Method for producing a drilled fibre

Abstract

The invention relates to a method for producing a drilled fibre. The problem addressed by the present invention, namely that of providing a method for producing a drilled fibre, which enables drilling of any drilled hole diameter that does not lead to extremely rough and defective inner drilled surfaces in the sintered end product (glass preform) due to tension-related, random chipping, and that does not require any post-treatment (grinding, polishing or microwave and plasma treatment), is solved in that the method comprises the following successive steps: producing a fibre precursor in the form of a porous green body (1) from doped or undoped SiO2 nanopowder by pressing the SiO2 nanopowder, mechanically drilling into the porous green body (1) to form a drilled hole (21) in the form of a cavity, a hollow space or a continuous recess and post-treating this drilled porous green body (1) to a vitrified preform (3), and finally drawing the preform (3) into a drilled fibre, wherein the SiO2 nanopowder of the green body (1) is free from organic auxiliary materials, polymer binding materials, polymerizable monomers, resins or their precursors, wherein the SiO2 nanopowders are pressed at 100 to 600 kN to a final density of 0.9 g / cm3 to 1.5 g / cm3, so that a cylindrical green body (2) with an outer diameter between 10 mm and 50 mm and a length of up to 15 cm is created, and the absence of defects on the inner drilled surface of the green body (2) produced by drilling is created by subsequent thermal and chemical processing of the drilled green body (1), and thus a healing of the original inner drilled surface produced by drilling is achieved without the need for a final polishing of the original inner surface of the drilled hole (21).

Description

[0001] Method for producing a drilled fiber

[0002] Method for producing a drilled fiber from doped or undoped silica glass or from doped or highly doped glasses with a high silica content.

[0003] From DE 41 30 440 A1 a process for producing shaped bodies made of ceramic or glass is known, in which a porous green body is formed from the starting material for the shaped body in the form of a suspension containing highly dispersed solid particles (e.g. powder ceramic material), water as a dispersant and an organic binder soluble in the dispersant, and is then dried and sintered, one or more monomers being added to the suspension as a binder and a polymerization initiator.

[0004] Injection-molded and powder-pressed green bodies are known, for example, from the disclosure of DE 10 2006 036 690 A1.

[0005] DE 44 34 025 A1 discloses that drilling methods are known in which drills are used, comprising a drill rod, at the front end of which a drill head is arranged, which has a first drill bit which is rotatable about the longitudinal axis of the drill rod and provided with grinding or cutting means and has external dimensions to which a first enveloping circle is to be assigned when rotating about the longitudinal axis, and drills which are provided with a guide element which, viewed in the longitudinal axis direction towards the front end of the drill rod, is arranged behind the drill bit.

[0006] In order to specify a method on this basis which allows drilling of deep holes in brittle materials with low damage and precise guidance, and in order to provide a drill for this purpose, DE 44 34 025 A1 proposes that the drill head has a second drill bit which, viewed in the longitudinal axis direction towards the front end of the drill rod, is arranged in front of the first drill bit and which has external dimensions to which, upon rotation about the longitudinal axis, a second enveloping circle is to be assigned which runs coaxially to the first enveloping circle and whose diameter is smaller than that of the first enveloping circle, and, on the other hand, that the guide element has external dimensions to which, upon rotation about the longitudinal axis of the drill rod, an inner enveloping circle is to be assigned which runs coaxially to the outer enveloping circle and has a radius which is smaller than that of the first enveloping circle by a safety gap.

[0007] Based on DE 44 34 025 Al, DE 103 16 584 Al teaches a drill for drilling quartz glass (e.g. as a semi-finished product for an optical component), using a drill rod made of carbon fiber reinforced carbon.

[0008] In addition, other processes for drilling optical semi-finished products (e.g., fiber optic preforms) have been known for some time. For example, drilling of already glazed preforms or glass cylinders using ultrasonic technology (DMGMORI ULTRASONIC; DMG MORI Academy GmbH) or mechanical drilling of optical fiber preforms (Shiba R&D Ltd, http: / / www.shibagiken.com / ) are known.

