Sleeve for aligning hollow-core preform components

Abstract

For a hollow-core preform (from which a hollow-core fiber is ultimately drawn), alignment of an inner resonator tube within a cladding tube is accomplished by providing a sleeve with an opening through which the hollow-core preform moves. The sleeve holds a magnet that extends a magnetic field into the opening and, consequently, into the cladding tube and further into the resonator tube. When a ferromagnetic ball is placed within the resonator tube, there arises an attractive force between the magnet and the ferromagnetic ball. The outer surface of the resonator tube maintains a precise contact line with the inner surface of the cladding tube because of the attractive force between the ferromagnetic ball and the magnet. Furthermore, because the ball rolls, the contact line is maintained even when the cladding tube and the resonator tube are moved axially (along a longitudinal axis of the hollow-core preform).

Description

SLEEVE FOR ALIGNING HOLLOW-CORE PREFORM COMPONENTSCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisional patent application serial number 63 / 524,057, filed 2023-JUN-29, having the title "An Alignment Sleeve for Hollow Core Preform Assembly," which is incorporated herein by reference in its entirety.BACKGROUNDFIELD OF THE DISCLOSURE

[0002] The present disclosure relates generally to optics and, more particularly, to hollow-core preforms.DESCRIPTION OF RELATED ART

[0003] Manufacturing of hollow-core preforms (HCPs) is challenging because even slight misalignment of the components that constitute the HCP can result in deleterious effects on an intermediate hollow-core cane (HCC), which in turn adversely affects performance of a hollow-core fiber (HCF) that is drawn from the HCC.SUMMARY

[0004] Briefly described, in a hollow-core preform (HCP, from which a hollow-core fiber (HCF) is ultimately drawn), alignment of an inner resonator tube within a cladding tube is accomplished by providing a sleeve with an opening through which the HCP moves. The sleeve holds a magnet that extends a magnetic field into the opening and, consequently, into the cladding tube and further into the resonator tube. When a ferromagnetic ball (or rod, pin, or other object with a circular cross-sectional area) is placed within the resonator tube, an attractive force arises between the magnet and the ferromagnetic ball. Because of this attractive force, the outer surface of the resonator tube maintains a precise contact line with the inner surface of the cladding tube. Furthermore, because the ball rolls (or the pinds, rods, or other objects slide), a contact line is maintained even when the cladding tube and the resonator tube move axially (along a longitudinal axis of the HCP). Consequently, the sleeve permits better positional accuracy of the HCP components during assembly of the HCP.After assembly, the HCP is drawn into a corresponding hollow-core cane (HCC), which in turn is eventually drawn into a HCF.

[0005] Other systems, devices, methods, features, and advantages will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure.Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0007] FIG. 1 is a drawing showing a hollow-core preform (HCP) with preform supports on both axial ends of the HCP.

[0008] FIG. 2 is a diagram showing the HCP of FIG. 1 being drawn into a hollowcore cane (HCC).

[0009] FIG. 3 is a picture showing preform supports in greater detail.

[0010] FIG. 4 is a diagram showing an axial cross-section (cut along an axial direction (z-axis)) of a system with magnets that are used to align inner resonator tubes to their respective desired contact lines.

[0011] FIG. 5 is a diagram showing an enlarged portion of FIG. 4 in which a magnetic force between a ferromagnetic ball and a magnet is illustrated.

[0012] FIG. 6 is a diagram showing an axial cross-section (cut along an axial direction (z-axis)) of a system with magnets that are used to align nested resonator tubes to their respective desired contact lines.

[0013] FIG. 7 is a diagram showing a substantially axial view (substantially along the z-axis) of one embodiment in which resonator tubes are aligned in an HCP using magnets.

[0014] FIG. 8 is a diagram showing a different view of the embodiment of FIG. 7.

[0015] FIG. 9 is a picture showing one embodiment of an assembly with fivemagnets, five ferromagnetic balls, and five resonator tubes.

