Method for producing a hollow core fiber

Abstract

The present disclosure relates to a method of manufacturing a hollow core optical fiber by drawing a hollow core preform 100. A hollow core preform 100 includes an annular support structure 130 having an inner surface 132 defining an inner cavity 105. The inner cavity 105 comprises at least one tube 120 in direct contact with the inner surface of the annular support structure. The tube 120 includes a wall defining an inner opening 124, the inner opening 124 having a sealed end. There is an additional non-sealed tube 120. The tube 120 may form an anti-resonance coated capillary in the optical fiber. Drawing includes adjusting a pressure of the inner cavity to a predetermined pressure.

Description

[0001] This application claims the benefit of priority under 35 U.S.C. §120 to U.S. Provisional Application Serial No. 63 / 394,123, filed on August 1, 2022, the contents of which are hereby relied upon and incorporated herein by reference in its entirety.

[0002] background Technical Field

[0003] The present specification relates generally to methods for producing optical fibers, and more particularly to methods for producing hollow core optical fibers. Background Art

[0004] Hollow core optical fibers transmit light through a hollow core. Some hollow core optical fibers include capillaries as cladding elements, but manufacturing such hollow core optical fibers can be difficult. Specifically, when drawing a preform into a hollow core optical fiber, maintaining the desired configuration can be challenging because the capillaries can collapse during the drawing process. Therefore, there is a need for improved methods of manufacturing hollow core optical fibers. Summary of the invention

[0005] According to a first aspect of the present disclosure, a method for producing an optical fiber comprises: drawing a hollow-core optical fiber from a hollow-core preform, the hollow-core preform comprising an annular support structure having an inner surface defining an inner cavity, the inner cavity comprising a sealing tube in contact with the inner surface, the sealing tube comprising a wall defining an inner opening, the inner opening having a sealed end, the drawing comprising adjusting the pressure of the inner cavity to a predetermined pressure from -1.0 psig to 3.0 psig.

[0006] A second aspect of the present disclosure may include the first aspect or aspects 53 to 54, wherein the inner cavity includes two or more sealed tubes.

[0007] A third aspect of the present disclosure may include the first or second aspect or aspects 53 to 54, wherein the inner cavity further comprises an open tube in contact with the inner surface, the open tube comprising a wall defining an inner opening, the inner opening lacking a sealed end.

[0008] A 4th aspect of the present disclosure may include any one of aspects 1 to 3 or aspects 53 to 54, wherein the method further comprises forming a sealed end of the inner opening.

[0009] A fifth aspect of the present disclosure may include the fourth aspect or aspects 53 to 54, wherein forming the sealed end portion includes heating the end portion of the inner opening.

[0010] A sixth aspect of the present disclosure may include the fourth aspect or any of aspects 53 to 54, wherein forming the sealed end portion includes laser welding the end portion of the inner opening.

[0011] A 7th aspect of the present disclosure may include the 4th aspect or any of aspects 53 to 54, wherein forming the sealed end portion includes plasma welding the end portion of the inner opening.

[0012] An 8th aspect of the present disclosure may include the 4th aspect or the 53rd to 54th aspects, wherein a sealed end flame welded opening end is formed.

[0013] A 9th aspect of the present disclosure may include any one of aspects 1 to 8 or aspects 53 to 54, wherein the sealing tube is in direct contact with the inner surface of the annular support structure.

[0014] A tenth aspect of the present disclosure may include any one of aspects 1 to 9 or aspects 53 to 54, wherein drawing changes the diameter of the hollow core optical fiber, and the capillary is formed by the sealing tube during the drawing process.

[0015] An 11th aspect of the present disclosure may include any one of aspects 1 to 10 or aspects 53 to 54, wherein drawing changes the thickness of the wall of a capillary of the optical fiber, the capillary being formed by the sealing tube during the drawing process.

[0016] A 12th aspect of the present disclosure may include any one of aspects 1 to 11 or aspects 53 to 54, wherein drawing changes the diameter of the hollow core of the hollow core optical fiber, the hollow core being formed by a hollow section of the inner cavity during the drawing process.

[0017] A 13th aspect of the present disclosure may include any one of aspects 1 to 12 or aspects 53 to 54, wherein the drawing is performed at a temperature of 1700°C to 2150°C.

[0018] A 14th aspect of the present disclosure may include any one of aspects 1 to 13 or aspects 53 to 54, wherein the hollow core preform is drawn at a rate of 10 m / min to 60 m / s.

[0019] A 15th aspect of the present disclosure may include any one of aspects 1 to 14 or aspects 53 to 54, wherein the hollow core preform is drawn at a tension of 30 g to 400 g.

[0020] A sixteenth aspect of the present disclosure may include any one of aspects one to fifteen, wherein the predetermined pressure varies with time.

[0021] A 17th aspect of the present disclosure may include any one of aspects 1 to 16, wherein the predetermined pressure is from -0.5 psig to 2.0 psig.

[0022] An eighteenth aspect of the present disclosure may include any one of aspects 1 to 17, wherein adjusting the pressure of the hollow cavity includes increasing the pressure in the hollow cavity.

[0023] Aspects 19 of the present disclosure may include any one of aspects 1 to 17, wherein adjusting the pressure of the hollow cavity includes reducing the pressure in the hollow cavity.

[0024] 20 aspects of the present disclosure may include any one of aspects 1 to 19, wherein adjusting the pressure of the hollow cavity comprises delivering one or more gases into the hollow cavity.

[0025] Aspect 21 of the present disclosure may include any one of aspects 1 to 20, wherein adjusting the pressure of the hollow cavity comprises delivering an inert gas into the hollow cavity.

[0026] Aspect 22 of the present disclosure may include any one of aspects 1 to 21, wherein adjusting the pressure of the hollow cavity comprises delivering air into the hollow cavity.

[0027] A 23rd aspect of the present disclosure may include any one of aspects 1 to 22, wherein adjusting the pressure changes the diameter of a capillary of the hollow core optical fiber, the capillary being formed by the sealing tube.

[0028] 24 aspects of the present disclosure may include any one of aspects 1 to 23, wherein adjusting the pressure changes the thickness of a wall of a capillary of the hollow core optical fiber, the capillary being formed by a sealed tube.

[0029] A 25th aspect of the present disclosure may include any one of aspects 1 to 24, wherein adjusting the pressure changes the diameter of a hollow core of the hollow core optical fiber, the hollow core being formed by a hollow section of the inner cavity.

[0030] A 26th aspect of the present disclosure may include any one of aspects 1 to 25 or aspects 53 to 54, wherein the annular support structure comprises silica-based glass.

[0031] A 27th aspect of the present disclosure may include any one of aspects 1 to 26 or aspects 53 to 54, wherein the wall of the sealing tube comprises silica-based glass.

[0032] A 28th aspect of the present disclosure may include any one of aspects 1 to 27 or aspects 53 to 54, wherein the inner cavity contains one or more gases.

[0033] A 29th aspect of the present disclosure may include any one of aspects 1 to 28 or aspects 53 to 54, wherein the inner cavity is substantially composed of air.

[0034] A 30th aspect of the present disclosure may include any one of aspects 1 to 29 or aspects 53 to 54, wherein the inner cavity is substantially composed of an inert gas.

[0035] Aspect 31 of the present disclosure may include any one of aspects 1 to 30 or aspects 53 to 54, wherein the hollow core preform further includes an overclad, and the annular support structure is positioned between the overclad and the hollow cavity.

[0036] A 32nd aspect of the present disclosure may include the 31st aspect or the 53rd to 54th aspects, wherein the outer coating comprises a silica-based glass.

[0037] A 33rd aspect of the present disclosure may include any one of aspects 1 to 32 or aspects 53 to 54, wherein the sealing tube comprises a nested tube in contact with an inner surface of a wall of the sealing tube.

[0038] A 34th aspect of the present disclosure may include the 33rd aspect, wherein the nested capillary tube contacts the inner surface of the wall of the sealing tube at a point proximate to the inner surface of the annular support structure.

