JP2008047199A - Optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup which can efficiently guide a laser beam to two objective lenses in a simple configuration without using a polarization conversion element. <P>SOLUTION: The laser beam emitted by the semiconductor laser 101 is circularly polarized on the λ/4 plate 103 to input to a beam splitting mirror 104. The half (S polarized component) of the input circularly polarized laser beam is reflected in the Y axis direction on a polarizing mirror plane 104a. The other half (P polarized component) passed through the polarizing mirror plane 104a is reflected in the Y axis direction on a mirror plane 104b. Those laser beams are input to the objective lens 111 for an HD and the objective lens 112 for a BD through the erecting mirrors 108, 109. The return beams respectively passing through the objective lenses are separated on the polarizing diffraction element 115 and radiated to each different position on the optical detector 116. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup device, and is particularly suitable for use in a compatible optical pickup device in which two or more objective lenses are arranged.

  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 light is in the first direction, the laser light is reflected in the direction toward the first objective lens 7 by the polarization beam splitter 4. 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 conventional configuration example, since the polarization conversion element 3 is separately required, there arises a problem that the cost of the optical system increases. Further, in order to switch the laser beam to be used, the polarization conversion element 3 must be switched at any time. For this reason, a configuration for actively controlling the polarization conversion element 3 is required on the drive side.

  Further, in this configuration example, since the laser beams that have passed through the respective objective lenses are incident on the photodetector system 9 in a state where the optical axes thereof coincide with each other, no separate means for separating the optical axes is provided. As long as these two laser beams are guided onto the same sensor pattern. In this case, the laser beam not used for reproduction becomes unnecessary light, which may adversely affect the reproduction signal.

  The present invention has been made to solve such a problem, and it is possible to guide a laser beam to two objective lenses with a simple configuration, and from a disk via these two objective lenses. It is an object of the present invention to provide an optical pickup device capable of smoothly guiding the reflected light of the light to the corresponding sensor pattern.

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

  According to the first aspect of the present invention, in the optical pickup device, a light source that emits laser light, a first λ / 4 plate that converts the laser light into circularly polarized light, and the laser light that has been converted into circularly polarized light are incident. A polarizing beam splitter, a first objective lens for converging the laser light reflected by the polarizing beam splitter on a recording medium, and a first objective lens for converging the laser light transmitted through the polarizing beam splitter on the recording medium. 2 objective lenses, a second λ / 4 plate disposed between the first objective lens and the polarization beam splitter, and a second λ / 4 plate disposed between the second objective lens and the polarization beam splitter. 3 λ / 4 plate, a photodetector for receiving the laser beam reflected by the recording medium, an optical path between the polarization beam splitter and the second λ / 4 plate, and the polarization beam splitting. And having a said third lambda / 4 plates of the optical path and the polarizing beam splitter and the polarizing diffraction element disposed on any one of the optical path of the light path between the light detector.

  According to a second aspect of the present invention, in the optical pickup device, a light source that emits laser light, a first λ / 4 plate that converts the laser light into circularly polarized light, and the laser light that has been converted into circularly polarized light are incident. A polarizing beam splitter, a mirror that reflects the laser light transmitted through the polarizing beam splitter in the same direction as the traveling direction of the laser light reflected by the polarizing beam splitter, and the laser reflected by the polarizing beam splitter A first objective lens for converging light onto the recording medium; a second objective lens for converging the laser light reflected by the mirror onto the recording medium; the first objective lens; and the polarizing beam splitter. A second λ / 4 plate disposed between the second objective lens and the polarization beam splitter, and a recording medium. A photodetector for receiving the laser beam reflected by the light beam, an optical path between the polarization beam splitter and the second λ / 4 plate, an optical path between the polarization beam splitter and the third λ / 4 plate, and the polarization A polarizing diffractive element is disposed in any one of the optical paths between the beam splitter and the photodetector.

  According to a third aspect of the present invention, in the optical pickup device according to the second aspect, the laser light reflected by the polarization beam splitter and the laser light reflected by the mirror are converted into the first and second objectives. It further comprises a rising mirror that reflects in the direction of the lens.

  According to a fourth aspect of the present invention, in the optical pickup device, a light source that emits laser light, a first λ / 4 plate that converts the laser light into circularly polarized light, and the laser light that has been converted into circularly polarized light are incident. A polarizing beam splitter, a mirror that reflects the laser light reflected by the polarizing beam splitter in the same direction as the traveling direction of the laser light that has passed through the polarizing beam splitter, and the laser light that has passed through the polarizing beam splitter. A first objective lens that converges on the recording medium, a second objective lens that converges the laser light reflected by the mirror on the recording medium, and between the first objective lens and the polarizing beam splitter A second λ / 4 plate disposed on the second objective lens, a third λ / 4 plate disposed between the second objective lens and the polarization beam splitter, and the recording medium. A photodetector for receiving the reflected laser beam; an optical path between the polarizing beam splitter and the second λ / 4 plate; an optical path between the polarizing beam splitter and the third λ / 4 plate; and the polarizing beam splitter. And a polarizing diffraction element arranged in any one of the optical paths between the optical detector and the photodetector.

According to a fifth aspect of the present invention, in the optical pickup device according to the fourth aspect, the laser light transmitted through the polarization beam splitter and the laser light reflected by the mirror are transmitted to the first and second objective lenses. Further comprising a rising mirror that reflects in the direction,
It is characterized by that.

