High-birefringence multi-core elliptical polarization maintaining optical fiber and preparation method thereof

Abstract

The invention relates to a high-birefringence multi-core elliptical polarization-maintaining optical fiber and a preparation method thereof, the high-birefringence multi-core elliptical polarization-maintaining optical fiber comprises a common cladding and at least three stress areas and polarization-maintaining core areas which are distributed in the common cladding, the stress areas are uniformly distributed along the circumferential direction at equal intervals, and the center connecting lines of the adjacent stress areas form a regular polygon. One elliptical polarization-maintaining core is arranged at the middle point of each side of the regular polygon, the long axis of each elliptical polarization-maintaining core is flush with each corresponding side of the regular polygon, and each elliptical polarization-maintaining core and two adjacent stress areas are configured to form a polarization-maintaining core area. According to the invention, by designing the plurality of elliptical fiber cores and adding the stress rods, more transmission channels are provided, the birefringence performance is stronger, and the process requirement of manufacturing is reduced. The arrangement of the shared stress area forms multiple independent channels, the structure is compact, crosstalk is small, higher density and larger capacity of the multi-core polarization maintaining optical fiber are achieved, and the multi-core polarization maintaining optical fiber has wide application prospects in the aspect of miniaturization of optical fiber gyroscopes and devices.

Description

Technical Field

[0001] The invention relates to a high-birefringence multi-core elliptical polarization-maintaining optical fiber and a preparation method thereof, and belongs to the technical field of optical communication and sensing. Background Art

[0002] Polarization-maintaining fibers are widely used in various sectors of the national economy, including aerospace, aviation, navigation, industrial manufacturing, and communications. In interferometric fiber sensors based on optical coherence detection, using polarization-maintaining fibers ensures a constant linear polarization direction, improving the coherent signal-to-noise ratio (SNR) and enabling high-precision measurement of physical quantities. Common types of polarization-maintaining fibers currently include panda, bowtie, and elliptical. Panda and bowtie polarization-maintaining fibers achieve polarization maintenance through stress-induced birefringence, while elliptical polarization-maintaining fibers achieve this through geometric birefringence. Elliptical polarization-maintaining fibers are more compact than other types of polarization-maintaining fibers. Existing polarization-maintaining fibers are mostly single-core structures, meaning they have only one transmission channel. Their transmission capacity is gradually failing to meet increasing transmission demands. Multi-core polarization-maintaining fibers utilize space-division multiplexing (SDM) to achieve higher density, greater capacity, and improved polarization-maintaining performance. While multi-core elliptical polarization-maintaining fibers offer the advantages of compactness and high density, they also require high manufacturing precision, making it difficult to guarantee polarization performance and inter-core crosstalk. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a high-birefringence multi-core elliptical polarization-maintaining optical fiber and its preparation method in response to the above-mentioned deficiencies in the prior art. The optical fiber has a compact structure, stronger birefringence performance, and enables the polarization-maintaining optical fiber to achieve higher density and larger capacity.

[0004] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows: it includes a common cladding and stress zones and polarization-maintaining core zones distributed in the common cladding, wherein there are at least three stress zones, which are evenly spaced along the circumference, and the center lines connecting adjacent stress zones form a regular polygon. An elliptical polarization-maintaining core is arranged at the midpoint of each side of the regular polygon, and the major axis of the elliptical polarization-maintaining core is flush with the corresponding sides of the regular polygon. Each elliptical polarization-maintaining core is configured with its two adjacent stress zones to form a polarization-maintaining core zone.

[0005] According to the above solution, the radial distance (radius) between the stress zone and the center of the optical fiber is 12~35μm.

[0006] According to the above solution, the diameter of the stress region is 8-30 μm, and the stress region is a boron-doped quartz glass layer, with a molar percentage of boron being 15-25%.

[0007] According to the above solution, the elliptical polarization-maintaining core includes a circular core and an elliptical cladding surrounding the core, which are evenly spaced along the circumference.

