JP2010267307A - Optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup which can appropriately suppress the spherical and coma aberration. <P>SOLUTION: The optical pickup 1 has a light source 11, an objective lens 17 to focus the light from the light source 11 on the information recording layer of an optical recording medium, a movable lens 15 disposed on the optical path between the light source 11 and the objective lens 17 and free to move to correct the spherical aberration, and a lens moving mechanism 4 to translate the movable lens 15 in the predetermined direction. This predetermined direction is aslant to the optical axis of the light incident to the movable lens 15. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical pickup used for reading information recorded on an optical recording medium and writing information on the optical recording medium.

  Some optical discs (an example of an optical recording medium) are provided with a plurality of information recording layers in the thickness direction of the optical disc (multilayer optical disc) for the purpose of increasing the recording capacity. For example, in a Blu-ray disc (hereinafter referred to as BD), it is standard to provide two information recording layers according to the standard.

  In a multilayer optical disc, a transparent cover layer provided for protecting the information recording layer for each information recording layer (here, an intermediate layer provided between the two information recording layers is also expressed as a transparent cover layer) ) Are different in thickness. For this reason, when reading or writing information recorded on a multilayer optical disk using an optical pickup (hereinafter, sometimes referred to as “reading” or the like), the information recording layer to be read or the like has certain information. When moving from the recording layer to another information recording layer (hereinafter referred to as interlayer jump), the influence of spherical aberration may be a problem. In particular, an optical pickup compatible with BD uses an objective lens with a high NA (numerical aperture), and thus is easily affected by spherical aberration due to interlayer jump.

  For this reason, conventionally, optical pickups configured to be able to correct spherical aberration have been developed. As a configuration example for correcting spherical aberration, for example, a collimating lens provided in the optical system of the optical pickup can be moved along the optical axis, thereby adjusting the convergence and divergence state of light incident on the objective lens. In some cases, spherical aberration is corrected (see, for example, Patent Documents 1 and 2).

JP 2004-103087 A JP 2008-186537 A

  By the way, the objective lens provided in the optical pickup may have coma aberration due to a manufacturing error. For this reason, in the optical pickup, when the objective lens has coma aberration, the optical axis of the objective lens is inclined with respect to the optical axis of incident light incident on the objective lens so that the coma aberration is corrected. There are things to do. However, in an optical pickup installed with the objective lens tilted in this way, if the collimator lens is moved to correct spherical aberration, information cannot be read properly due to the effects of coma aberration. There is.

  In this regard, it is conceivable to provide a tilt mechanism for tilting the objective lens in the optical pickup to suppress the influence of coma aberration caused by the movement of the position of the collimating lens. However, in this configuration, since it is necessary to provide a tilt mechanism, there are problems such as an increase in the number of parts. Further, in the configuration in which the coma aberration is corrected using the tilt mechanism, it is necessary to learn how much the objective lens needs to be tilted according to the collimating lens position after manufacturing the optical pickup, which is troublesome. .

  In view of the above points, an object of the present invention is to provide an optical pickup capable of appropriately suppressing spherical aberration and coma aberration.

  In order to achieve the above object, an optical pickup of the present invention includes a light source, an objective lens that condenses light emitted from the light source on an information recording layer of an optical recording medium, and a space between the light source and the objective lens. An optical pickup comprising: a movable lens disposed in an optical path and movably provided so as to be able to correct spherical aberration; and a lens moving unit that translates the movable lens in a predetermined direction. Is tilted with respect to the optical axis of the incident light incident on the movable lens.

  According to this configuration, since the direction of moving the movable lens (predetermined direction) is inclined with respect to the optical axis incident on the movable lens, the optical axis of the incident light incident on the objective lens due to the movement of the movable lens Changes. Therefore, it is possible to simultaneously correct coma while correcting spherical aberration by moving the position of the movable lens.

  As a specific configuration of the optical pickup having the above configuration, an optical axis of light from the light source to the objective lens when the movable lens is arranged at a predetermined position so that substantially parallel light is incident on the objective lens. Is the reference optical axis, the optical axis of the objective lens and the predetermined direction may be inclined with respect to the reference optical axis. Further, as a more specific configuration of this configuration, the objective lens is inclined so as to cancel the coma aberration of the objective lens when the movable lens is disposed at the predetermined position, and the predetermined direction is: The moving lens may be in a direction that cancels coma generated when the movable lens is translated from the predetermined position along the reference optical axis.

