Experimental measurements of RXI concentrators

A small series of nonimaging RXI concentrators designed for concentrating radiation on a 1 mm2 photodiode have been manufactured by injection molding of PMMA (polymethyl methacrylate). Their entry aperture diameter is 40 mm and the design acceptance angle is +/- 2.24 degrees. Measurements done at (lambda) equals 890 nm show an optical efficiency of 33.8% and the relative transmission drops from 90% to 10% when the incidence angle varies from 1.2 to 3.4 degrees. A computer model of the concentrator which takes into account the different optical losses shows that optical efficiency is increased up to 57.1 % using silver metallization and (lambda) equals 800 nm. Moreover if photodiode position error is corrected, then the efficiency grows up to 76.2%, and if profile errors are also corrected, then the efficiency reach 88.2%. A more stepped angular transmission requires a most accurate manufacture process.