Research On Terahertz Amplitude Modulators Based On Composite Metasurface

Terahertz wave is an electromagnetic wave band,which has been proposed and rapidly becomes a research hotspot all over the world in recent years.With the development of micro-nano technology,terahertz functional devices such as filters,polarizers and modulators develop shaply.In contrast,active control devices for modulating terahertz waves are still very lacking,and there are problems to varying degrees such as less variety,larger size,poor performance,great difficulty in processing and importantly,very high price.Therefore,it is of significance to develop all kinds of terahertz wave active control devices with compact,high performance,high flexible design and high efficiency to the terahertz science and technology.In this thesis,we studied the terahertz amplitude modulator of composite structures based on graphene,ion-gel and artificial metasurface.The details are as follows:(1)Terahertz amplitude modulators based on graphene/ion-gel/metasurface composite structures.A terahertz amplitude modulator based on graphene/ion-gel/metasurface composite structure was designed and fabricated.The device was composed of monolayer graphene,ion-gel and metal metasurface successively constructed on quartz substrate,and its modulation depth was 64% at resonant frequency 0.51 THz by 3 V external bias voltage.The research showed that the terahertz amplitude modulators can modulate terahertz wave in a wide range at a lower voltage,and the modulation effect was the result of the interaction of metal structure,graphene and ion-gel.(2)Terahertz amplitude modulators based on the symmetrical structure of double layer graphene.On the basis of the above monolayer graphene modulator,a terahertz amplitude modulator based on the symmetrical structure of double layer graphene was designed and fabricated.Experiments showed that the device achieved 73% modulation depth at the resonant frequency of 0.51 THz by 3 V external bias voltage.The results showed that the conductivity of the upper and lower layers of graphene increases with the increase of applied bias voltage,and they has a short circuit effect on the resonance of the metal structure.Thus,the structure can further increase the modulation depth of terahertz waves.(3)Amplitude modulators of anomalous refracted terahertz based on graphene/iongel/metasurface.Amplitude modulators of anomalous refracted terahertz was fabricated by combining the metasurface with a linear phase gradient with graphene and ion-gel.Through the terahertz time domain spectroscopy system based on optical fiber test,it was shown that the device achieved 18.4 degree deflection and 48% modulation depth at the terahertz wave frequency of 0.58 THz under 3 V external bias voltage.