JP2012104184A - Optical pickup device and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a servo signal and a reproduction signal stable to a positional deviation of a light receiving surface with a simple configuration.SOLUTION: An optical pickup device 2 includes a laser light source unit 20 housing a first light source 20a and a second laser light source 20b for emitting light fluxes at least independent of each other in one casing, a light splitting unit 26 for splitting the light fluxes emitted from the laser light source unit 20 and reflected to an information layer of an optical disk 5, and a photodetector 27 provided with a plurality of light receiving surfaces for receiving light fluxes split by the light splitting unit 26. The light splitting unit 26 includes a first light splitting element for splitting a first light flux 200a emitted from the first laser light source 20a into a plurality of regions, and a second light splitting element for splitting a second light flux 200b emitted from the second laser light source 20b into a plurality of regions and is arranged at a position at which only a light flux reflecting information of the optical disk 5 is made incident.

Description

  The present invention relates to an optical pickup device and an optical disk device, and is particularly suitable for application to an optical pickup device and an optical disk device that perform recording and reproduction of a plurality of types of optical disks.

  In general, an optical pickup device includes an optical component that guides a laser beam emitted from a laser light source to an optical disc and guides a light beam reflected by the optical disc to a photodetector. The optical pickup device is used for reproducing and recording optical disks such as DVD (Digital Versatile Disk) and CD (Compact Disk).

  In recent years, it has been proposed to use a two-wavelength multi-laser light source in an optical pickup device when recording or reproducing optical discs having different wavelengths such as DVD and CD. The two-wavelength multi-laser light source is a laser light source in which a CD semiconductor laser and a DVD semiconductor laser are stored in a common housing. Use of the two-wavelength multi-laser light source makes it possible to reduce the size of the optical pickup device, such as space-saving arrangement of the laser light source, elimination of prisms for two-wavelength synthesis, and sharing of optical components such as lenses and photodetectors. This is advantageous in terms of cost reduction.

  A DVD and CD compatible optical pickup device using a two-wavelength multi-laser light source generally uses a three-beam optical system as disclosed in Patent Document 1, for example. In the three-beam optical system, the light beam emitted from the laser light source is separated into three light beams by an outward diffraction grating, condensed on the information layer of the optical disk, and separated into three light beams reflected by the information layer. Focus on the information layer. Then, by detecting three light fluxes reflected from the information layer by an astigmatism method, a focus error signal (FES), a tracking error signal (TES), or a reproduction signal that is a servo signal is detected. An RF signal (RF: Radio Frequency) is generated.

  In general, the optical pickup device controls the position of the objective lens using a focus error signal and a tracking error signal in order to correctly irradiate a spot on a predetermined recording track in the optical disk. Specifically, by detecting the focus error signal, the objective lens is displaced in the focus direction and adjustment is performed in the focus direction. Further, by detecting the tracking error signal, the objective lens is displaced in the radial direction of the optical disc to perform tracking adjustment.

JP 2009-48756 A

  However, when the above-described three-beam optical system is used, in order to detect a light beam with high accuracy on the light receiving surface of the diffraction grating, the arrangement direction of the three light beams condensed on the information layer of the optical disk is set to the track direction of the optical disk. It was necessary to attach with very high accuracy. Also, when trying to realize a three-beam optical system with a two-wavelength multi-laser light source, the two lasers are housed in a single casing, so the direction of each light beam has to be adjusted.

  Furthermore, the three-beam optical system requires a diffraction grating that divides the light beam emitted from the light source into three beams, and a light receiving element that separately detects the three light beams. There was a drawback that the structure would be complicated.

  Conventionally, the astigmatism method used to obtain the servo signal is greatly deteriorated due to the positional deviation of the light beam incident on the light receiving surface of the photodetector, and the sensitivity due to the positional deviation is also large. This is an issue. That is, there is a problem that the smaller the spot shape of the light beam incident on the light receiving surface of the photodetector is, the greater the influence on the vertical and horizontal deviation of the light beam incident on the photodetector is.

  Therefore, it is desirable to use a so-called one-beam optical system that collects one light beam on the information layer of the optical disk and generates a servo signal or an RF signal using the reflected light beam. In addition, it is desirable to use a signal generation method having a smaller positional deviation sensitivity than the astigmatism method.

  The present invention has been made in consideration of the above points. In a DVD / CD compatible optical pickup apparatus using a two-wavelength multi-laser light source, a servo signal and reproduction that are stable with respect to the positional deviation of the light receiving surface with a simple configuration. An optical pickup device capable of generating a signal and an optical disk device equipped with the optical pickup device are proposed.

  In order to solve such a problem, in the present invention, a laser light source unit in which at least a first laser light source and a second laser light source that emit light beams independent from each other are stored in one housing, and the laser light source unit emits light. Further, an objective lens for condensing the light flux on the information layer of the optical disc, a light splitting unit for splitting the light flux emitted from the laser light source unit and reflected on the information layer of the optical disc, and the light splitting unit. And a photodetector having a plurality of light receiving surfaces for receiving the light flux, wherein the light splitting unit divides the first light flux emitted from the first laser light source into a plurality of regions. 1 light splitting element, and a second light splitting element that splits the second light flux emitted from the second laser light source into a plurality of regions, Only light flux reflected by the information disk is characterized in that it is disposed at a position where the incident.

  In the present invention, a laser light source unit storing at least a first laser light source and a second laser light source that emit light beams independent from each other in one housing, and the light beams emitted from the laser light source unit. An objective lens for focusing on the information layer of the optical disc, a light splitting unit for splitting the light flux emitted from the laser light source unit and reflected by the information layer of the optical disc, and the light flux split by the light splitting unit. A light detector having a plurality of light receiving surfaces for receiving light, wherein the light splitting unit splits the first light flux emitted from the first laser light source into a plurality of regions. An optical element, and a second light splitting element that splits the second light beam emitted from the second laser light source into a plurality of regions, and reflects information on the optical disk An optical pickup device that is arranged at a position where only the incident light beam is incident, a laser lighting circuit for driving the laser light source unit, and a detection signal obtained by a photodetector of the optical pickup device In order to stably reproduce the information recorded on the optical disc from the servo signal generation circuit for generating a stable servo signal for the optical disc and the detection signal obtained by the photodetector of the optical pickup And a control circuit that controls the laser lighting circuit, the servo signal generation circuit, and the information signal reproduction circuit.

  According to the present invention, in an optical pickup device using a two-wavelength multi-laser light source, it is possible to generate a servo signal and an RF signal that are stable with respect to the positional deviation of the light receiving surface with a simple configuration.

1 is a block diagram illustrating a configuration example of an optical disc device according to a first embodiment. It is a top view which shows the structural example of the optical pick-up apparatus by 1st Embodiment. It is an enlarged view which shows the structural example of a 2 plane diffraction grating. It is the figure seen from the incident direction of the light beam which shows an example of the shape of a diffraction grating. It is the figure which looked at the structural example of the light-receiving surface of a photodetector from the incident direction of the light beam. It is a figure which shows the example which signal light condensed on the light-receiving surface of the photodetector. It is the figure seen from the incident direction of the light beam which shows the modification of the light-receiving surface of the photodetector by 1st Embodiment. It is the figure seen from the incident direction of the light beam which shows the example which signal light condensed on the light-receiving surface of the photodetector of FIG. It is the figure seen from the incident direction of the light beam which shows an example of the shape of the diffraction grating by 2nd Embodiment. It is the top view seen from the incident direction of the light beam which shows the structural example of the light-receiving surface of the photodetector by 2nd Embodiment. It is the figure seen from the incident direction of the light beam which shows the example which condensed DVD signal light on the light-receiving surface of a photodetector. It is the figure seen from the incident direction of the light beam which shows the example which condensed CD signal light on the light-receiving surface of a photodetector. It is an enlarged view of the information layer and objective lens of a two-layer optical disk. It is the figure seen from the incident direction of the light beam which shows the example which the signal light and the stray light entered into the DVD diffraction grating surface. It is the figure seen from the incident direction of the light beam which shows the example which 0th-order stray light entered on the photodetector. It is the figure seen from the incident direction of the light beam which shows the example which + 1st-order and -1st-order stray light entered on the photodetector. It is the figure seen from the incident direction of the light beam which shows the example which the signal light and the stray light entered into the DVD diffraction grating surface. It is the figure seen from the incident direction of the light beam which shows the example which the + 1st-order and -1st-order stray light entered on the photodetector. It is the figure seen from the incident direction of the light beam which shows the example which the signal light and the stray light entered into the DVD diffraction grating surface. It is the figure seen from the incident direction of the light beam which shows the example which the + 1st-order and -1st-order stray light entered on the photodetector.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(1-1) First Embodiment FIG. 1 shows an optical disk device 1 on which an optical pickup device 2 according to this embodiment is mounted. The optical disk device 1 includes an optical pickup device 2, a spindle motor 3, a spindle motor drive circuit 4, a servo signal generation circuit 6, an information signal reproduction circuit 7, an actuator drive circuit 8, a control circuit 10, an access control circuit 11, and a laser lighting circuit 12. And an information signal recording circuit 13.

