JP4482809B2 - Spherical aberration detection device and method, optical pickup, and optical disk device - Google Patents

Description

The present invention relates to a spherical aberration detection device and method , an optical pickup , and an optical disc device, and is suitable for application to an optical disc device , for example.

  Conventionally, CD (Compact Disc) and DVD (Digital Versatile Disc) are widely distributed as optical disks. In recent years, optical discs of new formats such as Blu-ray and HD-DVD, which have a higher capacity by higher density recording than those of CDs and DVDs, have appeared and are on the market.

  In this case, the size of the beam spot formed on the optical disk by the light beam is proportional to λ / NA, where λ is the wavelength of the light beam for recording and reproduction, and NA is the numerical aperture of the objective lens. Therefore, the recording density of the optical disk is almost limited by this λ / NA. Therefore, in order to increase the capacity of the optical disk by high-density recording, it is necessary to shorten the wavelength of the recording / reproducing light beam or to increase the numerical aperture (NA) of the objective lens. .

  Therefore, in recent years, development of a semiconductor laser (for example, a blue-violet semiconductor laser) having a shorter wavelength of the emitted light beam has been promoted by various companies, and in conjunction with this, development of a technique for increasing the numerical aperture of the objective lens. Is also underway. For example, Japanese Patent Laid-Open No. 11-195299 discloses a method in which the numerical aperture can be increased to 0.85 from 0.6 of the current DVD by using two groups of two objective lenses.

  However, since a spherical aberration is generally generated in the light beam that has passed through the objective lens, the light beam is not condensed at one point as shown in FIG. 8A, but as shown in FIG. 8B. The component passing through the inner peripheral side of the objective lens 1 and the component passing through the outer peripheral side are condensed at different positions. The spherical aberration increases as the numerical aperture of the objective lens 1 increases.

  Therefore, when the numerical aperture of the objective lens is increased as a technique for increasing the capacity by high-density recording of the optical disk, the recording / reproduction irradiated to the optical disk when the substrate thickness varies between the optical disks or within one optical disk. There is a problem that large spherical aberration occurs in the optical beam for recording, and the recording / reproducing characteristics deteriorate.

  In order to solve this problem, it is necessary to detect the amount of spherical aberration generated in the light beam and correct this spherical aberration using some method. Therefore, in the conventional optical disc apparatus, the spherical aberration is corrected so that the RF signal and the push-pull signal are maximized during the calibration operation, thereby controlling the amount of spherical aberration to be minimized.

  However, according to such a method, since spherical aberration itself is not detected, high-precision correction cannot be performed, and real-time correction cannot be performed. There has been a problem that even if the content deviates from the time of calibration, this cannot be detected.

  On the other hand, conventionally, the reflected light of the light beam reflected on the reflecting surface of the optical disk is separated into an outer peripheral component with an equivalently large numerical aperture and an inner peripheral component with an equivalent small numerical aperture using a beam splitter. The state of the spherical aberration is detected based on the light receiving output of the outer peripheral component and the light receiving output of the inner peripheral component of the reflected light, and the interval between the two groups of two objective lenses is changed based on the detection result. A method for compensating for spherical aberration is disclosed (for example, see Patent Document 1).

According to this spherical aberration compensation method, it is considered that the spherical aberration generated in the light beam can be detected in real time and can be corrected in real time.
JP 2002-367197 A

  However, according to the method of separating the reflected light of the light beam on the reflecting surface of the optical disc into the outer peripheral side component and the inner peripheral side component as described above, the light amount of both the outer peripheral side component and the inner peripheral side component of the reflected light is the original. Therefore, the light reception output with a sufficient signal level cannot be obtained by either the outer peripheral component or the inner peripheral component of the reflected light.

  For this reason, for example, either the outer peripheral side component or the inner peripheral side component of the reflected light is affected by thermal noise or shot noise generated in the light receiving element, and only a light receiving output having a low S / N can be obtained. Even if an attempt is made to obtain a reproduction output based on one of the light reception output of the outer peripheral component and the light reception output of the inner peripheral component of the reflected light, there is a problem that only a low quality reproduction output with low S / N can be obtained. . The same applies to the case where the light receiving output of the outer peripheral component and the light receiving output of the inner peripheral component of the reflected light are added to obtain the reproduction output as disclosed in Patent Document 1.

  Further, according to the method of separating the reflected light of the light beam on the reflecting surface of the optical disk into the outer peripheral side component and the inner peripheral side component, only a light receiving output with a low S / N can be obtained as described above. There is a problem that it is difficult to perform accurate spherical aberration correction based on the light receiving output of the outer peripheral component and the light receiving output of the inner peripheral component.

The present invention has been made in consideration of the above points, and proposes a spherical aberration detection apparatus and method , an optical pickup , and an optical disc apparatus capable of performing spherical aberration correction with higher accuracy while obtaining a high-quality reproduction output. It is what.