  In the optical pickup configured as described above, the movable lens may be a collimating lens. According to this configuration, spherical aberration can be corrected with a simple optical configuration, and the occurrence of coma can be suppressed.

  In the optical pickup configured as described above, the objective lens may be arranged so that coma aberration of the objective lens is generated in a radial direction.

  In the optical pickup configured as described above, the optical recording medium may include a Blu-ray disc.

  According to the present invention, an optical pickup capable of appropriately suppressing spherical aberration and coma aberration can be provided. For this reason, if the optical pickup of the present invention is used, it is possible to suppress deterioration in information recording / reproduction quality due to aberrations, for example, during an interlayer jump, and it is possible to maintain stable recording / reproduction quality.

Schematic showing the configuration of the optical pickup of the present embodiment The figure which shows the optical structure of the optical pick-up of this embodiment. FIG. 2 is a diagram when a part of the optical configuration of the optical pickup shown in FIG. 2 is viewed from the side. The figure for demonstrating the reason for the movement direction of the collimating lens in the optical pick-up of this embodiment being inclined with respect to the reference | standard optical axis. The figure for demonstrating the reason for the movement direction of the collimating lens in the optical pick-up of this embodiment being inclined with respect to the reference | standard optical axis. The figure which shows the change of the optical axis accompanying the movement of a collimating lens in the optical pick-up of this embodiment. Graph showing the simulation result of coma aberration that occurs when the collimating lens is moved in parallel to correct spherical aberration The figure which shows the structure of the lens drive unit with which the optical pick-up of this embodiment is provided.

  Hereinafter, embodiments of an optical pickup according to the present invention will be described in detail with reference to the drawings. Here, the case where the present invention is applied to an optical pickup capable of reading and writing information on a BD is taken as an example.

  1A and 1B are schematic views showing the configuration of the optical pickup of the present embodiment. FIG. 1A is a schematic plan view, and FIG. 1B is a schematic side view. As shown in FIG. 1, the optical pickup 1 of the present embodiment includes a pickup base 2 and an objective lens actuator 3 mounted on the pickup base 2.

 Bearing portions 2 a and 2 b are provided on the left and right sides of the pickup base 2. The bearing portions 2a and 2b are fixedly disposed on a base (not shown) and engaged with two guide shafts 101 extending in the radial direction (the radial direction of the optical disc 100). As a result, the optical pickup 1 can slide in the radial direction. The optical pickup 1 is moved in the radial direction by a known moving mechanism (not shown). As an example of a known moving mechanism, there is a configuration using a rack attached to the pickup base 2 and a pinion rotated by a motor attached to a base (not shown) different from the pickup base.

  FIG. 2 is a diagram illustrating an optical configuration of the optical pickup according to the present embodiment. FIG. 2 is a schematic plan view when viewed from the optical disc 100 side along the focus direction (direction perpendicular to the information recording layers L0 and L1; see FIG. 1B).

  As shown in FIG. 2, the optical pickup 1 of the present embodiment includes a light source 11, a diffraction element 12, a polarizing beam splitter 13, a quarter wavelength plate 14, a collimator lens 15, and a rising mirror 16. , An objective lens 17, a sensor lens 18, and a light receiving element 19. Among these members, members other than the objective lens 17 are mounted on the pickup base 2. The objective lens 17 is mounted on the objective lens actuator 3 (see FIG. 1).

  The light source 11 is a semiconductor laser that emits laser light for BD (for example, laser light having a wavelength of 405 nm band). Note that linearly polarized light is emitted from the light source 11. The laser light emitted from the light source 11 is sent to the diffraction element 12.

  The diffraction element 12 divides the laser beam transmitted from the light source 11 into main light and two sub-lights. The reason for dividing the main light and the sub-light in this way is to obtain a track error signal necessary for track control. The optical pickup 1 according to the present embodiment is formed so that a track error signal can be obtained by using a DPP (Differential Push-Pull) method which is a known method. The laser beam emitted from the diffraction element 12 is sent to the polarization beam splitter 13.

