JPH09115185A - Optical recording medium and optical information detection device - Google Patents

Abstract

The present invention provides an optical recording medium and an optical information recording / reproducing apparatus capable of high density recording in which land-and-groove recording reduces crosstalk and cross erase. An optical recording medium capable of land-and-groove recording is characterized in that the groove depth is larger than the land width and the groove width. Desirably, the depth of the focus signal is not less than the depth of focus determined by the objective lens. A magneto-optical recording medium having such a groove depth that the land width is larger than the groove width and a spatial frequency filter including a converging lens and a pinhole or a slit are arranged. An optical recording medium and an optical information detecting device, each of which is composed of an optical recording / reproducing device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium capable of land and groove recording and an optical information detecting device, that is, an optical disk drive device.

[0002]

2. Description of the Related Art At present, optical disks are used as recording media capable of reproducing audio signals and image signals. Magneto-optical disks and phase change disks have been actively developed as rewritable high density recording media.

In order to increase the recording density of an optical disk recording medium for recording information in a spiral or concentric form, there are two methods: shortening the track pitch and improving the linear recording density. In any case, it is realized by shortening the wavelength of the semiconductor laser used for recording and reproduction. However, it seems that it will take some time before semiconductor lasers of short wavelength such as blue and green continuously oscillate stably at room temperature and they are available for commercial use at low cost. Under such circumstances, the optical super-resolution method using the temperature distribution of the refractive index and the method of maximizing the recording density while using the laser of the current wavelength as in the MSR of the magneto-optical disk. Is being sought.

A RAM disk such as a phase-change disk or a magneto-optical disk uses light of the same wavelength when writing and reproducing information, whereas a ROM disk in which information is recorded in advance has a short wavelength. Pits are formed by using a gas laser having a wavelength. From the viewpoint of the RAM disk, the ROM disk has the same reproduction condition, but is, so to speak, like writing information by light that can be used in the future, and RA in terms of writing information at high density.
The M disc is a disadvantage. Therefore, even in the DVD standard, which is drawing attention as a next-generation home video recording medium, the recording capacity of a full-ROM disc is the same as that of the R-type.
It is in a situation where there is no plan to support it with an AM disc.

The land-and-groove recording is an attractive technique for developing a high-density optical recording medium because the recording density can be doubled with the same linear recording density and the same track pitch. In particular, most of the RAM disks currently in use carry out land recording or groove recording on a substrate on which grooves have been previously formed, and it is desired that recording can be performed on both.

[0006]

By narrowing the track pitch, there is a problem of cross-erasure in which adjacent data signals are mixed in the output signal during reproduction, and cross-erasing in which adjacent data is rewritten during writing. Become. In land recording or groove recording, since there are grooves or lands between lands or between lands and there is a gap between areas where information is written, crosstalk and cross erase can be suppressed.

However, in the land & groove recording, since the information recording areas are adjacent to each other, there is a great influence on the recording / reproducing characteristics of crosstalk and cross erase. Japanese Unexamined Patent Publication (Kokai) No. 5-62250 provides means for optically suppressing crosstalk by defining the groove depth to an integral multiple of ¼ wavelength. Using this method, 0
Since the second-order and first-order diffracted lights cancel each other out, the push-pull method cannot be used as a tracking means, and the amount of light reflected from the recording medium and reaching the photodetector is reduced. is there.

Proc. Int. Symposium
Optical Memory '91, PP. 413
-416 (1991), a method of reducing crosstalk by providing a metal guide band between recording areas has been proposed, but it is difficult to manufacture a substrate at low cost.

In the current land recording or groove recording, the step difference between the land portion and the groove portion is 100 nm at most.
Since the depth is about the same, it is not sufficient to prevent heat diffusion when writing information at a high temperature with a focused laser beam such as a phase change type disc or a magneto-optical disc. Therefore, it is difficult to reduce the cross erase even if the crosstalk is suppressed by the above method.

Therefore, an object of the present invention is to reduce crosstalk in which adjacent data signals are mixed in the output signals during reproduction,
Another object of the present invention is to provide an optical recording medium for land & groove recording and an optical information detection device that reduce cross erase that rewrites adjacent data at the time of writing.

