Multi-core polarization maintaining optical fiber and preparation method thereof

Abstract

The invention relates to a multi-core polarization maintaining optical fiber and a preparation method thereof.The optical fiber comprises a common cladding, a plurality of core layers and stress areas, the number of the stress areas is four, the four stress areas are evenly distributed at equal intervals in the circumferential direction corresponding to the center of the optical fiber, the centers of the four stress areas are connected to form a regular quadrangle, one core layer is arranged at the middle point position of each of the four sides of the regular quadrangle, and the core layers are arranged at the middle point positions of the four sides of the regular quadrangle. And each core layer and the two adjacent stress regions are configured to form a polarization maintaining core region. The multi-core polarization-maintaining optical fiber is reasonable in structural arrangement, multi-core polarization-maintaining position layout can be achieved through the arrangement of the common stress area, and the multi-core polarization-maintaining optical fiber with multiple independent channels for simultaneous transmission is formed, so that the spectrum efficiency is enhanced, and the transmission capacity of the optical fiber is multiplied. The stress areas and the core layers are symmetrically arranged at intervals and specific structure parameters are selected, so that four polarization maintaining core areas can be realized, the optical signal coupling influence among the fiber cores can be weakened, and the transmission quality of the multi-core optical fiber is improved.

Description

Technical Field

[0001] The present invention relates to a multi-core polarization-maintaining optical fiber and a preparation method thereof, which has polarization-maintaining characteristics and multi-channel transmission performance, and belongs to the technical field of optical fibers. Background Art

[0002] Polarization-maintaining fiber is widely used in various sectors of the national economy, including aerospace, aviation, navigation, industrial manufacturing technology, and communications. In interferometric fiber sensors based on optical coherence detection, the use of polarization-maintaining fiber ensures a constant linear polarization direction, improving the coherent signal-to-noise ratio (SNR) and enabling high-precision measurement of physical quantities. Polarization-maintaining multi-core fiber utilizes spatial division multiplexing to achieve higher density, greater capacity, and improved polarization-maintaining performance, offering broad application prospects in fiber-optic gyroscopes and device miniaturization.

[0003] Existing PANDA-type polarization-maintaining optical fibers consist of a single core and two stress rods. Their transmission capacity is insufficient to meet increasing transmission demands. For example, in fiber optic gyros, increasing the effective length of the fiber coil requires increasing the number of windings by reducing the fiber diameter. To address this issue, Chinese patent CN106489087B proposes a multi-core polarization-maintaining optical fiber comprising multiple cores; a cladding surrounding the multiple cores; and multiple stress-applying sections, each arranged within a region enclosed by the cladding's periphery to sandwich the multiple cores. Multiple stress-applying sections are arranged along one direction in a cross-section perpendicular to the cladding's longitudinal direction, and multiple stress-applying sections are arranged along different directions. This solution aims to increase transmission capacity while simultaneously suppressing deformation of the PANDA-type polarization-maintaining optical fiber. However, the use of more than three core rods and stress rods limits their dimensions, making it difficult to achieve a sufficient stress-birefringence effect. Chinese patent CN113075763A provides a multi-core polarization-maintaining fiber with a panda structure and a coupling and connection device thereof. The multi-core panda structure polarization-maintaining fiber comprises a coaxially arranged core layer and a stress layer. The stress layer comprises a plurality of circumferentially evenly distributed stress rods. The core layer comprises a plurality of circumferentially evenly distributed fiber cores, each located at the midpoint of a line connecting adjacent stress rods. A cladding is also provided, covering the stress rods and the cores. The patent aims to address the difficulty in maintaining the polarization state of light waves when transmitting signals in multi-core optical fibers. However, due to the limited size of the optical fiber cladding, it is difficult to ensure sufficient stress birefringence. Summary of the Invention

[0004] The problem to be solved by the present invention is to provide a multi-core polarization-maintaining optical fiber and a preparation method thereof in view of the above-mentioned deficiencies in the prior art. The optical fiber has a reasonable structure and has high birefringence performance and multi-core transmission capability.

