Classifications

• • 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
  • G02B6/02342—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes characterised by cladding features, i.e. light confining region
  • G02B6/02357—Property of longitudinal structures or background material varies radially and/or azimuthally in the cladding, e.g. size, spacing, periodicity, shape, refractive index, graded index, quasiperiodic, quasicrystals
• • 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
  • C03B37/01228—Removal of preform material
  • C03B37/01231—Removal of preform material to form a longitudinal hole, e.g. by drilling
• • 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
  • C03B2203/00—Fibre product details, e.g. structure, shape
  • C03B2203/02—External structure or shape details
• • 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
• • 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
  • C03B2203/42—Photonic crystal fibres, e.g. fibres using the photonic bandgap PBG effect, microstructured or holey optical fibres
• • 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
• • 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
  • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
  • G02B6/102—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type for infrared and ultraviolet radiation
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P40/00—Technologies relating to the processing of minerals
  • Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
  • Y02P40/57—Improving the yield, e-g- reduction of reject rates

Definitions

• the present invention relates to a method for the manufacture of an optical component having longitudinal holes.
• the optical component having longitudinal holes is a microstructured optical fiber or a preform from which a microstructured optical fiber can be obtained by way of drawing.
• Microstructured optical fibers such as .photonic crystal fibers (PCF)", ,,holey fibers”, ..optical hollow fibers", or so-called ,,air-clad fibers", represent a special form of optical fibers of quartz glass, as are used in many fields regarding telecommunications, material treatment, or medical and analytical engineering.
• PCF photonic crystal fibers
• ,holey fibers ..optical hollow fibers
• so-called ,,air-clad fibers represent a special form of optical fibers of quartz glass, as are used in many fields regarding telecommunications, material treatment, or medical and analytical engineering.
• the light guidance in a microstructured optical fiber with longitudinal holes is influenced by cavities which are running through the fibers over their whole length and which are arranged in a specific geometric arrangement around the core region.
• the microstructured optical fiber has a core region surrounded by a jacket region with cavities running therethrough.
• JP-2005-247620 A proposes a method, in which an assembly is assembled that consists of an inner core rod and a multitude of capillary tubes that are closed on one end and are arranged around said inner core rod.
• the capillary tubes and the core rod are arranged in the densest packing possible with their longitudinal axes being parallel to each other inside the inner bore of a cladding tube having a polygonal internal cross-section.
• the air inside the capillary tubes is replaced by argon or nitrogen and thereafter the assembly is heated and collapsed zone-by-zone starting from the open side and, in this process, it is simultaneously drawn out into a microstructured optical fiber.
• a "preform element” is first produced, with capillary tubes of quartz glass with a diameter of 0.8 mm being fixed in a cladding tube in hexagonal arrangement while leaving a central inner bore, and the arrangement being elongated into the "preform element”.
• a monomode fiber is inserted without a plastic jacket into the central inner bore of the "preform element”, and additional jacket material is added in the form of a cladding tube.
• This assembly is then drawn at a negative pressure into the microstructured optical fiber while the annular gap between monomode fiber and central bore is collapsing.
• One problem consists in completely eliminating the cavities between the capillary tubes when the assembly is being collapsed without also having the inner bores of the capillary tubes collapse or taper excessively.
• a glass block forming the core material of the later fiber is mechanically provided with longitudinal holes having a diameter of 3 mm and is surrounded with a tube of tellurite glass and drawn into the fiber.
• the propagation of light proceeds essentially within the core rod material. For this reason, the requirements relating to its purity, homogeneity, and dimensional stability are especially high and its manufacture is cost-intensive.
• the core rod usually is the most valuable component of the preform. It consists of a core region that is clad in most cases by a jacket region having a different refractive index.
• WO 02/072489 A1 also reveals a method for the manufacture of a microstructured optical fiber, wherein the cavities of the microstructured optical fiber are produced by the outsides of rods or tubes being provided with longitudinal grooves (in the case of tubes also with longitudinal slits), and by subsequently elongating the components treated in this way into an assembly.
