JP2007200456A - Optical pickup device, optical disk driving unit, and spherical aberration correcting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device capable of preventing variation in a rim strength by properly correcting spherical aberration and being made compact, an optical disk driving unit mounted with the optical pickup device, and a spherical aberration correcting method. <P>SOLUTION: The optical pickup device 6 is provided with a relay lens 35 between a divergence angle variable device (liquid crystal element) 34 for correcting the spherical aberration and an objective lens 38. Thus, it is possible to maintain rim strength constant while properly correcting the spherical aberration even when the liquid crystal element 34 is not arranged very close to an aperture diaphragm 37 and the objective lens 38. In addition, the optical pickup device can be made compact. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical pickup device that performs at least one of optically recording a signal on an optical recording medium and reproducing the recorded signal, an optical disk driving device equipped with the optical pickup device, and a spherical aberration correcting method. .

  In recent years, in order to increase the signal recording density, a next-generation optical disc format using a light source having a wavelength of about 400 to 410 nm by a blue-violet semiconductor laser and an objective lens having an NA (numerical aperture) of 0.85 is used. It has been adopted. An optical disk using a laser beam having a wavelength of about 400 nm has been put into practical use with a structure in which the cover layer protecting the signal recording layer is thin, for example, 0.1 mm. In addition, in such an optical disc using a laser beam having a wavelength of about 400 nm, a disc having a plurality of signal recording layers has been proposed in order to increase the amount of information recorded, similarly to an optical disc using a light having a wavelength of 650 nm. Yes.

  When a signal is recorded on such a multi-layer disc, or when a recorded signal is reproduced, the amount of spherical aberration largely changes due to the difference in depth from the disc surface of each signal recording layer, Correction of spherical aberration is required. In particular, in an optical disc using a laser beam having a wavelength of about 400 nm, the amount of change in spherical aberration appears significantly.

  Even in the case of an optical disk having a single signal recording layer, if an error occurs in the thickness of the disk substrate itself, the spherical aberration changes. In particular, in an optical disc using laser light having a wavelength of about 400 nm, the substrate thickness of the disc is as thin as 0.1 mm. Therefore, it has become difficult to reduce the error of spherical aberration by increasing the dimensional accuracy of the substrate thickness in the optical disc manufacturing process (see, for example, Patent Document 1).

  A liquid crystal element may be used as a means for correcting such spherical aberration. Specifically, it is described in paragraph [0014] of the specification of Patent Document 1. For example, laser light is incident on the liquid crystal element, and a voltage is applied to electrodes formed concentrically in the liquid crystal element, whereby the refractive index of the incident laser light is partially changed. As a result, a phase change partially occurs in the incident laser beam, and thus the spherical aberration is corrected so as to be canceled. Specific examples of the liquid crystal element include the liquid crystal element described in Patent Document 2.

As a means for correcting the spherical aberration, an element of a system in which a mirror is driven by a piezoelectric body, for example, may be used instead of a liquid crystal element (for example, see Patent Document 3).
JP 2004-185758 A (paragraphs [0008] to [0015]) JP 2002-109776 A (paragraphs [0007], [0008]) JP 2005-100513 A (paragraphs [0054] to [0057], [0072])

  However, when liquid crystal elements as described in Patent Documents 1 and 2 are used, the refractive index of the incident laser light is changed, so that the laser light emitted from the liquid crystal element diverges or converges. As a result, the effective emission angle of the laser beam varies and the effective beam diameter varies. As the effective beam diameter varies, the rim intensity varies. As described in Patent Document 1, the rim intensity is an index representing the intensity distribution of laser light incident on the objective lens, and the outer edge of the effective diameter of the objective lens when the intensity peak of the laser light is 1. It is represented by the intensity ratio. When the rim intensity changes, the numerical aperture changes substantially, and the spot diameter of the laser beam focused on the optical disk changes, resulting in a problem that the reproduction characteristics deteriorate.

  On the other hand, when a mirror as described in Patent Document 3 is used, for example, it is necessary to arrange a critical angle prism 13 as shown in FIG. 1 of Patent Document 3, resulting in a complicated optical path. The device becomes larger.

  In view of the circumstances as described above, an object of the present invention is to appropriately correct spherical aberration, prevent fluctuations in rim strength, and further mount an optical pickup device that can realize downsizing. An optical disk drive and a spherical aberration correction method are provided.

