In this paper, a new sensor system for relative humidity measurements based on a SnO2 sputtering deposition on a microstructured optical fiber (MOF) low-finesse Fabry-Perot (FP) sensing head is presented and characterized. The interrogation of the sensing head is carried out by monitoring the Fast Fourier Transform phase variations of the FP interference frequency. This method is low-sensitive to signal amplitude variations and also avoids the necessity of tracking the evolution of peaks and valleys in the spectrum. The sensor is operated within a wide humidity range (20%-90% relative humidity) with a maximum sensitivity achieved of 0.14rad/%. The measurement method uses a commercial optical interrogator as the only active element, this compact solution allows real time analysis of the data.
The deposition of a non-metallic thin-film in a symmetrically coated tapered optical fiber leads to the generation of resonances due to guidance of a mode in the thin-film. At certain conditions, the resonances overlap each other, which can be avoided with an asymmetric coated tapered optical fiber, which permits to obtain resonances for TM and TE polarization separately. Numerical results showing the sensitivity to coating thickness and surrounding medium refractive index are also presented for both polarizations.
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.
This work presents the development and characterization of an optical fiber current transducer based on lossy mode resonances (LMRs) to work in high voltage networks. A multilayer structure was created in order to be able to shift the LMR by an electro-optic material deposited in the middle of two electrodes. The optical resonance has a displacement range of 200 nm on its TM component, what makes this device suitable for current sensing. Furthermore, dip coating of polyvinylidene difluoride has enhanced the nanofilm uniformity with respect to previous devices.
This work presents the development and test of an anti-gliadin antibodies biosensor based on lossy mode resonances (LMRs) to detect celiac disease. Several polyelectrolites were used to perform layer-by-layer assembly processes in order to generate the LMR and to fabricate a gliadin-embedded thin-film. The LMR shifted 20 nm when immersed in a 5 ppm anti-gliadin antibodies-PBS solution, what makes this bioprobe suitable for detecting celiac disease. This is the first time, to our knowledge, that LMRs are used to detect celiac disease and these results suppose promising prospects on the use of such phenomena as biological detectors.
This work addresses a humidity sensor using long-period fiber gratings (LPG) coated with silica nanospheres film. SiO2-nanospheres coating is deposited onto the LPG using the electrostatic self-assembly technique (ESA). The polymeric
overlay changes its optical properties when exposed to different humidity levels, resulting in a shift of the resonance
wavelength of the LPG. The obtained results are accordant with the theoretical simulations. Wavelength shifts up to
12nm in a humidity range from 20% to 80% are reported, maintaining the same dependence at different temperatures.
In this work a new nano-biofilm is proposed for the detection of celiac disease (CD). A long-period fiber grating (LPFG)
is used as a transducer and the surface of the fiber is coated with a precursor layer of SiO2-nanospheres using the
electrostatic self-assembly technique (ESA). This layer has been designed in order to create a substrate of high porosity
where the gliadins could be deposited. Under the presence of specific antibodies antigliadin antibodies (AGA) the
refractive index of the overlay changes giving a detectable shift in the resonance wavelength of the LPFG.
Concentrations as low as 5 ppm were detected.
CdTe Quantum Dots (4 nm of diameter) have been successfully deposited on the inner part of hollow core fibers using
the Layer-by-Layer Electrostatic Self-Assembly method. The architecture of the sensor consists on a short section of a
hollow core fiber tapered at both ends and spliced to standard multimode optical fibers. Taking advantage of the
dependence on temperature of the green fluorescent emission of the Quantum Dot sensitive nanofilms, optical fiber
sensors were fabricated and experimentally demonstrated.
A fiber-optic biosensor for glucose concentration detection has been designed, based on electrostatic self-assembly. The end face of a multimode fiber is coated with poly(allylamine hydrochloride) in combination with Prussian blue and the enzyme glucose oxidase. The glucose concentration that can be measured ranges between 0.06 and 2 mM. The initial velocity of change of the output biosensor signal has been found to be linear in the glucose concentration. The sensor recovers after immersion in ascorbic acid. The pH values analyzed range between 5 and 7. The sensitivity of the device has been increased by adjusting the number of bilayers and by adding some capping bilayers at the end of the structure.
We experimentally study the behavior of one multimode fiber–hollow core fiber–multimode fiber structure when nanofilms are deposited on it with the aim of developing practical evanescent field-based devices, such as sensors, filters, etc. The electrostatic self-assembly (ESA) method is used as the deposition technique and the chosen polymers are PDDA and Poly R-478 because of their well-known optical properties and their potential application as humidity sensors. Three different types of hollow core, fibers are used for the fabrication of the devices and at two different wavelengths. An oscillatory-decreasing transmitted optical power is obtained as the thickness of the nanofilms is increased.
In this work a new condition monitoring scheme using a fiber optic sensor is proposed. It has been specifically designed for the detection of damages in large electrical machines where the prevention of faults can be achieved through the vibration monitoring in the low frequency range. This sensor has been optimized to achieve a minimum detectable acceleration amplitude of 0.05g in the frequency range 2-500Hz. Also, high robustness and stability is achieved with the use of hollow core fiber to create the interferometric low-finesse cavity. The sensor has been tested in experimental induction machine test-rigs showing good performance both in the detection of magnetic and mechanical nature vibrations.
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