  The polarization beam splitter 13 reflects linearly polarized light having the same polarization direction as the linearly polarized light emitted from the light source 11 and transmits linearly polarized light whose polarization direction is rotated by 90 degrees with respect to the linearly polarized light emitted from the light source 11. Is formed. For this reason, the laser beam sent from the diffraction element 12 to the polarization beam splitter 13 is reflected by the polarization beam splitter 13. The laser beam reflected by the polarization beam splitter 13 is sent to the quarter wavelength plate 14.

  The quarter-wave plate 14 has a function of converting incident linearly polarized light into circularly polarized light and converting incident circularly polarized light into linearly polarized light. The laser beam sent from the polarization beam splitter 13 and passing through the quarter wavelength plate 14 is converted from linearly polarized light to circularly polarized light and sent to the collimating lens 15.

  The collimating lens 15 is mounted on the lens driving unit 4 and is movable in a direction (in the direction of arrow MD shown in FIG. 2) in contact with and away from the rising mirror 16 in plan view. Although details will be described later, when the optical pickup 1 shown in FIG. 2 is viewed along the tangential direction (direction perpendicular to the radial direction), the movement direction of the collimating lens 15 is the same as that of the collimating lens 15. It is adjusted so as to be inclined with respect to the optical axis of incident light.

  The reason why the collimator lens 15 can be moved as described above is to make the state of the laser light emitted from the collimator lens 15 parallel light or convergent light. The light state can be changed in this way because the information recording layer to be read by the optical pickup 1 is moved from L0 to L1 or from L1 to L0 (interlayer jump). This is to enable correction of spherical aberration that occurs in some cases. The laser light emitted from the collimating lens 15 is sent to the rising mirror 16.

  The above-described L0 indicates an information recording layer on the back side when viewed from the surface 100a side of the optical disc 100 having two information recording layers, and L1 indicates information on the near side when viewed from the surface 100a side of the optical disc 100. It refers to the recording layer (see FIG. 1B). In the optical pickup 1, when the information recording layer to be read of information is L0, the collimating lens 15 is disposed at a position (predetermined position) where the laser light incident on the objective lens 17 is substantially parallel. Is done. When the information recording layer that is the target of information reading or the like is L1, the collimating lens 15 is moved in the direction approaching the rising mirror 16 from the above-mentioned predetermined position, and convergent light is applied to the objective lens 17. Incident.

  The rising mirror 16 is formed of a substantially rectangular parallelepiped member and has a reflecting surface 16a that is covered with a metal thin film or the like and reflects all incident laser light. The laser light sent from the collimating lens 15 to the rising mirror 16 by the rising mirror 16 is converted in the traveling direction and sent to the objective lens 17.

  The objective lens 17 is an objective lens designed for BD, and condenses the laser beam sent from the rising mirror 16 on the information recording layer (L0 or L1) of the optical disc 100. The laser beam condensed on the information recording layer (L0 or L1) by the objective lens 17 is reflected by the information recording layer (L0 or L1).

  The objective lens 17 is mounted on the objective lens actuator 3 as described above, and can be moved in the focus direction and the track direction (direction parallel to the radial direction). The objective lens 17 can be moved in the focus direction in order to control (focus control) so that the focal position of the objective lens 17 always matches the information recording layer to be read. The reason why the objective lens 17 can be moved in the track direction is that the light spot collected by the objective lens 17 is controlled so as to always follow the track of the optical disc 100 (track control).

  Although the configuration of the objective lens actuator 3 is not particularly limited, in the optical pickup 1 of the present embodiment, a lens holder that holds the objective lens 17 is suspended by a wire (a rod-shaped elastic member) so as to be able to swing, and electromagnetic force The objective lens 17 can be moved in the focus direction and the track direction together with the lens holder using the lens holder. Since the configuration of this type of objective lens actuator is known, the detailed configuration is omitted here.

  The return light reflected by the information recording layer (L0 or L1) passes through the objective lens 17 and is reflected by the rising mirror 16. Then, after passing through the collimating lens 15, the ¼ wavelength plate 14 converts the circularly polarized light into linearly polarized light. The polarization direction of the linearly polarized light is a direction obtained by rotating the polarization direction of the linearly polarized light emitted from the light source 11 by 90 degrees. For this reason, the return light that has passed through the quarter-wave plate 14 passes through the polarization beam splitter 13. That is, the polarizing beam splitter 13 and the quarter wavelength plate 14 function as an optical isolator in cooperation with each other.

