Center-Shift Circular Transformation Cavity.

We analyzed the characteristics of conformal whispering gallery modes according to pure spatial refractive index variation without boundary deformation in two-dimensional center-shift circular transformation cavity designed in an alternative scheme without using resizable parameter. Through this, we confirmed that the isotropic emission of whispering gallery mode in the circular cavity with homogeneous refractive index is transformed into the bi-directional emission of conformal whispering gallery mode as the degree of center-shift increased. Also, using a newly defined purity factor that quantitatively measures the modulus of distortion, it was verified that the internal wave property of the whispering gallery mode maintained almost intact in the conformal whispering gallery mode.