Spiral structure waveguide for vortex light topological charge conversion and implementation method thereof

Abstract

The invention discloses a spiral structure waveguide for vortex light topological charge conversion and an implementation method thereof, and belongs to the field of optical waveguides. The circular waveguide and the spiral structure are combined, the spiral structure is used for regulating and controlling the vortex light mode according to the mode conversion matching condition, and vortex light conversion between any topological charge orders is achieved; according to the invention, complete conversion between different vortex lights is realized, two vortex light mixed beams with different proportions can be generated, and the requirements of generation and utilization of vortex lights with different orders in an integrated photonics on-chip structure are met. According to the method, the problem that topological charges cannot be freely converted among different vortex light modes in a waveguide structure is solved, the application value of the waveguide structure in the aspect of vortex light regulation and control is expanded, and the possibility is provided for an integrated photon platform to utilize vortex light topological charge degree-of-freedom coding information and process calculation tasks. According to the invention, information coding, optical communication, calculation and other applications are carried out by changing the topological charge of the vortex light.

Description

Technical Field

[0001] This invention relates to the field of optical waveguides, specifically to a spiral waveguide for topological charge conversion of vortex light and its implementation method. Background Technology

[0002] Vortex light, due to its non-uniform phase distribution, possesses non-zero orbital angular momentum, providing a novel degree of freedom for optical field manipulation. By encoding the topological charge corresponding to the orbital angular momentum, important functions such as high-dimensional information encoding, ultra-high resolution imaging, and diffraction neural network calculations can be realized. However, most current manipulations of vortex light are based on spatial structures. Common spatial vortex light conversion structures include spatial light modulators, spiral phase plates, metasurfaces etched with subwavelength structures, and cylindrical lens converters. By carefully designing the shape, size, and orientation of these structures, the phase, amplitude, and polarization of light waves can be arbitrarily manipulated. Although these structures offer significant conversion effects and high conversion efficiency, their large overall size makes them difficult to integrate into on-chip structures.

[0003] Currently, researchers have also studied some methods for controlling vortex beams based on on-chip integrated platforms. Due to its infinitely orthogonal mode space, vortex beams are considered one of the important technological directions for improving the capacity of information transmission systems on on-chip integrated platforms. How to directly and flexibly generate, convert, and exchange vortex beam modes within waveguides has become one of the key challenges in the development of information transmission technology. Current mainstream solutions are mainly based on structures such as micro-ring resonators, waveguides with special cross-sections (such as cross-shaped and corner-cut cross-sections), and grating couplers. Micro-ring resonators utilize the principle of resonance enhancement to efficiently excite specific vortex modes and have good compatibility with existing photonic integrated platforms. Cross-shaped waveguides and corner-cut cross-section waveguides, through special design, ensure that the two components of the synthesized vortex beam have the same effective mode refractive index, supporting stable transmission of fixed-order vortex beams on the chip. Specially designed on-chip grating couplers (such as circular gratings) can directly map waveguide modes into free-space vortex beams, which is a key solution for achieving efficient interface between on-chip and free space. However, these schemes can only be used for on-chip generation and detection of vortex light, and cannot truly realize the conversion between different modes of vortex light, that is, the conversion between vortex light topological charges, on-chip.

[0004] The difficulty in on-chip vortex topological charge conversion stems from the fact that fixed waveguide structures often only support one fixed vortex mode, failing to support stable long-distance propagation of other modes. Even if a waveguide structure can simultaneously support multiple vortex modes, these modes, being orthogonal to each other, cannot naturally convert during transmission. To simultaneously support multiple vortex modes and achieve conversion between them, meticulous optimization of the waveguide structure is required to support stable transmission of multiple modes, along with specially designed auxiliary structures to facilitate conversion between different orthogonal modes. Therefore, achieving vortex topological charge conversion remains a pressing issue for on-chip integrated photonics platforms. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a helical waveguide for topological charge conversion of vortex light and its implementation method. By flexibly controlling the generation, conversion and exchange of vortex light modes, this invention can conveniently adjust the mixing ratio between different vortex light modes; it provides a new device foundation for mode division multiplexing systems, offers new ideas for applications such as signal processing and spectral shaping, and also lays a theoretical foundation for the development of reconfigurable, programmable and multifunctional vortex light processing devices.

