JPS6332746A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To control tracking accurately by specifying effective depth of a guide groove and a pit groove in a recording medium having the guide groove for tracking and the pit groove forming preformat. CONSTITUTION:Guide grooves G for tracking and a pit PL that form preformat are formed on one face of a transparent substrate 10A. The effective depth of guide grooves G is made to 0.075-0.20 times the wavelength of laser light for record reproducing in the substrate 10A. When the variation of the level of various signals is measured in changing the effective depth of pit PL groove within the range of 0-0.4 times the wavelength, tracking signals is made stable in the extent in which the depth of pit PL groove is 0.26-0.45 times the wavelength, and tracking signal errors can be detected in preformat within allowable error. Thus, accurate tracking control is made possible.

Description

[Detailed description of the invention] (Technical field) The present invention relates to an optical information recording medium.

(Prior art) Guide grooves for tracking are formed in parallel, concentric circles, or spirally, and in a part of the information track set as an intermediate area between the guide grooves, by discontinuing the grooves, As an optical information recording medium, a light-absorbing and reflective recording film is provided on the surface of a transparent substrate on which a preformat such as address information is formed, on which the groove is formed.
It is intended as shown in the figure.

In FIG. 3, reference numeral 100 indicates an optical information recording medium, and FIG. 3 is an explanatory diagram.

The optical information recording medium lOO is composed of a transparent substrate 100A and a recording film 100B.

A tracking guide groove G is formed on one surface of the transparent substrate 100A.

The formation form of the guide grooves may be parallel to each other, concentric circles, or spiral, depending on the form of the optical information recording medium. When the optical information recording medium is disk-shaped, the guide groove is formed concentrically or spirally.

For concreteness of explanation, it is assumed that the optical information recording medium 100 shown in FIG. 3 is disk-shaped, and the guide dG is drawn as a straight line in FIG. 3, but in reality it is a concentric circle. Suppose that

Now, the intermediate area between the guide grooves 6 is set as an information track, and a part of this information track L is provided with a groove PL.
Address information and the like are formed in a preformat due to the discontinuation of the .

The flat part of the information track L is called a land part.

Furthermore, in the following description, each 11PL forming a preformat will be referred to as a pit PL.

911%100B is light absorbing and reflective, and the transparent substrate 1
It is formed on the grooved side surface of 00A.

For example, a dye coating film can be used as the recording film 100B. Optical information to be recorded is recorded in the land portion of the information track L as minute holes in the recording film or as a phase change with different reflectance.

The laser beam for recording and reproduction shown with the symbol H in FIG.
Laser light used for recording or reproducing optical information is incident from the side of the transparent substrate 100A, and is incident on the recording film 1.
It is focused on the 00B position.

Now, whether recording information on an optical information recording medium or reproducing information, a laser beam for recording and reproduction must be guided correctly on an information track.

This operation is called tracking control. This tracking control will be briefly explained using an example of reproducing optical information.

In FIG. 4, the recording/reproducing laser beam H is.

The light enters the polarizing prism 50, and the fourth polarizing prism 50
When reflected downward in the figure, it enters the objective lens 70 via the 174-wave plate 60. The light becomes focused by the action of the objective lens 70, enters the optical information recording medium 100 from the transparent substrate side, and is focused on the recording film. The light reflected by the recording film enters the polarizing prism 50 via the objective lens 70 and the quarter-wave plate 60, and after passing through the prism, enters the light-receiving surfaces 80A and 80B of the two-split light-receiving element. From each light receiving surface 80A, 80B.

Photoelectric conversion outputs A and B are output, respectively, and these are applied to an analog adder 90A and a subtracter 90B, respectively.

Therefore, an output (A + 8) is obtained from the adder 90A, and an output (A - 8) is obtained from the subtracter 90B.

The output (A+B) obtained from the adder 90A is an RF multiplied signal and is a reproduction signal of information recorded on the optical information recording medium 100.

On the other hand, the output (A-B) is a tracking signal (to be precise, it is a tracking error signal, but in this specification, it is referred to as a tracking signal), and the tracking control is
Servo control is performed to move the recording/reproducing laser beam relative to the optical information recording medium so as to make this tracking signal zero.

Since there is a track guide groove in the part of the optical information recording medium where the recording film is formed, a phase difference occurs in one reflected laser beam depending on its reflection position, and as a result,
Interference occurs. Light receiving surface 80A.

