JP2008108386A - Optical pickup and optical disc drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup applicable to a plurality of optical discs each having different disc substrate thickness using a semiconductor laser having the same wavelength, which solves the problem that it takes a long time to determine the type of an optical disc since a predetermined number of disc determination operations are required to determine the optical disk according to possible disc types. <P>SOLUTION: Polarized states of a light beam are switched by a polarization rotation element provided in front of the semiconductor laser. The amplitude of a focus error signal or a sum signal for a polarized state is compared with a predetermined slice level for the purpose of determination. Thereby, an operation speed to determine an optical disc is increased compared with conventional techniques. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup and an optical disc apparatus, and more particularly to an optical disc discrimination operation.

  As background art in this technical field, there is, for example, JP-A-9-17003. The purpose of this publication is as follows: “There is little loss in the amount of light when splitting or switching the light beam incident on the objective lens, the beam switching mechanism is simple, there is no angle change at the time of switching, and one objective lens The objective of the present invention is to provide an optical pickup that can reduce the size of the device by using a driving device and that can also reduce the size of the signal detection unit and can easily handle a plurality of types of optical discs. As a means, (1) an objective lens driving device for converging a light beam emitted from a light source and mounting a plurality of objective lenses for irradiating the converged light onto a recording medium and controlling movement in a predetermined direction; A polarization direction conversion element that converts the polarization direction of the incident linearly polarized light, and first and second polarization components having different reflectances or emission directions depending on the polarization direction of the light beam. An optical pickup comprising: a light beam from the light source side divided by the polarization separation unit; the divided light beams are respectively incident on the plurality of objective lenses and reflected by the recording medium; Returning to the first polarization separation means, the light beam transmitted and reflected here is divided into light beams of different polarization directions by the second polarization separation means, and each light beam is divided into at least two light detectors. (2) the first polarization separation means is a polarization beam splitter, and the second polarization separation means is a Wollaston prism. (3) A light beam incident on a plurality of objective lenses by setting the polarization direction of the light beam converted by the polarization direction conversion element to a predetermined direction. Determining the division ratio, and (4) mounting a plurality of objective lenses for converging the light beam emitted from the light source and irradiating the converged light onto the recording medium, and controlling movement in a predetermined direction An optical pickup comprising: an objective lens driving device for driving; a polarization separating unit having a different reflectance depending on a polarization direction of the light beam; and a polarization direction converting element for converting the polarization direction of the light beam incident on the polarization separating unit. By switching the polarization direction of the light beam by the polarization direction conversion element, the objective lens among the plurality of objective lenses is switched and the light beam is transmitted through the polarization separation means. The light beam reflected by the recording medium is transmitted again through the polarization separation means, while the light beam reflected by the polarization separation means and reflected by the recording medium is reflected. The reflected light is reflected again by the polarization separating means, so that both reflected lights are received by a common photodetector, and (5) the polarization direction changing element is a half-wave plate. The polarization direction of the light beam is switched by inserting / removing the half-wave plate with respect to the optical path, and (6) the polarization direction conversion element is a half-wave plate, The polarization direction of the light beam is switched by rotating the half-wave plate by a predetermined angle. Is described.

JP-A-9-17003

  As a next generation optical disc, an optical disc system using a blue semiconductor laser such as a BD (Blu-ray Disc) or an HD DVD has been proposed. The BD and HD DVD are systems having the same semiconductor laser specifications but different disk physical specifications. For example, the substrate thickness of the disc is 0.1 mm for BD and 0.6 mm for HD DVD, and NA is 0.85 for BD and 0.6 for HD DVD. When trying to realize a compatible optical pickup compatible with any of the optical discs with different physical specifications, in the optical disc discrimination operation for first discriminating which disc is loaded, the respective optical discs are assumed in order. The discriminating operation needs to be repeated, which causes a problem that it takes time to discriminate the disc.

  However, in Patent Document 1 described above, consideration is given to the fact that it corresponds to optical disks with different physical specifications, but there is no description about shortening the time required for disc determination for a plurality of optical disks.

  An object of the present invention is to shorten the time required for discriminating optical disks.

  The above object can be achieved by, for example, the configuration described in the claims.

  According to the present invention, the time required for discriminating an optical disk can be shortened.

