JP3413496B2 - Magneto-optical information reproducing device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical information reproducing apparatus for reproducing information recorded on a magneto-optical recording medium by a pit edge recording system.

[0002]

2. Description of the Related Art In recent years, a magneto-optical information recording / reproducing apparatus using a magneto-optical disk as a recording medium is portable.
There are great expectations for its large storage capacity and its ability to be erased and rewritten. FIG. 3 is a block diagram showing an optical system of the conventional magneto-optical information recording / reproducing apparatus. In FIG. 3 , 101 is a semiconductor laser used as a recording / reproducing light source. A divergent light beam emitted from the semiconductor laser 101 is collimated by a collimator lens 102 and is corrected by a beam shaping prism 103 into a parallel light beam having a circular cross section. The parallel light flux passes through the polarization beam splitter 104, and is further imaged as a minute light spot on the magnetic layer of the magneto-optical recording medium 106 by the objective lens 105. Further, the magnetic head 10 is attached to the light spot irradiation section.
An external magnetic field is applied from 7 to record information pits on the magnetic layer.

The reflected light from the magneto-optical recording medium 106 is returned to the polarization beam splitter 104 via the objective lens 105, where a part of the reflected light is separated and introduced to the control optical system. In the control optical system, the separated light beam is further separated by the separately prepared polarization beam splitter 109, and one of them is supplied to the reproduction optical system 110 to generate a reproduction signal. Further, the other light flux separated by the polarization beam splitter 109 is guided to the half prism 117 via the condenser lens 116, and is split into two here, one of which is the photodetector 11.
8 through the knife edge 119 to the photodetector 12
Lead to zero. Then, a servo error signal for auto-tracking control or auto-focusing control is generated based on the detection signals of the photodetectors 118 and 120 of these control optical systems.

The reproducing optical system 110 changes the polarization direction of a light beam to 4
A half-wave plate 111 for rotating 5 degrees, a condenser lens 112 for condensing a light flux, a polarization beam splitter 113,
It is composed of photodetectors 114 and 115 that detect the light beams separated by the polarization beam splitter 113, respectively. The signals detected by the photodetectors 114 and 115 are differentially detected by a differential amplifier (not shown) and reproduced as a magneto-optical signal.

By the way, in a magneto-optical recording medium, information is recorded by the difference in the direction of perpendicular magnetization. When this is irradiated with linearly polarized light, the polarization direction of the reflected light is right due to the difference in the direction of magnetization. Rotate either clockwise or counterclockwise. For example, the polarization direction of linearly polarized light incident on the magneto-optical recording medium as shown in FIG. 4, a coordinate axis P direction, the light reflected against the downward magnetization R ₊ rotated + theta _K, rotated reflected light - [theta] _K for upward magnetization R _- to. Therefore, FIG.
When the analyzer is placed in the direction as shown in, the light passing through the analyzer becomes A for R _{+ and} B for R ₋ , and when this is detected by the photodetector, information is obtained as the difference in light intensity. Obtainable. In the example of FIG. 3 , the polarization beam splitter 113 serves as an analyzer, and for one of the separated light beams,
+45 degrees from the P-axis, -45 degrees from the P-axis for the other beam
It becomes an analyzer in the direction of degrees. That is, the photodetectors 114 and 1
Since the signal components obtained in 15 have opposite phases, a reproduced signal with reduced noise can be obtained by differentially detecting individual signals.

Information pits (hereinafter abbreviated as pits) are recorded on the magneto-optical recording medium as described above as the difference in the magnetization direction. In the recording form, the pits that give the meaning of information to the center position of the pits are recorded. There are a position recording method and a pit edge recording method in which the position of the edge of the pit has meaning of information. When information is recorded on a magneto-optical recording medium by using optical means, if the recording sensitivity of writing pits on the magneto-optical recording medium is gentle with respect to heat generated by a light spot, the pit size may vary. Will occur.
However, the position of the center of the pit does not change. Conventionally,
For this reason, in many cases, pit position recording is performed in a magneto-optical recording medium using optical means. On the other hand, when the recording sensitivity of writing pits on the magneto-optical recording medium is steep with respect to the heat generated by the light spot, the variation in the size of the pits can be reduced to a certain amount or less.
Pit edge recording becomes possible and the recording density can be increased. Therefore, recently, a magneto-optical recording medium suitable for pit edge recording and a pit recording system have been developed, and the pit position recording is being changed to the pit edge recording.

