JPH09245366A - Optical recording / reproducing method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce cross talk from an adjacent track and to precisely reproduce the recorded data. SOLUTION: Light outgoing from a laser 1 is converged through a beam shaping part 2, a beam splitter 3 and an objective lens 4, and an optical recording medium A is irradiated with the light, and when recorded information is reproduced from its reflection light, the central part of the reflection light, that is, the part affected seriously by the cross talk from the adjacent track is advanced in the direction of a light absorbing element 9 by a spec-troscopic element 6 to be absorbed, and the light of the remaining part affected less by the cross talk from the adjacent track is converged by a condenser lens 7 to be detected by a photodetector 8, and by reproducing the recorded information, the cross talk from the adjacent track is reduced.

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 recording medium such as an optical disk.

[0002]

2. Description of the Related Art In a conventional optical recording / reproducing method of this type, light emitted from a light source such as a semiconductor laser is recorded on an optical recording medium via an optical system, as disclosed in JP-A-1-245433. Irradiate by narrowing down to one point of the track, collecting the reflected light from the one point through the optical system, guiding it to the photodetector, and detecting the change in the light intensity and the polarization direction of the reflected light,
The information recorded at one point on the track is reproduced.

However, in such a conventional method, when the track density is increased, the influence (crosstalk) of the information of the adjacent tracks contained in the reflected light beam from the optical recording medium becomes large and the information cannot be reproduced accurately. However, it was difficult to improve the track density.

As a method for suppressing the above-mentioned crosstalk and improving the track density, a paper J of the Japan Society of Applied Physics is available.
pn. J. Appl. Phys. , Volume 32, 199
3, High-Density Land / Groov
e Recording for Digital V
video File System, P5449-54
50, there is a method disclosed. This is to irradiate three light beams on one track and adjacent tracks on both sides of the optical recording medium, and to obtain a main signal obtained by the light beam irradiated on one track and the light beam irradiated on the adjacent tracks. The two sub-signals obtained by the above are input to a crosstalk cancel circuit to remove crosstalk and obtain a reproduced signal.

However, this method requires three light sources such as semiconductor lasers having uniform characteristics in order to generate three light beams, which is expensive, and the beam formed by these laser beams. There is a problem that a complicated reproducing circuit system for compensating the positional deviation of the reproducing signal due to the spot interval is required.

Further, as a method of improving the track density depending on the medium structure, a paper Jpn. J.
Appl. Phys. 32, 1993, Land
and Grove Recording for
High Track Density on Ph
ase-Change Optical Disks,
There are methods disclosed in P5324 to 5328. In this method, since information is recorded on the land portion and the groove portion on the optical recording medium, the optical recording medium is designed so that the information recorded on each portion can be reproduced with substantially the same signal amplitude.
Further, the depth of the groove is adjusted in advance so that the crosstalk from the adjacent track can be reduced most. As a result, the information recorded in the narrow track can be accurately reproduced.

However, this method has a problem that the structure of the optical recording medium needs to be significantly changed.

Further, as a method of reducing crosstalk and improving track density by using only one light beam, there is a method disclosed in Japanese Patent Laid-Open No. 7-50030. In this method, a reproduction light from the optical recording medium is diffracted in each area by using a hologram element having an area divided in a direction perpendicular to the information string direction recorded on the optical recording medium, and each diffracted light is independent. The crosstalk is reduced by performing weighted addition on the signals obtained by the detection.

However, this method has a problem that it is necessary to use a hologram element and a split detector, and the structure of the optical pickup is complicated and expensive.

Further, as a method for improving the recording density by providing a light-shielding band, JP-A-2-12624, JP-A-4-324129 and JP-A-4-337 are available.
There are methods disclosed in Japanese Patent Application Laid-Open No. 530, Japanese Patent Application Laid-Open No. 7-129962, and Japanese Patent Application Laid-Open No. 7-141684. In these methods, a super-resolution spot is formed on the optical recording medium by placing a light-shielding band in the irradiation optical system in the direction perpendicular to the track, and the recorded information is reproduced by this.

[0011]

However, since the super-resolution spot has a large side lobe, a slit or the like is provided in the reproducing optical system, signal processing is performed using an equivalent circuit, or the side lobe is detected separately. Therefore, it is necessary to reduce the influence of the side lobes.
In these disclosed methods, the shading band does not mention reduction of crosstalk, and none of them can reduce crosstalk.

It is an object of the present invention to provide an optical recording / reproducing method and apparatus capable of reducing crosstalk from adjacent tracks and reproducing recorded data with high accuracy.

