Multi-core optical fiber using cane and method for forming the same

Abstract

A method of making an optical fiber includes mounting a glass sleeve in a selective etching apparatus, the sleeve having one or more axial holes therethrough, the etching apparatus including a first end cap having a central opening disposed therethrough, the first end cap mounted on a first surface of the sleeve. The method further includes exposing the sleeve to an acidic solution such that a first portion of the first surface is exposed to the acidic solution and a second portion of the first surface is not exposed to the acidic solution. The first portion is adjacent to the central opening when the sleeve is mounted in the selective etching apparatus, and the second portion is covered by the first end cap when the sleeve is mounted in the selective etching apparatus.

Description

Priority

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 191543, filed on 21 May 2021, on which its contents are based and which are incorporated herein by reference. [Technical Field]

[0002] This disclosure broadly relates to multi-core optical fibers using cane, and more particularly to a method for forming multi-core optical fibers using cane using a vacuum-based method. [Background technology]

[0003] The transmission capacity of communication systems using multi-core optical fibers is increasing at a rate exceeding that of single-core optical fibers. In multi-core optical fibers, multiple cores are surrounded by a single cladding that allows light to propagate through each core. To manufacture multi-core optical fibers, an all-glass process can be used, and in multi-core optical fibers, bulk clad glass with one or more precisely formed axial holes is used. Each of these holes houses a cane, which forms the core of the multi-core optical fiber.

[0004] The whole-glass process may be preferable to depositional processes (e.g., external deposition (OVD) methods) that involve soot layer formation, sintering, and solidification to convert the soot into glass. In the whole-glass process, the clad glass can be precisely ground to a selected diameter, which provides both precision and flexibility in selecting various spacings, shapes, and arrangements of one or more axial holes when forming the glass preform.

[0005] However, the entire glassmaking process is relatively expensive and time-consuming. Precision drilling is time-consuming, one or more canes must be formed to define the selected refractive index profile and then added to the clad glass, and the entire structure must be solidified in a furnace to form a solid glass preform. To produce a glass preform of sufficient length, separate glass clad sections may need to be joined axially, which involves precise alignment of the axial holes. The solidification process typically requires dedicated support fixtures to hold the glass clad sections and canes in the solidification furnace to form the resulting solid glass preform. The solid glass preform must then be removed from the support fixtures so that it can be moved from the solidification furnace to a drawing furnace for drawing the preform into optical fibers. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Conventional all-glass processes not only require a significant number of resources to complete but are also extremely time-consuming. More specifically, the entire process takes approximately two days for the clad glass to cool completely between each step. Furthermore, this process involves a considerable number of steps. Embodiments of the present disclosure reduce the number of steps and resources involved in manufacturing optical fibers from clad glass. For example, embodiments of the present disclosure reduce the number of steps so that the entire process can be completed in one day. Moreover, embodiments of the present disclosure do not require separate solidification furnaces and drawing tower furnaces. Therefore, embodiments of the present disclosure provide a more economical and resource-efficient process for manufacturing optical fibers from conventional processes. [Means for solving the problem]

[0007] An exemplary method for solving this problem is described in the independent claim. Various embodiments are defined in the dependent claims.

[0008] Aspects of the present disclosure include a method for manufacturing an optical fiber. The method includes the step of mounting a glass sleeve in a selective etching apparatus, the sleeve having one or more axial through holes, the etching apparatus including a first end cap through which a central opening is positioned, the first end cap being mounted on a first surface of the sleeve. The method further includes the step of exposing the sleeve to an acidic solution such that a first portion of the first surface is exposed to the acidic solution, but a second portion of the first surface is not exposed to the acidic solution. The first portion is adjacent to the central opening when the sleeve is mounted in the selective etching apparatus, and the second portion is covered by the first end cap when the sleeve is mounted in the selective etching apparatus.

[0009] Aspects of the present disclosure include a method for manufacturing an optical fiber. The method includes the step of forming a concave recess on the first surface of a glass sleeve, the concave recess being surrounded by a raised edge of the sleeve, and the sleeve having one or more axial through holes. The method further includes the steps of inserting a glass cane core into each of the axial through holes, and vacuum sealing the sleeve with one or more additional glass components to form an assembly.

[0010] Aspects of the present disclosure include a method for manufacturing an optical fiber. The method includes the steps of forming an optical fiber by drawing the assembly, while simultaneously inserting a glass cane core into an axial through-hole of a glass sleeve and vacuum sealing the sleeve with one or more additional glass components to form an assembly.

[0011] Many different embodiments are listed, but embodiments may exist individually or in any combination as far as possible. Hereafter, illustrative embodiments will be shown and described. [Brief explanation of the drawing]

[0012] [Figure 1] A flowchart illustrating the process of manufacturing a multi-core optical fiber according to an embodiment of the present disclosure. [Figure 2]A diagram showing a sleeve including one or more axial through-holes according to an embodiment of the present disclosure [Figure 3] A diagram showing a selective etching apparatus according to an embodiment of the present disclosure [Figure 4A] An enlarged partial view of the selective etching apparatus of FIG. 3 according to an embodiment of the present disclosure [Figure 4B] An enlarged partial view of the selective etching apparatus of FIG. 3 according to an embodiment of the present disclosure [Figure 4C] An enlarged partial view of the selective etching apparatus of FIG. 3 according to an embodiment of the present disclosure [Figure 5A] An additional enlarged partial view of the selective etching apparatus of FIG. 3 according to an embodiment of the present disclosure [Figure 5B] An additional enlarged partial view of the selective etching apparatus of FIG. 3 according to an embodiment of the present disclosure [Figure 5C] An additional enlarged partial view of the selective etching apparatus of FIG. 3 according to an embodiment of the present disclosure [Figure 5D] An additional enlarged partial view of the selective etching apparatus of FIG. 3 according to an embodiment of the present disclosure [Figure 6] Another enlarged partial view of the selective etching apparatus of FIG. 3 according to an embodiment of the present disclosure [Figure 7] Schematic diagrams showing the sleeve before, during, and after a selective etching process according to an embodiment of the present disclosure [Figure 8] A diagram showing the sleeve attached to the selective etching apparatus after the selective etching process [Figure 9] A diagram showing another embodiment of a selective etching process according to an embodiment of the present disclosure [Figure 10A] A diagram showing the process of inserting a cane core into a sleeve according to an embodiment of the present disclosure [Figure 10B] A diagram showing the process of inserting a cane core into a sleeve according to an embodiment of the present disclosure [Figure 10C] Cross-sectional view of a cane core [Figure 10D] Cross-sectional view of a sleeve with a cane core inserted therein [Figure 11]Cross-sectional view of a cane clad assembly located in a drawing tower furnace and connected to a vacuum system according to an embodiment of the present disclosure [Figure 12] Figure showing an internal passage of a cane clad assembly according to an embodiment of the present disclosure [Figure 13] Schematic diagram illustrating an exemplary drawing system DETAILED DESCRIPTION OF EMBODIMENTS

[0013] Additional features and advantages of the present disclosure will be set forth in the following detailed description, will be apparent to those skilled in the art from the description, or will be recognized by practicing the present disclosure as described in the following detailed description, taken together with the claims and the accompanying drawings.