80B is capable of detecting a far field image of the interference of the reflected laser beam, and a pattern change in this far field image is detected as a tracking signal.

By the way, generally, the pitch of the guide groove in an optical information recording medium and the diameter of the 1/e2 intensity at the converging part of the laser beam for recording and reproduction are set to approximately the same value.
This value is 1.6 μm.

Such guide groove pitch and 1/e2 at the focusing part
The intensity diameter (the diameter of the spot that gives an intensity of 1/e2 of the maximum intensity) is approximately equal, and the value thereof is.

When the distance is approximately 1.6 μm, an accuracy of ±1.0 μm is required for accurate tracking control. Accurate tracking refers to tracking with less reduction in RF signal strength, less crosstalk, and less risk of missing the information track.

Now, plastic is used for the transparent substrate of optical information recording media, but with the current technology, when the transparent substrate is made from this plastic, subtle deformations such as warping inevitably occur in the transparent substrate. . Therefore, it is unavoidable that the optical information recording medium is tilted relative to the optical axis of the optical pickup, and this tilt is currently about 40 minutes. Note that the tilt of the optical information recording medium relative to the optical axis is hereinafter referred to as tilt.

In this way, assuming a 40-minute tilt, in the case of the tracking control method shown in Fig. 4, the tracking signal is already (
b) A guide groove having a rectangular cross-sectional shape that is difficult to manufacture;
Even in the case of a pit, there is an error of 0.09 μm to 0.12 μI, and (b) even in the case of a guide groove with a figure 7 cross-sectional shape, which is relatively easy to manufacture, and a pit with a rectangular cross-sectional shape. An error of 18 μm = 0.24 μm occurs. Further, tracking servo control has an error of about 0.03 μm. Therefore, when the tracking signal error and the tracking servo control error are added, the error in the preformat section exceeds the tracking control tolerance of 0.1 μm, making it impossible to obtain sufficient tracking accuracy and causing tracking control failure. Easy to occur.

(Objective) The present invention has been made in view of the above-mentioned circumstances, and its object is to provide novel optical information that enables sufficiently accurate tracking control even in the preformat section. The purpose is to provide recording media.

(composition) The present invention will be explained below.

The optical information recording medium of the present invention has a transparent substrate and a recording film.

On one side of the transparent substrate, there is a guide groove for tracking.
They are formed parallel to each other, concentrically, or spirally. The information track is set as an intermediate area between the guide grooves. Then, address information and the like are formed as a preformat in a part of this information track by discontinuing grooves, that is, pits.

The recording film is light-absorbing and is formed on the surface of the transparent substrate on which the grooves are formed, and optical information is recorded as minute holes in this recording film or phase changes with different reflectances. Ru. The recording/reproducing laser beam is irradiated from the side of the transparent substrate of the optical information recording medium.

Now, assume that the wavelength of the laser beam for recording and reproduction is λ in the transparent substrate. The wavelength in vacuum is λ. , if the refractive index of the transparent substrate is n, then λ=λo/n.

The effective depth of the guide groove in the optical information recording medium is 0.075 to 0.20 times the wavelength λ.

Further, the effective depth of the grooves forming the preformat, that is, the pits, is 0.26 to 0.45 times the wavelength λ.

As before, the pitch of the guide groove for tracking is approximately the same as the 1/e" intensity diameter of the focused spot of the laser beam for recording and reproduction, and is generally about 1.6 μm (1,
2 μrs to 2.4 μ+*).

Furthermore, as servo control for tracking control,
A method of displacing the objective lens, a method of tilting the incident light to the objective lens with a carbano mirror, a method of moving the optical pickup, or a method of displacing the optical information recording medium itself in a direction perpendicular to the tracking guide groove. There are methods etc.

When using the optical information recording medium of the present invention, servo control for tracking control may be performed by any of the above methods.

This will be explained below with reference to the drawings.

FIG. 1 diagrammatically shows an embodiment of the present invention.

The optical information recording medium 10 includes a transparent substrate 10A and a recording film 1.
0B.

A guide groove for tracking and pits constituting a preformat are formed on one surface of the transparent substrate 10A. In FIG. 1, symbols G, L, and PL indicate guide grooves, information tracks, and pits as in FIG.
are shown respectively.

In the embodiment shown in FIG. 1, both the guide groove G and the pit PL have a rectangular cross-sectional shape. In addition, the pitch P of the guide groove G is 1/1 of the focused spot of the laser beam for recording and reproduction.
It is equal to the e2 intensity diameter and is approximately 1.6 μm.

