Study On Terahertz Photoconductive Antenna Based On Dielectric Lens

Terahertz waves have extremely broad application prospects in medical,biological,detection,and security fields.How to use terahertz photoconductive antennas to generate high-gain radiation signals is a hot topic at home and abroad.In this dissertation,various factors affecting the radiation efficiency of terahertz photoconductive antennas have been deeply studied,and a terahertz photoconductive antenna based on a dielectric lens and a plasma structure is designed.Firstly,the antenna is researched by using electromagnetic field theory,and the classic butterfly antenna is selected as the research object;and CST software is used to simulate and analyze it.The simulation result shows that the gain of the antenna changes with the angle of the antenna.When the angle of the butterfly antenna is 90°,the maximum gain can be obtained;and the thickness of the substrate significantly affects the size of the radiation power.Therefore,it is necessary to reasonably select the antenna angle and substrate thickness to obtain excellent radiation efficiency.Secondly,the plasmon theory is applied to theoretically analyze the plasma structure between the photoconductive antenna electrodes;and the micro-nano structure is designed through the finite difference time domain algorithm;and the surface plasmon polaritons and localized surface plasmon resonance are used.The coupling of surface plasmon and localized surface plasmon resonance is used to achieve the purpose of improving radiation efficiency.The simulation results show that under the same material conditions,the radiation efficiency of photoconductive antennas with regular hexagonal prisms,cylinders,and quadrangular prisms as the plasma micro-nano structure decreases successively;under the same shape and structure,the radiation efficiency of silver materials,gold materials,and Gallium arsenide materials decreases successively.By effectively combining the structure,shape and material of the plasma,10 times of the radiation efficiency of the traditional photoconductive antenna is achieved.Finally,in order to weaken the limitation of terahertz radiation caused by the surface wave effect of the terahertz photoconductive antenna,a method of adding a dielectric lens is adopted.After analyzing the characteristics of several dielectric lenses,it can be seen that the effect of the ellipsoidal lens is relatively good.However,due to its difficult manufacturing process,the relatively simple processing of the expanded hemispheric lens and the ellipsoidal lens are selected to fit on the mathematical model,and CST is further applied to its design.The simulation results verify the effective suppression of the surface wave effect of the dielectric lens.The obtained high-efficiency terahertz photoconductive antenna provides a new solution for improving the radiation efficiency of the terahertz photoconductive antenna,and can be widely used in research fields such as terahertz sources,terahertz detection,and semiconductors.