[0006] One object of the present invention is to propose a spiral waveguide for topological charge conversion in vortex optical systems.

[0007] The spiral waveguide for vortex topology charge conversion of the present invention comprises: a circular waveguide and a spiral structure; wherein, the circular waveguide is a solid cylinder with a circular cross-section, supporting the stable transmission of vortex light of arbitrary topology charge order as an eigenmode within the waveguide, and supporting vortex light of arbitrary polarization state; a spiral structure is provided on the sidewall surface of the circular waveguide, the spiral structure comprising one or more helical lines, the helical lines being equally spaced along the axial direction and uniformly distributed along the circumference; the spiral structure is used to control the vortex light mode, the vortex light mode including topology charge order and polarization state; the vortex light is incident on the spiral waveguide in an initial vortex light mode, transmitted through the spiral waveguide, the spiral structure converts the topology charge order of the vortex light, and after complete conversion, it becomes a converted vortex light mode, the converted vortex light mode being related to the number and direction of the helical lines of the spiral structure; the outgoing vortex light includes the initial vortex light mode and the converted vortex light mode, and the outgoing vortex light is adjusted to an arbitrary mixing ratio between the two different vortex light modes by adjusting the length of the spiral structure.

[0008] The vortex light is directly incident from one end of the helical waveguide via end-face coupling, and its carried topological charge is modulated by a spatial light modulator or a helical phase plate in front of the waveguide. During propagation within the helical structure, the converted vortex light mode transitions from the initial vortex light mode. The polarization states of the initial and converted vortex light modes are the same, but the order of the topological charge changes. The relationship between the initial and converted vortex light modes and the helical structure satisfies the following: when the order of the topological charge of the initial and converted vortex light modes is the same, the number of helical elements in the helical structure... The spiral direction of the spiral structure is opposite to the polarization state of the initial vortex optical mode and the converted vortex optical mode; when the topological charge orders of the initial vortex optical mode and the converted vortex optical mode have opposite signs, the number of spiral elements in the spiral structure... At the same time The rotation direction of the helical structure is the same as the polarization state of the initial vortex optical mode and the converted vortex optical mode. The rotation direction of the spiral structure is opposite to the polarization state of the initial vortex optical mode and the converted vortex optical mode, where j is the absolute value of the topological charge order of the initial vortex optical mode and k is the absolute value of the topological charge order of the converted vortex optical mode. The number of helical lines in the helical structure.

[0009] According to the conditions Determine the period length L of the helical structure, where, These are the propagation constants for the initial vortex mode and the converted vortex mode, respectively. The propagation constants are related to the refractive index of the effective mode.

[0010] The spiral waveguide of this invention allows for convenient control of the mixing ratio between different vortex light modes. Traditional vortex light manipulation involves completely converting vortex light of one topological charge order into vortex light of another. In the spiral waveguide of this invention, the incident vortex light includes only the initial vortex light mode, while the outgoing vortex light includes two initial vortex light modes and a converted vortex light mode. The ratio between the different vortex light modes is related to the length of the spiral structure, i.e., the transmission distance of the vortex light within the spiral structure. The vortex light state at a transmission distance z is a mixture of the initial vortex light mode and the converted vortex light mode; the transmission distance at which the vortex light is completely converted from the initial vortex light mode to the converted vortex light mode in one complete conversion is the complete conversion length. , The coupling coefficient is [value missing]. At the full conversion length, the vortex optical state only has the converted vortex optical mode. By flexibly designing and adjusting the length of the spiral structure, the transmission distance z can be adjusted to be within the full conversion length. Within, by adjusting the arbitrary mixing ratio between two different vortex light modes, namely the initial vortex light mode and the converted vortex light mode, the emitted vortex light state can be achieved as a mixture of the two different vortex light modes in any proportion.

