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

Abstract

The invention provides a stress enhanced panda type polarization maintaining optical fiber preform, a manufacturing method and an optical fiber. According to the method, a quartz round rod with a fiber core hole and two stress holes is provided; wherein the fiber core hole is located in the center of the quartz round rod, and the two stress holes are in central symmetry relative to the fiber core hole; and two symmetrical grooves are formed in the surface of the quartz round rod and between the two stress holes. The stress area where the stress rod is located can be pulled to deform in the wire drawing process, the stress area appearance similar to a panda eye is finally formed, the acting force on a fiber core is increased, a higher birefringence coefficient is obtained, the polarization maintaining performance of the panda type polarization maintaining optical fiber is improved, and the application range of the panda type polarization maintaining optical fiber is widened. And the stress enhanced panda type polarization maintaining optical fiber with high yield is obtained.

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 rod, a manufacturing method and an optical fiber. Background Art

[0002] Polarization-maintaining fiber is a special type of fiber that overcomes the influence of environmental factors on the polarization state in the fiber during transmission by increasing the inherent birefringence of the fiber, and keeps the polarization state of the light wave transmitted in the fiber unchanged. In the field of optical fiber communication, it can improve the stability and communication capacity of the optical transmission system, and in the optical fiber sensing system, it can significantly reduce the error caused by polarization coupling in the optical path. Stress-type polarization-maintaining fiber mainly relies on the difference in thermal expansion coefficients between the embedded stress rod and the optical fiber core to generate thermal stress, which causes the change of the refractive index of the material under the action of thermal stress, thereby producing a birefringence effect. At present, the manufacturing process of panda-type stress-area polarization-maintaining fiber does not need to be completed in one step. The independent manufacturing of each component can effectively control the structure and composition of the optical fiber. It can ensure that each preform can be drawn into a uniform polarization-maintaining fiber product of tens of kilometers or even more than one hundred kilometers, which is suitable for mass production. Therefore, panda-type polarization-maintaining fiber is commonly used in China. However, there are many shortcomings of panda-type stress-area polarization-maintaining fiber, the most prominent of which is the low birefringence coefficient, which will seriously limit the polarization-maintaining ability of polarization-maintaining fiber.

[0003] Under the limitation 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; ③ increasing the boron doping concentration in the stress zone; the first way will cause the quartz between the holes to generate greater stress during the drilling process, thereby causing the preform rod to burst; the second way cannot be achieved due to the limitation of the optical fiber size; the third way will cause large stress inside the preform rod, which is prone to bursting 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-area 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 round rod having a core hole and two stress holes; wherein the core hole is located at the center of the quartz round rod, and the two stress holes are centrally symmetrical with respect to the core hole; There are two symmetrical grooves on the surface of the quartz rod between the two stress holes.

[0006] In a possible implementation manner, each groove is in a V-shape, a semicircular arc shape, or a slit shape.

[0007] In a possible implementation, the depth of each groove is 0-90% of the radius of the quartz rod.

[0008] In a possible implementation, the width of each groove is 0-30% of the radius of the quartz rod.

[0009] 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.

[0010] 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: A quartz round rod having a core hole and two stress holes is taken; wherein the core hole is located at the center of the quartz round rod, and the two stress holes are centrally symmetrical with respect to the core hole; Two symmetrical grooves are formed on the surface of the quartz round rod at positions between the two stress holes; A stress-enhanced panda-shaped polarization-maintaining optical fiber preform is manufactured based on a quartz round rod with grooves formed therein.

[0011] 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: 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.

[0012] 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 above.

[0013] The embodiment of the present invention provides a method for manufacturing a stress-enhanced panda-type polarization-maintaining optical fiber preform, a preform, and an optical fiber. By setting a groove to change the cross-sectional shape of a quartz round rod, the surface tension at various positions on the side of the quartz round rod can be changed during the drawing process. During the drawing process of the preform, the surface tension of the quartz glass in a high-temperature molten state will gradually restore it to a perfect circle. At the same time, the stress area where the stress rod is located is pulled and deformed during this process, and finally forms a stress area appearance similar to a panda eye, which increases the force on the fiber core and obtains a higher birefringence coefficient. In addition, during the drawing process, the stress rod is in a heated molten state and is not prone to bursting, which can improve the yield rate of the stress-enhanced panda-type polarization-maintaining optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative labor.

