Method for treating glass filaments

Abstract

1. A method of processing a glass filament, comprising the steps of: providing a length of glass filament, a portion of which is to be separated from the remainder of the filament; directing energy at the filament to reduce the width of the filament at a desired location to separate the portion; and causing relative longitudinal movement between the portion and the remainder of the filament to separate the portion from the remainder of the filament at the desired location.

Description

[Technical Field]

[0001] The present invention relates to a method for processing glass filaments, and in particular to a method for separating portions, such as canes, from glass filaments. The glass filaments may be filaments for forming optical fibers. [Background technology]

[0002] Optical fiber is typically manufactured by assembling multiple glass components into a preform assembly. The preform assembly has a cross-sectional configuration corresponding to the desired structure for the fiber and a diameter much larger than the desired fiber diameter. The preform is "drawn" on a fiber drawing tower by heating the preform to soften the glass and then pulling a continuous filament, maintaining the same cross-section but at a reduced diameter. The diameter is typically intermediate between the preform size and the intended fiber size, although the smaller diameter may be the intended fiber diameter. In the latter case, the filament is conveniently separated into shorter sections as the filament is drawn from the preform. The shorter sections, called canes, are then drawn into a continuous filament of optical fiber.

[0003] Originally, optical fibers had a solid structure. As such, preforms comprised solid glass rods corresponding to the desired cross-sections of the core and inner cladding for the finished fiber, inserted into hollow tubes intended to form the outer cladding of the fiber. More recent fiber designs employ longitudinal holes or lumens that run the length of the fiber and define the structure of either or both the core and inner cladding. Preforms for such fibers can be made by stacking hollow tubes and capillaries, and optionally solid rods, into the desired cross-sectional pattern.

[0004] One technique for separating a filament into individual canes is known as cleaving, and cleaving is a suitable mechanical technique for preparing optical fiber end faces. A notch, scratch, crack, or score is created in the outer glass surface of the filament (e.g., using a saw, grinding wheel, diamond blade, ceramic blade, or steel blade), resulting in a tensile stress in the area adjacent to the end of the notch that exceeds the tensile strength of the glass. This causes the notch to propagate through the glass, thereby separating the cane from the rest of the filament at the notch location. Cleavage can produce end faces with edges that are flat, smooth, or at a controlled angle, such as perpendicular to the longitudinal axis of the filament, and that are generally clean and free of nicks or scratches (except typically at the location of the notch). Nevertheless, cleaving and other mechanical techniques can be problematic for separating the cane from the filament. If nicks or scratches occur on the cleave surface, it may not be possible to successfully draw the cane into fiber because cracks can propagate from the defect. Also, debris may accumulate on and around the cane ends. This is a particular risk for fiber structures with one or more lumens, as debris may enter the lumens. The debris may introduce defects into the fiber subsequently drawn from the cane, which may manifest as increased optical loss or mechanical weakness in the fiber. All these problems can necessitate the scrapping of significant lengths of fiber and cane, thus reducing yield and increasing costs.

[0005] If cane separation is performed in a drawing tower as the filaments are formed, an additional problem is the potential for perturbations of the glass filaments, which can locally vary the diameter of the cane from the desired diameter. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, alternative methods of processing glass filaments to separate the cane from the filaments are of interest. [Means for solving the problem]

[0007] Aspects and embodiments are set out in the accompanying claims.

[0008] According to a first aspect of certain embodiments described herein, there is provided a method of processing a glass filament, the method including the steps of: providing a length of glass filament, a portion of which is to be separated from the remainder of the filament; directing energy at the filament to reduce a width of the filament at a desired location to separate the portion; and moving the portion away from the remainder of the filament to obtain the portion separated from the remainder of the filament.

[0009] According to a second aspect of certain embodiments described herein, there is provided a cane suitable for drawing into optical fiber, the cane being obtained by separation from a glass filament using the method according to the first aspect.

[0010] According to a third aspect of certain embodiments described herein, there is provided a device for drawing glass filaments from a preform, the device comprising a pair of rotatable belts, each having a movable surface rotatable about an axis of rotation, the belts positionable where the movable surfaces face a separator to receive and grip the glass filament, the movement of the surfaces acting to pull the filament away from the preform along the direction of the filament's longitudinal axis, the belts' axes of rotation positionable at an opposite, approximately equal, non-perpendicular angle to the pulling direction to impart rotation to the filament about its longitudinal axis.

[0011] These and further aspects of certain embodiments are set forth in the accompanying independent and dependent claims. It will be understood that features of the dependent claims can be combined with each other and with features of the independent claims in combinations other than those explicitly set forth in the claims. Furthermore, the techniques described herein are not limited to specific embodiments such as those described below, but are intended to include any suitable combination of features presented herein. For example, methods and apparatus can be implemented in accordance with the techniques described herein that include any one or more of the various features described below, as appropriate.

[0012] For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a flow chart illustrating a method for treating glass filaments according to an example of the present disclosure. [Figure 2] FIG. 1 is a transparent side view showing a glass filament to which the method of the present disclosure can be applied. [Figure 3A] FIG. 3 is a cross-sectional view illustrating an exemplary filament such as that of FIG. 2. [Figure 3B] FIG. 3 is a cross-sectional view illustrating an exemplary filament such as that of FIG. 2. [Figure 3C] FIG. 3 is a cross-sectional view illustrating an exemplary filament such as that of FIG. 2. [Figure 4] FIG. 1 is a schematic side view illustrating an apparatus for processing filaments according to an example of the present disclosure. [Figure 5A] FIG. 5 is a schematic diagram illustrating an exemplary energy source and beam guidance system that may be included in the apparatus of FIG. 4. [Figure 5B] 5B is a cross-sectional view illustrating an elongated focus of an energy beam produced by the beam guidance system of FIG. 5A. [Figure 6A]5 is a schematic diagram illustrating a further example of an energy source and beam guidance system that can be included in the apparatus of FIG. 4. [Figure 6B] 5 is a schematic diagram illustrating a further example of an energy source and beam guidance system that can be included in the apparatus of FIG. 4. [Figure 6C] 5 is a schematic diagram illustrating a further example of an energy source and beam guidance system that can be included in the apparatus of FIG. 4. [Figure 7] 1 is a schematic side view showing an alternative apparatus for treating glass filaments according to an example at an intermediate point in the treatment method performed on the filaments. FIG. [Figure 8] 7 or 4 at a further intermediate point in the processing method, including the use of crimping jaws. [Figure 9] 8 is a schematic side view of the apparatus of FIG. 7 at the end of the processing method, showing the cane portions separated from the filaments. [Figure 10] FIG. 10 is a schematic side view illustrating a further alternative apparatus for processing filaments according to a further exemplary method, at an intermediate point in the method. [Figure 11] 11 is a schematic side view of the apparatus of FIG. 10 at the end of the processing method, showing the cane portions separated from the filaments. [Figure 12] FIG. 12 is a schematic side view of an exemplary vapor handling system suitable for inclusion in the apparatus of FIGS. 10 and 11. [Figure 13] FIG. 11 is a schematic side view of a modified version of the device of FIG. 10. [Figure 14A] FIG. 1 is an orthogonal side view showing a cane pulling machine, by which glass filaments can be pulled or drawn from a glass preform. [Figure 14B] FIG. 1 is an orthogonal side view showing a cane pulling machine, by which glass filaments can be pulled or drawn from a glass preform. [Figure 15A] FIG. 1 is an orthogonal side view of an exemplary cane pulling machine according to aspects of the present disclosure. [Figure 15B]FIG. 1 is an orthogonal side view of an exemplary cane pulling machine according to aspects of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0014] Aspects and features of certain examples and embodiments are discussed / described herein. Some aspects and features of certain examples and embodiments may be implemented conventionally and will not be discussed / described in detail for the sake of brevity. Accordingly, it will be understood that aspects and features of the apparatus and methods discussed herein that are not described in detail may be implemented according to any conventional techniques for implementing such aspects and features.