[0016] FIG. 10 is a diagram showing a cutaway view in an antero-posterior plane (cut along the x-axis) that illustrates rolling of the ferromagnetic balls as the HCP moves in the axial direction (in the +z direction).DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] Manufacturing of hollow-core preforms (HCPs) is challenging because even slight misalignment of the HCP components (such as inner resonant tubes) can result in adverse effects on an intermediate hollow-core cane (HCC), which in turn adversely affects performance of a hollow-core fiber (HCF) that is drawn from the HCC. Primarily, misalignment or deformation results from various forces that are applied to the inner HCP components. For example, force bowing, gravity sagging, inherent curvature, static charging of the thin- walled tubes.

[0018] These problems arise because the inner resonant tubes are usually secured in place by spacers and support members, such as those shown in FIG. 1, FIG. 2, and FIG. 3. For example, FIG. 1 shows a conventional HCP 100 with a cladding tube 105 in which inner resonant tubes 110 are held in specific positions by spacers 115 and a central support structure 120. As shown in FIG. 1, the each of the spacers 115 maintains a separation between adjacent resonant tubes, while the central support structure 120 prevents the resonant tubes 110 and the spacers 115 from collapsing to the center of the cladding tube 105. However, the central support structure 120 and the spacers 115 are placed at the ends of the HCP 100 as preform supports 125, 130, with only a central draw region 135 eventually being drawn into the HCF.

[0019] Consequently, as shown in FIG. 2, as a heated HCP 200 is drawn through a furnace 205 to form an HCC 210, the preform support 125 (which includes the central support structure 120, the inner resonant tubes 110, and the spacers) holds the HCP 200 in place while the draw region 135 passes through the furnace 205 (or other heat source or, generally, heat zone) to form the HCC 210. For clarity, FIG. 3 shows a cross-section of a conventional dual-resonant-tube HCP with a cladding tube 305, resonant tubes 310, nested tubes 355 (within the resonator tube 310), spacers 315, and a central support structure 320. As one can appreciate from FIG. 1 through 3, because the preform support 125 supports theHCP 100, 200, 300 from one end, distortions can arise in the draw region 135. Poor positional accuracy also makes it difficult to maintain a uniform contact line as the HCP 100, 200, 300 moves axially through the furnace 205.

[0020] To mitigate these (and other) deleterious effects, alignment of an inner resonator tube is accomplished by providing a sleeve with an opening through which the HCP moves. The sleeve holds a magnet that extends a magnetic field into the opening and, consequently, into the cladding tube and further into the resonator tube. When a ferromagnetic ball is placed within the resonator tube, an attractive force arises between the magnet and the ferromagnetic ball. Because of this attractive force, the outer surface of the resonator tube maintains a precise contact line with the inner surface of the cladding tube. Furthermore, because the ball rolls, the contact line is maintained even when the cladding tube and the resonator tube move axially (along a longitudinal axis of the HCP). Consequently, the sleeve permits better positional accuracy of the HCP components as the HCP is assembled. The assembled HCP is drawn into a corresponding hollow-core cane (HCC), which in turn is eventually drawn into a HCF.

[0021] Having provided a broad technical solution to a technical problem, reference is now made in detail to the description of the embodiments as illustrated in the drawings. While several embodiments are described in connection with these drawings, there is no intent to limit the disclosure to the embodiment or embodiments disclosed herein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents.

[0022] FIG. 4 is a diagram showing an axial cross-section (cut along an axial direction (z-axis)) of a system 400 with magnets 430 that are used to align inner resonator tubes 420 to their respective desired contact lines within a cladding tube 405. For reference, a two-dimensional Cartesian coordinate system (with x-axis and y-axis) is provided at a radial center of the cross-section, with a normal axis (z-axis) extending outward from FIG. 4. Unless otherwise stated, the z-axis represents a longitudinal axis of a HCF and an axial direction in which the HCF is drawn into an HCC (or an HCF).

[0023] As shown in FIG. 4, the system 400 shows a cladding tube 405 with a cladding tube outer surface 410 (having a cladding tube outer diameter) and a cladding tube inner surface 415 (having a cladding tube inner diameter that is smaller than the cladding tube outer diameter). Based on the reference coordinate system, the cladding tube innersurface 415 is located radially inward from the cladding tube outer surface 410.

