JPH04141828A - Optical recording medium and information recording erasing method using this medium - Google Patents

Abstract

PURPOSE:To improve recording density by providing a group of bit recording cells arranged on an arbitrary track at intervals less than the minimum read intervals of a laser head and a clock mark provided on the same track as the bit recording cell group and in a position where the laser head can identify. CONSTITUTION:An optical recording film 1a is formed on the recording surface of an optical recording medium substrate 1, and the clock mark 2 formed on the recording surface in a projecting shape or in a recessed shape is arranged along the recording track. The bit recording cell group 3 which is vertically arranged is formed on the same track as the clock mark 2 in the projecting shape or in the recessed shape by equivalent to one bit. The center interval between the arbitrary bit recording cell 3a and the adjacent bit recording cell in the bit recording cell group 3 is set within the minimum read interval (=lambda/2NA) of the optical head used for reproducing recording information. Thus, recording density can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical recording medium in which information is recorded using the heat of a focused laser beam, and a method for recording and erasing information using this medium.

Background of the Prior Art Although higher S/N and higher recording density of optical recording media are being considered, the following description will be made with reference to the drawings. It also shows a diagram of the configuration of a conventional optical recording medium.
In FIG. 8, 10 is an optical recording medium substrate, and 20
The bit recording cells 20 may be bit recording cells formed concave or convex on the optical recording medium substrate.The bit recording cells 20 are arranged at intervals longer than the minimum reading resolution of the laser head so that they can be identified from the laser head. The minimum reading resolution mentioned here is λ/2 N where the wavelength of the laser head is λ and the aperture ratio is NA.
The length indicated by A.

The operation of the optical recording medium configured as described above will be explained below.

When recording information on the optical recording medium, selectively irradiate an arbitrary bit recording cell 20 with a strong laser beam,
Information is recorded using that heat.

