JP2008269756A - Optical pickup device and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately record or reproduce information on a multi-layer type disk-shaped recording medium by suppressing a decrease in the intensity of main light and shielding stray light collected before a light receiving element. An object is to obtain an optical pickup device and an optical disk device.
A collimator lens 3 for converting laser light into substantially parallel light, and a first signal for recording or reproducing information from a plurality of signal recording layers, the laser light having passed through the collimator lens 3 being used. An objective lens 6 for condensing on the recording layer, a light receiving element 9 having a light receiving portion 9a for condensing the first return light 10 from the first signal recording layer and receiving the first return light 10; Among the signal recording layers farther from the objective lens 6 than the first signal recording layer, the second recording layer is provided so as to coincide with the condensing position of the second return light from at least one second signal recording layer. And a light shielding element 8 having a light shielding portion 8a for shielding the return light.
[Selection] Figure 1

Description

  The present invention relates to an optical pickup device capable of recording or reproducing information with respect to an optical recording medium having a plurality of signal recording layers, and an optical disk device provided with the optical pickup device.

  In the optical pickup device, the laser light emitted from the light emitting element is condensed on the signal recording layer of the optical recording medium by the objective lens, and the return light from the signal recording layer is condensed on the light receiving element and received. Information is recorded on and reproduced from the recording layer. On the other hand, as an optical recording medium, there is a multi-layered disk-shaped optical recording medium in which a plurality of signal recording layers are stacked in order to improve the information recording density. When such a multi-layer disc-shaped optical recording medium is used, the return light from other signal recording layers is received as stray light in addition to the main light that is the return light from the signal recording layer to be recorded and reproduced. Since the light is incident on the element, there is a problem that information cannot be recorded or reproduced accurately. Therefore, an optical pickup device has been proposed in which a pinhole is provided in front of the light receiving element, the return light is once condensed at the pinhole portion, and only the main light is passed through the pinhole. (For example, refer to Patent Document 1.) Further, an optical pickup device has been proposed in which a light shielding member that shields at least part of stray light in the optical path of return light is installed. (For example, refer to Patent Document 2.)

JP-A-8-185640 (paragraph 0027, FIG. 1) Japanese Patent Laying-Open No. 2005-63595 (paragraph 0072, FIG. 3)

  However, in the method of passing the return light through the pinhole as described above, an extra condensing lens is required, and a part of the stray light passes through the pinhole and is incident on the light receiving element. There was a problem that could not be cut off. Further, in the method of shielding a part of the stray light, depending on the installation position of the light shielding member, the stray light collected before the light receiving element cannot be sufficiently shielded, and the intensity of the main light is reduced, thereby recording information. Or there was a problem that reproduction could not be performed accurately.

  The present invention has been made to solve the above-described problems, and suppresses a decrease in the intensity of main light and efficiently blocks stray light that is collected in front of the light receiving element. It is an object of the present invention to provide an optical pickup device and an optical disc apparatus capable of accurately recording or reproducing information on the disc-shaped recording medium.

  An optical pickup device according to the present invention is an optical pickup device for recording or reproducing information on an optical recording medium having a plurality of signal recording layers on a disk substrate, the light emitting element emitting laser light, A collimator lens that converts laser light into substantially parallel light and the laser light that has passed through the collimator lens are collected in a first signal recording layer that is a target of information recording or reproduction among the plurality of signal recording layers. A light-receiving objective lens; a light-receiving element having a light-receiving portion for collecting first return light from the first signal recording layer and receiving the first return light; and the plurality of signal recording layers When the signal recording layer closer to the objective lens is the first signal recording layer, at least one second of the signal recording layers farther from the objective lens than the first signal recording layer. Provided so as to match the second return light condensing position of the signal recording layer, and to and a shielding element having a light shielding portion for shielding the second return beam.

  According to the present invention, of the plurality of signal recording layers, the second return from the second signal recording layer farther from the objective lens than the first signal recording layer to be recorded or reproduced is information. By providing a light-shielding element so as to coincide with the light condensing position, it is possible to efficiently prevent stray light from entering the light-receiving element without reducing the intensity of the main light, and to provide a multilayer disk-shaped recording medium In contrast, it is possible to obtain an optical pickup device and an optical disc device capable of accurately recording or reproducing information.

Embodiment 1 FIG.
1 to 10 are diagrams for explaining an optical pickup device according to Embodiment 1 of the present invention, and FIG. 1 shows an entire configuration of the optical pickup device and an optical path of laser light in the optical pickup device. FIG. 2 shows an external configuration of a light shielding element provided in the optical pickup device. FIG. 3 shows the optical path of the return light from each signal recording layer in the vicinity of the light receiving element. 4 and 5 show the optical path of the return light in the vicinity of the light receiving element when the light blocking element is installed. FIG. 6 is a cross-sectional view showing the layer structure of the optical recording medium. FIG. 7 shows the condensing position of the return light from each signal recording layer when the signal recording layer to be recorded or reproduced is changed. 8 and 9 show the condensing state of the return light in the vicinity of the light receiving element. FIG. 10 shows a light receiving state at the light receiving element.

  In FIG. 1, an optical pickup device 100 includes a light emitting element 1, a polarizing prism 2, a collimator lens 3, a mirror 4, a wave plate 5, an objective lens 6, a light shielding element 8, and a light receiving element 9, and includes a moving base of an optical disk device (not shown). Is arranged. Since the objective lens 6 is disposed so as to face the signal recording layer 7a of the disc-shaped optical recording medium 7, the moving base moves in the radial direction of the optical recording medium 7, thereby allowing the optical recording medium 7 to be arbitrarily set. Information can be recorded and reproduced at the position. Details will be described below.

  As the light emitting element 1, for example, a semiconductor laser diode that emits laser light having a wavelength of about 405 nm is used. The light emitting element 1 is arranged in the optical pickup device 100 so that the optical axis of the light emitting element 1 coincides with the optical axis A of the optical pickup device 100 passing through the centers of the collimator lens 3 and the objective lens 6. The emitted laser light passes through the optical axis A and enters the polarizing prism 2.

