Parametric studies of whispering-gallery mode resonators

Abstract

This report characterizes the whispering-gallery mode (WGM) resonators with the design of waveguide and microdisk coupling microstructure. In order to understand and optimize the design, studies over a broad range of resonator configuration parameters including the microdisk size, the gap separating the microdisk and waveguide, and the waveguide width are numerically conducted. The finite element method is used for solving the Maxwell's equations which govern the propagation of electromagnetic (EM) field and the radiation energy transport in the micro/nano-structured WGM systems. The EM field and the radiation energy distributions in the WGM resonator are obtained and compared between the on-resonance and off-resonance cases. A very brilliant ring with strong EM field and high radiation intensity is found inward the peripheral surface of the microdisk under the first-order resonance. While under the second-order resonance, there are two bright rings; and the outer ring inward the peripheral surface is thin and weaker than the internal ring. The microdisk size affects significantly the resonant frequencies and their intervals. The gap also has a slight effect on the resonant frequencies. The effect of waveguide width on the resonant frequencies is negligible. However, the gap as well as the waveguide width does obviously influence the qualify factor and the finesse of the resonant modes.