JPWO2007108446A1 - OPTICAL HEAD, OPTICAL DISK DEVICE, AND OPTICAL HEAD MANUFACTURING METHOD - Google Patents

Abstract

An optical head or the like in which the position of an optical element that corrects chromatic aberration is adjusted is provided. The optical head is disposed on the optical path from the light source to the objective lens and the light collecting optical system including the light source that emits light, the objective lens that collects the light on the optical disk, and is caused by the fluctuation of the wavelength of the light. A correction element that corrects chromatic aberration of the generated objective lens and a diffraction grating that deflects light reflected by the optical disk in a plurality of directions are provided. The diffraction grating and the correction element constitute a composite element that is integrated so that the optical axes thereof coincide with each other. The position of the composite element is adjusted so that the optical axis of the composite element coincides with the optical axis of the condensing optical system.

Description

  The present invention relates to an optical head manufacturing method for optically recording and / or reproducing information on an information recording medium such as an optical disk, and the optical head. More specifically, the present invention relates to a method for adjusting the arrangement of optical elements in an optical head, and an optical head in which the arrangement of optical elements is adjusted.

  As the amount of data to be recorded increases, there is a demand for optical disks with higher recording density and larger capacity.

  In order to increase the recording density of the optical disc, it is necessary to shorten the wavelength of light used for recording and reproduction and to reduce the size of the light spot. Therefore, in recent years, a light source having a wavelength of about 405 nm shorter than the wavelengths used for CDs and DVDs (about 780 nm and about 650 nm) and a relatively large objective lens having a numerical aperture of 0.65 to 0.85 are used. It is getting to be.

  For wavelengths as short as about 405 nm, the dispersion of the optical material such as glass forming the objective lens becomes large, so that the refractive index of the objective lens becomes large. In addition, as the numerical aperture increases, the depth of focus decreases. As a result, when the wavelength of the light source fluctuates, the influence of axial chromatic aberration appears greatly, which causes the performance of the optical head to deteriorate. Laser light generally has a single wavelength and no axial chromatic aberration should occur, but in practice the wavelength fluctuates with a width of several nanometers due to temperature changes, output changes, and the like. As a result, axial chromatic aberration appears. Although axial chromatic aberration occurred even at wavelengths of CD and DVD, since the dispersion of the optical material forming the objective lens is small in these wavelength bands, the amount of axial chromatic aberration was negligibly small. However, as the wavelength becomes shorter, the depth of focus becomes shallower and the dispersion becomes larger, increasing the amount of axial chromatic aberration. Therefore, in an optical head having a short wavelength light source and an objective lens having a relatively large numerical aperture, it is necessary to correct axial chromatic aberration.

  For example, Patent Document 1 discloses a conventional optical head in which axial chromatic aberration of an objective lens is corrected. FIG. 11 shows a configuration of a conventional optical head. The conventional optical head includes a laser light source 101, a beam splitter 102, a diffraction integrated collimator 103, an objective lens 104, a detection optical system 106, and a light detection unit 107. The diffractive integrated collimator 103 is a lens composed of, for example, a refractive surface and a diffractive lens surface, and the diffractive lens surface has a positive power. Here, positive power means the same refractive power as the power of the convex lens. FIG. 11 shows the optical axis 108 of the diffraction integrated collimator 103.

  The light emitted from the laser light source 101 is reflected by the beam splitter 103, converted into substantially parallel light by the diffraction integrated collimator 103, and condensed on the information recording surface of the optical disk 105 by the objective lens 104. The light reflected by the optical disk 105 passes through the objective lens 104 again, is converted into convergent light by the diffraction integrated collimator 103, passes through the beam splitter 102, and is guided to the light detection unit 107 by the detection optical system 106.

  The principle of correcting axial chromatic aberration by the above-described optical system is as follows.

  As the wavelength becomes shorter, the power (refractive power) of the objective lens increases, and the position of the focal point approaches the objective lens. As a result, the influence of axial chromatic aberration of the objective lens appears greatly.

  On the other hand, when the wavelength is shortened, the diffraction angle decreases, so the power of the diffractive lens surface decreases. Since the diffractive lens surface has a positive power, if the power is reduced, the power of the entire diffractive integrated collimator 103 is also reduced, and the light that has passed through is incident on the objective lens 104 as divergent light. Since the divergent light moves the focal position of the objective lens in a direction away from the objective lens, it has the effect of canceling the axial chromatic aberration when the wavelength of the light source fluctuates. Therefore, the axial chromatic aberration of the objective lens 104 can be corrected by appropriately distributing the power of the refracting surface and the diffractive lens surface of the diffractive integrated collimator 103.

This principle is not limited to the above configuration. For example, even if one surface of the objective lens is a diffractive lens surface, it is possible to correct axial chromatic aberration by the same principle. However, the above-described conventional technique suppresses the manufacturing cost of the optical head by forming a diffractive lens surface on a collimator having a shape that can be easily processed.
Japanese Patent Laid-Open No. 2001-108894 (page 4-11, FIG. 1)

  However, the conventional techniques have the following problems.

  In general, if a lens that generates chromatic aberration and a lens that corrects chromatic aberration are relatively decentered (that is, if the optical axes of the two do not match), the amount of decentering is determined in a direction perpendicular to the optical axes. Chromatic aberration (hereinafter referred to as “lateral chromatic aberration”) occurs. This lateral chromatic aberration appears in the optical head as a phenomenon in which the position of the light spot moves in the plane of the optical disk.

  The wavelength of the laser light varies depending on the output light amount. Therefore, the wavelength is different between information reproduction with a relatively small amount of output light and information recording with a large amount of output light. It should be noted that the wavelength variation occurs instantaneously when switching between the recording operation and the reproducing operation. Due to the lateral chromatic aberration caused by this wavelength variation, the light spot position moves instantaneously. If this instantaneous movement occurs in a direction perpendicular to the information track of the optical disk (that is, the disk radial direction), the tracking servo cannot follow and the tracking control becomes unstable.

  The above-described problem becomes more apparent when an optical disk corresponding to a laser beam having a center wavelength of 405 nm is multilayered and accessed by higher rotation. In either case, the output light amount of the laser beam must be increased during the recording operation, so the difference from the output light amount during the reproduction operation increases, and the amount of movement of the light spot position due to lateral chromatic aberration increases. .

  The optical head is preferably assembled so that the optical axes of the optical systems are matched. However, since light propagates in parallel between the objective lens and the collimator, it is difficult to align their optical axes, and relative eccentricity remains. Furthermore, since the objective lens moves in a direction perpendicular to the information track (radial direction of the optical disk) for accessing the information track, the relative eccentricity increases. In the conventional optical head, since the chromatic aberration of the objective lens is corrected by the collimator, lateral chromatic aberration due to the relative decentration thereof occurs, and tracking control becomes unstable.

  An object of the present invention is to provide a structure for adjusting the position of an optical element that corrects chromatic aberration, and an optical head that matches the optical axis of the optical element with the optical axis of the objective lens by the structure, and An object of the present invention is to provide an optical disc apparatus provided with the optical head.

  An optical head according to the present invention is disposed on an optical path from a light source that emits light, a condensing optical system that includes an objective lens that condenses the light onto an optical disc, and from the light source to the objective lens. A correction element that corrects chromatic aberration of the objective lens caused by wavelength variation; and a diffraction grating that deflects the light reflected by the optical disc in a plurality of directions. In the optical head, the diffraction grating and the correction element constitute a composite element integrated so that their optical axes coincide with each other, and the optical axis of the composite element and the condensing optical system The optical axis is adjusted to match.

