JPH0454301B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a flat information recording carrier such as an optical disk memory medium (hereinafter referred to as a disk) capable of recording, reproducing, or erasing video signals, digital signals, and the like.

Conventional Technology Write-once optical disks that can read and write video signals, digital information signals, etc., or rewritable optical disks that can also be erased and rewritten have a track density that is nearly two orders of magnitude higher than that of conventional magnetic disks. The recordable capacity is also increasing accordingly.

In order to access such high-density tracks with high accuracy and high speed, a preformat signal is required on the surface of the recording medium on which information is recorded and reproduced on the optical disk. The preformat signal has a guide track section on which the user can record information, and address information for specifying a track or sector address. This is done by coating a glass master with photoresist and exposing it to laser light.
After development, a nickel mold is made based on the fine relief structure formed. A replica disk is made from this mold using various molding methods. A guide track and necessary address information are formed on this replica disk. A recordable optical disc is produced by forming a recording film thereon by vacuum evaporation or the like.

When recording and reproducing information signals on optical discs, it is extremely important to improve the C/N ratio, improve the read signal quality, and reduce the bit error rate. FIG. 4 shows an enlarged view of a conventional disk preformat signal. The information signal is recorded on the guide track 1 in a group recording manner.

FIG. 5 shows a second conventional example. This is a land recording method in which address signal pits 2 are provided between the guide tracks, and information signals are recorded between the guide tracks 1.

Since the land recording method is less affected by grooves than the groove recording method, it is easier to obtain a good C/N. In both conventional examples, the optical groove depth is set around λ/8 (λ: wavelength of the reproduction light source) in order to improve the efficiency of far-field detection of the tracking error signal. The guide track part is set to an optical depth of around λ/8, and the address signal pit part is set to a depth of around λ/4 where the diffraction efficiency is maximized. A method has also been proposed in which the coating is applied to a thickness of around 4, and the depth is varied by controlling the recording laser power and development conditions.

Problems to be solved by the invention The tracking method using the far-field method is
Used in recordable or rewritable optical discs. When following the guide track of an optical disk using this method, the following problems arise.

The optical system shown in FIG. 6 is an optical system used in a write-once type, rewritable type optical pickup. The light from the semiconductor laser light source 7 is made parallel by the collimator lens 6, and after passing through the converging lens 5,
It is focused on the guide track of the disk 4. The reflected light from the disk is reflected by a beam splitter 9 and is incident on a tracking signal detector 8.
The output of the two-split detector is connected to a differential amplifier 10, and a tracking signal can be obtained.
The converging lens 5 is adapted to move in a direction perpendicular to the guide track in order to cause the spot converged on the disk surface to follow the guide track. If the converging lens 5 is displaced with respect to the incident light beam, this will not cause much of a problem as long as the incident light beam is large enough, but usually, the amount of vignetting of the incident light to the converging lens 5 is generally adjusted in consideration of laser light utilization efficiency. has been kept below 50%. Therefore, the converging lens 5
When shifts in the direction of deviation as shown in Figure 6,
The state of vignetting of the incident light changes, and the reflected light beam 11 from the disk on the tracking signal detector 8 becomes
As shown in FIG. 7, it moves like 12 and 13. If the polarity of this light flux movement and the polarity of the tracking servo loop are in the same phase and are in negative feedback, the servo loop will be stable and the tracking servo will not become disconnected. However, there are two polarities of tracking: the polarity for following the guide track and the polarity for deflection of the luminous flux, and these cannot be controlled individually.

In tracking using the far-field method, if the optical depth of the guide track is around λ/8, if the spot is to be followed on the guide track, the tracking polarity and the movement of the light flux on the tracking detector will be in the same phase and the spot will be tracked. When the king servo loop is turned on, it can be made to follow the guide track stably. However, from the point of view of signal recording and reproduction, it is better in terms of C/N to follow between guide tracks, that is, on lands, than to follow on guide tracks. This is due to the process of exposing and developing the photoresist when creating the master disc, and the etched surface and the edges of the grooves become quite rough microscopically, resulting in poorer properties compared to the surface of the glass master disc. .

In order to improve this problem, a method has been proposed in which the width of the formed groove is made as small as possible and signals are recorded and reproduced on the land. According to this method, the C/N of signal recording and reproduction itself can be improved, but the polarity of the signal output due to the deflection of the light flux on the tracking detector as described above and the polarity of the tracking itself are in reverse phase, resulting in the problem of convergence. In a range where the deflection of the lens 5 in the tracking direction is small, that is, in a range where there is little vignetting of the light beam incident on the converging lens 5, the stability of the servo loop itself does not pose much of a problem. However, when performing high-speed access, it is necessary to keep a wide tracking range, and if the servo signal becomes unstable due to a defect on the disk, etc., the servo loop itself becomes unstable, causing significant damage. In some cases, the servo may not retract and may slip in and out.