  The optical disk 5 held on the turntable (not shown) of the spindle motor 3 is rotationally driven around the central axis by the spindle motor drive circuit 4. The optical pickup device 2 has a function of optically recording and reproducing information on the information layer of the optical disc 5. In the following, a CD and a DVD will be described as an example of the optical disk 5, but the present invention is not limited to this example, and other recording media may be used.

  Further, the signal detected from the photodetector in the optical pickup device 2 is sent to the servo signal generation circuit 6 and the information signal reproduction circuit 7.

  The servo signal generation circuit 6 generates a focus error signal, a tracking error signal, a tilt control signal, and the like suitable for the optical disc 5 based on the signal detected by the optical pickup device 2. Then, the position of the objective lens 9 is controlled by driving the objective lens actuator in the optical pickup device 2 through the actuator drive circuit 8 based on these signals.

  The information signal reproduction circuit 7 reproduces the information signal recorded on the optical disk 5 from the signal detected by the optical pickup device 2.

  A part of the signals obtained by the servo signal generation circuit 6 and the information signal reproduction circuit 7 is sent to the control circuit 10. The control circuit 10 transmits a laser driving signal to the laser lighting circuit 12, drives the laser lighting circuit 12, and supplies a laser driving current to the two-wavelength multi-laser light source in the optical pickup device 2. The laser lighting circuit 12 can be incorporated in the optical pickup device 2.

  Signals obtained by the servo signal control circuit 6, the information signal advance circuit 7, the spindle motor drive circuit 4 and the access control circuit 11 are input to the control circuit 10. The control circuit 10 performs rotation control of the spindle motor 3, position control of the objective lens 9, access direction position control of the optical pickup device 2, and the like.

  Further, the control circuit 10 has a function of discriminating the type of the optical disk 5 to be reproduced. After determining the type of the optical disk 5, the control circuit 10 drives the laser lighting circuit 12 so as to emit a light beam having a desired oscillation wavelength. In addition, the control circuit 10 performs a process of enabling the light receiving surface on the photodetector that receives a light beam having a desired oscillation wavelength.

  During recording, the information signal recording circuit 13 provided between the control circuit 10 and the laser lighting circuit 12 drives the laser lighting circuit 12 to record information on the optical disc 5 based on the recording control signal.

  Next, the optical system of the optical pickup device 2 mounted on the optical disk device 1 of FIG. 1 will be described. As shown in FIG. 2, the optical pickup device 2 includes a two-wavelength multi-laser light source 20, a polarization beam splitter 21, a front monitor 22, a collimator lens 23, a quarter-wave plate 24, a rising mirror 25, an objective lens 9, 2 A surface diffraction grating 26 and a photodetector 27 are provided.

  The two-wavelength multi-laser light source 20 includes a semiconductor laser light source 20a and a semiconductor laser light source 20b. The semiconductor laser light source 20a is a semiconductor laser light source for DVD that emits a light beam having a wavelength of about 660 nm, for example. The semiconductor laser light source 20b is, for example, a CD semiconductor laser light source that emits a light beam having a wavelength of about 785 nm. When recording / reproducing a DVD, a DVD light beam 200a is emitted as divergent light from the semiconductor laser light source 20a for DVD. When recording / reproducing a CD, a CD light beam 200b is emitted as divergent light from the CD semiconductor laser light source 20b.

  In FIG. 2, the DVD light beam 200a is indicated by a solid line, and the CD light beam 200b is indicated by a dotted line. The semiconductor laser generally emits a linearly polarized light beam, and it is assumed that the linearly polarized light beam 200a or 200b is also emitted from the two-wavelength multi-laser light source 20.

  Furthermore, it is assumed that the semiconductor laser light source for DVD 20a and the semiconductor laser light source for CD 20b are respectively arranged at positions separated by Ta as shown in FIG.

  The light beam 200 a or the light beam 200 b emitted from the two-wavelength multi-laser light source 20 is separated into a light beam that passes through a polarizing beam splitter 21 (PBS) and a light beam that reflects from the polarizing beam splitter 21. The polarization beam splitter 21 is an element that transmits linearly polarized light in a predetermined direction and reflects linearly polarized light in a direction orthogonal to the direction. Here, the polarization is controlled so as to reflect most of the light beam 200a or the light beam 200b.

  The light beam that has passed through the polarization beam splitter 21 is incident on the front monitor 22, and the light beam that has been reflected by the polarization beam splitter 21 is incident on the collimator lens 23.

  In general, in order to improve the accuracy of the recording / reproducing operation of the optical disc 5, the light quantity of the light beam 200a or 200b irradiated on the optical disc 5 is detected by the front monitor 22 and controlled to a desired value by the control circuit 206. Is required. The front monitor 22 detects a change in the light amount of the light beam 200a or the light beam 200b emitted from the two-wavelength multi-laser light source 20, and feeds it back to the control circuit 206 in FIG. This makes it possible to control the amount of light flux. For simplification, the light beam 200a or the light beam 200b incident on the front monitor 22 is not shown in FIG.

  Further, the light beam 200a or the light beam 200b reflected by the polarization beam splitter 21 and incident on the collimator lens 23 is converted into a light beam substantially parallel to the optical axis. Subsequently, the light beam 200a or the light beam 200b passes through the quarter-wave plate 24 and is converted into circularly polarized light. Then, after reflecting off the rising mirror 15, the light passes through the objective lens 9 mounted on an actuator (not shown) and is condensed on the information layer of the optical disk 5. Since there is no element that splits the light beam in the forward optical path from the two-wavelength multi-laser light source 20 to the information layer of the optical disk 5, one light beam is incident on the information layer, that is, one beam.

  The light beam 200a or the light beam 200b reflected from the information layer of the optical disk 5 travels in the reverse direction on the same optical path as the forward light beam, and passes through the objective lens 9, the rising mirror 25, the quarter wavelength plate 24, and the collimating lens 23. The light passes through and enters the polarization beam splitter 21. At this time, since the light beam 200a or the light beam 200b passes through the quarter-wave plate 24 twice, it is linearly polarized light in a direction orthogonal to the forward path. Accordingly, the light beam 200 a or the light beam 200 b passes through the polarization beam splitter 21. The light beam 200 a or the light beam 200 b that has passed through the polarization beam splitter 21 passes through the two-surface diffraction grating 26 and is collected on the photodetector 27.

  The light detector 27 has a light receiving surface configuration that can collect the light beam 200a or the light beam 200b. In the light detector 27, an RF signal or a focus error signal that is a reproduction signal according to the amount of light irradiated on the light receiving surface. And a tracking error signal are generated.

  In FIG. 2, the center of the light beam 200a from the DVD semiconductor laser 10a is drawn so as to pass through the center of the optical component. However, the present invention is not limited to this. The center of the light beam 200b from the CD semiconductor laser 10b may pass through the center of the optical component, and the center of the optical component may be between the center of the light beam 200a and the center of the CD light beam 200b.

  FIG. 3 is a diagram showing the relationship between the light beam 200a and the light beam 200b incident on the two-plane diffraction grating 26 in FIG. 2 and the light beam 200a and the light beam 200b emitted from the side surface of the grating. The two-plane diffraction grating 26 shown in FIG. 3A has two surfaces, a DVD diffraction grating surface 30 where the DVD light beam 200a is diffracted and a CD diffraction grating surface 31 where the CD light beam 200b is diffracted.

