Mounting device for a light guide

Abstract

The invention describes a mounting device for an optical fiber, comprising a sleeve with an end face and at least one fiber bundle, wherein the fiber bundle is at least partially or sectionarily fused to a glass tube around its circumference. The fiber bundle and the glass tube share a common end face and taper towards this common end face. The common end face forms a fused, rigid section with the glass tube and can be designed or manufactured as a ground and / or polished surface. In the region of the taper, the fiber bundle and the glass tube are or can be fixed in or onto the sleeve, at least partially or sectionarily, by means of an adhesive, in or on the fixing section of the sleeve.The common end surface of the fiber bundle with the glass tube is offset from the fixing section of the sleeve containing the adhesive, such that the common end surface is or can be arranged at a distance from the fixing section containing the adhesive. This separates or allows the fixing section and the common end surface from each other.

Description

Field of invention

[0001] The invention relates to a mounting device for an optical fiber, comprising a sleeve with an end face and at least one fiber bundle, wherein the fiber bundle is at least partially or sectionarily fused to a glass tube around its circumference. The fiber bundle shares an end face with the glass tube. The fiber bundle and the glass tube form a tapered section towards the shared end face, and the shared end face has a fused, rigid section. The shared end face is or can be designed as a ground and / or polished surface. Furthermore, the fiber bundle and the glass tube are or can be fixed in or on the sleeve in the area of ​​the tapered section by means of an adhesive, at least partially or sectionally, in or on the fixing section of the sleeve.

[0002] Such optical fibers with a fiber bundle fused to a glass tube are described in the applicant's German patent application DE 3620368C2. This patent shows a fiber optic optical fiber with an end-face region consisting of one end of an optical fiber bundle and a glass tube section applied to this end, the end-face being polished. It is provided that both the glass tube section and the optical fiber bundle are made of high-temperature-resistant glass, and that the glass tube section is applied to the optical fiber bundle in a molten state over a defined length such that the gaps between the individual optical fibers and / or between the optical fibers and the tube section are at least partially filled by the material of the glass tube section and / or by the material of the optical fiber sheaths.

[0003] This process for manufacturing such optical fibers is also known as GTF (Glass Tube Fusion). These optical fibers are then mounted in a metal sleeve or further processed into fiber optic cables and are primarily used in medical applications.

[0004] The two documents DE19703515C1 and DE10013482C2 also describe fiber bundles with a fused glass tube section. In both cases, the glass tube is intended to be detached again for further assembly of the fiber bundles in a sleeve. This involves complex procedures that can lead to damage to the optical fibers.

[0005] DE3534280C1 and DE3247500C2 each disclose a fiber bundle mounted in a sleeve, with an end face and a circumferential surface fused to a glass tube and forming a tapered area with the glass tube towards the common end face.

[0006] However, when mounting such glass-tube-fused fiber bundles into a mounting sleeve, usually made of stainless steel, using an adhesive, it has been shown that this can lead to stresses in the fiber composite, which can then induce cracks. This occurs particularly in the medical technology application of such optical fibers when they must be reprocessed after use through thermal processes, such as steam sterilization, for further, multiple uses. These processes involve high temperature fluctuations, which can damage the optical fiber and render it unusable after only a few such cycles.

[0007] In US patent 2016 / 011356 A1, a flexible optical fiber with at least one fused fiber end secured in an end piece is described to prevent damage to a fused fiber end. A layer of cushioning material is placed between the fused fiber end and the end piece. This cushioning layer is intended to compensate for differences in the thermal expansion and contraction of the fused fiber end and the end piece, thus preventing damage to the fused fiber end, such as that which can occur during repeated autoclaving. The cushioning layer can be created, for example, by wrapping the fused fiber end with PTFE tape, thread sealant tape, or similar material.

[0008] This initially appears to be a viable approach, particularly for avoiding stress. However, this approach has the disadvantage that such cushioning layers cannot guarantee a compact body. Microscopically fine gaps can allow germs to colonize these spaces, and even autoclaving cannot completely eliminate them, thus increasing the risk of contamination. This can lead to serious complications for patients, especially in medical technology settings.

