JP3140515B2 - Optical head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for an information recording / reproducing apparatus using an optical recording medium such as an optical disk or a magneto-optical disk.

[0002]

2. Description of the Related Art Information recording / recording using the optical head described above
In a reproducing apparatus, a laser beam emitted from a light source such as a semiconductor laser is converged by an objective lens and irradiated as a spot on an optical recording medium, and the laser beam reflected by the recording medium and modulated by recording information is used as an object. Information is reproduced by condensing with a lens and detecting with a photodetector. Conventional optical heads require many optical components such as an objective lens, a semiconductor laser, a beam splitter, and a photodetector, so it has been difficult to reduce the size and weight of the optical head.

As one proposal for reducing the size and weight of an optical head, for example, Japanese Patent Application Laid-Open No.
A laser diode, a photodetector and a reflecting surface that reflects the laser beam emitted from the laser diode toward the objective lens and is reflected by the recording medium, and transmits the laser beam condensed by the objective lens through the reflecting surface. There is disclosed an optical head in which a prism leading to a photodetector is integrally provided on a semiconductor substrate, and the semiconductor substrate is attached to a support member together with an objective lens. Thus, by providing the semiconductor substrate and the objective lens fixed to the support means, the positional shift between the objective lens and other optical members is less likely to occur. In such an optical head, it is necessary to perform tracking and focusing in order to correctly record and reproduce information. That is, a tracking error signal and a focusing error signal are detected from the optical information detected by the photodetector, and the tracking actuator and the focusing actuator are driven based on these error signals to drive the objective lens in the tracking direction and the focusing direction. Like that.

In the conventional optical head described in Japanese Patent Application Laid-Open No. 1-273238, the semiconductor substrate integrally provided with the laser diode, the photodetector and the prism and the objective lens are supported as described above. The entire supporting member is driven in a tracking direction and a focusing direction by a tracking actuator and a focusing actuator.

[0005]

As described above, in the conventional optical head, regarding the tracking control,
Although the whole supporting member for supporting the semiconductor substrate and the objective lens is driven in the tracking direction, the weight of the whole supporting member becomes considerably heavy, so that a device capable of generating a large amount of force is required as the tracking driving means. However, there is a disadvantage that the weight becomes large, and in particular, the dimension in the thickness direction becomes large. Also, considering that the driving force is small and light, there is a limit to generating a large driving force. Therefore, the sensitivity of the tracking control cannot be sufficiently increased due to the restriction from the miniaturization, and high-speed control cannot be performed. There were also disadvantages.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical head which eliminates the above-mentioned drawbacks of the prior art and which can reduce the size and weight of a tracking driving means and can perform high-sensitivity and high-speed tracking control. It is.

[0007]

In an optical head according to the present invention, a semiconductor laser light source and a galvanomirror for deflecting a laser beam emitted from the semiconductor laser light source in a tracking direction to perform at least tracking control are integrated with a semiconductor substrate. The semiconductor substrate and an objective lens for irradiating the laser beam deflected by the galvanomirror onto a recording medium are fixed to a holding member, and the holding member is fixed to the base in the optical axis direction of the objective lens. A focusing coil is fixed to the holding member while being movably mounted, and a permanent magnet arranged so as to face the focusing coil is fixed to the base, and the holding member is moved in the optical axis direction with respect to the recording medium surface. It is characterized in that focusing control is performed by driving only.

[0008]

According to the optical head of the present invention,
Since the tracking control is performed by driving the galvanomirror provided on the semiconductor substrate, the tracking driving means can be reduced in size and weight.

[0009]

1 and 2 are a plan view and a sectional view, respectively, showing the structure of a first embodiment of the optical head according to the present invention.
A laser diode 1 for emitting a laser beam, a silicon substrate 5 integrally provided with a galvanometer mirror 2 for deflecting the laser beam in the tracking direction, and photodetectors 3 and 4, a diffraction grating 6 and a hologram 7 The optical unit 9 having the glass block 8 provided with the lens is mounted near one end of the holding member 10. An objective lens 11 and a mirror 12 are fixed near the other end of the holding member 10. The light beam emitted from the optical unit 9 is reflected upward by the mirror 12 and enters the objective lens 11, where it is converged and projected as a minute spot on the optical recording medium 13. The light beam reflected by the recording medium 13 is condensed by the objective lens 11, is reflected by the mirror 12, and enters the optical unit 9.