[0039] A 35th aspect of the present disclosure may include any of the 33rd or 34th aspects, wherein the nested tube is in direct contact with the inner surface of the wall of the sealing tube.

[0040] A 36th aspect of the present disclosure may include any one of aspects 33 to 35, wherein the nested tube has a sealed end proximate to a sealed end of the inner opening of the sealing tube.

[0041] A 37th aspect of the present disclosure may include any one of aspects 33 to 36, wherein the nested tubes comprise silica-based glass.

[0042] According to the 38th aspect of the present disclosure, a hollow core optical preform comprises an annular support structure having an inner surface defining an inner cavity, the inner cavity comprising a sealing tube in contact with the inner surface, the sealing tube comprising a wall defining an inner opening, the inner opening having a sealed end.

[0043] A 39th aspect of the present disclosure may include the 38th aspect or any of aspects 55 to 56, wherein the sealing tube is in direct contact with the inner surface of the annular support structure.

[0044] A 40th aspect of the present disclosure may include the 38th or 39th aspect or the 55th to 56th aspects, wherein the hollow cavity includes two or more sealed tubes.

[0045] Aspect 41 of the present disclosure may include any one of aspects 38 to 40 or aspects 55 to 56, wherein the inner cavity further comprises an open tube in contact with the inner surface, the open tube comprising a wall defining a second inner opening, the second inner opening lacking a sealed end.

[0046] A 42nd aspect of the present disclosure may include the 41st aspect, wherein the open tube is in direct contact with the inner surface of the annular support structure.

[0047] A 43rd aspect of the present disclosure may include any one of aspects 38 to 42 or aspects 55 to 56, wherein the annular support structure comprises silica-based glass.

[0048] A 44th aspect of the present disclosure may include any one of aspects 38 to 43 or aspects 55 to 56, wherein the wall of the sealing tube comprises silica-based glass.

[0049] A 45th aspect of the present disclosure may include any one of aspects 38 to 44 or aspects 55 to 56, wherein the inner cavity contains one or more gases.

[0050] A 46th aspect of the present disclosure may include any one of aspects 38 to 45 or aspects 55 to 56, wherein the inner cavity is substantially composed of air.

[0051] A 47th aspect of the present disclosure may include any one of aspects 38 to 46 or aspects 55 to 56, wherein the inner cavity is substantially composed of an inert gas.

[0052] A 48th aspect of the present disclosure may include any one of aspects 38 to 47 or aspects 55 to 56, wherein the sealing tube comprises a nested tube, wherein the nested tube contacts an inner surface of a wall of the sealing tube.

[0053] A 49th aspect of the present disclosure may include the 48th aspect, wherein the nested tube is in direct contact with the inner surface of the wall of the sealing tube.

[0054] A 50th aspect of the present disclosure may include the 48th aspect or the 49th aspect, wherein the nested tube contacts the inner surface of the wall of the sealing tube at a point proximate to the inner surface of the annular support structure.

[0055] A 51st aspect of the present disclosure may include any one of aspects 48 to 50, wherein the nested tube has a sealed end proximate to a sealed end of the inner opening of the sealing tube.

[0056] A 52nd aspect of the present disclosure may include any one of aspects 48 to 51, wherein the nested tubes comprise silica-based glass.

[0057] According to the 53rd aspect of the present disclosure, a method for producing a hollow core optical fiber includes: drawing a hollow core optical fiber from a hollow core preform, wherein the hollow core preform includes an annular support structure having an inner surface defining an inner cavity, the inner cavity having a sealed end and including a tube in contact with the inner surface.

[0058] A 54th aspect of the present disclosure may include the 53rd aspect, wherein the tube is a sealed tube comprising a wall defining an inner opening having a sealed end.

[0059] According to the 55th aspect of the present disclosure, a hollow core optical fiber preform comprises an annular support structure having an inner surface defining an inner cavity, the inner cavity having a sealed end and comprising a sealing tube in contact with the inner surface, the sealing tube comprising a wall defining an inner opening, the inner opening having a sealed end.

[0060] A 56th aspect of the present disclosure may include the 55th aspect, wherein the tube is a sealed tube comprising a wall defining an inner opening having a sealed end.

[0061] A 57th aspect of the present disclosure may include any one of aspects 1 to 56, wherein the sealed end comprises material of the tube fused to itself.

[0062] Additional features and advantages are set forth in the following detailed description, and in part will be apparent to those skilled in the art from that description or may be learned by practicing the embodiments described herein, including the following detailed description, claims, and accompanying drawings.

[0063] It should be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overall review or framework for understanding the nature and characteristics of the claimed subject matter. The included drawings provide a further understanding of the various embodiments, and the drawings are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein and, together with the description, are used to explain the principles and operation of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1A schematically shows a cross-sectional view of a hollow core preform according to one or more embodiments described herein;

[0065] Figure 1B Schematically showing a cross-sectional view of a hollow core optical fiber drawn from a hollow core preform according to one or more embodiments described herein;

[0066] Figure 2A schematically shows a cross-sectional view of a hollow core preform according to one or more embodiments described herein;

[0067] Figure 2B Schematically showing a cross-sectional view of a hollow core optical fiber drawn from a hollow core preform according to one or more embodiments described herein;

[0068] Figure 3 Schematically showing a drawing production system according to one or more embodiments described herein;

[0069] Figure 4A A cross section of the hollow core optical fiber of Example 1 is shown;

[0070] Figure 4B A cross section of the hollow core optical fiber of Example 1 is shown;

[0071] Figure 4C A cross section of the hollow core optical fiber of Example 1 is shown;

[0072] Figure 4D A cross section of the hollow core optical fiber of Example 1 is shown;

[0073] Figure 4E A cross section of the hollow core optical fiber of Example 1 is shown;

[0074] Figure 4F A cross section of the hollow core optical fiber of Example 1 is shown;

[0075] Figure 5 Graphically showing the diameter of the capillary of the hollow core optical fiber of Example 1 as a function of the centerline pressure;

[0076] Fig. 6A A cross section of the hollow core optical fiber of Example 2 is shown;

[0077] Figure 6B A cross section of the hollow core optical fiber of Example 2 is shown;

[0078] Figure 6C A cross section of the hollow core optical fiber of Example 2 is shown;

[0079] Fig.6D A cross section of the hollow core optical fiber of Example 2 is shown;

[0080] Fig. 6E A cross section of the hollow core optical fiber of Example 2 is shown;

[0081] Fig. 6F A cross section of the hollow core optical fiber of Example 2 is shown;

[0082] Figure 7 Graphically showing the diameter of the hollow core of the hollow core optical fiber of Example 2 as a function of the centerline pressure;

[0083] Figure 8 Graphically showing the inner diameter and outer diameter of the capillary of the hollow core optical fiber of Example 2 as a function of the centerline pressure;

[0084] Fig. 9A A cross section showing the hollow core optical fiber of Example 3; and

[0085] Fig. 9B A cross section of the hollow core optical fiber of Example 3 is shown. DETAILED DESCRIPTION

[0086] Reference will now be made in detail to various embodiments of hollow core optical fibers. Whenever possible, the same reference numerals will be used throughout the drawings to represent the same or similar components. In an embodiment, a method of producing a hollow core optical fiber may include drawing an optical fiber from a hollow core preform. The hollow core preform may include an annular support structure having an inner surface defining a hollow cavity. The hollow cavity may include a tube in direct contact with the inner surface. The tube may include a wall defining an inner opening, and the inner opening may have a sealed end. Drawing may include adjusting a pressure of the hollow cavity to a predetermined pressure.

[0087] Herein, ranges may be expressed as starting from "about" another specific value and / or ending at "about" another specific value. When such a range is expressed, another embodiment includes starting from the one specific value and / or ending at the other specific value. Similarly, when a value is expressed as an approximation using the antecedent "about," it is understood that the specific value constitutes another embodiment. It will also be understood that the endpoints of each range are significant both in relation to the other endpoint and independently of the other endpoint.

