We theoretically analyze acousto-optic (AO) mode conversion between optical orbital angular momentum (OAM) modes using an elastic vortex wave (EVW) carrying OAM in a squared graded index (GI) fiber. The AO mode conversion from the fundamental mode to the higher order optical OAM mode is a useful technology to generate optical OAM modes in the GI fiber. This paper clarify the contribution of each component of the dielectric constant perturbation caused by the EVW to the AO mode conversion
