Curved lightguide in a see-through shell

A head mounted display comprising:

• a light engine configured to output display light;
• and
• a lens comprising:
• an optical shell having a world-facing spherical surface and an opposing eye-facing surface;
• and
• a curved lightguide disposed in the optical shell and having an incoupler surface adjacent to the light engine, a first freeform surface facing the world-facing spherical surface, and a second freeform surface facing the eye-facing surface, wherein the curved lightguide is configured to propagate the display light from the incoupler surface to an outcoupler region of the second freeform surface via total internal reflection between the first and second freeform surfaces facilitated by a first region of nanostructures at the first freeform surface and a second region of nanostructures at the second freeform surface.

A method of operating a head mounted display (HMD), the method comprising:

• receiving display light at an incoupler surface of a curved lightguide implemented in a curved optical shell;
• propagating the display light along the curved lightguide via total internal reflection between a first freeform surface of the curved lightguide that has a first low refractive index region and a second freeform surface of the curved lightguide that has a second low refractive index region;
• outputting the propagated display light toward a user's eye via an outcoupler region of the second freeform surface;
• transmitting ambient light incident on a first spherical surface of the curved optical shell through the curved optical shell to an opposing second surface of the curved optical shell;
• outputting the transmitted ambient light from the second surface of the curved optical shell toward the user's eye;
• and
• wherein at least one of the first low refractive index region or the second low refractive index region comprises at least one of:
• at least one layer of nanostructures;
• or at least one low refractive index coating.