JP2005285219A - Optical pickup and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain successful recording and reproducing characteristics while the occurrence of aberration is suppressed even in a high temperature environment. <P>SOLUTION: An optical pickup is provided with; an objective lens 7 designed to have non-aberration at a predetermined temperature; a lens holder 9 holding the objective lens 7 movably in the direction of focusing and the direction of tracking, and also having a heating means 13 which is prepared avoiding an optical path of the objective lens 7 to heat the upper objective lens 7 to the predetermined temperature; and a temperature control means 26 to control the heating means 13 to keep the objective lens 7 at the temperature at which the non-aberration is caused. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical pickup device that records and / or reproduces an information signal with respect to an optical disc, and an optical disc device provided with the optical pickup device, and more particularly, to irradiate a laser beam onto the optical disc and to reflect light from the optical disc. The present invention relates to an incident objective lens.

  2. Description of the Related Art Conventionally, there is an optical pickup device that includes an objective lens that irradiates an optical disc with laser light and receives reflected light from the optical disc. The optical pickup device includes a light emitting element such as a semiconductor laser that emits laser light, a diffraction member such as a prism that diffracts the laser light emitted from the light emitting element, and an optical path of the laser light. Objective lens for focusing on the signal recording surface and a light receiving element for receiving the reflected light from the optical disk.

  The laser light emitted from the light emitting element is reflected substantially at right angles by the diffractive member and is focused on the signal recording surface of the optical disc by passing through the objective lens. The return laser beam reflected by the signal recording surface of the optical disk travels between the optical disk and the objective lens along the same path, and is guided to the light receiving element by the diffraction member.

  Such an optical pickup device is incorporated in an optical disk device that uses an optical disk as a recording medium, such as a disk recording and / or reproducing device, a game machine, or an imaging device.

  By the way, in this type of optical disk apparatus, the aberration characteristic of the objective lens that focuses the laser beam on the optical disk affects the recording / reproducing characteristics. In particular, when the optical disk device is driven, heat is generated, and when the optical pickup device is placed in a high temperature environment, spherical aberration occurs in the objective lens due to a change in refractive index due to temperature conditions and a change in wavelength of the light source, The recording / reproducing characteristics are deteriorated.

Hereinafter, an objective lens designed so that the spherical aberration becomes almost zero at room temperature (25 ° C.) will be described as an example. The aspherical surface of this objective lens satisfies the following condition.
R ₁ : radius of curvature of the first surface R ₂ : radius of curvature of the second surface d: lens thickness K ₁ : cone coefficient of the first surface K ₂ : cone coefficient of the second surface A _2i (1): first surface 2i-order aspheric coefficient A _2i (2): 2i-order aspheric coefficient of the second surface l: Cover glass or protective layer thickness W. Refractive index for wavelength 660 nm is 1.578098. D: Working distance n: Refractive index, when f (focal length of lens) is 3.05 mm with respect to wavelength 660 nm,
R ₁ = 1.88056
R ₂ = −9.16061
d = 1.7 mm
l = 0.6
n = 1.540783
W. D = 1.718808
It is.

  Moreover, the coefficient shown by the well-known aspherical formula (1) shown below is shown.

K ₁ = −0.7724
A ₄ (1) = 0.520388E-02
_{A 6 (1) = 0.216731E-} 03
_{A 8 (1) = 0.490875E-} 04
A ₁₀ (1) = − 0.141805E−04
K ₂ = −72.1106
_{A 4 (2) = 0.328614E-} 02
A ₆ (2) = − 0.105921E-02
_{A 8 (2) = 0.155050E-} 03
A ₁₀ (2) = − 0.954978E-05
Note that E represents a power whose base is 10 and the number on the right of E is an exponent. For example, the value of the fourth-order aspheric coefficient on the first surface, [0.520388E-02] is [0 .00520388].

  As shown in FIG. 8, the objective lens 7 has substantially zero spherical aberration when heated to about 25 ° C., and the spherical aberration increases as the temperature rises or falls after 25 ° C. . Therefore, when the optical pickup device provided with the objective lens is used in an optical disc apparatus used in an environment higher than 25 ° C., the spherical aberration deteriorates as the temperature of the objective lens rises to 25 ° C. or higher. It is difficult to maintain good recording / reproduction characteristics.

  In addition, in an optical disc having two signal recording surfaces, such as a DVD (digital versatile disk), an intermediate layer is formed between the first layer and the second layer. The lens is designed in anticipation of the aberration caused by this, and a spot that can be detected is connected even if some aberration occurs. In order to secure a margin to absorb this spherical aberration, the aberration in a high temperature environment It is necessary to suppress the deterioration of characteristics as much as possible.

