Concave diffraction grating for whispering-gallery mode selection

Using simulation in the FDTD technique it was demonstrated that the strip-like diffraction gratings are the promising candidate for whispering-gallery mode selection. The essence of the selection process is as follows: The incident wave is transformed to the surface one by a strip-like diffraction grating at the dielectric substrate if the condition λ / 2 = P is fulfilled. If the diffraction grating applies to the lateral surface of the dielectric resonator, the direction of the surface wave is coincident with the propagation direction of the whispering-gallery mode. If geometrical dimentions of the grating and resonator are chosen in such a way that the integer number of half waves n fits the lateral surface of the resonator, the surface wave serves to excite the whispering-gallery mode with azimuthal number n. The other waves go off into outer space.