  The polarization prism 2 plays a role of a polarization beam splitter that switches between reflection and transmission according to the polarization direction of incident light. The polarization prism 2 transmits the laser beam incident from the light emitting element 1 as it is, and the transmitted laser beam is collimator. The light enters the lens 3.

  The collimator lens 3 converts divergent light emitted from the light emitting element 1 into substantially parallel light. Further, by moving the collimator lens 3 along the direction of the optical axis A, the transmitted laser light is changed from convergent light to divergent light to correct spherical aberration generated on the signal recording layer 7a of the optical recording medium 7. It can be performed. In the first embodiment, the collimator lens 3 is moved in the direction of the optical axis A in order to correct the spherical aberration, but the spherical aberration generated on the signal recording layer 7a is small, which hinders information recording or reproduction. If not, it can be fixed.

  The laser beam that has passed through the collimator lens 3 and has become substantially parallel (converged light or divergent light depending on the generated spherical aberration for correcting spherical aberration) is reflected by the mirror 4 and enters the wave plate 5.

  The wave plate 5 converts the transmitted laser light from linearly polarized light to circularly polarized light. The laser light incident from the mirror 4 is converted into circularly polarized light by the wave plate 5 and enters the objective lens 6.

  The laser light incident on the objective lens 6 is focused on the first signal recording layer to be recorded or reproduced, of the signal recording layer 7 a of the optical recording medium 7 facing the objective lens 6. The optical recording medium 7 is configured by laminating a plurality of signal recording layers 7 a in the thickness direction of the optical recording medium 7, which is the direction facing the objective lens 6.

  The laser light focused on the first signal recording layer of the optical recording medium 7 is modulated according to the information signal recorded on the first signal recording layer when reflected by the first signal recording layer. The return light is in the state of light and travels toward the objective lens 6.

  The return light that has passed through the objective lens 6 enters the wave plate 5 again in a substantially parallel light state (in the case of correcting spherical aberration, in the state of convergent light or divergent light depending on the generated spherical aberration). .

  When the return light passes through the wave plate 5, it is converted from circularly polarized light to linearly polarized light, contrary to the forward path, and the polarization direction at this time is different from the forward path by about 90 degrees. The return light transmitted through the wave plate 5 is reflected by the mirror 4, passes through the collimator lens 3, becomes a condensed light beam, and enters the polarizing prism 2.

  The polarizing prism 2 transmits the laser light emitted from the light emitting element 1, but due to its polarization dependence, the return light whose polarization direction is different from the forward path by about 90 degrees is reflected, and the return light is deflected by 90 degrees from the optical axis A. Then, the light is guided toward the light receiving element 9.

  As shown in FIG. 2, a light shielding element 8 having a light shielding portion 8 a that does not transmit light is disposed on a part of the surface of the condensed light flux directed toward the light receiving element 9. The substrate 8b of the light shielding element 8 is made of a general glass base material, for example, BK7. Of course, a plastic material etc. may be sufficient. As the light shielding portion 8a, a material to which an absorbing film that absorbs light is attached is used. However, the light shielding portion 8a is not limited to this, and can be formed by attaching a material having a light shielding effect such as a reflective film. Further, if the light intensity can be sufficiently reduced, a film having a dimming effect can be used. The return light from the polarizing prism 2 toward the light receiving element 9 is shielded in the part where the light shielding part 8a exists in the optical path, and only the return light that has passed through the part other than the light shielding part 8a reaches the light receiving element 9. The light-shielding element 8 focuses the laser light on the first signal recording layer to be recorded or reproduced, among the plurality of signal recording layers 7a of the optical recording medium 7. The light shielding portion 8a coincides with the position where the stray light 11 as the second return light from the signal recording layer (second signal recording layer) farther from the objective lens than the first signal recording layer is condensed. Has been placed.

  The main light 10 that is the return light from the first signal recording layer that has passed through the light shielding element 8 enters the light receiving element 9. In the light receiving element 9, the return light is received by the light receiving portion 9a and is converted into an electric signal in accordance with the modulation state.

  Here, the collection state of the return light in the vicinity of the light receiving element 9 will be described. FIG. 3 shows the main light 10 that is the return light from the first signal recording layer to be recorded or reproduced, and the signal recording layers from the signal recording layers other than the first signal recording layer. The relationship of the condensing state of the stray light 11 which is return light is shown. Since the reflective layer on the optical recording medium 7 is different, the main light 10 which is the return light from the first signal recording layer to be recorded or reproduced of information and the first of the plurality of signal recording layers 7a. In the stray light 11 reflected by a signal recording layer (second signal recording layer) other than the one signal recording layer, the condensing position in the vicinity of the light receiving element 9 is different. The main light 10 is collected at the light receiving portion 9 a of the light receiving element 9. On the other hand, of the stray light 11, the stray light 11 a from the third signal recording layer closer to the objective lens 6 than the first signal recording layer is condensed behind the light receiving portion 9 a of the light receiving element 9. Of the stray light 11, stray light 11 b from the second signal recording layer farther from the objective lens 6 than the first signal recording layer is on the near side of the light receiving portion 9 a of the light receiving element 9, that is, on the polarizing prism 2 side. Condensate. Here, it is expressed that the laser beam travels from the near side to the far side along the optical axis A in correspondence with the direction in which the laser beam travels (downward in FIG. 3).

  As shown in FIG. 1, the optical recording medium 7 has a plurality of signal recording layers 7a stacked in the thickness direction. The optical pickup device 100 adjusts the position of the objective lens 6 to record a plurality of signals. Of the layer 7a, the laser beam is focused on the first signal recording layer to be recorded or reproduced. When correcting spherical aberration, the collimator lens 3 also moves along the optical axis A direction.

