Fiber optic light guide with molded end

Abstract

SOLUTION: To provide a fiber optic light guide (1) comprising a plurality of optical fibers (10) collected as a flexible fiber bundle having a substantially constant diameter d1 (11), in which the whole circumference of at least a partial region of the length, at one end at least, is surrounded by a covering material (20), the optical fibers (10) are fused mutually and preferably also with the covering material (20) so that a rigid region including a lengthwise direction axis (16) is formed, and in a region of the covering material (20), the fiber optic light guide (1) is bent from its lengthwise direction axis (16) according to actions of pressure and heat, and / or are deformed relating to a lateral cross-section geometric shape of the fiber optic light guide (1), wherein the fiber optic light guide (1) may be formed by being tapered in the rigid region.EFFECT: A glass sleeve remains on a fiber bundle even after tapering a lateral cross-section, and contributes as a rigid composite to shape stabilization of a fiber optic light guide.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical fiber light guide comprising a plurality of optical fibers which are or can be assembled into a flexible fiber bundle having a substantially constant diameter d1, wherein at least one end of the optical fiber light guide is surrounded by a coating material all around at least a partial region of the length of the optical fiber light guide, wherein the optical fibers are fused to each other and preferably also to the coating material to form a rigid section.

[0002] The main application field of optical fiber light guides are, for example, light guides for endoscopes, in particular for medical or industrial applications. These light guides are required in that, on the one hand, with a first end (proximal end) or its end face, the light guide is coupled to a light source and, on the other hand, with a second end (distal end), is introduced into a subject, in order to, in particular, guide light thereto or receive light therefrom. In general, a light source with a high light output is desired. The larger the entrance surface and thus the diameter of the light guide, the better or easier it is to efficiently couple the light guide to the light source, but the larger the diameter of the light guide, the more difficult it is to introduce the light guide into the subject. For this reason, some endoscopic light guides have several partial regions, for example a first partial region with a substantially constant, larger diameter d1, which is usually followed by another partial region consisting of a conically tapered region made of an additional light guide, in which the diameter of the light guide is reduced to a smaller diameter d2. In this case, a further light guide with a smaller diameter d2 can be connected to the tapered region as a further partial region, which can be introduced into the specimen or object to be examined.

[0003] In some configurations of such endoscopes, especially at their distal end, further components, e.g., cameras or camera chips as well as light sources, for image transmission or image capture, may also be included. Fiber optic illumination here must ensure adequate illumination, especially for image capture. This can be achieved by adapted geometry of devices and / or light guides provided on or around such further components.

[0004] In a conventional manufacturing method, the tapered region is formed by deforming a separate fiber bundle into a cone and then joined to a light guide having a certain diameter, for example by fusing, resulting in an interface between the light guide and the tapered region where the fiber structure of the entire light guide is interrupted, and in operation, the total light transmittance of the light guide is reduced due to partial reflection, since the light guided or guided through the light guide is lost.

[0005] Furthermore, light guides are generally present as loose fiber bundles, in which each optical fiber consists of a core-clad fiber. A core-clad fiber is a fiber consisting of a light-guiding core surrounded all around along the fiber axis by a cladding made of a material with a lower refractive index than the material of the core. Light guiding in the fiber core is made possible by total internal reflection at the interface between the core and the cladding. By providing a separate tapered region, it is not possible to ensure that the fiber core of the light guide region, which has a constant diameter, is coupled to the fiber core of the tapered region. Instead, at the interface between the first partial region and the tapered region, a statistical distribution of fibers coupled to the fiber cladding and at least partially to the core occurs. However, this also leads to a decrease in the total light transmittance of the light guide, since light cannot be guided in the fiber cladding or can only be guided very poorly.

[0006] DE 10013482 describes a method for producing an optical fiber light guide comprising a bundle of optical fibers which is crushed at a suitable temperature in a glass sleeve before being inserted into a holder, which comprises removing the glass sleeve from the bundle of fibers before crushing and before inserting the fibers into the holder, and furthermore inserting an intermediate layer between the bundle of fibers and the glass sleeve before crushing, allowing an improved removal of the glass sleeve from the bundle of fibers after crushing. In this case, the method envisages inserting as intermediate layer a layer of a powdery, particulate or pasty separating medium whose melting point is above the softening temperature of the fibers and the softening temperature of the glass sleeve, and at least partially roughening the inner surface of the glass sleeve before inserting the intermediate layer.

[0007] According to the German patent DE 19703515, an optical fiber guide consisting of a fiber bundle is insertable into a holder and is optically effective at least at one end thereof, the end insertable into the holder being crushed before being inserted into a glass sleeve, the glass sleeve being removed before the end is inserted into a socket.

[0008] In both cases, the glass sleeve is applied temporarily and is removed before assembly into the ferrule or holder or sleeve, in particular after the end portion has been partially processed in a laborious manner.

[0009] The Applicant has developed a light guide and a method for its manufacture, in which the glass sleeve remains on the fiber bundle, especially after tapering of the cross section, and contributes to the shape stabilization of the optical fiber light guide as a strong composite, i.e. the light guide is formed rigidly in the region of the coating, so that damages during further processing, such as for example damage to the outer edge layer of the optical fibers, can be precluded, especially when the glass sleeve is removed.

[0010] This approach allows particularly circular cross sections to be produced, particularly at tapered end faces or end sections with tapers.

[0011] Taking into account the construction space provided at the distal end of an endoscope, for example in relation to relatively new requirements in particular endoscopes, the object of the present invention is to provide a light guide which has not only a circular end face but also a non-circular end face, or a light guide which has a purely conical, substantially uniform tapering portion, i.e. a geometry which differs from, for example, a substantially constant cross-sectional geometry, thereby providing a light guide which, in addition to rigid shaped regions, also contains inherently flexible regions which follow the rigid regions continuously and without interruption.

[0012] Disclosure of the Invention The object of the present invention is achieved by an optical fiber light guide having the features set forth in claim 1.

