Abstract

Evanescent wave devices operating on guided waves in single-mode fibers have led to highly efficient devices such as couplers and polarizers. This paper is concerned with the use of external grating structures introduced into the evanescent fields of single-mode fibers to perform mode coupling. Such devices could have application in fiber-optic communication and sensing where they can act as frequency and polarization selective couplers. A dielectric grating used to couple the guided fiber mode to external radiation modes propagating at ~90° angles with regard to the fiber axis has been re- ported.¹ Our purpose is to investigate the use of gratings having a much smaller spatial period for efficient coupling of the incident wave in the fiber to a guided backward wave In the fiber. Such coupling has been observed with periodic internal distributions of optical-induced photorefractive damage within the cores of Ge-doped fibers.²

© 1985 Optical Society of America