[0015] Figure 1 is a schematic cross-sectional view of an existing panda-type polarization-maintaining optical fiber provided by an embodiment of the present invention; Figure 2 1 is a schematic cross-sectional view of a stress-enhanced Panda-type polarization-maintaining optical fiber preform provided by an embodiment of the present invention; Figure 3A 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; Figure 3B 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; Figure 4 is a schematic cross-sectional view of a stress-enhanced Panda-type polarization-maintaining optical fiber provided by an embodiment of the present invention; Figure 5 It is a flow chart of a method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber provided in one embodiment of the present invention. DETAILED DESCRIPTION

[0016] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

[0018] The nouns involved in the present invention include: Stress birefringence: photoelastic effect, the refractive index characteristics of a transparent isotropic medium will change under the action of pressure or tension, thus showing optical anisotropy; Stress rod: used to apply stress to the fiber core, usually a boron rod.

[0019] Figure 1 Figure 2 is a cross-sectional diagram of an existing Panda-type polarization-maintaining optical fiber. Figure 1 As shown, Figure 1The 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.

[0020] At present, bowtie-type polarization-maintaining optical fiber is also used to replace panda-type polarization-maintaining optical fiber. A pair of "bowtie"-type preform rods in the bowtie-type polarization-maintaining optical 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.

[0021] The existing bowtie polarization-maintaining optical fiber preparation method is based on a liner, uniformly depositing a borosilicate glass layer, and then using chemical vapor etching to symmetrically "eliminate" the local borosilicate glass layer to form a "quasi-elliptical" structure, and then continue to deposit a cladding and core layer inside to form a waveguide structure, and finally melt the preform to form an end face structure to form a "bowtie" shape. Although this method has good continuity in the preparation process of the preform, the preparation process of this method is complicated, the geometric dimensions of the fiber core and the preform are difficult to control, and it is not suitable for mass production. In addition, the stress birefringence of the prepared polarization-maintaining optical fiber is low.

[0022] 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: The stress-enhanced Panda-type polarization-maintaining optical fiber preform 2 comprises a quartz round 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 round rod 21, and the two stress holes 212 are centrally symmetrical with respect to the core hole 211; There are two symmetrical grooves 213 on the surface of the quartz round rod 21 between the two stress holes 212 .

[0023] In this embodiment, after grooves are set on the surface of the quartz round rod, when the preform rod is used to manufacture the optical fiber, the surface tension of the quartz glass in the high-temperature molten state during the drawing process can be used 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.

[0024] Specifically, surface tension refers to the tension on any boundary line along the surface caused by the uneven molecular attraction of the liquid surface layer. In a high-temperature furnace, the polarization-maintaining optical fiber preform will be close to a molten state due to the influence of temperature, so there will also be surface tension on the surface of the preform, and different materials have different viscosities. Therefore, during the drawing process, the surface of the preform satisfies the following formula under the combined influence of viscosity, temperature, and surface tension:

[0025]

[0026] in, u represents the surface slip velocity; t Represents time; F Represents external force; µ Represents the viscosity coefficient.

[0027] For polarization-maintaining optical fiber, 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. Usually, 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 by cold processing.

[0028] 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 part of the quartz round rod will gradually deform during the wire drawing process until the cross section of the quartz round 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 upward force, and the stress rods in the lower part are subjected to downward force. The area between the two stress rods is almost free of force in the lateral direction. The final cross section of the optical fiber 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 core part also becomes larger accordingly.

[0029] 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.

[0030] As can be seen from the above, the embodiment of the present invention can change the cross-sectional shape of the quartz round rod by setting grooves, so that the surface tension at various positions on the side of the quartz round rod can be changed during the drawing process. During the drawing process of this preform rod, the surface tension of the quartz glass in the high-temperature molten state will gradually restore it to a perfect circle. At the same time, the stress area where the stress rod is located is pulled and deformed during this process, and finally forms a stress area appearance similar to a panda eye, which increases the force on the fiber core and obtains a higher birefringence coefficient. In addition, during the drawing process, the stress rod is in a heated and molten state, and is not easy to explode, which can improve the yield rate of stress-enhanced panda-type polarization-maintaining optical fiber.

[0031] In a possible implementation manner, each groove is in a V-shape, a semicircular arc shape, or a slit shape.

[0032] 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 schematic diagram of a semicircular arc groove. Figure 3A is a cross-sectional schematic diagram of a V-shaped groove. Figure 3B Schematic diagram of the cross section of the slit-type groove.

[0033] The optical fibers manufactured from preforms with the same cross-sectional area and grooves of different shapes were tested for parameters, and the test results are shown in Table 1.

[0034] Table 1

[0035] In a possible implementation, the depth of each groove is 0-90% of the radius of the quartz rod.

