JPS63173242A - Optical recording medium - Google Patents

Abstract

PURPOSE:To make effective use of an optical disk by forming tracking regions of a low reflectivity to a recording member, which is decreased in the reflectivity by quick cooling after heating and is increased in the reflectivity by slow cooling after heating, to a spiral shape centering at the center of the rotation thereof except recording and reproducing regions of a high reflectivity. CONSTITUTION:A thin recording film 22 consisting of a resin which is constituted of the two components; vinylidene fluoride copolymer and methacrylate copolymer and is formed as a thin film. Transmittance which is initially about 80% is degraded to about 10% with about 175 deg.C as threshold when the film 22 is heated. On the other hand, about 80% transmittance is restored by slow cooling and about 10% transmittance is maintained by quick cooling when the film 22 heated once in excess of the threshold is cooled. The tracking regions 24 of the optical disk 2 are the parts where the transmittance of the thin film 22 is low and the recording and reproducing regions 25 are the part where the transmittance of the film 22 is high.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical recording medium on which new information can be freely recorded.

BACKGROUND OF THE INVENTION Information recording on this type of optical recording medium is performed by forming pits on the recording surface of the optical recording medium. Conventional methods for forming pits include irradiating a recording surface with a laser beam to cause a minute change in density in the area, or
There are methods such as forming microscopic holes or bubbles. Here, FIG. 5 shows an example in which an optical disk is used as the optical recording medium. A disk-shaped substrate 1 is provided.

A recording layer 2 is formed on this substrate 1, and a protective layer 3 is formed thereon to constitute an optical disc 4. To further explain the recording layer 2, tracks 5 are formed protruding from the recording layer 2. This track 5 is
When looking at the optical disc 4 as a whole, it is formed in a spiral shape around its rotation center. Further, the recording layer 2 has physical properties such that when the recording M2 is irradiated with a laser beam having thermal energy of a certain value or more, pits (not shown) are formed in the irradiated portion.

Next, information is recorded on the optical disc 4 as described above,
An example of a conventional device capable of reading this information will be explained based on FIGS. 5 to 8(a), (b), and (c). The outline of this device is as follows:
It is composed of a semiconductor laser 6 and an optical system 8 that focuses a laser beam L emitted from the semiconductor laser 6 onto the optical disk 4 and focuses reflected light from the optical disk 4 onto a photosensor 7. . This optical system 8
teeth.

Anterograde optical system 8 used for recording, playback, and control
a, and a retrograde optical system 8b which partially overlaps with the prograde optical system 8a and is used only for reproduction and control. Hereinafter, the antegrade optical system 8a and the retrograde optical system 8b will be separated.

First, the antegrade optical system 8a will be explained.

A collimator lens 9 is provided to convert the laser beam L emitted from the semiconductor laser 6 into parallel light, and a shaping prism 10 is provided to correct the traveling direction of the laser beam L after passing through the collimator lens 9. A polarizing beam splitter 11 and a quarter wavelength plate 12 are located at the position where the laser beam L after passing through the shaping prism 10 passes.
are provided in order. Also, a reflection mirror 1 that reflects the laser beam L after passing through the quarter-wave plate 12 at right angles.
3, and a focus lens 14 that focuses the reflected laser beam L onto the recording layer 2 of the optical disc 4. This focus lens 14 can move toward and away from the optical disc 4 .

Next, the retrograde optical system 8b will be explained.

This retrograde optical system 8b is a system that focuses the laser beam L reflected on the optical disk 4 onto the photosensor 7, and shares some parts with the antegrade optical system 8a. The common parts are the focus lens 14, the reflection mirror 13, the quarter wavelength plate 12, and the polarization beam splitter 11. On the other hand, the only unique components of this retrograde optical system 8b are the two cylindrical lenses 15. The cylindrical lenses 15 are arranged at a 45 degree direction with respect to the cemented surface 11a of the polarizing beam splitter 11, and at an intermediate position between the photosensor 7 and the polarizing beam splitter 11 arranged in this direction. be.

Next, the photosensor 7 will be explained.

The light receiving surface 16 of this photosensor 7 is divided into four squares having the same area. First light receiving surface 16a, second light receiving surface 1
6b, the third light receiving surface 16c, and the fourth light receiving surface 16d, respectively. As for their arrangement positions, the first light receiving surface 16a and the third light receiving surface 16c are arranged diagonally, and the second light receiving surface 16b and the fourth light receiving surface 16d are arranged diagonally.