[0015] This disclosure presents a method for processing glass filaments by separating a cane from the remainder of a length of filament for formation into optical fiber using the application of energy instead of mechanical techniques known to produce debris and chipped end faces that compromise the quality of the optical fiber drawn from the cane. The use of energy to separate the cane produces clean end faces that are substantially free of debris and defects and, in some cases, can be sealed to prevent the ingress of contaminants. Also, while mechanical techniques such as cleaving may be less suitable for severing larger diameter filaments, energy-based approaches can be adapted to the filament diameter by appropriately selecting energy characteristics.

[0016] FIG. 1 shows a flowchart describing steps in an exemplary method for glass filament processing as described herein. In a first step S1, the method includes providing a glass filament. This is a length of filament formed from a glass material, such as fused silica, having a cross-sectional configuration suitable for the desired structure for the optical fiber, but with a larger diameter than that intended for the fiber. The filament is typically produced by drawing it from a glass preform or preform assembly, which also has a suitable configuration but still a larger scale, created by stacking or otherwise arranging glass tubes, capillaries, and rods to form the desired structure. Drawing the filament from the preform can be performed in a drawing tower, as will be understood by those skilled in the art. To produce the final optical fiber, the filament will be split or separated into individual shorter lengths or sections, which can be called "canes," each of which can be drawn into optical fiber. The method of Figure 1 shows steps to achieve separation of the cane from the rest of the filament, which steps can be performed on a filament freshly drawn from a preform in a draw tower, so that processing removes continuous cane portions from the filament as it is drawn. Alternatively, the filament may be drawn in continuous lengths from a preform and processed into separate portions in separate stages outside of the draw tower.

[0017] In the second step S2, energy is applied to the filament. This can be done in a variety of ways, as described further below. Energy is directed at the filament at desired locations to split the filament into pieces or portions. The pieces or portions are separated to form a cane and a remaining piece or portion of the filament (additional canes can be separated from the remaining piece or portion by repeating the process). In the third step S3, applied energy is used to reduce the width or diameter of the filament at desired locations. As will be appreciated, the application of energy to the glass material results in a material change in the glass. The application of energy can be suitably managed and directed to form a constriction in the filament. Techniques for achieving this are described further below.

[0018] In a fourth step S4, the cane portion of the filament and the remainder of the filament, i.e., the portions of the filament on either side of the reduced width at the desired location, are separated. Specifically, the cane portion is separated from the remainder, and in this manner, a separate cane portion is obtained, separated from the remainder at the desired location. The movement of the cane portion can be achieved in various ways.

[0019] In one example, the application of energy in step S3 is performed to reduce the diameter of the filament to a non-zero value. In other words, the filament becomes thinner in the desired locations, but the cane portion remains integral with the remaining portion. The cane portion is then separated from the remaining portion by introducing a relative longitudinal motion between the two portions. Here, longitudinal refers to the direction along the length of the filament (along its longitudinal axis). Depending on where the process is being performed, one or both portions may be moved. In a draw tower, for example, both portions can advance as the filament is drawn from the preform, and the relative motion is achieved by increasing the advancement of the cane portion at the distal end of the filament. The reduced width and / or change in the texture of the glass in the desired locations introduces weakness into the filament. The glass has reduced structural integrity at this point. Therefore, moving the two portions away from each other causes the glass to break, snap, shear, pull apart, or otherwise split, resulting in the cane portion being separated from the remainder of the filament. Similar splitting can be achieved by relative movement of the cane segments along different directions, such as sideways or bending movement of the segments.

[0020] In another example, the application of energy in step S3 is performed to reduce the diameter of the filament to zero, so that the cane portion is no longer integral with the remaining portion but is still immediately adjacent thereto. Typically, this can be achieved by applying more energy at the desired location, such as energy delivered at a higher power or for a longer time. Thus, the application of energy alone is sufficient to cause complete separation or severance of the cane portion from the remaining portion. Therefore, the movement in step S4 is to remove the cane portion from its position adjacent to the remaining portion, so that it is isolated from the remaining portion and in a condition suitable for storage or further processing. The movement may or may not be a relative longitudinal movement between the two portions, as in the previous example.

[0021] FIG. 2 shows a schematic see-through side view of a length of glass filament 10 to which the method of the present disclosure can be applied. Filament 10 has a length L (extending above and below the depicted portion of the filament), a longitudinal axis A, and a width or diameter W. Filament 10 is nominally divided into cane portion 12 and remainder or remainder portion 14 at a desired location D across filament 10, typically perpendicular to longitudinal axis A. Remainder portion 14 may or may not extend from the preform or preform assembly (not shown) from which filament 10 is drawn. The method of the present disclosure, regarding the separation of cane portion 12 from remainder portion 14 at desired location D, can be performed either during or after drawing of filament 10 from the preform.

[0022] The filament 10 has a cross-sectional configuration formed from glass material that corresponds, on a larger scale, to the desired configuration of the final optical fiber. The methods herein are applicable to any fiber configuration and are not limited in this respect.

[0023] FIG. 3 shows some examples of possible cross-sectional structures of the filament 10. FIG. 3A shows a structure for forming an all-solid optical fiber, whereby the filament comprises a solid glass rod 16 in which the core and cladding of the fiber structure are defined by different values of refractive index. FIG. 3B shows a structure for a simple hollow-core fiber, where the filament comprises a glass tube 18 with a hollow center 20 that will form the core of the fiber. FIG. 3C shows a structure for a more complex hollow-core optical fiber, where the filament comprises a hollow glass tube 18 that forms the outer cladding, or part of it, of the fiber, and multiple nested pairs of hollow glass capillaries 22 arranged in a ring around the interior of the tube 18 that form the inner cladding of the fiber. A hollow space 20 remains inside the ring of capillaries 22, which will form the hollow core of the fiber. This particular design of hollow-core fiber can be described as a nested antiresonant nodeless fiber (NANF).