  According to a sixth aspect of the present invention, in the optical pickup device according to any one of the second to fifth aspects, the polarizing beam splitter and the mirror are integrally formed.

  According to a seventh aspect of the invention, in the optical pickup device according to any one of the first to sixth aspects, the first λ / 4 plate has a spectral ratio of P-polarized light and S-polarized light of 1 in the polarization beam splitter. : 1 is adjusted.

  According to an eighth aspect of the present invention, in the optical pickup device according to any one of the first to sixth aspects, the first λ / 4 plate has a spectral ratio of P-polarized light and S-polarized light in the polarizing beam splitter. It is characterized by being adjusted to be balanced.

  According to the first aspect of the present invention, the laser beam is incident on the polarization beam splitter in a circularly polarized state by the optical action of the first λ / 4 plate. For this reason, the laser light is transmitted and reflected according to the spectral ratio of the P-polarized light and the S-polarized light in the polarization beam splitter. Therefore, the laser light emitted from the light source is distributed to the first objective lens and the second objective lens according to the spectral ratio of P-polarized light and S-polarized light in the polarization beam splitter.

  As described above, according to the first aspect of the present invention, the laser light is distributed to the first objective lens and the second objective lens by the optical action of the first λ / 4 plate and the polarization beam splitter. There is no need to provide a polarization conversion element. Since the λ / 4 plate is considerably less expensive than the polarization conversion element, even if the first λ / 4 plate is used separately as in the first aspect of the invention, the optical system can be compared with the conventional example. Cost can be suppressed. Further, according to the first aspect of the present invention, it is not necessary to actively control the polarization conversion element as in the above-described conventional example, so the burden on the drive side can be reduced.

  Further, according to the first aspect of the present invention, the light reflected from the disk via the first objective lens and the light reflected from the disk via the second objective lens are reflected on the photodetector by the polarizing diffraction element. Therefore, when recording / reproduction is performed using one objective lens, the reflected light via the other objective lens is incident on the sensor that receives the reflected light via the objective lens. Therefore, stable recording / reproducing operation can be realized.

  According to the invention of claim 2, as in the invention of claim 1 above, the laser light is converted into the first objective lens and the second objective lens by the optical action of the first λ / 4 plate and the polarization beam splitter. Therefore, it is not necessary to separately provide a polarization conversion element. For this reason, as in the first aspect of the invention, the cost of the optical system can be reduced, and the burden on the drive side can be reduced. In addition, by providing a polarizing diffraction element, when recording / reproduction is performed using one objective lens, the sensor that receives the reflected light that passes through the objective lens is reflected by the other objective lens. Light can be prevented from entering, and stable recording / reproducing operation can be realized.

  In addition, according to the invention of claim 3, since the optical system from the light source to the rising mirror can be arranged on a plane orthogonal to the optical axes of the first and second objective lenses, the optical pickup device Can be made thinner.

  According to a fourth aspect of the invention, as in the first and second aspects of the invention, the laser light is transmitted to the first objective lens and the second by the optical action of the first λ / 4 plate and the polarization beam splitter. Since the light is distributed to the objective lens, it is not necessary to separately provide a polarization conversion element. For this reason, as in the first and second aspects of the invention, the cost of the optical system can be reduced, and the burden on the drive side can be reduced. In addition, by providing a polarizing diffraction element, when recording / reproduction is performed using one objective lens, the sensor that receives the reflected light that passes through the objective lens is reflected by the other objective lens. Light can be prevented from entering, and stable recording / reproducing operation can be realized.

  In addition, according to the invention of claim 5, as in the invention of claim 3, the optical system from the light source to the rising mirror is arranged on a plane orthogonal to the optical axes of the first and second objective lenses. Therefore, the optical pickup device can be thinned.

  Further, if the polarizing beam splitter and the mirror are integrated as in the sixth aspect of the invention, the number of parts can be reduced, the optical system can be simplified, and the arrangement of the optical parts can be facilitated. .

  According to the invention of claim 7, the laser light from the light source is evenly distributed to the first objective lens and the second objective lens. In this case, the first λ / 4 plate is adjusted so that the laser beam is incident on the polarization beam splitter as circularly polarized light. According to the present invention, when recording and reproduction are performed using laser light from each objective lens, laser light in a limited output range can be smoothly distributed to each objective lens.

  According to the invention of claim 8, the laser light from the light source is disproportionately distributed between the first objective lens and the second objective lens. In this case, the first λ / 4 plate is adjusted so that the laser beam is incident on the polarization beam splitter as elliptically polarized light. Here, the degree of imbalance is adjusted from the following viewpoints.

  For example, when one objective lens is used for recording and the other is used exclusively for reproduction, it is preferable to distribute the laser light from the light source more with the objective lens used for recording. Even when both objective lenses are used exclusively for reproduction, there is a difference in the utilization efficiency of the laser light due to the difference in effective diameter and numerical aperture of the objective lens, resulting in a difference in the amount of spot light on the recording medium. May occur. In this case as well, it is preferable to adjust the amount of laser light distributed to each objective lens in order to optimize the amount of spot light. Note that the unbalance of the spot light amount is also caused by a difference in optical elements arranged in the optical path from the polarization beam splitter to each objective lens. Therefore, in this case as well, it is preferable to adjust the amount of laser light distributed to each objective lens in order to optimize the amount of spot light. Furthermore, the laser power required for recording / reproducing may differ from recording medium to recording medium. In such a case as well, each objective lens is irradiated with a laser beam having an appropriate power. It is necessary to adjust the amount of laser light to be distributed.

