JP2001176108A - Aberration correcting optical element and pickup device, information reproducing device and information recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suitably correct the influence of aberration owing to an information recording medium. SOLUTION: An aberration correcting optical element 4 for correcting aberration is arranged in an optical path between a light source emitting information recording or information reproducing light and an objective lens. Electrode parts 12, 13 holding a liquid crystal element 14 are provided in the aberration correcting optical element 4, and mutually facing relational transparent electrode layers A1-Ai, B1-Bj, C1-Ci, D1-Dj are formed in these electrode parts 12, 13. Further, these transparent electrode layers A1-Ai, B1-Bj, C1-Ci, D1-Dj are formed with a multilayerd structure along the liquid crystal element 14 side. Owing to such a multilayerd structure, the transparent electrodes B1-Bj are faced to gaps W1 formed among the transparent electrode layers A1-Ai, and the transparent electrodes D1-Dj are faced to gaps W2 formed among the transparent electrode layers C1-Ci. Thus, all transparent electrodes are faced to the liquid crystal 14 without any gaps, the change of oriented stats is caused within the liquid crystal 14 without any gaps, and whereby aberration correcting precision is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aberration correcting optical element for correcting aberration when information is recorded or reproduced on an information recording medium such as an optical disk, and a pickup device provided with the aberration correcting optical element. And an information recording / reproducing device.

[0002]

2. Description of the Related Art CDs (Compact disks) and DVDs are used as information recording media for optically recording or reproducing information.
Optical disks such as (Digital Video Disk or Digital Versatile Disk) are known.
Different types of optical disks have been developed, such as a write-once optical disk on which information can be additionally recorded and a rewritable optical disk on which information can be erased and re-recorded.

[0003] Further, research and development of higher density optical discs and pickup devices and information recording / reproducing apparatuses corresponding to the higher densities have been promoted, and there is a so-called compatibility in which different types of optical discs can be used. Research and development of the pickup device and the information recording / reproducing device are also progressing.

In order to cope with the increase in the density of the optical disk, the optical disk is irradiated with a light beam having a small irradiation diameter by increasing the numerical aperture (NA) of an objective lens provided in the pickup device. Is considered. In addition, it has been considered that the use of a short-wavelength light beam corresponds to high density.

However, if the numerical aperture NA of the objective lens is increased or a short-wavelength light beam is used, the influence of the aberration on the light beam by the optical disk increases, and it is difficult to improve the accuracy of information recording and information reproduction. Problem arises.

For example, when the numerical aperture NA of the objective lens is increased, the range of the incident angle of the light beam on the optical disk is widened, so that the distribution width of the amount of birefringence, which depends on the incident angle, on the pupil plane of the optical disk is also increased. . For this reason, there is a problem that the influence of the spherical aberration caused by the birefringence increases. Also, if the numerical aperture NA of the objective lens is increased and a short-wavelength light beam is used, the optical disk tilts during information recording or information reproduction, and the incident angle (tilt angle) of the light beam with respect to the normal direction of the optical disk is reduced. When tilted, the influence of coma cannot be ignored.

[0007] Further, since the structure and recording density of an optical disk differ depending on the type, such as a CD and a DVD, the effects of aberrations such as the above-mentioned spherical aberration and coma are different depending on the type of the optical disk. It becomes difficult to develop a pickup device and an information recording / reproducing device having the above.

In order to reduce the influence of such aberrations, a pickup device having a liquid crystal unit for correcting aberrations has been proposed (Japanese Patent Laid-Open No. 10-20263).

This liquid crystal unit has a structure in which a liquid crystal element C is sandwiched between transparent electrodes A and B facing each other as shown schematically in FIG. 14, and adjusts an applied voltage between the transparent electrodes A and B. When the light incident on one of the transparent electrodes A (or B) passes through the liquid crystal element C, a change in the birefringence according to the alignment state occurs when the light incident on the transparent electrode A (or B) side passes through the liquid crystal element C. To emit light to the other transparent electrode B (or A) side.

Further, at least one of the transparent electrodes A and B is, for example, a plurality of transparent electrodes a1, a2, a3 and b1,
b2, b3 and the transparent electrodes a1, a3
2 and a3 are electrically separated from each other and the transparent electrode b
1, b2 and b3 are also electrically separated from each other.

