Design of a compact four-lens collimation system with integrated light recycling

High-radiance LED illumination systems utilizing incoherent light sources are typically limited by an inherent trade-off between achievable radiance and overall system volume. To overcome this constraint, we designed and fabricated a compact four-lens collimation system with integrated light recycling (ILRC) that combines a freeform surface lens group with a reflective ring structure to efficiently redistribute and recapture divergent light. Ray tracing analysis was performed by three discrete wavelengths (385, 430, and 475 nm) to evaluate key system parameters, including aperture, reflectivity, scattering behavior, and LED chip area. Compared to commercially available alternatives, the ILRC system achieves a reduction in total volume by nearly 50% while increasing the radiant intensity at 385 nm by approximately 65%. When implemented in optical microscopy, the system provided significantly enhanced effective radiance at the sample plane and improved image contrast, confirming its utility as a compact, energy-efficient, and high-radiance illumination solution.