A bidirectional vortex fiber laser based on intracavity superstructure surface assistance

Abstract

The application provides a bidirectional vortex fiber laser based on intracavity superstructure surface assistance, which comprises a pump light source, a wavelength division multiplexer, a first collimator, a second collimator, a first polarization beam splitter, a second polarization beam splitter and a superstructure surface; two output ends of the wavelength division multiplexer are connected with the first collimator and the second collimator respectively, the first collimator and the second collimator are connected with the first polarization beam splitter and the second polarization beam splitter respectively, output ends of the first polarization beam splitter and the second polarization beam splitter are connected with the superstructure surface, the superstructure surface comprises a substrate layer and a nano unit layer, the first polarization beam splitter outputs to the nano unit layer of the superstructure surface, and the second polarization beam splitter outputs to the substrate layer of the superstructure surface; the first polarization beam splitter and the second polarization beam splitter are further provided with laser output ports, and two laser output ports output vortex beams with different topological charges.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and in particular to a bidirectional vortex fiber laser based on intracavity metasurface assistance. Background Technology

[0002] In recent years, vortex beams, a special type of structured beam carrying orbital angular momentum (OAM), have attracted widespread attention from researchers. The most significant characteristic of vortex beams is their spiral phase, which is related to both azimuth and helicity. Due to their near-zero center (donut-shaped) intensity distribution, topological orthogonality, and ability to carry orbital angular momentum, vortex beams have demonstrated enormous application potential in fields such as optical communication, optical tweezers, and optical measurement.

[0003] Compared to generating vortex beams outside the cavity using phase elements (vortex phase plates, spatial light modulators, etc.), active vortex beams generated inside the cavity often have advantages such as high purity and high conversion efficiency. Vortex lasers offer a more efficient and integrated solution for generating vortex beams.

[0004] Fiber lasers, using doped fiber as the gain medium, offer significant advantages such as compactness, high gain, low maintenance costs, and high stability. Vortex fiber lasers, as an important vortex source, have been widely used in various fields. To generate a vortex beam within the fiber laser cavity, the intracavity optical field needs to be modulated or mode-selected. In previous work, vortex fiber lasers typically generated vortex beams through fiber gratings, mode-selective couplers, and offset splicing. These methods can stably and efficiently output vortex beams within the cavity, but they are often limited by limited modulation capabilities, low vortex order (<3), and relatively low output degrees of freedom.

[0005] Meanwhile, the degrees of freedom related to the propagation direction of bidirectional lasers from the ring cavity are often ignored. Although some works can achieve asymmetric control of bidirectional beams, they often achieve simple temporal adjustment of bidirectional pulse beams by only controlling polarization or intensity. Summary of the Invention

[0006] In view of this, embodiments of the present invention provide a bidirectional vortex fiber laser based on intracavity metasurface assistance to eliminate or improve one or more defects existing in the prior art.

[0007] One aspect of the present invention provides a bidirectional vortex fiber laser based on an intracavity metasurface-assisted structure, the laser comprising a pump source, a wavelength division multiplexer, a first collimator, a second collimator, a first polarization beam splitter, a second polarization beam splitter, and a metasurface. The two output terminals of the wavelength division multiplexer are respectively connected to a first collimator and a second collimator. The first collimator and the second collimator are respectively connected to a first polarization beamsplitter and a second polarization beamsplitter. The output terminals of the first polarization beamsplitter and the second polarization beamsplitter are both connected to the metasurface. The metasurface includes a substrate layer and a nanounit layer. The first polarization beamsplitter outputs at the nanounit layer of the metasurface, and the second polarization beamsplitter outputs at the substrate layer of the metasurface. The first polarization beam splitter and the second polarization beam splitter are also provided with laser output ports, and the two laser output ports output vortex beams with different topological charges.

[0008] Using the above scheme, this scheme can achieve drastically different optical responses depending on the incident direction. After introducing additional polarization-dependent degrees of freedom, it can achieve full phase (2π) of the bidirectional optical field without breaking the Lorentz reciprocity effect. (Control). Taking a pair of linearly polarized incident orthogonal bases (x- or y-polarized bases) as an example, when light is incident in the forward direction, the Jones matrix of the metasurface can be represented as... When the incident direction is reversed, the Jones matrix of the reverse incident direction will transform into... As the incident direction is reversed, the cross-polarized light field switches once, while the same-polarized light field remains unchanged. This means that the polarization-dependent metasurface has the ability to simultaneously control both symmetric and asymmetric bidirectional light fields, separating them into different polarization states. Here, this scheme integrates a metasurface into a fiber laser, realizing asymmetric control of the bidirectional light field within the spatial cavity. It also enables the control of bidirectional laser beams within a structurally simple laser, simultaneously generating a pair of high-quality vortex beams with a large span of topological charge within the cavity.