[0011] The circular waveguide and helical structure are made of resin or silicon dioxide and are fabricated on the sidewall surface of the circular waveguide using 3D printing or femtosecond laser direct writing. The cross-sectional shape of the helical structure on the sidewall surface of the circular waveguide is rectangular, with a radial thickness of 1 / 5 to 1 / 10 of the diameter of the circular waveguide. The diameter of the circular waveguide needs to match the wavelength of the vortex light to support stable propagation of the mode corresponding to the operating wavelength. The axial width is L / (2l). The helical structure is either convex or concave, achieving the same modulation effect. The helical structure provides external perturbations, thereby affecting the evolution of the eigenstates.

[0012] Another objective of this invention is to propose a method for implementing a helical waveguide for topological charge conversion in vortex optical systems.

[0013] The present invention provides a method for implementing a helical waveguide for topological charge conversion in vortex optical systems, comprising the following steps:

[0014] 1) A spiral structure is set on the sidewall surface of the circular waveguide; the circular waveguide is a solid cylinder with a circular cross-section, which supports the stable transmission of vortex light of arbitrary topological charge order as an eigenmode within the waveguide, and supports vortex light of arbitrary polarization state; the spiral structure includes one or more spirals, which are equally spaced along the axial direction and uniformly distributed along the circumference.

[0015] 2) The vortex light is directly incident on the helical structure from one end of the helical waveguide in the initial vortex light mode via end-face coupling; the helical structure converts the topological charge order of the vortex light, and after complete conversion, it becomes the converted vortex light mode. The converted vortex light mode is related to the number of helical lines and the direction of rotation of the helical structure.

[0016] 3) After the vortex light is incident, it propagates in the spiral structure. As the propagation distance increases, the converted vortex light mode changes from the initial vortex light mode.

[0017] 4) The emitted vortex light includes an initial vortex light mode and a converted vortex light mode. By adjusting the length of the spiral structure, the emitted vortex light can be adjusted to any mixing ratio between the two different vortex light modes, so as to realize that the vortex light state is a mixture of the two different vortex light modes in any ratio.

[0018] In step 1), the circular waveguide and the helical structure are made of resin or silicon dioxide and are fabricated on the sidewall surface of the circular waveguide using 3D printing or femtosecond laser direct writing. The cross-sectional shape of the helical structure located on the sidewall surface of the circular waveguide is rectangular; the helical structure can be either convex or concave.

[0019] In step 2), a spatial light modulator or a spiral phase plate is placed in front of the spiral waveguide to modulate the topological charge carried by the vortex light.

[0020] In step 3), the conversion between the initial vortex light mode and the transformed vortex light mode satisfies the following two conditions: (1) When the topological charge order has the same sign. Or when the order of the topological charge has the opposite sign and (2) , denoted by , j represents the absolute value of the topological charge order of the initial vortex optical mode, and k represents the absolute value of the topological charge order of the converted vortex optical mode. are the propagation constants for the initial vortex optical mode and the converted vortex optical mode, respectively, and L is the period length of the spiral structure.

[0021] In step 4), the transmission distance during which the vortex light is completely converted from the initial vortex light mode to the converted vortex light mode in one step is the complete conversion length. , The coupling coefficient is used; at the full conversion length, the vortex optical state only converts to the vortex optical mode. Adjusting the length of the spiral structure adjusts the transmission distance z to be within the full conversion length. Internally, the emitted vortex light is adjusted to an arbitrary mixing ratio between two different vortex light modes. Based on the complete conversion length, according to The initial ratio of the vortex light modes is used to calculate the transmission distance and determine the length of the spiral structure, resulting in an outgoing vortex light from a mixture of two vortex light modes in any ratio.

[0022] It also includes using a probe light to detect the emitted vortex light. The probe light is interfered with by a coherent Gaussian spatial beam, or by using a time-domain spectral system in the terahertz band to split the probe light into two beams for differential detection, and then performing Fourier transform analysis to obtain the phase distribution corresponding to the emitted vortex light.

