  Spectral splitting of the sunlight using diffractive optical elements (DOEs)
is an effective method to increase the efficiency of solar panels. Here, we
design phase-only DOEs by using an iterative optimization algorithm to
spectrally split and simultaneously concentrate solar spectrum. In our
calculations, we take material dispersion into account as well as the
normalized blackbody spectrum of the sunlight. The algorithm consists of the
local search optimization and is strengthen with an outperforming logic
operation called MEAN optimization. Using the MEAN optimization algorithm, we
demonstrate spectral splitting of a dichromatic light source at 700 nm and 1100
nm with spectral splitting efficiencies of 92% and 94%, respectively. In this
manuscript, we introduce an effective bandwidth approach, which reduces the
computation time of DOEs from 89 days to 8 days, while preserving the spectral
splitting efficiency. Using our effective bandwidth method we manage to
spectrally split light into two separate bands between 400 nm - 700 nm and 701
nm - 1100 nm, with splitting efficiencies of 56% and 63%, respectively. Our
outperforming and effective bandwidth design approach can be applied to DOE
designs in color holography, spectroscopy, and imaging applications.
