In an optical display system that includes a waveguide (330) with multiple diffractive optical elements (310,340), an in-coupling diffractive optical element (340) couples light into the waveguide (330), an intermediate diffractive optical element provides exit pupil expansion in a first direction, and an out-coupling diffractive optical element (310) provides pupil expansion in a second direction and couples light out of the waveguide. The intermediate diffractive optical element is configured with a crossed grating which is a three-dimensional microstructure that is periodic in two directions. The crossed grating provides multiple optical paths to a given point in the diffractive optical element in which differences in optical path lengths are larger than the coherence length. The crossed grating in the intermediate diffractive optical element may provide increased display uniformity in the optical display system by reducing the "banding" resulting from optical interference that is manifested as dark stripes in the display. The crossed grating can further enable the optical display system to be more tolerant to manufacturing variations.