JP4222988B2 - Optical pickup device and optical disk device - Google Patents

Description

The present invention relates to an optical pickup device and an optical disc device, and is particularly suitable for use in recording / reproducing on a land / groove recording type optical disc.

  Conventionally, an astigmatism method is known as a focus error detection method of an optical pickup device, and has already been widely used in optical pickup devices for CD and MD. However, in a land / groove recording type optical disk such as a DVD-RAM, when the astigmatism method is used as it is, a phenomenon called “tracking interference” occurs, and noise called “tracking crossing noise” occurs in the focus error signal. Is known (see, for example, Patent Document 1 below). For this reason, it is generally preferable to use another focus error detection method such as a beam size method as a focus error detection method for this type of disc.

  FIG. 12 shows a configuration example of an optical system when the beam size method is used.

  In the figure, the reflected light from the optical disk is divided into 0th order diffracted light and ± 1st order diffracted light by the hologram element and received by the corresponding optical sensors. The hologram element is given a lens effect (hologram pattern) such that the focal positions of the ± first-order diffracted lights move back and forth in the optical axis direction. At this time, the focal position of the 0th-order diffracted light is located at an intermediate position between the focal positions of ± 1st-order diffracted light. For this reason, the position where the beam spot of the ± 1st order diffracted light becomes a substantially circular shape of the same size (the detection position of ± 1st order diffracted light) is also the focal position of the 0th order diffracted light. If an optical sensor corresponding to the 0th-order diffracted light is arranged, the spot size of the 0th-order diffracted light cannot be made sufficiently large.

On the other hand, in Patent Document 2 below, in FIG. 12, an optical element for expanding or converging only the 0th-order diffracted light is arranged immediately before the optical sensor so that the focal position of the 0th-order diffracted light is moved back and forth in the optical axis direction. ing. Specifically, as shown in FIG. 13, a concave lens portion or a convex lens portion is formed at the 0th-order diffracted light incident position of the optical element, or a step portion is provided at this incident position, and the thickness thereof is compared with other portions. Thick or thin. In this way, the beam spot of the 0th-order diffracted light has a sufficient spread at the detection position of ± 1st-order diffracted light, and even if a split sensor or the like is provided at this position, the beam spot can be positioned in a balanced manner in each divided region. become able to.
JP 2001-101681 A JP 2003-6917 A

  However, since the diffraction angle of ± 1st order diffracted light is usually several degrees, the incident positions of 0th order diffracted light and ± 1st order diffracted light with respect to the optical element are very close. For this reason, when projecting a stepped portion having a different thickness (see FIG. 13 (d)), the height of the stepped portion is set to be considerably small so that ± 1st-order diffracted light is not applied to the stepped portion. Will have to.

  However, if the height of the step portion is reduced in this way, the refractive difference of the 0th-order diffracted light with respect to the ± 1st-order diffracted light cannot be increased. Cannot be shifted greatly in the direction. On the contrary, if the height of the step portion is increased in order to increase the refractive index difference, the width of the step portion has to be set considerably small in order to prevent ± first-order diffracted light from being applied to the step portion. In this case, in addition to the extremely difficult formation of the stepped portion, there arises a problem that it is considerably difficult to position the 0th-order diffracted light on the upper surface of the stepped portion.

  Similarly, when the convex lens portion (see FIG. 13B) is formed on the optical element, the height of the convex lens portion must be made small so that ± 1st order diffracted light is not applied. As a result, there is a problem that the formation of processing becomes extremely difficult. In this case, the 0th-order diffracted light must be aligned with the convex lens portion more strictly than in the case of the stepped portion, which causes a problem that the adjustment work becomes considerably complicated.

  Further, when forming a stepped portion (see FIG. 13 (c)) or a concave lens portion (see FIG. 13 (a)) recessed in the optical element, these widths are not applied to the incident position of ± first-order diffracted light. It is necessary to set it as small as possible. Also in this case, there is a problem that it is difficult to process and form the stepped portion and the concave lens portion, and it is difficult to position the 0th-order diffracted light so as to be incident on them. Further, in order to greatly shift the focal position of the 0th order diffracted light, it is necessary to considerably increase the thickness of the optical element.

