High-birefringence polarization maintaining optical fiber stress layer and preparation method and device thereof

Abstract

The invention relates to the technical field of optical fiber preparation, in particular to a high-birefringence polarization-maintaining optical fiber stress layer and a preparation method and device.Two pairs of blowtorches are used for stress layer deposition and include the first pair of blowtorches and the second pair of blowtorches, the first pair of blowtorches is responsible for the long-axis direction of the aperture of a deposition pipe, and the second pair of blowtorches is responsible for the long-axis direction of the aperture of the deposition pipe; and the second pair of blowtorches is responsible for stress layer deposition in the short axis direction of the aperture of the deposition pipe. According to the preparation method disclosed by the invention, the processes of mechanical grinding, sleeve splicing, high-temperature extrusion and the like are avoided, better optical fiber strength can be obtained, and particularly, the preparation of the small-diameter polarization maintaining optical fiber is facilitated.

Description

Technical Field

[0001] This invention relates to the field of optical fiber fabrication technology, specifically to a high birefringence polarization-maintaining fiber stress layer and its fabrication method and apparatus. Background Technology

[0002] Polarization-maintaining fiber, a special type of optical fiber, has the function of maintaining a stable polarization state. It plays a crucial role in lasers and communications by maintaining polarization invariance through a special structure. Its core lies in the fiber's unique structure, which allows light to maintain its polarization direction during transmission. This characteristic is essential in many optical applications, such as laser communication, precision optical measurement, and optical signal processing. A common method for introducing high birefringence is to introduce geometrically symmetrical non-uniform stress into the fiber core of the preform. This can be achieved by adding two stress bars with modified glass compositions having different coefficients of thermal expansion on both sides of the core. For example, elliptical, bowtie, and panda shapes achieve different stress effects through geometric shapes, producing enhanced birefringence. Stable polarization transmission can be achieved without additional stress, simplifying the manufacturing process. Elliptical stress layer or elliptical core polarization-maintaining fiber has advantages over bow-tie and panda type polarization-maintaining fibers in terms of bending resistance and lower temperature dependence. It is not sensitive to external interference such as bending and twisting, and can maintain polarization stability, especially when the ambient temperature changes. It is suitable for high-temperature environment applications. At the same time, the fusion splicing loss of elliptical stress layer polarization-maintaining fiber is lower than that of elliptical core polarization-maintaining fiber, making it more suitable for applications with high-precision polarization-maintaining performance requirements.

[0003] Methods for fabricating elliptical polarization-maintaining fibers generally employ grinding and sleeve splicing, pressure reduction and collapse, and directional etching one-time forming methods. Patent CN117263513A discloses a method and product for fabricating elliptical cladding polarization-maintaining fibers. This method first prepares an elliptical stress layer rod using positive or negative pressure methods, then prepares a core rod, drills a circular hole in the center of the elliptical stress layer rod, and etches the core rod to a suitable size. Finally, it uses the RIT tube-rod method for fiber drawing. However, the drilling process on the high-stress elliptical stress layer rod during this method easily causes stress layer breakage. Patent CN103253860A discloses a method for manufacturing elliptical stress-zone polarization-maintaining fibers. This involves drilling three connecting holes longitudinally into a quartz rod to form a sleeve, then inserting the core rod and fixing it to a fiber drawing tower for drawing to obtain an elliptical stress layer polarization-maintaining fiber. In this tube-rod drawing method, the stress layer deforms during drawing, and the fiber core is also prone to deformation. US Patent No. 2006 / 0191295A1 discloses Polarization Controlling Optical Fiber Preform and Fabrication Methods, employing a cold-working method. This involves depositing and collapsing a symmetrical preform with a stress zone on an MCVD lathe. Appropriate quartz portions are then symmetrically cut off from both sides of the preform, which is then drawn into an optical fiber on a drawing tower. This method requires cold working; improper handling can affect fiber strength. Achieving high birefringence requires significant stretching of the stress layer during drawing, easily leading to core deformation. Patent No. CN1632629A discloses a "I"-shaped polarization-maintaining fiber and its production method, using a directional etching in-line one-step forming method. This involves depositing and collapsing a preform on an MCVD lathe, followed by appropriate etching, to form a single preform, which is then drawn into a polarization-maintaining fiber on a tower. While the process is relatively simple, it is complex. Unlike butterfly-shaped polarization-maintaining fibers, the "I"-shaped or elliptical stress layer requires directional etching of most of the stress layer area, making batch consistency difficult to achieve due to the complexity of the etching process.

