Linear Variable Filter Coatings for Multispectral FPAs

The Thin Film Engineering Laboratory at Santa Barbara Research Center (SBRC) has recently developed a multispectral Focal Plane Array (FPA) for the 3.0-5.5µm region using a Linear Variable Filter (LVF) mounted directly onto a linear or two-dimensional indium antimonide (InSb) detector array. This technology involves depositing a "wedged" thickness interference filter coating on a single filter substrate and then mounting it directly to the detector assembly using a new proximal mounting technique (patent pending) currently under development at SBRC. Each layer in the coating is wedged by use of a mechanically varying shutter on the substrate tooling during the deposition. The purpose of the wedged coating is to provide a spectral bandpass which varies linearly with position along the length of the substrate such that each element of the detector array responds to a different spectral band.