JP4312214B2 - Optical pickup device - Google Patents

Description

  The present invention relates to an optical pickup device, and is particularly suitable for use in a compatible optical pickup device having a plurality of objective lenses.

  In a compatible optical pickup that can handle several types of disks with different substrate thicknesses, a method using two or more objective lenses can be considered. In this case, a configuration in which the objective lens to which the laser beam is guided can be appropriately set in the optical system. As this structure, the structure shown in the following patent documents 1 and 2 can be used, for example.

  FIG. 11 shows a configuration example described in Patent Documents 1 and 2. In the figure, 1 is a semiconductor laser, 2 is a collimator lens, 3 is a polarization conversion element, 4 is a polarization beam splitter, 5 is a mirror, 6 is a λ / 4 wave plate, 7 is a first objective lens, and 8 is a second objective lens. An objective lens 9 is a light detection system.

The laser light emitted from the semiconductor laser 1 is converted into parallel light by the collimator lens 2 and then the polarization direction is adjusted by the polarization conversion element 3. When the polarization direction of the laser beam is in the first direction, the laser beam is reflected by the polarization beam splitter 4 in the direction toward the first objective lens 7. Further, when the polarization direction of the laser light is in a second direction orthogonal to the first direction, the laser light is transmitted through the polarization beam splitter 4 and incident on the second objective lens 8 via the mirror 5. The As described above, the polarization lens 3 switches the polarization direction of the laser light between the first direction and the second direction, thereby changing the objective lens on which the laser light is incident.
JP-A-9-212905 JP 2001-344803 A

  However, in the above-described conventional configuration example, the reflected light (first reflected light) from the disk via the first objective lens 7 and the reflected light (second reflection) from the disk via the second objective lens 8 are used. The problem arises that it is difficult to guide the reflected light) onto the corresponding sensor pattern on each photodetector.

  In the case of the above configuration example, normally, after arranging the optical elements from the semiconductor laser 1 to the photodetector 9 on the chassis, for example, the first reflected light is appropriately irradiated onto the corresponding sensor pattern. As described above, the position of each optical element is adjusted. However, depending on this adjustment, the second reflected light is not necessarily properly irradiated onto the corresponding sensor pattern, and usually, the positional deviation (light) of the second objective lens 8 with respect to the normal position is not achieved. The second reflected light is irradiated to a position deviated from the corresponding sensor pattern due to a direction perpendicular to the axis or a position shift in the tilt direction.

  However, in the above configuration example, since the position of each optical element has already been adjusted in relation to the first reflected light, the position of these optical elements is further adjusted to change the irradiation position of the second reflected light. It cannot be adjusted. In this case, if the position of each sensor pattern corresponding to the first and second reflected light can be individually adjusted on the photodetector, the second reflected light can be irradiated onto the corresponding sensor pattern. However, this causes a problem that the configuration becomes complicated. Further, this method can be used when the sensor patterns are individually arranged corresponding to the first and second reflected lights, and the first and second reflected lights are irradiated onto the common sensor pattern. If you do, you can no longer even take this approach.

  Thus, in the above configuration example, there is a problem that it is difficult to position both the first reflected light and the second reflected light on the corresponding sensor pattern.

  The present invention has been made in order to avoid such a problem, and can easily adjust the positions of the first and second reflected lights with respect to the sensor pattern on the photodetector by adding a simple configuration. It is an object to provide a pickup device.

  In view of the above problems, the present invention has the following features.

According to a first aspect of the present invention, in the optical pickup device, a first light source that emits laser light, a polarization beam splitter that receives laser light emitted from the first light source, and the laser for the polarization beam splitter. A polarization conversion element that switches a polarization direction of light according to a control signal, and a first objective that causes the first laser light that has passed through the polarization beam splitter to be incident and converges the first laser light on a recording medium. A lens, a second objective lens that receives the second laser beam reflected by the polarization beam splitter and converges the second laser beam on a recording medium, the polarization beam splitter, and the first beam And a λ / 4 plate disposed between the first objective lens and the second objective lens, and light detection for receiving the first and second laser beams reflected by the disk When the diffraction action in accordance with the polarization direction only either one of the lambda / 4 plate and the light detector and the first and reflected by the disc with disposed between the second laser beam expression A polarizing diffractive element that adjusts the position of the polarizing diffractive element so that the first and second laser beams reflected by the disk are irradiated onto a corresponding sensor pattern on the photodetector. It is characterized by being.

