JP2004171682A - Optical information recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information recording and reproducing device capable of properly correcting spherical aberration for a desired information recording layer caused by the variance in thickness of an optical information recording medium. <P>SOLUTION: The optical information recording and reproducing device has a laser light source 1 for emitting a diverging light beam 10, a collimator lens 3 for collimating the diverging light beam 10 into a parallel light beam 11, an electrostatic deformable mirror 4 for deflecting the parallel light beam 11 and also correcting the spherical aberration, an objective lens 5 for varying the deflected light beam 11 into a converging light beam 12, a beam splitter 2 for separating the light beam returning from a disk 6 from the light beam going to the disk 6, and a detector 7 for detecting the light beam returning from the disk 6. The objective lens 5 is so designed that the spherical aberration at the optical focusing point of the light beam 12 converged thereby is minimized at a farther position from the surface of the disk 6 than the farthest information recording layer from the surface of the disk 6 on the side near the objective lens 5. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical information recording / reproducing apparatus for recording / reproducing information on / from an optical information recording medium.
[0002]
[Prior art]
Japanese Patent Application Laid-Open No. 3-54740 discloses that each information recording layer of an optical information recording medium having a plurality of information recording layers is inserted by appropriately inserting a transparent flat plate having a predetermined optical path length between the objective lens and the optical recording medium. Discloses an optical information recording / reproducing device corresponding to.
[0003]
In this optical information recording / reproducing apparatus, the objective lens is designed to focus on the information recording layer farthest from the objective lens with the minimum spherical aberration. Also, for the information recording layer located closer to the objective lens than the information recording layer farthest from the objective lens, an appropriate thickness corresponding to the reduction in the thickness (optical path length) of the cover layer is used. The spherical aberration is corrected by appropriately inserting a transparent flat plate between the objective lens and the optical recording medium.
[0004]
[Patent Document 1]
JP-A-3-54740
[0005]
[Problems to be solved by the invention]
The above-described optical information recording / reproducing apparatus has no means for correcting spherical aberration for the information recording layer farthest from the objective lens. For this reason, for example, when the thickness (optical path length) of the cover layer with respect to the information recording layer farthest from the objective lens becomes larger than an ideal dimension due to variation in the thickness of the optical information recording medium, the spherical aberration is appropriately reduced. Correction may not be possible.
[0006]
The thickness of the transparent flat plate for correcting spherical aberration is determined in advance based on an optical information recording medium having ideal dimensions. For this reason, even when the thickness (optical path length) of the cover layer with respect to the information recording layer of the reading candidate greatly deviates from the ideal dimension due to, for example, variation in the thickness of the optical information recording medium, the spherical aberration is appropriately corrected. It may not be possible.
[0007]
Such a risk is particularly large in an apparatus that employs an objective lens having a large numerical aperture as the density of an optical information recording medium increases.
[0008]
The present invention has been made in view of such a situation, and an object of the present invention is to appropriately correct spherical aberration with respect to a desired information recording layer, which is caused by variation in the thickness of an optical information recording medium. An object of the present invention is to provide an optical information recording / reproducing apparatus which can obtain the same.
[0009]
[Means for Solving the Problems]
The present invention relates to an information recording / reproducing method that irradiates an optical information recording medium having a plurality of information recording layers with a light beam and records information thereby, or reproduces information by detecting reflected light from the optical information recording medium. Is directed at the device.
[0010]
An information recording / reproducing apparatus according to the present invention includes a light source that emits a light beam, an objective lens that converges the light beam, and an electrostatically deformable spherical aberration correcting lens disposed in an optical path between the light source and the objective lens. The objective lens has a spherical aberration at a focal point of the light beam converged thereby farther than the information recording layer farthest from the surface of the optical information recording medium on the side of the objective lens. Designed to be minimal in position.
[0011]
Another information recording / reproducing apparatus of the present invention includes a light source that emits a divergent light beam, a collimating lens that converts the divergent light beam from the light source into a parallel light beam, an objective lens that converges the light beam, and a collimator. An electrostatically deformable mirror for correcting spherical aberration disposed in an optical path between the lens and the objective lens, wherein the objective lens has a spherical aberration at a focal point of the light beam converged thereby. Is designed to be minimized at the position between the information recording layer farthest from the surface of the optical information recording medium on the side of the objective lens and the information recording layer closest to the surface, and furthermore, the electrostatic deformable mirror and the objective lens Has a concave lens disposed in the optical path between them.
