Showing papers by "Ignacio R. Matias published in 2017"

Recent Developments in Fiber Optics Humidity Sensors.

Abstract: A wide range of applications such as health, human comfort, agriculture, food processing and storage, and electronic manufacturing, among others, require fast and accurate measurement of humidity. Sensors based on optical fibers present several advantages over electronic sensors and great research efforts have been made in recent years in this field. The present paper reports the current trends of optical fiber humidity sensors. The evolution of optical structures developed towards humidity sensing, as well as the novel materials used for this purpose, will be analyzed. Well-known optical structures, such as long-period fiber gratings or fiber Bragg gratings, are still being studied towards an enhancement of their sensitivity. Sensors based on lossy mode resonances constitute a platform that combines high sensitivity with low complexity, both in terms of their fabrication process and the equipment required. Novel structures, such as resonators, are being studied in order to improve the resolution of humidity sensors. Moreover, recent research on polymer optical fibers suggests that the sensitivity of this kind of sensor has not yet reached its limit. Therefore, there is still room for improvement in terms of sensitivity and resolution.

Optical sensors based on lossy-mode resonances

Abstract: Lossy-mode resonance (LMR)–based optical sensing technology has emerged in the last two decades as a nanotechnological platform with very interesting and promising properties. LMR complements the metallic materials typically used in surface plasmon resonance (SPR)–based sensors, with metallic oxides and polymers. In addition, it enables one to tune the position of the resonance in the optical spectrum, to excite the resonance with both transverse electric (TE) and transverse magnetic (TM) polarized light, and to generate multiple resonances. The domains of application are numerous: as sensors for detection of refractive indices voltage, pH, humidity, chemical species, and antigens, as well as biosensors. This review will discuss the bases of this relatively new technology and will show the main contributions that have permitted the optimization of its performance to the point that the question arises as to whether LMR–based optical sensors could become the sensing platform of the near future.

Micro and Nanostructured Materials for the Development of Optical Fibre Sensors.

Abstract: The measurement of chemical and biomedical parameters can take advantage of the features exclusively offered by optical fibre: passive nature, electromagnetic immunity and chemical stability are some of the most relevant ones. The small dimensions of the fibre generally require that the sensing material be loaded into a supporting matrix whose morphology is adjusted at a nanometric scale. Thanks to the advances in nanotechnology new deposition methods have been developed: they allow reagents from different chemical nature to be embedded into films with a thickness always below a few microns that also show a relevant aspect ratio to ensure a high transduction interface. This review reveals some of the main techniques that are currently been employed to develop this kind of sensors, describing in detail both the resulting supporting matrices as well as the sensing materials used. The main objective is to offer a general view of the state of the art to expose the main challenges and chances that this technology is facing currently.

A self-referenced optical colorimetric sensor based on silver and gold nanoparticles for quantitative determination of hydrogen peroxide

Abstract: In this work, a self-referenced colorimetric sensor for the quantitative determination of hydrogen peroxide is presented This optical sensor is based on the presence of the Localized Surface Plasmon Resonances of silver and gold nanoparticles which are capped with the same encapsulating agent of poly(diallylammonium chloride) (PDDA) These metallic nanoparticles are synthesized by a chemical reduction method of their corresponding inorganic precursors and characterized by UV–vis spectroscopy and transmission electron microscopy, respectively A remarkable difference in sensitivity related to both LSPR absorption bands is observed as a function of variable molar concentration of the target molecule The LSPR band of the silver nanoparticles is gradually decreased whereas the LSPR of the gold nanoparticles is practically unaltered when the hydrogen peroxide molar concentration is increased as a result of its better chemical stability This stable absorbance LSPR band of the AuNPs is used as an optical reference and the molar concentration of the target molecule is obtained by measuring the changes of the absorbance strength maxima of both LSPR absorption bands As a result, a very good sensitivity with a high robustness and a linear response over a wide concentration range from 125 μM to 1250 μM is obtained This self-referenced method opens up a new perspective for the chemical detection of other reactive oxygen species or well for the determination of other type of analytes in the future

