JPH0963106A - Optical recording and reproducing method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording/reproducing method and a device therefor of a low cost capable of suppressing crosstalk from an adjacent track by simple constitution and improving the track density. SOLUTION: A light beam emitted from a laser 1 is converged through a beam forming part 2, a beam splitter 3 and an objective lens 4, to irradiate an optical recording medium A, its reflected beam is converged by a condenser lens 6, detected by a photodetector 7 and recorded information is reproduced. At this time, by shielding the center part, i.e., a part largely affected by crosstalk from an adjacent track, the crosstalk from the adjacent track is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing method and apparatus using an optical disk or the like.

[0002]

2. Description of the Related Art A conventional optical recording / reproducing method of this type, as disclosed in Japanese Patent Laid-Open No. 1-245433, condenses light emitted from a light source such as a semiconductor laser through an optical system to form a beam. Form a spot, irradiate the recording track on the optical recording medium, guide the reflected light to a photodetector through an optical system, and detect the change in the light intensity and polarization direction of the reflected light, It was intended to reproduce the information recorded on the track.

[0003]

However, in such a conventional method, when the track density is increased, the influence (crosstalk) of the information of the adjacent tracks included in the reflected light beam from the optical recording medium is increased, and the accuracy is increased. It is difficult to improve the track density because the information cannot be reproduced well.

As a method for suppressing the above-mentioned crosstalk and improving the track density, a paper Jp of the Japan Society of Applied Physics has been proposed.
nJAppl.Phys., Volume 32, 1993, High-Density L
and / Groove Recording for Digital Video File Syste
m, p 5449-5450. This is 3
One beam spot is applied to a recording track on an optical recording medium, and a main detection signal and two sub detection signals obtained by these are input to a crosstalk cancel circuit to remove crosstalk and reproduce information. It is a thing.

However, this method requires three light sources such as semiconductor lasers having uniform characteristics in order to form three light beam spots, which is expensive, and the distance between the beam spots results. There is a problem that a complicated reproducing circuit system for compensating for the positional deviation of the detection signal is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical recording / reproducing method and an apparatus therefor capable of suppressing crosstalk from adjacent tracks with a simple structure and improving track density at low cost.

[0007]

In order to solve the above-mentioned problems, the present invention collects light emitted from a light source and irradiates it onto an optical recording medium, and detects reflected light or transmitted light to record information. In the optical recording / reproducing method for reproducing, the central portion of the light beam from the optical recording medium is shielded, and the shielded light beam is detected to reproduce the recorded information.

As a result, the central portion of the light beam, which is greatly affected by the crosstalk from the adjacent tracks, can be removed, and the crosstalk from the adjacent tracks can be suppressed.

If the light-shielding region is sandwiched by two straight lines parallel to the track direction, the change in signal amplitude due to off-focus and off-track can be reduced.

Further, if the boundary line of the light-shielded area is a concentric circle having the same center as the light beam, the central portion of the light beam, which is greatly affected by crosstalk from the adjacent track, can be removed, and the cross from the adjacent track can be removed. Talk can be suppressed, low frequency components in the track direction can be removed, and linear recording density can be improved.

Further, in the optical recording / reproducing apparatus for condensing the light emitted from the light source and irradiating the optical recording medium and detecting the reflected light or the transmitted light to reproduce the recorded information, the light from the optical recording medium is detected. According to the apparatus in which the light shielding element for shielding the central portion of the light beam is arranged in the optical path of the beam, it is only necessary to insert the light shielding element in the conventional apparatus, and low cost and space saving high density recording can be realized. .

Further, according to the arrangement in which the apodizing element is arranged in the optical path for irradiating the optical recording medium with the light emitted from the light source, the light irradiating the optical recording medium can be used as a super-resolution beam spot. As a result, the linear recording density in the track direction can also be improved.

[0013]

1 shows a first embodiment of the present invention, in which 1 is a light source, here is a laser, 2 is a beam shaping unit, 3 is a beam splitter, and 4 is an objective lens. 5, a light shielding element, 6 a condenser lens, 7 a photodetector, A
Is an optical recording medium.

The light shielding element 5 shields the central portion of the reflected light from the optical recording medium A. Here, as shown in FIG. 2, a streamlined light shielding surrounded by two curves of the same curvature on a glass plate. The band 5a is used. The light shielding element 5
Means that the wide surface of the shading band 5a is orthogonal to the beam (axis thereof) direction and the longitudinal direction of the streamline of the shading band 5a is the optical recording medium A.
It is arranged so as to coincide with the upper track direction (beam traveling direction).

In the above structure, the light 11 emitted from the laser 1 is shaped into parallel light by the beam shaping unit 2, the direction is changed by the beam splitter 3, and the light is condensed by the objective lens 4 to form a beam spot 12. , A recording track (not shown) on the optical recording medium A is irradiated. The reflected light 13 from the recording track on the optical recording medium A by the beam spot 12 passes through the objective lens 4 and the beam splitter 3, and reaches the light shielding element 5.

