JP2000155979A - Aberration-detecting device and optical information recording/reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aberration-detecting device for controlling the aberration of an optical disk or the like with a speedy closed loop. SOLUTION: A light beam at a return path that is emitted from a light source 101 and is reflected from an optical disk 106 is separated by a half mirror 102 and is split into a light beam through a specific region and that through the other regions by a hologram 109 for deflection. The light beam through the specific region is received by a plurality of photo detectors 107, and the obtained signals are compared, thus detecting aberration. An aberration correction element 104 is driven in real time based on it, thus reducing the aberration of an optical system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The first invention relates to an optical information recording medium such as an optical disk (hereinafter sometimes referred to as an information carrier).
The present invention relates to an aberration detection device for an optical system used in an optical information recording / reproducing device for recording information on or reproducing the recorded information.

[0002] The second invention relates to an optical information recording / reproducing apparatus for recording a large amount of information on an optical information recording medium (information carrier) using a laser beam or reproducing the recorded information. In particular, it relates to an optical information recording / reproducing apparatus for an information carrier such as an optical disk having a plurality of recording information layers.

[0003]

2. Description of the Related Art Conventionally, as an aberration correcting means for an optical disc, one described in Japanese Patent Application Laid-Open No. 8-212611 is known.

FIG. 20 shows a schematic configuration of a conventional wavefront aberration correction method. 20, reference numeral 801 denotes a magneto-optical disk,
811 denotes a semiconductor laser, 812 denotes a collimator lens for converting a divergent light beam from the semiconductor laser 811 into a parallel light beam,
Reference numeral 813 denotes an anamorphic prism for correcting a light beam into a circular cross section, 814 a reflection mirror, 816 a reflection mirror, 81
7, an objective lens; and 818, a liquid crystal element. Also, 82
0 is a compound prism, 822 is an APC sensor for detecting and controlling the power of laser light, 825 is a half-wave plate, 826 is a polarizing beam splitter, and 829 and 83.
0,833 is a light receiving element, 850 is a liquid crystal control circuit, 854
Is a microcomputer.

In the apparatus shown in FIG. 20, a liquid crystal control circuit 850 is driven based on information from a memory to control a liquid crystal element 818 to perform aberration correction. Specifically, when an aberration occurs, the phase of the liquid crystal aberration correction element 818 is controlled in an open loop so as to minimize the wavefront aberration. When the wavefront aberration changes due to temperature or the like,
Temperature detection is performed, and wavefront aberration is corrected based on the detected temperature and control information stored in advance in association with the temperature.

In the example of FIG. 20, the light receiving element 8 for detecting a signal is used.
29, 830 and a signal from the light receiving element 833 for detecting an error signal are inputted to the microcomputer 854, and the liquid crystal control circuit 850 applies an applied voltage to each element of the liquid crystal element 818 so that the detection signal of the light receiving element becomes good. Is determined.

[0007] Further, in the publication, a method of measuring wavefront aberration using an interference system is described as an aberration detection method.
In addition, it is possible to obtain the type of the disc and the control information of the liquid crystal necessary for correcting the wavefront aberration generated when the disc is used, and to correct the wavefront aberration based on a table calibrated in advance. It has been disclosed. For this purpose, an interference system is constructed outside and a measuring device is formed to measure the wavefront aberration, but the specific configuration of the interference system is not disclosed.

[Second Invention] As a so-called read-only optical information recording medium for reproducing a signal using a laser beam, an optical disk called a compact disk (CD) and an optical disk called a laser disk (LD) And an optical disk called a digital video disk.

At present, 4.7 GB of DVD-ROM is currently used among the commercially available reproduction-only optical information recording / reproducing apparatuses on which signals are recorded at the highest density.

A read-only DVD having a diameter of 120 mm has a single-side read single-layer type with a maximum user capacity of 4.7 GB.
Formats such as a double-sided reading single-layer type having the same capacity of 9.4 GB at the maximum and a single-sided reading two-layer type of the same capacity at the maximum of 8.5 GB are determined by the standard.

FIG. 21 shows an example of the structure of a single-sided readout two-layer type optical disk. In the present optical disc, the substrate 918 is used.
The first recording information layer 919 and the second recording information layer 92 are irradiated through the substrate 918 by irradiating a laser beam from the side.
Signals recorded in any one layer can be reproduced.
Between the first recording information layer 919 and the second recording information layer 921, the laser beam incident from the substrate 918 is optically separated into the first recording information layer 919 and the second recording information layer 921. An optical separation layer 920 is provided. Also, the second
The second recording information layer 92 is provided on the lower surface side of the recording information layer 921 of FIG.
1 is provided. In addition,
A method of manufacturing a read-only optical disk having a multilayer structure is disclosed in, for example, US Pat. No. 5,126,996.

Optical information recording media on which signals can be recorded and reproduced using laser light include phase-change optical disks, magneto-optical disks, dye disks, and the like.

Of these, in a recordable phase-change optical disk, a chalcogenide is generally used as a recording thin film material. In general, a signal is recorded by setting the recording thin film material in a crystalline state to an unrecorded state, irradiating a laser beam, melting and rapidly cooling the recording thin film material to an amorphous state. On the other hand, when erasing a signal, the recording thin film is brought into a crystalline state by irradiating a laser beam having a lower power than during recording.

From the viewpoint of improving the recording density of a recordable or recordable / erasable optical disc, a signal is recorded in both a guide groove (groove) and a guide groove (land) provided on the surface of the substrate. Groove recording has been proposed (for example, Japanese Patent Application Laid-Open No. 5-282705).

From the viewpoint of increasing the recording capacity of a recordable or recordable / erasable phase-change optical disc, a disc having a two-layer structure has been proposed (for example, see Japanese Patent Application Laid-Open No. Hei 9 (1998)).
-212917).

In order to increase the recording / reproducing density of these discs, a high numerical aperture (NA Numerical Aperture) is required.
It is desired to perform recording and reproduction using an objective lens having the following. In the conventional optical disk device, there is no example in which an objective lens having a high NA is used so that the thickness error of the substrate becomes a problem, and the thickness error of the substrate is not particularly considered.

An idea for correcting the spherical aberration of a two-layer disc by a reproducing apparatus is described in Japanese Patent Application Laid-Open No. 7-77031. Here, the predicted amount of spherical aberration that occurs when an objective lens and a two-layer disc are used is corrected. A liquid crystal layer is described as an embodiment as an element for generating an optical phase difference for aberration correction.
When the NA is low, the correction can be sufficiently performed by this method.

That is, the thickness variation of the disk substrate is usually 30 to 60 microns even if it is manufactured with high accuracy, and the thickness of a CD or the like has a variation of about 100 microns. CD
A lens having an NA of 0.4 to 0.45 is used for reproduction of. NA = 0.5 for a recordable CD-R device
A lot of lenses are used. Furthermore, since the density of DVD is increased, a lens having NA = 0.6 is used. A recording / reproducing system with an NA of 0.6 or less can manage and reproduce a disk with a thickness of several tens to 100 microns. However, when the NA is 0.6 or more, variations in the thickness of the substrate and aberrations possessed by the lens itself become problems.

