A METHOD FOR OBTAINING AN ACCURATE CONCENTRIC FASTENING OF AN OPTICAL FIBRE IN A CONNECTOR

Abstract: Connector (1) provided with an optical fibre (3) in an axial through-bore (2). The bore (2) has an enlargement (4) in the end of the connector. A solid rod (6) of a non-elastical ductile material is inserted in the recess. An axial force from outside the connector is applied to the rod, thereby expanding the rod radially to fixed position in the recess. A hole (6) is made in the rod with an accurate concentricity relative to the circumference of the connector. The optical fibre is inserted into the hole in the rod. Finally, an axial force from outside the connector is applied to the rod for radial expansion thereof resulting in a reduction of the hole in the rod and thereby obtaining an accurate concentric fastening of the optical fibre.

Description: A METHOD FOR OBTAINING AN ACCURATE CONCENTRIC FASTENING OF AN OPTICAL FIBRE IK A CONNECTOR FIELD OF THE INVENTION The present inventor relates to a ' connector provided with an optical fibre, which connector is provided with an axial through-hole for the optical fibre and provided wit a bushing for concentric fixing of the fibre within the connector. The bushing is arranged to be compressed in axial direction by means of a tool in order to obtain a radial deformation resulting in a centering of the optical fibre within the connector. BACKGROUND OF THE INVENTION Such optical connectors are known in several embodiments, for instance as described in the British Patent No. 1 478135 and in the U.S.Patent No. 4 190 317. In the connector (ferrule) described in* the British Patent the bushing is positioned at a considerable distance inside the mouth (end) of the connector and is compressed axially in order to be expanded radially by means of a piston fixed within the connector by varnish, while the end of the optical fibre is after the compression of the bushing resulting in the concentric fastening of the fibre fixed by means of resin in the mouth of the connector. Besides a rela¬ tively complicated construction accuracy is with necessi- ty lost by said distance from the mouth of the connec¬ tor so that in all probability desired low optical damp¬ ing can not be achieved. Errors in accuracy .are also obtained by the method described in said patent by the fact that the free end will wabble during the turning of the surface, so that different thickness of material is obtained in the bushing. The connector assembly described in said U.S. patent is also a relatively comp¬ licated construction. The bushing (insert member) is OMPI tapered in order to hold the fibre after a forced inser¬ tion of the bushing into a narrow bore, which according to the preferred embodiment is made in a second bushing arranged in a recess in the mouth of the connector. Due to several details errors in accuracy are added resulting in a deteriorated optical damping. During the forced in¬ sertion of the tapered body there is also a risk for skew setting or "swelling" meaning deteriorated accuracy. SUMMARY OF THE INVENTION The present invention is based in the realization, that the concenctric fastening of the fibre requires for the decisive optical damping in the connector an accuracy in the order of magnitude of a few micrometers. The faste¬ ning should accordingly take place immediately at the mouth (end) of the connector. Moreover, as few means as possible enclosing the fibre should be utilized and the bushing be made in non-elastic material in order to keep as close tolerances as possible.upon the manufac¬ ture of the bore for the fibre. The invention renders an improvement of the optical damping compared with previous technic possible and discloses a simplified method for obtaining the concentric holding of the op¬ tical fibre i the connector. This is achieved by the following steps: a) inserting into the recess a solid rod of a non-elas- tic ductile material ? b) applying from outside relative to the connector an axial force to the rod for obtaining an expansion there¬ of in radial direction resulting in a fixing relative to the inner wall of the recess; c) taking up a hole in the rod with an accurate concent¬ ricity relative to the outer surface of the connector; d) inserting the optical fibre into said hole in the rod being fixed in the recess in the connector; e) applying from outside relative to the axial force to the rod for obtaining an expansion there¬ of in radial direction resulting in a reduction of the hole in the rod, thereby obtaining the accurate concent¬ ric fastening of the optical fibre. