second spin response structure units are interleaved, and each layer is spaced apart by a transmission wavelength λ. SPP The integer multiple setting.

[0058] In one embodiment of this invention, multilayer first spin response structure units and multilayer second spin response structure units are arranged alternately, with each layer spaced apart by a transmission wavelength λ. SPP In this embodiment, each layer is spaced apart by a transmission wavelength λ. SPP The setting refers to the following: when the equivalent radius of the first-layer second spin response structure unit is smaller than the equivalent radius of the first-layer first spin response structure unit, the first-layer first spin response structure unit and the first-layer second spin response structure unit are spaced apart by a transmission wavelength λ. SPP The second-layer second spin response structure unit is configured to be spaced apart from the first-layer first spin response structure unit by a transmission wavelength λ. SPP The second-layer first spin response structure unit is configured to be spaced apart from the second-layer first spin response structure unit by a transmission wavelength λ. SPPThe settings are similar; when the equivalent radius of the first-layer second spin response structure unit is greater than the equivalent radius of the first-layer first spin response structure unit, the first-layer first spin response structure unit and the first-layer second spin response structure unit are spaced apart by a transmission wavelength λ. SPP The second-layer first spin response structure unit is configured to be spaced apart from the first-layer second spin response structure unit by a transmission wavelength λ. SPP The second spin response structure unit of the second layer is configured to be spaced apart from the first spin response structure unit of the second layer by a transmission wavelength λ. SPP The settings follow the same pattern.

[0059] As a preferred embodiment of this invention, the metasurface structure may include three layers of first spin-response structural units and three layers of second spin-response structural units. Figure 8 An exemplary three-layer spin-response structure is shown. Repeated experiments demonstrate that this three-layer structure enables the cylindrical vector beam to achieve optimal focusing on the metasurface structure.

[0060] It should be noted that the metasurface structure according to any embodiment of the first aspect of this application can realize the on-chip focusing function of cylindrical vector beams without the need for multiple optical devices, a large optical system, a complex detection process, or low diffraction efficiency. Its structure is simple but powerful, which significantly reduces the application cost, significantly improves the application value of cylindrical vector beams, and expands the application range of cylindrical vector beams.

[0061] According to an embodiment of the second aspect of this application, such as Figure 9 As shown, an on-chip detection device 300 for detecting the order of a cylindrical vector beam is provided, which may include:

[0062] A cylindrical vector beam generator 310 is used to generate a cylindrical vector beam.

[0063] According to any embodiment of the first aspect of this application, the metasurface structure 320 is provided, wherein the optical axis of the cylindrical vector beam generated by the cylindrical vector beam generator 310 is perpendicular to the metasurface structure 320 to excite surface plasmons on the metasurface structure 320.

[0064] Near-field acquisition device 330, used to acquire the electric field distribution of excited surface plasmons; and

[0065] The processor 340 is configured to: receive the electric field distribution acquired by the near-field acquisition device 330, calculate the focal point of the surface plasmon on the metasurface structure 320 based on the electric field distribution, calculate the distance x between the focal point and the origin of the semi-circular trajectory, and calculate the order m of the cylindrical vector beam based on the distance x.

[0066] In this embodiment, the cylindrical vector beam generator 310 may include, but is not limited to, one or more of the following: a laser, a polarizer, a lens, a mirror, a spatial light modulator, a waveplate, and a beam splitter. Furthermore, the laser, polarizer, lens, mirror, spatial light modulator, waveplate, and beam splitter are not limited to specific types and models; any combination of one or more of them is sufficient to generate a cylindrical vector beam.

[0067] In this embodiment, the description of the metasurface structure 320 can be referred to the metasurface structure described in any embodiment of the first aspect of this application, and will not be repeated here.

[0068] In this embodiment, the near-field acquisition device 330 may include, but is not limited to, one or more of the following: a probe, an optical fiber, a signal enhancement device, a camera, etc. Furthermore, the probe, optical fiber, signal enhancement device, camera, etc., are not limited to specific types and models; any combination of one or more of them is sufficient to acquire the electric field distribution of the excited surface plasmons.