[0004] Meanwhile, the birefringence of polarization-maintaining fiber with an elliptical stress layer is directly related to the ellipticity of the stress layer. For a given doping concentration in the stress layer, high birefringence requires high ellipticity; that is, a larger major axis / minor axis ratio results in higher birefringence. In existing methods for fabricating polarization-maintaining fiber with an elliptical stress layer, obtaining the elliptical stress layer generally involves two approaches. First, obtaining a circular stress layer is achieved through high-temperature extrusion or stretching. However, this is difficult while maintaining the core's roundness. Second, the elliptical stress layer shape can be obtained through grinding and splicing or directional etching during the fabrication process. While this can achieve high ellipticity, grinding easily causes the high-stress layer to crack, splicing and melting readily generate dust bubbles and cause stress layer deformation, and the directional etching process is complex and difficult to guarantee consistent shape. Summary of the Invention

[0005] The purpose of this invention is to provide a stress layer for a high birefringence polarization-maintaining fiber and its preparation method and apparatus, thereby solving the technical problem that the higher the birefringence of a polarization-maintaining fiber, the more difficult it is to prepare.

[0006] This invention discloses a method for preparing a stress layer in a high birefringence polarization-maintaining optical fiber. Two pairs of torches are used for stress layer deposition. The two pairs of torches are a first pair of torches and a second pair of torches. The first pair of torches is responsible for the deposition of the stress layer along the long axis of the deposition tube aperture, and the second pair of torches is responsible for the deposition of the stress layer along the short axis of the deposition tube aperture.

[0007] Furthermore, when the torch returns to the initial end after each deposition cycle, it rotates the deposition tube by 180°, but the deposition tube does not rotate during the deposition process.

[0008] Furthermore, the ratio of the major axis to the minor axis of the stress layer is greater than 1.

[0009] Furthermore, the stress layer is elliptical or rhomboid.

[0010] Furthermore, each pair of torches is symmetrically distributed across the cross-section of the deposition tube.

[0011] Furthermore, the two pairs of torches are arranged perpendicular to each other along the longitudinal direction of the deposition tube.

[0012] Furthermore, the distance S between the first pair of blowtorches and the second pair of blowtorches is 10-150mm. For example, S can be 10mm, 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm, 140mm or 150mm.

[0013] Furthermore, the distance d1 between the head of the first pair of blowtorches and the outer wall of the deposition tube is 10-100 mm, and the temperature range of the first pair of blowtorches is 1300-1900℃. For example, d1 can be 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, or 100 mm, and the temperature of the first pair of blowtorches can be 1300℃, 1400℃, 1500℃, 1600℃, 1700℃, 1800℃, or 1900℃.

[0014] Furthermore, the distance d2 between the head of the second pair of blowtorches and the outer wall of the deposition tube ranges from 5 to 100 mm, and the temperature range of the second pair of blowtorches is 1200-1800℃. For example, d2 can be 5 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, or 100 mm, and the temperature of the second pair of blowtorches can be 1200℃, 1300℃, 1400℃, 1500℃, 1600℃, 1700℃, or 1800℃.

[0015] Furthermore, before the stress layer is deposited, a high-purity quartz tube is selected as the deposition tube. After cleaning, ordinary quartz tubes are welded to both ends of the deposition base tube as the inlet tube and the outlet tube, respectively.

[0016] Furthermore, an isolation layer is deposited after the stress layer is deposited, and then the core layer is deposited.

[0017] Furthermore, the core layer is deposited and then sintered to obtain a polarization-maintaining fiber preform.

[0018] Further, the polarization-maintaining fiber preform is drawn into an optical fiber to obtain the final product.

[0019] Furthermore, after the stress layer is deposited, the stress layer is softened and a uniform circular aperture isolation layer is formed for redeposition.