[0014] As used herein, when the term "and / or" is used in a list of two or more items, it means that any one of the listed items may be used by itself, or any combination of two or more of the listed items may be used. For example, if a composition is described as containing components A, B and / or C, the composition may contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B and C in combination.

[0015] In this document, relative terms such as first and second, upper and bottom are only used to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions.

[0016] As used herein, the expression "comprises" includes the term "consists of" as a special case, so for example, the expression "A comprises B and C" is understood to include the case where "A consists of B and C".

[0017] The term “solidified” as used here means providing an assembly made from different glass components that are not bonded to each other, and heating the assembly slightly above the softening point of the glass components so that the glass components can flow and bond or seal to each other to form a unified glass component that maintains the overall structure of the glass components, that is, so that the glass components do not substantially change their basic form.

[0018] The terms "axial hole" or "axial through-hole" refer to a hole that extends parallel to the axial direction, that is, parallel to the central axis or centerline.

[0019] The term "cylinder" used here refers to a three-dimensional shape formed by taking a two-dimensional shape and projecting it onto a third dimension perpendicular to the plane of that two-dimensional shape. Therefore, the cylinder used here may have a cross-sectional shape other than a circle.

[0020] Those skilled in the art will understand that the structures and other components described in the disclosure are not limited to any particular material. Other exemplary embodiments of the disclosure disclosed herein may be formed from a wide variety of materials unless otherwise specified.

[0021] It is also important to note that the structure and arrangement of the elements of this disclosure, as shown in the exemplary embodiments, are for illustrative purposes only. Although only a few embodiments are described in detail in this disclosure, it will be readily apparent to those skilled in the art who have studied this disclosure that many modifications are possible (e.g., modifications to the size, dimensions, structure, shape and proportions, parameter values, mounting arrangement, material use, color, orientation, etc.) without significantly deviating from the novel and non-obvious teachings and advantages of the enumerated subject matter. For example, an element shown as integrally molded may consist of numerous parts, or an element shown as numerous parts may be integrally molded; the operation of the interface may be reversed or otherwise altered; the length or width of the structure, and / or system components, or connectors, or other elements may be altered; and the nature or number of adjustment positions provided between multiple elements may be altered. It should be noted that the elements and / or assemblies of the system may consist of a wide variety of materials that provide sufficient strength or durability, in any wide variety of colors, textures, and combinations. Accordingly, all such modifications are intended to be within the scope of this disclosure. Without departing from the spirit of this disclosure, other substitutions, modifications, changes, and omissions may be made to the designs, operating conditions, and arrangements of desired and other exemplary embodiments.

[0022] Herein, we refer in detail to currently preferred embodiments of the present disclosure, the examples of which are shown in the accompanying drawings. Whenever possible, the same reference numerals are used across the drawings to refer to the same or similar parts.

[0023] Referring here to Figure 1, an exemplary process 1 according to an embodiment of the present disclosure is shown. Process 1 is a system for manufacturing a multi-core optical fiber. However, process 1 may also be used to manufacture a single-core optical fiber. As can be seen from Figure 1, step 10 of process 1 includes the step of forming holes in a glass sleeve. Each hole is sized to accommodate a cane core. Next, in step 20, a selective etching process is performed on the sleeve, which creates recessed areas at one end of the sleeve. These recessed areas are later used during a vacuum sealing process to seal multiple glass components together and provide a preform assembly. Then, in step 30, the cane core is inserted into the holes. In step 40, the vacuum sealing process is performed together with the drawing process. It is convenient that the vacuum sealing process is performed simultaneously with the drawing process in step 40 of process 1. Each of the steps of process 1 is described in more detail later.

[0024] As shown in Figure 2, in step 10 of process 1, a hole 110 is formed in the sleeve 100. In some embodiments, the hole 110 is formed by precision drilling, such as diamond abrasive core drilling and / or ultrasonic-assisted core drilling. The sleeve 100 is a cylindrical glass body having a top surface 102 and a bottom surface 104. Furthermore, the sleeve 100 is made of silica (e.g., pure silica or doped silica). As shown in Figure 2, the sleeve 100 has a diameter Ds and a height Hs. In some embodiments, the diameter Ds is in the range of about 25 mm to about 200 mm or about 50 mm to about 125 mm, and the height Hs is in the range of about 50 mm to about 2 m or about 75 mm to about 1 m. In one exemplary embodiment, the diameter Ds is about 70 mm and the height Hs is about 110 mm. Other diameters and heights are also conceivable, as will be recognized by those skilled in the art.

[0025] Each of the holes 110 is an axial through-hole formed within the internal volume of the sleeve 100. Although four holes 110 are shown in Figure 2, the sleeve 100 may have more or fewer holes 110. For example, the sleeve 100 may have one or more holes, two or more holes, four or more holes, six or more holes, eight or more holes, ten or more holes, or twelve or more holes. Furthermore, the holes 110 may have a circular cross-sectional shape, as shown in Figure 2. The holes 110 may have other cross-sectional shapes, and one or more holes may have a different cross-sectional shape from one or more other holes.

[0026] Each hole 110 has an upper end that opens into the upper surface 102 of the sleeve 100 and a lower end that opens into the bottom surface 104 of the sleeve 100. Therefore, each hole 110 forms a continuous opening from the upper surface 102 to the bottom surface 104. In some embodiments, the holes 110 have diameters ranging from about 2 mm to about 60 mm, or from about 5 mm to about 45 mm, or from about 10 mm to about 30 mm. It is also conceivable that one or more holes 110 have a different diameter from one or more other holes.

[0027] The holes 110 may be spaced equidistant from each other. Furthermore, the holes 110 may be arranged in any configuration and layout known in the art.