[0088] Directional terms used herein, such as up, down, right, left, front, back, top, and bottom, are only used with reference to the drawings in which they are drawn and are not intended to imply an absolute orientation.

[0089] The various components described herein may be referred to as being "directly connected" or "indirectly connected". Components are directly connected when they are joined to each other without an intervening structure. Components may be joined by fusion, melting, welding, soldering, adhesives, or any other suitable attachment means. Components are "indirectly connected" when they are joined to each other with an intervening structure. Examples of intervening structures include welding aids (e.g., glass frits, solders, fluxes), adhesives, and bonding materials. In an embodiment, indirectly connected components are connected only by welding aids, adhesives, or bonding materials. The term "connected" means "directly connected" or "indirectly connected". Components that are "directly connected" to each other are said to be in direct contact with each other. Components that are "indirectly connected" to each other are said to be in indirect contact with each other. Components that are "connected" to each other are in direct or indirect contact with each other.

[0090] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "an" component includes aspects having two or more such components unless the context clearly dictates otherwise.

[0091] Hollow core optical fiber can be produced by drawing a preform into an optical fiber. Some hollow core optical fibers contain capillaries as cladding elements or cladding elements containing capillaries. The capillaries serve to confine light to the hollow core of the optical fiber. The capillaries are formed by a tube in a preform used to form a hollow core optical fiber. In conventional preforms, the tube is directly connected to an annular support structure and is located at the center of the hollow cavity of the preform. During the drawing process of the preform, the tube may collapse or deform in any other way. This may affect the shape or size of the capillary formed by the tube and reduce the effectiveness of the capillary as a cladding element to confine light to the hollow core of the optical fiber. In order to prevent the collapse or deformation of the tube, methods have been proposed to control the pressure in the hollow cavity and tube of the preform during the drawing process. However, it has been proven that it is challenging to independently control the pressure in the tube and in the hollow cavity (especially when it is produced on a large scale or for a long time). Conventional methods of controlling pressure include separately inputting gas into the hollow cavity and tube of the preform, which requires multiple pressure manifolds and precise control of the respective pressures. The production method of the hollow core optical fiber discussed herein simplifies the process of independently controlling the pressure in the hollow cavity and tube of the preform. Specifically, the method disclosed herein includes sealing one or more tubes of the preform at the end opposite to the end of the preform being drawn. The sealed end realizes the pressure control in the tube during the drawing process. The gas transmission can be made through the hollow cavity of the preform to control the pressure difference between the hollow cavity and the tube, thereby preventing the deformation or collapse of the tube during the drawing process. This method can simplify the pressure manifold required to provide gas to the hollow cavity, because the manifold does not need to separately provide or adjust the gas delivery to each tube. In addition, the method simplifies pressure control because the pressure difference between the hollow cavity and the tube is adjusted by making the gas transmission through the hollow cavity when the one or more tubes are sealed.

[0092] The production method of optical fiber includes drawing the optical fiber from a hollow core preform. Figure 1A , the hollow core preform 100 may include an annular support structure 130 having an inner surface 132 defining an inner cavity 105. The inner cavity 105 includes a hollow section 110 and a tube 220. The hollow section 110 is the central portion of the inner cavity 105 and corresponds to the hollow core region of the hollow core optical fiber 200 drawn from the hollow core preform 100. The tube 120 is in contact with the inner surface 132. Figure 1A In the illustrated embodiment, the tube 120a is in direct contact with the inner surface 132. It should be noted that Figure 1AThe illustrated embodiment of the hollow core preform 100 includes six tubes 120a, 120b, 120c, 120d, 120e, and 120f, which may be generally referred to as tubes 120 or collectively referred to as tubes 120. It should also be noted that similar notations are used for other repeating structures appearing in the figures of the present disclosure.

[0093] In an embodiment, the hollow core preform 100 may include two or more tubes 120. For example, the hollow core preform 100 may include two or more, three or more, four or more, five or more, or even six or more tubes 120, but is not limited thereto. In an embodiment, each tube 120 may be directly connected to the inner surface 132 of the annular support structure 130. For example, during the production process of the hollow core preform 100, each tube 120 may be fused to the inner surface 132, but is not limited thereto.

[0094] In an embodiment, each tube includes a wall 122 (i.e., walls 122a, 122b, 122c, 122d, 122e, and 122f) defining an inner opening 124 (i.e., inner openings 124a, 124b, 124c, 124d, 124e, and 124f). In an embodiment, at least one inner opening 124 of the tube 120 has a sealed end. In an embodiment, at least two tubes 120 have inner openings 124 with sealed ends. For example, at least two, at least three, at least four, at least five, or even at least six of the tubes 120 may have inner openings 124 with sealed ends, but are not limited thereto. In an embodiment where multiple tubes 120 have inner openings 124 with sealed ends, the sealed end of each tube 120 may be on the same end of the hollow core preform 100. Tubes with sealed ends are referred to herein as "sealed tubes." Tubes lacking sealed ends are referred to herein as "open tubes." The open tube has an open end. In an embodiment, the hollow core preform 100 includes only a sealed tube, only an open tube, or a combination of a sealed tube and an open tube. Unless otherwise specified, the reference numeral 120 refers to either a sealed tube or an open tube. When it is necessary to distinguish between a sealed tube and an open tube in the specification, the terms "sealed" and "open" are added as qualifiers when referring to the tube 120 (for example, "sealed tube 120" or "open tube 120"). In some embodiments, the inner cavity 105 has a sealed end. The inner cavity 105 with a sealed end is referred to as a "sealed inner cavity" herein. The inner cavity 105 lacking a sealed end is referred to as an "open inner cavity" herein. In an embodiment, the hollow core preform 100 includes an open inner cavity 105 and one or more tubes (sealed) 120. In an embodiment, the hollow core preform 100 includes a sealed inner cavity 105 and one or more sealed tubes 120. In an embodiment, the hollow core preform 100 includes a sealed inner cavity 105 and one or more open tubes 120. In an embodiment with a sealed tube or a sealed inner cavity, the tube or the inner cavity preferably has a sealed end and an open end. The one sealed end is preferably the end opposite to the drawing end of the hollow core preform 100.

[0095] The methods described herein for producing optical fibers may include a preliminary step to form sealed ends of one or more tubes 120. In an embodiment, the ends of the open tubes 120 may be heated to seal the ends to form sealed tubes. For example, the sealed ends of the tubes 120 may be formed by laser welding, plasma welding, flame welding, or by applying a bonding or filling compound to the open ends, but are not limited thereto. The heating may include heating the ends of the tubes 120 to a temperature suitable for softening the material of the tubes 120 so that the material flows together, thereby sealing the ends of the tubes 120. The same method may be used to form the sealed ends of the inner cavity 105. When the sealed ends of the tubes 120 are formed by heating, laser welding, plasma welding, or flame welding, the material of the tubes 120 fuses with itself to form a seal.

[0096] In an embodiment, the hollow core preform 100 further includes an outer cladding 140. The outer cladding is in contact with the outer surface of the annular support structure 130. In an embodiment, the outer cladding is in direct contact with the outer surface of the annular support structure 130. In such an embodiment, the annular support structure 130 may be located between the outer cladding 140 and the inner cavity 105.

[0097] See now Figure 2A In an embodiment, at least one tube 120 in the hollow core preform 100 may include a nested tube 150. As used herein, a "nested tube" refers to a tube positioned within another tube such that an outer surface of the nested tube is connected to an inner surface of the other tube. In an embodiment, the nested tube 150 may directly contact the inner surface 126 of the wall 122 of the tube 120. For example, in Figure 2A In the illustrated embodiment, the nested tubes 150a are in direct contact with the inner surface 126a of the wall 122a of the tube 120a. In an embodiment, each tube 120 in the hollow core preform 100 may include a nested tube 150 (i.e., Figure 2A The nested tubes 150a, 150b, 150c, 150d, 150e and 150f in the illustrated embodiment).

