![]() ![]() Optical metasurfaces consisting of meta-atoms arranged on the sub-wavelength scale can display holographic images over a wide viewing angle without multiple diffraction orders. The optical metasurface with sub-wavelength scale features allows cross-talk-free stereoscopic display with a wide viewing angle. Observation of 2D holographic images created at the same plane (the grey dashed line) provides the perception of floating 3D objects. The optical metasurface consists of several hologram pieces (the green and blue boxes), which are in charge of displaying different 2D holographic projections of the target 3D object depending on the observation direction (the green and blue arrows). b) Schematic of the generation of transmissive holographic stereograms based on the optical metasurface. The difference between the two images observed by the left and right eyes produces the cues for the brain to perceive the depth and distance of the 3D object. Metasurface based holographic stereogram. 7, 15, 16 To widen the viewing angle, complex optics, such as multiple spatial light modulators 8 and microlens arrays, 9 and their precise control are required. However, conventional holographic stereograms using micrometer-scale pixels suffer from undesired multiple diffraction orders, that duplicate the same holographic images, and the narrowing of the viewing angle by only a few degrees. The observation of the two different floating 2D holographic images by both eyes produces binocular disparity without the vergence-accommodation conflict. 6 Recently, the holographic stereoscopic 7- 10 and multiview displays 11- 14 have been suggested as a promising alternative to the eyeglasses-based stereoscopic. 5 Eyeglasses-based stereoscopy has been representative for raising binocular depth cues, but the vergence-accommodation conflict limits their comfort and applicability significantly. In particular, binocular disparity is the most sensitive physiological depth cue for 3D objects with a size and distance of ≈10 m or less ( Figure 1a). The physiological cues of convergence and binocular disparity originate from the difference in the direction and location of both eyes. 4 The physiological depth cues of the motion parallax, accommodation of the eyes, and the psychological depth cues are all monocular. 1- 3 The perception of 3D objects in the human visual system arises from the physiological and psychological depth cues. ![]() The results will open avenues to advanced eyeglasses-free 3D displays that can provide rich and well-defined depth cues.ģD displays to overcome the limits of 2D flat images and visualize the complexity of real objects have been intensively investigated. A Gerchberg–Saxton algorithm modified with a spatial Fourier filter calculates the phase and amplitude distribution of meta-atoms. The demonstrated optical metasurface is an ensemble of several hologram pieces, which produce the different 2D projections of the target 3D structure depending on the observation direction, and displays the holographic stereogram of 25 × 25 × 25 µm 3 over a wide viewing angle of more than ☓0°. Here, a novel method is presented based on optical metasurfaces for obtaining a binocular holographic stereopsis. Optical metasurfaces with sub-wavelength-scale features have recently been leading amongst the state-of-the-art technologies in 3D holograms but employing only monocular depth cues. However, conventional holographic stereograms based on micrometer-scale pixels suffer from multiple diffraction orders and narrow viewing angles.
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