[0012]
Another information recording / reproducing apparatus of the present invention corrects spherical aberration, which is disposed in a light source for emitting a divergent light beam, an objective lens for converging the light beam, and an optical path between the light source and the objective lens. The objective lens has an electrostatically deformable mirror, and the objective lens has a spherical aberration at the focal point of the light beam converged thereby, the information recording layer being farthest from the surface of the optical information recording medium on the side of the objective lens. Designed to be minimal at the location between the closest information recording layers, and furthermore, the divergent electrostatically deformable mirror located in the optical path between the light source and the electrostatically deformable mirror It has a lens for allowing a light beam to enter.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0014]
First embodiment
FIG. 1 shows an optical information recording / reproducing apparatus according to the present embodiment.
[0015]
In the optical information recording / reproducing apparatus of the present embodiment, the optical information recording medium on which information is recorded / reproduced is a double-layer disc 6 having two information recording layers 6a and 6b.
[0016]
The optical information recording / reproducing apparatus includes a laser light source 1 that emits a divergent light beam 10, a collimating lens 3 that converts the divergent light beam 10 into a parallel light beam 11, and deflects the parallel light beam 11 and reduces spherical aberration. An electrostatic deformable mirror 4 for correction, an objective lens 5 for converting the deflected and spherical aberration corrected light beam 11A into a convergent light beam 12, a light beam heading for the disk 6 and a light beam returning from the disk 6; And a detector 7 for detecting a light beam returning from the disk 6.
[0017]
The objective lens 5 is located at a position where the spherical aberration at the converging point of the light beam 12 converged thereby is farther from the surface of the disk 6 than the information recording layer farthest from the surface of the disk 6 closer to the objective lens 5. It is designed to be minimal.
[0018]
The objective lens 5 can be moved along an optical axis for focus control and can be moved along an axis orthogonal to the optical axis for tracking control by a drive mechanism (not shown). More specifically, the objective lens 5 is moved along the optical axis with respect to the electrostatically deformable mirror 4 during focus control. In tracking control, the objective lens 5 is moved together with the electrostatically deformable mirror 4 along an axis orthogonal to the optical axis.
[0019]
FIG. 2 shows the configuration of the electrostatically deformable mirror 4. As shown in FIG. 2, the electrostatic deformable mirror 4 includes a semiconductor substrate 21 having a void 24, and an electrode layer 27 provided on the bottom surface of the void 24 of the semiconductor substrate 21 via an insulating film 26. An insulating film 22 covering an air gap 24 of the semiconductor substrate 21; an electrode layer 23 formed on the insulating film 22; and a reflective film 25 formed on the electrode layer 23. are doing.
[0020]
When a voltage is applied between the electrode layer 23 and the electrode layer 27, the electrostatically deformable mirror 4 generates an electrostatic attraction between the electrode layer 23 and the electrode layer 27. The reflection film 25 is deformed into a concave surface, mainly a paraboloid or an arbitrary curved surface close to a paraboloid, depending on the magnitude of electrostatic attraction generated between the electrode layer 23 and the electrode layer 27.
[0021]
The voltage applied between the electrode layer 23 and the electrode layer 27 is adjusted according to the spherical aberration to be corrected. More specifically, the voltage applied between the electrode layer 23 and the electrode layer 27 is adjusted so that the reflective film 25 is deformed into a shape that appropriately corrects the spherical aberration to be corrected. As a result, the electrostatically deformable mirror 4 corrects the spherical aberration generated due to the deviation of the thickness of the cover layer of the disk 6 from the design value.
[0022]
The electrostatically deformable mirror 4 is deformed in only one direction due to its structure. That is, the reflection surface (that is, the reflection film 25) of the electrostatically deformable mirror 4 can be deformed from a plane that is not deformed to a concave surface, but cannot be deformed to a convex surface. Due to such one-way deformation, the electrostatically deformable mirror 4 can correct the spherical aberration generated when the cover layer of the disk 6 becomes thinner than the designed value.