In order to achieve the above object, an optical pickup device according to the present invention includes a light source that emits laser light, a beam diameter regulating element that regulates a beam diameter of the laser light emitted from the light source,
An objective lens for condensing the laser beam, the beam diameter of which is regulated by the beam diameter regulating element, onto a disc-shaped recording medium capable of recording a signal, and a divergence angle of the laser beam emitted from the light source is changed. And a relay optical system that is disposed between the liquid crystal element and the beam diameter regulating element and guides the laser light to the beam diameter regulating element so that the optical coupling efficiency of the laser light is substantially constant. It comprises.

  In the present invention, since the laser light is guided to the beam diameter regulating element by the relay optical system so that the optical coupling efficiency of the laser light is constant, the fluctuation of the rim intensity is corrected while appropriately correcting the spherical aberration by the liquid crystal element. Can be prevented. Thereby, the quality of the recording signal or the reproduction signal can be improved.

  In particular, even if a relay optical system is not used, it is possible to suppress fluctuations in the effective beam diameter or rim intensity by arranging the liquid crystal element very close to the beam diameter regulating element. The fluctuation is inevitable. On the other hand, in the present invention, since the relay optical system is used, it is not necessary to dispose the liquid crystal element near the beam diameter regulating element, and the fluctuation of the effective beam diameter and the fluctuation of the rim intensity are eliminated.

  In addition, since a liquid crystal element is provided as means for changing the divergence angle of the laser beam, the number of optical components is reduced as compared with a case where a correction element for correcting the spherical aberration is provided by driving the mirror as described above, for example. The spherical aberration is corrected with a simple configuration. Therefore, it is possible to further reduce the size of the optical pickup device. In this case, the liquid crystal element is preferably a transmissive type.

  As described above, in the present invention, the effect of providing the liquid crystal element and the relay optical system in combination is great, preventing fluctuations in the rim strength, realizing downsizing or thinning of the apparatus, reducing manufacturing costs, and designing the arrangement of the liquid crystal elements The effect of improving the degree of freedom is obtained.

  “Arranged between the liquid crystal element and the beam diameter regulating element” means that it is arranged on the optical path of the laser beam between the liquid crystal element and the beam diameter regulating element.

  In the present invention, the relay optical system may have a form having two relay lenses. Thereby, a telecentric optical system can be realized, and fluctuations in effective beam diameter and rim intensity are eliminated. Alternatively, in order to realize a reduction in thickness or size of the optical pickup device, the relay optical system may have a mirror disposed between the two relay lenses.

  In the present invention, the optical pickup device further includes a conversion element that is disposed between the relay optical system and the beam diameter regulating element and converts an angle of an optical axis of the laser light emitted from the relay optical system. To do. This makes it possible to reduce the thickness of the optical pickup device. In the case where the conversion element for converting the angle of the optical axis is provided as described above, when there is no relay optical system, it is considered that the thickness can be reduced if a liquid crystal element is arranged between the conversion element and the beam diameter regulating element. However, in reality, it is almost impossible to dispose the liquid crystal element in a narrow space between the conversion element and the beam diameter regulating element. In the present invention, by providing the relay optical system, it is possible to reduce the thickness of the optical pickup device.

  In the present invention, it is particularly advantageous when the light source is a blue semiconductor laser and the numerical aperture of the objective lens is 0.85.

  An optical disk drive apparatus according to the present invention regulates a rotational drive mechanism that rotationally drives a disk-shaped recording medium capable of recording signals, a light source that emits laser light, and a beam diameter of the laser light emitted from the light source. A beam diameter regulating element, an objective lens for condensing the laser beam whose beam diameter is regulated by the beam diameter regulating element on the recording medium, and a divergence angle of the laser beam emitted from the light source is changed. And a relay optical system that is disposed between the liquid crystal element and the beam diameter regulating element and guides the laser light to the beam diameter regulating element so that the optical coupling efficiency of the laser light is substantially constant. It comprises.

  The “optical disk drive device” is a device capable of at least one of recording a signal on a recording medium and reproducing the recorded signal.

  The spherical aberration correction method according to the present invention emits a laser beam, changes a divergence angle of the emitted laser beam, regulates a beam diameter of the emitted laser beam by a beam diameter regulating element, and The laser beam is guided to the beam diameter regulating element so that the optical coupling efficiency of light is substantially constant, and the laser beam whose beam diameter is regulated by the beam diameter regulating element is a disc-shaped disk capable of recording a signal. Focus on the recording medium.

  In the present invention relating to this spherical aberration correction method, the order of the steps is not limited unless otherwise specified in the specification of the invention or in the description of the function and effect thereof.

  As described above, according to the present invention, it is possible to appropriately correct spherical aberration, prevent fluctuations in rim intensity, and further achieve downsizing of the optical pickup device and the optical disk drive device.

