A film stack adapted to enable optical readings on a film stack. Multiple gratings layers are disposed within transparent layers, and include a topmost grating layer, a bottommost grating layer, and at least one intervening grating layer. Each one of the grating layers have a pitch between substantially opaque portions of the grating layer and substantially transparent portions of the grating layer. The substantially opaque portions of the bottommost grating layer are laterally disposed at an offset from the substantially opaque portions of the topmost grating layer. The substantially opaque portions of the at least one intervening grating layer are laterally disposed between the opaque portions of the bottommost grating layer and the substantially opaque portions of the topmost grating layer.