JPS63200346A - Magneto-optical recording and reproducing head - Google Patents

Abstract

PURPOSE:To miniaturize a reproducing optical system and make it light and to facilitate the adjustment of the system, by providing a composite wavelength plate in which two wavelength plates are joined, and a wedge prism which divides a beam of light on the same line as the junction line of the wavelength, in the optical path of a reproducing beam. CONSTITUTION:A laser beam 1 is projected on a magneto-optical recording medium 6, and a reflected reproducing beam of light is optically divided with a beam splitter 4, and they are detected with the composite wavelength plate 7 in which the two wavelength plates are joined and an analyzer 8. Next, a detected beam of light is introduced to the wedge prism 9 which divides the beam of light on the same line as the junction line of the wavelength plate 7, and is amplitude-divided with angles in two directions centering an optical axis, and each beam of light is condensed on a bi-sected optical detector 11. The detected beam of light, since whose phase being shifted by (pi), can be differentially amplified by a differential amplifier 12. Thus, since the composite wavelength plate is used, it is possible to simplify the reproducing optical system and also, to apply the adjustment with resulting high accuracy, and to miniaturize and make it light.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magneto-optical recording/reproducing head using a magneto-optical recording medium, and in particular to an optical head having a structure that allows the optical system for magneto-optical reproduction to be made smaller and simpler. The present invention relates to a magneto-optical recording/reproducing head equipped with an element.

[Conventional technology]

A method for reproducing magnetically recorded information from a magneto-optical recording medium on which information signals are recorded utilizes magneto-optical effects called the Kerr effect and the Faraday effect.

FIG. 5 shows a conventional magneto-optical recording/reproducing head that utilizes the Kerr effect. However, the optical system for obtaining a control signal for driving the actuator 5 is omitted. In this magneto-optical recording/reproducing head, a laser beam emitted from a semiconductor laser 1 is converted into a parallel beam by a collimator lens 2, passes through a polarizer 3° beam splitter 4, and is finely divided by an objective lens 5a provided on an actuator 5. The light is focused into a light spot, irradiated onto the surface of the magneto-optical recording medium 6, and reflected. At this time, the polarization state of the reflected light changes depending on the magnetization state of the irradiated magneto-optical recording medium. The reflected light passes through the objective lens 5a again, has its optical path bent by the beam splitter 4, is sent to the analyzer 8, and then passes through the condenser lens 10.
The light is focused on the photodetector 13, and a signal corresponding to the magnetization state of the medium is output.

FIG. 6 is a diagram for explaining the reproduction principle of magneto-optical recording using the magnetic Kerr effect, and P in the figure.

is the polarized light incident on the magneto-optical recording medium 6, R is the polarized light reflected from a magnetized region below the medium film surface, and R is the polarized light incident on the magneto-optical recording medium 6.
- represents the polarized light reflected from the magnetized region above the medium film surface. Further, θ is called the Kerr rotation angle and represents the amount by which the plane of polarization of light is rotated due to the magneto-optic effect.

At this time, when the reproducing light spot scans the alternately magnetized areas of the magneto-optical recording medium 6, the analyzer 8 is mechanically rotated by θ from the extinction position, with the light intensity incident on the analyzer 8 being P. The light intensity S of the modulated light when

5=Psin2θkSin2θ (1) [Problem to be solved by the invention] In this case, the analyzer 8 is mechanically rotated so as to maximize the signal-to-noise ratio (SN ratio) of the reproduced signal, and the optimum setting is made. Angle θ. It is necessary to set it to . The setting angle θ of this analyzer.

The noise on the photodetector 13 and the magneto-optical recording medium 6 are
Noise caused by fluctuations in reflected light from the source has a large effect. Therefore, a differential detection method as shown in FIGS. 7(a) and 7(b) has been conventionally used as a method for removing common-mode noise caused by fluctuations in reflected light.

In the differential type magneto-optical recording/reproducing head shown in FIG. 7(a), a laser beam emitted from a semiconductor laser 1 is converted into parallel light by a collimator lens 2, passes through a polarizer 3, a beam splitter 4, and then passes through an objective lens 5a. The light is focused into a minute light spot, and is irradiated onto the surface of the magneto-optical recording medium 6 and reflected. The reproduction beam from the magneto-optical recording medium 6 is amplitude-divided by beam splinters 4 and 4a, and each analyzer 8a.

8b, and then the condenser lens 10a.

10b, the light is focused on each photodetector 13a, 13b,
The configuration is such that photoelectric conversion is performed, a reproduced output is obtained, and a differential amplifier 12 performs differential amplification.

On the other hand, in the differential type magneto-optical recording/reproducing head shown in FIG. 7(b), the laser light emitted from the semiconductor laser 1 is converted into parallel light by the collimator lens 2, and the polarizer 3. The light passes through the beam splinter 4, is focused into a minute light spot by the objective lens 5a, is irradiated onto the surface of the magneto-optical recording medium 6, and is reflected.

