Chapter 6 - Polarization Effects

Abstract

Publisher Summary This chapter focuses on the polarization effects and considers the coupling between the two orthogonally polarized components of an optical field induced by the non-linear phenomenon—known as the cross-phase modulation (XPM). The XPM is always accompanied with SPM and can also occur between two optical fields of different wavelengths. The non-degenerate case involving different wavelengths is also discussed. It discusses the origin of the non-linear birefringence, and reviews the derivation of a set of two coupled non-linear Schrodinger (NLS) equations—that describes evolution of the two orthogonally polarized components of an optical field. A single-mode fiber supports two orthogonally polarized modes with the same spatial distribution. In practice, all the fibers exhibit some modal birefringence because of the unintentional variations in the core shape and anisotropic stresses along the fiber length. In the polarization-maintaining fibers, the built-in birefringence is made much larger than the changes occurring due to stress and core-shape variations. Therefore, such fibers exhibit constant birefringence along their entire length, known as the linear birefringence. The vector modulation instability, in contrast with the scalar case can occur even in the normal-dispersion regime of a birefringent fiber, which is also illustrated in the chapter. The chapter concludes by discussing the vector modulation instability occurring in the birefringent fibers and elaborates polarization-mode dispersion (PMD) occurring in fibers, with randomly varying birefringence along their length and its implications for lightwave systems.