  The DVD diffraction grating surface 30 diffracts the light beam 200a having only the DVD wavelength in a predetermined direction and transmits the CD light beam 200b. Further, the CD diffraction grating surface 31 diffracts the light beam 200b having only the CD wavelength in a predetermined direction and transmits the light beam 200a having the DVD wavelength.

  The two-plane diffraction grating 26 is made of a transparent substrate made of glass or the like, for example, and is provided with periodic uneven grooves on the light incident surface. As a result, the light beam 200a and the light beam 200b incident on the incident surface side are diffracted into three types of light beams, that is, the 0th-order diffracted light that is the main beam, the + 1st-order diffracted light that is the sub-beam, and the −1st-order diffracted light. Furthermore, the + 1st-order diffracted light or the first-order diffracted light is diffracted in a predetermined direction according to the angle and interval of the concave and convex grating grooves on the light incident surface of the two-surface diffraction grating 26.

  FIG. 3B shows a state where the DVD light beam 200 a is diffracted by the DVD diffraction grating surface 30. First, when the DVD light beam 200a is incident on the two-surface diffraction grating 26, it is diffracted by the DVD diffraction grating surface 30, and as shown in FIG. 3B, the 0th-order diffracted light 201a, the + 1st-order diffracted light 202a, and the −1st-order diffracted light. Diffracted to 203a. Thereafter, the 0th-order diffracted light, the + 1st-order diffracted light, and the −1st-order diffracted light of the diffracted DVD light beam 200a pass through the CD diffraction grating surface 31 and enter the photodetector 27.

  On the other hand, FIG. 3C shows a state where the CD light beam 200 b is diffracted by the CD diffraction grating surface 31. First, when the CD light beam 200 b is incident on the two-sided diffraction grating 26, it passes through the DVD diffraction grating surface 30 and enters the CD diffraction grating surface 31. Then, as shown in FIG. 3C, the CD light beam 200b is diffracted by the CD diffraction grating surface 31 into 0th-order diffracted light 201b, + 1-shaped diffracted light 202b, and -1st-order diffracted light 203b. Incident.

  The diffracted light from the DVD diffraction grating surface 30 and the CD diffraction grating surface 31 is mainly composed of 0th-order diffracted light, + 1st-order diffracted light, and -1st-order diffracted light.

  FIG. 4A is an example of a schematic plan view of the DVD diffraction grating surface 30 viewed from the direction along the optical axis direction. A circle drawn with a solid line indicates the DVD light beam 200 a incident on the DVD diffraction grating surface 30. The DVD diffraction grating surface 30 is divided into eight diffraction regions 30a, 30b, 30c, 30d, 30e, 30f, 30g, and 30h. For each region, the angle and interval of the grating grooves are determined so as to diffract the DVD light beam 200a incident on the DVD diffraction grating surface 30 in a predetermined direction.

  The DVD diffraction grating surface 30 is provided with a central dividing line 32 in a direction substantially parallel to the track direction, that is, an optical disc tangential direction (hereinafter abbreviated as Tan direction). The DVD light flux 200a indicated by a circle is arranged so that the substantial center of the optical axis overlaps. Further, the eight regions of the DVD diffraction grating surface 30 are arranged so as to be line symmetric with respect to the central dividing line 32 as a central axis.

  A region composed of 30a, 30b, 30c, and 30d is referred to as a region B, and a region composed of regions A, 30e, 30f, 30g, and 30h will be described below.

  FIG. 4B is an example of the grating shape of the CD diffraction grating surface 31. A circle drawn with a dotted line indicates the CD light beam 200b incident on the DVD diffraction grating surface 30. The CD light beam 200b has a smaller spot diameter than the DVD light beam 200a because of the numerical aperture of the objective lens 9.

  The CD diffraction grating surface 31 is divided into eight diffraction areas 31a, 31b, 31c, 31d, 31e, 31f, 31g and 31h, and the angle of the grating grooves so as to diffract the CD light beam 200b in a predetermined direction. And intervals are defined.

  Similarly, the CD diffraction grating surface 31 is provided with a central dividing line 33 in the Tan direction, and is arranged so that the approximate center of the optical axis of the CD light beam 200b indicated by the dotted circle overlaps with the central dividing line 33. Has been. Further, the eight regions of the CD diffraction grating surface 31 are arranged so as to be line symmetric with respect to the central dividing line 33 as a central axis.

  A region composed of 31a, 31b, 31c and 31d is referred to as a region B ', and a region composed of regions A', 31e, 31f, 31g and 31h will be described below.

  Further, as shown in FIG. 2, the DVD semiconductor laser light source 20a and the CD semiconductor laser light source 20b are arranged at positions where the intervals between the light emitting points are separated by Ta. For this reason, the approximate center of the optical axis of the CD light beam 200 b incident on the CD diffraction grating surface 31 is located at a position separated from the approximate center of the optical axis of the DVD light beam 200 a incident on the DVD diffraction grating surface 30 by Tb.

  FIG. 5 is an example of the configuration of the photodetector 27 in FIG. The light detector 27 includes a plurality of light receiving surfaces for receiving the condensed DVD diffracted light and CD diffracted light. There are a total of 21 light receiving surfaces from D0 to D20. Of these light receiving surfaces, the 0th-order diffracted light of DVD is incident on D0, and the 0th-order diffracted light of CD is incident on D20. Note that the diffracted light of DVD is represented by black dots, and the diffracted light of CD is represented by white dots.

  The interval between the condensing position of the 0th-order diffracted light of the DVD indicated by black dots and the condensing position of the 0th-order diffracted light of the CD indicated by white dots corresponds to the interval between the emission points of the semiconductor laser. As described above, the DVD semiconductor laser light source 20a and the CD semiconductor laser light source 20b are arranged at positions where the light emission point intervals are separated from each other by Ta. The condensing position of the 0th-order diffracted light is separated by Ta. The shaded area represents a dark line part for allowing the focused signal light to enter.

  FIG. 6A shows a light receiving position when the DVD diffracted light enters the photodetector 27. The + 1st order diffracted lights of the light beams diffracted in the regions 30a, 30b, 30c and 30d (region A) and 30e, 30f, 30g and 30h (region B) of the DVD diffraction grating surface 30 are the light receiving surfaces D1, D2, D3 and D4, respectively. , D5, D6, D7 and D8. The -1st order diffracted light beams diffracted in the regions 30e, 30f, 30g, and 30h (region B) are dark line portions between the light receiving surfaces D10 and D11, dark line portions between D14 and D15, and dark lines between D12 and D13, respectively. And the dark line part between D16 and D17. The 0th-order diffracted light that has passed through the two-plane diffraction grating 26 is incident on D0. The -1st order diffracted light of the light beam diffracted in the regions 30a, 30b, 30c and 30d enters the photodetector 27 while avoiding the light receiving surface at a position in a range 24 indicated by a broken line in FIG.

  FIG. 6B shows a light receiving position when CD diffracted light enters the photodetector 27. The + 1st order diffracted lights of the light beams diffracted by the regions 31a, 31b, 31c, 31d (region A ′) and 31e, 31f, 31g, and 31h (region B ′) of the CD diffraction grating surface 31 are the light receiving surfaces D1, D2, respectively. , D3, D4, D9, D6, D7 and D8. The -1st order diffracted light beams diffracted in the regions 31e, 31f, 31g, and 31h (region B ') are dark line portions between the light receiving surfaces D14 and D15, dark line portions between D10 and D11, and between D18 and D19, respectively. The light enters the dark line portion, the dark line portion between D12 and D13. The 0th-order diffracted light that has passed through the two-plane diffraction grating 26 is incident on D20. The first-order diffracted light of the light beams diffracted in the regions 31a, 31b, 31c, and 31d (region A ′) avoids the light receiving surface at a position in a range 25 indicated by a broken line in FIG. Is incident on.

