Optical fiber with large dispersion coefficient and preparation method thereof

Abstract

The invention provides an optical fiber with a large dispersion coefficient and a preparation method thereof, and belongs to the technical field of special optical fibers, the optical fiber with the large dispersion coefficient comprises an inner fiber core, an inner cladding, an outer fiber core and an outer cladding which are concentrically arranged in sequence from inside to outside, and a plurality of air holes are formed in the inner cladding and penetrate through the inner cladding in the axial direction. The invention provides a large-dispersion-coefficient optical fiber and a preparation method thereof, and aims to solve the problems that the dispersion coefficient of a dispersion optical fiber in the prior art is not large enough, and the requirement of a time stretching technology in the field of microwave photonics on an ultra-large-dispersion-coefficient optical fiber cannot be met.

Description

Technical Field

[0001] The invention belongs to the technical field of special optical fibers, and more specifically, relates to an optical fiber with a large dispersion coefficient and a preparation method thereof. Background Art

[0002] Different light components (different modes or different frequencies, etc.) are usually transmitted at different speeds in optical fibers. Dispersion is an important optical property of optical fibers. Dispersion causes the broadening of light pulses and severely limits the transmission capacity and bandwidth of optical fibers.

[0003] Optical time stretching technology in microwave photonics uses optical dispersion to perform equivalent frequency reduction on the microwave signal of the input optical link, which has a series of advantages such as large input bandwidth, low-frequency detection, and anti-electromagnetic interference. Optical time stretching technology requires a large dispersion amount to reduce the high-frequency signal to a low frequency for detection. If the dispersion coefficient of the large dispersion coefficient light is not large enough, the required optical fiber length will be very long, resulting in a large system delay, and the dispersion module will cause a large loss in the system, and the dispersion module will also occupy a large volume. Therefore, it is necessary to develop a large dispersion coefficient optical fiber.

[0004] The existing large dispersion coefficient optical fiber structure generally dopes a low refractive index fluorine-doped silica layer between the inner core and the annular core, so that the mode refractive index of the optical fiber changes dramatically near the dispersion wavelength, thereby achieving a large dispersion coefficient. However, due to the limitations of the manufacturing process, the concentration of fluorine doped into the large dispersion coefficient optical fiber is limited, and the refractive index of the inner cladding cannot be reduced to a preset range. Therefore, in order to meet the demand for large dispersion coefficient optical fiber in the time stretching technology in the field of microwave photonics, a large dispersion coefficient optical fiber structure that can achieve a larger dispersion coefficient is needed. Summary of the invention

[0005] The purpose of the present invention is to provide a large dispersion coefficient optical fiber and a preparation method thereof, aiming to solve the problem that the dispersion coefficient of the optical fiber in the prior art is not large enough to meet the demand for large dispersion coefficient optical fiber in the time stretching technology in the field of microwave photonics.

[0006] To achieve the above object, the technical solution adopted by the present invention is: In a first aspect, a large dispersion coefficient optical fiber is provided, comprising an inner core, an inner cladding, an outer core and an outer cladding which are concentrically arranged in sequence from the inside to the outside, wherein the inner cladding has a plurality of air holes which penetrate the inner cladding axially.

[0007] In combination with the first aspect, in a possible implementation manner, the plurality of air holes are arranged in a ring shape around the outer circumference of the inner fiber core.

[0008] In combination with the first aspect, in a possible implementation manner, the inner cladding is a fluorine-doped quartz layer.

[0009] The beneficial effect of the large dispersion coefficient optical fiber provided by the present invention is that: compared with the prior art, the large dispersion coefficient optical fiber of the present invention is provided with a plurality of air holes in the inner cladding, and the air holes are located outside the inner core. Since the refractive index of the air holes is much smaller than the refractive index of quartz, the refractive index of the inner cladding after the air holes are provided is greatly reduced compared with when the inner cladding is solid. When the inner core and the outer core exist independently, the mode refractive index of the fundamental mode of the dispersion optical fiber is equal at the dispersion wavelength point, and the mode refractive index changes dramatically near the dispersion wavelength point, thereby achieving a large dispersion coefficient, which fully meets the requirements of the time stretching technology in the field of microwave photonics for large dispersion coefficient optical fiber. In addition, since the refractive index of air is much lower than the refractive index of the fluorine-doped layer, the present invention can achieve a sudden change in the mode refractive index compared with the solution of only providing the fluorine-doped layer in the prior art, thereby improving the dispersion coefficient.

