Optical fiber preform, multi-core sensing optical fiber and manufacturing method of multi-core sensing optical fiber

Abstract

The invention discloses an optical fiber preform, a multi-core sensing optical fiber and a manufacturing method of the multi-core sensing optical fiber, and belongs to the field of optical fiber manufacturing. Comprising the following steps: accommodating a fiber core in a second sleeve, and filling a second quartz capillary rod between the fiber core and the second sleeve to form an integrated body; the multiple integrated bodies are contained in a first sleeve, the space between the integrated bodies and the first sleeve is filled with first quartz capillary rods, the positions of all the integrated bodies and the shape of the stack structure are kept unchanged, and an optical fiber preform is obtained; and performing wire drawing on the optical fiber preform to form the multi-core sensing optical fiber. The quartz capillary rod is used for stacking and filling, the filling rod is located between the optical fiber core and the cladding, the sensing capacity of the optical fiber is enhanced by means of air holes and gaps of the solid core rod, and the optical fiber can be applied to the design of the multi-core optical fiber with the circular fiber core, is easy to implement in the process and has good universality.

Description

Technical Field

[0001] The invention belongs to the field of optical fiber manufacturing, in particular to an optical fiber preform rod, a multi-core sensing optical fiber and a manufacturing method thereof. Background Art

[0002] According to the type of optical fiber, optical fiber shape sensing technology can be roughly divided into two types: single-mode optical fiber beam combination and multi-core optical fiber. Among them, multi-core optical fiber grating shape sensing technology has the characteristics of simple structure, stability, high transmission quality, etc. It has a more compact volume when applied to sensors, and is more convenient to package and use. Multi-core optical fiber grating shape sensing technology has become more mature after years of development. In practical applications, in order to improve the accuracy of measuring the shape of an object, it is necessary to design a reasonable grating distribution configuration scheme based on the shape change characteristics of the object to be measured, on the premise that the main key points and the entire area of ​​other areas to be measured can be measured. The realization of multi-core optical fiber can play an increasingly important and unique role in technical applications such as sensing, and will continue to break through the bottleneck of single-mode optical fiber or conventional optical fiber sensors in sensing applications, and broaden the new dimension of special optical fiber in the field of sensing applications. However, for the difficulty of preparing multi-core optical fiber preform rods, multi-core optical fiber sensing technology still has room for improvement in the basic manufacturing link. Summary of the invention

[0003] In order to overcome the above technical defects, the present invention provides an optical fiber preform, a multi-core sensing optical fiber and a manufacturing method thereof to solve the problems involved in the background technology.

[0004] In a first aspect, the present invention provides an optical fiber preform, comprising:

[0005] First set of pipes;

[0006] A plurality of integrated bodies, one of which is located at the center of the first sleeve, and the remaining integrated bodies are evenly and equidistantly distributed around the one integrated body; the integrated body comprises a second sleeve, a fiber core arranged at the center of the second sleeve, and a plurality of second quartz capillary rods in the second sleeve and respectively covering around the fiber core;

[0007] A plurality of first quartz capillary rods are tightly filled in the gaps between the first sleeve and the integrated body and between the integrated bodies.

[0008] Preferably or optionally, the diameter of the second sleeve is 2 to 3 times the diameter of the fiber core; the diameter of the first sleeve is 3 to 5 times the diameter of the second sleeve.

[0009] Preferably or optionally, the ratio of the diameter of the first quartz capillary rod to the diameter of the second quartz capillary rod is 1.2:1 to 2:1.

[0010] Preferably or optionally, the refractive index of the first sleeve and the first quartz capillary rod are both 1.444, and the difference in refractive index between the two is no more than 10 -4 Order of magnitude;

[0011] The refractive index of the second quartz capillary rod is 1.444, and that of the second sleeve is 1.450.

[0012] Preferably or optionally, the fiber core is a germanium-doped quartz fiber core or a rare earth-doped fiber core, and its refractive index is 1.454-1.464.

[0013] Preferably or optionally, the first sleeve is made of high-purity quartz glass, and the second sleeve is made of high-purity quartz doped fluorine sleeve.