  The “imbalance of the spectral ratio between the P-polarized light and the S-polarized light” in the eighth aspect of the invention is adjusted so that the laser light having the appropriate power is distributed to each objective lens. For example, when the laser power required for recording / reproduction differs for each recording medium, the maximum value of the laser power required for the corresponding recording medium is set for the first and second objective lenses, The spectral ratio of P-polarized light and S-polarized light is set so as to be equal to the ratio between the maximum value of the laser power set for the first objective lens and the maximum value of the laser power set for the second objective lens. Of course, when other factors are taken into consideration, the spectral ratio of P-polarized light and S-polarized light is further adjusted accordingly.

  According to the invention of claim 8, by thus making the spectral ratio of the P-polarized light and the S-polarized light unbalanced, the laser light is efficiently distributed to each objective lens, whereby the target recording is performed. It is possible to irradiate the medium with laser light having an appropriate power.

The features of the present invention will become more apparent from the following description of embodiments. However, the following embodiments are merely illustrative examples, and the meanings of the terms of the present invention or each constituent element are not limited to those described in the following embodiments.

  Embodiments of the present invention will be described below with reference to the drawings. Note that this embodiment is a reproduction-only compatible optical pickup device that is compatible with HDDVD (High Definition Digital Versatile Disc) with a substrate thickness of 0.6 mm and BD (Blu-ray disc) with a substrate thickness of 0.1 mm. Is applied.

  First, FIG. 1 shows an optical system of an optical pickup device according to the embodiment. For the sake of convenience, the circuit side configuration (reproduction circuit 301, servo circuit 302, drive circuit 303) is also shown in FIG.

  As shown in the figure, the optical system of the optical pickup device has a semiconductor laser 101, a collimator lens 102, a λ / 4 plate 103, a spectroscopic mirror 104, a liquid crystal element 105, and λ / 4 plates 106 and 107. Mirrors 108 and 109, a holder 110, an HD objective lens 111, a BD objective lens 112, an objective lens actuator 113, an anamorphic lens 114, a polarizing diffraction element 115, and a photodetector 116 are provided.

  The semiconductor laser 101 emits a laser beam having a blue wavelength (about 405 nm). The collimator lens 102 converts the laser light incident from the semiconductor laser 101 into parallel light. The λ / 4 plate 103 converts laser light incident from the collimator lens 102 side into circularly polarized light.

  The spectroscopic mirror 104 is formed of a translucent material, and has a polarizing mirror surface 104a and a mirror surface 104b inside. The spectroscopic mirror 104 has a rectangular parallelepiped shape, and the side surface facing the λ / 4 plate 103 and the side surface facing the liquid crystal element 105 each have an optical axis of the laser light emitted from the semiconductor laser 101 (X axis in the figure). ) And an axis perpendicular to this (Y axis in the figure). The polarizing mirror surface 104a and the mirror surface 104b are arranged in a state inclined by 45 ° with respect to the optical axis of the laser light emitted from the semiconductor laser 101, respectively.

  Half of the circularly polarized laser light incident on the spectral mirror 104 from the λ / 4 plate 103 is reflected in the Y-axis direction by the polarizing mirror surface 104a. The remaining half of the laser light (P-polarized component) transmitted through the polarizing mirror surface 104a is reflected in the Y-axis direction by the mirror surface 104b.

  The liquid crystal element 105 changes the wavefront state of the laser light in accordance with the drive signal from the drive circuit 303, and corrects aberrations on the optical disc and the photodetector 116. Aberration correction (spherical aberration correction) using a liquid crystal element is described in, for example, Japanese Patent Application Laid-Open No. 10-269611.

  In the configuration example of FIG. 1, the polarization direction of laser light (incident laser light) incident on the liquid crystal element 105 from the spectroscopic mirror 104 side and the laser light (reflected laser light) incident on the liquid crystal element from the λ / 4 plates 106 and 107 side. Are orthogonal to each other by the action of the λ / 4 plates 106 and 107. For this reason, the liquid crystal element 105 is configured by stacking two liquid crystal elements for incident laser light and reflected laser light. The drive circuit 303 drives and controls each liquid crystal element so that the amplitude of the reproduction RF signal is optimized.

  A laser beam (hereinafter referred to as “HD incident laser beam”) traveling from the polarizing mirror surface 104a to the λ / 4 plate 106 is referred to as a laser beam (hereinafter referred to as “BD”) from the λ / 4 plate 107 to the mirror surface 104b. The direction of polarization coincides with that of the “reflected laser light” and the laser light (hereinafter referred to as “HD reflected laser light”) from the λ / 4 plate 106 toward the polarizing mirror surface 104a is λ from the mirror surface 104b. The direction of polarization coincides with laser light traveling to the / 4 plate 107 (hereinafter referred to as “BD incident laser light”). Therefore, when one (first liquid crystal element) of the two liquid crystal elements constituting the liquid crystal element 105 is for HD incident laser light and the other (second liquid crystal element) is for HD reflected laser light, BD Aberration correction for incident laser light and BD reflection laser light is performed using the first liquid crystal element for BD reflection laser light and the second liquid crystal element for BD incident laser light. As described above, the drive circuit 303 switches the control of the two liquid crystal elements included in the liquid crystal element 105 according to whether the used laser light is the HD laser light or the BD laser light.

