Abstract: A near infrared zoom optical system with large focal depth and large field of view, which uses the wavefront coding technology, is designed to meet the current imaging requirements of search-tracking in fog, rain and snow, reduce the difficulty of processing and adjusting of optical system, and lessen the influence of thermal effect on image quality. Optical design software can be used to obtain the maximum extended focal depth at any focal length in the zoom range by placing a cubic phase encoding plate at the aperture of the system and optimizing the parameters of the phase plate. The extended focal depth ratio of the system at different focal lengths is analyzed. The operating band of the system is 1.20- 1.67 μm, which has good imaging performance in fog. The focal length of the system is 18- 90 mm. The target surface of detector is the full frame, and the system has a large search field of view, which is beneficial to find a target. In different zoom positions, the focal depth of the zoom optical system is 6.43 times of that of the traditional system at short-EFL, and is 3.21 times of that of the traditional system at long-EFL, which greatly reduces the sensitivity of the continuous zoom system to image positioning accuracy. This method not only makes the system have good image quality, but also makes the requirements of design, processing and assembly more relaxed, and is conducive to eliminate the influence of thermal effect.

Key words: zoomopticalsystem, nearinfraredoptics, wavefrontcoding, focusdepthexpansion