Polarisation characteristics of fibres for coherent detection systems

Abstract

Coherent transmission systems utilising the optical heterodyning principle require a stable polarisation state for both the local oscillator and incoming signal waves. For a fixed input state the output polarisation of a single-mode fibre in general varies according to the prevailing environmental conditions. Efficient heterodyning can be obtained only by stabilising the output state. This may be accomplished by either (i) designing the fibre polarisation properties to be intrinsically immune to the environment, or (ii) by actively controlling the output to maintain the required state of polarisation at the detector. In this paper the design, manufacture and properties of fibres suited to both these approaches will be considered