Twist effect on spectral properties of two-mode fiber acousto-optic filters.

The splitting and the shift of resonance peaks in the output spectrum of two-mode fiber acousto-optic devices caused by twist perturbation are described. An elliptical-core two-mode fiber and a two-mode photonic-crystal fiber are used for the analysis. The splitting of the resonance peaks are found to be almost linearly proportional to the twist angle of the fiber with the slopes of about 0.58 nm/(rad/m) for the elliptical-core fiber and about 0.29 nm/(rad/m) for the photonic crystal fiber. The experimental results compare well with the theoretical predictions.