Vacuum-Based Method for Forming Cane-Based Glass Optical Fiber Preforms

Abstract

A vacuum-based method for forming an optical fiber preform includes applying a vacuum to a preform assembly. The preform assembly includes at least one glass cladding section having one or more axial through-holes and a cane residing within each of the one or more axial through-holes. Opposite ends of the at least one glass cladding section are capped to define a substantially sealed interior chamber. A vacuum is applied to the substantially sealed interior chamber to form a vacuum-held preform assembly. The method also includes heating the vacuum-held preform assembly to just above the glass softening point to coalesce the vacuum-held preforms to form a cane-based glass preform. The cane-based glass preform is pulled to form an optical fiber. The same furnace used to coalesce the vacuum-held preforms can be used to draw the optical fiber.

Description

Related Applications

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62 / 811,842, filed Feb. 28, 2019, the entire content of which is incorporated herein by reference.

Technical Field

[0002] The present disclosure relates to optical fibers, and in particular to a vacuum-based method for forming a cane (glass rod)-based optical fiber preform and a method for forming an optical fiber using the cane-based optical fiber preform.

Background Art

[0003] Multi-core fiber technology for spatial multiplexing transmission is considered for both long-distance communication and short-distance optical fiber interconnections used within data centers and high-performance computers. The connection of multi-core fibers requires very precise positioning of the individual cores, with a standard tolerance of a fraction of 1 micrometer. This important requirement affects the choice of materials and processes when forming an optical fiber preform.

[0004] Single-core fibers and multi-core fibers can be manufactured from glass preforms made using a process called the all-glass process in the art. The all-glass process utilizes bulk cladding glass having one or more precisely formed axial holes sized to accommodate canes that each form the core of an optical fiber formed from the preform and thus the glass preform.

[0005] The all-glass process is preferred over vapor deposition-based processes (e.g., outside vapor deposition (OVD) processes) that include soot (glass oxide particles) layer formation, soot compression and sooting, sintering, and consolidation to turn the soot into glass. The ability to precisely grind the outer surface of the cladding glass to a selected diameter and the ability to perform precision sooting of the cladding glass provide both precision and flexibility in selecting various spacings, shapes, and arrangements of one or more axial holes when forming the glass preform.

Summary of the Invention

Problems to be Solved by the Invention

[0006] Unfortunately, the all - glass process is relatively expensive and time - consuming. Precision drilling is time - consuming, and one or more canes need to be formed to have a selected refractive index profile and inserted into the cladding glass. The entire structure needs to be assembled in a furnace to form a solid glass preform. To make a glass preform of sufficient length, it may be necessary to join separate glass cladding portions along the axis, which requires precise alignment of the axial holes. The assembly process usually requires special fixtures to hold the glass cladding portions and the canes in the assembly furnace, and then removing the resulting solid glass preform from the furnace, lowering the glass preform from the fixture, and then movably supporting it in the drawing furnace of the drawing system to make an optical fiber.

Means for Solving the Problems

[0007] Aspects of the methods disclosed herein are directed to forming a cane - based glass preform and using the cane - based glass preform to draw an optical fiber. These methods can be used to form a single - core cane - based glass preform or a multi - core cane - based glass preform. The method uses one or more glass cladding portions, each glass cladding portion having an upper end with a recess defined by an outer peripheral lip and one or more precision axial holes formed therein. When multiple glass cladding portions are used, these cladding portions are stacked such that the axial holes are aligned. Next, a cane is inserted into the one or more axial holes to form a cane - cladding assembly.

[0008] Attach an upper lid and a bottom lid to the upper and lower ends of the cane clad assembly respectively to form a preform assembly. The upper lid closes the recess at the upper end of the glass clad portion. The bottom lid may have a raised lip and a recess that closes when the bottom lid is aligned with the lower end of the cane clad assembly. The closed recess and the gap formed by the cane in the shaft hole define an internal chamber that is substantially sealed. By drawing a selected cleaning gas (e.g., chlorine) through a small passage in the bottom lid that leads to the internal chamber, the preform assembly can be dried and purified. Apply a vacuum through the upper lid to create a pressure difference between the internal chamber and the surrounding environment. The pressure difference holds the components of the preform assembly together. This is referred to as the preform assembly held by vacuum in this document. The preform assembly held by vacuum constitutes a preform assembly product formed using the method disclosed in this document.

[0009] When the preform assembly held by vacuum is heated in a furnace to just above the glass softening point to be combined, the glass clad portion, the cane, the upper lid, and the bottom lid (all made of glass) seal to each other. Also, the flow of the glass eliminates the internal chamber. As a result, a solid glass preform that can be immediately pulled (especially when the furnace used for combination is a wire drawing furnace used for drawing optical fibers) is obtained. The cane-based preform constitutes a preform product formed using the method disclosed in this document.

[0010] An embodiment of the present disclosure is a method of forming a cane-based preform. This method includes the step of applying a vacuum to a preform assembly, wherein the preform assembly includes at least one glass clad portion having one or more shaft holes, an upper end, a lower end, and a cane present in each of the one or more shaft holes, and the upper end and the lower end are covered so as to define a substantially sealed internal chamber; and the step of heating the preform assembly held by vacuum to just above the glass softening point to combine the preform held by vacuum to form a cane-based glass preform.

[0011] Another embodiment of the present disclosure is a method of forming a cane-based glass preform. The method includes forming one or more axial holes in each of a plurality of glass cladding portions each having a body, an upper end, a bottom end, and an outer periphery, wherein each upper end has a lip extending around the outer periphery and defining an upper recess and each axial hole is defined by a cylindrical inner surface within the body; stacking the plurality of glass cladding portions such that the axial holes formed within each glass cladding portion are aligned along an axis, the stacked plurality of glass cladding portions having an overall stacked length LS, a topmost glass cladding portion, and a bottommost glass cladding portion; inserting one or more glass canes into the one or more aligned axial holes of the plurality of glass cladding portions, such that there is a gap between each glass cane and the cylindrical inner surface of the axial hole in which the glass cane is located; aligning a glass top cover with the upper end of the topmost glass cladding portion and aligning a glass bottom cover with the bottom end of the bottommost glass cladding portion to define a preform assembly having a substantially sealed internal chamber, the internal chamber including the upper recess and the gap; applying a vacuum through the glass top cover to the substantially sealed internal chamber to create a pressure differential with respect to the ambient environment, the pressure differential holding the preform assembly together to form a preform assembly held in vacuum; and heating the preform assembly held in vacuum to just above the glass softening point to fuse the preform assembly held in vacuum to form a glass preform.

[0012] Another embodiment of the present disclosure is a method of forming a cane-based glass preform assembly. The method includes the steps of forming one or more axial holes in at least one glass cladding portion, wherein the at least one glass cladding portion has an upper end and a bottom end; inserting one or more canes into the one or more axial holes, such that each axial hole contains one cane; forming a preform assembly having a lid on the upper end and the bottom end and having a substantially sealed internal chamber, wherein the internal chamber is in air communication connection with the upper end and the bottom end through the axial holes; and applying a vacuum to the substantially sealed internal chamber to create a pressure difference between the substantially sealed internal chamber and the surrounding environment to form a preform assembly held in vacuum.

[0013] Another embodiment of the present disclosure is a method of forming a cane-based glass preform assembly for forming a multi-core optical fiber. The method includes the steps of stacking a plurality of glass cane portions each having a plurality of axial holes such that the axial holes are aligned, wherein adjacent glass cane portions contact each other with a raised lip that forms an internal cavity, and wherein there is a top glass cane portion and a bottom glass cane portion; inserting one cane into each of the aligned axial holes to define a gap within the axial holes, wherein the gap provides air communication between the internal cavities; forming a preform assembly having a lid on the top and bottom glass cane portions and having a substantially sealed internal chamber, wherein the internal chamber includes the internal cavities and the gap; and applying a vacuum to the substantially sealed internal cavity to form a preform assembly held in vacuum.

[0014] Another embodiment of the present disclosure is a cane-based preform. The process of forming this preform includes applying a vacuum to a preform assembly, the preform assembly comprising at least one glass clad portion having one or more axial holes, an upper end, a bottom end, and canes present within each of the one or more axial holes, with an upper lid attached to the upper end and a bottom lid attached to the bottom end; and heating the preform assembly held in vacuum to just above the glass softening point to fuse the preform held in vacuum to form a cane-based glass preform.

[0015] Another embodiment of the present disclosure is a cane-based glass preform product. The process of forming this preform product includes the steps of forming one or more axial holes in each of a plurality of glass clad portions, each having a body, an upper end, a bottom end, and an outer periphery, wherein each upper end has a lip extending around the outer periphery and defining an upper recess, and each axial hole is defined by a cylindrical inner surface within the body; stacking the plurality of glass clad portions such that the axial holes formed within each glass clad portion are aligned along an axis, the stacked plurality of glass clad portions having an overall stacked length LS, a topmost glass clad portion, and a bottommost glass clad portion; inserting one or more glass canes into the one or more aligned axial holes of the plurality of glass clad portions, such that there is a gap between each glass cane and the cylindrical inner surface of the axial hole in which the glass cane is located; aligning a glass top cover with the upper end of the topmost glass clad portion and a glass bottom cover with the bottom end of the bottommost glass clad portion to define a preform assembly having a substantially sealed internal chamber, the internal chamber including the upper recess and the gap; applying a vacuum through the glass top cover to the substantially sealed internal chamber to create a pressure differential with respect to the ambient environment, the pressure differential holding the preform assembly together to form a preform assembly held in vacuum; heating the preform assembly held in vacuum to just above the glass softening point to fuse the preform assembly held in vacuum to form a glass preform; including.

