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CN-122018081-A - Spiral structure waveguide for vortex light topology charge conversion and implementation method thereof

CN122018081ACN 122018081 ACN122018081 ACN 122018081ACN-122018081-A

Abstract

The invention discloses a spiral structure waveguide for vortex rotation topological charge conversion and an implementation method thereof, and belongs to the field of optical waveguides. The invention combines the circular waveguide and the spiral structure, regulates vortex optical mode by utilizing the spiral structure according to mode conversion matching conditions, realizes vortex optical conversion between random topological charge orders, not only realizes complete conversion between different vortex lights, but also can generate two vortex light mixed beams with different proportions, thereby meeting the requirements of generating and utilizing vortex optical rotation with different orders in an integrated photonics on-chip structure. The invention solves the problem that the random conversion of the topological charges can not be realized among different vortex optical modes in the waveguide structure, expands the application value of the waveguide structure in the aspect of regulating and controlling vortex rotation, and provides possibility for the integrated photon platform to encode information and process calculation tasks by utilizing the degree of freedom of vortex rotation topological charges. The invention can be used for information coding, optical communication, calculation and the like by changing the topological charge of vortex rotation.

Inventors

  • GAO JINZE
  • HU XIAOYONG
  • GONG QIHUANG

Assignees

  • 北京大学

Dates

Publication Date
20260512
Application Date
20260227

Claims (10)

  1. 1. A spiral structure waveguide for vortex light topological charge conversion is characterized by comprising a round waveguide and a spiral structure, wherein the round waveguide is a solid cylinder, the cross section of the round waveguide is circular, the spiral structure is arranged on the side wall surface of the round waveguide and comprises one or more spiral lines which are uniformly distributed along the circumferential direction at equal intervals along the axial direction, vortex light enters the spiral structure waveguide in an initial vortex rotation mode, the spiral structure converts the topological charge order of vortex rotation, the vortex rotation mode is converted into a conversion vortex rotation mode after complete conversion, the conversion vortex rotation mode is related to the number of spiral lines and the rotation direction of the spiral structure, the emergent vortex light comprises the initial vortex rotation mode and the conversion vortex rotation mode, and the emergent vortex light is adjusted to be any mixing proportion between two different vortex light modes by adjusting the length of the spiral structure.
  2. 2. The waveguide according to claim 1, wherein the polarization states of the initial vortex rotation mode and the converted vortex rotation mode are the same, and the relationship between the initial vortex rotation mode and the converted vortex rotation mode and the helix is such that the number of helices of the helix is such that when the topological orders of the initial vortex rotation mode and the converted vortex rotation mode are the same The spiral line number of the spiral structure when the topological charge order of the initial vortex rotation mode and the conversion vortex rotation mode are different in number At the same time when The helix direction of the helix structure is the same as the polarization state of the initial vortex rotation mode and the conversion vortex rotation mode when The spiral direction of the spiral structure is opposite to the polarization states of the initial vortex rotation mode and the conversion vortex rotation mode, j is the absolute value of the topological order of charge of the initial vortex rotation mode, and k is the absolute value of the topological order of charge of the conversion vortex rotation mode.
  3. 3. The helical structured waveguide of claim 2, wherein, depending on conditions The period length L of the spiral structure is determined, wherein, The propagation constants of the initial vortex rotation mode and the converted vortex rotation mode, respectively.
  4. 4. A spiral structure waveguide according to claim 3, wherein the material of the circular waveguide and the spiral structure is resin or silicon dioxide, the cross-section of the spiral structure is rectangular, the thickness of the spiral structure along the radial direction is 1/5-1/10 of the diameter of the circular waveguide, the width along the axial direction is L/(2L), Is the number of spiral lines of the spiral structure.
  5. 5. A method for realizing a helical structured waveguide for vortex optical topological charge conversion according to any one of claims 1 to 4, comprising the steps of: 1) The circular waveguide is a solid cylinder, the cross section of the circular waveguide is circular, the spiral structure comprises one or more spiral lines, and the spiral lines are uniformly distributed along the circumferential direction at equal intervals along the axial direction; 2) The spiral structure converts the topological order of the vortex rotation, changes into a vortex rotation conversion mode after complete conversion, and the vortex rotation conversion mode is related to the number of spiral lines and the spiral direction of the spiral structure; 3) The vortex rotation is transmitted in the spiral structure, and along with the increase of the transmission distance, the vortex rotation mode is converted with the initial vortex optical mode; 4) The emergent vortex light comprises an initial vortex rotation mode and a conversion vortex rotation mode, and the emergent vortex light is adjusted to be any mixing proportion between two different vortex light modes by adjusting the length of the spiral structure.
  6. 6. The method according to claim 5, wherein in step 1), the material of the circular waveguide and the spiral structure is resin or silicon dioxide, and the material is prepared on the side wall surface of the circular waveguide by 3D printing or femtosecond laser direct writing.
  7. 7. The method according to claim 5, wherein in step 2), a spatial light modulator or a spiral phase plate is disposed before the spiral waveguide to modulate the topological charge carried by the vortex light.
  8. 8. The method according to claim 5, wherein in step 3), the conversion between the initial vortex rotation mode and the converted vortex rotation mode satisfies two conditions of (1) topological order of charge is same in number Or when the topological charge order is different from the sign And (2) , The number of the spiral lines is the number of the spiral lines, j is the absolute value of the topological order of the initial vortex rotation mode, k is the absolute value of the topological order of the converted vortex rotation mode, The propagation constants of the initial vortex rotation mode and the converted vortex rotation mode are respectively, and L is the period length of the spiral structure.
  9. 9. The method according to claim 5, wherein in step 4), the transmission distance of the vortex rotation from the initial vortex rotation mode to the converted vortex rotation mode is the full conversion length at one time , For coupling coefficient, adjusting the length of the spiral structure to adjust the transmission distance to be at the full conversion length And (3) adjusting the emergent vortex light to be any mixing proportion between two different vortex light modes.
  10. 10. The implementation method according to claim 9, characterized in that, based on the full conversion length, according to And calculating the transmission distance to determine the length of the spiral structure to obtain the emergent vortex rotation of the two vortex optical modes mixed in any proportion.

