Toleranced freeform optical design with extended sources using ray targeting

Abstract

Freeform optics are limited to design with simplified source models. With a realistic extended source, the resulting design is limited by the ability to hold the source and optic to the desired tolerances. For example, a design is made around the nominal emitter characteristics, such as an encapsulated LED die. This process is called tailoring. Positioning and spectral output can vary appreciably for these emitters. A method to design optics with extended sources with tolerances taken into account is presented. This method uses targeted ray tracing to specify particular points on optical surfaces. In the method presented here, the source is represented instead as a collection of non-ideal sources, each weighted according to the statistics of the dimensional and color variations that are expected in the source. The design is iteratively developed over its extent where each step accounts for the multitude of tolerances potential ray paths through the optics. The end result is to design optics that are tolerant to the predicted level of error, while maintaining the desired level of efficiency and distribution at the target. This method notably samples the differential étendue aspects of the source as it propagates through the system. Upon solution of the iteratively generated reflector control points, an optimization run can be performed to improve performance. We present a wall-wash example to illustrate the method.