JPS61267953A - Processing system for photomagnetic information - Google Patents

Abstract

PURPOSE:To simplify a signal detecting system, and to prevent a data from being omitted, by converting a detecting signal in which magnetizing information and phase information is mixed, to a binary-coding signal, by each separate threshold, and thereafter, taking OR, and synthesizing both the signals. CONSTITUTION:An optical beam is irradiated from a semiconductor laser 3 to a recording medium 1 having magnetizing information which is recorded by a heat magnetic effect and phase information which is recorded by an uneven pit, and its reflected light is detected by a photodetector 9 through an optical analyzer 8. In this photomagnetic information system, the detecting signal in which the magnetizing information and the phase information is mixed is converted to a binary-coding logical signal by a comparator 1 and a comparator 2 by each separate threshold, and thereafter, both the signals are synthesized by taking OR by an OR gate 13. In this case, a rotational angle of the analyzer 8 is set in advance so that S/N of a reproducing signal of the magnetizing information becomes maximu, and a signal modulation degree depending on a depth of the uneven pit of the phase information becomes maximum. In this way, a signal detecting system is simplified and a data omission can be prevented.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a magneto-optical disk device, and particularly to signal processing suitable for reproducing a magneto-optical disk in which phase information and magnetization information are recorded in a mixed manner. Regarding the method.

[Background of the invention]

An example of a magneto-optical information recording and reproducing device that performs recording and erasing using the thermomagnetic effect and reproducing using the magneto-optic effect is proposed in Technical Report CPM83-53° pp. 13-19 of the Institute of Electronics and Communication Engineers. In this device.

Address information is recorded as a phase signal of uneven pits.

Data is intended for media recorded with magnetization signals. However, there is no description of information processing methods or binarization (digitization) of analog signals.

[Purpose of the invention]

The purpose of the present invention is to detect both information using only a polarization rotation detection system and to utilize the difference in signal amplitude between the two when reproducing a magneto-optical disk on which both phase information and magnetization information are recorded. , after digitizing at the separate slice level,
By logically combining data into a series of data, the present invention aims to simplify the signal detection optical system and provide a signal processing method that does not cause data loss.

[Summary of the invention]

A method for realizing the above purpose will be explained.

How to handle phase information and magnetization information together.

This is because it is convenient from a data management standpoint.

In other words, the address information for tracks and sectors on the disk, the self-clock for signal reproduction, the sector mark for recognizing the beginning of a sector, etc. are fixed information that does not need to be changed by the user. It can be provided in advance as uneven pits at the replica stage of disk production. In other words, the header area is recorded as phase information. On the other hand, areas where user data and the like need to be rewritten are handled as magnetization information.

This is not only advantageous in terms of mass production of disks, but also in recording and erasing magnetized information.

This eliminates the possibility of accidentally destroying information in the header area. The method of managing information in units of sectors is also effective for magneto-optical disks.

Now, as a method for reproducing a disc on which such mixed and dissimilar signals are recorded, the following methods can be considered.

The first method is to separately provide means for detecting polarization plane rotation using an analyzer or the like and means for detecting only changes in light intensity without using an analyzer. There is a method of detecting information and then switching between the header area and the data area to switch and combine both pieces of information into a series of digital data. In this case, it is possible to detect phase information using a polarization plane rotation detection system, but since the signal amplitudes of phase information and magnetization information after passing through an analyzer are generally different, the signal-to-noise ratio is reduced at the slice level of Rin. It is difficult to binarize without

The second method is to detect both phase information and magnetization information using only a polarization plane rotation detection means using an analyzer, match the amplitude and polarity of both signals by selecting the analyzer rotation angle, and then There is a method of binarizing based on the slice level.

In this case, there is a drawback that the signal-to-noise ratio of the magnetization signal is not necessarily maximized at the above-mentioned analyzer selection angle. Therefore, it is necessary to match the amplitude and polarity of the two signals while maintaining the maximum signal-to-noise ratio of the magnetization signal by setting the signal modulation degree of the one-phase information.

