JP4648633B2 - Liquid crystal optical element and optical device - Google Patents

Description

  The present invention relates to a liquid crystal optical element for phase modulation and an optical apparatus using the same, and in particular, liquid crystal optics for correcting wavefront aberration of a light beam (high coherence light) such as laser light. The present invention relates to an element and an optical device using the element.

  In an optical pickup device that reads or writes a recording medium such as a DVD or a next-generation high-density DVD, the light beam from the light source 1 is converted into substantially parallel light by a collimator lens 2 as shown in FIG. The light is condensed on the recording medium 4 by the objective lens 3 and the reflected light beam from the recording medium 4 is received to generate a light intensity signal. When reading or writing the recording medium 4 with such an optical pickup device, it is necessary to accurately focus the light beam on the track of the recording medium 4 by the objective lens 3.

  However, the distance from the objective lens 3 to the track surface is not constant or is always the same due to uneven thickness of the light transmission protective layer on the track surface in the recording medium 4 (direction B in FIG. 8A). In some cases, the light spot cannot be collected. In addition, when a plurality of track surfaces are provided in the recording medium 4 in order to increase the recording capacity of the recording medium 4, it is necessary to adjust the positional relationship between the objective lens 3 and each track surface.

  As described above, when unevenness occurs in the distance between the objective lens 3 and the track surface, spherical aberration occurs in the substrate of the recording medium 4, and light generated based on the reflected light beam from the recording medium 4. It causes deterioration of the intensity signal. An example of the spherical aberration 20 converted at the entrance pupil position of the objective lens 3 is shown in FIG. In addition, when a plurality of track surfaces are provided in the recording medium, spherical aberration occurs when reading or writing a second track surface other than the first track surface at the focal position of the objective lens 3, and similarly, This becomes a cause of deteriorating the light intensity signal generated based on the reflected light beam from the recording medium 4.

  Therefore, as shown in FIG. 9, there is an attempt to correct the spherical aberration generated in the substrate of the recording medium 4 by arranging the liquid crystal optical element 5 between the collimator lens 2 and the objective lens 3 (for example, Patent Document 1). reference.). Such a liquid crystal optical element 5 works by changing the phase of the light beam passing through the liquid crystal and thereby canceling out the spherical aberration by utilizing the fact that the orientation of the liquid crystal changes according to the potential difference generated in the liquid crystal. .

  FIG. 10A shows an example of the transparent electrode pattern 40 for generating a phase distribution in the liquid crystal according to the voltage applied to the liquid crystal optical element 5 for correcting the spherical aberration. In FIG. 10A, nine concentric electrode patterns 41 to 49 are provided within the range of the effective diameter 10. A voltage 21 as shown in FIG. 10B is applied to each region. When a voltage 21 as shown in FIG. 10 (b) is applied to the electrode pattern 40 as shown in FIG. 10 (a), a potential difference is generated between the opposing transparent electrodes, and the orientation of the liquid crystal therebetween is a potential difference. It changes according to. Therefore, the light beam passing through this portion is subjected to an action that advances its phase in accordance with the potential difference. Thereby, the spherical aberration 20 generated in the substrate of the recording medium 4 is corrected like the spherical aberration 22 shown in FIG. A voltage is applied to the transparent electrode pattern 40 through the wiring 6 (see FIG. 9).

  However, in addition to the problem of spherical aberration occurring in the substrate of the recording medium 4 described above, there also arises a problem that the track of the recording medium 4 and the optical axis of the objective lens 3 are shifted (axis misalignment). Therefore, as shown in FIG. 11, a tracking actuator 7 is attached to the objective lens 3 so that the optical axis of the objective lens 3 follows the track of the recording medium 4. The actuator 7 has a wiring 8 for supplying power. The actuator 7 moves the objective lens 3 in the direction of arrow A in the figure, so that the light beam condensed by the objective lens 3 accurately follows the track of the recording medium 4.