[0024] 3B and 3C include one or more lumens, which are holes or hollow spaces, extending longitudinally along the filament and into the finished fiber formed from the cane cut from the filament. Any other lumen-based structures can also be processed with the presently presented methods. These include hollow-core photonic-bandgap (or photonic crystal) fiber structures with an inner cladding defined by a periodic arrangement of lumens or capillaries, more or fewer, spaced or not spaced apart, nested or not nested within an inner core ring, and other anti-resonant hollow-core fiber structures, which can include kagome fiber structures that also utilize a periodic arrangement of lumens. The present disclosure is in no way limited in this respect and can be applied to glass structures for any optical fiber design.

[0025] FIG. 4 shows a schematic diagram of an apparatus configured to perform an exemplary method of separating cane from filaments according to the present disclosure. A glass filament 10, viewed from the side and which may have any cross-sectional configuration as described above with respect to FIGS. 2 and 3, is positioned to perform the separation. As depicted, the filament 10 is positioned vertically, as it would be if it were drawn in a downward direction from a preform (not shown) in a draw tower. If not actively drawn, the filament may be suspended within the draw tower after being drawn from the preform or during draw down periods. Alternatively, the filament may be processed away from the draw tower after being drawn. In this case, the filament may be oriented vertically as depicted, although it could equally well be processed in a horizontal or intermediate position, as convenient.

[0026] The location of filament 10, a specified distance from the free (bottom) end of the filament (not shown) corresponding to the desired length of cane, is designated as desired location D, which is the desired longitudinal location or position where filament 10 should be separated into a cane portion and a remainder filament portion. The filament is secured for processing by a first clamping apparatus 24, which includes one or more clamps or clamping devices that hold filament 10 on one side (in this example, above) of desired location D. Thus, first clamping apparatus 24 holds the portion of filament 10 that will become remainder portion 14 after separation. A second clamping apparatus 26, which includes one or more clamps or clamping devices, holds filament 10 on the other side (in this example, below) of the desired location. Thus, second clamping apparatus 26 holds the portion of filament 10 that will become cane portion 12 after separation. In the first stage, before applying energy to filament 10, the clamps are separated by a distance d1.

[0027] Energy is applied to the filament from an energy source. The purpose of applying the energy is to deliver energy into the glass material, raising its temperature and causing a change in state that results in a change in the shape of the filament. As described further below, the change in state may be softening or cutting. Thus, any form of energy capable of producing this effect can be used. In the example of FIG. 4, the energy source is a laser 28 that emits a beam of laser light 30. In this simple example, the beam 30 is focused with one or more lenses 32 to form a focal point 34 that is directed onto the outer surface of the filament 10 along the desired location D.

[0028] Lens 32 can be considered a beam guidance system, which can be configured in various ways depending on the nature of the energy and energy source, the size of the filament, and where the separation method is performed. In the case of a beam of laser light, the beam can be focused, as in FIG. 4, to form a focal spot on the filament surface that is approximately circular, or approximately linear, or some intermediate or other shape. Alternatively, the beam guidance system can approximately collimate the energy toward the filament, where the collimated beam can have a circular, linear, intermediate, or other cross-sectional shape. Usefully, energy can be delivered to a distributed location around the circumference of filament 10 rather than a single point as depicted in FIG. 4, although this arrangement may be practical if sufficient energy can be delivered in a localized manner. Thus, energy can be applied at desired locations to one or more regions circumferentially disposed around the filament; the regions can be discrete points or can have the shape of continuous or substantially continuous rings; the rings can be formed by simultaneous delivery around the circumference or can be made up of adjacent or overlapping regions to which energy is applied.

[0029] 5A shows a simplified diagram of an exemplary beam guidance system 32 for delivering a laser beam 30 from a laser 28. The beam 30 emanates from the laser source 28 with a circular beam cross-section and passes through the beam guidance system 32, which comprises a negative cylindrical lens 36 followed by a positive cylindrical lens 38 with parallel axes. These lenses 36, 38 act to shape the beam into an elongated elliptical cross-section, and the beam is directed through a spherical lens 40 to a focal point 34 and onto the filament.

[0030] 5A shows the resulting elliptical focus 34. Usefully, the major axis of the ellipse point can be positioned perpendicular to the longitudinal axis of the filament, so that the point can extend significantly around the circumference of the filament at the desired location without reaching far along the length of the filament above or below the desired location. This aids in efficient energy delivery to the desired location.

[0031] When a laser is used as the energy source, its light wavelength, output power, and mode of operation (e.g., continuous wave or pulsed output) can be selected with reference to the filament characteristics, such as diameter and glass composition, as well as the configuration of the beam delivery system, to maximize the efficiency of delivering the appropriate amount of energy to the filament. By way of example, a continuous wave carbon dioxide laser operating at 10.6 μm or 9.3 μm can be used. Alternatively, the laser output can be in the form of ultrashort pulses of picosecond or femtosecond duration. Other useful wavelengths are in the green region of the spectrum, such as at or around 532 nm.

[0032] However, the energy source need not be a laser. In other examples, the energy source may be a combustion source that delivers energy in the form of combustion, such as hydrogen-oxygen combustion. A further alternative embodiment is the use of plasma as the energy delivered from the energy source, for example in the form of a plasma torch.

[0033] FIG. 6A shows a schematic diagram of a further exemplary beam guidance system configured to deliver optical energy in the form of a laser beam simultaneously to three regions circumferentially disposed around the filament, as viewed from above and below along the longitudinal axis of the filament. An initial output beam 30 from a laser 28 is incident on a first beam splitter BSa, which splits the light into two portions. One of the portions, 30a, is reflected by the beam splitter BSa and directed by a first pair of mirrors Ma1 and Ma2 to a first region on the filament 10 via a first lens La, which focuses the beam 30a to a focal point 34a at the surface of the filament. A second portion of the original beam 30 is transmitted by the first beam splitter BSa to a second beam splitter BSb, which also splits the light into two portions. One portion 30b is reflected by a second beam splitter BSb to a second pair of mirrors Mb1 and Mb2, which directs beam portion 30b to a second region on filament 10 via a second lens Lb, which focuses beam 30b to a focal point 34b on the surface of filament 10. Finally, the remaining portion of light 30c is transmitted by the second beam splitter BSb to a third region on filament 10 via a third lens Lc, which focuses beam 30c to a focal point 34c on the surface of filament 10. The three regions 34a, 34b, and 34c are evenly spaced around the circumference of filament 10 at desired location D. Thus, a larger percentage of the circumference is exposed to the laser beam energy than would be possible with a single beam. The exposure can be expanded when lenses La, Lb, and Lc are configured to shape the beam into an elongated focus, as in the example of FIG. 5B. Multiple elongated points can be arranged to wrap around most or all of the circumference, thus exposing the filament all around the desired location. If the beam splitter specifications are appropriately selected, each beam portion can contain the same amount of laser energy to deliver a more even distribution of energy to the filament, although this is not essential.

[0034] In other examples, the laser beam can be split into more or fewer portions by providing more or fewer beam splitters and lenses. Each portion can be directed onto a different circumferentially spaced region on the filament. If the spacing is even and each beam portion has approximately the same energy, an even distribution of energy is delivered around the desired location. The lenses and flat mirrors in the example of FIG. 6A can be replaced with non-flat mirrors, such as parabolic mirrors. Also, separate lasers can be used to deliver each beam portion directly, eliminating the need for beam splitters to split the beam.

[0035] Depending on factors including focal spot size, the amount of energy in the beam portion, and the size and structure of the filament, statically delivering energy to one or more regions around the circumference of the filament may be suitable to achieve the required energy in the glass. In other cases, ensuring a larger area or the complete circumference receives energy may be more suitable. To achieve this, a full beam delivery system, such as that shown in FIG. 6A , can be configured to be rotatable about an axis coincident with the longitudinal axis of the filament so that one or more focal points of the beam or beam portion follow the filament completely or partially around the filament. In this manner, exposure of a continuous circumferential region to energy can be achieved. Or, if the energy is not delivered continuously, a circumferential arrangement of spaced regions can be achieved. Alternatively, various groups of mirrors and lenses can be moved to direct corresponding beam portions to different regions of desired locations, for example, in a scanning arrangement.

[0036] FIG. 6B shows a schematic diagram, in side view, of another exemplary beam guidance system configured to deliver optical energy in the form of a laser beam in a substantially continuous ring around the filament. A plane mirror 82 is positioned to direct the output beam 30 from the laser 28 substantially coaxially with the filament 10 to form a reflected beam 88. The output beam 30 is configured to have a diameter wider than the width of the filament 10 so that a substantial portion passes through the filament 10 to reach the plane mirror 82. The plane mirror 82 is provided with a hole 84 or other means for allowing the filament 10 to pass therethrough. An optional baffle 86 can be included to block the portion of the output beam 30 that would otherwise be incident on the filament 10 and allow the remainder of the output beam to pass through the baffle 86 and reach the plane mirror 82. The reflected beam 88 has a cylindrical shape that substantially surrounds the filament 10 but propagates along the length of the filament to impinge on a parabolic mirror 90. Similar to the planar mirror 82, the parabolic mirror 90 is provided with an aperture 92 or other means for allowing the filament 10 to pass therethrough. The parabolic mirror 90 is configured to focus the reflected beam 88 in a ring around the filament 10, focusing at or near the outer surface of the filament at the desired location D. For example, because of areas in the reflected beam 88 that are shadowed by the filament 10 or the baffle 86, the ring focus may not be continuous around the filament; complete circumferential exposure of the filament to laser energy at the desired location D can be achieved by relative rotational motion of the beam guidance system and the filament.

[0037] When a beam guidance system such as the example of FIGS. 6B and 6C is employed while the filament is being drawn from the preform assembly in the draw tower, it is useful to have a parabolic mirror 90 mounted on a carriage 94 that is arranged for movement parallel to the drawing direction and the longitudinal axis of the filament.

[0038] FIG. 6C shows a schematic diagram, in side view, of yet another exemplary beam guidance system configured to deliver optical energy, in this case in the form of a laser beam swept around a substantially continuous ring around the filament at a desired location D. This system includes a plane mirror 84 and a facing parabolic mirror 90 annularly arranged around the filament 10, as in the example of FIG. 6B. However, this system is configured differently prior to the plane mirror 84. The output beam 30 from the laser 28 is directed toward a plane sweep mirror 96 along a propagation direction that is approximately parallel to but offset from the longitudinal axis of the filament 10. The beam waist of the output beam 30 can be positioned coincident with the plane of the sweep mirror 96. The sweep mirror 96 is mounted on a shaft 98 driven by a motor 100 for rotational motion centered at the point of incidence of the output beam 30 on the sweep mirror 96. However, the sweep mirror 96 is mounted such that there is an angle between the axis of the shaft 98 (the axis of rotation) and the normal to the plane of the mirror 96. Thus, as the shaft 98 and sweep mirror 96 rotate, the propagation direction imparted to the beam 102 reflected from the sweep mirror changes according to the rotational position of the shaft 98. This changing propagation direction is illustrated in FIG. 6C in a first position by reflected beam 102a and in phantom by reflected beam 102b in a second position. Thus, the reflected beam 102 travels over the surface of a cone as the sweep mirror 96 rotates. An alternative method for sweeping the reflected beam in a similar manner includes the use of a prism-prism pair (a Risley prism). The reflected beam 102 is incident on an off-axis parabolic mirror 104. The off-axis parabolic mirror 104 can have a hole 106 or other means, if desired, to allow the output beam 30 from the laser 28 to pass through it. The parabolic mirror 104 has a propagation direction that is independent of the position of the shaft 98 because the doubly reflected beam 108 leaving its surface always propagates along the same parallel direction relative to the plane mirror 82. This directs the beam 88 onto the focusing parabolic mirror 90, which focuses the beam at the desired location D as before. The change in propagation direction of the reflected beam 102 leaving the sweep mirror 96 causes the focal point of the beam at the filament surface to sweep around the circumference of the filament. In this manner, the beam guidance system Or, the energy can be exposed on the filament along a continuous ring around the filament without the need to rotate either of the filaments.

[0039] As mentioned, the energy does not have to be optical energy in the form of a laser beam. Similar delivery devices that allow for simultaneous exposure in multiple regions around the filament can be provided for other energy types. For example, if the energy is from combustion, several combustion sources can be arranged around the filament, optionally in a rotatable arrangement. If the energy is plasma delivered as a plasma jet from a plasma torch, several plasma torches can be arranged around the filament, also optionally in a rotatable arrangement.

[0040] FIG. 7 shows a schematic side view of an exemplary apparatus similar to that shown in FIG. 4 , but after energy begins or is being applied to the filament 10. In this example, the energy source is combustion 40 delivered to one (as shown) or multiple regions around the filament 10 at a desired location D. In this example, the amount of energy delivered is selected with reference to the nature and characteristics of the filament 10 to soften or partially melt the glass material of the filament at the desired location. Softening enables deformation of the filament 10, such that the width W of the filament 10 is reduced at the desired location to form a neck, waist, or “necked” portion or region having a smaller, non-zero width W′. Deformation can be enabled by any of a variety of means. If the filament has a cross-sectional structure that includes one or more lumens, softening may cause distortion of the internal structure and collapse of the lumens. This also causes the outer wall of the filament to collapse inward, reducing its width.

