Microoptics for homogeneous LED-illumination

LED-optics for homogeneous illumination of rectangular areas - as required for reading lamps or lighting of imagers - employ a primary optics which acts as collimator and a secondary optics for beam shaping, homogenization and relaying the light onto the illuminated plane. Efficient primary optics are realized by concentrators which are either simple reflecting or combined refractivereflective devices. Different design algorithms based on the modelling of the concentrators by Bezier splines were developed: A modification of the edge-ray principle allows the formulation of the merit function in geometrical terms (for instance the divergence after collimator), while a more general algorithm with direct Powell optimization allows for combined optimization criteria like efficiency and homogeneity in near- and/or farfield. Concentrator prototypes were realized by direct diamond-turning into PMMA. Telecentric, homogeneous illumination of rectangular areas is achieved by a subsequent secondary optics with tandem lens array integrators. We describe design rules for array integrator optics derived from a simple ABCD-matrix formalism. Based on these rules, sequential real raytracing is used for the actual optics system design and analysis of aberrations, which deteriorate homogeneity and useful system transmission. We realized miniaturized array integrators with monolithic tandem microlens arrays, which remarkably reduce overall system length compared to light-pipe approaches. Double-sided cylindrical microlens arrays with large fill-factor over 99%, realized by polymer-on-glass replication of reflow lenses, relax system assembly by shifting critical adjustment steps into element manufacturing