Metasurface-based compact light engine for AR headsets

Despite the great advances, potentials of augmented reality to fundamentally transform the way people use computers is partially hindered by the size and weight of the AR headsets. In waveguide-based devices, the light engine constitutes a significant portion of the total volume and weight. Dielectric metasurfaces have in recent years been used to demonstrate various high performance optical elements like blazed gratings and wide field of view lenses with small thicknesses, high efficiencies, and little stray light. Here, we report our work on the design of a compact light engine based on multi-metasurface optics with wide fields of view, integrated with three monochrome μ-LED displays for red, green, and blue. The metasurfaces image the μ-LEDs on the prism or grating couplers. This design avoids an important shortcoming of μ-LEDs and metasurface lenses, i.e., each work well for a single wavelength. As an example, we present a design for 532 nm, with over 3000 resolved angular points in an 8-mm-diameter field of view, and a total volume less than 0.65 cc (<2 cc for the three wavelengths). Limited by the total internal reflection region inside a waveguide with a 1.78 refractive index, the light engine can produce an image with over 1500x1500 points over a field of view slightly larger than 85°x85° in air. To the best of our knowledge, this is the first proposal and demonstration of such a system and therefore opens the path towards exploring the potentials of the metasurface diffractive optics technology for compact AR headsets with enhanced optical capabilities.