By the way, when reproducing the information of the pit edge recording, the reproduction signal obtained by the reproduction optical system of FIG. 3 is compared with a predetermined slice level, and the position where the reproduction signal crosses the slice level is detected. The pit edge is detected. Then, the information is reproduced according to the obtained edge position, and the original recorded information is restored. However, if the density of information is further increased and the size of the minimum pit becomes equal to or smaller than the size of the light spot, the transfer characteristics of the optical head and the like deteriorate, and the optical The DC component of the detected signal fluctuates, and there is a problem that an edge shift occurs when trying to detect a pit edge at a constant slice level.

Therefore, in order to solve this, differential detection is performed by using a divided photodetector divided in the direction orthogonal to the track, thereby optically performing differential detection to suppress the fluctuation of the DC component and to make the pit. There is a method of detecting edges. Specifically, for example, in Japanese Unexamined Patent Publication No. 62-188047, a reflected light beam from an information recording medium is converted into circularly polarized light, and a split light is generated by a phase difference between the respective reflected circularly polarized lights generated by upward magnetization and downward magnetization. A method of detecting the light amount distribution on the detector is disclosed. However, in the method of converting into circularly polarized light, it is difficult to accurately detect the edge of the pit because the phase difference is very small and the detection signal is weak.

In addition, "Detecting Transition Regions I
n Magnetooptical Disk Systems, Appl.Phys.Lett.55
(8), 716-7 (1989) ”describes detection of an autofocus control signal and an autotracking control signal by one multi-divided photodetector and a pit edge detection method by optical differentiation. However, also in this example, since circularly polarized light is incident on the information recording medium and an edge is detected by using the phase difference, the detection signal is still weak.

On the other hand, as is clear from FIG. 4 , S ₊ , S
_- the two components of a component displaced by the same magnitude phase [pi. That is, if attention is paid only to the S-polarized component, the magneto-optical pit can be regarded as a phase pit having a phase difference of π. Therefore, Japanese Patent Laid-Open No. 61-198458 discloses that
This has been described, and a method of correcting the phase difference between the S-polarized component and the P-polarized component to improve the quality of the reproduced signal is disclosed. However, this method is intended to improve the quality of the reproduced signal and does not optically reproduce the edge of the pit. Also, it is known that the light quantity distribution of the reflected light from the edge of the phase pit changes conventionally.
For example, in Japanese Utility Model Application Laid-Open No. 56-90744, the fact that the light amount distribution of the reflected light from the edge portion of the concavo-convex phase pit is asymmetric on the far field surface is used to perform optical differentiation with a multi-division photodetector. , A method of obtaining a reproduction signal is disclosed. However, since the magneto-optical pit is not a concave-convex pit, the asymmetry on the far field surface is very small with only S-polarized light, and it cannot be applied to reproduction of the magneto-optical pit as it is.

Further, Japanese Patent Laid-Open No. 2-46544 discloses that
A method is disclosed in which the S-polarized component of the reflected light from the edge portion of the magneto-optical pit has an asymmetric light amount distribution. However, even in this method, as described above, the asymmetry on the far field surface is very small only with S-polarized light, and it cannot be applied to reproduction of magneto-optical pits as it is, and the amount of light is very small only with S-polarized light component. Therefore, accurate information reproduction is difficult.
In addition, `` Edge Detection For MagnetoopticalData Stor
age .Appl.Opt.30.232-252 (1991) "and Japanese Patent Laid-Open No. 3-1
Japanese Patent No. 20645 discloses a method of optically detecting the edge portion of a pit by using both the S-polarized component and the P-polarized component. However, this method has a problem that the number of parts of the optical system increases and the configuration becomes complicated.