[0009] Furthermore, RU 2521260 CI discloses a method for laser-mechanical drilling of SiO2-containing materials.

[0010] This drilling method for SiO2-containing materials is used in the field of mining and geology, e.g. for drilling thin diagnostic deep holes in meter-high concrete walls and local side holes in deposits of radioactive materials.

[0011] For this purpose, laser radiation is guided via a quartz optical fiber with a diameter of 0.2 to 1 mm into the drilling surface on a drill base, so that the absorbed laser radiation heats up the end face of the SiO2-containing material to the melting and boiling point and leads to thermal escape (= evaporation) of the material, which escapes through the inner cavity of the drilling tool, whereby the drilling tool has an outer rib crown which mechanically carries out the drilling itself, whereby the laser radiation weakens the irradiated material in that the drilling is carried out cyclically and in each cycle the end face is irradiated with the laser light for a certain time, whereby the end face is heated to temperatures in the range of the melting and boiling points of the material and is then cooled with coolant.

[0012] DE 10 2007 015 663 A1 teaches a molded body obtainable by treating a ceramic green body and a method for producing such a molded body. For this purpose, a ceramic green body, after its compression molding, is subjected to a treatment for 2 to 10 days at a temperature of 50 to 100°C in an oxidative atmosphere. In this way, defects such as chipping, flaking, abrasion, or cracks that occur on the green body during green machining processes such as milling, grinding, turning, drilling, cutting, or punching are significantly reduced or, in some cases, even prevented.

[0013] The disadvantage of all known technical processes for drilling semi-finished products for an optical component, such as quartz glass, is that the commercial systems mentioned above either generate stresses during drilling or extremely rough and defective inner drill surfaces due to stress-induced random spalling, whereby the stresses can lead to cracking of the preform and the extremely rough and defective inner drill surfaces lead to high attenuation losses at the interface between the original drill surface and a subsequently inserted core rod.

[0014] Therefore, in these cases, post-processing of the inner surface (e.g., by grinding, polishing, or significant reduction of surface roughness using microwaves and plasma according to DE 10 2018 132 338 Al) or the production of extremely large preforms (i.e., several centimeters in diameter) is always necessary. In addition, commercially available drilling technologies are currently only available for synthetic quartz glass, but not for doped synthetic quartz glass, and especially not for highly doped quartz glass materials, e.g., in cylindrical and hollow fiber form. Doping, for example, with Al2O3 or Se2O3, leads to intrinsically high stresses and is subjected to such severe stresses by ultrasonic drilling, laser-mechanical drilling, or purely mechanical drilling that the partial or complete destruction of the doped preform is the result.

[0015] The disadvantage of the technical solution according to the disclosure of DE 10 2007 015 663 A1 is that the defects such as breakouts, flaking, abrasion or cracks that occur on the green body during green machining processes such as milling, grinding, turning, drilling, separating or punching are considerably reduced. However, when drilling fiber precursors to produce hollow fibers from doped and highly doped silica glass or doped and highly doped glasses with a high silica content, these defects are still present due to the doping, so that post-treatment of the inner surface after drilling by grinding, polishing or microwave and plasma treatment according to DE 10 2018 132 338 A1 is still necessary in order to provide cavities with largely defect-free interfaces in specifically doped fiber precursors (such as doped silica glass preforms), which can be used, among other things, for filling with other materials, such asGlass rods for structured preforms.

[0016] A further disadvantage of the technical solution disclosed in DE 10 2007 015 663 A1 is that this process requires polymerizable additives to ensure the green body's drillability, which must be completely removed in time- and energy-consuming subsequent steps. Particularly for the functionality of an optical fiber, the resulting decomposition products, such as water and carbon or its compounds, must be completely removed. The production of green bodies and doped preforms has also been known for some time.

