Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
  • C03B37/01—Manufacture of glass fibres or filaments
  • C03B37/012—Manufacture of preforms for drawing fibres or filaments
  • C03B37/01205—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
  • C03B37/01211—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments by inserting one or more rods or tubes into a tube
  • C03B37/0122—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments by inserting one or more rods or tubes into a tube for making preforms of photonic crystal, microstructured or holey optical fibres
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B23/00—Re-forming shaped glass
  • C03B23/04—Re-forming tubes or rods
  • C03B23/07—Re-forming tubes or rods by blowing, e.g. for making electric bulbs
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
  • C03B37/01—Manufacture of glass fibres or filaments
  • C03B37/012—Manufacture of preforms for drawing fibres or filaments
  • C03B37/01205—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
  • C03B37/01—Manufacture of glass fibres or filaments
  • C03B37/012—Manufacture of preforms for drawing fibres or filaments
  • C03B37/01205—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
  • C03B37/01225—Means for changing or stabilising the shape, e.g. diameter, of tubes or rods in general, e.g. collapsing
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
  • C03B37/01—Manufacture of glass fibres or filaments
  • C03B37/012—Manufacture of preforms for drawing fibres or filaments
  • C03B37/01205—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
  • C03B37/01225—Means for changing or stabilising the shape, e.g. diameter, of tubes or rods in general, e.g. collapsing
  • C03B37/01228—Removal of preform material
  • C03B37/01234—Removal of preform material to form longitudinal grooves, e.g. by chamfering
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
  • C03B37/01—Manufacture of glass fibres or filaments
  • C03B37/012—Manufacture of preforms for drawing fibres or filaments
  • C03B37/01205—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
  • C03B37/01225—Means for changing or stabilising the shape, e.g. diameter, of tubes or rods in general, e.g. collapsing
  • C03B37/0124—Means for reducing the diameter of rods or tubes by drawing, e.g. for preform draw-down
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
  • C03B37/01—Manufacture of glass fibres or filaments
  • C03B37/02—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor
  • C03B37/025—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from reheated softened tubes, rods, fibres or filaments, e.g. drawing fibres from preforms
  • C03B37/027—Fibres composed of different sorts of glass, e.g. glass optical fibres
  • C03B37/02781—Hollow fibres, e.g. holey fibres
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/08—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant
  • C03B2201/12—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant doped with fluorine
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2203/00—Fibre product details, e.g. structure, shape
  • C03B2203/10—Internal structure or shape details
  • C03B2203/14—Non-solid, i.e. hollow products, e.g. hollow clad or with core-clad interface
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2203/00—Fibre product details, e.g. structure, shape
  • C03B2203/10—Internal structure or shape details
  • C03B2203/14—Non-solid, i.e. hollow products, e.g. hollow clad or with core-clad interface
  • C03B2203/16—Hollow core
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2203/00—Fibre product details, e.g. structure, shape
  • C03B2203/32—Eccentric core or cladding
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2203/00—Fibre product details, e.g. structure, shape
  • C03B2203/42—Photonic crystal fibres, e.g. fibres using the photonic bandgap PBG effect, microstructured or holey optical fibres

Definitions

• the invention relates to a method for producing an anti-resonant hollow core fiber which has a hollow core extending along a longitudinal axis of the fiber and a cladding area surrounding the hollow core which comprises a number of anti-resonant elements, with the method steps:
• the invention also relates to a method for producing a preform for an anti-resonant hollow core fiber, which has a hollow core extending along a longitudinal axis of the fiber and surrounding the hollow core, which comprises several anti-resonant elements, with the method steps:
• the refractive index of the core is smaller than that of the cladding, so that light transmission through total reflection is not possible and the light would normally escape from the core into the cladding.
• hollow core fibers are divided into “photonic bandgap fibers” and “anti-resonance reflection fibers”.
• the hollow core area is surrounded by a cladding in which small hollow channels are periodically arranged.