[0016] Another embodiment of the present disclosure is a cane-based glass preform assembly product. The process of forming this assembly product includes a step of forming one or more axial holes in at least one glass cladding portion, wherein the at least one glass cladding portion has an upper end and a bottom end; a step of inserting one or more canes into the one or more axial holes respectively, so that each axial hole contains one cane; a step of forming a preform assembly having an internal chamber that is substantially sealed by covering the upper end and the bottom end, wherein the internal chamber is in air communication connection with the upper end and the bottom end through the axial holes; and a step of applying a vacuum to the substantially sealed internal chamber to generate a pressure difference between the substantially sealed internal chamber and the surrounding environment to form a preform assembly held in a vacuum.

[0017] Another embodiment of the present disclosure is a cane-based glass preform assembly product for forming a multi-core optical fiber. The process of forming this assembly product includes a step of stacking a plurality of glass cane portions each having a plurality of axial holes so that the axial holes are aligned, wherein adjacent glass cane portions contact each other with a raised lip that forms an internal cavity, and there are a top glass cane portion and a bottom glass cane portion; a step of inserting one cane into each of the aligned axial holes to define a gap within the axial holes, wherein the gap provides air communication between the internal cavities; a step of forming a preform assembly having an internal chamber that is substantially sealed by covering the top and bottom glass cane portions, wherein the internal chamber includes the internal cavities and the gaps; and a step of applying a vacuum to the substantially sealed internal cavity to form a preform assembly held in a vacuum.

[0018] The method disclosed in this book provides a solid and cost-effective process for manufacturing precision single-core or multi-core preforms. Drilling provides precision and robustness. Sealing of glass cladding portions aligned and stacked along an axis allows the use of short and thick precision-drilled glass cladding portions. The use of a substantially sealed internal chamber and the application of a vacuum to hold the preform assembly eliminate the need for special fixtures to hold the preform assembly while mating. The sealing of the various glass components of the vacuum-held preform assembly is achieved simultaneously in all directions, eliminating the need to seal in one direction (e.g., vertically) and then in another direction (e.g., horizontally). The use of a temperature just above the glass softening point (and thus well below the glass melting point) allows the surfaces of the various glass components to be finished by fine grinding rather than polishing. However, polishing can of course be used.

[0019] Additional features and advantages are described in the following detailed description, will be apparent to those skilled in the art from that description, or will be recognized by practicing the embodiments described in the following description, claims, and accompanying drawings. It is to be understood that both the foregoing general description and the following detailed description are exemplary only and are intended to provide an overview or framework for understanding the nature and characteristics of the claims.

Brief Description of the Drawings

[0020] The accompanying drawings are included to provide a further understanding and are incorporated herein and form a part hereof. The drawings illustrate one or more embodiments and, together with the detailed description, explain the principles and operation of the various embodiments. That is, the present disclosure will be more fully understood from the following detailed description in conjunction with the accompanying drawings.

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[0021] Some of the drawings include cross-sectional views with diagonal hatching, and the diagonal hatching represents the glass material in this disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0022] Various embodiments of the present disclosure, examples of which are shown in the accompanying drawings, will be described in detail. Whenever possible, the same or similar reference numerals are used throughout the drawings to refer to the same or similar parts. The drawings are not necessarily to scale, and those skilled in the art will recognize where the drawings are simplified to illustrate important aspects of the present disclosure.

[0023] The appended claims are incorporated into and form a part of this detailed description.

[0024] Cartesian coordinates are shown in some of the figures for reference purposes, but are not intended to limit the direction or orientation. The vertical direction is along the z-axis and along the direction of gravity, which is assumed to act in the -z direction.

[0025] The English phrase "comprises" as used in this document includes, as a special case, the term "consists of", for example, the expression "A comprises B and C" is understood to include the case of "A consists of B and C".

[0026] Relative terms such as upper, lower, side, horizontal, vertical, etc. are used for convenience and ease of explanation and are not intended to limit the direction or orientation, except that the term "vertical" is an exception and its special use regarding the direction of gravity will be understood from the context of the description.

[0027] The symbol "μm" is micron or micrometer, i.e., 10-6 represents meters, and the symbol "nm" represents nanometers, that is, 10 -9 represents meters.

[0028] As used herein, the term "fused" refers to taking a set consisting of separate glass parts that are not adhered to each other, heating this set up to just above the softening point of the glass parts so that the glass parts flow and adhere or seal to each other to form an integrated glass part, and the integrated glass part maintains the general overall configuration of the glass parts, that is, the glass parts do not substantially change their basic shape.

[0029] The term "axial hole" means a hole that extends parallel to the axial direction, that is, parallel to the central axis or center line.

[0030] As used herein, the term "cylindrical" refers to a three-dimensional shape formed by considering a two-dimensional shape and projecting the two-dimensional shape along a third dimension perpendicular to the plane of the two-dimensional shape. Therefore, when used herein, a cylinder can have a cross-sectional shape other than circular.

[0031] Glass cladding part FIG. 1A is a top-oblique view of an example glass cladding portion 10. FIG. 1B is an xz cross-sectional view of the glass cladding portion 10 of FIG. 1A, and FIG. 1C is a top view of the glass cladding portion of FIGS. 1A and 1B.

[0032] The glass cladding portion 10 is defined by a cylindrical glass body 11 made of a glass material containing silica such as pure silica or doped silica. The glass cladding portion 10 has a central axis or center line AC, an upper surface 12 at the upper end 13, a bottom surface 14 at the bottom end 15, and an outer surface 16 that defines an outer circumference 18. The glass cladding portion 10 has a diameter DS and a height HS. In one example, the diameter DS can be in the range of 50 mm to 150 mm, and the height HS can be in the range of 50 mm to 200 mm. In one example in this document, the diameter DS is about 70 mm and the height HS is about 110 mm. It will be apparent to those skilled in the art that other diameters DS and heights HS of the glass cladding portion 10 that are consistent with the principles and limitations of the methods described herein can be effectively used. To obtain an accurate diameter DS, the outer surface 16 can be ground and then polished. The flat upper surface 12 and bottom surface 14 of the glass cladding portion 10 can also be polished. In one example, polishing is performed to obtain a flatness of about 2 μm across the flat surface.

[0033] The glass cladding portion 10 includes a raised lip 20 at the upper end 13. The raised lip 20 goes around the outer circumference 18. Thus, the raised lip 20 can also be referred to as a raised outer lip or an outer peripheral lip. FIG. 1B includes an enlarged insert view showing a cross-sectional view of the raised lip 20. The raised lip 20 has a flat surface parallel to the upper surface 12. In one example, the raised lip 20 is finely ground or polished. The raised lip 20 has an inner wall 22. The inner wall 22 and the upper surface 12 define a recess 24 at the upper end 13. The raised lip 20 has a width WL and a height HL. In one example, the width WL can be in the range of 2.5 mm to 10 mm (e.g., 5 mm), and the height HL can be in the range of 0.25 mm to 1 mm (e.g., 0.5 mm). The purposes of the raised lip 20 and the recess 24 will be described in more detail below.

[0034] Consider a glass cladding portion 10 having a diameter DS of 70 mm, a height DH of 100 mm, and a raised lip 20 with a width WL of 5 mm and a height HL of 0.5 mm. The volume VS of the solid glass cladding portion 10 (without the recess 24 or the following shaft hole) is VS = π[DS / 2] 2 (HS) = π[35 mm] 2(100 mm) ≒ 3.8×10 5 mm 3 is. The volume VR of the concave portion 24 is VR = π[(DS - 2(WL)) / 2] 2 (HL) = 1.4×10 3 mm 3 is. The relative size (volume) of the concave portion 24 compared to the total volume of the solid glass cladding portion 10 is VR / VS ≒ 0.004 or about 0.4%.

[0035] The glass cladding portion 10 includes one or more through-axis holes 40 with a diameter DH. The glass cladding in an example of FIGS. 1A - 1C shows eight axis holes 40. Each axis hole 40 is defined by an open upper end 42, an open lower end 44, and a cylindrical inner surface 46 of the glass body 11. An example axis hole 40 is shown as having the same diameter DH as, for example, a circular cross-sectional shape. In other embodiments, the axis holes 40 can have different sizes (diameters) and different cross-sectional shapes. One or more axis holes 40 can be formed by precision drilling, such as diamond abrasive core drilling and / or ultrasonic-assisted core drilling.

[0036] The use of a glass cladding portion 10 with a larger diameter allows for a less stringent absolute tolerance positioning of the axis holes considering the shrinkage rate effect during the drawing process in optical fiber formation. In one example, the relative tolerance between the center positions of the axis holes 40 is about 0.2% with respect to the diameter DS of the glass cladding portion. As an example, this results in a 0.25 mm tolerance when the glass cladding portion diameter DS = 125 mm, corresponding to a 0.25 μm tolerance for the position of an individual core within a 125 μm fiber. Precision drilling of the axis holes 40 using hole drilling techniques known in the art can meet the accuracy goals of this example.

