JP2011065697A - Optical pickup and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup which can obtain a stable servo signal from a multilayer disk which has three or more information recording layers, and to provide an optical disk device. <P>SOLUTION: The optical pickup includes: a laser package which includes in one casing, a main light source which outputs a main beam for recording or reproducing a signal to the optical disk, a first sub-light source which outputs a first sub-beam for servo which is incoherent to the main beam, and a second sub-light source which outputs a second sub-beam for servo which is incoherent to the main beam and the sub-beam 1; an objective lens which condenses the main beam, the first sub-beam and the second sub-beam to the optical disk; and a photodetector which receives light from the main beam, the first sub-beam and the second sub-beam. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to an optical pickup and an optical disc apparatus.

  As background art in this technical field, Patent Document 1 describes the configuration of an optical pickup that splits a light beam with a diffraction grating, and Patent Documents 2 and 3 describe an optical pickup configured with two laser light sources. ing.

Japanese Patent Laid-Open No. 2007-164922 JP 2006-53953 A

  In recent years, the amount of information owned by an individual tends to increase due to an increase in the number of pixels of an image. In order to answer the need to store increasing information, storage with a larger capacity is required.

  Until now, the capacity of optical disks has been increased by increasing the density of information recording surfaces, such as CD (Compact Disc), DVD (Digital Versatile Disc), and BD (Blu-ray Disc). In particular, in DVDs and BDs, a large capacity has already been realized with two signal recording surfaces. Currently, in order to further increase the capacity, a multi-layer disc having three or more layers is being studied. That is, an optical pickup and an optical disc apparatus capable of recording / reproducing a multilayer disc having three or more layers are required.

  Patent Document 1 describes an ordinary three-beam optical pickup. A light beam emitted from one semiconductor laser light source is branched into three light beams of 0 and ± 1st order by a diffraction grating, 0th order light is a main light beam for signal recording and reproduction, and ± 1st order light is used for servo. The technique used for the secondary light beam is general.

  When a recording / reproducing operation of a multi-layer disc having three or more layers is performed with such an optical pickup, stray light is generated from an adjacent layer different from the signal recording surface to be recorded / reproduced. This stray light interferes with the servo sub-light beam on the surface of the photodetector, and greatly fluctuates the servo signal obtained from the sub-light beam. That is, since the servo performance is remarkably deteriorated, the conventional three-beam optical pickup cannot cope with a multi-layer disc having three or more layers.

  Patent Document 2 describes an optical pickup having one semiconductor laser light source dedicated for signal recording and reproduction and one semiconductor laser light source dedicated for servo. However, it is intended to easily adjust the position of the light spot formed on the optical disk and to simultaneously correct the divergent light distribution of the semiconductor laser, and does not describe any technique related to recording and reproduction of a multilayer disk having three or more layers. Absent.

  It is an object of the present invention to provide an optical pickup and an optical disc apparatus that can obtain a stable servo signal from a multilayer disc having three or more information recording layers.

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

  According to the present invention, it is possible to provide an optical pickup and an optical disc apparatus that can obtain a stable servo signal in a multilayer disc having three or more information recording layers.

Schematic explaining the optical system configuration of the optical pickup in the first embodiment Schematic explaining the semiconductor laser package 1 in Example 1 Schematic explaining the light spot arrangement on the information recording surface in Example 1 Schematic explaining stray light generated in the multilayer disk in Example 1 Schematic explaining the condensing spot of signal light and stray light in the photodetector in Embodiment 1 FIG. 6 is a graph for explaining the relationship between the light spot interval d and the amplitude of the TE signal when reproduction of a 100 μm eccentric disk in Example 1 is assumed. Schematic explaining the semiconductor laser package 50 in the second embodiment Schematic explaining the semiconductor laser package 60 in the third embodiment Schematic explaining the light spot arrangement on the information recording surface in Example 3 Schematic explaining the condensing spot of the signal light and stray light in the photodetector in Example 3 A graph illustrating the relationship between the light spot interval d and the off-track amount of the TE signal, assuming reproduction of a 100 μm eccentric disk in Example 3. Schematic explaining the semiconductor laser package 70 in Example 4 Schematic explaining the semiconductor laser package 80 in Example 5 Schematic explaining the configuration of the optical disc device in Embodiment 6

  Embodiment 1 of the present invention will be described in detail with reference to the drawings. Here, assuming a three-layer disc based on the BD standard, an optical pickup capable of recording or reproducing the three-layer disc will be described. Of course, a BD having three or more layers, a multi-layer disc based on the DVD standard, or a multi-layer disc of another standard may be used.

  FIG. 1 is a diagram illustrating a configuration of an optical pickup according to the first embodiment of the present invention. First, the configuration of the optical pickup according to the present invention will be described with reference to FIG. In the following description, the optical path from the semiconductor laser package 1 to the objective lens 8 is referred to as the forward path, and the optical path from the objective lens 8 to the photodetector 10 is referred to as the return path.

  First, the outward path will be described. The semiconductor laser package 1 is a laser light source that independently emits three light beams, which are one main light beam and two sub-light beams, using divergent light beams. Usually, a light beam having a wavelength of 405 nm band (405 nm ± 10 nm) is used for recording / reproducing of BD. For this reason, it is assumed that the three light beams are 405 nm ± 10 nm. The configuration of the semiconductor laser package 1 will be described later.

  An alternate long and short dash line 11 illustrates the optical paths of the three light beams. The main light beam and the two sub light beams pass through the same optical path. Hereinafter, for simplicity, the configuration of the optical pickup will be described using the main light beam.

  The main light beam emitted from the semiconductor laser package 1 as divergent light enters the beam splitter 2. The beam splitter 2 has a function of branching an incident light beam by transmission and reflection. Here, the forward path is used for reflection and the return path is used for transmission. The main light beam that has reached the beam splitter 2 is reflected and travels to the collimating lens 3. The main light beam is converted into a substantially parallel light beam by the collimating lens 3.

