JP4797650B2 - Optical pickup device - Google Patents

Description

  The present invention relates to an optical pickup device, and more particularly to an optical pickup device capable of recording and / or reproducing information interchangeably with different optical disks.

  In recent years, research and development of a high-density optical disk system capable of recording / reproducing information using a blue-violet semiconductor laser having a wavelength of about 400 nm is rapidly progressing. As an example, an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (BD), is the same size as DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4, 7 GB). On an optical disk with a diameter of 12 cm, information of 20 to 30 GB can be recorded on one surface, and an optical disk that records and reproduces information with specifications of NA 0.65 and light source wavelength 405 nm, so-called HD DVD In addition, it is possible to record information of 15 to 20 GB per side on an optical disk having a diameter of 12 cm. Hereinafter, in this specification, such an optical disc is referred to as a “high-density optical disc”.

By the way, it cannot be said that the value of the optical pickup device as a product is sufficient only by appropriately recording / reproducing information on such a high-density optical disk. In light of the reality that DVDs and CDs that record a wide variety of information are currently being sold, it is not only possible to record / reproduce information appropriately for high-density optical discs. For example, conventional DVDs owned by users Alternatively, it is possible to record / reproduce information appropriately for a CD as well, which leads to an increase in the value of a product as a compatible type optical pickup device. From such a background, the optical system used for the compatible type optical pickup device has, of course, a low-cost and simple configuration. In addition to this, for high-density optical discs, conventional DVDs, and CDs, It is desired to obtain a good spot in order to properly record / reproduce information. In addition, an optical pickup device capable of recording and / or reproducing information in a manner compatible with DVD and CD has been put into practical use, but further downsizing, thinning, and cost reduction with respect to the current configuration. Etc. are desired. Patent Document 1 discloses a conventional optical pickup device.
Japanese Patent Laying-Open No. 2005-141884

  However, in an optical pickup device having a thin configuration, generally, a light beam from a light source is bent by a rising mirror before entering the objective lens. In such a case, most of the components must be arranged between the two rails arranged to guide the carrier carrying the carrier in the radial direction of the optical disc. There is a problem that a large interval between the two rails cannot be secured in order to avoid interference.

  In order to make compatible use of optical discs, it is necessary to mount a plurality of light sources having different wavelengths, but in order to achieve compactness, the objective lens is used in common and the drive unit is designed to be as small as possible. In this case, it is necessary to allow light beams emitted from different light sources to enter the common optical path using a light beam coupling element such as a dichroic prism having a wavelength selection system that reflects or transmits light according to the wavelength of the incident light beam. In such a case, the problem is how to arrange the light sources.

  The present invention has been made in view of the problems of the prior art, and provides an optical pickup device capable of appropriately recording and / or reproducing information with respect to different optical information recording media while having a compact configuration. The purpose is to do.

The optical pickup device according to claim 1, a first light source that irradiates a light beam having a wavelength λ1, a second light source that emits a light beam having a wavelength λ2 (λ1 <λ2), and a wavelength λ3 (λ2 <λ3). A third light source that emits a light beam and a light beam emitted from the first light source are collected on the information recording surface via the protective substrate of the first optical information recording medium having a protective substrate thickness t1. The light beam emitted from the second light source is condensed on the information recording surface via the protective substrate of the second optical information recording medium having a protective substrate thickness t2 (t1 ≦ t2). And a condensing optical system including an objective lens for condensing the information recording surface through the protective substrate of the third optical information recording medium, wherein the thickness of the protective substrate is t3 (t2 <t3), and the information recording surface have a, a photodetector for receiving reflected light from, movable on the carrier along the rail In location optical pickup apparatus,
Each of the first light source, the second light source, and the third light source is a semiconductor laser, and the far-field pattern of the emitted light beam is elliptical, and the minor axis direction and the polarization vibration direction are substantially the same. The light beam is incident on the objective lens so that the elliptical shape of the far field pattern is maintained and the major axis direction of the elliptical shape is substantially matched with the track direction of the optical information recording medium, and 2 One light source is housed in the first package and the remaining light sources are housed in the second package;
A polarizing beam splitter is disposed between the first light source, the second light source, the third light source, and the objective lens, and λ is disposed between the polarizing beam splitter and the objective lens. / 4 wavelength plate is placed,
The light beams emitted from the first light source, the second light source, or the third light source enter the light beam coupling element to enter the common optical path incident on the polarization beam splitter, and further to the objective Reflected by the rising mirror before entering the lens,
The light beams emitted from the first light source, the second light source, and the third light source pass through the polarization beam splitter while maintaining the relationship between the minor axis direction of the ellipse of the far field pattern and the polarization vibration direction. The incident light is P-polarized light, and the transmitted light is incident on the objective lens.
Of the first package and the second package, a light beam emitted from a light source housed in one package passes through the light beam coupling element and is emitted from a light source housed in the other package. The light beam is reflected by the light beam coupling element, and then enters the polarization beam splitter, and the rail is orthogonal to the axis of the light beam emitted from the one package, and is opposite to the side from which the light beam is emitted. Provided,
The reflected light from the information recording surface of the optical information recording medium is at least partially reflected by the polarization beam splitter and is condensed on the photodetector.
The photodetector is a single detector, and receives light beams from the first light source, the second light source, and the third light source in order to record and / or reproduce information. And