  According to a second aspect of the present invention, in the optical pickup device according to the first aspect, the photodetector detects a first sensor pattern that receives the first laser beam and a second sensor that receives the second laser beam. The polarization diffractive element is positioned so that the first and second laser beams reflected by the disk are irradiated onto the first and second sensor patterns, respectively. It is characterized by being.

  According to a third aspect of the present invention, in the optical pickup device according to the first aspect, the photodetector has a common sensor pattern that receives the first and second laser beams, and the polarizing diffraction element is The position of the first and second laser beams reflected by the disk is adjusted so as to be irradiated onto the common sensor pattern.

  According to a fourth aspect of the present invention, in the optical pickup device according to any one of the first to third aspects, the polarization conversion element has a first polarization direction in which the laser light is substantially totally transmitted through the polarization beam splitter. The polarization direction of the laser beam is switched between the second polarization direction in which the laser beam is substantially totally reflected by the polarization beam splitter.

According to a fifth aspect of the present invention, in the optical pickup device according to any one of the first to fourth aspects, the polarizing diffractive element is configured such that the first and second laser beams reflected by the disk are convergent lights. It is arrange | positioned on the optical path used as follows.

According to a sixth aspect of the present invention, in the optical pickup device according to any one of the first to fifth aspects, the second light source that emits laser light having a wavelength different from that of the laser light emitted from the first light source. The laser light from the second light source has an optical axis aligned with the laser light from the first light source, and has a polarization direction in one of the first and second laser lights. The light beam is incident on the polarization beam splitter in a coincident state.

  According to the present invention, by adjusting the position of the polarizing diffraction element, the first and second laser beams reflected by the disk are appropriately irradiated onto the corresponding sensor pattern on the photodetector. That is, according to the present invention, the first and second laser beams are detected by the optical detector by newly arranging the polarizing diffraction element in the optical path and adjusting the position in the optical axis direction and the rotational direction. The corresponding sensor pattern on the upper side is properly irradiated. According to the present invention, the position of the first and second reflected lights can be adjusted smoothly with respect to the sensor pattern on the photodetector by adding a simple configuration.

  The features and effects of the present invention will become more apparent from the following description of embodiments. However, the following embodiment is merely an example when the present invention is implemented, and the meaning of the term of the present invention or each constituent element is limited to that described in the following embodiment. Is not to be done.

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

  The present embodiment is a reproduction-only type capable of supporting HDDVD (High Definition Digital Versatile Disc: hereinafter referred to as “HD”) having a substrate thickness of 0.6 mm and BD (Blu-ray Disc) having a substrate thickness of 0.1 mm. The present invention is applied to a compatible optical pickup device.

  FIG. 1 shows an optical system of an optical pickup device according to the embodiment.

  As shown in the figure, the optical system of the optical pickup device includes a semiconductor laser 11, an active polarizing element 12, a polarizing beam splitter 13, a collimator lens 14, a mirror 15, a collimator lens 16, a rising mirror 17, and a λ. / 4 plate 18, HD objective lens 19, BD objective lens 20, lens holder 21, objective lens actuator 22, polarizing diffractive element 23, detection lens 24, photodetector 25, lens An actuator 26 and a drive motor 27 are provided.

  The semiconductor laser 11 emits a laser beam having a blue wavelength (about 400 nm). In accordance with the control signal, the active polarization element 12 changes the polarization direction of the laser light, the first polarization direction (S-polarized light) in which the laser light is substantially totally reflected by the polarization beam splitter 13, and the laser light is the polarization beam splitter 13. Is switched to the second polarization direction (P-polarized light) that transmits almost all of the light. The active polarizing element 12 corresponds to the polarization conversion element 3 having the configuration example shown in FIG.

  The polarization beam splitter 13 substantially totally reflects the laser beam (first laser beam) having the first polarization direction (S-polarized light), and the laser beam (second laser beam) having the second polarization direction (P-polarized light). Light). The collimator lens 14 converts the first laser light reflected by the polarization beam splitter 13 into parallel light. The mirror 15 reflects the second laser light transmitted through the polarization beam splitter 13 in the direction of the collimator lens 16. The collimator lens 16 converts the second laser light reflected by the mirror 15 into parallel light.

  The raising mirror 17 reflects the first and second laser beams converted into parallel beams by the collimator lenses 14 and 16 in a direction toward the HD objective lens 19 and the BD objective lens 20, respectively. The λ / 4 plate 18 converts the first and second laser light incident from the rising mirror 17 side into circularly polarized light and the first incident light from the HD objective lens 19 and the BD objective lens 20 side. The second laser beam is converted into linearly polarized light orthogonal to the polarization direction when incident from the rising mirror 17 side.

