Super resolution near field structure study

In conventional optical data storage devices, diffraction ultimately limits the data density which can achieved. The density is proportional to the ratio (NA//spl lambda/), where /spl lambda/ is the wavelength of the laser source and NA is the numerical aperture of the playback optical system. One way to exceed this limit is to use a super resolving imaging technique. A technique that has been proposed as a means of exceeding the density restriction imposed by the diffraction limit is the super resolution near field structure (SR or super-RENS). In SR an additional thin material layer, such as AgO is added to the disc storage medium. When the silver oxide layer is heated with a laser, that layer's material changes its optical properties in such a way that its transmission increases in the region over which the material has become sufficiently hot, which generally occurs only in the vicinity of the center of the focused laser beam. Since this region can be substantially smaller in diameter than the focused light spot itself, it effectively becomes a small (relative to the diameter of the focused playback spot) aperture in the SR layer. Further, because the spot's diameter is already very near its diffraction limit, the SR aperture is sub-wavelength in size.