The advantage of this optical recording medium (L) is that recording with high S/N and low jitter can be easily achieved. Moreover, even though they are formed in a concave and convex shape with almost uniform size, each bit recording cell is thermally isolated even when irradiated with a strong laser beam, so it does not affect adjacent bit recording cells. It is possible to record signals only in the desired bit recording cells 20, and variations in the size of recording marks that cause jitter and noise in photothermal recording do not occur. When recording information by increasing the laser power, the laser beam must be positioned approximately at the center of the bit recording cell 20 to be recorded in advance. A strong laser beam is irradiated between the bit recording cells, and two bits may not be generated halfway. Therefore, when recording information, the laser head accurately determines the position of the bit recording cell 20 to be recorded in advance. (-In the conventional example, even if the position of the bit recording cell 20 is recognized from the change in the amount of reflected light when scanning the bit recording cell 20 with a laser beam, as shown in FIG. When scanning near the center of the bit recording cell 20, the amount of reflected light takes a minimum value (D in the figure).Therefore, this minimum value is checked, a clock signal is generated from this, and the laser is activated at that timing. If you emit a strong light, it will definitely become bit recording cell 2.
Although it is possible to record information accurately in 0 (for example, U.S. Pat. No. 4,811.331), problems to be solved by the invention. However, in the above configuration, if any adjacent bits If the interval between recording cells is narrowed, each bit recording cell becomes indistinguishable, and there is a limit to the number of recording densities.9 In other words, as mentioned earlier, when the wavelength of the laser beam is λ and the aperture ratio is NA, This means that the bit recording cells must be formed at intervals sufficiently wider than λ/2NA; below this, the amount of reflected light when scanning the bit recording cells will not change at all, so any bit recording cell 2
In view of the above-mentioned problems, the present invention has been made in view of the above-mentioned problems.
x To provide an optical recording medium with good S/N and high recording density. Means for Solving the Problems In order to solve the above problems, the optical recording medium of the present invention is
a bit recording cell group consisting of a plurality of bit recording cells arranged on an arbitrary track at intervals of λ/2NA or less;
The laser head is provided with a clock mark provided on the same track as the bit recording cell group and at a distance of λ/2 NA or more from the bit recording cell group. can identify the clock mark and calculate the position of each bit recording cell constituting the bit recording cell group from the position of the clock mark, so that the laser head cannot identify each of the bit recording cells. and L It is possible to correctly record information in any bit recording cell, and as a result, it is possible to improve the recording density.EmbodimentThe following describes an optical recording medium according to an embodiment of the present invention with reference to the drawings. 2 shows a perspective view of an optical recording medium according to a first embodiment of the present invention, and FIG. 1 shows a sectional view thereof. 1st @
In FIG. 2, 1 is an optical recording medium substrate on which an optical recording film 1a is formed, and 2 is a clock mark formed in a convex or concave shape on the recording surface. The bit recording cells arranged along the track 3 are a group of bit recording cells arranged in columns, and even if they are formed in a convex or concave shape corresponding to one bit on the same track as the clock mark, in the bit recording cell group 3 The center interval between any bit recording cell 3a and its adjacent bit recording cell is set within the minimum reading interval (=λ/2NA) of the optical head used to reproduce recorded information. However, the clock mark 2 and the edge of the bit recording cell group 3 are separated by an appropriate distance (>λ/2NA), and no uneven marks are formed between them (1) Regarding the optical recording medium configured as above, The operation will be explained below with reference to Figure 1 @ Figure 2 and Figure 3.In the conventional example and the same machine, the information signal is sequentially recorded in the bit recording cell group 3 channel by channel bit by a pulsed laser beam. When recording 0", the laser does not emit light or emit light with a sufficiently weak power, and when recording 1", it emits light with strong power, changing the physical properties of the optical recording film 1a. It is also possible to use a phase change type material based on tellurium oxide and a magneto-optical recording material. In order to do this, it is necessary to strongly ramp up the laser power when scanning exactly near the center of the bit recording cell where you want to record the laser palm (1"). To do this, the optical head identifies the position of each bit recording cell. Must be able to do it (℃
In the conventional example, if the interval between adjacent bit recording cells (ζ) is sufficiently longer than the reading limit of the reading laser head, the center position of each bit cell can be identified from the change in the amount of light reflected from the optical recording surface.However, in this embodiment, each recording Since the bit cells are arranged at a pitch of λ/2NA or less, it is impossible to identify each recording bit cell. Therefore, in this embodiment, Even though the clock mark 2 is provided at a predetermined position, the amount of reflected light when the laser beam scans the clock mark 2 and the bit recording cell group 3 is shown in FIG.

Level 1 (thin solid line in the figure) is the amount of reflected light when the laser beam is irradiating the mirror surface (where no unevenness is formed) of the optical recording medium, and the amount of reflected light when the laser beam is irradiating the uneven surface. The level of the clock mark 2 is represented by level 2 (dashed line in the figure).The front and back of the clock mark 2 are surrounded by mirror surfaces.When the laser beam crosses the mirror surface, the clock mark 2, and the mirror surface sequentially, the amount of reflected light is level 1. (A in the diagram
), Level 2 (B in the figure), Level 1 (C in the figure) The bit recording cells are not observed independently of each other.In other words, the amount of light reflected by the bit recording cell group 3 remains constant at level 2 (D in the figure).

Therefore, it is possible to obtain a synchronization signal by reading the clock mark when the amount of reflected light changes from A to B to C, and by appropriately interpolating this synchronization signal, it is possible to obtain a synchronization signal corresponding to the center position of each bit recording cell group. If it is possible to obtain a clock that occurs at the same time, then the laser beam can be blinked at the appropriate time in synchronization with that clock.
Although information can be recorded in any bit cell, the recorded information can be reproduced as shown below.When a laser beam scans a bit recording cell in which information is recorded, the amount of reflected light is level 2. 11) If the level is lower than level 3 (F in the figure), information ""1" should correspond to level 3, information "0" should correspond to level 2, and the threshold level should be set in the middle. For example, information can be easily read out from changes in the amount of reflected light.As described above, according to this embodiment, a bit recording cell in which an appropriate number of uneven recording bit cells are arranged at a pitch below the reading limit of the optical head. By providing the clock mark 2 on the same track as the group 3 and at a fixed position that is distinguishable from the group 3, it is possible to realize an optical recording medium with a higher recording density than the conventional one.