[0024] Within the cladding tube 405 are four (4) inner resonant tubes 420. Each of the inner resonant tubes 420 holds a corresponding ferromagnetic ball 425 (or bearing). Thus, structurally, each ferromagnetic ball 425 is located within a corresponding inner resonant tube 420, which is in turn located within the cladding tube 405.

[0025] External to the cladding tube are magnets 430. For purposes of illustration, the magnets 430 are shown with a negative pole 435 being radially farther from the radial center and a positive pole 440 being radially closer to the radial center and in proximity to the outer surface 410. Based on the configuration of FIG. 4, the positive pole 440 (which faces the cladding tube 405) extends a magnetic field inwardly toward the radial center. Each ferromagnetic ball 425 is located within a corresponding magnetic field and, consequently, each ferromagnetic ball 425 is magnetically coupled to a corresponding magnet 430 with an attractive force being created between each ferromagnetic ball 425 and its corresponding magnet 430. The effect of this attractive magnetic force is described in greater detail with reference to FIG. 5, which shows an enlarged section 450 of FIG. 4.

[0026] Before moving to FIG. 5, it should be appreciated that although four (4) resonant tubes 420, four (4) ferromagnetic balls 425, and four (4) magnets are shown in FIG. 4 for illustrative purposes, those having skill in the art will understand that the number of resonant tubes 420, number of magnets 430, and the number of ferromagnetic balls 425 can be increased or decreased, depending on the desired properties of the eventually drawn HCF. For example, some embodiments employ multiple ferromagnetic balls (e.g., 5 balls, each with a 2mm outer diameter) into each tube, which form a linear chain, which can be attracted by a single magnet. As another example, multiple magnets can be aligned either radially outward or vertically (along the z-axis) to shape the magnetic field as desired.

[0027] Furthermore, although both a negative pole 435 and a positive pole 440 are shown in a particular arrangement for FIG. 4 (with negative pole 435 being radially farther from the radial center and the positive pole 440 being radially closer to the radial center), one having ordinary skill in the art will understand that the poles for one or more of the magnets 430 may be reversed with no significant impact on the attractive forces experienced by their respective ferromagnetic balls 425. Furthermore, it should be appreciated that, for some embodiments, the magnets 430 are movable axially to shape a magnetic field.

[0028] Turning now to FIG. 5, the enlarged portion 450 of FIG. 4 is shown in which a magnetic force between a ferromagnetic ball 425 and a magnet 430 is illustrated. For consistency, the reference coordinate system (x, y, and z) are the same as that shown in FIG. 4. As shown in FIG. 5, there is an attractive force (represented by Fl and F2) that pulls the ferromagnetic ball 425 toward the magnet 430 and, correspondingly, the magnet 430 toward the ferromagnetic ball 425. Between the ferromagnetic ball 425 and the magnet 430 resides the inner resonant tube 420 and the cladding tube 405. The embodiment of FIG. 5 shows a gap 525 between the magnet 430 and the cladding tube outer surface 410.

[0029] Because of the differing diameters (and consequently the differing radii of curvatures) between the ferromagnetic ball 425 and the inner resonant tube 420, the attractive force (Fl, F2) maintains a precise contact point (first contact point) between the ferromagnetic ball 425 and an inside surface of the inner resonator tube 420. Similarly, because of the differing diameters (and radii of curvatures) between the inner resonant tube 420 and the cladding tube 405, the attractive force (Fl, F2) maintains a precise contact point (second contact point) between the outside surface of the inner resonator tube 420 and the cladding tube inner surface 415.

[0030] Insofar as the attractive force (Fl, F2) extends radially outward, and insofar as the curvatures permit a single contact point at each interface, the radial center and the first contact point and the second contact point are all collinear with each other along radial lines. This collinearity permits nesting of multiple resonator tubes, as shown in FIG. 6.