In the method described in Japanese Patent Application Laid-Open No. 7-77031, when the thickness of the substrate changes, spherical aberration caused by the change cannot be corrected. Further, since the correcting element is located in the middle of the optical system, it becomes a spherical aberration correcting element having an optical axis different from the optical axis of the objective lens.
The spherical aberration that changes with the power increases and cannot be applied to an optical system with a high NA.

[0020]

[Problems to be Solved by the Invention] [First Invention]
In the above-described conventional aberration correction method, the wavefront aberration is changed by trial and error so that the S / N of the signal is best,
A correction method for forming a closed loop so as to reduce the wavefront aberration as a result is shown.

However, in this method, since the best point is obtained in a hill-climbing manner (by trial and error) while judging whether the signal is good or bad, control is not performed by a closed loop which takes a long time for detection and has a fast response.

The first aspect of the present invention solves the above-mentioned conventional problems and provides an aberration detection apparatus which can detect aberrations in real time or time in accordance with real time and perform high-speed closed loop control. With the goal.

[Second Invention] The idea of doubling the recording capacity by making a recordable / erasable optical disk a two-layer structure has already been proposed (for example, Japanese Patent Application Laid-Open No. 9-2).
No. 12917) has not been put to practical use because a method for solving the following problems has not been found.
In the present invention, the first recording information layer is a recordable layer in front of the recording / reproducing laser beam as viewed from the incident side, and the second recording information layer is a recording / reproducing laser. Refers to a recordable layer at the back as viewed from the light incident side.

1. An optical system for recording / erasing / reproducing a signal, means for performing good recording / reproducing at the same level on both the first recording information layer and the second recording information layer using an objective lens having a high NA. Not found.

2. An optical system for recording / erasing / reproducing signals, and no means has been found to reduce spherical aberration in both the first recording information layer and the second recording information layer using an objective lens having a high NA. .

3. No configuration of an optical system capable of overwriting at high speed has been found in either the first recording information layer or the second recording information layer.

The structure of the optical information recording medium according to the present invention is as follows.
A plurality of recording information layers are provided on a substrate in the order of a first recording information layer / optical separation layer / second recording information layer /..., And the plurality of recording information layers are capable of storing and reproducing information. Including materials. A typical material is a recording material that reversibly changes phase between an amorphous state and a crystalline state by irradiation with a laser beam, and records, erases, and reproduces a signal by irradiating the laser beam through the substrate. It is a possible material.

When recording or reproducing data on or from an optical disk having the above-described substrate, the actual thickness is determined by the design substrate thickness used in designing the lens (hereinafter simply referred to as “design substrate thickness”).
Aberrations are generated depending on the separation.

The spherical aberration W ₄₀ that occurs when the thickness variation from the designed substrate thickness is t, the refractive index of the substrate is n, and the aperture ratio of the objective lens is NA is expressed as follows.

W ₄₀ = (1/8) (1 / n−1 / n ³ ) t (NA) ⁴ If the amount of this aberration exceeds 35 mλ (milli-lambda) when the working wavelength is λ, the recording / reproducing characteristics are degraded. Has a major adverse effect.

For example, NA = 0.60, n = 1.5, W ₄₀
= 35 mλ, t = 14.5 μm.

For the sake of simplicity, in the case of a two-layer disc having two recording information layers, if the thickness of the design substrate is exactly the middle thickness of the two-layer disc, the maximum thickness change is ± 14.
Since the thickness is 5 μm, the thickness between the two layers needs to be 29 μm or less. On the other hand, if the thickness between the two layers is small, interference from the layers is large, which has an adverse effect on the recording / reproducing characteristics. For example, assuming that the interlayer distance is about 10 μm, when recording / reproducing one layer, the focus servo is affected by stray light from the other layer, and good recording / reproduction cannot be performed.

Therefore, the substantially allowable interlayer thickness is 15 μm.
m to 29 μm, but it is difficult to actually manufacture such a disk.

According to the second aspect of the present invention, the optical information capable of stably recording / reproducing information with respect to an information carrier having two or more recording information layers by correcting spherical aberration caused by a thickness error. An object of the present invention is to provide a recording and reproducing device.

[0035]

Means for Solving the Problems [First invention] In order to achieve the above object, the present invention provides a method capable of detecting aberrations in real time. Focusing on the occurrence of a random distribution, the aberration is detected by detecting this distribution. Although it is difficult to quantitatively determine the amount of aberration,
It is relatively easy to detect the type of aberration and whether the aberration is above a certain value.

The aberration is detected, and the aberration correcting element is driven within a time corresponding to a real time or a real time to correct the aberration, thereby improving the characteristics of the condensed beam. Can be obtained.

The first invention has the following configuration.

The aberration detecting device according to the first configuration of the first invention comprises a radiation light source for emitting a light beam, an objective lens for condensing the light beam on an information carrier, and an objective lens reflected on the information carrier. A light beam branching unit that separates the light beam on the return path that has passed through the objective lens from the light beam on the outward path, and the light beam on the return path separated by the branching unit passes through the light beam that passes through a specific region and other regions And a plurality of light detecting means for receiving the light beam passing through the deflected specific area, and comparing signals from the plurality of light detecting means. And detecting aberration.

Further, the aberration detecting device according to the second configuration of the first invention comprises a radiation light source for emitting a light beam, an objective lens for condensing the light beam on an information carrier, The reflected light beam on the return path that has passed through the objective lens is split into a light beam that passes through a specific region and a light beam that passes through other regions, and the light beam that passes through the specific region is different from the radiation light source. A light deflecting means for deflecting light in a direction, and a plurality of light detecting means for receiving a light beam passing through the deflected specific area, and detecting aberration by comparing signals from the plurality of light detecting means. It is characterized by the following.

According to the first and second configurations, the aberration of the optical system can be detected in real time or near real time. Therefore, if the aberration correction element is driven based on the detection result, the aberration of the optical system can be reduced. Therefore, it is possible to reproduce information carriers (disks) having large surface deviations and information carriers (disks) having different substrate thicknesses, which were difficult in the past. Further, since the tolerance of the information carrier can be relaxed, the production of the information carrier becomes easy.

In the first and second configurations, it is preferable that the light deflecting means is a hologram that divides a light beam into a plurality of parts and diffracts the light beam. By using such a hologram element, a light beam can be efficiently split by one element, and the optical system can be made compact.

In the first and second configurations, the plurality of light detecting means include at least two divided photodetectors, and a light beam passing through the specific area is divided into the two divided photodetectors. It is preferable to be installed so as to irradiate on a line. According to this configuration, when the aberration occurs, the distribution of the light beam spot changes and a difference occurs in the output between the two divided photodetectors. Therefore, by detecting this difference, the aberration can be stabilized with a simple configuration. Can be detected.

In the first and second configurations, one of two regions obtained by dividing the region through which the light beam on the return path passes by a plane including the optical axis of the light beam into two parts. It can be a substantially central region. According to such a configuration, coma aberration can be detected.