[0069] In this embodiment, the processor 340 can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor.

[0070] Based on the above embodiments, an on-chip detection device 300 according to another embodiment of the second aspect of this application, such as... Figure 10 As shown, it possesses the basic technical features of the above embodiments. Based on the above embodiments, the near-field acquisition device 330 may include a probe 331 for detecting the focal point and a photomultiplier tube 332 connected to the probe 331. The photomultiplier tube 332 is connected to the processor. In this embodiment, since the photoelectric signal directly detected by the probe 331 may be weak, a photomultiplier tube 332 is used to amplify the signal acquired by the probe for subsequent computational processing.

[0071] In this embodiment, the probe used to detect the focusing electric field distribution of surface plasmons can be any suitable probe known in the art, and the photomultiplier tube can be any type and model of photomultiplier tube.

[0072] As a preferred embodiment of the various embodiments of the second aspect of this application, the order m of the cylindrical vector beam can be calculated according to the following formula:

[0073]

[0074] Exemplary, and not limiting, it is still assumed that the incident wavelength of the cylindrical vector beam is 633 nm, and the propagation wavelength of the surface plasmons excited on the metasurface structure is... The radial distance S and angular distance d between the first and second nanoslits of the same first spin-response structural unit are both λ. SPP / 4≈150nm, and the angular distance D between two adjacent first nanoslits is λ. SPP / 2≈300nm. Exemplarily, and not limitingly, the thickness of the metasurface structure can be 200nm. Exemplarily, and not limitingly, the length and width of the first and second nanoslits can be 200nm and 40nm, respectively. The above data examples are only for illustrating specific experimental results and are not intended to impose a specific limitation on the size of the metasurface structure of this application. Undoubtedly, the size of the metasurface structure of this application, as well as the size and number of slits therein, can be determined according to actual needs. The results obtained through simulation based on the above data are as follows... Figure 11 As shown in the figure, it can be seen that the order m of the cylindrical vector beam is linearly related to the distance x from the focal point to the origin.

[0075] It should be noted that the metasurface structure according to any embodiment of the second aspect of this application does not require a variety of optical devices, a large optical system, a complex detection process, or low diffraction efficiency, and can realize on-chip detection of the order m of the cylindrical vector beam. Its structure is simple but powerful, which significantly reduces the application cost, significantly improves the application value of the cylindrical vector beam, and expands the application range of the cylindrical vector beam.

[0076] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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. Such 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 this application, and should all be included within the protection scope of this application.

Claims

1. A metasurface structure for on-chip focusing of a column vector beam, characterized in that, Comprising: a plurality of first spin response structure units, wherein each of the first spin response structure units comprises: an elongated first nanoslit; and an elongated second nanoslit, wherein the long axis of the second nanoslit is perpendicular to the long axis of the first nanoslit, and the size of the first nanoslit is the same as the size of the second nanoslit; wherein the center points of the plurality of first nanoslits are arranged along a uniform interval on an upper half-ring trajectory, the plurality of second nanoslits are respectively located on the radially outer side of the upper half-ring trajectory, and for the same first spin response structure unit, the angle bisector between the long axis of the first nanoslit and the long axis of the second nanoslit is the same as the direction of the tangent line of the half-ring trajectory at the center point of the first nanoslit, so that the cylindrical vector beam is vertically irradiated on the metasurface structure and focused at a point on the metasurface structure; the metasurface structure further comprises a plurality of second spin response structure units, wherein each of the second spin response structure units comprises: an elongated third nanoslit; and an elongated fourth nanoslit, wherein the long axis of the fourth nanoslit is perpendicular to the long axis of the third nanoslit, Wherein, the center points of the third nanometer slits are arranged along the lower half ring trajectory with uniform intervals respectively, the fourth nanometer slits are respectively located on the radial outside of the lower half ring trajectory, and the lower half ring trajectory is a concentric half ring trajectory arranged at an interval of an integer multiple of the transmission wavelength of the upper half ring trajectory. ​ for the same second spin response structure unit, the angle bisector between the long axis of the third nanoslit and the long axis of the fourth nanoslit is the same as the direction of the tangent line of the lower half-ring trajectory at the center point of the third nanoslit, wherein: when the leftmost first spin response structure unit of the plurality of first spin response structure units is in an inverted herringbone shape, the leftmost second spin response structure unit of the plurality of second spin response structure units is in a herringbone shape; when the leftmost first spin response structure unit of the plurality of first spin response structure units is in a herringbone shape, the leftmost second spin response structure unit of the plurality of second spin response structure units is in an inverted herringbone shape; The order of the cylindrical vector beam is calculated according to the following formula m : wherein x is the distance between the focal point and the origin of the upper semicircular trajectory.

