JPH0235641A - Optical pickup using for magneto-optical disk also for draw type disk - Google Patents

Abstract

PURPOSE:To miniaturize a device, to reduce an occupant space, and to reduce a cost by fixing a rotary member having a phase contrast plate on a ball bearing. CONSTITUTION:One pickup can be used for a magneto-optical disk also for a DRAW (direct-read-after-write) type disk by switching the direction of the optical axis of the phase contrast plate 20 by rotating, and in addition to that, the direction of the optical axis of the phase contrast plate 20 can be switched by utilizing and fixing the phase contrast plate 20 on the outer ring or the inner ring of the ball bearing 30. In such a way, the ball bearing 30 can be arranged in the neighborhood of the optical axis of the pickup, and to form the constitution of an actuator for the switching of the phase contrast plate 20 compactly, therefore, the optical pickup of combination type can be formed compactly.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical pickup that can be used whether the recording medium is a magneto-optical disk or a write-once optical disk.

(Conventional Technique t#) Optical pickups that use optical disks as recording media for information signals are classified into various types depending on the type of optical disk used.

For example, one example is one that uses a magneto-optical disk, and a conventional example thereof will be shown in Part 11. In FIG. 11, a laser beam emitted from a semiconductor laser 1 is made into parallel light by a coupling lens 2, and the beam is shaped by a beam shaping prism 3. The light flux that has passed through the beam shaping prism 3 is reflected by the roof prism 4 as shown by the dotted line, and is reflected by the first beam splinter 5 toward the carriage side of the optical pickup. The carriage is movable in the radial direction of the magneto-optical disk 8. A second beam splitter 6 is arranged on the carriage to make the parallel light guided from the beam splitter 5 enter the objective lens 7. The objective lens 7 focuses the light beam from the beam splitter 6 onto the optical disk 8 as a light spot with a diameter of about 1 μm.

The reflected light from the optical disk 8 passes through the objective lens 7 and reaches the beam splitter 6. A portion of the light is guided to the track detection light receiving element 9, and the rest is reflected toward the first beam splitter 5. The light beam reflected to the beam splitter 5 side passes through the beam splitter 5 and becomes convergent light by the condenser lens 10. This convergent light is split by a splitting mirror (naifetsu) 11, and part of it passes through a λ/2 plate 12 and a Wollaston prism 13, and then passes through a magneto-optical signal detector 14.
The remaining light flux that is not reflected by the 0-divided mirror 11 is reflected by the mirror 15, and is guided to the focus detection light receiving element 1.6.

There is also an optical pickup that uses a write-once optical disc as a recording medium. Figure 12 shows a conventional example.
6. In FIG. 12, components that are functionally the same as those of the optical pickup for a magneto-optical disk shown in FIG. 1 are given the same reference numerals.

The light beam from the semiconductor laser 1 is linearly polarized light (S-polarized light), is made into parallel light by the coupling lens 2, is transmitted through the polarized beam splinter 18, and is transmitted through the λ/4 plate 19 and the objective lens 7 to the write-once optical disc 17. The light is focused on. The light irradiated onto the optical disc 17 passes through the λ/4 plate 19, and therefore becomes circularly polarized light. The reflected light from the optical disc 17 is also circularly polarized light. This reflected light passes through the λ/4 plate 19 again and becomes linearly polarized light again. The linearly polarized light is
P whose phase is shifted by 90 degrees with respect to the emitted light of the semiconductor laser 1
It becomes polarized light. More than 99% of this P-polarized light is reflected by the polarizing beam splitter 18 and guided to the condenser lens 10 side. The convergent light that has passed through the condenser lens 1.0 is guided to a focus detection light receiving element 16 and a track detection light receiving element 9. As is well known, each light-receiving element 16.9 has a divided light-receiving surface, and by inputting the output of each divided light-receiving surface of the light-receiving element 16 to the differential amplifier 50, a focusing signal can be detected. Furthermore, a tracking signal can be detected by inputting the output of each divided light-receiving surface of the light-receiving probe 9 to the differential amplifier 51.

