High-efficiency free-form nonimaging condenser overcoming rotational symmetry limitations

Abstract

The importance of condenser optics is the fact that it is the bottleneck limiting efficiency in commercially available projection systems. Conventional condensers use rotational symmetric devices, most of them being elliptic or parabolic mirrors. They perform very far from the theoretical limits for sources such as arc lamps or halogen bulbs. Typical small displays in the 5-15 mm 2 etendue range have geometrical efficiencies about 40-50% for the best condensers; although theory allows about 100% (no reflection nor absorption losses are considered). The problem is in the coma aberration of the reflectors and the rotational symmetric image of the source making the source projected image to unfit with the target. Thus, the only way to improve this performance is to generate a free form design that is able to control the shape and rotation of the source projected images. As yet, this can only be done with the SMS3D design method. We present here one of such designs achieving a collection efficiency 1.8 times that of an elliptical condenser for a 4:1 target aspect ratio and for the range of target etendue with practical interest and 1.5 for 16:9 target. These designs use only 1 additional reflection, i.e., use a total of 2 reflections from the source to the target. A prototype of one type of free form condenser has already been built.

Design of a novel free-form condenser overcoming rotational symmetry limitations

“…When target etendue is small, the slope of the XX curve in Fig. 12 is less than the theoretical slope, because the XX does not fill completely and uniformly the circular field of view (see the intensity distribution in ref [17]). …”

“…The "shoulder" of the XX efficiency curve is rounded (in contrast to the theoretical one, which shows a slope discontinuity). This is due to the non-stepped transitions of the illuminance distribution on the target plane and also to the rounded contour lines of that illuminance distribution (see [17]). …”

“…Although the design for a cylindrical source is conceptually similar to the one done above, the details are significantly different. These details are given in [17].…”