  The HD objective lens 19 and the BD objective lens 20 converge the first and second laser beams incident from the λ / 4 plate 18 side onto the HD and BD, respectively. The HD objective lens 19 is designed so that the blue wavelength laser light can be properly converged on the HD having a substrate thickness of 0.6 mm, and the BD objective lens 20 is configured to apply the blue wavelength laser light to the substrate. It is designed to properly converge on a BD with a thickness of 0.1 mm. The HD objective lens 19 and the BD objective lens 20 are integrally held by a lens holder 21.

  The objective lens actuator 22 drives the lens holder 21 in the focus direction and the tracking direction according to the servo signal. As a result, the HD objective lens 19 and the BD objective lens 20 are integrally driven in the focus direction and the tracking direction. The objective lens actuator 22 is, for example, a conventionally known electromagnetic drive type actuator.

  The polarizing diffractive element 23 does not give a diffracting action to the first reflected light (P-polarized light) that passes through the polarizing beam splitter 13 out of the reflected light from the disk, and is substantially reflected by the polarizing beam splitter 13. A diffraction action is imparted to the second reflected light (S-polarized light) to change the traveling direction of the second reflected light by a certain angle. Details of the polarizing diffraction element 23 will be described later with reference to FIG.

  The detection lens 24 converges the first and second reflected lights reflected by the disk on the photodetector 25. The detection lens 24 includes a condenser lens and a cylindrical lens, and introduces astigmatism into the reflected light from the disk.

  The photodetector 25 has a sensor pattern for deriving a reproduction RF signal, a focus error signal, and a tracking error signal from the intensity distribution of the received reflected light. Here, the sensor 25 is provided with two sensor patterns for individually receiving the first and second laser beams. In this embodiment, an astigmatism method and a one-beam push-pull method are employed as a method for generating a focus error signal and a tracking error signal.

  The collimator lenses 14 and 16 are held by a lens actuator 26 so as to be integrally displaceable in the optical axis direction of the laser light. The drive motor 27 applies a driving force to the lens actuator 26 according to the servo signal. As a result, the collimator lenses 14 and 16 are integrally displaced in the optical axis direction of the laser light.

  For example, the collimator lenses 14 and 16 are servoed so that the reproduction RF signal is optimized. By this servo operation, aberrations on the optical disc and the photodetector 25 are suppressed.

  The operation of this optical system is as follows.

  When the laser light emitted from the semiconductor laser 11 is guided to the HD objective lens 19, the active polarization element 12 is driven and controlled so that the laser light is incident on the polarization beam splitter 13 in the first polarization direction (S-polarized light). The As a result, the laser light is substantially totally reflected by the polarization beam splitter 13 and guided to the HD objective lens 19. At this time, the reflected light from the disk is incident on the polarization beam splitter 13 as P-polarized light by the action of the λ / 4 plate 18. For this reason, the reflected light passes through the polarization beam splitter 13 almost completely and enters the polarizing diffraction element 23. In this case, since the reflected light is incident on the polarizing diffraction element 23 in the P-polarized state, the reflected light travels straight without being diffracted by the polarizing diffraction element 23 as will be described later. The sensor pattern is irradiated.

  When the laser beam emitted from the semiconductor laser 11 is guided to the BD objective lens 20, the active polarization element 12 is driven so that the laser beam is incident on the polarization beam splitter 13 in the second polarization direction (P polarization). Be controlled. As a result, the laser light is substantially totally transmitted through the polarization beam splitter 13 and guided to the BD objective lens 20. At this time, the reflected light from the disk is incident on the polarization beam splitter 13 as S-polarized light by the action of the λ / 4 plate 18. Therefore, the reflected light is substantially totally reflected by the polarization beam splitter 13 and enters the polarizing diffraction element 23. In this case, since the reflected light is incident on the polarizing diffraction element 23 in the S-polarized state, the traveling direction is bent by the diffractive action by the polarizing diffraction element 23 as will be described later. Irradiates onto the corresponding sensor pattern.

  FIG. 2 shows the configuration of the polarizing diffraction element 23. 1 is a cross-sectional structure when the polarizing diffraction element 23 in FIG. 1 is cut along a plane parallel to the XY plane.

  As shown in the figure, the polarizing diffraction element 23 is configured by forming a blazed diffraction structure 232 made of a birefringent material on a transparent substrate 231, and forming a glass layer 233 and a transparent substrate 234 thereon. . The blazed diffractive structure 232 is formed by forming a sawtooth hologram having a constant height at a constant pitch.