[0013]

In order to solve the above problems, the present invention provides an optical recording / reproducing method for reproducing information recorded on an optical recording medium by using a light beam, in which a light beam is formed on the optical recording medium. Irradiation is performed to change the traveling direction of the central portion of the light from the optical recording medium to a direction different from other portions, and only the light of the other portions is condensed and detected to reproduce recorded information. I made it.

Further, in the optical recording / reproducing apparatus for reproducing the information recorded on the optical recording medium by using the light beam, the light irradiating means for irradiating the optical recording medium with the light beam and the center of the light from the optical recording medium. A spectroscopic element for changing the traveling direction of the part to a direction different from that of the other part, and an information reproducing means for condensing and detecting only the light of the other part that has passed through the spectroscopic element and reproducing the recorded information. Prepared

As a result, the central portion of the light from the optical recording medium, which is greatly affected by the crosstalk from the adjacent tracks, can be removed, the crosstalk from the adjacent tracks can be reduced, and the center which is not detected can be removed. It is possible to prevent the light of a part from becoming stray light and increasing noise.

Further, according to the present invention, in an optical recording / reproducing method of reproducing information recorded on an optical recording medium by using a light beam, the optical beam is irradiated onto the optical recording medium to emit light from the optical recording medium. The central portion is dimmed, the passing light is collected and detected, and the recorded information is reproduced.

Further, in an optical recording / reproducing apparatus for reproducing information recorded on an optical recording medium by using a light beam, a light irradiation means for irradiating the optical recording medium with the light beam and a center of light from the optical recording medium. The light-reducing element for dimming a portion and the information reproducing means for condensing the light passing through the light-reducing element to detect the light and reproduce the recorded information are provided.

As a result, crosstalk can be reduced and a decrease in the amplitude of the reproduction signal can be suppressed.

Further, by using a dimming element in which the transmittance of the dimming portion differs depending on the position, the crosstalk component can be removed according to the distribution characteristic of the crosstalk included in the reproduction light, so that the crosstalk can be efficiently reduced. can do.

Further, according to the invention, in which a spectral element or a light attenuating element is provided with a shutter for inserting / removing into / from the optical path of the light from the optical recording medium, when the influence of crosstalk from an adjacent track is small, That is, the spectroscopic element or the light attenuating element can be removed when reproducing an optical recording medium before the present invention having a sufficiently wide track interval and a low recording density, and compatibility with the recording method and apparatus before the present invention is provided. It is possible.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 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 a beam splitter. The objective lens, 5 is a spectroscopic element mounting portion, 6 is a spectroscopic element, 7 is a condenser lens, 8 is a photodetector, 9 is a light absorbing element, and A is an optical recording medium.

The operation of this example will be described below.

The light output from the laser 1 is shaped into parallel light by the beam shaping unit 2, and passes through the beam splitter 3 to
The objective lens 4 is irradiated with the light and the light is focused on the optical recording medium A by the objective lens 4. The reflected light from the optical recording medium A becomes parallel light 10 by the objective lens 4 and its polarization direction can be changed by the beam splitter 3 (in order to change the direction, a known quarter-wave plate is inserted, PB
You may use S etc. ), Toward the spectral element 6 of the spectral element mounting portion 5.

Here, the spectroscopic element 6 is composed of a rectangular mirror surrounded by two straight lines parallel to the traveling direction of the beam on the optical recording medium on the upper surface as shown in FIG.
As shown in FIG. 6A, the side surface is incorporated into the spectroscopic element mounting portion 5 at an angle of 45 degrees with respect to the light beam direction.

In this example, the reproduction light beam 1 is transmitted through the mirror.
Although it is inclined by 45 degrees with respect to the traveling direction of 0, the beam can be dispersed if it is larger than 0 degree and 90 degrees or less, so that it may be within this range.

FIG. 3 shows a region 11 passing through the spectroscopic element 6.
The area a of the reproduction light beam removed by the spectroscopic element 6 is shown, and the intensity distribution of the reproduction light beam immediately after passing through the spectroscopic element is also shown. As described above, the reproduction light beam is removed by the region 11a that passes through the spectroscopic element in the track width direction and the spectroscopic element with a straight division boundary line according to the shape of the spectroscopic element 6 in the beam traveling direction on the optical recording medium A. It is divided into a region 11b. The light intensity distribution immediately after passing is such that the vicinity of the center of the reproduction light beam is shielded.

