JPH02249137A - Optical disk erasing method - Google Patents

Abstract

PURPOSE:To reduce unerased part on a phase change type optical disk by setting laser wavelength in erasure larger than that in recording and reproduction. CONSTITUTION:The spot diameter of a laser beam in the erasure can be set larger than the diameter of a recording pit by setting the laser wavelength in the erasure larger. This is due to the fact that the spot diameter of the laser beam converged on an optical recording medium layer is proportional to a value in which the number of apertures of a lens is divided by the laser wavelength, and it is possible to increase the spot diameter of the laser beam on the optical recording medium layer by increasing the laser wavelength in the erasure under the constant number of apertures. In other words, the erasure is performed with the spot diameter larger than the recording pit. In such a way, when the reproduction is performed with the spot diameter with the same size as that of the recording pit, the unerased part can be scarsely generated in a reproducing spot diameter area.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method of erasing a rewritable phase-change optical disk used for data files, etc., on which information can be recorded, reproduced, and erased using light.

2. Description of the Related Art In recent years, rewritable phase change optical disks that can be recorded, reproduced, and erased using light have been increasingly being applied to data files and the like due to their advantages such as high density, large capacity, and high speed access.

The recording and erasing uses the heat of laser light (heat mode).

Conventionally, recorded pits (amorphous state) are erased (crystalline state) by irradiation with a laser beam (one beam overrite) that is slightly weaker than the recording power in the phase change type, and reproduction is performed using a very weak laser beam. irradiated with light and read the changes in reflectance. Since only the laser power was changed during recording, reproduction, and erasing in this way, the spot diameter of the laser beam on the optical recording medium layer did not change. (For example, Chabanise Journal of Physics.

Vol. 26 (1987) P61-66, and Optical Memory Symposium 86 Proceedings P81-86) Problems to be Solved by the Invention In order to perform erasing with a laser beam having the same spot diameter as the spot diameter of the laser beam during recording, In the phase change type, the temperature around the recording pit becomes low due to heat flow to the vicinity of the pit, which tends to cause a crystalline state that remains unerasable.

In view of the above-mentioned problems, the present invention provides an erasing method that leaves almost no unerased data on a phase change optical disc using a heat mode.

Means for Solving the Problems In order to solve the above problems, the method for erasing an optical disk of the present invention involves making the laser wavelength during erasing longer than the laser wavelength during recording and reproduction, and recording the spot diameter of the laser beam during erasing. This method of erasing an optical disc is characterized in that the spot diameter is made larger than the original spot diameter, and erasing is performed so as to completely cover the recorded pits.

Function: As described above, in the present invention, by lengthening the laser wavelength during erasing, the spot diameter of the laser beam during erasing becomes larger than the diameter of the recording pit. This means that the diameter of the focused spot of the laser beam on the optical recording medium layer is the numerical aperture of the lens (N
This is because it is proportional to the value obtained by dividing A) by the laser wavelength, and NA
Under a constant condition (common to lenses), the spot diameter of the laser beam on the optical recording medium layer can be increased by increasing the laser wavelength during erasing.

Since erasing is performed with a spot diameter larger than the recording pit, when reproducing with a spot diameter the same as the recording pit, there is almost no unerased portion in the reproduced spot diameter region.

Embodiment A method for erasing an optical disc according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the signal level after erasing with respect to erasing power in this embodiment. In FIG. 1, the solid line indicates what was recorded with a laser beam with a wavelength of 740 nm, erased with a laser beam with a wavelength of 830 nm, and reproduced with a laser beam with a wavelength of 740 nm.

The dotted line indicates recording, erasing, and reproduction using a conventional 830 nm laser beam. This example will be described below.

ZnS on a polycarbonate substrate as an optical disk
A protective film made of +S i 02 was prepared by sputtering, a TeGe-3e-3b layer was formed as a recording medium layer on top of it, and a protective film of ZnS+S to □ and gold was sputtered as a reflective layer on top of it. Using. The optical disk is rotated at 240 rpm, and a wavelength tunable laser (740A-830A) is used on top of the optical disk to rotate the optical disk at a wavelength of 740 rpm.
Pit positions were recorded using a 0 nm laser beam.

At this time, the NA of the lens was 0.53, the recording power was 181, the erasing power was 10 mW, and the reproducing power was 1 eW.

Next, erase with a laser beam with a wavelength of 830 nm, and erase with a laser beam with a wavelength of 740 nm.
Regeneration was performed at nm. As a result, the amount of unerased data has been significantly reduced from -24 dB to -36 dB.

The recording pit diameter at this time was 0.70 μm, and the laser beam spot diameter during erasing was about 0.78 μm. This erasing method has been effective not only for phase change type optical disks but also for heat mode storage such as magneto-optical disks.

Effects of the Invention As described above, the erasing method of the present invention provides an erasing method that makes it possible to significantly suppress unerased data in heat mode recording, particularly in phase change optical discs.

[Brief explanation of drawings]

The figure is a diagram showing the signal level after erasing with respect to the erasing power in one embodiment of the present invention. 11... This embodiment, 12... Conventional example.

Claims (2)

[Claims] (1) A method for erasing an optical disc, characterized in that the laser wavelength during erasing is longer than the laser wavelength during recording and reproduction. (2) The optical disk erasing method according to claim (1), wherein the lasers for recording, reproducing, and erasing are made of the same semiconductor.