  The optical axis of the composite element may be fixed at a position that coincides with the optical axis of the condensing optical system among positions on a plane orthogonal to the optical axis of the condensing optical system.

  The optical head may further include a base having at least one end face defining a plane perpendicular to the optical axis of the condensing optical system, and the composite element may be fixed on the at least one end face. .

  Around the fixed composite element, there may be a space in which the composite element before being fixed can move.

  The optical head further includes a light receiving unit that detects light reflected by the optical disc, and the diffraction grating includes a plurality of diffraction regions for detecting a push-pull signal in the radial direction of the optical disc based on the reflected light. You may have.

  The optical disc has one or more tracks, the diffraction grating has two diffraction regions divided by a dividing line corresponding to a direction along the tracks, and the composite element is on the plane. Of the range movable in the direction orthogonal to the dividing line, the optical axis of the composite element may be adjusted and fixed at a position that coincides with the optical axis of the condensing optical system.

  The optical disc has one or more tracks, and the diffraction grating is divided by a first dividing line corresponding to a direction along the track and a second dividing line orthogonal to the first dividing line. The composite element has four diffractive regions, and the composite element is movable in the first plane perpendicular to the first dividing line and the direction perpendicular to the second dividing line on the plane. The optical axis of the composite element may be adjusted and fixed at a position that coincides with the optical axis of the condensing optical system.

  The composite element may include the correction element, the diffraction grating, and a member that physically fixes the correction element and the diffraction grating.

  The composite element may be configured by adhering the correction element and the diffraction grating.

  An optical disc apparatus according to the present invention includes an optical head having any one of the above-described features, a motor that rotates the optical disc, and a controller that controls the optical head and the motor. The control unit controls the optical head based on a signal output from the optical head so as to continuously collect light on the recording layer of the optical disc, and performs information recording and / or reproduction. .

  The method of manufacturing an optical head according to the present invention includes a light source that emits light, a condensing optical system that includes an objective lens that condenses the light on an optical disc, and an optical path from the light source to the objective lens. To produce an optical head comprising a correction element that corrects chromatic aberration of the objective lens caused by fluctuations in the wavelength of the light, and a diffraction grating that deflects the light reflected by the optical disc in a plurality of directions. To be implemented. The optical head manufacturing method includes the steps of preparing the condensing optical system, preparing a composite element integrated so that the optical axis of the diffraction grating and the optical axis of the correction element coincide with each other, Adjusting the optical axis of the composite element to coincide with the optical axis of the condensing optical system on a plane orthogonal to the optical axis of the condensing optical system.

  The adjusting step may be performed such that an optical axis of the composite element coincides with an optical axis of the condensing optical system while bringing the composite element into contact with a base having the flat surface.

  According to the present invention, since the optical axes of the lens that generates chromatic aberration in the optical head and the lens that corrects chromatic aberration coincide with each other, lateral chromatic aberration caused by decentration of the optical system can be reduced. Thereby, an optical head capable of stable tracking control even when a sudden wavelength change occurs can be manufactured.

It is a figure which shows the optical head 50 in the assembly by embodiment of this invention. 3 is a diagram illustrating an example of a configuration of a chromatic aberration correction element 4. FIG. 3 is a diagram illustrating an example of a configuration of a diffraction element 3. FIG. It is a figure which shows the end surface (pressing surface) 54 of the base 55 which prescribes | regulates the base 55 and the plane orthogonal to the optical axis of the objective lens 7. FIG. (A) is a figure which does not show the position of the light 14 which passes the diffraction element 3, (b) is a figure which shows each waveform of signal S12 and S13. (A) is a figure which shows the light 14 equally divided into 2 by the dividing line 15, (b) is a figure which shows the level change of signal S12 and S13 when the position of a composite element is adjusted. It is a figure which shows the optical head 56 after an assembly. 3 is a diagram illustrating an example of the configuration of a diffraction element 30 having two parting lines 20 and 21. FIG. 1 is a diagram showing a schematic configuration of an optical disc device 90 according to an embodiment of the present invention. It is a figure which shows the example of the base provided with the processus | protrusion 60. FIG. It is a figure which shows the structure of the conventional optical head.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Beam splitter 3,30 Diffraction element 4 Chromatic aberration correction element 5 Collimator 6 Aperture stop 7 Objective lens 8 Optical disk 9 Main beam of condensing optical system 10 Optical axis of collimator 11 Optical detection part 50 Optical head 51 Control circuit 52 Actuator 54 End surface (pressing surface)
55 base

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows an optical head 50 during assembly according to this embodiment. FIG. 1 shows a process in which components of the optical head 50 are incorporated and the arrangement thereof is adjusted.

  The optical head 50 includes a light source 1, a beam splitter 2, a diffraction element 3 that splits light, a chromatic aberration correction element 4, a collimator 5, an aperture stop 6, an objective lens 7, and a photodetector 11. ing. In FIG. 1, an optical disk 8 is also shown for reference.

  Note that an optical system of a general optical head further requires a focus detection unit, a tracking detection unit, an information signal detection unit, etc., but these are not shown in FIG. These configurations will be described later with reference to FIG.

  In FIG. 1, a solid line 9 indicates the principal ray (optical axis) of the condensing optical system from the light source 1 to the objective lens 7. A one-dot chain line 10 indicates the optical axis of the collimator 5.

  Although the optical axis of the light source 1 is assembled so as to coincide with the optical axis of the collimator 5, this optical axis does not coincide with the optical axis of the condensing optical system. FIG. 1 shows a state where the optical axis of the condensing optical system 7 and the optical axis 10 of the collimator are decentered. The eccentricity occurs because light propagates in parallel between the objective lens and the collimator and it is difficult to align their optical axes. The chief ray 9 passes through the center of the aperture stop 6. In general, since the aperture stop 6 is arranged close to the objective lens 7 without being decentered, the principal ray 9 substantially coincides with the optical axis of the objective lens 7. In the following description, the principal ray 9 is described as being the optical axis of the objective lens 7.

  The diffraction element 3 and the chromatic aberration correction element 4 are integrally held by a holder 53. When fixed by the holder 53, the respective optical axes of the diffraction element 3 and the chromatic aberration correction element 4 are adjusted so as to coincide with each other, and the state is maintained after the fixing. The optical axis of the diffractive element 3 is an axis perpendicular to the paper surface passing through a point (for example, the midpoint of the dividing line 15) on the dividing line 15 (FIG. 3 described later) of the diffractive element 3.

  Hereinafter, the integrated diffraction element 3 and chromatic aberration correction element 4 are also referred to as a “composite element”. In addition, since the two optical axes of the diffraction element 3 and the chromatic aberration correction element 4 overlap each other and are recognized as one optical axis, the one optical axis is hereinafter referred to as “optical axis of the composite element”.

  Here, the configurations of the diffraction element 3 and the chromatic aberration correction element 4 will be described with reference to FIGS. 2 and 3.

  FIG. 2 shows an example of the configuration of the chromatic aberration correction element 4. The chromatic aberration correcting element 4 has a concave refracting surface and a diffractive lens surface. For example, the concave surface is disposed on the light source 1 side. The diffractive lens surface facing the concave surface has positive power. Since the positive power cancels out the negative negative power, the overall power of the chromatic aberration correction element 4 is small.

