Fabrication of high-temperature tilted fiber Bragg gratings using a femtosecond laser.

We developed a new method to fabricate tilted fiber Bragg gratings (TFBGs) by using a femtosecond laser with a phase mask. During the laser processing, the fiber was obliquely moved at a tilt angle, in which the laser beam and the phase mask were fixed. The peak loss of the cladding modes with a tilt angle of 4.9° reaches to ~-8 dB, and the insertion loss is less than -0.2 dB. The TFBG was stable at temperature up to 700°C and slight degraded at 800 °C. The temperature sensing of the TFBG was demonstrated at a high temperature up to 800°C. The temperature sensitivities of the Bragg mode, the ghost mode, and the cladding mode were measured to be 15.72 pm/°C, 15.56 pm/°C, and 15.52 pm/°C, respectively. The refractive index response of the TFBGs was also measured.