JP2007018566A - Pickup and optical disk using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup which has high efficiency and is low-cost and compact as an optical pickup adaptive to two optical disks which have the same wavelength and differ in disk substrate thickness like Blu-ray Disc and HD DVD. <P>SOLUTION: The optical pickup has optical pickup constitution comprising one semiconductor laser, a polarized light rotating element capable of rotating the polarization direction of a light beam to a desired polarization direction with an external signal, a polarized light branching element which is disposed behind the polarized light rotating element and has two reflective surfaces, two objectives, and one optical detector, and the polarization direction of the light beam projected from the polarized light rotating element is rotated to switch the light beam reflected by the optical branching element between the objectives. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical pickup of an optical disc apparatus used for reproducing an information signal recorded on an optical disc, and more particularly to an optical pickup corresponding to optical discs having different substrate thicknesses with respect to the oscillation wavelength of the same semiconductor laser.

  Optical disc apparatuses such as DVD (Digital Versatile Disc) and CD (Compact Disc) are widely used as information recording / reproducing apparatuses characterized by non-contact, large-capacity, high-speed access, and low-cost media. In order to record and store such information, next-generation optical disc devices such as BD (Blu-ray Disc) and HD DVD have been proposed.

  Both BD and HD DVD are optical disk apparatuses that use a 400 nm band blue-violet semiconductor laser and both use a 12 cm diameter optical disk. However, the substrate thickness of the optical disk is 0.1 mm and 0.6 mm, respectively, and the numerical aperture NA (Numerical Aperture) of the objective lens mounted on the optical pickup used for reproducing the signal on the optical disk is 0. Since the basic physical characteristics are different from 85 and 0.65, the amount of information that can be stored in one optical disk is 27 GB and 15 GB, respectively. That is, the BD is an optical disk having a very large storage capacity, while the HD DVD is characterized in that the DVD and the optical pickup configuration can be easily interchanged due to the specifications in which many of the physical characteristics other than the laser wavelength match the current mainstream DVD. It has.

  In the market, there are two conflicting demands for recording and reproducing digital broadcasts with high definition and handling large volumes of information, and for ensuring compatibility with DVDs that are currently popular. For this reason, it is expected that BD and HD DVD will be compatible for the time being as a next-generation optical disk device, and it is strongly desired to realize an optical drive and an optical pickup compatible with both specifications. It is a situation.

In order to realize an optical pickup compatible with BD and HD DVD, it is necessary to focus an optical beam emitted from a semiconductor laser of the same wavelength on an information recording layer at a position of a different disc substrate thickness by using an objective lens having a different NA. There is. When trying to cope with one objective lens, the generation of a light beam component on the unused optical disk cannot be avoided, and this unnecessary light beam component becomes stray light on the original optical disk to be reproduced. May cause disturbance. In terms of light utilization efficiency, when trying to deal with one objective lens, compared to the case where each dedicated lens is provided, the stray light described above becomes a cause of light loss, so that it has a high output on the optical disk. This is a disadvantageous configuration for high-speed recording that requires a light amount.
On the other hand, in order to reduce the cost of the optical pickup itself, it is effective to reduce the number of parts by sharing optical parts as much as possible. In particular, it is possible to obtain a great effect in reducing the cost of the optical pickup by sharing the semiconductor laser, the photodetector, etc., which are expensive parts, in common.

  Here, in Patent Document 1, two semiconductor lasers that emit light beams having different polarization states, two objective lenses, and a polarization beam splitter are provided for two optical disks that use semiconductor lasers having two different wavelengths. An optical system configuration of an optical pickup to be combined has been proposed. In such a configuration, by switching the lit semiconductor laser, the light beam can be guided with high efficiency to the objective lens suitable for the optical disk to be used, and a part of the optical system and the photodetector can be shared. It has a configuration that can.

Japanese Patent Laid-Open No. 9-17015

  The problem to be solved is to provide two objective lenses optimized for each optical disc system when dealing with two different optical discs using optical discs of different substrate thicknesses for semiconductor lasers of the same wavelength, Since two semiconductor lasers having the same wavelength whose polarization directions are substantially orthogonal to each other are required, it is difficult to reduce the cost of the optical pickup. Also, the use of two semiconductor lasers is a point that reduces the entire optical system.