A holding member 10 for supporting the optical unit 9, the objective lens 11, and the mirror 12 is provided integrally with the base 14 so as to be movable with respect to the base 14 in a focusing direction parallel to the optical axis of the objective lens. Four elastic wires having one end fixed to the raised member 14a and the other end fixed to the holding member 10 are provided. In FIG. 1, the wires arranged on each side of the holding member 10 are indicated by reference numerals 15 and 16, respectively. Further, in order to drive the holding member 10 in the focusing direction, first and second yokes 17 and 18 are attached to the base 14, and one leg of these yokes is fixed to the first and second yokes which are fixed to the holding member. Pass through focusing coils 19 and 20, respectively.

Further, permanent magnets 21 and 22 are fixed to the inner surfaces of the other legs of the yokes 17 and 18, respectively, to generate a magnetic flux passing through the focusing coils 19 and 20. Therefore, when a current corresponding to the focusing error signal is applied to the focusing coils 19 and 20, a force in the focusing direction is generated in the focusing coil, and the holding member 10 is moved in the focusing direction against the elastic force of the wires 15 and 16. To perform focusing control.

FIG. 3 is a plan view showing a detailed configuration of the optical unit 9. A concave portion is formed in the silicon substrate 5, and the laser diode 1 is fixed to the bottom surface so that the laser beam is emitted in the horizontal direction. One side surface of the concave portion is formed as an inclined surface having an angle of approximately 45 degrees. The galvanometer mirror 2 is disposed on the inclined surface, and the galvanometer mirror is rotated about an axis parallel to a tangential direction of an information track formed on the recording medium 13. And a tracking drive electrostatic motor for deflecting the laser beam in the tracking direction. This drive motor will be described later.

The first and second photodetectors 3 and 4 are mounted on the front surface of the silicon substrate 5 so as to sandwich the optical axis.
Each of these photodetectors 3 and 4 has three light receiving elements, and the central light receiving element has a light receiving area divided into three. On the back of the glass block 8,
A diffraction grating 6 is attached, and the laser beam emitted from the laser diode 1 and reflected by the galvanomirror 2 is diffracted. In this example, 0 order, +1 order and -1
The next laser beam is used to read information and to detect a focusing error and a tracking error. The hologram 7 is attached to the surface of the glass block 8. The hologram 7 has a function of a diffraction grating for further diffracting the laser beam reflected by the recording medium 13 and an optical element for giving astigmatism to the laser beam for detecting a focusing error.

The laser beam emitted from the laser diode 1 and reflected by the galvanomirror 2 is diffracted by the diffraction grating 6, and its 0th, + 1st and -1st order beams are taken out, and as shown in FIG. The light is reflected upward, converged by the objective lens 11, and irradiated on the recording medium 13 as three laser beam spots. Of these three laser beam spots, the center spot of the 0th-order beam is located at the center of the information track, and the spots of the + 1st-order beam and the -1st-order beam are located at the left and right edges of the same information track. The three laser beams reflected by the recording medium 13 are condensed by the objective lens 11 and
And is returned to the optical unit 9 again.

In the optical unit 9, the three laser beams are diffracted by the hologram 7 and are given astigmatism. Of the diffracted light beams, the + 1st-order and -1st-order beams are respectively incident on the first and second photodetectors 3 and 4, and the 0th-order beam is not used. The return signal of the 0-order beam diffracted by the diffraction grating 6 is diffracted by the hologram 7 to process the output signal of the central light receiving element for receiving the + 1st-order and -1st-order beams, thereby processing the information signal and the focusing error. The signals are taken out, and the output signals of the light receiving elements at both ends for receiving the +1 order and −1 order beams obtained by diffracting the return beam of the +1 order and −1 order beams diffracted by the diffraction grating 6 by the hologram 7 are obtained. Processing can extract the tracking error signal. A part of the circuit for processing the output signals of the photodetectors 3 and 4 may be formed in the silicon substrate 5. Since the configurations of the photodetectors 3 and 4 and the circuit configuration for extracting these signals are well known, they will not be described in further detail.

