New erasable thermal phase-change superresolution (EPSR) disks composed of mask and recording layers can increase recording density by the detection of the below-diffraction-limited marks within the readout spot. The formation of the aperture and the readout signal on the EPSR disk were analyzed. The feasibility of optically designed EPSR disks was evaluated by thermal simulation. A carrier-to-noise ratio of 32 dB at a mark size of 0.4 mum, 8 dB higher than that of a conventional disk, was obtained by application of a pulse-read method to the EPSR disks at a wavelength of 780 nm and a numerical aperture of 0.55.
High density optical disks are progressing rapidly recently. Shrinking the track pitch and the size of recorded pits are among the key technologies to attain higher density storage. However, the decrease in track pitch requires that the tracking servo control system be more precisely than conventional system. Scalar diffraction theory is usually used to calculate the optical readout of conventional optical disk storage system. However, scalar diffraction theory is valid only as long as the wavelength of the incident light is small compared with characteristic transverse dimensions of the scattering structure. As the transverse dimension of track pitch is no longer larger than the wavelength for higher density optical disks, vector diffraction theory1,2 becomes necessary to analyze the optical readout.
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