The second embodiment of the present invention will be described below with reference to the drawings. Fig. 4 is a block diagram of an optical recording medium showing the second embodiment of the present invention. 1 is a disc-shaped light beam. 2 is a recording medium substrate, and an optical recording film 1a is formed on the recording surface thereof. 2 is a clock mark; 3 is a bit recording cell group;
Both clock marks 2 are formed in a concavo-convex shape on the recording surface, and 43a is an arbitrary bit recording cell in the bit recording cell group 3.The feature of this embodiment is that all the clock marks 2 are arranged in a line in the radial direction of the disk. The optical recording medium configured as above is explained below because the number of recording bit cells constituting the recording bit cell group 3 is different between the inner circumference and the outer circumference of the disk. To explain the operation, first, the clock marks 2 are present in the same number and at equal intervals on all tracks (this is to speed up track access and information recording/reproduction). As mentioned above, in the present invention, the clock mark 2 serves as a reference for obtaining a synchronization signal for accurately recording information near the center of each bit cell of the recording bit cell group 3. Nara (
-Here, if the clock marks are different for each track, a pull-in operation for extracting the synchronization signal must be performed for each track each time. For example, track jump from one track to another track. If there is a difference in phase or frequency between the clock mark on the jump destination track and the clock mark on the original track, synchronization will occur on the new track, and it will take time to resynchronize. There may be cases where information cannot be recorded or reproduced immediately after the clock is finished. Therefore, the clock marks must be arranged so that they can be detected in the same phase across all tracks, and the arrangement shown in Figure 3 is inevitable. However, in this case, the interval between the recording bit cells is the same regardless of the outer circumference.If the number of recording bit cells constituting the recording bit cell group 3 is the same on the inner and outer circumferences, the interval between each recording bit cell is necessarily the same. 4 If the spacing between recording bit cells is sufficiently wider than the reading limit, each recording bit cell can be identified. This may seem advantageous from a conventional point of view (
In the present invention, there is a possibility of causing a malfunction.In other words, as described in the first embodiment, in the present invention, all recording and reproduction of information on an optical recording medium is performed based on clock mark 2. If the interval between the bit recording cells is sufficiently wide and a change in the amount of reflected light from each bit recording cell is observed, it becomes difficult to distinguish between the clock mark 2 and the bit recording cell 3a based on the change in the amount of reflected light. Conversely, if the spacing between the bit recording cells on the outer periphery is made below the reading limit, the spacing between the bit recording cells on the inner periphery will become too close, making it impossible to form cells with convexes and convexities where each bit is independent.

E. In this embodiment, the number of recording bit cells on the outer circumference of the disk is greater than on the inner circumference, so that the interval between each recording bit cell is almost constant.

A third embodiment of the present invention will be described below.

This embodiment relates to the method of recording information on the optical recording medium shown in the first or second embodiment. An optical recording film 1a is formed. Therefore, it is possible to record information by changing the physical properties of the optical recording film 1a using the heat of the laser beam. In particular, when the optical recording film 1a is oxidized. In the case of phase change materials whose main component is tellurium or the like, it is possible not only to record and reproduce information, but also to erase and rewrite information. In this case, three levels of laser power settings are required: weak power for playback, strong power for recording (writing ``1''), and medium power for erasing (writing ``0''). Figure 6 shows the intensity modulation waveform of the laser beam when overwriting the information "0010100" on this optical recording film 1a even with a power of about P2 is the power when writing 0″, and the power when recording (″
The power of 1" writing) is set as P3. In other words, the board
When reading the clock mark 2, the laser is emitted steadily at power P1, and when recording or erasing information in any bit recording cell 3a, the laser power is set to P1, P2.
, Pl, or Pl, P3, Pl. This is for the following reason. In other words, the optical recording film 1a formed on the bit recording cell 3a is thermally isolated from that formed on the adjacent bit recording cell. As already mentioned, it is possible to record and erase only information.If there is a timing error in the laser startup and part of the adjacent bit recording cell is irradiated with laser light, the information in the adjacent bit recording cell will be erased. Therefore, in this embodiment, in order to secure a margin for such timing errors, the L laser is emitted in a pulsed manner both during recording and during erasing, and the L laser is emitted in a pulsed manner near the boundary of the bit recording cell. The fourth embodiment of the present invention will be described below even if the laser power when the laser beam passes is reduced to a level below P1.
This is a timing chart of the fourth embodiment. Similar to the third embodiment, information is transmitted using a pulsed laser beam.
00101000” 4
This embodiment differs from the third embodiment in that recording and erasing are not performed by switching the laser power, but are switched by the laser pulse width while the power remains constant (P4). This is due to the following reasons.

