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 In2O3 coating the lower the sensitivity, but the better the FWHM. Thus, a compromise is required depending on the necessities of the application.
A pH optical fiber sensor based on electromagnetic resonances generated in a waveguide-nanocoating interface is presented here. The incorporation of gold nanoparticles (AuNPs) into polymeric thin films has been deeply studied and the deposition of these thin-films onto an optical fiber core has been performed in order to obtain a resonance-based optical fiber device. The presence of both the metal nanoparticles and the polymers in the coating allows the generation of two different electromagnetic resonances: localized surface plasmon resonance (LSPR) and lossy mode resonance (LMR). These phenomena can be simultaneously observed in the transmitted spectrum. The resultant device has shown a high sensitivity to pH changes from pH 4.0 to pH 6.0, with a large dynamical range and a very fast response.
Optical fiber sensors are of great interest due to their intrinsic advantages over electronic sensors. In this work, the sensing characteristics of two different and novel optical fiber devices are compared, after simultaneously depositing a thin-film using the layer-by-layer assembly deposition process. The first one is an SMS structure, formed by splicing two single-mode fiber pigtails on both sides of a coreless multimode fiber segment. This structure induces an interferometric phenomenon that generates several attenuation and transmission bands along the spectrum. These bands are sensitive to variations in the surrounding refractive index, although this sensitivity has been enhanced by a TiO2/PSS thin-film. The other device is a 40 mm uncladded segment of a 200 μm-core multimode optical fiber. When coated by a TiO2/PSS thinfilm, part of the light transmitted into the uncladded core is coupled into the thin-film, generating a lossy mode resonance (LMR). The absorption peaks due to these phenomena red-shift as long as the thin-film thickness increases or the external RI becomes higher. The performance of these devices as refractometers and relative humidity sensors are tested. Results show that the LMR-based sensor is more sensitive in both situations, in spite of its lower sensitivity. Particularly, it presents a 7-fold sensitivity enhancement when measuring surrounding medium refractive index changes and a 10-fold sensitivity enhancement when measuring environmental relative humidity. To our knowledge, this is the first time that a comparative study between SMS and LMR sensors is performed.
An optical fiber device showing simultaneously two optical phenomena, localized surface plasmon resonance (LSPR) and lossy mode resonance (LMR), is presented here for the first time. It consists of a fragment of stripped optical fiber coated with a polymeric film that includes gold nanoparticles. The absorption peaks related to both phenomena were captured during the deposition of the coating, showing a different evolution. In addition, the behavior of both phenomena to variations of the surrounding medium refractive index (SMRI) was monitored, studying the different responses of LSPR and LMR.
In this work, the fabrication and characterization of novel humidity sensors based on Lossy Mode Resonances (LMR) is presented. Tin oxide (SnO2) coatings fabricated onto optical fibers are used as LMR supporting coatings. The SnO2 based refractometers showed an average sensitivity of 6715 nm/refractive index unit (RIU) in the range 1.333–1.420 RIU. The behavior of this optical fiber device as relative humidity (RH) sensor was also tested, monitoring its response to different surrounding humidity levels. The results show a sensitivity of 0.1 nm/RH% in the range from 20% to 80% RH.
In this work, the fabrication and characterization of refractometers based on lossy mode resonances (LMR) is presented.
Tin dioxide (SnO2) films deposited on optical fibers are used as the LMR supporting coatings. These resonances shift to
the red as a function of the external refractive index, enabling the fabrication of robust and highly reproducible
wavelength-based optical fiber refractometers. The obtained SnO2-based refractometer shows an average sensitivity of
7198 nm/refractive index unit (RIU) in the range 1.333-1.420 RIU.
In this work, it is described the fabrication and characterization of optical fiber refractometers based on lossy-mode
resonances (LMR) originated by deposition of different thin-film coatings around the optical fiber core. Two devices
with different coating materials are compared: one coated with conducting tin doped indium oxide (ITO) coatings and
the other one coated with semiconducting indium oxide. The response of these devices is characterized and compared as
a function of the external refractive index. The sensitivity obtained for indium oxide based refractometers resulted 39%
higher than that of ITO based ones when the resonance is located in the same spectral region. This behaviour is attributed
to the spectral characteristics of indium oxide, which allow an earlier generation of the resonance thanks to its higher
refractive index as well as permitting the accomplishment of LMR conditions in a wider spectral range. Moreover, these
devices are an adequate platform for the development of a wide variety of sensors by the addition of the suitable layer
onto the transparent oxide coating.
In this work, lossy mode resonance (LMR) based optical fiber refractometers are fabricated by using a transparent
coating (indium oxide), as the LMR supporting layer. The utilization of indium oxide coatings permits the fabrication of
highly sensitive optical fiber refractometers and enables the tunability of the LMR by adjusting the fabrication
parameters, such as the coating thickness. The detection technique is based on the wavelength shift of the LMR. In this
work it has been studied the influence of the external refractive index, achieving a maximum sensitivity of 2.24e-4
refractive index units per nanometer. Moreover, by adequated parameterization, more than one LMR can be observed in
the wavelength range analyzed in the experiments, which leads to a more accurate measurement of the refractive index.
In this work, surface plasmon resonance (SPR) based optical fiber sensors are proposed by using a transparent
conductive coating, Indium Tin Oxide (ITO) in our case, as the SPR supporting layer. The utilization of these ITO
coatings instead of using a thin film of gold or silver shifts the plasmon resonance band to the infra-red region and allows
the tunability of the SPR wavelength by adjusting the film fabrication parameters. The spectral response of these novel
devices is characterized, achieving a sensitivity of 0.00025 refractive index units per nanometer, which opens the door
for a wide range of applications.
Here, the fabrication and characterization of a novel optical fiber humidity sensor based on surface plasmon resonance
(SPR) in the infra-red region is presented. Firstly, an indium tin oxide (ITO) coating is deposited onto a 200 μm core
diameter optical fiber causing the shift of the SPR wavelength to the infra-red region. Then, the LbL method is used to
deposit a polymeric coating onto the ITO layer. The variations in the external humidity originated changes in the
thickness and refractive index of the polymeric coating and hence in the resonance.
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