Research On Terahertz Wave Front Manipulation Based On Guided Wave Structure

Terahertz wave has many excellent characteristics because of its special location,so it can be widely used in biomedical,communications,public safety and other fields,and be one of the hot research directions in several decades.This paper first introduces the background,significance and research status of terahertz wave front manipulation.Then it focuses on the detailed description of the theory of metal parallel plate waveguide,the theory of metal rectangular waveguide and the generalized Snell's law.The main research work of this dissertation is to introduce the principle of phase abruptly change in the generalized Snell's law into the metal waveguide theory,and jointly realize the wavefront manipulation in the terahertz region.The research focuses on three kinds of structures,which are the generation of Airy beam,the focus of the lens and the resolution of the spectrum.The main research work of this paper is summarized as follows:?1?We have designed and numerically characterized the characteristics of the launching of Airy beam in the terahertz region using parallel plate waveguiding structures.The structure consists of stacked copper plates forming an array of parallel plate waveguides.These plates are arranged in parallel,with different slit separations,the same length,and the same period.The interval between metal plates in the odd group is d1,and the interval between metal plates in the even number group is d2.The phase changes produced when the metal plate interval is d₁ and d₂are in accordance with the phase requirement of the Airy function,and the number of metal plate in each group needs to conform to the amplitude distribution of the Airy function.In addition to the design of the Airy beam,many properties of the Airy beam,such as self-bending property and self-healing property,were also verified by modifying the parameters.This method based on metal parallel plate waveguide to produce Airy beam is simpler and more effective than the method proposed in previous articles,and it hopes to get more different applications in terahertz and microwave frequencies.?2?We designed and simulated three terahertz ultrathin lenses based on metal waveguides,including terahertz two-dimensional lenses and bifocal lenses based on metal parallel slab waveguides,and terahertz three-dimensional lenses based on metal rectangular waveguides.The width of the slits between the metal plates and the length of the metal plate in the two-dimensional lens and the bifocal lens are determined by the polarization state of the incident light,the operation mode of the waveguide,and the phase distribution requirements of the lens.The x-direction width,the y-direction width,and the thickness of the rectangular waveguide in a three-dimensional lens are determined by the polarization state of the incident light,the mode of operation of the waveguide,and the phase distribution requirements of the lens.The method of producing the focusing effect based on metal waveguides is simpler and easier to fabricate than the method mentioned in the previous article,and can produce a full width at half maximum close to the beam diffraction limit.?3?We have designed and simulated a terahertz beam splitter based on a metal parallel plate waveguide.We have designed a parallel plate waveguide array with an equal phase gradient.The distinguishable wavelength range of this structure is from 0.80 mm to 1.15 mm,and the intensity changes of the transmission electric field can be detected even if the incident wavelength only changes by 0.01 mm.The maximum coordinate position of the electric field intensity is recorded when the wavelength changes,the corresponding relation curve can be obtained,and the effect of the spectral resolution can be achieved.The terahertz spectrometer based on a metal parallel slab waveguide array has the advantages of simple design,small size,and portability,and is an excellent alternative to the traditional spectrometer.