JPH04251456A - Magneto-optical pickup device - Google Patents

Abstract

PURPOSE:To prevent any adverse influence such as reducing a signal level or the like because of C/N deterioration by elliptically polarizing a laser beam even when an objective lens or the like has birefringence by setting the advanced phase axis or delayed phase axis of a birefringence optical element in a prescribed direction. CONSTITUTION:When an angle formed between a deflecting phase 33 of the laser beam made incident an objective lens 10 or the like and an advanced phase axis 31 of the lens 10 having birefringence is set at + or -90 deg., the polarizing phase 33 is coincident with a delayed phase axis 32, and the laser beam is elliptically polarized. Thus, the level of the signal through the lens 10 is made maximum and even when the optical equipment such as the objective lens or the like has birefringence, the adverse influence such as reducing the signal level or the like by the C/N deterioration caused by the birefringence is prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical pickup device used in an optical information recording and reproducing apparatus that records and reproduces information, or records, reproduces, and erases information using laser light.

0002

[Prior Art] In recent years, with the dramatic increase in the amount of information handled in offices, etc., information is being recorded, reproduced, recorded and
Information recording devices that perform playback and erasing are used. As this information recording device, magneto-optical disk memory has a high density and large capacity, and as access time is shortened, it has progressed as an alternative to the conventionally used magnetic disk memory.

As shown in FIG. 7, the magneto-optical disk memory converts laser light emitted from a semiconductor laser 100 into a collimator lens 101 and a beam splitter 10.
2 and the magneto-optical disk 104 via the objective lens 103.
The reflected light from the magneto-optical disk 104 is focused on the
The light is reflected in the right angle direction by the beam splitter 102 through the optical path opposite to the above, and is detected by the detector 105, thereby reproducing information. The magneto-optical disk 104 has a disk substrate 1
06 and a recording film 107 made of a magnetic material formed on this disk substrate 106. In this magneto-optical disk 104, the recording film 107 is irradiated with a linearly polarized laser beam as described above through the disk substrate 106, and the polarization plane of the laser beam changes depending on the magnetization direction of the recording film 107 of the magneto-optical disk 104. Magneto-optical effect (Kerr effect)
is used to record, reproduce, or rewrite information.

0004

However, the above-mentioned prior art has the following problems. That is, the objective lens 103 that focuses the laser beam onto the magneto-optical disk 104 may be manufactured by injection molding of plastic, etc. In this case, the objective lens 103
exhibits birefringence due to optical anisotropy caused by the molecular orientation of the plastic during the manufacturing process. in this way,
If birefringence exists in the objective lens 103, when the recording film 107 is irradiated with linearly polarized laser light through the disk substrate 106 and the reflected and refracted laser light is detected,
There is a problem in that the laser beam becomes elliptically polarized, resulting in adverse effects such as deterioration of C/N and reduction in signal level.

[0005]

[Means for Solving the Problems] Therefore, the present invention has been made to solve the problems of the above-mentioned prior art.
The purpose of this is that even if optical components such as objective lenses have birefringence, the laser beam becomes elliptically polarized.
It is an object of the present invention to provide a magneto-optical pickup device that can prevent adverse effects such as a decrease in signal level due to deterioration of C/N.

That is, the present invention focuses a laser beam emitted from a laser light source onto an optical recording medium through an optical element having birefringence to provide a magneto-optical pickup device for recording and reproducing information. , the fast axis or the slow axis of the optical element having birefringence is configured to match the polarization plane of the laser beam incident on the optical element.

[0007] As the optical element, for example, an objective lens or the like which is a plastic optical element manufactured by injection molding is applied. However, the above-mentioned optical element is not limited to this, but two lenses are arranged on the optical axis to perform focusing control, and focusing control is performed by varying the distance between the two lenses. A combination lens may also be used.

[0008] Further, the above-mentioned optical element is, for example, a plastic optical element manufactured by injection molding,
The direction of injection passing through the injection port mark created when manufacturing the plastic optical element by injection molding or the direction perpendicular to the injection direction is set to match the polarization plane of the laser beam incident on the optical element.

[0009]

[Operation] In this invention, by making the fast axis or slow axis of an optical element having birefringence coincide with the polarization plane of the laser beam incident on the optical element, birefringence exists in the optical element. The inventors of the present invention have discovered that it is possible to suppress the decrease in signal level that occurs in .

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on the illustrated embodiments.

FIG. 2 shows an embodiment of a magneto-optical pickup device according to the present invention.

