JP2007066360A - Objective lens unit and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective lens unit used for compatible use, for which the risk of deterioration in image formation accuracy due to the influence of a tracking coil and a focusing coil is suppressed. <P>SOLUTION: Since a holder 30 supports the side of a second lens part 22 for allowing a relatively large spot diameter (for DVD or CD) of a compound objective lens 20, even when the holder 30 is heated by the high load operation of the tracking coil and the focusing coil, the heating does not easily affect on a first lens part 21 where highly accurate image formation is required. That is, since the first lens part 21 of a high requirement level relating to a using environment or the like is operated under a relatively advantageous environment and a relatively small first spot diameter formed of the laser beam of a wavelength 405nm for BD is surely maintained with high reliability, high image formation accuracy and information reproducing and recording accuracy are secured. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an objective lens unit suitable as an objective system for an optical pickup, and further relates to an optical pickup device provided with such an objective lens unit.

Up to now, various optical pickup devices for reproducing and recording information on optical information recording media such as CD (compact disc) and DVD (digital versatile disc) have been developed and manufactured, and are widely used. Yes. “Reproduction / recording of information” means reproduction and / or recording of information. As an objective lens incorporated in such an optical pickup device, there is a composite objective lens in which a plurality of lens elements are combined and integrally molded, and information can be easily reproduced and recorded on a different type of recording medium. (See Patent Documents 1 to 4). There is also an objective lens formed by embedding two microlenses having different focal lengths in a glass substrate having a relatively low refractive index (see Patent Document 5). Among these, some objective lenses (see Patent Document 4) include a movable body that supports the objective lens, and one of the two lens elements is positioned on the optical path by the magnetic body at the distal end of the movable body, and the tracking coil The lens element can be switched by instantaneously increasing the energization of the lens element.
JP-A-9-115170 Japanese Patent Application Laid-Open No. 9-306021 JP-A-10-275356 JP-A-9-63083 JP 2000-90472 A

  However, none of the objective lenses as described above is designed on the assumption of a high NA short wavelength application such as a BD (Blu-ray Disc), that is, an application in which the spot diameter is extremely small on the disk surface. For this reason, when the objective lens having the above-described structure is used for BD, the lens elements and the like are heated by the influence of the tracking coil and the focusing coil, and there is a possibility that the imaging accuracy is lowered during use.

  Therefore, the present invention is an objective lens unit for an optical pickup device used in compatible applications including a case where the spot diameter is extremely small, and there is a risk that the imaging accuracy may be reduced due to the influence of the tracking coil and the focusing coil. An object is to provide a suppressed objective lens unit.

  The present invention also provides a compatible optical pickup device incorporating an objective lens unit including a plurality of lens elements, which can maintain high imaging accuracy even when used for a long time under a high load. For the purpose.

  In order to solve the above problems, an objective lens unit for an optical pickup device according to the present invention includes (a) a first lens portion that enables a first spot diameter, and a second lens that is larger than the first spot diameter. An integrated objective lens including a second lens portion that enables a spot diameter, and the first lens portion and the second lens portion are disposed adjacent to each other; and (b) a portion of the objective lens on the second lens portion side. And a holder to support. Note that the objective lens can include three or more lens portions. In this case, at least one side of the remaining lens portions other than the lens portion that realizes the smallest spot diameter is supported by the holder.

  In the objective lens unit, since the objective lens is an integral type in which the first lens portion and the second lens portion are arranged adjacent to each other, depending on which of the first and second lens portions is arranged on the optical path, information Information can be easily reproduced and recorded on two types of optical information recording media having different spot diameter standards on the recording surface. In addition, in the case of the objective lens unit, the holder supports a portion of the objective lens on the second lens portion side that enables a relatively large second spot diameter, so that the holder is heated by the tracking coil or the focusing coil. Even if it is done, the first lens part is less likely to be affected by heating. Therefore, the first lens unit, which normally requires a high level of usage environment, can be operated in a relatively advantageous environment, a relatively small first spot diameter can be reliably maintained, and high image formation can be achieved. Accuracy can be ensured.

  According to a specific aspect or aspect of the present invention, in the objective lens unit, the numerical aperture of the first lens unit is larger than the numerical aperture of the second lens unit. For example, when the wavelength of light used in the first lens unit and the wavelength of light used in the second lens unit are equal or approximate, a spot diameter having a magnitude relationship opposite to the magnitude relationship of the numerical aperture is set for each lens unit. Can be set. That is, the first lens unit having a relatively large numerical aperture can be operated in an environment that is not easily affected by thermal error factors.