  The return light transmitted through the polarization beam splitter 13 is given a predetermined astigmatism by the sensor lens 18 and is condensed on the light receiving surface of the light receiving element 19. The light receiving element 19 converts the received optical signal into an electrical signal and outputs it, and the output electrical signal is processed to become a reproduction signal, a servo signal (focus error signal, track error signal, etc.), and the like.

  The sensor lens 18 may be any means for providing astigmatism. For example, a cylindrical lens or a hologram element is used. The reason why the sensor lens 18 gives a predetermined astigmatism is to obtain an astigmatism focus error signal.

  The schematic configuration of the optical pickup 1 of the present embodiment is as described above. Next, the characteristic configuration of the optical pickup 1 will be described in detail.

  FIG. 3 is a view of a part of the optical configuration of the optical pickup shown in FIG. 2 as viewed from the side. 3 is a diagram of the optical pickup shown in FIG. 2 as viewed along the tangential direction (see FIG. 2) perpendicular to the radial direction. Further, the reference optical axis in FIG. 3 indicates the optical axis when the collimating lens 15 is arranged so that incident light emitted from the light source 11 and incident on the objective lens 17 becomes substantially parallel light. In the present embodiment, the reference optical axis coincides with the optical axis when reading the information recording layer L0. The reference optical axis is parallel to the radial direction at the position of the collimating lens 14, and is parallel to the focus direction after being reflected by the reflecting surface 16a of the rising mirror 16.

  The objective lens 17 usually has coma aberration (hereinafter, this coma aberration is expressed as intrinsic coma aberration) due to a manufacturing error. For this reason, it is necessary to avoid the influence of the intrinsic coma aberration. Therefore, in the optical pickup 1 of the present embodiment, coma aberration of light emitted from the objective lens 17 in a state where substantially parallel light is incident on the objective lens 17 (a state in which information is read from the information recording layer L0). The inclination of the optical axis OLA of the objective lens 17 with respect to the reference optical axis is determined so that (based on the intrinsic coma aberration) becomes as small as possible.

  In the present embodiment, the objective lens 17 has an objective lens actuator so that the inherent coma aberration is generated on one side in the radial direction (one of the left and right sides in FIG. 3) for reasons such as easy design. 3 lens holders. Then, the objective lens 17 is rotated by a predetermined amount in a direction around an axis perpendicular to the radial direction and the focus direction (counterclockwise direction in this embodiment) so that the intrinsic coma aberration is canceled, and the optical axis of the objective lens 17 The OLA is inclined with respect to the reference optical axis (inclination angle α) (see FIG. 3).

  Incidentally, the intrinsic coma aberration of the objective lens 17 may of course be zero. In such a case, it is not necessary to tilt the objective lens 17 for the purpose of correcting the intrinsic coma aberration. However, in the present embodiment, the case where the intrinsic coma aberration of the objective lens 17 is zero is excluded.

  The optical pickup 1 of the present embodiment is optically designed so that spherical aberration is minimized when information is read from the information recording layer L0. When an interlayer jump is performed from the information recording layer L0 to L1, the collimating lens 15 is moved to correct spherical aberration. However, when the objective lens 17 is tilted as described above, the collimating lens 15 is moved along the reference optical axis from the state shown in FIG. When moving to the state shown in (b), coma aberration occurs. This coma aberration may adversely affect information reading and writing quality. For this reason, as shown in FIG. 3, the moving direction of the collimating lens 15 is inclined with respect to the reference optical axis (inclined by an inclination angle β in the focus direction). In the movement, the collimating lens 15 is configured to move in parallel along a predetermined moving direction, and the optical axis CLA of the collimating lens 15 moves while being parallel to the reference optical axis.

  FIG. 4 is a diagram for explaining the reason why the moving direction of the collimating lens in the optical pickup of this embodiment is inclined with respect to the reference optical axis. FIG. 4A shows a state in which information is read from the information recording layer L0, and this state is the same in the optical pickup 1 of the present embodiment. FIG. 4B shows a state when information is read from the information recording layer L1, and this state is different from the configuration of the present embodiment in that the collimating lens 15 is aligned along the reference optical axis. A state is shown in which a predetermined amount is translated toward the reflecting surface 16a. In the state of FIG. 4B, convergent light enters the objective lens 17. Therefore, when the objective lens 17 is inclined as in the optical pickup 1 of the present embodiment, large coma aberration is likely to occur.