[0014] In a second aspect, the present invention provides a method for manufacturing a multi-core sensing optical fiber, comprising:

[0015] The fiber core is contained in a second sleeve, and a second quartz capillary rod is filled between the fiber core and the second sleeve to form an integrated body;

[0016] Accommodating a plurality of integrated bodies in a first sleeve, filling a first quartz capillary rod between the integrated body and the first sleeve, keeping the position of each integrated body and the shape of the stacking structure unchanged, and obtaining an optical fiber preform;

[0017] The optical fiber preform is drawn to form a multi-core sensing optical fiber.

[0018] Preferably or optionally, it also includes: using high frequency CO 2 Laser inscription of long-period fiber gratings on multi-core sensing optical fibers.

[0019] Preferably or optionally, it also includes: during the optical fiber drawing process, controlling the gas pressure at various locations in the stack structure in the optical fiber preform to effectively modulate the spacing between the fiber cores, the size of the fiber cores, and the air duty cycle.

[0020] In a third aspect, the present invention provides a multi-core sensing optical fiber, comprising:

[0021] an outer barrier formed by the first sleeve;

[0022] A core portion, wherein one core portion is located at a central position, and the other core portions are evenly and equidistantly distributed around one of the core portions; the core portion comprises an inner spacer, a central core arranged at a central position of the inner spacer, and a plurality of inner claddings respectively covering around the core and located in the inner spacer;

[0023] The outer cladding layer is formed and filled between the outer spacer layer and the core part, and between the core parts.

[0024] Preferably or optionally, the distance between the core portion located at the center and the remaining core portions is the same, the spacing between two adjacent remaining core portions is the same, the distance between the core portion located at the center and the remaining core portions is set to 50-70 μm, and the thickness of the core portion is 20-40 μm;

[0025] The multi-core sensing optical fiber is inscribed to form multiple groups of long-period optical fiber gratings with a grating interval of 300 μm, and the spacing of each group of gratings is set to 1-2 cm.

[0026] The present invention relates to an optical fiber preform, a multi-core sensing optical fiber and a manufacturing method thereof, which have the following beneficial effects compared with the prior art:

[0027] 1. The present invention uses a stack of quartz capillary rods for filling. The filling rods are located between the optical fiber core and the cladding. The air holes and gaps of the solid rods enhance the sensing ability of the optical fiber. The present invention can be applied to the design of multi-core optical fibers with circular cores, is easy to implement in terms of technology, and has good universality.

[0028] 2. The main benefit of the present invention of setting two layers of quartz capillary rods is to enhance the sensing ability of the optical fiber. By filling the second quartz capillary rod between the fiber core and the second sleeve, and filling the first quartz capillary rod between the first sleeve and the integrated body, the pores and gaps of the solid core rod can be used to enhance the sensing ability of the optical fiber. This structural design allows for more precise control of the spacing and size between the fiber cores, thereby improving the sensitivity and accuracy of the optical fiber in sensing applications.

[0029] 3. The present invention designs the diameter ratio between the first quartz capillary rod and the second quartz capillary rod and the size of the gap so that the air gap formed therebetween can constrain the optical mode field and make the mode field more concentrated in the sensing area, thereby enhancing the sensing capability of the optical fiber. If the ratio is not appropriate, the air gap may be too large or too small, resulting in leakage of optical field energy or failure to effectively constrain, thereby reducing the sensing performance.

[0030] 4. The structure of the present invention is simple and clear, the manufacturing process is easy to operate, and the preparation process is controllable. Because the microstructure stacking technology is adopted, the influence of the processing process on the optical fiber performance is reduced, and the complex process in the preparation of the optical fiber preform is reduced; by controlling the shape, size, distribution density and other parameters of the quartz capillary rod, various process parameters more suitable for the selected optical fiber are selected.

[0031] 5. The traditional tube-based optical fiber rod making process and the microstructured quartz capillary rod are combined to achieve the effective preparation of multi-core optical fiber preform rods for sensing. At the same time, the multi-core optical fiber is drawn using an optical fiber drawing tower, resulting in a microstructured optical fiber process that is easy to operate and has low preparation requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic cross-sectional view of an optical fiber preform or a multi-core optical fiber in the present invention.

