Micromirrors Improve Detectors

Hank Hogan

Researchers at Southern Methodist University have proposed a design for better infrared detectors. The micromachined devices promise to measure the actual temperature of objects and to enable multicolor IR imaging with video frame rates, characteristics absent from uncooled IR arrays.

Today's micromachined IR detectors do not measure the temperature of a body. Rather, they determine the power radiated at a given wavelength and from it estimate the temperature based on the output of an ideal radiator of heat. The real world, unfortunately, lacks perfection, so this approach is inaccurate.

The ability to take readings at multiple wavelengths would improve performance, so the team has designed a two-color micromachined IR detector. The key element is a mirror that sits below the detector and is mounted on a cantilevered silicon arm. Applying a voltage moves the arm, which changes the size of the optical cavity and alters the response of the detector. Using this approach, a single detector should be able to capture information from two parts of the spectral region and to rapidly switch between wavelengths.

Typically, the mirrors are the approximate size of a bolometer, or in the range of 25 x 25 or 40 x 40 µm, said Donald P. Butler, who led the research effort. Vladimir N. Leonov, now with XenICs of Louvain, Belgium, assisted Butler on the project, which they reported in the June 1 issue of Applied Optics.

Toward realization

At present, the micromirror-based two-color detector is only a theory, but Butler noted that nothing in the scheme is beyond current technology. For their part, the researchers are planning to construct a prototype.

"That's one thing we would like to do, and we're really looking for funding now to go and build one," Butler said.