[0009] In some embodiments of the present invention, the laser further includes a first lens and a second lens, wherein the first lens is disposed between a first polarizing beam splitter and a metasurface, and the second lens is disposed between a second polarizing beam splitter and a metasurface.

[0010] In some embodiments of the present invention, on the orthographic projection plane of one side of the nanounit layer of the metasurface, the metasurface is provided with an array of nanopillars, and the nanopillars are provided with a rotation angle.

[0011] In some embodiments of the present invention, the nanopillars are all cuboids, the height of the nanopillars is a preset first height value, and the array period of the nanopillars is set to a first period length.

[0012] In some embodiments of the present invention, the nanopillars are all connected to the substrate layer and extend along the same surface of the substrate layer to a first height value.

[0013] In some embodiments of the present invention, the nanopillars of the nanounit layer are made of silicon, and the substrate layer is made of silicon dioxide.

[0014] In the specific implementation process, the first height value is 680-720nm, and the first period length is 430-470nm.

[0015] In some embodiments of the present invention, based on obtaining a first phase map and a second phase map corresponding to two output channels respectively, the first polarization, the second polarization and the rotation angle corresponding to each nanounit are calculated based on the first phase map and the second phase map, wherein the first polarization corresponds to the length value of the nanounit and the second polarization corresponds to the width value of the nanounit.

[0016] In some embodiments of the present invention, in the step of calculating the first polarization, second polarization, and rotation angle corresponding to each nanounit based on the first phase map and the second phase map, the position of the nanounit in the preset first phase map and the second phase map is determined based on the position of the nanounit in the nanounit layer, the phase value of the nanounit in the first phase map and the second phase map is determined respectively, and the corresponding first polarization, second polarization, and rotation angle are calculated based on the phase value of the nanounit in the first phase map and the second phase map.

[0017] In some embodiments of the present invention, in the step of calculating the corresponding first polarization, second polarization, and rotation angle based on the phase values ​​of the nanounit in the first phase map and the second phase map, the first polarization, second polarization, and rotation angle are calculated using the following formula: in, This represents the phase value of the nanounit in the first phase diagram. This represents the phase value of the nanounit in the second phase diagram. Indicates the first polarization. Indicates the second polarization. Indicates the rotation angle.

[0018] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows, and will also become apparent in part to those skilled in the art upon studying the text, or may be learned by practice of the invention. The objects and other advantages of the invention will become apparent from the description and the accompanying drawings.

[0019] Those skilled in the art will understand that the objectives and advantages achievable with the present invention are not limited to those specifically described above, and that the above and other objectives achievable with the present invention will become clearer from the following detailed description. Attached Figure Description

[0020] The accompanying drawings, which are provided to further illustrate the invention and form part of this application, are not intended to limit the scope of the invention.

[0021] Figure 1 This is a schematic diagram of the bidirectional vortex fiber laser based on intracavity metasurface assistance in this scheme. Figure 2 This is a schematic diagram illustrating the operation and simulation of metasurfaces; Figure 3 This is a schematic diagram of the first phase diagram and the second phase diagram; Figure 4 The simulation results are for nanopillars under x-polarized incident light. Figure 5 This is a schematic diagram of the measurement results for a Gaussian-like beam. Figure 6 This is a schematic diagram of bidirectional asymmetric optical field manipulation within the cavity; Figure 7 This is a schematic diagram of the laser output of this scheme. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments and accompanying drawings. Here, the illustrative embodiments and descriptions of this invention are used to explain the invention, but are not intended to limit the invention.

[0023] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the structures and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0024] Due to the lack of bidirectional asymmetric elements within the cavity, current technology has not yet achieved asymmetric full-phase modulation of the bidirectional optical field within the cavity. Since the intracavity elements need to simultaneously ensure mode self-consistency and decoupled bidirectional optical field output, this requires the elements to possess partial symmetry to ensure normal oscillation of the cavity and partial asymmetry to ensure the asymmetric optical field output within the cavity.