[0017] For example, EP 2 215 025 A1 discloses a process for producing doped quartz glass, in which a suspension is provided which contains SiO2 particles and a starting compound for at least one dopant in an aqueous liquid, the liquid is removed to form a doped intermediate product which contains particles of the dopant or particles of a precursor substance of the dopant, and the doped quartz glass is formed from the doped intermediate product by sintering, wherein at least some of the particles of the dopant or of the particles of the precursor substance thereof are produced in the suspension as a precipitate of a precipitation reaction from the starting compound which takes place at a specific pH value.

[0018] Furthermore, to produce co-doped quartz glass, a starting compound for a first dopant and a starting compound for a second dopant can be added to the suspension, wherein at least a portion of the particles of the first dopant and the second dopant or the particles of precursor substances thereof are produced in the suspension as a precipitate of the precipitation reaction of the starting compounds, wherein the liquid is removed to form a co-doped intermediate product containing particles of the dopant and particles of the second dopant or particles of precursor substances of the dopants, and the co-doped quartz glass is formed from the co-doped intermediate product by sintering, wherein

[0019] • nitrogen hydrides, in particular ammonia, ammonium salts, hydrazine or amines such as hydroxylamine, are used as alkali-free bases,

[0020] • when adding the starting compounds, the liquid content of the suspension is increased by adding water, ammonia and / or aqueous solutions,

[0021] • the suspension contains water and at least one other auxiliary agent, • fluorine or one or more oxides of the following group of elements are used as dopant: Al, B, P, Nb, Ta, Mg, Ga, Zn, Ca, Sr, Ba, Sc, La, Sb, Ge, Y, Ce, Hf, Zr and Ti,

[0022] • the solids content of the suspension during the precipitation of at least one dopant is less than 80 wt.%, preferably less than 70 wt.%,

[0023] • the drying of the suspension is preceded by a process step in which the solids contained in the suspension and the liquid are separated by means of a mechanical separation process,

[0024] • before sintering the doped SiO2 intermediate product, the intermediate product is compacted under a compaction atmosphere at a temperature below the sintering temperature, the SiO2 particles have particle sizes in the range between 0.5 pm and 100 pm, preferably between 1 pm and 10 pm,

[0025] • the SiO2 particles are present as aggregates of SiO2 primary particles, with the SiO2 primary particles in the range between 5 nm and 300 nm making up the largest volume fraction, and

[0026] • at least 80% by weight, preferably at least 90% by weight of the SiO2 primary particles are spherical.

[0027] The object of the present invention is therefore to provide a method for producing a drilled fiber which does not have the aforementioned disadvantages of the prior art, in particular which enables drilling of any desired borehole diameter, which does not lead to extremely rough and defective internal bore surfaces in the sintered end product (glass preform) due to stress-induced random spalling, but rather provides cavities with largely defect-free interfaces in specifically doped fiber precursors (such as doped silica glass preforms) without post-treatment (grinding, polishing or microwave and plasma treatment), which can be used, among other things, for filling with other materials, such as glass rods or glass powder for structured preforms. Furthermore, the method should be usable for drilling in order to create small, smooth cavities orTo create cavities in small, specifically doped silica glass preforms, which can be filled with a core rod of another material and drawn into a fiber with low attenuation.

[0028] According to the invention, this object is achieved by the features of the first patent claim. Further advantageous embodiments of the invention are specified in the subordinate patent claims.

[0029] The essence of the invention is that cavities, hollow spaces or continuous recesses are created by mechanical drilling into a porous green body, wherein this porous green body consists of doped SiO2 nanopowder (it is also within the scope of the invention that the green bodies can consist of undoped SiO2 nanopowder), wherein this green body is free of organic binders as well as polymer binders, polymerizable monomers, resins or their precursors and wherein the freedom from defects at the interface between the original drilled inner surface of the green body created by drilling and, for example,a core rod or SiO2 nanopowder inserted into the bore (or without an inserted core rod, which is also within the scope of the invention) is carried out by a subsequent thermal and chemical processing of the drilled green body including (or without) the inserted core rod and thereby a healing of the original inner bore surface created by the drilling is achieved, whereby:.

