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In this paper, we present the preliminary results of a fiber optic sensor based on fluorescence quenching induced by mercury (Hg) concentrations presence in aqueous solutions. The fabrication of the sensor head consists of a methyl red coating over multimode fiber tip using thermoplastic polyurethane to immobilize the thin layer. The sensor device was tested in a Hg molar concentration ranges 10-10,000 nmol/L. The experimental results show a linear dependence of the induced fluorescence quenching related to the Hg molar concentration. This work was supported in part by the PRODEP-SEP under Grant UAT-CA-154 (IDCA-23742). Yadira A. Fuentes-Rubio thanks CONACyT for the doctoral stay scholarship assigned. more...

An optical fiber tip interferometer for the measurement of relative humidity (RH) and temperature is proposed. The optical fiber structure used, a dual-cavity optical fiber Fabry-Perot interferometer (DFFPI), is simply-to-fabricate, compact, and robust. The reflectance (RDFFPI) of the interferometer is sensitive to the refractive index (RI) and temperature of the external medium. Consequently, when the cross-section of the fiber tip was coated with a SnO 2 thin film, whose RI changes according to the humidity of the surrounding ambient, the measurement of the RH was possible. An increment of the RH produced a decrement of RI of the SnO 2 thin film, then the reflectance of the fiber tip end-face diminished, and this produced a decrement of the visibility of the interference fringes. The analysis of the RDFFPI was carried out in the Fourier domain, using a novel processing method it was possible to establish that the amplitude of two peaks of Fourier spectrum changed at a ratio of 39.49 × 10 -3 %RH -1 in the range of 40 to 90 RH%. On the other hand, the temperature of the humidity chamber was monitored, from 25 to 60 °C at a fixed RH%, by analyzing the phase shift of the interference pattern produced by the changes in the optical path length of the cavities. The good sensitivity, stability, reproducibility, and compactness of the fiber tip RH sensor make this proposal very appealing in a wide range of applications. This work was supported in part by the Consejo Nacional de Ciencia y Tecnología (CONACyT) from Mexico through the CIENCIA BÁSICA under Project 257046 and Project LN-293442, and in part by the Spanish Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) under Grant TEC2016-79367-C2-2-R. The work of Carmen E. Domínguez-Flores and Osvaldo Rodríguez-Quiroz were supported by the CONACyT for Ph.D. Scholarship. more...

Lossy mode resonance (LMR) based refractometers obtained by means of copper oxide thin-films fabricated onto side-polished (D-shaped) are presented in this work. The high refractive index of copper oxide combined with the propagation mode isolation capabilities of D-shaped fibers allows for the observation of narrow (30 nm) and high sensitive (10,336 nm per refractive index unit) LMRs, which could enable to improve the performance of LMR-based refractometers as well as provide an alternative label-free sensing platform for LMR-based sensors. The authors would like to acknowledge the support from the Spanish Agencia Estatal de Investigación (AEI) (PID2019-106231RB-I00) and the Public University of Navarra (PJUPNA26). A. O. C. would also like to thank the Spanish Ministry of Universities (FPU15/05663). more...

In this work, an optical fiber vacuum sensor based on a single-mode multimode single-mode (SMS) structure coated with polydimethylsiloxane (PDMS) is studied. The SMS structure generates an interferometric pattern based on multimode interference. The structure is dip-coated with a layer of PDMS, whose optical properties change when it is subjected to varying vacuum pressure. Different strategies are applied in an attempt to improve the final performance of the sensor, such as decreasing the diameter of the fiber and modifying the properties of the coating by modifying the proportion of solvent. Decreasing the diameter of the optical fiber and using toluene as a solvent are both proved to be successful strategies for increasing the sensitivity of the sensor. The devices are studied in the 1×10-3–10 mbar range with a maximum wavelength shift of 12 nm, leading to a maximum sensitivity of 35 nm/mbar. The simplicity of the fabrication process, which can be applied to more sensitive structures, suggests that PDMS may be a good choice for the development of optical fiber vacuum sensors. This work was supported by the Spanish Agencia Estatal de Investigación (AEI), Fondo Europeo de Desarrollo Regional (FEDER) (TEC2016-79367-C2-2-R) and a Torres-Quevedo grant from the Science and Innovation Ministry (PTQ2018-010221). more...