In the first and second configurations,
The specific region is made substantially coincident with one region obtained by dividing a region sandwiched between two concentric circles having different diameters about the optical axis of the light beam on the return path into two planes including the optical axis. Can be. According to such a configuration, spherical aberration can be detected.

In the first and second configurations, it is preferable that the light deflecting means is a blazed hologram. According to this configuration, it is possible to use the deflection unit with higher efficiency than a normal hologram, and thus it is possible to detect aberration with high sensitivity.

[0046] In the second configuration, it is preferable that the plurality of light detection means are arranged near the radiation light source and symmetrically with respect to the radiation light source. According to such a configuration, when a hologram is used as the light deflecting means, it is possible to efficiently receive + 1st-order and -1st-order diffracted lights that appear at symmetrical positions with respect to the radiation light source with the same diffraction efficiency. A good optical system can be formed.

In the second configuration, the light deflecting means comprises a hologram for diffracting only a predetermined polarized light and a quarter-wave plate, and in the hologram, an outgoing light from the radiation light source toward the information carrier. Preferably, the beam is not diffracted, and the light beam on the return path is divided into a plurality of parts and diffracted in different directions. According to such a configuration, the light use efficiency of the optical system can be increased.

[Second Invention] In the present invention, an optical device for correcting spherical aberration is provided in order to eliminate the influence of spherical aberration and enable recording and reproduction of an information carrier having a multilayer structure. There are various means for correcting spherical aberration. Here, a method for correcting spherical aberration by adjusting the position of the lens system in the optical axis direction and a method for correcting spherical aberration by correcting the optical phase of a light beam incident on the objective lens are provided.

To change the distance between lenses, a micromachine, an electromagnetic actuator, a piezo element, an ultrasonic motor, or the like can be used.

To correct the optical phase of the light beam incident on the objective lens, it is necessary to change the phase distribution of the light beam. Therefore, the inside of the effective pupil of the light beam is divided into minute regions, and the phase advance or phase delay is corrected for each region. For example, a liquid crystal element can be used as the element for performing the phase correction.

The second invention has the following configuration.

The optical information recording / reproducing apparatus according to the first structure of the second invention is a device for recording / reproducing information on a recordable / reproducible information carrier having a plurality of recording information layers and an optical separation layer sandwiched between the recording information layers. Recording, or an optical information recording and reproducing apparatus for reproducing the recorded information, a radiation light source that emits a light beam, and a light beam from the radiation light source at least of the plurality of recording information layers The light beam condensing means for converging light on one recording information layer and a spherical aberration correcting means integrally formed with the light beam condensing means are provided. According to such a configuration, even if the information carrier has a thickness deviated from the design substrate thickness, the spherical aberration is corrected by the spherical aberration correcting means, and the spherical aberration is reduced with respect to the recording information layer. Recording and reproduction characteristics can be obtained. Thereby, even if spherical aberration caused by a thickness error of the substrate occurs, it is possible to stably perform recording / reproducing on each recording information layer from one surface side of the information carrier having a plurality of recording information layers. it can. As a result, a large-capacity optical information recording medium and an optical information recording / reproducing device therefor can be realized.

In the above-mentioned first configuration, the light beam condensing means may comprise two groups of convex lenses, and the spherical aberration correcting means may change the distance between the two groups of convex lenses. Changing the distance between the two groups of convex lenses changes the spherical aberration. Therefore, by automatically adjusting this distance with respect to the recordable recording information layer of the optical disc so as to minimize spherical aberration, optimal recording and reproduction can be performed.

In the above-mentioned first configuration, the light beam focusing means comprises two aspherical lenses, and the spherical aberration correcting means changes the distance between the two aspherical lenses. be able to. There is a method of configuring a high NA objective lens by combining a plurality of convex lenses, and the above configuration corresponds to such a case. However, two lenses can be formed by using an aspheric lens. By optimizing the distance between the two aspheric lenses, spherical aberration can be minimized.

In the first configuration, the light beam condensing means comprises one aspherical lens and one spherical lens, and the spherical aberration correcting means comprises the aspherical lens and the spherical lens. The distance between them may be changed. To construct a high NA objective lens, a combination of an aspheric lens and a spherical lens can be used. By optimizing the distance between the aspherical lens and the spherical lens, spherical aberration can be minimized.

An optical information recording / reproducing apparatus according to a second configuration of the second invention is characterized in that a recording / reproducing information carrier having a plurality of recording information layers and an optical separation layer sandwiched between the recording information layers is provided with information. Recording, or an optical information recording and reproducing apparatus for reproducing the recorded information, a radiation light source that emits a light beam, and a light beam from the radiation light source at least of the plurality of recording information layers A light beam focusing means for focusing on one recording information layer; a spherical aberration correcting means integrally formed with the light beam focusing means between the radiation light source and the light beam focusing means; Wherein the spherical aberration correcting means changes optical phases which are equal in a circumferential direction of a circle centered on an optical axis of the light beam condensing means and different in a radial direction. According to such a configuration, by adding the same amount of optical phase with the opposite polarity to the optical phase distribution in the radial direction around the optical axis generated by spherical aberration, the light distribution in the pupil becomes uniform as a whole, Spherical aberration can be canceled out and reduced. As a result, even if the information carrier has a thickness deviating from the design board thickness,
By correcting the aberration by the spherical aberration correcting means and reducing the spherical aberration with respect to the recording information layer, good recording / reproducing characteristics can be obtained. Thereby, even if spherical aberration caused by a thickness error of the substrate occurs, it is possible to stably perform recording / reproducing on each recording information layer from one surface side of the information carrier having a plurality of recording information layers. it can. As a result, a large-capacity optical information recording medium and an optical information recording / reproducing device therefor can be realized.

[0057]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic configuration diagram of an aberration detection apparatus according to Embodiment 1.

A light beam emitted from a light source 101 such as a semiconductor laser passes through a half mirror 102, is converted into substantially parallel light by a collimating lens 103, passes through a wavefront conversion element 104, and passes through a substrate of an optical disk 106 by an objective lens 105. At the recording / reproducing information surface.

The light beam reflected on the recording / reproducing information surface passes through the substrate again, and the objective lens 105, the wavefront conversion element 10
4. The light passes through the collimator lens 103, is reflected by the half mirror 102, is transmitted through the hologram 109, is diffracted, and is incident on the photodetector 107 for signal detection. The photodetector 107 includes an information signal, a control signal such as a focus signal and a tracking signal, and a photodetector such as a pin diode for detecting aberration of the light beam. These detection elements may be configured independently for each signal detection, or may be integrated to have a plurality of functions. The detected aberration is processed by the signal processing circuit 108, and the wavefront conversion element 1
04 is driven.

As the wavefront conversion element 104, for example, the following method can be used, and a liquid crystal sealed in a portion sandwiched between two glass substrates can be used. When a portion through which a light beam passes is divided into a plurality of regions, and a voltage is independently applied to each region, the refractive index of each corresponding portion can be changed. By utilizing this change in the refractive index, the phase of the wavefront can be changed. If the light beam has an aberration, the phase of the light beam partially changes. Therefore, the aberration can be corrected by driving the wavefront conversion element 104 so as to complement the changed phase. When the voltage is applied according to the degree of aberration, it is possible to correct the aberration more accurately.

