A multi-core polarization maintaining optical fiber and a method for manufacturing the same

Abstract

The present application relates to a kind of multicore polarization maintaining optical fiber and its preparation method, the optical fiber includes common cladding and multiple core layer and stress zone, the stress zone is 4, 4 stress zones correspond to the equidistant distribution of optical fiber center along circumference, the center line of 4 stress zones forms regular quadrilateral, 1 core layer is respectively arranged at the midpoint of the four sides of regular quadrilateral, and each core layer is configured with its adjacent 2 stress zones to form a polarization maintaining core zone.The structure of the present application is reasonable, the layout of the common stress zone can realize the position of multicore polarization maintaining, form the multicore polarization maintaining optical fiber of multiple independent channel simultaneous transmission, so as to enhance spectral efficiency, expand fiber transmission capacity by several times.The symmetric interval arrangement of stress zone and core layer and the selection of specific structure parameters not only can realize 4 polarization maintaining core zones, but also can weaken the influence of optical signal coupling between core, improve the transmission quality of multicore optical fiber.

Description

Technical Field

[0001] This invention relates to a multi-core polarization-maintaining optical fiber and its fabrication method, which possesses polarization-maintaining characteristics and multi-channel transmission performance, and belongs to the field of optical fiber technology. Background Technology

[0002] Polarization-maintaining fibers are widely used in various sectors of the national economy, including aerospace, aviation, marine, industrial manufacturing, and communications. In interferometric fiber optic sensors based on optical coherence detection, polarization-maintaining fibers ensure that the linear polarization direction remains unchanged, improving the coherence signal-to-noise ratio and enabling high-precision measurement of physical quantities. Polarization-maintaining multi-core fibers, utilizing space division multiplexing, offer advantages such as higher density, greater capacity, and better polarization-maintaining performance, showing broad application prospects in fiber optic gyroscopes and device miniaturization.

[0003] Existing PANDA-type polarization-maintaining fibers are configured with a single core and two stress bars, achieving single-core polarization maintenance. Their transmission capacity is insufficient to meet increased transmission demands. For example, in fiber optic gyroscopes, to increase the effective length of the fiber coil, the only solution is to increase the number of windings by reducing the fiber diameter. To address this issue, Chinese patent CN106489087B provides a multi-core polarization-maintaining fiber: it has multiple cores; a cladding surrounding the cores; and multiple stress-applying sections. These stress-applying sections are arranged within the area surrounded by the cladding, clamping the cores into each section. Multiple stress-applying sections are arranged along one direction in a cross-section perpendicular to the long side of the cladding, and also along different other directions. This solution aims to improve transmission capacity while suppressing deformation of the PANDA-type polarization-maintaining fiber's shape. However, because this solution uses more than three core bars and stress bars, it limits the size of the stress bars and core bars, making it difficult to guarantee sufficient stress birefringence. Chinese patent CN113075763A discloses a multi-core panda structure polarization-maintaining optical fiber and its coupling connection device. The multi-core panda structure polarization-maintaining optical fiber includes a core layer and a stress layer arranged coaxially. The stress layer includes multiple circumferentially distributed stress bars, and the core layer includes multiple circumferentially distributed fiber cores. The fiber cores are located at the midpoint of the line connecting adjacent stress bars. A cladding layer is also provided, covering the stress bars and fiber cores. The purpose of this patent is to solve the problem of maintaining the optical wave polarization state during signal transmission in multi-core optical fibers. However, due to the limited size of the fiber cladding, it is difficult to guarantee sufficient stress birefringence effect. 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 its preparation method, which addresses the shortcomings of the prior art. The fiber has a reasonable structure and 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, multiple core layers, and stress zones. There are 4 stress zones, which are evenly distributed circumferentially around the center of the optical fiber. The center lines of the 4 stress zones form a regular quadrilateral. One core layer is arranged at the midpoint of the four sides of the regular quadrilateral (at 1 / 2 of the side length). Each core layer and its two adjacent stress zones are configured to form a polarization-maintaining core zone.

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

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

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

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

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

[0011] According to the above scheme, the core layer is surrounded by a recessed cladding layer with a diameter of 10~25μm and a relative refractive index difference Δ2 of -0.3~-0.6%.