[0013] The present invention provides an optical fiber light guide having at its original end face a flexible region of length l1 with a substantially constant diameter d1 and another region with a coating, in which the optical fiber light guide which then becomes rigid there is bent, distorted or folded, for example by the action of pressure and heat, away from its longitudinal axis, i.e. for example by being bent at least once in at least one partial region of the region with the coating, and / or is deformed in terms of its cross-section or its cross-sectional geometry in this rigid region. This allows a 3D-shaped optical fiber light guide to be realized, which can be mounted in an endoscope, in particular where the construction space provided is generally limited, or which can avoid collisions with other components in the endoscope. In other words, there is an optical fiber light guide having a flexible region whose end face is connected or can be connected or can be arranged correspondingly to a light source. The light guide has at least one bend or fold from its original longitudinal axis or from the direction of this longitudinal axis in its region surrounded by the covering material and therefore rigid, i.e. the optical fiber light guide is shaped, in particular folded or bent at least once in the rigid region, and / or the optical fiber light guide has at least one region in this rigid region in which the cross-sectional geometry is changed or deformed, i.e. the cross-sectional geometry of the optical fiber light guide is shifted or deformed, for example from an initially originally circular shape to a non-circular shape, for example an elliptical or polygonal shape. The bent and / or deformed cross-sectional geometry of the optical fiber light guide thus usually forms a distal end opposite the proximal end of the light guide, which in operative condition emits and supplies light incident on the proximal end. By shaping from the longitudinal axis we mean in particular bending or folding, and by deformation of the cross-sectional geometry we mean a change in the geometry or a change in the cross-sectional shape.In this case, the longitudinal axis or the original longitudinal axis is considered to be the axis that is set or can be set by the region surrounded by the covering material and therefore rigid, before this region is bent or folded at least once.

[0014] One embodiment envisages an optical fiber light guide having a flexible region of length l1 with a substantially constant diameter d1 at the original end face, followed by at least one tapered region of length l2, in which the diameter of the light guide decreases from diameter d1 to diameter d2. In this case, the tapered region is surrounded by a coating material all around at least in a partial region of its length, and the fiber structure continues without interruption from the region with the substantially constant diameter to the tapered region, with the tapered region having a tapered end face in which the optical fibers are fused to each other and preferably also to the coating material. In this case, the length l2 may include a region which initially extends after the original tapering, i.e. in particular before a further shaping, bending or folding section, with a constant cross section or diameter d2 and cross-sectional geometry. In the region of the coating material, the optical fiber light guide may also be bent from its longitudinal axis by the action of pressure and heat and / or deformed with respect to its cross-sectional geometry, in particular also in the region of length l2. In other words, there is a fiber optic light guide having a flexible region, connected or connectable or compliant at its end face (proximal end) to a light source, surrounded by a covering and thus having a tapered region of length l2 with an original diameter d1 tapering to a diameter d2 in a rigid region, and having at least one bend or fold from or in the direction of the original longitudinal axis, i.e. the fiber optic light guide is molded, folded or bent once at least in the rigid region and / or the fiber optic light guide has at least one region in the rigid region where the cross-sectional geometry is deformed and changed, i.e. the cross-sectional geometry of the fiber optic light guide is transferred, for example, from an initially originally circular shape to a non-circular shape, for example an elliptical or polygonal shape. Thus, the bent and / or deformed cross-sectional geometry of the rigid tapered region of the optical fiber light guide typically forms a distal end opposite the proximal end of the light guide that outputs and delivers light incident on the proximal end in an operative state.In this case, the longitudinal axis or the original longitudinal axis is considered to be the axis that is set or can be set by the region surrounded by the covering material and therefore rigid, before this region is bent or folded at least once.

[0015] On the one hand, this allows the light to be concentrated in the near field, i.e. at a short distance between the light exit surface of the light guide and the object (e.g. tissue surface). On the other hand, in the case of fiber optic components, the acceptance angle and thus the possible emission angle increases at the taper of such components. This effect is stronger the greater the difference between the diameters d1 and d2. What is important here is the so-called "étendue" or retention of the light guide value, which characterizes the maximum light beam that is transmitted or can be transmitted. This retention describes the ability of the optical system geometry to transmit light. The value of the retention is obtained from the product of the aperture size of the optical system and the solid angle of transmission. In the case of optical fiber light guides in particular, the numerical aperture or acceptance angle, through which light can still be guided in the light guide, determines the possible solid angle.

[0016] This fact can be seen by the following relationship: NA1×D1=NA2×D2(1) and NA1 = sin(α1) (2a) NA2 = sin(α2) (2b) where D1 is the original fiber diameter, D2 is the tapered fiber diameter, NA1 is the original fiber numerical aperture, and NA2 is the tapered fiber numerical aperture, where α1 or α2 is the acceptance angle for the numerical aperture NA1 or NA2. In this way, a wider acceptance angle and thus a wider illumination can be achieved, which is advantageous, especially when a wide-angle camera module is integrated into the endoscope. Thus, for example, an optical fiber with an NA of 0.68 (corresponding to a doubling of the acceptance angle of about 85°) can be increased to about 0.79 by reducing the fiber diameter, for example, from D1=70 μm to about D2=60 μm, corresponding to a taper of the light guide diameter from diameter d1 to diameter d2, for example from 4 mm (d1) to about 3.4 mm (d2), which corresponds to a doubling of the acceptance angle from 42.5° to about 52.2° or a doubling of the amount of light received to 104.4°. This allows, for example, to adapt the emissivity of the light guide to the viewing angle of the camera.

[0017] It should be pointed out here that the taper, i.e. the ratio D1 / D2 with respect to the diameter of the optical fiber or the ratio d1 / d2 with respect to the fiber bundle, must not be arbitrarily large in order to obtain the above-mentioned light spreading effect. That is, in the case of an optical fiber with an exit NA of, for example, 0.57, which corresponds to a double acceptance angle of about 70°, only a D1 / D2 or d1 / d2 ratio of a little more than 1.75 can be achieved. In the case of another optical fiber with a higher exit NA, for example NA=0.68, which corresponds to a double acceptance angle of about 85°, a maximum taper ratio of 1.47 can be achieved. It should also be noted that the tapering of the optical fiber leads to a corresponding reduction in the thickness of the cladding of the optical fiber, so that for wall thicknesses in the range of 1-2 times the maximum transmitted light wavelength (for example up to 1 μm), due to quantum mechanical effects, the total internal reflection in the transition region from the core to the cladding is lost and the light guide emits light uncontrollably to the sides and thus loses its light guiding properties. The significant taper ratio is therefore in the range of up to 1.5 to up to 1.7 depending on the NA of the optical fiber.