  The light receiving surfaces D0, D1, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, D14, D15, D16, D17, D18, D19, and D20 of the photodetector 27, respectively. S0, S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, S11, S12, S13, S14, S15, S16, S17, S18, S19 and S20 are obtained in order. Can do. The servo signal generation circuit 6 described above generates a focus error signal, a tracking error signal, and an RF signal using the signal light incident on each of the light receiving surfaces.

  For example, a double knife edge method is used to detect the focus error signal. In order to generate the focus error signal by the double knife edge method, the signal light is incident on the dark line portion between the light receiving surfaces divided into two in the light collection state. The dark line portion detects light with a predetermined sensitivity according to the distance from the light receiving surface, even with light away from the light receiving surface. By using this dark line portion, the focus error with sensitivity to defocusing is detected. A signal can be generated.

  Defocusing is a state in which the position of the information layer of the optical disc 5 approaches or moves away from the focal length of the objective lens 9. In the defocus state, a part of the light beam is incident on one of the light receiving surfaces divided into two. And the difference of the signal detected by the divided | segmented 2-part light-receiving surface is taken, and when a difference becomes 0 shows a condensing state. Therefore, the actuator drive circuit 8 controls the objective lens 9 so that the difference becomes zero. Since the double knife edge method is a known technique, detailed description thereof is omitted.

  In this embodiment, using the double knife edge method described above, the signals S10, S11, S12, S13, S14, S15, S16, S17, S18, and S19 are used to calculate DVD and CD using the arithmetic expressions shown in Expression 1 and Expression 2. Generate a focus error signal.

  On the other hand, for detection of the tracking error signal, for example, a one-beam differential push pull method (DPP: Differential Push Pull) (hereinafter referred to as DPP method) is used.

  The DPP method is a method of generating a tracking error signal using a push-pull signal without causing an offset when a lens is shifted. The push-pull signal can be generated by dividing the light beam reflected by the information layer of the optical disc into two by a dividing line that is substantially parallel to the Tan direction on the diffraction grating and passes through the center of the light beam, and taking the difference between the left and right light beams. it can. However, with only a signal including a push-pull component, when the objective lens 9 is displaced in the radial direction of the optical disk (hereinafter abbreviated as the Rad direction), that is, when the lens is shifted, the light quantity unbalance between the right and left light beams occurs, and the direct current is generated. Component offset occurs, resulting in an unstable tracking error signal. Therefore, a stable tracking error signal can be obtained by performing an operation for canceling the offset using a signal including an offset component. Performing the DPP method with one beam is called a one-beam DPP method. Since 1-beam DPP is a known technique, further explanation is omitted.

  Using the above-described one-beam DPP method, DVD and CD tracking error signals are generated from the signals S1, S2, S3, S4, S5, S6, S7, and S8, S9 by the arithmetic expression shown in Equation 2. A signal including the push-pull component is referred to as a main push-pull (hereinafter abbreviated as MPP) signal, and a signal for canceling the offset component of the MPP signal is referred to as an offset cancel (hereinafter abbreviated as OC) signal.

  K1 and k2 in Equation 2 correct the offset component included in the signal of the first term in the equation of the tracking error signal and the offset component included in the signal of the second term in the equation when the objective lens is lens-shifted. It is a coefficient to do. By performing such calculation, it is possible to generate a stable tracking error signal without offset even when the objective lens is shifted.

  Further, an RF signal is generated on the basis of a signal obtained from the 0th-order diffracted light, as shown in the following equation (3). Since the RF signal is generated only by the condensed 0th-order diffracted light, it can be realized by one light receiving surface. Thus, since there are few light-receiving surfaces, a signal with little noise can be obtained. Also, an RF signal with a good S / N ratio can be generated by increasing the light amount of the 0th-order diffracted light.

  As in the present embodiment, the configuration using the two-surface diffraction grating in the return path can solve the problem caused by the one-beam optical system using the two-wavelength multi-laser light source 20. This will be described below.

  As described above, in the two-wavelength multi-laser light source 20, the interval between the emission points of the DVD semiconductor laser light source 20a and the CD semiconductor laser light source 20b is shifted by Ta. That is, the optical axes are shifted from each other. Therefore, the centers of the optical axes of the DVD light beam and the CD light beam are also shifted from each other even on the two-surface diffraction grating 26 that divides the light beam.

  The distance Tb between the center division line 33 in the Tan direction of the CD diffraction grating surface 31 shown in FIG. 4B and the center division line 32 in the Tan direction of the DVD diffraction grating surface 30 shown by the alternate long and short dash line is the distance between the emission points. This is the amount of deviation of the optical axis center on the diffraction grating caused by the deviation of Ta. If a common central dividing line is used in a state where the center of the optical axis is deviated, the division of one or both light beams becomes asymmetric in the Rad direction of FIG. If it becomes asymmetric, there arises a problem that an offset occurs in the signal.

  In the two-wavelength multi-laser light source 20, the oscillation wavelength of DVD is approximately 660 nm, and the oscillation wavelength of CD is approximately 785 nm, which is approximately 1.2 times different. For this reason, it is necessary to increase the number of light receiving surfaces of the photodetector 27 or to increase the size of the light receiving surface. When the size of the light receiving surface is increased, a problem that signal noise is increased occurs.

  However, if the two-surface diffraction grating 26 is used, it is possible to determine the dividing line in the Tan direction independently. As a result, the asymmetry between the DVD light flux and the CD light flux does not occur, and the signal offset problem can be solved.

  Further, in the two-plane diffraction grating 26, it is possible to independently design the pitch interval of the concave and convex grating grooves carved in each region of each grating surface. Therefore, the diffraction directions of the DVD light beam 200a and the CD light beam 200b having different wavelengths can be determined freely.

  Conventionally, when the same grating surface is used for light beams having different wavelengths, the diffraction groove direction is determined depending on the wavelength because the pitch interval of the grating grooves is constant. It was difficult to share the light receiving surface.

  However, the condensing position of the divided light flux on the photodetector 27 can be freely designed for DVD and CD, and as a result, a part of the light receiving surface can be shared. That is, even when light beams having different wavelengths are used, it is not necessary to increase the size of the light receiving surface, and the photodetector 27 can be made compact. Further, by using a common light receiving surface for DVD and CD except for a part, the arithmetic expressions for DVD and CD can be realized by using the same signal, except for a part, as in equations (1) and (2). . In other words, it is possible to have a configuration with little arithmetic switching.

  Further, when the two-surface diffraction grating 26 is arranged in the round-trip optical path, the light beam is divided into a plurality of parts by the two-surface diffraction grating 26 in the forward path, and these divided unnecessary light beams reflect the information layer of the optical disk 5; There was a problem that it was detected by the photodetector 27 as stray light. Therefore, in the present embodiment, it is possible to prevent stray light from being generated by arranging the two-surface diffraction grating 26 on the return path and configuring the outgoing light flux to be one beam.

  Furthermore, this embodiment can reduce the signal performance degradation due to the position shift as compared with the astigmatism method. In the case of the astigmatism method, for example, a light beam having an effective diameter of, for example, about 40 to 60 μm is generally incident on the quadrant light receiving surface of the photodetector. Here, when the position of the photodetector is shifted by 2 to 5 μm, the balance of the signal light incident on the light receiving surface is deteriorated, and the performance of the focus error signal and the tracking error signal is deteriorated.

  However, when the light beam is collected on the light receiving surface as in the present embodiment, the tracking error signal performance is not degraded unless the photodetector is displaced from the light receiving surface. Further, by adjusting the dark line width of the focus error signal, it is possible to alleviate the performance deterioration of the focus error signal with respect to the positional deviation.

  Specifically, in the present embodiment, the two-surface diffraction grating 26 having the DVD diffraction grating surface 30 and the CD diffraction grating surface 31 shown in FIGS. 3 and 4 is arranged in the return optical path, and the light reception shown in FIG. A photodetector 27 having a surface configuration is provided. Accordingly, light that generates a servo signal and an RF signal that are stable with respect to the positional deviation of the light receiving surface without being limited by the difference in the emission point position of the two-wavelength multi-laser light source 20 or the difference in wavelength between the DVD and the CD. The pickup device 2 can be realized. In addition, a part of the light receiving surface of the photodetector 27 can be shared. Further, since no special parts other than the two-surface diffraction grating 26 are used, a simple optical system configuration with a small number of parts is realized.

