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A metamaterial terahertz modulator based on negative differential conductance effect

A new metamaterial modulator based on a metamaterial absorber is proposed for the first time by utilizing the negative differential conductance (NDC) effect in n-GaAs. The modulator consists of gold square resonators on an n-GaAs substrate integrated with a gold film on the bottom. This device's absorption spectrum, which is in the range of terahertz (THz), can be modulated by applying high bias voltages between the resonators and the bottom gold film. The nonlinear response of this modulator operating under the ideal mode is investigated in detail by FDTD Solutions. The simulation results show that the bias voltage causes a redshift of the resonance frequency of the absorber and an increase in the resonance strength. This phenomenon can be attributed to the NDC effect resulting from the transferred-electron mechanism, which reduces the electron mobility and increases the electron effective mass under the bias voltage high enough. The absorption of modulators with square resonators of different sizes has also been investigated, and similar trends on the change of resonance frequency and resonance strength appear. This kind of device enables the dynamic control of THz waves by applying different voltages, which can be used as a terahertz modulator.