Objective With the rapid development of infrared imaging systems, target recognition of infrared images can achieve the determination of ultra long range targets and the guidance of long-range weapons. To accurately analyze the performance of infrared systems, it is necessary to improve the simulation ability of the infrared simulator itself to match high-resolution and high dynamic range infrared images. The research on domestic infrared dynamic scene simulators mainly focuses on small field of view, short exit pupil distance, and the projection system adopts a one-time imaging method, which can meet the requirements of low resolution MTF. The DMD type infrared simulator requires a light source for illumination as the DMD is a radiation modulation device. The illumination method mainly uses Kohler illumination, where the filament of the light source is imaged at the entrance of the optical system through a condenser and a variable aperture. Although it can improve the uniformity of the system, the lens composition and the system are more complex. The lighting system adopts TIR splitter prisms, which require complex splitter prism design and reduce energy utilization efficiency; Adopting an off-axis system can avoid interference and occlusion between the projection system and the lighting system. However, due to the characteristics of DMD itself, it requires a large aperture angle, resulting in a large size of the lighting system. Based on the current development status of DMD type infrared simulators, the optical mechanical system design of compact infrared simulators is carried out, which effectively reduces the size of the simulator, improves energy utilization efficiency, and improves lighting uniformity.
Methods Due to the large exit pupil and field of view angle of the system, the infrared projection system in this article adopts the telecentric optical path method of secondary imaging (Fig.3); The splitting method did not adopt the design of splitting prisms and off-axis, but adopted the critical illumination method of blackbody combination mirrors for design. In the selection of light sources, a high-accuracy surface source blackbody with adjustable temperature and wide range was selected as the system's light source (Fig.8). On the premise of ensuring high resolution, two reflective mirrors are added to the optical path to compress the overall volume of the system (Fig.8). Due to the overall reduction of the system, the mechanical structure of the system has also been designed and analyzed to ensure that it can provide stable mid-wave infrared simulation (Fig.12-16).
Results and Discussions This article designed a compact telecentric optical path projection system and a critical illumination method using a blackbody combination mirror, effectively compressing the overall size of the system and improving its uniformity. Using ZEMAX for optical path analysis, the design results show that the MTF of the projection system is better than 0.5 at 36 lp/mm (Fig.4), the wavefront aberration is less than 0.076 7 \lambda (Fig.5), and the distortion is less than 1% (Fig.7). The uniformity of the lighting system is greater than 98% (Fig.9). Using ANSYS for mechanical analysis, it was found that the first-order modal frequency is 212 Hz (Fig.12), the maximum deformation of the radial X-direction medium wave simulator is 0.054 mm (Fig.13), and the maximum stress is 17.116 MPa (Fig.14). The maximum deformation of the radial Y-direction medium wave simulator is 0.028 mm (Fig.15), and the maximum stress is 5.27 MPa (Fig.16), which meets the requirements for use. Finally, an infrared simulator system was established, with a volume of less than 400 mm × 300 mm × 400 mm. By inputting images and using a thermal image for testing, it was shown that the overall design of the system is compact, the imaging quality is high, and stable infrared image simulation can be provided in the medium wave band.
Conclusions This article designs the optomechanical system of a compact infrared simulator. Through analysis of current infrared simulators, in order to make the system more compact, reduce system size, and improve system uniformity, while ensuring high resolution, a compact telecentric optical path projection system is designed. The critical illumination method of a blackbody combination mirror is adopted, effectively reducing the volume of the system. Finally, an infrared simulator system was established, with a volume of less than 400 mm×300 mm×400 mm. By inputting images and using a thermal image for testing, it was shown that the overall design of the system is compact, the imaging quality is high, and stable infrared image simulation can be provided in the medium wave band.
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