By inputting the signal to the adder 52, the information signal recorded on the disk 17 can be read out.

(Problems to be Solved by the Invention) Information signals are recorded as different magnetization directions on a magneto-optical disk 8 as a recording medium of an optical pickup shown in FIG. The information signal can be read out by detecting, by the light receiving element 14, a minute difference in polarization angle caused by the difference in the magnetization direction as a difference in intensity between two light beams separated by the Wollaston prism 13. However, since the difference in the polarization angle (referred to as "Kerr rotation angle") is minute, highly accurate linearly polarized light must be incident on the magneto-optical disk 8. Therefore.

In a magneto-optical pickup, unlike a write-once optical pickup, it is not possible to use a configuration in which incident light and reflected light are separated using a λ/4 beam splitter and a polarizing beam splitter. A portion of the reflected light is reflected by the beam splitter 5 and returns to the semiconductor laser 1. Since the semiconductor laser 1 and the disk 8 are in a conjugate relationship via the coupling lens 2 and the objective lens 7, when a part of the emitted light from the semiconductor laser 1 returns to the semiconductor laser 1, the semiconductor laser 1. A phenomenon occurs in which the optical path formed by the coupling lens 2°, the objective lens 7, and the disk 8 becomes a resonator, and the amount of light from the semiconductor laser 1 fluctuates. this"
"Semiconductor laser output fluctuation due to returned light." The output fluctuation of the semiconductor laser due to this returned light generally has a relationship as shown in FIG. 13 with respect to the output light amount of the semiconductor laser (LD), and the smaller the output light amount, the larger the light amount fluctuation.

Also, in the case of magneto-optical disks, information signals are recorded by magnetization reversal, whereas in the case of write-once disks, information is recorded by melting and removing the medium, so if the light intensity during playback is increased too much, the medium will Because of the deterioration, the amount of light emitted by the semiconductor laser during write-once reproducing is lower than that during magneto-optical reproducing, and is about 115.

For this reason, when the optical pickup shown in Figure 11 is used as a dual-purpose magneto-optical and write-once type reproducing machine, the fluctuation of the scene due to the returned light, which is hardly a problem during magneto-optical playback, increases rapidly during write-once playback, causing serious problems. This becomes a problem. In particular, fluctuations in light intensity due to returned light occur when the light spot is focused on the disc, so the power is higher during actual playback when the focus servo is always in focus than when setting the playback power. increases, leading to deterioration of the medium. Also, this light amount fluctuation.

This becomes noise to the reproduced signal and has an adverse effect.

The present invention has been made in order to solve the problems of the prior art, and it is possible to improve the playback of magneto-optical disks and the write-once type by reducing the light amount fluctuation due to the return light during write-once type playback to an almost non-problematic level. It enables both disc playback and playback to be performed with a single optical pickup, and also allows easy switching between magneto-optical disc playback and write-once disc playback using a small, space-occupying, and low-cost mechanism. An object of the present invention is to provide a magneto-optical/write-once type optical pickup that can perform the following functions.

(Means for Solving the Problems) The present invention fixes a rotating member having a retardation plate to one of the outer ring and the inner ring of a ball bearing having a relatively rotatable outer ring and an inner ring, and The other of the magnets is fixed to the optical pickup main body, and a permanent magnet and a yoke are arranged at a constant interval near the rotating member to form a magnetic field approximately perpendicular to the rotating surface of the rotating plate. A coil is fixed to the rotating member and is wound so that the current flows in a direction substantially perpendicular to the direction of the magnetic field and is positioned within the magnetic field. It is characterized by generating thrust in a direction perpendicular to each other.