1. IA is a transparent substrate, and 11B is a recording film. Also in this optical information recording medium, the pitch of the guide grooves is approximately 1.
．． It is 6 μm.

In the optical information recording medium 11, a sag occurs in the guide groove G, and its cross-sectional shape is a figure 7 shape.

As shown in Fig. 1, guide grooves and pitches having a rectangular cross-sectional shape are difficult to manufacture in practice, and sagging occurs even in the preformat pitch PL with an inclination of usually 10° to 85°. is the actual situation.

In addition, the transparent substrates 10A and 10B in the optical information recording medium 10.11 of the embodiment shown in FIGS. 1 and 2 are P
It is an MMA plate, and the guide grooves G and pits PL are formed by being transferred from a stamper using a photopolymer method. In addition, the recording films 10B and IIB are coated with a light-absorbing and reflective dye having the following structural formula using a spinner to an average thickness of 650 mm.
It is formed by applying it to a person.

Further, the optical information recording medium 10.11 is disk-shaped, and the guide groove G is formed in a concentric shape.

Furthermore, in these optical information recording media 10.11, the effective depth of the guide groove G is 0.075λ to 0.20% with respect to the wavelength λ of the laser beam for recording and reproduction in the transparent substrate.
In addition, the effective depth of the pit PL is set to 0 so as to satisfy λ.
．． It is manufactured to satisfy 26λ to 0.45λ. For example, when the cross-sectional shape becomes V-shaped due to sagging, as in the case of the guide groove G in FIG.
If the groove is shaped like a letter, the peak depth is approximately 1.4X, where X is the effective depth difference.

Now, when information is to be reproduced from an optical information recording medium as shown in FIGS. 1, 2, and 3 using an optical pickup as shown in FIG. When moving across orthogonally,
RF multiplied signal A + 8) and tracking signal (A-
[3) changes as shown in FIG.

In FIG. 5, one curve TI, T2. T3 indicates a tracking signal, which is an average value in a preformat area where lands and pits coexist in a ratio of 1=1, and curve T1
is the first curve T2. without the above-mentioned tilt. T3 represents a case where there is a tilt. It can be seen that an offset occurs in the tracking signal due to the tilt of the optical information recording medium with respect to the optical axis of the optical pickup, that is, the tilt.

Regarding the RF multiplied signal, in Fig. 5, the RF multiplied signal FI is generated from the land portion, and the RF multiplied signal F2
This occurs in the pit portion of the preformat.

Therefore, the preformat information can be expressed as a high level signal for RFI and a low level signal for RF2.

It is important that the zero-crossing point of the tracking signal does not deviate from the center of the information track, regardless of the tissue.If the offset increases until there is no zero-crossing point, it becomes impossible to perform tracking servo control on the information track.

Now, FIG. 6 shows the type of optical information recording medium shown in FIG. It shows changes in the levels of various signals when changing within a range of 0.4 times.

The transparent substrate of the optical information recording medium was a PMMA plate, and the recording film was a coating film of the above-mentioned light-absorbing and reflective dye with an average thickness of 650 mm.

In addition, the pitch of the guide groove is 1.6 μm, and the 1/e2 intensity diameter of the focused spot of the laser beam for recording and reproduction is also 1.6 μm.
The signal is extracted by the optical pickup shown in FIG. A semiconductor laser that emits a laser beam with a wavelength of 690 nm was used as a light source for the laser beam for recording and reproduction. The vertical axis in FIG. 6 is the level given by signal level/M, where M is the reflection level of the mirror.

In FIG. 6(1), the width of the guide groove G of the optical information recording medium is 0.45 μm, and the width of the pit changes from 0.24 μm to 0.48 μI as the depth increases. Straight line 6-11 shows the RF signal change obtained from the land portion. Further, a curve 6-21 shows a change in the XRF signal obtained from the pit portion of the preformat.

Further, curve 6-31 shows the change in value of 1/2 of the P-P value of the tracking signal when the pre-format is crossed, and curve 6-41 shows that the disc-shaped optical information recording medium It shows the change in the offset value of the tracking signal when a tilt occurs at an angle of 1.43° with respect to the pickup optical axis.

In addition, in FIG. 6 (II), the width of the guide groove G is 0.60 μm.
Except that, the other conditions are the same as in the case of FIG. 6 (1), and the curve
42 are curves 6-11 and 6-2 in Figure 6 (1), respectively.
Corresponds to 1.6-31.6-41.