[0023]
In FIG. 1, a divergent light beam 10 emitted from a laser light source 1 passes through a beam splitter 2 and is converted into a parallel light beam 11 by a collimating lens 3. The parallel light beam 11 is bent at right angles by the electrostatically deformable mirror 4 and directed to the objective lens 5. That is, the electrostatically deformable mirror 4 also functions as a so-called rising mirror. Thereafter, the deflected light beam 11A whose spherical aberration has been corrected is converted into a convergent light beam 12 by the objective lens 5.
[0024]
The convergent light beam 12 focuses on one of the information recording layer 6a and the information recording layer 6b of the disk 6 when the objective lens 5 is moved along the optical axis by a driving mechanism (not shown) during normal driving. Is adjusted. Further, the electrostatically deformable mirror 4 corrects spherical aberration caused by a difference in the thickness of the cover layer of the disk 6 (a protective layer formed on the disk surface and a transparent layer disposed between recording layers). Is done.
[0025]
The light beam converged on the information recording layer 6a or the information recording layer 6b of the disk 6 is reflected by being modulated according to the information recorded thereon. The returning light beam from the disk 6 passes through the objective lens 5 and the electrostatically deformable mirror 4 and is converted into a converging light beam by the collimating lens 3. This convergent light beam is partially reflected by the beam splitter 2, and the reflected light beam enters the detector 7. The detector 7 outputs an electric signal reflecting the amount of the incident light beam. The electric signal output from the detector 7 is read as an information signal.
[0026]
The electrostatically deformable mirror 4 (more precisely, its reflection surface, that is, the reflection film 25) is not deformed when no voltage is applied, and is usually flat. In this state, the spherical aberration has not been corrected.
[0027]
When the spherical aberration is not corrected by the electrostatically deformable mirror 4, the objective lens 5 is located at a position several microns farther than the information recording layer 6b farthest from the surface of the disk 6 closer to the objective lens 5. Is designed to minimize spherical aberration. In other words, the objective lens 5 is optimally designed for a cover layer having a thickness equal to the distance from the surface of the disk 6 to the information recording layer 6b plus several microns.
[0028]
The reason for designing the objective lens 5 in this way is that the electrostatically deformable mirror 4 can be deformed only in a concave shape in principle as described above, so that the thickness of the cover layer is smaller than the design value. This is because it is possible to correct only the spherical aberration generated when the thickness becomes thin. That is, the design is made in consideration of a case where an error such as an increase in the thickness occurs at the time of manufacturing each cover layer. Here, the position of a few microns farther from the information recording layer 6b than the information recording layer 6b is equivalent to a value obtained by integrating errors in manufacturing the thickness of each cover layer when the errors increase. Therefore, if the number of layers increases, it may be ten and several microns. In addition, similar to the spherical aberration caused by the increase in the thickness of the cover layer, due to a manufacturing error or an assembly error of the objective lens or the deformable mirror, or an error in the parallelism of the parallel beam incident on the objective lens, or the like. Spherical aberration occurs. These errors may be evaluated by another means in advance, and may be taken into account when designing the objective lens.
[0029]
When the thickness of the cover layer of the disk 6 is almost the designed value or smaller than the designed value, as shown in FIG. When the objective lens 5 is driven along the optical axis by a drive mechanism (not shown) so that the spherical aberration at the focal point of the convergent light beam 12 from the lens 5 is minimized, the convergence from the objective lens 5 is reduced. The focal point of the light beam 12 is located a few microns farther from the surface of the disk 6 than the information recording layer 6b.
[0030]
When the converging point of the convergent light beam 12 from the objective lens 5 is adjusted to the information recording layer 6b farther from the surface of the disk 6, as shown in FIG. The electrostatic deformable mirror 4 is deformed into a concave surface so as to correct the spherical aberration caused by the reduction of the distance, and the objective lens 5 is moved along the optical axis by a driving mechanism (not shown) so that the objective lens 5 Is focused on the information recording layer 6b. The parallel light beam incident on the electrostatically deformable mirror 4 is reflected there and converted into a convergent light beam. This convergent light beam is converted into a light beam 12 that is converged by the objective lens 5 and converges on the information recording layer 6b.
