Optical fiber article, its manufacture and use

Abstract

Optical fiber article comprising at least one optical fiber and a functional layer arranged on the surface of the optical fiber; wherein the functional layer comprises at least one functional silane having the following structural formula: wherein Z is a branched or unbranched alkyl or aryl group having 1 to 18 carbon atoms, wherein R1, R2 and R3 are independently selected from hydrogen, oxygen, alkyl, alkyloxy, hydroxyalkyl and hydroxyl, and wherein one, two or three of the groups R1, R2 or R3 are directly or indirectly connected to the surface of the optical fiber via a covalent bond, and wherein R4 is selected from -NH2, -NHR', -NR'R'', glycidyloxy and -SH, wherein R' and R'' are independently selected from alkyl, aminoalkyl, hydroxyalkyl and -(CH2)mNH2 with m from 1 to 6, wherein the proportion of the functional silane in the functional layer is at least 1.5 wt.% and at most 70 wt.%.-% and wherein the content of polyvinyl polymers is less than 1 wt% based on the mass of the functional layer, wherein the content of photopolymerized polymers, in particular polyacrylates, polymethacrylates, polyvinyl polymers, polystyrene and / or derivatives thereof, in the functional layer is less than 1 wt% based on the mass of the functional layer.

Description

The present invention relates to an optical fiber article and a method for manufacturing the optical fiber article. The present invention also relates to the use of the optical fiber article in a fiber bundle as light sources and / or image guides, for example in an endoscope. Optical fiber products, such as fiber optic cables, can transmit data and / or transport light as light guides and / or image guides. Optical fiber products are frequently used in the medical field, for example, for therapeutic and / or diagnostic procedures. Light guides and / or image guides are used, for instance, for the flexible transmission of light in measuring instruments, microscopes, spectroscopes, inspection cameras, and endoscopes. Medical devices such as endoscopes are very often autoclaved and / or sterilized. During steam sterilization, the materials are exposed to high pressures, temperatures, and simultaneously high humidity. Therefore, light guides and / or image guides for use in medical devices such as endoscopes must exhibit good autoclavability or sterilizability and high corrosion resistance to ensure long-term usability.Therefore, optical fiber products are needed that increase the lifespan of medical devices and reduce corrosion. Furthermore, optical fiber products with high temperature and humidity resistance would be desirable. At the same time, the optical fiber product should exhibit high flexibility and good mechanical stability, especially for use in endoscopes. Optical fibers are often coated with sizing as a protective layer. Typically, optical fibers are coated with polymerizable coatings that cure upon UV irradiation. Such coatings often contain acrylates, methacrylates, and other polymerizable components. However, these polymerizable coatings are not entirely safe for human health. Furthermore, such coatings contain photoinitiators, the effects of which on human health are increasingly viewed with concern. The use of such photopolymerizable substances in medical devices, especially those that come into contact with human organs, is critical. Therefore, optical fiber products that can be manufactured without harmful components would be desirable. In particular, the materials should be as low-toxicity as possible, ideally non-toxic, and pose no risk to the patient.The provision of optical fibers with improved biocompatibility and reduced toxicity would therefore be desirable. US 2003 / 0045600 A1 describes a sizing that may include silanes such as polyalkoxysilanes and polyhalosilanes. The sizing described in US 2003 / 0045600 A1 may also contain halides such as chlorine or fluorine. Furthermore, US 2003 / 0045600 A1 describes a sizing that may contain polyether urethane acrylate as its main component. WO 01 / 49625 A1 describes an optical fiber with a UV-curable sizing that may contain photopolymerizable compounds such as caprolactone (meth)acrylate or 4-hydroxybutyl (meth)acrylate. Furthermore, the sizing of WO 01 / 49625 A1 may contain photoinitiators such as 1-hydroxycyclohexyl phenyl ketone or 2,2-dimethoxy-2-phenylacetophenone. US 2008 / 0050529A1 describes compositions for treating the surface of glass, e.g., flat glass or hollow glass, or glass in the form of fibers, wherein the compositions are applied as a thin layer to the glass. The silane coupling agent (3-Aminopropyl)triethoxysilane is known in the prior art (CAS: 919-30-2). US 6 577 802 B1 describes a method for applying an adhesion-promoting intermediate layer to an optical fiber using a carrier gas. JP 2017 - 7 875 A describes an optical transmission body with a core consisting of a first and a second glass, wherein the transmission body comprises a fiber element wire consisting of a cladding that encloses an outer circumferential surface of the core and a coating that encloses an outer circumferential surface of the cladding. The coating has a variety of organic silicon compounds with a functional group at one end and contains a variety of nonionic surfactants, wherein the organic silicon compound siloxane binds to the cladding. It is therefore an object of the present invention to overcome the disadvantages of the prior art. In particular, it is an object to provide an improved optical fiber article for use in medical and diagnostic devices such as endoscopes. The optical fiber article should be characterized in particular by high corrosion resistance, even during steam sterilization, a long service life, good flexural strength, as well as particularly high biocompatibility and reduced toxicity. The problems are solved by the subject matter of the patent claims. In particular, the problems are solved by an optical fiber article comprising at least one optical fiber and a functional layer arranged on its surface. The optical fiber can have a fiber core and a cladding arranged on the fiber core. The functional layer can comprise at least one functional silane with the following structural formula: where Z is a branched or unbranched alkyl or aryl group with 1 to 18 carbon atoms, wherein R1, R2 and R3 are independently selected from hydrogen, oxygen, alkyl, hydroxyalkyl and hydroxyl, and wherein one, two or three of the groups R1, R2 or R3 are directly or indirectly connected to the surface via a covalent bond, and where R4 is selected from, -NH 2 , -NHR', -NR'R'', glycidyloxy and -SH, where R' and R'' are independently selected from alkyl, aminoalkyl, hydroxyalkyl and -(CH 2 ) m NH 2 with m from 1 to 6, wherein the proportion of the functional silane in the functional layer is at least 1.5 wt.% and at most 70 wt.% and wherein the content of polyvinyl polymers is less than 1 wt.% based on the mass of the functional layer, wherein the content of photopolymerized polymers, in particular polyacrylates, polymethacrylates, polyvinyl polymers, polystyrene and / or derivatives thereof, in the functional layer is less than 1 wt.% based on the mass of the functional layer. In one embodiment, the functional layer in the IR spectrum is additionally characterized by the following absorption: a. a ratio of the maximum absorption band height in the range of 800 cm⁻¹ to 1200 cm⁻¹ to the maximum absorption band height in the range of 1500 cm⁻¹ to 1900 cm⁻¹ is at least 2.0; b. a ratio of the maximum absorption band height in the range of 2700 cm⁻¹ to 3000 cm⁻¹ to the maximum absorption band height in the range of 1500 cm⁻¹ to 1900 cm⁻¹ is at least 2.0; and c. a ratio of the maximum absorption band height in the range of 800 cm⁻¹ to 1200 cm⁻¹ to the maximum absorption band height in the range of 2700 cm⁻¹ to 3000 cm⁻¹ is at least 1.1 and at most 2.0. The optical fiber article with such an IR spectrum is obtained by implementing the measures described herein. In particularly preferred embodiments, the functional layer has an IR spectrum substantially according to Fig. 2 or Fig. 3. An "optical fiber" is a fiber that can transmit light over short or long distances. One example of such an optical fiber is a glass fiber. An optical fiber comprises a core layer (also called the "fiber core"), a cladding layer (also called the "cladding"), and a functional layer located on the surface of the cladding layer. "Optical fiber bundle" refers to a plurality of optical fibers. For example, an optical fiber bundle can consist of 10 or more optical fibers. "Optical fiber article" refers to an article that includes at least one optical fiber. An optical fiber article can also include multiple optical fibers. Optical fibers and optical fiber articles can be used, for example, in light guides and / or image guides. For use in such light guides and / or image guides, several optical fiber articles can, for example, be bonded together and embedded within a sleeve. "Functional layer" refers to a layer arranged on the surface of the cladding layer, which covers the optical fiber at least partially, and in particular substantially completely. The functional layer serves, among other things, to protect the optical fiber from damage, for example, from breakage. The functional layer can, for example, be formed from a sizing agent. "Plain" refers to a composition used to apply the functional layer to optical fibers. It can be applied after fiber production, for example by dipping, spraying, or using a roll-to-roll process. "Functional silane" refers to a silane compound that includes at least one functional group capable of undergoing chemical reactions. Such a functional group could, for example, be an amino group. The functional silane can, for instance, act as an adhesion promoter, bridging the gap between the surface of the coating layer and an adhesive. The term "cladding layer" refers to a layer located beneath the functional layer and surrounding a core layer. The cladding layer can contain, for example, glass or a polymer such as polyimide. The cladding layer contributes significantly to the light transmission function of the optical fiber. The "core layer" refers to the inner layer of the optical fiber and is surrounded by the cladding layer. The core layer can contain, for example, glass or a polymer such as polycarbonate. Together with the cladding layer, the core layer contributes significantly to the light transmission function of the optical fiber. The following detailed description lists measures and features that can contribute to the success of the invention. It is not necessary to implement all measures in an optical fiber article. Rather, the intended improvements can already be achieved if only some of the following measures are applied. In one embodiment, the functional layer comprises a functional silane. This functional silane has free functional groups, such as amino groups, that have not been de-reacted by acrylates or other reactive compounds. The functional silane ensures good adhesion of the functional layer to the surface of the cladding layer. This good adhesion of the functional layer to the optical fiber serves to protect the functional layer, for example, from microcracks and fractures, especially under repeated and increased bending stress on the fiber article. Additionally, the functional silane provides the functional layer with good adhesion-promoting properties on the side facing away from the optical fiber. This enables the functional layer to form good bonds with other materials, such as adhesives. The functional silane thus ensures good bondability of the optical fiber article.For example, if several optical fiber components are embedded and bonded within a sleeve, improved adhesion of the optical fiber components to each other and to the sleeve is achieved. Such a sleeve can be made of materials such as stainless steel or plastic. Preferably, the alkyl group in Z comprises at least one carbon atom, at least two carbon atoms, at least three carbon atoms, or at least four carbon atoms. More preferably, the alkyl group in Z comprises at most 25 carbon atoms, more preferably at most 20 carbon atoms, more preferably at most 15 carbon atoms, more preferably at most 12 carbon atoms, more preferably at most 10 carbon atoms, more preferably at most 9 carbon atoms, more preferably at most 8 carbon atoms, and more preferably at most 7 carbon atoms. In embodiments, the alkyl group in Z comprises 1 to 25 carbon atoms, more preferably 1 to 20 carbon atoms, more preferably 2 to 15 carbon atoms, or 3 to 12 carbon atoms. In particularly preferred embodiments, the alkyl group in Z comprises 3 to 8 carbon atoms. The number of carbon atoms influences the sliding properties of the optical fibers.This allows the optical fibers or the optical fiber article to be bent more frequently and more sharply without breaking. Improved sliding properties also ensure that the optical fibers slide smoothly against each other without sticking together. Preferably, the alkyl group in Z is an unbranched alkyl group. The groups R1, R2, and R3 can be independently selected from hydrogen, oxygen, alkyl, alkyloxy, hydroxyalkyl, and hydroxyl, wherein one, two, or three of the groups R1, R2, or R3 are directly or indirectly bonded to the surface of the optical fiber via a covalent bond. In other words, for example, one of the groups R1, R2, or R3 can be an alkyl group (e.g., a methyl group) or an alkyloxy group (e.g., a methoxy group), and two other groups are oxygen and bonded to the surface of the fiber via a siloxane group (see Fig. 1). The alkyl component of R1, R2, and / or R3 can have a chain length of 1 to 6, particularly 1 to 3 carbon atoms. In particular, one, two, or three of the groups R1, R2, or R3 of the functional silane are directly or indirectly bonded to the surface of the fiber via a covalent bond.Preferably, one, two, or three of the groups R1, R2, and R3 are a (-X-R''') group, wherein X is selected from oxygen, selenium, and sulfur, and wherein R''' is selected from an alkyl group, hydrogen, and the fiber surface. Further preferably, one, two, or three of the groups R1, R2, and R3 are a (-X-R''') group, wherein X is oxygen and wherein R''' is selected from an alkyl group, hydrogen, and the fiber surface. Further preferably, one, two, or three of the groups R1, R2, and R3 are a (-X-R''') group, wherein X is oxygen and wherein R''' is the fiber surface. Further preferably, two or three of the groups R1, R2, and R3 are a (-X-R''') group, wherein X is oxygen and wherein R''' is the fiber surface. The alkyl group can have a carbon chain length in the range of 1 to 6, particularly 1 to 3 carbon atoms.For example, the functional silane forms one, two, or three siloxane compounds with the surface of the cladding layer. The functional silane