Azimuth angle coding orbital angular momentum vortex light beam switching holographic channel design method

Abstract

The invention provides an azimuth angle coding orbital angular momentum vortex beam switching holographic channel design method, which comprises the following steps: dividing orbital angular momentum according to an azimuth angle to obtain a plurality of angular regions, and coding different topological charges for the plurality of angular regions; permutation and combination are carried out on the plurality of topological charges, the topological charges are coded in different azimuth angle areas, and a target azimuth angle coding orbital angular momentum with orthogonal light beams is screened out; performing phase conversion and phase superposition on the holographic picture by using a GSW algorithm and the target azimuth coding orbital angular momentum to obtain a multi-channel holographic phase; the method comprises the following steps: constructing a nanorod array structure, and encoding a corner of the nanorod array structure by using a multi-channel holographic phase to obtain an encoded extremely-simple metasurface; and determining the current azimuth coding orbital angular momentum carried by the incident light, and decoding according to a matching result of the current azimuth coding orbital angular momentum and the target azimuth coding orbital angular momentum. Therefore, the dynamic switching convenience and the information security can be improved.

Description

Technical Field

[0001] The present application relates to the field of optical holography technology, and in particular to a method for designing an azimuthally encoded orbital angular momentum vortex beam switching holographic channel. Background Art

[0002] Among related technologies, metasurface is a two-dimensional planar optical device composed of sub-wavelength artificial structures. It has shown revolutionary potential in the field of micro-nano photonics by precisely controlling the phase, amplitude and polarization state of light. Its core advantage lies in breaking through the volume limitations of traditional optical devices. It is widely used in the fields of holographic multiplexing, high-resolution imaging and optical encryption, and provides a new solution for integrated photonic systems.

[0003] Orbital Angular Momentum (OAM) vortex beams have opened up a new physical dimension for holographic displays due to their unique spiral wavefront distribution. The OAM modes carried by this beam are mathematically infinitely orthogonal (the topological charge l is an arbitrary integer) and can be used as independent information carriers in metasurface holography. When OAM modes with different l values are used to encode information, their orthogonal properties allow a single hologram to carry a large amount of independent channel information. This feature makes OAM-based metasurface holographic devices extremely promising in the fields of ultra-high capacity storage and multi-channel communications. For example, studies have reported the realization of OAM four-channel selective holography using cylindrical nanoarray metasurfaces in the visible light band. By switching the topological charge carried by the incident vortex beam (such as switching from l=1 to l=2), the holographic channels can be dynamically switched. However, despite the significant theoretical advantages of OAM multiplexing, traditional OAM holographic technology still faces the following key challenges: 1. Dynamic switching requires switching the incident light source: the OAM mode of the incident light needs to be adjusted through a spatial light modulator (SLM) or a mechanical device, resulting in a bulky system and limited response speed. 2. Insufficient security: attackers can directly intercept all information by traversing different l values, and there is a lack of encryption mechanism. 3. High complexity of metasurface preparation: traditional schemes require a combination of multi-sized nanostructures to achieve multi-channel encoding, resulting in complex lithography processes. The above problems have seriously restricted the practical application of OAM holographic technology, and it is urgent to achieve a synergistic breakthrough in dynamics, security and preparation efficiency through innovative designs (such as azimuth coding, minimalist metasurface structures, etc.).

[0004] In the prior art, a polymer-based complex amplitude metasurface is prepared by three-dimensional laser printing technology. The amplitude and phase are independently regulated by controlling the height and size of birefringent nanocolumns, realizing multiplexing of OAM complex amplitude holography in momentum space. However, the prior art has the following technical defects: high preparation complexity: high-precision three-dimensional laser printing technology is required, and the preparation process is complex. Moreover, dynamic switching depends on external devices. Switching holographic channels requires switching the incident light source, which is complex in operation and limited in switching speed. At the same time, there is insufficient security: the encryption mechanism depends on the combination of OAM modes, and there is a risk of brute-force cracking of integer OAM. Summary of the Invention

[0005] This application aims to solve at least one of the technical problems existing in the prior art. Therefore, this application proposes a method for designing a switching holographic channel of an azimuth-encoded orbital angular momentum vortex beam, aiming to improve the convenience of dynamic switching and information security.