[0023] Advantages of this invention:

[0024] This invention combines a helical outer structure with a circular waveguide inner structure. Based on mode conversion matching conditions, the helical structure provides the absolute value of the topological charge difference required before and after the conversion of vortex light modes, achieving vortex light conversion between arbitrary topological charge orders. The period length of the helical structure is determined by the effective mode refractive index and topological charge of the preceding and following vortex light modes. The complete conversion length of the helical structure is inversely proportional to the coupling coefficient. Furthermore, by adjusting the length of the helical structure, the arbitrary mixing ratio between two different vortex light modes can be adjusted. The vortex light topological charge conversion method proposed in this invention is not only applicable to the complete conversion between different vortex lights, but can also be used to generate mixed beams of two vortex lights in different ratios, meeting the needs of generating and utilizing vortex lights of different orders in integrated photonics on-chip structures. This invention solves the problem of the inability to achieve arbitrary topological charge conversion between different modes of vortex light in waveguide structures, expanding the application value of waveguide structures in controlling vortex light, and providing the possibility for integrated photonics platforms to use the topological charge of vortex light as a degree of freedom to encode information and process computational tasks. This invention achieves information encoding, optical communication, and computational applications by changing the topological charge of vortex light. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the spiral structure of the spiral waveguide for vortex optical topological charge conversion of the present invention, which is convex.

[0026] Figure 2 This is a schematic diagram of the concave spiral structure of the spiral waveguide for vortex optical topological charge conversion of the present invention.

[0027] Figure 3 The electric field intensity distribution diagram of a spiral waveguide for vortex topological charge conversion according to an embodiment of the present invention is shown when the initial vortex optical mode is completely converted into the converted vortex optical mode.

[0028] Figure 4 This is a phase distribution diagram of a spiral waveguide for vortex topology charge conversion according to an embodiment of the present invention, showing the complete conversion from an initial vortex optical mode to a converted vortex optical mode. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 1 and 2As shown, the helical waveguide for topological charge conversion of vortex light in this embodiment includes a circular waveguide and a helical structure. The circular waveguide is a solid cylinder with a circular cross-section, supporting the stable transmission of vortex light of any topological charge order as an eigenmode within the waveguide, and supporting vortex light of any polarization state. The sidewall surface of the circular waveguide is provided with a helical structure, which includes two helical lines that are equidistant along the axial direction and uniformly distributed along the circumference.

[0031] The relationship between the initial vortex optical mode, the transformed vortex optical mode, and the helical structure satisfies the following equation:

[0032]

[0033] In this equation, the left side represents the initial vortex light mode, the middle side represents the direction of rotation and the number of helical lines, and the right side represents the converted vortex light mode. j is the absolute value of the topological charge order of the initial vortex light mode, k is the absolute value of the topological charge order of the converted vortex light mode, -1 indicates that the polarization state of the vortex light or the direction of rotation of the helical structure is right-handed, and +1 indicates that the polarization state of the vortex light or the direction of rotation of the helical structure is left-handed. The initial vortex light mode and the converted vortex light mode have the same polarization state. From the above equation, it can be seen that when the initial vortex light mode and the converted vortex light mode have the same polarization state and the same sign of the topological charge order, the number of helical lines is the absolute value of the difference between the absolute values ​​of the topological charge orders of the converted vortex light mode and the initial vortex light mode. The spiral direction of the helical structure is opposite to the polarization state of the initial vortex mode and the converted vortex mode; when the polarization states of the initial vortex mode and the converted vortex mode are the same and their topological charge orders have opposite signs, the number of spiral elements is the sum of the absolute values ​​of the topological charge orders of the converted vortex mode and the initial vortex mode. At the same time The rotation direction of the helical structure is the same as the polarization state of the initial vortex optical mode and the converted vortex optical mode. The direction of rotation of the spiral structure is opposite to the polarization state of the initial vortex light mode and the converted vortex light mode.