[0028] In step 20 of process 1, a selective etching process is performed on the sleeve 100. Prior to this selective etching process, one or more surfaces of the sleeve 100 can be polished or finely ground. For example, the outer surface of the sleeve 100 can be polished or finely ground to obtain a precise diameter Ds and / or a precise height Hs. In addition, or instead, the inner surface of the hole 110 may be polished or finely ground. To obtain precise flatness, the top surface 102 and / or the bottom surface 104 may also be polished or finely ground. In some embodiments, the top and bottom surfaces 102 and 104 are finely ground to obtain a surface roughness (RMS) of about 2 micrometers or less, or about 1 micrometer or less.

[0029] The selective etching process etches only a portion of the sleeve 100 to provide recessed areas on the top surface 102 and / or bottom surface 104 of the sleeve 100. These recessed areas are used in the vacuum sealing process, as will be further described below. For the selective etching process, first the etching apparatus 200 is fixed to the sleeve 100. At this point, the sleeve 100 is a cylindrical member with flat, uniform top and bottom surfaces 102, 104. Therefore, at this point, the sleeve 100 does not yet have any recessed areas. As shown in Figure 3, when the sleeve 100 is installed in the etching apparatus 200, it is firmly fixed between the first end cap 210 and the second end cap 220 of the apparatus 200. The first end cap 210 is connected to the top surface 102 of the sleeve 100, and the second end cap 220 is connected to the bottom surface 104 of the sleeve 100. As will be further described below, multiple rods 230 extend from the first end cap 210 to the second end cap 220, securely fixing the etching apparatus 200 on and around the sleeve 100.

[0030] Each of the first and second end caps 210, 220 may be a flange member that helps to securely maintain the connection between the sleeve 100 and the etching apparatus 200. The end caps 210, 220 may be cylindrical members with a central opening extending from the top surface to the bottom surface of the end cap. Therefore, the end caps 210, 220 may be donut-shaped.

[0031] Figure 4A shows a perspective view of the first end cap 210, and Figure 4B shows a cross-sectional view of the end cap 210 through line AA in Figure 4A. The end cap 210 has a central opening 212 for alignment with the sleeve 100. In addition, the end cap 210 has a number of outer openings 214, each of which is sized to accommodate the rod 230, as will be further described below. All of the central opening 212 and outer openings 214 extend along the entire length of the first end cap 210, from the first surface 211 to the second surface 213. The central opening 212 has a diameter ranging from approximately 30 mm to approximately 60 mm, or approximately 40 mm to approximately 50 mm, or approximately 42 mm to approximately 48 mm. The central opening 212 has a diameter smaller than the diameter Ds of the sleeve 100. In some embodiments, the diameter of the central opening 212 is about 5 mm to about 10 mm smaller than the diameter Ds of the sleeve 100.

[0032] Furthermore, the central opening 212 has a larger diameter than each of the outer openings 214, each of which has a diameter ranging from approximately 10 mm to approximately 30 mm, or approximately 15 mm to approximately 25 mm, or approximately 18 mm to approximately 22 mm, or approximately 20 mm. However, the diameter of the outer openings 214 will vary depending on the size of the rod 230. The outer openings 214 may be uniformly spaced around the central opening 212, and thus the outer openings 214 are radially outward from the central opening 212.

[0033] The total outer diameter D of the first end cap 210 FEC The length may range from approximately 120 mm to approximately 160 mm, or from approximately 130 mm to approximately 150 mm, or be approximately 140 mm. In addition, the first end cap 210 has a height H of approximately 30 mm to approximately 50 mm, or from approximately 35 mm to approximately 45 mm, or from approximately 37 mm to approximately 39 mm. FEC(From the first surface 211 to the second surface 213) may be present. The first end cap 210 may also have a projection 215 that extends radially outward from the first surface 211. Figure 4C shows an enlarged view of area B in Figure 4B, where the projection 215 is shown. The projection 215 may extend from the first surface 211 for a length of approximately 0.5 mm to approximately 1.5 mm, or approximately 0.75 mm to approximately 1.25 mm, or approximately 1 mm. Therefore, the height of the first end cap 210 is the length from the second surface 213 to the projection 215 (H FEC This is the length of the projection 215 (plus the length of the projection 215). As shown in Figure 4C, the projection 215 frames the central opening 212. As will be further described below, a gasket may be placed around the projection 215 to securely fasten the sleeve 100 to the first end cap 210.

[0034] Figures 5A and 5B show the first and second perspective views of the second end cap 220. Figure 5C shows a cross-sectional view of the second end cap 220 through line CC in Figure 5A. The second end cap 220, like the first end cap 210, has a central opening 222 for alignment with the sleeve 100. In addition, the second end cap 220 also has several outer openings 224, each of which is sized to accommodate the rod 230, as will be further described below. All of the central opening 222 and outer openings 224 extend along the entire length of the second end cap 220, from the first surface 221 to the second surface 223. Figure 5A shows the open ends of the openings 222 and 224 on the first surface 221 of the end cap 220, and Figure 5B shows the open ends of the openings 222 and 224 on the second surface 223 of the end cap 220.

[0035] Similar to the first end cap 210, the central opening 222 of the second end cap 220 has a diameter ranging from about 30 mm to about 60 mm, or from about 40 mm to about 50 mm, or from about 42 mm to about 48 mm. The central opening 222 has a diameter smaller than the diameter Ds of the sleeve 100. In some embodiments, the diameter of the central opening 222 is about 5 mm to about 10 mm smaller than the diameter Ds of the sleeve 100.

[0036] Furthermore, the central opening 222 has a larger diameter than each of the outer openings 224, each of which has a diameter ranging from approximately 10 mm to approximately 30 mm, or approximately 15 mm to approximately 25 mm, or approximately 18 mm to approximately 22 mm, or approximately 20 mm. However, the diameter of the outer openings 224 will vary depending on the size of the rod 230. The outer openings 224 may be uniformly spaced around the central opening 222, and thus the outer openings 224 are radially outward from the central opening 222.

[0037] The second surface 223 of the second end cap 220 may have a plurality of recesses 227, so that each outer opening 224 is centered within a recess 227. Thus, the opening of each outer opening 224 is formed on the recess 227. As will be further described below, the recesses 227 help to securely fix the rod 230 on the etching apparatus 200.

