Long-period fiber grating with multi resonant wavelengths fabricated by a CO2 laser for distributed sensing

A multi long-period grating (multi-LPG) sensor was investigated and fabricated by a CO₂ laser for distributed sensing to detect abnormal high temperatures of a nuclear power generator and a large-scale chemical plant. To fabricate the multi-LPG sensor, a carved LPG was introduced for easy fabrication of the multi-LPGs with different resonant wavelengths in a similar loss spectrum. It was investigated experimentally how the CO₂ laser beam is scanned for the carving. The influence of the irradiated energy of the CO₂ laser on carving has been clarified, and it was found that a minimum irradiated energy of the CO₂ laser existed, and the value was determined to be 0.23 J/mm. As a result, the carved LPG could be fabricated and the resonant wavelength could be shifted successfully for the distributed sensor. The procedures for the fiber carving and the fundamental characteristics of the carving are described in details.