[0009] Another approach to preventing cracks during or due to temperature changes is the use of permanently elastic adhesives. However, it turns out that such adhesives often lack the long-term stability required for, for example, several hundred autoclave cycles. Over time, chemical bonds in the adhesive break down, causing it to decompose or even liquefy with each reprocessing cycle, rendering the optical fiber unusable. Object of the invention

[0010] It is therefore an object of the invention to provide a mounting device that avoids the above disadvantages and enables a robust, long-term stable and temperature-resistant optical fiber or such an optical fiber mounting for continuous use, especially in the medical technology environment. Brief description of the invention

[0011] The object of the invention is already solved by the subject matter of the independent claim. Advantageous embodiments and further developments are the subject matter of the dependent claims.

[0012] According to the invention, the mounting device has an offset between the common end surface of the fiber bundle and the glass tube relative to the fixing section of the sleeve containing the adhesive, such that the common end surface is or can be arranged at a distance from the fixing section containing the adhesive. The particularly crack-prone common end surface of the glass tube fusion forms a projection or extends a certain distance beyond the sleeve end surface, so that the fixing section containing the adhesive is isolated from the sensitive area of ​​the common end surface. This prevents or at least reduces stresses on the common end surface of the fiber bundle and glass tube that are induced by the adhesive or the bonding process.

[0013] In other words, a mounting device for an optical fiber is provided, comprising a sleeve with an end face and at least one fiber bundle, wherein the fiber bundle is surrounded by a glass tube at its circumferential surface and is at least partially or sectionarily fused circumferentially, and the fiber bundle and the glass tube share a common end face. Furthermore, the fiber bundle and the glass tube form a tapered section towards the common end face, and this common end face and the glass tube form a fused, rigid section. The common end face is, or can be, designed as a ground and / or polished surface. Furthermore, the fiber bundle and the glass tube are, or can be, fixed in or on the sleeve at the fixing section of the sleeve, at least partially or sectionally, by means of an adhesive.The material bond is therefore formed particularly in or at the fixing section, but can also continue inside the sleeve, facing away from the end faces, i.e., behind the fixing section in or at the sleeve. The common end face of the fiber bundle is further offset from the fixing section of the sleeve, so that the common end face of the fiber bundle is or can be arranged at a distance from the fixing section of the glass tube, and the fixing section and the common end face are or can be separated from each other.

[0014] According to the invention, the mounting device comprises, in particular, a sleeve in which the fiber bundle with the fused glass tube can be mounted or glued in place using adhesive. Such a fused fiber bundle can be positioned in an optical fiber at either the distal or proximal end, or at both ends. The mounting device is also understood to be a device that enables the attachment, connection, or integration of the fiber bundle with other devices, assemblies, or components. These may include light sources, camera modules, or endoscopic handpieces, as well as those used in other application areas, such as in medical settings.

[0015] Such an optical fiber comprises, at least as a light guide element or elements, a multitude of optical fibers that then form a fiber bundle. It is also possible that the fiber bundle is at least partially or sectionally enclosed in a sheath, thus forming a sheathed optical cable. In the area of ​​a sleeve or ferrule, the sheath can be removed, and only the optical fibers are fixed in the sleeve by a material-fit and / or form-fit connection, possibly also by force-fit. Fixation in a sleeve together with the sheath is also possible. An optical fiber element or optical fibers are preferably glass-based fibers (glass optical fibers - GOF) and are usually designed as so-called core-cladding systems.

