The advent of high-definition television as well as the increased use of video-on-demand over the internet continue to foster demand for high-density recording media. Researchers from the Swinburne University of Technology in Australia1 have now demonstrated a novel optical recording scheme that uses a five-dimensional parameter space to achieve world-leading storage densities.

Their new recording technique exploits surface plasmons in gold nanorod structures. Surface plasmons are collective electronic excitations that interact strongly with light at the matching wavelength. In the case of gold nanorods, the wavelength of the plasmon resonance depends strongly on the rod length and orientation in relation to the polarization of incident light.

The team constructed their recording medium by depositing a thin film containing nanorods of various lengths and with random orientations onto a glass substrate. They then scanned areas of the surface using a laser with a specific wavelength and polarization. The gold nanorods with size and orientation producing a plasmon resonance matching the laser absorbed the light, heated up and melted, while other nanorods were unaffected.

To read this information, the area was scanned with a laser of the same wavelength and polarization but with lower intensity. Where the nanorods had been melted, light reflection was stronger because there were no longer any nanorods with matching plasmon absorption.

Fig. 1: Schematic diagram illustrating the 5D plasmonic recording scheme. Images are imprinted in different layers at different wavelengths and polarizations.

When the same surface was written using a laser with either different wavelength or orthogonal light polarization, other nanorods melted, leading to a different read-out pattern for these parameters. By stacking several layers on top of each other (as in DVDs), the researchers created a five-dimensional parameter space — three spatial dimensions plus the wavelength and polarization of the laser beam (Fig. 1).

The storage density achieved was more than one terabit per square centimeter — more than 340 times that of a DVD. “To our best knowledge, this is the highest demonstrated optical density so far,” says James Chon from the research team. Although a few obstacles remain before this technique can be commercialized, Chon is optimistic. “I believe our work provides an exciting new method of multidimensional multiplexing. Unlike previous methods, it is cross-talk free, stable and practical.”