[0036] In this embodiment, the depth of the grinding portion cannot extend to the core portion of the core rod, and 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.

[0037] In a possible implementation, the width of each groove is 0-30% of the radius of the quartz rod.

[0038] In this embodiment, in order to ensure that the stress rod is subjected to only longitudinal force and not lateral force during the drawing process, the width of the groove is limited to ensure the performance of the output optical fiber.

[0039] 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.

[0040] In this embodiment, the preform rod is used for drawing to produce a stress-enhanced Panda-type polarization-maintaining optical fiber, and the optical fiber cross section 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 manufactured stress-enhanced panda-type polarization-maintaining optical fiber, and the better the stress birefringence effect.

[0041] It should be understood that the order of execution of the steps in the above embodiment does not necessarily 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 embodiment of the present invention.

[0042] The following is an embodiment of the device of the present invention. For details not described in detail therein, reference may be made to the corresponding method embodiment described above.

[0043] Figure 5 The following is a flowchart of a method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber according to an embodiment of the present invention. For ease of explanation, only the part related to the embodiment of the present invention is shown, which is described in detail as follows: Step 501, taking a quartz round rod having a core hole and two stress holes; wherein the core hole is located at the center of the quartz round rod, and the two stress holes are centrally symmetrical with respect to the core hole; Step 502, two symmetrical grooves are formed on the surface of the quartz round rod at a position between the two stress holes; Step 503: manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber preform based on the quartz round rod with the grooves formed therein.

[0044] In a possible implementation, two symmetrical grooves are opened on the surface of the quartz round rod at a position between two stress holes, including: Two symmetrical grooves are opened on the surface of the quartz round rod between two stress holes by grinding.

[0045] In a possible implementation, the method further includes: Before or after two symmetrical grooves are formed 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 core hole and the stress rods of the two stress holes.

[0046] In this embodiment, grinding can be performed before or after assembling the core rod and the stress rod. The timing of assembling the core rod and the stress rod can be determined based on the effect of grinding the quartz round rod before or after assembling.

[0047] The embodiment of the present invention can change the cross-sectional shape of the quartz round rod by setting grooves, so that the surface tension at various positions on the side of the quartz round rod can be changed during the drawing process. During the drawing process of the preform rod, the surface tension of the quartz glass in the high-temperature molten state will gradually restore it to a perfect circle. At the same time, the stress area where the stress rod is located is pulled and deformed during this process, and finally forms a stress area appearance similar to a panda eye, which increases the force on the fiber core and obtains a higher birefringence coefficient. In addition, the stress rod is in a heated and molten state during the drawing process, and is not easy to explode, which can improve the yield rate of stress-enhanced panda-type polarization-maintaining optical fiber.

[0048] The embodiment of the present invention also provides a method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber, comprising: 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.

[0049] The 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.

[0050] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0051] 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 the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A stress-enhanced Panda-type polarization-maintaining optical fiber preform, characterized in that: A quartz round rod comprising a core hole and two stress holes; wherein the core hole is located at the center of the quartz round 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 round rod at positions between the two stress holes.

2. The method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber preform according to claim 1, characterized in that: The shape of each groove is V-shaped, semicircular arc-shaped or slit-shaped.

3. 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 round rod.

4. 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 round rod.

5. 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, and the birefringence coefficient of the panda-type polarization-maintaining optical fiber increases with the increase of the depth and / or width of each groove.

6. A method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber preform, characterized in that: include: Take a quartz round rod having a core hole and two stress holes; wherein the core hole is located at the center of the quartz round rod, and the two stress holes are centrally symmetrical with respect to the core hole; Two symmetrical grooves are formed on the surface of the quartz round rod at a position between the two stress holes; A panda-shaped polarization-maintaining optical fiber preform is manufactured based on a quartz round rod with grooves formed therein.

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

8. The method for manufacturing a stress-enhanced Panda-type polarization-maintaining optical fiber preform according to claim 6, characterized in that: Also includes: Before or after two symmetrical grooves are formed on the surface of the quartz round rod at the position between the two stress holes, a core rod and a stress rod are respectively assembled in the core hole and the stress rods in the two stress holes.

9. 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 5 is drawn to obtain a stress-enhanced PANDA-type polarization-maintaining optical fiber.

10. A stress-enhanced Panda-type polarization-maintaining optical fiber, characterized in that: The method for manufacturing a stress-enhanced PANDA-type polarization-maintaining optical fiber according to claim 9 is used for manufacturing the stress-enhanced PANDA-type polarization-maintaining optical fiber.

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