JPS62172542A - Optical disk - Google Patents

Abstract

PURPOSE:To improve the erasure efficiency of an objective track without signal deterioration of adjacent recording tracks and to reduce the noise of a read signal by providing a medium having a lower heat conductivity and lower reflectance than those of a recording medium between a recording field and adjacent recording fields. CONSTITUTION:In using an optical disk 1 consisting of an amorphous recording medium 4 provided between recording tracks 3 of crystal state recording medium by an optical disk drive, the heat generated from a light beam irradiated to the track 3 at the recording and erasure is confined in the object track 3 by the medium 4. Thus, a written signal of adjacent tracks 3 to the object track 3 is hardly erased and the erasure efficiency of the object track 3 is improved. Since the reflectance of the medium 4 is low, the noise component read from the medium 4 is reduced at the signal reproduction.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to optical discs, and more specifically, to narrowing laser light into a minute light beam with a diameter of about 171 m using a lens, etc., and forming a spiral or concentric guide groove. and irradiates the light beam onto a recording area centered on the guide groove or a recording area centered on a midpoint between the guide groove and a guide groove adjacent to the guide groove (hereinafter also referred to as a recording track). The present invention relates to an optical disc on which signals are recorded.

Conventional technology The optical discs that have been developed so far can be roughly divided into two types: those that change the amount of reflected light by forming holes or bubbles in the recording medium by irradiating the recording medium with a light beam such as a laser beam, and those that change the amount of reflected light. There are so-called phase-change types that change optical constants such as the refractive index n and extinction coefficient while keeping the same shape, and utilize the resulting change in reflectance or transmittance, and even while applying a magnetic field to the recording medium. There are three types: the so-called magneto-optical type, in which a light beam is irradiated and the magneto-optical properties of the recording medium (such as the Kerr rotation angle due to the Faraday effect) are utilized while the shape of the recording medium remains unchanged. Conventional examples of phase change type optical disks are shown below, but since all of the three types mentioned above utilize heat from a light beam, all of them have problems that will be described later.

Examples of phase-change optical disks that have been developed so far, which can reversibly change between a crystalline state and an amorphous state depending on the light beam irradiation method and record signals, include chalcogen glass thin films. It has been known. In such a recording medium, optical constants such as the refractive index n and extinction coefficient are changed while preserving the shape, and signals are recorded and erased using the resulting change in reflectance. usually,
By heating and rapidly cooling the recording medium, the recording medium becomes amorphous and the reflectance becomes low. Conversely, heating up the recording medium
By slow cooling, the recording medium becomes crystalline and its reflectance increases. Optical disks can perform heating, rapid cooling, heating and slow cooling
Examples of ways to achieve this in a drive include irradiating a roughly circular light beam with a diameter of about 1 μm for heating and rapid cooling, and irradiating a long oval light beam in the direction of the recording trunk for heating and slow cooling. Methods are known. The recording state of the signal can be selected as either high reflectance or low reflectance (generally, low reflectance is selected). At this time, the erased state (including the initial state) should have a reflectance that is opposite to the recorded state.

Incidentally, this type of recording medium is formed by a manufacturing method such as vapor deposition or sputtering. As a result, the recording medium as formed usually becomes amorphous. In the general case where the recording medium thus formed is used in a recording state with a low reflectance, that is, in an amorphous state, it is necessary to set the area to be recorded in a crystalline state in advance so that the reflectance is high. Conventional methods of creating a crystalline state include using open beams and using high-power laser light. The latter uses a high-power laser beam with a diameter of several 10/j
This is a method of irradiating a rotating optical disk with a relatively large light beam of m while sequentially sending the beam in the radial direction.

In all of the above methods, the recording medium over the entire surface of the optical disk is in a crystalline state. As a result, the entire recording medium between the recording track and the adjacent recording trunk becomes an optical disk in a crystalline state.

