JPH04241232A - Multibeam optical head - Google Patents

Abstract

PURPOSE:To perform tracking on respective tracks with high accuracy when recording and reproducing are simultaneously performed on plural parallel tracks by using plural light beams. CONSTITUTION:The plural light beams from a multibeam semiconductor laser 1 are guided to torsion mirrors 21b which are arranged corresponding to the respective light beams and can be deflected by respective tracking control signals 23. By controlling the torsion mirrors 21b in accordance with the tracking control signals 23 from the respective beams and moving the light spot on an optical disk 7 in a beam train direction, tracking control is performed. Thus, the tracking control is performed for every light beam.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam optical head for optical discs that uses a plurality of light beams to simultaneously perform recording and reproduction on a plurality of parallel tracks.

0002

2. Description of the Related Art FIG. 4 shows an example of the configuration of an optical system of a conventional multi-beam optical head. In this example, a case of a four-beam multi-beam optical head will be explained. The light beam emitted from the multi-beam semiconductor laser 1 is made into parallel light by a collimating lens 2, and the parallel light passes through a polarizing beam splitter 3, a Dove prism 4, and a quarter-wave plate 5.
The light is further focused by an objective lens 6 and irradiated onto an optical disk 7 as a light spot array.

The light reflected from the optical disk 7 follows the same optical path as the outgoing path in the opposite direction, is reflected by the polarizing beam splitter 3 in a direction perpendicular to the outgoing path, and is further split into two optical paths by the beam splitter 8. One of the lights (reflected light) is collected by a condenser lens 9 and detected as four light spots on a signal detector 10.

A tracking error signal is obtained from the signal detector 10 along with the reproduction signal of each beam. The other light (transmitted light) that has passed through the beam splitter 8 enters the prism 11, and due to the difference in the angle of incidence of the incident light, only one of the four light beams is detected as having a focus error. Guided to vessel 12.

A focus error signal is obtained from the focus error detector 12, and a focus control signal 14 generated by a focus control circuit 13 in accordance with this focus error signal is supplied to an actuator 15 attached to the objective lens 6. Focus control of the objective lens 6 is performed.

In the conventional multi-beam optical head,
Since the spacing between the four beams is fixed, the angle around the optical axis of the optical head is adjusted in advance so that the track spacing on the optical disk 7 matches the beam spacing, and one of the four beams is By applying tracking control only to the beam, recording and reproduction are performed on four tracks.

Further, the Dove prism 4 disposed in the optical path can be rotated around the optical axis by a rotation mechanism (not shown), and by utilizing this rotation, the beam array on the optical disk 7 can be rotated.

Therefore, by controlling the rotation mechanism according to the tracking error signal from the signal detector 10, the Dove prism 4 is rotated around the optical axis, and the radial position on the optical disk 7 is changed by rotating the beam array thereby. It is possible to correct the positional deviation between the light beam and the track due to the difference.

[0009]

In other words, in the conventional multi-beam optical head, alignment to each track is performed by tracking control using one of the plurality of light beams and rotation of the beam array. Since the beam spacing is fixed, accurate tracking is performed on one track, but if the track spacing changes or the light emitting position of the multi-beam semiconductor laser shifts, etc. The problem with the track was that accurate recording and playback could not be performed.

The present invention has been made in view of the drawbacks of the prior art, and its object is to provide a multi-beam optical head that can track each of a plurality of parallel tracks with high precision.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the present invention emits a plurality of light beams lined up in the beam row direction from a multi-beam semiconductor laser, and simultaneously projects the plurality of light beams onto an optical disk. A multi-beam optical head that performs recording and reproduction on the optical disk by inputting the light beam, a plurality of torsion mirrors arranged to individually deflect each of the plurality of light beams emitted from the multi-beam semiconductor laser; means for irradiating the optical disc with a plurality of emitted lights polarized by a plurality of torsion mirrors as a light spot array consisting of a plurality of light spots; and receiving reflected light from the optical disc;
means for generating a plurality of tracking error signals corresponding to each of the plurality of light beams; and means for individually controlling each of the plurality of torsion mirrors in accordance with the plurality of tracking error signals; It is characterized by comprising means for individually moving the plurality of upper light spots in the direction of the beam array to perform tracking control.

