Polarization in Optical Fibers

Abstract

Optical fibers exhibit particular polarization properties. The guided electromagnetic fields in optical fiber waveguides are called inhomogeneous plane waves since their amplitudes are not stable within the plane wave and the fields are characterized, in most cases, by non-transverse components. In the description of polarization phenomena in optical fibers there are generally two approaches [1]. The first one treats an optical fiber as an optical waveguide in which light being a kind of electromagnetic wave of optical frequencies can be guided in the form of waveguide modes. This approach identifies basic polarization eigenmodes of a fiber and relates them to the polarization state of the guided light. Changes in output polarization are described in terms of polarization-mode coupling due to birefringence changes acting as perturbations along the fiber. Another approach treats an optical fiber like any other optical device which transmits light and the fiber can be divided into separated sections behaving like . polarization state shifters. Here, polarization evolution in a fiber can be described by one of the three general formalisms: by the Jones vectors and matrices formalism, by the Stokes vectors and Mueller matrices formalism, or by the Poincare sphere representation. Since optical fibers allow very large propagation distances even very small birefringence effects can cumulate along fiber and their random distribution over the large lengths causes polarization properties of guided light generally difficult to determine. Although polarization effects in optical fibers have initially played a minor role in the development of light-wave systems their importance is still growing. Before 1980 it was impossible to exploit the polarization modulation in a fiber for