JP2009043350A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a configuration capable of downsizing an optical pickup device with a lens driving unit as a component of a means for correcting spherical aberrations. <P>SOLUTION: In the optical pickup device 1, a collimator lens 5 is made movable in an optical axis direction by a lens driving unit 11. The collimator lens 5 is moved in an optical axis direction, thereby roughly adjusting a spherical aberration correction. A refractive index varying element 3 is disposed between a light source 2 and the collimator lens 5. The refractive index varying element 3 can change the refractive index of a passing laser beam, thereby finely adjusting the spherical aberration correction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup device that enables reading and writing of information by irradiating an optical recording medium with a light beam, and more particularly to a configuration of an optical pickup device having means for correcting spherical aberration.

  Optical recording media such as compact discs (hereinafter referred to as CDs) and digital versatile discs (hereinafter referred to as DVDs) are widely used. Furthermore, in recent years, in order to increase the amount of information recorded on an optical recording medium, research on increasing the density of information recorded on the optical recording medium has been promoted. An optical recording medium such as BD is also in practical use. In addition, in an optical recording medium aiming at high-density recording such as BD, an optical recording medium having a plurality of recording layers in the thickness direction of the optical recording medium has been actively developed.

  Such reading (reproduction) of information from the optical recording medium and writing (recording) of information to the optical recording medium are performed using an optical pickup device. By the way, when reading information using an optical pickup device for an optical recording medium having a plurality of recording layers, the thickness of the transparent cover layer that protects the recording layer differs depending on the position of the recording layer. Occurrence becomes a problem.

  Further, even in an optical pickup device that supports a plurality of types of optical recording media, the occurrence of spherical aberration may be a problem because the thickness of the transparent cover layer that protects the recording layer differs depending on the type of optical recording medium. For example, in the case of CD, DVD, and BD, the thickness of the transparent cover layer is 1.2 mm for CD, 0.6 mm for DVD, and 0.1 mm for BD.

  The problem of spherical aberration described above is likely to be a problem particularly in an optical pickup device using a blue light source that requires an objective lens having a large numerical aperture (NA). In recent years, an optical pickup device that can appropriately correct spherical aberration is proposed. The demand is getting stronger. For this reason, conventionally, various proposals have been made for optical pickup devices including means for correcting spherical aberration (see, for example, Patent Documents 1 to 4).

  An example of a conventionally proposed means for correcting spherical aberration is as follows. For example, the spherical aberration is corrected by changing the convergence or divergence state of the light beam emitted from the light source and entering the objective lens. There is. Specifically, examples include an expander lens having two lenses and at least one of which is movable, and an example in which the collimator lens is configured to be movable in the optical axis direction.

  As another means for correcting spherical aberration, for example, a liquid crystal element is arranged in an optical system of an optical pickup device, and a voltage applied to the liquid crystal element is controlled so that a wavefront passing through the optical element has an arbitrary phase distribution. Some of them correct spherical aberration. In this case, the transparent electrode constituting the liquid crystal element needs to be configured to have a pattern corresponding to the spherical aberration distribution shape.

In addition, as shown in Patent Document 1, there is also an example in which the above-described means for correcting the two spherical aberrations are combined. According to Patent Document 1, one of the two aberration correction means changes the divergence or convergence of the light beam incident on the objective lens by changing the relative position with respect to the objective lens in the optical axis direction. Among the wavefront aberrations generated by the disc cover layer thickness, low-order wavefront aberration is corrected. On the other hand, by arbitrarily controlling the magnitude of the voltage applied to the electrodes constituting the liquid crystal element, an arbitrary transmitted wavefront having an arbitrary phase difference can be formed in an arbitrary shape, and higher-order wavefront aberration can be reduced. It is supposed to be corrected. That is, Patent Document 1 aims at correcting aberrations by compensating for deficiencies of each means by combining two aberration correcting means for correcting spherical aberration by different methods.
JP 2005-122861 A JP 2005-158093 A JP 2005-327396 A JP 2005-327401 A

  However, the configuration for correcting the spherical aberration by generating a phase difference in the incident laser beam using the liquid crystal element described above has the following problems. That is, in this configuration, since it is necessary to form and use an electrode pattern composed of a plurality of regions on the transparent electrode of the liquid crystal element, wiring is likely to be complicated. In addition, it is required to accurately form an electrode pattern to be formed on the transparent electrode and to dispose the liquid crystal element in the optical system with high attachment accuracy. This is because if the accuracy is low, the phase difference of the light beam that has passed through the liquid crystal element is different from the target, and the spherical aberration cannot be sufficiently corrected.