[0006] In a first aspect, an embodiment of this application provides a method for designing a switching holographic channel of an azimuth-encoded orbital angular momentum vortex beam, including:

[0007] Dividing the orbital angular momentum according to the azimuth angle to obtain a plurality of angular regions, and encoding different topological charges for the plurality of angular regions respectively, where one of the angular regions corresponds to one of the topological charges;

[0008] Performing permutation and combination on the plurality of topological charges and encoding them in different azimuth angle regions, and screening out the target azimuth-encoded orbital angular momentum with orthogonal beams;

[0009] Using the GSW algorithm and the target azimuth-encoded orbital angular momentum to perform phase transformation and phase superposition on the holographic image to obtain a multi-channel holographic phase;

[0010] Constructing a nanocolumn array structure, and encoding the rotation angle of the nanocolumn array structure with the multi-channel holographic phase to obtain an encoded minimalist metasurface;

[0011] Determining the currently carried azimuth-encoded orbital angular momentum of the incident light, and performing decoding according to the matching result between the currently carried azimuth-encoded orbital angular momentum and the target azimuth-encoded orbital angular momentum.

[0012] According to some embodiments of this application, the dividing the orbital angular momentum according to the azimuth angle to obtain a plurality of angular regions, and encoding different topological charges for the plurality of angular regions respectively, includes:

[0013] Dividing the azimuth angle equally to obtain n angular regions, where the angular ranges corresponding to the n angular regions are respectively

[0014] Encode n different topological charges for the n angular regions respectively, where the n different topological charges are l1, l2... l n 。

[0015] According to some embodiments of the present application, arranging and combining the multiple topological charges and encoding them in different azimuthal regions, and screening out the target azimuthal encoded orbital angular momentum with orthogonal beams, includes:

[0016] Arrange and combine the n different topological charges to obtain kinds of combination results;

[0017] Use the inner product judgment formula to screen out the target azimuthal encoded orbital angular momentum with orthogonal beams from the kinds of combination results, where the inner product judgment formula is: u1 and u2 represent the azimuthal encoded orbital angular momentum, is the azimuth.

[0018] According to some embodiments of the present application, using the GSW algorithm and the target azimuthal encoded orbital angular momentum to perform phase conversion and phase superposition on the holographic picture to obtain a multi-channel holographic phase, includes:

[0019] Use the GSW algorithm to perform phase conversion on the holographic picture to be encoded to obtain multiple single-channel holographic phases;

[0020] Superimpose the target azimuthal encoded orbital angular momentum on each single-channel holographic phase;

[0021] Superimpose the multiple single-channel holographic phases with the target azimuthal encoded orbital angular momentum superimposed on them to obtain a multi-channel holographic phase.

[0022] According to some embodiments of the present application, constructing a nano-pillar array structure, and using the multi-channel holographic phase to encode the rotation angle of the nano-pillar array structure to obtain an encoded minimalist metasurface, includes:

[0023] Construct a nano-pillar array structure, and use numerical simulation to obtain the transmission efficiency and phase of the transmitted light of the nano-pillars;

[0024] Determine the major axis and minor axis of the nano-pillars according to the transmission efficiency and the phase;

[0025] Use the multi-channel holographic phase to encode the rotation angle of the nano-pillar array structure after determining the major axis and minor axis to obtain an encoded minimalist metasurface.

[0026] According to some embodiments of the present application, the Jones matrix of the nano-pillars at the rotation angle is expressed as:

[0027]

[0028] Wherein, the A and the B represent transmittance parameters in the major axis and minor axis directions of the nanorods;

[0029] The Jones vector of circularly polarized light is When circularly polarized light is incident and regulated by the nanorods of the minimalist metasurface, the outgoing light is expressed as: The polarization light with opposite circular polarization of the outgoing light introduces a phase of twice the nanorod rotation angle.

[0030] The geometric phase regulation satisfies: Wherein, represents the geometric phase, and θ is the nanorod rotation angle.

[0031] According to some embodiments of the present application, decoding according to the matching result of the current azimuth-encoded orbital angular momentum and the target azimuth-encoded orbital angular momentum includes:

[0032] When the current azimuth-encoded orbital angular momentum matches the target azimuth-encoded orbital angular momentum, a holographic image is decoded.

[0033] According to some embodiments of the present application, decoding according to the matching result of the current azimuth-encoded orbital angular momentum and the target azimuth-encoded orbital angular momentum includes:

[0034] When the current azimuth-encoded orbital angular momentum does not match the target azimuth-encoded orbital angular momentum, a holographic image cannot be decoded.

