Machining an insulated optical fibre

[0001] This invention concerns the processing of an insulated optical fibre.

[0002] Optical fibres are usually provided with an insulation, which can comprise several layers. The optical fibre must be stripped before a connecting member, e.g. a connector can be mounted on it. Even if two fibres are to be connected together permanently or temporarily, e.g. in order to conduct optical measurements, both fibres must be stripped at the ends that are to be brought into contact with each other.

[0003] An apparatus for removing the insulation from an optical fibre is known from WO 98/33082. This apparatus has a retention device into which an insulated fibre to be processed can be placed and which clamps the insulated fibre placed into it. The apparatus also has a holder-bracket assembly with two heatable holder brackets, between which a projecting section of the insulated fibre extends beyond the retention device in a starting position. In relation to each other, the holder brackets can be adjusted substantially perpendicular to the fibre and can clamp and heat a section of the fibre insulation in a holding position. Moreover, the familiar apparatus comprises a cutting device, which cuts into the fibre insulation at a substantially perpendicular angle. In relation to the holder-bracket assembly, the retention device can be adjusted in parallel to the fibre, whereby the fibre is fixed in relation to the retention device when this device is adjusted, while the cut-off insulation is fixed in relation to the holder-bracket assembly, as this is clamped between the holder brackets. The adjusting movement of the retention device draws out the optical fibre from its insulation.

[0004] In order to realise a relatively high-quality optical connection with the lowest possible transmission losses, an interface must be created at the end of the stripped fibre, which is as even as possible. In the case of optical fibres, in particular glass fibres, even interfaces can be realised by means of a cleaving method in which the fibre is cleaved substantially perpendicular to its lengthwise direction. Cleaving tools are available to this end, e.g. from the company of York Technology in the United Kingdom, into which the fibre with its stripped end section is placed. The stripped fibre is clamped in two positions, which are a particular distance apart, and cleaved using a cutting element which is perpendicular to this, in particular with a diamond blade, perpendicular to the lengthwise direction of the fibre.

[0005] An apparatus is known from U.S. Pat. No. 6,023,996, which on the one hand enables the fibre to be stripped and on the other allows it to be cleaved. To this end, the insulated fibre is placed in a holder and subsequently clamped. This holder is positioned on a base plate of the apparatus in an initial station, in which the fibre is stripped. In this situation, the end section of the fibre to be stripped extends into a stripping tool, in which the insulation is first heated. Following adequate heating, two handles are operated that are used to operate a cutting device, which cuts perpendicularly into the fibre insulation to be removed. The handles and the cutting device are mounted on a slide which can be moved parallel to the longitudinal axis of the fibre. By operating the handles, the cutting device can be used to entirely remove the cut-in fibre insulation so that the fibre has a stripped end section from now on. After the fibre is stripped, the holder is manually positioned in a second station on the base plate, where the stripped fibre can be cleaved.

[0006] The end section of the stripped and cleaved fibre can now be inserted into an adapter or into any other connecting member, in order to realise an optical coupling, for example using a measurement and/or testing device. It is similarly possible to optically connect together two stripped and cleaved fibre ends. To this end, both fibre ends can, for example, be placed in a linear adjustment groove, in which both cleaved fibre ends abut each other face-on. In this position, both fibres can be clamped to the adjustment groove or to a support in the adjustment groove, in particular with a holding-down clamp. Special coupling fluids can be used in order to improve the optical coupling, e.g. in order to reduce the effects of optical refraction at the media boundaries.

[0007] Alternatively, two optical fibres can also be optically connected together in such a way that their stripped and cleaved ends are welded or fused together, for example by means of a laser or a welding arc. The connection of two fibres is called splicing; Splicing devices that connect two fibre ends together by means of a fused or welded connection are called fusion splicers. Examples of fusion splicers are the FSM40S and FSM30R from the company of Fujikura.