Development of DNA and RNA biosensors and the associated diagnostic tests have gained growing interest in recent years. In particular, short RNA chains (around 25 oligonucleotides), known as micro RNAs, can be associated different stroke and neurodegenerative diseases. Here, we present the utilization of highly sensitive fiber optic sensor based on Lossy Mode Resonance (LMR) for the detection of single strand complementary DNA (ssDNA) associated to Huntington Disease (Hsa-miR-34b). more...

The application of an etching process in a single-mode multimode single-mode (SMS) fiber allows monitoring the change of refractive index of wind turbine gearbox oil due to temperature and degradation with a limitation at short temperatures, where the transmission and attenuation bands in the optical spectrum fade. The application of a black tin oxide nanocoating solves this issue and allows tuning the refractive index region where the sensitivity is maximum. The SMS was designed for operating at short wavelengths, where the setup is less expensive. The experimental results were contrasted with a theoretical analysis developed with FIMMWAVE, which allowed understanding better the phenomena involved in the experiments. This work was supported in part by the Spanish Ministry of Education and Science-FEDER TEC 2016-78047 and in part by the Government of Navarre through its project with reference 2017/PI044. more...

Trabajo presentado a la 18th IEEE Sensors Conference. Montreal, 2019 This work studies the behavior of polydimethylsiloxane (PDMS) as a transducer for optical vacuum pressure measurements. The optical structure chosen for this device is a modal interferometer achieved by splicing a coreless multimode optical fiber between two single mode fibers. Then, an etching process is applied to the obtained device, in order to decrease the diameter of the fiber and increase the sensitivity. Finally, the fiber is coated by dip-coating with a layer of PDMS, which changes its volume with pressure changes. The device has been studied in the 1x10(-3) mbar to 10 mbar range with a wavelength shift of 4 nm. A maximum sensitivity of 35 nm/mbar was obtained. The simple fabrication process, which can be applied to more sensitive structures, suggest that PDMS can be a good choice for the development of optical fiber vacuum sensors. This work was supported by Spanish Agencia Estatal de Investigacion (AEI). Fondo Europeo de Desarrollo Regional (FEDER) (TEC2016-79367-C2-2-R and TEC2016-78047-R). more...

In this paper, a multiplexing system for simultaneous interrogation of optical fiber sensors which measure different parameters is presented and validated. The whole system has been tested with 6 different sensing heads with different purposes: one temperature sensing head, two relative humidity sensors and three VOCs leak sensors; all of them based on microstructured optical fibers. The interrogation system uses the FFT technique to isolate each sensor's interference, enabling their simultaneous interrogation. The system interrogates all the sensors at frequencies up to 1 KHz, showing a good performance of each measurement without crosstalk between sensors. The developed system is independent of the sensors' purpose or of the multiplexing topology. This work was supported in part by the Spanish Comisión Interministerial de Ciencia y Tecnología within projects under Grant TEC2016-76021-C2-1-R, Grant TEC2016-78047-R, and Grant TEC2016-79367-C2-2-R, in part by the Cost Action MP1401, and in part by the FEDER funds from the European Union. more...

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. more...

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. more...

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. more...

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. more...

Fabrication and characterization of an optical fiber refractometer based on Lossy Mode Resonances is presented. Tin oxide (SnO 2 ) coatings deposited on cladding etched single mode optical fibers are used as LMR supporting coatings, which are sensitive to the external medium refractive index. These refractometers showed an average sensitivity of 3680 nm/RIU with a dynamic range of 196 nm, for a surrounding medium refractive index range of 1.3339 to 1.3865. Chemical etching of the single mode optical fiber provides a simple method to get access to the evanescent field of light, without affecting the core of the optical fiber and with highly repeatable results on the final dimensions. LMRs have been proved, for the first time, to be a good phenomenon to make this structure sensitive to the surrounding medium refractive index. more...

DNA sequence detection has a broad range of applications in different fields such as genetics, pathology, criminology, pharmacogenetics, public health, food safety, agriculture, defense and environmental monitoring. However, common DNA detection techniques present several drawbacks such as bulky size, restricted to laboratory environments, high equipment cost and time consuming experiments. Here, we present an alternative DNA detection technique by means of the utilization of label-free lossy mode resonance (LMR) based optical fiber refractometers and compare two different DNA immobilization techniques. more...