  Further, in an optical pickup device that reads or writes data on a recording medium such as a compact disc (CD) or a digital video disc (DVD), as shown in FIG. Thus, the light is converted into substantially parallel light, condensed by the objective lens 3 onto the recording medium 14, and the reflected light beam from the recording medium 14 is received to generate an information signal. In such an optical pickup device, when reading or writing a recording medium, it is necessary to cause the light beam condensed by the objective lens 3 to accurately follow the track of the recording medium 14. However, the recording medium 14 may be inclined due to warping or bending of the recording medium 14, a defect in the drive mechanism of the recording medium 14, and the like. Since the optical axis of the light beam condensed by the objective lens 3 is tilted with respect to the track of the recording medium 14 in this way, coma aberration occurs in the substrate of the recording medium 14. When converted in terms of the pupil position, coma aberration 120 as shown in FIG. 12B is generated, which causes the information signal generated based on the reflected light beam from the recording medium 14 to deteriorate.

  Therefore, as shown in FIG. 13, there is an attempt to correct the coma caused by the inclination of the recording medium 14 by arranging a liquid crystal optical element 15 between the collimator lens 2 and the objective lens 3 (see, for example, Patent Document 2). ). Such a liquid crystal optical element 15 uses the fact that the orientation of the liquid crystal changes according to the potential difference generated in the liquid crystal, thereby changing the phase of the light beam passing through the liquid crystal, thereby canceling the coma aberration. It is.

  A transparent electrode pattern 30 for generating a phase distribution in the liquid crystal according to the voltage applied to the liquid crystal optical element 15 for correcting such coma aberration is shown in FIG. In FIG. 14A, two regions 32 and 33 for advancing the phase and 2 for delaying the phase are within the region having the same size as the effective diameter 10 of the light beam incident on the liquid crystal optical element 15. There are two regions 34 and 35. In the figure, reference numeral 31 denotes a region for applying a reference potential.

  When a positive (+) voltage is applied to the regions 32 and 33, a potential difference is generated between the opposing transparent electrodes (not shown), and the orientation of the liquid crystal therebetween changes according to the potential difference. Therefore, in the case of a general P-type liquid crystal, the light beam passing through this portion is subjected to an action that allows the phase to be advanced. When a negative (-) voltage is applied to the regions 34 and 35, a potential difference is generated between the transparent electrodes (not shown) facing each other, and the orientation of the liquid crystal therebetween changes according to the potential difference. Therefore, in the case of a general P-type liquid crystal, the light beam passing through this portion is subjected to an action of delaying the phase. A reference potential (for example, 0 v in this case) is applied to the region 31. A voltage is applied to the transparent electrode pattern 30 through the wiring 6 (see FIG. 13).

  FIG. 14B shows the voltage 121 applied to each region on the X axis. The coma aberration 120 is corrected by applying such a voltage to the transparent electrode pattern 30. FIG. 14C shows the coma aberration 122 after correction. As shown in FIG. 14C, by using the liquid crystal optical element 15, the coma aberration generated in the substrate of the recording medium 14 is corrected so as to be suppressed.

  However, in addition to the above-described problem that the recording medium 14 is tilted, there is a problem that the track of the recording medium 14 and the optical axis of the objective lens 3 are shifted (optical axis deviation). Therefore, as shown in FIG. 15, a tracking actuator 7 is attached to the objective lens 3 so that the optical axis of the objective lens 3 follows the track of the recording medium 14. The actuator 7 has a wiring 8 for supplying power. The actuator 7 moves the objective lens 3 in the direction of arrow A in the figure, so that the light beam condensed by the objective lens 3 is corrected so as to accurately follow the track of the recording medium 14 (FIG. 15). The light beam 11 is corrected to the light beam 12).

  In the above two examples, in order for the liquid crystal optical elements 5 and 15 to function correctly, the centers of the electrode patterns 40 and 30 formed on the liquid crystal optical elements 5 and 15 and the optical axis of the objective lens 3 are It was necessary to mount with an accuracy of several μm. Therefore, by fixing the objective lens and the phase control element, each of which has a positioning mark for center axis alignment, to the holder, the eccentricity of the objective lens and the phase control element that occurs during assembly of the optical device is stabilized below the allowable value. (For example, refer to Patent Document 3). If this technique is applied to the optical apparatus described above, it is impossible for the naked eye to accurately position the electrode patterns 40 and 30 of the liquid crystal optical elements 5 and 15 and the objective lens 3. Therefore, the objective lens 3 and the liquid crystal optical elements 5 and 15 need to be photographed with a video camera or the like and aligned on the screen while performing image processing such as enlargement. Therefore, a complicated process is required only for the alignment between the objective lens 3 and the liquid crystal optical elements 5 and 15, which is a reason for inviting an increase in cost of the element and the device.