Optimization in nanocoated D-shaped optical fiber sensors

Abstract: Nanocoated D-shaped optical fibers have been proven as effective sensors. Here, we show that the full width at half minimum (FWHM) of lossy mode resonance can be reduced by optimizing the nanocoating width, thickness and refractive index. As a counterpart, several resonances are observed in the optical spectrum for specific conditions. These resonances are caused by multiple modes guided in the nanocoating. By optimizing the width of the coating and the imaginary part of its refractive index, it is possible to isolate one of these resonances, which allows one to reduce the full width at half minimum of the device and, hence, to increase the figure of merit. Moreover, it is even possible to avoid the need of a polarizer by designing a device where the resonance bands for TE and TM polarization are centered at the same wavelength. This is interesting for the development of optical filters and sensors with a high figure of merit.

Wavelength and Phase Detection Based SMS Fiber Sensors Optimized With Etching and Nanodeposition

Abstract: The development of an optical fiber refractometer by hydrogen fluoride etching and sputtering deposition of a thin-film of indium tin oxide on a single-mode-multimode-single-mode fiber structure has been analyzed with the aim of improving the sensitivity to the changes of the refractive index (RI) of the external medium. The device is sensitive to the RI changes of the surrounding medium, which can be monitored by tracking the spectral changes of an attenuation band or with a fast Fourier transform (FFT) analysis. By using an optical spectrum analyzer combined with a simple FFT measurement technique, the simultaneous real-time monitoring is achieved. The results show that the sensitivity depends on the thin-film thickness. A maximum of 1442 nm/RIU (refractive index unit) in the 1.32–1.35 RIU range has been attained. In addition, a theoretical analysis has been performed, where simulations matched with the experimental results. As a practical application of the developed optical fiber structure, a °Brix (°Bx) sensor has been implemented with a sensitivity of 2.13 nm/°Bx and 0.25 rad/°Bx respectively for wavelength and phase shift detection.

Fiber-Optic Immunosensor Based on an Etched SMS Structure

Abstract: A novel and high sensitive IgG – anti-IgG biosensor based on multimode interference induced through a single-mode–multimode–single-mode (SMS) optical fiber structure is developed in this contribution. First, an improvement of the performance of a basic 125-μm-diameter SMS structure is carried out by etching the optical waveguide cladding to a diameter of 15 μm. This leads to sensitivity values eight times higher than the original SMS structure. Then, 3-glycidopropyl-trimethoxysilane is used to attach the IgGs to the optical substrate. Finally, a phosphate buffer saline solution containing an increasing concentration of antigoat IgGs is used to detect biological interactions up to 104 μg/ml. High-resolution mass spectrometry was used to corroborate the attachment of the biomolecules to the optic fiber. The analyzed bioprobe presents no cross sensitivity to other biomolecules immersed in the same detection solution.

Enhancement of luminescence-based optical fiber oxygen sensors by tuning the distance between fluorophore layers

Abstract: In this work, different luminescence-based optical fiber oxygen sensors have been fabricated by means of the Layer-by-Layer nanoassembly technique. The sensing material employed has been a platinum metalloporphyrin, platinum tetrakis pentafluorophenylporphine (Pt-TFFP), which has been entrapped into anionic micelles. Poly(diallyldimethylammonium chloride) (PDDA), polyethyleneimine (PEI) and poly(allylamine hydrochloride) (PAH) have been utilized as cationic polyelectrolytes. With the aim of avoiding self-quenching and optimizing sensors in terms of sensitivity and linearity of the calibration curves, the spacing (thickness) between the fluorophore films has been tuned by introducing poly(acrylic acid) (PAA) between the cationic layers. The morphology of the resultant sensors has been analyzed with an Atomic Force Microscope. It has been found that the number of spacing layers between the luminescent ones is determined by the features of the employed polycation.

