JP2011129247A - Optical element for optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element for an optical pickup for preventing degradation of characteristics due to temperature and stably obtaining good optical characteristics without increasing its mass. <P>SOLUTION: The optical element for the optical pickup has an objective lens 1 for condensing an optical beam, an aberration corrector for correcting aberration, and a holder for fixing a relative position between the objective lens 1 and aberration corrector. The aberration corrector has a plurality of aberration correcting elements 2 and 3 including an aberration correcting element 3 with a negative power, the holder has a first holder 32 holding at least the aberration correcting element 3 with the negative power and a second holder 31 holding at least the objective lens 1, and the objective lens 1 has a numerical aperture of ≥0.75. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical element for an optical pickup provided in an optical disc drive apparatus for optically recording / reproducing information.

  In recent years, in order to increase the recording capacity of an optical disk drive device, a CD using a laser beam having a wavelength of 780 nm, a DVD using a laser beam having a wavelength of 650 nm, and a disc using a laser beam having a wavelength of 405 nm have been adopted. In addition, higher density is being promoted by shortening the wavelength.

  In such an optical disc drive apparatus, in order to make use of the past assets, even a disc apparatus using a laser beam with a wavelength of 405 nm, a DVD using a laser beam with a wavelength of 650 nm, or a CD using a laser beam with a wavelength of 780 nm. It is desirable to be able to record and reproduce.

  By the way, an optical pickup that irradiates a recording medium with laser light to perform recording and reproduction is mounted on the optical disk drive device, and an objective lens that condenses the laser light onto the recording medium is attached to the optical pickup. ing.

  This optical pickup and objective lens are designed to be dedicated to one wavelength, and by mounting a plurality of optical pickups and objective lenses, it is easy to cope with recording and reproduction of disks of various wavelengths.

  However, mounting an optical pickup corresponding to each wavelength in this way is disadvantageous for downsizing and cost reduction of the apparatus, so that one optical pickup is required to support a plurality of wavelengths. . The objective lens mounted on the optical pickup is not equipped with a plurality of objective lenses corresponding to each wavelength, and they are used by switching them according to the wavelength, but a single objective lens can handle a plurality of wavelengths. It is demanded.

  However, when the wavelength is shortened, the allowable amount of optical characteristics with respect to various aberrations is reduced, and it becomes difficult to handle a plurality of wavelengths with only one objective lens. For this reason, in addition to the objective lens that collects light, an aberration correction element that corrects aberrations caused by different wavelengths is required. In addition, this aberration correction element needs to align its optical axis with the optical axis of the objective lens with high accuracy in order to ensure the optical performance of the optical pickup.

  On the other hand, as a conventional optical pickup, for example, a focusing means for condensing a light beam on the signal recording surface of an optical disc, and one of the ordinary light component and abnormal light component of the light beam is transmitted and the other component is diffracted. And a polarizing hologram element that converges and a holding means for fixing the relative position of these elements are known (for example, see Patent Document 1).

  By applying the technique disclosed in Patent Document 1 and replacing the polarization hologram element with an aberration correction element, the relative position between the aberration correction element and the objective lens as the focusing means can be accurately maintained by the holding means, It is possible to ensure good optical characteristics.

  By the way, in order to increase the numerical aperture, if the aberration correction element has a negative power, the aberration correction becomes easy, which is advantageous in terms of optical characteristics. Moreover, chromatic aberration can be corrected by a concave lens having negative power. However, when negative power is given, the influence of misalignment and the like is greater than that of an optical element having positive power.

  In addition, the holder that is a holding means for the aberration correction element and the objective lens that is the focusing means is often made of synthetic resin for weight reduction and cost reduction, but the linear expansion coefficient of the synthetic resin is large. There is a problem that the distance between the aberration correction element and the objective lens held by the temperature or the distance between the aberration correction elements changes when there are a plurality of aberration correction elements.

  For this reason, as described above, in the case of an aberration correction element having a negative power, the influence of the positional deviation is large, and this is also accompanied by a decrease in the allowable amount of optical characteristics due to a shorter wavelength or a higher numerical aperture. Thus, there is a problem that the optical characteristics are not allowed to be deteriorated due to the positional deviation due to the temperature of the synthetic resin.

  As a method for solving this problem, for example, it is conceivable to make the holder made of metal and reduce the positional deviation due to temperature. However, in this case, the optical pickup has an increased mass and the resonance frequency of the movable part of the optical pickup that follows the surface deviation of the disk or the track shift due to eccentricity is lowered or the drive current is increased. There is a concern that the performance of the system will be lowered.