0012

[Operation] In the present invention, each beam is provided with a torsion mirror that can be deflected by an electric signal, and by applying a tracking control signal from each beam to the torsion mirror, each optical axis is moved in the direction of the beam array. , performs tracking control. Therefore, in the conventional technology, since the beam interval is fixed, tracking control of individual beams is not possible, whereas with the present invention, tracking control of individual beams of a plurality of beams is possible. .

As a result, the multi-beam optical head of the present invention has high tracking accuracy, and its operation is stable even when the track interval of the optical disk changes or the light emitting position of the multi-beam semiconductor laser shifts.

[0014]

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

FIG. 1 shows the configuration of an optical system and a control system in an embodiment of a multi-beam optical head according to the present invention. In this embodiment, a four-beam multi-beam optical head will be described as an example. Multi-beam semiconductor laser 1
A plurality of light beams arranged in the beam row direction are emitted. Each of the plurality of light beams is guided to a plurality of torsion mirror devices 21 which are allocated and arranged for each beam, and each beam is deflected by each torsion mirror 21b.

The structure and function of the torsion mirror device 21 will now be explained with reference to FIGS. 2 and 3. Figure 2
3 shows the structure of the entire torsion mirror device 21, and FIG. 3 shows the structure of each torsion mirror portion of this torsion mirror device 21 in an enlarged manner.

In FIGS. 2 and 3, 21a is a silicon substrate, 21b is a torsion mirror, and 21c is a mirror 2.
These mirrors 21b and torsion bars 21c support the silicon substrate 2.
It is formed by punching out 1a by etching. Furthermore, a metal film such as aluminum is deposited on the surface of the mirror 21b to form a mirror surface.

On the other hand, on the glass substrate 21d, there is a rectangular depression 21h and a fulcrum 21 inside this depression 21h.
e is formed by etching, and two electrodes 2
1f and 21g are formed on both sides of the fulcrum 21e.

A torsion mirror device 21 is formed by attaching a silicon substrate 21a to a glass substrate 21d.

The operation of the torsion mirror device 21 is such that the mirror 21b supported by a silicon torsion bar 21c twists and moves by applying a voltage to the two electrodes 21f and 21g.

Therefore, for four beam rows, FIG.
By arranging the torsion mirror 21b as shown in , it becomes possible to deflect the individual beams in the direction of the beam array, and furthermore, it becomes possible to move the optical spot on the optical disk 7 in the direction of the beam array. Tracking control, which will be described later, is performed.

The light reflected by the torsion mirror device 21 is made into parallel light by the collimating lens 2, passes through the polarizing beam splitter 3 and the quarter-wave plate 5, is condensed by the objective lens 6, and is directed onto the optical disc 7. It is irradiated as four light spot rows at the top.

The light reflected from the optical disk 7 follows the same optical path as the outgoing path in the opposite direction, is reflected by the polarizing beam splitter 3 in a direction perpendicular to the outgoing path, and is then split into two optical paths by the beam splitter 8.

One of the lights (reflected light) is focused by a condenser lens 9 and detected by a signal detector 10 as four light spots.

After the other light (transmitted light) that has passed through the beam splitter 8 enters the prism 11, only one of the four light beams is guided to the focus error detector 12 due to the difference in the angle of incidence. It will be destroyed.

A focus error signal is obtained from the focus error detector 12, and a focus control signal 14 generated by the focus control circuit 13 in accordance with the focus error signal is supplied to an actuator 15 attached to the objective lens 6. Focus control of the objective lens 6 is performed.

