Investigation of an optical method for determining the average radius of curvature of micro-optical lenticular lens arrays

摘要

Micro-optical elements are of great importance in areas of optoelectronics and informationprocessing. Establishing fast, reliable methods for characterization and quality control of theseelements is important in order to maintain the optical performance in a high volume productionprocess. We investigate an optical technique, applied to a polymer-based, injection moulded,lenticular array, but the method is also applicable for the tooling for these elements. Thecylindrical lenses have feature sizes of 1-15 rm. The method is based on observation of theintensity distribution, which can be obtained in the far field of surface reflections resulting froma plane wave incident on the lenticular array. The intensity distribution of the diffraction ordersis highly correlated with the shape of the illuminated lenslets. This is exploited to attaininformation about possible defects and shape variations that have arisen in the mouldingprocess. The experimental results are compared with a model, based on the Fraunhoferapproximation to the Huygens—Fresnel principle. Furthermore, the optical elements underinvestigation are probed using a scanning probe microscope. Hence, access to accuratetopological data of the elements is attained and used to confirm the validity of the proposedoptical technique.