Here, the behavior of the amplitude and polarity of the phase signal and magnetization signal with respect to the analyzer rotation angle will be briefly explained. Considering the polarity of the signal after passing through the analyzer in a range where the rotation angle from the extinction position of the analyzer is small, the magnetization signal is reversed depending on the rotation direction of the analyzer, but the 1-phase signal does not change. Also, regarding the signal amplitude, the magnetization signal and phase signal are
They are proportional to the first power and the square of the magnitude of the analyzer rotation angle, respectively. Furthermore, the amplitude of the phase signal also depends on the degree of modulation with the depth of the uneven bit, and the amplitude of the magnetization signal depends on the depth of the uneven bit.

It depends on the Kerr rotation angle and the reflectance of the polarizing prism used in the reproduction optical system. In addition, the polarity of the magnetization signal.

It also depends on the magnetization direction of the magnetized domain. Therefore, by considering these parameters and selecting the rotation angle and rotation direction of the analyzer, it is possible to match the signal amplitude and polarity of both signals.

Now, as a problem with the first method, in addition to the above-mentioned problem, there is a possibility that data may be lost by the time required for the switching waveform to rise. This problem can be solved by allocating dummy data that is not directly related to the necessary information to the data bit string corresponding to the switching operation in advance, but this will waste storage capacity for this amount of data. The switching position may shift due to rotational jitter and the like that occur during recording and reproduction.

Regarding the second method, in addition to the above-mentioned problems, it is necessary to accurately set the degree of signal modulation of the phase information, taking into account the disk reflectance, the polarization rotation angle of the perpendicularly magnetized film, and the polarization characteristics. be. Therefore, it is necessary to take measures according to the differences in disk characteristics.

The method of the present invention uses the second method as a detection method, that is, a method of reproducing with a photodetector after passing through an analyzer.
Regarding the amplitude and polarity of the phase signal and the magnetization signal, threshold values for binarization are set for each of the phase signal and the magnetization signal, without considering special coincidence, and after binarization, 1 and 2 are set. This involves taking the logical sum of the valued signals and creating a series of data strings. According to this method, the rotation angle of the analyzer can be set so that the signal-to-noise ratio of the magnetization signal becomes a liquid hole, and there is no need to particularly consider amplitude matching with the phase signal.
The bit depth may be determined so that the degree of modulation of the phase signal is excessive. Furthermore, as described above, the problem of data loss due to switching that occurs in the first method can also be solved.

[Embodiments of the invention]

The present invention will be described below with reference to Examples.

FIG. 1 is a diagram showing the configuration of a magneto-optical disk device which is an embodiment of the present invention. In fig.

Reference numeral 1 denotes a magneto-optical disk, which is rotated by a one-rotation motor 2. A perpendicularly magnetized film having a magneto-optical effect is formed on the disk 1 . Recording, erasing, and reproducing magnetization information are performed as follows.

The light emitted from the semiconductor laser 3 is passed through the coupling lens 4.
is converted into a parallel light beam by and passed through a polarizing prism 5,
The light is made incident on the aperture lens 6 and focused on the perpendicular magnetization pattern of the disk 1 as a minute spot. When recording information, the drive current of the semiconductor laser 3 is modulated with the information signal,
The heat of the optical pulse corresponding to the information causes the temperature of the perpendicularly magnetized film on the disk l to rise above the Curie temperature, thereby causing the magnetization to be lost. If a magnetic field in the opposite direction to the magnetization of the unrecorded area is applied externally using the electromagnetic coil 7,
Only the light-irradiated portion becomes a recording domain with magnetization in the opposite direction. K for erasing recorded information may be achieved by applying a magnetic field in the opposite direction to that used for recording at the same time as light irradiation. 3~
9 is arranged in a carriage movable in the radial direction of the disk.

It is configured so that a light beam can be irradiated onto a desired position on the disc. However, all of 3 to 9.

It is not necessary to make it movable relative to the disk, and it is sufficient if at least the objective lens 6 and the electromagnetic coil 7 are movable. Further, although the explanation is omitted here, the aperture lens 6 is attached to, for example, a two-dimensional actuator, and is used for automatic focus control to constantly irradiate a minute light spot onto the disc, and for tracking to follow a track on the disc. Of course, control is performed.