[0020] Furthermore, the stress layer is softened and a uniform circular aperture is formed through the MCVD system.

[0021] Furthermore, the heating temperature of the blowtorch in the MCVD system is 1000-1800℃. For example, the heating temperature can be 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700 or 1800℃.

[0022] Furthermore, the stress layer includes SiO2 and a component with a high coefficient of thermal expansion, wherein the component with a high coefficient of thermal expansion includes one or more of B2O3, GeO2, P2O5 and SiF4.

[0023] Furthermore, the components of the isolation layer used for refractive index and viscosity adjustment include one or more of SiO2, GeO2, SiF4, and P2O5.

[0024] Furthermore, the fiber core layer includes SiO2 and components for adjusting the refractive index and viscosity, wherein the components for adjusting the refractive index and viscosity include one or more of SiO2, GeO2, SiF4, and P2O5.

[0025] An apparatus for preparing a stress layer for a high birefringence polarization-maintaining optical fiber is used in the above method.

[0026] A high birefringence polarization-maintaining fiber stress layer is prepared by the above method.

[0027] A method for preparing high birefringence polarization-maintaining optical fiber, wherein a stress layer is prepared using the above method.

[0028] A high birefringence polarization-maintaining optical fiber is prepared using the method described above.

[0029] Compared with the prior art, the beneficial effects of the present invention are: The preparation method disclosed in this patent is to directly obtain an elliptical stress layer through selective region deposition in a quartz tube. A deposition tube with a high ellipticity is selected as the deposition tube. Using the method disclosed in this patent, a high-ellipticity stress region can be obtained, making it easier to obtain high birefringence performance in the preparation of polarization-maintaining fibers with elliptical stress layers. It also makes it easier to ensure longitudinal uniformity of the stress region in the preform. Polarization-maintaining fibers with elliptical stress layers prepared using the method of this invention can achieve higher birefringence and better uniform polarization-maintaining performance. The preparation method disclosed in this invention avoids processes such as mechanical grinding, sleeve splicing, and high-temperature extrusion, which is beneficial for obtaining better fiber strength and is particularly convenient for the preparation of small-diameter polarization-maintaining fibers. Attached Figure Description To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 The diagram shown is a schematic diagram of the stress layer deposition according to the present invention.

[0031] Figure 2 The diagram shows a schematic of the stress layer deposition heating quartz torch device of the present invention.

[0032] Figure 3 The diagram shown is a schematic diagram of the torch position in the cross-section direction of the deposition tube during the deposition of the elliptical stress layer according to the present invention.

[0033] Figure 4 The diagram shows the longitudinal torch position of the deposition tube during the deposition of the elliptical stress layer according to the present invention.

[0034] Figure 5 The diagram shown is a schematic diagram of the quartz tube rotation during the elliptical stress layer deposition process of the present invention.

[0035] Figure 6 The diagram shows the deposition process of the final circular deposition aperture of the elliptical stress layer according to the present invention.

[0036] Figure 7The diagram shows the deposition process of the isolation layer and the fiber core according to the present invention.

[0037] Figure 8 The diagram shown is a schematic representation of the polarization-maintaining fiber end face of the elliptical stress layer according to the present invention.

[0038] Figure 9 The diagram shown is a schematic diagram of other deposition tubes suitable for this invention.

[0039] Figure 10 The figure shown is a cross-sectional view of the optical fiber in Embodiment 1 of the present invention.

[0040] Figure 11 The figure shown is a cross-sectional view of the optical fiber in Embodiment 2 of the present invention.