FIG. 3 shows a region where the reflected light 13 is blocked by the light blocking element 5 and a region through which the reflected light 13 passes.
3 is a light-shielding band 5 with respect to the beam traveling direction on the optical recording medium A.
It is divided into a light-shielding area 13a and a passing area 13b in the track width direction with a curved division boundary line according to the shape of a.

The light beam 14 which has passed through the above-mentioned passage region 13b is received by the photodetector 7 through the condenser lens 6,
Converted to electrical (reproduction) signal.

In the above-mentioned reproducing system, the leak signal from the adjacent track on the optical recording medium is distributed to each region in the intensity distribution of the parallel beam on the plane having the light-shielding band which is the Fourier transform surface on the medium. Appear differently. Therefore, by blocking the region containing a large amount of leak signal with a light-shielding band, the influence from an adjacent track can be suppressed and the signal recorded on the medium can be accurately reproduced.

According to the above construction, the Fourier transform of the light lens can be used to suppress the crosstalk from the adjacent tracks, and the data on the optical recording medium A can be reproduced with high accuracy. Moreover, the shielded area of the reflected light is ±
Matches the region where the 1st-order diffracted light and the 0th-order diffracted light overlap,
Since this is the portion where the variation due to crosstalk appears most, it is possible to efficiently reduce the influence of crosstalk from the adjacent track and also to compensate the signal from the target track. Furthermore, crosstalk can be reduced only by inserting a light-shielding element in the conventional reproducing system, and it is possible to realize at low cost and in a small space.

A known quarter-wave plate may be inserted between the beam splitter 3 and the objective lens 4 in order to pass through the beam splitter 3, or a polarization sum splitter may be used as the beam splitter 3. Although omitted here, a well-known method may be used for detecting and controlling the focus signal and tracking signal necessary for actual information reproduction.

FIG. 4 shows a second embodiment of the present invention, in which the apodization element is added to the first embodiment. That is, in the figure, 1 is a laser, 2
Is a beam shaping unit, 3 is a beam splitter, 4 is an objective lens, 5 is a light shielding element, 6 is a condenser lens, 7 is a photodetector, and 8
Is an apodization element, and A is an optical recording medium.

The apodization element 8 changes the intensity distribution of the light 11 emitted from the laser 1 so that the diameter of the beam spot formed on the optical recording medium A becomes small, and more precisely, attenuates the central portion of the light 11. Here, as shown in FIG. 5, a mirror 8a made of a rectangular metal film or the like on a glass plate is used here.
Is used. The apodizing element 8 is
The wide surface of the mirror 8a is arranged so as to be perpendicular to the beam (axis thereof) direction, and the longitudinal direction of the mirror 8a is arranged so as to be perpendicular to the track direction (beam traveling direction) on the optical recording medium A.

In the above structure, the light 11 emitted from the laser 1 is shaped into parallel light by the beam shaping unit 2 and reaches the apodization element 8.

FIG. 6 shows a region of the light 11 shielded by the apodizing element 8 and a region through which the light 11 passes.
Is a mirror 8a with respect to the beam traveling direction on the optical recording medium A.
The light-blocking area 11a and the passing area 11b are divided in the track direction with a linear division boundary line conforming to the shape.

The light 15 that has passed through the above-mentioned passage area 11b
Is changed in direction by the beam splitter 3, and the objective lens 4
The beam spot 16 is formed by being condensed by the laser beam and is irradiated onto a recording track (not shown) on the optical recording medium A.

At this time, as shown in FIG. 7, the beam spot 16 is a super-resolution spot in which the width of the central main lobe is narrow and the side lobe is large in the traveling direction of the light beam as compared with the case without the apodizing element. Becomes This allows
The high frequency component of the reproduction signal is emphasized, and the information recorded with higher linear density can be reproduced.

The reflected light 17 from the recording track on the optical recording medium A by the above-mentioned beam spot 16 passes through the objective lens 4 and the beam splitter 3, and further the light shielding element 5 is provided.
Passing through the adjacent tracks to form a light beam 18 with reduced crosstalk, and passing through the condenser lens 6 to the photodetector 7
The light is received by and is converted into an electric (reproduction) signal.

According to the above construction, by using the apodizing element for the incident light to the optical recording medium and the light shielding element for the reflected light (reproducing light), the linear density and the track density can be simultaneously improved. The other configurations and effects are similar to those of the first embodiment.

FIG. 8 shows another example of the light shielding element. That is, in the figure, 21 is a light shielding element, and here, a mirror 21a made of a rectangular metal film or the like is formed on a glass plate. The light shielding element 21 is arranged such that the wide surface of the mirror 21a is orthogonal to the beam (axis thereof) direction and the longitudinal direction of the mirror 21a is coincident with the track direction (beam traveling direction) on the optical recording medium A.

