Miniature Computer-Tomography-imaging-spectrometer.

Abstract

A novel design methodology for the miniature imaging spectrometer has been demonstrated. The Computer-Tomography detection scheme is applied because of its inherently large etendue and snap-shot function. As opposed to the traditional CTIS design that employs only one dispersive element to generate all different spectral and spatial information mixing, the idea of independent information collection and multiple-channel array structure is introduced. Based on this idea our design will not only achieve a very compact sensor structure for limited system aperture size, but also dramatically reduce the alignment and assembly difficulty compared with other micro imaging spectrometers.

By combining diffractive, refractive and graded-index (GRIN) optics into single optical element, every information channel consists of three quarter-pitch GRIN lenses (diameter of 250um) with an on-axis dispersion imaging function. By rotating the information channel to arbitrary azimuthal directions along the optical axis, different dispersion mixing is introduced to the same object's image. This scheme provides the freedom of increasing information channels for higher spectral resolution.

One miniature CTIS sensor was designed with 16 information channels in a 1mm x 1mm x 2mm cube. A single channel was fabricated and tested. A Focused-Ion-Beam Etch method was employed to directly fabricate the grating on the cylinder GRIN lens. A simple but efficient hyper-spectral information reconstruction algorithm was built up and successfully tested with NASA AVIRIS satellite hyperspectral data. The designed sensor performance was tested with different polychromatic objects.