[0008] According to the above solution, the diameter of the common cladding is 40 to 125 μm, and the common cladding is a pure silica glass layer.

[0009] According to the above solution, the relative refractive index difference Δ1 of the circular core is 0.5-1.3%, and the diameter d1 is 1-2.5 μm.

[0010] According to the above solution, a circular inner cladding is tightly coated on the outside of the circular core, the diameter d2 of the circular inner cladding is 2 to 6.2 μm, and the relative refractive index difference Δ2 is -0.8 to 0%.

[0011] According to the above scheme, the relative refractive index difference Δ3 of the elliptical cladding is -1.5 to -0.7%, the major axis 2a of the elliptical cladding is 7 to 25 μm, the ellipticity 1-b / a of the elliptical cladding is 0.1 to 0.5, and b is the minor axis of the elliptical cladding.

[0012] According to the above solution, there are 3 to 4 elliptical polarization-maintaining core areas, which are evenly spaced along the circumference.

[0013] According to the above scheme, the birefringence coefficient of the polarization-maintaining optical fiber is 6.0×10 -4 ~6.5×10 -4 .

[0014] According to the above solution, the macrobending loss of the polarization-maintaining optical fiber is ≤0.1 dB when it is wound 10 times with a bending diameter of 10 mm.

[0015] The preparation method technical solution of the present invention is: Make round core rods and stress rods, Production of elliptical cladding core rod: Use a pure silica glass tube of a certain thickness to perform doping deposition inside the tube, and after deposition, burn and melt it into a solid circular core rod with a doped core layer. Heat the circular core rod with the doped core layer until it is in a molten state and apply radial pressure to make the circular core rod form a doped core layer core rod with an elliptical or quasi-elliptical radial cross section. Then, grind the elliptical cladding into a core rod with a circular outer circumference and an elliptical doped core layer inside. Preparation of elliptical polarization-maintaining core rod: punch a center hole in the core rod containing the elliptical doped core layer, insert the round fiber core rod and melt it into a solid elliptical polarization-maintaining core rod. Preparation of multi-core elliptical polarization-maintaining optical fiber preform: holes are punched on a solid pure silica glass rod according to the number and spacing of polarization-maintaining cores, and the number and spacing of stress rods. The solid elliptical polarization-maintaining core rods and stress rods are inserted into the holes according to the orientation to form a multi-core elliptical polarization-maintaining optical fiber preform. The multi-core elliptical polarization-maintaining optical fiber preform is clamped into an optical fiber drawing furnace and drawn into a multi-core elliptical polarization-maintaining optical fiber.

[0016] According to the above solution, the circular core rod is covered with an inner cladding.

[0017] According to the above scheme, the elliptical cladding core rod is deposited by PCVD (plasma chemical vapor deposition) process, using SiCl4 (tetrachlorosilane), BCl3 (boron trichloride), O2 (oxygen), and C2F6 (hexafluoroethane) as deposition raw materials. By adjusting the flow rate and proportion of the gases, a core rod with the required diameter and refractive index is prepared. During the deposition process, the SiCl4 flow rate is 500-2000sccm (sccm is the unit of volume flow rate, referring to standard milliliters per minute), the BCl3 flow rate is 250-800sccm, the O2 flow rate is 1500-5000sccm, and the C2F6 flow rate is 20-300sccm.

[0018] According to the above scheme, the circular fiber core rod is deposited by PCVD process, using SiCl4 (tetrachlorosilane), GeCl4 (germanium tetrachloride) and O2 (oxygen) as deposition raw materials. By adjusting the flow rate and proportion of the gas, a core rod with the required diameter and refractive index is prepared. During the deposition process, the SiCl4 flow rate is 500-800sccm, the GeCl4 flow rate is 20-50sccm, and the O2 flow rate is 1000-1500sccm. After the deposition is completed, it is fired and melted into a solid core rod.

