Distribution of Cavity-modes in Narrowband Filters with Chirped Thin-Films

Thin-Film devices with Fabry-Pérot configuration are commonly applied as narrowband filters in spectroscopic measurements or as base element for lasers. The cavity in this layout can be described as an additional layer thickness localized at a central position of a quarterwave multi-layer stack. In our approach this additional layer thickness is distributed over many periods of the multilayer-stack leading to a chirped filter with slightly varying layer thicknesses. Distribution of the cavity layer over the filter leads to wider distribution of the related cavity mode as well, which is beneficial for applications where less localized electric fields are desired. The fundamental properties of chirped filters with distributed cavities are presented and numerical calculations for the optimization of devices are shown. Results of the fabrication and optical characterization of narrowband filters with positive and negative chirp functions are given and discussed.