JPH0664766B2 - Magneto-optical information recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical information recording / reproducing apparatus, and in particular, it has a magnetization signal recorded by a thermomagnetic effect and a phase signal recorded by an uneven pit. The present invention relates to a magneto-optical disc information recording / reproducing apparatus using a recording medium.

[Background of the Invention]

An example of a magneto-optical information recording / reproducing apparatus that records and erases information by using the thermomagnetic effect and reproduces the information by using the magneto-optical effect is known as a technical research report of the Institute of Electronics and Communication Engineers CPM83.
-53, PP 13-19. This apparatus uses a recording medium in which information is recorded by a magnetization signal and address information is recorded by a phase signal of the concave and convex pits.

[Object of the Invention]

It is an object of the present invention to read the magnetization information recorded by the thermomagnetic effect and the phase information recorded by the concavo-convex pits even if the same photodetector reads the slice level during signal processing. It is to provide a magnetic information recording / reproducing apparatus.

[Outline of Invention]

In order to achieve the above object, in the present invention, the polarization plane passing axis angle of the analyzer installed in front of the photodetector is selected so that the polarities and amplitudes of the reproduction signals of the magnetization information and the phase information match. Is characterized by. Considering the polarity of the signal after passing through the analyzer in a range where the rotation angle from the erase position of the analyzer is small, the magnetization signal is inverted depending on the rotation direction of the analyzer, but the phase signal does not change. Regarding the signal amplitude, the magnetization signal and the phase signal are proportional to the first power and the second power of the magnitude of the analyzer rotation angle, respectively. Furthermore, the amplitude of the phase signal also depends on the degree of modulation associated with the depth of the uneven pit, and the amplitude of the magnetization signal is the polarization rotation angle of the recording material represented by the Kerr rotation angle and the polarization prism used in the reproduction optical system. Depends on the reflectance of. In addition, the polarity of the magnetization signal also depends on the magnetization direction of the magnetization domain. Therefore, the amplitude and polarity of the magnetization signal and the phase signal can be matched by selecting the magnitude of the rotation angle and the rotation direction of the analyzer in consideration of these parameters. By making the amplitudes and polarities of both signals the same, it is not necessary to distinguish the slice level at the time of data processing between the magnetization signal and the phase signal. Therefore, simplification of the signal processing circuit and data read by fluctuation of the level slice It has the effect of suppressing the decrease in reliability.

Example of Invention

 Hereinafter, the present invention will be described together with examples.

FIG. 1 is a diagram showing the configuration of a magneto-optical disk device which is an embodiment of the present invention. In the figure, reference numeral 1 is a magneto-optical disk, which is rotated by a rotary motor 2. A perpendicular magnetic film having a magneto-optical effect is formed on the magneto-optical disk 1. The recording / erasing / reproducing of the magnetization information is performed as follows.

The light emitted from the semiconductor laser 3 is coupled to the coupling lens 4
To convert it into a parallel light beam, and through the polarizing prism 5,
The light is made incident on the objective lens 6 and focused on the perpendicularly magnetized film of the disk 1 as minute spots. The objective lens 6 is attached to the voice coil 7 so that the objective lens 6 is moved so as to follow the vertical shake accompanying the rotation of the disk 1. When recording information, the drive current of the semiconductor laser 3 is modulated with an information signal, and the temperature of the perpendicular magnetization film on the disk 1 is locally raised by the heat of the optical pulse corresponding to the information. The perpendicular magnetization film has a property of losing its magnetization when the temperature exceeds the Curie temperature. Therefore, when the magnetization of the magnetized film is lost, if a magnetic field is applied from the outside by the electromagnetic coil 8 in the direction opposite to the magnetization of the unrecorded portion, only the light-irradiated portion has the opposite magnetization. It becomes a part. That is, the formation of this magnetization domain is the recording of information. In order to erase the already written information, the disk 1 is irradiated with light, and at the same time, the magnetization direction of the magnetic field generated by the electromagnetic coil 8 is applied in the opposite direction to that at the time of recording. In this way, the magnetization direction of the perpendicular magnetization film is returned to the same direction as the magnetization direction of the unrecorded portion, thereby erasing.