[0031] Specifically, FIG. 6 shows an axial cross-section (cut along an axial direction (z-axis) and in an x-y plane) of a system 600 with magnets 430 that are used to align nested resonator tubes 610, 620 to their respective desired contact lines. Insofar as many of the components of FIG. 6 have been described in detail with reference to FIGS. 4 and 5, only the nested resonator tubes 610, 620 are described with reference to FIG. 6. As shown in FIG. 6, the system 600 comprises one resonator tube 620 (nested resonator tube 620) nested within another resonator tube 610 (inner resonator tube 610). Because the diameters of the resonator tubes 610, 620 differ, the attractive force (Fl, F2, FIG. 5) maintains a precise contact point (third contact point) between the inside surface of the inner resonator tube 610 and the outer surface of the nested resonator tube 620. As one can appreciate the radial center, the first contact point, the second contact point, and the third contact point are allcollinear with each other.

[0032] Having described the principles of operation in FIGS. 4 through 6, attention is turned to FIGS. 7 and 8, which show different views of a system 700, 800 in which inner resonator tubes 420 are aligned in an HCP using magnets 430. Again, the reference coordinate system is designated by the x-axis, the y-axis, and the z-axis as shown in FIGS. 7 and 8.

[0033] One embodiment 700, 800 (as shown in FIGS. 7 and 8) comprises a sleeve 710 with a substantially circular opening 720 extending in an axial direction through the sleeve 710. As those having skill in the art will appreciate, the axial direction (z-direction) corresponding to a longitudinal axis of the HCF. The substantially circular opening comprises a radial center, a circumference (at a substantially fixed radial distance from the radial center), and an opening diameter that is larger than an outer diameter of the HCP. Thus, for a HCP in which the outermost layer is the cladding tube 405, a gap 725 will exist between the cladding tube outer surface 410 and the opening 720. This gap 725 permits the HCP to rotate along its longitudinal axis (meaning, rotate about the z-axis) as it travels (along the z-axis) through the opening 720 (as shown in FIG. 8). Although such a rotation is permissible, preferred embodiments require the HCP and the sleeve to rotate together so as to prevent pulling the tubes out of position. In other words, if there is coordinated rotation, then this coordinated rotation prevents the resonator tubes 420 from becoming twisted as the cladding tube 405 rotates. The gap 725 also permits the HCP to move through the sleeve 710 without touching the sleeve 710 as it travels in the axial direction (z-axis) through, for example, a heat source 810 (or furnace), such as that shown in FIG. 8.

[0034] Channels 730 are located in the sleeve 710 in proximity to the circumference of the opening 720. Each magnet 430 is located in a corresponding channel 730. Although five (5) channels 730 and five (5) magnets 430 are shown in FIG. 7, it should be appreciated that there can be more channels 730 than there are magnets 430, thereby permitting different configurations of magnetic fields. In the specific embodiment 700, 800 of FIGS. 7 and 8, the channels 730 are shown to be positioned at approximately equidistant azimuthal angles from each other (so, for five (5) channels, at every 2TI / 5 radians or thereabouts). However, as one can appreciate, the channels 730 can be re-positioned to different azimuthal angles to generate different magnetic fields and, consequently, different resonant-tube configurations.

[0035] A pictorial representation 900 of the system 700, 800 of FIGS. 7 and 8 is shown in FIG. 9 (namely, an assembly with five magnets, five ferromagnetic balls, and five resonator tubes).

[0036] FIG. 10 is a diagram 1000 showing a cutaway view in an antero-posterior plane (cut along the x-axis) that illustrates rolling of the ferromagnetic balls 425 as the HCP moves in the axial direction (in the +z direction), with a coordinate system being provided for reference. For simplicity, only the inner resonant tube 420, the ferromagnetic ball 425, and the magnet 430 are shown in FIG. 10. Because of the attractive forces between the magnets 430 and their respective ferromagnetic balls 425, the ferromagnetic balls 425 maintain contact with the walls of their respective inner resonant tubes 420, specifically, at the point closest to their respective magnets 430. Additionally, because the ferromagnetic balls 425 are spherical, as the inner resonant tubes 420 move along the longitudinal axis (shown in the +z direction), the ferromagnetic balls 425 roll, thereby maintaining their respective contact lines, which, in turn, maintains positional accuracy of the inner resonant tubes 420 vis-a-vis the cladding tube 405.