• the periodic structure of the hollow channels in the cladding causes the effect known as the “photonic band gap” based on semiconductor technology, according to which light from certain wavelength ranges scattered on the cladding structures interferes constructively in the central cavity due to Bragg reflection and cannot propagate transversely in the cladding.
• the hollow core area is surrounded by an inner cladding area in which so-called “antiresonant elements” (or “antiresonant elements”; in short: “ AREs ”) are arranged.
• the walls of the anti-resonance elements evenly distributed around the hollow core can act as anti-resonance-operated Fabry-Perot cavities that reflect the incident light and guide it through the fiber core.
• This fiber technology promises low optical attenuation, a very broad transmission spectrum (also in the UV or IR wavelength range) and low latency in data transmission. '
• hollow core fibers are in the field of data transmission, high-performance beam guidance, for example for material processing, modal filtering, non-linear optics, in particular for supercontinuous generation, from the ultraviolet to the infrared wavelength range.
• high-performance beam guidance for example for material processing, modal filtering, non-linear optics, in particular for supercontinuous generation, from the ultraviolet to the infrared wavelength range.
• a disadvantage of antiresonant hollow core fibers is that higher order modes are not necessarily suppressed, so that they are often not purely single-mode over long transmission lengths and the quality of the output beam deteriorates.
• the effective mode suppression depends on the center wavelength of the transmitted light and on structural parameters of the fiber design, such as the radius of the hollow core and the difference in diameter between nested ring structures in the anti-resonance elements.
• An anti-resonant hollow core fiber is known from EP 3 136 143 A1 (referred to there as “hollow core fiber without band gap”), in which the core can conduct other modes in addition to the fundamental mode. For this purpose, it is surrounded by an inner jacket with “non-resonant elements”, which provide a phase matching of antiresonant modes with the higher modes.
• the hollow core fiber is manufactured using a so-called “stack-and-draw technique”, in which the starting elements are arranged in an ensemble parallel to the axes and fixed in a preform, and the preform is then elongated.
• a cladding tube with a hexagonal inner cross-section is used and six so-called “ARE preforms” (anti-resonance element preforms) are fixed in the inner edges of the cladding tube.
• This preform is drawn into a hollow core fiber in two stages.
• a method for producing a preform for anti-resonant hollow core fibers is known in which a first cladding area comprises a plurality of rods and a second cladding area comprises a plurality of tubes which are surrounded by an outer cladding tube. Rods, tubes and cladding tubes are joined together using the “stack and draw” technique to form a preform.
• the preform end is sealed, which is done by applying a sealing compound.
• a UV adhesive for example, is used as the sealing compound.
• Antiresonant hollow core fibers and especially those with nested structural elements have complex internal geometries, which makes their exact and reproducible manufacture difficult. This is all the more true because, in order to maintain the resonance or anti-resonance conditions, even small dimensional deviations in the order of magnitude of the working wavelength of the light to be conducted cannot be tolerated. Deviations from the target geometry can be caused by the configuration of the fiber preform, and they can also occur as a result of undesired, out-of-scale deformations during the fiber drawing process.
• Antiresonance element preforms each consisting of an anti-resonance preform outer tube (short: ARE outer tube) and an anti-resonant preform inner tube (short: ARE inner tube) welded on one side of the inner surface of the ARE outer tube, can be attached to the inside of a cladding tube.
• the azimuthal position of the anti-resonance elements within the cladding tube is also important. This cannot easily be realized with the "stack and draw" technique.
• the aim of the invention is to provide a method for the cost-effective production of a Specify anti-resonant hollow core fiber that avoids limitations of conventional manufacturing processes.
• the aim of the invention is to provide a method for producing an anti-resonant hollow core fiber and a preform for anti-resonant hollow core fibers with which high precision of the structural elements and exact positioning of the anti-resonant elements in the fiber can be achieved in a sufficiently stable and reproducible manner can.