[0037] Cane cladding assembly FIG. 2A is a developed view similar to FIG. 1A, showing the glass cladding portion 10 and eight canes 50 operably arranged with respect to eight axis holes 40 in the process of forming the cane cladding assembly 120. FIG. 2B shows an assembled cane cladding assembly 120 in one example. FIG. 2C is an xz cross-sectional view, and FIG. 2D is a top view of an example cane cladding assembly 120.

[0038] FIG. 2A includes an enlarged insert view showing a cane 50 of an example. Each cane 50 has a glass body 51 that defines an upper end 52, a bottom end 54, and an outer surface 56 of the cane. The cane 50 has an axial length LC. The glass body 51 may include a core section 51c and an inner cladding section 51i that directly surrounds the core section. The inner cladding section 51i may have one or more inner cladding portions with different refractive indices. The glass body may also consist of only the core section 51c. In one example, the cladding section 51i may consist of one or more undoped or lightly doped inner cladding sections. Generally speaking, the cane 50 may have any refractive index profile that can be made using techniques known in the art to appropriately achieve the desired properties of the resulting optical fiber.

[0039] The cane 50 has a diameter DC that is slightly smaller than the diameter DH of the axial hole so that it can fit into the corresponding axial hole 40. In one example, there is a gap G between the outer surface 56 of the cane 50 and the inner surface 46 of the axial hole, and the gap has a gap size δG (see also the enlarged insert view of FIG. 5C). In one example, the size of the gap G is such that the cane 50 just fits into the axial hole 40, for example, the fit is firmly fixed but not a press fit. For example, the axial hole diameter DH may be 10 mm, the cane diameter DC may be 9.98 mm, and the gap size δG = (DH - DC) / 2 = 0.01 mm or 10 μm. On the other hand, the gap size δG may be relatively large because in the following fitting process, the relatively large gap inside the glass cladding portion 10 can be crushed. In one example, the gap size δG is preferably about 0.1 mm or less (for example, 0 < δG ≦ 0.1 mm) so that there is no large distortion of the glass body 11 of the glass preform portion 10 during the fitting process.

[0040] As described in more detail below, the gap forms an annular passage that supports the flow of gas when evacuated. Each axial hole 40 has a volume VH = π[DH / 2] 2 (HS). When DH = 10 mm and HS = 100 mm, VH ≒ 7850 mm 3On the other hand, the volume VC of the cane 50 is VC = π[DC / 2] 2 2 >(HS), and when DC = 9.98 mm, VC = 7818 mm 3 3 The clearance volume is VG = VH - VC, and in the above example, it is 32 mm 3 3 which is about 0.4% of the shaft hole volume. As described above, a larger gap size δG, and thus a larger clearance volume VG, can also be used.

[0041] Figure 2E is similar to Figure 2D and shows an example where not all of the shaft holes 40 have the same diameter DH, and not all of the canes 50 also have the same cane diameter DC. In the example shown in Figure 2C, the bottom cover 90 can be used to support the cane 50 in the shaft hole 40 while the cane clad assembly 120 is in a vertical position. The configuration of an example of the bottom cover 90 will be described in more detail below.

[0042] Figures 3A - 3C are top views similar to the top view of Figure 2D, but show examples having a single shaft hole 40 that houses a single cane 50. Figure 3A shows an example where the shaft hole 40 has a round cross - sectional shape and is coaxial with the center line AC of the glass clad portion 10. Figure 3B is similar to Figure 3A except that the shaft hole 40 and the corresponding cane 50 have an elliptical cross - sectional shape. Figure 3C is similar to Figure 3B and shows an example where the single shaft hole 40 and the corresponding single cane 50 are offset from the axis.

[0043] Preform assembly Figure 4A is a partial development view of an example of a pre - formed article assembly 150 formed using the cane clad assembly 120 of Figure 2B. The pre - formed article assembly 150 includes an upper cover 70 that mates with a raised lip 20 at the upper end 13 of the glass clad portion 10. The pre - formed article assembly 150 also includes the above - mentioned bottom cover 90 that mates with the bottom end 15 of the glass clad portion 10. Both the upper cover 70 and the bottom cover 90 are made of glass, for example, the same glass as the glass clad portion 10.

[0044] In one example, the upper lid 70 has a main body 71, a central axis AT, an upper end 72, and a bottom surface 74 at the bottom end 75. The upper lid 70 also includes an axially penetrating hole 78 that is open at the upper end 72 and the bottom end 74. In one example, the axial hole 78 is coaxial with the central axis AT.

[0045] Figure 4B is similar to Figure 4A, and the preform assembly 150 uses two glass cladding portions 10 arranged along the axis, and the axial keel holes 40 of the two different glass cladding portions are aligned along the axis. In this example, the keel 50 has a keel length LC such that the keel extends through the aligned axial keel holes 40 of the two stacked and aligned glass cladding portions 10. Thus, in this example, the two keel cladding assemblies 120 share the same keel 50, and this keel has a keel length LC that is generally the same as the axial length LS of the stacked glass cladding portions 10 of the preform assembly 150 in one example. Thus, in some embodiments, the keel length LC is greater than the height HS of a single glass cladding portion 10. In other examples, three or more glass cladding portions 10 are joined to form the preform assembly 150 using an appropriately long keel 50. When the preform assembly 150 consists of stacked glass cladding portions 10, there is a top glass cladding portion that receives the upper lid 70 and a bottom glass cladding portion that receives the bottom lid 90.

[0046] Referring to FIGS. 4A and 4B, in one example, the bottom cap 90 is made of glass (e.g., the same glass as the glass cladding 10) and has a conical shape that serves as the final shape of the preform for drawing out the optical fiber. The bottom cap 90 includes an upper surface 92 at the upper end 93, a conical portion 95 of the outer surface 96, and a bottom end 94. The cap 90 has an outer periphery 98 at the upper end 93. In one example, the upper end 93 can consist of a flat surface 92. In the illustrated example, the upper end 93 includes a raised lip 100 at the outer periphery 98 of the upper end 93. The raised lip has a flat polished surface and defines an inner wall 102. The inner wall 102 and the upper surface 92 define a recess 104. In one example, the raised lip 100 optionally includes a small passage 101 that connects the recess 104 to the outer surface 96. The purpose of the optional passage 101 is described below. In one example, the various glass components of the preform assembly 150 are cleaned, e.g., washed with pickled DI water, before assembly.

[0047] Preform system FIG. 5A is a top - down perspective view of an example preform system 200 formed using the preform assembly 150. The example preform assembly 150 shown in FIG. 5A is formed using four cane - cladding assemblies 120 and a suitably long cane 50 (e.g., a cane 50 having a length LC approximating the length LS of the four combined cane - cladding assemblies 120). The preform system 200 includes a vacuum system 210. The vacuum system 210 is air - communicatively connected to the preform assembly 150 at the upper lid 70 via a vacuum conduit 216. The preform system 200 is illustrated as being in an ambient air environment 230A. The preform assembly 150 is illustrated as having an upper end portion 152, a central portion 153, and a bottom end portion 154. The preform system 200 is used to perform a vacuum - based method of forming the cane - based glass preforms disclosed herein. Note that one example of the preform system 200 has an upper end portion 152 closest to the vacuum system and a bottom end portion 154 at the opposite end.

[0048] Figure 5B is an enlarged partial development view of the upper end portion 152 of the preform assembly 150, viewed obliquely downward, and illustrates how the upper lid 70 aligns with the lip 20 at the upper end 13 of the glass clad portion 10 of the uppermost cane clad assembly 120. Figure 5C is an enlarged cross-sectional view of the upper portion of the preform assembly 150 and the upper lid 70 operably disposed thereon. In one example, the vacuum conduit 216 is attached to the upper end 72 of the upper lid 70 using a fixing member 220, such that the vacuum conduit is in air communication with the axial hole 78 of the upper lid. In one example, both the upper lid 70 and the vacuum conduit 216 are made of glass, and the fixing member 220 is made of welded glass. In one example, the vacuum conduit 216 is configured to mechanically support the preform assembly 150 while allowing the preform assembly 150 to be movable in the z direction, as described below.

[0049] In the example best seen in Figure 5B, the upper lid 70 may include a lip 80 on the outer periphery of the bottom end 75. The lip 80 defines an inner wall 82 that, together with the bottom surface 74, defines a recess 84. In one example, the lip 80 of the upper lid 70 aligns with the lip 20 of the glass clad portion 10 of the uppermost cane clad assembly 120 of the preform assembly 150. These flat and finely ground surfaces become substantially airtight when drawn into a vacuum, as described below.

[0050] As best seen in the cross-sectional view of Figure 5C and the full cross-sectional view of Figure 5D, the preform assembly 150 includes an internal cavity 250 formed by the axial hole 40 of the glass clad portion 10 of the uppermost cane clad assembly 120 and the recess 24 at the upper end 13 of the glass clad portion 10 of the uppermost cane clad assembly 120. The internal cavity 250 may also be partially defined by an optional recess 84 in the upper lid 70 and an optional recess 104 in the bottom lid 90. The internal cavity 250 is actually partially defined by a gap G, which is defined as the gap between the outer surface 56 of the cane 50 and the inner surface 46 of the axial hole 40, as described above. Thus, the internal cavity 250 is composed of relatively small gaps and recesses, which is advantageous when drawn into a vacuum. Figure 5E shows another example similar to the example shown in Figure 5D, where the cane 50 may have a length sufficient to contact the upper surface 92 of the bottom lid 90 and the bottom surface 74 of the upper lid 70.

