Monte Carlo ray-tracing simulations for diffractive optics

Diffractive optic elements offer significant advantages in optical system design, enabling lightweight and compact architectures compared with conventional refractive and reflective components. However, accurately modeling wave-optical effects in such systems remains challenging because characteristic wavelengths of light are much smaller than the overall dimensions of typical optical assemblies. Conventional ray-tracing methods generally neglect these effects, while full-wave simulations become computationally prohibitive for large-scale systems. To overcome these limitations, we introduce a numerical implementation of the Monte Carlo ray-tracing approach based on the Huygens-Fresnel principle to predict key optical parameters, including focusing efficiency, focal spot size, and diffraction patterns with high fidelity. This approach is validated through systematic comparisons of dedicated experimental, theoretical, and numerical results, demonstrating accurate performance over a broad range of optical configurations. We further demonstrate that photon sieves incorporating large numbers of pinholes distributed across Fresnel zones can focus light into spots smaller than the smallest pinhole diameter while strongly suppressing higher diffractive orders and sidelobes. These results highlight the potential of the ray-tracing approach as a practical tool for both the design and optimization of next-generation diffractive optical elements.