The problems of maximum allowable cone of incidence and peak shift with angle of incidence have been examined both theoretically and experimentally for multilayer Fabry—Perot interference filters. It is shown that both effects can be characterized by a monolayer with an effective refractive index. Explicit expressions for the effective index (which is intermediate between that of the high and low components), the peak transmission, and the half-width are given. The method is extended to the case of double-half-wave filters, and the effective index deduced.
C. R. PIDGEON and S. D. SMITH, "Resolving Power of Multilayer Filters in Nonparallel Light," J. Opt. Soc. Am. 54, 1459-1464 (1964)