The light in the region 11b whose traveling direction is changed by the spectroscopic element 6 strikes the light absorbing element 9 and is absorbed.
The light in the region 11a that passes through the spectroscopic element 6 is condensed by the condenser lens 7 on the photodetector 8, and a reproduction signal is output.

That is, the light intensity distribution on the plane perpendicular to the traveling direction of the reproduction light beam located where the Fourier transform surface on the optical recording medium is located is the recording mark sequence on the optical recording medium. It is given by the convolution of the diffraction pattern by and the far field pattern of the intensity distribution of the light condensed on the medium surface. Then, it changes as shown in FIG. 4A depending on the presence or absence of crosstalk.

As shown in FIG. 4A, it can be seen that the light intensity distribution is greatly reduced due to crosstalk in the vicinity of the center of the light beam, and is increased outside. Therefore, as shown in FIG. 4B, if the light near the center of the reproduction beam is removed by using the spectroscopic element and only the light passing through is detected by the method described above,
Even if the light intensity distribution changes due to crosstalk, the energy of light detected by the photodetector does not change. As a result, the reproduced signal is not affected by crosstalk. Therefore, by removing the vicinity of the center of the reproduction light, which greatly reduces the light intensity due to crosstalk, by the spectroscopic element, it is possible to suppress the influence of the recording marks of the adjacent tracks and reproduce the signal recorded on the medium with high accuracy.

FIG. 5 shows a result obtained by simulation of the relationship between the width w (%) of the region removed by the spectroscopic element and the crosstalk. Here, w is shown as a ratio to the diameter of the reproduction light beam. Further, w = 0% represents the case where no spectroscopic element is inserted. From FIG. 5, crosstalk can be reduced when w is larger than 0% and smaller than 50%, and in the simulation, w = 30%.
It can be seen that the crosstalk can be reduced most when. In addition, from 20% to 43%, it is below -26 dB which is a standard of crosstalk.

Based on these results, an optical recording / reproducing apparatus based on this example was prototyped with w = 25%, and the results of recording / reproducing experiments are shown in FIG. FIG. 6A shows the results of measuring the signals when the recording mark is recorded and reproduced on only one track on the optical recording medium, with and without the spectroscopic element. Further, in FIG. 6B, recording marks are recorded on adjacent tracks on both sides of one track on the optical recording medium,
It is a result of measuring a leak signal (crosstalk) from an adjacent track when the one track is reproduced, with and without a spectroscopic element.

From these measurement results, it was experimentally clarified that the crosstalk can be reduced to 1/2 or less by inserting the spectroscopic element. The focus signal and tracking signal necessary for detecting the actual signal are detected from the light separated by the beam splitter (not shown), but a well-known detection method may be used, and a description thereof will be omitted here.

Further, as means for removing the central portion of the reproduction light beam, instead of the spectroscopic element and the spectroscopic element mounting portion shown in FIGS. 1 and 2, fixed to both sides in the longitudinal direction of a rectangular mirror as shown in FIG. You may use the spectroscopic element 12 which attached the handle for. Further, in the figure, the spectroscopic element 12 is arranged in a plane perpendicular to the beam direction, that is, at an angle of 90 degrees with respect to the beam direction so that the light of the central portion of the beam of the read light beam travels in the direction opposite to the beam direction of the beam. It is arranged. Here, since the purpose of the spectroscopic element is to change the direction of the portion of the reproduction light beam to be removed as described above, the angle with respect to the beam direction may be set to more than 0 degree and 90 degrees or less. Beam direction and 45 as shown
They may be arranged at an angle of degrees. According to this spectroscopic element, the spectroscopic element mounting portion is unnecessary, and the crosstalk can be reduced at a low cost as in the case of the above embodiment.

Further, instead of using a flat mirror as in the spectroscopic element shown in FIGS. 1 and 2, a spectroscopic element 13 including a prism as shown in FIG. 9 is used to change the traveling direction of the light near the center of the reproduction light beam. A method of changing and removing it is also conceivable. This method is easy to realize because the prism which is already widely used can be used.

Further, as means for removing the central portion of the reproduction light beam, as shown in FIG. 10, a ½ wavelength plate 14 and a polarization beam splitter 15 may be used instead of the spectroscopic element. In this method, it is not necessary to incorporate the spectroscopic element in the spectroscopic element mounting portion, the components used in the conventional optical disc device can be used, and the high track density can be realized at low cost.

