JP2644840B2 - optical disk - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical memory system for recording and reproducing information by light, and more particularly, to a preformat structure of an optical disk.

[Conventional technology]

In recent years, with the progress of the information society, the demand for inexpensive and large-capacity memories has increased, and optical disk systems have been developed and commercialized. Among them, a device that forms a row of fine pits on the recording surface and only reproduces information using the diffraction phenomenon of the incident laser beam in the fine pits,
A laser beam is applied to the surface of the recording medium to form a portion where the reflectance changes, and at the time of reproduction, the change in the reflectance at this portion is detected with a laser beam, and not only reproduction but also additional recording is possible. So-called DRAW (Direct Read After Writ
The e) type device has been put to practical use.

On the other hand, as a rewritable optical disk that also has an information erasing function, a magnetic thin film of a magneto-optical recording medium having an easy axis of magnetization perpendicular to the magnetic film surface is irradiated with a laser beam to partially raise the temperature. By reducing the coercive force of the magnetic thin film at the irradiated part, magnetic domains are arranged according to the direction of the external magnetic field acting on the magnetic thin film, and information is recorded and erased, and information is recorded. There is a magneto-optical disc that irradiates a weak laser beam to a portion (data bit) that has been reproduced and reproduces information by a magneto-optical effect.

In the above optical disk system, 1 μm
It has a recording track width of about m, so that when recording or reproducing with a laser beam narrowed down narrowly, the laser beam deviates from a recording track so that data is not recorded or reproduced on another recording track. There is a need. Therefore, a servo system provided with some guide track is required.

Here, in the above-described apparatus that performs only reproduction, since a row of fine pits as information is fixedly recorded at the time of manufacturing the optical disc, the laser light follows the recording track composed of the fine pits as a guide. Servo control may be performed so that

However, since DRAW type devices and rewritable optical disks are used to newly write information in areas where information is not recorded, glass is required to accurately guide the light beam to a predetermined position on the optical disk. A guide track and a guide address for identifying the order of the guide track on a substrate made of a transparent resin or a transparent resin must be formed in advance when an optical disc is manufactured. For this purpose, a method is generally used in which an uneven groove is formed in a substrate of an optical disk, and information is recorded or reproduced along the groove. The uneven groove has a shape interrupted in the circumferential direction, and this gives bit information indicating the address of the groove. Several methods of forming the uneven groove have already been proposed. For example, a method of transferring irregular grooves directly to a resin substrate such as acrylic or polymer carbonate by injection molding using a Ni stamper with irregular grooves, or a groove stamper having irregular grooves with glass or acrylic substrate A method of inserting a UV curable resin between the two and transferring the uneven grooves to the UV curable resin (2P method), or applying a photoresist on a glass substrate when using glass as the substrate, The resist pattern corresponding to the guide grooves and pits is formed by selectively irradiating laser light or ultraviolet light through a photomask to form a resist pattern. Then, etching is performed once while the resist pattern is covered. A method of forming guide grooves and pits at one time has been proposed.

Next, the above-described guide track has a rectangular, V-shaped, U-shaped, or Ω-shaped cross section, and is formed in a spiral or concentric shape. Track number information is added to each guide track, and this information is called a pre-pit, and the pre-pit, the guide track, and the like are collectively called a pre-format.

Specifically, as shown in FIG.
... and data bits (in the case of a magneto-optical disk, the direction of magnetization is inverted at this portion) 3 ... and pre-pits 2
.. Are recorded, and a land-type preformat is used to record data bits 3 and pre-pits 2 between adjacent guide tracks 1 and 1 as shown in FIG.

The guide track 1 is "shifted" to the laser beam focusing position in order to focus the laser beam at an accurate position.
Is determined so that a large error signal is output when the error occurs. On the other hand, the shapes of the pre-pits 2... Are determined so that a signal indicating the track number is output in large amounts. Therefore, the optimum size of the pre-pit 2 and the optimum size of the guide track 1 are usually different from each other.

According to the group type, since the guide tracks 1 are not formed at the places where the pre-pits 2 are formed, the track error signal tends to be difficult to be output at such places. On the other hand, according to the land type, since the guide tracks 1 also exist at the positions where the pre-pits 2 are formed, there is an advantage that a track error signal can be easily obtained also at this position.

[Problems to be solved by the invention]

However, in the land type, as described above, since the guide tracks 1 also exist at the positions where the pre-pits 2 are formed, there is an advantage that a track error signal is easily obtained. Has the disadvantage that the track error signal is adversely affected.

In order to avoid this adverse effect, it is conceivable to set the groove depth of the pre-pits 2 to 1/4 of the wavelength of the laser beam.
And the prepits 2 ... have different groove depths,
This leads to a new problem that it becomes difficult to manufacture a preformat.

[Means for solving the problem]

In order to solve the above problem, the optical disk according to the present invention is adjacent to a guide track composed of concentric or spiral continuous grooves involved in control of the laser beam condensing position, corresponding to recorded information. Data bits formed on the land between the guide tracks, and prepits formed in the land in a concave shape corresponding to the information of the track number, wherein the width of the prepit is larger than the width of the guide track. Is also set to be narrow.

