Background
Lightguide technologies are widely used in augmented and virtual reality systems to improve compactness. Planar lightguide geometries are currently most common, but when expanding to a large field of view, planar lightguides become very wide and require a large range of light emission angles. Furthermore, since the eye rolls on a spherical surface but the geometry of the lightguide is flat, the range of focus of the eye must change relative to the display as the eye stares at different fields in the simulated scenario. A curved display drastically reduces the emission ray angle variation and maintains the focus of the eye. However, a curved homogeneous lightguide propagates light in a nonuniform and complicated way and does not preserve imaging conditions for the rays.
Technology Overview
Researchers at the University of Rochester have invented an optimal curved lightguide spherical gradient index (GRIN) profile, primarily intended for dis- or continuous visible spectra, which simultaneously enables a curved lightguide design and conserves ray angle of incidence internally for all rays as they propagate inside the sphere. The GRIN construction can be optimally chosen so that the surfaces of equal index are concentric with the prevailing external optical surfaces of the lightguide, or non-concentric in order to achieve other functionalities such as aberration correction of the ambient scene. Making the lightguide concentric with the eye results in less variation in reflection or diffraction angle at each of the display pixels, improving design performance. Further, the spherical nature of the construction will allow for variable or symmetric focusing of the eye through the entire field of view.
Benefits
The GRIN spherical lightguide can guide light similarly to a planar lightguide but is more compact and has an improved eyebox without any special complicated additions to the guide itself. This system would be advantageous in both geometric and diffraction grating lightguide display systems.
Applications
Augmented and Virtual Reality display systems