Japanese Patent Laid-Open No. 10-269611 (page 3-5, FIGS. 1-3, FIG. 5) JP 2001-143303 A (page 3, FIG. 1) JP 2001-6203 A (page 3, page 7, FIG. 10)

  Therefore, an object of the present invention is to provide a liquid crystal optical element that does not require a complicated alignment step and an optical device using such a liquid crystal optical element.

  In order to solve the above problems, a liquid crystal optical element according to the present invention is configured integrally with an objective lens for condensing a light beam from a light source onto a recording medium, and includes a first transparent substrate, a second transparent substrate, and a second transparent substrate. A wavefront aberration electrode pattern formed on one of the transparent substrate, the liquid crystal sealed between the first and second transparent substrates, and the first or second transparent substrate, and advances the phase of the light beam. It has a region for correcting wavefront aberration of the light beam by delaying or delaying, and the region is arranged only in the inner region of the effective diameter of the light beam.

In order to solve the above problems, an optical device according to the present invention includes a light source, an objective lens for condensing a light beam from the light source onto the recording medium, and a liquid crystal configured integrally with the objective lens. An optical element, and a liquid crystal optical element is
A first transparent substrate, a second transparent substrate, a liquid crystal sealed between the first and second transparent substrates, and a wavefront aberration electrode formed on one of the first or second transparent substrates A pattern having a region for correcting wavefront aberration of the light beam by advancing or retarding the phase of the light beam, and the region is arranged only in an inner region of the effective diameter of the light beam .

  Furthermore, in the liquid crystal optical element and the optical device according to the present invention, the electrode pattern is preferably a spherical aberration electrode pattern.

  Further, in the liquid crystal optical element and the optical device according to the present invention, the electrode pattern preferably has a plurality of small regions for advancing or delaying the phase of the light beam.

  Furthermore, in the liquid crystal optical element and the optical device according to the present invention, the electrode pattern is preferably an electrode pattern for coma aberration.

  Furthermore, in the liquid crystal optical element and the optical device according to the present invention, the electrode pattern includes a first region for advancing the phase of the light beam, a second region for retarding the phase of the light beam, and the phase of the light beam. It is preferable to have a third region that does not substantially change

  Furthermore, in the liquid crystal optical element and the optical device according to the present invention, it is preferable that the region is set to the inside of 10 μm to 75 μm from the effective diameter of the light beam.

  Furthermore, the optical apparatus according to the present invention preferably has a tracking means for moving the objective lens in order to correct the axial deviation of the objective lens.

  Furthermore, the optical device according to the present invention preferably has voltage applying means for applying a voltage to the electrode pattern.

  According to the present invention, since the area for correcting the wavefront aberration is set in the area inside the effective diameter of the light beam, the liquid crystal optical element can be easily fixed, attached or integrated with the objective lens. It becomes.

  In addition, according to the present invention, it is possible to perform sufficient wavefront aberration correction regardless of the mounting error between the objective lens and the liquid crystal optical element.

  A liquid crystal optical element and an optical device according to the present invention will be described below with reference to the drawings.

  An optical apparatus 100 using a liquid crystal optical element according to a second embodiment of the present invention is shown in FIG.

  In FIG. 1, the light beam (405 nm) emitted from the light source 1 is converted into substantially parallel light having an effective diameter 10 by the collimator lens 2, passes through the polarization beam splitter 50, passes through the liquid crystal optical element 70, and The light enters the quarter wave plate 55. The light beam that has passed through the liquid crystal optical element 70 is condensed on the recording medium 104 by the objective lens 13 (aperture ratio NA = 0.85). In the present embodiment, the effective diameter 10 (φ) is set to 3 mm.