  As for the polarization state on the optical disk, it is generally desirable to use circularly polarized light or linearly polarized light having a direction of about 45 degrees in the radial direction of the disk in consideration of reproduction characteristics. Therefore, it is important that the polarization direction is circularly polarized light or linearly polarized light in the 45 degree direction for any of two different optical disks.

  In the present invention, in order to solve the above-described problems, in an optical pickup, a polarization rotation element capable of rotating the polarization direction of a light beam emitted from a semiconductor laser light source in a substantially orthogonal direction as necessary, and the light beam is polarization-rotated. A light branching element that is disposed after passing through the element and reflects or transmits the light according to the polarization state of the light beam, and a first objective that is disposed downstream of the light branching element and focuses the light beam on the first optical disk. A second optical system that collects a light beam emitted from the same semiconductor laser as that of the first optical disk on a second optical disk that has a lens and a substrate thickness different from that of the first optical disk. Objective lens and a photodetector for detecting the reflected light from the first and second optical discs, and any of the reflected light from the first and second optical discs travels through the optical branching element. Similarly reflection, or the most important feature that the like reaches the light detector arrangement by transmitting forward as well.

  The optical pickup according to the present invention has an optical system configuration including one semiconductor laser and one detection system while supporting two different optical disc systems using optical discs having different substrate thicknesses with respect to a semiconductor laser having the same wavelength. There is an advantage that an optical system configuration with low cost and high light utilization efficiency can be realized.

  A configuration in which the optical system of the semiconductor laser and the detection system are shared for the purpose of corresponding to two different optical disk systems using optical disks of different substrate thicknesses for the same wavelength semiconductor laser. As a result, an optical pickup optical system that is simple, low cost, has high light utilization efficiency, and does not generate unnecessary light that causes disturbance is realized.

  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 blue-violet semiconductor laser that oscillates at a wavelength of 400 nm band, and an oscillation wavelength at room temperature is 405 nm. The light beam emitted from the semiconductor laser 1 is a light beam in a polarization state (hereinafter referred to as P-polarized light) in a direction parallel to the paper surface, and passes through the diffraction grating 2 and reaches the half mirror 3. Here, the diffraction grating 2 is for splitting an incident light beam into three light beams of zero-order light and ± first-order light and generating three light spots on the optical disk. The half mirror 3 is disposed at an angle of 45 ° with respect to the optical axis of the light beam emitted from the semiconductor laser 1, and is a light beam having a wavelength of 400 nm band formed on the surface of the half mirror 3. Is an optical element that reflects approximately 80%. Further, about 20% of the light beam passes through the half mirror 3, and a part thereof reaches the front monitor 14 for monitoring the light quantity of the light beam.

  The light beam reflected by the reflection film of the half mirror 3 is converted into a parallel light beam by the collimating lens 4. The light beam emitted from the collimating lens 4 passes through the polarization rotation element 5. Here, when the light beam transmitted through the collimating lens 4 is P-polarized light, the polarization rotation element 5 is an element capable of rotating the polarization angle of P-polarized light transmitted in accordance with an input signal from the outside by 90 degrees. When the P-polarized light is rotated by 90 degrees, the polarization direction of the light beam is a direction perpendicular to the paper surface (hereinafter referred to as S-polarized light).

  The light beam that has passed through the polarization rotation element 5 enters the PBS 6. The PBS 6 has a structure having two film surfaces 6a and 6b having an inclination of 45 degrees inside. The film surface 6a reflects about 100% when the polarization state of the incident light beam is P-polarized light and transmits about 100% when it is S-polarized light. The film surface 6b has a characteristic of reflecting the light beam by about 100% regardless of the polarization state of the incident light beam.

