Beam displacement and distortion effects in narrowband optical thin-film filters

A three-dimensional model for beam propagation through optical interference filters is presented. The model predicts a wavelength-dependent lateral beam displacement of tens or hundreds of micrometers in narrowband filters at an angle of incidence of only 3 degrees to 5 degrees . The effects of filter bandwidth, wavelength offset, angle of incidence, and beam size are investigated. The effect is experimentally confirmed for a 100 GHz filter at a 3.5 degrees angle of incidence.