  On the other hand, in order to prevent problems such as tilting of the objective lens due to thermal expansion deformation due to the temperature of the lens holder made of synthetic resin, paying attention to the hot water flow during molding of synthetic resin, the lens holder adjusts the optical axis of the objective lens. There is also known a lens holder in which a synthetic resin injection gate is provided on a plane passing through the optical axis when divided into a symmetrical shape on the plane passing through (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 10-3690 Japanese Patent Laid-Open No. 9-35296

  According to the technique disclosed in Patent Document 2, the flow of the resin is symmetric with respect to a bilaterally symmetric plane passing through the optical axis, so that thermal expansion deformation due to temperature change is also symmetric. Can be prevented.

  However, when the technique disclosed in Patent Document 2 is applied to a holder that holds the objective lens and the aberration correction element, the tilt of the optical axis of the objective lens and the aberration correction element due to thermal expansion deformation of the holder can be prevented. Since the distance between the aberration correction element and the objective lens and the change in distance between the aberration correction elements when there are a plurality of aberration correction elements cannot be prevented, the optical characteristics are deteriorated.

  Accordingly, an object of the present invention made in view of such circumstances is to provide an optical element for an optical pickup that can prevent deterioration in characteristics due to temperature without causing an increase in mass and stably obtain good optical characteristics. It is in.

An optical element for an optical pickup according to the present invention that achieves the above object includes an objective lens that focuses a light beam, an aberration correction unit that corrects aberration, and a holder that fixes the relative positions of the objective lens and the aberration correction unit. An optical element for an optical pickup having
The aberration correction means has a plurality of aberration correction elements including an aberration correction element having a negative power,
The holder includes a first holder that holds at least the aberration correction element having the negative power, and a second holder that holds at least the objective lens,
The objective lens has a numerical aperture of 0.75 or more.

  It is preferable that the aberration correction element having a negative power corrects an aberration that occurs when light having a different wavelength enters the objective lens.

  According to the present invention, as an optical element for an optical pickup having an objective lens for focusing a light beam, an aberration correction means having a plurality of aberration correction elements including an aberration correction element having a negative power, and a holder for fixing them. Therefore, it is possible to obtain an optical element for an optical pickup that can prevent deterioration of characteristics due to temperature without causing an increase in mass and stably obtain good optical characteristics.

It is a partial top view of an optical pickup according to a first reference example developed together with the present invention. It is a conceptual diagram of the optical pick-up which shows a part in the AA cross section of FIG. It is a perspective view which shows the optical element part group which is an optical element for optical pick-ups mounted in the optical pick-up shown in FIG. Similarly, it is an exploded perspective view. It is sectional drawing of the optical element part group in the AA cross section of FIG. It is a figure for demonstrating the manufacturing method of the lens barrel which is a holder of the optical element part group in a 1st reference example. Similarly, it is a figure for demonstrating the manufacturing method of a lens-barrel. It is a disassembled perspective view of the optical element part group which is an optical element for optical pick-ups concerning the 1st reference example developed with the present invention. It is sectional drawing of the optical element part group which is an optical element for optical pick-ups concerning 1st Embodiment of this invention. Similarly, it is sectional drawing of the optical element part group which is an optical element for optical pick-ups concerning 2nd Embodiment.

  The present invention will be described below with reference to the drawings.

(First Reference Example)
1 to 7 show an optical pickup according to a first reference example developed together with the present invention. FIG. 1 is a partial top view of the optical pickup, and FIG. 2 is a partial cross-sectional view taken along line AA of FIG. FIG. 3 is a perspective view showing an optical element unit set that is an optical element for an optical pickup, FIG. 4 is an exploded perspective view, and FIG. 5 is a cross-section of the optical element unit in the AA cross section of FIG. FIG. 6, FIG. 6 and FIG. 7 are diagrams for explaining a method of manufacturing a lens barrel as a holder.

  In FIG. 1 and FIG. 2, a holder 51 made of a synthetic resin such as a liquid crystal polymer has an objective lens 1, aberration correction elements 2 and 3 as aberration correction means, a lens barrel 11 as a holder, and an aperture member 14. An optical element assembly 10 that is an optical element for use is bonded and fixed. The optical element unit set 10 will be described in detail later.