  When the light beam incident on the PBS 6 is P-polarized light, the light beam is reflected by the film surface 6 a and is incident on the objective lens 7. The objective lens 7 is focused on the information recording surface of the first optical disk 12 having a substrate thickness of 0.1 mm, such as a Blu-ray Disc, when a 400 nm band light beam is incident as parallel light. It is a lens with a possible function. On the other hand, when the light beam incident on the PBS 6 is S-polarized light, almost all of the light beam is transmitted through the film surface 6a, reflected by the film surface 6b, and then incident on the objective lens 8. The objective lens 8 can focus on the information recording surface of the second optical disk 13 having a substrate thickness of 0.6 mm, such as HD DVD, when a 400 nm band light beam is incident as parallel light. This lens has a function. The objective lens 7 and the objective lens 8 are 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. For this reason, the objective lens 7 and the objective lens 8 are moved in a substantially radial direction of the optical disc 12 or the optical disc 13 and in a direction perpendicular to the disc surface by energizing the drive coil 10 and generating a driving force by a reaction force from the magnet 11. Is possible.

  Here, the light beam transmitted through the objective lens 7 or the objective lens 8 is based on the amount of light detected by the front monitor 14, or the amount of light beam transmitted through the objective lens 7 or the objective lens 8, respectively, or the optical disc 12 or optical disc. The light quantity of the light spot condensed on 13 can be estimated.

The light beam reflected from the optical disc 12 returns to the PBS 6 through the objective lens 7 through the same optical path as that of the outward light in the opposite direction. The light beam reflected from the optical disk 12 and incident on the PBS 6 is reflected by the film surface 6 a because most of the polarization direction is the same as that in the forward path, and enters the collimating lens 4 through the polarization rotating element 5. The collimating lens 4 converts the light beam from parallel light into convergent light and reaches the half mirror 3. About 20% of the light beam reaching the half mirror 3 is transmitted through the half mirror 3 by the film surface of the half mirror 3.
Similarly, the light beam reflected from the optical disc 13 returns to the PBS 6 through the objective lens 8 through the same optical path as the forward light in the opposite direction to the forward light. The light beam reflected from the optical disk 13 and incident on the PBS 6 is first reflected by the film surface 6b. Furthermore, since most of the polarization direction of the light beam is the same S-polarized light as in the forward path, it passes through the film surface 6 a and enters the collimating lens 4 through the polarization rotating element 5. The collimating lens 4 converts the light beam from parallel light into convergent light and reaches the half mirror 3. About 20% of the light beam reaching the half mirror 3 is transmitted through the half mirror 3 by the film surface of the half mirror 3.

  Here, the light beam that passes through the half mirror 3 has already become convergent light by passing through the collimating lens 4, and passes through the half mirror 3 that is inclined at 45 ° with respect to the traveling direction of the light beam. In doing so, astigmatism is given to the light beam. Thereafter, the light beam passes through the detection lens 15 and is then focused on a predetermined light detection surface of the light detector 16. The detection lens 15 is a lens for canceling coma generated in the half mirror 3 and enlarging the combined focal length on the detection system side. The photodetector 16 can output a servo signal or a reproduction signal from the optical disc 12 or the optical disc 13 from the received light beam.

  The optical pickup 17 is configured by the combination of the optical component and the electrical component described above.

  Next, the polarization direction of the light beam after emitting the semiconductor laser will be described with reference to FIG. In FIG. 2, the laser chip 21 is mounted inside the semiconductor laser 1. A light beam emitted from the end face of the active layer 22 in the laser chip 21 in a direction substantially parallel to the longitudinal direction of the laser chip 21 has a direction θh (horizontal direction) parallel to the active layer 22 with respect to the optical axis of the light beam. The spread angle is narrow and the spread angle in the direction θv (vertical direction) perpendicular to the active layer 22 is wide. In general, the spread angles are approximately 9 ° and 18 °, and the light beam spread 23 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 21 is substantially the same as the plane parallel to the active layer 22, that is, the θh direction, and 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 polarization rotation element will be described with reference to FIG. In FIG. 3, the polarization rotating element 25 can convert P-polarized light transmitted through the polarization rotating element 25 into S-polarized light whose plane of polarization is rotated by 90 degrees with respect to the optical axis in conjunction with the on / off of an electric signal from the outside. Element. Although the element itself is configured using a liquid crystal element, detailed description thereof is omitted here because the configuration of the element is not related to the present invention.

