KEYWORDS: Diffusion, Germanium antimony tellurium, Super resolution, Laser stabilization, Laser optics, Laser marking, Digital signal processing, Near field, Laser applications, High power lasers
We report the readout stability improvement results of super-resolution near field structure (Super-RENS) write-once
read-many (WORM) disk at a blue laser optical system. (Laser wavelength 405nm, numerical aperture 0.85) By using diffusion barrier structure (GeSbTe sandwiched by GeN) and high transition temperature recording material (BaTiO3), material diffusion of phase change layer and recording mark degradation were greatly improved during high power (Pr=2.0mW) readout process up to 1X105 times.
Selecting a binary compound (Sb-Te, Zn-Sb and Ge-Te) with its composition at around a eutectic point generated a
better super-resolution effect. The thickness optimization of the super-resolution readout layer was also effective for the
property improvement. The temperature estimation indicated thinner the layer thickness is better as far as the readout
laser can easily increase its temperature.
KEYWORDS: Super resolution, Polarization, Near field optics, Signal processing, Optical properties, Reflectivity, Near field, Platinum, Signal detection, Silver indium antimony tellurium
KEYWORDS: Near field, Light scattering, Scattering, Near field optics, Super resolution, Finite-difference time-domain method, Optical storage, Diffraction, Signal detection, Optical discs
We describe the angular dependence of near-field signals generated in super-resolution near-field structure (Super- RENS) disks. The carrier-to-noise ratio (CNR) of transmitted signals using different numerical aperture's (NA's) lenses, were mostly the same values, experimentally. While on computer simulation by finite-difference time-domain (FDTD) method, it was found that most scattered signals were trapped around the optical axis.
Optical near-field recording with a super-resolution near- field structure (Super-RENS) records and retrieves small marks with dimensions beyond the diffraction limit. A thin layer of an antimony (Sb) film, added to the usual phase-change optical disk structure, is the key material of this technique. We investigated the nonlinear optical properties of the Sb film, especially the optical switching behavior in the stationary state using a nanosecond pulsed laser. Clear switching was observed under microscopic measurement. Time response of the optical switching properties were examined and found to show fast rise-up and slow decaying times.
KEYWORDS: Near field scanning optical microscopy, Near field, Super resolution, Near field optics, Silver, Light scattering, Optical discs, Optical storage, Plasmons, Oxides
The principle and recent progress of super-resolution near- field structure (super-RENS) were introduced. Super-RENS is a unique method to retrieve optical near-field without any probes at high speeds approximately millions times faster than that of any other scanning near-field optical microscopes (SNOMs). First super-RENS disks were developed using an optically transparent aperture, and recently we found that a light-scattering-center using nano-explosion of silver oxide (AgOx) is also available in super-RENS.
Organic material with pronounced thermochromism is used as a mask layer in a phase change optical disk. The thermochromic material exhibits significant change in optical properties at increased temperatures as well as fast response upon pulsed laser irradiation. Recording and retrieving signals from marks smaller than that of the diffraction limit is investigated under high speed disk rotation.
Readout characteristics of light-scattering-mode super- resolution near-field structure (super-RENS) disks are described in detail. Readout intensities in reflected and transmitted signals are compared. Both signals showed mostly the same carrier-to-noise ratios (CNRs) using objective lenses with NA of 0.6. The formation mechanism of light scattering centers in the super-RENS disks ia also described in comparison with several different disks. As increasing oxygen ratio during the deposition of silver oxide (AgOx) layers, two different chemical reactions were identified. It was found that the super-RENS disks with oxygen-rich AgOx films have both characteristics of transparent and light- scattering apertures in one disk. Further study also revealed that the AgOx dynamic nonlinearity is not so high and less than 6% by the film itself; however, it is enhanced to 12% in super-RENS. It is supposed that the imaginary refractive index k of the films is less than 0.1; therefore, it is hard to heat itself to the decomposition temperature without a heat source (GeSbTe film) underneath. This result would be a hint to further increase CNRs in a light- scattering-mode super-RENS disks.
KEYWORDS: Optical storage, Modulation, Finite-difference time-domain method, Near field optics, Optical discs, Antimony, Thermography, Analytical research, Super resolution, Near field
Recently a super-resolution near-field structure (Super-RENS) has been proposed. A storage density of a conventional optical disk has been limited by the diffraction limit of the light. During the readout process of a Super-RENS, a small aperture is formed in a masklayer by a readout laser power. The mask layer is laid very close to a recording layer, and the aperture produced in the mask layer acts as an optical near-field probe. We have retrieved marks as small as 60 nm.
Near-field optics has been applied to optical data storage systems with a high recording density beyond the diffraction limit. However, the actual data storage has not been realized, yet. The difficulty applying a near-field optics to optical data storage is caused by a narrow space between a near-filed probe and a recording medium.
KEYWORDS: Near field optics, Near field scanning optical microscopy, Modulation, Near field, Phase shift keying, Refractive index, Objectives, Optical storage, Crystals, Optical microscopes
We have observed near-field optical images of phase change marks and evaluated the readout signals including the optical near-field. Samples were composed of multilayered structures on glass substrates. Crystalline marks were recorded by a focused laser beam with an optical microscope in the as-deposited amorphous films. In readout, the optical and the topographical images of the recorded marks were evaluated at the same time by a collection mode near-field scanning optical microscope (NSOM). The surface profiles showed less than 1 nm dips around the marks. Therefore it means that the NSOM image of phase change marks depends on the refractive index change. The evaluated signal modulation of the optical image showed a sinusoidal curve to the top SiN layer thickness, and the maximum modulation was 60 percent.
A new optical RAM-bus (ORAM-bus) memory has been proposed. This memory has three- dimensional memory structure with the vertical optical interconnection. Data are vertically transferred in this memory by the optical coupling sense amplifier which acts as a cache memory and also as an amplifier to amplify the signal read-out from a memory cell. It was confirmed in the computer simulation that a very high data transfer speed of 64 Gbit/s can be achieved in the ORAM-bus memory with the configuration of 256 Kbits X 4 layers. The new parallel computer system with such ORAM-bus memories is also proposed.
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