Micromirrors are key to optical measurement

17 Jun 2002

A new optical measuring device offers a cheaper, quicker alternative to confocal microscopy.

Researchers at the Fraunhofer Institute for Production Technology (IPT) have developed a prototype optical device, which they claim can measure an object's location and height to within a thousandth of a millimeter.

In the past, scientists have relied on confocal microscopy, a technique that uses a focussed beam to scan an object layer by layer to build up a three-dimensional image. A rotating perforated Nipkow disk positioned between the light source and the object filters the light in such a way that each layer can be scanned separately. But according to Frank Bitte, an engineer at IPT, these disks have serious drawbacks.

"Nipkow scanning disks are expensive and produced only in small numbers," he said. "Also, [varying the quality of the image] requires different disks and changing them is a time-consuming procedure." To combat this, the researchers have replaced the Nipkow disks with digital micromirror devices (DMD). These lower-cost, mass-produced alternatives are already widely used in digital video projection.

In the researchers' new optical measuring device, the DMD contains half a million micromirrors on a surface the size of a thumbnail. By electronically tilting each micromirror independently, the team is able to reflect multiple, tightly focussed light beams in the required direction to obtain the dimensions of an object.

"Because the DMD can be adjusted electronically, the [optical device] is more flexible," said Bitte. "Moreover, there is no interference from vibration or friction, as occurs with rotating disks."

The researchers expect their optical devices to find use in applications such as measuring and testing strip conductors in microelectronic circuits.