A new nano-optical device can focus laser light tighter than traditional optics, which could lead to higher-density data storage.

As gigabytes of movies, pictures, audio, and text fill up more and more CDs and DVDs, there's clearly a need for better ways to save more data. A research team at Harvard University has developed a technique that could help to significantly boost the capacity of conventional optical discs. They've fabricated a nano antenna--built directly onto an inexpensive, off-the-shelf laser--that focuses light to a much smaller spot size than is possible with even the best traditional lenses, potentially enabling more bits to be written onto an optical disc.

The storage capacity of a disc increases as the wavelength of light used to write data to it decreases; CDs are written and read using light with a wavelength of 780 nanometers, DVDs use 650 nanometers, and HD-DVDs and Blu-ray discs use 405 nanometers. Wavelengths shorter than 405 nanometers would require light sources far too expensive for consumer electronics.
The problem is that conventional lenses can only focus light to half their wavelength, a physical barrier called the diffraction limit. The Harvard researchers sidestepped this limit, however, by abandoning traditional optics in favour of nano-optical techniques. "We can get around the wavelength limitation by using an antenna," says Ken Crozier, assistant professor of electrical engineering at Harvard.

The team of Crozier, Federico Capasso, professor of applied physics at the university, and graduate students Eric Kort and Ertugrul Cubukcu designed the optical antenna to focus light from a commercial laser (with a wavelength of 830 nanometers) to a spot size of 40 nanometers. With this resolution, "you'd be able to pack more than three terabytes [3,000 gigabytes] worth of data onto something the size of a CD," Crozier estimates. That's enough to hold more than 300 feature-length movies. By comparison, a dual-layer HD-DVD or Blu-ray disc can hold 30 gigabytes or 50 gigabytes, respectively.

Crozier says his team is also exploring alternatives to the gold metal that currently coats their nano rods. Silver, for instance, could focus light more efficiently than gold at the wavelengths used by the consumer electronics industry.

written by Florin C.

Source: technologyreview.com