  The λ / 4 plate 106 converts the HD incident laser light reflected by the polarizing mirror surface 104a into circularly polarized light, and the HD reflected laser light reflected by the disk is orthogonal to the polarization direction when entering the disk. Convert to linearly polarized light. As a result, the HD reflected laser light reflected by the disk becomes P-polarized light with respect to the polarizing mirror surface 104a, passes through the polarizing mirror surface 104a, and is guided to the photodetector 116.

  The λ / 4 plate 107 converts the BD incident laser light reflected by the mirror surface 104b into circularly polarized light and orthogonally intersects the polarization direction when the BD reflected laser light reflected by the disk is incident on the disk. Convert to linearly polarized light. As a result, the BD reflected laser light reflected by the disc becomes S-polarized light with respect to the polarizing mirror surface 104a, is reflected by the polarizing mirror surface 104a, and is guided to the photodetector 116.

  The rising mirrors 108 and 109 reflect the HD incident laser light and the BD incident laser light converted into circularly polarized light by the λ / 4 plates 106 and 107 in the directions of the objective lenses 111 and 112 (Z-axis direction in the figure). .

  The holder 110 integrally holds the HD objective lens 111 and the BD objective lens 112. The HD objective lens 111 is designed so that a laser beam with a blue wavelength can be properly converged on an HDDVD having a substrate thickness of 0.6 mm. Further, the BD objective lens 112 is designed so that the blue wavelength laser beam can be properly converged on the BD having a substrate thickness of 0.1 mm.

  The objective lens actuator 113 drives the holder 110 in the focus direction and the tracking direction according to the servo signal from the servo circuit 302. Thereby, the HD objective lens 111 and the BD objective lens 112 are integrally driven in the focus direction and the tracking direction. As the objective lens actuator 113, for example, a conventionally known electromagnetic drive type actuator is used.

  The anamorphic lens 114 converges the laser beam reflected by the disk on the photodetector 116. The anamorphic lens is composed of a condenser lens and a cylindrical lens, and introduces astigmatism into the reflected light from the disk.

  The polarizing diffractive element 115 does not give a diffractive action to the BD reflected laser light (S-polarized light) out of the reflected light from the disk, but gives a diffractive action to the HD reflected laser light (P-polarized light). Change the traveling direction of light by a certain angle. Details of the polarizing diffraction element 115 will be described later with reference to FIG.

  The photodetector 116 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 laser beam. The photodetector 116 is provided with two sensor patterns that individually receive the HD reflection laser light and the BD reflection laser light. Signals from the sensors are output to the reproduction circuit 301, the servo circuit 302, and the drive circuit 303.

  The reproduction circuit 301 calculates the sensor signal received from the photodetector 116 to derive a reproduction RF signal, and demodulates it to generate reproduction data.

  The servo circuit 302 performs arithmetic processing on the sensor signal received from the photodetector 116 to derive a tracking error signal and a focus error signal, generates a tracking servo signal and a focus servo signal based on the tracking error signal and the focus error signal, and supplies them to the objective lens actuator 113. Output.

  As described above, the drive circuit 303 sequentially monitors the reproduction RF signal and applies a servo to the liquid crystal element 105 so that the reproduction RF signal is optimized.

  FIG. 2 shows the configuration of the polarizing diffraction element 115. 1 is a cross-sectional structure when the polarizing diffraction element 115 in FIG. 1 is cut along a plane parallel to the XZ plane.

  As shown in the figure, the polarizing diffraction element 115 is configured by forming a blazed diffraction structure 115b made of a birefringent material on a transparent substrate 115a, and forming a glass layer 115c and a transparent substrate 115d thereon. . The blazed diffractive structure 115b is formed by forming a sawtooth hologram having a constant height at a constant pitch.

  Here, the refractive index of the blazed diffraction structure 115b 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 the laser light is incident on the polarizing diffraction element 115 as S-polarized light, there is no difference between the refractive index (ns) of the blazed diffraction structure 115b and the refractive index (n1) of the glass. The blazed diffraction structure 115b does not function as a diffraction grating. On the other hand, when the laser light is incident on the polarizing diffraction element 115 as P-polarized light, a difference occurs between the refractive index (np) of the blazed diffraction structure 115b and the refractive index (n1) of the glass. The type diffraction structure 115b 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 115 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 diffracting action is imparted to the laser light only when the laser light is incident on the polarizing diffraction element 115 as P-polarized light, BD reflected laser light (S-polarized light) out of the reflected light from the disk. ) Is not given a diffractive action, but is given a diffractive action to HD reflected laser light (P polarized light). Therefore, the traveling direction of the HD reflected laser light is changed by a certain angle when passing through the polarizing diffraction element 115, whereby the BD reflected laser light and the HD reflected laser light are separated, and on the photodetector 116, Irradiate onto different sensor patterns.