For this reason, between the transparent electrodes facing each other, for example, between the transparent electrodes a1 and b1, and between the transparent electrodes a2 and b
When different voltages are respectively applied between the two electrodes and between the transparent electrodes a3 and b3, the liquid crystal element C can be adjusted to a plurality of different alignment states, and the incident light can be adjusted according to the respective alignment states. The birefringence change is given at the same time.

The liquid crystal unit is arranged in an optical path between a light source for emitting laser light and an objective lens. When the laser light is emitted from the light source, the liquid crystal unit gives the laser light a birefringence change corresponding to the plurality of alignment states described above and transmits the laser light to the objective lens side, and the objective lens converges the transmitted laser light. To generate a light beam to irradiate the optical disk. When the reflected light generated by the light beam irradiation on the optical disk enters the liquid crystal unit via the objective lens, the reflected light is transmitted by giving a birefringence change corresponding to the plurality of alignment states. The reflected light is detected by a photodetector. By properly adjusting the plurality of alignment states of the liquid crystal unit, the influence of aberrations such as spherical aberration and coma is reduced.

[0013]

However, the above-mentioned conventional liquid crystal unit includes a plurality of transparent electrodes a1, a2, a3.
As shown in FIG. 14, a gap SP for electrical insulation is provided between the transparent electrodes to electrically isolate the electrodes b1, b2, and b3 from each other. That is, the gap SP is provided along the boundary between the transparent electrodes a1, a2, and a3, and the transparent electrodes b1, b
A gap SP is provided along each boundary portion between 2 and b3.

For this reason, no voltage is applied to these gaps SP, so that the alignment state in the liquid crystal element C corresponding to these gaps SP cannot be controlled. As a result, the transparent electrodes a1, a2, a3 and b1, b
Aberration correction can be performed on a light beam or reflected light passing through 2 and b3, whereas aberration cannot be corrected on a light beam or reflected light passing through the gap SP. In some cases, highly accurate aberration correction cannot be performed on the light beam or the reflected light as a whole.

To increase the number of divisions of the transparent electrode in order to finely correct the influence of aberration, many transparent electrodes are electrically insulated within a limited effective optical path range through which laser light or reflected light passes. Therefore, there is a problem that the number and the occupied area of the gaps SP increase, and as a result, fine aberration correction becomes difficult.

Further, when different voltages are applied to the transparent electrodes adjacent to each other, there is another problem that the alignment state in the liquid crystal element C corresponding to the gap SP becomes a steep discontinuous state.

The present invention has been made to overcome the problems of the prior art, and has an aberration correcting optical element, a pickup device, and an information processing device capable of accurately correcting the influence of aberration due to an information recording medium. An object of the present invention is to provide a recording and reproducing device.

It is another object of the present invention to provide an aberration correcting optical element capable of accurately correcting the influence of aberration accompanying the increase in the density of an information recording medium, a pickup device, and an information recording / reproducing device.

[0019]

An aberration correcting optical element according to the present invention is arranged in an optical path between a light source and an optical element for irradiating the information recording medium with light emitted from the light source, in alignment with the optical axis. An aberration correction optical element that corrects aberration of light generated in the information recording medium, comprising: a liquid crystal element that exhibits a predetermined alignment state by a predetermined voltage; and an opposing electrode that applies a voltage to the liquid crystal element. And at least one of the electrodes facing each other is formed of a plurality of electrodes having a multilayer structure arranged in the optical axis direction.

In the aberration correcting optical element according to the present invention, the plurality of electrodes formed in the multilayer structure are formed in the multilayer structure arranged in the optical axis direction without overlapping each other. .

Further, the aberration correcting optical element of the present invention is characterized in that the plurality of electrodes formed in the multilayer structure are formed in the multilayer structure arranged in the optical axis direction while partially overlapping each other. I do.

Further, the aberration correcting optical element according to the present invention is characterized in that a voltage is applied to the electrode to produce an electro-optical effect having characteristics opposite to the aberration characteristics of the information recording medium.

