A volumetric full-color display realized by frequency upconversion of a transparent composite incorporating dispersed nonlinear optical crystals

Popular three-dimensional (3D) TV or film media primarily relies on misleading our visual system by presenting our two eyes with spatially offset two-dimensional (2D) images. In comparison, volumetric displays generate moving objects in three physical dimensions with unlimited viewing angles. In a static volumetric display, voxels instead of pixels are usually addressed by luminescence, scattering or deflection. Although various prototype volumetric display technologies have been developed, the generation of full-color moving objects remains a challenge. Herein, we demonstrate the generation of voxels by frequency upconversion based on second-harmonic generation (SHG) in nonlinear optical crystals that are dispersed in solid-state composite materials that serve as a transparent solid display. Notably, voxels that radiate all colors with near-monochromatic color purity can be created by pumping at different near-infrared wavelengths and thus enable a simple solution to realize a full-color display. A computer-controlled scanner allows the generation of moving 3D objects that are viewable from any direction in a prototype device at a 25 × 25 × 25 mm3 scale, and larger displays that are based on the colloidal dispersion of SHG crystals are envisioned. Our methodology may have important implications for the application of the transparent crystal-in-glass composites in both 3D and 2D display technologies. Creating colorful three-dimensional pixels, or voxels, in panes of transparent composites can bring true depth perception to imaging devices. Xiaofeng Liu from Zhejiang University, China, and co-workers have demonstrated this approach with barium–titanium–silicate (BTS) glasses that contain a uniform distribution of small crystallites. When stimulated by a femtosecond pulse laser, the BTS crystals double the photon frequency, enabling localized red, blue or green glowing voxels to be generated through small tweaks in the laser wavelength. The team constructed a one-inch, see-through cube out of the BTS glass ceramic and used a computer-controlled arrangement of mirrors and mechanical scanners to manipulate the laser. This proof-of-concept device mixed the red, blue, and green voxels to produce full-color, moving 3D images viewable at any angle without the need for clunky goggles. A full-color, solid-state, volumetric display based on second harmonic generation in a transparent glass-ceramic (GC) containing second-order optical nonlinear crystals is described. The device uses infrared femtosecond laser beams that focus inside the GC to address red, green and blue voxels. Three-dimensional images are drawn by scanning the point of focus of the lasers inside of the material. The prototype device is demonstrated using conventional focusing optics and mechanical scanners, and the image is bright enough to be seen in ambient room lighting conditions.