[0037] The embodiments of FIGS. 4 through 10 are implementable in a vertical lathe. The HCP is initially prepared by inserting multiple pristine inner resonator tubes into an outer cladding tube. Clean ferromagnetic balls (or ball bearings) are individually loaded into the ends and rolled inward to establish their respective magnetic couplings with their respective magnets. The HCP is then mounted to an upper chuck and suspended downward. One or more sleeves are attached at different heights with reference to a heating source (e.g., furnace, torch, etc.). For some embodiments, the sleeves are attached using rotary bushings or bearings, which permit free or controlled rotation of the sleeves (preferably in conjunction with the rotation of the HCP, thereby preventing the tubes from being pulled out of alignment). A passive (un-heated) full excursion of the HCP may be used to test whether or not the longitudinal travel will be smooth during actual operation. To begin tacking / fusing (to form the fused HCP for eventual draw into a HCC), the HCP is pulled upward with the heating source active. As one can appreciate, the vertical lathe permits multiple heated passes.

[0038] As those having skill in the ait will appreciate, the embodiments in FIGS. 4 through 10 demonstrate systems and processes that maintain a more-consistent position ofthe inner resonant tubes 420 within HCPs, even when the HCPs move linearly (through, for example, a heat source, a furnace, or generally a heat zone) or rotationally. The improved precision produces more consistent contact lines, which in turn reduces undesirable gaps, asymmetries, or other deformities that adversely affect optical properties of HCCs or HCFs that are eventually drawn from the HCPs. r0039] Furthermore, because the opening of the sleeve is placed concentrically outside of the outer glass tube with the attractive magnetic forces being used to hold the components in place, the embodiments of FIG. 4 through 10 exhibit additional advantages over conventional processes that require spacers or other fixed structural support members.

[0040] First, because the ferromagnetic balls make contact at a single point and roll along the inside wall of the inner resonant tube, the ferromagnetic balls trace only a small contact line with in the inside wall. The small trace line is one advantage.

[0041] Second, because the attractive forces extend radially outward, the inner resonant tubes self-center along the radial line (and collinearly with the direction of the magnetic force). In other words, as long as the magnets do not move azimuthally, the inner resonant tubes will also not move azimuthally. This self-aligning (or self-centering) feature is another advantage.

[0042] Third, because the only magnetic components within the HCP are the ferromagnetic balls, there is no need to painstakingly mount fixtures within the cladding tube (other than the resonator features that eventually become part of the HCF). Furthermore, because the magnetic components are relatively small ferromagnetic balls, they can be readily introduced into the HCP once the magnets are properly aligned outside of the HCP. Simplicity is yet another advantage.

[0043] Fourth, because only the ferromagnetic balls are introduced into the cladding tube, there is a reduced likelihood of contamination.

[0044] Fifth, due to the radial forces that exceed the rolling friction of the ferromagnetic balls, the HCP is free to travel both axially and rotationally while conserving the azimuthal alignment of the inner resonant tubes with reference to each other (and the other internal components). Conventional fixtures do not readily permit such rotations without risk of misalignment.

[0045] Sixth, because the sleeve can be configured as a substantially flat disc withradially aligned channels for magnets, multiple sleeves can be stacked at different axial locations (different z-coordinates).

[0046] Seventh, because the ferromagnetic balls pull the inner resonant tubes to the cladding tube for continuous contact, this reduces the possibility of gaps between the resonant tubes and the cladding tube. Gaps are undesirable because the gaps decrease the likelihood of fusion and correspondingly increase the likelihood of deformation and, thus, the creation of defects. Reducing the possibility of gaps is, therefore, yet another advantage.

