JP3841993B2 - Aberration correcting optical element, pickup device, information reproducing device, and information recording device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aberration correction optical element that performs aberration correction when information recording or information reproduction is performed on an information recording medium such as an optical disc, a pickup device including the aberration correction optical element, and an information recording / reproducing apparatus. It is.
[0002]
[Prior art]
Optical discs such as CDs (Compact disks) and DVDs (Digital Video Disks or Digital Versatile Disks) are known as information recording media on which information is recorded or reproduced optically. Different types of optical discs have been developed, such as a recordable optical disc that can be recorded and a rewritable optical disc that can erase and re-record information.
[0003]
Further, as the density of optical discs is increased, and research and development of a pickup device and an information recording / reproducing device corresponding to the higher density are being promoted, a so-called compatible pickup device capable of using different types of optical discs. Research and development of information recording and playback devices are also underway.
[0004]
In order to cope with the higher density of the optical disk, it is possible to irradiate the optical disk with a light beam having a small irradiation diameter by increasing the numerical aperture (NA) of the objective lens provided in the pickup device. ing. Further, it is considered to cope with higher density by using a light beam with a short wavelength.
[0005]
However, if the numerical aperture NA of the objective lens is increased or a light beam with a short wavelength is used, the influence of the aberration on the light beam by the optical disk increases, making it difficult to improve the accuracy of information recording and information reproduction. Problems arise.
[0006]
For example, when the numerical aperture NA of the objective lens is increased, the incident angle range of the light beam with respect to the optical disc is widened, so that the distribution width on the optical disc pupil plane of the birefringence amount that is an amount dependent on the incident angle is also increased. For this reason, the problem that the influence of the spherical aberration resulting from this birefringence becomes large arises. In addition, when the numerical aperture NA of the objective lens is increased and a light beam having a short wavelength is used, the optical disk is tilted 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 When tilted, the influence of coma aberration cannot be ignored.
[0007]
Also, since the structure and recording density of optical discs differ depending on the type, such as CD and DVD, the effects of aberrations such as spherical aberration and coma aberration differ depending on the type of optical disc, and a compatible pickup Development of a device and an information recording / reproducing device becomes difficult.
[0008]
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).
[0009]
As schematically shown in FIG. 14, 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, and an applied voltage between the transparent electrodes A and B is adjusted by adjusting the voltage applied between the transparent electrodes A and B. When the alignment state of the liquid crystal element C is changed and light incident on one transparent electrode A (or B) side passes through the liquid crystal element C, a birefringence change corresponding to the alignment state is given to the light. The light is emitted to the other transparent electrode B (or A) side.
[0010]
Further, at least one of the transparent electrodes A and B is formed, for example, by being divided into a plurality of transparent electrodes a1, a2, a3 and b1, b2, b3, and the transparent electrodes a1, a2, a3 are electrically separated from each other. At the same time, the transparent electrodes b1, b2, b3 are also electrically separated.
[0011]
For this reason, when different voltages are applied between the transparent electrodes in a mutually facing relationship, for example, between the transparent electrodes a1 and b1, between the transparent electrodes a2 and b2, and between the transparent electrodes a3 and b3, the liquid crystal element C is A plurality of different alignment states can be adjusted, and birefringence changes corresponding to the respective alignment states are simultaneously given to incident light.
[0012]
The liquid crystal unit is disposed in the optical path between the light source that emits laser light and the objective lens. When laser light is emitted from the light source, the liquid crystal unit gives the laser light birefringence changes according to the above-mentioned plurality of alignment states and transmits the laser light to the objective lens, and the objective lens converges the transmitted laser light. In this way, a light beam is generated and applied to the optical disk. Further, when the reflected light generated by the light beam irradiation to the optical disk enters the liquid crystal unit through the objective lens, the reflected light is transmitted through the birefringence change according to the plurality of orientation states, and the transmitted light is transmitted. The reflected light is detected by a photodetector. The influence of aberrations such as spherical aberration and coma is reduced by appropriately adjusting the plurality of alignment states of the liquid crystal unit.
[0013]
[Problems to be solved by the invention]
However, in the conventional liquid crystal unit, the plurality of transparent electrodes a1, a2, a3 and b1, b2, b3 are electrically separated from each other as shown in FIG. A gap SP for electrical insulation is provided. That is, the gap SP is provided along each boundary portion of the transparent electrodes a1, a2, and a3, and the gap SP is provided along each boundary portion of the transparent electrodes b1, b2, and b3.
