Voltage controlled Fabry–Perot modulator
Here we propose a voltage-controlled Fabry–Perot modulator made of two overlapping graphene sheets separated by a hafnium oxide layer, manufactured on a silicon substrate. The applied voltage shifts the Fermi level in both layers thus changing the total surface conductivity. This in turn changes the optical parameters of the system. Due to the architecture of the modulator, ≈50% of THz power is absorbed and the applied voltage controls the ratio between the reflection and transmittance. At the resonance frequency of 414 GHz, the transmission through the Fabry–Perot modulator can be doubly reduced in a voltage range of –1.5 to 10 V. In DC measurements, it is revealed that the electrical properties of graphene sheets dramatically depend on the technological process. The proposed multilayer structure can be manufactured on any THz-transparent substrate, compatible with photolithography and atomic layer deposition (ALD) processes.Voltage-controlled surface conductivity could find its application in sensing or modulation of electromagnetic waves.