Accordingly, an object of the present invention is to provide an optical pickup device and an optical disc device that can solve such problems and can smoothly detect a focus error with a simple configuration. In addition, it intends to solve the following problems in a progressive manner.
(1) Suppress the DC offset of the tracking error signal.
(2) In a compatible pickup device that emits laser beams of a plurality of wavelengths, the pattern arrangement of the photodetector can be easily performed.
(3) To provide a sensor pattern that can receive diffracted light satisfactorily even when the diffraction angle fluctuates due to the wavelength shift of laser light.

  The invention of claim 1 is a laser means for irradiating a recording medium with laser light, an optical element for separating the laser light reflected from the recording medium, and a photodetector for receiving the laser light separated by the optical element. And a means for generating a tracking error signal based on a detection signal from the optical detector, wherein the optical element is; a first that gives a lens effect to the first polarization component of the laser light; And second optical means for separating the second polarization component different from the first polarization component by diffraction and giving the separated diffracted light a focal position back and forth in the optical axis direction, The photodetector includes: first sensor means for receiving the first polarization component; and two sets of sensor groups for receiving the separated ± first-order diffracted lights, respectively. Comprises three sensor regions divided by two parallel dividing lines along the track direction, and the center of the beam spot of the ± first-order diffracted light is at the center in the width direction of the central sensor region among the three sensor regions. And means for generating the tracking error signal, comprising: the sensor group and second sensor means whose optical axis of the ± first-order diffracted light is adjusted so as to be positioned; three means of the two sets of sensor groups; Of the sensor regions, the central sensor region is region 1, region 2 is in one direction orthogonal to the dividing line, and region 2 is region 2 in the other direction orthogonal to the dividing line. Then, the detection signal from region 2 of one sensor group of the two sets of sensor groups and the detection signal from region 3 of the other sensor group are added, and the result of the addition is added. The resulting two signals are subtracted respectively and generates a tracking error signal.

  According to the present invention, the DC offset of the tracking error signal can be suppressed. That is, when the tracking error signal is generated in this way, the DC component is canceled at the time of subtraction, and an appropriate tracking error signal can be generated. As a result, stable tracking servo can be realized.

  According to a second aspect of the present invention, in the optical disc apparatus according to the first aspect, the first sensor means is disposed between the two sets of sensor groups, and the second optical means is the first optical means. The first-order diffracted light is separated such that the sensor means can be arranged between the two sets of sensor groups.

  In this way, the sensor pattern of the photodetector can be simplified or integrated, and the effective size of the photodetector can be reduced.

  According to a third aspect of the present invention, in the optical disc apparatus according to the first aspect, the second optical means is adjusted in position so that a laser beam separation direction by the diffraction is along the track direction. .

  In this way, a wavelength shift occurs in the laser beam due to a temperature change or the like. As a result, even if the separation angle of the laser beam due to diffraction varies, the beam spot of the separated ± first-order diffracted beam is separated on the corresponding sensor group. Accordingly, the amount of the beam spot applied to each divided region does not change. Therefore, no error occurs in the detection signal from each divided region, and an appropriate servo signal can be generated based on this detection signal.

  According to a fourth aspect of the present invention, there is provided the optical disk apparatus according to the first aspect, further comprising laser means for emitting several types of laser light, and separation of the laser light by the optical axis misalignment direction of the laser light and the second optical means. The position of the second optical means is adjusted so that the directions are substantially orthogonal to each other.

  In this way, the sensor patterns for each optical axis can be shifted in the optical axis misalignment direction, and the respective sensor patterns can be integrated on one photodetector.

  According to the present invention, it is possible to provide an optical pickup device and an optical disc apparatus that can smoothly detect a focus error with a simple configuration. In addition, the above problems (1) to (3) can be solved.