• the longitudinal slits and longitudinal grooves can be produced by sawing or mechanical drilling.
• US 6,944,380 B1 describes an optical fiber for transmitting UV radiation, and the fiber may here be configured as a microstructured optical fiber.
• a cladding tube with a central inner bore and with longitudinal holes is inserted into the wall.
• step (d) collapsing the assembly while forming the optical component, wherein providing the perforated cladding tube according to method step (b) comprises measures in which a thick-walled starting hollow cylinder is provided by mechanical drilling with longitudinal holes and is subsequently elongated into a cladding tube strand from which a plurality of perforated cladding tubes are cut to size.
• the method according to the invention refers to the technique in which an assembly consisting of cylindrical components is assembled, and the assembly is collapsed while being simultaneously elongated in this process into the optical component with longitudinal holes.
• the optical component is obtained in the form of a microstructured optical fiber or in the form of a preform from which a microstructured optical fiber can then be drawn.
• the essential component of the assembly is the perforated cladding tube which is cladding a core rod or a plurality of core rods.
• the assembly may comprise further components, particularly tubes, rods or capillaries, as is otherwise also known in coaxial assemblies of the prior art.
• the perforated cladding tube surrounds the core rod directly or indirectly.
• these are statistically distributed in the wall of the cladding tube, or they are arranged in the form of one or a plurality of perforated rims with circular or polygonal cross-section around the longitudinal axis of the cladding tube.
• the following explanations will also concern the embodiment with only one longitudinal hole although these explanations only deal with the embodiment with several longitudinal holes for the sake of clarity.
• the longitudinal holes, or at least some of them are maintained after collapsing of the assembly and form fine channels distributed around the core region and extending in parallel with the longitudinal axis of the fiber in the optical fiber.
• At least one of the cladding tubes comprises a perforated wall through which one longitudinal hole or several longitudinal holes are running that extend in parallel with the longitudinal axis of the cladding tube.
• providing the perforated cladding tube according to method step (b) comprises the following measures: (I) A starting hollow cylinder is provided having a wall equipped with mechanically generated longitudinal holes.
• the starting hollow cylinder is elongated into a cladding tube strand.
• the longitudinal holes of the perforated cladding tube are produced separately with respect to the remaining components of the assembly, particularly separately with respect to the core rod, so that in case of defective holes the loss of material will be comparatively small.
• the diameter of the longitudinal holes and their geometric distribution inside the wall can be easily adapted to the requirements, which permits a flexible production of a microstructured component.
• a single starting hollow cylinder yields multiple (at least two) perforated cladding tubes with an almost identical geometry. This facilitates the reproducible manufacture of identical fibers, and the efforts spent on the generation of the longitudinal holes in the starting hollow cylinder must only be taken once, which has an advantageous effect on the productivity of the method.
• the longitudinal holes of the starting hollow cylinder are generated by mechanical drilling, which ensures high accuracy and variability. Moreover, deviations from the specified size in the subsequent elongation process are downscaled according to the draw ratio and are thus less noticeable in the cladding tube (in absolute terms). All of this contributes to a high reproducibility. (5) Moreover, after elongation of the starting hollow cylinder the resulting longitudinal holes are distinguished by a smooth inner wall generated in the molten state. This applies equally to the inner and outer cylindrical jacket surface of the cladding tube. A smooth inner wall can be cleaned comparatively easily and reduces adhesion and deposition of particles.
• the at least one core rod comprises a core region made of a glass material of a higher refractive index or of a glass material doped with active components, as is known from laser fibers or reinforcement fibers.
• the core rod itself may be provided with through-holes, which is not preferred for the above reasons.
• the optical fiber obtained according to the method may be configured as a so-called “monomode fiber” or a “multimode fiber”.
• At least part of the whole jacket region of the microstructured optical fiber is provided by way of the perforated cladding tube.
