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Publications

Publications by CAP

2011

Fiber-Optic Inclinometer Based on Taper Michelson Interferometer

Authors
Amaral, LMN; Frazao, O; Santos, JL; Ribeiro, ABL;

Publication
IEEE SENSORS JOURNAL

Abstract
A compact fiber-optic inclinometer based on a fiber-taper Michelson interferometric sensor is constructed and demonstrated. The sensor consist of a single symmetrically taper waist of 80 mu m distanced 30 mm from the single-mode fiber end-tip right-angled cleaved. The amplitude of the bending angle of the fiber taper interferometer is obtained by passive interferometric interrogation based on the generation of two quadrature phase-shifted signals from two fiber Bragg gratings with different resonant wavelengths. Optical phase-to-bending sensitivity of similar to 1.13 rad/degree and a bend angle resolution of similar to 0.014 degree/root Hz were achieved.

2011

Simultaneous Measurement of Humidity and Temperature Based on an SiO2-Nanospheres Film Deposited on a Long-Period Grating In-Line With a Fiber Bragg Grating

Authors
Viegas, D; Hernaez, M; Goicoechea, J; Santos, JL; Araujo, FM; Arregui, F; Matias, IR;

Publication
IEEE SENSORS JOURNAL

Abstract
A novel configuration able to measure simultaneously relative humidity and temperature is proposed. The sensing head is based on a long-period fiber grating (LPG) coated with silica nanospheres in-line with a fiber Bragg grating. The polymeric overlay that changes its optical properties when exposed to different humidity levels is deposited onto the LPG using the electrostatic self-assembly technique (ESA), resulting into a humidity-induced shift of the resonance wavelength of the LPG. Considering the humidity range from 20% to 50% RH, a system resolution of 1.6% RH and 2.5 degrees C was achieved. At higher humidity, from 50% to 80% RH, the corresponding resolution values were 2.4% RH and 0.4 degrees C.

2011

Multiwavelength Raman Fiber Lasers Using Hi-Bi Photonic Crystal Fiber Loop Mirrors Combined With Random Cavities

Authors
Pinto, AMR; Frazao, O; Santos, JL; Lopez Amo, M;

Publication
JOURNAL OF LIGHTWAVE TECHNOLOGY

Abstract
Different multiwavelength Raman fiber lasers based on a hybrid cavity setup are proposed. The lasing schemes are based in highly birefringent photonic crystal fiber loop mirrors combined with random cavities. The Hi-Bi PCF loop mirrors are characterized by an interferometric output; whereas the random mirrors are created by cooperative Rayleigh scattering due to Raman gain. This configuration allows suppression of Rayleigh associated noise growth, while taking advantage of it as an active part of the laser cavity, enhancing the achievable gain. The proposed fiber lasers present stable operation at room temperature although different output maxima and shapes depending on the fiber loop mirror/random mirror combination.

2011

Temperature and strain-independent curvature sensor based on a singlemode/multimode fiber optic structure

Authors
Silva, S; Frazao, O; Viegas, J; Ferreira, LA; Araujo, FM; Xavier Malcata, FX; Santos, JL;

Publication
MEASUREMENT SCIENCE & TECHNOLOGY

Abstract
This work describes a fiber optic sensing structure that is sensitive to curvature, and features a low temperature-and strain cross-sensitivity. It is based on multimode interference, and relies on a singlemode-step index multimode-singlemode fiber structure. It was observed that the transmitted optical power in such a layout is highly sensitive to the wavelength of operation, and to the length of the multimode fiber. The optical spectrum exhibits two dominant loss bands, at wavelengths that have similar responses both to temperature and strain, but different responses to curvature. Based on this result, an interrogation approach is proposed that permits substantial sensitivity to curvature (8.7 +/- 0.1 nm m) and residual sensitivities to temperature and strain (0.3 +/- 0.1 pm degrees C(-1) and (-0.06 +/- 0.01) x 10(-6) m m(-1), respectively). The beam-propagation method was employed for modeling the propagation of light along the optical fiber sensing device proposed.

2011

Fiber Bragg Grating Structures with Fused Tapers

Authors
Silva, SFO; Ferreira, LA; Araujo, FM; Santos, JL; Frazao, O;

Publication
FIBER AND INTEGRATED OPTICS

Abstract
Fiber structures based on the combination of abrupt tapers and fiber Bragg gratings are studied. Two situations are exploredin one, the taper is fabricated in the fiber region with a fiber Bragg grating; in the other, the taper is first fabricated followed by the fiber Bragg grating. It is shown that the first device presents the properties of a Fabry-Perot cavity and the other of a phase-shifted Bragg grating, where the phase shift is associated to the tapered fiber region. The sensing characteristics of these structures are studied, and it is shown that the temperature sensitivities are similar but with observable different responses to strain.

2011

Gene Delivery into Mesenchymal Stem Cells: A Biomimetic Approach Using RGD Nanoclusters Based on Poly(amidoamine) Dendrimers

Authors
Pandita, D; Santos, JL; Rodrigues, J; Pego, AP; Granja, PL; Tomas, H;

Publication
BIOMACROMOLECULES

Abstract
Poly(amidoamine) dendrimers (generations 5 and 6) with amine termini were conjugated with peptides containing the arginine-glycine-aspartic acid (RGD) sequence having in view their application as gene delivery vectors. The idea behind the work was to take advantage of the cationic nature of dendrimers and of the integrin targeting capabilities of the RGD motif to improve gene delivery. Dendrimers were used as scaffolds for RGD clustering and, by controlling the number of peptides (4, 8, and 16) linked to each dendrimer, it was possible to evaluate the effect of RGD density on the gene delivery process. The new vectors were characterized in respect to their ability to neutralize and compact plasmid DNA (pDNA). The complexes formed by the vectors and pDNA were studied concerning their size, zeta potential, capacity of being internalized by cells and ability of transferring genes. Transfection efficiency was analyzed, first, by using a pDNA encoding for Enhanced Green Fluorescent Protein and Firefly Luciferase and, second, by using a pDNA encoding for Bone Morphogenetic Protein-2. Gene expression in mesenchymal stem cells was enhanced using the new vectors in comparison to native dendrimers and was shown to be dependent on the electrostatic interaction established between the dendrimer moiety and the cell surface, as well as on the RGD density of nanoclusters. The use of dendrimer scaffolds for RGD cluster formation is a new approach that can be extended beyond gene delivery applications, whenever RGD clustering is important for modulating cellular responses.

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