SINGAPORE, May 26, 2023 — Researchers at the National University of Singapore (NUS) developed a light-field sensor that detects 3D light fields across the x-ray to visible light spectrum. The sensor relies on a pixelated color conversion strategy that is based on perovskite nanocrystal arrays.
The color conversion strategy developed by the researchers further supported absolute spatial positioning, 3D imaging, and visible light and x-ray phase-contrast imaging in addition to 3D light-field detection.
Current light-field detection techniques either require complex microlens arrays or are limited to the ultraviolet (UV) to visible wavelength ranges. The ability to detect light direction beyond optical wavelengths, using color-contrast encoding, could be useful for bio-imaging, robotics, virtual reality, autonomous navigation, and other fields.
The researchers surmised that, based on the versatility of color encoding in data visualization, color-contrast encoding could be useful for visualizing the direction of light. The team used inorganic perovskite nanocrystals to build a systems to test this hypothesis; these nanocrystals are known to have strong optoelectronic properties.
A large-scale angle-sensing structure comprising nanocrystal phospors, a key component of the sensor, is illuminated under ultraviolet light. Three light-emitting phosphors that produce red, green, and blue light are arranged in a pattern to capture detailed angular information, which is then used for 3D image construction. The team is exploring the use of other materials for the structure. Courtesy of the National University of Singapore.
The researchers combined pixelated perovskite nanocrystal arrays with a color CCD camera to demonstrate 3D object imaging and visible light and x-ray phase-contrast imaging. They patterned perovskite crystals onto a transparent thin-film substrate and integrated the perovskites into the CCD camera to create a crystal conversion system for the sensor. When incident light hit the light-field sensor, the nanocrystals became excited and emitted light in colors that varied depending on the angle of the incoming light. The CCD captured the color that was emitted, and the captured colors were then used for 3D image reconstruction. 
These multicolor nanocrystal arrays enabled the researchers to convert light rays from specific directions into pixelated color outputs at a very high angular resolution of 0.0018°.
Still, researcher Yi Luying said, “A single angle value, however, is not enough to determine the absolute position of the object in a three-dimensional space.”