described here thus contributes significantly to the adhesion of the functional layer to the optical fiber. R4 can be selected from -NH2, -NHR', -NR'R'', glycidyloxy, and -SH, wherein R' and R'' are independently selected from alkyl, aminoalkyl, hydroxyalkyl, and -(CH2)mNH2 with m from 1 to 6, particularly 1 to 3. In preferred embodiments, R4 is selected from -NH2, -NHR', and -NR'R'', wherein R' and R'' are independently selected from alkyl, aminoalkyl, hydroxyalkyl, and -(CH2)mNH2 with m from 1 to 6, more preferably m from 1 to 5, more preferably m from 1 to 4, more preferably m from 1 to 3, and more preferably m from 1 to 2. Particularly preferably, R4 is selected from -NH2 and -NHR', wherein R' is selected from alkyl, aminoalkyl, hydroxyalkyl, and -(CH2)mNH2 with m from 1 to 6, more preferably m from 1 to 5, and more preferably m from 1 to 2. to 4, more preferably from 1 to 3, more preferably from 1 to 2. R4 is particularly preferably selected from -NH2 and -NHR', wherein R' is alkyl. In a particularly preferred embodiment, R4 is -NH2.In a particularly preferred embodiment, R4 is -(CH2)2NH2. The functional silane with such a group R4 enables good adhesion mediation and bonding, for example when optical fiber articles are embedded in a sleeve with an adhesive. In a particularly preferred embodiment, the functional silane has the following structural formula: where R1, R2 and R3 is a (-XR''') group, where X is oxygen and where R''' is the surface of the fiber; where Z is an unbranched alkyl group with 3 carbon atoms; and where R4 is selected from, -NH 2 , -NHR' where R''-(CH 2 ) m NH 2 with m = 2. In a particularly preferred embodiment, the functional silane has the following structural formula: where R1, R2 and R3 is a (-X-R''') group; where X is oxygen and where R''' is the surface of the fiber; where R4 is -NH 2 is; and wherein Z is an unbranched alkyl group with 1 to 10 carbon atoms, more preferably with 2 to 9 carbon atoms, more preferably with 3 to 8 carbon atoms. In another particularly preferred embodiment, the functional silane has the following structural formula: where R1, R2 and R3 is a (-X-R''') group, where X is oxygen and where R''' is the surface of the fiber; where R1, R2 and R3 are directly connected to the surface of the fiber via a covalent bond; where R4 is -NHR'; where R' is -(CH 2 ) m NH 2 with m = 2; and where Z is an unbranched alkyl group with 1 to 10 carbon atoms, more preferably with 2 to 9 carbon atoms, more preferably with 3 to 8 carbon atoms. In a preferred embodiment, Z=3 and R4 is NH2 or NHR' with R' = -(CH2)mNH2 and m = 2. Examples of functional silanes preferably used according to the invention are N-[3-(trimethoxysilyl)propyl]ethylenediamine, 3-aminopropyl diethoxymethylsilane, 3-glycidyloxypropyl triethoxysilane, 3-glycidoxypropyl dimethoxymethylsilane and combinations thereof or their reaction products with the surface of the fiber, in particular their derivatives connected to the surface of the fiber via one, two or three covalent bonds. In certain embodiments, the functional layer comprises a plurality of functional silanes. In certain embodiments, the functional layer comprises at least two functional silanes, at least three functional silanes, or at least four functional silanes. Preferably, the functional layer comprises the functional silane in a proportion of at least 1.8 wt.%, more preferably at least 2 wt.%. More preferably, the functional layer comprises the functional silane in a proportion of at most 60 wt.%, more preferably at most 50 wt.%, more preferably at most 40 wt.%, more preferably at most 30 wt.%, more preferably at most 25 wt.%, more preferably at most 15 wt.%. In preferred embodiments, the functional layer comprises the functional silane in a proportion of 0.1 to 70 wt.%, more preferably 0.5 to 50 wt.%, more preferably 0.9 to 40 wt.%, more preferably 1.2 to 30 wt.%, more preferably 1.5 to 15 wt.%. In particularly preferred embodiments, the functional layer comprises the functional silane in a proportion of 1 to 40 wt.%, or 2 to 15 wt.%.If the proportion of functional silane is too low, the functional layer adheres poorly to the surface of the cladding layer, making the optical fiber more prone to microcracking and breakage. If the proportion of functional silane is too high, the optical fibers slide against each other less smoothly and tend to stick together. This leads to increased formation of microcracks and breaks under repeated and increased bending loads. It should be noted that the functional silane content in the functional layer is comparatively high compared to prior art functional layers, since the sizing agents used to produce the functional layer preferably contain essentially no polymerizable solvents, such as acrylates or methacrylates. The solvents used in the sizing agents do not remain in the functional layer after drying. In embodiments, the functional layer comprises, alternatively or additionally to the functional silane, at least one alkylsilane. Preferably, the functional layer comprises an alkylsilane covalently bonded to the surface of the fiber. Preferably, the alkylsilane has the following structural formula: wherein R5, R6 and R7 are independently selected from hydrogen, oxygen, alkyl, alkyloxy, hydroxyalkyl and hydroxyl, and wherein one, two or three of the groups R5, R6 or R7 are directly or indirectly connected to the surface of the fiber via a covalent bond, where R8 is selected from branched and unbranched alkyl groups with 1 to 25 carbon atoms. The alkylsilane improves the hydrolytic resistance of the optical fiber and reduces the surface energy. Preferably, the alkyl group in R8 of the alkylsilane has at least one carbon atom, at least two carbon atoms, at least five, or at least eight carbon atoms. More preferably, the alkyl group in R8 has at most 25 carbon atoms, more preferably at most 20 carbon atoms, more preferably at most 15 carbon atoms, more preferably at least at most 12 carbon atoms, and more preferably at most 10 carbon atoms. In embodiments, the alkyl group in R8 has 1 to 25 carbon atoms, more preferably 1 to 20 carbon atoms, more preferably 1 to 15 carbon atoms, and more preferably 3 to 12 carbon atoms. In particularly preferred embodiments, the alkyl group in R8 has 5 to 10 carbon atoms or 8 to 15 carbon atoms.The chain length of the alkylsilane according to the invention improves the sliding of the optical fibers, for example within an optical fiber bundle, and prevents the optical fibers from sticking together. This leads to improved handling and re-separation of the optical fibers in optical fiber bundles. Preferably, the alkyl group in R8 of the alkylsilane is an unbranched alkyl group. Preferably, one, two, or three of the groups R5, R6, and R7 are a (-X-R''') group, wherein X is selected from oxygen, selenium, and sulfur, and wherein R''' is selected from an alkyl group, hydrogen, and the surface of the fiber. Further preferably, one, two, or three of the groups R5, R6, and R7 are a (-X-R''') group, wherein X is oxygen and wherein R''' is selected from an alkyl group, hydrogen, and the surface of the fiber.Preferably, one, two, or three of the groups R5, R6, and R7 form a (-X-R''') group, where X is oxygen and R''' is the fiber surface. For example, the alkylsilane forms one, two, or three siloxane compounds with a Si-OH group on the fiber surface. The alkylsilane described here improves the adhesion of the functional layer to the fiber surface. Furthermore, the alkylsilane described here improves the flexibility of the optical fibers, for example, in an optical fiber bundle, and reduces the mutual friction of the optical fibers. Preferably, the alkylsilane has the following structural formula: wherein R5, R6 and R7 is a (-X-R''') group; wherein X is oxygen and wherein R''' is the surface of the fiber; wherein R5, R6 and R7 are directly connected to the surface of the fiber via a covalent bond; and wherein R8 is an unbranched alkyl group having 1 to 15 carbon atoms, more preferably having 1 to 12 carbon atoms, more preferably having 1 to 10 carbon atoms, more preferably having 1 to 9 carbon atoms, more preferably having 3 to 8 carbon atoms. Examples of alkylsilanes used according to the invention are trimethoxypropylsilane, trimethoxyoxysilane, trimethoxymethylsilane, n-propyltriethoxysilane, triethoxymethylsilane, dimethoxydimethylsilane, diethoxydimethylsilane, or their reaction products with the surface of the fiber, in particular their derivatives connected to the surface of the fiber via one, two or three covalent bonds. In certain embodiments, the functional layer comprises a plurality of alkylsilanes. In certain embodiments, the functional layer comprises at least two alkylsilanes, at least three alkylsilanes, or at least four alkylsilanes. Preferably, the functional layer comprises the alkylsilane in a proportion of at least 0.8 wt.%, more preferably at least 1 wt.%, more preferably at least 2 wt.%, more preferably at least 3 wt.%, more preferably at least 4 wt.%, more preferably at least 5 wt.%, and more preferably at least 6 wt.%. More preferably, the functional layer comprises at least one alkylsilane in a proportion of at most 65 wt.%, more preferably at most 60 wt.%, more preferably at most 55 wt.%, more preferably at most 50 wt.%, more preferably at most 45 wt.%, more preferably at most 40 wt.%, and more preferably at most 35 wt.%. In preferred embodiments, the functional layer comprises the alkylsilane in a proportion of 0.8 to 65 wt.%, more preferably 1 to 60 wt.%, more preferably 29 to 55 wt.%, more preferably 3 to 50 wt.%, and more preferably 4 to 45 wt.%.In particularly preferred embodiments, the functional layer comprises the alkylsilane in a proportion of 6 to 35 wt.%. If the proportion of alkylsilane is too low, the optical fibers exhibit reduced flexibility and chemical resistance, and increased friction occurs between the optical fibers, for example, in an optical fiber bundle. This leads to the faster formation of microcracks and fractures. Furthermore, an insufficient proportion of alkylsilane reduces the chemical stability of the optical fiber, for example, against acids. If the proportion of alkylsilane is too high, the cohesion between the optical fibers, for example, in an optical fiber bundle, is reduced. In embodiments, the functional layer comprises, alternatively or additionally to the functional silane and / or the alkylsilane, a polyethylene glycol (PEG) silane. Preferably, the functional layer comprises a PEG silane covalently bonded to the surface of the fiber. Preferably, the PEG silane has the following structural formula: wherein R9, R10 and R11 are independently selected from hydrogen, oxygen, alkyl, alkyloxy, hydroxyalkyl and hydroxyl, and wherein one, two or three of the groups R9, R10 and R11 are directly or indirectly connected to the surface of the fiber via a covalent bond, and R12 contains, consists of, or is a derivative of a polyethylene glycol group with a chain length of 5 to 900 ethylene oxide units. The PEG-silane improves the hydrolytic stability of the optical fiber. Preferably, the polyethylene glycol group or derivative thereof in R12 has a chain length of at least 3, more preferably at least 4, more preferably at least 5, more preferably at least 6, more preferably at least 7, and more preferably at least 8 ethylene oxide units. More preferably, the polyethylene glycol group or derivative thereof has a chain length of at most 30, more preferably at most 25, more preferably at most 20, more preferably at most 15, and more preferably at most 12 ethylene oxide units. In embodiments, the polyethylene glycol group has a chain length of 3 to 30, more preferably 4 to 25, and more preferably 5 to 20 ethylene oxide units. In particularly preferred embodiments, the polyethylene glycol group has a chain length of 8 to 12 ethylene oxide units.The chain length of the polyethylene glycol group or its derivative according to the invention improves the cohesion of the optical fibers, for example in an optical fiber bundle, without causing them to stick together. This improves the flexibility of the optical fibers, for example in an optical fiber bundle. The polyethylene glycol group in R12 can have an end group at its free end. The end group can be a hydroxyl or alkyloxy group, in particular a methoxy group. Preferably, one, two, or three of the groups R9, R10, and R11 form a (-X-R''') group, wherein X is selected from oxygen, selenium, and sulfur, and wherein R''' is selected from an alkyl group, hydrogen, and the fiber surface. Further preferably, one, two, or three of the groups R9, R10, and R11 form a (-X-R''') group, wherein X is oxygen and wherein R''' is selected from an alkyl group, hydrogen, and the fiber surface. Further preferably, one, two, or three of the groups R9, R10, and R11 form a (-X-R''') group, wherein X is oxygen and wherein R''' is the fiber surface. Further preferably, two or three of the groups R9, R10, and R11 form a (-X-R''') group, wherein X is oxygen and wherein R''' is the fiber surface. For example, the PEG-silane forms one, two, or three siloxane compounds with a silicon group on the fiber surface.The PEG-silane described here improves the adhesion of the functional layer to the fiber surface. Furthermore, the PEG-silane described here improves the flexibility of the optical fibers, for example in an optical fiber bundle, and reduces the mutual friction between the optical fibers. In particularly preferred embodiments, the PEG-silane has the following structural formula: wherein R9, R10 and R11 is a (-X-R''') group; wherein X is oxygen and wherein R''' is the surface of the fiber; wherein R9, R10 and R11 are directly connected to the surface of the fiber via a covalent bond; and wherein R12 has a polyethylene glycol group, consists thereof or is a derivative thereof with a chain length of 3 to 30, more preferably 4 to 25, more preferably 5 to 20, more preferably 8 to 12 ethylene oxide units. Examples of PEG silanes used according to the invention are 2-[Methoxy(polyethyleneoxy)9-12propyl]trimethoxysilane, [Hydroxy(polyethyleneoxy)propyl]triethoxysilane, and their reaction products with the surface of the fiber, in particular their derivatives connected to the surface of the fiber via one, two or three covalent bonds. In certain embodiments, the functional layer comprises a plurality of PEG silanes. In certain embodiments, the functional layer comprises at least two PEG silanes, at least three PEG silanes, or at least four PEG silanes. Preferably, the functional layer comprises at least one PEG-silane with a proportion of at least 1 wt.%, more preferably at least 5 wt.%, more preferably at least 8 wt.%, more preferably at least 11 wt.%, more preferably at least 13 wt.%, more preferably at least 15 wt.%, and more preferably at least 21 wt.%. More preferably, the functional layer comprises at least one PEG-silane with a proportion of at most 90 wt.