JPH04192130A - Optical head and using same optical information reproducing device - Google Patents

Abstract

PURPOSE:To reduce jitters and cross talk of a reproduction signal by forming a two-dimensional shape of an information reproducing sensor of an optical head to be approximately similar to a two-dimensional shape of a pit recorded on a recording medium. CONSTITUTION:The pit (domain) 21 recorded on an information track is recorded parallel with the direction of a track (A-direction). A reproducing light spot 22 is imaged on the sensor 23 via an objective lens 3 and a condenser lens 10 after reflecting upon the surface of a magneto-optical disk. The two-dimensional shape of the sensor 23 is formed to be approximately similar to a standard shape of the domain 21 showing a fundamental period of the pit on the medium surface. By this method, jitter components generated dependant on the domain shape and the spot shape can drastically be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical head for reproducing optical information and an optical information reproducing apparatus using the same.

[Prior Art] In recent years, optical memories such as optical disks and optical cards have attracted attention as memories with large capacity and low price per bit. Among these, since information can be erased on magneto-optical disks, there is a lot of research into applying them as external storage devices for combiators and memory for image files.

By the way, optical modulation and magnetic field modulation are known as recording methods for such magneto-optical disks. The optical modulation method is a method in which intensity-modulated laser light is irradiated while a constant bias magnetic field is applied to the disk. Further, the magnetic field modulation method is a method in which a modulated bias magnetic field is applied while a laser beam of a constant intensity is irradiated. Of these two recording methods, the magnetic field modulation method is advantageous because it has a simple disk medium structure in order to perform so-called override, in which new information is recorded while erasing previously recorded information. Currently, the most common method for recording information is the so-called mark-to-mark recording method, in which information is recorded by modulating the spacing between marks called domains (magnetic domains) on a disk. In contrast to this current method, research is also being conducted on a mark length recording method that can theoretically double the recording density, that is, a mark length recording method in which information is recorded by modulating the length of the mark. Even in such high-density recording using mark length recording, the magnetic field modulation method is said to be advantageous because it is less likely to be limited by the size of the optical spot or the light intensity distribution.

FIG. 7 is a configuration diagram showing the magnetic field modulation type disk and its surroundings. In the figure, 7 is a semiconductor laser used as a light source, and after the laser beam is collimated by a collimator lens 6, it is passed through a beam shaping prism 5.
is converted into sunlight flux. The light also passes through the beam splitter 4, is narrowed down by the objective lens 3, and is focused on the recording layer of the magneto-optical disk 2 as a minute light spot. A magnetic head 1 is mounted on the upper surface of the magneto-optical disk 2, facing the objective lens 3.
is located.

On the other hand, the light reflected from the magneto-optical disk 2 is guided to the beam splitter 8 via the objective lens 3 and the beam splitter 4. The beam splitter 8 separates the reflected light into two parts, and guides one to the reproduction optical system on the wavelength plate 9 side and the other to the control optical system on the condenser lens 14 side. In the reproduction optical system, the light that has passed through the local wavelength plate 9 is guided to the beam splitter 13 via the condenser lens 10, where it is further separated into two parts.

The separated lights are each received by photodetectors 11 and 12, and an information signal is obtained from the output of the received light. In addition, in the control optical system, the light passing through the condenser lens 14 is separated into two by a beam splitter 15. One of the separated lights is received by a photodetector 16, and the other is received by a knife detector 1.
The light is received by the photodetector 18 via the photodetector 7 . Then, a servo signal is obtained from the light reception signal of the photodetectors 16 and 18.

Next, when recording information, a laser beam of constant intensity is irradiated from the semiconductor laser 7, and a thermal bias is applied to the magneto-optical disk 2. As a result, the temperature of the recording layer rises above the Curie point temperature, and in this state, a bias magnetic field is applied from the magnetic head 1 to the temperature raised region. The bias magnetic field is modulated according to the recording signal, and the magnetization direction of the recording layer is aligned in the same direction as the bias magnetic field. Then, the moment the temperature of the recording layer falls below the Curie point temperature, the direction of magnetization is maintained, and domains representing information are formed. In this case, since the normal light spot has a Gaussian light intensity distribution, the temperature distribution of the heated medium is a smooth temperature distribution that reflects the light intensity distribution, and the shape of the Curie point temperature contour line is not rectangular. Therefore,
The recorded domain is in the shape of an arrow feather, as shown in FIG. FIG. 5A shows a domain recorded by inter-mark recording, in which each mark has the same shape and the interval between the marks is modulated. Further, FIG. 6B shows a domain of mark length recording, in which the length of each mark is modulated and the interval between the edges represents information.

