Manufacturing of a Linear Variable Filter for Spectral Order Sorting

An analytical thin film thickness model based on the geometry of a commercial vacuum coating system is proposed. This model can calculate the profiles of linear variable filters (LVFs), which are used to eliminate overlapping orders of spectra due to the use of a diffraction grating and which are fabricated using a local mask, producing a linearly variable thickness. While the filter transmits the first-order wavelength and blocks the second-order wavelength. The 75% and 25% relative thicknesses deviation between the evaporated film and the theoretical model is less than 5%, indicating good suitability for LVF design and fabrication.