The effects and significance of the present invention will become more apparent from the following description of embodiments. However, the following embodiment is an exemplary form of the present invention, and the meaning of the term of the present invention or each constituent element is not limited to that described in the following embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a configuration of an optical pickup device according to the embodiment. This optical pickup device is used as a compatible pickup for CD / DVD / next-generation DVD.

  This optical pickup device includes a three-wavelength laser 101, a λ / 2 plate 102, an optical axis correction diffraction grating 103, a polarization BS (beam splitter) 104, a collimator lens 105, a mirror 106, and a wavefront correction. A liquid crystal lens 107, a λ / 4 plate 108, a wavelength-selective aperture limiting element 109, an objective lens 110, an optical element 111, and a photodetector 112 are provided.

  The three-wavelength laser 101 includes three laser elements that emit laser light for CD (wavelength 780 nm), laser light for DVD (wavelength 655 nm), and laser light for next-generation DVD (wavelength 408 nm) in the same CAN. Contained. Here, the laser elements are arranged with a predetermined gap so as to be aligned on one straight line. Further, the laser beams emitted from the respective elements have parallel polarization planes. The arrangement of each laser element will be described later.

  The λ / 2 plate 102 rotates the polarization plane of the laser light of each wavelength by 90 degrees, and the rotational position about the optical axis is adjusted so that the laser light of each wavelength is totally transmitted to the polarization BS104. The

  The optical axis correcting diffraction grating 103 aligns the optical axis of the DVD laser light out of the laser light emitted from the three-wavelength laser 101 with the optical axis of the next-generation DVD laser light by diffraction action. That is, the optical axis correcting diffraction grating 103 is formed with a pattern designed to correct the optical axis shift of the DVD laser beam. The configuration of the diffraction grating and the optical axis deviation correcting action will be described later.

  The polarized light BS 104 totally transmits the laser light from the three-wavelength laser 101 and totally reflects the laser light from the disk 100.

  The collimator lens 105 converts the laser light of each wavelength incident from the polarization BS 104 into parallel light. Here, the collimator lens 105 is formed, for example, by bonding a plurality of lenses whose Abbe number and curvature (spherical surface) are adjusted so as to realize an achromatic effect on laser light of each wavelength.

  The mirror 106 raises the optical path of the laser light from the polarization BS 104 toward the objective lens 110.

  The liquid crystal lens 107 corrects the wavefront state of the laser light in accordance with a servo signal from a servo circuit (not shown). As described above, the laser light of each wavelength emitted from the three-wavelength laser 101 is converted into parallel light by the collimator lens 105. On the other hand, when the objective lens 110 is designed to be a finite system only for laser light of a predetermined wavelength, for example, it is necessary to correct the wavefront state of the laser light of that wavelength accordingly. In such a case, the liquid crystal lens 107 imparts a wavefront correcting action to the laser light of the wavelength so that the wavefront state of the laser light of the wavelength becomes an appropriate state.

  In the present embodiment, the objective lens 110 is infinite for the laser beam for DVD (wavelength 655 nm) and the laser beam for next-generation DVD (wavelength 408 nm), and for the laser beam for CD (wavelength 780 nm). Are designed to be finite systems. Accordingly, the liquid crystal lens 107 is driven when the CD laser light is used, and corrects the wavefront state of the CD laser light to a wavefront state that meets the specifications of the objective lens 110.

  A specific configuration of the liquid crystal lens 107 is described in, for example, Japanese Patent No. 2895150. That is, a plurality of concentric ring-shaped transparent electrodes are arranged so as to sandwich the liquid crystal element in the optical axis direction, and the liquid crystal elements are arranged so that the optical axis of the laser light passes through the center of the concentric ring-shaped transparent electrode. By applying a voltage to the transparent electrode, the refractive index of the liquid crystal element is differentiated in a ring shape, thereby curving the wavefront state of the laser light. Here, the refractive index of the transparent electrode position can be adjusted by the magnitude of the applied voltage. That is, by adjusting the applied voltage, the wavefront state of the laser light can be adjusted to an appropriate state.