  The effects of the present invention will be described with reference to the drawings. FIG. 3A is a diagram showing the positional relationship between the far field pattern FFP related to the intensity distribution of the light beam emitted from the light source and the region BR captured by the objective lens. In FIG. 3A, the elliptical long axis direction of the far field pattern FFP coincides with the track direction of the optical disk, and in FIG. 3B, the long axis direction of the condensed elliptical spot SPT is the radial direction of the optical disk. I'm doing it. FIG. 3B is a perspective view showing a state in which a focused spot is formed on the information recording surface on the optical disc.

  When the far field pattern of the light beam incident on the objective lens is in an elliptical state (when the beam is not shaped), when the light is condensed on the optical disk recording surface, the long axis direction of the far field pattern is short and the short axis of the far field pattern is short. An elliptical spot whose axial direction corresponds to the major axis direction is a first precondition. First, as a first precondition, the focused spot is set so that its minor axis direction substantially coincides with the track direction. This is preferable because the resolution can be improved. On the other hand, as a second precondition, if a film that mainly transmits P-polarized light and mainly reflects S-polarized light among the light beams incident on the polarizing beam splitter, the degree of freedom in designing the film is increased. In addition, since it can be realized with a small number of layers, it is preferable to use a polarizing beam splitter having such specifications because the optical margin of the optical pickup device can be widened and the cost of the polarizing beam splitter can be reduced.

  Here, consider an arrangement example in which the optical path from the light source LD to the objective lens OBJ is parallel to the rail SR in FIG. 5 (the far field pattern FFP is indicated by a one-dot chain line and the polarization direction is indicated by an arrow D). In such an arrangement example, since the track direction of the optical disc OD is perpendicular to the rail SR at the position where the spot on the optical disc recording surface is condensed, the first condition and the second condition are simultaneously adapted. The direction of the light source LD is set so that the long axis direction of the far field pattern of the light beam emitted from the light source LD coincides with the track direction of the optical disk OD, and the same light beam is P-polarized light with respect to the polarization beam splitter PBS. It is necessary to provide an optical element (for example, a λ / 2 wavelength plate HWP shown by a dotted line) for rotating the polarization direction between the polarizing beam splitter PBS and the light source LD so that the light enters, which causes an increase in cost.

  On the other hand, in FIG. 6 (far field pattern FFP is indicated by a one-dot chain line and the polarization direction is indicated by arrow D), an arrangement example in which the optical path from light source LD to objective lens OBJ is perpendicular to rail SR is considered. . With such an optical arrangement, an optical element for rotating the polarized light by 90 ° is not required between the light source LD and the polarization beam splitter PBS, and the first and second preconditions are satisfied. is there.

  On the other hand, when trying to realize compatibility using light sources LD1 and LD2 having two different wavelengths, an arrangement example of light sources as shown in FIG. 7 can be considered. At this time, by arranging the optical axes of the two light sources LD1 and LD2 to be orthogonal and using a dichroic prism DBS or the like as a light beam coupling element, each light beam can be guided into the same optical path. In this case, by setting the distances from the light sources LD1 and LD2 to the dichroic prism DBS to be equal, the length of the optical path from the light source LD1 to the photodetector is set equal to the length of the optical path from the light source LD2 to the same photodetector. By making the relationship between each light source and the light detector a conjugate relationship through a spot condensed on the optical disk information recording surface, the light detector can be used in common, thereby reducing costs and optical pickup. The size of the apparatus can be reduced. In this specification, the conjugate relationship means an optically conjugate relationship.