[0011]

According to the present invention, in an optical recording medium capable of land-and-groove recording, the groove depth, that is, the step between land and groove is made larger than both the land width and the groove width. In particular, an optical recording medium characterized in that the groove depth is larger than the focal depth determined by the objective lens, and the groove depth is smaller than the pull-in range of the focus signal, and the signal recorded on the optical recording medium described above. An optical information detecting device used for reproduction is composed of a lens and an optical information detecting device in which a spatial frequency filter consisting of a pinhole or a slit is arranged at a position before or after incidence of an optical signal detecting optical system.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In land and groove recording,
By making the groove depth larger than both the land width and the groove width, the landing portion and the groove portion have different focusing positions. As a result, the defocus in the groove or land adjacent to the land or groove that collects the laser light increases, and crosstalk is optically reduced. Due to the above-mentioned defocus, the temperature rise due to the absorption of the laser beam in the adjacent land or groove is suppressed, and the large distance between the land and the groove in the depth direction suppresses the diffusion of heat. Erase can be prevented.

Further, by setting the groove depth to be within the focusing pull-in range above the depth of focus determined by the objective lens of the optical information detecting device used for reproducing the signal recorded on the optical recording medium, the land portion is formed. It is possible to clearly distinguish the focus positions of the groove part and the groove part, and to easily focus on each part.

By making the groove depth equal to or larger than the focal depth, the geometrical optical difference between the land and the groove becomes large when the laser light is focused. When light is incident from the substrate side and condensed on the land portion, the kick of the light by the groove becomes large. Therefore, by making the land width larger than the groove width, the influence of kicking by the groove can be reduced.

By disposing a spatial frequency filter composed of a converging lens and a pinhole or a slit in the optical information detecting device, it is possible to remove the reflected light from the adjacent land or groove which is largely deviated from the focal point, so that crosstalk is reduced To be done.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical recording medium and an optical information detecting device according to embodiments of the present invention will be described in detail below with reference to the drawings. In the present embodiment, a case where a magneto-optical disk is used as an optical recording medium will be described, but the same effect can be obtained even with a phase change type disk or the like as the optical recording medium capable of land and groove recording according to the present invention. .

FIG. 1 is a schematic view showing a cross section of an optical disk substrate used in the present invention and a condensed state of light used for recording and reproduction. The lands 1 and the grooves 2 are alternately formed while having a groove depth 3, a land width 4, and a groove width 5. The laser light represented by the geometrical optical beam 6 has a finite wave-optically finite size when condensed and has a beam waist 7. The depth of focus 8 is the distance from the portion where the divergence of the geometrical optics beam and the divergence of the wave optics beam are of the same order to the beam waist 7.

In this example, a 1.2 mm-thick glass substrate was coated with a photoresist to form a high-power Ar film.
The substrate is spirally exposed using a laser and then subjected to a development treatment, which is used as a substrate. As the substrate, a stamper is prepared and injection-molded with polycarbonate or polymethylmethacrylate, or a product molded by the 2P method is used in the present invention, like a normal compact disc or laser disc. This effect can be obtained.

By exposing and developing as described above, a glass substrate having lands and grooves is formed.
A magneto-optical recording film having a four-layer structure of dielectric layer / magnetic recording layer / dielectric layer / metal reflective layer was formed by a sputtering method. The magnetic recording film has a good perpendicular magnetic anisotropy of about 8 kOe at room temperature and a Curie temperature of about 200 ° C.
An amorphous alloy thin film composed of a transition metal and a rare earth metal is used.

FIG. 2 is a schematic diagram of an optical information detecting device according to an embodiment of the present invention. The above magneto-optical disk 10 is rotated using the spindle motor 9. Light emitted from the semiconductor laser 11 having a wavelength of 680 nm is focused on the magneto-optical disk 10 by the objective lens 14 having a numerical aperture of 0.55 via the collimator lens 12 and the polarization beam splitter (PBS) 13. The light reflected from the magneto-optical disk 10 passes through the PBSs 13 and 15, one of which is focused on the four-division photodiode 18 by the converging lens 17 via the cylindrical lens 16. Focusing is performed by the astigmatism method and tracking is performed by the push-pull method using the signals obtained from the four-division photo detector. The other light passing through the PBS passes through the spatial frequency filter 22 composed of the converging lenses 19 and 21 and the pinhole 20,
Converging lens 2 via half-wave plate 23 and PBS 24
The light beams 5 and 26 are focused on photodetectors 27 and 28 for detecting the magneto-optical signal. The signal writing is performed by the magnetic field modulation method using the floating magnetic head 29.

