Optical-fibre-bundle holographic coupler

The difficulty of realising effective couplers for single-mode fibres imposes a significant obstacle to their application. The paper is concerned with the use of a holographic element, which substantially reduces the sensitivity to tolerance errors in the manufacture of such a coupler. The approach is based on the use of a hologram output window for the cable end, the coupling between the two windows proceeding by means of pseudoplane waves. The effect is to transfer the need for precision to the factory, the coupler to be assembled in the field being relatively undemanding. The system is applicable to bundles of fibres; preliminary experimental results for the coupling between one pair of fibres to another pair are described.