Analysis of a plasmonic based optical fiber optrode with phase interrogation

Abstract

Optical fiber optrodes are attractive sensing devices due to their ability to perform point measurement in remote locations. Mostly, they are oriented to biochemical sensing, quite often supported by fluorescent and spectroscopic techniques, but with the refractometric approach considered as well when the objective is of high measurement performance, particularly when the focus is on enhancing the measurand resolution. In this work, we address this subject, proposing and analyzing the characteristics of a fiber optic optrode relying on plasmonic interaction. A linearly tapered optical fiber tip is covered by a double overlay: the inner one -a silver thin film and over ita dielectric layer, with this combination allowing to achieve, at a specific wavelength range, surface plasmonic resonance (SPR) interaction sensitive to the refractive index of the surrounding medium. Typically, the interrogation of the SPR sensing structures is performed, considering spectroscopic techniques, but in principle, a far better performance can be obtained, considering the reading of the phase of the light at a specific wavelength located within the spectral plasmonic resonance. This is the approach which is studied here in the context of the proposed optical fiber optrode configuration. The analysis performed shows the combination of a silver inner layer with a dielectric titanium oxide layer with tuned thicknesses enables sensitive phase reading and allows the operation of the fiber optic optrode sensor in the third telecommunication wavelength window.

Plasmonic Fiber Optic Refractometric Sensors: From Conventional Architectures to Recent Design Trends

“…A less common interrogation technique used in SPR fiber sensors is phase interrogation. The method relies on analyzing the phase difference between two light polarizations, p- and s-, at the resonance in the transmitted or back-reflected light [ 29 , 30 , 31 ]. This technique offers advantages of lower resolution and higher dynamic range when compared to other methods [ 31 ].…”

Plasmonic Optical Fiber-Grating Immunosensing: A Review

“…Additional interrogation techniques have been reported making use of polarization analysis to evaluate the sensor response with respect to the interactions produced in the surrounding medium. The measurement of the phase of the light at a wavelength matching the SPR [ 110 ] or the use of the polarization-dependent loss (PDL) [ 111 ] are two techniques that have been proven to exhibit a good performance, especially when associated with nanoparticles [ 112 , 113 ]. In the case of fiber gratings, the PDL spectrum relates to the difference between orthogonally polarized spectra [ 114 ], which therefore contains information about (L)SPR.…”

Surface plasmon resonance refractive index sensor based on fiber-interface waveguide inscribed by femtosecond laser

“…However, one difficulty of the trade-off between the mechanical strength of the fiber and the intensity of evanescent field to excite SPR effect significantly blocks the practical applications of SPR fiber sensor. The commonly used methods to obtain strong evanescent field includes removing all or part of the cladding (via etching, side polishing, or femtosecond laser micromaching) and tapering the fiber to allow the light to escape to the cladding [3][4][5][6]. Unfortunately, these SPR fiber sensors are very fragile due to the destroyed physical structure, thus it becomes one of blocks in the practical implications.…”