Problems to be Solved by the Invention However, if the recording medium between the recording tracks of the above-mentioned optical disc is in a crystalline state, it is easy to erase signals on adjacent recording tracks during recording and erasing, and it is difficult to achieve the desired recording when erasing. There have been problems in that the erasing efficiency on the track is reduced and the read signal is noisy during playback. This problem will be explained below. Generally, the thermal conductivity in a crystalline state is about one order of magnitude higher than that in an amorphous state. Therefore, the heat of the light beam applied to the target recording track for recording or erasing tends to flow to the adjacent recording track. As a result, signals of adjacent recording tracks are easily erased, which is inconvenient. Similarly, during erasing, the heat during slow cooling tends to escape, resulting in a decrease in erasing efficiency. The reason why the readout signal has large noise during reproduction is due to the high reflectance of the crystalline state. That is, this is because the amount of light reflected from adjacent recording tracks increases due to the spread of the reproduction beam (usually Gaussian distribution). However, this comparison is based on the assumption that the granularity in the size before and after the reproduction light beam, which causes noise, is almost the same in the crystalline state and the amorphous state. Generally, the granularity of the crystalline state is rougher than that of the amorphous state, so the readout signal noise is also larger.

These problems are true of any of the three types of optical discs mentioned above. In other words, if the medium existing between the recording tracks has higher thermal conductivity and higher reflectance than the recording medium above the recording tracks, it will tend to have a thermal effect on the adjacent recording tracks, and the heat utilization efficiency within the target recording track will decrease. If the noise is small, the noise of the reproduced signal during reproduction will be large.

In view of these problems, the present invention provides an optical disc in which signals on adjacent recording tracks are difficult to erase during recording and erasing, high erasing efficiency is achieved on the target recording track during erasing, and low noise in read signals during reproduction. The purpose is to

Means for Solving the Problems The present invention has a spiral or concentric guide groove, and a region centered on the guide groove or an intermediate point between the guide groove and a guide groove adjacent to the guide groove. An optical disc with a central area as a recording area (recording track), where the area between the recording area and the recording area adjacent to the recording area (hereinafter referred to as "between recording tracks") has a temperature lower than that of the recording medium in the recording area. An optical disc provided with a medium of low conductivity and/or low reflectivity.

Function: As described above, the present invention makes the medium between the recording tracks have lower thermal conductivity and lower reflectance than the recording medium, so that the light beam emitted from the light beam irradiated onto the target recording track during recording/erasing is reduced. By using a medium with low thermal conductivity, it is possible to suppress the heat from flowing into the adjacent recording track, making it difficult to erase the signal on the adjacent recording track. High,
Furthermore, noise read from between recording tracks during reproduction can be reduced by using a medium with low reflectivity.

Embodiments Hereinafter, embodiments of the present invention will be described by taking a phase change type optical disk as an example. In this example of an optical disk, the recording medium on the recording track is made into a crystalline state in advance, and a signal is recorded by irradiating the recording medium with a fine/JX light beam to make the recording medium amorphous. Let's move on with the story. In this case, the medium between the recording tracks, which is a means for realizing the purpose of the present invention, is an amorphous recording medium.

FIGS. 1a and 1b are a plan view and a cross-sectional view, respectively, showing the structure of an optical disc in a first embodiment of the present invention. In this case, it is an optical disc whose recording tracks are recording areas centered around the guide grooves.

In FIGS. 1a and 1b, 1 is an optical disk. Figure 1 a, b
In the enlarged view inside, 2 is a guide groove for tracking control known in an optical disk drive, 3 is a crystalline recording medium, and 4 is an amorphous recording medium. The recording medium 3 in a crystalline state is wider than the guide groove 3 in the next area with the guide groove 2 as the center, and the width of the recording signal pit (not shown) is the same as or smaller than the width of the guide groove 3. In the following description, the crystalline recording medium 3 will be referred to as a recording track, and will be given the same number 3.

When the optical disc 1 configured as described above is used in an optical disc drive, the heat generated from the light beam applied to the recording track 3 during recording and erasing is transferred to the amorphous state, which has a lower thermal conductivity than the crystalline state. By using the recording medium 4 in this state, it is possible to confine the information to only the target recording track 3. Therefore, during recording/erasing, it is difficult to erase the signal already written in the recording track 3 adjacent to the target recording track 3, and during erasing, the erasing efficiency of the target recording track 3 is improved. Furthermore, since the reflectance of the amorphous recording medium 4 is low, the noise component read from the amorphous recording medium 4 during signal reproduction is reduced.

