JP2590832B2 - Tracking error detection method for optical disk - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an optical disk (including a magneto-optical disk or the like) provided with a pre-groove in which the depth of the pre-groove is made shallower than in the past, and the reflectance is reduced. By increasing, the servo is stabilized and the amplitude of the HF signal is increased.

[Conventional technology]

2. Description of the Related Art As an optical disk for recording and reproducing information, a write-once type disk and a recording / erasing (Erasable) type disk which can be written by a user are known.

Write-once discs allow information to be played back immediately after recording,
Further, additional recording can be performed as necessary. The recording / erasing type disc is a disc capable of erasing recorded data and rewriting.

 FIG. 2 shows an example of the structure of a conventional write-once disc.

This optical disc 1 is made of tellurium (T) on the surface of a transparent disc substrate 10 such as polycarbonate or acrylic (PMMA).
e) A thin film 12 of a metal having a thickness of about 100 nm made of aluminum or the like is formed. In this case, two thin films 12 are laminated with the thin film 12 side facing each other and bonded with an adhesive 14.

A pre-groove (guide groove) 16 is formed in the substrate 10 and the thin film 12, and a portion of the thin film 12 on the pre-groove 16 is burned out by a laser beam to form a hole. The hole is formed by a pit 18 for recording information. It has become. In some cases, pits 18 are formed on lands 17 between the pregrooves 16 as shown in FIG.

Here, the pregroove 16 is provided for the purpose of facilitating tracing of the optical pickup at the time of writing and increasing the writing density, and is formed in advance at the time of manufacturing a disc. That is, the write / playback pickup forms pits with laser light (in the case of a magneto-optical disk, changes the magnetization direction of the disk medium) while tracking this pre-groove by the push-pull method, and the information is read. Record.

In the conventional optical disc 1, the depth of the pre-groove 16 is set so that a push-pull signal and a pre-pit signal (pits indicating addresses formed in advance on the disc) are largely output during tracking by the push-pull method during writing. 70-80 nm (1/8 of the laser light wavelength λ,
In consideration of the refractive index, the value was set at about 1 / 1.5).

[Problems to be solved by the invention]

The depth of the pre-groove like the conventional optical disk
In the case of 70 to 80 nm, the reflectivity is low, the load on the focus servo circuit is increased, and the HF signal output is small.

An object of the present invention is to provide a method for detecting a tracking error of an optical disk which solves the drawbacks of the conventional technique, increases the reflectivity, stabilizes the servo, and increases the amplitude of the HF signal. is there.

[Means for solving the problem]

The present invention is characterized in that a pregroove having a depth of 20 to 30 nm is formed on an optical disk, and a tracking error is detected by using a push-pull method at the time of recording and a three-beam method at the time of reproduction.

(Operation)

According to the solution of the present invention, since the depth of the pre-groove is set to 20 to 30 nm, the reflectivity increases, the focus servo gain increases, and the three-beam tracking servo gain during reproduction also increases. Therefore, the load on the servo circuit is reduced. Also, the HF signal increases. Although the level of the tracking error signal by the push-pull method is reduced, the servo is stable and there is no practical problem.

〔Example〕

FIG. 1 shows an embodiment of the present invention. In this example,
A case where the present invention is applied to a write-once optical disc that records information as pits will be described.

This optical disc 2 is made of polycarbonate or acrylic (PM
MA) and the like, a thin film 12 of several tens nm thick made of tellurium (Te), aluminum, etc. is formed on the surface of a transparent disk substrate 10,
This is used in the form of a single plate.

A pre-groove (guide groove) 16 'is formed in the substrate 10 and the thin film 12, and the thin film 12 on the pre-groove 16' is burned off by laser light to form a hole, and the hole records information. It is pit 18. Pregroove 16 'depth is 20 ~
It is set to 30nm.

The pits 18 can be formed on the lands 17 as shown in FIG. Also in this case, the depth of the pregroove 16 'is set to 20 to 30 nm.

A description will be given of how various characteristics change depending on the depth of the pregroove.

5 to 8 show the results of measuring various characteristics of a structure having pits formed on the land 17 (shown in FIG. 4).

Reflectivity (FIG. 5) The reflectivity of an unrecorded disk changes as shown in FIG. 5 depending on the depth of the pregroove. That is, both the land and the groove have a higher reflectance as the depth of the pre-groove is smaller. Therefore, a higher reflectance can be obtained in the present invention than in the conventional one.

Tracking error detection sensitivity (FIG. 6) Before recording (at the time of writing), a tracking error is detected by the push-pull method, and after recording (at the time of reproduction), the tracking error is detected by the three-beam method.

The detection sensitivity by the push-pull method before recording is maximum when the pre-groove is around 70 nm, and conventionally it is 70 to 80 nm in consideration of this
Was set to. Pregrooves 20 to 30 as in the present invention
If it is nm, it is about 50% lower than the conventional one,
Experiments have shown that the tracking servo operates stably.

Further, the detection sensitivity by the three-beam method after recording is higher when the pre-groove is shallower. Therefore, according to the present invention, the detection sensitivity of the three-beam method is higher than that of the conventional one, and the load on the servo circuit during reproduction is reduced. Therefore, in the optical disc of the present invention, it is preferable that the tracking error is detected by using the push-pull method at the time of recording and the three-beam method at the time of reproduction.

Focus gain after recording (FIG. 7) The focus gain after recording changes as shown in FIG. 7 depending on the depth of the pre-groove. According to this, according to the present invention, the servo gain is increased by about 2 dB as compared with the conventional one, and the load on the servo circuit is reduced.

HF output The HF output changes as shown in Fig. 8 depending on the pregroove depth.

According to this, the level of the HF signal of the present invention is increased by about 2 dB as compared with the conventional one.

[Modification example]

In the above-described embodiment, the case where the present invention is applied to the write-once optical disc is described.

Further, in the above-mentioned embodiment, the disk is used in a single-plate type and used for one side, but it is of course possible to use them for both sides by opposing and bonding them in the same manner as in the configuration of FIG.

〔The invention's effect〕

As described above, according to the present invention, by setting the depth of the pre-groove to 20 to 30 nm, the reflectivity increases, and the focus servo gain and the tracking servo gain at the time of reproduction when using the three-beam method are used. And the load on the servo circuit can be reduced.

Further, since the amplitude of the HF signal increases, the S / N can be improved.

[Brief description of the drawings]

FIG. 1 is a partially enlarged perspective view of an optical disc showing an embodiment in which the present invention is applied to an optical disc having pits formed in a pre-groove portion. FIG. 2 is a perspective view showing the entire conventional optical disc and a partially enlarged sectional perspective view thereof. FIG. 3 is a partially enlarged cross-sectional perspective view showing another conventional optical disk having pits formed in a land portion. FIG. 4 is a partially enlarged cross-sectional perspective view showing another embodiment in which the present invention is applied to an optical disk having pits formed on land portions. 5 to 8 are diagrams showing changes in various characteristics depending on the depth of the pregroove, respectively. 1,2 ... optical disk, 16,16 '... pre-groove, 17 ...
Land, 18 ... pit.

Claims (1)

(57) [Claims] 1. A tracking error detection method for an optical disk, wherein a pregroove having a depth of 20 to 30 nm is formed on an optical disk, and a tracking error is detected by a push-pull method during recording and a three-beam method during reproduction. Method.