(Function) When a current is passed through the coil, the thrust generated in the coil rotates the retardation plate together with the rotating member, and its optical axis rotates. The rotational position of the retardation plate is changed by switching the direction of the current flowing through the coil. The direction of vibration of light passing through the retardation plate changes depending on the rotational position of the retardation plate. By setting the rotational position of the coil so that the vibration direction of the light reflected by the disk is the direction in which the beam splitter is transmitted through the optical system that includes the beam splitter and reaches the light receiving element, Output fluctuations can be suppressed.

(Embodiments) Before describing embodiments of the magneto-optical/write-once optical pickup according to the present invention, the basic configuration of the present invention will be explained. FIG. 1 schematically shows the basic configuration of the present invention, and in addition to the configuration of the conventional optical pickup shown in FIG. , a first λ/4 plate 2 which is a retardation plate
0 is arranged, and the 1-split mirror 11 and the λ/2 plate 12
A second λ/4 plate 25 is arranged between.

Whereas the second λ/4 plate 25 is fixed.

The first λ/4 plate 20 is rotatably provided so that its optical axis can be switched between the magneto-optical mode and the write-once mode. The rest of the configuration is similar to the configuration of the optical pickup shown in FIG. 11, so the common components are given the same reference numerals and a detailed explanation of the configuration will be omitted.

Next, the operation of the above basic configuration will be explained for each mode.

In the write-once mode, as shown in FIG. 2, the light emitted from the semiconductor laser 1 is passed through the coupling lens 2. The light passes through the shaping prism 3° and the roof prism 4, and enters the beam splitter 5 as S-polarized light. Beam splitter 5 reflects 75% of the S-polarized light,
It transmits 25% of the light, and transmits more than 99% of the P-polarized light. 75% of the light beam reflected by the beam splitter 5 passes through the λ/4 plate 20 and becomes circularly polarized light. In this write-once mode, the λ/4 plate 20 is installed so that its optical axis 56 is at an angle of 45 degrees with respect to the vibration direction of the S-polarized light.

The circularly polarized light that has passed through the λ/4 plate 20 is reflected upward by the second beam splitter 6 and is focused onto the write-once optical disk 17 by the objective lens 7 . The reflected light from the disk 17 returns as circularly polarized light and becomes linearly polarized light by passing through the λ/4 plate 20 again. The vibration direction of this linearly polarized light is perpendicular to the S-polarized light described above, and becomes P-polarized light with respect to the beam splitter 5. Beam splitter 5 is Pa
Since 99% or more of the light is transmitted, almost no reflected light from the disk 17 returns to the semiconductor laser 1 side. The light transmitted through the beam splitter 5 is guided to the focus detection light receiving element 16 and the magneto-optical detector 14, and the 6-write-once information signal is detected as a sum signal of the outputs of the detector 14. In this way, since the information signal is detected using the sum signal of the detector 14, the second λ/4 plate 25 and the λ/2 plate 12 have no effect on information detection.

In the case of magneto-optical mode, Figures 3 and 4 show the operation in magneto-optical mode.As shown in Figure 3, in the case of magneto-optical mode, the first λ/4
The plate 20 is rotated to align the vibration direction of the S-polarized light from the beam splitter 5 with the optical axis 56. In this way, S
The polarized light passes through the λ/4 plate 20 and is irradiated onto the magneto-optical disk 8 as linearly polarized light. The reflected light from the magnetic disk 8 becomes KM polarized light rotated by the Kerr rotation angle α according to the magnetization direction of the recorded data. When this linearly polarized light enters the λ/4 plate 20 again, it becomes elliptically polarized light because it is tilted by a small angle of Kerr rotation angle α with respect to the optical axis. Beam splitter 5 splits S-polarized light by 75% and P-polarized light by 99%.
%, the ellipticity of the elliptically polarized light changes and the elliptically polarized light reaches the splitting mirror 11 side.The elliptically polarized light reflected by the 0 splitting mirror 11 passes through the second λ/4 plate 25. λ/4
The plate 25 has the role of returning this elliptically polarized light to linearly polarized light again, and its optical axis is at an angle of 90° with respect to the first λ/4 plate 20.
It is installed at a degree angle. Since the returned linearly polarized light rotates according to the magnetization direction of the information, the difference in polarization angle is determined by the λ/2 plate 12. They are separated by the Wollaston prism 13 and detected as a difference signal by the two-split detector 14.In this way, by rotating the λ/4@20 as a retardation plate and changing the direction of its optical axis 56, One optical pickup can be used as a dual-purpose optical pickup for magneto-optical and write-once types.