  At this time, of the second signal recording layer that is a layer other than the first signal recording layer, the second signal recording layer on the side close to the objective lens 6 is not condensed on the first signal recording layer. The second signal recording layer on the side far from the objective lens 6 reflects the laser light after being condensed by the first signal recording layer.

  FIG. 4 shows an optical path of stray light 11b reflected by the second signal recording layer far from the objective lens 6 and condensed on the front side of the light receiving element 9 (between the collimator lens 3 and the light receiving element 9). It is. As shown in FIG. 4, the stray light 11b collected on the near side of the light receiving element 9 is collected at one point. Therefore, of the stray light 11b, the stray light 11b which is the second return light in which the light shielding portion 8a of the light shielding element 8 is arranged at the light condensing position is shielded with a very small area corresponding to the light condensing area. Thus, it is possible to prevent the light from entering the light receiving portion 9a. In FIG. 4, the stray light 11b is reflected from one signal recording layer, but may be reflected from a plurality of signal recording layers.

  FIG. 5 is a diagram showing an optical path of stray light 11 a that is reflected by the second signal recording layer on the side close to the objective lens 6 and collected on the back side of the light receiving element 9. As shown in FIG. 5, the stray light collected at the back side of the light receiving element 9 cannot be shielded with a small area, unlike the stray light 11b collected at the near side. However, as shown in FIG. 5, the stray light 11a is received by setting the area of the light shielding portion 8a of the light shielding element 8 so that only the size of the stray light 11a incident on the light receiving portion 9a is shielded. It is possible not to reach 9a. However, when the area of the light shielding portion 8a is increased, the intensity of the main light 10 reaching the light receiving portion 9a is decreased. For example, assuming that the cross-sectional area of the optical path when the main light 10 passes through the light shielding element 8 is α and the area of the light shielding portion 8a is β, the intensity distribution of the main light 10 is due to the presence of the light shielding portion 8a. In a fixed case, it becomes ((α−β) / α), and if the intensity of the central portion is strong like a semiconductor laser, it will decrease to ((α−β) / α) or less. In FIG. 5, the stray light 11a is reflected from one layer, but may be reflected from a plurality of layers.

  Next, the arrangement and operation of the light shielding element 8 in the optical pickup device 100 according to the first embodiment will be described. Here, as the optical recording medium 7 to be recorded or reproduced information, a multi-layer disc-shaped optical recording medium having a five-layer structure in which a plurality of signal recording layers 7a are laminated at an equal interval of 10 μm is used. The case will be described.

  FIG. 6 is a cross-sectional view showing the layer structure of the optical recording medium 7. The optical recording medium 7 is provided by laminating a plurality of signal recording layers 7a on a substrate 7b. Of the plurality of signal recording layers 7a, the layer farthest from the objective lens 6 is the signal recording layer L0. The signal recording layer L0 to the signal recording layer L1, the signal recording layer L2, the signal recording layer L3, and the signal recording layer As it goes to the layer L4, it approaches the objective lens 6 at intervals of 10 μm.

  In the first embodiment, as described above, the collimator lens 3 is moved in the direction of the optical axis A in order to correct spherical aberration. For example, when reproducing the signal recording layer L0 as the first signal recording layer, the collimator lens 3 moves to a position close to the light emitting element 1, and when reproducing the signal recording layer L4 as the first signal recording layer, the collimator. The lens 3 moves to a position far from the light emitting element 1. Similarly, the positions of the collimator lenses 3 are determined in the order of the signal recording layers in the optical recording medium 7 in the other layers.

  The collimator lens 3 allows the first signal to be recorded even when the laser beam is condensed as the first signal recording layer for which information recording or reproduction is to be performed on any signal recording layer (L0 to L4). The main light 10 that is the return light from the recording layer is condensed at substantially the same position on the optical axis A of the optical pickup device 100, and can be received by the light receiving portion 9a without moving the light receiving element 9. it can.

  FIG. 7 shows the return from each signal recording layer when one of the signal recording layers (L0 to L4) is set as the first signal recording layer to be recorded or reproduced. The light condensing position in the vicinity of the light receiving element 9 is shown. The horizontal axis indicates the number of the signal recording layer set as an information recording or reproducing target, and the vertical axis indicates the condensing position of the return light from each signal recording layer by the distance (in mm) from the polarizing prism 2 It is. In the figure, the main light 10 that is the return light from the first signal recording layer and the stray light 11 that is the return light from the second signal recording layer are not distinguished and are simply expressed as return light. In the drawing, the portion surrounded by the broken line is the arrangement position (12.5 mm) of the light receiving element 9 and the condensing position of the main light 10. The lower side from the broken line is the front side from the light receiving element 9, and the upper side from the broken line is the back side from the light receiving element 9. That is, as the setting of the first signal recording layer is changed from the signal recording layer L0 to the signal recording layer L4, the condensing position from each signal recording layer moves linearly to the near side. In the first embodiment, since the signal recording layers L0 to L4 are arranged at equal intervals, the layer number is taken on the horizontal axis. However, when the layer intervals are different, the distance from the reference layer is different. If the horizontal axis is taken, the same linear relationship can be obtained. The numerical value on the vertical axis is the numerical value in the first embodiment, and is a design value determined by the focal length of the lens to be used, the size of each component, etc., and the present invention is not limited to this numerical value. .

  As shown in FIG. 7, when a certain signal recording layer (L0 to L4) is reproduced, the return light (stray light) from the signal recording layer one layer before the signal recording layer is condensed at substantially the same position. . Further, when a certain signal recording layer (L0 to L4) is reproduced, the return light (stray light) from the layer one layer behind that layer is also condensed at substantially the same position. For example, the return light from the L1 layer when reproducing the L2 layer (square: ■) and the return light from the L3 layer when reproducing the L4 layer (diamond: ◆) are almost at the same position. Condensate. The same applies to return light (stray light) from a signal recording layer separated into a plurality of layers. That is, when reproducing each signal recording layer, the position where the return light from the adjacent signal recording layer far from the objective lens of each signal recording layer is collected is substantially the same, and the signal recording layer being reproduced As the position is further away from the objective lens, the condensing position moves to the near side at equal intervals.

