Defect-Free Phononic Crystal Waveguides on GaAs

A phononic crystal waveguide is presented that consists of the inverse of a typical structure. Instead of a defect waveguide within an extended phononic crystal, this waveguide consists of a phononic crystal of finite width, and the phononic crystal itself is composed of a shallow array of holes. The acoustic velocity is actually reduced in the phononic crystal region, which subsequently enables the waveguiding of the acoustic wave underneath the micro-structured surface. As the width of the waveguide increases with the number of inclusions, the waveguide morphs from an unstructured surface to an extended phononic crystal with a transitional modal region of an intermediate number of inclusions that is suitable for waveguiding. For the chosen phononic crystal parameters in terms of the hole depth and filling fraction, the optimum waveguide width of four inclusions is determined.