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

  FIG. 1 is a schematic perspective view of an optical disk drive apparatus according to an embodiment of the present invention.

  An optical disk drive 1 shown in FIG. 1 records and reproduces information with respect to an optical disk (DVD ± R / RW, CD-R / RW, BD (Blu-ray Disc (registered trademark))) 2 as a recording medium. It is a device to perform. The optical disc 2 may have a single signal recording layer or a plurality of signal recording layers.

  The optical disk drive 1 includes a disk table 3 on which an optical disk 2 such as a BD is mounted, a movable base 4 provided so as to be movable, a guide shaft 5 for guiding the movable base 4, and information on the optical disk 2. An optical pickup device 6 that records and reproduces and a housing 7 that houses them are provided.

  The disk table 3 is provided with a chucking mechanism for mounting the optical disk 2. Accordingly, the optical disk 2 is mounted on the disk table 3 and can be rotated.

  The moving base 4 is provided so as to be slidable in the radial direction of the optical disc 2, for example. The moving base 4 is mounted with an optical pickup device 6 and a feed motor described later.

  The guide shaft 5 guides the moving base 4 in the radial direction of the optical disc 2.

  The optical pickup device 6 includes a biaxial actuator 8, and the biaxial actuator 8 displaces the objective lens 38 in the focusing direction and the tracking direction to perform drive control such as focus servo and tracking servo. Instead of the biaxial actuator 8, a triaxial actuator capable of displacing the objective lens 38 in the direction of the relative tilt angle (tilt angle) between the objective lens 38 and the optical disc 2 may be provided. .

  FIG. 2 is a block diagram showing a configuration of the optical disk drive device 1 shown in FIG.

  As shown in FIG. 2, the optical disk drive 1 includes a spindle motor 9, a feed motor 10, a system controller 11, a servo control circuit 12, a preamplifier 13, a signal modulator / demodulator in addition to the optical pickup device 6 described above. And an ECC (error correction code) unit 14, an interface 15, a D / A converter and A / D converter 16, an audio / visual processing unit 17, an audio / visual signal input / output unit 18, and a laser control unit. 19.

  The spindle motor 9 is a motor for rotationally driving the optical disc 2.

The feed motor 10 is a motor for moving the moving base 4 shown in FIG. 1 in the radial direction of the optical disc 2. Thereby, the system controller 11 in which the optical pickup device 6 is moved in the radial direction of the optical disc 2 is provided for the entire optical disc driving device 1 and for individual control such as signal processing and servo control.

  The servo control circuit 12 generates a focus servo signal and a tracking servo signal based on signals (focus error signal and tracking error signal) obtained from the preamplifier 13 and sends these signals to the optical pickup device 6 and the feed motor 10.

  The preamplifier 13 generates a focus error signal, a tracking error signal, and an RF signal) from the signal obtained by the optical pickup device 6.

  The signal modulator / demodulator and ECC (error correction code) unit 14 demodulates the RF signal, demodulates the recording signal, and performs error correction coding processing. For example, ECC is added to the recording signal, and error correction is performed on the reproduction signal (RF signal).

  The interface 15 exchanges signals with the external computer 21.

  The D / A converter and the A / D converter 16 convert the reproduction signal from a digital signal to an analog signal, and convert the recording signal from an analog signal to a digital signal.

  The audio / visual processing unit 17 and the audio / visual signal input / output unit 18 exchange audio signals and video signals with external devices.

  The laser control unit 19 controls the output and wavelength of the semiconductor laser mounted on the optical pickup device 6 according to recording and reproduction, the type of the optical disc 2 and the like.

  The optical disk drive device 1 configured as described above rotates the optical disk 2 by the spindle motor 9 and drives and controls the feed motor 10 in accordance with a control signal from the servo control unit 12. As a result, the optical disc driving apparatus 1 moves the optical pickup device 6 to a position corresponding to a desired recording track of the selected signal recording layer of the optical disc 2, so that the selected signal recording layer of the optical disc 2 is moved. Record and play back information.

  FIG. 3 is a diagram showing an optical system of the optical pickup device 6 shown in FIG.

  The optical pickup device 6 includes a light source 31, a beam splitter 32, a collimator lens 33, a divergence angle variable element 34, a relay lens 35, a rising mirror 36, an aperture stop 37, an objective lens 38, a condensing lens 39, and a photodetector 40.

  As the light source 31, for example, a blue semiconductor laser having a wavelength of about 400 to 410 nm, specifically about 405 nm is used. However, the present invention is not limited to this, and laser light with a wavelength of 780 nm can be selectively emitted to support CD-R and CD-RW, and laser light with a wavelength of 650 nm can be selectively emitted to support DVD-R and DVD-RW. A light source may be used.

