Flying solid immersion lens offers alternate approach to high-density data storage
A near-field, flying solid immersion lens for writing optical data reduces the beam spot size below the diffraction limit. Researchers at IBM Almaden Research Center (San Jose, CA) used an 830-nm source to record data with a 375-nm bit size at a density of 67.7 kbit/in. Density is a function of beam spot size, which can be reduced by increasing the numerical aperture (NA) of the focusing system or decreasing the wavelength. Near-field optical recording combined with an unconventional optical system offers a method of decreasing the spot size.
The solid immersion lens consists of a truncated sphere placed between the focusing objective and the storage disk. Light is brought to an unaberrated focus inside the sphere, increasing the effective NA by a factor of n2. A sub-diffraction-limited spot inside the lens can be coupled out by evanescent waves in the near-field. The lens was mounted on a flying head (such as is used for magnetic read/write heads) 150 nm above the write surface. These early results were reported in paper Th3.4 last month at the SPIE Optical Data Storage Conference (San Diego, CA); the researchers expect higher rates from an optimized system.