[0051] The full xz cross-sectional view of FIG. 5D shows a preform assembly 150 of an example consisting of two glass clad portions 10, and shows an example of an internal cavity 250. An example of the internal cavity 250 is defined by two recesses 24 of the glass clad portion 10, a gap G defined by the keel 50 and the shaft hole 40 containing the keel, and a recess 104 of the bottom cover 90. The internal cavity 250 is configured to provide an air passage between the recess 24 and the recess 84 to the upper surface 92 of the bottom cover 90 or to the recess 104 of the bottom cover 90. An optional passage 101 is not shown in the bottom cover 90. The various contacting surfaces are sufficiently smooth to maintain a pressure difference when a vacuum is applied to the internal cavity, so the internal cavity 250 is said to be generally sealed. The raised lip 20 of the glass clad portion 10 and the raised lip 100 of the bottom cover 90 help to form a seal by reducing the amount of surface area in contact with adjacent surfaces and increasing the force per area (i.e., pressure).

[0052] The preform assembly 150 is held together by applying a vacuum from the vacuum system 210 to the internal cavity 250 via the vacuum conduit 216 and the shaft hole 78 of the upper cover 70. The vacuum draws air out of the internal cavity 250 as shown by the air streamline 218 in FIG. 5A. Since the internal cavity 250 is generally sealed, drawing a vacuum creates a significant pressure difference ΔP between the internal cavity 250 and the surrounding environment 230A. This pressure difference ΔP acts to tightly press together the bottom cover 90, the stacked keel clad assemblies 120, and the upper cover 70 of the preform assembly 150 when acting vertically against gravity. In one example, the pressure difference ΔP between a full vacuum and normal ambient pressure at sea level applies an axial compressive force of 98 kg to a representative assembly having an outer diameter DS of 122 mm and an inner chamber diameter of 112 mm. More generally, the pressure difference can be approximately 100 kg, and it will be apparent to those skilled in the art that the exact value depends on the weights of the various components of the preform assembly 150 and the sizes of the various portions of the internal chamber 250. Thus, applying a vacuum forms a preform assembly 150 held together by vacuum ( "held by vacuum"). It is this preform 150 held by vacuum that is processed in the steps below.

[0053] When a vacuum is applied, the above-described vacuum conduit 216 can have sufficient strength to mechanically support the preform assembly 150 in a vertical orientation. In one example, the preform system 200 is configured such that the preform assembly 150 can move vertically as indicated by the movement arrow AR-M in FIG. 5A. This can be accomplished in various ways known in the art, including having an expandable vacuum conduit 216, for example, consisting of telescoping vacuum pipes (not shown) that can slide axially relative to each other in a controlled manner so as to expand and contract while maintaining a vacuum.

[0054] The example of FIG. 5A shows an optional passage 101 in the bottom cover 90. This narrow passage allows a small amount of air in the ambient air environment 230A to flow into the internal chamber 250 when drawn by the vacuum. In one example, the ambient environment can be other than air, for example, filtered nitrogen or other inert gas or an inert gas containing chlorine, which can dry the internal chamber, remove impurities from the internal chamber 250, and / or prevent impurities from entering the internal chamber.

[0055] FIG. 5F is similar to FIG. 5C and shows an example configuration of the preform assembly 150 where the upper end 52 of the cane 50 is in contact with the bottom surface 74 of the upper cover 70. This embodiment is useful when the vacuum force is strong enough to pull the cane 50 out of the shaft hole 40.

[0056] FIG. 5G is similar to FIGS. 5C and 5F and shows an example where the bottom surface 74 of the upper cover 70 is flat (i.e., without a lip 80) and the uppermost portion of the internal chamber 250 is defined by the recess 24 of the glass clad portion 10 of the uppermost cane clad assembly 120. FIG. 5G also shows an example of the expanding shaft hole 78 in the upper plate 70. Such a shape of the shaft hole 78 can assist the flow of air (gas) to the vacuum conduit 216 through the internal chamber 250.

[0057] FIG. 5H is similar to FIG. 5E and shows an example where the glass clad portion 10 includes vacuum holes 40V. In fact, one or more of the vacuum holes 40V form part of the internal chamber 250 and can be used to help draw a vacuum and thus maintain the desired pressure differential ΔP. At least one vacuum hole 40V can be used when the gap size δG is small enough and / or the number of shaft holes 40 supporting the cane 50 is small (e.g., one or two) and an additional volume of the internal chamber 250 is desired to draw a stronger vacuum. The vacuum holes 40V need not be precisely formed since they remain empty and collapse with the remaining region of the internal chamber 250 during the coalescence as described below. In one example, the vacuum holes 40V are cylindrical and extend axially through the glass body 11 of the glass clad portion 10. The vacuum holes 40V can have any reasonable diameter, shape, size, etc. such that the glass body 11 of the glass clad portion 10 is hardly distorted when collapsed during the coalescence process.

[0058] Form a glass preform from the preform assembly FIG. 6A is similar to FIG. 5A and shows a preform system 200 movably disposed relative to a furnace 300 having an upper opening 302, a bottom opening 304, and an interior 306 in which heat 310 is generated and generally contained. The furnace interior 306 includes a furnace ambient atmosphere 230F of a gas 232 that can optionally contain one or more selected gases.

[0059] An initial configuration of the preform system 200 is shown, with the bottom end portion 154 of the preform assembly 150 within the furnace interior 306, initiating a coalescence process to form a glass preform. The bottom end portion 154 is heated to a temperature that bonds the various glass parts of the preform assembly 150.

[0060] Typically, when the preform assembly 150 enters the hottest part of the furnace interior 306, the lips 20 of the glass clad portions 10 adjacent to the aligned lips 100 of the bottom cover 90 seal at the respective bottom ends 15 of the glass clad portions. Next, the other adjacent surfaces within the preform assembly are gradually sealed from the outer surface inward. As heat 310 diffuses radially inward through the thickness of the components of the preform assembly 150, the recesses 24 between the adjacent cane clad assemblies 120 and the recess 104 associated with the bottom cover 90 close. As the preform assembly moves downward, the cane 50 seals within its axial hole 40 and the upper recess 24 seals to the upper cover 70.

[0061] In one example, the entire preform assembly 150 is heated to a temperature of about 1100 °C, and the gas 232 in the furnace ambient environment 230F contains chlorine gas and is drawn through the internal chamber 250 by the applied vacuum of the vacuum system 210. This serves to dry and purify the preform assembly 150. In this step, the entire preform assembly is inserted into the furnace interior 306 and the temperature is controlled to the above drying and cleaning temperature of about 1100 °C.

[0062] Next, the temperature is raised just above the glass softening temperature. The softening temperature is in the range of about 1400 °C to about 1500 °C for silica glass. Alternatively, the preform assembly 150 is further lowered into the hotter zone 306H within the furnace interior 306 at a temperature in the range of about 1400 °C to about 1500 °C or higher. This is done to seal the various glass surfaces as described above. In this step, the gas 232 can be helium or other inert gas or simply a vacuum. The above temperature range is an example, and those skilled in the art will understand that a polished silica surface can chemically bond at a temperature as low as about 600 °C. Bonds formed at about 1500 °C can be fairly or fully cured, have substantially no residual stress, and have the same strength as solid glass and can thus often be advantageous. Another advantage of the consolidation at or just above the glass softening temperature is that it allows the polished surfaces of the preform assembly 150 to deform and contact each other despite low flatness, polishing quality, relatively large gap sizes, and / or surface contamination.

[0063] Figure 6B is similar to Figure 6A and shows a preform assembly 150 further inserted into the hotter zone 306H of the furnace interior 306. The white arrow AR-C schematically illustrates how the consolidation process progresses over time. In particular, when the preform assembly 150 moves downward in the furnace interior 306, the consolidation process rises from the bottom end portion 154 to the central portion 153 and then successively to the upper end portion 152, and also moves inward from the outer surface of the preform assembly. Also, the glass flow at a temperature just above the glass softening temperature is used to eliminate the internal chamber 250 consisting of relatively small gaps and recesses that provide a vacuum path for generating the pressure difference ΔP that holds the preform assembly 150 together before consolidation, as described above.

[0064] Figure 6C is similar to Figure 6B and shows the resulting cane-based glass preform (the "preform") 400 in the furnace interior 306 after completion of the consolidation process. The glass preform 400 is called a "cane-based" preform because it includes and is formed of one or more canes 50. The glass preform 400 has a preform axis AP.

[0065] It should be noted that the consolidation of the integrally held preform assembly 150 is carried out in a single process step, namely, heating of the preform assembly near, at, or just above the glass softening temperature. This single heating step seals all the glass surfaces of the various parts of the preform assembly 150.

[0066] At this point in the process, the glass preform 400 can be removed from the furnace 300. Alternatively, if the furnace 300 includes a drawing furnace of the fiber drawing system as described below, the glass preform 400 can be immediately used for fiber drawing. Note that removing the glass preform 400 obtained by charging the preform assembly 150 into the furnace 300 is preferably carried out with care to avoid damage. In one example, the furnace temperature is lowered to 900 °C, and the charging and removal processes can take up to 1 hour to prevent damage. This is one of the many reasons why it may be preferable to perform the consolidation process in a drawing furnace to form the glass preform 400 and then start the fiber drawing process using the resulting preform.