  The beam splitter 32 transmits the laser light emitted from the light source 31 and reflects the 90 ° polarized return light to guide it to the photodetector 40.

  The collimator lens 33 causes the laser light transmitted through the beam splitter 32 to enter the divergence angle variable element 34 as substantially parallel light.

  The divergence angle variable element 34 changes the divergence angle of the incident laser light in order to correct spherical aberration caused by an error in the structure of the optical disc 2 or the design of the optical system. The divergence angle variable element is composed of, for example, a liquid crystal element, and a voltage is applied to an electrode (not shown) so that the alignment of liquid crystal molecules is biased according to the applied voltage. As a result, the refractive power of the liquid crystal element changes, and the refractive index of the incident laser beam partially changes. As a result, the divergence angle of the laser light changes. The electrode arrangement is preferably concentric, for example, but is not limited thereto. Here, the divergence angle includes both positive and negative divergence angles, and the negative divergence angle means a convergence angle. This will be described in detail later.

  The relay lens 35 guides the laser light to the aperture stop 37 so that the optical coupling efficiency of the laser light is substantially constant. Specifically, the relay lens 35 is composed of, for example, two lenses 35a and 35b. For example, a Kepler type is used as the relay lens 35, but is not limited thereto. The optical design of the lens 35a and the lens 35b is the same, but they may be different. The optical coupling efficiency here is represented by the ratio of the power incident on the aperture stop to the power of the laser light emitted from the light source 31, that is, the ratio of the power actually used in the total power.

  The rising mirror 36 converts the angle of the optical axis of the laser light emitted from the relay lens 35. In this example, the laser beam traveling in the horizontal direction is raised substantially vertically. As described above, the optical axis is not limited to 90 degrees, and the optical axis may be converted at an angle of less than 90 degrees or greater than 90 degrees.

  The aperture stop 37 is a beam diameter regulating element that regulates the beam diameter of the laser light incident on the objective lens 38.

  The objective lens 38 condenses the laser light whose beam diameter is regulated on the optical disc 2. When a laser having a wavelength of about 400 to 410 nm is used as the light source 31, the numerical aperture of the objective lens 38 is 0.85. When a laser having a wavelength of about 650 nm is used, the numerical aperture of the objective lens 38 is 0.6. When a laser having a wavelength of about 780 nm is used, the numerical aperture of the objective lens 38 is 0.45. The numerical aperture may be other numerical apertures and depends on the wavelength of the laser beam.

  The condensing lens 39 condenses the return light reflected by the beam splitter 32 on the photodetector 40.

  The photodetector 40 converts, for example, the detected return light into an electrical signal, and generates a tracking error signal, a focus error signal, an RF signal, and the like.

  The operation of the optical pickup device 6 configured as described above will be described.

  The laser light emitted from the light source 31 passes through the beam splitter 32 and enters the collimator lens 33. The incident laser light is collimated by the collimator lens 33. The reason for the parallel light is to efficiently use the energy of the laser light incident on the divergence angle variable element 34 and further minimize the variation in the optical coupling efficiency of the laser light. When parallel light is used in this way, the laser light propagates as a plane wave. A laser beam whose divergence angle is changed is emitted by the divergence angle variable element 34. When the divergence angle of the laser beam is changed by the divergence angle variable element 34, it propagates as a spherical wave laser beam whose phase is selectively controlled and enters the relay lens 35.

  The divergence angle variable element 34 is driven based on the control by the system controller 11. In this case, it may be controlled by an open loop system or may be dynamically controlled by a closed loop system, that is, a feedback system.

  The laser light emitted from the relay lens 35 is raised almost vertically by the raising mirror 36, and the laser light is incident on the aperture stop 37 and the objective lens 38 with a certain optical coupling efficiency. By providing the relay lens 35, a telecentric optical system can be realized even when the divergence angle of the laser beam is changed by the divergence angle variable element 34, and the aperture stop 37 can emit the laser beam with a substantially constant optical coupling efficiency. It becomes possible to make it enter. This will be described in detail later. The laser light focused on the optical disk 2 by the objective lens 38 is reflected by the signal recording layer, and the reflected return light is reflected by the beam splitter 32 and enters the photodetector 40 in the reverse order. .

  In the present embodiment, even when the spherical aberration is corrected, the laser light is incident on the objective lens 38 with a substantially constant optical coupling efficiency, so that the signal can be stably recorded or reproduced. The quality of the recording signal and the reproduction signal can be improved.

