Unidirectional ultrabroadband and wide-angle absorption in graphene-embedded photonic crystals with the cascading structure comprising the Octonacci sequence
The band-gap effects in Bragg structures are currently applied in high quality reflectors and band-pass filters; they are typically narrow-band. In this work, Guo et al. aimed at designing broadband absorbers, whose performance will exceed that of the ideal periodic structures. They compared the scattering properties of several types of quasi-periodic structures and demonstrated that carefully designed Octonacci sequences in combination with several units of periodic structure containing dielectric layers can provide high absorption in a wide frequency range for a wide range of angles of incidence. The authors predict that this structure shows absorption with a wider bandwidth than pure periodic structures or even other more common quasi-periodic structures. Due to inherent spatial asymmetry, the proposed devices show low loss and high reflectivity when the wave is incident from the opposite side of the structure – thus the structure is called an asymmetric absorber. The authors also propose that by inserting graphene layers, which are tuned by external voltage, the absorbing properties of the structure can by dynamically controlled.