GB1558605A

GB1558605A - Optical waveguides

Info

Publication number: GB1558605A
Application number: GB2885476A
Authority: GB
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1975-07-10
Filing date: 1976-07-12
Publication date: 1980-01-09
Also published as: JPS5931042B2; FR2317669A1; FR2317669B1; JPS5210150A; NL7607666A

Description

(54) IMPROVEMENTS IN OR RELATING TO OPTICAL WAVEGUIDES (71) We, SIEWENS AKTIENGESELL SCHAFT, a German Company of Berlin and Munich, German Federal Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement.

The invention relates to methods of connecting single fibre optical waveguides and to apparatus for performing such methods.

For the connection of single fibre optical waveguides, expensive devices and intricate methods are often necessary in order to obtain an good optical low-loss joint between the waveguides. Because of the small diameter of such waveguides it is very difficult to complete a connection without any axial misalignment or angular deviation, and equipment of a very expensive design may often be required. For that purpose, as is described in the German Patent Specification No. 2,237,444, electro-optical measuring means and associated adjusters are used in an attempt to keep coupling losses as low as possible. Another example of a connecting arrangement is described in the United States Patent Specification No.

3,870,395 where single waveguides are inserted in capillary tubes for the purpose of alignment and centring of the single optical waveguides. However, the insertion of a single waveguide is very difficult due to its small diameter, and the operation therefore requires a great deal of skill. Similar considerations apply when using connecting arrangements with flute-type grooves as explained, of the type described in the Canadian Patent Specification No. 969,744.

A further device for adjusting two optical components is described in the United States Patent Specification No. 3,800,388.

One object of the present invention is to provide a method by means of which insertion of single optical waveguides into a centring groove of a suitable splicing element may be effected in an uncomplicated manner, without repeated measurements or adjustments, and thus eliminate the need for precise mechanical skill and assembly operations.

The invention consists in a method of connecting single fibre optical waveguides, in which a splicing element provided with a centring guidance groove is positioned between two clamping devices, said method comprising clamping a respective single fibre optical waveguide in each said clamping device to extend at an acute angle to the base of said splicing element, causing relative movement between said clamping devices and said splicing element to bring respective ends of said waveguides into the centring groove of the splicing element moving said two ends together by movement of said clamping devices towards each other, bending said waveguides at their ends to cause them to lie completely in contact with the walls of the centring groove for the purpose of axial alignment, and subsequently joining said ends whilst the two waveguides have their respective ends positively aligned to one another.

The essenoe of the method in accordance with the invention is the fact that the waveguides which are clamped and aligned to one another at an obtuse angle in a groove in the splicing element, being positioned therein by relative movement of the clamping devices with respect to the splicing element so that a lowering of the waveguides which are to be connected into the centring groove takes place, whereby a positive mutual alignment is achieved. The ends of the single light waveguides are then brought into contact with one another by moving the clamping devices towards each other until waveguides come into mutual contact and, finally, as a result of bending adjacent the ends of the waveguides, the latter are lowered completely into the centring slot to ensure axial alignment. With these sequences of movement, waveguide manufacturing tolerances do not have a disadvantageous effect on the quality of the connection of the waveguides, as automatic compensation of length variations is effected by bending the waveguides more or less.

The apparatus for carrying out the method is not dependent on a specific drive for the required sequences of movement.

This drive can, for example, be effected mechanically by a lever system or pneumatically or electro-magnetically, whichever is found to be most convenient, in any given case. Further, it is advantageous to provide means for removing the covering at the ends of the waveguides, and preferably also a fibre-breaker equipment. The sequences for the method are, in this way, extended by two steps at the beginning after clamping the ends of the single light waveguides during which steps removal of the covering and shearing of the waveguides to the required length takes place. This is achieved in an advantageous manner by positioning the appropriate devices at the position of the splicing element situated between the holders, so that the distances and lengths do not have to be adjusted anew for the further operation. Additional supplements are a dosing equipment for the supply of an adhesive for the material-locking fixing of the waveguides together, or a press device for the force-locking fixing of the waveguides in the centring groove. A magazine containing replacement splicing elements is provided for the latter type of jointing, so that automatic supply of the splicing elements can be achieved.

