Design Of Cassegrain Non-focus Coaxial Common-path Optical System

The requirement of modern battlefield for target detection and recognition is increasing.However,the battlefield camouflage makes target detection difficult.If only using the single wavelength imaging,it has been unable to satisfy the needs of battlefield.Visible light imaging and mid-IR imaging have a very good complementarity.Dual band imaging technology can greatly improve the probability of target detection and recognition.For the above problems,this paper designs a dual-band common-caliber optical system based on Cassegrain system.This scheme can achieve the technical requirements,which is the Visible system can detect the target-medium tank 10 km outside and identify 12 km outside,the mid-IR system can detect the tank target 10 km outside and identify the target 7km outside.Firstly,the scheme in this paper designs a front part used the improved Cassegrain common-caliber system,The optical parameters of Visible system is: the visible light wavelength: 0.45 ~ 0.9 μm,F number was 4.5,with 1920 x 1080 CCD,pixel size is 5.5μm;In the mid-IR system: working wavelength of 3.6 ~ 4.8 μm,F number was 4,640×512refrigeration type infrared coagulation as the focal plane array detector,the pixel size is 17μm,MTF in the spatial frequency of 91lp/mm of visible light system is higher than 0.4,at the spatial frequency of 29lp/mm of mid-IR system is about 0.2,close to the diffraction limit.Then,the system adopted the method of electromechanical active way of athermalization,the image quality meets design requirements after realizing mid-IR optical system’sathermalization under the temperature of-40~60℃.Finally,for the mid-IR system,the paper analyzes the cold reflection,and tolerance analysis of the whole system.The system meets the requirements of Engineering Optics,can be well imaging,and can realize the visible /mid-IR infrared distance recognition.