[0018] In a preferred embodiment, it may be envisaged that the cross section of the end face of the light guide or the tapered end face of the tapered light guide is shaped or deformed substantially non-circularly, i.e. for example elliptical, D-shaped or kidney-shaped, or even polygonal. This allows, for example, a light exit surface arranged around the periphery of the normally square camera tip, particularly at the distal end, to be realised, which ensures a uniform illumination at the distal end of the endoscope. Thus, by appropriately deforming the distal end face from its own circular shape, the entire diameter provided at the distal end of the endoscope can be optimally utilised. This also applies if further working channels are provided in or on the endoscope, for example for the introduction or placement of minimally invasive instruments therein for use.

[0019] In some embodiments, a plastic optical fiber (POF) or a quartz-based light guide may also be used. It is particularly advantageous if the optical fiber is a core-clad fiber made of glass, in particular a multicomponent glass, and the coating is made of glass and is constructed in the form of a glass sleeve, the thermal expansion coefficient of the coating differing from that of the core glass of the optical fiber by at most 50%, preferably by at most 30%. This approach offers very good optical properties as well as advantages in processing and subsequent handling relative to plastic or quartz fibers.

[0020] With regard to the reduction of scattered light that may emerge from the light guide in the operating state, i.e. when light is incident into the light guide, in particular towards the sides, i.e. from the sides of the light guide, it has been found to be advantageous in another embodiment if the coating comprises or consists of colored or tinted glass, in particular brown or black glass, and / or comprises or consists of glass with a light-absorbing coating. Such tinted glass is obtainable by suitable colored glasses, in particular brown or black glass. Alternatively, glass that is colorless per se can be tinted, at least on the surface thus treated, by a so-called pickling process, which may be thermally assisted, for example with a silver nitrate solution. Such glass can therefore be tinted later. Alternatively or additionally, the coating may comprise a light-absorbing coating or may comprise or consist of a light-absorbing coated glass. The coating of the optical fiber light guide thus comprises or consists of colored glass, preferably black or brown glass, and / or comprises or consists of tintable glass, in particular black or brown tintable glass, and / or the coating comprises or consists of glass with a light-absorbing coating. It should be mentioned here that in the context of plastic optical fibers (POF), the coating preferably comprises or consists of a light-absorbing plastic sleeve, whether tinted or color-coated. In this way, for example, in the operating state of an endoscope equipped with a light guide according to the invention, scattered light of the light entering this light guide and exiting in particular laterally from the light guide can be reduced or minimized, and possibly even completely prevented. In this case, such a light-absorbing material can be adapted to the light to be applied, which can possibly be located in the visible wavelength range (VIS) and also in the infrared wavelength range (IR) and / or ultraviolet wavelength range (UV) of the light spectrum. In this way, for example, crosstalk of scattered light onto or into a camera mounted in the endoscope can be prevented or at least reduced, which improves the display of the object to be examined.

[0021] Particularly preferred are optical fibers made of lead-free glass systems for the core and the cladding. Such fibers are very often used in the field of medical technology and are known, inter alia, from the applicant's US Pat. No. 1,103,4612. Depending on the fiber configuration, which may be influenced in particular by the combination of the core glass and the optical cladding of the glass fiber, the optical fiber has a numerical aperture NA of at least 0.50, typically in the range of 0.57, preferably at least 0.60, typically in the range of 0.64 to 0.68, particularly preferably at least 0.80, typically 0.86, where a higher NA is fundamentally advantageous for a higher transmittable light flux. Furthermore, especially in the case of endoscopic applications, improved illumination can be achieved at the distal end of the light guide.

[0022] In the case of such optical fiber light guides, the following geometric shapes can be obtained, for example, depending on the diameter of the individual optical fibers: For example, in the case of an optical fiber diameter of (30±4) μm, a fiber bundle is obtained with a typical diameter d1 in the range of 0.5 mm to 3.0 mm, preferably in the range of 2.5 mm to 3.0 mm. In the case of thicker optical fibers with a diameter of (50±4) μm or (70±4) μm, the diameter d1 may typically be in the range of 0.5 mm to 8.0 mm, preferably in the range of 2.5 mm to 6.5 mm. These are examples of typical fibers. Basically, fibers with different, larger or smaller diameters can also be processed and used, in which case the preferred fiber bundle diameter is shifted rather to the larger or smaller range.

[0023] The thickness of the coating, in the as-processed or treated state, i.e. in the area of ​​the possibly tapered light guide surrounded by the coating, is in the range of 0.1 mm to 0.5 mm, preferably 0.15 mm to 0.25 mm, with a typical value being about 0.2 mm, where in thinner fiber bundles the thickness tends to be somewhat greater than in larger fiber bundles.

[0024] It is particularly advantageous if the glass sleeve formed as a covering has a collar or an inwardly located cone on the side facing the flexible part of the light guide containing the optical fiber, which provides an insertion aid for the optical fiber or a bundle thereof. This preferred configuration has the advantage that the optical fibers can be tightly packed and inserted into the glass sleeve with little effort. It is sufficient for this insertion aid to be formed to a size of only a few tenths of a millimeter.

[0025] In one further preferred configuration, it may be envisaged that at least the shaped and / or tapered end of the optical fiber light guide with the tapered end face in the tapered region and the other end with the original end face following the region with the substantially constant diameter d1 are respectively integrated into end sleeves made of metal or plastic, with a layer made of plastic being at least partially located between the optical fiber light guide and the inner surface of the end sleeve. The plastic is generally formed as a casting compound or adhesive. Besides the mechanical protection function for the end of the light guide, each end sleeve forms a mechanical interface for connection to a light source and / or an instrument, which may for example have a screw thread, a bayonet connection or a plug-in or locking connection.

[0026] A preferred use of the optical fiber light guide as described above envisages its use in medico-technical or industrial endoscopic instruments and / or as a light guide between a light source and an endoscopic instrument or an analysis device or as a light guide between a container and a detector unit. Due to the particularly good optical transmission properties of the Applicant's glass fibers, in particular in connection with light sources which may comprise lighting means based on halogen, LED and / or laser, a very high luminous intensity with low color shifts, i.e. poor color transmission, can be achieved. This can be shown, for example, as a difference in color temperature. Furthermore, in the case of lighting systems with several light-guiding components connected in series, as in the case of endoscopes, advantages are obtained in the overall light transmission efficiency, whether they are designed as reusable / reprocessable or disposable endoscopes. Further fields of application can also be found in dental, surgical or dermatological environments in medical technology, in particular in the field of robot-assisted medical examination procedures or surgical procedures also called "robotic surgery". In this case, the total length of the optical fiber light guide can typically be up to 6 m, and in many cases even more than 10 m. Preference is given here to light guides based on the above-mentioned glass fibers, which have a small color shift, particularly over such lengths of use.

