Dynamically tunable ultra-narrowband perfect absorbers for the visible-to-infrared range based on a microcavity integrated graphene pair.

Dynamically tunable ultra-narrowband perfect absorbers are important to next-generation active photonic devices. A composite structure of a graphene pair and a microcavity with Bragg mirrors are proposed for this purpose. Based on the electrically controllable doping of graphene and critical coupling of the incident light, the microcavity-graphene composite structure achieves peak absorptance higher than 99.5%, a relative peak width ($\Delta \lambda /{\lambda _0}$) smaller than 1.1%, and a modulation depth larger than 92.0% throughout the visible-to-mid-infrared range, surpassing other structures in comprehensive performance. By changing the number of the dielectric pairs in the Bragg mirrors, the device can become an amplitude or a spectral modulator. The results are based on the optical constants from experiment data, including the surface conductivity of graphene with relatively low mobility, so they are more useful in practical situations.