DLP Technology In Near Infrared (NIR) Spectroscopy

A new approach to performing the wavelength analysis that promises to provide greater performance than the traditional methods utilizes digital light projection (DLP) technology. The key to this new approach is the use of a digital micromirror device (DMD) that takes the place of the detector array or scanning mechanism and acts as a programmable wavelength filter, as shown in Figure I.2. The DMD consists of an array of mirrors constructed using MEMS technology. The tilt of each mirror can be changed to direct light towards the detector or away from the detector and is controlled electronically from a DLP control board. Each column of mirrors in the array is illuminated by a narrow range of wavelengths in a manner similar to the detectors in the linear array, but the extra height presented by the column collects more optical power from the grating than a single, small detector can collect. A range of wavelengths is selected for analysis by selecting the mirror tilt of the column to direct light to the detector. Using the mirrors eliminates inter-pixel noise in detector arrays and allows the use of a larger area point detector since the dimensions of the mirrors are the responsible for the wavelength resolution of the spectrometer. An added advantage of this method is that measurements can be readily limited to known wavelengths of interest if desired (i.e. if the spectral lines of a sample compound are well known) so that the time and processing power needed to complete the measurement can potentially be greatly reduced.

Figure I-2: DLP-based approach to making spectrographic measurements using MEMS technology

In the following pages, the components and operating principles inherent to the DLP-based spectrometer approach are discussed in more detail and specific examples of the method are provided based on the NIR Nano compact spectrometer system.