Development Of A Near-infrared Polarizing Chip Based On Metamaterials

Infrared polarization imaging technology plays a key role in astronomy,medicine,military and other fields,and has important research value and application prospects.At present,the infrared device technology is very mature,but the traditional infrared detection system can only obtain the intensity information of the target,and the infrared polarization detection system can only obtain the polarization information of the target,so it is difficult to give full play to its fusion advantages.With the development of infrared detection and polarization technology,the infrared polarization imaging system has been successfully developed.However,the existing infrared polarization imaging system is large in size and low in energy utilization,which has become a bottleneck problem in the application of infrared devices.The key to solving this problem is to design and fabricate a compact and lightweight near-infrared polarization(imaging)chip with high signal-to-noise ratio and high stability that integrates polarization and imaging.With the maturity of micro-nano preparation technology,the emergence of metamaterials provides a new way to meet the above needs.Therefore,in this paper,the design,fabrication and characterization of nearinfrared polarizing chips based on metamaterials are carried out.The specific research contents and results are as follows:In terms of theoretical research,based on the detection requirements of polarization imaging in the near-infrared band,a near-infrared metamaterial metal polarization structure is designed.The excellent polarization selective transmission characteristics of subwavelength metal gratings was taken into account together in this design.A simulation model based on subwavelength metal gratings was constructed by the finite difference time domain(FDTD)method.The effects of parameters as metal film materials,grating period,duty cycle and thickness on the super-transmission polarization filtering and extinction in the near-infrared band were analyzed.Three materials of Au,Ag and Al were chosed as research objects.In the band range from 0.8μm to 1.1μm,Au has the highest transmittance of the three,Al has the highest extinction ratio,and the polarization property of Ag is weaker than those of Au and Al.Therefore,Au and Al were selected in the following simulation study.When change the structural parameters,it was found that the grating period and thickness were proportional to the transmittance and extinction ratio.The duty cycle was proportional to the transmittance and inversely proportional to the extinction ratio.The structural parameters were optimized according to the actual machining accuracy.Based on these optimized results,Au was selected as the metal material.The grating period P was set at 500 nm,the duty cycle F was set at 6 and the metal film thickness h was set at 100 nm.Based on the simulation results,a near-infrared polarizing filter was fabricated using focused ion beam etching equipment and magnetron sputtering technology.Its surface structure was also characterized.According to the principle of polarization test,a performance test system for near-infrared polarization filters was designed and built.The test results showed that the maximum transmittance can get to 58.5% and the extinction ratio can reach 4.58 in the band range from 0.8μm to 1.1μm.The transmittance was reduced by 26.5%and the extinction ratio was increased by 12.9% compared with the simulated value.The reason is that the irregular splashing of particles during the etching causing the grating line width to be larger than the theoretical value.It causes the simultaneous reduction for the TM and TE wave,which resulting in a decrease in transmittance and an increase in extinction ratio.Further,the near-infrared polarization chip was integrated with the near-infrared polarization filter and a near-infrared detector.The grayscale images of the light source spots in the near-infrared band at different polarization angles were obtained by using this polarization chip.The extinction ratio of the polarizing chip was calculated to be 4.85,which verified the polarizing imaging capability of the polarizing chip in the near-infrared band.This research realizes the polarization properties of subwavelength metal metamaterial structures and its application value in polarization imaging.It also provides a design route and original model for miniaturized and low-cost polarization imaging chips.