Optical Design Of Visible/Mid-Infrared Dual-band-seeker

Interference and concealment technique in guidance get improved continuously with the development of technology. In order to deal with the situation, according to the characters that the visible light can provide high-resolution images while the MIR can work in day and night, a dual-band-seeker was designed by combining the imaging seeker in two bands.The poor aerodynamic performance of the conventional spherical cover-nose becomes a growing trouble in pace with the increasing speed of the aircraft. The flight efficiency might be lowered by the huge air resistance while the image quality might be deteriorated by the severe aerodynamic heating. A conformal cover-nose was used to improve aerodynamic performance which is the primary task of this research.Large quantity of hard-to-correct asymmetric aberrations including coma and astigmatism are brought in by conformal cover-nose. In order to correct the aberrations with a simpler structure, static correction methods are chosen over dynamic correction methods. Different static correction methods are used in different bands according to the parameters of the two subsystems. The aberrations in visible light and MIR are corrected with Wassermann-Wolf aspherical surfaces and DOE respectively.Due to the severe thermal expansion of the IR optical materials, the image quality of MIR optical system is affected by temperature. Optical passive athermalisation technique was used to make sure the IR optical system can work during -40°～+65°.Image motion is inevitable produced by the movement of optical system with the aircraft gets compensated by digital image processing method without additional agency.Design results can be described as follow:the MTF of the visible optical system is 0.6 in 601p/mm,0.33 in 1201p/mm, spot diagram is less than 10um; the MTF of MIR optical system is 0.768 on axis and 0.7 off axis in 201p/mm, where the diffraction limit is 0.78.The RMS of spot diagram is close to airy disk’s. The spot is almost in one pix range under every field. The image quality hardly changes with temperature by using thermal compensation.The design results show that the two sub systems are good in image quality. The combined system could work in day and night, so that the abilities of capturing, following and recognizing the targets are improved. What’s more, the combined system is compact in structure.The whole system fits the design require well.