Periodic microbending-induced mode coupling in microstructured optical fiber

Abstract

Microstructured optical fiber (MOF) is a new class of optical fiber that has emerged in recent years. It is formed by an array of air holes running along the fiber length. They are fascinating because of various novel properties, including endlessly single-mode operation, scalable dispersion and nonlinearity, and the surprising phenomenon of a short wavelength bend loss edge, etc. These optical characteristics make possible wide-ranging applications in optical communication. In this paper, we investigate the mode coupling characteristics induced by periodic microbending in MOF. Coupling between various modes in normal single mode fiber (SMF) and polarization maintaining fiber (PMF) have already been investigated theoretically as well as experimentally. Periodic microbending created by a corrugated fixture on a SMF is known to induce the mode coupling between a codirectional propagating core (LP01) and cladding mode (LP11). In our experiment, a core-cladding mode coupler was built and tested based on a section of endlessly single mode MOF (fabricated with the stack-and-draw process). The fiber was bended between a pair of identical grooved plates with 250μm periodicity, thus this can be treated as a mechanical-stress-induced long period grating (LPG). The effect of microbending is controlled using stress gauge. The coupling strength is compared between single mode fiber and MOF under the same stress gage condition. The modal coupling coefficient enhancement is observed in MOF because of the complex index distribution.