Traditional photoelectric reconnaissance equipment belongs to the single-aperture optical system, but the single-aperture optical system cannot effectively obtain the depth, precise position, and velocity of the target. In addition, although the resolution of the telephoto system in a single-aperture optical system is high, and the detection distance is far, the field-of-view angle for detection is small. Thus, it is difficult to carry out a real-time search in a wide area. Moreover, wide-angle cameras are usually short in focus and low in resolution and are not suitable for remote target detection and recognition. As a consequence, the single-aperture optical system cannot achieve a large field-of-view and high resolution at the same time, thereby being unable to give full play to the parallel processing ability. The single-band optical system is subject to the influence of external factors such as light and poor anti-interference performance and cannot achieve all-weather target detection. Given the above background, a dual-band composite aperture optical system is proposed in this paper.

This paper analyzes the design concept of the composite aperture optical system and calculates its relevant design data by building a mathematical model for the field-of-view stitching. The conditions of the dual-band confocal and common image plane are analyzed to ensure the synchronization and consistency of image acquisition in different bands. Through the theoretical calculation of the relay image conversion system, the problem that the curved image formed by the composite aperture system cannot match with the plane detector is solved, and the composite aperture optical system is finally designed. The imaging wavebands of the composite aperture optical system consist of the medium wave infrared waveband and long wave infrared waveband. The main and subordinate apertures are used to cooperate with detection and search. The main aperture is used for remote detection, and the subordinate aperture is used for large field-of-view searches to achieve wide-area and long-distance detection.

First of all, the front end of the composite aperture optical system is composed of a main sub-eye and four subordinate sub-eyes to improve the field of view and detection distance of the system. The main aperture is for the telephoto high-resolution identification of the target, and the subordinate aperture is for the large field-of-view detection and search of the target. In addition, the system can achieve all-weather detection and identification of the target in complex environments due to its medium wave/long wave infrared common optical path design. Finally, the design scheme of the relay image conversion system is selected through comparison and demonstration to solve the problem of image plane matching in the composite aperture system. The relay image conversion system can convert the focal curve image plane of the composite aperture system into a focal plane image, which can be received and collected by the photodetector. The design indexes of the main aperture system (Table 3) can meet the requirement of the 20-km long-range detection of the system, and the design indexes of the four subordinate aperture systems (Table 4) can satisfy the large field-of-view search requirement of the system. According to related design theory and models of the composite aperture system, the design indexes of the system (Table 2) and the relay image conversion system (Table 5) can be calculated.

The composite aperture optical system designed in this paper consists of a main sub-eye and four subordinate sub-eyes. The imaging bands are 3.7-4.8 μm and 7.7-9.5 μm. The main aperture system has a focal length of 200 mm, a field-of-view angle of ±6°, and a detection distance of up to 20 km. The subordinate aperture system has a focal length of 50 mm and a field-of-view angle of ±12°. The optical axis angle of the main and subordinate apertures is 6°, and the combined total field-of-view angle is 24°. The imaging quality of the main and subordinate aperture systems and the relay receiving system is good, and there is no thermal difference in the temperature range of -40 ℃ to 60 ℃. Compared with the homo-type composite aperture system, the system has the characteristics of long-range detection, wide-field-of-view search, and good adaptability to temperature change and has broad application prospects in long-range detection and identification, military reconnaissance, and other fields.