Table 1 shows parameters indicating the groove shape of the optical disk substrate used in the examples of the present invention. The track pitch was 1.4 μm in all cases. The groove depth is
It was adjusted by the thickness of the photoresist applied to the glass substrate. The duty of the land and groove width was adjusted by changing the beam profile of the Ar laser by changing the diaphragm of the exposure device. The groove shape was examined by breaking the optical disc after the measurement and observing the cross section with a scanning electron microscope.

The depth of focus Z is the numerical aperture (N
From A) and the wavelength λ of the light used, Z≈λ / (2 × NA
Given in ² ). In this embodiment, λ = 680 nm, N
Since A = 0.55, Z≈1.1 μm. In the embodiment, the condition of claim 2 is satisfied. In addition, the pull-in range of the recording surface detection signal in this embodiment is about 10 μm.
m.

Table 2 shows the values of crosstalk and cross erase measured in the magneto-optical disk of this embodiment without using the spatial frequency filter 22. The amount of crosstalk is such that the data in five adjacent lands or grooves is erased using a constant magnetic field and laser light, and then a mark with a mark length of 0.8 μm is recorded on the central land or groove by the magnetic field modulation method. Then, after measuring the carrier level C _CENTER , the land or groove on both sides adjacent to each other is reproduced, and the higher one of the measured carrier levels is set as C _MAX , and the crosstalk is determined.
C _CROSS = C _MAX -C _CENTER was _calculated . The crosstalk amount was measured for each of the land and the groove, and the one having the larger value including the sign is shown in Table 2. Writing recording power C _CENTER measures the write power dependence of C _CENTER, was set to a power P _S whose value is saturated.

The cross erase amount is obtained by first erasing the data in three adjacent land or groove areas, recording a mark having a mark length of 0.8 μm on the central land or groove under the same conditions as the crosstalk, and determining the carrier level C
After measuring the _A, the adjacent sides of the land or groove, after the data erase operation with laser light having a constant magnetic field and intensity P _S, and measuring the carrier level C _B about the center of the land or groove again Then, the cross erase amount C _E = C _B −C _A was obtained. The cross erase amount was measured for each of the land and the groove, and the one with the smaller value including the sign is shown in Table 2.

[0025]

[Table 1]

[0026]

[Table 2]

From the measurement results of crosstalk and cross erase in Table 2, it can be seen that the effect of reducing cross talk and cross erase according to claim 1 of the present invention is great. The difference in the amount of crosstalk between the first and third embodiments is defined by claim 2.
The depth of the groove is deeper than the depth of focus, which clearly distinguishes the focal positions of the land and the groove, indicating that almost no signal is read from the adjacent land or groove area. ing. Further, as described in claim 4, since the groove depth is within the pull-in range of the focus, it is easy to track to the land and the groove respectively, and the focusing state is maintained even if the track jump is performed. Be drunk

[0028]

[Table 3]

Table 3 shows the improvement in the amount of crosstalk when the spatial frequency filter is arranged as described in claim 5 in the optical information detecting device according to the embodiment of the present invention. In each case where the light is focused on the land or the groove, the center carrier C _{CE NTER} does not change C
Pinhole 20 in Figure 2 to minimize _CROSS
The position was adjusted and the measurement was performed. It was confirmed that the spatial frequency filter has an effect of reducing crosstalk by 3 dB. The same effect can be obtained even if the pinhole 20 is a slit.

In the second embodiment, the land has a smaller amount of light that reaches the photodetector of the magneto-optical signal by being reflected compared to the groove, so that the carrier level is 0.5 dB.
It is low and the noise level is high by 1 dB. When the surface roughness of the land part and the groove part was examined using a scanning tunneling electron microscope, the land part had a larger surface roughness than the groove part. Therefore, as described in claim 3, in Example 3, when the land width was made larger than the groove width, there was almost no difference in crosstalk and cross erase, but the C / N in the land portion was improved. did. When the recording / reproducing characteristics of a 1-7 modulated random signal having a shortest mark length of 0.48 μm were examined using the magneto-optical disk of Example 3, a jitter characteristic of 10% or less was obtained in both the land and the groove. Was given.