  Hereinafter, the configuration of an optical pickup as Example 1 of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of an optical pickup in Embodiment 1 of the present invention. In FIG. 1, a semiconductor laser 1 is a semiconductor laser that can oscillate at a wavelength of 405 nm band, and an oscillation wavelength at room temperature is 405 nm. The 405 nm band is a wavelength capable of recording / reproducing BD and HD DVD. FIG. 1 shows a state where a light beam having a wavelength of 405 nm is emitted. The semiconductor laser 1 emits a light beam so that the light beam emitted from the semiconductor laser 1 becomes a light beam in a polarization state (hereinafter referred to as P-polarized light) parallel to a plane parallel to the paper surface as indicated by an arrow in the figure. The rotational position is determined around the optical axis.

  The light beam emitted from the semiconductor laser 1 reaches the liquid crystal element 2 just before the semiconductor laser 1. Here, the liquid crystal element 2 is an element capable of rotating the polarization angle of the P-polarized light transmitted in accordance with an input signal from the liquid crystal element driving circuit 25 provided outside the optical pickup by about 90 degrees. When the switch of the liquid crystal element driving circuit 25 is turned on, the polarization direction of the light beam after passing through the liquid crystal element 2 is the same as the double circle in the figure where the P-polarized light is rotated by 90 degrees. The direction is vertical (hereinafter referred to as S-polarized light).

  The light beam transmitted through the liquid crystal element 2 reaches the diffraction grating 3. The diffraction grating 3 is for splitting an incident light beam into three light beams of zero-order light and ± first-order light to generate three light spots on the optical disk. It reaches PBS4 which is a polarization beam splitter. The PBS 4 has a cubic shape in which two triangular prisms are combined, and a film surface 4a that forms an angle of 45 ° with respect to the emission optical axis of the light beam emitted from the semiconductor laser 1 is formed therein. . The film surface 4a reflects about 100% of the S-polarized component of the light beam having a wavelength of 405 nm as described later. On the other hand, about 100% of the P-polarized light component is transmitted. For this reason, in the light beam that has reached the PBS 4, the S-polarized component is reflected in the 90 ° direction with respect to the incident direction, and the P-polarized component is transmitted by an amount corresponding to the polarization state.

  The light beam reflected on the film surface 4 a of the PBS 4 is converted into a parallel light beam by the collimating lens 5. The light beam emitted from the collimating lens 5 is transmitted through the quarter-wave plate 6. Here, the light beam that has passed through the collimating lens 4 passes through the quarter-wave plate 6, and then the optical axis of the light beam 12 is converted with respect to the surface of the optical disk by the rising mirror 7. The incident angle is set to be substantially perpendicular. The light beam 12 emitted from the rising mirror 7 enters the objective lens 8. The objective lens 8 is focused on the information recording surface 14 of the first optical disc 13 having a substrate thickness of 0.1 mm such as BD, for example, when a light beam 12 having a wavelength of 405 nm is incident as parallel light. It is a lens with possible characteristics. The objective lens 8 is held by an actuator 9 integrated with the drive coil 10, and a magnet 11 is disposed at a position facing the drive coil 10. Therefore, it is possible to move the objective lens 8 in a substantially radial direction of the optical disk 13 and a direction perpendicular to the disk surface by energizing the drive coil 10 and generating a driving force due to a reaction force from the magnet 11. Yes.

  The light beam reflected from the optical disk 13 returns to the quarter-wave plate 6 through the objective lens 8 and the rising mirror 7 through the same optical path as that of the outward light in the opposite direction to the outward light. Thereafter, the light beam enters the collimating lens 5, and the collimating lens 5 converts the light beam from parallel light into convergent light and reaches the PBS 4. Although the details will be described later, the return light beam that has reached the PBS 4 passes through the film surface 4 a inside the PBS 4, so that the return light beam is directed to the detection lens 23.

  Here, the light beam passing through the PBS 4 has already become convergent light by passing through the collimating lens 5. The detection lens 23 is a lens for enlarging the combined focal length on the detection system side. Since one of the two surfaces is a concave surface and the other is a cylindrical surface, light is transmitted when passing through the detection lens 23. Astigmatism is given to the beam. The light beam is focused on a predetermined light detection surface of the photodetector 24 after passing through the detection lens 23. The photodetector 24 can output a servo signal, a reproduction signal, and the like from the optical disc 13 from the received light beam.

  On the other hand, when the polarization direction of the light beam after passing through the liquid crystal element 2 is set to remain as P-polarized light, the polarization state of the light beam that passes through the diffraction grating 3 and reaches the PBS 4 is P-polarized light. As described above, the PBS 4 transmits about 100% of the P-polarized light component. Therefore, the P-polarized light beam that has reached the PBS 4 passes through the PBS 4.