As a means for removing the central portion of the reproduction light beam, a divided condensing element 16 as shown in FIG. 11 is used to divide the reproduction light into the light of the region to be removed and the light of the region to be detected. The light in a desired area is absorbed by the photodetector 17 together with the photodetector 17a.
Absorb by. With this method, the number of parts used can be reduced, so that it is possible to realize space saving.

In addition, in FIG.
The spectroscopic element mounting portion 5 was formed by sandwiching and fixing the two triangular prism-shaped glasses. However, as shown in FIG. 12A, the spectroscopic element mounting portion 18 having triangular prism-shaped projections on a flat glass plate is used. The spectroscopic element may be fixed. In addition, FIG.
Alternatively, the spectroscopic element may be fixed to the slope of the spectroscopic element mounting portion 19 in which a glass plate is provided with a triangular prism-shaped cut as shown in FIG. Furthermore, as shown in FIG. 12C, a spectroscopic element 20 in which a prism is fixed on a glass flat plate and the traveling direction near the center of the reproduction light beam is changed to the direction of the light absorbing element may be used. good.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. The difference between this embodiment and the first embodiment is the transmittance of the mirror used as the spectroscopic element. That is, instead of using a total reflection mirror, a dimming element, that is, a half mirror is used. The other configuration of this embodiment is the same as that of the first embodiment, and the description thereof is omitted.

As shown in FIG. 13B, the dimming element 21 is a rectangular half mirror surrounded by two straight lines parallel to the traveling direction of the beam on the optical recording medium as shown in FIG. As shown in a), it is incorporated in the dimming element mounting portion 22 in a plane perpendicular to the reproduction light beam on the side surface, that is, at an angle of 90 degrees with respect to the light beam direction.

Here, since the purpose of the light attenuating element is to reflect a part of the light of the reproducing light beam to be dimmed, change its direction, and pass the rest, the angle with respect to the beam direction is set to 0. The angle may be greater than 90 degrees and less than 90 degrees, for example, as shown in FIG.
As shown in FIG. 4, the dimming element mounting portion 24 may be arranged at an angle of 45 degrees with the beam direction.

As shown in FIG. 15, the reproduction light beam has a region 23a that passes through the dimming element in the track width direction and a region that is dimmed by the dimming element with a straight division boundary line according to the shape of the dimming element 21. 23b. FIG.
The figure on the right side of FIG. 3 shows the light intensity distribution along the x-axis of the reproduction light beam immediately after passing through the dimming element 21. As shown here, the light intensity distribution immediately after passage is such that the vicinity of the center of the reproduction light beam is dimmed.

FIG. 16 shows the relationship between the width of the dimming element, the transmittance and the crosstalk. The width of the dimming element is standardized by the diameter of the reproduction light beam. In the figure, the white portion represents the least crosstalk, and the darker the black portion, the more crosstalk. From the drawing
Regarding the width of the shading element, 30% of the diameter of the reproduction light beam
It can be seen that from 70% to 70% is a good range because a wide margin of transmittance can be secured, and when it is 55%, it is an optimum value in which the margin of transmittance is widest. Regarding the transmittance, the range in which the crosstalk is −30 dB or less appears at 35% or less, which is a desirable range.

In FIG. 17, the transmittance is 0% (equivalent to shading), 2
The relationship between the width of the dimming element and the crosstalk at 0% and 30% is shown. From the drawing, although the crosstalk value in the optimum width of the dimming element is slightly increased, the design margin of the width of the dimming element becomes wider as the transmittance of the dimming element approaches 30%. I understand.

According to the present embodiment, the use of the dimming element can reduce the crosstalk and can secure the signal that has been excessively removed in the light shielding element, so that the reduction of the S / N ratio can be prevented. it can. Further, the design margin of the width and the transmittance of the light attenuating element can be widened.

Further, instead of using the rectangular dimming element as shown in FIG. 13, a dimming element 25 having a shape as shown in FIG. 18 may be used. The light attenuating element shown in FIG. 18 is composed of a half mirror having a streamlined shape surrounded by two curves of the same curve on the upper surface, the wide surface of which is orthogonal to the axial direction of the beam and the longitudinal direction of the streamlined optical recording medium. It is installed so that it exists in the same plane as the traveling direction of the upper light beam.

Further, of the light in the region that is dimmed by the dimming element, the reflected light may travel in a direction other than the traveling direction of the reproduction light beam, so that, for example, as shown in FIG. The portion 24 is arranged so that the angle formed by the wide surface and the axial direction of the beam is 45 degrees, and the traveling direction of the reflected light of the light in the region dimmed by the dimming element 25 is the reproduction light. You may make it the 90 degree | times with the advancing direction of a beam.

