Research On Terahertz Devices Of Amplitude Modulation And Phase Modulation

Amplitude,phase,polarization,etc.are important characteristic parameters of terahertz waves.In recent years,researchers have carried out a lot of research on the regulation of these parameters,and have designed many metasurfaces for making amplitude modulators,polarization converters,metalens,beam splitter and other terahertz functional devices.This paper aims to explore new types of amplitude modulators and phase modulators in order to realize more convenient and efficient active modulation devices.A novel design of the amplitude modulator is carried out based on the metasurface lattice mode theory;the pump optical control scheme is innovatively combined with the digital micromirror system,and is used in the design of amplitude and phase modulation devices.The research work of this paper mainly includes the following four aspects:1.In-depth study of lattice mode theory.By means of experiments and simulations,as well as theoretical calculations and comparisons of spectral lines,the metasurface period,terahertz incidence angle,and metasurface substrate that affect the frequency of lattice modes are analyzed in detail.During the analysis,it was found that the red shift of the lattice mode frequency would affect the amplitude of the metasurface eigenmode and accordingly,an amplitude modulator was designed to control the amplitude by changing the incident angle.The reason why the lattice mode suppresses the eigenmode is explored by designing experiments and simulations.2.Two kinds of metasurfaces with super cell as the unit structure are designed,and there is a phase difference between the two U-shaped unit cells in the super cell.The experimental and simulation results of these two metasurfaces are analyzed,and the results show that the phase mismatch is the fundamental reason for the suppressed amplitude of higher-order eigenmode.Further explore the super cell composed of two U-shapes,and design a metasurface in combination with lattice modes to achieve tunable Fano resonance peaks.3.Explore the light control scheme combined with the spatial light modulator to realize the ternary coded amplitude modulator.Combined with the digital micromirror system,the local precise control of the metasurface area is realized.A metasurface capable of generating three resonance peaks is designed using the Barbinet-like structure.Using the proposed optical control scheme,on-off control of the three resonant peaks is realized,and a ternary encoder with eight encoding states is realized.4.Using the proposed optical control scheme,combined with the control of the phase by the metasurface,a terahertz beam splitter with dynamically adjustable beam splitting ratio is realized.Designing a metasurface with two phase gradients can divide a beam of terahertz light into two beams,and use a digital micromirror system to manipulate the responses of the two phase gradient structures to achieve dynamic control of the splitting ratio of the two beams.