[0014]
For this reason, no voltage is applied to these gaps SP, and therefore the alignment state in the liquid crystal element C corresponding to these gaps SP cannot be controlled. As a result, aberration correction can be performed on the light beam or reflected light passing through the transparent electrodes a1, a2, a3 and b1, b2, b3, whereas the light beam or reflected light passing through the gap SP is used. As a result, aberration correction cannot be performed. For this reason, there is a case where aberration correction with high accuracy cannot be performed on the entire light beam or reflected light.
[0015]
In addition, when trying to increase the number of divisions of the transparent electrode in order to finely correct the influence of aberration, a large number of transparent electrodes are electrically insulated and formed within a limited effective optical path range through which laser light or reflected light passes. Therefore, the number and the occupied area of the gaps SP are increased, resulting in a problem that fine aberration correction becomes difficult.
[0016]
In addition, when different voltages are applied to adjacent transparent electrodes, there is a problem that the alignment state in the liquid crystal element C corresponding to the gap SP becomes a steep discontinuous state.
[0017]
The present invention has been made to overcome the problems of the prior art, and provides an aberration correction optical element, a pickup device, and an information recording / reproducing device that can accurately correct the influence of aberration caused by an information recording medium. The purpose is to provide.
[0018]
It is another object of the present invention to provide an aberration correction optical element, a pickup device, and an information recording / reproducing device that can accurately correct the influence of aberration associated with an increase in the density of an information recording medium.
[0019]
[Means for Solving the Problems]
The invention described in claim 1 In the optical path between the light source and the optical element that irradiates the information recording medium with the light emitted from the light source In Arranged, By a plurality of aberration correction regions intersecting the optical axis of the optical path An aberration correction optical element that corrects light aberration generated in the information recording medium, the liquid crystal element showing a predetermined alignment state by a predetermined voltage, and a voltage applied to the liquid crystal element Preferably, the electrodes are opposed to each other in a face-to-face relationship in the optical axis direction with the liquid crystal element interposed therebetween, and each of the plurality of aberration correction regions is defined via a gap portion for electrical insulation, In the above facing relationship At least one of the opposing electrodes is Make up for the gap It is formed of a plurality of electrodes having a multilayer structure arranged in the optical axis direction.
[0022]
According to a second aspect of the present invention, in the aberration correction optical element according to the first aspect, the electrodes facing each other in the facing relationship include: A voltage that causes an electro-optic effect opposite to the aberration characteristic of the information recording medium is applied.
[0023]
In these claims 1 and 2 According to the aberration correcting optical element of the present invention, by adjusting the voltage applied to the electrodes facing each other, an electro-optical effect opposite to the aberration characteristic due to the information recording medium can be generated in the liquid crystal element. The aberration of light transmitted through the liquid crystal element can be corrected 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 to the liquid crystal element side without a gap. For this reason, when a voltage is applied to the plurality of electrodes, an electro-optic effect is produced in the liquid crystal element without a gap, and aberrations can be corrected without omission. Also. Aberrations can be finely corrected.
[0024]
Invention of Claim 3 is a pick-up apparatus provided with the aberration correction optical element of Claim 2, Comprising: Said pickup Reflected by the information recording medium Said It comprises a photodetector for detecting reflected light transmitted through the aberration correction optical element.
[0025]
Invention of Claim 3 According to this, it is possible to perform accurate information reproduction based on the reflected light in which the influence of the aberration is corrected.
[0026]
According to a fifth aspect of the present invention, there is provided an information reproducing apparatus including the pickup device according to the third aspect, wherein the voltage is applied to the electrode of the aberration correcting optical element, and the light source includes the light. And driving means for emitting light for reproducing information, and reproducing means for reproducing information based on the output of the photodetector. According to such a configuration, it is possible to perform accurate information reproduction based on the reflected light in which the influence of the aberration is corrected.
[0027]
A sixth aspect of the present invention is an information recording apparatus comprising the pickup device according to the third aspect, wherein the voltage is applied to the electrode of the aberration correcting optical element, and the light source includes the light. And a driving means for emitting light for information recording. According to this 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]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a pickup device provided in an information recording / reproducing apparatus.