[0025] An optical metasurface is a planar optical element composed of subwavelength-scale artificial units. It possesses advantages such as extreme thinness and low weight, while also allowing arbitrary modulation of the beam phase across multiple degrees of freedom (incident wavelength, polarization, etc.). These advantages mean that metasurfaces can serve as compact and powerful intracavity phase modulation elements.

[0026] The metasurface in this scheme is a general term for metasurfaces with bidirectional properties, which can produce drastically different optical responses depending on the incident direction. By introducing additional polarization-dependent degrees of freedom, it is possible to achieve full-phase (2π / 2) coherence of the bidirectional optical field without breaking the Lorentz reciprocity effect. (Control). Taking a pair of linearly polarized incident orthogonal bases (x- or y-polarized bases) as an example, when light is incident in the forward direction, the Jones matrix of the metasurface can be represented as... When the incident direction is reversed, the Jones matrix of the reverse incident direction will transform into... .

[0027] like Figure 1 As shown, this invention proposes a bidirectional vortex fiber laser based on an intracavity metasurface-assisted structure. The laser includes a pump source, a wavelength division multiplexer, a first collimator, a second collimator, a first polarization beam splitter, a second polarization beam splitter, and a metasurface. The first collimator and the second collimator correspond to respectively Figure 1 Collimators 1 and 2 are included; the first polarization beam splitter and the second polarization beam splitter correspond to... Figure 1 The polarization beam splitter 1 and polarization beam splitter 2 are shown in the figure.

[0028] The two output terminals of the wavelength division multiplexer are respectively connected to a first collimator and a second collimator. The first collimator and the second collimator are respectively connected to a first polarization beamsplitter and a second polarization beamsplitter. The output terminals of the first polarization beamsplitter and the second polarization beamsplitter are both connected to the metasurface. The metasurface includes a substrate layer and a nanounit layer. The first polarization beamsplitter outputs at the nanounit layer of the metasurface, and the second polarization beamsplitter outputs at the substrate layer of the metasurface. Metasurface Correspondence Figure 1 JMS in; The first polarization beam splitter and the second polarization beam splitter are also provided with laser output ports, and the two laser output ports output vortex beams with different topological charges.

[0029] Using the above scheme, this scheme can achieve drastically different optical responses depending on the incident direction. After introducing additional polarization-dependent degrees of freedom, it can achieve full phase (2π) of the bidirectional optical field without breaking the Lorentz reciprocity effect. (Control). Taking a pair of linearly polarized incident orthogonal bases (x- or y-polarized bases) as an example, when light is incident in the forward direction, the Jones matrix of the metasurface can be represented as... When the incident direction is reversed, the Jones matrix of the reverse incident direction will transform into... As the incident direction is reversed, the cross-polarized light field switches once, while the same-polarized light field remains unchanged. This means that the polarization-dependent metasurface simultaneously possesses the ability to control both symmetric and asymmetric bidirectional light fields, separated into different polarization states. Here, this scheme integrates a metasurface into a fiber laser, achieving asymmetric control of the bidirectional light field within the spatial cavity. It also enables the control of bidirectional laser beams within a structurally simple laser, simultaneously generating a pair of high-quality vortex beams with a large span of topological charge within the cavity.

[0030] In some embodiments of the present invention, the laser further includes a first lens and a second lens, wherein the first lens is disposed between a first polarizing beam splitter and a metasurface, and the second lens is disposed between a second polarizing beam splitter and a metasurface.

[0031] In some embodiments of the present invention, on the orthographic projection plane of one side of the nanounit layer of the metasurface, the metasurface is provided with an array of nanopillars, and the nanopillars are provided with a rotation angle.

[0032] In some embodiments of the present invention, the nanopillars are all cuboids, the height of the nanopillars is a preset first height value, and the array period of the nanopillars is set to a first period length.

[0033] In some embodiments of the present invention, the nanopillars are all connected to the substrate layer and extend along the same surface of the substrate layer to a first height value.

[0034] In some embodiments of the present invention, the nanopillars of the nanounit layer are made of silicon, and the substrate layer is made of silicon dioxide.

[0035] In the specific implementation process, the first height value is 680-720nm, and the first period length is 430-470nm.