[0012] According to the above scheme, the core layer is surrounded by a recessed cladding layer with a diameter of 13~19μm and a relative refractive index difference Δ2 of -0.3~-0.5%.

[0013] According to the above scheme, the diameter of the common cladding layer is 40~125μm, and the common cladding layer is a pure silicon dioxide glass layer.

[0014] According to the above scheme, the diameter of the common cladding is 60~80μm. When a lower cladding diameter is applied to a fiber optic gyroscope, more loops can be made in the same fiber ring volume, thereby increasing the effective length of the fiber.

[0015] According to the above scheme, the birefringence of the polarization-maintaining fiber is 3×10⁻⁶. -4 ~5×10 -4 .

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

[0017] The technical solution of the optical fiber fabrication method of the present invention is as follows:

[0018] Preparation of mandrel: The cladding and core layers are deposited separately in a quartz liner using PCVD, and then melted and shrunk to form the desired mandrel.

[0019] Preparation of stress bars: A boron-doped stress layer was deposited in a quartz liner using PCVD. After deposition, the layer was melted, shrunk, and polished to obtain the desired stress bars.

[0020] Preparation of optical fiber preform: Drill holes in the pure silica quartz rod at the locations of the core rod and stress rod to make a quartz sleeve. Insert the four core rods and four stress rods into the quartz sleeve to make a multi-core polarization-maintaining optical fiber preform.

[0021] Drawing multi-core polarization-maintaining fiber: The multi-core polarization-maintaining fiber preform is clamped into a drawing furnace and drawn to form a multi-core polarization-maintaining fiber.

[0022] According to the above scheme, the core rod is prepared using PCVD (plasma chemical vapor deposition) technology. The core layer and the recessed cladding layer are prepared using SiCl4, GeCl4, C2F6, and O2 as raw materials. Specifically, during the recessed cladding layer preparation process, the flow rate of SiCl4 is 500–1500 sccm, the flow rate of C2F6 is 50–200 sccm, and the flow rate of O2 is 1500–3500 sccm. During the core layer preparation process, the flow rate of SiCl4 is 200–1000 sccm, the flow rate of C2F6 is 10–100 sccm, the flow rate of GeCl4 is 5–100 sccm, and the flow rate of O2 is 750–2500 sccm. (sccm is a unit of volumetric flow rate, referring to standard milliliters per minute.)

[0023] According to the above scheme, the stress bar is prepared by PCVD process, and a boron doped layer is prepared by using SiCl4 (tetrachlorosilane), BCl3 (boron trichloride) and O2 (oxygen) as raw materials. During the preparation process of boron doped layer, the flow rate of SiCl4 is 500-2000 sccm; the flow rate of BCl3 is 250-800 sccm; and the flow rate of O2 is 1500-5000 sccm.

[0024] The beneficial effects of this invention are as follows: 1. The structure is rationally designed. The arrangement of the shared stress zone allows for a multi-core polarization-maintaining layout, forming a multi-core polarization-maintaining fiber with multiple independent channels transmitting simultaneously, thereby enhancing spectral efficiency and significantly expanding the fiber transmission capacity. 2. Through the symmetrical spacing of the stress zone and core layer and the selection of specific structural parameters, not only can four polarization-maintaining core regions be achieved, but the influence of optical signal coupling between fiber cores can also be reduced, improving the transmission quality of the multi-core fiber. 3. The use of a widely fluorine-doped recessed cladding structure in the fiber core can improve the fiber's bending resistance and also increase the effective refractive index of the fiber core, reducing inter-core crosstalk and improving birefringence performance. It is particularly suitable for applications in fiber optic gyroscopes. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a radial cross-sectional structure according to an embodiment of the present invention. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings.