[0047] Eighth, because of the radial magnetic forces, multiple nested resonant tubes can be concurrently fused for the cane, thereby eliminating the conventional multi-step process for nested resonant tubes. Specifically, conventional processes required the nested tubes to be fabricated first and thereafter incorporated into the cladding tube. The disclosed system and process in FIGS. 4 through 10 simplifies the process.

[0048] Ninth, because the ferromagnetic balls can be placed both inside the resonant tube and between adjacent resonant tubes, different components within the cladding tube can be aligned with different configurations of magnets combined with ferromagnetic balls.

[0049] As one can appreciate, the principles of operation for the magnetic embodiments (as shown in FIGS. 4 through 10) are remarkably different than static nonmagnetic fixtures that have been used in conventional systems.

[0050] Any process descriptions or blocks in flow charts should be understood as representing specific functions or steps in a process, and alternate implementations are included within the scope of the preferred embodiment of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the ail of the present disclosure.

[0051] Although exemplary embodiments have been shown and described, it will be clear to those of ordinary skill in the ail that a number of changes, modifications, or alterations to the disclosure as described may be made. For example, the term "ferromagnetic ball" as used herein is expressly defined to mean, either, any ball that experiences a magnetic force from a magnet, or any ferrogmagnetic object that has either a substantially circular cross-section or other known effective cross-sectional shape. Thus, the ferromagnetic ball does not need to be completely ferromagnetic but, instead, can includeferromagnetic components in conjunction with other ingredients.

[0052] In some embodiments, the ferromagnetic balls may be positioned in series or combined and encased in a thin-walled tube of materials (e.g., Teflon, Rulon, PEEK, etc.) and optionally sealed at one end or both ends. Alternatively, a small pin or other shaped element (e.g., hexagon, triangle, etc.) can be used as a stopper at one or both ends of the thinwalled tube. In some embodiments, a low-friction coating can be applied to enhance sliding. Low-carbon steel can be used to maximize magnetic attractive forces. Either a permanent magnet or an electromagnet can be used. Chromium- free alloys can be used to minimize contamination. A plating (e.g., nickel) or a coating (e.g., polyimide) can be used to reduce contamination of the glass from the ferromagnetic balls. In some embodiments, instead of placing the ferromagnetic balls within the inner resonant tubes, the ferromagnetic balls may be placed outside of the inner resonant tubes, thereby acting as rolling spacers. For some embodiments, the ferromagnetic balls need not be passive magnetic bodies but, rather, can be magnetized shapes.

[0053] All such changes, modifications, and alterations should therefore be seen as within the scope of the disclosure.

Claims

What is claimed is:

1. A system comprising: a sleeve; a substantially circular opening extending in an axial direction through the sleeve, the axial direction corresponding to a longitudinal axis of a hollow-core preform, the substantially circular opening comprising: a radial center; a circumference at a substantially fixed radial distance from the radial center; and an opening diameter that is larger than an outer diameter of the hollow-core preform; channels located in the sleeve, each channel being located in proximity to the circumference of the opening; magnets, each magnet being located in a corresponding channel, each magnet comprising: a first pole in proximity to the circumference of the opening; and a second pole extending in a radial direction from the first pole and away from the radial center; magnetic fields, each magnetic field extending inwardly from a corresponding first pole toward the radial center; ferromagnetic balls, each ferromagnetic ball being located within the substantially circular opening, each ferromagnetic ball being located within a corresponding magnetic field, each ferromagnetic ball being magnetically coupled to a corresponding magnet with an attractive force being created between each ferromagnetic ball and its corresponding magnet; a cladding tube of the hollow-core preform, the cladding tube being positioned within the substantially circular opening, the cladding tube comprising: a cladding tube outer surface having a cladding tube outer diameter and being located radially inward from the circumference of the substantially circular opening; and a cladding tube inner surface having a cladding tube inner diameter and being located radially inward from the cladding tube outer surface;a gap separating the cladding tube outer surface from the sleeve; and inner resonator tubes located within the cladding tube, each inner resonator tube comprising: an inner resonator tube outside diameter that is smaller than the cladding tube inner diameter; an inner resonator tube inside surface in contact with a corresponding ferromagnetic ball, the contact with the corresponding ferromagnetic ball being maintained by the attractive force between the corresponding ferromagnetic ball and the corresponding magnet; and an inner resonator tube outside surface in contact with the cladding tube inner surface, the contact with the cladding tube inner surface being maintained by the attractive force between the corresponding ferromagnetic ball and the corresponding magnet.

