JPH03156726A - Erasure method for optical information - Google Patents

Abstract

PURPOSE:To obtain a reproduction signal with excellent quality by radiating a converged laser beam spot while being shifted not in excess of the width of a recessed part or a projection in both adjacent directions from the center of the recessed part or the projection. CONSTITUTION:The optical information is erased by radiating a converged laser beam spot 3 to a position from the center of a projection 1 or a recessed part 2 in the direction of both adjacent projection or recessed parts by a shift quantity not in excess of the width of the recessed part or the projection once. Thus, sufficient erasure is attained with an erasure laser power less than the recording laser power. Then the erasure of information suitable for obtaining a reproduction signal with excellent quality is attained with a power less than the recording laser power.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for recording, reproducing, and erasing digital or analog signals on an optical information recording medium having a pregroove consisting of a convex portion and a concave portion that move at high speed. Person in charge, especially
Related to a method of erasing an optical information signal suitable for obtaining a highly reliable reproduced signal [Prior art] As a method of recording information on an optical information recording medium having a pregroove consisting of a convex part and a concave part, a microscopic method is used. A laser beam of constant intensity narrowed down to a small diameter is irradiated onto the convex part or any of the four parts of the recording medium moving at high speed, the laser beam is made to follow the convex part or the concave part, and is emitted for a predetermined time (pulse) depending on the desired pit length. A method has been developed in which pits are formed using heat generated by irradiating a laser beam during the width (also called width). For example, (1) heat causes a phase transition, creating a region where optical properties such as refractive index and reflectance differ from the original state, and this region becomes a pit; (2) heat causes a medium to move upward or A method that reduces the coercive force of vertical magnetization that is aligned downward and simultaneously applies a reversal magnetic field to reverse the direction of magnetization, creating a region where the direction of magnetization is opposite to the original state, and making this region a pit ( Information recording methods such as magneto-optical recording have already been proposed and some have been put into practical use.

The information recorded in this way is then recorded by irradiating a laser beam onto either the convex or concave portions of the recording medium moving at high speed, taking advantage of the fact that the optical properties of the formed bits are different from the surroundings. The information is reproduced by detecting an optical change in the recording medium using a beam reflected by the recording medium or a beam transmitted through the recording medium.

The recorded information obtained in this way is produced by irradiating a laser beam with a constant intensity narrowed to a minute diameter onto the position where the recorded information exists, either in the convex or concave portions of a recording medium moving at high speed, and the heat generated by the laser beam is emitted. is used to restore the optical properties of the bit to its original state.

[Problem that the invention aims to solve]

However, in this method of erasing information using heat generated by laser beam irradiation, sufficient consideration has not been given to the optimal erasing method for obtaining a high-quality reproduced signal.

An object of the present invention is to provide an optical information erasing method suitable for obtaining a high-quality reproduction signal.

(Means for Solving the Problems) The optical information erasing method of the present invention is characterized in that one piece of information is recorded on either the convex part or the concave part of a recording medium having a convex part and a pregroove consisting of four parts. The laser beam spot focused on is shifted from the center of the convex part or concave part in the direction of the convex parts or concave parts on both sides by an amount that does not exceed the width of each concave part or convex part, and the laser beam spot is shifted once at less than the recording laser power. It is characterized by irradiating and erasing laser power.

[Effect]

Generally, when bits are erased using heat, the recording medium has a minimum critical temperature (erasable temperature T) required to erase the focus.
, 1) are determined, and the bit will be erased only when T is exceeded.

Therefore, as a result of measuring the relationship between erasure laser beam power and erasure rate with respect to recording laser power, as shown in Figure 2, in order to obtain an erasure rate that can obtain a high quality reproduction signal, it is necessary to exceed the recording laser power. It was found that it was necessary to irradiate the surface of the recording medium with an erasing laser power of . However, the output of semiconductor lasers is limited, and when the laser beam is made to follow the convex or concave portions of the recording medium, there may be a misalignment between the laser beam and the center of the pregroove made of the convex and concave portions of the recording medium. Occur.