[0038] The total diameter D of the second end cap 220 SEC The diameter may range from approximately 120 mm to approximately 160 mm, or from approximately 130 mm to approximately 150 mm, or be approximately 140 mm. Therefore, the first and second end caps 210, 220 may have the same overall diameter. In addition, the second end cap 220 may range from approximately 40 mm to approximately 60 mm, or from approximately 45 mm to approximately 55 mm, or have a height H of approximately 50 mm. SEC (From the first surface 221 to the second surface 223) may be present. Therefore, the second end cap 220 has a height H of the first end cap 210. FEC Larger height H SEC They may have it.

[0039] The second end cap 220 may also include a projection 225 that extends radially outward from the first surface 221. Figure 5D shows an enlarged view of area D in Figure 5C, where the projection 225 is shown. The projection 225 may extend from the first surface 221 for a length of approximately 0.5 mm to approximately 1.5 mm, or approximately 0.75 mm to approximately 1.25 mm, or approximately 1 mm. Therefore, the height of the second end cap is the length (H) from the second surface 223 to the projection 225. SEC This is the length of the sleeve 100 plus the length of the projection 225. As shown in Figure 5D, the projection 225 frames the central opening 222. A gasket 240 may be positioned around the projection 225 to securely fasten the sleeve 100 to the second end cap 220. Figure 5A shows the gasket 240 securely fastened to the first surface 221 of the second end cap 220. The projection 225 helps to maintain the gasket 240 securely fastened on the first surface 221. In some embodiments, the projection 225 forms a press fit with the gasket 240. Although not shown in Figure 4A, a gasket 240 may also be attached to the first surface 211 of the first end cap 210 in the same manner as described with respect to the end cap 220.

[0040] Figure 6 shows a gasket 240 that provides a joint between the sleeve 100 and the first end cap 210. The gasket 240 is positioned between the first end cap 210 and the sleeve 100 when the sleeve 100 is fixed to the etching apparatus 200. Thus, the gasket 240 provides a clearance such that the first end cap 210 does not come into direct contact with the sleeve 100. This is advantageous in preventing the first end cap 210 from applying pressure to the sleeve 100. As shown in Figure 6, the gasket 240 overlaps the sleeve 100 in the radial width direction of the sleeve 100 for a length of about 1 mm or less, or about 0.5 mm or less, or about 0.25 mm or less. Although the gasket 240 is disclosed herein with respect to the first end cap 210 with respect to Figure 6, the gasket 240 functions similarly for the second end cap 220.

[0041] Referring again to Figure 3, the rod 230 is firmly secured to the first and second end caps 210, 220 by extending inward within the outer openings 214, 224. Therefore, when the etching apparatus 200 is assembled, the rod 230 extends inward within the openings 214, 224 so as to protrude outward from both the first and second surfaces 211, 213 of the first end cap 210 and from both the first and second surfaces 221, 223 of the second end cap 220. To maintain each rod 230 in place on the etching apparatus 200, nuts 232 may be tightened around the protruding end of each rod 230. Furthermore, recesses 227 on the second end cap 220 provide further means for firmly securing the nuts 232 to the rod 230. More specifically, the recesses 227 may reduce any relative displacement between the rod 230 and the end caps 210, 220. Note that the sleeve 100 should also be positioned so that the first and second end caps 210 and 220 are not too close to each other.

[0042] In an alternative embodiment, the second end cap 220 does not use a nut 232 to securely fasten the rod 230 to its end cap. Instead, in this embodiment, the rod 230 is welded to the second end cap 220. Thus, the rod 230 and the second end cap 220 form a single integrated component. In another embodiment, the first and second end caps 210, 220 are held and securely fastened on the rod solely by friction.

[0043] When the etching apparatus 200 is assembled and attached to the sleeve 100, the rods 230 are spaced radially away from the sleeve 100. For example, the rods 230 are spaced approximately 15 mm from the outer diameter of the sleeve 100. In addition, the rods 230 may be spaced radially away from adjacent rods, as shown in Figure 3. The distance between each rod 230 may be approximately 36 mm.

[0044] As also shown in Figure 3, the etching apparatus 200 further comprises a fastener 250, which may form a U-shaped member for suspension from a hook. The fastener 250 is used to suspend the etching apparatus 200 from a hook in the etching tank. The fastener 250 may also have other shapes and structures than those shown in Figure 3.

[0045] Once the sleeve 100 is installed in the etching apparatus 200 and the apparatus is placed in the etching tank, the sleeve 100 is exposed to an acidic solution and etched. In some embodiments, the acidic solution contains hydrofluoric acid (HF), which may be diluted with deionized water. In addition to or instead, the acidic solution contains nitric acid (HNO3) or sulfuric acid (H2SO4). Exemplary acidic solutions include (i) 10 vol% hydrofluoric acid and 15 vol% nitric acid, (ii) 5 vol% hydrofluoric acid and 7.5 vol% nitric acid, or (iii) 2.5 vol% hydrofluoric acid and 3.75 vol% nitric acid.

[0046] In some embodiments, a surfactant is added to an acidic solution. The surfactant can be any suitable surfactant that dissolves in the acidic solution and does not react with the acid in the acidic solution. For example, the surfactant may be a fluorinated surfactant such as Capstone® FS-50 or "Capstone" FS-54. The concentration of the surfactant in the acidic solution (in mL of surfactant per L of acidic solution) may be about 1, about 1.1, about 1.2, about 1.3, about 1.4, about 1.5, about 1.6, about 1.7, about 1.8, about 1.9, or about 2 or more.

[0047] The sleeve 100 may be exposed to an acidic solution for a total time of approximately 10 hours to approximately 5 minutes, or approximately 15 minutes to approximately 30 minutes (i.e., the total etching time). When the sleeve 100 is exposed to the acidic solution, the solution may be at a temperature of approximately 25°C to approximately 35°C. In some embodiments, the acidic solution is ultrasonically agitated while the sleeve 100 is exposed to the acidic solution.

[0048] During the selective etching process, when the sleeve 100 is attached to the etching apparatus 200 and exposed to the acidic solution, the acidic solution can come into contact with only specific portions of the sleeve 100. More specifically, referring to the first end cap 210, the acidic solution flows through the central opening 212 and can come into contact with a portion of the upper surface 102 of the sleeve. This portion is smaller than the entire upper surface 102. Furthermore, as previously mentioned, the central opening 212 of the first end cap 210 has a diameter smaller than the diameter Ds of the sleeve 100. Therefore, at least a portion of the upper surface 102 of the sleeve 100 is covered by the first end cap 210. More specifically, as shown in Figure 7, the radially outer portion of the upper surface 102 is covered by the first end cap 210 during the etching process. Therefore, the acidic solution does not come into contact with this radially outer portion of the sleeve 100 during the etching process, and thus this radially outer portion is not etched by the acidic solution during the etching process. Only the central portion of the upper surface 102 (the portion of the upper surface 102 exposed by the central opening 212) is etched during the etching process. As also shown in Figure 7, this results in the formation of a recess 120 surrounded by a raised edge 130 on the upper surface 102 after the etching process. The central portion of the upper surface 102 (the portion of the upper surface 102 exposed by the central opening 212) forms the recess 120 after the etching process, and the radially outer portion of the upper surface 102 (the portion covered by the first end cap 210) forms the raised edge 130 after the etching process.

