Field Enhancement with Waveguide Resonance by the Structure Dielectric Grating/Dielectric Layer/Metal Substrate

Abstract

In this work, the results of modelling the diffraction of a plane wave by the structures of type dielectric grating/dielectric layer/metal substrate are presented. The strongest field enhancement is achieved for TE polarization under of waveguide mode resonance. In addition, the reflection coefficient is zero under such resonance conditions. Waveguide mode resonance can be realized in a wide range of wavelengths by changing the grating parameters. The spectral characteristics of three types of periodic structures were modelled. The first and second structures contain a dielectric layer, while the third one does not. The waveguide mode resonance and, accordingly, zero reflection coefficient can be obtained with carefully selected structure parameters. Resonant values of the grating thicknesses and periods were determined. Numerical modelling was done with Rigorous Coupled Wavelength Analysis. The thicknesses different from the resonant ones significantly affect the reflection coefficient from the periodic structure, as was established. Absolute permissible deviation values of the thicknesses of the gratings and dielectric layers from the calculated resonance values were estimated. The waveguide mode resonance is sensitive to the incident wavelength on the periodic structure. The reflection coefficient and the field distribution along the grating period were calculated. Studied structures can be effectively used as substrates for SERS-type devices due to field enhancement and zero reflection coefficient under waveguide resonance. The strongest field on the grating surface is observed for the structure without a dielectric layer, namely, dielectric grating deposited on the metal substrate. In addition, the benefits of such periodic structures include lower manufacturing costs.