Melody Encoded onto Plasmonic Nanostructure

With data storage capacity 5600 times greater than magnetic film, a chip made of tiny gold bow ties could be the next best place to store all your MP3s.

Researchers from the University of Illinois at Urbana-Champaign recently created the first-ever optically encoded audio recording using a plasmonic nanostructure. Using the device as a “nano piano,” they were able to input and then play back the melody of “Twinkle, Twinkle, Little Star.”

The device is made of an array of 250-nm gold bow tie nanoantennas supported on 500-nm-tall SiO₂ posts. The researchers demonstrated that these pillar-supported bow tie nanoantennas (pBNAs) could be used to store sound information either as a temporally varying intensity waveform or a frequency varying intensity waveform.

Arrays of pillar-supported bow tie nanoantennas (pBNAs) can be used to record distinct musical notes. Courtesy of the University of Illinois.

Audio signals were recorded by using a microscope to scan a sound-modulated laser beam directly onto the bow ties. When the gold is illuminated, it melts slightly and its optical response changes.

“Originating from a plasmon-induced thermal effect, well-controlled nanoscale morphological changes allow as much as a 100-nm spectral shift from the nanoantennas,” said postdoctoral researcher Hao Chen. “By employing this spectral degree of freedom as an amplitude coordinate, the storage capacity can be improved.”

Retrieval is achieved by using the same microscope to image the recorded waveform, after which the signal is processed and played back as sound.

“Although our audio recording focused on analog data storage, in principle it is still possible to transform to digital data storage by having each bow tie serve as a unit bit 1 or 0,” Chen said. “By modifying the size of the bow tie, it’s feasible to further improve the storage capacity.”

Professor Dr. Kimani Toussaint said the technique could be of use in archival storage. The technology also holds potential for on-chip, plasmonic information processing, he said.

The research was published in Scientific Reports (doi: 10.1038/srep09125).

For more information, visit www.illinois.edu.