Javier Bravo

Optical Fiber Humidity Sensors Using Nanostructured Coatings of SiO

In this paper, a new optical fiber humidity sensor based on superhydrophilic coating is proposed. The electrostatic self-assembly technique has been used to create a nanometric scale surface on the tip of a standard single-mode pigtail. The fabricated sensor has demonstrated a good linearity in the range from 40% to 98% of relative humidity (RH). A variation of 10 dB in reflected optical power is achieved with a response time of only 150 ms. Among other applications, this sensor is intended to be used for monitoring the human breathing, so high dynamic performances are required, specially in the higher RH ranges.

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The transmitted optical power of two different fiber optic based structures when a nanofilm is being deposited onto them is experimentally studied. The technique used to build the nanofilms is Electrostatic Self Assembly (ESA), which has been widely reported in the literature. For the shake of comprehensibility, the comparative analysis of this phenomenon is accomplished for a particular sensing measure, humidity. The two structures selected towards development of practical humidity evanescent field sensors are hollow core fibers and tapered optical fibers. Some preliminary experimental studies of depositing humidity sensitive thin films and demonstrating their feasibility are presented. Depending on the working point selected, up to 10dB of variation in the optical output power is obtained when the environmental humidity changes. Both configurations exhibit similar dynamic behavior and response times shorter than 300msec, making these evanescent field sensors good candidates to monitor human breathing

Nanoparticles

Quantum dot nanocoatings have been deposited by means of the Layer-by-Layer technique on the inner holes of Photonic Crystal Fibers (PCFs) for the fabrication of temperature sensors. The optical properties of these sensors including absorbance, intensity emission, wavelength of the emission band, and the full width at half maximum (FWHM) have been experimentally studied for a temperature range from to .

Evanescent Field Fiber-Optic Sensors for Humidity Monitoring Based on Nanocoatings

A new humidity sensor has been developed by coating a tapered single-mode standard communications fiber with a humidity sensitive nanofilm using the electrostatic self-assembled (ESA) monolayer technique. Power changes up to 20 dB have been recorded during the coating process. In order to take advantage of both the potential sensitivity of the tapered fiber and the precise thickness control, which is possible to achieve using the ESA technique, the optimal layer thickness has been adjusted to the maximum slope point of the transmitted optical power curve as a function of the overlay thickness. An optimal working point sensor is compared to a nonoptimal one demonstrating the sensitivity difference between both.

Photonic Crystal Fiber Temperature Sensor Based on Quantum Dot Nanocoatings

In this work, a new method for the detection of the negative effects of a particular unbalanced voltage and inverter harmonics on the performance of an induction motor using fiber sensors is proposed. Supplying a three-phase induction motor with unbalanced voltages causes an oscillating electromagnetic torque that generates vibrations, increased losses, efficiency reduction, and an extra temperature rise that leads to a reduction on insulation life of the machine. A new in-line fiber etalon accelerometer has been designed to detect these vibrations in the range DC-500 Hz. The in-line fiber etalon scheme used provides high robustness and stability, giving enough sensitivity to monitor the low-frequency and low-amplitude oscillations in the stator of the machine that exist in a voltage unbalance situation. To prove this claim, a 1.5-kW squirrel cage induction motor is analyzed under different unbalance levels. It is shown that a precise unbalance factor can be detected without accessing to the electric part of the machine and an accurate monitoring can be obtained using the high-resolution analysis proposed

Nonadiabatic tapered single-mode fiber coated with humidity sensitive nanofilms

The optical characteristics of one multimode fiber (MMF)-hollow core fiber (HCF)-structure when a nanofilm is deposited on it has been theoretically and experimentally studied. The electrostatic self-assembly method has been used as the deposition technique, and the polymers chosen are polydiallyldimethylammonium and Poly R-478. Two different types of HCF have been used for the fabrication of the devices: 10/150 and 50/150 /spl mu/m inner and outer diameters, respectively. Depending on several design parameters, the transmitted optical-power characteristic of the device experiences important changes that could be interesting towards development of several practical optical devices. The length and thickness of the HCF segment, the refractive index of the material deposited, the angle of the light when it reach the HCF section, and the wavelength of the light source will be analyzed.

Unbalance and harmonics detection in induction motors using an optical fiber sensor

In this paper, a way to build a nanostructured coating on the inner surface of a hollow core fiber (HCF) is presented. This coated HCF is subsequently spliced to two standard multimode fibers (MMF) obtaining an encapsulated all fiber structure that protects the nanocoating from the environment. Using quantum dot (QD) nanofilms in this structure, an improvement in the photobleaching effect is observed with respect to previous fiber optic temperature sensors based on similar QD nanofilms. When the film is deposited on the outer surface of the fiber, the sensors suffered an 80% decrease in the fluorescence emission after 1.5 h of continuous illumination. The enhanced structure presented here achieves a diminution of only 6.3% after 4 h at the same conditions. In addition, it is experimentally shown that these sensors can be used in a parallel setup to measure temperature changes simultaneously in two different locations.

Nanofilms on hollow core fiber-based structures: an optical study

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.

Encapsulated Quantum Dot Nanofilms Inside Hollow Core Optical Fibers for Temperature Measurement

In this paper a new fiber optic sensor for the detection of antibodies to gliadin, in order to aid the diagnosis of celiac disease, is presented. Optical fibers of 200/230 mum (core and cladding diameters respectively) were tapered to a waist diameter in the range of 15-20 mum, and then the specific antigen was deposited using the Electrostatic Self-Assembly (ESA) method. Optimal deposition parameters have been selected using an in-situ interferometric characterization technique. The high sensitivity and continuous monitoring of the proposed scheme can reduce importantly the time and serum volume required for celiac disease tests. Performance time is shorter due to the absence of many washing and blocking steps as needed in conventional methods. Additionally, the ESA method allows the construction of nanometric scale recognition surfaces on the fiber optic, which helps to create fast response sensors for real time observation of the binding process.

Fiber optic temperature sensor depositing quantum dots inside hollow core fibers using the layer by layer technique

Temperature sensitive nanofilms based on quantum dots (QDs) has been deposited on the inner holes of a photonic crystal fiber (PCF) using the layer by layer electrostatic self-assembly method. The sensing structure is based on a PCF fiber segment spliced between two multimode fibers (MMF) of different diameters. The sensors showed a linear variation of the intensity and wavelength emission for a temperature range from -20degC to 70degC.