Therefore, for the information recorded on either the convex part or the concave part of the recording medium, a single focused laser beam is directed from the center of the convex part or concave part to the convex part or concave part on both sides, respectively. If an erasing method is used in which the data is shifted by an amount that does not exceed the width of the area and irradiated once at a time, sufficient erasing is possible with an erasing laser power that is less than the recording laser power, and a high-quality reproduction signal can be obtained.

〔Example〕

Examples of the present invention will be described below.

FIG. 3 shows a cross-sectional view of the recording medium 5 used in the experiment. This recording medium consists of a magneto-optical recording film 2 made of TbFeCo sandwiched between a protective film 25 made of SiN and a transparent substrate 24 made of polycarbonate with a convex part interval of 1.6 μm.
6 is provided.

FIG. 1 is a diagram illustrating a method of erasing the recording medium 5.
The single focused laser beam spot 3 is shifted once from the center of the convex portion 1 or the concave portion 2 in the direction of the convex portions or concave portions on both sides by an amount that does not exceed the width of the concave portion or convex portion, respectively. Erase by irradiating one by one.

In order to confirm the effectiveness of this erasing method, a recording/reproducing experiment was conducted using the recording medium 5 using the apparatus shown in FIG. Fourth
The device shown in the figure consists of an actuator, an 8° lens, and a 9. Beam splitter 10.11.12.8 Optical filter 13. Reproduction signal detection light receiving element 14. Error detection light receiving element 15.16
．． Magneto-optical recording head 4 consisting of a laser light source 17
, a laser light source modulation circuit 18, a recording medium heating laser light source circuit 19, and a servo control circuit 20.2.
1, an amplifier circuit 22, a shift circuit 23, a current source 6, and a magnetic field application device 7; a laser light source modulation circuit 18; and a recording medium heating laser q.
- A laser beam pulse was generated by the light source circuit 19, a reversal magnetic field was applied by the magnetic field application device 7, and bit recording and reproduction was performed by the magneto-optical recording head 4.

Linear speed 5.6ta/s, recording laser beam power 8mW
, IM under the condition of recording laser beam irradiation time of 500 ns.
A signal in Hz was recorded. After that, when the shift circuit 23 was stopped and erasing was performed using the conventional method of irradiating once, the erasing rate was 56 dB at a reproduction laser beam power of 1 mW.
An erasing laser beam power of IOmW was required to obtain .

Similarly, the IMllz signal was recorded under the conditions of a linear velocity of 5.6 m/s, a recording laser beam power of 81, and a recording laser beam irradiation time of 500 ns, and using the shift circuit 23,
When erasing was performed using the method shown in Figure 1 in which the recording area was shifted by 0.2 μm from the center of the recording area toward the inner and outer circumferences, an erasure laser power of 6n+H was sufficient to obtain an erasure rate of 56 dB at a reproduction laser beam power of 1IIIW. there were.

As a result, according to the present invention, it was possible to erase information suitable for obtaining a high-quality reproduction signal with a power smaller than the recording laser power.

〔Effect of the invention〕

According to the present invention, an optical information erasing method suitable for obtaining a high-quality reproduction signal can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the erasing laser beam irradiation method according to the present invention, FIG. 2 is a diagram showing the relationship between the erasing rate and the recording laser power, and FIG. 3 is a schematic cross-sectional view of the optical recording medium used in the present invention. FIG. 4 is a diagram showing an apparatus for implementing the erasing method according to the present invention. 3...Laser beam 4...Magneto-optical recording head 5...Magneto-optical disk 7...Magnetic field applying device 23...Shift circuit 26...・Magneto-optical recording film

Claims (1)

[Claims] (1) A single focused laser beam spot is directed from the center of the convex or concave portion to information recorded on either the convex or concave portions of a recording medium that has a pregroove consisting of convex portions and concave portions. An information erasing method characterized by shifting in the direction of adjacent convexes or concave portions by an amount that does not exceed the width of each concave or convex portion, and irradiating the laser power less than the recording laser power once to erase the information. .