Ultrawideband Solid-State Terahertz Phase Shifter Electrically Modulated by Tunable Conductive Interface in Total Internal Reflection Geometry

Phase modulation plays a crucial role in various terahertz applications, including radar detection, biomedical imaging, and data communication. Existing terahertz phase shifters typically rely on tuning the resonant effect of metamaterial structures to achieve a narrow bandwidth phase shift. However, the terahertz band offers a wide bandwidth resource, which has great advantages in high longitudinal resolution detection, high-capacity communication, spectral imaging, and so on. Here, we propose and demonstrate an ultrawideband terahertz phase shifting mechanism that utilizes an optical conductivity tunable interface combined with a nonresonant metasurface operating in the total internal reflection geometry. This approach effectively modulates the phase of the reflected terahertz signal in an ultrawideband. To implement this mechanism, we designed a structure consisting of graphene-loaded nonresonant periodic metal microslits arranged in the total internal reflection geometry. By controlling the gate voltage of the graphene within a range of ±5 V, an averaged ∼120° continuous phase shift in the frequency range of 0.4 to 1.2 THz was achieved, with a group delay less than 50 ps. Notably, in the frequency range of 1 to 1.2 THz, the phase modulation exhibited a linear relationship with the driving voltage. Our device demonstrated minimal fluctuations in the reflected amplitude, with a deviation of less than 1 dB and an insertion loss of less than 10 dB. Additionally, the modulation speed of this solid-state device reached the kHz level. Remarkably, the phase modulation bandwidth (Δf/f) achieved approximately 100% of the arithmetic center frequency at 0.8 THz, surpassing the definition of ultrawideband, which typically encompasses 20% of the center frequency. To the best of our knowledge, this is the first and most wideband phase shifter developed for the terahertz regime with the lowest recorded group delay to date.