Study On Modulation Of Graphene Terahertz Wave Enhanced By Micro-nanostructures

In the development of terahertz technology,the terahertz modulator is one of the essential key devices.For a long time,people have been seeking for the Terahertz high-speed modulators with stable performances and a large modulation depth.Among these investigations,the modulation material is one of the keys.Graphene is an ideal material for fabricating the terahertz modulator due to its high-speed and adjustable electronic properties,but because of its ultrathin thickness(0.35 nm),the interaction between graphene and the electromagnetic wave is very weak,resulting in the modulation depth of graphene is very limited.While micro-nano structure can be strong interaction with the terahertz owing to its special structural characteristics.In order to improve the modulation depth,the thesis combines graphene and micro-nanostructures to fabricate terahertz modulation devices with a higher modulation depth.Research contents and results are summarized as follows:In theory,based on the theoretical studies of electronic conductivity and micro-nanostructure enhancement mechanism of graphene,and according to the actual working mode and structural requirement of the terahertz modulator,the reflection-type graphene phase modulator with a butterfly hollow structure and the transmission-type graphene amplitude modulator with a ring-shaped hollow structure were designed,and the corresponding equivalent circuit theoretical model was established.Using this model,the terahertz modulator enhancement analysis was carried out,and the parameter optimization was performed by a numerical calculation method.For the optimized structure,the results show that the phase modulation exceeds 150 degrees,50 degrees higher than the graphene-only device.For transmission modulators,the maximal modulation depth is 71.3%,more than three times of the single-layer graphene device.This indicates that the micro-nanostructures can significantly enhance the ability of graphene to modulate the depth of terahertz waves.In the aspect of process,the preparation technology of the transmission-type amplitude modulation device is studied according to the structure feature of the substrate-/-micro-nano structure layer-/-dielectric layer-/-electrode and graphene layer.In our work,a PET film with low transmission loss was used as the substrate of the modulator in the terahertz band.In line with the theoretical design results.The hard substrate supporting method and the UV lithography process were used to prepare the reinforced structure.Magnetron sputtering,and graphene wet transfer process were used to fabricate the device.Results show that the preparation process of the structures is good and less-defects.In the test,the terahertz modulator test was performed using the terahertz time domain spectroscopy system,and the modulation performance of the prepared modulator was tested and analyzed.The results show that when the modulation voltage changes from 0 V to 20 V,the transmission amplitude modulation depth reaches 71%at 0.6 THz,which is consistent with theoretical results.When the AC square wave modulation was applied to the device,it was found that the amplitude modulation performance of the modulator is stable in the process of continuous modulation.The work of this thesis has laid a technical foundation for advancing the practical development of terahertz modulator.