Augmented reality solution based on nanoimprinted metalens array

Researchers have developed a see-through augmented reality (AR) prototype based on an ultrathin nanoimprinted metalens array, creating a full-color, video-rate, and low-cost 3D near-eye display solution.

According to MEMS Consulting, integrated imaging (II) display is a form of light field display that uses lens/pinhole arrays to capture and reproduce light fields. It was invented by Nobel Prize winner Gabriel Lippmann more than a century ago. This technology reconstructs the entire image through a large number of small lens arrays, similar to the mechanism of a fly's eye. The generated image includes all the light field information of the original three-dimensional (3D) object, similar to holography. Unlike holography, this technology is not limited to coherent light sources. Integrated imaging display itself has properties such as full parallax and quasi-continuous viewpoints, presenting a true 3D display and avoiding visual fatigue, which is a common problem caused by convergence and accommodation conflicts in binocular parallax 3D displays.

Prior to the 21st century, the development of integrated imaging displays was slow due to technological limitations. In recent years, integrated imaging display technology has developed rapidly, especially in the past decade, due to algorithm enhancements, improved manufacturing capabilities, and the emergence of high-speed digital cameras. Planar meta-optics is a promising candidate for the next generation of 3D display technology, and ultrathin meta-lenses are emerging as an ideal replacement for conventional large-size lenses. Meta-lenses have demonstrated unprecedented capabilities to manipulate light at subwavelength scales, including precise control of the amplitude, phase, polarization, and dispersion of light emitted or reflected by dielectric or plasma meta-atoms. Recently, meta-lenses have shown great potential in integrated imaging displays, solving the severe chromatic aberration problem encountered by conventional micro-lens arrays. However, fabricating large-scale meta-lens arrays and using them in commercial micro-displays for integrated imaging displays remains a challenging task. In addition, the computational algorithms used to encode 3D objects and create elemental image arrays are still too slow to achieve real-time rendering of 3D objects for integrated imaging displays at practical video rates.

According to MEMS Consulting, in a paper titled "Integral Imaging Near-eye 3D Display Using a Nanoimprint Metalens Array" recently published in the journal eLight, a research team led by Professor Dong Jianwen and Associate Professor Qin Zong of Sun Yat-sen University introduced the application of large-scale nanoimprinted meta-lens arrays in 3D near-eye integrated imaging display. The developed system combines large-scale meta-lens arrays, commercial microdisplays and real-time rendering algorithms to produce high-quality 3D images with motion parallax and focus cues. The full-color, real-time, perspective meta-structure prototype highlights the application of the developed device in virtual reality (VR) and augmented reality (AR). The researchers used nanoimprint manufacturing technology to fabricate large-scale (1.84 mm × 1.84 mm) meta-lens arrays on an adhesive material with a refractive index of 1.9. The 4×4 high-quality meta-lens array was integrated with a commercial microdisplay via a 3D printed bracket. To achieve video-rate integrated imaging display, the researchers also introduced a new rendering method that exploits the static mapping between voxels and pixels in the integrated imaging display. This rendering method can bypass traditional geometric projection and achieve real-time performance through lookup tables. To verify the true 3D display capability of the hyperstructure system, the researchers also demonstrated a perspective prototype that can merge 3D images with surrounding objects, demonstrating the application of augmented reality.

Schematic diagram of near-eye integrated imaging display based on meta-lens array

Conceptual image of augmented reality based on nanoimprinted meta-lens array

Although nanoimprint lithography and real-time rendering algorithms for high-throughput metasurface fabrication can advance the development of integrated imaging displays for future virtual and augmented reality applications, several challenges remain in this field. For example, high-resolution image acquisition remains a huge obstacle, requiring micro-display sensors with ultra-small pixel sizes down to the sub-micrometer scale. However, fabricating such small sensors poses considerable challenges. In this context, time-multiplexed light fields with high refresh rate monitors may provide a viable solution. Second, the refractive index of existing nanoimprint adhesives is still low, requiring high-aspect-ratio nanopillars to construct metalenses, which results in a shadowing effect that reduces the diffraction efficiency at high spatial frequencies. Third, the development of truly interactive 3D displays requires the use of dynamic metasurfaces for fast tunability and low power consumption. Although various mechanisms (e.g., phase change and electro-optical effects) have been proposed to realize dynamic metasurfaces, this development is still in its infancy. Notably, the unique ability of metasurfaces to interact with multiple optical degrees of freedom (e.g., polarization, wavelength, orbital angular momentum, and spatiotemporal beams) opens the door to further enhance the dynamic functionality and image capacity of metasurface-based displays. In addition to hardware efforts, the rapid development of machine learning, neural networks, and artificial intelligence (AI) can improve the software part of future 3D display technology.