DMD spectrometers are Digital Micromirror Devices (DMD), which is a two-dimensional array of tiny MEMS-based mirrors. The technology Ibsen is using is the Digital Light Processing (DLP®) DMD from Texas Instruments.
This technology is extensively used in projectors in offices, homes, and cinemas but, the DMD technology can also be used for spectroscopy as described on this page.
A DMD based spectrometer like the PEAK XNIR, provides the following key benefits over other types of spectroscopy:
- Lower cost than diode array-based spectroscopy in the NIR range
- More robust than scanning grating type monochromators
- Advanced scan options like Hadamard to improve SNR, speed, or other parameters
The picture below shows a close op of an array of micro-mirrors in a DMD. Each mirror can have three positions: ON, OFF, and Neutral.
How a DMD based spectrometer works
The picture below shows schematically the construction of a DMD based spectrometer in a very simplified case with only three micromirrors.
The first part of the spectrometer is very similar to a regular diode array spectrometer (DDA) with a slit, a collimating lens, and a diffraction grating. The function of the diffraction grating is to separate the wavelengths into different angles as illustrated by the blue, green, and red light rays in the picture. Normally, in a DDA spectrometer, we would place an array of photodetectors after the diffraction grating to detect the amount of intensity of each wavelength. However, in a DMD spectrometer, we place the micro-mirror array at this location. This enables us to select one or more wavelengths by setting the mirrors in the ON or OFF position. At the output end of the DMD spectrometer, we have placed a single photodetector that detects the wavelength(s) we have selected.
To illustrate a simple scanning through the spectrum the pictures a), b), and c) show how the blue, green, and red wavelengths are being selected and measured by the photo-detector one by one.