[0034] The vortex light is directly incident from one end of the helical waveguide via end-face coupling, and its carried topological charge is modulated by a spatial light modulator or a helical phase plate in front of the helical waveguide. After incident, the vortex light propagates in the helical structure. As the propagation distance z increases, the converted vortex light mode transforms from the initial vortex light mode. The transformation process satisfies the coupled-mode theory, as expressed by the following equation:

[0035]

[0036] Where A and B are the amplitudes of the initial vortex optical mode and the converted vortex optical mode, respectively. These are the propagation constants for the initial vortex optical mode and the transformed vortex optical mode, respectively. The propagation constant is equal to the product of the wavenumber of light in vacuum and the effective mode refractive index. This represents the coupling coefficient between the initial vortex optical mode and the converted vortex optical mode. , and These represent the electric fields of the initial vortex optical mode and the converted vortex optical mode, respectively, and L is the period length of the helical structure, i.e., the length of the helix along the axis after rotating 360°. Mode conversion occurs when the following two conditions are met: (1) the topological charge orders have the same sign. Or when the order of the topological charge has the opposite sign and (2) , Let L be the number of helical lines in the helical structure. Determine the period length L of the helical structure according to condition (2).

[0037] The period length of the helical structure is determined by the effective mode refractive index and topological charge order corresponding to the initial vortex optical mode and the converted vortex optical mode. The complete conversion length of the helical structure is the transmission distance required for a complete conversion from the initial vortex optical mode to the converted vortex optical mode in one step, and the complete conversion length is inversely proportional to the coupling coefficient. The same helical waveguide will modulate right-handed light corresponding to -1 and left-handed light corresponding to +1 differently, which is related to the helix direction of the helix.

[0038] The ratio between different vortex light modes is related to the length of the helical structure, i.e., the transmission distance of the vortex light within the helical structure. The specific correspondence is derived using the following formula: Hamiltonian of a helical waveguide supporting inter-mode conversion. Write it in the following form:

[0039]

[0040] in, The coupling coefficient is a real number, representing the coupling coefficient between the initial vortex optical mode and the converted vortex optical mode; the helical waveguide supports two eigenstates. and They are respectively:

[0041]

[0042] The incident vortex light state is decomposed into:

[0043]

[0044] in, The incident vortex light state has an initial vortex light mode of 1 and a converted vortex light mode of 0, meaning that the incident vortex light state only has the initial vortex light mode.

[0045] Vortex optical state when propagating a distance z in a spiral structure Decomposed into:

[0046]

[0047] The vortex optical state at a transmission distance z is a mixture of the initial vortex optical mode and the converted vortex optical mode; the transmission distance at which the vortex optical light completely converts from the initial vortex optical mode to the converted vortex optical mode in one complete transformation is the complete conversion length. When the conversion length is fully achieved, the vortex optical state only exhibits the converted vortex optical mode; by flexibly designing and adjusting the length of the spiral structure, the transmission distance z can be adjusted to be within the fully converted length. Inside, the emitted vortex light is adjusted to be any mixture ratio between two different vortex light modes, namely the initial vortex light mode and the converted vortex light mode, so that the emitted vortex light state is a mixture of the two different vortex light modes in any ratio.

[0048] After being manipulated by a helical waveguide, the topological charge order of the outgoing vortex light differs from that of the incident vortex light. It may be completely converted to another integer order, or it may lie between the incident topological charge order and the converted topological charge order. Detection methods include interferometry using another coherent Gaussian spatial beam, or using a terahertz time-domain spectral system to split the probe light into two beams for differential detection, followed by Fourier transform analysis to obtain the corresponding phase distribution.

[0049] In this embodiment, the circular waveguide and helical structure are made of resin with a refractive index of 1.7, fabricated by 3D printing on the sidewall surface of the circular waveguide. The wavelength of the vortex light is 750 μm, the cross-sectional diameter of the circular waveguide is 1200 μm, the thickness of the helical line is 240 μm, and the width of the helical line is L / 4 = 942 μm. The surrounding material is air. The helical structure can be either convex or concave. The convex type involves adding a helical structure to the surface of the circular waveguide. The outer radius of the helical structure is larger than that of the circular waveguide, while the inner radius is the same as that of the circular waveguide. Figure 1 As shown, the difference between the outer radius and the inner radius of the helical structure is the thickness of the helix; the concave type involves etching a helical structure onto the surface of a circular waveguide, where the outer radius of the helical structure is the same as the radius of the circular waveguide, and the inner radius is smaller than that of the circular waveguide, as shown in the figure. Figure 2 As shown.

