JPS63157341A - Magneto-optical recording/reproducing head - Google Patents

Abstract

PURPOSE:To obtain a compact the light-weight optical system and at the same time to improve the light availability by providing a multi-split photodetector to a 2nd optical system which detects the reflected light sent from a recording medium to detect the information signals out of two luminous fluxes that are divided with polarization in parallel to an optical axis. CONSTITUTION:A semiconductor laser light is projected on an optical recording medium 6 via an objective lens 5 and the reflected light of the medium 6 is reflected by a beam splitter 4. This reflected light is led to a multi-split photodetector 11 via a critical angle prism 7 which can apply a critical angle method, a 1/2 wavelength plate 8 which turns a polarized surface by pi/4 and a several plate 10. The detector 11 leads one of two beams divided with polarization in parallel to an optical axis to a photodetecting part 11a. Then a focus error signal is outputted by a critical angle method and the other beam is led to a photodetecting part 11b for output of a track error signal. In such a constitution, a compact and light-weight optical system is obtained together with improvement of the light availability. Then the load of a light source is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magneto-optical recording/reproducing head using a magneto-optical recording medium, and in particular to an optical element having a configuration that allows the magneto-optical system to be made smaller and simpler. This relates to the mounted magneto-optical recording/reproducing head. [Prior Art] When recording and reproducing information signals on the surface of a magneto-optical recording medium using an optical head, focal plane detection and track position detection are first important. Conventionally, various methods have been devised for focal plane detection. Representative methods include the Naifetsu method, the astigmatism method, and the critical angle method. this house,
An outline of the critical angle method related to the present invention will be described. 8th
The figure shows a conceptual diagram of the critical angle method. When the disk is at the focal point B of the objective lens 25, the reflected light from the disk becomes parallel. At this time, a prism 26 whose incident angle is adjusted to be a critical angle is arranged, and a two-split photodetector 27 is arranged behind it to constitute a critical angle method. As shown in FIG. 8(b), when the disc is at the focus position B, all the incident angles to the prism 26 are critical angles, and the total luminous flux reaches the two-split photodetector 27 through total reflection. Next, when the disk is at position A, as shown in FIG. 8(a),
The light exiting the objective lens 25 becomes focused light, and the lower half of the light beam with the optical axis as a boundary has an incident angle less than the critical angle, and the upper half of the light beam has an incident angle greater than or equal to the critical angle. Since the light is partially transmitted, an output difference occurs between the two divided photodetectors 27. In addition, when the disk is in position C, as shown in Figure 8(c), the upper half of the light beam is not totally reflected but partially transmitted, as shown in Figure 8(a), and the light beam is divided into two parts. In the device 27, an output difference opposite to that shown in FIG. 8(a) is produced. A focus error signal is obtained from this output difference.

On the other hand, in the prism 26, the light is totally reflected in a direction perpendicular to the dividing line of the photodetector 27 without being affected by the critical angle.

Therefore, since diffraction light is generated when guide grooves are formed on the disk substrate in advance, a two-split photodetector having a dividing line perpendicular to the dividing line of the two-split photodetector 27 described above is conventionally used. A certain push-pull method can be applied, and a tracking error signal can be obtained from the output difference of the two-split photodetector. Therefore, by using a four-part photodetector as shown in FIG. 9, the servo error signal can be detected with one photodetector.

On the other hand, the Kerr effect is used in a method of reproducing magnetically recorded information from a magneto-optical recording medium on which information signals are recorded.

A magneto-optical effect called the Faraday effect is used.

FIGS. 7(a) and 7(b) show a conventional magneto-optical recording/reproducing head that utilizes the Kerr effect. In the magneto-optical recording/reproducing head shown in FIG. 7(a), the laser light emitted from the semiconductor laser 1 is converted into parallel light by the collimator lens 2,
The light passes through a beam splitter 3 and a beam splitter 4, is focused into a minute light spot by an objective lens 5 installed on an actuator, and is irradiated onto the surface of a 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 from the magneto-optical recording medium passes through the objective lens 5 again, and the optical path is bent by the beam splitter 4.
It reaches the half-wave plate 8. At this time, the half-wave plate rotates the polarization plane of the reflected light by π/4, and the analyzer 12
The light is transmitted to the photodetectors 13a and 13b by the lens 9, and a signal corresponding to the magnetization state of the magneto-optical recording medium is output, and a differential amplifier 17 forms a difference signal. At this time, a portion of the light transmitted through the beam splitter 4 is reflected by the beam splitter 3 and guided to a servo optical system consisting of a critical angle prism 7 and a four-split photodetector 16. As mentioned above, in the servo optical system, a focus error signal and a track error signal are obtained using, for example, the critical angle method, and the light beam is positioned on the surface of the magneto-optical recording medium.