[0035] According to the technical solution of the embodiment of the present application, it has at least the following beneficial effects: First, the embodiment of the present application divides the orbital angular momentum according to the azimuth angle to obtain multiple angular regions, and encodes different topological charges for the multiple angular regions respectively, where one angular region corresponds to one topological charge; then, the embodiment of the present application screens out the target azimuth angle encoding orbital angular momentum of the orthogonal beam; then, the embodiment of the present application uses the GSW algorithm and the target azimuth angle encoding orbital angular momentum to perform phase conversion and phase superposition on the holographic image to obtain a multi-channel holographic phase; then, the embodiment of the present application constructs a nano-pillar array structure, and encodes the rotation angle of the nano-pillar array structure by using the multi-channel holographic phase to obtain an encoded minimalist metasurface; then, the embodiment of the present application determines the currently azimuth angle encoding orbital angular momentum carried by the incident light, and decodes according to the matching result between the currently azimuth angle encoding orbital angular momentum and the target azimuth angle encoding orbital angular momentum. The embodiment of the present application realizes channel switching by rotating the incident target azimuth angle encoding orbital angular momentum beam, without replacing the light source or complex modulation equipment, with simple operation and improved dynamic switching convenience; in addition, the embodiment of the present application adopts double encryption, that is, combines azimuth angle encoding with OAM topological charge, and can only be decrypted when the rotation angle of the incident light matches the encoded phase, improving information security.

[0036] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings are used to provide a further understanding of the technical solution of the present application, and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present application, and do not constitute a limitation to the technical solution of the present application.

[0038] Figure 1 is a flowchart of a method for designing a holographic channel for switching azimuth angle encoding orbital angular momentum vortex beams provided by an embodiment of the present application;

[0039] Figure 2 is a schematic diagram of traditional OAM and azimuth angle encoding orbital angular momentum provided by an embodiment of the present application;

[0040] Figure 3 is a schematic diagram of calculating holographic phase provided by an embodiment of the present application;

[0041] Figure 4 is a schematic diagram of a nano-pillar provided by an embodiment of the present application;

[0042] Figure 5 is a transmission efficiency and phase scan diagram of a nano-pillar provided by an embodiment of the present application;

[0043] Figure 6 Schematic diagram of the relationship between polarization conversion efficiency and PB phase provided by an embodiment of the present application;

[0044] Figure 7 Calculated total holographic phase provided by an embodiment of the present application;

[0045] Figure 8 Decoding simulation effect diagram provided by an embodiment of the present application. Detailed implementation manners

[0046] Embodiments of the present application will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary only for explaining the present application and should not be construed as limiting the present application.

[0047] In the description of the present application, it should be understood that the orientation or positional relationship indicated by terms such as up, down, front, back, left, right, etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for facilitating the description of the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present application.

[0048] In the description of the present application, the meaning of several is one or more, the meaning of multiple is two or more, greater than, less than, exceeding, etc. are understood as not including the recited number, and above, below, within, etc. are understood as including the recited number. If there is a description of first and second, it is only for the purpose of distinguishing technical features and should not be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence of the indicated technical features.

[0049] In the description of the present application, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present application in combination with the specific content of the technical solution.

[0050] In some cases, a metasurface is a two-dimensional planar optical device composed of sub-wavelength artificial structures, which shows revolutionary potential in the field of micro-nano photonics by precisely controlling the phase, amplitude, and polarization state of light. Its core advantage lies in breaking through the volume limitation of traditional optical devices and is widely used in fields such as holographic multiplexing, high-resolution imaging, and optical encryption, providing a new solution for integrated photonics systems.

