Optical Design of a Thin Curved Lightguide and Manufacturing Using Ophthalmic Approaches

We present an underexplored variation of the classical optical freeform prism design that incorporates 3 optical surfaces. This optical architecture can make use of one, two, or three freeform surfaces. Our initial prototype uses a single freeform surface along with a sphere and a flat surface to simplify manufacturing complexity. There are two key contributions in this paper that to our knowledge have not been achieved previously: 1) the design of a thin, 4 mm to 1 mm gradient thickness, curved freeform lightguide (nearly 4x thinner than the original freeform prism), and 2) lightguide fabrication utilizing ophthalmic machines. This particular optical design makes combined use of total internal reflections and partial reflections. The advantages of this optical architecture include the curved optical surfaces that eliminate the optical collimator requirement in flat lightguides, a relatively large eyebox, and a manufacturing approach that reuses the standard ophthalmic process for fabricating the eyeside and worldside optical surfaces. The limitations of the optical design are low efficiency (∼ 5%), multiple image artifacts, and lack of optical see-through.

• General Science