[0033] Figure 2 It is a schematic cross-sectional view of an optical fiber preform or a multi-core optical fiber in the present invention.

[0034] Figure 3 It is a perspective view of the optical fiber long period grating in the present invention.

[0035] The reference numerals are: 110, first sleeve; 120, integrated body; 121, second sleeve; 122, fiber core; 123, second quartz capillary rod; 130, first quartz capillary rod;

[0036] 210, outer spacer; 220, core part; 221, inner spacer; 222, central core; 223, inner cladding; 230, outer cladding; 240, fiber Bragg grating. DETAILED DESCRIPTION

[0037] In the following description, a large number of specific details are provided to provide a more thorough understanding of the present invention. However, it is apparent to those skilled in the art that the present invention can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present invention, some technical features well known in the art are not described.

[0038] See attached Figure 1 , an optical fiber preform rod, comprising: a first sleeve, a plurality of integrated bodies and a plurality of first quartz capillary rods.

[0039] The first sleeve is a high-purity quartz sleeve, and a plurality of integrated bodies are arranged in the first sleeve, one of which is located at the center of the first sleeve, and the other integrated bodies are evenly and equidistantly distributed around one of the integrated bodies; the integrated body includes a second sleeve, a fiber core arranged at the center of the second sleeve, and a plurality of second quartz capillary rods in the second sleeve that cover the fiber core respectively; the first sleeve and the first quartz capillary rod are made of pure quartz glass. The first quartz capillary rod is tightly filled in the gap between the first sleeve and the integrated body, and between the integrated bodies.

[0040] The main benefit of setting two layers of quartz capillary rods in this embodiment is to enhance the sensing ability of the optical fiber. By filling the second quartz capillary rod between the fiber core and the second sleeve, and filling the first quartz capillary rod between the first sleeve and the integrated body, the pores and gaps of the solid core rod can be used to enhance the sensing ability of the optical fiber. This structural design allows more precise control of the spacing and size between the fiber cores, thereby improving the sensitivity and accuracy of the optical fiber in sensing applications.

[0041] In a further embodiment, the diameter of the second sleeve is 2 to 3 times the diameter of the fiber core; the diameter of the first sleeve is 3 to 5 times the diameter of the second sleeve. This arrangement ensures that the optical fiber has sufficient mechanical strength and support, while allowing the optical signal to propagate effectively, reducing losses and optimizing optical transmission efficiency.

[0042] In a further embodiment, the diameter ratio between the first quartz capillary rod and the second quartz capillary rod and the size of the gap formed directly affect the mode field distribution, light field intensity and sensing sensitivity of the optical fiber. When the diameter ratio is appropriate: the air gap formed between the two can constrain the light mode field, making the mode field more concentrated in the sensing area, thereby enhancing the sensing ability of the optical fiber. If the ratio is not appropriate, the air gap may be too large or too small, resulting in leakage of light field energy or failure to effectively constrain, reducing the sensing performance. Specifically, the ratio of the diameter of the first quartz capillary rod to the diameter of the second quartz capillary rod is 1.2:1 to 2:1, so that after the first quartz capillary rod and the second quartz capillary rod are drawn into an optical fiber, the size of the air gap formed is between 0.3μm and 0.5μm.

[0043] In a further embodiment, the refractive index of the first sleeve and the first quartz capillary rod are both 1.444, and the difference between the refractive indexes of the first sleeve and the first quartz capillary rod is not more than 10 -4 The refractive index of the second quartz capillary rod is 1.444, and that of the second sleeve is 1.450. There is a slight difference in refractive index between the second quartz capillary rod and the second sleeve, which is used to control the propagation path and mode field distribution of the optical signal, ensuring that light can be efficiently transmitted between the fiber cores while maintaining good optical isolation.

[0044] In a further embodiment, the fiber core is a germanium-doped quartz fiber core or a rare earth-doped fiber core, which has a higher refractive index than the first sleeve and the first quartz capillary rod, and its refractive index is 1.454-1.464. The fiber core with a higher refractive index can enhance the confinement ability of light and increase the nonlinear effect.

