An optical waveguide plug assembly

Abstract: This invention relates to a beam waveguide plug comprising: a plug casing (5) which has for each beam waveguide cable (2) a plug segment (6) and a clamping segment (7) for fixing the beam waveguide cable (2) to the plug (1). The clamping segment (7) has a socket (15) with a plurality of serrations (8) pressed by their edges into the beam waveguide sheathing and extending substantially transversely of the beam waveguide axis, and recesses (9) disposed between the serrations (8), to accommodate (15) the sheathing material displaced by the serrations.

Description: This invention relates to an optical waveguide plug assembly. Optical waveguide plugs of this kind are required to connect optical waveguide cables to equipment in which the light signals are converted, amplified, transmitted or processed. Optical waveguide plugs are required in large numbers in systems operating with light signals, so that if it is possible to reduce the costs of manufacture of such plugs it will have a considerable effect on the overall costs of such a system. To enable a large number of plugs to be accommodated in the minimum amount of space the plugs must not occupy too much space. Also, they must be of robust design for frequent plug-in and pull-out loading, and ensure high resistance to tearing out. In addition, the precision of construction, and particularly the contact of the end face of the optical waveguide on a corresponding companion element, are required to meet high specifications in order not to cause attenuation losses in the optical waveguide core end. A number of different methods have already been adopted to solve the above requirements. For example, multipart metal optical waveguide plugs are known which are similar in construction to coaxial cables known in electronics. Their construction from a plurality of parts screwed together by way of screwthreads is very complicated and miniaturisation is practically impossible because of the fact that the screw connections are not easy to handle. In addition, plastic optical waveguide plugs are known wherein the cable end is partially stripped, the stripped part is passed through a bore in defined relationship as far as the front end of the plug, and wherein the plug is secured to the cable in the rear part of the plug. In a known optical waveguide plug system this fixing is by means of double clamping yokes made of metal, which are inserted into slots provided for the purpose in the plug casing in orderto pinch or cut into the sheathing of the optical waveguide cable between their limbs, at two spaced points of the cable. The disadvantage of these plugs is that they consist of a plurality of parts, and this renders production expensive, limits miniaturisation as a result of the metal clamps, while in addition the high pinching stress on the optical waveguide core at the clamping points does not prevent changes of the interface layer between the core and the sheathing such as is essential for multiple reflection and hence light transport, and consequently attenuation losses occur. Abstract of JP-A-60186811 discloses an optical connector comprising a ferrule having at least a part of its inner surface made uneven and directly engaging to the projecting part of the uneven section with a clad of the plastic-clad optical fiber. Further to the plastic-clad two other outer sheaths are provided together with strengthening fibers, which are wrapped over the outer sheath within the ferrule. Apart of the serrations gripped directly into the plastic-cladding of the optical fiber another part attacks the strengthening fibers laying on the outer surface of the outer protective sheath. This is done to prevent a displacement of the end face of the strand within the connector due to the difference in the coefficient of thermal expansion of the core and the sheath. US 2,147,356 describes a contracted sleeve hose coupling. The hose comprises separate layers, one of them is a wire braid reinforcement to strengthen the hose against radial forces. The sleeve comprises at its inner wall surface circumferentially spaced apart teeth biting into the outer layer of the hose to fix them. The teeth are asymmetrical in section in order to raise the pull-out force of the hose. Due to the wire braid reinforcement of the hose, radial forces are not further transmitted to the inner wall of the hose, which local deformation is uncritical in this context. Further, the radial forces during crimping the hose are considerably high due to the deformation of the outer sheath material which has to be brought into the shape of the space between the sheath to achieve the desired crimping depth which goes down to the wire braid reinforcement. Such radial forces would be unacceptable for the crimping of an optical fiber cable due to the high impact on the fiber. EP 0 152 225 A3 describes a plastic optical fiber cord with a ferrule. Such a ferrule corresponds to the plug as described in the preamble portion of patent claim 1. The serrations biting into the plastic sheath of the optical fiber cord are not further specified. Especially, their section and the space between the serrations, which are important features as to the radial impact on the optical fibers while crimping, are not described in detail. The object of this invention is so to improve an optical waveguide plug assembly as to require considerable tear-out forces, make it inexpensive to manufacture, highly suitable for miniaturisation, while preventing any adverse effect on the optical properties of the optical waveguide in the plug zone. This problem is solved by the claims. The subclaims refer to preferred embodiments of the optical waveguide plug assembly according to the invention. The optical waveguide plug is preferably made in one piece from plastics, this having a positive influence on costs and ease of handling. Clamping is distributed over a relatively large zone of the optical waveguide cable outer surface, thus guaranteeing high tear-out forces while providing non-damaging support. The construction of the optical waveguide plugs allows rational and, if required, automated or manual cable installation. The invention is explained in detail below with reference to one exemplified embodiment and the drawing, the exemplified embodiment having no limiting force. In the drawing: Fig. 1 is a partial longitudinal section of one exemplified embodiment of the optical waveguide plug before beeing crimped. Fig. 2 shows the optical waveguide plug of Fig. 1 after crimping. Fig. 1 illustrates one embodiment of an optical waveguide plug 1 before beeing crimped. The right-hand part of the drawing shows a sheathed optical waveguide cable 2 onto which the plug is pushed. Its end zone is stripped. The stripped fibre core 3 is taken as far as the end of the plug 1 through a cylindrical opening in the segment 6 thereof. Here the core end is fused positively by hot plate technique to the plug 1, which widens out at the plug segment end 6. This also increases the tensile strength of the plug connection. In this exemplified embodiment the plug segment 6 is tubular so that its outer surface is also cylindrical. Clamping elements are provided in the clamping segment 7 of the optical waveguide plug, on the inner wall situated opposite the surface of the optical waveguide cable sheathing 4. In longitudinal section these clamping elements constitute a serration 8. The serration 8 are in the form of a screwthread, and this gives certain advantages in the removal of the cast plug 1 from the mould. The important point is that crimping of the clamping segment 7 on the optical waveguide sheathing 4 results in a pinching of the sheath material at a number of places distributed over the sheath surface 4 of the optical waveguide cable, the peripheral material displaced by the serration 8 being capable of accommodation in sufficiently large recesses 9 between the serrations 8. The flanks of the serration 8 are asymmetrical in respect of inclination transversely of the cable axis. In this way greater retaining forces are achieved if the flank of each serration rib 8 situated towards the head end of the plug 1 occupies a small angle transversely of the cable axis, whereas the corresponding angle on the side towards the cable is larger. A value of about 15° has proved satisfactory for the first angle and about 35° for the second angle. Fig. 2 shows the plug 1 of Fig. 1 after crimping. This means that an appropriate tool has constricted the plug material in the clamping segment 7 either by cross-crimping or hexagonal crimping. It will be clearly seen that the material of the sheathing 4 has been displaced by the tips of the burrs of the serrations 8 and has been bulgingly displaced into the recesses 9 between the ribs. The large number of points of engagement of the serrations 8 on the surface 4 of the sheathing causes a pressure distributed over a relatively large area to be applied to the cable sheath 4, thus avoiding intensely local pinching effects which might be transmitted from the sheath 4 to the core 3. In the exemplified embodiment illustrated, a silicone spring 10 is positively applied to the cable entry end of the plug 1. In a casing (not shown), it serves to ensure that the end face of the plug 11 is pressed onto an appropriate contact surface by bearing against a corresponding back wall. Sealing rings 13 can be recessed into grooves 14 provided for the purpose on the plug segment 6, which is cylindrical here, or a groove 12 with flat side walls can be provided to form the plug 1 as a jack plug. The above-described embodiment of the optical waveguide plug according to the invention is particularly suitable for production from plastic material by injection moulding. However, it is also possible to make such plugs from not too hard a metal, e.g. brass, particularly in the case of advanced miniaturisation. Here again crimping is possible. The present invention is equally suitable for multiple plugs in which two or more optical waveguide cables are mounted side by side in a plug casing.

