Earle Wilson
(Morehouse College)

The experimental set-up for this experiment was relatively simple. The major components were an Interferometer (which we used solely as a laser source for most of the experiment), a Texas Instruments Digital Micro-Mirror Device (DMD Chip) and a Charged Couple Device (CCD camera). As shown in the diagram above, the DMD and CCD were mounted on translation stages that allowed them to move back and forth.

For our experiment, we allowed laser light from the interferometer to illluminate the DMD chip. The light then diffracts off the DMD's surface and the subsequent diffraction pattern is detected by the CCD camera, which sends it to our main computer.

The DMD Chip

The crux of the experiment was the DMD chip. The DMD chip is also a digital light processor (DLP). Our DMD chip comes from a TI line of DLP chips that was designed to be used in Home Theatre Systems and Laptop Projectors. Our model was a TI DMD Discovery 1100.

• The DMD surface is a 1024 by 768 micro-mirror array mounted on a circuit board.
• The micro-mirror array is arranged in a square-grid pixel arrangement.
• Each micro-mirror is 13 by 13 microns with approximately a 1 micron spacing between each.
• Each micro-mirror is capable of moving in either an "ON" or an "OFF" position.
• "ON" is defined as when the micro-mirror is tilted at +12.5 degrees off axis. "OFF" is defined as when the micro-mirror is tilted at -12.5 degrees off axis. This is illustrated in the diagram below
• Therefore, depending on the viewer's position relative to the DMD chip ON or OFF could either be a dark or bright mirror.
• By manipulating ON and OFF positions virtually any pattern can be created. In other words, each micro-mirror acts a pixel that can either be dark or bright
• Examples of such patterns are shown below.

The next step of the experiment was to choose an appropriate pattern to put on the DMD's mirror array.