Low-loss anti-resonant hollow core fiber and method of making same

Abstract

The application belongs to the technical field of optical fiber manufacturing, and discloses a low-loss anti-resonant hollow-core optical fiber and a preparation method thereof. The low-loss anti-resonant hollow-core optical fiber comprises an inner cladding and an outer cladding. The inner cladding comprises an outer cavity unit, a plurality of first units and a plurality of second units. The outer cavity unit is in a polygonal structure. End points of the outer cavity unit abut against the outer cladding. A plurality of air regions are formed between outer walls of the outer cavity unit and the outer cladding. The plurality of first units and the plurality of second units are all arranged in the inner cavity of the outer cavity unit. An inner wall of each outer cavity unit abuts against one first unit. A central region defined by the plurality of first units is a fiber core. The second units are arranged staggeredly with the first units. The low-loss anti-resonant hollow-core optical fiber is simple in assembly and positioning, high in processing efficiency, low in transmission loss and capable of realizing long-distance optical transmission.

Description

Technical Field

[0001] This invention relates to the field of optical fiber manufacturing technology, and in particular to a low-loss anti-resonant hollow optical fiber and its preparation method. Background Technology

[0002] Traditional silica optical fibers rely on the principle of total internal reflection to confine light within a solid fiber core. Antiresonant hollow-core optical fibers, however, differ in that, based on the principle of antiresonance, light can be effectively confined within the central air layer, thus suppressing the interaction between light and the solid glass material. Antiresonant hollow-core optical fibers possess characteristics such as low loss, low latency, low nonlinearity, low dispersion, wide bandwidth, and a high laser damage threshold, offering significant advantages in optical communication, fiber optic sensing, and high-power laser transmission. Figure 1 As shown, existing antiresonant hollow-core optical fibers symmetrically arrange multiple glass tubes within the cladding. During assembly, the positioning of the glass tubes requires high precision, making the assembly process relatively difficult and inefficient. Furthermore, the loss of existing low-loss antiresonant hollow-core optical fibers is approximately between 0.2 dB / km and 1 dB / km, limiting the optical transmission distance. Therefore, reducing the transmission loss of antiresonant hollow-core optical fibers and achieving long-distance signal transmission are also major challenges in their development.

[0003] Therefore, there is an urgent need for a low-loss anti-resonant hollow fiber and its fabrication method to solve the above-mentioned technical problems. Summary of the Invention

[0004] The purpose of this invention is to provide a low-loss anti-resonant hollow fiber and its preparation method, which can not only solve the problems of difficult assembly and low processing efficiency of existing anti-resonant hollow fibers, but also reduce the transmission loss of anti-resonant hollow fibers and realize long-distance signal transmission.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] A low-loss anti-resonant hollow-core optical fiber, comprising:

[0007] The fiber comprises an inner cladding layer and an outer cladding layer. The inner cladding layer includes an outer cavity unit, a plurality of first units, and a plurality of second units. The radial cross-section of the outer cavity unit is polygonal. The endpoints of the outer cavity unit abut against the outer cladding layer, and an air region is formed between the outer cavity unit and the outer cladding layer. The plurality of first units and the plurality of second units are all located inside the outer cavity unit. Each sidewall of the outer cavity unit abuts against one of the first units. The central region defined by the plurality of first units is the fiber core. The second units are staggered from the first units.

[0008] As a preferred technical solution for low-loss anti-resonant hollow optical fiber, a gap is left between adjacent first units.

[0009] As a preferred technical solution for low-loss anti-resonant hollow optical fiber, a second unit is provided at each included corner inside the outer cavity unit.

[0010] As a preferred technical solution for low-loss anti-resonant hollow optical fiber, the second unit is spaced apart from the first unit.

[0011] As a preferred technical solution for low-loss anti-resonant hollow optical fiber, the first unit is a single glass tube or a nested glass tube.

[0012] The second unit is a single glass tube or a nested glass tube.

[0013] As a preferred technical solution for low-loss anti-resonant hollow optical fiber, the nested glass tube includes two or more layers of glass tubes with different radii.