  Incidentally, as shown in FIG. 5, instead of tilting the objective lens 17, the optical axis of convergent light incident on the objective lens 17 is tilted with respect to the optical axis OLA of the objective lens 17 (FIG. 5B). As in FIG. 4B, coma aberration occurs. FIG. 5A shows a state in which parallel light is incident on the objective lens 17 in a state where the optical axis of the objective lens 17 and the optical axis of the incident light coincide with each other. FIG. 5B shows a state in which convergent light is incident on the objective lens 17 in a state where the optical axis of the incident light is inclined with respect to the optical axis of the objective lens 17.

  FIG. 6 is a diagram illustrating a change in the optical axis accompanying the movement of the collimating lens in the optical pickup according to the present embodiment. As described above, in the optical pickup 1, the parallel movement direction of the collimating lens 15 is inclined with respect to the reference optical axis. For this reason, when the collimating lens 15 is moved along with the interlayer jump from the information recording layer L0 to L1, the direction of the optical axis changes. When the direction of the optical axis changes in this way, coma aberration occurs as described above.

  Here, the simulation result is shown about the coma aberration which generate | occur | produces with the collimating lens movement demonstrated above. FIG. 7 is a graph showing a simulation result of coma aberration generated when the collimating lens is moved in parallel to perform spherical aberration correction. In FIG. 7, the horizontal axis is the spherical aberration amount, and the vertical axis is the coma aberration amount. In performing the simulation whose result is shown in FIG. 7, when reading information from the information recording layer L0, substantially parallel light is incident on the objective lens 17, and at this time, the generation amount of spherical aberration becomes zero. Yes.

  First, the simulation result A shown in FIG. 7 will be described. In this simulation, the optical axis OLA of the objective lens 17 reads the information recording layer L0 so that the coma aberration (due to the intrinsic coma aberration of the objective lens 17) becomes zero when information is read from the information recording layer L0. Inclined with respect to the optical axis of the optical system (that is, the reference optical axis). The inclination at this time is 15 minutes in the radial direction (the angle α in FIG. 3 is 15 minutes). Further, the direction in which the collimator lens 15 is moved in order to correct spherical aberration is a direction along the reference optical axis. Such movement of the collimating lens 15 is the same as the situation where the state shown in FIG. 4A is changed to the state shown in FIG. 4B. From the simulation result A, it can be seen that the coma aberration is generated as described above by moving the collimating lens from the information recording layer L0 to L1 to correct the spherical aberration in accordance with the interlayer jump.

  Next, the simulation result B shown in FIG. 7 will be described. In this simulation, the optical axis OLA of the objective lens 17 coincides with the reference optical axis. Further, the direction in which the collimator lens 15 is translated in order to correct spherical aberration is inclined with respect to the reference optical axis. The inclination with respect to the reference optical axis is 10 minutes in the focus direction (the angle β in FIG. 3 is 10 minutes). From the simulation result B, it can be seen that coma aberration occurs with the movement of the position of the collimating lens 15 by tilting the direction of parallel movement of the collimating lens 15 with respect to the reference optical axis.

  In FIG. 7, the simulation result C is a result of adding the simulation results A and B. In this case, even if the spherical aberration amount changes, the coma aberration hardly occurs. Therefore, when moving the collimating lens 15 to correct the spherical aberration, the collimating lens 15 is moved with respect to the reference optical axis in a direction to cancel the coma generated when the collimating lens 15 is moved along the reference optical axis. It can be seen that the spherical aberration and the coma aberration can be appropriately suppressed even when the interlayer jump is performed by inclining and moving in parallel.

  Considering this point, in the optical pickup 1 of the present embodiment, the objective lens 17 is inclined in the radial direction by an angle α (see FIG. 3), and at the same time, the direction in which the collimating lens 15 is translated is set with respect to the reference optical axis. Thus, it is inclined by an angle β (see FIG. 3) in the focus direction.

