JP3354214B2 - Optical recording medium reproducing method and reproducing apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The method of recording the invention high-density information recording capable optical recording medium BACKGROUND OF THE, a reproducing method and apparatus.

[0002]

2. Description of the Related Art Among recording technologies currently in practical use, an optical recording technology for recording / reproducing by using a laser beam can realize the highest recording density. is there. The recording density in these optical recordings is determined mainly by the diffraction limit of the laser beam, and is approximately 1 bit / μm.
In order to meet the recent demand for large capacity, various studies have been made to further improve the recording density.

One of the promising next-generation ultra-high-density optical memories is a three-dimensional memory. As shown in FIG. 7, a conventional optical memory has two layers on the recording layer 120.
While information is recorded two-dimensionally (planar), information is recorded two-dimensionally (plane) in a three-dimensional memory, as shown in FIG. 8, for a recording layer 120 having a film thickness greater than the focal depth of a laser used. In addition to information recording, information is also recorded in the depth direction of the layer.
With the 00 layer recording, it is possible to easily achieve a recording density 100 times that of the current recording.

[0004] Research reports on such three-dimensional memories are not intended for recording / reproducing when the recording medium is in a disk state. For example, the Optical Alliance Symposium Kyoto '9
2 Proceedings of the Lectures P39-40 and Proceedings of the 40th Lectures on Applied Physics, 29p-B-11 and 29p-B-12.

[0005]

In recording / reproducing an optical disk, focus servo and tracking servo are generally performed in order to accurately record or reproduce a recording mark. In the recording / reproducing of the conventional optical disk as shown in FIG. 7 , the beam 5 for recording / reproducing could be used simultaneously as the beam for focus servo and tracking servo .

[0006] This is because the thickness of the recording layer 120 is smaller than the depth of focus of the beam radiated toward the recording layer 120, and the focus is adjusted to the position of the reflective layer 130 so that the diffraction limit is formed on the recording layer 120. This is because the spot could be irradiated.

On the other hand, in the case of a three-dimensional memory as shown in FIG. 8, the thickness of the recording layer 120 is much larger than the depth of focus. There has been a problem in that defocusing occurs at a part of the recording mark 121 at a distant position, and recording or reproduction cannot be performed.

Also, when the beam is focused on the recording mark 121 itself, light is not reflected on the layer corresponding to the recording mark 121, so that there is a problem that focus servo cannot be executed.

In view of the above-mentioned problems of the prior art, the present invention efficiently irradiates a three-dimensional optical memory having a reflective layer with a beam for focus servo and tracking servo and a beam for reproduction to achieve high-density recording. The purpose is to achieve the reproduction of information .

[0010]

According to the present invention, there is provided a method for reproducing an optical recording medium, comprising the steps of: forming a reflective layer, a recording layer, and a protective layer in this order on an optical recording medium; A first beam for focus servo or tracking servo is focused on the reflective layer surface using an objective lens system, and a second beam for reproduction is focused on a spot of the first beam using the objective lens system. The light was condensed at different points in the depth direction of the recording layer, and the reflected light from the optical recording medium at this light condensing point was condensed so as to pass through a pinhole, and passed through the pinhole. a method of reproducing an optical recording medium for reproducing information multiplexed recording by detecting the reflected light by the light detector, the position in the depth direction of the recording layer of the point where the second beam is condensed Layer selection signal More varied, it is a method for displacing the pinhole in accordance with the changed position.

[0011] As an apparatus for realizing this method,
An optical recording medium, a first light source that emits a beam for focus servo or tracking servo, an objective lens system for converging a first beam from the first light source onto the medium, Means for performing focus servo or tracking servo by detecting reflected light of the first beam, a second light source for emitting a second beam for reproducing information recorded on the medium, and the first and second light sources. Means for synthesizing first and second beams from a light source, first condensing means for converging the first and second beams respectively to different points in a depth direction of the medium, A second condensing means for condensing the reflected light of the second beam from a medium, a pinhole disposed at a condensing point of the reflected light of the second beam by the second condensing means, Pinho A photodetector for detecting the light passing through the Le, varying the layer selection signal the position of the depth direction of the medium point the second beam is condensed by the optical recording medium
Means for converting, and the second signal changed by the layer selection signal.
It is desirable that the apparatus includes means for displacing the pinhole in accordance with the position of the condensing point of the two beams .

[0012]

According to the above method, the optical recording medium 10 shown in FIG.
0, the focus servo beam 6 indicated by a solid line
The focus servo is performed so that the focus is directed to the reflective layer 130 (shown by a solid line in the figure), while the recording / reproducing beam 5 (shown by the broken line in the figure) is applied to the optical recording medium 100 by the same objective lens 4. ) Focuses on a point that is separated from the focus of the servo beam 6 in the depth direction by a distance equal to or greater than the depth of focus.