  Multilayer discs have different substrate thicknesses from the surface to each signal recording surface, and different amounts of spherical aberration are generated in the light beams applied to each information recording surface. For this reason, in order to cope with a multilayer disk, a function for correcting spherical aberration is required. As means for correcting the spherical aberration, it is common to use the divergence and convergence state of a light beam. For this reason, the collimating lens 3 is preferably configured to be movable in the optical axis direction so that the main light beam can be diverged and the focusing state can be changed. Detailed description of spherical aberration correction by the collimating lens is omitted.

  The main light beam that has passed through the collimating lens 3 is then reflected by the raising mirror 7 and raised in the direction perpendicular to the paper surface, and is focused and irradiated onto a disk (not shown) by the objective lens 8. In general, spherical aberration occurs in a cover glass of a disk in a light beam condensed by an objective lens. Therefore, the objective lens is designed so that the spherical aberration of the light beam collected on the disk is minimized by generating a spherical aberration that cancels the spherical aberration. Therefore, in order to cope with a multi-layer disc having three or more layers, the spherical aberration is minimized when the light beam is condensed at an intermediate position between the information recording surface close to the front surface side of the disc and the innermost information recording surface. It is recommended to design an objective lens. The amount of spherical aberration generated on the information recording surface close to the front side and the innermost information recording surface can be equalized, and any information recording surface can correct the spherical aberration by driving the collimating lens 3 described above. For this reason, it is assumed that the objective lens 8 is designed so that the spherical aberration is minimized when the light beam is focused at an intermediate position between the information recording surface close to the disk surface side and the innermost information recording surface. ing.

  At the time of recording or reproducing, the distance between the objective lens 8 and the disk varies in the optical axis direction due to the surface vibration of the disk. In order for the focal position of the main light beam condensed by the objective lens 8 to follow this fluctuation on the predetermined information recording surface of the disc, the objective lens 8 needs to be focus-controlled. Further, the objective lens 8 and the disk fluctuate in the radial direction of the disk due to eccentricity of the disk. In order for the main light beam condensed by the objective lens 8 to follow a predetermined track in the disc, the objective lens 8 needs to be subjected to tracking control. For the focus control and the tracking control, the objective lens 8 is mounted on an actuator (not shown) and is movable in the tracking direction and the focus direction.

  Next, the return path will be described. The main light beam reflected by the disk travels through the collimator lens 3 through the objective lens 8 and the raising mirror 7 which are the optical paths opposite to the forward path, and reaches the beam splitter 2 again. In the return path, the main light beam passes through the beam splitter 2 and travels to the detection lens 9.

  When the light passes through the detection lens 9, a predetermined astigmatism is given to the main light beam, which is used for detection of a focus error signal by a differential astigmatism method (hereinafter referred to as a DAD method).

  Finally, the main light beam travels to the photodetector 10. The detection lens 10 receives the main light beam and the two auxiliary light beams described above on a predetermined light detection surface. The photodetector 10 can receive the main light beam and the two auxiliary light beams independently, and the photodetector 10 will be described later. The photodetector 10 outputs a signal photoelectrically converted according to the amount of received light beam, and a tracking error signal based on the DAD method, tracking based on a differential push-pull method (hereinafter referred to as DPP method). An error signal (hereinafter referred to as a TE signal), a recording / reproducing signal, and the like are generated. Detailed description of the DPP method is omitted.

  As described above, the optical pickup of this embodiment has the semiconductor laser package 1 capable of independently emitting at least one main light beam and two sub light beams, the beam splitter 2, and the collimating lens 3. And an objective lens 8 and a photodetector 10 capable of receiving three light beams.

Next, the configuration of the semiconductor laser package 1 will be described with reference to FIG.
FIG. 2 is a schematic view of the semiconductor laser package 1 as viewed from the beam splitter 2. A heat sink 12 is disposed in the semiconductor laser package 1, and a main light beam semiconductor laser chip 14 and two sub light beam semiconductor laser chips 13 and 15 are mounted on the heat sink 12.

Although not shown in the drawings, in this embodiment, the circuit configuration is such that the amount of light beams emitted from the main laser beam semiconductor laser chip 14 and the two sub light beam semiconductor laser chips 13 and 15 can be changed independently. Is assumed to take.
The heat sink 12 has a function of radiating heat generated from the semiconductor laser chip.

  The main light beam semiconductor laser chip 14 is disposed substantially at the center of the sub light beam semiconductor laser chips 13 and 15. This is because the DPP method is assumed as described above. In the DPP method, when the chip intervals h of the semiconductor laser chips 13 and 15 for the sub light beam with respect to the semiconductor laser chip 14 for the main light beam are different, an offset occurs in the TE signal. For this reason, it is preferable to install the chips so that the chip intervals h substantially coincide. Further, the emission power of the two auxiliary light beams emitted from the semiconductor laser chips 13 and 15 for the auxiliary light beam is set to be weaker than the emission power of the main light beam emitted from the semiconductor laser chip 14 for the main light beam. . This is to avoid erroneous recording due to the auxiliary light beam. The emission powers of the two auxiliary light beams emitted from the auxiliary light beam semiconductor laser chips 13 and 15 are preferably substantially the same. This is intended to prevent TE signal offset caused by eccentricity of the disk. For this reason, for example, a drive circuit (not shown) for driving the semiconductor laser chips 13 and 15 for the sub light beam may be shared.

  The main light beam emitted from the main light beam semiconductor laser chip 14 and the two sub light beams emitted from the sub light beam semiconductor laser chips 13 and 15 are not incoherent. Incoherent light, that is, incoherent light, means that interference does not occur when the light beams overlap each other. A light beam having no coherence can be realized by means such as slightly changing the wavelength of the light beam emitted from the semiconductor laser chip or changing the phase of the emitted light beam.

  In order to realize incoherent light, a semiconductor laser may be used as the main light beam, and an LED (Light Emitting Diode) may be used as the sub light beam. Since an LED can be manufactured at a lower cost than a semiconductor laser, it can be expected that the semiconductor laser package 1 can be manufactured at a lower cost.

  For example, assuming an optical pickup equipped with a semiconductor laser chip that emits a coherent light beam, interference fringes are generated in the light beam emitted from the CP lens 3, but the CP lens 3 is used in the optical pickup of this embodiment. Interference fringes are not generated in the light beam emitted from.