[0019] According to the above scheme, the inner cladding is deposited by PCVD process, using SiCl4 (tetrachlorosilane), C2F6 (hexafluoroethane) and O2 (oxygen) as deposition raw materials. During the deposition process, the SiCl4 flow rate is 800-1200sccm, the C2F6 flow rate is 50-150sccm, and the O2 flow rate is 2000-3000sccm, and the cladding is deposited before the core layer.

[0020] According to the above scheme, the stress rods are prepared using a PCVD process to deposit a boron-doped layer. SiCl4 (tetrachlorosilane), BCl3 (boron trichloride), and O2 (oxygen) are used as deposition materials. By adjusting the gas flow rates and ratios, stress rods with the required diameter and refractive index are produced. 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. After deposition, the rods are sintered and melted to form a solid core rod.

[0021] The beneficial effects of the present invention are: 1. By designing multiple elliptical cores and adding stress rods, it is possible to simultaneously increase the effective length of the optical fiber and achieve polarization-maintaining performance, provide more transmission channels, have stronger birefringence performance, and reduce crosstalk between cores. The addition of stress rods can not only increase birefringence performance, but also reduce the requirements for the elliptical core ellipticity and reduce the process requirements for production. 2. The layout of the shared stress zone can realize the positional layout of multi-core polarization-maintaining, forming a multi-core polarization-maintaining optical fiber that transmits multiple independent channels simultaneously, thereby enhancing spectral efficiency. Its structure is compact and has low crosstalk, which is conducive to setting more polarization-maintaining core areas in a limited optical fiber cross-section, so that the elliptical multi-core polarization-maintaining optical fiber can achieve higher density and larger capacity of multi-core polarization-maintaining optical fiber by using space division multiplexing, as well as the advantages of better polarization-maintaining performance, and has broad application prospects in the miniaturization of optical fiber gyroscopes and devices. 3. Each elliptical polarization-maintaining core area is evenly spaced along the circumference, and the short axis of the elliptical cladding points to the center of the common cladding, forming a corresponding iso-azimuth structure, which is conducive to controlling the cladding roundness of the optical fiber during drawing and is also conducive to crosstalk control between cores. 4. A circular inner cladding is tightly wrapped around the circular fiber core, which is beneficial to reducing the drawing stress and distortion of the fiber core and further reducing the crosstalk between cores. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the radial structure of an embodiment of the present invention.

[0023] Figure 2 It is a schematic diagram of the radial structure of the second embodiment of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below in conjunction with the embodiments of the present invention and the accompanying drawings.

[0025] One embodiment of the present invention is Figure 1As shown, the fiber comprises a common cladding 1, stress zones 2 distributed within the common cladding, and a polarization-maintaining core region. The common cladding has a diameter of 80 μm and is composed of a pure silica glass layer. Three stress zones are equally spaced circumferentially, with a radial distance (radius) of 20 μm from the fiber center and a diameter of 19 μm. These stress zones are made of boron-doped silica glass with a boron content of 15-25% by mole. The birefringence provided by the stress zones effectively reduces the required core rod ellipticity. The centers of adjacent stress zones are connected to form an equilateral triangle. An elliptical polarization-maintaining core is positioned at the midpoint of each side of the triangle. The long axis of each elliptical polarization-maintaining core is aligned with the corresponding side of the triangle, and the short axis points toward the center of the common cladding. Each elliptical polarization-maintaining core, combined with its two adjacent stress zones, forms a polarization-maintaining core region. Each of the elliptical polarization-maintaining core regions has the same structure. The elliptical polarization-maintaining core comprises a circular core 3, wherein the relative refractive index difference Δ1 of the circular core is 0.5 to 1.3%, and the diameter d1 is 2 μm. A circular inner cladding 4 is tightly coated on the circular core, wherein the diameter d2 of the circular inner cladding is 4 μm, and the relative refractive index Δ2 is -0.8 to 0%. The circular inner cladding is surrounded by an elliptical cladding 5, wherein the relative refractive index difference Δ3 of the elliptical cladding is -1.5 to -0.7%, the major axis 2a of the elliptical cladding is 17 μm, and the ellipticity 1-b / a of the elliptical cladding is 0.1 to 0.5. The birefringence coefficient of the polarization-maintaining optical fiber of this embodiment is 6.0×10 -4 ~6.5×10 -4 ; When the optical fiber is wound 10 times with a bending diameter of 10mm, the macrobending loss is ≤0.1dB.