According to the aberration correcting optical element of the present invention having the above-described configuration, by adjusting the voltage applied to the electrodes facing each other, the electro-optical effect opposite to the aberration characteristic of the information recording medium can be obtained. The liquid crystal element can be corrected for aberration by the electro-optic effect. Further, when at least one of the electrodes facing each other is formed of a plurality of electrodes having a multilayer structure, the plurality of electrodes can be directed toward the liquid crystal element without gaps. For this reason, when a voltage is applied to the plurality of electrodes, an electro-optical effect is generated without any gap in the liquid crystal element, and it is possible to correct aberrations without omission. Also. The aberration can be finely corrected.

A pickup apparatus according to the present invention includes the above-described aberration correction element, and further includes a photodetector that detects reflected light reflected by the information recording medium and transmitted through the aberration correction optical element.

According to this configuration, accurate information reproduction can be performed based on the reflected light in which the influence of the aberration has been corrected.

An information reproducing apparatus according to the present invention includes the above-mentioned pickup device, and reproduces information by emitting light for information recording and detecting light reflected from an information recording medium. . According to such a configuration, accurate information reproduction can be performed based on the reflected light in which the influence of the aberration has been corrected.

An information recording apparatus according to the present invention includes the pickup device described above, and emits light for information recording to record information on an information recording medium. According to such a configuration, it is possible to perform accurate information reproduction based on the reflected light reflected from the information recording medium and corrected for the influence of aberration.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a pickup device provided in an information recording / reproducing device.

In FIG. 1, the present pickup device PU
Comprises a light source 1 for emitting a laser beam H1, a polarization beam splitter 3, an aberration correction optical element 4, an objective lens 5, a condenser lens 6, and a photodetector 7. These components 1 to 7 , Are arranged along the optical axis OA. Also,
A control circuit 8 for controlling the aberration correction optical element 4 is provided in the present pickup device PU or the information recording / reproducing device.

Here, the aberration correcting optical element 4 is formed of an electro-optical element whose electro-optic effect changes by an electric field. More specifically, it is formed of a liquid crystal optical element that causes a birefringence change according to a control voltage Vi applied by the control circuit 8.

That is, as shown schematically in FIG. 2, the variable optical element 4 has a liquid crystal (liquid crystal) between two insulating substrates 10 and 11 such as a transparent glass substrate.
The device has a structure in which the element 14 is sealed, and electrode portions 12 and 13, insulating films 23 and 24, and liquid crystal alignment films 21 and 22 are formed on opposing surfaces of the glass substrates 10 and 11 facing each other.

When a control voltage Vi is applied between the electrodes 12, 13, an electric field Ei generated by the control voltage Vi is generated.
, The arrangement of the liquid crystal elements 14 changes. As a result, the light passing through the liquid crystal element 14 undergoes birefringence of the liquid crystal element 14 and changes its polarization state (phase).
Can be controlled by the control voltage Vi applied to the liquid crystal element 14.

Further, the aberration correction optical element 4 has bidirectional light transmission, so that either side of the insulating substrates 10 and 11 may be arranged to face the objective lens 5 side. I have.

When the aberration correction optical element 4 is viewed from the optical axis OA side, as shown in the plan view of FIG. 3, a plurality of aberration correction areas AR1, AR1 determined in correspondence with the distribution of aberrations generated in the optical disk 9. AR2 to ARi, and these aberration correction regions AR1 and AR2 to ARi are
This is realized by the transparent electrode (ITO) layers formed on the substrates 2 and 13. FIG. 3 shows aberration correction areas AR1 and AR1 for correcting spherical aberration caused by the optical disc 9.
This shows a typical example of AR2 to ARi, and is actually divided into various shapes in accordance with the aberration distribution of the optical disk 9. For example, when correcting coma caused by tilting the optical disk 9 during information recording or information reproduction, the aberration correction area BR1 having a shape as shown in FIG.
To BR9. Further, the number of sections of these aberration correction areas is also determined in association with the distribution of aberration of the optical disc 9.

