Abstract
Abstract 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.
Highlights
The eigenfrequencies of open dielectric particle are complex because of leakage of the electromagnetic (EM) power from particle
Real parts response for positions of resonances while imaginary parts do for the resonant widths which can be measured by light scattering
The compact dielectric cavity is open to the radiation continuum whose spectrum is given by light cone ω = ck which have no cutoffs and the resonant width of the supercavity mode cannot turn to zero and cannot be true bound state in the continuum (BIC) [5, 6]
Summary
The eigenfrequencies of open dielectric particle are complex because of leakage of the electromagnetic (EM) power from particle. In practice material losses and structural losses restrict the number of cavities [13, 16,17,18] This way of engineering of quasi-BICs goes away the dielectric structures (DS) from compactness when DS dimension do not exceed the wavelength. The underlying principle of enhancement of the Q-factor is the ACR of two resonances [21] of dielectric disk under variation of the aspect ratio. The presence of the second coaxial disk substantially expands a number of ACRs due to crossing of resonances and allows elevating the Q-factor of disk’s dimer by two orders remaining in the subwavelength range [25]. For the DS consisted of symmetrically disposed three/four silicon disks the ACRs at the subwavelength range ka ≈ 2.2 give rise to quality factors around 105 and 106, respectively, where a is the radius of disks
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