In a situation where the optical system has no aberration, the photodetector 10
7, no aberration is detected, and therefore, there is no change in the wavefront conversion element 104, and the element becomes equivalent to a simple glass parallel plate.
However, when an aberration occurs, the manner of the detection signal differs depending on the type of the aberration.

Hereinafter, three typical examples of aberration will be described.

As a first example, for example, the optical disk 106
When tilted, coma occurs when the light beam passes through the substrate of the optical disk. This coma is detected by the photodetector 107, and the wavefront conversion element 10 is set so as to cancel the coma.
4 can be driven to correct aberrations. As a method of wavefront conversion for correcting coma, a method using a wavefront conversion element composed of multi-divided liquid crystal can be used.

A method for detecting coma will be described below.

FIG. 2 shows the wavefront aberration when coma aberration occurs. With respect to the reference wavefront 11 in the aperture, there is an advance 11a and a delay 11b of the wavefront with the optical axis 10 as a boundary. When the reference wavefront 11 is converged, the wavefront 11a is advanced and the wavefront 11b is delayed
Are all defocused. Therefore, by detecting only the advanced wavefront or delayed wavefront and detecting the focus state, it is possible to know the state of occurrence of coma.

FIG. 3 shows an example of an optical system for detecting coma. The optical axis 10 passes through the origin of the XY coordinate system, and a case where coma aberration occurs in the Y-axis direction is considered. In the return light beam 12 that is reflected and condensed from the optical disk, only the light beam that passes through the substantially central portion 13 of the region where Y> 0 is separated from the light beam that passes through the region other than the region 13 to be divided into two. Photodetectors 17a, 17
b, and the light spot 14 is formed. here,
When no aberration occurs, the light spot 14 is formed so as to be focused on the dividing line of the photodetectors 17a and 17b. When coma aberration occurs in the Y-axis direction, the light beam passing through the region 13 has a phase advanced or delayed with respect to the light beam passing through the other regions. In other words, the region 1 is selected so that a light beam whose phase is advanced or delayed can be extracted.
Set 3. In the example of FIG. 3, the region 13 is illustrated as a semicircle, but is not limited thereto, and may be a circle, an ellipse, a rectangle,
It may have an arc shape or the like.

FIG. 4 shows a light beam 14 on a two-segment photodetector.
The shape and the formation position are shown.

FIG. 4A shows a case where the phase of the light beam passing through the area 13 is delayed, and the light beam becomes a light beam condensed behind the detection surface of the photodetector. At this time, since the light beam passes through the photodetector 17a,
The output of the light detector 17a becomes larger than the output of the light detector 17b.

FIG. 4B shows a case where there is no advance or delay of the phase of the light beam passing through the area 13 (that is, when there is no aberration), and the light beam is on the detection surface of the photodetectors 17a and 17b. Thus, the light beam is condensed on the two dividing lines. At this time, the output of the photodetector 17a and the output of the photodetector 17b have the same magnitude.

FIG. 4C shows a case where the phase of the light beam passing through the region 13 is advanced, and the light beam becomes a light beam that is focused ahead of the detection surface of the photodetector. At this time, since the light beam passes through the photodetector 17b,
The output of the light detector 17a becomes smaller than the output of the light detector 17b.

As described above, the two-split photodetectors 17a and 17b
By detecting the difference signal between the respective output signals of
If the coma is minute, the amount and sign of the coma can be known. When an aberration larger than a certain level occurs, the difference signal is saturated. Therefore, even if the sign of the coma is known, the amount of the coma cannot be known. In such a case, the amount of coma can be measured by calculating the signal by dividing the photodetector into multiple parts.

As a second example, in FIG. 1, for example, if the thickness of the optical disk 106 is different, a spherical aberration occurs when the light beam passes through the substrate. This spherical aberration is detected by detector 1
At 07, the wavefront conversion element 104 is driven so as to cancel the spherical aberration, and the aberration can be corrected. As a method of wavefront conversion for correcting spherical aberration, a method using a wavefront conversion element composed of multi-divided liquid crystal can be used.

The method for detecting spherical aberration will be described below.

FIG. 5 shows wavefront aberration in which spherical aberration occurs. Wavefront delays 21a and 21b are symmetrical to the optical axis 10 with respect to the reference wavefront 21 in the aperture. When the reference wavefront 21 is converged, the positions where the delayed wavefronts 21a and 21b converge with respect to the converging point are defocused. Therefore, by detecting only the delayed wavefront and detecting the focus state, the occurrence state of the wavefront aberration can be known. Note that, contrary to the above, wavefront aberration also occurs when the wavefront advances symmetrically with respect to the optical axis 10.

FIG. 6 shows an example of an optical system for detecting spherical aberration. The optical axis 10 passes through the origin of the XY coordinate system. The return light beam 22 reflected from the optical disk and condensed passes through a region (semi-ring-shaped region) 23 of Y> 0 of a region between two concentric circles having different diameters centered on the optical axis 10. Is separated from the light beam passing through the area other than the area 23,
The light is condensed on the divided photodetectors 17a and 17b to form a light spot 24. Here, when no aberration occurs, the light spot 24 is formed so as to be focused on the division line of the photodetectors 17a and 17b.
When the spherical aberration occurs, the light beam passing through the region 23 has a phase advanced or delayed with respect to the light beam passing through the other regions. In other words, the region 23 is set so that a light beam whose phase is advanced or delayed can be extracted. The radius of the ring and the width in the radial direction of the semi-ring region 23 can be set according to the state of the wavefront aberration of the light beam.

FIG. 7 shows the light beam 24 on the two-segment photodetector.
The shape and the formation position are shown.

FIG. 7A shows a case where the phase of the light beam passing through the region 23 is delayed, and the light beam becomes a light beam that is focused behind the detection surface of the photodetector. At this time, since the light beam passes through the photodetector 17a,
The output of the light detector 17a becomes larger than the output of the light detector 17b.

FIG. 7B shows a case where there is no advance or delay in the phase of the light beam passing through the area 23 (ie, when there is no aberration), and the light beam is on the detection surface of the photodetectors 17a and 17b. Thus, the light beam is condensed on the two dividing lines. At this time, the output of the photodetector 17a and the output of the photodetector 17b have the same magnitude.

FIG. 7C shows a case where the phase of the light beam passing through the region 23 is advanced, and the light beam becomes a light beam that is focused forward of the detection surface of the photodetector. At this time, since the light beam passes through the photodetector 17b,
The output of the light detector 17a becomes smaller than the output of the light detector 17b.

As described above, the two-split photodetectors 17a and 17b
By detecting the difference signal between the respective output signals of
If the spherical aberration is minute, the amount and sign of the spherical aberration can be known. When an aberration larger than a certain level occurs, the difference signal is saturated, so that the sign of the spherical aberration is known but the amount of the spherical aberration cannot be known. In such a case, the amount of spherical aberration can be measured by calculating the signal by dividing the photodetector into multiple parts.

