▎ 摘　　要

We show that, on general theoretical grounds, transmission of light in graphene always presents a non-vanishing minimum value independently of any material and physical condition, the transmission coefficient being higher in the presence of a substrate, and getting increasing when QED corrections higher than a come into play. Explicit numerical calculations for typical cases are carried out when an external magnetic field is applied to the sample, showing that, in epitaxial graphene, a threshold effect exists leading to a non-trivial minimum transmission, for a non-vanishing light frequency, only for field values larger than a critical one, both in the large and in the intermediate chemical potential regime. Such a threshold effect manifests even in the maximum Faraday rotation polarization of light, which is substantially controlled by the applied magnetic field. Instead, more transmission minima in suspended graphene enters in the considered light frequency region for increasing magnetic field, displaying an effective shift of frequency bands where the sample gets more or less absorptive with a suitable tuning of the external field. Two transition regions in different magnetic field ranges are found, where the shift effect towards higher frequency values occurs both in the transmission coefficient and in the Faraday rotation angle. Potential technological application of the results presented are envisaged.