  In FIG. 3A, the switch 24 is in an OFF state, and the polarization rotator 25 is not energized from the outside. In this state, since no electrical action is generated in the polarization rotation element 25, the P-polarized light incident from the incident side passes through the polarization rotation element 25 as it is and is emitted as P-polarized light from the emission side. On the other hand, in FIG. 3B, the switch 24 is in an on state, and the liquid crystal element in the polarization rotation element 25 is in an electrically acted state. In this state, the P-polarized light incident from the incident side is rotated by 90 degrees in the polarization plane within the polarization rotation element 52, and is emitted as an S-polarized light beam from the emission side. As described above, in the polarization rotation element 25, the output polarization can be rotated by 90 degrees with respect to the incident polarization by turning on / off the energized state. This polarization rotation 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 half mirror on the film surface 6 a of the PBS 6. In FIG. 4, the horizontal axis indicates the wavelength of the light beam incident on the film surface 6a, and the vertical axis indicates the transmittance of the incident light beam. On the film surface 6a arranged at an angle of 45 degrees with respect to the light beam, approximately 100% of light is transmitted 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 6a, and are transmitted and reflected.

  FIG. 5 is a diagram showing a configuration of the optical pickup, and shows a situation at the time of reproduction of the first disc. The detailed description of each component has already been described and will not be repeated. The semiconductor laser 1 emits a P-polarized light beam having a polarization plane parallel to the paper surface indicated by the arrow in the figure. Here, when the first optical disk 12 is mounted on an optical disk device (not shown), the switch 24 of the polarization rotation element 5 is set to an on state. Therefore, the polarization plane of the light beam transmitted through the polarization rotation element 5 is rotated by approximately 90 degrees, and converted to S-polarized light having a polarization plane in a direction perpendicular to the paper surface indicated by a circle in the drawing. Thereafter, the light enters the PBS 6. Since the light beam incident on the film surface 6a of the PBS 6 is incident as S-polarized light, about 100% of the light amount of the light beam is reflected to the objective lens 7 side. Thereafter, the light beam is condensed on the information recording surface of the optical disk 12 by the objective lens 7.

  The light beam reflected by the optical disk 12 follows a path opposite to the forward path in the order of the objective lens 7 and the PBS 6 and reaches the polarization rotation element 5. In the polarization rotation element 5, S-polarized light is converted to P-polarized light, contrary to the forward path, and the light beam reaches the collimating lens 4. About 20% of the light amount of the light beam converted into convergent light by the collimating lens 4 is transmitted through the half mirror 3. Thereafter, the light beam that has passed through the lens 15 reaches the photodetector 16 and can output various servo signals and information reproduction signals. That is, in the configuration as shown in FIG. 5, the light beam emitted from the semiconductor laser 1 can be efficiently guided to the objective lens 7 and condensed on the optical disk 12 by energizing the switch 24 and selecting the ON state. It becomes possible.

  FIG. 6 is a diagram showing the configuration of the optical pickup, and shows the situation during reproduction of the second disc. The semiconductor laser 1 emits a P-polarized light beam having a plane of polarization parallel to the paper surface indicated by the arrow in the figure, as in the case of the first disk 12 described in FIG. is there. The semiconductor laser 1 emits a P-polarized light beam having a polarization plane parallel to the paper surface indicated by the arrow in the figure. Here, in FIG. 6, the second optical disk 13 is used, and the switch 24 of the polarization rotation element 5 is set to an off state. For this reason, the light beam transmitted through the polarization rotation element 5 remains in the polarization state as P-polarized light. Thereafter, the light enters the PBS 6. Since the light beam incident on the film surface 6a of the PBS 6 is incident as P-polarized light, it passes through the film surface 6a of the PBS as it is and is reflected on the film surface 6b toward the objective lens 8 side. Thereafter, the light beam is condensed on the information recording surface of the optical disc 13 by the objective lens 8.