(Operation)

According to the above configuration, it is possible to avoid a situation in which the track error signal is adversely affected by the pre-pits, so that a good track error signal can be obtained even in a portion where the pre-pits are formed. Further, the groove depth of the pre-pit is set to 1/4 of the wavelength of the laser beam.
And the groove depth of the pre-pits and the groove depth of the guide track can be set to be the same, thereby facilitating the production of the preformat.

〔Example〕

One embodiment of the present invention will be described below with reference to FIGS. 1 to 7 taking a magneto-optical disk as an example.

In the preformatting of the magneto-optical disk, as shown in FIG. 1, grooves on the magneto-optical disk 11 are concentrically or spirally formed on the magneto-optical disk 11 as guide tracks 12 involved in controlling the condensing position of the laser light. Is formed. The guide tracks 12 are "shifted" to the laser light focusing position in order to focus the laser light at an accurate position.
The shape is determined so that a large error signal (hereinafter, referred to as a tracking error signal) is output when the error occurs. Adjacent guide tracks
Data bits corresponding to the recorded information (the direction of magnetization is inverted, not unevenness)
, And pre-pits 14 corresponding to track number information on lands (recording tracks) are formed.

Here, a configuration for reading the data bits 13 is as follows. In the magneto-optical disk device of the embodiment, when reproducing a signal, linearly polarized light is incident on the magneto-optical disk 11, which is a magneto-optical recording medium, and a change in the polarization direction corresponding to the magnetization direction of the magneto-optical disk 11 is detected as a reproduced signal. I do. That is,
The linearly polarized light obtained through the polarizer is made incident on the magneto-optical disk 11 to obtain reflected light having a changed polarization direction in accordance with the magnetization direction of the magneto-optical disk 11, and this reflected light is made incident on the analyzer. The change in the polarization direction in the reflected light is converted into a change in light intensity, and the obtained change in intensity is converted into an electric signal by a light receiving element.

For example, it has an optical system for signal reproduction shown in FIG. In this optical system, a laser beam projected from a semiconductor laser 21 is converted into parallel light by a collimator lens 22 and passes through a polarizer 23, as shown in FIG. Become. This linearly polarized light is focused on the magneto-optical disk 11 by the objective lens 25.
The magneto-optical disk 11 has an insulating layer 31 made of AlN and an amorphous magnetic thin film layer 3 made of GdTbFe on a substrate 30.
2. An insulating layer 33 made of AlN and a metal reflective layer 34 made of Al are formed by stacking in this order.

The linearly polarized light condensed on the magneto-optical disk 11 as described above is reflected as linearly polarized light having the polarization direction B or C corresponding to the direction of the magnetic domain of the amorphous magnetic thin film layer 32.
The reflected light is guided by the half mirror 24 to a signal detection optical path 28 in a direction orthogonal to the optical path between the semiconductor laser 21 and the magneto-optical disk 11. Then, an analyzer 26 having a direction different from that of the polarizer 23 uses a polarization direction B ·
C is converted into an intensity D · E, and the linearly polarized light obtained in this manner is extracted as an electric signal by the light receiving element 27, and reproduction is performed. On the other hand, for reading the information of the above-mentioned pre-pits 14,... As described above, when writing and reading of the data bits 13, reading of the pre-pits 14, and scanning of the laser beam spot by the guide track 12 are performed by one optical head, this optical head has three optical systems, A condensing optical system for irradiating a laser beam on a magneto-optical disk with a minute spot, a servo optical system for stably scanning the minute spot along a guide track, and an optic for reproducing information signals and track address signals (See “Magneto-optical disk device for file memory” CPM83-53, published by the Institute of Electronics, Communication and Engineers on November 25, 1983).

Here, the width X of each pre-pit 14 is set to be narrower than the width wg of the guide track 12, and according to this configuration, the pre-pits 14 ...
It is possible to avoid a situation in which the track error signal in the portion where the is formed is adversely affected, and it is possible to perform reliable control of the optical disk system. That is, the track error signal is at the reference 0 level when the laser light condensing position is at the center position of the land (when there is no “shift”), and changes to a positive level or a negative level as the position deviates from the center position. The change has the characteristic that the direction and amount of the "shift" from the center position can be known.
Is set smaller than the width wg of the guide track 12, it is possible to reliably prevent such characteristics from deteriorating.

For example, the width wg of the guide track 12 is set to 0.4 μm, the groove depth of both the guide track 12 and the prepit 14 is set to 60 nm, and the width X of the prepit 14 is 0.2 μm (1), 0.4 μm. (2), 0.6 μm
(3), 0.8 μm (4), and the case where the width of the pre-pit 14 is 0 μm, that is, when there is no pre-pit 14 (0), the track for the “deviation” between the laser light focusing position and the land center position FIG. 2A shows the change (signal level) of the error signal. The wavelength of the laser beam is 0.78 μm, and the NA (Numerical Aper
) is set to 0.6 and the track pitch is set to 1.6 μm to calculate the numerical values. Also, to detect a track error signal,
The push-pull method of the far field pattern is adopted.