[0041] 8 shows a schematic side view of an exemplary apparatus for enabling width reduction. After the glass has softened (conveniently, but not necessarily, after energy delivery is complete), crimping jaws 42 or similar devices can be applied to the filament at desired locations, operating to apply inward pressure (a pinching or compressing action) in the plane of the desired location to reshape the glass into a thinner shape and create a neck. This is applicable to both solid filaments and hollow or partially hollow filaments.

[0042] Alternatively, some relative movement can be performed between cane portion 12 and remaining portion 14 to effect width reduction or expansion. The movement can be longitudinal, along the axis of the filament, so that the softened glass is stretched over a longer length and therefore adopts a smaller width. Or, the movement can be rotational, to effect a twisting action that deforms and compresses the softened glass.

[0043] Once the narrow neck portion is created, the cane portion 12 is separated from the remainder 14 of the filament 10 while the glass is still flexible (so energy may continue to be applied to maintain the elevated temperature).

[0044] FIG. 9 shows the example apparatus of FIG. 7 after separation has been performed. To effect separation, cane portion 12 and remaining portion 14 are moved longitudinally away from one another. The movement is relative, in that one or both portions can be moved. In this example, the movement can be accomplished by increasing the distance between first clamping device 24 and second clamping device 26 from distance d1 in FIGS. 4 and 7 to a larger distance d2. The softened glass material stretches and necks down, becoming increasingly narrower until the material of the two portions 12, 14 is pulled apart and the portions separate, as shown in FIG. 9.

[0045] Alternatively, the amount of energy applied to soften the glass, optionally assisted by crimping jaws or the like, may be sufficient to effect separation by reducing the filament under the necked region to zero width. Inter-portion movement can then be effected to move the already separated cane portion away from the remaining portion to a different location.

[0046] When the glass-softening approach is used, the glass on the outer surface of the filament moves inward and eventually closes over the ends of each of the sections 12, 14, leaving a teardrop or ogive shape at the section ends. This is generally beneficial in that it eliminates end-face defects that can be introduced by mechanical cane separation techniques. In the particular case of filaments having one or more lumens within their internal structure, the glass-closing shaping at the ends of the cane sections and the remaining section serves to close or seal the lumens. This prevents the ingress of contaminants into the lumens both during the separation process and during later stages, such as storage and further processing. Therefore, the quality of optical fiber subsequently drawn from canes produced in this manner is potentially improved over that from mechanically separated canes.

[0047] The amount by which the spacing or separation d1 must be increased to d2 to cause separation depends on the diameter of the filament and the size of the reduced width W'. Thicker filaments may require greater relative longitudinal movement to neck down to zero width, at which point separation occurs.

[0048] Once separated from the filament, the cane section or cane can be moved to a different location for storage or further processing, such as by a manipulator or robotic arm, in accordance with known cane and fiber drawing procedures. A second clamping device 26 can be used for this purpose.

[0049] As an alternative, one or other of the first and second clamping devices can be omitted, and the filament can be secured for processing by only a single clamping device. In such a configuration, if the filament is secured in a vertical orientation, as in the drawing tower, gravity can be used to effect movement between the cane portion and the remainder of the filament. Once the glass in the desired location has softened, if this is the only clamping device used, the cane portion will fall under its own weight under the action of gravity, possibly aided by the weight of the second clamping device, until the neck portion narrows to zero width and the cane is separated. By rapidly applying sufficient energy, a zero-width neck portion is created, after which the cane portion begins to fall. Thus, the force of gravity moves the already separated portion apart.

[0050] 10 shows a simplified diagram of an apparatus for carrying out a method of cane separation according to a further example. As in the method described with respect to FIG. 4, the filament 10 is first clamped vertically, such as inside a drawing tower, by a first clamping device 24 at an upper position and a second clamping device 26 at a lower position on either side of a desired location D for dividing the filament 10 into a remaining filament portion 14 and a cane portion 12 to be separated from the remaining filament portion 14. As before, the first and second clamping devices are separated by a distance d1.

[0051] Also, as before, the apparatus includes an energy source in the form of a laser 28 emitting a beam of laser light 30 that is focused onto and directed toward the filament face at a desired location D by a lens arrangement 32 that forms a focal point 34. As before, the laser energy source may consist of a suitable beam guidance system for applying one, two, or more foci or collimated points of light around the circumference of the filament 10, with the option to rotate around the filament to deliver light to some or all of the circumferential region. Similarly, the energy source may alternatively comprise one or more combustion or plasma sources.

[0052] This example differs from the previous example in that energy is delivered primarily in a manner that ablates the glass material of the filament at the desired location, rather than softening it. In softening, due to a suitable temperature increase caused by the applied energy, the glass material undergoes a state change: melting, i.e., progressing from solid glass to softened, liquid-like glass. In contrast, ablation causes the glass material to change state from solid to gas or plasma, depending on the density of the delivered energy. At lower densities or flow rates, solid glass is converted to gas by evaporation or sublimation, while at higher densities, solid material can be directly converted to plasma. Ablation therefore causes the physical removal of material from the filament. The removal can be limited to one or more layers on the exterior or surface of the filament, thus reducing the width of the filament at the desired location, similar to but using a different mechanism than the necking-based width reduction achieved in the glass-softening example. Alternatively, ablation can remove enough material to effectively sever the filament, reducing its width to zero at that point.

[0053] Those skilled in the art will be able to select suitable operating parameters for the energy source to deliver energy to the filament in a manner that results in ablation rather than softening. Generally, a higher energy density is required to achieve ablation rather than softening.

[0054] Ablation is accomplished by directing energy at desired locations to remove material to create cuts, grooves, or slots 44 in the filament. The slots 44 are preferably circumferentially oriented, where the slots 44 are aligned around the circumference of the filament approximately perpendicular to the longitudinal axis of the filament. One or more slots 44 can be created at desired locations by relatively rotating one or more points around the filament at which an energy beam, such as the example laser beam 30 in FIG. 10, is applied (as previously described). The slots 44 can be cut as a continuous slot around the filament, for example, by sweeping a single beam immediately around the filament, or as a series of overlapping or adjacent slots, each cut by a different one of multiple beams spaced around the filament.

[0055] The reduction in filament width to a non-zero width caused by the presence of one or more slots 44 weakens the filament at a desired location, so that the filament can be broken at a desired location by providing relative longitudinal motion between cane portion 12 and remaining portion 14 such that the two portions move apart.

[0056] FIG. 11 shows the apparatus of FIG. 10 with the cane 12 separated from the remainder of the filament 14 after a relative longitudinal movement of the cane 12 and the remainder of the filament 14, corresponding to an increase in the spacing of the clamping device from d1 to d2. This can be performed after applying energy to effect ablation. Therefore, the energy source (laser) 28 is shown in an inactive state without an output beam. The strain caused by the longitudinal movement preferentially breaks the filament at the weak points in the desired locations, allowing the cane 12 to separate from the remainder of the filament 10. The slots 44 can be cut to any depth, with the slot depth being a greater percentage of the filament width, increasing the weakness in the desired locations and thus facilitating separation of the cane 12. A convenient depth for hollow-core filaments is approximately the wall thickness of the outer glass tube. Alternatively, one or more slots may be deep enough to completely cut the cane 12 from the filament, creating a zero reduced width.

