Tracking Concentrator - Reflection

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This is an assembled tracking concentrator designed to work in reflection. The Fresnel lens at bottom is metallized on the faceted surface so that light reflects upward from the facets and converges above the device. The gray band just above the Fresnel mirror represents a quarter-wave plate (QWP), which has the effect of rotating the polarization of the light by 90° after it has passed through the QWP twice. The QWP is a passive, unpowered component and can be made from something as simple as a couple of layers of birefringent polymer film. The polarization which had been actively steered by the steering panel on the way down becomes the polarization which is not steered at all on the way up (since the refractive index of the film matches the ordinary refractive index of the liquid crystal). In this manner a single steering panel can be used to keep half of the incident unpolarized light focused on a target.