[0045] In a further embodiment, the first sleeve is made of high-purity quartz glass, and the second sleeve is made of high-purity quartz doped with fluorine. The first sleeve is made of different materials from the second sleeve, the first sleeve is made of high-purity quartz glass to provide high optical purity and mechanical strength, and the second sleeve is made of fluorine-doped quartz glass to optimize the refractive index and environmental adaptability.

[0046] In order to facilitate understanding of the technical solutions of optical fiber preform and multi-core optical fiber, a brief description of the manufacturing method of multi-core optical fiber is given: the fiber core is contained in a second sleeve, and a second quartz capillary rod is filled between the fiber core and the second sleeve to form an integrated body; a plurality of integrated bodies are contained in a first sleeve, and a first quartz capillary rod is filled between the integrated body and the first sleeve, and the position of each integrated body and the shape of the stacking structure remain unchanged to obtain an optical fiber preform; the optical fiber preform is drawn to form a multi-core sensing optical fiber; and a high-frequency CO is used to generate a plurality of optical fiber preforms. 2 The laser writes long-period fiber gratings on the prepared multi-core optical fiber. During the fiber drawing process, the gas pressure in the stack structure of the optical fiber preform is actively and precisely controlled to effectively modulate the spacing between the fiber cores, the size of the fiber cores, and the air duty cycle, and has higher sensitivity and accuracy when restoring the structure of the object through three-dimensional structure sensing.

[0047] See attached Figure 2 , a multi-core sensing optical fiber, comprising: an outer spacer, a core part and an outer cladding. During the drawing process, the first sleeve forms the outer spacer; the integrated body forms the core part, in which the second sleeve forms the inner spacer, the core forms the central core, the second quartz capillary rod forms the inner cladding; the first quartz capillary rod forms the outer cladding. Specifically, one of the core parts is located at the center, and the remaining core parts are evenly and equidistantly distributed around one of the core parts; the core part includes an inner spacer, a central core arranged at the center of the inner spacer, and a plurality of inner claddings respectively covering around the core and located in the inner spacer; the outer cladding is formed and filled between the outer spacer and the core part, and between the core part and the core part.

[0048] The distance between the core part located at the center and the other core parts is the same, the spacing between two adjacent other core parts is the same, the distance between the core part located at the center and the other core parts around is about 50-70 μm, and the distance between the outer core sleeve (i.e., the first sleeve) and the quartz glass sleeve 3 (i.e., the second sleeve) is controlled to be about 20-30 μm; the thickness of the quartz glass sleeve is 20-40 μm; the multi-core sensing optical fiber is written to form multiple groups of long-period fiber gratings with a grating spacing of 300 μm, and the spacing of each group of gratings is set to 1-2 cm;

[0049] The present invention will be further described below in conjunction with embodiments. The examples of the embodiments are intended to explain the present invention and should not be construed as limiting the present invention.

[0050] Example 1

[0051] A germanium-doped quartz fiber core (with a diameter of 2 cm and a refractive index of 1.460) was manufactured using PCVD, and then a quartz glass sleeve (i.e., the second sleeve, with a diameter of 5.5 cm and a refractive index of 1.450) was put on the outside of the fiber core, and a quartz capillary rod (i.e., the second quartz capillary rod, with a diameter of 1 cm and a refractive index of 1.444) was filled in the middle gap to prepare a fiber core sleeve. Fix one of the fiber core tubes (i.e., the second tube, which includes the fiber core and the second quartz capillary rod) in position, and place the remaining fiber core tubes at equal distances. The distance between each fiber core tube (i.e., the second tube) is kept at 1 cm, and the distance between the outer fiber core tube (i.e., the first tube) and the quartz glass tube (i.e., the second tube) is controlled at about 0.5 cm. After all the fiber core tubes are fixed with a clamp, a high-purity quartz doped fluorine tube (i.e., the first tube, with a diameter of 18 cm and a refractive index of about 1.444) is put on, and then a quartz capillary rod (i.e., the first quartz capillary rod, with a diameter of 1.2 cm and a refractive index of 1.444) is filled in the gap between the fiber core tubes. The quartz capillary rod is wrapped around the fiber core tube, and the ratio of the outer diameter of the core rod to the core diameter is fixed, that is, the core ratio is 3.0. Finally, the already tightly packed optical fiber preform rod is hung on the drawing tower, and the equipment is operated to draw an optical fiber with a diameter of 125μm. Then, the number and spacing of the long-period fiber gratings are flexibly configured according to the sensing requirements. The distance of the gratings can be set to 300μm, and the spacing of each group of gratings can be adjusted to 1cm.