  When the wavelength is shortened, the positive power of the diffractive lens surface is reduced and the negative power of the concave surface is superior, so that the light passing therethrough is more diverged. Therefore, when the wavelength is shortened, the light from the light source 1 is intensified in the divergence state by the chromatic aberration correction element 4. As a result, the light output from the chromatic aberration correcting element 4 and passing through the collimator 5 becomes divergent light. Thereby, the axial chromatic aberration of the objective lens 7 is corrected.

  FIG. 3 shows an example of the configuration of the diffraction element 3. The diffractive element 3 has two diffractive regions 12 and 13 in which diffraction gratings having different periods or directions are formed. The diffraction regions 12 and 13 are arranged with the dividing line 15 as a boundary. The dividing line 15 corresponds to a direction parallel to the information track (a direction along the information track). For reference, the passing light 14 is shown in FIG. When adjusting the arrangement of the composite elements, the diffractive element 3 is moved together with the chromatic aberration correcting element 4 in the X direction indicated by the double arrow in FIG.

  Next, the path of light traveling through the optical head 50 will be described with reference to FIG. 1 again. The laser light emitted from the light source 1 passes through the beam splitter 2, the diffraction element 3, and the chromatic aberration correction element 4, is converted into parallel light by the collimator 5, passes through the aperture stop 6, and is information on the optical disk 8 by the objective lens 7. Focused on the recording surface.

  The light reflected by the optical disk 8 enters the diffraction element 3 again through the objective lens 7, the aperture stop 6, the collimator 5, and the chromatic aberration correction element 4. The diffraction element 3 splits and diffracts the light. The diffracted light is reflected by the beam splitter 2, guided to the photodetector 11, and the amount of each divided light is detected.

  If the optical axis of the objective lens 7 that generates chromatic aberration and the optical axis of the composite element having the function of correcting the chromatic aberration described above are deviated (that is, decentration occurs), lateral chromatic aberration corresponding to the decentration amount is generated. It occurs in a direction perpendicular to their optical axes.

  Therefore, in the present embodiment, a configuration has been introduced in which the holder 53 is moved so that the optical axis of the composite element can coincide with the optical axis of the objective lens 7. Specifically, a base having the plane is provided so that the composite element can be moved on a plane orthogonal to the optical axis of the objective lens 7.

  FIG. 4 shows a base 55 and an end surface (pressing surface) 54 of the base 55 that defines a plane orthogonal to the optical axis of the objective lens 7. A composite element composed of the diffraction element 3 and the chromatic aberration correction element 4 is disposed in contact with the end face 54. By moving the holder 53 in the direction along the plane, the position of the composite element is adjusted. At the time of movement, the composite element is pressed against the end face 54, and the optical axis of the composite element and the optical axis of the objective lens 7 are always parallel. The chromatic aberration correcting element 4 is in contact with the end face 54, but this is an example. The end face 54 may be provided on the diffraction element 3 side so that the diffraction element 3 is in contact with the end face 54.

  The movement direction of the holder 53 is the X direction shown in FIG. 4 when the diffraction element 3 shown in FIG. 3 is used. The X direction in FIG. 3 and the X direction in FIG. 4 correspond to the same direction. On the other hand, when the diffraction element 30 shown in FIG. 8 to be described later is used, the moving direction of the holder 53 is the X direction and the Y direction shown in FIG. The X direction and the Y direction in FIG. 8 correspond to the same directions as the X direction and the Y direction in FIG. 4, respectively.

  An example of a configuration in which the diffraction element 3 and the chromatic aberration correction element 4 are not movable is shown in FIG. FIG. 10 shows an example of a base having a protrusion 60. The protrusion 60 is not for adjusting the positions of the diffraction element 3 and the chromatic aberration correction element 4 but for determining the positions of the diffraction element 3 and the chromatic aberration correction element 4. In the optical head having such a protrusion 60, the position adjusting method according to the present invention cannot be adopted.

  The holder 53 is moved by the control circuit 51 and the actuator 52 shown in FIG. Specifically, it is as follows.

  The control circuit 51 receives at least two signals output from the photodetector 11. The level of each signal corresponds to the amount of light incident on a different light receiving area of the photodetector 11. The control circuit 51 generates a control signal based on these signals and outputs it to the actuator 52. The actuator 52 is physically connected to the holder 53 and moves the holder 53 based on a control signal. The direction indicated by the arrow in FIG. 1 corresponds to the X direction in FIG.

  Next, a method for adjusting the position of the composite element will be described.

  First, the light source 1 is caused to emit light and the laser light is condensed on the optical disk 8. Then, the light reflected by the optical disk 8 and divided by the diffraction element 3 is detected by the photodetector 11. In order to focus the laser beam on the optical disk 8, so-called focus control is preferably performed. Therefore, the focus control may be performed by incorporating the optical head 50 being assembled into a device having a function equivalent to that of FIG. 9 described later.

  Before the adjustment of the position of the composite element, the optical axis of the composite element and the optical axis of the objective lens 7 do not coincide with each other, so that the laser light is incident on a position off the optical axis of the diffraction element 3.

  For example, FIG. 5A shows the position of the light 14 that passes through the diffraction element 3. The light transmitted through the diffraction regions 12 and 13 of the diffraction element 3 is separately detected by the photodetector 11. Now, it is assumed that the light diffracted by the diffraction region 12 is detected by the photodetector 11 and a signal S12 is output. Further, it is assumed that the light diffracted by the diffraction region 13 is detected by the photodetector 11 and a signal S13 is output.

  FIG. 5B shows the waveforms of the signals S12 and S13. The level of the signal S12 is a, and the level of the signal S13 is b (<a). As shown in FIG. 5A, since the amount of light passing through the diffraction region 12 is larger than the amount of light passing through the diffraction region 12, the level of the signal S12 is higher than that of the signal S13.

  The control circuit 51 adjusts the position of the composite element (that is, the diffraction element 3) by controlling the actuator 52 so that the signals S12 and S13 are at the same level. This means that the position of the composite element is adjusted so that the light is equally divided into two by the dividing line 15.

  In the present embodiment, the optical disc 8 is a disc having a reflective layer without pits / marks. This is because the levels of the signals S12 and S13 are very easy to adjust. Since the waveform component of the pit / mark of the optical disk 8 is not superimposed on the reflected light, the waveform in FIG. 5B is a straight line. When a disc having pits / marks is used, a waveform component due to the pits / marks is superimposed on both signals S12 and S13.

  FIG. 6A shows the light 14 that is equally divided into two by the dividing line 15. FIG. 6B shows the level change of the signals S12 and S13 when the position of the composite element is adjusted. The composite element is moved from the position shown in FIG. 5A to the position shown in FIG. At this time, the light 14 itself does not fluctuate.

  When the levels of the signals S12 and S13 are both c, the driving of the actuator 52 is stopped and the movement of the composite element is completed. At this position, the composite element is fixed to the base 55 with an adhesive or the like. The control circuit 51 and the actuator 52 are removed from the optical head 50 when the adjustment is completed.

  As is clear from the comparison between FIG. 4 and FIG. 10, when the composite element shown in FIG. 4 is fixed, there is a space around it. This space extends in the direction (X direction in the above example, X direction and Y direction in the example described later) in which the composite element before being fixed was movable during adjustment. In the configuration shown in FIG. 10, there is a moving space for introducing the composite element on the optical path, but there is no movable space for adjusting the position of the composite element.

