JPWO2006126466A1 - Optical pickup device and objective lens - Google Patents

Abstract

In order to provide an optical pickup device and an objective lens excellent in tracking characteristics, an optical pickup device having a driving means D for tilting according to the shift amount of the objective lens OBJ from a predetermined reference position is provided. Good tracking characteristics can be obtained by shifting and tilting the objective lens OBJ.

Description

  The present invention relates to an optical pickup device, and more particularly to an optical pickup device and an objective lens capable of recording and / or reproducing appropriate information by correcting astigmatism when the objective lens is shifted.

  In a general optical pickup device, a light beam from a semiconductor laser is focused on an information recording surface of an optical disk such as a CD or a DVD by an objective lens, thereby recording and / or reproducing information on the information recording surface. Is supposed to do. However, in a rotating optical disk, it is necessary to accurately form a condensing spot along the track. However, the converging spot is separated from the track because the optical disk itself deviates and the rotating shaft shakes. In order to avoid this, the objective lens is moved in the radial direction of the optical disc while detecting the track. This is called tracking.

  Here, in an optical pickup device using a finite conjugate objective lens as shown in Patent Document 1, if the objective lens is moved in a direction perpendicular to the optical axis with respect to the light source by tracking, the off-axis incident on the objective lens will be described. The light beam is condensed on the information recording surface of the optical disk. Therefore, if tracking is premised, an objective lens in which aberrations are favorably corrected both on and off the axis is required. However, normally, an objective lens for an optical disk is often a full aplanate single aspherical lens due to limitations such as cost and weight. In this case, off-axis aberration is expressed as a quadratic function with respect to the image height. It will be dominated by increasing astigmatism. Further, at that time, astigmatism is generated in which the convergence point of the light ray in the meridian plane is located in front of the convergence point of the light ray in the spherical surface (on the objective lens side). Therefore, it can be said that it is difficult to obtain an objective lens that is well corrected both on and off the axis.

Therefore, in the objective lens shown in Patent Document 1, astigmatism is given in advance so that the maximum value of astigmatism is suppressed even when the objective lens is shifted by tracking, so that the tracking characteristic is good. An objective lens is realized.
JP-A-8-136801

  However, in the case of the objective lens of Patent Document 1, astigmatism inherently remains even when the light beam emitted from the semiconductor laser is incident along the optical axis of the objective lens. There is a problem that it is difficult to obtain a spot shape. Such a problem becomes more conspicuous when a condensed spot is formed by a high numerical aperture objective lens using a short wavelength light beam.

  The present invention has been made in view of the problems of the prior art, and an object thereof is to provide an optical pickup device and an objective lens excellent in tracking characteristics.

  The optical pickup device according to claim 1 is configured to condense the light beam emitted from the first light source on the information recording surface of the first optical information recording medium. And an optical detector for receiving the light beam reflected by the information recording surface, and recording and / or reproducing information on the information recording surface of the first optical information recording medium In the pickup apparatus, the pickup device includes a driving unit that tilts the objective lens in accordance with a shift amount of the objective lens from a predetermined reference position.

  The principle of the present invention will be described with reference to the drawings. FIG. 1 is a graph showing an example of an objective lens according to the present invention and a comparative example, with astigmatism on the vertical axis and shift amount of the objective lens on the horizontal axis. First, in the case of the objective lens of the prior art (Comparative Example 1) indicated by the dotted line, since the astigmatism is inherently designed, for example, the astigmatism is 0 when the shift amount is near 0.21 mm. Although as small as .007λrms, astigmatism remains on the axis (shift amount is zero) by 0.024λrms.

  On the other hand, in the objective lens (Comparative Example 2) designed with zero astigmatism on the axis, as shown by the two-dot chain line in FIG. Aberration increases, for example, the shift amount exceeds 0.07λ rms at 0.4 mm, and the tracking characteristics are poor.

  Therefore, as for an example of the objective lens according to the present invention, the objective lens of Comparative Example 2 is tilted according to the shift amount. More specifically, as the shift amount increases to 0.1 mm, 0.2 mm, 0.3 mm, and 0.4 mm, the tilt angles are 0.01 °, 0.04 °, 0.12 °,. It is given as 23 °. According to the present invention, by tilting the objective lens of Comparative Example 2 indicated by the two-dot chain line according to the shift amount, the characteristic as indicated by the solid line in FIG. 1 is obtained, and the characteristic of Comparative Example 1 indicated by the dotted line is obtained. In comparison, the astigmatism becomes small when the shift amount is between zero and 0.16 mm, and the astigmatism becomes the same level when the shift amount is 0.4 mm. On the other hand, astigmatism is reduced in the entire region as compared with the characteristics of Comparative Example 2 indicated by the two-dot chain line.