FIG . 5 shows, when linearly polarized light is incident on the magneto-optical recording medium, the amplitude distribution, the phase distribution, and the polarization distribution of the reflected light beam, the position reflected from the recording medium, the far field surface, and the condenser lens. It is the figure shown by the convergence surface by. However, it is assumed that there is no influence of the phase plate and the analyzer. First, FIG. 5A shows the magnetization state of the magneto-optical recording medium and the irradiation position of the reproducing light spot narrowed down by the objective lens.
It is the figure shown in four cases of- (D). (A) is all downward magnetization, and one of them is irradiated with a light spot,
In (B), all are upward magnetization, and one of them is irradiated with a light spot. Further, in (C), the left side of the drawing is downward magnetization,
The right side is upward magnetization, and the edge of the pit at the boundary is irradiated with a light spot. Further, in (D), the left side in the drawing is upward magnetization and the right side is downward magnetization, and a light spot is applied to the edge of the pit at the boundary. Arrow T
(T ') is the moving direction of the light spot.

FIG . 5B is a diagram showing the distribution of reflected light immediately after being reflected by the magneto-optical recording medium in each of the above (A) to (D). The incident light flux is P-polarized linearly polarized light as described above. (B-1) is the amplitude distribution of P-polarized light,
(B-2) is the amplitude distribution of S-polarized light (ignoring the magnitude), (b
-3) is a phase distribution of S-polarized light when P-polarized light is used as a reference,
(B-4) is a diagram showing a polarization state on the left side of the light flux with reference to the objective lens, and (b-5) is a diagram showing a polarization state on the right side of the light flux. The right side and the left side of this light flux correspond to before and after the light spot in the track direction advances.

[0014] FIG. 5 (c) is a diagram showing the distribution of the reflected light beam in the far field plane for each similarly (A) ~ (D). (C-1) is the amplitude distribution of P-polarized light, (c-1)
-2) is the amplitude distribution of S-polarized light (ignoring the magnitude), (c-
3) is a phase distribution of S-polarized light when P-polarized light is used as a reference,
(C-4) is the polarization state on the left side of the light flux, and (c-5) is the polarization state on the right side of the light flux. Further, FIG. 5 (d) is also the same as (A).
FIG. 5 is a diagram showing distributions of reflected light beams on the converging surface of the condenser lens for each of (D) to (D). (D-1) is the amplitude distribution of P-polarized light, (d-2) is the amplitude distribution of S-polarized light (ignoring the size), (d-3) is the phase distribution of S-polarized light when P-polarized light is the reference, (D-4) is the polarization state on the left side of the luminous flux, and (d-
5) is the polarization state on the right side of the light flux.

When reproducing the downward magnetization of (A), (b)
As shown in -1) and (b-2), the amplitude distributions of the P-polarized light and the S-polarized light immediately after being reflected by the magneto-optical recording medium are bilaterally symmetrical. Further, the left and right light beams have the same polarization state on the left and right as shown in (b-4) and (b-5), and are linearly polarized light rotated clockwise. The phase difference between the P-polarized light and the S-polarized light at this time is 0 as shown in (b-3). In the far field plane and the convergence plane, (c-
1), (c-2) and (d-1), (d-2), the amplitude distributions of P-polarized light and S-polarized light are symmetrical, and the phase of S-polarized light is (c-3), ( 0 as shown in d-3)
Becomes The polarization states of the left and right light fluxes are also (c-4), (c
As shown in -5), (d-4), and (d-5), the left and right are the same, and are in a clockwise rotated state.

In the case of reproducing the upward magnetization of (B), the amplitude distributions of P-polarized light and S-polarized light become bilaterally symmetrical just after being reflected by the magneto-optical recording medium. However, the phase of S-polarized light differs from that of P-polarized light by π. The left and right polarization states are linearly polarized lights that are rotated counterclockwise as compared with the case of downward magnetization. Also on the far field plane and the converging plane, the amplitude distributions of the P-polarized light and the S-polarized light are bilaterally symmetric, the phase difference of the S-polarized light is π, and the left and right polarization states are linearly polarized lights rotated counterclockwise.

