JPH0831015A - Optical information recording medium and optical information recording / reproducing apparatus - Google Patents

Abstract

PURPOSE:To linearize the nonlinear reproduction characteristics generated when phase pits are formed in proximity to each other according to increase in density. CONSTITUTION:The plural phase pits varying in depth are used and are provided with an optical phase difference between the adjacent pits 10 and 11, thereby the pits are made into the linear system of a reproduced signal level increasing monotonously with an increase in the number of the pits included within a light spot. Then, the application of linear signal processing is possible even with the phase pits and, therefore, the formation of the pits in proximity to each other is made possible and the higher densities are attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium such as an optical disk and an optical information recording / reproducing apparatus, and particularly to reproducing information recorded at a high density so that intersymbol interference between adjacent data occurs during reproduction. Therefore, the present invention relates to an optical information recording medium and an optical information recording / reproducing apparatus suitable for applying signal processing such as waveform equalization or partial response.

[0002]

2. Description of the Related Art An optical disc records image information, audio information, digital data, or the like as recording marks, that is, an array of recording magnetic domains or pits, and irradiates a reproducing light to the reflected light detection signal modulated by the recording marks. It demodulates and reproduces data.

For example, as shown in FIG. 7, an optical information recording medium for storing data in pits has a pit 31 having a diameter of about 0.4 μm on a transparent substrate 30 such as polycarbonate.
Are formed with a track pitch of about 1.2 μm, and an aluminum film is formed thereon as the reflection film 32. The pit 31 has a constant depth, and is set to a depth of λ / 6 to λ / 4 with respect to the light source wavelength λ in order to obtain a large reproduction signal amplitude. When a laser beam having a wavelength of 680 nm is used as the light source, the pit depth is about 0.1 μm. As shown in FIG. 7, the light source 33 and the beam splitter 3
4. In the reflection system using the optical head 36 including the photodetector 35, this depth corresponds to an optical phase difference of 2π / 3 to π. Here, the optical phase difference can be mainly expressed by the phase difference between the reflected light from the pit portion in the spot and the reflected light from other portions.

In an optical disc, if the distance between marks is reduced to increase the recording density, intersymbol interference between adjacent data occurs, and errors during data reproduction increase. As a method for solving this, there are two signal processing approaches. One is a waveform equalization process that reduces intersymbol interference between adjacent data, and the other is a partial response method that positively utilizes intersymbol interference.

Waveform equalization processing is performed, for example, as described in "Digital Video Recording Technology", page 59, published by Nikkan Kogyo Shimbun, written by Eto, Mita, Doi. The signal of adjacent data point is weighted and added to the signal of (1) to remove the inter-waveform interference from the adjacent mark and detect the signal of high S / N.

Further, the partial response and the multilevel recording method are described in, for example, the Institute of Electronics, Information and Communication Engineers, Vol.
J70-C, No. 3, Osawa, Okamoto, Tasaki As described in “Performance comparison of signal detection methods for multilevel recording code”, the reproduction signal level is multileveled by reducing the data interval more than the resolution of the reproduction signal system. In addition, the multilevel is set by changing the length, width or depth of the recording mark in multiple steps.

[0007]

It is desirable that the response characteristics of the reproduced signals are such that the reproduced signals are superposed. Linearity is established when differential detection is performed in a magneto-optical recording medium, but other media, especially R
Since the phase pit medium, which is a medium for OM, is reproduced by utilizing the diffraction phenomenon of light, there is a problem that the linearity is not established and the signal cannot be reproduced when the density is increased.

FIG. 8 shows a reproduced signal waveform obtained when an isolated recording pit 2 is scanned with a light spot.
The presence of the phase pit 2 reduces the amount of reflected light, and the minimum level of the reproduced signal waveform 3 becomes the signal level 4. However, when the pits come close to each other, the reproduction signal level becomes lower than that when the isolated phase pit is scanned. In Figure 9,
The change in the signal level 4 with respect to the ratio of the mark 2 occupying the light spot 1 is shown. The level 5 of the reproduction signal for the phase pit and the level 6 of the differential detection signal in the magneto-optical medium are shown for comparison. When the marks come close to each other, the signal level of the magneto-optical signal increases in proportion to the increase in the area occupied by the mark.
This indicates that the reproduction signal characteristic is linear. on the other hand,
In the phase pit medium, the reproduction signal level becomes saturated and further decreases. This is a non-linear reproduction characteristic, which is unsuitable for linear signal processing, and the above-described signal processing for increasing the density cannot be applied.