[0027] The subject of the invention is also a method according to claim 12.

[0028] The problem with this method is to produce an optical fiber light guide having a plurality of optical fibers arranged in a flexible fiber bundle having a substantially constant diameter d1, by the following method steps: Inserting the optical fibers as a fiber bundle into a cladding tube that surrounds a predetermined partial length of the fiber bundle; heating the fiber bundle and the cladding tube present within at least a predetermined portion of the length of the cladding tube until at least the optical fiber and the cladding tube soften; - collapsing the cladding tube towards the optical fiber bundle, which may be assisted by a press and / or, for example, by negative pressure, whereby a rigid region is formed; Shaping the light guide in the rigid region away from its longitudinal axis or from the direction of its original longitudinal axis and / or deforming the cross-section or the cross-sectional geometry of the light guide. This is solved by including

[0029] By these method steps, various geometries can be realized, both with regard to axial shaping of the light guide and with regard to changing the cross-sectional geometry along the axis of the light guide, where the cross-section is constant.

[0030] In other words, in this way, an optical fiber guide is obtained, which comprises a number of optical fibers which are or can be gathered into a flexible fiber bundle having a substantially constant diameter d1, and which, at at least one end of the optical fiber guide, is surrounded all around in at least a partial region of its length by a coating, thereby forming a rigid section which includes the longitudinal axis (16), in which the optical fibers are fused to one another and preferably also to the coating, in the rigid section, and in which the optical fiber guide is bent from its longitudinal axis at least once in the region of the coating and / or the cross-sectional geometry of the optical fiber guide is deformed at least once in the region of the coating.

[0031] With regard to the additional cross-sectional modification, an embodiment of the method which is also preferred comprises, after heating of the fiber bundle and the cladding tube present in the cladding tube, additionally carrying out the following method steps: stretching the heated region until the fiber bundle present in the cladding tube, in particular together with the cladding material (20), has a diameter d2 in at least one partial region and thus a tapered region is formed in which the fiber structure is not interrupted; cutting the cladding tube and the fiber bundle present therein at a point of diameter d2 in the tapered region; It is expected that the following will be implemented.

[0032] Based on this, at least one light guide is produced which has a region surrounded by a covering material and therefore rigid, a region having a diameter d1 and a region tapering from d1 to a diameter d2, where the tapered region or tapered region has a length l2.

[0033] This is followed by the shaping process described above with respect to at least one bend and / or at least one deformation or change in cross-sectional geometry. This also allows for a light guide that is shaped at its end and whose cross section is reduced towards the end. In this case, the shaping is performed in a region having a length l2 in another preferred embodiment. That is, there is an optical fiber light guide that has a flexible region of length l1 with a substantially constant diameter d1 at its original end face and at least one rigid tapered region of length l2 following the flexible region, where the diameter of the light guide is reduced from diameter d1 to diameter d2. In this case, the tapered region is surrounded by the coating material all around in at least a partial region of its length, the fiber structure continues uninterrupted from the region having a substantially constant diameter into the tapered region, the tapered region having a tapered end face in which the optical fibers are fused with each other and preferably with the coating material, and the optical fiber light guide is bent from its longitudinal axis at least once in the region of the coating material and / or the cross-sectional geometry of the optical fiber light guide is deformed at least once in the region of the coating material.

[0034] In another embodiment, it may be assumed that in the above-mentioned method steps, the used sheathing tube already has a non-circular, in particular D-shaped, cross section, whereby it is already present as a non-circular tube itself or the tube has been formed, for example in a previous process, from a circular cross section itself to a non-circular, for example elliptical or substantially D-shaped cross section over its entire length. A sheathing tube formed or deformed in this way has the advantage that a relatively small degree of deformation of the optical fiber can be achieved during the drawing, pressing, tapering, bending or deformation of the light guide, which is advantageous in terms of reducing light losses. Furthermore, advantages in compression arise in terms of a significantly denser fusion. In comparison with a circular sheathing tube with a section formed only at the end, a further advantage arises that a sheathing tube preformed over its entire length or a light guide based on this sheathing tube can be more advantageously fitted into the often insufficiently provided construction space in an endoscope.

[0035] In one alternative method embodiment, it may additionally be envisaged that the sheath is closed on one side and that before shaping or stretching the heated region, negative pressure is applied to the sheath and the optical fiber, so that the optical fiber is fused to each other and preferably also to the sheath, which serves to compress the optical fiber further, so that the optical fibers are brought into almost ideal abutment and air intermediate spaces, so-called gussets, are largely avoided, which prevents ingress of body fluids, particularly in medical endoscopes, or of cleaning fluids, for example during processing.

[0036] In this case, once the heated region has cooled prior to cutting the cladding tube and the fiber bundle present therein, the light guide can be ground and / or polished, for example at its end face or at the tapered end face terminating the cut tapered region, thereby achieving high value optical quality of the fiber end face.

[0037] The present invention will be described in more detail below with reference to the illustrated embodiments. [Brief description of the drawings]

[0038] [Figure 1] FIG. 2 is a schematic diagram of a tapered optical fiber light guide. [Diagram 2] FIG. 1 shows a micrograph of a tapered end face of a light guide. [Diagram 3] Figures 3a to 3i are schematic diagrams illustrating examples of 3D shaped regions of a lightguide. [Figure 4] 4a to 4f are schematic diagrams showing a sequence of a manufacturing process for a light guide with a tapered circular end face of the light guide. [Diagram 5] 1A-1C show schematic diagrams of the deformation process at a rigid end of a fiber optic light guide.

[0039] 1 shows a schematic longitudinal cross section of a fiber optic light guide 1. The fiber optic light guide 1 comprises a number of optical fibers 10 which continue, without interruption in the fiber structure, along a longitudinal axis 16 from a region having a substantially constant diameter d111 and length l1 to a tapered region 12 having a length l2 and in which the diameter of the fiber optic light guide 1 decreases from d111 to a diameter d214. The tapered region 12 terminates in a tapered end face 13, and the region of substantially constant diameter d111 terminates in a natural end face 15.