[0057] As discussed with respect to FIG. 9, only one clamping device can be used to secure the filaments in a vertical orientation and use gravity to provide the relative longitudinal movement to separate the canes.

[0058] The use of laser light or energy delivered as combustion or plasma to effect ablation allows the slots to be cut without generating solid debris, such as bits of glass filament material, that may be created when mechanical cleaving techniques relying on saws, grinding wheels, or diamond, ceramic, or steel blades are used.

[0059] In contrast to glass-softening embodiments, where the cane ends to be closed allow for sealing of any lumen, ablation approaches allow for cane separation to be achieved with minimal strain on the internal structure of the filament, thereby allowing the lumen to remain open and the cane ends to be drawn into optical fiber. Keeping some or all of the lumen open is related to fiber drawing methods in which one or more internal pressures are controlled. This reduces waste and maximizes fiber output. Applied energy parameters can be selected with reference to the internal filament structure to minimize internal wall distortion and lumen closure. In other words, energy application can be formulated to maximize the ablation effect and minimize glass melting or softening.

[0060] As mentioned, ablation by application of a laser beam or other form of energy is a process that typically creates a vapor or plasma. Any vapor may subsequently condense. In this case, the condensation may be on the outer surface of the filament, on the end face exposed by the cutting slot, and on the inner surface of the filament, if a lumen is present. This condensation is effectively contaminant, in that material (whether glass material from the filament itself) is deposited where it should not be. This can affect the drawing of the separate cane into fiber and may alter the optical properties of the fiber, such as resulting in increased light propagation loss. Therefore, to reduce condensation and preserve filament quality, it is proposed to remove the ablation byproducts as they are generated.

[0061] 10 and 11, the apparatus further includes a vapor handling system 50, shown in simplified form. The vapor handling system 50 includes an air handling unit 52 and a duct 54 connected at one end to the air handling unit. The other remote end(s) 56 of the duct 54 is positioned adjacent the filament 10 and is proximate the desired location D and the region of the filament 10 where the energy spot 34 is to be applied.

[0062] FIG. 12 shows a simplified diagram of an exemplary air handling unit in more detail. The vapor handling unit 50 includes a first air handling unit 52a having an associated first duct(s) 54a. The first air handling unit 52a delivers clean, dry air (or an alternative gas, such as nitrogen) through the first duct 54a. The first duct 54a discharges to one or more nozzles 58a, 58b at the distal end 56 of the first duct 54a. In the case of two or more nozzles, these can be positioned around the circumference of the filament 10, proximate the desired location D and spaced slightly from the filament plane. Alternatively, the nozzles 58a, 58b can be in the form of one or more slots circumferentially disposed around the axis of the filament 10. The nozzles 58a, 58b each discharge air delivered from the first air handling unit 52a as an air stream 60a, 60b from a respective nozzle. The air streams 60a, 60b are positioned to impinge on the filament 10 in a manner that entrains vapors and / or particles generated by the impact of energy (not shown) applied to the filament 10 at the desired location D. The air streams 60a, 60b carry the entrained vapors and particles (sometimes commonly referred to as debris or ablation by-products) so that they move away from the filament 10. For example, the flowing air can impinge on the filament surface and bounce outward, carrying the debris with it. In this manner, debris is removed from the vicinity of the filament 10, reducing the risk of debris deposition on the outer and / or inner surfaces of the filament 10. To enhance the effectiveness of this removal, the air handling capacity of the vapor handling unit 50 can be supplemented by a second air handling unit 52b equipped with an extraction duct 54c. The second air handling unit 52b is an air intake unit rather than an air discharge unit. The distal end 56 of the extraction duct 54c has a suitably positioned nozzle 58c for collecting the flowing air 60a, 60b laden with vapors and particles. More than one extraction duct 54c may be provided or the extraction duct 54c may have more than one end nozzle 58c.

[0063] Returning to FIG. 10 , note that ablative energy, such as laser beam 30, is delivered onto the filament surface along a direction generally perpendicular to the longitudinal axis of the filament (horizontal to the depicted orientation of the vertical filament). In instances where filament 10 has an internal cross-sectional structure with a lumen, such as the example of FIG. 3C , it will be apparent that outer tube 18 is truncated before the wall of internal capillary 22. If energy is in the beam 30 delivered to focal point 34 at desired location D, the energy beam 30 will diverge after focal point 34 before passing through filament 10. The diverged beam will be incident on the internal structure of the filament, including the opposite inner surface of outer tube 18. With a horizontally directed beam, the diverged energy will extend both above and below the desired location, thus impinging on both cane portion 12 and the remaining filament portion 14. This may generate vapors that are inaccessible to the vapor handling system 50 and may subsequently condense inside both cane portion 12 and the remaining filament portion 14. Therefore, both portions of the filament 10 can become internally contaminated.

[0064] Figure 13 shows a simplified side view of an apparatus modified to address this situation. The beam guidance system (which includes a lens 32 in the depicted simple arrangement, but which can be significantly more complex to handle multiple beams or have multiple beam directions as described with respect to Figures 6A, 6B, or 6C) is positioned so that one or more energy beams 30 are directed in a downwardly tilted direction (relative to the depicted vertical orientation of the filament 10). This allows a focal point 34 to be incident on the outside of the filament 10 at the desired location D, allowing separation of the cane portion 12 at the correct location, while the diverging beam after the focal point 34 is incident on the internal structure of the filament 10 over one or more regions 35 (shaded in Figure 13) that are mostly or completely within the cane portion 12, i.e., below the desired location D. In this way, any vapor condensation can be limited to mostly within the cane portion 12.

[0065] While the examples thus far have been described primarily in the context of separating canes from larger lengths of glass filaments either while the filaments are being drawn from the preform in a draw tower or after they have been drawn, the separation method is not limited in this respect. In particular, any of the examples and modifications can be used to cut existing canes to different lengths by removing portions at one or both ends of the cane. This may be, for example, to achieve a specific cane length. For example, if a glass softening separation method is used to obtain canes from drawn filaments such that the canes have closed or necked ends, an ablation separation method can be used to remove the ends. In such cases, application of an oblique beam, as described with respect to FIG. 13 , can be used to limit internal vapor condensation to the removed ends, thereby avoiding contamination of the lumen in the final cane. Accordingly, references in the preceding description to “filament” can apply to filaments that have been drawn or are being drawn from a preform and need to be cut into canes or other shorter lengths, as well as to already separated canes from which one or more portions are to be separated. References to "cane portion" can mean the cane that has been separated from the filament, or any portion that has been separated from the cane, such as a necked or closed end. References to "remainder of filament" (and similar terms) can apply to the filament remaining after separation of the cane, or the mass of cane that remains after separation of one or both ends. The method can also be used to cut the finished optical fiber to a desired length or to trim the ends.