  FIG. 7 shows the optical head 56 after assembly. According to the adjustment method described above, the chromatic aberration correcting element 4 is moved together with the diffractive element 3, so that the optical axis of the objective lens 7 (the optical axis of the principal ray 9) coincides with the optical axis of the chromatic aberration correcting element 4. Thereby, the eccentric component in the direction perpendicular to the information track in the plane of the optical disc 8 is removed, and the occurrence of lateral chromatic aberration can be suppressed.

  According to the adjustment method described above, the position of the optical axis of the chromatic aberration correction element 4 and the principal ray 9 (that is, the optical axis of the objective lens 7) is adjusted so that tracking control becomes unstable even if a sudden wavelength change occurs. Thus, an optical head that does not generate the light spot movement can be realized.

  In the present embodiment, the holder 53 is an example for holding the diffraction element 3 and the chromatic aberration correction element 4 in a state where the optical axes coincide with each other. Other configurations may be employed as long as the diffraction element 3 and the chromatic aberration correction element 4 can be simultaneously moved in a state where the optical axes coincide with each other. For example, the diffraction element 3 and the chromatic aberration correction element 4 may be fixed by an arm, or the diffraction element 3 and the chromatic aberration correction element 4 may be bonded to each other.

  In the above description, the coincidence optical axis of the composite element and the light of the objective lens 7 are formed by forming one end surface of the base 55 that is a structure of the optical head as a plane orthogonal to the optical axis of the objective lens 7. It was assumed that the axis was kept parallel. However, this structure is an example. As long as a plane orthogonal to the optical axis of the objective lens 7 can be defined, an example in which the base 55 is not used may be adopted. Further, as long as the composite element is moved along such a plane, it may be adjusted by a human instead of using the control circuit 51 and the actuator 52.

  In the above description, the diffraction region of the diffraction element 3 is divided into two by one dividing line. However, the number of dividing lines may be plural.

  For example, FIG. 8 shows an example of the configuration of a diffraction element 30 having two dividing lines 20 and 21. The diffraction element 30 is used in place of the diffraction element 3 described above.

  The diffraction element 30 is divided into four regions 16, 17, 18 and 19 by two dividing lines 20 and 21. In each region, diffraction gratings having different periods or orientations are formed. For reference, FIG. 8 shows light 22 passing therethrough. The dividing line 20 corresponds to a direction perpendicular to the information track, and the dividing line 21 corresponds to a direction parallel to the information track.

  By employing the diffractive element 30, the position of the composite element composed of the diffractive element 30 and the chromatic aberration correcting element 4 can be adjusted in both the X direction and the Y direction shown in FIG. The optical axis of the diffractive element 30 and the optical axis of the chromatic aberration correcting element 4 are the same. The optical axis of the diffractive element 30 is an axis perpendicular to the paper surface that passes through the intersection of the dividing lines 20 and 21 of the diffractive element 3.

  The adjustment method is the same as the adjustment method shown in FIGS. That is, by collecting the light on the optical disk 8 and measuring the signal detected by dividing the reflected light by the diffraction element 3, the amount of the light that has passed through the regions 16 to 19 is detected. The position of the composite element may be adjusted so that the signal levels are equal. Since the principal ray 9 is adjusted so as to pass through the intersection of the dividing lines 20 and 21, the optical axis of the chromatic aberration correcting element 4 and the principal ray 9, that is, the optical axis of the objective lens 7 can be matched.

  By using the diffractive element 30 described above, the occurrence of lateral chromatic aberration is prevented in both the direction perpendicular to the information track and the direction parallel to the information track in the plane of the optical disc 8, and tracking is performed when a sudden wavelength change occurs. It is possible to produce an optical head that does not generate a light spot movement that makes the recording state of control and information unstable.

  In the above description, the composite element is disposed between the light source 1 and the collimator 5. However, the same effect can be obtained by arranging the composite element between the collimator 5 and the objective lens 7.

  The optical head described in the above embodiment has been described as being incorporated in the optical disc apparatus. Therefore, the configuration of an optical disc apparatus provided with such an optical head will be described with reference to FIG.

  FIG. 9 shows a schematic configuration of the optical disc apparatus 90 according to the present embodiment. The optical disk device 90 includes an optical head 70, a disk motor 72 that rotates the optical disk 8, and a portion that performs various signal processing.

  The optical head 70 is an optical head obtained by replacing the optical head 51 shown in FIG. 7 or the diffraction element 3 of the optical head 51 with the diffraction element 30 shown in FIG.

  In the configuration example shown in FIG. 9, the output of the optical head 70 is sent to the encoder / decoder 78 via the front end signal processing unit 76. The encoder / decoder 78 decodes data recorded on the optical disc 2 based on a signal obtained by the optical head 70 when reading data. The decrypted data is output to a host device (not shown). At the time of data writing, the encoder / decoder 78 encodes user data, generates a signal to be written on the optical disc 2, and sends it to the optical head 70.

  The front end signal processing unit 76 generates a reproduction signal based on the output of the optical head 70, while generating a focus error signal FE and a tracking error signal TE. The focus error signal FE and the tracking error signal TE are sent to the servo control unit 80. The servo controller 80 controls the disk motor 72 via the driver amplifier 74, and controls the position of the objective lens via an actuator (not shown) in the optical head 70.

  Specifically, the servo control unit 80 controls the position of the objective lens in a direction perpendicular to the information recording layer of the optical disc 8 based on the focus error signal FE. As a result, the focus of light continues and is positioned on the information recording layer to be reproduced or recorded. The servo controller 80 controls the position of the objective lens in the radial direction of the optical disc 8 based on the tracking error signal TE. As a result, the focus of light continues to follow the track of the information recording layer to be reproduced or recorded. Components such as the encoder / decoder 78 and the servo controller 80 are controlled by the CPU 79.

  The optical head of the present invention and the optical disk apparatus using the same are useful for an optical disk apparatus for BD (Blu-ray Disc) or HD-DVD, etc., in which the objective lens has a large numerical aperture and axial chromatic aberration correction is required.

  The present invention relates to an optical head manufacturing method for optically recording and / or reproducing information on an information recording medium such as an optical disk, and the optical head. More specifically, the present invention relates to a method for adjusting the arrangement of optical elements in an optical head, and an optical head in which the arrangement of optical elements is adjusted.

  As the amount of data to be recorded increases, there is a demand for optical disks with higher recording density and larger capacity.

  In order to increase the recording density of the optical disc, it is necessary to shorten the wavelength of light used for recording and reproduction and to reduce the size of the light spot. Therefore, in recent years, a light source having a wavelength of about 405 nm shorter than the wavelengths used for CDs and DVDs (about 780 nm and about 650 nm) and a relatively large objective lens having a numerical aperture of 0.65 to 0.85 are used. It is getting to be.

