All dielectric band pass filters typically consist of all dielectric mirrors made up of quarter-wave optical thick layers and half-wave thick cavity layers. The cavity layers can also be thicker as long as they have multiple half-wave optical thickness. Filters with a single cavity layer will have a triangular shape. Filters with multiple cavity layers can have a square shape. In this paper we will discuss what happens when the cavity layers are made very thick, resulting in multiple pass bands within the quarter-wave stack rejection region.
