Dynamically actuable diffractive optical element

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 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 dynamically actuable DOE comprising:
• a substrate having a surface;
• a metasurface diffractive optical element (DOE) formed on the surface of the substrate, wherein the metasurface DOE includes a plurality of raised portions protruding above the surface, wherein the metasurface DOE defines a plurality of recesses between adjacent raised portions;
• a movable cover overlying the metasurface DOE and comprising a hydrophilic material;
• a quantity of a fluid disposed on the movable cover;
• and
• a drive mechanism coupled to the movable cover, the drive mechanism configured to:
• upon receiving a control signal in a first state, move the movable cover toward the metasurface DOE to displace a portion of the quantity of the fluid into the plurality of recesses, thereby rendering the metasurface DOE in an “off” state;
• and
• upon receiving a control signal in a second state, move the movable cover away from the metasurface DOE, causing the portion of the quantity of the fluid retracting from the plurality of recesses, thereby rendering the metasurface DOE in an “on” state.