As shown in FIG. 20, the reproduction light beam passes through the dimming element in the track width direction with a curved division boundary line according to the shape of the dimming element 25 in the beam traveling direction on the optical recording medium A. It is divided into a region 26a and a region 26b that is dimmed by the dimming element. The diagram on the right side of FIG. 20 shows the light intensity distribution along the x-axis of the reproduction light beam immediately after passing through the dimming element 25.

When this dimmer is used, the dimming region of the reproduced light coincides with the region where the ± 1st-order diffracted light and the 0th-order diffracted light in the track direction overlap, and is the portion where the fluctuation due to crosstalk appears most. By dimming this region, the effect of crosstalk from adjacent tracks can be efficiently reduced.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIG. The difference between the present embodiment and the second embodiment lies in the transmittance distribution of the half mirror used as the dimming element. That is, in the second embodiment, the transmittance of the half mirror is constant regardless of the location, but in the present embodiment, the transmittance of the half mirror differs depending on the location. The other configuration of this embodiment is the same as that of the first embodiment, and the description thereof is omitted.

As shown in FIG. 21B, the light attenuating element 27 has the lowest light transmittance in the central portion, and extends along the direction (track width direction) orthogonal to the traveling direction of the beam on the optical recording medium. The transmittance increases continuously toward the outside (however, in the drawing, there are three types of step expressions due to drawing problems). Further, the dimming element 27 is the dimming element mounting portion 2
8 is installed perpendicular to the beam direction.

Here, since the reflected light of the light in the region dimmed by the light attenuating element may proceed in a direction other than the traveling direction of the reproduction light beam, for example, as shown in FIG. You may arrange | position so that the angle formed by and may be 45 degrees. The transmittance is the same in the traveling direction of the beam on the optical recording medium. Further, as shown in FIG. 7A, the light-receiving element mounting portion 30 is incorporated at an angle of 45 degrees with the traveling direction of the reproduction light beam on the side surface.

FIG. 23 shows the light intensity distribution of the reproduction light beam dimmed by the dimming element 27 whose transmittance of light continuously changes immediately after passing through the dimming element. As shown, in the x-axis direction, the ratio of the extinction is highest near the center and decreases toward the outside, and in the y-axis direction, the extinction ratio is the same.

Further, FIG. 24 shows an example of the light blocking rate distribution of the dimming element.
Shown in As shown in the figure, in (a), the center of the reproduction light beam has the highest light blocking rate, and the light blocking rate decreases linearly toward the outside. In (b), the light blocking rate is similar to that of Gaussian. The rate is falling.

FIG. 25 shows the relationship between the width of the dimmed region and the crosstalk in the case of using the dimming element having the shading ratio distribution shown in FIGS. 24A and 24B. It is also shown together with the case. From the figure, in the case of using a Gaussian and a dimming element having a linear shading rate distribution, -26d
It can be seen that the design margin of the dimming element that satisfies B is wider than that when the light shielding element is used. Further, the value of the crosstalk in the optimum width where the crosstalk can be most reduced is as low as or more than that in the case where the light shielding element is used.

According to this embodiment, crosstalk is reduced and S
Both / N ratio can be secured at a high level. Further, by designing the transmittance distribution of the light attenuating element, it is possible to optimize the reduction of crosstalk and the securing of S / N according to the recording / reproducing characteristics. As a result, the design margin of the optical recording / reproducing device is widened, and it can be widely applied to the same type of optical recording / reproducing device having different characteristics using various methods to reproduce the information recorded in the narrow track, and to output it. It is also possible to make the characteristics of the signal applied almost uniform.

Further, instead of using the dimming element whose transmittance changes continuously as shown in FIG. 21, it is also possible to use a shading band group in which thin shading elements having different widths are arranged as shown in FIG.

Here, as shown in FIG. 7A, the light-shielding band group 31 shields light in a plane perpendicular to the beam direction such that the longitudinal direction of the light-shielding band is parallel to the beam traveling direction on the optical recording medium. It is incorporated in the belt mounting portion 32. Further, when a mirror is used for the light shielding band, in order to make the axis of the reflected light deviate from the reproduction light beam, for example, as shown in FIG. Light-shielding band group mounting portion 3 so as to form an angle of 45 degrees with the traveling direction of the beam
4 may be incorporated.