[0049] Furthermore, the selective etching process described above is also applied to the second end cap 220. During the etching process, the acidic solution flows through the central opening 222 of the second end cap 220 and comes into contact with a portion of the bottom surface 104 of the sleeve. This portion is smaller than the entire bottom surface 104. The central opening 222 of the second end cap 220, like the first end cap 210, has a diameter smaller than the diameter Ds of the sleeve 100. Therefore, at least a portion of the bottom surface 104 of the sleeve 100 is covered by the second end cap 220. The radially outer portion of the bottom surface 104 is covered by the second end cap 220. Therefore, the acidic solution does not come into contact with the radially outer portion of the sleeve 100 during the etching process, and thus this radially outer portion is not etched by the acidic solution during the etching process. Therefore, only the central portion of the bottom surface 104 (the portion of the bottom surface 104 exposed by the central opening 222) is etched during the etching process. As a result, after the etching process, a recess 120 surrounded by a raised edge 130 is formed on the bottom surface (similar to what was previously described with respect to the first end cap 210).

[0050] Therefore, the etching process described above exposes the top surface 102 (first surface) of the sleeve 100 to the acidic solution such that the first portion of the top surface 102 is exposed to the acidic solution, while the second portion of the top surface 102 is not. Similarly, the etching process described above exposes the bottom surface 104 (second surface) of the sleeve 100 to the acidic solution such that the first portion of the bottom surface 104 is exposed to the acidic solution, while the second portion of the bottom surface 104 is not. Note that in Figure 7, the first end cap 210 is shown partially cut off for clarity.

[0051] The shape and dimensions of the recess 120 depend on the etching time of the acidic solution. In some embodiments, the recess 120 (on the upper surface 102 and / or bottom surface 104 of the sleeve 100) has a maximum depth of about 20 micrometers or more, or about 40 micrometers or more, or about 60 micrometers or more, or about 80 micrometers or more, or about 100 micrometers or more. In addition, or alternatively, the recess 120 has a maximum depth of about 10 mm or less, or about 7 mm or less, or about 5 mm or less, or about 4 mm or less, or about 3 mm or less, or about 2 mm or less, or about 1 mm or less. In some embodiments, the maximum depth of the recess 120 is in the range of about 40 micrometers to about 5 mm, or about 6 micrometers to about 4 mm.

[0052] Furthermore, the recess 120 has a diameter in the range of approximately 30 mm to approximately 60 mm, or approximately 40 mm to approximately 50 mm, or approximately 42 mm to approximately 48 mm. In some embodiments, the diameter of the recess 120 is the same as the diameter of the opening 212 and / or opening 222. Thus, the raised edge 130 has a length in the width direction of the sleeve 100 in the range of approximately 2.5 mm to approximately 10 mm, or approximately 3 mm to approximately 5 mm. In some embodiments, as shown in Figure 8, the recess 120 (above the top surface 102 and / or bottom surface 104 of the sleeve 100) has a concave shape. As will be further described below, this concave shape provides advantages during the vacuum sealing process. The concave shape may be, for example, spherical or elliptical. Figures 7 and 8 show the recess 120 having a circular cross-sectional shape, but the recess 120 may also have other cross-sectional shapes, such as square or rectangular.

[0053] As previously mentioned, the raised edge 130 was not etched during the selective etching process. Therefore, the raised edge 130 forms the polished surface of the upper surface 102 and / or bottom surface 104 of the sleeve 100.

[0054] During the selective etching process 20 of process 1, the sleeve 100 is selectively etched to create recesses 120. In addition, the selective etching process conveniently provides acid cleaning to remove contaminants from the sleeve 100 and polish the surface of the sleeve 100. Therefore, separate acid cleaning and polishing steps are not required. Instead, with respect to the process disclosed herein, the selective etching process combines these steps into a single step. Note that a longer etching time (as described above) may be used when only the top surface 102 and bottom surface 104 are etched, compared to when the entire sleeve 100 is etched (except for the portion of the sleeve 100 covered by the first and second end caps 210, 220).

[0055] As shown in Figure 9, the assembled preform assembly 300 includes a handle 310, a sleeve 100, and a nose cone 320, each formed from glass. These components are sealed together during a vacuum sealing process, as will be further described below. The selective etching process described earlier discloses that the top surface 102 and bottom surface 104 of the sleeve 100 are selectively etched to form recesses 120 and raised edges 130 on the sleeve 100. However, in alternative embodiments, the bottom surface of the handle 310 and the top surface of the nose cone 320 are selectively etched. In these embodiments, the sleeve 100 is not selectively etched. Therefore, the recesses and raised edges are formed on the handle 310 and the nose cone 320, rather than on the sleeve 100. In some embodiments, the recesses formed on the handle 310 and / or the nose cone 320 have a concave shape (as previously described). In these embodiments, where the handle 310 and nose cone 320 are etched, longer etching times may be used, for example, about 10 hours. In additional embodiments, it is conceivable that only one of the handle 310 and nose cone 320 is selectively etched. Thus, in this embodiment, either the upper surface 102 or the lower surface 104 of the sleeve 100 is also etched.

[0056] Referring again to FIG. 1, after completion of the selective etching process, in step 30 of process 1, a cane core is inserted into the hole 110 of the sleeve 100. FIG. 10A shows a cane 140 operably disposed relative to the hole 110 of the sleeve 100 during the process of forming a cane-clad assembly 150. FIG. 10B shows an exemplary assembled cane-clad assembly 150, and FIG. 10C shows a cross-sectional view of one cane 140. Each cane 140 is formed from a glass body that includes a core section 142 and an inner clad section 144 surrounding the core section 142. Further, the inner clad section 144 may include one or more inner clad portions having different refractive indices. In some embodiments, it is also contemplated that the glass body of the cane 140 consists only of the core section 140 (does not include a clad section). When the cane-clad assembly 150 is formed into a preform and then drawn into an optical fiber, the sleeve 100 surrounds each cane 140. Therefore, the sleeve 100 forms an outer clad section in the drawn optical fiber.