  However, when compatibility is to be realized using the light sources LD1, LD2, and LD3 having three different wavelengths, the arrangement becomes a problem. Even in such a case, in order to use the photodetector in common, as shown in FIG. 8, it is conceivable to provide two dichroic prisms DBS1 and DBS2 as light beam coupling elements and guide the three light beams into the common optical path. . However, in the arrangement example of FIG. 8, another dichroic prism DBS1 must be inserted between the light sources LD1 and LD2 and the dichroic prism DBS2, and still the light detection common to the light sources LD1, LD2, and LD3. In order to make the relationship between the light source LD3 and the dichroic prism DBS2 large, the distance between the light source LD3 and the dichroic prism DBS2 must be increased. There is a risk of inviting. Note that a common photodetector for the light beams of the light sources LD1, LD2, and LD3 has a plurality of light receiving portions in the same plane so that light beams of different wavelengths are received by different light receiving portions. This includes the case of a photodetector in which all light receiving parts are sealed in one package.

  Therefore, in the present invention, a so-called two-laser one-package type composite light source in which two light sources having different wavelengths are accommodated in one package is employed. If such a composite light source is used, only one dichroic prism DBS as a light beam coupling element is required, so that the light source LD1, LD2, LD3 is shared as a photodetector for receiving reflected light from the optical disk OD. Even if one is used, the distance between the light source LD2, the light source 3 (FIG. 9), the light source LD3 (FIG. 10) and the dichroic prism DBS is small, and these light sources (ie, LD2, LD3 (FIG. 9)), the light source LD3 ( The risk of interference between the mechanisms of FIG. 10)) and the rail SR is reduced. In addition, since only one dichroic prism and two laser packages are required for the light source, not only the direction of the rail SR but also the entire optical system can be reduced in size.

  According to a second aspect of the present invention, in the optical pickup device of the first aspect, a coupling lens is disposed between the light source accommodated in the one package and the light beam coupling element. It is characterized by.

  According to the present invention, when the light source accommodated in the one package is disposed at a position close to a guide member for moving the optical pickup device, the light source is accommodated in the one package. By arranging a coupling lens between the light source and the light beam coupling element, the light source and the photodetector can maintain the conjugate relationship through the spot condensed on the optical disc information recording surface. The distance from one package to the light beam coupling element can be kept short, and the optical pickup device can be efficiently arranged in the vicinity of a guide member whose arrangement position is generally limited.

  The optical pickup device according to claim 3 is characterized in that, in the invention according to claim 1 or 2, the light beam coupling element is a wavelength selective prism, so that by using such a wavelength selective prism, A three-wavelength light beam can be efficiently guided to the same optical path. For example, when a blue-violet light beam is used as the light beam having the wavelength λ1, a red light beam is used as the light beam having the wavelength λ2, and a near-infrared light beam is used as the light beam having the wavelength λ3, a transmittance of 90% or more is obtained for the red wavelength light beam and the near-infrared color light beam. Using a wavelength-selective prism (dichroic prism) having a reflectivity of 90% or more for a blue-violet wavelength light beam, two light sources for emitting a red wavelength light beam and a near-infrared color wavelength light beam (identical) By arranging the LD of the package to be transmitted light and the blue wavelength light beam to be reflected light, the three wavelength light beam can be efficiently guided to the common optical path. However, in the case of two lasers and one package, the position of the light emitting point is slightly different (for example, about 110 μm), but here, the light beams emitted from these two light sources are considered to be in a common optical path.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the light source accommodated in the one package emits a light beam having a wavelength of 600 nm or more. .

  FIG. 1 is a schematic configuration diagram of an optical pickup device used for explaining the effects of the present invention. In FIG. 1, the light beam emitted from the point A in the direction and the polarization direction (corresponding to the minor axis direction) of the far field pattern FFP shown in the figure is reflected by the dichroic prism DBS, and is polarized by the polarization beam splitter PBS, collimating lens COL, λ / 4 wave plate QWP, reflected by the rising mirror M, and condensed by the objective lens OBJ at a point C on the information recording surface of the optical disc OD. The reflected light passes through the objective lens OBJ, is reflected by the rising mirror M, passes through the λ / 4 wave plate QWP and the collimating lens COL, is reflected by the polarization beam splitter PBS, and is transmitted through the servo lens SL. Light is received at a point D on the light receiving surface of the detector PD.