  The light beam reflected from the recording medium 104 passes through the objective lens 13, the quarter wavelength plate 55, and the liquid crystal optical element 70 again, the optical path is changed by the polarization beam splitter 50, and the light receiver 52 passes through the condenser lens 51. It is focused on. The light beam is amplitude-modulated by information (pits) recorded on the track surface of the recording medium 104 when reflected by the recording medium 104. The light receiver 52 outputs the received light beam as a light intensity signal. Record information is read from this light intensity signal (RF signal).

  When writing to the recording medium 104, the intensity of the light beam emitted from the light source 1 is modulated in accordance with the data signal for writing, and the recording medium is irradiated with the modulated light beam. In the recording medium, data is written by changing the refractive index and color of the thin film sandwiched between the disks or generating pits in accordance with the intensity of the light beam. It should be noted that the intensity modulation of the light beam can be performed by modulating the current flowing through the semiconductor laser element used for the light source 1.

  A tracking actuator 7 is attached to the objective lens 13. The actuator 7 moves the objective lens 13 in the direction of arrow A in the figure, so that the light beam condensed by the objective lens 13 accurately follows the track of the recording medium 104. A wiring 8 for driving is attached to the actuator 7. Wiring 54 for driving a transparent electrode pattern, which will be described later, is attached to the liquid crystal optical element 70.

  As will be described later, the liquid crystal optical element 70 includes a transparent electrode pattern 40 for correcting spherical aberration (and / or a transparent electrode pattern for correcting coma aberration as shown in FIG. 3A and / or FIG. 6A). And 30) a transparent electrode pattern for wavefront aberration correction.

  The recording medium 104 is a next-generation high-density DVD and has a disk shape with a diameter of 12 cm and a thickness of 1.2 mm. Further, on the track surface on which information is recorded, a light transmission protective layer made of polycarbonate of about 0.1 mm is provided. The track pitch is about twice that of a conventional DVD (0.32 μm), and a light spot area using a blue laser (1) of 405 nm and an objective lens (13) with an aperture ratio (NA) = 0.85. Is about 1/5 of the conventional DVD, and a maximum capacity of about 27 GB is realized on one side.

  In such a recording medium 104, the light intensity signal output from the light receiver 52 is deteriorated due to spherical aberration caused by the uneven thickness of the light transmission protective layer that protects the track surface as compared with the conventional DVD. . Therefore, the control circuit 53 detects the spherical aberration based on the light intensity signal from the light receiver 52, and the electrode pattern (and / or the coma) for correcting the spherical aberration through the wiring 54 so as to cancel the detected spherical aberration. A voltage is applied to the transparent electrode pattern 30) for aberration correction. Note that the spherical aberration generated in the substrate of the recording medium 104 is reduced by applying a voltage to the spherical aberration correcting electrode pattern so as to maximize the amplitude of the light intensity signal (RF signal) from the light receiver 52. It is possible to cancel.

  FIG. 2 is a sectional view of the liquid crystal optical element 70 shown in FIG. The direction indicated by the arrow in FIG. 10 indicates the direction in which the light beam emitted from the light source 1 in FIG. 1 enters the liquid crystal optical element 70 after passing through the polarization beam splitter 50. In FIG. 2, a transparent electrode 72 for spherical aberration correction and an alignment film 73 are formed on the transparent substrate 71 on the light source 1 side. A transparent counter electrode 76 and an alignment film 75 are formed on the transparent substrate 77 on the recording medium 703 side. The liquid crystal 78 is sealed between the two transparent substrates 71 and 77 and the seal member 74. Each element shown in FIG. 2 is exaggerated for convenience of explanation, and is different from an actual thickness ratio.

  FIG. 3 shows an example of a method for fixing the liquid crystal optical element 70 and the objective lens 13 described with reference to FIGS. In FIG. 3, the objective lens 13 is assumed to be attached to the frame member 80 in advance. The frame member 80 has two orthogonal reference surfaces 81 and 82 for mounting the liquid crystal optical element 70. The frame member 80 is formed of resin or the like, and can create a reference surface having an accuracy of about ± 10 μm.