[0057] FIG. 10D is a cross-sectional view of the cane-clad assembly 150 of FIG. 10B. As shown in FIG. 10D, in some embodiments, each cane 140 has a diameter D of the corresponding hole 110 into which the cane 140 is inserted H has a diameter D slightly smaller than CIt has a gap G between the cane 140 and the hole 110, thereby allowing the cane 140 to slide easily within the hole 110. More specifically, the gap G is provided between the outer surface of the cane 140 and the inner surface of the hole 110. In some embodiments, the gap G has a length of about 2 mm or less, or about 1.5 mm or less, or about 1 mm or less, or about 0.75 mm or less, or about 0.5 mm or less, or about 0.25 mm or less. In addition, or instead, the length of the gap G is about 0.1 mm or more, or about 0.2 mm or less, or about 0.4 mm or less, or about 0.6 mm or less, or about 0.8 mm or less, or about 1 mm or more. In some embodiments, the length of the gap G is in the range of about 0.1 mm to about 1 mm, or about 0.2 mm to about 0.8 mm. It should be further noted that the length of the gap G is a function of the size of the sleeve 100. Smaller diameter D S A smaller sleeve 100 having a smaller gap G length is required.

[0058] Next, in process 1 of Figure 1, the cane 140 is inserted into the sleeve 100 to form the cane-clad assembly 150, after which in process 40, a vacuum sealing and wire drawing process is performed. This vacuum sealing and wire drawing process is performed to manufacture a preform and to wire the preform into an optical fiber. First, the handle 310, the sleeve 100 (with the cane 140 inserted inside), and the nose cone 320 are assembled into a laminated structure. When the laminated structure is formed, the handle 310 is positioned vertically on the sleeve 100, and the sleeve 100 is positioned vertically on the nose cone 320. In some embodiments, the laminated structure may include multiple sleeves. Figure 11 shows an exemplary laminated structure in which four sleeves 100 are positioned between the handle 310 and the nose cone 320. In this embodiment, each of the canes 140 is positioned through all four sleeves 100. Therefore, all four sleeves share the same cane 140. As shown in Figure 11, in the laminated structure, the handle 310 is in direct contact with the uppermost sleeve 100, and each sleeve 100 is in direct contact with the adjacent sleeve 100. Furthermore, the lowermost sleeve 100 is in direct contact with the nose cone 320. The handle 310, sleeves 100, and nose cone 320 may be cleaned (for example, by acid cleaning and then rinsing with deionized water) before being assembled into the laminated structure.

[0059] As also shown in Figure 11, this laminated structure is connected to a vacuum system 400, and thus the laminated structure and the vacuum system 400 together constitute a preform system 500. The vacuum system 400 further comprises conduits 410 that support the laminated structure and provides an airflow connection between the vacuum system 400 and the laminated structure. As will be further described below, the vacuum system 400 uses air pressure to seal the handle 310, sleeve 100, and nose cone 320 together when the laminated structure is in place.

[0060] Figure 12 shows a partial cross-sectional view of part A of the preform system 500 of Figure 11, showing that two sleeves 100 are in a laminated structure. The upper sleeve 100 is connected to the handle 310. Note that the nose cone 320 is not shown in this partial view. As shown in Figure 12, a first recess 120 on the bottom surface of the uppermost sleeve 100 is connected to a second recess 120 on the top surface of the adjacent sleeve 100. Furthermore, all of the recesses 120 of the multiple sleeves 100 are connected, along with the space formed by the gap G (between the sleeve 100 and the cane 140), and are connected to a passage through the conduit 410, forming a continuous internal passage 420. This passage 420 is substantially sealed for contact between the handle 310, the sleeves 100, and the sufficiently smooth glass surfaces of the nose cone 320. Although not shown in Figure 12, the passage 420 extends through the entire laminated structure to the nose cone 320. Furthermore, the passage 420 is connected to the vacuum system 400 to provide an air passage.

[0061] When the vacuum system 400 is activated, it draws air into the vacuum system 400 from the passage 420, as shown by the airflow line B in Figure 12. Since the passage 420 is substantially sealed, the vacuum suction creates a considerable pressure difference ΔP between the passage 420 and the ambient environment 430 surrounding the preform system 500. This pressure difference ΔP compresses and seals the handle 310, sleeve 100, and nose cone 320 together when they are oriented vertically in a laminated structure. Thus, these components are compressed and seal each other against gravity. In one example, the pressure difference ΔP between the vacuum system 400 and the normal ambient pressure at sea level provides an axial compressive force of 98.5 kg to a typical assembly where the sleeve 100 has a diameter Ds of 122 mm and the passage has a maximum diameter of 112 mm. In other embodiments, the pressure difference ΔP may be approximately 100 kg, and the exact value depends on the mass of the various components of the preform system 500 and the size of the various sections of the passage 420, as will be obvious to those skilled in the art.

[0062] The vacuum suction of the vacuum system 400 forms a cane-clad assembly 150 that is held together in vacuum ("vacuum-held"). Thus, the handle 310, sleeve 100, and nose cone 320 are compressed and sealed together, eliminating the passage 420. When the handle 310, sleeve 100, and nose cone 320 are compressed and sealed together, the recess 120 (if it has the concave shape in Figure 8) deforms by sealing the glass parts first in the radially outer portion of the recess 120, before the central portion of the recess 120. Thus, the sealing of the glass parts (handle 310, sleeve 100, and / or nose cone 320) begins in the radially outer portion of the recess 120 and then moves radially inward until the glass parts are sealed together. This results in a stronger bond between the glass parts than would be possible if a non-concave recess 120 were used. In contrast, when using a non-concave recess 120, the glass components are sealed to each other simultaneously in the radially outer portion and the central portion of the recess.

[0063] It should also be noted that in some embodiments, the recess 120 is formed in the handle 310 and / or nose cone 320, rather than in the sleeve 100, as previously described with respect to Figure 9. In these embodiments, as previously described with respect to Figure 12, the passage 420 is formed by the recess 120 in the handle 310 and / or nose cone, and these parts are sealed to each other.