  The light beam transmitted through and emitted from the film surface 4a of the PBS 4 is converted into the optical axis direction of the light beam by 90 degrees by the reflection surface set to 45 degrees with respect to the optical axis of the light beam inside the reflection prism 15. The collimating lens 16 is reached. In the collimating lens 16, the light beam is converted into a substantially parallel light beam, and the light beam emitted from the collimating lens 16 is transmitted through the quarter-wave plate 17. Here, the light beam after passing through the quarter-wave plate 17 is set so that the optical axis of the light beam is converted by 90 degrees by the rising mirror 7 and the optical axis of the light beam is directed in the surface direction of the optical disk. The light beam 20 emitted from the rising mirror 18 enters the objective lens 19. The objective lens 19 is focused on the information recording surface 22 of the second optical disc 21 having a substrate thickness of 0.6 mm, such as HD DVD, for example, when a 405 nm band light beam 20 is incident as parallel light. It is a lens with a possible function. The objective lens 19 is held by an actuator 9 integrated with the drive coil 10, and a magnet 11 is disposed at a position facing the drive coil 10. Therefore, by energizing the drive coil 10 and generating a driving force due to a reaction force from the magnet 11, the objective lens 19 can be moved in a substantially radial direction of the optical disc 21 and in a direction perpendicular to the disc surface. Yes. In the optical pickup of the first embodiment, since the objective lens 8 and the objective lens 19 are integrally held by the common actuator 9, the objective lens 8 and the objective lens 19 are integrally formed by energizing the drive coil 10. It will be driven.

  The light beam reflected from the optical disk 21 returns to the quarter-wave plate 17 through the objective lens 19 and the rising mirror 18 through the same optical path as the forward light in the reverse direction. Thereafter, the light beam enters the collimating lens 16, the light beam is converted from parallel light into convergent light by the collimating lens 16, and the optical axis direction of the 90 ° light beam is converted by the reflecting prism 15 before reaching the PBS 4. . As will be described in detail later, the return light beam from the second optical disk that has reached the PBS 4 is reflected by the film surface 4 a inside the PBS 4, so that the return light beam is directed toward the detection lens 23.

  Here, the light beam passing through the PBS 4 has already become convergent light by passing through the collimating lens 16. As described above, the detection lens 23 is a lens in which one of the two surfaces is a concave surface and the other is a cylindrical surface. Therefore, astigmatism is given to the light beam when passing through the detection lens 23. Will be. Thereafter, the light beam passes through the detection lens 23 and is then condensed on a predetermined light detection surface of the photodetector 24. The detection lens 23 is a lens for enlarging the combined focal length on the detection system side. The photodetector 24 can output a servo signal, a reproduction signal, and the like from the optical disc 13 from the received light beam.

  As described above, the optical pickup 26 is composed of a combination of one semiconductor laser, a liquid crystal element that rotates polarized light, PBS, a plurality of objective lenses, and one photodetector.

  Next, the laser chip mounted on the semiconductor laser and the polarization will be described with reference to FIG. In FIG. 2, a laser chip 27 emits a 405 nm band light beam, is mounted on a substrate 29, and is mounted inside the semiconductor laser 1 described in FIG. An active layer 28 is formed inside the laser chip 27, and a light beam is emitted from the end face of the active layer. A light beam in the 405 nm band emitted from the end face of the active layer 28 in the laser chip 27 in a direction substantially parallel to the longitudinal direction of the laser chip 27 has a direction θh (horizontal) parallel to the active layer 28 with respect to the optical axis of the light beam. The spread angle in the direction θv (vertical direction) perpendicular to the active layer 28 is wide. For example, the spread angles are approximately 9 ° and 18 °, and the light beam spread 30 has an elliptical intensity distribution that is long in the θv direction. Here, the vibration plane of the light beam emitted from the laser chip 27 is substantially the same as the plane parallel to the active layer 28, that is, the θh direction, and is so-called P-polarized light that vibrates in the direction indicated by the arrow in the figure. The polarization state is.

  Next, the operation of the liquid crystal element will be described with reference to FIG. In FIG. 3, the liquid crystal element 2 is polarized light that can convert P-polarized light transmitted through the liquid crystal element 2 into S-polarized light whose polarization plane is rotated by 90 degrees with respect to the optical axis in conjunction with the on / off of an electric signal from the outside. It is a rotating element. Since the structure of the element itself has little relation to the present invention, a detailed description is omitted here.

