## 5 Discussion  
This study developed a solar radiation simulation system to meet the key requirements of ground-based Sun outage interference simulation. The system features high spectral uniformity, high irradiance homogeneity, wide-range dynamic power modulation and ultralow stray light. A co-path beam output configuration was also implemented by integrating a signal light module, enabling the simulation of realistic communication interference scenarios. Experimental validation of all key performance indicators demonstrates that the system fulfills the core parameter requirements for Sun outage simulation and exhibits both engineering feasibility and functional completeness. Nevertheless, the following limitations and areas for improvement remain:  
While our _BRDF_-based ray-tracing simulations demonstrate consistent stray light suppression (5.13 \(\times\) 10\({}^{-12}\) W achieved in Section 4.3.3), we acknowledge the inherent limitation of relying solely on numerical modeling. The co-propagating architecture fundamentally precludes conventional stray light measurement techniques (e.g., _VGI/PST_) that require separable optical paths. Even emerging coherent detection methods, despite their high sensitivity in other applications, face three inherent constraints in our system: the 200 mm output aperture significantly exceeds the active area of available coherent detectors (<10 mm diameter) and the 10\({}^{10}\) dynamic range between solar background and target stray light exceeds the linear operation range of balanced homodyne detection.  
Spectral control performance is inherently constrained by filter manufacturing tolerances. Although the system achieves 78% average spectral matching (exceeding the 75% minimum requirement), localized transmittance deviations at critical edge wavelengths (1540-1541 nm) exceed theoretical predictions by \(\leq\)5%--a fundamental challenge in multilayer deposition. The power-spectrum co-optimization (Section 3.2) provides adaptive tolerance through nonlinearity compensation, maintaining >75% uniformity even with edge wavelength deviations. While the 78% mean uniformity suffices for sun outage simulation, future designs will prioritize edge wavelength control to further enhance spectral precision.  
While the current system is optimized for the 1540-1560 nm communication band to address Sun outage simulation, the underlying methodology exhibits notable extensibility to broader spectral ranges. The key distinction lies in the adaptation of spectral matching criteria: our precision wavelength control approach (achieving 78% point-by-point match in narrowband) would transition to integrated irradiance matching for broadband applications (e.g., 400-2500 nm solar monitoring), where maintaining total spectral energy distribution supersedes individual wavelength accuracy. This scalability is facilitated by the modular design of both the homogenization optics (maintaining >85% uniformity regardless of spectral width) and the _BRDF_-based stray light suppression (effective across UV-NIR). However, full spectral extension would require source reconfiguration--replacing the tunable laser with a supercontinuum source and optimizing the apodizer's chromatic performance, representing a focused area for future development.  
In summary, while the system meets all its key performance objectives, further improvements are needed in spectral range scalability and stray light measurement capabilities.