  In the liquid crystal optical element 70, as described above, liquid crystal is injected between the two transparent substrates 71 and 77 and the sealing member 74 and sealed with the sealing material 173. The transparent substrates 71 and 77 are made of a glass material, but by processing the end portion by a dicing method or the like, two orthogonal reference surfaces 171 and 172 having an accuracy of about ± 50 μm can be created. . In addition, a transparent electrode pattern 400 described later is formed on the transparent substrate 71 so as to be accurately positioned with respect to the reference surfaces 171 and 172 by a lithography method or the like.

  The liquid crystal optical element 70 and the objective lens 13 are positioned, fixed, or integrated by fixing them with an adhesive so that the reference surfaces 171 and 172 of the liquid crystal optical element 70 are aligned with the reference surfaces 81 and 82 of the frame member 80. It can be performed. However, when the liquid crystal optical element 70 is attached to the frame member 80 without a special tool, the attachment error between the frame member 80 and the objective lens 13, and the attachment between the frame member 80 and the liquid crystal optical element 70. Due to the error, an error between the center of the transparent electrode pattern 400 and the optical axis of the objective lens 13 occurs about 50 μm or less.

  FIG. 4 shows an example of a transparent electrode pattern 400 for correcting spherical aberration formed on the liquid crystal optical element 70 according to the present invention. As shown in FIG. 4A, six regions 42 to 47 for advancing the phase are arranged concentrically in the inner region 18 that is 50 μm inside from the effective diameter 10 of the light beam incident on the liquid crystal optical element 70. Arranged in a shape. Note that a reference potential is applied to the region 41 and does not have a function of advancing the phase of the incident beam.

  Here, the “inner region” refers to a region that is provided with an electrode pattern for wavefront aberration correction and enters a predetermined length inside from the effective diameter 10, which corresponds to the effective diameter of the liquid crystal optical element described above. . The “effective diameter” refers to the diameter of the main light beam on the liquid crystal optical element that is effectively used in the objective lens 3 in the geometrical optical design when there is no positional deviation or change in the diameter of the light beam. Say.

  When a positive (+) voltage is applied to the regions 42 to 47 with respect to the reference potential, a potential difference is generated between the transparent counter electrode 76 and the orientation of the liquid crystal therebetween changes according to the potential difference. Therefore, the light beam passing through this portion is subjected to an action that can advance its phase. A reference potential (for example, 0 v in this case) is applied to the region 41. A voltage is applied to the spherical aberration correcting electrode pattern 410 by the wiring 54 (see FIG. 1) from the control circuit 253 described above.

  FIG. 4B shows a voltage waveform 23 applied to each region on the X axis. When such a voltage is applied to each of the regions 41 to 47 of the inner region 18, the liquid crystal optical element 70 works so as to cancel the spherical aberration 20 caused by the uneven thickness of the light transmission protective layer of the recording medium 104. .

  FIG. 4C shows the corrected spherical aberration 24. The spherical aberration 20 in FIG. 4B is corrected so as to become the spherical aberration 24 in FIG. In other words, it is understood that the spherical aberration generated in the substrate of the recording medium 104 is corrected by using the liquid crystal optical element 70.

  In the description of FIG. 4, a positive (+) voltage is applied to each region of the spherical aberration correcting transparent electrode pattern 400 so that the phase of the light beam passing through this portion is advanced. Controlled. However, when the spherical aberration generated in the substrate of the recording medium 104 occurs in the direction opposite to that shown in FIG. 4B, the negative (−) opposite to that shown in FIG. ) Can be controlled to be applied. In that case, the light beam passing through each region of the electrode pattern 400 is subjected to an action such that its phase is delayed.

  In the description of FIG. 4A, six regions 42 to 47 for advancing the phase are arranged concentrically in the inner region 18 that is 50 μm inside from the effective diameter 10 of the light beam incident on the liquid crystal optical element 70. However, this is merely an example, and is not limited to 50 μm, and is within a range where an attachment error between the center of the electrode pattern and the optical axis of the objective lens is expected to occur (with an attachment error of It is preferable to be set within the range. For example, the inner region 18 is preferably set in a range larger than the inner side by 10 μm and smaller than the inner side by 75 μm with respect to the effective diameter. If the inner region is 10 μm or less with respect to the effective diameter, the objective lens and the liquid crystal optical element must be assembled by image processing. On the other hand, when the inner region is set to 75 μm or more with respect to the effective diameter, the transparent electrode pattern region for correcting the aberration is reduced accordingly, so that it is not possible to perform a good aberration correction. Therefore, it is preferable that the range is larger than the inner side of 10 μm and smaller than the inner side of 75 μm.