[0030] • chemical cleaning of the inner surface of the porous green body with Cl2 gas can be carried out to remove any contamination in the interface area (subgroup elements, drill abrasion, etc.) and

[0031] • the drilled porous green body is then thermally treated for sintering and vitrification, whereby the viscous state of the doped or undoped SiO2 nanopowder achieved in this process creates a smooth interface in the vitrified preform, so that a final polishing of the original inner drill surface is not necessary.

[0032] The method according to the invention for producing drilled fibers, in particular for drilling a porous green body for producing a hollow fiber from doped or highly doped silica glass or from doped or highly doped glasses with a high silica content, requires specially prefabricated porous preforms and comprises the following successive sub-steps:

[0033] To get a drilled porous green body:

[0034] • a doped and / or undoped SiO2-containing powder material is produced, for example according to EP 2 215 025 A1, in order to obtain a nanoparticle powder mixture,

[0035] • this SiO2-containing nanoparticle powder mixture is processed into a green body by isostatic pressing,

[0036] • this green body is held metal-free on a drilling device and aligned centrally,

[0037] • a cavity is created by repeated mechanical drilling with intermittent removal of the drilling residue,

[0038] • The cavity is then cleaned (borehole cleaning) with oil-free gas flow,

[0039] • If necessary, a core rod or SiO2 nanopowder can be added,

[0040] • the final processing is carried out with thermal and chemical treatment in accordance with EP 2 215 025 A1.

[0041] In order to obtain the porous green body, one can proceed in a manner analogous to the technical teaching of EP 2 215 025 A1, in which the nanoparticles used in the powder to be pressed are SiO2 particles in the form of SiO2 particles produced by a CVD process.

[0042] Equivalently, any SiO2 particles produced in any other way can be processed into the porous green body, for example, using the Stöber method. Doped powder mixtures obtained from liquid suspension as described above or by mixing differently doped fractions in the dry state can also be used.

[0043] The doping of the SiO2 particles can be done by adding fluorine or one or more oxides of the following group of elements: Al, B, P, Nb, Ta, Mg, Ga, Zn, Ca, Sr, Ba, Sc, La, Sb, Ge, Y, Yb, Tm, Nd, Ce, Hf, Ho, Zr and Ti.

[0044] After its production, the doped silica glass mixture is pressed into the porous green body by forming it into a cylinder shape, for example by isostatic pressing.

[0045] Green bodies with outer diameters between 10 mm and 50 mm and lengths up to 15 cm are advantageously produced. Green bodies with outer diameters between 10 mm and 24 mm and lengths up to 8 cm are particularly advantageous.

[0046] Green bodies with densities between 0.9 and 1.5 g / cm 3 produced at pressing pressures between 100 kN and 600 kN. Green bodies with pressing densities between 0.9 and 1.3 g / cm 3 generated at pressing pressures between 200 kN and 600 kN.

[0047] This porous cylinder is advantageously held in a metal-free holder and then machined with a twist drill. The desired borehole length is achieved by repeated drilling. If the drill length is shorter than the required borehole length, and the green body is shorter than twice the drill length, the green body can be removed from the holder, rotated 180°, re-held, centered, and drilled again. After the drilling process, the end face is straightened, and the bore cavity is flushed with an oil-free gas flow.

[0048] It is advantageous to achieve a ratio of borehole diameter to compact diameter in the range, for example, of 1:2 to 1:20, and particularly advantageously of 1:2.5 to 1:10. The thus structured green body is then chemically and thermally treated according to previously known methods.

[0049] Compared to the process of DE 41 30 440 A1, the process described above enables the structuring of green bodies that are free of polymers, resins or their polymerizable precursors.

[0050] The inventive method enables mechanical drilling of any hole diameter into a porous green body (which is made of nanoparticles, such as doped or undoped SiO2 nanopowders).

