Holographic volume dual-element as an optical variable beamsplitter

Kogelnik's coupled wave theory is used to obtain the relative phase and dir ections of the coupled waves at the output of a planar volume grating. This allows us to obtain the energy coupling on a planar volume grating when it is illuminated by two waves related by diffraction. We illustrate this cou pling with a two grating beamsplitter that splits an incident polarized bea m into two transmitted beams whose intensity ratio may be continuously vari ed without altering the other beam parameters.