  In this regard, when using a configuration for moving the collimating lens in the optical axis direction or a configuration using an expander lens as a means for correcting spherical aberration, it is possible to avoid the complexity of the wiring described above. It is. However, in the case of such a configuration, a lens driving unit which is a means for moving the lens is required, and the conventional configuration has the following problems.

  First, in the conventional configuration, the lens driving unit has a very large shape because the lens is moved using a lead screw and a motor. Further, in the conventional lens driving unit, in order to accurately manage the position of the movable lens, it is necessary to use a stepping motor and further include a photo interrupter. For this reason, the cost of the motor increases, and an extra space is required to provide the photo interrupter, which causes an increase in the size of the optical pickup device. Furthermore, since the lens is moved by rotation with the lead screw, there is a problem that it takes time to change the setting when changing the setting for correcting the spherical aberration.

  In view of the above points, an object of the present invention is to provide a configuration capable of reducing the size of an optical pickup device including a lens driving unit as a component of means for correcting spherical aberration. Another object of the present invention is to provide a configuration capable of suppressing the manufacturing cost in an optical pickup device including a lens driving unit as a component of means for correcting spherical aberration. Furthermore, another object of the present invention is to provide an optical pickup device having a lens driving unit as a component of means for correcting spherical aberration, and capable of switching the correction amount for correcting spherical aberration at high speed. It is to be.

  In order to achieve the above object, the present invention is provided between a light source, an objective lens that focuses a light beam emitted from the light source on a recording surface of an optical recording medium, and the light source and the objective lens. In an optical pickup device comprising a movable lens movable in the optical axis direction and a lens drive unit for driving the movable lens, the movement of the movable lens by the lens drive unit corrects spherical aberration. Used for coarse adjustment when performing, provided between the light source and the objective lens so that the refractive index of the passing light beam can be changed, and used for fine adjustment when correcting spherical aberration A variable refractive index element is provided.

  According to this configuration, spherical aberration can be corrected appropriately because of the configuration in which coarse adjustment means and fine adjustment means are provided for correcting spherical aberration. Since the movable lens is used for coarse adjustment of spherical aberration correction, high accuracy is not required for the movement accuracy of the movable lens. For this reason, the lens driving unit can be manufactured at low cost, and the motor can be deleted. Conventionally, a motor requires a large space, and according to the configuration of the present invention, the optical pickup device can be miniaturized. In addition, since the variable refractive index element that finely adjusts the correction of spherical aberration is provided, the range in which the movable lens can be moved can be shortened, and the correction amount for correcting the spherical aberration can be switched faster than before. It becomes possible.

  Further, in the optical pickup device having the above-described configuration, the present invention provides that the spherical aberration correction using the movable lens and the lens driving unit and the spherical aberration correction using the refractive index variable element are both described above. It may be performed by changing the convergence or divergence state of the light beam incident on the objective lens.

  According to this configuration, the electrode constituting the refractive index variable element does not have to be an electrode pattern composed of a plurality of regions, and the configuration of the refractive index variable element can be simplified. In addition, since the electrode can be a solid electrode, the requirement for mounting position accuracy can be reduced when the refractive index variable element is arranged in the optical system of the optical pickup device.

  In the optical pickup device having the above configuration according to the present invention, it is preferable that the movable lens is a collimating lens. According to this configuration, it is not necessary to significantly change the means for correcting the spherical aberration from the conventional configuration, and thus it is easy to realize downsizing and the like of the optical pickup device.

  In the optical pickup device having the above configuration according to the present invention, it is preferable that the variable refractive index element is disposed between the light source and the movable lens. According to this configuration, it is easy to appropriately correct spherical aberration even in the case where the refractive index variable element for fine adjustment is a solid electrode.

  According to the present invention, in the optical pickup device configured as described above, the lens driving unit includes a coil and a magnet, and a magnetic field formed by passing a current through the coil and a magnetic field formed by the magnet. The movable lens can be moved by the interaction.

