The limitations of focussing a light spot on to recording medium (that is, diffraction effects) has been a fundamental restriction on achievable density of data storage. The work reported by a group led by Professor Sergei Kazarian from the Department of Chemical Engineering at Imperial College London can circumvent that problem. The summary from Imperial comments that, until now, optical storage media such as DVD or BluRay, lag significantly behind in capacity compared with hard drives, flash memory and other solid state drives. However, storing a higher density of data using light cannot be accomplished due to restrictions imposed by the so-called "diffraction limit".
This term refers to a physical phenomenon - the inability to focus a beam on the surface of objects whose size is smaller than the wavelength of the light (about 400 nm in the case of BluRay). For this reason, the density of recording information on all optical storage media is noticeably inferior to what is possible in magnetic or electronic data recording systems.
This work represents an increase in recording density to [the equivalent of] hundreds of terabytes per square inch, using two things - organic dyes based on azobenzene, and a special light antenna. The researchers found that shining a laser on azobenzene molecules in an electric field causes them to flip. This creates a change in the optical properties of the dye molecules allowing them to act as information carriers. In this way the researchers can use azobenzene films to create optical memory which “violates” the diffraction limit.