JP4162949B2 - Optical information recording / reproducing head device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical information recording / reproducing head apparatus that guides a light beam emitted from a light source onto an optical disc, and records, reproduces, and erases optical information.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an optical information recording / reproducing head device is a device that records, reproduces, and erases information on an optical disc by irradiating a laser beam onto an optical disc, which is a recording medium, and detecting the polarization state of the reflected light. It is.
[0003]
In recent years, the density of optical disks has been increasing, and various optical recording media have been proposed. Conditions for increasing the density of the optical disk include shortening the wavelength of the semiconductor laser, which is a light source, and increasing the NA of the objective lens that focuses the laser beam on the pits. By achieving these two conditions, it is possible to irradiate a smaller spot on the optical disc. Therefore, even if the information written on the optical disk is made smaller, the information can be processed. As a result, the density of the optical disk can be increased.
[0004]
However, as the wavelength of semiconductor lasers as in recent years is shortened and the NA of objective lenses is increased, spherical aberration due to various errors (for example, the thickness of the optical disk is not uniform) is more easily It will occur more greatly. Even in the case of an error that does not cause a problem when using a conventional optical disk, spherical aberration easily easily occurs in a recent high-density optical disk, and the SN ratio of a reproduced signal is greatly deteriorated. It becomes a problem.
[0005]
Therefore, a beam expander is generally provided between the light source and the objective lens as a mechanism for correcting the spherical aberration of the high-density optical disc. When spherical aberration is detected by a sensor or the like, the beam expander changes the lens interval, and as a result, this spherical aberration is corrected.
[0006]
However, when the beam expander changes the lens interval, the diffused light and the convergent light are emitted toward the objective lens in addition to the parallel light depending on the lens interval, so that the NA changes. Further, even if an aperture is provided in order to prevent a change in NA, the amount of light incident on the objective lens changes because the aperture scatters light depending on the state of light. Since the amount of light of the beam changes, the polarization state of the light reflected from the pits also changes, making it difficult to read and write from the optical disc well. In order to solve this problem, a method of controlling the output of the semiconductor laser so as to keep the light quantity of the beam incident on the objective lens substantially constant is used.
[0007]
[Problems to be solved by the invention]
However, as described above, when the output of the semiconductor laser is controlled so as to keep the amount of light incident on the objective lens substantially constant, such a mechanism must be provided inside the apparatus. As a result, the apparatus becomes larger, the configuration becomes complicated, and the cost increases.
[0008]
Accordingly, in view of the above circumstances, the present invention can perform good reading and writing from an optical disk without controlling the output of a semiconductor laser, and therefore, downsizing, simplification, and cost reduction of the apparatus can be achieved. It is an object of the present invention to provide an optical information recording / reproducing head device capable of performing the following.
[0009]
[Means for Solving the Problems]
The optical information recording and reproducing head apparatus according to an embodiment of the present invention to solve the above problem, a light beam emitted from the light source guided on an optical disk by the objective lens, the recording of optical information, related to an apparatus for performing reproduction, or erasure It is a thing. The optical information recording / reproducing head device is disposed between a light source and an objective lens, and includes at least two of a first lens group disposed on the objective lens side and a second lens group disposed on the light source side. An aberration correction optical system having two lens groups, which has an aberration correction optical system that corrects spherical aberration generated on an optical disk by changing the divergence or convergence of light . The objective lens principal point of the objective lens is arranged to be positioned substantially at the focal position of the first lens group of the objective lens side. By disposing each optical element in this way, even when diffused light or convergent light is emitted from the aberration correction optical system toward the objective lens, the first lens group has a substantially focal position on the objective lens side. Since the principal point of the objective lens is located, the beam diameter formed on the principal point of the objective lens is substantially constant regardless of the state of the beam emitted from the aberration correction optical system. As a result, it is possible to suppress a change in the light amount of the spot used for reading and writing on the optical disk, and it is possible to read and write from the optical disk satisfactorily.
[0010]
Here, the aberration correction optical system moves at least one lens group of the first lens group and the second lens group to vary the distance between the first lens group and the second lens group. It is good also as a structure which changes the divergence degree or convergence degree of light.
[0011]
Further, the optical information recording / reproducing head device according to the present invention may have a configuration in which an aperture is disposed in the vicinity of the objective lens. When the objective lens is arranged so that the principal point of the objective lens is located at the focal position of the first lens group, the aperture can be arranged at an arbitrary position , for example, in the vicinity of the objective lens . As a result, the degree of freedom in design is improved.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a perspective view showing a configuration of an optical information recording / reproducing head device 100 according to an embodiment of the present invention. The optical information recording / reproducing head device 100 is generally composed of a light source unit 10, a pickup unit 50, a spindle motor 90, and a fixed table 91.