  According to this configuration, the lens driving unit that drives the movable lens used for coarse adjustment of spherical aberration is configured to erase the motor. Therefore, the optical pickup device can be reduced in size. Further, since the configuration for moving the movable lens is a configuration using magnets and coils, the cost required for the lens driving unit can be reduced. Further, since the movable lens is moved using the force of the magnet, the movable lens can be quickly moved, and the switching of the correction amount for correcting the spherical aberration can be speeded up.

  According to the present invention, in the optical pickup device configured as described above, the refractive index variable element includes a liquid crystal capable of changing a refractive index according to an applied voltage, and an electrode for applying a voltage to the liquid crystal. Further, the refractive index variable element may include an electro-optic crystal whose refractive index can be changed according to an applied voltage, and an electrode for applying a voltage to the electro-optic crystal. The configuration using the electro-optic crystal is particularly suitable for the purpose of switching the correction amount for correcting the spherical aberration at a high speed because the response speed is faster than the case of using the liquid crystal.

  According to the present invention, in an optical pickup device including a lens driving unit as a component of means for correcting spherical aberration, downsizing of the device, cost reduction, and switching of a correction amount for correcting spherical aberration are performed at high speed. It is possible to realize at least one of the following.

  Hereinafter, embodiments of an optical pickup device of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram showing the configuration of the optical pickup device of the present embodiment. The optical pickup device 1 of the present embodiment is provided so as to be able to read and write information on an optical disc (optical recording medium) having one recording layer on which information is recorded and an optical disc having two recording layers. . In FIG. 1, a two-layer optical disc having two recording layers L0 and L1 is shown.

  As shown in FIG. 1, the optical system of the optical pickup device 1 includes a light source 2, a refractive index variable element 3, a polarizing beam splitter 4, a collimator lens 5, a rising mirror 6, and a quarter wavelength plate. 7, an objective lens 8, a sensor lens 9, and a photodetector 10.

  The light source 2 is a semiconductor laser. The type of semiconductor laser differs depending on what type of optical disk the optical pickup device 1 supports. That is, for example, when the optical pickup device 1 is compatible with BD, a laser beam of 405 nm band is used, when the optical pickup device 1 is compatible with DVD, a laser beam of 650 nm band is used; A semiconductor laser that emits light is used.

  The refractive index variable element 3 is an element that can change the refractive index by changing the applied voltage, and can control the refractive index by controlling the applied voltage. The laser light passing through the variable refractive index element 3 is given refractive power according to the refractive index of the variable refractive index element 3, and its divergence state (divergence angle) is changed. That is, spherical aberration can be generated by controlling the refractive index variable element 3. Then, the spherical aberration can be corrected by setting the spherical aberration generated by the refractive index variable element 3 to have the opposite polarity to the spherical aberration generated due to the difference in the thickness of the transparent cover layer.

  FIG. 2 is a schematic plan view showing the configuration of the refractive index variable element 3 provided in the optical pickup device 1 of the present embodiment. In the refractive index variable element 3, the liquid crystal 21 is used as a material whose refractive index can be changed by changing the applied voltage. In order to apply a voltage to the liquid crystal 21, the liquid crystal 21 is sandwiched between two electrodes 22a and 22b made of, for example, ITO (Indium Tin Oxide). The electrodes 22a and 22b constituting the refractive index variable element 3 are both solid electrodes, and no electrode pattern is particularly formed. The two electrodes 22a and 22b are supported by the glass substrates 23a and 23b, respectively.

In this embodiment, liquid crystal is used as a material whose refractive index can be changed by changing the voltage to be applied, but the present invention is not limited to this. For example, instead of the liquid crystal, an electro-optic crystal such as LiNbO ₃ (lithium niobate) may be used. The configuration using the electro-optic crystal has an advantage that the response speed is faster than the configuration using the liquid crystal, and the correction amount for correcting the spherical aberration can be switched more quickly.

  The polarization beam splitter 4 has a function of transmitting one of two linearly polarized light whose polarization directions are orthogonal to each other and reflecting the other. In the optical pickup device 1 of the present embodiment, the laser beam is transmitted in the forward path and the laser beam is reflected in the return path. The polarization beam splitter 4 functions as an optical isolator in cooperation with a quarter wave plate 7 described later.