[0051] The advantage of this method according to the invention is that

[0052] • the green body is free from organic binding substances as well as polymer-free, resin-free and free from polymerizable precursors,

[0053] • a defect-free interface between the original drill inner surface and the core material is obtained in the sintered final product and

[0054] • that time-consuming polishing, etching, etc. is no longer necessary.

[0055] This enables the more effective production of microstructured fibers compared to the state of the art, which are used as transport fibers or special sensor fibers or laser-active fibers, whereby a high-quality internal interface of this fiber is achieved.

[0056] The invention is explained in more detail below with reference to the exemplary embodiments and the figures, without being limited to these.

[0057] They show:

[0058] Fig. 1 : a schematic representation of the process steps from an embodiment of a porous green body, through the drilled green body to the vitrified preform

[0059] Fig. 2: A schematic representation of a second embodiment of a porous green body with a core rod. To obtain the porous green body (1) shown in Fig. 1, powder processing into a green body is carried out via a special pressing process, which proceeds as follows:

[0060] • Pouring the powder into a press mold,

[0061] • Pressing, e.g. isostatic pressing,

[0062] • Removing the compact from the mold,

[0063] • If necessary, the cylinder surface can be mechanically reworked (grinding / straightening), whereby the powder parameters correspond to the technical teaching of EP 2 215 025 A1.

[0064] The subsequent drilling of the porous green body (1) prepared in this way is carried out by holding it in a metal-free manner, a first centering hole is made, and then drilling is carried out several times until the desired dimension of the borehole (21) is reached.

[0065] The end surface is then straightened mechanically.

[0066] The drilled preform (2) is provided with a glass rod (doped or undoped) in the form of a core rod (22) and further treated chemically and thermally according to the technical teaching of EP 2 215 025 A1 in order to obtain the vitrified preform (3).

[0067] 1. Example

[0068] A SiO2 granulate, prepared by suspension precipitation and dried and doped with Yb2O3 and A12O3, is compressed at 500 kN to a final density of 1.09 g / cm 3pressed. The diameter is 20 mm, the length 71 mm. A center hole is first drilled using a 1.8 mm diameter twist drill with a length of 40 mm, followed by periodic deep drilling.

[0069] 2. Example a pierced doped

[0070] A SiO2 granulate, prepared by suspension precipitation and dried, doped with Yb2O3 and Al2O3, is compressed with 500 kN to a final density of 1.09 g / cm 3 pressed. The diameter is 20 mm, the length 71 mm. A center hole is first drilled using a 1.8 mm diameter twist drill with a length of 40 mm, followed by periodic deep drilling.

[0071] The partially drilled green body is then removed from the holder and, rotated 180°, reinserted. A new center hole is drilled, followed by periodic deep-hole drilling.

[0072] 3. Example

[0073] Production of a pierced doped silica glass body as a vitrified preform

[0074] A SiO2 granulate, prepared by suspension precipitation and dried and doped with Yb2O3 and Al2O3, is compressed with 500 kN to a final density of 1.09 g / cm 3 Pressed. The diameter is 20 mm, the length 71 mm. A 1.8 mm diameter twist drill with a length of 40 mm is used to first drill a center hole, then the hole is periodically deep-drilled.

[0075] The partially drilled green body is then removed from the holder and replaced after being rotated 180°. A new center hole is drilled, followed by periodic deep-hole drilling. The two end surfaces are straightened. The cavity is flushed with an oil-free gas flow.

[0076] The hollow cylinder thus obtained is subjected to further chemical and thermal treatments according to the technical teaching of EP 2 215 025 A1.

[0077] 4. Example

[0078] Production of a pierced doped silica glass body as a vitrified preform with core rod

[0079] A SiO2 granulate, prepared by suspension precipitation and dried and doped with Yb2O3 and Al2O3, is compressed with 500 kN to a final density of 1.09 g / cm 3 Pressed. The diameter is 20 mm, the length 71 mm. A 1.8 mm diameter twist drill with a length of 40 mm is used to first drill a center hole, followed by periodic deep hole drilling. The partially drilled green body is then removed from the holder and, rotated 180°, reinserted. Another center hole is drilled, followed by periodic deep hole drilling.

