JPS59121639A - Opto-magnetic optical device - Google Patents

Abstract

PURPOSE:To omit a beam splitter to be used for guiding light to an error signal detector and to improve SN in a reproduced signal by adjusting a relative angle made by the polarizing surface of reflected light from a medium and the polarizing surface of an analyzer by a wavelength plate and fixing the analyzer. CONSTITUTION:Light beams projected from a laser diode 1 are made into parallel light by a colimate lens 2 and then reflected by a beam splitter 3 to guide the optical path in the direction of a magneto-optical recording medium 4. An objective lens 5 converges the light beam guided in the medium 4 direction on the medium 4. The medium 4 turns the polarizing surface of the light beam by a fixed angle (angle of Kerr rotation) on the basis of magnetic Kerr effect. The reflected light beam is made into parallel light again by the objective lens 5 and reaches a half-wave length plate 24 through the beam splitter 3. The half- wave length plate 24 turns the polarizing surface of the light beam by a precribed angle and sends the light to an analyser 21. The analyser 21 detects the component of the light beam to the polarizing surface as a reproduced signal component and sends the component to a reproduced signal detecting device 23 and reflects other components in the direction of a focusing/tracking error signal detecting device 22.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to
The present invention relates to a magneto-optical device that performs recording and reproduction using effects.

A conventional magneto-optical device of this type has a configuration as shown in FIG. That is, in the figure, 1 is a laser diode, and 2 is a collimating lens for collimating the light beam emitted from the laser diode.

Reference numeral 3 designates a first beam splitter for reflecting a part of the light beam, which has been made into parallel light by the collimating lens 2, toward the magneto-optical recording medium 4.

Reference numeral 5 denotes an objective lens for converging the light beam reflected by the first beam splitter 3 onto the magneto-optical recording medium 4. Furthermore, a numeral 6 reflects a part of the light beam that has been completely reflected by the magneto-optical recording medium 4 and has become parallel light again by the objective lens 5 in the direction of the 4-split detector 7, and transmits other light beams. 2 beam splitter. A cylindrical lens 8 is installed on the optical path of the light beam reflected by the second beam splitter 6 and in front of the four-split detector 7. The four-part detector 7 and the cylindrical lens 8 constitute a device for detecting seven tracking error signals.

On the other hand, 9 is an analyzer for decomposing and detecting reproduced signal components from the light beam transmitted through the 26th beam splitter, and generally a polarizing beam splitter, Glan-Thompson prism, Polaroid plate, etc. are used. . This analyzer 9 is provided so as to be rotatable and adjustable around the optical axis.

Reference numeral 10 denotes a lens for converging the light beam transmitted through the above-mentioned two analyzers 9 onto a detector 11 for detecting a reproduced signal. As the detector 11, an APD (avalanche photodiode) is generally used in order to obtain a good signal-to-noise ratio (S/N ratio).

In a conventional magneto-optical device having such a configuration,
The plane of polarization of the light beam incident on the magneto-optical recording medium 4 is rotated by a fixed angle υ (Kerr rotation angle) according to the magnetic recording signal due to the so-called Kerr effect, and then reflected. The light beam with the rotated plane of polarization is then
A part of the light is reflected by the beam splitter 6 and enters the cylindrical lens 8, and is converted into a focusing and tracking error signal by the 4-split detector 7.

-75, the other light beams that entered the second beam sinter 6 pass through as they are and reach the analyzer 9. The analyzer 9 detects the reproduced signal component of the original beam for that plane of polarization. The light beam, which is a reproduced signal component detected by the analyzer 9, is converged by a lens 10, reaches a detector 11, and is converted into a reproduced signal.

By the way, the conventional magneto-optical device that operates as described above has the following problems. That is, the 8/N ratio of the reproduced signal h output by the detector 11 is the
In the conventional magneto-optical device described above, the light beam is split by the second beam splitter 6 and further split by the analyzer 9, so the amount of light incident on the detector 11 is As a result, the S of the reproduced signal detected by the detector 1)
/N ratio was poor, causing problems in terms of reproduction accuracy.

It is also possible to consider a configuration in which the second beam splitter 6 is removed and focusing and tracking errors are detected using the light beam reflected by the analyzer 9. However, in this case, each time the relative angle between the polarization plane of the light beam reflected by the medium 4 and the polarization plane of the analyzer 9 is adjusted by rotating the analyzer 9, the direction of reflection of the light beam reflected by the analyzer 9 changes. The position of the focusing and tracking error signal detection device must be adjusted accordingly.

Therefore, there is considerable difficulty in implementing it.

Additionally, beam sintering is generally formed by coating a rectangular prism with multiple layers of dielectric film, and then bonding another rectangular prism to this multilayer coated surface, which makes the prism itself expensive. . Therefore, in an apparatus in which the beam sinter is used in two places like the conventional apparatus described above, there is a problem in that the manufacturing cost is extremely high and expensive.