  The collimating lens 5 is an optical member having a function of converting incident laser light into parallel light. In the present embodiment, the collimating lens 5 is moved in the optical axis direction (direction indicated by arrow A in FIG. 1) by the lens driving unit 11. It is a possible movable lens. For this reason, by controlling the position of the collimating lens 5 by the lens driving unit 11, the convergence angle or the divergence angle of the laser light incident on the objective lens 8 can be changed. That is, spherical aberration can be generated by adjusting the position of the collimating lens 5. The spherical aberration can be corrected by setting the spherical aberration generated by adjusting the position of the collimating lens 5 to the opposite polarity to the spherical aberration generated due to the difference in the thickness of the transparent cover layer.

  FIG. 3 is a schematic perspective view showing the configuration of the lens driving unit 11 that drives the collimating lens 5 in the optical axis direction. As shown in FIG. 3, the lens driving unit 11 includes a lens holder 31, two guide shafts 33 a and 33 b, a permanent magnet 34, a coil 35, and a stopper 36.

  The resin lens holder 31 has a through hole 32 at a substantially central portion thereof, and holds the collimating lens 5 at this portion. In addition, two guide shafts 33a and 33b pass through the lens holder 31, and the lens holder 31 is slidable along the guide shafts 33a and 33b. The two guide shafts 33a and 33b are fixedly arranged so as to be parallel to each other. The guide shafts 33a and 33b are made of a nonmagnetic material.

  In a portion of the lens holder 31 through which the guide shaft 33a passes, a permanent magnet 34 having a donut shape in cross section is inserted. A coil 35 is wound around the guide shaft 33a on the side where the permanent magnet 34 is provided. The coil 35 is connected to an electrode (not shown), and the magnitude and direction of the current flowing through the coil 35 can be controlled by the control unit 14 described later.

  In such a configuration, when a current is passed through the coil 35, a magnetic field is formed, and this magnetic field interacts with the magnetic field formed by the permanent magnet. Therefore, by controlling the current flowing through the coil 35, the lens holder 31 can be slid along the guide shafts 33a and 33b, and the collimating lens 5 can be driven. However, since the stopper 36 is fixedly arranged, the movement range of the lens holder 31 is restricted by the stopper 36.

  In this embodiment, the permanent magnet 34 and the coil 35 are provided only on the one guide shaft 33a side. However, the present invention is not limited to this configuration, and the permanent magnet 34 and the coil are also provided on the guide shaft 33b side. Of course, it is possible to provide 35. In the present embodiment, the coil 35 is wound around the guide shaft 33a made of a nonmagnetic material. However, the present invention is not limited to this configuration. That is, in order to increase the magnetic force generated when a current is passed through the coil 35, the coil 35 may be wound around a material having a high magnetic permeability and joined to the tip of the guide shaft 33a.

  Returning to FIG. 1, the rising mirror 6 has a function of reflecting the laser beam sent from the collimating lens 5 and changing the optical axis direction to a direction orthogonal to the recording layers L <b> 0 and L <b> 1 of the optical disc 20.

  The quarter-wave plate 7 is arranged so as to convert it into circularly polarized light when linearly polarized light emitted from the light source 2 enters. In this arrangement, the circularly polarized light reflected by the optical disk 20 and incident on the quarter-wave plate 7 is converted into linearly polarized light whose polarization direction is rotated by 90 ° with respect to the linearly polarized light emitted from the light source 2. The For this reason, the laser light reflected by the optical disk 20 is reflected without passing through the polarization beam splitter 4. That is, as described above, the quarter wavelength plate 7 and the polarization beam splitter 4 cooperate to function as an optical isolator.

  The objective lens 8 focuses the incident laser light on the recording layer L0 (or recording layer L1) of the optical disc 20. The objective lens 8 is mounted on the actuator 12 and is movable in a focus direction parallel to the optical axis direction and a tracking direction parallel to the radial direction of the optical disc 20. Thereby, focusing control for controlling the focal position of the objective lens 8 to always coincide with the recording layer of the optical disc 20 becomes possible. In addition, tracking control for controlling the beam spot formed by being focused by the objective lens 8 to always follow the track formed on the optical disc 20 is also possible.

  In addition, a focus jump that causes the focal position of the objective lens 8 to jump from one recording layer to another recording layer (for example, the recording layer L0 to the recording layer L1) also causes the position of the objective lens 8 to be in the focus direction by the actuator 12. It is possible by moving. Note that the configuration of the actuator 12 is a well-known configuration in which the objective lens 8 is moved using the electromagnetic action of the current flowing through the coil and the magnetic field generated by the permanent magnet, and therefore the description thereof is omitted here. .

