2019/11/08 by Lan, Jun, Zhang, Xiaowei, Wang, Liwei +2
#Applied Physics (physics.app-ph) #FOS: Physical sciences #Optics (physics.optics)
paper · doi:10.48550/arxiv.1911.03138
Negative refraction plays an important role in acoustic wave manipulation and imaging. However, conventional systems based on acoustic metamaterials suffer from the limits induced by loss-related and resolution issues. In this work, a parity-time (PT)-symmetric system is introduced to realize loss-free bidirectional acoustic negative refraction. The system is composed of a pair of locally PT-symmetric multi-layer metasurfaces sandwiching a region of free space, which also forms a global PT-symmetry. The property of bidirectional negative refraction, which is rare for regular PT-symmetric structures, is related to the coexistence of amplification and absorption in the locally PT-symmetric metasurfaces at their PT broken phases. Such metasurfaces can freely switch their states between coherent perfect absorber (CPA) and amplifier depending on the direction of incidence. Our results provide a new physical mechanism for realizing bidirectional functions in PT-symmetric systems.