BUSCADOR RECOLECTA

Coverslips deposited with a metallic oxide can be employed for generating lossy mode resonances by lateral incidence of light on the coverslip. Here it is demonstrated that with copper oxide the fading observed with other materials in the near infrared (NIR) wavelength range is avoided and LMRs can be obtained in a broadband range from 400 to 1700 nm, which permitted to observe the better performance in the NIR region compared to the visible region: the sensitivity to humidity is improved by more than a factor of two. However, copper oxide is not adequate for sensing humidity. The sensitivity of the device was optimized initially with a tin oxide coating and later with an additional layer of agarose, specifically adequate for the detection of humidity. The best performance was obtained with an agarose concentration 1% w/v, which permitted to observe a 10-fold sensitivity increase compared to the same device without agarose. This opens the path towards the development of environmental, chemical or biological sensors with an optimized sensitivity to a specific parameter to detect., The authors would like to acknowledge the support of the Agencia Estatal de Investigación (AEI) del Ministerio de Ciencia, Innovación y Universidades of Spain through the research project PID2019-106231RB-I00 and the predoctoral research grant from the Public University of Navarra.

With the goal of ultimate control over the light propagation, photonic crystals currently represent the primary building blocks for novel nanophotonic devices. Bloch surface waves (BSWs) in periodic dielectric multilayer structures with a surface defect is a well-known phenomenon, which implies new opportunities for controlling the light propagation and has many applications in the physical and biological science. However, most of the reported structures based on BSWs require depositing a large number of alternating layers or exploiting a large refractive index (RI) contrast between the materials constituting the multilayer structure, thereby increasing the complexity and costs of manufacturing. The combination of fiber–optic-based platforms with nanotechnology is opening the opportunity for the development of high-performance photonic devices that enhance the light-matter interaction in a strong way compared to other optical platforms. Here, we report a BSW-supporting platform that uses geometrically modified commercial optical fibers such as D-shaped optical fibers, where a few-layer structure is deposited on its flat surface using metal oxides with a moderate difference in RI. In this novel fiber optic platform, BSWs are excited through the evanescent field of the core-guided fundamental mode, which indicates that the structure proposed here can be used as a sensing probe, along with other intrinsic properties of fiber optic sensors, as lightness, multiplexing capacity and easiness of integration in an optical network. As a demonstration, fiber optic BSW excitation is shown to be suitable for measuring RI variations. The designed structure is easy to manufacture and could be adapted to a wide range of applications in the fields of telecommunications, environment, health, and material characterization., Fundación para la Promoción de la Investigación y la Tecnología-Banco de la República of Colombia (Contract 202103); Universidad Nacional de Colombia (Hermes code 46509); Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (TEC2016-78047-R and PID2019-106231RB-I00).
E.G.V. acknowledges the support of COLCIENCIAS through the Doctoral Scholarship program.

Multi-parameter detection is key in the domain of sensors. Here it is demonstrated that an indium tin oxide (ITO) nanocoating can be used to generate multiple lossy mode resonances (LMRs) in the optical spectrum. To achieve this, a nanocoating with a gradient in thickness is generated on the surface of a planar waveguide, permitting broadening of the LMR because the position of an LMR in the optical spectrum is directly related to the nanocoating thickness. The nanocoating with a gradient in thickness contributes multiple LMRs, each one centred at a different wavelength. With a further etching or deposition using a mask, a pattern of deposited and non-deposited regions can be created, resulting in isolation of the LMRs by preventing LMR overlap. This enables tracking of each central wavelength separately, which can be tuned through control of the gradient or nanocoating pattern. The array of LMR-based sensors is a photonics analogue to the interdigital concept in electronics, enabling multiple resonances to be used for multiparameter sensing., The authors would like to acknowledge the partial support to the Spanish Ministry of Economy and Competitiveness TEC2016-79367-C2-2-R and PID2019-106231RB-I00 research fund, the STARDUST project (European Commission) and the pre-doctoral research grants of the Public University of Navarra.

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., This work has been supported by the Spanish Ministry of Universities through the FPU18/03087 grant (Formación de Profesorado Universitario) and the Spanish Ministry of Science and Innovation PID2019-106231RB-I00 TEC Research fund.

There exists an increasing interest in monitoring low concentrations of biochemical species, as they allow the early-stage detection of illnesses or the monitoring of the environment quality. Thus, both companies and research groups are focused on the development of accurate, fast and highly sensitive biosensors. Optical fiber sensors have been widely employed for these purposes because they provide several advantages for their use in point-of-care and real-time applications. In particular, this review is focused on optical fiber biosensors based on luminescence and absorption. Apart from the key parameters that determine the performance of a sensor (limit of detection, sensibility, cross-sensibility, etc.), other features are analyzed, such as the optical fiber dimensions, the sensing set ups and the fiber functionalization. The aim of this review is to have a comprehensive insight of the different aspects that must be taken into account when working with this kind of sensors., This research was funded by the Spanish AGENCIA ESTATAL DE INVESTIGACIÓN (AEI), through the project with reference PID2019-106231RB-I00—ESPADA and also by the Regional Government of Navarra, through the project with reference 0011-1365-2020-000061–BREATHALYSER (FEDER).