[0064] In conventional sealing and drawing processes, the cane-clad assembly is first vacuum-sealed and then solidified in a solidification furnace at a temperature of approximately 1100°C and in a chlorine atmosphere. This solidification process bonds the glass components of the cane-clad assembly together. After the solidification process, the assembly is annealed at a temperature of approximately 1400°C to 1500°C. After the annealing process is complete, the assembly is now a preform, which is moved from the solidification furnace to a drawing tower furnace for drawing the preform into optical fibers. Thus, in the conventional process, the preform assembly is first vacuum-sealed before being moved to a drawing tower furnace for drawing the optical fibers. Embodiments of the present disclosure combine these two processes by simultaneously vacuum-sealing the assembly during the drawing process. Furthermore, embodiments of the present disclosure do not have separate solidification and annealing processes as in the conventional process. Thus, embodiments of the present disclosure reduce the total number of processes, thereby shortening the time and saving costs. Furthermore, in conventional processes, the glass assembly must be cooled and relaxed between processes (such as the annealing and drawing processes). Each cooling process introduces the possibility of breakage due to inherent stresses resulting from the uneven heating and cooling of the large glass pieces. Embodiments of the present disclosure reduce the total number of processes and thus reduce such possibilities of inherent stresses in the glass. Moreover, embodiments of the present disclosure do not require moving the preform from the solidification furnace to the drawing tower furnace (during which the preform may be scratched or chipped). And embodiments of the present disclosure do not require two separate solidification furnaces and drawing tower furnaces.

[0065] As previously stated, embodiments of the present disclosure perform the vacuum sealing process and the wire drawing process simultaneously. Therefore, during the vacuum sealing process described above, the cane-clad assembly 150 is placed in a wire drawing tower furnace 520, which is heated by a lower heater 510. As shown in Figure 11, the lower heater 510 creates a high-temperature zone 515 within the furnace having a temperature in the range of about 1500°C or higher, or about 1600°C or higher, or about 1700°C or higher, or about 1800°C or higher, or about 1900°C or higher, or about 2000°C or higher. In some embodiments, the temperature of the high-temperature zone 515 is in the range of about 1600°C to about 2200°C, or about 1800°C to about 2100°C. The temperature of the high-temperature zone 515 is sufficient to solidify the cane-clad assembly 150 (bond the glass components together) and to heat the cane-clad assembly 150 to its glass melting temperature (for the wire drawing process). Please note that the temperature in high-temperature zone 515 is higher than that of conventional solidification furnaces, as mentioned earlier.

[0066] When the cane-clad assembly 150 is placed in the furnace 520, it slowly descends toward the lower heater 510 as the cane-clad assembly 150 is consumed and drawn into the optical fiber. Furthermore, the previously disclosed vacuum sealing process is performed simultaneously with the slow processing of the cane-clad assembly 150 toward the lower heater 510. Thus, vacuum suction from the vacuum system 400 is performed while the cane-clad assembly 150 is consumed and drawn into the optical fiber. The furnace 520 may contain one or more inert gases in addition to the cane-clad assembly 150.

[0067] Figure 13 shows a drawing system 600 for drawing optical fibers according to an embodiment disclosed herein. The exemplary drawing system 600 comprises a furnace 520 as previously described. Furthermore, the drawing system 600 comprises non-contact measuring sensors 610, 615 for measuring (e.g., diameter control) the size of the drawn (bare) fiber 620 coming out of the furnace 520. A cooling station 630 is located downstream of the measuring sensors 610, 615 and is configured to cool the bare fiber 620. A coating station 640 is located downstream of the cooling station 630 and is configured to deposit protective coating material 645 onto the bare fiber 620 to form a coated fiber 625. A tensioner 650 is located downstream of the coating station 640. The tensioner 650 has a surface 655 for pulling (drawing) the coated fiber 625. A pair of guide wheels 660, each having a surface 665, are located downstream of the tensioner 650. The guide wheels 660 guide the coated fiber 625 to the fiber winding spool ("spool") 670, thereby storing the coated fiber 625. Embodiments of the present disclosure can be used to form single-core or multi-core optical fibers.

[0068] While various embodiments have been described herein, these embodiments are presented only as examples and not as limitations. Based on the teachings and guidance presented herein, it should be apparent that adaptations and modifications are intended to be within the meaning and scope of the equivalents of the disclosed embodiments. Accordingly, it will be apparent to those skilled in the art that various changes in form and detail can be made to the embodiments disclosed herein without departing from the spirit and scope of this disclosure. The elements of the embodiments presented herein are not necessarily mutually exclusive and may be substituted to meet various needs, as will be recognized to those skilled in the art.

[0069] It should be understood that the expressions and terminology used herein are for illustrative purposes only, not limitations. The breadth and scope of this disclosure should not be limited by any of the exemplary embodiments described herein, but should be defined solely in accordance with the following claims and their equivalents.

[0070] Preferred embodiments of the present invention are described below in separate sections.

[0071] Embodiment 1 In a method for manufacturing optical fibers, A step of installing a glass sleeve inside a selective etching apparatus, The sleeve is provided with one or more axial through holes, The etching apparatus includes a first end cap through which a central opening is positioned, and the first end cap is attached to the first surface of the sleeve, and the process is as follows: A step of exposing the sleeve to an acidic solution such that a first portion of the first surface is exposed to the acidic solution, but a second portion of the first surface is not exposed to the acidic solution, The first portion is adjacent to the central opening when the sleeve is installed in the selective etching apparatus, The second part is covered by the first end cap when the sleeve is installed in the selective etching apparatus, A method comprising [a certain characteristic].

[0072] Embodiment 2 The method according to Embodiment 1, wherein a recess is formed in the first portion of the sleeve by the step of exposing the sleeve to the acidic solution.

[0073] Embodiment 3 The method according to Embodiment 2, wherein the recess is surrounded by a raised edge of the sleeve 100, and the raised edge is the second portion of the sleeve.

[0074] Embodiment 4 The method according to embodiment 2 or 3, further comprising the step of inserting a glass cane core into each of the one or more axial through holes.

[0075] Embodiment 5 The method according to Embodiment 4, wherein there is a gap of approximately 1 mm in diameter or less between the cane core and the axial through hole.

[0076] Embodiment 6 The method according to Embodiment 4, further comprising the step of attaching the sleeve, through which the cane core is inserted, to a glass handle and a glass nose cone to form an assembly.

[0077] Embodiment 7 The method according to embodiment 6, wherein the assembly includes an internal passage formed by the recess.

[0078] Embodiment 8 The method according to embodiment 7, further comprising the step of subjecting the assembly to a vacuum sealing process in which a vacuum system generates vacuum suction in the passage.

[0079] Embodiment 9 The method according to embodiment 8, wherein the vacuum sealing process is performed inside a wire drawing tower furnace.