  Focus coils 52 a and 52 b and tracking coils 53 a to 53 d are bonded to the holder 51. Also, one end of four wire springs 54a to 54d (54a not shown) made of beryllium copper is bonded to the holder 51. Further, one end of wire springs 54a to 54d and terminals of focus coils 52a and 52b and tracking coils 53a to 53d are connected to the substrates 55a and 55b fixed to the holder 51 (terminals are not shown).

  The other ends of the wire springs 54a to 54d are bonded to the spring spacer 56, whereby the holder 51 is supported so as to be movable in the vertical direction (Z direction) and the radial direction (X direction) of the recording medium 59 via the wire springs 54a to 54d. Will be. A two-dot chain line 79 in the recording medium 59 indicates a recording surface when the cover glass is 0.1 mm, and a two-dot chain line 80 shown inside the objective lens 1 and the like is a light flux when the cover glass is 0.1 mm. Is shown.

  A substrate 57 is fixed to the spring pocket 56, and the other ends of the wire springs 54 a to 54 d are soldered to the substrate 57. The wire springs 54a to 54d are further connected to an external electric circuit via a flexible substrate (not shown). The spring bush 56 is fixed to a bent up part 61 a of an iron base 58. Magnets 62a and 62b for generating a magnetic field are also fixed to the bending rising portions 61a and 61b. The mechanism for moving the optical element assembly 10 assembled on the base 58 is referred to as the lens actuator 60. In FIG. 2, only this lens actuator 60 is shown by the AA cross section of FIG. 1, and other optical components are shown as conceptual diagrams.

  Next, the optical element unit set 10 will be described in detail with reference to FIGS.

  The lens barrel 11 is made of, for example, a liquid crystal polymer containing 30% carbon fiber. As shown in FIGS. 4 and 5, the objective lens 1 and the aberration correction elements 2 and 3 are bonded and fixed to the lens barrel 11. Has been. The objective lens 1 is made of a glass lens.

  The aberration correction element 2 is made of synthetic resin, and an annular diffraction grating is formed on both surfaces 6 and 7 thereof. Similarly, the aberration correction element 3 is made of synthetic resin, but a ring-shaped diffraction grating is formed on one surface 9 and the other surface 8 is an aspherical concave surface having negative power. ing. Here, the diffraction gratings of the surfaces 6, 7 and 9 have a cover glass thickness of 0.1 mm, a wavelength of 405 nm, a numerical aperture of 0.85, a cover glass thickness of 0.6 mm, a wavelength of 650 nm, and a numerical aperture of 0.6. Various aberrations that occur when the light corresponding to the DVD or the CD having a cover glass thickness of 1.2 mm, a wavelength of 780 nm, and a numerical aperture of 0.45 is incident on the objective lens 1 are corrected. That is, by utilizing the difference in wavelength, the diffraction grating allows light to pass through different spaces at each wavelength so as to correspond to different cover glass thicknesses, and to correct spherical aberration and chromatic aberration. Further, the concave surface having negative power on the surface 8 spreads the light flux, thereby facilitating optical design correspondence to a large numerical aperture of 0.85 at a wavelength of 405 nm, such as improvement of aberration.

  As shown in FIG. 5, adhesive reservoirs 13 a to 13 c through which excess adhesive escapes when the corresponding elements are bonded are provided at the fixed portions of the objective lens 1 and the aberration correction elements 2 and 3 of the lens barrel 11. This prevents the adhesive from spreading on the optical working surface.

  The lens barrel 11 is made of a liquid crystal polymer containing 30% carbon fiber as described above. In this reference example, it is manufactured by injection molding using a mold. At this time, as shown in FIG. 7, the side provided at two places on the Z-end side surface of the lens barrel 11 from the runners 26a and 26b. The resin is filled through the gates 27a and 27b, and the lens barrel 11 is formed. In FIG. 7, the lens barrel 11 is depicted in a simplified manner. 1 to 6 indicate the remaining gate after the gate cut (hereinafter, the protrusions 12a and 12b are also referred to as gates). As shown in FIGS. 4 and 5, the positional relationship between the gates 12 a and 12 b is two rotationally symmetric with respect to the optical axis 22. The gates 12a and 12b are provided on the side surfaces in the XY direction in contact with the end surface 30 in the Z-direction.

