Ultra-narrow perfect graphene absorber based on critical coupling

A polarization-independent perfect graphene absorber is numerically demonstrated. The novel absorber is composed of an array of dielectric square resonators and a graphene monolayer on a Bragg reflector. An absorption peak at a wavelength of 1550 nm with an absorbance of up to similar to 99% is achieved, owing to the critical coupling effect. Moreover, the designed graphene absorber exhibits an ultra-narrow spectrum bandwidth with an ultra-high quality factor, owing to the combined effects of the guided mode resonance achieved with the dielectric square resonators and photonic band gap with the Bragg reflector. In addition to the numerical results, an analysis model based on the coupled-mode theory is presented. Moreover, the electromagnetic field intensity distributions are plotted to provide a physical interpretation of the complete absorption. This study paves the way for the development of a perfect ultra-narrow spectrum-selective graphene absorber.