JP-A-6-76333

  Accordingly, an object of the present invention is to provide an optical pickup device including an objective lens that suppresses the occurrence of aberrations even under a high temperature environment and has good recording / reproducing characteristics, and an optical disk device including the optical pickup device.

  In order to solve the above-described problems, an optical pickup device according to the present invention includes an objective lens designed to be free of aberration at a predetermined temperature, and holds the objective lens movably in a focusing direction and a tracking direction. The lens holder is provided avoiding the optical path of the objective lens, and has a heating means for heating the objective lens to the predetermined temperature, and the heating means is controlled to maintain the objective lens at a temperature at which no aberration occurs. Temperature control means.

  An optical disk apparatus according to the present invention is an optical disk apparatus that records and / or reproduces information signals with respect to an optical disk. The objective lens is designed to be free of aberration at a predetermined temperature, and the objective lens is in a focusing direction. And a lens holder that is movably held in the tracking direction and is provided so as to avoid the optical path of the objective lens, and has a heating means for heating the objective lens to the predetermined temperature, and a temperature at which the objective lens is free from aberrations. And an optical pickup device for recording and / or reproducing information signals with respect to the optical disc.

  According to the optical pickup device and the optical disk device using the same according to the present invention, even when the temperature of the objective lens fluctuates due to the usage environment of the optical pickup device and the aberration characteristics fluctuate, the temperature control means provides the lens holder. The heating means can maintain the temperature of the objective lens at a predetermined temperature. As a result, the optical pickup device and the optical disk device using the same can suppress the spherical aberration of the objective lens to the minimum, and realize good recording / reproducing characteristics.

  Hereinafter, an optical pickup apparatus to which the present invention is applied and an optical disk apparatus using the same will be described in detail with reference to the drawings. As shown in FIG. 1, the optical pickup device 1 includes a semiconductor laser 3 that emits laser light, a photodiode IC 4 that forms a light receiving element made of a photodiode, and a beam splitter 5, and further includes a beam splitter. A grating 6 for performing a so-called three-spot method is disposed between 5 and the semiconductor laser 3. In addition, above the beam splitter 5 and on the optical path of the laser light, an objective lens 7 that condenses the laser light LF emitted from the semiconductor laser 3 onto the optical disk 8 and a lens holder 9 that holds the objective lens 7. Is arranged.

  Laser light LF emitted from the semiconductor laser 3 is reflected by the surface of the beam splitter 5, converged by the objective lens 7, and reflected by the signal recording surface of the optical disk 8. The returned laser light LR is again directed to the beam splitter 5 through the objective lens 7, refracted at the surface of the beam splitter 5, passes through the inside of the beam splitter 5, and is condensed on the photodiode IC 4. The beam splitter 5 is set with the position, angle, and transmittance of the laser beam at the surface so that the outgoing light LF and the return light LR travel as described above.

  The objective lens 7 is a single lens made of, for example, optical glass, and has a first surface and a second surface in order from the optical disk 8 side. The objective lens 7 is an aspherical lens having positive power in which both the first surface and the second surface are convex surfaces. The objective lens 7 has a flange portion 7a formed on a side surface perpendicular to the optical axis direction, and the flange portion 7a is held by the lens holder 9 by being supported by a lens holding portion 10 of the lens holder 9 described later. ing.

  The objective lens 7 is designed so as to eliminate spherical aberration when heated to a predetermined temperature. That is, the objective lens 7 is heated by a heating coil wound around a lens holder 9 to be described later, and is designed so as to eliminate spherical aberration by being set to 60 ° C., for example. Accordingly, even when the optical disk device incorporating the optical pickup device 1 is driven to heat and the objective lens 7 is heated and the aberration characteristics are changed, the objective lens 7 has the lens holder 9. Since the spherical aberration is made zero by being heated by the heating coil wound around, good recording / reproducing characteristics can be maintained even when the temperature environment changes.

Among such objective lenses 7, an aspheric surface of the objective lens 7 whose spherical aberration becomes zero by being heated to 60 ° C. satisfies the following condition.
R ₁ : radius of curvature of the first surface R ₂ : radius of curvature of the second surface d: lens thickness K ₁ : cone coefficient of the first surface K ₂ : cone coefficient of the second surface A _2i (1): first surface 2i-order aspheric coefficient A _2i (2): 2i-order aspheric coefficient of the second surface l: Cover glass or protective layer thickness W. Refractive index for wavelength 660 nm is 1.578098. D: Working distance n: Refractive index, when f (focal length of lens) is 3.05 mm with respect to wavelength 660 nm,
R ₁ = 1.87378
R ₂ = -8.90155
d = 1.7 mm
l = 0.6
n = 1.5372
W. D = 1.702853
It is.

