Spatially multiplexed volume Bragg gratings with varied refractive index modulations for waveguide display
A waveguide display includes a waveguide transparent to visible light, a first volume Bragg grating (VBG) on the waveguide and characterized by a first refractive index modulation, and a second reflection VBG on the waveguide and including a plurality of regions characterized by different respective refractive index modulations. The first reflection VBG is configured to diffract display light in a first wavelength range and a first field of view (FOV) range such that the display light in the first wavelength range and the first FOV range propagates in the waveguide through total internal reflection to the plurality of regions of the second reflection VBG. The plurality of regions of the second reflection VBG are configured to diffract the display light in different respective wavelength ranges within the first wavelength range and the first FOV range.
1. A waveguide display comprising:
a waveguide transparent to visible light;
a first reflection volume Bragg grating (VBG) on the waveguide and characterized by a first refractive index modulation; and
a second reflection VBG on the waveguide and including a plurality of regions characterized by different respective refractive index modulations,
wherein the first reflection VBG is configured to diffract display light in a first wavelength range and a first field of view (FOV) range such that the display light in the first wavelength range and the first FOV range propagates in the waveguide through total internal reflection to the plurality of regions of the second reflection VBG;
wherein the plurality of regions of the second reflection VBG are configured to diffract the display light in different respective wavelength ranges within the first wavelength range and the first FOV range;
wherein the plurality of regions of the second reflection VBG are configured such that the display light in the first wavelength range and the first FOV range reaches a first region of the plurality of regions having a second refractive index modulation before reaching a second region of the plurality of regions having a third refractive index modulation that is greater than the second refractive index modulation; and
wherein the first region is configured to diffract the display light in a first wavelength sub-range of the first wavelength range, the second region is configured to diffract the display light in a second wavelength sub-range of the first wavelength range, and the second wavelength sub-range includes the first wavelength sub-range and is wider than the first wavelength sub-range.
2. The waveguide display of claim 1 , wherein the first reflection VBG and the second reflection VBG have a same grating vector in a plane perpendicular to a surface normal direction of the waveguide.
3. The waveguide display of claim 1 , wherein the first refractive index modulation and at least one of the different respective refractive index modulations of the plurality of regions of the second reflection VBG are greater than a minimum refractive index modulation for diffraction efficiency saturation.
4. The waveguide display of claim 1 , wherein:
the first reflection VBG is configured to couple the display light in the first wavelength range and the first FOV range into the waveguide; and
the second reflection VBG is configured to couple the display light in the first wavelength range and the first FOV range out of the waveguide and is transparent to visible light from an ambient environment.
5. The waveguide display of claim 1 , further comprising a third grating and a fourth grating, wherein:
the third grating is configured to diffract the display light in the first wavelength range and the first FOV range from the first reflection VBG to the fourth grating;
the fourth grating is configured to diffract the display light in the first wavelength range and the first FOV range at two or more regions of the fourth grating to the second reflection VBG; and
the third grating and the fourth grating have a same grating vector in a plane perpendicular to a surface normal direction of the waveguide.