[0066] As previously mentioned, the use of a single clamping apparatus (or similar securing or holding device) and gravity to cause separation by relative longitudinal movement may be useful and advantageous in situations where portions are being removed from an existing cane.

[0067] As will be appreciated, while the method is employed according to the examples described herein, the apparatus for enabling the method can include a system or device for pulling the filament downwardly from the preform to achieve continuous drawing as the filament is drawn from the preform assembly in a draw tower.

[0068] 14A and 14B show simplified diagrams of an exemplary device for this purpose, commonly referred to as a "cane puller." Device 70 includes a pair of rotatable belts 72, each in the form of a continuous loop passing around a pair of spaced-apart drive wheels 74 that hold the belts in a predetermined configuration. Rotating the two drive wheels in the pair in the same direction pulls the belts around in the same direction. The axis X about which this rotation occurs is midway between the axes of the two drive wheels. The two belts 72 are arranged in a parallel, opposing configuration with their axes of rotation X parallel, so that as the belts 72 rotate, the outwardly facing surfaces 76 of the belts 72, each providing a moving surface, face each other to provide opposing, parallel moving surfaces 76. The opposing moving surfaces 76 are spaced apart by a width W corresponding to the width of the filament 10 (conveniently, the relative positions of the belts 72 can be adjusted to move the belts in and out of this arrangement). Thus, the filament 10 can be gripped between the two opposing surfaces 76 of the belts 72, with its longitudinal axis A oriented perpendicular to the rotational axis X of the belts 72 and parallel to the direction of movement of the movable surfaces 76. When the drive wheel 74 of one belt 72 is driven in the opposite direction to the drive wheel 74 of the other belt 72, the two movable surfaces 76 move in the same direction, as indicated by the arrows. Thus, the filament 10 is continuously fed in that same direction (downward in the depicted orientation) through the space between the movable surfaces 76. This continuously pulls new filament 10 from the preform (not shown), thereby enabling a continuous supply of new filament 10 from which the cane can be separated.

[0069] The drive wheel 74 is under the control of a drive mechanism (not shown) which may include a computerized controller that is programmed to allow automatic control of the tension on the filament 10 .

[0070] 14A shows a side view of the cane pulling machine 70 in a plane transverse to the rotation axis X of the belt 72. FIG. 14B shows a vertical side view of the cane pulling machine 70 (without the filaments) in a plane parallel to the rotation axis X of the belt 72. From this, it can be seen that the two belts 72 have the same configuration (because one is hidden behind it from all but this viewing angle) in that their rotation axes X are parallel to each other and perpendicular to the filament axis A, and the moving surface moves in a direction also parallel to the filament axis.

[0071] 15A and 15B show simplified side views of an exemplary cane pulling machine 80 according to embodiments of the present disclosure. The cane pulling machine 80 includes a pair of opposing rotatable belts 72 a, 72 b configured and operable in the manner described with respect to FIGS. 14A and 14B, providing a pair of opposing movable surfaces 76 spaced a distance W apart that act to grip and continuously feed the filament 10 downwardly by the oppositely driven belts 72 a, 72 b.

[0072] In this example, however, the rotation axes Xa, Xb of belts 72a, 72b are not parallel to one another. Instead, they lie in parallel planes that are also parallel to filament axis A, but each is positioned at a substantially equal but opposite non-perpendicular angle relative to filament axis A (and thus relative to the direction of travel or feed of the filament through the cane pulling machine). This can be seen in FIG. 15B, which shows each belt 72a, 72b tilted away from the vertical (filament axis A) in opposite directions within the plane of moving surface 76. Thus, there is an angle Y between the two rotation axes Xa, Xb. The rotation axis Xa of one belt 72a is disposed above horizontal at an angle Y' (perpendicular to filament axis A), while the rotation axis Xb of the other belt 72b is disposed below horizontal at the same angle Y', where 2Y'=Y. Similarly, the two rotational axes are disposed at equal and opposite non-perpendicular angles 90°-Y′ to the filament axis A, which is also the longitudinal direction in which the filament is pulled or drawn from the preform. This can also be described as the direction of travel of the moving surfaces 76 of the two belts 72 a, 72 b separated by angle Y, each disposed at angle Y′ on either side of the filament axis A.

[0073] The effect of this angled arrangement of the two rotating belts is to impart a twisting motion to the filament 10, indicated by the spiral arrow R in FIG. 15A, as it is fed downward through the cane puller 80. Thus, the filament 10 rotates about its longitudinal axis A as it is pulled through the cane puller 80. This motion can be used to achieve relative rotational motion between the applied energy beam and the filament to deliver energy circumferentially around the filament at a desired location, as described above. Thus, the beam guidance system 32, such as those shown in FIGS. 4, 5A, 6A, 6B, and 6C, can remain stationary while the filament rotates about its rotational axis A. Alternatively, the two motions can be combined, with the beam guidance system 32 rotating around the filament in a first direction and the filament rotating within the beam guidance system in a second, opposite direction.

[0074] The cane tensioning machine 80 can be configured so that the belt angle is fixed, thereby providing a constant torsional motion while pulling the filament. Alternatively, the belts can be movable (e.g., under the control of the same controller that operates the rotation of the rotating belt), so that their relative angle can be adjusted. This can allow the rotation of the filament to be turned on and off (by switching the angle of the belt rotation axis between non-perpendicular and perpendicular to the filament axis), between rotation in one direction and rotation in the opposite direction (by reversing the angle of the non-perpendicular belt rotation axis), or to change speed (by making the angle of the non-perpendicular belt rotation axis smaller or larger).

[0075] Other methods for achieving filament rotation within the energy beam guidance system may alternatively be used.

[0076] The filament processing method proposed herein is generally applicable to filaments made of glass materials. The filaments can be made from materials known for the manufacture of solid, luminal optical fibers of existing designs, particularly glass materials such as silica. In filaments with internal structures, the various tubes and capillaries can be made from the same or different materials. Examples of glass types include "silicate glasses" or "silica-based glasses" based on silica compounds (silicon dioxide, or quartz), among many others. Other glasses from which filaments can be made useful and suitable for optical applications include, but are not limited to, chalcogenides, tellurite glasses, fluoride glasses, and doped silica glasses. Glass materials can contain one or more dopants to adjust optical properties, such as modifying absorption / transmission or enabling optical pumping.

[0077] The method is also generally applicable to a wide range of filament widths or diameters, for example, from a typical optical fiber diameter of about 100 μm to a typical cane diameter of 20 mm or more.