5 to 10 show examples of a rotation mechanism for the λ/4 plate 20. FIG. 5 to 9, the reference numeral 30 indicates a ball bearing, and the ball bearing 3
0 is a relatively rotatable outer ring 3, similar to the generally known one.
5 and an inner ring 48. A ring-shaped rotating member 34 is fixed to one end of the inner ring 48 of the bearing 30,
The λ/4 plate 20 is fixed to the rotating member 34.

On the other hand, the outer ring 35 of the bearing 30 is fixed to the optical pickup main body 36. Therefore, the substantially integral inner ring 4
8, the rotating member 34, and the λ/4 plate 20 can freely rotate relative to the optical pickup main body 36 and the outer ring 35 fixed thereto. The central axis of the bearing 30 is arranged to coincide with the optical axis between the first beam splitter 5 and the second beam splitter 6. A frame-shaped coil 31 is fixed to the outer circumference of the rotating member 34. Appropriate means may be used for fixing the coil 31 to the rotating member 34, but in the illustrated embodiment, 1 is used.
The coil 31 is fixed to the rotating member 34 by fitting and attaching an inverted U-shaped mounting member 43 fixed to the outer surface of the coil 31 to a block 44 formed integrally protruding from the outer periphery of the rotating member 34. has been done. Optical pickup body 3
A yoke 40 formed in a U-shape is fixed to 6 in the vicinity of the 5-rotation member 34, and one side of the yoke 40 provides a sufficient distance between the inside of the coil 31 and the inner surface of the coil 31. It penetrates through. A permanent magnet 3 is attached to the inner surface of one side opposite to one side of the yoke 40 passing through the coil 31.
2 is fixed, and a magnetic field is formed between one side of the yoke 40 and the permanent magnet 32, which are arranged at regular intervals. This magnetic field is formed in a direction substantially perpendicular to the rotating surface of the rotating member 34. The coil 31 is in this magnetic field.
is located. A direct current is passed through the coil 31 in the forward direction or in the reverse direction depending on whether the magneto-optical mode is the write-once mode. The direction of this current is approximately perpendicular to the direction of the magnetic field. Therefore, by passing a current through the coil 31, a thrust force is generated in a direction perpendicular to the direction of the magnetic field and the direction of the current according to the principle of a voice coil motor or a linear motor, and the motor is fixed to the rotating member 34! /4 made of 2 plates Rotate in a plane perpendicular to the 0 axis.

The limit of rotation of the rotating member 34 in the counterclockwise direction in FIG. The limit of rotation in the clockwise direction is determined by the step 46 on the outer periphery of the rotating member 34 coming into contact with a stopper that is substantially integral with the pickup body 36.

Each end of the rotation range of the rotating member 34 corresponds to the magneto-optical mode and the write-once mode, respectively. The determination between the magneto-optical mode and the write-once mode may be made by the user's judgment, or it may be made automatically by reading a mark or the like attached to the optical disc cartridge. Then, the direction of the current flowing through the coil 31 is switched depending on whether the mode is magneto-optical mode or write-once mode. By doing this, the direction of the optical axis of the λ/4 plate 20, which is one retardation plate, is switched depending on whether the recording medium is a magneto-optical disk or a write-once disk. Fluctuations in light amount due to return light from the semiconductor laser can be prevented.