• one or several jacket tubes of quartz glass can contribute to the jacket material of the fiber, or one or several layers of SiO 2 soot which are applied to the outer wall of the cladding tube or of jacket tubes.
• the at least one cladding tube has an annular cross-section.
• the inner wall of the cladding tube or the outer wall of the cladding wall may however have different geometries independently of one another, such as an oval or polygonal geometry.
• a cladding tube with an inner wall of a hexagonal cross-section can particularly be used in an advantageous manner.
• Collapsing the assembly yields a preform.
• collapsing of the assembly according to method step (d) is accompanied by an elongation of the assembly.
• a preform or an optical fiber is obtained. Collapsing and elongation of the assembly may here be carried out in method steps succeeding one another in time or in simultaneous method steps. Predetermined dimensions of the final product (preform or fiber) can be observed more easily by simultaneous elongation.
• a starting hollow cylinder which has an outer diameter ranging from 100 mm to 250 mm, the draw ratio during elongation into the cladding tube strand being at least 8.
• these may have a small outer diameter preferably ranging from 25 mm to 98 mm.
• the longitudinal holes of the cladding tube are due to an initial mechanical drilling operation on the starting hollow cylinder.
• the mechanical processing of the starting hollow cylinder Thanks to the mechanical processing of the starting hollow cylinder, predetermined dimensions can be exactly observed.
• the outer wall of the starting hollow cylinder is also obtained by mechanical processing. Possible dimensional deviations are downscaled by the subsequent elongation process, and surface roughnesses are eliminated in this process at the same time.
• a plurality of longitudinal holes are produced that are distributed over an enveloping circle around the longitudinal axis of the cladding tube.
• the longitudinal holes form a perforated rim around the circumference of which they are distributed (preferably evenly).
• a cylindrical symmetry of the longitudinal holes has an advantageous impact on the transmission properties of the optical fiber.
• step (c) comprises surrounding the perforated cladding tube with at least one additional second perforated cladding tube having a larger inner diameter that comprises a wall provided with a multitude of longitudinal holes extending parallel to the longitudinal axis of the cladding tube.
• the optical properties of the assembly can be easily adapted to the needs.
• forming the coaxial assembly according to method step (c) comprises surrounding the perforated cladding tube with at least one additional jacket tube having a longitudinal axis and a larger inner diameter.
• the inner cross-section of the jacket tube is normally round, but may also be polygonal, which facilitates a tight arrangement of possible additional capillaries or rods inside the inner bore of the jacket tube.
• the surfaces of the assembly are acted upon with an etching gas, which leads to a superficial removal of the freely accessible SiO 2 surfaces. Contaminated surface layers are thereby removed and adhering contamination clusters are thereby also undermined by the etching gas and detached and discharged by means of the etchant stream. With gas phase etching there is hardly any risk that residues will remain inside the assembly, and the elimination of hydroxyl groups from a near-surface layer of the quartz glass is especially facilitated.
• the etching gas is an etchant chemically reacting with SiO 2 , such as SF 6 or C 2 F 6 .
• Gas phase etching is preferably carried out as a hot etching process at a temperature above 1 ,400°C, resulting in a high solubility of impurities. To be more specific, it is only in this way that hydroxyl groups can be removed from deep layers in economically acceptable treatment periods.
• This variant of the method is particularly preferred when the assembly comprises a jacket tube cladding the remaining components. The etching gas is then introduced into the inner bore of the jacket tube.
• a negative pressure or an overpressure is maintained with respect to the externally applied pressure. This facilitates the observance or setting of a predetermined inner diameter of the longitudinal holes after collapsing.
• the longitudinal holes can be closed by means of plugs, or the like. This ensures that, when the assembly is manufactured and further processed into the microstructured optical fiber, impurities originating from the environment do not pass into the longitudinal holes, which could have a disadvantageous impact in a later hot process, nor do possible impurities pass from the longitudinal holes into other regions of the assembly where they might have particularly harmful effects.
