Ultra-broadband terahertz bandpass filter with dynamically tunable attenuation based on a graphene–metal hybrid metasurface

We propose an ultra-broadband terahertz bandpass filter with dynamically tunable attenuation based on a graphene-metal hybrid metasurface. The metasurface unit cell is composed of two metal stripes enclosed with a graphene rectangular ring. Results show that when the metasurface is normally illuminated by a terahertz wave polarized along the metal stripes, it can act as an ultra-broadband bandpass filter over the spectral range from 1.49 THz to 4.05 THz, corresponding to a fractional bandwidth of 92%. Remarkably, high transmittance above 90% covering the range from 1.98 THz to 3.95 THz can be achieved. By changing the Fermi level of graphene, we find that the attenuation within the passband can be dynamically tuned from 2% to 66%. We expect that the proposed ultra-broadband terahertz bandpass filter with tunable attenuation will find applications in terahertz communication and detection and sensing systems.