Linear Variable Filters for Hyperspectral Imaging
The spectral content of an image contains a wealth of information about the chemical composition of the captured scene. While hyperspectral imaging has been popular for a number of years, recent advances in filter technology have enabled the miniaturization of these systems, leading to widespread deployment. Commonly, a linear variable filter (LVF) is positioned directly on top of a sensor array or camera to provide spectral separation along one axis. In combination with a drone or conveyorbelt providing motion in the other axis, a “hypercube” of x,y,λ data is obtained.This basic technique can be used by farmers to assess crops, for counterfeit detection by characterizing ink composition and in earth science to determine glacier size. The possibilities are endless!
Linear variable filters exhibit a rainbow-like gradient where the wavelength of the spectral feature of interest (long or short pass edge, or center wavelength) increases along the length of the part. Each wavelength is a function of position on the part. Omega has produced spectral gradients up to ~80 nm per mm using environmentally stable, hard oxide coatings well suited to indoor and outdoor applications. With full blocking of the out-of-band spectral range, high transmission in the wavelengths of interest, and exceptional linearity across the filter, Omega’s linear variable filters are a precision solution for hyperspectral applications.