Optical systems with modulated surface relief gratings

A display system comprising:

• a waveguide configured to propagate image light via total internal reflection;
• and
• a surface relief grating (SRG) structure on the waveguide, wherein:
• the SRG structure has a first region, a second region, and a third region, the second region being laterally interposed between the first region and the third region,
• the SRG structure comprises a first SRG configured to contribute a first amount of diffraction to the image light in the first region, a second amount of diffraction to the image light in the second region, and a third amount of diffraction to the image light in the third region, the second amount of diffraction being less than the first amount of diffraction and the third amount of diffraction being less than the second amount of diffraction,
• the SRG structure comprises a second SRG that at least partially overlaps the first SRG, the second SRG being configured to contribute the third amount of diffraction to the image light in the first region, the second amount of diffraction to the image light in the second region, and the first amount of diffraction to the image light in the third region, and
• the SRG structure is configured to couple the image light out of the waveguide.

A head mounted display device comprising:

• a waveguide;
• an input coupler configured to couple image light into the waveguide;
• and
• a surface relief grating (SRG) structure on the waveguide, wherein the SRG structure is configured to expand the image light, the SRG structure is configured to couple the expanded image light out of the waveguide, the SRG structure has a brow region and a cheek region, and the SRG structure comprises:
• a first SRG having a first strength that decreases from the brow region to the cheek region, and
• a second SRG that at least partially overlaps the first SRG and that has a second strength that decreases from the cheek region to the brow region.