We present a magnetic field optical fiber sensor. The configuration chosen for this purpose is a tapered single mode optical fiber coated with a thin film of a magneto-optic alloy, which is made of cobalt and nickel. The coating has been fabricated by means of sputtering. This alloy was used to build the nano-coating which produces the Lossy Mode Resonance (LMR) and that is sensitive to magnetic fields. Then, the device was placed in the air gap of an electrical transformer for applying magnetic field. Wavelength shifts of 2 nm have been achieved for 330 mT of magnetic field. This is the first time, for the best of our knowledge, that LMRs have been used for magnetic field sensing. more...

A novel immunosensor based on lossy mode resonances (LMRs) induced in optical fibers is developed in this contribution. Indium tin oxide (ITO) is sputtered on the optical substrate to generate an LMR in the transmission spectrum. Type G immunoglobulins (IgGs) are then attached to the ITO-coated fiber using (3-glycidyloxypropyl)trimethoxysilane (GPTMS). A phosphate buffer saline solution containing anti-IgGs is used to detect the biological reactions. The presented device is capable of detecting anti-IgG concentrations up to 10 nM. These results will permit the fabrication of biosensors based on a covalent attachment of bioreceptors over an LMR inducing thin-film. more...

A fiber optic liquid-level sensor based on a long period grating (LPG) is proposed and experimentally validated. The principle of operation is based on a technique used to analyze microwave photonics filters. A 4-cm-long LPG cascaded with a high-reflectivity fiber Bragg grating is employed to achieve a continuous liquid-level sensor. The measurements have been performed using a modulator and a photo-detector with a modest bandwidth of less than 500 MHz, showing a sensitivity of −12.71 dB/cm and a standard deviation of 0.52 dB. One of the significant advantages of such sensing structure is that it is based on low-bandwidth radio frequency and off-the-shelf photonic components. In addition, the simple proposed scheme presents good repeatable performance and proves to be intrinsically robust against environmental changes, stable, and easy to reconfigure., This work was supported in part by the Accion Financiada por el Ministerio de Educacion, Cultura y Deporte through the framework of the Programa de Campus de Excelencia Internacional VLC/Campus, in part by the Spanish MINECO under Project TEC2014-60378-C2-1-R, in part by the Grant of the SANTIAGO GRISOLIA Program, in part by the Research Excellency Award Program GVA PROMETEO 2013/012, in part by the Project TEC2013-43679-R, and in part by an UPNA Predoctoral Grant. The associate editor coordinating the review of this paper and approving it for publication was Dr. Anna G. Mignani. more...

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. This work was supported by a Public University of Navarra PhD Grant and by the Spanish Economy and Competitiveness Ministry, TEC-2013-43679-R. more...

Here we present a new structure to fabricate optical fiber sensors. This structure consists on an etched single mode optical fiber coated with a thin film of a semiconductor material by means of sputtering. The optical fiber was etched with hydrofluoric acid until it reaches 19 µm of diameter. Then it was attached to a U-holder and coated with the indium oxide nanocoating. The thin film generates a lossy mode resonance and when the relative humidity increases, the wavelength of the resonance shifts. Changes of 30% to 80% RH have been applied to the device obtaining a wavelength shift of 12 nm. more...

In this work we present a high sensitivity optical fiber humidity sensor. The configuration chosen for this purpose is a Fabry-Perot interferometer. The device has been fabricated by means of sputtering. A semiconductor material was used to build the nano-cavity which produces the interferometry. Then the device was introduced into a climatic chamber in order to change relative humidity. Changes of 88 nm have been obtained for relative humidity varying from 20% to 90%, which implies a sensitivity of 1.27 nm/%RH. more...

A single mode-multimode-single mode structure (SMS) has been used for developing a magnetic field sensor without using magnetic fluids. The SMS optical fiber was coated with a magneto-optical material by means of sputtering. The sputtering process was monitored in order to achieve the optimum thickness of the coating and the best sensitivity. Sensitivities of 1.45 dB/T and 6 nm/T have been achieved. Repeatability in the fabrication and in the behaviour of the device has been checked. more...