In the case of reproducing the edge of the pit at the boundary between the downward magnetization and the upward magnetization of (C), the amplitude distribution of P-polarized light is symmetric right after being reflected by the magneto-optical recording medium, but that of S-polarized light. The amplitude distribution is divided into two corresponding to the magnetization direction, and the phase distribution is 0 on the left side and π on the right side. The polarization state at this time is a linearly polarized light that is rotated clockwise on the left side and a linearly polarized light that is rotated counterclockwise on the right side. On the far field plane, the amplitude distribution of P-polarized light is symmetrical, and the amplitude distribution of S-polarized light is still divided into two, but the phase distribution of S-polarized light changes and the left side is −π / 2 and the right side is + π / 2. Becomes That is, the polarization state is, for example, clockwise elliptically polarized light on the left side and counterclockwise elliptically polarized light on the right side. The ellipticity and size of each elliptically polarized light are the same, and the major axis of the ellipse is in the P polarization direction.
On the converging surface of the condenser lens, the amplitude distribution of P-polarized light is left-right symmetric, and the amplitude distribution of S-polarized light remains divided into two.
The phase distribution of S-polarized light returns again to 0 on the left and π on the right.
Becomes Therefore, the polarization state is a left-handed linearly polarized light and a right-handed linearly polarized light.
In the case of reproducing the pit edge at the boundary between the upward magnetization and the downward magnetization of (D), the left and right are reversed as compared with the case of (C).

In Japanese Patent Application No. 2-279710, as described with reference to FIG. 5 , focusing on the fact that the left and right polarization states on the converging surface are linearly polarized in different directions, the two-split light detection divided in the track direction is detected. It has been proposed that a pit edge signal and a pit position signal be detected by arranging a device near the converging surface and detecting the difference or sum signal of the detection signals of the photodetector. Hereinafter will be described in detail with reference to FIGS. 6-8.
First, FIG. 6 is a diagram showing a reproducing optical system in the optical head. In the figure, 111 is a half-wave plate, 112 is a condenser lens,
Reference numeral 113 is a polarization beam splitter .
It is the same as that shown in 3 . Reference numerals 121 and 122 each denote a two-divided photodetector divided into two in a direction orthogonal to the track direction (T, T'direction) of the information recording medium.
The detection signals of the detection pieces 121a and 121b of the two-division photodetector 121 are differentially detected by the differential amplifier 123, and the other 2
The detection signals of the detection pieces 122a and 122b of the split photodetector 122 are differentially detected by the differential amplifier 124. And
The differential detection signal thus obtained is further differentially detected by the differential amplifier 125 to obtain a reproduction signal of the pit recorded by the pit edge recording, that is, a pit edge detection signal for detecting the edge of the pit.

[0019]Figure 7Is the light spot a pit with downward magnetization?
From the upper direction through the boundary (edge) where the magnetization is reversed.
On the two-division photodetectors 121 and 122 when shifting to
It is a figure showing the change of the light intensity of.Figure 7(A)-(c)
Is a two-segment photodetector 121,Figure 7(D) to (f) are divided into two
Each corresponds to the photodetector 122. Also, the X-axis in the figure
The position on the two-division photodetector shown below, the Y-axis is the light intensity
It is the size. The Y-axis is on the dividing line of the 2-split photodetector.
It 2 if the light spot is on a pit with downward magnetization
The distribution of intensities on the split photodetectors 121 and 122 isFigure 7
As shown in (a) and (d). Each distribution is Y
Symmetric about the axis, the intensity peak is on the Y axis. Pee
The size of kuFigure 7The photodetector 121 in (a) is larger
Yes. In this case, each of the two-divided photodetectors 121 and 122
Detection pieces 121a and 121b and detection pieces 122a and 122
The detection signals obtained in b are the same, and
The signals obtained by differential detection with
Both are 0. Therefore, the output signal of the differential amplifier 125
The number is also 0.

On the contrary, when the light spot is on the pit having the upward magnetization, the light intensity distributions on the two-divided photodetectors 121 and 122 are as shown in FIGS. 7 (c) and 7 (d). 7 (a) and 7 (d) are reversed. Also in this case, the detection signals of the detection pieces 121a and 121b and the detection pieces 122a and 122b of the two-divided photodetectors 121 and 122 are the same, so that the differential amplifier 12
The differential detection signal of 3,124 becomes 0, and the differential amplifier 12
The output signal of 5 also becomes 0.