  For wavelengths as short as about 405 nm, the dispersion of the optical material such as glass forming the objective lens becomes large, so that the refractive index of the objective lens becomes large. In addition, as the numerical aperture increases, the depth of focus decreases. As a result, when the wavelength of the light source fluctuates, the influence of axial chromatic aberration appears greatly, which causes the performance of the optical head to deteriorate. Laser light generally has a single wavelength and no axial chromatic aberration should occur, but in practice the wavelength fluctuates with a width of several nanometers due to temperature changes, output changes, and the like. As a result, axial chromatic aberration appears. Although axial chromatic aberration occurred even at wavelengths of CD and DVD, since the dispersion of the optical material forming the objective lens is small in these wavelength bands, the amount of axial chromatic aberration was negligibly small. However, as the wavelength becomes shorter, the depth of focus becomes shallower and the dispersion becomes larger, increasing the amount of axial chromatic aberration. Therefore, in an optical head having a short wavelength light source and an objective lens having a relatively large numerical aperture, it is necessary to correct axial chromatic aberration.

  For example, Patent Document 1 discloses a conventional optical head in which axial chromatic aberration of an objective lens is corrected. FIG. 11 shows a configuration of a conventional optical head. The conventional optical head includes a laser light source 101, a beam splitter 102, a diffraction integrated collimator 103, an objective lens 104, a detection optical system 106, and a light detection unit 107. The diffractive integrated collimator 103 is a lens composed of, for example, a refractive surface and a diffractive lens surface, and the diffractive lens surface has a positive power. Here, positive power means the same refractive power as the power of the convex lens. FIG. 11 shows the optical axis 108 of the diffraction integrated collimator 103.

  The light emitted from the laser light source 101 is reflected by the beam splitter 103, converted into substantially parallel light by the diffraction integrated collimator 103, and condensed on the information recording surface of the optical disk 105 by the objective lens 104. The light reflected by the optical disk 105 passes through the objective lens 104 again, is converted into convergent light by the diffraction integrated collimator 103, passes through the beam splitter 102, and is guided to the light detection unit 107 by the detection optical system 106.

  The principle of correcting axial chromatic aberration by the above-described optical system is as follows.

  As the wavelength becomes shorter, the power (refractive power) of the objective lens increases, and the position of the focal point approaches the objective lens. As a result, the influence of axial chromatic aberration of the objective lens appears greatly.

  On the other hand, when the wavelength is shortened, the diffraction angle decreases, so the power of the diffractive lens surface decreases. Since the diffractive lens surface has a positive power, if the power is reduced, the power of the entire diffractive integrated collimator 103 is also reduced, and the light that has passed through is incident on the objective lens 104 as divergent light. Since the divergent light moves the focal position of the objective lens in a direction away from the objective lens, it has the effect of canceling the axial chromatic aberration when the wavelength of the light source fluctuates. Therefore, the axial chromatic aberration of the objective lens 104 can be corrected by appropriately distributing the power of the refracting surface and the diffractive lens surface of the diffractive integrated collimator 103.

This principle is not limited to the above configuration. For example, even if one surface of the objective lens is a diffractive lens surface, it is possible to correct axial chromatic aberration by the same principle. However, the above-described conventional technique suppresses the manufacturing cost of the optical head by forming a diffractive lens surface on a collimator having a shape that can be easily processed.
JP 2001-108894 A (page 4-11, FIG. 1)

  However, the conventional techniques have the following problems.

  In general, when a lens that generates chromatic aberration and a lens that corrects chromatic aberration are relatively decentered (that is, if the optical axes of the two do not match), the amount of decentering is determined in a direction perpendicular to the optical axes. Chromatic aberration (hereinafter referred to as “lateral chromatic aberration”) occurs. This lateral chromatic aberration appears in the optical head as a phenomenon in which the position of the light spot moves in the plane of the optical disk.

  The wavelength of the laser light varies depending on the output light amount. Therefore, the wavelength is different between information reproduction with a relatively small amount of output light and information recording with a large amount of output light. It should be noted that the wavelength variation occurs instantaneously when switching between the recording operation and the reproducing operation. Due to the lateral chromatic aberration caused by this wavelength variation, the light spot position moves instantaneously. If this instantaneous movement occurs in a direction perpendicular to the information track of the optical disk (that is, the disk radial direction), the tracking servo cannot follow and the tracking control becomes unstable.

  The above-described problem becomes more apparent when an optical disk corresponding to a laser beam having a center wavelength of 405 nm is multilayered and accessed by higher rotation. In either case, the output light amount of the laser beam must be increased during the recording operation, so the difference from the output light amount during the reproduction operation increases, and the amount of movement of the light spot position due to lateral chromatic aberration increases. .

  The optical head is preferably assembled so that the optical axes of the optical systems are matched. However, since light propagates in parallel between the objective lens and the collimator, it is difficult to align their optical axes, and relative eccentricity remains. Furthermore, since the objective lens moves in a direction perpendicular to the information track (radial direction of the optical disk) for accessing the information track, the relative eccentricity increases. In the conventional optical head, since the chromatic aberration of the objective lens is corrected by the collimator, lateral chromatic aberration due to the relative decentration thereof occurs, and tracking control becomes unstable.

  An object of the present invention is to provide a structure for adjusting the position of an optical element that corrects chromatic aberration, and an optical head that matches the optical axis of the optical element with the optical axis of the objective lens by the structure, and An object of the present invention is to provide an optical disc apparatus provided with the optical head.

  An optical head according to the present invention is disposed on an optical path from a light source that emits light, a condensing optical system that includes an objective lens that condenses the light onto an optical disc, and from the light source to the objective lens. A correction element that corrects chromatic aberration of the objective lens caused by wavelength variation; and a diffraction grating that deflects the light reflected by the optical disc in a plurality of directions. In the optical head, the diffraction grating and the correction element constitute a composite element integrated so that their optical axes coincide with each other, and the optical axis of the composite element and the condensing optical system The optical axis is adjusted to match.

  The optical axis of the composite element may be fixed at a position that coincides with the optical axis of the condensing optical system among positions on a plane orthogonal to the optical axis of the condensing optical system.

  The optical head may further include a base having at least one end face defining a plane perpendicular to the optical axis of the condensing optical system, and the composite element may be fixed on the at least one end face. .

  Around the fixed composite element, there may be a space in which the composite element before being fixed can move.

  The optical head further includes a light receiving unit that detects light reflected by the optical disc, and the diffraction grating includes a plurality of diffraction regions for detecting a push-pull signal in the radial direction of the optical disc based on the reflected light. You may have.

  The optical disc has one or more tracks, the diffraction grating has two diffraction regions divided by a dividing line corresponding to a direction along the tracks, and the composite element is on the plane. Of the range movable in the direction orthogonal to the dividing line, the optical axis of the composite element may be adjusted and fixed at a position that coincides with the optical axis of the condensing optical system.

  The optical disc has one or more tracks, and the diffraction grating is divided by a first dividing line corresponding to a direction along the track and a second dividing line orthogonal to the first dividing line. The composite element has four diffractive regions, and the composite element is movable in the first plane perpendicular to the first dividing line and the direction perpendicular to the second dividing line on the plane. The optical axis of the composite element may be adjusted and fixed at a position that coincides with the optical axis of the condensing optical system.

  The composite element may include the correction element, the diffraction grating, and a member that physically fixes the correction element and the diffraction grating.

  The composite element may be configured by adhering the correction element and the diffraction grating.

  An optical disc apparatus according to the present invention includes an optical head having any one of the above-described features, a motor that rotates the optical disc, and a controller that controls the optical head and the motor. The control unit controls the optical head based on a signal output from the optical head so as to continuously collect light on the recording layer of the optical disc, and performs information recording and / or reproduction. .