[0052] Example 2

[0053] A germanium-doped quartz fiber core (with a diameter of 2 cm and a refractive index of 1.460) was manufactured using PCVD, and then a quartz glass sleeve (i.e., the second sleeve, with a diameter of 5.5 cm and a refractive index of 1.450) was put on the outside of the fiber core, and a quartz capillary rod (i.e., the second quartz capillary rod, with a diameter of 1 cm and a refractive index of 1.444) was filled in the middle gap to prepare a fiber core sleeve. Fix one of the fiber core tubes (i.e., the second tube, which includes the fiber core and the second quartz capillary rod) in position, and place the remaining fiber core tubes at equal distances. The distance between each fiber core tube (i.e., the second tube) is kept at 1 cm, and the distance between the outer fiber core tube (i.e., the first tube) and the quartz glass tube (i.e., the second tube) is controlled at about 0.5 cm. After all the fiber core tubes are fixed with a clamp, a high-purity quartz doped fluorine tube (i.e., the first tube, with a diameter of 18 cm and a refractive index of about 1.444) is put on, and then a quartz capillary rod (i.e., the first quartz capillary rod, with a diameter of 1.3 cm and a refractive index of 1.444) is filled in the gap between the fiber core tubes. The quartz capillary rod is wrapped around the fiber core tube, and the ratio of the outer diameter of the core rod to the core diameter is fixed, that is, the core ratio is 3.0. Finally, the already tightly packed optical fiber preform rod is hung on the drawing tower, and the equipment is operated to draw an optical fiber with a diameter of 125μm. Then, the number and spacing of the long-period fiber gratings are flexibly configured according to the sensing requirements. The distance of the gratings can be set to 300μm, and the spacing of each group of gratings can be adjusted to 1cm.

[0054] Example 3

[0055] A germanium-doped quartz fiber core (with a diameter of 2 cm and a refractive index of 1.460) was manufactured using PCVD, and then a quartz glass sleeve (i.e., the second sleeve, with a diameter of 5.5 cm and a refractive index of 1.450) was put on the outside of the fiber core, and a quartz capillary rod (i.e., the second quartz capillary rod, with a diameter of 1 cm and a refractive index of 1.444) was filled in the middle gap to prepare a fiber core sleeve. One of the fiber core tubes (i.e., the second tube, which includes the fiber core and the second quartz capillary rod) is fixed in position, and the remaining fiber core tubes are placed at equal distances, with the distance between each fiber core tube (i.e., the second tube) maintained at 1.2 cm, and the distance between the outer fiber core tube (i.e., the first tube) and the quartz glass tube (i.e., the second tube) controlled at about 0.8 cm. All the fiber core tubes are fixed with a clamp and then covered with a high-purity quartz doped fluorine tube (i.e., the first tube, with a diameter of 18 cm and a refractive index of about 1.444), and then the gap between the fiber core tubes is filled with a quartz capillary rod (i.e., the first quartz capillary rod, with a diameter of 2 cm and a refractive index of 1.444). The quartz capillary rod is wrapped around the fiber core tube, and the ratio of the outer diameter of the core rod to the core diameter is fixed, i.e., the core ratio is 3.0. Finally, the already tightly packed optical fiber preform rod is hung on the drawing tower, and the equipment is operated to draw an optical fiber with a diameter of 125μm. Then, the number and spacing of the long-period fiber gratings are flexibly configured according to the sensing requirements. The distance of the gratings can be set to 300μm, and the spacing of each group of gratings can be adjusted to 1cm.