[0014] As a preferred technical solution for low-loss anti-resonant hollow optical fiber, the nested glass tube includes circular glass tubes of different radii, which are tangent to each other at a point, and the outer circular glass tube is tangent to the inner wall of the outer cavity unit.

[0015] And / or, the nested glass tubes include arc-shaped glass tubes of different radii, which intersect with the inner wall of the outer cavity unit.

[0016] As a preferred technical solution for low-loss anti-resonant hollow optical fiber, the wall thickness of the glass tube satisfies the anti-resonance condition:

[0017]

[0018] Where, λ m λ is the wavelength of the resonant light, t is the wall thickness of the nested glass tube, n is the refractive index of the fiber optic glass material, and m is a positive integer representing the resonant order.

[0019] As a preferred technical solution for low-loss anti-resonant hollow optical fiber, the cross-sectional shape of the outer cladding is circular.

[0020] A method for fabricating a low-loss anti-resonant hollow-core optical fiber, used to fabricate the low-loss anti-resonant hollow-core optical fiber as described in any one of the above-mentioned methods, the method comprising the following steps:

[0021] Multiple first glass tubes and multiple second glass tubes are selected, wherein the first glass tubes constitute a first unit and the second glass tubes constitute a second unit;

[0022] Select multiple glass plates, and fix one of the first glass tubes on the inner side of each glass plate;

[0023] Select a third glass tube, and sequentially splice the glass plates with the first glass tube installed on them and connect them to the inner boundary of the third glass tube to form the outer cavity unit, with the first glass tube facing the center direction of the third glass tube.

[0024] The second glass tube is installed on the glass plate and is staggered from the first glass tube. The multiple glass plates, the multiple first glass tubes and the multiple second glass tubes constitute the inner cladding layer.

[0025] A positive pressure is applied to the inner cladding and the interior of the third glass tube to draw an intermediate body.

[0026] Select a fourth glass tube and insert the intermediate into the fourth glass tube to form a secondary preform.

[0027] Positive pressure is applied to the inner cladding and the interior of the third glass tube in the secondary preform, and negative pressure is applied between the third glass tube and the fourth glass tube to draw and form an optical fiber.

[0028] Compared with existing technologies, the low-loss anti-resonant hollow-core optical fiber provided by this invention has the following advantages:

[0029] 1. The low-loss anti-resonant hollow fiber provided by the present invention forms multiple air regions between the outer cladding and the inner cladding. The increased glass / air interface increases the number of reflections of the light transmitted in the fiber core, which can effectively reduce the leakage loss of the fiber core fundamental mode.

[0030] 2: The low-loss anti-resonant hollow fiber provided by the present invention has no contact between adjacent first units, adjacent second units, and between first and second units, which can avoid the formation of nodes inside the outer cavity unit and cause Fano resonance, and can reduce the leakage loss of the fiber core fundamental mode.

[0031] 3: The low-loss anti-resonant hollow fiber provided by the present invention has a core formed by the central region defined by the first unit boundary, which is negative curvature, and can effectively reduce the leakage loss of the fiber core fundamental mode.

[0032] 4. The low-loss anti-resonant hollow-core optical fiber provided by this invention allows workers to assemble the first unit simply by aligning the different inner walls of the first unit with those of the outer cavity unit. Compared to the existing layout where glass tubes are symmetrically arranged inside the cladding, this simplifies positioning during assembly and improves the processing efficiency of the low-loss anti-resonant hollow-core optical fiber.

[0033] The method for preparing low-loss anti-resonant hollow optical fiber provided by this invention has the advantages of easy positioning during the initial preform assembly, rapid preparation of low-loss anti-resonant hollow optical fiber, low transmission loss and long-distance optical transmission. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of anti-resonant hollow optical fiber in the prior art;

[0035] Figure 2 This is a schematic diagram of the first structure of the low-loss anti-resonant hollow optical fiber provided by the present invention.