The present invention has been made to solve the above-mentioned problems, and its purpose is to provide a magneto-optical device that can improve the S/N ratio of reproduced signals (two signals) and reduce the cost. be.

Hereinafter, the present invention will be explained based on examples shown in the drawings.

FIG. 2 and subsequent figures are diagrams showing the configuration of an embodiment of the present invention. Note that the same parts or corresponding parts as shown in FIG.

FIG. 2 is a diagram showing the configuration of the first embodiment of the present invention.

In the figure, 21 is an analyzer consisting of a polarizing beam splitter, a Glan-Thompson prism, etc. The analyzer 21 is provided on the optical path of the light beam reflected by the magneto-optic recording medium 4 and between the beam splitter 3 and the lens 10 with the plane of polarization fixed. In this analyzer 2, of the incident light beam, only the component corresponding to the polarization plane of the analyzer 2 is transmitted, and the other components are reflected. A focusing system consisting of a cylindrical lens 8 and a 4-split detector 7 is placed on the optical path of the light beam reflected by the analyzer 2.

A tracking error signal detection device 22 is provided. The focusing/tracking error signal detection device 22 detects the focusing error signal by a so-called astigmatism method, and also detects the tracking error signal by changing the light intensity distribution of the light beam in the four-split detector 7. It is.

- On the optical path of the light beam transmitted through the analyzer 21, a reproduced signal detection device 23 consisting of a lens 10 and a detector 11 is provided.

1. On the optical path of the light beam reflected by the magneto-optical recording medium 4 and between the analyzer 21 and the beam splitter 3, a % wavelength plate 24 is provided so as to be rotatable around the optical axis. There is.

Next, the operation of this embodiment configured as described above will be explained. That is, a light beam emitted from a laser diode 1 is converted into parallel light by a collimating lens 2, and further reflected by a beam splitter 3 to guide the optical path toward a magneto-optic recording medium 4. The objective lens 5 focuses the light beam directed toward the medium 4 onto the medium 4 . In the medium 4, the plane of polarization of the light beam is rotated by a certain angle (Kerr rotation angle) by a so-called Kerr effect in response to the magnetic recording signal, and the light beam is reflected toward the objective lens 5. The light beam reflected in this way is made into parallel light again by the objective lens 5, passes through the beam splitter 3, and reaches the iAm long plate 24. This % wavelength plate 24 rotates the polarization plane of the light beam by a predetermined angle and sends it to the analyzer 2. The analyzer 21 detects the components of the light beam corresponding to the polarization plane as reproduced signal components and sends them to the reproduced signal detection device 23, and reflects the other components in the direction of the focusing and tracking error signal detection device 22.

The reproduced signal detection device 23 detects a reproduced signal using a light beam that is focused by the lens 10 and is incident on the detector 11. On the other hand, the focusing/tracking error signal detection device 22 performs focusing using the so-called astigmatism method, which utilizes the fact that the spot on the four-split detector 7 of the light beam that has passed through the cylindrical lens 8 is deformed according to the shift in focus and depression. Detect error signals. At the same time, a tracking error signal is detected by utilizing the fact that the light intensity distribution of the light beam spot on the four-division detector 7 changes due to tracking error.

In this embodiment, which operates as described above, in order for the analyzer 2 to detect more reproduced signal components from the incident light beam, it is necessary to adjust the relative angle between the polarization plane of the analyzer 2 and the polarization plane of the light beam. It is necessary to set the angle between 2° and 20°,
This angle setting can be performed by rotating the wavelength plate 24 about the optical axis. Suwachi, hammer wave plate 24
When rotated simultaneously, the polarization plane of the light beam also rotates with the rotation, so that a predetermined set angle can be obtained with respect to the analyzer 2. In this embodiment, the relative angle between the polarization plane of the analyzer 2 and the polarization plane of the light beam can be set by the 3A wavelength plate 24.
can remain fixed. Therefore, focusing,
Focusing and tracking error signals can be easily detected from the light components reflected by the analyzer 2 up to the reed where the tracking error signal detection device 22 is placed at a fixed position, and as a result, the amount of light incident on the detector 11 increases. The S/N ratio of the reproduced signal can be improved. In addition, the beam splitter 6 in the conventional device shown in FIG. 1 is not required, making it possible to reduce the cost.

FIG. 3 is a diagram showing the configuration of a second embodiment of the present invention.

That is, in this embodiment, the reproduced signal detection device 23 is disposed on the optical path of the light beam reflected by the analyzer 2 in the first embodiment, and the light beam transmitted through the analyzer 2 is The focusing and tracking error signal detection device 22 is disposed on the optical path of the optical system. in this case,
The relative angle between the polarization plane of the analyzer 21 and the polarization plane of the light beam is set to about 70° to 88° by the % wavelength plate 24, and the reproduced signal component of the light beam is reflected at the analyzer 21.