[0008] An apparatus is referred to in U.S. Pat. No. 5,999,682 that can be used to strip and cleave the end sections of two fibres and subsequently connect them in an adjustment groove. The apparatus in question has a holder for each fibre, in which the respective fibre is clamped so that a free end section projects from the holder. Each of these holders is placed in a support, which can be adjusted in the lengthwise direction of the fibre. The apparatus has a cutting tool for each fibre, which cuts into the fibre insulation when operated. Moreover, there is a separate cleaving unit for each fibre, which clamps and tensions the stripped fibre by means of special holder brackets in order to cleave it by means of a suitable cleaving tool. The individual holders, supports, cutting tools and cleaving units of both fibres are configured symmetrically to each other, while a connecting unit comprising an adjustment groove and holding-down clamp is configured centrally between them. The apparatus operates with a rotary drive, comprising cams to activate and operate the individual components of the apparatus.

[0009] The fibres are stripped and cleaved as follows: The blades of the cutting tool move perpendicular to the fibre until they cut into the insulation. The blades remain in this position while the support containing the holder is removed from this parallel to the lengthwise direction of the fibre. Since the fibre is clamped in the holder, the fibre is therefore drawn out of its insulation, thereby subsequently presenting a stripped end section. The blades are then moved away again, while the holder brackets move towards the stripped fibre in order to hold it from now on. After the stripped fibre is secured between the holder brackets, the support is again adjusted so that it is parallel to the axis of the lengthwise direction of the fibre in order to tension the fibre. When the fibre has been tensioned, the cutting tool is operated in order to cleave the fibre. The holder brackets then release the removed section of stripped fibre and the supports now move towards each other to insert the stripped and cleaved fibre end into the adjustment groove of the connecting unit.

[0010] In order to create a high-quality cleaved surface at the fibre end, the individual tools and components must be positioned together with a high level of precision. For example, the cutting tool must be adjusted relatively precisely in respect of the support or the holders in order to avoid damaging the fibre during the cutting procedure. Similarly, the holder brackets must be aligned relatively precisely to the holder in order to avoid random bending stresses in the fibre during the cleaving procedure. The higher the quality of the cleaved surface created in this way, the higher the quality of the optical connection, which can then be created.

[0011] Another apparatus for removing insulation and for fusion-splicing an optical fibre is known from EP 0 899 594 A2. This apparatus also has a retention device for placing and clamping the fibre to be stripped as well as a holder-bracket assembly with two holder brackets for clamping the fibre end projecting from the retention device. When the fibre end is clamped between the holder brackets, two blades cut into the fibre insulation. The holder brackets can be heated in order to soften the insulation to be removed. When the insulation to be removed has been adequately heated, the retention device can be removed from the holder-bracket assembly in the direction of the fibre, during which the blades and the holder brackets hold onto the softened insulation so that the optical fibre is completely drawn out of its insulation. A cleaving procedure and a splicing procedure can then be carried out by means of a method not described in greater detail here.

[0012] A manufacturing procedure for cutting and prior removal of the casing from cables and wires, and an apparatus for carrying out this procedure is known from DE 692 08 235 T2. This apparatus can be used to cut several cables contained in a cable bundle simultaneously and remove their casing in advance. To this end the apparatus comprises at least an initial cutting device, which splits the cable cores without splitting their mantles or insulation completely. At least a second cutting device splits the mantles or insulation of several cables in a different position without cutting into the cable cores.

[0013] Moreover, U.S. Pat. No. 4,046,298 describes a procedure and an apparatus for stripping a protective layer from a fibre bundle containing several optical fibres. To this end, the fibre bundle is placed on a rotatable, cylindrical wheel, whereby a blade cuts into the protective layer. In this case, the wheel is rotated in order to cut the protective layer, while at the same time the fibre is bent in the best possible way to allow the subsequent procedure of breaking or cleaving the fibre to be carried out.

[0014] The task of the present invention is to simplify the manufacture of a high-quality optical connection. This task is resolved by the features of the independent claim. The dependent claims describe advantageous embodiments.

[0015] The invention is based on the concept of allocating a dual function to the holder-bracket assembly, namely on the one hand a holding function when the fibre is drawn out of its insulation and on the other hand a holding function when tensioning the fibre for the cleaving procedure. This construction means that the fibre, retention device and holder-bracket assembly always have the same alignment orientation when the fibre is being stripped and cleaved; it is no longer necessary to change the clamping tools. This can increase the overall precision of the cleaving procedure, making it possible to improve the quality of the attainable optical coupling. In the case of the apparatus according to the invention, the end section of the fibre is not completely stripped, unlike in conventional procedures, rather a fibre end remains in the removed section of insulation. In order to tension the stripped fibre section, it is clamped indirectly by both the retention device and the holder-bracket assembly indirectly via the insulation, thereby avoiding any damage to the fibre. In contrast to this, all the conventional procedures fist fully strip the fibre end section and then clamp the stripped fibre directly in order to carry out the cleaving procedure, which may cause damage to the fibre.

