Diffractive optical elements with asymmetric profiles
In an optical display system that includes a waveguide with multiple diffractive optical elements (DOEs), gratings in one or more of the DOEs may have an asymmetric profile in which gratings may be slanted or blazed. Asymmetric gratings in a DOE can 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. Banding may be more pronounced when polymeric materials are used in volume production of the DOEs to minimize system weight, but which have less optimal optical properties compared with other materials such as glass. The asymmetric gratings can further enable the optical system to be more tolerant to variations—such as variations in thickness, surface roughness, and grating geometry—that may not be readily controlled during manufacturing particularly since such variations are in the submicron range.
1. An optical display system, comprising:
a substrate of planar optical material;
a first diffractive optical element (DOE) arranged on the substrate, the first DOE having an input surface and configured as an in-coupling grating to receive one or more optical beams as an input; and
a second DOE arranged on the substrate which receives one or more optical beams from the first DOE and couples the received one or more optical beams to a third DOE, and in which the second DOE is configured as an intermediate DOE for pupil expansion of the received one or more optical beams along a first direction,
wherein at least a portion of the second DOE includes grating features each having a slant angle to a respective axis orthogonal to the plane of the substrate, such that each grating feature is asymmetric about the axis, and
wherein the second DOE is configured with uniform grating features that are periodic in only a single direction.
2. The optical display system of claim 1 in which the third DOE is arranged on the substrate, the third DOE having an output surface and configured for pupil expansion of the one or more optical beams along a second direction, and further configured as an out-coupling grating to couple, as an output from the output surface, one or more optical beams with expanded pupil relative to the input.
3. The optical display system of claim 2 in which at least a portion of the third DOE includes gratings that are configured with a second slant angle to a direction orthogonal to a plane of the output surface.
4. The optical display system of claim 3 in which at least a portion of the first DOE includes gratings that are configured with a third slant angle to a direction orthogonal to a plane of the input surface.
5. The optical display system of claim 1 in which the one or more optical beams received at the first DOE emanate as a virtual image produced by a micro-display or imager.