Tunable and ultra-narrowband multifunctional terahertz devices using anisotropic graphene based hyperbolic metamaterials.

In this paper, we propose a novel structure of anisotropic graphene-based hyperbolic metamaterial (AGHMM) sandwiched as a defect between two one-dimensional photonic crystals (PCs) in the terahertz (THz) region. The proposed structure is numerically simulated and analyzed using the transfer matrix method, effective medium theory and three-dimensional finite-difference time-domain. The defect layer of AGHMM consists of graphene sheets separated by subwavelength dielectric spacers. According to the presented results, a sharp defect mode originated from the optical Tamm state (OTS) takes place at the interfaces between PCs and AGHMM. The platform is then applied as various THz devices with outstanding characteristics compared with their previous counterparts. The performance of all the proposed devices can be tuned by changing the incident angle and graphene chemical potential. Our designed electro-optical modulator exhibits a high extinction ratio of 24.75 dB. The required switching voltage and insertion loss are as low as 9.94 V and 0.05 dB, respectively. Owing to the anisotropy of graphene, a tunable polarizer over wide incident angles is attained. The highest polarization extinction ratios (PERs) for TE- and TM-pass polarizers are 42.4 dB and 76.8 dB, respectively, which are the highest PER ever reported. By introducing more AGHMM defects, multiband tunable filters with quality factors of as high as 75314 are realized. Finally, a narrowband perfect absorber is proposed so that a high absorption of 99.8% with an ultra-narrow FWHM of 0.00055 THz is achieved. Hence, the proposed structure is a promising platform that could have many potential THz applications.