When the light spot is at the position where the downward magnetization is reversed to the upward magnetization, the two-divided photodetectors 121, 1
The light intensity distribution on 22 is as shown in FIGS. 7 (b) and 7 (e). Both light intensity distributions are centered on the Y axis and + on the X axis.
It is divided into a side and a − side, and the peak is larger on the − side in FIG. 7 (b) and larger on the + side in FIG. 7 (e). Therefore, when the differential amplifier 123 differentially detects the signals of the two detection pieces 121a and 121b of the two-split photodetector 121, a negative signal is obtained, and the differential amplifier 124 splits the two-split photodetector 1 into two.
When the signals of the detection pieces 122a and 122b of 22 are differentially detected, a positive signal is obtained. Further, when the obtained positive and negative signals are differentially detected by the differential amplifier 125, a positive value signal is obtained. That is, when the light spot moves from the downward magnetization to the upward magnetization, it is possible to obtain a signal having a peak in the positive direction at the position where the magnetization direction is reversed, that is, the position of the edge of the pit.

On the other hand, when the light spot moves from the upward magnetization to the downward magnetization, a signal having a peak in the negative direction is obtained at the position of the edge of the pit where the magnetization direction is reversed, contrary to the above. FIG. 8 shows the pit edge detection signal described above. FIG. 8A shows a pit row on the information track, and the pits indicated by diagonal lines have upward magnetization, and the other pits have downward magnetization. FIG. 8B shows a pit edge detection signal obtained by the differential amplifier 125. When the light spot moves in the direction of the arrow, as described above, a positive direction signal is obtained at the edge position where the downward magnetization is changed to the upward magnetization, and a negative direction signal is obtained at the edge position where the upward magnetization is changed to the downward magnetization. The pit edge can be detected by the positive and negative peak positions. According to the above detection method, the signal on the pit becomes 0, and the signal appears only at the edge of the pit, so that it is possible to reduce the influence of the difference in the transfer characteristics of the optical head or the like due to the difference in the size of the pit. .
Therefore, the fluctuation of the DC component also becomes small, and the problem of edge shift can be solved.

Further, in FIG. 6 , 127 and 128 are 2
An addition amplifier 129 for adding the detection signals of the detection pieces of the split photodetectors 121 and 122, respectively, is a differential amplifier for differentially detecting the addition signals obtained by the addition amplifiers 127, 128. The output signal of the differential amplifier 129 becomes a reproduction signal of the pit recorded in the pit position recording, that is, a pit position detection signal. The pit position detection signal obtained here is a signal having a peak at the center of the pit, similar to the signal obtained by the reproducing optical system shown in FIG .

[0024]

The pit edge detection method described with reference to FIGS. 6 to 8 can effectively solve the problem of edge shift and accurately detect the pit edge. To detect using 2
There is a problem that the position adjustment of the split photodetector, that is, the position adjustment with the light spot becomes complicated. Further, in the above-mentioned conventional example, there is no edge shift in the detection of the pit edge, and it is possible to accurately detect, but when detecting the pit position, if the size of the pit becomes smaller,
After all, there was a problem that the direct current component fluctuates due to the influence of the deterioration of the transfer characteristics of the optical head and the like.

The present invention has been made in order to solve such a problem, and enables detection of pit edges with an ordinary single photodetector, without requiring complicated optical adjustment of the photodetector. An object of the present invention is to provide a magneto-optical information reproducing device capable of accurately detecting a pit edge.

[0026]

SUMMARY OF THE INVENTION An object of the present invention is to irradiate a magneto-optical recording medium with a light beam, and to emit light beams in two directions orthogonal to each other.
In a magneto-optical information reproducing apparatus that reproduces recorded information based on reflected light containing a polarized component in the opposite direction, the reflected optical path of the recording medium
Inside , corresponding to the front and back of the reflected light beam, one of which is recorded
Linearly polarized light orthogonal to the direction of linearly polarized light incident on the medium
The phase of is advanced by 1 / 2π and the other is delayed by 1 / 2π
A phase plate set as described above, a lens and an analyzer for converging the light flux passing through the phase plate are provided, and a photodetector having a single light receiving surface is arranged on the rear surface of the analyzer. By detecting the change in the amount of light flux passing through
This is achieved by a magneto-optical information reproducing device characterized by detecting edges of information pits recorded on the recording medium.

