Polarization-maintaining homogenized optical fiber and laser using polarization-maintaining homogenized optical fiber

Abstract

The utility model relates to a polarization-maintaining homogenized optical fiber and a laser using the polarization-maintaining homogenized optical fiber, and belongs to the technical field of optical shaping. The laser comprises a step-shaped heat sink, laser chips, fast axis collimating lenses, slow axis collimating lenses, a reflector, a coupling lens and a polarization-maintaining homogenizing optical fiber, the laser chips are arranged on steps of the step-shaped heat sink respectively, the fast axis collimating lenses are arranged on the light emitting sides of the laser chips respectively, and the slow axis collimating lenses are arranged on the light emitting sides of the coupling lens. One side of the fast axis collimating lens is sequentially provided with a slow axis collimating lens and a reflector along a light path, one side of the reflector is provided with a coupling lens, and the coupling lens couples a light beam to the polarization-maintaining homogenizing optical fiber. By adjusting the ellipse ratio and the ellipse size of the ellipse fiber core and setting the fiber core structure with specific refractive index distribution, the flat-topped light beam with high birefringence is obtained, the mode field area of the optical fiber is increased, and the nonlinear effect is reduced.

Description

Technical Field

[0001] This utility model relates to a polarization-maintaining homogenizing optical fiber and a laser using the polarization-maintaining homogenizing optical fiber, belonging to the field of optical shaping technology. Background Technology

[0002] Since the advent of lasers, laser communication technology has developed rapidly. In fiber optic sensing technology and coherent optical communication technology, high requirements have been placed on the polarization performance of optical fibers. Ensuring the stability of the polarization state of light during optical transmission has become an important research direction in fiber optic technology.

[0003] Polarization-maintaining fibers are widely used in many fields, such as dense wavelength division multiplexing, fiber optic gyroscopes, fiber optic amplifiers and other fiber optic communication systems, as well as polarization-sensitive integrated optical components. They can also be combined with polarizers to generate stable polarization modes. Currently, the methods for preparing high birefringence polarization-maintaining fibers are usually to prepare high birefringence polarization-maintaining fibers by utilizing geometric shapes, such as elliptical core fibers, or based on the photoelastic effect, using stress-induced high birefringence fibers, such as elliptical and bowtie fibers.

[0004] Flat-top beams can effectively improve the thermal damage threshold and nonlinear threshold. Flat-top beams are currently widely used in laser holographic illumination, second harmonic generation, inertial confinement fusion and material heat treatment. Increasing the mode field area of ​​optical fibers can effectively improve the limitation of nonlinear effects on fiber lasers. However, traditional Gaussian beams have a small mode field area and suffer from polarization mode dispersion and polarization crosstalk problems, so there is still room for optimization. Utility model content:

[0005] To address the shortcomings of existing technologies, this invention proposes a polarization-maintaining homogenized optical fiber and a laser using the polarization-maintaining homogenized optical fiber. By adjusting the ellipticity ratio and elliptic size of the elliptical core and setting a core structure with a specific refractive index distribution, a flat-top beam with high birefringence can be obtained, thereby increasing the mode field area of ​​the optical fiber and reducing nonlinear effects.

[0006] Polarization-maintaining homogenized fiber can effectively overcome polarization mode dispersion, polarization crosstalk, and polarization-dependent loss problems, optimize the stability of optical devices and fiber optic communication systems, and meet the application requirements of polarization-sensitive applications such as fiber optic gyroscopes, high-power fiber lasers, and fiber polarizers.

[0007] The technical solution of this utility model is as follows:

[0008] A polarization-maintaining homogenizing optical fiber includes a cladding and an elliptical core. The cladding is disposed on the outside of the elliptical core, and the refractive index distribution of the elliptical core satisfies the following:

[0009] n = n1 × sqrt(1 + 2Δ × (r / η)) 2 )

[0010] Where n is the refractive index distribution of the elliptical fiber core, n1 is the minimum refractive index, r is the radial variable of the elliptical fiber core in polar coordinates, η is the elliptic ratio, and Δ is the relative refractive index difference. By adjusting the elliptic ratio of the elliptical fiber core, the elliptical fiber core as a whole exhibits a concave refractive index distribution that first decreases and then increases as the fiber core diameter increases.

[0011] According to a preferred embodiment of this invention, the relative refractive index difference satisfies Δ=(n2) 2 -n1 2 ) / 2n1 2 , where n2 is the maximum refractive index.