[0098] In an embodiment, the nested tube 150 may be directly or indirectly connected to the inner surface 126 of the wall 122 of the tube 120 at a point proximate to the inner surface 132 of the annular support structure 130. As described herein, a point may be proximate to the annular support structure 130 when it is the point closest to the annular support structure 130 as assessed in the radial direction 190. In an embodiment, the nested tube 150 may be directly or indirectly connected to the inner surface 126 of the wall 122 of the tube 120 at a point within 30° of the point proximate to the annular support structure 130. For example, the nested tube 150 may be directly or indirectly connected to the inner surface 126 of the wall 122 of the tube 120 at a point within 30°, 25°, 20°, 15°, 10°, 5°, or even 1° of the point proximate to the annular support structure 130, but is not limited thereto.

[0099] In an embodiment, the nested tubes 150 may include sealed ends proximate to the sealed ends of the inner opening of the sealed tube 120. The nested tubes 150 may be sealed in the same manner as the tubes 120 in which they are placed. For example, the nested tubes 150 may be sealed by heating the ends of the nested tubes 150, but is not limited thereto. In an embodiment, the ends of the nested tubes 150 may be sealed by laser welding, plasma welding, or flame welding. Heating may include heating the ends of the nested tubes 150 to a temperature suitable for softening the material of the nested tubes 150 so that the material flows together, thereby sealing the ends of the nested tubes 150.

[0100] In an embodiment, the hollow core preform 100 may include a drawing end. As described herein, the "drawing end" of the hollow core preform 100 is the end of the preform from which an optical fiber is drawn during the drawing process. In an embodiment, the sealed end of the inner opening 124 of the tube 120 is opposite the drawing end of the hollow core preform 100. In an embodiment where the hollow core preform 100 further includes a nested tube 150, the sealed ends of the tube 120 and the nested tube 150 may be opposite the drawing end of the hollow core preform 100. In such embodiments, the drawing end of the tube or nested tube may remain open.

[0101] Without intending to be limited by theory, sealing one end of the tube 120 (and, when included, the nested tube 150) can create a positive pressure in the tube during the drawing process. Sealing the ends of the tube 120 can trap gas in the tube 120 during the drawing process. As the gas is heated during the drawing process, the pressure of the gas in the sealed tube increases. This can result in a constant pressure in the capillary throughout the drawing process without the need for a separate device configured to pressurize and independently control the pressure of the tube 120. The temperature and environment of the drawing process establish and stabilize the gas pressure in the sealed tube 120. The stabilized gas pressure is consistent over time during the drawing process and acts to prevent the tube from collapsing during the drawing process. The gas pressure is also consistent and uniform across each of the multiple sealed tubes 120. The consistency and uniformity of the gas pressure in the sealed tube 120 helps to form a hollow core optical fiber drawn from the hollow core preform 100 having a capillary having uniform dimensions (diameter and wall thickness) over the extended length of the optical fiber. It should also be noted that although the drawing end of the tube 120 remains open when the hollow core preform 100 is initially heated during the drawing process, during the drawing process, the drawing end of the tube 120 eventually reaches a temperature at which the gas at the drawing end spit (gob) to seal the drawing end of the tube as the fiber is drawn. The diameter of the capillary 220 formed from the tube 120 during the drawing process is small enough to maintain a constant pressure in the tube 120 during the drawing process as the fiber is drawn.

[0102] In an embodiment, various components of the hollow core preform 100 may include silica-based glass. The silica-based glass may include pure silica or silica doped with one or more dopants to modify the refractive index or viscosity of the silica. In an embodiment, the annular support structure 130 may include silica-based glass. In an embodiment, the wall 122 of one or more tubes 120 includes silica-based glass. In an embodiment, the wall 122 of each tube 120 consists of or consists essentially of silica-based glass. In an embodiment, one or more nested tubes 150 may include silica-based glass. In an embodiment, the outer cladding 140 may include silica-based glass. Further, in an embodiment, any combination of the annular support structure 130, the tubes 120, the nested capillaries 150, and the outer cladding 140 may include silica-based glass.

[0103] In an embodiment, the space between the hollow section 110, the inner opening 124 and / or the tube 120 contains a gas. For example, the space between the hollow section 110, the inner opening 124 and / or the tube 120 may contain air, but is not limited thereto. In an embodiment, the space between the hollow section 110, the inner opening 124 and / or the tube 120 is substantially composed of air or even composed of air. In an embodiment, the space between the hollow section 110, the inner opening 124 and / or the tube 120 is substantially composed of an inert gas. As described herein, an inert gas refers to any gas that is not reactive during the drawing process. Inert gases may include, but are not limited to, nitrogen, argon, and helium. For example, the space between the hollow section 110, the inner opening 124 and / or the tube 120 may be substantially composed of one or more of nitrogen, argon, or helium, but is not limited thereto.

[0104] The method for producing a hollow core optical fiber may include drawing a hollow core preform 100 into an optical fiber. The hollow core preform 100 may be drawn from the end of the hollow core preform 100 opposite to the sealed end of the tube 120 (or, when included, the sealed end of the nested tube or the sealed end of the inner cavity) in the hollow core preform 100. The hollow core preform 100 may be drawn in any suitable drawing production system currently known in the art.

[0105] For example, the hollow core preform 100 can be drawn into an optical fiber in a drawing production system 1100, such as Figure 3 Schematically illustrated, but not limited thereto. Drawing production system 1100 includes a drawing furnace 1102, which is heated to an elevated temperature (e.g., greater than 1000° C.). Hollow core preform 100 is vertically arranged in drawing furnace 1102, and drawing furnace 1102 supplies heat to hollow core preform 100. In an embodiment, the drawing furnace may have a hot zone located about 0.5 inches to about 1 inch toward the bottom of preform 100, heated to a temperature sufficient to soften the drawing end (lower end) of preform 100 (e.g., 1700° C. or higher); however, it should be understood that in the method for producing hollow core optical fiber described herein, a drawing furnace with a larger or smaller hot zone may be used.

[0106] The drawing production system 1100 includes a manifold 1120 attached to the hollow core preform 100. The manifold 1120 can be attached to the end of the hollow core preform opposite the drawing end of the hollow core preform 100. The manifold 1120 can be fluidly connected to a gas supply 1122, and the manifold 1120 can operatively supply gas to the hollow core of the hollow core preform 100. The flow of gas from the gas supply 1122 to the hollow core preform 100 via the manifold 1120 can be controlled to adjust the pressure of the hollow core of the hollow core preform 100 during the drawing process. The flow of gas from the gas supply 1122 to the hollow core preform can be controlled by any suitable means. For example, the gas flow rate from the gas supply to the hollow core preform 110 can be controlled manually or by an automatic control system, but is not limited thereto.

[0107] During the fiber drawing process, the optical fiber 10 is pulled from the bottom portion (softened drawing end) of the hollow core preform 100 by the tractor 1106. After leaving the drawing furnace 1102, the optical fiber 10 encounters a diameter monitoring device 1108, which provides a signal for a feedback control loop to adjust the speed of the tractor 1106 and maintain a constant fiber diameter. The optical fiber 10 then passes through a fiber tension measurement device 1110, which measures the tension of the optical fiber 10 and provides a feedback control loop to adjust the tension of the optical fiber 10 and maintain a desired drawing tension setting.

[0108] Still see Figure 3 Once the optical fiber 10 is drawn from the hollow core preform 100, the optical fiber 10 is cooled in a cooling tube 1112 or other controlled cooling process device that can be connected to or remote from the outlet of the drawing furnace 1102, and then coated with a coater 1114, which can apply a polymer-based coating material to the outer surface of the optical fiber 10. The optical fiber 10 can also pass through a coating curing device 1116, which cures the polymer coating (for example, by ultraviolet light). The optical fiber 10 is then wound onto a spool or reel 1118. Various optical properties of the optical fiber (including bandwidth) are usually measured offline.