  In FIG. 3A, the switch 25 is in an off state, and the liquid crystal element 2 is not energized from the outside. In this state, since no electrical action is generated in the liquid crystal element 2, the P-polarized light incident from the incident side passes through the liquid crystal element 2 as it is and is emitted as P-polarized light from the emission side. On the other hand, in FIG. 3B, the switch 25 indicates the on state, and the liquid crystal element 2 is in an electrically operated state. In this state, the P-polarized light that has entered from the incident side has its polarization plane rotated by 90 degrees within the liquid crystal element 2 and is emitted as an S-polarized light beam from the emission side. As described above, in the liquid crystal element 2, the output polarization can be rotated by 90 degrees with respect to the incident polarization by turning on / off the energized state. This liquid crystal element rotates the polarization plane of the light beam, and can ensure a transmittance of 95% or more regardless of the polarization state of the emitted light beam.

  FIG. 4 is a diagram showing the characteristics of the membrane surface 4a of PBS4. In FIG. 4, the horizontal axis indicates the wavelength of the light beam incident on the film surface 4a, and the vertical axis indicates the transmittance of the incident light beam. On the film surface 4a arranged at an angle of 45 degrees with respect to the light beam, approximately 100% of light is transmitted at around 405 nm in the case of a P-polarized light beam, and almost at 405 nm for an S-polarized light beam. It has the characteristic of not transmitting light. Therefore, for the light beam near 405 nm, the P-polarized light is hardly reflected and transmitted, and the S-polarized light is reflected by about 100%. That is, the P-polarized light and the S-polarized light are substantially separated by the film surface 4a and are transmitted and reflected.

  Next, the polarization state of the light beam in the optical pickup will be described with reference to FIGS.

  FIG. 5 is a diagram showing a polarization state when the first optical disc is being reproduced. Note that each component in FIG. 5 has already been described with reference to FIG. In FIG. 5, the light beam emitted from the semiconductor laser 1 enters the liquid crystal element 2. When the first optical disk 13 is reproduced, by turning on the switch of the liquid crystal element driving circuit 25, the polarization state of the light beam passing through the liquid crystal element 2 is changed to P parallel to the paper surface indicated by the arrow in the figure. The polarized light is rotated to S-polarized light perpendicular to the paper surface indicated by a double circle in the figure. Thereafter, the light beam is branched into three light beams of 0th order and ± 1st order by the diffraction grating 3 and reaches the PBS 4. Since the S-polarized light reflects about 100% in the PBS 4, the light beam is reflected by the film surface 4 a of the PBS 4 in the S-polarized state and exits the PBS 4. The S-polarized light beam passes through the collimating lens and reaches the quarter-wave plate 6. In the quarter-wave plate 6, the polarization state of the light beam is converted into circularly polarized light, reflected by the rising mirror 7, and then incident on the objective lens 8. Thereafter, the light is reflected by the recording surface 14 of the first disk 13 and again reaches the quarter-wave plate 6 through the objective lens 8 and the rising mirror 7 in a circularly polarized state. In the return path, when passing through the quarter-wave plate 6, the zero-order light is converted into linearly polarized light in a direction orthogonal to the forward path. That is, it becomes P polarized light which is a polarization direction parallel to the paper surface indicated by an arrow in the drawing. Thereafter, the light beam enters the collimating lens 5 and is converted from parallel light to convergent light by the collimating lens 5, but reaches the PBS 4 while maintaining the polarization state as P-polarized light. As described above, since the film surface 4a of the PBS 4 transmits about 100% of the P-polarized light beam, the reflected light from the first optical disk passes through the PBS 4 and is emitted toward the detection lens 23 and the photodetector 24. To do. That is, in the PBS 4 of FIG. 5, the forward light beam is reflected because of S polarization, and the return light is transmitted because of P polarization.

  Next, the polarization state when the second optical disc is reproduced will be described with reference to FIG.