[0013]
FIG. 2 is a perspective view showing a configuration of the light source unit 10 according to the embodiment of the present invention. The light source unit 10 includes a laser diode 11, a collimator lens 12, a first anamorphic prism 13, a second anamorphic prism 14, a mirror 15, a right angle prism 16, a Wollaston prism 17, and a condenser lens 18. And the composite sensor 19.
[0014]
The laser diode 11 is a semiconductor laser that emits divergent laser light having an elliptical cross section. The divergent laser light from the laser diode 11 is emitted toward the collimator lens 12.
[0015]
The collimator lens 12 converts the divergent laser light incident from the laser diode 11 into a parallel light beam. The converted parallel light flux is emitted toward the first anamorphic prism 13.
[0016]
The first anamorphic prism 13 and the second anamorphic prism 14 shape the parallel light beam incident from the collimator lens 12 into a parallel light beam having a substantially circular cross-sectional shape. The shaped parallel light beam is emitted toward the mirror 15.
[0017]
The mirror 15 bends the parallel light beam incident from the second anamorphic prism 14 by 90 degrees and guides it to the pickup unit 50. And this parallel light beam injects into the SA correction | amendment lens part 61 which the lens actuator part 60 has as shown in FIG.
[0018]
FIG. 3 is a cross-sectional view of the lens actuator unit 60 according to the embodiment of the present invention. This cross-sectional view is a view cut by a plane including the optical axis from the light source unit 10 to the objective lens 66 shown in FIG. . The lens actuator unit 60 includes an SA (Spherical aberration) correction lens unit 61, a carriage 63, a right-angle prism 64, a biaxial actuator 65, and an objective lens 66.
[0019]
The SA correction lens unit 61 includes a beam expander 62. The beam expander 62 is an optical system that corrects spherical aberration. In the embodiment of the present invention, the beam expander 62 includes a first lens group 62a in which one positive lens and one negative lens are bonded together, and one negative lens. The second lens 62b is configured. The first lens group 62a is held by the first lens frame 61a, and the second lens 62b is held by the second lens frame 61b. The first lens frame 61 a is fixed to a carriage 63 that is an outer frame of the lens actuator unit 60. The first lens frame 61a and the second lens frame 61b are respectively screwed with helicoids 61A and 61B, and the helicoids cause the second lens frame 61b to move the beam expander 62 relative to the first lens frame 61a. It can move in the direction of arrow A parallel to the optical axis.
[0020]
FIG. 4 is a diagram showing the state of the light flux at various intervals between the first lens group 62a and the second lens 62b according to the embodiment of the present invention. In order to simplify the drawing, the SA correction lens unit 61 and the objective Only the lens 66 and the optical disc 200 are shown. As the second lens frame 61b moves in the direction of arrow A, the distance between the first lens group 62a and the second lens 62b changes. As shown in FIG. 4A, when the second lens frame 61b is at the reference position that is a design value, the beam expander 62 converts the parallel light beam incident from the light source unit 10 into the objective lens 66 as an expanded parallel light beam. Inject towards.
[0021]
When excessive spherical aberration occurs on the recording surface of the optical disk due to an error in the thickness of the optical disk 200, the second lens 62b is moved from the reference position toward the first lens group 62a as shown in FIG. 4B. The beam expander 62 emits the parallel light beam incident from the light source unit 10 toward the objective lens 66 as a divergent light beam. When the light beam incident on the objective lens 66 changes from a parallel light beam to a divergent light beam, the spherical aberration generated in the objective lens 66 changes in the under direction, so that the spherical aberration on the optical disk recording surface can be corrected.
[0022]
When under spherical aberration occurs on the optical disk recording surface, the second lens 62b moves away from the first lens group 62a from the reference position as shown in FIG. Emits the parallel light beam incident from the light source unit 10 toward the objective lens 66 as a convergent light beam. In this case, since the spherical aberration generated in the objective lens 66 changes in the over direction, the spherical aberration on the optical disk recording surface can be corrected.
[0023]
The light beam emitted from the beam expander 62 is bent 90 degrees by a right-angle prism 64 fixed to the carriage 63 and travels toward the objective lens 66. The objective lens 66 is fixed to the biaxial actuator 65.
[0024]
The biaxial actuator 65 causes the objective lens 66 to move in the direction of the arrow B (focus direction) parallel to the optical axis of the objective lens 66 and the arrow C perpendicular to the optical axis of the objective lens 66 according to the detection result of the composite sensor 19 described later. In the direction (tracking direction). The biaxial actuator 65 has an aperture 65a in the vicinity of the objective lens 66 on the SA correction lens unit 61 side. The aperture 65a is a convex portion formed on the biaxial actuator 65 and has a diaphragm function (fixed diaphragm).
