Low-Coherence Interferometric Fiber-Optic Sensors with Potential Applications as Biosensors.

Marzena Hirsch,Matthieu Weber,Daria Majchrowicz,Paweł Wierzba,Małgorzata Jędrzejewska-Szczerska,Mikhael Bechelany

doi:10.3390/s17020261

Abstract

Fiber-optic Fabry-Pérot interferometers (FPI) can be applied as optical sensors, and excellent measurement sensitivity can be obtained by fine-tuning the interferometer design. In this work, we evaluate the ability of selected dielectric thin films to optimize the reflectivity of the Fabry-Pérot cavity. The spectral reflectance and transmittance of dielectric films made of titanium dioxide (TiO2) and aluminum oxide (Al2O3) with thicknesses from 30 to 220 nm have been evaluated numerically and compared. TiO2 films were found to be the most promising candidates for the tuning of FPI reflectivity. In order to verify and illustrate the results of modelling, TiO2 films with the thickness of 80 nm have been deposited on the tip of a single-mode optical fiber by atomic layer deposition (ALD). The thickness, the structure, and the chemical properties of the films have been determined. The ability of the selected TiO2 films to modify the reflectivity of the Fabry-Pérot cavity, to provide protection of the fibers from aggressive environments, and to create multi-cavity interferometric sensors in FPI has then been studied. The presented sensor exhibits an ability to measure refractive index in the range close to that of silica glass fiber, where sensors without reflective films do not work, as was demonstrated by the measurement of the refractive index of benzene. This opens up the prospects of applying the investigated sensor in biosensing, which we confirmed by measuring the refractive index of hemoglobin and glucose.

Highlights

Optoelectronic instruments based on spectroscopic techniques are currently applied in medicine, especially for diagnosis and imaging.these measurement methods are expensive, as they often require high-end measurement equipment, expensive consumables and complex methods of sample preparation
We evaluate the ability of different thin films—namely titanium dioxide (TiO2 ) and aluminum oxide (Al2 O3 )—with different thicknesses to tune the reflectivity of the Fabry-Pérot cavity, and we illustrate this modelling work with an experimental fiber using a TiO2 film
As the best modelling results were obtained with TiO2 films, we experimentally investigated the ability of an atomic layer deposition (ALD)-grown TiO2 thin film to tune the reflectivity of the Fabry-Pérot interferometers (FPI) cavity, by measuring the influence of TiO2 thin films on the intensity of reflected interfering beams

Summary

Introduction

Optoelectronic instruments based on spectroscopic techniques (e.g., absorption [1,2], Raman [3,4], optical tomography [5,6]) are currently applied in medicine, especially for diagnosis and imaging. These measurement methods are expensive, as they often require high-end measurement equipment, expensive consumables (e.g., reagents, dedicated trays, or substrates) and complex methods of sample preparation. Fiber-optic sensors possess several advantages in comparison to electronic sensors Their design often makes use of dielectric materials, which makes them insensitive to electric and magnetic fields generated by other medical devices. The small dimensions of such sensors (below hundreds of micrometers) reduce their impact on the investigated area, allowing for extremely precise measurements [9,10]

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Conclusion