%, more preferably at most 85 wt.%, more preferably at most 80 wt.%, more preferably at most 75 wt.%, more preferably at most 70 wt.%, more preferably at most 65 wt.%, and more preferably at most 62 wt.%. In preferred embodiments, the functional layer comprises the PEG-silane in a proportion of 1 to 90 wt.%, more preferably 5 to 85 wt.%, more preferably 8 to 80 wt.%, more preferably 11 to 75 wt.%, more preferably 13 to 70 wt.%.In a particularly preferred embodiment, the functional layer comprises PEG-silane in a proportion of 21 to 65 wt.%. If the proportion of PEG-silane is too low, the cohesion of the optical fibers, for example in an optical fiber bundle, is reduced. If the proportion of PEG-silane is too high, the cohesion of the optical fibers to each other, for example in an optical fiber bundle, is reduced. Furthermore, an insufficient proportion of PEG-silane reduces the chemical stability of the optical fiber. If the proportion of PEG-silane is too high, the optical fibers tend to adhere too strongly to each other, and their flexibility is reduced. This leads to a faster formation of microcracks and fractures. In certain embodiments, the mass fraction of the alkylsilane and / or PEG-silane exceeds the mass fraction of the functional silane. In certain embodiments, the mass fraction of the alkylsilane and / or PEG-silane exceeds the mass fraction of the functional silane by a factor of at least 1.05, more preferably 1.1, more preferably 1.2, more preferably 1.3, more preferably 1.4, more preferably 1.5, more preferably 1.6. Preferably, the mass fraction of the alkylsilane and / or PEG-silane exceeds the mass fraction of the functional silane by a factor of at most 100, more preferably at most 80, more preferably at most 60, more preferably at most 40, more preferably at most 30, more preferably at most 20, more preferably at most 10. In another embodiment, the mass fraction of the functional silane exceeds the mass fraction of the alkyl silane and / or PEG silane. In one embodiment, the mass fraction of the functional silane exceeds the mass fraction of the alkyl silane and / or PEG silane by a factor of at least 1.05, more preferably 1.1, more preferably 1.2, more preferably 1.3, more preferably 1.4, more preferably 1.5, more preferably 1.6. Preferably, the mass fraction of the functional silane exceeds the mass fraction of the alkyl silane and / or PEG silane by a factor of at most 100, more preferably at most 80, more preferably at most 60, more preferably at most 40, more preferably at most 30, more preferably at most 20, more preferably at most 10. In one embodiment, the functional layer comprises the following compounds: <row> <cell>Functional silane< / cell> <cell> 0,1-70< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 0,8-65< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> -< / cell> < / row> <p xml:id="_ab747a0134" n="0051">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 0,1-70< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> -< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> 1-90< / cell> < / row> <p xml:id="_ab747a0151" n="0052">In another embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 0,1-70< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 0,8-65< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> 1-90< / cell> < / row> <p xml:id="_ab747a0168" n="0053">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 2-40< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 6-35< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> -< / cell> < / row> <p xml:id="_ab747a0185" n="0054">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 2-40< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> -< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> 21-65< / cell> < / row> <p xml:id="_ab747a0202" n="0055">In another embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 2-40< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 6-35< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> 21-65< / cell> < / row> <p xml:id="_ab747a0219" n="0056"> Preferably, the functional layer comprises at least one fatty acid, either alternatively or in addition to at least one of the silanes. The fatty acid can be saturated or unsaturated. In particularly preferred embodiments, the fatty acid is saturated. The fatty acid increases the mechanical stability of the optical fiber and reduces friction between the optical fibers. Furthermore, the fatty acid can form a hydrophobic protective layer around the fiber. <p xml:id="_ab747a0220" n="0057">Preferably, the fatty acid has a chain length of at least 10 carbon atoms, more preferably at least 11, more preferably at least 12, more preferably at least 13, more preferably at least 14, more preferably at least 15, more preferably at least 16. Preferably, the fatty acid has a chain length of at most 40 carbon atoms, more preferably at most 35, more preferably at most 30, more preferably at most 28, more preferably at most 26, more preferably at most 24, more preferably at most 22. In preferred embodiments, the fatty acid has a chain length of 10 to 40 carbon atoms, more preferably from 11 to 35, more preferably from 12 to 30, more preferably from 13 to 28. In particularly preferred embodiments, the fatty acid has a chain length of 14 to 22 carbon atoms.If the chain length is too short, the adhesion of the functional layer to the surface of the cladding layer is reduced. If the chain length is too long, the optical fibers tend to stick together too strongly. <p xml:id="_ab747a0221" n="0058">Preferably, the fatty acid has a melting point of at least 35°C, more preferably at least 39°C, more preferably at least 42°C, more preferably at least 48°C, more preferably at least 52°C, more preferably at least 54°C, more preferably at least 56°C, more preferably at least 58°C, more preferably at least 60°C, more preferably at least 65°C, more preferably at least 70°C. Preferably, the fatty acid has a melting point of at most 180°C, more preferably at most 160°C, more preferably at most 140°C, more preferably at most 120°C, more preferably at most 100°C, more preferably at most 95°C, more preferably at most 90°C. Preferably, the fatty acid has a melting point of 35°C to 180°C, 39°C to 160°C, or 42°C to 100°C. In particularly preferred embodiments, the fatty acid has a melting point of 53°C to 90°C.If the melting point of the fatty acid is too low, this reduces the adhesion of the functional layer to the optical fiber. This results in reduced protection of the optical fiber, for example, against microcracks and breaks. If the melting point of the fatty acid is too high, the optical fibers stick together too strongly. This reduces flexibility and, under increased and repeated bending stress, leads to microcracks and breaks. Preferably, the fatty acid has a boiling point of at least 200°C, more preferably at least 220°C, more preferably at least 240°C, more preferably at least 260°C, more preferably at least 280°C, and more preferably at least 300°C. Preferably, the fatty acid has a boiling point of at most 500°C, more preferably at most 400°C, more preferably at most 380°C, and more preferably at most 330°C.Preferably, the fatty acid has a boiling point of 200°C to 500°C, of ​​220°C to 400°C, or of 240°C to 380°C. Examples of fatty acids usable according to the invention are capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, and arachidic acid. <p xml:id="_ab747a0222" n="0059"> In certain embodiments, the functional layer comprises a plurality of fatty acids. In certain embodiments, the functional layer comprises at least two fatty acids, at least three fatty acids, or at least four fatty acids. <p xml:id="_ab747a0223" n="0060">Preferably, the majority of fatty acids in their mixture have a melting point of at least 35°C, more preferably at least 39°C, more preferably at least 42°C, more preferably at least 48°C, more preferably at least 52°C, more preferably at least 54°C, more preferably at least 56°C, more preferably at least 58°C, more preferably at least 60°C, more preferably at least 65°C, and more preferably at least 70°C. Preferably, the majority of fatty acids in their mixture have a melting point of at most 180°C, more preferably at most 160°C, more preferably at most 140°C, more preferably at most 120°C, more preferably at most 100°C, more preferably at most 95°C, and more preferably at most 90°C. Preferably, the majority of fatty acids as a mixture have a melting point of 35°C to 180°C, of ​​39°C to 160°C, or of 42°C to 140°C.The melting point of a mixture refers to the melting point of a mixture of the individual fatty acids that make up the majority of the fatty acids, in the proportions used. If the melting point of the majority of fatty acids is too low, this reduces the adhesion of the functional layer to the optical fiber. This results in reduced protection of the optical fiber, for example, against microcracks and breaks. If the melting point of the majority of fatty acids is too high, the optical fibers stick together too strongly. This reduces flexibility, and under increased and repeated bending stress, microcracks and breaks can occur. <p xml:id="_ab747a0224" n="0061">Preferably, the functional layer comprises one or more fatty acids with a proportion of at least 1 wt.%, more preferably at least 2 wt.%, more preferably at least 3 wt.%, more preferably at least 4 wt.%, more preferably at least 5 wt.%, more preferably at least 6 wt.%, and more preferably at least 7 wt.%. More preferably, the functional layer comprises at least one fatty acid with a proportion of at most 85 wt.%, more preferably at most 80 wt.%, more preferably at most 75 wt.%, more preferably at most 70 wt.%, more preferably at most 65 wt.%, more preferably at most 60 wt.%, and more preferably at most 56 wt.%. In preferred embodiments, the functional layer comprises at least one fatty acid with a proportion of 1–85 wt.%, more preferably 2–80 wt.%, more preferably 3–75 wt.%, and more preferably 4–70 wt.%.In a particularly preferred embodiment, the functional layer comprises one or more fatty acids in a total proportion of 7 to 56 wt.%. If the proportion of the at least one fatty acid is too low, the optical fibers slide past each other less smoothly. If the proportion of the at least one fatty acid is too high, the optical fibers stick together. <p xml:id="_ab747a0225" n="0062">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 0,1-70< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> -< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> -< / cell> < / row> <row> <cell>fatty acid< / cell> <cell> 1-85< / cell> < / row> <p xml:id="_ab747a0245" n="0063">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 2-40< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> -< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> -< / cell> < / row> <row> <cell> fatty acid< / cell> <cell> 7-56< / cell> < / row> <p xml:id="_ab747a0265" n="0064">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 0,1-70< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 0,8-65< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> -< / cell> < / row> <row> <cell> fatty acid< / cell> <cell> 1-85< / cell> < / row> <p xml:id="_ab747a0285" n="0065">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 2-40< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 6-35< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> -< / cell> < / row> <row> <cell> fatty acid< / cell> <cell> 7-56< / cell> < / row> <p xml:id="_ab747a0305" n="0066">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 0,1-70< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 0,8-65< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> 1-90< / cell> < / row> <row> <cell> fatty acid< / cell> <cell> 1-85< / cell> < / row> <p xml:id="_ab747a0325" n="0067">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 2-40< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 6-35< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> 21-65< / cell> < / row> <row> <cell> fatty acid< / cell> <cell> 7-56< / cell> < / row> <p xml:id="_ab747a0345" n="0068">In embodiments, the functional layer comprises, alternatively or additionally to at least one of the silanes, at least one polyvalent alcohol. Polyvalent alcohols according to the invention are glycerol, diethylene glycol, or 1,5-pentanediol, as well as alkane polyols, such as alkanediols and alcanetriols, in particular alkane polyols with chain lengths of 2 to 10 carbon atoms, preferably 3 to 8 carbon atoms. Preferably, the functional layer comprises at least one polyvalent alcohol in a proportion of at least 3 wt.%, more preferably at least 5 wt.%, more preferably at least 10 wt.%, more preferably at least 15 wt.%, more preferably at least 20 wt.%, more preferably at least 25 wt.%, and more preferably at least 30 wt.%. More preferably, the functional layer comprises at least one polyvalent alcohol in a proportion of at most 90 wt.%, more preferably at most 87 wt.%, and more preferably at most 84 wt.%.-%, more preferably at most 81 wt.%, more preferably at most 79 wt.%, more preferably at most 77 wt.%, more preferably at most 75 wt.%. In preferred embodiments, the functional layer comprises the polyvalent alcohol in a proportion of 3 to 90 wt.%, more preferably 5 to 87 wt.%, more preferably 10 to 84 wt.%, more preferably 15 to 81 wt.%. In particularly preferred embodiments, the functional layer comprises the polyvalent alcohol in a proportion of 30 to 75 wt.%. The polyvalent alcohol improves the sliding of optical fibers against each other and thus reduces the occurrence of microcracks and breaks.The polyvalent alcohol improves the handling, packing density and re-singleability of the optical fiber, for example in an optical fiber bundle; in particular, the polyvalent alcohol leads to a desired "wet behavior", i.e. the property of a fiber article to behave like a wet fiber article. <p xml:id="_ab747a0346" n="0069">The functional layer can alternatively or additionally comprise at least one polyalkylene oxide in addition to at least one of the silanes. Polyalkylene oxides according to the invention are, in particular, polyglycols such as polyethylene glycol and polypropylene glycol, as well as other polyalkylene oxides made from monomers with 2 to 6 carbon atoms. Preferably, the functional layer comprises at least one polyalkylene oxide in a proportion of at least 2 wt.%, more preferably at least 3 wt.%, more preferably at least 4 wt.%, more preferably at least 5 wt.%, more preferably at least 6 wt.%, more preferably at least 7 wt.%, and more preferably at least 8 wt.%. More preferably, the functional layer comprises at least one polyalkylene oxide in a proportion of at most 90 wt.%, more preferably at most 85 wt.%, more preferably at most 80 wt.%, more preferably at most 75 wt.