Stress-enhanced panda-shaped polarization-maintaining optical fiber preform, manufacturing method, and optical fiber

Abstract

The present invention provides a stress-enhanced Panda-type polarization-maintaining optical fiber preform, a manufacturing method, and an optical fiber. The method comprises: a quartz rod having a core hole and two stress holes; wherein the core hole is located at the center of the quartz rod, and the two stress holes are centrally symmetrical with respect to the core hole; and two symmetrical grooves are provided on the surface of the quartz rod, between the two stress holes. The present invention can cause the stress region where the stress rod is located to be pulled and deformed during the drawing process, ultimately forming an appearance of the stress region similar to a panda's eye. This increases the force acting on the core, resulting in a higher birefringence coefficient, and improves the polarization maintenance performance of the Panda-type polarization-maintaining optical fiber, resulting in a stress-enhanced Panda-type polarization-maintaining optical fiber with a high yield.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber technology, and in particular to a stress-enhanced panda-type polarization-maintaining optical fiber preform, a manufacturing method and an optical fiber. Background Art

[0002] Polarization-maintaining fiber (PMF) is a specialized optical fiber that, by enhancing its inherent birefringence, overcomes the effects of environmental factors on the polarization state during transmission, maintaining the polarization state of the light waves transmitted through the fiber. In fiber-optic communications, this improves the stability and capacity of optical transmission systems and significantly reduces errors caused by polarization coupling in optical fiber sensing systems. Stress-type PMF relies on the difference in thermal expansion coefficients between embedded stress rods and the fiber core to generate thermal stress. This thermal stress causes a change in the material's refractive index, resulting in birefringence. Currently, Panda-type stress-region PMF is commonly used in China because its manufacturing process does not require a single step. Independent manufacturing of each component allows for effective control of the fiber's structure and composition. This ensures that each preform can produce tens or even hundreds of kilometers of uniform PMF, making it suitable for mass production. However, Panda-type stress-region PMF has several drawbacks, the most prominent of which is its low birefringence, which severely limits its polarization-maintaining ability.

[0003] Within the limitations of the panda-type optical fiber structure, there are three main ways to increase stress birefringence, including ① reducing the hole spacing; ② increasing the area of the stress zone; and ③ increasing the boron concentration in the stress zone. The first approach will cause the quartz between the holes to generate greater stress during the drilling process, thereby causing the preform rod to explode. The second approach cannot be achieved due to the limitations of the optical fiber size. The third approach will lead to high stress inside the preform rod, which is prone to explosion when assembled with the preform rod. Summary of the Invention

[0004] The embodiments of the present invention provide a stress-enhanced Panda-type polarization-maintaining optical fiber preform, a manufacturing method, and an optical fiber to solve the problem of low birefringence coefficient of Panda-type stress-region polarization-maintaining optical fiber.

[0005] In a first aspect, an embodiment of the present invention provides a stress-enhanced Panda-type polarization-maintaining optical fiber preform, comprising a quartz rod having a core hole and two stress holes; wherein the core hole is located at the center of the quartz rod, and the two stress holes are centrally symmetrical with respect to the core hole;

[0006] There are two symmetrical grooves on the surface of the quartz rod between the two stress holes.

[0007] In a possible implementation, each groove is V-shaped, semicircular arc-shaped, or slit-shaped.

[0008] In a possible implementation, the depth of each groove is 0-90% of the radius of the quartz rod.

[0009] In a possible implementation, the width of each groove is 0-30% of the radius of the quartz rod.

[0010] In a possible implementation, the stress-enhanced PANDA-type polarization-maintaining optical fiber preform is used to manufacture the stress-enhanced PANDA-type polarization-maintaining optical fiber, and the birefringence coefficient of the stress-enhanced PANDA-type polarization-maintaining optical fiber increases with the increase of the depth and / or width of each groove.