  In another aspect of the invention, the first wavelength used for the first lens portion is shorter than the second wavelength used for the second lens portion. For example, when the numerical aperture of the first lens unit and the numerical aperture of the second lens unit are equal or approximate, a spot diameter having a size relationship similar to the size relationship of the used wavelengths can be set for each lens unit. That is, the first lens unit used at a shorter wavelength can be operated in an environment that is less susceptible to thermal error factors.

  The objective lens can be formed from various resins that can be normally used for optical applications such as a lens. In particular, it is preferable to use a resin containing a polymer having an alicyclic structure, and among them, it is more preferable to use a cyclic olefin resin.

In addition, an athermal resin can be used as the resin material as described above. The athermal resin is a material in which particles of, for example, 30 nm or less are dispersed in a resin as a base material. The athermal resin has a characteristic that the refractive index change with respect to the temperature change is smaller than that of a resin for normal optical use. Therefore, when the phase structure is formed in the first lens part or the second lens part, the temperature characteristic of the phase structure The improvement effect can be moderated, thereby reducing the deterioration of the wavelength characteristics due to the phase structure, increasing the design freedom of the optical element, and increasing the tolerance of manufacturing error and assembly accuracy. Can do.
In general, when powder is mixed with a transparent resin material, light scattering occurs and the transmittance decreases, so that it has been difficult to use as an optical material. It has been found that by using fine particles having a diameter of, for example, 30 nm or less, scattering can be substantially prevented. By utilizing such a phenomenon, materials having different temperature characteristics can be mixed macroscopically and the temperature change of the refractive index and the root thermal expansion can be suppressed, and thus A material that has an artificial effect of suppressing temperature characteristics is called an athermal resin. The athermal resin is preferably a material in which fine particles with an average particle diameter of 30 nm or less having a refractive index change rate larger than a refractive index change rate accompanying a temperature change of the resin as a base material are dispersed. In addition, when the sign of the refractive index change rate of the resin that is the base material is negative, the refractive index change rate is large. It includes both of positive refractive index change rates.

  In yet another aspect of the present invention, the objective lens and the holder are integrally formed. In this case, the bonding process between the objective lens and the holder is not necessary, and the cost can be reduced by reducing the number of parts.

  Further, an optical pickup device according to the present invention includes (a) reading the information of the first optical information recording medium via the objective lens unit described above and (b) the first lens unit, or using the first optical information recording medium. An optical device for writing information, reading information on the second optical information recording medium via the second lens unit, or writing information on the second optical information recording medium.

  In the optical pickup device, the objective lens unit described above is used, and information can be easily reproduced and recorded on the first and second optical information recording media having different spot diameter standards. Further, by operating the first lens unit having a small spot diameter and a high required level in a relatively advantageous environment, high imaging accuracy can be ensured for the first optical information recording medium.

  The specific aspect of the optical pickup further includes a driving device that drives the holder and displaces it together with the first and second lens portions. In this case, the first and second lens portions can be arranged in place by displacing the holder.

  In yet another aspect of the present invention, the drive device includes a tracking coil and a focusing coil, and either one of the first lens unit and the second lens unit is switched and disposed on the optical path. In this case, the first and second lens units can be switched, and tracking and focusing can be performed for each lens unit.

[First Embodiment]
The objective lens unit according to the first embodiment of the present invention will be described below with reference to the drawings. FIGS. 1A and 1B are a plan view and a side view for explaining the objective lens unit of the first embodiment, and FIG. 1C is a view of a compound objective lens constituting the objective lens unit. It is a side view.

  An objective lens unit 10 shown in FIG. 1A and the like includes a composite objective lens 20 that is an objective optical system arranged to face an optical disc (not shown), and a composite objective lens 20 that supports the composite objective lens 20. And a holder member 30 that is displaced together, and two actuator portions 71 that are made of a coil or the like and are fixed to a side surface of the holder member 30.

  The compound objective lens 20 includes a first lens portion 21 that can collect incident light on an information recording surface provided in an optical disk (not shown) with a relatively small spot diameter, and another type of incident light with a relatively large spot diameter. 2nd lens part 22 which can be condensed on the information recording surface provided in the optical disc of this. Both lens portions 21 and 22 are supported and fixed to the connecting portion 23 from the periphery, and substantially along a specific plane (a surface parallel to the paper surface of FIG. 1A) perpendicular to the optical axes OA1 and OA2. Arranged adjacent to each other. The compound objective lens 20 is a single component that is molded from, for example, a plastic material or the like, and the first lens portion 21 and the second lens portion 22 are integrated via the connecting portion 23.

