Laser radio-frequency and cavity-enhanced interrogation techniques for strain sensing by fiber Bragg gratings

Year: 2006

Authors: Gagliardi G., Salza M., Ferraro P., De Natale P.

Autors Affiliation: CNR – Istituto Nazionale di Ottica Applicata, Via Campi Flegrei 34, 80078 Pozzuoli (NA), Italy

Abstract: We report on the implementation of novel, highly sensitive methods for strain measurements using FBG-based sensors. Basically, the strain detection technique rely on frequency modulation of a 1560-nm pig-tailed diode laser in the radio-frequency range with phase-sensitive detection of the FBG reflected signals. In one set-up, the power directly reflected by the fiber grating is demodulated at multiples of the sideband frequency. A different approach is based instead on using as a sensor an in-fiber Fabry-Pdrot cavity, made of an FBG pair with very high peak reflectivity (> 99 %). Static and dynamic deformation can be applied to the sensors in a controlled manner thanks to a piezoelectric actuator and a loud speaker. In the first case, a minimum detectable strain of the order of 100 n epsilon/root Hz, in the quasi-static domain (0.5 divided by 2 Hz), and 2 nE/root Hz around 1 kHz. An FFT analysis of the output signals reveals the possibility of tracing dynamic strains up to 20 kHz, this limit being set only by the test device bandwidth. For the fiber interferometer set-up, similar tests have been performed using an electrical strain gauge as a reference probe. The diode laser, in this case, is actively frequency-locked to the FBG cavity, using the Pound-Drever-Hall technique. The resulting error signal is used as a monitor of strain suffered by the cavity fiber. We show that a sensitivity gain of at least one order of magnitude can be obtained with this scheme.


Volume: 6162      Pages from: 616208  to: 616208

More Information: This work was funded by the Italian Ministry for Education, University and Research in the framework of \”Progetto PON-Simona\”. Authors wish to thank Roberto Abbate for his technical support in mounting and testing of electronic circuits, and Torsten Thiel (AOS GmbH, Dresden) for helpful and stimulating discussions.
KeyWords: strain sensors; fiber Bragg grating; diode laser; frequency modulation; high-finesse cavity
DOI: 10.1117/12.674952

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