  By using the semiconductor laser package 1 described above, a stable servo signal can be obtained from a multilayer disk having three or more layers. Details will be described later.

Next, the arrangement of light spots on the information recording surface will be described with reference to FIG.
FIG. 3 is a schematic view of the information recording surface as viewed from the objective lens 8. Information tracks 16 are arranged on the information recording surface at a constant interval T. Since BD is assumed, the information track interval T is 0.32 μm.
There are three light spots 17, 18, and 19 on the information recording surface. The light spot 18 is a condensing spot of the main light beam, and the light spots 17 and 19 are condensing spots of the sub light beam. As described above, since the chip interval h of the sub-light beam semiconductor laser chips 13 and 15 with respect to the main light beam semiconductor laser chip 14 is substantially the same, the light spot interval d between the light spot 18 and the light spots 17 and 19 is It almost agrees. In order to realize the DPP method, the light spots 17 and 19 of the secondary light beam need to be arranged by being shifted by 1/2 track in the disc radial direction with respect to the light spot 18 of the main light beam. For this reason, as shown in FIG. 3, the light spots 17 and 19 of the sub light beam are arranged so as to be shifted from the light spot 18 of the main light beam by exactly 1/2 track in the disc radial direction. In general DPP, when the light spot arrangement as shown in FIG. 3 is used, the TE signal can obtain the maximum amplitude. Thus, the arrangement of the spots on the information recording surface can be realized by adjusting the rotation of the semiconductor laser package 1. For this reason, it is preferable that the semiconductor laser package 1 has a mechanism capable of rotational adjustment. For example, the semiconductor laser package 1 may be fixed with a holder, and the outer shape of the optical pickup may be devised so that the holder can rotate.

  Next, stray light generated in the multilayer disk will be described.

FIG. 4 shows the main light beam collected by the objective lens 8 on the three-layer disc. 4A shows the optical path of signal light, and FIGS. 4B and 4C show the optical path of stray light.
The three-layer disc 20 has three information recording surfaces 21, 22, and 23. In FIG. 4, it is assumed that the information recording surface 22 is a recording / reproducing target layer and the information recording surfaces 21 and 23 are adjacent layers.
A solid line 24 indicates a light beam outside the main light beam which is signal light. Dashed lines 25 and 26 indicate light rays outside the main light beam that become stray light.

First, the optical path of signal light will be described with reference to FIG. The main light beam is incident on the objective lens 8 as a parallel light beam as indicated by a solid line 24 and is then focused on the three-layer disc 20. The main light beam passes through the information recording surface 23 and is condensed on the information recording surface 22. Let this condensing point be P point. Point P corresponds to the focal position of the objective lens 8. The main light beam is reflected by the information recording surface 22, returns to the objective lens 8, and is converted again into a parallel light beam. That is, the signal light refers to a light beam that travels on substantially the same optical path (solid line 24) before and after reflecting the recording / reproducing target layer.
Next, the optical path of stray light will be described with reference to FIGS. As described above, there is an optical path through which the main light beam that has traveled to the information recording surface 22 transmits in addition to reflection. Therefore, a part of the main light beam passes through the information recording surface 22 and reaches the information recording surface 21. FIG. 4B shows the optical path of the main light beam that reaches the information recording surface 21. The main light beam is reflected by the information recording surface 21 and then returns to the objective lens 8 again. At this time, since the main light beam that has traveled again to the objective lens 8 is reflected by the recording information surface 21 at a position different from the focal point P, the Q point further behind the recording information surface 21 is a virtual light emitting point. appear. Therefore, the main light beam reflected by the information recording surface 21 is converted into focused light when passing through the objective lens 8. The main light beam reflected by the information recording surface 21 is indicated by a broken line 25.

  In addition, the main light beam that has traveled to the information recording surface 23 has an optical path for reflecting as well as transmitting as described above. Therefore, a part of the main light beam is reflected by the information recording surface 23 and wants to reach the information recording surface 22. FIG. 4C shows the optical path of the main light beam reflected by the information recording surface 22. The main light beam is reflected by the information recording surface 23 and then returns to the objective lens 8 again. At this time, the main light beam that has traveled again to the objective lens 8 is reflected by the recording information surface 23 at a position different from the focal point P, so that the R point further in front of the recording information surface 23 is a virtual light emitting point. appear. Therefore, the main light beam reflected by the information recording surface 23 is converted into divergent light when passing through the objective lens 8. The main light beam reflected by the information recording surface 23 is indicated by a broken line 26. That is, stray light refers to a light beam that travels on an optical path (broken lines 25 and 26) different from the optical path of signal light (solid line 24) because it reflects an adjacent layer different from the recording / playback target layer. In a multi-layer disc, stray light is generated as described above.

A technique for removing the disturbance of the signal light due to the stray light will be described below.
A technique for removing disturbance from the relationship between signal light and stray light on the photodetector will be described. FIG. 5 illustrates the light receiving surface in the photodetector 10 and the condensing spots of the main light beam and the sub light beam signal light and the stray light of the main light beam.

  The photodetector 10 includes a main light beam light receiving surface 28 and two sub light beam light receiving surfaces 27 and 29. The photodetector 10 is assumed to be a general 12-divided light receiving surface based on the DAD method and the DPP method. The photodetector 10 can convert the intensity of the light beam received by the light receiving surface into an electric signal, and generate a recording / reproducing signal and a servo signal.

  The signal light of the main light beam is condensed on the main light beam receiving surface 28 to form a signal light spot 31. Similarly, the signal light of the two sub light beams is condensed on the light receiving surfaces 27 and 29 for the sub light beam to form signal light spots 30 and 32.

