A phase-shifted long period fiber grating based on filament heating method for simultaneous measurement of strain and temperature

We proposed and fabricated a $\pi -phase-shifted$ long period fiber grating (PS-LPG) for simultaneous measurement of strain and temperature. The $\pi -PS-LPG$ is fabricated by inscribing micro-tapers on a pre-tapered fiber using the filament heating method. When the temperature or strain varies, the wavelengths of both transmission notches shift in the same direction, whereas the depths of the notches change in different directions. Therefore, the sensitivity of the PS-LPG can be improved by detecting the depth difference between the two notches, and simultaneous temperature and strain measurements can be achieved from the variation of the wavelength and the depth difference. Experimental results show that the wavelength sensitivities can reach a maximum of respectively −1.5 nm mϵ ⁻¹ and $52pm{}^{\circ }{C}^{-1}$ for strain and temperature, and the depth sensitivities are as high as −4.6 dB mϵ ⁻¹ and −0.06 dB °C⁻¹, respectively. (paper)