Iñaki Bikandi

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.

Computational Analysis of the Power Spectral Shifts and Widths Along Dye-Doped Polymer Optical Fibers

Polymer optical fibers doped with organic dyes can be used as efficient optical amplifiers and lasers in the visible region. We computationally analyze the spectral features of both their fluorescence and their amplified emission for different amounts of overlap between the emission and absorption spectra of the dyes employed. Representative cases are compared by calculating the respective evolutions along the doped fiber of the average wavelength, peak wavelength, and full-width at half-maximum of the output power obtained.

A comprehensive analysis of scattering in polymer optical fibers

The aim of this paper is to investigate the properties of the inhomogeneities that give rise to light scattering in polymer optical fibers (POFs). We perform several measurements in two commercial POFs of identical characteristics: these measurements, based on the side-illumination technique, consist in the detection of the total amount of scattered light guided along a POF sample under different launching conditions and in the acquisition of the corresponding near- and far-field patterns. We carry out complementary computer simulations considering inhomogeneities of different sizes at different positions inside the POF. The comparison of these simulated results with the experimental measurements will provide us with valuable information about the size and placement of the most influential inhomogeneities.

Scattering in step-index polymer optical fibers by side-illumination technique: theory and application

In this paper we present a detailed theoretical study that describes the generation of scattered light in step-index polymer optical fibers by using the side-illumination scattering measurement technique. A detailed analysis of the variation of the maximum angle of acceptance within the fiber has been carried out in order to calculate the scattered light as a function of different launching conditions. The theoretical model has been developed by using the Mie theory for spheres in the independent-scatterer approximation.

Luminescence Study of Polymer Optical Fibers Doped With Conjugated Polymers

The characterization of the spectral emission and of the photostability of polymer optical fibers (POFs) doped with conjugated polymers has been carried out taking into account the distribution of the dopant in the fiber core. Four different conjugated polymers embedded in the matrix of the typical POF material have been analyzed. Measurements include, among others, evolutions of the emission with excitation wavelength and time, spectral changes for different excitation irradiances, and the influence of the propagation distance along the fiber.

Side-illumination fluorescence critical angle: theory and application to F8BT-doped polymer optical fibers

In this work we have analyzed theoretically and experimentally the critical angle for the emission generated in doped polymer optical fibers as a function of different launching conditions by using the side-illumination fluorescence technique. A theoretical model has been developed in order to explain the experimental measurements. It is shown that both the theoretical and experimental critical angles are appreciably higher than the meridional critical angle corresponding to the maximum acceptance angle for a single source placed at the fiber axis. This increase changes the value of several important parameters in the performance of active fibers. The analysis has been performed in polymer optical fibers doped with a conjugated polymer.

U-Shaped and Surface Functionalized Polymer Optical Fiber Probe for Glucose Detection

In this work we show an optical fiber evanescent wave absorption probe for glucose detection in different physiological media. High selectivity is achieved by functionalizing the surface of an only-core poly(methyl methacrylate) (PMMA) polymer optical fiber with phenilboronic groups, and enhanced sensitivity by using a U-shaped geometry. Employing a supercontinuum light source and a high-resolution spectrometer, absorption measurements are performed in the broadband visible light spectrum. Experimental results suggest the feasibility of such a fiber probe as a low-cost and selective glucose detector.

Spectral Dependence of Scattered Light in Step-Index Polymer Optical Fibers by Side-Illumination Technique

In this study, we investigate the spectral distribution of the light scattered in step-index polymer optical fibers by illuminating the fibers transversely to their symmetry axis. For that purpose, we have performed wavelength-dependent scattering measurements over the spectral range 400-750 nm in three different commercial step-index polymer optical fibers. We have estimated the mean size of the most influential scattering centers in these polymer optical fibers, analyzing theoretically the experimental results obtained.

A novel liquid-filled microstructured polymer optical fiber as bio-sensing platform for Raman spectroscopy

One approach to overcome the poor efficiency of the Raman scattering as a sensing platform is to use microstructured optical fibers. In this type of fibers with a longitudinal holey structure, light interacts with the target sample, which is confined in the core, giving rise to a light intensity increase of the obtained Raman spectra due to the large interaction distances and the guidance of the scattered light. In this work, we present an ad-hoc fabricated liquid-core microstructured polymer optical fiber (LC-mPOF) as a bio-sensing platform for Raman Spectroscopy. Arising from an initial simulation stage, we create the desired preform using the drilling technique and afterwards the LC-mPOF is drawn in our fiber drawing tower. The guiding mechanism of the light through the solution has a major importance, being a key factor to obtain appreciable enhancements in Raman scattering. In this case, in order to optimize the Raman scattering signal of dissolved glucose (target molecule), we have filled the core with an aqueous solution of the target molecule, enabling in this way the modified total internal reflection mechanism. Experimental Raman measurements are performed and results are discussed.

Mechanical properties of polymer-optical fibres

Abstract This chapter describes the mechanical properties of POFs, such as Young’s modulus, strain, stress, or strength, which result relevant in the performance of POFs, as well as in the aging and in the fabrication of new POF designs. All these physical properties vary drastically depending on the designed POF type, going from conventional step-index POFs (SI-POF) to hollow-core or solid-core microstructured POFs (mPOF), multicore POFs (MCPOF) or dye-doped POFs. The chapter begins with a description of the key parameters that characterize the mechanical performance of POFs. Afterwards, a review of the mechanical performance and properties of available POFs with different geometries, sizes and materials is performed. Finally, different mechanical models for thermoplastic polymers are summarized. The use of these mechanical models will be helpful in the design process of new and optimized POF types.