• a semifinished product is thus used for the manufacture of a microstructured optical fiber in the form of a perforated cladding tube having a longitudinal axis, which comprises a wall through which a longitudinal hole or multiple longitudinal holes are running that extend in parallel with the longitudinal axis, the manufacture of the at least one longitudinal hole by mechanical drilling comprising a starting hollow cylinder, from which the cladding tube is obtained by elongation and cutting to size.
• the longitudinal holes of the perforated cladding tube are produced separately from the remaining components of the assembly, particularly separately from the core rod, so that in the case of defective bores the loss of material is comparatively small.
• the diameter of the longitudinal holes and their geometric distribution within the wall can be easily adapted to the needs, which permits a flexible manufacture of a microstructured component.
• a single starting hollow cylinder yields multiple (at least two) perforated cladding tubes with an almost identical geometry. This facilitates the reproducible manufacture of identical fibers, and the efforts for generating the longitudinal holes in the starting hollow cylinder must only be taken once, which has an advantageous impact on the productivity of the method.
• the longitudinal holes obtained are distinguished by a smooth inner wall generated in the molten state. This is equally true for the inner and outer cylindrical jacket surface of the cladding tube. A smooth inner wall can be cleaned comparatively easily and reduces adhesion and deposition of particles.
• the longitudinal holes of the perforated cladding tube comprise an inner wall generated in the molten state.
• the inner wall of the longitudinal holes generated in the molten state is obtained because the perforated cladding tube is produced in an elongation method.
• a thick-walled starting hollow cylinder is provided with longitudinal holes in parallel with the longitudinal axis of the cylinder and is subsequently elongated into a cladding tube strand.
• Multiple cladding tubes are obtained therefrom. It is not only the longitudinal holes that have an inner wall generated in the molten state, but also the remaining cylindrical jacket surfaces of the cladding tube.
• the jacket region of the fiber or part thereof and all of the capillary cavities or part thereof are provided by a perforated cladding tube or a plurality of perforated cladding tubes within the meaning of the present invention by collapsing a corresponding assembly of components and elongating it into a preform for the optical fiber or directly into the optical fiber. Thereafter, the longitudinal holes of the cladding tube(s) form capillary cavities of the fiber.
• Figure 1 a first embodiment of a perforated cladding tube for use in the method according to the invention, in a radial cross-section;
• Figure 2 a second embodiment of a perforated cladding tube for use in the method according to the invention, in a radial cross-section;
• Figure 3 an embodiment of an assembly consisting of jacket tube, perforated cladding tube, and core rod, in a lateral view;
• Figure 4 a microstructured optical fiber obtained by elongation from the assembly according to Figure 3 with its hollow space structure being shown, in a radial cross-section.
• Fig. 1 shows a cladding tube 1 consisting of synthetic quartz glass having an outer jacket of round cross-section and an inner bore 2 of round cross-section.
• the cladding tube 1 has an outer diameter of 45 mm, an inner diameter of 21 mm and a length of 700 mm.
• the wall of the cladding tube 1 is perforated by multiple continuous longitudinal holes 3 extending in parallel with the longitudinal axis 4 of the cladding tube.
• the longitudinal holes 3 are evenly distributed over an enveloping circle 5 around the longitudinal axis 4 and have a diameter of 7 mm.
• the cladding tube 1 is obtained by elongating a starting cylinder in the wall of which through-holes are mechanically generated.
• the draw ratio in the elongation process is about 13, the ratio of the radial cross-sectional dimensions (outer diameter, inner diameter and diameter of the holes) relative to one another being maintained in the elongation process.
• the through-holes of the starting cylinder form the continuous longitudinal holes in the cladding tube 1. Due to the elongation process the inner walls of the longitudinal holes 3 and the inner wall 6 of the inner bore 2 and the outer wall 7 of the cladding tube 1 are generated in the molten state.
