JPH08297883A - Magneto-optical disk device - Google Patents

Abstract

PURPOSE: To provide a magneto-optical disk device with an excellent read/white charac teristic performing optimum phase difference compensation according to then even when a phase difference occurring optical parts such as a reflection mirror, a beam splitter, etc., constituting an optical system of an optical head of an optical disk device is changed according to an ambient change, and the phase difference occurring in a magneto-optical disk substrate is different according to a medium and a generated phase difference amount in the medium substrate is changed according to the ambient change. CONSTITUTION: This device is the optical system for the magneto-optical disk provided with a convergence optical system for irradiating a magneto-optical recording medium with a minute spot of linear polarized light and a reproducing optical system reproducing information from reflection light reflected by the magneto-optical recording medium. A Soleil/Babinet phase plate 30 compensating the phase difference occurring between orthogonally intersecting two linear polarization is provided in an optical path from the magneto-optical recording medium of the reproducing optical system to reproducing detectors 22, and the phase difference of the Soleil/Babinet phase plate 30 is set in optionally by a command from a microcomputer 40, and the phase difference compensation is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical disk device, and more particularly to a magneto-optical disk device which enables improvement of reproduction signal quality.

[0002]

2. Description of the Related Art As a conventional optical head for a magneto-optical disk, Japanese Patent Publication No. 1-229445 is known.

This conventional optical head for a magneto-optical disk will be described with reference to the drawings.

FIG. 4 is a diagram for explaining the reflected light for signal detection (without phase difference), FIG. 5 is a diagram for explaining the reflected light for signal detection (with phase difference), and FIG. 6 is a conventional magneto-optical system. It is a figure which shows one Example of the optical head for discs.

In FIG. 6, the light emitted from the laser diode 11 is converted into parallel light by the collimator lens 12, and the intensity distribution becomes a perfect circle by the perfect circle correction prism 13. The laser light is incident on the joint surface of the first beam splitter 14 as P-polarized light (hereinafter, the P-polarized component and the S-polarized component are distinguished based on the joint surface of the first beam splitter). After passing through the first beam splitter, the laser light is reflected by the reflection mirror 15, narrowed down by the objective lens 16, and reaches the magneto-optical disk surface (not shown) (the optical path up to this point is shown by the solid line in FIG. 6). .

Next, referring to FIG. 4, when the laser light L ₁ which is linearly polarized light composed of only P-polarized light component is reflected by the disk surface, the polarization plane is rotated by the Keer rotation angle θ _k due to the Keer effect. It becomes the reflected light L ₂ or L ₃ .
The direction of rotation depends on the direction of magnetization of the medium.

After being reflected by the disk surface, the laser light is reflected by the objective lens 16, the reflection mirror 15, the first beam splitter 14,
One of the light beams passing through the second beam splitter 17 and split by the second beam splitter 17 passes through the lens 18 to the servo signal detector 19, and the other light beam is polarized by the half-wave plate 20 and polarized. The beam goes through the beam splitter 21 to the detector 22 for the reproduction signal (the optical path shown by the broken line in FIG. 6). The half-wave plate 20 has its main direction (optical axis) tilted by 22.5 ° with respect to the direction of the P-polarized component. Therefore, after passing through the half-wave plate 20, the P-polarized component (S
The polarization component) is inclined at 45 °. Polarization beam splitter 21
Reflects vertical polarization components and transmits horizontal polarization components. Therefore, assuming that the reflected light from the disk is only the P-polarized component, that is, θ _K = 0 in FIG. 4, the outputs of the two detectors 22 become equal, and if θ _K ≠ 0, one output becomes large. . The detector that increases the output changes depending on the direction of Keer rotation. The reproduced signal is obtained by taking the difference between the outputs of the two detectors 22.

Ideally, the reflected light from the magneto-optical disk should be incident on the half-wave plate 20 as it is as linearly polarized light, but an optical system in the middle (reflection mirror, beam splitter, etc.).
Therefore, a phase difference occurs between the P-polarized component and the S-polarized component, so that elliptically polarized light is actually obtained as seen in FIG. When it becomes elliptically polarized light, the amplitude l ₂ of the projection in the direction of 45 ° with respect to the P-polarized component becomes small, and the level of the reproduction signal also decreases.

Therefore, the second beam splitter 17 and 1 /
A wave plate 31 is inserted between the two wave plates 20 as a phase compensating means. The phase compensating wave plate 31 is made of a quartz plate and has a main direction (optical axis) parallel to the P-polarized component (or S-polarized component) (the half-wave plate 20 has a P-polarized component (S-polarized component). 22.5 ° from)). This phase compensation wavelength plate has a phase difference that is opposite to the phase difference generated in the optical system (reflection mirror, beam splitter, magneto-optical disk, etc.) in the middle and is inserted in the optical system in the middle. The phase difference is canceled.

