Multi-core polarization-maintaining photonic crystal fiber

Abstract

The application discloses a kind of multicore polarization maintaining photonic crystal fiber, including cladding region, stress region and core region, the cladding region uses glass material base, the core region is located cladding region center, the stress region is thermal expansion area, symmetrically distributed in the two sides of core region, the core region is multicore microstructure, and periodically arranged into hexagonal air hole array.The application can realize large-mode-area polarization maintaining supermode transmission, and can be well applied to high-power polarization laser technology field.

Description

Technical Field

[0001] The present invention relates to a polarization-maintaining optical fiber, in particular to a multi-core polarization-maintaining photonic crystal optical fiber. Background Art

[0002] In the field of high-power laser generation and transmission, appropriately increasing the mode field area of ​​an optical fiber can effectively reduce the nonlinear effects of the optical fiber and increase the damage threshold, which is of great research significance for high-power, high-beam-quality laser transmission. In recent years, the concept of multi-core photonic crystal fiber has been proposed. The light fields between the cores can couple with each other to form a so-called "supermode", whose mode field area increases proportionally with the number of cores, and the mode field distribution is insensitive to heat. Splitting the light field in a single core across multiple cores can effectively avoid the self-focusing and thermal lensing effects that single-core fiber lasers cannot overcome.

[0003] Currently, many studies have adopted a hexagonal air hole array structure, with an appropriate number of cores designed within the air holes, primarily focusing on a 7-core photonic crystal fiber structure, to achieve supermode transmission. However, in practical applications, polarization mode coupling and other issues can occur when light is transmitted through multi-core fibers. Therefore, polarization-maintaining design is required for these multi-core fibers to achieve better application performance.

[0004] Existing polarization-maintaining photonic crystal fibers (PMCFs) primarily target traditional single-core PMCFs, achieving polarization-maintaining performance by disrupting the periodic arrangement of air holes or by adding stress rods outside the core region to achieve asymmetric refractive index changes. Folkenberg, J. et al., Optics Express 12.5 (2004): 956, reported a large-mode-field PMCF design. The fiber comprises a core region, a stress region, and a cladding region. The entire cladding region is made of pure quartz glass, while the core region comprises a hexagonal array microstructure formed by four layers of air holes. The light field is primarily concentrated in the core region, while two boron-doped high-stress regions are symmetrically introduced on either side of the core region. Due to the different thermal expansion coefficients of the stress regions and other materials, the polarization-maintaining effect of the fiber can be achieved. Patent US7289709B2 introduces several PMC fiber designs based on the aforementioned design, also using a combination of a microstructure array and stress rods to achieve polarization-maintaining performance.

[0005] The above-mentioned fiber design introduces a boron-doped high-stress region based on the traditional photonic crystal fiber structure, which can not only maintain the unique properties of photonic crystal fiber such as tunable dispersion and infinite single-mode cutoff, but also ensure the polarization characteristics of the fiber.

[0006] However, the design of the aforementioned polarization-maintaining optical fibers often focuses on optimizing single-core optical fibers. In recent years, with the development of multi-core optical fibers, especially in the field of high-power pulse transmission, the mode characteristics of multi-core optical fibers are superior to those of traditional single-core optical fibers. However, the design of these multi-core optical fibers ignores the polarization maintenance issue of their modes. Therefore, the invention of a multi-core polarization-maintaining photonic crystal fiber is very necessary for high-performance optical fiber communication technology. Summary of the Invention

[0007] The present invention proposes a multi-core polarization-maintaining photonic crystal fiber for existing large-mode-field polarization-maintaining photonic crystal fibers. This fiber not only has the large-mode-field characteristics of the multi-core photonic crystal fiber, but also can effectively reduce the influence of polarization mode coupling, so that the fiber has a polarization-maintaining function and can be applied in the field of high-power polarization laser technology.

[0008] The technical solution of the present invention:

[0009] A multi-core polarization-maintaining photonic crystal fiber comprises a cladding region, a stress region, and a core region. The cladding region is formed of a glass substrate, the core region is located at the center of the cladding region, and the stress region is a thermal expansion region symmetrically distributed on both sides of the core region. The fiber is characterized in that the core region has a multi-core microstructure and a periodically arranged hexagonal air hole array.

[0010] The diameter of the core region is 10 to 100 μm, the diameter of the stress region is 20 to 300 μm, and the diameter of the cladding of the multi-core polarization-maintaining photonic crystal optical fiber is 100 to 800 μm.

[0011] The multi-core polarization-maintaining photonic crystal fiber core is a multi-core structure, including 7 cores or 19 cores, etc. The mode fields of the cores are coupled to form a supermode, and the mode field area is relatively large.

[0012] The ratio of the air hole diameter d to the air hole spacing Λ in the fiber core region satisfies d / Λ=0.30-0.9;

[0013] The thermal expansion coefficient of the stress region is different from that of the cladding region material, and its refractive index is lower than the refractive index of the cladding.