[0051] Orbital angular momentum vortex beams have opened up a new physical dimension for holographic display due to their unique spiral wavefront distribution. The OAM mode carried by this beam is infinitely orthogonal in mathematics (topological charge l is an arbitrary integer) and can be used as an independent information carrier in metasurface holography. When using OAM modes with different l values for information encoding, their orthogonal characteristics allow a single hologram to carry a large amount of independent channel information. This feature makes OAM-based metasurface holographic devices extremely promising in the fields of ultra-high capacity storage and multi-channel communications. For example, studies have reported the use of cylindrical nanoarray metasurfaces in the visible light band to achieve OAM four-channel selective holography. By switching the topological charge carried by the incident vortex beam (such as switching from l = 1 to l = 2), the holographic channel can be dynamically switched. However, despite the significant theoretical advantages of OAM multiplexing, traditional OAM holographic technology still faces the following key challenges: 1. Dynamic switching requires switching the incident light source: the OAM mode of the incident light needs to be adjusted by a spatial light modulator (SLM) or mechanical device, resulting in a bulky system and limited response speed. 2. Insufficient security: attackers can directly intercept all information by traversing different l values, and there is a lack of encryption mechanism. 3. High complexity of metasurface preparation: Traditional solutions require a combination of multi-sized nanostructures to achieve multi-channel encoding, which leads to complex lithography processes. The above problems seriously restrict the practical application of OAM holographic technology, and it is urgent to achieve a synergistic breakthrough in dynamics, security and preparation efficiency through innovative designs (such as azimuth coding, minimalist metasurface structures, etc.).

[0052] Existing technology uses 3D laser printing technology to prepare polymer-based complex amplitude metasurfaces, and uses the height and size of birefringent nanocolumns to independently control the amplitude and phase, realizing the multiplexing of OAM complex amplitude holography in momentum space. Multi-channel capability: supports up to 200 orthogonal OAM channels, realizes lensless holographic image reconstruction through Fourier transform, and dynamically switches holograms by switching the l carried by the incident light. Encryption application: Information is dispersed into multiple OAM modes through random encoding, and the holographic image can only be decrypted when the vortex light opposite to the encoded OAM is incident.

[0053] However, the existing technology has the following technical defects: high preparation complexity: high-precision three-dimensional laser printing technology is required, and the preparation process is complicated. In addition, dynamic switching depends on external equipment. Switching the holographic channel requires switching the incident light source, which is complicated to operate and has limited switching speed. At the same time, the security is insufficient: the encryption mechanism depends on the combination of OAM modes, and the integer OAM is at risk of being cracked by brute force.

[0054] Based on the above situation, an embodiment of the present application proposes a method for designing an azimuthally encoded orbital angular momentum vortex beam switching holographic channel, aiming to improve the convenience of dynamic switching and information security.

[0055] The following further elaborates on various embodiments of the method for designing a holographic channel for switching azimuthally encoded orbital angular momentum vortex beams in conjunction with the accompanying drawings.

[0056] As Figure 1 shown, Figure 1 FIG. 7 is a flowchart of a method for designing a holographic channel for switching azimuthally encoded orbital angular momentum vortex beams provided by an embodiment of the present application. The method for designing a holographic channel for switching azimuthally encoded orbital angular momentum vortex beams includes, but is not limited to, steps S110, S120, S130, S140, and S150.

[0057] Step S110: Divide the orbital angular momentum according to the azimuth angle to obtain a plurality of angular regions, and encode different topological charges for the plurality of angular regions respectively, where one angular region corresponds to one topological charge;

[0058] Step S120: Perform permutation and combination on the plurality of topological charges and encode them in different azimuth angle regions, and screen out the target azimuthally encoded orbital angular momentum with orthogonal beams;

[0059] Step S130: Use the GSW algorithm and the target azimuthally encoded orbital angular momentum to perform phase transformation and phase superposition on the holographic image to obtain a multi-channel holographic phase;

[0060] Step S140: Construct a nano-pillar array structure, and use the multi-channel holographic phase to encode the rotation angle of the nano-pillar array structure to obtain an encoded minimalist metasurface;

[0061] Step S150: Determine the currently carried azimuthally encoded orbital angular momentum of the incident light, and perform decoding according to the matching result between the currently carried azimuthally encoded orbital angular momentum and the target azimuthally encoded orbital angular momentum.

[0062] In the embodiment of the present application, channel switching is achieved by rotating the incident azimuthally encoded orbital angular momentum beam, without the need to replace the light source or complex modulation equipment, with simple operation and improved convenience of dynamic switching; in addition, the embodiment of the present application adopts double encryption, that is, combining azimuthal encoding and OAM topological charge, and can only be decrypted when the rotation angle of the incident light matches the encoded phase, improving information security.

[0063] In one embodiment, the light in the embodiment of the present application is different from the traditional OAM. The traditional OAM is azimuthally encoded, making its angular distribution non-uniform. In different angular regions, different OAMs are carried respectively, and we call it an azimuthally encoded orbital angular momentum (AE-OAM) vortex beam.