  The sensor lens 9 is reflected by the optical disk 20, passes through the objective lens 8, the quarter wavelength plate 7, the rising mirror 6, and the collimating lens 5 in this order, and the laser beam reflected by the polarization beam splitter 4 is detected by the photodetector 10. The light is focused on a light receiving area (not shown).

  The photodetector 10 receives the laser beam reflected by the optical disc 20 in a light receiving region (not shown), and changes the optical information into an electrical signal. The electrical signal output from the photodetector 10 is sent to the signal processing unit 13.

  The signal processing unit 13 processes the electrical signal received from the photodetector 10 to generate an RF signal, a focus error signal (FE signal), a tracking error signal (TE signal), a jitter signal, and the like. Information is read by the RF signal, and the above focusing control and tracking control are performed based on the FE signal and the TE signal. The jitter signal is used as an index for determining the setting of the refractive index variable element 3. This point will be described later.

  The control unit 14 has a function of controlling the entire operation of the optical pickup device 1. For example, the control unit 14 controls the refractive index variable element 3, the lens driving unit 11, the actuator 12, and the like.

  The overall configuration of the optical pickup device 1 is as described above. However, in the optical pickup device 1 of this embodiment, it is possible to correct spherical aberration that occurs mainly due to the difference in the thickness of the transparent cover layer 20a. The refractive index variable element 3 and the collimating lens 5 movable in the optical axis direction by the lens driving unit 11 are provided. The reason for providing two means for correcting spherical aberration in this way will be described.

  In the optical pickup device 1, spherical aberration occurs when information is read from or written to the two-layer optical disc, when information is read from or written to the recording layer L 0, and when information is read from the recording layer L 1. It is necessary to change the correction amount. In the dual-layer optical disc, the positions where the recording layers L0 and L1 are formed are determined according to the standard. For example, in BD, the disc is formed so that the recording layer L0 has a transparent cover layer 20a thickness of 0.1 mm, and the recording layer L1 has a transparent cover layer 20a thickness of 0.075 mm. Here, the transparent cover layer including the intermediate layer between the recording layer L0 and the recording layer L1 is also expressed.

  For this reason, ideally, the amount of correction of spherical aberration is a predetermined value, and when correcting spherical aberration, the collimating lens 5 may be configured to be switched between two positions. . However, the spherical aberration cannot be corrected with the ideal value due to, for example, manufacturing variations of the optical disc 20 or a wavelength shift of the laser light emitted from the light source 2. Accordingly, it is necessary to provide a configuration in which the correction amount of the spherical aberration can be finely adjusted after the configuration of switching the position of the collimating lens 5 at two positions.

  Considering the above points, in this embodiment, two means for correcting spherical aberration are provided. That is, the configuration in which the spherical aberration is corrected by moving the collimating lens 5 by the lens driving unit 11 is a rough adjustment means having only a function of switching between two positions, and the refractive index is controlled by controlling the applied voltage. The refractive index variable element 3 capable of performing the above is provided as means for fine adjustment.

  Next, when the target recording layer from which information is read or written is moved from the recording layer L0 to the recording layer L1, or from the recording layer L1 to the recording layer L0 by the optical pickup device 1 of the present embodiment ( In other words, how to change the setting for correcting the spherical aberration in the case of a focus jump will be described with reference to FIG. FIG. 4 is a flowchart showing a procedure for changing the setting for correcting the spherical aberration during the focus jump.

  When a focus jump command is issued, the collimating lens 5 is moved from the current position to the other position by the lens driving unit 11 (step S1). Specifically, a predetermined current is passed through the coil 35 according to a command from the control unit 14, and the position of the collimating lens 5 is moved by moving the lens holder 31 with a magnetic attractive force or repulsive force. This movement simply moves the collimating lens 5 between the two ends of the stopper 36, and corresponds to rough adjustment for spherical aberration correction.

  When the spherical aberration is roughly adjusted, the control unit 14 determines whether or not the setting for correcting the spherical aberration may be the current setting (step S2). In this embodiment, this determination is made using a jitter signal sent from the signal processing unit 13. Specifically, if the jitter value is smaller than a predetermined threshold value prepared in advance (data is stored in the memory), it is determined that the correction amount for correcting the spherical aberration is good, If it is equal to or greater than the predetermined threshold, it is determined that the correction amount for correcting the spherical aberration is inappropriate.