  Further, a diaphragm member 14 having a diaphragm 16 is bonded and fixed to the lens barrel 11. The diaphragm member 14 is provided with relief portions 15a and 15b for the remaining gate protrusions 12a and 12b. The Z-side surface 17 of the aperture member 14 has a conical side surface shape. This is to prevent the light incident on the optical element group 10 from reflecting on the diaphragm member 14 in the opposite direction of 180 degrees and returning to the optical system to adversely affect signal detection, laser, and the like. The conical side surface 17 reflects the light with the direction and angle from which it comes and prevents light from returning to the optical system.

  Next, an optical system other than the optical element unit set 10 will be described along an optical path from the laser diode 63 that emits laser light having a wavelength of 405 nm to the optical element unit set 10 with reference to FIG.

  Laser light from the laser diode 63 enters the collimator lens 64. The collimator lens 64 is adjusted in position in the optical axis direction so that incident laser light is emitted as parallel light. The laser light that has passed through the collimator lens 64 passes through a dichroic prism 65 that synthesizes the laser light and laser light having a wavelength of 650 nm, and further passes through a dichroic prism 66 that synthesizes the laser light and laser light having a wavelength of 780 nm. / 4 wavelength plate 68 is joined to polarization beam splitter 67. The laser light emitted from the laser diode 63 follows the above path, and then passes through the relay lens system including the concave lens 69 and the convex lens 70 that slightly converges or diverges the parallel light, and enters the optical element group 10. To reach.

  A part of the laser light emitted from the laser diode 63 is reflected by the polarization beam splitter 67. A photodetector 71 is disposed at a position where the reflected light travels. Further, the return light from the recording medium is reflected by the polarization beam splitter 67 and reaches the photodetector 73 via the condenser lens 72.

  In addition to the laser diode 63, a laser diode 74 that emits laser light having a wavelength of 650 nm and a laser diode 76 that emits laser light having a wavelength of 780 nm are also arranged.

  Laser light having a wavelength of 650 nm from the laser diode 74 is incident on the collimator lens 75. The collimator lens 75 is adjusted in position in the optical axis direction so that incident laser light is emitted as parallel light. The laser light that has passed through the collimator lens 75 is incident on the dichroic prism 65 that combines the laser light and the laser light having a wavelength of 405 nm and is reflected. Thereafter, the laser beam having a wavelength of 405 nm follows the same optical path and reaches the optical element unit set 10.

  Laser light having a wavelength of 780 nm from the laser diode 76 enters the collimator lens 78 via the grating 77 in order to detect a tracking error by the three-beam method. The collimator lens 78 is adjusted in position in the optical axis direction so that incident laser light is emitted as parallel light. The laser light that has passed through the collimator lens 78 is incident on the dichroic prism 66 that combines the laser light, the laser light having a wavelength of 405 nm, and the laser light having a wavelength of 650 nm, and is reflected. Thereafter, the laser beam having a wavelength of 405 nm follows the same optical path and reaches the optical element unit set 10.

  The photodetector 71 and the photodetector 73 are shared by all wavelengths. Each of the optical elements described above is fixed to a housing (not shown) via an appropriate holder, a mounting plate, or the like.

  Next, the operation of the reference example configured as described above will be described.

  When a recording medium 59 corresponding to a laser beam having a wavelength of 405 nm is used, the laser diode 63 is caused to emit light. The laser light emitted from the laser diode 63 enters the collimator lens 64 to be converted into parallel light, and passes through the dichroic prisms 65 and 66, the polarization beam splitter 67, the quarter wavelength plate 68, and the relay lenses 69 and 70. A spot is formed on the recording medium 59 by the objective lens 1 through the aberration correction elements 3 and 2 of the optical element group 10.

  Part of the laser light incident on the polarization beam splitter 67 is reflected and received by the photodetector 71, and the light emission amount of the laser diode 63 is adjusted based on the output.

  The reflected light (returned light) from the recording medium 59 passes through the objective lens 1 again, and reaches the polarization beam splitter 67 along a path opposite to the forward path. Here, the return light is reflected and received by the photodetector 73 through the condenser lens 72, and the focus error, tracking error and recording signal are detected based on the output. Further, spherical aberration is also detected.

  When a focus error is detected, the holder 51 is driven in a direction perpendicular to the recording medium 59 by passing a current through the focus coils 52a and 52b. When a tracking error is detected, current is passed through the tracking coils 53a to 53d to drive the holder 51 in a direction crossing the track of the recording medium 59. When the recording medium 59 is a disk, it is driven in the radial direction. Further, when accessing different tracks, the holder 51 together with the housing is driven in a direction crossing the track of the recording medium 59 by a driving means (not shown). As described above, the holder 51 and the optical element group 10 fixed thereto are subjected to focus control, tracking control, and access control.