[0031]
When the focal point of the convergent light beam 12 from the objective lens 5 is adjusted to the information recording layer 6a closer to the surface of the disk 6, as shown in FIG. Further, the electrostatic deformable mirror 4 is further deformed into a concave surface so as to correct the spherical aberration caused by the further reduction of the objective lens, and the objective lens 5 is moved along the optical axis by a drive mechanism (not shown) to The focusing point of the convergent light beam 12 from 5 is adjusted to the information recording layer 6a. The parallel light beam incident on the electrostatically deformable mirror 4 is reflected there and converted into a convergent light beam. The convergence of this light beam is stronger than in the case of FIG. The convergent light beam from the electrostatically deformable mirror 4 is converted into a light beam 12 that is converged by the objective lens 5 and converges on the information recording layer 6a.
[0032]
When the thickness of the cover layer of the disk 6 is several microns larger than the design value due to a manufacturing error or the like, the information recording layer 6b is larger than the information recording layer 6b shown in FIG. 5 is located near the focal point of the convergent light beam 12.
[0033]
In order to match the converging point of the convergent light beam 12 from the objective lens 5 with respect to the information recording layer 6b, a spherical surface generated due to a reduction in the thickness of the cover layer is used in the same manner as described above. The electrostatic deformable mirror 4 is deformed into a concave surface so as to correct the aberration, and the objective lens 5 is moved along the optical axis by a drive mechanism (not shown) so that the convergent light beam 12 from the objective lens 5 is The focal point is adjusted to the information recording layer 6b. The deformation of the electrostatically deformable mirror 4 required at that time is smaller than the deformation of the electrostatically deformable mirror 4 in FIG.
[0034]
FIG. 4 shows characteristics of spherical aberration after correction with respect to the thickness of the cover layer in the present embodiment. In FIG. 4, the characteristics of the spherical aberration after correction are generalized to an optical information recording medium having n information recording layers. For comparison, FIG. 4 also shows the characteristic of the spherical aberration in the case where the aberration is not corrected by the electrostatically deformable mirror 4 by a dashed line.
[0035]
As shown in FIG. 4, the corrected spherical aberration is good even when the thickness of the cover layer is larger than the distance between the surface of the disk and the information recording layer farthest therefrom. Therefore, the information recording / reproducing apparatus of the present embodiment can correct the spherical aberration even for a disk in which the thickness of the cover layer of the information recording layer farthest from the surface of the disk is larger than the design value.
[0036]
In the present embodiment, an information recording / reproducing apparatus for a multilayer recording medium is described as an example, but the technology of the present embodiment may be applied to an information recording / reproducing apparatus for a single-layer recording medium. The technology of the present embodiment particularly has a light source that emits light of a short wavelength and an objective lens with a large numerical aperture for high recording density, and requires correction of spherical aberration during focus adjustment. This is suitable for an information recording / reproducing apparatus for a single-layer recording medium.
[0037]
In the present embodiment, the adjustment of the focal position is performed by a drive mechanism (not shown) that moves the objective lens 5 along the optical axis. However, instead of such a drive mechanism, an electrostatically deformable mirror is used. 4 may be performed. That is, the electrostatically deformable mirror 4 may adjust the focal position in addition to correcting the spherical aberration.
[0038]
Second embodiment
The optical information recording / reproducing apparatus according to the present embodiment has a configuration in which a concave lens is added near the electrostatically deformable mirror to the optical information recording / reproducing apparatus according to the first embodiment. FIG. 5 shows the configuration of the peripheral portion of the objective lens of the optical information recording / reproducing apparatus of the present embodiment. The configuration of a portion not shown in FIG. 5 is the same as that of the first embodiment, and is therefore shown in FIG. 1, so that the illustration of that portion is omitted.
[0039]
As shown in FIG. 5, the optical information recording / reproducing apparatus of the present embodiment has an electrostatic deformable mirror 4 and an objective lens in addition to the configuration of the optical information recording / reproducing apparatus of the first embodiment shown in FIG. 5 further comprises a concave lens 8 arranged between them. As shown in FIG. 5A, the concave lens 8 changes the parallel light beam 11 traveling from the electrostatically deformable mirror 4 to the objective lens 5 into a divergent light beam.
[0040]
The objective lens 5 can be moved along the optical axis for focus control by a drive mechanism (not shown), whereas the concave lens 8 is fixed and its relative position with respect to the electrostatically deformable mirror 4. The relationship does not change.
[0041]
The concave lens 8 is fixed at a fixed position with respect to the electrostatic deformable mirror 4. Therefore, during focus control, the objective lens 5 is moved along the optical axis with respect to the concave lens 8, but the relative positional relationship between the concave lens 8 and the electrostatically deformable mirror 4 does not change. In tracking control, the concave lens 8, the electrostatically deformable mirror 4, and the objective lens 5 are moved together along an axis orthogonal to the optical axis.
