The Improvement of the Backward Cladding–Core Coupling in a Tilted Fiber Grating by Two Acoustic Flexural Waves

The cladding modes of a tilted fiber grating can be coupled back to the core modes by acoustooptic interactions. However, the coupling of high-order diffractions by acoustic-optic interaction is not apparent, owing to the insufficiency of acoustic power. In this paper, we will demonstrate that as two acoustic flexural waves with appropriate frequency are launched to a tilted fiber Bragg grating, high-order harmonic acoustic waves can be superposed to improve the coupling efficiency between the backward cladding modes and core modes. This phenomenon may be applied to induce several optical channels for multichannel laser and wavelength-division multiplexing filters.