[0011] In a second aspect, an embodiment of the present invention provides a method for manufacturing a stress-enhanced panda-type polarization-maintaining optical fiber preform, comprising:

[0012] A quartz rod having a core hole and two stress holes is prepared; wherein the core hole is located at the center of the quartz rod, and the two stress holes are centrally symmetrical with respect to the core hole;

[0013] Two symmetrical grooves are opened on the surface of the quartz rod between the two stress holes;

[0014] A stress-enhanced panda-shaped polarization-maintaining optical fiber preform is manufactured based on a quartz round rod with grooves formed therein.

[0015] In a third aspect, an embodiment of the present invention provides a method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber, comprising:

[0016] The stress-enhanced PANDA-type polarization-maintaining optical fiber preform according to the first aspect or any possible implementation of the first aspect is drawn to obtain a stress-enhanced PANDA-type polarization-maintaining optical fiber.

[0017] In a fourth aspect, an embodiment of the present invention provides a stress-enhanced PANDA-type polarization-maintaining optical fiber, which is manufactured based on the manufacturing method of the stress-enhanced PANDA-type polarization-maintaining optical fiber according to the third aspect.

[0018] Embodiments of the present invention provide a method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber preform, a preform, and an optical fiber. By providing grooves to modify the cross-sectional shape of a quartz rod, the surface tension at various locations on the rod's side can be varied during the drawing process. During the drawing process, the surface tension of the quartz glass, in its high-temperature, molten state, gradually restores it to a perfect circle. Simultaneously, the stress zone where the stress rods are located is stretched and deformed during this process, ultimately forming an appearance similar to a panda's eye. This increases the force acting on the fiber core and results in a higher birefringence coefficient. Furthermore, the stress rods remain in a heated, molten state during the drawing process, making them less susceptible to cracking. This improves the yield rate of stress-enhanced Panda-type polarization-maintaining optical fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 1 is a schematic cross-sectional view of an existing panda-type polarization-maintaining optical fiber provided by one embodiment of the present invention;

[0021] Figure 2 1 is a schematic cross-sectional view of a stress-enhanced panda-type polarization-maintaining optical fiber preform provided by one embodiment of the present invention;

[0022] Figure 3A 1 is a schematic cross-sectional view of a stress-enhanced panda-type polarization-maintaining optical fiber preform provided by another embodiment of the present invention;

[0023] Figure 3B 1 is a schematic cross-sectional view of a stress-enhanced panda-type polarization-maintaining optical fiber preform provided by another embodiment of the present invention;

[0024] Figure 4 1 is a schematic cross-sectional view of a stress-enhanced Panda-type polarization-maintaining optical fiber provided in one embodiment of the present invention;

[0025] Figure 5 This is a flowchart of a method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber provided in one embodiment of the present invention. DETAILED DESCRIPTION

[0026] In the following description, specific details such as particular system structures and techniques are provided for purposes of illustration, not limitation, to facilitate a thorough understanding of the embodiments of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below with reference to the accompanying drawings.

[0028] The nouns involved in the present invention include:

[0029] Stress birefringence: Photoelastic effect, transparent isotropic media will change their refractive index properties under the action of pressure or tension, thus showing optical anisotropy;

[0030] Stress rod: used to apply stress to the fiber core, usually a boron rod.

[0031] Figure 1 Figure 2 is a cross-sectional diagram of an existing Panda-type polarization-maintaining optical fiber. Figure 1 As shown, Figure 1 The largest light-colored part in the middle area is the optical fiber cladding, the center is the fiber core, and the circular parts on both sides of the fiber core are stress rods. The stress rods exert pressure on the fiber core, producing a birefringence effect.

[0032] At present, bowtie-type polarization-maintaining fiber is also used to replace panda-type polarization-maintaining fiber. A pair of "bowtie"-shaped preform rods in the bowtie-type polarization-maintaining fiber are obtained by chemical vapor etching during the chemical vapor deposition preparation process. The chemical vapor etching process can realize the preparation of continuous preform rods and can provide a stress area with a larger cross-sectional area.