The drawing on the left side of FIG. 28 shows the reproduction light beam cross section 3
3 shows an area group 33a that passes through the shading band group and an area group 33b that is partially shaded by the shading band group, and the right diagram shows the light intensity distribution immediately after passing through the shading band group. ing. As shown in the figure, in the x-axis direction, the width of the light-shielded region near the center is wide, and the width of the light-shielded region becomes narrower toward the outside.

The use of this light-reducing element does not require a high-level manufacturing technique for continuously changing the transmittance of the light-reducing element, so that the cost can be reduced and the transmittance continuously changes. Crosstalk can be reduced in the same manner as when using a dimming element.

Further, instead of using the light shielding band group shown in FIG. 26, as shown in FIG. 29, a minute line divided by a plurality of straight lines parallel to the beam traveling direction on the optical recording medium and a plurality of straight lines perpendicular to the beam traveling direction. The light-shielding element group 35 in which minute light-shielding bands are arranged in some of the plurality of regions may be incorporated in the light-shielding band group mounting portion 36 and used. Also, as in FIG. 27, as shown in FIG. 30, the light-shielding band group 35 is incorporated in the light-shielding band group mounting portion 38 so that the arrangement direction of the light-shielding bands on the side surface forms an angle of 45 degrees with the traveling direction of the light beam. You can

By using this light-attenuating element, minute light-shielding elements can be arranged two-dimensionally, so that the influence of the fluctuation of the light intensity distribution due to the recording marks of the adjacent tracks can be finely controlled two-dimensionally. Therefore, it is possible to reduce crosstalk in the same manner as in a dimming element in which the transmittance changes two-dimensionally.

Further, as an example of a dimming element in which the light transmittance changes continuously, as shown in FIG. 31, the light transmittance is directed from the center to the outside in the traveling direction of the beam on the optical recording medium. There is a method to increase continuously. Here, as shown in FIG. 4A, the light attenuating element 39 is incorporated in the light attenuating element mounting portion 40 so as to exist in a plane perpendicular to the beam direction.

Further, in order to make the axis of the reflected light from the dimming element deviate from the reproduction light beam, for example, as shown in FIG. 32, the dimming element 39 is arranged at 45 degrees with respect to the traveling direction of the light beam on the side surface. You may make it incorporate in the light-shielding band group mounting part 42 so that it may make an angle.

In the examples shown in FIGS. 31 and 32, the point where the central axis of the light beam on the light attenuating element passes has the lowest transmittance, and from there, the light beam is concentrically and continuously outward in the radial direction of the beam. The transmittance is increasing (However, in the drawing, there are about 3 types of step representation due to drawing problems.)

The light attenuated by the light attenuating element 39 passes through the light attenuating element 41a as shown in FIG.
And a region 41b that is dimmed by the dimming element. In the region 41b that is dimmed, the rate of decrease in light intensity is greatest near the center of the light beam, and the rate of decrease is smaller toward the outside. Has become.

By using this light attenuating element, not only the crosstalk from the adjacent track can be reduced but also the linear recording density can be increased. This is because the intensity distribution of the light beam at the position of the light attenuating element is given by the Fourier transform of the light beam reflected on the optical recording medium, so that much dimming near the center is the spatial frequency of information on the optical recording medium. This is because it is equivalent to emphasizing the high range of the distribution.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIG. The difference between this embodiment and the first to third embodiments is that a spectral (light-shielding) element or a dimming element is mounted on the shutter, and the light-shielding element or the dimming element is inserted into the reproduction light beam as necessary. To remove it. Further, this shutter is controlled by the shutter control section with reference to the output signal from the photodetector.

In the figure, 1 is a laser, 2 is a beam shaping unit, and 3 is a beam shaping unit.
Is a beam splitter, 4 is an objective lens, 7 is a condenser lens, 8 is a photodetector, 51 is a light-shielding or dimming element, 52 is a shutter, 53 is a shutter controller, and A is an optical recording medium.

The operation of this example will be described below.
Since the light output from the above reaches the light blocking or dimming element 51 incorporated in the shutter 52, the description is omitted because it is the same as in the first embodiment.

In the initial state, the shutter 52 holds the state where the light blocking or dimming element 51 is not irradiated with the reproduction light beam. The shutter control unit 53 determines whether the optical recording medium A is a medium having a high recording density or a medium having a low recording density by referring to the signal from the photodetector 8, and a medium having a high recording density as used in the present invention. In this case, the light shielding or light attenuating element 51 is inserted to shield or dimm the vicinity of the center of the reproduction light beam to reduce the crosstalk from the adjacent track as shown in each of the above-mentioned modes. On the other hand, in the case of a medium having a low recording density as used in the recording method before the present invention, the reproduction light is allowed to pass as it is without removing the light shielding or attenuating element 51.

