Open Access
Optical fiber thermo-refractometer
(Optica, 2022) Imas González, José Javier; Ruiz Zamarreño, Carlos; Del Villar, Ignacio; Cardozo da Silva, Jean Carlos; Oliveira, V.; Matías Maestro, Ignacio; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
This work presents the implementation of a thermo-refractometer, which integrates the measurement of both refractive index and temperature in a single optical fiber structure. To this purpose, a lossy mode resonance (LMR)-based refractometer is obtained by means of the deposition of a titanium dioxide (TiO2) thin film onto a side-polished (D-shaped) single mode fiber. Measurement and subsequent temperature compensation are achieved by means of a fiber Bragg grating (FBG) inscribed in the core of the D-shaped region. The LMR wavelength shift is monitored in transmission while the FBG (FBG peak at 1533 nm) displacement is observed in reflection. The LMR is sensitive to both the surrounding refractive index (SRI), with a sensitivity of 3725.2 nm/RIU in the 1.3324-1.3479 range, and the temperature (- 0.186 nm/°C); while the FBG is only affected by the temperature (32.6 pm/°C in the 25°C - 45°C range). With these values, it is possible to recover the SRI and temperature variations from the wavelength shifts of the LMR and the FBG, constituting a thermo-refractometer, where it is suppressed the effect of the temperature over the refractometer operation, which could cause errors in the fourth or even third decimal of the measured SRI value.
Open Access
A systemic model for lossy mode resonances (LMRs)
(Elsevier, 2024-11-07) Imas González, José Javier; Del Villar, Ignacio; Halir, Robert; Wangüemert-Pérez, J. Gonzalo; Ortega-Moñux, Alejandro; Matías Maestro, Ignacio; Molina-Fernández, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Lossy mode resonances (LMRs) have been widely employed for the development of sensors in the last years. However, the theoretical frameworks for LMRs are scarce and difficult to systematize, hampering the development of this technology. In this work, we propose a new systemic model for assessing LMRs in arbitrary waveguide configurations, based solely on modal analysis of the unperturbed waveguide and the waveguide with a thin film optimized for LMR generation. The model is first developed for a generic waveguide, and leveraged to design, for the first time, LMRs in a silicon nitride photonic wire waveguide. It is furthermore demonstrated that the model only requires a few modes to reliably describe LMRs in D-shaped fibers, reducing the computational cost of simulating them. Therefore, the suggested model is valid for both high and low contrast waveguides, and it is considered it provides new insights about LMRs, which will help in the design of new LMR-based devices and its extension to novel platforms.
Open Access
A comprehensive study of optical resonances in metals, dielectrics, and excitonic materials in double interface structures
(Elsevier, 2025-02-01) Imas González, José Javier; Matías Maestro, Ignacio; Del Villar, Ignacio; Ozcariz Celaya, Aritz; Vitoria Pascual, Ignacio; Ruiz Zamarreño, Carlos; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
From an optical perspective, depending on the relationship between the real (n) and imaginary (k) parts of its refractive index, three broad categories of materials can be distinguished: metals (k ¿ n), dielectrics (n ¿ k), and materials in which n ¿ k (termed here excitonic materials). The modes and optical resonances that appear in a thin film bounded by two dielectrics with similar refractive index, what we call here a double interface structure, have been widely studied in the case of metals, but not for dielectrics, or materials with n ¿ k. In this work, we propose a new approach, based on employing the phase matching condition to correlate the resonances that appear in the wavelength versus incident angle color maps of the reflected power with the modal analysis of the cross section of the structure. This analysis is performed, using an attenuated total reflection (ATR) setup, for thin film materials that belong to each of the mentioned categories: a metal (gold, Au), a dielectric (titanium dioxide, TiO2), and a material with n ¿ k (chromium, Cr). The theoretical analysis is supported with experimental results. It is demonstrated that this method enables to identify any resonance at any wavelength or incident angle, being valid for all three types of materials. Therefore, it is considered the suggested approach will help the research in these materials and in the double interface structure in the optics and photonics field.
Open Access
Multi-sensing platform design with a grating-based nanostructure on a coverslip substrate
(Springer, 2023) Imas González, José Javier; Del Villar, Ignacio; Ruiz Zamarreño, Carlos; Mukhopadhyay, Subhas C.; Matías Maestro, Ignacio; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
Two different thin film designs with a grating pattern are simulated on a soda lime coverslip, which acts as optical waveguide, with the purpose of generating both a lossy mode resonance (LMR) in transmission and reflection bands. This way both phenomena can be made sensitive to different parameters, leading to a multi-sensing device. The first design consists of a grating patterned in a SnO2 thin film deposited on the coverslip. The performance of the device in both transmission and reflection is numerically studied in air for different values of the grating pitch. Small grating pitches (in the order of the µm) are more suitable for generating the reflection bands while larger values (500 µm or more) are required to produce the LMR, when the reflection bands are no longer visible. Due to the inability to obtain both phenomena with this design, a second design is assessed, where the grating is combined with a section of constant thickness. In this case the desired response is obtained, which opens the path to use this device for multi-sensing applications, measuring several parameters at the same time.

Imas González, José Javier

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