Spectral characteristics of cascaded long-period gratings

The transmission spectrum of cascaded long-period fiber grating has many advantages, such as large amplitude of diffraction peak, various spectral types and so on. The transmission spectra of cascaded long-period grating (LPG) were analyzed by using transfer matrix method. The effects of distance, position and phase-shift related to the LPGs on the cascaded spectral characteristics were discussed. And the cascaded and phase-shifted long-period grating spectra were compared. The results show that the spectra of phase-shifted LPG and cascaded LPG have great consistency when the cascading position is near the end of the cascaded LPG or the distance between the cascading fibers is small. And for phase-shifted LPG, when several phase-shifts are inserted, the interval of the two main-stop-bands broadens with the increase of the number of phase-shifts inserted.