[0040] The tapered region 12 is completely surrounded along its outer periphery by a coating 20. According to the embodiment shown, the coating 20 also extends beyond the tapered region 12 into a region with a substantially constant diameter d111. As already explained, the coating 20 preferably has a thermal expansion coefficient that is adapted to the thermal expansion coefficient of the material of the optical fibers 10. As also already explained, the optical fibers 10 may be disjointed, which means that the relative positions of the individual optical fibers in the input matrix of optical fibers at the original end face 15 do not coincide with the relative positions of the optical fibers in the output matrix at the tapered end face 13. This disjointed arrangement may even be intentional for illumination applications, such as in endoscopes, which can be used precisely disjointed, since by disjointing the individual optical fibers 10 a particularly uniform brightness distribution can be achieved at the tapered end face 13 formed as a light exit face. If light enters at the original end face 15 and exits at the tapered end face 13 of the tapered region 12, the optical fiber light guide 1 acts, as it were, as a light concentrator due to the change in cross section. Of course, it is equally possible for light to enter at the tapered end face 13 and exit at the original end face 15. In this case, as can be seen from Figures 1, 3a-3i, 4a and 5a, the longitudinal axis 16 is regarded as an axis that is set or can be set through the region surrounded by the coating 20 and thus rigid. The flexible region is shown simply next to the longitudinal axis 16.

[0041] Similarly, it is also possible according to the invention to arrange the optical fibers 10 for the optical fiber light guide 1 according to the invention such that the relative positions of the individual optical fibers 10 in the input matrix of the original end face 15 correspond to the relative positions of the optical fibers 10 in the output matrix of the tapered end face 13. In this case, they are referred to as aligned fiber bundles. These fiber bundles are capable of transmitting image information. When image information is coupled into the larger original end face 15, a reduced image can be received at the smaller tapered end face 13. In the opposite coupling direction, image magnification is achieved.

[0042] As also previously discussed, the light guide 10 may be rigid or flexible. Hybrid configurations are also possible, with some areas being rigid and some areas being flexible. The areas of the optical fiber light guide 1 surrounded by the coating 20 are typically rigid, with the coating 20 forming transition areas 19 where the flexible areas of the optical fiber 10 transition to fused rigid areas.

[0043] In FIG. 2, a photograph of the tapered end face 13 at the end of the tapered region 12 of an optical fiber light guide 1 according to the invention is shown. As can be seen, the optical fibers 10 are surrounded in an annular manner at their common circumferential surface by a coating material 20, which in this way contributes to the shape stabilization of the optical fibers 10. Here, the optical fibers 10 are fused to one another. This is achieved by stretching the tapered region 12 while applying a negative pressure. The negative pressure causes the optical fibers to be pressed together and to assume a substantially polygonal, in particular substantially hexagonal, well-defined shape. There is preferably no longer any intermediate space between the fused optical fibers 10, so that there is no longer any risk of media penetrating the end face 13. This is particularly advantageous in the medical application of the light guide 1 according to the invention, since in this way the light guide 1 can be autoclaved better.

[0044] At the other end of the light guide 1 or the portion of the light guide 1 that is not surrounded or formed by a cladding material, it is generally assumed that the optical fibers 10 are not necessarily fused together and are therefore considered a flexible fiber bundle. The optical fibers 10 still have a circular cross section and there are intermediate spaces between them.

[0045] Typically, the light guide 1 is fitted or integrated at its ends into corresponding end sleeves, by means of which the light guide 1 is connected or can be connected, for example, to other light guides and / or light sources and / or other objects, such as measuring instruments or endoscopic instruments, etc. These end sleeves, which may consist of metal, for example stainless steel, or plastic, for example PPS, PPSU, PC, are internally processed to accommodate, for example, the tapered region of the light guide. A casting compound, for example a one- or two-component adhesive, is usually used for fixing.

[0046] In another embodiment, it is advantageously provided that at least the flexible part of the light guide 1 or the optical fiber 10 located therein is surrounded by a flexible covering, for example as a spiral hose, for example a hose, a woven fabric or a net, made of a polymer or metal or a combination thereof. Such a flexible covering may also continue and / or at least partially surround the rigid parts of the end sleeve and / or the light guide 1 surrounded by the covering material 20. This flexible covering may comprise or consist of a so-called shrink hose material and / or may be formed in several parts from several different materials, which may also at least partially overlap.

[0047] The invention further envisages that the optical fiber light guide is not tapered at its end, but rather that a coating 20 formed as a glass sleeve surrounds the optical fibers 10 for subsequent shaping of one end of the light guide 1, crushing the bundle of optical fibers 10 during the manufacturing process to compress the optical fibers 10 so that each has a substantially dense hexagonal packing as shown in Fig. 2. Then, by a further shaping step using a press tool 150 (see Fig. 5), a contour of the light guide 1 other than cylindrical (deformation of the cross-sectional geometry) and / or a precise bending of the previously cylindrical part of the light guide 1 from the original longitudinal axis 16 of the light guide 1 can be achieved.

[0048] It should be mentioned here that this shaping process can also be applied to a previously conically tapered light guide 1, resulting in a fiber optic light guide 1 that is both tapered and deformed at the same time.

[0049] 3a to 3i show corresponding embodiments of a light guide 1 produced in this way. Each optical fiber light guide 1 shown consists of a bundle of optical fibers 10, at one end of which the light guide 1 has a shaped region 18, which is surrounded all around by a coating 20 formed as a sheath tube and in which the optical fibers 10 are fused to each other and preferably also to the coating 20 in the region of the coating 20 to form a rigid section. In this case, a transition region 19 is formed in which the optical fibers 10 transition from the non-fused region, where the fiber bundle is flexible or pliable, to the fused, i.e. rigid, region leading to the end of the light guide 1. Both this transition region 19 and the shaped region 18 are completely surrounded by the coating 20, which provides sufficient mechanical stabilization of the transition region 19. By means of a deformation process as described in Figures 5a to 5e, in the present invention the light guide 1 can be bent from its longitudinal axis 16 and / or deformed with respect to its cross-sectional geometry, for example by influencing pressure and temperature.

[0050] In the example shown in Fig. 3a-c, the light guide 1, whose cross section is constant along its longitudinal axis 16, is deformed at the end and has a shaped or deformed end face 17 which is different from a circular shape here. Exemplarily, Fig. 3a shows a shaped or deformed end face 17 with an elliptical geometry or which is compressed flat. Fig. 3b shows a shaped or deformed end face 17 with a substantially D-shaped geometry, and Fig. 3c shows a shaped or deformed end face with a kidney-shaped geometry. Furthermore, substantially polygonal, in particular square, rectangular, trapezoidal as well as triangular geometries are conceivable. Basically, any geometric shape can be formed, although in this case, depending on the material of the optical fiber 10 of the light guide 1, there are limitations on the formation of sharply formed edges or corners or, for example, pointed extending geometries due to the viscosity properties of the material in the forming process as a function of the temperature. The geometric shape that is formed will therefore always have a slight degree of rounding in such areas and thus will substantially correspond to the required or desired geometric shape that is to be achieved.