• the formation of the anti-resonant element precursors comprises the formation of elongated pressure chambers, each of which is connected to an under pressure and in the area of the target positions of the anti-resonant elements Adjacent heat deformable wall, and when carrying out a process according to process step (c) as a result of pressure and heat, a portion of the deformable wall bulges in the direction of the cladding tube inner bore with the formation of an anti-resonance element or a precursor therefor.
• the starting point for the manufacture of the anti-resonant hollow core fiber is a preform, which is also referred to here as a “primary preform”. It comprises a cladding tube in which or on which precursors or preforms for shaping anti-resonant elements in the hollow core fibers (here referred to as “anti-resonant elements” for short) are contained.
• the primary preform can be elongated into the hollow core fiber; As a rule, however, additional jacket material is added to the primary preform in order to create a preform, referred to here as a “secondary preform”.
• the hollow core fiber is created by elongating the secondary preform.
• the primary preform or the second The secondary preform is surrounded by the formation of a coaxial ensemble of components with an overlay cylinder or with several overlay cylinders, and the coaxial ensemble is elongated directly to form the hollow core fiber.
• the general term “preform” is understood here to denote that component or that coaxial ensemble of components from which the hollow core fiber is ultimately drawn.
• the accuracy of the positioning of the anti-resonance elements is improved in that the preliminary stages for anti-resonance elements are implemented in the form of elongated pressure chambers which are formed in the area of the target positions of the anti-resonance elements.
• the pressure chambers are designed to turn the adjoining wall sections of the inner cladding tube inside out in the direction of the cladding tube longitudinal axis when these wall sections are softened and a gas pressure is applied in the pressure chambers.
• the elongated pressure chambers cause an elongated eversion of an elongated portion of the deformable wall in the direction of the cladding tube inner bore to form an elongated Antiresonanzele element or a precursor therefor when a process is carried out according to method step (c) as a result of pressure and heat.
• the relevant, inverted wall sections of the deformable wall are elongated and run along the pressure chambers and the target positions of the antiresonance element precursors in the preform.
• the wall sections to be turned over belong to the deformable wall of a glass tube.
• the pressure chambers are in a first preferred variant of the method
• the pressure chambers are provided by a separate component that adjoins the outer surface of the deformable glass tube wall.
• they form hollow channels, which run parallel to the longitudinal axis of the glass tube from one end to the other end along the glass tube wall and which are delimited on one side by the glass of the glass tube.
• the pressure chambers are formed in recesses in the outer jacket surface of the glass tube wall; in this case they also form hollow channels which run parallel to the glass tube longitudinal axis from one end to the other along the glass tube wall and are delimited by the glass of the glass tube in the region of the recess.
• the antiresonance element precursors are generated at these positions in a manufacturing step by turning the relevant wall sections in the direction of the inner glass tube bore by applying a pressure acting from the outer side of the glass tube. This can be done, for example, when elongating the preform to form a hollow core fiber or a semi-finished product.
• a positioning and fixing of prefabricated anti-resonance element preforms at the relevant positions of the cladding tube inner wall - as known in the stack-and-draw technique - can thus be completely omitted or the number of anti-resonance element preforms to be positioned in this way can be at least reduced.
• anti-resonant hollow core fibers and preforms for them can be produced precisely and reproducibly.
• the pressure chambers are advantageously designed as hollow channels to which the wall sections of a glass tube to be deformed adjoin.
• the hollow channels form pressure chambers into which a pressurized gas can be introduced in a manufacturing step, so that the wall sections of the glass tube accessible to the pressurized gas are deformed as a result of the gas pressure.
• Hollow channels created by drilling inside the tube wall of a deformable glass tube
• hollow channels are formed within the glass tube wall which run parallel to the glass tube longitudinal axis.
• the cross section of the hollow channels can be round or polygonal, in particular triangular or rectangular.
• the long side of the rectangle runs tangentially to the wall section to be formed (to be turned out).
• one of the triangle sides runs tangentially to the wall section to be reshaped (to be turned out).
• the gas pressure acts more strongly on this wall section than in other directions.