[0036] Figure 3 This is a simulation diagram of the transmission loss of the first structure low-loss anti-resonant hollow optical fiber provided by the present invention;

[0037] Figure 4 This is a schematic diagram of the second structure of the low-loss anti-resonant hollow fiber provided by the present invention;

[0038] Figure 5 This is a simulation diagram of the transmission loss of the second structure low-loss anti-resonant hollow fiber provided by the present invention;

[0039] Figure 6 This is a flowchart illustrating the fabrication process of the low-loss anti-resonant hollow-core optical fiber provided by this invention.

[0040] In the picture:

[0041] 1. Fiber core; 2. Inner cladding; 21. First unit; 211. Inner glass tube; 212. Outer glass tube; 22. Outer cavity unit; 23. Second unit; 3. Air region; 4. Outer cladding. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0043] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or a thermal weld; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0044] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0045] In the description of this embodiment, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0046] Example 1

[0047] like Figure 2 and Figure 4 As shown in the illustration, this embodiment provides a low-loss anti-resonant hollow-core optical fiber, including an inner cladding 2 and an outer cladding 4. The inner cladding 2 includes an outer cavity unit 22, a plurality of first units 21, and a plurality of second units 23. The outer cavity unit 22 has a polygonal structure, and its endpoints abut against the outer cladding 4, thus forming a plurality of air regions 3 between the outer wall of the outer cavity unit 22 and the outer cladding 4. The formation of multiple air regions 3 between the outer cladding 4 and the inner cladding 2 forms a glass / air interface, which enhances the reflection of the light transmitted in the fiber core and effectively reduces the leakage loss of the fiber core's fundamental mode.

[0048] Multiple first units 21 and multiple second units 23 are placed inside the outer cavity unit 22. The inner wall of each outer cavity unit 22 abuts against a first unit 21. The central area defined by multiple first units 21 forms the fiber core 1. The fiber core 1 is defined by the boundaries of multiple first units 21. The fiber core 1 is negative curvature, which can effectively reduce the leakage loss of the fiber core fundamental mode.

[0049] The second unit 23 is staggered from the first unit 21. There is no contact between adjacent first units 21, between the first unit 21 and the second unit 23, and between adjacent second units 23. This can prevent the formation of nodes inside the outer cavity unit 22 and cause Fano resonance, and can reduce the leakage loss of the fiber core fundamental mode.

[0050] Meanwhile, when assembling the first unit 21, the staff only needs to attach the first unit 21 to the corresponding inner walls of the outer cavity unit 22. Compared with the existing layout of symmetrically setting the glass tube inside the outer cladding layer 4, the staff can position the fiber more easily during assembly, which can improve the processing efficiency of low-loss anti-resonant hollow fiber.

[0051] Based on data comparison and calculation, the low-loss antiresonant hollow-core optical fiber provided in this embodiment theoretically has a transmission loss of less than 0.1 dB / km in the S+C+L+U bands, enabling long-distance optical transmission. The S-band has wavelengths of 1460 nm-1530 nm, the C-band 1530 nm-1565 nm, the L-band 1565 nm-1625 nm, and the U-band 1625 nm-1675 nm.

[0052] In this embodiment, the outer cavity unit 22 has a cross-section that is a regular pentagon. The inner cladding 2 includes five first units 21, which are attached to the five sides of the outer cavity unit 22 in a one-to-one correspondence. The central region defined by the five first units 21 is the fiber core 1. Of course, the cross-sectional shape of the outer cavity unit 22 can also be an irregular polygon, as long as an air region 3 of appropriate thickness can be formed. The structure of the outer cavity unit 22 is not specifically limited here.

[0053] In this embodiment, a gap is left between adjacent first units 21. This avoids the formation of nodes due to mutual contact between adjacent first units 21, which could cause Fano resonance during optical transmission and further reduce leakage loss during optical transmission. Fano resonance is a common asymmetric resonance phenomenon in physical systems and is considered standard knowledge in the field of physics.