[0027]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a magneto-optical information reproducing apparatus of the present invention. It should be noted that FIG. 1 shows only the configuration of the reproducing optical system, which is a main part of the present invention. In FIG. 1, reference numeral 1 is a quarter-wave plate composed of two quarter-wave plates 1a and 1b having different phase characteristics. 1 /
The four-wave plate 1 is separated corresponding to the front part and the rear part of the light beam reflected from the information recording medium, and the 1/4 wave plate 1a on the right side of the drawing is on the front part of the reflected light beam and on the left quarter of the reflected light beam. Wave plate 1b
Are arranged corresponding to the rear part of the reflected light flux.
The quarter-wave plate 1a is constructed such that its fast axis coincides with the direction of the incident linearly polarized light, and the other quarter-wave plate 1b is constituted so that its slow axis coincides with the direction of the incident linearly polarized light. Therefore, if the incident linearly polarized light is linearly polarized light in the P-axis direction (P-polarized light),
The light beam incident on the right side in the figure is P by the quarter wavelength plate 1a.
The phase of S-polarized light is advanced by 1/4 wavelength (1 / 2π) with respect to the polarized light, and the light flux incident on the left side is delayed by 1/4 wavelength with respect to P-polarized light by the quarter-wave plate 1b. It has become.

[0028] 111 half-wave plate, 112 a condenser lens, 113 by the polarization beam splitter, which are the same as those both shown in FIG. 2 and 3 are photodetectors, and 4 is a differential amplifier. The photodetectors 2 and 3 may be arranged on the converging surface of the condenser lens 112 or may be arranged in the middle thereof. Although in Figure 1 the other configurations are omitted, otherwise it is possible to use the one shown in FIG. Therefore, the light flux reflected from the information recording medium 106 is the objective lens 105 and the polarization beam splitter 10.
It is guided to the quarter-wave plate 1 via 4,109.

FIG. 2 is a diagram showing the amplitude distribution, the phase distribution, and the polarization distribution of the reflected light flux when the information recording medium is irradiated with the linearly polarized light, with respect to the far field surface and the converging surface of the condenser lens 112, respectively. is there. Similar to FIG. 5 , FIG. 2A shows the magnetization state of the information recording medium and the irradiation position of the reproduction light spot narrowed down by the objective lens in 4 of (A) to (D).
It is the figure shown in two cases. In (A), all of the magnetizations are directed upward, and one of them is irradiated with a light spot, and in (B), the magnetizations are all directed upward and one of them is irradiated with a light spot. Further, in (C), the left side in the drawing is downward magnetization, and the right side is upward magnetization, and a light spot is applied to the edge of the pit at the boundary. Further, in (D), the left side of the drawing is upward magnetization, and the right side is downward magnetization, and the light spot is applied to the edge of the pit at the boundary. The arrow T (T ') is the scanning direction of the light spot.

FIG. 2 (e) is a diagram showing the distribution of the luminous flux on the far field surface for each of the above (A) to (D). Here, in order to provided a quarter-wave plate 1 in the optical path of the light beam reflected from the information recording medium is converted as shown in FIG. 2 (e) from the state of FIG. 5 (c). First, (A)
When reproducing downward magnetization of P, the amplitude distribution of P-polarized light is the same as that of FIG.
The amplitude distribution of the polarized light is the phase advance action of the quarter-wave plate 1a.
It changes as shown in (e-2) by the phase delay action of the quarter wave plate 1b. Therefore, as shown in (e-3), the phase distribution of S-polarized light based on P-polarized light is such that the left-side light flux is delayed by π / 2 and the right-side light flux is advanced by π / 2. -4), the linearly polarized light (R ₊ ) rotated in the clockwise direction is changed to the elliptically polarized light in the clockwise direction, and the right side light flux is (e−
As shown in 5), the clockwise linearly polarized light is converted into the counterclockwise elliptically polarized light.