[0036] In some embodiments of the present invention, based on obtaining a first phase map and a second phase map corresponding to two output channels respectively, the first polarization, the second polarization and the rotation angle corresponding to each nanounit are calculated based on the first phase map and the second phase map, wherein the first polarization corresponds to the length value of the nanounit and the second polarization corresponds to the width value of the nanounit.

[0037] In some embodiments of the present invention, in the step of calculating the first polarization, second polarization, and rotation angle corresponding to each nanounit based on the first phase map and the second phase map, the position of the nanounit in the preset first phase map and the second phase map is determined based on the position of the nanounit in the nanounit layer, the phase value of the nanounit in the first phase map and the second phase map is determined respectively, and the corresponding first polarization, second polarization, and rotation angle are calculated based on the phase value of the nanounit in the first phase map and the second phase map.

[0038] like Figure 3 As shown, 3(a) is the first phase diagram and 3(b) is the second phase diagram. In some embodiments of the present invention, in the step of calculating the corresponding first polarization, second polarization, and rotation angle based on the phase values ​​of the nanounit in the first and second phase diagrams, the first polarization, second polarization, and rotation angle are calculated using the following formula: in, This represents the phase value of the nanounit in the first phase diagram. This represents the phase value of the nanounit in the second phase diagram. Indicates the first polarization. Indicates the second polarization. The rotation angle is the angle between the length direction of the nanounit and the vertical axis in a Cartesian coordinate system constructed by the orthographic projection plane on one side of the nanounit layer of the metasurface.

[0039] In summary, this scheme can simultaneously control the bidirectional optical field within a ring fiber cavity, outputting a pair of topologically decoupled vortex beams within a simple and compact laser cavity. Through proper design, metasurfaces can decouple and control beams from different directions, enabling the direct emission of multiple, wide-span topologically charged vortex beams from a fiber laser, thus expanding the design possibilities for vortex fiber lasers.

[0040] Specifically, such as Figure 2 As shown, the metasurface used to assist in the generation within the bidirectional vortex cavity in this scheme consists of a half-wavelength plate (HWP), i.e., the substrate layer, and a single-layer non-staggered silicon monorod metasurface (MS), i.e., a nanounit layer. The goal of the MS is to generate a pair of phase distributions for the same polarization terms (xx, yy) in the Jones matrix, as shown below. Figure 3 The decoupled vortex beam is shown, and a beam with the highest possible Gaussian mode is generated within the cross-polarization channel to ensure consistency between the laser's vortex output and the intracavity mode. For a beam with a rotation angle... The Jones matrix of a rectangular nanopillar can be represented as: in The rotation matrix is ​​completely determined by the rotation angle of the nanopillar, and can be expressed as: To maximize the efficiency of the metasurface, this scheme... and will Substituting into Eq.(1), we can obtain Since the independent variable only contains three degrees of freedom There are also certain inherent physical constraints among the six dependent variables, which can be derived as follows: It can be observed that and It is completely decoupled, thus enabling the generation of a pair of completely decoupled vortex beams in two co-polarized channels, while due to the cross-polarization components... Received and Due to limitations, it cannot achieve the generation of a completely Gaussian light field while ensuring the quality of the vortex beam. However, as shown below, the purity of the Gaussian mode can be maximized through a special setting of n1, which is called a Gaussian-like (GL) beam. In this case, the Jones matrix of the metasurface can be expressed as... Based on the Jones matrix described above, formulas for calculating the first polarization, the second polarization, and the rotation angle are derived. By carefully selecting the MS, which is determined by the length and width of the basic unit... , (like Figure 4 As shown, Figure 4 (a) represents transmittance. Figure 4 (b) is the phase ( (Diagram showing the relationship between length and width) and the rotation angle of each unit. It can achieve the output of one cross-polarized and one co-polarized channel when incident in the opposite direction (corresponding to the CW direction in the cavity below). The OAM beam and a GL beam are produced. When incident in the forward direction (corresponding to the intracavity CCW direction below), it is possible to emit one beam in each of the cross-polarization and co-polarization channels. An OAM beam and a GL beam. Simulation results of the metasurface are as follows: Figure 2 As shown in (b), the initial phase of the GL beam can be adjusted by appropriate selection. Numerical implementation: When the phase of the Gaussian-like beam is equal to At this time, n1 will be reduced by 1. The GL beam is then a special fractional vortex beam, with the initial complex amplitude of the optical field being... .in Representing polar coordinates. This fractional vortex can be decomposed into a set of integer OAM states, whose complex amplitude can be expressed as... in, It is a positive integer. The pattern corresponds to a Gaussian beam. Indicates having The probability amplitude and state of the occurrence of a topological charge beam probability of occurrence .

