Suppression of high-radial-order whispering-gallery modes and directional emission of anisotropic cylindrical microcavity

Suppression of high-radial-order whispering-gallery modes in a cylindrical microcavity made of electric anisotropic medium was studied by the finite-difference time-domain method. While the electric anisotropy of the microcavity medium increases, the quality factors of high-radial-order whispering-gallery modes decrease more quickly to zero than those of first-radial-order whispering-gallery modes. Thus, for an anisotropic cylindrical microcavity with large enough anisotropy, the spectrum consists of only those resonant peaks corresponding to first-radial-order whispering-gallery modes. This novel characteristic results in widening of the free spectral range of the cylindrical microcavity. Therefore, the anisotropic cylindrical microcavity has potential applications in single-mode low-threshold microlasers and narrow-linewidth wavelength-selective filters.