  The light shielding portion 8a of the light shielding element 8 is arranged at a position where the signal recording layer L4, which is the layer closest to the objective lens, is reproduced as the first signal recording layer. The light shielding element 8 may be disposed at each position where return light (stray light) from the recording layer L0, signal recording layer L1, signal recording layer L2, and signal recording layer L3 is collected. Further, even when the return light from any one of the signal recording layers is disposed only at the position where the light is condensed, at least the stray light where the light shielding element 8 is disposed at the light condensing position is directed to the light receiving portion 9a of the light receiving element 9. Incident can be prevented.

  Here, the intensity of stray light from the second signal recording layer, that is, the influence on the recording and reproduction of information will be examined. FIG. 8 is a diagram showing an optical path of return light from each signal recording layer (L0 to L4) when the signal recording layer L2 is set as the first signal recording layer to be recorded or reproduced. It is. The main light 10L2 from the signal recording layer L2 is collected by the light receiving portion 9a of the light receiving element 9, and the stray light 11 includes the signal recording layer L0 and the stray light 11bL0 and 11bL1 from the signal recording layer L1 on the front side of the light receiving element 9. The light is condensed, and the stray lights 11aL3 and 11aL4 from the signal recording layer L3 and the signal recording layer L4 are condensed on the back side of the light receiving element 9.

  FIG. 9 is a diagram showing an optical path of return light from each signal recording layer (L0 to L4) when the signal recording layer L4 is set as an information recording or reproducing target. The main light 10L4 from the signal recording layer L4 is collected by the light receiving portion 9a of the light receiving element 9, and among the stray light 11, the stray lights 11bL0, 11bL1, 11bL2, and 11bL3 from the signal recording layers L0 to L3 are in front of the light receiving element 9. Concentrate on the side.

  In consideration of the area of stray light incident on the light receiving element 9 when reproducing the signal recording layer L2 in FIG. 8, the areas of the stray light 11bL1 and 11aL3 from the signal recording layer L1 and the signal recording layer L3 are It is obvious that the area is smaller than the area of the stray light 11bL0 and 11aL4 from the recording layer L0 and the signal recording layer L4. Further, when the area of the stray light incident on the light receiving element 9 is taken into consideration when reproducing the signal recording layer L4 in FIG. 9, the area of the stray light 11bL3 from the signal recording layer L3 is the signal from the signal recording layer L0. It is clear that the area of the stray light 11bL0, 11bL1, 11bL2 from the recording layer L2 is smaller. That is, when the intensity of the return light from each of the signal recording layers (L0 to L4) is the same, the light intensity per unit area becomes stronger when the area when entering the light receiving element 9 is smaller. As the influence becomes stronger. That is, when the influence of the stray light from each signal recording layer (L0 to L4) is considered, when the first signal recording layer is set to the signal recording layer L2, the stray light 11bL1, 11aL3 from the signal recording layers L1 and L3 is set. When the first signal recording layer is set to the signal recording layer L4, the influence of the stray light 11bL3 from the signal recording layer L3 is the largest. Therefore, the influence of the stray light 11 from the signal recording layer adjacent to the first signal recording layer is the largest among the second signal recording layers.

  Then, the stray light 11bL1 from the signal recording layer L1 when the first signal recording layer is set to the signal recording layer L2, and the stray light from the signal recording layer L3 when the first signal recording layer is set to the signal recording layer L4. From FIG. 7, 11bL3 collects light at substantially the same position (10 mm) before the light receiving element 9 surrounded by a broken line. That is, in the second signal recording layer, the position where the stray light 11b from the signal recording layer adjacent to the first signal recording layer and farther from the objective lens than the first signal recording layer is collected is received light. The light is condensed at substantially the same position in front of the element 9.

  Therefore, when the signal recording layer L2 is the first signal recording layer, the light shielding element 8 having the light shielding portion 8a at the position where the stray light 11bL1 from the signal recording layer L1 is condensed in the second signal recording layer. It is possible to shield stray light 11bL1 having the greatest influence. When the signal recording layer L4 is the first signal recording layer, the light shielding element 8 having the light shielding portion 8a at the position where the stray light 11bL3 from the signal recording layer L3 is condensed in the second signal recording layer. When arranged, stray light 11bL3 having the greatest influence can be shielded. Therefore, when the first signal recording layer to be recorded or reproduced of information is set as a signal recording layer having another signal recording layer on the side farther than the objective lens 6 among the plurality of signal recording layers 7a. That is, when the signal recording layer closer to the objective lens 6 is set as the first signal recording layer, the first signal recording layer is adjacent to the first signal recording layer and is further away from the objective lens than the first signal recording layer. If the stray light 11b from the second signal recording layer is disposed at a position where the stray light 11b is collected, the stray light 11b having the greatest influence can be shielded.

  In the case where the light shielding element 8 is installed at the position as described above, in the first embodiment, the light shielding element 8 is incorporated in the optical pickup device 100 as shown in FIG. 1, but is formed on another element. You may do it. For example, when the astigmatism method is used for focus error signal detection, a cylindrical lens that gives astigmatism to the main light 10, an optical plate disposed obliquely with respect to the optical axis A, and the like are focused on the main light 10. Although arranged in the light beam, it may be formed on these optical surfaces. The light receiving portion 9a of the light receiving element 9 is generally protected by a glass substrate, a plastic substrate or the like, but may be formed thereon. Of course, the light shielding element 8 used in the optical pickup device 100 of the present invention is not limited to these elements, and may be formed on an optical element disposed in the condensed light beam of the main light 10. A similar effect can be obtained.