[0016] Moreover, the new procedure made possible by the apparatus according to the invention has the great advantage that at least part of the cleaved and stripped fibre end section is still located in the insulation, making it significantly easier to dispose of the fibre section, which is detrimental to health.

[0017] In a special embodiment, the holder brackets of the holder-bracket assembly can be controlled so that a retention force by which the holder brackets hold the fibre insulation when tensioning the fibre for the cleaving process is greater than when the fibre is drawn out of its insulation. In this way, greater tensile forces can be exerted on the fibre to tension it than when the fibre is being drawn out of the insulation after it has been stripped.

[0018] In a special embodiment, the stripped fibre can be cleaved during the relative adjustment between the retention device and the holder-bracket assembly. This makes continuous processing possible, in which the stripping procedure is terminated seamlessly by the cleaving procedure.

[0019] An embodiment is particularly advantageous, in which the retention device has a seating for mounting an adapter, into which the insulated fibre to be processed can be placed and which clamps the insulated fibre placed within it, wherein this adapter can be connected to an optical device, e.g. a measurement and/or testing device or a positioning device. A stripped and cleaved fibre must usually be inserted or threaded into such an adapter with care, wherein the even cleaved surface at the fibre end can easily be damaged. This difficult threading procedure can be dispensed with in the proposed embodiment.

[0020] In a specific further development, the fibre can be positioned in or on the adapter after having been cleaved and after the adapter has been removed from the seating in such a way that without further difficult manipulations in the adapter, particularly with respect to positioning, the fibre contained in the adapter can be optically connected directly to the relevant device, e.g. a measurement and/or testing device or a positioning device.

[0021] In accordance with a different special embodiment, at least two retention devices can be provided so that at least two fibres can be stripped and cleaved, wherein moreover a splicing tool is provided, which connects together two stripped and cleaved optical fibres that have been positioned together. According to the invention, the two retention devices can be adjusted in relation to each other in such a way that the splicing tool uses these retention devices to position the fibres to be optically connected together in relation to each other. These measures mean that the retention devices have a dual function, namely on the one hand holding the fibre while it is being stripped and cleaved and on the other hand holding the fibre to position it within the splicing procedure. This means that the fibre only has to be positioned in the retention device at the beginning of the process, and it is no longer necessary to make any adjustment during the remainder of the process, wherein the overall precision and quality of the connection between the two fibres created in this way increases.

[0022] The invention is described in the following by referring to the diagrams, wherein the same reference symbols refer to the same or functionally identical or similar features. Schematic representations are provided of the following,

[0023] FIGS. 1 through 5 top views of a highly simplified representation of the apparatus according to the invention involving an initial embodiment and various operating phases,

[0024] FIG. 6 a side view of the apparatus according to FIG. 5,

[0025] FIGS. 7 and 8 top views of the apparatus according to the invention, but of a second embodiment and various operating phases,

[0026] FIG. 9 a top view of the apparatus according to the invention, but of a third embodiment,

[0027] FIGS. 10 through 12 top views of the apparatus according to the invention, but of a fourth embodiment and various operating phases, and

[0028] FIGS. 13 through 15 top views of the apparatus according to the invention, but of a fifth embodiment and various operating phases.

[0029] In accordance with FIGS. 1 through 6 an initial embodiment of the apparatus 1 according to the invention has a retention device 2, comprising a holder 3, into which an insulated fibre can be placed. In the figures, the insulated fibre is constantly identified by the number 4, while the actual fibres are referred to as 5 and their insulation as 6. It is evident that insulation 6 can be comprised of a single layer or multiple layers. The figures only illustrate an end section of insulated fibre 4; at the other end of insulated fibre 4, which is not illustrated, this may lead to an optical module or device.

[0030] Holder 3 can have a permanent connection to retention device 2. In a different embodiment, it is possible to remove holder 3 and holder 2 that are clamped together, to which end holder 2 has a corresponding seating 7. In a special embodiment, holder 3 can be provided as an adapter, which can be connected to an optical measurement and/or testing device.

