Dynamically actuable diffractive optical element

1. A dynamically actuable diffractive optical element (DOE) comprising:

a waveguide having a surface, the surface including a first region and a second region laterally displaced from the first region;

a diffraction grating disposed on the first region of the surface of the waveguide, the diffraction grating including a plurality of ridges protruding from the surface of the waveguide and a plurality of grooves between adjacent ridges, the plurality of ridges comprising a hydrophobic material with a first index of refraction;

a quantity of a fluid disposed on the second region of the surface of the waveguide, the fluid having a second index of refraction that substantially matches the first index of refraction of the plurality of ridges;

an optical window overlying the first and second regions;

an edge seal supporting the optical window to form an internal space in which the first region is located;

a truss overlying the optical window overlying the second region;

an actuator disposed between the truss and the optical window; and

a drive signal source coupled to the actuator and configured to send an electric signal to the actuator, the electric signal having a first state and a second state;

wherein the actuator is configured to:

upon receiving the electric signal in the first state, exert a force on the optical window to cause the optical window to flex, thereby compressing the edge seal and causing a portion of the quantity of the fluid to be displaced from the second region of the surface into the grooves of the diffraction grating; and

upon receiving the electric signal in the second state, cause the optical window to retract to an original position, thereby causing the portion of the quantity of the fluid to retract from the grooves of the diffraction grating to the second region of the surface.

2. The dynamically actuable DOE of claim 1 wherein the actuator comprises one of a piezoelectric element, a voice coil motor, or a thermally expandable body.

3. The dynamically actuable DOE of claim 1 wherein the second region of the surface of the waveguide is hydrophilic.

4. The dynamically actuable DOE of claim 1 wherein the hydrophobic material comprises a polymer.

5. The dynamically actuable DOE of claim 1 wherein, upon receiving the electric signal in the first state, the actuator exerts a force on the optical window to cause the optical window to flex relative to the first region and the second region.

6. An eyepiece for projecting image light to an eye of a viewer for forming an image of virtual content, the eyepiece comprising:

a first planar waveguide configured to propagate light in a first wavelength range centered at a first wavelength;

a first dynamically actuable diffractive optical element (DOE) formed on a first region of a surface of the first planar waveguide in a first lateral position and configured to receive image light incident thereon, the first dynamically actuable DOE comprising:

a diffraction grating disposed on the first region of the surface of the first planar waveguide, the diffraction grating including a plurality of ridges protruding from the surface of the first planar waveguide and a plurality of grooves between adjacent ridges, the plurality of ridges comprising a hydrophobic material with a first index of refraction;

a quantity of a fluid disposed on a second region of the surface of the first planar waveguide, the fluid having a second index of refraction that substantially matches the first index of refraction of the plurality of ridges;

an optical window overlying the first and second regions;

an edge seal supporting the optical window to form an internal space in which the first region is located;

a truss overlying the optical window overlying the second region;

an actuator disposed between the truss and the optical window; and

a drive signal source coupled to the actuator and configured to send an electric signal to the actuator, the electric signal having a first state and a second state;

wherein the actuator is configured to:

upon receiving the electric signal in the first state, exert a force on the optical window to cause the optical window to flex, thereby compressing the edge seal and causing a portion of the quantity of the fluid to be displaced from the second region of the surface into the grooves of the diffraction grating; and

upon receiving the electric signal in the second state, cause the optical window to retract to an original position, thereby causing the portion of the quantity of the fluid to retract from the grooves of the diffraction grating to the second region of the surface;

wherein the diffraction grating is configured to:

diffract a portion of the image light incident thereon into the first planar waveguide to be propagated therein while in the “on” state; and

transmit the image light incident thereon while in the “off” state;

a second planar waveguide positioned substantially parallel to a plane of the first planar waveguide and configured to propagate light in a second wavelength range centered at a second wavelength different from the first wavelength; and

a second DOE formed on a region of a surface of the second planar waveguide in a second lateral position substantially aligned with the first lateral position, the second DOE configured to:

receive the image light transmitted by the diffraction grating while the diffraction grating is in the “off” state; and

diffract a second portion of the image light into the second planar waveguide to be propagated therein.

7. The eyepiece of claim 6 wherein the image light includes light in the first wavelength range and light in the second wavelength range time-multiplexed in a plurality of subframe time periods, and wherein the drive signal source is configured to:

send the electrical signal in the first state in subframe time periods corresponding to the light in the second wavelength range; and

send the electrical signal in the second state in subframe time periods corresponding to the light in the first wavelength range.

8. The eyepiece of claim 6 wherein the actuator comprises one of a piezoelectric element, a voice coil motor, or a thermally expandable body.

9. The eyepiece of claim 6 wherein the second region of the surface of the first planar waveguide is hydrophilic.

10. The eyepiece of claim 6 wherein the hydrophobic material comprises a polymer.

11. The eyepiece of claim 6 wherein, upon receiving the electric signal in the first state, the actuator exerts a force on the optical window to cause the optical window to flex relative to the first region and the second region.