  As described above, stray light from the second signal recording layer close to the first signal recording layer and close to the objective lens, that is, stray light 11a collected on the back side of the light receiving element 9, is blocked as described above. This can be dealt with by adjusting the size of the light shielding portion 8a of the element 8. However, in the case of the stray light 11a condensed on the back side of the light receiving element, it is not necessary to block the stray light 11b from the signal recording layer far from the objective lens in front of the light receiving element 9 as described above. In order to increase the intensity of the main light 10 that reaches the light receiving portion 9a, a light shielding element may be separately provided at a position closer to the collimator lens and the objective lens than the condensing position.

  As described above, the stray light 11bL1 for the main light 10L2 or the stray light 11bL3 for the main light 10L4, that is, the second signal recording layer adjacent to the first signal recording layer and far from the objective lens. The light receiving state of the light receiving element 9 when the light shielding element 8 is arranged at the position where the stray light 11b from the light is condensed will be described. FIG. 10 is a diagram showing a light receiving state at the light receiving portion 9 a of the light receiving element 9. Of the plurality of signal recording layers 7a, the light receiving portion 9a includes main light 10 (return light from the first signal recording layer to be recorded and reproduced) (main light 10L2 in the setting of FIG. 8, FIG. In the setting of 9, the main light 10L4) is condensed. For the stray light in the figure, only stray light from the signal recording layer adjacent to the first signal recording layer having a strong influence is described. The stray light 11b (the stray light 11bL1 in the setting of FIG. 8, the stray light 11bL3 in the setting of FIG. 9), which is the second return light from the second signal recording layer farther from the objective lens than the first signal recording layer, Since the light is blocked by the light blocking portion 8a at the position where the light is condensed before the light receiving element 9, the light does not enter the light receiving element 9. On the other hand, the stray light 11a from the signal recording layer closer to the objective lens than the first signal recording layer (stray light 11aL3 in the setting of FIG. 8) is incident on the light receiving portion 9a by adjusting the area of the light shielding portion 8a. With respect to the influence on the main light 10, only the central white portion is shielded as described with reference to FIG. In FIG. 10, the light receiving portion 9a is described as having a simple square shape. However, even when the light receiving portion 9a is configured in another shape, the stray light 11b does not enter the light receiving element 9, and the light blocking portion By adjusting the size and shape of 8a, it is possible to prevent stray light 11a (stray light 11aL3 in the setting of FIG. 8) from entering the light receiving portion 9a.

  The light receiving element 9 shown in FIG. 10 is a simple square-shaped light receiving element for signal detection using one beam, but the light blocking element can be used even when other light receiving elements for signal detection are used. It is effective to arrange 8 at the position where stray light 11b (stray light 11bL1 in the setting of FIG. 8, stray light 11bL3 in the setting of FIG. 9) is collected. For example, in the case of a signal detection method using a plurality of beams, such as a three-beam method or a differential push-pull method, which is a tracking error signal detection method, which is common in an optical pickup device, stray light 11b is applied to the light receiving element 9. The stray light 11a (stray light 11aL3 in the setting of FIG. 8) can be prevented from entering the light receiving portion 9a by adjusting the size and shape of the light shielding portion 8a.

  FIG. 11 shows, as an example of another light receiving element, light receiving portions 9b that receive the main light beam 10m in the main light 10 (main light 10L2 in the setting of FIG. 8, main light 10L4 in the setting of FIG. 9) and on both sides thereof. It is a top view which shows the light reception state in the light receiving element 9 at the time of comprising with the light-receiving part 9c which light-receives the two sub-beams 10e arrange | positioned. For the stray light in the figure, only stray light from the signal recording layer adjacent to the first signal recording layer having a strong influence is described. This configuration is obtained by disposing a diffractive element between the light emitting element 1 and the objective lens 6 and spectroscopically analyzing the main light 10 (the main light 10L2 in the setting of FIG. 8 and the main light 10L4 in the setting of FIG. 9). The sub-beam 10e is used for signal detection or the like. In the embodiment of the present invention, the astigmatism method is used for focus error signal detection, and the differential push-pull method is used for tracking error signal detection. As for the stray light 11a, only the stray light 11a for the main light beam 10m having a high intensity is illustrated.

  As described above, by forming the light shielding portion 8a corresponding to the light receiving element 9, it is the return light from the second signal recording layer different from the first signal recording layer among the plurality of signal recording layers 7a. The stray light 11 (11a, 11b) is shielded by the light shielding portion 8a and does not enter the light receiving portion 9b and the light receiving portion 9c. For this reason, when the tracking error signal detection is performed using the sub-beam 10e whose light intensity is lower than that of the main beam 10m, the stray light 11 of the main beam 10m does not enter the light receiving portion 9c for detecting the sub-beam 10e. , Tracking servo can be stabilized. Of course, the present invention is not applied only to the error signal detection described above, and the stray light 11 can be reduced by applying other methods.

  That is, according to Embodiment 1 of the present invention, the signal recording layer closer to the objective lens 6 among the plurality of signal recording layers 7a stacked on the optical recording medium 7 is used as the first signal recording layer. At this time, light shielding is performed so as to coincide with the condensing position of the second return light from at least one second signal recording layer among the signal recording layers farther from the objective lens 6 than the first signal recording layer. By providing the light-shielding element 8 having the portion 8a, the stray light 11 is effectively prevented from entering the light-receiving element 9 without reducing the intensity of the main light 10, and the multi-layer disc-shaped recording medium 7 is used. In contrast, the optical pickup device 100 capable of accurately recording or reproducing information can be obtained.

  In particular, since the light shielding element 8 is formed so that the area of the light shielding portion 8a coincides with the light collecting area of the stray light 11b, the stray light 11b can be prevented from entering the light receiving portion 9a and the rate of shielding the main light 10 can be suppressed. Thus, the main light 10 can be incident on the light receiving portion 9a without reducing the intensity.

  In addition, since the light shielding element 8 is arranged so as to coincide with the position where the stray light 11b from the second signal recording layer adjacent to the first signal recording layer of the second signal recording layer is collected, Large stray light 11b can be efficiently blocked, and information can be recorded or reproduced accurately.