[0016] In an advantageous embodiment of the mounting device for an optical fiber, the offset between the common end surface of the fiber bundle and the glass tube and the sleeve end surface is in the range of 0.1 mm to 2 mm, preferably in the range of 0.5 mm to 1.0 mm. It has been shown that such an offset, or offset dimension, between the common end surface of the fiber bundle and the glass tube and the adhesive surrounding the fiber bundle in the fixing section is advantageous. This is due, on the one hand, to the fact that the free-standing protrusion must not be too large with regard to its mechanical stability. In principle, larger offset dimensions than the maximum of 2 mm are conceivable, but are not very practical due to the increased mechanical fragility of such an embodiment.On the other hand, a certain minimum distance is necessary between the fusion zone, i.e., the fused area of ​​the fiber bundle and glass tube, particularly in or near the common end face, and the adhesive edge or the bond between the fiber bundle and the glass tube in the sleeve, to ensure sufficient isolation of mechanical stresses from the fusion zone. These stresses result, for example, from differences in thermal expansion, especially between the adhesive and the sleeve compared to the glass. This prevents, or at least reduces or minimizes, the introduction of mechanical stress into the common end face, allowing the optical fiber to withstand repeated thermal stresses without damage, such as cracks, chipping, or delamination.Such stresses occur regularly in the medical field, for example, during the required reprocessing, particularly through thermal process steps in sterilization, such as autoclaving, after use or before reuse of a fiber optic cable.

[0017] In a further advantageous embodiment of the invention, it is alternatively or additionally provided that a gap of 0.05 mm to 0.2 mm is formed or can be formed partially or section by section within the fixing section between the glass tube and the sleeve as an adhesive gap. Excessively large adhesive gaps promote excessive eccentricity of the fiber bundle in the sleeve or can negatively affect the positional tolerance of the fiber bundle in the sleeve. This can be detrimental during operation, particularly during light coupling or extraction, or during the positioning of the optical fiber relative to other connected components. An insufficient adhesive gap can result in insufficient adhesive wetting of the surfaces in certain areas, potentially leading to air gaps, which can be disadvantageous during processing and use.Such air gaps can fill with media, germs or contaminants, which is unacceptable, especially in medical applications in or on the body, or can lead to further damage to the adhesive bond during processing with chemical components, ultimately resulting in the failure of the optical fiber.

[0018] In another preferred embodiment of the mounting device for a fiber optic cable, the sleeve is alternatively or additionally designed such that the fixing section is or can be arranged at a distance from the sleeve end face by the offset, and a ring is formed or can be formed, so that in the assembled state a circumferential groove is formed between the ring and the glass tube in the area of ​​the common end face, and wherein the sleeve end face and the common end face of the fiber bundle and glass tube form a plane. This allows for circumferential lateral mechanical protection of the freestanding fiber bundle fused to the glass tube. It should be noted that, in principle, the ring of the sleeve can also project beyond the common end face of the fiber bundle and glass tube.However, this may not be beneficial to the manufacturing process, as the light guide or its end surface is usually subjected to a grinding and polishing process together with the fiber bundle mounted or glued into the sleeve, thus removing any protrusion of the collar.

[0019] To avoid excessively narrow gaps, which, as mentioned earlier, promote bacterial growth, the width of the groove (groove width) between the rim of the mounting sleeve and the glass tube is at least 0.3 mm, preferably at least 0.5 mm. This ensures that a sufficiently large opening or surface area is provided for sterilization processes used in medical environments, such as steam sterilization, autoclaving, or plasma sterilization processes, e.g., the Sterrad™ process, and thus a sufficiently high reduction of germs, for example, a multiple, e.g., 6-fold, log reduction, can be achieved.Depending on the design of the light guide or the possible, permitted or required overall geometry of the mounting device, in particular with regard to its width or diameter transverse to its axis, the groove can have widths in the range of up to a few 0.1 mm, in any case greater than 0.3 mm, or up to a few millimeters, e.g. in the range of greater than or equal to 0.3 mm to 3 mm, preferably greater than or equal to 0.3 mm to 1.5 mm.

[0020] In an advantageous embodiment of the mounting device for a light guide, the sleeve comprises or consists of stainless steel, for example, materials 1.4301 or 1.4305, plastic, or a combination of both material classes, for example, in the case of a multi-part sleeve. In the medical technology sector, plastics based on materials such as PPSU (polyphenylsulfone) or PEEK (polyetheretherketone) have proven particularly effective in plastic versions. These are characterized by sufficiently good thermal stability on the one hand and particularly high mechanical stiffness on the other.

