Design of Infrared Telephoto Lenses for Joint Transform Correlator

Infrared optical system has been widely used in many fields, especially in target detection and recognition. While the virtue of infrared optical system is that it can not only detect great distance but also detect the target in the poor conditions such as turbid air or smoke, flog and snow. Hybrid optoelectronic joint transform correlator (HOJTC) is very useful for target detection and recognition. Exploiting the Fourier transform property of a lens, it can implement target detection in real time. Designing perfect optical system is one of key technology of target detection. In this paper, the infrared detector which we adopted is infrared focal plane arrays with working waveband 3-5 mu m. Its resolving power is 30 lp/mm. For the infrared optical system, the effective focal length, relative aperture and the field of view should be large enough to ensure the long distance and large field of view target can be detected. In hybrid optoelectronic joint transform correlator, the light weight and big aperture of infrared optical system is required. For this purpose, an aspheric surface is introduced and the telephoto lens is composed of the three pieces of lenses. The MTF curve of the telephoto lens is close to diffraction limit. The result shows that the aspheric surface can not only simplify and reduce the structure and weight of the system respectively, but also can effectively improve the image quality of the system. This telephoto lens can be used in HOJTC for infrared target detection.