  Here, the refractive index of the blazed diffraction structure 232 is np = n1, ns, where np and ns are the refractive indexes when the laser light is incident as P-polarized light and S-polarized light, respectively, and n1 is the refractive index of the glass. ≠ n1 is set. Therefore, when laser light is incident on the polarizing diffraction element 23 as P-polarized light, there is no difference between the refractive index (np) of the blazed diffraction structure 232 and the refractive index (n1) of the glass. The blazed diffraction structure 232 does not function as a diffraction grating. On the other hand, when the laser light is incident on the polarizing diffraction element 23 as S-polarized light, a difference occurs between the refractive index (ns) of the blazed diffraction structure 232 and the refractive index (n1) of the glass. The type diffraction structure 232 functions as a diffraction grating.

  The principle of a polarizing diffraction element using a birefringent material is disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-365416.

  In the polarizing diffraction element 23 shown in FIG. 2, since the diffractive action is given to the laser light by the blazed diffraction structure, the diffractive action by only the + 1st order light or only the −1st order light is given to the laser light. Therefore, the diffraction efficiency of laser light can be increased.

  In the present embodiment, since the laser beam is diffracted only when the laser beam is incident on the polarizing diffraction element 23 as S-polarized light, the laser beam from the semiconductor laser 11 is used as the HD objective as described above. When the light is guided to the lens 19, the diffracting action by the polarizing diffraction element 23 is not given to the reflected light (P-polarized light) from the disk, and when the laser light from the semiconductor laser 11 is guided to the BD objective lens 20, The diffracting action by the polarizing diffraction element 23 is given to the reflected light (S-polarized light). For this reason, the reflected light from the disc that has passed through the HD objective lens 19 travels straight through the polarizing diffraction element 23 and is irradiated onto one of the two sensor patterns on the photodetector 25. The reflected light from the disc that has passed through the BD objective lens 20 has its traveling direction bent by the polarizing diffraction element 23 and is irradiated onto the other sensor pattern.

  FIG. 3A is a diagram illustrating a configuration of the photodetector 25.

  As shown in the drawing, on the photodetector 25, the reflected light from the disk via the HD sensor 251 for receiving the reflected light from the disk via the HD objective lens 19 and the BD objective lens 20 is reflected. Two sensor patterns (four-divided sensors) of the BD sensor 252 for receiving light are arranged.

  When the optical system shown in FIG. 1 is mounted on the chassis, each optical element is placed at a corresponding position, the semiconductor laser 11 is turned on, and the laser light from the semiconductor laser 11 is S-polarized light. The active polarizing element 12 is driven so as to enter the polarizing beam splitter 13. Then, while monitoring the sensor output of the HD sensor 251, the positions of these optical elements are adjusted so that the reflected light from the disk that has passed through the HD objective lens 19 is appropriately irradiated onto the HD sensor 251. . Next, the drive of the active polarization element 12 is switched so that the laser light from the semiconductor laser 11 is incident on the polarization beam splitter 13 as P-polarized light, and the BD objective lens 20 is moved while monitoring the sensor output of the BD sensor 252. The optical axis direction position and the rotational direction position of the polarizing diffraction grating 23 are adjusted so that the reflected light from the passing disk is appropriately irradiated onto the BD sensor 252. After this adjustment is completed, the position of each optical element is fixed. Thereby, the arrangement of the optical system with respect to the chassis is completed.

  As described above, according to the present embodiment, by adjusting the position of the polarizing diffraction element 23, the BD laser light reflected by the disk can be appropriately guided onto the BD sensor 252. According to the present embodiment, by adding only the polarizing diffraction element 23 to the optical system, it is possible to smoothly adjust the positions of the HD laser beam and the BD laser beam with respect to the sensor pattern on the photodetector. it can.

  In the present embodiment, the polarizing diffraction element 23 is arranged in the optical path where the HD laser light (reflected light) and the BD laser light (reflected light) are converged. This is because the irradiation position of the BD laser light on the light receiving surface of the photodetector 25 can be changed smoothly by displacing the polarizing diffraction element 23 in the optical axis direction.

  FIG. 4 is a diagram showing an imaging state when the polarizing diffraction grating 23 is arranged in parallel light. Note that the dotted line in the figure indicates the convergence state of the laser light when it is not diffracted by the polarizing diffraction grating 23.

