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 diffraction grating;
- a truss overlying the optical window adjacent the second region of the surface of the first planar waveguide;
- 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 downward toward the diffraction grating, thereby 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.