  FIG. 3 is a diagram illustrating the configuration of a sensor pattern arranged in the photodetector 116 and an arithmetic circuit that performs arithmetic processing on signals from each sensor. For convenience, the arithmetic circuit is shown only for one of the two sensor patterns. The arithmetic circuit for the other sensor pattern is the same as that shown in the figure.

  Note that the arithmetic circuit in the figure is arranged on a corresponding circuit among the reproduction circuit 301, the servo circuit 302, and the drive circuit 303. Alternatively, the arithmetic circuit shown in the figure may be arranged on the optical pickup device side, and the reproduction RF signal, tracking error signal, and focus error signal may be output to the corresponding circuits.

  As shown in the drawing, the photodetector 116 includes two quadrant sensors 20 and 30 each having a sensor area of A to D. The HD reflected laser beam and the BD reflected laser beam are converged on the four-divided sensors 20 and 30 so that their optical axes pass through the intersections of the dividing lines of the four-divided sensors 20 and 30, respectively. In the drawing, the condensed spot of each reflected light in the on-focus state is indicated by a dotted line.

  The operational amplifier circuit 201 describes signals output from the sensor areas A to D of the quadrant sensor 20 (hereinafter, the signals output from the sensor areas A, B, C, and D are denoted as A, B, C, and D). ), An operational amplification of (A + C) − (B + D) is executed to generate a focus error signal FE. The generated focus error signal FE is input to the servo circuit 302.

  The operational amplification circuit 202 performs operational amplification of A + B + C + D based on the signals output from the sensor areas A to D of the quadrant sensor 20 to generate a reproduction signal RF. The generated reproduction signal RF is input to the reproduction circuit 301 and the drive circuit 303.

  The operational amplification circuit 203 performs operational amplification of (A + B) − (C + D) based on signals output from the sensor areas A to D of the quadrant sensor 20 to generate a tracking error signal. The generated tracking error signal FE is input to the servo circuit 302.

  In the present embodiment, since the two laser beams separated by the spectroscopic mirror 104 are simultaneously incident on the HD objective lens 111 and the BD objective lens 112, the polarizing diffraction element 115 described above must be provided. For example, the HD reflected laser light passing through the HD objective lens 111 and the BD reflected laser light passing through the BD objective lens 112 are simultaneously guided to the same position on the photodetector 116. For this reason, when reproduction is performed using one objective lens, unnecessary reflected light that has passed through the other objective lens is guided to the photodetector 116, and this unnecessary reflected light is converted into a reproduction RF signal, The focus error signal and tracking error signal may be adversely affected.

  However, in the present embodiment, by providing the polarizing diffraction element 115, the HD reflected laser light and the BD reflected laser light are separated on the photodetector 116, and each reflected light converges on a different sensor pattern. Is done. Therefore, in this embodiment, when reproduction is performed using one objective lens, unnecessary reflected light via the other objective lens is incident on the sensor pattern that receives the reflected light via the objective lens. There is no possibility that the unnecessary reflected light will adversely affect the reproduction RF signal, focus error signal, and tracking error signal.

  As described above, according to the present embodiment, the laser light can be guided to the HD objective lens 111 and the BD objective lens 112 without using the polarization conversion element as in the conventional example. Therefore, the polarization conversion element can be omitted as compared with the conventional example, and the cost of the optical system can be suppressed. Further, since it is not necessary to actively control the polarization conversion element as in the conventional example, the burden on the drive side can be reduced.

  Further, according to the above embodiment, since the polarizing mirror surface 104a and the mirror surface 104b are integrally arranged in the spectroscopic mirror 104, the number of parts of the optical system is reduced as compared with the case where the polarizing beam splitter and the mirror are individually arranged. It is possible to reduce the number of optical components and facilitate the arrangement of the optical components.

  Further, according to the above embodiment, since the HD incident laser beam and the BD incident laser beam are reflected by the rising mirrors 108 and 109 in the direction of the HD objective lens 111 and the BD objective lens 112, the semiconductor laser The optical components from the 101 to the rising mirrors 108 and 109, the anamorphic lens 114 and the photodetector 116 can be arranged on one XY plane, so that the thickness dimension of the optical pickup device (dimension in the Z-axis direction) Can be reduced.

  Furthermore, according to the present embodiment, since the reflected light that has passed through the HD objective lens 111 and the reflected light that has passed through the BD objective lens 112 are separated on the photodetector 116, one objective lens is used. When reproduction is performed, unnecessary reflected light that has passed through the other objective lens does not enter the sensor pattern that receives reflected light that has passed through the objective lens. There is no possibility of adversely affecting the focus error signal and tracking error signal.

  In addition, embodiment which concerns on this invention is not limited above, In addition, a various change is possible suitably.

  For example, although the aberration correction (spherical aberration) is performed by the liquid crystal element 105 in the above embodiment, the aberration correction may be performed using the beam expander 123 as shown in FIG. In this case, the drive circuit 303 controls the actuator that drives the movable lens of the beam expander 123 so that the reproduction RF signal is the best.

  Further, as shown in FIG. 4, the polarization beam splitter 121 and the mirror 122 may be arranged separately. However, in this case, the number of parts of the optical system is increased as compared with the case where the polarizing mirror surface 104a and the mirror surface 104b are integrally disposed in the spectroscopic mirror 104 as in the above embodiment.