Information is reproduced by utilizing the magneto-optical effect represented by the Kerr effect. The Kerr effect is an effect in which the polarization directions of incident light slightly rotate in opposite directions corresponding to the upward and downward magnetization directions of the perpendicular magnetization film. The reflected light from the disk 1 that has caused the rotation of the polarization plane passes through the objective lens 6, is separated by the polarization prism 5, and is guided to the analyzer 9. The analyzer 9 is an optical element that passes only a specific polarization component. Therefore, due to the Kerr effect, when the light whose polarization plane is rotated corresponding to the presence or absence of the magnetization domain is incident on the analyzer 9, it is converted into a change in the light amount. This change in the amount of light is converted into an electric signal by the photodetector 10 and then amplified by the amplifier 11 to a desired level. Since the signal light from the disk 1 contains noise due to defects and dust on the disk 1, the slice level setting circuit 1
At the level set in 2, the comparator 13 outputs only a signal having a certain amplitude or more. Generally, the slice level is set at the level of half the amplitude of the signal amplified by the amplifier 11. The principle of information reproduction by such a detection optical system will be described with reference to FIG. 2 centering on rotation detection of the polarization plane of the analyzer.

In FIG. 2, the axis 21 is the polarization axis of the laser light with which the disk 1 is irradiated. In the polarization state of the light reflected from the disk 1, the incident polarization angle is rotated by the Kerr rotation angle θ _{K due} to the Kerr effect in the portion having the magnetization domain.
In the part without the magnetization domain, the Kerr rotation angle in the opposite direction −
It rotates by θ _K , and the angle difference becomes 2 θ _K. The axis 22 rotated by 90 ° with respect to the axis 21 is called the extinction axis,
When the polarization plane passing axis of the analyzer 9 is aligned with the erasing axis 21, the amount of passing light of the polarization state of the axis 21 is minimized. If the polarization plane passing axis of the analyzer is set by rotating it from the extinction axis 21 by θ _A, the amount of light that passes through the analyzer will be the amount of light projected on the θ _A axis. That is, the amount of transmitted light P _T1 of the analyzer when the reflected light from the portion having the magnetization domain is incident on the analyzer 9 is P _T1 = P ₀ sin ² (θ _A + θ _K ) (1) The amount of transmitted light P _{T2 with} respect to the reflected light from the portion having no domain is P _T2 = P _O sin ² (θ _A −θ _K ) (2) Here, P ₀ is the amount of light incident on the analyzer. By the way, since the magnetization information signal is detected as a difference in which the amount of light passing through the analyzer increases or decreases depending on the presence or absence of the magnetization domain, the magnetization signal S _M detected by the photodetector 10 is as follows. Represented.

_{S M = P T1 -P T2 =} P 0 sin 2 (θ A + θ K) -P 0 sin 2 (θ A -θ K) = P 0 sin2θ A sin2θ K ...... (3) where, Kerr rotation angle theta _{Since K} is uniformly determined by the characteristics of the perpendicular magnetization film, the amplitude of the magnetization signal changes depending on the incident light amount P _{0 on the} analyzer and the rotation angle θ _A of the polarization plane passing axis of the analyzer. Furthermore, it can be seen that the polarity of the magnetization signal is inverted depending on whether the rotation angle θ _A is positive or negative. Next, what happens when the signal light of the phase information formed in the shape of the concave and convex pits on the disk 1 passes through the analyzer.

The amount of light reflected from the uneven pit depends on the depth of the pit.
The modulation of the signal changes. Since the magneto-optical effect does not occur in the uneven pit, the Kerr rotation angle θ _K can be considered to be zero. Therefore, as is clear from FIG. 2, the signal S _{P of the} uneven pit is given by the following equation.

S _P = η · P _T0 = η · P ₀ sin ² θ _A (4) Here, η is the modulation degree of the pit signal, and P _T0 is the transmitted light amount of the analyzer. That is, the phase signal due to the concave and convex pits corresponds to the change in the modulation degree. Furthermore, the amount of light after passing through the analyzer depends on the analyzer rotation angle θ _A. Here, the polarity of the phase signal S _P does not depend on whether the rotation angle θ _A is positive or negative, but only the amplitude depends on the absolute value of the rotation angle θ _A.

Here, the conditions under which the magnetization signal S _M and the phase signal S _P coincide with each other are shown from the expressions (3) and (4). That is, the following equation is derived from S _M = S _P.