2. A system comprising: a sleeve; a substantially circular opening extending in an axial direction through the sleeve, the axial direction being substantially parallel to a longitudinal axis of a hollow-core preform, the substantially circular opening comprising: a radial center; a circumference at a substantially fixed radial distance from the radial center; and an opening diameter that is larger than an outer diameter of the hollow-core preform; channels located in the sleeve, each channel being located in proximity to the circumference of the opening; magnets, each magnet being located in a corresponding channel, each magnet comprising: a first pole in proximity to the circumference of the opening; and a second pole extending in a radial direction from the first pole and away from the radial center; and magnetic fields, each magnetic field extending inwardly from a corresponding firstpole toward the radial center.

3. The system of claim 2, further comprising: ferromagnetic balls located within the substantially circular opening, each ferromagnetic ball being located within a corresponding magnetic field, each ferromagnetic ball being magnetically coupled to a corresponding magnet with an attractive force being created between the ferromagnetic ball and its corresponding magnet.

4. The system of claim 3, further comprising: a cladding tube of the hollow-core preform, the cladding tube being positioned within the substantially circular opening, the cladding tube comprising: a cladding tube outer surface having a cladding tube outer diameter and being located radially inward from the circumference of the substantially circular' opening; and a cladding tube inner surface having a cladding tube inner diameter and being located radially inward from the cladding tube outer surface; a gap separating the cladding tube outer surface from the sleeve; and inner resonator tubes located within the cladding tube, each inner resonator tube comprising: an inner resonator tube outside diameter that is smaller than the cladding tube inner diameter; an inner resonator tube inside surface in contact with a corresponding ferromagnetic ball, the contact with the corresponding ferromagnetic ball being maintained by the attractive force between the corresponding ferromagnetic ball and its corresponding magnet; and an inner resonator tube outside surface in contact with the cladding tube inner surface, the contact with the cladding tube inner surface being maintained by the attractive force between the corresponding ferromagnetic ball and its corresponding magnet.

5. The system of claim 3, further comprising: a cladding tube of the hollow-core preform, the cladding tube being positioned within the substantially circular opening, the cladding tube comprising:a cladding tube outer surface having a cladding tube outer diameter and being located radially inward from the circumference of the substantially circular’ opening; and a cladding tube inner surface having a cladding tube inner diameter and being located radially inward from the cladding tube outer surface; a gap separating the cladding tube outer surface from the sleeve; and inner resonator tubes located within the cladding tube, each inner resonator tube comprising: an inner resonator tube outside diameter that is smaller than the cladding tube inner diameter; an inner resonator tube inside surface; and an inner resonator tube outside surface in contact with the cladding tube inner surface, the contact with the cladding tube inner surface being maintained by the attractive force between the corresponding ferromagnetic ball and its corresponding magnet; and nested tubes, each nested tube being located within a corresponding inner resonator tube, each nested tube comprising: a nested tube outer diameter that is smaller than its corresponding inner resonator tube inside diameter; a nested tube inner surface in contact with its corresponding ferromagnetic ball, the contact with the corresponding ferromagnetic ball being maintained by the attractive force between the corresponding ferromagnetic ball and its corresponding magnet; and a nested tube outer surface in contact with its corresponding inner resonator tube inside surface, the contact with the corresponding inner resonator tube inside surface being maintained by the attractive force between the corresponding ferromagnetic ball and its corresponding magnet.

6. The system of claim 3, further comprising: a heat zone through which the hollow-core preform travels in the axial direction.

7. The system of claim 6, wherein each ferromagnetic ball rolls as the hollow-core preform travels in the axial direction through the heat zone.

8. The system of claim 2, wherein the channels are separated from adjacent channels by substantially the same azimuthal angle.