[0010] In a second aspect, an embodiment of the present invention further provides a method for preparing a large dispersion coefficient optical fiber, comprising: S100, preparing an optical fiber preform, wherein the optical fiber preform comprises an inner core, an inner cladding, an outer core and an outer cladding which are concentrically arranged in sequence from the inside to the outside; S200, opening air holes along the axial direction of the inner cladding, wherein the air holes penetrate two ends of the inner cladding; S300, heating the optical fiber preform having the air hole, and then extending the optical fiber preform so that the diameter of the optical fiber preform is between 0.5 and 4 mm; S400, heating and re-stretching the optical fiber preform that has completed the preliminary stretching in S300 to form a large dispersion coefficient light with a diameter of ≤125 μm.

[0011] In combination with the first aspect, in a possible implementation manner, the S100 specifically includes: S110, fixing the quartz reaction tube to the vapor deposition equipment, and rotating the quartz reaction tube; S120, respectively introducing SiCl4, GeCl4 and O2 into the quartz reaction tube and heating them to generate SiO2 and GeO2 by reaction, and SiO2 and GeO2 are deposited on the inner wall of the quartz reaction tube to form the annular outer core; S130, introducing SiCl4 and O2 into the inner hole of the outer core and heating, so that SiO2 generated by the reaction is deposited on the inner wall of the inner core, and the SiO2 deposition forms the annular inner cladding; S140, introducing SiCl4, GeCl4 and O2 into the inner hole of the inner cladding and heating them to react and generate SiO2 and GeO2, which are deposited on the inner wall of the inner cladding to form the inner core; S150, heating and shrinking the formed part in S140; S160, a pure quartz tube is arranged outside the quartz reaction tube and heated, the quartz reaction tube and the pure quartz tube are melted into one, forming the outer cladding, and completing the preparation of the optical fiber preform.

[0012] In combination with the first aspect, in a possible implementation, in S130, while SiCl4 and O2 are introduced into the quartz reaction tube, SF6 is also introduced to heat and form a fluorine-doped quartz layer, namely, the inner cladding.

[0013] In combination with the first aspect, in a possible implementation, in S200, an ultrasonic punch is used to open a plurality of air holes in the inner cladding, each of the air holes extending along the axial direction of the inner cladding.

[0014] In combination with the first aspect, in a possible implementation, in S300, the optical fiber preform is heated to 1750° C.-2150° C. in a heating furnace of a drawing tower, and then the optical fiber preform is preliminarily extended to form a rod-shaped component with a diameter between 0.5-4 mm.

[0015] In combination with the first aspect, in a possible implementation manner, the S400 specifically includes: S410, placing the optical fiber preform formed in S300 into a sleeve; S420, heating the optical fiber preform in S410, and extending the optical fiber preform until the optical fiber preform forms a large dispersion coefficient optical fiber with a diameter of ≤125 μm.

[0016] In combination with the first aspect, in a possible implementation manner, the S420 specifically includes: S421, placing the optical fiber preform and the sleeve in S410 into a heating furnace of an optical fiber drawing tower for heating; S422, introducing gas into the air hole to form a positive pressure in the air hole, and forming a negative pressure in the gap between the sleeve and the optical fiber preform, until the optical fiber preform forms a large dispersion coefficient optical fiber with a diameter of ≤125 μm.

[0017] The beneficial effect of the preparation method provided by the present invention is that: compared with the prior art, the preparation method of the large dispersion coefficient optical fiber of the present invention adopts a secondary extension process for the optical fiber preform, firstly extending the optical fiber preform to form an intermediate with a smaller diameter, and then placing the intermediate into a sleeve and extending it again to form a dispersion coefficient optical fiber, which can not only extend the optical fiber preform to form a large dispersion coefficient optical fiber with a smaller diameter, and achieve a very small core-cladding ratio, but also is easier to implement in terms of processing technology, reducing the scrap rate. The existing preparation method of large dispersion coefficient light usually adopts a one-time extension molding method, resulting in high requirements for wire drawing during extension, and because the diameter difference between the optical fiber preform and the large dispersion coefficient light is large, the air hole processed by the ultrasonic punching machine in the optical fiber preform becomes the air hole in the dispersion optical fiber, and the reduction factor is nearly 1000 times, resulting in difficult process implementation and high scrap rate. BRIEF DESCRIPTION OF THE DRAWINGS 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 work.

