Efficient Inscription of High Quality FBGs on ZBLAN Fiber With a Femtosecond Laser

An efficient inscription method for low insertion loss fiber Bragg gratings in ZBLAN fiber is presented, and the effects of femtosecond laser with different pulse numbers and repetition rate on the morphology of the refractive index modulation region and the insertion loss of ZBLAN fiber gratings were investigated. It is experimentally proved that the thermal effect of multiple pulses of high repetition rate femtosecond lasers avoid the generation of microcracks in the process of grating preparation, which greatly reduces the insertion loss. At the same time, the efficiency of grating inscription was greatly improved by utilizing the spherical aberration, the self-focusing effect in ZBLAN fiber and the parallel inscription technique. Finally, a parallel-integrated fiber Bragg grating consisting of three fiber Bragg gratings was inscribed on a ZBLAN fiber in 2.5 minutes by using 1 MHz femtosecond laser burst mode with a reflectivity of 99.6% and an insertion loss of only 0.1 dB, and the temperature sensitivity of this FBG was tested to be 26.17 pm/ °C.