Whispering gallery modes in a dielectric cylinder with circular cross-section

As a result of diffraction of a plane monochromatic TE-wave by an ideal homogeneous dielectric cylinder with a wavelength-scale resonant radius, two on-axis near-surface focal spots are generated at the cylinder output. The first subwavelength focal spot is formed by a whispering gallery mode. Its peak intensity is 50 times the intensity of the incident plane wave, and its full width at half maximum can reach 0.155 of the incident wavelength. The second focal spot intensity is half as much as that of the first one. This focal spot, which is also known as the photonic nanojet, is stretched towards the optical axis. Its width is 0.44 of the wavelength, while the length can reach two wavelengths. In this paper, we numerically analyze the focusing ability of a two-layered cylinder and effects of the material absorption on the results of focusing of the whispering gallery mode.