In order to solve such a problem, in the present invention, in the spherical aberration detection apparatus, the first region that is the range through which the first light beam emitted toward the optical disc passes is located from the center in the first region. Second and third regions in which blazed gratings each having a groove offset in a direction opposite to each other by a predetermined distance in the center and cross-sectional shapes of grooves in opposite directions are formed, respectively. And a fourth region in which a groove having a rectangular cross-sectional shape is formed. The first region allows a part of the first light beam to pass as zero-order light and the second region. A part of the first light beam is divided and generated as a second light beam composed of primary light by the regions and the fourth region, and one part of the first light beam is generated by the third region and the fourth region. - Divided generate a third light beam having a next light, and the first light beam, a first light beam when the second light beam and third light beam is incident on a predetermined objective lens, the Beam split generation in which the second light beam and the third light beam are respectively inclined with respect to the first light beam so that the centers of the second light beam and the third light beam pass through the center of the objective lens. means and, based on the reflected light in the optical disc of the first light beam to generate a focus error information of the first light beam, a focus error of the second light beam based on the reflected light in the optical disc of the second light beam generates information, focus error information generating means for generating a focus error information of the third light beam based on the reflected light in the optical disk of the third light beam, focus the first light beam Error information, based on the focus error information, and the focus error information of the third light beam of the second light beam, and to provide a spherical aberration detecting means for detecting a spherical aberration generated in the first light beam.

In this spherical aberration detection device, the combination of the blazed grating and the rectangular grating splits and generates the second and third light beams corresponding to the case where the numerical aperture is lower than that of the first light beam, and the objective lens. Each of the focus error information can be generated by passing through the central portion of each . As a result, this spherical aberration detector can obtain a light reception output with a high S / N based on the reflected light of the first light beam on the optical disk. Therefore, a reproduction output with a high S / N based on this light reception output. And accurate spherical aberration correction can be performed based on the three types of focus error information .

According to the present invention, in the spherical aberration detection method, the first region that is the range through which the first light beam emitted toward the optical disc passes is predetermined in the opposite directions from the center of the first region. Second and third regions each having a blazed grating in which the cross-sectional shapes of the grooves are opposite to each other centered at a location offset by a distance, and grooves adjacent to the second and third regions, respectively. And a fourth region in which a grating having a rectangular cross section is formed, and the first region allows a part of the first light beam to pass as zero-order light, and the second region and the fourth region. A part of the first light beam is divided and generated as a second light beam made up of primary light by the region, and a part of the first light beam is made −1st order light by the third region and the fourth region. The third light bee Division generated as was, and the first light beam, a first light beam when the second light beam and third light beam is incident on a predetermined objective lens, the second light beam and third light A first step in which the second light beam and the third light beam are respectively inclined with respect to the first light beam so that the center of the beam passes through the center of the objective lens, and the first light beam Focus error information of the first light beam is generated based on the reflected light on the optical disc, focus error information of the second light beam is generated on the basis of the reflected light of the second light beam on the optical disc , and the third light a second step of generating a focus error information of the third light beam based on the reflected light in the beam of the optical disc, the focus error information of the first light beam, a focus error of the second light beam Based on the focus error information over information and third light beam, and to provide a third step of detecting a spherical aberration generated in the first light beam.

In this spherical aberration detection method, by combining a blazed grating and a rectangular grating, the second and third light beams corresponding to a case where the numerical aperture is lowered than that of the first light beam are divided and generated, and the objective lens Each of the focus error information can be generated by passing through the central portion of each . As a result, according to this spherical aberration detection method, a light reception output having a high S / N can be obtained based on the reflected light of the first light beam on the optical disk. Therefore, a high S / N is obtained based on this light reception output. A reproduction output can be obtained, and spherical aberration correction with high accuracy can be performed based on three types of focus error information .