  On the other hand, the light beam emitted from the point B in the direction and the polarization direction (corresponding to the minor axis direction) of the far field pattern FFP shown in the figure passes through the dichroic prism DBS, and is polarized beam splitter PBS, collimating lens COL, λ / 4 The light passes through the wave plate QWP, is reflected by the rising mirror M, and is focused on the point C on the information recording surface of the optical disc OD by the objective lens OBJ. The reflected light passes through the objective lens OBJ, is reflected by the rising mirror M, passes through the λ / 4 wave plate QWP and the collimating lens COL, is reflected by the polarization beam splitter PBS, and is transmitted through the servo lens SL. Light is received at a point D on the light receiving surface of the detector PD. Note that the light flux emitted from the point A and the light flux emitted from the point B have the same minor axis direction when entering the objective lens OBJ.

  Here, in order to reduce the size and simplify the optical pickup device, if a single photodetector PD is used, the light source and the photodetector are conjugated via a spot condensed on the optical disk information recording surface. In order to secure this relationship, it is necessary to match the length of the optical path from point A to point D with the length of the optical path from point B to point D. However, in order to provide a rail as a guide member for guiding the carrier in the vicinity of the point B, the distance Δ from the point B to the dichroic prism DBS must be shortened. Therefore, in the present invention, by inserting a coupling lens CUL (shown by a dotted line) between the point B and the dichroic prism DBS, the spot condensed on the optical disk information recording surface is obtained by the light source and the photodetector. The distance from the point B to the dichroic prism DBS is shortened while maintaining the conjugate relationship.

  By the way, the light source arranged at the point B has a problem of whether a blue-violet laser light source or another laser light source is preferable. In general, a CD or DVD requires a light amount of a light beam used for recording and / or reproducing information as compared with a high-density optical disk. This is because, compared with blue-violet laser light, since the beam diameter of red laser light or the like is not much reduced by the objective lens, the light density tends to be low. In addition, since the pit interval on the optical disk is large, when rotating at a high speed to increase the signal transfer speed, it is necessary to form a spot with higher light intensity and read the pit. As described above, in the present invention, as the light source disposed at the point B close to the rail, a red laser light source or a near infrared laser light source, that is, a light source capable of emitting a light beam having a wavelength of 600 nm or more is disposed.

  FIG. 2 is a diagram for explaining the effect of arranging the coupling lens. The light beam emitted from the position of the point B shown in FIG. 2A is smaller than the range BR of the light beam incident on the objective lens, as shown by hatching in FIG. As shown by hatching in FIG. 2B, the light beam emitted from the point B ′ shown in FIG. 2B and passing through the coupling lens CUL has a wide range BR of light incident on the objective lens. Therefore, according to the present invention, the luminous flux of the emitted light can be used more efficiently.

  Note that, in any light beam incident on the polarization beam splitter PBS, if the far-field pattern FFP is an ellipse that is long in the track direction of the optical disk and is P-polarized light, the light use efficiency is high, and the optical disk recording surface There is an advantage that a spot with high resolution of recording and reproduction can be obtained.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, a part of the light beam from the light source is reflected by the polarization beam splitter, and the reflected light is received and received. Since it has the monitor element which outputs the signal according to quantity, the intensity | strength of emitted light can be monitored.

  For example, the monitor optical system is configured so that light beams of three different wavelengths incident on the polarization beam splitter are partially reflected by the light beam splitting surface and guided to a monitor element for monitoring the intensity of the light beam emitted from the light source. In this case, it is not necessary to provide a separate beam splitting element for guiding to the monitor element. Also, instead of providing a light beam splitting element, compared to a structure in which a part of the light beam from the light source is transmitted through the reflecting surface of the rising mirror and a monitor element is placed ahead of it, there is a problem of mechanical interference with the actuator. It can be avoided. This is an advantageous optical arrangement especially when the optical pickup device is thin.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the coating on the light beam splitting surface of the polarizing beam splitter has a transmittance (referred to as Tp) of P-polarized light beam of 70. %, And the reflectance (referred to as Rs) of the S-polarized light beam is 90% or more, the light beam traveling toward the objective lens is efficiently captured, and the light from the optical information recording medium is efficiently captured by the photodetector. Reflected light can be guided.

  According to a seventh aspect of the present invention, in the optical pickup device according to the sixth aspect, the polarizing beam splitter has a cubic shape, and an incident angle of a light beam incident on the polarizing beam splitter is 7 ° or less. Features.