[0051] It may further be assumed that the light guide 1, whose cross section is constant along its original longitudinal axis 16, is shaped from this longitudinal axis 16. In other words, the light guide 1 is thus formed at least once bent or folded. In Fig. 3d an example is shown in which the light guide is folded or bent at the end. In Fig. 3e an example is shown in which the light guide has two bending regions.

[0052] The light guide 1 shown exemplarily in FIG. 3f has, on the one hand, two bends relative to its longitudinal axis 16 and, on the other hand, additionally has at its ends shaped end faces 17 which here exhibit an elliptical geometric shape.

[0053] Figures 3g and 3h show examples of shaped light guides 1, in which the cross section of the light guide additionally tapers towards its shaped end in a tapered region 12. Besides the two bends from the longitudinal axis 16, the light guide 1 shown in Figure 3g furthermore has an elliptically shaped or deformed end face 17. In contrast, the light guide shown in Figure 3h only has a tapered end face 13 with a still circular cross section.

[0054] The two light guides 1 shown exemplarily in Fig. 3i are each shaped similarly to the light guide 1 shown in Fig. 3g, i.e. have a combination of bends and shaped end faces 17. In this case, the arrangement of the two light guides 1 is selected such that between each light guide, a working channel and / or an electrical supply line leading to a camera chip or a fiber optic image guide, for example when mounted in an endoscopic instrument, may be arranged between the shaped end faces 17 of the light guide according to the invention (not shown in Fig. 3i). By the illustrated configuration at each end of each light guide 1, it can be achieved that the specimen, for example a tissue surface, can be illuminated without shadows.

[0055] It is pointed out that the embodiment shown in figures 3a-3i is merely exemplary. Any combination of cross-sectional variation and shaping of the light guide 1 can be achieved. For example, the per se circular cross-section of the light guide 1 may be compressed, for example flattened, only in one particular area, as in the deformation method shown diagrammatically in figures 5a-5e.

[0056] As mentioned above, the method of manufacturing an optical fiber light guide 1 having a plurality of optical fibers 10 organized in a flexible fiber bundle having a substantially constant diameter d111 comprises the following main method steps: Inserting the optical fiber 10 as a fiber bundle into a cladding tube 21 surrounding a predetermined partial length of the fiber bundle; heating the fiber bundle and the cladding tube 21 present in at least a predetermined partial length of the cladding tube until at least the optical fiber 10 and the cladding tube 21 are softened; - collapsing the cladding tube 21 towards the fiber bundle of the optical fiber 10, for example by negative pressure and / or by applying a predetermined force, whereby a rigid region is formed in which the cladding tube 21 and the optical fiber 10 are at least partially fused to the cladding tube 21 and to itself and in which the cladding tube 21 forms the cladding 20; shaping or bending the light guide 1 from its longitudinal axis 16 in the region of the cladding tube 21 and / or deforming it with respect to its cross-sectional geometry; Includes.

[0057] This applies when the cross-section along the longitudinal axis 16 of the light guide 1 remains constant, as shown diagrammatically in Figures 4a and 4b, followed by deformation process steps also diagrammatically shown in Figures 5a to 5e.

[0058] If it is additionally desired to provide a taper whose cross section decreases towards the end 13, then after heating of the fiber bundle present in the cladding tube 21 and the cladding tube 21, and additionally before the shaping process, the following method steps can be carried out: stretching the heated region until the fiber bundle present in the cladding tube 21 or thus surrounded by the cladding 20, i.e. together with the cladding 20, forms a tapered region 12 having a diameter d214 in at least one partial region and thus an uninterrupted fiber structure; cutting the cladding tube 21 and the fiber bundle present in the cladding tube 21 at a point of diameter d2 in the tapered region 12; The following will be implemented.

[0059] That is to say, the sequence of method steps for a light guide 1 including a cross-sectional taper as shown in Figures 4a to 4f is followed by the modified process steps which are also shown diagrammatically in Figures 5a to 5e.

[0060] In a first method step, shown in FIG. 4a, the optical fiber 10 is inserted into a cladding 20 formed as a cladding tube 21, thus forming a fiber bundle. In FIG. 4a, a cladding tube 21 is used, which is previously manufactured by known methods and is closed on one side. Since the cladding tube 21 remains in the light guide 1 according to the invention as the cladding 20 surrounding the tapered region 12, the material of the cladding tube 21 is preferably selected such that its thermal expansion coefficient is adapted to that of the optical fiber 10. If a core-clad fiber is used, the thermal expansion coefficient of the core material is used for the adaptation, since the core material generally constitutes the main component of the individual core-clad optical fiber 10. The optical fiber 10 itself can be manufactured in a previously known drawing process and cut to the required length. This allows standard optical fibers to also be used in the optical fiber light guide 1 according to the invention.

[0061] In Fig. 4b, another method step is shown. In this case, the optical fiber 10 inserted in the cladding tube 21 is surrounded at its end protruding from the cladding tube 21 by a vacuum chamber 100 designed to withstand the vacuum to be applied. This can be, for example, a metal tube. The connection between the cladding tube 21 and the vacuum chamber 100 is sealed by suitable means, so that when the volume formed by the vacuum chamber 100 and the cladding tube 21 is evacuated by the pump 110, there is no risk of air ingressing through the connection, or at least there is no risk of undesirable large amounts of air ingressing. At least one heating device 120 is installed so that the cladding tube 21 and partial regions of the optical fiber 10 inserted therein can be heated. As heating device 120, for example, an electric tube furnace can be used, but other devices such as burners or laser beams etc. are known to those skilled in the art and can also be used. The heating device 120 and / or the device to which the cladding tube 21 containing the optical fiber 10 is attached or to which it can be attached may also be designed to be movable, so that the cladding tube on or containing the optical fiber 10 can be collapsed and / or melted over a desired length or in a predetermined position. The closed end of the cladding tube is usually cut off (not shown) and thus an optical fiber light guide 1 is obtained which initially has a substantially constant diameter d111.