[0033] The existing bowtie polarization-maintaining fiber production method uses a liner tube as the foundation, uniformly depositing a borosilicate glass layer. Chemical vapor etching is then used to symmetrically "eliminate" the borosilicate glass layer in certain areas, forming a "quasi-elliptical" structure. Cladding and core layers are then deposited internally to form the waveguide structure. Finally, the end face structure formed by melting and collapsing the preform forms the "bowtie" shape. While this method offers good continuity during the preform production process, it is complex and difficult to control the geometric dimensions of the core and preform, making it unsuitable for mass production. Furthermore, the resulting polarization-maintaining fiber exhibits low stress birefringence.

[0034] See also Figure 2 , which shows a cross-sectional schematic diagram of a stress-enhanced panda-type polarization-maintaining optical fiber preform 2 provided in an embodiment of the present invention, and is described in detail as follows:

[0035] The stress-enhanced Panda-type polarization-maintaining optical fiber preform 2 includes a quartz rod 21 having a core hole 211 and two stress holes 212 ; wherein the core hole 211 is located at the center of the quartz rod 21 , and the two stress holes 212 are centrally symmetrical with respect to the core hole 211 ;

[0036] There are two symmetrical grooves 213 on the surface of the quartz rod 21 between the two stress holes 212 .

[0037] In this embodiment, after grooves are provided on the surface of the quartz rod, when a preform rod is used to manufacture an optical fiber, the surface tension of the quartz glass in the high-temperature molten state during the drawing process can be utilized to change the shape of the boron rod in the preform rod, so that the boron rod exerts greater stress on the fiber core, resulting in a better stress birefringence effect.

[0038] Specifically, surface tension refers to the tension acting on any boundary along the surface of a liquid due to the uneven attraction of molecules. Polarization-maintaining optical fiber preforms are placed in a high-temperature furnace, approaching a molten state due to the influence of temperature. Therefore, surface tension also exists on the preform surface, and different materials have different viscosities. Therefore, during the drawing process, the preform surface satisfies the following equation under the combined influence of viscosity, temperature, and surface tension:

[0039]

[0040]

[0041] in, u represents the surface slip velocity; t Represents time; F Represents external forces; µ Represents the viscosity coefficient.

[0042] For polarization-maintaining optical fibers, the greater the force exerted by the stress zone on the core, the more obvious the stress birefringence effect. The magnitude of the force exerted by the stress zone on the core mainly depends on the following aspects: first, the doping concentration of the boron rod in the stress zone. The higher the doping concentration, the greater the force generated; second, the size of the stress zone and the distance between the stress zone and the core. The larger the area of the stress zone and the closer the distance between the stress zone and the core, the greater the force exerted on the core, and the more obvious the stress birefringence effect. Under normal circumstances, due to the limitations of the stress preform preparation process, it is difficult to obtain stress rods with a high boron doping concentration. Therefore, it is necessary to start with the structure of the stress zone. However, due to the large stress of the stress rod itself, it is very easy to burst during mechanical processing. Therefore, it is difficult to obtain anisotropic stress preforms through cold processing.

[0043] according to Figure 2 It can be seen that the line connecting the two grooves is perpendicular to the line connecting the two stress holes. Based on the positional relationship between the grooves and the stress holes, the groove portion of the quartz rod will gradually deform during the wire drawing process until the cross section of the quartz rod returns to a circular shape. During this process, the stress rod in the stress hole is also subjected to deformation force, specifically Figure 2 The stress rods in the upper part of the middle are subjected to an upward force, while the stress rods in the lower part are subjected to a downward force. The area between the two stress rods is almost free of force in the transverse direction. The final fiber cross section is as follows: Figure 4 It can be determined that the longitudinal area between the two stress rods becomes larger after drawing, and the area where the force is applied to the fiber core also becomes larger accordingly.

[0044] Figure 2 The shape of the middle groove is only an example, and different groove shapes can be set according to actual requirements for polarization-maintaining optical fiber parameters.

