Information can be stored in many ways, and for many systems the density it is stored at is very important. There can be limits to the density though, such as with the wavelength of light. By using a plasmonic film though, researchers at the University of Illinois have recorded optical information at sub-wavelength scale, and in real time.
The plasmonic film is actually an array of gold, pillar-bowtie nanoantennas (pBNAs) that reacts to laser light. The reaction is analogous to how photographic film behaves when exposed to light, but the effect occurs in real time, and does more than store an image. When exposed to laser light, the pBNAs actually create optofluidic channels without walls, allowing the researchers to affect the trajectory of particles in a solution. Other optofluidic systems have been made that achieve the same goal, but do have physical walls.
When the researchers tested it, the bit size was around 425 nm, which is directly related to the spacing of the antennas. If this were applied to an optical disc that would be around 28.6 GB of data, but by modifying the spacing of the array and the antennas, it could be scaled up to 75 GB a disk. That is of course only considering data storage applications, but this discovery could have many other photonic uses.