On the other hand, the stray light of the main light beam forms stray light spots 33 and 34 that are largely blurred on the photodetector 10 as described above. Since the stray light spots 33 and 34 are largely blurred, the light enters the main light beam light receiving surface 28 and the sub light beam light receiving surfaces 27 and 29. Further, the signal light spots 30 and 32 and the stray light spots 33 and 34 are overlapped on the photodetector 10.
Since the stray light spots 33 and 34 are largely blurred, the amount of light entering the light receiving surface 28 for the main light beam and the light receiving surfaces 27 and 29 for the sub light beam on the photodetector is sufficiently small. For this reason, it does not become a big disturbance. Further, since the main light beam and the two sub light beams are not coherent with each other, they interfere even if a region where the stray light spots 33 and 34 and the signal light spots 30 and 32 overlap on the photodetector 10 is generated. There is no. Therefore, a high quality servo signal can be obtained stably.

  In a general optical pickup, a light beam emitted from one semiconductor laser chip is branched into one main light beam and two sub light beams by a diffraction grating. However, the secondary light beam and the main light beam branched by the diffraction grating in this way are coherent with each other. When the signal light spots 30 and 32 and the stray light spots 33 and 34 overlap on the photodetector 10 as shown in FIG. 5, light interference occurs. Due to this interference, the intensity of the light spots 33 and 34 of the secondary light beam fluctuates unpredictably with the rotation of the disk. The disturbance due to this interference has caused the servo signal in the conventional optical pickup to deteriorate significantly.

  In the present embodiment, as described above, the stray light of the main light beam can be reduced to 2 by using the semiconductor package composed of three semiconductor laser chips having no coherence between one main light beam and two sub light beams. The problem that the secondary light beams interfere with each other on the same light receiving surface is solved. Therefore, if the configuration of the optical pickup shown in this embodiment is adopted, a high quality servo signal can be stably obtained.

  Next, the problem of the TE signal when reproducing a disk having a large eccentricity, that is, an eccentric disk will be described. The eccentric disk refers to a disk in which the center of rotation and the center of the disk are eccentric.

  When such an eccentric disk is reproduced, it changes as if the information track 16 is rotating around the light spot 18 in FIG. On the other hand, the light spots 17, 18, and 19 are irradiated to a certain position when the eccentric disk is reproduced. In other words, it looks as if the light spots 17, 18, 19 are rotating around the light spot 18 with respect to the information track.

  As described above, the TE signal using the DPP method can obtain the maximum amplitude when the light spots 17 and 19 are shifted from the light spot 18 by 1/2 track in the radial direction. Conversely, when the light spots 17 and 19 deviate from the optimum ½ track in the disk radial direction, the amplitude of the TE signal decreases. That is, the problem of the TE signal when reproducing the eccentric disk is a decrease in the amplitude of the TE signal.

  The amplitude of the TE signal becomes smaller in inverse proportion to the light spot interval d when the eccentric amount of the eccentric disk is constant. This is because, when the light spot interval d is large, even if the amount of change in the angle of the information track is constant, the amount of deviation of the light spots 18 and 19 with respect to the light spot 18 in the disc radial direction becomes large.

In an optical disk device for reproducing BD, when reproducing a generally assumed 100 μm eccentric disk, if the TE signal has an amplitude of 90% or more, stable servo performance can be obtained. Similarly, in the present embodiment, when a 100 μm eccentric disk is reproduced, the TE signal ensures an amplitude of 90% or more.
FIG. 6 shows the result of calculating the relationship between the light spot interval d and the amplitude of the TE signal, assuming reproduction of an eccentric disk of 100 μm. The horizontal axis indicates the light spot interval d, and the vertical axis indicates the TE signal amplitude. The TE signal amplitude on the vertical axis is calculated assuming that the reproduction of a disc with no eccentricity is 100%. Since BD is assumed, the track pitch in the calculation is 0.32 μm.

  As described above, it is reproduced that the TE signal amplitude decreases as the light spot interval d increases. From the graph, it can be seen that the light spot interval may be set to 8 μm or less in order to ensure the amplitude of the TE signal of 90% or more.

  In general, the forward path magnification M, the chip interval h of the semiconductor laser package 1 and the light spot interval d on the information recording surface have a relationship expressed as in Equation 1. The forward magnification M is the ratio of the focal lengths of the collimating lens 3 and the objective lens 8.

h / M = d [Formula 1]
In the optical pickup of this embodiment, the forward path magnification M and the chip interval h in Equation 1 may be determined so that the light spot interval d is 8 μm or less.

  Now, one of the design items of the optical pickup is the RIM intensity. RIM intensity is the ratio of the light intensity at the pupil edge to the maximum light intensity in the entrance pupil of the objective lens. In the BD standard, the RIM intensity in the disk radial direction and the rotational direction is determined to be 65% and 60%.

  The RIM intensity depends on the outgoing light distribution of the semiconductor laser chip and the forward magnification F. In order to realize the RIM intensity, when a normal semiconductor laser chip is used, the forward magnification M is generally set to about 10 times. Similarly in this embodiment, the forward magnification M may be set to 10 times or more.

  When the forward path magnification M is determined, the semiconductor laser chip interval h is obtained from the above equation 1. For example, in order to set the light spot interval d to 8 μm or less, if the forward magnification M is set to 10 times, the chip interval h may be set to 80 μm or less. Normally, when the forward path magnification M increases, the amount of light emitted from the objective lens 8 decreases. For this reason, the forward magnification M is not set larger than 15 times. When the forward magnification M is 15 times, in order to make the light spot interval d 8 μm or less, the chip interval may be 120 μm or less according to Equation 1. That is, it is understood that the chip interval h of the semiconductor laser package 1 may be set to 80 μm or less in the range of 10 to 15 times of the forward path magnification M actually used.

  As described above, in this embodiment, by using a semiconductor laser package that emits a main light beam and a sub light beam having no coherency, a high-quality servo signal can be stably obtained from a multi-layer disk having three or more layers. Can do.

  Further, the eccentric disk can be stably reproduced by setting the chip interval of the semiconductor laser package 1 to 80 μm or less at most.

  In addition, since the optical pickup of the present embodiment does not have a diffraction grating for generating three beams, unlike the conventional optical pickup, the number of components is small and the effect of facilitating the manufacture of the optical pickup can be obtained.

  A second embodiment of the present invention will be described in detail with reference to the drawings. Here, a modification of the semiconductor laser package 1 of the first embodiment will be described.