[0029]
In FIG. 1, the pickup apparatus PU includes a light source 1 that emits laser light 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. Further, a control circuit 8 for controlling the aberration correcting optical element 4 is provided in the pickup apparatus PU or the information recording / reproducing apparatus.
[0030]
Here, the aberration correction optical element 4 is formed of an electro-optical element whose electro-optic effect is changed by an electric field. More specifically, it is formed of a liquid crystal optical element that causes a birefringence change according to the control voltage Vi applied by the control circuit 8.
[0031]
That is, in the variable optical element 4, as schematically shown in FIG. 2, a liquid crystal element 14 is enclosed between two insulating substrates 10 and 11 such as a transparent glass substrate. The electrode portions 12 and 13, the insulating films 23 and 24, and the liquid crystal alignment films 21 and 22 are formed on the opposing surfaces of the glass substrates 10 and 11 that have the configuration and face each other.
[0032]
When the control voltage Vi is applied between the electrode parts 12 and 13, the arrangement of the liquid crystal elements 14 changes according to the electric field Ei generated by the control voltage Vi. 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), and the polarization state (phase) is controlled by the control voltage Vi applied to the liquid crystal element 14. can do.
[0033]
Further, the aberration correcting optical element 4 has bidirectional light transmission, and either side of the insulating substrates 10 and 11 may be arranged facing the objective lens 5 side.
[0034]
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, AR2 to ARi determined in association with the distribution of aberrations generated in the optical disk 9. These aberration correction regions AR1, AR2 to ARi are realized by a transparent electrode (ITO) layer formed on the electrode portions 12 and 13. FIG. 3 shows typical examples of the aberration correction areas AR1, AR2 to ARi for correcting the spherical aberration caused by the optical disk 9. In actuality, there are various examples corresponding to the aberration distribution of the optical disk 9. Divided into shapes. For example, when correcting coma aberration generated by tilting of the optical disc 9 during information recording or information reproduction, aberration correction regions BR1 to BR9 having shapes as shown in FIG. 6 are provided. Further, the number of sections of these aberration correction regions is also determined in correspondence with the aberration distribution of the optical disc 9.
[0035]
When the concentric aberration correction regions AR1 to ARi as shown in FIG. 3 are provided, as shown in the cross-sectional view of FIG. 4 (the cross-sectional structure taken along the line XX of FIG. 3), the electrode portion 12 Is insulated against the transparent electrode layers A1, A2 to Ai embedded in the transparent insulating layer 15 so as to be electrically separated from each other, and a plurality of gaps W1 existing between the transparent electrode layers A1, A2 to Ai. The transparent electrode layers B1, B2-Bj embedded in the layer 15 are provided. The group of transparent electrode layers A1, A2 to Ai and the group of transparent electrode layers B1, B2 to Bj are formed in a two-stage structure in the insulating layer 15 along the optical axis OA. For convenience of explanation, in the cross-sectional view of FIG. 4, the insulating films 23 and 24 and the liquid crystal alignment films 21 and 22 are omitted (hereinafter, FIG. 5, FIG. 7, FIG. 11, FIG. 12, FIG. 13 are also shown). The same).
[0036]
Here, the transparent electrode layer A1 is formed in a shape (circular shape in FIG. 3) according to the aberration correction area AR1, and the transparent electrode layer A2 is a shape (in FIG. 3 according to FIG. 3). The remaining transparent electrode layers A3 to Ai are similarly shaped in accordance with the aberration correction regions AR3 to ARi.
[0037]
The transparent electrode layer B1 is formed in an extremely narrow annular shape in accordance with the shape of the gap W1 for electrically separating the transparent electrode layers A1 and A2, and the transparent electrode layer B2 is similarly formed of a transparent electrode. An extremely narrow annular shape is formed in accordance with the shape of the gap W1 for electrically separating the layers A2 and A3, and the remaining transparent electrode layers B3 and Bj are similarly formed.
[0038]
In other words, the aberration correction areas AR1, AR2 to ARi shown in FIG. 3 are realized by electrically separating the transparent electrode layers A1, A2 to Ai, and between the aberration correction areas AR1, AR2 to ARi. The gaps BK1, BK2 to BKj are realized by forming the transparent electrode layers B1, B2 to Bj.
