All-optical signal gating in cascaded long-period fiber gratings

An all-optical signal gating has been demonstrated in cascaded long-period fiber gratings using cross-phase modulation by means of Q-switched pump wav e packets. The obtained cascaded twin long-period fiber gratings showed an extremely narrow band of rejection of 0.5-nm bandwidth, Using this narrowba nd rejection filter, all-optical switching efficiency in long-period fiber grating devices could he enhanced so that they can be operated with relativ ely lo iv pump intensities. Approximately a 20% modulation depth of a signa l wave at 1565 nm was obtained with a pump intensity of 1 GW/cm(2) at 1064 nm, The experimental results are in good agreement with numerical expectati ons by the discretized coupled-mode theory, which was previously proposed f or the nonlinear long-period fiber grating analysis.