  The λ / 4 plate 108 converts the laser light (linearly polarized light) converted into parallel light by the collimator lens 105 into circularly polarized light. Further, the laser beam (circularly polarized light) reflected from the disk 100 is converted into linearly polarized light orthogonal to the polarization direction at the time of incidence. Therefore, the laser beam reflected from the disk is almost totally reflected by the polarized beam BS104.

  The aperture limiting element 109 shields the outer periphery of the laser beam according to the substrate thickness of each disk, and thereby adjusts the numerical aperture (NA) of each laser beam with respect to the objective lens 110. That is, the numerical aperture of the objective lens 110 is determined in advance for each laser beam in accordance with the substrate thickness for each disk. The aperture limiting element 109 shields the outer periphery of the laser beam so as to have a numerical aperture corresponding to the substrate thickness of the disk, and causes each laser beam to enter the objective lens 110 with an appropriate effective diameter.

  When the optical pickup device is compatible with CD / DVD / next-generation DVD (substrate thickness 0.6 mm) as in this embodiment, only the substrate thickness (1.2 mm) of the CD is compared to other disks. For this reason, only the NA of the laser beam for CD is set smaller than the others. The aperture limiting element 109 shields the outer periphery of only the CD laser beam and adjusts the effective diameter of the CD laser beam with respect to the objective lens 110. Thereby, the numerical aperture of the laser beam for CD is adjusted to a set value.

  As the aperture limiting element 109, for example, a diffraction element can be used. In this diffraction element, a wavelength-selective diffraction pattern is formed at a position where the outer peripheral portion of the laser light is incident, and the outer peripheral portion of the laser light having the wavelength is diverged by the diffraction action of this pattern. In the case of the present embodiment, a diffraction pattern for diffracting only the laser beam for CD (wavelength 780 nm) is formed at the outer peripheral incident position. Thereby, the outer peripheral part of the laser beam for CD is diverged by diffraction, and only the central part is guided toward the objective lens 110. In addition, a wavelength-selective dichroic filter can be used as the aperture limiting element 109.

  The objective lens 110 is designed to properly converge the laser light of each wavelength on the recording layer. The objective lens 110 is driven in the focus direction and the tracking direction by an objective lens actuator (not shown). That is, it is driven in the focus direction and the tracking direction in accordance with servo signals (tracking servo signal and focus servo signal) from the servo circuit. The configuration of the objective lens actuator is well known in the art and will not be described.

  The optical element 111 separates the laser light in accordance with the polarization component, and simultaneously imparts a lens effect and a separation effect by diffraction to each separated laser light. Details of the optical element 111 will be described later.

  The photodetector 112 has a sensor pattern for deriving a reproduction RF signal, a focus error signal, and a tracking error signal from the intensity distribution of the received laser beam. The signal from each sensor is output to the reproduction circuit and servo circuit on the disk device side. The sensor pattern of the photodetector 112 and the generation of the error signal will be described in detail later.

  FIG. 2 shows the configuration of the three-wavelength laser 101. FIG. 2B is a right side view of FIG. 1A viewed from the right side.

  In the figure, reference numerals 101a to 101c denote laser elements. As illustrated, the laser elements 101a to 101c are mounted on the base body 101d so as to be aligned in a straight line when viewed from the emission port side. Here, the interval between the laser elements is such that the laser light emitted from the laser element 101a (wavelength: 655 nm) is emitted from the laser element 101b by the optical axis correcting diffraction grating 103 (wavelength: 408 nm). ) To be diffracted to coincide with the optical axis.

  FIG. 3 shows the relationship between the laser elements 101 a to 101 c and the optical axis correcting diffraction grating 103.

