Optical design for multi-functional IRST system using high-definition detector

Abstract

Infrared Search and Track (IRST) system has been widely applied to cover a wide field-of-view in surveillance systems to passively search, detect, track, classify several objects at as long ranges as possible. In order to achieve that wide area of coverage the optical system must have a relatively large field of view which ultimately limits the observation range due to the fixed size of detector and optical performance of the system. The IRST system could integrate with a Forward-Looking-Infrared (FLIR) camera with longer focal length which increases the observation distance in required situations; this solution would make the IRST system become unnecessarily complex with two separate optical cameras. This paper introduces a mid-wave infrared (MWIR) lens design which has both abilities of high-speed scanning and optical zooming for Infrared Search and Track (IRST) system. A reflecting mirror is integrated within the optical system to perform the scanning function by stabilizing light-of-sight of the optical axis. The scanning mirror is placed to be conjugated with an afocal telescope which has the function of optical magnification. In scanning mode, the field of view is 20° x 16° for a single frame at a maximum scanning angle of 4.32°. In optical zooming mode, the minimum field of view is 6.7° x 5.3° which makes the optical zoom power of 3X. All configurations of the optical system are designed to work with a F/2 SXGA (1280 x 1024) cooled detector having a pixel pitch of 15µm.