[0005] The optical fiber technology solution adopted by the present invention to solve the above-mentioned problems is as follows: it includes a common cladding and multiple core layers and stress zones. The four stress zones are evenly distributed along the circumference corresponding to the center of the optical fiber. The centers of the four stress zones are connected to form a regular quadrilateral. A core layer is arranged at the midpoint of each of the four sides of the regular quadrilateral (at 1 / 2 the length of the side). Each core layer is configured with its two adjacent stress zones to form a polarization-maintaining core zone.

[0006] According to the above solution, the radial distance (radius) between the stress zone and the center of the optical fiber is 12~35μm.

[0007] According to the above solution, the diameter of the stress region is 10-30 μm, and the stress region is a boron-doped quartz glass layer, with a molar percentage of boron of 15-25%.

[0008] According to the above solution, the diameter of the stress zone is 13-19 μm.

[0009] According to the above scheme, the diameter of the core layer is 4-18 μm, and the relative refractive index difference (relative to pure silica) Δ1 is 0.5-0.8%.

[0010] According to the above scheme, the diameter of the core layer is 9~13μm, and the relative refractive index difference Δ1 is 0.7~0.8%.

[0011] According to the above solution, the core layer is wrapped with a depressed cladding, the diameter of the depressed cladding is 10-25 μm, and the relative refractive index difference Δ2 is -0.3-0.6%.

[0012] According to the above solution, the core layer is wrapped with a depressed cladding, the diameter of the depressed cladding is 13-19 μm, and the relative refractive index difference Δ2 is -0.3-0.5%.

[0013] According to the above solution, the diameter of the common cladding is 40-125 μm, and the common cladding is a pure silica glass layer.

[0014] According to the above solution, the diameter of the common cladding is 60-80 μm. When the lower cladding diameter is applied to the fiber optic gyroscope, more turns can be made under the same fiber ring volume, thereby increasing the effective length of the fiber.

[0015] According to the above scheme, the birefringence coefficient of the polarization-maintaining optical fiber is 3×10 -4 ~5×10 -4 .

[0016] According to the above solution, the macrobending loss of the polarization-maintaining optical fiber is ≤0.1 dB when the polarization-maintaining optical fiber is wound 10 times with a bending diameter of 10 mm.

[0017] The technical solution of the optical fiber preparation method of the present invention is: Preparation of core rod: PCVD is used to deposit the depressed cladding layer and core layer in the quartz liner, and after the deposition is completed, they are melted and shrunk to form the required core rod; Preparation of stress rods: using PCVD to deposit a boron-doped stress layer in a quartz liner, and then melting and polishing it to obtain the desired stress rods; Preparation of optical fiber preform: drilling holes at the positions of core rods and stress rods on a pure silica quartz rod to make a quartz sleeve, and inserting the four core rods and the four stress rods into the quartz sleeve respectively to prepare a multi-core polarization-maintaining optical fiber preform; Drawing a multi-core polarization-maintaining optical fiber: clamping the multi-core polarization-maintaining optical fiber preform rod into a drawing furnace, and drawing the multi-core polarization-maintaining optical fiber.

[0018] According to the above scheme, the core rod is prepared using a PCVD (plasma chemical vapor deposition) process, using SiCl4, GeCl4, C2F6, and O2 as raw materials to prepare the core layer and depressed cladding. During the depressed cladding preparation process, the SiCl4 flow rate is 500-1500 sccm, the C2F6 flow rate is 50-200 sccm, and the O2 flow rate is 1500-3500 sccm. During the core layer preparation process, the SiCl4 flow rate is 200-1000 sccm, the C2F6 flow rate is 10-100 sccm, the GeCl4 flow rate is 5-100 sccm, and the O2 flow rate is 750-2500 sccm. (sccm is a unit of volume flow, referring to standard milliliters per minute) According to the above scheme, the stress rod is prepared by PCVD process, and SiCl4 (tetrachlorosilane), BCl3 (boron trichloride) and O2 (oxygen) are used as raw materials to prepare the boron doping layer. During the preparation process of the boron doping layer, the SiCl4 flow rate is 500~2000sccm; the BCl3 flow rate is 250~800sccm, and the O2 flow rate is 1500~5000sccm.