  Next, the relay lens 35 will be described in more detail. Before that, the optical principle and operation in the case where the optical pickup device 6 does not have the relay lens 35 will be described. FIG. 4 is a diagram showing an optical system from the light source 31 to the objective lens 38 when “there is no relay lens 35”.

  In FIG. 4, a light source 31, a collimator lens 33, a divergence angle variable element 34, an aperture stop 37, and an objective lens 38 are arranged. The divergence angle variable element 34 is disposed at a position where the distance between the divergence angle variable element 34 and the aperture stop 37 satisfies the following expression (1).

((1.5 / 4.4) × 10 ³ ) · (ΔSA3 / NA ³ ) (λ · L / φ ² ) ≦ 0.1 (1)
However, in Formula (1),
ΔSA3: a difference (λrms) in the amount of spherical aberration generated due to a difference in thickness from the disk surface on which the laser beam is incident to the signal recording layer between the two most separated layers of the two or more signal recording layers,
NA: numerical aperture of the objective lens 38,
λ: wavelength of the laser beam emitted from the light source 31 (mm),
L: distance (mm) between the divergence angle variable element 34 and the aperture stop 37;
φ: Aperture diameter (mm) regulated by the aperture stop 37
And

  The optical pickup device 6 prevents the optical coupling efficiency from changing greatly by being arranged at a predetermined position so that the divergence angle variable element 34 satisfies the above-described formula (1).

  Here, it will be described in detail that the divergence angle variable element 34 is arranged at a position satisfying the expression (1).

  In the optical pickup device 6, as shown in FIG. 3, when the refracting power of the divergence angle variable element 34 is changed, the aperture is restricted by the aperture stop 37, so that the effective emission angle of the laser light emitted from the light source 31 is increased. Changes.

  Here, the effective emission angle of the laser beam means that the laser beam emitted from the light source 31 passes through each optical component arranged in the optical system, is limited by the aperture stop 37, and is optical disc by the objective lens 38. 2 shows the angle of the laser light collected at 2 and emitted from the light source 31, in other words, the effective coupling angle.

  For example, when the refractive power of the divergence angle variable element 34 changes and the laser beam is converged, the effective emission angle at the light source 31 is increased. On the other hand, when the refractive power of the divergence angle variable element 34 changes and the laser beam is diverged, the effective emission angle at the light source 31 becomes small.

  When the divergence angle variable element 34 is not arranged at a position satisfying the above-described formula (1), it is effective to change the refractive power of the divergence angle variable element 34 in order to correct the difference in spherical aberration due to the interlayer thickness. The beam diameter changes, that is, the effective emission angle of the laser light changes. Further, the amount of light (power) of the laser beam condensed on each signal recording layer of the optical disc 2 changes, the intensity distribution in the pupil, that is, the intensity distribution within the effective diameter (or rim intensity) changes, When the tracking error signal is generated using three beams, the spot interval on the signal recording layer may change. For example, when the laser beam is diverged by the divergence angle variable element 34, the effective beam diameter is reduced and the amount of light is reduced, and when converged, the effective beam diameter is increased and the amount of light is increased.

  Due to this change in the amount of light, proper recording of information signals is prevented by deviating from the optimum recording power. Also, by reproducing from the optimum reproduction power at a predetermined power or higher, recording is performed by heat generated by condensing the laser beam, so that recording / reproduction characteristics such as causing a problem in reproduction durability are deteriorated. Sometimes.

  Next, Formula (1) showing the positional relationship between the divergence angle variable element 34 and the aperture stop 37 will be described.

  In the optical pickup device 6 including the optical components as described above, spherical aberration is generated by changing the divergence angle of the laser light incident on the objective lens 38, that is, by causing the light to diverge or converge. Think.

  Here, as shown in FIG. 3, the inclination angle of the laser light incident on the objective lens 38 from the optical axis direction to the divergence direction is α (rad). That is, α = 0 in the case of parallel light, and α takes a negative value in the case of convergent light.

In the optical pickup device 6, the generated spherical aberration SA3 is proportional to the tilt angle α (rad) of the laser light incident on the objective lens and the focal length f (mm) of the objective lens. Further, spherical aberration SA3 that occurs, the fourth power of the numerical aperture NA, i.e., proportional to NA ^4. Therefore, the generated spherical aberration SA3 (λrms) satisfies the following expression (2).

SA3 = k ₀ · α · (f / λ) · NA ⁴ (2)
However, in Formula (2),
α: inclination angle (rad) of the laser light incident on the objective lens,
f: Focal length (mm) of the objective lens,
λ: wavelength of laser light (mm),
NA: numerical aperture k _{0 of the} objective lens: coefficient.