  In the case where the polarizing diffraction grating 23 is disposed in parallel light, the polarizing diffraction grating 23 gives an angle of view α to the lens L by the diffraction action on the laser light. When laser light is incident on the lens L in the state of parallel light, the condensing point of the laser light is determined by the angle of view α with respect to the lens L. However, as shown in the figure, when the polarizing diffraction grating 23 is arranged in parallel light, the diffraction angle of the laser light is constant regardless of the position of the polarizing diffraction grating 23 on the optical axis. The angle of view α with respect to the lens L is constant even when the polarizing diffraction grating 23 is displaced in the optical axis direction. For this reason, the condensing point of the laser beam does not change even when the polarizing diffraction grating 23 is displaced in the optical axis direction. Therefore, the converging point of the laser beam when not receiving the diffraction action and the polarizing diffraction grating 23 The distance (image height) between the converging points of the diffracted laser light does not change even when the polarizing diffraction grating 23 is displaced in the optical axis direction.

  Accordingly, in the optical system of FIG. 1 as well, when the polarizing diffraction grating 23 is disposed in, for example, parallel light between the collimator lens 16 and the λ / 4 plate 18, the polarizing diffraction grating 23 is displaced in the optical axis direction. Even if it makes it, the irradiation position of the laser beam for BD on the light-receiving surface of the photodetector 25 will not change.

  FIG. 5 is a diagram showing an imaging state when the polarizing diffraction grating 23 is arranged in the diffused light. In addition, the dotted line in the figure shows the convergence state of the laser light when it is not diffracted by the polarizing diffraction grating 23, as in FIG.

  When the polarizing diffraction grating 23 is arranged at the position (1) in the figure, the real image and the virtual image are formed at the positions of the image height (1) and the virtual image height (1) by the diffraction action by the polarizing diffraction grating 23. In this case, the lateral magnification M is given by M = image height / virtual image height.

  In the figure, when the position of the polarizing diffraction grating 23 is displaced in the optical axis direction, the virtual image height changes accordingly. That is, the polarizing diffraction grating 23 acts to change the virtual image height. Here, from the relational expression of the lateral magnification M, since the image height = M × (virtual image height), when the virtual image height changes with the displacement of the polarizing diffraction grating 23 in the optical axis direction, The image height also changes. For example, as shown in FIG. 6, when the polarizing diffraction grating 23 is displaced from the position (1) to the position (2), the virtual image height changes from the virtual image height (1) to the virtual image height (2). Accordingly, the image height changes from the image height (1) to the image height (2). Therefore, by displacing the polarizing diffraction grating 23 in the optical axis direction, the distance between the convergence point of the laser light when not receiving the diffraction action and the convergence point of the laser light diffracted by the polarizing diffraction grating 23 ( The image height 1, 2) can be changed.

  This phenomenon similarly occurs when the polarizing diffraction grating 23 is arranged in the convergent light based on the same theory. In other words, if the polarizing diffraction grating 23 is disposed in the convergent light, the polarizing diffraction grating 23 is displaced in the optical axis direction, and the convergence point of the laser light when not receiving the diffractive action, and the polarizing diffraction grating 23. It is possible to change the distance (image height 1, 2) between the convergence points of the laser light diffracted by.

  Therefore, in the optical system of FIG. 1 as well, if the polarizing diffraction grating 23 is arranged in the convergent light, the polarizing diffraction grating 23 is displaced in the optical axis direction, so that the light receiving surface of the photodetector 25 can be displaced. The irradiation position of the laser beam for BD can be changed.

  For this reason, the polarizing diffraction grating 23 is disposed between the polarizing beam splitter 13 and the detection lens 24 in the optical system of FIG. As is clear from the above description, the arrangement position of the polarizing diffraction grating 23 is not limited to this, and may be set to any other position as long as the laser light is in the optical path in the state of convergent light.

  The description with reference to FIG. 4 is based on the premise that no aberration (astigmatism, coma, etc.) occurs in the laser light due to the angle of view α (diffraction angle). That is, the description with reference to FIG. 4 assumes an ideal lens L.

  However, when the lens L is not ideal, and an aberration (astigmatism, coma aberration, etc.) is generated in the laser beam due to the angle of view α (diffraction angle), the laser beam is concentrated at one point. The intensity distribution is not spread and has a certain spread. In this case, the height of the principal ray on the image plane changes according to the height at which the principal ray passes through the lens L.