An object of the present invention is to provide an optical information recording medium and an optical information recording / reproducing apparatus which can solve the above problems in a phase pit medium and can effectively apply signal processing for high density.

[0010]

As shown in FIG. 8, when only one phase pit 2 is included in the light spot 1,
The reflected light of the pit portion and the reflected light of the other portion cancel each other out due to the interference due to the phase difference, and as a result, the amount of reflected light is reduced, and the reproduction signal level greatly changes. However, FIG.
As shown in 0 (a), the pits are close to each other and the light spot 1
When about 2 pits 2 are included in the inside,
Adjacent pits 2, 2'as schematically shown in the sectional view of (b)
Since there is no optical phase difference between them, the reflected light 37, 40 on the reflective layer on the substrate surface and the reflected light 3 by the pits 2, 2 '
Since 8 and 39 have a phase difference, they interfere and cancel each other.
There is no cancellation of the light intensity due to interference between the reflected lights 38 and 39 reflected by the pit 2 and the pit 2 ', and a change in the signal level cannot be obtained. That is, the reproduction signal waveform changes from the waveform for the magneto-optical recording medium such that the reproduction signals are superposed as indicated by the broken line to the waveform for the solid line,
The playback signal level drops. This is the cause of the nonlinear reproduction characteristics of the phase pit medium shown in FIG.

According to the present invention, a plurality of phase pits having different depths are used and an optical phase difference is provided between adjacent pits, so that the reproduction signal characteristic is increased as the number of pits included in the light spot increases. Achieves the above-mentioned object by using a linear system in which C increases monotonically. That is, the optical information recording medium according to the present invention has a region on which information is recorded as an array of phase pits on a transparent substrate provided with a reflective film, and scans a light spot of a light source wavelength λ emitted from the transparent substrate side to scan the phase pits. In an optical information recording medium that reproduces information by detecting changes in reflected light due to columns, the minimum interval between adjacent phase pits is approximately half the light spot diameter, and phase pits are multiple types of phase pits with different depths. The depth of each phase pit is such that when the array of phase pits is scanned with a light spot, the signal intensity obtained for each pit is such that the difference between the level of light reflected from the reflective film and the level of light shielding is 100%. It is characterized in that it is set to be 50% or more of the signal level.

The phase pits have different depths from the first and second phases.
The optical phase difference between the light reflected by the reflective film of the transparent substrate and the light reflected by the first phase pit is the position of the light reflected by the first phase pit and the light reflected by the second phase pit. It is preferable that the difference is substantially equal to the phase difference. The optical phase difference with respect to the unrecorded portion having the adjacent phase pitch at the shortest distance is π / 2 and 3π / 2, 4π / 3 and 8π / 3, and 2π / 3.
And 4π / 3 are desirable. However, practically π / 2 ± π
/ 40 and 3π / 2 ± π / 40, 4π / 3 ± π / 40 and 8
π / 3 ± π / 40, 2π / 3 ± π / 40 and 4π / 3 ± π
It can be / 40.

The optical information recording medium has a guide groove having irregular periodicity in the radial direction, the land interval is substantially equal to the spot diameter, and the widths of the groove portion and the groove portion are substantially equal.
It can be of the groove type. When the refractive index of the transparent substrate is N, the depth of the groove portion is approximately λ / (6 ×
N), and the depth of the phase pits provided in the groove portion and the inter-groove portion is preferably approximately λ / (6 × N).

Further, an optical information recording / reproducing apparatus according to the present invention, the optical information recording medium, a means for driving the optical information recording medium, a light spot is emitted from the transparent substrate side of the optical information recording medium, and reflected light is received. And an optical head driving means for driving the optical head with respect to the optical information recording medium, and means for performing equalization processing or multi-valued processing on a light reception signal by the optical head.

[0015]

By using a plurality of phase pits having different depths without making the depths of the phase pits constant, an optical phase difference is generated between the light reflected by the adjacent pits. Therefore, interference also occurs between the light reflected by the adjacent pits, and the reproduction light intensity decreases. Therefore, the reproduction signal characteristic is substantially linear as the reproduction signal level monotonically increases as the number of pits included in the light spot increases. It becomes a system. Since the reproduced signal characteristic is a substantially linear system, signal processing such as waveform equalization can be applied, and high recording density can be achieved.

Since the depth of each phase pit is set so that the signal intensity obtained for each pit when the array of phase pits is scanned with a light spot is 50% or more of the reproduction signal level, the error rate is increased. S / N having a reliability of 10 ^-4 or less was obtained. Phase pit with different depth 1st
And the second phase pit, and the optical phase difference between the light reflected on the surface of the transparent substrate and the light reflected by the first phase pit is reflected by the light reflected by the first phase pit and the light reflected by the second phase pit. If the phase difference of the light is substantially equal to the reproduction signal detection level, the slice level and the like for obtaining the binarized data can be easily set.

