A typical autostereoscopic 3D display only needs to integrate two components: an optical element and an off-the-shelf refreshable display panel (e.g., liquid crystal display, organic light-emitting diode display, light-emitting diode display) ( Dodgson, 2005). Moreover, by modulating the irradiance pattern of each view, only a small number of views are required to reconstruct the light field. The properly arranged perspective views can approximate the 3D images with motion parallax and stereo parallax. In contrast, autostereoscopic 3D displays reduce computing costs by discretizing a continuously distributed light field of 3D objects into multiple “views”. Both the holographic 3D display and volumetric 3D display require a large amount of data to provide 3D content, which brings challenges to data processing and transportation. These image points form 3D graphics that can be observed within 360° ( Kumagai et al., 2015 Kumagai et al., 2018 Smalley et al., 2018 Hirayama et al., 2019). Volumetric 3D display is another technology that generates luminous image points (i.e., voxels) in space via special media, such as trapped particles and fluorescent screens. In the future, real-time holographic 3D displays will have wide applications in mobile displays and AR displays ( Peng et al., 2021 Lee et al., 2022). ![]() Currently, powerful acceleration chips or video processors have enabled the reproduction of high-quality 3D holograms at video rates ( An et al., 2020 Shi et al., 2021). Furthermore, by using a spatial light modulator that directly modulates the coherent wave, computer-generated hologram systems can be implemented via numerical simulation. A holographic 3D display is a technology that records both the amplitude and phase information of a real object and reproduces it through specific mediums (e.g., photorefractive polymers) ( Tay et al., 2008 Blanche et al., 2010). Generally, we assign glasses-free 3D displays into three main categories: holographic 3D displays, volumetric 3D displays and autostereoscopic 3D displays ( Geng, 2013). Therefore, glasses-free 3D displays are regarded as next-generation display technology. The visualization of 3D images will have a huge impact on improving work efficiency. According to a survey, people spend an average of 5 h every day watching display panel screens. As a more natural way to present virtual data, glasses-free 3D displays show great prospects in various fields including education, military, medical, entertainment, automobile, etc. ![]() Since Charles Wheatstone first invented stereoscopy, the research interest in three-dimensional (3D) displays has extended for 150 years, and its history is as long as that of photography ( Charles, 1838). Finally, the current status, future direction and potential applications for glasses-free 3D displays and glasses-free AR 3D displays are summarized. Therefore, multiple micro/nanofabrication methods used in 3D displays are highlighted. Fabrication technologies are important challenges that hinder the development of 3D displays. As a specific application and an appealing feature, augmented reality (AR) 3D displays enabled by planar optics are comprehensively discussed. The promising solutions offered by planar optics for glasses-free 3D displays are introduced in detail. ![]() In this review, the limitations of geometric optics-based glasses-free 3D displays are analyzed. ![]() As a result, planar optics hold great promise to tackle the critical challenges for glasses-free 3D displays, especially for portable electronics and transparent display applications. Recently, planar optical elements (e.g., diffraction gratings, diffractive lenses and metasurfaces) have shown superior light manipulating capability in terms of light intensity, phase, and polarization. However, many geometric optics-based 3D displays suffer from a limited field of view (FOV), severe resolution degradation, and visual fatigue. Glasses-free three-dimensional (3D) displays are one of the technologies that will redefine human-computer interfaces. 3SVG Optronics, Co., Ltd, Suzhou, China.2Key Lab of Advanced Optical Manufacturing Technologies of Jiangsu Province and Key Lab of Modern Optical Technologies of Education Ministry of China, Soochow University, Suzhou, China.1School of Optoelectronic Science and Engineering, Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou, China.Jianyu Hua 1,2 Wen Qiao 1,2* Linsen Chen 1,2,3*
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