  Here, as shown in FIG. 10A, a case where a region (or a region that delays the phase) is formed over the entire inside of the effective diameter 10, and as shown in FIG. 4A. A difference in the case where a region for advancing the phase (or a region for delaying the phase) is formed only in the inner region 18 of the effective diameter 10 will be described.

  In the spherical aberration correction in the case of FIG. 10A, as shown in FIG. 5A, the light beam is captured in all regions within the effective diameter 10, and the light beam is made the effective diameter of the liquid crystal optical element. Comparing with the correction. However, when an attachment error occurs between the objective lens 3 and the effective diameter of the liquid crystal optical element deviates from the range of the field of view of the objective lens (see FIG. 5B), the spherical aberration correction is effectively performed. I can't.

  On the other hand, the spherical aberration correction in the case of FIG. 4A, as shown in FIG. 6A, captures the light beam only within the range of the inner region having an effective diameter of 10 to 50 μm, and the liquid crystal optics. This is equivalent to performing correction in the inner region 18 corresponding to the effective diameter of the element. In this case, if an attachment error occurs between the objective lens 3 and the liquid crystal optical element 70, the center (optical axis position) of the field of view of the objective lens deviates from the center of the inner region 18, but this inner region 18 still remains. It stays within the field of view of the objective lens (see FIG. 6B). Accordingly, the spherical aberration is sufficiently corrected, although it is slightly lower than when the light beam is captured at the center of the optical axis (see FIG. 6A).

  Since a region (or a region for delaying the phase) is provided only for the inner region 18 of the effective diameter 10 without providing a region (or a region for delaying the phase) within the effective diameter 10 range. Even when an attachment error occurs between the objective lens 3 and the liquid crystal optical element 70, the spherical aberration can be corrected effectively.

  In other words, the mounting error between the objective lens 3 and the liquid crystal optical element 70, and the region where the phase is substantially advanced (or delayed) is set so as to remain within the range of the visual field of the objective lens. In addition, spherical aberration correction can be performed.

  In the above case, the case where the electrode pattern 400 for correcting spherical aberration is formed on the transparent electrode 72 of the liquid crystal optical element 70 has been described. However, instead of the electrode pattern 400 for correcting spherical aberration, the electrode for correcting coma aberration is used. A pattern 300 (described later) can also be provided. Further, an electrode pattern 400 for correcting spherical aberration is formed on the transparent electrode 72 of the liquid crystal optical element 70, and an electrode pattern 300 (described later) for correcting coma aberration is formed on the transparent electrode 76 of the liquid crystal optical element 70. You can also.

  Hereinafter, a case where the coma aberration correcting electrode pattern 300 is formed on the transparent electrode 72 of the liquid crystal optical element 70 will be described.

  FIG. 7A shows a transparent electrode pattern 30 for correcting coma aberration. As shown in FIG. 7 (a), two regions 32 and 33 for advancing the phase to the inner region 18 that enters the inner side of the effective diameter 10 to 50 μm of the light beam incident on the liquid crystal optical element 70, and Two regions 34 and 35 for delaying the phase are arranged. In the figure, reference numeral 31 denotes a reference region for applying a reference potential.

  When a positive (+) voltage is applied to the regions 32 and 33 with respect to the reference voltage applied to the region 31, a potential difference is generated between the transparent counter electrode 76, and the orientation of the liquid crystal therebetween is determined according to the potential difference. Change. Therefore, the light beam passing through this portion is subjected to an action that can advance its phase. In addition, when a negative (−) voltage is applied to the regions 34 and 35 with respect to the reference voltage applied to the region 31, a potential difference is generated between the transparent counter electrode 76 and the liquid crystal orientation between them is changed to the potential difference. Will change accordingly. Therefore, the light beam passing through this portion is subjected to an action that delays the phase. A reference potential (for example, 0 v in this case) is applied to the region 31. A voltage is applied from the control circuit 53 to the electrode pattern 300 for correcting the coma aberration of the transparent electrode 72 by the wiring 54 (see FIG. 1).