When this equation (2) is transformed using the following equation (3) showing the relationship between the aperture diameter φ (mm) of the objective lens 38, the focal length f (mm), and the numerical aperture NA, the equation (4) is obtained. become.
φ = 2 · f · NA (3)
SA3 = k · α · (φ / λ) · NA ³ (4)
However, in Formula (3) and Formula (4),
φ: aperture diameter of objective lens (mm),
k: a coefficient.

Further, the relationship between the coefficient k ₀ in Expression (2) and the coefficient k in Expression (4) is as shown in the following Expression (5).

_{k = k 0/2 ··· (} 5)
In the above formula (4), the objective lens 38 is changed by changing the aperture diameter φ (mm) of the objective lens 38, the tilt angle α (rad) of the laser light incident on the objective lens 38, and the numerical aperture NA of the objective lens 38. When the spherical aberration amount SA3 (λrms) included in the laser beam emitted from the laser beam is actually calculated, it is as shown in FIG. From FIG. 4, when the coefficient k is calculated, it becomes 8.8 × 10 ⁻³ , and the expression (4) is expressed as the following expression (6).

SA3 = (8.8 × 10 ⁻³ ) · α · (φ / λ) · NA ³ (6)
Equation (6) is modified to obtain the following equation (7).

α = ((1 / 8.8) × 10 ³ ) · (SA3 / NA ³ ) (λ / φ) (7)
Further, the change amount Δφ ₀ (mm) of the opening diameter φ ₀ (mm) in the divergence angle variable element 34 is the following equation (8). Using the relationship between this equation (8) and φ ₀ ≈φ, When the equation (7) is modified, the following equation (9) is obtained.

φ ₀ = −2 · α · L (8)
φ ₀ / φ ₀ = ((− 1 / 4.4) × 10 ³ ) · (SA3 / NA ³ ) (λ · L / φ ² ) (9)
However, in Formula (8) and Formula (9),
φ ₀ : Effective aperture diameter (mm) of the divergence angle variable element 34,
Δφ ₀ : Effective amount of change in aperture diameter (mm) of the divergence angle variable element 34,
L: Distance between variable divergence element 34 and aperture stop 37 (mm)
And

(Δφ ₀ / φ ₀ ) shown in the equation (9) is an equation showing the change rate of the effective beam diameter in the divergence angle variable element 34. Here, if there is no change, (Δφ ₀ / φ ₀ ) is zero. Also, (Δφ ₀ / φ ₀ ) shown in this equation (9) is the rate of change of Sinθ when the effective emission angle of the laser light emitted from the light source 31 is θ, that is, the rate of change of the effective beam diameter. I can say that.

  Even if the laser beam emitted from the light source 31 is controlled to have a predetermined value due to the change in the effective beam diameter, the spherical aberration is corrected by changing the refractive power of the divergence angle variable element 34. The light quantity (power) of the focused laser beam in the signal recording layer 2 changes, the intensity distribution in the pupil, that is, the intensity distribution within the effective diameter changes, and the tracking error signal uses three beams. In the case of generation, the spot interval on the signal recording layer may change.

Here, when a semiconductor laser is used as the light source 31, since the intensity is Gaussian, the relationship between the change ratio of the effective beam diameter and the change ratio of the light amount slightly changes depending on the intensity distribution in the pupil. A system in which the optical coupling efficiency of pure laser light excluding the component transmittance is considered to be a representative example is about 35% (when the light intensity at the outermost effective diameter with respect to the center of the pupil is about 55 to 70%) ) Is about 1.5 (Δφ ₀ / φ ₀ ).

  The change rate of the light amount needs to be suppressed within 10% in consideration of the power margin at the time of recording and the reproduction durability at the time of reproduction. For example, in the case of an optical disc using an objective lens with NA = 0.85 and laser light having a wavelength of about 400 nm, there is a phenomenon that when the reproduction power is increased by 10%, the reproduction durability number is reduced to 1/10 or less. This is a serious disadvantage in practical use.

  And since the change rate of a light quantity is less than 10%, the relationship of following Formula (10) is obtained.

1.5 (Δφ ₀ / φ ₀ ) ≦ 0.1 (10)
Substituting Equation (9) above into Equation (10), and further, the difference in the amount of spherical aberration caused by the difference in thickness from the disk surface on which the laser light is incident to the signal recording surface, in the two most separated layers Is ΔSA3 (λrms), and when this is substituted into SA3 in the equation, when the wavelength λ (mm), the numerical aperture NA of the objective lens, and the effective diameter φ (mm)), the divergence angle variable element 34 and the aperture stop As a relational expression to be satisfied by the distance L (mm) from 37, the relation of the following expression (11) is obtained.

