JPS61192047A - Optical disc - Google Patents

Abstract

PURPOSE:To increase the capacity and density of recording as well as prevent crosstalk by forming light beam guide grooves respectively in the convex track and the concave track and performing tracking about the both tracks by said guide grooves. CONSTITUTION:When a laser light beam 4 is incident on a light beam guide groove 2 with a optical axis 4A normal to the center M of the groove, light is scattered by surfaces exactly mirror image with respect to the optical axis 4A, and each of the right and left halved light detector receives exactly equal amount of light, giving a mirror image curve with respect to the optical axis 4A as shown by curve QR. When the laser beam 4 is incident with its optical axis 4A at the bank A of the groove 2, scattered light is distributed asymmetric with respect to the optical axis 4A, and the right and left halved light detectors receive unequal amount of light, giving a curve PQ. This difference in amount of light received by the halved light detector due to misalignment of the optical axis with the center of the light beam guide groove 2 is fed as the tracking signal for the servo-control.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a general optical disk including a magneto-optical disk, and more specifically to an optical disk used as a recording medium of an optical information recording/reproducing device.

[Conventional technology]

Optical information recording and reproducing technology using optical discs is a recording medium that can perform high-density, large-capacity recording, random access, and fast access, as well as high reliability and non-contact recording and reproducing. Magneto-optical disks have undergone remarkable development in recent years due to their many features and advantages, such as the fact that they do not suffer from abrasion and deterioration, and magneto-optical disks in particular can be erased and re-recorded on the recording medium.

In order to further develop the feature of high-density, large-capacity recording in optical information recording and reproducing technology, improvements have been made to the optical discs used in recording media, and recently, for example, the technology disclosed in Japanese Patent Application Laid-Open No. 139147/1983 has been improved. Optical discs have been developed that allow

This is shown in FIG. In this way, spiral or concentric convex tracks 11 and concave tracks 12 are alternately provided adjacent to each other in the radial direction, and recording pits 3 are provided on both of the convex tracks 11 and concave tracks 12.
In order to increase the density and capacity of recording, a convex track 11 is formed for tracking.
or the recessed track 12 is an adjacent recessed track 12
Alternatively, it is configured to serve as a guide groove for the convex track 11.

[Same ff 1 point to be solved] The above-mentioned improved optical disc is different from the initial optical disc with the optical guide groove, but the width of the optical guide groove on the disc is the same as the total width of the optical guide groove on the disc.
i! Contrary to the decrease in recording capacity, the convex track 11 or the concave track 12 is VAF! The concave track 12 or convex track 11 serves as an id groove and is used exclusively for guiding the optical head, and since there is no groove in which recording pits are formed, the recording capacity increases accordingly. However, it has the following drawbacks.

That is, the convex tracks or concave tracks in the prior art are used as optical guide grooves, but at the same time, recording pits are also formed thereon.
It must have a relatively large width, at least not smaller than the recording pit diameter, and as a result, if the response speed for servo-controlling the optical head is the same,
The tracking accuracy decreases accordingly, and as shown by the symbol 3A in FIG. 4, the track deviation of the recorded pits occurs, and as a result, the recorded pits overlap with those of the adjacent tracks, resulting in cross-talk (cross-talk). )
There is a drawback that it is easy to cause.

(Means for Solving the Problems) This invention solves the above-mentioned disadvantages, increases the storage capacity,
The purpose is to provide a new optical disc that achieves high density and eliminates the drawback of crosstalk at the same time.Specifically, it is disc-shaped, and the convex tracks and concave tracks on which recording pits are to be formed are In an optical disk provided in a spiral shape or a concentric shape so as to appear alternately adjacent to each other in the radial direction, a light guide groove extending along the tracks of the convex portion and the concave portion is formed in each of both the convex portion tracks and the concave portion tracks, The present invention provides an optical disk 8 characterized in that the optical guide groove allows tracking of a convex track or a concave track to which the optical guide groove belongs.

[Effect]

Since each convex track and concave track in which a recording pit is formed is provided with a light guide groove having a relatively narrow width, tracking accuracy is improved and there is no risk of crosstalk v1.

Furthermore, since recording pits are formed on both the convex tracks and the concave tracks, the recording capacity is sufficiently large.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS. 1 to 3.

On the surface of the disc-shaped optical disc 1, spiral or concentric convex tracks 11 and concave tracks 12 are formed so as to appear adjacent to each other in the radial direction and alternately appear. The convex track 11 and the concave track 12 are both tracks on which the recording pit 3 is to be recorded, as shown in the second cause of the enlarged perspective view of the partial breakage of the π arrow indicated part in FIG. A light guide groove 2 is provided approximately in the middle of each convex trunk 11 and concave track 12 in the width direction.

As shown more clearly in FIG.
1, /8 to 1, /4) λ, and the material of the optical disk 1 may be a suitable synthetic resin plate such as acrylic (particularly in the case of a magneto-optical disk). As is well known, the surface may be formed with an appropriate amorphous alloy WIllI1 containing iron (Fe) as the main component and mixed with rare earth metals such as cadrinium (Gd) and terbium (Tb), but the material Of course, it is not limited to this.Also, the optical disc 1
As for the overall structure, two sheets may be bonded together facing each other with the recording pit forming surface facing inside so as not to expose the recording pit forming surface.

