Theoretical analysis of acoustic-optic frequency shifter by dual mode fiber

Abstract

The frequency shifting between two modes in an optical fiber resulting from acoustic wave propagation has been studied theoretically. Our theoretical results confirm the earlier experimental work. The polarization effect introduced by acoustic waves has been examined as well. The analysis shows that the polarization characteristic and symmetry property of the modes are not preserved in the coupling process of acoustic-optic frequency shifting for arbitrary ratio of the fiber cladding radius to the acoustic wavelengthd/λa, in contrast to stable mechanical microbending, and that for the givend/λa = 0.397, the polarized light signal at frequencyω2, shifted from that at frequencyω1, is quasi-linearly polarized for any acoustic-optic interaction length. However, the polarization effect can be neglected when the fiber cladding radius is much smaller than the acoustic wavelength.