FIG. 9 shows a region where the reflected light is shielded by the light shielding element 21 and a region where the reflected light passes therethrough. The reflected light is in the track direction according to the shape of the mirror 21a with respect to the beam traveling direction on the optical recording medium A. With parallel dividing boundaries,
It is divided into a light blocking area 22a and a passing area 22b in the track width direction.

According to this light-shielding element, since the division boundary line of the reflected light is parallel to the track direction, the change in signal amplitude due to off-track and off-focus is small, which is advantageous for off-track and off-focus. Be practical. Further, the light-shielding element itself can be easily manufactured without requiring complicated processing.

FIG. 10 shows still another example of the light shielding element. That is, in the figure, 31 is a light shielding element, and here, a mirror 31a made of a circular metal film or the like is formed on a glass plate. The light shielding element 31 is arranged so that the wide surface of the mirror 31a is orthogonal to the beam (axis thereof) direction.

FIG. 11 shows a region where the reflected light is shielded by the light shielding element 31 and a region through which the reflected light passes. The reflected light is directed toward the beam traveling direction on the optical recording medium A by the mirror 31a.
With a concentric division boundary line conforming to the shape of the above, the cross section is divided into a light shielding region 32a and a passage region 32b.

According to this light-shielding element, the dividing boundary line of the reflected light is concentric with respect to its cross section, so that the track density and the linear density are simultaneously obtained only by the light-shielding element used in the first embodiment. Can be improved. That is, regarding the track density, the shielded area of the reflected light is almost the same as the area where the ± 1st-order diffracted light and the 0th-order diffracted light in the track width direction are overlapped, and the mirror shields the area where a lot of variation due to crosstalk appears. Therefore, the influence of crosstalk from adjacent tracks can be efficiently reduced, and the track density can be improved. Regarding the linear density, the low-frequency component of the information recorded on the optical recording medium is gathered at the center of the reflected light, and the low-frequency component is removed by the mirror, so that the high-frequency information is reproduced accurately. be able to.

Thus, by shielding the center of the reflected light with the light shielding element, it is possible to reproduce information having a high linear recording density and a high track density.

[0036]

As described above, according to the present invention,
Crosstalk can be suppressed by utilizing the Fourier transform effect of the light lens, and the recorded information on the optical recording medium can be detected with high accuracy. Further, it is only necessary to insert the light-shielding element into the conventional device, and it is possible to realize high-density recording at low cost and space.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory view showing details of a light shielding element in FIG.

FIG. 3 is an explanatory diagram showing a region shielded by the light shielding element of FIG. 2 and a region passing therethrough.

FIG. 4 is a configuration diagram showing a second embodiment of the present invention.

5 is an explanatory diagram showing details of the apodizing element in FIG. 4. FIG.

6 is an explanatory view showing a region shielded by the apodizing element of FIG. 5 and a region passing therethrough.

FIG. 7 is an explanatory diagram showing a change in light intensity distribution of a beam spot by an apodizing element.

FIG. 8 is an explanatory diagram showing another example of the light shielding element.

9 is an explanatory diagram showing a region shielded by the light shielding element of FIG. 8 and a region passing therethrough.

FIG. 10 is an explanatory diagram showing still another example of the light shielding element.

11 is an explanatory view showing a region shielded by the light shielding element of FIG. 10 and a region passing therethrough.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser, 2 ... Beam shaping part, 3 ... Beam splitter, 4 ... Objective lens, 5, 21, 31 ... Shading element, 6 ...
Condensing lens, 7 ... Photodetector, 8 ... Apodizing element, A ...
Optical recording medium.

Claims (5)

[Claims] 1. An optical recording / reproducing method for condensing light emitted from a light source, irradiating the same onto an optical recording medium, and detecting reflected light or transmitted light to reproduce recorded information. An optical recording / reproducing method characterized in that the central portion of the beam is shielded, and the light beam after the shielding is detected to reproduce the recorded information. 2. The light-shielding area is parallel to the track direction.
The optical recording / reproducing method according to claim 1, wherein the region is defined by a straight line of a book. 3. The optical recording / reproducing method according to claim 1, wherein a boundary line of the light shielding region is a concentric circle having the same center as the light beam. 4. An optical recording / reproducing apparatus for condensing light emitted from a light source to irradiate the optical recording medium and detecting reflected light or transmitted light thereof to reproduce recorded information. An optical recording / reproducing apparatus, wherein a light shielding element for shielding the central portion of the light beam is arranged in the optical path of the beam. 5. The optical recording / reproducing apparatus according to claim 4, wherein an apodizing element is arranged in an optical path for irradiating the optical recording medium with the light emitted from the light source.