  In the above embodiment, an example in which the present invention is applied to a compatible optical pickup device for reproduction only has been shown. However, the present invention can also be applied to a compatible optical pickup device for recording / reproduction.

  FIG. 5 shows an optical system in this case. In this optical system, a diffraction grating 131 is added compared to FIG.

  The diffraction grating 131 splits the laser beam emitted from the semiconductor laser 101 into three beams. In the configuration example of FIG. 4, for example, a DPP (Differential Push-Pull) method is employed as a tracking error signal generation method.

  The liquid crystal element 105 may be provided with an electrode pattern for correcting coma aberration in addition to spherical aberration. The correction of coma using a liquid crystal element is described in, for example, Japanese Patent Laid-Open No. 10-289465.

  FIG. 6 is a diagram showing the sensor pattern on the photodetector 116 and the configuration of the arithmetic circuit. For convenience, the arithmetic circuit is shown only for one of the two sets of sensor patterns. The arithmetic circuit for the other set of sensor patterns is the same as that shown in the figure.

  Note that the arithmetic circuit in the figure is one in which the DPP method is used as a method for generating a tracking error signal. This arithmetic circuit is arranged on a corresponding circuit among the reproduction circuit 301, the servo circuit 302, and the drive circuit 303. Alternatively, the arithmetic circuit shown in the figure may be arranged on the optical pickup device side, and the reproduction RF signal, tracking error signal, and focus error signal may be output to the corresponding circuits.

  As shown in the figure, the photodetector 116 includes quadrant sensors 20a and 30a composed of sensor regions A to D, two-divided sensors 20b and 30b composed of E and F sensor regions, and G and H sensor regions. Two split sensors 20c and 30c are provided. Among these, the four-divided sensors 20 a and 30 a receive the main beam among the three beams divided by the diffraction grating 131. The two-divided sensors 20b and 30b receive a sub beam (preceding sub beam) preceding the main beam in the track scanning direction on the disk, and the two-divided sensors 20c and 30c are in the track scanning direction on the disk than the main beam. The sub-beam (following sub-beam) delayed after is received.

  The operational amplifier circuit 201 describes signals output from the sensor areas A to D of the quadrant sensor 20a (hereinafter, the signals output from the sensor areas A, B, C, and D are denoted as A, B, C, and D). ), An operational amplification of (A + C) − (B + D) is executed to generate a focus error signal FE. The generated focus error signal FE is input to the servo circuit 302.

  The operational amplification circuit 202 performs operational amplification of A + B + C + D based on signals output from the sensor areas A to D of the quadrant sensor 20a, and generates a reproduction signal RF. The generated reproduction signal RF is input to the reproduction circuit 301 and the drive circuit 303.

  The operational amplification circuit 203 performs operational amplification of (A + B) − (C + D) based on the signals output from the sensor areas A to D of the quadrant sensor 20a to generate a signal MPP.

  The operational amplifier circuit 204 includes signals output from the sensor areas E and F of the two-divided sensor 20b (hereinafter, each signal output from the sensor areas E and F will be referred to as E and F) and the two-divided sensor 20c. Based on the signals output from the sensor areas G and H (hereinafter, the signals output from the sensor areas G and H are described as G and H), the operation amplification of (E + G) − (F + H) is executed. The signal SPP is generated.

  The amplifier circuit 205 amplifies the signal SPP generated by the operational amplifier circuit 204 at a preset magnification.

  The operational amplifier circuit 206 subtracts the signal SPP generated by the operational amplifier circuit 204 from the signal MPP generated by the operational amplifier circuit 203 to generate a tracking error signal TE. The generated tracking error signal TE is input to the servo circuit 302.

  Also in this configuration example, as in the case of FIG. 1 and FIG. 4 described above, the polarizing diffractive element 115 is arranged, so that when recording / reproduction is performed using one objective lens, the objective lens passes through the objective lens. It is possible to prevent unnecessary reflected light from entering the sensor pattern that receives the reflected light via the other objective lens. Therefore, a smooth recording / reproducing operation can be realized.

  When only one of the HD incident laser light and the BD incident laser light is used for recording and the other is used exclusively for reproduction, the laser that uses the spectral ratio of P-polarized light and S-polarized light on the polarizing mirror surface 104a for recording. What is necessary is just to set so that the intensity | strength of light may become high. For example, when recording is performed with BD incident laser light and HD incident laser light is exclusively used for reproduction, the spectral ratio of the polarizing mirror surface 104a is set to P polarized light: S polarized light = 8: 2. As a result, the power of the BD incident laser light can be effectively increased within the output limit range of the semiconductor laser 101.

  Note that the spectral ratio on the polarizing mirror surface 104a can be adjusted by making the laser light incident on the polarizing mirror surface 104a as elliptically polarized light, as shown in FIG. As shown in the center of the figure, when the laser beam is incident on the polarizing mirror surface 104a as circularly polarized light, the spectral ratio at the polarizing mirror surface 104a is 1: 1. When the λ / 4 plate 103 is rotated around the laser optical axis from the center of the figure and the laser light is incident on the polarizing mirror surface 104a as elliptically polarized light, the ratio of the P-polarized component and the S-polarized component changes. As a result, the spectral ratio in the polarizing mirror surface 104a becomes unbalanced. In the case of the figure, when the laser light is incident on the polarization mirror surface 104a in the elliptically polarized state shown at both ends, the ratio of the P-polarized component and the S-polarized component becomes P-polarized: S-polarized light = 8: 2, and as a result, the semiconductor 80% of the laser light from the laser 101 is transmitted through the polarizing mirror surface 104a, and the remaining 20% is reflected by the polarizing mirror surface 104a. As a result, 80% of the laser light emitted from the semiconductor laser 101 can be incident on the BD objective lens 112.

