Deeply Nonlinear Magnonic Directional Coupler.

Abstract

Dipolar coupling between closely spaced magnetic waveguides enables magnonic directional couplers serving as signal combiners, power splitters, demultiplexers, and more. The wavelength-dependent coupling, combined with the weak nonlinear variation of spin-wave wavelength at constant frequency, introduces power-dependent characteristics of directional couplers. This property has been utilized in magnonic logic elements and other applications. Here, we explore a different nonlinear phenomenon in a directional coupler arising purely from the spin-wave nonlinear frequency shift. A strong nonlinear frequency shift causes the coupler to behave as if composed of nonidentical waveguides, suppressing energy transfer between the waveguides. The transition from complete to negligible energy transfer exhibits a sharp threshold behavior, with the critical power determined by the coupling strength and nonlinear frequency shift parameter. Based on these findings, a switchable directional coupler with potential to operate at higher frequencies of exchange-dominated spin waves for magnonic circuits is designed and validated by micromagnetic simulations.