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
  • C03B37/02—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
  • 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
  • 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
  • C03B37/012—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
  • C03B37/01257—Heating devices therefor
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/02—Optical fibres with cladding with or without a coating
  • G02B6/02295—Microstructured optical fibre
  • G02B6/02314—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes
  • G02B6/02319—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes characterised by core or core-cladding interface features
  • G02B6/02323—Core having lower refractive index than cladding, e.g. photonic band gap guiding
  • G02B6/02328—Hollow or gas filled 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
  • C03B2203/10—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
  • C03B2203/42—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:
• a hollow core area and a jacket area which comprises at least one jacket tube, which has a jacket tube inner bore and a jacket tube longitudinal axis, along which a jacket tube wall defined by an inner jacket surface and an outer jacket surface extends, wherein in the jacket region a number of tubular and / or hollow channel-shaped anti-resonance element preforms are arranged,
• the invention also relates to a method for producing a preform for an anti-resonant hollow core fiber which extends along a longitudinal fiber axis having extending hollow core and the shell region surrounding the hollow core, which comprises several anti-resonance elements, with the method steps:
• a hollow core area and a jacket area which comprises at least one jacket tube, which has a jacket tube inner bore and a jacket tube longitudinal axis, along which a jacket tube wall defined by an inner jacket surface and an outer jacket surface extends, wherein in the jacket region a number of tubular and / or hollow-channel anti-resonance element preforms are arranged, and
• hollow core fibers in which the core comprises an evacuated, gas or liquid-filled cavity.
• the interaction of the light with the glass is less than in solid core fibers.
• the refractive index of the core is smaller than that of the clad, 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.
• 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 phase matching of anti-resonant 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 axially parallel ensemble 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 from WO 2018/169487 A1, in which a first cladding area comprises a large number of rods and a second cladding area comprises a multiplicity of tubes which are surrounded by an outer cladding tube. Rods, tubes and cladding are put together using the “stack and draw” technique to form a preform. Before the preform is elongated, 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 antiresonance element outer tube (short: ARE outer tube) and an antiresonant element 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 important in addition to a uniform wall thickness of the walls of the anti-resonance elements. This cannot be easily realized with the “stack-and-draw” technique.
• the aim of the invention is to provide a method for the cost-effective production of an anti-resonant hollow core fiber which avoids the limitations of conventional production 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.
• this object is achieved according to the invention, based on a method of the type mentioned at the beginning, in that a secondary preform is formed which has an outer diameter in the range of 30 to 90 mm, and that before the hollow core fiber is drawn according to Method step (c) at least one of the front ends of the anti-resonance element preforms is closed.
• the starting point for the manufacture of the anti-resonant hollow core fiber is a preform, which is referred to here as the “primary preform”. It comprises a cladding tube in which or on which precursors or preforms for the shaping of antiresonant elements are contained in the hollow core fibers (here referred to as “antiresonant elements” for short).
• 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 produce a preform, referred to here as a “secondary preform”. If necessary, the hollow core fiber is produced by elongating the secondary preform.
• the primary preform or the secondary preform are surrounded by components with an overlay cylinder or with a plurality of overlay cylinders, forming a coaxial ensemble, 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.
• Adding cladding material includes collapsing a barrel cylinder onto the primary preform.
• the coaxial arrangement of the primary preform and the cover cylinder is elongated when the cover cylinder collapses, or it is not elongated.
• the anti-resonance element preforms are changed in their shape or arrangement, or they are not changed in their shape or arrangement.
• the production of the preform comprises a number of process steps in which starting elements of the hollow core fiber are produced and positioned with respect to one another, and at least one hot deformation step.