As shown in the figure, the optical axis correcting diffraction grating 103 has a hologram grating pattern formed on the surface on which laser light is incident. In the figure, a lattice pattern with the number of steps = 3 is shown. Here, when the grating pitch is p, the relationship between the diffraction angle θ and the wavelength λ of the primary light of the laser beam is
λ = p sin θ (1)
θ = sin ⁻¹ λ / p (2)
It is prescribed. Therefore, if the optical axis of the laser light from the laser element 101a is made to coincide with the optical axis of the laser light from the laser element 101b by diffraction by the optical axis correcting diffraction grating 103, the emission point interval d1 between the laser elements is ,
d1 = Ltan θ1 (3)
From the emission wavelength λa of the laser element 101a and the grating pitch p of the optical axis correcting diffraction grating 103, the emission point interval d1 between the laser elements is
d1 = Ltan (sin ⁻¹ λa / p) (4)
Set as Accordingly, the simple optical path length L is obtained from the emission wavelength λa and the light emitting point interval d1, and the optical axis correcting diffraction grating 103 is disposed at this position, whereby the light of the laser light (first-order diffracted light) emitted from the laser element 101a. The axis can be aligned with the laser beam emitted from the laser element 101b.

  FIG. 4 shows the optical axis of laser light of each wavelength. The optical axis of the DVD laser beam (wavelength: 655 nm) is aligned with the optical axis of the next-generation DVD laser beam (wavelength: 408 nm) by the optical axis correcting diffraction grating 103, and then in the optical path to the photodetector 112. The alignment state of the optical axis is maintained. On the other hand, the optical axis of the laser beam for CD (wavelength: 780 nm) is shifted from the optical axis of the laser beam for next-generation DVD (wavelength: 408 nm) in all optical paths. Therefore, the laser beam for CD is incident on the photodetector 112 in a state where the optical axis is deviated from other laser beams.

  Next, the optical element 111 will be described with reference to FIG.

  As shown in the figure, the optical element 111 is configured by superposing a polarizing lens 111a and a polarization hologram element 111b. Among these, the polarization lens 111a gives a lens effect as a converging lens only to a specific polarization component (first polarization component) of incident laser light. Further, the polarization hologram element 111b has a diffraction effect and a focal position of ± first-order diffracted light that move back and forth in the optical axis direction only for a specific polarization component (second polarization component) of the incident laser light. Give a lens effect. That is, the polarization hologram 111b is formed with a hologram pattern that imparts such an optical action.

  Here, the polarization lens 111a and the polarization hologram element 111b are superposed such that the polarization direction of the first polarization component and the polarization direction of the second polarization component are orthogonal to each other. The laser beam reflected by the disk 100 is disposed in the optical path so that the polarization direction of the laser beam is 45 ° with respect to both the polarization direction of the first polarization component and the polarization component of the second polarization component. The Therefore, the laser beam is transmitted through the optical element 111 to be separated into the first polarized light component and the second polarized light component having an equal light amount. At the same time, the first polarized light component is subjected to the lens effect by the polarizing lens 111a. In addition, the second polarization component is given a diffraction effect by the polarization hologram element 111b and a lens effect such that the focal position of ± first-order diffracted light moves back and forth in the optical axis direction.

  Note that the hologram pattern of the polarization hologram element 111b is a pattern in which the diffraction efficiency of 0th-order diffracted light is 0% and the diffraction efficiency of ± 1st-order diffracted light is 100%. The ± 1st order diffracted light is separated in a direction that is symmetrical with respect to the optical axis of the 0th order diffracted light and that is along the track direction of the disk.

  The polarization lens 111a can be configured by a polarization hologram element. In this case, the polarization hologram element is formed with a hologram pattern that gives a lens effect only to the first polarization component.

  The photodetector 112 includes a sensor group that receives laser light (first polarization component) converged by the polarization lens 111a and two sets of sensors that respectively receive ± first-order diffracted light separated by the polarization hologram element 111b. Holding a group. Here, the light detection surfaces of the sensor groups are placed on the same plane. That is, the light detection surface of each sensor group is placed at a position where the beam spots of ± first-order diffracted light (second polarization component) separated by the polarization hologram element 111b are approximately the same size. At this time, the laser beam (first polarization component) converged by the polarization lens 111a is not focused on the light detection surface due to the lens effect of the polarization lens 111a, and becomes a beam spot having a certain spread. .