[0026] The preparation method of this embodiment is as follows: (1) Preparation of a circular fiber core rod: The circular fiber core rod is coated with an inner cladding, and the core layer and the inner cladding are prepared separately by PCVD (plasma chemical vapor deposition) process; the core layer is prepared by SiCl4 (tetrachlorosilane), GeCl4 (germanium tetrachloride), and O2 (oxygen) as raw materials, and the inner cladding is prepared by SiCl4 (tetrachlorosilane), C2F6 (hexafluoroethane), and O2 (oxygen) as raw materials. By adjusting the flow rate and ratio of the gas, a core rod with the required diameter and refractive index is prepared under appropriate deposition speed conditions. Among them, during the core layer preparation process, the SiCl4 flow rate is 600-700sccm (sccm is the unit of volume flow rate, referring to standard milliliters per minute); the GeCl4 flow rate is 30-40sccm, and the O2 flow rate is 1200-1400sccm; during the inner cladding preparation process, the SiCl4 flow rate is 900-1100sccm, the C2F6 flow rate is 70-90sccm, and the O2 flow rate is 2200-2800sccm.

[0027] (2) Fabrication of circular stress rods: The stress rods are prepared by depositing a boron-doped layer using a PCVD process. SiCl4 (tetrachlorosilane), BCl3 (boron trichloride), and O2 (oxygen) are used as deposition materials. By adjusting the flow rates and ratios of these gases, stress rods with the required diameter and refractive index are prepared. 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 2000-2800 sccm. After deposition, the rods are sintered and melted to form solid core rods.

[0028] (3) Then, an elliptical cladding core rod is made: a pure silica glass tube of a certain thickness is used for in-tube doping deposition, and an elliptical cladding is prepared by PCVD process; specifically, SiCl4 (tetrachlorosilane), BCl3 (boron trichloride), O2 (oxygen), and C2F6 (hexafluoroethane) are used as raw materials to prepare the elliptical cladding. 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 speed conditions. During the preparation process, the SiCl4 flow rate is 900-1500sccm (sccm is a unit of volume flow rate, referring to standard milliliters per minute); the BCl3 flow rate is 300-500sccm, the O2 flow rate is 2000-3500sccm, and the C2F6 flow rate is 80-250sccm; after the deposition is completed, the circular core rod of the doped core layer is fired and melted to form a solid core, and radial pressure is applied to the circular core rod of the doped core layer when it is in a molten state so that the circular core rod forms a doped core layer core rod with an elliptical or quasi-elliptical radial cross-section and a cladding, and then the elliptical cladding is ground into a core rod with a circular outer circumference and an elliptical doped core layer inside through processing.

[0029] (4) Preparation of an elliptical polarization-maintaining core rod: Punch a center hole in the core rod containing the elliptical doped core layer, insert a circular fiber core rod into the center hole, and then melt and shrink it into a solid elliptical polarization-maintaining core rod.

[0030] (5) Preparation of multi-core elliptical polarization-maintaining optical fiber preform: holes are punched on a solid pure silica glass rod according to the number and spacing of polarization-maintaining cores and the number and spacing of stress rods, and the solid elliptical polarization-maintaining core rods and stress rods are inserted into the holes according to the orientation to make a multi-core elliptical polarization-maintaining optical fiber preform.

[0031] (6) The multi-core elliptical polarization-maintaining optical fiber preform is clamped into an optical fiber drawing furnace and drawn into a multi-core elliptical polarization-maintaining optical fiber.