[0031] The insulated fibre 4 placed in holder 3 can be clamped in holder 3 to which end holder 3 has corresponding holding implements that are not illustrated.

[0032] Moreover, apparatus 1 has a holder-bracket assembly 8, which has two holder brackets 9. Holder brackets 9 are oriented parallel to fibre 5 and in the starting position illustrated in FIG. 1 form a gap 10 between them, into which the projecting section 13 of insulated fibre 4 extends while clamped in holder 3 via retention device 2.

[0033] Furthermore, a cutting device 11 is provided, which when operated can cut perpendicularly into the insulation 6 of fibre 5, which is to be removed. To this end, cutting device 11 can be constructed in the conventional way and have in particular two V-shaped blades, which are not illustrated, which are adjusted to cut into insulation 6 perpendicular to fibre 5, thereby gripping and cutting into insulation 6 with their cutting flanks.

[0034] Moreover, the apparatus has a cleaving unit 12, which makes it possible to cleave stripped fibre 5 substantially perpendicular to its lengthwise direction, provided that fibre 5 is tensioned in the lengthwise direction. For example, this kind of cleaving unit 12 has a cleaving blade, which is not illustrated, and which can be adjusted against fibre 5 perpendicular to the lengthwise direction of the fibre.

[0035] Apparatus 1, which is in accordance with the invention, as illustrated in FIGS. 1 through 6, operates as follows: Insulated fibre 4, the end section of which is to be stripped and which is to be provided with cleaved end, is placed and clamped in holder 3. According to FIG. 1, insulated fibre 4 is positioned in holder 3 so that the free end section 13 of insulated fibre 4 extends by means of an axial length 14 into the gap 10 formed between holder brackets 9. Here, holder 3 is configured so that fibre section 13 and holder brackets 9 are automatically oriented in parallel.

[0036] In the next step, according to FIG. 2 the holder brackets 9 are adjusted in relation to each other, wherein this adjustment moves perpendicular to the lengthwise direction of the fibre. In this way, both holder brackets 9 clamp fibre section 13 between them. Holder-bracket assembly 8 is provided with heating elements 15, which are integrated here in holder brackets 9. This means that at least one of the holder brackets 9 can be heated. The purpose of heating elements 15 is to heat insulation 6 in the cable section clamped between holder brackets 9 and thereby reduce the stability of insulation 6, which is regularly manufactured from a polymer. As soon as the heating procedure is complete, cutting device 11 is operated, which cuts into insulation 6 at the boundary between insulated fibre 4 and the fibre section to be stripped. The cutting procedure can also be carried out before or during the heating procedure accordingly.

[0037] According to FIG. 3 retention device 2 and holder-bracket assembly 8 can be adjusted in relation to each other and parallel to fibre 5. The figures represent this adjustment option symbolically by means of a pair of rails 16. According to FIG. 3 retention device 2 moves away from holder-bracket assembly 8, by which fibre 5 is drawn out of the cut-off insulation 6. As soon as stripped fibre 5 is drawn sufficiently far out of cut-off insulation 6, cleaving tool 12 is operated to cleave fibre 5 perpendicular to the lengthwise direction of the fibre.

[0038] Accordingly, holder brackets 9 and therefore holder-bracket assembly 8 have a dual function, as holder brackets 9 clamp the section of insulation to be removed during stripping and exert a corresponding tensile stress on stripped fibre 5 during the cleaving procedure. Furthermore, it is preferable to provide holder brackets 9 with a heating facility so that these have an additional function.

[0039] According to FIG. 4 the cleaving procedure at an end 17 of stripped fibre 5 produces an even cleaved surface, which is particularly suited to creating an optical coupling. According to the invention, the cleaving procedure is only possible because when cleaving unit 12 is operated, stripped fibre 5 is still tensioned between retention device 2 and holder-bracket assembly 8. In order to exert a tensile stress on fibre 5 that is suitable for cleaving it, it may be practical for holder brackets 9 to be controlled according to a preferred embodiment, in which a retention force used by holder brackets 9 to clamp fibre insulation 6 is increased to tension the fibre, in order to increase the removal resistance of fibre 5 from its insulation 6.