As a third example, in FIG. 1, astigmatism occurs when a light beam passes through a substrate due to, for example, birefringence of the optical disk 106 or the like. This astigmatism is detected by the detector 107
The wavefront conversion element 1 is detected so as to cancel the astigmatism.
04 can be driven to correct aberrations. As a method of wavefront conversion for correcting astigmatism, a method using a wavefront conversion element composed of multi-divided liquid crystal can be used.

The method for detecting astigmatism can be performed based on the same concept as the method for detecting coma and spherical aberration described above.

In FIG. 1, the hologram 109 as the light deflecting means may be a blazed hologram.
This makes it possible to use deflection means with higher efficiency than a normal hologram.

The photodetector 107 is a photodetector divided into a plurality of areas such as an information signal, a control signal such as a focus signal and a tracking signal, and a pin diode for detecting the aberration of the light beam. The part to be detected also includes at least two divided light detection elements, and is set so that the light beam deflected by the hologram 109 falls on the dividing line of the two divided light detection elements.

(Embodiment 2) FIG. 8 is a schematic configuration diagram of an aberration detection apparatus according to Embodiment 2.

A light beam emitted from a light source 101 such as a semiconductor laser passes through a hologram 109, is converted into substantially parallel light by a collimator lens 103, passes through a wavefront conversion element 104, and passes through an objective lens 105 over a substrate of an optical disk 106. It is incident on the recording / reproducing information surface.

The light beam reflected on the recording / reproducing information surface passes through the substrate again, and the objective lens 105, the wavefront conversion element 10
4. The hologram 1 transmitted through the collimating lens 103
It is diffracted at 09 and enters the photodetectors 107 and 111 for signal detection. Each of the photodetectors 107 and 111 includes an element for detecting an information signal, a control signal such as a focus signal and a tracking signal, and an aberration of a light beam. These detection elements may be configured independently for each signal detection, or may be integrated to have a plurality of functions. The detected aberration is processed by the signal processing circuit 108 and the wavefront conversion element 10
4 is driven.

In a situation where the optical system has no aberration, the photodetector 10
No aberration is detected at 7, 111, and therefore the wavefront conversion element 1
04 has no change, and is an element equivalent to a simple glass parallel plate. When an aberration occurs, it is detected by the same detection method as described in the first embodiment.

According to the present embodiment, a more compact aberration detector can be obtained as compared with the first embodiment.

(Embodiment 3) FIG. 9 shows a specific method of detecting coma aberration.

The hologram 109 has a plurality of regions 109a to 109a.
The photodetectors 107a to 107h are provided corresponding to the respective regions. That is, the area 109
a corresponds to the photodetectors 107g and 107h,
b corresponds to the photodetectors 107a and 107b,
c corresponds to the photodetectors 107e and 107f,
d corresponds to the photodetectors 107c and 107d. The area division of the hologram 109 is performed according to the concept described with reference to FIG. As described above, in order to deflect the light beam into a plurality of light beams in accordance with the region through which the light beam passes, for example, the spatial frequency (pitch) and the diffraction direction of the hologram 109 can be appropriately set for each region. .

Assuming that coma occurs in the Y-axis direction, the area 109 on the detection hologram 109
The phase error is largest between a and the region 109b, and the phase error is relatively small in the regions 109c and 109d. Therefore, when each of these four regions is detected, coma can be detected. Since coma is an aberration symmetric with respect to the X axis, it can be detected from a combination of the region 109a and the region 109c. Area 1
It is also possible to detect from the combination of 09b and the area 109d.

The photodetector 107 is located near the light beam converging point and employs a so-called knife-edge method.

The detection of the far-field tracking error signal can be obtained by detecting the difference in the light amount between the light beam passing through the portion of Y> 0 of the hologram and the light beam passing through the portion of Y <0. That is, the far-field tracking signal TE is given by: TE = [(107a) + (107b) + (107c) +
(107d)]-[(107e) + (107f) + (1
07g) + (107h)].

FIG. 10 shows a state of a light spot (hatched portion) by a light beam on the detector 107 when focus detection is performed by the knife edge method. In this case, assuming that there is no coma aberration, all the light beams are converged on the dividing line of the two-part photodetector as shown in FIG.
When the focus is shifted and, for example, the optical disc 106 and the objective lens 105 move in a direction approaching each other, FIG.
The elements 107a, 107c, 107f, 1 as shown in FIG.
The output at 07h increases. When the optical disk 106 and the objective lens 105 move away from each other, FIG.
The elements 107b, 107d, 107e, 1 as shown in FIG.
The output of 07g increases. Therefore, a focus signal can be obtained by processing these signals. That is, the focus signal FE is given by FE = [(107c) + (107f)]-[(107
d) + (107e)].

FIG. 11 shows a state of a light spot (hatched portion) by the light beam on the photodetector 107 when the focus is set (when the focus is achieved).

When no coma aberration occurs, FIG.
As shown in (B), the outputs of all the photodetectors do not change substantially equally.

When coma of a certain polarity occurs, the coma aberration shown in FIG.
As shown in (A), the outputs of the photodetectors 107a and 107g increase and the outputs of 107b and 107h decrease, but the outputs of the photodetectors 107c, 107d, 107e and 107f do not change.

When coma of the opposite polarity occurs, FIG.
As shown in (C), the outputs of the photodetectors 107b and 107h increase and the outputs of 107a and 107g decrease, but the outputs of the photodetectors 107c, 107d, 107e and 107f do not change.

Therefore, by processing these signals, it is possible to obtain a coma aberration detection signal. That is, coma aberration C
M is: CM = [(107a) + (107g)] − [(107
b) + (107h)] can be detected.

(Embodiment 4) FIG. 12 shows a specific method for detecting spherical aberration.

The hologram 109 has a plurality of areas 109e-
The photodetectors 107a to 107h are provided corresponding to the respective regions. That is, the area 109
e corresponds to the photodetectors 107g and 107h,
f corresponds to the photodetectors 107a and 107b,
g corresponds to the photodetectors 107c and 107d, and
h corresponds to the photodetectors 107e and 107f. The area division of the hologram 109 is performed according to the concept described with reference to FIG. As described above, in order to deflect the light beam into a plurality of light beams depending on the region through which the light beam passes, for example, the spatial frequency (pitch) and the diffraction direction of the hologram 109 can be appropriately set for each region. .

Assuming that spherical aberration has occurred,
On the detection hologram 109, regions 109e, 109
The phase error between f and the regions 109g and 107h is largest. Therefore, when these two regions are respectively detected, spherical aberration can be detected. Since the spherical aberration is an aberration symmetric with respect to the X axis and the Y axis, it can be detected from a combination of the region 109e and the regions 109g and 109h. Similarly, the region 109f and the region 109g, 1
It is also possible to detect from the combination with 09h.

FIG. 13 shows a state of a light spot (shaded portion) by a light beam on the photodetector 107 when the focus is set.

When no spherical aberration occurs, FIG.
As shown in (B), the outputs of all the photodetectors do not change substantially equally.