[0010]

The phase difference generated in optical parts such as a reflection mirror and a beam splitter used in the optical system of an optical head of an optical disk device ideally does not change with respect to the environment (particularly temperature). Is desirable, but it actually changes slightly. In addition, the phase difference generated in the magneto-optical disk substrate is different for each medium,
Furthermore, even with the same medium, the amount of phase difference generated varies within the plane. Furthermore, the change in the amount of generated phase difference in the magneto-optical disk medium substrate caused by the temperature change is so large that it cannot be ignored. Therefore, in the phase difference correction according to the above-mentioned conventional method, only the phase difference in a certain environment and at a specific place of a specific medium is compensated.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to stably compensate the phase difference generated in the reflected light from the magneto-optical disk regardless of the type of medium and environmental conditions.

Therefore, the magneto-optical disk device of the present invention comprises a condensing optical system for irradiating the magneto-optical recording medium with linearly polarized light in a minute spot and a reproducing optical system for reproducing information from the reflected light reflected by the magneto-optical recording medium. In a magneto-optical disk device having a system and a phase compensating means for compensating a phase difference between two orthogonal linearly polarized lights generated in the optical path of the reproducing optical system in the optical path of the condensing optical system or the reproducing optical system. The phase compensating means has a function of arbitrarily setting the compensating phase difference by a command from the micro computer.

The magneto-optical disk apparatus of the present invention is characterized in that the phase compensating means compensates the phase difference between the P-polarized component and the S-polarized component generated in the optical path of the reproducing optical system.

The magneto-optical disk apparatus of the present invention is characterized in that the phase compensating means is composed of a Soleil-Babinet phase plate.

[0015]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a diagram for explaining an embodiment of an optical system of a magneto-optical disk device of the present invention, and FIG. 2 is a diagram for explaining a Soleil-Babinet phase plate of the magneto-optical disk device of FIG. FIG. 3 is a flow chart for explaining the phase difference correction value setting method of the magneto-optical disk device of FIG.

In FIG. 1, the light emitted from the laser diode 11 is converted into parallel light by the collimator lens 12,
The intensity distribution becomes a perfect circle by the perfect circle correction prism 13. The laser light is incident on the joint surface of the first beam splitter 14 as P-polarized light (hereinafter, the P-polarized component and the S-polarized component are distinguished based on the joint surface of the first beam splitter). After passing through the first beam splitter, the laser light is reflected by the reflection mirror 15, narrowed down by the objective lens 16, and reaches the magneto-optical disk surface (not shown) (the optical path up to this point is shown by the solid line in FIG. 1). ).

Next, referring to FIG. 4, when the laser light L ₁ which is linearly polarized light composed of only P-polarized light component is reflected by the disk surface, the polarization plane is rotated by the Keer rotation angle θ _k due to the Keer effect. It becomes the reflected light L ₂ or L ₃ .
The direction of rotation depends on the direction of magnetization of the medium.

After being reflected by the disk surface, the laser light is reflected by the objective lens 16, the reflecting mirror 15, the first beam splitter 14,
One of the light beams passing through the second beam splitter 17 and split by the second beam splitter 17 passes through the lens 18 to the servo signal detector 19, and the other light beam is polarized by the half-wave plate 20 and polarized. The beam goes through the beam splitter 21 to the detector 22 for the reproduction signal (the optical path shown by the broken line in FIG. 1). The half-wave plate 20 has its main direction (optical axis) tilted by 22.5 ° with respect to the direction of the P-polarized component. Therefore, after passing through the half-wave plate 20, the P-polarized component (S
The polarization component) is inclined at 45 °. Polarization beam splitter 21
Reflects vertical polarization components and transmits horizontal polarization components. Therefore, assuming that the reflected light from the disk is only the P-polarized component, that is, θ _K = 0 in FIG. 4, the outputs of the two detectors 22 become equal, and if θ _K ≠ 0, one output becomes large. The detector that increases the output changes depending on the direction of Keer rotation. The reproduced signal is obtained by taking the difference between the outputs of the two detectors 22.

Ideally, the reflected light from the magneto-optical disk should be incident on the half-wave plate 20 as it is as linearly polarized light, but the optical system in the middle (reflection mirror, beam splitter, etc.).
Therefore, a phase difference occurs between the P-polarized component and the S-polarized component, so that elliptically polarized light is actually obtained as seen in FIG. When it becomes elliptically polarized light, the amplitude l ₂ of the projection in the direction of 45 ° with respect to the P-polarized component becomes small, and the level of the reproduction signal also decreases.

Therefore, the second beam splitter 17 and 1 /
A Soleil-Babinet phase plate 30 is inserted between the two wave plates 20 as a phase compensating means.

The operation of the Soleil-Babinet phase plate 30 used in the magneto-optical disk apparatus of this embodiment will be described with reference to the drawings.