Next, tracking w4 in the case of the optical disc of this invention
- will be explained with reference to M5a and FIG. The tracking method is not particularly different from that of conventional grooved disks, so it will be briefly explained.

Figure 5 shows a laser beam 4 emitted from an optical head (not shown) (its leading axis is indicated by line 4A).
FIG.
) is when the laser beam 4 is irradiated at a position where its leading axis 4A just hits the edge A of the groove 2 for light guide, and (b) of the same figure shows that the laser beam 4 is irradiated at a position where its leading axis 4A is for light guiding. If the irradiation is perpendicular to the center M of the groove 2, I! 11il(c) shows the case where the laser beam 4 is irradiated so that its front axis 4A hits the opposite edge B of the light guide groove 2.

In each case described above, the reflected light of the laser beam is received by the two-split photodetector, and the light reflected to the left side of the optical axis 4A is received by one of the two-split photodetectors, and the light reflected to the right side of the optical axis 4A is The light reflected by the two detectors is received by the other detector of the two-split photodetector, and if the amount of light entering each detector is compared, it is expressed as the graph in FIG.

In other words, the most obvious case is the case of factor 5 (b), in which case the situation of the reflecting surface is completely symmetrical with respect to the optical axis 4A, so each detection by the two-split photodetector The amount of light received by the device is exactly the same on the left and right sides, and if it is expressed by a light amount distribution curve with the horizontal axis representing the left and right deviation from the center M of the light guide groove 2, then, for example, the sixth factor, song 1! As represented by QR, it becomes a symmetrical curve with respect to the optical axis 4A.

However, if the position of the optical head that emits the laser beam 4 is shifted and the laser beam 4 is irradiated in the state shown in Fig. 5(a), the state of the reflecting surface will change to the left or right with respect to the optical axis 4A. Since it is not symmetrical, the amount of reflected light entering each detector of the two-split photodetector is not equal on the left and right sides, and the light amount distribution curve in the above sense becomes, for example, curve PQ in FIG. 6.

The reason for this difference in the amount of light received by each detector of the two-split photodetector is that the depth of the light guide groove 2 is (1778~1,
/4) λ, so there is a gap between (1, /4)λ or C between the light reflected from the surface of the convex track 11 or the concave track 12 and the light reflected from the bottom surface of the light guide groove 2.
This is because an optical path difference of 1/2) λ is generated, and in combination with the excellent coherence of the laser beam 4, strong interference between reflected lights occurs.

As mentioned above, if the position of the optical head deviates from the center position of the light guide m2, a difference will occur between the rain detectors of the two-split photodetector caused by the laser beam 4. This difference will be used as a tracking signal to move the optical head towards the optical disc. If the laser beam is moved in the radial direction and servo controlled so that the laser beam irradiation state is always in the state shown in FIG. 5(b), accurate automatic tracking becomes possible. In this invention, since the width of the light guide groove 2 is small, more precise tracking becomes possible.

〔effect〕

According to this invention, (1) each convex track and concave track where recording pits are formed is provided with a light guide groove, so tracking 1112 is improved and there is no possibility of O-stalk; (1) Moreover, since recording pits are formed on both the convex track and the concave track, there is an effect that the recording capacity jlt3 is sufficiently large.

Furthermore, in this embodiment, (1) the width of the optical guide groove is relatively narrow, smaller than the diameter of the recording pit, so there is an advantage that the tracking accuracy is even better.

[Brief explanation of drawings]

Fig. 1 is a diagrammatic plan view showing the entire optical disc of the present invention, Fig. 2 is a partially broken enlarged perspective view of the part indicated by the □ arrow in Fig. SI, and Fig. 3 is the same FIG. 4 is a diagram similar to FIG. 2 of a conventional optical disc, and FIG. 5 is a diagram showing a case where a laser beam beam is irradiated onto the surface of a convex track or a concave track including a light guide groove. FIG. 6 is a simplified side sectional view illustrating the light amount distribution curve of reflected light in each case of FIG. 5. DESCRIPTION OF SYMBOLS 1... Optical disc, 11... Convex track, 12... Concave track, 2... Optical guide groove, 3... Recording. pit. Applicant NEC Home Electronics Co., Ltd. Agent Patent Attorney Masu 1) Takeo Figure 4 Figure 5 Figure 6

Claims (1)

[Scope of Claims] 1. The disc-shaped convex track (11) and the concave track (12) on which the recording pits (3) are to be formed are arranged in a spiral shape so that they appear alternately adjacent to each other in the radial direction. Or in an optical disc (1) provided concentrically,
A light guide groove (2) is formed in each of the convex track and the concave track, and the light guide groove (2) allows the convex track to which the light guide groove belongs to be formed. Or an optical disc characterized in that tracking is performed on concave tracks. 2. The width of the optical guide groove (2) is smaller than the recording pit diameter, and its depth is (with respect to the wavelength (λ) of the laser beam).
1/4 to 1/8) λ.