[Problems to be Solved by the Invention] However, in the conventional magnetic field modulation method described above, when reproducing a feather-shaped domain corresponding to a bit of information, a circular light spot whose light intensity distribution is a Gaussian distribution is used to reproduce the feather-shaped domain. It will be scanned. Therefore, the correlation between the light spot and the domain is different before and after the fletching.
Problems arise such that the crosstalk from the domains before and after the reading comparison is also asymmetrical, and the shape of the pointed portion of the feather-shaped domain, that is, the portion with a high spatial frequency, tends to be unstable. Therefore, in the past, these defects and poor MTF of the optical system caused an increase in signal jitter, leading to an increase in error rate and a decrease in reliability. In particular, in the mark length recording shown in FIG. 8(b), since the position of the edge of a domain represents information, the error rate increased significantly due to jitter.

The present invention has been made to solve these problems, and its purpose is to provide an optical head that can reduce jitter and reproduce information with high reliability, and an optical information reproducing device using the same. Our goal is to provide the following.

[Means for Solving the Problems] An object of the present invention is to provide an optical head having an information reproducing sensor for detecting reflected light or transmitted light of a reproducing light beam irradiated onto an information recording medium. This is achieved by an optical head characterized in that the two-dimensional shape of the sensor is formed to be substantially similar to the two-dimensional shape of the bit recorded on the recording medium.

Further, in an optical head having an information reproducing sensor for detecting reflected light or transmitted light of a reproducing light beam irradiated onto an information recording medium, the sensor may be moved in a one-dimensional reading direction of the bit to detect an edge shape of the bit. This is achieved by an optical head that is divided into at least two parts by a dividing line that is substantially similar to the above.

Furthermore, an optical head having an information reproducing sensor divided into at least two parts by a dividing line substantially similar to the edge shape of the bit in a one-dimensional reading direction of the bit, and a difference signal between the outputs of the divided sensors. and means for detecting the maximum and minimum peak positions of the amplitude of the difference signal,
This is achieved by an optical information reproducing apparatus characterized in that the edge position of the bit is detected by the pressure of the peak position detecting means.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram showing a first embodiment of the optical head of the present invention. In FIG. 1, the same parts as those of the conventional device shown in FIG. 7 are given the same reference numerals.

In FIG. 1, the reference numeral 3 designates an objective lens for focusing the light beam of the light source into a minute light spot, and the reference numeral 10 designates a condenser lens provided in the optical path of the reproduction optical system, which are the same as those in FIG. 7. In addition, there are actually the same components as shown in FIG. 7 other than the objective lens 3 and the condenser lens 10, but they are omitted here. Reference numeral 21 denotes bits (domains) recorded on the information track of the magneto-optical disk, which are recorded side by side in the track direction (six directions) as shown. Note that B in the figure represents the track cross direction. Reference numeral 22 indicates a reproduction light spot irradiated onto the information track, which is the light beam of the semiconductor laser focused by the objective lens 3. This reproducing light spot is reflected by the surface of the magneto-optical disk, is returned to parallel light by the objective lens 3, and is further imaged onto the sensor 23 by the condenser lens 10.

As shown in the figure, the two-dimensional shape of the sensor 23 is formed to be substantially similar to the single shape of the domain 21 representing the fundamental period of the bit on the medium surface. Furthermore, in the imaging optical system shown in FIG. 1, the image is in an inverted relationship with respect to the object, so the sensor 23 is arranged so as to have an inverted positional relationship with respect to the domain 21 accordingly.

Here, the focal length fo of the objective lens 3, the condenser lens 1
When the focal length of 0 is f, the lateral magnification β of the optical system is expressed by the following equation.