[0054] Preferably, a second unit 23 is provided at each included corner inside the outer cavity unit 22, which further restricts the transmission space of the core-guided light and can further reduce the leakage loss of the core fundamental mode. Spacing is left between the multiple second units 23 and the multiple first units 21, thus preventing the formation of nodes due to contact between the first units 21 and the second units 23, which could lead to Fano resonance during light transmission and reduce leakage loss. At the same time, workers can quickly assemble the second units 23, reducing the operational difficulty of assembling low-loss anti-resonant hollow-core fibers and improving the production efficiency of low-loss anti-resonant hollow-core fibers.

[0055] In this embodiment, the first unit 21 can be a single glass tube or a nested glass tube. Similarly, the second unit 23 can be a single glass tube or a nested glass tube.

[0056] For example, on one hand, the nested glass tubes include circular glass tubes of different radii, with each nested circular glass tube having an equal wall thickness. The outermost glass tube of each first unit 21 is tangent to the side wall of the outer cavity unit 22, and the inner glass tube is internally tangent to the outer glass tube. The outermost glass tube of each first unit 21 is correspondingly tangent to the inner wall of the outer cavity unit 22, thereby forming a fiber core 1 at the center of the outer cavity unit 22. On the other hand, the nested glass tubes include multiple arc-shaped glass tubes of different radii, with the same wall thickness. All arc-shaped glass tubes of different radii intersect the inner wall of the outer cavity unit 22, and the multiple arc-shaped glass tubes are arranged sequentially in ascending order of radius. Each side wall of the outer cavity unit 22 is provided with nested arc-shaped glass tubes of different radii, thereby forming a fiber core 1 at the center of the outer cavity unit 22. Regarding the number of nested glass tube layers in the first unit 21, it can be 3, 4, 5, or more. There are no specific restrictions on the number of nested glass tube layers in the first unit 21. As for the structure of the inner cladding layer 2, it can be a combination of the outer cavity unit 22 and circular glass tubes of different radii, or a combination of the outer cavity unit 22, circular glass tubes of different radii, and circular glass tubes of different radii. There are no restrictions on the specific structure of the inner cladding layer 2.

[0057] Specifically, the low-loss anti-resonant hollow-core optical fiber provided in this embodiment has a first unit 21, which is a nested glass tube. The first unit 21 includes two nested glass tubes with different radii: an inner glass tube 211 and an outer glass tube 212. The radius of the inner glass tube 211 is smaller than that of the outer glass tube 212, and the inner glass tube 211 is nested inside the outer glass tube 212. The second unit 23 is a single glass tube, consisting of only one glass tube. The cross-sectional shapes of the inner glass tube 211 and the outer glass tube 212 in the first unit 21 can be regular polygons, circles, or irregular polygons, and are not specifically limited here. Similarly, the cross-sectional shape of the glass tube selected as the second unit 23 is also not limited.

[0058] In this embodiment, the wall thickness of the glass tube satisfies the anti-resonance condition:

[0059]

[0060] Where: λ m λ is the wavelength of the resonant light, t is the wall thickness of the nested glass tube, n is the refractive index of the fiber optic glass material, and m is a positive integer representing the resonant order.

[0061] To facilitate the assembly of low-loss anti-resonant hollow optical fibers, the outer cladding layer 4 is preferably circular in cross-section, i.e., the outer cladding layer 4 is a circular glass tube. The use of a circular glass tube for the outer cladding layer 4 is only one preferred technical solution; of course, the outer cladding layer 4 can also be a regular polygonal glass tube or an irregular polygonal glass tube, as long as an air region 3 of appropriate thickness is maintained between the inner cladding layer 2 and the outer cladding layer 4. No specific restrictions are imposed here.

[0062] Furthermore, the structure of the low-loss anti-resonant hollow fiber of the present invention will be described in conjunction with specific embodiments.

[0063] First structure:

[0064] like Figure 2 As shown, in the inner cladding 2 of the low-loss anti-resonant hollow fiber, the distance between adjacent first units 21 is 4.5 μm, and the diameters of the glass tubes in the first units 21 are 31.9 μm and 19.1 μm, respectively; the distance between adjacent second units 23 is 41.34 μm, and the diameter of the glass tube in the second unit 23 is 15.5 μm; the thickness of the outer cavity unit 22 of the inner cladding 2 is 9.84 μm.