  As for the amount (angle β) of inclining the parallel movement direction of the collimator lens 15 with respect to the reference optical axis, the coma aberration included in the laser light emitted from the objective lens 17 is minimized. At the time of assembly, it is preferable to determine the amount of coma of the light emitted from the objective lens 17 disposed at an inclination while measuring it. In this way, coma aberration of light emitted from the objective lens 17 can be appropriately suppressed.

  Further, if the amount of tilting the parallel movement direction of the collimating lens 15 with respect to the reference optical axis is excessively increased, astigmatism occurs at a level where the influence cannot be ignored. For this reason, it is preferable that the amount by which the parallel movement direction of the collimating lens 15 is tilted with respect to the reference optical axis be kept at a level that is not affected by astigmatism.

  Here, the configuration of the lens driving unit (lens moving means) 4 provided in the optical pickup 1 of the present embodiment will be described. The configuration of the lens driving unit 4 shown here is merely an example, and other configurations may be used as long as the collimating lens 15 can be translated in a predetermined direction with respect to the reference optical axis.

  8A and 8B are diagrams illustrating the configuration of the lens driving unit included in the optical pickup according to the present embodiment. FIG. 8A is a schematic plan view viewed along the focus direction, and FIG. 8B is along the tangential direction. FIG. As shown in FIG. 8, the lens driving unit 4 includes a unit base 41, a movable holder 42, a guide shaft 43, a pressurizing spring 44, a stepping motor 45, a lead screw 46, and a lead nut 47. Prepare.

  The movable holder 42 is provided with a holding portion (not shown) that holds the collimating lens 15. The movable holder 42 is slidable along two guide shafts 43 arranged in parallel to each other. The two guide shafts 43 are fixedly disposed on the unit base 41 while being supported by the support portion 48, and are substantially parallel to the base surface 41 a of the unit base 41. A coil-shaped pressurizing spring 44 is loosely fitted on one of the two guide shafts 43. The pressurizing spring 44 urges the lens holder 42 to the right in FIG.

  The stepping motor 45 is fixedly disposed on the unit base 41, and a lead screw 46 is attached to the output shaft. Thereby, the lead screw 46 is rotated by driving the stepping motor 45. The lead screw 46 is disposed so as to be substantially parallel to the guide shaft 43. The lead nut 47 is screwed with the lead screw 46 and moves in a direction parallel to the radial direction by the rotation of the lead screw 46.

  The operation of the lens driving unit 4 configured as described above will be described. When the lead screw 46 is rotated by driving of the stepping motor 45 and the lead nut 47 moves away from the stepping motor 45, the movable holder 42 is pushed by the lead nut 47 along the guide shaft 43 from the stepping motor 45. Move away. On the other hand, when the lead nut 47 moves in the direction approaching the stepping motor 45, the movable holder 42 moves in the direction approaching the stepping motor 45 along the guide shaft 43 by the biasing force of the pressurizing spring 44.

  The lens drive unit 4 is provided with a photo interrupter (not shown) so that the reference position can be detected by this photo interrupter. The position of the collimating lens 15 can be adjusted to a desired position based on the number of steps of the stepping motor 45 from this reference position.

  As described above, in the optical pickup 1 of the present embodiment, the moving direction of the collimating lens 15 is configured to be inclined with respect to the reference optical axis. Therefore, the unit base 41 of the lens driving unit 4 is inclined with respect to the base surface 2a of the pickup base 2 as shown in FIG. The inclination may be adjusted by, for example, the adjustment screw 49, and the optimum amount of the inclination is selected while measuring the amount of coma aberration of the outgoing light emitted from the objective lens 17, for example.

  Note that the collimating lens 15 held by the movable holder 42 is held by the movable holder 42 in a state where the optical axis CLA is adjusted to be parallel to the reference optical axis, regardless of the position. ing. As described above, in the optical pickup 1, when the information recording layer L0 is read or the like, the optical axis is the reference optical axis, and when the collimating lens 15 is in a position to read the information recording layer L0 or the like, The optical axis CLA of the collimating lens 15 coincides with the reference optical axis.