In order to correctly position the optical axis of the λ/4 plate 20 in each mode, it is necessary to prevent the rotating member 34 from moving erroneously when the rotating member 34 rotates to the limit position. To do this, after the coil 31 is energized to rotate the rotating member 34, the coil 31 is continuously energized to generate thrust, and the protrusion 45 or step 46 is brought into contact with the stopper. or the 10th
As shown in the figure, permanent magnets 54 may be fixed to both sides of the coil 31 in the rotational direction, and the permanent magnets 54 may be attracted to the pickup body or the like at the rotation limit position of the coil 31, the example of FIG. 10. In this case, after the coil 31 is energized and rotated, it is not necessary to continue energizing the coil 31.

Note that the inner ring side of the ball bearing may be fixed, the outer ring side may be set as the rotating side, and the rotating member and the retardation plate may be fixed to this.

The yoke 40 may be formed in an arc shape along the rotation direction of the coil 31.

(Effects of the Invention) According to the present invention, by rotating the retardation plate and switching the direction of its optical axis, one pickup can be used for both a magneto-optical disk and a write-once disk. , the direction of the optical axis of the retardation plate is switched by fixing the retardation plate to the outer ring or inner ring using a ball bearing, so the ball bearing can be placed around the optical axis of the pickup. The configuration of seven cut units for switching one retardation plate can be made compact, thereby making it possible to make a dual-purpose optical pickup compact. Moreover, since a commercially available bearing can be used as the bearing, the cost can be reduced.

[Brief explanation of the drawing]

FIG. 1 is an optical layout diagram schematically showing an embodiment of a magneto-optical/write-once optical pickup according to the present invention. FIG. 2 is an optical layout diagram showing the operation in the write-once mode of the above embodiment, and FIG. 3 is an optical layout diagram showing the operation in the magneto-optical mode. FIG. 5 is a perspective view showing a specific example of the rotation mechanism of the retardation plate in the above embodiment, FIG. 6 is a front view of the same, and FIG. 7 is a diagram showing the rotating member in the rotation mechanism. 8 is a sectional view taken along the line A-A in FIG. 6, FIG. 9 is an exploded perspective view of the rotation mechanism, and FIG. 10 is a rotation mechanism of a retardation plate applicable to the present invention. FIG. 3 is a front view showing another example. FIG. 11 is an optical layout diagram showing an example of a conventional magneto-optical optical pickup, FIG. 12 is an optical layout diagram showing an example of a conventional write-once optical pickup, and FIG. 13 is an optical layout diagram showing an example of a conventional write-once optical pickup. FIG. 3 is a diagram showing output fluctuations. 8...Magneto-optical disk 17...Writable optical disk 2o...Retardation plate 30...Ball bearing 31...Coil 32...Permanent magnet 3
4...Rotating member 35...Outside @ 36...
Optical pickup body 40... Yoke 48...
・Inner ring 56...Optical axis 4 Uijiku 5 ヅσ G] Shape 40 I Amo D Mouth 1 Z round nok

Claims (1)

[Scope of Claims] A magneto-optical/write-once optical pickup in which the direction of the optical axis is switched by rotating a retardation plate depending on whether the recording medium is a magneto-optical disk or a write-once disk, A rotating member having the retardation plate is fixed to one of the outer ring and the inner ring of a ball bearing having a relatively rotatable outer ring and an inner ring, and the other of the outer ring and the inner ring is fixed to the optical pickup main body, and the above-mentioned A permanent magnet and a yoke are arranged at regular intervals near the rotating member to form a magnetic field in a direction substantially perpendicular to the rotating surface of the rotating member. and a coil wound so that a current flows substantially perpendicular to the direction of the magnetic field is fixed so that the coil generates a thrust in a direction perpendicular to the direction of the magnetic field and the direction of the current, respectively. A magneto-optical/write-once optical pickup that is characterized by the following: