Abstract

A number of fibre based devices have been shown to be capable of performing all-optical switching. These include, polarisation discriminators ^[1], Mach-Zehnder interferometers ^[2], Sagnac interferometers ^[3] and coherent couplers ^[4]. The crucial feature common to these devices is the existence of two modes which can propagate independently in the linear regime. Polarisation based devices and couplers are described by a simple set of coupled equations which can either be in terms of the local modes (mode of a single core for the coupler, circular modes for polarisation) or the global (true) modes (symmetric and antisymmetric modes of the coupler, linear modes for polarisation). The latter choice exemplifies the connection with the interferometer based devices since the linear coupling operation is described in terms of the beating of the true modes in much the same way as the linear properties of the interferometer are described in terms of the beating between the fields in the two arms.

© 1991 Optical Society of America