The magneto-optical recording/reproducing head shown in FIG. 7(b) is an example in which the beam splitter 3 is provided in the optical path of the reflected light from the beam splitter 4, and the other structure is the same as that in FIG. 7(a).

FIG. 6 is a diagram for explaining the reproduction principle of magneto-optical recording that makes extensive use of the magnetic Kerr effect.

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 12 is mechanically rotated by θ from the extinction position, with the light intensity incident on the analyzer 12 being P. The light intensity S of the modulated light when

5=Psin2θgsin2θ [Problem to be solved by the invention] In the conventional magneto-optical recording/reproducing head shown in FIG. Since the beam splitter is inserted between the beam splitter and the magneto-optical recording medium, not only the efficiency of light utilization deteriorates, but also it is necessary to use two expensive beam splitters. On the other hand, the seventh
In the conventional magneto-optical recording/reproducing head shown in Figure (b), it is possible to use one beam splitter between the laser and the magneto-optical recording medium to increase the efficiency of laser light utilization, but the number of beam splitters is limited. remains at two, and the signal-to-noise ratio (S
(N ratio) deteriorates, leading to drawbacks such as a decrease in servo error tracking performance and a decrease in the S/N ratio of the recorded information signal. These Figure 7(a).

The conventional magneto-optical recording/reproducing head shown in FIG. 3(b) uses both transmitted light and reflected light from the analyzer, so it has a spatially large configuration. Further, there are disadvantages in that it is necessary to use two photodetectors with uniform characteristics, the light-receiving area of the photodetectors is small, and it takes time and effort to adjust the individual light-receiving positions.

In addition, in this case, the servo error signal is obtained by a separate optical system, resulting in a spatially large configuration, which reduces the size of the device.
This was a major drawback to lower prices.

The purpose of the present invention is to improve the above-mentioned drawbacks and to provide a magneto-optical recording/reproducing head that can reduce the size and weight of the optical system for magneto-optical reproduction and has an optical system configuration that has high light utilization efficiency. be.

[Means for solving problems]

The magneto-optical recording/reproducing head of the present invention includes a light source, a first optical system for condensing and irradiating a light beam emitted from the light source onto the surface of a magneto-optical recording medium and extracting reflected light or transmitted light thereof, and a first optical system for collecting the reflected light or transmitted light. Alternatively, a beam splitter that is installed in the optical path of the transmitted light and splits the reflected light or transmitted light, and a beam splitter that is installed in the optical path of the transmitted light of the beam splitter or the reflected light from the beam splitter and that allows the critical angle method to be applied. a prism, a second optical system installed in the optical path of the reflected light of the reflecting prism, which rotates the plane of polarization by π/4 and splits the light beam into polarized light parallel to the optical axis; It is characterized by comprising a multi-division photodetector that detects information signals from the light beam.

[Effect]

By simplifying the reproducing optical system, it is possible not only to make the magneto-optical recording/reproducing head smaller and lighter, but also to reduce the burden on the light source by increasing the light utilization efficiency of the light source. For this reason, increasing the number of rotations of the disk ultimately leads to an increase in data transfer speed. At the same time, it is also possible to significantly shorten the access time of the magneto-optical disk system itself. On the other hand, since only one photodetector is required, the effort required for adjustment can be significantly reduced.

〔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 which is a light source, and a collimator lens 2 which condenses and irradiates the light beam emitted from the semiconductor laser onto the surface of a magneto-optical recording medium 6. A beam splitter 4, an objective lens 5, a critical angle prism (reflection prism) 7 provided in the optical path of the reflected light from the magneto-optical recording medium 6 to which the critical angle method can be applied, and a polarization plane set to π.
A half-wave plate 8 with a rotation mechanism that rotates /4, a condensing lens 9, a Savart plate 10 that polarizes and splits a luminous flux parallel to the optical axis, and information signals from both polarized luminous fluxes, respectively. The multi-division photodetector 11 has a function of outputting a recording information signal at the same time as a servo error signal.

