05.12.22 -- Understanding Thin-Film Optical Filters

Thin-film optical filters are made by depositing alternating thin layers of materials with special optical properties onto a substrate, such as optical-grade glass. As light makes its way through the optical filter, its direction changes as it passes from one layer to the next, resulting in internal interference.

This paper defines major filter types and discusses how to specify key attributes while also optimizing cost. The filter types discussed include band pass types of ultra-square high cavity count, ultra-narrow and soft coating replacements, and dichroic and polychroic tilted beamsplitter filters.

Alluxa’s thin-film optical filter technology has advanced to the point where the spectral slopes and blocking levels are challenging even the best metrology equipment and techniques. This paper discusses challenges and provides solutions for measuring the spectral response of this new class of high-performance filters.