Miniaturized UAV Carrying Pod Double Band Common-aperture Optical System Design

Single-band optical system can no longer meet its mission requirements due to the complex and ever changing application environment of UAV onboard optoelectronic imaging system.In order to meet such mission requirements of UAV onboard photoelectric imaging systems,multi-band imaging optical system has become an important development direction in the future because of its unique imaging advantages.It can not only take advantage of the imaging advantages of multiple band imaging systems at the same time,but also observe the information of the same target at the same time around the clock.In order to avoid the disadvantages of reflective common aperture optical imaging system that include difficult installation and adjustment,a certain blocking ratio and low energy utilization,a dual band common aperture optical imaging system with a refractive common aperture and a beam splitter is designed in this paper.The main works in this paper as follow:Analyze and then select the most suitable materials for the design of the common aperture in this paper because of the lack of optical materials in the wide band;The designed and optimized refractive common aperture optical imaging system was evaluated for image quality using transfer functions and spot arrays,the optical system was subjected to passive optical athermalization in a working environment of-40℃～+60 ℃,and the thermal defocusing and MTF curve were used to evaluate the athermal effect.Based on the Johnson criterion and the minimum resolvable temperature difference(MRTD)model,the visible light system and the medium wave infrared system was analyzed for the detection distances for the designed system,and a cold reflection analysis was conducted for the medium wave infrared optical system.The cold reflection effect of the system was evaluated from two aspects,namely,the cold reflection ray reverse trace map and the NITD contribution value of some lens surfaces.Finally,the zoom curve of the system was drew by using multi-point fitting process and a comprehensive tolerance analysis was performed on the system.The final design result shows that the mechanical compensation zoom method is used in this paper to implement 10× zoom of 17～170mm of the visible light system and 3× zoom of30～90mm of the medium wave infrared system.In a working environment of –40 ～ +60 ℃,after athermalization the modulation transfer function values of each configuration of the visible light system are greater than 0.28 at the cutoff frequency of 145lp/mm with the maximum 26.4° field of view;the modulation transfer function values of each configuration of the medium wave infrared system are greater than 0.3 at the cutoff frequency of 31lp/mm with the maximum 22.6° field of view.The detection distances of the visible light system and the medium wave infrared optical system designed in this paper are more than 10 km and 5km respectively,and for the medium wave infrared optical system,cold reflection effect is negligible.With multi-point fitting process,the cam curve of the system is smooth without inflection points,which meets the design requirements of the system.Finally,with Monte Carlo Method used the tolerance analysis of the optical system demonstrate that the dual band common aperture continuous zoom system designed in this paper meets the imaging quality requirements.