At this time, a surface wobble occurs with the rotation of the disk (optical recording medium 100). However, the objective lens 4 is displaced by the action of the servo beam 6 in such a manner as to correct the surface wobble, and as a result, the recording is performed. The reproducing beam 5 always focuses on a position in the recording layer in a certain depth direction.
In this way, it is possible to correctly focus on the recording mark 121 located at a position distant from the reflective layer 130.

The servo beam 6 can be used for recording / reproducing with respect to the recording mark 122 located at a position close to the reflection layer 130, similarly to the conventional optical memory.

[0015]

Reproducing method and re EXAMPLES The following optical recording medium of the present invention
Reference examples and examples of the raw device will be described in detail with reference to the drawings.

REFERENCE EXAMPLE FIG. 2 is a block diagram showing an apparatus for realizing a recording / reproducing method for achieving a four-fold increase in density in the depth direction.

In FIG. 1, second to fourth light sources 1102-1 to 110-1
Numeral 104 radiates beams for recording or reproducing information with respect to the three-dimensional memory 100 as an optical recording medium. The first light source 1101 emits a beam for performing a focus servo or a tracking servo.
However, it is also possible to use the radiation beam of the first light source for recording or reproduction.

Numerals 901 to 904 and 801 to 803 denote half mirrors for synthesizing beams emitted from the light sources 1101 to 1104 and for converting the light which has reached the memory 100 and reflected by the photodetector 14.
02 to 1404.

The wavelengths of the radiation beams from the light sources 1101 to 1104 may be the same or different. For example, the wavelength of the radiation beam from the light source 1101 may be different from the wavelength of the radiation beam from the light sources 1102 to 1104. If the half mirror 801 is a dichroic mirror, these beams can be completely separated.

On the other hand, assuming that the wavelengths of the beams are all the same, the beams from the light sources 1102 to 1104 are converted into P-polarized light by the polarization beam splitter 801 using a polarization beam splitter instead of the half mirror 801.
In addition, by setting the beam from the light source 1101 so as to enter as S-polarized light, it is possible to completely separate the beam in the reflected light from the memory 100.

Here, the necessity of increasing the beam separation efficiency in the half mirror 801 is based on the fact that the focus error or tracking error detection system 15 needs to be controlled by the memory 100 using the beams from the light sources 1102 to 1104.
This is because it is possible to prevent the reflected light from entering the device from causing undesirable effects on error detection.

When recording or reproduction is performed with the radiation beam from the light source 1101, the error detection system 15 creates the sum of the outputs from the divided photodetectors (not shown) in the system to generate the reproduction signal SIG1.
Is obtained.

On the other hand, the beams emitted from the light sources 1102 to 1104 are focused by the objective lens 4 at different positions in the recording layer in the depth direction. Here, a method of displacing the focal position will be described with reference to FIGS.

First, in FIG.
A case where the radiation beam from the light source 1100 representing the light sources 2 to 1104 is correctly collimated by the collimator lens 1000 and normally collected by the objective lens 4 is defined as a standard focal position.

On the other hand, when the collimating lens 1000 is slightly displaced in the opposite direction with respect to the light source 1100 as shown in FIG. 3B, the radiation beam becomes slightly more focused light than in the case of FIG. As a result, the beam spot by the objective lens 4 is displaced slightly toward the objective lens 4 from this (a).

Also, by displacing the light source 1100 in a direction slightly away from the collimator lens 1000 as shown in FIG. 3C, the beam spot by the objective lens 4 It can be displaced to the side.

The beam spot displaced in the depth direction of the memory 100 obtained as described above is used for the memory 10.
0 is recorded with information. At the time of reproducing the recorded information, as shown in FIG. 4, a recording signal corresponding to each layer of the recording layer 120 is read out from each beam spot (indicated by a small black circle in the drawing). The problem is how to separate the plurality of beams to be used to reduce the crosstalk between the read signals.

As described in the prior art document described in the section of the prior art, such a problem is disclosed in the photodetector 1 by the lenses 1202 to 1204 in FIG.
When the beams are focused on 402 to 1404, the problem can be solved by providing pinholes 1302 to 130 at corresponding focusing points.

That is, as shown in FIG. 5, the reflected light from the memory 100 has a different divergence angle. Therefore, the reflected light collected by the sensor lens 1202 can efficiently pass through the pinhole 1302 and reach the photodetector 1402 in the case of the beam indicated by the dashed line, but can have another beam having a different divergence angle (indicated by a chain line). ) For pinhole 1
This pinhole 1302 is defocused on 302
Can hardly pass through.

Therefore, each of the photodetectors 1402 to 14
By providing such pinholes 1302 to 1304 on the entire surface of the optical disk 04, unnecessary beams can be efficiently removed from the reproduction light.

In this reference example , the objective lens 4
Is driven by a signal from the servo circuit S during focusing servo or tracking servo to perform focusing or tracking.

Embodiment FIG. 6 shows an optical recording / reproducing apparatus according to an embodiment of the present invention. This apparatus is for recording or reproducing a plurality of layers in the recording layer 120 with a radiation beam from a single recording / reproducing light source 1102. The optical system corresponding to the servo light source 1101 is the same as that shown in FIG.

