Review of bandgap characteristics and acousto-optical coupling in phoxonic crystals

Phoxonic crystals are periodic structures which possess photonic and phononic bandgaps simultaneously. Phoxonic crystals can be applied as systematic platforms for manipulating electromagnetic and elastic waves simultaneously, and can be utilized in various fields such as optical, acoustic and acouto-optical devices, and cavity optomechanics. This paper firstly introduces the basic concepts of phoxonic crystals, including the constituting materials, their classifications according to spatial periodicity, the numerical calculation methods of band structures. We elaborate the characteristics of phoxonic dual bandgaps for different systems, and the topology optimization method applied in optimizing the bandgap width of phoxonic dual bandgaps. The field of cavity optomechanics, as well as the quasistatic method and optomechanical coupling coefficient method for evaluating the acousto-optical coupling strength are introduced. The acousto-optical coupling phenomena in various phoxonic crystal structures are summarized. Then this paper introduces the research works related to phoxonic crystal waveguides and sensors. Finally, we outline the prospects of phoxonic crystals based on state of the art, including the enhancements of acousto-optical interaction in phoxonic crystal cavities, the investigations of three-dimensional phoxonic crystals, the designs of different phoxonic metamaterials, the phoxonic crystal device designs and related applications, and so on.