Design and fabrication of novel optical fiber architectures for sensing applications

Optical fiber sensors have experienced an important progress in recent years with the employment of structures based on gratings, interferometers or electromagnetic resonances, among others; and the development of nanotechnology, that has enabled the deposition of coatings at the micro- and nanometric level on the fiber. These advances have allowed the manufacture of optical fiber sensors for measuring physical variables, chemical parameters or biosensing applications. This thesis contributes to the analysis and optimization, both theoretical and experimental, of different configurations and structures in optical fiber, applied to the development of sensors. Several structures are studied in this thesis, including Lossy Mode Resonances (LMRs) and optical fiber gratings: FBGs (fiber Bragg gratings), LPGs (long period fiber gratings) and TFBGs (tilted fiber Bragg gratings). The main research lines that are presented in this thesis are the fabrication of multisensing devices based on LMRs and the enhancement of the mode transition in optical fiber gratings: LPGs in double clad fibers and TFBGs. The common element between both research lines is the employment of thin films of high refractive index materials: tin oxide (SnO2), indium tin oxide (ITO) and titanium dioxide (TiO2). The results shown in this thesis reveal the potential of combining several structures and/or phenomena in optical fibers to improve the performance of optical fiber sensors.