[0041] Explanation of the labels in the diagram: 1-First pair of torches, 2-Second pair of torches, 3-Deposition tube, 4-Fixing device, 5-Hydrogen / oxygen pipeline, 6-Deposited elliptical stress layer, 7-Deposited aperture during stress layer deposition, 8-Final circular aperture of the deposited stress layer, 9-Deposited isolation layer, 10-Deposited fiber core layer, 11-Aperture after core layer deposition, 12-Elliptical stress layer of optical fiber, 13-Optical fiber isolation layer, 14-Optical fiber core layer, 15-Optical fiber cladding, 16-Diamond aperture deposition tube, 17-Rectangular aperture deposition tube, 18-Polygonal aperture deposition tube, d1: Distance from the head of the first pair of torches to the outer wall of the deposition tube, d2: Distance from the head of the second pair of torches to the outer wall of the deposition tube, S: Distance between the first pair of torches and the second pair of torches. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0043] Example 1: Fabrication of polarization-maintaining fiber with elliptical stress layer This embodiment discloses a high birefringence polarization-maintaining fiber stress layer and its fabrication method and apparatus, such as... Figures 1-9 As shown, it includes the following steps: Step S1: Select a high-purity quartz tube with a circular outer diameter and an elliptical aperture as the deposition tube 3. After cleaning, weld ordinary quartz tubes to both ends of the deposition base tube as the inlet tube and the outlet tube, and connect them to the MCVD lathe for rotary sealing.

[0044] Step S2: As Figure 2As shown, a hydrogen / oxygen pipeline 5 is connected to the fixed device 4, and the hydrogen / oxygen pipeline 5 connects to the first pair of blowtorches 1 and the second pair of blowtorches 2. The first pair of blowtorches 1 is positioned directly opposite the major axis of the elliptical aperture of the deposition tube along the air intake direction, and the second pair of blowtorches 2 is positioned directly opposite the minor axis of the elliptical aperture of the deposition tube. Then, stress layer deposition is performed. A lathe rotary motor is set so that the deposition tube rotates 180° each time the blowtorches return to their initial position after each deposition pass; the deposition tube does not rotate during the deposition process. The distance d1 between the head of the first pair of blowtorches 1 and the outer wall of the deposition tube is set to 30mm, and the distance d2 between the head of the second pair of blowtorches 2 and the outer wall of the deposition tube is set to 25mm. The longitudinal distance S between the first pair of blowtorches 1 and the second pair of blowtorches 2 along the deposition tube is 30mm. The temperature of the first pair of blowtorches 1 is set to 1600°C, and the temperature of the second pair of blowtorches 2 is set to 1300°C for stress layer deposition.

[0045] Since MCVD deposition primarily relies on a thermophoretic mechanism, the MCVD deposition efficiency can be approximated as:

[0046] Where Te is the equilibrium temperature between the heated gas flow and the tube wall, and Tr is the deposition efficiency due to changes in reaction temperature. Both Te and Tr can be altered. For a specific product, the reaction temperature Tr is fixed; therefore, increasing the equilibrium temperature can reduce the deposition efficiency. In the stress layer deposition heating quartz torch device designed in this invention, the first pair of torches along the air inlet direction are directly opposite the major axis of the elliptical inner hole of the deposition tube, serving as the primary heating source for the deposition reaction. After the reaction, the gas will be deposited behind it. The second pair of torches along the air inlet direction are directly opposite the minor axis of the elliptical inner hole of the deposition tube, increasing the tube wall temperature and equilibrium temperature Te in the minor axis direction. This makes the deposition efficiency in the minor axis direction much lower than that in the major axis direction, i.e., εminor axis < εmajor axis, thereby obtaining elliptical stress deposition.

[0047] When depositing a stress layer, the deposition is completed when the major axis of the elliptical aperture of the deposition tube is preferentially deposited until the aperture is nearly circular. Figure 5 The diagram shows, from the outside in, the deposition tube 3, the deposited elliptical stress layer 6, and the deposition pore size 7 during the deposition of the stress layer. The stress layer consists of SiO2 and B2O3.

[0048] Step S3: After stress layer deposition is completed, the lathe is continuously rotated, the MCVD system's conventional blowtorch is turned on, and the blowtorch heating temperature is set to 1450℃. This softens the stress layer, and under the rotation of the lathe, the deposited pore size gradually becomes a uniform circular pore size. Figure 6 The diagram shows, from the outside in, the deposition tube 3, the deposited elliptical stress layer 6, and the final circular aperture 8 of the deposited stress layer.

[0049] Step S4: Continue with the above steps to complete the deposition of the isolation layer, which consists of SiO2, GeO2, and SiF4.