According to FIG. 2A, the width X of the pre-pit 14 is
In the case of 0.2 μm (1) and when there is no pre-pit (0), a positive level signal is output with respect to “shift” in the direction A (shown in FIG. 1) from the land center position. It can be confirmed that the characteristics of the track error signal are not adversely affected. On the other hand, the width X of the pre-pit 14 is 0.4
In the case of μm (2), 0.6 μm (3), and 0.8 μm (4), a signal of a negative level is output for “displacement” in the A direction, or a positive level and a negative level are mixed. It can be confirmed that the characteristics of the track error signal are adversely affected. In such a case, there is a possibility that the track servo is deviated.

FIG. 3B shows the result when the width wg of the guide track 12 is 0.2 μm. In this case, it can be confirmed that the track error signal is not adversely affected only when there is no pre-pit 14 (0). .

FIG. 3A shows that the width wg of the guide track 12 is 0.4 μm,
FIG. 4B shows the results when the groove depth of the guide track 12 is 50 nm, and FIG.
m, the results are for the case where the groove depth of the guide track 12 is 50 nm. As is apparent from these figures, the tendency of the influence on the track error signal depends on the guide track 12.
It can be confirmed that it is substantially constant regardless of the groove depth.

4 (a) and 4 (b), it can be confirmed that the tendency of the influence on the track error signal is substantially constant irrespective of the groove depth of the guide track 12.

Further, as is clear from FIGS. 5A and 5B, it can be confirmed that the track error signal is not adversely affected only when the width X of the pre-pit 14 is smaller than the width wg of the guide track 12. .

As described above, according to the preformat of the magneto-optical disk according to the present invention, it is possible to obtain a good track error signal even in the portion where the prepits 14 are formed. Further, the tendency of the influence on the track error signal is substantially constant irrespective of the groove depth of the guide track 12. In addition, since the groove depth of the guide track 12 and the groove depth of the pre-pits 14 may be of course the same, the groove depth of the pre-pits 14 may be reduced to 1/4 of the wavelength of the laser beam as in the related art. There is an advantage that it is not necessary to set, and the preparation of the preformat is easy.

Note that "S" in FIGS. 2 to 5 is the signal intensity, and the reflected light from the optical disk in a flat place having no grooves or pits is 1000. For example, in FIG. 2A, when there is no pre-pit 14 (0), S = 957, and the width X of the pre-pit 14 is 0.2 μm.
In the case of (1), S = 632. And S = 957 and S
325 which is the difference from = 632, the width X of the pre-pit 14 is 0.2μ
The signal amplitude at m (1), which indicates that the larger the signal amplitude, the easier the signal detection. The same applies when the width X of the pre-pit 14 is 0.4 μm (2),
389, which is the difference between S = 568 and S = 957, is the signal amplitude when the width X of the prepit 14 is 0.4 μm (2).

〔The invention's effect〕

As described above, the optical disc according to the present invention is, as described above, a guide track composed of concentric or spiral continuous grooves involved in controlling the focus position of laser light, and corresponding to the recorded information, the adjacent guide tracks Data bits formed on the land between them, and prepits formed in the land in a concave shape corresponding to the information of the track number, and the width of the prepit is set smaller than the width of the guide track. It is a configuration consisting of

As a result, a good track error signal can be obtained even in a place where the pre-pits are formed, and the effect of making such a preformat extremely easy is also provided.

[Brief description of the drawings]

1 to 7 show an embodiment of the present invention. FIG. 1 is an explanatory diagram showing a preformat of an optical disk, and FIGS. 2 (a) and 2 (b) are diagrams each showing a track error signal. Graphs showing characteristics, FIGS. 3 (a) and (b)
Is a graph showing the characteristics of the track error signal.
5A and 5B are graphs showing the characteristics of a track error signal, respectively. FIGS. 5A and 5B are graphs showing the characteristics of a track error signal, respectively. FIG. 6 is an optical system for signal reproduction. FIG. 7 is an explanatory view showing the principle of reproduction by changing the polarization direction, FIGS. 8 and 9 are views showing a conventional example, and FIG. 8 shows a groove type preformat. FIG. 9 is an explanatory view showing a land-type preformat. 11 is a magneto-optical disk, 12 is a guide track, 13 is a data bit, and 14 is a pre-pit.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenji Ota 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Toshihisa 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (72) Inventor Kazuo Ban, 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-61-214246 (JP, A)

Claims (1)

(57) [Claims] 1. A guide track comprising concentric or spiral continuous grooves involved in control of a laser beam condensing position and a land formed between adjacent guide tracks corresponding to recorded information. It has a data bit and a pre-pit formed in a concave shape on the land corresponding to the information of the track number, and the width of the pre-pit is set smaller than the width of the guide track. Optical disk.