[0021] Besides stainless steel, other metallic materials are also conceivable, such as nickel silver or brass. However, stainless steel is preferred with regard to corrosion resistance and biocompatibility, especially in a medical technology environment. The following selection criteria are generally advantageous for the material: firstly, the material must be mechanically stable enough to be clamped in a fixture during the final grinding and polishing process. Secondly, the material must not be prone to "lubrication," meaning it should preferably be rather brittle and / or filled with glass fibers (glass fiber-reinforced plastics) or other fillers, such as ceramic or glassy materials. These also bond well to the fiber bundle of the optical fiber.

[0022] In advantageous embodiments of the mounting device for a light guide, the adhesive comprises or consists of highly cross-linked, brittle epoxy adhesives. These are used to ensure sufficiently good reprocessing capabilities. Often, more than 100 to 1000 reprocessing cycles, particularly autoclave cycles, are required. Crucial adhesive properties for such brittle, highly cross-linked adhesives include: the highest possible tensile shear strength, the highest possible glass transition temperature (which, like high or increased hardness, is also an indicator of the degree of cross-linking), the lowest possible coefficient of thermal expansion, the lowest possible modulus of elasticity, and a relatively low Poisson's ratio or shear modulus, which are usually not available in datasheets. Often, only the modulus of elasticity is specified.

[0023] Typical suitable adhesives, when cross-linked, cured, or processed, generally exhibit Shore hardnesses of 75 to 95 and typically have a glass transition temperature of > 95°C. The tensile shear strength is typically > 13.5 N / mm². 2 This corresponds to approximately > 2000 psi. Shore hardness correlates with the modulus of elasticity and shear strength. However, the precise curing conditions of the adhesive and any fillers are usually more crucial. In particular, high degrees of cross-linking can be achieved through long curing times and / or elevated temperatures. Depending on the chemical composition of the adhesive, combination cross-linking processes are also conceivable, which can occur in several stages. For example, pre-cross-linking with UV light followed by thermal cross-linking can lead to high degrees of cross-linking.

[0024] It should be noted that this is essentially a conflict of objectives. On the one hand, particularly stable adhesives are required that can withstand several hundred processing cycles, especially during autoclaving, and correspondingly high chemical bond stability is also required during plasma sterilization. On the other hand, these very adhesives induce stresses that can lead to stress cracks in the glass tube-fiber composite even during curing. However, this can be avoided or at least significantly reduced by the design according to the invention, as described above.

[0025] A particularly advantageous use of the mounting device, as described above in its various embodiments, involves its use with a fiber optic cable and / or a fiber optic cable, which can be repeatedly sterilized after each use in medical applications. This approach according to the invention can be particularly advantageous for fiber optic cables or fiber optic cables used as a connection between a light source and an endoscope, or for connecting to such assemblies, and / or for fiber optic cables integrated within the endoscope. Applications in industrial environments are also conceivable, for example, in the fields of energy technology and aerospace, where high temperatures or large temperature fluctuations play a significant role. Character description

[0026] The invention is described in more detail below with reference to figures.

[0027] They show: Fig. 1. Schematic representation of a mounting device according to the state of the art, Fig. 2 schematically a mounting device according to the invention, Fig. 3 schematically a variant of the mounting device with a sleeve which forms a ring and Fig. 4 schematically another variant to the one in Fig. 3 variants shown.

[0028] Fig. Figure 1 schematically shows the assembly device according to the prior art for an optical fiber 1, consisting of a fiber bundle 2, which has been fused to a glass tube 3 at its circumferential surface 2.5 according to the GTF process described above. The fiber bundle 2 exhibits a taper 2.4. The taper 2.4 results from the increasing packing density of the individual fibers as a consequence of progressive fusion with itself and the glass tube 3 until complete fusion or a completely fused portion in or near the region of the common end surface 2.3 and encompassing it. The fiber bundle 2 with the glass tube 3 thus has, at least near the surface at its common end surface 2.3, a fused and therefore rigid section 2.2, followed by a transition region in which the fibers are only partially fused, which then transitions into an unfused section 2.1.In this, the fibers in fiber bundle 2 are arranged to move freely.

