JP3766524B2 - Optical system for optical information recording / reproducing head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical system for an optical information recording / reproducing head.
[0002]
[Problems to be solved by the invention]
Recently, development of a magneto-optical disk apparatus having a surface recording density exceeding 10 Gbit / (inch) ² is in progress. In this apparatus, for example, the incident angle of the laser beam with respect to the objective optical system provided at the tip of a coarse motion arm that rotates, for example, in a direction intersecting the track of the magneto-optical disk is finely adjusted by a deflecting means such as a galvo mirror. It is considered that the tracking is performed accurately at a narrow track pitch level of 0.34 μm, for example. In this case, if the rotation axis of the deflecting mirror is tilted, the light spot on the magneto-optical disk moves, for example, in the tangential direction (track tangential direction) with fine movement tracking, and as a result, the jitter component is included in the reproduced signal. Has occurred and the signal quality is degraded.
[0003]
[Means for Solving the Problems]
The present invention has been made in view of the above-described background. The invention of claim 1 is a method in which a light beam emitted from a laser light source is converted into a parallel light beam and then incident on an objective optical system via a deflecting unit. An optical system of an optical information recording / reproducing apparatus for focusing on an optical disc, wherein a relay optical system is disposed between the deflecting unit and the objective optical system, and the vicinity of the deflecting surface of the deflecting unit and the objective optical system And the principal plane position of the light source is substantially conjugated, and the light beam incident on the deflecting means is converted so that the light beam shape on the deflecting surface is linear in the direction perpendicular to the rotation axis of the deflecting means. In addition, the linear light beam is returned to the original light beam before the linear light beam enters the objective optical system.
[0004]
DETAILED DESCRIPTION OF THE INVENTION
First, recording called near field recording (NFR) technology, which was proposed to meet the increasing demand for external storage devices, especially the demand for large storage capacity, due to recent advances in hardware and software related to computers An outline of a magneto-optical disk recording / reproducing apparatus using a reproducing method will be described with reference to FIGS.
[0005]
FIG. 1 is an overall schematic diagram of the optical disk apparatus. In the disk drive device 1, an optical disk 2 is mounted on a rotating shaft of a spindle motor (not shown). On the other hand, a rotating (coarse movement) arm 3 is attached so as to be parallel to the recording surface of the optical disc 2 in order to reproduce or record information on the optical disc 2. The rotating arm 3 can be rotated about a rotating shaft 5 by a voice coil motor 4. A floating optical head 6 on which an optical element is mounted is mounted on the tip of the rotating arm 3 facing the optical disk 2. Further, a light source module 7 including a light source unit and a light receiving unit is disposed in the vicinity of the rotation shaft 5 of the rotation arm 3, and is configured to be driven integrally with the rotation arm 3.
[0006]
2 and 3 illustrate the tip of the rotating arm 3, and in particular, the floating optical head 6 will be described in detail. The floating optical unit 6 is attached to the flexure beam 8 and is disposed to face the optical disc 2. The flexure beam 8 is fixed to the rotating arm 3 at the other end, and is pressurized in a direction in which the floating optical unit 6 at the tip is brought into contact with the optical disc 2 by the elastic force of the flexure beam 8.
[0007]
The flying type optical unit 6 includes a flying slider 9, an objective lens 10, a solid immersion lens (SIL) 11, and a magnetic coil 12, and converges a parallel laser beam 13 emitted from the light source module 7 onto the optical disk 2. To work. Further, a rising mirror 31 is fixed to the tip of the rotating arm 3 in order to guide the laser beam 13 to the floating optical unit 6. The laser beam 13 incident on the objective lens 10 by the rising mirror 31 is converged by the refraction action of the objective lens 10. A solid immersion lens (SIL) 11 is disposed in the vicinity of the condensing point, and irradiates the optical disc 2 with the convergent light as finer evanescent light 15.
[0008]
A magnetic coil 12 for recording by a magneto-optical recording system is formed around a solid immersion lens (SIL) 11 facing the optical disk 2, and a magnetic field necessary for recording is applied on the recording surface of the optical disk 2. It can be applied.