9. The system of claim 2, wherein the first pole of each magnet is movable to different radial distances from the radial center.

10. The system of claim 2, wherein each magnet is movable axially to shape a magnetic field.

11. A system comprising: a sleeve; a substantially circular opening extending in an axial direction through the sleeve, the axial direction being substantially parallel to a longitudinal axis of a hollo w-corc preform, the substantially circular opening comprising: a radial center; a circumference at a substantially fixed radial distance from the radial center; and an opening diameter that is larger than an outer diameter of the hollow-core preform; a channel located in the sleeve, the channel being located in proximity to the circumference of the opening; a magnet located in the channel, the magnet comprising: a first pole in proximity to the circumference of the opening; and a second pole extending in a radial direction from the first pole and away from the radial center; and a magnetic field extending inwardly from the first pole toward the radial center.

12. The system of claim 11, further comprising: a ferromagnetic ball located within the substantially circular opening, the ferromagnetic ball being located within the magnetic field, the ferromagnetic ball being magnetically coupled to the magnet with an attractive force being created between theferromagnetic ball and the magnet.

13. The system of claim 12, further comprising: a cladding tube of the hollow-core preform, the cladding tube being positioned within the substantially circular opening, the cladding tube comprising: a cladding tube outer surface having a cladding tube outer diameter and being located radially inward from the circumference of the substantially circular opening; and a cladding tube inner surface having a cladding tube inner diameter and being located radially inward from the cladding tube outer surface; a gap separating the cladding tube outer surface from the sleeve; and an inner resonator tube located within the cladding tube, the inner resonator tube comprising: an inner resonator tube outside diameter that is smaller than the cladding tube inner diameter; an inner resonator tube inside surface in contact with the ferromagnetic ball, the contact with the ferromagnetic ball being maintained by the attractive force between the ferromagnetic ball and the magnet; and an inner resonator tube outside surface in contact with the cladding tube inner surface, the contact with the cladding tube inner surface being maintained by the attractive force between the ferromagnetic ball and the magnet.

14. The system of claim 12, further comprising: a cladding tube of the hollow-core preform, the cladding tube being positioned within the substantially circular opening, the cladding tube comprising: a cladding tube outer surface having a cladding tube outer diameter and being located radially inward from the circumference of the substantially circular opening; and a cladding tube inner surface having a cladding tube inner diameter and being located radially inward from the cladding tube outer surface; a gap separating the cladding tube outer surface from the sleeve; and an inner resonator tube located within the cladding tube, the inner resonator tube comprising:an inner resonator tube outside diameter that is smaller than the cladding tube inner diameter; an inner resonator tube inside surface; and an inner resonator tube outside surface in contact with the cladding tube inner surface, the contact with the cladding tube inner surface being maintained by the attractive force between the ferromagnetic ball and the magnet; and a nested tube located within the inner resonator tube, the nested tube comprising: a nested tube outer diameter that is smaller than the inner resonator tube inside diameter; a nested tube inner surface in contact with the ferromagnetic ball, the contact with the ferromagnetic ball being maintained by the attractive force between the ferromagnetic ball and the magnet; and a nested tube outer surface in contact with the inner resonator tube inside surface, the contact with the inner resonator tube inside surface being maintained by the attractive force between the ferromagnetic ball and the magnet.

15. The system of claim 12, further comprising: a heat zone through which the hollow-core preform travels in the axial direction.

16. The system of claim 15, wherein the ferromagnetic ball rolls as the hollow-core preform travels in the axial direction through the heat zone.

17. The system of claim 11, wherein the channel is a first channel, wherein the magnet is a first magnet, wherein the magnetic field is a first magnetic field, wherein the system further comprises: a second channel located in the sleeve, the second channel being located at an azimuthal angle away from the first channel, the second channel being in proximity to the circumference of the opening; a second magnet located in the second channel; and a second magnetic field extending inwardly from the second magnet toward the radial center.1 18. The system of claim 11, wherein each magnet is movable axially to shape a magnetic2 field.

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