Design Of Terahertz Broadband Filter With Simple Periodic Binary Subwavelength Structure

Terahertz broadband filter is an important component of terahertz functional devices.It is of great significance in the application of terahertz technology in medical imaging,safety inspection and product testing.At present,the implementation methods of terahertz broadband filter include surface plasmas,metamaterials,etc.,but all of them have some problems,such as complicated structure,difficult fabrication,high cost,and unsatisfactory filtering effect.Therefore,the design of terahertz filter with simple structure and high performance has important academic significance and application value.In this paper,a terahertz broadband filter based on the simple periodic binary subwavelength structure is proposed and designed by combining the rigorous coupled wave analysis(RCWA)with genetic algorithm,achieves the filtering effect of broadband and high transmission efficiency,and breaks through the limitation of the design of above methods.The main contents of this paper are as follows: 1.A terahertz broadband filter design method based on RCWA and genetic optimization algorithm is proposed.Based on the rigorous coupled wave theory,the diffraction efficiency of terahertz broadband filter is mapped to structural parameters(period d,duty ratio f,groove depth h).For the diffraction efficiency and bandwidth of the sub-wavelength grating terahertz filter in the filter band,set an appropriate evaluation function.In combination with the genetic optimization algorithm,various weighting factors in the evaluation function are constantly adjusted according to the optimization results to find the most suitable weighting factors and structural parameters.2.A terahertz broadband filter based on the simple periodic binary subwavelength structure is designed.A terahertz broadband filter with a center frequency of 4.07 THz and a filter frequency range of 2.94-5.27 THz is designed by using the method of RCWA and genetic optimization algorithm.Among them,the highest transmission efficiency in the main lobe was nearly 50%,the average transmission efficiency in the main lobe was more than 40%,and the 3dB bandwidth reached 2.33 THz.3.Perform tolerance analysis on structural parameters.This paper introduces the fabrication error of grating structure parameters and the influence on the performance of subwavelength grating broadband filter.The structure parameters of the filter are analyzed,and the optimum fabrication parameters are obtained.4.According to the tolerance analysis,production and performance testing were conducted.A terahertz broadband filter with a period of 127.19?m,a duty ratio of 0.417,and a groove depth of 29.81?m is made from silicon-based materials.The test results are close to the results of simulation.In this paper,a terahertz broadband filter based on the simple periodic binary subwavelength structure is designed by using the vector theory of binary optical.By combining the RCWA with genetic algorithm,the ideal values of the structure parameters such as period,duty ratio and groove depth are given.Through the tolerance analysis of the structure parameters,the error range of the structure parameters of the filter may appear during processing,which makes the design and manufacture of terahertz broadband filter more feasible.This paper adopts simple structure to realize high-performance broadband filtering,breaking through the limitation of narrow bandwidth and low transmission efficiency of the medium and high frequency terahertz broadband filter,which has broader bandwidth,higher transmission rate,simple structure and convenient fabrication,and is expected to be applied in terahertz communication and imaging systems.