A monomaterial-based resonator structure is proposed here, which can replace the multilayer-based narrowband transmission filter. This new concept of introducing the effect of multilayered structures of different materials into a single material is based on etching out repeatable structures of two different dimensions on the same material. As the etched-out repeatable structures are of different dimensions, it is possible to obtain periodic layers of two different-effective refractive indices. This type of monomaterial-based optical filters avoids the challenges generally faced while fabricating multilayer structures of different heterogeneous materials having different refractive indices. The dependence of the filter action on the number of bilayers of two different-effective refractive-index materials formed by etching and on the cavity region thicknesses is studied. Although the study is done mainly on lithium niobate on insulator, but it is seen that similar effects occur for materials of varying refractive indices. © 1989-2012 IEEE.