High-sensitive lossy mode resonance-based optical fiber refractometers by means of sputtered indium oxide thin-films

Abstract

ABSTRACT Three different optical fiber refractometers based on lossy mode resonances (LMRs) have been fabricated by means of the deposition of indium oxide thin-films. The sensitivity of the devices as well as the full-width at half maximum (FWHM) has been characterized as a function of the surrounding medium refractive index (from 1.332 to 1.471. Obtained results revealed that thinner coating possess higher sensitivities. However, the FWHM is better for thicker coatings. As a general rule, the thicker the In 2 O 3 coating the lower the sensitivity, but the better the FWHM. Thus, a compromise is required depending on the necessities of the application. Keywords: Optical fiber, Refractometer, Indium oxide, DC - Sputtering 1. INTRODUCTION Different optical fiber sensing applications have been developed in fields like biomedical, chemical and environmental monitoring. One of the most interesting groups of optical fiber sensors are those based on spectral response because their response is highly immune to fluctuations of the optical source power. This kind of optical fiber sensors are represented mostly by the groups based on long-period gratings [1], fiber Bragg gratings [2], interferometers [3] or resonances [4]. In the last few years, optical fiber refractometers have attr acted the attention of many authors as a promising label-free sensing platform. Lossy Mode Resonances (LMRs) have been recently described by our group as a novel type of resonances that present several remarkable and interesting pr operties, such as independence with the polarization of light or easy generation of multiple resonances [5]. Additionally, LMRs can be generated by using a wide range of materials from transparent conductive oxides [6-7] to polymeric films [8] or hybrid polymer/metal oxide nanoparticle coatings [9]. LMRs shift as a function of the refractive index of the medium in contact with the supporting layer and enable the fabrication of highly sensitive refractometers [6, 9]. Here, it is first described the fabrication of LMR-based optical fiber refractometers by means of the deposition of a thin indium oxide (In