Furthermore, according to the present invention, in the optical pickup, a predetermined distance in a direction opposite to each other from the center in the first region is within a first region that is a range through which the first light beam emitted toward the optical disc passes. The second and third regions each having a blazed grating with the cross-sectional shapes of the grooves directed in opposite directions with each offset point as the center, and adjacent to the second and third regions, respectively. And a fourth region in which a grating having a rectangular cross-section is formed. The first region allows a part of the first light beam to pass as zero-order light, and the second region and the fourth region. A part of the first light beam is divided and generated as a second light beam composed of primary light depending on the region, and a part of the first light beam is divided into −1st order light by the third region and the fourth region. A third light beam Divided generated, and the first light beam, a first light beam when the second light beam and third light beam is incident on a predetermined objective lens, the second light beam and third as the center of the light beam passes through the center of the objective lens, a beam splitting generating means for advancing to the first light beam by tilting the second light beam and third light beam respectively, the first light beam of generating a focus error information of the first light beam based on the reflected light of the optical disc, based on the reflected light in the optical disc of the second light beam to generate a focus error information of the second light beam, the third a focus error information generating means for generating a focus error information of the third light beam based on the reflected light in the optical disc of the light beam, a focus error information of the first light beam, a second optical Bee Based on the focus error information, and the focus error information of the third light beam, a first spherical aberration detecting means for detecting a spherical aberration generated in the light beam, so as to eliminate the spherical aberration generated in the first light beam And spherical aberration generating means for generating a spherical aberration in the first light beam based on the control of a predetermined control means.
In this optical pickup, by combining the blazed grating and the rectangular grating, the second and third light beams corresponding to the case where the numerical aperture is lowered than that of the first light beam are divided and the center of the objective lens is formed. Each part can be passed and the respective focus error information can be generated. As a result, this optical pickup can obtain a light reception output having a high S / N based on the reflected light of the first light beam on the optical disk, and therefore a reproduction output having a high S / N can be obtained based on this light reception output. In addition, accurate spherical aberration correction can be performed based on the three types of focus error information .
Furthermore, according to the present invention, in the optical disc apparatus, a predetermined distance in a direction opposite to each other from the center in the first region is within a first region that is a range through which the first light beam emitted toward the optical disc passes. The second and third regions each having a blazed grating with the cross-sectional shapes of the grooves directed in opposite directions with each offset point as the center, and adjacent to the second and third regions, respectively. And a fourth region in which a grating having a rectangular cross section is formed. The first region allows a part of the first light beam to pass as zero-order light, and the second region and the fourth region. A part of the first light beam is divided and generated as a second light beam composed of primary light depending on the region, and a part of the first light beam is divided into −1st order light by the third region and the fourth region. A third light beam Divided generated, and the first light beam, a first light beam when the second light beam and third light beam is incident on a predetermined objective lens, the second light beam and third as the center of the light beam passes through the center of the objective lens, a beam splitting generating means for advancing to the first light beam by tilting the second light beam and third light beam respectively, the first light beam of generating a focus error information of the first light beam based on the reflected light of the optical disc, based on the reflected light in the optical disc of the second light beam to generate a focus error information of the second light beam, the third a focus error information generating means for generating a focus error information of the third light beam based on the reflected light in the optical disc of the light beam, a focus error information of the first light beam, a second optical Bee Based on the focus error information, and the third light beam focusing error information, the spherical aberration detecting means for detecting a spherical aberration generated in the first light beam, the first light beam, freely adjust the aberration amount Spherical aberration generating means for generating spherical aberration, and spherical aberration generated in the first light beam by the spherical aberration generating means so as to eliminate the spherical aberration generated in the first light beam based on the detection result of the spherical aberration detecting means. And a control means for generating.

In this optical disc apparatus, by combining the blazed grating and the rectangular grating, the second and third light beams corresponding to the case where the numerical aperture is lowered than that of the first light beam are divided and the center of the objective lens is formed. Each part can be passed and the respective focus error information can be generated. As a result, this optical disk apparatus can obtain a light reception output with a high S / N based on the reflected light of the first light beam on the optical disk, and thus a reproduction output with a high S / N can be obtained based on this light reception output. In addition, accurate spherical aberration correction can be performed based on the three types of focus error information .

According to the present invention, by combining the blazed grating and the rectangular grating, the second and third light beams corresponding to the case where the numerical aperture is lowered than that of the first light beam are divided and the objective lens is used. Each focus error information can be generated by passing through the central portion. As a result, in the present invention, a light reception output having a high S / N can be obtained based on the reflected light of the first light beam on the optical disk, and a reproduction output having a high S / N can be obtained based on the light reception output. Accurate spherical aberration correction can be performed based on the three types of focus error information . As a result, it is possible to realize a spherical aberration detection apparatus and method capable of performing spherical aberration correction with higher accuracy while obtaining a high-quality reproduction output.

According to the invention, the combination of the blazed grating and the rectangular grating splits and generates the second and third light beams corresponding to the case where the numerical aperture is lower than that of the first light beam, and the objective lens. Each of the focus error information can be generated by passing through the central portion of each . As a result, in the present invention, a light reception output having a high S / N can be obtained based on the reflected light of the first light beam on the optical disk, and a reproduction output having a high S / N can be obtained based on the light reception output. Accurate spherical aberration correction can be performed based on the three types of focus error information . As a result, it is possible to realize an optical pickup and an optical disc apparatus that can perform spherical aberration correction with higher accuracy while obtaining a high-quality reproduction output.

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

(1) Principle Consider two objective lenses 2 and 3 having different numerical apertures as shown in FIGS. When there is no spherical aberration, the first light beam L1 transmitted through the objective lens 2 having a large numerical aperture and the second light beam L2 transmitted through the objective lens 3 having a small numerical aperture converge at the same position. Even when there is spherical aberration, spherical aberration having a magnitude corresponding to the numerical aperture of the objective lenses 2 and 3 is generated in the first and second light beams L1 and L2, respectively. The light beams L1 and L2 are condensed at different positions.

  This is equivalent to when the objective lens 2 is not shielded as shown in FIG. 1A and when the outer peripheral side of the objective lens 2 having the same numerical aperture is shielded as shown in FIG. The same can be said when the numerical aperture is lowered. In other words, when there is spherical aberration, the first light beam L1 that passes through the objective lens 2 whose outer peripheral side is not shielded and the third light beam L3 that passes through the objective lens 2 whose outer peripheral side is shielded are each of the beams. Since spherical aberration is generated in accordance with the diameter (that is, the numerical aperture of the portion of the objective lens 2 through which the first or third light beam L1, L3 passes), the first and third light beams L1, L3 are Concentrate at different positions.