  That is, according to the present invention, it is possible to obtain a good tracking characteristic by tilting the objective lens according to the shift amount of the objective lens from the predetermined reference position by the driving means. Here, the “predetermined reference position” refers to, for example, a position where the optical axis of the optical pickup device and the optical axis of the objective lens coincide with each other, and “shift” refers to the optical axis of the objective lens of the optical pickup device. “Tilting” refers to a movement in which the optical axis of the objective lens is tilted with respect to an axis parallel to the optical axis of the optical pickup device. The tilt direction is such that when the objective lens is shifted, the optical axis of the optical pickup device and the optical axis of the objective lens are tilted in a direction intersecting the objective lens on the disk side.

  The optical pickup device according to claim 2 is the invention according to claim 1, wherein the light beam emitted from the first light source is incident on the objective lens in a finite divergence state. It is characterized by. In the case of the configuration in which the objective lens is incident in a finite divergence state, the coupling lens and the like can be omitted, the configuration is simplified, and off-axis rays are easily incident due to the shift of the objective lens. Can demonstrate.

  The optical pickup device described in claim 3 is characterized in that, in the invention described in claim 1 or 2, the objective lens does not satisfy the sine condition.

  The principle of the present invention will be described with reference to the drawings. FIG. 2 shows an example of an objective lens according to the present invention and another example. Astigmatism (AS), coma aberration (COMA) and wavefront aberration (RMS) are plotted on the vertical axis, and the shift amount of the objective lens is plotted on the horizontal axis. It is a graph which shows the amount of tilts. First, in FIG. 2A, as indicated by the solid line, astigmatism can be suppressed by tilting the objective lens according to the shift amount, as described above. However, when a normal objective lens designed to satisfy the sine condition is tilted, the coma increases as shown by the dotted line in FIG. 2A. Therefore, the total aberration of astigmatism and coma is added. There is a case where the wavefront aberration is increased (two-dot chain line). Such coma aberration itself can be corrected by using a liquid crystal element or the like, but the liquid crystal element is expensive and may not be suitable for use in a simple optical pickup device.

  Therefore, in another example of the present invention, an objective lens in which coma aberration is likely to occur is obtained by designing with the sine condition broken. More specifically, as shown by the dotted line in FIG. 2B, when the objective lens is shifted by 0.3 mm without being tilted, a coma aberration of 0.05 λrms or more is generated. If the objective lens designed in this way is tilted according to the shift amount, both astigmatism and coma can be suppressed.

  In the example shown in FIG. 2C, the tilt angle of the objective lens designed in this way is 0.11 as the shift amount increases to 0.1 mm, 0.2 mm, 0.3 mm, and 0.4 mm, respectively. By giving the angle, 0.23 °, 0.35 °, and 0.48 °, the coma aberration when the shift amount is 0.4 mm is set to 0 with respect to the objective lens that is designed to satisfy the sine condition. 0.03λrms (FIG. 2A) is significantly reduced to 0.009λrms (FIG. 2C). The astigmatism when the shift amount is 0.4 mm is also reduced from 0.048 λrms (FIG. 2A) to 0.024 λrms (FIG. 2C). Such an objective lens is particularly suitable for specifications with a high numerical aperture (for example, NA 0.65 or more) using a short wavelength light beam.

  The optical pickup device described in claim 4 is the optical pickup device according to any one of claims 1 to 3, wherein the driving means is configured to adjust the inclination of the first optical information recording medium. Accordingly, since the objective lens is tilted, information can be appropriately recorded and / or reproduced even when the first optical information recording medium is warped or tilted.

  The optical pickup device according to claim 5 is the second light source that emits a light beam having a wavelength λ2 (λ1 ≠ λ2) in the invention according to any one of claims 1 to 4. And condensing the light beam emitted from the second light source on the information recording surface of the second optical information recording medium via the objective lens, so that the information recording surface of the second optical information recording medium is Since information is recorded and / or reproduced, information can be appropriately recorded and / or reproduced on different types of optical information recording media.

