Dynamically actuable diffractive optical element
A dynamically actuable diffractive optical element (DOE) includes a substrate and a diffraction grating disposed on a first region of a surface of the substrate. The DOE further includes a quantity of a fluid disposed on a second region of the surface of the substrate, a fluid displacer disposed adjacent the second region of the surface of the substrate, and a drive signal source configured to send an electric signal to the fluid displacer. The fluid displacer is configured to, upon receiving the electric signal in a first state, causing a portion of the quantity of the fluid to be displaced from the second region of the surface into grooves of the diffraction grating, and upon receiving the electric signal in a second state, 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.
1. A dynamically actuable diffractive optical element (DOE) comprising:
a waveguide having a surface;
a diffraction grating disposed on 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 transparent substrate overlying the diffraction grating, the transparent substrate having a first surface facing the diffraction grating;
a transparent spacer positioned on the first surface of the transparent substrate, the transparent spacer comprising a hydrophilic material;
a quantity of a fluid disposed on a surface of the transparent spacer, the fluid having a second index of refraction that substantially matches the first index of refraction of the plurality of ridges;
a seal engaging the surface of the waveguide and the first surface of the transparent substrate, wherein the seal forms a sealed space around the diffraction grating between the surface of the waveguide and the first surface of the transparent substrate;
one or more electromechanical transducers mechanically coupled to the surface of the waveguide and the first surface of the transparent substrate; and
a drive signal source electrically coupled to the one or more electromechanical transducers, and configured to send an electric signal to the one or more electromechanical transducers, the electric signal having a first state and a second state;
wherein the one or more electromechanical transducers are configured to:
upon receiving the electric signal in the first state, causing a distance between the surface of the transparent spacer and the surface of the waveguide to be decreased so as to force a portion of the quantity of the fluid into the grooves of the diffraction grating, thereby causing the diffraction grating to be in an “off” state; and
upon receiving the electric signal in the second state, causing the distance between the surface of the transparent spacer and the surface of the waveguide to be increased so as to allow the portion of the quantity of the fluid to retract from the grooves of the diffraction grating, thereby causing the diffraction grating to be in an “on” state so that the diffraction grating diffracts a portion of a light beam that is incident on the diffraction grating into the waveguide to be propagated therein.
2. The dynamically actuable DOE of claim 1 wherein the hydrophilic material comprises glass, and the hydrophobic material comprises a polymer.
3. The dynamically actuable DOE of claim 1 wherein each of the one or more electromechanical transducers comprises a piezoelectric element.
4. 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 surface of the first planar waveguide in a first lateral position and configured to receive the image light that is incident thereon, the first dynamically actuable DOE comprising:
a 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 transparent substrate overlying the diffraction grating, the transparent substrate having a first surface facing the diffraction grating;
a transparent spacer positioned on the first surface of the transparent substrate, the transparent spacer comprising a hydrophilic material;
a quantity of a fluid disposed on the surface of the transparent spacer, the fluid having a second index of refraction that substantially matches the first index of refraction of the plurality of ridges;
a seal engaging the surface of the first planar waveguide and the first surface of the transparent substrate, wherein the seal forms a sealed space around the diffraction grating between the surface of the first planar waveguide and the first surface of the transparent substrate;
one or more electromechanical transducers mechanically coupled to the surface of the first planar waveguide and the first surface of the transparent substrate; and
a drive signal source electrically coupled to the one or more electromechanical transducers, and configured to send an electric signal to the one or more electromechanical transducers, the electric signal having a first state or a second state;
wherein the one or more electromechanical transducers are configured to:
upon receiving the electric signal in the first state, causing a distance between the surface of the transparent spacer and the surface of the first planar waveguide to be decreased so as to force a portion of the quantity of the fluid into the grooves of the diffraction grating, thereby causing the diffraction grating to be in an “off” state; and
upon receiving the electric signal in the second state, causing the distance between the surface of the transparent spacer and the surface of the first planar waveguide to be increased so as to allow the portion of the quantity of the fluid to retract from the grooves of the diffraction grating, thereby causing the diffraction grating to be in an “on” state so that the diffraction grating diffracts a portion of a light beam into the first planar waveguide to be propagated therein;
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 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.
5. The eyepiece of claim 4 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.
6. The eyepiece of claim 4 wherein the hydrophilic material comprises glass, and the hydrophobic material comprises a polymer.
7. The eyepiece of claim 4 wherein each of the one or more electromechanical transducers comprises a piezoelectric element.