Imas González, José Javier
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Imas González
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José Javier
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Ingeniería Eléctrica, Electrónica y de Comunicación
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Publication Open Access Mode transitions and thickness measurements during deposition of nanoscale TiO2 coatings on tilted fiber Bragg gratings(IEEE, 2022) Imas González, José Javier; Albert, Jacques; Del Villar, Ignacio; Ozcariz Celaya, Aritz; Ruiz Zamarreño, Carlos; Matías Maestro, Ignacio; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de ComunicaciónThe mode transition is a phenomenon observed in thin film coated long period fiber gratings (LPGs) and singlemode multimode single-mode (SMS) fibers for certain values of the coating thickness and refractive index, resulting in increased sensitivity for sensing applications. It is shown here that mode transitions occur simultaneously for a large number of mode resonances in the transmission spectra of tilted fiber Bragg gratings (TFBG) measured during the deposition of ~350nm thick TiO2 coatings by Atomic Layer Deposition (ALD). In TFBGs, the mode transition shows up as an acceleration of the resonance wavelength shift vs thickness, but without fading of the resonance amplitude. Furthermore, the results show that the mode transition for cladding modes with predominantly “TE” polarization at the cladding boundary is significantly sharper than that of predominantly “TM” polarized modes and that it occurs at a smaller coating thickness (<100 nm vs >200 nm). Finally, using a separately determined coating refractive index (2.14, by ellipsometry on witness flats deposited simultaneously) and simulations of the resonance shifts of the TFBG with coating thickness, it is demonstrated that a TFBG connected to a spectral interrogation system can be used to measure the growth of a coating on the surface of the fiber in real time.Publication Open Access Improving the width of lossy mode resonances (LMRs) in double-clad fibers(IEEE, 2023) Imas González, José Javier; Del Villar, Ignacio; Zubiate Orzanco, Pablo; Ruiz Zamarreño, Carlos; Matías Maestro, Ignacio; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio IngeniaritzarenIn this work, the characteristics of lossy mode resonances (LMRs) in double-clad fibers where the refractive index (RI) of the second cladding is lower than that of the first cladding are analyzed both numerically and experimentally. In the first place, the LMRs spectra obtained with a 75 nm TiO 2 thin film are simulated, and it is observed that a thicker second cladding improves the width of the resonances, making them narrower. Then, two experimental cases (no second cladding, and second cladding with thickness of 1.13 μm) are assessed, showing a good agreement with the previous simulations. Finally, an experimental refractometric study is carried out in liquids (surrounding medium refractive index in the 1.34 - 1.40 range) for both fibers, calculating the full width at 1 dB (FW 1dB ), the sensitivity, and the figure of merit (FOM). The FW 1dB is better for the LMR obtained on the fiber with second cladding while the sensitivity is slightly greater for the fiber without second cladding. In the case of the FOM, it is higher for the double-clad fiber as the narrowing of the resonances outweighs the lower sensitivity. These results show that the performance of LMR-based optical fiber sensors can be improved by employing double-clad fibers.