[0039]
These transparent electrode layers B1, B2 to Bj may be provided so as to face all the existing gaps W1, but are formed so as to face the necessary number or gaps W1 depending on the characteristics of the aberration to be corrected. You may do it.
[0040]
On the other hand, in the same manner, the electrode section 13 is also formed between 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 between the transparent electrode layers C1, C2 to Ci. The transparent electrode layers D1, D2 to Dj embedded in the insulating layer 16 so as to face the existing gap W2 have a two-stage structure, and the transparent electrode layers C1, C2 to Ci are The transparent electrode layers A 1, A 2 to Ai are in a face-to-face relationship, and the transparent electrode layers D 1, D 2 to Dj are in a face-to-face relationship with the transparent electrode layers B 1, B 2 to Bj of the electrode portion 12.
[0041]
These transparent electrode layers D1, D2 to Dj may also be provided to face all the existing gaps W2, but they are formed to face the required number or gaps according to the characteristics of the aberration to be corrected. May be.
[0042]
Then, as schematically shown in FIG. 5, the transparent electrode layers (A1, C1) to (Ai, Ci) in the aberration correction regions AR1 to ARi that are in a directly-facing relationship with each other by the control voltage Vi from the control circuit 8. When different unique voltages V1 to Vk are applied to the transparent electrode layers (B1, D1) to (Bj, Di) in the gaps BK1 to BKj, the liquid crystal element 14 is applied to the applied voltages V1 to Vk. A plurality of alignment states are generated in the inside. These voltages V1 to Vk are determined so that the orientation of the liquid crystal element 14 in each of the aberration correction areas AR1 to ARi and the gaps BK1 to BKj is opposite to the characteristics of the aberration caused by the optical disc 9. It is done.
[0043]
Thus, even if there are gaps BK1 to BKj between the aberration correction areas AR1 to ARi, since the transparent electrode layers B1 to Bj and D1 to Dj are provided in the gaps BK1 to BKj, the liquid crystal element 14 It is possible to adjust the alignment state for aberration correction over the entire area of the lens, and to finely adjust the alignment state.
[0044]
Further, when the voltages V1 to Vk between the transparent electrode layers (B1, D1) to (Bj, Di) are appropriately adjusted, the alignment state is generated by the transparent electrode layers (A1, C1) to (Ai, Ci). Instead of a steep change with respect to the state, it can be a continuous change.
[0045]
Further, also in the case of the aberration correction optical element 4 including the aberration correction regions BR1 to BR9 for correcting the coma aberration shown in FIG. 6, the cross-sectional view of FIG. 7 (the cross-sectional structure along the line XX of FIG. 6 is used). As shown in the figure), a transparent electrode layer (reference numeral omitted) corresponding to the aberration correction regions BR1 to BR9 and a transparent electrode layer corresponding to the gaps between the aberration correction regions BR1 to BR9 are provided on the electrode portions 12 and 13, respectively. It is formed with a two-stage structure. 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 indicated by reference numerals F1 to F4 and G1 to G4. The case where it provided only in the location of the clearance gap which should reduce the influence of a coma aberration is shown.
[0046]
Next, the operation of the pickup apparatus PU including the aberration correcting optical element 4 having such a structure will be described with reference to FIGS. 1 and 6 to 10. As a representative example, the operation when the aberration correction optical element 4 for correcting coma shown in FIGS. 6 and 7 is provided in the pickup apparatus PU will be described.
[0047]
When the optical disk 9 is loaded at a so-called clamp position of the information recording / reproducing apparatus and an instruction to start information reproduction is given from the user, a system controller (not shown) provided in the information recording / reproducing apparatus instructs the control circuit 8. The control voltage Vi for correcting the coma aberration is output. Thereby, the transparent electrode layer F1 in a facing relationship corresponding to the gap and the transparent electrode layer in the facing relationship corresponding to each of the aberration correction regions BR1 to BR9 of the aberration correcting optical element 4 shown in FIGS. Appropriate voltages are respectively applied between ˜F4 and G1 to G4, and a plurality of alignment state changes corresponding to the electric field generated by the applied voltages are generated in the liquid crystal element 14.
[0048]
Next, the system controller rotates and drives a spindle motor (not shown) provided in the information recording / reproducing apparatus, and a carriage (not shown) for moving the pickup device PU in the radial direction of the optical disk 9. By driving, the optical disk 9 is rotated at a predetermined linear velocity.
