Less distortion of illumination light at device (image of integrating rod) due to lower illumination angles produces less overfill losses, and higher efficiencies. However, some or all of this can be negated by prism coating efficiency losses due to high angles of incidence in the TIR air gap.
The system can be packaged such that projection-lens offset displacement will not add to package height (see Figure 3). In this case, lens offset is vertical toward the long dimension of the prism, and does not add height to the package. Also, note that offset direction is away from flat- and off-state light paths in this configuration, minimizing the chance for stray light to enter the lens aperture and diminish contrast.
Projection and illumination paths (for prism design) can be designed independently, allowing multiple optical sources and interchangeable lenses. This can speed time to market by having parallel development of illumination and projection optics.
2510332 - February 2009
Figure 3. Telecentric TIR Prism Design Layout for Minimum Package Height Due to Projection-Lens Offset
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