Topologically protected dual-wave rainbow trapping and robust acousto-optic interaction in valley phoxonic crystals

Abstract Rainbow trapping, which involves the separation and confinement of waves of different frequencies at various spatial positions, has garnered significant attention due to its promising applications in energy harvesting, selective filtering, and the slowing down of light and sound. However, previous studies on the rainbow trapping of electromagnetic waves and elastic waves have been conducted independently. This has limited applications in dual optomechanical devices. In this study, we present topological rainbow trapping of electromagnetic and elastic waves along a gradient waveguide composed of two phoxonic crystals featuring distinct valley topological phases. Subsequently, a phoxonic crystal cavity is constructed by a double-directional gradient waveguide, which shows robust cavity modes and acoustic-optic interaction. Our work offers an alternative approach for simultaneously trapping electromagnetic and elastic waves within the same waveguide across various frequencies, holding the potential for innovative topological optomechanical devices.