%, and more preferably at most 70 wt.%.-%, more preferably at most 68 wt.%, more preferably at most 65 wt.%. In preferred embodiments, the functional layer comprises at least one polyalkylene oxide with a proportion of 1 to 90 wt.%, more preferably 2 to 85 wt.%, more preferably 3 to 80 wt.%, more preferably 4 to 75 wt.%. In a particularly preferred embodiment, the functional layer comprises the polyalkylene oxide with a proportion of 8 to 65 wt.%. The polyalkylene oxide reduces the friction between the optical fibers and improves the mechanical stability of the optical fibers. The polyalkylene oxide also improves the cohesion of optical fibers, for example in an optical fiber bundle. <p xml:id="_ab747a0347" n="0070">In preferred embodiments, the polyalkylene oxide has a chain length of at least 3, more preferably at least 4, more preferably at least 5, more preferably at least 6, more preferably at least 7, and more preferably at least 8 alkylene oxide units. Preferably, the polyalkylene oxide has a chain length of at most 100, more preferably at most 75, more preferably at most 50, more preferably at most 20, and more preferably at most 14 alkylene oxide units. In embodiments, the polyalkylene oxide has a chain length of 3 to 100, more preferably 4 to 50, and more preferably 6 to 20 alkylene oxide units. In particularly preferred embodiments, the polyalkylene oxide has a chain length of 7 to 14 alkylene oxide units. It is advantageous to use polyalkylene oxides that are liquid at room temperature (20°C, 1013 hPa). <p xml:id="_ab747a0348" n="0071">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 0,1-70< / cell> < / row><row> <cell> Alkylsilane< / cell> <cell> 0,8-65< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> -< / cell> < / row> <row> <cell> fatty acid< / cell> <cell> -< / cell> < / row> <row> <cell> Polyvalent alcohol< / cell> <cell> -< / cell> < / row> <row> <cell>Polyalkylene oxide< / cell> <cell> -90< / cell> < / row> <p xml:id="_ab747a0374" n="0072">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 2-40< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 6-35< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> -< / cell> < / row> <row> <cell> fatty acid< / cell> <cell> -< / cell> < / row> <row> <cell> Polyvalent alcohol< / cell> <cell> -< / cell> < / row> <row> <cell> Polyalkylene oxide< / cell> <cell> 8-65< / cell> < / row> <p xml:id="_ab747a0400" n="0073">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 0,1-70< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 0,8-65< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> -< / cell> < / row> <row> <cell> fatty acid< / cell> <cell> 1-85< / cell> < / row> <row> <cell> Polyvalent alcohol< / cell> <cell> -< / cell> < / row> <row> <cell> Polyalkylene oxide< / cell> <cell> -90< / cell> < / row> <p xml:id="_ab747a0426" n="0074">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 2-40< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 6-35< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> -< / cell> < / row> <row> <cell> fatty acid< / cell> <cell> 7-56< / cell> < / row> <row> <cell> Polyvalent alcohol< / cell> <cell> -< / cell> < / row> <row> <cell> Polyalkylene oxide< / cell> <cell> 8-65< / cell> < / row> <p xml:id="_ab747a0452" n="0075">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 0,1-70< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 0,8-65< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> 1-90< / cell> < / row> <row> <cell> fatty acid< / cell> <cell> 1-85< / cell> < / row> <row> <cell> Polyvalent alcohol< / cell> <cell> 3-90< / cell> < / row> <row> <cell> Polyalkylene oxide< / cell> <cell> -90< / cell> < / row> <p xml:id="_ab747a0478" n="0076">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 2-40< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 6-35< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> 21-65< / cell> < / row> <row> <cell> fatty acid< / cell> <cell> 7-56< / cell> < / row> <row> <cell> Polyvalent alcohol< / cell> <cell> 30-75< / cell> < / row> <row> <cell> Polyalkylene oxide< / cell> <cell> 8-65< / cell> < / row> <p xml:id="_ab747a0504" n="0077">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 0,1-70< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 0,8-65< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> 1-90< / cell> < / row> <row> <cell> fatty acid< / cell> <cell> 1-85< / cell> < / row> <row> <cell> Polyvalent alcohol< / cell> <cell> 3-90< / cell> < / row> <row> <cell> Polyalkylene oxide< / cell> <cell> -90< / cell> < / row> <p xml:id="_ab747a0530" n="0078">In one embodiment, the functional layer comprises the following compounds: <title desc="title">< / title> <row> <cell> Functional silane< / cell> <cell> 2-40< / cell> < / row> <row> <cell> Alkylsilane< / cell> <cell> 6-35< / cell> < / row> <row> <cell> PEG-silane< / cell> <cell> 21-65< / cell> < / row> <row> <cell> fatty acid< / cell> <cell> 7-56< / cell> < / row> <row> <cell> Polyvalent alcohol< / cell> <cell> 30-75< / cell> < / row> <row> <cell> Polyalkylene oxide< / cell> <cell> 8-65< / cell> < / row> <p xml:id="_ab747a0556" n="0079">IR spectra of functional layers can be recorded by pressing an ATR crystal onto the functional layer. Since the spectra are recorded in ATR mode, the spectrum of a fiber corresponds to the spectrum of the functional layer. The functional layer exhibits characteristic absorption in the infrared region in the Fourier-transform infrared attenuated total reflection (FTIR-ATR) spectrum. The IR spectra of the functional layer on the fibers of this invention are characteristic due to their unique composition. In particular, they differ from the IR spectra of functional layers in the prior art. For example, the functional layers of this invention exhibit—if any—only very weak bands in the wavenumber range around 1750 cm⁻¹. <hi rend="superscript"> -1< / hi> (±25 cm <hi rend="superscript"> -1< / hi> ) which is due to the preferential absence of polyacrylates and polymethacrylates. The same applies to bands in the range of 1590 cm. <hi rend="superscript"> -1< / hi> (±25 cm <hi rend="superscript"> -1< / hi> ) which is due to the preferred absence of aromatic components. Many aromatic compounds are carcinogenic and therefore undesirable. <p xml:id="_ab747a0561" n="0080">Preferably, the functional layer exhibits a ratio of maximum absorption band height in the FTIR-ATR spectrum in the range of 3200 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 3600 cm <hi rend="superscript"> -1< / hi> to the maximum absorption band height in the range of 3800 cm <hi rend="superscript"> -1< / hi> up to 4000 cm <hi rend="superscript"> -1< / hi> of at least 1.3, more preferably of at least 1.4, more preferably of at least 1.5, more preferably of at least 1.6, more preferably of at least 1.7, more preferably of at least 1.8, more preferably of at least 1.9, more preferably of at least 2.0, more preferably of at least 2.1, more preferably of at least 2.2. Preferably, the functional layer exhibits a ratio of the maximum absorption band height in the FTIR-ATR spectrum in the range of 3200 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 3600 cm <hi rend="superscript"> -1< / hi> to the maximum absorption band height in the range of 3800 cm <hi rend="superscript"> -1< / hi> up to 4000 cm <hi rend="superscript"> -1< / hi> of at most 35, more preferably of at most 30, more preferably of at most 25, more preferably of at most 20, more preferably of at most 15, more preferably of at most 10, more preferably of at most 9, more preferably of at most 8, more preferably of at most 7, more preferably of at most 6. Preferably, the functional layer exhibits a ratio of the maximum absorption band height in the FTIR-ATR spectrum in the range of 3200 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 3600 cm <hi rend="superscript"> -1< / hi> to the maximum absorption band height in the range of 3800 cm <hi rend="superscript"> -1< / hi> up to 4000 cm <hi rend="superscript"> -1< / hi> from 1.3 to 35, more preferably 1.4 to 30, more preferably 1.5 to 25, more preferably 1.6 to 6. The absorption described here is caused, for example, by an advantageous ratio of the functional silane and / or the optional polyvalent alcohol to the other components of the functional layer. The relative absorption described here is 3200 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 3600 cm <hi rend="superscript"> -1< / hi> If the ratio of functional silane to the other components of the functional layer is too low, the functional layer's adhesion to the cladding layer is poor. Furthermore, the bondability of the functional layer to other layers, such as an adhesive layer in a composite of optical fiber bundles, is reduced. Is the relative absorption described here of 3200 cm⁻¹ <hi rend="superscript"> -1< / hi> up to 3600 cm <hi rend="superscript"> -1< / hi> Conversely, if the ratio of functional silane to the other components of the functional layer is too high, the friction between the optical fibers increases, and the sliding properties decrease. <p xml:id="_ab747a0578" n="0081">Preferably, the functional layer exhibits a ratio of maximum absorption band height in the FTIR-ATR spectrum in the range of 800 cm. <hi rend="superscript"> -1< / hi> up to 1200 cm <hi rend="superscript"> -1< / hi> to the maximum absorption band height in the range of 1500 cm <hi rend="superscript"> -1< / hi> up to 1900 cm <hi rend="superscript"> -1< / hi> of at least 1.1, more preferably of at least 1.2, more preferably of at least 1.3, more preferably of at least 1.4, more preferably of at least 1.5, more preferably of at least 1.6, more preferably of at least 1.7, more preferably of at least 1.8, more preferably of at least 1.9, more preferably of at least 2.0. Preferably, the functional layer exhibits a ratio of the maximum absorption band height in the FTIR-ATR spectrum in the range of 800 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 1200 cm <hi rend="superscript"> -1< / hi> to the maximum absorption band height in the range of 1500 cm <hi rend="superscript"> -1< / hi> up to 1900 cm <hi rend="superscript"> -1< / hi> of at most 300, more preferably of at most 200, more preferably of at most 100, more preferably of at most 50, more preferably of at most 30, more preferably of at most 20, more preferably of at most 10, more preferably of at most 7, more preferably of at most 6, more preferably of at most 5. Preferably, the functional layer exhibits a ratio in the FTIR-ATR spectrum of the maximum absorption band height in the range of 800 nm to 1200 nm to the maximum absorption band height in the range of 1500 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 1900 cm <hi rend="superscript"> -1< / hi> from 1.3 to 300, more preferably 1.4 to 250, more preferably 1.5 to 200, more preferably 2.0 to 10. The absorption described here is caused, for example, by an advantageous ratio of the functional silane, the optional alkylsilane and / or the optional PEG-silane, particularly to undesired photopolymerizable or photopolymerized compounds. The relative absorption described here is 800 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 1200 cm <hi rend="superscript"> -1< / hi> If the concentration is too low, the ratio of photopolymerizable or photopolymerized compounds is too high. Such functional layers are not without health risks. <p xml:id="_ab747a0591" n="0082">Preferably, the functional layer exhibits a ratio of the maximum absorption band height in the FTIR-ATR spectrum in the range of 2700 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 3000 cm <hi rend="superscript"> -1< / hi> to the maximum absorption band height in the range of 1500 cm <hi rend="superscript"> -1< / hi> up to 1900 cm <hi rend="superscript"> -1< / hi> of at least 1.1, more preferably of at least 1.2, more preferably of at least 1.3, more preferably of at least 1.4, more preferably of at least 1.5, more preferably of at least 1.6, more preferably of at least 1.7, more preferably of at least 1.8, more preferably of at least 1.9, more preferably of at least 2.0. Preferably, the functional layer exhibits a ratio of the maximum absorption band height in the FTIR-ATR spectrum in the range of 2700 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 3000 cm <hi rend="superscript"> -1< / hi> to the maximum absorption band height in the range of 1500 cm <hi rend="superscript"> -1< / hi> up to 1900 cm <hi rend="superscript"> -1< / hi> of at most 300, more preferably of at most 200, more preferably of at most 100, more preferably of at most 50, more preferably of at most 30, more preferably of at most 20, more preferably of at most 10, more preferably of at most 7, more preferably of at most 6, more preferably of at most 5. Preferably, the functional layer exhibits a ratio of the maximum absorption band height in the FTIR-ATR spectrum in the range of 2700 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 3000 cm <hi rend="superscript"> -1< / hi> The maximum absorption band height in the range of 1500 and 1900 nm is from 1.3 to 300, more preferably from 1.4 to 250, more preferably from 1.5 to 200, and more preferably from 2.0 to 5. The absorption described here is caused, for example, by an advantageous ratio of the functional silane, the optional alkyl silane, the optional PEG silane, and / or the optional fatty acid, particularly to undesired photopolymerizable or photopolymerized compounds. The relative absorption described here is 2700 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 3000 cm <hi rend="superscript"> -1< / hi> If the amount of photopolymerizable or photopolymerized compounds is too low, the ratio of these functional layers is too high. Such layers are not harmless to health and can cause harm to the patient. <p xml:id="_ab747a0604" n="0083">Preferably, the functional layer exhibits a ratio of maximum absorption band height in the FTIR-ATR spectrum in the range of 3200 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 3600 cm <hi rend="superscript"> -1< / hi> to the maximum absorption band height in the range of 1500 cm <hi rend="superscript"> -1< / hi> up to 1900 cm <hi rend="superscript"> -1< / hi> of at least 1.1, more preferably of at least 1.2, more preferably of at least 1.3, more preferably of at least 1.4, more preferably of at least 1.5. Preferably, the functional layer exhibits a ratio of the maximum absorption band height in the FTIR-ATR spectrum in the range of 3200 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 3600 cm <hi rend="superscript"> -1< / hi> The maximum absorption band height in the range of 1500 to 1900 nm is at most 3.0, more preferably at most 2.5, more preferably at most 2.2, and more preferably at most 2.0. Preferably, the functional layer exhibits a ratio of the maximum absorption band height in the FTIR-ATR spectrum in the range of 3200 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 