Increasing the Sensitivity of an Optic Level Sensor With a Wavelength and Phase Sensitive Single-Mode Multimode Single-Mode Fiber Structure

Abstract: The sensitivity of a liquid level sensor based on a single-mode-multimode-single-mode fiber structure has been increased by hydrofluoric acid etching. The etching process was analyzed and monitored both theoretical and experimentally, which permitted to observe that a sinusoidal spectrum can be obtained for low diameters. As an example, a 2.77 fold sensitivity increase was attained by etching from diameter 125 to $50~\mu \text{m}$ . Moreover, the sinusoidal shape of the optical spectrum permitted to monitor liquid level changes both in wavelength and phase. The cross sensitivity of the sensor to refractive index and temperature was also studied.

Humidity Sensor Based on Bragg Gratings Developed on the End Facet of an Optical Fiber by Sputtering of One Single Material.

Abstract: The refractive index of sputtered indium oxide nanocoatings has been altered just by changing the sputtering parameters, such as pressure. These induced changes have been exploited for the generation of a grating on the end facet of an optical fiber towards the development of wavelength-modulated optical fiber humidity sensors. A theoretical analysis has also been performed in order to study the different parameters involved in the fabrication of this optical structure and how they would affect the sensitivity of these devices. Experimental and theoretical results are in good agreement. A sensitivity of 150 pm/%RH was obtained for relative humidity changes from 20% to 60%. This kind of humidity sensors shows a maximum hysteresis of 1.3% relative humidity.

Smart Carbon fiber transtibial prosthesis based on embedded fiber Bragg gratings

Abstract: This paper presents the utilization of optical fiber Bragg gratings (FBGs) embedded into a carbon fiber reinforced polymer transtibial prosthesis to evaluate the user's gait, and its own performance. Static mechanical tests were performed to characterize the sensors. Vertically and horizontally positioned FBGs within the structure have been used for load and strain force evaluation during real-time experiments with a candidate at different speeds on a treadmill. For simplicity, one non-amputee candidate performed the experiments using a mechanical adaptation. Distinctive patterns of response of the FBGs located at different points within the prosthetic structure enabled the differentiation between slow and fast motion gait cycle and the force distribution during the tread. This optical instrumentation contributes to the development of a new tool for the evaluation of prosthesis design and amputee patients rehabilitation and to the assessment of the performance of athletes during training or competition.

Luminescence-based optical sensors fabricated by means of the layer-by-layer nano-assembly technique

Abstract: Luminescence-based sensing applications range from agriculture to biology, including medicine and environmental care, which indicates the importance of this technique as a detection tool. Luminescent optical sensors are required to be highly stable, sensitive, and selective, three crucial features that can be achieved by fabricating them by means of the layer-by-layer nano-assembly technique. This method permits us to tailor the sensors′ properties at the nanometer scale, avoiding luminophore aggregation and, hence, self-quenching, promoting the diffusion of the target analytes, and building a barrier against the undesired molecules. These characteristics give rise to the fabrication of custom-made sensors for each particular application.

Strain Mapping in Carbon-Fiber Prosthesis Using Optical Fiber Sensors

Abstract: This letter presents the utilization of optical fiber Bragg grating sensors for strain mapping of carbon fiber reinforced polymer below-knee prosthesis at different positions. Optical fiber sensors embedded within the prosthetic structure have a minimal impact on the design and enable real-time monitoring of the structure deformation. Tests were performed with a volunteer who is not amputated using a mechanical adaptor. The results obtained show the deformation of the mechanical structure of the prosthesis at different points, which can be helpful to record training sessions, detect material failures, or study ground reaction forces during periodic evaluations.

Comparative study of polymeric matrices embedding oxygen-sensitive fluorophores by means of Layer-by-Layer nanosassembly

Abstract: In this work, a comparative study of luminescent optical fiber oxygen sensors fabricated by means of Layer-by-Layer nanoassembly technique (LbL) has been carried out. The oxygen-sensitive fluorophore is the same in all the cases, the metalloporphyrin platinum tetrakis pentafluorophenylporphin (Pt-TFPP), which was deposited using LbL method by entrapping it into anionic micelles formed with a surfactant. As cationic counterpart to form the anionic-cationic bilayer, different polyelectrolytes acting as the polymeric matrices embedding the sensing material have been studied: poly(diallyldimethylammonium chloride) (PDDA), polyethyleneimine (PEI) and poly(allylamine hydrochloride) (PAH). Absorbance spectra, contact angle, Atomic Force Microscope and Scanning Electronic Microscope analysis were performed on the sensing films. The kinetics, resolution and sensitivity of the sensors for different number of bilayers were also determined. It has been found a remarkable difference on these characteristics depending on the polymer used.

