Wideband THz Filtering by Graphene-Over-Dielectric Periodic Structures with and without MgF2Defect Layer

Abstract

Investigation of the spectral response of graphene-dielectric (SiO2)-based periodic structure was made in the far-infrared (IR) to the mid-IR frequency range, and the effects of different parametric and operational conditions on the transmission characteristics were explored. The presence of stop-bands, followed by Bragg reflection harmonics, in the low-frequency regime was observed exploiting the bilayer graphene (BLG) sheets. The width of stop-bands could be tuned by altering the number of periods as well as the chemical potential of BLG. The formation of a stop-band (with a transmission dip positioned at 16 THz) having a span of 3 THz was noticed, which is possibly a very large stop-bandwidth reported so far. The structure was also analyzed upon introducing a defect layer of MgF2 having a thickness smaller than the dielectric medium. This results in shifting the position of stop-bands of the structure. The characteristics of transmission spectra were found to be greatly depending on the chemical potential (of BLG) and other operating conditions - the feature that triggers the usefulness of the proposed structure in the design of optical modulators, tunable narrow-band filters, broad-band reflectors and biosensing applications.