[0109] See now Figure 1B , shows a hollow core optical fiber 200. The hollow core optical fiber 200 can be obtained by, for example, Figure 1AThe hollow core preform 100 shown is drawn to form a hollow core optical fiber 200. The hollow core optical fiber 200 may include a substrate 230 having an inner surface 232 defining an inner space 205. The inner space 205 includes a hollow core 210 and a capillary 220. The hollow core 210 is the central portion of the inner space 205 and corresponds to a region in the hollow core optical fiber 200 where optical signals are confined. The capillary 220 is a cladding element of the hollow core optical fiber 200. The capillary 220 is in contact with the inner surface 232. Figure 1B In the illustrated embodiment, the capillary 220 is in direct contact with the inner surface 232. It should be noted that Figure 1B The illustrated embodiment of the hollow core fiber 200 includes six capillaries 220a, 220b, 220c, 220d, 220e, and 220f, which may be generally referred to as capillaries 220 or collectively as capillaries 120. The capillaries 220 are formed from corresponding tubes 120 of the hollow core preform 100 during the drawing process (e.g., capillary 220a is formed from tube 120a, etc.). The hollow core 210 is formed from the hollow section 110 of the hollow core preform 100. As the hollow core preform 100 is drawn, the tubes 120 thin and shrink in diameter to form the capillaries 220 of the hollow core fiber 200. Corresponding thinning and shrinking of the annular support structure 130 occurs to form the substrate 230. Corresponding shrinking of the hollow section 110 also occurs to form the hollow core 210. The hollow core fiber 200 can be considered as a scaled-down version of the hollow core preform 100. As discussed further below, pressure variations in the inner cavity 105 of the hollow core preform 100 during the drawing process and / or sealing of the tube 120 of the hollow core preform 100 enable control of the diameter and wall thickness of the capillary 220 and substrate 230, as well as the diameter of the hollow core 210.

[0110] In an embodiment, the hollow core fiber 200 may include two or more capillaries 220. For example, the hollow core fiber 200 may include two or more, three or more, four or more, five or more, or even six or more capillaries 220, but is not limited thereto. In an embodiment, each capillary 220 may be in direct contact with the inner surface 232 of the substrate 230.

[0111] In an embodiment, each capillary 220 includes a wall 222 (ie, walls 222a, 222b, 222c, 222d, 222e, and 222f) defining an inner opening 224 (ie, inner openings 224a, 224b, 224c, 224d, 224e, and 224f).

[0112] In an embodiment, the hollow core optical fiber 200 further includes an outer cladding 240 derived from the outer cladding 140 of the hollow core preform 100. The outer cladding 240 is in contact with the outer surface of the substrate 230. In an embodiment, the outer cladding 240 is in direct contact with the outer surface of the substrate 230. In such an embodiment, the substrate 230 is located between the outer cladding 240 and the hollow core 210.

[0113] See now Figure 2B , shows a hollow core optical fiber 200. The hollow core optical fiber 200 can be obtained by, for example, Figure 2A The hollow core preform 100 shown is drawn to form a hollow core optical fiber 200. In an embodiment, at least one capillary 220 in the hollow core optical fiber 200 may include a nested capillary 250. As used herein, a "nested capillary" refers to a capillary positioned within another capillary such that the outer surface of the nested capillary is connected to the inner surface of the other capillary. In an embodiment, the nested capillary 250 may directly contact the inner surface 226 of the wall 222 of the capillary 220. For example, in Figure 2B In the illustrated embodiment, the nested capillary 250a is in direct contact with the inner surface 226a of the wall 222a of the capillary 220a. In an embodiment, each capillary 220 in the hollow core optical fiber 200 may include a nested capillary 250 (i.e., Figure 2B Nested capillaries 250a, 250b, 250c, 250d, 250e, and 250f in the illustrated embodiment).

[0114] In embodiments, the nested capillary 250 may be directly or indirectly connected to the inner surface 226 of the wall 222 of the capillary 220 at a point that is proximate to the inner surface of the substrate 230. As described herein, a point may be proximate to the substrate 230 when it is the point closest to the substrate 230 as assessed in the radial direction 190. In embodiments, the nested capillary 250 may be directly or indirectly connected to the inner surface 226 of the wall 222 of the capillary 220 at a point that is within 30° of the point that is proximate to the substrate 230. For example, the nested capillary 250 may be directly or indirectly connected to the inner surface 226 of the wall 222 of the capillary 220 at a point that is within 30°, 25°, 20°, 15°, 10°, 5°, or even 1° of the point that is proximate to the substrate 230, but is not limited thereto.

[0115] See again Figure 1A In an embodiment, the drawing of the hollow core preform 100 changes the inner diameter D of the inner opening 124 of the one or more tubes 120. 1p Thus, a 1f Specifically, the drawing of the hollow core preform 100 can reduce the inner diameter D of the inner opening 124 of one or more tubes 120 to1p When the inner diameter D of the capillary 220 is formed, 1f When the capillary 220 is formed from the sealing tube 120, it is particularly easy to control the inner diameter D of the capillary 1f In an embodiment, the drawing of the hollow core preform 100 may reduce the inner diameter D of the inner opening 124 of each tube 120 by 1p Thus, a 1f The inner diameter D of the capillary 220 is 1f For example, but not limited to, 12 μm to 50 μm, 16 μm to 50 μm, 20 μm to 50 μm, 24 μm to 50 μm, 28 μm to 50 μm, 32 μm to 50 μm, 36 μm to 50 μm, 40 μm to 50 μm, 44 μm to 50 μm, 48 μm to 50 μm, 12 μm to 46 μm, 12 μm to 42 μm, 12 μm to 38 μm, 12 μm to 34 μm, 12 μm to 30 μm, 12 μm to 26 μm, 12 μm to 22 μm, 12 μm to 18 μm, 12 μm to 16 μm, or any combination or subset of these ranges. In an embodiment, each capillary may have the same inner diameter. In an embodiment, for example, Figure 2A In the illustrated embodiment, the drawing of the hollow core preform 100 changes the inner diameter D of one or more nested tubes 150. 2p Thus, a 2f For example, the drawing of the hollow core preform 100 can reduce the inner diameter D of one or more nested tubes 150 or even each nested tube 150. 2p Thus, a 2f The nested capillaries 250 are, but not limited to, these.

[0116] In an embodiment, the drawing of the hollow core preform 100 changes the diameter D of the hollow section 110. 3p As described herein, the diameter D of the hollow section 110 is 3p is the diameter of a circle that is concentric with the annular support structure 130 and tangential to the tube 120, shown as circle 170 in FIGS. 1 and 2. 3p The associated region is the hollow section 110 which defines the hollow core 210 of the hollow core optical fiber 200 drawn from the hollow core preform 100. The circle 170 defines the boundary of the hollow section 110 of the inner cavity 105. The diameter D 3p is twice the radius of the hollow section 110, wherein the radius of the hollow section 110 is the shortest distance from the center of the hollow section 110 to the outer surface 122 of the tube 120. 1pIn embodiments where the diameter and wall thickness are the same, the radius of the hollow section 110 is the same for all tubes 120. In some embodiments, the D of the tube 120 may be increased during the manufacturing process. 1p and / or small differences in wall thickness. In such embodiments, the radius of the hollow section 110 is taken to be the smallest radius of the different tubes 120; that is, the smallest distance from the center of the hollow section 110 to the point tangent to the tube 120. In embodiments, the drawing of the hollow core preform 100 can reduce the diameter D of the hollow section 110 3p Thus, a hollow core optical fiber 200 having a diameter D is formed. 3f The hollow fiber core 210 is provided.