  The first lens unit 21 is designed for laser light having a wavelength of 405 nm for BD. That is, as shown in FIG. 1C, when a laser beam having a wavelength of 405 nm parallel to the optical axis OA1 is incident along the optical axis OA1 from the lower surface 21a side of the first lens unit 21, the first lens unit 21 A laser beam is emitted from the upper surface 21b side, and this laser beam is condensed at a focal position F1 on the optical axis OA1, and a relatively small condensed spot is formed here.

  The second lens unit 22 is designed for laser light with a wavelength of 655 nm for DVD and laser light with a wavelength of 780 nm for CD. That is, as shown in FIG. 1C, when a laser beam having a wavelength of 655 nm parallel to the optical axis OA2 is incident along the optical axis OA2 from the lower surface 22a side of the second lens unit 22, the second lens unit 22 A laser light beam having a wavelength of 655 nm is emitted from the upper surface 22b side, and this laser light beam is condensed at a focal position F2 on the optical axis OA2 to form a relatively large condensing spot. Further, when a laser beam having a wavelength of 780 nm, for example, parallel to the optical axis OA2 is incident from the lower surface 22a side of the second lens unit 22, a laser beam having a wavelength of 780 nm is emitted from the upper surface 22b side of the second lens unit 22. The laser beam is condensed at a focal position F3 on the optical axis OA2, and a relatively large condensing spot is formed here.

  In the second lens portion 22, a diffractive structure or a step structure can be formed on the lower surface 22a and the upper surface 22b. Further, a region where a laser beam having a wavelength of 655 nm for DVD is incident and a wavelength of 780 nm for CD are used. The region where the laser beam is incident can be set differently. Thereby, the space | interval of a pair of focus position F2, F3 on optical axis OA2 can be changed and adjusted freely.

  Hereinafter, materials for manufacturing the composite objective lens 20 will be described. That is, the composite objective lens 20 can be formed from a resin material that can be normally used for optical applications, and it is particularly preferable to use a resin material containing a polymer having an alicyclic structure, such as a cyclic olefin resin. .

Further, an athermal resin can be used as the material of the composite objective lens 20. The athermal resin is a material in which, for example, particles of 30 nm or less are dispersed in a resin material as a base material. In general, a resin material that serves as a base material has a refractive index that decreases as the temperature rises, but dispersion and mixing of inorganic particles can reduce a change in the refractive index of the entire material.
When an athermal resin is used, the refractive index change, which was conventionally about −1.2 × 10 ⁻⁴ , can be suppressed to an absolute value of less than 8 × 10 ^−5, but the refractive index change is further reduced to an absolute value of 6 By making it less than × 10 ^−5, the performance of the composite objective lens 20 can be further enhanced.
More preferably, the change in refractive index is less than 4 × 10 ⁻⁵ in absolute value. As a material of the composite objective lens 20, a fine particle having a size of 30 nm or less, preferably 20 nm or less, more preferably 10 to 15 nm with respect to a resin material as a base material, and a refractive index that tends to cancel the refractive index change of the base material By using a material in which fine particles made of inorganic particles having characteristics are dispersed, an optical element having no temperature dependency of the refractive index or having a reduced temperature dependency can be provided.

The fine particles dispersed in the base material are preferably inorganic substances, and more preferably oxides. It is more preferable that the oxide is saturated and does not oxidize any more.
The inorganic substance is preferable from the viewpoint that the reaction with the resin as a base material, which is a high molecular organic compound, is kept low, and the oxide can prevent deterioration due to actual use such as laser light irradiation. it can. In particular, oxidation of the resin is easily promoted under severe conditions such as high temperature and laser light irradiation. However, such inorganic oxide fine particles can prevent deterioration due to oxidation.

  Of course, an antioxidant may be added to the resin material in order to prevent the resin from being oxidized by other factors.

As a specific example of the athermal resin, for example, niobium oxide (Nb ₂ 0 ₅ ) fine particles are dispersed in an acrylic resin. The volume ratio of the resin as the base material is 80, and the ratio of niobium oxide is about 20, and these are uniformly mixed. Although the fine particles tend to aggregate, a necessary dispersion state can be generated by a technique such as applying a charge to the surface of the particles for dispersion. Instead of niobium oxide, it may be used fine particles of silicon oxide (Si0 _2).

