Spectra of long-period fiber grating fabricated by 800 nm femtosecond laser pulses

Long-period fiber gratings(LPFGs) with the periods of 100, 200, 300 and 400 m were fabricated in standard telecommunication fibers in air using laser direct writing method. Spectra of the LPFGs from 1 280 nm to 1 680 nm were obtained under different experimental conditions, in which the resonant wavelengths, the maximum transmission losses and the insertion losses were observed. By optimizing the experimental parameters, LPFGs were fabricated with the resonant wavelengths of 1 407, 1 311, 1 669, and 1 551 nm, respectively. The maximum transmission losses were about 24.0 ， 22.3 ， 27.8 , and 23.4 dB, and the insertion losses were about 2.5 ， 1.7 ， 3.2 ， and 2.0 dB, respectively.