[0056] Example 4

[0057] A germanium-doped quartz fiber core (with a diameter of 2 cm and a refractive index of 1.460) was manufactured using PCVD, and then a quartz glass sleeve (i.e., the second sleeve, with a diameter of 5.5 cm and a refractive index of 1.450) was put on the outside of the fiber core, and a quartz capillary rod (i.e., the second quartz capillary rod, with a diameter of 1 cm and a refractive index of 1.444) was filled in the middle gap to prepare a fiber core sleeve. Fix one of the fiber core tubes (i.e., the second tube, which includes the fiber core and the second quartz capillary rod) in position, and place the remaining fiber core tubes at equal distances. The distance between each fiber core tube (i.e., the second tube) is kept at 1.5 cm, and the distance between the outer fiber core tube (i.e., the first tube) and the quartz glass tube (i.e., the second tube) is controlled at about 1 cm. Fix all the fiber core tubes with a clamp and then put on a high-purity quartz doped fluorine tube (i.e., the first tube, with a diameter of 18 cm and a refractive index of about 1.444), and then fill the gap between the fiber core tube and the quartz capillary rod (i.e., the first quartz capillary rod, with a diameter of 1.5 cm and a refractive index of 1.444). The quartz capillary rod is wrapped around the fiber core tube, and the ratio of the outer diameter of the core rod to the core diameter is fixed, that is, the core ratio is 3.0. Finally, the already tightly packed optical fiber preform rod is hung on the drawing tower, and the equipment is operated to draw an optical fiber with a diameter of 125μm. Then, the number and spacing of the long-period fiber gratings are flexibly configured according to the sensing requirements. The distance of the gratings can be set to 300μm, and the spacing of each group of gratings can be adjusted to 1cm.

[0058] Example 5

[0059] A germanium-doped quartz fiber core (with a diameter of 2 cm and a refractive index of 1.460) was manufactured using PCVD, and then a quartz glass sleeve (i.e., the second sleeve, with a diameter of 5.5 cm and a refractive index of 1.450) was put on the outside of the fiber core, and a quartz capillary rod (i.e., the second quartz capillary rod, with a diameter of 1 cm and a refractive index of 1.444) was filled in the middle gap to prepare a fiber core sleeve. Fix one of the core tubes (i.e., the second tube, which includes the core and the second quartz capillary rod) in position, and place the remaining core tubes at equal distances. Keep the distance between each core tube (i.e., the second tube) at 2 cm, and control the distance between the outer core tube (i.e., the first tube) and the quartz glass tube (i.e., the second tube) at about 1 cm. Fix all the core tubes with a clamp and then put on a high-purity quartz doped fluorine tube (i.e., the first tube, with a diameter of 18 cm and a refractive index of about 1.444), and then fill the gap between the core tube and the quartz capillary rod (i.e., the first quartz capillary rod, with a diameter of 1.8 cm and a refractive index of 1.444). The quartz capillary rod is wrapped around the core tube, and the ratio of the outer diameter of the core rod to the core diameter is fixed, i.e., the core ratio is 3.0. Finally, the already tightly packed optical fiber preform rod is hung on the drawing tower, and the equipment is operated to draw an optical fiber with a diameter of 125μm. Then, the number and spacing of the long-period fiber gratings are flexibly configured according to the sensing requirements. The distance of the gratings can be set to 300μm, and the spacing of each group of gratings can be adjusted to 1cm.

[0060] Test example

[0061] The multi-core sensing optical fibers obtained in the above examples 1 to 5 were subjected to performance testing, and the results were as follows:

[0062]

[0063] Combined with the above table, the multi-core sensing optical fiber of Example 1 is superior to other embodiments in key performance indicators such as optical fiber loss, crosstalk between cores, sensing capability, tensile strength and temperature stability. This proves that the technical solution of the present application has significant advantages in the manufacture of multi-core sensing optical fibers and can provide higher performance optical fiber products.