  It is preferable that the mixing / dispersing step of the resin material and the particles as the base material is performed in-line when the composite objective lens 20 is injection molded. In other words, after mixing and dispersing, it is preferable not to be cooled and solidified until the composite objective lens 20 is formed.

  The volume ratio can be appropriately increased or decreased in order to control the rate of change of the refractive index with respect to the temperature, or a plurality of types of fine particles can be blended and dispersed. That is, in the above example, the volume ratio is 80:20, that is, 4: 1, but can be appropriately adjusted between 90; 10 (9: 1) and 60:40 (3: 2). Increasing the amount of fine particles more than 9: 1 increases the effect of suppressing temperature change, and conversely, reducing the amount of fine particles less than 3: 2 is preferable without causing problems in the moldability of the optical element. .

  The holder member 30 is a part molded from a plastic material or the like, for example, similarly to the composite objective lens 20, and supports a portion of the composite objective lens 20 on the second lens portion 22 side on the upper surface 30 a. The holder member 30 has an opening 31, and the edge portion of the opening 31 supports an annular portion 32 c around the second lens portion 22. The edge portion of the opening 31 and the annular portion 32c of the second lens portion 22 are fixed to each other with, for example, a UV curable adhesive, and the compound objective lens 20 is aligned with the holder member 30. Can be fixed. Note that the shape of the opening 31 can be freely designed within a range that does not interfere with the support of the annular portion 32 c and does not interfere with the lower surface 22 a of the second lens portion 22, and a step or the like that simplifies the alignment of the compound objective lens 20. It can also be provided. Since the holder member 30 is often heated by the heat generated by the actuator portion 71 and the like, it is desirable that the holder member 30 be formed of a material having low thermal conductivity so as to reduce heat conduction to the composite objective lens 20. In order to prevent the driving accuracy from being lowered, it is desirable to form it with a heat resistant material having a small coefficient of thermal expansion.

  The actuator portion 71 is formed of a coil or the like that is fixed to the holder member 30 or integrated with the holder member 30, and is along the optical axes OA1 and OA2 by interaction with another actuator portion (not shown) made of a magnet or the like. The holder member 30 can be finely displaced in the focus direction and the track direction perpendicular to the optical axes OA1 and OA2. Further, the actuator portion 71 largely moves in the AB direction in the plane in which both the lens portions 21 and 22 are arranged together with the first and second lens portions 21 and 22 by the interaction with the actuator portion (not shown). The positions of both lens parts 21 and 22 can be selectively switched and arranged on a single optical path for pickup.

  In the objective lens unit 10, a laser beam having a wavelength of 405 nm for BD is applied to the first lens unit 21 in a state where the first lens unit 21 is disposed at an operation position on the optical path for pickup by position control of the holder member 30. Is incident from the light source side, the laser light passing through the first lens unit 21 has a relatively small spot diameter with a relatively large numerical aperture of 0.85 on the BD information recording surface (corresponding to the focal position F1). It is focused on. On the other hand, in the objective lens unit 10, a laser beam having a wavelength of 655 nm for DVD is incident on the second lens unit 22 from the light source side in a state where the second lens unit 22 is arranged on the optical path by the position control of the holder member 30. In this case, the laser beam that has passed through the second lens unit 22 is focused on the information recording surface of the DVD (corresponding to the focal position F2) so as to have a relatively large spot diameter with a relatively small numerical aperture of 0.65. In addition, when a laser beam having a wavelength of 780 nm for CD is incident on the second lens unit 22 from the light source side in a state where the second lens unit 22 is arranged on the optical path, the laser beam that has passed through the second lens unit 22 is The light is condensed on the CD information recording surface (corresponding to the focal position F3) so as to have a larger spot diameter with a smaller numerical aperture of 0.53.