[0045] As can be seen from the above, the embodiments of the present invention modify the cross-sectional shape of the quartz rod by providing grooves, which can alter the surface tension at various locations on the rod's side during the drawing process. During the drawing process of this preform, the surface tension of the quartz glass in its high-temperature molten state gradually restores it to a perfect circle. Simultaneously, the stress zone where the stress rods are located is stretched and deformed during this process, ultimately forming an appearance similar to a panda's eye. This increases the force acting on the fiber core and results in a higher birefringence coefficient. Furthermore, since the stress rods remain in a heated and molten state during the drawing process, they are less likely to crack, thereby improving the yield of stress-enhanced panda-type polarization-maintaining optical fibers.

[0046] In a possible implementation, each groove is V-shaped, semicircular arc-shaped, or slit-shaped.

[0047] In this embodiment, the groove shape can be designed and changed according to the size of the stress birefringence enhancement, such as "V-shaped", "semi-circular arc-shaped", "slit-shaped", etc., and the depth and width of the groove are also related to the size of the stress birefringence enhancement. Figure 2 is a cross-sectional diagram of a semicircular arc groove. Figure 3A is a cross-sectional diagram of a V-shaped groove. Figure 3B Schematic diagram of the cross section of the slit-type groove.

[0048] Parameter tests were performed on optical fibers manufactured from preforms with the same cross-sectional area and grooves of different shapes. The test results are shown in Table 1.

[0049] Table 1

[0050]

[0051] In a possible implementation, the depth of each groove is 0-90% of the radius of the quartz rod.

[0052] In this embodiment, the depth of the grinding portion cannot extend to the core portion of the core rod. The grinding depth is set to 0-90% of the preform rod radius to ensure that the core portion has a certain reserved thickness to avoid damage during the production process.

[0053] In a possible implementation, the width of each groove is 0-30% of the radius of the quartz rod.

[0054] In this embodiment, in order to ensure that the stress rod is subjected to only longitudinal forces and not lateral forces during the drawing process, the width of the groove is limited to ensure the performance of the produced optical fiber.

[0055] In a possible implementation, the stress-enhanced PANDA-type polarization-maintaining optical fiber preform is used to manufacture the stress-enhanced PANDA-type polarization-maintaining optical fiber, and the birefringence coefficient of the stress-enhanced PANDA-type polarization-maintaining optical fiber increases with the increase of the depth and / or width of each groove.

[0056] In this embodiment, the preform rod is used for drawing to produce a stress-enhanced Panda-type polarization-maintaining optical fiber, the cross section of which is as follows: Figure 4 As shown in the calculation formula of the surface tension in the above embodiment, it can be seen that the greater the depth and width of the groove, the greater the force on the stress rod during drawing, the greater the birefringence coefficient of the stress-enhanced panda-type polarization-maintaining optical fiber produced, and the better the stress birefringence effect.

[0057] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0058] The following are device embodiments of the present invention. For details not fully described therein, reference may be made to the corresponding method embodiments described above.

[0059] Figure 5 A flowchart illustrating a method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber according to an embodiment of the present invention is shown. For ease of illustration, only the portion related to the embodiment of the present invention is shown, which is described in detail as follows:

[0060] Step 501: Take a quartz rod having a core hole and two stress holes; wherein the core hole is located at the center of the quartz rod, and the two stress holes are centrally symmetrical with respect to the core hole;

[0061] Step 502: Two symmetrical grooves are formed on the surface of the quartz rod between the two stress holes.

[0062] Step 503 : manufacturing a stress-enhanced panda-type polarization-maintaining optical fiber preform based on the quartz rod with the grooves formed therein.

[0063] In a possible implementation, two symmetrical grooves are opened on the surface of the quartz rod between the two stress holes, including:

[0064] Two symmetrical grooves are opened on the surface of the quartz round rod at a position between two stress holes by grinding.

[0065] In a possible implementation, the method further includes:

[0066] Before or after two symmetrical grooves are opened on the surface of the quartz round rod at the position between the two stress holes, the core rod and the stress rod are respectively assembled in the fiber core hole and the two stress holes and stress rods.