Therefore, as shown in FIG. 2, the side beams L12A and L12B are divided and generated from the light beam L10 emitted from the semiconductor laser 11 by the grating 12 in an equivalent manner, and this is divided into the collimator lens 13 and the objective lens 14. When there is no spherical aberration, the light beams L10 after splitting the side beams L12A and L12B (hereinafter referred to as the main beam L11), the side beams L12A, When there is spherical aberration, the main beam L11 and the side beams L12A and L12B are condensed at different positions, respectively, while L12B is condensed at the same position.

Here, FIG. 3 shows the beam diameter of the main beam L11 (that is, the main beam L11 of the objective lens 14) corresponding to the beam diameter of the side beams L12A and L12B (that is, the numerical aperture of the portion through which the side beams L12A and L12B of the objective lens 14 are transmitted). When the substrate thickness of the optical disk 15 is changed by 10 [μm] from 50 [μm] to 120 [μm], each substrate thickness (50 [μm] to 120 [mu] m) is obtained. [Μm]), the focus error signals of the main beam L11 (solid lines FE ₅₀ to FE ₁₂₀ ) and the focus error signals of the side beams L12A and L12B (respectively broken lines FE ₅₀ ′ to FE ₁₂₀ ′) obtained in [μm]). The simulation results are shown respectively. FIG. 4 shows a simulation result obtained when the substrate thickness of the optical disk 15 is 90 [μm]. 3 and 4, the vertical axis indicates the signal level, and the horizontal axis indicates the focus error signals FE ₉₀ of the main beam L11 and the side beams L12A and L12B when the substrate thickness is 90 [μm]. The amount of displacement of the objective lens 14 from the position of the objective lens 14 (hereinafter referred to as the reference position) when both FE ₉₀ ′ are zero is taken.

As apparent from FIGS. 3 and 4, the focus of the main beam L11 when the substrate thickness of the optical disk 15 is a certain value (in this simulation, it is 85 [μm], hereinafter referred to as the reference substrate thickness). When the error signals FE _{50 to} FE ₁₂₀ and the focus error signals FE ₅₀ ′ to FE ₁₂₀ ′ of the side beams L12A and L12B are both set to zero, if the substrate thickness of the optical disc deviates from that value, the main beam Since spherical aberration having a magnitude corresponding to the beam diameter (numerical aperture of the corresponding portion of the objective lens 14) occurs in each of L11 and side beams L12A, L12B, the focus positions of the main beam L11 and side beams L12A, L12B lag behind, as a result, the focus error signal FE ₅ of the main beam L11 A position where the signal level is zero ~FE _120, side beams L12A, deviation occurs in the position where the focus error signal _{FE 50'~FE 120} of L12B 'is zero.

In this case, the main beam L11 when the signal level of the focus error signals FE ₅₀ ′ to FE ₈₀ ′ of the side beams L12A and L12B is zero depending on whether the substrate thickness of the optical disk is smaller or larger than the reference substrate thickness. (in FIG. 4, the signal level of the portion surrounded by "○" on the focus error signal _FE 50 _{~FE 120)} the signal level of the focus error signal _FE 50 _{~FE 80} sign of the value (positive or negative) is different.

For example, in the example of FIG. 3, when the substrate thickness of the optical disk is smaller than the reference substrate thickness, the focus of the main beam L11 when the signal levels of the focus error signals FE ₅₀ ′ to FE ₈₀ ′ of the side beams L12A and L12B are zero. When the signal levels of the error signals FE _{50 to} FE ₈₀ are always negative values and the substrate thickness of the optical disk is larger than the reference substrate thickness, the signal levels of the focus error signals FE ₉₀ ′ to FE ₁₂₀ ′ of the side beams L12A and L12B. The signal level of the focus error signals FE _{90 to} FE ₁₂₀ of the main beam L11 when is zero is always a positive value.

  Therefore, for example, based on the sign of the value of the focus error signal of the main beam L11 (or side beams L12A, L12B) when the focus error signal of the side beams L12A, L12B (or main beam L11) is zero, The state of spherical aberration occurring at that time, such as in which direction the condensing position of the side beams L12A and L12B is shifted with respect to the condensing position, can be detected in real time.

  In this case, for example, in the optical system as shown in FIG. 2, in order to obtain the focus error signals of the side beams L12A and L12B separately from the focus error signal of the main beam L11 as described above, the main beam L11 on the optical disc 15 is obtained. It is necessary to guide the reflected light to a light receiving element (not shown) for generating a focus error signal so that the reflected light and the reflected light of the side beams L12A and L12B on the optical disk 15 do not overlap.

  For this purpose, the side beams L12A and L12B must be focused on the recording surface 15A of the optical disc 15 at a position away from the focusing position of the main beam L11. This condition is as shown in FIG. The side beams L12A and L12B can be satisfied by entering the objective lens 14 obliquely.

  In order to make the side beams L12A and L12B enter the objective lens 14 obliquely, as is apparent from FIG. 2, the collimator lens 13 is asymmetric with respect to the center of the collimator lens 13 (of the collimator lens 13). It is necessary to make side beams L12A and L12B having a beam diameter smaller than that of the main beam L11 incident (offset from the center).