Two embodiments of methods for actually manufacturing the optical disc 1 described above will be described below. Here, it is assumed that the recording medium of the optical disc 1 is in an amorphous state before the recording trunk is formed. In addition, the same numbers as in FIG. 1 are given to the same parts in FIGS. 2, 3, and 4 below.

FIG. 2 is a diagram illustrating a first method of manufacturing the optical disc 1 of the present invention. In FIG. 2a, 5 is an oval light beam for forming recording tracks 3 on the optical disc 1. In FIG. The light energy distribution of the light beam 5 in the longitudinal direction of the guide groove 3 is set to such a condition that the recording medium in an amorphous state can be heated and slowly cooled, as shown at T1 to T3 in FIG. The recording medium is crystallized by moving the light beam 6 along the guide groove 3 and relatively advancing in the direction of the arrow 6 using known tracking control. Actually, the recording track 3 is created by fixing the light beam 6 and rotating the optical disk 1. Once the desired recording track has been created, the light beam 6 is
is sent in the radial direction.

FIG. 3 is a diagram illustrating how the width of the recording track 30 is determined when the recording track 3 is created by the method described above. FIG. 3a is a diagram showing an example of the optical energy distribution of the light beam S in the lateral direction of the guide groove 3. FIG. 7 is the crystallization energy of the recording medium, and a recording medium irradiated with light energy exceeding this value becomes in a crystalline state. When the optical energy distribution is as wide as 11, the width of the recording track 3 is larger than the pitch of the guide groove 2, and when the recording tracks 3 are formed sequentially, the amorphous recording medium is between the recording tracks. Since no residue remains, this is contrary to the purpose of the present invention. Conversely, when the optical energy distribution is narrow like I3, the width of the recording track 3 becomes smaller than the width of the guide groove 2. In this case, when a signal is recorded later, the space between the recording tracks will be in an amorphous state, but
This is inconvenient because the reproduced signal amplitude becomes small.

Therefore, in this embodiment, the optical energy distribution is selected as I2. That is, the width of the recording track 30 is equal to the width of the guide groove 2.
It is smaller than the pitch of , and larger than the width of the guide groove 2 .

As a result, an amorphous recording medium remains between the recording tracks, and the reproduced signal amplitude of the recorded signal does not decrease.
This is the second method of manufacturing. In Figure 4, 5-1.5-
2.5-3 is a light beam having the same optical energy distribution as the light beam shown in FIG. irradiated. Formation of a recording track can be achieved by rotating the optical disc 1, rotating it once or a necessary number of times, and then sending the light beams 5-1 to 5-3 in the radial direction by one recording track. . In this way, the time required to process one optical disc can be reduced by 20% compared to the time required to process one optical disc using only one light beam. Furthermore, since the light beams are irradiated onto separate recording tracks, the concentration of heat can be suppressed compared to the method where the light beams are irradiated onto consecutive recording tracks. As a result, the base material can also be protected from thermal destruction.

As explained above, according to this embodiment, by making the recording medium between the recording tracks of the optical disc into an amorphous state, it is difficult to erase the signals of the adjacent recording tracks during recording/erasing, and it is difficult to erase the signals of the adjacent recording tracks during erasing. It is possible to increase the erasing efficiency of recording tracks and reduce the noise of the reproduced signal during reproduction.

FIG. 5 is a diagram showing an optical disc according to a second embodiment of the present invention. In this case, a so-called groove-to-groove recording method is used, in which a recording area centered at the midpoint of adjacent guide grooves is used as a recording track. This is an optical disc.

FIGS. 6 and 6C are a sectional view and a plan view of the optical disc, respectively, similar to FIG. 1. Figure 6.