This embodiment with such a configuration also provides the same effects as the first embodiment described above.

FIG. 4 is a diagram showing the configuration of a third embodiment of the present invention.

That is, in this embodiment, the focusing error signal in the first embodiment described above is detected using the so-called critical angle method. This focusing error signal detection means based on the critical angle method is disclosed in detail in Japanese Patent Application Laid-open No. 7246/1983. That is, in this embodiment using the critical angle method, the critical angle prism 25 is placed on the optical path of the light beam reflected by the analyzer 2 so that its reflective surface is almost critical to the incident light beam in a focused state. It is arranged so as to take a corner, and a four-split detector 26 is arranged on the optical path of the light beam that passes through the critical angle prism 25.

It should be noted that there are 3
A wavelength plate 27 is interposed.

In this embodiment with such a configuration, the light beam reflected by the analyzer 21 along the same path as in the first embodiment is modified into P-polarized light by the 3A wavelength plate 27 and then enters the critical angle prism 25. do. In the critical angle prism 25, if the light beam is incident on the reflective surface in a focused state, the light beam will be totally reflected, and if the light beam is out of focus and incident on the reflective surface, the light beam will be totally reflected. The reflected intensity of the beam changes drastically on the left and right sides of the optical axis. A focusing error signal can be detected by detecting a change in the reflected intensity of this light beam with the four-division detector 26. In addition to detecting the focusing error signal, the four-division detector 26 can also detect a tracking error signal based on a change in the light intensity distribution with respect to the tracking error.

FIG. 5 is a diagram showing the configuration of a fourth embodiment of the present invention.

That is, in this embodiment, when the light beam passes through the % wavelength plate 24, it becomes elliptically polarized to some extent depending on the accuracy of the % wavelength plate 24, etc.
/ It may reduce the N ratio. Therefore, in this embodiment, the 174 wavelength plate 28 interposed between the analyzer 21 and the spoon wave plate 24 is used to correct the elliptical polarization of the light beam, and the S/ This further improves the N ratio.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

As explained above, according to the present invention (2), the relative angle between the polarization plane of the reflected light beam from the medium and the polarization plane of the analyzer is adjusted by the wave plate, and the analyzer remains fixed. With this configuration, one of the light beams split into two by the analyzer can be guided by a reproduction signal detection device (two) installed at a fixed position, and the other can be guided by a focusing and tracking error signal detection device installed at a fixed position. As a result, a beam splitter and a ritter for guiding the beam to the focusing and tracking error signal detection device are no longer necessary, and the S/N ratio of the reproduced signal is improved.
It is possible to provide a magneto-optical device that can realize a reduction in price.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the structure of a conventional magneto-optical device, FIG. 2 and the following figures show embodiments of the present invention, and FIG. FIG. 2 is a configuration diagram showing the configuration of an example. 1... Laser diode, 2... Collimating lens, 3... First beam splitter, 4... Magneto-optical recording medium, 5... Objective lens, 6... Second beam splitter, 7...4-split detector, 8...Cylindrical lens, 9...Analyzer, 10...Lens, 1...
・Detector, 21... Analyzer, 22... Focusing and tracking error signal detection device, 23...
Reproduction signal detection device, 24...3A wavelength plate, 25...
Critical angle prism, 26... 4-segment detector, 27.
...3A wave plate, 28...]/4 wave plate. Applicant's representative Patent attorney Takehiko Suzue (Figure 4 Figure 5 Procedural amendments filed on December 2, 1982 by Kazuo Wakasugi, Commissioner of the Japan Patent Office 1, Patent Application for Indication of Case 1982-'231345 No. 3, Amendments Relationship with the case of a person who does

Claims (3)

[Claims] (1) In a magneto-optical device that performs recording and reproduction using the magneto-optic effect in a magneto-optic recording medium, a magneto-optical device is provided on the optical path of the reflected light beam from the medium so as to be rotatable and adjustable about the optical axis. At least one wavelength plate, an analyzer with the plane of polarization fixed on the optical path of the light beam that has passed through the wave plate, and a portion of the light beam that is split into two by this analyzer. Magneto-optical optics, characterized by comprising a focusing and tracking error signal detection device provided on the road, and a reproduced signal detection device provided on the other optical path of the light beam split into two by the analyzer. Device. (2) The wavelength plate provided on the optical path of the reflected light beam from the medium in a rotatable manner around the optical axis is a % wavelength plate. magneto-optical device. (3) The wavelength plate provided on the optical path of the reflected light beam from the medium for rotational adjustment around the optical axis is a % wavelength plate and a 174 wavelength plate into which the light beam transmitted through the 3A wavelength plate is incident. Claim No. fil 11 is characterized in that
Magneto-optical device.