Temperature Sensor Using a Multiwavelength Erbium-Doped Fiber Ring Laser

Abstract: A novel temperature sensor is presented based on a multiwavelength erbium-doped fiber ring laser. The laser is comprised of fiber Bragg grating reflectors as the oscillation wavelength selecting filters. The performance of the temperature sensor in terms of both wavelength and laser output power was investigated, as well as the application of this system for remote temperature measurements.

Multimode Interference Fiber Sensors for the Monitoring of Gasoline/Ethanol Blends

Abstract: Multimode interference (MMI) devices have attracted a great deal of interest due to their simplicity of fabrication. The MMI device is ready for testing after splicing a section of multimode fiber (MMF) between two single-mode fiber (SMF). In this chapter we provide an overview of the fundamentals behind the formation of self-images in MMI fiber devices, as well as the basic mechanisms for tuning their operational wavelength which is related with their application for sensing applications. The sensitivity enhancement of these MMI fiber sensors is also investigated by reducing the diameter of the MMF via wet chemical etching, as well as coating the MMF with a high refractive index overlay. The MMI fiber sensors are applied to the quality control of gasolines and in particular the real time monitoring of gasohol, mixtures of gasoline and ethanol, which is critical for the proper operation of flexible-fuel vehicles (FFV). The results demonstrate that MMI fiber sensors are well suited for such applications, as well as other applications were the binary mixture of liquids has to be controlled or monitored.

Fabrication of Bragg Gratings on the End Facet of Standard Optical Fibers by Sputtering the Same Material

Abstract: A sputtering process has been applied to deposit quarter-wavelength stacks on the end facet of cleaved optical fibers by using only one sputtering target. Standard multimode optical fibers were used as substrates to fabricate broadband filters, and the experimentally measured spectral responses of these devices are shown. Periodical changes in the refractive index of the coating have been achieved by changing the vacuum chamber pressure. A reflected peak with a full-width at half-maximum of 20 nm centered at 440 nm has been obtained, which provides a good structure for the development of optical fiber sensors working with the wavelength detection technique. This optical structure can be used for several purposes: as tunable wavelength filters or optical fiber sensors or to improve the performance of fluorescence sensors. A theoretical analysis of these structures corroborates the experimental results and allows some rules to be obtained.

Distributed optical fiber microphone

Abstract: A distributed acoustic sensing (DAS) optical fiber system has been studied using intensity-based optical time-domain reflectometry (i-OTDR). The fiber strain originated by sound waves (pressure waves) is in general quite small to enable the detection using conventional Rayleigh backscattering intensity based systems (low signal to noise ratio). Here, a 10 m portion of optical fiber has been rolled following a plane spiral shape in order increase the fiber surface subjected to the acoustic waves pressure and improve the signal to noise ratio (SNR). The performance of the system within the human voice frequency range (300–3400Hz) has been studied showing to effectively acquire voice signals at different points along a ∼2.5 Km fiber.

High Sensitivity Optical Structures for Relative Humidity Sensing

Abstract: This chapter is focused in the different optical structures and materials that have been used for the development of optical fiber humidity sensors. First, we will start with a short introduction of what relative humidity is, and why it has been extensively investigated. We will make also a brief summary of the different options that have been developed by now, showing the evolution of this research field. Then we will look more closely at the most used structures, the most common materials and the devices having greater sensitivity and resolution.