[0032] The second embodiment of the present invention is Figure 2As shown, the main difference from the first embodiment is that four stress zones 2 and four elliptical polarization-maintaining cores are arranged in the common cladding 1. The four stress zones are evenly spaced along the circumference. The radial distance (radius) between the stress zones and the center of the optical fiber is 19 μm, and the diameter of the stress zones is 15 μm. The centers of adjacent stress zones are connected to form a regular quadrilateral, i.e., a square. An elliptical polarization-maintaining core is arranged at the midpoint of each side of the regular quadrilateral. The major axis of the elliptical polarization-maintaining core is aligned with the corresponding side of the regular quadrilateral, and the minor axis points toward the center of the common cladding. Each elliptical polarization-maintaining core, together with its two adjacent stress zones, forms a polarization-maintaining core. The elliptical polarization-maintaining cores have the same structure. The elliptical polarization-maintaining core includes a circular core 3, the relative refractive index difference Δ1 of the circular core is 0.5 to 1.3%, and the diameter d1 is 1.8 μm. The circular core is tightly coated with a circular inner cladding 4, the diameter d2 of the circular inner cladding is 4 μm, the relative refractive index Δ2 is -0.8 to 0%, and the circular inner cladding is surrounded by an elliptical cladding 5, the relative refractive index difference Δ3 of the elliptical cladding is -1.5 to -0.7%, the major axis 2a of the elliptical cladding is 15 μm, and the ellipticity 1-b / a of the elliptical cladding is 0.1 to 0.5. The birefringence coefficient of the polarization-maintaining fiber of this embodiment is 6.0×10 -4 ~6.5×10 -4 When the optical fiber is wound 10 times with a bending diameter of 10 mm, the macrobending loss is ≤ 0.1 dB. The remaining structure is the same as that of the first embodiment.

Claims

1. A high birefringence multi-core elliptical polarization-maintaining optical fiber, comprising a common cladding and a stress region and a polarization-maintaining core region distributed in the common cladding, characterized in that There are at least three stress zones, which are evenly distributed along the circumference. The center lines of adjacent stress zones form a regular polygon. An elliptical polarization-maintaining core is arranged at the midpoint of each side of the regular polygon. The major axis of the elliptical polarization-maintaining core is flush with the corresponding sides of the regular polygon. Each elliptical polarization-maintaining core and its two adjacent stress zones are configured to form a polarization-maintaining core zone.

2. The high birefringence multi-core elliptical 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 high birefringence multi-core elliptical polarization-maintaining optical fiber according to claim 1 or 2, characterized in that The diameter of the stress region is 8-30 μm, and the stress region is a boron-doped quartz glass layer, with a molar percentage of boron being 15-25%.

4. The high birefringence multi-core elliptical polarization-maintaining optical fiber according to claim 1 or 2, characterized in that The elliptical polarization-maintaining core comprises a circular fiber core and an elliptical cladding surrounding the fiber core, which are evenly spaced along the circumference.

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

6. The high birefringence multi-core elliptical polarization-maintaining optical fiber according to claim 4, characterized in that The relative refractive index difference Δ1 of the circular fiber core is 0.5-1.3%, and the diameter d1 is 1-2.5 μm.

7. The high birefringence multi-core elliptical polarization-maintaining optical fiber according to claim 6, characterized in that A circular inner cladding is tightly coated on the outside of the circular core. The diameter d2 of the circular inner cladding is 2 to 6.2 μm, and the relative refractive index difference Δ2 is -0.8 to 0%.

8. The high birefringence multi-core elliptical polarization-maintaining optical fiber according to claim 4, characterized in that The relative refractive index difference Δ3 of the elliptical cladding is -1.5 to -0.7%, the major axis 2a of the elliptical cladding is 7 to 25 μm, the ellipticity 1-b / a of the elliptical cladding is 0.1 to 0.5, and b is the minor axis of the elliptical cladding.

9. The high birefringence multi-core elliptical polarization-maintaining optical fiber according to claim 1 or 2, characterized in that There are 3 to 4 elliptical polarization-maintaining core areas, which are evenly spaced along the circumference.

