The prism-taper coupler for the excitation of single modes in optical transmission fibres

A coupler is described which allows the excitation of pure single guided fibre modes with a single mode laser. The coupler uses a prism and precision taper fibre end to access any of the fibre modes. The conditions for obtaining excitation of single modes are discussed and the technique for producing the tapers is described. In the first tests, an excitation efficiency of approximately ?16 dB has been obtained.