[0040] The cleaving process can in principle be carried out intermittently, i.e. retention device 2 and holder-bracket assembly 8 are fixed in relation to each other at the moment of cleaving, and the adjusting motion of retention device 2, by which this moves away from the holder-bracket assembly 8, is therefore interrupted for the cleaving process. It is similarly possible to continuously integrate the cleaving procedure in the adjusting motion of retention device 2 so that the adjusting motion of retention device 2 moves without interruption from the starting position according to FIG. 2 via the cleaving position according to FIG. 3 to the end position according to FIG. 4.

[0041] The cleaving procedure is preferably controlled so that a predetermined axial length of the stripped fibre section projects over insulation 6 at the side of retention device 2. Moreover, apparatus 1 can be configured in such a way that retention device 2 and holder-bracket assembly 8 can be rotationally adjusted in relation to each other and concentrically to fibre 5. When a torsion moment is exerted on axially tensioned fibre 5 during the cleaving process, the even surface at end 17 of fibre 5 can be provided with an advantageous angle in relation to a surface positioned vertically in relation to fibre 5.

[0042] Axial length 14 with which end section 13 extends into gap 10 between holder brackets 9 (cf. FIG. 1), is preferably chosen to be greater as the adjustment path of retention device 2 in relation to holder-bracket assembly 8 from the starting position according to FIG. 2 to the cleaving position according to FIG. 3. The result of this measure is that another section of fibre 5 is located in the insulation section clamped between holder brackets 9. This safeguards the facility of exerting an adequate tensile force in fibre 5 via holder brackets 9.

[0043] Moreover, the adjustment path of retention device 2 until the cleaving procedure and the position of cutting device 11 are oriented to each other in such a way that after fibre 5 has been cleaved, part of fibre 5 is still present in the insulation section clamped between holder brackets 9. This means that fibre 5 is easy to remove, in particular by hand.

[0044] FIGS. 5 and 6 illustrate apparatus 1 according to the invention with open holder brackets 9, wherein the cleaved fibre section and the removed insulation have already been removed from gap 10 of holder brackets 9.

[0045] Provided that holder 3 is configured as an adapter, it may be practical to carry out the insulation and cleaving processes in such a way that after removing the adapter (holder 3) from seating 7, the stripped and cleaved fibre 5 is positioned in or on the adapter in such a way that the fibrewithout further manipulationcan be optically connected using adapter 3 to the appropriate optical device, e.g. a measurement and/or testing device and/or a positioning device.

[0046] The embodiment of apparatus 1 according to the invention illustrated in FIGS. 1 through 6 forms a unit 18, which makes it possible to strip and cleave an optical fibre 4 or 5 in an automatic procedure. Although only one individual fibre 4 is processed in the sample execution, apparatus 1 can also be configured in such a way to simultaneously process several fibres 4, which are integrated in a fibre bundle, i.e. apparatus 1 can then strip and cleave all fibres 4 of such a fibre bundle simultaneously.

[0047] FIGS. 7 through 15 represent various embodiments of apparatus 1 according to the invention, which have been provided with an additional splicing tool 19. In the figures, splicing tool 19 is represented only by a frame outlined by dotted lines. Splicing tool 19 can be used to connect together two stripped und cleaved fibre ends with a high optical quality. Various techniques are available here for the splicing and connection process. For example, the fibre ends can be placed in an accurately prepared, linear adjustment groove to allow the fibre ends to come into contact with each other face-on. However, an embodiment is preferred in which the fibre ends are fused together. In that case, splicing tool 19 is actually a fusion-splicing tool.

[0048] The common feature of all embodiments of FIGS. 7 through 15 is that apparatus 1, which is provided with splicing tool 19 has two retention devices 2 for splicing together two stripped, cleaved fibre ends 17. This means that retention device 2 has a dual function. On the one hand, during the stripping procedure, retention device 2 serves to draw out fibre 5 from the cut-off insulation 6 and to tension stripped fibre 5 for the cleaving procedure. On the other hand, retention device 2 serves to position the allocated, stripped and cleaved fibre ends 17 in splicing tool 19.

[0049] At least for the case in which splicing tool 19 is a fusion splicer, both retention devices 2 can be adjusted three-dimensionally to each other in order to optimally position both fibre ends 17 to be connected together.