[0027] One embodiment of the present invention is as follows: Figure 1 As shown, the optical fiber includes a common cladding 1 and four stress zones 2. These four stress zones are evenly distributed circumferentially around the fiber center. The radial distance (radius) between each stress zone and the fiber center is 17 μm. The centers of the four stress zones form a regular quadrilateral. A core layer 3 is placed at the midpoint (half the side length) of each of the four sides of the quadrilateral. Each core layer and its two adjacent stress zones form a polarization-maintaining core region. The diameter of each stress zone is 15 μm, and the stress zone is a boron-doped silica glass layer with a boron molar percentage of 15-25%. The core layer has a diameter of 5.5 μm and a relative refractive index difference (relative to pure silica) Δ1 of 0.7-0.8%. A recessed cladding 4 surrounds the core layer, with a diameter of 14 μm and a relative refractive index difference Δ2 of -0.3 to -0.6%. The common cladding has a diameter of 60 μm and is a pure silica glass layer. The birefringence of the polarization-maintaining fiber described in this embodiment is 4.8 × 10⁻⁶. -4 ~5×10 -4 When the optical fiber is wound 10 times with a bending diameter of 10mm, the macrobending loss is ≤0.1dB. The design scheme with a cladding diameter of 60μm can be wound with more bundles in the same volume, thereby increasing the effective length of the optical fiber.

[0028] Examples of the preparation method of the present invention are as follows:

[0029] (1) Preparation of core rod: fluorine-doped cladding and core layer are deposited in a quartz liner using PCVD, and the core rod is formed by melting and shrinking after deposition;

[0030] (2) Preparation of stress bars: Boron-doped stress layer is deposited in quartz liner tube using PCVD. After deposition, the stress bar is obtained by melting, shrinking and polishing.

[0031] (3) Preparation of optical fiber preform: Drill holes in the pure silica quartz rod at the locations of the core rod and stress rod to make a quartz sleeve, and insert the four core rods and four stress rods into the quartz sleeve to make a multi-core polarization-maintaining optical fiber preform.

[0032] (4) The multi-core polarization-maintaining fiber preform is clamped into a drawing furnace and drawn to produce a multi-core polarization-maintaining fiber.

[0033] 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 a sunken cladding layer. By adjusting the flow rate and ratio of the gases, a core rod with the required diameter and refractive index is prepared under appropriate deposition rate conditions. Specifically, in the sunken cladding layer 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. In 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 rod is prepared with a boron-doped layer using PCVD (plasma chemical vapor deposition) technology. Specifically, in this application, the stress rod uses SiCl4 (tetrachlorosilane), BCl3 (boron trichloride), and O2 (oxygen) as raw materials to prepare the boron-doped layer. By adjusting the flow rate and ratio of the gases, a boron rod with the required diameter and refractive index is prepared under appropriate deposition rate conditions. During the boron-doped layer preparation process, the flow rate of SiCl4 is 500–700 sccm, the flow rate of BCl3 is 500–700 sccm, and the flow rate of O2 is 1500–3000 sccm. (sccm is a unit of volumetric flow rate, referring to standard milliliters per minute).

[0034] Example 2:

[0035] Another embodiment of the present invention is also as follows Figure 1 As shown, the fiber includes a common cladding and four stress zones. These four stress zones are evenly distributed circumferentially around the fiber center. The radial distance (radius) between each stress zone and the fiber center is 32 μm. The centers of the four stress zones form a regular quadrilateral. A core layer is placed at the midpoint (half the side length) of each side of the quadrilateral. Each core layer, along with its two adjacent stress zones, forms a polarization-maintaining core region. The diameter of each stress zone is 28 μm, and the stress zone is a boron-doped silica glass layer with a boron molar percentage of 15-25%. The core layer has a diameter of 6 μm and a relative refractive index difference (relative to pure silica) Δ1 of 0.7-0.8%. A recessed cladding with a diameter of 16 μm and a relative refractive index difference Δ2 of -0.3 to -0.6% surrounds the core layer. The diameter of the common cladding is 125 μm, and the common cladding is a pure silica glass layer. The birefringence of the polarization-maintaining fiber described in this embodiment is 4.3 × 10⁻⁶. -4 ~4.5×10 -4 The macrobending loss is ≤0.1dB when the optical fiber is wound 10 times with a bending diameter of 10mm. The design scheme with a cladding diameter of 125μm facilitates matching and splicing.

[0036] The preparation method in this embodiment is the same as that in the first embodiment.

