Design Of Guided-Mode Resonance Filters For Segmented Planar Imaging Detection System

In order to improve the resolution of remote sensing satellites,the aperture of the optical system needs to be increased to collect enough light energy for imaging.The size,weight,and power for the traditional optical system are dominated by the optical telescope,bulky stiff structures,and thermal controls needed to maintain precise alignment,respectively.The volume,weight and power consumption of optical system will increase with the increase of aperture.The bulky stiff structures and the thermal controls not only occupy huge space and consume a lot of power,but also greatly improve the difficulty on engineering implement of the system.In a segmented planar imaging detector for electro-optical reconnaissance(SPIDER),an image is formed by making measurements for all of the baselines and interferometer orientations,and then numerically reconstructing the object intensity distribution.SPIDER provides a large effective aperture for fine-resolution imaging,while minimizing system volume,mass,power,and cost.However,due to the defects of structure and core components,SPIDER exhibits low efficiency of light energy collection and few spectral channels,which result in poor image quality.In this paper,the working principle and imaging simulation of SPIDER system were studied.A scheme to improve the spectral characteristics of SPIDER system by using guided mode resonance filter(GMRF)was proposed,and the designs of GMRFs were studied.Firstly,the working principle of SPIDER system was studied,and the influence of the number of spectral channels on imaging quality was analyzed by imaging simulation.According to the existing scheme parameters,the numerical simulations were calculated,and a method of using GMRF to obtain tunable spectra with narrow bandwidth,high peak value and low sideband was proposed.Thus the design method of GMRF was studied.Rigorous coupled wave analysis(RCWA)was used to calculate the GMRF,and the formulas were deduced and analyzedSecondly,the guided mode resonance(GMR)effect and its principle in periodic sub-wavelength grating structures were analyzed in detail.The influence of the incident angle and the number of waveguide layers on the reflection resonance spectra were analyzed to determine the incident angle and structure parameters.According to the analysis results,the angular rotation tunable GMRFs of one-dimensional structure in infrared band and visible band were designed respectively.Angular rotation tunable GMRF has the advantages of wide spectrum tuning range and high peak value,but the angular rotation needs to be adjusted by mechanical equipment,which results in the slow spectral tuning speed of this method.Thirdly,in order to improve the spectral tuning speed of GMRF,a spectral tuning method that changing the refractive index of waveguide layer material instead of rotation angle was proposed.Since liquid crystal(LC)materials have the advantages of the tunable refractive index through applied voltage and fast response speed,high-speed tunable spectra can be obtained by using LC as the waveguide layer in the GMRF devices.Then the photoelectric characteristics of LC materials were analyzed,and one-dimensional tunable photoelectric GMRFs with LC layer were designed in infrared band and visible band,respectively.Finally,the polarization characteristics of the above one-dimensional GMRFs were analyzed,and it can be concluded that the spectra of the one-dimensional GMRFs are very sensitive to the polarization characteristics of the incident light.In order to eliminate the dependence of GMRF on the polarization of incident light and obtain the non-polarization spectra,the polarization characteristics of two-dimensional cylindrical array and rectangular array GMRFs under normal and oblique incidence were analyzed.By adjusting the structure parameters,two-dimensional structure GMRFs with non-polarization characteristics were designed.In view of the difficulty of processing two-dimensional structure,one-dimensional GMRF element with two one-dimensional grating structures placed vertically cross was designed.The relationship between the spectra of the element and the incident light angle was analyzed.By choosing different grating periods,the two-grating structure unpolarized GMRF was obtained.When LC material was used in these two kinds of unpolarized elements,the unpolarized reflection peak with narrow band,high peak value and low sideband can be tuned by adjusting the refractive index of LC layer.