Optical performance of a versatile illumination system for high divergence LED sources

Abstract

An efficient flat-top illuminating optical system optimized for an extended light source is presented. The source is a high-brightness high divergence light emitting diode (LED), sized 1mm×1mm, producing monochromatic emission (525±5nm) with viewing angle of 130°. The design is based on a rotationally symmetrical catadioptric system, developed on a geometrical optics basis, and modelled with ZEMAX® software. The device consists of two optical systems: (i) a collimating system which, in turn, is formed by an aspheric lenses system (low numerical apertures, NA<0.26) and two-mirror system (0.26<NA<0.86), and (ii) an external mirror (NA>0.86) designed and optimized for each purpose. By itself, the collimating system works with a residual divergence of θC=1.46°. The external mirror can be adequately designed to produce some given conditions. For instance, a flat-top profile is obtained in the selected focusing plane, with a maximum transversal intensity variation of 2.5% over 18mm. In addition, when the focusing mirror is allowed to move along the optical axis in a ±1mm range, other interesting profiles can be reached for a given working distance, therefore increasing the versatility of the system.