  Note that each component shown in FIG. 6 has already been described with reference to FIG. In FIG. 6, the light beam emitted from the semiconductor laser 1 enters the polarization rotation element 2. When reproducing the second optical disc 21, the polarization state of the light beam passing through the liquid crystal element 2 is changed to P parallel to the paper surface indicated by the arrow in the figure by turning off the switch of the liquid crystal element drive circuit 25. It passes through the liquid crystal element while being polarized. Thereafter, the light beam is branched into three light beams of 0th order and ± 1st order by the diffraction grating 3 and reaches the PBS 4. Since approximately 100% of the P-polarized light is transmitted through the PBS 4, the light beam passes through the film surface 4a of the PBS 4 in the P-polarized state and exits the PBS 4. The P-polarized light beam is converted 90 degrees in the optical axis direction by the reflecting prism 15, and then reaches the quarter-wave plate 17 through the collimating lens 16. In the quarter-wave plate 17, the polarization state of the light beam is converted into circularly polarized light, reflected by the rising mirror 18, and then incident on the objective lens 19. Thereafter, the light is reflected by the recording surface 22 of the second disk 21 and again reaches the quarter-wave plate 17 through the objective lens 19 and the rising mirror 18 in the circularly polarized state. In the return path, when passing through the quarter-wave plate 17, the 0th-order light is converted into linearly polarized light in a direction orthogonal to the forward path. That is, the S polarization is a polarization direction perpendicular to the paper surface indicated by a double circle in the drawing. Thereafter, the light beam enters the collimating lens 16 and is converted from parallel light to convergent light by the collimating lens 16, but reaches the PBS 4 while maintaining the polarization state as S-polarized light. As described above, since the film surface 4a of the PBS 4 reflects the S-polarized light beam by about 100%, the reflected light from the second optical disk reflects the PBS 4 and exits toward the detection lens 23 and the photodetector 24. To do. That is, in the PBS 4 of FIG. 6, the forward light beam is transmitted because of P-polarized light, and the return light is transmitted because of S-polarized light.

  As described above, in the first embodiment, in the liquid crystal element 2, the polarization direction is set to S-polarized light or P-polarized light, so that in the case of S-polarized light, the light beam is guided to the first objective lens 8 side. It is possible to guide the light beam to the objective lens 19 side of 2 and detect the reflected light from the optical disk with a photodetector in any case.

  Next, a focus error signal and a sum signal at the time of disc reproduction will be described.

  FIG. 7 shows a state where the optical disk is reproduced by the first objective lens. In the case where the first optical disk 13 is reproduced with respect to the objective lens 8, the light beam 12 is incident on the first objective lens 8 as substantially parallel light, for example, a first BD which is a BD. It is possible to focus the light beam on the recording surface 14 having a disc substrate thickness of 0.1 mm on the optical disc. On the other hand, when the second optical disc made of HD DVD having a disc substrate thickness which is not optimal with respect to the first objective lens 8, for example, the disc substrate thickness is 0.6 mm, is reproduced. Since the light beam 12 incident on the light 8 as parallel light cannot be condensed on the recording surface 27 as shown by the broken line in the figure, the reflected light from the first optical disk is parallel to the first objective lens in the same way as the forward path. The light beam cannot be returned and becomes like a light beam 28 shown by a broken line in the figure. Therefore, the signal detected by the photodetector when reproducing the second optical disk is detected because the light beam is blurred compared with the optimum state, compared with the case where the first optical disk is reproduced. The signal itself becomes smaller.

  FIG. 8 shows a focus error signal and a sum signal when the optical disk is reproduced by the first objective lens. The horizontal axis shows time, and the vertical axis shows the signal level. FIG. 8A shows a case where the first optical disk is reproduced, and both the focus error signal and the sum signal have sufficient signal levels. On the other hand, FIG. 8B shows a case where the second optical disk is reproduced. Since the light beam at the photodetector is blurred, both the focus error signal and the sum signal have low signal levels. Become.

  FIG. 9 shows a state where the optical disk is reproduced by the second objective lens. When the second optical disk 21 is reproduced with respect to the objective lens 19, the light beam 20 is incident on the second objective lens 19 as substantially parallel light, so that the second optical disk 21 is, for example, an HD DVD. It is possible to focus the light beam on the recording surface 22 having a disc substrate thickness of 0.6 mm on the optical disc. On the other hand, when the disc substrate thickness is not optimal with respect to the second objective lens 19, for example, when the first optical disc made of BD having a disc substrate thickness of 0.1 mm is reproduced, the second objective lens 19 is reproduced. Since the light beam 20 that is incident as parallel light on the recording surface 29 cannot be condensed on the recording surface 29 as shown by the broken line in the figure, the reflected light from the first optical disk is the same parallel light as the forward path through the second objective lens. In this state, the light beam 30 cannot be returned and becomes a broken light beam 30 in the figure. Therefore, compared with the case where the second optical disk is reproduced, the signal detected by the photodetector when reproducing the first optical disk is detected because the light beam is blurred compared with the optimum state. The signal itself becomes smaller.