• Each of the output elements has a certain deviation from its target geometry and each step of positioning and reshaping inevitably leads to Geometry deviations that add up to an absolute geometrical error in the finished preform.
• the hot forming of glass can lead to undesired and non-reproducible deformation in the event of the slightest deviations from an ideal, usually cylinder-symmetrical temperature profile of the heating zone.
• the preform used in the method according to the invention for the fiber drawing process is characterized by an outer diameter in the range from 30 to 90 mm, preferably in the range from 40 to 90 mm. This is a large outer diameter compared to the current state of the art. Since the absolute geometry errors present during fiber drawing are scaled down with increasing outer diameter of the preform, a more precise production of the hollow core fiber is basically made possible.
• the outer diameter of the preform is a maximum of 90 mm. With larger diameters, temperature gradients form within the preform volume in the fiber drawing process, which result in deviations in the wall thickness of the anti-resonance elements in the hollow core fiber of more than 3.5%.
• the reference value for the percentage is the mean wall thickness.
• the outer diameter of the preform is at least 30 mm, preferably at least 40 mm. It has been shown that anti-resonance element preforms can be produced in which the wall thickness deviation is approximately
• All anti-resonance element preforms or at least some of them form hollow channels and are usually open on both sides.
• the free inner diameter of the hollow channels is small and is typically in the preform Range of a few millimeters.
• the preform is heated from the outside so that a radial temperature gradient is established in the preform volume. This is - with otherwise the same process conditions - the greater the thicker the preform.
• the hollow channels will shrink differently as a result of the surface tension and depending on the local temperature.
• the greater the radial temperature gradient and the thicker the preform the greater the risk.
• the temperature gradient has no significant effects on the central hollow core.
• the core area (hollow core) is left open in the fiber drawing process with vertical orientation of the longitudinal axes, but the otherwise open upper end is closed in at least some of the anti-resonance element preforms.
• each hollow channel has an initial volume of gas.
• the gas is heated and the pressure in the hollow channels is increased, so that these expand from the bottom upwards.
• the temperature difference between the lower and upper preform end largely determines the degree of expansion, essentially independent of the original hollow channel diameter.
• this temperature difference is approximately the same for all hollow channels, regardless of their radial position, so that all hollow channels expand to approximately the same extent. As a result, the original distribution of the hollow channel sizes in the thick preform is also retained in the final hollow core fiber.
• This concept is also suitable for a reproducible and precise manufacturing process for anti-resonant hollow core fibers on an industrial scale. It is particularly suitable for the precise production of anti-resonant hollow core fibers with nested anti-resonance elements that have internal diameters that differ greatly from one another.
• a primary preform is formed which has an outer diameter in the range from 20 to 70 mm, preferably in the range from 30 to 70 mm. having.
• the outside diameter of the primary preforms is typically 4 to 6 mm.
• the primary preform in the secondary preform forms an inner jacket area which has an outer diameter in the range from 7 mm to 50 mm, preferably in the range from 20 mm to 50 mm.
• the hollow core area and the material for the inner cladding area of the secondary preform are given by the primary preform.
• An increase in the outside diameter of the primary preform can be achieved both by increasing the size of the hollow core (associated with lower attenuation) and by reducing the outside diameter of the final hollow core fiber (which involves less material input).
• an internal pressure in the core area is set in the range between 0.05 mbar to 20 mbar, preferably in the range between 3 mbar to 20 mbar. At an internal pressure of less than 0.05 mbar it can happen that the antiresonance element preforms or antiresonance element precursors expand too much. Conversely, an internal pressure of more than 20 mbar in the core area can mean that the gas pressure within the hollow channels of the anti-resonance element preforms is insufficient for them to expand sufficiently in the hot molding process.
• the temperature of the heating zone during the hot forming process should be as constant as possible.
• a temperature-controlled heating element is therefore advantageously used in the hot forming process according to method step (d), the set temperature of which is kept to within +/- 0.1 ° C.
• providing the primary preform comprises arranging the antiresonance element preforms at target positions on the inside of the cladding tube wall, the arrangement of the antiresonance element preforms and / or the drawing of the hollow core fiber according to method step (c) a Fixing measure and / or a sealing measure using a seal containing amorphous SiC particles