A concentric aberration correction area AR as shown in FIG.
1 to ARi, the cross-sectional view of FIG.
(A diagram showing a cross-sectional structure along X-rays), the electrode portion 12 includes transparent electrode layers A1, A2 to Ai embedded in the transparent insulating layer 15 so as to be electrically separated from each other. The transparent electrode layers B1, B2 embedded in the insulating layer 15 facing the plurality of gaps W1 existing between the transparent electrode layers A1, A2 to Ai.
Bj is provided. Also, the transparent electrode layer A
The group of 1, A2 to Ai and the group of transparent electrode layers B1, B2 to Bj are formed in the insulating layer 15 in a two-stage structure along the optical axis OA. For convenience of description, the cross-sectional view of FIG. 4 omits the insulating films 23 and 24 and the liquid crystal alignment films 21 and 22 (hereinafter, FIGS. 5, 7, 11, 12, 13). The same).

Here, the transparent electrode layer A1 is formed in a shape (circular in FIG. 3) corresponding to the aberration correction region AR1, and the transparent electrode layer A2 is formed in a shape (FIG. 3) corresponding to the aberration correction region AR2. The remaining transparent electrode layers A3 to Ai are similarly formed in the aberration correction regions AR3 to ARi.
It has a shape according to.

Further, the transparent electrode layer B1 is formed of a transparent electrode layer A1.
And A2 are formed in a very narrow annular shape according to the shape of the gap W1 for electrically separating the transparent electrode layer B from the transparent electrode layer B2.
Similarly, the second transparent electrode layers B3 and Bj are formed in an extremely narrow annular shape in accordance with the shape of the gap W1 for electrically separating the transparent electrode layers A2 and A3. ing.

In other words, the aberration correction area A shown in FIG.
R1, AR2 to ARi are the transparent electrode layers A1, A2 to Ai
Are electrically separated from each other to form gaps BK1, BK2 between the aberration correction areas AR1, AR2 to ARi.
To BKj are realized by forming the transparent electrode layers B1, B2 to Bj.

The transparent electrode layers B1, B2 to Bj
May be provided so as to face all the existing gaps W1, but a necessary number or gaps W may be provided according to the characteristics of the aberration to be corrected.
1 may be formed.

On the other hand, similarly, the electrode section 13 also includes a group of transparent electrode layers C1, C2 to Ci embedded in the transparent insulating layer 16 so as to be electrically separated from each other, and the respective transparent electrode layers C1, C2 to C2.
and a group of transparent electrode layers D1, D2 to Dj embedded in the insulating layer 16 facing a plurality of gaps W2 existing between i, and has a two-stage structure. The transparent electrode layers C1, C2 to Ci are The transparent electrode layers A1, A2 to Ai of the electrode section 12 are directly opposed to each other, and the transparent electrode layers D1, D2 to Dj are formed by the transparent electrode layer B of the electrode section 12.
1, B2 to Bj.

The transparent electrode layers D1, D2 to Dj
May be provided so as to face all existing gaps W2, or may be formed so as to face a required number or gaps according to the characteristics of aberration to be corrected.

Then, as schematically shown in FIG. 5, the control voltage Vi from the control circuit 8 causes the transparent electrode layers (A) of the aberration correction areas AR1 to ARi, which are directly opposed to each other, to intersect.
When different unique voltages V1 to Vk are applied to the respective transparent electrode layers (B1, D1) to (Bj, Di) of the gaps BK1 to BKj and (C1, 1) to (Ai, Ci),
A plurality of alignment states occur in the liquid crystal element 14 at those applied voltages V1 to Vk. Note that these voltages V1 to Vk are:
Each of the aberration correction areas AR1 to ARi and the gap BK1
The alignment state of the liquid crystal element 14 in BKj is
The voltage is determined so as to have the opposite characteristic to the characteristic of the aberration caused by the above.

As described above, the aberration correction areas AR1 to ARi
Between the gaps BK1 through BKj,
Since the transparent electrode layers B1 to Bj and D1 to Dj are provided in K1 to BKj, the alignment state for aberration correction can be adjusted over the entire area of the liquid crystal element 14, and the alignment state can be finely adjusted. Is possible.