[0065] Simulation results of transmission loss of low-loss antiresonant hollow fiber in the S+C+L+U bands are as follows: Figure 3 As shown, the average transmission loss of optical fiber across the entire band is 0.1 dB / km, with the lowest transmission loss at 1550 nm wavelength being 0.06 dB / km and the limiting loss being 0.002 dB / km.

[0066] The second structure:

[0067] like Figure 4 As shown, in the inner cladding 2 of the low-loss anti-resonant hollow fiber, the distance between adjacent first units 21 is 4.5 μm, and the diameters of the glass tubes in the first units 21 are 31.9 μm and 19.1 μm, respectively; the distance between adjacent second units 23 is 32.7 μm, and the diameter of the glass tube in the second unit 23 is 19.1 μm; the thickness of the outer cavity unit 22 of the inner cladding 2 is 1.64 μm.

[0068] Simulation results of transmission loss of low-loss antiresonant hollow fiber in the S+C+L+U bands are as follows: Figure 5 As shown, the average transmission loss of the optical fiber across the entire band is 0.09 dB / km, with a transmission loss of 0.06 dB / km and a confinement loss of 0.004 dB / km at a wavelength of 1550 nm.

[0069] Example 2

[0070] like Figure 6As shown in the illustration, this embodiment provides a method for fabricating a low-loss anti-resonant hollow-core optical fiber, used to fabricate the low-loss anti-resonant hollow-core optical fiber in Embodiment 1. The method for fabricating the low-loss anti-resonant hollow-core optical fiber includes the following steps:

[0071] Select multiple first glass tubes and multiple second glass tubes, wherein the first glass tubes are designated as first unit 21 and the second glass tubes are designated as second unit 23; specifically, prepare five first glass tubes and five second glass tubes, wherein the first glass tubes are nested glass tubes, including an inner glass tube 211 and an outer glass tube 212, and the second glass tubes are single glass tubes, including only one glass tube.

[0072] Select multiple glass plates and fix a first glass tube on the inner side of each glass plate; preferably, place the first glass tube at the center of the inner side of the glass plate. Specifically, select five glass plates, mark the center of each glass plate, and place the five first glass tubes at the corresponding centers of the five glass plates.

[0073] A third glass tube is selected, and glass plates with first glass tubes installed on them are sequentially spliced ​​together and internally connected to the inner boundary of the third glass tube to form an outer cavity unit 22, with the first glass tube facing the center direction of the third glass tube. Specifically, a third glass tube is selected, wherein the radius of the third glass tube is larger than the radius of the outer glass tube 212, and the glass plates can be internally connected to the third glass tube. Five glass plates, each with a first unit 21 installed on them, are fixed to the inner wall of the third glass tube in a pentagonal form, with the first unit 21 facing the center direction of the third glass tube. At this time, the central area defined by the multiple first units 21 is the fiber core 1. In this case, to facilitate the assembly of low-loss anti-resonant hollow fiber, a regular pentagonal glass tube can also be directly selected and placed inside the third glass tube, and then the five first glass tubes are installed on the five inner side walls of the regular pentagonal glass tube. The multiple glass plates can be spliced ​​and internally connected to the third glass tube by flame heating, laser heating, or glass adhesive bonding, or a combination of the above methods can be used to complete the splicing and internal connection.

[0074] A second glass tube is installed on a glass plate, and the second glass tube is staggered from the first glass tube. Multiple glass plates, multiple first units 21, and multiple second units 23 constitute the inner cladding 2. Specifically, the glass plate connected to the third glass tube, five first units 21, and five second units 23 constitute the inner cladding 2 of the low-loss anti-resonant hollow fiber.

[0075] A positive pressure is applied to the inner cladding 2 and the inside of the third glass tube, and the intermediate is drawn to obtain the intermediate body;

[0076] A fourth glass tube is selected, and the intermediate body is inserted into the fourth glass tube to form a secondary preform; wherein the fourth glass tube is the outer cladding layer of the low-loss anti-resonant hollow fiber, and the whole formed by the third glass tube and the fourth glass tube in the intermediate body corresponds to the outer cladding layer 4 of the low-loss anti-resonant hollow fiber in this embodiment, which is a conventional step in the fabrication of low-loss anti-resonant hollow fiber.