  As apparent from FIG. 4, when the position of the polarizing diffraction grating 23 on the optical axis is changed, the height of the principal ray when passing through the lens L changes. Therefore, when the lens L is not ideal, the position of the principal ray on the image plane changes according to the displacement of the polarizing diffraction grating 23 on the optical axis, and accordingly, on the image plane. Since the intensity distribution of the laser light changes, a phenomenon equivalent to the displacement of the focal point on the image plane occurs.

  Thus, when the lens L is not ideal, even if the polarizing diffraction grating 23 is arranged in parallel light, the position of the polarizing diffraction grating 23 on the optical axis is changed to change the image. An effect equivalent to the displacement of the condensing point on the surface can be expressed. Therefore, even in the optical system of FIG. 1, the collimator lens 16 is not ideal, and when the field angle α (diffraction angle) causes aberrations (astigmatism, coma aberration, etc.) in the laser light. Even if the polarizing diffraction grating 23 is arranged in, for example, parallel light between the collimator lens 16 and the λ / 4 plate 18, the position of the polarizing diffraction grating 23 is adjusted so that the BD with respect to the BD sensor 252 can be obtained. The irradiation position of the laser beam can be adjusted.

  However, since the amount of adjustment in this case is smaller than that in the case where the polarizing diffraction grating 23 is arranged in the convergent light, in order to make the adjustment more smoothly, the polarizing diffraction grating 23 is used as shown in FIG. It is preferable to arrange in the convergent light.

  Although the embodiment of the present invention has been described above, the embodiment of the present invention is not limited to the above, and various other modifications are possible.

  For example, in the above embodiment, the present invention is applied to a reproduction-only compatible optical pickup device, but the present invention can also be applied to a recording / reproduction type compatible optical pickup device.

  FIG. 7 shows a configuration example of an optical system when the present invention is applied to a compatible recording / reproducing optical pickup device.

  In this optical system, a diffraction grating 28 is added compared to the case of FIG. Further, the sensor pattern of the photodetector 25 is changed as shown in FIG. That is, in this configuration example, a DPP (Differential Push Pull) method is used as a method for generating a tracking error signal. When the in-line DPP method is used, a diffraction grating in which the phase of the grating groove is adjusted can be used as the diffraction grating 28 (see, for example, Japanese Patent Application Laid-Open No. 2004-145915).

  In the configuration example of FIG. 7, the laser light from the semiconductor laser 11 is divided into a main beam and two sub beams by the diffraction grating 28. When a recording type HD is installed in the drive, the active polarization element 12 is driven and controlled so that the laser beam is incident on the polarization beam splitter 13 with S polarization. As a result, the main beam and the two sub beams are substantially totally reflected by the polarization beam splitter 13 and converged on the HD via the HD objective lens 19.

  Reflected light from the HD is incident on the polarization beam splitter 13 as P-polarized light by the action of the λ / 4 plate 18. As a result, the reflected light is substantially totally transmitted through the polarization beam splitter 13 and is incident on the polarizing diffraction element 23. In this case, since the reflected light is incident on the polarizing diffraction element 23 in the state of P-polarized light, the reflected light travels straight without being diffracted by the polarizing diffraction element 23 and enters the HD sensor 251 on the photodetector 25. Irradiated. Of the reflected light, the main beam is guided to the sensor 251a, and the two sub beams are guided to the sensors 251b and 251c, respectively.

  When a recording type BD is attached to the drive, the active polarization element 12 is driven and controlled so that the laser beam is incident on the polarization beam splitter 13 with P polarization. As a result, the main beam and the two sub beams pass through the polarization beam splitter 13 and are converged on the BD via the BD objective lens 20.

  Reflected light from the BD is incident on the polarization beam splitter 13 as S-polarized light by the action of the λ / 4 plate 18. As a result, the reflected light is substantially totally reflected by the polarization beam splitter 13 and is incident on the polarizing diffraction element 23. In this case, since the reflected light is incident on the polarizing diffraction element 23 in the S-polarized state, the path is bent due to the diffraction action by the polarizing diffraction element 23, and the reflected light is applied to the BD sensor 252 on the photodetector 25. Irradiated. Of the reflected light, the main beam is guided to the sensor 252a, and the two sub beams are guided to the sensors 252b and 252c, respectively.

  The present invention can also be applied to a compatible optical pickup apparatus that is compatible with CD (Compact Disc) and DVD (Digital Versatile Disc) in addition to HD and BD.

  FIG. 8 shows a configuration example of an optical system when the present invention is applied to an HD / BD / CD / DVD compatible optical pickup device.