In this paper we report the experimental results of a fiber optic refractometer based in multimodal interference effects (MMI) using an Indium Tin Oxide (ITO) coating. The MMI sensor is able to detect different liquid concentrations of glycerin and other substances. In addition, the use of ITO coating, deposited by the sputtering technique, allows a significant increment in the device sensitivity. In specific, we obtained a sensitivity around 297.12 nm/RIU for 18nm ITO coating thickness. more...

The fabrication and characterization of an optical fiber pH sensor based on Lossy Mode Resonances (LMRs) is presented. PAH/PAA polymeric thin-films fabricated onto side-polished D-shaped optical fibers are used as LMR supporting coatings. The thickness of PAH/PAA coatings can be modified as a function of the external medium pH. As a consequence of this variation, the effective refractive index of the structure will change, producing a shift of the LMR. The fabricated sensor has been used to measure pH from 4.0 to 5.0. This pH sensor showed a sensitivity of 101.3 nm per pH unit, which means a resolution of ∼6×10−4 pH units by using a conventional communications Optical Spectrum Analyzer (OSA), which is an improvement over commercial pH sensors. more...

Nanometer scale coatings with a complex refractive index deposited on optical fibre permit to obtain attenuation bands in the transmission spectrum, whose central wavelength coincides with the moment when a mode guided in the optical fibre cladding starts to be guided in the coating. Due to the complex refractive index of the coating, the guided mode is a lossy mode. Consequently, these attenuation bands receive the name of lossy mode resonances. This phenomenon can be used for development of ultra-high sensitivity photonic devices (for detection, among others, of volatile organic compounds, pH and refractive index) or for optical filtering. In this work, rules for adequate design are indicated based on numerical results obtained with FIMMWAVE and on experimental results that corroborate the theoretical predictions. more...

In this work, the fabrication and characterization of a small and portable exhaled breath sensor based on Lossy Mode Resonances (LMR) is presented. Tin oxide (SnO2) coatings fabricated onto optical fibers are used as LMR supporting coatings. The principle of operation is based on the measurement of refractive index changes by the LMR device (with an average sensitivity of 8355 nm/RIU) originated by the condensation of micro water droplets in the surroundings of the SnO2 coating during the breath natural process. The sensor shows a repetitive response with less than 100 ms of response time and a wavelength shift of 150 nm from inhalation to exhalation. more...

In this work a new optical fiber pH sensor based on the deposition of poly(acrylic acid) (PAA) using the electrospinning technique is presented. The optical fiber structure consists of a 4 cm segment of hollow core fiber (50/150μm) spliced between two standard multimode fibers onto which the nanoweb is deposited. The sensitive layer is a membrane composed by PAA nanofibers deposited onto the surface of an optical fiber. The sensor has a repetitive behavior and low hysteresis in the pH range 4-7, with an average sensitivity of 0,53 dB/pH. more...

The particular behavior of poly(sodium phosphate) (PSP) when it is deposited by means of the spraying layer-by-layer (LbL) technique has been used here to enhance the response of optical fiber humidity sensors. The roughness of the PSP films varies depending on the concentration of the polymeric solutions. In this work, it is demonstrated that this special feature of PSP allows the fabrication of optical fiber humidity sensors with different responses. Particularly, multilayer thin-films made of 10-3 and 10-4 M PSP and poly(allylamine hydrochloride) (PAH) solutions have been studied and used for the fabrication of optical fiber interferometers sensitive to humidity. To our knowledge this is the first time that the spray-assisted LbL technique has been used for the fabrication of optical fiber sensors. more...

By coating a single-mode–multimode–single-mode (SMS) structure with a complex refractive index thin-film the central wavelength of the transmission and attenuation bands of the optical spectrum can be shifted. By adequate selection of multimode segment length and diameter, the thin-film thickness and the thin-film refractive index, the sensitivity of the device to the surrounding medium refractive index, the thickness of the thin-film or the refractive index of the thin-film can be optimized. Experimental results are corroborated numerically with the transfer matrix method. This work was supported in part by the Spanish Ministry of Education and Science - FEDER TEC2006-12170 and TEC2007-67987-C02-02/MIC. more...