In C, 8 is an optical disk (as in the first embodiment, the recording medium is in an amorphous state before recording tracks are formed), 9 is a guide groove, 1o is a recording medium in a crystalline state, and 11 is an amorphous state. It is a recording medium. The recording track of this optical disk 8 has the same width as the recording medium 10 in a crystalline state (the recording track is also given the same number 10). The width of the recording track 10 is usually determined by calculating the width of the guide groove 9 from the pitch of the guide groove 9. Make it smaller than the value you subtracted. The width of the recording pit (not shown) is recording track 1.
Make it smaller than the width of ゜.

In FIG. 5a, part 4 shows the optical energy distribution in the short direction of the guide groove in a light beam (not shown) similar to the light beam 5 shown in FIG. 2 for forming the recording track 1o,
A recording medium corresponding to a width greater than or equal to the crystallization energy of No. 7 is brought into a crystalline state. This width becomes the width of the recording track 10 described above, and forms an amorphous recording medium 11 between the recording tracks.

In this case, the position where the peak value of the light energy distribution device 4 is irradiated is the midpoint between adjacent guide grooves.

The optical disc 8 as described above can be manufactured by a method similar to that shown in FIG. Furthermore, it can also be realized by the method shown in FIG. The difference between each method is
When manufacturing the optical disk 1 shown in FIG. 1, the light beam is irradiated onto the guide groove, whereas when manufacturing the optical disk 8 shown in FIG. 5, the light beam irradiation position is at the midpoint between adjacent guide grooves. The point is that there is.

As explained above, according to the present embodiment, similarly to the first embodiment, by making the recording medium between the recording tracks of the optical disc into an amorphous state, the signals of the adjacent recording tracks are erased during recording and erasing. This makes it possible to increase the erasing efficiency of the target recording track during erasing and reduce the noise of the reproduced signal during reproduction.

In the first and second embodiments, the recording medium of the optical disc is in an amorphous state before recording tracks are formed.
If this is in a crystalline state, the recording medium between the recording tracks can be brought into an amorphous state by irradiating the space between the recording tracks with a light beam that satisfies the heating and quenching conditions (for example, a minute approximately circular light beam). can. In addition, in Figure 4, the number of light beams is three, but in order to improve the processing speed, four light beams are used.
It is also possible to use more than one light beam.

In addition, in the above embodiments, a phase change type optical disk is taken as an example to facilitate understanding, and the medium between the recording tracks is an amorphous recording medium, but the medium between the recording tracks is It is obvious that similar effects can be obtained by making the recording medium lower in thermal conductivity and reflectance than those in the recording medium. Furthermore, it is obvious that the same effect can be obtained by not attaching the recording medium between the recording tracks in advance or by removing the recording medium already attached between the recording tracks. According to the invention, it is possible to obtain an optical disc that does not deteriorate the signals of adjacent recording tracks during recording and erasing, increases the erasing efficiency of the target recording track during erasing, and suppresses the noise of the reproduced signal during reproduction. The effect is great.

[Brief explanation of drawings]

FIG. 1 is a structural diagram showing an optical disc according to a first embodiment of the present invention, FIGS. 2 and 3 are explanatory diagrams of a first method for manufacturing an optical disc according to the same embodiment, and FIG. 4 is a diagram showing the same embodiment. FIG.
FIG. 2 is a structural diagram showing an optical disc according to an embodiment of the present invention. 1.8... Optical disc, 2,9... Guide groove, 3°10... Recording medium in crystalline state, 4,
11...Recording medium in amorphous state, 5, 5-1
, 6-2, 5-3... light beam. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure J: jt crystal yt'i: q:zn#+%7; f roar I
-/! Kanade, Ruggegi 2nd figure? l Figure 3 Figure 5

Claims (3)

[Claims] (1) Has a spiral or concentric guide groove,
An optical disc whose recording area is an area centered on the guide groove or an area centered on a midpoint between the guide groove and a guide groove adjacent to the guide groove, the recording area being adjacent to the recording area. An optical disc characterized in that a medium having lower thermal conductivity and/or lower reflectance than the recording medium of the recording area is provided between the recording area and the recording area. (2) The optical disc according to claim 1, wherein the recording medium between a recording area and a recording area adjacent to the recording area is amorphous. (3) The optical disc according to claim 1, wherein there is no recording medium between a recording area and a recording area adjacent to the recording area.