Programmable freeform optics with extended white light sources: possibilities and limitations

Abstract

Freeform optics can be used in lighting applications to generate accurate prescribed illumination patterns from compact light sources such as LEDs. When targeting dynamic illumination systems, a time-variable optical functionality is needed. Phase-only spatial light modulators (SLMs) have been used in the past for various dynamic beam shaping applications with monochromatic, zero-étendue illumination under paraxial conditions. Such limitations can no longer hold when considering lighting applications. In this paper, a novel algorithm for the calculation of smooth phase shift patterns is presented in order to generate arbitrary target patterns from arbitrary incident wave fronts for non-paraxial conditions. When applying such phase shift patterns to SLMs, these devices can be considered as programmable freeform optics. The experimental performance of the calculated phase patterns is analyzed on a real SLM, with a maximal phase shift of 6π, for collimated laser beams and white LEDs. The possibilities and limitations of generating accurate prescribed target patterns are critically discussed in terms of the angular extent of the target pattern, the consider spectrum of the light source and the étendue of the incident light beam.

Creation of One- and Two-Dimensional Copper and Zinc Oxides Semiconductor Structures

“…Two groups of typical beam shaping tasks presented in [132] are shown in Figure 8. The first group includes tasks of redistributing only the intensity distribution of the incident light beam to create a given illuminance in the target plane or a given intensity distribution in the distant zone [133][134][135][136]. When solving tasks of the second group, the both intensity distribution and phase distribution of the incident light beam are redistributed to obtain a predefined illuminance distribution with a predetermined output phase distribution [137][138][139][140].…”

Adaptive illumination systems with programmable freeform optics?

“…The resulting smooth, continous wavefront W can now be used to calculate the required SLM phase shift, such that the incident wavefront S will be converted into the outgoing wavefront W. Following Fermat's principle, the optical path length from the source grid points on S (which are directly connected to the grid points on S ) to the corresponding grid points at W, should be equal. The additional optical path length that should be induced by the SLM, to transform S in W, can thus be calculated from the optical path lengths from S to S , and from S to W [7]. The resulting optical path length difference, can then simply be wrapped to a phase shift pattern with a maximal retardation of 2π, 4π or 6π (see Figure 2).…”