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Publications

Publications by Paulo Caldas

2010

Monitoring the quality of frying oils using a nanolayer coated optical fiber refractometer

Authors
Abe, I; Oliveira, J; Simoes, E; Caldas, P; Frazao, O;

Publication
TALANTA

Abstract
The analysis of the quality of food oils is of paramount importance because the degradation of oils can lead to formation of harmful substances to the human organism With the increase of the degradation of oils an increase of its refractive index occurs The objective of this work is to develop and to characterize optical fiber refractometers sensitive to variations of refractive index of food oil samples The optical fiber refractometers thanks to the intrinsic characteristics make them suitable for monitoring the quality of frying oils They possess the advantages to require small volumes of sample for analysis do not contaminate the sample and supply the response in real time In this work a long period grating (LPG) as refractometer is used because of their sensitivity to refractive index of the external media degraded and not degraded frying oil samples The oil samples had been characterized by the analysis of total polar components The refractive index of oil is above 1 47 this region the LPG does not show enough sensitivity a nanolayer of an organic material was coated onto the fiber Using the Langmuir-Blodgett technique the response of LPG is modified according to the refractive index and thickness of the film (he deposition of the film modifies the rates effective modes of cladding thus improving the response of the changes in the refractive index of the external media higher than that the refractive index of the cladding (n = 1 457)

2011

Comparative study of different parameters of fibre Bragg gratings and long period gratings sensors for high-temperature measurements

Authors
Melo, LB; Angelo, N; Alberto, N; Marques, C; Monteiro, J; Rego, G; Caldas, P; Nogueira, R;

Publication
INTERNATIONAL CONFERENCE ON APPLICATIONS OF OPTICS AND PHOTONICS

Abstract
This paper presents a comparative study of the behaviour of different kinds of optical fibre sensors in response to high temperatures. It compares the performance of regenerated fibre Bragg gratings (FBGs) written in hydrogen-loaded and non-loaded fibres with long period gratings (LPGs) written through the two different processes of ultraviolet (UV) irradiation and electrical arc discharges. This work shows the importance of the use of hydrogen-loaded fibres to achieve regenerated FBGs capable of withstanding high temperatures as high as 955 degrees C. In addition, the results demonstrated that LPGs recorded by electric arc discharges have higher thermal resistance than LPGs written by UV radiation.

2010

20 mW, 70 nm bandwidth ASE fibre optic source at 1060 nm wavelength region for Optical Coherence Tomography

Authors
Trifanov, I; Caldas, P; Neagu, L; Romero, R; Berendt, MO; Salcedo, JR; Podoleanu, AG; Lobo Ribeiro, ABL;

Publication
FIBER LASERS VII: TECHNOLOGY, SYSTEMS, AND APPLICATIONS

Abstract
Optical coherence tomography (OCT) imaging at 1060 nm region proved to be a successful alternative in ophthalmology not only for resolving intraretinal layers, but also for enabling sufficient penetration to monitor the sub-retinal vasculature in the choroids when compared to most commonly used OCT imaging systems at 800 nm region. To encourage further clinical research at this particular wavelength, we have developed a compact fiber optic source based on amplified spontaneous emission (ASE) centered at similar to 1060 nm with similar to 70 nm spectral bandwidth at full-width half maximum (FWHM) and output power >20 mW. Our approach is based on a combination of slightly shifted ASE emission spectra from a combination of two rare-earth doped fibers (Ytterbium and Neodymium). Spectral shaping and power optimization have been achieved using in-fiber filtering solutions. We have tested the performances of the source in an OCT system optimized for this wavelength.

2010

Characterization of nanolayer LPG refractometer according surrounding refractive index

Authors
Simoes, E; Abe, I; Oliveira, J; Pinto, JL; Caldas, P; Frazao, O;

Publication
FOURTH EUROPEAN WORKSHOP ON OPTICAL FIBRE SENSORS

Abstract
In this work the behavior of an optical fiber Long Period Grating (LPG) refractometer with the variations of the surrounding refractive index is discussed. The objective is to characterize optical fiber refractometers sensitive to surrounding refractive index, higher and lower than the cladding. For values of surrounding refractive index higher than the cladding, the LPG does not show enough sensitivity. For this reason, a nanolayer of an organic material was coated onto the fiber, using the Langmuir-Blodgett technique. We characterized LPG covered with different nanolayers thickness (110 and 120 nm) relatively to changes in surrounding refractive index.

2007

Origin of coupling to antisymmetric cladding modes in arc-induced long-period fiber gratings - art. no. 66190X

Authors
Ivanov, IV; Caldas, P; Rego, G;

Publication
Third European Workshop on Optical Fibre Sensors

Abstract
We study the origin of antisymmetric perturbation of the fiber in are-induced long-period gratings that couple the core mode into the antisymmetric cladding modes. We demonstrate that this perturbation is caused by a temperature gradient in the fiber, which is induced, in turn, by a temperature gradient in the arc discharge.

2007

<title>In-fibre Mach-Zehnder configuration based on fibre multimode interference structure combined with a long period grating</title>

Authors
Frazão, O; Viegas, J; Caldas, P; Araújo, FM; Ferreira, LA; Santos, JL; Farahi, F;

Publication
Third European Workshop on Optical Fibre Sensors

Abstract

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