[0042]
The objective lens 5 is designed such that the spherical aberration at the converging point of the light beam 12 converged thereby is minimized in the disk 6. More preferably, the objective lens 5 minimizes the spherical aberration at the converging point of the light beam 12 converged thereby at a position between the information recording layer 6b far from the surface of the disk 6 and the information recording layer 6a near. Is designed to be Most preferably, the objective lens 5 minimizes the spherical aberration at the focal point of the light beam 12 converged thereby at an intermediate position between the information recording layer 6b far from the surface of the disk 6 and the information recording layer 6a near. It is designed to be.
[0043]
The concave lens 8 converts the parallel light beam 11 from the electrostatically deformable mirror 4 into a divergent light beam before entering the objective lens 5 so that the convergent light beam 12 from the objective lens 5 is focused. The position at which the spherical aberration is minimized is moved from the above-mentioned disk 6 to a position several microns farther from the surface of the disk 6 than the information recording layer farthest from the surface of the disk 6 closer to the objective lens 5. .
[0044]
When the electrostatic deformable mirror 4 is a plane that is not deformed, the parallel light beam 11 is reflected by the electrostatic deformable mirror 4 and then by the concave lens 8 as shown in FIG. Can be converted to a divergent light beam. The divergent light beam is then converted by the objective lens 5 into a convergent light beam 12. When the objective lens 5 is driven along the optical axis by a drive mechanism (not shown) so that the spherical aberration at the focal point of the convergent light beam 12 from the objective lens 5 is minimized, the convergence from the objective lens 5 Of the light beam 12 is located a few microns farther from the surface of the disk 6 than the information recording layer 6b.
[0045]
When adjusting the focal point of the convergent light beam 12 from the objective lens 5 to the information recording layer 6b farther from the surface of the disk 6, as shown in FIG. The electrostatic deformable mirror 4 is deformed into a concave surface so as to correct the spherical aberration caused by the reduction of the distance, and the objective lens 5 is moved along the optical axis by a driving mechanism (not shown) so that the objective lens 5 Is focused on the information recording layer 6b. The parallel light beam incident on the electrostatically deformable mirror 4 is reflected there and converted into a convergent light beam. After the convergent light beam is weakened by the concave lens 8, the convergent light beam is converted into a light beam 12 converged on the information recording layer 6 b by the objective lens 5.
[0046]
When the focal point of the convergent light beam 12 from the objective lens 5 is adjusted to the information recording layer 6a closer to the surface of the disk 6, as shown in FIG. Further, the electrostatic deformable mirror 4 is further deformed into a concave surface so as to correct the spherical aberration caused by further reduction of the objective lens, and the objective lens 5 is moved along the optical axis by a drive mechanism (not shown) to The focusing point of the convergent light beam 12 from 5 is adjusted to the information recording layer 6a. The parallel light beam incident on the electrostatically deformable mirror 4 is reflected there and converted into a convergent light beam. The convergence of this light beam is stronger than in the case of FIG. The convergence light beam from the electrostatically deformable mirror 4 is converted into a light beam 12 that converges on the information recording layer 6a by the objective lens 5 after the convergence is weakened by the concave lens 8.
[0047]
FIG. 6 shows characteristics of spherical aberration after correction with respect to the thickness of the cover layer in the present embodiment. The characteristic of the spherical aberration after correction shown in FIG. 6 is such that the spherical aberration at the focal point of the convergent light beam 12 is designed such that the spherical aberration is minimized at an intermediate position between the information recording layer 6b and the information recording layer 6a. This is for a combination of a lens 5 and a concave lens 8. In FIG. 6, the characteristics of the spherical aberration after the correction are generalized to an optical information recording medium having n information recording layers. For comparison, FIG. 6 shows the characteristics of the spherical aberration (only the objective lens and the combination of the objective lens and the concave lens) in the case where the aberration is not corrected by the electrostatically deformable mirror 4 together with the one-dot chain line. It is shown.
[0048]
As shown in FIG. 6, the spherical aberration after the correction is good in a range where the thickness of the cover layer is a distance from the surface of the disk to a position farthest from the information recording layer n farthest from the surface of the disk. is there.
