CHAPTER 20

Acousto-Optic Interaction in Few-Mode Optical Fibers

Helge E. Engan* and Kjell Bløtekjær,     Department of Electronics & Telecommunications, Norwegian University of Science and Technology, Trondheim, Norway

1 INTRODUCTION

Optical fibers are usually characterized as single-mode or multimode. Multimode in general means a large number of modes, typically several hundred. There is, however, an interesting regime where only a few modes can propagate; in particular, a two-mode fiber supports only two transverse spatial modes.

Two-mode fibers are primarily used for sensing purposes, using the phase change between the two spatial modes induced by a measurand such as strain, pressure, or temperature. The sensitivity to temperature and ...

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