[0117] The hollow core preform 100 may be drawn at a temperature of 1700°C to 2150°C. For example, the temperature for drawing the hollow core preform 100 may be 1700° C. to 2150° C., 1700° C. to 2100° C., 1700° C. to 2050° C., 1700° C. to 2000° C., 1700° C. to 1950° C., 1700° C. to 1900° C., 1700° C. to 1850° C., 1700° C. to 1800° C., 1700° C. to 1750° C., 1750° C. to 2150° C., 1800° C. to 2150° C., 1850° C. to 2150° C., 1900° C. to 2150° C., 1950° C. to 2150° C., 2000° C. to 2150° C., 2050° C. to 2150° C., 2100° C. to 2150° C., or any combination or subset of these ranges, but is not limited thereto.

[0118] In an embodiment, the hollow core optical fiber 200 may be drawn from the hollow core preform 100 at a rate of 0.1 m / s to 60 m / s. For example, the hollow core optical fiber 200 may be drawn from the hollow core preform 100 at the following rates: 0.1 m / s to 60 m / s, 0.5 m / s to 60 m / s, 1 m / s to 60 m / s, 5 m / s to 60 m / s, 10 m / s to 60 m / s, 20 m / s to 60 m / s, 30 m / s to 60 m / s, 40 m / s to 60 m / s, 50 m / s to 60 m / s / s to 60m / s, 0.1m / s to 50m / s, 0.1m / s to 40m / s, 0.1m / s to 30m / s, 0.1m / s to 20m / s, 0.1m / s to 10m / s, 0.1m / s to 5m / s, 0.1m / s to 1m / s, 0.1m / s to 0.5m / s, or any combination or subset of these ranges, but not limited to.

[0119] In an embodiment, the hollow core preform 100 may be drawn at a tension of 30 g to 400 g to form the hollow core optical fiber 200. For example, the tension for drawing the hollow core preform 100 may be 30 g to 400 g, 50 g to 400 g, 100 g to 400 g, 150 g to 400 g, 200 g to 400 g, 250 g to 400 g, 300 g to 400 g, 350 g to 400 g, 30 g to 350 g, 30 g to 300 g, 30 g to 250 g, 30 g to 200 g, 30 g to 150 g, 30 g to 100 g, 30 g to 50 g, or any combination or subset of these ranges, but is not limited thereto.

[0120] Drawing of the hollow core preform 100 may include adjusting the pressure of the inner cavity 105 to a predetermined pressure. In embodiments, the predetermined pressure may vary over time during the drawing process. Without intending to be limited by theory, the predetermined pressure may be a pressure that prevents the tube 120 from collapsing or deforming during the drawing process. During the drawing process, the pressure in the tube 120 may be greater than the pressure in the inner cavity 105, thereby preventing the capillary from collapsing. Adjusting the pressure difference between the tube 120 and the inner cavity 105 may achieve an inner diameter D of the inner opening 124 of the tube 120. 1p and the diameter D of the hollow section 110 of the hollow core preform 110 3p When the tube 120 is sealed, the pressure difference between the pressure in the capillary and the pressure in the inner cavity 105 can be adjusted by adjusting the pressure in the inner cavity 105. In an embodiment, the pressure of the inner cavity 105 can be adjusted by transmitting one or more gases through or into the inner cavity 105 via a manifold.

[0121] In an embodiment, the predetermined pressure of the inner cavity 105 can be 0.1 pounds-force per square inch (gauge) (psig) to 1.0 psig (689.5 Pascals (Pa) (gauge) to 6895 Pa (gauge) (wherein 0.0 psig = 14.7 psia (pounds-force per square inch (absolute)). For example, the predetermined pressure can be: -2.0 psig to 4.0 psig, -1.0 psig to 3.0 psig, -0.5 psig to 2.0 psig, 0.0 psig to 1.5 psig, 0.1 psig to 1.0 psig, 0.2 psig to 1.0 psig, 0.3 psig to 1.0 psig, 0. 4psig to 1.0psig, 0.5psig to 1.0psig, 0.6psig to 1.0psig, 0.7psig to 1.0psig, 0.8psig to 1.0psig, 0.9psig to 1.0psig, 0.1psig to 0.9psig, 0.1psig to 0.8psig, 0.1psig to 0.7psig, 0.1psig to 0.6psig, 0.1psig to 0.5psig, 0.1psig to 0.4psig, 0.1psig to 0.3psig, 0.1psig to 0.2psig, or any combination or subset of these ranges, but not limited to.

[0122] The effect of changing the pressure of the inner cavity 105 on the pressure in the opening 124 of the tube 120 is different for an open tube 120 and a sealed tube 120. The pressure in the opening 124 of the open tube 120 will closely correspond to the pressure of the inner cavity 105. However, the pressure in the opening 124 of the sealed tube 120 will be different from the pressure of the inner cavity 105 because the sealed end of the sealed tube 120 prevents the gas introduced into the inner cavity 105 from continuing to flow through the sealed tube 120. Preferably, the pressure in the opening 124 of the sealed tube 120 is greater than the pressure in the inner cavity 105. In embodiments with a sealed inner cavity 105, it is also possible to establish a difference in the pressure of the opening 124 of the tube 120 (whether sealed or open) and the pressure in the sealed cavity 105. For example, in some embodiments, because the diameter of the opening 124 is much smaller than the diameter of the hollow section 110, the gas transferred to the sealed inner cavity 105 may result in a difference in the gas flow rate into the open or sealed tube 120 and the sealed inner cavity 105. The difference in gas flow rate may result in a pressure difference, which enables control of the diameter of the capillary formed by the sealing tube when drawing the hollow core preform 100 having the inner cavity 105 with sealed ends.

[0123] In an embodiment, the pressure regulation of the inner cavity 105 includes increasing the pressure in the inner cavity 105. Without intending to be limited by theory, increasing the pressure of the inner cavity 105 (relative to the baseline pressure) during the drawing process can reduce the inner diameter D of the inner opening 224 of the capillary 220 in the hollow core optical fiber. 1f (Inner diameter D relative to baseline pressure 1f As the inner diameter D of the inner opening 224 of the capillary 220 increases 1f The diameter D of the hollow core 210 is reduced. 3f The wall thickness of the inner opening 224 of the capillary tube 220 increases.

[0124] In an embodiment, regulating the pressure of the inner cavity 105 includes reducing the pressure in the inner cavity 105. For example, a baseline pressure can be established in the inner cavity 105, and the pressure of the inner cavity 105 can be reduced from the baseline pressure to affect the inner diameter D of the inner opening 124 of the tube 120. 1p and / or the inner diameter D of the inner opening 224 of the capillary tube 220 1f Without intending to be bound by theory, reducing the pressure in the inner cavity 105 during the drawing process may increase the inner diameter D of the inner opening 124 of the tube 120. 1p and / or the inner diameter D of the inner opening 224 of the capillary 220 in the hollow core optical fiber 200 1f With the inner diameter D 1p As the pressure in the inner cavity 105 increases, the wall thickness of the tube 120 also decreases. In addition, reducing the pressure in the inner cavity 105 can reduce the diameter D of the hollow section 110 of the hollow core preform 100. 3p and / or the diameter D of the hollow core 210 of the hollow core optical fiber 200 3f .

[0125] In an embodiment, the pressure regulation of the inner cavity 105 includes delivering one or more gases into the inner cavity 105. In an embodiment, the one or more gases may include one or more inert gases. For example, the one or more inert gases may include nitrogen, argon, and helium. In one or more embodiments, the one or more gases may include air.