  Even when the laser power required for recording / reproduction differs between BD and HD, the HD objective lens 111 and the BD objective lens 112 are converted into elliptically polarized laser light that is incident on the polarizing mirror surface 104a as described above. What is necessary is just to adjust the intensity | strength of the laser beam which injects into. For example, the maximum laser power required for HD (reproduction only, write once type, rewritable type, single recording layer type, multiple recording layers) is Pw1, BD (reproduction only, write once type, rewritable type, single recording layer) When the maximum value of the laser power required for the mold and the plurality of recording layers is Pw2, the intensity of the laser light incident on the HD objective lens 111 and the BD objective lens 112 is elliptically polarized light with HD: BD = Pw1: Pw2. Thus, the laser beam is made incident on the polarizing mirror surface 104a.

  In the above embodiment, the laser light transmitted through the polarizing mirror surface 104a is reflected by the mirror surface 104b. However, the laser light reflected by the polarizing mirror surface may be reflected by the mirror surface. it can.

  FIG. 8 is a diagram showing a configuration example of the optical system in this case.

  In this optical system, of the laser light incident on the spectroscopic mirror 104, the laser light (S-polarized component) reflected by the polarizing mirror surface 104a is reflected in the Y-axis direction by the mirror surface 104b. The laser light is converted into circularly polarized light by the λ / 4 plate 107, reflected by the rising mirror 109 in the Z-axis direction, and incident on the BD objective lens 112. The laser light transmitted through the polarizing mirror surface 104 a is converted into circularly polarized light by the λ / 4 plate 106, reflected by the rising mirror 108 in the Z-axis direction, and incident on the HD objective lens 111.

  Also in the configuration example of FIG. 8, the same effects as in the case of FIGS. 1 to 5 can be obtained. In the configuration example of FIG. 8, since the BD reflected laser light is incident on the polarizing diffraction element 115 as P-polarized light, the traveling direction of the BD reflected laser light is different from that in FIG. Will be changed by. In the configuration example of FIG. 8, when the traveling direction of the HD reflected laser light is changed, the blazed diffraction structure 115b shown in FIG. 2 may be made of a birefringent material that satisfies ns ≠ n1 and np = n1.

  1 to 8, the laser beam from the semiconductor laser 101 is incident on the polarization mirror surface 104a or the polarization beam splitter 121 from the X-axis direction, and the laser beam divided thereby is raised by the rising mirror 108. , 109 is reflected in the direction of the HD objective lens 111 and the BD objective lens 112 (Z-axis direction), but as shown in FIG. 9, the laser reflected by the polarizing mirror surface 104a and the mirror surface 104b. The light can be directly incident on the HD objective lens 111 and the BD objective lens 112 without passing through the rising mirrors 108 and 109. However, in this case, an arrangement space for the anamorphic lens 114 and the photodetector 116 is required in the Z-axis direction, so that the optical pickup device is hindered from being made thinner than the above embodiment.

  1 to 9, the polarizing diffraction element 115 is arranged between the anamorphic lens 114 and the photodetector 116. However, as shown in FIG. 10, it is between the liquid crystal element 105 and the λ / 4 plate 106. The polarizing diffractive element 140 can also be arranged on the front.

  In this case, since the HD incident laser light directed from the liquid crystal element 105 toward the λ / 4 plate 106 is S-polarized light, the HD incident laser light is not diffracted by the polarizing diffractive element 140, and the The diffractive action by the polarizing diffraction element 140 is imparted to the P-polarized HD reflected laser light that is directed. Also in this case, the traveling direction of the HD reflection laser light is changed by the polarizing diffraction element 140, and the irradiation positions of the HD reflection laser light and the BD reflection laser light on the photodetector 116 are different.

  In order to change the traveling direction of the BD reflection laser light, a polarizing diffraction element may be disposed between the liquid crystal element 105 and the λ / 4 plate 107. In this case, however, the blazed diffractive structure 115b shown in FIG. 2 must be made of a birefringent material satisfying ns ≠ n1 and np = n1 in view of providing a diffraction action to S-polarized laser light. .

  By the way, in the above-described embodiment, laser light having a blue wavelength is incident on the HD objective lens 111 and the objective lens 112 such as a BD, but the laser light incident on each objective lens is not limited thereto. It can be appropriately changed according to the specifications of the optical pickup device.

  In the present embodiment, as shown in FIG. 2, a polarizing diffractive element having a blazed diffractive structure is used. Instead, a polarizing diffractive element having a stepped diffractive structure is used. May be used. Note that the diffraction efficiency of the + 1st order light or the −1st order light can be increased more than the light of other orders even with the stepped diffraction structure. However, in this case, due to the diffraction efficiency, unnecessary order light may be incident on the photodetector as unnecessary light, which may adversely affect the detection signal.