3600 cm <hi rend="superscript"> -1< / hi> to the maximum absorption band height in the range of 1500 cm <hi rend="superscript"> -1< / hi> up to 1900 cm <hi rend="superscript"> -1< / hi> from 1.1 to 3, more preferably 1.1 to 2.5, more preferably 1.1 to 2.0, or 1.2 to 2.5. The absorption described here is caused, for example, by an advantageous ratio of the functional silane and / or the optional polyvalent alcohol, particularly to undesired photopolymerizable or photopolymerized compounds. The relative absorption described here is 3200 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 3600 cm <hi rend="superscript"> -1< / hi> If the concentration is too low, the ratio of photopolymerizable or photopolymerized compounds is too high. Such functional layers are not without health risks. <p xml:id="_ab747a0617" n="0084">Preferably, the functional layer exhibits a ratio of maximum absorption band height in the FTIR-ATR spectrum in the range of 800 cm. <hi rend="superscript"> -1< / hi> up to 1200 cm <hi rend="superscript"> -1< / hi> to the maximum absorption band height in the range of 2700 cm <hi rend="superscript"> -1< / hi> up to 3000 cm <hi rend="superscript"> -1< / hi> of at least 1.1, more preferably of at least 1.2, more preferably of at least 1.3, more preferably of at least 1.4. Preferably, the functional layer exhibits a ratio of the maximum absorption band height in the FTIR-ATR spectrum in the range of 800 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 1200 cm <hi rend="superscript"> -1< / hi> to the maximum absorption band height in the range of 3200 cm <hi rend="superscript"> -1< / hi> up to 3600 cm <hi rend="superscript"> -1< / hi> preferably at most 35, more preferably at most 30, more preferably at most 25, more preferably at most 20, more preferably at most 15, more preferably at most 10, more preferably at most 9.0, more preferably at most 5, more preferably at most 3.0, more preferably at most 2.0. Preferably, the functional layer exhibits a ratio of the maximum absorption band height in the FTIR-ATR spectrum in the range of 800 cm⁻¹. <hi rend="superscript"> -1< / hi> up to 1200 cm <hi rend="superscript"> -1< / hi> to the maximum absorption band height in the range of 3200 cm <hi rend="superscript"> -1< / hi> up to 3600 cm <hi rend="superscript"> -1< / hi> from 1.1 to 35, more preferably 1.2 to 15, more preferably 1.3 to 2.0. The absorption described here is caused, for example, by an advantageous ratio of the functional silane and / or the optional polyvalent alcohol, in particular to functional silane, optional alkyl silane, and / or optional PEG silane. If the relative absorption described here is too low from 800 nm to 1200 nm, the ratio of functional silane is too low. If the relative absorption described here is too low from 800 nm to 1200 nm, the ratio of functional silane is too low. <hi rend="superscript"> -1< / hi> up to 1200 cm <hi rend="superscript"> -1< / hi> The ratio of functional silane is too high. <p xml:id="_ab747a0632" n="0085">For good sliding action between optical fibers without them sticking together, the functional layer should have suitable coefficients of friction. The coefficient of friction can be measured on the surface of the functional layer using a method known to those skilled in the art. For example, the measurement can be carried out by moving an optical fiber article or a corresponding glass rod made of the same material as the fiber article (test article) at an angle of 90° to a friction partner, which is also formed from an optical fiber article or corresponding glass rod, with a normal force Fn of 0.5 N at a speed of 10 mm / min. The movement is longitudinal, relative to the test article. The friction partner is also formed from an optical fiber article or corresponding glass rod.Depending on the coefficient of friction, a frictional force is generated, which is determined as a measure of the coefficient of friction (coefficient of friction = quotient of frictional force and normal force). Preferably, the functional layer has a coefficient of friction of at most 0.5, more preferably at most 0.45, more preferably at most 0.35, more preferably at most 0.3, more preferably at most 0.2, more preferably at most 0.15. Preferably, the functional layer has a coefficient of friction of at least 0.001, more preferably at least 0.01, more preferably at least 0.03, more preferably at least 0.05. In preferred embodiments, the functional layer has a coefficient of friction of 0.001 to 0.5, more preferably from 0.01 to 0.35, more preferably from 0.03 to 0.2. In particularly preferred embodiments, the functional layer has a coefficient of friction of less than 0.2.If the coefficient of friction is too high, the optical fibers slide against each other less smoothly, leading to microcracks and breaks. If the coefficient of friction is too low, the optical fibers, for example within an optical fiber bundle, do not hold together as well.<p xml:id="_ab747a0633" n="0086">The surface of the functional layer should have a suitable contact angle to ensure, for example, good wettability of the optical fiber with an adhesive in a composite of optical fiber bundles. The contact angle can be measured on the surface of the functional layer using a method known to those skilled in the art (for example, according to ISO DIN 55660-2:2011). Preferably, the functional layer has a contact angle of at least 10°, more preferably at least 20°, more preferably at least 40°, more preferably at least 60°, and more preferably at least 80°. Preferably, the functional layer has a contact angle of at most 125°, more preferably at most 100°. In preferred embodiments, the functional layer has a contact angle of 20° to 120°, more preferably from 40° to 100°, and more preferably from 60° to 100°.In particularly preferred embodiments, the functional layer has a contact angle of 50° to 85°. If the contact angle is too small, the surface of the functional layer is too hydrophilic, resulting in reduced chemical protection. If the contact angle is too large, the wettability of the surface of the functional layer, for example with an adhesive layer in a composite, is reduced. <p xml:id="_ab747a0634" n="0087">The functional layer should adhere well to the fiber surface, allow good but limited adhesion between the fibers, and enable good bonding of a fiber article, especially a fiber bundle, to other materials, e.g., a sleeve. The result obtained in the squeeze-out test described below is a measure of the adhesion of the fibers to one another. In the squeeze-out test, a fiber bundle, or for comparison, several (possibly different) fiber bundles with a diameter of 5 mm, are bonded into stainless steel sleeves using identical adhesive, for example, a two-component epoxy resin adhesive, preferably solvent-free and room-temperature curing (e.g., Araldite AY103-1 hardener; REN HY 956, Huntsman; curing at 60°C for 2 hours). The end surface of the fiber bundles is ground and polished. Using a test mandrel with a round cross-section, a diameter of 2.5 mm, and a flat end surface, the squeeze-out forces are then measured, at least qualitatively.The force relative to each other is determined by pressing the test mandrel in the fiber direction onto the fibers bonded in the sleeve. The ejection speed is 6 mm / min. Two failure modes occur. In the first case, the bond between the fiber bundle and the stainless steel sleeve fails (the entire fiber bundle is pushed out of the sleeve). In the second case, the bond between the fibers themselves fails. In the first case, the adhesion between the fibers is better than the adhesion of the fiber bundle to the stainless steel sleeve. In the second case, this indicates insufficient adhesion of the adhesive to the glass fiber, which suggests inadequate adhesion of the functional layer. The detected maximum force required to displace the bonded fiber bundle located under the test mandrel relative to the stainless steel sleeve, or the surrounding fibers, is the ejection force. <p xml:id="_ab747a0635" n="0088">Preferably, the optical fiber article has a pull-out force of at least 250 N, more preferably at least 300 N, more preferably at least 350 N, more preferably at least 400 N, and more preferably at least 500 N. In embodiments, the optical fiber article has a pull-out force of at most 5,000 N, more preferably at most 4,500 N, more preferably at most 4,000 N, more preferably at most 3,500 N, and more preferably at most 3,000 N. In preferred embodiments, the optical fiber article has a pull-out force of 100 to 5,000 N, more preferably from 150 to 4,500 N, and more preferably from 200 to 4,000 N. If the pull-out force is too low, the functional layer adheres poorly to the surface of the cladding layer, or the adhesion-promoting agent of the functional layer is insufficient. <p xml:id="_ab747a0636" n="0089">Preferably, the optical fiber article comprises fibers with a high break length, in particular at least 20 m. More preferably, the fibers have a break length of at least 30 m, more preferably at least 40 m, more preferably at least 50 m, more preferably at least 60 m, more preferably at least 70 m, more preferably at least 80 m, and more preferably at least 90 m. If the length is too short, the optical fibers break too frequently and are unsuitable for use as light guides and / or image guides. Furthermore, broken optical fibers pose a health hazard. The break length can be measured as follows: The test fiber is provided as a continuous fiber with a length of at least 2 km on a spool (e.g., a standard polystyrene spool with a circumference of 0.49 m).A tensile-bending device subjects the fiber under test to a defined bending load by rewinding it over four rollers with a radius of 6 mm. The test fiber, which is under constant tension, is unwound from a braked spool and wound onto a second, motor-driven spool. If a fiber break occurs, the unwinding process is stopped by a breakage sensor. The fiber is then re-laid to continue the measurement. The break length is the fiber length at which the probability of breakage is 63% (Weibull distribution). Preferably, at least 10 measurements, and preferably 25 measurements, are performed for the calculation. The test is carried out at a tensile force of 25 ± 1 cN and a rewinding speed of 25 ± 1 rpm (corresponding to 12.5 m / min). <p xml:id="_ab747a0637" n="0090">The optical fiber article should contain fibers that exhibit high mechanical stability and are as resistant to breakage as possible. The fibers' susceptibility to breakage can be measured using the break loop test according to DIN 58141-6:2011. This test serves to determine the basic strength of a fiber article. The method determines the mechanical bending radius of optical fibers by subjecting them to a stressed 360° loop of decreasing tension until fiber breakage occurs (destructive testing). The result of the break loop test is a bending radius, i.e., a measure of how far the fiber can be bent without breaking. The fibers of the optical fiber article preferably have a bending radius of less than 10 mm, particularly less than 5 mm or even less than 3 mm. The fibers also retain a very small bending radius even after hydrolytic stress.Thus, the bending radius of the fibers preferably remains below 12 mm, 8 mm, or 6 mm even after storage in water at 50°C for 5 days. The fact that the fibers largely retain their good bending properties even under hydrolytic stress is a major advantage with regard to the cleaning and sterilization of optical fiber products. <p xml:id="_ab747a0638" n="0091">Acrylates, methacrylates, vinyl and styrene compounds, and other unsaturated compounds that cure under UV radiation are potentially harmful to the environment and can cause health problems in humans. The functional layer should therefore contain the lowest possible proportion of photopolymerizable and / or photopolymerized substances. <p xml:id="_ab747a0639" n="0092">Preferably, the optical fiber article has a content of photopolymerized polymers in the functional layer, based on the mass of the functional layer, of less than 0.8 wt.%, more preferably less than 0.6 wt.%, more preferably less than 0.4 wt.%, more preferably less than 0.2 wt.%, more preferably less than 0.1 wt.%, more preferably less than 0.05 wt.%, more preferably less than 0.01 wt.%, more preferably less than 0.005 wt.%, more preferably less than 0.001 wt.%. In particularly preferred embodiments, the functional layer is free of photopolymerized polymers. "Photopolymerized polymers" means polymers that can be produced by polymerizing UV-curable mono- or oligomers. Photopolymerized polymers preferably avoided according to the invention are, for example, polyacrylates, polymethacrylates, polyvinyl polymers, polystyrene, and / or derivatives thereof.If the proportion of photopolymerized polymers in the functional layer is too high, the optical fiber article may pose potential health risks. Particularly in medical devices that are frequently autoclaved, photopolymerized polymers may release residual monomers or photoinitiators. Therefore, especially in medical devices that come into contact with human organs, such as endoscopes, the proportion of photopolymerized polymers should not exceed the levels described here. In particular, the content of photopolymerizable mono- and / or oligomers in the functional layer should also be low. Specifically, the content of acrylates, methacrylates, styrene, and vinyl compounds in the functional layer is preferably limited to less than 1 wt%, less than 0.1 wt%, or less than 0.01 wt%. <p xml:id="_ab747a0640" n="0093">Photoinitiators are potentially harmful to human health. In preferred embodiments, the optical fiber article has a photoinitiator and / or derivative content in the functional layer of less than 5 wt.%, more preferably less than 4 wt.%, more preferably less than 3 wt.%, more preferably less than 2 wt.%, more preferably less than 1 wt.%, more preferably less than 0.8 wt.%, more preferably less than 0.6 wt.%, more preferably less than 0.4 wt.%, more preferably less than 0.2 wt.%, more preferably less than 0.1 wt.%, more preferably less than 0.05 wt.%, more preferably less than 0.01 wt.%, more preferably less than 0.005 wt.%, more preferably less than 0.001 wt.%.In particularly preferred embodiments, the functional layer is free of photoinitiators and / or their derivatives. "Photoinitiators and / or their derivatives" refers to chemical compounds that, upon absorption of photons such as UV light, form reactive species capable of initiating a reaction such as polymerization. Photoinitiators and / or their derivatives can also refer to the already reacted compounds. Photoinitiators according to the invention include, for example, radical photoinitiators, cationic photoinitiators, and / or thermolatent photoinitiators. Such photoinitiators include, for example, acylphosphine oxide, alpha-alkoxy aryl ketone, or aryldiazonium, or combinations thereof. If the proportion of photoinitiators and / or their derivatives in the functional layer is too high, the optical fiber article may pose potential health risks. This is particularly undesirable in medical devices. <p xml:id="_ab747a0641" n="0094">The functional layer should be thoroughly dried and have a low water content. Preferably, the optical fiber article has a residual water content in the functional layer, based on the mass of the functional layer, of less than 5 wt.