In other words, the power of a semiconductor laser is used as the light source of the laser beam.
The optical system of the laser head, especially the objective lens, may have chromatic dispersion.When the power of the laser beam is changed, the focal point moves, and as a result, the desired bit recording cell 3
Therefore, in this example, the laser power is kept constant during recording and erasing, and the laser pulse width is changed to change the thermal energy input to the optical recording medium. In this way, it is possible to suppress fluctuations in the emission wavelength of the laser and achieve more reliable erasing of records. By providing a bit recording cell group consisting of a plurality of bit recording cells arranged at intervals of It is possible to calculate the position of each bit recording cell that makes up the bit recording cell group from the clock mark identified by the laser head, and from this it is possible to correctly record information in any bit recording cell, and as a result, the recording density can be increased. It is possible to improve

[Brief explanation of drawings]

FIG. 1 is a strabismus doctor according to an embodiment of the present invention. FIG. 2 is a cross-sectional doctor according to an embodiment of the present invention. FIGS. 3 and 4 are timing diagrams showing the operation of an embodiment of the present invention. Top view of the second embodiment of the present invention FIG. 6 is a timing diagram showing the operation of the third embodiment of the present invention FIG. 7 is a timing diagram showing the operation of the fourth embodiment of the present invention FIG. Figure 9 is a timing diagram showing the operation of the conventional example.
Optical recording medium substrate 2... Kuro Tsukumakyu 3...
Bit recording cell beads 3a... Name of the dead agent on the bit recording Patent attorney Akira Odori and two others Figure Laser beam Figure Laser beam Figure Figure Figure θ θ θ θ

Claims (1)

[Scope of Claims] (1) A unit information recording area is formed in a concave or convex shape with respect to the substrate, and an optical head records and reproduces one unit of information in the unit information recording area. An optical recording medium comprising: a group of unit information recording areas formed by arranging a plurality of unit information recording areas on one track; and a clock mark formed on the same track as the group of unit information recording areas. The plurality of unit information recording areas constituting the group of unit information recording areas are arranged at intervals equal to or less than the minimum reading interval of the optical head, and the clock mark is characterized in that:
An optical recording medium characterized in that the optical head is provided at an interval greater than a minimum reading interval of the optical head with respect to the group of unit information recording areas so that the optical head can be identified. (2) The optical recording medium according to claim 1, wherein an optical recording film is formed in the unit information recording area. (3) When the wavelength of the laser beam from the optical head is λ and the aperture ratio is NA, the interval between each of the plurality of unit information recording areas constituting the unit information recording area group is shorter than λ/2NA. 2. The optical recording medium according to claim 1, wherein the interval between the unit information recording area group and the clock mark is longer than λ/2NA. (4) A clock mark and a group of unit information recording areas are formed on a track provided in a circumferential or spiral shape on a disk-shaped substrate, and the clock mark is provided in the same number on each track, and the clock mark is provided in the same number on each track. 2. The optical recording medium according to claim 1, wherein the number of unit information recording areas constituting the unit information recording area group is formed differently depending on the track. (5) The optical recording medium according to claim 2, wherein information is recorded on the optical recording film by light having a first intensity, and information is erased by light having a second intensity. (6) A method for recording and erasing information on an optical recording medium according to claim 5, wherein when recording information, each unit information recording area is irradiated with light having a first intensity in a pulsed manner. An information recording and erasing method characterized in that when erasing information, each unit information recording area is irradiated with light having a second intensity in a pulsed manner. (7) The information recording/erasing method according to claim 6, wherein the first and second intensities are substantially obtained by changing the pulse width of the light irradiated to each unit information recording area.