[0067] Manufacture an optical fiber Figure 7 is a schematic diagram of an example optical fiber drawing system ("drawing system") 500 for pulling a glass preform 400 as formed using the above-described system and method into an optical fiber ("fiber") 600. The glass preform 400 can be used to form a single-core optical fiber or a multi-core optical fiber. In the illustrated example, the formation of a multi-core optical fiber having eight cores is depicted as an example.

[0068] The fiber 600 can be produced using standard optical fiber drawing techniques using the drawing system 500. An example drawing system 500 includes a drawing furnace 502 for heating the glass preform 400 to the glass melting temperature. In one example, the drawing furnace 502 is the same as the furnace 300 used to consolidate the preform assembly 150 to form the glass preform 400, and there is no need to transfer the glass preform 400 to another furnace to perform the fiber drawing process. In one example, the fiber drawing process is carried out at a glass melting temperature in the range of 1800 °C to 1900 °C.

[0069] The wire drawing system 500 also includes non-contact measurement sensors 504A and 504B for measuring the size (diameter) of the drawn (bare) fiber 600B exiting the wire drawing furnace 502 for size control. The cooling station 506 is located downstream of the measurement sensors 504A and 504B and is configured to cool the bare fiber 600B. The coating station 507 is located downstream of the cooling station 506 and is configured to deposit a protective coating material 507M on the bare fiber 600B to form the coated fiber 600. The tensioner 620 is located downstream of the coating station 507. The tensioner 620 has a surface 622 for pulling the coated fiber 600. A set of guide wheels 530 is located downstream of the tensioner 620, each having a surface 532. The guide wheels 530 serve to guide the coated fiber 600 to a fiber take-up spool ("spool") 550 and store the coated fiber 600.

[0070] The enlarged insert view I1 of FIG. 7 shows a cross-sectional view of the glass preform 400. The glass preform 400 includes a preform outer cladding 410 formed by the body 11 of one or more glass cladding portions 10 used to form the glass preform 400. The glass preform 400 includes a cane 50 embedded therein and extending along the axis, i.e., parallel to the preform axis AP. As shown in the enlarged insert view I2, the cane 50 includes the core region 50c and the inner cladding region 50i. Other configurations of the cane 50 may also be used. The preform outer cladding 410 serves as an outer cladding directly adjacent to the inner cladding region 50i of the cane or, if the inner cladding region is not included in the cane, to the core region 50c.

[0071] The enlarged insert view I3 shows a cross-sectional view of a coated fiber 600 which is, in one example, a multi-core fiber. The coated fiber 600 includes an outer cladding 610 in which a core 620 is embedded and extends along the axis, i.e., parallel to the fiber central axis AF. As shown in the enlarged insert view I4, the core 620 is formed by the cane 50 of the glass preform 400 and may include a corresponding core region 620c and an inner cladding 620i. Other configurations of the core 620 may also be used. The coated fiber 600 has an outer surface 626 on which a protective coating 630 made of a coating material 507M is formed. In one example, the coating material 507 is a non-glass material such as a polymer or acrylate.

[0072] Aspect 1 of the disclosure is A method of forming a cane-based preform, comprising: Applying a vacuum to a preform assembly, the preform assembly comprising at least one glass cladding portion having one or more axial holes, an upper end, a bottom end, and canes present within each of the one or more axial holes, the upper end and the bottom end being capped so as to define a substantially sealed internal chamber; Heating the preform assembly held in vacuum to just above the glass softening point to fuse the preform held in vacuum to form a cane-based glass preform; A method including the above steps.

[0073] Aspect 2 of the disclosure is Before the step of applying the vacuum, forming the one or more axial holes by drilling the at least one glass cladding portion; And operably disposing the one or more canes within the one or more axial holes; The method according to aspect 1, wherein capping comprises attaching an upper glass lid and a bottom glass lid to the upper end and the bottom end of the at least one glass cladding portion respectively to define a substantially sealed internal chamber. Including the steps formed by

[0074] Aspect 3 of the disclosure is said at least one glass cladding portion consists of two or more glass cladding portions that are stacked and whose said axial holes are aligned and have one axial length, the uppermost glass cladding portion that defines the upper end, and the lowermost glass cladding portion that defines the bottom end, and each of said one or more canes has a cane length that is at least substantially equal to or greater than said axial length, the method according to Aspect 1 or 2.

[0075] Aspect 4 of the disclosure is each of said one or more canes comprises a glass core region surrounded by a glass inner cladding region, the method according to any one of Aspects 1 to 3.

[0076] Aspect 5 of the disclosure is at least one of said glass core region and said glass inner cladding region consists of doped silica glass, the method according to Aspect 4.

[0077] Aspect 6 of the disclosure is said glass inner cladding region consists of one or more undoped or lightly doped inner cladding portions, the method according to Aspect 4 or 5.

[0078] Aspect 7 of the disclosure is the upper end of each glass cladding portion includes a recess defined by a raised outer lip, the method according to any one of Aspects 1 to 6.

[0079] Aspect 8 of the disclosure is said bottom glass lid has an outer surface and an outer peripheral lip that defines a recess forming part of said substantially sealed inner chamber, the method according to any one of Aspects 2 to 7.

[0080] Aspect 9 of the disclosure is said bottom glass lid includes a passage from said recess to said outer surface, and said passage allows gas from the ambient environment to flow through said inner chamber, the method according to Aspect 8.

[0081] Aspect 10 of the disclosure is The method according to aspect 9, wherein the gas from the ambient environment contains chlorine.

[0082] Disclosed aspect 11 is The method according to any one of aspects 8 to 10, wherein applying the vacuum is performed through the axial hole of the upper glass lid.

[0083] Disclosed aspect 12 is The method according to aspect 11, wherein the vacuum is provided from a vacuum system through a telescopic vacuum conduit glass-welded to the upper glass lid.

[0084] Disclosed aspect 13 is The method according to any one of aspects 1 to 12, wherein the one or more axial holes consist of a single axial hole, and the one or more canes consist of a single cane present in the single axial hole.

[0085] Disclosed aspect 14 is The method according to any one of aspects 1 to 13, wherein heating the integrally held preform assembly is performed using a furnace.

[0086] Disclosed aspect 15 is The method according to aspect 14, wherein the furnace includes an optical fiber drawing furnace.

[0087] Disclosed aspect 16 is The method according to aspect 15, further comprising the step of drawing an optical fiber from the cane-based glass preform using the drawing furnace without removing the cane-based preform from the drawing furnace.

[0088] Disclosed aspect 17 is The method according to any one of aspects 1 to 16, wherein the substantially sealed internal chamber comprises at least one vacuum hole defining a part of the substantially sealed internal chamber.

[0089] Disclosed aspect 18 is Each cane has a cane diameter DC, each shaft hole has a hole diameter DH > DC, and the substantially sealed internal chamber includes a gap formed by the difference between the hole diameter and the cane diameter for each shaft hole, the method according to any one of Aspects 1 to 17.

[0090] Aspect 19 of the disclosure is The gap has a gap size δG = (DH - DC) / 2, and the gap size δG satisfies 0 < δG ≦ 0.1 mm, the method according to Aspect 18.

[0091] Aspect 20 of the disclosure is The method according to any one of Aspects 1 to 19, further comprising the step of drawing out an optical fiber using the cane-based glass preform.

[0092] Aspect 21 of the disclosure is A method of forming a cane-based glass preform, comprising: Forming one or more shaft holes in each of a plurality of glass cladding portions each having a body, an upper end, a bottom end, and an outer periphery, wherein each upper end has a lip extending around the outer periphery and defining an upper concave portion, and each shaft hole is defined by a cylindrical inner surface within the body; Stacking the plurality of glass cladding portions such that the shaft holes formed in each glass cladding portion are aligned along an axis, the stacked plurality of glass cladding portions having an overall stacked length LS, a topmost glass cladding portion, and a bottommost glass cladding portion; Inserting one or more glass canes into the one or more aligned shaft holes of the plurality of glass cladding portions, such that a gap exists between each glass cane and the cylindrical inner surface of the shaft hole in which the glass cane is located; Aligning a glass top cover with the upper end of the topmost glass cladding portion and aligning a glass bottom cover with the bottom end of the bottommost glass cladding portion to define a preform assembly having a substantially sealed internal chamber, the internal chamber including the upper concave portion and the gap; Applying a vacuum through the glass top cover to the substantially sealed internal chamber to create a pressure differential with respect to the ambient environment, the pressure differential forming a preform assembly integrally held and held in vacuum, the step of, Heating the preform assembly held in vacuum to just above the glass softening point to combine the preform assembly held in vacuum to form a glass preform, the step of A method comprising.

[0093] Aspect 22 of the disclosure is Each cane has a cane length LC that is at least as long as the stacking length LS, the method according to aspect 21.

[0094] Aspect 23 of the disclosure is Each cane comprises a glass core region surrounded by a glass inner cladding region, the method according to aspect 21 or 22.

[0095] Aspect 24 of the disclosure is At least one of the glass core region and the glass inner cladding region consists of doped silica glass, the method according to aspect 23.

[0096] Aspect 25 of the disclosure is The glass inner cladding region consists of one or more undoped or lightly doped inner cladding portions, the method according to aspect 23 or 24.

[0097] Aspect 26 of the disclosure is The glass bottom cover has an outer periphery lip defining a recess that forms part of the outer surface and the substantially sealed internal chamber, the method according to any one of aspects 21-25.

