Ultrahigh-Q system of a few coaxial disks

Resonant modes of high contrast dielectric disk have finite Q-factors in the subwavelength range due to radiation leakage into the surrounding space. That leakage can be reduced considerably (a few times) by exploiting of the mechanism of destructive interference of two modes for avoided crossing of resonances (ACR) (Rybin et al. M. V. Rybin, K. L. Koshelev, Z. F. Sadrieva, et al., “High-Q Supercavity Modes in Subwavelength Dielectric Resonators,” Phys. Rev. Lett., vol. 119, p. 243901, 2017.). In the present paper we report suppression of radiation leakage by a few orders in magnitude via the ACR in the structure of three and four different coaxial disks. For fine multi-scale tuning of disks we reveal the ultrahigh-Q resonances of order 105 for the case of three disks and of order 106 for the case of four coaxial disks of equal radii.

Mie Resonance Engineering in Two Disks

Recently the recipes to achieve the high-Q subwavelength resonances in an isolated dielectric disk have been reported based on avoided crossing (anticrossing) of the TE resonances under variation of the aspect ratio of the disk. In a silicon disk that recipe gives an enhancement of the Q factor by one order of magnitude. In the present paper we present the approach based on engineering of the spherical Mie resonances with high orbital index in two coaxial disks by two-fold avoided crossing of the resonant modes of the disks. At the first step we select the resonant modes of single disk which are degenerate because of the opposite symmetry. Approaching of the second disk removes this degeneracy because of interaction between the disks. As a result at certain distances we realize the hybridized anti-bonding resonant modes whose morphology becomes close to the spherical Mie resonant mode with high orbital index. Respectively the Q factor of the anti-bonding resonant mode can be enhanced by three orders of magnitude compared to the case of single disk.

A Fast-Converging Scheme for the Electromagnetic Scattering from a Thin Dielectric Disk

In this paper, the analysis of the electromagnetic scattering from a thin dielectric disk is formulated as two sets of one-dimensional integral equations in the vector Hankel transform domain by taking advantage of the revolution symmetry of the problem and by imposing the generalized boundary conditions on the disk surface. The problem is further simplified by means of Helmholtz decomposition, which allows to introduce new scalar unknows in the spectral domain. Galerkin method with complete sets of orthogonal eigenfunctions of the static parts of the integral operators, reconstructing the physical behavior of the fields, as expansion bases, is applied to discretize the integral equations. The obtained matrix equations are Fredholm second-kind equations whose coefficients are efficiently numerically evaluated by means of a suitable analytical technique. Numerical results and comparisons with the commercial software CST Microwave Studio are provided showing the accuracy and efficiency of the proposed technique.

Increasing the Q-factor of thin planar dielectric resonator with whispering gallery modes

The spectral and energy characteristics of the tunable thin planar dielectric resonator with the movable metal mirror are researched. It is found that the high-Q HE-polarized whispering gallery modes (WGMs) are effectively excited in such a resonator by the dielectric waveguide. A mode set of the tunable thin planar dielectric resonator depends on the presence of an air gap in its design. Changing the height of the air gap affects the energy characteristics of the tunable thin planar dielectric resonators (DR). Shifting the resonant fields of WGMs from the dielectric disk to the air gap is the reason for this effect. It is shown that at certain heights of the air gap, increasing the unloaded Q-factor of the tunable thin planar DR and improving the excitation efficiency of WGMs in it is achieved.