Experimental verification of spectral grating interference in multiplexed volume holograms employed as broadband dispersive elements for solar concentrators

Using diverse bandgap photovoltaic cells can improve solar conversion efficiency, but these systems also require efficient dispersive optics to direct portions of the solar spectrum onto the appropriate optimized cells. We use an extended coupled-mode model to show how multiplexed volume gratings interact with one another reducing efficiency in the diffraction orders of interest as well as increasing stray light under certain conditions. We conducted experiments with multiplexed gratings in dichromated gelatin to verify our theory. This technique reveals effects that cannot be seen through superposition of single grating models, which suggests that multiplexed gratings must be treated simultaneously when designing such a system.