[0080] The two end surfaces are straightened. The cavity is flushed with an oil-free gas flow.

[0081] A SiO2 rod with an outer diameter of 1.5 mm is inserted into the cavity. The resulting cylinder is subjected to further chemical and thermal treatments according to the technical teaching of EP 2 215 025 A1.

[0082] 5. Example a pierced doped pebble

[0083] A SiO2 granulate prepared by suspension precipitation and dried, doped with Yb2O3 and A12O3, is compressed with 250 kN to a final density of 1.13 g / cm 3 pressed. The diameter is 26 mm, the length 76 mm. A 2.0 mm diameter twist drill with a length of 50 mm is used to first drill a center hole, then the hole is periodically deep-drilled.

[0084] The partially drilled green body is then removed from the holder and, rotated 180°, reinserted. A new center hole is drilled, followed by periodic deep-hole drilling.

[0085] 6. Example

[0086] Production of a pierced doped silica glass body with core rod Production of a pierced doped silica glass body according to embodiment 5.

[0087] Afterward:

[0088] A SiO2 rod with an outer diameter of 1.8 mm is inserted into the cavity. The resulting cylinder is subjected to further chemical and thermal treatments according to the teachings of EP 2 215 025 A1. 7. Embodiment a pierced doped pebble

[0089] A SiO2 granulate, prepared by suspension precipitation and dried and doped with Yb2O3 and Al2O3, is compressed with 500 kN to a final density of 1.07 g / cm 3Pressed. The diameter is 20 mm, the length 59 mm. A center hole is first drilled using a 2.0 mm diameter twist drill bit with a length of 50 mm. The hole is then periodically deep-drilled using a 5 mm diameter and 7 cm long twist drill bit.

[0090] The partially drilled green body is then removed from the holder and, rotated 180°, reinserted. A new center hole is drilled, followed by periodic deep-hole drilling.

[0091] 8. Embodiment of a drilled doped Kieseh as v

[0092] Preform with core rod with an outer diameter of 4.8 mm

[0093] A SiO2 rod with an outer diameter of 4.8 mm is inserted into the cavity. The resulting cylinder is subjected to further chemical and thermal treatments according to the teachings of EP 2 215 025 A1.

[0094] 9. Example a pierced undoped as

[0095] Preform

[0096] An undoped SiO2 granulate produced by suspension precipitation and dried is compressed at 750 kN to a final density of 1.28 g / cm 3 Pressed. The diameter is 20 mm, the length 22 mm. A center hole is first drilled using a 2 mm diameter twist drill bit with a length of 50 mm. The hole is then periodically drilled deeper with a 5 mm drill bit (length 70 mm).

[0097] The two end surfaces are then straightened. The cavity is flushed with an oil-free gas flow. 10. Example

[0098] Production of a perforated undoped silica glass body as a vitrified preform with core rod

[0099] An undoped SiO2 granulate produced by suspension precipitation and dried is compressed at 750 kN to a final density of 1.28 g / cm 3Pressed. The diameter is 20 mm, the length 22 mm. A center hole is first drilled using a 2 mm diameter twist drill bit with a length of 50 mm. The hole is then periodically drilled deeper with a 5 mm drill bit (length 70 mm).

[0100] The two end surfaces are then straightened. The cavity is flushed with an oil-free gas flow.

[0101] A SiO2 rod with an outer diameter of 4.8 mm is then inserted into the cavity. The resulting cylinder is subjected to further chemical and thermal treatments according to the teachings of EP 2 215 025 A1.

[0102] 11. Example

[0103] Production of a fifth perforated undoped silica glass body as a vitrified preform

[0104] An undoped SiO2 granulate produced by suspension precipitation and dried is compressed with 500 kN to a final density of 1.16 g / cm 3pressed. The diameter is 20 mm, the length 26 mm. A center hole is first drilled using a 1.8 mm diameter twist drill with a length of 40 mm, followed by periodic deep drilling.