When the optical information recording medium is a land-groove type, the depth of the groove portion is approximately λ / (6 × N), and the depth of the phase pits provided in the groove portion and the groove portion is approximately If λ / (6 × N), R due to land and groove
Crosstalk between adjacent tracks in the AM data section can be reduced, linear signal processing between phase pits between adjacent tracks is possible, and high S / N reproduction is possible. Individual pit signals can be detected separately by subjecting the reproduced signal to equalization processing or multilevel processing.

[0018]

EXAMPLES The present invention will be described in detail below with reference to examples. [Embodiment 1] FIG. 1 shows a sectional structure of an optical disk ROM (read only memory) using phase pits having a plurality of depths according to the present invention. FIG. 1A is a sectional view, FIG.
(B) is a plan view.

The optical disk has a structure in which an aluminum film 8 is sputtered as a reflective film on a disk substrate 7 made of polycarbonate (refractive index N = 1.5) in which phase pits 10 and 11 corresponding to information are formed by a known injection method. Have. The phase pits are arranged on the two-dimensional lattice points 12. Each pit has a diameter of 0.25 μm, the track pitch is 0.45 μm, and the lattice point spacing in the track direction is 0.30 μm. The phase pits 10 and 11 adjacent to each other at the closest distance have different depths, and the reflected light reflected by these pits has an optical phase difference. In addition to this,
As shown in (a), a laser beam having a wavelength of 630 nm is irradiated from the side of the substrate 7 by the focusing lens 9 as a light spot having a diameter of 1.0 μm and scanning is performed. Then, the change of the reflected light modulated by the presence or absence of the pit is converted into an electric signal to reproduce the data.

As shown in FIG. 2, the depth of the phase pit is (1/8) λ and (3/8) λ with respect to the wavelength λ (630 nm) of the reproduction light, that is, 52.5 nm and 157.5 n.
There are two types, m, and the depth between the adjacent phase pits 41 and 42 is different. By changing the depth of the adjacent phase pits, as shown in the cross-sectional view of FIG. 2B, the reflected light 13 and 16 at the reflection layer on the substrate surface and the phase of depth (1/8) λ Light reflected by pit 41, and depth (3/8) λ
Since the reflected light 15 due to the phase pit 42 of FIG. 2 can have an optical phase difference, the reproduced signal waveform is as shown in FIG.
As indicated by the solid line in (c), the reproduced signal level does not saturate or fall even when the pits are moved closer to each other.
Therefore, even in the case of recording by the phase pits, it is possible to obtain a substantially linear characteristic like the differential detection reproduction characteristic in the magneto-optical medium of FIG.

Individual pits recorded at high density can be detected separately from each other by performing the signal processing described in JP-A-5-44875 and JP-A-5-253960. FIG. 11 shows an example of a two-dimensional equalization processing circuit. Three spots are positioned on three adjacent tracks, and the center spot 2 is the target track. At this time, the signal leak from the adjacent track is detected from the spots 1 and 3. The detection signals from the spots 2 and 3 are delayed by the delay circuits 51 and 52 by τ and 2τ, respectively, and added by the adder 53. At this time, the signals from the spots 1 and 3 scanning the adjacent tracks are multiplied by a weighting coefficient β of 1 or less. The time constant τ is set to correct the deviation of each spot in the circumferential direction. Also, regarding the signal obtained from spot 2,
In order to detect the leak of the adjacent data in the track direction, the delay circuits 54 to 57 use the lattice point intervals ± T and ± 2.
Output the signal from T and weight each signal α, α ² Are added and added by the adder 58 to obtain an EQ signal from which the inter-waveform interference is removed.

Next, optimization of the phase pit depth will be described with reference to FIG. FIG. 3 shows the reproduction signal level with respect to the optical phase difference of the phase pits with respect to the reflective layer. The conditions for optimization are adjacent portions included in the light spot without significantly reducing the absolute value of the reproduction signal level, in FIG. 2, reflected light 13 and 14, reflected light 14 and 15,
The optical phase difference between the reflected lights 15 and 16 is substantially the same, or the optical phase difference between at least two reflected lights is substantially the same. This is because when these optical phase differences are substantially equal to each other, or when the optical phase differences between at least two reflected lights are substantially equal to each other, the reproduction signal detection level does not fluctuate, so that the slice level for obtaining the binarized data is obtained. This is because it becomes easy to set such as. Further, the reproduction signal level is preferably 0.5 or more in order to secure the S / N which realizes an error rate of 10 ^-4 or less.

