Geometric optics analysis of inverted graded index fibers

We derive a general solution based on geometric optics that describes the light propagation properties in multimode optical fibers with inverted refractive index profiles. Using this general solution, we classify rays according to their propagation properties and calculate the analytical expressions of the ray trajectories inside these fibers under different launching conditions. In addition, we discuss the most suitable propagation conditions that maximize the confinement of light power in the vicinity of the core-cladding interface for sensing purposes.hese results are part of the Grant Nos. PID2021-122505OB- C31, TED2021-129959B-C21 and PDC2022-133053-C21, funded by MCIN/AEI/10.13039/501100011033, by ‘ERDF A way of making Europe’ and by the ‘European Union Next GenerationEU/PRTR’, and also of the Grant Nos. IT1452-22, ELKARTEK KK 2021/00082 and ELKARTEK KK 2021/000 funded by the Gobierno Vasco/Eusko Jaurlaritza

Laser sintonizagarriak: titanio : zafiro laserraren sintonizazioa kristalaren beraren birrefringentziaz baliatuz

Lan honetan, laser sintonizagarrien (hau da uhin-luzera aldakorra duten laserren) funtzionamenduaren ezaugarriak laburbilduko dira eta adibide gisa, gailu jakin baten garapena aurkeztuko da. Laser sintonizagarri honen berezitasun nagusia bere sinpletasunean datza: laserraren igorpena lortzeko kitzikatzen den materiala (material aktiboa) eta sintonizatze efektua eragiten duen osagaia bat dira, alegia anplifikazioa eta sintonizazioa osagai bakarrekin lortzen da alegia. Sintonizazioaren eragileak kristalaren propietate birrefringenteak dira. Hainbat material gai diren arren, Ti:zafiro kristala aukeratu dugu, ikuspegi praktikotik erakargarriena delako. Ti:zafiro laserraren uhin-luzeraren "autosintonizazioa" bere igorpen-bandan lortu dugu sintonizatze efektua delako prozedura hori erabiliz. Teorikoki kalkulatutako sintonizazioaren uhin-luzerak eta igorpenaren beste ezaugarriak nahiko ados daude esperimentuetan neurtutakoekin. Ikuspegi praktikotik gailu hau erresonadorearen barneko osagai sintonizatzaileak erabiltzen ez delarik, merkeagoa eta eraginkorragoa da eta efizientzia irabazi. Bere trinkotasuna dela medio, beste sistema konplexuago batzuetan erabil daiteke akoplatuta eta bereziki interesgarria izango da laser jarraietan erabiltzeko

Characterization of Chromatic Dispersion and Refractive Index of Polymer Optical Fibers

The chromatic dispersion and the refractive index of poly(methyl methacrylate) polymer optical fibers (POFs) have been characterized in this work by using a tunable femtosecond laser and a Streak Camera. The characterization technique is based on the measurement of the time delays of light pulses propagating along POFs at different wavelengths. Polymer fibers of three different lengths made by two manufacturers have been employed for that purpose, and discrepancies lower than 3% have been obtained in all cases.This work has been funded in part by the Fondo Europeo de Desarrollo Regional (FEDER); by the Ministerio de Economia y Competitividad under project TEC2015-638263-C03-1-R, and by the Gobierno Vasco/Eusko Jaurlaritza under projects IT933-16 and ELKARTEK (KK-2016/0030, KK-2017/00033, KK-2017/00089 and KK-2016/0059). The work of Mikel Azkune was supported in part by a research fellowship from the Universidad del Pais Vasco/Euskal Herriko Unibertsitatea (UPV/EHU), Vicerrectorado de Euskera y Formacion Continua, while working on a Ph.D. degree

Fabrication of Active Polymer Optical Fibers by Solution Doping and Their Characterization

This paper employs the solution-doping technique for the fabrication of active polymer optical fibers (POFs), in which the dopant molecules are directly incorporated into the core of non-doped uncladded fibers. Firstly, we characterize the insertion of a solution of rhodamine B and methanol into the core of the fiber samples at different temperatures, and we show that better optical characteristics, especially in the attenuation coefficient, are achieved at lower temperatures. Moreover, we also analyze the dependence of the emission features of doped fibers on both the propagation distance and the excitation time. Some of these features and the corresponding ones reported in the literature for typical active POFs doped with the same dopant are quantitatively similar among them. This applies to the spectral location of the absorption and the emission bands, the spectral displacement with propagation distance, and the linear attenuation coefficient. The samples prepared in the way described in this work present higher photostability than typical samples reported in the literature, which are prepared in different ways.This research was funded by European Regional Development Fund (ERDF), by Ministerio de Economia y Competitividad (MINECO) (TEC2015-638263-C03-1-R) and by Eusko Jaurlaritza (ELKARTEK KK-2016/0030, ELKARTEK KK-2016/0059, ELKARTEK KK-2017/00033, ELKARTEK KK-2017/00089, IT933-16). The work of Mikel Azkune was supported in part by a research fellowship from the Universidad del Pais Vasco/Euskal Herriko Unibertsitatea (UPV/EHU), Vicerrectorado de Euskera y Formacion Continua, while working on a Ph.D. degree