  In particular, a polarizing beam splitter (so-called cubic shape: a surface formed by vertical and horizontal sides) having a substantially cubic shape and a light beam splitting surface inclined by 45 ° with respect to the incident optical axis. (Including a rectangular parallelepiped polarization beam splitter such that length = width ≠ height), a collimating lens is difficult to produce astigmatism even when the light beam passing through the polarization beam splitter is non-parallel light. Need not be placed between the polarizing beam splitter and the light source, but can be placed between the polarizing beam splitter and the objective lens. For this reason, it is suitable for miniaturization of the optical pickup device.

  On the other hand, the film characteristic of the light beam splitting surface of the polarizing beam splitter generally has an incident angle dependency. For this reason, when non-parallel light is incident on the beam splitting surface of the polarizing beam splitter, the incident angle dependency is reduced by setting the number of coating layers on the splitting surface to a high number of layers, for example, 60 layers. However, the polarization beam splitter is not preferable because it increases the cost. However, in the case of the present invention, with respect to the light beam condensed by the objective lens, if the incident angle with respect to the incident surface of the polarizing beam splitter (such as a glass surface instead of the light beam splitting surface) is 7 ° or less for light beams of different wavelengths It is possible to obtain a film having a relatively small number of layers such as Tp and Rs of about 40 layers or less.

  An optical pickup device according to an eighth aspect of the present invention is the optical pickup device according to any one of the first to seventh aspects, wherein the wavelength λ1 is 350 to 450 nm, the wavelength λ2 is 600 to 700 nm, and the wavelength λ3 is 700. It is ˜800 nm.

  According to the present invention, it is possible to provide an optical pickup device capable of appropriately recording and / or reproducing information with respect to different optical information recording media while having a relatively simple configuration and a compact configuration. .

  Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 4 is a schematic configuration diagram of the optical pickup device according to the present embodiment. In an optical pickup apparatus PU capable of appropriately recording / reproducing information with respect to BD or HD DVD, DVD and CD which are optical information recording media having different thicknesses of protective layers, parallel main rail MR and sub rail SR (guide member) And a carrier CY that is movably supported by an actuator (not shown) is provided between the rails. The optical pickup device PU includes a first semiconductor laser LD1 mounted on a carrier CY and housed in a second package PA and capable of emitting a light beam having a wavelength λ1, a second semiconductor laser capable of emitting a light beam having a wavelength λ2, and a wavelength λ3. A second laser 1 package 2L1P in which a third semiconductor laser capable of emitting a light flux of the same in a first package PB, a coupling lens CUL, a dichroic prism DBS as a light beam coupling element, a polarization beam splitter PBS, and a monitor lens ML, a monitor detector MD as a monitor element, an expander lens EXP including lenses L1 and L2, a λ / 4 wavelength plate QWP, a rising mirror M as a reflective optical element, and an actuator ACT. Supported by the objective lens OBJ and the cylindrical adjustment member AM Including a Borenzu SL, and the polarization beam splitter PS, a photodetector PD. The lens L2, which is a movable optical element, is moved in the optical axis direction with respect to the lens L1 fixed to the carrier CY by the driving device DR. The driving device DR moves the holder EH held by the lens L2 in an arbitrary direction at an arbitrary speed along the driving axis DS by expanding and contracting the piezoelectric element PZ fixed to the fixed portion FX in a predetermined pattern. be able to.

  Note that the coating on the light beam splitting surface of the polarizing beam splitter PBS has a transmittance of 70% or more for the P-polarized light beam and a reflectance of 90% or more for the S-polarized light beam. The polarization beam splitter PBS has a cubic shape, and the incident angle of the light beam incident on the incident surface is 7 ° or less. Further, the emitted light from the second and third semiconductor lasers of the first semiconductor lasers LD1 and 2 and the laser 1 package 2L1P has an elliptical far field pattern, and the minor axis direction and the polarization vibration direction are almost equal. In addition, the light beam is made incident on the objective lens OBJ so that the elliptical shape of the far field pattern is maintained and the major axis direction of the elliptical shape and the optical disc track direction are substantially matched. Further, the light beams emitted from the second semiconductor laser and the third semiconductor laser of the first semiconductor laser LD1, 2 laser 1 package 2L1P are polarized while maintaining the relationship between the minor axis direction of the far field pattern ellipse and the polarization oscillation direction. It is assumed that the P-polarized light is incident on the beam splitter PBS and the transmitted light is incident on the objective lens OBJ.