[0064] In one embodiment, for the angular region division and encoding in step S110, specifically, it can be: First, the azimuth angle is equally divided into n angular regions, where the angular ranges corresponding to the n angular regions are respectively Next, the n angular regions are respectively encoded with n different topological charges, obtaining combinatorial results. Among them, the n different topological charges are l1, l2... l n .

[0065] In one embodiment, for the combination and screening process in step S120, specifically, it can be: The inner product judgment formula is used to screen out the target azimuth angle encoded orbital angular momentum with orthogonal beams from combinatorial results. Among them, the inner product judgment formula is: u1 and u2 represent the azimuth angle encoded orbital angular momentum, is the azimuth angle.

[0066] In one embodiment, for the phase conversion and phase superposition process in step S130, specifically, it can be: First, the GSW algorithm is used to perform phase conversion on the holographic image to be encoded, obtaining multiple single-channel holographic phases; then, the target azimuth angle encoded orbital angular momentum is superimposed on each single-channel holographic phase; next, the multiple single-channel holographic phases superimposed with the target azimuth angle encoded orbital angular momentum are superimposed to obtain a multi-channel holographic phase.

[0067] In one embodiment, for the construction and encoding process of the minimalist metasurface in step S140, specifically, it can be: First, a nano-pillar array structure is constructed, and the transmission efficiency and phase of the transmitted light of the nano-pillars are obtained by numerical simulation; then, the major axis and minor axis of the nano-pillars are determined according to the transmission efficiency and phase; next, the rotation angle of the nano-pillar array structure after determining the major axis and minor axis is encoded using the multi-channel holographic phase, obtaining the encoded minimalist metasurface.

[0068] In one embodiment, the Jones matrix of the nano-pillars at the rotation angle is expressed as:

[0069]

[0070] Among them, A and B represent the transmittance parameters in the directions of the major axis and minor axis of the nano-pillars.

[0071] The Jones vector of circularly polarized light is When circularly polarized light is incident and regulated by the nano-pillars of the minimalist metasurface, the outgoing light is expressed as: The outgoing polarized light with the opposite circular polarization introduces a phase of twice the nano-pillar rotation angle.

[0072] The geometric phase regulation satisfies: Among them, represents the geometric phase, and θ is the rotation angle of the nanocolumn.

[0073] In one embodiment, for the decoding process of the minimalist metasurface in step S150, it can be specifically:

[0074] If the currently azimuth-encoded orbital angular momentum matches the target azimuth-encoded orbital angular momentum, a holographic image is decoded;

[0075] If the currently azimuth-encoded orbital angular momentum does not match the target azimuth-encoded orbital angular momentum, a holographic image cannot be decoded.

[0076] Based on the azimuth-encoded orbital angular momentum vortex beam switching holographic channel design methods of the above various embodiments, the overall embodiments of the azimuth-encoded orbital angular momentum vortex beam switching holographic channel design method of the present application are respectively proposed below.

[0077] In one embodiment, the traditional OAM has a uniform angular phase, that is, the phase changes by l*2π as the azimuth angle rotates by 2π. Due to this characteristic, the vortex beams carrying different l are orthogonal to each other (similar to left-handed light and right-handed light, x-polarized light and y-polarized light in light polarization). In theory, l can be infinitely large, so there are infinitely many orthogonal OAMs. As a new degree of freedom, OAM is consistent with polarization, phase, etc. and can be used as a channel for carrying holographic information.

[0078] The light in the embodiments of the present application is different from the traditional OAM. The traditional OAM is azimuth-encoded, making its angular distribution non-uniform. In different angular regions, different OAMs with l are carried respectively, and we call it the azimuth-encoded orbital angular momentum vortex beam. The number of angular regions can be freely designed. The traditional OAM only carries one l.

[0079] The azimuth-encoded orbital angular momentum needs to equally divide the azimuth angle into n regions, which are respectively The n regions are respectively encoded with n different topological charges, represented by l1, l2......l n The orbital angular momentum spectrum of the azimuth-encoded orbital angular momentum is much more complex, not only including the n ls that make up the azimuth-encoded orbital angular momentum n , but also including other components.

[0080] Arrange and combine the l n encoded in each azimuth angle region. There are a total of possibilities. Select a set of completely orthogonal azimuth-encoded orbital angular momenta. These n phases can be obtained by continuously rotating a phase by 2π / n. The way to judge the orthogonality of the beams is: when the inner product of the azimuth-encoded orbital angular momenta is zero: At this time, the two beams of light are orthogonal, and u1 and u2 represent the azimuth-encoded orbital angular momentum, where \(\varphi\) is the azimuth.

