Miguel A. Basurto-Pensado

Stimulated Raman scattering in a fiber with bending loss

Stimulated Raman scattering is investigated in a 100-m long single mode fiber with bend-induced loss which has a steep wavelength dependence. The wavelength dependent loss can be used to suppress the second Stokes conversion resulting in an increased first Stokes intensity. Our experiments with a Q-switch Nd:YAG laser produced a rectangular first Stokes pulse at the fiber output.

Fiber Optic Pressure Sensor using Multimode Interference

Based on the theory of multimode interference (MMI) and self-image formation, we developed a novel intrinsic optical fiber pressure sensor. The sensing element consists of a section of multimode fiber (MMF) without cladding spliced between two single mode fibers (SMF). The MMI pressure sensor is based on the intensity changes that occur in the transmitted light when the effective refractive index of the MMF is changed. Basically, a thick layer of Polydimethylsiloxane (PDMS) is placed in direct contact with the MMF section, such that the contact area between the PDMS and the fiber will change proportionally with the applied pressure, which results in a variation of the transmitted light intensity. Using this configuration, a good correlation between the measured intensity variations and the applied pressure is obtained. The sensitivity of the sensor is 3 μV/psi, for a range of 0-60 psi, and the maximum resolution of our system is 0.25 psi. Good repeatability is also observed with a standard deviation of 0.0019. The key feature of the proposed pressure sensor is its low fabrication cost, since the cost of the MMF is minimal.

Fiber Optic Pressure Sensor Using a Conformal Polymer on Multimode Interference Device

We report experimental results on an optical fiber pressure sensor based on multimode interference effects (MMIs). The key component is a small multimode fiber (MMF) section without cladding, which is placed on a direct contact with a polydimethilsiloxane polymer layer previously attached to a pressure-sensitive membrane. When the applied pressure is increased, both the polymer contact area and the induced stress on the MMF increase directly proportional with the applied pressure. Both effects contribute to losses of the propagating modes, and since the MMI spectrum is formed by the interference of the propagating modes, the net effect is that the intensity of the spectral response of the MMI is reduced as the pressure is increased. Therefore, by tracking a single wavelength, the intensity changes are correlated to the applied pressure values. The response of the sensor is highly linear within a pressure range of 0-960 kPa with a sensitivity of - 0.145 ×10-3 mW/kPa. The key features of the MMI pressure sensor are its low-cost and high repeatability.

Optical Fiber Sensor for Pressure Based on Multimode Interference as Sensitive Element

The experimental results of applications on a novel intrinsic fiber optic pressure sensor based on multimode interference are presented. The sensitive element consists in a SM-MM-SM (MMI) fiber structure embedded in a membrane.

Fiber Optic Pressure Sensor of 0–0.36 psi by Multimode Interference Technique

This paper presents the design, development and tests made to a fiber optic pressure sensor using the multimodalinterference methodology (MMI) thus, we propose an alternative sensor to the ones available which are limited byhigh robust environments where the use of them is a potential hazard (explosive gases, corrosion and evenelectromagnetic fields). The range of work for this sensor is 0 to 0.36 psi, the arrangement used is formed by a laserdiode, a sensing element, an electronic amplifying circuit, a data acquisition board and a computer. The sensingelement used is a SMS fiber optic structure (singlemode–multimode–singlemode, where a multimode fiber isembedded between two singlemode fibers) placed within the contact surface (diaphragm) made of a polymericmaterial; the body of the sensor was made of nylamid. The bending produced in the diaphragm by the pressure insidethe body of the sensor generates changes in the transmitted power response carried inside the fiber.

Estimation of LiBr-H2O Using Multimode Interference (MMI)

We use multimode interference (MMI) as an alternative optical technique to estimate lithium bromide (LiBr)concentration, of the work pair LiBr-H2O, in absorption heat pumps (AHP). The sensing element is a singlemodemultimode-singlemode (SMS) fiber optic structure. This is fabricated by splicing a precisely dimensioned multimodefiber (MMF) section between two singlemode fibers (SMFs). The operation principle is based on the multimodeinterference (MMI) effect occurring in the MMF section. For that purpose, different concentrations of the mixture wereprepared (from 44.30% to 60.69%) to study their optical response. The input field profile entering the sensing element,which is the naked (no cladding) MMF section of the SMS fiber structure, produced different transmitted intensityresponses for each of these concentrations. Thus the optical characterization of the mixture was used to establish amathematical relation to estimate the LiBr concentration. A linear fit for solutions with concentrations ranging from43.30% to 50.87% and refractive indices between 1.421 and 1.439 is demonstrated.