[0067] In this embodiment, grinding can be performed before or after the core rod and the stress rod are assembled. The timing of assembling the core rod and the stress rod can be determined based on the grinding effect of the quartz round rod before and after assembly.

[0068] By modifying the cross-sectional shape of the quartz rod through the provision of grooves, the present invention allows the surface tension at various locations on the rod's side to vary during the drawing process. During the drawing process, the surface tension of the molten quartz glass gradually restores the preform to a perfect circle. Simultaneously, the stress zone where the stress rods are located is stretched and deformed during this process, ultimately forming a panda-eye-like appearance. This increases the force acting on the fiber core and results in a higher birefringence coefficient. Furthermore, since the stress rods remain in a heated and molten state during the drawing process, they are less likely to crack, thereby improving the yield of stress-enhanced panda-shaped polarization-maintaining optical fibers.

[0069] An embodiment of the present invention further provides a method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber, comprising:

[0070] The stress-enhanced PANDA-type polarization-maintaining optical fiber preform provided in the above embodiment is drawn to obtain a stress-enhanced PANDA-type polarization-maintaining optical fiber.

[0071] An embodiment of the present invention further provides a stress-enhanced PANDA-type polarization-maintaining optical fiber, which is manufactured based on the manufacturing method of the stress-enhanced PANDA-type polarization-maintaining optical fiber provided in the above embodiment.

[0072] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0073] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the scope of protection of the present invention.

Claims

1. A stress-enhanced panda-type polarization-maintaining optical fiber preform, characterized in that: A quartz rod having a core hole and two stress holes; wherein the core hole is located at the center of the quartz rod, and the two stress holes are centrally symmetrical with respect to the core hole; Two symmetrical grooves are provided on the surface of the quartz rod between the two stress holes. The line connecting the two grooves is perpendicular to the line connecting the two stress holes. Each groove is V-shaped, semicircular, or slit-shaped.

2. The method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber preform according to claim 1, characterized in that: The depth of each groove is 0-90% of the radius of the quartz rod.

3. The method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber preform according to claim 1, characterized in that: The width of each groove is 0-30% of the radius of the quartz rod.

4. The method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber preform according to claim 1, characterized in that: The panda-type polarization-maintaining optical fiber preform is used to manufacture a panda-type polarization-maintaining optical fiber. The birefringence coefficient of the panda-type polarization-maintaining optical fiber increases with the increase of the depth and / or width of each groove.

5. A method for manufacturing a stress-enhanced panda-type polarization-maintaining optical fiber preform, characterized in that: include: A quartz rod having a core hole and two stress holes is prepared; wherein the core hole is located at the center of the quartz rod, and the two stress holes are centrally symmetrical with respect to the core hole; Two symmetrical grooves are provided on the surface of the quartz rod between the two stress holes, wherein the line connecting the two grooves is perpendicular to the line connecting the two stress holes, and each groove is V-shaped, semicircular arc-shaped or slit-shaped; A panda-shaped polarization-maintaining optical fiber preform is manufactured based on a quartz round rod with grooves formed therein.

6. The method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber preform according to claim 5, characterized in that: The two symmetrical grooves are provided on the surface of the quartz rod between the two stress holes, including: Two symmetrical grooves are opened on the surface of the quartz round rod at a position between the two stress holes by grinding.

7. The method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber preform according to claim 5, characterized in that: Also includes: Before or after two symmetrical grooves are formed on the surface of the quartz round rod at a position between the two stress holes, a core rod and a stress rod are respectively assembled in the core hole and the two stress holes and stress rods.

8. A method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber, characterized in that: include: The stress-enhanced PANDA-type polarization-maintaining optical fiber preform according to any one of claims 1 to 4 is drawn to obtain a stress-enhanced PANDA-type polarization-maintaining optical fiber.

9. A stress-enhanced Panda-type polarization-maintaining optical fiber, characterized in that: The stress-enhanced PANDA-type polarization-maintaining optical fiber is manufactured based on the manufacturing method of claim 8.

Images