  FIG. 2 is a schematic view of the semiconductor laser package 50 as viewed from the beam splitter 2. A heat sink 12 is disposed in the semiconductor laser package 50, and a semiconductor laser chip 51 is mounted on the heat sink 12.

  The semiconductor laser chip 51 is provided with three light emitting points, a main light emitting point 36 and sub light emitting points 35 and 37. The light emitting point refers to a point that emits a light beam. The main light emitting point 36 corresponds to the semiconductor laser chip 14 for the main light beam of the semiconductor laser package 1. The sub-light emitting points 35 and 37 correspond to the sub-light beam semiconductor laser chips 13 and 15 of the semiconductor laser package 1, respectively.

  Although not shown, in the present embodiment, it is assumed that the circuit configuration is such that the amount of light beams emitted from the main light emitting point 36 and the two sub light emitting points 15 and 37 can be changed independently. .

  In recent years, a multi-semiconductor laser chip capable of emitting a plurality of light beams from one semiconductor laser chip has been used, and the semiconductor laser package 50 is assumed to be mounted with the multi-semiconductor laser chip. In such a multi-semiconductor laser chip, light emitting points are arranged in a direction parallel to the active layer. Therefore, the main light emitting point 36 and the sub light emitting points 35 and 37 of the semiconductor laser chip 51 are arranged side by side in a direction parallel to the contact surface with the heat sink 12.

  On the other hand, the light beams emitted from the main light emitting point 36 and the sub light emitting points 35 and 37 must be arranged in a direction parallel to the information track as shown in FIG. Therefore, the heat sink 12 is rotated 90 degrees with respect to the semiconductor laser package 1. The heat sink 12 has a function of radiating heat generated from the semiconductor laser chip.

  Similarly to the semiconductor laser package 1, in the semiconductor laser package 50, the emission power of the two sub light beams emitted from the sub light emission points 35 and 37 is weaker than the emission power of the main light beam emitted from the main light emission point 36. Power. The emission powers of the two sub light beams emitted from the sub light emission points 35 and 37 are preferably substantially the same. Further, for example, a drive circuit (not shown) for driving the sub light emission points 35 and 37 may be shared.

  Also in the semiconductor laser package 50, the distance between the main light emitting point 36 and the sub light emitting points 35, 37, in other words, the chip interval of the semiconductor laser package 1 is at most 80 μm or less, as in the first embodiment. Can be reproduced stably.

  Of course, as in the semiconductor laser package 1, the main light beam emitted from the main light emitting point 36 and the two sub light beams emitted from the sub light emitting points 35 and 37 are not incoherent. For this reason, even if the semiconductor laser package 50 is used, high-quality servo signals can be stably obtained from a multi-layer disc having three or more layers as in the first embodiment.

  In the semiconductor laser package 1, since three semiconductor laser chips are mounted, the mounting position accuracy becomes a problem. However, in the semiconductor laser package 50, the interval between the light emitting points is determined by the semiconductor process. For this reason, it can be expected that the semiconductor laser package 50 has an effect that the mounting accuracy is improved as compared with the semiconductor laser package 1.

  Embodiment 3 of the present invention will be described in detail with reference to the drawings. Here again, a modification of the semiconductor laser package 1 of the first embodiment will be described.

  FIG. 8 is a schematic view of the semiconductor laser package 60 viewed from the beam splitter 2. A heat sink 12 is disposed in the semiconductor laser package 60, and a main light beam semiconductor laser chip 61 and a sub light beam semiconductor laser chip 62 are mounted on the heat sink 12.

Although not shown, the present embodiment also adopts a circuit configuration in which the amount of light beams emitted from the main light beam semiconductor laser chip 61 and the sub light beam semiconductor laser chip 62 can be changed independently. Assumed.
The heat sink 12 has a function of radiating heat generated from the semiconductor laser chip.
A sub light beam semiconductor laser chip 62 is disposed on the main light beam semiconductor laser chip 61. This is because the DPP method is assumed as described above. The main light beam semiconductor laser chip 61 and the sub light beam semiconductor laser chip 62 are arranged with a chip interval h therebetween.

In the DPP method using two light beams as compared with the DPP method using three light beams, the TE signal is largely offset when the eccentric disk is reproduced when the chip interval h is widened. For this reason, it is preferable that the chip interval h is set to 80 μm or less. This chip interval will be described later. The emission power of the sub light beam emitted from the sub light beam semiconductor laser chip 62 is set to be weaker than the emission power of the main light beam emitted from the main light beam semiconductor laser chip 61. This is to avoid erroneous recording due to the auxiliary light beam.
The main light beam emitted from the main light beam semiconductor laser chip 61 and the sub light beam emitted from the sub light beam semiconductor laser chip 62 are not incoherent.

Next, differences from the first embodiment when the semiconductor laser package 60 is used will be described.
FIG. 9 is a schematic view of the information recording surface as viewed from the objective lens 8. Information tracks 16 are arranged on the information recording surface at a constant interval T. Since this figure also assumes BD, the information track interval T is 0.32 μm. There are two light spots 40 and 41 on the information recording surface. The light spot 40 is a condensing spot of the main light beam, and the light spot 41 is a condensing spot of the sub-light beam, and they are arranged separated by a light spot interval d. The relationship between the light spot interval d and the chip interval h can be expressed by Equation 1 as described above.

  In order to realize the DPP method, the light spot 41 of the sub light beam needs to be shifted from the light spot 40 of the main light beam by 1/2 track in the disk radial direction. For this reason, also in FIG. 9, the light spot 41 is shifted from the light spot 40 by exactly 1/2 track in the disc radial direction. In the DPP using two light beams, the phase difference between the TE signal and the track position is minimized when the light spot 41 is arranged with a shift of exactly 1/2 track with respect to the light spot 40 in the disk radial direction. . On the other hand, if the track deviates from 1/2 track, a phase shift between the TE signal and the track position, so-called off-track occurs.