FIG. 4 shows an example of the configuration of a tracking drive motor for driving the galvanometer mirror 2. FIG.
As shown in A, the surface of the silicon substrate 5 is selectively etched to form a mirror base 2b rotatably supported by a rotation shaft 2a, and the surface of the mirror base is coated with a reflection film 2c. I do. Also, as shown in FIG. 4B, an electrode 2d is formed on the back surface of the mirror base 2b, and two opposing electrodes 2e and 2f are opposed to this electrode.
Is provided on the surface of the silicon substrate. Therefore, the electrode 2d
Voltage E1 is applied between the electrode 2d and the electrode 2d.
By applying a voltage E2 between the electrode and the counter electrode 2f, an attractive force acts between these electrodes,
The mirror base 2 can be selectively applied by applying this voltage.
b rotates around the rotation shaft 2a. As described above, the mirror base is rotated about the rotation axis 2a extending in the direction parallel to the tangential direction of the information track on the recording medium 13 by the tracking drive unit also called an electrostatic motor. The laser beam can be deflected in the tracking direction, so that the voltage E1 or E2 is applied to the electrode 2d based on the tracking error signal.
The tracking control can be performed by applying the voltage between the electrode 2d and the counter electrode 2e or between the electrode 2d and the counter electrode 2f.

As described above, in the optical head according to the present invention, the silicon substrate 5 on which the laser diode 1, the galvanometer mirror 2, and the photodetectors 3 and 4 are integrally provided.
Optical unit 9, including objective lens 11, mirror 1
2 are supported by the holding member 10 and the focusing coils 19 and 2 displace the holding member in the focusing direction.
Focusing control is performed by driving in a focusing direction by a focusing driving means including a motor 0, yokes 17 and 18, and permanent magnets 21 and 22, and the galvano mirror 2 is controlled by an electrostatic motor type driving means provided on the silicon substrate 5 for tracking control. Since the driving is performed in the tracking direction, the tracking control is performed by driving the extremely small galvanometer mirror 2 by the electrostatic motor, so that the tracking driving means can be made small and lightweight, and as a result, the tracking control can be performed. Control sensitivity and responsiveness can be improved. In addition, the drive axis for focusing control and the drive axis for tracking control are independent of each other, so that the focusing drive and the tracking drive do not interfere with each other, and accurate focusing control and tracking control are performed. Can be.

FIG. 5 shows the configuration of a second embodiment of the optical head according to the present invention. In this example, the same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted because they are duplicated. In this example, a silicon substrate 5 integrally provided with a laser diode 1, a galvanometer mirror 2, and a photodetector 30 is provided on the upper surface of a holding member 10. By providing the silicon substrate 10 on the upper surface in this manner, heat radiation characteristics are improved. Further, the optical unit 9 is further provided with a prism 31, and the laser diode 1 is provided.
The laser beam emitted from the prism is reflected by the reflecting surface of the prism, and then is incident on the galvanometer mirror 2. After the laser beam reflected by the galvanometer mirror 2 is directed in the horizontal direction by the mirror 32 fixed to the holding member 10, the reflection surface 33a fixed to the holding member 10 at an angle of 45 degrees with respect to the horizontal plane. To the aspherical objective lens 33 having Then, the lens surface 33
The light is focused on the recording medium 13 in b.

The return laser beam from the recording medium 13 is condensed by the objective lens 33, is deflected in the horizontal direction by the reflection surface 33a, enters the mirror 32, enters the prism 31 via the galvanometer mirror 2, and enters the prism 31. After being reflected by the reflection surface, the light is incident on the photodetector 30. The holding member is supported by the pair of elastic members 34 so as to be displaceable in the focusing direction with respect to the base 14. Driving means for driving the holding member 10 in the focusing direction includes a yoke 17 fixed to the base 14,
18, focusing coils 19 and 20 fixed to the holding member so as to pass through the legs of the respective yokes, and permanent magnets 21 and 22 fixed to the other legs of the yoke. They are only different.

FIG. 6 shows the configuration of a third embodiment of the optical head according to the present invention. In this example, the same parts as those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. In this example, an optical unit 9 having a silicon substrate 5 integrally provided with a light source, a galvanometer mirror, and a photodetector, and an aspheric objective lens 33 having a reflection surface are attached to a holding member 10.
The wires 15 and 16 (only one wire 15 is visible in FIG. 6) are supported so as to be displaceable in the focusing direction. In this case, the position where one end of each of the wires 15 and 16 is connected to the holding member 10 is made to coincide with the position of the center of gravity of the holding member. With this configuration, when the holding member 10 is driven in the focusing direction, undesired rotation of the holding member can be suppressed.