[0081] Meanwhile, the improved GSW algorithm is needed to obtain the phase of the minimalist metasurface to be encoded. As Figure 3 shown, first, for a single channel, the GSW algorithm is used to convert the holographic image to be encoded into a single-channel holographic phase. On this basis, the azimuth-encoded orbital angular momentum phase is superimposed to introduce the azimuth-encoded orbital angular momentum information into the holographic phase of each channel. Finally, the phases of multiple channels after the above processing are superimposed to obtain a holographic phase containing multi-channel information. In this way, the information of different channels is integrated into a hologram to achieve effective encoding of multi-channel information.

[0082] After obtaining the multi-channel holographic phase, the process of encoding the metasurface is as follows: 1. Design the basic structure of the minimalist metasurface. The substrate is a cube. An xoy coordinate system is established along two sides parallel to the substrate. The nanocolumns are elliptical on the xoy plane. The major and minor axes of the nanocolumns are parallel to the substrate and have different lengths. The rotation angle of the nanocolumns is the angle between the major axis of the nanocolumns and the x-axis. The substrate material of the metasurface is selected as SiO2, and the nanocolumn material is selected as TiO2, which can achieve a high conversion efficiency in the visible light band. 2. When determining the geometric dimensions of the minimalist metasurface, first determine the height of the nanocolumns and the period of the substrate unit. Through electromagnetic simulation, the major and minor axis dimensions of the nanocolumns are scanned in the visible light band of 400nm - 700nm, and the optimized parameters include the length L1 and width L2 of the nanostructure, the period P = 300nm, and the nanocolumn thickness H = 600nm remain unchanged. The metasurface is encoded according to the calculated phase information using the geometric phase of the structure.

[0083] The Jones matrix of the nanocolumn with a rotation angle of \(\theta\) is expressed as:

[0084]

[0085] A and B represent the transmittance-related parameters in the major and minor axis directions of the nanocolumns. The Jones vector of circularly polarized light is where \(i\) is the imaginary part. When circularly polarized light is incident and regulated by the nanocolumns of the minimalist metasurface, the outgoing light is expressed as: The outgoing polarized light with the opposite circular polarization will introduce a phase of twice the nanocolumn rotation angle. The geometric phase regulation satisfies: where represents the geometric phase, and \(\theta\) is the nanocolumn rotation angle. The additional phase is independent of the wavelength. Therefore, the minimalist metasurface designed using the PB phase can achieve broadband regulation. The rotation angles of the nanocolumn arrays are encoded using the PB phase. where is the calculated total holographic phase.

[0086] In a specific embodiment, a four-channel holographic design method for switching orbital angular momentum vortex beams with rotation incident azimuth angle encoding based on a minimalist metasurface includes the following steps:

[0087] 1. Figure 2 is a schematic diagram of traditional OAM and azimuth angle encoded orbital angular momentum. Traditional OAM only carries one l, and it can also be seen from the orbital angular momentum spectrum that only one OAM component is carried. After four-channel azimuth angle encoding of OAM, the azimuth angle is divided into four regions, which are respectively encoded with 4 different topological charges represented by l1, l2, l3, and l4, and a set of four completely orthogonal azimuth angle encoded orbital angular momenta is taken. At this time, the orbital angular momentum spectrum not only contains the four encoded ls, but also contains other components, which becomes more complex for decoding. Among them, Figure 2 the abscissa in represents the topological charge, and the ordinate represents the weight.

[0088] 2. Calculate the holographic phase: The process is as Figure 3 shown. First, obtain the single-channel holographic phase, use the weighted GSW algorithm to transform the holographic image to be encoded into a holographic phase, and superimpose the azimuth angle encoded orbital angular momentum phase. Finally, superimpose the phases of the four single channels to obtain the multi-channel holographic phase.