• a procedural variant has proven to be favorable in which a coaxial glass tube arrangement is formed, comprising an inner peripheral row of hollow channels in the tube wall of an inner glass tube and an outer peripheral Row of Hohlka channels in the tube wall of an outer glass tube, the hollow channels of the inner and outer peripheral row in the radial direction on a common connecting line and are spatially separated by at least one peripheral and inwardly deformable glass wall.
• the peripheral glass wall separates the pressure spaces of the inner and outer peripheral rows of hollow channels from one another and is turned inside out during the hot forming process through the hollow channels of the outer peripheral row. If the peripheral glass wall is part of the inner glass tube, the deformation of the outer glass tube can take place in a protuberance of the inner glass tube, whereby an anti-resonance element preform is produced for a nested anti-resonance element. Hollow channels, created by longitudinal slots in an intermediate pipe wall adjoining a deformable glass pipe
• Another particularly elegant procedure for forming the hollow channels comprises a measure in which an intermediate tube is arranged between the glass tube and an outer tube which has an intermediate tube longitudinal axis along which an intermediate tube wall, delimited by an inner side and an outer side, extends , wherein longitudinal slots are made in the intermediate pipe wall, hollow channels being formed from the longitudinal slots when a process is carried out according to method step (c).
• the longitudinal slots penetrate the wall of the intermediate tube (preferably with the exception of the two end regions). They have parallel longitudinal edges.
• the intermediate tube can rest against the outer wall of the glass tube and be fused with it, and it can rest against the inner wall of the outer tube and be fused with it.
• the longitudinal slots are located between the glass tube and the outer tube at the positions of the glass tube wall sections to be inverted. There they form hollow channels or preliminary stages of hollow channels, via which pressure can be applied to the outside of the glass tube in a later manufacturing step in order to invert the softened material of the glass tube in the direction of its inner bore.
• the hollow channels are formed into the elongated protuberances as a result of pressure and heat.
• One advantage of this embodiment is that the distance between the hollow channels and the inner bore becomes particularly uniform over their length and among one another.
• an internal pressure is generated in the hollow channels by introducing a compressed gas, and the wall sections of the glass tube that are accessible to the compressed gas through the longitudinal slots are thereby deformed.
• elongated bulges pointing inward - in the direction of the inner bore of the glass tube and in the direction of the hollow core - are formed on the glass tube, which serve as anti-resonance element preforms or as anti-resonance elements.
• the longitudinal slots preferably end in front of the front ends of the intermediate tube in order to ensure that the remaining longitudinal webs are held together.
• a procedural variant has proven to be favorable in which a coaxial tube arrangement is formed, comprising an inner glass tube, an inner intermediate tube, an inner outer tube, which is also an outer glass tube forms, an outer intermediate tube and an outer outer tube, the longitudinal slots of the inner and the äuße Ren intermediate tube lie in the radial direction on a common connecting line and are spatially separated by at least one peripheral and inwardly deformable glass wall.
• Such coaxial tube arrangements are used to produce at least two hollow channels or pressure chambers which, viewed in the radial direction, are arranged in pairs one behind the other.
• the peripheral glass wall separates the pressure spaces of the inner and outer peripheral rows of hollow channels from one another and is turned inside out during the hot forming process through the hollow channels of the outer peripheral row. If the peripheral glass wall is part of the inner glass tube, the outer glass tube can be deformed into a protuberance of the inner glass tube, whereby an anti-resonance element preform for a nested anti-resonance element is produced.
• an intermediate tube with a circular inner cross-section is provided and machined.
• the longitudinal slots are continuous in the radial direction and can be manufactured easily and precisely; for example by milling, drilling or cutting.
• the internal geometry of the longitudinal slots or grooves is, for example, rectangular or V-shaped.
• the longitudinal slots are preferably produced by machining the intermediate pipe wall, in particular by cutting, drilling, sawing, milling or grinding.
• Machining is understood to mean abrasive mechanical processing techniques such as turning, cutting, drilling, sawing, milling or grinding. These machining techniques provide compared to other known ones Forming techniques using heat and pressure more precise and filigree structures and they avoid contamination of the surfaces by molding tools such as nozzles, presses or melt molding.