10. The high birefringence multi-core elliptical polarization-maintaining optical fiber according to claim 1 or 2, characterized in that The birefringence coefficient of the polarization-maintaining optical fiber is 6.0×10 -4 ~6.5×10 -4 .

11. The high birefringence multi-core elliptical 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.

12. A method for preparing a high birefringence multi-core elliptical polarization-maintaining optical fiber according to any one of claims 1 to 11, characterized in that Making a circular fiber core rod and a stress rod; making an elliptical cladding core rod: using a pure silica glass tube of a certain thickness to perform doping deposition inside the tube, firing and melting the tube after deposition to form a circular core rod with a solid doped core layer, heating the circular core rod with the doped core layer so that it is in a molten state and applying radial pressure to the circular core rod so that the circular core rod forms a doped core layer core rod with an elliptical or quasi-elliptical radial cross section, and then grinding the elliptical cladding into a core rod with a circular outer circumference and an elliptical doped core layer inside through processing; making an elliptical polarization-maintaining core Zone core rod: Punch a center hole in a core rod containing an elliptical doped core layer, insert a round fiber core rod, and then melt and shrink it into a solid elliptical polarization-maintaining core zone core rod; Prepare multi-core elliptical polarization-maintaining optical fiber preform: Punch holes on a solid pure silica glass rod according to the number and spacing of polarization-maintaining cores, and the number and spacing of stress rods, and insert the solid elliptical polarization-maintaining core zone core rod and stress rods into the holes according to orientation to form a multi-core elliptical polarization-maintaining optical fiber preform; Clamp the multi-core elliptical polarization-maintaining optical fiber preform into an optical fiber drawing furnace to draw it into a multi-core elliptical polarization-maintaining optical fiber.

13. The method for preparing a high birefringence multi-core elliptical polarization-maintaining optical fiber according to claim 12, characterized in that The circular fiber core rod is covered with an inner cladding.

14. The method for preparing a high birefringence multi-core elliptical polarization-maintaining optical fiber according to claim 12, characterized in that The elliptical cladding core rod is deposited using a PCVD process, using SiCl4, BCl3, O2, and C2F6 as deposition raw materials. By adjusting the flow rates and proportions of the gases, a core rod with the required diameter and refractive index is prepared. During the deposition process, the SiCl4 flow rate is 500-2000sccm, the BCl3 flow rate is 250-800sccm, the O2 flow rate is 1500-5000sccm, and the C2F6 flow rate is 20-300sccm.

15. The method for preparing a high birefringence multi-core elliptical polarization-maintaining optical fiber according to claim 12, characterized in that The circular fiber core rod is deposited using the PCVD process, using SiCl4, GeCl4, and O2 as deposition raw materials. By adjusting the flow rate and ratio of the gases, a core rod with the required diameter and refractive index is prepared. During the deposition process, the SiCl4 flow rate is 500-800sccm, the GeCl4 flow rate is 20-50sccm, and the O2 flow rate is 1000-1500sccm. After deposition, the rod is fired and melted into a solid core rod.

16. The method for preparing a high birefringence multi-core elliptical polarization-maintaining optical fiber according to claim 13, characterized in that The inner cladding is deposited by PCVD process, using SiCl4, C2F6 and O2 as deposition raw materials. During the deposition process, the SiCl4 flow rate is 800-1200sccm, the C2F6 flow rate is 50-150sccm, and the O2 flow rate is 2000-3000sccm, and the cladding is deposited before the core layer.

17. The method for preparing a high birefringence multi-core elliptical polarization-maintaining optical fiber according to claim 12, characterized in that The stress rod is prepared by depositing a boron-doped layer using a PCVD process, with SiCl4, BCl3, and O2 as deposition raw materials. By adjusting the flow rate and ratio of the gases, a stress rod with a diameter and refractive index that meets the requirements is prepared. In 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. After deposition, the rod is fired and melted into a solid core rod.

Images