  For example, when a common objective lens is used when recording and / or reproducing information on different types of optical information recording media, generally, the off-axis characteristics are improved when both optical information recording media are used. Since it is difficult to maintain, off-axis characteristics are expected to deteriorate with respect to at least one of the optical information recording media. When off-axis rays are incident on such an objective lens, coma is always generated. Therefore, when recording and / or reproducing information on one optical information recording medium, the objective lens is not tilted, and the occurrence of coma aberration is suppressed only by the original off-axis characteristics, and the other optical information is recorded. When recording and / or reproducing information on a recording medium, the objective lens can be tilted to suppress coma.

  The optical pickup device described in claim 6 is the optical pickup device according to claim 5, wherein the driving means tilts the objective lens according to an inclination of the second optical information recording medium. It is characterized by that.

  The objective lens according to claim 7 is an objective lens used in the optical pickup device according to any one of claims 1 to 6 in the direction orthogonal to the optical axis without being tilted. Since the coma aberration of 0.015 λ rms or more and 0.15 λ rms or less occurs when shifted by 0.2 mm, the above-described effects can be achieved.

  The objective lens according to claim 8 is the objective lens used in the optical pickup device according to any one of claims 1 to 6, wherein a shift amount A (mm in the direction perpendicular to the optical axis) is used. When the tilt angle at which the objective lens is tilted to minimize the wavefront aberration is B (°), the following conditional expression is satisfied. Therefore, the above-described effect can be achieved.

B / A ≧ 0.60
In the present specification, the objective lens refers to an optical element having a light condensing function, which is disposed to face the optical information recording medium in a state where the optical information recording medium is loaded in the optical pickup device. When there is an optical element that is integrated with the optical element and can be driven at least in the optical axis direction by an actuator, the set of these optical elements is defined as an objective lens in this specification.

  According to the present invention, an optical pickup device and an objective lens excellent in tracking characteristics can be provided.

It is a graph which shows an example of the objective lens concerning this invention, and a comparative example by taking the astigmatism on the vertical axis and the shift amount of the objective lens on the horizontal axis. As for an example and another example of the objective lens according to the present invention, the vertical axis represents astigmatism (AS), coma aberration (COMA) and wavefront aberration (RMS), and the horizontal axis represents the shift amount and tilt amount of the objective lens. It is a graph shown. 1 is a diagram schematically showing a configuration of an optical pickup device capable of recording / reproducing information so as to be compatible with an optical information recording medium (optical disc) CD and DVD. It is a perspective view which shows the drive means of an objective lens. It is a perspective view which shows the drive means D concerning 2nd Embodiment. In the objective lens according to Example 1, (a) longitudinal spherical aberration diagram when using DVD, (b) diagram showing sine conditions when using DVD, (c) longitudinal spherical aberration diagram when using CD, (d) CD It is a figure which shows the sine condition at the time of use. (A) Longitudinal spherical aberration diagram when using DVD, (b) Diagram showing sine conditions when using DVD, (c) Longitudinal spherical aberration diagram when using CD, (d) CD It is a figure which shows the sine condition at the time of use. In the objective lens according to Example 3, (a) longitudinal spherical aberration diagram when using DVD, (b) diagram showing sine conditions when using DVD, (c) longitudinal spherical aberration diagram when using CD, (d) CD It is a figure which shows the sine condition at the time of use. FIG. 6 is a diagram illustrating characteristics of an objective lens according to Example 3; In the objective lens according to Example 4, (a) Longitudinal spherical aberration diagram when using DVD, (b) Diagram showing sine condition when using DVD, (c) Longitudinal spherical aberration diagram when using CD, (d) CD It is a figure which shows the sine condition at the time of use. FIG. 6 is a diagram illustrating characteristics of an objective lens according to Example 4; The horizontal axis represents the shift amount A (mm) of the objective lens in the direction orthogonal to the optical axis, and the vertical axis represents the tilt angle B (°) that minimizes the wavefront aberration when the shifted objective lens is tilted. It is a graph shown.