  For example, if the beam diameter of the main beam L11 in the collimator lens 13 and the objective lens 14 is set to a radius of 4 [mm] and the numerical apertures of the side beams L12A and L12B are limited to this half, the beam diameter is set to a radius of 2 [ mm]. Then, on the recording surface 15A of the optical disc 15, the spots of the side beams L12A and L12B are offset by 20 [μm] with respect to the spot of the main beam L11, the focal length of the objective lens 14 is 2 [mm], and the collimator lens If the distance to 13 is 40 [mm], the side beams L12A and L12B can be, for example, light beams with a radius of 2 [mm] offset from the center of the collimator lens 13 by 400 [μm] on the collimator lens 13. It will be good.

  In order to obtain such side beams L12A and L12B, as is clear from FIG. 2, when the side beams L12A and L12B are divided and generated from the light beam L10 in the grating 12, the entire range of the light beam L10 is obtained. Instead, it is necessary to divide and generate the side beams L12A and L12B from only a part of the inner circumference.

  For example, in order to obtain two such side beams L12A and L12B, it is necessary to divide and generate these two side beams L12A and L12B in different ranges in the light beam L10. It should be noted that the ranges in which the side beams L12A and L12B are divided and generated in the light beam L10 may overlap, and in this case, two side beams L12A and L12B are generated simultaneously in the same range as in the conventional grating.

  And as a structure of the grating 12 for dividing and generating such side beams L12A and L12B in two, the structure as shown in FIG. 5 can be considered.

  That is, the grating 12 is, for example, circular first and second regions 21 and 22 formed on the one surface 20A side of the glass disk 20 by being offset by a predetermined distance in the opposite direction from the center of the one surface 20A. A third region 23 that is an overlapping portion of the first and second regions 21 and 22 and a fourth region 24 that is a region other than the first to third regions 21 to 23 are formed. It is comprised by.

  In this case, the first region 21 is formed as a so-called blazed grating having a sawtooth cross-sectional shape of the groove, and the direction of the blaze is from the center of the second region 22 toward the center of the first region 21. These are selected in parallel so that the primary light that becomes one side beam L12A can be divided and generated from the light beam L10 emitted from the semiconductor laser 11.

  The second region 22 is formed as a blazed grating having a blazed direction opposite to that of the first region 21. As a result, the light beam L10 emitted from the semiconductor laser 11 becomes the other side beam L12B. The primary light can be divided and generated.

  Further, the third region 23 is formed as a normal grating having a groove having a rectangular cross-sectional shape, whereby primary light that becomes one side beam L12A from the light beam L10 emitted from the semiconductor laser 11, and The first-order light that becomes the other side beam L12B can be divided and generated. The third region 23 may be omitted depending on the design.

  Further, the fourth region 24 is a portion of the transparent flat plate that is not formed with a groove or the like and generates the 0th-order light of the transmitted light beam L10.

  By configuring the grating 12 in this manner, the zero-order light of the light beam L10 that has passed through the first to fourth regions 21 to 24 becomes the main beam L11 through the collimator lens 13 and the objective lens 14 in order. The first light of the light beam L10 divided and generated in the first area 21 and the −1st order of the light beam L10 generated and divided in the second area 22 while being condensed on the 15 recording surfaces 15A. The light is condensed as side beams L12A and L12B on the recording surface 15A of the optical disk 15 through the collimator lens 13 and the objective lens 14, respectively, at a position away from the spot of the main beam L11.

  Thus, by adopting such a configuration as the grating 12, it is possible to generate a focus error signal so that the reflected light of the main beam L11 on the optical disk 15 and the reflected light of the side beams L12A and L12B on the optical disk do not overlap. The light beams can be individually guided to a light receiving element (not shown), whereby the focus error signals of the side beams L12A and L12B can be obtained separately from the focus error signal of the main beam L11.

  Based on these two focus error signals, the focus error signal of the main beam L11 (or side beams L12A, L12B) when the focus error signal of the side beams L12A, L12B (or main beam L11) is zero as described above. By correcting the spherical aberration so that the value of Y converges to zero, it is possible to correct in real time the spherical aberration caused by the variation in the substrate thickness of the optical disk.

  Hereinafter, an optical disc apparatus according to the present embodiment to which such a principle is applied will be described.

(2) Configuration of Optical Disc Device According to this Embodiment FIG. 6 shows a partial configuration of the optical disc device 30 according to this embodiment.

  In this optical disc apparatus 30, the light beam L20 emitted from the semiconductor laser 32 under the control of the laser drive circuit 31 during the recording operation and the reproducing operation is converted into one main in the grating 33 having the configuration described above with reference to FIG. The beam is divided into a beam L21 and two side beams L22A and L22B.

  The main beam L21 and the two side beams L22A and L22B are then incident on the collimator lens 35 via the beam splitter 34, converted into parallel light in the collimator lens 35, and then incident on the objective lens unit 36. .

  The objective lens unit 36 includes two groups of two objective lenses 36A and 36B, and condenses the incident main beam L21 and the two side beams L22A and L22B on the recording surface 37A of the optical disc 37 in a predetermined state. To do.