When reproducing the upward magnetization of (B), P
Although the amplitude distribution of polarized light is the same, the amplitude distribution of S polarized light, S
The phase distribution of the polarized light with respect to the P-polarized light is completely opposite to that in the case of (A). Therefore, regarding the polarization state, the left-side light flux is converted from the counterclockwise rotated linearly polarized light (R ₋ ) to the counterclockwise elliptically polarized light, and the right-side light beam is converted from the counterclockwise rotated linearly polarized light to the clockwise elliptically polarized light. When reproducing the edges of the downward magnetization and the upward magnetization of (C), the amplitude distributions of P-polarized light and S-polarized light are distributions as shown in (e-1) and (e-2), and the phase distribution of S-polarized light is As shown in (e-3), both the left and right light fluxes have a phase advanced by π. As a result, the left light flux is converted from right-handed elliptically polarized light into left-handed rotated linearly polarized light (R ₋ ) and the right-handed light flux is also converted from left-handed elliptically polarized light into left-handed rotated linearly polarized light. . Further, at the edge of the upward magnetization and the downward magnetization of (D), S
The phase distribution of the polarized light becomes 0, and the left light flux is converted from left-handed elliptically polarized light to right-handed linearly polarized light (R ₊ ), and the right-handed light flux is also rotated from right-handed elliptically polarized light to right-handed straight line. It is converted to polarized light.

FIG. 2 (f) is a diagram showing the distribution of the luminous flux on the converging surface of the condenser lens 112 for each of the above (A) to (D). On the converging surface of the condenser lens 112, when reproducing the downward magnetization of (A), the amplitude distributions of P-polarized light and S-polarized light are (f-1) and (f-, respectively).
2), the phase distribution of S-polarized light becomes (f−
As shown in 3), it becomes squid. The polarization state of the left-side light flux changes from right-handed elliptically-polarized light on the far field plane to linearly-polarized light (R ₊ ) rotated clockwise as shown in (f-4), and the right-side light flux of (f-5). As shown in, the counterclockwise elliptically polarized light changes to the counterclockwise rotated linearly polarized light (R ₋ ). When reproducing the upward magnetization of (B), the amplitude distribution and the phase distribution of the S-polarized light are opposite to those in the case of (A), and the polarization state on the left side is linearly polarized light rotated counterclockwise on the right side. The light flux changes to linearly polarized light that is rotated clockwise.

On the other hand, at the edge positions of the downward magnetization and the upward magnetization of (C), the amplitude distribution of P-polarized light, the amplitude distribution of S-polarized light, and the phase distribution of S-polarized light are (f-1) and (f, respectively).
-2) and (f-3) show a squirrel. Further, the polarization state is the same as the far field plane as shown in (f-4) and (f-5), and the left and right light fluxes are both linearly polarized lights rotated counterclockwise. Further, at the edges of the upward and downward magnetizations of (D), the polarization state is the same as that of the far field plane, and both the left and right light beams are linearly polarized light rotated clockwise.

The luminous flux reflected from the information recording medium is 1/4
The light enters the polarization beam splitter 113 through the wave plate 1, the half wave plate 111, and the condenser lens 112, and is separated into two light beams of P polarization and S polarization by the polarization characteristic thereof. The photodetectors 2 and 3 are respectively provided on the converging surface of the condenser lens 112 or in the middle thereof corresponding to the two separated light beams, and the detection signals of the photodetectors 2 and 3 are supplied to the differential amplifier 4
The edge of the pit is detected by differentially detecting at. Here, when reproducing the downward magnetization of (A) of FIG. 2, since the polarization states of the left and right light beams are canceled by the linearly polarized light rotated left and right as described above, the photodetector 2 and The signals of 3 are the same. As a result, the edge detection signal obtained by differentially detecting the differential amplifier 4 becomes zero.
Similarly, in the upward magnetization of (B), since the left and right polarization states are different, the detection signals of the photodetectors 2 and 3 are the same, and the edge detection signal of the differential amplifier 4 is 0.

On the other hand, in FIG. 2C, since the polarization states of the left and right light fluxes are both linearly polarized lights rotated counterclockwise, a difference occurs between the detection signals of the photodetectors 2 and 3. Also in (D), since the polarization states of the left and right light fluxes are linearly polarized lights that are rotated clockwise, the photodetectors 2 and 3 are similarly detected.
A difference occurs in the detection signal of. Therefore, as described in FIG. 7 , when the light spot moves from the downward magnetization to the upward magnetization of (C), a positive edge detection signal can be obtained at the edge position. (D) When the light spot moves from the upward magnetization to the downward magnetization, on the contrary, a negative edge detection signal is obtained at the edge position. That is, the pit detection signal obtained here is exactly the same as the signal obtained using the two-division photodetector as shown in FIG. 8 , and positive or negative edge detection is performed corresponding to the front end and the rear end of the pit. You can get a signal.