[0049]
Further, when the system controller supplies a drive signal with a predetermined power to the light source 1, a linearly polarized laser beam H 1 with a constant power is emitted from the light source 1. The laser light H1 is converted into parallel light by the collimator lens 2, passes through the polarization beam splitter 3, and enters the aberration correction optical element 4.
[0050]
When the laser light incident on the aberration correction optical element 4 passes through the aberration correction optical element 4, it is birefringent according to the orientation state of the liquid crystal element 14, and the birefringent laser light is converged by the objective lens 5. Thus, the optical disk 9 is irradiated with a light beam having a small irradiation diameter.
[0051]
Further, the reflected light generated by reflecting the light beam on the pupil plane of the optical disk 9 enters the objective lens 5, and the reflected light that has passed through the objective lens 5 is again birefringent and transmitted by the aberration correction optical element 4. The light is reflected by the polarizing beam splitter 3 toward the condenser lens 6 side. The condensing lens 6 condenses the reflected light and causes the photodetector 7 to receive it. The photodetector 7 photoelectrically converts the received reflected light to output a photoelectric conversion signal having information recorded on the optical disc 9, and a reproduction signal processing circuit provided in the information recording / reproducing apparatus. The reproduction signal processing circuit performs so-called decoding processing and decoding processing based on the photoelectric conversion signal to generate a reproduction signal such as an audio signal and a video signal.
[0052]
Here, when the optical disc 9 is tilted and the incident angle (tilt angle) of the light beam is tilted with respect to the normal direction of the optical disc 9, coma aberration occurs on the pupil plane of the optical disc 9.
[0053]
FIG. 8 is a characteristic diagram showing the amount of wavefront aberration obtained by normalizing the influence of coma aberration generated on the pupil plane of the optical disk 9, and the horizontal axis shows the effective optical path range (lens diameter) of the objective lens 5.
[0054]
When the coma aberration shown in FIG. 8 occurs, the aberration correction optical element 4 gives birefringence to the laser beam incident from the polarization beam splitter 3 side as described above so as to reduce the influence of the coma aberration. Thus, the optical disk 9 is irradiated with a light beam that can reduce the influence of coma aberration in advance through the objective lens 5. Further, when the reflected light returning from the optical disk 9 under the influence of coma aberration is incident on the aberration correction optical element 4 via the objective lens 5, the reflected light is reflected again by giving birefringence. The influence of coma is reduced and the light is transmitted to the polarization beam splitter 3 side. For this reason, the reflected light in which the influence of the coma aberration is suppressed is incident on the photodetector 7 through the condenser lens 6, thereby enabling accurate information reproduction.
[0055]
Further, as shown in FIGS. 6 and 7, the transparent electrode layers F1 to F4 and G1 to G4 are provided facing each other in the gaps between the aberration correction regions BR1 to BR9 of the aberration correction optical element 4. The coma aberration can be reduced in the entire region of the aberration correction optical element 4, and the coma aberration can be accurately reduced.
[0056]
FIG. 9 is a characteristic diagram showing the amount of wavefront aberration normalized by the coma aberration reduced by the aberration correction optical element 4, and the horizontal axis shows the effective optical path range (lens diameter) of the objective lens 5. . As is clear from the figure, a significant improvement can be seen compared to the uncorrected coma aberration shown in FIG.
[0057]
FIG. 10 shows a case where aberration correction is performed only in the aberration correction regions BR1 to BR9 without providing a transparent electrode layer in the gaps between the aberration correction regions BR1 to BR9 of the aberration correction optical element 4, that is, FIG. FIG. 10 is a diagram showing the influence of coma aberration obtained when aberration correction is performed without providing transparent electrode layers F1 to F4 and G1 to G4, in contrast to the characteristic diagram of FIG.
[0058]
In the characteristic diagram of FIG. 10, large peaks P1 to P4 occur in the aberrations in the portions where the transparent electrode layers F1 to F4 and G1 to G4 are not provided, whereas in the characteristic diagram of FIG. It can be seen that is significantly reduced.
[0059]
As is apparent from the experimental results, according to the aberration correction optical element 4 of the present embodiment, the coma aberration is obtained by providing the transparent electrode layers F1 to F4 and G1 to G4 in the gaps between the aberration correction regions BR1 to BR9. It has been confirmed that the influence of can be greatly reduced.