[0037] 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 a sunken cladding layer. By adjusting the flow rate and ratio of the gases, a core rod with the required diameter and refractive index is prepared under appropriate deposition rate conditions. Specifically, in the sunken cladding layer preparation process, the SiCl4 flow rate is 800–900 sccm (sccm is a volumetric flow rate unit, referring to standard milliliters per minute), the C2F6 flow rate is 50–150 sccm, and the O2 flow rate is 2000–3000 sccm; in 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 bar is prepared with a boron-doped layer using PCVD (plasma chemical vapor deposition) technology. Specifically, in this application, the stress bar is prepared with SiCl4 (tetrachlorosilane), BCl3 (boron trichloride), and O2 (oxygen) as raw materials. By adjusting the flow rate and ratio of the gases, boron bars with the required diameter and refractive index are prepared under appropriate deposition rate conditions. During the boron-doped layer preparation process, the SiCl4 flow rate is 500–700 sccm (sccm is a volumetric flow rate unit, referring to standard milliliters per minute), the BCl3 flow rate is 500–700 sccm, and the O2 flow rate is 1500–3000 sccm.

Claims

1. A multi-core polarization-maintaining optical fiber, comprising a common cladding, multiple core layers, and a stress region, characterized in that... There are four stress zones, which are evenly distributed circumferentially around the center of the optical fiber. The center lines of the four stress zones form a regular quadrilateral. A core layer is placed at the midpoint of each of the four sides of the quadrilateral. Each core layer and its two adjacent stress zones are configured to form a polarization-maintaining core region. The core layer is surrounded by a recessed cladding with a diameter of 10~25μm and a relative refractive index difference Δ2 of -0.3~-0.6%. The core layer has a diameter of 4~18μm and a relative refractive index difference Δ1 of 0.5~0.8%.

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 12~35μm.

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

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

5. The multi-core polarization-maintaining optical fiber according to claim 1 or 2, characterized in that... The core layer has a diameter of 9~13μm and a relative refractive index difference Δ1 of 0.7~0.8%.

6. The multi-core polarization-maintaining optical fiber according to claim 1 or 2, characterized in that... The diameter of the sunken cladding is 13~19μm, and the relative refractive index difference Δ2 is -0.3~-0.5%.

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

8. The multi-core polarization-maintaining optical fiber according to claim 7, characterized in that... The diameter of the common cladding is 60~80μm.

9. The multi-core polarization-maintaining optical fiber according to claim 1 or 2, characterized in that... The birefringence of the polarization-maintaining fiber is 3 × 10⁻⁶. -4 ~5×10 -4 .

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

11. A method for fabricating a multi-core polarization-maintaining optical fiber as described in any one of claims 1-10, characterized in that... Preparation of mandrel: The cladding and core layers are deposited separately in a quartz liner using PCVD, and then melted and shrunk to form the desired mandrel. Preparation of stress bars: A boron-doped stress layer was deposited in a quartz liner using PCVD. After deposition, the layer was melted, shrunk, and polished to obtain the desired stress bars. Preparation of optical fiber preform: Drill holes in the pure silica quartz rod at the locations of the core rod and stress rod to make a quartz sleeve. Insert the 4 core rods and 4 stress rods into the quartz sleeve to make a multi-core polarization-maintaining optical fiber preform. Drawing multi-core polarization-maintaining fiber: The multi-core polarization-maintaining fiber preform is clamped into a drawing furnace and drawn to form a multi-core polarization-maintaining fiber.

12. The method for fabricating a multi-core polarization-maintaining optical fiber according to claim 11, characterized in that... The core rod is prepared using PCVD technology, with SiCl4, GeCl4, C2F6, and O2 as raw materials to prepare the core layer and the sunken cladding. During the sunken 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.

13. The method for fabricating a multi-core polarization-maintaining optical fiber according to claim 11 or 12, characterized in that... The stress bar is prepared using PCVD process, and a boron doped layer is prepared using SiCl4, BCl3 and O2 as raw materials. During the preparation process of the boron doped layer, the flow rate of SiCl4 is 500-2000 sccm, the flow rate of BCl3 is 250-800 sccm, and the flow rate of O2 is 1500-5000 sccm.

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