  FIG. 10 shows a focus error signal and a sum signal when the optical disk is reproduced by the second objective lens. The horizontal axis shows time, and the vertical axis shows the signal level. FIG. 10A shows a case where the second optical disk is reproduced, and both the focus error signal and the sum signal have sufficient signal levels. On the other hand, FIG. 10B shows a case where the first optical disk is reproduced. Since the light beam at the photodetector is blurred, both the focus error signal and the sum signal have low signal levels. Become.

  Next, the relationship among the liquid crystal drive signal, the focus error signal, and the sum signal will be described.

  FIG. 11 shows the relationship between the liquid crystal drive signal, the focus error signal, and the sum signal when various disks are reproduced. 11A shows the case where the first optical disk is played back, FIG. 11B shows the case where the second optical disk is played back, FIG. 11C shows the case where other optical disks are played back, and FIG. In other cases, the horizontal axis represents time, and the vertical axis represents signal amplitude. When the first optical disk in FIG. 11A is reproduced, the reflected light from the first optical disk can be optimally detected as described above by turning on the liquid crystal drive signal. Therefore, only when the liquid crystal drive signal is on, a focus error signal or sum signal exceeding a preset slice level can be detected. On the other hand, when the liquid crystal drive signal is off, the reflected light from the optical disc cannot be detected sufficiently, and a focus error signal or sum signal exceeding the slice level cannot be detected. Therefore, when a focus error signal or sum signal exceeding the slice level is detected when the liquid crystal drive signal is on, the optical disc being reproduced has the characteristics of the first optical disc. Can be determined. When the second optical disk of FIG. 11B is reproduced, only when the liquid crystal drive signal is turned off, a focus error signal or sum signal exceeding a preset slice level can be detected. When is turned off, a focus error signal or sum signal exceeding the slice level cannot be detected. Therefore, it is possible to determine whether or not the optical disc being reproduced has the characteristics of the second optical disc by determining the level of the focus error signal and the sum signal when the liquid crystal drive signal is off. When reproducing an optical disc having another thickness of the disc substrate shown in FIG. 11C, the light beam that can be detected by the photodetector is blurred regardless of whether the liquid crystal drive signal is on or off. However, it is impossible to detect a focus error signal or a sum signal that exceeds the slice level. That is, it is possible to discriminate the optical disc being reproduced by determining the on / off state of the liquid crystal drive signal and the level of the focus error signal or the sum signal. As shown in FIG. 11 (d), when the first optical disk is reproduced, the operation time in the on / off state of the liquid crystal drive signal is switched to be shorter than the period of the focus error signal. With such a configuration, when the objective lens is in the vicinity of the focal position with respect to each optical disc, the liquid crystal element can be set to two operation states of an on state and an off state. The level of the focus error signal or the sum signal can be determined by moving the objective lens in the focus direction, and the discriminating operation of the optical disc being played back can be performed in a shorter time.

  In this embodiment, it is assumed that there is one photodetector. By using one photodetector as described above, there is an advantage that the reflected light from the optical disk can be obtained from either the objective lens 1 or the objective lens 2 without performing any switching operation by the photodetector. .

  Next, an optical disc discrimination sequence will be described.

  FIG. 12 shows an optical disc discrimination sequence. After the optical disk is mounted on a turntable (not shown), the optical disk is rotated and the laser is turned on. Thereafter, the actuator equipped with the objective lens is vibrated in the focus direction, and the drive signal for driving the liquid crystal element is turned on or off. In this case, the drive signal ON / OFF timing of the liquid crystal element is set to several milliseconds to several tens of milliseconds. This is a value close to the upper limit of the operation speed of the liquid crystal element. Simultaneously with the on / off driving of the liquid crystal element, the focus error signal and the sum signal are detected, and whether the level of each detected signal is higher than a preset slice level and the driving timing of the liquid crystal element It is determined whether it is synchronized with. Based on the determination result, the optical disc is discriminated whether it is the first optical disc, the second optical disc, or any other optical disc, and the optical disc discrimination sequence is terminated.

  As described above, in the present invention, the polarization state of the light beam is switched by driving a liquid crystal element in front of the semiconductor laser at high speed, and the liquid crystal element drive signal used for switching the polarization state is turned on. By monitoring the / off state and the signal level of the focus error signal and the sum signal, it is possible to discriminate the loaded optical disc in a single disc discriminating operation in a short time.