In the case of this device, a layer selection signal corresponding to each layer of the recording layer 120 on which recording or reproduction is performed is input to the driving circuit A of the actuator 1012, and the actuator 1012 displaces the collimating lens 1002.

As a result, the divergence angle of the recording (or reproducing) beam changes, and the beam is condensed at a desired depth in the recording layer 120 by the operation described with reference to FIG.
A dimensional recording is performed.

At the time of reproduction, a pinhole 1302 is provided to prevent crosstalk due to the servo beam as described above. This pinhole 1302 is also displaced by the driving actuator 1310 according to the layer selection signal.

In this manner, a beam spot for recording or reproduction can be connected to a desired position, so that all the reproduction signals SIG1
To SIG4 can be sequentially obtained.

The switching of the layer selection signal can also be performed by detecting an address signal preformatted on the memory 100 with the servo beam.

Further, as the three-dimensional memory material in the above embodiment, it is needless to say that a photochromic material or the like which reacts nonlinearly can be used in addition to the photopolymer and the photorefractive crystal described in the above-mentioned prior art document.

[0039]

According to the present invention as the above description, it can perform effective focus servo or tracking servo with respect to three-dimensional optical memory medium, further beam for reproduction
When the position of the focal point in the depth direction of the medium changes
The pinhole is displaced accordingly
Makes it possible to remove unnecessary beams efficiently.
Thus, an effect that stable recording of information or reproduction of recorded information can be expected can be expected.

[Brief description of the drawings]

FIG. 1 is a sectional view of a medium for explaining the principle of an optical recording / reproducing method according to the present invention.

FIG. 2 is a block diagram showing a first optical recording / reproducing apparatus.

FIGS. 3A to 3C are main block diagrams illustrating an operation of displacing the focal point of a recording or reproducing beam.

FIG. 4 is a cross-sectional view of a medium showing a state in which a plurality of recording or reproducing beams are focused on a recording layer of the medium.

FIG. 5 is a main block diagram illustrating a means for selecting a recording layer on which a recording or reproducing beam is focused.

FIG. 6 is a block diagram showing a first optical recording / reproducing device.

FIG. 7 is a diagram illustrating a conventional beam focusing state on a two-dimensional memory.

FIG. 8 is a diagram illustrating a state of focusing of a beam on a three-dimensional memory.

[Explanation of symbols]

Reference Signs List 110 transparent substrate or protective layer 120 recording layer 130 reflective layer 121, 122 recording mark 4 objective lens system 5 recording / reproducing beam 6 servo beam 100 three-dimensional optical memory (optical recording medium) 1101-1104 light source 1001-1004 lens 901-904 Half mirror 801 to 803 Half mirror 1202 to 1204 Lens 1402 to 1404 Photodetector 15 Focus error or tracking error detection system 1000 Lens 1100 Light source 1012 Collimating lens 1310 Actuator for pinhole

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-157816 (JP, A) JP-A-4-301226 (JP, A) JP-A-1-188816 (JP, A) JP-A-3-18886 200915 (JP, A) JP-A-61-140914 (JP, A) Sumitomo Hashiguchi "High-sensitivity optical memory, part 2" 100− 101

Claims (2)

(57) [Claims] 1. An optical recording medium formed by laminating a reflective layer, a recording layer, and a protective layer in this order, a first beam for focus servo or tracking servo is applied to the reflective layer using an objective lens system. While focusing on the surface,
A second beam for reproduction is focused on a spot of the first beam at a different point in a depth direction of the recording layer using the objective lens system, and the optical recording at the focused point is performed. A method of reproducing an optical recording medium that collects reflected light from a medium so as to pass through a pinhole, and reproduces multiplex-recorded information by detecting the reflected light passing through the pinhole with a photodetector. The position of the point where the second beam converges in the depth direction of the recording layer is determined by a layer selection signal.
A method for reproducing an optical recording medium, comprising: changing the pinhole according to the changed position . 2. An optical recording medium, a first light source that emits a beam for focus servo or tracking servo,
An objective lens system for converging a first beam from the first light source on the medium, and means for performing focus servo or tracking servo by detecting reflected light of the first beam from the medium; A second light source for emitting a second beam for reproducing information recorded on the medium; a unit for combining first and second beams from the first and second light sources; First condensing means for condensing beams at different points in the depth direction of the medium, and second condensing means for condensing reflected light of the second beam from the medium, respectively. And the second
A pinhole arranged at a condensing point of the reflected light of the second beam by the condensing means, a photodetector for detecting light passing through the pinhole, and the second beam condensed on the optical recording medium Select the position in the depth direction of the medium at the point
Means for changing by a signal, and means for changing by the layer selection signal.
According to the position of the focal point of the second beam
An apparatus for reproducing an optical recording medium, comprising: means for displacing the pinhole.