As a combination of two types of phase pits satisfying such conditions, three combinations of a circle white blank mark, a triangle white blank mark and a square white blank mark shown in FIG. 3 are effective. These phase differences are caused by the phase pit depths of λ / (3N) and 2λ / (3N), λ / (8N) and 3λ / (8N), and λ / (6N) and λ / (3N) in the reflection system. ) Corresponds to. However, the refractive index of the substrate is N. Since light is actually incident through the substrate, the combination of phase pit depths is λ / (3N) ± λ / (90N) and 2λ / (3N) ±.
λ / (90N), λ / (8N) ± λ / (90N) and 3λ
/ (8N) ± λ / (90N), λ / (6N) ± λ / (9
0N) and λ / (3N) ± λ / (90N) are effective.

Further, in the above-mentioned embodiment, there are two kinds of the depth of the phase pit, but if the reproduction signal level can satisfy 50% or more, the pits of three or more kinds of depth are used. Good.

[Embodiment 2] Next, an embodiment in which the phase pit recording of the present invention is applied to a land groove structure will be described. As shown in FIG. 4, the land-groove structure is provided with grooves having a period substantially equal to the diameter of the light spot 1, the data area 17 is assigned to both the inter-groove portion and the groove portion as an information track, and marks 27 are recorded to achieve high density. This is a system for recording / reproducing (see Japanese Patent Laid-Open No. 5-28275).

In this case, the problematic crosstalk between adjacent tracks can be reduced by setting the groove depth to λ / 6. However, this crosstalk reducing effect is applicable to phase change recording and magneto-optical recording, but is not applicable to the phase pit 24. Therefore, Japanese Patent Laid-Open No. 5-
According to the publication No. 282705, as shown in FIG. 4, the inter-groove address portion 18 and the groove address portion 19 are separated in the track direction so that crosstalk does not occur. However, the format efficiency is reduced by the amount of separation of both address portions 18 and 19 in the track direction, and high density cannot be achieved. Further, not only the address portion but also the ROM portion for recording information using the phase pits causes the same problem.

On the other hand, in this embodiment, as shown in FIG. 5, the inter-groove portion and the groove portion are commonly used for the address area 20 formed of the phase pits, so that the density is increased. At that time, an optical phase difference is provided between the adjacent pits 25 and 26 as in the first embodiment. However, it is necessary to keep the groove depth 23 at approximately λ / 6 depending on the crosstalk reducing groove structure condition of the data area 17 in which the recording mark 21 is recorded by phase change recording or magneto-optical recording. Therefore, as shown in the enlarged view of the address area in FIG. 6, the inter-groove phase pit depth 21 and the groove phase pit depth 2
2 may both be λ / 6, and practically λ / 6 ± λ / 24. As a result, the difference in depth between the parts is approximately λ /
6, λ / 3, that is, approximately 2π / 3 as the optical phase difference
4π / 3, which corresponds to the phase difference shown by the white square marks in FIG. 3, the same signal level can be obtained, and a linear characteristic can be obtained.

The distance between the land portion and the groove portion is 0.5 μm
As shown in FIG. 5, a diameter of 0.25 μm is formed in the adjacent land portion and groove portion of the optical recording medium having the land-groove structure.
An address portion was formed by using the phase pits 26 having a depth of 70 nm, the reproduction was performed with the laser light 1 having a wavelength of 630 nm which was narrowed down to a spot diameter of 1.0 μm, and an equalization process was performed in the same manner as in the above-described example, and good reproduction was performed. The signal was obtained.

[0029]

Since the reproduction signal characteristics of the phase pits used in the ROM disk or the pre-header portion can be substantially linearized, the equalization process which is a linear signal process and the high density achieved by applying the partial response method are the phase pits. It is also possible to record.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a phase pit medium according to the present invention.

FIG. 2 is an explanatory diagram of a reproduced signal waveform by the phase pit medium of the present invention.

FIG. 3 is an explanatory diagram of a phase difference between adjacent marks and a reproduction signal level.

FIG. 4 is a schematic view of a land groove structure.

FIG. 5 is an explanatory diagram of a disk structure according to a second embodiment of the present invention.

6 is an enlarged view of the pit portion of FIG.

FIG. 7 is a schematic cross-sectional view of a conventional phase pit medium.

FIG. 8 shows a reproduced signal waveform for an isolated phase pit.