As shown in FIG. 2, this magneto-optical pickup device 1 includes a semiconductor laser 2 that emits a laser beam, and a collimator lens that converts the laser beam having an elliptical cross section that is emitted from the semiconductor laser 2 into parallel light. 3 and
A beam shaping prism 4 that shapes this laser light into a beam with a circular cross section, a beam splitter 5 that splits the beam, and a beam splitter 5 that once converges the laser light that has passed through the beam splitter 5 and then converts it into parallel light again. By moving one lens along the optical axis,
Relay lenses 6 and 7 that perform focusing control on the magneto-optical disk 8, which will be described later, a reflecting prism 9 that reflects laser light guided by the relay lenses 6 and 7 toward the magneto-optical disk 8, and the reflecting prism 9. an objective lens 10 that focuses the laser beam reflected by the magneto-optical disk 8 onto the magneto-optical disk 8; and a floating slider 11 that holds the objective lens 10 in a floating state to maintain a constant distance between the objective lens 10 and the magneto-optical disk 8. It is equipped with

Further, in the magneto-optical pickup device 1, the laser beam that is converged onto the magneto-optical disk 8 by the objective lens 10 and is reflected and refracted by the magneto-optical disk 8 is transmitted through the objective lens 10 and the reflecting prism. 9. The polarization plane of the laser beam guided through the relay lenses 6 and 7 and reflected by the beam splitter 5 is 45
1/2 wavelength plate 12 to be rotated and this 1/2 wavelength plate 1
a Wollaston prism 13 that separates the laser light that has passed through the Wollaston prism 13; and a lens 15 that focuses the laser light that has passed through the Wollaston prism 13 onto the detector 14.
and a beam splitter 16 that further separates the laser beam reflected by the Wollaston prism 13.
A lens 19 focuses the laser light transmitted through the beam splitter 16 onto a detector 18 via a knife edge 17, and a lens 21 focuses the laser light reflected by the beam splitter 16 onto the detector 20.
It is configured to have the following.

A magneto-optical disk 8 as a magneto-optical recording medium on which information is recorded, reproduced or rewritten by the magneto-optical pickup device 1, as shown in FIG. The recording film 26 is made of a magnetic material.

This magneto-optical disk 8 has a recording film 26
A linearly polarized laser beam is irradiated through the disk substrate 25, and information is recorded using the magneto-optic effect (Kerr effect) in which the polarization plane of the laser beam changes depending on the magnetization direction of the recording film 26 of the magneto-optical disk 8. Recording, reproducing, rewriting, etc. are performed. To explain further, as shown in FIG. 4(A), a laser beam is irradiated to the recording film 26 while a magnetic field is applied in the direction of the arrow, and the Kerr rotation angle is changed by reversing the magnetization direction of the irradiated area. The change in the Kerr rotation angle is used to record and reproduce information (see Figure 4 (B)), while the direction of the magnetic field is reversed from that during recording, as shown in Figure 4 (C). In this method, a laser beam is irradiated onto the recorded area of the recording film 26, and the magnetization direction of the irradiated area is returned to the state before recording, thereby erasing information.

In the magneto-optical pickup device 1, the laser beam with an elliptical cross section emitted from the semiconductor laser 2 is collimated by the collimator lens 3, and then converted into a laser beam with a circular cross section by the beam shaping prism 4. Shaped by light. After that, this laser light passes through the beam splitter 5 and relay lenses 6 and 7,
The light is reflected by the reflection prism 9 and focused by the objective lens 10, and then irradiated onto the magneto-optical disk 8.

The reflected light from the magneto-optical disk 8 returns along the same optical path as above, is reflected by the beam splitter 5, and is reflected by the beam splitter 5.
After passing through the /2 wavelength plate 12, the light is separated into two directions by a Wollaston prism 13. The laser beam that has passed through this Wollaston prism 13 is focused onto a detector 14 by a lens 15.
An RF reproduction signal is obtained.

Further, the laser beam reflected by the Wollaston prism 13 is transmitted to the beam splitter 16.
further separated by The laser beam that has passed through the beam splitter 16 is focused by a lens 19 and is partially blocked by a knife edge 17, and is irradiated onto a detector 18.
A focusing error signal is obtained by: on the other hand,
The laser beam reflected by the beam splitter 16 is focused onto a detector 20 by a lens 21, and a tracking error signal is obtained by this detector 20.

By the way, the optical parts such as the objective lens 10 are made of PMMA in order to reduce the weight of the pickup device 1.
The objective lens 1 is manufactured from plastic such as (polymethyl methacrylate) or PC (polycarbonate).
0 exhibits a certain level of birefringence due to optical anisotropy caused by the molecular orientation of the plastic during the manufacturing process. In this way, when birefringence exists in optical components such as the objective lens 10, the linearly polarized laser beam is irradiated onto the magneto-optical disk 8 through the objective lens 10 and reflected and refracted by the recording film 26 of the magneto-optical disk 8. The light becomes elliptically polarized and C
/N deteriorates and the signal level decreases.