[0098] Aspect 27 of the disclosure is The glass bottom cover includes a passage from the recess to the outer surface, the passage allowing gas from the ambient environment to flow through the internal chamber while substantially maintaining the pressure differential, the method according to aspect 26.

[0099] Aspect 28 of the disclosure is The method according to aspect 27, wherein the gas from the surrounding environment contains chlorine.

[0100] The disclosed aspect 29 is The method according to any one of aspects 21 to 28, wherein applying the vacuum is performed through the shaft hole of the upper lid.

[0101] The disclosed aspect 30 is The method according to aspect 29, wherein the vacuum is provided via a telescopic vacuum conduit that is glass-welded to the upper lid from a vacuum system and is in air communication with the shaft hole of the upper lid.

[0102] The disclosed aspect 31 is The method according to any one of aspects 21 to 30, wherein the one or more shaft holes consist of a single shaft hole, and the one or more canes consist of a single cane present within the single shaft hole.

[0103] The disclosed aspect 32 is The method according to any one of aspects 21 to 31, wherein heating the preform assembly held in the vacuum is performed using a furnace.

[0104] The disclosed aspect 33 is The method according to aspect 32, wherein the furnace includes an optical fiber drawing furnace.

[0105] The disclosed aspect 34 is The method according to aspect 33, further comprising the step of drawing an optical fiber from the cane-based glass preform using the drawing furnace without removing the cane-based preform from the drawing furnace.

[0106] The disclosed aspect 35 is The method according to any one of aspects 21 to 34, wherein the substantially sealed internal chamber comprises at least one vacuum hole that defines a part of the substantially sealed internal chamber.

[0107] The disclosed aspect 36 is Each cane has a cane diameter DC, each shaft hole has a hole diameter DH > DC, and the internal chamber includes a gap formed by the difference between the hole diameter and the cane diameter for each shaft hole, the method according to any one of aspects 21 to 35.

[0108] Aspect 37 of the disclosure is The gap has a gap size δG = (DH - DC) / 2, and the gap size δG is within the range of 0 < δG ≦ 0.1 mm, the method according to aspect 36.

[0109] Aspect 38 of the disclosure is The method according to any one of aspects 21 to 37, further comprising the step of drawing out an optical fiber using the cane-based glass preform.

[0110] Aspect 39 of the disclosure is A method of forming a cane-based glass preform assembly, comprising: Forming one or more shaft holes in at least one glass cladding portion, the at least one glass cladding portion having an upper end and a bottom end; Inserting one or more canes into the one or more shaft holes respectively, such that each shaft hole contains one cane; Forming a preform assembly having an internal chamber substantially sealed by covering the upper end and the bottom end, the internal chamber being in air communication connection with the upper end and the bottom end through the shaft holes; Applying a vacuum to the substantially sealed internal chamber to generate a pressure difference between the substantially sealed internal chamber and the surrounding environment, and forming a preform assembly held in vacuum; and the method comprising.

[0111] Aspect 40 of the disclosure is The method according to aspect 39, further comprising the step of heating the preform assembly held in vacuum to just above the glass softening point to combine the preforms held in vacuum to form a cane-based glass preform.

[0112] Aspect 41 of the disclosure is A method of forming a cane-based glass preform assembly for forming a multi-core optical fiber, comprising: stacking a plurality of glass cane portions each having a plurality of axial holes such that the axial holes are aligned, wherein adjacent glass cane portions contact each other with a raised lip forming an internal cavity, and there are a top glass cane portion and a bottom glass cane portion; inserting one cane into each of the aligned axial holes to define a gap within the axial holes, the gap providing air communication between the internal cavities; covering the top and bottom glass cane portions to form a preform assembly having a substantially sealed internal chamber, the internal chamber including the internal cavities and the gaps; applying a vacuum to the substantially sealed internal cavity to form a preform assembly held by the vacuum; and a method comprising the steps of.

[0113] Aspect 42 of the disclosure is The method according to aspect 41, further comprising heating the preform assembly held by the vacuum to just above the glass softening point to combine the preform assembly held by the vacuum to form a cane-based glass preform.

[0114] Aspect 43 of the disclosure is The method according to aspect 42, further comprising drawing an optical fiber using the cane-based glass preform.

[0115] Aspect 44 of the disclosure is The method according to aspect 43, wherein the combining is performed using a furnace and the drawing is performed using the furnace.

[0116] Aspect 45 of the disclosure is A cane-based preform product, wherein the process of forming the preform product is Applying a vacuum to a preform assembly, the preform assembly comprising at least one glass clad portion having one or more axial holes, an upper end, a bottom end, and a cane present within each of the one or more axial holes, and an upper lid attached to the upper end and a bottom lid attached to the bottom end, the step; A cane-based preform product, comprising heating the preform assembly held in a vacuum to just above the glass softening point to combine the preforms held in the vacuum to form a cane-based glass preform.

[0117] Aspect 46 of the disclosure is A cane-based glass preform product, the process for forming the preform product being Forming one or more axial holes in each of a plurality of glass clad portions, each having a body, an upper end, a bottom end, and an outer periphery, each upper end having a lip extending around the outer periphery and defining an upper recess, and each axial hole being defined by a cylindrical inner surface within the body, the step; Stacking the plurality of glass clad portions such that the axial holes formed within each glass clad portion are aligned along an axis, the stacked plurality of glass clad portions having an overall stacked length LS, a topmost glass clad portion, and a bottommost glass clad portion, the step; Inserting one or more glass canes into the one or more aligned axial holes of the plurality of glass clad portions, such that there is a gap between each glass cane and the cylindrical inner surface of the axial hole in which the glass cane is present, the step; Aligning a glass upper lid with the upper end of the topmost glass clad portion and aligning a glass bottom lid with the bottom end of the bottommost glass clad portion to define a preform assembly having a substantially sealed internal chamber, the internal chamber including the upper recess and the gap, the step; Applying a vacuum through the glass top cover to the substantially sealed internal chamber to create a pressure differential with respect to the ambient environment, the pressure differential integrally holding the preform assembly to form a preform assembly held in vacuum; Heating the preform assembly held in vacuum to just above the glass softening point to join the preform assembly held in vacuum to form a glass preform; A cane-based glass preform product comprising.

[0118] Aspect 47 of the disclosure is A cane-based glass preform assembly product, the process for forming the assembly product comprising Forming one or more axial holes in at least one glass cladding portion, the at least one glass cladding portion having an upper end and a bottom end; Inserting one or more canes into the one or more axial holes, each axial hole thus containing one cane; Forming a preform assembly having a lid at the upper end and the bottom end and having a substantially sealed internal chamber, the internal chamber being in air communication connection with the upper end and the bottom end through the axial holes; Applying a vacuum to the substantially sealed internal chamber to create a pressure differential between the substantially sealed internal chamber and the ambient environment to form a preform assembly held in vacuum; A cane-based glass preform assembly product comprising.

[0119] Aspect 48 of the disclosure is A cane-based glass preform product, the process for forming the preform product comprising The process according to aspect 47; and Heating the preform assembly held in vacuum to just above the glass softening point to join the preform held in vacuum to form a cane-based glass preform. A cane-based glass preform product comprising.

[0120] Aspect 49 of the disclosure is a cane-based glass preform assembly product for forming a multi-core optical fiber, and the process for forming the assembly product is stacking a plurality of glass cane portions each having a plurality of axial holes so that the axial holes are aligned, wherein adjacent glass cane portions contact each other with a raised lip forming an internal cavity, and there are the uppermost glass cane portion and the lowermost glass cane portion; inserting one cane into each of the aligned axial holes to define a gap within the axial holes, the gap providing air communication between the internal cavities; covering the uppermost and lowermost glass cane portions to form a preform assembly having a substantially sealed internal chamber, the internal chamber including the internal cavities and the gaps; applying a vacuum to the substantially sealed internal cavity to form a preform assembly held in vacuum; A cane-based glass preform assembly product comprising.

[0121] Aspect 50 of the disclosure is a cane-based glass preform product, and the process for forming the preform product is the process described in Aspect 49 and heating the preform assembly held in vacuum to just above the glass softening point to join the preform assembly held in vacuum to form a cane-based glass preform. A cane-based glass preform product comprising.

[0122] It will be apparent to those skilled in the art that various partial modifications can be made to the preferred embodiments of the disclosure described herein without departing from the spirit and scope of the disclosure claimed in the appended claims. Accordingly, the present disclosure includes those partial modifications and variations when they fall within the scope of the appended claims and their equivalents.

[0123] Hereinafter, preferred embodiments of the present invention will be described item by item.

[0124] Embodiment 1 A method of forming a cane-based preform, comprising: applying a vacuum to a preform assembly, the preform assembly comprising at least one glass clad portion having one or more axial holes, an upper end, a bottom end, and canes present within each of the one or more axial holes, the upper end and the bottom end being capped so as to define a substantially sealed internal chamber; heating the preform assembly held in vacuum to just above the glass softening point to combine the preforms held in vacuum to form a cane-based glass preform; and a method comprising the steps of.

[0125] Embodiment 2 Prior to the step of applying the vacuum, the preform assembly is drilled in the at least one glass clad portion to form the one or more axial holes; and operatively disposing the one or more canes within the one or more axial holes; forming by; capping comprises attaching an upper glass cap and a bottom glass cap to the upper end and the bottom end of the at least one glass clad portion, respectively, to define a substantially sealed internal chamber, the method according to Embodiment 1.