Trabajo presentado en la IEEE Sensors Conference, celebrada en Taipei del 28 al 31 de octubre de 2012., An optical fiber sensor using an aptamer receptor has been developed for the detection of thrombin. The sensitive coating consists of an aptamer-polymer structure fabricated using the layer-by-layer electrostatic self assembly technique onto novel optical fiber refractometers based on lossy mode resonances (LMRs). LMR based refractometers enable to overcome the traditional drawbacks of surface Plasmon resonance (SPR) based devices, such as the utilization of polarized light for example. The refractometer is based on an indium tin oxide thin layer deposited by DC-sputtering onto the cladding removed multimode fiber. These refractometers enable to monitor the variations of the surrounding medium refractive index (RI). Hence, RI variations of the outer film induced by thrombin can be referenced to the LMR wavelength shift. The described configuration has enabled the detection of low concentrations of thrombin (100nM) as well as obtaining a maximum wavelength shift of 50 nm at higher (1μM) concentrations. more...

A novel humidity sensor based on polymer electrospun nanofibers coating onto an optical fiber is proposed in this work. The coating is composed of poly(acrylic acid), and its fabrication was performed by the electrospinning technique using an optical fiber core as substrate. This technique allows the fabrication of sensitive films with high surface area in a fast and simple way compared to other overlay fabrication techniques. The sensor was tested in a programmable temperature and humidity climatic chamber. Relative Humidity (RH) was varied in the range from 20%RH to 80%RH at room temperature. The results showed a monotonic variation of the absorbance spectra to RH changes, thus obtaining a successful humidity sensor. more...

This work presents the fabrication of optical fiber refractometers based on indium tin oxide (ITO) coatings deposited by sputtering with response in the visible spectral region. ITO thin-films have been sputtered by employing a rotating mechanism that enables the fabrication of smooth and homogeneous coatings onto the optical fiber core. Fabricated ITO coated optical fiber devices present several resonances in the visible and near infrared region. These resonances show high optical power attenuations (more than 10 dB) in the visible spectral region, which produces changes in the colour of the output visible light. Therefore, since these resonances shift as a function of the refractive index (RI) of the surrounding medium it is feasible to determine the RI of the outer medium in contact with the ITO coating by simply monitoring the chromatic coordinates (colour change), x and y, of the visible output light. more...

This contribution presents a pH sensor based on the combination of two technologies: tapered standard-single mode optical fiber (S-SMF) and an electromagnetic resonance phenomenon called Lossy Mode Resonance (LMR). This last phenomenon is produced by coating the optical structure with a thin polymeric film, which for specific values of the coating refractive index and thickness causes a maximum coupling of light guided in the tapered S-SMF region. Layer-by-layer electrostatic self assembly technique was used for the fabrication of a polymeric sensing nanostructure. The construction process was optimized in order to visualize the LMR behavior with a device length of 5 mm. The sensing combination produces a 250 nm wavelength-shift and a 20 dB attenuation variation of the LMR when varying the pH from 4 to 6. more...

In this work it is presented for the first time the fabrication of optical fiber relative humidity (RH) sensors by means of polymeric thin-films as lossy mode resonance (LMR) supporting coatings. In particular, LMRs have been observed thanks to the fabrication of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) polymeric coatings onto cladding-removed multimode optical fibers (CRMMF) employing the Layer-by-Layer (LbL) self assembly method. More than one LMR can be generated as a function of the coating thickness. This generation of multiple LMRs produces a band pass filter with a transmission band in the visible region. PAH/PAA film thickness and refractive index can be modified as a function of the surrounding medium relative humidity (SMRH). Thus, SMRH can be easily determined by measuring the wavelength shift of the transmission band (∼15nm between 20% and 60% RH). more...

Here, it is presented a study of optical fiber refractometers based on resonances supported by different thin-film coatings. These coatings consist of different materials, such as noble metals and metal oxides fabricated onto the core of the optical fibers. The dielectric constants of the deposited materials determine the presence of the resonances. Thus, noble metals, such as gold and silver, thanks in part to their negative real part of the optical permittivity enable the generation of surface plasmon resonances (SPR). Meanwhile, conductive metal oxides, such as titanium dioxide (TiO 2 ) and indium tin oxide (ITO), with a positive real part of its optical permittivity make it possible to produce lossy mode resonances (LMR). Gold, silver, TiO 2 and ITO refractometers show sensitivities of 1468, 3617, 114 and 1546 nm/refractive index unit (RIU) respectively. Fabricated devices present a promising platform for the fabrication of multipurpose sensors by the addition of the adequate coating. more...