FIG. 7 shows the structure of an optical head according to a fourth embodiment of the present invention. Also in this example, the same parts as those in the previous example are denoted by the same reference numerals, and detailed description thereof will be omitted. Optical unit 9, mirror 31, and reflecting surface 3
An aspherical objective lens 33 having a 3a is mounted on the holding member 10, and the holding member is supported by a wire so as to be displaceable in the focusing direction with respect to the base 14, and a focusing coil, a yoke, and a permanent magnet are provided for driving in the focusing direction. This embodiment is the same as the third embodiment in that a focusing drive means is provided. Although not shown in the previous example, the base 14 is configured to move in the tracking direction to perform a seek to a desired track. In this example, not only the galvanomirror provided in the optical unit 9 is rotated around the tangential direction of the information track as an axis to perform tracking control, but also can be displaced in a direction perpendicular to the surface of the galvanomirror. Is changed to perform focusing control.

FIGS. 8A and 8B are a sectional view and a plan view showing the structure of the galvanomirror 41 constructed so as to be displaceable in the tracking direction and the focusing direction. Also in this example, the silicon substrate is selectively etched, and the mirror base 4 connected to the silicon substrate via the connecting portions 41a and 41b extending in the tangential direction of the information track.
1c is provided, and a reflecting surface 41d is attached to the surface of the mirror base. Front electrodes 42a and 42b are provided on the front surface of the mirror base 41c, and rear electrodes 43a and 43b are provided on the rear surface.
b are provided, and the front facing electrodes 44a, 44b and 45
a and 45b are provided.

A voltage E1 is applied between the front electrode 42a and the front facing electrode 44a, and a voltage E4 is applied between the back electrode 43b and the back facing electrode 45b. 8A, the mirror base 41c can be rotated clockwise in FIG. 8A around the axis OO, and a voltage E2 is applied between the front electrode 42b and the front facing electrode 44b, and By applying a voltage E3 between the electrode 43a and the back surface facing electrode 45a, an electrostatic attraction acts between these electrode pairs, and the mirror base 41c is moved counterclockwise in FIG. 8A around the axis OO. Can be rotated. Thus, the voltages E1, E according to the tracking error signal
By applying E4 or E2 or E3 as described above, the tracking control can be performed by rotating the mirror base 41c about the axis OO. Further, a voltage E1 is applied between the surface electrode 42a and the surface counter electrode 44a, and the surface electrode 42b and the surface counter electrode 44b are applied.
When the voltage E2 is applied between the pair of electrodes, an electrostatic attractive force acts between these electrode pairs, and the mirror base 41c can be moved in a direction perpendicular to the plane, thereby performing focusing control. Can be.

As described above, in the present embodiment, the reflecting surface 41d constituting the galvanomirror is displaced in the tracking direction and the focusing direction. Therefore, the connecting portions 41a and 4b supporting the mirror base 41c are provided.
1b has a structure in which the mirror base can be easily displaced in both directions.

Further, in this embodiment, a current is applied to the focusing coil to drive the entire holding member 10 in the focusing direction, and a voltage is applied to the electrodes of the galvanometer mirror to move the galvanometer mirror in a direction perpendicular to the surface thereof. Focusing control is performed by displacing, and a circuit for creating signals to be supplied to these focusing coils and electrodes is shown in FIG.

In FIG. 9, an output signal of a photodetector 51 for receiving a laser beam reflected from a recording medium is processed by a signal processing circuit 52 to create a focusing error signal, and this focusing error signal is converted to a low-pass filter. A low-pass component is extracted through a filter 53 and a high-pass component is extracted through a high-pass filter. Low-pass filter 5
The low-frequency component of the focusing error signal obtained from 3 is supplied to the first drive circuit 55 to generate a current corresponding to the low-frequency component of the focusing error signal, and the current is supplied to the focusing coil 56. The high-frequency component of the focusing error signal obtained from the high-pass filter
And generates a voltage corresponding to the high frequency component, and supplies the generated voltage to the focusing electrostatic motor 58 including the surface electrode 42a, the surface counter electrode 44a, the surface electrode 42b, and the surface counter electrode 44b. Apply. In this way, a focusing control signal corresponding to the low-frequency component and the high-frequency component of the focusing error signal is created, and these are supplied to the focusing coil and the focusing electrostatic motor, respectively, thereby reducing the high-order resonance of the drive system. And more accurate focusing control can be performed.