The light beam emitted from the semiconductor laser 1 passes through the collimator lens 2
．． The light passes through the beam splinter 4 in order, and is focused and irradiated onto the surface of the magneto-optical recording medium 6 by the objective lens 5 installed in the actuator. A part of the focused beam is reflected by the magneto-optical recording medium. The reflected light beam is split by a beam splinter 4. At this time, the beam splitter 4 is configured to reflect 100% of the information signal component on the magneto-optical recording medium and partially reflect the component whose polarization plane differs by π/2 from the information signal component. The reflected light from the magneto-optical recording medium reflected by the beam splitter 4 is reflected by a reflecting prism 7 configured to be able to apply the critical angle method, and the polarization plane is changed to π/4 by a half-wave plate 8 with a rotating mechanism. can only be rotated. Next, this reflected light passes through a condenser lens 9, and is guided to a multi-segment photodetector 11 where the light flux is polarized and split parallel to the optical axis by a Savart plate 10 according to the present invention.

FIG. 2 shows a configuration example of the multi-division photodetector 11 according to the present invention. Of the two light beams polarized and split parallel to the optical axis, one light beam is guided to the photodetection section 11a of the multi-split photodetector 11 and a focus error signal is detected by the critical angle method in the conventional technology. F. This is a configuration that outputs . On the other hand, other light beams are guided to the photodetector 11b. At this time, the photodetector 11b outputs information from the guide groove on the disk medium surface as a track error signal using the Pufschable method, which is a conventional technique. On the other hand, the recorded information signal on the magneto-optical recording medium is obtained by introducing the sum signals of each of the photodetectors 11a and llb to a differential amplifier and performing differential calculation. In addition, in the multi-division photodetector 11, in order to differentially amplify the sum signal of the photodetector 11a and the sum signal of the photodetector 11b, it is necessary to make the same amount of light incident on both photodetectors. For this purpose, the half wavelength plate 8 with a rotation mechanism is rotated around the optical axis for adjustment. Of course, the plane of polarization should be theoretically set to π/4 in advance.
If the optical axis of the half-wave plate 8 is designed so that it can be rotated, there is no need for a rotation mechanism, but in reality, the characteristics may change due to mechanical misalignment or environmental conditions. , it is better to provide a rotation mechanism.

FIG. 3 shows an example of the configuration of the half-wave plate 8 with a rotating mechanism. FIG. 3(a) is a front view, and FIG. 3(b) is a side view. The rotation mechanism includes a support base 18, on which a support column 20 is rotatably supported.

A gear 19 is fixed to one end of the support column, and a through hole 21 is provided in the support column 20 and the gear 19. Inside this through hole, there is a 1/2 wavelength plate 2.
2 is fixed. According to this half-wave plate with a rotating mechanism, when the gear 19 is rotated, the half-wave plate 22 is rotated.

FIG. 4 is a diagram illustrating the optical properties of the Savart plate 10 according to the present invention. In FIG. 4, the separation width d of the Savart plate is proportional to the thickness t in the optical axis direction and is expressed by the following equation.

Here, No is the refractive index of ordinary rays, N is the refractive index of extraordinary rays, and the Savard plates are composed of quartz and calcite.
For example, when using calcite, it is given by d~0.106t. Therefore, the multi-division photodetector 11a, ll
The separation width d is set so as to be symmetrical with respect to the dividing line between b. Furthermore, when the Savart plate is rotated around the optical axis, the separation width d of the light beam does not change, but the direction in which it is separated rotates. A split photodetector 11 is installed.

FIG. 5 shows a second embodiment of the magneto-optical recording/reproducing head of the present invention. This magneto-optical recording/reproducing head uses a semiconductor laser 1 as a light source, as in the first embodiment of the present invention, and condenses and irradiates the light beam emitted from the light source onto the surface of a magneto-optical recording medium 6.
A beam splitter 4 is disposed in the optical path of the reflected light, and a reflecting prism 7 configured to apply the critical angle method to the optical path of the reflected light from the beam splitter, a condensing lens 9, and a light beam directed toward the optical axis. Savart plate 2 with rotation mechanism that splits polarized light in parallel
3, and a multi-division photodetector 11 that detects information signals from both polarized light beams, the multi-division photodetector 1
1 has a function of outputting a servo error signal and a recording information signal at the same time.

In the first embodiment described above, the Savart plate according to the present invention is arranged in a fixed state, and the plane of polarization is set to π/
The amount of light polarized and split by the Savart plate was equalized by four rotations, but in the second embodiment, the half-wave plate was removed and the Savart plate itself was placed in the rotation mechanism, and the Savart plate with rotation mechanism 2 was used.
3) This is a configuration in which the same effect can be obtained by rotating around the optical axis.