[0018] Figure 1 A schematic diagram of the structure of a large dispersion coefficient optical fiber provided by an embodiment of the present invention; Figure 2 Another schematic diagram of the structure of a large dispersion coefficient optical fiber provided in an embodiment of the present invention.

[0019] In the figure: 1, outer cladding; 2, outer core; 3, inner cladding; 301, air hole; 4, inner core. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0021] In the claims, specification and the above drawings of the present invention, unless otherwise clearly defined, the terms "first", "second" or "third" are used to distinguish different objects, rather than to describe a specific order. Unless otherwise specified, other directional words, such as "vertical", "clockwise", "counterclockwise", etc., indicating directions or positional relationships are based on the directions and positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction or be constructed and operated in a specific direction, so it cannot be understood as limiting the specific protection scope of the present invention. In the claims, specification and the above drawings of the present invention, unless otherwise clearly defined, the terms "fixed connection" or "fixed connection" should be understood in a broad sense, that is, any connection method without a displacement relationship and relative rotation relationship between the two, that is, including non-detachable fixed connection, detachable fixed connection, integrated connection and fixed connection through other devices or elements. In the claims, specification and the above drawings of the present invention, the terms "including", "having" and their variations are used, and the intention is to "include but not limited to".

[0022] It should be noted that an optical fiber preform is a quartz glass rod with a specific refractive index profile and is used to manufacture optical fibers (abbreviated as optical fibers). The diameter of an optical fiber preform is generally a few millimeters to tens of millimeters (commonly known as an optical rod). The internal structure of the optical fiber is formed in the optical fiber preform.

[0023] Please also read Figure 1 to Figure 2 The large dispersion coefficient optical fiber provided by the present invention and its preparation method are now described. The large dispersion coefficient optical fiber comprises an inner core 4, an inner cladding 3, an outer core 2 and an outer cladding 1 which are arranged concentrically from the inside to the outside, and the inner cladding 3 has a plurality of air holes 301, and the air holes 301 penetrate the inner cladding 3 along the axial direction.

[0024] Compared with the prior art, the large dispersion coefficient optical fiber provided by the present invention has a plurality of air holes 301 arranged in the inner cladding 3, and the air holes 301 are located outside the inner core 4. Since the refractive index of the air holes 301 is much smaller than the refractive index of quartz, the refractive index of the inner cladding 3 after the air holes 301 are arranged is greatly reduced compared with when the inner cladding 3 is solid. When the inner core 4 and the outer core 2 exist independently, the mode refractive index of the fundamental mode of the large dispersion coefficient light is equal at the dispersion wavelength point, and the mode refractive index changes dramatically near the dispersion wavelength point, thereby achieving a large dispersion coefficient, which fully meets the requirements of the time stretching technology in the field of microwave photonics for large dispersion coefficient optical fiber. In addition, since the refractive index of air is much lower than the refractive index of the fluorine-doped layer, the present invention can achieve a sudden change in the mode refractive index compared with the solution of only setting the fluorine-doped layer in the prior art, thereby improving the dispersion coefficient.

[0025] It should be noted that the mode refractive index values ​​of the inner and outer cores are adjusted when they are independent, so that the two intersect at a certain wavelength (value matching), but the two curves separate quickly at other wavelengths. According to the coupled mode theory, the closer the mode refractive index values ​​are, the stronger the mode coupling is. The coupling is strong near the intersection and weak at other wavelengths, resulting in a sudden change in the value of the mode refractive index of the inner and outer cores only at the intersection, and then forming a curve in which the entire mode refractive index changes with wavelength near this point, thereby generating large dispersion. That is, the greater the change of the mode refractive index curve of the inner core 4 and the outer core 2 of the large dispersion coefficient light near the intersection (the greater the change near the region of equal wavelength), the greater the dispersion coefficient of the optical fiber.