%, more preferably less than 4 wt.%, more preferably less than 3 wt.%, more preferably less than 2 wt.%, more preferably less than 1 wt.%, more preferably less than 0.8 wt.%, more preferably less than 0.6 wt.%, more preferably less than 0.4 wt.%, even more preferably less than 0.2 wt.%, more preferably less than 0.1 wt.%, more preferably less than 0.05 wt.%, more preferably less than 0.01 wt.%, more preferably less than 0.005 wt.%, and more preferably less than 0.001 wt.%. In particularly preferred embodiments, the functional layer is free of water.If the proportion of water is too high, the insulating protective effect of the functional layer is reduced and the mechanical and chemical stability of the optical fiber article is reduced. <p xml:id="_ab747a0642" n="0095">The functional layer should be thoroughly dried and have a low residual content of water-miscible solvents. Such solvents are, in particular, aliphatic ethers or alcohols with up to 10 carbon atoms and / or carboxylic acids with up to 6 carbon atoms. Examples of water-miscible solvents according to the invention are acetic acid, ethanol, isopropanol, dipropylene glycol monomethyl ether, or tripropylene glycol monomethyl ether. Preferably, the optical fiber article has a residual content of water-miscible solvents in the functional layer, based on the mass of the functional layer, of less than 5 wt%, more preferably less than 4 wt%, and more preferably less than 3 wt%. <p xml:id="_ab747a0643" n="0096">wt.%, further preferably less than 2 wt.%, further preferably less than 1 wt.%, further preferably less than 0.8 wt.%, further preferably less than 0.6 wt.%, further preferably less than 0.4 wt.%, even more preferably less than 0.2 wt.%, further preferably less than 0.1 wt.%, further preferably less than 0.05 wt.%, further preferably less than 0.01 wt.%, further preferably less than 0.005 wt.%, further preferably less than 0.001 wt.%. In particularly preferred embodiments, the functional layer is free of water-miscible solvents. If the proportion of water-miscible solvents is too high, the insulating protective effect of the functional layer is reduced, and the mechanical and chemical stability of the optical fiber article is reduced. <p xml:id="_ab747a0644" n="0097">In particularly preferred embodiments, the optical fiber article has a residual content of short-chain carboxylic acids with up to 10 carbon atoms in the functional layer, based on the mass of the functional layer, of less than 5 wt.%, more preferably less than 4 wt.%, more preferably less than 3 wt.%, more preferably less than 2 wt.%, more preferably less than 1 wt.%, more preferably less than 0.8 wt.%, more preferably less than 0.6 wt.%, more preferably less than 0.4 wt.%, even more preferably less than 0.2 wt.%, more preferably less than 0.1 wt.%, more preferably less than 0.05 wt.%, more preferably less than 0.01 wt.%, more preferably less than 0.005 wt.%, and more preferably less than 0.001 wt.%. Examples of such short-chain carboxylic acids are acetic acid or citric acid.In particularly preferred embodiments, the functional layer is free of short-chain carboxylic acids with up to 10 carbon atoms. <p xml:id="_ab747a0645" n="0098">In particularly preferred embodiments, the optical fiber article has a residual content of aliphatic alcohols with up to four carbon atoms in the functional layer, based on the mass of the functional layer, of less than 5 wt.%, more preferably less than 4 wt.%, more preferably less than 3 wt.%, more preferably less than 2 wt.%, more preferably less than 1 wt.%, more preferably less than 0.8 wt.%, more preferably less than 0.6 wt.%, more preferably less than 0.4 wt.%, even more preferably less than 0.2 wt.%, more preferably less than 0.1 wt.%, more preferably less than 0.05 wt.%, more preferably less than 0.01 wt.%, more preferably less than 0.005 wt.%, and more preferably less than 0.001 wt.%. Examples of such short-chain carboxylic acids are ethanol or isopropanol.In particularly preferred embodiments, the functional layer is free of aliphatic alcohols with up to four carbon atoms. <p xml:id="_ab747a0646" n="0099">The optical fiber product should be well-suited for use in medical devices such as endoscopes. For medical applications, the optical fiber product should be as resistant as possible, even with frequent autoclaving. Therefore, it is important that the optical fiber product contains as few halogens as possible.Preferably, the optical fiber article has a halogen content in the functional layer of less than 500 ppm (w / w), more preferably less than 400 ppm (w / w), more preferably less than 300 ppm (w / w), more preferably less than 250 ppm (w / w), more preferably less than 200 ppm (w / w), more preferably less than 150 ppm (w / w), more preferably less than 100 ppm (w / w), more preferably less than 80 ppm (w / w), more preferably less than 60 ppm (w / w), more preferably less than 40 ppm (w / w), more preferably less than 20 ppm (w / w), and even more preferably less than 10 ppm (w / w). In particularly preferred embodiments, the functional layer is free of halogens. Halogens include, for example, chlorine, fluorine, bromine, and / or iodine or their anions. The term "halogen" includes in particular the halides, and preferably also other halogen compounds.An excessively high concentration of halogens in the functional layer leads to the formation of the corresponding halo acids, particularly during steam sterilization. These halo acids can reduce the durability of the optical fiber and may even leach out of it. In particular, halo acids attack materials such as the stainless steel used in autoclaves and endoscopes, leading to the formation of unwanted rust. <p xml:id="_ab747a0647" n="0100">In particular, residual chloride content in the functional layer can lead to the formation of hydrochloric acid. Therefore, the optical fiber article should contain as little chloride as possible. Preferably, the optical fiber article has a chloride content in the functional layer of less than 500 ppm (w / w), more preferably less than 400 ppm (w / w), more preferably less than 300 ppm (w / w), more preferably less than 250 ppm (w / w), more preferably less than 200 ppm (w / w), more preferably less than 150 ppm (w / w), more preferably less than 100 ppm (w / w), more preferably less than 80 ppm (w / w), more preferably less than 60 ppm (w / w), more preferably less than 40 ppm (w / w), more preferably less than 20 ppm (w / w), and even more preferably less than 10 ppm (w / w). In particularly preferred embodiments, the functional layer is chloride-free.An excessively high chloride content reduces the corrosion resistance of the optical fiber product. <p xml:id="_ab747a0648" n="0101">For the optical fiber article to be suitable for medical or diagnostic applications, it should be biocompatible. Preferably, the fiber article is biocompatible according to ISO 10993-1:2018. Preferably, the optical fiber article is biocompatible in the cytotoxicity test according to ISO 10993-5:2009. <p xml:id="_ab747a0649" n="0102"> Preferably, the optical fiber product is biocompatible according to ISO 10993-1:2018 and / or ISO 10993-5:2009. Preferably, the optical fiber product is biocompatible according to USP Class VI. <p xml:id="_ab747a0650" n="0103">The optical fiber product should only contain compounds that pose as few risks to human health as possible. For example, people come into contact with the optical fiber product during its manufacture and processing. Preferably, the optical fiber product contains a proportion of compounds with a maximum workplace concentration (MAK value) of less than 240 mg / m³. <hi rend="superscript"> -3< / hi> in the functional layer, based on the mass of the functional layer, of less than 5 wt.%, more preferably less than 4 wt.%, more preferably less than 3 wt.%, more preferably less than 2 wt.%, more preferably less than 1 wt.%, more preferably less than 0.8 wt.%, more preferably less than 0.6 wt.%, more preferably less than 0.4 wt.%, even more preferably less than 0.2 wt.%, more preferably less than 0.1 wt.%, more preferably less than 0.05 wt.%, more preferably less than 0.01 wt.%, more preferably less than 0.005 wt.%, more preferably less than 0.001 wt.%. <p xml:id="_ab747a0652" n="0104">Preferably, the optical fiber comprises a fiber core and a cladding or cladding layer, with the functional layer then arranged on the cladding layer. In preferred embodiments, the core layer consists of a core glass. In other embodiments, the fiber core consists of a core polymer. Suitable core polymers are, for example, polyacrylate, polymethacrylate, polyurethane, polyester, polyamide, and mixtures thereof. The core glass can be a multi-component glass; in particular, the core glass can have a combination of several oxides, i.e., it can be an oxide glass. Quartz glass is also suitable as a core glass in principle, but unlike multi-component glasses, it has a very high melting point, which makes processing more difficult and, above all, more energy-intensive. <p xml:id="_ab747a0653" n="0105">Preferably, the optical fiber comprises a cladding layer that surrounds the fiber core. In preferred embodiments, the cladding layer comprises a cladding glass. The cladding glass can be a multi-component glass; in particular, the cladding glass can have a combination of several oxides, i.e., be an oxide glass. In other embodiments, the cladding layer comprises a cladding polymer. Examples of cladding polymers according to the invention are polyacrylate, polymethacrylate, polyurethane, polyester, polyamide, and mixtures thereof. <p xml:id="_ab747a0654" n="0106">In certain embodiments, the optical fiber is a quartz fiber. In one particular embodiment, the cladding layer and / or the fiber core has a quartz content of at least 76 wt.%, more preferably at least 81 wt.%, more preferably at least 84 wt.%, more preferably at least 88 wt.%, more preferably at least 92 wt.%, more preferably at least 95 wt.%, more preferably at least 97 wt.%, and more preferably at least 98 wt.%. A higher quartz content results in increased chemical resistance and increased temperature resistance. <p xml:id="_ab747a0655" n="0107">In a particular embodiment, the core glass has the following features: Preferably, the core glass contains at least 8 wt.%, more preferably at least 23 wt.%, more preferably at least 24 wt.%, and particularly preferably at least 25 wt.% or even at least 26 wt.% SiO₂. <hi rend="subscript"> 2< / hi> In a special embodiment, the core glass can even contain at least 28.3 wt.% SiO₂. <hi rend="subscript"> 2< / hi> containing, most preferably at least 34 wt.% SiO₂ <hi rend="subscript"> 2< / hi> In some preferred embodiments, the core glass even comprises at least 35 wt.% SiO₂. <hi rend="subscript"> 2< / hi> , preferably at least 42 wt.%. <p xml:id="_ab747a0660" n="0108">Preferred core glasses of these inventions have the following composition in weight percent: <title desc="title">< / title> <row> <cell>B <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> < / cell> <cell> 0< / cell> <cell> 24< / cell> < / row> <row> <cell>Not. <hi rend="subscript"> 2< / hi> < / cell> <cell> 23< / cell> <cell> 62,1< / cell> < / row> <row> <cell>Al <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> < / cell> <cell> 0< / cell> <cell> 10< / cell> < / row> <row> <cell>Li <hi rend="subscript"> 2< / hi> About< / cell> <cell> 0< / cell> <cell> 10< / cell> < / row> <row> <cell>So <hi rend="subscript"> 2< / hi> O< / cell> <cell> 0< / cell> <cell> 18,5< / cell> < / row> <row> <cell>K <hi rend="subscript"> 2< / hi> O< / cell> <cell> 0< / cell> <cell> 25,7< / cell> < / row> <row> <cell> BaO< / cell> <cell> 0< / cell> <cell> 57,8< / cell> < / row> <row> <cell> ZnO< / cell> <cell> 0< / cell> <cell> 40< / cell> < / row> <row> <cell>to <hi rend="subscript"> 2< / hi> A <hi rend="subscript"> 3< / hi> < / cell> <cell> 0< / cell> <cell> 25< / cell> < / row> <row> <cell>ZrO <hi rend="subscript"> 2< / hi> < / cell> <cell> 0< / cell> <cell> 10< / cell> < / row> <row> <cell>HfO <hi rend="subscript"> 2< / hi> < / cell> <cell> 0< / cell> <cell> 14,2< / cell> < / row> <row> <cell>SnO <hi rend="subscript"> 2< / hi> < / cell> <cell> >0< / cell> <cell> 2< / cell> < / row> <row> <cell> MgO< / cell> <cell> 0< / cell> <cell> 8< / cell> < / row> <row> <cell> CaO< / cell> <cell> 0< / cell> <cell> 8< / cell> < / row> <row> <cell> SrO< / cell> <cell> 0< / cell> <cell> 24,4< / cell> < / row> <row> <cell>The <hi rend="subscript"> 2< / hi> The <hi rend="subscript"> 5< / hi> < / cell> <cell> 0< / cell> <cell> 22< / cell> < / row> <row> <cell>AND <hi rend="subscript"> 2< / hi> EITHER <hi rend="subscript"> 3< / hi> < / cell> <cell> 0< / cell> <cell> 11,9< / cell> < / row> <row> <cell>Rb <hi rend="subscript"> 2< / hi> Oh< / cell> <cell> 0< / cell> <cell> 15< / cell> < / row> <row> <cell>Cs <hi rend="subscript"> 2< / hi> A< / cell> <cell> 0< / cell> <cell> 21< / cell> < / row> <row> <cell>GeO <hi rend="subscript"> 2< / hi> < / cell> <cell> 0< / cell> <cell> 7,5< / cell> < / row> <row> <cell> F< / cell> <cell> 0< / cell> <cell> 2< / cell> < / row> <row> <cell>S R <hi rend="subscript"> 2< / hi> The< / cell> <cell> 5< / cell> <cell> 20< / cell> < / row> <row> <cell> Σ MgO, CaO, SrO,ZnO< / cell> <cell> 20< / cell> <cell> 42< / cell> < / row> <p xml:id="_ab747a0782" n="0109">R <hi rend="subscript"> 2< / hi> O is the sum of the contents of all alkali metal oxides. <p xml:id="_ab747a0784" n="0110">It may contain one or more of the following components: Cs <hi rend="subscript"> 2< / hi> O, Rb <hi rend="subscript"> 2< / hi> O, MgO, CaO, SrO, Gd <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , Lu <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , Sc <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , Y <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , In <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , Ga <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> and where <hi rend="subscript"> 3< / hi> . <p xml:id="_ab747a0800" n="0111">The following components should preferably not be present in the core glass, or only in concentrations resulting from unavoidable impurities in the raw materials: TiO₂ <hi rend="subscript"> 2< / hi> , CEO <hi rend="subscript"> 2< / hi> , Nb <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 5< / hi> , MoO <hi rend="subscript"> 3< / hi> , Bi <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , PbO, CdO, Tl <hi rend="subscript"> 2< / hi> O, As <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , Sb <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , SO <hi rend="subscript"> 3< / hi> , SeO <hi rend="subscript"> 2< / hi> , TeO <hi rend="subscript"> 2< / hi> BeO, radioactive elements and coloring components, unless otherwise described in the text. In particular TiO <hi rend="subscript"> 2< / hi> This component should be omitted because it can lead to pronounced absorption in the UV range. In preferred embodiments, the component WO is also omitted. <hi rend="subscript"> 3< / hi> abstained. <p xml:id="_ab747a0818" n="0112">The components TiO <hi rend="subscript"> 2< / hi> , CEO <hi rend="subscript"> 2< / hi> , Nb <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 5< / hi> and / or bi <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> These components can be present in the core glass up to a maximum of 0.5 wt.