When a spherical aberration of a certain polarity is generated, FIG.
As shown in FIG. 12A, the holograms 109g and 109h of FIG.
The focal point of the light beam passing through is focused behind the photodetector 107. As a result, the outputs of the photodetectors 107a and 107h increase, and the outputs of the photodetectors 107b and 107g decrease, but the photodetectors 107c, 107d, 107e, 107
The output of f does not change.

When spherical aberration of the opposite polarity occurs, FIG.
As shown in FIG. 12C, the holograms 109g and 109h of FIG.
Is focused on the front of the photodetector 107. As a result, the outputs of the photodetectors 107b and 107g increase, and the outputs of the photodetectors 107a and 107h decrease, but the photodetectors 107c, 107d, 107e, 107
The output of f does not change.

Therefore, by processing these signals, a signal for detecting spherical aberration can be obtained. That is, spherical aberration S
A is: SA = [(107a) + (107h)]-[(107
b) + (107 g)].

The detection of the far-field tracking error signal can be obtained by detecting the difference in light amount between the light beam passing through the portion of Y> 0 of the hologram and the light beam passing through the portion of Y <0. That is, the far-field tracking signal TE is given by: TE = [(107a) + (107b) + (107e) +
(107f)]-[(107c) + (107d) + (1
07g) + (107h)].

(Embodiment 5) Astigmatism can be detected by applying the principle of the present invention. FIG. 14 shows a specific method of detecting astigmatism.

The hologram 109 has a plurality of regions 109i to
109m (109l is a missing number), and photodetectors 110a to 110m (110l is a missing number) are provided corresponding to each area. That is, the region 109i is the photodetector 1
10i, 110j, 110k, and 110m, and the region 109j includes the photodetectors 110a, 110b, 110c, and 1
10d, the region 109k includes the photodetectors 110e, 1
10f, and the region 109m includes the photodetectors 110g and 1g.
10h. The hologram 109 is divided into regions as described below. First, a region (ring-shaped region) sandwiched between two concentric circles having different diameters about the optical axis.
And the other area. The former ring-shaped area is further divided into four parts by the X-axis and the Y-axis, and the opposing areas are set as one set to be two sets of detection areas 109i and 109j. Further, the latter area is divided into an area of Y> 0 and an area of Y <0, and these areas are set to 109k and 109m, respectively. As described above, in order to deflect the light beam into a plurality of light beams depending on the region through which the light beam passes, for example, the spatial frequency (pitch) and the diffraction direction of the hologram 109 can be appropriately set for each region. .

Assuming that astigmatism has occurred,
On the detection hologram 109, the region 109i and the region 1
09j, the phase error becomes largest, and the region 1
The phase error between 09k and the area 109m has a value intermediate between them. Therefore, when each of these three regions is detected, astigmatism can be detected.

FIG. 15 shows a state of a light spot (hatched portion) of the light beam on the photodetector 110 when the focus is set.

When no astigmatism occurs, FIG.
As shown in (B), the outputs of all the photodetectors 110 do not change substantially equally.

When astigmatism of a certain polarity occurs, FIG.
14A, the focus of the light beam passing through the hologram 109i in FIG. 14 is focused behind the photodetector 110, and the focus of the light beam passing through the hologram 109j is detected by the photodetector 1.
Light is collected in front of 10. As a result, the photodetectors 110a,
The outputs of 110d, 110j, 110k increase, and the outputs of photodetectors 110b, 110c, 110i, 110m decrease. Photodetectors 110e, 110f, 110g, 11
The output at 0h does not change.

When astigmatism of the opposite polarity occurs, FIG.
As shown in FIG. 14C, the focus of the light beam passing through the hologram 109j in FIG. 14 is focused behind the photodetector 110, and the focus of the light beam passing through the hologram 109i is detected by the photodetector 1.
Light is collected in front of 10. As a result, the photodetectors 110a,
The outputs of 110d, 110j, 110k decrease, and the outputs of photodetectors 110b, 110c, 110i, 110m increase. Photodetectors 110e, 110f, 110g, 11
The output at 0h does not change.

Therefore, by processing these signals, a signal for detecting astigmatism can be obtained. That is, astigmatism A
S is: AS = [(110a) + (110d) + (110j) +
(110k)]-[(110b) + (110c) + (1
10i) + (110m)].

Each embodiment using the above hologram is
An example in which + 1st-order diffracted light or -1st-order diffracted light is used for simplification of a photodetector is described. A blazed hologram can also be used, and in this case, the aberration detection device can be formed as it is in this mode. By using a blazed hologram, the amount of light received by the photodetector increases, so that highly sensitive aberration detection can be performed. In the case of a hologram that is not blazed, the above method can be used naturally. In this case, it is necessary to design the photodetector so that the + 1st-order and -1st-order diffracted light do not interfere with each other.

In the second embodiment (FIG. 8), when a hologram that is not blazed is used as the hologram 109, the + 1st-order and -1st-order diffracted lights are received at substantially symmetric positions near both sides of the light source 101. The photodetectors 107 and 111 are installed so that they can be
11 may be configured to perform the above-described aberration detection. With such a configuration, the amount of received light is doubled as compared with the case where aberration is detected by only one of the photodetectors, and an aberration detection signal with a high S / N ratio can be obtained.

Alternatively, in the second embodiment (FIG. 8), a polarization hologram that diffracts only polarized light may be used as hologram 109, and this and a quarter-wave plate may constitute an optical deflection unit. That is, as shown in FIG.
A radiation light source that emits polarized light is used as the light source 101, and the polarization hologram 109 is set in a direction in which the emitted polarized light is transmitted. Also, the quarter-wave plate 115 is connected to the wavefront conversion element 1.
It is installed between the object lens 04 and the objective lens 105. The light beam emitted from the polarized light source 101 is transmitted through the polarization hologram 109 and becomes a circularly polarized light by the quarter-wave plate 115. The circularly polarized beam reflected by the disk 106 is applied to the quarter wave plate 11
5 again, the light beam becomes a light beam polarized in a direction perpendicular to the polarization direction of the outward light beam. When this light beam enters the polarization hologram 109, most of the light beam is diffracted and enters the photodetectors 107 and 111. here,
The light detectors 107 and 111 are installed at substantially symmetric positions near both sides of the light source 101. Aberration detection is performed using signals from both the photodetectors 107 and 111. As described above, by using the polarization hologram and the quarter-wave plate, the utilization efficiency of the light beam incident on the photodetector can be improved, and an aberration detection signal with a high S / N ratio can be obtained. it can.

In each of the above embodiments, the method of detecting aberrations at high speed by using a two-divided photodetector has been described. However, if the response speed of the photodetector can be increased, a plurality of photodetectors can be divided in the same direction as the two-division A more accurate aberration detection can be performed using the photodetector described above. 10, 11, 13, and 15
As is clear from FIG. 7, when the aberration occurs, the light distribution on the photodetector is greatly expanded. The magnitude of the spread is proportional to the magnitude of the aberration. Therefore, the larger the output is, the more the output is output from the photodetector away from the center of the optical axis of the light beam. It is also possible to process signals output from a plurality of photodetectors and control and drive the aberration correction device (wavefront conversion element 104) stepwise with analog values to perform more accurate aberration correction. . Since the liquid crystal used in the aberration correction device can change the refractive index substantially in proportion to the applied voltage, it is suitable as a device for controlling in a stepwise manner with an analog value.

