A Fresnel lens imaging performance can be seriously impaired by chromatic dispersion which typically doubles the diameter of the focused sun image in a solar concentrator. This problem can be alleviated by means of a molded diffraction grating whose diffraction-induced dispersion offsets and substantially cancels the lens intrinsic refractive index dispersion. The grating lines would comprise a second tier of small-scale, Fresnel-type facets superimposed on the lens facets, with a typical grating facet height of about 40 micro-inches and a facet width ranging from about 1 milli-inch at the edge of the lens to around 5 or 10 milli-inches near the center. In its primary intended application the grating would function in a core daylighting system to improve the optical performance of a collector which focuses direct sunlight into fiber optic couplers. For this application chromatic dispersion would be reduced by an order of magnitude with only a 2% loss in optical efficiency.
BT - SPIE Optical Materials Technology for Energy Efficiency and Solar Conversion Conf. XIII C1 -Windows and Daylighting Group
C2 - LBL-27950 CY - San Diego, CA DA - 08/1989 LA - eng N2 -A Fresnel lens imaging performance can be seriously impaired by chromatic dispersion which typically doubles the diameter of the focused sun image in a solar concentrator. This problem can be alleviated by means of a molded diffraction grating whose diffraction-induced dispersion offsets and substantially cancels the lens intrinsic refractive index dispersion. The grating lines would comprise a second tier of small-scale, Fresnel-type facets superimposed on the lens facets, with a typical grating facet height of about 40 micro-inches and a facet width ranging from about 1 milli-inch at the edge of the lens to around 5 or 10 milli-inches near the center. In its primary intended application the grating would function in a core daylighting system to improve the optical performance of a collector which focuses direct sunlight into fiber optic couplers. For this application chromatic dispersion would be reduced by an order of magnitude with only a 2% loss in optical efficiency.
PP - San Diego, CA PY - 1989 T2 - SPIE Optical Materials Technology for Energy Efficiency and Solar Conversion Conf. XIII T3 - SPIE Optical Materials Technology for Energy Efficiency and Solar Conversion Conf. XIII TI - Chromatic Dispersion Compensation in a Fresnel Lens by Means of a Diffraction Grating ER -