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, th...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.展开更多
基金supported by Research Grants Council of Hong Kong(C6013-18G,15211918,and 15205219)the National Natural Science Foundation of China(11774297)+4 种基金support from the National Natural Science Foundation of China(12104383)Internal Research Fund of The Hong Kong Polytechnic University(ZZLC)supported by Hong Kong Research Grants Council(12302420,12300419,and 22302718)the National Natural Science Foundation of China(11922416 and 11802256)Hong Kong Baptist University(RC-SGT2/18-19/SCI/006)。
文摘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.