Further, each of the transparent electrode layers (B1, D1) to
By appropriately adjusting the voltages V1 to Vk of (Bj, Di),
The alignment state of the transparent electrode layers (A1, C1) to (A
Instead of a steep change with respect to the orientation state caused by i, Ci), the orientation state can be changed continuously.

Also, in the case of the aberration correction optical element 4 having the aberration correction regions BR1 to BR9 for correcting coma aberration shown in FIG. 6, the sectional view of FIG. 7 (along the line XX in FIG. 6). As shown in the cross-sectional structure, transparent electrode layers (reference numerals are omitted) corresponding to the aberration correction regions BR1 to BR9 in each of the electrode portions 12 and 13, and transparent electrodes corresponding to gaps between the aberration correction regions BR1 to BR9. The electrode layer is formed in a two-stage structure. still,
In FIG. 7, the transparent electrode layers corresponding to the gaps between the aberration correction regions BR1 to BR9 are not formed so as to face all the gaps as shown by reference numerals F1 to F4 and G1 to G4. The case where it is provided only at the location of the gap to reduce the influence of is shown.

Next, the operation of the pickup device PU provided with the aberration correcting optical element 4 having such a structure will be described with reference to FIGS.
0 will be described. Further, as a representative example, an operation in a case where the aberration correction optical element 4 for correcting coma aberration shown in FIGS. 6 and 7 is provided in the pickup device PU will be described.

When the optical disk 9 is loaded at the so-called clamp position of the information recording / reproducing apparatus and an instruction for starting information reproduction is given by the user, a system controller (not shown) provided in the information recording / reproducing apparatus operates the control circuit 8. To output a control voltage Vi for correcting coma aberration. Thereby, the transparent electrode layer having a direct relationship corresponding to each of the aberration correction regions BR1 to BR9 of the aberration correction optical element 4 shown in FIGS. 6 and 7, and the transparent electrode layer F1 having a direct relationship corresponding to the gap. To F4, G1 to G4, an appropriate voltage is applied, and a plurality of changes in the alignment state according to the electric field generated by the applied voltages occur in the liquid crystal element 14.

Next, the system controller drives a spindle motor (not shown) provided in the information recording / reproducing apparatus to rotate, and the pickup device P
By driving a carriage (not shown) for moving U in the radial direction of the optical disk 9, the optical disk 9 is rotated at a predetermined linear velocity.

Further, the system controller controls the light source 1
By supplying a drive signal of a predetermined power to the light source 1, a linearly polarized laser beam H1 having a constant power is emitted from the light source 1. This laser light H1 is converted into parallel light by the collimator lens 2,
The light passes through the polarization beam splitter 3 and enters the aberration correction optical element 4.

When the laser beam incident on the aberration correcting optical element 4 passes through the aberration correcting optical element 4, it is birefringent in accordance with the orientation of the liquid crystal element 14, and the birefringent laser light is transmitted through the objective lens 5 Is converged, and a light beam having a small irradiation diameter is irradiated on the optical disc 9.

Further, reflected light generated by the light beam being reflected by the pupil plane of the optical disk 9 is incident on the objective lens 5, and the reflected light transmitted through the objective lens 5 is further reflected by the aberration correcting optical element 4.
Then, the light is again birefringent and transmitted, and is reflected by the polarizing beam splitter 3 toward the condenser lens 6. Then, the condenser lens 6 condenses the reflected light and makes the photodetector 7 receive the reflected light. The photodetector 7 performs photoelectric conversion of the received reflected light to output a photoelectric conversion signal having information recorded on the optical disk 9, and outputs a reproduced signal processing circuit provided in the information recording / reproducing apparatus. (Not shown), and the reproduction signal processing circuit performs a so-called decoding process or decoding process based on the photoelectric conversion signal, thereby generating a reproduction signal such as an audio signal or a video signal.

Here, when the optical disk 9 is tilted and the incident angle (tilt angle) of the light beam is tilted with respect to the normal direction of the optical disk 9, coma aberration occurs on the pupil plane of the optical disk 9.

FIG. 8 is a characteristic diagram showing the effect of coma aberration generated on the pupil plane of the optical disk 9 as a normalized wavefront aberration amount, with the horizontal axis showing the effective optical path range (lens diameter) of the objective lens 5. I have.