[0105] The two end surfaces are then straightened. The cavity is flushed with an oil-free gas flow.

[0106] 12. Example a fifth pierced undoped as Preform

[0107] An undoped SiO2 granulate produced by suspension precipitation and dried is compressed with 500 kN to a final density of 1.16 g / cm 3 pressed. The diameter is 20 mm, the length 26 mm. With a

[0108] A 1.8 mm diameter twist drill with a length of 40 mm is used to first drill a center hole, then the hole is periodically deep drilled.

[0109] The two end surfaces are then straightened. The cavity is flushed with an oil-free gas flow.

[0110] A SiO2 rod with an outer diameter of 1.5 mm is inserted into the cavity. The resulting cylinder is subjected to further chemical and thermal treatments according to the teachings of EP 2 215 025 A1.

[0111] 13. Example

[0112] Production of a perforated undoped silica glass body as a vitrified preform

[0113] An undoped SiO2 granulate produced by suspension precipitation and dried is compressed with 250 kN to a final density of 1.13 g / cm 3 pressed. The diameter is 26 mm, the length 46 mm. With a

[0114] A centering hole is first drilled using a 1.8 mm diameter twist drill with a length of 40 mm, then the hole is periodically deep drilled (drill diameter 2 mm, length approx. 50 mm).

[0115] The partially drilled green body is then removed from the holder and, rotated 180°, reinserted. A new center hole is drilled, followed by periodic deep-hole drilling.

[0116] The two end surfaces are then straightened. The cavity is flushed with an oil-free gas flow.

[0117] 14. Example a sixth pierced undoped as a preform

[0118] An undoped SiO2 granulate produced by suspension precipitation and dried is compressed with 250 kN to a final density of 1.13 g / cm 3 pressed. The diameter is 26 mm, the length 46 mm. With a

[0119] A centering hole is first drilled using a 1.8 mm diameter twist drill with a length of 40 mm, then the hole is periodically deep drilled (drill diameter 2 mm, length approx. 50 mm).

[0120] The partially drilled green body is then removed from the holder and, rotated 180°, reinserted. A new center hole is drilled, followed by periodic deep-hole drilling.

[0121] The two end surfaces are then straightened. The cavity is flushed with an oil-free gas flow.

[0122] A SiO2 rod with an outer diameter of 1.8 mm is inserted into the cavity. The resulting cylinder is subjected to further chemical and thermal treatments according to the teaching of EP 2 215 025 A1.

[0123] The advantage of this manufacturing process (or variants) is that the interfaces formed during drilling can be treated in the porous precursor in a single step, together with the core rod (if used). Complex processing steps such as grinding, polishing, etching, etc., are unnecessary, increasing processability.

[0124] All features presented in the description, the embodiments and the following claims can be essential to the invention both individually and in any combination with one another.

[0125] List of reference symbols 1 - porous green body

[0126] 2 - porous, drilled green body (hollow cylinder)

[0127] 21 - Borehole / Recess / Cavity

[0128] 22 - Core rod

[0129] 3 - glazed preform

Claims

1. A method for producing a drilled fiber comprising the successive substeps: - producing a fiber precursor in the form of a porous green body (1) made of doped or undoped SiO 2 - Nanopowder by pressing the SiO 2 - nanopowder, - mechanical drilling in this porous green body (1) to form a borehole (21) in the form of a cavity, a hollow space or a continuous recess and - post-treatment of this drilled porous green body (1) to form a vitrified preform (3) and final drawing of the preform (3) to form a drilled fiber, characterized in that • the SiO 2 - nanopowder of the green body (1) is free from organic binders, polymer binders, polymerizable monomers, resins or their precursors, • pressing the SiO 2- Nanopowder at 100 to 600 kN to a final density of 0.9 g / cm 3 up to 1.5 g / cm 3 so that a green body (2) in cylindrical shape with an outer diameter between 10 mm and 50 mm and a length of up to 15 cm is produced, and • chemical cleaning of the inner surface of the porous green body with Cl 2 -Gas to remove any contamination in the interface area and • the drilled porous green body (3) is then thermally treated to sinter and vitrify it, thereby achieving healing of the original internal surface of the drill produced by drilling.