Explanation of symbols

2L1P 2 laser 1 package 12 base 14 lens holder 18 suspension base 20 elastic metal wire 26a magnet 28 focusing coil 30a tracking coil 32a radial tilt coil 34a bracket 36a bracket 38 radial skew sensor AP aperture D drive means LD1 semiconductor laser LD2 semiconductor laser OBJ objective Lens PBS Polarizing beam splitter PD Photodetector QWP λ / 4 wave plate

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a diagram schematically showing a configuration of an optical pickup device capable of recording / reproducing information in a manner compatible with CD and DVD, which are optical information recording media (optical disks). In the present embodiment, a so-called two-laser one package 2L1P in which two semiconductor lasers are housed in one package is used. The objective lens OBJ can be tilted by driving means D (not shown in FIG. 3) described later.

  In FIG. 3, when recording and / or reproducing information on a DVD, a light beam having a wavelength of 660 nm emitted from the semiconductor laser LD1 of the two-laser one package 2L1P is reflected by the polarization beam splitter PBS as indicated by a solid line. , Λ / 4 wavelength plate QWP, aperture AP, and incident on the objective lens OBJ in a finite divergence state as shown in the figure, through the objective lens OBJ through the 0.6 mm thick protective layer, DVD Is condensed on the information recording surface.

  The reflected light beam modulated by the information pits on the information recording surface of the DVD again passes through the objective lens OBJ, and further passes through the stop AP, the λ / 4 wavelength plate QWP, and the polarization beam splitter PBS, and is received by the photodetector PD. The light is received by the surface. Since the photodetector PD detects the focused spot based on the astigmatism method, a read signal of information recorded on the DVD can be obtained using the output signal.

  In addition, focus detection and track detection are performed by detecting spot shape change and light quantity change on the photodetector PD. Based on this detection, the objective lens OBJ is moved for tracking and focusing so that the driving means D (described later) of the objective lens OBJ appropriately forms a light beam from the semiconductor laser LD1 on the information recording surface of the DVD. It is like that. At this time, since the objective lens OBJ is tilted according to the shift amount by the driving means D, astigmatism and coma can be suppressed.

  Next, when recording and / or reproducing information with respect to a CD, the light beam having a wavelength of 790 nm emitted from the semiconductor laser LD2 of the two-laser one package 2L1P is reflected by the polarization beam splitter PBS as indicated by a dotted line, The λ / 4 wave plate QWP and the aperture stop AP are passed through the objective lens OBJ in a finite divergence state as shown in the figure, and the objective lens OBJ is passed through the protective layer having a thickness of 1.2 mm through the objective lens OBJ. It is condensed on the information recording surface.

  The reflected light beam modulated by the information pits on the information recording surface of the CD again passes through the objective lens OBJ, and further passes through the aperture AP, the λ / 4 wavelength plate QWP, and the polarization beam splitter PBS, and is received by the photodetector PD. The light is received by the surface. Since the photodetector PD detects the focused spot based on the astigmatism method, a read signal of information recorded on the CD can be obtained using the output signal.

  In addition, focus detection and track detection are performed by detecting spot shape change and light quantity change on the photodetector PD. Based on this detection, the objective lens OBJ is moved for tracking and focusing so that the driving means D (described later) of the objective lens OBJ appropriately forms a light beam from the semiconductor laser LD2 on the information recording surface of the CD. It is like that. At this time, since the objective lens OBJ is tilted according to the shift amount by the driving means D, astigmatism and coma can be suppressed.

  FIG. 4 is a perspective view showing the driving means D for the objective lens. In FIG. 4, the driving means D includes an iron base 12 and a plastic lens holder 14. The lens holder 14 is fixed with an objective lens OBJ for forming a light spot on the recording surface of the optical disc.

  A plastic suspension base 18 is fixed on the base 12, and the suspension base 18 and four elastic metal wires 20, which have base ends fixed to the suspension base 18, extend in parallel to each other. Thus, a suspension mechanism is configured. The tips of the four elastic metal wires 20 are connected to the lens holder 14. The elastic metal wire 20 has strength and elasticity capable of supporting the lens holder 14, and when the elastic metal wire 20 is bent, the lens holder 14 has a focusing direction indicated by an arrow in FIG. It is movable in the tracking direction and the radial tilt (also simply referred to as tilt) direction. Of these three directions, the focusing direction is a direction perpendicular to the recording surface (nominal recording surface) of an optical disc when an ideal optical disc having no shape error is accurately loaded in the optical disc drive. is there. The tracking direction is the radial direction of the optical disk, and the radial tilt direction is the rotation direction when the objective lens is tilted in the radial direction of the optical disk. FIG. 4 further shows the tangential direction of the optical disk as the tangential direction.