[0026] It should be noted that the main materials of the inner cladding 3 and the outer cladding 1 are both quartz, and the refractive index of air is much smaller than that of quartz, so opening air holes 301 in the inner cladding 3 can reduce its refractive index.

[0027] It should be noted that, since the refractive index of air is much smaller than that of the inner cladding 3 , the larger the area occupied by the air hole 301 , the lower the final refractive index of the inner cladding 3 , which is more conducive to improving the dispersion coefficient.

[0028] Specifically, the inner fiber core 4 is circular, and the outer fiber core 2 is annular.

[0029] Optionally, the cross section of the air hole 301 is annular, such as circular or elliptical.

[0030] Optionally, the cross section of the air hole 301 is fan-shaped.

[0031] It should be noted that a sector refers to a figure formed by an arc and two radii passing through the two ends of the arc. The sector in the present application may be a conventional sector, that is, the two radii passing through the arc directly intersect, or the other ends of the two radii may be connected by a short arc line, which bulges toward the side away from the arc (see Appendix Figure 2 ).

[0032] It should be noted that the radius of the inner core 4 is in the range of 0.1μm-5μm, the inner radius of the outer core 2 is in the range of 1μm-10μm, the outer radius of the outer core 2 is in the range of 1.5μm-15μm, the diameter of the air hole is in the range of 0.1μm-10μm, the refractive index difference Δn1 between the inner core 4 and the inner cladding 3 is in the range of 0.01-0.06, the refractive index difference Δn2 between the outer core 2 and the inner cladding 3 is in the range of 0.002-0.05, and the number of air holes is 2-30. By optimizing the optical fiber structural parameters within the above range, the absolute value of the dispersion coefficient of the optical fiber at a wavelength of 1550nm can reach more than 18000ps / nm / km.

[0033] As a specific embodiment of the above scheme, the radius of the inner core 4 is 1.3µm, the inner diameter of the outer core 2 is 5.5µm, the outer diameter of the outer core 2 is 7.8µm, the minimum distance between the air hole wall and the outer wall of the inner core 4 is 0.8µm, the radius of the air hole is 4.2µm, the refractive index difference Δn1 between the inner core 4 and the inner cladding 3 is 0.0298, and the refractive index difference Δn2 between the outer core 2 and the inner cladding 3 is 0.0116. Figure 1 The dispersion coefficient of the optical fiber at 1550nm can be as high as -18270ps / nm / km through the dispersion calculation formula.

[0034] In some embodiments, see Figure 1 to Figure 2 , multiple air holes 301 are arranged in a ring shape around the outer periphery of the inner fiber core 4.

[0035] Multiple air holes 301 are arranged in a ring shape around the outer circumference of the inner core 4, which can not only make the refractive index of each position of the inner cladding 3 uniform, but also increase the number of air holes 301 opened in the inner cladding 3 and the area of ​​the inner cladding 3 occupied by the air holes 301, thereby reducing the refractive index of the inner cladding 3.

[0036] It should be noted that when the cross section of the air hole 301 is fan-shaped, the gap between two adjacent air holes 301 is the smallest, and the air holes 301 can be opened on the inner cladding 3 to a maximum extent. In some embodiments, see Figure 1 to Figure 2 , the inner cladding 3 is a fluorine-doped quartz layer.

[0037] The existing inner cladding 3 is mostly made of quartz material. After fluorine is doped into the quartz material, a fluorine-doped quartz layer is formed. Compared with the inner cladding 3 formed by the pure quartz layer, its refractive index is effectively reduced. Under the premise that the refractive index of the inner cladding 3 is reduced due to fluorine doping, an air hole 301 is opened in the inner cladding 3 to further reduce the refractive index of the inner cladding 3, which can greatly improve the dispersion coefficient of the large dispersion coefficient optical fiber. Based on the same inventive concept, the present invention also provides a method for preparing a large dispersion coefficient optical fiber. The method for preparing a large dispersion coefficient optical fiber comprises: S100, preparing an optical fiber preform, the optical fiber preform comprising an inner core 4, an inner cladding 3, an outer core 2 and an outer cladding 1 which are concentrically arranged in sequence from the inside to the outside; S200, opening an air hole 301 along the axial direction of the inner cladding 3, wherein the air hole 301 passes through both ends of the inner cladding 3; S300, heating the optical fiber preform with the air hole 301, and then extending the optical fiber preform to make the diameter of the optical fiber preform between 0.5-4 mm; S400, heating and re-stretching the optical fiber preform that has completed the initial stretching in S300 to form a large dispersion coefficient light with a diameter of ≤125 μm.

