Jon Arrue

Dependence of bending losses on cladding thickness in plastic optical fibers.

Our main goal is to provide a comprehensive explanation of the existing differences in bending losses arising from having step-index multimode plastic optical fibers with different cladding thickness and under different types of conditions, namely, the variable bend radius R, the number of fiber turns, or the fiber diameter. For this purpose, both experimental and numerical result of bending losses are presented for different cladding thicknesses and conditions. For the measurements, two cladding thicknesses have been considered: one finite and another infinite. A fiber in air has a finite cladding thickness, and rays are reflected at the cladding-air interface, whereas a fiber covered by oil is equivalent to having an infinite cladding, since the very similar refractive index of oil prevents reflections from occurring at the cladding-oil interface. For the sake of comparison, numerical simulations based on ray tracing have been performed for finite-cladding step-index multimode waveguides. The numerical results reinforce the experimental data, and both the experimental measurements and the computational simulations turn out to be very useful to explain the behavior of refracting and tunneling rays along bent multimode waveguides and along finite-cladding fibers.

A Self-Referencing Intensity Based Polymer Optical Fiber Sensor for Liquid Detection

A novel self-referencing fiber optic intensity sensor based on bending losses of a partially polished polymer optical fiber (POF) coupler is presented. The coupling ratio (K) depends on the external liquid in which the sensor is immersed. It is possible to distinguish between different liquids and to detect their presence. Experimental results for the most usual liquids found in industry, like water and oil, are given. K value increases up to 10% from the nominal value depending on the liquid. Sensor temperature dependence has also been studied for a range from 25 °C (environmental condition) to 50 °C. Any sector requiring liquid level measurements in flammable atmospheres can benefit from this intrinsically safe technology.

Analysis of the use of tapered graded-index polymer optical fibers for refractive-index Sensors.

The behavior of tapered graded-index polymer optical fibers is analyzed computationally for different refractive indices of the surrounding medium. This serves to clarify the main parameters affecting their possible performance as refractive-index sensors and extends an existing study of similar structures in glass fibers. The ray-tracing method is employed, its specific implementation is explained, and its results are compared with experimental ones, both from our laboratory and from the literature. The results show that the current commercial graded-index polymer optical fibers can be used to measure a large range of refractive indices with several advantages over glass fibers.

New method to calculate mode conversion coefficients in SI multimode optical fibers

A simple method is proposed for the experimental calculation of the mode conversion coefficients in multimode optical fibers. It only requires observing the far-field output pattern from a fixed length of fiber as the launching angle changes, as well as the intersection point between two far-field output patterns corresponding to two different input angles. The results obtained with this method are quite insensitive to small variations of the experimental parameters. A good agreement between theoretical and experimental results is also found.

Design of mode scramblers for step-index and graded-index plastic optical fibers

We analyze the internal evolution of light power angular distribution in typical mode scrambling configurations by comparing the resultant far fields, obtained either experimentally or computationally, with the experimental equilibrium mode distribution (EMD) far field for the plastic optical fibers (POF) considered, so as to provide an insight that helps to adapt existing scramblers to new types of POF that are coming onto the market.

Comparing polymer optical fiber, fiber Bragg grating, and traditional strain gauge for aircraft structural health monitoring

Systems for structural health monitoring in aeronautical structures use methods of measuring the elongation that normally require too heavy setups or difficult assembly jobs, such as those based on traditional strain gauges. Alternative methods based on fiber Bragg gratings tend to be very expensive. We analyze the possibility of improving the existing designs with the aid of low-cost plastic optical fiber sensors. For this purpose we test these sensors in a rudder flap subjected to different types of bending forces. The results show that they offer good stability and repeatability, and the measured values are very similar to those obtained with Bragg sensors.

Geometric Optics Analysis of Multi-Step Index Optical Fibers

The double aim of the present article is to give a brief description of our research groups main results achieved in recent years and to provide a comprehensive analysis of light propagation properties in multi-step index (MSI) fibers based on the geometric optics method. Therefore, in the initial part we present our research team and its main lines of research on plastic optical fibers (POF). Afterward, the discussion focuses on a new theory we have developed for the propagation in MSI fibers. First of all, we derive the ray invariants ˜β and ˜l, which allow us to instantly determine the direction of the ray at any position along its trajectory, and we discuss the characteristics of the ray path, setting the classification of rays into bound, refracting and tunneling categories. Then, we calculate the ray-path parameters, namely the path length Lp, the ray half period zp and the ray transit time t. Furthermore, we analyze the ray temporal dispersion. Specifically, we take a practical case in which the width of each layer is maintained constant, allowing, in contrast, for the respective refractive indices to take any value, and we derive closed expressions for the ray dispersion. Finally, we investigate the light power acceptance properties of an MSI fiber, calculating the effectiveness of both diffuse and collimated light sources in launching bound rays and the coupling losses with lateral and longitudinal misalignments.

Passive device based on plastic optical fibers to determine the indices of refraction of liquids.

We have designed and measured a passive device based on plastic optical fibers (POFs) that one can use to determine the indices of refraction of liquids. A complementary software has also been designed to simulate the behavior of the device. We report on the theoretical model developed for the device, its implementation in a simulation software program, and the results of the simulation. A comparison of the experimental and calculated results is also shown and discussed.

Amplified spontaneous emission in graded-index polymer optical fibers: theory and experiment.

In this work we analyze experimentally and theoretically the properties of amplified spontaneous emission (ASE) in a rhodamine-6G-doped graded-index polymer optical fiber. A theoretical model based on the laser rate equations describes the ASE features successfully. The dependence of the ASE threshold and efficiency on fiber length is analyzed in detail.

Analysis of a plastic optical fiber-based displacement sensor

An easy-to-manufacture setup for a displacement sensor based on plastic optical fiber (POF) is analyzed, showing computational and experimental results. If the displacement is the consequence of force or pressure applied to the device, this can be used as a force or pressure transducer. Its principle of operation consists of bending a POF section around a flexible cylinder and measuring light attenuation when the whole set is subjected to side pressure. Attenuations are obtained computationally as a function of side deformation for different design parameters. Experimental results with an actually built prototype are also provided.