  On the other hand, the reflected light L30 of the main beam L21 on the optical disk 37 and the reflected lights L31A and L31B of the two side beams L22A and L22B on the optical disk 37 are converted into parallel light through the objective lens unit 36, respectively, and then collimator lenses. It enters the beam splitter 34 via 35. These reflected lights L30, L31A, and L31B are all reflected in a predetermined direction on the polarization plane 34A of the beam splitter 34, and thereafter enter the light receiving surface 40A of the light receiving element 40 through the condenser lens 38 and the cylindrical lens 39 in sequence. To do.

  At this time, on the light receiving surface 40A of the light receiving element 40, as shown in FIG. 7, there are four divided areas for the main beam L21 (hereinafter referred to as main divided four areas) and two for each side beam. Four divided regions (hereinafter referred to as first and second side beam four-divided regions) 42A and 42B, and the reflected light L30 of the main beam L21 on the optical disc 37 is divided into four main-beam divided regions. In addition to being condensed on the region 41, the reflected lights L31A and L31B of the side beams L22A and L22B on the optical disc 37 are condensed on the corresponding side beam quadrants 42A and 42B.

  The outputs of the four divided regions of the main beam four-divided region 41 on the light-receiving surface 40A of the light-receiving element 40 and the outputs of the four divided regions of the first and second side beam four-divided regions 42A and 42B. Is provided to a logic circuit 43 provided integrally with the light receiving element 40.

  Thus, the logic circuit 43 sets the outputs of the four regions of the main beam four-divided region 41 denoted by reference characters A to D in FIG.

The RF signal S _RF is generated by executing the above calculation process, and is sent to the reproduction circuit 44 (FIG. 6). Thus, the reproduction circuit 44 performs predetermined signal processing on the _RF signal SRF, thereby generating a reproduction signal S1.

  Further, the logic circuit 43 has the following formula:

The focus error signal _{SFE (M)} of the main beam L21 is generated by executing this calculation, and is sent to the focus control circuit 45.

Thus, the focus control circuit 45 controls the main beam L21 by controlling the biaxial actuator 48 that holds the two groups of objective lenses 36A and 36B of the objective lens section 36 based on the focus error signal _{SFE (M).} If necessary, the two objective lenses 36A and 36B are moved together in the direction approaching or separating from the optical disc 37 so that the light is always condensed on the recording surface 37A of the optical disc 37.

Further, the logic circuit 43 outputs the outputs of the four divided areas of the first side beam four-divided area 42A to which the reference numerals E1 to H1 are assigned in FIG. 7 respectively, and E2 to H2 in FIG. The outputs of the four divided areas of the second divided side beam quadrant area 42B are denoted as E2 to H2, respectively, and the outputs of the first and second side beam quadrant areas 42A and 42B are output. E1～H1, generates a tracking error signal _{S TE} by executing a predetermined arithmetic processing based on E2～H2, and sends it to the tracking control circuit 46.

Thus, the tracking control circuit 46 controls the biaxial actuator 48 based on the tracking error signal _STE , so that the main beam L21 can scan the track formed on the recording surface 37A of the optical disc 37 in a just-tracked state. As described above, the two objective lenses 36 </ b> A and 36 </ b> B are integrally moved in the radial direction of the optical disk 37 as necessary.

  Further, the logic circuit 43 is based on the outputs E1 to H1 and E2 to H2 of the respective regions of the first and second side beam quadrants 42A and 42B.

The focus error signal SFE _{(M) of the} main beam L21 normalized by the total reflected light amount of the main beam L21 and these normalized by the total reflected light amounts of the side beams L22A and L22B A spherical aberration error signal S _SA representing a difference from the sum of the focus error signals S _{FE (S 1)} and S _{FE (} S ₂₎ of the side beams L 22 A and L 22 B is generated and sent to the spherical aberration correction control circuit 47. In addition, the logic circuit 43 also sends the focus error signal _{SFE (M) of} the main beam L21 obtained as described above to the spherical aberration correction control circuit 47.

Thus, the spherical aberration correction control circuit 47 controls the uniaxial actuator 49 that holds one objective lens 36A, 36B of the objective lens section 36 based on the spherical aberration error signal _SSA and the focus error signal _{SFE (M).} As a result, when the signal level of the focus error signal _{SFE (M)} is zero, the value of the spherical aberration error signal _SSA converges to zero (that is, the spherical aberration is eliminated). 36B is moved in a direction close to or away from the other objective lenses 36B and 36A.

  In this manner, the optical disc apparatus 30 can correct the spherical aberration in real time in response to the occurrence of the spherical aberration caused by the variation in the substrate thickness of the optical disc 37 and the like.

(3) Operation and effect of the present embodiment In the above configuration, the optical disk apparatus 30 divides the light beam L20 emitted from the semiconductor laser 32 into the main beam L21 and the two side beams L22A and L22B. A focus error signal SFE _(M) obtained based on the reflected light L30 on the optical disk 37 of the beam L21 and a focus error signal SFE _(S1) obtained based on the reflected lights L31A and L31B on the optical disk 37 of the two side beams L22A and L22B. _{) And SFE (S2)} , spherical aberration correction is performed so that the value of the spherical aberration error signal _SSA converges to zero when the signal level of the focus error signal _{SFE (M)} is zero.

