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Sensitivity enhancement in a multimode interference-based SMS fibre structure coated with a thin-film: Theoretical and experimental study 

A.B. Socorro, I.D. Villar, J.M. Corres, F.J. Arregui, I.R. Matias

Multimode interference in a single-mode-multimode-single-mode (SMS) fibre structure leads to the generation of transmission bands and attenuation bands in the optical spectrum. in this work, the progressive deposition, with layer-by-layer assembly technique, of a high refreactive index thin-film onto the SMS structure permits to observe the evolution of the bands as a function of the coating thickness. The results show that it is possible to increase the sensitivity of the device to variations of the coating thickness, what indicates the adequateness of this structure as a sensing platform. The experimental results are corroborated with a numerical method based on coupled-mode theory. As a practical application, a sensitivity improvement has been obtained a pH sensor by increasing the coating thickness.


Comparative study of layer-by-layer deposition techniques for poly(sodium phosphate) and poly(allylamine hydrochloride) 

C. Elosua, D. Lopez-Torres, M. Hernaez, I.R. Matias, F.J. Arregui

An inorganic short chain polymer, poly(sodium phosphate), PSP, together with poly(allylamine hydrochloride), PAH, is used to fabricate layer-by-layer (LbL) films. The thickness, roughness, contact angle, and optical transmittance of these films are studied depending on three parameters: the precursor solution concentrations (10-3 and 10-4 M), the number of bilayers deposited (20, 40, 60, 80, and 100 bilayers), and the specific technique used for the LbL fabrication (dipping or spraying). In most cases of this experimental study, the roughness of the nanofilms increases with the number of bilayers. This contradicts the basic observations made in standard LbL assemblies where the roughness decreases for thicker coatings. In fact, a wide range of thickness and roughness was achieved by means of adjusting the three parameters mentioned above. For instance, a roughness of 1.23 or 205 nm root mean square was measured for 100 bilayer coatings. Contact angles close to 0 were observed. Moreover, high optical transmittance is also reported, above 90%, for 80 bilayer films fabricated with the 10-4 M solutions. Therefore, these multilayer structures can be used to obtain transparent superhydrophilic surfaces.


Tunable electro-optic wavelength filter based on lossy-guided mode resonances 

J.M. Corres, J. Ascorbe, F.J. Arregui, I.R. Matias 

In this work an optical fiber tunable filter based on lossy guided-mode resonances (LGMR) is proposed. It consists of a multilayer structure deposited onto the surface of a plastic cladding removed multimode fiber. The first layer is used to generate the LGMR and to work as the first electrode as well; the second one to tune the filter and the outer layer forms the other electrode. The fabricated filter has demonstrated a good sensitivity to the applied voltage showing a change of the LGMR wavelength of 0.4 nm/V. Among other applications, this filter is intended to be used as electro-optic wavelength filter or modulator.


High sensitivity optical fiber pH sensor using poly (acrylic acid) nanofibers 

J.M. Corres, F.J. Arregui, I.R. Matias, Y. Rodriguez 

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.


Multicolor Layer-by-Layer films using weak polyelectrolyte assisted synthesis of silver nanoparticles 

P.J. Rivero, J. GoicoecheaA. Urrutia, I. R. Matías, F. J. Arregui 

In the present study, we show that silver nanoparticles (AgNPs) with different shape, aggregation state and color (violet, green, orange) have been successfully incorporated into polyelectrolyte multilayer thin films using the layer-by-layer (LbL) assembly. In order to obtain colored thin films based on AgNPs is necessary to maintain the aggregation state of the nanoparticles, a non-trivial aspect in which this work is focused on. The use of Poly(acrylic acid, sodium salt) (PAA) as a protective agent of the AgNPs is the key element to preserve the aggregation state and makes possible the presence of similar aggregates (shape and size) within the LbLcolored films. This approach based on electrostatic interactions of the polymeric chains and the immobilization of AgNPs with different shape and size into the thin films opens up a new interesting perspective to fabricate multicolornanocomposites based on AgNPs.


A Lossy Mode Resonance optical sensor using silver nanoparticles-loaded films for monitoring human breathing.

Pedro J. Rivero, A. Urrutia, J. Goicoechea, I. R. Matías, F. J. Arregui

This work is focused on the fabrication of a human breathing sensor based on the in situ synthesis of silver nanoparticles (Ag-NPs) inside a polymeric coating previously deposited on an optical fiber core by means of the Layer-by-Layer self-assembly. The Ag-NPs were created using a synthesis protocol consisting of a loading step of the Ag+ cations into the polymeric film and a further reduction step using dimethylamine borane (DMAB). The morphology and distribution of the Ag-NPs inside the polymeric coating have been studied using atomic force microscopy (AFM). Furthermore, UV–VIS spectroscopy and energy dispersive X-ray (EDX) were also used to confirm the synthesis of the Ag-NPs within the resultant coating. The amount of Ag-NPs increases when the number of loading/reduction cycles is higher. Therefore the incorporation of the Ag-NPs affects the refractive index of the overlay promoting the observation of a resonant attenuation band in the infrared region (NIR), known as Lossy Mode Resonance (LMR), which can be used as a sensing signal to monitor the human breathing. The quality of the device has been experimentally tested with good sensitivity (0.455 nm per RH%) and fast response time (692 ms and 839 ms for rise/fall). 


Fiber-optic biosensor based on lossy mode resonances

Socorro, A.B., Villar, I.D. ,  Corres, J.M. ,  Arregui, F.J. ,  Matias, I.R.

In this work, a novel fiber-optic immunoglobulin G biosensor based on lossy mode resonances is proposed. This physical phenomenon is obtained by depositing a PAH/PSS layer-by-layer thin-film on a cladding removed optical fiber. A reflective configuration is used to track the generation and response of the electromagnetic resonance in the different phases of the process. According to the results, wavelength displacements of 10 nm are visualized when detecting immunoglobulins with a response time of 12 min for a 50 μg/ml concentration. 


Optical fiber humidity sensors based on Localized Surface Plasmon Resonance (LSPR) and Lossy-mode resonance (LMR) in overlays loaded with silver nanoparticles.

Pedro J. Rivero, A. Urrutia, J. GoicoecheaF. J. Arregui

In this work, it is presented for the first time the fabrication and characterization of a novel optical fiber humidity sensor based on both Lossy-mode resonance (LMR) and Localized Surface Plasmon Resonance (LSPR). Those resonances were created using Layer-by-Layer (LbL) polymeric coating loaded with Ag nanoparticles (Ag NPs) and fabricated onto an optical fiber core. Firstly, it was observed a LSPR attenuation band, inherent to the presence of the Ag NPs in the coating. This LSPR band showed a slight intensity variation with Relative Humidity (RH) changes but no significant wavelength dependence was observed. Otherwise several LMR attenuation bands were observed in the 400–1100 nm spectral range as the thickness coating was increased. The LMR maxima depend strongly on the thickness and refractive index of the LbL overlay, and therefore, they show a strong wavelength response to Relative Humidity (RH) changes. A wavelength-based optical humidity sensor was achieved and the dynamic range (42.4 nm), transfer function, response time (476 ms and 447 ms for rise/fall respectively) were characterized. The results confirm that this sensor could be used even for monitoring human breathing. 


Tapered Single-Mode Optical Fiber pH Sensor Based on Lossy Mode Resonances Generated by a Polymeric Thin-Film

Socorro, A.B., Villar, I.D. ,  Corres, J.M. ,  Arregui, F.J. ,  Matias, I.R.

Lossy mode resonances can be generated with certain polymeric nanostructures, such as those obtained with a multilayered assembly of poly(allylamine hydrochloride) and poly(acrylic acid). This coating is adsorbed by the electro-static self-assembly technique onto a tapered single-mode optical fiber, in order to evaluate its performance when detecting pH. According to the results reported in this paper, the high sensitivity given by a tapering process in a single-mode optical fiber is increased by the effect of this kind of electromagnetic resonances. Particularly, in a pH range from 4.0 to 6.0, the overall wavelength shift of this sensor reaches 200 nm, and the transmission at the resonance wavelengths can fall down to -50 dB. These data provide results which can be taken into account to detect pH with high accuracy. 


A novel luminescent optical fibre probe based on immobilized tridentate bis(phosphinic amide)...

F.J. Sainz-Gonzalo, C. Elosua, J.F. Fernández-Sánchez, C. Popovici, I. Fernández, F.L. Ortiz, F.J. Arregui, I.R. Matias, A. Fernández-Gutiérrez

A novel optical fibre probe based on a tridentate bis(phosphinic amide)-phosphine oxide PhPO(C6H4POPhN(CH(CH3)2)2)2 (ligand 1) has been developed for the detection of europium(III) ions in water. The dip coating technique was used to deposit the ligand 1 encapsulated on a poly(vinyl chloride) membrane onto an optical fibre. The optimum deposition thickness of the membrane was 280 ± 40 nm. The sensing mechanism relies on the reaction between europium(III) ion and ligand 1, which produces a strong luminescent complex of stoichiometry 1:2 Eu(III):Ligand 1 with a maximum emission peak around 612 nm. Two different configurations, aerial and aqueous, were tested for measuring the luminescence off-line and on-line, respectively. The proposed probe showed a response time of 92 s in the aqueous configuration (in situ detection of europium(III) ions in water). The luminescence of the proposed probe displayed a power-law response for the europium(III) concentration in a broad range of concentrations of at least 5 orders of magnitude, from 10 nM to 1 mM, with a correlation coefficient (R2) of the fitted curve better than 0.99.


Lossy mode resonances dependence on the geometry of a tapered monomode optical fiber

Socorro, A.B., Villar, I.D. ,  Corres, J.M. ,  Matias, I.R.,  Arregui, F.J. ,

The geometry of a tapered single-mode optical fiber influences the formation and sensitivity of lossy mode resonances generated by the deposition of a polymeric thin-film employing the layer-by-layer electrostatic self assembly technique. In this work, several waist diameters and waist lengths of a monomode optical fiber are analyzed both experimentally and theoretically to obtain some conclusions about their influence on the behavior of this kind of devices. The transmitted optical power is studied as a function of the wavelength to estimate the sensitivity of this system. According to the results obtained, this sensitivity increases as a function of the waist length, whereas it decreases as a function of the waist diameter. What is more, depending on the combination of waist length and waist diameter, important power changes up to 45 dB can be reached at specific wavelength ranges of the electromagnetic spectrum, which can be used for accurate detection of small changes in the nanocoating properties induced by a specific analyte. This behavior can lead to sensing applications based on the combination of lossy mode resonances and tapered monomode optical fibers.


Humidity sensor based on silver nanoparticles embedded in a polymeric coating

Pedro J. Rivero, Aitor Urrutia, Javier Goicoechea, Francisco J. Arregui, Ignacio R. Matías

In this work, it is presented a novel optical fiber humidity sensor based on silver nanoparticle-loaded polymeric coatings built onto an optical fiber core. The polymeric film was fabricated using the Layer-by-Layer assembly technique. The silver nanoparticles (Ag NPs) were characterized using transmission electron microscopy (TEM and UV-VIS spectroscopy. A Localized Surface Plasmon Resonance (LSPR) attenuation band is observed when the thickness of the coating increases, and showed a very good sensitivity to Relative Humidity (RH) variations, suitable for high performance applications such as human breathing monitoring.


Influence of Waist Length in Lossy Mode Resonances Generated With Coated Tapered Single-Mode Optical Fibers.

Socorro, A.B.;  Del Villar, I.; Corres, J.M.; Arregui, F.J.; Matias, I.R.;

In this work, the generation of electromagnetic resonances due to the deposition of a nanocoating on a tapered single-mode optical fiber is analyzed. The layer-by-layer technique is used to control the thickness of the nanocoating. According to the results that have been obtained, the depth of the resonance depends on the length of the waist region. Variations in the transmitted optical power of 40 dB are observed in just a few layers. This can be considered in the fabrication of both highly sensitive resonance-based sensors and optical filters.


Optical Fiber Humidity Sensors using PVdF Electrospun Nanowebs

Corres, J.M.; Rodriguez, Y.R.; Arregui, F.J.; Matias, I.R.;

In this paper, a new optical fiber humidity sensor based on PVdF nanowebs is presented. The electrospinning technique has been used to create a nanometric scale membrane onto the surface of a hollow core fiber (HCF). The fabricated sensor has demonstrated a repetitive response in the range from 50 to 70 % of relative humidity with a rise time of 100 ms. Among other applications, this sensor is intended to be used for monitoring the human breathing. Therefore, high dynamic performances are required, especially in the higher relative humidity ranges.


Lossy Mode Resonance-based pH sensor using a tapered single mode optical fiber coated with a polymeric nanostructure

Socorro, A.B.;  Del Villar, I.; Corres, J.M.; Arregui, F.J.; Matias, I.R.;

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.