Anti-resonance ring fiber supporting multiple orbital angular momentum modes

[0019] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings, but the implementation and protection of the present invention are not limited to this. It should be pointed out that if there are processes or symbols that are not specifically described in detail below, those skilled in the art can follow the current situation. There is technical understanding or realization.

[0020] This embodiment provides an anti-resonant toroidal fiber that supports multiple orbital angular momentum modes. The cross-section of the anti-resonant toroidal fiber for supporting multiple orbital angular momentum (OAM) transmission is as follows figure 1 Shown. The anti-resonant ring optical fiber includes: the fiber substrate 1 is made of a single quartz glass material, the ring core 2 is a ring silica glass tube, the cladding air holes 3 are arranged in a ring on the outer wall of the ring core 2, and the negative curvature silica glass tube 4 The ring is arranged on the outer layer of the air holes 3 of the cladding layer. Among them, the radius of the outer wall of the annular core 2 r 7 microns, inner wall radius of annular core 2 r 0 The ratio ρ to the outer wall radius r is 0.65, and the cladding air hole duty ratio d /Λ is 0.8 (where d is the diameter of the cladding air holes, and Λ is the distance between the centers of the two adjacent cladding air holes), the thickness of the negative curvature glass tube 4 t 1.2 microns, the inner radius of the negative curvature glass tube 4 R 9 microns, 1 tube inner diameter of fiber base D It is 61.2 microns and the working wavelength is 1550 nanometers. The anti-resonant ring fiber can support a total of 26 modes of 7-order OAM, and the effective refractive index difference between adjacent vector modes is Δ n eff Are greater than 10 -4 Magnitude. When Δ n eff Greater than 10 -4 When the same group of eigenvector modes will not be re-coupled into linear polarization mode (LP). At the same time, the fiber also has the characteristics of insensitive to bending, low nonlinear coefficient and flat dispersion.

[0021] figure 2 It is the ratio of each eigenvector mode of the anti-resonant ring fiber supporting the transmission of multiple orbital angular momentum modes to the inner and outer radius of the ring core 2 tube wall according to the present invention ρ And effective normalized frequency V eff The cut-off conditions. Among them, TE, TM, HE/EH represent transverse electric mode, transverse magnetic mode and mixed mode respectively; the first subscript of each mode is called the azimuth modulus, which represents the period of the electric field change of the core along the azimuth angle; The second subscript is called the radial modulus, which represents the number of half cycles of the electric field change from the core center to the interface between the core and the cladding. As can be seen from the figure, ρ The valid range of is 0.6~0.8. Because when ρ Greater than 0.6 and V eff When it is less than 11, the radial high-order mode can be cut off. when ρ When it is less than 0.8, the thickness of the annular core 2 will not be too small so as to ensure the quality of the orbital angular momentum mode.

[0022] image 3 The limiting loss of the anti-resonant ring optical fiber supporting multiple orbital angular momentum mode transmission according to the present invention is relative to the thickness of the negative curvature glass tube 4 t Dependencies. It can be seen from the figure that the anti-resonance interval of each eigenvector mode is different, and this feature can be used to cut off unwanted modes. For example, when the orbital angular momentum mode is excited, the radial higher-order mode is the mode that needs to be cut off, then t It can cut off the radial high-order mode TE at 1.2 microns 02 And HE 12 And at the same time restrain other modes. So when V eff When greater than 11, you can change t Value to further cut off the radial higher-order modes.

[0023] Figure 4 The mode intensity distribution and electric field distribution diagram of each order of OAM mode supported by the anti-resonant ring fiber supporting the transmission of multiple orbital angular momentum modes in this example. Among them, σ+ and σ− respectively represent right-handed and left-handed polarization directions; in the expression of OAM±m,n, + and − represent right-handed and left-handed phase wavefronts, respectively, m represents the topological charge, and n represents the radial order. The size of the ring core and the thickness of the ring core determine the number of modes and the degree of separation of the effective refractive index of the modes. Therefore, the anti-resonant ring fiber can support 26 OAM modes and effective refraction between each adjacent eigenvector mode. The rate difference can be guaranteed to be greater than 10-4 magnitude. Moreover, it has the characteristics of insensitive to bending, low nonlinear coefficient and flat dispersion in the C+L band.

[0024] The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, etc. made without departing from the spirit and principle of the present invention Simplified, all should be equivalent replacement methods, and they are all included in the protection scope of the present invention.