Highly efficient Y-junctions with arc-bend branch structures of sunlight guiding systems for indoor illumination

This paper proposes both symmetrical and asymmetric Y-junctions with arc-bend branch structures for auxiliary indoor-illumination applications. These arc-bend branch structures can be used as a concave-mirror-like light guide, to change the direction of beam propagation and also to converge the beam spread angle. Optical simulation results show that the proposed arc-bend Y-junctions can achieve an inner coupling efficiency, not including plastic/air interfaces, above 90% in both usages: beam combiner and splitter. Particularly, when the applied branch opening angle becomes large, this high optical efficiency becomes more significant than those of linear straight Y-junctions. Moreover, it is also confirmed that the coupling efficiency of the symmetric arc-bend junction can be as high as 90.0%, and the asymmetric coupling efficiency is 93.4%, even if the branch opening angle is quite large.