  In this configuration example, semiconductor lasers 31 and 32, dichroic prisms 33 and 34, and an aperture limiting element 35 are added compared to the case of FIG. The HD objective lens 19 is designed so that, in addition to the HD laser light, the CD laser light and the DVD laser light can be properly converged on the CD and DVD. When the CD laser light is used, the aperture limiting element 35 limits the entrance pupil of the CD laser light to the HD objective lens 19.

  The semiconductor laser 31 emits red laser light (DVD laser light) having a wavelength of about 650 nm. The semiconductor laser 32 emits infrared laser light (CD laser light) having a wavelength of about 780 nm. The dichroic prism 33 reflects the DVD laser light emitted from the semiconductor laser 31 and transmits the CD laser light emitted from the semiconductor laser 32. The dichroic prism 34 reflects the DVD laser light and CD laser light emitted from the semiconductor lasers 31 and 32, and transmits the laser light (HD / BD laser light) emitted from the semiconductor laser 11.

  The positions of the semiconductor lasers 31 and 32 are adjusted so that the DVD laser beam and the CD laser beam are incident on the polarization beam splitter 13 as S-polarized light. The semiconductor lasers 31 and 32 and the dichroic prisms 33 and 34 are arranged so that the optical axes of the DVD laser light and the CD laser light when entering the polarization beam splitter 13 are aligned with the optical axes of the HD / BD laser light. The position has been adjusted.

  The aperture limiting element 35 blocks the outer periphery of only the CD laser light and limits the entrance pupil of the CD laser light to the HD objective lens 19. As the aperture limiting element 35, for example, a wavelength selective aperture limiting element can be used. In this case, the aperture limiting element 35 is provided with a wavelength-selective diffraction grating at the position of the outer periphery of the CD laser beam, whereby the outer periphery of the CD laser beam is diffused outward.

  In this configuration example, the operation when the HD / BD laser beam is used is the same as in the case of FIG. When DVD laser light or CD laser light is used, the laser light is incident on the polarization beam splitter 13 as S-polarized light, and therefore is substantially totally reflected by the polarization beam splitter 13 and guided to the HD objective lens 19. .

  Reflected light from the disc (DVD / CD) is incident on the polarization beam splitter 13 as P-polarized light by the action of the λ / 4 plate 18. For this reason, the reflected light passes through the polarization beam splitter 13 almost completely and enters the polarizing diffraction element 23. In this case, since the reflected light is incident on the polarizing diffraction element 23 in the P-polarized state, the reflected light travels straight without being diffracted by the polarizing diffraction element 23, and the HD sensor 251 (on the photodetector 25 ( (See FIG. 3A).

  In this configuration example, in addition to the HD / BD laser light, the DVD laser light and the CD laser light are incident on the polarizing diffraction element 23, so that the laser light in the blue wavelength band is P-polarized light. In addition to the case where the light is incident, the diffraction structure 232 is also formed so that the refractive index np of the diffractive structure 232 matches the refractive index n1 of the glass when laser light in the red wavelength band and the infrared wavelength band is incident as P-polarized light. It is necessary to select a birefringent material to constitute. That is, a birefringent material whose refractive index dispersion for the blue wavelength band, red wavelength band, and infrared wavelength band substantially matches the refractive index dispersion of glass is selected as the birefringent material constituting the diffractive structure 232.

  By the way, in the above-described embodiment, two sensor patterns (HD sensor 251 and BD sensor 252) for individually receiving the HD laser beam and the BD laser beam are arranged on the photodetector 25. The polarizing diffractive element 23 is adjusted so that the BD laser beam is appropriately irradiated onto the BD sensor 252. However, the HD laser beam and the BD laser beam are shared on the photodetector 25. It is also possible to arrange one sensor pattern for receiving light and adjust the polarizing diffraction element 23 so that the HD laser beam and the BD laser beam are appropriately irradiated onto the sensor pattern. .

  FIG. 9 shows a configuration example of the optical system in this case. In this configuration example, the sensor pattern on the photodetector 25 is the same as that of the optical system of FIG. 1 except that the sensor pattern is composed of only one sensor pattern (four-divided sensor) as shown in FIG. It is. However, in the optical system of FIG. 1, the position of the polarizing diffraction element 23 is adjusted so that the optical axis of the BD laser light is separated from the optical axis of the HD laser light. The position of the polarizing diffraction element 23 (the optical axis direction position and the rotational direction position) is adjusted so that the optical axis of the BD laser beam is brought closer to the optical axis.

