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Publicações

2021

Femtosecond laser-written long period fibre gratings coated with titanium dioxide for improved sensitivity

Autores
Viveiros, D; de Almeida, JMMM; Coelho, L; Vasconcelos, H; Amorim, VA; Maia, JM; Jorge, PAS; Marques, PVS;

Publicação
Optical Sensing and Detection VI

Abstract

2021

Preliminary assessment on the detection of putrescine using long period fiber gratings coated with titanium dioxide and poly(ethylene-co-vinyl acetate)

Autores
Vasconcelos, H; de Almeida, JMMM; Saraiva, C; Viveiros, D; Jorge, PAS; Coelho, L;

Publicação
Proceedings of SPIE - The International Society for Optical Engineering

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. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.

2021

Mach-Zehnder interferometer-based evanescent refractometer inscribed at the surface of Eagle2000 by femtosecond laser writing

Autores
Amorim, VA; Maia, JM; Viveiros, D; Marques, PVS;

Publicação
IEEE Sensors Journal

Abstract

2021

Intensity-modulated refractometer based on mode-mismatch in surface waveguides inscribed by femtosecond laser direct writing

Autores
Amorim, VA; Viveiros, D; Maia, JM; Marques, PVS;

Publicação
OPTICS AND LASER TECHNOLOGY

Abstract
Optical waveguides were fabricated at the surface of Eagle2000 glass substrates, using femtosecond laser direct writing and wet etching, and their potential as intensity-modulated refractometers was assessed. Through the analysis of their broadband spectral response to different refractive index oils, we observed that mode mismatch is present when the guided mode reaches the surface of the substrate and interacts with the external medium, thus enabling the use of such optical waveguides in refractive index sensing. Refractive indices equal to or greater than that of the substrate also induced a coupling mechanism that was shown not to be suitable in these devices. The device's wavelength of operation was found to be tunable by controlling the distance between the surface and the center of the optical waveguide. However, the sensitivity was seen to diminish by increasing the latter, being nonexistent for distances greater than 5.5 mu m. In this study, the maximum sensitivity values were found for a surface to core center distance between 1 and 2 mu m, in the biological range, and 2.5 to 3 mu m, for a refractive index nearing that of the substrate. Accordingly, maximum sensitivities of approximate to 25 dB/RIU and approximate to 1200 dB/RIU were found between 1.300 < n(D)(25)degrees(C) < 1.400 and 1.490 < n(D)(25)degrees(C) < 1.500, respectively.

2021

Effect of low-doses of gamma radiation on electric arc-induced long period fiber gratings

Autores
Mesonero Santos, P; Fernandez Medina, A; Coelho, LCC; Viveiros, D; Jorge, PA; Belenguer, T; Heredero, RL;

Publicação
Sensors

Abstract
This work presents an experimental study on the effects of gamma radiation on Long Period Fiber Gratings (LPFGs) in a low-dose test campaign to evaluate their eventual degradation. The study was carried out with standard single-mode fibers where the grating was inscribed using the Electric-Arc Discharge (EAD) technique. Before the gamma campaign, a detailed optical characterization was performed with repeatability tests to verify the accuracy of the setup and the associated error sources. The gamma-induced changes up to a dose of 200 krad and the recovery after radiation were monitored with the Dip Wavelength Shift (DWS). The results show that the gamma sensitivity for a total dose of 200 krad is 11 pm/krad and a total DWS of 2.3 nm has been observed with no linear dependence. Post-radiation study shows that recovery from radiation-induced wavelength shift is nearly complete in about 4000 h. Experimental results show that the changes suffered under gamma irradiation of these LPFGs are temporary making them a good choice as sensors in space applications. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.