In order to make the amplitude and polarity of the magnetization signal and the phase signal coincide with each other, which is the object of the present invention, the modulation degree η of the phase signal and the disk 1 at the time of incidence on the analyzer 9 are satisfied so as to satisfy the relationship of equation (5). The analyzer rotation angle may be set to the value on the right side calculated from the polarization plane rotation angle (Kerr rotation angle) θ _K of the reflected light.
Here, the polarization rotation angle θ _K has an effect of increasing the Kerr rotation angle of the recording material itself when the polarization prism 5 having a reflectance of S polarization higher than that of P polarization is used.

That is, it also depends on the reflectance of the polarizing prism 5.

Therefore, in the calculation of the equation (5), it is necessary to use the Kerr rotation angle at the time of incidence on the analyzer 9. Next, a description will be added to each of the two purposes of the present invention.

The first object of the present invention, that is, in order to match the polarity of the magnetization information and the polarity of the phase information, the rotation angle direction of the analyzer 9 may be set as follows.

In the case of the header signal, the amount of reflected light decreases when there are unevenness pits. Therefore, the rotation angle θ of the analyzer 9 also decreases in the direction in which the amount of signal light decreases when the magnetization signal has a magnetization domain.
Set _A. Since the direction of this setting angle depends on the initial magnetization setting direction of the recording medium, the initial magnetization setting direction and the analyzer rotation angle direction are uniformly determined. For example, in FIG. 2, it is assumed that the rotation angle of the polarization plane depending on the magnetization direction in the initial magnetization setting state, that is, the unrecorded state is θ _A. Therefore, when the recording domain is formed, the rotation angle of the polarization plane of the reflected light from the recording portion becomes −θ _K. In this case, by setting the rotation angle θ _A of the analyzer 9 in the direction as shown in FIG. 2, the polarities of the magnetization signal and the phase signal can be matched.

The second object of the present invention, that is, in order to set the amplitude of the magnetization information to the same level as the amplitude of the phase information, the magnitude of the rotation angle of the analyzer 9 is set so as to satisfy the relationship shown in the equation (5). Just set it. As can be seen from equations (3) and (4), this is because the magnetization signal is proportional to sin2θ _A and the phase signal is sin
^{2 This} utilizes the property that the amplitude changes in proportion to θ _A.

FIG. 3 (a) shows an example in which the polarities and amplitudes of two signals are made to match in accordance with the present invention, and FIG. 3 (b) shows that the polarities of the signals are reversed by reversing the direction of the rotation angle of the analyzer 9. An example in which it is reversed is shown. To give concrete values for the matched examples, if the polarization rotation angle θ _{K of the} light incident on the analyzer 9 is 1 ° and the signal modulation degree η of the concave and convex pits is 50%, then according to equation (5), If the rotation angle θ _A of the photon 9 is set to about 8 °, the state shown in FIG. 3 (a) can be obtained.

If the amplitude and polarity of the magnetization signal and the phase signal can be matched, a certain fixed slice level can be used when level slicing the data, and the signal processing circuit can be simplified.

〔The invention's effect〕

According to the present invention, when reproducing information from a magneto-optical recording medium in which magnetization information and phase information are recorded in a mixed manner, it is possible to optimize the magnitude of the polarization plane passing axis angle and the rotation direction of the analyzer. As a result, the amplitude and polarity of the reproduction signal can be optically matched, which has the effect of reducing the load and scale of the signal processing circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a diagram showing the principle of magneto-optical reproduction, and FIG. 3 is a diagram showing the relationship between the amplitude and polarity of a reproduction signal of phase information and magnetization information. 1 ... Magneto-optical disk, 3 ... Semiconductor laser, 8 ... Electromagnetic coil, 9 ... Analyzer, 13 ... Comparator.

Claims (2)

[Claims] 1. A light source for irradiating a recording medium having a magnetization information recorded by a thermomagnetic effect and phase information recorded by uneven pits with a light beam, and light reflected from the recording medium is converted into an electric signal. In the magneto-optical information recording / reproducing apparatus having a photodetector, an analyzer is arranged in front of the photodetector, and an angle of a polarization plane passing axis of the analyzer is detected by the photodetector. And a magneto-optical information recording / reproducing apparatus, which are selected so that the polarities and amplitudes of the electric signals of the phase information coincide with each other. 2. An apparatus according to claim 1, further comprising an amplifier for amplifying an electric signal from the photodetector and a comparator for comparing an output signal of the amplifier with a predetermined slice level. Magneto-optical information recording / reproducing apparatus.