In such a configuration, the laser beam L emitted from the semiconductor laser 6 is made into parallel light beams by the collimator lens 9, and the direction is corrected by the shaping prism 10, so that the polarizing beam splitter 11 and the quarter-wave plate 12 are aligned in a straight line. pass through. As it passes through, the laser beam becomes circularly polarized light.

Thereafter, the laser beam L is reflected at right angles by the reflecting mirror 13 and focused by the focus lens 14 onto the track 5 formed on the recording layer 2 of the optical disc 4. At this time, if the laser beam L has thermal energy exceeding a certain value, pits will be formed in the recording layer 2 in the portion irradiated with the laser beam L. In this way, information is recorded on the optical disc 4 by selectively forming pits while tracing the track 5.

On the other hand, when reading information from the optical disc 4, the forward optical system 8a
The laser beam L with less thermal energy is applied to the recording layer 2.
and trace track 5. Information is then read by detecting the reflectance of the recording layer 2, which varies depending on the presence or absence of pits. That is, the laser beam focused on the recording layer 2 is reflected by the recording layer 2 and focused onto the photosensor 7 by the retrograde optical system 8b. In detail, the laser beam L reflected by the recording layer 2 and passed through the quarter-wave plate 12 becomes linearly polarized light rotated by 90 degrees from the time of incidence. Therefore, the joining surface 1 of the polarizing beam splitter 11
It is refracted in the right angle direction at 1a. Thereafter, the light passes through two cylindrical lenses 15 and is focused on the photosensor 7, forming a laser spot 17. Therefore,
In this photosensor 7, the difference in reflectance of the recording layer 2, that is, the presence or absence of pits, is detected by determining the strength of the laser beam L, and information on the optical disc 4 is read here.

Next, focusing control and tracking control will be explained. When tracing the track 5 using the laser beam, the irradiation position of the laser beam L is continuously shifted toward the center of the optical disc 4 in synchronization with the rotational speed of the optical disc 4.

This is to match the irradiation position of the laser beam L to the spiral shape of the track 5. Therefore, theoretically, the irradiation position of the laser beam L and the arrangement position of the track 5 are always constant. However, in reality, focusing errors (hereinafter simply referred to as FE) occur due to surface fluctuations of the optical disc 4.
Also, tracking errors (hereinafter simply referred to as TE) may occur due to eccentric rotation of the optical disc 4 and waviness of the track 5.
occurs. Therefore, focusing control and tracking control are necessary.

First, a method of focusing control will be explained. In the case of just focus, the laser spot 17 formed on the photosensor 7 has a perfect circular shape. Moreover,
The light is applied to the same area on each light receiving surface 16 of the photosensor 7.

The appearance of the light receiving surface 16 in such a case is shown in FIG. 6(b). On the other hand, when a focusing error occurs, the laser spot 17 becomes elliptical. As for the direction of the ellipse, FIGS. 6(a) and 6(c) show the orientation of the light-receiving surface 16 when the major axis direction and the minor axis direction are respectively diagonal directions of each light-receiving surface 16.

Here, 0□...Output of the first light receiving surface 16a 0□...Output of the second light receiving surface 16b 03...Output of the third light receiving surface 16c○,...Output of the fourth light receiving surface 16d shall be. Therefore, when FE is expressed in a proportional equation using the output of each light receiving surface 16, it becomes FEoc (Q□+03) −(O□+04).

Therefore, focusing control is (o1+o,)
The optical disc 4 may be irradiated with the laser beam L so that (02+04)=0. Specifically, the focal length of the laser beam L is changed by moving the focus lens 14 closer to and away from the optical disk 4.

Next, a tracking control method will be explained. FIG. 7(b) shows the state of irradiation of the laser beam L onto the optical disk 4 when the laser beam L is accurately tracing the track 5. On this occasion.

In the photosensor 7, the area of the laser spot 17 on the first light-receiving surface 16a and the second light-receiving surface 16b matches the area of the laser spot 17 on the third light-receiving surface 16c and the fourth light-receiving surface 16d. The same applies even if FE occurs. The appearance of the light-receiving surface 16 in such a case is shown in FIG. 8(b) and FIG. 6(a), (b), and (c). On the other hand, the seventh
Figures (a) and (c) show the state of irradiation of the laser beam onto the optical disc 4 when track deviation occurs.