POF-Based Solar Concentrators Incorporating Dyes and Europium Chelates

In this paper, useful models that enable time-efficient computational analyses of the performance of luminescent solar concentrators (LSCs) are developed and thoroughly described. These LSCs are based on polymer optical fibers codoped with organic dyes and/or europium chelates. The interest in such dopants lies in the availability of new dyes with higher quantum yields and in the photostability and suitable absorption and emission bands of europium chelates. Time-efficiency without compromising accuracy is especially important for the simulation of europium chelates, in which non-radiative energy transfers from the absorbing ligands to the europium ion and vice versa are so fast that the discretization in time, in the absence of some simplifying assumptions, would have to be very fine. Some available experimental results are also included for the sake of comparison.This research was funded by Gobierno de España, Ministerio de Economía y Competitividad, with grant RTI2018-094669-B-C31. They also acknowledge funding support from Departamento de Educación del Gobierno Vasco, Grant IT933-16, and SPRI ELKARTEK projects KK-2019/00101 (μ4Indust), and ELKARTEK KK-2019/00051 (SMARTRESNAK)

Fabrication and characterization of active polymer optical fibers with a ring-doped structure

This paper employs the solution-doping technique for the fabrication of polymer optical fibers (POFs) doped with two perylene derivatives, Lumogen Yellow 083 and Lumogen Red 305, in different combinations. With the solution-doping technique is very easy to control the amount of dopant penetration into the core of non-doped uncladded fibers, allowing the fabrication of active POFs with a novel ring-doped structure. In addition to manufacturing the fibers, these have also been optically characterized. Specifically, the influence of the combination of dopants, pumping power and wavelength, as well as the light propagation distance, have been measured and analyzed. Furthermore, time-resolved emission characteristics have also been measured to determine the fluorescence lifetimes and to extract information about the energy transfer between the dopants. Finally, the aim of this work has been to investigate the performance of the aforementioned POFs for fluorescent lighting applications, with a special focus on tunable light sources, and also for sensing applications.These results are funded in part by the Ministerio de Ciencia e Innovación -under projects RTC2019-007194-4, PID2021-122505OB-C31 and TED2021-129959B-C21,- and in part by Gobierno Vasco/Eusko Jaurlaritza under projects IT1452-22 and ELKARTEK (KK‑2021/00082, KK‑2021/00092)

Effects of Fabrication Methods on the Performance of Luminescent Solar Concentrators Based on Doped Polymer Optical Fibers

In this work, we detail two types of fabrication processes of four polymer optical fibers doped with lumogen dyes. The fiber preforms have been manufactured with two different methods: extrusion and casting. We have compared the performance of the two types of fibers as luminescent solar concentrators by calculating their optical efficiencies and concentration factors. The obtained results show better performance for those fibers manufactured by the casting process. We have also studied the photostability of the two types of fibers doped with the dye lumogen red under solar light radiation. A high thermal stability of the doped fibers has been observed.This work was funded in part by the Fondo Europeo de Desarrollo Regional (FEDER), in part by the Ministerio de Ciencia, Innovación y Universidades under projects RTC2019-007194-4, RTI2018-094669-B-C31 and MAT2014-5742-R and in part by the GobiernoVasco/Eusko Jaurlaritza IT933-16, ELKARTEK KK-2019/00101 (μ4Indust), and ELKARTEK KK-2019/00051 (SMARTRESNAK)

Optical Fiber Sensors for Aircraft Structural Health Monitoring

Aircraft structures require periodic and scheduled inspection and maintenance operations due to their special operating conditions and the principles of design employed to develop them. Therefore, structural health monitoring has a great potential to reduce the costs related to these operations. Optical fiber sensors applied to the monitoring of aircraft structures provide some advantages over traditional sensors. Several practical applications for structures and engines we have been working on are reported in this article. Fiber Bragg gratings have been analyzed in detail, because they have proved to constitute the most promising technology in this field, and two different alternatives for strain measurements are also described. With regard to engine condition evaluation, we present some results obtained with a reflected intensity-modulated optical fiber sensor for tip clearance and tip timing measurements in a turbine assembled in a wind tunnelThe authors would like to thank Professor A. Guemes for the permission to use the FBG responses shown in Figure 2. This work has been sponsored by the Ministerio de Economia y Competitividad (Spain) and FEDER funds under project TEC2012-37983-C03-01, the Gobierno Vasco/Eusko Jaurlaritza under projects IT664-13, ETORTEK14/13 and by the University of the Basque Country (UPV/EHU) through programs UFI11/16, US13/09 and EUSKAMPUS

Optical Characterization of Doped Thermoplastic and Thermosetting Polymer-Optical-Fibers

The emission properties of a graded-index thermoplastic polymer optical fiber and a step-index thermosetting one, both doped with rhodamine 6G, have been studied. The work includes a detailed analysis of the amplified spontaneous emission together with a study of the optical gains and losses of the fibers. The photostability of the emission of both types of fibers has also been investigated. Comparisons between the results of both doped polymer optical fibers are presented and discussed.This work has been funded in part by the Fondo Europeo de Desarrollo Regional (FEDER); by the Ministerio de Economia y Competitividad under project TEC2015-638263-C03-1-R; by the Gobierno Vasco/Eusko Jaurlaritza under projects IT933-16 and ELKARTEK (KK-2016/0030 and KK-2016/0059); by the University of the Basque Country UPV/EHU under program UFI11/16; and by the Japan Society for the Promotion of Science through the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program), initiated by the Council for Science and Technology. The work carried out by I. Parola has been funded by a research grant given by the Departamento de Educacion, Politica Linguistica y Cultura del Gobierno Vasco/Eusko Jaurlaritza for her PhD thesis. We also thank Stela Diamant and Oleg Palchik, from the company Intellisiv Ltd, for providing the thermosetting samples