When the coma aberration shown in FIG. 8 occurs, the aberration correcting optical element 4 performs birefringence so as to reduce the influence of the coma aberration on the laser beam incident from the polarizing beam splitter 3 as described above. , The objective lens 5
The optical disk 9 is irradiated with a light beam capable of reducing the influence of coma aberration through the optical disk 9 in advance. Further, when the reflected light returning from the optical disk 9 under the influence of the coma aberration and entering the aberration correcting optical element 4 via the objective lens 5, the reflected light is again subjected to the birefringence to thereby produce the reflected light again. The light is transmitted to the polarization beam splitter 3 while reducing the influence of coma. For this reason, the reflected light, in which the influence of the coma is suppressed, enters the photodetector 7 via the condenser lens 6, thereby enabling accurate information reproduction.

Further, as shown in FIGS. 6 and 7, transparent electrode layers F1 to F4, G1 to G4 are provided facing each other in the gap between the aberration correction regions BR1 to BR9 of the aberration correction optical element 4. Therefore, the coma can be reduced in the entire area of the aberration correction optical element 4 and the coma can be accurately reduced.

FIG. 9 is a characteristic diagram showing the effect of coma aberration reduced by the aberration correction optical element 4 as a normalized wavefront aberration amount. The horizontal axis represents the effective optical path range (lens diameter) of the objective lens 5. Is shown. As can be seen from the figure, a significant improvement is seen as compared to the coma aberration before correction shown in FIG.

FIG. 10 shows a case where the transparent electrode layer is not provided in the gap between the aberration correction regions BR1 to BR9 of the aberration correction optical element 4 and the aberration correction is performed only in the aberration correction regions BR1 to BR9, that is, FIG. 7, the transparent electrode layers F1 to F shown in FIG.
FIG. 10 is a diagram showing the influence of coma aberration obtained when aberration correction is performed without providing G1 to G4, in comparison with the characteristic diagram of FIG. 9.

In the characteristic diagram of FIG. 10, the transparent electrode layers F1 to F
4, while large peaks P1 to P4 occur in the aberration at the portion where G1 to G4 are not provided, it can be seen from the characteristic diagram of FIG. 9 that these peaks are greatly reduced.

As is clear from the experimental results, according to the aberration correction optical element 4 of the present embodiment, the transparent electrode layers F1 to F4, G1 are provided in the gaps between the aberration correction regions BR1 to BR9.
It was confirmed that the influence of coma aberration can be significantly reduced by providing G4.

Next, a pickup device P for recording information
The operation of U will be described. When a user gives an instruction to start information recording, the system controller provided in the information recording / reproducing apparatus instructs a recording signal processing circuit (not shown) to input an audio signal or a video signal supplied from the outside. A modulation process, an encoding process, or the like is performed based on the signal, and a recording signal generated by the modulation process or the
To emit a laser beam H1 modulated by the recording signal.

The laser beam H1 is transmitted to the collimator lens 2
, And is transmitted through the polarizing beam splitter 3.
The light enters the aberration correction optical element 4. Here, when the laser light incident on the aberration correction optical element 4 passes through the aberration correction optical element 4, the laser light is birefringent according to the orientation state of the liquid crystal element 14, and the birefringent laser light is transmitted to the objective lens 5. As a result, a light beam with a small irradiation diameter is radiated to the optical disk 9 and information recording is performed by the light energy of the light beam.

Further, reflected light generated by reflecting the light beam on the pupil plane of the optical disk 9 is incident on the objective lens 5, and further, reflected light transmitted through the objective lens 5 is converted into the aberration correcting optical element 4.
Then, the light is again birefringent and transmitted, and is reflected by the polarizing beam splitter 3 toward the condenser lens 6. Then, the condenser lens 6 condenses the reflected light and makes the photodetector 7 receive the reflected light. Further, the photodetector 7 photoelectrically converts the received reflected light and supplies the photoelectrically converted signal to a servo circuit (not shown) provided in the information recording / reproducing apparatus.

Here, the servo circuit detects a focus error by, for example, the astigmatism method, and performs focus servo of the objective lens 5 based on the detection result. Also in this focus servo, the focus servo is performed based on the photoelectric conversion signal in which the influence of the coma aberration is greatly reduced, so that the focus servo can be performed with high accuracy.