[0060]
Next, the operation of the pickup device PU during information recording will be described.
When an instruction to start information recording is given by the user, the system controller provided in the information recording / reproducing apparatus instructs a recording signal processing circuit (not shown) to input an audio signal, a video signal, or the like supplied from the outside. Based on the signal, modulation processing, encoding processing, and the like are performed, a recording signal generated thereby is supplied to the light source 1, and laser light H1 modulated by the recording signal is emitted.
[0061]
The laser light H1 is converted into parallel light by the collimator lens 2, passes through the polarization beam splitter 3, and enters the aberration correction optical element 4. Here, when the laser light incident on the aberration correcting optical element 4 is transmitted through the aberration correcting optical element 4, it is birefringent according to the orientation state of the liquid crystal element 14, and the birefringent laser light is converted into the objective lens 5. As a result, the optical disc 9 is irradiated with a light beam having a small irradiation diameter, and information recording is performed by the light energy of the light beam.
[0062]
Further, the reflected light generated by reflecting the light beam on the pupil plane of the optical disk 9 enters the objective lens 5, and the reflected light that has passed through the objective lens 5 is again birefringent and transmitted by the aberration correction optical element 4. The light is reflected by the polarizing beam splitter 3 toward the condenser lens 6 side. The condensing lens 6 condenses the reflected light and causes the photodetector 7 to receive it. The photodetector 7 photoelectrically converts the received reflected light and supplies the photoelectric conversion signal to a servo circuit (not shown) provided in the information recording / reproducing apparatus.
[0063]
Here, the servo circuit detects a focus error by, for example, an astigmatism method, and performs focus servo on the objective lens 5 based on the detection result. Also in this focus servo, since the focus servo is performed based on the photoelectric conversion signal in which the influence of the coma aberration is greatly reduced, the focus servo with high accuracy is possible.
[0064]
Incidentally, even when the spherical aberration correcting optical element 4 shown in FIGS. 3 and 4 is provided, the coma aberration correcting optical element 4 shown in FIGS. 6 and 7 is provided. Since the same effect can be obtained, the influence of various aberrations can be greatly reduced.
[0065]
As described above, according to the pickup apparatus PU and the information recording / reproducing apparatus of the present embodiment, the pickup apparatus PU includes 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, the influence of the aberration caused by the optical disk 9 can be greatly reduced, and the aberration reduction can be finely controlled.
[0066]
In the above embodiment, the case where the transparent electrode layer is provided corresponding to the gap generated between the aberration correction regions of the aberration correction optical element 4 has been described. However, the aberration correction optical element of the present invention is limited to such a structure. It is not something.
[0067]
As shown in the cross-sectional view of FIG. 11, one electrode portion 12 is provided with a transparent electrode layer corresponding to the gap generated between the aberration correction regions, and the other electrode portion 13 is transparent over the entire effective optical path range. An electrode layer 17 may be provided, and the transparent electrode layer 17 may be a so-called common electrode, and a specific voltage may be applied between each transparent electrode layer in the electrode portion 13 and the transparent electrode layer 17.
[0068]
In addition, as shown in the cross-sectional view of FIG. 12, a shape corresponding to the aberration correction region is formed in each electrode portion 12, 13 with a multi-stage structure in which a plurality of transparent electrode layers are overlapped along the optical axis OA. A specific voltage may be applied between the transparent electrode layers that are in a directly-facing relationship with each other. That is, aberration correction can be performed by matching the portion of each transparent electrode layer released to the liquid crystal element 14 side with the shape of the aberration correction region. According to such a structure, since no gap is generated between the aberration correction regions, the transparent electrode layer corresponding to the gap as shown in FIGS. 4 and 7 is not necessary, and a voltage is applied to the transparent electrode layer. 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.
[0069]
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 single transparent electrode layer is used as a common electrode. Also good.
[0070]
Furthermore, 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 multistage structure along the optical axis OA, and a unique voltage between the transparent electrode layers facing each other. May be applied.
[0071]
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 generated between the transparent electrode layers, the transparent electrode layer corresponding to the gap as shown in FIGS. 4 and 7 is not necessary, and the number of wires for applying a voltage to the transparent electrode layer can be reduced. Since the types of voltages to be applied can be reduced, effects such as simplification of the control circuit 8 can be achieved.