Embodiment 2. FIG.
FIG. 12 shows the overall configuration of the optical pickup device according to Embodiment 2 of the present invention. FIG. 13 shows the configuration of the diffraction element 13 according to the second embodiment. In the second embodiment, stray light is prevented from entering the light receiving element by using a diffraction element instead of the light shielding element in the first embodiment. Other configurations are the same as those in the first embodiment, and the description of corresponding portions is omitted.

  In FIG. 13, the diffractive element 13 is obtained by forming a diffractive part 13a made of a diffraction grating in a part where the light-shielding part 8a of the light-shielding element 8 in the first embodiment is formed. The light that has entered the diffractive portion 13 a has its optical path bent by diffraction, and is incident on a portion other than the light receiving portion 9 a of the light receiving element 9. The substrate 13b of the diffractive element 13 is made of a general glass base material, for example, BK7. Of course, a plastic material etc. may be sufficient. Further, if the light intensity of the stray light incident on the light receiving portion of the light receiving element 9 can be reduced, the stray light reduction effect can be obtained even if there are diffraction components of other orders instead of perfect diffraction.

  In the second embodiment, the diffractive element 13 is incorporated in the optical pickup device 100 as shown in FIG. 12, but may be formed on another element. For example, when the astigmatism method is used for focus error signal detection, a cylindrical lens that gives astigmatism to the main light 10, an optical plate arranged obliquely with respect to the optical axis A, and the like are arranged in the condensed light flux. However, it may be formed on these optical surfaces. The light receiving portion 9a of the light receiving element 9 is generally protected by a glass substrate, a plastic substrate or the like, but may be formed thereon. Of course, the diffractive element 13 used in the optical pickup device 100 of the present invention is not limited to these elements, and is formed on an optical element arranged in the condensed light flux of the return light main light 10. Then, the same effect can be obtained.

  FIG. 14 is a diagram showing the optical path of the return light diffracted by the diffraction element 13. As shown in the figure, for the stray light 11b condensed on the near side of the light receiving element 9, the diffraction portion 13a is arranged so as to coincide with the condensing position, and thus a small area corresponding to the condensing range. Thus, the stray light 11b can be diffracted and the stray light 11b can be prevented from entering the light receiving portion 9a of the light receiving element 9. FIG. 14 shows a state in which the stray light 11b is reflected from one layer, but may be reflected from a plurality of layers.

  FIG. 15 is a diagram illustrating stray light collected on the back side of the light receiving element 9. As shown in FIG. 15, the stray light 11a collected on the back side of the light receiving element 9 is diffracted in a small area so as not to be obtained by the light receiving portion 9a like the stray light 11b collected on the near side. I can't do it. However, as shown in FIG. 15, the stray light 11a is received by setting the area of the diffractive portion 13a of the diffractive element 13 so that only the magnitude of the stray light 11a incident on the light receiving portion 9a is diffracted. It is possible not to reach 9a. However, when the area of the diffractive portion 13a is increased, the intensity of the main light 10 reaching the light receiving portion 9a is decreased. For example, assuming that the cross-sectional area of the optical path when the main light 10 passes through the diffraction element 13 is γ and the area of the diffraction portion 13a is δ, the intensity distribution of the main light 10 is due to the presence of the diffraction portion 13a. In a fixed case, it becomes ((γ−δ) / γ), and if the intensity of the central portion is strong like a semiconductor laser, it will decrease to ((γ−δ) / γ) or less. In FIG. 15, the stray light 11a is reflected from one layer, but may be reflected from a plurality of layers.

  As described above, the diffraction element 13 is disposed at a position where the stray light 11b from the signal recording layer far from the objective lens 6 is condensed with respect to the first signal recording layer to be recorded or reproduced. The light receiving state at the light receiving element 9 will be described. FIG. 16 is a diagram showing a light receiving state at the light receiving portion 9 d of the light receiving element 9. Of the plurality of signal recording layers 7a, the main light 10 that is the return light from the signal recording layer to be recorded and reproduced is condensed on the light receiving portion 9d. For the stray light in the figure, only stray light from the signal recording layer adjacent to the first signal recording layer having a strong influence is described. The stray light 11 which is the return light from the layers other than the first signal recording layer is diffracted by the diffraction portion 13a before the light receiving element 9, and becomes stray light 11c and is incident on a position off the light receiving portion 9d. Of the stray light 11, stray light 11b collected before the light receiving element 9 is diffracted by the diffraction portion 13a and does not enter the light receiving portion 9d. Further, the stray light 11a (stray light 11aL3 in the setting of FIG. 8) from the signal recording layer closer to the objective lens than the first signal recording layer does not enter the light receiving portion 9d by adjusting the area of the diffraction portion 13a. As for the influence on the main light 10, only the central white portion is shielded as described with reference to FIG. Of the main light 10, the portion 10 c that has passed through the diffraction portion 13 a is incident on a position that is off the light receiving portion 9 d in the same manner as the stray light 11 c.

  Note that the light receiving element 9 shown in FIG. 16 is a simple square-shaped light receiving element for signal detection using one beam, but the diffraction element 13 is also used when other light receiving elements for signal detection are used. Is effective at the position where stray light 11b is condensed. For example, in the case of signal detection using a plurality of beams, such as the three-beam method and the differential push-pull method, which are tracking error signal detection methods that are common in optical pickup devices, the stray light 11b is incident on the light receiving element. Of course, the stray light 11a can be prevented from entering the light receiving portion 9d by adjusting the size and shape of the diffraction portion 13a.