• the longitudinal slots have longitudinal edges and the glass tube and the outer tube are connected to the longitudinal edges by softening.
• the coaxial tube ensemble consisting of the outer tube, longitudinally slotted inter mediate tube and glass tube is heated and the cut edges of the longitudinal slots are connected over their entire length to the outer wall of the glass tube and the inner wall of the outer tube.
• a simultaneous elongation suppresses undesirable deformations in the radial direction.
• the pipes are connected to one another in pairs in two process steps.
• Hollow channels created by longitudinal grooves on a deformable glass tube and / or on an intermediate tube adjoining the glass tube
• the formation of the hollow channels includes a measure in which a glass tube and an intermediate tube are inserted, which surrounds the glass tube coaxially, the glass tube being a Has the outer surface of the glass tube, in which longitudinal grooves are made which run parallel to the longitudinal axis of the glass tube, and / or the intermediate tube has an inner surface of the intermediate tube into which longitudinal grooves are made which run parallel to the longitudinal axis of the intermediate tube, wherein hollow channels are formed from the longitudinal grooves when carrying out a process according to method step (c), and the hollow channels are deformed into the elongated protuberances as a result of pressure and heat.
• the longitudinal grooves in the outer circumferential surface of the glass tube, together with a tube wall surrounding the glass tube, also form channels and thus pressure chambers for deforming the wall sections in which the longitudinal grooves run.
• the longitudinal grooves on the inner circumferential surface of the intermediate tube serve to form the hollow channels in a manner similar to the longitudinal slots of the intermediate tube, as explained in detail above.
• the longitudinal grooves are continuous, that is: they preferably extend from one end of the respective pipe res to the opposite end.
• the formation of the antireso nanzelement precursors comprises the formation of elongated pressure chambers, each in the area of the target positions of the anti-resonance elements adjoin a wall that is deformable under pressure and heat, and when a process is carried out according to method step (c), as a result of pressure and heat, a portion of the deformable wall is turned out in the direction of the cladding tube inner bore to form an anti-resonance element or a precursor cause for it.
• the preform is the starting point for the manufacture of the anti-resonant hollow core fibers.
• the anti-resonant hollow core fiber is drawn directly or a semi-finished product is first produced from which the anti-resonant hollow core fiber is then drawn.
• the production of the preform includes the turning in of wall sections of the glass tube in the area of the target positions of the anti-resonance elements by applying pressure in the pressure chambers.
• the wall sections of the glass tube to be turned over are elongated and run along the target positions of the antiresonance element precursors in the preform.
• the antiresonance element precursors are generated at these positions in a production step by turning the relevant wall sections in the direction of the inner casing tube by applying a pressure acting from the opposite wall side.
• a positioning tion and fixation of prefabricated anti-resonance element preforms at the relevant positions of the cladding tube inner wall - as known in the stack-and-draw technology - can be completely eliminated or the number of anti-resonance element preforms to be positioned in this way can at least be reduced. Measures for producing the preform are explained above in connection with the production of the hollow core fiber and these explanations are hereby incorporated.
• the anti-resonance elements can be simple or nested structural elements of the hollow core fiber. They have at least two walls that, when viewed from the direction of the hollow core, have a negative curvature (convex) or have no curvature (flat, straight). They usually consist of a material that is transparent to the work light, for example glass, in particular doped or undoped S1O 2 , a plastic, in particular a polymer, a composite material or a crystalline material.
• anti-resonance element preforms Components or parts of the preform are referred to as anti-resonance element preforms, which essentially become anti-resonance elements in the hollow core fiber by simply elongating during the fiber drawing process. Components or constituents of the preform which are only formed into anti-resonance element preforms or become anti-resonance elements directly.
• the anti-resonance element preforms can be simple or nested components on which positioning aids can also be fixed. They are originally in the primary preform.