1.5 (Δφ ₀ / φ ₀ ) = ((1.5 / 4.4) × 10 ³ ) · (ΔSA3 / NA ³ )
(Λ · L / φ ² ) ≦ 0.1 (11)
In this formula (11), for example, in an optical disk using a blue-violet semiconductor laser, the wavelength is λ = 0.405 × 10 ⁻³ (mm), the numerical aperture is NA = 0.85, the recording layer Since the thickness is 0.25 (λrms) in terms of spherical aberration SA3 from 25 μm, the relationship of equation (12) is obtained.

L / φ ² ≦ 1.8 (12)
As described above, in the optical pickup device 6 to which the present invention is applied, the spherical aberration due to the interlayer thickness of the signal recording layer is corrected by arranging the divergence angle variable element 34 at a position satisfying the above-described formula (1). In addition, the optical coupling efficiency can be prevented from changing greatly.

  However, it is often inconvenient in practice to arrange the divergence angle variable element 34 at a position satisfying the expression (1). The position satisfying the expression (1) is that the divergence angle variable element 34 is very close to the aperture stop 37. In particular, in order to realize a thin optical pickup device provided with the rising mirror 36, the divergence angle variable element 34 is provided. Must be arranged between the raising mirror 36 and the aperture stop 37. This is almost impossible.

  Therefore, the optical pickup device 6 according to the present embodiment includes a relay lens 35. FIG. 5 is a diagram showing an optical system from the divergence angle variable element 34 to the objective lens 38 when the relay lens 35 is provided.

  When the divergence angle variable element 34 corrects the spherical aberration, for example, when the laser beam 44 is diverged and emitted as shown by a solid line in FIG. 5, that is, between the two lenses 35a and 35b. The focal position at is the position of point A. The divergence angle variable element 34 is disposed at the focal position on the left side of the lens 35a in the drawing. The aperture stop 37 is disposed at the focal position on the right side of the lens 35b in the drawing. In order to correct the spherical aberration, the divergence angle variable element 34 conversely has a negative divergence angle, that is, when the laser light 45 is converged and emitted as shown by a broken line in FIG. 5, the two lenses 35a and 35b The focal position in between is the position of point B.

  Here, even if the focal position changes between A and B, the beam angles diverging from the focal points A and B are the same at β. Thus, if the beam angles diverging from the focal points A and B are the same, the beam diameter incident on the aperture stop 37 can be made constant. Such an optical system is called a telecentric optical system. If the beam diameter is constant, the optical coupling efficiency can be made constant, and the rim intensity can be made constant.

  That is, according to the present embodiment, the provision of the relay lens 35 makes it possible to maintain the rim intensity constant while appropriately correcting the spherical aberration without satisfying the above formula (1). Become. Further, depending on the design of the relay lens 35, the position of the divergence angle variable element 34 with respect to the relay lens 35a or the position of the aperture stop 37 (objective lens 38) with respect to the relay lens 35a is appropriately adjusted in the manufacturing process of the optical pickup device 6. can do.

  In addition, since the liquid crystal element is provided as the divergence angle variable element 34, the number of optical components is reduced and the configuration is simple compared to the conventional method in which, for example, a correction element that corrects spherical aberration by driving a mirror is provided. Spherical aberration is corrected. Accordingly, it is possible to further reduce the size or thickness of the optical pickup device.

  Further, by providing the relay lens 35, the degree of freedom in designing the optical system of the entire optical pickup device 6 can be increased.

  As described above, in the present embodiment, the effect that the divergence angle variable element 34 and the relay lens 35 are provided in combination is great, the fluctuation of the rim strength is prevented, the optical pickup device 6 is downsized or thinned, and the manufacturing cost is increased. And the like, and the like, the degree of freedom in the arrangement design of the divergence angle variable element 34, and the like are obtained.

  FIG. 6 is a plan view showing an optical pickup device according to another embodiment of the present invention. In the following description, the same members, functions, and the like of the optical pickup device 6 according to the embodiment shown in FIG. 3 and the like will not be described or will be mainly described.

  The optical pickup device 56 is different from the optical system of the optical pickup device 6 in that the arrangement of the optical components is more realistic. The light source 31 is attached to one end of the moving base 4, and a collimator lens 33 is disposed between the light source 31 and the beam splitter 32. The laser light converted into parallel light by the collimator lens 33 is reflected at an angle of 90 degrees by the reflecting prism 41 disposed on the opposite side of the moving base 4 from the position where the light source 31 is disposed. The laser beam reflected by the reflecting prism 41 is reflected by the mirror 42 at an angle of 90 degrees.