Copper oxide (CuO) allows the generation of lossy mode resonance (LMR) in a wide wavelength range of the optical spectrum, both in the visible and the near-infrared (NIR). For this, it is necessary to use a configuration based on the lateral incidence of light on the edge of a planar waveguide structure. On the other hand, the use of additional coatings of tin oxide (SnO2) and agarose allows an increase in the sensitivity of the sensor, in response to the breathing monitoring. The sensors were characterized, both in intensity and wavelength. In both cases their behavior depends on the position of the LMR in the optical spectrum. Therefore, it is convenient to extract the design rules that allow an optimal behavior of the sensor. In this sense, sensors located in the NIR presented a better behavior in terms of sensitivity and quality of the signal. In addition, the devices were tested in different conditions: repetitive tests at different distances, oral and nasal breathing, and breathing after doing physical exercise., The authors would to acknowledge the partial support to the Agencia Estatal de Investigacion (AEI) from the Spanish Ministry of Economy and Competitiveness (PID2019-106231RB-I00 and PID2019-106070RB-I00 research funds) and the predoctoral research grant of the Public University of Navarra.

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., Ministerio de Ciencia, Innovación y Universidades (FPU18/03087); Agencia Estatal de Investigación (PID2019-106231RB-I00 TEC); Universidad Pública de Navarra.

DNA is becoming increasingly important in the domain of optical fiber sensors, either as a tool for biosensing, or as a target to detect. In this review the main contributions of the last years are presented both in the domain of wavelength and intensity based configurations. This review comprises the use of natural single strand DNA (ssDNA) sequences as receptors for the detection of ssDNA sequences through hybridization, synthetic nucleic acids receptors for detection of complementary ssDNA sequences, and sensors based on natural and synthetic ssDNA receptors used for the detection of non-DNA targets. Parameters such as sensitivity, detection range and limit of detection are analyzed and discussed in detail to the purpose of comparing the different technologies and knowing the future lines to follow in the domain of fiber optic DNA-based sensors., This work was supported in part by the Spanish Agencia Estatal de Investigación (AEI) under Grant PID2019-106231RB-I00, in part by the Public University of Navarra under Grant PJUPNA26, in part by the Ph.D. Research Grants, and in part by the ATTRACT Call financed by the European Union’s Horizon 2020 Research and Innovation Program under Grant 777222.

This letter presents the fabrication of dual lossy mode resonance (LMR) refractometers based on titanium dioxide (TiO2) and tin oxide (SnO2) thin films deposited on a single side-polished D-shaped optical fiber. For the first time, to the best of our knowledge, two independent LMRs are obtained in the same D-shaped optical fiber, by using a step-shaped nanostructure consisting of a first section of TiO2 with a thickness of 120 nm and a second section with a thickness of 140 nm (120 nm of TiO2 and 20 nm of SnO2). Each section is responsible for generating a first-order LMR with TM-polarized light (LMRTM). TiO2 is deposited by atomic layer deposition and SnO2 by electron-beam deposition. The theoretical results show that the depth of each of the resonances of the dual LMR depends on the length of the corresponding section. Two experimental devices were fabricated with sections of different lengths, and their sensitivities were studied, achieving values ∼ 4000 nm/refractive index unit (RIU) with a maximum of 4506 nm/RIU for values of the SRI between 1.3327 and 1.3485., Ministerio de Ciencia, Innovación y Universidades (FPU18/03087); Agencia Estatal de Investigación (PID2019-106231RB-I00).

A planar waveguide consisting of a coverslip for a microscope glass slide was deposited in one of its two faces with two materials: silver and indium tin oxide (ITO). The incidence of light by the edge of the coverslip permitted the generation of both surface plasmon and lossy mode resonances (SPRs and LMRs) in the same transmission spectrum with a single optical source and detector. This proves the ability of this optical platform to be used as a benchmark for comparing different optical phenomena generated by both metal and dielectric materials, which can be used to progress in the assessment of different sensing technologies. Here the SPR and the LMR were compared in terms of sensitivity to refractive index and figure of merit (FoM), at the same time it was demonstrated that both resonances can operate independently when silver and ITO coated regions are surrounded by different refractive index liquids. The results were supported with numerical results that confirm the experimental ones., The authors would like to acknowledge the partial support to the Agencia Estatal de Investigacion (AEI) PID2019-106070RB-I00 and PID2019-106231RB-I00 research funds, and the predoctoral research grants of the Public University of Navarra.