Description

Spiral structure waveguide for vortex light topology charge conversion and implementation method thereof Technical Field The invention relates to the field of optical waveguides, in particular to a spiral structure waveguide for vortex rotation topological charge conversion and an implementation method thereof. Background The vortex rotation has non-zero orbital angular momentum due to the non-uniform phase distribution carried by the vortex rotation, and provides a brand-new degree of freedom for light field regulation. By encoding the topological charge corresponding to the orbital angular momentum, the important functions of high-dimensional information encoding, ultra-high resolution imaging, diffraction neural network computing and the like can be realized. However, most of the current regulation of eddy current rotation is based on spatial structure. The common vortex light conversion structure in space comprises a spatial light modulator, a spiral phase plate, a super surface carved with a sub-wavelength structure, a cylindrical lens converter and the like, and the phase, amplitude and polarization of light waves can be controlled randomly by carefully designing the shape, size and orientation of the structure. These structures, although having a remarkable conversion effect and high conversion efficiency, have a disadvantage in that integration in an on-chip structure is difficult due to a large overall size. At present, some regulation means for eddy current rotation are also studied based on an on-chip integration platform. Vortex rotation is considered to be one of the important technical directions in on-chip integrated platforms to increase the capacity of information transfer systems because it has an infinitely orthogonal modal space. How to directly and flexibly generate, convert and exchange vortex optical modes inside a waveguide becomes one of the key challenges for the development of information transfer technology. The current mainstream scheme is mainly based on micro-ring resonant cavities, waveguides with special cross sections (such as cross-shaped and unfilled-corner cross sections), grating couplers and other structures. The micro-ring resonant cavity can efficiently excite a specific vortex mode by utilizing a resonance enhancement principle, has good compatibility with the existing photon integration platform, enables two components of a synthesized vortex beam to have the same effective mode refractive index by special design, can support stable transmission of fixed-order vortex light on a chip, and can directly map a waveguide mode into a free space vortex beam aiming at an on-chip grating coupler (such as a circular grating) with special design, thereby being a key scheme for realizing an on-chip and free space efficient interface. However, these schemes can only be used for on-chip generation and detection of vortex light, and cannot truly realize conversion between vortex light in different modes on-chip, i.e. conversion between vortex light topological charges. The reason why the vortex light topological charge conversion is difficult to carry out on the chip is that a fixed waveguide structure often only supports one vortex light mode, long-distance stable propagation of vortex light of other modes cannot be supported, and even if the waveguide structure can support vortex light of a plurality of modes at the same time, different modes are orthogonal to each other, and natural conversion cannot be carried out in the transmission process. If it is desired to support simultaneous multiple modes of vortex light transmission and to achieve switching between different modes of vortex light transmission, it is necessary to fine-tune the waveguide structure to support stable transmission of multiple modes while designing the auxiliary structure specifically to achieve switching between different orthogonal modes. Therefore, the realization of conversion between vortex optical topology charges is still a urgent problem for the on-chip integrated photonics platform. Disclosure of Invention Aiming at the problems existing in the prior art, the invention provides the spiral structure waveguide for vortex optical topological charge conversion and the implementation method thereof, the invention can conveniently regulate and control the mixing proportion among different vortex optical modes by flexibly controlling the generation, conversion and exchange of vortex optical modes, provides a new device foundation for a mode division multiplexing system, provides a new thought for applications such as signal processing, spectrum shaping and the like, and lays a theoretical foundation for developing a reconfigurable, programmable and multifunctional vortex optical processing device. It is an object of the present invention to propose a spiral structured waveguide for eddy-current topological charge conversion. The spiral structure waveguide for vortex light topological charge conversion c