  In the present embodiment, it is configured to determine whether or not the correction amount for correcting the spherical aberration is good using the jitter signal, but the present invention is not limited to this. That is, an index indicating the quality of the reproduction signal may be used. For example, whether or not the correction amount for correcting the spherical aberration is good using the tracking error signal amplitude, the RF signal amplitude, the error rate, or the like. It does not matter as a configuration for judging the above.

  If it is determined that the setting for correcting the spherical aberration may be the current setting, the operation for correcting the spherical aberration ends without changing the setting of the refractive index variable element 3. On the other hand, if it is determined that the correction amount for correcting the spherical aberration is inappropriate under the current setting, the setting of the refractive index variable element 3 is changed (step S3). Specifically, when the setting of the applied voltage is changed and the setting is changed, the process returns to step S2, and it is confirmed again whether or not the correction amount for correcting the spherical aberration is good, and the correction is performed. This operation is repeated until the quantity is good. That is, fine adjustment of spherical aberration correction is performed by the refractive index variable element 3.

  As described above, in the optical pickup device 1 of the present embodiment, correction of spherical aberration due to movement of the collimator lens 5 is used as rough adjustment for correction of spherical aberration, and no stepping motor is used for movement of the collimator lens 5. It is configured. For this reason, the motor that conventionally required a large space can be eliminated from the configuration of the lens driving unit, and the optical pickup device 1 can be downsized. In addition, although the refractive index variable element 3 is newly arranged for fine adjustment, the effect of removing the motor is great, and the optical pickup device 1 can be downsized.

  In addition, as described above, since the collimating lens 5 has a simple configuration that moves using the force of the magnet, it is possible to reduce the cost as compared with the conventional configuration using a stepping motor or a photo interrupter. .

  Further, regarding the movement of the collimating lens 5, in the case of the present embodiment, since the collimating lens 5 is moved by the attractive force or repulsive force of the magnetic force, the collimating lens 5 is moved while rotating the lead screw by the stepping motor. Compared with the case, the position of the collimating lens 5 can be moved at high speed. Further, since the fine adjustment of the spherical aberration correction is performed by the refractive index variable element 3, as shown in FIG. 5, the collimator is compared with the case of correcting the spherical aberration only by changing the position of the collimator lens 5. The moving range of the lens 5 can be shortened (in the example of FIG. 5, it is shortened by about 1.2 mm). Therefore, it is possible to set the correction of spherical aberration at a higher speed than in the prior art. FIG. 5 is a graph showing the relationship between the driving amount of the collimating lens and the generation amount of spherical aberration.

  The embodiment described above is an example, and the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the object of the present invention.

  For example, in the present embodiment, the refractive index variable element 3 provided for fine adjustment of spherical aberration correction is arranged between the light source 2 and the collimating lens 5, but the present invention is not limited to this. Not the purpose. That is, it may be configured to be disposed between the collimating lens 5 and the objective lens 8.

  However, when the arrangement is made between the collimating lens 5 and the objective lens 8, if the two electrodes 22a and 22b included in the refractive index variable element 3 are solid electrodes as in this embodiment, spherical aberration is obtained. The amount that can be corrected becomes smaller. Therefore, when the refractive index variable element 3 is arranged between the collimating lens 5 and the objective lens 8, at least one of the two electrodes 22a and 22b provided in the refractive index variable element 3 is a concentric electrode. A configuration having a pattern is preferable. However, in this case, since the high mounting accuracy is required for the refractive index variable element 3, the configuration of this embodiment is preferable.

  Even when the refractive index variable element 3 is arranged between the light source 2 and the collimating lens 5 as in the present embodiment, at least one of the two electrodes 22a and 22b provided in the refractive index variable element 3 is concentric. However, in consideration of the above-mentioned problem of the accuracy of attaching the variable refractive index element 3, the two electrodes 22a and 22b provided in the variable refractive index element 3 are solid electrodes. Is preferred.