  The method of manufacturing an optical head according to the present invention includes a light source that emits light, a condensing optical system that includes an objective lens that condenses the light on an optical disc, and an optical path from the light source to the objective lens. To produce an optical head comprising a correction element that corrects chromatic aberration of the objective lens caused by fluctuations in the wavelength of the light, and a diffraction grating that deflects the light reflected by the optical disc in a plurality of directions. To be implemented. The optical head manufacturing method includes the steps of preparing the condensing optical system, preparing a composite element integrated so that the optical axis of the diffraction grating and the optical axis of the correction element coincide with each other, Adjusting the optical axis of the composite element to coincide with the optical axis of the condensing optical system on a plane orthogonal to the optical axis of the condensing optical system.

  The adjusting step may be performed such that an optical axis of the composite element coincides with an optical axis of the condensing optical system while bringing the composite element into contact with a base having the flat surface.

  According to the present invention, since the optical axes of the lens that generates chromatic aberration in the optical head and the lens that corrects chromatic aberration coincide with each other, lateral chromatic aberration caused by decentration of the optical system can be reduced. Thereby, an optical head capable of stable tracking control even when a sudden wavelength change occurs can be manufactured.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows an optical head 50 during assembly according to this embodiment. FIG. 1 shows a process in which components of the optical head 50 are incorporated and the arrangement thereof is adjusted.

  The optical head 50 includes a light source 1, a beam splitter 2, a diffraction element 3 that splits light, a chromatic aberration correction element 4, a collimator 5, an aperture stop 6, an objective lens 7, and a photodetector 11. ing. In FIG. 1, an optical disk 8 is also shown for reference.

  Note that an optical system of a general optical head further requires a focus detection means, a tracking detection means, an information signal detection means, etc., but these are not shown in FIG. These configurations will be described later with reference to FIG.

  In FIG. 1, a solid line 9 indicates the principal ray (optical axis) of the condensing optical system from the light source 1 to the objective lens 7. A one-dot chain line 10 indicates the optical axis of the collimator 5.

  Although the optical axis of the light source 1 is assembled so as to coincide with the optical axis of the collimator 5, this optical axis does not coincide with the optical axis of the condensing optical system. FIG. 1 shows a state where the optical axis of the condensing optical system 7 and the optical axis 10 of the collimator are decentered. The eccentricity occurs because light propagates in parallel between the objective lens and the collimator and it is difficult to align their optical axes. The chief ray 9 passes through the center of the aperture stop 6. In general, since the aperture stop 6 is arranged close to the objective lens 7 without being decentered, the principal ray 9 substantially coincides with the optical axis of the objective lens 7. In the following description, the principal ray 9 is described as being the optical axis of the objective lens 7.

  The diffraction element 3 and the chromatic aberration correction element 4 are integrally held by a holder 53. When fixed by the holder 53, the respective optical axes of the diffraction element 3 and the chromatic aberration correction element 4 are adjusted so as to coincide with each other, and the state is maintained after the fixing. The optical axis of the diffractive element 3 is an axis perpendicular to the paper surface passing through a point (for example, the midpoint of the dividing line 15) on the dividing line 15 (FIG. 3 described later) of the diffractive element 3.

  Hereinafter, the integrated diffraction element 3 and chromatic aberration correction element 4 are also referred to as a “composite element”. In addition, since the two optical axes of the diffraction element 3 and the chromatic aberration correction element 4 overlap each other and are recognized as one optical axis, the one optical axis is hereinafter referred to as “optical axis of the composite element”.

  Here, the configurations of the diffraction element 3 and the chromatic aberration correction element 4 will be described with reference to FIGS. 2 and 3.

  FIG. 2 shows an example of the configuration of the chromatic aberration correction element 4. The chromatic aberration correcting element 4 has a concave refracting surface and a diffractive lens surface. For example, the concave surface is disposed on the light source 1 side. The diffractive lens surface facing the concave surface has positive power. Since the positive power cancels out the negative negative power, the overall power of the chromatic aberration correction element 4 is small.

  When the wavelength is shortened, the positive power of the diffractive lens surface is reduced and the negative power of the concave surface is superior, so that the light passing therethrough is more diverged. Therefore, when the wavelength is shortened, the light from the light source 1 is intensified in the divergence state by the chromatic aberration correction element 4. As a result, the light output from the chromatic aberration correcting element 4 and passing through the collimator 5 becomes divergent light. Thereby, the axial chromatic aberration of the objective lens 7 is corrected.

  FIG. 3 shows an example of the configuration of the diffraction element 3. The diffractive element 3 has two diffractive regions 12 and 13 in which diffraction gratings having different periods or directions are formed. The diffraction regions 12 and 13 are arranged with the dividing line 15 as a boundary. The dividing line 15 corresponds to a direction parallel to the information track (a direction along the information track). For reference, the passing light 14 is shown in FIG. When adjusting the arrangement of the composite elements, the diffractive element 3 is moved together with the chromatic aberration correcting element 4 in the X direction indicated by the double arrow in FIG.

  Next, the path of light traveling through the optical head 50 will be described with reference to FIG. 1 again. The laser light emitted from the light source 1 passes through the beam splitter 2, the diffraction element 3, and the chromatic aberration correction element 4, is converted into parallel light by the collimator 5, passes through the aperture stop 6, and is information on the optical disk 8 by the objective lens 7. Focused on the recording surface.

  The light reflected by the optical disk 8 enters the diffraction element 3 again through the objective lens 7, the aperture stop 6, the collimator 5, and the chromatic aberration correction element 4. The diffraction element 3 splits and diffracts the light. The diffracted light is reflected by the beam splitter 2, guided to the photodetector 11, and the amount of each divided light is detected.

  If the optical axis of the objective lens 7 that generates chromatic aberration and the optical axis of the composite element having the function of correcting the chromatic aberration described above are deviated (that is, decentration occurs), lateral chromatic aberration corresponding to the decentration amount is generated. It occurs in a direction perpendicular to their optical axes.

  Therefore, in the present embodiment, a configuration has been introduced in which the holder 53 is moved so that the optical axis of the composite element can coincide with the optical axis of the objective lens 7. Specifically, a base having the plane is provided so that the composite element can be moved on a plane orthogonal to the optical axis of the objective lens 7.

  FIG. 4 shows a base 55 and an end surface (pressing surface) 54 of the base 55 that defines a plane orthogonal to the optical axis of the objective lens 7. A composite element composed of the diffraction element 3 and the chromatic aberration correction element 4 is disposed in contact with the end face 54. By moving the holder 53 in the direction along the plane, the position of the composite element is adjusted. At the time of movement, the composite element is pressed against the end face 54, and the optical axis of the composite element and the optical axis of the objective lens 7 are always parallel. The chromatic aberration correcting element 4 is in contact with the end face 54, but this is an example. The end face 54 may be provided on the diffraction element 3 side so that the diffraction element 3 is in contact with the end face 54.

  The movement direction of the holder 53 is the X direction shown in FIG. 4 when the diffraction element 3 shown in FIG. 3 is used. The X direction in FIG. 3 and the X direction in FIG. 4 correspond to the same direction. On the other hand, when the diffraction element 30 shown in FIG. 8 to be described later is used, the moving direction of the holder 53 is the X direction and the Y direction shown in FIG. The X direction and the Y direction in FIG. 8 correspond to the same directions as the X direction and the Y direction in FIG. 4, respectively.