[0089] 3. Construct the nano-unit structure. The schematic diagram of the nano-pillar is as Figure 4 shown. The long axis is represented by L1, the short axis is represented by L2, and the rotation angle is represented by θ. Use numerical simulation to obtain the transmission efficiency and phase of the transmitted light of the TiO2 nano-pillar. Select the working wavelength of 488 nm and the period of 300 nm to obtain the transmission efficiency and phase scan diagram of the nano-pillar as Figure 5 shown. Select the structure with higher conversion efficiency, that is, the structure of the pentagram in the figure. In Example 1, select the nano-pillar with L1 = 260 nm and L2 = 100 nm, and use the PB phase to encode the rotation angle of the nano-pillar array. The polarization conversion efficiency and PB phase are as Figure 6 shown. The solid line on the right represents the theoretical PB phase, and the pentagram represents the relationship between the PB phase obtained by simulation and the structure rotation angle. Figure 6 The upper line in represents the polarization conversion efficiency, a double Y graph, which is marked by small arrows in the figure, and the orientation angle represents the rotation angle.

[0090] 4. After encoding the minimalist metasurface, the incident azimuth angle encodes the orbital angular momentum. When the azimuth angle encoding angle and the carried l match the azimuth angle encoded orbital angular momentum encoded by the designed metasurface, the encoded hologram can be decoded. Rotate the incident light by 90°, and the second hologram can be obtained. Continue to rotate by 90° and 180°, and the third and fourth holograms can be obtained.Figure 7 is the calculated total holographic phase, Figure 8 is the decoded simulation effect diagram.

[0091] When the azimuth-encoded orbital angular momentum carried by the incident light is inconsistent with the encoded angle, accurate decoded information cannot be obtained either. Therefore, compared with traditional OAM holography, using azimuth-encoded orbital angular momentum as the holographic channel greatly improves the security of information transmission and realizes dynamic switching without changing the incident light source.

[0092] Based on the azimuth-encoded orbital angular momentum vortex beam switching holographic channel design method of the above various embodiments, the embodiments of the present application have the following characteristics:

[0093] 1. Design of azimuth-encoded orbital angular momentum vortex beam: Divide the 2π angular position of the beam phase into n regions, which can be evenly divided or arbitrarily partitioned, and different integer topological charges (l i ) are encoded in each region, and completely orthogonal azimuth-encoded orbital angular momentum modes are selected through the orthogonality condition .

[0094] 2. Arbitrary design of holographic channels: By designing the partition of azimuth-encoded orbital angular momentum, the number of independent dynamic holographic channels can be determined, and there is a direct connection between them. The number of direction angle partitions is the number of holographic channels.

[0095] 3. Dynamic switching and encrypted transmission mechanism: Trigger holographic channel switching by rotating the incident azimuth-encoded orbital angular momentum beam, and the image can be decoded only when the azimuth of the incident azimuth-encoded orbital angular momentum matches the azimuth of the encoded phase.

[0096] Based on the azimuth-encoded orbital angular momentum vortex beam switching holographic channel design method of the above various embodiments, the embodiments of the present application have the following technical effects:

[0097] 1. Convenience of dynamic switching:

[0098] Defects of the prior art: Dynamic switching of holograms requires switching the incident OAM mode, with slow response speed and complex operation.

[0099] Improvement of the embodiments of the present application: Channel switching is realized by rotating the incident azimuth-encoded orbital angular momentum beam, without the need to replace the light source or complex modulation equipment, and the operation is simple.

[0100] 2. Significantly improved information security:

[0101] Defects of the prior art: Traditional OAM holography is easily traversed and cracked (such as brute-force scanning of l values).

[0102] Improvements in the embodiments of this application: Double encryption: Combining azimuth encoding and OAM topological charge, it can be decrypted only when the rotation angle of the incident light matches the encoded phase (deviation < 5°).

[0103] It should be understood that in this application, "at least one (item)" means one or more, and "a plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that there can be three relationships. For example, "A and / or B" can mean: only A exists, only B exists, and both A and B exist at the same time. Among them, A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after. "At least one (item) of the following" or its similar expression refers to any combination of these items, including any combination of single item (item) or plural items (items). For example, at least one (item) of a, b, or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0104] In several embodiments provided in this application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. For example, the device embodiments described above are only illustrative. For example, the division of units is only a logical function division. In actual implementation, there can be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed coupling or direct coupling or communication connection between each other can be through some interfaces, and the indirect coupling or communication connection of devices or units can be in electrical, mechanical, or other forms. The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they can be located in one place, or they can be distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0105] It should also be understood that the various embodiments provided in the embodiments of this application can be combined arbitrarily to achieve different technical effects.

