Development of a triple-band terahertz metamaterial absorber with frequency switching and amplitude modulation characteristics

A triple-band absorber with typical three-layer structure is proposed in the terahertz region. Pattern layer consists of two concentric rings with different sizes, and photosensitive silicon is put into the symmetric double gaps of the inner one. The conductivity of silicon is taken as one regulating method. Under the action of a suitable pump laser, dynamic switching of the resonance frequency is realized through manipulating the conducting state of photosensitive silicon. Concretely, without excitation, there are three resonance absorption peaks at 1.000 THz (f1), 1.550 THz (f2), and 2.090 THz (f3). While pumped by an excitation laser, peak f2 generates a red shift to 1.500 THz and peak f3 to 2.075 THz. Taking polarization angle of the incident THz wave as another regulating method, we can modulate the absorption amplitude with or without excitation by device rotation. Thus, we obtain the characteristics of frequency switching and amplitude modulation simultaneously. It is even more crucial that continuous modulation of the absorption amplitude is achieved at each fixed resonant point without any frequency shift. The maximum value of amplitude modulation depths is up to 100%. The proposed device provides a new perspective to explore future multifunctional terahertz absorbers.