[0062] The light guide 1 with the tapered region 12 with the diameter d214 is obtained by applying further method steps. In FIG. 4c, another method step is shown, which is the drawing of the tapered region 12. Once the cladding tube 21 and the optical fiber 10 present therein have been sufficiently heated, the cladding tube 21 is drawn along the axis of the optical fiber 10, again by suitable means known per se. This causes the heated region to be elongated, which constricts it and forms the tapered region 12. The longer it is drawn, the smaller the diameter of the drawn region. The length of drawing makes it possible to adjust the desired minimum diameter d214. When a vacuum is applied inside the vacuum chamber 100 and the cladding tube 21 as described above, the pressure of the surrounding medium, usually air pressure, exerts a force perpendicular to the fiber axis of the optical fiber 10 on the optical fiber 10, so that the optical fiber 10 fuses under pressure to each other and to the inner wall of the cladding tube 21. For example, by suitably performing this process using a heating device 120, possibly including multiple heating zones, with a variable temperature profile or one or more movable heating devices, it is possible to achieve a tapered region 12 that also has a substantially constant diameter d2 after the actual tapering.

[0063] In a further method step shown in Fig. 4d, the preheated area is cooled. This can be preferably performed in a controlled manner depending on the material selection of the optical fiber 10 and the cladding tube 21, i.e. the heating device 120 is not simply switched off, but its heating power is gradually reduced, thus preventing rupture or tearing of the preheated area. Furthermore, during cooling, it is possible to continue to apply a stretching force to the optical fiber light guide 1, so that the optical fiber light guide 1 does not shrink too much during the cooling process, which would lead to a possibly undesirable change in the diameter d214.

[0064] In a further method step shown in Fig. 4e, the heating device 120 and the vacuum chamber 100 are removed and the stretched region is cut at a suitable location by means of a suitable cutting device 130. For this purpose, a location is selected where the stretched region has the desired diameter d214, possibly with a required tolerance insert for further processing.

[0065] The result of the manufacturing process according to the invention, shown in Fig. 4f, is an optical fiber light guide 1 according to the invention, in which the optical fibers 10 continue into the tapered region 12 without interruption of the fiber structure. The cladding tube 21 or the stretched region of the cladding tube 21 surrounds the tapered region 12 as a coating 20 and shape-stabilizes it. The cladding tube 21 is thus endowed with at least a double function, namely the function of assembling the optical fibers 10 into a fiber bundle for the manufacturing process and the function of protecting the delicate transition region 12 at the end of the optical fiber light guide 1 as a coating 20 in the final product. Optionally, the cladding tube 21, insofar as it is closed on the side opposite the flexible end, can also have the further function of making it possible to apply a negative pressure during the stretching of the transition region 12, thus enabling the fusion of the optical fibers 10 with each other, and preferably also with the cladding tube 21, particularly in the transition region 12, to be further improved.

[0066] In another embodiment, it may be assumed that in the above-mentioned method steps, the cladding tube 21 already has a non-circular cross-section and / or has been formed in a previous process from a per se circular cross-section into a non-circular cross-section, in particular into an elliptical or substantially D-shaped cross-section. In such or per se non-circular embodiments, the maximum transverse dimension is understood to be the diameter d1 or d2, respectively.

[0067] To manufacture one preferred embodiment of the optical fiber light guide 1 according to the invention, for example 2200-2500 flexible core-clad optical fibers 10, glass fibers with a diameter of 70 μm, are assembled into one fiber bundle with a diameter of 3.80 mm-4.25 mm, and the optical fiber light guide 1 is formed by the described method with a tapered region with a length l2 of 15-20 mm, which is also surrounded by glass as cladding material 20 having substantially the same thermal expansion coefficient as the core glass of the optical fiber 10. In this case, the diameter d214 of the optical fiber 10 fused at the tapered end face 13 of the tapered region 12 is 2.20 mm. L1 can be chosen arbitrarily, but is typically a few tens of centimeters to a few meters, but can also reach a length of 10 m or more. The end faces 13, 15 may be incorporated into a generally metal sleeve, and the area between the metal sleeves may be surrounded by a flexible protective cover made of plastic. The metallic end sleeve at the end of the tapered region 12 preferably has a cylindrical outer geometry. However, since the tapered region 12 is substantially conical, the metallic sleeve preferably has a conical inner geometry that matches the tapered region 12, so that a substantially form-locking connection between the outer circumferential surface of the transition region 12 and the inner circumferential surface of the end sleeve can be produced. The invention also includes the case where a layer, for example of a plastic, in particular for example of an adhesive, is located between the outer circumferential surface of the transition region 12 and the inner circumferential surface of the end sleeve.

[0068] The optical fiber light guide 1 according to the invention has an improved transmission compared to light guides known from the prior art due to an uninterrupted fiber structure at the transition to the tapered region 12. The optical fiber light guide 1 can be produced from standard optical fibers inexpensively by the method according to the invention. This makes the manufacturing process of the optical fiber light guide 1 flexible, and various geometries and diameters d1 of the guide region and diameters d2 of the tapered region 12 can be produced economically as required.

[0069] 5a to 5e show diagrammatically how a shaped feature can be produced at the rigid end of the optical fiber light guide 1, ie the end surrounded and fixed by a coating 20 or a coating tube .

[0070] The optical fiber 10 and its coating 20 previously fused to the optical fiber 10, shown on the left of FIG. 5a as a cylinder with a constant cross section or on the right as a cylinder with a tapered cross section, are heated by a heating device 140 (FIG. 5b) so that the actual deformation can be carried out in the next step (FIG. 5c). In this case, the desired contour is pressed or generated by a deformation or shaping means, for example by a pressing or deformation tool 150, into the optical fiber 1, so that the optical fiber 1 has a deformation region 18 as shown in FIG. 5d. This deformation region may have various forms, as illustrated in FIGS. 3a to 3i. In this case, it may be possible or necessary, especially in the case of complex embodiments as desired or required, to be applied or provided in two or more shaping steps in succession, in particular also by means of different pressing or deformation tools 150. That is, for example, a bending can first be produced at the rigid end of the light guide 1 from its original longitudinal axis 16, then, in particular, a further bending can be produced in a different direction, followed by a deformation or rigid region at the end face 13 and / or a further cross-sectional region of the bent end. This can involve several heating steps, and corresponding forming or deformation processes can be carried out simultaneously (in parallel) and / or sequentially (successively), as appropriate. At the end of the light guide, in particular if the covering material 20 has been melted beforehand, excess parts of the covering material 20 are possibly cut off (FIG. 5e). This is generally followed by a grinding and polishing process of the end face or tapered end face 13. [Explanation of symbols]

