Waveguide with coherent interference mitigation
A pupil-replicating waveguide suitable for operation with a coherent light source is disclosed. A waveguide body has opposed surfaces for guiding a beam of image light. An out-coupling element is disposed in an optical path of the beam for out-coupling portions of the beam at a plurality of spaced apart locations along the optical path. Electrodes are coupled to at least a portion of the waveguide body for modulating an optical path length of the optical path of the beam to create time-varying phase delays between the portions of the beam out-coupled by the out-coupling element.
1. A waveguide comprising:
a waveguide body for guiding a beam of image light;
an out-coupling element in an optical path of the beam for out-coupling a plurality of portions of the beam at a plurality of spaced apart locations along the optical path; and
electrodes coupled to at least a portion of the waveguide body for modulating an optical path length of the optical path of the beam to provide time-varying phase delays between different portions of the plurality of portions of the beam out-coupled by the out-coupling element.
2. The waveguide of claim 1 , wherein the out-coupling element and one of the electrodes comprise a same electrically conductive diffraction grating.
3. The waveguide of claim 1 , wherein the waveguide body comprises: a substrate for propagating the beam of image light therein; and
an electrically responsive layer disposed between the electrodes and configured to modulate the optical path length of the beam upon application of an electrical signal to the electrodes.
4. The waveguide of claim 3 , wherein the electrical signal comprises voltage, and wherein the electrically responsive layer comprises an elastic polymer material deformable by an electrostatic attraction force between the electrodes upon application of the voltage.
5. The waveguide of claim 4 , wherein the elastic polymer material comprises a nanovoided polymer.
6. The waveguide of claim 5 , wherein the nanovoided polymer has a thickness of between 0.1 micrometers and 20 micrometers.
7. The waveguide of claim 3 , wherein the electrical signal comprises voltage, and wherein the electrically responsive layer comprises a liquid crystal layer.
8. The waveguide of claim 1 , wherein the waveguide body comprises an electro-optic substrate disposed between the electrodes, and wherein the electro-optic substrate has a refractive index responsive to electric field between the electrodes upon application of voltage thereto.
9. The waveguide of claim 8 , wherein the at least a portion of the waveguide body comprises a piezoelectric material for modulating a physical length of the optical path of the beam of image light.
10. The waveguide of claim 1 , wherein the waveguide body comprises:
a substrate for propagating the beam of image light therein; and
an acoustic actuator coupled to the substrate and comprising an electrically responsive layer between the electrodes, wherein a thickness of the electrically responsive layer is variable by applying an electrical signal to the electrodes.
11. The waveguide of claim 10 , wherein the acoustic actuator is coupled at a side of the substrate and configured to provide a volume acoustic wave in the substrate.
12. The waveguide of claim 10 , wherein the waveguide body comprises opposed surfaces for guiding the beam of image light therebetween, wherein the acoustic actuator is mechanically coupled to one of the surfaces and configured to provide a surface acoustic wave in that surface.
13. A display device comprising:
a light source for providing a beam of image light carrying a plurality of image frames at a frame rate;
a waveguide comprising: a waveguide body for guiding the beam of image light;
an out-coupling element in an optical path of the beam for out-coupling a plurality of portions of the beam at a plurality of spaced apart locations along the optical path; and
electrodes coupled to at least a portion of the waveguide body for modulating an optical path length of the optical path of the beam to create time-varying phase delays between different portions of the plurality of portions of the beam out-coupled by the out-coupling element; and
a controller operably coupled to the electrodes of the waveguide and configured to apply an electrical signal to the electrodes to modulate the optical path length.
14. The display device of claim 13 , wherein a rate of modulation of the optical path length is higher than the frame rate.
15. The display device of claim 14 , wherein each image frame comprises a time sequence of frame lines at a line rate higher than the frame rate, and wherein the rate of modulation of the optical path length is higher than the line rate.
16. The display device of claim 14 , wherein each frame line comprises a time sequence of line pixels at a pixel rate higher than the line rate, and wherein the rate of modulation of the optical path length is higher than the pixel rate.
17. The display device of claim 14 , wherein a rate of modulation of the optical path length is randomly varying relative to a rate at which individual pixels of an image frame are updated.
18. A method for expanding a beam of image light, the method comprising:
propagating the beam along an optical path in a waveguide;
out-coupling, using an out-coupling element in an optical path of the beam, a plurality of portions of the beam at a plurality of spaced apart locations along the optical path; and
modulating, by applying an electrical signal to electrodes coupled to at least a portion of the waveguide, an optical path length of the optical path of the beam to create time-varying phase delays between different portions of the plurality of portions of the beam out-coupled by the out-coupling element.
19. The method of claim 18 , wherein the electrical signal comprises voltage, and wherein the optical path length is modulated using an electrically responsive layer between the electrodes, by applying the voltage thereto.
20. The method of claim 18 , wherein the beam of image light carries a plurality of image frames at a frame rate, and wherein a rate of modulation of the optical path length is randomly varying relative to the frame rate.