Furthermore, when optical parts such as the objective lens 10 are manufactured in the injection molding manufacturing process as described above, birefringence appears in the optical parts such as the objective lens 10. The refractive index distribution of the component becomes uniaxially crystalline. Therefore, as shown in FIG. 1, the objective lens 10 has a fast axis 31 in a plane perpendicular to the optical axis 30.
and the slow axis 32 appear perpendicular to each other.

Now, if the angle between the polarization plane 33 of the laser beam incident on the objective lens 10 and the fast axis 31 of the objective lens 10 is θ, then this angle θ and the presence of birefringence in the objective lens 10 A graph showing the relationship between the signal level and the decrease in the signal level that occurs in FIG. 5 is shown in FIG. Note that in FIG. 5, when the angle θ is ±90°, the polarization plane 33 of the laser beam and the slow axis 32 of the objective lens 10 match.

As is clear from the above graph, when the polarization plane 33 of the laser beam incident on the objective lens 10 coincides with the fast axis 31 or the slow axis 32 of the objective lens 10, the maximum signal level is reached. The present inventors have found that the following can be obtained. This signal level will be equivalent to that without birefringence.

In this example, based on the above facts,
As shown in FIG. 1, the polarization plane 33 of the laser beam incident on the objective lens 10 is made to match the fast axis 31 of the objective lens 10.

That is, when manufacturing the objective lens 10 by plastic injection molding, as shown in FIG.
Inlet traces 34 are formed on the edge of the objective lens 10, and
In the center of the objective lens 10, the injection port trace 34
The refractive index distribution is such that the fast axis 31 exists in the diametrical direction passing through. Note that the objective lens 10 has the injection port trace 3
4 remains as is.

By doing this, the polarization plane 33 of the linearly polarized laser light incident on the objective lens 10 is made to coincide with the diameter direction passing through the injection port trace 34 of the objective lens 10 or the direction perpendicular to the diameter direction within the plane of the lens 10. As a result, as shown in FIG. 5, it is possible to suppress a decrease in the signal level due to the presence of birefringence in the objective lens 10.

FIG. 6 shows a second embodiment of the present invention, in which the same parts as in the previous embodiment are denoted by the same reference numerals. In this embodiment, a relay lens for performing focusing control is shown. When birefringence exists in both lenses 6 and 7, the fast axes 31 of these two relay lenses 6 and 7
Alternatively, by aligning the slow axis 32 with the polarization plane 33 of the linearly polarized laser light incident on these lenses 6 and 7, the reduction in signal level due to birefringence can be suppressed as in FIG. 5 of the above embodiment. It is composed of

In this way, even when there are multiple optical components such as lenses having birefringence, the fast axis 3 of each optical component
1 or the slow axis 32 coincide with the polarization plane 33 of the linearly polarized laser light incident on these optical components, it is possible to suppress a reduction in signal level due to birefringence.

The rest of the structure and operation are the same as those of the previous embodiment, so their explanation will be omitted.

[0029]

[Effects of the Invention] This invention has the above-described structure and operation. Even when optical components such as an objective lens have birefringence, the laser beam becomes elliptically polarized light, and the C/N deteriorates and the signal level decreases. It is possible to provide a magneto-optical pickup device that can prevent adverse effects such as

[Brief explanation of the drawing]

FIG. 1 is a perspective view of essential parts of an embodiment of a magneto-optical pickup device according to the present invention.

FIG. 2 is a configuration diagram showing an embodiment of the magneto-optical pickup device.

FIG. 3 is a sectional view showing a magneto-optical disk.

FIG. 4 is an explanatory diagram showing the principles of recording, erasing, etc. on a magneto-optical disk.

FIG. 5 is a graph showing the relationship between angle θ and signal level.

FIG. 6 is a perspective view showing another embodiment.

FIG. 7 is a configuration diagram showing a conventional magneto-optical pickup device.

[Explanation of symbols]

1 Magneto-optical pickup device 6 Relay lens 7 Relay lens 8 Magneto-optical disk 10 Objective lens 30 Optical axis direction 31 Advance axis

Claims (3)

[Claims] 1. A magneto-optical pickup device for recording and reproducing information by condensing a laser beam emitted from a laser light source onto an optical recording medium via an optical element having birefringence, wherein the birefringent 1. A magneto-optical pickup device characterized in that a fast axis or a slow axis of an optical element having the above-mentioned optical element is made to coincide with a polarization plane of a laser beam incident on the optical element. 2. The magneto-optical pickup device according to claim 1, wherein the optical element is a plastic optical element manufactured by injection molding. 3. The optical element is a plastic optical element manufactured by injection molding, and the injection direction passing through the injection hole mark created when manufacturing the plastic optical element by injection molding or the direction perpendicular to the injection direction is
2. The magneto-optical pickup device according to claim 1, wherein the polarization plane of the laser beam incident on the optical element is made to coincide with the polarization plane of the laser beam.