An expression for the frequency dependence of the phase of reflections from quarter-wave multilayers is deduced. The result is included in a general formula for the resolving power of single half-wave filters and extended to the synthesis of multi-half-wave, or “coupled,” filters.
J. S. SEELEY, "Resolving Power of Multilayer Filters," J. Opt. Soc. Am. 54, 342-346 (1964)