  An example of a configuration in which the diffraction element 3 and the chromatic aberration correction element 4 are not movable is shown in FIG. FIG. 10 shows an example of a base having a protrusion 60. The protrusion 60 is not for adjusting the positions of the diffraction element 3 and the chromatic aberration correction element 4 but for determining the positions of the diffraction element 3 and the chromatic aberration correction element 4. In the optical head having such a protrusion 60, the position adjusting method according to the present invention cannot be adopted.

  The holder 53 is moved by the control circuit 51 and the actuator 52 shown in FIG. Specifically, it is as follows.

  The control circuit 51 receives at least two signals output from the photodetector 11. The level of each signal corresponds to the amount of light incident on a different light receiving area of the photodetector 11. The control circuit 51 generates a control signal based on these signals and outputs it to the actuator 52. The actuator 52 is physically connected to the holder 53 and moves the holder 53 based on a control signal. The direction indicated by the arrow in FIG. 1 corresponds to the X direction in FIG.

  Next, a method for adjusting the position of the composite element will be described.

  First, the light source 1 is caused to emit light and the laser light is condensed on the optical disk 8. Then, the light reflected by the optical disk 8 and divided by the diffraction element 3 is detected by the photodetector 11. In order to focus the laser beam on the optical disk 8, so-called focus control is preferably performed. Therefore, the focus control may be performed by incorporating the optical head 50 being assembled into a device having a function equivalent to that of FIG. 9 described later.

  Before the adjustment of the position of the composite element, the optical axis of the composite element and the optical axis of the objective lens 7 do not coincide with each other, so that the laser light is incident on a position off the optical axis of the diffraction element 3.

  For example, FIG. 5A shows the position of the light 14 that passes through the diffraction element 3. The light transmitted through the diffraction regions 12 and 13 of the diffraction element 3 is separately detected by the photodetector 11. Now, it is assumed that the light diffracted by the diffraction region 12 is detected by the photodetector 11 and a signal S12 is output. Further, it is assumed that the light diffracted by the diffraction region 13 is detected by the photodetector 11 and a signal S13 is output.

  FIG. 5B shows the waveforms of the signals S12 and S13. The level of the signal S12 is a, and the level of the signal S13 is b (<a). As shown in FIG. 5A, since the amount of light passing through the diffraction region 12 is larger than the amount of light passing through the diffraction region 12, the level of the signal S12 is higher than that of the signal S13.

  The control circuit 51 adjusts the position of the composite element (that is, the diffraction element 3) by controlling the actuator 52 so that the signals S12 and S13 are at the same level. This means that the position of the composite element is adjusted so that the light is equally divided into two by the dividing line 15.

  In the present embodiment, the optical disc 8 is a disc having a reflective layer without pits / marks. This is because the levels of the signals S12 and S13 are very easy to adjust. Since the waveform component of the pit / mark of the optical disk 8 is not superimposed on the reflected light, the waveform in FIG. 5B is a straight line. When a disc having pits / marks is used, a waveform component due to the pits / marks is superimposed on both signals S12 and S13.

  FIG. 6A shows the light 14 that is equally divided into two by the dividing line 15. FIG. 6B shows the level change of the signals S12 and S13 when the position of the composite element is adjusted. The composite element is moved from the position shown in FIG. 5A to the position shown in FIG. At this time, the light 14 itself does not fluctuate.

  When the levels of the signals S12 and S13 are both c, the driving of the actuator 52 is stopped and the movement of the composite element is completed. At this position, the composite element is fixed to the base 55 with an adhesive or the like. The control circuit 51 and the actuator 52 are removed from the optical head 50 when the adjustment is completed.

  As is clear from the comparison between FIG. 4 and FIG. 10, when the composite element shown in FIG. 4 is fixed, there is a space around it. This space extends in the direction (X direction in the above example, X direction and Y direction in the example described later) in which the composite element before being fixed was movable during adjustment. In the configuration shown in FIG. 10, there is a moving space for introducing the composite element on the optical path, but there is no movable space for adjusting the position of the composite element.

  FIG. 7 shows the optical head 56 after assembly. According to the adjustment method described above, the chromatic aberration correcting element 4 is moved together with the diffractive element 3, so that the optical axis of the objective lens 7 (the optical axis of the principal ray 9) coincides with the optical axis of the chromatic aberration correcting element 4. Thereby, the eccentric component in the direction perpendicular to the information track in the plane of the optical disc 8 is removed, and the occurrence of lateral chromatic aberration can be suppressed.

  According to the adjustment method described above, the position of the optical axis of the chromatic aberration correction element 4 and the principal ray 9 (that is, the optical axis of the objective lens 7) is adjusted so that tracking control becomes unstable even if a sudden wavelength change occurs. Thus, an optical head that does not generate the light spot movement can be realized.

  In the present embodiment, the holder 53 is an example for holding the diffraction element 3 and the chromatic aberration correction element 4 in a state where the optical axes coincide with each other. Other configurations may be employed as long as the diffraction element 3 and the chromatic aberration correction element 4 can be simultaneously moved in a state where the optical axes coincide with each other. For example, the diffraction element 3 and the chromatic aberration correction element 4 may be fixed by an arm, or the diffraction element 3 and the chromatic aberration correction element 4 may be bonded to each other.

  In the above description, the coincidence optical axis of the composite element and the light of the objective lens 7 are formed by forming one end surface of the base 55 that is a structure of the optical head as a plane orthogonal to the optical axis of the objective lens 7. It was assumed that the axis was kept parallel. However, this structure is an example. As long as a plane orthogonal to the optical axis of the objective lens 7 can be defined, an example in which the base 55 is not used may be adopted. Further, as long as the composite element is moved along such a plane, it may be adjusted by a human instead of using the control circuit 51 and the actuator 52.

  In the above description, the diffraction region of the diffraction element 3 is divided into two by one dividing line. However, the number of dividing lines may be plural.

  For example, FIG. 8 shows an example of the configuration of a diffraction element 30 having two dividing lines 20 and 21. The diffraction element 30 is used in place of the diffraction element 3 described above.

  The diffraction element 30 is divided into four regions 16, 17, 18 and 19 by two dividing lines 20 and 21. In each region, diffraction gratings having different periods or orientations are formed. For reference, FIG. 8 shows light 22 passing therethrough. The dividing line 20 corresponds to a direction perpendicular to the information track, and the dividing line 21 corresponds to a direction parallel to the information track.

  By employing the diffractive element 30, the position of the composite element composed of the diffractive element 30 and the chromatic aberration correcting element 4 can be adjusted in both the X direction and the Y direction shown in FIG. The optical axis of the diffractive element 30 and the optical axis of the chromatic aberration correcting element 4 are the same. The optical axis of the diffractive element 30 is an axis perpendicular to the paper surface that passes through the intersection of the dividing lines 20 and 21 of the diffractive element 3.

  The adjustment method is the same as the adjustment method shown in FIGS. That is, by collecting the light on the optical disk 8 and measuring the signal detected by dividing the reflected light by the diffraction element 3, the amount of the light that has passed through the regions 16 to 19 is detected. The position of the composite element may be adjusted so that the signal levels are equal. Since the principal ray 9 is adjusted so as to pass through the intersection of the dividing lines 20 and 21, the optical axis of the chromatic aberration correcting element 4 and the principal ray 9, that is, the optical axis of the objective lens 7 can be matched.

