NASA Langley Research Center has developed a novel spectral analysis system that provides rapid multispectral analysis and imaging in a miniaturized system design. Typical spectrometers make use of linear gratings with linear slits or charge-coupled device (CCD) arrays to separate and detect light in its component wavelengths to build a spectrum across a range of wavelengths. Such conventional spectrometers are difficult to miniaturize below a few centimeters. Creating an image with these systems also requires physical rastering of the light beam and detection system across an area to build up the individual data points of an image. The NASA Micro-Ring Thin-Film Spectrometer technology makes use of a microring grating to separate the component wavelengths of the light signal for detection and spectral analysis. Due to the miniaturized design obtained by Fresnel diffraction, an array of these micro-ring grating-based spectrometers can be constructed to enable extremely small-size, multi-spectral imaging of an analysis area.
The NASA Micro-Ring Thin-Film Spectrometer technology is based on a series of concentric rings created in a thin-film structure of micron dimensions. The rings alternate between opaque and transparent and cause the light beam to diffract into a continuum of focal points as a function of wavelength along the axis of the light beam itself. Thus, by detecting and scanning along the axis, different wavelengths of light can be detected to create the spectral response. Alternatively, by using an electro-optic layer that changes refractive index as a function of applied voltage, various wavelengths can be selectively focused at a fixed focal point into an aperture slit. No additional lenses or mirrors are necessary because the micro-ring grating serves to focus the light at the same time as dispersing it into its component wavelengths on the optical axis. The small size of the micro-ring gratings and the simplistic design allow for extreme miniaturization of the spectrometer or spectrometer array. The volume of optical path between the grating and detector can be as small as 1 mm3 and the diameter as low as 0.75 mm.
This technology can potentially be used in micro-optical spectral analysis and imaging for semiconductors, materials analysis, and implanted or embedded spectral analysis.