Open Access
Micro sized interdigital capacitor for gases detection based on graphene oxide coating
(Springer, 2023) Vitoria Pascual, Ignacio; Armas, Dayron; Coronel Camones, Carlos Manuel; Algarra González, Manuel; Ruiz Zamarreño, Carlos; Matías Maestro, Ignacio; Mukhopadhyay, Subhas C.; Institute for Advanced Materials and Mathematics - INAMAT2; Institute of Smart Cities - ISC
A micro sized interdigital capacitor sensible to CO2 and NO is studied in this work. The photolithography technique enables to obtain fingers with dimensions of 10 × 500 µm and separated 7 µm between them. The deposition of a film composed of graphene oxide particles as the dielectrics of the capacitor allows to measure the gas concentration of CO2 and NO mixed with N2. The sensors were characterized in a gas chamber with a constant flow, obtaining promising results in changes of capacitance at 100 Hz. The sensors have a good linearity and sensitivity with a R2 = 0.996 and 5.026·10-1 pF/ % v/v for CO2 and R2=0.972 and 1.433·10-1 pF/ppb for NO.
Open Access
HMR-based optical gas detection with CuO and ZnO coatings
(IEEE, 2025-07-02) Gallego Martínez, Elieser Ernesto; Ruiz Zamarreño, Carlos; Matías Maestro, Ignacio; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This work presents the fabrication of hyperbolic mode resonance-based optical sensors by means of sputtered copper oxide (CuO) and zinc oxide (ZnO), and the study of their performance for gas sensing purposes. Two sensors were fabricated in a planar waveguide configuration with an intermediate gold thin film, and resonances were observed in the visible region of the electromagnetic spectrum. Both materials were analyzed with X-ray diffraction techniques, and their response was characterized by different concentrations of a group of gases comprised of nitric oxide, acetylene (C2H2), ethanol, carbon dioxide, and relative humidity. The best performance corresponds to the CuO sensor for C2H2 gas, presenting a sensitivity of 1.11 nm/parts per million (ppm) and a limit of detection of 12.6 ppb, with response and recovery times of 70 and 68 s, respectively. ZnO-based sensors allowed for a comprehensive study of ethanol in a range of thousands of ppm, while CuO-based sensors showed exceptional sensitivity for most gases in the range of a few ppm. All measurements were performed at room temperature.
Open Access
Beyond near-infrared lossy mode resonances with fluoride glass optical fiber
(Optica, 2021) Vitoria Pascual, Ignacio; Ruiz Zamarreño, Carlos; Ozcariz Celaya, Aritz; Imas González, José Javier; Matías Maestro, Ignacio; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The objective of this Letter consists of the exploration of the lossy mode resonance (LMR) phenomenon beyond the nearinfrared region and specifically in the short wave infrared region (SWIR) and medium wave infrared region (MWIR). The experimental and theoretical results show for the first time, to the best of our knowledge, not only LMRs in these regions, but also the utilization of fluoride glass optical fiber associated with this phenomenon. The fabricated devices consist of a nanometric thin-film of titanium dioxide used as LMR generating material, which probed extraordinary sensitivities to external refractive index (RI) variations. RI sensitivity was studied in the SWIR and MWIR under different conditions, such as the LMR wavelength range or the order of resonance, showing a tremendous potential for the detection of minute concentrations of gaseous or biological compounds in different media.
Embargo
Photoisomerization-induced LMR shift for UV radiation detection
(Elsevier, 2024) Gallego Martínez, Elieser Ernesto; Ruiz Zamarreño, Carlos; Matías Maestro, Ignacio; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
This work presents an optical sensor for ultraviolet radiation (UV) detection, based on the combined effects of Lossy Mode Resonance (LMR) in the mid infrared (MIR) spectral region and the photoisomerization of a polymeric dye coating. LMR was obtained by means of a sputtered SnO2 thin film on a tetrafluoroethylene-perfluoro (or alkoxy Vinyl Ether, PFA) substrate, along with a photo sensitive coating based on poly R-478. Obtained devices shown response and recovery times of 12 and 43 s, respectively, for an UV excitation of 71 mW at 365 nm. Sensitivity as a function of the excitation wavelength was studied with the highest value of 26 nm/mW obtained at 280 nm. For this excitation wavelength, the limit of detection (LoD) obtained was 0.024 mW. Four different excitation wavelengths were used to cover all UV regions (280, 310, 365 and 395 nm). All measurements were performed at room temperature and humidity (25 ¿C ± 1 ¿C and 13% R.H. ± 2% R.H. respectively). As far as we know, it is the first time that the LMR effect has been recognized in combination with a photoisomerization process.
Open Access
Ammonia gas optical sensor based on lossy mode resonances
(IEEE, 2023) Armas, Dayron; 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 Ingeniaritzaren
This letter presents the fabrication and characterization of an ammonia (NH 3) gas optical sensor based on lossy mode resonances (LMRs). A chromium (III) oxide (Cr 2 O 3) thin film deposited onto a planar waveguide was used as LMR supporting coating. The obtained LMR shows a maximum attenuation wavelength or resonance wavelength centered at 673 nm. The optical properties of the coating can be modified as a function of the presence and concentration of NH 3 in the external medium. Consequently, the refractive index of the Cr 2 O 3 thin film will change, producing a red-shift of the resonance wavelength. Obtained devices were tested for different concentrations of NH 3 as well as repetitive cycles. Concentrations as low as 10 ppbv of NH 3 were detected at room temperature. Machine learning regression models were used to mitigate the cross-sensitivity of the device under temperature and humidity fluctuations.