FIG. 9 is an explanatory diagram of reproduction signal characteristics for each medium.

FIG. 10 is a diagram for explaining a decrease in reproduction signal level in a conventional phase pit medium.

FIG. 11 is an explanatory diagram of a two-dimensional equalization processing circuit.

[Explanation of symbols]

1 ... light spot, 2 ... phase pit, 3 ... reproduction signal, 4 ...
Reproduction signal level, 10, 11 ... Phase pit, 12 ... Lattice point, 13-16 ... Reflected light, 21 ... Inter-groove phase pit depth, 22 ... Groove phase pit depth, 23 ... Groove depth, 24,
25, 26 ... Phase pits, 27 ... Marks, 30 ... Transparent substrate, 31 ... Pits, 32 ... Reflective film, 33 ... Light source, 34 ...
Beam splitter, 35 ... Photodetector, 36 ... Optical head,
37-40 ... Reflected light, 51, 52, 54-57 ... Delay circuit, 53, 58 ... Adder

Claims (11)

[Claims] 1. A reflected light by the phase pit row having a region on which information is recorded as an array of phase pits on a transparent substrate provided with a reflective film, scanning a light spot of a light source wavelength λ irradiated from the transparent substrate side. In an optical information recording medium that reproduces information by detecting a change in the phase difference, the minimum interval between adjacent phase pits is approximately half the diameter of the light spot, and the phase pits consist of multiple types of phase pits with different depths. The depth of each phase pit is such that the signal intensity obtained for each pit when the array of phase pits is scanned with the light spot is such that the difference between the reflected light level from the reflective film and the light shield level is 100%. An optical information recording medium, which is set to be 50% or more of a signal level. 2. The phase pits are composed of first and second phase pits having different depths, and the optical phase difference between the light reflected by the reflective film of the transparent substrate and the light reflected by the first phase pits is different from each other. 2. The optical information recording medium according to claim 1, wherein the phase difference between the light reflected by the first phase pit and the light reflected by the second phase pit is substantially equal. 3. The optical phase difference between the unrecorded portions of the phase pits adjacent to each other at the shortest distance is about π / 2 and about 3π /, respectively.
The optical information recording medium according to claim 2, wherein the optical information recording medium is 2. 4. The optical phase difference with respect to the unrecorded portion having the adjacent phase pitch at the shortest distance is about 4π / 3 and about 8π, respectively.
3. The optical information recording medium according to claim 2, wherein the optical information recording medium is / 3. 5. The optical phase difference with respect to the unrecorded portion having the adjacent phase pitch at the shortest distance is about 2π / 3 and about 4π, respectively.
The optical information recording medium according to claim 1, wherein the optical information recording medium is / 3. 6. A guide groove having an irregular periodicity in a radial direction, the periodic interval being substantially equal to a spot diameter, and the widths of the groove portion and the inter-groove portion being substantially equal.
The optical information recording medium described. 7. When the refractive index of the transparent substrate is N,
9. The optical information recording medium according to claim 8, wherein the depth of the groove portion is approximately λ / (6 × N). 8. The optical information recording medium according to claim 7, wherein the depth of the phase pits provided in the groove portion and the inter-groove portion is approximately λ / (6 × N). 9. An optical information recording medium according to claim 1, and means for driving the optical information recording medium,
An optical head that irradiates a light spot from the transparent substrate side of the optical information recording medium and receives reflected light, an optical head driving unit that drives the optical head with respect to the optical information recording medium, and a light reception signal by the optical head. An optical information recording / reproducing apparatus comprising: 10. The optical information recording medium according to claim 1, a means for driving the optical information recording medium, and a light spot irradiated and reflected from the transparent substrate side of the optical information recording medium. An optical head comprising: an optical head for receiving light; an optical head driving means for driving the optical head with respect to the optical information recording medium; and a means for multi-value processing a light reception signal from the optical head. Information recording / reproducing apparatus. 11. Information is recorded as an array of phase pits on a transparent substrate having a reflective film, and a light spot of a light source wavelength λ irradiated from the transparent substrate side is scanned to detect a change in reflected light due to the phase pit row. In the optical information recording / reproducing method for reproducing information by doing so, the minimum interval between adjacent phase pits is approximately half of the light spot diameter, and the phase pits have different depths from the first and second.
Optical phase difference between the light reflected on the surface of the transparent substrate and the light reflected by the first phase pit, the light reflected by the first phase pit and the light reflected by the second phase pit. The optical information recording / reproducing method is characterized in that it is substantially equal to the phase difference.