Splicing elements which have centring, open grooves with preferably U- or Vshaped cross-sections are especially suitable for this latter jointing method. Splicing elements of that kind for accommodating the waveguides which are to be connected may consist of faces of thin-walled material which are inclined to one another at an acute angle and form a centring longitudinal groove.

The special advantage of exemplary embodiments in accordance with the invention resides in the fact, that for centring the ends of the waveguides no expensive measuring equipment or centring devices are required, as the alignment to a common axis in the centring groove takes place spontaneously when inserting is effected. The prismatic groove base preferably has a radius which is smaller than half the diameter of a single waveguide. Production of such a splicing element is effected comparatively simple by breaking off the thin-walled material, e.g.

of suitable metal or synthetic foils, whereby the resulting bend forms the centring groove. The design of a groove base which has a concavely vaulted shape in the longitudinal direction leads to the fact that a force component which is directed to the groove base effects automatically the ends of the single light waveguides, which ends are brought into contact with one another and are pressed against one another. This force component has an advantageous effect, if the adhesive, as a result of its surface tension, tries to lift the ends of the single light waveguides from the base plate.

The invention will now.be described with reference to the drawings, in which: Figure 1 shows a preferred apparatus in an initial position; Figure 2 shows the apparatus in a second stage of the operation; Figure 3 shows the apparatus at a third stage; Figure 4 shows the final stage; Figure 5 shows one preferred splice element; Figure 6 to 8 show one alternative splice element; Figures 9 and 10 show another alternative splice element.

In the stage of the method shown in Figure 1, single fibre optical waveguides 1 are clamped in respective clamping devices 4 at each end of a splicing element 2 having a centring groove, which splicing element is held in place on a splicing-element holder 3 for the assembly operation.

Figure 2 shows the state reached after a first relative movement by means of which a change of position of the clamping devices 4 with respect to the splicing-element holder 3 takes place to give a height difference 5.

Here, the two ends of the waveguides 1 have been lowered into the centring groove of the splicing element 2, by lowering the clamping devices 4 or by raising the splicing element 2, or by moving both. In this way, a lateral alignment of the single light waveguides 1 with respect to one another takes place, which alignment is maintained during the following steps. Figure 3 shows the state after the two clamping devices 4 have been moved towards one another to bring the two ends of the waveguides 2 together in the centring groove of the splicing element 2. As the single light waveguides 1 have initially been cut to the required length, the point of contact in the centring groove is defined quite accurately. Variations within given tolerances are insignificant, as they are automatically absorbed by the degree of bending of the waveguides 1. In the next step, a further relative movement of the clamping devices 4 and the splicing element holder 3 to one another in the direction of the first stage now takes place, so that the increased height difference 7 is obtained. Thus, further lowering of the wave guides 1 into the centring groove of the splicing element 2 takes place, due to which an axial alignment of the waveguides 1 is effected. The differences which occur also during this step are equilised by appropriate bending of the waveguides 1 in the free regions between the clamping devices 4 and the splicing element 2. While in this adjusted final stage, the joint faces between the waveguides 1 are wetted with a suitable adhesive and thus fixed in a materiallocking manner. When the adhesive has hardened, the connection of the single light waveguides 1 can be removed from the clamping devices 4. Another possibility of fixing the single light waveguides 1 in the centring groove of the splicing element 2 is made possible by press-fitting the splicing element 2. In that case, the wave-guides 1 are held in place in the centring groove by friction forces.

In Figure 5 a splicing element for waveguides without any protective covering is represented, as an example, which splicing element is subject to the conditions relating to a centering longitudinal groove and with which the method in accordance with the invention is feasible. The ends of the single light waveguides 1 are inserted into the alignment groove 9 for the purpose of lateral alignment groove 9 is formed by two parallel-arranged faces 10. Finally, during the third process of movement, the axial alignment takes place in the V-shaped groove base 8, formed by the faces inclined to one another at an acute angle. The upper ends of the two parallel-arranged faces 10 are angled off to the outside to serve as insertion aid 11, whereby any possibly lateral misalignment of the clamping devices 4 is compensated for.