  Accordingly, the suspension mechanism of the driving means D is interposed between the base 12 and the lens holder 14, and supports the lens holder 14 so as to be movable in the focusing direction, the tracking direction, and the radial tilt direction. The four elastic metal wires 20 of the suspension mechanism further function as energization wires for energizing coils described later.

  The driving unit D further includes a driving mechanism that drives the lens holder 14 in the focusing direction, the tracking direction, and the radial tilt direction. The driving mechanism includes a pair of magnets 26a and 26b fixed to the base 12, a focusing coil 28 fixed to the lens holder 14, a pair of tracking coils 30a and 30b fixed to the lens holder 14, A pair of radial tilt coils 32a and 32b fixed to the base 12 is included.

  The pair of magnets 26 a and 26 b are attached to a first pair of iron brackets 34 a and 34 b erected on the base 12. The brackets 34a and 34b constitute a yoke in cooperation with the base 12, and the yoke and the magnets 26a and 26b constitute a first fixed-side magnetic circuit.

  The focusing coil 28 is disposed on the lens holder 14 so that its axis extends in the same direction as the optical axis of the objective lens OBJ. The focusing coil 28 is connected to a focusing servo means (not shown) for controlling a current flowing through the focusing coil 28 using a focusing error signal output from a focusing error detector (not shown) as a feedback signal. This connection is made through two of the four elastic metal wires 20 of the suspension mechanism 22. As the focusing error detection unit, various configurations have been proposed, and an appropriate one may be selected and used. When a current flows, the focusing coil 28 generates an electromagnetic force that drives the lens holder 14 in the focusing direction by electromagnetic interaction with the first fixed-side magnetic circuit.

  The tracking coils 30a and 30b are arranged on the lens holder 14 side by side so that their axial centers extend in the tangential direction. The tracking coils 30a and 30b have tracking servo means (not shown) for controlling the current flowing through the tracking coils 30a and 30b using a tracking error signal output from a tracking error detector (not shown) as a feedback signal. The connection is made through another two of the four elastic metal wires 20 of the suspension mechanism 22. Various tracking error detection units have been proposed, and an appropriate one may be selected and used. When a current is passed, the tracking coils 30a and 30b generate an electromagnetic force that drives the lens holder 14 in the tracking direction by electromagnetic interaction with the first fixed-side magnetic circuit.

  The pair of radial tilt coils 32 a and 32 b are attached to a second pair of iron brackets 36 a and 36 b erected on the base 12. The brackets 36a and 36b function as iron cores of the radial tilt coils 32a and 32b and constitute a yoke in cooperation with the base 12. The yoke and the radial tilt coils 32a and 32b are used as the second. A fixed-side magnetic circuit is configured. Further, the pair of radial tilt coils 32 a and 32 b have their axial centers on the same straight line and extend in the radial direction (tracking direction) of the optical disc, and the coils 32 a and 32 b are on both sides of the focusing coil 28. It is disposed on the base 12 so as to be positioned.

  A sensor 38 is provided on one side of the objective lens OBJ on the lens holder 14 to detect the inclination of the optical axis of the objective lens OBJ with respect to the information recording surface of the actual optical disc facing the objective lens OBJ. The sensor 38 is arranged in such a direction as to detect the inclination in the radial tilt direction. Hereinafter, the sensor 38 is referred to as a radial skew sensor. Various sensors that can be used as the radial skew sensor 38 have been proposed and known, and an appropriate one may be selected and used. Moreover, the sensor used for this invention is not restricted to the kind of illustration example. For example, a sensor that detects the tilt of the lens holder 14 with respect to the base 12 and a sensor that detects the tilt of the information recording surface of the optical disc with respect to the base 12 are used, and the lens holder 14 with respect to the information recording surface of the optical disc is output from the sensors. The inclination of the optical axis of the upper objective lens OBJ may be obtained, and in that case, if these sensors are mounted on the base 12, it is advantageous in reducing the weight of the movable part of the optical pickup device. It becomes composition. Furthermore, the optical pickup device according to the present invention may use only a sensor for detecting the tilt of the lens holder 14 with respect to the base 12 or only a sensor for detecting the tilt of the information recording surface of the optical disc with respect to the base 12. In some cases, the sensor is not used at all. Whether or not to use a sensor and what kind of sensor to use depends on what is controlled and what method is used for radial tilt control. This will be explained later.

