Temperature and strain measurement by using cascaded chirped long period fiber gratings

Highly precise fiber optic strain and temperature measurements using chirped long period fiber grating (CLPG) are proposed and demonstrated, in which cascaded CLPGs (C-CLPGs) are employed as the sensing element and a Fourier transform technique is applied for the interrogation scheme. In this technique, strain and/or temperature-induced wavelength shift is determined precisely from the cross-correlation or cross-spectrum between the original and shifted channeled spectrum. In the experiment, C-CLPGs are fabricated by UV-irradiation technique, and strain and temperature characteristics are investigated. The highly precise measurements are confirmed by comparing with the results of the peak tracking method.