## 4 Experimental Validation and Results Analysis
### Stray Light Simulation and Path Analysis
#### 4.3.3 Evaluation of the Suppression Effect of the Light Trap Structure  
To reduce energy leakage from secondary stray light paths caused by multiple reflections within the system cavity, a U-shaped reflective light trap was designed. The structure utilizes highly absorptive inner wall materials and an extended reflective geometry to achieve structural suppression of background illumination. The fabricated prototype and main light tracing principle, shown in Figure 12, has been assembled and demonstrates good engineering feasibility. As shown in the simulation results (Figure 13), the stray light power from secondary paths is reduced from \(1.0\times 10^{-7}\) W to \(5.13\times 10^{-12}\) W after introducing the light trap, achieving more than five orders of magnitude of attenuation. This confirms the effectiveness of the design in suppressing background leakage under high-interference conditions.  
To ensure the accuracy of the stray light simulation model, an empirical _BRDF_ model (Equation (9)) was employed to characterize the angular distribution of scattered energy from key reflective surfaces. The model parameters A, B, and g were determined through fitting with measured or typical material data, and the results are listed in Table 4. Additionally, to describe the scattering behavior of the highly absorptive inner walls of the light trap, an improved microstructure _BRDF_ model (Equations (12) and (13)) was used, and the  
Figure 11: Simulation results of different roughness levels: (a) 2 nm specular scattering stray light; (b) 5 nm specular scattering stray light.  
Figure 12: Light trap main light tracing principle and physical image.  
Figure 14: Optical design results of the solar outage simulation system.  
Figure 15: Design curve of system output variation with the change of light source output.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Gear** & **T*** & **Output** \\ \hline
1 & 1 & 52.94–130.56 \\
2 & 0.50 & 27.89–52.94 \\
3 & 0.25 & 12.94–27.89 \\
4 & 0.11 & 5.5–12.94 \\
5 & 0.05 & 2.5–5.5 \\ \hline \hline \end{tabular}  
* T represents the transmittance of different attenuators.  
\end{table}
Table 6: System output with different gear (mW).  
To verify the power control accuracy, the system was configured with six discrete power levels spanning 2.5-130 mW. Each target output level was calibrated using an optical power meter. Figure 16 presents the deviation between the theoretical and the measured power values. The test results show that the output deviation across the full range remained within 0.9%, confirming the effectiveness of the programmable attenuation module in achieving precise power control. These results also demonstrate the system's reliable power response capability, enabling accurate reproduction of the desired Sun outage irradiance conditions.  
To provide a more intuitive understanding of the engineering implementation of the proposed Sun outage simulation system, the physical setup is shown in Figure 17. The complete system consists of the solar illumination module, the signal light simulation module, and the co-propagating beam combination structure. Key components such as the homogenization unit, rotational stage, and light trap have been fully integrated and tested, ensuring stable system output performance.  
Figure 16: The errors curve between the theoretical and the measured power values.  
Figure 17: Physical diagram of Sun Outage Simulation System: (**a**) Appearance of testing system; (**b**) inside testing system.