  In the configuration of the illustrated example including the radial skew sensor 38, the radial tilt coils 32 a and 32 b use the radial skew detection signal output from the radial skew sensor 38 as a feedback signal, and the radial tilt coils 32 a and 32 b Since a radial tilt servo means (not shown) for controlling the current to be supplied is connected and the radial tilt coils 32a and 32b are fixed on the base 12, this connection is made via the lead wire 40. . The radial tilt coils 32a and 32b generate an electromagnetic force that drives the lens holder 14 in the radial tilt direction by electromagnetic interaction with the focusing coil 28 when an electric current flows.

  By using such a driving means D, the objective lens OBJ is tracked so that the driving means D of the objective lens OBJ appropriately forms an image of the light beams from the semiconductor lasers LD1 and LD2 on the information recording surface of the DVD or CD. And can be moved for focusing. Furthermore, since the objective lens OBJ is tilted according to the shift amount by the driving means D, astigmatism and coma can be suppressed. The shift amount can be calculated based on the (tracking) signal from the photodetector PD, but the method of obtaining it is not limited thereto.

  In the above embodiment, the shift amount of the objective lens is detected, and the tilt amount is given according to the detected shift amount. However, the present invention is not limited to this, and as in the embodiment described below. Also good.

  FIG. 5 is a perspective view showing the driving means D according to the second embodiment. In FIG. 5, the objective lens OBJ is supported by the lens holder HLD. The lens holder HLD has a pair of flange portions FL attached to the side surfaces. The flange portion FL is supported in a swingable manner by a support shaft S fixed to a case (not shown). Further, the lens holder HLD is driven from the side by a direct acting actuator ACT.

  When the lens holder HLD is driven by the linear actuator ACT, the objective lens OBJ is shifted and tilted about the support shaft S. According to the present embodiment, since the tilt amount corresponding to the shift amount is mechanically given to the objective lens OBJ, detection of the shift amount is not required as in the above-described embodiment, and a simpler drive configuration is provided. realizable.

Next, examples suitable for the above-described embodiment will be described. 6A is a longitudinal spherical aberration diagram when using a DVD, FIG. 6B is a diagram showing sine conditions when using a DVD, and FIG. 6C is a longitudinal spherical aberration diagram when using a CD. (D) It is a figure which shows the sine condition at the time of CD use. The lens data of Example 1 are shown in Tables 1 and 2. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is expressed by using E (for example, 2.5E-3). The objective lens shown in Example 1 corresponds to the two-dot chain line and the solid line shown in FIG. 1 and the objective lens shown in FIG.

  The optical surface of the objective optical system is formed as an aspherical surface that is symmetric about the optical axis and is defined by a mathematical formula in which the coefficient shown in each table is substituted into the following formula (1).

  Further, the optical path length given to the light flux of each wavelength by the diffractive structure is defined by a mathematical formula in which the coefficient shown in each table is substituted for the optical path difference function of the following equation (2).

  7A is a longitudinal spherical aberration diagram when using a DVD, FIG. 7B is a diagram showing sinusoidal conditions when using a DVD, and FIG. 7C is a longitudinal spherical aberration diagram when using a CD. (D) It is a figure which shows the sine condition at the time of CD use. The lens data of Example 2 are shown in Tables 3 and 4. The objective lens shown in Example 2 corresponds to the objective lens shown in FIGS. 2B and 2C described above. In the case of the objective lens according to Example 2, as shown in FIG. 2B, when the lens is shifted by 0.2 mm without being tilted, a coma aberration of 0.042 λ rms is generated. On the other hand, as shown in FIG. 2C, the amount of aberration can be greatly reduced by tilting.

  8A is a longitudinal spherical aberration diagram when using a DVD, FIG. 8B is a diagram showing sine conditions when using a DVD, and FIG. 8C is a longitudinal spherical aberration diagram when using a CD. (D) It is a figure which shows the sine condition at the time of CD use. Further, FIG. 9 is a diagram showing the characteristics of the objective lens according to Example 3. (a) The aberration amount with respect to the shift amount when not tilted and (b) the aberration amount with respect to the shift amount when tilted. Show. In the case of the objective lens according to Example 3, as shown in FIG. 9A, when the lens is shifted by 0.2 mm without being tilted, a coma aberration of 0.082 λ rms is generated. On the other hand, as shown in FIG. 9B, the amount of aberration can be significantly reduced by tilting. The lens data of Example 3 are shown in Tables 5 and 6.