Surface plasmon resonances and lossy mode resonances can be generated with Indium Tin Oxide (ITO) coated optical fibers. Both phenomena are analyzed and compared. Lossy mode resonances present important advantages: they do not require a specific polarization of light, it is possible to generate multiple attenuation bands in the transmission spectrum, and the sensitivity of the device to external parameters can be tuned. The key parameter is the thickness of the ITO coating. The work is supported with both theoretical and experimental results. The main purposes are sensing and generation of multiple-wavelength filters. This work was supported in part by the Spanish Ministry of Education and Science-FEDER TEC2006-12170 and TEC2007-67987-C02-02/MIC. more...

An optical fiber sensor to detect Volatile Organic Compounds (VOCs) is presented in this work. A material that shows a color change (from orange to green) in presence of organic vapors, is fixed onto a cleaved ended pigtail by Electrostatic Self Assembly method [1]. This way, when an optical signal is guided to the device head, changes in the sensing material produce variations in the reflected optical power. Standard Mono mode fiber (9/125 µm) and a DBF laser (@ 1550nm) have been used. Typically, wider fibers (62.5/125 µm) and lower wavelengths (laying in the visible spectral) are used to measure the effect of color change, but working at 1550nm makes easier multiplexing several optical signals. A sensor was implemented and exposed to saturated concentrations of several VOCs, registering a change in the reflected optical power, especially significant for acetic acid. more...

A resonance based optical fiber sensor using a transparent conducting oxide (TCO) coating as the SPR supporting layer is presented here. Traditional resonance based sensors, such as surface plasmon resonance sensors, have been restricted to the utilization of noble metals such as gold and silver as resonance supporting layers. In this work, we present the fabrication of a novel optical fiber resonance based sensor by using a TCO, Indium Tin Oxide (ITO) as the resonance supporting layer with the resonance wavelength in the infra-red region. The refractive index (RI) in the interface ITO/sample can be obtained by monitoring the changes originated in the resonance wavelength peak. The fabricated sensors have been used as refractometers in order to determine the RI of different samples in contact with the ITO layer. These sensors showed high repeatability and a sensitivity in the order of 0.0003 RIU per nm. more...

An interferometric optical fiber sensor based on two nanoFabry-Perot interferometers (nFPs) in-line is experimentally demonstrated. The proposed sensing scheme takes advantage of both nFPs which individually act as humidity sensors and in this arrangement serve as a dual head sensor which improves the output range in 3 dB. more...

Temperature sensitive nanofilms based on quantum dots (QDs) has been deposited on the inner holes of a photonic crystal fiber (PCF) using the layer by layer electrostatic self-assembly method. The sensing structure is based on a PCF fiber segment spliced between two multimode fibers (MMF) of different diameters. The sensors showed a linear variation of the intensity and wavelength emission for a temperature range from -20degC to 70degC. more...

Presented is the material and gas sensing properties of graphene-like nano-sheets deposited on 36deg YX lithium tantalate (LiTaO3) surface acoustic wave (SAW) transducers. The graphene-like nano-sheets were characterized via scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The graphenelike nano-sheet/SAW sensors were exposed to different concentrations of hydrogen (H2) gas in a synthetic air at room temperature. The developed sensors exhibit good sensitivity towards low concentrations of H2 in ambient conditions, as well as excellent dynamic performance towards H2 at room temperature. more...

A new biosensor has been developed by coating a tapered optical fiber with an anti-gliadin antibodies (AGAs) sensitive nanofilm using the electrostatic self-assembled (ESA) monolayer technique in order to aid the diagnosis of celiac disease. Optical fibers were tapered and then the specific antigen was deposited using the ESA method which allows the construction of nanometric scale recognition surfaces on the fiber optic and helps to create fast response sensors for real time observation of the binding process. Power changes up to 6 dB have been recorded during the antibodies binding process with concentrations in the range 1–15 ppm. Optimal deposition parameters have been selected using an in situ interferometric characterization technique which allows to state the working point of the sensor accurately. The high sensitivity and continuous monitoring of the proposed scheme can reduce importantly the time and serum volume required for celiac disease tests. more...