  Therefore, in the optical disc device 30, even when spherical aberration occurs on the optical disc 37 due to variations in the substrate thickness or the like, this can be detected in real time to correct the spherical aberration.

  In this case, in the optical disc apparatus 30, the occurrence of such spherical aberration is achieved by dividing the light beam L20 emitted from the semiconductor laser 32 without separating the main beam L21 into an inner peripheral component and an outer peripheral component. Since detection is performed based on the obtained main beam L21 and side beams L22A and L22B, the reflected light L30 of the main beam L21 on the optical disk 37 is separated into an inner peripheral component and an outer peripheral component. Therefore, a larger amount of light as the reflected light L30 can be incident on the main beam quadrant 41 of the light receiving element 40.

  As a result, in this optical disc apparatus 30, the received light output of the main beam L20 reflected by the optical disc 37 is not affected by thermal noise or shot noise generated in the light receiving element 40 and has a high signal level. Obtainable. Accordingly, based on this light reception output, a reproduction output with a high S / N can be obtained based on this light reception output, and spherical aberration correction with high accuracy can be performed.

According to the above configuration, the light beam L20 emitted from the semiconductor laser 32 is divided into the main beam L21 and the two side beams L22A and L22B, and the focus error obtained based on the reflected light L30 on the optical disc 37 of the main beam L21. Based on the signal SFE _(M) and the focus error signals SFE _(S1) and SFE _(S2) obtained based on the reflected lights L31A and L31B of the two side beams L22A and L22B on the optical disk 37, the focus error signal Since the spherical aberration correction is performed so that the value of the spherical aberration error signal _SSA converges to zero when the signal level of _{SFE (M)} is zero, the reflected light L30 of the main beam L21 on the optical disk 37 is changed. Light reception output with high S / N can be obtained based on this light reception. And to obtain a high reproduction output S / N ratio based on the force, it is possible to perform accurate spherical aberration correction. In this way, an optical disc apparatus capable of correcting spherical aberration with higher accuracy while obtaining a high-quality reproduction output can be realized.

(4) Other Embodiments In the above-described embodiment, the optical system of the optical disc device 30 is configured as shown in FIG. 6, but the present invention is not limited to this, and other configurations are also possible. Various configurations can be widely applied.

  In the above-described embodiment, the case where the grating 33 is configured as described above with reference to FIG. 3 has been described. However, the present invention is not limited to this, and various other configurations can be widely applied. .

  In this case, in the above-described embodiment, the case where only the 0th-order light of the incident light beam L20 is generated in the fourth region 24 that is the transparent flat plate portion of the grating 33 has been described. The present invention is not limited to this, and in this fourth region 24, the n-th light other than the 0th-order light (n is an integer other than 0) of the light beam L20 is prevented from entering the optical disc 37 (that is, the n It may be generated (so that the next light does not enter the aperture of the collimator lens 35). By doing in this way, the malfunction that the transmittance | permeability of the light beam L20 in this 4th area | region 24 becomes high with respect to the other 1st-3rd area | regions 21-23 can be eliminated.

  The present invention can be widely applied to optical disc devices compliant with various optical disc standards, in addition to optical disc devices compliant with CD standards and DVD standards.

It is a conceptual diagram with which the principle of this invention is provided. It is a conceptual diagram with which the principle of this invention is provided. It is a wave form diagram with which the principle of this invention is provided. It is a wave form diagram with which the principle of this invention is provided. It is the top view which shows the structural example of a grating, and a rough-line sectional drawing. It is a basic diagram which shows schematic structure of the optical disk apparatus by this Embodiment. It is a conceptual diagram with which it uses for description of a light receiving element. It is a conceptual diagram with which it uses for description of spherical aberration.

Explanation of symbols

11, 32 ... Semiconductor laser, 12, 33 ... Grating, 14, 36A, 36B ... Objective lens, 15, 37 ... Optical disc, 15A, 37A ... Recording surface, 21-24 ... Area, 36 ... Objective lens group 40... Light receiving element 40 A... Light receiving surface 41... Main beam quadrant area 42 A, 42 B Side beam quadrant area 47. Spherical aberration correction control circuit 49. 1-axis actuator, L10, L20 ...... light beam, L11, L21 ...... main beam, L12A, L12B, L22A, L22B ...... side beams, L30, L31A, L31B ...... reflected _{light, S TE} ...... tracking error signal, S _SA …… Spherical aberration error signal.