Moreover, when the coefficient shown in the known aspherical expression (1) is shown,
K ₁ = −0.77162
A ₄ (1) = 0.523693E-02
A ₆ (1) = 0.216936E-03
_{A 8 (1) = 0.496810E-} 04
A ₁₀ (1) = − 0.143369E-04
K ₂ = −68.6955
A ₄ (2) = 0.328227E-02
A ₆ (2) = − 0.1006204E-02
_{A 8 (2) = 0.156495E-} 03
A ₁₀ (2) = − 0.970625E-05
As shown in FIG. 2, the objective lens 7 has substantially zero spherical aberration when heated to about 60 ° C., and the spherical aberration increases as the temperature rises or falls at 60 ° C. as a boundary. .

  As shown in FIG. 3, the lens holder 9 that holds the objective lens 7 includes a lens holding unit 10 that holds the objective lens 7 and a tracking coil winding around which a tracking coil that moves the objective lens 7 in the tracking direction is wound. A heating portion 13, a focusing coil winding portion 12 around which a focusing coil for moving the objective lens 7 in the focusing direction is wound, and a heating coil 13 that constitutes a heating means for heating the objective lens 7. And a coil winding portion 14.

  The lens holding portion 10 is formed with a support surface 10a that supports the flange portion 7a of the objective lens 7 around the optical path of the emitted light from the semiconductor laser 3 opened vertically and the return light from the optical disc 8. The lens holding portion 10 supports the flange portion 7a of the objective lens 7 with the support surface 10a, thereby holding the first surface and the second surface of the objective lens 7 on the optical path of the laser light.

  A heating coil winding portion 14 around which a heating coil 13 for heating the objective lens 7 is wound is formed on the support surface 10 a of the lens holding portion 10. The heating coil winding portion 14 is formed by intermittently standing a plurality of winding walls 15 around which the heating coil 13 is wound along the outer surface of the objective lens 7. When the heating coil 13 is wound around the winding wall 15, the heating coil winding unit 14 is configured so that the outer surface of the objective lens 7 held by the lens holding unit 10 is shown in FIGS. 4 and 5. The objective lens 7 can be heated by being brought into contact with the flange portion 7a formed in the above.

  Specifically, in the lens holder 9, after the heating coil 13 for heating the objective lens 7 is wound around the heating coil winding portion 14, the flange portion 7 a of the objective lens 7 is placed on the heating coil 13. It is held so as to be placed. As shown in FIG. 5, since the heating coil 13 is brought into contact with the lower side of the flange portion 7a, the objective lens 7 is heated to a predetermined temperature when the heating coil 13 is conducted.

  If the heating coil 13 is formed on a flexible substrate (not shown) disposed on the support surface 10a of the lens holding portion 10, there is no need to provide the winding wall 15 of the heating coil winding portion 14, and light Space saving, size reduction, and weight reduction of the pickup device 1 can be achieved.

  FIG. 6 shows a servo mechanism of the optical pickup device 1 that drives the lens holder 9. As shown in FIG. 6, in the optical pickup device 1, a focus error signal is output from the focus error signal generation unit 20 to the focus servo circuit 21 when recording or reproduction processing is being performed. Then, the lens holder 9 is moved in the focusing direction in which the focal position of the laser beam is brought close to and away from the optical disc 8 based on the drive signal generated by the focus servo circuit 21 that has received the focus error signal. Specifically, the focus servo circuit 21 forms a servo loop in which negative feedback is formed so that the focus error signal becomes 0, and drives the lens holder 9.

  In the optical pickup device 1, the tracking error signal is output from the tracking error signal generation unit 22 to the tracking servo circuit 23. The lens holder 9 is moved in the tracking direction orthogonal to the recording track of the optical disk 8 based on the drive signal generated by the tracking servo circuit 23 that has received the tracking error signal. Specifically, the tracking servo circuit 23 forms a servo loop in which negative feedback is formed so that the tracking error signal becomes 0, and drives the lens holder 9.

  In the optical pickup device 1, a tilt error signal is output from the tilt error signal generation unit 24 that detects the tilt of the optical disk 8 to the tilt servo circuit 25. The lens holder 9 is tilt-controlled so that the optical beam is irradiated perpendicularly to the optical disk 8 based on the drive signal generated by the tilt servo circuit 25 that has received the tilt error signal.

  Further, in the optical pickup device 1, a heating signal is output from the temperature control unit 26 that detects the temperature of the objective lens 7 to the objective lens heating servo circuit 27. The objective lens 7 is maintained at a predetermined temperature, for example, 60 ° C., when the heating coil 13 wound around the lens holder 9 is energized.