  When the spherical aberration generated due to the variation in the cover glass thickness of the recording medium 59 is detected, the lens 69 and / or 70 constituting the relay lens system is driven to correct the spherical aberration. In this method, by moving the lens 69 and / or 70, the convergence / divergence of light that is originally parallel light incident on the optical element unit set 10 is changed, and spherical aberration that changes thereby is used.

  In the above-described configuration, the optical element unit 10 has a stricter required accuracy in the distance 18 between the aberration correction elements 2 and 3 than in the distance 19 between the objective lens 1 and the aberration correction element 2. This is because the surface 8 of the aberration correction element 3 has a negative power, and the influence of the shift in the distance between the surface having the negative power and the next optical action surface has no positive power or no power. This is because the deviation of the distance between the surface and the next optical action surface is larger. For this reason, when the lens barrel 11 is made of synthetic resin in order to reduce the weight and cost, the synthetic resin has a large linear expansion coefficient due to temperature, and the distance 18 between the aberration correction elements 2 and 3 depends on the temperature. This change is unacceptable because the cover glass is thin, the wavelength is short, and the numerical aperture is increased, the margin for optical properties is also reduced.

  In this reference example, since the positions of the gates 12a and 12b are provided on the side surface of the Z-end, the flow of hot water at the time of injection molding is XY at the end of the Z-side as indicated by an arrow 28 in FIG. The hot water flows in a direction parallel to the XY plane for spreading in the plane direction, but in the Z-side region 20 excluding the Z-side end, the whole is parallel to the Z direction as indicated by an arrow 29. The flow is directed in the Z + direction.

Here, the linear expansion coefficient of the synthetic resin is small in the hot water flow direction and large in the perpendicular direction. For example, in a liquid crystal polymer containing 30% carbon, the former is 0.2 × 10 ⁻⁵ / ° C., whereas the latter is as large as 5 × 10 ⁻⁵ / ° C. In this reference example, the portion between the aberration correction elements 2 and 3 is in the region 20, and the linear expansion coefficient related to this distance 18 is 0.2 × 10 ⁻⁵ / ° C. Even if the temperature rises by 30 ° C. due to the environmental temperature or the heat generated by the focus coils 52a and 52b and the tracking coils 53a to 53d, the change in distance is as small as 0.06 μm per 1 mm and can be ignored. If the direction is a right angle, it changes greatly to 1.5 μm per 1 mm, which is a problem.

The hot water flow is somewhat disturbed, and even the region 20 may not be completely parallel to the Z direction. In this case, the coefficient of linear expansion is intermediate between 0.2 × 10 ⁻⁵ / ° C. and 5 × 10 ⁻⁵ / ° C., but the flow parallel to the Z direction is fundamental even when turbulence occurs. The coefficient of linear expansion is close to 2 × 10 ⁻⁵ / ° C., and the change in distance is negligible.

  The change due to the temperature in the XY plane direction is large because it is perpendicular to the hot water flow direction. However, even if the dimensions change in the XY plane direction, the receiving surface is also parallel to the XY plane, so that there is no displacement in the Z direction. In addition, the lens barrel 11 has a shape that is symmetrical with respect to the optical axis 22 in the XY plane direction, and the dimensions change symmetrically with respect to the optical axis 22 in the XY plane direction. Absent.

  As described above, by providing the gates 12a and 12b at the Z-end of the aberration correction element 3 having a negative power whose position accuracy is severe, a change in the distance 18 between the aberration correction elements 2 and 3 due to temperature can be suppressed. ing.

  In the region 21 far from the gates 12a and 12b, hot water flows in the Z + direction at a position close to the gates 12a and 12b in the XY plane direction, but at a far position, the hot water flows closer to the Z + end at a position closer to the hot water flowing in the Z + direction. Since the hot water turns around from the Z-direction, the entire hot water does not flow parallel to the Z-direction. Furthermore, since the far position in the region 21 is a portion to be filled at the end, the hot water flow is disturbed even in the process where the gas accumulates and escapes. For this reason, since the Z direction does not become a direction parallel to the hot water flow, the change in the distance in the Z direction due to temperature increases.

  As described above, in this reference example, the gates 12a and 12b are provided rotationally symmetric with respect to the optical axis 22, so that the hot water flow is symmetric with respect to the optical axis, and the region 20 is disturbed in a direction not parallel to the Z direction. Can be suppressed. Further, the expansion in the XY plane direction can be made symmetric, and the movement of the optical axis can also be suppressed.