SUMMARY OF THE INVENTION An object of the present invention is to provide a disk having a guide track that can solve these problems, stabilize the tracking servo loop, and obtain high-quality recording and reproduction signals. .

Means for Solving the Problem The tracking differential signal output changes polarity as the guide track depth changes. The boundary of polarity change is λ/2 (λ: reproduced signal optical wavelength).
Therefore, in the present invention, the guide track depth is set from 0 to
It is possible to invert the polarity up to λ/4 and in the range of λ/4 to λ/2, so that the polarity of fluctuations in the DC component due to movement of the light beam on the tracking detector is matched.

Effect Adjust the optical depth of the guide track from λ/4 to λ/2.
By doing this, the polarity of the tracking differential output signal can be reversed from that when the guide track depth is 0 to λ/4, and therefore, the polarity of the tracking differential output signal can be reversed from that when the guide track depth is 0 to λ/4. , Mizoma (on land)
A tracking signal output capable of canceling the polarity change at λ/4 to λ/2 can be obtained in the groove depth region of λ/4 to λ/2. Therefore, the polarity of the tracking signal can be kept constant, and the servo characteristics can be stabilized. At the same time, C/
It is possible to realize N-good groove (land) recording.

As shown in Figure 3, Figure a shows the tracking state between the grooves (lands) with a depth of λ/8, and Figure b shows the tracking state between the grooves (lands) with a depth of λ/8.
It shows the polarity of the output signal in the case of land tracking of a groove with a depth of 3λ/8. In a, the polarities of the tracking differential output and the differential light intensity change component at the center of the land are reversed, and the servo system is unstable. At b, both are in phase and the servo system is stable. As described above, by configuring a groove with a depth of 3λ/8, the polarity change when changing the tracking position from above the groove to between the grooves can be eliminated, and when a disturbance occurs during high-speed access, the servo Stability during pull-in can be greatly improved, and at the same time, by recording between grooves, high-quality signal recording and playback can be performed, and the characteristics of trackable and rewritable optical discs can be significantly improved. Yes, the effect is extremely large.

Example As shown in FIG. 2, the guide track depth is greater than λ/4 and smaller than λ/2. In order to set the guide track depth to a predetermined value, a photosensitive photoresist of a predetermined thickness is spin-coated onto a glass master disk, and after prebaking, it is exposed to laser light and then developed to form guide tracks. The photoresist is applied to a specified thickness,
It is also possible to control the depth of the grooves formed by controlling the exposure power and development time.

1a to 1c show diagrams of an embodiment of the optical disk guide track and address pit of the present invention. First, the first embodiment a has address pits between consecutive guide tracks, and both optical depths are
3λ/8. This can be easily achieved by applying the photoresist to a uniform thickness of 3λ/8 and controlling the exposure and development conditions so that the surface of the glass master disk is exposed by development. Assuming that λ=8300 Å and the refractive index of the disk base material n=1.5, the resist should be coated to a thickness of d=3λ/8n=2075 Å. Although the coating needs to be thicker than the conventional thickness of around 800 Å, it has the advantage of reducing pinholes during coating.

The resist thickness is coated thicker than this thickness and controlled by exposure and development conditions, making it virtually
Guide tracks and address pits with a depth of around 2000 Å may be formed. In the former case, a groove with a nearly trapezoidal cross section is formed; in the latter case, a groove of the desired depth can be formed by not developing the photoresist until it reaches the glass surface and then stopping halfway. .

In the second embodiment b, the guide track depth is 3λ/
8, and the depth of the address pit portion is λ/2. The depth of the address pit portion is set to a depth of λ/2, which is shallower than the guide track, by controlling the exposure and development conditions. By doing this, the tracking signal and the address signal can each be extracted with maximum efficiency, and the efficiency of the servo system and the efficiency of address detection can be set to the maximum, which is ideal for the structure of the groove of the disk.

A third embodiment is shown in c. The guide track is
Only the area adjacent to the address signal is made discontinuous, and the distances W ₁ and W ₂ between the address signal and the adjacent track, as shown in the conventional example shown in FIGS. It has the effect of preventing changes in

Also, if the depth of the address pit is set to λ/8 and recording is done shallowly, the polarity when tracking to the address pit as shown in Figure 2 and the tracking polarity of the guide track when the depth is 3λ/8 are reversed. Therefore, if the polarity is set so that tracking occurs between the guide tracks, the track area will follow the land, and the address pit portion will follow the pit.

As a result, stable tracking characteristics can be obtained over the entire range, increasing the stability and reliability of the system.