  When the recording type optical system is used (see FIG. 7), the sensor pattern on the photodetector 25 is changed to that shown in FIG.

  In this configuration example, the sensor pattern disposed on the photodetector 25 is shared by the HD laser beam and the BD laser beam, so that the configuration of the photodetector 25 can be simplified. On the other hand, when the diffraction efficiency of the polarizing diffraction element 23 is not 100%, unnecessary diffracted light is irradiated on the sensor pattern, which may appear as noise in the sensor output. In order to avoid such an inconvenience, as shown in FIG. 1, the polarizing diffraction element 23 clearly separates the HD laser beam and the BD laser beam, and individually separates each laser beam into a sensor pattern. It is better to receive light at.

  In addition, the embodiment of the present invention can be variously modified as appropriate within the scope of the technical idea shown in the claims.

The figure which shows the optical system of the optical pick-up apparatus which concerns on embodiment The figure which shows the structure of the polarizing diffraction element which concerns on embodiment The figure which shows the structure of the photodetector which concerns on embodiment The figure explaining arrangement | positioning of the polarizing diffraction element which concerns on embodiment The figure explaining arrangement | positioning of the polarizing diffraction element which concerns on embodiment The figure explaining arrangement | positioning of the polarizing diffraction element which concerns on embodiment The figure which shows the optical system of the optical pick-up apparatus which concerns on the example of a change of embodiment The figure which shows the optical system of the optical pick-up apparatus which concerns on the example of a change of embodiment The figure which shows the optical system of the optical pick-up apparatus which concerns on the example of a change of embodiment The figure which shows the structure of the photodetector which concerns on the example of a change of embodiment. A diagram for explaining a conventional example

Explanation of symbols

11 Semiconductor laser (first light source)
12 Active polarization element (polarization conversion element)
13 Polarizing Beam Splitter 18 λ / 4 Plate 19 HD Objective Lens 20 BD Objective Lens 23 Polarizing Diffraction Element 25 Photodetector 31, 32 Semiconductor Laser (Second Light Source)
33, 34 Dichroic prism 251 HD sensor (sensor pattern)
252 BD sensor (sensor pattern)
253 HD / BD sensor (sensor pattern)

Claims (6)

A first light source that emits laser light;
A polarizing beam splitter on which the laser light emitted from the first light source is incident;
A polarization conversion element that switches a polarization direction of the laser light with respect to the polarization beam splitter according to a control signal;
A first objective lens that receives the first laser beam that has passed through the polarization beam splitter and converges the first laser beam on a recording medium;
A second objective lens that receives the second laser beam reflected by the polarization beam splitter and converges the second laser beam on a recording medium;
A λ / 4 plate disposed between the polarizing beam splitter and the first and second objective lenses;
A photodetector for receiving the first and second laser beams reflected by the disk;
Polarized light that is arranged between the λ / 4 plate and the photodetector and that exhibits a diffractive action corresponding to the polarization direction only in one of the first and second laser beams reflected by the disk. An diffractive element,
The polarizing diffractive element is positioned so that the first and second laser beams reflected by the disk are irradiated onto corresponding sensor patterns on the photodetector. Optical pickup device. In claim 1,
The photodetector individually includes a first sensor pattern that receives the first laser light and a second sensor pattern that receives the second laser light,
The polarization diffractive element is positioned so that the first and second laser beams reflected by the disk are irradiated onto the first and second sensor patterns, respectively.
An optical pickup device characterized by that. In claim 1,
The photodetector has a common sensor pattern that receives the first and second laser beams,
The polarization diffractive element is positioned so that the first and second laser beams reflected by the disk are irradiated onto the common sensor pattern.
An optical pickup device characterized by that. In any one of Claims 1 thru | or 3,
The polarization conversion element includes a first polarization direction in which the laser light is substantially totally transmitted through the polarization beam splitter, and a second polarization direction in which the laser light is substantially totally reflected by the polarization beam splitter. Switching the polarization direction of the laser light;
An optical pickup device characterized by that. In any one of Claims 1 thru | or 4,
The polarizing diffraction element is disposed on an optical path where the first and second laser beams reflected by the disk become convergent light.
An optical pickup device characterized by that. In any one of Claims 1 thru | or 5,
A second light source that emits laser light having a wavelength different from that of the laser light emitted from the first light source;
The laser light from the second light source is in a state in which the optical axis is aligned with the laser light from the first light source and the polarization direction is aligned with one of the first and second laser lights. Is incident on the polarizing beam splitter,
An optical pickup device characterized by that.

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