• the sealing or bonding compound used for sealing or fixing contains amorphous SiC particles which are absorbed, for example, in a dispersion liquid. This mass is applied between the surfaces to be connected or sealed and is usually pasty when used. When drying at low temperature, the dispersion liquid is partially or completely removed and the mass solidifies.
• the sealing or bonding compound and in particular the solidified SiC -containing sealing or bonding compound obtained after drying meets the requirements for fixation and compression.
• the low temperature below 300 ° C required for this makes it easier to maintain the dimensional accuracy of the preform and prevents thermal impairment.
• the sealing or bonding compound is also suitable, opaque or to form transparent glass.
• the sealing or bonding compound does not decompose and it releases little impurities. It is thus characterized by thermal stability and purity during the hot forming process and it avoids deformations due to different thermal expansion coefficients.
• the provision of the primary preform according to method step (a) comprises arranging the antiresonance element preforms at desired positions on the inside of the cladding tube wall, with the antiresonance element preforms being arranged by means of an in the cladding tube inner Bore to be introduced positioning template takes place, the holding elements for positioning the anti-resonance element preforms at the target positions.
• the positioning template has, for example, a shaft which protrudes into the inner bore of the casing tube and is provided with holding elements in the form of a plurality of holding arms pointing radially outward.
• the structurally predetermined star-shaped arrangement of the holding elements facilitates the exact positioning of the anti-resonance element preforms at the respective target positions and their fixing, for example by means of the sealing or bonding compound explained above.
• the positioning template is preferably used exclusively in the area of the cladding tube end faces, preferably in the area of both cladding tube end faces.
• the accuracy of the positioning of the preforms on the inner circumferential surface of the cladding tube is improved in that the cladding tube inside is generated by machining, in particular by drilling, milling, grinding, honing and / or polishing.
• these processing techniques provide more precise and filigree structures using heat and pressure and they avoid contamination of the surfaces by molding tools such as nozzles, presses or melt molding.
• the metal-cutting machining preferably also comprises structuring the inside of the cladding tube in the area of target positions of the anti-resonance element preforms by providing them with a longitudinal structure extending in the direction of the longitudinal axis of the cladding tube.
• This longitudinal structure comprises, for example, longitudinal slots and / or longitudinal grooves in the cladding tube inner wall which run parallel to the cladding tube longitudinal axis and which are preferably produced by drilling, sawing, milling, cutting or grinding.
• the longitudinal structure extending in the direction of the longitudinal axis of the cladding tube serves as a positioning aid for the anti-resonance element preforms. It makes it easier for the antiresonance element preforms to assume predetermined, defined positions on the inside of the cladding tube.
• a procedure has also proven itself in which, when drawing the hollow core fiber according to method step (c), several components of the secondary preform made of quartz glass are jointly heated and softened, with the quartz glass containing at least some of the preform components at least one dopant that increases the viscosity lowered by quartz glass.
• Components of the preform include the cladding tube and the anti-resonance element preforms arranged therein, as well as additional jacket material, which, for example, is provided in the form of an overlay cylinder or several overlay cylinders and is collapsed onto the primary preform.
• Fluorine, chlorine and / or hydroxyl groups are preferably used as dopants which lower the viscosity of quartz glass.
• the doping makes it possible to adapt the thermal expansion coefficients of neighboring preform components in order to avoid or reduce stresses. It can also be used to reduce the thermal stability of one component in favor of the stability of an adjacent component.
• the quartz glass of the cladding tube is at least 0.5 dPa.s. at a measuring temperature of 1250 ° C has a higher viscosity, preferably a viscosity that is at least 0.6 dPa.s higher than that of the quartz glass of additionally applied jacket material (when the viscosity is given as a logarithmic value in dPa s).
• the anti-resonance elements are arranged around the hollow core with an uneven symmetry.
• the accuracy of the positioning of the preforms in the cladding tube is further improved by providing tubular structural elements, at least some of which have a wall thickness in the range of 0.2 and 2 mm, preferably a wall thickness in the range of 0.25 and 1 mm, and wherein a cladding tube with an external diameter in the range of 90 and 250 mm and preferably with an external diameter in the range of 120 to 200 mm is provided.