[0050] Step S5: After depositing the isolation layer, deposit the core layer, such as... Figure 7 The structure shown, from the outside to the inside, consists of a deposition tube 3, a deposited elliptical stress layer 6, a deposited isolation layer 9, a deposited core layer 10, and a pore size 10 after the core layer is deposited. The core layer is composed of SiO2, GeO2, and SiF4.

[0051] Step S6: After the fiber core deposition is completed, the deposited quartz deposition base tube is sintered to obtain a solid elliptical stress layer polarization-maintaining fiber preform.

[0052] Step 7: The obtained elliptical stress layer polarization-maintaining fiber preform is drawn into an optical fiber using an optical fiber drawing tower to obtain an elliptical stress layer polarization-maintaining fiber.

[0053] The actual cross-sectional diagram of the polarization-maintaining fiber with elliptical stress layer prepared in this embodiment is shown below. Figure 10 As shown in the diagram, the structural schematic is as follows: Figure 8 As shown, from the inside out, the layers are fiber core layer 14, fiber isolation layer 13, fiber elliptical stress layer 12, and fiber cladding 15.

[0054] Example 2: Fabrication of polarization-maintaining optical fiber with rhombic stress layer Step S1: Select a circular diamond-shaped aperture deposition tube 16 as the deposition tube 3. After cleaning, weld ordinary quartz tubes to both ends of the deposition tube as the inlet tube and the outlet tube, and connect them to the MCVD lathe for rotary sealing.

[0055] Step S2: Position the first pair of blowtorches 1 directly opposite the long axis of the rhomboid aperture of the deposition tube 3 along the air intake direction, and the second pair of blowtorches 2 directly opposite the short axis of the rhomboid aperture of the deposition tube 3. Then, perform stress layer deposition. Set the lathe rotary motor so that the deposition tube 3 rotates 180° each time the blowtorches return to the initial position after each deposition pass. The deposition tube 3 does not rotate during the deposition process. Set the distance between the head of the first pair of blowtorches 1 and the outer wall of the deposition tube 3 to d1: 30mm, and the distance between the head of the second pair of blowtorches 2 and the outer wall of the deposition tube 3 to d2: 25mm. Set the distance between the first pair of blowtorches 1 and the second pair of blowtorches 2 along the longitudinal direction of the deposition tube 3 to S: 30mm. Set the temperature of the first pair of blowtorches 1 to 1550℃ and the temperature of the second pair of blowtorches 2 to 1250℃ for stress layer deposition.

[0056] The deposition of the stress layer is completed when the long axis of the rhomboid aperture of the deposition tube 3 is preferentially deposited until the aperture is close to a circle. The stress layer consists of SiO2, B2O3, P2O5, and GeO2.

[0057] Step S3: After completing the stress layer deposition, the lathe is turned on to rotate continuously, the conventional blowtorch of the MCVD system is turned on, and the blowtorch heating temperature is set to 1350℃ to soften the stress layer and form a uniform circular aperture under the action of lathe rotation.

[0058] Step S4: Continue with the above steps to complete the deposition of the isolation layer, which consists of SiO2 and SiF4.

[0059] Step S5: After the isolation layer is deposited, the core layer is deposited. The core layer consists of SiO2, GeO2, and SiF4.

[0060] Step S6: After the fiber core deposition is completed, the deposited quartz deposition substrate is sintered to obtain a solid rhomboid stress layer polarization-maintaining fiber preform.

[0061] Step 7: The obtained rhombic stress layer polarization-maintaining fiber preform is drawn into an optical fiber using an optical fiber drawing tower to obtain rhombic stress layer polarization-maintaining fiber.

[0062] The cross-sectional diagram of the rhomboid stress layer polarization-maintaining fiber prepared in Example 2 is shown below. Figure 11 As shown.

[0063] like Figure 9 As shown, in some embodiments, this method can be used as a deposition tube 3 with a rectangular aperture 17 or a polygonal aperture 18 to achieve the same effect.

[0064] Comparative Example 1 Based on Example 1, the only change was to use the first pair of torches for deposition. Although there was a deposition difference in the fast axis and slow axis of the deposition tube ellipse, the slow axis deposition was not easy to control, and opacity or even bubbles were likely to occur, resulting in failure to prepare the preform.

