Temperature sensor using a Long Period Fiber Grating Fabricated by 800 nm Femtosecond Laser Pulses

In this letter, LPFGs in standard telecommunication fibers without hydrogen loading were fabricated in air using laser direct writing method, by femtosecond laser pulses with pulse duration of 200 fs and output wavelength of 800 nm. The loss peak of 1430 nm, the transmission loss of 22.86 dB and the FWHM of 6.6 nm were obtained. Temperature dependence of wavelength shift in air was measured by placing the LPFG in a temperature chamber that is temperature controlled in the range of 70-150 degrees C. The temperature sensitivities (Delta lambda/Delta T) are estimated by using linearly regression fits, which was 43.2 pm/degrees C. The linearity of the temperature sensitivities is high and the R-squared values for Delta lambda/Delta T is larger than 0.9979.