[0126] Embodiment 3 The at least one glass clad portion comprises two or more glass clad portions stacked and their axial holes aligned and having a single axial length, a top glass clad portion defining the upper end, and a bottom glass clad portion defining the bottom end, and the one or more canes each have a cane length at least substantially equal to or greater than the axial length, the method according to Embodiment 1 or 2.

[0127] Embodiment 4 The method according to any one of Embodiments 1 to 3, wherein each of the one or more canes comprises a glass core region surrounded by a glass inner cladding region.

[0128] Embodiment 5 The method according to Embodiment 4, wherein at least one of the glass core region and the glass inner cladding region is made of doped silica glass.

[0129] Embodiment 6 The method according to Embodiment 4 or 5, wherein the glass inner cladding region consists of one or more undoped or lightly doped inner cladding portions.

[0130] Embodiment 7 The method according to any one of Embodiments 1 to 6, wherein the upper end of each glass cladding portion includes a recess defined by a raised outer lip.

[0131] Embodiment 8 The method according to any one of Embodiments 2 to 7, wherein the bottom glass lid has an outer periphery lip that defines a recess that forms part of the substantially sealed internal chamber.

[0132] Embodiment 9 The method according to Embodiment 8, wherein the bottom glass lid includes a passage from the recess to the outer surface, and the passage permits gas from the ambient environment to flow through the internal chamber.

[0133] Embodiment 10 The method according to Embodiment 9, wherein the gas from the ambient environment contains chlorine.

[0134] Embodiment 11 The method according to any one of Embodiments 8 to 10, wherein applying the vacuum is performed through the axial hole of the upper glass lid.

[0135] Embodiment 12 The method according to Embodiment 11, wherein the vacuum is provided from a vacuum system through a flexible vacuum conduit glass-welded to the upper glass lid.

[0136] Embodiment 13 The method according to any one of Embodiments 1 to 12, wherein the one or more shaft holes consist of a single shaft hole, and the one or more canes consist of a single cane present in the single shaft hole.

[0137] Embodiment 14 The method according to any one of Embodiments 1 to 13, wherein heating of the integrally held preform assembly is performed using a furnace.

[0138] Embodiment 15 The method according to Embodiment 14, wherein the furnace includes an optical fiber drawing furnace.

[0139] Embodiment 16 The method according to Embodiment 15, further comprising the step of drawing an optical fiber from the cane-based glass preform using the drawing furnace without removing the cane-based preform from the drawing furnace.

[0140] Embodiment 17 The method according to any one of Embodiments 1 to 16, wherein the substantially sealed internal chamber comprises at least one vacuum hole defining a part of the substantially sealed internal chamber.

[0141] Embodiment 18 The method according to any one of Embodiments 1 to 17, wherein each cane has a cane diameter DC, each shaft hole has a hole diameter DH > DC, and the substantially sealed internal chamber includes a gap formed by a difference between the hole diameter and the cane diameter for each shaft hole.

[0142] Embodiment 19 The method according to Embodiment 18, wherein the gap has a gap size δG = (DH - DC) / 2, and the gap size δG satisfies 0 < δG ≦ 0.1 mm.

[0143] Embodiment 20 The method according to any one of Embodiments 1 to 19, further comprising the step of drawing an optical fiber using the cane-based glass preform.

[0144] Embodiment 21 A method of forming a cane-based glass preform, comprising: forming one or more axial holes in each of a plurality of glass cladding portions, each having a body, an upper end, a bottom end, and an outer periphery, wherein each upper end has a lip extending around the outer periphery and defining an upper recess, and each axial hole is defined by a cylindrical inner surface within the body; stacking the plurality of glass cladding portions such that the axial holes formed within each glass cladding portion are aligned along an axis, the stacked plurality of glass cladding portions having an overall stacked length LS, a topmost glass cladding portion, and a bottommost glass cladding portion; inserting one or more glass canes into the one or more aligned axial holes of the plurality of glass cladding portions, such that a gap exists between each glass cane and the cylindrical inner surface of the axial hole in which the glass cane is located; aligning a glass top cover with the upper end of the topmost glass cladding portion and aligning a glass bottom cover with the bottom end of the bottommost glass cladding portion to define a preform assembly having a substantially sealed internal chamber, the internal chamber including the upper recess and the gaps; applying a vacuum through the glass top cover to the substantially sealed internal chamber to create a pressure differential with respect to the ambient environment, the pressure differential holding the preform assembly together to form a preform assembly held in vacuum; heating the preform assembly held in vacuum to just above the glass softening point to fuse the preform assembly held in vacuum to form a glass preform; and a method comprising the steps of:

[0145] Embodiment 22 The method according to embodiment 21, wherein each cane has a cane length LC that is at least of the same order as the stacked length LS.

[0146] Embodiment 23 The method according to embodiment 21 or 22, wherein each cane comprises a glass core region surrounded by a glass inner cladding region.

[0147] Embodiment 24 The method according to embodiment 23, wherein at least one of the glass core region and the glass inner cladding region is made of doped silica glass.

[0148] Embodiment 25 The method according to embodiment 23 or 24, wherein the glass inner cladding region consists of one or more undoped or lightly doped inner cladding portions.

[0149] Embodiment 26 The method according to any one of embodiments 21 to 25, wherein the glass bottom cover has an outer peripheral lip defining a recess that forms part of the outer surface and the substantially sealed inner chamber.

[0150] Embodiment 27 The method according to embodiment 26, wherein the glass bottom cover includes a passage from the recess to the outer surface, the passage allowing gas from the ambient environment to flow through the inner chamber while substantially maintaining the pressure difference.

[0151] Embodiment 28 The method according to embodiment 27, wherein the gas from the ambient environment contains chlorine.

[0152] Embodiment 29 The method according to any one of embodiments 21 to 28, wherein applying the vacuum is performed through the axial hole of the upper cover.

[0153] Embodiment 30 The method according to embodiment 29, wherein the vacuum is provided via a flexible vacuum conduit that is glass-welded to the upper cover from a vacuum system and is in air communication with the axial hole of the upper cover.

[0154] Embodiment 31 The method according to any one of Embodiments 21 to 30, wherein the one or more shaft holes consist of a single shaft hole, and the one or more canes consist of a single cane present in the single shaft hole.

[0155] Embodiment 32 The method according to any one of Embodiments 21 to 31, wherein the heating of the preform assembly held in the vacuum is performed using a furnace.

[0156] Embodiment 33 The method according to Embodiment 32, wherein the furnace includes an optical fiber drawing furnace.

[0157] Embodiment 34 The method according to Embodiment 33, further including the step of drawing an optical fiber from the cane-based glass preform using the drawing furnace without removing the cane-based preform from the drawing furnace.

[0158] Embodiment 35 The method according to any one of Embodiments 21 to 34, wherein the substantially sealed internal chamber includes at least one vacuum hole that defines a part of the substantially sealed internal chamber.

[0159] Embodiment 36 The method according to any one of Embodiments 21 to 35, wherein each cane has a cane diameter DC, each shaft hole has a hole diameter DH > DC, and the internal chamber includes a gap formed by the difference between the hole diameter and the cane diameter for each shaft hole.

[0160] Embodiment 37 The method according to Embodiment 36, wherein the gap has a gap size δG = (DH - DC) / 2, and the gap size δG is in the range of 0 < δG ≤ 0.1 mm.

[0161] Embodiment 38 The method according to any one of Embodiments 21 to 37, further including the step of drawing an optical fiber using the cane-based glass preform.

[0162] Embodiment 39 A method of forming a cane-based glass preform assembly, comprising: forming one or more axial holes in at least one glass cladding portion, said at least one glass cladding portion having an upper end and a bottom end; inserting one or more canes into said one or more axial holes respectively, so that each axial hole contains one cane; forming a preform assembly having an internally sealed chamber substantially sealed by covers at said upper end and bottom end, said internal chamber being in air communication connection with said upper end and bottom end through said axial holes; applying a vacuum to said substantially sealed internal chamber to create a pressure difference between said substantially sealed internal chamber and the surrounding environment to form a preform assembly held in vacuum; and a method comprising:

[0163] Embodiment 40 The method according to embodiment 39, further comprising heating the preform assembly held in vacuum to just above the glass softening point to combine the preform assemblies held in vacuum to form a cane-based glass preform.

[0164] Embodiment 41 A method of forming a cane-based glass preform assembly for forming a multi-core optical fiber, comprising: stacking a plurality of glass cane portions each having a plurality of axial holes so that the axial holes are aligned, adjacent glass cane portions contacting each other with a raised lip forming an internal cavity, and there being a top glass cane portion and a bottom glass cane portion; inserting one cane into each of said aligned axial holes to define a gap within said axial holes, said gap providing air communication between said internal cavities; forming a preform assembly having an internally sealed chamber substantially sealed by covers on said top and bottom glass cane portions, said internal chamber including said internal cavities and said gaps; Applying a vacuum to the substantially sealed internal cavity to form a preform assembly held in a vacuum A method comprising.

[0165] Embodiment 42 The method according to embodiment 41, further comprising heating the preform assembly held in the vacuum to just above the glass softening point to combine the preform assemblies held in the vacuum to form a cane - based glass preform.

[0166] Embodiment 43 The method according to embodiment 42, further comprising drawing an optical fiber using the cane - based glass preform.