  FIG. 6 shows a sensor pattern of the photodetector 112.

  As shown in the figure, the photodetector 112 receives sensor groups A1, B1, and C1 that receive CD laser light, sensor groups A2, B2, and C2 that receive next-generation DVD laser light, and DVD laser light. Sensor groups A2, B3 and C3 for receiving light are arranged. Among these, the laser light (first polarization component) converged by the polarization lens 111a is received by the four-divided sensors A1 and A2, and ± 1st order diffracted light (second polarization component) separated by the polarization hologram element 111b. ) Are received by the three-divided sensors B1, B2, B3 and C1, C2, C3, respectively.

  Here, the three-divided sensors B 1 to B 3 and C 1 to C 3 are divided by two parallel dividing lines along the track direction of the disk 100. Therefore, the direction of the dividing line is the same as the direction of separating ± first-order diffracted light by the polarization hologram element 111b.

  In the above-described three-wavelength laser 101, the optical axis shift direction between the laser beam of the next-generation DVD laser beam (wavelength: 408 nm) and the laser beam of CD laser beam (wavelength: 780 nm) is the photodetector 112. Above, it arrange | positions so that it may become a direction orthogonal to the dividing line direction (track direction) of 3-part dividing sensors B1-B3 and C1-C3. The sensor groups A1, B1, and C1 that receive the laser beam for CD correspond to the optical axis deviation from the sensor groups A2, B2, C2, and A2, B3, and C3 that receive the next-generation DVD laser beam and the DVD laser beam. It is arranged at a position separated by a distance.

  As shown in FIG. 6B, when the next-generation DVD laser light is emitted from the three-wavelength laser 101, the laser light (first polarization component) converged by the polarization lens 111a is obtained by the four-divided sensor A2. The ± first-order diffracted light (second polarization component) received and separated by the polarization hologram element 111b is received by the three-divided sensors B2 and C2, respectively.

  On the other hand, when the DVD laser light is emitted from the three-wavelength laser 101, the laser wavelength is larger than that of the next-generation DVD laser light. Become. For this reason, the spot position of ± 1st-order diffracted light on the light detection surface is farther from the center position of the quadrant sensor A2 than in the case of FIG. In this case, as shown in FIG. 5C, the ± first-order diffracted light is received by the three-divided sensors B3 and C3 arranged at positions further away from the center position of the four-divided sensor A2.

  When the CD laser light is emitted from the three-wavelength laser 101, the irradiation position of the laser light on the light detection surface is shifted by an amount corresponding to the optical axis shift with respect to the next-generation DVD laser light. Further, since the laser wavelength is large, the spot position of the ± first-order diffracted light on the light detection surface is further away from the center position of the four-divided sensor than in the case of FIG. In this case, as shown in FIG. 5A, the laser beam (first polarization component) converged by the polarization lens 111a is arranged at a position separated by a distance corresponding to the optical axis deviation. Is received by. Further, the ± first-order diffracted light is received by the three-divided sensors B1 and C1, which are arranged at positions far away from the center position of the four-divided sensor A1.

  FIG. 7 shows a configuration of an arithmetic circuit that generates a focus error signal, a tracking error signal, and a reproduction RF signal from the detection signal from the photodetector 112.

  For the sake of convenience, only the arithmetic circuit for the next-generation DVD sensor group (four-divided sensor A2 and three-divided sensors B2, C2) is shown in FIG. By adopting the same configuration for the DVD sensor group (4-divided sensor A2, 3-divided sensors B3, C3) and CD sensor group (4-divided sensor A1, 3-divided sensors B1, C1), the focus An error signal, a tracking error signal, and a reproduction RF signal can be generated.

