The tunable single-/narrow-band terahertz metamaterial absorber through photoconductivity

In this work, a photo-excited terahertz metamaterial absorber (PETMA) switched between single-band and narrow-band absorption is reported. Such an absorber includes three layers, which are a metal plate on the bottom, a dielectric layer, and a top unit attached to the dielectric substrate. The upper unit of the proposed PETMA is composed of an innermost ring-shaped and a middle truncated ring-shaped high-impedance surfaces (HISs), a nested split ring-shaped resonator connected with an outer square ring-shaped metal resonator. It is noted that four corners of the square ring-shaped metallic resonator are embedded in photoconducting semiconductors (silicon), respectively. Furthermore, the quadrate air columns (ACs) are inserted in the dielectric substrate to promote the absorption effect of this absorber. The single-band (at 1.16 THz) and the narrow-band absorption (at 1.458–1.538 THz) conversion can be realized through the variation of the conductivity of silicon tuned by an optical pump beam. Besides, the absorption principle of the devised PETMA is analyzed by describing the surface currents, the electric field diagrams, the magnetic field distributions, and the power flow distributions. In addition, the simulations show that the proposed PETMA exhibits stable absorption performance at a wider incident angle