Open Access
Deposition of coatings on long-period fiber gratings: tunnel effect analogy
(Springer, 2006) Del Villar, Ignacio; Matías Maestro, Ignacio; Arregui San Martín, Francisco Javier; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Gobierno de Navarra / Nafarroako Gobernua
The sensitivity of Long-period fiber gratings (LPFGs), coated with high-refractive-index thin film overlays, to the refractive index and the thickness of the overlay, and to the ambient refractive index, can be enhanced with a design based on a two-overlay coating of an LPFG. The first overlay of lower refractive index than the cladding affects the guidance of a cladding mode in the second overlay of higher refractive index than the cladding. This causes a more abrupt cladding modal redistribution than with the deposition of a unique high-refractive-index overlay. The phenomenon is analyzed with a method based on a vectorial analysis of modes and the application of coupled mode theory.
Open Access
Influence in cladding mode distribution of overlay deposition on long-period fiber gratings
(Optical Society of America, 2006) Del Villar, Ignacio; Matías Maestro, Ignacio; Arregui San Martín, Francisco Javier; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Gobierno de Navarra / Nafarroako Gobernua
A thin overlay of higher refractive index than that of the cladding of a long-period fiber grating induces in cladding modes strong variations in effective index, mode profile, cross-coupling coefficient with the core mode, and self-coupling coefficient. Some conditions must be met in order to obtain the highest inducement. The key parameters are the thickness and the refractive index of the overlay, and the ambient refractive index. Under optimum conditions, the sensitivity of the device to variations in any of the critical parameters is improved in a great manner. The result is large shifts of the attenuation bands in the transmission spectrum. 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 solved in two steps: a vectorial analysis of the modes and the application of coupled-mode theory
Open Access
Nanosensor for detection of glucose
(SPIE, 2004-06-09) Del Villar, Ignacio; Matías Maestro, Ignacio; Arregui San Martín, Francisco Javier; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
A novel fibre-optic sensor sensitive to glucose has been designed based on electrostatic self-assembly method. The polycation of the structure is a mixture of poly(allylamine hydrochloride) (PAH) and Prussian Blue, whereas the polyanion is well-known enzyme glucose oxidase (GOx). The range of glucose concentration that can be measured is submilimolar and is located between 0.1 and 2 mM. Measures are based on a new detection scheme based on the slope of the change of signal produced by injection of glucose, yielding to a linear response. The sensor responses in a PH range between 4 and 7.4, which includes the physiological PH of blood. Some rules for estimation of the refractive index of the material deposited and the thickness of bilayers are also given.
Open Access
Long period fiber gratings with overlay of variable refractive index
(IEEE, 2005) Del Villar, Ignacio; Matías Maestro, Ignacio; Arregui San Martín, Francisco Javier; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Gobierno de Navarra / Nafarroako Gobernua
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.
Open Access
Analysis of one-dimensional photonic band gap structures with a liquid crystal defect towards development of fiber-optic tunable wavelength filters
(Optical Society of America, 2003) Del Villar, Ignacio; Matías Maestro, Ignacio; Arregui San Martín, Francisco Javier; Claus, Richard O.; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Gobierno de Navarra / Nafarroako Gobernua
A theoretical analysis of a fiber optical photonic band gap based tunable wavelength filter is presented. The design presented here is based on the quarter wave reflector with a liquid crystal defect layer in the middle of the structure. The filter generated by the structure is shifted in wavelength as the voltage applied to the structure is modified. Some critical parameters are analyzed: the effect of the consideration of fiber as the first layer and not the input medium in the shape of the filter, the number of layers of the structure, and the thickness of the defect layer. This last parameter determines the width of the wavelength sweep of the filter, but is limited by the creation of more defects. Some rules of practical implementation of this device are also given.
Open Access
Enhancement of sensitivity in long period fiber gratings with deposition of low refractive index materials
(Optical Society of America, 2005) Del Villar, Ignacio; Matías Maestro, Ignacio; Arregui San Martín, Francisco Javier; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
It was proved [Opt. Lett. 30, 720 (2005)] that the deposition of an overlay of higher refractive index than that of the cladding on a long-period fiber grating (LPFG) causes large shifts in the attenuation bands induced by the grating. The result is an enhancement of the sensitivity of the LPFG to variations in the ambient and overlay refractive indices or the overlay thickness. The limitation of the previous design to materials with higher refractive indices than that of the cladding of the LPFG is overcome with a five-layer model. To this purpose, a first overlay of higher refractive index than that of the cladding of the LPFG will enhance the sensitivity of the device to variations in the refractive index of a second overlay of lower refractive index than that of the cladding of the LPFG. Moreover, it is proved that, if the second overlay is thick enough, its behavior resembles that of an infinite layer
Open Access
Deposition of an overlay with electrostactic self-assembly method in long period fiber gratings
(Optical Society of America, 2005) Del Villar, Ignacio; Achaerandio Alvira, Miguel; Matías Maestro, Ignacio; Arregui San Martín, Francisco Javier; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Gobierno de Navarra / Nafarroako Gobernua
It was proved that the deposition of an overlay material onto a long-period fiber grating causes important shifts in the wavelengths of the typical attenuation bands that are caused by coupling between cladding and core modes [Opt. Lett. 27, 682 (2002)]. A theoretical model for analyzing a multilayer cylindrical waveguide is presented that permits the phenomenon to be understood and predicted. An overlay of higher refractive index than the cladding starts to guide a mode if a certain thickness value is exceeded. This causes large shifts in the resonance wavelength induced by the grating. One important application of this phenomenon to sensors is enhancement of the sensitivity of a long-period fiber grating to ambient conditions. Theoretical results are corroborated with experimental ones obtained by electrostatic self-assembly.
Open Access
ESA-based in-fiber nanocavity for hydrogen–peroxide detection
(IEEE, 2005) Del Villar, Ignacio; Matías Maestro, Ignacio; Arregui San Martín, Francisco Javier; Claus, Richard O.; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Gobierno de Navarra / Nafarroako Gobernua
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
Open Access
Strategies for fabrication of hydrogen peroxide sensors based on electrostatic self-assembly (ESA) method
(Elsevier, 2004) Del Villar, Ignacio; Matías Maestro, Ignacio; Arregui San Martín, Francisco Javier; Echeverría Morrás, Jesús; Claus, Richard O.; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Gobierno de Navarra / Nafarroako Gobernua
An optical fiber sensor has been fabricated for detection of 5 M–0.1mM concentrations of hydrogen peroxide with a linear response. The deposition method used is electrostatic self-assembly (ESA) of polymer cationic and anionic layers. Prussian Blue (PB) has been included in the polycation layers. The optical fiber sensor is included in a reflection setup, where the measuring technique is based on the slope of the optical reflected power change caused by oxidation of Prussian White (PW) to Prussian Blue. The sensor recovers after immersion in a reductive agent and is immune against a variety of components. Measurement of hydrogen peroxide has been proved successfully in a wide range pHs between 3 and 9. Some techniques have been applied in order to avoid the lost of indicator.
Open Access
Generation of selective fringes with cascaded long-period gratings
(IEEE, 2006) Del Villar, Ignacio; Achaerandio Alvira, Miguel; Arregui San Martín, Francisco Javier; Matías Maestro, Ignacio; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Gobierno de Navarra / Nafarroako Gobernua
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.