[0049]
Therefore, the information recording / reproducing apparatus of the present embodiment can correct the spherical aberration even for a disk in which the thickness of the cover layer of the information recording layer farthest from the surface of the disk is larger than the design value. In particular, when the objective lens 5 is designed so that the spherical aberration at the converging point of the convergent light beam 12 is minimized at a position between the information recording layers 6b and 6a, the spherical surface after the aberration correction is used. The amount of aberration deterioration can be made uniform between the information recording layer 6b and the information recording layer 6a. Further, when the disc has three or more information recording layers, as can be easily imagined from FIG. 6, the deterioration amount of the corrected spherical aberration in each information recording layer can be suppressed to a small value.
[0050]
Further, the information recording / reproducing device of the present embodiment can use an objective lens used in a normal information recording / reproducing device.
[0051]
In the present embodiment, an information recording / reproducing apparatus for a multilayer recording medium is described as an example, but the technology of the present embodiment may be applied to an information recording / reproducing apparatus for a single-layer recording medium. The technology of the present embodiment particularly has a light source that emits light of a short wavelength and an objective lens with a large numerical aperture for high recording density, and requires correction of spherical aberration during focus adjustment. This is suitable for an information recording / reproducing apparatus for a single-layer recording medium.
[0052]
In the present embodiment, the adjustment of the focal position is performed by a drive mechanism (not shown) that moves the objective lens 5 along the optical axis. However, instead of such a drive mechanism, an electrostatically deformable mirror is used. 4 may be performed. That is, the electrostatically deformable mirror 4 may adjust the focal position in addition to correcting the spherical aberration.
[0053]
Although the concave lens 8 is fixed to the electrostatically deformable mirror 4 in the present embodiment, it may be moved together with the objective lens 5 during focus control.
[0054]
Although the concave lens 8 is disposed between the electrostatic deformable mirror 4 and the objective lens 5 in the present embodiment, as shown in FIG. 7 as a modification of the present embodiment, the electrostatic deformable mirror 4 is provided. 4 may be arranged at the preceding stage.
[0055]
Alternatively, instead of arranging the concave lens 8 in the optical path from the collimating lens 3 to the objective lens 5, the light beam traveling from the collimating lens 3 to the electrostatically deformable mirror 4 is not a parallel light beam, but a divergent light beam. May be adopted.
[0056]
Third embodiment
The optical information recording / reproducing apparatus of the present embodiment has a wedge-shaped optical plate instead of the electrostatically deformable mirror in order to correct the spherical aberration with respect to the optical information recording / reproducing apparatus of the first embodiment. are doing. FIG. 8 shows the configuration of the peripheral portion of the objective lens of the optical information recording / reproducing apparatus of the present embodiment. The configuration of a portion not shown in FIG. 8 is the same as that of the first embodiment, and is therefore shown in FIG. 1, so that the illustration of that portion is omitted.
[0057]
As shown in FIG. 8, the optical information recording / reproducing device of the present embodiment uses a collimating lens 3 instead of the electrostatically deformable mirror 4 of the optical information recording / reproducing device of the first embodiment shown in FIG. And a wedge-shaped optical plate 9 that is appropriately movably inserted between the objective lens 5 and the disk 6 to deflect the parallel light beam toward the objective lens 5.
[0058]
The wedge angle 9a of the wedge-shaped optical plate 9 is so small that the influence of coma caused by refraction when the convergent light beam 12 from the objective lens 5 passes through the optical plate 9 can be ignored.
[0059]
The objective lens 5 records information farthest from the surface of the disk 6 closer to the objective lens 5 when the wedge-shaped optical plate 9 is not arranged in the optical path, that is, when the spherical aberration is not corrected. It is designed so that the spherical aberration is minimized at a position a few microns farther than the layer 6b.
[0060]
Here, the position of a few microns farther than the information recording layer 6b and the position of a few microns is the same as in the first embodiment in that the error in manufacturing the thickness of each cover layer is integrated with respect to the case where the error increases. Is equivalent to Therefore, if the number of layers increases, it may be ten and several microns.
[0061]
When the thickness of the cover layer of the disc 6 is as designed, as shown in FIG. 8A, the convergence from the objective lens 5 in a state where the optical plate 9 is not arranged in the optical path. When the objective lens 5 is driven along the optical axis by a drive mechanism (not shown) so that the spherical aberration at the converging point of the light beam 12 is minimized, the converging point of the convergent light beam 12 from the objective lens 5 Comes further away from the surface of the disk 6 by several microns than the information recording layer 6b.
[0062]
When the converging point of the convergent light beam 12 from the objective lens 5 is adjusted to the information recording layer 6b farther from the surface of the disk 6, as shown in FIG. The optical plate 9 is inserted into the optical path so as to correct the spherical aberration caused by the reduction of the distance, and the objective lens 5 is moved along the optical axis by a driving mechanism (not shown), so that the convergence from the objective lens 5 is improved. Is focused on the information recording layer 6b. The parallel light beam from the rising mirror 4A is converted into a convergent light beam 12 by the objective lens 5, and then the optical plate 9 corrects the spherical aberration. The degree of correction of the spherical aberration by the optical plate 9 is appropriately adjusted by the insertion amount of the optical plate 9 inserted into the optical path.
[0063]
When the focal point of the convergent light beam 12 from the objective lens 5 is adjusted to the information recording layer 6a closer to the surface of the disk 6, as shown in FIG. Further, the optical plate 9 is further inserted into the optical path so as to correct the spherical aberration caused by the further reduction, and the objective lens 5 is moved along the optical axis by a drive mechanism (not shown) so that the light from the objective lens 5 The focal point of the convergent light beam 12 is adjusted to the information recording layer 6a. The parallel light beam from the rising mirror 4A is converted into a convergent light beam 12 by the objective lens 5, and then the optical plate 9 corrects the spherical aberration. The optical plate 9 is inserted deeper into the optical path than in the case of FIG. 8B, and strongly corrects spherical aberration.
[0064]
FIG. 9 shows characteristics of spherical aberration after correction with respect to the thickness of the cover layer in the present embodiment. In FIG. 9, the characteristic of the spherical aberration after correction is generalized to an optical information recording medium having n information recording layers. For comparison, FIG. 9 also shows the characteristics of the spherical aberration in the case where the aberration correction is not performed by the optical plate 9 together with a dashed line.
[0065]
As shown in FIG. 9, the spherical aberration after the correction is obtained when the thickness of the cover layer is equal to or less than the distance obtained by adding a predetermined distance to the distance from the disk surface to the information recording layer farthest from the disk surface. , Small enough and constant. Therefore, the information recording / reproducing apparatus of the present embodiment can correct the spherical aberration even for a disk in which the thickness of the cover layer of the information recording layer farthest from the surface of the disk is larger than the design value.
[0066]
In the present embodiment, an information recording / reproducing apparatus for a multilayer recording medium is described as an example, but the technology of the present embodiment may be applied to an information recording / reproducing apparatus for a single-layer recording medium. The technology of the present embodiment particularly has a light source that emits light of a short wavelength and an objective lens with a large numerical aperture for high recording density, and requires correction of spherical aberration during focus adjustment. This is suitable for an information recording / reproducing apparatus for a single-layer recording medium.
[0067]
In the present embodiment, the objective lens 5 has a spherical aberration at the converging point of the convergent light beam 12 changed from the parallel light beam 11 in a state where the wedge-shaped optical plate 9 is not arranged in the optical path. Is designed to be minimum at a position farther than the information recording layer 6b farthest from the surface of the disk 6, but when the wedge-shaped optical plate 9 is slightly inserted into the optical path, this is the case. It may be designed as follows.
[0068]
Although the embodiments of the present invention have been described with reference to the drawings, the present invention is not limited to these embodiments, and various modifications and changes may be made without departing from the spirit of the present invention. May be done.
[0069]
【The invention's effect】
According to the present invention, there is provided an optical information recording / reproducing apparatus capable of appropriately correcting a spherical aberration with respect to a desired information recording layer, which is caused by a variation in the thickness of an optical information recording medium.
[Brief description of the drawings]
FIG. 1 shows an optical information recording / reproducing apparatus according to a first embodiment.
FIG. 2 shows a configuration of the electrostatically deformable mirror shown in FIG.
FIG. 3 shows several states of an objective lens and a deformable mirror with respect to a disk when the thickness of a cover layer is as designed or thin, and FIG. The state where the objective lens is arranged at a position where the spherical aberration at the focal point of the convergent light beam from the lens is minimized is shown. (C) A state in which the focal point of the convergent light beam from the objective lens is aligned with the information recording layer farther from the disk surface, and FIG. Are shown.
