A light-diffractive binary grating structure has a microscopic mesa structure
(2)
whose plateaux (5) are separated by valleys (4) of substantially
rectangular cross-section, wherein the arrangement of the valleys (4) is
periodically repeated. Within a period (T) of the mesa structure (2) at
least N valleys (4) separate the plateaux (5), N being an integer
and greater than 2. The mesa structure (2) is an additive superimposition
of N phase-shifted rectangular structures which have the same period (T) of the
mesa structure (2). Each of the rectangular structures has a phase shift
such that the plateaux (5) of the one rectangular structure fall into the
valleys (4) of the N-1 other rectangular structures. In addition the resulting
mesa structure (2) has only a single valley between two plateaux (5),
which is of a width greater than a seventh of the period (T). The binary grating
structures are suitable for use in optically diffractive security elements as the
binary grating structures cannot be copied with holographic means.