[0126] The one or more gases may be routed through a manifold (e.g., Figure 31120) into the inner cavity 105. In an embodiment, a method for producing a hollow core fiber 200 may include attaching a manifold 1120 to the hollow core preform 100 before drawing the hollow core preform 100 to form the hollow core fiber 200. The manifold 1120 may be any device suitable for delivering one or more gases to the inner cavity 105 during the drawing process. The manifold 1120 may be attached to the hollow core preform 100 by any suitable means. For example, the manifold 1120 may be formed of glass and may be welded to the hollow core preform 100, but is not limited thereto. It should be understood that the manifold 1120 may be attached to the hollow core preform 100, near the sealed end of the tube 120. Thus, the manifold 1120 can be used to supply gas to the inner cavity 110 of the hollow core preform 100 without also introducing gas into the sealed ends of the tubes 120 (and, when included, the nested tubes 150). Thus, the inclusion of the tubes 120 with sealed ends (and, when included, the nested tubes 150 with sealed ends) can simplify the connection of the manifold 1120 to the hollow core preform 100 by eliminating the need for a single manifold 1120 connected to the tubes 120 (and, when included, the nested tubes 150) to separately and independently regulate the pressure within each tube.

[0127] Drawing of the hollow core preform 100 can produce the hollow core optical fiber 200. As noted above, Figure 1A and 2A The drawing of the hollow core preform 100 shown produces Figure 1B and 2B The hollow core fiber 200 shown. The number, arrangement and size of the tubes 120 in the hollow core preform 100 can be changed to produce hollow core fibers 200 of various designs. In addition, by adjusting the pressure of the inner cavity 105 during the drawing process, the inner diameter D of the opening 224 of the capillary 220 can be controlled when the hollow core fiber 200 is drawn from a given hollow core preform 100. 1f , the inner diameter D of the opening of the nested capillary 250 2f , the wall thickness of the capillary 220 and the nested capillary 250, and the diameter D of the hollow core 210 of the hollow core optical fiber 200 3fThat is, by adjusting the pressure in the inner cavity 105 during the drawing process, various hollow core optical fibers 200 having different inner dimensions can be produced from the same hollow core preform 100. For example, during the drawing process of a specific hollow core preform 100, the pressure in the inner cavity 105 can be adjusted to a first predetermined pressure in a first time period to produce a hollow core optical fiber 200 having a first set of inner dimensions, and adjusted to a second predetermined pressure in a second time period to produce a hollow core optical fiber 200 having a second set of inner dimensions.

[0128] In an embodiment, the capillary 220 of the hollow core fiber 200 is configured by adjusting the pressure in the inner cavity 105 of the hollow core preform 100 to a predetermined pressure, thereby providing an anti-resonance effect to increase confinement of the optical signal in the hollow core 210 .

[0129] As used herein, "anti-resonance effect" refers to the effect that when the material thickness (e.g., the wall thickness of the capillary 220) is proportional to the wavelength of light passing through the hollow core fiber, the light passing through the hollow core fiber is confined to the hollow core. Without intending to be limited by theory, the anti-resonance effect exists when the material thickness satisfies the quarter wavelength condition (the phase accumulated over a single pass is one quarter of 2π, and any odd multiple of a quarter wave). When the material thickness applies this regime, the light is confined to the hollow core with minimized leakage to the cladding. In other words, this regime helps suppress coupling between the core mode and the cladding mode, resulting in low transmission losses and increased confinement of the optical signal in the hollow core. In one embodiment, the anti-resonance effect can be satisfied by a material having a thickness given by the following equation 1:

[0130]

[0131] In equation 1, t AR is the thickness of the material that satisfies the anti-resonance condition, λ is the wavelength of the optical signal, m is an integer greater than or equal to 1, and n is the refractive index of the material. It should be noted that Equation 1 represents the ideal thickness of the material that will satisfy the anti-resonance effect and is not exactly equal to t AR The material thickness can also provide increased light confinement in the hollow core. For example, the expected thickness is related to t AR The difference is within 10% (90% t AR Up to 110%t AR ) can be a material that is operable to confine light in a hollow fiber core, but is not limited to this.

[0132] In an embodiment, the capillary 220 is an anti-resonance element that can operatively confine the optical signal to the hollow core by suppressing the coupling mechanism. As used herein, "suppressing the coupling mechanism" refers to the effect that occurs when a cladding element having a negative curvature suppresses the coupling between the core mode and the cladding mode, thereby reducing light leakage from the hollow core. As used herein, "negative curvature" refers to a cladding element whose surface has a convex shape facing the central longitudinal axis of the hollow core optical fiber. Without intending to be limited by theory, the use of a cladding element having a convex shape on the surface facing the central longitudinal axis of the hollow core optical fiber can reduce the amount of light contacting the cladding element and can also reduce light leakage through the cladding elements and the gaps between these cladding elements. This in turn can reduce the attenuation of the optical signal caused by leakage through the cladding elements and the gaps between them, and can also reduce light scattering that may occur when light contacts the surface of the cladding element.

[0133] Example

[0134] The embodiments described herein are further illustrated by the following examples.

[0135] Example 1: Production of optical fiber, constant centerline pressure

[0136] An optical fiber is produced from a hollow core preform comprising an annular support structure, an outer cladding, a sealing tube and five open tubes arranged as shown in FIG1 . The annular support structure, the outer cladding and the tubes comprise silica-based glass. A core handle is welded to the hollow core preform. The core handle comprises a manifold that delivers gas to the inner cavity of the hollow core preform in an operative manner. The sealed end of the one sealing tube is arranged adjacent to the core handle and opposite to the drawing end. At a temperature of 1975° C., the hollow core preform is subjected to a gob at the drawing end to start the drawing process. The hollow core optical fiber is drawn at a temperature of 1925° C. The downward feed of the hollow core preform is 7 mm / min, and the drawing speed of the hollow core optical fiber is about 20 m / min. During the drawing process, no centerline pressure is applied to the inner cavity of the hollow core preform. The outer diameter of the drawn hollow core optical fiber is approximately 250 μm.

[0137] The hollow core fibers were cut in cross sections and observed every 5 to 10 minutes during the drawing process to determine how the sealed capillaries performed relative to the open capillaries. Figures 4A-4F is an image of the cross section of the optical fiber over time. Figure 5 The times associated with A-5F are 17 minutes, 22 minutes, 28 minutes, 38 minutes, 50 minutes, and 62 minutes. Figure 5As shown in FIG. 5A-5F, capillary 220a is formed by a sealed tube of a hollow core preform and capillaries 220b, 220c, 220d, 220e and 220f are formed by an open tube of a hollow core preform. Capillaries formed by a sealed tube and an open tube are referred to herein as "sealed capillaries" and "open capillaries", respectively. Figures 4A-4C shows the increase in diameter of the sealing capillary 220a over time, and Figures 4D-4F The diameter of the sealed capillary 220a is shown to stabilize at a diameter of about 30 μm for a draw time of more than about 30 minutes (corresponding to a draw length of about 600 m). The open capillaries 220b, 220c, 220d, 220e, and 220f maintain the same diameter throughout the draw process. Figure 5 The diagram shows the inner diameter and outer diameter of the sealing capillary 220a over time.

[0138] After drawing 1000 m of optical fiber, the downward feed of the hollow core preform was increased to 9 mm / min to check whether there was stabilization of the diameter of the sealing capillary 220a under different conditions. After increasing the downward feed rate, the inner and outer diameters of the sealing capillary also increased and then stabilized, as shown in FIG. Figure 5 As shown. Figure 5 The vertical dashed lines indicate the points where the feed rate increases downward.

[0139] Example 2: Optical fiber production, varying centerline pressure

[0140] An optical fiber is produced from a hollow core preform comprising an annular support structure, an outer cladding, a sealing tube and five open tubes arranged as shown in Figure 1. The annular support structure, the outer cladding and the tubes comprise silica-based glass. A core handle is welded to the hollow core preform. The core handle comprises a manifold, which operatively transmits gas to the hollow core of the hollow core preform and provides pressure to the inner cavity of the hollow core preform. The sealed end of the one sealing tube is arranged near the core handle and opposite to the drawing end. At a temperature of 1975°C, the hollow core preform is subjected to a gob at the drawing end to start the drawing process. The hollow core optical fiber is drawn at a temperature of 1925°C. The downward feed of the hollow core preform is 7 mm / min, and the drawing speed of the hollow core optical fiber is about 20 m / min. Argon gas is delivered to the inner cavity of the hollow core preform through the core handle to control the pressure in the inner cavity during the drawing process. The outer diameter of the drawn optical fiber is approximately 250 μm.

