The Research Of Large Zoom Ratio Long Focal Length MWIR Zoom Optical System

With the development of infrared imaging technology, infrared zoom system hasbeen widely used in guidance, monitoring, infrared forward-looking, target detectionand tracking fields. Compared with switch zoom system, Continuous zoom systemhas the advantage of not missing target in field of view during the switching process,which makes it is easy to realize the function of search target in large field view anddistinguish target in small field view. A lot of research work has been launched in thisfield both at home and abroad. And increasing the zoom ratio, reducing the systemweight and complexity is still the hot spot. In addition, in some special fields, thesystem should not only have a large zoom ratio but also required to have a long focallength, then it can observe target in large distance more easy, which makes it is moredifficult to design the system. At present, the MWIR zoom system reported at homeand abroad does not have the characteristics of large zoom ratio and long focal lengthat telephoto end at the same time. Based on this, the paper carried out the design andsimulation research of large zoom ratio long focal length MWIR continuous zoomoptical system. that is to integrated the requirements of optical materials,opticalcomponents,elements processing, mechanical structure and system alignment. Andwe develop a large zoom ratio of long focal length MWIR zoom system to meet thepractical application. Meanwhile, in order to reduce the complexity of the system, wecarried out the design of hybrid diffractive-refractive MWIR zoom system; then we carried out a stray light analysis of the refractive zoom lens system to further improveits image quality.For the Research of large zoom ratio long focal length MWIR Zoom OpticalSystem, this paper carried out the following research work:Firstly, research of infrared continuous zoom system program: research theoptical structure and corresponding techniques of large zoom ratio infrared continuouszoom optical system, analysis the advantages and disadvantages of the variousstructural forms and the feasibility of technology.Secondly, design and simulation of the refractive infrared continuous zoomoptical system: conduct research of infrared continuous zoom lens patent and paper athome and abroad; use the optical design software to design and simulation the largezoom ratio and long focal length MWIR zoom system; use new asphericfunction,then the significant digit to characterize the aspheric surface will be reducedextremely,Ashperic coefficient can directly reflect its impact on image quality, whichmakes it is possible to tolerance analysis of aspheric coefficient; control thecomponent tolerance sensitivity and the cam angle of moveable group, which ensurethe system can be realized in practice and have a better as-built image quality. Useindependent temperature and distance focusing element, the system can has strongenvironment adaptability.Thirdly, design and simulation of the hybrid diffractive-refractive infraredcontinuous zoom system: the diffractive optical elements have the characteristics ofarbitrary phase modulation and negative dispersion,we use it in MWIR zoom system,then we conduct the design and simulation the large zoom ratio and long focal lengthhybrid diffractive-refractive MWIR zoom system; At the same time we assess theworkability of diffractive elements;Fourth, stray light analysis of refractive infrared continuous zoom system:According to the results of mechanical and optical system design, we establish thestray light analysis model; conduct the research of stray light analysis based on thismodel, analysis the main stray light paths, the analysis result provides a useful guide to improve the mechanical system design and an effective guarantee to furtherimprove the image quality.The final study results show that: the large zoom ratio long focal length MWIRzoom system we designed can satisfy the requirements of practical application,thehybrid diffractive-refractive MWIR zoom system have the characteristics of highzoom ratio, long focal length and simple structure at the same time.