The evanescent light 15 and the magnetic coil 12 enable high-density recording and reproduction on the optical disc 2. Note that the floating optical unit 6 floats by a minute amount due to the air flow caused by the rotation of the optical disc 2, and follows surface vibration of the optical disc 2. For this reason, the focus control (focus servo) of the objective lens, which was necessary in the conventional optical disc apparatus, is not required.
[0009]
Hereinafter, the light beam guided to the light source module 7 and the floating optical unit 6 mounted on the rotating arm 3 will be described in detail with reference to FIGS. The rotating arm 3 has a floating optical unit 6 mounted at the tip, and a driving coil 16 for driving the voice coil motor 4 is fixed to the other end. The drive coil 16 is a flat coil, and is inserted and disposed in a magnetic circuit (not shown) with a gap. The rotating shaft 5 and the rotating arm 3 are fastened by bearings 17 and 17 so as to be rotatable. When a current is applied to the drive coil, the rotating arm 3 is rotated about the rotating shaft 5 by the electromagnetic action with the magnetic circuit. Can be moved.
[0010]
The light source module 7 mounted on the rotating arm 3 includes a semiconductor laser 18, a laser driving circuit 19, a collimating lens 20, a composite prism assay 21, a laser power monitor sensor 22, a reflecting prism 23, a data detection sensor 24, and tracking detection. A sensor 25 is arranged. The divergent light beam emitted from the semiconductor laser 18 is converted into a parallel light beam by the collimator lens 20. The cross-sectional shape of the parallel light flux is oblong due to the characteristics of the semiconductor laser 18, and it is inconvenient to finely focus the light beam on the optical disk 2, so it is necessary to convert it into a substantially circular cross-section. Therefore, the cross-sectional shape of the parallel light beam is shaped by causing the parallel light beam having an elliptical cross section emitted from the collimator lens 20 to enter the composite prism assay 21.
[0011]
The incident surface 21a of the composite prism assay 21 forms a predetermined slope with respect to the incident optical axis, and the sectional shape of the parallel light beam can be shaped from an oval shape to a substantially circular shape by refracting the incident light. . The shaped laser beam travels through the composite prism assay 21 and enters the first half mirror surface 21b. The first half mirror surface 21b is set to guide the information obtained from the optical disc 2 to the data detection sensor 24 and the tracking detection sensor 25, but the output of the laser emitted from the semiconductor laser 18 in the forward path. It plays the role of separating the light flux to the laser power monitor sensor 22 for detecting the power.
[0012]
Since the laser power monitor sensor 22 outputs a current proportional to the intensity of the received light, the output of the semiconductor laser 18 can be stabilized by feeding back this output to a laser power control circuit (not shown). The laser beam 13 having a substantially circular cross-sectional shape emitted from the composite prism assay 21 is irradiated to the deflection mirror 26, and the traveling direction of the laser beam 13 is changed. The deflecting mirror 26 is attached to a galvano motor 27 having an axis perpendicular to the paper surface as the center of rotation, so that the laser beam 13 can be swung by a minute angle in a direction parallel to the paper surface.
[0013]
The galvano motor 27 is provided with a deflection mirror position detection sensor 28 for detecting the rotation angle of the deflection mirror 26. The laser light beam 13 reflected by the deflection mirror 26 passes through the first relay lens 29 and the second relay lens (imaging lens) 30 and is reflected by the rising mirror 31 to reach the floating optical unit 6. The first relay lens 29 and the second relay lens 30 have a conjugate relationship between the reflecting surface of the deflecting mirror 26 and the pupil plane (main plane) of the objective lens 10 arranged in the floating optical unit 6. Thus, a relay lens optical system is formed. That is, when the focused beam on the optical disc 2 slightly deviates from a predetermined track, the laser beam 13 incident on the objective lens 10 is tilted by slightly rotating the deflection mirror 26 to move the focal point on the optical disc 2. To correct. However, when the focus is corrected by this method, if the optical distance between the deflecting mirror 26 and the objective lens 10 is long, the amount of movement of the laser beam 13 incident on the objective lens 10 becomes large, and can enter the objective lens 10. It may disappear.