  As shown in FIG. 9, the arrangement of the light spot on the information recording surface can be realized by adjusting the rotation of the semiconductor laser package 60. For this reason, it is preferable that the semiconductor laser package 60 has a mechanism capable of rotational adjustment. For example, the semiconductor laser package 60 may be fixed with a holder, and the outer shape of the optical pickup may be devised so that the holder can rotate.

  FIG. 10 illustrates the light receiving surface in the photodetector 65 and the condensing spots of the signal light of the main light beam and the sub light beam and the stray light of the main light beam. The photodetector 65 includes a main light beam light receiving surface 43 and a sub light beam light receiving surface 42. The photodetector 65 is assumed to be an eight-divided light receiving surface based on the DAD method and the DPP method. The photodetector 65 can convert the intensity of the light beam received by the light receiving surface into an electric signal, and generate a recording / reproducing signal and a servo signal.

  The signal light of the main light beam is condensed on the light receiving surface 43 for main light beam to form a signal light spot 45. Similarly, the signal light of the sub light beam is condensed on the light receiving surface 42 for the sub light beam to form a signal light spot 44. On the other hand, the stray light of the main light beam forms stray light spots 33 and 34 that are largely blurred on the photodetector 65. Since the stray light spots 33 and 34 are largely blurred, the light enters the main light beam light receiving surface 43 and the sub light beam light receiving surface 42. Further, the signal light spots 44 and 45 and the stray light spots 46 and 47 are overlapped on the photodetector 65.

  Since the stray light spots 33 and 34 are largely blurred, the amount of light incident on the light receiving surface 43 for the main light beam and the light receiving surface 42 for the sub light beam on the photodetector is sufficiently small. For this reason, it does not become a big disturbance. Further, since the main light beam and the two sub light beams are not coherent with each other, they interfere even if a region where the stray light spots 33 and 34 and the signal light spots 42 and 43 overlap on the photodetector 10 is generated. There is no. Therefore, a high quality servo signal can be obtained stably.

  In this embodiment, as described above, the stray light of the main light beam and the two sub-light beams are used by using the semiconductor package composed of two semiconductor laser chips having no coherence. The problem that the light beam interferes on the same light receiving surface is solved. Therefore, the optical pickup device of this embodiment can stably obtain a high-quality servo signal.

  When the eccentric disk is reproduced, the information track 16 changes as if it is rotating around the light spot 40 in FIG. On the other hand, the light spots 40 and 41 are irradiated to a certain position when reproducing the eccentric disk. In other words, it looks as if the light spots 40 and 41 are rotating around the light spot 40 with respect to the information track. For this reason, as described above, in the DPP using two light beams, the light spot 41 is shifted from the light spot 40 by exactly 1/2 track in the radial direction of the disk. The phase shift is minimal. On the other hand, if the track deviates from 1/2 track, a phase shift between the TE signal and the track position, so-called off-track occurs. That is, the TE signal when reproducing an eccentric disk in a DPP using two light beams has a problem that the TE signal is off-tracked.

  This off-track increases substantially in inverse proportion to the light spot interval d when the eccentric amount of the eccentric disk is constant. This is because, when the light spot interval d is large, even if the amount of change in the angle of the information track is constant, the amount of deviation of the light spot 41 with respect to the light spot 40 in the disc radial direction becomes large.

  In an optical disc apparatus that reproduces BD, when reproducing a generally assumed 100 μm eccentric disc, stable servo performance can be obtained if the off-track amount of the TE signal is suppressed to 1/10 track or less.

  Similarly, in the present embodiment, when a 100 μm eccentric disc is reproduced, the amount of TE signal off-track is suppressed to 1/10 track or less. FIG. 11 shows the result of calculating the relationship between the light spot interval d and the off-track amount of the TE signal, assuming the reproduction of a 100 μm eccentric disk. The horizontal axis represents the light spot interval d, and the vertical axis represents the off-track amount. The off-track amount on the vertical axis is normalized by the track pitch, and is calculated as 100% when the off-track amount is 0.32 μm. Since BD is assumed, the track pitch in the calculation is also 0.32 μm.

  As described above, it is reproduced that the off-track amount increases as the light spot interval d increases. From the graph, it can be seen that the light spot interval may be set to 8 μm or less in order to suppress the off-track amount to 1/10 track, that is, 10% or less. That is, in the DPP method using two light beams, the light spot interval d may be set to 8 μm or less as in the DPP method using three light beams, so that the chip interval d is 80 μm or less as in the first embodiment. By doing so, the eccentric disk can be reproduced stably.

  Embodiment 4 of the present invention will be described in detail with reference to the drawings. Here, a modification of the semiconductor laser package 60 of the third embodiment will be described.

  FIG. 12 is a schematic view of the semiconductor laser package 70 as viewed from the beam splitter 2. A heat sink 12 is disposed in the semiconductor laser package 70, and a semiconductor laser chip 71 is mounted on the heat sink 12.

  The semiconductor laser chip 71 is provided with two light emitting points, a main light emitting point 72 and a sub light emitting point 73. The main light emitting point 72 corresponds to the semiconductor laser chip 61 for the main light beam of the semiconductor laser package 60. The sub-light emitting points 73 correspond to the sub-light beam semiconductor laser chips 62 of the semiconductor laser package 70, respectively. Although not shown, it is assumed in this embodiment that the circuit configuration is such that the amount of light beams emitted from the main light emission point 72 and the sub light emission point 73 can be changed independently.

  The semiconductor laser package 70 is assumed to be equipped with a multi-semiconductor laser chip. Therefore, the main light emission point 72 and the sub light emission point 73 of the semiconductor laser chip 71 are arranged side by side in a direction parallel to the contact surface with the heat sink 12. On the other hand, the light beams emitted from the main light emitting point 72 and the sub light emitting point 73 must be arranged in a direction parallel to the information track as shown in FIG. Therefore, the heat sink 12 is rotated 90 degrees with respect to the semiconductor laser package 70.

  The semiconductor laser package 70 is obtained by modifying the light emitting points of the semiconductor laser package 50 of the second embodiment from three to two. The heat sink 12 has a function of radiating heat generated from the semiconductor laser chip.