[0077] Positive pressure is applied to the inner cladding 2 and the interior of the third glass tube in the secondary preform, and negative pressure is applied between the third and fourth glass tubes to draw and form an optical fiber.

[0078] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A low-loss anti-resonant hollow-core optical fiber, characterized in that, include: The inner cladding (2) and the outer cladding (4) are provided. The inner cladding (2) includes an outer cavity unit (22), a plurality of first units (21) and a plurality of second units (23). The radial cross-section of the outer cavity unit (22) is polygonal. The endpoints of the outer cavity unit (22) abut against the outer cladding (4). An air region (3) is formed between the outer cavity unit (22) and the outer cladding (4). The plurality of first units (21) and the plurality of second units (23) are all located inside the outer cavity unit (22). Each sidewall of the outer cavity unit (22) abuts against a first unit (21). The central region defined by the plurality of first units (21) is the fiber core (1). The second units (23) are staggered from the first units (21).

2. The low-loss anti-resonant hollow-core optical fiber according to claim 1, characterized in that, There is a gap between adjacent first units (21).

3. The low-loss anti-resonant hollow-core optical fiber according to claim 2, characterized in that, The second unit (23) is provided at each included corner inside the outer cavity unit (22).

4. The low-loss anti-resonant hollow-core optical fiber according to claim 3, characterized in that, The second unit (23) is separated from the first unit (21).

5. The low-loss anti-resonant hollow-core optical fiber according to claim 1, characterized in that, The first unit (21) is a single glass tube or a nested glass tube; The second unit (23) is a single glass tube or a nested glass tube.

6. The low-loss anti-resonant hollow-core optical fiber according to claim 5, characterized in that, The nested glass tubes include two or more layers of glass tubes with different radii.

7. The low-loss anti-resonant hollow-core optical fiber according to claim 6, characterized in that, The nested glass tubes include circular glass tubes of different radii, which are tangent to each other at a point, and the outer circular glass tube is tangent to the inner wall of the outer cavity unit (22). And / or, the nested glass tubes include arc-shaped glass tubes of different radii, which intersect with the inner wall of the outer cavity unit (22).

8. The low-loss anti-resonant hollow-core optical fiber according to claim 6, characterized in that, The wall thickness of the nested glass tube satisfies the anti-resonance condition: Where, λ m λ is the wavelength of the resonant light, t is the wall thickness of the nested glass tube, n is the refractive index of the fiber optic glass material, and m is a positive integer representing the resonant order.

9. The low-loss anti-resonant hollow-core optical fiber according to any one of claims 1-8, characterized in that, The outer cladding layer (4) has a circular cross-sectional shape.

10. A method for fabricating a low-loss anti-resonant hollow-core optical fiber, characterized in that, The method for preparing the low-loss anti-resonant hollow-core optical fiber according to any one of claims 1-9 includes the following steps: Select multiple first glass tubes and multiple second glass tubes, wherein the first glass tubes are the first unit (21) and the second glass tubes are the second unit (23); Select multiple glass plates, and fix one of the first glass tubes on the inner side of each glass plate; Select a third glass tube, and sequentially splice the glass plates with the first glass tube installed on them and connect them to the inner boundary of the third glass tube to form the outer cavity unit (22), with the first glass tube facing the center direction of the third glass tube; The second glass tube is installed on the glass plate and the second glass tube is staggered from the first glass tube. The multiple glass plates, the multiple first glass tubes and the multiple second glass tubes constitute an inner cladding layer (2). A positive pressure is applied to the inner cladding (2) and the interior of the third glass tube to draw an intermediate body. Select a fourth glass tube and insert the intermediate into the fourth glass tube to form a secondary preform. Positive pressure is applied to the inner cladding (2) in the secondary preform and the interior of the third glass tube, and negative pressure is applied between the third glass tube and the fourth glass tube to draw and form an optical fiber.

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