Reproduction of information is! This is done using the pneumatic effect.

The magneto-optic effect is an effect in which the plane of polarization of incident light is rotated depending on the direction of magnetization, and the Kerr effect is one such effect.

The reflected light from the disk 1 whose plane of polarization has been rotated is passed through a diaphragm lens 6, an optical pre-prism 5, and an analyzer 8.
guided by. Since the analyzer is an optical element that allows only a specific polarized light component to pass through, the rotation of the polarized light image can be converted into a change in the amount of light. This change in light amount is converted into an electrical signal by the photodetector 9, and then amplified to a desired level by the amplifier IO. The principle of information reproduction using such a detection optical system will be explained with reference to FIG. 2, focusing on the detection of rotation of the polarization plane of the analyzer.

In FIG. 2, an axis 21 is the polarization axis of the laser beam irradiated onto the disk l. Suppose that the plane of polarization of the light reflected from the disk 1 is rotated, for example, by the Kerr rotation angle θ in a certain portion of the magnetized domain.

The unrecorded portion rotates only at the Kerr rotation angle -θ in the opposite direction. The axis 22 rotated 900 degrees with respect to the axis 21 is called the extinction axis, and when the polarization plane passing axis of the analyzer 8 is aligned with this extinction axis 22, the amount of light passing through the polarization state of the axis 21 is minimized. Become.

If the polarization plane passing axis of the analyzer 8 is set to be rotated by .theta..mu. from the extinction axis 22, the amount of light passing through the analyzer will be the amount of light obliquely reflected on the .theta..mu. axis. That is, a change in the amount of light corresponding to the presence or absence of a magnetized domain is obtained as a magnetization signal. Here, the magnetization signal 8m detected by the photodetector 9 is expressed as follows.

8M = Posia” (θmu+θg) −rosi
n” (θmu θK)=Posin2θmu・5i112
θK −”...” (1) Here, since the Kerr rotation angle θ is uniformly determined by the characteristics of the perpendicular magnetization film,
The amplitude and polarity of the magnetization signal SM change depending on the amount of light incident on the analyzer Po and the rotation angle θm of the analyzer.

The signal-to-noise ratio of the magnetization signal is affected by amplifier noise generated by the amplifier 10, shot noise generated by the photodetector 9, laser noise generated by fluctuations in the light amount of the semiconductor laser 3, and minute irregularities on the surface of the disk 1. It is determined by disk noise etc. generated due to fluctuations in the amount of reflected light. Here, disk noise is expressed as a value proportional to the average amount of light passing through the analyzer as shown in the following equation.

No=ε・Po (s♂θmu+C) ・・・・・・・・・
(2) Here, the disc noise No. is expressed as the product of the disc noise factor ε and the average light amount. Furthermore, even at the extinction position, that is, when θm is zero, there is a small amount of leaked light that passes through the analyzer.

In equation (2), C indicates this leakage light component and is associated with the extinction ratio. If the disk noise ND is dominant as a noise component, the signal-to-noise ratio of the e&magnetization signal is expressed by the following equation.

The direct expression of equation (3) is:

θ,=s* −at I V− ・・・・
It becomes maximum when the analyzer rotation angle is set to (4).

Next, we will show what happens when the phase correction signal light recorded in the form of concave and convex pits on the disk 1 passes through an analyzer.

The amount of light reflected from the uneven bit depends on how quiet the pit is.
The degree of modulation of the signal changes. The phase signal 8p is expressed as the product of the degree of modulation and the average amount of light passing through the analyzer as shown in the following equation.

8p-η・Po(Si11!θmu+C)・・・・・・
...(5) The modulation degree of the phase signal is 178% of the laser light wavelength.
The maximum value (modulation depth of about 60%) is obtained when the pit has a depth of .

