Compact computational spectrometer using a solid wedged low finesse etalon.

Abstract

A novel, to the best of our knowledge, two-layer hybrid solid wedged etalon was fabricated and combined with a traditional imager to make a compact computational spectrometer. The hybrid wedge, comprised of ${{\rm Nb}_2}{{\rm O}_5}$ and Infrasil 302, was designed to operate from 0.4-2.4 µm. Initial demonstrations, however, used a complementary metal-oxide semiconductor (CMOS) imager and demonstrated operation from 0.4-0.9 µm with spectral resolutions ${\lt}\;{30}\;{{\rm cm}^{- 1}}$ from single snapshots. The computational spectrometer itself operates similarly to a spatial Fourier transform spectrometer (FTIR), but rather than use conventional Fourier-based methods or assumptions, the spectral reconstruction used a non-negative least-squares fitting algorithm based on analytically computed wavelength response vectors determined from extracted physical thicknesses across the entire two-dimensional wedge. This new computational technique resulted in performance and spectral resolutions exceeding those that could be achieved from Fourier processing techniques applied to this wedge etalon. With an additional imaging lens and translational scanning, the system can be converted into a hyperspectral imager.