Facebook's Reality Labs has teased a working prototype of a VR 'headset' that shrinks the technology down into something akin to a pair of sunglasses. To make this possible, Facebook's researchers have combined holographic optics and polarization-based optical folding which would replace the traditional refractive lens approach.
https://www.notebookcheck.net/Facebook-teases-sunglasses-like-wearable-VR-prototype-featuring-holographic-lens-tech.478491.0.html