In the above embodiment, only the case where the far-field tracking method is used as the tracking method has been described. However, the phase difference detection tracking method, the three-beam tracking method, etc., which are usually used, are combined in a design that is not so difficult. It is also possible.

Next, an embodiment in which the above-described aberration detecting device is applied to an optical information recording / reproducing device will be described.

(Embodiment 6) FIG. 17 shows a schematic configuration of an optical information recording apparatus according to a sixth embodiment.

In FIG. 17, a light beam 202 emitted from a semiconductor laser 201 is converted into substantially parallel light by a collimating lens 220, transmitted through an objective lens 205 composed of two aspheric lenses 203 and 204, and subjected to first recording. It is incident on an information carrier 209 comprising a possible recordable information layer 206, a second recordable recordable information layer 208 and an optical separation layer 207 between the two recordable information layers. A distance adjustment mechanism 210 that can change the distance between the two aspheric lenses 203 and 204 is provided between the two aspheric lenses 203 and 204. In the present embodiment, a piezo element is used, and when a high voltage is applied, the distance between the two aspheric lenses 203 and 204 is increased, and when the voltage is reduced, the two aspheric lenses 203 and 204 are reduced.
The distance between 204 becomes shorter. When the light beam converged by the objective lens 205 is converged on the first recordable recording information layer 206, the voltage applied to the piezo element is reduced to reduce the distance between the two aspheric lenses 203 and 204. Shorten to correct spherical aberration. When the light beam converged by the objective lens 205 is focused on the second recordable recording information layer 208, the voltage applied to the piezo element is increased to increase the distance between the two aspheric lenses 203 and 204. Lengthen to correct spherical aberration. By reducing spherical aberration with respect to the recording information layer by such a method, good recording / reproducing characteristics can be obtained.

In the sixth embodiment, an electromagnetically driven actuator or motor can be used instead of the piezo element. Also, an actuator driven by ultrasonic waves can be used instead of the piezo element.

Also, the two aspheric lenses 203 and 204
May be used instead of two convex lens groups, or one aspherical lens and one spherical lens.

(Embodiment 7) FIG. 18 shows a schematic configuration of an optical information recording apparatus according to a seventh embodiment.

In FIG. 18, a light beam 202 emitted from a semiconductor laser 201 is converted into substantially parallel light by a collimating lens 220, passes through an objective lens 205 composed of two aspheric lenses 203 and 204, and performs first recording. It is incident on an information carrier 209 comprising a possible recordable information layer 206, a second recordable recordable information layer 208 and an optical separation layer 207 between the two recordable information layers. Between the objective lens 205 and the semiconductor laser 201, a spherical aberration correction element 230 capable of changing the optical phase that is equal in the circumferential direction of the circle around the optical axis of the objective lens 205 and different in the radial direction.
Are arranged integrally with the objective lens 205.

Since a phase error symmetric with respect to the optical axis occurs due to a thickness error of the base material, the same amount of optical phase having the opposite polarity to the optical phase different in the radial direction due to spherical aberration and having the opposite polarity is added. Thereby, the spherical aberration of the light beam focused on the recording information layer can be canceled.

In this embodiment, the spherical aberration correction element 230
Is a liquid crystal element divided into a plurality of three to seven regions in the radial direction by a concentric circle centered on the optical axis, and controls the voltage applied to the plurality of regions according to the amount of generated spherical aberration. Optimize phase differences.

In this embodiment, instead of using two aspheric lenses 203 and 204, two convex lens groups are used.
Alternatively, one aspherical lens and one spherical lens can be used.

(Embodiment 8) In Embodiments 6 and 7, a spherical aberration detection method using a hologram can be used for detecting spherical aberration. A method for detecting the spherical aberration of the optical disk will be described with reference to FIG.

In FIG. 19, a light beam 202 emitted from a semiconductor laser 201 is made substantially collimated by a collimator lens 220, passes through an objective lens 205 composed of two aspheric lenses 203 and 204, and performs first recording. The light is incident on an information carrier 209 comprising a recording information layer 206, a second recordable recording information layer 208, and an optical separation layer 207 between both recording information layers. Two aspheric lenses 203 and 204
Between them, there is a distance adjusting mechanism 210 for keeping the distance between both aspheric lenses constant. In this embodiment, a piezo element is used as the distance adjusting mechanism 210.

The light beam reflected from the disk is reflected by the half mirror 302, passes through the hologram 309 for detecting aberration, and enters the photodetector 307. The detected signal is processed by the signal amplification processing circuit 308 to drive the piezo element 210. By applying a high voltage in accordance with the detection signal, the distance between the two aspheric lenses 203 and 204 increases, and by decreasing the voltage, the distance between the two aspheric lenses 203 and 204 decreases. Become.

When the light beam converged by the objective lens 205 converges on the first recordable recording information layer 206, a spherical aberration detection signal is detected, and the voltage applied to the piezo element 210 is reduced to 2 The distance between the aspherical lenses is shortened to correct the spherical aberration.

When the light beam converged by the objective lens 205 is converged on the second recordable recording information layer 208, the spherical aberration detection signal is detected with the opposite polarity to the above and applied to the piezo element 210. The voltage is increased to increase the distance between the two aspheric lenses to correct spherical aberration.

As a specific method for detecting spherical aberration, the method described in FIGS. 5 to 7 or the fourth embodiment can be used.

In this embodiment, instead of using two aspheric lenses 203 and 204, two convex lens groups are used.
Alternatively, one aspherical lens and one spherical lens can be used.

In the present embodiment, an example in which the spherical aberration detecting device is combined with the optical information recording device of the sixth embodiment has been described. However, the optical information recording device of the seventh embodiment may be combined with the spherical aberration detecting device. it can.

Further, in the present embodiment, the case where the spherical aberration detecting device having the configuration shown in FIG. 1 is combined has been described, but the spherical aberration detecting device having the configuration shown in FIG. 2 can be similarly combined.

The present invention described above is not limited to the configuration specifically shown in the drawings, and various variations can be assumed.

[0144]

According to the first aspect of the present invention, the aberration of the optical system can be detected in real time or near real time. Therefore, if the aberration correction element is driven based on the detection result, the aberration of the optical system can be reduced. Therefore, it is possible to reproduce information carriers (disks) having large surface deviations and information carriers (disks) having different substrate thicknesses, which were difficult in the past. Further, the production of the information carrier is facilitated.

Further, according to the second aspect of the invention, even if the information carrier has a thickness deviating from the design substrate thickness, the spherical aberration is corrected by the spherical aberration correcting means, and the spherical aberration is reduced with respect to the recording information layer. By reducing, good recording / reproducing characteristics can be obtained. Thereby, even if spherical aberration caused by a thickness error of the substrate occurs, it is possible to stably perform recording / reproducing on each recording information layer from one surface side of the information carrier having a plurality of recording information layers. it can. As a result, a large-capacity optical information recording medium and an optical information recording / reproducing device therefor can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an aberration detection device according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram illustrating a wavefront aberration when a coma aberration occurs.