  In the objective lens unit 10 of this embodiment, since the composite objective lens 20 in which the first lens portion 21 and the second lens portion 22 having different specifications are adjacently used is used, the first lens portion 21 and the second lens portion 22 are arranged. By arranging one of them on the optical path, spots conforming to the standards can be formed on the information recording surface of the BD and the information recording surface of the DVD or CD. At this time, the spot diameter formed on the information recording surface of the BD by the first lens portion 21 is about 0.41 μm, and the spot diameter formed on the information recording surface of the DVD or CD by the second lens portion 22 is 0 respectively. .87, about 1.2 μm. In the case of the objective lens unit 10 of the present embodiment, the holder member 30 is connected to the second lens portion 22 side that enables a relatively large spot diameter (for DVD or CD) in the composite objective lens 20, so that tracking is performed. Even if the holder member 30 is heated by the high load operation of the coil or the focusing coil, the first lens portion 21 that is required to form an image with high accuracy is less likely to be affected by the heating. That is, the first lens unit 21 for BD having a high requirement level regarding the use environment and the like can be operated in a relatively advantageous environment, and a relatively small first lens formed by a laser beam having a wavelength of 405 nm for BD. Since the spot diameter can be maintained with high reliability, it is possible to set the imaging accuracy, and hence the information reproduction / recording accuracy, to a high level.

  FIG. 2 is a diagram schematically showing the configuration of an optical pickup device incorporating the objective lens unit 10 shown in FIG.

  In this optical pickup device, laser light from each of the semiconductor lasers 61B, 61D, and 61C is applied to the optical discs DB, DD, and DC, which are optical information recording media, using the shared objective lens unit 10, and the optical discs DB, The reflected light from DD and DC is finally guided to the photodetectors 67B, 67D, and 67C through the shared objective lens unit 10. In addition to the semiconductor lasers 61B, 61D, and 61C and the photodetectors 67B, 67D, and 67C, the polarization beam splitters 63B, 63C, 63D, 64D, and 64C, the cylindrical lenses 65B, 65D, and 65C, and the quarter wavelength plate 69 are used. Etc. function as an optical device for recording / reproducing information on / from each optical disc DB, DD, DC.

  Here, the first semiconductor laser 61B generates laser light for information reproduction (for example, for BD, wavelength 405 nm) of the first optical disc DB, and this laser light is emitted from the objective lens unit 10 at the first operating position. A spot condensed by the first lens unit 21 and having an NA equivalent to 0.85 is formed on the information recording surface MB. The second semiconductor laser 61D generates laser light for reproducing information from the second optical disk DD (for example, for DVD, wavelength 655 nm), and then the laser light is the second lens of the objective lens unit 10 in the second operating position. A spot condensed by the portion 22 and corresponding to NA 0.65 is formed on the information recording surface MD. The third semiconductor laser 61C generates laser light for information reproduction (for example, for CD, wavelength 780 nm) of the third optical disk DC, and then the laser light is the second lens of the objective lens unit 10 in the second operating position. A spot condensed by the portion 22 and having an NA equivalent to 0.53 is formed on the information recording surface MC. On the other hand, the first photodetector 67B detects the information recorded on the first optical disc DB as an optical signal (for example, for BD, wavelength 405 nm), and the second photodetector 67D is recorded on the second optical disc DD. The information is detected as an optical signal (for example, for DVD, wavelength 655 nm), and the third photodetector 67C detects the information recorded on the third optical disc DC as an optical signal (for example, CD for wavelength 780 nm). Note that when the light source is switched from the first semiconductor laser 61B to the second and third semiconductor lasers 61D and 61C, the objective lens unit 10 is slid by the actuator 73 which is a driving device (the position indicated by the one-dot chain line). Instead of the lens unit 21, the second lens unit 22 is arranged on the optical path.

  The detailed structure and specific operation of the optical pickup device shown in FIG. 2 will be described below. First, when reproducing the first optical disc DB, laser light having a wavelength of, for example, 405 nm is emitted from the first semiconductor laser 61B, and the emitted light beam becomes a parallel light beam by the collimator 62B. This light beam passes through the polarization beam splitters 63B, 64D, 64C and the quarter wavelength plate 69, and then is condensed on the information recording surface MB of the first optical disc DB by the corresponding first lens unit 21 of the composite objective lens 20. Is done.

  The light beam modulated and reflected by the information bit on the information recording surface MB is again transmitted through the first lens unit 21 and the like, and is incident on the polarization beam splitter 63B. The light beam is reflected and given astigmatism by the cylindrical lens 65B. Then, the light is incident on the first photodetector 67B, and a read signal of information recorded on the first optical disc DB is obtained using the output signal.