[0019] The beneficial effects of the present invention are: 1. The structure is reasonably set up, and the layout of the shared stress zone can realize the position layout of multi-core polarization-maintaining optical fibers, forming a multi-core polarization-maintaining optical fiber that transmits multiple independent channels at the same time, thereby enhancing the spectrum efficiency and multiplying the optical fiber transmission capacity. 2. The symmetrical spacing of the stress zone and the core layer and the selection of specific structural parameters can not only realize four polarization-maintaining core areas, but also reduce the effect of optical signal coupling between the cores, thereby improving the transmission quality of the multi-core optical fiber. 3. The setting of a sunken cladding structure with wide fluorine doping in the core can improve the bending resistance of the optical fiber, while also increasing the effective refractive index of the core, reducing crosstalk between cores, and improving birefringence performance. It is particularly suitable for application in optical fiber gyroscopes. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the radial cross-sectional structure of an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below in conjunction with the embodiments of the present invention and the accompanying drawings.

[0022] One embodiment of the present invention is Figure 1 As shown, the fiber optic cable comprises a common cladding 1 and four stress zones 2, equidistantly spaced circumferentially relative to the fiber center. Each stress zone has a radial distance (radius) of 17 μm from the fiber center. The centers of the four stress zones are connected to form a regular quadrilateral. A core layer 3 is positioned at the midpoint of each of the four sides of the quadrilateral (at half the length of each side). Each core layer, along with its two adjacent stress zones, forms a polarization-maintaining core. The stress zones have a diameter of 15 μm and are made of boron-doped silica glass with a boron molar percentage of 15-25%. The core layer has a diameter of 5.5 μm and a relative refractive index difference (Δ1) (relative to pure silica) of 0.7-0.8%. The core layer is surrounded by a depressed cladding 4 with a diameter of 14 μm and a relative refractive index difference (Δ2) of -0.3-0.6%. The common cladding has a diameter of 60 μm and is made of pure silica glass. The birefringence coefficient of the polarization-maintaining optical fiber in this embodiment is 4.8×10 -4 ~5×10 -4 The macrobending loss is ≤ 0.1dB when the fiber is wound 10 times with a 10mm bend diameter. The 60μm cladding diameter design allows for more windings within the same volume, increasing the effective length of the fiber.

[0023] The preparation method of the present invention is as follows: (1) Preparation of core rod: Use PCVD to deposit fluorine-doped depressed cladding and core layer in the quartz liner, and melt and shrink to form the required core rod after deposition; (2) Preparation of stress rods: Use PCVD to deposit a boron-doped stress layer in a quartz liner. After deposition, melt and grind to obtain the required stress rods. (3) Preparation of optical fiber preform: drilling holes at the positions of the core rods and stress rods on a pure silica quartz rod to make a quartz sleeve, and inserting the four core rods and the four stress rods into the quartz sleeve respectively to prepare a multi-core polarization-maintaining optical fiber preform; (4) The multi-core polarization-maintaining optical fiber preform is clamped into a drawing furnace, and a multi-core polarization-maintaining optical fiber is drawn.

[0024] Specifically, this application uses SiCl4 (tetrachlorosilane), GeCl4 (germanium tetrachloride), C2F6 (hexafluoroethane), and O2 (oxygen) as raw materials to prepare a pure silicon core layer or depressed cladding. By adjusting the flow rates and ratios of these gases, a core rod with the required diameter and refractive index is prepared at an appropriate deposition rate. During the depressed cladding preparation process, the SiCl4 flow rate is 800-900 sccm; the C2F6 flow rate is 50-150 sccm; and the O2 flow rate is 2000-3000 sccm. During the core layer preparation process, the SiCl4 flow rate is 200-500 sccm, the GeCl4 flow rate is 20-50 sccm, the C2F6 flow rate is 10-50 sccm, and the O2 flow rate is 1000-1500 sccm. The stress rods are prepared using a PCVD (plasma chemical vapor deposition) process to form a boron-doped layer. Specifically, the stress rods in this application use SiCl4 (tetrachlorosilane), BCl3 (boron trichloride), and O2 (oxygen) as raw materials to form the boron-doped layer. By adjusting the flow rates and ratios of these gases, boron rods with a desired diameter and refractive index are prepared at an appropriate deposition rate. During the boron-doped layer preparation process, the SiCl4 flow rate is 500-700 sccm, the BCl3 flow rate is 500-700 sccm, and the O2 flow rate is 1500-3000 sccm. (sccm is a unit of volume flow, referring to standard milliliters per minute).

