Generation of lossy mode resonances with different nanocoatings deposited on coverslips.

Omar Fuentes,Ignacio Del Villar,Jesus M Corres,Ignacio R Matias,Aritz Ozcariz,Javier Goicoechea

doi:10.1364/oe.28.000288

Abstract

The generation of lossy mode resonances (LMRs) with a setup based on lateral incidence of light in coverslips is a simple platform that can be used for sensing. Here the versatility of this platform is proved by studying the deposition of different coating materials. The devices were characterized with both SEM and AFM microscopy, as well as ellipsometry, which allowed obtaining the main parameters of the coatings (thickness, refractive index and extinction coefficient) and relating them with the different sensitivities to refractive index attained with each material. In this way it was possible to confirm and complete the basic rules observed with lossy mode resonance based optical fiber sensors towards the design of simpler and more compact applications in domains such as chemical sensors or biosensors.

Highlights

The generation of lossy mode resonances (LMR) with polymers and metallic oxides deposited on optical fiber is a topic that has attracted much interest during the last decade thanks to the properties it presents: ability to generate the resonance both for TE and TM polarized light, possibility to obtain multiple resonances and the capability to tune its position in the optical spectrum [1,2,3,4,5,6,7], which has resulted in many publications where LMR based optical fiber sensors are used for detecting refractive index variation [8,9,10,11], humidity [12], pH [3], chemical or biological species [6,13], gases [14] or even voltage [15,16]
The deposition process was stopped in all cases when an attenuation corresponding to the first LMR started to be observed in the optical spectrum
There, it is interesting to observe that, for the SnO2 coating, the first TE LMR is present at about 570 nm as a side lobe and the TM LMR is visible at a shorter wavelength (450 nm), as observed in other works [28]

Summary

Introduction

The generation of lossy mode resonances (LMR) with polymers and metallic oxides deposited on optical fiber is a topic that has attracted much interest during the last decade thanks to the properties it presents: ability to generate the resonance both for TE and TM polarized light, possibility to obtain multiple resonances and the capability to tune its position in the optical spectrum [1,2,3,4,5,6,7], which has resulted in many publications where LMR based optical fiber sensors are used for detecting refractive index variation [8,9,10,11], humidity [12], pH [3], chemical or biological species [6,13], gases [14] or even voltage [15,16].The idea of a thin-film inducing attenuation maxima in the transmission spectrum was first proposed in the domain of semiconductor waveguides [17,18,19]. The basic rules that determine the sensitivity of the device can be summarized in tracking the first LMR (i.e. the LMR that is generated with a thinner coating), to operate with substrate and outer medium refractive indices that are as similar to each other as possible, and to use a nanocoating material whose refractive index is as high as possible [7,20] Another important question is the width of the resonance [21], which can be greatly reduced by using a configuration where a single mode is transmitted and the contribution in the optical spectrum of TM and TE resonance can be separated. It is necessary to use in-line polarizer and a polarization controller that permits to control the polarization in a standard single-mode fiber [10], or to employ a side-polished polarization maintaining fiber [8]

Methods

Results

Conclusion