• Nested antiresonance element preforms form nested antiresonance elements in the hollow core fiber. They are composed of an outer tube and at least one further structural element which is arranged in the inner hole of the outer tube.
• the further structural element can be a further tube which rests against the inner circumferential surface of the outer tube.
• the outer tube is referred to as the "anti-resonance element outer tube” or “ARE outer tube” for short, and the other tube as the “anti-resonance element inner tube” or “ARE inner tube” for short or as a “nested ARE inner tube”.
• At least one further structural element can be arranged in the inner bore of the nested ARE inner tube, for example a third tube resting on the inner surface of the nested ARE inner tube.
• a distinction is made between “outer nested ARE inner tube” and “inner nested ARE inner tube”.
• cross-section in connection with cylindrical anti-resonance element preforms and their cylindrical structural elements always refers to the cross section perpendicular to the respective cylinder longitudinal axis, namely - unless otherwise stated - the cross section of the outer contour (not: the cross section of the inner contour) for tubular components.
• the preform is the component from which the anti-resonant hollow core fiber is drawn. It is a primary preform or a secondary preform produced by further processing the primary preform.
• the primary preform can be present as an enmul of at least one cladding tube and preforms or precursors for anti-resonance elements loosely received or firmly fixed therein.
• the further processing of the primary preform into a secondary preform, from which the hollow core fiber is drawn can include one or more of the following hot forming processes:
• a core preform is a preform obtained by collapsing and / or elongating a primary preform. Typically, it is covered with additional sheath material before or when the hollow core fiber is drawn.
• the primary preform When elongating, the primary preform is elongated.
• the elongation can take place without collapsing at the same time.
• the elongation can take place to scale, so that, for example, the shape and arrangement of components or constituents of the primary preform are reflected in the elongated end product.
• the primary preform When elongating, however, the primary preform can also be drawn not to scale and its geometry can be changed. When it collapses, an inner bore is narrowed or annular gaps between the tubular component are closed or narrowed. Collapse is usually accompanied by elongation.
• the ensemble of at least one cladding tube and preforms or precursors for anti-resonance elements loosely received or firmly fixed therein is also referred to here as a “primary preform”.
• the primary preform includes the hollow core and a cladding area.
• This cladding area is also referred to as the “inner cladding area” if there is also an “outer cladding area” that has been created, for example, by collapsing onto the ensemble, and if a distinction is to be made between these cladding areas.
• the terms “inner cladding area” and “outer cladding area” are also used for the corresponding areas in the hollow core fiber or in intermediate products that are obtained through further processing of the primary preform.
• pipe inside is also used as a synonym for “pipe inner jacket surface” and the term “pipe outside” is also used as a synonym for “pipe outer jacket surface”.
• inner bore in connection with a pipe does not mean that the inner bore was created by a drilling process.
• This processing creates a longitudinal structure which extends in the direction of the longitudinal axis of the filler tube and which serves as a positioning aid for the anti-resonance element preforms.
• the longitudinal structure is accessible from the inside of the cladding tube; it can also extend through the entire cladding tube wall to the outside.
• Particle size and particle size distribution of the Si0 2 particles are characterized on the basis of the Dso values. These values are taken from particle size distribution curves which show the cumulative volume of the Si0 2 particles as a function of the particle size.
• the particle size distributions are often characterized using the respective D10, D50 and D9o values.
• the Dio value characterizes the particle size that is not achieved by 10% of the cumulative volume of the Si0 2 particles, and accordingly the D50 value and the D9o value those particle sizes that are 50% and 90% of the cumulative volume, respectively the Si0 2 particles is not reached.
• the particle size distribution is determined by light scattering and laser diffraction spectroscopy according to ISO 13320.