(1-2) Other Embodiments In the first embodiment described above, the divided region configuration of the two-plane diffraction grating 26 and the light receiving surface configuration of the photodetector 27 are as shown in FIGS. However, the present invention is not limited to this. For example, the photodetector 27 may have the configuration shown in FIG.

  In FIG. 7, the light receiving surfaces D1 to D4 are arranged in a row in the Tan direction in FIG. 5, whereas two light receiving surfaces D1 to D4 are arranged in the Tan direction so as to face the 0th-order diffracted light. Arranged. At this time, the light receiving position when the DVD diffracted light enters the photodetector 27 is as shown in FIG. Further, the light receiving position when the CD diffracted light enters the photodetector 27 is shown in FIG. Further, the shape of the two-surface diffraction grating 26 and signal generation are the same as those in FIG. With the configuration of the light receiving surface shown in FIG. 7, the size of the photodetector can be made smaller in the Tan direction than the configuration of the light receiving surface shown in FIG. 5.

  The two-surface diffraction grating 26 and the light detector 27 are free from the limitation of the difference in the emission point position of the two-wavelength multi-laser light source 20 and the difference in the wavelength of DVD and CD, Any configuration may be used as long as an RF signal can be generated.

As described above, the dihedral diffraction grating 26 diffracts the DVD light beam 200a while not diffracting the CD light beam 200b, and the CD diffraction grating surface 31 diffracts the CD light beam 200b. The DVD light beam 200a may not have a wavelength selective function such as not diffracting. For example, the DVD diffraction grating surface 30 may diffract only P-polarized light, and the CD diffraction grating surface 31 may have a polarization-selective function such as diffracting only S-polarized light. Specifically, in FIG. 3B, the DVD light beam 200a is a polarized light beam (P-polarized light) in a direction substantially parallel to the paper surface, and in FIG. 3C, the CD light beam 200b is a light beam substantially perpendicular to the paper surface. It is assumed that a polarized light beam (referred to as S-polarized light) enters each of them. At this time, the DVD light beam 200a can be diffracted only on the DVD diffraction grating surface 30 and the CD light beam 200b can be diffracted only on the CD diffraction grating surface 31 without having wavelength selectivity. In addition, such an element having polarization can be realized by using a crystal plate or a polymer crystal material having birefringence.
As described above, the dihedral diffraction grating 26 can be any structure as long as it has a function of diffracting only the light beam having the oscillation wavelength of the DVD on the DVD diffraction grating surface and diffracting only the light beam having the oscillation wavelength of the CD on the CD diffraction grating surface. Such a lattice may be used.

(1-3) Effects of this Embodiment As described above, according to the optical pickup device 2 according to this embodiment, in the DVD and CD compatible optical pickup device 2 using the two-wavelength multi-laser light source 20, two-plane diffraction is performed. When the grating is used, the dividing line in the Tan direction can be determined independently, and the optical pickup device 2 capable of generating a stable servo signal and RF signal with respect to the positional deviation of the light receiving surface with a small signal offset, and It is possible to provide an optical disc apparatus 1 equipped with the same.

(2-1) Second Embodiment FIG. 9 is an example of a schematic plan view of the two-surface diffraction grating 26 used in the optical pickup device 2 according to the second embodiment viewed from a direction along the optical axis direction. Indicates. The difference from the first embodiment is that the DVD diffraction grating surface 40 and the CD diffraction grating surface 41 of the two-surface diffraction grating 26 have different shapes from the DVD diffraction grating surface 30 and the CD diffraction grating surface 31. . The optical system has the same configuration as that shown in FIG. 2, and the configuration for reflecting and transmitting the light beam by the two-surface diffraction grating 26 is the same as that shown in FIG.

  As shown in FIG. 9A, the DVD diffraction grating surface 40 has 13 diffraction regions of regions 40a, 40b, 40c, 40d, 40e, 40f, 40g, 40h, 40i, 40j, 40k, 40l and 40m. I know. The direction of the grating grooves is determined so that the light beams incident on the DVD diffraction grating surface 40 are each diffracted in a predetermined direction.

  The DVD diffraction grating surface 40 is provided with a center dividing line 32 in the Tan direction. The central dividing line 32 is arranged so that the approximate center of the optical axis of the DVD light beam 200a indicated by a solid circle overlaps. Further, the 13 regions of the DVD diffraction grating surface 40 are arranged so as to be line symmetric with respect to the central dividing line 32 as a central axis.

  In the two-surface diffraction grating 26 according to the second embodiment, the region composed of 40a, 40b, 40c, and 40d is defined as the region composed of regions E, 40e, 40f, 40g, and 40h. Hereinafter, the region composed of 40j, 40k and 40l will be described as region H composed of regions G and 40m.

  FIG. 9B is an example of the grating shape of the CD diffraction grating surface 41. The CD diffraction grating surface 41 is divided into 12 diffraction regions 41a, 41b, 41c, 41d, 41e, 41f, 41g, 41h, 41i, 41j, 41k and 41l. The direction of the grating grooves is determined so that the light beams incident on the CD diffraction grating surface 41 are each diffracted in a predetermined direction.

  Similarly, the CD diffraction grating surface 41 is also divided so that the center dividing line 33 in the Tan direction passes through the center of the optical axis of the CD light beam 200b indicated by the dotted circle. Further, the 12 regions of the CD diffraction grating surface 41 are arranged so as to be line symmetric with respect to the central dividing line 32 as a central axis.

  It should be noted that an area composed of 41a, 41b, 41c and 41d is an area composed of areas E ′, 41e, 41f, 41g and 41h, and an area composed of areas F ′, 41i, 41j, 41k and 41l is an area. This will be described below as G ′.

  As shown in FIG. 9, in this embodiment, the region of each diffraction grating surface is divided into 12 or 13 divisions. By dividing in this way, it becomes possible to avoid stray light of the double-layer disc. The avoidance of stray light will be described in detail later.

  FIG. 10 is an example of the configuration of the photodetector 27 used in the optical pickup device 2 according to the present embodiment. As shown in FIG. 10, the light receiving surface of the photodetector 27 is composed of a total of 26 surfaces from D0 to D25. Of these light receiving surfaces, the 0th-order diffracted light of DVD is incident on D0, and the 0th-order diffracted light of CD is incident on D25. Note that the diffracted light of DVD is represented by black dots, and the diffracted light of CD is represented by white dots. As described above, the DVD semiconductor laser light source 20a and the CD semiconductor laser light source 20b are arranged at positions where the light emission point intervals are separated by Ta, respectively. The condensing position of the next diffracted light is separated by Ta. The shaded area represents a dark line part for allowing the focused signal light to enter.

  FIG. 11 is a diagram showing a state in which DVD diffracted light is incident on the light receiving surface of the photodetector 27 from the incident direction of the light flux. The luminous fluxes diffracted by the regions 40a, 40b, 40c and 40d (region E), 40e, 40f, 40g and 40h (region F) and 40i, 40j, 40k and 40l (region G) of the DVD diffraction grating surface 40 The + 1st order diffracted light is incident on the light receiving surfaces D1, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, and D12, respectively. Further, the −1st order diffracted light of the light beam diffracted in the regions 40a, 40b, 40c and 40d (region E) of the DVD diffraction grating 40 is a dark line portion between the light receiving surfaces D17 and D18, a dark line portion between D14 and D15, and D16, respectively. And the dark line part between D17 and the dark line part between D13 and D14.

  Further, the 0th-order diffracted light that has passed through the two-plane diffraction grating 26 is incident on D0. The -1st order diffracted light of the light beam diffracted by the regions 40e, 40f, 40g and 40h (region F) and 40i, 40j, 40k and 40l (region G) of the DVD diffraction grating 40 is indicated by a broken line in FIG. The light is incident on the photodetector while avoiding the light receiving surface at the position of the range 42 shown. Further, the + 1st order light and the −1st order diffracted light of the light beam diffracted in the region 40m (region H) of the DVD diffraction grating 40 are diffracted to a position far away from the light receiving surface, for example, in a range 43 indicated by a broken line in FIG. Let By not receiving the diffracted light in the region 40m of the DVD diffraction grating 40, it becomes possible to avoid stray light of the double-layer disc. The avoidance of stray light will be described in detail later.