  Next, an optical disk apparatus equipped with the optical pickup of Example 1 will be described. FIG. 13 is a schematic block diagram of an optical disc apparatus equipped with an optical pickup according to an embodiment of the present invention. A part of the signal detected by the optical pickup 26 is sent to the optical disc discrimination circuit 51. The optical disc discriminating operation in the optical disc discriminating circuit 51 is performed by comparing the on / off state of the drive signal output from the liquid crystal drive circuit 60 with the slice level in which the signal levels of the focus error signal and the sum signal are set in advance. Is. The optical disc discrimination result is sent to the control circuit 54. Further, a part of the detection signal detected by the optical pickup 26 is sent to the servo signal generation circuit 52 or the information signal detection circuit 53. The servo signal generation circuit 52 generates a focus error signal and a tracking error signal suitable for the optical disc 13 from various signals detected by the optical pickup 26 and sends them to the control circuit 54. On the other hand, the information signal detection circuit 53 detects the information signal recorded on the optical disc 13 from the detection signal of the optical pickup 26 and outputs it to the reproduction signal output terminal. The control circuit 54 sets the optical disc 13 based on the signal from the optical disc discrimination circuit 51, and in response to the focus error signal and tracking error signal generated by the servo signal generation circuit 52, the objective lens drive signal is supplied to the actuator. This is sent to the drive circuit 55. Based on this objective lens drive signal, the actuator drive circuit 55 drives the actuator 10 in the optical pickup 26 to control the positions of the objective lens 8 and the objective lens 19. The control circuit 54 controls the position of the optical pickup 26 in the access direction by the access control circuit 56, and controls the rotation of the spindle motor 58 by the spindle motor control circuit 57 to rotate the disk 13.

  Further, the control circuit 54 drives the laser lighting circuit 59 so that the semiconductor laser 1 mounted on the optical pickup 26 is appropriately lit according to the optical disk 13 to realize a recording / reproducing operation in the optical disk device. . The control circuit 54 turns on / off the switch 25 of the polarization rotation element 2 based on the discrimination result of the optical disc discrimination circuit 51. As a result, the polarization state of the light beam in the optical pickup 26 can be optimally controlled, and good signals can be detected from the optical disc 13.

In the first embodiment of the present invention described above, the optical disk 13 is irradiated with S-polarized light and the optical disk 21 is irradiated with P-polarized light. However, the present invention limits the polarization state of each disk. Needless to say, the arrangement of the objective lens 8 and the objective lens 19 may be changed to use a different polarization state depending on the configuration of the optical system. In the description of the first embodiment, the liquid crystal element is used to switch the polarization state of the light beam. However, the liquid crystal element is not necessarily used as long as the polarization state of the light beam can be selectively switched. But it doesn't matter. For example, the polarization state of the light beam may be switched by mechanically moving the position of a wave plate element having two different wave plate characteristics.

The figure which shows the structure of the optical pick-up in Example 1. FIG. Diagram showing laser chip and polarization mounted on semiconductor laser Diagram showing the operation of the liquid crystal element Diagram showing the characteristics of the membrane surface of PBS The figure which shows the polarization state at the time of reproducing | regenerating the 1st optical disk The figure which shows the polarization state at the time of reproducing | regenerating the 2nd optical disk The figure which shows the state at the time of reproducing | regenerating an optical disk in a 1st objective lens The figure which shows the focus error signal and sum signal at the time of reproducing | regenerating an optical disk in a 1st objective lens The figure which shows the state at the time of reproducing | regenerating an optical disk in a 2nd objective lens The figure which shows a focus error signal and a sum signal at the time of reproducing | regenerating an optical disk in a 2nd objective lens The figure which shows the relationship between the liquid crystal drive signal, the focus error signal, and the sum signal when playing various discs Diagram showing optical disc discrimination sequence Optical disc apparatus equipped with the optical pickup of Example 1

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Liquid crystal element, 4 ... PBS, 5, 16 ... Collimator lens,
6, 17 ... quarter-wave plate, 8, 19 ... objective lens, 13, 21 ... optical disc,
24 ... photodetector, 25 ... liquid crystal element drive circuit, 26 ... optical pickup

Claims (11)

