With the growth of military demand for multi-spectrum, high-resolution, long-range photoelectric reconnaissance and surveillance, large-aperture multispectral optical system with common aperture is widely used in airborne optoelectronic mission payloads. At the flight altitude of 10000 meters, the optical system actually works at -30℃ ambient temperature, while it is assembled and tested at room temperature. Therefore, the airborne optical system should ensure excellent image performance in the wide temperature range, such as from -50℃ to +70℃. A large aperture catadioptric optical system with long focal length is designed. The optical model with zoom multi-configuration structures at room temperature, high temperature and low temperature is established, and it is based on the linear thermal expansion thermal-structural-optical integrated model. Optical focusing variables are introduced at high temperature and low temperature to optimize the image quality at the respective temperature. The optical system has excellent image performance at both high temperature and low temperature. The design results show that the waveband is 0.7μm~0.9μm. The MTF of the catadioptric optics with relative aperture F/3.6 and focal length 900mm is close to the optical diffraction limit at +20℃, -50℃ and +70℃, which ensures good image quality from -50℃ to +70℃.
The abbe number of diffractive optical element is negative, which is opposite to that of traditional refraction optical element. So diffractive optical element has unique advantages on achromatic and thermal compensation. Therefore, it can be applied to diffractive and refraction hybrid optical systems to simplify the optical structure and improve the imaging quality. However, the diffraction efficiency of the single-layer diffractive optical element depends on the wavelength mightily , However, the diffraction efficiency of the design order of the double-layer diffractive optical element in the whole working band is coincident basically and more than 90%, which can significantly suppress the stray light of the non-design order and advance the image contrast. Therefore, the double-layer diffractive optical elements are adopted in this long-wave infrared wide waveband optical system, and the design idea of superposing the diffractive surface on the aspheric surface is proposed. Only two lenses and two materials were used to realize the optimal design. By matching the microstructure parameters of the double-layer diffractive elements ,the diffraction efficiency of the whole working band reached more than 97%. Imaging quality analysis shows that the chromatic aberration of 8μm-14μm is well corrected. the secondary spectrum is well controlled also, and the MTF is close to the diffraction limit, which meets the design requirements.
Super-wide FOV lens has a short focal length, making the detection distance shorter. To suit the need of long detection distance, the inversed telephoto structure is used. In this paper, we designed a super-wide FOV camera system with a negative-positive inversed telephoto structure, whose FOV is 95°×71.25°.And optical aberration were analyzed detailedly, the structure of foreside and backside were made certain respectively, based on these, optical optimum design was accomplished.The result shows that in the entire field of view, the MTF at 60lp/mm is more than 0.4, the diameter RMS of spot diagram dispersion circle is less than 5 microns and the maximum distortion is less than 5%. The result shows that it meets the requirement of system well.
When the field of operation of precision strike missiles is more and more complicated, autonomous seekers will soon encounter serious difficulties, especially with regard to low signature targets and complex scenarios. So the dual-mode sensors combining an imaging sensor with a semi-active laser seeker are conceived to overcome these specific problems. Here the sensors composed a dual field of view mid-infrared thermal imaging camera and a laser range finder have the common optical aperture which produced the minization of seeker construction. The common aperture optical systems for mid-infrared and laser dual-mode guildance have been developed, which could meet the passive middle infrared high-resolution imaging and the active laser high-precision indication and ranging. The optical system had good image quality, and fulfilled the performance requirement of seeker system. The design and expected performance of such a dual-mode optical system will be discussed.
For the realization of target detection and monitoring of a wide range with the unmanned aerial vehicle (UAV), an UAV-based reconnaissance and surveillance system was proposed. The main optical system was consisted of visible camera with narrow field of view (FOV), mid-wave infrared camera (MWIR) and long-wave infrared camera (LWIR). The aperture was shared and the spectrum was disparted in the terminal. The diameter of primary mirror was 170mm. The focal length was 880mm and field of view was 0.86º for visible camera with narrow FOV, the focal length was 880mm and field of view was 0.8º for MWIR camera, the focal length was 220mm and field of view was 3.2º for LWIR camera. Considering the influence of temperature on the imaging quality, a kind of material with good thermal property was used as mirror substrate. The athermalization method was introduced to realize a high image quality in a wide temperature range of -40℃~+65℃. Zoom optical system was adopted in the visible camera with middle FOV and wide FOV, the view of it was 3.4º~34º. The operating distance of laser channel was designed to 20km. The results of the design indicated that this set of optical system could be used for ground target detection and monitoring of a wide range, met user’s requirement.
With the demand of autonomous precision guidance of air defense missile, the system scheme of the IR imaging/Ladar dual-mode seeker with a common aperture was proposed, and the optical system used in was designed. The system had a common receiving aperture, and its structure was very compact, so it could meet the requirement for the miniaturization of the seeker. Besides, it also could meet the demands of a wide field of view for searching target, and the demands for accurately recognizing and tracking the target at the same time. In order to increase the narrow FOV tracking performance, the dual FOV infrared optical used the zooming mode which some components flip in or out the optical system to firm the target signal. The dual FOV optics are divided into the zooming part, with dual variable focal length, and the reimaging part which was chosen in such a way to minimize the objective lens while maintaining 100% cold shield efficiency. The final infrared optics including 4°×3°(NFOV) and 16°×12°(WFOV) was designed. The NFOV lens composed of two common IR/Ladar lens, three relay lens, a beam splitter and two reflective fold mirrors, while WFOV lens increased two lens such as Germanium and Silicon. The common IR/Ladar lens ZnS and ZnSe could refractive the IR optics and Laser optics. The beam splitter which refractived IR optics and reflected Laser optics was located in the middle of Germanium and Silicon. The designed optical system had good image quality, and fulfilled the performance requirement of seeker system.
With the demand on Infrared and Electro-Optical sensors’ detectability, Large aperture optics have been widely used. But the deform of the opto-mechanical system has been induced by heavy deadweight of the large aperture optical elements and by the change of environment temperature could lead to the attenuation of the Infrared and Electro-Optical sensors’ detectability. For weakening the influence of deadweight deform and temperature change, people utilize the fruits of adaptive optical technology achieved the unattenuated performance of Electro-Optical sensors. A infrared adaptive optical system based on Hartmann-Shack wave-front sensor is designed. The wave-front sensor has adopted in the visual spectrum for lower cost and higher precision. So the fore large aperture telescope must work in the dual waveband such as middle-infrared wavelength and visual wavelength. The final dual-waveband telescope achieved 4’ collimation at the visual wavelength and 10’ collimation at the middle-infrared wavelength. The dual-waveband optical system for IR adaptive system achieved high-resolution middle-infrared imaging and real-time visual-waveband wave-front distortion measuring.
A compact mid-wavelength infrared zoom camera with a zoom range of 15:1 and active athermalization has been
developed. The moving groups for a wide zoom range are only two lens groups and moving machanisms of zoom are
very simple, which allows easy access of opto-mechanical and electromechanical design. The final design adopts the
configuration of reflective mirror fold, comprising of two mirrors and eleven refractive lenses made of two infrared
materials such as germanium or silicon. The movement of the lens groups and the focal length of the system are smooth
and continuous. The zoom lens has the advantages of simple structure, high image quality, simple moving lens groups,
short zoom path and smooth zoom locus.
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