Fernando Martínez-Piñón

Polymer optical fiber moisture sensor based on evanescent-wave scattering to measure humidity in oil-paper insulation in electrical apparatus

An optical fiber moisture sensor is prepared by coating a 1 mm polymer optical fiber with a film 30 micron thick of Polyvinyl Acetate PVA. We have experimentally studied how the light transmission characteristics of such coated optical fiber changes as a function of moisture conditions within an oil-paper insulation, to which the coating is exposed. An optical fiber moisture sensor that can be used to sense moisture present in liquid transformer oil and composite paper insulation in a wide range of concentrations is characterized. The resulting optical fiber sensor can be used for on-line measurements in electrical apparatus that use oil-paper insulation under large electrical field gradients. A light guide such as an optical polymer fiber operating in the 400 nm to 970 nm wavelength range is embedded in a body of paper insulation material immersed in oil, with the free ends of the fiber extending to or beyond the edges of the structure so that radiation such as light can be directed through one end of the carrier, and measured at the other end thereof, to monitor and detect the presence of moisture in the interior of the structure. Under normal operating conditions of power transformers the moisture concentration in the oil is in the range of 10 to 100 ppm and 0.5 to 5% in paper for a temperature range of 0 to 100degC. In order to compensate for the oil optical properties, an additional optical polymer fiber in contact with the transformer oil is used as a cero reference outside of the paper structure, since amount of moisture in oil is at least 200 times smaller than the moisture in the paper.

Surface Plasmon Resonance-Based Optical Fiber Embedded in PDMS for Temperature Sensing

A compact, simple-to-fabricate, low-cost, and highly sensitive optical fiber temperature sensor based on surface plasmon resonance (SPR) is reported. The sensor consists of a core mismatch fiber structure fabricated by splicing a small piece of single-mode fiber (SMF) between two multimode fibers (MMF). SPR is generated when evanescent field interacts with the gold layer deposited over the SMF cladding. Then, the sensor was embedded in polydimethylsiloxane (PDMS), which acts as a temperature to refractive index transducer. Due to PDMS high thermooptic coefficient, the SPR dip underwent a noticeable wavelength shift when a variation of temperature occurred. The device was tested in the 20-60 °C range showing a linear response and a sensitivity of 2.60 nm/°C. This sensor is appealing for temperature monitoring in microfluidic devices made of PDMS due to its high performance and simply fabrication process.

Temperature sensing through long period fiber gratings mechanically induced on tapered optical fibers

In this work the feasibility of employing two well-known techniques already used on designing optical fiber sensors is explored. The first technique employed involves monomode tapered fibers, which were fabricated using a taper machine designed, built, and implemented in our laboratory. This implementation greatly reduced the costs and fabrication time allowing us to produce the desired taper length and transmission conditions. The second technique used fiber Bragg gratings, which we decided to have mechanically induced and for that reason we devised and produced our own mechanical gratings with the help of a computer numerical control tool. This grating had to be fabricated with aluminum to withstand temperatures of up to 600°C. When light traveling through an optical fiber reaches a taper it couples into the cladding layer and comes back into the core when the taper ends. In the same manner, when the light encounters gratings in the fiber, it couples to the cladding modes, and when the gratings end, the light couples back into the core. For our experimentation, the tapering machine was programmed to fabricate single-mode tapers with 3 cm length, and the mechanically induced gratings characteristics were 5 cm length, and had a period of 500 μm and depth of the period of 300 μm. For the conducting tests, the tapered fiber is positioned in between two aluminum slabs, one grooved and the other plane. These two blocks accomplish the mechanically induced long period grating (LPG); the gratings on the grooved plaque are imprinted on the taper forming the period gratings. An optical spectrum analyzer is used to observe the changes on the transmission spectrum as the temperature varies from 20°C to 600°C. The resultant attenuation peak wavelength in the transmission spectrum shifts up to 8 nm, which is a higher shift compared to what has been reported using nontapered fibers. As the temperature increases there is no longer a shift, but there is significant power loss. Such a characteristic can be used as well for sensing applications.