[0012] According to the preferred embodiment of this utility model, the elliptic ratio η = b / a, where a is the length of the minor axis of the elliptical fiber core and b is the length of the major axis of the elliptical fiber core.

[0013] According to the preferred embodiment of this utility model, the elliptical fiber core material is selected from quartz (SiO2) doped with high refractive index material. The refractive index increases with the increase of doping concentration, and the refractive index is the highest at the boundary between the fiber core and the cladding.

[0014] The Gaussian beam undergoes total internal reflection within the elliptical fiber core. Each reflection generates a virtual sub-point light source, and the original angular domain is divided into multiple angular channels, with each virtual point light source corresponding to a sub-channel. After each reflection, the originally freely propagating distribution of the corresponding channel is reversed once, and finally, the distributions of each channel are superimposed at the exit to form a uniform light intensity distribution.

[0015] A laser employing polarization-maintaining homogenizing fiber includes a stepped heat sink, a laser chip, a fast-axis collimating lens, a slow-axis collimating lens, a reflector, a coupling lens, and a polarization-maintaining homogenizing fiber. Each step of the stepped heat sink is equipped with a laser chip, and a fast-axis collimating lens is provided on the light-emitting side of each laser chip. A slow-axis collimating lens and a reflector are sequentially arranged along the optical path on one side of the fast-axis collimating lens, and a coupling lens is provided on one side of the reflector. The coupling lens couples the light beam to the polarization-maintaining homogenizing fiber.

[0016] The beneficial effects of this utility model are as follows:

[0017] This invention achieves a flat-top beam with high birefringence by adjusting the ellipticity ratio and elliptic size of the elliptical fiber core and setting a core structure with a specific refractive index distribution, thereby increasing the mode field area of ​​the optical fiber and reducing nonlinear effects.

[0018] Polarization-maintaining homogenizing fibers can effectively overcome problems such as polarization mode dispersion, polarization correlation loss, and polarization crosstalk, further improving the stability of lasers and optical communication systems. Simultaneously, flat-top beams have a larger mode field area than Gaussian beams, increasing the mode field area of ​​the fiber and effectively mitigating the limitations imposed by nonlinear effects on fiber laser performance. Compared to traditional panda-type polarization-maintaining fibers, elliptical-core polarization-maintaining fibers possess a higher polarization extinction ratio, lower thermal correlation performance, and higher coupling efficiency, while being insensitive to bending and stress, making them more promising for applications. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the laser structure of this utility model;

[0020] Figure 2 This is a schematic diagram of the polarization-maintaining and homogenizing optical fiber structure of this utility model, where a is the length of the minor axis of the elliptical fiber core and b is the length of the major axis of the elliptical fiber core.

[0021] Figure 3 This is a schematic diagram of the optical path of the incident light in the polarization-maintaining homogenizing fiber of this invention, where θc is the critical angle for total internal reflection and θ is the incident angle.

[0022] Figure 4 This is a schematic diagram of the non-uniform light spot before fiber insertion;

[0023] Figure 5 This is a schematic diagram of the slow-axis light intensity distribution of the beam before it enters the fiber.

[0024] Figure 6 This is a schematic diagram of the homogenized light spot after passing through the polarization-maintaining homogenizing fiber of this utility model.

[0025] Figure 7 This is a schematic diagram of the slow-axis intensity distribution of the beam after passing through the polarization-maintaining homogenizing fiber of this utility model.

[0026] Figure 8 This is a schematic diagram of the beam phase before it enters the fiber.

[0027] Figure 9 This is a schematic diagram of the beam phase after passing through a polarization-maintaining homogenizing fiber.

[0028] The components include: 1. Laser chip; 2. Fast-axis collimating lens; 3. Slow-axis collimating lens; 4. Reflector; 5. Coupler lens; 6. Polarization-maintaining homogenizing fiber.

[0029] 61. Cladding; 62. Elliptical core. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments and accompanying drawings. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, it should be understood that after reading the description of the present invention, those skilled in the art can make various modifications or alterations to the present invention, and these equivalent forms also fall within the scope defined in this application.

[0031] Example 1:

[0032] like Figure 2 As shown, this embodiment provides a polarization-maintaining homogenizing optical fiber, including a cladding 61 and an elliptical core 62. The cladding 61 is disposed around the outside of the elliptical core 62, and the refractive index distribution of the elliptical core 62 satisfies:

[0033] n = n1 × sqrt(1 + 2Δ × (r / η)) 2 )

[0034] Where n is the refractive index distribution of the elliptical fiber core, n1 is the minimum refractive index, r is the radial variable of the elliptical fiber core in polar coordinates, η is the elliptic ratio, and Δ is the relative refractive index difference. By adjusting the elliptic ratio of the elliptical fiber core, the elliptical fiber core as a whole exhibits a concave refractive index distribution that first decreases and then increases as the fiber core diameter increases.