[0038] The present invention provides a method for preparing a large dispersion coefficient optical fiber. The method for preparing a large dispersion coefficient optical fiber adopts a secondary extension process for an optical fiber preform. The optical fiber preform is first extended to form an intermediate with a smaller diameter, and then the intermediate is extended again to form an optical fiber with a large dispersion coefficient. Not only can the optical fiber preform be extended to form an optical fiber with a smaller diameter and a large dispersion coefficient, and a very small core-cladding ratio is achieved, but it is also easier to achieve in terms of processing technology, and the scrap rate is reduced. The existing method for preparing a large dispersion coefficient optical fiber usually adopts a one-time extension molding method, resulting in a very high extension requirement during extension, and due to the large difference in diameter between the optical fiber preform and the large dispersion coefficient optical fiber, the process is difficult to achieve and the scrap rate is high.

[0039] It should be noted that the optical fiber preform prepared by the existing one-time extension process can be used to prepare ordinary large dispersion coefficient light. However, since the large dispersion coefficient light in the present invention requires air holes to be opened in the inner cladding, the requirements for the optical fiber preform are relatively high, and thus the optical fiber preform prepared by the one-time extension in the prior art cannot meet the requirements.

[0040] Specifically, the diameter of the optical fiber preform is between 0.5-4 mm, which means that the diameter of the optical fiber preform can be any value between 0.5 mm and 4 mm, and can be 0.5 mm or 4 mm.

[0041] Optionally, in S300 and S400, when the optical fiber preform is extended, it is necessary to ensure that the air hole 301 does not deform, and gas may be introduced into the air hole 301 to prevent the air hole 301 from deforming due to the extension.

[0042] In some embodiments, S100 specifically includes: S110, fixing the quartz reaction tube to the vapor deposition equipment, and rotating the quartz reaction tube; S120, respectively introducing SiCl4, GeCl4 and O2 into the quartz reaction tube and heating them to react and generate SiO2 and GeO2, which are deposited on the inner wall of the quartz reaction tube to form a ring-shaped outer fiber core 2; S130, SiCl4 and O2 are introduced into the inner hole of the outer core 2 and heated, and the SiO2 generated by the reaction is deposited on the inner wall of the inner core 4, and the SiO2 deposition forms an annular inner cladding 3; S140, SiCl4, GeCl4 and O2 are introduced into the inner hole of the inner cladding 3 and heated to react to generate SiO2 and GeO2, which are deposited on the inner wall of the inner cladding 3 to form an inner core 4; S150, heating and shrinking the component formed in S140; S160, a pure quartz tube is arranged outside the quartz reaction tube and heated, the quartz reaction tube and the pure quartz tube are melted into one, forming an outer cladding 1, and the preparation of the optical fiber preform is completed. In the process of preparing the optical fiber preform, the material is evenly covered on the tube wall by rotating it, and the preparation is carried out step by step from the outside to the inside, which can ensure that the thickness of the inner material is uniform.

[0043] Optionally, in S110, the quartz reaction tube rotates at a speed of 30±5 rpm.

[0044] Optionally, in S120, the heating temperature is 1600°C-2010°C, and SiCl4, GeCl4 and O2 undergo the following chemical reactions under the above temperature environment: SiCl4+O2→SiO2+Cl2↑, GeCl4+O2→GeO2+2Cl2↑. In this step, high-purity oxygen is selected as the reaction raw material.

[0045] Optionally, in S130, the heating temperature is 1600°C-2010°C, and SiCl4 and O2 undergo the following chemical reaction under the above temperature environment: SiCl4+O2→SiO2+Cl2↑. In this step, high-purity oxygen is selected as the reaction raw material.

[0046] Optionally, in S140, the heating temperature is 1600°C-2010°C, and the chemical reaction formula is the same as that in S120.