[0071] 1 Optical fiber light guide 10 Optical Fiber 11 diameter d1 12 Tapered Area 13 Tapered End Face 14 diameter d2 15 Original end face 16 Longitudinal axis 17 Molded End Face 18 Molding area 19 Transition Zone 20 Covering material 21 Cladding tube 100 Negative pressure chamber 110 Pump 120 Heating device 130 Cutting device 140 Heating device 150 Press Tools

Claims

1. Substantially constant diameter d １ 1. An optical fiber light guide (1) comprising a plurality of optical fibers (10) that are or can be gathered into a flexible fiber bundle having a longitudinal axis (16), wherein at least one end of the optical fiber light guide (1) is surrounded by a coating material (20) around the entire circumference of at least a portion of the length of the optical fiber light guide (1), thereby forming a rigid section that includes a longitudinal axis (16); the optical fibers (10) are fused together and preferably also to the coating material (20) in the rigid section; the optical fiber light guide (1) is bent from its longitudinal axis (16) at least once in the region of the coating (20) and / or the cross-sectional geometry of the optical fiber light guide (1) is deformed at least once in the region of the coating (20); Optical fiber light guide (1).

2. The optical fiber light guide (1) has a substantially constant diameter d at its original end face (15). １ (11) with length l １ and the diameter of the light guide (1) following the flexible region is d １ (11) from the diameter d ２ (14) At least one length l reduced to ２ and a tapered region (12) of the tapered region (12) is surrounded by the coating material (20) over at least a portion of its length, and the fiber structure continues uninterrupted from the region of substantially constant diameter into the tapered region (12); The tapered region (12) has tapered end faces (13) where the optical fibers (10) fuse together and preferably also with the coating material (20).

2. The optical fiber light guide (1) according to claim 1.

3. 3. The optical fiber light guide (1) according to claim 2, wherein the cross section of the end face of the light guide (1) or the tapered end face (13) of the tapered light guide (1) is shaped substantially non-circular, elliptical, D-shaped, kidney-shaped or polygonal.

4. 3. The optical fiber light guide (1) according to claim 1 or 2, wherein the optical fiber (10) is a core-clad fiber made of glass, and the cladding material (20) is made of glass whose thermal expansion coefficient differs by at most 50%, preferably by at most 30%, from the thermal expansion coefficient of the core glass of the optical fiber (10).

5. The cladding material (20) comprises colored glass, preferably black or brown glass. The cladding material (20) comprises tintable glass, in particular black or brown tintable glass. The cladding (20) comprises a light-absorbing coated glass.

5. The optical fiber light guide (1) according to claim 4, characterized in that at least one of the following is true:

6. 5. The optical fiber light guide (1) according to claim 4, wherein the optical fiber (10) is made of a lead-free glass system for the core and the cladding, and the optical fiber (10) has a numerical aperture NA of at least 0.50, preferably at least 0.60, particularly preferably at least 0.

80.

7. When the diameter of the optical fiber (10) is (30±4) μm, the diameter d １ (11) is in the range of 0.5 mm to 3.0 mm, preferably in the range of 2.5 mm to 3.0 mm; When the diameter of the optical fiber (10) is (50±4) μm or (70±4) μm, the diameter d １ (11) is in the range of 0.5 mm to 8.0 mm, preferably in the range of 2.5 mm to 6.5 mm; 3. An optical fiber light guide (1) according to claim 1 or 2.

8. The optical fiber light guide (1) according to claim 1 or 2, wherein the thickness of the coating (20) is in the range of 0.1 mm to 0.5 mm, preferably in the range of 0.15 mm to 0.25 mm.

9. 5. The optical fiber light guide (1) according to claim 4, wherein the covering material (20) is formed as a glass sleeve, which has a collar or an inner cone formed on the side facing the flexible part of the light guide (1) containing the optical fiber (10).

10. The shaped and / or tapered end of the optical fiber light guide (1) has at least the tapered end face (13) in the tapered region (12) and the substantially constant diameter d １ 3. The optical fiber light guide (1) according to claim 2, wherein the other end with the original end face (15) following the region having the optical fiber (11) is incorporated into an end sleeve made of metal or plastic, and a layer made of plastic is at least partially located between the optical fiber light guide (1) and the inner surface of the end sleeve.

11. 3. Use of an optical fiber light guide according to claim 1 or 2 in a medical-technical or industrial endoscopic instrument and / or as a light guide between a light source and an endoscopic instrument or an analytical device or as a light guide between a container and a detector unit.

12. Substantially constant diameter d １ 1. A method for manufacturing an optical fiber light guide (1) having a plurality of optical fibers (10) that are or can be grouped together in a flexible fiber bundle having a plurality of optical fibers (11), the method comprising: Inserting the optical fibers (10) as a fiber bundle into a cladding tube (21) that surrounds a predetermined partial length of the fiber bundle; heating the fiber bundle and the cladding tube (21) present within the cladding tube (21) until at least the optical fiber (10) and the cladding tube (21) soften in at least a predetermined partial length of the cladding tube; collapsing the cladding tube (21) towards the fiber bundle of the optical fiber (10); Shaping the light guide (1) and / or modifying the cross-sectional geometry of the light guide (1) from its longitudinal axis (16) in the region of the covering tube (21). A method including each of the method steps of

13. After heating the fiber bundle and the cladding tube (21) present in the cladding tube (21), additionally: The fiber bundle present in the cladding tube (21) together with the cladding material (20) has a diameter d ２ stretching the heated region until a tapered region (12) is formed having a diameter (14) and an uninterrupted fiber structure; The cladding tube (21) and the fiber bundle present in the cladding tube (21) are tapered to the diameter d ２ Step of cutting at 13. The method of claim 12, comprising the method steps of:

14. 14. A method according to claim 12 or 13, wherein the cladding tube (21) has a non-circular, preferably elliptical or substantially D-shaped cross section.

15. 14. The method according to claim 12 or 13, wherein the cladding tube (21) is closed on one side and, before shaping or stretching the heated region, a negative pressure is applied to the cladding tube (21) and the optical fiber (10), thereby fusing the optical fiber (10) to each other and preferably also to the cladding tube (21).

16. 14. The method of claim 12 or 13, wherein the heated region is cooled before cutting the cladding tube (21) and the fiber bundle present within the cladding tube (21).

17. 14. The method according to claim 12 or 13, wherein the end face or the tapered end face (13) terminating the cut tapered region (12) is ground and / or polished.

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