  As shown in the figure, the signal F1 is generated by adding the signal from the center sensor area of the three-divided sensor B2 and the signal from the sensor areas at both ends of the three-divided sensor C2, and the center sensor area of the three-divided sensor C2. The signal F2 is added to the signal from the sensor region at both ends of the three-divided sensor B2, and the signal F2 is generated. Further, the signal F2 is subtracted from the signal F1, thereby generating a focus error signal according to the beam size method. Can do.

  Further, a signal T1 is generated by adding a signal from the leftmost sensor region of the three-divided sensor B2 and a signal from the rightmost sensor region of the three-divided sensor C2, and a signal from the rightmost sensor region of the three-divided sensor B2 A signal T2 is generated by adding signals from the leftmost sensor region of the three-divided sensor C2, and a tracking error signal can be generated by subtracting the signal T2 from the signal T1.

  Here, when calculating the signal T1 and the signal T2, among the signals from the sensor areas at both ends of each three-divided sensor, the signals from the sensor areas opposite to each other are added together. This is because the beam pattern on the spot (the distribution pattern of the light and dark areas corresponding to the tracks) is inverted between the + 1st order light and the −1st order light. That is, with this configuration, a tracking error signal according to the push-pull method can be generated.

  Further, a reproduction RF signal is generated by adding the sensor outputs from the quadrant sensor A2. The output from the quadrant sensor A2 is also used for adjusting the optical axis of the laser light. That is, while emitting the laser beam for the next-generation DVD, the sensor output from each divided area of the four-divided sensor A2 is monitored, and the optical axis and light detection of the laser light are performed so that the sensor output from each divided area becomes equal. The relative position of the instrument 112 is finely adjusted.

  Finally, effects in the present embodiment will be described with reference to FIG.

  (1) According to this embodiment, the separation direction of ± first-order diffracted light is made to coincide with the dividing line direction of the three-divided sensor (the track direction of the disk). Thus, even if the wavelength variation occurs in the laser beam, and the separation angle of the ± first-order diffracted light varies, the spot displacement of the ± first-order diffracted light on the three-divided sensor changes to the dividing line as shown in FIG. The directions are parallel, and the amount of the beam spot applied to each sensor area does not change at all. Therefore, even if the wavelength fluctuates, the output from each sensor region does not change, and the focus error signal and the tracking error signal can be generated and output appropriately.

  (2) Even if a lens shift occurs in the objective lens, as shown in FIG. 8B, the ± first-order diffracted light spot shifts in the same direction on the corresponding three-divided sensor. When the signal is calculated, the DC component based on the lens shift is canceled. Therefore, the DC offset of the tracking error signal can be suppressed, and a stable tracking servo can be realized.

  (3) Since the lens effect is individually provided by the polarizing lens 111a as shown in FIG. 5, the spot shape on the four-divided sensor can have a sufficient spread.

  (4) As shown in FIG. 6, the sensor pattern can be simplified and integrated. Further, by making the optical axis misalignment direction of the laser light orthogonal to the dividing line direction of the three-divided sensor or the separation direction of the ± first-order diffracted light, the CD laser light sensor pattern is changed to the next generation DVD and DVD sensor pattern. The sensor patterns corresponding to all the laser beams can be efficiently arranged on one photodetector.

  Needless to say, the present invention is not limited to the above-described embodiment, and various other modifications are possible.

  For example, in the above embodiment, as shown in FIG. 6, the three-divided sensors B2 and C2 that receive next-generation DVD laser light (± first-order diffracted light) and the DVD laser light (± first-order diffracted light) are received. Although the three-divided sensors B3 and C3 are arranged individually, they may be integrated as shown in FIG.

  In the above embodiment, only the optical axis of the laser beam for CD is deviated from the optical axis of the other laser beam. In addition to this, all the optical axes are aligned, or all the optical axes are aligned. It is also possible to adopt a form in which the optical axes are not aligned. When all the optical axes are aligned, for example, the sensor pattern can be configured as shown in FIG. At this time, each sensor area of the three-divided sensor B2 and each corresponding sensor area of the three-divided sensor B3 may be integrated, or each sensor area of the three-divided sensor B3 may be integrated with a DVD laser. You may make it isolate | separate into the area | region which receives light, and the area | region which receives the laser beam for CD separately. Further, when all the optical axes are not aligned, the configuration can be as shown in FIG.