%, preferably up to 0.3 wt.%, and particularly preferably up to 0.2 wt.%. In a preferred embodiment, the core glass is free of these components. <p xml:id="_ab747a0825" n="0113">Preferably the core glass is free of optically active components, in particular Sm <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , Nd <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , Dy <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , Pr <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , Eu <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , Yb <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , Tb <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , He <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , Tm <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> and / or Ho <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> CEO <hi rend="subscript"> 2< / hi> absorbs in the UV range, so preferred core glasses do not contain CeO <hi rend="subscript"> 2< / hi> contain. <p xml:id="_ab747a0848" n="0114">The content of the components alkaline earth metal oxides, La <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> , Ta <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 5< / hi> , ZrO <hi rend="subscript"> 2< / hi> and HfO <hi rend="subscript"> 2< / hi> The total amount of these components is preferably, and especially for core glasses with refractive indices greater than 1.65, at least 40 wt.%, more preferably at least 42 wt.%, more preferably at least 50 wt.%, and particularly preferably at least 55 wt.%. If the content of these components is too low, the preferred refractive index cannot normally be achieved. Due to formulation requirements, this total should not exceed 72 wt.%. In a specific embodiment, the jacket glass has the following features: <p xml:id="_ab747a0856" n="0115">Preferably the cladding glass contains SiO₂. <hi rend="subscript"> 2< / hi> of >60 wt.%, more preferably >65 wt.% and particularly preferably of at least 69 wt.%. The SiO <hi rend="subscript"> 2< / hi> The SiO₂ content is preferably at most 75 wt.% and particularly preferably up to 73 wt.%. The cladding glass tends to be exposed to stronger environmental influences than the core glass. A high SiO₂ content <hi rend="subscript"> 2< / hi> The presence of this component provides better chemical resistance. Consequently, the content of this component is preferably higher in the cladding glass than in the core glass. <p xml:id="_ab747a0860" n="0116">The coefficient of thermal expansion (CTE) in a temperature range of 20 to 300°C can be the same or different for the fiber core and sheath. In particular, the CTE is different. Preferably, the CTE of the sheath is smaller than the CTE of the fiber core, preferably by at least 1.0 × 10⁻⁶. <hi rend="superscript"> -6< / hi> / K smaller or particularly preferably at least by 2.5*10 <hi rend="superscript"> -6< / hi> / K. The fiber core preferably has a CTE of 6.5*10 <hi rend="superscript"> -6< / hi> up to 10*10 <hi rend="superscript"> -6< / hi> / K on, the mantle has a CTE of 4.5*10 <hi rend="superscript"> -6< / hi> up to 6*10 <hi rend="superscript"> -6< / hi> / K. <p xml:id="_ab747a0867" n="0117">The following table shows some preferred compositions of cladding glasses that can be used together with the core glasses. The cladding glasses contain (in wt.% oxide-based): <title desc="title">< / title> <row> <cell>Not. <hi rend="subscript"> 2< / hi> < / cell> <cell> 70 - 78< / cell> <cell> 63 - 75< / cell> <cell> 75 - 85< / cell> <cell> 62 - 70< / cell> < / row> <row> <cell>Al <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> < / cell> <cell> 5 - 10< / cell> <cell> 1 - 7< / cell> <cell> 1 - 5< / cell> <cell> 1 - 10< / cell> < / row> <row> <cell>B <hi rend="subscript"> 2< / hi> O <hi rend="subscript"> 3< / hi> < / cell> <cell> 5 - 14< / cell> <cell> 0 - 3< / cell> <cell> 10 - 14< / cell> <cell> > 15< / cell> < / row> <row> <cell>Li <hi rend="subscript"> 2< / hi> About< / cell> <cell> free< / cell> <cell> 0 - 1< / cell> <cell> 0 - 3< / cell> <cell> < 0,1< / cell> < / row> <row> <cell>So <hi rend="subscript"> 2< / hi> O< / cell> <cell> 0 - 10< / cell> <cell> 8 - 20< / cell> <cell> 2 - 8< / cell> <cell> 0 - 10< / cell> < / row> <row> <cell>K <hi rend="subscript"> 2< / hi> O< / cell> <cell> 0 - 10< / cell> <cell> 0 - 6< / cell> <cell> 0 - 1< / cell> <cell> 0 - 10< / cell> < / row> <row> <cell> MgO< / cell> <cell> 0 - 1< / cell> <cell> 0 - 5< / cell> <cell> free< / cell> <cell> 0 - 5< / cell> < / row> <row> <cell> CaO< / cell> <cell> 0 - 2< / cell> <cell> 1 - 9< / cell> <cell> free< / cell> <cell> 0 - 5< / cell> < / row> <row> <cell> SrO< / cell> <cell> 0 - 1< / cell> <cell> free< / cell> <cell> free< / cell> <cell> 0 - 5< / cell> < / row> <row> <cell> BaO< / cell> <cell> 0 - 1< / cell> <cell> 0 - 5< / cell> <cell> free< / cell> <cell> 0 - 5< / cell> < / row> <row> <cell> halogen< / cell> <cell> free< / cell> <cell> free< / cell> <cell> free< / cell> <cell> free< / cell> < / row> <p xml:id="_ab747a0952" n="0118"> Chalcogenide glasses are also suitable as core and / or cladding glass, in particular the glasses disclosed in DE 4011553 C1 and EP 0 217195 A1.<p xml:id="_ab747a0953" n="0119">The optical fiber article can comprise one or more optical fibers. The optical fibers can be arranged randomly in a bundle or in optical fiber bundles. The optical fiber article can comprise one or more optical fiber bundles. The optical fiber bundles can be arranged randomly in a bundle or in groups of fiber bundles. The optical fiber article can comprise one or more groups of optical fiber bundles. <p xml:id="_ab747a0954" n="0120">In one embodiment, the optical fiber article comprises at least one optical fiber, more preferably at least two optical fibers, more preferably at least three optical fibers, more preferably at least five optical fibers, more preferably at least seven optical fibers, more preferably at least nine optical fibers, more preferably at least ten optical fibers, and more preferably at least eleven optical fibers. In particularly preferred embodiments, the optical fiber article comprises at least 15 optical fibers, more preferably at least 50 optical fibers, more preferably at least 100 optical fibers, more preferably at least 300 optical fibers, more preferably at least 700 optical fibers, more preferably at least 1,600 optical fibers, more preferably at least 2,800 optical fibers, and more preferably at least 4,700 optical fibers. <p xml:id="_ab747a0955" n="0121">Optical fiber bundles can be bonded together with adhesives to form larger assemblies and / or embedded in sleeves. In preferred embodiments, the optical fiber article has no adhesive layer. In one embodiment, the optical fiber article comprises, in addition to the functional layer, one or more adhesives that can be arranged on or within the functional layer. The optical fiber article can then at least partially contain the reaction product of the functional silane with a reactive adhesive component. Preferably, not the entire optical fiber article is bonded with an adhesive, but only a portion of the article contains the reaction product of the functional silane and at least one adhesive.In one embodiment, the optical fiber article has one or more adhesives on or in the functional layer only over a length of at most 25 mm, in particular at most 15 mm or at most 10 mm. If too large a section of the optical fiber article is bonded, the risk of fiber breakage increases. In another embodiment, the optical fiber article has one or more adhesives on or in the functional layer over a length of at least 1 mm, in particular at least 3 mm. <p xml:id="_ab747a0956" n="0122">Adhesives suitable for use according to the invention, with which optical fibers can be bonded to each other or to other materials, include, for example, epoxy resin adhesives, acrylate adhesives, cyanoacrylate adhesives, polyurethane adhesives, silicone adhesives, phenolic resin adhesives, polysulfide adhesives, and / or bismaleimide adhesives. In embodiments, the fiber article contains less than 10% by weight of adhesive, more preferably less than 8% by weight, more preferably less than 6% by weight, more preferably less than 4% by weight, more preferably less than 2% by weight, more preferably less than 1% by weight, more preferably less than 0.8% by weight, more preferably less than 0.6% by weight, more preferably less than 0.4% by weight, and more preferably less than 0.1% by weight. <p xml:id="_ab747a0957" n="0123">Preferably, the optical fiber article has a functional layer proportion on the optical fiber of at most 10 wt.%, more preferably at most 8 wt.%, more preferably at most 6 wt.%, more preferably at most 4 wt.%, more preferably at most 2 wt.%, more preferably at most 1 wt.%, more preferably at most 0.5 wt.%, more preferably at most 0.2 wt.%, more preferably at most 0.1 wt.%. Preferably, the optical fiber article has a protective layer proportion on the optical fiber of at least 0.001 wt.%, more preferably at least 0.005 wt.%, more preferably at least 0.009 wt.%, more preferably at least 0.012 wt.%, more preferably at least 0.02 wt.%, more preferably at least 1 wt.%, more preferably at least 0.04 wt.%, more preferably at least 0.06 wt.%.-%, more preferably at least 0.08 wt.%. In preferred embodiments, the optical fiber article has a proportion of the protective layer on the optical fiber of 0.001 to 10 wt.%, more preferably 0.005 to 8 wt.%, and more preferably 0.009 to 6 wt.%. If the proportion of the protective layer is too low, the optical fiber loses mechanical, chemical, and thermal stability. If the proportion of the protective layer is too high, the cohesion of the optical fibers, for example in an optical fiber bundle, is reduced. <p xml:id="_ab747a0958" n="0124">Preferably, the functional layer has a thickness of at least 0.1 nm, more preferably at least 0.9 nm, more preferably at least 1.2 nm, more preferably at least 1.5 nm, more preferably at least 1.8 nm, more preferably at least 2.1 nm, and more preferably at least 3 nm. Preferably, the functional layer has a thickness of at most 500 nm, more preferably at most 200 nm, more preferably at most 100 nm, more preferably at most 50 nm, and more preferably at most 20 nm. If the thickness of the functional layer is too small, the optical fiber loses mechanical, chemical, and thermal stability. If the thickness of the functional layer is too large, the cohesion of the optical fibers, for example in an optical fiber bundle, is reduced. <p xml:id="_ab747a0959" n="0125">The optical fiber preferably comprises at least one functional layer. In other embodiments, the optical fiber comprises at least two, three, or four functional layers. Multiple functional layers increase the bending strength of the optical fiber and improve its protection against microcracks. <p xml:id="_ab747a0960" n="0126"> Preferably, the method for manufacturing an optical fiber article comprises the steps: a. providing at least one optical fiber; b. coating at least one part of the optical fiber with a sizing; c. drying the sizing. <p xml:id="_ab747a0961" n="0127"> The optical fiber can be provided, for example, using a drawing process known to those skilled in the art, such as from a preform or using a nozzle process. <p xml:id="_ab747a0962" n="0128"> The coating of the optical fiber can be carried out using a method known to those skilled in the art, for example in a dipping tank, by spraying the fiber or in a roll-to-roll process. <p xml:id="_ab747a0963" n="0129">The dried sizing forms the functional layer. The drying of the sizing influences the properties of the functional layer. The functional layer is preferably dried using a gas mixture. In preferred embodiments, the gas mixture is air. <p xml:id="_ab747a0964" n="0130">The humidity of the gas mixture influences the drying process and the material properties of the functional layer. The term "humidity" refers to relative humidity. Preferably, the gas mixture has a humidity of at least 10%, more preferably at least 15%, more preferably at least 20%, more preferably at least 25%, more preferably at least 30%, and more preferably at least 35%. Preferably, the gas mixture has a humidity of at most 95%, more preferably at most 85%, more preferably at most 75%, more preferably at most 60%, and even more preferably at most 55%. In preferred embodiments, the gas mixture has a humidity of 10% to 95%, 15% to 85%, or 20% to 60%. If the humidity of the gas mixture is too low, the functional silane and / or the optional alkylsilane and / or the optional PEG-silane, in particular, react less effectively with the fiber surface.This results in poorer adhesion of the functional layer to the fiber. If the humidity of the gas mixture is too high, the sizing dries too slowly, impairing the mechanical and chemical resistance of the optical fiber. Furthermore, excessively high humidity leads to an excessive residual content of water and / or water-miscible solvents in the functional layer. <p xml:id="_ab747a0965" n="0131">Temperature influences the drying process and the material properties of the functional layer. Temperature refers to the temperature of the gas mixture surrounding the fiber during drying and / or any contact surface with which the fiber may be in contact during drying, e.g., a heated or unheated spool and / or other fibers. Preferably, the fiber is exposed to a temperature of no more than 120°C during drying, more preferably no more than 100°C, more preferably no more than 80°C, more preferably no more than 50°C, more preferably no more than 40°C, and even more preferably no more than 30°C. Preferably, the fiber is exposed to a temperature of at least 8°C during drying, more preferably no more than 15°C, more preferably no more than 18°C, more preferably no more than 20°C, more preferably no more than 21°C, and even more preferably no more than 22°C.In preferred embodiments, the fiber is exposed to a temperature of 8 to 120°C during drying, more preferably 15 to 100°C, and even more preferably 18 to 30°C. If the temperature of the gas mixture is too high during drying, undesirable chemical side reactions and byproducts occur. Furthermore, an excessively high temperature of the gas mixture during drying leads to poorer adhesion of the functional layer to the fiber surface. If the temperature of the gas mixture is too low during drying, the sizing dries too slowly, impairing the mechanical and chemical resistance of the optical fiber and resulting in an excessively high residual content of water and / or aqueous solvents in the functional layer. <p xml:id="_ab747a0966" n="0132"> Often, sizing agents are irradiated with UV radiation for curing. However, it is preferable that the optical fiber article is not subjected to any curing process and is not dried by UV radiation. <p xml:id="_ab747a0967" n="0133">In one embodiment, the method comprises treating the dried sizing (dry sizing) with a liquid component to obtain a wet sizing as a functional layer, wherein the liquid component has a boiling point at 1013 hPa of more than 100°C or more than 200°C. The liquid component can be selected from the group consisting of silicone oil, polyethylene glycol, alcohols (e.g., long-chain or polyhydric), esters, ethers, ketones, acetates, and combinations thereof. The dry sizing typically comprises less than 50 wt.