As shown in FIGS. 2 (a) and 2 (b), the Soleil-Babinet phase plate is composed of two wedge-shaped crystal plates, and one of the crystal plates is moved by a micrometer to increase its thickness. The thickness x can be continuously changed, and FIG. 2A shows a case where the thickness is thin, and FIG. 2B shows a case where the thickness is thick. The Soleil-Babinet phase plate has a phase difference y that occurs in proportion to its thickness x.
Is a phase plate that continuously changes. The relationship between the thickness x of this Soleil-Babinet phase plate and the phase difference y generated there is shown in FIG. 2 (c).

In this embodiment, the Soleil-Babinet phase plate 30 is adapted to delay or advance the phase of the P-polarized component. Then, the thickness x (compensation phase difference) of the Soleil-Babinet phase plate 30 is set so as to cancel the phase difference between the P-polarized component and the S-polarized component generated in the optical system (reflection mirror, beam splitter, magneto-optical disk substrate, etc.) on the way. ) Is set at any time by a command from the microcomputer 40 to cancel the phase difference generated in the optical system on the way.

In the present embodiment, the training by the microcomputer 40 is carried out when the recording medium (magneto-optical disk) is loaded and the temperature is 0 ° C., 15 ° C., 30 ° C., 45 ° C., 60.
It was set to be carried out at 0 ° C.

The microcomputer 40 carries out training as shown in the flowchart of FIG.

FIG. 3 (a) is a flow chart, and FIG. 3 (b).
Indicates a loop count phase difference to be set, and FIG. 3C shows a result table.

First, the loop count and result table are initialized (step 301). As shown in FIG. 3B, the set value of the loop count is such that k = 0 is the phase difference generated by the Soleil-Babinet phase plate −20 deg, and k = 1 is the phase difference generated by the Soleil-Babinet phase plate −15 deg. It has a one-to-one correspondence with the phase difference generated by the Soleil-Babinet phase plate. Then, in the present embodiment, the generated phase difference of the Soleil-Babinet phase plate 30 of FIG. 1 is set to −20 deg.
The setting is made from (k = 0) to 20 deg (k = 8) in steps of 5 deg.

First, the loop count is set to k = 0 (the phase difference generated by the Soleil-Babinet phase plate-20 deg) (step 302). Then, write verification is performed for one track (step 303), the number of errors at that time is checked, and l = 0 in the result table is set (step 304). Next, k = k + 1 and l = l + 1 are set (step 305), and steps 303, 304 and 305 are repeated until k = 8 (the phase difference generated by the Soleil-Babinet phase plate is 20 deg), and k = 8. Then, the process proceeds to the next step 307 (step 306). In step 307, the result l having the smallest number of errors is selected from the result table, and the value of k (phase difference of the Soleil-Babinet phase plate) corresponding to the l is selected from the result.

Therefore, even if the use condition changes, optimum phase compensation can be performed depending on the situation.

[0031]

As described above, in the optical disk device of the present invention, the phase difference generated in the optical components such as the reflection mirror and the beam splitter used in the optical system changes due to the environmental change, and the magneto-optical disk. Even if the phase difference generated on the substrate differs depending on the medium and the amount of the phase difference generated on the medium substrate changes due to temperature change, optimum phase compensation can be performed depending on the occasion, and an optical disc with excellent read / write characteristics. There is an effect that a device can be provided.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of an optical system of a magneto-optical disk device of the present invention.

FIG. 2 is a diagram for explaining a Soleil-Babinet phase plate of the magneto-optical disk device of FIG.

3 is a flow chart for explaining a phase difference correction value setting method of the magneto-optical disk device of FIG.

FIG. 4 is a diagram for explaining reflected light for signal detection (no phase difference).

FIG. 5 is a diagram for explaining reflected light for signal detection (with a phase difference).

FIG. 6 is a diagram showing an example of a conventional optical head for a magneto-optical disk.

[Explanation of symbols]

 Reference Signs List 11 laser diode 12 collimator lens 13 perfect circle correction prism 14 first beam splitter 15 reflecting mirror 16 objective lens 17 second beam splitter 18 lens 19 four-division detector 20 1/2 wavelength plate 21 polarization beam splitter 22 playback signal detector 30 soleil・ Babinet phase plate 31 Phase compensation wavelength plate 40 Microcomputer

Claims (3)

[Claims] 1. A condensing optical system for irradiating a magneto-optical recording medium with linearly polarized light in a minute spot, a reproducing optical system for reproducing information from reflected light reflected by the magneto-optical recording medium, and the condensing optical system. Alternatively, in a magneto-optical disk device having a phase compensating means for compensating for a phase difference between two linearly polarized light beams orthogonal to each other which are in the optical path of the reproducing optical system and occur in the optical path of the reproducing optical system, the phase compensating means However, the magneto-optical disk device has a function of arbitrarily setting the compensation phase difference by a command from a micro computer. 2. The magneto-optical disk device according to claim 1, wherein the phase compensating means compensates a phase difference between the P-polarized component and the S-polarized component generated in the optical path of the reproducing optical system. 3. The magneto-optical disk device according to claim 1, wherein the phase compensating means is composed of a Soleil-Babinet phase plate.