[0047] Optionally, in S150, the heating temperature is 2010°C-2300°C.

[0048] In some embodiments, in S130, while SiCl4 and O2 are introduced into the quartz reaction tube, SF6 is also introduced to heat and form a fluorine-doped quartz layer, namely, inner cladding 3.

[0049] Since the refractive index of the fluorine-doped quartz layer is lower than that of the pure quartz layer, the scheme in this embodiment can further reduce the refractive index of the inner cladding 3 and increase the dispersion coefficient. In this embodiment, the following chemical reaction occurs: SiCl4+O2+SF6→SiO2+Si2O3F2+SO2+SiF4.

[0050] In some embodiments, in S200 , an ultrasonic puncher is used to open a plurality of air holes 301 in the inner cladding 3 , and each air hole 301 extends along the axial direction of the inner cladding 3 . An ultrasonic punch is a device that uses ultrasonic high-frequency vibration to penetrate the surface material of a workpiece. The principle is to generate high-frequency vibrations by passing high-frequency oscillating electrical signals through transformers, amplifiers and other components into the ultrasonic oscillator. This vibration is then transmitted to the surface of the workpiece through a resonator. When the wave intersects the surface, it causes high-frequency vibrations on the surface, generating increasing stress. Ultimately, this vibration will produce a small point-shaped hole, achieving drilling. Compared with traditional mechanical drilling, ultrasonic punching does not damage the equipment in contact with the surface, and can also reduce manual operations.

[0051] In some embodiments, in S300, the optical fiber preform is heated to 1750°C-2150°C in a heating furnace of a drawing tower, and then the optical fiber preform is preliminarily extended to form a rod-shaped component with a diameter of 0.5-4 mm.

[0052] In this embodiment, the optical fiber preform is first extended to form a rod with a diameter between 0.5-4 mm. Compared with the initial state, the diameter of the optical fiber preform is reduced, but compared with the large dispersion coefficient light to be formed in the end, its diameter is still large, thereby avoiding the problem of low product qualification rate and production difficulties caused by one-time extension molding.

[0053] It should be noted that there is a graphite furnace in the drawing tower, which can generate a high temperature of more than 1700℃ to soften the optical fiber preform rod, which is then wound by the extension wheel and drawn into a thin optical fiber. The drawing tower has a feedback system to feedback the furnace temperature and winding speed, etc., so as to accurately control the optical fiber diameter through the laser wire diameter meter.

[0054] It should be noted that in order to increase the strength of the optical fiber, a thin layer of resin can be applied to the optical fiber during the drawing process and cured in time to avoid adhesion.

[0055] In some embodiments, S400 specifically includes: S410, placing the optical fiber preform formed in S300 into a sleeve; S420, heating the optical fiber preform in S410, and when the optical fiber preform reaches a preset extension temperature, extending the optical fiber preform until the optical fiber preform forms a large dispersion coefficient light with a diameter of ≤125 μm.

[0056] Before extending the optical fiber preform, the optical fiber preform is first placed in a sleeve, and then the sleeve and the optical fiber preform are heated together. When the optical fiber preform reaches a preset temperature, the optical fiber preform is extended to finally form a large dispersion coefficient light with a diameter of ≤125μm.

[0057] Specifically, the preset stretching temperature is between 1750°C and 2150°C.

[0058] In some embodiments, S420 specifically includes: S421, placing the optical fiber preform and the sleeve in S410 into a heating furnace of an optical fiber drawing tower for heating; S422, introducing gas into the air hole 301 to form a positive pressure in the air hole 301, and at the same time forming a negative pressure in the gap between the sleeve and the optical fiber preform, until the optical fiber preform forms a large dispersion coefficient light with a diameter of ≤125μm. In this embodiment, gas is introduced into the air hole 301 to form a positive pressure in the air hole 301, which can avoid the problem that the air hole 301 is compressed and deformed during the extension of the optical fiber preform, thereby affecting the refractive index of the inner cladding 3. In addition, a negative pressure is formed in the gap between the sleeve and the optical fiber preform, which further ensures the pressure difference between the inside and outside of the air hole 301 and ensures that the air hole 301 does not deform during the extension process.