Figures 6 to 8 represent a splicing element which, likewise, has a centring longitudinal groove 14, formed by two faces 12 which are inclined to one another at an acute angle 13, as can be seen from Figure 7. The fold at the base of the longitudinal groove 14 is slotted at both ends, so that the joint faces 15 can be angled apart to serve for accommodating waveguides having protecting coverings, to which they are connected by glueing after the unwrapped ends of the single light waveguides have been brought together. Thus, the traction relief upon the joint of the ends of the waveguides in the axial direction is secured. The joint faces 15 can also be seen from Figures 7 and 8, more especially in Figure 8, which clearly reveals the angling apart. Insertion of the waveguides into the centring longitudinal groove 14 and the condition for its bending radius have already been described introductorily.

Figure 9 shows a longitudinal section of a splicing element 16, likewise suitable for the proposed. method, having a concave vault 19 of the groove base of a longitudinal groove 17. Widenings 18 for the accommodation of protecting coverings are provided at both ends. The centring longitudinal groove 17 of prismatic cross-section can be seen in Figure 10. This splicing element 16 has the advantage that it can be produced very simply by injection moulding of synthetic resin material. Production using thin-walled material, e.g. of metal, glass or ceramics, presents no significant problem.

When the waveguides have been lowered into the centring grooves, 8, 14 or 17, the ends of the waveguides are fixed by a suitable adhesive, serving at the same time as an immersion substance.

In the case of the exemplary embodiments, as already mentioned, force-locking fastening of the ends of the single light waveguides in the centring longitudinal grooves is made possible by press-fitting the splicing elements, if the splicing elements are made of a suitable material.

WHAT WE CLAIM IS: 1. A method of connecting single fibre optical waveguides, in which a splicing element provided with a centring guidance groove is positioned between two clamping devices, said method comprising clamping a respective single fibre optical waveguide in each said clamping device to extend at an acute angle to the base of said splicing element, causing relative movement between said clamping devices and said splicing element to bring respective ends of said waveguides into the centring groove of the splicing element, moving said two ends together by relative movement of said clamping devices towards each other, bending said waveguides at their ends to cause them to lie completely in contact with the walls of the centring groove for the purpose of axial alignment, and subsequently joining said ends whilst the two waveguides have their respective ends positively aligned to one another.

2. A method as claimed in Claim 1, in which said waveguides are positioned in said groove of the splicing element by lowering said clamping devices.

3. A method as claimed in Claim 1, in which said waveguides are positioned in said groove of the splicing element by raising the splicing element.

4. A method as claimed in any preceding Claim, in which said ends of said waveguides are stripped of any covering by a device prior to cutting them to the required length after the waveguides have been clamped in said clamping devices.

5. A method as claimed in any preceding Claim, in which said ends of said waveguides are cut to the required lengths by

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. guides 1 into the centring groove of the splicing element 2 takes place, due to which an axial alignment of the waveguides 1 is effected. The differences which occur also during this step are equilised by appropriate bending of the waveguides 1 in the free regions between the clamping devices 4 and the splicing element 2. While in this adjusted final stage, the joint faces between the waveguides 1 are wetted with a suitable adhesive and thus fixed in a materiallocking manner. When the adhesive has hardened, the connection of the single light waveguides 1 can be removed from the clamping devices 4. Another possibility of fixing the single light waveguides 1 in the centring groove of the splicing element 2 is made possible by press-fitting the splicing element 2. In that case, the wave-guides 1 are held in place in the centring groove by friction forces. In Figure 5 a splicing element for waveguides without any protective covering is represented, as an example, which splicing element is subject to the conditions relating to a centering longitudinal groove and with which the method in accordance with the invention is feasible. The ends of the single light waveguides 1 are inserted into the alignment groove 9 for the purpose of lateral alignment groove 9 is formed by two parallel-arranged faces 10. Finally, during the third process of movement, the axial alignment takes place in the V-shaped groove base 8, formed by the faces inclined to one another at an acute angle. The upper ends of the two parallel-arranged faces 10 are angled off to the outside to serve as insertion aid 11, whereby any possibly lateral misalignment of the clamping devices 4 is compensated for. Figures 6 to 8 represent a splicing element which, likewise, has a centring longitudinal groove 14, formed by two faces 12 which are inclined to one another at an acute angle 13, as can be seen from Figure 7. The fold at the base of the longitudinal groove 14 is slotted at both ends, so that the joint faces 15 can be angled apart to serve for accommodating waveguides having protecting coverings, to which they are connected by glueing after the unwrapped ends of the single light waveguides have been brought together. Thus, the traction relief upon the joint of the ends of the waveguides in the axial direction is secured. The joint faces 15 can also be seen from Figures 7 and 8, more especially in Figure 8, which clearly reveals the angling apart. Insertion of the waveguides into the centring longitudinal groove 14 and the condition for its bending radius have already been described introductorily. Figure 9 shows a longitudinal section of a splicing element 16, likewise suitable for the proposed. method, having a concave vault 19 of the groove base of a longitudinal groove 17. Widenings 18 for the accommodation of protecting coverings are provided at both ends. The centring longitudinal groove 17 of prismatic cross-section can be seen in Figure 10. This splicing element 16 has the advantage that it can be produced very simply by injection moulding of synthetic resin material. Production using thin-walled material, e.g. of metal, glass or ceramics, presents no significant problem. When the waveguides have been lowered into the centring grooves, 8, 14 or 17, the ends of the waveguides are fixed by a suitable adhesive, serving at the same time as an immersion substance. In the case of the exemplary embodiments, as already mentioned, force-locking fastening of the ends of the single light waveguides in the centring longitudinal grooves is made possible by press-fitting the splicing elements, if the splicing elements are made of a suitable material. WHAT WE CLAIM IS:

1. A method of connecting single fibre optical waveguides, in which a splicing element provided with a centring guidance groove is positioned between two clamping devices, said method comprising clamping a respective single fibre optical waveguide in each said clamping device to extend at an acute angle to the base of said splicing element, causing relative movement between said clamping devices and said splicing element to bring respective ends of said waveguides into the centring groove of the splicing element, moving said two ends together by relative movement of said clamping devices towards each other, bending said waveguides at their ends to cause them to lie completely in contact with the walls of the centring groove for the purpose of axial alignment, and subsequently joining said ends whilst the two waveguides have their respective ends positively aligned to one another.

a fibre-breaker equipment prior to insertion into the centring groove of the splicing element after being clamped in said clamping devices.

6. A method of connecting single fibre optical waveguides substantially as described with reference to Figures 1 to 4 and any one of Figures 5 to 10.

7. Apparatus for performing the method as claimed in Claim 1, comprising a splicing element positioned between two clamping devices provided with means for gripping respective waveguides with their ends projecting towards said splicing element, means for effecting relative movement on parallel paths between said clamping devices and said splicing element, means for moving said clamping devices towards one another, means for bending said waveguides adjacent their ends to lie in contact with the walls of a guide groove in said splicing element, and means for joining said ends whilst said waveguides are thus positively aligned.

8. Apparatus as claimed in Claim 7, in which a dosing equipment is provided for adhesives for the joining of the waveguides in the groove of the splicing element.

9. Apparatus as claimed in Claim 7 or Claim 8, in which a pressure plate provides said means for bending said waveguides in the groove of the splice element

10. Apparatus as claimed in any one of Claims 7 to 9, in which a magazine is provided for the automatic supply of splicing elements.

11. Apparatus as claimed in any one of Claims 7 to 10, in which said splicing element consists of faces of thin-walled material which are inclined to one another at an acute angle to form said centring longitudinal groove for accommodating said waveguides.

12. Apparatus as claimed in any one of Claims 7 to 10, in which said splicing element has a centring, prismatic longitudinal groove with a concave longitudinal base exhibiting a low point at the joint positive for said waveguides.

113. Apparatus as claimed in any one of Claims 7 to 10, in which said splicing element has a roundness radius at the base of the prismatic longitudinal groove which is smaller than half the diameter of said waveguides.

14. Apparatus as claimed in any one of the Claims 7 to 10, in which said splicing element is slotted in the two outer regions along a buckling line in the groove base of the longitudinal groove, and the joint faces which extend up to the slot ends are angled apart.

15. Apparatus as claimed in any one of Claims 7 to 10, in which said splicing element has a centring longitudinal groove that is continued at its upper edges by an alignment groove formed from faces which run parallel, and that these faces are angled off to the outside to serve as insertion aid of the respective waveguides, by widening the alignment groove in the upper region.

16. Apparatus as claimed in Claim 7, substantially as described with reference to Figures 1 to 4 and any one of Figures 5 to 10.