Temperature sensing on tapered single mode fiber using mechanically induced long period fiber gratings

The modeling of a temperature optical fiber sensor is proposed and experimentally demonstrated in this work. The suggested structure to obtain the sensing temperature characteristics is by the use of a mechanically induced Long Period Fiber Grating (LPFG) on a tapered single mode optical fiber. A biconical fiber optic taper is made by applying heat using an oxygen-propane flame burner while stretching the single mode fiber (SMF) whose coating has been removed. The resulting geometry of the device is important to analyze the coupling between the core mode to the cladding modes, and this will determine whether the optical taper is adiabatic or non-adiabatic. On the other hand, the mechanical LPFG is made up of two plates, one grooved and other flat, the grooved plate was done on an acrylic slab with the help of a computerized numerical control machine (CNC). In addition to the experimental work, the supporting theory is also included.

Implantable blood pressure sensor for analyzing elasticity in arteries

MEMS technology could be an option for the development of a pressure sensor which allows the monitoring of several electronic signals in humans. In this work, a comparison is made between the typical elasticity curves of several arteries in the human body and the elasticity obtained for MEMS silicon microstructures such as membranes and cantilevers employing Finite Element analysis tools. The purpose is to identify which types of microstructures are mechanically compatible with human arteries. The goal is to integrate a blood pressure sensor which can be implanted in proximity with an artery. The expected benefits for this type of sensor are mainly to reduce the problems associated with the use of bulk devices through the day and during several days. Such a sensor could give precise blood pressure readings in a continuous or periodic form, i.e. information that is especially important for some critical cases of hypertension patients.

Mechanically induced long period fiber gratings on single mode tapered optical fiber for structure sensing applications

The modal characteristics of tapered single mode optical fibers and its strain sensing characteristics by using mechanically induced long period fiber gratings are presented in this work. Both Long Period Fiber Gratings (LPFG) and fiber tapers are fiber devices that couple light from the core fiber into the fiber cladding modes. The mechanical LPFG is made up of two plates, one flat and the other grooved. For this experiment the grooved plate was done on an acrylic slab with the help of a computer numerical control machine. The manufacturing of the tapered fiber is accomplished by applying heat using an oxygen-propane flame burner and stretching the fiber, which protective coating has been removed. Then, a polymer-tube-package is added in order to make the sensor sufficiently stiff for the tests. The mechanical induced LPFG is accomplished by putting the tapered fiber in between the two plates, so the taper acquires the form of the grooved plate slots. Using a laser beam the transmission spectrum showed a large peak transmission attenuation of around -20 dB. The resultant attenuation peak wavelength in the transmission spectrum shifts with changes in tension showing a strain sensitivity of 2pm/μɛ. This reveals an improvement on the sensitivity for structure monitoring applications compared with the use of a standard optical fiber. In addition to the experimental work, the supporting theory and numerical simulation analysis are also included.

Flavin and porphyrin-micro optical fibre biosensor: analysis and design

Micro Optical Fibre Biosensors (MOFBs) are emerging as one of the most sensitive bio-detection system technologies which do not require of labelling or amplification of the analyte. In these devices, a short region of the fibre core is exposed to the external environment so that the evanescent field can interact with biological species such as cells, proteins, and DNA. In order to increase the sensitivity and selectivity, MOFBs are often used in combination with other optical transduction mechanisms such as changes in refractive index, absorption, fluorescence and surface plasmon resonance. In this work we present the full characteristics, analysis and design of a MOFBs for Flavin and Porphyrin detection.

Modeling of temperature sensitivity on tapered Yb-doped fiber lasers

The temperature sensitivity of a tapered Yb-doped fiber laser is numerically investigated. The laser rate equations are modified to analyze the output characteristics of the tapered fiber laser in the continuous wave regime under different temperature conditions. Numerical analysis shows that for different pump schemes, high sensitivity can be achieved when the pump power is reduced to close to the threshold value. Our results are reproducible and contribute new information to the development and optimization of tapered Yb-doped fiber lasers and temperature fiber laser sensors.

PZR transducer for monitoring blood pressure

Results on a designed piezo resistive transducer (PZR) are presented in this work. The PZR will be specially manufactured for accurately measuring human blood pressure levels. Such transducer consists of four indifussed piezoresistors within a 10-μm Si membrane. The voltage signal response (VSR) is predicted when pressure is applied to the membrane, using a MEMS design tool that includes Finite Element Analysis (FEA). This transducer has the purpose of serving as a basis for the integration of an implantable Bio-MEMS BP sensor.