• Two-stage concentrator system achieves 2 0,328×theoretical concentration ratio . • Optical model defines spot size and convergence angle design limits. • 1000 µm fiber (NA=0.37) relaxes alignment tolerance for broadband coupling. • Achieved 87.8% fiber coupling efficiency with 0.46 mm focused spot diameter. To address the challenge of efficiently coupling broadband, high-energy-density sunlight into a single optical fiber, this study proposes a two-stage concentrator architecture. A two-stage optical system based on a Fresnel lens and a plano-convex lens was constructed, established an optical transmission model defines two critical coupling criteria: the short-wavelength spot diameter must be smaller than the fiber core diameter, and the convergence angle must match the fiber's acceptance angle. Through parametric optimization and aberration suppression simulation, the system achieved a theoretical concentration ratio of 20,328. Experimental validation across the broadband spectrum (520–1064 nm) demonstrated that the focal spot diameter was compressed from 5.75 mm in the primary stage to 0.46 mm in the secondary stage (representing a 92% reduction in spot diameter), achieving an optical fiber coupling efficiency of 87.8%. The high alignment tolerance provided by the 1000 μm core silica fiber (NA = 0.37) guaranteed the engineering feasibility of the two-stage system for efficient broadband solar coupling. This study validates the feasibility of the two-stage concentrator for high-efficiency broadband solar energy coupling.
Li et al. (Sun,) studied this question.