At this time, information indicating that the medium is a high-density optical recording medium is recorded in advance on the medium, and the shutter control unit 53 determines the medium based on the signal obtained by reading the information. The difference between the media may be determined based on the change in the tracking signal or the focus signal caused by the difference in the shape of the groove on the optical recording medium.

The light thus passing through the shutter 52 is detected by the condenser lens 7 and a reproduction signal is output.

FIG. 35 shows the details of the shutter. As shown in the figure, the light shielding or dimming element 51 is fixed by a guide groove 54 and has a mechanism capable of moving in parallel with the traveling direction of the beam on the optical recording medium. Shading or dimming element 51
Since the power for moving the can be the power that is already generally used, a detailed description thereof will be omitted.

According to this embodiment, high density recording can be realized by reducing crosstalk, and both the high density optical recording medium used in the optical recording apparatus of the present invention and the conventionally used optical recording medium can be used. Recording and reproduction can be performed, and these media can be made compatible with each other.

Further, instead of using the slide type shutter shown in FIG. 35, a shutter having a mechanism as shown in FIG. 36 may be used. As shown in the figure, the light shielding or dimming element 55 is an elongated quadrangular prism, one side of which is the motor 5
It is fixed to the rotary shaft of 6. The light-shielding or light-attenuating element positioning jig 57 has a cylindrical shape and is fixed so that its central axis coincides with the central axis of the reproduction light beam. A notch 57a is provided so that the light shielding or dimming element 55 can be fixed near the center of the reproduction light beam spot described above during reproduction.

The light shielding or dimming element 55 can be removed by rotating the motor 56 in the clockwise direction in FIG. On the contrary, when inserting, the motor 56 may be rotated counterclockwise. According to this configuration, since it is not necessary to move the elements in parallel, the mechanism can be simplified, and the shutter function can be provided in a space-saving manner.

Further, instead of using the light shielding element or the light reducing element and the shutter, a liquid crystal element mounting portion 58 and a liquid crystal element 59 as shown in FIG. 37 may be used. Compatibility with a conventional optical recording medium can be realized by the liquid crystal element control unit 60 referring to the reproduction signal from the photodetector 8 to determine the type of medium and turning the liquid crystal element 59 on and off.

Since the area where the liquid crystal element 59 absorbs light is determined by the shape of the electrode in the element, the shape of the electrode is made to match the area where light is to be shielded or dimmed. When dimming, the voltage applied to the electrodes is determined so that the liquid crystal has a desired transmittance.

According to this structure, since the light-shielding band and the dimming band are electrically turned on / off, high-speed switching is possible.

[0081]

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 possible to realize a compatible optical recording / reproducing apparatus capable of reproducing a medium having a conventional low recording density.

[Brief description of drawings]

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

FIG. 2 is a diagram showing details of a spectroscopic element in FIG.

FIG. 3 is a diagram showing the distribution of the reproduction light beam and the light intensity distribution by the spectroscopic element of FIG.

FIG. 4 is a diagram showing the influence of crosstalk on reproduction light in the first embodiment.

FIG. 5 is a diagram showing a result of simulating a relationship between a width of a region removed by the spectroscopic element and crosstalk in the first embodiment.

FIG. 6 is a reproduction signal waveform and leakage signal waveform diagram in the first embodiment.

FIG. 7 is a view similar to FIG. 2 showing another example of the spectroscopic element.

FIG. 8 is a view similar to FIG. 2 showing still another example of the spectroscopic element.

FIG. 9 is a view similar to FIG. 2 showing still another example of the spectroscopic element.

FIG. 10 is a diagram showing another configuration example of the first embodiment of the present invention.

FIG. 11 is a diagram showing still another configuration example of the first embodiment of the present invention.

FIG. 12 is a view similar to FIG. 2 showing still another example of the spectroscopic element.

FIG. 13 is a diagram showing a main part of a second embodiment of the present invention.

FIG. 14 is a view similar to FIG. 13 showing another example of the dimming element.

FIG. 15 is a view similar to FIG. 3 in the second embodiment.

FIG. 16 is a diagram showing the relationship between the width, the transmittance, and the crosstalk of the light attenuating element in the second embodiment.

FIG. 17 is a view similar to FIG. 5 in the second embodiment.

