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基于矢量像差理论的离轴反射式宽波段红外目标模拟器研究

Study on Off-axis Relfective Broadband IR Simulator Based on the Theory of Vector Aberrations

【作者】 王健

【导师】 卢振武;

【作者基本信息】 中国科学院研究生院(长春光学精密机械与物理研究所) , 光学, 2012, 博士

【摘要】 随着各种红外双色及多波段制导武器的出现,单一波段的红外目标模拟器已经难以满足半实物仿真试验的需求。利用离轴反射式光学投影镜头克服红外材料对工作波段的限制,是实现宽波段红外目标模拟器的有效途径。本论文针对红外半实物仿真试验对新型目标模拟器的需求,基于矢量像差理论展开对离轴反射式光学投影镜头的像差特性和设计方法的研究,以此为基础设计并研制了宽波段红外目标模拟器。研究内容包括:1.对离轴光学系统矢量像差理论的现阶段研究进行了全面概括,讨论了离轴光学系统三级像差场理论。在离轴光学系统中,并没有新的像差类型产生,但是原有像差的形式产生了变化,主要体现在像差对视场的依赖性发生了改变,在共轴光学系统的像差表达式下增加了降幂项;介绍了像差场偏心矢量的计算方法。2.提出了光阑离轴系统的矢量像差处理方法。利用光阑离轴系统中的光瞳变换关系,引入光瞳偏心矢量,根据共轴系统的像差系数推导出光阑离轴系统的像差场函数,这一方法避免了已有像差场计算方法对局部光学参数(如元件的曲率半径、离轴量、像差系数等)的依赖。对光阑离轴系统的像差研究表明,光阑离轴使球差、彗差、像散、场曲和畸变这五种像差衍生出其它形式的像差,这些像差通过光阑平移矢量交叉耦合在一起。三级像差框架下,彗差具有单节点、像散双节点、畸变具有三节点特性。如果系统在共轴状态下实现对各种像差的校正,那么在光阑离轴后光学系统中同样不会产生像差。这一结论作为光阑离轴系统设计的指导性思想,可以直接用于指导离轴反射式投影光学镜头的设计;3.根据光阑离轴系统像差场的特点,对共轴反射系统的初始结构参数进行了计算;利用光阑离轴实现了由共轴反射式光学系统到离轴反射系统的变换,通过对光学结构参数和像差节点进行控制,完成了用于目标模拟器投影镜头的离轴反射系统的设计。离轴反射式投影镜头的视场角为±3°,出瞳大小100mm,出瞳距500mm,具有像质高、畸变小的优点,并且公差宽松,易于加工和装调;4.完成了宽波段红外目标模拟器系统整机的设计、加工及检测。红外目标模拟器整体采用桁架式结构,并对较大的镜片进行减重处理,实现了红外目标模拟器轻量化设计;系统采用中继散射照明形式,解决了传统衰减方法无法实现红外宽波段连续调节的问题,确保在不同能量状态下投影系统出瞳与被测系统出瞳的匹配关系;系统中的镜片都采用单点金刚石车削的方式加工完成,镜面镀制在红外波段反射率最高的金膜。目标模拟器系统研制完成后,分别用中波和长波红外热像仪对其输出图像进行了观察,结果表明,基于离轴反射的宽波段红外目标模拟器,能够实现从中波到长波红外的均匀面源目标图像输出。

【Abstract】 With the advent of dual-color and even multi-color IR guided weapons, IR targetsimulators of single waveband have become incompetent to meet the needs ofhardware-in-the loop (HWIL) simulations. How to overcome the restriction of IRmaterials on the operating waveband and thus realize broadband IR target simulatorsare of great importance and urgency. The primary objective of this thesis is to developa method to design an off-axis three-mirror IR target simulator whose waveband cancover all the IR bands based on the theory of vector aberration, for the use ofadvanced HWIL simulation on IR guided missiles. The specific research contentsinclude:1. Vector aberration characteristics of off-axis optical systems are summarized,and the nodal theory of third-order aberrations in nonsymmetrical systems isdiscussed. In off-axis optical systems, there are no new aberrations, but the fielddependence of an aberration often changes and the lower field-power dependentaberration items arise in nonsymmetric systems. The method to calculate theaberration field center is discussed.2. A new method is proposed to obtain the aberration field of a pupil-decenteredoptical system. By introducing the pupil decentration vector, the off-axis aberrationfield is deduced from the aberration coefficients of an axially rotational system, so that the nodal features of optical aberrations are insightfully revealed. The methodshows great convenience since parameters of individual surface such as radius ofcurvature, decenter as well as the shifted center of the aberration field are not used inthe analysis. The field characteristics of single-node coma, dual-node astigmatism,triple-node distortion are analyzed. If an axially rotational system has its aberrationswell corrected, then the aberrations in the pupil-decentered state does not exist either.The aberration theory can be applied in the design of off-axis projection systembecause decentering the aperture is a frequently-used method to obtain an unobscuredoff-axis system.3. The detailed method to design an off-axis target simulator is proposed. Withaberration theory the co-axis system structure is calculated at first, then the pupil isdecentered and the system parameters are optimized under the control of layoutstructure and nodal positions. Finally an off-axis reflective projection system with alarge field of view of±3°, large pupil diameter of100mm, large exit pupil distance of500mm and high image quality is obtained. The tolerance is loose compared to that ofan imaging system and the system can be easily manufactured and aligned.4. A broadband IR target simulator is designed, manufactured and tested. Thesimulator adopts a trussed framework and has a lightweight by reducing the weight ofits mirrors. The exit pupil of the illuminating system is kept unchanged for therequirement of pupils’ match between the IR target simulator and the unit under test,by using the relay illuminating system. The reflectors of the system are manufacturedby diamond turning and coated with highly-reflective gold material. MWIR andLWIR thermal imagers are respectively used to obtain the images of the IR targetsgenerated by the simulator. The results show that the broadband IR target simulatorbased on reflective structure can provide a uniform IR target which has a widespectral range from MW to LW infrared.

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