Open Access
Tunable sensitivity in long period fiber gratings during mode transition with low refractive index intermediate layer
(IEEE, 2022) Del Villar, Ignacio; Montoya-Cardona, Jorge; Imas González, José Javier; Reyes-Vera, Erick; Ruiz Zamarreño, Carlos; Matías Maestro, Ignacio; Cruz, José Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
Double-clad fibers where the second cladding has a lower refractive index than the first cladding, prove to be ideal structures for potentiating and tuning the sensitivity in long-period fiber gratings (LPFGs) operating in mode transition. When a thin film is deposited on the optical fiber, the second cladding performs acts as a barrier that initially prevents the transition to guidance in the thin film of one of the modes guided in the first cladding. Finally, the transition to guidance occurs with a sensitivity increase, in analogy to the tunnel effect observed in semiconductors. This improvement has been demonstrated both as a function of the thin film thickness and the surrounding medium refractive index, with enhancement factors of 4 and 2, respectively. This idea reinforces the performance of LPFGs, adding a new degree of freedom to the mode transition and the dispersion turning point phenomena. Moreover, the control of the variation of the effective index of cladding modes could be applied in other structures, such as tilted-fiber gratings or evanescent wave sensors.
Open Access
Photonic chip breath analyzer
(SpringerOpen, 2025-06-03) Gallego Martínez, Elieser Ernesto; Matías Maestro, Ignacio; Ruiz Zamarreño, Carlos; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This work introduces a novel single-package optical sensing device for multiple gas sensing, which is suitable for breath analysis applications. It is fabricated on a coverslip substrate via a sputtering technique and uses a planar waveguide configuration with lateral incidence of light. It features three sequentially ordered strips of different materials, which serve to increase the multivariate nature of the response of the device to different gases. For the proof-of-concept, the selected materials are indium tin oxide (ITO), tin oxide (SnO2), and chromium oxide III (Cr2O3), while the selected gases are nitric oxide (NO), acetylene (C2H2), and ammonia (NH3). The sensing mechanism is based on the hyperbolic mode resonance (HMR) effect, with the first-order resonance obtained for each strip located in the near infrared region. The multivariate response of the resonances and the correlation with the concentration of each gas allow training a machine learning (ML) model based on a nonlinear autoregressive neural network, enabling the accurate prediction of the concentration of each gas. The obtained limit of detection for all the gases was in the order of a few parts per billion. This innovative approach coined as the multivariate optical resonances spectroscopy demonstrates the potential of HMR-based optical sensors in combination with ML techniques for ultra-sensitive multi-gas detection applications using a single device.
Open Access
Low-cost optical fiber multimode interference biosensor based on a glucose sensitive Glucose-Oxidase enzyme thin-film
(Elsevier, 2024-12-04) Rodríguez Rodríguez, Wenceslao Eduardo; Rodríguez Rodríguez, Adolfo Josué; Juárez-Saldivar, Alfredo; Ruiz Zamarreño, Carlos; Matías Maestro, Ignacio; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
In this research we report a contribution for the development of low-cost fiber optical biosensors fabricated by the Single Mode-Multi Mode-Single Mode configuration applied for the glucose monitoring considering clinical concentrations ranges in aqueous analytes. Designed devices are evaluated using health standard detection ranges, such as healthy, pre-diabetic, and diabetic stages operating at the visible spectral region. The sensing regions has been prepared by the etching technique in order to improve the interaction between the evanescent wave with the surrounding medium followed by functionalization of enzyme oxidase glucose via the electrostatic self-assembly using by Poly(allylamine hydrochloride) as an immobilizer matrix. The increase of bilayers number over the sensor surface permits us to demonstrate the enhancement of sensitivity and limit of detection. Experimental results permitted the glucose characterization in the range from 0.3 to 2.4 mg mL-1 obtaining a response time of 9 s and a sensitivity of 1.8 nm/(mg mL-1) allowing to detect hypoglycemia and diabetes stages according to the World Health Organization standards.
Open Access
Optimization of fiber Bragg gratings inscribed in thin films deposited on D-shaped optical fibers
(MDPI, 2021) Imas González, José Javier; Ruiz Zamarreño, Carlos; Del Villar, Ignacio; Matías Maestro, Ignacio; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
A fiber Bragg grating patterned on a SnO2 thin film deposited on the flat surface of a D-shaped polished optical fiber is studied in this work. The fabrication parameters of this structure were optimized to achieve a trade-off among reflected power, full width half maximum (FWHM), sensitivity to the surrounding refractive index (SRI), and figure of merit (FOM). In the first place, the influence of the thin film thickness, the cladding thickness between the core and the flat surface of the D-shaped fiber (neck), and the length of the D-shaped zone over the reflected power and the FWHM were assessed. Reflected peak powers in the range from −2 dB to −10 dB can be easily achieved with FWHM below 100 pm. In the second place, the sensitivity to the SRI, the FWHM, and the FOM were analyzed for variations of the SRI in the 1.33–1.4 range, the neck, and the thin-film thickness. The best sensitivities theoretically achieved for this device are next to 40 nm/RIU, while the best FOM has a value of 114 RIU−1.
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.