## 1 Introduction  
With the rapid development of space optical payload technology, the design of optical payload has shifted from focusing solely on basic indicators such as resolution and field of view (FOV) to a systematic indicator of multi-purpose and high-efficiency applications. Among them, the multifunctional and multispectral imaging capability of single payload based on highly integrated detectors is an important developmental direction to enhance the observation capability of payloads. Judging from the current development of payloads in the world, many satellite payloads adopt the idea of multi-spectral integrated design. For example, the United States commercial satellite Worldwide-3 has 1 Panchromatic band, 8 Multispectral bands, 8 Multiband in SWIR (Shortwave Infrared) and 12 CAVIS (Corrects for Clouds, Aerosols, Vapors, Ice, & Snow) bands [1]. In addition to obtaining high-resolution optical images, Worldview-3 can also obtain short-wave infrared band images, which has a good application prospect in fire detection and mineral detection [2]. For another example, South Korea's KompSat-3A satellite not only has 1 Panchromatic band and 4 Multispectral bands, but also has a 3.3-5.2 um mid-wave infrared imaging capability [3,4]. The Goodrich SYERS-2 detector used by the ORS-1 satellite, launched by the United States in 2011, has seven imaging spectrum bands, including panchromatic band, near-infrared band, two short-wave infrared bands, one mid-wave infrared band and red band and green band [5]. The GaoFen-4 (GF-4) satellite launched by China in 2015 can achieve a resolution of 50m in the visible and near-infrared bands of 400-900 nm and a resolution of 400m in the mid-wave infrared band of 3.5 um to 4.1 um in an orbit of about 36,000 km [6]. The advantage of infrared imaging is that it mainly relies on the radiation imaging of the target and the background, and generally does not require external environmental light sources. The infrared imaging system is less affected by severe weather such as rain, snow, wind and frost, and can also image normally at night [7]. It has the ability to work all day, and has a certain ability to recognize camouflaged and anti-interference targets. However, the infrared detector is not sensitive to the brightness changes of the scene, and the imaging resolution and clarity are relatively low, which is not conducive to human eye judgment [8]. The visible light band remote sensing camera can obtain high-resolution images, the images are clear, in line with human visual habits, and can show the true color characteristics of the target. However, the visible light band camera is greatly affected by weather conditions, and its observation ability is limited in rain, snow, and cloudy environments, and its night observation ability is relatively weak [9]. The low-light detector can effectively enhance the camera's ability to acquire information in the visible light band in low-illumination environments, extend the effective working time of the camera, and to a certain extent make up for the camera's weak night observation ability [10]. The single-spectrum detector imaging system can acquire very limited spectral information in the target area, while the use of multi-detector integrated cameras working in different spectral bands can make use of the data complementarity and redundancy of different detectors. This results in a single payload owning the ability to simultaneously acquire high-resolution images of multiple spectral bands in the target area, which greatly enhances the camera's ability to adapt to the environment and the ability to acquire information about the target. According to the current demand for multi-band imaging equipment, this paper proposes a compact visible/long-wave infrared dual-band common aperture design. By sharing the primary and secondary mirrors and the separate field of view design, the two bands can be imaged on one device at the same time.