Note that, even when the aberration correcting optical element 4 for correcting spherical aberration shown in FIGS. 3 and 4 is provided, FIGS.
Since the same effect as in the case where the aberration correction optical element 4 for correcting coma aberration is provided is obtained, the influence of various aberrations can be greatly reduced.

As described above, according to the pickup device PU and the information recording / reproducing device of the present embodiment, the pickup device PU is provided with the aberration correction optical element 4 and, as shown in FIGS. Since the transparent electrode layer is provided corresponding to the gap generated between the aberration correction regions of the element 4, the influence of the aberration by the optical disk 9 can be greatly reduced and the reduction of the aberration can be finely controlled.

In the above embodiment, the case where the transparent electrode layer is provided corresponding to the gap generated between the aberration correction areas of the aberration correction optical element 4 has been described. However, the aberration correction optical element of the present invention has such a structure. However, the present invention is not limited to this.

As shown in the cross-sectional view of FIG. 11, one electrode section 12 is provided with a transparent electrode layer corresponding to the gap generated between the aberration correction areas, and the other electrode section 13 is provided with an effective optical path range. The transparent electrode layer 17 may be provided on the entire surface, and the transparent electrode layer 17 may be used as a so-called common electrode, and a unique voltage may be applied between each transparent electrode layer in the electrode portion 13 and the transparent electrode layer 17.

As shown in the sectional view of FIG. 12, a plurality of transparent electrode layers are formed along each optical axis OA in a multistage structure in the electrode portions 12 and 13 so as to overlap with each other. A unique voltage may be applied between the transparent electrode layers having the corresponding shape and facing each other.
That is, the aberration can be corrected by adjusting the portion of each transparent electrode layer opened to the liquid crystal element 14 to the shape of the aberration correction region. According to this structure, no gap is formed between the aberration correction regions, so that the transparent electrode layer corresponding to the gap as shown in FIGS. 4 and 7 becomes unnecessary, and a voltage for applying a voltage to the transparent electrode layer is eliminated. Since the number of wirings can be reduced and the types of voltages to be applied can be reduced, effects such as simplification of the control circuit 8 can be achieved.

In the case of FIG. 12, one transparent electrode layer similar to the transparent electrode layer 17 shown in FIG. 11 is formed on one electrode portion 12 (or 13), and this one transparent electrode layer is formed. It may be a common electrode.

Further, as shown in the cross-sectional view of FIG. 13, a transparent electrode layer having a shape corresponding to the aberration correction region is formed in a multi-stage structure along the optical axis OA, and the transparent electrode layers facing each other are directly opposed to each other. A unique voltage may be applied.

According to such a structure, the shape of the transparent electrode layer can be formed in accordance with the shape of the aberration correction region, so that the alignment state to be generated in the liquid crystal element 14 can be finely adjusted. For this reason, a more accurate aberration correction optical element can be realized. Further, since no gap is formed between the transparent electrode layers, a transparent electrode layer corresponding to the gap as shown in FIGS. 4 and 7 becomes unnecessary, and the number of wirings for applying a voltage to the transparent electrode layer can be reduced. The control circuit 8 can reduce the types of voltages to be applied.
And the like can be achieved.

[0072]

As described above, according to the present invention, at least one of the electrodes facing each other for applying a voltage to the liquid crystal element of the aberration correction optical element is formed by a plurality of electrodes having a multilayer structure. A plurality of electrodes can be directed to the liquid crystal element without gaps. Accordingly, when a voltage is applied to the plurality of electrodes, an electro-optical effect is generated without any gap in the liquid crystal element, and it is possible to correct aberration without omission. Also. The aberration can be finely corrected.

Furthermore, as a result of properly correcting aberrations due to the information recording medium, it is possible to promote a higher NA of the objective lens and a shorter wavelength of light emitted from the light source as the density of the information recording medium increases. It is possible to provide an aberration correction optical element that is effective for increasing the density.

