Design Of Infrared Optical System Based On Cassegrain-type

In the precision compound detection system,Infrared/Microwave(IR/MW)dual-mode compound detection technique has been widely concerned,which can greatly improve the target tracking and acquisition capabilities,and also antiinterference ability of the detection system.Dual-mode dichroism technique is one of the key techniques of IR/MW dual-mode compound detection.Nowadays,the dualmode dichroism technique of IR/MW dual-mode compound detection adopts mainly thin-film dichroism technique,whereas the following problems exist: thin-film dichroism technique is difficult to achieve a high transmittance of the microwave signal,and even worse,the reflection energy of microwave directly enters into the infrared detector,which interferes with infrared detection system and affects the quality and stability of infrared imaging.In this paper,with respect to the problem of dual-mode dichroism technique of IR/MW dual-mode compound detection,metallic mesh is employed as the dichroic component to achieve the dichroism of IR/MW.Dual-mode compound detection infrared optical system is designed to provide the physical simulation for verifying the effects of utilizing metallic mesh as dichroic component on the IR/MW dualmode compound detection infrared optical system.Firstly,characteristics of the microwave reflection and infrared transmission of the metallic mesh are simulated to verify the feasibility of the IR/MW dual-mode compound detection with metallic mesh as the dichroic component.Cassegrain system is chosen as the basic structure of dual-mode compound detection infrared optical system based on the work characteristics and the design principles of the infrared optical system,by introducing the correction lens group to increase the field of view and balance the aberration.The above research provides the theoretical basis for the overall scheme design of dual-mode compound detection infrared optical system.Further,an infrared optical system has been designed based on the above scheme.Firstly,the shape dimensions and face coefficients of the primary and secondary mirror of the Cassegrain-type R-C system are calculated on the basis of the near-axis optical theory of the Cassegrain system and the theory of the aspherical primary aberration.Secondly,the correction lens group and dichroic component are introduced into the infrared optical system for optimization design by using ZEMAX optical simulation software,and accordingly a dual-mode compound detection infrared optical system has been attained with the focal length of 100 mm,F/# of 2,the block ratio of 0.4048,and imaging of the diffraction limit for 8 ～ 12μm band.Lastly,the tolerance and stray light of designed infrared optical system are analyzed,and the reasonable tolerance and improvement measures for suppressing stray light relating to the structure and processing technique are given.Finally,the imaging effects of infrared optical system are tested.The energy transmittance of infrared optical system is greater than 60% by testing the infrared reflectance of the primary and secondary mirror and the infrared transmittance of the correction lens group;the imaging effects of the infrared optical system are tested by using micro-bolometer with non-cooled infrared focal plane detector,which can successfully identify the shooting target;by analyzing the required parameters of infrared optical system and the imaging properties of infrared detection,it can be seen that the infrared optical system can get an ideal imaging quality.To sum up,the designed infrared optical system can be applied to verify the effects of utilizing metallic mesh as the dichroic component on infrared optical properties of dual-mode compound detection infrared optical system.