β-”-f a / f O... (1) For simplicity, we ignore the effects of other optical elements such as the disk substrate and the molded resin of the sensor. Of course, it is possible to find the magnification.

From this result, the ratio of the sensor 23 to the domain 21 is set approximately equal to the optical system lateral magnification 1β1. Further, 24 indicates an imaginary dividing line that equally divides the upper and lower areas of the sensor 23 in the direction orthogonal to the track. The sensor 23 is arranged so that the dividing line 24 intersects with the optical axis of the reproduction light beam.

As described above, in this embodiment, since the two-dimensional shape of the sensor 23 is similar to the two-dimensional shape of the main body,
It is possible to significantly reduce jitter components that occur depending on the domain shape and spot shape.

FIG. 2 is a second embodiment of the present invention, and is a schematic diagram showing various modifications of the sensor 23. FIG. 5A shows an example in which the length of the domain (in the A direction) and the width of the domain (in the B direction) are approximately equal. Further, FIG. 2B shows the shape of the sensor 23 when the basic period, that is, the domain length and the domain width are different, and here, the domain length is larger than the domain width. The width in the B direction is narrower than that in the example in FIG. This is an example of
d) is an example applied to an optical modulation type reproduction system, and the basic synchronization bit (domain) is circular, so sensor 2
The shape of No. 3 is formed into a circular shape accordingly. Figure (e) is an example of a sensor 23 that is similarly adapted to an oval bit, and Figure (f) is an example in which the width of the sensor 23 is narrowed to reduce crosstalk from adjacent tracks and the influence of groups. be.

In this way, the sensor 23 can be modified in various ways depending on the shape of the domain. Incidentally, regardless of the sensor 23 shown in FIG. 2, as in the example shown in FIG. shall be placed in In addition, in the embodiments shown in FIGS. 1 and 2, if the light intensity distribution of the light spot is point symmetrical and small at the periphery, such as a Gaussian distribution, it is not simply a position where the area is equally divided ( , it is possible to correct the sensor position to a position that takes into account the light intensity distribution.In this case, for example, the light spot 22 and domain 2 on the medium shown in FIG.
It is possible to correct the position where the correlation of 1 is maximum, and thereby the output of the sensor 23 can be maximized.

FIG. 3 is a schematic diagram showing a third embodiment of the present invention. In the figure, a curve 25 represents the edge shape of the bit (domain), and a polygonal line 26 represents the shape of the sensor 23. To explain each embodiment in detail, the embodiment shown in FIG. 3(a) is an example in which the polygonal line 26 of the sensor 23 is inscribed in the curve 25 of the bit.

Further, the embodiment shown in FIG. 2B is an example in which, on the contrary, i$126 of the sensor 23 is formed so as to be circumscribed with respect to the curve 25.

In the above embodiment, since the curved portion of the sensor 23 is formed into a polygonal shape, there is an advantage that the sensor 23 can be easily manufactured. Further, the shape of the polygon is not limited to the above, and may be set depending on the edge shape of the bit.

Even if the sensor 23 has a polygonal shape as described above, there is no practical problem as long as the jitter of the reproduced signal can be finally reduced to a permissible value or less. In addition, Fig. 3(a),
In the embodiment (b), the sensor 23
is slightly shifted inward and outward, which affects the jitter reduction effect accordingly.

FIG. 3(c) shows an embodiment that solves this problem, and is an example in which the polygonal line 26 of the edge of the sensor 23 is formed to approximate the curve 25 of the pit edge. That is, i
l! This is an example in which the sensor 23 is arranged so that the area inside and the area outside of the curve 25 divided by 26 are approximately equal.

Therefore, in the embodiment shown in FIG. 3(c), not only is it easy to fabricate the sensor, but it is also possible to obtain the same effect in reducing jitter as the embodiments shown in FIGS. 1 and 2. can.

FIG. 4 is a schematic diagram showing a fourth embodiment of the present invention.

This embodiment is particularly effective for reproducing the mark length recording shown in FIG. 8(b).

