Fiber grating-assisted investigation on surface plasmon resonance of fiber cladding modes

This article reports a novel method of deriving the effective refractive index and losses of fiber cladding modes in surface plasmon resonance (SPR) from the transmission spectrum of long-period fiber gratings in metal-plated optical fibers. Focusing on the SPR-related behavior of the cladding modes, the presented semi-analytical method presented is based on an appropriate slab waveguide model combined with an algorithm derived from coupled mode theory. The method avoids elaborate numerical calculations and is a convenient tool for the design of fiber-optic SPR sensors. The reliability of the method is confirmed by experimental work on gold-plated fibers.