Nanooptics and photonics

Topological vortices on dispersion maps 
of resonant metal-dielectric coatings
Lymarenko R.A., Ilchenko S.G., Taranenko V.B.
International Center “Institute of Applied Optics” of the NAS of Ukraine
10G Kudryavska street, Kyiv, 04053, Ukraine. 
E-mail: kit@iao.kiev.ua

We propose the classification of resonant modes for nanoscale metal dielectric multilayer structures, not only by the dependence of the reflectivity on the wavelength and angle of incidence, but also on the spectral-angular phase distribution of the reflected beam and enhance electromagnetic (evanescent) field in the structure. We show the existence of singularities (topological vortices) on the dispersion map of the phase of the reflection coefficient for the interface between two media with adding dielectric layers. The topological vortices pattern analysis on spectral angular space for resonant properties of dielectric layer characterization is investigated. Types of resonant curves of a modification of Bragg mirror (several pairs of unmatched quarter-wave layers with high (TiO2) and low (SiO2) refractive index with larger thickness of terminal layer) is analyzed. It is shown that resonance curves start from a singular point. These curves correspond to the amplification lines of an evanescent electromagnetic field in the structure and do not appear in the reflection amplitude at a zero attenuation coefficient of the layer material. The points of convergence of the phase curves near the total internal reflection angle and the glide angle are described. The existence of a resonance mode (Bragg mode), which is characterized by a significant amplification of the electromagnetic field in the resonant dielectric structure and a narrow angular width of the reflection peak, is shown. A mechanism is proposed for the resonance curve for visualizing the Bragg mode in reflection coefficient by adding a layer with a nonzero imaginary part of the dielectric constant (), i.e., a metal or dielectric with extinction. The behavior of dispersion resonance curves in case of it intersecting by the interaction of topological charges on a dispersion map is explained. It is shown that the intersection of the Bragg mode with the band of the minimum reflection coefficient (like optical Tamm states [1]) is possible and gives a narrow reflection peak, which is promising for creating laser angular selectors or modulators.

1.	Yongkang Gong et al. Perfect absorber supported by optical Tamm states in plasmonic waveguide // Optics Express 19(19):18393-8, 2011.