At this time, in the photosensor 7, the laser spot 1
The area covered by 7 on the first light receiving surface 16a and the second light receiving surface 16b and the area covered on the third light receiving surface 16c and the fourth light receiving surface 16d change. The appearance of the light receiving surface 16 in such a case is shown in FIGS. 8(a) and 8(C). Here, if TE is expressed in a proportional formula using the output of each light receiving surface 16, TEcX: (○
X + OZ ) (○, +04). Therefore, the tracking control is (o1+oz) (0
The focusing position of the laser beam L on the optical disc 4 may be corrected so that 3+04)=0.

Problems to be Solved by the Invention Once information is recorded on the optical disc 4, the information is fixed. Therefore, it has the disadvantage that once recorded information cannot be erased and the information cannot be recorded again.

Further, for tracking control, it is necessary to form tracks 5 on the recording layer 2 of the optical disc 4 in advance. Moreover, for accurate tracking, the track 5 must be formed with a certain degree of positional accuracy. T
This is because there is a limit to the correction of E. For this reason, there is a drawback that manufacturing the optical disc 4 takes time and effort.

Means for Solving the Problems A recording member is formed into a disk shape, in which the reflectance decreases when rapidly cooled after heating, and increases when slowly cooled after heating. Then, a tracking area with a low reflectance is formed in a spiral shape around the center of rotation of the recording member, leaving a recording/reproducing area with a high reflectance.

Operation To record on an optical disc, a laser beam is selectively irradiated onto the recording/reproducing area. Then, the reflectance of the portion irradiated with the laser beam decreases, and information is recorded. After that, when the part is rapidly cooled, the decrease in reflectance is maintained,
Information is fixed on the optical disc. Therefore, information is read by irradiating a recording/reproducing area with a weak laser beam and detecting the reflected light.

Furthermore, in order to erase information on the optical disc, the recording/reproducing area is irradiated with a laser beam again. Then, the irradiated area is slowly cooled. As a result, the recording/reproducing area returns to a state of high reflectance, and information is erased. Therefore, once information is erased, it is possible to record on the optical disc again and again as many times as desired.

Furthermore, the tracking area for tracking control is formed only by complete chemical change of the recording member. Therefore, it is not necessary to form structural tracks, making it easy to manufacture the optical disc.

Embodiment of the Invention An embodiment of the present invention will be described with reference to FIGS. 1 to 4(a) and (b). Portions that are the same as those shown in the conventional example are indicated by the same reference numerals, and explanations thereof will be omitted.

In this example, a 2° optical disc was used as the optical recording medium. FIG. 2 shows its vertical side view. That is, a disk-shaped substrate 21 is provided, and a recording thin film 22 as a recording member is formed on one side of the substrate 21. and,
The optical disc 20 is constructed by forming a protective layer 23 on the recording thin film 22.

The recording thin film 22 is a thin film formed of a resin composed of two components: a vinylidene fluoride copolymer and a methacrylate copolymer. Its characteristics are shown in Figure 4(a)
These graphs shown in (b) show the relationship between the heating and cooling temperature and the transmittance of the recording thin film 22 when the recording thin film 22 is heated and then cooled. The difference between the two graphs is the difference in cooling rate. Figure 4 (a
) shows the characteristics when cooled slowly, and FIG. 4(b) shows the characteristics when cooled rapidly. As can be seen from these graphs, when the recording thin film 22 is heated, the recording thin film 2
In case of No. 2, the transmittance which was initially about 80% deteriorates to about 10% with a threshold value of around 175°C.

On the other hand, when the recording thin film 22, which has been heated once beyond the threshold value, is cooled, the transmittance returns to about 80% when it is slowly cooled, and the transmittance is maintained at about 10% when it is rapidly cooled.

Next, on the optical disc 20, a tracking area 24 and a recording/reproducing area 25 are formed in advance. The tracking area 24 is a portion of the recording thin film 22 with poor transmittance, and the recording/reproducing area 25 is a portion of the recording thin film 22 with excellent transmittance. To form these tracking areas 24 and recording/reproducing areas 25.

If the entire record book 11% 22 is in a state of excellent reflectance at the beginning, only the tracking area 24 may be formed. That is, the recording thin film 22 is once heated to a temperature exceeding a threshold value, and then the spiral-shaped portion centered on the rotation center of the optical disk 20 is rapidly cooled. As a result, the tracking area 24 is formed in the rapidly cooled spiral-shaped part, and the recording/reproducing area 24 is formed in the other part.
5 is formed. Note that these tracking areas 24
The recording/reproducing area 25 is formed to have approximately the same width, and the specific value thereof is approximately 1 μm.

On the other hand, as a recording/reproducing apparatus for the above-mentioned optical disc 20, an apparatus is used in which a tracking control section and a heater (not shown) are added to the apparatus shown in the conventional example.

