Design of a thin see-though optical viewer with a freeform surface

Using a see-through optical viewer with a prism combiner is an affordable solution for head mounted devices. Free-form surfaces are a general way to correct off-axis aberrations generated by combiners. A glass high index wedge prism is used as a combiner to keep the wedge angle small while maintaining total internal reflection and the combiner becomes thinner. Free-form surfaces, on the other hand, are used in relay lenses to correct off-axis aberrations. The diagonal FOV is 44° and the exit pupil diameter is 4.8 mm. After two optical design using XY and Zernike polynomial, we confirm which free-form expression is superior in aberration correction for the viewer.