Temperature sensing based on optical transmission in a LiBr heat pump

A new technique, based on Optical Methods, has been tested for the evaluation of the lithium bromide (LiBr) concentration, a corrosive substance frequently used in heat pumps. Those solutions have large oxidizing capabilities. This technique avoids the direct contact between the electrodes and the LiBr aqueous solution within a thermodynamic absorption cycle. The viability of this technique in a potential commercial device, resides on its capability to detect working fluid concentrations within a temperature range from 25 °C up to 70 °C, those limiting temperature values correspond to the operating wavelengths of 1.33 μm and 1.55 μm, respectively. Our system determines the correlation among the signal and temperature data, for various concentrations, between 49 and 58 mass percentages. This function of two variables is represented as a surface with the transmittance, concentration and temperature as parameters and wavelength as reference. We discuss the adequate parameters characterization used in this technique.

Physicochemical and Luminescent Properties of Copolymers Composed of Three Monomers: Polythiophenes Based on 3-Hexylthiophene and 3,4-Ethylenedioxythiophene

The chemical synthesis and physicochemical and luminescent characterizations of polymers based on 3-HT, EDOT, and 2,2′-(9,9-dioctyl-9H-fluorene-2,7-diyl) bisthiophene (fluorene) or (E)-2-(ethyl(4-((4-nitrophenyl)diazenyl)phenyl)amino)ethyl 2-(thiophen-3-yl)acetate (TDR1) are reported. The fluorene unit was bound to the conjugate backbone, while the Disperse Red 1 (DR1) chromophore was present as a pendant group. Characterizations by 1H NMR, FT-IR, DSC-TGA, GPC, UV-vis, cyclic voltammetry, fluorescence quantum yield, excited state lifetime, and two-photon absorption cross-section were carried out. These polymers combined the physicochemical properties of EDOT and 3-HT, such as high electron density, high charge mobility, low oxidation potential, and good processability. The optical properties of these copolymers were highly dependent on the presence of EDOT, the molecular weight, and the regioregularity rather than the presence of the third component (fluorene or TDR1). The good nonlinear absorption and luminescent properties exhibited by these copolymers were exploited to fabricate nanoparticles used as fluorescent tags for the imaging of microstructures.

Failure Analysis to Blades Of Steam Turbines At Normal Conditions Of Operations And Resonance

The need to provide quality services, accurate diagnosis, timely rehabilitation and improvement in materials and operation of the turbines, have given way to scientific research crack initiation and crack propagation, the impending fracture and estimating life of the turbine components at normal conditions and resonance. The L-1 stage blades suffer high alternating stresses, for its size, exposure to high temperatures, and mechanical loads under repetitive strain of cyclic load. The lasts stages of blades are also subjected to severe centrifugal loads stress that, when combined with the alternating stress, is responsible for fatigue failures. In this work, the last stage L-1 blades of a steam turbine under cyclic load or fatigue were analyzed, the first instance to observe and measure the initiation crack and propagation crack under normal conditions operation and conditions on resonance; making the comparison to estimate the life time of the blade at both conditions.

Optical fiber trap: radiation pressure effect on inorganic and organic micro-particles

An optical fiber trap operates by radiation pressure and transverse force gradient while conventional optical trap operates on longitudinal gradient to trap particles. This subtle difference translates into easy setup and many advantages over conventional single-beam optical tweezers. In this work, we present a brief review of the current situation of fiber optic trap and their applications. Subsequently, we discuss the effect of radiation pressure on micro-organic and inorganic particles. Using a single optical fiber, radiation pressure transfers movement to the micro-particles, so velocity and acceleration are quantified. After that, micro particles are trapped, but now using two optical fibers. Finally, we discuss the results and problems involved with this research.