  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 sensor pattern and arithmetic circuit of the photodetector which concern on embodiment The figure which shows the example of a change of the optical system of the optical pick-up apparatus which concerns on embodiment The figure which shows the example of a change of the optical system of the optical pick-up apparatus which concerns on embodiment The figure which shows the sensor pattern and arithmetic circuit of the photodetector which concern on embodiment The figure explaining the spectral ratio in the polarization mirror surface concerning an embodiment The figure which shows the example of a change of the optical system of the optical pick-up apparatus which concerns on embodiment The figure which shows the example of a change of the optical system of the optical pick-up apparatus which concerns on embodiment The figure which shows the example of a change of the optical system of the optical pick-up apparatus which concerns on embodiment A diagram for explaining a conventional example

Explanation of symbols

101 Semiconductor laser 103 λ / 4 plate (first λ / 4 plate)
104 Spectroscopic mirror 104a Polarizing mirror surface 104b Mirror surface 106 λ / 4 plate (second λ / 4 plate)
107 λ / 4 plate (third λ / 4 plate)
108 Rising Mirror 109 Rising Mirror 111 HD Objective Lens 112 BD Objective Lens 115 Polarizing Diffraction Element 116 Photodetector 121 Polarizing Beam Splitter 122 Mirror 140 Polarizing Diffraction Element

Claims (8)

A light source that emits laser light;
A first λ / 4 plate for converting the laser light into circularly polarized light;
A polarizing beam splitter on which the laser beam converted into circularly polarized light is incident;
A first objective lens that converges the laser light reflected by the polarizing beam splitter onto a recording medium;
A second objective lens that converges the laser light transmitted through the polarizing beam splitter onto a recording medium;
A second λ / 4 plate disposed between the first objective lens and the polarizing beam splitter;
A third λ / 4 plate disposed between the second objective lens and the polarizing beam splitter;
A photodetector for receiving the laser beam reflected by the recording medium;
Any one of an optical path between the polarizing beam splitter and the second λ / 4 plate, an optical path between the polarizing beam splitter and the third λ / 4 plate, and an optical path between the polarizing beam splitter and the photodetector. A polarizing diffractive element arranged in one optical path,
An optical pickup device characterized by that. A light source that emits laser light;
A first λ / 4 plate for converting the laser light into circularly polarized light;
A polarizing beam splitter on which the laser beam converted into circularly polarized light is incident;
A mirror that reflects the laser light transmitted through the polarizing beam splitter in the same direction as the traveling direction of the laser light reflected by the polarizing beam splitter;
A first objective lens that converges the laser light reflected by the polarizing beam splitter onto a recording medium;
A second objective lens for converging the laser beam reflected by the mirror on a recording medium;
A second λ / 4 plate disposed between the first objective lens and the polarizing beam splitter;
A third λ / 4 plate disposed between the second objective lens and the polarizing beam splitter;
A photodetector for receiving the laser beam reflected by the recording medium;
Any one of an optical path between the polarizing beam splitter and the second λ / 4 plate, an optical path between the polarizing beam splitter and the third λ / 4 plate, and an optical path between the polarizing beam splitter and the photodetector. A polarizing diffractive element arranged in one optical path,
An optical pickup device characterized by that. The optical pickup device according to claim 2,
A rising mirror that reflects the laser light reflected by the polarizing beam splitter and the laser light reflected by the mirror in the direction of the first and second objective lenses;
An optical pickup device characterized by that. A light source that emits laser light;
A first λ / 4 plate for converting the laser light into circularly polarized light;
A polarizing beam splitter on which the laser beam converted into circularly polarized light is incident;
A mirror that reflects the laser light reflected by the polarizing beam splitter in the same direction as the traveling direction of the laser light transmitted through the polarizing beam splitter;
A first objective lens that converges the laser light transmitted through the polarizing beam splitter onto a recording medium;
A second objective lens for converging the laser beam reflected by the mirror on a recording medium;
A second λ / 4 plate disposed between the first objective lens and the polarizing beam splitter;
A third λ / 4 plate disposed between the second objective lens and the polarizing beam splitter;
A photodetector for receiving the laser beam reflected by the recording medium;
Any one of an optical path between the polarizing beam splitter and the second λ / 4 plate, an optical path between the polarizing beam splitter and the third λ / 4 plate, and an optical path between the polarizing beam splitter and the photodetector. A polarizing diffractive element arranged in one optical path,
An optical pickup device characterized by that. The optical pickup device according to claim 4,
A rising mirror that reflects the laser light transmitted through the polarizing beam splitter and the laser light reflected by the mirror in the direction of the first and second objective lenses;
An optical pickup device characterized by that. The optical pickup device according to any one of claims 2 to 5,
The polarizing beam splitter and the mirror are formed integrally.
An optical pickup device characterized by that. The optical pickup device according to any one of claims 1 to 6,
The first λ / 4 plate is adjusted so that the spectral ratio of P-polarized light and S-polarized light in the polarization beam splitter is 1: 1.
An optical pickup device characterized by that. The optical pickup device according to any one of claims 1 to 6,
The first λ / 4 plate is adjusted so that the spectral ratio of P-polarized light and S-polarized light in the polarization beam splitter is unbalanced.
An optical pickup device characterized by that.

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