  FIG. 12 shows a light receiving surface when CD diffracted light enters the photodetector 27. As shown in FIG. 12, all the CD diffracted light is indicated by white dots. Diffraction of regions 41a, 41b, 41c and 41d (region E ′), 41e, 41f, 41g and 41h (region F ′) and 41i, 41j, 41k and 41l (region G ′) of the CD diffraction grating surface 41 The + 1st order diffracted light of the luminous flux is incident on the light receiving surfaces D1, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11 and D12, respectively. Further, the −1st order diffracted light beams of the light beams diffracted in the regions 41a, 41b, 41c and 41d (region E ′) of the CD diffraction grating surface 41 are dark line portions between the light receiving surfaces D23 and D24 and dark line portions between the D20 and D21, respectively. , Incident on the dark line portion between D22 and D23 and the dark line portion between D19 and D20.

  Also, the 0th-order diffracted light that has passed through the two-plane diffraction grating 26 is incident on D25. Note that the −1st order diffracted light of the light beams diffracted by the regions 41e, 41f, 41g, and 41h (region F ′) and 41i, 41j, 41k, and 41l (region G ′) avoid the light receiving surface, and FIG. It enters the position of the range 44 shown by the broken line inside.

  The light receiving surfaces D0, D1, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, D14, D15, D16, D17, D18, D19, D20, D21 of the photodetector 27. , D22, D23, D24, and D25, the signals obtained by detecting them respectively in order S0, S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, S11, S12, S13, S14, S15. , S16, S17, S18, S19, S20, S21, S22, S23, S24 and S25. Using the signal light incident on each of the light receiving surfaces, the servo signal generation circuit 6 described above generates a focus error signal, a tracking error signal, and an RF signal that is a reproduction signal.

  The server signal generation circuit 6 detects the focus error signal using, for example, a double knife edge method. Specifically, the server signal generation circuit 6 calculates the focus error between the DVD and CD from the signals S13, S14, S15, S16, S17, S18, S19, S20, S21, S22, S23, and S24 using the equation shown in Equation 4. Generate a signal.

  On the other hand, the server signal generation circuit 6 detects the tracking error signal using, for example, a 1-beam DPP method. The server signal generation circuit 6 generates a tracking error signal for DVD and CD from the signals S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, S11, and S12 by the arithmetic expression shown in Equation 5. . A signal including a push-pull component is an MPP signal, and a signal for canceling an offset component of the MPP signal is an OC signal.

  K1 and k2 in Formula 5 correct the offset component included in the signal of the first term in the equation of the tracking error signal and the offset component included in the signal of the second term in the equation when the objective lens is lens-shifted. It is a coefficient to do. The light receiving surfaces D1 to D12 used for generating the tracking error signal are all the same light receiving surfaces for DVD and CD. For this reason, the arithmetic expressions for DVD and CD can be realized by the same expression, except for the offset correction coefficients k1 and k2, as shown in Equation 2 above. In other words, it is possible to adopt a configuration that does not require calculation switching when detecting the tracking error signal.

  Further, an RF signal is generated using a signal obtained from the 0th-order diffracted light as in the arithmetic expression shown in Equation 6. Since the RF signal is generated only by the condensed 0th-order diffracted light, the RF signal can be generated using one light receiving surface. As described above, since the light receiving surface is small, it is possible to obtain a signal with less noise, and it is possible to generate an RF signal with a good SN ratio by increasing the light amount of the 0th-order diffracted light.

  As in the present embodiment, the configuration using the two-surface diffraction grating in the return path can solve the problem of stray light that becomes a problem in a DVD having two layers. Hereinafter, stray light will be described.

  A DVD has a two-layer optical disk having two information layers for increasing the capacity. When a two-layer optical disk is used, a part of the light amount is not reflected by the target information layer but is reflected by the non-target information layer. For this reason, not only the desired signal light reflected by the target information layer but also stray light reflected by an information layer other than the target information layer is incident on each light receiving surface of the photodetector. is there. As described above, when stray light is incident on the light receiving surface, unnecessary noise leaks into the signal. Therefore, it is necessary to prevent stray light from other layers from entering the light receiving surface.

  The DVD diffraction grating surface 40 shown in FIG. 9A and the photodetector 27 shown in FIG. 10 are configured to solve the problem of stray light described above.

  FIG. 13 shows the relationship between the DVD light beam 200a, which is signal light immediately after reflecting the information layer of the double-layer optical disc 50, and the stray light 220a. Of the information layers of the two-layer DVD shown in FIG. 13, the information layer located behind the objective lens 9 is the information layer 51, the information layer located in front is the information layer 52, and the layer interval between the information layers is L. .

  FIG. 13A is a diagram illustrating a state in which the light beam 200 a is condensed on the information layer 51 and reflected on the information layer 51. The light beam 200a collected by the back information layer 51 is reflected by the information layer 51 and travels in the optical path as signal light. However, of the light beam 200a, a part of the light beam is reflected by the front information layer 52 and travels in the optical path as stray light 220a. As shown in FIG. 13A, the stray light 220a travels in the optical path with a light beam diverging weaker than the light beam 200a that is signal light.

  On the other hand, FIG. 13B shows a state of reflected light when a light beam is condensed on the information layer 52. The light beam collected by the information layer 52 is reflected and travels in the optical path as signal light 200a. However, some of the light beams 200a pass through the front information layer 52 and are reflected by the back information layer 51, and travel along the optical path as stray light 220a. This stray light 220a travels in the optical path with a light beam that converges weaker than the signal light 200a as shown in the figure.

  FIG. 14 shows the signal light 200a and the stray light 220a on the DVD diffraction grating surface 40 of the two-surface diffraction grating 26 when the information layer 51 in the back of the two-layer optical disk is recorded and reproduced as shown in FIG. It shows a state. The signal light 200a is indicated by a solid circle, and the stray light 220a is indicated by a dotted circle. As shown in FIG. 14, the stray light 220a generated by the information layer 52 is weaker than the signal light 200a, and thus becomes larger than the signal light on the DVD diffraction grating surface 40.

  On the DVD diffraction grating surface 40, the luminous flux is mainly divided into 0th-order diffracted light, + 1st-order diffracted light, and -1st-order diffracted light, so that stray light also generates 0th-order stray light, + 1st-order diffracted stray light, and -1st-order diffracted stray light. First, FIG. 15 shows a state when 0th-order stray light is incident on the photodetector 27. Signal light is indicated by black dots, and zero-order stray light is indicated by shaded areas. As shown in FIG. 15, the 0th-order stray light is not diffracted but is defocused and incident on the 0th-order signal light incident on the light receiving surface D0. Therefore, by arranging the DVD light receiving surface outside the 0th-order stray light, it is possible to avoid the 0th-order stray light.

  Next, FIG. 16 shows a state when the + 1st order diffraction stray light and the −1st order stray light are incident on the photodetector 27. In FIG. 16, the signal light is indicated by a black dot, and the + 1st order diffraction stray light and the −1st order diffraction stray light are indicated by shaded areas. Like the signal light, the + 1st order diffracted stray light and the −1st order diffracted stray light are divided into the number of regions incident on the DVD diffraction grating surface 40. Therefore, as shown in FIG. 14, since the stray light 220a is incident on all 13 regions 40a to 40m, a total of 26 + 1st order diffracted stray light and −1st order diffracted stray light is divided into 13 on the photodetector 27. Pieces of diffracted stray light are incident.

  However, as shown in FIG. 16, the stray light avoids the DVD light receiving surface, and the signal light and the stray light do not overlap. This is because the diffraction grating region is divided into 13 and the light receiving surface is arranged at a position where stray light is effectively avoided. That is, stray light is incident on the light receiving surfaces D1 to D4 and D13 to D18 that receive the light beams in the regions 40a to 40d while being shifted in the Rad direction with respect to the signal light. For this reason, the light receiving surfaces are arranged in a row in the Tan direction to prevent stray light from entering each light receiving surface. Further, the stray light is incident on the light receiving surfaces D5 to D12 that receive the light flux of the region 40e to 40l with a deviation from the signal light in the Tan direction. Therefore, the arrangement is such that stray light is prevented from entering the light receiving surface by arranging the light receiving surfaces in a row in the Rad direction. Although stray light is incident on D19 to D25, which are CD light receiving surfaces, signals obtained from these light receiving surfaces are not used, and therefore do not cause DVD signal noise. Further, even when the lens shift is performed and the stray light is displaced in the Rad direction, it is possible to minimize the influence of the stray light.

