Design Of Infrared Continuous Zoom Optical System Based On Diffraction Optics

With the rapid development of infrared imaging technology,its application in zoom lens is extensive.The infrared zoom lens is divided into continuous zoom and multistage zoom system.Multiple zoom system can only image clearly at the fixed focal length for its fixed design,while continuous zoom system can achieve clear imaging within the scope of design by zooming stably for the existence of cam.Consequently,the infrared continuous zoom system is widely used in security,temperature measurement and detection guidance military and civil field.As UAV(Unmanned Aerial Vehicle)technology developing rapidly,infrared continuous zoom system is frequently applied to airborne photoelectric load in recent years.Due to the size and weight limit of UAV load,the optical system with large zoom range and small system volume is more favored.Studying the MWIR(Medium Wave Infrared)continuous zoom optical system with a large F number,it is generally found that the zoom ratio is 30 times and the total optical length is difficult to control within 200 mm.Therefore,it is a great significance to design the 30× MWIR continuous zoom system with the total length of optical less than 170 mm for improving comprehensive performance of airborne photoelectric load.Traditional infrared continuous zoom system cannot achieve high zoom ratio and miniaturization simultaneously.Considering this problem,this paper proposes a new composite continuous zoom mode which a piece of lens is isolated from the front fixed set as two-speed moving group,and combines the two-speed moving group,zoom group,compensation group,and back fixed group into a composite continuous zoom system.This kind of composite continuous zoom mode helps to achieve the goal of design High magnification optical system.The establishment of the composite continuous zoom model was completed.For 640×512 cooled mid-wave infrared focal plane detector array,a continuous zoom optical system with a focal length range of 12?360mm,F-number of 4,and a working band of 3.7? 4.8?m was designed by using the composite continuous zoom model.This system uses several diffraction optical elements combined with the use of aspheric surface,and achieves the goal of correcting aberration,improving image quality and shortening the total length.There is no requirement of adding mirror folding optical path for the system,and the total optical length is only 160 mm.The system adopts secondary imaging technology to achieve 100% efficiency of cold stop.The processing parameters and diffraction efficiency of the diffraction optical element in the composite continuous zoom optical system are also analyzed,the cold reflection suppression ability of the system is evaluated,and the fitting of the cam curve is optimized.The optical system has the advantage of high zoom ratio,miniaturization,excellent image quality,high diffraction efficiency and smooth cam curve,and hence it has a good application prospect in the field of photoelectric detection.