Photonic crystals are optical nanostructures in which the refractive index changes periodically². This periodic change affects the propagation of light in a similar way to how the structure of natural crystals gives rise to X-ray diffraction and how the atomic lattices (crystal structure) of semiconductors affect their conductivity of electrons².
Photonic crystals can be fabricated for one, two, or three dimensions. One-dimensional photonic crystals can be made of thin film layers deposited on each other. Two-dimensional ones can be made by photolithography, or by drilling holes in a suitable substrate. Fabrication methods for three-dimensional ones include drilling under different angles, stacking multiple 2-D layers on top of each other, direct laser writing, or, for example, instigating self-assembly of spheres in a matrix and dissolving the spheres².
Photonic crystals can, in principle, find uses wherever light must be manipulated. For example, dielectric mirrors are one-dimensional photonic crystals which can produce ultra-high reflectivity mirrors at a specified wavelength. Two-dimensional photonic crystals called photonic-crystal fibers are used for fiber-optic communication, among other applications. Three-dimensional crystals may one day be used in optical computers, and could lead to more efficient photovoltaic cells².
In essence, photonic crystals are materials patterned with a periodicity in dielectric constant, which can create a range of 'forbidden' frequencies called a photonic bandgap. Photons with energies lying in the bandgap cannot propagate through the medium. This provides the opportunity to shape and mould the flow of light for photonic information technology⁵.
Source: Conversation with Bing, 10/18/2023 (1) Photonic crystal - Wikipedia. https://en.wikipedia.org/wiki/Photonic_crystal. (2) Photonic crystals: putting a new twist on light - Nature. https://www.nature.com/articles/386143a0.pdf. (3) . https://bing.com/search?q=photonic+crystals. (4) Introduction to Photonic Crystals: Bloch’s Theorem, Band Diagrams, and .... http://ab-initio.mit.edu/photons/tutorial/photonic-intro.pdf. (5) Photonic Crystal Research - Massachusetts Institute of Technology. http://ab-initio.mit.edu/photons/
"Pseudogravity" my ass. The science is interesting, the headline is clickbait.