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Publications

Publications by CAP

2002

Nonlinear mode coupling in a CW operating Ti: Sapphire laser oscillator

Authors
Cataluna, MA; Crespo, H; Guerreiro, A; Mendonca, JT;

Publication
PHYSICA SCRIPTA

Abstract
We experimentally observe a high-contrast intensity modulation in the multimode CW output of a Titanium:Sapphire laser, This modulation has a very low frequency (in the hundreds of Hz range), being stable and self-sustaining, unlike previously reported regimes which require external perturbations such as a periodic change in the resonant cavity length. This effect results from the nonlinear coupling of several longitudinal modes with very large frequency spacing (of the order of tens of THz) which arise due to mode competition violation (promoted by dispersion control within the laser cavity), associated with the large gain bandwidth of Ti:Sapphire, To our knowledge, this is a previously unreported phenomenon. for which we are currently developing an adequate theoretical model. These results may prove useful in the further understanding of the onset of mode-locked operation in ultrashort lasers and other highly nonlinear systems.

2001

Temperature and strain insensitive bending measurements with D-type fibre Bragg gratings

Authors
Araujo, FM; Ferreira, LA; Santos, JL; Farahi, F;

Publication
MEASUREMENT SCIENCE & TECHNOLOGY

Abstract
We present a new sensor configuration based on the intrinsic bend sensitivity of Bragg gratings written in D-type fibres. This sensor can be embedded in any layer of a composite material to evaluate curvature in a way independent of axial strain and temperature. It can also be used to measure other parameters such as acceleration, angle and acoustic pressure.

2001

Twin all-optical magnetic probe for current metering and relaying applications

Authors
Caldas, P; Jorge, PAS; Ferreira, LA; Lobo Ribeiro, AB; Santos, JL;

Publication
2001 IEEE Porto Power Tech Proceedings

Abstract
A twin polarimetric configuration based on the Faraday effect for the measurement of electric currents in high voltage environments is presented. Field test results are shown that indicate the device suitability for current metering and relaying applications. © 2001 IEEE.

2001

Passive interrogation of low-finesse Fabry-Perot cavities using fiber Bragg gratings

Authors
Dahlem, M; Santos, JL; Ferreira, LA; Araujo, FM;

Publication
IEEE PHOTONICS TECHNOLOGY LETTERS

Abstract
An investigation on the application of fiber Bragg gratings for the interrogation of interferometric low-finesse Fabry-Perot cavities is reported. The proposed scheme is based on the generation of two quadrature phase-shifted signals that allows the recovering of the change in the cavity length. Besides being totally passive, this technique offers a high degree of flexibility and has the potential to be used in the interrogation of very short cavities.

2001

Interrogation of low-finesse Fabry-Perot cavities based on modulation of the transfer function of a wavelength division multiplexer

Authors
Misas, CJ; Araujo, FMM; Ferreira, LA; Santos, JL; Lopez Higuera, JM;

Publication
JOURNAL OF LIGHTWAVE TECHNOLOGY

Abstract
A theoretical and experimental investigation is reported on a novel all-fiber technique for interrogation of interferometric low-finesse Fabry-Perot cavities, It is based on the modulation of the spectral transfer function of a wavelength-division multiplexer, Results are given when both serrodyne and sinusoidal modulation formats are considered.

2001

Multiplexing of fibre optic intensity sensors using fused biconical wavelength selective couplers

Authors
Abad, S; Araujo, FM; Ferreira, LA; Santos, JL; Lopez Amo, M;

Publication
ELECTRONICS LETTERS

Abstract
Fused biconical wavelength division multiplexers have been used to replace standard couplers in an intensity-sensor multiplexing network. The wavelength-selective power splitting and the low insertion losses of these devices (< 0.2dB) improve the power budget, while providing network overall optical isolations > 30dB. With this isolation, crosstalk effects in the network are proven to be negligible.

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