In Fig. 6(m), except that the width of the guide groove G is 0.75μ, the other conditions are the same as in Fig. 6(1), and the curve 6-13.6-23 .6-33.6-43
are curves 6-11.6-21. in FIG. 6(1), respectively.
6-31° corresponds to 6-41.

Signal representing the change in curve 6-31.6-32.6-33.

That is, the value of 172 of the P-P value of the tracking signal when crossing the preformat is temporarily called the TP times signal, and is based on the curve 6-41.6-42.6-43.

If the offset value of the tracking signal indicating the change is simply called the offset value, the TP multiplied signal,
The larger the offset value is, the better the tracking signal is, and the less likely it is to go off track. In other words, at this time, the vicinity of the center of the information track can be tracked.

As is clear from Figure 6 (1), (II), and (III).

For pit depths of 0.1λ to 0.25λ, the tracking signal is extremely sensitive to tilt of the optical information storage medium. Also, the depth of the pit is 0.26
It can be seen that the tracking signal is stabilized between λ and 0.4λ. Furthermore, the tracking signal tends to be stable even when the depth of the pit is 0.1λ or less;
In this region, the contrast of the RF multiplied signal between the land and the pit becomes low, making the RF multiplied signal unusable.

The larger the difference between the preformat land and pit, the more advantageous it is, but if the difference is too large, crosstalk to adjacent tracks will increase, so the contrast will be 0.3.
~0.7 is appropriate.4 Also, as mentioned above, due to the processing of the groove, shallow grooves tend to become V-shaped like the guide groove G in Figure 2 due to sag. ,Also,
Deep grooves tend to be rectangular or trapezoidal.

Figure 7 shows the case of a guide groove having a V-shaped cross section with a width of 0.3μ and a maximum depth of 0.175λ, and a pit with a rectangular cross-section of 0.55μ in width. ~0
．． 0 songs 1i7-11.7-21.7-31.7-4 showing changes in various signals when changed over a range of 5λ]
As shown in Fig. 6 (1) 4-niotttre curve a6-11゜6-21.6-31.6-41, the R of the land part
F times signal change, RF times signal change in pit area, TPff
The change in No. 1 and the change in the offset value are reported.

In this case, the tracking signal becomes stable at a pit depth of 0.26λ to 0.45λ. In addition, considering the RF signal contrast, the depth of the pit is 0.28λ to 0.3
8λ is better.

In addition, in the case of a guide groove with a figure 7 cross-sectional shape, the maximum tracking signal is obtained around 0.175λ, but this is due to the influence of the shape, and the effective depth is
Correcting the influence of shape, it is 0.125λ or 0.17
5λ/1.4. The effective depth of the guide groove is optimally 0.125λ in order to obtain a tracking signal.
If it is in the range of 0.75λ to 0.20λ, it can withstand practical use.

(Effects) As described above, according to the present invention, a novel optical information recording medium can be provided.

According to the present invention, the tracking signal can be detected with a detection error of 1/1.2 to 1/3 of the conventional method, particularly in the preformat section. This is because the tracking signal has the same polarity at the guide groove portion and the pit portion.

Furthermore, the RF multiplied signal in the preformat section does not become larger than necessary, and the adverse effect on adjacent tracks can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining one embodiment of the present invention, FIG. 2 is a diagram for explaining another embodiment, and FIGS. 3 and 4 are for explaining the prior art and its problems. , and FIGS. 5 to 7 are diagrams for explaining the present invention. IO...Optical information recording medium, IOA...Transparent substrate, 10B...Recording film, G...Guide groove, PL...
-・Pit (preformat groove). Voice 15, C8, right? ■ 4 “0olr>△Dokami N Kuni

Claims (1)

[Scope of Claims] A tracking guide groove is formed in a parallel, concentric, or spiral shape, and a part of the information track set as an intermediate area between the above-mentioned guide grooves is pre-printed by discontinuing the groove. An optical information recording medium in which a light-absorbing and reflective recording film is provided on the surface of a transparent substrate on which a format is formed, on which the groove is formed, the effective depth of the guide groove being It is 0.075 to 0.20 times the wavelength of the laser beam for recording and reproduction in the substrate, and the effective depth of the groove of the preformat is 0.075 to 0.20 times the wavelength of the recording/reproducing laser beam in the substrate.
．． An optical information recording medium characterized in that the magnification is 26 to 0.45 times.