2020
Autores
Paiva, JS; Jorge, PAS; Ribeiro, RSR; Balmaña, M; Campos, D; Mereiter, S; Jin, C; Karlsson, NG; Sampaio, P; Reis, CA; Cunha, JPS;
Publicação
Scientific Reports
Abstract
An amendment to this paper has been published and can be accessed via a link at the top of the paper. © 2020, The Author(s).
2020
Autores
Viveiros, D; de Almeida, JMMM; Coelho, L; Vasconcelos, H; Maia, JM; Amorim, VA; Jorge, PAS; Marques, PVS;
Publicação
SENSORS
Abstract
Long period fiber gratings (LPFGs) were fabricated in a standard single mode fiber (SMF-28e) through femtosecond (fs) laser direct writing. LPFGs with longer and shorter periods were fabricated, which allows coupling from the fundamental core mode to lower and higher order asymmetric cladding modes (LP(1,6)and LP1,12, respectively). For the grating periods of 182.7 and 192.5 mu m, it was verified that the LP(1,12)mode exhibits a TAP at approximately 1380 and 1448 nm in air and water, respectively. Characterization of the LPFGs subjected to high-temperature thermal treatment was accomplished. Fine-tuning of the resonance band's position and thermal stability up to 600 degrees C was shown. The temperature sensitivity was characterized for the gratings with different periods and for different temperature ranges. A maximum sensitivity of -180.73, and 179.29 pm/degrees C was obtained for the two resonances of the 182.7 mu m TAP LPFG, in the range between 250 and 600 degrees C.
2020
Autores
Vasconcelos, H; de Almeida, JMMM; Saraiva, C; Viveiros, D; Jorge, PAS; Coelho, L;
Publicação
OPTICAL SENSING AND DETECTION VI
Abstract
Biogenic amines, such as putrescine are potential indicators of food storage condition and deterioration. The real time measurement of their concentration in food may become an important method of food control. It was found that putrescine diffuses through a thin layer made from a solution of Poly(ethylene-co-vinyl acetate) (PEVA) and maleic anhydride. Poly(ethylene-co-vinyl acetate) is a common non-chlorinated vinyl capable to adsorb specific analytes as putrescine which upon diffusion, reversibly binds to the maleic anhydride causing the polymer swelling resulting in spectral changes from the optical point of view. Long Period Fiber Gratings coated with 30 nm titanium dioxide, a high refractive index material used to increase the intrinsic sensitivity to the external refractive index, were overcoated with a thin layer of maleic anhydride doped Poly(ethylene-co-vinyl acetate). When exposed to solutions containing small concentrations of putrescine the resonant band corresponding to the LP1,6 cladding mode was found to move to shorter wavelengths. The observed blue shift corresponds to the increasing concentration of putrescine in the fiber sensor structure. Further work is being carried out to improve the sensitivity and the limit of detection of the sensing system as well as to increase range of operation, which is presently limited to 0.3 to 0.5 M.
2020
Autores
Ferreira, WSJ; dos Santos, PSS; Caldas, P; Jorge, PAS; Sakamoto, JMS;
Publicação
EPJ Web of Conferences
Abstract
2020
Autores
Mendes, JP; Coelho, L; Pereira, CM; Jorge, PAS;
Publicação
U.Porto Journal of Engineering
Abstract
The study of sensing materials to the detection of carbon dioxide (CO2) was achieved using p-nitrophenol (pNPh) as a colorimetric indicator. The sensing material was polymerized (NPLn), functionalized with 3-triethoxysilyl propyl isocyanate (IPTES) which sensitivity was tested in the form of a membrane as is and encapsulated in hollow silica nanoparticles. The sensing membranes were tested in a closed gas system comprising very precise flow controllers to deliver different concentrations of CO2 (vs. N2). The combination of the sensing membranes with multimode optical fibers and a dual-wavelength diode (LED) allows the measurement of the CO2 through the analysis of the induced absorbance changes with a self-referenced ratiometric scheme. The analysis of the sensing materials have shown significant changes in their chemical and physical properties and the results attest these materials with a strong potential for assessing CO2 dynamics in environmental, medical, and industrial applications.
2020
Autores
Viveiros, D; De Almeida, JMMM; Coelho, L; Vasconcelos, H; Maia, JM; Amorim, VA; Jorge, PAS; Marques, PVS;
Publicação
Optics InfoBase Conference Papers
Abstract
The fabrication of Turn Around Point Long Period Fiber Grating in standard SMF-28e fibers through femtosecond laser direct writing is demonstrated and its sensing sensitivity is improved by coating the fiber with titanium dioxide through physical vapor deposition. © 2021 The Author(s).
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