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1-3 illustrates schematically different manufactu¬ ring steps of an optical fibre connector according to the invention. Figs. 4 and 5 show a coupling device for two connectors in a section along the line IV-IV in Fig. 5 and a sec¬ tion along the line V-V in Fig. 4, respectively. DESCRIPTION OF THE PREFERRED EMBODIMENT The connector 1 shown in Fig. 1 has an axially bore 2 for an optical fibre 3. The bore is in the forward end or the coupling end enlarged to a recess 4 and a bushing 5 having a hole 6 in alignment with the extension of the bore 2 is inserted in the recess 4. Fig. 1 also shows the front end of a punch 7 having a hole 8 for receiving the optical fibre 3. The bushing 5 is made of a soft metallic material, pre¬ ferably a tin alloy, and the punch 7 is arranged for compressing the bushing in axial direction for obtaining a radial deformation. Fig. 2 illustrates the shape of the conductor and the bushing after performed compres- sion and Fig. 3 shows the final shape of the conductor after grinding the coupling end. By a method as described above and using a bushing of a soft metallic material,a non-elastic and with maximum accuracy determined concentric fixing of an optical fibre is made possible. Since the concentricity is coun- OMPI ted relative to the outer surface of .the conductor 1 , the bushing 5 may preferably be manufactured in such a way, that the solid rod is inserted into the recess 4 and is fixed therein by a limited compression by means 5 of a suitable tool, whereupon the axial hole 6 is bored in the rod. Due to the obtained accurate centering an optical fibre in a connector can definitely guaranteed be . lined up with another connector in an optical coupling device. 10 An appropriate embodiment of such a coupling device is shown in Figs. 4 and 5. The coupling device 10 shown in Figs. 4 and 5 consists of a middle sleeve 11 having a central through-hole 12, in which a rod 13 is- fixed. A longitudinal groove 14 15 with vails 15 is formed in. the rod 13 for obtaining an inwardly decreasing cross-section of the groove. The hole 12 has above the groove 14 a portion 16 being some¬ what enlarged and extending along the groove, said por¬ tion 16 being concentrically formed relative to a con- 20 nector 1 inserted into the groove. The sleeve 1 is at the ends provided with projecting flanges 17 having ex¬ ternal thread 18 and internal tapered surface 19. The threads 18 are arranged for co-operation with nuts 20 having internal threads 21 and the tapered surfaces 19 25 are arranged for co-operation with annular tapered wedge elements 22, which preferably have an axial slit. • * When coupling two connectors 1 together by means of the . coupling device 10 shown in Figs. 4 and 5, the connec¬ tors are inserted from the ends of the groove 14 to the 30 abutment shown in Fig. 5. The nuts 20 are positioned so far outwardly, that wedgo effect clooπ not exist between the wedgo elements 22 and the surfaces co-ope¬ rating with the elements in order to allow the inser¬ tion of'the connector. The nuts are thereafter'screwed^^ upon the threads 18 and the wedge elements are wedged up between the tapered surfaces 9 of the sleeve 11 and the outer surface of the connector 1 faced to the portion 16 and the roll 13. An extraordinarily rigid coupling of the connectors 1 with high accuracy concerning the up-lining of the fibre ends relative each other is obtained by means of a coup¬ ling device 10. Moreover, the construction is simple in manufacture and allows a simple and rapid handling. OMPI •v/ WIPO

Claims: r CLAIM: • A method for obtaining an accurate concentric fastening of an optical fibre in a connector, wherein a ductile bushing is arranged to surround the fibre in a recess in the end of the connector, c h a r a c t e r i z e d in the following steps: (a) inserting into the recess (4) a solid rod (5) of a non-elastic ductile material; (b) applying from outside relative to the connector (1) an axial force to the rod for obtaining an expansion thereof in radial direction resulting in a fixing rela¬ tive to the inner wall of the recess; (c) taking up a hole (6) in the rod with an accurate concentricity relative to the outer surface of the connector; (d) inserting the optical fibre (3) into said hole in the rod being fixed in the recess in the connector; (e) applying from outside relative to the connector an axial force to the rod for obtaining an expansion there¬ of in radial direction resulting in a reduction of the hole in the rod, thereby obtaining the accurate concent¬ ric fastening of the optical fibre.

Inventors: ROGSTADIUS I
Applicants: ROGSTADIUS I
Application year: 1981
Main classification: G02B7
IPC codes: G02B6