  Note that the gates 12a and 12b may not be provided rotationally symmetrical. In this case, the level of hot water flow in the Z direction is slightly worse, but there is no problem. Further, in this reference example, the gates 12a and 12b are provided in contact with the end surface 30 in the vicinity of the end surface on the side where the aberration correction element 3 having negative power in the optical axis direction is present. However, it may be provided on the side where the aberration correction element 3 having a negative power in the optical axis direction exists. However, the closer the end face 30 is, the greater the effect is, and it is desirable that the end face 30 on the side where the aberration correction element 3 having negative power in the optical axis direction is present is within a range of 1 mm in the optical axis direction. Thus, it is more preferable if it contacts the end face 30.

  Needless to say, the aberration correction element 3 having negative power is not limited to a lens having a concave aspherical surface but may be a spherical surface. Further, not a lens but a diffraction grating having negative power may be used. As a form of the diffraction grating, for example, one having a blaze-shaped annular zone shape is conceivable.

  Further, the aberration correcting element 3 having negative power is not limited to correcting aberration when the numerical aperture is increased, but corrects chromatic aberration due to wavelength variation of the laser beam by a combination of the objective lens 1 that is a convex lens and a concave lens. Alternatively, it is also possible to correct the aberration such as spherical aberration when light of different wavelengths is incident on the objective lens 1. Also, the numerical aperture may be 0.65 instead of 0.85. However, the larger the numerical aperture, the smaller the allowable amount of misalignment. In particular, since the allowable amount is small at 0.75 or more, a great effect can be obtained.

  In addition, the lens barrel 11 is not limited to a liquid crystal polymer containing carbon fibers, and the same effect can be obtained as long as it is a synthetic resin such as polyphenylin sulfide, polyether imide, or thermoplastic polyimide. Furthermore, it is not necessary to insert fibers into the resin, but it is desirable to include fibers in order to increase rigidity. Moreover, the fiber-containing direction has a greater difference in linear expansion coefficient depending on the direction of hot water flow, and the effect of reducing the positional deviation due to temperature is also great. In the case of containing fibers, the optical element unit set 10 is mounted on the holder 51 which is a movable part, and is desired to be lightweight and highly rigid. In addition, it may be a glass fiber or whisker that is inexpensive and has high rigidity. In particular, there are various types of whiskers and can be selected according to required characteristics.

  By mounting the optical element assembly 10 according to this reference example on an optical pickup, as described above, it is possible to realize a high-performance optical pickup that suppresses characteristic deterioration due to temperature.

(Second reference example)
FIG. 8 is an exploded perspective view of an optical element unit set which is an optical element for an optical pickup according to a second reference example developed together with the present invention. In addition, the same number is attached | subjected to the part same as a 1st reference example.

  This reference example differs from the first reference example in the position of the gate of the lens barrel 11. That is, in the first reference example, the side gate is provided on the side surface of the Z-end of the lens barrel 11, but in this reference example, two pin gates 23a and 23b are provided on the Z-end surface. . To be precise, the pin gates 23a and 23b are provided in portions 24a and 24b that are slightly recessed from the Z-end surface 25. This is to make it easier to make the gate. The pin gates 23a and 23b are rotationally symmetric with respect to the optical axis 22 as in the first reference example. Other configurations and operations are substantially the same as those in the first reference example.

  In this reference example, since the pin gates 23a and 23b are provided on the surface of the Z-end, the hot water flow at the time of injection molding can be made more parallel to the Z direction near the Z-end, and is described in the first reference example. The effect of suppressing the fluctuation of the distance 18 between the aberration correction elements 2 and 3 due to the temperature change becomes higher.

(First embodiment)
FIG. 9 is a cross-sectional view of an optical element section set which is an optical element for an optical pickup according to the first embodiment of the present invention. In addition, the same number is attached | subjected to the part same as a 1st reference example.

  In the present embodiment, the configuration of the lens barrel is different from that of the first reference example. That is, in the first reference example, one lens barrel 11 is provided, but in the present embodiment, two lens barrels 31 and 32 are provided, and aberration is added to the lens barrel 32 serving as the first holder. The correction elements 2 and 3 are fixed, and the objective lens 1 and the lens barrel 32 are fixed to a lens barrel 31 that is a second holder. The objective lens 1 and the aberration correction elements 2 and 3 are bonded and fixed in the same manner as in the first reference example, and adhesive reservoirs 34a to 34c are provided at their bonded portions. The lens barrel 32 is fixed to the lens barrel 31 by bonding, and an adhesive reservoir 35 is provided at the fixing portion. The lens barrels 31 and 32 are both made of synthetic resin. The diaphragm 33 is not attached to the lens barrel 32 but is formed integrally with the lens barrel 32. Other configurations and operations are substantially the same as those in the first reference example.