FIG. 4(a) shows an example in which the sensor 23 is divided into two parts in the bit (domain) scanning direction (track direction) A. In this case, the area of both divided sensor surfaces is approximately the same. The shape of the dividing line is approximately similar to the edge shape of the bit, as in the embodiment shown in FIG. 1.2, and the ratio thereof is set approximately equal to the lateral magnification of the optical system. The divided outputs of the sensors 27 and 28 are output to an addition circuit 29 and a subtraction circuit 30, respectively, and an addition output 31 and a subtraction output 32 are obtained. In this embodiment, as will be described in detail later, recorded information is reproduced using these two outputs. Further, in this embodiment, by taking the spatial difference as described above, spatial differentiation is realized and the reproduction performance of mark length recording is improved.

The reproduction operation of this embodiment will be explained below with reference to FIG.

3A shows a signal waveform 33 obtained by converting the output current of the divided sensor 27 into a voltage, and Tb in the same figure shows a signal waveform 34 obtained by converting the output current of the other sensor 28 into a voltage.

Note that each sensor pressure is assumed to be a sine wave for simplicity. Further, in FIG. 5, it is assumed that bits are continuously recorded on the information track at a fundamental period T of modulation. The sensor 23 is
As mentioned above, since it is similar to the bit of the fundamental period T, 2
The outputs of the divided sensors 2, 7, and 28 are shifted in phase by π/2 as shown.

Here, the amplitude of the outputs of the sensors 27 and 28 is normalized to 1
Then, the output Vat of the sensor 27 and the 8-force V of the sensor 28 are expressed by the following equation. However, the initial phase shall be ignored.

V2te=cos ωt+Va...(2)Vt
s=CO8((+Jt +i/2) +Va= -5i
nωt+V, + (3) Note that ■ is a standardized dc acid component. The difference between these two outputs Vs+ and the sum ■
. is obtained by the following equation. V31 is the output of the adder circuit 29, and V31 is the output of the subtracter circuit 30.

V a+= V sq+ V is= Nin (ωt
+3π/4)+2V.

...(4) v s2= v xq-V 21 &= , /'rsi
n ((Al tax /4) - (5) Figure 5 (
c) is the Vat signal waveform 35 obtained by equation (4),
Figure 5(d) shows the signal waveform 3 of V12 obtained by equation (5).
It is 6. Note that in the past, detection was performed using a sensor with a large area capable of detecting the total amount of light reaching the sensor surface, so its output was close to the signal waveform 35.

Here, in order to detect the edge of the recorded bit from the signal obtained as described above, in the signal waveform 35 shown in FIG.
It is sufficient to detect the intersection of the c acid component terms. Specifically, after cutting the DC acid component using an electrical high-pass filter, binarization can be performed using the zero-crossing point of the sine term as a threshold. This is the obtained binary signal 37, and the pulse is a bit (domain).
, and its rising and falling edges correspond to edges.

In addition, in this embodiment, since the dc acid component has already been removed from the differential signal waveform 36 shown in FIG. 5(d), that is, the equation (5), if this is used, the All you have to do is value it. Fifth
Figure (f) shows the binary signal 38 obtained in this way. In addition, in this embodiment, the peak position of the differential signal waveform 36 is detected by a peak detection circuit (not shown), and is shown in FIG.
A pulse signal 39 indicating a peak position as shown in g) is obtained. The specific peak detection circuit can be realized by various known detection circuits, so the explanation thereof will be omitted here. In this embodiment, when detecting the edge of a bit, a binary signal 3 obtained from a signal waveform 35 indicating a sum signal is used.
Bit edges are detected and reproduced using a pulse signal 39 obtained from a signal waveform 36 indicating a difference, instead of a signal waveform 36 indicating a difference.

Note that by using the binary signal 38 as a gate for the edge position during edge detection, the reliability of edge detection using the pulse signal 39 can be improved.

As described above, in this embodiment, bit edges are detected from the difference signal, but compared to edge detection using a sum signal, it is difficult to detect edges when bits are repeated in a single cycle as in this example. However, in reality, the arrangement of modulated and recorded bits is random, and edge detection using a difference signal is advantageous in such practical edge detection. Hereinafter, edge detection using a sum signal and edge detection using a difference signal will be compared and explained using FIG.

