System Uses Quaternary Code to Optically Store Data

A space-saving method of storing digital data uses a quaternary (four-symbol) code to store the data, and uses heat and UV light to write and read fluorescence output from polymer film. This method could potentially require about half the space as existing data storage methods.

Instead of numerals, this optical storage system uses the absence of color and three colors produced by two dyes as the symbols representing information to be stored.

Researchers from Case Western Reserve University loaded a small amount — less than .4 percent by weight — of the two dye molecules into a flexible sheet of polymethyl methacrylate (PMMA). The PMMA remained clear and colorless in ambient light and temperature after patterning.

Two dyes were used: cyano-substituted oligo(p-phenyene vinylene), which fluoresces green when exposed to heat; and o-nitrobenzyl ester of benzoic acid, which fluoresces ultramarine when exposed to UV light. When the dyes are overlapped and exposed to both heat and UV light, they fluoresce as cyan.

The team wrote quaternary code by laying metal or wood templates over the dye-containing film, then applying heat and UV light.

CWRU chemists developed a space-saving method to store digital data optically, using four-symbol, or quaternary code. The four symbols are the absence of color and three colors -- fluorescent green, ultramarine and cyan -- produced when dyes contained in a common polymer are exposed to heat, ultraviolet light or both. Courtesy of Emily Pentzer.

The circular symbols in the template were each 300 micrometers across, with 200 micrometers between them. The polymer film showed that it could be removed from the substrate and mechanically deformed without damaging the pattern. The system demonstrated its durability, retaining the data and remaining legible even after the film had been rolled, bent, written on with permanent marker, submerged in boiling water and half the surface had been rubbed away with sandpaper.

Currently the team is investigating the use of specialized lasers to shrink the spatial resolution in order to further increase the data density (similar to Blu-ray vs. CD).

The team is also researching whether a third dye could be added that would respond to different stimuli and remain distinct from the other two dyes. If this is possible, the colorless film, plus all the color combinations available, would allow the research team to develop a method of storing data using a septenary, or seven-symbol code, further shrinking storage size.

The researchers believe that chemistry-based approaches could be required to move beyond current limitations and meet future needs for data storage. Their system, which is scalable, demonstrates the use of simple and robust chemical reactions to improve data storage capabilities, and has the potential to exponentially increase information density.

“We’re using chemistry instead of engineering to address data storage, but it’s really complementary to what engineers are doing,” said professor Emily Pentzer.

The research was published in Journal of Materials Chemistry C (doi: 10.1039/c7tc00929a).