  Furthermore, in the above embodiment, a compatible optical pickup device for CD / DVD / next-generation DVD is exemplified, but other compatible optical pickup devices such as a CD / DVD compatible type and a DVD / next-generation DVD compatible type are also included. Is also applicable as appropriate. In the above description, the optical axis correction is performed using the optical axis correcting diffraction grating 103. However, other correction elements may be used. Further, the optical axis correction element may be disposed immediately before the photodetector 112.

The embodiments of the present invention can be appropriately modified in various ways within the scope of the technical idea shown in the claims.

The figure which shows the optical system of the optical pick-up apparatus which concerns on embodiment The figure which shows the structure of 3 wavelength laser which concerns on embodiment The figure explaining the effect | action of the diffraction grating for optical axis correction concerning embodiment The figure which shows the optical axis of the laser beam of each wavelength which concerns on embodiment The figure explaining the structure and effect | action of the optical element which concerns on embodiment The figure which shows the sensor pattern of the photodetector which concerns on embodiment FIG. 10 is a diagram illustrating a configuration of an arithmetic circuit according to an embodiment. The figure explaining the effect of an embodiment The figure which shows the example of a change of the sensor pattern which concerns on embodiment The figure which shows the example of a change of the sensor pattern which concerns on embodiment The figure which shows the example of a change of the sensor pattern which concerns on embodiment The figure which shows the structure of the optical pick-up apparatus which concerns on a prior art example. The figure which shows the structure of the optical pick-up apparatus which concerns on a prior art example.

Explanation of symbols

101 Three-wavelength laser 111 Optical element 111a Polarization lens 111b Polarization hologram element 112 Photodetector

Claims (4)

Laser means for irradiating the recording medium with laser light, an optical element for separating the laser light reflected from the recording medium, a photodetector for receiving the laser light separated by the optical element, and the photodetector And an optical disc device comprising means for generating a tracking error signal based on the detection signal of
The optical element;
First optical means for imparting a lens effect to the first polarization component of the laser light;
Comprising second optical means for separating a second polarized light component different from the first polarized light component by diffraction and giving the separated diffracted light a focal position back and forth in the optical axis direction;
The photodetector is;
First sensor means for receiving the first polarization component;
The sensor group includes two sensor groups that respectively receive the separated ± first-order diffracted light, and each sensor group includes three sensor regions divided by two parallel dividing lines along the track direction, The sensor group and the optical axis of the ± 1st order diffracted light are secondly adjusted so that the center of the beam spot of the ± 1st order diffracted light is positioned at the center in the width direction of the center sensor region among the three sensor regions. Sensor means,
The means for generating the tracking error signal is;
Of the three sensor regions of the two sets of sensor groups, the central sensor region is region 1, the region in one direction perpendicular to the dividing line from region 1 is region 2, and the region 1 is orthogonal to the dividing line. When the region in the other direction is region 3,
The detection signal from region 2 of one sensor group and the detection signal from region 3 of the other sensor group of the two sets of sensor groups are added, and the two signals obtained as a result of the addition are subtracted, respectively. To generate a tracking error signal,
An optical disc device characterized by the above. In claim 1,
The first sensor means is disposed between the two sets of sensor groups;
The second optical means separates the ± first-order diffracted light so that the first sensor means can be disposed between the two sets of sensor groups;
An optical disc device characterized by the above. In claim 1,
The second optical means is position-adjusted so that the laser beam separation direction by the diffraction is along the track direction.
An optical disc device characterized by the above. In claim 1,
The laser means emits laser light of several wavelengths, and the position of the second optical means is such that the optical axis misalignment direction of the laser light and the laser light separating direction by the second optical means are orthogonal to each other. Has been adjusted,
An optical disc device characterized by the above.

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