FIG. 6(a) is a diagram showing a state in which a domain 40a with a basic period IT is recorded on an information track sandwiched between domains 40b with two basic periods.

Note that the domains 40a and 40b have opposite magnetization directions. FIG. 4B shows a sum signal obtained by scanning the information track with a reproducing light beam. That is, a signal waveform 41 of the addition output 31 of the addition circuit 29 that adds the outputs of the sensors 27 and 28 is shown. In the same figure (b), when this addition output is passed through a high-pass filter to cut the dc acid component, the original zero cross level becomes the dc component 2 of the signal waveform 41.
Although the level of V a is 42, the frequency characteristic of the optical system, that is, the MTF is not flat, so the amplitude of period 2T is IT
is larger than the amplitude of Therefore, as a result, when the signal is passed through a high-pass filter, the zero-cross level shifts to the level shown as 43. FIG. 6(C) shows the binarized signal 44 obtained from the sum signal in FIG. 6(b), and since the zero cross level has shifted, the edge position of the binarized signal has also shifted. I understand. Therefore, in edge detection using a sum signal, the detected pit edge position includes an error corresponding to the shift of the zero cross level, and the edge position cannot be detected accurately.

FIG. 6(d) shows a signal waveform 45 of the difference signal.

That is, the waveform of the subtraction output 32 of the subtraction circuit 30 that calculates the difference between the sensors 27 and 28 is shown. In this difference signal, since the dc acid component is removed by spatial differentiation (difference),
The maximum and minimum peak positions do not change with respect to the edge of the domain 40a. FIG. 2(e) shows a binary signal obtained from the difference signal, which is used as a gate signal as described above.

Further, (f) in the figure is a pulse signal 47 indicating the peak position of the difference signal, and is a signal indicating the edge position of the domain. Since the jitter component is thus removed from the difference signal, edges can be detected accurately and information can be reproduced with high reliability. Furthermore, since jitter is reduced and accurate edge detection is achieved, it is particularly effective for information reproduction of high-density recording such as mark length recording.

The above was an explanation of the embodiment shown in FIG. 4(a), but
FIG. 4(b) is an example in which the overall shape of the sensor 23 is similar to the bit (domain) shape. The similarity ratio is set approximately equal to the lateral magnification of the optical system.

In this embodiment, crosstalk from bits arranged in the track direction (inward direction) can be reduced, so that the jitter reduction effect is further improved. Further, FIG. 4(c) shows an embodiment in which the sensor width is reduced, and crosstalk from adjacent tracks can be reduced.

In the embodiment shown in FIG. 4, the sensor 23 may be arranged as follows with respect to the optical axis. That is, as shown in FIG. 4(a), the virtual dividing line 24 is divided so that the area of the sum of the shaded areas 27a and 27b of the sensor 27 is equal to the area of the shaded area 28a of the sensor 28. In some cases, the optical axis may be positioned so as to intersect with the virtual dividing line 24. With this positioning, when the edge of the bit is on the optical axis, the difference signal 32 between the sensors 27 and 28
is the peak. Of course, the edge positions have a distribution in the B direction, so depending on where you actually set the edge,
All you have to do is change the dividing line of the sensor. To adjust the sensor position specifically, align the optical axis with the predetermined edge position of the bit, move the sensor in the track direction from this state, and position the sensor as the position where the difference signal peaks. . At that time, positioning is performed including correction for the influence of the light intensity distribution of the light spot.

Further, the dividing line shape of the sensor of the embodiment shown in FIG. 4 may be a multi-use approximation similar to that shown in FIG. Furthermore, the number of divisions is not limited to the two-divided sensor, and may be an optimal number of divisions depending on crosstalk and jitter.

In the embodiments shown in FIGS. 1 to 4 above, the information recording medium is a magneto-optical disk, but the present invention is not limited to this, and the present invention is not limited to this, but may be applied to a bit-shaped disk or a disk with a change in reflectance. Of course, it is also possible to use a phase change or dye-based medium. Further, although not shown in the embodiment, by making the reproducing system have a differential detection configuration as shown in FIG. 7, medium noise, laser noise, etc. can be reduced and the signal level can be doubled.