  The relay lens 35 includes lenses 35a and 35b, and another mirror 43 is disposed between these lenses. The laser beam reflected by the mirror 42 enters the lens 35a, is reflected by the mirror 43, passes through the lens 35b, is reflected almost vertically by the rising mirror 36 (see FIG. 3) not shown in FIG. The light enters the diaphragm 37 (see FIG. 3) and the objective lens 38.

  The optical path from the light source 31 to the lens 35b of the relay lens 35 or from the light source 31 to a rising mirror (not shown) is preferably provided so as to be substantially horizontal. However, it is not limited to such a form.

  As described above, by arranging an appropriate mirror 43 between the lenses 35a and 35b, the optical pickup device 56 can be reduced in size and thickness.

  The present invention is not limited to the embodiment described above, and various modifications are possible.

  The optical pickup device 6 or 56 in the above embodiment is a pickup including the rising mirror 36. This is because the optical pickup device 6 or 56 is mounted on the thin optical disk drive device 1, and the raising mirror 36 is not necessarily required. If the optical disk drive 1 is not thin, the raising mirror 36 may be unnecessary.

  In the optical system of the optical pickup devices 6 and 56, for example, the arrangement of the light source 31, the beam splitter 32, and other optical components is not limited to the form shown in FIG. 3 and FIG. Further, depending on the arrangement, another optical component (not shown) may be further provided.

1 is a schematic perspective view of an optical disk drive device according to an embodiment of the present invention. It is a block diagram which shows the structure of the optical disk drive device shown in FIG. It is a figure which shows the optical system of the optical pick-up apparatus shown in FIG. It is a figure which shows the optical system from the light source to an objective lens in "when there is no relay lens." It is a figure which shows the optical system by an objective lens from a divergence angle variable element in case a relay lens is provided. It is a top view which shows the optical pick-up apparatus which concerns on other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical disc drive device 2 ... Optical disc 6, 56 ... Optical pick-up device 31 ... Light source 34 ... Divergence angle variable element 35, 35a, 35b ... Relay lens 37 ... Aperture stop 38 ... Objective lens 44, 45 ... Laser beam

Claims (7)

A light source that emits laser light;
A beam diameter regulating element that regulates a beam diameter of the laser light emitted from the light source;
An objective lens that focuses the laser beam, the beam diameter of which is regulated by the beam diameter regulating element, onto a disc-shaped recording medium capable of recording a signal;
A liquid crystal element that changes a divergence angle of the laser light emitted from the light source;
A relay optical system that is disposed between the liquid crystal element and the beam diameter regulating element and guides the laser light to the beam diameter regulating element so that the optical coupling efficiency of the laser light is substantially constant. A characteristic optical pickup device. The optical pickup device according to claim 1,
The relay optical system has two relay lenses, and is an optical pickup device. The optical pickup device according to claim 2,
The optical optical pickup apparatus, wherein the relay optical system includes a mirror disposed between the two relay lenses. The optical pickup device according to claim 1,
An optical pickup device further comprising a conversion element that is disposed between the relay optical system and the beam diameter regulating element and converts an angle of an optical axis of the laser light emitted from the relay optical system. . The optical pickup device according to claim 1,
The light source is a blue semiconductor laser;
An optical pickup device having a numerical aperture of the objective lens of 0.85. A rotational drive mechanism for rotationally driving a disk-shaped recording medium capable of recording a signal;
A light source that emits laser light;
A beam diameter regulating element that regulates a beam diameter of the laser light emitted from the light source;
An objective lens for condensing the laser beam, the beam diameter of which is regulated by the beam diameter regulating element, on the recording medium;
A liquid crystal element that changes a divergence angle of the laser light emitted from the light source;
A relay optical system that is disposed between the liquid crystal element and the beam diameter regulating element and guides the laser light to the beam diameter regulating element so that the optical coupling efficiency of the laser light is substantially constant. An optical disk drive device. Emits laser light,
Change the divergence angle of the emitted laser light,
The beam diameter of the emitted laser light is regulated by a beam diameter regulating element,
The laser beam is guided to the beam diameter regulating element so that the optical coupling efficiency of the laser beam is substantially constant,
A method for correcting spherical aberration, comprising: condensing the laser beam, the beam diameter of which is regulated by the beam diameter regulating element, on a disk-shaped recording medium capable of recording a signal.

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