Restoring whispering gallery modes with transformation optics

Whispering gallery modes (WGMs) have ultra-high quality factor but only non-directional light emission property. We suggest a novel way to restore WGM in resonant cavity of deformed boundary shape with Transformation optics. Conformal mapping make it possible with only density controlled isotropic material. FEM and microwave near-field scanning result prove that our idea is working. It is expected to be applied to wide range of optical cavity.