  As described above, in the present embodiment, the objective lens 1 is held in the lens barrel 31 and the aberration correction elements 2 and 3 are held in the lens barrel 32 separate from the lens barrel 31. A precise distance 18 between the surface 8 having a negative power of 3 and the surface 7 of the aberration correction element 2 facing the surface 8 is determined by the lens barrel 32. Therefore, since the lens barrel 32 can be reduced in size and the structure thereof can be simplified, the hot water flow when forming the lens barrel 32 can be simplified, and the hot water flow along the Z direction can be easily made. The influence of the dimensional change due to can be reduced.

  Note that the gate for forming the lens barrel 32 is provided near the end surface 36 or the end surface 37 when the lens barrel 32 has an annular shape with a hole through which light passes in the center as in the present embodiment. Desirably, it may be provided within a range of 1 mm from the end surface 36 or the end surface 37 in the direction of the optical axis 22 (Z direction), more preferably on the end surface 36 or the end surface 37. Further, as described in the first reference example and the second reference example, it is more preferable to provide a gate at a rotationally symmetric position with respect to the optical axis 22.

  In addition, since the lens barrel 32 holds only the aberration correction elements 2 and 3 and is small in size, a gate may be provided on either the end surface 36 or the end surface 37, but the size is large or the shape is complicated. In such a case, it is desirable to provide a gate near the end face 36 on the side where the aberration correction element 3 having negative power is provided, as in the first reference example. With respect to the synthetic resin constituting the lens barrel 32 and the fibers to be put therein, the same ones as described in the first reference example can be considered, and the same effect can be obtained.

  The lens barrel 32 may be formed of the same material as that of the lens barrel 31, or may be made of a material having a smaller linear expansion coefficient than that of the lens barrel 31, for example, a metal such as aluminum. Thus, if the lens barrel 32 holding the aberration correction elements 2 and 3 is made of metal, the variation of the distance 18 due to temperature can be further suppressed, the optical characteristics can be improved, and the lens barrels 31 and 32 can be improved. Compared to the case where both are made of metal, an increase in mass of the movable part of the optical pickup can be minimized, so that deterioration in mechanical performance such as resonance characteristics of the optical pickup can be suppressed.

  In the case where the lens barrel 32 is made of metal, preferably, the lens barrel 32 is disposed on the Z− side opposite to the Z + side where the objective lens 1 having a large mass is disposed, so that the optical element unit 10 You may give the role of the balancer for making a gravity center into the center vicinity of the Z direction. That is, the holder 51 to which the optical element unit set 10 is attached is a movable part, and it is desirable that the center of gravity is in the vicinity of the center in the Z direction. Therefore, the mass of the lens barrel 32 is effectively used to serve as a balancer. If a balancer is added separately as described above and the mass is substantially the same as viewed from the holder 51, it is not necessary to separately provide a balancer, and the number of parts can be reduced. It should be noted that the center of gravity of the optical element unit set 10 is not a problem as long as it is within the range of 1 mm from the center even if it does not exactly coincide with the center in the Z direction.

  The lens barrel 32 can also be made of a magnesium alloy. In this way, since the magnesium alloy is a metal and also has a small linear expansion coefficient, the change in the distance 18 due to temperature can be suppressed. In addition, since magnesium alloy is lightweight while being a metal, even if the lens barrel 31 is made of magnesium alloy, there is no problem in terms of mass. However, since magnesium alloy is expensive, in order to reduce costs. Only the lens barrel 32 is preferably made of a magnesium alloy. In addition, since the magnesium alloy is difficult to process, it is easier to manufacture the lens barrel 32 only by using the magnesium alloy.

  The lens barrel 32 may be made of a synthetic resin having a relatively small linear expansion coefficient. Resins having such special characteristics are expensive, and by adopting only the lens barrel 32, an increase in price can be suppressed.