2. A method for producing a drilled fiber according to claim 1, characterized in that the mechanical drilling of the porous green body (1) is carried out with a twist drill in which the porous green body (1) is held metal-free, a first drilling is carried out and then drilled several times until the desired dimension of the borehole (21) is reached, so that a ratio of borehole diameter to compact diameter in the range of 1:2 to 1:20 is realized.

3. A method for producing a drilled fiber according to claim 1 or 2, characterized in that after drilling, the end surface of the borehole (21) is mechanically straightened and the cavity is filled with Cl by an oil-free gas flow. 2 -Gas is flushed to remove any contamination present in the interface area of ​​the borehole (21).

4. A method for producing a drilled fiber according to claim 1, 2 or 3, characterized in that the drilled preform (2) is finally chemically and thermally treated by sintering and vitrification in order to arrive at the vitrified preform (3), wherein due to the viscous state of the doped or undoped SiO 2- nanopowder creates a smooth interface on the vitrified preform (3), so that a final polishing of the original inner surface of the borehole (21) is not necessary.

5. A method for producing a drilled fiber according to one or more of claims 1 to 4, characterized in that a doping of the SiO 2 - particles by adding fluorine or one or more oxides of the following group of elements: Al, B, P, Nb, Ta, Mg, Ga, Zn, Ca, Sr, Ba, Sc, La, Sb, Ge, Y, Yb, Tm, Nd, Ho, Ce, Hf, Zr and Ti, 6. A method for producing a drilled fiber according to one or more of claims 1 to 5, characterized in that a Yb-containing fiber prepared and dried by suspension precipitation 2 O 3 and A1 2 O 3 doped SiO 2 - Granules with 500 kN to a final density of 1.09 g / cm 3is pressed so that a green body (2) in cylindrical shape with an outer diameter of 20 mm and a A length of 71 mm is created, whereby a hole is first drilled with a 1.8 mm diameter twist drill with a length of 40 mm and then the resulting hole is periodically deep drilled until a continuous recess is created, the two end surfaces of which are straightened and finally the continuous recess is flushed with an oil-free gas flow.

7. A method for producing a drilled fiber according to one or more of claims 1 to 5, characterized in that an undoped SiO produced by suspension precipitation and dried 2 - Granules with 500 kN to a final density of 1.16 g / cm 3is pressed so that a green body (2) in cylindrical shape with an outer diameter of 20 mm and a length of 26 mm is created, whereby a centering hole is first drilled with a 1.8 mm diameter twist drill with a length of 40 mm and then the hole created is periodically deep-drilled until a continuous recess is created, the two end surfaces of which are straightened and finally the continuous recess is flushed with an oil-free gas flow.

8. A method for producing a drilled fiber according to one or more of claims 1 to 5, characterized in that if the drill length is shorter than the required borehole length and the green body is shorter than twice the drill length, the porous green body (1) is removed from its holder, rotated by 180°, held again, centered and drilled again in order to obtain a continuous recess.

9. A method for producing a drilled fiber according to claim 1, 2, 6, 7 or 8 with a core, characterized in that after flushing the borehole of the drilled preform (2), a doped or undoped SiO 2 - Rod of suitable diameter in the form of a fiber core rod (22) or SiO 2 - nanopowder is partially or completely introduced into the borehole (21) of the porous green body (1) and finally, it is further treated chemically and thermally by sintering and vitrification to obtain a vitrified fiber preform (3) with a fiber core.

10. Method for producing a drilled fiber according to the Claims 1 to 9, characterized in that the pressing of the SiO 2 - Nanopowder is isostatic.

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