The present invention is not limited only to the above-described embodiment, and many modifications and variations are possible. For example, the configuration of the optical unit is not limited to that described above, and various configurations are possible. Further, various configurations are possible for a mechanism for movably supporting the holding member and a mechanism for driving the same in the focusing direction.

[0028]

As described above, according to the optical head of the present invention, the semiconductor substrate integrally provided with the semiconductor laser light source and the galvanomirror and the objective lens are held by the holding member, and this holding member is used as the objective. Focusing control is performed by driving in the direction of the optical axis of the lens, and tracking control is performed by rotating a galvanomirror provided integrally with the semiconductor substrate about an axis extending in a tangential direction of the information track of the recording medium. With this configuration, the tracking driving unit can be made small and lightweight, and therefore, the sensitivity and the response speed can be improved. Further, since the tracking control is performed by rotating an extremely small galvanometer mirror provided integrally with the semiconductor substrate, the entire apparatus including the driving means can be made small and lightweight.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of a first embodiment of an optical head according to the present invention.

FIG. 2 is a sectional view showing the configuration of the first embodiment.

FIG. 3 is a sectional view showing a detailed configuration of the optical unit.

FIGS. 4A and 4B are a perspective view and a sectional view, respectively, showing the configuration of the galvanomirror driving means.

FIG. 5 is a schematic sectional view showing a configuration of a second embodiment of the optical head according to the present invention.

FIG. 6 is a schematic sectional view showing the configuration of a third embodiment of the optical head according to the present invention.

FIG. 7 is a schematic sectional view showing the configuration of an optical head according to a fourth embodiment of the present invention.

8A and 8B are a cross-sectional view and a plan view, respectively, showing a detailed configuration of the galvanomirror.

FIG. 9 is a circuit diagram showing a configuration of a galvanomirror driving circuit in the same manner.

[Explanation of symbols]

1 laser diode, 2 galvanometer mirror, 3
Photodetector, 4 Photodetector, 5 Silicon substrate, 6
Diffraction grating, 7 hologram, 8 glass block, 9 optical unit, 10 holding member, 11
Objective lens, 12 mirror, 13 recording medium, 14
Base, 15 wires, 16 wires, 17
Yoke, 18 yoke, 19 focusing coil, 20 focusing coil, 21 permanent magnet,
Reference Signs List 22 permanent magnet, 2a rotation axis, 2b mirror base, 2c reflection surface, 2d electrode, 2e, 2f counter electrode, 30 photodetector, 31 prism, 32
Mirror, 33 aspherical objective lens, 34 spring member, 41a, 41b connecting portion, 41c mirror base, 41d reflecting surface, 42a, 42b surface electrode,
43a, 43b back electrode, 44a, 44b front facing electrode, 45a, 45b back facing electrode, 51 photodetector, 52 signal processing circuit, 53 low pass filter, 54 high pass filter, 55 first drive circuit, 56 focusing Coil, 57 second drive circuit, 58 electrostatic motor for focusing

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 7/09 G11B 7/095 G11B 7/135

Claims (3)

(57) [Claims] 1. A semiconductor substrate integrally provided with a semiconductor laser light source and a galvanomirror for performing at least tracking control by deflecting a laser beam emitted from the semiconductor laser light source in a tracking direction, the semiconductor substrate, and the galvanometer. An objective lens for irradiating the laser beam deflected by the mirror onto the recording medium is fixed to a holding member, and the holding member is attached to the base so as to be movable in the optical axis direction of the objective lens, and a focusing coil is attached to the holding member. And a permanent magnet arranged so as to face the focusing coil is fixed to the base, and the holding member is driven only in the optical axis direction with respect to the recording medium surface to perform focusing control. An optical head having a configuration. 2. The optical head according to claim 1, wherein the objective lens is an objective lens including a reflecting mirror surface and an aspherical lens. 3. A galvanomirror driving means for driving the galvanomirror in a direction perpendicular to the reflection surface thereof to perform focusing control, and supplies a low-frequency component of the focusing error signal to the focusing coil and a focusing error signal. 3. The optical head according to claim 1, wherein the high-frequency component is supplied to the galvanomirror driving means.