[0141] The fibers were cut and observed every 5 to 10 minutes to determine how the sealed capillaries performed relative to the open capillaries. Figures 6A-6F is an image of the cross section of a hollow core optical fiber over time. Figures 6A-6FAs shown, capillary 220a is sealed, and capillaries 220b, 220c, 220d, 220e, and 220f are open. Figures 6A-6C It shows how the diameter of the sealing capillary 220a increases over time when no pressure is added to the inner cavity. Figures 6A-6C The pressure of the internal cavity of the hollow core fiber cross section shown is a baseline pressure associated with the process and process environment (approximately 1 atm). Figure 6C The diameter of the sealing capillary 220a shown corresponds to the stabilized diameter of the sealing capillary 220a when the pressure of the inner cavity of the hollow core preform is not regulated. Figure 6C After the conditions shown, the drawing process is modified to adjust the pressure in the inner cavity of the hollow core preform. An inert gas at a controlled pressure is introduced into the inner cavity to increase the pressure above the baseline pressure. Fig.6D The effect of increasing the pressure by 0.2 psi is shown. Specifically, Fig.6D In FIG. 2 , a reduction in the diameter of the sealing capillary 220 a is observed. Fig. 6E shows the effect of a 0.4 psi increase in pressure, and Fig. 6F Shown is the effect of a 0.75 psi pressure increase. Fig. 6E and 6F It shows that as the pressure in the inner cavity increases, the diameter of the sealed capillary 220a continues to decrease. In contrast, the open capillaries 220b, 220c, 220d, 220e and 220f maintain the same diameter throughout the drawing process. Figure 7 and 8 The diameter of the hollow fiber core (labeled as "fiber inner diameter") and the inner diameter and outer diameter of the sealing capillary 220a (labeled as "capillary ID" and "capillary OD", respectively) at different centerline pressures (pressure applied to the inner cavity) are graphically shown. Figures 6A-6F , 7 and 8, the diameter of the sealing capillary can be controlled by changing the centerline pressure applied to the inner cavity of the preform. In addition, the diameter of the hollow core can be controlled by changing the centerline pressure applied to the inner cavity.

[0142] Example 3: Production of optical fiber, six sealed capillaries

[0143] An optical fiber is produced from a hollow core preform comprising an annular support structure, an outer cladding and six sealing capillaries arranged as shown in Figure 1. The annular support structure, the outer cladding and the capillaries comprise silica-based glass. A core handle is welded to the hollow core preform. The core handle comprises a manifold, which operatively transmits gas to the inner cavity of the hollow core preform and provides pressure to the inner cavity of the preform. The sealed ends of the six sealing tubes are arranged near the core handle and opposite to the drawing end. At a temperature of 1975°C, the preform is spitted (gob) at the drawing end to start the drawing process. The hollow core optical fiber is drawn at a temperature of 1925°C. The downward feed of the hollow core preform is 7 mm / min, and the drawing speed of the hollow core optical fiber is about 20 m / min. During the drawing process, argon gas was delivered to the hollow core through the core handle to increase the pressure in the inner cavity (relative to the process baseline pressure) by 0.5 psi. The outer diameter of the drawn optical fiber was approximately 250 μm.

[0144] Observe the beginning and end of the hollow core fiber and Fig. 9A and 9B The hollow core fiber has a length of about 1250 m and is formed from a hollow core preform of about 400 mm. Fig. 9A and 9B As shown, the structure of the hollow core fiber remains consistent over the length of the hollow core fiber, showing almost no deviation from the target structure of the hollow core fiber. That is, a hollow core fiber containing multiple capillaries with controlled dimensions (diameter, wall thickness) can be produced, wherein the centerline pressure applied to the hollow core preform is controlled only by the drawing process. That is, through the methods described herein, a hollow core fiber with controlled capillary and hollow core dimensions can be produced through a single process variable (the pressure applied to the inner cavity of the hollow core preform).

[0145] The present disclosure relates to various embodiments of optical fiber manufacturing methods. The method may include drawing an optical fiber from a hollow core preform. The hollow core preform may include an annular support structure having an inner surface defining a hollow cavity. The hollow cavity may include a capillary in direct contact with the inner surface of the annular support structure. The capillary may include a wall defining an inner opening, the inner opening having a sealed end. Drawing may include adjusting a pressure of the hollow cavity to a predetermined pressure.

[0146] It is obvious to those skilled in the art that various modifications and changes can be made to the embodiments described herein without departing from the spirit and scope of the subject matter claimed for protection. Therefore, this specification is intended to cover modifications and variations of the various embodiments described herein, as long as these modifications and variations fall within the scope of the attached claims and their equivalents.

Claims

1. A method for producing a hollow core optical fiber, the method comprising: Drawing a hollow core optical fiber from a hollow core preform, the hollow core preform comprising an annular support structure having an inner surface defining an inner cavity, the inner cavity comprising a sealing tube in contact with the inner surface, the sealing tube comprising a wall defining an inner opening, the inner opening having a sealed end, the drawing comprising adjusting the pressure of the inner cavity to a predetermined pressure from -1.0 psig to 3.0 psig.

2. The method of claim 1, wherein: The inner cavity includes two or more sealed tubes.

3. The method according to claim 1 or 2, wherein: The inner cavity also includes an open tube in contact with the inner surface, the open tube including a wall defining an inner opening, the inner opening lacking a sealed end.

4. The method of any of claims 1-3, further comprising forming a sealed end portion of the inner opening.

5. The method according to any one of claims 1 to 4, wherein: The sealing tube is in direct contact with the inner surface of the annular support structure.

6. The method according to any one of claims 1 to 5, wherein: Drawing changes the diameter of the hollow core fiber's capillary, which is formed by the sealing tube during the drawing process.

7. The method according to any one of claims 1 to 6, wherein: Drawing changes the wall thickness of the hollow core fiber's capillary tube, which is formed by the sealing tube during the drawing process.

8. The method according to any one of claims 1 to 7, wherein: The predetermined pressure varies with time.

9. The method according to any one of claims 1 to 8, wherein: Regulating the pressure of the hollow cavity includes delivering one or more gases into the hollow cavity.

10. The method according to any one of claims 1 to 9, wherein: Adjusting the pressure changes the diameter of the hollow core fiber's capillary, which is formed by the sealing tube.

11. The method according to any one of claims 1 to 10, wherein: The sealing tube includes a nested tube that contacts the inner surface of the wall of the sealing tube.

12. A hollow core optical fiber preform, comprising: An annular support structure has an inner surface defining an inner cavity, the inner cavity including a sealing tube in contact with the inner surface, the sealing tube including a wall defining an inner opening, the inner opening having a sealed end.

13. The hollow core optical fiber preform according to claim 12, wherein: The sealing tube is in direct contact with the inner surface of the annular support structure.

14. The hollow core optical fiber preform according to claim 12 or 13, wherein: The inner cavity also includes an open tube in contact with the inner surface, the open tube including a wall defining a second inner opening, the second inner opening lacking a sealed end.

15. The hollow core optical fiber preform according to any one of claims 12 to 14, wherein: The sealing tube includes a nested tube that contacts the inner surface of the wall of the sealing tube.

16. A hollow core optical fiber preform, comprising: An annular support structure has an inner surface defining an inner cavity having sealed ends and containing a tube in contact with the inner surface.

17. The hollow core optical fiber preform according to claim 16, wherein: The tube is a sealed tube including a wall defining an inner opening having a sealed end.

18. The method of any of claims 1-11, wherein: The sealed end comprises the material of the tube fused to itself.

19. The hollow core optical fiber preform according to any one of claims 12 to 15, wherein: The sealed end comprises the material of the tube fused to itself.

20. The hollow core optical fiber preform according to claim 16 or 17, wherein: The sealed end comprises the material of the tube fused to itself.

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