  As shown in FIG. 13A, when recording / reproducing the information layer 51 in the back of the two-layer optical disc, the light receiving surface on the photodetector 27 avoids stray light.

  FIG. 17 shows signal light 200a and stray light 220a on the DVD diffraction grating surface 40 of the two-sided diffraction grating 26 when recording and reproducing the front information layer 52 of the two-layer optical disk as shown in FIG. 13B. The state of is shown. The signal light 200a is indicated by a solid circle, and the stray light 220a is indicated by a dotted circle. As shown in FIG. 17, the stray light 220a by the information layer 51 in the back is weaker than the signal light 200a, and therefore becomes smaller than the signal light 200a on the DVD diffraction grating surface 40. Here, it is assumed that the stray light 220a is incident only on the area 40i to 40m.

  When the 0th-order stray light enters the photodetector 27, the 0th-order diffracted light is defocused and incident. Accordingly, the state of incidence of the 0th-order stray light is the same as in FIG.

  FIG. 18 shows a state when the + 1st order diffraction stray light and the −1st order stray light are incident on the photodetector 27. In FIG. 18, the signal light is indicated by a black dot, and the zero-order stray light is indicated by a shaded area. Like the signal light, the + 1st order diffracted stray light and the −1st order diffracted stray light are divided into the number of regions incident on the DVD diffraction grating surface 40. Therefore, as shown in FIG. 17, since the stray light 220a is incident on five regions 40i to 40m, a total of ten stray lights of five divisions are incident on the photodetector in the + 1st order and the −1st order.

  However, as shown in FIG. 18, the stray light avoids the DVD light receiving surface, and the signal light and the stray light do not overlap. This is because the diffraction grating region is divided into 13 and the light receiving surface is arranged at a position where stray light is effectively avoided. That is, stray light is incident on the light receiving surfaces D9 to D12 that receive the light fluxes in the regions 40i to 40l with a deviation from the signal light in the Tan direction. Therefore, the configuration is such that stray light is prevented from entering each light receiving surface by arranging the light receiving surfaces in the Rad direction in a line. Further, even when the lens shift is performed and the stray light is displaced in the Rad direction, it is possible to minimize the influence of the stray light.

  FIG. 19 shows a two-plane diffraction grating when recording and reproducing the front information layer 52 of the two-layer optical disk as shown in FIG. 13B and assuming that the information layer has a large layer spacing L. The state of the signal light 200a and the stray light 220a on the 26 DVD diffraction grating surfaces 40 is shown. The standard is that the layer spacing L is in the range of 45 μm to 70 μm in a DVD dual layer disc. Thus, since the layer spacing L of the DVD layers varies as much as 25 μm, it is necessary to cope with the case where the stray light 220a is incident only on the region 40m so as to be focused on the diffraction grating surface as shown in FIG. is there.

  FIG. 20 shows a state when the + 1st order diffracted stray light and the −1st order diffracted stray light are incident on the photodetector 27. The signal light is indicated by a black dot, and the zero-order stray light is indicated by a shaded area. Like the signal light, the + 1st order diffracted stray light and the −1st order diffracted stray light are split in the region incident on the DVD diffraction grating surface 40. Accordingly, as shown in FIG. 19, since the stray light 220a is incident only on the region 40m, two substantially circular + 1st-order diffracted stray light and −1st-order diffracted stray light are incident on the photodetector 27. However, the signal light in the region 40m is diffracted to a position far away from the light receiving surface without being used for signal generation. For this reason, as shown in FIG. 20, it can be seen that the stray light avoids the DVD light receiving surface, and the signal light and the stray light do not overlap. Further, even when the lens shift is performed and the stray light is displaced in the Rad direction, it is possible to minimize the influence of the stray light.

  Of course, even when the stray light 220a smaller than the signal light 200a on the DVD diffraction grating surface 40 is incident on the entire area 40m from the area 40a, it is possible to avoid the stray light as shown in FIG.

  As described above, when the information layer 52 of the two-layer optical disk is recorded and reproduced as shown in FIG. 13B, the light receiving surface on the photodetector 27 avoids stray light.

  In general, the stray light divided in each region of the diffraction grating is incident on the light detector 27 around the condensing position of the signal light. Since the regions 40a to 40l do not include the region at the center of the light beam, the stray light can be incident away from the signal light and separated from the signal light. However, since only the region 40m includes a region at the center of the light beam, the stray light necessarily enters the signal light so as to overlap. Therefore, in this embodiment, only the region 40m including the light beam center is largely diffracted without being used for signal generation. As a result, this embodiment can separate any stray light from the two-layer optical disc from the signal light. In addition, the influence of stray light can be minimized even during lens shift. Therefore, a stable servo signal and RF signal can be generated.

  Since the stray light 220a on the DVD diffraction grating surface 40 is displaced in the Rad direction due to the lens shift, the center of the light beam falls within the area 40m within the allowable lens shift range. Therefore, as shown in FIG. 9A, it is desirable that the side of the region 40m parallel to the Rad direction is longer than the side parallel to the Tan direction.

  Further, since there is no double-layer optical disc for CD, it is not necessary to consider stray light. Further, a part of the incident light beam may be diffracted by a surface that is not a desired diffraction grating surface of the two-surface diffraction grating 26. For example, the DVD light beam is diffracted by the DVD diffraction grating surface 40 and transmitted through the CD diffraction grating surface 41. However, a part of the DVD light beam is transmitted through the DVD diffraction grating surface 40 and is diffracted by the CD diffraction grating surface 41 due to the influence of the depth of the grating grooves and the variation in polarization. In this case, the diffracted light diffracted by the CD diffraction grating surface 41 enters the photodetector 18 as stray light. This stray light is referred to as dihedral lattice stray light.

  When this two-plane lattice stray light is incident on, for example, a DVD light-receiving surface, there is a problem that signal offset occurs due to noise. However, since the wavelength of DVD and CD has a wavelength difference of about 1.2 times, the dihedral grating stray light on the CD diffraction grating surface 41 is closer to the 0th-order diffracted light receiving surface D0 than the signal light indicated by the black dots in FIG. Concentrate to a close position. Since this embodiment has a configuration in which the light receiving surfaces are arranged in a radial pattern with respect to the optical axis, it is possible to avoid this two-plane lattice stray light. A case where a part of the CD light beam is diffracted by the DVD diffraction grating surface 40 and transmitted by the CD diffraction grating surface 41 can be similarly avoided.

  Another reason why the region of the DVD diffraction grating surface 40 and the CD diffraction grating surface 41 is divided into 13 to 12 is to improve the balance of the focus error signal. For example, the photodetector 27 according to the first embodiment detects the signal light from the light beam diffracted on the eight-divided region (30a to 30h) of the DVD diffraction grating surface 30 (FIG. 4A) and outputs a focus error signal. It was generated. In this case, the focus error signal is unbalanced due to the influence of the intensity distribution of the light beam, and the focus control performance is deteriorated.

  As a method for improving the balance of the focus error signal, there is a method that does not use a part of the center of the light beam with a large amount of light. For this reason, in this embodiment, the center of the luminous flux is used by generating a focus error signal by the double knife edge method using the diffracted light of the four divided regions (40a to 40d) of the 13-divided DVD diffraction grating 40. Without generating a focus error signal. The reason why the CD diffraction grating surface is divided into 12 parts is to improve the balance of the focus error signal as in the DVD diffraction grating surface 40.

  In addition, since the optical pickup device according to the present embodiment uses the two-surface diffraction grating 26 as in the first embodiment, there is a problem caused by the one-beam optical system using the two-wavelength multi-laser light source. It is possible to solve.

