Research Of Tunable Terahertz Devices Based On Liquid Crystal And Metamaterials

Terahertz(THz)wave is electromagnetic wave with a frequency range of 0.1 THz to10 THz,and its frequency lies at the intersection of electronics and photonics.Compared with the mature infrared and microwave technologies,the development of terahertz wave technology has been relatively backward.Because it has unique properties such as transient,low radiation and large bandwidth,THz technology shows great application prospects in high-speed wireless communication,biomedical detection,high-resolution imaging of objects,environmental monitoring,security inspection and military radar.In order to realize these applications,it is very important to develop a THz functional device capable of actively controlling the polarization state,phase and amplitude of the THz wave.In this thesis,the electromagnetic properties of a tunable two-layer sub-wavelength metal plasma metamaterial(MM)array structure based on nematic liquid crystal(NLC)are studied.Two electrically tunable THz devices were designed,manufactured and tested in the frequency range of 220-500 GHz.The numerical calculations and experiments have verified the tunable THz transmission characteristics of the double-layer metal arc array structure based on NLC.According to the requirements of electromagnetic performance,a metal-dielectric-metal array structure with an operating frequency of 283.91 GHz was designed.The theoretical calculation results show that the amplitude modulation depth(MD)and insertion loss(IL)of the design prototype at its operating frequency are 86.1%and 0.72d B,respectively.A sample containing an array of 33×33 cells was fabricated on a quartz substrate with an area of 2×2 cm~2 by using the UV lithography process.Experimental results show that for vertically incident THz electromagnetic waves,the sample can obtain an amplitude modulation depth higher than 70.56%and an insertion loss lower than 1.9d B at285.45GHz.By applying a bias voltage of 0-4.8 V on the intermediate dielectric layer,the sample showed a frequency tunability of more than 13.5%.In order to further improve the modulation performance,an NLC-based tunable THz plasmonic MMs with large MD and IL is designed and experimentally verified at 325-500 GHz.The proposed structure includes two-layered MM that is immersed in LC.The tunable device with a 46×46 array of sub-wavelength metal arc was fabricated on a quartz glass substrate,with 2×2 cm~2 area and 220?m thickness.The obtained results show that the amplitude MD and IL for normally incident electromagnetic waves are about 96%and1.19 d B at 421.2 GHz,respectively,when the bias voltage applied to the NLC layer varies from 0 to 16 V.Meanwhile,the transmission peak frequency gradually decreases from421.2 to 381.8 GHz,and the frequency tunability of the proposed structure is greater than9.35%.