FIG. 4 shows characteristics of spherical aberration after correction with respect to the thickness of a cover layer in the first embodiment.
FIG. 5 is a diagram showing a configuration of a peripheral portion of an objective lens of the optical information recording / reproducing apparatus according to the second embodiment, wherein the objective lens and the deformable mirror for a disc when the thickness of a cover layer is as designed or thin. (A) shows the state where the objective lens is located at a position where the spherical aberration at the converging point of the convergent light beam from the objective lens is minimized when the deformable mirror is not deformed. (B) shows a state where the converging point of the convergent light beam from the objective lens is adjusted to the information recording layer farther from the surface of the disk, and (C) shows a state where the convergent light beam is focused from the objective lens. This shows a state where the focal point of the convergent light beam is adjusted to the information recording layer closer to the surface of the disk.
FIG. 6 shows characteristics of spherical aberration after correction with respect to the thickness of a cover layer in the second embodiment.
FIG. 7 shows a modification of the optical information recording / reproducing device of the second embodiment.
FIG. 8 is a diagram showing a configuration of a peripheral portion of an objective lens of the optical information recording / reproducing apparatus according to the third embodiment, wherein the objective lens and the wedge shape for a disc when the thickness of a cover layer is as designed or thin. 7A shows several states of the optical plate, and FIG. 7A shows a state in which the spherical aberration at the converging point of the convergent light beam from the objective lens is minimized when the wedge-shaped optical plate is not arranged in the optical path. (B) shows a state in which the focal point of the convergent light beam from the objective lens is adjusted to the information recording layer farther from the disk surface, C) shows a state in which the focal point of the convergent light beam from the objective lens is adjusted to the information recording layer closer to the surface of the disk.
FIG. 9 shows characteristics of spherical aberration after correction with respect to the thickness of a cover layer in the third embodiment.
[Explanation of symbols]
1 Laser light source
2 Beam splitter
3 Collimating lens
4 Electrostatic deformable mirror
5 Objective lens
6 disks
6a, 6b Information recording layer
7 Detector

Claims (3)

In an information recording / reproducing apparatus that irradiates an optical information recording medium having a plurality of information recording layers with a light beam and thereby records information or reproduces information by detecting reflected light from the optical information recording medium, An objective lens having a light source that emits a beam, an objective lens that converges the light beam, and an electrostatically deformable mirror that corrects spherical aberration and is disposed in an optical path between the light source and the objective lens. Is designed so that the spherical aberration at the focal point of the light beam converged thereby is minimized at a position farther from the information recording layer farthest from the surface of the optical information recording medium on the side of the objective lens. Optical information recording and reproducing device. In an information recording / reproducing apparatus which irradiates an optical information recording medium having a plurality of information recording layers with a light beam and thereby records information, or reproduces information by detecting reflected light from the optical information recording medium, divergence occurs. A light source that emits a non-uniform light beam, a collimating lens that converts the divergent light beam from the light source into a parallel light beam, an objective lens that converges the light beam, and an optical path between the collimating lens and the objective lens. Further, the objective lens has an electrostatically deformable mirror that corrects spherical aberration, and the objective lens has a spherical aberration at a focal point of a light beam converged by the mirror. It is designed to be minimized at the position between the information recording layer farthest from and the information recording layer closest to the information recording layer, and is further arranged in the optical path between the electrostatically deformable mirror and the objective lens. And it has a concave lens, an optical information recording and reproducing apparatus. In an information recording / reproducing apparatus which irradiates an optical information recording medium having a plurality of information recording layers with a light beam and thereby records information, or reproduces information by detecting reflected light from the optical information recording medium, divergence occurs. A light source that emits a neutral light beam, an objective lens that converges the light beam, and an electrostatically deformable mirror that corrects spherical aberration and is disposed in an optical path between the light source and the objective lens. The lens minimizes the spherical aberration at the focal point of the light beam converged by the lens at the position between the information recording layer farthest from the surface of the optical information recording medium on the side of the objective lens and the nearest information recording layer. And further comprising a lens disposed in an optical path between the light source and the electrostatically deformable mirror, for causing a divergent light beam to be incident on the electrostatically deformable mirror, Optical information Reproducing apparatus.

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