[0050] This embodiment utilizes FDTD (Finite-Difference Time-Domain) simulation to calculate the intensity and phase distribution of the incident vortex light after passing through the spiral structure. Since the inner circular waveguide in this embodiment exhibits degeneracy of polarization modes in both the x and y directions, there are no restrictions on the polarization mode of the incident vortex light. Vortex light incident in any polarization direction will be modulated by the topological charge of the outer spiral structure, and the polarization direction remains unchanged between the incident and outgoing paths. In this embodiment, by calculating and adjusting parameters such as the effective mode refractive index of the vortex light carrying a first-order topological charge, the effective mode refractive index of the vortex light carrying a third-order topological charge, and the complete conversion length, a structure capable of converting incident vortex light carrying a first-order topological charge into vortex light carrying a third-order topological charge for outgoing emission is designed. When the incident vortex light is a vortex light carrying a first-order topological charge, the rotation direction of the vortex light is matched with the rotation direction of the spiral structure, and the length of the spiral structure is the same as the complete conversion length between the vortex light carrying a first-order topological charge and the vortex light carrying a third-order topological charge. A vortex light carrying a third-order topological charge will be obtained at the exit port. According to condition (1), the spiral structure consists of two helices. The topological charge order of the initial vortex light mode and the converted vortex light mode is the same, and the polarization state is right-handed. The rotation direction of the spiral structure is left-handed. According to condition (2), the period length L of the spiral structure is 3768 μm. The electric field intensity distributions of the vortex light carrying a first-order topological charge and the vortex light carrying a third-order topological charge before and after the conversion of the spiral structure are as follows: Figure 3 As shown, the phase distributions of the vortex beams carrying first-order topological charges and third-order topological charges before and after the transformation are as follows: Figure 4 As shown.

[0051] In this embodiment, to completely convert the initial vortex light mode to the converted vortex light mode, the length of the spiral structure is the complete conversion length. Based on this length value, according to The proportion of the initial vortex light mode is used to calculate the transmission distance. The length of the spiral structure is equal to the transmission distance, allowing for arbitrary conversion of the initial vortex light mode. This results in an output vortex light that is a mixture of the two vortex light modes in any proportion before and after conversion. For example, to convert 1 / 2 of the initial vortex light mode to the converted vortex light mode, then... , , , To change 2 / 3 of the initial vortex light mode to a vortex light mode, then... , , , To convert 1 / 3 of the initial vortex light mode to the converted vortex light mode, then... , , , .

[0052] Finally, it should be noted that the purpose of disclosing the embodiments is to help further understand the present invention. However, those skilled in the art will understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the scope of protection of the present invention is defined by the claims.

Claims

1. A helical waveguide for topological charge conversion in vortex optical systems, characterized in that, The spiral waveguide includes a circular waveguide and a spiral structure. The circular waveguide is a solid cylinder with a circular cross-section. A spiral structure is provided on the sidewall surface of the circular waveguide. The spiral structure includes one or more helical lines, which are equally spaced along the axial direction and uniformly distributed along the circumference. Vortex light is incident on the spiral waveguide in an initial vortex light mode. The spiral structure converts the topological charge order of the vortex light, and after complete conversion, it becomes a converted vortex light mode. The converted vortex light mode is related to the number and direction of the helical lines in the spiral structure. The emitted vortex light includes the initial vortex light mode and the converted vortex light mode. The emitted vortex light can be adjusted to any mixture ratio between the two different vortex light modes by adjusting the length of the spiral structure.