[0029] Typical diameters of such fused fiber bundles 2 range from 0.5 to 10 mm. The length of the taper 2.4, or the transition zone between the unfused section 2.1 of the fiber bundle 2 and the common end face 2.3 of the fiber bundle 2 and the glass tube 3, is typically between 0.5 mm and 20 mm. The transition zone between the unfused section 2.1 and the fully fused section 2.2 can have typical values ​​of 2 mm to 10 mm. Accordingly, the diameter of the mounting device is of a similar order of magnitude, in any case larger than the diameter of the fiber bundle used. For a fiber bundle with a diameter of 2 mm, a total diameter of the mounting device of at least 3 mm can be assumed.The minimum possible wall thicknesses of the sleeve 4 are certainly determined by its material, and the maximum permissible or required overall diameters are often determined by the application of such mounted light guides.

[0030] This GTF fiber bundle is then fixed in a sleeve 4 in the area of ​​a fixing section 4.3 of the sleeve 4 using an adhesive 5. Ideally, the applied adhesive 5 fills the gap up to the common end surface 2.3 to prevent gaps or holes. The sleeve 4 is ideally made of stainless steel, but can also be made of fiber-reinforced or filled plastics, as described previously. The final common end surface 2.3 of the fiber bundle 2 is then created together with the end surface of the sleeve 4 by a subsequent grinding and polishing process. A disadvantage, as described previously, is the stress induced in the fused section 2.2 of the fiber bundle 2, which is introduced as soon as the adhesive 5 cures. Further stresses arise from temperature changes during processing, for example, by steam sterilization. This often leads to cracks at the common end surface 2.3, which on the one hand significantly reduces the yield in production and on the other hand considerably limits the service life or the number of reprocessing cycles.

[0031] Fig. Figure 2 schematically shows an embodiment according to the invention. In this embodiment, the fiber bundle 2 produced using the GTF process projects beyond the sleeve 4 by the offset dimension 6, so that the adhesive 5 in the adhesive gap or in the fixing section 4.3 has a sufficient distance from the fused section 2.2 of the fiber bundle 2. This reduces stress input both during assembly or adhesive curing and during the processing cycles in use, thus significantly minimizing the risk of cracking. In a preferred embodiment of the invention, it has been found that an offset 6, or the offset dimension between the common end surface 2.3 of the fiber bundle 2 and the glass tube and the adhesive 5 surrounding the fiber bundle 2 or the fixing section 4.3, of at least 0.1 mm to 2 mm is advantageous, with an offset dimension of 0.5 mm to 1.0 mm being particularly preferred.Tests have shown that this offset dimension 6 is largely independent of the diameter of the fiber bundle 2 with the glass tube 3. The adhesive or bond should have an adhesive gap between the glass tube 3 and the inner surface of the sleeve 4 of 0.05 mm to 0.2 mm.

[0032] A potential disadvantage of this in Fig. The difference in the embodiment shown in Figure 2 is that the edges of the common end surface 2.3 of the fiber bundle 2 produced by the GTF process are poorly protected and exposed. Therefore, in Fig. Figure 3 shows a further embodiment variant schematically, in which the sleeve 4 is designed such that the fixing section 4.3 is spaced from the end surface 4.1 by the offset 6 and a ring 4.2 is formed, so that in the assembled state a circumferential groove 7 is formed between the ring 4.2 and the glass tube 3 in the area of ​​the common end surface 2.3, and the sleeve end surface 4.1 and the common end surface 2.3 of the fiber bundle 2 and the glass tube 3 form a plane. This allows for circumferential lateral mechanical protection of the free end of the glass tube-fused fiber bundle.

[0033] To avoid excessively narrow gaps, which promote or hinder the formation or accumulation of germs or contamination, as mentioned above, the groove 7 has a groove width 7.1 of at least 0.3 mm, preferably at least 0.5 mm. During assembly, care must be taken to ensure that this groove 7 between the rim 4.2 and the glass tube 3 is not covered or filled with adhesive 5.