  When recording and / or reproducing information on a first optical disk (not shown) (for example, BD or HD DVD), in the optical pickup device PU of FIG. Is reflected by the dichroic prism DBS, passes through the polarization beam splitter PBS, passes through the λ / 4 wave plate QWP, passes through the lens L1 of the expander lens EXP, and is driven by the driving device DR. The light passes through the lens L2 moved to the first position, is converted into a substantially parallel light beam, and is incident on the rising mirror M. A part of the light beam reflected by the polarization beam splitter PBS passes through the monitor lens ML, enters the monitor detector MD, and is used for monitoring the laser power.

  The light beam incident on the rising mirror M is reflected there, is incident on the objective lens OBJ, and is collected from here on the information recording surface of the first optical disk (the thickness of the protective layer is 0.1 mm or 0.6 mm). The

  The reflected light beam modulated by the information pits on the information recording surface again passes through the objective lens OBJ, is reflected by the rising mirror M, then passes through the lenses L2 and L1 of the expander lens EXP, and the λ / 4 wavelength plate QWP. , Is reflected by the polarization beam splitter PBS, passes through the servo lens SL and the adjustment member AM, is reflected in the polarization beam splitter PS, and is collected on the light receiving surface of the photodetector PD. Using the output signal of the photodetector PD, a read signal for information recorded on the first optical disk is obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the actuator ACT performs the focusing actuator, tracking actuator, and tilt adjustment operation of the objective lens.

  When recording and / or reproducing information on a second optical disk (not shown) such as a DVD, the optical pickup apparatus PU shown in FIG. 4 uses a semiconductor laser (second light source) having a light source wavelength of 600 to 700 nm. The emitted light beam is emitted from the 2 laser 1 package 2L1P, and the divergence angle is changed by passing through the coupling lens CUL, passes through the dichroic prism DBS and the polarization beam splitter PBS, and is then transmitted through the λ / 4 wavelength plate QWP. , Passes through the lens L1 of the expander lens EXP, passes through the lens L2 moved to the second position by the driving device DR, is converted into a substantially parallel light beam, and enters the rising mirror M. A part of the light beam reflected by the polarization beam splitter PBS passes through the monitor lens ML, enters the monitor detector MD, and is used for monitoring the laser power.

  The light beam incident on the rising mirror M is reflected there, is incident on the objective lens OBJ, and is collected from here on the information recording surface (thickness of the protective layer 0.6 mm) of the second optical disk.

  The reflected light beam modulated by the information pits on the information recording surface again passes through the objective lens OBJ, is reflected by the rising mirror M, then passes through the lenses L2 and L1 of the expander lens EXP, and the λ / 4 wavelength plate QWP. , Is reflected by the polarization beam splitter PBS, passes through the servo lens SL and the adjustment member AM, is reflected in the polarization beam splitter PS, and is collected on the light receiving surface of the photodetector PD. Using the output signal of the photodetector PD, a read signal for information recorded on the second optical disk is obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the actuator ACT performs the focusing actuator, tracking actuator, and tilt adjustment operation of the objective lens.

  When recording and / or reproducing information on a third optical disc (not shown) such as a CD, the optical pickup apparatus PU shown in FIG. 1 uses a semiconductor laser (third light source) having a light source wavelength of 700 to 800 nm. The emitted light beam is emitted from the 2 laser 1 package 2L1P, and the divergence angle is changed by passing through the coupling lens CUL, passes through the dichroic prism DBS and the polarization beam splitter PBS, and is then transmitted through the λ / 4 wavelength plate QWP. , Passes through the lens L1 of the expander lens EXP, passes through the lens L2 moved to the third position by the driving device DR, is converted into a finite divergent light beam, and enters the rising mirror M. A part of the light beam reflected by the polarization beam splitter PBS passes through the monitor lens ML, enters the monitor detector MD, and is used for monitoring the laser power.

  The light beam incident on the rising mirror M is reflected there, is incident on the objective lens OBJ, and is collected from here on the information recording surface (the thickness of the protective layer is 1.2 mm) of the third optical disk.