2. The metasurface structure of claim 1, wherein, For the same first spin response structure unit, the perpendicular segment distance from the center point of the second nanoslit to the tangent of the upper semi-circular track at the center point of the first nanoslit is S , and the intersection point of the extension line of the perpendicular segment and the upper semi-circular track is on the circular arc of the upper semi-circular track to the center point of the first nanoslit, and the circular arc distance is d , and S and d respectively satisfy the following relationship: S / d>0.5 ， wherein, is the incident wavelength of the cylindrical vector beam, is the dielectric constant of air, is the dielectric constant of the metasurface structure, is the transmission wavelength of the surface plasmon excited by the cylindrical vector beam on the metasurface structure, wherein the arc distance of the center points of two adjacent first nanoslits on the upper half-ring trajectory is D, and D=2d.

3. The metasurface structure of claim 1, wherein, For the same second spin-response structural unit, the distance between the perpendicular segment from the center point of the fourth nanoslit to the tangent line of the lower semi-circular trajectory at the center point of the third nanoslit is... S The intersection of the extension of the vertical line segment and the lower semi-circular trajectory is a circular arc distance from the center point of the third nanometer slit on the lower semi-circular trajectory. d The arc distance between the center points of two adjacent third nano-slits on the lower semi-circular trajectory is D.

4. The metasurface structure of claim 3, wherein, The metasurface structure comprises a plurality of layers of first spin- responsive structure units and a plurality of layers of second spin-responsive structure units positioned according to a plurality of upper half-loop trajectories and a plurality of lower half-loop trajectories, wherein the plurality of layers of first spin-responsive structure units and the plurality of layers of second spin-responsive structure units are arranged in an alternating fashion, and each layer is spaced by an integer multiple of the transmission wavelength .

5. The metasurface structure of claim 4, wherein, The metasurface structure comprises three layers of first spin response structure units and three layers of second spin response structure units.

6. An on-chip detection apparatus for detecting an order of a cylindrical vector beam, characterized by, Comprising: a cylindrical vector beam generator for generating a cylindrical vector beam; the metasurface structure according to any one of claims 1-5, wherein the optical axis of the cylindrical vector beam generated by the cylindrical vector beam generator is perpendicular to the metasurface structure to excite surface plasmons on the metasurface structure; a near-field acquisition device for acquiring the electric field distribution of the excited surface plasmons; and a processor configured to: receive the electric field distribution collected by the near-field collection device, calculate a focal point of the surface plasmon on the metasurface structure according to the electric field distribution, calculate a distance between the focal point and an origin of the upper semi-annular track x , and determine whether the distance is greater than a preset threshold value x , and if so, calculate an order of the cylindrical vector beam m ; The order of the cylindrical vector beam is calculated according to the following formula m : 。 7. The on-chip detection apparatus according to claim 6, wherein the near-field acquisition device comprises a probe for detecting the focal point and a photomultiplier connected to the probe, wherein the photomultiplier is connected to the processor.

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