The tracking control section has a structure that performs tracking control by irradiating the tracking area 24 with a laser beam as a tracking signal and detecting the reflected light, and the heater has a structure that heats the recording thin film 22. be.

In such a configuration, for the optical disc 2o,
Information can be recorded, and the information can also be reproduced and erased. At this time, the optical disk 20 is rotated and the recording/reproducing area 25 is traced by the laser beam L.

At the same time, tracking control is performed by irradiating the tracking region 24 with a laser beam as a tracking signal and detecting the reflected light while tracing the tracking region 24.

Therefore, in order to record on the optical disc 20, the recording/reproducing area 25 is selectively irradiated with a laser beam L having thermal energy exceeding the threshold value.

Then, the temperature of the portion irradiated with the laser beam L increases locally, the reflectance decreases to about 10%, and -star information is written there. Thereafter, the portion of the recording/reproducing area 25 irradiated with the laser beam releases heat into the air, so the temperature of that portion drops rapidly. As a result, the recording/playback area 2
The portion with reduced reflectance, ie, the information recording portion of No. 5, remains as it is, and the information is fixed on the optical disc 2o. FIG. 3 shows an example of the optical disc 20 after recording on the recording/reproducing area 25. As shown in FIG. Therefore, the information is read by irradiating the recording/reproducing area 25 after information has been recorded with a laser beam L having thermal energy not exceeding the threshold value and detecting the reflected light.

Next, in order to erase the information once recorded on the optical disc 20, the recording/reproducing area 25 is irradiated with a laser beam L having thermal energy exceeding the threshold value. At this time, turn on the heater. Then, since the heat dissipation speed of the recording/reproducing area 25 is delayed, the portion irradiated with the laser beam L is gradually cooled, and the reflectance of the entire recording/reproducing area 25 is restored to about 80%. In this way, the optical disc 20
returns to its original state and its information is erased.

Therefore, the optical disc 20 can be rerecorded any number of times.

On the other hand, the tracking area 24 used for tracking control
is formed only by a complete chemical change of the recording thin film 22. Moreover, this chemical change can be achieved by an extremely easy method of simply heating and then rapidly or slowly cooling. Therefore, there is no need to form structural tracks on the recording thin film 22, making it easy to manufacture the optical disc 20.

In this example, the threshold value is 175° C. when the vinylidene fluoride copolymer and the methacrylic acid ester copolymer are synthesized at a ratio of 1:1. On the other hand, by changing the synthesis ratio of both substances, the threshold value can be changed arbitrarily. In addition, in implementation,
The recording thin film 22 is not limited to being composed of two components, vinylidene fluoride copolymer and methacrylic acid ester copolymer, but any type of material used may be used as long as it has the same characteristics. No questions asked.

For example, a compatible amorphous polymer may be added to these vinylidene fluoride copolymers and methacrylic acid ester copolymers.

In this case, the @ value drops to about 120°C.

Effects of the Invention The present invention forms a recording member in the shape of a disc, which reduces the reflectance when rapidly cooled after heating and increases the reflectance when slowly cooled after heating,
Since the tracking area with low reflectance is formed in a spiral shape around the center of rotation while leaving the recording/reproducing area with high reflectance on the recording member, information can be recorded in the recording/reproducing area by changing the cooling rate after laser beam irradiation. This makes it possible to erase information and repeat recording of information over and over again, making it possible to use optical discs effectively. This simplifies its formation and contributes to the ease of manufacturing optical discs.

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged plan view of an optical disc showing an embodiment of the present invention, FIG. 2 is a vertical side view thereof, and FIG. Figure 4 (
a) (b) are graphs showing the physical properties of the recording thin film, Fig. 5 is an overall side view showing an example of a conventional example, Fig. 6 (a) (b)
(c) is a plan view showing the shape of the laser spot formed on the photosensor; FIGS. 7(a), (b), and (c)
8(a), 8(b), and 8(c) are plan views showing aspects of a laser spot formed on a photosensor. FIG. 22...Recording*@(recording member), 24...Tracking area, 25...Recording/reproducing area ratio Request Person Tokyo Electric Co., Ltd. J3" Figure JSu

Claims (1)

[Claims] When rapidly cooled after heating, the reflectance decreases, and when slowly cooled after heating, the reflectance increases.A recording member is formed into a disk shape, and a tracking area with a low reflectance is left in a recording/reproducing area with a high reflectance on the recording member. An optical recording medium characterized in that it is formed in a spiral shape around the center of rotation of a recording member.