[0078] The various embodiments described herein are proposed solely to aid in understanding and teaching the claimed features. These embodiments are provided merely as representative sample embodiments and are not intended to be exhaustive and / or exclusive. The advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein should not be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and it is understood that other embodiments may be utilized and modifications may be made without departing from the scope of the claimed invention. Various embodiments of the present invention may suitably comprise, consist of, or consist essentially of any suitable combination of the disclosed elements, components, features, parts, steps, means, etc., other than those specifically described herein. In addition, the present disclosure may include other inventions not currently claimed but which may be claimed in the future. [Explanation of symbols]

[0079] 10 Glass filament, filament 12 Cane part 14 Remaining part, remaining filament part 16 solid glass rods 18 Glass tube, outer tube 20. The center, the hollow space 22 Hollow glass capillary, internal capillary, capillary 24 First clamping device 26 Second clamping device 28 Lasers, laser sources, energy sources 30 Laser light, laser beam, beam, output beam, energy beam 30a beam 30b Beam, beam part 30c light, beam 32 Lenses, beam guidance systems, lens devices 34 Focus, elliptical focus, energy spot 34a focus 34b focus 34c focus 35 areas 36 Negative cylindrical lens, lens 38 Positive cylindrical lens, lens 40 Spherical lens, burning 42 Crimping Jaws 44 slots 50 Steam handling systems, steam handling units 52 Air Handling Unit 52a First Air Handling Unit 52b Second Air Handling Unit 54 Duct 54a First Duct 54c Extraction duct 56 End, distal end 58a nozzle 58b nozzle 58c nozzle 60a Airflow, Air 60b Air flow, air 70 Device, cane tensioning machine 72 Belt 72a Belt 72b Belt 74 Drive Wheel 76 Movable surface, outward facing surface 80 Cane Pulling Machine 82 Plane mirror 84 holes, plane mirror 86 Baffle, Reflected Beam 88 Reflected beam, beam 90 Parabolic mirror 92 holes 94 Carriage 96 Plane sweep mirror, mirror 98 Shaft 100 motor 102 beam, reflected beam 102a Reflected beam 102b Reflected beam 104 Off-axis parabolic mirror 106 holes 108 Double Reflection Beam BSa First beam splitter BSb Second beam splitter La First Lens Lb Second Lens Lc third lens Ma1 Mirror Ma2 Mirror Mb1 mirror Mb2 Mirror

Claims

1. providing a length of glass filament, a portion of which is separated from the remainder of the filament; directing energy to the filament to cause a reduction in width of the filament at a desired location to separate the portion; moving the portion away from the remainder of the filament to obtain the portion separated from the remainder of the filament; 1. A method for treating glass filaments, comprising: the length of glass filament is drawn from a glass preform, and the filament is run through a drawing tower while being drawn from the glass preform; the filament is drawn from the glass preform using a cane puller comprising a pair of opposing rotating belts positioned to grip opposite sides of the filament and pull the filament longitudinally away from the preform; wherein the pair of opposing rotating belts are arranged so that the belt rotation axes are at opposite and approximately equal non-perpendicular angles to the longitudinal direction to cause rotation of the drawn filament about its longitudinal axis.

2. The method of claim 1 , wherein the separated portion forms a cane that can be drawn into optical fiber.

3. 3. The method of claim 1 or 2, wherein the energy is in the form of one or more laser beams or combustion or plasma beams applied to the filament.

4. The method of claim 3 , wherein the energy is directed to at least one focal point approximately in a plane of the filament at the desired location.

5. 5. The method of claim 1, wherein directing energy onto the filament comprises directing energy onto two or more regions circumferentially disposed around the filament at the desired location.

6. 6. The method of claim 1, further comprising inducing relative rotational motion between the filament and the energy while directing the energy onto the filament to direct the energy onto one or more regions circumferentially disposed around the filament at the desired location.

7. 7. The method of claim 1, wherein directing energy onto the filament causes the width of the filament to reduce to zero at the desired location, thereby separating the portion from the remainder of the filament.

8. 7. The method of claim 1, wherein directing energy onto the filament reduces the width of the filament to a value greater than zero at the desired location, and wherein moving the portion away from the remainder of the filament includes causing relative longitudinal movement between the portion and the remainder of the filament to separate the portion from the remainder of the filament at the desired location.

9. 10. The method of claim 8, further comprising, during the directing energy step, holding the remainder of the filament with a first clamping device at a first position, holding the portion with a second clamping device at a second position longitudinally spaced from the first position, and causing the relative longitudinal movement by increasing a spacing between the first clamping device and the second clamping device.

10. 9. The method of claim 8, further comprising, during the directing energy step, holding the one of the remainders and the portion of the filament with a clamping device and causing the relative longitudinal movement by allowing the portion to move under gravity.

11. 11. The method of claim 1, comprising directing sufficient energy onto the filament to cause softening and deformation of the glass of the filament into a necked region at the desired location.

12. The method of claim 11 further comprising applying crimping jaws to the softened glass to assist deformation into the necked region.

13. 13. The method of claim 11 or 12, wherein the filament has an internal structure with one or more longitudinal lumens, and the deformation of the glass into the necked region comprises collapsing the one or more lumens.

14. 14. The method of claim 13, wherein the deformation, and optionally also the step of moving the portion away from the remainder of the filament, causes a width of the necked region to decrease to zero, thereby closing the lumen at a separated end of the portion.

15. 11. The method of claim 1, comprising directing energy onto the filament sufficient to cause ablation of glass of the filament at the desired location.

16. 16. The method of claim 15, wherein glass is ablated to form a circumferential slot around the filament at the desired location.

17. 17. The method of claim 15 or 16, further comprising removing vapors and / or debris generated by the ablation by providing a flow of air to carry the vapors and / or debris away from the filament.

18. 18. The method of any one of claims 15 to 17, wherein the filament has an internal structure with one or more longitudinal lumens, and wherein directing energy onto the filament includes directing energy toward the portion at an angle that is not perpendicular to a longitudinal axis of the filament so as to reduce condensation of vapor generated by the ablation inside the lumens in the remainder of the filament.

19. 2. The method of claim 1, wherein the pair of opposing rotating belts are arranged so that the axis of rotation of each belt is perpendicular to the longitudinal direction.

20. a pair of rotatable belts, each having a movable surface rotatable about an axis of rotation, the belts positionable in a position where the movable surfaces face the separator to receive and grip the glass filaments, the movement of the surfaces acting to pull the filaments along the longitudinal axis of the filaments and away from the preform; a belt, the rotation axis of which is configurable at a non-perpendicular angle that is opposite and substantially equal to the pulling direction to impart rotation to the filaments about their longitudinal axes; 1. A device for drawing glass filaments from a preform, comprising:

21. 21. The device of claim 20, wherein the rotational axes of the belts are additionally positionable parallel to one another and substantially perpendicular to the pulling direction to pull the filaments without imparting rotation.

22. 22. A device according to claim 20 or 21, wherein opposite, substantially equal, non-orthogonal angles can be varied to change the speed of said rotation, including being reversed to reverse the direction of said rotation.

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