Study On The Fabrication And Polarization Performance Of Pixelated Polarizer Arrays

Polarization imaging detection technology provides a new imaging means for improving the ability to detect targets in special environments.Depending on the way the polarization information is collected and the scene in which the image is observed,the commonly used methods of polarization detection are time-division polarization detection,amplitude-division polarization detection,aperture-division polarization detection and devision of focal plane(Do FP).Do FP polarization detection method integrates four sub-wavelength metal micro-polarizers with four different polarization directions into the pixels of camera,and it can realize the miniaturization of the polarization imaging system,which has the advantages of system stability,simple system structure,small size,good polarization performance and real-time polarization imaging.However,due to the constraints such as the pixel size,grating period,linewidth and preparation process,its extinction ratio and accuracy of polarization detection need to be further improved.In this thesis,the preparation method and polarization performance of Do FP sub-wavelength metal gratings are studied.In the simulation,a metal grating model with different structural parameters is established,and the transmittance and extinction ratio of the metal gratings with different periods,heights,line widths and oxide layer thicknesses are simulated,and the influences of structural parameters and oxide layer thickness on the polarization performance are studied.In the manufacturing,electron beam lithography and laser interference lithography are used to study the preparation of pixelated sub-wavelength metal gratings.The method of superlens enhanced laser interference lithography is proposed to prepare pixelated grating arrays,and the network structures are studied.The formation mechanism of the structure and the influence of the exposure parameters on the structure size and morphology during the preparation process are analyzed.In the performance testing,the polarization performance test system is designed and built for the fabricated pixel polarizer arrays in the visible light band,which provides a test method for the polarization performance measurement of the Do FP sub-wavelength metal grating arrays.The polarization performances of the fabricated pixel polarizers with different grating directions are tested and analyzed.The mechanism of selective transmission of subwavelength metal grating polarizers is studied,and the Al grating models with different structural parameters are established using the FDTD solutions simulation software.The effects of structural parameters(period,height and linewidth)and oxide layer thicknesses on the polarization performance are analyzed.In the wavelength range of 300-700 nm,the transmittance and extinction ratio of the grating with different periods(100/140/170/200 nm)and heights(50/100/150/200 nm)are simulated,and it is found that the smaller period has the higher TM transmittance,and the greater extinction ratio.Considering the limitation of preparation process conditions,this thesis will study the sub-wavelength Al metal grating arrays with the period of 170 nm.Based on the 170 nm period,different grating heights are studied,and the trends of TM transmittance and extinction ratio are considered comprehensively,and the grating height is determined to be 150 nm.The TM and TE transmittances and extinction ratios of pure Al gratings with different linewidths(60-110 nm and 110.6-125.7 nm)are studied.The results show that the wider linewidth has the lower TM transmittance and greater extinction ratio.When the difference between adjacent linewidths is 3-7 nm,the transmittance and extinction ratio have changed significantly.The transmittance and extinction ratio of different oxide layer thicknesses(4-12 nm)of the gratings are studied.It is found that the polarization performance of the Al metal grating whose surface layer is oxidized is lower than that of the pure Al grating,and the polarization performance is inversely proportional to the thickness of the oxide layer.A combination of electron beam lithography and inductively coupled plasma etching is used to fabricate a pixelated Do FP sub-wavelength Al grating array on a quartz substrate.The the grating direction of each focal plane pixel is 0°,45°,90°and 135°.The pixel size is6.4?m×6.4?m.The proximity effect on the structure in the electron beam exposure process is studied.In the experiment,the dose correction and pattern size compensation methods are used to effectively avoid the problems of overexposure,adhesion and underexposure of the grating structure caused by the proximity effect.The influence of the dose variation during electron beam exposures on the feature size of gratings is studied.The results show that the change of the electron beam exposure dose by 10?C/cm~2 will change the line width of the Al grating by 3-7 nm.In addition,a method for the efficient preparation of Si gratings by superlens enhanced laser interference lithography is proposed.The formation mechanism of the grid structure and the influence of different exposure doses and interference light intensity contrast on the structure morphology and feature size of the two-beam direct laser interference lithography are studied.Pt nano-network gratings,Pt gratings and Si grating structures are proposed using two-beam direct laser interference lithography technology,the mask is used to prepare the Do FP Si grating structures with the directions of 0°,45°,90°and 135°,which can be used in THz polarization detection system.For the prepared pixelated sub-wavelength metal grating arrays,a polarization performance test system was designed and built in the visible light band.Since the pixel size of the Do FP metal grating prepared in this thesis is small,and there are four pixelated sub-wavelength metal grating arrays at the same time,it is necessary to test the grating structure of each pixel unit in different directions.Thus,this thesis introduces the components of the test system and test methods,and sets up the Do LP and Ao P test optical system based on the polarization performance test system.The test results show that the linear polarization of the incident polarized light from the polarizer is very good.The constructed system is used to test the prepared grating structures,and the effect of oxidation time on the extinction ratio is studied.The correctness of the simulation results is verified,and the reasons for the difference between the test results and the simulation results are analyzed.