%, and in particular less than 35 wt.%, of the liquid component. The wet sizing preferably comprises at least 35 wt.%, and in particular at most 85 wt.%, of the liquid component. In one embodiment, the proportion of the liquid component in the wet sizing is between 35 and 65 wt.%. <p xml:id="_ab747a0968" n="0134">According to the invention, an optical fiber article with such a wet-applied sizing as a functional layer can also be produced, in particular by the method described herein. The optical fiber article with wet-applied sizing can have the features described herein as advantageous, provided that the functional layer contains at least 35 wt.% of the liquid component described for the wet-applied sizing. <p xml:id="_ab747a0969" n="0135">When processing fiber optic bundles, a distinction is made between so-called dry and wet sizing as functional layers. With wet sizing, the individual fibers in the bundle adhere slightly to each other. This reduces the tendency of the individual fibers to fan out and also minimizes electrostatic charging. This, in turn, significantly simplifies the threading of fiber bundles into ferrules, thus reducing assembly effort. In particular, this method allows for higher fiber packing densities, which improves light transmission. Furthermore, it also simplifies assembly handling, especially with relatively long optical fibers. <p xml:id="_ab747a0970" n="0136">In contrast, when using dry sizing, the individual fibers stick together less. This is advantageous when, for example, the individual fibers need to be separated and / or additionally mixed within the bundle (also known as a "randomization process") to achieve more homogeneous illumination, or, in the case of multi-arm bundles, when the fibers of the individual arms need to be mounted as evenly distributed as possible, i.e., statistically well distributed, into a common end sleeve. In these cases, a wet sizing would be rather detrimental. <p xml:id="_ab747a0971" n="0137">An advantage of the inventive approach is that a dry coating can first be applied as a functional layer to the fiber article. Only by adding a liquid component, which is a liquid with a high boiling point, preferably > 100°C, more preferably > 200°C, can a wet coating be provided from the dry coating in a customer-specific or application-specific manner, which offers significant advantages in the manufacturing process. In principle, it is conceivable to first apply a dry coating to the fiber article and, if required, add the liquid component in a subsequent coating process. Depending on customer requirements or the application, the coating properties can thus be specifically adjusted. The liquid component can be composed of at least one of the following components. Suitable components of the liquid component include silicone oil, polyethylene glycol, and alcohols (e.g.,...Long-chain or polyvalent esters, ethers, ketones, acetates, and combinations thereof. The concentration of the liquid component in the functional layer on the fiber article is typically less than 50 wt.% for a dry sizing, preferably less than 35 wt.%. For a wet sizing, the proportion is at least 35 wt.%, typically in the range of 35 to 65 wt.%. <p xml:id="_ab747a0972" n="0138"> Preferably, the optical fiber component is used in a fiber bundle as a light guide and / or image guide. For example, the optical fiber component can be used in endoscopes, inspection cameras, microscopes and / or spectroscopes. <p xml:id="_ab747a0973" n="0139">The optical fiber device is preferably used in a diagnostic or therapeutic procedure. For example, the optical fiber device can be used in endoscopy and / or surgery with flexible inspection cameras. Examples Example E1 <p xml:id="_ab747a0976" n="0140">To prepare a sizing solution, the following components (each from Sigma Aldrich) were weighed into a 1 L laboratory glass bottle and stirred on a standard laboratory magnetic stir plate for at least one hour to a solution of ethanol, deionized water and acetic acid. <title desc="title">< / title> <row> <cell> Stearic acid< / cell> <cell> 1,8 g< / cell> < / row> <row> <cell> Polyethylene glycol 40< / cell> <cell> 2 g< / cell> < / row> <row> <cell> Octyltrimethoxysilane< / cell> <cell> 1,2 g< / cell> < / row> <row> <cell> N-[3-(Trimethoxysilyl)propyl]ethylenediamine< / cell> <cell> 0,55 g< / cell> < / row> Examples E2-E22 <p xml:id="_ab747a0997" n="0141">To prepare sizing solutions, the components shown in Tables 1, 2, and 3 (each from Sigma-Aldrich) were weighed into a 1 L laboratory glass bottle and stirred on a standard laboratory magnetic stir plate for at least one hour, using a solution of ethanol, deionized water, acetic acid, and optionally other solvents such as dipropylene glycol monomethyl ether or tripropylene glycol monomethyl ether. Table 1 shows the components without solvents such as ethanol, deionized water, or acetic acid in relative wt% of examples E2-E18. PEG-Si = 2-[Methoxy(polyethyleneoxy)9-12propyl]trimethoxysilane, Ami-Si = N-[3-(Trimethoxysilyl)propyl]ethylenediamine, Alk-Si = Trimethoxy(octyl)silane. <p xml:id="_ab747a0998" n="0142">The sizing solution was then applied to optical fibers using a roll-to-roll process and allowed to dry at room temperature. Table 1 also shows the pull-out force and whether the fiber-to-sleeve (FS) or fiber-to-fiber (FF) connection failed in the pull-out test. The fracture length is also given. Table 1 <title desc="title"> Table 1< / title> PEG-Si60,6460,6060,61 Ami-Si39,3639,4039,3935,9532,3915,7510,50 Alk-Si17,6134,2522.83 PEG40064,0550,0033,33 Stearic acid 50.00 33.33 Glycerin Diethylene glycol 1,5-Pentanediol Expulsion force [N] 1250 1250 1300 650--750 FailureF HF-HF-HF-H--FH Breaking length [m] 350620 Table 2 Table 2 PEG-Si Ami-Si12,6514,1710,564,352,747,926,52 Alk-Si27,5030,8122,979,465,9617,2114,19 PEG40040,1544,9833,5413,818,7149,7458,58 Stearic acid 19.71 10.05 13.8 18.71 25.13 20.71 Glycerin 32,935 8,587 3,88 Diethylene glycol 1,5-Pentanediol Expulsion force 750700---14001500 Failure F-HF-H---F-HF-H Table 3 Table 3 PEG-Si Ami-Si5,552,3710,064,352,744,352,74 Alk-Si12,075,1521,889,465,969,465,96 PEG40064,7721,2436,1313,818,7113,818,71 Stearic acid 17,627,513,1,941,3,818,711,3,818,71 Glycerin 63,73 Diethylene glycol 58.58 73.88 1,5-Pentanediol 58,587 3,88 Expressing force 1150900----- Failure F-HF-H----- An IR spectrum was measured from a fiber bundle consisting of optical fibers coated with the sizing solution. The measurement was performed on a single device. For this purpose, the fiber bundle was repeatedly pressed onto the ATR crystal of the measuring instrument. Small amounts of the sizing solution were transferred to the crystal during this process and then measured. The FTIR-ATR spectrum of sample E14 is shown in Fig. 2 and that of sample E18 in Fig. 3. Brief description of the characters Fig. 1 is a schematic representation of an optical fiber with a fiber core (1) and a cladding (2). The functional layer (3) is connected to the surface of the cladding layer via covalent siloxane compounds (4) and non-covalent hydrogen bonds (5). The functional layer comprises, for example, an alkylsilane (6), an aminosilane (7), a polyethylene glycol (8), and a fatty acid (9). Fig. 2 shows the FTIR-ATR spectrum of example E14. Fig. 3 shows the FTIR-ATR spectrum of example E18. Fig. 4 shows the FTIR-ATR spectrum of a commercially available fiber product. Fig. 5 shows the FTIR-ATR spectrum of a commercially available fiber product. Fig. 6 shows the FTIR-ATR spectrum of a commercially available fiber product. List of reference symbols 1 Fiber core 2 Sheath 3 Functional layer 4 Siloxane compound between an alkylsilane of the functional layer and the surface of the sheath layer 5 Hydrogen bond between a functional group of the surface of the sheath layer and a polyethylene glycol of the functional layer 6 Alkylsilane 7 Aminosilane 8 Polyethylene glycol 9 Fatty acid

Claims

Optical fiber article comprising at least one optical fiber and a functional layer arranged on the surface of the optical fiber; wherein the functional layer comprises at least one functional silane with the following structural formula: where Z is a branched or unbranched alkyl or aryl group with 1 to 18 carbon atoms, wherein R1, R2 and R3 are independently selected from hydrogen, oxygen, alkyl, alkyloxy, hydroxyalkyl and hydroxyl, and wherein one, two or three of the groups R1, R2 or R3 are directly or indirectly connected to the surface of the optical fiber via a covalent bond, and where R4 is selected from, -NH 2 , -NHR', -NR'R'', glycidyloxy and -SH, where R' and R'' are independently selected from alkyl, aminoalkyl, hydroxyalkyl and -(CH 2 ) m NH 2 with m from 1 to 6, wherein the proportion of the functional silane in the functional layer is at least 1.5 wt.% and at most 70 wt.% and wherein the content of polyvinyl polymers is less than 1 wt.% based on the mass of the functional layer, wherein the content of photopolymerized polymers, in particular polyacrylates, polymethacrylates, polyvinyl polymers, polystyrene and / or derivatives thereof, in the functional layer is less than 1 wt.% based on the mass of the functional layer. Optical fiber article according to claim 1, wherein the fiber article comprises less than 500 ppm (m / m) of a halide. Optical fiber article according to at least one of the preceding claims, wherein the functional layer additionally comprises at least one fatty acid. Optical fiber article according to at least one of the preceding claims, wherein the at least one optical fiber has a bending radius of less than 10 mm in the break loop test according to DIN 58141-6:2011. Optical fiber article according to at least one of the preceding claims, with a push-out force of at least 250 N. Optical fiber article according to at least one of the preceding claims, wherein the fiber article is biocompatible according to ISO10993-1:2018, USP Class VI and / or ISO10993-5:2009. Optical fiber article according to at least one of the preceding claims, wherein the functional layer comprises an alkylsilane and / or polyethylene glycol silane covalently bonded to the surface of the fiber. Optical fiber article according to at least one of the preceding claims, wherein the functional layer comprises a polyvalent alcohol. Optical fiber article according to at least one of the preceding claims, wherein the functional layer comprises a polyalkylene oxide, in particular a polyglycol. Optical fiber article according to at least one of the preceding claims, wherein the optical fiber has a fiber core and a cladding and the functional layer is arranged on the cladding surface. Optical fiber article according to at least one of the preceding claims, wherein the fiber article comprises a fiber core and / or cladding made of a multi-component glass. Optical fiber article according to at least one of the preceding claims, wherein the functional layer in the IR spectrum is characterized by the following absorption: a. a ratio of the maximum absorption band height in the range of 800 cm⁻¹ to 1200 cm⁻¹ to the maximum absorption band height in the range of 1500 cm⁻¹ to 1900 cm⁻¹ is at least 2.0; b. a ratio of the maximum absorption band height in the range of 2700 cm⁻¹ to 3000 cm⁻¹ to the maximum absorption band height in the range of 1500 cm⁻¹ to 1900 cm⁻¹ is at least 2.0; c. a ratio of the maximum absorption band height in the range of 800 cm⁻¹ to 1200 cm⁻¹ to the maximum absorption band height in the range of 2700 cm⁻¹ to 3000 cm⁻¹ is at least 1.1 and at most 2.0; and d. The ratio of the maximum absorption band height in the range of 3200 cm-1 to 3600 cm-1 to the maximum absorption band height in the range of 1500 cm-1 to 1900 cm-1 is at least 1.

1. Optical fiber article according to claim 12, with an IR spectrum according to Fig. 2 or Fig.

3. Optical fiber article according to at least one of the preceding claims, comprising a dry functional layer comprising less than 35 wt.% of a liquid component having a boiling point at 1013 hPa of more than 100°C. Optical fiber article according to at least one of claims 1 to 14, comprising a moist functional layer comprising at least 35 wt.% of a liquid component having a boiling point at 1013 hPa of more than 100°C. Optical fiber article according to at least one of the preceding claims wherein the functional silane has formed a reaction product at least partially with one or more adhesives. A method for manufacturing an optical fiber article according to one of the preceding claims, comprising the steps: a. providing at least one optical fiber; b. coating at least one part of the optical fiber with a sizing; c. drying the sizing. The method of claim 17, comprising treating the dried sizing with a liquid component to obtain a wet sizing, wherein the liquid component has a boiling point at 1013 hPa of more than 100°C. The method of claim 18, wherein the liquid component is selected from the group consisting of silicone oil, polyethylene glycol, alcohols, esters, ethers, ketones, acetates and combinations thereof. Use of an optical fiber article according to one of claims 1 to 15 in a fiber bundle as a light guide and / or image guide, for example in an endoscope. Optical fiber article according to any one of claims 1 to 15 for use in a diagnostic or therapeutic procedure.

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