Augmented reality and virtual reality displays:emerging technologies and future perspectives

With rapid advances in high-speed communication and computation,augmented reality(AR)and virtual reality(VR)are emerging as next-generation display platforms for deeper human-digital interactions.Nonetheless,to simultaneously match the exceptional performance of human vision and keep the near-eye display module compact and lightweight imposes unprecedented challenges on optical engineering.Fortunately,recent progress in holographic optical elements(HOEs)and lithography-enabled devices provide innovative ways to tackle these obstacles in AR and VR that are otherwise difficult with traditional optics.In this review,we begin with introducing the basic structures of AR and VR headsets,and then describing the operation principles of various HOEs and lithography-enabled devices.Their properties are analyzed in detail,including strong selectivity on wavelength and incident angle,and multiplexing ability of volume HOEs,polarization dependency and active switching of liquid crystal HOEs,device fabrication,and properties of micro-LEDs(light-emitting diodes),and large design freedoms of metasurfaces.Afterwards,we discuss how these devices help enhance the AR and VR performance,with detailed description and analysis of some state-of-the-art architectures.Finally,we cast a perspective on potential developments and research directions of these photonic devices for future AR and VR displays.

Miniature planar telescopes for efficient,wide-angle,high-precision beam steering

Non-mechanical beam steerers with lightweight,compact,high-efficiency,high-precision,and/or large-angle are pivotal for light detection and ranging(LiDAR)of autonomous vehicles,eye-tracking for near-eye displays,microscopy,optical tweezers,and high-precision three-dimensional(3D)printing.However,even the most matured optical phased array can only provide quasi-continuous,efficient beam steering within a small angle range.A telescope module with an angle magnification function can be coupled to enlarge the steering range or precision.But obtaining a compact,low-cost,lightweight,high-quality telescope module with conventional optics remains challenging.Patterned liquid crystal-based planar optical elements offer great design freedom for manipulating the phase profile of light in 2D space.Owing to the advantages of high efficiency,thinness,low cost,easy processing,flexibility,and response to environmental stimuli,a plethora of high-quality optical devices have been demonstrated.Here,a miniature planar telescope mediated by liquid crystal polymers is proposed to offer angle magnification independent of incident spatial location.It consists of two cascaded liquid crystal planar optical elements,each performing a predefined mathematical transformation.By this concept,planar optical elements are fabricated using a new exposure method and assembled into planar telescopes with different magnification factors.Within the incident field range,over 84.6%optical efficiency is achieved with small wavefront distortion.Such a miniature planar telescope shows the potential of cascaded liquid crystal planar optical elements for realizing functionalities that cannot be fulfilled by single optical elements,and enables lightweight,low loss,passive optical transmitters for widespread applications.