Optical system design of a new type infrared dual-band seeker

Abstract

Based on the appearance of infrared dual-band device and the technical parameters of infrared seeker, a new-type Cassegrain optical system is designed. The main advantages of the system are large field-of-view, infrared dual-band common path and compact structure. In the Cassegrain optical system, the working wavelengths are 3.7μm~4.8μm and 8μm~12μm, the field-of-view 4° and the aperture 240mm. The paraboloidal primary mirror and hyperboloidal secondary mirror are all replaced by spherical surfaces. So the problems of high machining accuracy and alignment become much easier. In order to balance the aberrations, two compensating lenses are used in the system. The amounts of compensating lenses are much less than other optical systems. So the new optical system becomes much more economy, light and compact. The total length of system is 170mm. The ratio of total length to focal length is 0.62. So it can meet the operating requirement of seeker in limited space. Moreover, the system has a good performance of athermalization between negative 40°c and positive 50°c. The design results of the system show that the MTF value of each field is greater than 0.7 when the cut-off frequency is 11 lp / mm. Wavefront aberration is less than 0.038λ.