[0065] Comparative Example 2 The only change made in Example 1 is to change the distance between the first pair of torches and the second pair of torches to 200mm or even more. This will not only greatly reduce the effective deposition length of the quartz tube, but also make it easy for opaque surfaces or even bubbles to appear at the distance between the two pairs of torches at the beginning and end of the deposition tube, resulting in the failure of preform preparation.

[0066] The above are the embodiments listed in this example. However, this example is not limited to the optional embodiments described above. Those skilled in the art can arbitrarily combine the above methods to obtain other various embodiments. Anyone can derive other various forms of embodiments based on the inspiration of this example. The above specific embodiments should not be construed as limiting the scope of protection of this example. The scope of protection of this example should be determined by the claims, and the specification can be used to interpret the claims.

Claims

1. A method for preparing a stress layer in a high birefringence polarization-maintaining optical fiber, characterized in that: Two pairs of torches are used for stress layer deposition. The two pairs of torches are the first pair of torches (1) and the second pair of torches (2). The first pair of torches (1) is responsible for the long axis direction of the aperture of the deposition tube (3), and the second pair of torches (2) is responsible for the stress layer deposition in the short axis direction of the aperture of the deposition tube (3).

2. The method for preparing a stress layer for a high birefringence polarization-maintaining optical fiber according to claim 1, characterized in that: When the torch returns to the initial end after each deposition, the deposition tube (3) rotates 180°. During the deposition process, the deposition tube (3) does not rotate.

3. The method for preparing a stress layer for a high birefringence polarization-maintaining optical fiber according to claim 1, characterized in that: The ratio of the major axis to the minor axis of the stress layer is greater than 1.

4. The method for preparing a stress layer for a high birefringence polarization-maintaining optical fiber according to claim 3, characterized in that: The stress layer is elliptical or rhomboid.

5. The method for preparing a stress layer for a high birefringence polarization-maintaining optical fiber according to claim 1, characterized in that: Each pair of torches is symmetrically distributed across the cross section of the deposition tube (3); And / or the distance S between the first pair of blowtorches (1) and the second pair of blowtorches (2) is 10-150 mm; And / or the distance d1 between the head of the first pair of blowtorches (1) and the outer wall of the deposition tube (3) is 10-100 mm, and the temperature range of the first pair of blowtorches (1) is 1300-1900℃; And / or the distance d2 between the head of the second pair of blowtorches (2) and the outer wall of the deposition tube (3) is 5-100 mm, and the temperature range of the second pair of blowtorches (2) is 1200-1800℃.

6. The method for preparing a stress layer for a high birefringence polarization-maintaining optical fiber according to claim 5, characterized in that: Two pairs of torches are set perpendicular to each other along the longitudinal direction of the deposition tube (3); And / or the distance S between the first pair of blowtorches (1) and the second pair of blowtorches (2) is 20-150 mm; And / or the distance d1 between the head of the first pair of blowtorches (1) and the outer wall of the deposition tube (3) is 20-100 mm, and the temperature range of the first pair of blowtorches (1) is 1400-1900℃; And / or the distance d2 between the head of the second pair of blowtorches (2) and the outer wall of the deposition tube (3) is 5-90 mm, and the temperature range of the second pair of blowtorches (2) is 1200-1700℃.

7. An apparatus for fabricating a stress layer in a high birefringence polarization-maintaining optical fiber, characterized in that: Used in a method for preparing a high birefringence polarization-maintaining fiber stress layer according to any one of claims 1-6.

8. A high birefringence polarization-maintaining fiber stress layer, characterized in that: It is prepared in the method for preparing a high birefringence polarization-maintaining fiber stress layer according to any one of claims 1-6.

9. A method for fabricating high birefringence polarization-maintaining optical fiber, characterized in that: The stress layer is prepared using the method for preparing a high birefringence polarization-maintaining fiber stress layer according to any one of claims 1-6.

10. A high birefringence polarization-maintaining optical fiber, characterized in that: The stress layer obtained by the method for preparing a high birefringence polarization-maintaining fiber stress layer according to any one of claims 1-6 or the high birefringence polarization-maintaining fiber stress layer according to claim 8.

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