A compact and integrated terahertz (THz) wave photonic crystal switch is proposed in silicon. The switch operates based on a dynamic shift of the photonic bandgap by using an external applied electric field. The plane wave expansion method and the finite-difference time-domain method are used to verify and analyze the characteristics of the proposed THz wave switch. Numerical simulation results show that the THz wave switch has a high extinction ratio of $29.9\text{\hspace{0.17em} dB}$.

When metamaterial structures meet functional materials, what will happen? The recent rise of the combination of metamaterial structures and functional materials opens new opportunities for dynamic manipulation of terahertz wave. The optical responses of functional materials are greatly improved based on the highly-localized structures in metamaterials, and the properties of metamaterials can in turn be manipulated in a wide dynamic range based on the external stimulation. In the topical review, we summarize the recent progress of the functional materials-based metamaterial structures for flexible control of the terahertz absorption and polarization conversion. The reviewed devices include but are not limited to terahertz metamaterial absorbers with different characteristics, polarization converters, wave plates, and so on. We review the dynamical tunable metamaterial structures based on the combination with functional materials such as graphene, vanadium dioxide (VO₂) and Dirac semimetal (DSM) under various external stimulation. The faced challenges and future prospects of the related researches will also be discussed in the end.

We designed a terahertz bandpass filter based on double-layer frequency selective surface. Details of the proposed terahertz wave filter design and of the related parametric analysis are presented and discussed. The proposed terahertz filter was fabricated by laser technology. The transmission spectrum was characterized by terahertz time-domain spectroscopy. The results show that the center frequency of the terahertz filter is about 1 THz with 3-dB bandwidth of 400 GHz.

We report a polarization-insensitive dual-band tunable graphene absorber in the terahertz region, which is composed of a top patterned graphene and a gold ground plane, separated by a silicon dielectric layer. Numerical simulations verify the amplitude of the absorption peaks have reached 98.6% and 98.2% at 0.512THz and 1.467THz, respectively. It exhibits excellent performances with high absorptivity and wide incident angles for both transverse electric (TE) and transverse magnetic (TM) polarizations. The frequency and amplitude of the absorption peaks can be regulated by chemical potential of graphene via bias voltage. These characteristics provide great potential applications in imaging, detecting, and sensing in the terahertz regime.