A dual-polarization mode terahertz modulator based on metamaterial and HEMT structures

In this paper, we reported the design, fabricate, and characterize of an electronically controlled terahertz (THz) amplitude modulator composed of a four-open ring metamaterial structure and a high electron mobility transistor (HEMT) structure, HEMT area is located at the openings of the four-opening ring metamaterial structure. The concentration of 2D electron gas of the HEMT is adjusted by applying an external electrical field and results in the resonance shifts. Both static and dynamic characterizations of the modulator were carried out by using an optical fiber-coupled terahertz time-domain spectroscopy (THz-TDS) system in the transmission type. Experimental results show that the amplitude modulator can modulate the incident THz waves with two orthogonal polarization directions. The modulation depths are 56% at 0.32 THz for vertical polarized beam and 40% at 0.34 for horizontal polarized beam respectively. The modulator has potential application in wireless communication and real-time imaging.