  Similarly to the semiconductor laser package 60, in the semiconductor laser package 70, the emission power of the sub light beam emitted from the sub light emission point 73 is set to be weaker than the emission power of the main light beam emitted from the main light emission point 72. Also in the semiconductor laser package 70, the eccentric disk can be stably reproduced as in the third embodiment by setting the distance between the main light emitting point 72 and the sub light emitting point 73, that is, the chip distance to 80 μm or less. .

  Of course, as in the semiconductor laser package 1 or the like, the main light beam emitted from the main light emission point 72 and the sub light beam emitted from the sub light emission point 73 are not incoherent. For this reason, even if the semiconductor laser package 70 is used, high-quality servo signals can be stably obtained from a multi-layer disc having three or more layers as in the first embodiment.

  Since two semiconductor laser chips are mounted in the semiconductor laser package 60, the positional accuracy of mounting becomes a problem. However, in the semiconductor laser package 70, the interval between the light emitting points is determined by the semiconductor process. Therefore, it can be expected that the semiconductor laser package 70 has an effect that the mounting accuracy is improved as compared with the semiconductor laser package 60.

  A fifth embodiment of the present invention will be described in detail with reference to the drawings. Here again, a modification of the semiconductor laser package 60 of the third embodiment will be described.

  FIG. 13 is a schematic view of the semiconductor laser package 80 as viewed from the beam splitter 2. In the semiconductor laser package 80, two heat sinks 48 and 49 are arranged facing each other as shown in the figure. The main light beam semiconductor laser chip 81 is mounted on the heat sink 48, and the sub light beam semiconductor laser chip 82 is mounted on the heat sink 49.

  Further, the main light beam semiconductor laser chip 81 and the sub light beam semiconductor laser chip 82 are arranged with a chip interval h therebetween. That is, the main light beam semiconductor laser chip 81 corresponds to the main light beam semiconductor laser chip 61, and the sub light beam semiconductor laser chip 82 corresponds to the sub light beam semiconductor laser chip 62.

  Although not shown, it is assumed that the circuit configuration is such that the amount of light beams emitted from the main light beam semiconductor laser chip 61 and the sub light beam semiconductor laser chip 62 can be changed independently.

  Similar to the semiconductor laser package 60, the semiconductor laser package 80 is obtained by changing the light emitting points of the semiconductor laser package 50 from three to two. The heat sinks 48 and 49 have a function of radiating heat generated from the semiconductor laser chip. By using two heat sinks as compared with the semiconductor laser package 60, it is possible to expect an effect of obtaining a heat radiating performance approximately twice as large.

Similarly to the semiconductor laser package 60, in the semiconductor laser package 80, the emission power of the sub light beam emitted from the sub light beam semiconductor laser chip 82 is the emission power of the main light beam emitted from the main light beam semiconductor laser chip 81. Weaker output power.
Also in the semiconductor laser package 80, the eccentric disk can be stably reproduced as in the third embodiment by setting the chip interval h to 80 μm or less at most. Of course, the main light beam emitted from the semiconductor laser chip 81 for the main light beam and the sub light beam emitted from the semiconductor laser chip 82 for the sub light beam are not coherent with each other in the heat sink 49 as in the semiconductor laser package 1 or the like. Use things. For this reason, even if the semiconductor laser package 80 is used, a high-quality servo signal can be stably obtained from a multi-layer disc having three or more layers as in the first embodiment.

  The optical pickup of the present embodiment includes a semiconductor laser package capable of independently emitting at least one main light beam and one sub light beam, a beam splitter, a collimator lens, an objective lens, and light detection. Different from FIG. 1, an optical system deformed by a mirror or the like may be used.

  In the sixth embodiment, an optical disk device 400 on which the optical pickup described in the first embodiment is mounted will be described.

  FIG. 14 shows a block diagram of an optical disk device 400 on which the optical pickup 403 is mounted and a schematic circuit configuration of the optical disk device 400. In the optical disc apparatus 400, a three-layer optical disc 405 is fixed to a spindle 401, and the spindle 401 has a function of rotating the optical disc 405. In addition, a guide bar 402 is provided in the optical disc apparatus 400, and the optical pickup 403 can access a predetermined radial position of the optical disc 400 along the guide bar 402.

  The host 425 means an information home appliance using an optical disk device such as a personal computer. When an instruction to reproduce information on the optical disc 405 is input from the host 425 to the control circuit 412 in the optical disc apparatus 400, the control circuit drives the spindle motor drive circuit 419 and drives the spindle 401 to drive the optical disc 405. Start spinning.

  Next, the control circuit 412 drives the semiconductor laser chip driving circuit 418 to drive the semiconductor laser package 1 in the optical pickup 402, so that the main light beam semiconductor laser chip 14 and the two sub light beam semiconductor laser chips 13, 15 is turned on. As described above, the two sub-light beam semiconductor laser chips 13 and 15 are set to have a weaker emission power than the emission power of the main light beam semiconductor laser chip 14. In a conventional optical pickup using a diffraction grating, when the power of the main beam is 1, the sub beam is set in the range of 0.05 to 0.1. For this reason, it is preferable to use the emission powers of the two semiconductor laser chips 13 and 15 for the secondary light beam in the range of 0.05 to 0.1 with respect to the emission power of the semiconductor laser chip 14 for the main light beam.

  Next, the control circuit 412 drives the actuator drive circuit 415 to drive the actuator in the optical pickup 403 in the height direction. The signal detected from the photodetector 10 of the optical pickup 403 is sent to the servo signal generation circuit 410, and FES and TES are generated from the detection signal. The control circuit 412 drives the information recording surface selection circuit 413 to determine which information recording surface of the optical disc 405 is to be reproduced from the obtained FES. In a multilayer optical disc, the thickness of the cover layer differs for each information recording surface. For this reason, it is possible to determine which information recording surface is accessed by detecting the interval for each information recording surface of the optical disk 405 from the FES, that is, the thickness of the cover layer.

  A command to servo to the information recording surface selected from the information recording surface selection circuit 413 is sent from the control circuit 412 to the actuator driving circuit 415 to drive the actuator in the optical pickup 403 to control the position of the objective lens, A light beam is focused on the information recording surface. The control circuit 412 also has a function of driving the access control circuit 414 to move the optical pickup 403 along the guide bar 402 to a predetermined radial position.

