Research On Terahertz Wave Modulation Technology And Functional Devices

Terahertz(THz)wave is an electromagnetic wave with frequency in the range of 0.1-10 THz(wavelength in the range of 3000-30 ?m),and its spectrum is between microwave and infrared waves.The short-wave band of terahertz wave overlaps with infrared light and the long-wave band with microwaves and millimeter waves,which is in the transition area from electronics to photonics.Because of its special position in the electromagnetic spectrum,it also exhibits special physical properties not found in microwave and infrared waves.These special physical properties make terahertz technology show good prospects and applications in aerospace,biomedical detection,imaging,terahertz communications,military and other fields.Aiming at the problems that traditional terahertz functional devices are difficult to tune and the control method is difficult to achieve,this paper uses nematic liquid crystal as the tunable dielectric layer to design two active tunable terahertz functional devices.The main work is as follows:We proposed an F-band phase shifter based on the nematic liquid crystals(NLCs).The proposed phase shifter is formed by a voltage-controlled cavity through introducing an NLC layer between a dipole structure array and a metal floor.Under the action of electric field,the orientation of the NLC molecules will be deflected.We can adjust the resonant frequency and phase of the reflective electromagnetic(EM)wave by tuning the permittivity.The transmission characteristics of EM waves and the LC parameters are calculated and analyzed within the frequency range from 85 to 115 GHz.The LC-based device with a 30×30 array of two parallel unequal dipoles is printed on a quartz substrate,with 4 cm × 4 cm area and 490 ?m thickness.The experimental results show that phase shift of zero to 350.7° is achieved at 104.2 GHz by changing the applied bias voltage on the LC layer from 0 to 20 V.Considering the anisotropy and inhomogeneity of the LC,an accurate electrification model is established and compared with the test results.In addition,the phase modulation accuracy of the liquid crystal phase shifting unit under minimum voltages is explored.When the phase changes drastically,the minimum phase shift that can be adjusted is 4.08°@2 m V.The proposed phase shifter is expected to find several applications in millimeter wave and terahertz reconfigurable antenna systems.A terahertz amplitude control device based on a double-layer slotted array structure is designed.It is composed of nematic liquid crystals between the two-layer metal metamaterial structure.The metal metamaterial is not only used to generate electromagnetic resonance but also serves as an electrode to provide bias voltage.The transmission characteristics of the device in the range of 330 to 500 GHz were studied.By calculating the transmission spectrum of the device under different polarization angles and incident angles,the polarization insensitivity and wide incident angle characteristics of the device were verified.Based on the semiconductor processing technology,a device array composed of 35×35 slotted array structural units was fabricated.The experimental results that when the bias voltage is increased from 0 V to 40 V,the modulation depth and insertion loss of the sample at 371.3 GHz are 72.9% and 1.48 d B,In addition,a modulation depth above 60% and insertion loss below 2 d B can be provided between363.15 GHz and 377.3 GHz.