Mechanically-induced π-shifted long-period fiber gratings.

A band-pass filter based on mechanically-induced multi-π-shifted long-period fiber gratings is proposed. The pass band width of the filter depends on the number N of the sub-gratings divided by π-shifts in the long-period fiber grating. The depth of the two lateral rejection bands can be changed by the amount of pressure applied to the fiber. This paper demonstrates a multi-π-shifted long-period fiber grating created by pressing a fiber between two periodically grooved plates. For N = 7 and LP12 mode coupling, the extinction ratio is 22.22 dB, and the pass band loss is 0.85 dB. For LP12 mode coupling, the pass band width varies from 14.23 nm to 39.31 nm when N increases from 2 to 10.