As described above, in the present embodiment, the quarter wave plate having different phase characteristics is provided in the reflected light path from the information recording medium so as to correspond to the front part and the rear part of the reflected light beam, and thus the conventional It is possible to detect the pit edge using a normal single photodetector instead of such a two-division photodetector. Therefore, the complicated position adjustment of the photodetector and the light spot is not necessary, and the position of the photodetector is not limited to the converging surface of the condenser lens. Can be greatly simplified.

[0037]

As described above , according to the present invention ,
Corresponds to the front and back of the reflected light flux in the reflected light path of the recording medium,
One is the direction orthogonal to the direction of linearly polarized light incident on the recording medium
Of the phase of linearly polarized light of
Since the phase plate set to delay is provided, P
Information pit using both polarization component and S polarization component
Edge detection using a photodetector with a single light receiving surface.
You can Therefore, the conventional two-split photodetector is used.
Eliminates the need for troublesome positioning work, and
Using both P-polarized component and S-polarized component, the edge signal
Since detection is performed, a detection signal with better S / N can be obtained.
It is possible to

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a magneto-optical information reproducing apparatus of the present invention.

2 shows the amplitude distribution, phase distribution, and polarization distribution of the reflected light flux on the far field surface and the converging surface of the condenser lens, respectively, when linearly polarized light is incident on the recording medium in the embodiment of FIG. It is a figure.

FIG. 3 shows an optical system of a conventional magneto-optical recording / reproducing apparatus.
It is a block diagram .

FIG. 4 illustrates the principle of information reproduction in magneto-optical recording .
FIG .

FIG. 5 shows a linear polarization on a magneto-optical recording medium in a conventional optical system.
The position where the recording medium is reflected when light is incident,
On the far field surface and the converging surface of the condenser lens,
A diagram showing the amplitude distribution, phase distribution, and polarization distribution of the reflected light flux.
There is .

FIG. 6 is a diagram showing another conventional reproduction optical system .

7 is a diagram for explaining the information reproducing principle of the reproducing optical system of FIG .
It is a figure .

8 is a pit train reproduced by the reproduction optical system of FIG .
It is a figure showing a pit edge detection signal .

[Explanation of symbols]

1 1/4 wave plate A few photo detectors 4 differential amplifier 101 Semiconductor laser 105 Objective lens 106 information recording medium 111 1/2 wave plate 112 Condensing lens 113 Polarizing beam splitter

Front page continuation (51) Int.Cl. ⁷ identification code FI G11B 7/135 G11B 7/135 Z (72) Inventor Susumu Matsumura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference: JP-A-3-268252 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 11/105 G11B ^7/ 12-7/22

Claims (3)

(57) [Claims] 1. A magneto-optical information reproducing apparatus for irradiating a magneto-optical recording medium with a light beam, and reproducing recorded information based on reflected light containing polarized components in two directions orthogonal to each other , in the magneto-optical information reproducing apparatus. In the optical path , it corresponds to the front part and the rear part of the reflected light beam, one of which is directly parallel to the direction of the linearly polarized light incident on the recording medium.
Advances only the phase of linearly polarized light in the intersecting direction by 1 / 2π, while
Is provided with a phase plate set to delay by 1 / 2π, a lens and an analyzer for converging the light flux that has passed through the phase plate, and a light receiving surface having a single light receiving surface on the rear surface of the analyzer.
A magneto-optical information reproducing apparatus characterized in that an edge of an information pit recorded on the recording medium is detected by arranging a device and detecting a change in the light amount of a light flux that has passed through the analyzer. Wherein said optical detector is a magneto-optical information reproducing apparatus according to claim 1, characterized in that arranged on the way to the convergence position or converging position of the lens. 3. The analyzer is a polarization beam separating light beam.
Optical splitter, the photodetector is separated into two
2 are arranged to detect the respective luminous fluxes of
By differentially detecting the detection signals of two photodetectors,
The magneto-optical information reproducing apparatus according to claim 1 , wherein an edge of the information pit is detected .