[0041] like Figure 5 As shown, Figure 5 (a) shows the OAM mode spectrum formed by the theoretical phase distribution and mode decomposition of the GL beam. Figure 5 (b) is the intensity distribution map of the GL beam obtained by measurement. It can be seen from the mode decomposition by the above formula that the GL beam can contain more than 40% Gaussian mode without affecting the vortex beam of the cross polarization channel.

[0042] With the aid of metasurfaces, this scheme can output vortex beams with different topological charges from two directions (CW and CCW). The structure and principle of the laser are as follows: Figure 6 As shown, Figure 6 (a) is a network representation of the clockwise (CW) and counterclockwise (CCW) optical path operating states of the laser. Figure 6 (b) is a schematic diagram of the free-space optical path and polarization evolution of the laser. All fibers within the fiber laser are polarization-maintaining single-mode fibers to ensure that the beams in the fiber optical path are in the fixed-polarization LP01 mode. A 976 nm pump is injected into the resonant cavity through a 980 / 1030 nm wavelength division multiplexer. Ytterbium-doped polarization-maintaining fiber serves as the gain medium. The clockwise (CW) beam within the laser is output after passing through the first collimator. The y-polarization component (vortex) of the CW beam is modulated by the metasurface. The x-polarized component will be output outside the cavity by the first polarization beam splitter, while the Gaussian mode of the x-polarized component can be coupled back into the second polarization beam splitter. The CCW beam will be output through col.2, and the y-polarized component (vortex) will also be modulated by the metasurface. The x-polarized component (Gaussian-like component) will be output by the second polarization beam splitter, while the x-polarized component can be coupled back into col.1. In summary, the polarization state and transverse intensity distribution of both CW and CCW beams ensure self-consistent propagation within the cavity. Polarization-maintaining gain fiber and related optical components ensure laser emission around 1030 nm, corresponding to the design wavelength of the metasurface.

[0043] The intensity pattern of the vortex beam directly output from the cavity is as follows: Figure 7 As shown, Figure 7 (a) are scanning electron microscope images of the metasurface (scale bar represents 1 micrometer), the intensity of the bidirectional output vortex beam of the laser, and the interference pattern, respectively. Figure 7 (b) is a schematic diagram of the physical image of the metasurface; Figure 7 (c) shows the relationship between output power and pump power, with the blue dots representing the output of the beam in the CW direction; Figure 7 (d) is a schematic diagram of the output spectrum of the laser beam in two directions; Figure 7 (e) Schematic diagram of evaluating the mode purity of the emitted vortex beam using a spatial light modulator; measurements by a spectrometer show that the wavelengths of the vortex beams output by both CW and CCW are around 1028 nm. The OAM beams in both directions simultaneously possess an oscillation threshold of 79 mW and high slope efficiencies of 4.6% and 12.9%, respectively. By modulating the vortex beams output from the JVFL using spatial light modulators with different OAM order phase profiles, mode purity greater than 93% can be obtained for both intracavity vortex beams.

[0044] This patent proposes a novel vortex laser. As the core modulation element, the optical field manipulation capability of the polarization-dependent metasurface is perfectly matched to that of a bidirectional fiber cavity. With the aid of a carefully designed metasurface, bidirectional asymmetric full-phase manipulation within the laser cavity is demonstrated. Using an OAM beam as a demonstration, two vortex fields with completely different topological charges are generated within the cavity using only a single monolayer non-interlaced metasurface and a half-wave plate. Through interference with spherical waves, the topological charges of the vortex fields are verified, and further quantitative analysis shows that both vortex fields from different directions possess extremely high (93%) mode purity. In summary, a highly attractive direction is emerging: the simultaneous and independent manipulation of bidirectional optical fields within a resonant cavity. This directional degree of freedom, previously overlooked by other researchers, is not limited to ring cavities; it can be applied to linear cavities of other single-mode lasers or other single-mode resonant systems with bidirectional operating modes. Meanwhile, the final mode of the regulated light field is not limited to a vortex beam. Since the metasurface energy can completely decouple the bidirectional light field of cross-polarization, the actual target can be arbitrary, such as orbital angular momentum combs and self-accelerating beams, etc.