The reproduction beam light from the recording medium 6 has its polarization plane halved.
The wavelength plate 18 rotates the light by π/4, the analyzer 8 splits the light and the wave is detected, and then the condenser lenses 10a, 1
0b, the light is focused on each photodetector 13a, 13b, photoelectrically converted, a reproduced output is obtained, and a differential amplifier 12 performs differential amplification.

In the case of the magneto-optical recording/reproducing head shown in FIG. 7(a), it is necessary to use two expensive analyzers, and it is necessary to set the setting angle of each analyzer to the optimum angle. The drawback is that it is difficult to adjust. On the other hand, Fig. 7 (
In the case of the magneto-optical recording/reproducing head shown in b), there is no need to rotate the analyzer itself, but since both the transmitted light and reflected light of the analyzer are used, the magneto-optical recording/reproducing head shown in FIG. 7(a) Like the head, it has a spatially large configuration. Also, Fig. 7 (a
) and (b) both have drawbacks such as the need to use two photodetectors with the same characteristics and difficulty in adjusting the light reception.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magneto-optical recording/reproducing head having a configuration in which the optical system for magneto-optical reproduction can be made smaller and lighter, and the optical system can be easily adjusted by improving the above-mentioned drawbacks. It is in.

[Means for solving problems]

The magneto-optical recording/reproducing head of the present invention includes a light source, an optical system that focuses a light beam emitted from the light source onto the surface of a magneto-optical recording medium and extracts a reproduction beam from the magneto-optical recording medium, and the reproduction head. A composite wavelength plate in which two wavelength plates are joined, which are provided in the optical path of the beam light and have a boundary that divides the reproduced beam light into two; an analyzer provided in the optical path; and a joining line between the composite wavelength plate. a wedge prism that splits a beam on the same line as the beam, a two-split photodetector that receives each of the split beams, and a differential amplifier that differentially amplifies the output of each of the two split photodetectors. It is characterized by being prepared.

[Effect]

By using a composite wave plate in the optical system for magneto-optical reproduction, the reproduction optical system is simplified, which not only makes it easier to adjust the optical system stably and accurately, but also makes the magneto-optical head smaller and lighter. This makes it possible to greatly shorten the access time of the magneto-optical disk system itself.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a first embodiment of the magneto-optical recording/reproducing head of the present invention. This magneto-optical recording/reproducing head includes a semiconductor laser 1 as a light source, a collimator lens 2. Polarizer 3. An optical system consisting of a beam splinter 4 and an objective lens 5a, a composite wavelength plate 7 in which two wavelength plates are joined, which are provided in the optical path of the reproduced beam light and have a boundary that divides the reproduced beam light into two, and an analyzer 8.
, a wedge prism 9 that splits a beam on the same line as the joining line of the composite wavelength plate 7, a condenser lens 10 that focuses each of the split beams, and a two-split beam that receives the condensed beam. It is equipped with a detector 11 and a differential amplifier 12 that differentially amplifies the output of each of the two-split photodetectors, and the composite wave plate 7 aligns the crystal orientation axes of the two wave plates with respect to the joining line. It is set symmetrically. Note that in FIG. 1, the optical system for obtaining control signals for driving the actuator is omitted.

The light beam emitted from the semiconductor laser 1 passes through the collimator lens 2
．． Polarizer 3. The light passes through the beam splitter 4 in order and is focused and irradiated onto the surface of the magneto-optical recording medium 6 by the objective lens 5a installed on the actuator 5. A part of the focused beam is reflected by the magneto-optical recording medium. The reflected reproduction beam light is split by the beam splitter 4, and the reproduction beam light is transmitted to the composite wavelength plate 7 and the analyzer 8 according to the present invention.
The wave is detected by Next, the detected light beam is transferred to a composite wavelength plate 7.
Wedge prism 9 that splits the luminous flux on the same axis as the joining line of
and divides the amplitude at angles in two directions around the optical axis. Each of the amplitude-divided beams is detected by a two-split photodetector.
The light is condensed by a condenser lens 10, and its output is differentially amplified by a differential amplifier 12. At this time, for example, a half-wave plate is used as the composite wavelength plate 7, and the crystal orientation axes are set to be symmetrical, making an angle of 3π/8 from the joining line, for example.

FIG. 3 is a diagram illustrating the optical properties of the composite wavelength plate according to the present invention. In FIG. 3, each half-wave plate 21
．． The crystal orientation axis 23 of 22 is 3π/8 with respect to the joining line 24
It is created by tilting it. At this time, each wavelength plate 21.
The signal component S transmitted through the wave plate 22 and detected by the analyzer 8 is clearly equivalent to setting the setting angle θ to π/4 and 3π/4, respectively, from equation (1). The signals detected by the analyzer have a phase shift of π. Therefore, differential amplification can be performed from the output of one two-split photodetector.

