Strong field enhancement of resonance modes in dielectric microcylinders

Abstract

A loss-free compact dielectric microcylinder acting as an optical resonator is studied in the present work by means of the spectral element method. A specific whispering gallery mode (WGM) supported by the structure is constantly tracked under the same type of illumination while varying the diameter of the resonator between similar to 5 lambda and 8 lambda (lambda = wavelength of light). The parameter space of the optical resonator informs us that it is possible to have either a larger radius of microcylinder with a smaller refractive index or a smaller radius of microcylinder with a larger refractive index value. Two different scenarios are also considered in the current study in order to verify the strong field confinement; one is under Bessel beam illumination conditions and the other is the introduction of nonhomogeneity in the material forming the cylinder. Strong power enhancement up to 3 orders of magnitude is attainable with small microcylinders. While the refractive index changes from 1.50 to 2.25, the corresponding radius utilizing the same type of WGM has to be carefully captured with fine tuning. It is imperative to increase the number of significant digits from 3.9380 lambda to 2.6600939 lambda in order not to miss such huge field enhancement phenomena. Standard resonance condition for constructive interference does not give us targeted parameters. The study may pave the way toward a new technique to detect nanoscale objects below the diffraction limit and may contribute to a new ultramicroscopy technique for detecting single molecules by low-threshold microcavity lasers. Additionally there are nonlinear optics applications. (C) 2016 Optical Society of America