FIG. 3 is a schematic configuration diagram showing an example of an optical system for detecting coma aberration.

4 is an explanatory diagram showing the shape and formation position of a light beam spot formed on the two-segment photodetector in FIG.

FIG. 5 is a conceptual diagram showing wavefront aberration when spherical aberration occurs.

FIG. 6 is a schematic configuration diagram showing an example of an optical system for detecting spherical aberration.

FIG. 7 is an explanatory diagram showing the shape and formation position of a light beam spot formed on the two-segment photodetector in FIG.

FIG. 8 is a schematic configuration diagram of an aberration detection device according to a second embodiment of the present invention.

FIG. 9 is a configuration diagram showing a principle of detecting coma aberration according to the third embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a state of forming a light beam spot on the photodetector of FIG. 9 when focus detection is performed by the knife edge method.

FIG. 11 is an explanatory diagram showing a state of formation of a light beam spot on the photodetector in FIG. 9 when coma aberration occurs.

FIG. 12 is a configuration diagram illustrating a principle of detecting spherical aberration according to the fourth embodiment of the present invention.

FIG. 13 is an explanatory diagram showing a state of forming a light beam spot on the photodetector in FIG. 12 when spherical aberration occurs.

FIG. 14 is a configuration diagram showing a principle of detecting astigmatism according to the fifth embodiment of the present invention;

FIG. 15 is an explanatory diagram showing a state of forming a light beam spot on the photodetector in FIG. 14 when astigmatism occurs.

FIG. 16 is a schematic configuration diagram showing another configuration example of the aberration detection device of the present invention.

FIG. 17 is a schematic configuration diagram of an optical information recording apparatus according to Embodiment 6 of the present invention.

FIG. 18 is a schematic configuration diagram of an optical information recording device according to a seventh embodiment of the present invention.

FIG. 19 is a schematic configuration diagram of an optical information recording apparatus according to Embodiment 8 of the present invention.

FIG. 20 is a schematic configuration diagram showing a conventional wavefront aberration correction method.

FIG. 21 is a sectional view showing a configuration example of a single-sided readout two-layer type optical disc.

[Explanation of symbols]

 Reference Signs List 101 light source 102 half mirror 103 collimating lens 104 wavefront conversion element 105 objective lens 106 optical disk 107 photodetector 108 aberration signal processing circuit 109 hologram 111 photodetector 115 quarter-wave plate 201 semiconductor laser 202 light beam 203 first Lens 204 Second lens 205 Objective lens 206 First recording information layer 207 Optical separation layer 208 Second recording information layer 209 Information carrier 210 Distance adjustment mechanism (piezo element) 220 Collimating lens 230 Liquid crystal spherical aberration correction element 302 Half mirror 307 Photodetector 308 Signal amplification processing circuit 309 Hologram

Claims (14)

[Claims] A radiation source for emitting a light beam; an objective lens for condensing the light beam on an information carrier; and a forward light beam reflected on the information carrier and passing through the objective lens. A light beam branching unit that separates the light beam from the light beam, and a light deflecting unit that divides and deflects the light beam on the return path separated by the branching unit into a light beam passing through a specific region and a light beam passing through other regions. A plurality of light detecting means for receiving a light beam passing through the deflected specific region, and detecting aberration by comparing signals from the plurality of light detecting means. . 2. A radiation source for emitting a light beam, an objective lens for condensing the light beam on an information carrier, and a return light beam reflected on the information carrier and passing through the objective lens to a specific area. A light deflecting unit that divides the passing light beam into a light beam that passes through the other region and deflects the light beam that passes through the specific region in a direction different from that of the radiation light source. An aberration detection device, comprising: a plurality of light detection units that receive a passing light beam; and detecting aberration by comparing signals from the plurality of light detection units. 3. The aberration detecting device according to claim 1, wherein the light deflecting unit is a hologram that divides a light beam into a plurality of beams and diffracts the light beam. 4. The plurality of photodetectors comprise at least two photodetectors, and are installed so that a light beam passing through the specific area irradiates a split line of the two photodetectors. The aberration detection device according to claim 1 or 2, wherein 5. The specific region is a substantially central portion of one of two regions obtained by dividing a region through which the light beam on the return path passes by a plane including an optical axis of the light beam into two. Item 3. The aberration detection device according to item 1 or 2. 6. The one area obtained by dividing the area sandwiched by two concentric circles having different diameters centered on the optical axis of the light beam on the return path into two on a plane including the optical axis. The aberration detection device according to claim 1, wherein the aberration detection device substantially corresponds to: 7. The aberration detecting device according to claim 1, wherein the light deflecting unit is a blazed hologram. 8. The aberration detection device according to claim 2, wherein the plurality of light detection units are arranged near the radiation light source and symmetrically with respect to the radiation light source. 9. The light deflecting means includes a hologram for diffracting only predetermined polarized light and a quarter-wave plate, and the hologram does not diffract an outgoing light beam from the radiation light source to the information carrier. 3. The aberration detecting apparatus according to claim 2, wherein the light beam on the return path is divided into a plurality of beams and diffracts in different directions. 10. Optical information for recording information on a recordable / reproducible information carrier having a plurality of recording information layers and an optical separation layer sandwiched between the recording information layers, or reproducing the recorded information. A recording / reproducing apparatus, comprising: a radiation light source that emits a light beam; and a light beam focusing unit that focuses a light beam from the radiation light source on at least one recording information layer of the plurality of recording information layers. An optical information recording / reproducing apparatus comprising: a light beam condensing means; and a spherical aberration correcting means integrally formed. 11. The optical information recording / reproducing apparatus according to claim 10, wherein said light beam focusing means comprises two groups of convex lenses, and said spherical aberration correcting means changes a distance between said two groups of convex lenses. 12. The optical information recording / reproducing apparatus according to claim 10, wherein said light beam condensing means comprises two aspherical lenses, and said spherical aberration correcting means changes a distance between said two aspherical lenses. apparatus. 13. The light beam condensing means comprises one aspherical lens and one spherical lens, and the spherical aberration correcting means changes a distance between the aspherical lens and the spherical lens. The optical information recording / reproducing device according to claim 10. 14. Optical information for recording information on a recordable / reproducible information carrier having a plurality of recording information layers and an optical separation layer sandwiched between the recording information layers, or reproducing the recorded information. A recording / reproducing apparatus, comprising: a radiation light source that emits a light beam; and a light beam focusing unit that focuses a light beam from the radiation light source on at least one recording information layer of the plurality of recording information layers. And a spherical aberration correcting means integrally formed with the light beam condensing means between the radiation light source and the light beam condensing means. An optical information recording / reproducing apparatus characterized by changing optical phases which are equal in a circumferential direction of a circle centered on an optical axis of the means and different in a radial direction.