[0034] Fig. 4 shows a variant of the one in Fig. 3. The conically designed GTF fusion differs from the one shown in 3. Fig. 1, Fig. 2 to Fig. The fusions shown in section 3 are achieved by increasing the ratio of the diameters of the unfused bundle (i.e., the unfused section 2.1) and the fused section 2.2 through an additional manufacturing step compared to the other fusions. This ensures that the end surface 2.3 of the Fig. 4 compared to the variants of Fig. 1, Fig. 2 to Fig. 3 has a smaller or reduced diameter. The sleeve 4 can, as shown schematically here, also have further sections which, for example, have a partially or sectionally reduced wall thickness, especially in the area of ​​the end faces, and / or (not shown here) have additional clamping or locking elements, which in turn at least facilitate or enable the mounting of such a pre-assembled optical fiber to a light source, a camera module, or a handpiece, for example, of an endoscope. To facilitate the insertion or threading of the fiber bundle 2 into the glass tube 3 before the so-called GTF fusion, the glass tube 3 can have a collar 3.1 on the threading end. This collar 3.1 can be designed as a rounded collar, as shown, or as a conical section (not shown).

Claims

[1] Mounting device for an optical fiber (1) comprising a sleeve (4) with an end face (4.1) and at least one fiber bundle (2), wherein the fiber bundle (2) is at least partially or section by section fused around its circumferential surface (2.5) with a glass tube (3), and the fiber bundle (2) and the glass tube (3) have a common end surface (2.3), wherein the fiber bundle (2) with the glass tube (3) forms a tapered area (2.4) towards the common end surface (2.3), wherein the common end surface (2.3) with the glass tube (3) has a fused, rigid section (2.2), and wherein the common end surface (2.3) is or can be made to be ground and / or polished, and wherein the fiber bundle (2) is fixed or can be fixed to the glass tube (3) in the area of ​​the tapering (2.4) at least partially or sectionally in or on the sleeve (4) in or on the fixing section (4.3) of the sleeve (4) by means of an adhesive (5), wherein the common end surface (2.3) of the fiber bundle (2) with the glass tube (3) has an offset (6) relative to the fixing section (4.3) of the sleeve (4) with the adhesive (5), such that the common end surface (2.3) is or can be arranged with an offset (6) from the fixing section (4.3) with the adhesive (5) and the fixing section (4.3) and the common end surface (2.3) are or can be separated from each other. [2] Mounting device for a light guide (1) according to claim 1, wherein the offset (6) between the common end surface (2.3) of the fiber bundle (2) with the glass tube (3) and the sleeve end surface (4.1) is in the range of 0.1 mm to 2 mm, preferably in the range of 0.5 mm to 1.0 mm. [3] Mounting device for a light guide (1) according to claim 1 or 2, wherein in the fixing section (4.3) between the glass tube (3) and the sleeve (4) a distance of 0.05 mm to 0.2 mm is formed or can be formed partially or section by section as an adhesive gap dimension for the adhesive (5). [4] Mounting device for a light guide (1) according to at least one of the preceding claims, wherein the sleeve (4) is designed such that the fixing section (4.3) is or can be arranged spaced apart by the offset (6) from the sleeve end surface (4.1) and a ring (4.2) is formed or can be formed, so that in the assembled state a circumferential groove (7) is formed between the ring (4.2) and the glass tube (3) in the area of ​​the common end surface (2.3), and wherein the sleeve end surface (4.1) and the common end surface (2.3) of fiber bundle (2) and glass tube (3) form a plane. [5] Mounting device for a light guide (1) according to claim 4, wherein the groove (7) has a groove width (7.1) of at least 0.3 mm, preferably of at least 0.5 mm. [6] Mounting device for a light guide (1) according to at least one of the preceding claims, wherein the sleeve (4) comprises or consists of stainless steel, plastic or a combination of both material classes. [7] Mounting device for a light guide (1) according to at least one of the preceding claims, wherein the adhesive (5) comprises or consists of highly cross-linking, brittle epoxy adhesives. [8] Use of the mounting device according to one of the preceding claims for a light guide (1) and / or for a light guide cable which can be reprocessed multiple times in a medical technology environment by means of sterilization procedures.

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