  Since the optical pickup 1 of the present embodiment is configured as described above, the occurrence of spherical aberration and coma aberration is appropriately suppressed even when an interlayer jump is performed from the information recording layer L0 to L1 or from L1 to L0. it can. For this reason, in the optical pickup 1 of the present embodiment, the quality of reading information recorded on the BD and writing information on the BD can be made stable. Further, the optical pickup 1 of the present embodiment is advantageous in terms of cost and the like because it can be configured without a tilt mechanism for suppressing coma aberration.

  In addition, the range to which this invention is applied is not limited to the structure of embodiment shown above. That is, various modifications can be made without departing from the object of the present invention.

  For example, in the above-described embodiment, the collimator lens 15 is configured so that substantially parallel light is incident on the objective lens 17 when the collimator lens 15 is disposed at a position where the information recording layer L0 is read. The optical axis of the optical system when the collimating lens 15 is disposed at a position where the information recording layer L0 is read or the like is used as the reference optical axis. However, the present invention is not limited to this configuration. That is, for example, when the collimating lens 15 is disposed between a position where the information recording layer L0 is read and a position where the information recording layer L1 is read, substantially parallel light is incident on the objective lens 17. It is good also as a structure. The optical axis of the optical system when the collimator lens 15 is disposed at a position where substantially parallel light enters the objective lens 17 may be used as the reference optical axis.

  In the embodiment described above, the objective lens 17 is mounted on the lens holder of the objective lens actuator 3 so that the intrinsic coma aberration is generated on one side in the radial direction. However, the present invention is not limited to this configuration, and the objective lens may be arranged so that the generation direction of the intrinsic coma aberration is different. However, in this case, the direction in which the objective lens is tilted and the direction in which the collimator lens is translated must also be changed from the configuration of the present embodiment.

  In the embodiment described above, the collimating lens 15 is used as a movable lens to perform spherical aberration. However, when performing spherical aberration, there is a configuration in which a beam expander having a movable lens is arranged in the optical system of the optical pickup instead of using the collimating lens as a movable lens. The present invention can also be applied to such a configuration. That is, the direction in which the movable lens included in the beam expander is translated may be inclined with respect to the reference optical axis as in the case of this embodiment. The reference optical axis here refers to the optical axis of the optical system when the movable lens is arranged at a position where substantially parallel light is incident on the objective lens.

  In the embodiment described above, the optical pickup is configured to be able to read and write information on the BD. However, the scope to which the present invention is applied is not limited to this. That is, the present invention can be widely applied to an optical pickup having a movable lens so that the spherical aberration can be corrected by changing the convergence and divergence state of incident light incident on the objective lens. It is not limited. Of course, the present invention can be applied to an optical pickup corresponding to a plurality of types of optical disks.

  The present invention is suitable, for example, for an optical pickup that reads and writes information on a BD having two information recording layers.

1 Optical pickup 4 Lens drive unit (lens moving means)
11 Light source 15 Collimating lens (movable lens)
17 Objective lens 100 Optical disc L0, L1 Information recording layer OLA Optical axis of objective lens

Claims (6)

A light source;
An objective lens for condensing the light emitted from the light source onto the information recording layer of the optical recording medium;
A movable lens disposed in an optical path between the light source and the objective lens, the movable lens being movably provided so that spherical aberration can be corrected;
Lens moving means for translating the movable lens in a predetermined direction;
An optical pickup comprising:
The optical pickup according to claim 1, wherein the predetermined direction is inclined with respect to an optical axis of incident light incident on the movable lens. When the movable lens is arranged at a predetermined position so that substantially parallel light is incident on the objective lens, when the optical axis of the light from the light source to the objective lens is a reference optical axis,
The optical pickup according to claim 1, wherein an optical axis of the objective lens and the predetermined direction are inclined with respect to the reference optical axis. The objective lens is tilted so as to cancel the coma aberration of the objective lens when the movable lens is disposed at the predetermined position.
The optical pickup according to claim 2, wherein the predetermined direction is a direction that cancels coma aberration that occurs when the movable lens is translated from the predetermined position along the reference optical axis.   The optical pickup according to claim 1, wherein the movable lens is a collimating lens.   5. The optical pickup according to claim 1, wherein the objective lens is arranged so that coma aberration of the objective lens is generated in a radial direction. 6.   6. The optical pickup according to claim 1, wherein the optical recording medium includes a Blu-ray disc.

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