Chirality-switchable acoustic vortex emission via non-Hermitian selective excitation at an exceptional point

Abstract

Artificial structures provide an efficient method to generate acoustic vortices carrying orbital angular momentum (OAM) essential for applications ranging from object manipulation to acoustic communication. However, their flexibility in terms of chirality control has thus far been limited by the lack of reconfigurability and degrees of freedom like spin–orbit coupling. Here we show that this restriction can be lifted by controlling the individual on–off states of two coherent monopolar sources inside a passive parity-time-symmetric ring cavity at an exceptional point where the counter-propagating waves coalesce into one chiral eigenmode. One of the sources satisfies the chirality-reversal condition, generating a travelling wave field fully decoupled from and opposite to the chiral eigenmode, while the other source is phase-shifted such that the wave generated by the first source can be canceled out, and the remaining sound field circulates in the same direction as the chiral eigenmode. Such non-Hermitian selective excitation enables our experimental realization of acoustic vortex emission with switchable OAM but free of system reconfiguration. Our work offers opportunities for chiral sound manipulation as well as integrated and tunable acoustic OAM devices.