• These components each have a length of at least 1 m and are relatively large-volume structural elements for the formation of anti-resonance elements. This simplifies handling.
• the gravitational force supports the parallelism and the vertical alignment of the structural element longitudinal axes when the structural elements are each positioned and fixed at the target position at their obe Ren end face; for example, and preferably using the sealing or connecting compound explained in more detail above and additionally or alternatively by means of the positioning template explained in more detail above.
• a secondary preform which has an outer diameter in the range of 30 to 90 mm, and at least one of the front ends of the anti-resonance element preforms is closed.
• the secondary preform is the starting point for the manufacture of the anti-resonant hollow core fiber.
• the anti-resonant hollow core fiber is drawn by elongating the preform.
• a preform is produced which, compared to the previous state of the art, has a large outer diameter in the range of 30 to 90 mm, preferably in the range of 40 to 90 mm, so that the absolute geometry error present in the preform is scaled down more strongly during fiber drawing can be.
• At least one of the front ends of the anti-resonance element preforms is closed before the fiber drawing process.
• the front end to be closed is that which represents the upper end when elongating the preform with a vertically oriented longitudinal axis.
• the sealing of the anti-resonance element preform or the anti-resonance element preforms also remains in place during the fiber drawing process.
• 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 S1O2, 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.
• Antiresonance element precursors are components or parts of the preform that are only transformed into antiresonance element preforms or directly into antiresonance elements through reshaping.
• 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 bore 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.
• Preform / primary preform / secondary preform / core preform (cane)
• 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 performing one or more of the following hot forming processes once or repeatedly:
• a core preform (Cane) 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. Elongation / collapse
• 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 parts of the primary preform are reflected in the elongated end product.
• the primary preform can also be drawn out of scale and its geometry changed.
• the ensemble of at least one cladding tube and loosely received or firmly fixed preforms or precursors for anti-resonance elements is also referred to here as the “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. Machining
• 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 to the outside through the entire cladding tube wall.
• 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 on the basis of the respective D10, D50 and D90 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 Dso value and the D90 value those particle sizes that are 50% and 90% of the cumulative Volume of the Si0 2 particles is not reached.
• the particle size distribution is determined by scattered light and laser diffraction spectroscopy according to ISO 13320.
• FIG. 1 shows a primary preform with a cladding tube and anti-resonance element preforms positioned and fixed therein for the production of a preform for a hollow core fiber based on a plan view of the cross section
• FIG. 2 shows the primary preform from FIG. 1 after the anti-resistance element preforms have been closed for the purpose of carrying out the fiber drawing process.
• a sealing compound based on S1O2 is used, as is known from DE 10 2004 054 392 A1. Since an aqueous slip is produced by wet grinding of quartz glass grains, which contains amorphous Si0 2 particles with a particle size distribution which is characterized by a D 50 value of about 5 pm and a D90 value of about 23 pm. Further amorphous Si0 2 grains with an average grain size of about 5 ⁇ m are added to the base slip.
• the slip used as the bonding compound has a solids content of 90%, at least 99.9% by weight of which consists of S1O2.
• FIG. 1 schematically shows a primary preform with a cladding tube 1 with a cladding tube wall 2, on the inner circumferential surface of which antiresonance element preforms 4 are fixed at previously defined azimuthal positions at a uniform distance; in the exemplary embodiment there are six preforms 4; in another preferred embodiment, not shown, there is an odd number of preforms.
• the cladding tube 1 consists of quartz glass and has a length of 700 mm, an outer diameter of 27 mm and an inner diameter of 20 mm.
• the anti-resonance element preforms 4 are present as an ensemble of interlocking structural elements made up of an ARE outer tube 4a and an ARE inner tube 4b.
• the ARE outer pipe 4a has an outer diameter of 6.2 mm and the ARE inner pipe 4b has an outer diameter of 2.5 mm.
• the wall thickness of both structural elements (4a; 4b) is the same and is 0.3 mm.
• the lengths of ARE outer tube 4a and ARE inner tube 4b correspond to the cladding tube length 1.