2. The helical waveguide according to claim 1, characterized in that, The initial vortex optical mode and the converted vortex optical mode have the same polarization state; the relationship between the initial vortex optical mode, the converted vortex optical mode, and the helical structure satisfies the following: when the topological charge orders of the initial vortex optical mode and the converted vortex optical mode have the same sign, the number of helical lines in the helical structure... The spiral direction of the spiral structure is opposite to the polarization state of the initial vortex optical mode and the converted vortex optical mode; when the topological charge orders of the initial vortex optical mode and the converted vortex optical mode have opposite signs, the number of spiral elements in the spiral structure... At the same time The rotation direction of the helical structure is the same as the polarization state of the initial vortex optical mode and the converted vortex optical mode. The rotation direction of the spiral structure is opposite to the polarization state of the initial vortex optical mode and the converted vortex optical mode, j is the absolute value of the topological charge order of the initial vortex optical mode, and k is the absolute value of the topological charge order of the converted vortex optical mode.

3. The helical waveguide according to claim 2, characterized in that, According to the conditions Determine the period length L of the helical structure, where, These are the propagation constants for the initial vortex light mode and the converted vortex light mode, respectively.

4. The helical waveguide according to claim 3, characterized in that, The materials of the circular waveguide and the helical structure are resin or silicon dioxide; the cross-sectional shape of the helical structure is rectangular, the radial thickness is 1 / 5 to 1 / 10 of the diameter of the circular waveguide, and the axial width is L / (2l). The number of helical lines in the helical structure.

5. A method for implementing a helical waveguide for topological charge conversion in vortex optical systems according to any one of claims 1 to 4, characterized in that, The implementation method includes the following steps: 1) A helical structure is set on the sidewall surface of the circular waveguide; the circular waveguide is a solid cylinder with a circular cross-section; the helical structure includes one or more helical lines, which are equally spaced along the axial direction and uniformly distributed along the circumference. 2) The vortex light is directly incident on the helical structure from one end of the helical waveguide in the initial vortex light mode via end-face coupling; the helical structure converts the topological charge order of the vortex light, and after complete conversion, it becomes the converted vortex light mode. The converted vortex light mode is related to the number of helical lines and the direction of rotation of the helical structure. 3) As the transmission distance increases, the vortex light transmits through the spiral structure, and the converted vortex light mode changes from the initial vortex light mode. 4) The emitted vortex light includes an initial vortex light mode and a converted vortex light mode. By adjusting the length of the spiral structure, the emitted vortex light can be adjusted to any mixing ratio between the two different vortex light modes.

6. The implementation method according to claim 5, characterized in that, In step 1), the materials for the circular waveguide and the spiral structure are resin or silicon dioxide, which are fabricated on the sidewall surface of the circular waveguide by 3D printing or femtosecond laser direct writing.

7. The implementation method according to claim 5, characterized in that, In step 2), a spatial light modulator or a spiral phase plate is placed in front of the spiral waveguide to modulate the topological charge carried by the vortex light.

8. The implementation method according to claim 5, characterized in that, In step 3), the conversion between the initial vortex light mode and the transformed vortex light mode satisfies the following two conditions: (1) When the topological charge order has the same sign. Or when the order of the topological charge has the opposite sign and (2) , denoted by , j represents the absolute value of the topological charge order of the initial vortex optical mode, and k represents the absolute value of the topological charge order of the converted vortex optical mode. are the propagation constants for the initial vortex optical mode and the converted vortex optical mode, respectively, and L is the period length of the spiral structure.

9. The implementation method according to claim 5, characterized in that, In step 4), the transmission distance during which the vortex light is completely converted from the initial vortex light mode to the converted vortex light mode in one step is the complete conversion length. , The coupling coefficient is used to adjust the length of the spiral structure to adjust the transmission distance at the full conversion length. Inside, the emitted vortex light is adjusted to an arbitrary mixing ratio between two different vortex light modes.

10. The implementation method according to claim 9, characterized in that, Based on the complete conversion length, according to The initial ratio of the vortex light modes is used to calculate the transmission distance and determine the length of the spiral structure, resulting in an outgoing vortex light from a mixture of two vortex light modes in any ratio.

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