[0014]
In order to avoid such a phenomenon, the first relay lens 29 and the second relay lens 30 set the relationship between the reflection surface of the deflection mirror 26 and the pupil surface of the objective lens 10 to be a conjugate relationship, Even when the deflection mirror 26 rotates, the laser beam 13 incident on the objective lens 10 does not move, and accurate tracking control is possible. Note that the access operation over the inner circumference / outer circumference of the optical disk 2 is performed by rotating the rotating arm 3 by the voice coil motor 4, and only the very small tracking control is performed by rotating the deflection mirror 26.
[0015]
The return laser beam 13 that has been reflected back from the optical disk 2 travels in the opposite direction to the forward path, is reflected by the deflection mirror 26, and enters the composite prism assay 21. Thereafter, the light is reflected by the first half mirror surface 21b and travels toward the second half mirror surface 21c. The second half mirror surface 21c generates transmitted light toward the tracking detection sensor 25 and reflected light toward the data detection sensor 24, and separates the laser beam on the return path. The laser beam transmitted through the second half mirror surface 21c is irradiated to the tracking detection sensor 25, and a tracking error signal is output.
[0016]
On the other hand, the laser beam reflected by the second half mirror surface 21 c is polarized and separated by the Wollaston prism 32, converted into convergent light by the condenser lens 33, reflected by the reflecting prism 23, and irradiated on the data detection sensor 24. Is done. The data detection sensor 24 has two light receiving areas, and receives the two polarized beams separated by the Wollaston prism 32, thereby reading the data information recorded on the optical disc 2 and outputting a data signal. More precisely, the tracking error signal and the data signal are generated by a head amplifier circuit (not shown) and sent to a control circuit or an information processing circuit.
[0017]
Next, in the disk drive device configured as described above, if the rotation axis of the deflection mirror 26 is inclined, the beam spot moves on the optical disk 2 in the tangential direction of the track, and a jitter component is generated in the reproduction signal. As a result, the signal quality is lowered.
[0018]
Modifications configured to avoid such problems will be described with reference to FIGS. 6 is a view of the vicinity of the deflection mirror 26 as seen from the direction of the rotation axis of the deflection mirror 26, and FIG. 7 is a cross-sectional view taken along line AA in FIG.
[0019]
In this modification, as shown in FIGS. 6 and 7, a lens 40 is inserted between the composite prism assay 21 and the deflection mirror 26. The lens 40 has power only in the direction of the rotation axis of the deflection mirror 26, and the light beam having a substantially circular cross section emitted from the composite prism assay 21 is reflected on the reflection surface of the deflection mirror 26 with the rotation axis of the deflection mirror 26. It is configured to converge linearly in an orthogonal direction. Further, by using at least one toric aspherical surface for the relay lens system, the linear light beam on the reflecting surface of the deflecting mirror 26 is returned to the original light beam before entering the objective optical system, and various aberrations are obtained. Is configured to correct.
[0020]
For example, as shown in FIGS. 8 and 9, the first relay lens 29 in the above-described embodiment is a toric lens in which the power in the rotation axis direction of the deflection mirror 26 is different from the power in the direction orthogonal to the rotation axis. By replacing it with 29M, it converges linearly on the reflecting surface of the deflecting mirror 26, and when it enters the objective lens 10, it returns to a light beam having a substantially original circular cross section, thereby avoiding the influence of the surface tilt of the deflecting mirror 26. can do.
[0021]
FIG. 8 is a diagram showing the arrangement of the optical system on a plane orthogonal to the rotation axis of the deflection mirror 26, and FIG. 9 shows the arrangement of the optical system on a plane including the rotation axis of the deflection mirror 26. FIG. In order to simplify the drawing, the deflection mirror 26 is represented by a line segment, and the light beam incident on the deflection mirror 26 and the deflected light beam are shown on the same plane.