[0035] The relative refractive index difference satisfies Δ=(n2) 2 -n1 2 ) / 2n1 2 , where n2 is the maximum refractive index.

[0036] The elliptic ratio η = b / a, where a is the length of the minor axis of the elliptical fiber core and b is the length of the major axis of the elliptical fiber core.

[0037] The elliptical fiber core material is made of quartz (SiO2) doped with high refractive index material. The refractive index increases with increasing doping concentration, and the refractive index is highest at the boundary between the fiber core and the cladding.

[0038] Example 2:

[0039] like Figure 1 As shown, this embodiment provides a laser using polarization-maintaining homogenizing fiber, including a stepped heat sink, a laser chip 1, a fast-axis collimating lens 2, a slow-axis collimating lens 3, a reflector 4, a coupling lens 5, and a polarization-maintaining homogenizing fiber 6. The laser chip 1 is disposed on each step of the stepped heat sink. A fast-axis collimating lens 2 is disposed on the light-emitting side of the laser chip 1. A slow-axis collimating lens 3 and a reflector 4 are disposed sequentially along the optical path on one side of the fast-axis collimating lens 2. A coupling lens 5 is disposed on one side of the reflector 4. The coupling lens couples the light beam to the polarization-maintaining homogenizing fiber 6.

[0040] Simulation of the structure in this embodiment: Reference Figure 3After collimation along the fast and slow axes, the beam is focused and coupled into a polarization-maintaining homogenizing fiber. The beam undergoes sufficient total internal reflection within the elliptical fiber core. Each reflection generates a virtual sub-point source, dividing the original angular domain into multiple angular channels, with each virtual point source corresponding to a sub-channel. With each reflection, the originally freely propagating distribution of the corresponding channel is reversed once, and the distributions of all channels are superimposed at the fiber exit to form a uniform intensity distribution. (Reference) Figure 4-5 The slow-axis light intensity distribution of the light spot before fiber insertion is a Gaussian distribution, as referenced. Figure 6-7 After passing through the polarization-maintaining homogenizing fiber, a homogenized spot with a slow-axis flat-top intensity distribution is output, while simultaneously referencing... Figure 8-9 By adjusting the ellipticity ratio and refractive index distribution of the elliptical fiber core, a suitable mode of birefringence was obtained. The phase of the beam before and after fiber insertion did not change, and the polarization state of the beam remained unchanged.

Claims

1. A polarization maintaining homogenizing optical fiber, characterized by, The fiber includes a cladding and an elliptical core, the elliptical core is wrapped by the cladding, and the refractive index distribution of the elliptical core satisfies: n = nl x sqrt(l + 2Δ x (r / η) 2 ) Wherein, n is the refractive index distribution of the elliptical core, n1 is the minimum refractive index, r is a radial variable in the polar coordinate of the elliptical core, η is the ellipticity, Δ is the relative refractive index difference, by adjusting the ellipticity of the elliptical core, the overall elliptical core presents a concave refractive index distribution which first decreases and then increases with the increase of the core diameter.

2. The polarization maintaining, homogenizing optical fiber of claim 1, wherein, The relative refractive index difference satisfies Δ = (n2 2 - n1 2 ) / 2n1 2 where n2 is the maximum refractive index.

3. The polarization maintaining, homogenizing optical fiber of claim 2, wherein, The ellipticity η is b / a, wherein a is the length of the short axis of the elliptical core, and b is the length of the long axis of the elliptical core.

4. The polarization maintaining, homogenizing optical fiber of claim 3, wherein, The material of the elliptical core is quartz.

5. A laser using the polarization maintaining homogenizing optical fiber according to claim 1, characterized by The device comprises a stepped heat sink, a laser chip, a fast-axis collimating lens, a slow-axis collimating lens, a mirror, a coupling lens and a polarization maintaining homogenization optical fiber, the laser chips are arranged on each step of the stepped heat sink, the fast-axis collimating lenses are arranged on the light-emitting side of the laser chips, the slow-axis collimating lens and the mirror are sequentially arranged on one side of the fast-axis collimating lens along the light path, the coupling lens is arranged on one side of the mirror, and the coupling lens couples the light beam to the polarization maintaining homogenization optical fiber.

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