Design of a compact wide field of view HMD optical system using freeform surfaces

The design of a compact optical system with good image quality for head mounted display (HMD) is particularly demanding since the aberrations, weights, and center of gravity of the display are always critical. One more critical requirement is its wide field of view. We are presenting two designs of an HMD optical system, which have good optical performance while maintaining the compactness. The comparison of their optical performance and other parameters is also presented. Freeform optical surfaces are employed in one of these designs while one aspheric and some spherical surfaces are used in the other design. Freeform surfaces provide more degrees of freedom to design an optical system with less number of elements and hence to reduce the weight of the overall system. Generally, HMD optical systems are tilted and decentered in their nature; it is difficult to get rid of all the aberrations without adding extra optics in such systems. However, freeform optics also provides enough degrees of freedom in this aspect and facilitates the designer to overcome such limitations without additional optics. It is also mentioned that the fabrication technologies of freeform optics are developing now and hence allow the designers to employ such optics elements in their designs. The designing characteristics and results of the two proposed models are also discussed in this paper.