  FIG. 7B shows the voltage 123 applied to each region on the X axis. By applying such a voltage to each of the regions 31 to 35 of the transparent electrode pattern 30 in the inner region 18, the liquid crystal optical element 70 causes the coma aberration 120 generated when the recording medium 104 is inclined with respect to the optical axis. Work to counteract.

  FIG. 7C shows the coma aberration 124 after correction. That is, the coma aberration 120 in FIG. 7B is corrected like the coma aberration 124 in FIG. It will be understood that the liquid crystal optical element 70 corrects the coma aberration generated in the substrate of the recording medium 104 to be suppressed.

  Here, as shown in FIG. 14 (a), a case where a region where the phase is advanced and a region where the phase is delayed is formed over the entire inside of the effective diameter 10, and as shown in FIG. 7 (a). The difference in the case where the region for advancing the phase and the region for delaying the phase are formed only in the inner region 18 having the diameter 10 will be described.

  As shown in FIG. 5A, the coma aberration correction in the case of FIG. 14A is obtained by capturing the light beam in all regions within the effective diameter 10 and correcting the light beam with the effective diameter of the liquid crystal optical element. Comparable to doing. However, if an attachment error occurs between the objective lens 13 and the liquid crystal optical element 70, the effective diameter of the liquid crystal optical element is shifted from the range of the field of view of the objective lens (see FIG. 5B), which is effective. The coma aberration cannot be corrected.

  On the other hand, as shown in FIG. 6A, the coma aberration correction of FIG. 7A captures a light beam only within the inner region of an effective diameter of 10 to 50 μm, and the liquid crystal optical element This is equivalent to performing correction in the region 18 corresponding to the effective diameter. In this case, even if an attachment error occurs between the objective lens 13 and the liquid crystal optical element 70, the center of the field of view of the objective lens deviates from the center of the inner region 18, but the inner region 18 still remains in the objective lens. (See FIG. 6B). Therefore, coma aberration correction is sufficiently performed, although it is slightly lower than when the inner region 18 is captured at the center of the optical axis (see FIG. 6A).

  Since the region for advancing the phase and the region for delaying the phase are all provided within the range of the effective diameter 10, the region for advancing the phase and the region for delaying the phase are provided only for the inner region 18 of the effective diameter 10. Even if an attachment error occurs between the liquid crystal optical element 70 and the liquid crystal optical element 70, the coma aberration can be corrected effectively.

  That is, regardless of the mounting error between the objective lens 13 and the liquid crystal optical element 70, the region for advancing the phase and the region for delaying the phase are set so as to remain within the field of view of the objective lens. Therefore, coma aberration correction can be effectively performed. “Substantially stay” refers to a relationship in which coma can be corrected within a predetermined accuracy.