Monitoring the Etching Process in LPFGs towards Development of Highly Sensitive Sensors

Abstract: In this work, the monitoring of the etching process up to a diameter of 30 µm of two LPFG structures has been compared, one of them had initially 125 µm, whereas the second one had 80 µm. By tracking the wavelength shift of the resonance bands during the etching process it is possible to check the quality of etching process (the 80 µm fibre performs better than de 125 µm fibre), and to stop for a specific cladding mode coupling, which permits to obtain an improved sensitivity compared to the initial structure.

New organizational and assessment frameworks for company internship programs

Abstract: Old company internship programs in the pre-Bologna degrees dealt mainly with helping the students find a suitable company to stay for a time interval outside the academic periods. No assessments were implemented to evaluate the acquired competences and no especial procedures were required since these internships were not included in the student academic curricula. The new requirements for company internships in emerging European Higher Education Area make it necessary to lay down new organizational frameworks and stablish clear and efficient assessment procedures. This paper describes the initiatives carried out within the Engineering Degrees of the Public University of Navarre. The Degree in Engineering in Industrial Technologies is shown as a good example of the program. Results achieved so far are very satisfactory for both the companies participating in the program and the students taking part in the internships.

Detection of ethanol in human breath using optical fiber long period grating coated with metal-organic frameworks

Abstract: An optical fiber sensor for ethanol detection in exhaled breath has been developed. It has been fabricated by functionalizing a Long Period Grating with a metal-organic framework, ZIF-8. The sensor’s response was tested by exposure to exhaled breath of a person before and after the ingestion of alcoholic drinks, showing a higher wavelength difference between the resonance bands in the second case. Further work will analyze cross-sensitivity towards temperature, relative humidity and carbon dioxide.

Sensitivity enhancement by diameter reduction in low cutoff wavelength single-mode multimode singlemode (SMS) fiber sensors

Abstract: Two different low cutoff wavelength single-mode fibers were used in single-mode multimode single-mode (SMS) configuration with the aim of designing sensors operating at short wavelengths, where optical sources and spectrometers are less expensive than in telecommunications bands. The diameter of the SMS structure was reduced with an etching process based on hydrofluoric acid immersion. The results prove that the devices can operate at wavelength ranges from 600 to 1200 nm and that multiple peaks can be obtained, each one with a different sensitivity that is proportional to the wavelength. Moreover, a fivefold increase in sensitivity to refractive index can be obtained. This high sensitivity indicates the possibility to apply this simple and cost-effective device in other applications such as biosensors or chemical sensors.

Refractive index sensing performance of a Bragg grating built up on the tip of an optical fiber by reactive sputtering

Abstract: Bragg gratings have been fabricated by means of sputtering on the end facet of standard multimode optical fibers towards development of refractometers. Tin oxide was selected as the coating material, and argon and oxygen were used as sputtering gases. Changes on the refractive index of the material were achieved by varying the oxygen percentage in the sputtering gas flow. A reflected peak centered at 586 nm with a full width at half maximum of 70 nm has been obtained, which provides a good structure for the development of wavelength modulated optical fiber sensors. The sensitivity of this structure to the refractive index of the surrounding medium has been studied, obtaining a linear sensitivity of 173 nm/RIU, for refractive index varying from 1.333 to 1.442.

Study of ammonia and nitric oxide sensing performance of a Fabry-Perot interferometer

Abstract: In this work we report the performance of a fiber optic sensor towards ammonia and nitric oxide detection. The device is based on a Fabry-Perot interferometer which is fabricated by coating the tip of an optical fiber by means of sputtering with tin oxide (SnO2). The main advantage of this structure is its small size, which offers the possibility of making point to point measurements. Besides, this kind of optical devices enables working with the wavelength detection method in the UV-VIS-NIR range. The device was tested at room temperature under nitrogen flow with different concentrations of ammonia or nitric oxide in order to obtain the response of the sensor. The maximum sensitivity for ammonia concentration ranging from 0 ppm to 500 ppm is 4 pm/ppm, whereas wavelength shift while changing nitric oxide concentration from 0 to 375 ppb was 1.2 nm, which corresponds to a sensitivity of 10pm/ppb.