JP2636822B2 - Substrate for optical recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optically recordable and reproducible optical recording medium having address pits.

[0002]

2. Description of the Related Art Conventionally, a pre-groove for optically guiding irradiation light is previously formed on an optical disk for an optical disk file device, and the irradiation light is scanned along the pre-groove to enter the pre-groove. Information was recorded. Further, one round of the track is divided into several sectors, and an address pit such as a track address and a sector address is formed at the head of each sector, so that a search can be performed in sector units (for example, Nikkei Electronics November 21, 1983, 197
page).

In a conventional additional recording type optical disc,
Even if information was recorded in the pre-groove, the signal-to-noise ratio (S / N) could secure a sufficient value to satisfy the condition that no reading error occurred. However, if this method is adopted for an optical disk on which information can be rewritten, there is a problem that the S / N is small and the condition for lowering the error rate is not satisfied. Particularly, in the magneto-optical disc to a perpendicular magnetic film and the recording medium, so to reproduce information by detecting the polarization plane rotation of less than 1 degree due to magnetization, to enhance the S / N become an important technical challenges I have. Therefore, there has been proposed a groove-to-groove recording method for recording address pits on lands between pre-grooves (for example, JP-A-60-50733, JP-A-61-13458, and JP-A-61-2250).

FIG. 4A is an enlarged sectional view of a conventional substrate for an optical recording medium of the on-groove recording type. Pregroove P
G, groove width Wap ≦ 0.7 μm, groove depth of address pit AP

(Equation 4) It is. Since this is mainly used for a write-once medium having a high signal strength, no problem occurs in the system even if the width of the data pit DP is limited by the pre-group width and the S / N is slightly deteriorated. Next, in a rewritable medium having a low signal intensity, it is difficult to perform recording on a groove because deterioration in S / N degrades the reliability of the system, and an inter-groove recording type as shown in FIG. 4B has been proposed. According to this method, even in a magneto-optical recording medium having a low signal strength, the data bit D
S / N could be increased to record P. Since Wp = 0.5 [mu] m and WA = 0.45 [mu] m, the land width between grooves for recording the data pit DP is as wide as 1.1 [mu] m , contributing to an improvement in S / N. Pregroove PG depth

(Equation 5) Address pit AP depth

(Equation 6) Thus, the medium has a high S / N and the highest address modulation, which is an ideal configuration in principle.

[0005]

However, this inter-groove recording method has three problems. One is that the cutting cost of the inter-groove recording is technically advanced such as processing with two beams, so that the price of the device is very high, and the optical recording medium processed by this device becomes expensive. is there.
Another problem is that the width of the land between the grooves fluctuates due to uneven feed pitch of the cutting device because a signal is recorded between the grooves. Specifically, for a track pitch of 1.6 μm, the feed accuracy of the normal cutting device is within ± 0.1 μm. When the pregroove width Wp is 0.6 μm, the land portion between the grooves has a width of 1 μm,
A variation of ± 0.1 μm in the above-described feeding accuracy results in a variation in the land portion width. In other words, the land width between the grooves where the data signal DP is recorded / reproduced is 1.0 ± 0.1 μm, and has a fluctuation of ± 10%, which is a factor of the fluctuation of the S / N. In addition, there is a high possibility that dropouts will occur during the mastering process of making a stamper.Dropouts generated during the resist coating process will remain on the optical recording medium in the case of the groove-to-groove recording method, resulting in a bit error. It was a medium with a high (bad) rate BER.

SUMMARY OF THE INVENTION Accordingly, the present invention is to solve such a problem, and an object of the present invention is to provide a substrate for an optical recording medium which is inexpensive, has a high S / N, and has a small dropout, that is, a low BER. Where you do it.

[0007]

According to the present invention, there is provided a substrate for an optical recording medium, wherein the wavelength of a recording and reproducing beam is λ, the refractive index of a light transmitting layer through which the recording and reproducing beam passes is n,
The track pitch is P, the phase depth of the address pit is d,
The width W (However, when the top width and the bottom width of the address pit respectively W _T, and W _B,

(Equation 7) And )

(Equation 8) And

(Equation 9) Is satisfied.