In the first embodiment described above, the composite wavelength plate 7 according to the present invention
Although the explanation has been made on the assumption that the amount of each light transmitted by the analyzer is the same, in reality, the amount of light transmitted by the analyzer is the same, but in reality, the amount of light transmitted by the analyzer varies depending on various factors, such as the precision of manufacturing the composite wavelength plate 7, the installation of optical components, and differences in environmental conditions. The amount of light transmitted by the analyzer with respect to the wave plate may become unbalanced, and the S/N ratio of the reproduced signal may deteriorate.

FIG. 2 shows a second embodiment of the present invention that does not have this problem. This magneto-optical recording/reproducing head is the same as the first embodiment except that a rotation mechanism 19 is provided so that the analyzer 8 can be rotated around the optical axis, and the other configurations are the same as those of the first embodiment. Therefore, the same components are labeled with the same numbers as in FIG. 1.

FIG. 4 shows an example of the rotation mechanism 19 that rotates the analyzer 8. FIG. 4(a) is a front view, and FIG. 4(b) is a side view. This rotation mechanism 19 includes a support base 14, on which a support column 15 is rotatably supported. A gear 16 is fixed to one end of the support column, and a through hole 17 is provided in the support column 15 and the gear 16. An analyzer 8 is fixed within this through hole. According to this rotation mechanism, the analyzer 8 is rotated by rotating the gear 16.

In the second embodiment, the analyzer 8 is rotated by a rotating mechanism 19 shown in FIG.
By arranging it and slightly rotating it around the optical axis, it is possible to equalize the amount of light that passes through the analyzer 8 for each wavelength plate. As a result, the S/N ratio of the reproduced signal can be improved. Also, of course, contrary to the second embodiment, the analyzer 8 is fixed and the composite wavelength plate 7. A similar effect can be obtained by providing the wedge prism 9 and the two-split photodetector 11 integrally in a rotating mechanism.

In the above two embodiments, the light whose amplitude has been divided by the wedge prism 9 is focused on the two-split photodetector 11 by the condensing lens 10. A configuration may also be adopted in which the light is focused on a detector. Further, the condenser lens may be arranged over the entire surface of the composite wavelength plate according to the present invention. In this case, the magneto-optical recording/reproducing head can be further miniaturized than in the above embodiments. In addition, before the reproduction beam passes through the composite wavelength plate, a phase compensation plate is placed, which has a so-called phase compensation effect, which can alleviate the effects of turbulence caused by the reproduction optical system and the magneto-optical recording medium. It's okay.

〔Effect of the invention〕

As explained above, the magneto-optical recording/reproducing head of the present invention has
By using a composite wave plate in the optical system for magneto-optical reproduction, we were able to make the optical system smaller and lighter.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the magneto-optical recording/reproducing head of the present invention, FIG. 2 is a diagram showing a second embodiment of the present invention, and FIG. 3 is a composite wavelength plate according to the present invention. Figure 4 is a diagram of the rotation mechanism that mechanically rotates the analyzer; Figure 5 is a diagram showing the basic configuration of a conventional basic magneto-optical recording/reproducing head; Figure 6 7(a) and 7(b) are diagrams showing the basic configuration of a conventional differential type magneto-optical recording/reproducing head. be. 1...Semiconductor laser 2...Collimator lens 3...Polarizer 4.4a...Beam splitter 5...Actuator 5a...Objective lens 6... - Magneto-optical recording medium 7... Composite wavelength plate 8... Analyzer 9... Wedge prism 10.10a, 10b - Condensing lens 11...
・Two-split photodetector 12...Differential amplifier 13.13a, 13b...Photodetector 14...
Support stand 15...Support column 16...Gear 17...Through hole 18...Half wavelength plate 19...Rotation mechanism 21.22...・Wavelength plate agent Patent attorney Yoshiyuki Iwasa Figure 3 (a) (b) Figure 4 Bottom Figure 6 (a) 1-\White (b) Figure 7

Claims (3)

[Claims] (1) A light source, an optical system that focuses the light beam emitted from the light source onto the surface of a magneto-optical recording medium and extracts a reproduction beam from the magneto-optical recording medium, and is installed in the optical path of the reproduction beam. 2 having a boundary that divides the reproduction beam into two.
a composite wavelength plate in which two wavelength plates are joined together, an analyzer provided in the optical path of the analyzer, a wedge prism that splits a luminous flux on the same line as the joining line of the composite wavelength plate, and a wedge prism that splits a luminous flux on the same line as the joining line of the composite wavelength plate; A magneto-optical recording/reproducing head comprising a two-divided photodetector that receives light and a differential amplifier that differentially amplifies the output of each of the two-divided photodetectors. (2) In the magneto-optical recording/reproducing head according to claim 1, the composite wavelength plate is characterized in that the crystal orientation axes of the two wavelength plates are set symmetrically with respect to the joining line thereof. magneto-optical recording/reproducing head. (3) A magneto-optical recording/reproducing head according to claim 1 or 2, wherein the light source is a laser.