[0025] Example 2: Another embodiment of the present invention is also as follows Figure 1 The fiber optic cable comprises a common cladding and four stress zones, equidistantly spaced circumferentially relative to the fiber center. Each stress zone has a radial distance (radius) of 32 μm from the fiber center. The centers of the four stress zones are connected to form a regular quadrilateral. A core layer is positioned at the midpoint of each of the four sides of the quadrilateral (at half the length of each side). Each core layer, along with its two adjacent stress zones, forms a polarization-maintaining core. The stress zones have a diameter of 28 μm and are made of boron-doped silica glass with a boron molar percentage of 15-25%. The core layer has a diameter of 6 μm and a relative refractive index difference (Δ1) (relative to pure silica) of 0.7-0.8%. The core layer is surrounded by a depressed cladding with a diameter of 16 μm and a relative refractive index difference (Δ2) of -0.3-0.6%. The common cladding has a diameter of 125 μm and is made of pure silica glass. The birefringence coefficient of the polarization-maintaining optical fiber in this embodiment is 4.3×10 -4 ~4.5×10 -4 The macrobending loss is ≤ 0.1dB when the fiber is wound 10 times with a 10mm bend diameter. The 125μm cladding diameter design facilitates mating and splicing.

[0026] The preparation method of this embodiment is the same as that of the first embodiment.

[0027] Specifically, this application uses SiCl4 (tetrachlorosilane), GeCl4 (germanium tetrachloride), C2F6 (hexafluoroethane), and O2 (oxygen) as raw materials to prepare a pure silicon core layer or depressed cladding. By adjusting the flow rates and ratios of these gases, a core rod with the required diameter and refractive index is prepared at an appropriate deposition rate. During the depressed cladding preparation process, the SiCl4 flow rate is 800-900 sccm (sccm is a unit of volume flow, referring to standard milliliters per minute), the C2F6 flow rate is 50-150 sccm, and the O2 flow rate is 2000-3000 sccm. During the core layer preparation process, the SiCl4 flow rate is 200-500 sccm, the GeCl4 flow rate is 20-50 sccm, the C2F6 flow rate is 10-50 sccm, and the O2 flow rate is 1000-1500 sccm. The stress rods are prepared using a PCVD (plasma chemical vapor deposition) process to form a boron-doped layer. Specifically, the stress rods in this application use SiCl4 (tetrachlorosilane), BCl3 (boron trichloride), and O2 (oxygen) as raw materials to prepare the boron-doped layer. By adjusting the flow rates and ratios of these gases, boron rods with a desired diameter and refractive index are prepared at an appropriate deposition rate. During the boron-doped layer preparation process, the SiCl4 flow rate is 500 to 700 sccm (sccm is a unit of volume flow, referring to standard milliliters per minute), the BCl3 flow rate is 500 to 700 sccm, and the O2 flow rate is 1500 to 3000 sccm.

Claims

1. A multi-core polarization-maintaining optical fiber comprising a common cladding, multiple core layers, and a stress zone, characterized in that There are four stress zones, which are evenly distributed circumferentially corresponding to the center of the optical fiber. The centers of the four stress zones are connected to form a regular quadrilateral. A core layer is arranged at the midpoint of each of the four sides of the regular quadrilateral. Each core layer is configured with its two adjacent stress zones to form a polarization-maintaining core zone.

2. The multi-core polarization-maintaining optical fiber according to claim 1, characterized in that The radial distance between the stress zone and the center of the optical fiber is 12-35 μm.

