Berry's phase fiber loop mirror characteristics

Abstract

The tuneable reflectivity of a fiber loop mirror consisting of a Sagnac interferometer with a fixed ratio directional coupler is attributed to Berry's topological phase. Berry's phase is the phase acquired by a light beam when the direction of propagation is changed, while the optical path length remains unchanged. The nature of the topological phase is studied and exact relations characterizing Berry's phase fiber-optic mirror are derived.