  10A is a longitudinal spherical aberration diagram when using a DVD, FIG. 10B is a diagram showing a sine condition when using a DVD, and FIG. 10C is a longitudinal spherical aberration diagram when using a CD. (D) It is a figure which shows the sine condition at the time of CD use. Furthermore, FIG. 11 is a diagram illustrating the characteristics of the objective lens according to Example 4. (a) The aberration amount with respect to the shift amount when the tilt is not performed and (b) the aberration amount with respect to the shift amount when the tilt is performed. Show. In the case of the objective lens according to Example 4, as shown in FIG. 11A, when the lens is shifted by 0.2 mm without being tilted, a coma aberration of 0.021 λ rms is generated. On the other hand, as shown in FIG. 11B, the amount of aberration can be significantly reduced by tilting. Tables 7 and 8 show lens data of Example 4.

  As described in each of the objective lenses according to Examples 2 to 4 above, when the lens is shifted by 0.2 mm without being tilted, a coma aberration of 0.015 λ rms or more and 0.15 λ rms or less is generated. It is preferable to intentionally leave coma aberration. This upper limit value of 0.15λrms corresponds to the amount of residual coma aberration when the tilt angle at which the wavefront aberration is minimized when the objective lens is shifted by 0.2 mm is set to about 1 (°). . By setting the upper limit value in this way, the objective lens can be easily set to a desired tilt angle according to the shift amount without requiring a large torsional driving force for the driving means as shown in FIG. 4, for example. it can. As a result, power saving of the driving means can be achieved and durability can be easily ensured.

  In FIG. 12, the horizontal axis indicates the shift amount A (mm) of the objective lens in the direction orthogonal to the optical axis, and the vertical axis indicates the tilt angle B (the wavefront aberration is minimized when the shifted objective lens is tilted. In the objective lens according to the normal design, B / A is less than 0.6, but in the case of the objective lenses of Examples 2 to 4, all of the objective lenses have B / A = 0. You can see that it is over 6.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. The optical pickup device may be capable of recording and / or reproducing information with respect to an optical disc such as a Blu-ray Disc or an HD DVD, and the configuration of the driving means is not limited to the above-described embodiment. .

Claims (8)

A first light source that emits a light beam having a wavelength λ1, an objective lens that focuses the light beam emitted from the first light source on the information recording surface of the first optical information recording medium, and a light beam reflected by the information recording surface. In an optical pickup device having a photodetector for receiving light, and recording and / or reproducing information on an information recording surface of the first optical information recording medium,
An optical pickup device comprising: a drive unit that tilts the objective lens according to a shift amount of the objective lens from a predetermined reference position.   The optical pickup device according to claim 1, wherein the light beam emitted from the first light source is incident on the objective lens in a finite divergence state.   The optical pickup device according to claim 1, wherein the objective lens does not satisfy a sine condition.   4. The optical pickup device according to claim 1, wherein the driving unit tilts the objective lens according to an inclination of the first optical information recording medium. 5. .   A second light source that emits a light beam having a wavelength of λ2 (λ1 ≠ λ2), and the light beam emitted from the second light source is condensed on the information recording surface of the second optical information recording medium via the objective lens. The optical pickup device according to any one of claims 1 to 4, wherein information is recorded and / or reproduced on an information recording surface of the second optical information recording medium. .   6. The optical pickup device according to claim 5, wherein the driving unit tilts the objective lens according to an inclination of the second optical information recording medium.   In the objective lens used in the optical pickup device according to any one of claims 1 to 6, when the lens is shifted by 0.2 mm in the direction perpendicular to the optical axis without being tilted, 0.015 λrms or more, An objective lens in which coma of 0.15 λ rms or less occurs. The objective lens used in the optical pickup device according to any one of claims 1 to 6, wherein the objective lens is tilted when a shift amount A (mm) is given in a direction orthogonal to the optical axis. An objective lens characterized by satisfying the following conditional expression where B (°) is a tilt angle at which the wavefront aberration is minimized.
B / A ≧ 0.60