# Three-Band Spectral Camera Structure Design Based on the Topology Optimization Method
## 1 Introduction  
Compared to single-band imaging systems, multi-band imaging systems not only inherit the imaging advantages of multiple single-band optical systems but also capture target features across multiple spectral dimensions, significantly enhancing the spatial situational awareness capabilities [1, 2, 3]. With unique advantages such as cloud penetration, all-weather operation, and the ability to detect camouflaged targets [4], multi-band imaging systems have been widely applied in military reconnaissance, national defense development, aerial mapping, ground monitoring, environmental regulation, and intelligence gathering [5, 6, 7, 8, 9]. However, the implementation of these advanced functions often comes at the cost of increased system complexity and weight, imposing a heavier burden on platforms. A lightweight design is particularly crucial in this regard. By reducing the weight of the imaging system, it is possible to lower the carrier's energy consumption, improve the endurance and flexibility, and create valuable space and weight margins for the integration of additional functional components. This enablesthe incorporation of multi-band modules, higher-resolution sensors, or other advanced measurement devices, further enhancing the system's performance and multifunctional capabilities. The combination of multi-band imaging systems and a lightweight design not only optimizes the overall efficiency but also enhances their adaptability and competitiveness in harsh environments and complex tasks. With the continuous development of technology and increasing demand, compact and portable multi-band multispectral cameras have emerged. For instance, [PERSON] et al. [10] successfully achieved the simultaneous imaging of visible light and long-wave infrared while ensuring a compact system structure. These instruments are primarily designed to meet the imaging needs of diverse scenarios and applications, especially in complex environments and specific task conditions. The growing demand has driven advancements in both technology and performance requirements. Multi-band spectral cameras not only need an improved spatial resolution but must also adhere to stricter structural design standards [11; 12]. In recent years, various optimization methods have been adopted for optical cameras to enhance the design efficiency, becoming a popular focus of research. The lightweight multi-band camera currently primarily employs two methods: topology optimization and parameter optimization [13]. Among the different methods of structural optimization, topology optimization has recently attracted much interest across research teams [14]. However, discrepancies often arise in the weight reduction of the same structure when using these two methods. While parameter optimization provides optimization within an existing framework, topology optimization allows for a more radical redesign, often leading to superior weight savings and structural performance improvements. Parameter optimization allows the selective optimization of the model based on the given parameters and their value ranges. It can easily lead to globally optimal shape and size solutions for linear and convex problems, but it cannot optimize the topology of the structure [15]. For example, [PERSON] [16] performed parameter optimization on the thickness of the lens barrel wall, resulting in a significant weight reduction of approximately 33%. [PERSON] et al. [17] optimized the thickness and width of the frame for a wide-format push-broom camera, aiming to minimize the weight. This optimization effectively shifted the natural frequency away from the excitation frequency. [PERSON] et al. [18] achieved a weight reduction rate of 73.8% for a space-reflective mirror through dimensional optimization and material substitution.