Athermal Design of Infrared Telephoto Used in Joint Transform Correlator

Abstract

On the basis of optical correlation detection, joint transform correlator(JTC) is widely used in military, aviation and intelligentization and so on. It has the advantages of great flexibility and high precision of recognition. The optical system is applied to receive the infrared radiation of the target. Athermalization is the key to stabilizing the optical performance with respect to off-design temperature. Therefore, the image quality of optical system in different temperatures plays an important role in JTC. In order to improve the environmental adaptability of JTC, the infrared telephoto system with high image quality and high performance-price ratio is designed for wavelength 8μm～12μm to detect target in a large range of temperature. This telephoto lens is composed of four refractive lenses. Three materials, zinc selenide, germanium and zinc sulfide are used to compensate for the temperature. The focal length is 200 mm, the relative aperture is 1:3, and the field of view is 6.4°. This system has the characteristics of small volume and compact structure. The optical system image quality is evaluated with ZEMAX optical design software. The results have shown that MTFs in the range of -40°C to +60°C are all closed to the diffraction limited curve. The spot diagram RMS radius of each field is closed to the Airy disk radius. The system meets the requirements of technical specification and improves the ability of JTC in target tracking and recognition.