Unique temperature sensing characteristics of CO2-laser-notched long-period fiber gratings

Long-period fiber gratings (LPFGs) are written by use of a focused CO₂ laser beam to notch periodically on the surface of optical fibers. Temperature characteristics of the CO₂-laser-notched LPFG are investigated in detailed to develop its sensing applications. It is shown that, for such LPFG, temperature sensitivity of resonant wavelength can be increased by creating deeper notches. The coupling from the fundamental core mode to a cladding mode in the LPFG can be enhanced by increasing the ambient temperature. The polarization-dependent loss (PDL) of the LPFG depends strongly on the ambient temperature. Such unique temperature characteristics can be used to solve the cross-sensitivity problem between the temperature and the tensile strain. So, the LPFG is a promising temperature sensor based on the wavelength modulation, on the intensity modulation and/or on the PDL modulation.