This paper describes the use of free-standing electrically conductive low modulus materials as sensors for the measurement of large strains. Molecular-level wet-chemistry self-assembly processing methods have been used to form free-standing, highly elastomeric and highly electrically conductive nanocomposite thin films that exhibit a large change in resistance with strain. The processing details and sensor applications are presented. more...

In this work a new relative humidity sensor based on the deposition of a subwavelength thickness overlay of alumina (Al2O3) and poly(Sodium 4-Styrene Sulfonate) (PSS) on the cladding of a Long-Period Fiber Grating (LPFG) is presented. This material has a lower refractive index compared to the refractive index of the optical fiber. This characteristic limits the sensitivity of the sensor. In order to enhance the sensitivity to humidity it has been intercalated a high refractive index layer, which permits to improve the sensitivity of LPFG sensors by a ratio of four. The method proposed here widens the design of LPFG based sensors characterized by overlays of low refractive index, and could be used for other applications such as the design of optical filters. more...

The inscription of cascaded long-period gratings of different periods in optical fiber permits us to obtain both narrowband and wideband filters in the same spectrum. If used as an optical transducer, it may permit us to detect with the same device- wide and small parameter changes. The transmission spectra have been simulated using a theoretical model based on LP mode coupling and have been also experimentally demonstrated. This work was supported in part by the Spanish Ministerio de Ciencia y Tecnologia and FEDER under Grant CICYT-TIC 2004-05936-C02-01/MIC, by Gobierno de Navarra, and by FPU MECD. more...

A fiber-optic sensor sensitive to hydrogen peroxide has been designed based on the electrostatic layer-by-layer selfassembly method. Prussian blue has been deposited in a polymeric structure formed by Poly(allylamine hydrochloride) and poly(acrylic acid). The concentration that can be detected range between 10 6–10 3 M, and recovery of the sensor after immersion into a reductive agent was demonstrated. The response of the sensor is independent of thepHfor values that range between 4–7.4. Some rules for estimation of the refractive index of the material deposited and the thickness of the bilayers are also presented This work was supported by Spanish CICYT Research Grants TIC 2003-00909 and TIC 2001-0877-C02- 02; Gobierno de Navarra and FPU MECD grant. more...

An overlay of higher refractive index than the cladding is deposited on a Long Period Fiber Grating (LPFG). This permits to improve in a great manner the sensitivity of the device to ambient and overlay refractive index changes. This causes large shifts of the attenuation bands in the transmission spectrum. To obtain a maximum sensitivity for specific refractive indices of the overlay and the ambient, an optimum overlay thickness must be selected. If the refractive index of the overlay is complex there is an additional phenomenon of vanishing of the attenuation bands in the transmission spectrum. This occurs for specific thickness values of the overlay. The problem is analyzed with a numerical method based on LP mode approximation and coupled mode theory. Experimental results are contrasted with theoretical ones This work was supported by Spanish CICYT Research Grant TIC 2003-00909, Gobierno de Navarra and FPU MECD grant. more...

In this work, an indirect method for the detection of voltage unbalance in electrical engines using an optical fiber sensor is presented. The in-line fiber etalon structure has been designed and used to detect 0-5% voltage unbalances in the frequency range up to 500 Hz. The interferometric sensing mechanism of the sensor allows a high sensitivity with the additional advantages of EMI immunity and high dielectric isolation. In order to prove this claim, a 1.5 kW squirrel cage induction motor is unbalanced and its vibration analyzed. It is shown that a precise unbalance factor can be detected without accessing to the electric part of the machine and an accurate monitoring can be obtained using the analysis proposed. This scheme can be applied to reduce the oscillating electromagnetic torque, power losses and temperature rise due to unbalance, and leading to a higher efficiency and the extension of the life of the machine more...

A theoretical analysis is presented of a long-period fiber grating (LPFG) with an overlay of variable refractive index. The highest sensitivity of the resonance wavelengths to variations in the refractive index of the overlay can be optimized. There are two key points for a good design: the selection of an overlay refractive index close to that of the cladding of the LPFG and the overlay thickness. The problem is analyzed with a numerical method based on coupled-mode theory. This work was supported by Spanish Ministerio de Ciencia y Tecnologia and FEDER Research Grants CICYT-TIC 2003-00909, and by Gobierno de Navarra and FPU MECD Grant. more...