  The light beam reflected by the optical disk 13 follows the path opposite to the forward path in the order of the objective lens 8 and the PBS 6 and reaches the polarization rotation element 5. Since the polarization rotating element 5 is not energized, the light beam reaches the collimating lens 4 while remaining P-polarized light. About 20% of the light amount of the light beam converted into convergent light by the collimating lens 4 is transmitted through the half mirror 3. Thereafter, the light beam that has passed through the detection lens 15 reaches the light detector 16 and can output various servo signals and information reproduction signals. That is, in the configuration as shown in FIG. 6, by selecting the switch 24 in the OFF state, the light beam emitted from the semiconductor laser 1 can be efficiently guided to the objective lens 8 and condensed on the optical disc 13. Become.

  As described above, the configuration as shown in the first embodiment can be applied to two optical discs having the same wavelength and different disc substrate thicknesses by using one semiconductor laser 1 and one photodetector 16. An optical system of an optical pickup can be realized. Further, by adopting such a configuration, since only the PBS 6 has to be disposed immediately below the objective lens 7 and the objective lens 8, the height of the portion immediately below the objective lens can be reduced.

  FIG. 7 shows the polarization state on the optical disk. For convenience, the polarization state of the light beam in a state where it is emitted from both the objective lens 7 and the objective lens 8 is also shown. The objective lens 7 is arranged such that the center of the lens is shifted from the axis in the radial direction of the optical disc 12 (hereinafter referred to as the disc radial direction) that coincides with the feeding direction of the optical pickup 17. On the other hand, the objective lens 8 is arranged on an axis in the disk radial direction. In FIG. 7, the polarization state of the light beam focused on the optical disk 12 from the objective lens 7 is a direction that matches the disk radial direction in the figure, and the polarization state of the light beam emitted from the objective lens 8 is It coincides with a direction orthogonal to the radial direction (hereinafter referred to as the track direction).

  As described above, by using an optical pickup configuration in which the polarization state is changed according to the disc while using one semiconductor laser and one photodetector, optical discs having different substrate thicknesses while using the same wavelength are used. It is possible to realize a low-cost optical pickup that can be applied to two optical disc systems, for example, any of Blu-ray Disc and HD DVD optical disc systems. Furthermore, with this configuration, the optical component disposed immediately below the objective lens can be only PBS, which can greatly contribute to the thinning of the optical pickup.

  Next, a second embodiment of the present invention will be described. FIG. 8 is a diagram showing an optical system configuration of the optical pickup in the second embodiment, and FIG. 9 is a diagram showing a polarization state on the optical disc in the second embodiment. In FIG. 8, the difference from the configuration of the first embodiment described above is that a half-wave plate 18 is disposed above the film surface 6 b of the PBS 6. With such a configuration, the polarization direction after passing through the half-wave plate 18 can be rotated. For example, the output polarized light from the objective lens 8 as shown in FIG. It is possible to set the direction and the direction of the track in half. Here, as for the polarization direction on the optical disk, it has been empirically found that circular polarization is generally desirable for ensuring reproduction performance. In the second embodiment, by setting the polarization direction on the objective lens 8 side to approximately 45 degrees, linearly polarized components can be generated in the disk radial direction component and the track direction component, and an effect equivalent to circularly polarized light is obtained. It is possible. Since the reflected light beam from the optical disk 13 returns to the P-polarized light again at the half-wave plate 18, the behavior of the light beam in the subsequent return path is the same as in the first embodiment. The half-wave plate 18 only needs to be disposed between the PBS 6 and the objective lens 8, and it goes without saying that, for example, the same effect is exhibited even if it is installed on the lens holder 9 side.

