Mode conversion in nonlinear waveguides stimulated by the longitudinal bi-harmonic refractive index modulation

Abstract

We study specific features of resonant mode conversion in nonlinear waveguides stimulated by the bi-harmonic longitudinal modulation of its parameters, which includes changes of the waveguide depth as well as its bending (in the one-dimensional case) or spiraling (in the two-dimensional case). We demonstrate the possibility of simultaneous excitation of higherorder modes of different parities and topologies with controllable energy weights. The output mode composition is highly sensitive to the variation in the input power and detuning from the resonant modulation frequency.

Resonant Bloch-wave beatings

“…However, if the array consists of multimode waveguides, the rate of light energy transport across the structures and the amplitude of the collective Bloch oscillations may strongly depend on the particular superposition of the excited individual modes, due to difference in the overlap integrals of different modes with neighboring waveguides [19]. In that scenario, resonant mode conversion utilizing longitudinal waveguide modulation [15], affords rich possibilities for the dynamical control of the weights of guided modes and, therefore, the global diffraction rate [20,21]. Different approaches are available to realize resonant mode conversion, including periodic mechanical stress and photo-induced gratings [22][23][24].…”