  Further, a change in the amount of light due to a change in the shape of the spot and a change in position on the first photodetector 67B is detected to perform focus detection and track detection. Based on this detection, the actuator 73 moves the compound objective lens 20, that is, the first lens unit 21 in the optical axis direction so that the light beam from the first semiconductor laser 61B forms an image on the information recording surface MB of the first optical disc DB. The first lens unit 21 is moved in a direction perpendicular to the optical axis so that the light beam from the first semiconductor laser 61B is imaged on a predetermined track. The actuator 73 for performing focusing and tracking includes a first actuator portion 71 attached to the holder member 30 side of the objective lens unit 10 and a support device 75 that guides the movement of the holder member 30 and the composite objective lens 20. And a second actuator portion 72 attached to the side, and operates under the control of a control device (not shown).

  Next, when reproducing the second optical disk DD, laser light having a wavelength of, for example, 655 nm is emitted from the second semiconductor laser 61D, and the emitted light beam is converted into a parallel light beam by the collimator 62D. This light beam is transmitted through the polarizing beam splitter 63D, reflected by the polarizing beam splitter 64D, and then transmitted through the polarizing beam splitter 64C and the like, and then is transmitted from the second objective optical disk DD by the corresponding second lens portion 22 of the composite objective lens 20. It is condensed on the information recording surface MD.

  The light beam modulated and reflected by the information bit on the information recording surface MD is transmitted again through the second lens unit 22 and the like, reflected by the polarization beam splitter 64D and incident on the polarization beam splitter 63D, and reflected and reflected here by the cylindrical lens. Astigmatism is given by 65D, is incident on the second photodetector 67D, and a read signal of information recorded on the second optical disk DD is obtained using the output signal.

  Further, as in the case of the first optical disc DB, the spot shape change on the second photodetector 67D and the light quantity change due to the position change are detected to perform focus detection and track detection, which are attached to the objective lens unit 10. The compound objective lens 20, that is, the second lens unit 22 is moved by the actuator 73 for focusing and tracking.

  Next, when reproducing the third optical disc DC, a laser beam having a wavelength of, for example, 780 nm is emitted from the third semiconductor laser 61C, and the emitted light beam is converted into a parallel light beam by the collimator 62C, and transmitted through the polarization beam splitter 63C. After being reflected by the splitter 64C, it is condensed on the information recording surface MC of the third optical disc DC by the corresponding second lens portion 22 of the composite objective lens 20.

  The light beam modulated and reflected by the information bit on the information recording surface MC is again transmitted through the second lens unit 22 and the like, reflected by the polarization beam splitter 64C, and incident on the polarization beam splitter 63C, and reflected and cylindrical here. Astigmatism is given by the lens 65C, is incident on the third photodetector 67C, and a read signal of information recorded on the third optical disc DC is obtained using the output signal.

  As in the case of the first and second optical discs DB and DD, the spot shape change on the third photodetector 67C and the light quantity change due to the position change are detected, and focus detection and track detection are performed, and the objective is detected. The compound objective lens 20, that is, the second lens unit 22 is moved for focusing and tracking by an actuator 73 attached to the lens unit 10.

  In the above description, information is reproduced from the optical disks DB, DD, and DC. However, information is recorded on the optical disks DB, DD, and DC by adjusting the outputs of the semiconductor lasers 61B, 61D, and 61C. You can also.

[Second Embodiment]
The objective lens unit according to the second embodiment will be described below. The objective lens unit according to the second embodiment is a modification of the objective lens unit according to the first embodiment, and parts not specifically described are the same as those in the first embodiment.

  FIG. 3 is a plan view of the objective lens unit 110 of the present embodiment. In the illustrated objective lens unit 110, the connecting portion 123 constituting the compound objective lens 120 has an oval outline. Also in this case, the first lens unit 21 is designed for a laser beam having a wavelength of 405 nm for BD, and the second lens unit 22 is a laser beam having a wavelength of 655 nm for DVD or a laser having a wavelength of 780 nm for CD. Designed for light. Further, the connecting portion 123 on the second lens portion 22 side of the compound objective lens 120 having an oval outline is supported by being bonded to the flat upper surface 30 a of the holder member 30.

[Third Embodiment]
The objective lens unit according to the third embodiment will be described below. The objective lens unit according to the third embodiment is a modification of the objective lens unit according to the first embodiment, and parts not specifically described are the same as those in the first embodiment.

