Design Of Cooled Dual-band Infrared Continuous Zoom Optical System

With the development of infrared technology and airborne observation technology, the single-band infrared and fixed focus optical system could not have gradually meet diversification, facilitation and real-time requirements for access to information. The multi-band infrared integrated in a continuous zoom optical system to seek target has become the forefront of military science and technology. Contrast to single-band infrared optical system, the dual-band infrared system has so many benefits. It can eliminate effectively the target information camouflage signal and reduce greatly the false alarm rate and improve the access to information on the target amount. At the same time, continuous zoom system also has its unique advantage:not only used the large field for viewing, but also small field used to sight. And during the working process, it can be sustained tracking target capture through continuous zoom without switching, in order to have real-time, high efficiency, stability and other needs.Based on the analysis about the dual-band infrared systems and infrared continuous zoom system was studied at home and abroad in recent years in this thesis. And dual-band infrared continuous zoom optical system design methods, design consideration and design concept wrere studied in detail. By studying, the cooled dual-band infrared continuous zoom optical system, finally, is designed. This system adopted two-groups-mechanical-compensation-zoom type to achieve the dual-band image plane stable and common continuous zooming with 25x ratio. The zoom curve is smooth without inflection. Two zoom-compensation-groups have a short moving distance and a fast zoom speed. Moreover, this system used a difficult dual-band common optical path and all refraction-diffraction-hybrid structure. It allowed infrared seeker imaging spectrum is 3.6 to 4.8μm and 7.7 to 9.3 μm at the same time. In addition, in order to achieve 100% cold shield efficiency that is requested by cooled infrared system, it used a re-imaging system.The aberration curves, spot diagram and MTF show that the cooled dual-band infrared continuous zoom optical system has a good image quality, the MTF of MWIR still keep higher than 0.5 at 201p/mm and MTF of LWIR keep higher than 0.3 at 201p/mm throughout zooming process. So it is closed to the diffraction limit for the entire field. Moreover, the actual depth of focus both of MWIR and LWIR are less than the theoretical depth of focus. In addition, it achieve athermalized design within the range of -40- to+60-℃ by electromechanical device. Finally, the narcissus of this system is analyzed by reverse ray tracing.