• Figure 1 shows a first embodiment of an intermediate tube provided with longitudinal slots for use in the method according to the invention in a side view (a) and in a top view (b) on a cross section,
• FIG. 2 process steps for producing a preform (b) for a hollow core fiber using a pipe ensemble (a) with several slotted intermediate pipes based on a first example
• FIG. 3 shows the fiber drawing of the preform from FIG. 3 to form a hollow core fiber
• Figure 4 shows a second embodiment of one provided with longitudinal slots
• FIG. 5 process steps for producing a preform (b) for hollow core fibers using a pipe ensemble (a) with a slotted intermediate pipe based on a second example
• FIG. 6 shows the fiber drawing of the preform from FIG. 5 to form a hollow core fiber
• Figure 7 shows a coaxial arrangement of a glass tube with thermally deformable
• Wall containing hollow channels and an overlay cylinder in a plan view.
• FIG. 1 (a) shows an intermediate tube 10, in the wall of which at previously defined azimuthal positions elongated longitudinal slots 13 are cut at regular intervals, for example cutting by means of a mechanical saw, water jet, laser or the like.
• the longitudinal slots 13 are used to form anti-resonance elements in the finished hollow core fiber or to form anti-resonance element preforms in a fiber preform, and the number of longitudinal slots 13 corresponds to the number of anti-resonance element preforms or anti-resonance elements that can be produced with the intermediate tube 10 concerned.
• the longitudinal slots 13 end in front of the pipe ends, so that the front end regions 12 remain closed all the way round and connect the remaining webs 14 to one another. The cut edges are then glazed.
• the cutting width of the longitudinal slots 13 is uniform and is 2 mm.
• FIG. 2 (a) shows schematically a plan view of a coaxial arrangement 19 of a total of five quartz glass tubes, including two intermediate tubes 10; 20 each with longitudinal slots 13.
• the coaxial tube arrangement 19 is composed of two coaxial stacks, each composed of a glass tube (21; 22) to be deformed, an intermediate tube (10; 20) and a jacket tube (22; 23).
• the tube with the reference number 22 has a double function: in the inner stack it forms a "jacket tube” and its wall becomes part of the wall of hollow channels, and in the outer stack it forms a "glass tube” with a wall to be deformed.
• F320 quartz glass doped with fluorine / low viscosity
• Undoped undoped quartz glass / high viscosity
• the materials used differ in terms of their viscosity.
• the unprocessed tubes 21 and 22 consist of a commercially available, fluorine-doped quartz glass (trade name: F320) and have a lower viscosity than the slotted intermediate tube 10, 20 and than the outermost casing tube 23 (casing tube).
• FIG. 2 (b) shows that the coaxial pipe ensemble 19 subsequently collapses into a primary preform 26 and is lengthened at the same time.
• the annular gaps between the tubes and these are firmly connected to each other and form cladding tube with a common cladding tube wall 24.
• two pressure chambers 25a, 25b are located one behind the other in pairs, viewed in the radial direction.
• the primary preform 26 Before the fiber drawing process, at least one of the closed, longitudinally slot-free end regions of the primary preform 26 is removed, so that pressure chambers 25a, 25b which are open at the end are obtained, into which a compressed gas can be introduced.
• the primary preform 26 has a hollow core area 27 which is surrounded by a jacket (cladding tube wall 24).
• the pressure chambers 25a; 25b form precursors for antiresonance elements of the hollow core fiber to be drawn in the cladding tube wall 24.
• FIG. 3 (a) shows the pressure chambers 25a generated from the original longitudinal slots in the cladding tube wall 24; 25b in an enlargement.
• a differential pressure is applied between the pressure chambers 25a, 25b and that of the hollow core region 27, so that the pressure exerted on the pressure chambers 25a; 25b adjoining and deformable wall areas of the original glass tubes 21; 22 are inflated inwardly along the pressure chambers 25a, 25b.
• FIG. 3 (b) shows that in the case of the hollow core fiber 29 on the inside 27 of the former innermost glass tube, a first bulge 28a is created, which surrounds a second bulge 28b.
• the first and second bulges 28a; 28b form a nested anti-resonance element with two glass membranes with a negatively curved surface.
• FIG. 4 (a) shows another intermediate tube 110, in the wall of which at previously defined azimuthal positions elongated longitudinal slots 13 are cut at regular intervals, for example by means of a mechanical saw, water jet cutting, laser or the like.