Note that at this time, since the direction of separation by the Savart plate changes rotationally as the Savart plate rotates, the photodetector 11 is fixed to the Savart plate, for example, so that the light flux always reaches each photodetector in a stable manner. Configure it.

In the above embodiments, an example of a basic optical system was shown, but the influence of retardation occurring in optical elements and magneto-optical recording media can be suppressed by inserting a phase compensation plate having a phase compensation effect into the reproduction optical system. Good too.

In addition, in the above embodiment, the reflected light from the magneto-optical recording medium is split by a beam splitter and the reflected light from the beam splitter is used to obtain an information signal, but it is also possible to change the optical configuration of the beam splitter to transmit the information. A configuration in which light is used for signal detection may also be used. In this case, the configuration is such that the light from the light source is reflected by the beam splitter and focused on the magneto-optical recording medium.

-Also, in the above embodiments, the information signal is detected using reflected light from the magneto-optical recording medium, but a structure may also be adopted in which light transmitted through the magneto-optical recording medium is used.

〔Effect of the invention〕

As explained above, the magneto-optical recording/reproducing head of the present invention has
By using a Savart plate as the analyzer for magneto-optical reproduction and using the critical angle method for the servo error signal optical system, it is possible to obtain the recorded information signal and the servo error signal with a single multi-segment photodetector, and the optical We were able to make the system smaller and lighter. Furthermore, since the servo error signal optical system and the recording information signal optical system are integrated, the efficiency of using light from the light source can be increased. Therefore, the load on the light source can be reduced, and by increasing the rotational speed of the disk, the data transfer speed can be improved as a result. At the same time, it is also possible to significantly shorten the access time of the magneto-optical disk system itself. On the other hand, since only one photodetector is required, there is an advantage that the effort required for adjustment can be significantly reduced.

[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 an example of the configuration of a multi-division photodetector according to the present invention, and FIG. FIG. 4 is a diagram for explaining the optical properties of the Savart plate according to the present invention; FIG. 5 is a diagram for explaining the optical properties of the Savart plate according to the present invention; FIG. FIG. 6 is a diagram for explaining the reproduction principle of magneto-optical recording using the magnetic Kerr effect, and FIGS. 7(a) and (b) are diagrams showing the second embodiment of the conventional A diagram showing the basic configuration of a magneto-optical recording/reproducing head. FIG. 8 is a diagram for explaining a conceptual diagram of the critical angle method. FIG. 9 is a diagram showing a four-division diagram used in the conventional critical angle method and push-pull method. FIG. 3 is a diagram showing the configuration of a photodetector. 1...Semiconductor laser 2...Collimator lens 3.4...Beam splitter 5...Objective lens 6...Magneto-optical recording medium 7...Critical angle Prism 8...Half wavelength plate with rotating mechanism 9...Condensing lens 10...Savart plate 11...Multi-segment photodetector 12... Analyzers 13a, 13b ---Photodetector 1G...Four-split photodetector 17...Differential amplifier 18...Support stand 19...Gear 20...・Support column 21...Through hole 22...Half wavelength plate

Claims (5)

[Claims] (1) A light source, a first optical system that condenses and irradiates the light flux emitted from the light source onto the surface of the magneto-optical recording medium, and extracts the reflected light or transmitted light; a beam splitter that is provided to split the reflected light or the transmitted light; a reflective prism that is installed in the optical path of the transmitted light of the beam splitter or the reflected light from the beam splitter and to which the critical angle method can be applied; A second lens is installed in the optical path of the reflected light, rotates the plane of polarization by π/4, and splits the light flux into polarized light parallel to the optical axis.
1. A magneto-optical recording/reproducing head comprising: an optical system; and a multi-division photodetector that detects information signals from both of the polarized beams. (2) In the magneto-optical recording/reproducing head according to claim 1, the second optical system includes a half-wave plate that rotates the plane of polarization by π/4, a condenser lens, and a light beam. A magneto-optical recording/reproducing head comprising: a Savart plate that splits polarized light parallel to the optical axis; (3) In the magneto-optical recording/reproducing head according to claim 1, the second optical system is composed of a condenser lens and a Savart plate with a rotating mechanism. Recording/playback head. (4) The magneto-optical recording/reproducing head according to any one of claims 1 to 3, characterized in that the multi-division photodetector outputs a recording information signal at the same time as a servo error signal. magneto-optical recording/reproducing head. (5) A magneto-optical recording and reproducing head according to any one of claims 1 to 4, wherein the light source is a laser.