  By using the diffractive element 30 described above, the occurrence of lateral chromatic aberration is prevented in both the direction perpendicular to the information track and the direction parallel to the information track in the plane of the optical disc 8, and tracking is performed when a sudden wavelength change occurs. It is possible to produce an optical head that does not generate a light spot movement that makes the recording state of control and information unstable.

  In the above description, the composite element is disposed between the light source 1 and the collimator 5. However, the same effect can be obtained by arranging the composite element between the collimator 5 and the objective lens 7.

  The optical head described in the above embodiment has been described as being incorporated in the optical disc apparatus. Therefore, the configuration of an optical disc apparatus provided with such an optical head will be described with reference to FIG.

  FIG. 9 shows a schematic configuration of the optical disc apparatus 90 according to the present embodiment. The optical disk device 90 includes an optical head 70, a disk motor 72 that rotates the optical disk 8, and a portion that performs various signal processing.

  The optical head 70 is an optical head obtained by replacing the optical head 51 shown in FIG. 7 or the diffraction element 3 of the optical head 51 with the diffraction element 30 shown in FIG.

  In the configuration example shown in FIG. 9, the output of the optical head 70 is sent to the encoder / decoder 78 via the front end signal processing unit 76. The encoder / decoder 78 decodes data recorded on the optical disc 2 based on a signal obtained by the optical head 70 when reading data. The decrypted data is output to a host device (not shown). At the time of data writing, the encoder / decoder 78 encodes user data, generates a signal to be written on the optical disc 2, and sends it to the optical head 70.

  The front end signal processing unit 76 generates a reproduction signal based on the output of the optical head 70, while generating a focus error signal FE and a tracking error signal TE. The focus error signal FE and the tracking error signal TE are sent to the servo control unit 80. The servo controller 80 controls the disk motor 72 via the driver amplifier 74, and controls the position of the objective lens via an actuator (not shown) in the optical head 70.

  Specifically, the servo control unit 80 controls the position of the objective lens in a direction perpendicular to the information recording layer of the optical disc 8 based on the focus error signal FE. As a result, the focus of light continues and is positioned on the information recording layer to be reproduced or recorded. The servo controller 80 controls the position of the objective lens in the radial direction of the optical disc 8 based on the tracking error signal TE. As a result, the focus of light continues to follow the track of the information recording layer to be reproduced or recorded. Components such as the encoder / decoder 78 and the servo controller 80 are controlled by the CPU 79.

  The optical head of the present invention and the optical disk apparatus using the same are useful for an optical disk apparatus for BD (Blu-ray Disc) or HD-DVD, etc., in which the objective lens has a large numerical aperture and axial chromatic aberration correction is required.

It is a figure which shows the optical head 50 in the assembly by embodiment of this invention. 3 is a diagram illustrating an example of a configuration of a chromatic aberration correction element 4. FIG. 3 is a diagram illustrating an example of a configuration of a diffraction element 3. FIG. It is a figure which shows the end surface (pressing surface) 54 of the base 55 which prescribes | regulates the base 55 and the plane orthogonal to the optical axis of the objective lens 7. FIG. (A) is a figure which does not show the position of the light 14 which passes the diffraction element 3, (b) is a figure which shows each waveform of signal S12 and S13. (A) is a figure which shows the light 14 equally divided into 2 by the dividing line 15, (b) is a figure which shows the level change of signal S12 and S13 when the position of a composite element is adjusted. It is a figure which shows the optical head 56 after an assembly. 3 is a diagram illustrating an example of the configuration of a diffraction element 30 having two parting lines 20 and 21. FIG. 1 is a diagram showing a schematic configuration of an optical disc device 90 according to an embodiment of the present invention. It is a figure which shows the example of the base provided with the processus | protrusion 60. FIG. It is a figure which shows the structure of the conventional optical head.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Beam splitter 3,30 Diffraction element 4 Chromatic aberration correction element 5 Collimator 6 Aperture stop 7 Objective lens 8 Optical disk 9 Main beam of condensing optical system 10 Optical axis of collimator 11 Optical detection part 50 Optical head 51 Control circuit 52 Actuator 54 End surface (pressing surface)
55 base

Claims (12)

A light source that emits light;
A condensing optical system comprising an objective lens for condensing the light on an optical disc;
A correction element that is arranged on an optical path from the light source to the objective lens and corrects chromatic aberration of the objective lens caused by a variation in the wavelength of the light;
An optical head comprising: a diffraction grating that deflects the light reflected by the optical disc in a plurality of directions;
The diffraction grating and the correction element constitute a composite element that is integrated so that their optical axes coincide with each other, and the optical axis of the composite element coincides with the optical axis of the condensing optical system. An optical head that has been adjusted to.   2. The optical axis of the composite element is fixed at a position that coincides with the optical axis of the condensing optical system among positions on a plane orthogonal to the optical axis of the condensing optical system. Optical head. At least one end surface further comprises a base that defines a plane perpendicular to the optical axis of the condensing optical system,
The optical head according to claim 2, wherein the composite element is fixed on the at least one end face.   The optical head according to claim 3, wherein a space in which the composite element before being fixed is movable is present around the fixed composite element. A light receiving unit for detecting light reflected by the optical disc;
The optical head according to claim 2, wherein the diffraction grating has a plurality of diffraction regions for detecting a push-pull signal in the radial direction of the optical disk based on the reflected light. The optical disc has one or more tracks;
The diffraction grating has two diffraction regions divided by a dividing line corresponding to a direction along the track,
The composite element is adjusted and fixed at a position where the optical axis of the composite element coincides with the optical axis of the condensing optical system in the movable range in the direction perpendicular to the dividing line on the plane. The optical head according to claim 5. The optical disc has one or more tracks;
The diffraction grating has four diffraction regions divided by a first dividing line corresponding to a direction along the track and a second dividing line orthogonal to the first dividing line,
The composite element has an optical axis of the composite element that is movable with respect to a first direction orthogonal to the first dividing line and a direction orthogonal to the second dividing line on the plane. The optical head according to claim 5, wherein the optical head is adjusted and fixed at a position coinciding with the optical axis of the system.   The optical head according to claim 1, wherein the composite element includes the correction element, the diffraction grating, and a member that physically fixes the correction element and the diffraction grating.   The optical head according to claim 1, wherein the composite element is configured by bonding the correction element and the diffraction grating. An optical head according to claim 1;
A motor for rotating the optical disc;
A control unit that controls the optical head and the motor, and the control unit is configured to optically focus light on the recording layer of the optical disc based on a signal output from the optical head. An optical disc apparatus that controls a head and performs recording and / or reproduction of information. A light source that emits light;
A condensing optical system comprising an objective lens for condensing the light on an optical disc;
A correction element that is arranged on an optical path from the light source to the objective lens and corrects chromatic aberration of the objective lens caused by a variation in the wavelength of the light;
A method of manufacturing an optical head comprising: a diffraction grating that deflects the light reflected by the optical disc in a plurality of directions;
Providing the condensing optical system;
Providing a composite element integrated so that the optical axis of the diffraction grating and the optical axis of the correction element coincide;
Adjusting the optical axis of the composite element to coincide with the optical axis of the condensing optical system on a plane orthogonal to the optical axis of the condensing optical system.   The optical device according to claim 11, wherein the adjusting step adjusts the optical axis of the composite element to coincide with the optical axis of the condensing optical system while bringing the composite element into contact with a base having the flat surface. Manufacturing method of the head.

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