FIG. 18 is a view similar to FIG. 13 showing still another example of the dimming element.

FIG. 19 is a view similar to FIG. 13 showing still another example of the dimming element.

20 is a view similar to FIG. 15 in the case of using the dimming element of FIG. 18 or FIG.

FIG. 21 is a diagram showing an essential part of a third embodiment of the present invention.

FIG. 22 is a view similar to FIG. 21, showing another example of the dimming element.

FIG. 23 is a view similar to FIG. 3 in the third embodiment.

FIG. 24 is a diagram showing an example of a light blocking rate distribution of a dimming element.

FIG. 25 is a view similar to FIG. 5 in the third embodiment.

FIG. 26 is a view similar to FIG. 21, showing an example of a dimming element using a light-shielding band.

FIG. 27 is a view showing another example of a dimming element using a light-shielding band.
Figure similar to 1

28 is a view similar to FIG. 23 in the case of using the dimming element of FIG. 26 or FIG.

FIG. 29 is a view similar to FIG. 21, showing still another example of the light attenuating element using a light-shielding band.

FIG. 30 is a view similar to FIG. 21, showing still another example of the light attenuating element using a light-shielding band.

FIG. 31 is a view similar to FIG. 21, showing still another example of the light attenuating element.

FIG. 32 is a view similar to FIG. 21, showing still another example of the dimming element.

33 is a view similar to FIG. 23 in the case where the light attenuating element of FIG. 31 or 32 is used.

FIG. 34 is a configuration diagram showing a fourth embodiment of the present invention.

35 is a diagram showing details of the shutter in FIG. 34.

FIG. 36 is a diagram showing another example of the shutter.

FIG. 37 is a diagram showing another configuration example of the fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser, 2 ... Beam shaping part, 3 ... Beam splitter, 4 ... Objective lens, 5,18,19 ... Spectral element mounting part, 6, 12, 13, 20 ... Spectral element, 7 ... Condensing lens, 8, 17 ... Photodetector, 9 ... Photoabsorption element, 14 ... 1 /
2 wavelength plate, 15 ... Polarizing beam splitter, 16 ... Divided condensing element 21, 25, 27, 39 ... Dimming element, 22, 2
4, 28, 30, 40, 42 ... Attenuator mounting portion, 31,
35 ... Shading band group, 32, 34, 36, 38 ... Shading band group mounting section, 51, 55 ... Shading or dimming element, 52 ... Shutter, 53 ... Shutter control section, 56 ... Motor, 57 ...
Positioning jig for light-shielding or dimming element, 58 ... Liquid crystal element mounting portion, 59 ... Liquid crystal element, 60 ... Liquid crystal element control section, A ... Optical recording medium.

Claims (6)

[Claims] 1. An optical recording / reproducing method for reproducing information recorded on an optical recording medium by using a light beam, wherein a light beam is irradiated onto the optical recording medium, and a central portion of light from the optical recording medium travels. An optical recording / reproducing method characterized in that the direction is changed to a direction different from that of the other portion, and only the light of the other portion is condensed and detected to reproduce recorded information. 2. An optical recording / reproducing method for reproducing information recorded on an optical recording medium by using a light beam, wherein a light beam is irradiated onto the optical recording medium to reduce a central portion of light from the optical recording medium. An optical recording / reproducing method characterized by reproducing the recorded information by irradiating the light, condensing and detecting the passed light. 3. An optical recording / reproducing apparatus for reproducing information recorded on an optical recording medium by using a light beam, a light irradiating means for irradiating the optical recording medium with the light beam, and a center of light from the optical recording medium. A spectroscopic element for changing the traveling direction of the part to a direction different from that of the other part, and an information reproducing means for condensing and detecting only the light of the other part that has passed through the spectroscopic element and reproducing the recorded information. An optical recording / reproducing device characterized by being provided. 4. An optical recording / reproducing apparatus for reproducing information recorded on an optical recording medium by using a light beam, a light irradiating means for irradiating the optical recording medium with the light beam, and a center of light from the optical recording medium. An optical recording / reproducing apparatus comprising: a dimming element for dimming a part, and an information reproducing means for condensing light passing through the dimming element to detect the light and reproduce recorded information. 5. The optical recording / reproducing apparatus according to claim 4, wherein a light attenuating element is used in which a transmittance of a light attenuating portion differs depending on a position. 6. The optical recording / reproducing apparatus according to claim 3, further comprising a shutter for inserting / removing a spectroscopic element or a light attenuating element into / from an optical path of light from the optical recording medium as required. .