[0072]
【The invention's effect】
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 correcting optical element is formed of a plurality of electrodes having a multilayer structure. Can be directed to the liquid crystal element side. Accordingly, when a voltage is applied to the plurality of electrodes, an electro-optic effect is generated in the liquid crystal element without a gap, and aberrations can be corrected without omission. Also. Aberrations can be finely corrected.
[0073]
Furthermore, as a result of appropriately correcting the aberration due to the information recording medium, the NA of the objective lens accompanying the increase in the density of the information recording medium and the shortening of the wavelength of the light emitted from the light source can be promoted. It is possible to provide an aberration-correcting optical element that is effective for the improvement.
[0074]
In addition, since the pickup device, the information reproducing device, and the information recording device of the present invention include the aberration correcting optical element described above and perform aberration correction, it is possible to perform information recording and information reproduction with high accuracy.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a pickup device provided in an information recording / reproducing apparatus 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 an aberration correction optical element when viewed from the optical axis side.
FIG. 4 is a sectional view showing a longitudinal sectional structure of an aberration correction optical element.
FIG. 5 is a diagram for explaining the principle of aberration correction by an aberration correction optical element.
FIG. 6 is a plan view showing a shape of another aberration correction optical element when viewed from the optical axis side.
FIG. 7 is a cross-sectional view showing a longitudinal 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 the aberration correction optical element.
FIG. 10 is a characteristic diagram showing characteristics when coma is not sufficiently reduced.
FIG. 11 is a cross-sectional view showing another structure of the aberration correction optical element.
FIG. 12 is a cross-sectional view showing still another structure of the aberration correction optical element.
FIG. 13 is a cross-sectional view showing still another structure of the aberration correction optical element.
FIG. 14 is a diagram for explaining problems in a conventional liquid crystal unit.
[Explanation of symbols]
PU ... Pickup device
1 ... Light source
2 ... Collimator lens
3. Polarizing beam splitter
4. Aberration correction optical element
5 ... Objective lens
6 ... Condensing lens
7 ... Photodetector
8 ... Control circuit
9 ... Optical disc
10, 11 ... Insulating substrate
12, 13 ... Electrode part
14 ... Liquid crystal element
15, 16 ... Insulating layer
17, A1-Ai, B1-Bj, C1-Ci, D1-Dj ... Transparent electrode layer
AR1 to ARi: Aberration correction area
BK1 to BKj ... Gap
PU ... Pickup

Claims (6)

A light source, disposed in an optical path between the optical element for focusing the light emitted from the light source on the information recording medium, a plurality of aberration correction region intersecting the optical axis of said optical path, said information recording medium An aberration correction optical element for correcting the aberration of light generated in
A liquid crystal element exhibiting a predetermined alignment state by a predetermined voltage;
In order to apply a voltage to the liquid crystal element, the liquid crystal elements are sandwiched so as to face each other in the optical axis direction, and each of the plurality of aberration correction regions is defined through gap portions for electrical insulation. Having an electrode
Aberration correction optics characterized in that at least one of the electrodes facing each other in the facing relationship is formed of a plurality of electrodes having a multilayer structure arranged in the optical axis direction so as to compensate for the gap portion. element. The aberration correcting optical element according to claim 1 , wherein a voltage that causes an electro-optical effect having a characteristic opposite to the aberration characteristic of the information recording medium is applied to the electrodes facing each other in the facing relationship . A pickup apparatus comprising the aberration correction optical element according to claim 2 ,
A pickup apparatus comprising: a photodetector that detects reflected light reflected by the information recording medium and transmitted through the aberration correction optical element. The pickup apparatus according to claim 3 , further comprising a control unit that applies the voltage to the electrode of the aberration correction optical element. An information reproducing apparatus comprising the pickup device according to claim 3 ,
Control means for applying the voltage to the electrode of the aberration correcting optical element;
Driving means for emitting light for information reproduction as the light to the light source;
Information reproducing apparatus characterized by comprising a reproducing means for reproducing information based on the output of the photodetector. An information recording device comprising the pickup device according to claim 3 ,
Control means for applying the voltage to the electrode of the aberration correcting optical element;
The light source, the information recording apparatus characterized by comprising a driving means for emitting light for recording information as the light.

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