  According to such an optical pickup device 1, even when the optical disk device incorporating the optical pickup device is used in a high temperature environment and the aberration characteristics fluctuate due to an increase in the temperature of the objective lens 7, the temperature The heating coil 13 wound around the lens holder 9 is turned on by the control unit 26 and the objective lens heating servo circuit 27, and the objective lens 7 can be heated and maintained at 60 ° C., which is higher than the temperature of the optical disk device. . Thereby, the optical pickup device 1 can suppress the spherical aberration of the objective lens 7 to the minimum, and can realize good recording / reproducing characteristics.

  Further, the lens holder 9 is configured such that after the objective lens 7 is placed on the lens holding unit 10, the heating coil 13 is wound around the heating coil winding unit 14 and heated above the flange portion 7 a of the objective lens 7. The working coil 13 may abut. As shown in FIG. 7, since the heating coil 13 is brought into contact with the upper side of the flange portion 7a, the objective lens 7 is heated to a predetermined temperature when the heating coil 13 is conducted.

  In the optical pickup device 1 having such a configuration, since the heating coil 13 is wound so as to contact the upper portion of the flange portion 7a, the objective lens 7 is rattled on the lens holding portion 10 of the lens holder 9. It can be attached with high accuracy without any problems. Further, since the heating coil 13 is located between the objective lens 7 and the optical disk 8, it is possible to prevent the objective lens 7 and the optical disk 8 from directly colliding with each other.

  The optical pickup device 1 using the objective lens 7 designed to be free of aberrations at 60 ° C. has been described above. However, the objective lens 7 of the optical pickup device 1 to which the present invention is applied is incorporated in the optical pickup device 1. Depending on the use environment of the optical disk device, a temperature at which no aberration occurs at a temperature higher than the temperature of the optical disk device can be selected. For example, in an in-vehicle disc recording and / or reproducing apparatus, the temperature of the apparatus main body rises to about 70 ° C. to 80 ° C. Therefore, the objective lens is designed to have no aberration at 80 ° C. and is constantly heated to 80 ° C. Therefore, it is possible to suppress deterioration of aberration characteristics and maintain good recording / reproducing characteristics.

  The optical pickup device and the optical disk device to which the present invention is applied may be applied to an optical pickup device for a magneto-optical disk and a magneto-optical disk device in addition to an optical disk used as a recording medium.

It is a figure which shows the structure of the optical pick-up apparatus to which this invention was applied. It is a graph which shows the relationship between the temperature of the objective lens of an optical pick-up apparatus with which this invention was applied, and spherical aberration. It is a perspective view which shows the lens holder holding an objective lens. It is a top view which shows the lens holding part with which the objective lens was hold | maintained. It is sectional drawing which shows the lens holder with which the objective lens was attached. It is a block diagram which shows the servo mechanism which drives a lens holder. It is sectional drawing which shows the other example of a lens holder. It is a graph which shows the relationship between the temperature of a conventional objective lens, and spherical aberration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up apparatus, 7 Objective lens, 8 Optical disk, 9 Lens holder, 10 Lens holding part, 13 Heating coil, 14 Heating coil winding part, 15 Winding wall, 26 Temperature control part, 27 Objective lens heating servo circuit

Claims (6)

An objective lens designed to be free of aberrations at a given temperature;
A lens holder that holds the objective lens movably in a focusing direction and a tracking direction, has a heating means provided to avoid the optical path of the objective lens, and heats the objective lens to the predetermined temperature;
An optical pickup device comprising temperature control means for controlling the heating means so as to keep the objective lens at a temperature at which no aberration occurs.   2. The optical pickup device according to claim 1, wherein the objective lens is designed to be free from aberrations at a temperature higher than the temperature of the optical pickup device during driving.   3. The optical pickup device according to claim 2, wherein the objective lens is designed to be free from aberrations when heated to 60.degree. In an optical disc apparatus for recording and / or reproducing information signals with respect to an optical disc,
An objective lens designed to be free of aberrations at a predetermined temperature, the objective lens is movably held in a focusing direction and a tracking direction, and is provided to avoid the optical path of the objective lens. And a temperature control means for controlling the heating means so as to maintain the objective lens at a temperature at which no aberration occurs, and recording an information signal on the optical disc and / or An optical disc device including an optical pickup device for performing reproduction.   5. The optical disc apparatus according to claim 4, wherein the objective lens is designed to be free of aberrations at a temperature higher than the temperature of the optical pickup device during driving.   6. The optical disc apparatus according to claim 5, wherein the objective lens is designed to be free from aberrations when heated to 60.degree.

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