  In the present embodiment, the lens barrel 32 that holds the aberration correction elements 2 and 3 is separated from the lens barrel 31 that holds the objective lens 1, so that the aberration correction element 2 is Z + with respect to the lens barrel 32. From the side, the aberration correction element 3 can be fixed from both directions, from the Z-side. Here, as compared with the first reference example, in the first reference example, both the aberration correction elements 2 and 3 are fixed from the Z-side, so that the aberration correction outside the aberration correction element 2 fixed in the back is performed. The element 3 is larger in the XY plane direction. Further, the diaphragm 16 having an aperture smaller than that of the aberration correction element 2 or 3 in the XY plane direction cannot be integrally formed between the aberration correction elements 2 and 3 or outside the aberration correction element 3. It is necessary to provide the diaphragm member 14 having On the other hand, in the present embodiment, since the two lens barrels 31 and 32 are provided, the entire lens barrel is increased in size, but it is not necessary to enlarge the aberration correction element 3 or separate the diaphragm. Therefore, the size can be reduced in that respect. Therefore, even if the two barrels 31 and 32 are provided, the size is not necessarily increased, and in some cases, the size can be reduced. Further, since it is not necessary to fix the aberration correction element 2 in a deep place, workability is improved.

(Second Embodiment)
FIG. 10 is a cross-sectional view of an optical element unit set which is an optical element for an optical pickup according to the second embodiment of the present invention. In addition, the same number is attached | subjected to the part same as a 1st reference example.

  Although this embodiment has two lens barrels 31 and 32 as in the first embodiment, the first embodiment is different in that the aberration correction element 2 is bonded and fixed to the lens barrel 31. It is different from the form. After the aberration correction element 2 is fixed to the lens barrel 31, the lens barrel 32 is fixed to the lens barrel 31 in such a manner that it is brought into contact with the Z-direction surface 39 of the aberration correction element 2. The aberration correction element 3 is bonded and fixed to the lens barrel 32, but may be bonded before or after the lens barrel 32 is bonded to the lens barrel 31. As in the first embodiment, adhesive reservoirs 38a to 38c are provided in the lens barrels 31 and 32 at the adhesive fixing portion between the objective lens 1 and the aberration correction elements 2 and 3, respectively. Other configurations and operations are substantially the same as those in the first reference example.

  In the present embodiment, the lens barrel 32 holding the aberration correcting element 3 having negative power is in contact with the aberration correcting element 2 having the surface 7 facing the surface 8 having negative power of the aberration correcting element 3. Therefore, as in the first embodiment, the precise distance 18 is determined by the lens barrel 32, and the variation in the distance 18 due to temperature can be reduced as in the first embodiment. . In the present embodiment, the lens barrel 32 holds only the aberration correction element 3 having negative power, only contacts the aberration correction element 2, and does not have a holding portion for the aberration correction element 2. The structure of the cylinder 32 can be simplified compared to the first embodiment, and the size can be reduced. Thereby, the effect described in the first embodiment can be made more remarkable. Also in this embodiment, various modifications as described in the first embodiment are possible.

  The present invention is not limited to the above-described embodiment, and many variations or modifications are possible. In particular, the number of aberration correction elements does not have to be two, and the diffraction correction element or the like may not be provided on both sides but only on one side. Also, the shape of the aberration correction element does not have to be circular as viewed from the direction parallel to the optical axis, and various shapes such as a rectangle are conceivable.

DESCRIPTION OF SYMBOLS 1 Objective lens 2,3 Aberration correction element 6,7,8,9 surface 10 Optical element part set 11 Lens barrel 12a, 12b Gate 13a-13c Adhesive reservoir 14 Diaphragm members 15a, 15b Escape part 16 Diaphragm 17 surface 18,19 Distance 22 Optical axis 23a, 23b Pin gate 30 End surface 31, 32 Lens barrel 33 Diaphragm 34a-34c Adhesive reservoir 36, 37 End surface 38a-38c Adhesive reservoir 39 Surface 60 Lens actuator

Claims (2)

An optical element for an optical pickup, comprising: an objective lens that focuses a light beam; an aberration correction unit that corrects aberration; and a holder that fixes a relative position of the objective lens and the aberration correction unit.
The aberration correction means has a plurality of aberration correction elements including an aberration correction element having a negative power,
The holder includes a first holder that holds at least the aberration correction element having the negative power, and a second holder that holds at least the objective lens,
The optical element for an optical pickup, wherein the objective lens has a numerical aperture of 0.75 or more. 2. The optical element for an optical pickup according to claim 1, wherein the aberration correcting element having negative power corrects an aberration that occurs when light of different wavelengths enters the objective lens. .

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