[0106] The above is a specific description of the preferred embodiments of this application, but this application is not limited to the above-mentioned implementation manners. Those skilled in the art can also make various equivalent deformations or substitutions without violating the spirit of this application. These equivalent deformations or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A design method for switching holographic channels of azimuthally encoded orbital angular momentum vortex beams, characterized in that, Including: Dividing the orbital angular momentum according to the azimuth angle to obtain multiple angular regions, and encoding different topological charges for the multiple angular regions respectively, where one angular region corresponds to one topological charge; Performing permutation and combination on the multiple topological charges and encoding them in different azimuth angle regions, and screening out the target azimuth angle encoded orbital angular momentum with orthogonal beams; Using the GSW algorithm and the target azimuth angle encoded orbital angular momentum to perform phase transformation and phase superposition on the holographic image to obtain a multi-channel holographic phase; Constructing a nano-pillar array structure, and encoding the rotation angle of the nano-pillar array structure using the multi-channel holographic phase to obtain an encoded minimalist metasurface; Determining the currently azimuth angle encoded orbital angular momentum carried by the incident light, and performing decoding according to the matching result between the currently azimuth angle encoded orbital angular momentum and the target azimuth angle encoded orbital angular momentum.

2. The method according to claim 1, wherein The dividing the orbital angular momentum according to the azimuth angle to obtain multiple angular regions, and encoding different topological charges for the multiple angular regions respectively, includes: Divide the azimuth angle into equal angles to obtain n angular regions, where the angular ranges corresponding to the n angular regions are respectively Encode the n angular regions with n different topological charges, where the n different topological charges are l1, l2... l n .

3. The method according to claim 2, characterized in that The performing permutation and combination on the multiple topological charges and encoding them in different azimuth angle regions, and screening out the target azimuth angle encoded orbital angular momentum with orthogonal beams, includes: Arrange and combine the n different topological charges to obtain kinds of combination results; Using the inner product judgment formula, select the target azimuth encoded orbital angular momentum with orthogonal light beams from the combinatorial results, where the inner product judgment formula is: u1 and u2 represent azimuth encoded orbital angular momentum, is the azimuth.

4. The method according to claim 1, wherein The using the GSW algorithm and the target azimuth angle encoded orbital angular momentum to perform phase transformation and phase superposition on the holographic image to obtain a multi-channel holographic phase, includes: Using the GSW algorithm to perform phase transformation on the holographic image to be encoded to obtain multiple single-channel holographic phases; Superposing the target azimuth angle encoded orbital angular momentum to each single-channel holographic phase; Superposing the multiple single-channel holographic phases with the target azimuth angle encoded orbital angular momentum superposed thereon to obtain a multi-channel holographic phase.

5. The method according to claim 1, characterized in that, The constructing a nano-pillar array structure, and encoding the rotation angle of the nano-pillar array structure using the multi-channel holographic phase to obtain an encoded minimalist metasurface, includes: Constructing a nano-pillar array structure, and obtaining the transmission efficiency and phase of the transmitted light of the nano-pillars using numerical simulation; Determining the major axis and minor axis of the nano-pillars according to the transmission efficiency and the phase; Encoding the rotation angle of the nano-pillar array structure with the determined major axis and minor axis using the multi-channel holographic phase to obtain an encoded minimalist metasurface.

6. The method according to claim 5, wherein The Jones matrix of the nano-pillars at the rotation angle is expressed as: Wherein, the A and the B represent the transmittance parameters in the major axis and minor axis directions of the nano-pillars; The Jones vector of circularly polarized light is When circularly polarized light is incident and regulated by the nanocolumns of the minimalist metasurface, the outgoing light is expressed as: The polarization light with opposite circular polarization of the outgoing light introduces a phase of twice the nanocolumn rotation angle; The geometric phase modulation satisfies: wherein, represents the geometric phase, and θ is the rotation angle of the nanocolumn.

7. The method according to claim 1, characterized in that The performing decoding according to the matching result between the currently azimuth angle encoded orbital angular momentum and the target azimuth angle encoded orbital angular momentum, includes: When the currently azimuth angle encoded orbital angular momentum matches the target azimuth angle encoded orbital angular momentum, decoding to obtain a holographic image.

8. The method according to claim 1, wherein The performing decoding according to the matching result between the currently azimuth angle encoded orbital angular momentum and the target azimuth angle encoded orbital angular momentum, includes: When the currently azimuth angle encoded orbital angular momentum does not match the target azimuth angle encoded orbital angular momentum, it is impossible to decode to obtain a holographic image.

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