Adjustment of the chirp parameter of chirped fibre Bragg gratings

A method for accurately adjusting the chirp parameter of the fabricated chirped fibre Bragg gratings (CFBGs) is demonstrated experimentally. By establishing different strain gradients with proper profiles along the length of CFBGs, one can not only increase or decrease the chirp of the CFBG, but also change the sign of the chirp without exchanging the two ends of the grating. The variance of the chirp's amplitude can be accurately tuned through varying the amplitude of the strain gradient. Moreover, the grating's reflectivity hardly decreases and the shape of the reflection spectrum stays good during the adjustment of the chirp.