Hypersensitivity and Applications of Cladding Modes of Optical Fibers Coated with Nanoscale Metal Layers

Jacques Albert,Fu Liu,Violeta Marquez-Cruz

doi:10.3390/s18051518

Abstract

Theoretical and experimental results are presented to show that the complex effective index of the modes of optical fibers coated with non-uniform metal coatings of gold, silver, copper, or palladium, with thicknesses between 0 and 20 nm, acquire a greatly enhanced sensitivity to various forms of perturbations. Thickness changes of less than 1 nm can be measured as well as the binding of record low concentrations of chemical and biochemical species.

Highlights

IntroductionMetal coated optical fibers and waveguides (the acronym OWG will be used as a generic term covering all kinds of optical waveguiding structures, to simplify the text) are widely used in chemical and biochemical sensing applications for two interrelated reasons, namely: plasmonic enhancement of the sensitivity and well established techniques to attach functional layers, and bio-recognition elements on metals, most notably gold and silver [1,2,3,4,5]
Metal coated optical fibers and waveguides are widely used in chemical and biochemical sensing applications for two interrelated reasons, namely: plasmonic enhancement of the sensitivity and well established techniques to attach functional layers, and bio-recognition elements on metals, most notably gold and silver [1,2,3,4,5]
Wave from the edge of the metal layer, but this is only practical for a special class of ‘long range surface plasmon’ devices (LRSP) that are made up of very thin metal layers surrounded by materials with similar permittivity values [6], otherwise the propagation lengths of the SPP waves for any realistic metals do not exceed a fraction of millimeter [6]

Summary

Introduction

Metal coated optical fibers and waveguides (the acronym OWG will be used as a generic term covering all kinds of optical waveguiding structures, to simplify the text) are widely used in chemical and biochemical sensing applications for two interrelated reasons, namely: plasmonic enhancement of the sensitivity and well established techniques to attach functional layers, and bio-recognition elements on metals, most notably gold and silver [1,2,3,4,5] For such applications to work, the metal layers or metal particles must be thin enough or sparse enough to let some light through, so that it can interact with the measurands and result in measurable changes in the optical properties of the OWG. In the case of layers of metal particles, the plasmonic enhancement is usually attributed to so-called ‘localized SPR’ (LSPR), whereby the incident optical waves drive electronic resonances at very specific wavelengths, which are related to the metal plasma frequency and to the sizes and shapes of the particles (or equivalently, of holes in a uniform layer) [4,7]

Objectives

Methods

Results

Discussion

Conclusion