Therefore, by using the present invention together with the differential detection configuration, crosstalk, jitter, etc. can be further reduced. Further, although a reflective recording medium is used in the embodiment, a transmissive recording medium may be used.

[Effects of the Invention] As explained above, according to the present invention, since the two-dimensional shape of the information reproducing sensor is formed to be substantially similar to the two-dimensional shape of the bit on the recording medium, jitter components and crosstalk of the reproduced signal are reduced. can be significantly reduced compared to conventional methods. Furthermore, by dividing the sensor into at least two parts in the one-dimensional bit readout direction by a dividing line that is substantially similar in shape to the bit edge, it is possible to significantly reduce the jitter component and crosstalk of the reproduced signal. Furthermore, since the edge position of the bit is detected by the difference signal of the divided sensors, the error rate can be significantly reduced and highly reliable information reproduction can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the present invention, and FIG. 2 is a diagram showing a second embodiment of the present invention.
FIG. 3 is a diagram showing a third embodiment, FIG. 4 is a diagram showing a fourth embodiment, and FIG. 5 is a diagram showing a bit edge detection operation of the embodiment shown in FIG. 4. Figure 6 is a time chart that compares edge detection operations using sum and difference signals, Figure 7 is a configuration diagram showing a conventional optical modulation type optical head optical system, and Figure 8 is a diagram showing the edge detection operation between marks. FIG. 3 is a diagram showing domains according to recording and mark length recording. 3: Objective lens 10: Condensing lens 21 domain 22: Reproduction light spot 23: Sensor 27.28: Divided sensor 29; Addition circuit 30: Subtraction circuit Agent Patent attorney Yohei Yamashita Figure 2, Figure 3 Figure 4 Figure 6 Figure 8 (b) @2l

Claims (1)

[Claims] (1) Reflected light of a reproducing light beam irradiated onto an information recording medium;
Alternatively, an optical head having an information reproducing sensor for detecting transmitted light, wherein a two-dimensional shape of the sensor is formed to be substantially similar to a two-dimensional shape of a bit recorded on the recording medium. . (2) The optical head according to claim 1, wherein a similarity ratio of the sensor to the bit is approximately equal to an optical lateral magnification from the bit to the sensor. (3) The optical head according to claim 1, wherein the width of the sensor is slightly narrower than the bit. (4) The optical head according to claim 1, wherein the portion of the sensor corresponding to the bit edge is formed to be substantially similar by polygonal approximation. (5) The optical head according to claim 1, wherein the sensor is arranged such that a dividing line that divides the sensor into approximately equal areas in a direction orthogonal to the one-dimensional reading direction intersects the optical axis. . (6) In an optical head having an information reproducing sensor for detecting reflected light or transmitted light of a reproducing light beam irradiated onto an information recording medium, the sensor is positioned at the edge of the bit in a one-dimensional reading direction of the bit. An optical head characterized in that the shape is divided into at least two parts by a substantially similar dividing line. (7) The optical head according to claim 6, wherein a similarity ratio of the sensor to the bit is approximately equal to an optical lateral magnification from the bit to the sensor. (8) The optical head according to claim 6, wherein the sensor is divided by a polygonal approximation dividing line with respect to the bit edge shape. (9) The optical head according to claim 6, wherein the overall shape of the sensor is substantially similar to the shape of the bit. (10) The optical head according to claim 6, wherein the sensor is divided so that the area of the sensor surface divided by the dividing line is approximately equal. (11) The optical head according to claim 6, wherein the sensor is arranged such that a dividing line that divides the sensor into approximately equal areas in a direction orthogonal to the one-dimensional reading direction intersects the optical axis. . (12) An optical head having an information reproducing sensor divided into at least two parts by a dividing line substantially similar to the edge shape of the bit in the one-dimensional reading direction of the bit, and a difference signal between the output of the divided sensor. and means for detecting the maximum and minimum peak positions of the amplitude of the difference signal, and detecting the edge position of the bit based on the output of the peak position detecting means. information reproducing device. (13) The optical information reproducing apparatus according to claim 12, further comprising means for binarizing said difference signal, and said binarized signal being used as a gate signal for said edge detection.