• the longitudinal slots 13 are used to form anti-resonance elements in the finished hollow core fiber or anti-resonance element preforms in a fiber preform and the number of longitudinal slots 13 corresponds to the number of anti-resonance element preforms that can be generated with the intermediate tube 10 or anti-resonance elements. In the embodiment there are five antireso- nance element preforms or anti-resonance elements.
• the longitudinal slots 13 end in front of the pipe ends, so that the front end regions 12 remain closed all round and connect the remaining webs 14 with one another. The cut edges are then glazed.
• the cut width of the longitudinal slots 13 is uniform and is 2 mm.
• Figure 5 (a) shows a schematic plan view of a coaxial ensemble of a total of three quartz glass tubes, including the slotted intermediate tube 110.
• the coaxial tube ensemble is composed of a glass tube 21 to be deformed, the intermediate tube 110 with the longitudinal slots 13 and a jacket tube 22.
• F320 quartz glass doped with fluorine / low viscosity
• Undoped undoped quartz glass / high viscosity
• the materials used differ in terms of their viscosity.
• the mechanically unprocessed glass tube 21 consists of a commercially available, fluorine-doped quartz glass (trade name: F320) and has a lower viscosity than the slotted intermediate tube 110 and the jacket tube 22 (outer tube).
• FIG. 5 (b) shows that the coaxial pipe ensemble subsequently collapses into a primary preform 126. It is lengthened at the same time and the annular gaps between the tubes 21, 22, 110 disappear, so that these are firmly connected to one another so that they form a common cladding tube wall 124.
• the primary preform 126 has a hollow core area 127 which is surrounded by a jacket (cladding tube wall 124).
• the pressure chambers 125 form precursors for Antiresonanzele elements in the cladding area of the hollow core fiber to be drawn.
• At least one of the closed, longitudinally slot-free end regions of the preform 126 is removed so that the pressure chambers 125 can be opened at the end and a pressurized gas can be introduced.
• FIG. 6 (a) shows a pressure chamber 125 generated from an original longitudinal slot 13 in an enlargement.
• a differential pressure is applied between the pressure chambers 125 and the inner bore 16, so that the wall area adjacent to the pressure chambers 125 is inflated inward along the pressure chamber 125.
• FIG. 6 (b) shows that in the case of the hollow core fiber 129 on the inside 17 of the former glass tube, a bulge 128a is created which forms an anti-resonance element with a glass membrane with a negatively curved surface.
• the intermediate tubes 10, 20, 10 can also be provided with longitudinal grooves on their inner lateral surface. If necessary, the longitudinal grooves are generated by mechanical milling in the inner surface of the intermediate pipe.
• the glass tubes 21; 22 be provided with thermally deformable wall with longitudinal grooves on its outer surface.
• the longitudinal grooves are optionally produced by mechanical milling in the outer surface of the glass tube.
• the glass tubes 21; 22 be provided with thermally deformable wall with hollow channels.
• FIG. 7 schematically shows an exemplary embodiment.
• the coaxial arrangement comprises a glass tube 221 with a thermally deformable wall and a covering cylinder 22 (jacket tube).
• hollow channels 213 evenly distributed around the circumference run parallel to the longitudinal axis of the glass tube (extends perpendicular to the plane of the paper).
• the hollow channels 213 are produced by laser cutting and are continuous (they extend from one end of the wall to the other end). In the cross section shown, they have a rectangular shape, the long side of the rectangle being tangential to the adjacent wall portion of the inner jacket surface 221 a.
• F320 quartz glass doped with fluorine / low viscosity
• Undoped undoped quartz glass / high viscosity
• an internal pressure can be generated in the hollow channels 213 by introducing a compressed gas, and thereby the wall sections of the glass tube 221, which limit the hollow channels 213 inward, are deformed.
• elongated bulges are formed on the glass tube 221 in the direction of the inner bore 16 of the glass tube and serve as anti-resonance element preforms.

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• 2019
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