Laser Spot Aims at Storage Market

Kevin Robinson

A relatively simple solution to the problem of reducing a laser's spot size using near-field optics may lead to an optical storage system that could store as much as 500 Gb/in.² of data, up to 100 times current storage densities. Researchers at Lucent Technologies' Bell Laboratories are working with Siros Technologies Inc. of San Jose, Calif., to commercialize the very-small-aperture laser, which has built-in near-field optics.

Typically, laser spot size is determined by the wavelength of light. With conventional optics, you cannot get a spot smaller than half of the wavelength of light. However, passing light through a hole that is smaller than the light's wavelength enables a subwavelength spot in the near field of the hole.

As described in the Sept. 13, 1999, issue of Applied Physics Letters, the Bell Labs researchers created the laser by making a 250-nm hole in the mirrored end of a 980-nm diode laser, creating a 250-nm near-field spot. They then used the laser to write to an optical disk at a density of 7.5 Gb/in².

What is remarkable is the simplicity of the solution. Previous research, much of which sprang from near-field microscopy, used tapered optical fiber that was coated to be reflective. However, much of the laser power was lost as heat in the reflective coating. In the new solution, because the photons that do not escape through the hole are returned to the laser's gain medium, the laser loses far less power through heating. The increase of power in the near field topped 1 mW, 10,000 times the power of coated-fiber near-field devices.

Lucent and Siros recently broadened their intellectual property agreement. Siros officials would not comment on the technology; company statements said that the expansion would allow Siros to pursue applications of the laser beyond optical data storage.