Research On The Infrared Imaging System Based On Wavefront Coding

Compared with visible imaging system, application field of infrared imaging system ismore complicated and increasingly wide. Because of the thermal effect of infrared opticalmaterials is sensitive, the influence of ambient temperature to the infrared imaging systemis quite obvious compared with external factors. In order to ensure imaging quality inworking temperature range, athermalization is necessary for traditional infrared imagingsystem.Wavefront coding is a two-step imaging system which includes both optical image anddigital image processing. By adding a special phase mask on the pupil plane, the wave frontof incident light is encoded, and the OTF and PSF become insensitive to defocus within anextended range. Thus equal blurred middle images could be obtained from CCD. By usinga same digital filter which was decided by the designed optic system, the final clear imagein an extended depth of filed could be acquired. This is same as the athermalization theoryof infrared optical system. If the range of depth of focus extended by wavefront codingexceeds the thermal defocus caused by the variations of temperature, wavefront coding canbe an athermalization method applied in infrared imaging system to make the systeminsensitive to temperature.Firstly, the background and significance of the research are introduced. We discuss thepossibility of wavefront coding applying in infrared imaging system. The application ofwavefront coding and its research status both abroad and at home are also presented.Secondly, the theories of wavefront coding and decoding are introduced, the analyticalexpression of cubic phase plate is derived. The defocus invariance of wavefront coding isdiscussed. Thirdly, by analyzing the relationship between DM (the MTF difference wheredefocus is zero and maximum) and the two characteristics of wavefront coding: defocusinvariance and the image restorability, optimization method of phase plate based on MTFinvariance is established. Through simulation experiment, we test this optimization methodfrom spatial, frequency and light position. Fourthly, by designing control experiments,illustrating that wavefront coding can be an athermalization method applied in infrared imaging system, which can make the system insensitive to temperature, at the same timereduce complexity and cost of infrared imaging system. Finally, the designed lens andphase plate are manufactured and specific experiments is conducted to verify systemperformance.