Narrowband Absorption Platform Based on Graphene and Oblique Incidence in the Infrared Range

Abstract

Narrowband absorption spectrum is usually a critically important factor for a plasmonic absorber that works as a biosensor for narrower bandwidth which refers to higher sensitivity of sensor. To realize plasmonic biosensor of narrow bandwidth, absorption property of plasmonic absorber has been usually investigated under normally incident light with transverse magnetic polarization. Here we present numerically a structure of graphene-based metasurface to obtain reflection spectrum of narrow bandwidth, while incident light is at oblique angle and with transverse electric polarization in the infrared range. The presented structure includes a dielectric layer on top side, a buffer dielectric layer, graphene film, a dielectric layer of high refractive index with high-aspect-ratio nanotrench array, and a metal substrate. As a plasmonic absorber, its absorption bandwidth is 0.5 nm wide, and its peak absorption reaches 97% at the resonant wavelength. As a refractive index sensor, its bulk sensitivity and figure of merit are 500 nm/RIU and 1000/RIU (“RIU” is abbreviation of “Refractive Index Unit” and as unit of refractive index), respectively. It shows a novel configuration of obtaining narrow bandwidth plasmonic absorbers using transverse electric polarized incident light at oblique incidence angle. The presented graphene-based structure has a strong potential in biosensing applications, such as platform for sensing refractive index variation on the nanoscale while probing neural stem cell activities in the period of cell development.