[0080] Embodiment 10 The method according to Embodiment 8, further comprising the step of drawing optical fibers from the assembly while the assembly is undergoing the vacuum sealing process.

[0081] Embodiment 11 The method according to any one of embodiments 2 to 10, wherein the recess is a concave depression.

[0082] Embodiment 12 The method according to any one of embodiments 2 to 11, wherein the recess has a depth of approximately 40 micrometers or more.

[0083] Embodiment 13 The method according to any one of embodiments 2 to 12, wherein the recess has a depth of approximately 10 mm or less.

[0084] Embodiment 14 The method according to any one of embodiments 2 to 11, wherein the recess has a depth ranging from about 40 micrometers to about 5 mm.

[0085] Embodiment 15 The method according to any one of embodiments 2 to 14, further comprising the step of forming a second recess on the second surface of the sleeve.

[0086] Embodiment 16 The method according to any one of Embodiments 1 to 15, wherein the acidic solution contains hydrofluoric acid.

[0087] Embodiment 17 In a method for manufacturing optical fibers, A step of forming a concave recess on the first surface of a glass sleeve, wherein the concave recess is surrounded by a raised edge of the sleeve, and the sleeve has one or more axial through holes, The steps include inserting a glass cane core into each of the axial through holes, and A step of forming an assembly by vacuum sealing the sleeve with one or more additional glass components, A method comprising [a certain characteristic].

[0088] Embodiment 18 The method according to embodiment 17, further comprising the steps of vacuum sealing the sleeve to form the assembly and simultaneously drawing the assembly to form an optical fiber.

[0089] Embodiment 19 The method according to embodiment 17 or 18, further comprising the step of vacuum sealing the sleeve in a wire drawing tower furnace.

[0090] Embodiment 20 The method according to any one of embodiments 17 to 19, wherein the recess has a depth of approximately 40 micrometers or more.

[0091] Embodiment 21 The method according to any one of embodiments 17 to 20, wherein the recess has a depth of approximately 10 mm or less.

[0092] Embodiment 22 The method according to any one of embodiments 17 to 19, wherein the recess has a depth ranging from about 40 micrometers to about 5 mm.

[0093] Embodiment 23 The method according to any one of embodiments 17 to 22, further comprising the step of forming a second concave recess on the second surface of the sleeve.

[0094] Embodiment 24 The method according to any one of embodiments 17 to 23, wherein there is a gap of approximately 1 mm or less in diameter between the cane core and the axial through hole.

[0095] Embodiment 25 In a method for manufacturing optical fibers, A process of forming an optical fiber by inserting a glass cane core into an axial through-hole in a glass sleeve, simultaneously vacuum sealing the sleeve with one or more additional glass components to form an assembly, and then drawing the assembly. A method comprising [a certain characteristic].

[0096] Embodiment 26 The method according to embodiment 25, further comprising the step of vacuum sealing the sleeve in a wire drawing tower furnace.

[0097] Embodiment 27 The method according to embodiment 25 or 26, wherein the assembly includes the sleeve, glass handle, and glass nose cone.

[0098] Embodiment 28 The method according to Embodiment 27, wherein the assembly comprises an internal passage, and the vacuum sealing step generates vacuum suction through the internal passage.

[0099] Embodiment 29 The method according to embodiment 28, wherein the internal passage forms an internal connection between the sleeve, the handle, and the nose cone. [Explanation of symbols]

[0100] 100 sleeves 102 Top surface 104 Bottom 110 holes 120 recess 130 Raised edge 140 canes 142 Core Section 144 Inner clad section 150 Cane Clad Assembly 200 Etching equipment 210 First end cap 211 First surface of the first end cap 212 Center opening of the first end cap 213 Second side of the first end cap 214 Outer opening of the first end cap 215 Projection of the first end cap 220 Second end cap 221 First surface of the second end cap 222 Center opening of the second end cap 223 Second side of the second end cap 224 Outer opening of the second end cap 225 Protrusion of the second end cap 227 Depression 230 Multiple rods 232 nuts 250 fasteners 300 assembled preform assemblies 310 Handle 320 Nose Cone 400 Vacuum System 410 Conduit 420 Internal passage 430 Surrounding Environment 500 Preform System 510 Lower heater 515 High temperature area 520 Line-drawing tower furnace 600 Line Drawing System 610, 615 Non-contact measuring sensors 620 Exposed fiber 625 coated fiber 630 Cooling Station 640 Covering Station 650 Tensioner 660 Guide Wheel 670 Fiber Winding Spool

Claims

1. In a method for manufacturing optical fibers, A step of installing a glass sleeve inside a selective etching apparatus, The sleeve is provided with one or more axial through holes, The etching apparatus includes a first end cap with a central opening positioned through it, the first end cap being attached to the first surface of the sleeve, and the process is as follows: A step of exposing the sleeve to an acidic solution such that a first portion of the first surface is exposed to the acidic solution, but a second portion of the first surface is not exposed to the acidic solution, The first portion is adjacent to the central opening when the sleeve is installed in the selective etching apparatus. The second part is covered by the first end cap when the sleeve is installed in the selective etching apparatus, A method comprising [a certain characteristic].

2. The method according to claim 1, wherein a recess is formed in the first portion of the sleeve by the step of exposing the sleeve to the acidic solution.

3. The method according to claim 2, wherein the recess is surrounded by a raised edge of the sleeve, and the raised edge is the second portion of the sleeve.

4. The method according to claim 2, further comprising the step of inserting a glass cane core into each of the one or more axial through holes.

5. The method according to claim 4, wherein there is a gap of 1 mm or less in diameter between the cane core and the axial through hole.

6. The method according to claim 4, further comprising the step of attaching the sleeve, through which the cane core is inserted, to a glass handle and a glass nose cone to form an assembly.

7. The method according to claim 6, wherein the assembly includes an internal passage formed by the recess.

8. The method according to claim 7, further comprising the step of subjecting the assembly to a vacuum sealing process in which a vacuum system generates vacuum suction in the passage.

9. The method according to claim 8, wherein the vacuum sealing process is carried out in a wire drawing tower furnace.

10. The method according to claim 8, further comprising the step of drawing optical fibers from the assembly while the assembly is subjected to the vacuum sealing process.

11. The method according to any one of claims 2 to 10, wherein the recess is a concave depression.

12. The method according to any one of claims 2 to 10, wherein the recess has a depth in the range of 40 micrometers to 5 mm.

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