[0050] FIGS. 7 and 8 represent an embodiment, in which an entire unit 18 is provided for each insulated fibre 4. In this way, two insulated fibres 4 can be stripped and cleaved simultaneously. After the stripping and cleaving process, retention devices 2 assume the positions indicated in FIG. 7, both of which correspond to the positions indicated in FIG. 5. In order to splice both stripped and cleaved fibre ends 17 obtained in this way, both retention devices 2 are rotated 180 about a vertical axis, which is vertical to the plane of the diagram, so that both fibre ends 17 from now on are essentially axially facing each other. Corresponding adjusting motions of at least one of the retention devices 2 means that both fibre ends 17 can then be positioned in relation to each other in splicing tool 19 in such a way to carry out the splicing procedure. In this special embodiment, both units 18 are essentially aligned symmetrically with each other.

[0051] In the embodiment according to FIG. 9, both units 18 are positioned in relation to each other in such a way that both retention devices 2 only have to be rotated by 90 to be able to position fibre ends 17 in splicing tool 19 in relation to each other. It is evident that any number of other spatial arrangements are possible for both units 18.

[0052] FIGS. 10 through 12 represent a further special embodiment of apparatus 1 according to the invention, in which a common unit 18 comprising holder-bracket assembly 8, cutting device 11 and cleaving unit 12 is allocated to both retention devices 2. Here, both retention devices 2 can be adjusted, for example, using corresponding rails 16, one after the other, from an initial position according to FIG. 10 to a first position, in which they collaborate separately and independently of each other with common unit 18 in order to strip and cleave the fibre ends clamped in the respective retention device 2. Correspondingly, FIG. 11 shows lower retention device 2 in the starting position, while the upper retention device occupies the aforementioned first position. When both fibre ends have been stripped and cleaved, both retention devices 2 are moved to a second position according to FIG. 12, wherein both retention devices 2 are, for example, rotated 90 about a vertical axis, which is vertical to the plane of the diagram. The stripped and cleaved fibre ends 17 are then aligned to each other in splicing tool 19 and can be positioned in relation to each other by means of adjustable retention devices 2.

[0053] FIGS. 13 through 15 represent a further special embodiment of apparatus 1 according to the invention, wherein a common unit 18 is again allocated to both retention devices 2. In this embodiment common unit 18 has a common holder-bracket assembly 8 in a central section with holder brackets 9, the axial length of which is chosen to be approximately twice as long as the axial length of the embodiment illustrated in the other figures. Correspondingly, the fibre-end sections to be stripped are placed in one after the other in holder brackets 9. It is similarly possible to place the fibre-end sections one above the other in holder brackets 9, which can then in turn be shorter. A cutting device 11 and a cleaving tool 12 are then configured on both sides of holder-bracket assembly 8.

[0054] Both retention devices 2 can then be adjusted simultaneously from a starting position to an initial position according to FIG. 13, whereby the simultaneously collaborate with common unit 18. According to FIG. 13 the end sections 13 of insulated fibre 4 thereby extend simultaneously into the common gap 10 of common holder brackets 9. Clamping, heating and cutting into insulation 6 as well as removing and cleaving fibre 5 can then be conducted simultaneously for both insulated fibres 4. After the stripping and cleaving process, both retention devices 2 are, for example, located in the position illustrated in FIG. 14, and can be adjusted to a second position, in particular via suitable rails 16, according to FIG. 15, wherein retention devices 2 position fibre ends 17 prepared in this way in splicing tool 19 in relation to each other. The splicing procedure can then be carried out.

[0055] In the sample executions illustrated, apparatus 1, in particular its retention device 2, holder-bracket assembly 8, cutting tool 11, cleaving tool 12 and splicing tool 19, are configured in such a way that a couple of fibre ends 17 can be stripped, cleaved and connected together with the highest possible optical quality.

[0056] It is however possible in principle also to assemble such an apparatus 1 in such a way that several fibre pairs can be optically connected together. This is particularly advantageous, when several individual fibres are integrated to form a fibre bundle, so that apparatus 1 according to the invention can be used, for example, to optically connect together two such fibre bundles. This individual fibre pairs can for example, in principle, be connected in succession, if the fibre bundle in question was previously separated into individual fibres. It is likewise possible to connect together several or all fibre pairs simultaneously. In the case of separated fibre bundles apparatus 1 can have two separate retention devices 2 for each fibre pair.