[0045] Those skilled in the art will understand that the exemplary components, systems, and methods described in conjunction with the embodiments disclosed herein can be implemented in hardware, software, or a combination of both. Whether implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this invention. When implemented in hardware, it can be, for example, electronic circuits, application-specific integrated circuits (ASICs), appropriate firmware, plug-ins, function cards, etc. When implemented in software, the elements of this invention are programs or code segments used to perform the desired tasks. The programs or code segments can be stored in a machine-readable medium or transmitted over a transmission medium or communication link via data signals carried in a carrier wave.

[0046] It should be clarified that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of the present invention.

[0047] In this invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with or in place of features of other embodiments.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, various modifications and variations can be made to the embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A bidirectional vortex fiber laser assisted by an intracavity metasurface, characterized in that, The laser includes a pump source, a wavelength division multiplexer, a first collimator, a second collimator, a first polarization beam splitter, a second polarization beam splitter, and a metasurface; The two output terminals of the wavelength division multiplexer are respectively connected to a first collimator and a second collimator. The first collimator and the second collimator are respectively connected to a first polarization beamsplitter and a second polarization beamsplitter. The output terminals of the first polarization beamsplitter and the second polarization beamsplitter are both connected to the metasurface. The metasurface includes a substrate layer and a nanounit layer. The first polarization beamsplitter outputs at the nanounit layer of the metasurface, and the second polarization beamsplitter outputs at the substrate layer of the metasurface. The first polarization beam splitter and the second polarization beam splitter are also provided with laser output ports, and the two laser output ports output vortex beams with different topological charges; Obtain a first phase map and a second phase map corresponding to the two output channels respectively. Calculate the first polarization, second polarization, and rotation angle corresponding to each nanounit based on the first and second phase maps. Determine the position of the nanounit in the preset first and second phase maps based on the position of the nanounit in the nanounit layer. Determine the phase value of the nanounit in the first and second phase maps respectively. Calculate the corresponding first polarization, second polarization, and rotation angle based on the phase value of the nanounit in the first and second phase maps. The first polarization corresponds to the length value of the nanounit, and the second polarization corresponds to the width value of the nanounit.

2. The bidirectional vortex fiber laser based on intracavity metasurface assistance according to claim 1, characterized in that, The laser also includes a first lens and a second lens, wherein the first lens is disposed between a first polarizing beam splitter and a metasurface, and the second lens is disposed between a second polarizing beam splitter and a metasurface.

3. The bidirectional vortex fiber laser based on intracavity metasurface assistance according to claim 1, characterized in that, On the orthographic projection plane of one side of the nanounit layer of the metasurface, the metasurface is provided with an array of nanopillars, and the nanopillars are provided with a rotation angle.

4. The bidirectional vortex fiber laser based on intracavity metasurface assistance according to claim 3, characterized in that, All nanopillars are cuboids, and the height of each nanopillar is a preset first height value. The array period of the nanopillars is set to the first period length.

5. The bidirectional vortex fiber laser based on intracavity metasurface assistance according to claim 3, characterized in that, The nanopillars are all connected to the substrate layer and extend along the same surface of the substrate layer to a first height value.

6. The bidirectional vortex fiber laser based on intracavity metasurface assistance according to claim 1, characterized in that, The nanopillars of the nanounit layer are made of silicon, and the substrate layer is made of silicon dioxide.

7. The bidirectional vortex fiber laser based on intracavity metasurface assistance according to claim 4, characterized in that, The first height value is 680-720nm, and the first period length is 430-470nm.

8. The bidirectional vortex fiber laser based on intracavity metasurface assistance according to claim 1, characterized in that, In the step of calculating the corresponding first polarization, second polarization, and rotation angle based on the phase values ​​of the nanounit in the first and second phase maps, the first polarization, second polarization, and rotation angle are calculated using the following formula: in, This represents the phase value of the nanounit in the first phase diagram. This represents the phase value of the nanounit in the second phase diagram. Indicates the first polarization. Indicates the second polarization. Indicates the rotation angle.

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