  By using the two-plane diffraction grating 26, the DVD diffraction grating surface 40 and the CD diffraction grating surface 41 can be freely set without being limited by the difference in the emission point position or the wavelength difference between the DVD light beam 200 a and the CD light beam 200 b. It is possible to change the number of divided areas. Further, the pitch interval of the lattice grooves can be changed independently. As a result, the diffraction directions of the DVD light beam 200a and the CD light beam 200b having different wavelengths can be determined freely for each light beam, and a part of the light receiving surface can be made common, and the photodetector 27 can be made compact. Became possible.

  Further, when the two-surface diffraction grating 26 is arranged in the outward optical path, a part of the light beam divided into three by the two-surface diffraction grating 26 in the outward path is made finer depending on the track pitch of the information layer of the optical disc 5. It will be divided. There is a problem that the light beam thus finely divided becomes stray light and is detected by the photodetector 27. Therefore, in the present embodiment, it is possible to prevent the generation of stray light by disposing the two-plane diffraction grating 26 on the return path and configuring the forward path to have one beam.

  In addition, this configuration can reduce signal performance degradation due to misalignment as compared to the astigmatism method. In the case of the astigmatism method, a light beam having an effective diameter of, for example, about 40 to 60 μm is generally incident on the four-divided light receiving surface of the photodetector. Here, when the position of the photodetector is shifted by 2 to 5 μm, the balance of the signal light incident on the light receiving surface is deteriorated, and the performance of the focus error signal and the tracking error signal is deteriorated. However, when the light beam is collected on the light receiving surface as in the present embodiment, the performance of the tracking error signal does not deteriorate unless the photodetector is displaced from the light receiving surface. Further, by adjusting the dark line width of the focus error signal, it is possible to alleviate the performance deterioration of the focus error signal with respect to the positional deviation.

(2-2) Other Embodiments In the second embodiment described above, the divided region configuration of the two-plane diffraction grating 26 and the light receiving surface configuration of the photodetector 27 are as shown in FIGS. However, the present invention is not limited to this, and there is no limitation on the light emission point position of the wavelength multi-laser light source and the wavelength difference between the DVD and the CD. However, any configuration may be used as long as a stable servo signal and RF signal can be generated.

  Further, the two-surface diffraction grating 26 may have a wavelength selectivity function, a polarization selectivity function, or the other. Any structure may be used as long as it diffracts only the light flux having the DVD oscillation wavelength on the DVD diffraction grating surface and diffracts only the light flux having the CD oscillation wavelength on the CD diffraction grating surface.

(2-3) Effect of Second Embodiment As described above, the two-surface diffraction grating 26 having the DVD diffraction grating surface 40 and the CD diffraction grating surface 41 shown in FIG. 9 is arranged in the return optical path, and FIG. By providing the photodetector 27 having the light receiving surface configuration shown in the figure, the light receiving surface position is stable without being limited by the difference in the emission point position of the two-wavelength multi-laser light source or the wavelength difference between the DVD and the CD. An optical pickup device 2 that generates a servo signal and an RF signal can be realized. In addition, a part of the light receiving surface of the photodetector 27 can be shared. In addition, it is possible to generate a servo signal that is stable against stray light generated by a two-layer optical disc. Further, since no special parts other than the two-plane diffraction grating are used, a simple optical system configuration with a small number of parts is realized.

5 …… Optical disk,
9 …… Objective lens,
20 …… 2 wavelength multi-laser light source,
20a: DVD semiconductor laser light source,
20b …… CD semiconductor laser light source,
26: Two-plane diffraction grating,
27. Photodetector,
30, 40 ... DVD diffraction grating surface,
30a to 30h, 40a to 40m ... the region of the DVD diffraction grating surface,
31, 41 ... CD diffraction grating surface,
31a to 31h, 41a to 41m... Region of CD diffraction grating surface,
200a …… DVD luminous flux,
200b …… CD luminous flux,
201a: DVD 0th order diffracted light,
202a ... DVD + 1 character diffracted light,
203a ... DVD-1 diffracted light,
201b …… 0th-order CD diffracted light,
202b …… CD + 1 shaped diffracted light,
203b …… CD-1 diffracted light,
D0 to D25: Light receiving surface of the photodetector.

Claims (10)

A laser light source unit in which at least a first laser light source and a second laser light source that emit light beams independent of each other are stored in one housing;
An objective lens for condensing the luminous flux emitted from the laser light source unit on the information layer of the optical disc;
A light splitting unit that splits the luminous flux emitted from the laser light source unit and reflected by the information layer of the optical disc;
A photodetector having a plurality of light receiving surfaces for receiving the light beam divided by the light dividing unit;
With
The light splitting unit is:
A first light splitting element that splits the first light flux emitted from the first laser light source into a plurality of regions;
A second light splitting element for splitting the second light flux emitted from the second laser light source into a plurality of regions;
With
An optical pickup device, wherein the optical pickup device is disposed at a position where only a light beam reflecting information on the optical disk is incident. The first light flux and the second light flux have different wavelengths,
The first light splitting element selectively splits only the first light flux;
The second light splitting element selectively splits only the second light flux,
The optical pickup device according to claim 1, wherein the first and second light splitting elements have a predetermined wavelength selection function. The first and second light fluxes have orthogonal polarizations;
The first light splitting element selectively splits only the first light flux;
The second light splitting element selectively splits only the second light flux,
2. The optical pickup device according to claim 1, wherein the first and second light splitting elements have a predetermined polarization selection function. The first light splitting element and the second light splitting element are diffraction gratings divided into at least two regions by a predetermined parting line,
The optical pickup device according to claim 1, wherein the plurality of divided regions have different grating groove directions or grating pitches. The first light splitting element and the second light splitting element each have a split line in a direction substantially parallel to a direction corresponding to the track direction of the optical disc in the light splitting element,
A dividing line in a direction substantially parallel to the track direction of the first light splitting element is disposed so as to pass through a central optical axis of the first light beam incident on the first light splitting element,
A dividing line in a direction substantially parallel to the track direction of the second light splitting element is disposed so as to pass through a central optical axis of the second light beam incident on the second light splitting element. The optical pickup device according to claim 1. At least one light receiving surface of the photodetector is
Receiving at least a part of the first light beam divided into a plurality by the first light splitting element or at least a part of the second light beam split into a plurality by the second light splitting element; The optical pickup device according to claim 1. The photodetector is
The light receiving surface for receiving 0th-order diffracted light, + 1st-order diffracted light, or -1st-order diffracted light among the diffracted light that is reflected by the information grating of the optical disc and divided by the diffraction grating is provided. The optical pickup device described. Of the diffracted light divided by the diffraction grating, a reproduction signal is detected on the light receiving surface of the 0th order diffracted light,
The optical pickup device according to claim 7, wherein a tracking error signal and a focus error signal are detected on the light receiving surfaces of the + 1st order diffracted light and the −1st order diffracted light. The optical pickup device according to claim 1, wherein a focus error signal is detected by a knife edge method. A laser light source unit in which at least a first laser light source and a second laser light source that emit light beams independent of each other are stored in one housing;
An objective lens for condensing the luminous flux emitted from the laser light source unit on the information layer of the optical disc;
A light splitting unit that splits the luminous flux emitted from the laser light source unit and reflected by the information layer of the optical disc;
A photodetector having a plurality of light receiving surfaces for receiving the light beam divided by the light dividing unit;
An optical pickup device comprising:
A laser lighting circuit for driving the laser light source unit;
From the detection signal obtained by the photodetector of the optical pickup device, a servo signal generation circuit for generating a stable servo signal for the optical disc,
An information signal reproducing circuit for stably reproducing information recorded on the optical disc from a detection signal obtained by a photodetector of the optical pickup device;
In an optical disk apparatus comprising the laser lighting circuit, the servo signal generation circuit, and a control circuit for controlling the information signal reproduction circuit,
The light splitting unit provided in the optical pickup device is:
A first light splitting element that splits the first light flux emitted from the first laser light source into a plurality of regions;
A second light splitting element for splitting the second light flux emitted from the second laser light source into a plurality of regions;
With
An optical disc apparatus, wherein the optical disc apparatus is disposed at a position where only a light beam reflecting information on the optical disc is incident.