Publications

Publications by CAP

1999

<title>Active WDM demodulation scheme for fiber Bragg grating sensors</title>

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

Publication
Fiber Optic and Laser Sensors and Applications; Including Distributed and Multiplexed Fiber Optic Sensors VII

Abstract

1999

Demodulation of fiber Bragg grating sensors based on dynamic tuning of a multimode laser diode

Authors
Ferreira, LA; Diatzikis, EV; Santos, JL; Farahi, F;

Publication
APPLIED OPTICS

Abstract
Dither demodulation of fiber Bragg grating sensors illuminated with multimode light from laser diodes is theoretically and experimentally investigated. Quasi-static temperature and strain sensitivities of 0.09 degrees C/root Hz and 0.6 mu epsilon/root Hz are obtained. We show that it is possible to measure small ac signals that lie outside the feedback loop bandwidth by using a synchronous detection referenced to twice the dither frequency. In this situation, dynamic strain sensitivity of 3.3 n epsilon/root Hz is achieved. (C) 1999 Optical Society of America.

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1999

Simultaneous measurement of strain and temperature using Bragg gratings written in germanosilicate and boron-codoped germanosilicate fibers

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

Publication
IEEE PHOTONICS TECHNOLOGY LETTERS

Abstract
A new fiber Bragg grating sensor configuration is presented for simultaneous measurement of strain and temperature. The sensor utilizes the effect of boron codoping on the temperature dependence of the refractive index in germanosilicate fibers. By writing gratings with close wavelengths in undoped and boron doped fibers, different temperature sensitivities are obtained while strain sensitivities remain the same. These gratings are then spliced to obtain a simple sensor head suitable for applications in smart structures and composite materials.

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1999

Dynamic range enhancement in fiber Bragg grating sensors using a multimode laser diode

Authors
Moreira, PJ; Ferreira, LA; Santos, JL; Farahi, F;

Publication
IEEE PHOTONICS TECHNOLOGY LETTERS

Abstract
A signal processing scheme for fiber Bragg grating sensors based on the utilization of adjacent modes of a multimode laser diode light source is demonstrated which allows high sensitivity to be obtained over a large measurement range, For strain measurements, a range of 4800 mu epsilon is achieved with a resolution of 0.08 mu epsilon/root Hz, yielding a dynamic range of 95 dB.

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1999

Sagnac topology for a self-referencing fiber optic sensor

Authors
Baptista, JM; Santos, JL; Lage, AS;

Publication
Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS

Abstract
A sensor based on a Sagnac topology in reflection is described. The sensor uses the properties of its frequency response in order to obtain a self-referenced signal proportional to the measured signal. The sensor is a versatile structure for the monitoring of static and dynamic physical parameters, which require a small number of optical components and simple signal processing.

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1999

Dynamic tuning of a multimode laser diode for fibre Bragg grating demodulation

Authors
Ferreira, LA; Santos, JL; Diatzikis, EV; Farahi, F;

Publication
OFS-13: 13TH INTERNATIONAL CONFERENCE ON OPTICAL FIBER SENSORS & WORKSHOP ON DEVICE AND SYSTEM TECHNOLOGY TOWARD FUTURE OPTICAL FIBER COMMUNICATION AND SENSING

Abstract
Dither demodulation of fibre Bragg grating sensors illuminated with multimode light from cheap compact disc laser diodes is investigated. Quasi-static temperature and strain sensitivities of 0.09 degrees C/root Hz and 0.6 mu epsilon/root Hz are obtained. It is shown that small ac signals outside the loop bandwidth can be measured using synchronous detection at double the dither frequency.

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