[0008]

FIG. 1 shows an embodiment of an optical recording medium substrate according to the present invention. FIG. 2 shows the definition of the width W of the pregroove and the address pit. First, in the example of FIG. 1, the groove width W of the pre-groove PG and the address pit AP is set to half the track pitch P. That is

(Equation 10) Also groove depth

[Equation 11] And The present invention will be described with reference to FIG. First, it is shown in FIG. 3 that the S / N ratio is increased by the wide groove cut of the present invention.
(B)

(Equation 12) It can be seen from the fact that the reflected signal at the point increases in proportion to W. In addition, the diameter of the Airy disk of a normal optical head is
Since the thickness is 1.2 to 1.6 μm, if the flat recording area increases, the signal strength also increases, which is also a factor for increasing the S / N. Next, as a factor contributing to an increase in S / N, it is important to increase the tracking error signal. For this purpose, the groove depth is shown in FIGS. 3 (a) and 3 (b).

(Equation 13) Is best. Further, it is necessary that the modulation of the address pit AP is high.

[0009]

[Equation 14] Is good. When the three contradictory conditions of signal strength, tracking error signal strength, and address signal strength are applied to a medium having a low signal strength such as rewritable magneto-optical recording, first, the groove width W becomes

(Equation 15) Turned out to be good. However, as the groove width W approaches the track pitch P, the tracking error signal approaches 0,

(Equation 16) Is preferred.

On the other hand, if the groove width W is increased, the address signal will be reduced. Therefore, in order to increase the modulation of the address signal, the groove depth d is increased.

[Equation 17] It turned out that we should deepen. However, the groove depth d

(Equation 18) , The tracking error signal approaches 0

[Equation 19] In addition, the processing method of the present invention using a cutting apparatus is preferable.However, the numerical aperture NA of the objective lens is set to be higher than the normal exposure power, the laser beam is slightly defocused without being focused on the surface of the glass master. Normal 0.9-0.93 to 0.7-0.
The groove width, the groove depth, and the groove shape can be appropriately changed by a method such as lowering to 8, or a combination thereof.

[0011]

As described above, according to the present invention, the cutting device for forming the groove of the address pit may be a conventional low-cost one-beam device for cutting a compact disk or a laser disk, and therefore, is inexpensive. A rewritable optical disk. Furthermore, when data is recorded on the groove, the address signal strength can be increased by increasing the groove depth where the address signal decreases when the groove width is increased to increase the S / N. An object of the present invention is to provide an inexpensive optical recording medium having a high S / N ratio by recording on a monotone groove with a wide cut according to the present invention.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view of an optical recording medium substrate according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a groove shape of a pregroove and an address pit.

FIG. 3A is a diagram illustrating a relationship between a groove depth d and an address signal, a tracking error signal, and a reflection signal. (B)
The figure which shows the relationship between a groove width W and an address signal, a tracking error signal, and a reflection signal.

FIG. 4A is an enlarged sectional view of a conventional optical recording medium substrate. (B) is an enlarged cross-sectional view of a conventional optical recording medium substrate.

[Explanation of symbols]

 P: Track pitch d: Phase depth of pre-groove and address pit W: Groove width of pre-groove and address pit PG: Pre-groove AP: Address pit DP: Data pit

Claims (3)

(57) [Claims] 1. The wavelength of a recording and reproducing beam is λ, the refractive index of a light transmitting layer through which the recording and reproducing beam passes is n,
The track pitch is P, the phase depth of the address pit is d,
When the width is W (provided that the top width and bottom width of the address pit are WT and WB, respectively, And ), And [Equation 3] An optical recording medium substrate characterized by satisfying the following. 2. The method according to claim 1, wherein said groove depth d is: 2. The substrate for an optical recording medium according to claim 1, wherein: 3. The width W of the address pit is: 2. The substrate for an optical recording medium according to claim 1, wherein: