Nonresonant cascaded acousto-optic mode coupling

Nonresonant cascaded acousto-optic mode coupling under an overall phase-matching condition is presented, where phase matching is not satisfied for each of the coupling stages but the sum of the two acoustic momenta matches the optical phase detuning between the source mode and the destination mode. As a special nonresonant cascaded case, conversion from LP₀₁ to LP₂₁ and LP₀₂ driven by a single acoustic frequency is predicted theoretically and demonstrated experimentally.