  The reflected light beam modulated by the information pits on the information recording surface again passes through the objective lens OBJ, is reflected by the rising mirror M, then passes through the lenses L2 and L1 of the expander lens EXP, and the λ / 4 wavelength plate QWP. , Is reflected by the polarization beam splitter PBS, passes through the servo lens SL and the adjustment member AM, is reflected in the polarization beam splitter PS, and is collected on the light receiving surface of the photodetector PD. Using the output signal of the photodetector PD, a read signal for information recorded on the third optical disk is obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the actuator ACT performs the focusing actuator, tracking actuator, and tilt adjustment operation of the objective lens.

  FIG. 11 is a view of the polarizing beam splitter PS as viewed from above. In FIG. 11, the polarization beam splitter PS has a first reflection surface APL and a second reflection surface BPL. The incident surface and the exit surface of the polarization beam splitter PS are parallel to each other, and the reflection surfaces APL and BPL are also parallel. The reflected light from the optical disk is incident on the polarization beam splitter PS, then reflected by the first reflecting surface APL, then reflected by the second reflecting surface BPL and emitted, and received by the photodetector PD. ing. Here, the first reflective surface APL has a P-polarized light beam transmittance of 90% or more and a S-polarized light beam reflectance of 90% or more with respect to at least the light beam having the wavelength λ1.

  When the light beam passes through the resin protective layer of the optical disk, the polarization of the light beam irradiated on the optical disk receives a phase difference due to the birefringence. The luminous flux component accompanied by such a phase difference due to birefringence becomes noise for the reproduction of recorded information and causes a reduction in C / N of the reproduction signal. Of the polarized light of the light beam incident on the polarization beam splitter PS, the P-polarized light that has undergone the phase difference is almost transmitted, the light beam of the S-polarized component that has not undergone the phase difference is reflected, and then guided to the light receiving element. Thus, a high C / N optical disc information recording / reproducing signal can be obtained. In the case where a high C / N reproduction signal is not required, the first reflection surface APL may be a simple mirror instead of the polarization beam splitter as shown in FIG. In this case, bonding with another triangular prism as shown in FIG. 11 is unnecessary. Further, if the optical relationship with the light beam is set so that the first reflection surface APL is totally reflected, the reflection coating on the first reflection surface APL is unnecessary, and the cost of the optical pickup device can be further reduced.

  The second reflecting surface BPL is not limited to the vibration direction of polarized light, but only needs to be totally reflected, and it is not necessary to provide a coating for reflection. When the first reflection surface APL and the second reflection surface BPL are at an angle of 45 ° with respect to the incident surface and the output surface that are parallel to each other, the light beam traveling toward the photodetector PD can be obtained even when the polarization beam splitter PS is tilted. Since the direction does not change, it is not necessary to attach with high accuracy and the assembling property can be improved.

  Furthermore, in the present embodiment, the polarizing beam splitter PS has a shape in which a triangular prism is bonded to a parallelogram prism as shown in FIG. 11, but the shape as a polarizing beam splitter is limited to this. For example, a cubic polarizing beam splitter in which the slopes of two identical isosceles prisms are bonded to each other and a polarizing film is applied to the bonding surface, or a polarizing film is applied to one surface of a glass plate. Of course, other forms of polarization beam splitter such as the plate polarization beam splitter can suppress the C / N drop of the reproduction signal.

  According to the present embodiment, a two-laser one package 2L1P including a light source housed in a first package PB disposed at a position close to a rail SR for moving the optical pickup device PU, a dichroic prism DBS, Since the coupling lens CUL is arranged between the two lasers 1 package 2L1P, the distance from the riser mirror M to the two lasers 1 package 2 can be kept short, and the optical pickup is provided between the rails MR and SR whose distance is limited. The device PU can be arranged efficiently.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate.

It is a schematic block diagram of the optical pick-up apparatus used in order to demonstrate the effect of this invention. It is a figure for demonstrating the effect which arrange | positions a coupling lens. It is the figure which showed the positional relationship of far field pattern FFP regarding intensity distribution of the light beam radiate | emitted from the light source, and area | region BR captured by the objective lens of these. FIG. 3B is a perspective view showing a state in which a focused spot is formed on the information recording surface on the optical disc. It is a schematic block diagram of the optical pick-up apparatus concerning this Embodiment. It is a figure which shows the example of arrangement | positioning of a light source. It is a figure which shows the example of arrangement | positioning of a light source. It is a figure which shows the example of arrangement | positioning of a light source. It is a figure which shows the example of arrangement | positioning of a light source. It is a figure which shows the example of arrangement | positioning of a light source. It is a figure which shows the example of arrangement | positioning of a light source. It is a figure which shows a polarizing prism.