[0022]
If the focal length of the first relay lens 29M in FIG. 8 is fr1 and the focal length of the second relay lens 30 is fi, the deflection mirror 26, the first relay lens 29M, the second relay lens 30, and the objective lens 10 are used. The intervals are as shown in the figure. In FIG. 8, the reflecting surface of the deflection mirror 26 coincides with the front focal position of the first relay lens 29M, and the rear focal position of the first relay lens 29M and the front focal position of the second relay lens. The position matches. Further, the rear focal position of the second relay lens 30 and the front main plane position of the objective lens coincide. Accordingly, the reflecting surface of the deflection mirror 26 and the main plane of the objective lens are in a conjugate relationship.
[0023]
Assuming that the focal length of the first relay lens 29M in FIG. 9 is fr2, the second relay lens fr2 converges the light beam converged on the reflecting surface of the deflecting mirror 26 by the lens 40 from the first relay lens 29M again by the distance fr1. The value is set to converge at the side 30. On the plane including the rotation axis of the deflecting mirror 26, the rear focal position of the lens 40 coincides with the reflecting surface of the deflecting mirror 26, and the image on the deflecting mirror 26 is reflected by the first relay lens 29M to the second position. It converges to the position of the distance fr1 on the relay lens 30 side. The focal length of the second relay lens 30 is fi in FIG. 9, and therefore the light beam converged by the first relay lens 29M is emitted from the second relay lens 30 as parallel light and travels toward the objective lens 10.
[0024]
With the above configuration, the light beam shape on the reflecting surface of the deflecting mirror is made linear in a direction perpendicular to the rotation axis, and the linear light beam is returned to the original light beam before entering the objective optical system. Therefore, the deflection mirror 26 is not affected by the surface tilt.
[0025]
【The invention's effect】
As described above, according to the configuration of the above modification, the incident angle of the laser beam with respect to the objective optical system provided at the tip of the coarse movement arm moving in the direction intersecting the track of the magneto-optical disk is finely adjusted by the deflection mirror. Thus, in the optical system of the disk drive device that performs fine motion tracking, it is possible to prevent the deflection mirror from being affected by the tilting of the surface.
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic configuration of a magneto-optical disk apparatus according to an embodiment.
FIG. 2 is a view showing a distal end portion of a rotating arm.
FIG. 3 is a cross-sectional view showing a floating optical unit.
FIG. 4 is a plan view showing a deflection mirror and a floating optical unit.
FIG. 5 is a side sectional view of a rotating arm.
6 is a view of the vicinity of the deflection mirror 26 as seen from the direction of the rotation axis of the deflection mirror 26. FIG.
7 is a cross-sectional view taken along line AA in FIG.
FIG. 8 is a diagram illustrating an arrangement of an optical system according to a modified example on a plane orthogonal to the rotation axis of the deflection mirror.
FIG. 9 is a diagram illustrating an arrangement of an optical system according to a modified example on a plane including a rotation axis of the deflection mirror.
[Explanation of symbols]
2 Optical disk 3 Rotating arm 6 Floating optical unit 8 Flexure 26 Deflection mirror 29 First relay lens 29M First relay lens (modification)
30 Second relay lens (imaging lens)

Claims (1)

An optical system of an optical information recording / reproducing apparatus that converts a light beam emitted from a laser light source into a parallel light beam, then enters the objective optical system via a deflecting unit and collects it on an optical disc, the deflecting unit and the objective optical system A relay optical system is arranged between the optical system and the vicinity of the deflecting surface of the deflecting means and the main plane position of the objective optical system so that they are substantially conjugate with respect to the axial direction of the rotation axis of the deflecting means. while, as a linear light beam shape at the deflection surface and converts the light beam incident on the deflecting means in a direction orthogonal to the rotation axis the deflection means, and the linear light beam the objective optical system An optical system of an optical information recording / reproducing head, wherein the linear light beam is returned to the original light beam before entering the optical beam.

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