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DLP® Discovery System Optics Application Note - page 36 / 38

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2510332 - February 2009

Wedge Prism

0.17 QVGA DMD

Relay

RTIR Prism

Mirror

Projection Lens

Lens Array

The potential disadvantages of the fly-eye lens array are:

Cannot reshape the square LED die anamorphically, possibly reducing efficiency.

The degree of collimation must be high for efficient lens array operation. This is because rays entering the first lens in each pair of lenslets in the array should also go through the corresponding on-axis lens in the pair. If the collimation is not good going in, some marginal rays will diverge too much after the first lens and skew into the adjacent off-axis lenslets surrounding the second lens instead. This produces “ghost” array images at the DMD that can be seen at the top, bottom, and each side, made up of these skew rays. These rays not only are lost light for efficiency, but may also illuminate structures in or around the DMD which create indesirable image artifacts on the screen.

As DMD panel diagonal goes down, the size of the lens in the array gets smaller and the focal length gets shorter. This begins to strain existing manufacturing technologies, which become limited either by lens size or lens sag requirements.

Collimators

Dichroics

Red, Green, Blue LED s

Mirror

36

May not be reproduced without permission from Texas Instruments

Copyright 2009 Texas Instruments Incorporated

About the only thing laser sources have in common with LED sources is the ability to produce a very large color gamut. There are few similarities and many differences. Please refer to drawing 2509927 for more discussion about laser applications with DLP. Here are some of the potential advantages of laser sources:

5.2

Laser Sources

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