• Fig. 2 shows a further embodiment of such a semifinished product in the form of a cladding tube 21 of synthetic quartz glass. It also comprises an outer jacket which is round in radial cross-section, and a round inner bore 22.
• the cladding tube 21 has an outer diameter of 80 mm, an inner diameter of 24 mm and a length of 700 mm.
• the wall of the cladding tube 21 is perforated by multiple continuous longitudinal holes 23, 26 which extend in parallel with the longitudinal axis 24 of the cladding tube.
• the longitudinal holes 23, 26 are uniformly distributed around an inner enveloping circle 25 and an outer enveloping circle 27 about the longitudinal axis 24 of the cladding tube.
• the longitudinal holes 23 around the inner enveloping circle 25 have a diameter of 7 mm
• the longitudinal holes 26 around the outer enveloping circle 27 have a diameter of 10 mm.
• the cladding tube 21 is also obtained by elongating a starting cylinder in the wall of which the corresponding through-holes are produced mechanically.
• the draw ratio in the elongation process is about 13, the ratio of the radial cross-sectional dimensions (outer diameter, inner diameter and diameter of the bores) relative to one another being maintained in the elongation process.
• the through- holes of the starting cylinder form the longitudinal holes 23, 26 in the cladding tube 21.
• the inner walls of the longitudinal holes 23, 26 and the inner wall 28 of the inner bore 22 and the outer wall 29 of the cladding tube 21 are generated in the molten state.
• the cladding tubes 1 and 21 serve as semifinished products for making a preform for a microstructured optical fiber by means of a technique in which a coaxial assembly is assembled from the cladding tube 1 , 21 and further components, and the assembly is subsequently collapsed and elongated. This technique will be explained in the following in more detail with reference to Fig. 3 and with reference to the cladding tube 1 depicted in Fig. 1.
• Fig. 3 shows a lateral view of a coaxial assembly 30 using a perforated cladding tube 1 according to Fig. 1.
• the cladding tube 1 surrounds a core rod 31 while leaving an annular gap 35.
• Said rod is provided with an inner core region 32 and a jacket region 33.
• the assembly 30 comprises a jacket tube 34 which surrounds the cladding tube 1 while leaving a further annular gap 36.
• the core rod 31 has an outer diameter of 20 mm.
• the outer diameter of the jacket tube 34 is 160 mm and its inner diameter is 46 mm.
• the assembly 30 is subjected to gas phase etching, with an etching gas being passed in the form of SF 6 at a temperature of 1 ,450 °C through the inner bore of the jacket tube 34.
• the freely accessible quartz glass surfaces are thereby removed superficially and cleaned.
• the longitudinal holes 3 of the cladding tube 1 are closed on one side by the lower front side 37 of the cladding tube 1 being heated by means of a flame and slightly drawn lengthwise (not shown in Fig. 3).
• the assembly 30 is subsequently elongated into a preform by the assembly being continuously supplied, starting with its lower front side 37, to an annular heating zone where it is heated zone by zone.
• annular gaps 35, 36 are collapsing in this process zone by zone and the assembly is simultaneously elongated into the preform.
• the draw ratio in the elongation process is about 4.
• a radial cross-section of the preform 40 obtained in this way is shown in Fig. 4.
• the previous annular gaps 35, 36 of the assembly 30 are collapsed.
• the ratio of the radial cross-sectional dimensions with respect to one another has however been maintained.
• the preform 40 is drawn in a standard fiber drawing process into a microstructured optical fiber.
• the radial fiber cross-section is, except for its size, identical with the radial preform cross-section schematically shown in Fig. 4.
• the microstructured optical fiber obtained after drawing is particularly distinguished by high geometric precision. The optical properties predetermined by the fiber design are thereby achieved to a high degree also in practice.

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• 2007
  • 2007-07-15 DE DE102007033086A patent/DE102007033086A1/de not_active Withdrawn
• 2008
  • 2008-04-15 WO PCT/EP2008/054546 patent/WO2009010317A1/en active Application Filing

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