Dielectric optical waveguide joints
This is a continuation, of application Ser. No. 703,227, filed July 7, 1976 now abandoned. 
    
    
     The present invention relates to the jointing of dielectric optical waveguides. 
     In a known method of joining two dielectric optical waveguides, a groove is formed in a perspex plate by pressing a dielectric optical waveguide into the plate, two dielectric optical waveguides are then slid along the groove until their ends abut, and a second plate is clamped on top of the dielectric optical waveguides to complete the joint. Joints made by this technique are frequently bulky and require the use of adhesive or clamps to complete the joint. 
     The present invention seeks to provide a groove plate joint which is simple, readily made, and compact. The joint of this type has clear advantages for implementation in the field. 
     According to a first aspect of the present invention there is provided a dielectric optical waveguide joint comprising a groove disposed on a first face of a plate of a non-ductile material, first and second dielectric optical waveguides located in said groove with their ends abutting, said first and second dielectric optical waveguides being retained in said groove by a mass of ductile material which has been formed so as to flow into intimate contact with said plate and said first and second dielectric optical waveguides. 
     Preferably said plate has at least one hole passing therethrough from said first face to a second face, the hole being wider at said second face than said first face, said mass of ductile material extending through said hole. Said ductile material may be pure tin, or indium, or a material having like mechanical properties. 
     According to a second aspect of the present invention there is provided a method of joining a first and a second dielectric optical waveguide comprising positioning said first and second dielectric optical waveguides so that an end face of said first dielectric optical waveguide abuts an end face of said second dielectric optical waveguide in a groove formed on a face of a non-ductile plate, placing a mass of ductile material on said face of said non-ductile plate and deforming said mass of ductile material so that it flows into intimate contact with said first and second dielectric optical waveguides and said face of said non-ductile plate and attaches to said non-ductile plate. 
    
    
     The invention will be described now by way of example only with particular reference to the accompanying drawings. In the drawings: 
     FIG. 1 shows a section through a dielectric optical waveguide joint of known type; 
     FIG. 2 shows a section through a dielectric optical waveguide joint of known type; 
     FIG. 3 shows a longitudinal section through a dielectric optical waveguide joint according to the present invention, and 
     FIG. 4 shows a transverse section through a dielectric optical waveguide joint according to the present invention. 
    
    
     FIGS. 1 and 2 show two forms of dielectric optical waveguide joint which are produced by a known method of jointing. In this method a groove is formed in a perspex plate 10 by pressing a dielectric optical waveguide into the plate. Two dielectric optical waveguides 11 are then slid along the groove until their ends abut, and a second plate 12 is clamped on top of the dielectric optical waveguides to complete the joint. 
     Referring now to FIGS. 3 and 4 the initial stage in making a dielectric optical waveguide joint according to the invention is to form a groove 21 in a sheet 20 of non-ductile material such as plastics, copper, or anything that can be grooved, embossed etc. The term non-ductile is to be understood in a relative sense, i.e. as referring to a material which does not flow under pressure easily so that it is capable of offering at least some resistance to pressure. 
     The ends of two dielectric optical waveguides are then prepared by for example breaking using the fibre breaking device described in our co-pending application No. 29511/75. This produces plain end surfaces normal to the axis of the dielectric optical waveguides. The dielectric optical waveguides 23, 24 are then placed in the groove 21 on the top face of the plate 20 and slid along the groove until the two ends abut. The plate 20 is also provided with a set of four holes 25 each having a counter sunk end 26 on the opposite face of the plate to the groove. A mass of ductile material 28, e.g. indium or pure tin is then placed over the top of the joint between the two fibres and compressed. This forces the ductile material into intimate contact with the top surface of the plate 20, and the dielectric optical waveguides 23, 24. In addition ductile material is forced through the holes 25 and flows outwardly to fill in the counter sunk areas 26. This serves to retain the ductile material in position on the top surface of the plate when the pressure is removed from the mass of ductile material. 
     The best joint results are obtained if the pressure applying tool is slightly dished in the middle so that the pressure applied to the ductile material immediately over the junction between the two dielectric optical waveguides is somewhat lower than the pressure farther out along the dielectric optical waveguides. This has the effect, that the flow of ductile material tends to push the two dielectric optical waveguides being joined together thus ensuring good optical contact.