[0014] Compared with the existing large mode field polarization-maintaining photonic crystal fiber, the present invention has the following advantages:

[0015] 1. The fiber core of the present invention is a multi-core photonic crystal fiber structure. The light field modes between each fiber core can couple with each other to form a supermode. Its mode field area can be higher than that of the existing single-core large mode field polarization-maintaining photonic crystal fiber, and the output beam quality is improved.

[0016] 2. The multi-core optical fiber structure in the core area of ​​the present invention can be flexibly designed according to actual needs, including 7-core, 19-core, etc., which increases the design flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is a schematic structural diagram of an embodiment of a multi-core polarization-maintaining photonic crystal fiber according to the present invention;

[0018] Figure 2 This is a common diagram of existing Panda fiber;

[0019] Figure 3 Schematic diagram of the core microstructure region in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] In order to better understand the present invention, the content of the present invention is further described below in conjunction with examples, but this should not limit the scope of protection of the present invention.

[0021] Example 1

[0022] like Figure 1 As shown, the multi-core polarization-maintaining photonic crystal fiber of the present invention comprises a cladding region 1, a stress region 2, and a core region 3. The cladding region 1 utilizes a pure silica glass substrate (SiO2). The core region 3, located at the center of the cladding, comprises a multi-core microstructure consisting primarily of a regularly arranged hexagonal array of air holes. The two stress regions 2 are highly boron-doped regions (B2O3 / SiO2), symmetrically distributed on either side of the core region 3. The core region has a diameter of 16 to 20 μm, the stress region has a diameter of 40 μm, and the fiber diameter is 140 to 250 μm. The ratio of the air hole diameter d to the air hole spacing Λ in the core region satisfies d / Λ = 0.8. The stress region is a highly boron-doped region, i.e., boron-doped silica glass, with a boron doping concentration of 10 to 25 wt%.

[0023] Figure 2 The common structure of an existing Panda-type polarization-maintaining fiber is presented, including a cladding region 4, a stress region 5, and a core region 6. The core region 6 is made of germanium-doped silica glass (Ge / SiO2) and has a high refractive index. The relative refractive index difference between the core region 6 and the cladding region 4 is set according to the operating wavelength and specific application. The stress region 5 is made of boron-doped silica glass with a boron doping concentration of 10 to 25 wt%. The modal birefringence of the Panda-type polarization-maintaining fiber is related to the doping concentration, diameter, and spacing of the stress region 5, as shown in the equation:

[0024] Birefringence B

[0025]

[0026] Where r1 is the distance from the fiber core to the periphery of the stress region, R is the diameter of the stress region, and D is the outer diameter of the entire optical fiber.

[0027] Figure 2Given that the diameter of the fiber core region 6 is 5 μm, the diameter of the stress region 5 R is 40 μm, the distance r1 between the core and the stress region is 10 μm, and the outer diameter D of the fiber is 125 μm, its birefringence value can reach 2.134×10 -4 .

[0028] Analogous to the panda-type polarization-maintaining optical fiber, the birefringence characteristics of the multi-core polarization-maintaining optical fiber of the present invention should also satisfy the above formula.

[0029] like Figure 3 As shown, given Figure 1 The detailed structure of the fiber core region in Figure 1 shows a 7-core microstructured air hole array with an air hole diameter d of 1.45 μm. The spacing between adjacent air holes is Λ, where d / Λ is 0.8. Seven layers of air holes are arranged in a hexagonal array, with seven solid cores incorporated. The optical fields between each core can couple to form a supermode. The resulting core region has a radius of 12 μm. To maintain the fiber's birefringence, the diameter of stress region 2 remains 40 μm. The value of r1 is set between 16 and 20 μm. Under the above formula, the total outer diameter D of the fiber is calculated to be 140 to 250 μm.

[0030] The multi-core polarization-maintaining photonic crystal fiber of the present invention can achieve a large mode field area and maintain good polarization characteristics in light field transmission, thus meeting the requirements of high-performance optical fiber communication.

Claims

1. A multi-core polarization-maintaining photonic crystal fiber, comprising a cladding region (1), a stress region (2) and a core region (3), wherein the cladding region (1) is formed of a glass substrate, the core region (3) is located at the center of the cladding region, and the stress region (2) is a thermal expansion region symmetrically distributed on both sides of the core region (3), characterized in that: The core region (3) is a 19-core microstructure, which is periodically arranged into a hexagonal air hole array. The stress region (2) is composed of boron-doped quartz glass with a boron doping concentration of 10-25wt%. The core mode fields of the core region (3) are coupled to form a supermode, and the mode field area is relatively large; The thermal expansion coefficient of the stress region (2) is different from the thermal expansion coefficient of the material of the cladding region (1), and its refractive index is lower than the refractive index of the cladding region (1).

2. The multi-core polarization-maintaining photonic crystal fiber according to claim 1, characterized in that: The diameter of the core region (3) is 10-100 μm, the diameter of the stress region (2) is 20-300 μm, and the diameter of the cladding of the multi-core polarization-maintaining photonic crystal fiber is 100-800 μm.

3. The multi-core polarization-maintaining photonic crystal fiber according to claim 1, wherein: The ratio of the diameter d of the air holes in the core region (3) to the spacing Λ between the air holes satisfies d / Λ=0.3~0.9.

Images