This thesis investigates the concentration of solar light for the generation of entangled photons. Previous studies have demonstrated that pumping a nonlinear crystal with coherent laser light can produce entangled photons via spontaneous parametric down-conversion (SPDC). The objective of this work is to explore the feasibility of generating entangled photons using solar light as the pump source. An experimental setup is developed that efficiently collects approximately 1000 W/m² of sunlight and couples it into an optical fiber to pump a nonlinear ppKTP crystal. Primary focusing is achieved using a Fresnel lens with dimensions of 1 m × 1.4 m, while a secondary concentrator guides the focused light into a multimode optical fiber with a core diameter of 1500 µm. The efficiency of the secondary concentrator is identified as a key factor determining the usable pump power. Several concentrator designs are investigated through optical simulations and experimental testing. Initial approaches employing cascaded compound parabolic concentrators and conical segments yield low coupling efficiencies. To overcome these limitations, optimized geometries including a solid glass droplet and a single polished conical concentrator made of fused silica are developed. Simulations predict total efficiencies of up to 66.9 % for high-index materials. Outdoor experiments under real sunlight demonstrate that coupling solar light into an optical fiber is feasible, with up to 62 mW successfully coupled. The results provide a foundation for future solar-driven quantum optical systems and related free-space applications.
Jasvinder S. Brar (Wed,) studied this question.