[0025]
As shown in FIG. 4, the objective lens 66 is disposed so that the principal point 66a of the objective lens 66 is positioned on the focal point f on the objective lens 66 side of the first lens group 62a. Therefore, in any state of FIGS. 4A to 4C, the light beam incident from the SA correction lens unit 61 always has a constant beam diameter d on the principal point 66a of the objective lens 66. As a result, a change in the light amount of the spot used for reading and writing on the optical disc 200 can be substantially suppressed, and the spot profile (intensity distribution) can be made substantially constant. Writing can be performed.
[0026]
The optical disc 200 is set on the fixed table 91 shown in FIG. 1 and is rotated about the rotation shaft 90a by the spindle motor 90. As the optical disc 200 rotates, the optical information recording / reproducing head device 100 can read and write information on the optical disc 200. Further, the linear motor unit 70 can move the lens actuator unit 60 in the tracking direction.
[0027]
The spot light irradiated on the optical disc 200 is reflected and enters the light source unit 10 as return light via the lens actuator unit 60. Then, the return light is bent 90 degrees by the mirror 15 and guided to the second anamorphic prism 14, and by the half mirror 13 a provided between the first anamorphic prism 13 and the second anamorphic prism 14. It is bent 90 degrees, guided to the right-angle prism 16, further bent 90 degrees by the right-angle prism 16, and emitted to the Wollaston prism 17.
[0028]
The Wollaston prism 17 is a polarizing prism. In the embodiment of the present invention, the return light incident from the right-angle prism 16 is separated into three light beams having different polarization directions. Then, the three separated light beams are emitted toward the composite sensor 19 via the condenser lens 18.
[0029]
The composite sensor 19 includes a servo light receiving element and a data light receiving element (not shown). These light receiving elements are arranged on the same plane orthogonal to the return light emitted from the right-angle prism 16. Two of the three light beams separated by the Wollaston prism 17 are received by the data light receiving element, and are processed as information on the optical disc 200.
[0030]
The remaining one of the light beams separated by the Wollaston prism 17 is received by the servo light receiving element. The output of the light receiving element for servo is subjected to arithmetic processing by an arithmetic unit (not shown) and detected as a focus error signal and a tracking error signal.
[0031]
When the focus error signal is detected, the biaxial actuator 65 moves the objective lens 66 in the focus direction so as to correct this error, and when the tracking error signal is detected, the tracking direction so as to correct this error. The objective lens 66 is moved. Therefore, the principal point 66a of the objective lens 66 deviates from the focal point f on the objective lens 66 side of the first lens group 62a. However, since the amount of movement of the position of the objective lens 66 due to these error signals is very small, the change in the light amount of the spot in this case is not a problem in practice.
[0032]
The above is the embodiment of the present invention. The present invention is not limited to these embodiments and can be modified in various ranges.
[0033]
In the above embodiment, the spherical aberration is corrected by moving the second lens 62b away from the objective lens 66. However, the first lens group 62a may be moved to correct the spherical aberration. . However, in this case, the focal position of the second lens group 62a changes, but since the amount of change is very small, there is no practical problem.
[0034]
【The invention's effect】
As described above, in the optical information recording / reproducing head device of the present invention, the objective lens is disposed so that the principal point of the objective lens is located in the vicinity of the focal position of the lens on the objective lens side of the aberration correction optical system. Therefore, the beam diameter formed on the principal point of the objective lens is always substantially constant. As a result, a change in the amount of light of a spot used for reading and writing on an optical disk can be substantially suppressed, and a spot profile (intensity distribution) can be made substantially constant, so that good reading and writing can be performed. It can be performed.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a configuration of an optical information recording / reproducing head device according to an embodiment of the present invention.
FIG. 2 is a perspective view illustrating a configuration of a light source unit according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view of a lens actuator portion according to an embodiment of the present invention.
FIG. 4 is a diagram illustrating a state of light beams at various intervals between the first lens group and the second lens according to the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Light source part 50 Pickup part 60 SA correction lens part 62 Beam expander 66 Objective lens 100 Optical information recording / reproducing head apparatus 200 Optical disk

Claims (3)

In an optical information recording / reproducing head device that guides a light beam emitted from a light source onto an optical disk by an objective lens, and records, reproduces, or erases optical information.
An aberration having at least two lens groups, a first lens group disposed between the light source and the objective lens and disposed on the objective lens side, and a second lens group disposed on the light source side A correction optical system having an aberration correction optical system that corrects spherical aberration generated on an optical disk by changing the divergence or convergence of light,
The objective lens, said that the main point of the objective lens is arranged to be positioned substantially at the focal position of the objective lens side first lens group, an optical information recording and reproducing head apparatus according to claim. The aberration correcting optical system, the first of the lens group and moving at least one lens group of the second lens group, varying the distance between said first lens group and the second lens group 2. The optical information recording / reproducing head device according to claim 1, wherein the degree of light divergence or convergence is changed accordingly. 3. The optical information according to claim 1, wherein an aperture is disposed between the first lens group and the objective lens and in the vicinity of the objective lens. 4. Recording / reproducing head device.

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