[0059] Optionally, the air pressure in the air hole 301 ranges from 0 to 50 kPa, and the air pressure between the optical fiber preform and the sleeve ranges from -0.1 kPa to -20 kPa.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Large dispersion coefficient optical fiber, characterized in that: The invention comprises an inner core, an inner cladding, an outer core and an outer cladding which are arranged concentrically in sequence from the inside to the outside. The inner cladding has a plurality of air holes which penetrate the inner cladding along the axial direction.

2. The large dispersion coefficient optical fiber according to claim 1, characterized in that: The plurality of air holes are annularly arranged around the outer periphery of the inner core.

3. The large dispersion coefficient optical fiber according to claim 1, characterized in that: The inner cladding layer is a fluorine-doped quartz layer.

4. A method for preparing a large dispersion coefficient optical fiber, characterized in that: include: S100, preparing an optical fiber preform, wherein the optical fiber preform comprises an inner core, an inner cladding, an outer core and an outer cladding which are concentrically arranged in sequence from the inside to the outside; S200, opening air holes along the axial direction of the inner cladding, wherein the air holes penetrate two ends of the inner cladding; S300, heating the optical fiber preform having the air hole, and then extending the optical fiber preform so that the diameter of the optical fiber preform is between 0.5 and 4 mm; S400, heating the optical fiber preform that has completed the preliminary extension in S300 and extending it again to form a dispersion optical fiber with a diameter of ≤125 μm.

5. The method for preparing a large dispersion coefficient optical fiber according to claim 4, characterized in that: The S100 specifically includes: S110, fixing the quartz reaction tube to the vapor deposition equipment, and rotating the quartz reaction tube; S120, respectively introducing SiCl4, GeCl4 and O2 into the quartz reaction tube and heating them to generate SiO2 and GeO2 by reaction, and SiO2 and GeO2 are deposited on the inner wall of the quartz reaction tube to form the annular outer core; S130, introducing SiCl4 and O2 into the inner hole of the outer core and heating, so that SiO2 generated by the reaction is deposited on the inner wall of the inner core, and the SiO2 deposition forms the annular inner cladding; S140, introducing SiCl4, GeCl4 and O2 into the inner hole of the inner cladding and heating them to react and generate SiO2 and GeO2, which are deposited on the inner wall of the inner cladding to form the inner core; S150, heating and shrinking the component formed in S140; S160, a pure quartz tube is arranged outside the quartz reaction tube and heated, the quartz reaction tube and the pure quartz tube are melted into one, forming the outer cladding, and completing the preparation of the optical fiber preform.

6. The method for preparing a large dispersion coefficient optical fiber according to claim 5, characterized in that: In the S130, while SiCl4 and O2 are introduced into the quartz reaction tube, SF6 is also introduced to heat and form a fluorine-doped quartz layer, namely, the inner cladding.

7. The method for preparing a large dispersion coefficient optical fiber according to claim 4, characterized in that: In S200, an ultrasonic punch is used to open a plurality of air holes in the inner cladding, each of the air holes extending along the axial direction of the inner cladding.

8. The method for preparing a large dispersion coefficient optical fiber according to claim 4, characterized in that: In the S300, the optical fiber preform is heated to 1750°C-2150°C in a heating furnace of a drawing tower, and then the optical fiber preform is preliminarily extended to form a rod-shaped component with a diameter of 0.5-4 mm.

9. The method for preparing a large dispersion coefficient optical fiber according to claim 4, characterized in that: The S400 specifically includes: S410, placing the optical fiber preform formed in S300 into a sleeve; S420, heating the optical fiber preform in S410, and extending the optical fiber preform until the optical fiber preform forms a large dispersion coefficient optical fiber with a diameter of ≤125 μm.

10. The method for preparing a large dispersion coefficient optical fiber according to claim 9, characterized in that: The S420 specifically includes: S421, placing the optical fiber preform and the sleeve in S410 into a heating furnace of an optical fiber drawing tower for heating; S422, introducing gas into the air hole to form a positive pressure in the air hole, and forming a negative pressure in the gap between the sleeve and the optical fiber preform, until the optical fiber preform forms a large dispersion coefficient optical fiber with a diameter of ≤125 μm.

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