Study on asymmetric diffraction of acoustic parity-time-symmetric gratings using rigorous coupled-wave analysis

The method of rigorous coupled-wave analysis (RCWA) is developed to analyze the diffraction properties of acoustic parity-time-symmetric gratings. Asymmetric diffraction can be generated in these gratings, and the +1st order transmitted wave is suppressed completely at the diffraction vanishing point (DVP). The influence factors of the modulation ratio of the DVP, including the modulation amplitude and modulation approach, are systematically discussed using the method of RCWA. Two-beam diffraction with Bragg incident angle is studied in detail. The results show that the modulation ratio of the DVP changes with the modulation amplitude differently for different modulation approaches. The attenuation or enhancement of the sound energy depends on the sign of incident angle and the modulation ratio.