Further, since the pickup device, the information reproducing device and the information recording device of the present invention are provided with the above-mentioned aberration correcting optical element and perform aberration correction, accurate information recording and information reproduction can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a pickup device provided in an information recording / reproducing device according to an embodiment.

FIG. 2 is a diagram for explaining an operation principle of an aberration correction optical element provided in the pickup device.

FIG. 3 is a plan view showing a shape of the aberration correction optical element when viewed from the optical axis side.

FIG. 4 is a cross-sectional view showing a vertical cross-sectional structure of the aberration correction optical element.

FIG. 5 is a diagram for explaining the principle of aberration correction by the aberration correction optical element.

FIG. 6 is a plan view showing a shape when another aberration correction optical element is viewed from the optical axis side.

FIG. 7 is a cross-sectional view showing a vertical cross-sectional structure of another aberration correction optical element.

FIG. 8 is a characteristic diagram showing characteristics of coma aberration.

FIG. 9 is a characteristic diagram showing a result of reducing coma by an aberration correction optical element.

FIG. 10 is a characteristic diagram showing characteristics when coma is not sufficiently reduced.

FIG. 11 is a sectional view showing another structure of the aberration correction optical element.

FIG. 12 is a sectional view showing still another structure of the aberration correction optical element.

FIG. 13 is a sectional view showing still another structure of the aberration correction optical element.

FIG. 14 is a view for explaining a problem in a conventional liquid crystal unit.

[Explanation of symbols]

PU ... Pickup device 1 ... Light source 2 ... Collimator lens 3 ... Polarizing beam splitter 4 ... Aberration correcting optical element 5 ... Objective lens 6 ... Condensing lens 7 ... Photodetector 8 ... Control circuit 9 ... Optical disk 10, 11 ... Insulating substrate 12 , 13 ... electrode part 14 ... liquid crystal element 15, 16 ... insulating layer 17, A1-Ai, B1-Bj, C1-Ci, D1-D
j: transparent electrode layer AR1 to ARi: aberration correction area BK1 to BKj: gap PU: pickup

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H088 EA62 HA20 HA24 HA28 MA20 2K002 AA01 AA05 BA03 CA14 DA14 FA01 5D119 AA11 AA17 BA01 BB01 BB02 BB03 DA01 DA05 EA02 EA03 EC01 JA09 JA12 JA25 JB10

Claims (8)

[Claims] 1. An optical element disposed in an optical path between a light source and an optical element for irradiating the information recording medium with light emitted from the light source to correct an aberration of light generated in the information recording medium. An optical element for correcting aberration, comprising: a liquid crystal element that exhibits a predetermined alignment state by a predetermined voltage; and electrodes facing each other that apply a voltage to the liquid crystal element, and at least one of the electrodes facing each other. Is an aberration-correcting optical element comprising a plurality of electrodes having a multilayer structure arranged in the optical axis direction. 2. The aberration correction optics according to claim 1, wherein the plurality of electrodes formed in the multilayer structure are formed in a multilayer structure arranged in the optical axis direction without overlapping each other. element. 3. The aberration correction according to claim 1, wherein the plurality of electrodes formed in the multilayer structure are formed in a multilayer structure partially overlapped with each other and arranged in the optical axis direction. Optical element. 4. The device according to claim 1, wherein a voltage for generating an electro-optical effect having characteristics opposite to the aberration characteristics of the information recording medium is applied to the electrodes. Aberration correction optical element. 5. A pickup device comprising the aberration correction optical element according to claim 4, further comprising: a photodetector that detects reflected light reflected by the information recording medium and transmitted through the aberration correction optical element. A pickup device characterized by the following. 6. The pickup device according to claim 5, further comprising control means for applying the voltage to the electrode of the aberration correction optical element. 7. An information reproducing apparatus comprising the pickup device according to claim 5, wherein the control means applies the voltage to the electrode of the aberration correction optical element, and the light source is used for reproducing information as the light. An information reproducing apparatus comprising: a driving unit that emits light; and a reproducing unit that reproduces information based on an output of the photodetector. 8. An information recording apparatus comprising the pickup device according to claim 5, wherein the control unit applies the voltage to the electrode of the aberration correction optical element, and the light source is used for recording information as the light. An information recording device comprising: a driving unit that emits light.