An optical pickup that emits light to an optical disc and receives reflected light from the optical disc,
A laser light source;
A polarization rotation element capable of rotationally controlling the polarization direction of the light beam emitted from the laser light source;
A light branching element disposed at a position after the polarization rotation element as viewed from the laser light source and reflecting or transmitting the light beam according to a polarization state of the incident light beam;
A first objective lens for condensing the light beam reflected by the light branching element on a first optical disc;
A second objective lens for condensing the light beam transmitted by the light branching element onto a second optical disc;
A first actuator for moving the first objective lens;
A second actuator for moving the first objective lens;
With
The first actuator and the second actuator move the first objective lens and the second objective lens in a focus direction with or without a rotation operation of a light beam incident on the polarization rotation element. Move to
Optical pickup. An optical pickup that emits light to an optical disc and receives reflected light from the optical disc,
A laser light source;
A polarization rotation element capable of rotationally controlling the polarization direction of the light beam emitted from the laser light source;
A light branching element disposed at a position after the polarization rotation element as viewed from the laser light source and reflecting or transmitting the light beam according to a polarization state of the incident light beam;
A first objective lens for condensing the light beam reflected by the light branching element on a first optical disc;
A second objective lens for condensing the light beam transmitted by the light branching element onto a second optical disc;
A first actuator for moving the first objective lens;
A second actuator for moving the first objective lens;
With
The polarization rotation element performs a rotation operation in a polarization direction of an incident light beam when the first actuator and the second actuator move the first objective lens and the second objective lens in a focus direction. To
Optical pickup. The optical pickup according to claim 1 or 2,
A photodetector for receiving reflected light from the first and second optical discs;
Comprising
Optical pickup. An optical pickup that emits light to an optical disc and receives reflected light from the optical disc,
A laser light source;
A polarization rotation element capable of rotationally controlling the polarization direction of the light beam emitted from the laser light source;
A light branching element disposed at a position after the polarization rotation element as viewed from the laser light source and reflecting or transmitting the light beam according to a polarization state of the incident light beam;
A first objective lens for condensing the light beam reflected by the light branching element on a first optical disc;
A second objective lens for condensing the light beam transmitted by the light branching element onto a second optical disc;
A photodetector for receiving reflected light from the first and second optical discs;
With
Comparing the control signal output from the polarization rotation element control circuit to rotate the polarization direction of the light beam in the polarization rotation element and the amplitude of the focus error signal or the sum signal detected by the photodetector. Thus, it is determined whether the optical disk is the first optical disk or the second optical disk. An optical pickup that emits light to an optical disc and receives reflected light from the optical disc,
A laser light source;
A polarization rotation element capable of rotationally controlling the polarization direction of the light beam emitted from the laser light source;
A light branching element disposed at a position after the polarization rotation element as viewed from the laser light source and reflecting or transmitting the light beam according to a polarization state of the incident light beam;
A first objective lens for condensing the light beam reflected by the light branching element on a first optical disc;
A second objective lens for condensing the light beam transmitted by the light branching element onto a second optical disc;
A photodetector for receiving reflected light from the first and second optical discs;
With
The optical disk is the first optical disk or the second optical disk by comparing the polarization state of the light beam transmitted through the polarization rotation element and the amplitude of the focus error signal or the sum signal detected by the photodetector. An optical pickup characterized by determining whether or not. An optical pickup according to claim 4 or claim 5, wherein
The optical pickup element is a polarization beam splitter. An optical pickup according to any one of claims 4 to 6,
The optical pickup characterized in that the polarization state of the light beam transmitted through the polarization rotation element is substantially orthogonal to the case where there is a polarization rotation operation and the case where there is no polarization rotation operation. An optical pickup according to any one of claims 4 to 7,
The optical pickup according to claim 1, wherein the polarization rotation element is a wave plate driving element that can change the characteristics of the wave plate through which the light beam is transmitted by mechanically switching the position of the wave plate. An optical pickup according to any one of claims 4 to 7,
2. The optical pickup according to claim 1, wherein the polarization rotation element is a liquid crystal element capable of changing characteristics as a wave plate by changing a driving voltage. An optical pickup according to any one of claims 4 to 9,
The wavelength of the laser light source is in a 405 nm band, the first optical disc has a disc substrate thickness of about 0.1 mm, and the second optical disc has a disc substrate thickness of about 0.6 mm. And optical pickup. An optical pickup according to any one of claims 4 to 10,
A polarization rotation element control circuit that outputs a control signal for rotating the polarization direction of the light beam in the polarization rotation element,
The optical disk is the first optical disk or the second optical disk by comparing the control signal output from the polarization rotation element control circuit with the amplitude of the focus error signal or the sum signal detected by the photodetector. An optical disc apparatus characterized by determining whether or not.

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