3. The multi-core polarization-maintaining optical fiber according to claim 1 or 2, characterized in that The diameter of the stress region is 10-30 μm, and the stress region is a boron-doped quartz glass layer, with a molar percentage of boron being 15-25%.

4. The multi-core polarization-maintaining optical fiber according to claim 3, characterized in that The diameter of the stress zone is 13-19 μm.

5. The multi-core polarization-maintaining optical fiber according to claim 1 or 2, characterized in that The core layer has a diameter of 4 to 18 μm and a relative refractive index difference Δ1 of 0.5 to 0.8%.

6. The multi-core polarization-maintaining optical fiber according to claim 5, characterized in that The core layer has a diameter of 9-13 μm and a relative refractive index difference Δ1 of 0.7-0.8%.

7. The multi-core polarization-maintaining optical fiber according to claim 1 or 2, characterized in that The core layer is surrounded by a sunken cladding layer, the diameter of the sunken cladding layer is 10-25 μm, and the relative refractive index difference Δ2 is -0.3-0.6%.

8. The multi-core polarization-maintaining optical fiber according to claim 7, characterized in that The diameter of the depressed cladding is 13-19 μm, and the relative refractive index difference Δ2 is -0.3-0.5%.

9. The multi-core polarization-maintaining optical fiber according to claim 1 or 2, characterized in that The diameter of the common cladding is 40-125 μm, and the common cladding is a pure silica glass layer.

10. The multi-core polarization-maintaining optical fiber according to claim 9, characterized in that The diameter of the common cladding is 60-80 μm.

11. The multi-core polarization-maintaining optical fiber according to claim 1 or 2, characterized in that The birefringence coefficient of the polarization-maintaining optical fiber is 3×10 -4 ~5×10 -4 .

12. The multi-core polarization-maintaining optical fiber according to claim 1 or 2, characterized in that When the polarization-maintaining optical fiber is wound 10 times with a bending diameter of 10 mm, the macrobending loss is ≤0.1 dB.

13. A method for preparing a multi-core polarization-maintaining optical fiber according to any one of claims 1 to 12, characterized in that Preparation of core rod: PCVD is used to deposit the depressed cladding layer and core layer in the quartz liner, and after the deposition is completed, they are melted and shrunk to form the required core rod; Preparation of stress rods: using PCVD to deposit a boron-doped stress layer in a quartz liner, and then melting and polishing it to obtain the desired stress rods; Preparation of optical fiber preform: drilling holes at the positions of core rods and stress rods on a pure silica quartz rod to make a quartz sleeve, and inserting the four core rods and the four stress rods into the quartz sleeve respectively to prepare a multi-core polarization-maintaining optical fiber preform; Drawing a multi-core polarization-maintaining optical fiber: clamping the multi-core polarization-maintaining optical fiber preform rod into a drawing furnace, and drawing the multi-core polarization-maintaining optical fiber.

14. The method for preparing a multi-core polarization-maintaining optical fiber according to claim 13, characterized in that The core rod is prepared by PCVD process, and SiCl4, GeCl4, C2F6 and O2 are used as raw materials to prepare the core layer and the depressed cladding. In the process of preparing the depressed cladding, the SiCl4 flow rate is 500-1500sccm, the C2F6 flow rate is 50-200sccm, and the O2 flow rate is 1500-3500sccm; in the process of preparing the core layer, the SiCl4 flow rate is 200-1000sccm; the C2F6 flow rate is 10-100sccm, the GeCl4 flow rate is 5-100sccm, and the O2 flow rate is 750-2500sccm.

15. The method for preparing a multi-core polarization-maintaining optical fiber according to claim 13 or 14, characterized in that The stress rod is prepared by PCVD process, and SiCl4, BCl3 and O2 are used as raw materials to prepare the boron doping layer. During the preparation process of the boron doping layer, the SiCl4 flow rate is 500-2000sccm, the BCl3 flow rate is 250-800sccm, and the O2 flow rate is 1500-5000sccm.

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