Claims: An optical waveguide plug assembly comprising a plug casing (5) crimped onto an optical waveguide cable (2) the plug having a plug segment (6) and a clamping segment (7) fixing the optical waveguide cable (2) to the plug (1), the clamping segment (7) having several serrations for being fixed to the optical waveguide cable, wherein the serrations (8) are in the form of an internal screwthread which is pressed into the optical waveguide sheathing and extends around the optical waveguide axis and has an asymmetric substantially triangular cross section, the flank facing the front end of the plug being inclined at a small angle of about 15° relative to a plane perpendicular to the cable axis and the rear flank at a larger angle of about 35° and wherein between the serrations (8) recesses (9) receiving the sheathing material displaced by the crimping are provided, the sheathing material being bulgingly displaced into the recesses but not filling up the recesses, said recesses (9) being formed with rounded bottoms connecting the flanks of adjacent serrations (8). An optical waveguide plug assembly according to claim 1, characterised in that the plug casing (5) is made of plastic. An optical waveguide plug assembly according to claim 1, characterised in that the plug casing (5) is made of metal. An optical waveguide plug assembly according to claim 1, characterised in that the clamping segment (7) has a cylindrical outer surface and the crimping is a hexagonal or cross-crimping. An optical waveguide plug assembly according to any one of claims 1 to 4, characterised in that a silicone spring (10) or anti-buckle bush is positively secured to the cable end of the plug (1). An optical beam waveguide plug assembly according to any one of claims 1 to 5, characterised in that the plug segment (6) is cylindrical and the optical waveguide core end (11) is positively adapted by a hot plate technique to a widening of the inside diameter of the plug segment (6). An optical waveguide plug assembly according to any one of the preceding claims, characterised in that a detent groove (12) is provided on the plug segment (6) to form a jack plug. An optical waveguide plug assembly according to any one of the preceding claims, characterised in that a sealing ring (13) is disposed in a groove (14) on the plug segment (6). An optical waveguide plug assembly according to any one of the preceding claims, characterised in that the clamping segment (7) and the plug segment (6) are made in one piece.

Inventors: BESLER MARTIN, MAY GUNTRAM, BESLER, MARTIN, MAY, GUNTRAM
Applicants: FRAMATOME CONNECTORS INT, FCI
Application year: 1995
Main classification: G02B6
IPC codes: G02B6