Claims (5)

The cross section of the groove centering on a portion offset by a predetermined distance in the opposite direction from the center in the first region in the first region that is a range through which the first light beam emitted toward the optical disc passes. Second and third regions each having a blazed grating whose shapes are opposite to each other, and a grating having a rectangular cross-sectional shape adjacent to the second and third regions are formed. A first region that allows a portion of the first light beam to pass as zero-order light through the first region and the first light through the second region and the fourth region. A part of the beam is divided and generated as a second light beam composed of primary light, and a part of the first light beam is composed of −1 order light by the third region and the fourth region. Split generation as a light beam And the first light beam, said second light beam and said first optical beam in the third light beam is incident on a predetermined objective lens, the second light beam and said third like the center of the light beam passes through the center of the objective lens, a beam splitting generating means for advancing inclined the first to the light beam and the second light beam and said third light beam respectively,
Focus error information of the first light beam is generated based on the reflected light of the first light beam on the optical disc , and the second light beam is generated based on the reflected light of the second light beam on the optical disc. Focus error information generating means for generating focus error information of the third light beam based on reflected light of the third light beam on the optical disc ;
Spherical aberration generated in the first light beam is detected based on the focus error information of the first light beam, the focus error information of the second light beam, and the focus error information of the third light beam. A spherical aberration detector comprising: a spherical aberration detector. The beam splitting generation means is
The spherical aberration detection device according to claim 1 , wherein the first region generates the n-th (n is an integer other than 0) -order light of the first light beam so as not to enter the optical disc. The cross section of the groove centering on a portion offset by a predetermined distance in the opposite direction from the center in the first region in the first region that is a range through which the first light beam emitted toward the optical disc passes. Second and third regions each having a blazed grating whose shapes are opposite to each other, and a grating having a rectangular cross-sectional shape adjacent to the second and third regions are formed. A first region that allows a portion of the first light beam to pass as zero-order light through the first region and the first light through the second region and the fourth region. A part of the beam is divided and generated as a second light beam composed of primary light, and a part of the first light beam is composed of −1 order light by the third region and the fourth region. Split generation as a light beam And the first light beam, said second light beam and said first optical beam in the third light beam is incident on a predetermined objective lens, the second light beam and said third A first step in which the second light beam and the third light beam are respectively inclined and traveled with respect to the first light beam so that the center of the light beam passes through the center of the objective lens;
Focus error information of the first light beam is generated based on the reflected light of the first light beam on the optical disc , and the second light beam is generated based on the reflected light of the second light beam on the optical disc. A second step of generating focus error information of the third light beam based on the reflected light of the third light beam on the optical disc ;
The spherical aberration generated in the first light beam is detected based on the focus error information of the first light beam, the focus error information of the second light beam, and the focus error information of the third light beam. A spherical aberration detection method comprising: a third step. The cross section of the groove centering on a portion offset by a predetermined distance in the opposite direction from the center in the first region in the first region that is a range through which the first light beam emitted toward the optical disc passes. Second and third regions each having a blazed grating whose shapes are opposite to each other, and a grating having a rectangular cross-sectional shape adjacent to the second and third regions are formed. A first region that allows a portion of the first light beam to pass as zero-order light through the first region and the first light through the second region and the fourth region. A part of the beam is divided and generated as a second light beam composed of primary light, and a part of the first light beam is composed of −1 order light by the third region and the fourth region. Split generation as a light beam And the first light beam, said second light beam and said first optical beam in the third light beam is incident on a predetermined objective lens, the second light beam and said third like the center of the light beam passes through the center of the objective lens, a beam splitting generating means for advancing inclined the first to the light beam and the second light beam and said third light beam respectively,
Focus error information of the first light beam is generated based on the reflected light of the first light beam on the optical disc , and the second light beam is generated based on the reflected light of the second light beam on the optical disc. Focus error information generating means for generating focus error information of the third light beam based on reflected light of the third light beam on the optical disc ;
Spherical aberration generated in the first light beam is detected based on the focus error information of the first light beam, the focus error information of the second light beam, and the focus error information of the third light beam. Spherical aberration detection means;
And a spherical aberration generating means for generating a spherical aberration in the first light beam based on control of a predetermined control means so as to eliminate the spherical aberration generated in the first light beam. The cross section of the groove centering on a portion offset by a predetermined distance in the opposite direction from the center in the first region in the first region that is a range through which the first light beam emitted toward the optical disc passes. Second and third regions each having a blazed grating whose shapes are opposite to each other, and a grating having a rectangular cross-sectional shape adjacent to the second and third regions are formed. A first region that allows a portion of the first light beam to pass as zero-order light through the first region and the first light through the second region and the fourth region. A part of the beam is divided and generated as a second light beam composed of primary light, and a part of the first light beam is composed of −1 order light by the third region and the fourth region. Split generation as a light beam And the first light beam, said second light beam and said first optical beam in the third light beam is incident on a predetermined objective lens, the second light beam and said third like the center of the light beam passes through the center of the objective lens, a beam splitting generating means for advancing inclined the first to the light beam and the second light beam and said third light beam respectively,
Focus error information of the first light beam is generated based on the reflected light of the first light beam on the optical disc , and the second light beam is generated based on the reflected light of the second light beam on the optical disc. Focus error information generating means for generating focus error information of the third light beam based on reflected light of the third light beam on the optical disc ;
The spherical aberration generated in the first light beam is detected based on the focus error information of the first light beam, the focus error information of the second light beam, and the focus error information of the third light beam. Spherical aberration detecting means for
Spherical aberration generating means for generating spherical aberration in an adjustable amount of aberration in the first light beam;
Control means for generating the spherical aberration in the first light beam by the spherical aberration generating means so as to eliminate the spherical aberration generated in the first light beam based on the detection result of the spherical aberration detecting means. An optical disc apparatus having the following.

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