  FIG. 4 is a plan view of the objective lens unit 210 of the present embodiment. In the illustrated objective lens unit 210, a little more than half of the connecting portion 23 provided in the composite objective lens 20 is bonded and supported on the upper surface 30 a of the holder member 230. In this case, not only the connecting portion 23 that forms the periphery of the second lens portion 22 but also a part of the connecting portion 23 that forms the periphery of the first lens portion 21 (on the second lens portion 22 side) is supported by the holder member 230. Has been.

[Fourth Embodiment]
The objective lens unit according to the fourth embodiment will be described below. The objective lens unit according to the fourth embodiment is a modification of the objective lens unit according to the first embodiment, and parts that are not particularly described are the same as those in the first embodiment.

  FIG. 5 is a plan view of the objective lens unit 310 of the present embodiment. In the illustrated objective lens unit 310, the connecting portion 323 of the compound objective lens 320 has a structure that also serves as the holder member 30 shown in FIG. That is, in this case, the actuator portion 71 is directly attached to the composite objective lens 320, the number of parts is reduced, and the bonding step between the composite objective lens and the holder becomes unnecessary, so that the cost can be reduced.

[Fifth Embodiment]
FIG. 6 is a diagram schematically showing the configuration of the optical pickup device according to the fifth embodiment. In the illustrated optical pickup device, the objective lens unit 410 has the same structure as the objective lens unit 10 shown in FIG. 1 and the objective lens units 110 to 310 shown in FIGS. 3 to 5, but the second lens unit 22. Is designed not only for laser light with a wavelength of 655 nm for DVD and laser light with a wavelength of 780 nm for CD, but also for laser light with a wavelength of 405 nm for HD-DVD.

  In this optical pickup device, the laser beams from the semiconductor lasers 61B, 61D, and 61C are irradiated onto the optical discs DB, DD, DC, and DH, which are optical information recording media, using the shared objective lens unit 410, and each optical disc DB. , DD, DC, and DH are finally guided to photodetectors 67B, 67D, and 67C through a shared objective lens unit 410.

  Here, the first semiconductor laser 461B generates laser light for information reproduction (for example, for BD, wavelength 405 nm) of the first optical disc DB, and this laser light is emitted from the objective lens unit 410 at the first operating position. A spot condensed by the first lens unit 21 and having an NA equivalent to 0.85 is formed on the information recording surface MB. The first semiconductor laser 461B also serves as a light source for the fourth optical disk DH, and generates laser light for reproducing information on the fourth optical disk DH (for example, a wavelength of 405 nm for HD-DVD). The light is condensed by the second lens portion 22 of the objective lens unit 410 at the second operation position, and a spot corresponding to NA 0.65 is formed on the information recording surface MH.

  When reproducing the first optical disc DB, a laser beam having a wavelength of, for example, 405 nm is emitted from the first semiconductor laser 461B, and the emitted light beam passes through the polarization beam splitters 63B, 64D, 64C and the like, and then the first lens unit 21. Thus, the light is condensed on the information recording surface MB of the first optical disc DB. The light beam modulated and reflected by the information bit on the information recording surface MB is again transmitted through the first lens unit 21 and the like, and is incident on the polarization beam splitter 63B. The light beam is reflected and given astigmatism by the cylindrical lens 65B. Then, the light is incident on the first photodetector 467B, and a read signal of information recorded on the first optical disc DB is obtained using the output signal.

  On the other hand, when reproducing the fourth optical disk DH, a laser beam having a wavelength of, for example, 405 nm is emitted from the first semiconductor laser 461B, and the emitted light beam passes through the polarization beam splitters 63B, 64D, 64C, etc. The light is condensed on the information recording surface MH of the fourth optical disk DH by the unit 22. The numerical aperture at this time is 0.65, and the spot diameter is about 0.53 μm. The light beam modulated and reflected by the information bit on the information recording surface MH is transmitted again through the second lens unit 22 and the like, is incident on the polarization beam splitter 63B, is reflected here, and is given astigmatism by the cylindrical lens 65B. Then, the light is incident on the first photodetector 467B, and a read signal of information recorded on the fourth optical disc DH is obtained using the output signal.

  When reproducing the first optical disc DB or the fourth optical disc DH, the objective lens unit performs focus detection or track detection by detecting a change in the amount of light due to a change in the shape or position of the spot on the second photodetector 67D. The composite objective lens 20, that is, the first lens unit 21 and the second lens unit 22 are moved for focusing and tracking by an actuator 73 attached to 410. Note that when the fourth optical disk DH is reproduced, it may be necessary to control the tilt angle of the compound objective lens 20. In this case, the actuator 73 is provided with a coil for tilt control.