The guide track depth and address pit depth of the configuration described above are not limited to the single optical depth described, but may be substantially close to the value described. . Further, the cross section of the groove shape and the pit shape need not be the rectangular shape in the embodiment, but may be V-shaped with a rounded bottom.

Effects of the Invention As described above, in order to improve the characteristics of optical discs, magneto-optical discs, etc., it is preferable to record information signals between the guide tracks rather than on the guide tracks. There is an improvement effect of several dB in terms of C/N. However, in conventional recording between guide tracks at an optical depth of around λ/8, the polarity of tracking and the polarity of light intensity fluctuation caused by vignetting of the light flux due to movement of the converging lens are opposite on the tracking servo loop. Therefore, it is possible to track the groove, but it becomes a positive feedback when the light intensity changes on the tracking detector, making it impossible to track.
The servo loop becomes extremely unstable. There are few problems when the tracking follow-up range is narrow, but when high-speed access is required, the dynamic range needs to be increased, and the instability of the servo system becomes fatal. The polarity of tracking and the polarity of light intensity fluctuation depend on what kind of lens system,
Even through optical elements, the relative relationship is preserved and cannot be reversed.

In the present invention, the optical depth of the guide track is
By changing the intensity distribution of the diffracted light to around 3λ/8, the tracking polarity and the polarity of the light amount fluctuation are made to be in phase when recording between guide tracks, thereby realizing stabilization of the tracking servo, and It is also possible to improve the C/N ratio, and the results are extremely significant in optical disks and magneto-optical disks. Stan 110-It is necessary to make the resist coating thickness on the glass master disk thicker than before, but
Increasing the thickness of the resistor also has the effect of suppressing the occurrence of pinholes and improving quality.

[Brief explanation of the drawing]

FIG. 1 is a plan view and a sectional view showing a guide track and address pit of a flat information recording carrier according to an embodiment of the present invention, and FIG. 2 is a waveform diagram showing a normalized tracking differential signal with respect to the guide track depth. , FIG. 3 is a schematic diagram and characteristic diagram of the detection unit showing the relationship between the tracking signal and the light amount fluctuation (DC component) due to lens movement, and FIGS. 4 and 5 are plan views showing the guide groove and address pit of the conventional example. FIG. 6 is a side view showing a far-field tracking type optical pickup, and FIG. 7 is a plan view showing the displacement of the light beam on the tracking detector. 1... Guide track, 2... Address pit, 3... Recording bit, 4... Disk, 5...
Converging lens, 6...Collimator lens, 7...Light source, 8...Tracking detector, 9...Beam splitter, 11...Return light flux from the disk.

Claims (1)

[Scope of Claims] 1. A concentric or spiral guide groove for guiding a light spot for recording, reproducing or erasing information signals, and a pit row consisting of a plurality of pits having information signals between the guide grooves. has an uneven structure, the optical depth d ₁ of the guide groove is λ/4<d ₁ λ/2 (λ: wavelength of the light source for information signal reproduction), and the optical depth d ₂ of the pit row A flat information recording carrier characterized in that λ/16<d ₂ ≦λ/2. 2 Optical depths d ₁ and d ₂ of a pit row consisting of a plurality of pits having guide grooves and information signals are -
The flat information recording carrier according to claim 1, characterized in that λ/16≦d ₁ and d ₂ -λ/8≦λ/16. 3. The optical depth d ₁ of the guide groove is -λ/16≦d ₁ -3λ/8≦λ/16, and the optical depth d ₂ of the pit row consisting of a plurality of pits having information signals is -λ/16. The flat information recording carrier according to claim 1, characterized in that ≦d ₂ -λ/4n≦λ/16. 4. The optical depth d ₁ of the guide groove is -λ/16≦d ₁ -3λ/8≦λ/16, and the optical depth d ₂ of the pit row consisting of a plurality of pits having information signals is -λ/16. The flat information recording carrier according to claim 1, characterized in that ≦d ₂ -λ/8≦λ/16. 5 The optical depth d ₁ of the guide groove is λ/4<d ₁ <λ/2, and the optical depth d ₂ of the pit row consisting of a plurality of pits having information signals is λ/16<d ₂ ≦λ. 2. The flat information recording carrier according to claim 1, wherein the information recording carrier has a structure in which the guide track is desired to exist only in an area adjacent to the pit row having the information signal. 6 The optical depth d ₁ of the guide groove is λ/4<d ₁ <λ/2, and the optical depth d ₂ of the pit row consisting of a plurality of pits having information signals is −λ/16<d ₂ −λ 6. The flat information recording carrier according to claim 5, wherein the structure is such that /8<λ/16 and no guide track exists only in an area adjacent to the row of pits having the information signal.