  In the present embodiment, the configuration in which the rough adjustment is performed for the correction of the spherical aberration is a configuration in which the permanent magnet 34 and the coil 35 are used. However, the present invention is not limited to this. That is, since it is only necessary to roughly adjust the position of the collimating lens 5, for example, a configuration in which the position of the collimating lens 5 is adjusted using a DC motor may be used. However, in this case, since the motor is not erased as in the present embodiment, the effect of downsizing the optical pickup device 1 cannot be expected so much. However, cost reduction can be expected by using a DC motor as the stepping motor. Even in the case of a configuration using a DC motor, by providing the fine-tuning refractive index variable element 3, it is possible to shorten the distance that the collimating lens 5 is moved using the motor, and to correct spherical aberration. It is possible to switch the correction amount for this at high speed.

  Further, in the present embodiment, the case where the optical element provided for coarse adjustment for correcting the spherical aberration is a collimating lens that moves in the optical axis direction has been described. However, the present invention is not limited to this. That is, for example, the present invention can also be applied when the expander lens is used as an optical element for coarse adjustment when correcting spherical aberration.

  In the present embodiment, the optical pickup device 1 is configured to support one type of optical disk such as a BD, a DVD, and a CD. However, the present invention is not limited to this. In other words, the present invention is naturally applicable to an optical pickup device corresponding to a plurality of types such as BD, DVD, and CD. In the optical pickup device corresponding to a plurality of types of optical discs having different transparent cover layer thicknesses such as BD, DVD, and CD, the occurrence of spherical aberration becomes a problem as described above. By applying this, spherical aberration can be corrected.

  According to the present invention, in an optical pickup device including a lens driving unit as a component of means for correcting spherical aberration, downsizing of the device, reduction of manufacturing cost, and switching of a correction amount for correcting spherical aberration are performed. It is feasible for at least one of high-speed operations. Therefore, the optical pickup device of the present invention is useful.

These are the schematic diagrams which show the structure of the optical pick-up apparatus of this embodiment. These are the schematic plan views which show the structure of the refractive index variable element with which the optical pick-up apparatus of this embodiment is provided. These are the schematic perspective views which show the structure of the lens drive unit which drives the collimating lens with which the optical pick-up apparatus of this embodiment is provided in an optical axis direction. These are the flowcharts which showed the procedure in which the setting for correct | amending a spherical aberration at the time of a focus jump is changed in the optical pick-up apparatus of this embodiment. These are the graphs which show the relationship between the drive amount of a collimating lens and the generation amount of spherical aberration in the optical pickup device of the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up apparatus 2 Light source 3 Refractive index variable element 5 Collimate lens (movable lens)
8 Objective lens 11 Lens drive unit 20 Optical disc (optical recording medium)
21 Liquid crystal (or electro-optic crystal)
22a, 22b Electrode 34 Permanent magnet 35 Coil L0, L1 Recording layer

Claims (7)

A light source;
An objective lens for condensing the light beam emitted from the light source on the recording surface of the optical recording medium;
A movable lens provided between the light source and the objective lens and movable in the optical axis direction;
A lens driving unit for driving the movable lens;
In an optical pickup device comprising:
The movement of the movable lens by the lens driving unit is used for coarse adjustment when correcting spherical aberration,
A refractive index variable element is provided between the light source and the objective lens so that the refractive index of the light beam passing therethrough can be changed and used for fine adjustment when correcting spherical aberration. Optical pickup device.   The correction of spherical aberration using the movable lens and the lens driving unit and the correction of spherical aberration using the refractive index variable element both change to the convergence or divergence state of the light beam incident on the objective lens. The optical pickup device according to claim 1, wherein the optical pickup device is performed.   The optical pickup device according to claim 1, wherein the movable lens is a collimating lens.   The optical pickup device according to claim 3, wherein the refractive index variable element is disposed between the light source and the movable lens.   The lens driving unit includes a coil and a magnet, and moves the movable lens by an interaction between a magnetic field formed by flowing an electric current through the coil and a magnetic field formed by the magnet. The optical pickup device according to claim 1.   The said refractive index variable element is equipped with the liquid crystal which can change a refractive index according to the voltage to apply, and the electrode for applying a voltage to the said liquid crystal, In any one of Claim 1 to 5 characterized by the above-mentioned. Optical pickup device.   6. The refractive index variable element includes: an electro-optic crystal capable of changing a refractive index in accordance with an applied voltage; and an electrode for applying a voltage to the electro-optic crystal. The optical pick-up apparatus in any one.

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