Thz Wave Propagation Properties Of Polymer Electro-optic Modulator Based On Beam Propagation Method With Alternating Direction Implicit Method

With the great development of THz Technology in the fields of Plasma Physics,Biomedical Engineering, Spectral Imaging Technology, Information Science andMaterials Science in recent years, the technology of modulating terahertz radiationhas become increasingly urgent demand by people. Currently there are two majormethods for realizing the modulation of terahertz radiation. One way is based on theinternal antenna and the other is using external THz modulates. Though there areplenty types of THz modulator and each of them has its own advantage in one wayor another, but none of them can achieve the goals of high-speed, broadband, lowloss, and high efficiency THz modulation simultaneously. Meanwhile, the polymerelectro-optic modulator has been widely used in microwave communication fieldsdue to its advantages of high modulation rate, low insertion loss, high extinctionration and being convenient for production. The low absorption materials in thefrequency of THz people have currently found will provide the material basis of theMache-Zehnder type polymer electro-optic modulator for THz frequency wave.The key parts which decide the whole performance of Mache-Zehnder typepolymer electro-optic modulator are its THz band structure and electro-opticpolymer waveguide modulator electrode structure. According to the two partsmentioned above, we use effective index method(EIM) and full-vectorialthree-dimensional beam propagation (3D-FV-BPM)with alternating directionimplicit method(ADI) to simulate the characteristics of the THz frequency wavetransmission in different shape Mache-Zehnder waveguide with designed electrodestructure. The modulation depth of Mache-Zehnder type polymer electro-opticmodulator is also calculated.Beginning with the Maxwell equation, the3D-FV-BPM equation is derived withSlowly varying envelope approximation and the mixed partial derivative equationitems are processed by alternating direction implicit method. Then considering thecontinuity conditions of light field in at the interface of different refractive indexthe differential equations is derived and the waveguide modeling computational isbuiltaccording to different cross-sectional shapes. The compute nodes at boundary are calculated by transparent boundary condition(TBC). The characteristics of fullvector propagation eigenmodes propagating in the ladder and ridge polymerwaveguide constant of propagation are also discussed.Secondly, the characteristics of THz wave transmission in Y-branch waveguideof Mache-Zehnder polymer electro-optic modulator is simulated via3D-FV-BPMwith ADI algorithm, and the light transmission loss caused by different angle ofY-branch waveguide is discussed. In order to ensure the ensure the Mach-Zehnderelectro-optic modulator operating in the linear work area, two optical bias includingpath asymmetric and refractive index asymmetric designs are introduced and theiradvantages and disadvantages are compared in simulation.Finally, the Characteristics of THz wave propagating in Mach-Zehnderelectro-optic modulation system is simulated and the performance of micro-stripline electrode coplanar electrode is analysis. The modulation bandwidth, microwavephase speed, microwave equivalent refractive index, electrode impedance electrodecapacitance and electric potential distribution of three types of electrode incondition of50Impedance matching are calculated and analysis.