Design and Tuning of Substrate-Fabricated Dielectric Metasurfaces Supporting Quasi-Trapped Modes in the Infrared Range

Optical metasurfaces supporting resonances of trapped modes allow obtaining narrow features in their reflection and transmission spectra and are the technological basis for the fabrication of highly sensitive sensor coatings and near-field pumping systems for two-dimensional lasers. In the present work, we propose and experimentally verify the strategy for tuning the parameters of an all-dielectric metasurface placed on the substrate in order to implement the narrow resonance of a quasi-trapped mode (QTM) at the required wavelength. We use a Si disk with an eccentric hole as a building block irradiated by a linearly polarized plane wave normally incident to the disk's base. In this case, the normal components of the magnetic dipole moment are excited due to the bianisotropic response in the system. Using the electrostatic approximation for the polarizability of a single disk and solving the equation for the self-consistent dipole response of a lattice composed of such disks, we plot the parametric curve in the plane (wavelength vs geometric size of the disk) that corresponds to the conditions of QTM excitation accounting for the overcoming effect of diffraction into the substrate. Fixing the arbitrary wavelengths from the infrared (IR) range of the spectrum, we use this curve to select the disk's size and the period of the metasurface, which are the basis for the fabrication of the necessary metasurfaces. Analyzing the reflection spectra of the fabricated metasurfaces, we observe the narrow spectral features at given wavelengths and, using numerical simulation, identify them as QTM resonances. We demonstrate the polarization control of the amplitudes of the QTM, which allows switching of the intensity value of the electric field on the surface of the Si disks.