  Next, Embodiment 3 of the present invention will be described. FIG. 10 is a diagram showing an optical system configuration of the optical pickup in the third embodiment, and FIG. 11 is a diagram showing a polarization state on the optical disc in the third embodiment. In FIG. 10, the difference from the configuration of the second embodiment described above is that a half-wave plate 19 is disposed above the film surface 6 a of the PBS 6. By adopting such a configuration, the polarization direction after passing through the half-wave plate 18 and the half-wave plate 19 can be rotated. For example, an objective lens as shown in FIG. 7 and the output polarized light from the objective lens 8 can be set to a direction that divides the disk radial direction and the track direction into two. Therefore, it is possible to ensure good reproduction performance for both the optical disk 12 and the optical disk 13. Since the reflected light beam from the optical disk 12 returns to the P-polarized light again at the half-wave plate 19, the behavior of the light beam in the subsequent return path is the same as in the second embodiment. Note that both the half-wave plate 18 and the half-wave plate 19 may be disposed between the PBS 6, the objective lens 8, and the objective lens 7, for example, installed on the lens holder 9 side. Needless to say, the same effect can be achieved.

  Next, a fourth embodiment of the present invention will be described. FIG. 12 is a diagram showing an optical system configuration of the optical pickup in the fourth embodiment, and FIG. 13 is a diagram showing a polarization state on the optical disc in the fourth embodiment. In FIG. 12, the difference from the configuration of the first embodiment described above is that the PBS mirror 20 is provided in a portion corresponding to the PBS 6. A film surface 20 a having an inclination of 45 degrees is formed on the surface of the PBS mirror 20, and a film surface 20 b is formed inside the PBS mirror 20. Since the optical characteristics of the film surface 20a and the film surface 20b are the same as those of the film surface 6a and the film surface 6b in the first embodiment, the same operations and effects as described in the first embodiment can be obtained. It is. Therefore, on the optical disc, it is possible to obtain a polarization state similar to that described in FIG. 7 as shown in FIG.

  With such a configuration, an optical system of the optical pickup can be realized by the PBS mirror 20 that is lower in cost than the PBS 6, and the cost of the optical pickup can be reduced. Furthermore, also in the present invention, the second and third embodiments have been described by adopting a configuration in which a half-wave plate is disposed between the film surface 20a and the film surface 20b and the objective lens 7 and the objective lens 8. It goes without saying that the same effect can be obtained.

  Next, an optical disk device on which the optical pickup according to the first to fourth embodiments is mounted will be described. FIG. 14 shows a schematic block diagram of an optical disc apparatus equipped with an optical pickup in an embodiment of the present invention. A part of the signal detected by the optical pickup 17 is sent to the optical disc discrimination circuit 51. When the optical disc discriminating operation of the optical disc discriminating circuit 51 corresponds to the oscillation wavelength of the semiconductor laser in which the substrate thickness of the optical disc is lit, and when it corresponds to the different oscillation wavelength In addition, for example, the fact that the focus error signal amplitude level detected by the optical pickup 17 becomes larger in the former case is utilized. The determination result is sent to the control circuit 54. Further, a part of the detection signal detected by the optical pickup 17 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 12 or the optical disc 13 from various signals detected by the optical pickup 17 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 12 or the optical disc 13 from the detection signal of the optical pickup 17 and outputs it to the reproduction signal output terminal. The control circuit 54 sets the optical disk 12 or the optical disk 13 based on the signal from the optical disk discrimination circuit 51, and drives the objective lens based on the focus error signal and tracking error signal generated by the servo signal generation circuit 52 correspondingly. A signal is sent to the actuator drive circuit 55. Based on this objective lens drive signal, the actuator drive circuit 55 drives the actuator 9 in the optical pickup 17 to control the positions of the objective lens 7 and the objective lens 8. The control circuit 54 controls the position of the optical pickup 17 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 12 or the optical disk 13.

  Further, the control circuit 54 drives the laser lighting circuit 59 so that the semiconductor laser 1 mounted on the optical pickup 17 is appropriately lit according to the optical disk 12 or the optical disk 13, thereby realizing the recording / reproducing operation in the optical disk device. is doing. The control circuit 54 turns on / off the switch 24 of the polarization rotation element 5 based on the discrimination result of the optical disc discrimination circuit 51. Thereby, the polarization state of the light beam in the optical pickup 17 can be optimally controlled, and a good signal can be detected from the optical disc 12 or the optical disc 13, respectively.