When the analyzer rotation angle is set so that the signal-to-noise ratio of the magnetization signal is maximized, the amplitudes of the phase signal and magnetization signal generally differ by several times. For example, Kerr rotation angle θK is 0.5°
, the leakage light component (extinction ratio) C is 1/100, and the noise is dominated by disk noise No. From equation (4), the analyzer rotation angle at which the signal-to-noise ratio of the magnetization signal is maximum is determined. is found to be ±5.7°. At this time, from equation (1), the amount of light received for the magnetization signal is SM = ±3.4X1G-"P
o (W), and the amount of light received for the phase signal is + S p = 1-2 x 10 if the degree of modulation is 60-.
-” P o (W).

Here, the decoding of the magnetization signal SM indicates the polarity of the signal, and if the phase is positive when θm is positive, it means that if θm is rotated in the negative direction, the phase will be reversed.

In the above example, it can be seen that the amplitude of the phase signal is approximately 3.5 times larger than the amplitude of the magnetization signal.

Therefore, if the magnetization signal and the phase signal are binarized using different threshold values, only the phase signal can be read out. Furthermore, by taking the logical sum (0) of the logical data that has been binarized using each threshold value, it is possible to reproduce it as a series of data strings.

FIG. 3 is a time chart showing the method of binarization and synthesis. If the binarized 1gI4 values of the comparator 11 and comparator 12 are set as shown in the figure for the signal from the amplifier 10, the binarized signal from the comparator 11 will be only one phase value, and the comparator From 12 onwards, the binary signal becomes a mixture of 1 phase value number and magnetization signal. Here, if the header clearing information is recorded as a phase signal, it is also possible to separate only the header clearing signal by using the output of the comparator 11. To make a series of data columns,
The output of the comparator 11 and the comparator 12 can be logically summed.Also, if the direction of rotation of the analyzer is reversed from that shown in Figure 5g3, the output of the amplifier 10 will be as shown in Figure 4. A good signal can be obtained. Therefore, rI4 of comparator 11.12
If you set saliva like a cause, each 2 f
The i magnetization signal is only one phase value number or magnetization signal. If it is treated as a series of data strings, the outputs of both comparators 11 and 12 may be logically summed as in the case of FIG.

The present invention makes it possible to separate or combine both signals without switching by actively utilizing the behavior of one phase value and the magnetization signal with respect to the rotation of the analyzer. This makes it possible to prevent data from being read out.

Note that the comparator may be a commonly used analog comparator.

〔Effect of the invention〕

According to the present invention, when reproducing information from a magneto-optical recording medium in which a 1-phase signal and a magnetization signal are recorded together, the polarization plane passing axis angle of the analyzer is set such that the signal-to-noise ratio of the magnetization signal is maximum. Set it so that

Separate threshold values are set for the phase signal and magnetization signal for the signal obtained by the photodetector placed on the photodetector, and the signal is converted into a binary value, so the detection optical system can be made smaller and simpler. In addition, it has the effect of making it possible to reproduce information without data loss.

[Brief explanation of the drawing]

Figure g1 is a block diagram of a magneto-optical disk device showing an embodiment of the present invention, Figure 2 is a diagram showing the principle of magneto-optical reproduction, Figures 3 and 4 are diagrams showing phase information and magnetization information. 5 is a time chart showing binarization of a reproduced signal.

Claims (1)

[Claims] 1. A light beam is irradiated onto a recording medium having magnetization information recorded by thermomagnetic effect and phase information recorded by uneven bits, and the reflected light is passed through an analyzer. In a magneto-optical information processing method that detects using optical detection means, a detection signal containing a mixture of the magnetization information and the phase information is converted into a binary logic signal using separate threshold values, and then logically summed. A magneto-optical information processing method characterized by combining both signals. 2. In the magneto-optical information processing method according to claim 1, the rotation angle of the analyzer is set so as to maximize the signal-to-noise ratio of the reproduced signal of the magnetization information, and the rotation angle of the analyzer is set to maximize the signal-to-noise ratio of the reproduction signal of the magnetization information, A magneto-optical information processing method characterized in that a degree of signal modulation depending on the depth of a concavo-convex bit is set to be maximum. 3. In the magneto-optical information processing system according to claim 1 or 2, the rotation angle of the analyzer is such that the polarity of the magnetization signal and the phase signal are opposite, and the signal-to-noise ratio of the magnetization signal is A magneto-optical information processing method characterized by being set to maximize the