  The above description is for the case of reproducing information from the optical discs DB, DD, DC, DH. However, by adjusting the outputs of the semiconductor lasers 61B, 61D, 61C, etc., the optical discs DB, DD, DC, DH can be changed. Information can also be recorded.

  In the optical pickup device according to the fifth embodiment described above, the laser light for BD and HD-DVD is emitted from the first semiconductor laser 461B, but two LD chips are provided in the first semiconductor laser 461B. Thus, the laser beam for BD and the laser beam for HD-DVD can be generated individually. At this time, two sensor chips are also provided in the first photodetector 267B, and the BD laser beam and the HD-DVD laser beam can be individually detected. Furthermore, a dedicated semiconductor laser for HD-DVD can be provided and condensed on the information recording surface MH of the fourth optical disk DH through an optical path different from that of the first semiconductor laser 461B, and returned from the fourth optical disk DH. Light can be individually detected by a dedicated sensor for HD-DVD.

  Although the present invention has been described based on the above embodiments, the present invention is not limited to the above embodiments, and various modifications are possible. For example, in the first embodiment, the first lens unit 21 reproduces / records information on the BD, and the second lens unit 22 reproduces / records information on the DVD or CD. However, the first lens unit It is also possible to adopt an embodiment in which information is reproduced / recorded on the HD-DVD by 21 and information is reproduced / recorded on the DVD or CD by the second lens unit 22. Furthermore, the first lens unit 21 can reproduce / record information on the BD, and the second lens unit 22 can reproduce / record information on the HD-DVD. The first lens unit 21 can reproduce / record information on a DVD, and the second lens unit 22 can reproduce / record information on a CD.

  The compound objective lens 20 is not limited to having two lens portions 21 and 22, and may have three or more lens portions. In this case, too, it is used at a short wavelength or at a high NA. By fixing the lens portion having the smallest spot diameter away from the holder member 30, the imaging accuracy of the lens portion having the smallest spot diameter can be maintained high.

(A), (b) is the front view and side view of the objective lens unit of 1st Embodiment, ((c) is a side view of a compound objective lens. It is a figure which shows the structure of the optical pick-up apparatus incorporating the objective lens unit shown in FIG. It is a top view which shows the structure of the objective lens unit of 2nd Embodiment. It is a top view which shows the structure of the objective lens unit of 3rd Embodiment. It is a top view which shows the structure of the objective lens unit of 4th Embodiment. It is a figure which shows the structure of the optical pick-up apparatus of 5th Embodiment.

Explanation of symbols

10, 110, 210, 310, 410 ... objective lens unit, 20, 220, 320 ... compound objective lens, 21 ... first lens portion, 22 ... second lens portion, 23 ... connecting portion, 30 ... holder member, 61B, 61D, 61C ... Semiconductor laser, 63B, 63D, 64D, 64C ... Polarizing beam splitter, 67B, 67C, 67D ... Photo detector, 71, 72 ... Actuator part, 73 ... Actuator, 75 ... Supporting device, DB, DD, DC , DH ... optical disc, MB, MD, MC, MH ... information recording surface

Claims (7)

A first lens portion that enables a first spot diameter; and a second lens portion that enables a second spot diameter that is larger than the first spot diameter. An integral objective lens in which a lens portion is disposed adjacently;
A holder for supporting a portion of the objective lens on the second lens portion side;
Objective lens unit for optical pickup device.   The objective lens unit according to claim 1, wherein the numerical aperture of the first lens unit is larger than the numerical aperture of the second lens unit.   The objective lens unit according to claim 1, wherein a first wavelength used for the first lens unit is shorter than a second wavelength used for the second lens unit.   The objective lens unit according to any one of claims 1 to 3, wherein the objective lens and the holder are integrally formed. The objective lens unit according to any one of claims 1 to 4,
Read information on the first optical information recording medium through the first lens unit, or write information on the first optical information recording medium, read information on the second optical information recording medium through the second lens unit, Alternatively, an optical pickup device comprising: an optical device that writes information on the second optical information recording medium.   The optical pickup device according to claim 5, further comprising a driving device that drives the holder to displace the first and second lens portions together. 7. The optical pickup device according to claim 5, wherein the driving device includes a tracking coil and a focusing coil, and any one of the first lens unit and the second lens unit is switched on the optical path. .

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