• the antiresonance element preforms 4 are fixed on the inside of the cladding tube 1 by means of the connecting compound 5 based on S1O2.
• the compound 5 is applied locally to the cladding tube inner jacket surface in the area of the front ends and the antiresonance element preforms are placed thereon using a positioning template with a structurally given star-shaped arrangement of holding arms for the individual antiresonance element preforms 4.
• the positioning template is limited to the area around the two cladding tube ends.
• This method creates a precise and reproducible connection between the cladding tube 1 and the anti-resonance element preforms 4.
• the primary preform 1 is covered with a covering cylinder made of quartz glass, the covering cylinder collapsing onto the cladding tube 1, and at the same time the tube ensemble is elongated to form a secondary preform.
• the Studentsfangzy cylinder has an outside diameter of 63.4 mm and a wall thickness of 17 mm.
• the coaxial arrangement of cladding tube 1 and cover cylinder with a vertically oriented longitudinal axis is fed from below to a temperature-controlled heating zone and is softened zone by zone beginning with the upper end of the arrangement.
• the heating zone is kept at a target temperature of 1600 ° C with a control accuracy of +/- 0.1 ° C. This means that temperature fluctuations in the hot forming process can be limited to less than +/- 0.5 ° C.
• the secondary preform (core preform) formed in the collapsing and elongating process has an outside diameter of approximately 50 mm and a jacket wall thickness of 16.6 mm, made up of the outer jacket and inner jacket.
• the maximum fluctuation in wall thickness (largest value minus smallest value) of the anti-resistance element preforms is less than 4 ⁇ m.
• the secondary preform is then drawn into the anti-resonant hollow core fiber. Before this, all anti-resonance element preforms are sealed with the sealing or bonding compound. This state is indicated schematically in FIG. 2 by means of areas colored in dark gray.
• the sealing compound 51 is only applied to the end face of the anti-resonance element preforms 4 that faces upward during the fiber drawing process.
• the upward facing end is connected to a flalter tube made of quartz glass, which also serves as a gas connection.
• the holder is fixed to the cladding cylinder and the cladding tube by means of the sealing or connecting compound.
• the secondary preform is fed from above with a vertically oriented longitudinal axis to a temperature-controlled heating zone, where it is softened zone by zone starting with the lower end.
• gas is supplied to the core area (hollow core) so that an internal pressure of 4 mbar is established in the core area.
• the heating zone is kept at a target temperature of around 2100 ° C with a control accuracy of +/- 0.1 ° C. This allows temperature fluctuations in the hot forming process to be limited to less than +/- 0.5 ° C.
• the existing absolute geometric error is scaled down, so that in the hollow core fiber the anti-resonance elements obtained from the anti-resonance element preforms have a maximum deviation of less than 3.5% in wall thickness.
• the value for OD / ID in table column 2 is obtained by dividing the values in columns 4 (outside diameter of the secondary preform) and 5 (inside diameter of the previous primary preform in the secondary preform).
• the maximum deviation in the wall thickness of the antiresonance element preforms in the preform is approximately 4 ⁇ m in all exemplary embodiments. Hollow core fibers with an outer diameter of 200 ⁇ m or 230 mm were drawn from the preforms, as indicated in the table above, and the wall thicknesses of the anti-resonance elements were determined. In all examples, the error in the wall thickness of the anti-resonance elements was less than 3.5% (based on the mean wall thickness).
• Example No. 7 in the table corresponds to the exemplary embodiment described in detail above.
• Examples 8 and 9 are comparative examples.
• hollow core fibers were obtained in which the error in the wall thickness of the anti-resonance elements was more than 4%.
• this unsatisfactory result is attributed to the comparatively small draw ratio, and in comparative example 9 to temperature gradients within the preform volume during the fiber drawing process.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Geochemistry & Mineralogy (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Crystallography & Structural Chemistry (AREA)
• General Physics & Mathematics (AREA)
• Manufacture, Treatment Of Glass Fibers (AREA)
• Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=67402848

Family Applications (1)

Country Status (5)

Cited By (2)

Families Citing this family (11)

Citations (6)

Family Cites Families (16)

• 2019
  • 2019-07-17 EP EP19186745.6A patent/EP3766844B1/de active Active
• 2020
  • 2020-07-15 WO PCT/EP2020/069990 patent/WO2021009218A1/de not_active Ceased
  • 2020-07-15 JP JP2021574870A patent/JP7453259B2/ja active Active
  • 2020-07-15 US US17/618,274 patent/US12209045B2/en active Active
  • 2020-07-15 CN CN202080038448.6A patent/CN113939483B/zh active Active

Patent Citations (6)

Non-Patent Citations (5)

Also Published As

Similar Documents

Legal Events