  A detection signal detected from the photodetector 10 in the optical pickup 403 after being focused and irradiated on a predetermined information recording surface of the optical disk 405 is sent to the information signal reproducing circuit 435. The information signal reproduction circuit 435 reproduces the information signal recorded on the optical disc 405 from the detection signal, and the information signal is output to the host 425.

  The control circuit 412 drives the collimator lens drive circuit 416 so that the reproduction performance (for example, jitter and amplitude of the detection signal) of the information signal generated from the information signal reproduction circuit 435 is the best. The collimating lens 3 is moved to correct spherical aberration.

  By driving the circuit of the optical disc apparatus 400 as described above, the host 425 can acquire desired reproduction information.

  When an instruction to record information from the host 425 to the optical disk 405 is input to the control circuit 412, the same operation as in the above reproduction is performed, the laser light source suitable for the medium of the optical disk 405 is turned on, and the light beam is turned on. The optical disk 405 is focused and irradiated.

  Next, recording information to be recorded from the host 425 is input to the recording information signal conversion circuit 420, and the recording information signal conversion circuit 420 converts the recording information into a recording signal suitable for a predetermined medium. This recording signal is sent to the control circuit 412. The control circuit 412 drives the semiconductor laser chip driving circuit 418, controls the light amounts of the main light beam semiconductor laser chip 14 and the two sub light beam semiconductor laser chips 13 and 15, and records a recording signal on the optical disk 405. To do. The amount of light of the main light beam semiconductor laser chip 14 depends on the recording signal, and the amount of light of the two sub light beam semiconductor laser chips 13 and 15 is the ratio of the amount of light of the aforementioned main light beam semiconductor laser chip 14. If it is changed according to the above, the operation is the same as that of an optical pickup using a conventional diffraction grating.

  At this time, the control circuit 412 drives the access control circuit 414 and the spindle motor drive circuit 419 to perform access control of the optical pickup 402, rotation control of the optical disc 401, and the like according to the recording signal.

  Recording information received from the host can be recorded on the optical disk 405 by driving the circuit of the optical disk apparatus 400 as described above.

  As described above, the embodiment of the optical disk device 400 has been described. However, the present invention is not limited to this as long as at least the semiconductor laser chip driving circuit 418 and the information recording surface selection circuit 413 are mounted.

  As described above, according to the present invention, it is possible to provide an optical pickup and an optical disc apparatus capable of recording / reproducing a multilayer disc having three or more information recording layers.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  In addition, each of the above-described configurations may be configured such that some or all of them are configured by hardware, or are implemented by executing a program by a processor. Further, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser package, 2 ... Beam splitter, 3 ... Collimating lens, 8 ... Objective lens, 10 ... Photo detector, 13 ... Semiconductor laser chip for sub light beams, 14 ... Semiconductor laser chip for main light beams, 15 ... Sub Semiconductor laser chip for light beam

Claims (14)

In an optical pickup for reproducing or recording an optical disc having at least three information recording layers,
A main light source that emits a main beam for recording or reproducing a signal on the optical disc, a first sub light source that emits a first sub beam for servo that is incoherent, the main beam, A laser package including a second sub-light source that emits a second sub-beam for servo that is incoherent with the sub-beam 1;
An objective lens for condensing the main beam, the first sub beam, and the second sub beam on the optical disc;
An optical pickup comprising a photodetector for receiving the main beam, the first sub beam, and the second sub beam. The optical pickup according to claim 1,
The optical pickup is characterized in that the main light source is disposed between the first sub-light source and the second sub-light source. The optical pickup according to claim 2,
The laser package comprises an optical pickup comprising three light sources, the main light source, the first sub light source, and the second sub light source, in one laser chip. The optical pickup according to claim 2,
The laser package includes three laser chips: a main laser chip having the main light source, a first sub laser chip having the first sub light source, and a second sub laser chip having the first sub light source. An optical pickup comprising: The optical pickup according to claim 3 or 4,
The optical pickup characterized in that the main light beam, the first sub light beam, and the second sub light beam have a wavelength of 405 nm ± 10 nm. In an optical pickup for reproducing or recording an optical disc having at least three information recording layers,
A main light source that emits a main beam for recording or reproducing a signal on the optical disc and a sub light source that emits a sub beam for servo that is incoherent with the main beam are provided in one housing. Laser package,
An objective lens for condensing the main beam and the sub beam on the optical disc;
An optical pickup comprising a photodetector for receiving the main beam and the sub beam. The optical pickup according to claim 6,
2. The optical pickup according to claim 1, wherein the laser package comprises two light sources, the main light source and the sub light source, in one laser chip. The optical pickup according to claim 7,
2. The optical pickup according to claim 1, wherein the laser package comprises two laser chips, a main laser chip having the main light source and a sub laser chip having the sub light source. The optical pickup according to claim 7 or 8,
An optical pickup characterized in that the main light beam and the sub light beam have a wavelength of 405 nm ± 10 nm. The optical pickup according to claim 8, wherein
An optical pickup characterized in that a semiconductor laser is used as the main laser chip and an LED is used as the sub laser chip. The optical pickup according to claim 8 or 9, wherein
The laser package includes a main heat sink on which the main light source is mounted, and a sub heat sink on which the sub light source is mounted.
An optical pickup characterized in that the main heat sink and the sub heat sink are arranged facing each other inside the laser package. The optical pickup according to claim 7,
An optical pickup characterized in that an interval between the main light source and the sub light source is 80 μm or less. An optical pickup according to any one of claims 1 to 5,
A drive circuit for independently driving the main light source, the first sub light source, and the second sub light source of the optical pickup;
An optical disc apparatus comprising an information recording surface selection circuit for selecting a predetermined information recording surface of the optical disc from a focus error signal. An optical pickup according to any one of claims 6 to 12,
A drive circuit for independently driving the main light source and the sub-light source;
An optical disc apparatus comprising an information recording surface selection circuit for selecting a predetermined information recording surface of the optical disc from a focus error signal.

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