Based on the theory of coupled waves the amplitude of the first-order diffracted wave and the diffraction efficiency is calculated for sequentially superposed plane gratings that are stored in dielectric transmission volume holograms. Using suitable approximations, both the Bragg-angle incidence and any deviations can be described. The grating interaction effects make it possible to couple the incident energy from one wave to another and to build up beam-couplers and splitters with certain coupling parameters. These coupling properties are adjustable in a definite manner by the recording process.