[0031]

According to the optical recording medium capable of land-groove according to the present invention, by making the groove depth larger than the land width groove width, it is possible to condense light at the land portion and the groove portion. , Since the difference in the focal position becomes large, the focused lands or grooves are out of focus in the adjacent grooves or lands.
Crosstalk is significantly reduced. Further, due to the defocusing, the temperature rise in the adjacent region due to the light absorption is small, so that the cross erase is significantly improved. Further, since the distance between the adjacent land and the groove in the depth direction is larger than the distance in the horizontal direction, crosstalk due to heat diffusion to the adjacent region can be suppressed.

As described in claim 2, by making the groove depth deeper than the focal depth of the optical system, the focal positions of the land portion and the groove portion are clearly separated by geometrical optics. The effect of reducing crosstalk and cross erase described above is enhanced.

As described in claim 3, by making the land width larger than the groove width, when the light is focused on the land portion, the reproduction output is lowered due to the geometrical optical kick of the light by the groove. Can be improved. It also has an effect of improving the influence of noise in the land portion due to the mastering of the substrate.

By setting the groove depth within the range of the focus pull-in signal, it is possible to easily focus on each land or groove.

As described in claim 5, light is reproduced by reproducing the information of the above-mentioned optical recording medium by using the optical information detecting device in which the spatial frequency filter including the converging lens and the pinhole or the slit is arranged. Light reflected from the groove surface or land surface adjacent to the focused land or groove is cut by the above-mentioned spatial frequency filter, so that crosstalk is reduced.

According to the present invention, an optical recording medium having small crosstalk and cross erase and capable of land and groove recording can be manufactured in the same process as the conventional process without elaborating complicated means. Further, the crosstalk of the above-mentioned optical recording medium can be greatly improved only by disposing the condenser lens and the pinhole or the slit in the optical information detecting device. In adjusting the optical system, the pinholes or slits may be arranged at positions conjugate with the light converging surface of the recording medium, so that there is almost no problem in cost for manufacturing the drive.

In the optical recording medium and the optical information detecting device according to the present invention, when recording / reproducing of the magneto-optical recording medium is performed by using the magnetic field modulation method, the track pitch is 1.4 μm, which is almost the same as the 3.5-inch ISO standard 230 MB. In land-groove recording, a jitter value of 10% or less can be obtained by the 1-7 modulation method with the shortest mark length of 0.48 μm.
The effect that a magneto-optical disk having a recording capacity of about 1.5 GB, which is more than twice that of the O standard 640 MB magneto-optical disk, can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a relationship between a cross section of a substrate of an optical disc according to the present invention and a condensed light beam.

FIG. 2 is a schematic diagram showing an arrangement configuration of an optical information detection device according to the present invention.

[Explanation of symbols]

 1. Land 2. Groove 3. Groove depth 4. Land width 5. Groove width 6. Ray 7. Beam waist 8. Depth of focus 9. Spindle motor 10. Magneto-optical disk 11. Semiconductor laser 12. Collimator lens 13. Polarizing beam splitter (PBS) 14. Objective lens 15. PBS 16. Cylindrical lens 17. Converging lens 18.4 split photo detector 19. Converging lens 20. Pinhole 21. Converging lens 22. Spatial frequency filter 23.1 / 2 wave plate 24. PBS 25. Converging lens 26. Converging lens 27. Photo detector 28. Photo detector 29. Levitation magnetic head

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tomoaki Hara 3-78 Ina-cho, Kita-Adachi-gun, Saitama Kato Heights 306 (72) Inventor Kenji Morita 1-2 1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Tube Within the corporation

Claims (5)

[Claims] 1. An optical recording medium having a pair of spiral grooves and lands that serve as guide tracks on a substrate, wherein the step between the grooves and lands is larger than the width of any of the grooves and lands. Characteristic optical recording medium. 2. The step of the groove and land is larger than the depth of focus determined by the reproducing objective lens of the optical information detecting device used for reproducing the signal recorded on the optical recording medium. Item 2. The optical recording medium according to item 1. 3. The optical recording medium according to claim 1, wherein the land width is larger than the groove width. 4. An optical information detecting device for reproducing a signal recorded on the optical recording medium, wherein the pull-in range of the recording surface detection signal is larger than the step between the groove and the land. apparatus. 5. The optical information detection device as described above, wherein a spatial frequency filter including a converging lens and a pinhole or a slit is arranged at a position before or after incidence in the optical signal detection optical system. apparatus.