  In the first to fourth embodiments of the present invention described above, the optical disk 12 uses S-polarized light and the optical disk 13 uses P-polarized light. However, the present invention limits the polarization state for each disk. However, it goes without saying that the arrangement of the objective lens 7 and the objective lens 8 may be changed to use a different polarization state depending on the configuration of the optical system.

1 is a diagram illustrating a configuration of an optical pickup in Embodiment 1. FIG. It is a figure which shows the polarization direction of the light beam after radiate | emitting a semiconductor laser. It is a figure which shows operation | movement of a polarization rotation element. It is the figure which showed the characteristic of the film | membrane surface 6a of PBS. It is the figure which showed the polarization state at the time of the 1st optical disk reproduction | regeneration. It is the figure which showed the polarization state at the time of the 2nd optical disk reproduction | regeneration. It is the figure which showed the polarization state on an optical disk. 6 is a diagram illustrating a configuration of an optical pickup in Embodiment 2. FIG. 6 is a diagram showing a polarization state on an optical disc in Example 2. FIG. 6 is a diagram illustrating a configuration of an optical pickup in Embodiment 3. FIG. 6 is a diagram showing a polarization state on an optical disc in Example 3. FIG. FIG. 10 is a diagram illustrating a configuration of an optical pickup according to a fourth embodiment. FIG. 6 is a diagram showing a polarization state on an optical disc in Example 4. It is a schematic block diagram of the optical disk device carrying an optical pickup.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 5 ... Polarization rotation element, 6 ... PBS, 7 ... Objective lens, 8 ... Objective lens, 12 ... 1st optical disk, 13 ... 2nd optical disk, 17 ... Optical pick-up, 18 ... 1/2 Wave plate, 19 ... half-wave plate, 24 ... switch.

Claims (8)

A semiconductor laser light source, a polarization rotation element capable of rotating the polarization direction of the light beam emitted from the semiconductor laser light source in a substantially orthogonal direction as necessary, and the light beam disposed after passing through the polarization rotation element; A light branching element that reflects or transmits the light beam according to a polarization state of the light beam; a first objective lens that is disposed downstream of the light branching element and focuses the light beam on a first optical disk; and the light branching A second objective for condensing a light beam emitted from the same semiconductor laser as the first optical disc on a second optical disc disposed at a subsequent stage of the element and having a substrate thickness different from that of the first optical disc. An optical pickup comprising a lens and a photodetector for detecting reflected light from the first and second optical disks,
An optical pickup characterized in that each of reflected light from the first and second optical discs reaches the photodetector by reflecting or transmitting the light branching element in the same way as in the forward path.   2. The optical pickup according to claim 1, wherein a half-wave plate is disposed at a position after reflection or transmission of the optical branching element or both.   3. The optical pickup according to claim 2, wherein the polarization states of the light beams emitted from the objective lens 1 and the objective lens 2 are linearly polarized light in substantially the same direction or in directions orthogonal to each other.   4. The optical pickup according to claim 1, wherein an oscillation wavelength of the semiconductor laser light source is set in a 400 nm band.   5. The optical pickup according to claim 1, wherein the substrate thickness of the first optical disc is set to about 0.1 mm, and the substrate thickness of the second optical disc is set to about 0.6 mm. Features an optical pickup.   6. The optical pickup according to claim 1, wherein the optical branching element has two reflecting film surfaces, and the reflecting film surfaces are set substantially parallel to each other.   7. The optical pickup according to claim 1, wherein the optical branching element is a flat mirror. 8. An optical disc apparatus using the optical pickup according to claim 1, wherein an optical disc discriminating circuit for discriminating whether the mounted optical disc is the first optical disc or the second optical disc, and the polarization rotation element A polarization rotation element drive circuit that outputs a signal for rotating the polarization direction of the light beam that passes through the optical disk, and based on the signal from the optical disc discrimination circuit, the signal from the polarization rotation element drive circuit to the polarization rotation element An optical disc apparatus characterized by output.

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