Creating A More Human-Centric AR Experience with Volume Holography

摘要

AUGMENTED REALITY (AR) DEVICES SUCH AS SMART glasses and head-up displays (HUDs) are making their way to consumers, thanks to ambitious companies such as North (acquired by Google in June 2020), Microsoft, Vuzix, and Magic Leap. Diffractive optical elements, including holograms and surface relief structures, play a key role in directing the light in AR devices without compromising a transparent view of the real world. Today, companies use varying architectures to design near-to-eye (NTE) devices and HUDs, each of which has advantages and disadvantages. For example, Magic Leap achieves a full-color, multifocal device with multiple stacks of broadband waveguides. Microsoft's HoloLens mixed-reality smart glasses use laser beam scanning (LBS) butterfly waveguided geometry. Both use surface relief gratings on waveguides that require a microdisplay and a combination of imaging optics to achieve the transparent image overlay. Although necessary to create an optimized image and a wide field of view (FOV), the optics are conventional mirrors, lenses, and prisms that require a certain amount of volume. For NTE devices such as smart glasses, the extra space and weight can be the difference between sleek design and one that is bulky and obvious. Add this to a frame that must accommodate one or more microprojectors, sensors, and other hardware, and comfort and style lose out to functionality. Focals by North took a different approach with LBS freespace geometry and Luminit's volume hologram combiner, a system based on holographic optical elements (HOEs). The result is the first stylish, compact, prescription-compatible smart glasses (Fig. 1). Here, I detail how those glasses were manufactured, the differences between optical geometries, and how advancements in HOE technology are breaking down barriers to mass-market AR.