Optical Parameters in High-Efficiency Optical Receivers With a Parabolic Reflector Before and After Coating With Ag Film

Abstract

High-efficiency optical receivers before and after the coating of Ag film are composed of a parabolic reflector, a solid parabolic second optical element (SOE), and a Fresnel/aspheric concentrating lens. The optical receivers before the Ag-film coating are fabricated on a high-precision machine tool based on an optimum design attained from ray tracing software simulations. The real profiles of the reflector before and after coating the Ag film are found to be the average of the two orthogonal parabolic profiles. They are then compared to the perfect profile (without profile error and surface roughness) in order to investigate the influence of the profile error and the Ag film on optical performances. The optical parameters, including the total flux, the optical efficiency, and the maximum, minimum, and mean irradiances are evaluated for ray projection simulations in the ASTM G173-03 spectrum. Experiments for the same ray source are also carried out to compare with the simulation results. It is determined that Ag-film coating can improve the profile error and surface roughness of the reflector, thus resulting in all optical parameters being either equal to or higher than those of the reflector without Ag coating. The total flux and optical efficiency obtained from the module with the Fresnel lens has values relatively higher than those of the aspheric lens. The irradiance uniformity for the Fresnel lens is also determined to be better than that of the aspheric lens. The irradiance intensity of the reflector after coating the Ag film has a magnitude at various wavelengths higher than that of the reflector without the Ag-film coating. Due to the coating of the Ag film, the optical receiver shows an almost constant rise in optical efficiency for the two types of concentrating lenses. This characteristic is shown to be valid for both the simulation and experimental results.