On the other hand, a reproduction signal and a tracking error signal for each beam are obtained from the signal detector 10, and a tracking control signal 23 for each beam is obtained from the tracking error signal through a tracking control circuit 22. . These tracking control signals 23 are guided to a driver 24, which drives the torsion mirror device 21 for each beam to move the light spot on the optical disk 7 in the direction of the beam array. This allows tracking control to be performed for each beam.

Next, the results of recording and reproducing experiments using the multi-beam optical head of this example will be described. The interval between the light emitting points of the multibeam semiconductor laser 1 used in the multibeam optical head of this example was 100 μm, and its accuracy was about ±2 μm. The size of each mirror 21b in the torsion mirror device 21 was 70 μm square.

The optical disk 7 used was one in which an SbTe film was formed as a recording film on a polycarbonate substrate having a diameter of 130 mm. The guide grooves of the optical disk 7 were formed by the method for manufacturing an optical disk master disclosed in Japanese Patent Laid-Open No. 1-133237, which was filed by the present applicant, and consisted of four parallel spiral grooves with a groove interval of 1.6 μm. . The variation in the guide groove spacing was ±0.1 μm or less.

When the optical disk 7 was mounted on a recording/reproducing apparatus including a multi-beam optical head shown in FIG. 1 and a tracking experiment was conducted, stable tracking operation was confirmed. Furthermore, an attempt was made to record signals with different frequencies in each of the four guide grooves. As a result, it was confirmed by microscopic observation that a predetermined recording mark was formed at the center of each of the four guide grooves at any position on the disk.

[0031] In this embodiment, the case where there are four multi-beams is exemplified, but the present invention is not limited to this, and may be applied to the case where there are four or less or four or more beams. Needless to say, it is also possible.

[0032]

[Effects of the Invention] As explained above, according to the multi-beam optical head of the present invention, by providing a torsion mirror for each light beam, tracking control can be performed independently for each of the plurality of light beams. This has the advantage that the tracking accuracy is high and the operation is stable even when the track interval of the optical disk changes or the light emitting position of the multi-beam semiconductor laser shifts.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an optical system and a control system in an embodiment of a multi-beam optical head of the present invention.

FIG. 2 is a plan view showing the configuration of the torsion mirror in FIG. 1;

FIG. 3 is an enlarged perspective view of the structure of the illustrated torsion mirror.

FIG. 4 is a configuration diagram showing an optical system of a conventional multi-beam optical head.

[Explanation of symbols]

1 Multi-beam semiconductor laser 2 Collimating lens 3 Polarizing beam splitter 4 Dove Prism 5 1/4 wavelength plate 6 Objective lens 7 Optical disc 8 Beam splitter 9 Condensing lens 10 Signal detector 11 Prism 12 Focus error detector 13 Focus control circuit 14 Focus control signal 15 Actuator 21 Torsion mirror device 21a Silicon substrate 21b Mirror 21c Torsion bar 21d Glass substrate 21e Fulcrum 21f electrode 21g electrode 21h Hollow 22 Tracking control circuit 23 Tracking control signal 24 Driver

Claims (1)

[Claims] 1. A multi-beam optical head for recording and reproducing information on an optical disk by emitting a plurality of light beams lined up in a beam row direction from a multi-beam semiconductor laser and simultaneously making the plurality of light beams incident on the optical disk. a plurality of torsion mirrors arranged to individually deflect each of the plurality of light beams emitted from the multi-beam semiconductor laser; and a plurality of output lights polarized by the plurality of torsion mirrors to the optical disk. means for irradiating a plurality of light spots as a light spot array, and receiving reflected light from the optical disc;
means for generating a plurality of tracking error signals corresponding to each of the plurality of light beams; and means for individually controlling each of the plurality of torsion mirrors in accordance with the plurality of tracking error signals; A multi-beam optical head characterized by comprising: means for individually moving the plurality of upper light spots in the direction of the beam row to perform tracking control.