Tunable terahertz structure based on graphene hyperbolic metamaterials

Photoexcited graphene can behave as the gain medium aiming to come up with the coherent radiation at low THz spectral region. However, its response is very weak because of its atomic dimensions. Herein, a different design aiming to obtain effective tunable THz amplifiers, having small dimensions and lasers with broadband operation based on active THz hyperbolic metamaterials (HMM) is demonstrated. HMMs are considered by employing multiple stacked photoexcited graphene sheets divided by dielectric spacers. Herein, we study and characterize the hyperbolic THz regime of the studied atomic active HMM. A broadband slow-wave propagation regime takes place if the graphene-based HMM system is periodically patterned. This occurs due to the hyperbolic dispersion. Doing so, reconfigurable amplification of THz waves in a broad-spectrum region is attained. This might be engineered by tuning the quasi-Fermi level of graphene. Moreover, the mechanisms leading to the increase of the frequency region of bound surface wave have been proposed in the frame of the current study.