  FIG. 17 is a plan view showing a light receiving element 9 provided with a light receiving portion 9 f that receives the sub-beam 10 c diffracted by the diffraction element 13 of the main light 10 as an example of the other light receiving element 9. Of the plurality of signal recording layers 7a, the main light 10 that is the return light from the first signal recording layer is condensed on the light receiving portion 9e of the light receiving element 9. For the stray light in the figure, only stray light from the signal recording layer adjacent to the first signal recording layer having a strong influence is described. The stray light 11 that is the return light from the second signal recording layer different from the first signal recording layer is diffracted by the diffraction portion 13a of the diffraction element 13 at the light receiving portion 9e and received as stray light 11c. Since light is received at a position deviated from the portion 9e, the light receiving portion 9e does not receive light. Furthermore, since the light receiving portion 9f can receive the diffracted light 10c that is a part of the main light 10 that is the return light from the first signal recording layer, it is possible to add a new function to the optical pickup device 100. Become. For example, the sub-beam 10c can be used for focus error signal detection, spherical aberration error detection, RF signal compensation, and the like. In particular, when signal detection that does not require high sensitivity is performed at the light receiving portion 9f, the sub-beam 10c has a sufficiently high intensity with respect to the stray light 11c, so that the influence of the stray light 11c is small and a new function is provided. It becomes possible to give to 9f.

  In this way, by receiving the diffracted light 10c that is diffracted by the diffraction portion 13a of the diffractive element 13 and is part of the main light 10 that is the return light from the first signal recording layer, only the effect of reducing stray light is obtained. In addition, it is possible to add a new function to the optical pickup device 100.

  The light receiving element 9 shown in FIG. 17 is a simple square-shaped light receiving element for signal detection using one beam, but also when other light receiving elements for signal detection are used, the diffraction element 13 is caused to stray light. It is effective to arrange 11 at a position where light is condensed. For example, in the case of a signal detection method using a plurality of beams, such as a three-beam method or a differential push-pull method, which is a tracking error signal detection method that is common in an optical pickup device, the size of the diffraction portion 13a, By adjusting the shape, the stray light 11 can be prevented from entering the light receiving portion 9a.

  FIG. 18 shows, as examples of other light receiving elements, a light receiving portion 9g that receives the main light beam 10m of the main light 10, a light receiving portion 9h that receives the two sub light beams 10e arranged on both sides thereof, and It is a top view which shows the light reception state in the light receiving element 9 at the time of comprising by the light receiving part 9i which light-receives the diffracted light 10c diffracted by the diffraction part 13a of the diffraction element 13. For the stray light in the figure, only stray light from the signal recording layer adjacent to the first signal recording layer having a strong influence is described. In this configuration, a diffractive element (different from the diffractive element 13 of the second embodiment) is arranged between the light emitting element 1 and the objective lens 6, and the sub-light beam 10 e obtained by dispersing the main light 10 is obtained. This corresponds to the signal detection used. In the embodiment of the present invention, the astigmatism method is used for focus error signal detection, and the differential push-pull method is used for tracking error signal detection. As for the stray light, only the stray light 11m with respect to the main light beam 10m having a strong influence is illustrated.

  As described above, by forming the diffractive portion 13a corresponding to the light receiving element 9, stray light 11b which is return light from the second signal recording layer among the plurality of signal recording layers 7a is caused by the diffractive portion 13a. It is diffracted and does not enter the light receiving portions 9g and 9h. For this reason, when tracking error signal detection is performed using the sub-beam 10e having a light intensity lower than that of the main beam 10m, the stray light 11 of the main beam 10m does not enter the light receiving portion 9h for detecting the sub-beam 10e. , Tracking servo can be stabilized. Of course, the present invention is not applied only to the error signal detection method described above, and the stray light reduction effect can be obtained even when applied to other methods.

  Further, the light receiving element 9 is provided with a light receiving part 9 i for receiving the diffracted light 10 c from the main light beam 10 diffracted by the diffraction part 13 a of the diffraction element 13. Since the light receiving portion 9i can receive the return light 10c, which is a part of the return light 10 from the first signal recording layer, it is possible to add a new function to the optical pickup device 100. For example, functions such as focus error signal detection, spherical aberration error signal detection, and RF signal compensation can be provided.

  That is, according to the second embodiment of the present invention, the signal recording layer closer to the objective lens 6 among the plurality of signal recording layers 7a stacked on the optical recording medium 7 is the first signal recording layer. When the stray light coincides with the condensing position of the second return light from at least one second signal recording layer among the signal recording layers farther from the objective lens 6 than the first signal recording layer. By providing the diffractive element 13 having the diffractive portion 13a for diffracting 11b, the stray light 11b is effectively prevented from entering the light receiving element 9 without reducing the intensity of the main light 10, and a multilayer structure is obtained. An optical pickup device 100 capable of accurately recording or reproducing information on a disk-type recording medium 7 of a type can be obtained.

  In particular, since the diffractive portion 13a of the diffractive element 13 is formed so as to coincide with the condensing area of the stray light 11, the ratio of diffracting the main light 10 can be suppressed and the main light 10 can be efficiently incident on the light receiving portion 9a. it can.

  In addition, since the diffraction element 13 is arranged so as to coincide with the position where the stray light 11b from the second signal recording layer adjacent to the first signal recording layer of the second signal recording layer is collected, Large stray light can be efficiently blocked, and information can be recorded or reproduced accurately.

  Further, since the light receiving element 9 is provided with the second light receiving part 9i for receiving the diffracted light 10c from the main light beam 10 diffracted by the diffraction part 13a of the diffraction element 13, the focus error signal detection, spherical surface is provided. Functions such as aberration error signal detection and RF signal compensation can be provided.

Embodiment 3 FIG.
FIG. 19 is a diagram showing a basic configuration of an optical disc apparatus according to Embodiment 3 of the present invention. The optical disc device according to the third embodiment includes the optical pickup device 100 described in the first or second embodiment.

  The optical disk apparatus according to the third embodiment includes a rotation driving mechanism 102 that holds and rotates an optical disk 107 that is a multi-layer disk-shaped optical recording medium. The rotation drive mechanism 102 positions and rotates the optical disk 7 with reference to a chucking hole 107c provided at the center of the optical disk 107.