[0064] The multi-core optical fiber for sensing of the present invention can maintain a maximum outer diameter of the optical fiber drawn after the casing is installed below 200μm, and exhibits high sensitivity in optical fiber sensing applications based on a low diameter. In addition, the structure of the present invention is simple to prepare compared to the traditional casing method, and the simulation model is simple and easy to manufacture. The optical fiber sensing sensitivity in the experimental operating environment is similar to the simulation result and can be actually put into use. The appropriate grating spacing and demodulation method are selected in combination with the specific application scenario, and the measurement point resources are reasonably configured to improve the optical fiber performance within a relatively low preparation cost range. It has good application prospects in the fields of three-dimensional shape reconstruction, pressure sensing, temperature sensing, etc.

[0065] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. An optical fiber preform, characterized in that: include: First set of pipes; A plurality of integrated bodies, one of which is located at the center of the first sleeve, and the remaining integrated bodies are evenly and equidistantly distributed around the one integrated body; the integrated body comprises a second sleeve, a fiber core arranged at the center of the second sleeve, and a plurality of second quartz capillary rods in the second sleeve and respectively covering around the fiber core; A plurality of first quartz capillary rods are tightly filled in the gaps between the first sleeve and the integrated body and between the integrated bodies.

2. The optical fiber preform according to claim 1, characterized in that: The diameter of the second sleeve is 2 to 3 times the diameter of the fiber core; the diameter of the first sleeve is 3 to 5 times the diameter of the second sleeve.

3. The optical fiber preform according to claim 1, characterized in that: The ratio of the diameter of the first quartz capillary rod to the diameter of the second quartz capillary rod is 1.2:1 to 2:1; The refractive index of the first sleeve and the first quartz capillary rod are both 1.444, and the difference between the refractive indexes of the first sleeve and the first quartz capillary rod is not more than 10 -4 Order of magnitude; The refractive index of the second quartz capillary rod is 1.444, and that of the second sleeve is 1.

450.

4. The optical fiber preform according to claim 1, characterized in that: The fiber core is a germanium-doped quartz fiber core or a rare earth-doped fiber core, and its refractive index is 1.454-1.

464.

5. The optical fiber preform according to claim 1, characterized in that: The first sleeve is made of high-purity quartz glass, and the second sleeve is made of high-purity quartz doped fluorine sleeve.

6. A method for manufacturing a multi-core sensing optical fiber, characterized in that: include: The fiber core is contained in a second sleeve, and a second quartz capillary rod is filled between the fiber core and the second sleeve to form an integrated body; Accommodating a plurality of integrated bodies in a first sleeve, filling a first quartz capillary rod between the integrated body and the first sleeve, keeping the position of each integrated body and the shape of the stacking structure unchanged, and obtaining an optical fiber preform; The optical fiber preform is drawn to form a multi-core sensing optical fiber.

7. The method for manufacturing a multi-core sensing optical fiber according to claim 6, characterized in that: Also includes: High-frequency CO2 laser is used to write long-period fiber gratings on multi-core sensing optical fibers.

8. The method for manufacturing a multi-core sensing optical fiber according to claim 6, characterized in that: Also includes: During the optical fiber drawing process, the gas pressure at various locations in the stack structure in the optical fiber preform is controlled to effectively modulate the spacing between the fiber cores, the size of the fiber cores, and the air duty cycle.

9. A multi-core sensing optical fiber, characterized in that: include: an outer barrier formed by the first sleeve; A core portion, wherein one core portion is located at a central position, and the other core portions are evenly and equidistantly distributed around one of the core portions; the core portion comprises an inner spacer, a central core arranged at a central position of the inner spacer, and a plurality of inner claddings respectively covering around the core and located in the inner spacer; The outer cladding layer is formed and filled between the outer spacer layer and the core part, and between the core parts.

10. The multi-core sensing optical fiber according to claim 9, characterized in that: The distance between the core portion at the center and the other core portions is the same, the spacing between two adjacent other core portions is the same, the distance between the core portion at the center and the other core portions is set to 50 to 70 μm, and the thickness of the core portion is 20 to 40 μm; The multi-core sensing optical fiber is inscribed to form multiple groups of long-period optical fiber gratings with a grating interval of 300 μm, and the spacing of each group of gratings is set to 1-2 cm.

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