It is a conceptual diagram which shows the optical apparatus concerning this invention. It is a figure which shows an example of sectional drawing of the liquid crystal optical element used for FIG. It is a figure which shows an example of the attachment method of the liquid crystal optical element concerning this invention. (A) shows an example of an electrode pattern for correcting spherical aberration, (b) shows an example of a voltage applied to the electrode pattern shown in (a), and (c) shows an example of corrected spherical aberration. FIG. It is a figure for illustrating operation of the conventional liquid crystal optical element. It is a figure for demonstrating operation | movement of the liquid crystal optical element concerning this invention. (A) shows an example of an electrode pattern for correcting coma aberration, (b) shows an example of voltage applied to the electrode pattern shown in (b), and (c) shows an example of corrected coma aberration. FIG. (A) is a figure for demonstrating generation | occurrence | production of the spherical aberration of a recording medium, (b) is a figure which shows the example of the spherical aberration to generate | occur | produce. It is a figure which shows an example of the optical apparatus which has the liquid crystal optical element for the conventional spherical aberration correction. (A) shows an example of an electrode pattern for correcting spherical aberration of the liquid crystal optical element, (b) shows an example of voltage applied to the electrode pattern shown in (a), and (c) shows corrected spherical aberration. It is a figure which shows an example. It is a figure which shows the other example of the optical apparatus which has the liquid crystal optical element for the conventional spherical aberration correction. (A) is a figure for demonstrating generation | occurrence | production of the coma aberration by the surface tilt of a recording medium, (b) is a figure which shows an example of the coma aberration to generate | occur | produce. It is a figure which shows an example of the optical apparatus which has the liquid crystal optical element for the conventional coma aberration correction. (A) shows an example of an electrode pattern for correcting coma of a liquid crystal optical element, (b) shows an example of a voltage applied to the electrode pattern shown in (a), and (c) shows a corrected coma aberration. It is a figure which shows an example. It is a figure which shows the other example of the optical apparatus which has the liquid crystal optical element for the conventional coma aberration correction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light source 10 ... Effective diameter 13 ... Objective lens 18 ... Inner area | region 70 ... Liquid crystal optical element 71, 77 ... Transparent substrate 72, 76 ... Transparent electrode 78 ... Liquid crystal 80 ... Frame member 300 ... Electrode pattern 400 for coma aberration correction ... Electrode pattern for spherical aberration correction

Claims (14)

A liquid crystal optical element configured integrally with an objective lens for condensing a light beam from a light source onto a recording medium,
A first transparent substrate;
A second transparent substrate;
A liquid crystal sealed between the first and second transparent substrates;
An electrode pattern for wavefront aberration formed on one of the first and second transparent substrates, and having an area for correcting the wavefront aberration of the light beam by advancing or delaying the phase of the light beam. And
The region is disposed only in an inner region that is more than the attachment error between the center of the electrode pattern and the optical axis of the objective lens with respect to the effective diameter of the light beam.
A liquid crystal optical element characterized by the above.   The liquid crystal optical element according to claim 1, wherein the electrode pattern is a spherical aberration electrode pattern.   The liquid crystal optical element according to claim 2, wherein the electrode pattern has a plurality of small regions for advancing or delaying the phase of the light beam.   The liquid crystal optical element according to claim 1, wherein the electrode pattern is an electrode pattern for coma aberration.   The electrode pattern includes a first region for advancing the phase of the light beam, a second region for delaying the phase of the light beam, and a third region that does not substantially change the phase of the light beam. The liquid crystal optical element according to claim 4, comprising:   6. The liquid crystal optical element according to claim 1, wherein the region is set on the inner side of 10 μm to 75 μm from the effective diameter of the light beam. An optical device,
A light source;
An objective lens for condensing the light beam from the light source onto a recording medium;
A liquid crystal optical element configured integrally with the objective lens;
The liquid crystal optical element is
A first transparent substrate;
A second transparent substrate;
A liquid crystal sealed between the first and second transparent substrates;
An electrode pattern for wavefront aberration formed on one of the first and second transparent substrates, and having an area for correcting the wavefront aberration of the light beam by advancing or delaying the phase of the light beam. And
The region is disposed only in an inner region that is more than the attachment error between the center of the electrode pattern and the optical axis of the objective lens with respect to the effective diameter of the light beam.
An optical device.   The optical device according to claim 7, wherein the electrode pattern is a spherical aberration electrode pattern.   The optical device according to claim 8, wherein the electrode pattern has a plurality of small regions for advancing or retarding the phase of the light beam.   The optical apparatus according to claim 7, wherein the electrode pattern is an electrode pattern for coma aberration.   The electrode pattern includes a first region for advancing the phase of the light beam, a second region for delaying the phase of the light beam, and a third region that does not substantially change the phase of the light beam. The optical device according to claim 10.   The optical device according to any one of claims 7 to 11, wherein the region is set on the inner side of 10m to 75m from the effective diameter of the light beam.   The optical apparatus according to any one of claims 7 to 12, further comprising tracking means for moving the objective lens in order to correct an axial deviation of the objective lens.   The optical device according to any one of claims 7 to 13, further comprising a voltage applying unit for applying a voltage to the electrode pattern.

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