[0167] Embodiment 44 The method according to embodiment 43, wherein the combining is performed using a furnace and the drawing is performed using the furnace.

[0168] Embodiment 45 A cane - based preform product, wherein the process of forming the preform product Applying a vacuum to a preform assembly, the preform assembly comprising at least one glass cladding portion having one or more axial holes, an upper end, a bottom end, and canes present in each of the one or more axial holes, and an upper lid is attached to the upper end and a bottom lid is attached to the bottom end; Heating the preform assembly held in a vacuum to just above the glass softening point to combine the preform assemblies held in the vacuum to form a cane - based glass preform.

[0169] Embodiment 46 A cane - based glass preform product, wherein the process of forming the preform product Forming one or more axial holes in each of a plurality of glass clad portions each having a body, an upper end, a bottom end, and an outer periphery, wherein each of the upper ends has a lip extending around the outer periphery and defining an upper recess, and each of the axial holes is defined by a cylindrical inner surface within the body; Stacking the plurality of glass clad portions such that the axial holes formed within each glass clad portion are aligned along an axis, the stacked plurality of glass clad portions having an overall stacked length LS, a topmost glass clad portion, and a bottommost glass clad portion; Inserting one or more glass canes into the one or more aligned axial holes of the plurality of glass clad portions, such that there is a gap between each glass cane and the cylindrical inner surface of the axial hole in which the glass cane is located; Aligning a glass top cover with the upper end of the topmost glass clad portion and aligning a glass bottom cover with the bottom end of the bottommost glass clad portion to define a preformed assembly having a substantially sealed internal chamber, the internal chamber including the upper recess and the gap; Applying a vacuum through the glass top cover to the substantially sealed internal chamber to create a pressure differential with respect to the ambient environment, the pressure differential holding the preformed assembly together to form a preformed assembly held in vacuum; Heating the preformed assembly held in vacuum to just above the glass softening point to fuse the preformed assembly held in vacuum to form a glass preform; A cane-based glass preform product comprising.

[0170] Embodiment 47 A cane-based glass preform assembly product, wherein the process for forming the assembly product is Forming one or more axial holes in at least one glass clad portion, the at least one glass clad portion having an upper end and a bottom end; Inserting one or more canes into the one or more shaft holes respectively, such that each shaft hole contains one cane, and forming a preform assembly having an internal chamber substantially sealed by covers at the upper end and the bottom end, wherein the internal chamber is in air communication connection with the upper end and the bottom end through the shaft holes, and applying a vacuum to the substantially sealed internal chamber to create a pressure difference between the substantially sealed internal chamber and the surrounding environment to form a preform assembly held by vacuum A cane-based glass preform assembly product comprising:

[0171] Embodiment 48 A cane-based glass preform product, wherein the process of forming the preform product comprises the process according to Embodiment 47, and heating the preform assembly held by vacuum to just above the glass softening point to combine the preform held by vacuum to form a cane-based glass preform. A cane-based glass preform product comprising:

[0172] Embodiment 49 A cane-based glass preform assembly product for forming a multi-core optical fiber, wherein the process of forming the assembly product comprises stacking a plurality of glass cane portions each having a plurality of shaft holes such that the shaft holes are aligned, wherein adjacent glass cane portions contact each other with a raised lip forming an internal cavity, and there are a top glass cane portion and a bottom glass cane portion, and inserting one cane into each of the aligned shaft holes to define a gap within the shaft holes, the gap providing air communication between the internal cavities, and forming a preform assembly having an internal chamber substantially sealed by covers on the top and bottom glass cane portions, the internal chamber including the internal cavities and the gaps, and Applying a vacuum to the substantially sealed internal cavity to form a preform assembly held in a vacuum A cane-based glass preform assembly product comprising the above

[0173] Embodiment 50 A cane-based glass preform product, wherein the process for forming the preform product is the process according to Embodiment 49, and heating the preform assembly held in the vacuum to just above the glass softening point to join the preform assembly held in the vacuum to form a cane-based glass preform. A cane-based glass preform product comprising the above

Explanation of Reference Numerals

[0174] 10 Glass cladding portion 11 Cylindrical glass body 12 Upper surface 13 Upper end 14 Bottom surface 15 Bottom end 16 Outer surface 18 Outer circumference 20 Lip 24 Recess 40 Axial hole 42 Open upper end 44 Open bottom end 46 Cylindrical inner surface 50 Cane 51 Glass body 51c Core section 51i Inner cladding section 52 Upper end 54 Bottom end 56 Outer surface 70 Upper lid 71 Body 72 Upper end 74 Bottom surface 75 Bottom end 90 Bottom lid 92 Upper surface 93 Upper end 94 Bottom end 95 Conical portion 96 Outer surface 98 Periphery 100 Lip 101 Passageway 102 Inner wall 104 Recess 120 Can clad assembly 150 Preform assembly 152 Upper end portion 153 Central portion 154 Bottom end portion 200 Preform system 210 Vacuum system 216 Vacuum conduit 230A Ambient air environment 230F Furnace ambient atmosphere 250 Internal cavity / internal chamber 300 Furnace 400 Glass preform 600 Optical fiber

Claims

1. 1. A method of forming a cane-based glass preform, comprising: forming a vacuum-based preform assembly by applying a vacuum to a preform assembly, the vacuum creating a pressure differential relative to the surrounding environment sufficient to hold the preform assembly together, the preform assembly comprising at least one glass cladding portion having one or more axial holes and a top end and a bottom end, one or more canes within each of the one or more axial holes, and a top glass cover at the top end and a bottom glass cover at the bottom end, the top glass cover and the bottom glass cover defining a substantially sealed interior chamber; heating the vacuum-held preform assembly to combine the vacuum-held preforms to form a cane-base glass preform, the vacuum-held preform assembly being heated to a temperature that causes the glass cladding, the cane, the glass top cover, and the glass bottom cover to simultaneously seal to one another in all directions, the internal chamber disappears, and is ready to pull, does not require special fixtures to hold the vacuum-held preform assembly during combination, and allows the surface of the vacuum-held preform assembly to be finely ground rather than polished. The method includes:

2. Prior to the step of applying a vacuum, the preform assembly is drilling the at least one glass cladding portion to form the one or more axial holes; operably disposing the one or more canes within the one or more axial bores; attaching said top glass cover and said bottom glass cover to said top and bottom ends, respectively, of said at least one glass clad portion to define said substantially sealed internal chamber; The method of claim 1 , further comprising forming the first insulating layer by:

3. 3. The method of claim 1 or 2, wherein the at least one glass clad section comprises two or more glass clad sections stacked together with their axial holes aligned and having an axial length, an uppermost glass clad section defining the top end and a lowermost glass clad section defining the bottom end, and the one or more canes each having a cane length at least substantially equal to or greater than the axial length.

4. The method of any of claims 1 to 3, wherein each of the one or more canes comprises a glass core region surrounded by a glass inner cladding region.

5. The method of any of claims 1 to 4, wherein the upper end of each glass clad portion includes a recess defined by a raised outer lip.

6. The method of any of claims 2 to 5, wherein the glass bottom lid has an outer surface and a peripheral lip defining a recess that constitutes a portion of the substantially sealed internal chamber.

7. The method of claim 6 , wherein the glass bottom cover includes a passageway from the recess to the exterior surface, the passageway allowing gas from the surrounding environment to flow through the interior chamber.

8. The method of any one of claims 1 to 7, wherein the one or more axial bores comprise a single axial bore, and the one or more canes comprise a single cane residing within the single axial bore.

9. 9. The method of claim 1, wherein each cane has a cane diameter DC and each axial bore has a bore diameter DH>DC, and the substantially sealed interior chamber includes a gap formed by a difference between the bore diameter and the cane diameter for each axial bore, the gap having a gap size δG=(DH-DC) / 2, where 0<δG≦0.1 mm.

10. 1. A method of forming a cane-based glass preform, comprising: forming one or more axial bores in each of a plurality of glass clad portions, each having a body, a top end, a bottom end, and an outer periphery, each of said top ends having a lip extending around said periphery defining an upper recess, each of said axial bores being defined by an inner cylindrical surface within said body; stacking the plurality of glass clad sections such that the axial holes formed in each of the glass clad sections are aligned along an axis, the stacked plurality of glass clad sections having a total stack length LS, a topmost glass clad section, and a bottommost glass clad section; inserting one or more glass canes into the one or more aligned axial bores of the plurality of glass clad portions, respectively, so that there is a gap between each glass cane and the cylindrical inner surface of the axial bore within which the glass cane resides; aligning a top glass cover with the top end of the topmost glass clad portion and a bottom glass cover with the bottom end of the bottommost glass clad portion to define a preform assembly having a substantially sealed internal chamber, the internal chamber including the top recess and the gap; applying a vacuum to the substantially sealed interior chamber through the glass top cover to create a pressure differential with respect to an ambient environment, the pressure differential holding the preform assembly together to form a vacuum-held preform assembly; heating the vacuum-held preform assembly to combine the vacuum-held preform assemblies to form a cane-base glass preform, the vacuum-held preform assembly being heated to a temperature that causes the glass cladding portion, the glass cane, the glass top cover, and the glass bottom cover to simultaneously seal to one another in all directions, the internal chamber disappears, and the assembly to be ready to pull, does not require special fixtures to hold the vacuum-held preform assembly during combination, and allows the surface of the vacuum-held preform assembly to be finely ground rather than polished. The method includes:

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