The Design Of Dual-band Infrared Zoom Optical System

In recent years, with the development of infrared technology and detectorperformance, dual-band infrared zoom system has became an important direction ofthe countries in the development of infrared technology and applications. Comparedwith the traditional infrared systems, infrared zoom lens have unparalleledadvantages: it not only can detect the target in wide field, but also can observe thetarget in narrow field particularly. Furthermore, the dual-band detector reads theinformation of MWIR and LMIR simultaneously and the amount of informationwhich dual-band system gets is twice as much as the single-band.This article firstly summarizes the design theory of the system：basing on theprimary aberration theory, and optical system and refractive/diffractive hybridsystem are designed with CODEV and the tolerance is analyzed.Firstly, the imaging feasure of the dual-band system is summarized andcompared, the appropriate way of imaging and the detector of dual-band imagingsystem is selected; according to the parameters of the detector as well as the opticalengineering theory, the indicator parameters are computed; basing on the theory ofradiation transfer, the SNR of the system is calculated and whether the radiationenergy of the system is enough to extract the signal in detection range isdemonstrated.Secondly, the characteristics of different compensation methods are comparedand analyzed, then an appropriate zoom compensation way is selected; Then theequation of positive mechanical compensation system is established based on thetheory of gaussian optics, and the characteristics of the equation is discussed whichmake the preparation for calculating the initial structure of zoom system.Thirdly, the characteristic of infrared materials is analyzed; Basing on theprimary aberration theory, a focal length range of25~100mm, wavelength range of8~12μm, F/2mechanically positive continuously dual-band infrared zoom system isdesigned with CODEV. Then the image quality is evaluated by analyzing the MTF、 Spot diagrams and aberration curve of the system. The MTF of long-wave for spatialfrequency at20lp/mm achieves0.4, which achieves0.5of middle-wave, and thespot diameter of each wave is less than the size of detector pixel. Further the lateralchromatic aberration of the system is analyzed, which is below0.2μm. Finally,according to the requirements of actual processing, the tolerance of the opticalsystem is distributed using the reverse sensitivity analyzing method, and ultimatelya more relaxed tolerance margin is given.Finally, the differences of the optical properties between the binary opticalelements and the traditional refract lens are summarized. The final system isoptimized by adding two diffraction surfaces into the traditional optical system.Then, the image quality of the diffractive system and the traditional optical systemis compared.