Analysis of dielectric circular cylinder light spot narrowing by whispering gallery modes and influence of material absorption

Abstract

We present results of numerical analysis of the diffraction of a plane monochromatic TE-wave on an ideal homogeneous dielectric cylinder with several resonant wavelength scale radii. Two subsequent near-surface maxima of intensity (two focuses) generated at the cylinder output were found on the optical axis. The first subwavelength focus is formed by one of the whispering gallery mode lobes. Its intensity is 50 times the incident light intensity and its full width at the half maximum of the intensity is equal to 0.155 of the incident wavelength. The second focus is two times less in intensity. Its focal spot known as a photonic nanojet is stretched toward the optical axis. The second focus is formed at a distance about the wavelength from the cylinder surface. Its width is equal to 0.44 of the wavelength and its length is two wavelengths. The influence of material absorption on the light focusing is also examined by numerical simulation.