Explanation of symbols

2L1P Package ACT Actuator AM Adjusting member BR Region COL Collimating lens CUL Coupling lens CY Carrier DBS Dichroic prism DR Driving device DS Driving shaft EH Holder EXP Expander lens FFP Far field pattern FX Fixed portion L1 First lens L2 Second lens LD1 First semiconductor laser M Rising mirror MD Monitor detector ML Monitor lens MR Main rail OBJ Objective lens OD Optical disk PA Second package PB First package PBS Polarization beam splitter PD Photodetector PS Polarization beam splitter PU Optical pickup device PZ Piezoelectric element QWP λ / 4 wave plate SL Servo lens SPT Spot SR Sub rail

Claims (8)

A first light source that irradiates a light beam with a wavelength λ1, a second light source that emits a light beam with a wavelength λ2 (λ1 <λ2), a third light source that emits a light beam with a wavelength λ3 (λ2 <λ3), The light beam emitted from the first light source is condensed on the information recording surface via the protective substrate of the first optical information recording medium whose protective substrate thickness is t1, and is emitted from the second light source. The collected light beam is condensed on the information recording surface via the protective substrate of the second optical information recording medium whose protective substrate thickness is t2 (t1 ≦ t2), and the protective substrate thickness is t3 (t2). A condensing optical system including an objective lens for condensing on the information recording surface via the protective substrate of the third optical information recording medium at <t3), and a photodetector for receiving reflected light from the information recording surface; , have a, in the optical pickup device arranged on a movable carrier along the rail
Each of the first light source, the second light source, and the third light source is a semiconductor laser, and the far-field pattern of the emitted light beam is elliptical, and the minor axis direction and the polarization vibration direction are substantially the same. The light beam is incident on the objective lens so that the elliptical shape of the far field pattern is maintained and the major axis direction of the elliptical shape is substantially matched with the track direction of the optical information recording medium, and 2 One light source is housed in the first package and the remaining light sources are housed in the second package;
A polarizing beam splitter is disposed between the first light source, the second light source, the third light source, and the objective lens, and λ is disposed between the polarizing beam splitter and the objective lens. / 4 wavelength plate is placed,
The light beams emitted from the first light source, the second light source, or the third light source enter the light beam coupling element to enter the common optical path incident on the polarization beam splitter, and further to the objective Reflected by the rising mirror before entering the lens,
The light beams emitted from the first light source, the second light source, and the third light source pass through the polarization beam splitter while maintaining the relationship between the minor axis direction of the ellipse of the far field pattern and the polarization vibration direction. The incident light is P-polarized light, and the transmitted light is incident on the objective lens.
Of the first package and the second package, a light beam emitted from a light source housed in one package passes through the light beam coupling element and is emitted from a light source housed in the other package. The light beam is reflected by the light beam coupling element and then enters the polarization beam splitter, and the rail is perpendicular to the axis of the light beam emitted from the one package, and is opposite to the side from which the light beam is emitted. It is provided in
The reflected light from the information recording surface of the optical information recording medium is at least partially reflected by the polarization beam splitter and is condensed on the photodetector.
The photodetector is a single detector, and receives light beams from the first light source, the second light source, and the third light source in order to record and / or reproduce information. Optical pickup device.   The optical pickup device according to claim 1, wherein a coupling lens is disposed between the light source accommodated in the one package and the light beam coupling element.   3. The optical pickup device according to claim 1, wherein the light beam coupling element is a wavelength selective prism.   The optical pickup device according to claim 1, wherein the light source accommodated in the one package emits a light beam having a wavelength of 600 nm or more.   5. The monitor element according to claim 1, further comprising: a monitor element that reflects a part of a light beam from the light source by the polarization beam splitter, receives the reflected light, and outputs a signal corresponding to the amount of received light. The optical pickup device described in 1.   6. The coating on the light beam splitting surface of the polarizing beam splitter has a transmittance of 70% or more for P-polarized light beam and a reflectance of 90% or more for S-polarized light beam. The optical pick-up apparatus in any one.   The optical pickup device according to claim 6, wherein the polarization beam splitter has a cubic shape, and an incident angle of a light beam incident on the polarization beam splitter is 7 ° or less.   8. The optical pickup device according to claim 1, wherein the wavelength [lambda] 1 is 350 to 450 nm, the wavelength [lambda] 2 is 600 to 700 nm, and the wavelength [lambda] 3 is 700 to 800 nm.

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