  The optical pickup device 100 is disposed with the objective lens facing the signal recording layer 107 a of the optical disc 107 that is rotationally driven by the rotational drive mechanism 102, and moves in the radial direction of the optical disc 107 by the feed mechanism 103. The optical pickup device 100, the rotation drive mechanism 102, and the feed mechanism 103 are controlled by the control circuit 101. The optical pickup device 100 records and / or reproduces information with respect to the optical disc 107. A signal read from the optical disc 107 by the optical pickup device 100 is demodulated by the demodulation circuit 104.

  According to the third embodiment, by providing the optical pickup device 100 described in the first embodiment and the second embodiment, the information recording or reproducing target of the multilayer disk-shaped optical recording medium 107 can be obtained. Thus, it is possible to realize an optical disc apparatus capable of stably recording or reproducing information on the first signal recording layer by suppressing the influence of stray light from signal recording layers other than the first signal recording layer.

It is a figure which shows the whole structure of the optical pick-up apparatus in Embodiment 1 of this invention. It is a perspective view which shows the structure of the light shielding element in Embodiment 1 of this invention. It is a figure which shows the optical path of the return light in the light receiving element vicinity in Embodiment 1 of this invention. It is a figure which shows the optical path of the return light in case there exists a light shielding element in Embodiment 1 of this invention. It is a figure which shows the optical path of the return light in case there exists a light shielding element in Embodiment 1 of this invention. 1 is a cross-sectional view showing a layer structure of an optical recording medium in Embodiment 1 of the present invention. It is a figure which shows the relationship between the target signal recording layer in Embodiment 1 of this invention, and the condensing position of return light. It is a figure which shows the optical path of the return light in the light receiving element vicinity in Embodiment 1 of this invention. It is a figure which shows the optical path of the return light in the light receiving element vicinity in Embodiment 1 of this invention. It is a top view which shows the light reception state on the light receiving element in Embodiment 1 of this invention. It is a top view which shows the light reception state on the light receiving element in the modification of Embodiment 1 of this invention. It is a figure which shows the whole structure of the optical pick-up apparatus in Embodiment 2 of this invention. It is a perspective view which shows the structure of the diffraction element in Embodiment 2 of this invention. It is a figure which shows the optical path of the return light in case there exists a diffraction element in Embodiment 2 of this invention. It is a figure which shows the optical path of the return light in case there exists a diffraction element in Embodiment 2 of this invention. It is a top view which shows the light reception state on the light receiving element in Embodiment 2 of this invention. It is a top view which shows the light reception state on the light receiving element in the modification of Embodiment 2 of this invention. It is a top view which shows the light reception state on the light receiving element in the modification of Embodiment 2 of this invention. It is a figure which shows the whole structure of the optical disk device in Embodiment 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emitting element, 2 Polarizing prism, 3 Collimator lens, 4 Mirror, 5 Wavelength plate, 6 Objective lens, 7, 107 Optical recording medium, 7a Signal recording layer, 8 Light shielding element, 8a Light shielding part, 9 Light receiving element, 9a, 9b , 9c, 9d, 9e, 9f, 9g, 9h, 9i Light receiving part 10 Main light, 10e Sub-light beam, 10m Main light beam 11, 11a, 11b, 11c, 11d Stray light, 100 Optical pickup device, 101 Control mechanism, 102 Rotation Driving mechanism, 103 feeding mechanism, 104 demodulating circuit,

Claims (8)

An optical pickup device for recording or reproducing information on an optical recording medium having a plurality of signal recording layers on a disk substrate,
A light emitting element for emitting laser light;
A collimator lens that converts the laser light into substantially parallel light;
An objective lens that focuses the laser light that has passed through the collimator lens on a first signal recording layer to be recorded or reproduced, among the plurality of signal recording layers;
A light receiving element having a light receiving portion for collecting the first return light from the first signal recording layer and receiving the first return light;
When the signal recording layer closer to the objective lens among the plurality of signal recording layers is the first signal recording layer, the signal recording layer farther from the objective lens than the first signal recording layer A light shielding element that is provided so as to coincide with the condensing position of the second return light from at least one second signal recording layer, and that has a light shielding portion that shields the second return light;
An optical pickup device comprising: 2. The optical pickup device according to claim 1, wherein the light shielding element is formed such that an area of the light shielding portion coincides with a light collection area of the second return light. The optical pickup device according to claim 1, wherein the second signal recording layer is a signal recording layer adjacent to the first signal recording layer. An optical pickup device for recording or reproducing information on an optical recording medium having a plurality of signal recording layers on a disk substrate,
A light emitting element that emits laser light toward the optical recording medium;
A collimator lens that converts the laser light into substantially parallel light;
An objective lens that focuses the laser light that has passed through the collimator lens on a first signal recording layer to be recorded or reproduced, among the plurality of signal recording layers;
A light receiving element having a first light receiving portion for collecting the first return light from the first signal recording layer and receiving the first return light;
When the signal recording layer closer to the objective lens among the plurality of signal recording layers is the first signal recording layer, the signal recording layer farther from the objective lens than the first signal recording layer A diffractive element having a diffractive portion provided to coincide with a condensing position of the second return light from at least one second signal recording layer, and diffracting the second return light;
An optical pickup device comprising: 5. The optical pickup device according to claim 4, wherein the diffractive element is formed so that an area of the diffractive portion coincides with a condensing area of the second return light. 6. The optical pickup device according to claim 4, wherein the second signal recording layer is a signal recording layer adjacent to the first signal recording layer. The said light receiving element is equipped with the 2nd light-receiving part which light-receives one part of the said 1st return light diffracted by the said diffraction element, The Claim 4 thru | or 6 characterized by the above-mentioned. Optical pickup device. A rotational drive mechanism for rotationally driving the optical recording medium;
An optical pickup device according to any one of claims 1 to 7,
A feed mechanism for moving the optical pickup device in the radial direction of the optical recording medium;
An optical disc apparatus comprising:

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