JP3288083B2 - 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 an optical information reproducing apparatus for reproducing information recorded on an optical information recording medium, and more particularly to an optical information reproducing apparatus which records information on an optical information recording medium utilizing a magneto-optical effect. The present invention relates to an optical information reproducing apparatus having an improved optical head for reproducing information.

[0002]

2. Description of the Related Art A recording medium used in an optical information recording / reproducing method is effectively used as an external storage means of a computer in that a data recording capacity is large with respect to its size. Above all, a magneto-optical recording / reproducing recording medium is extremely useful in that data can be rewritten. As a method of recording information on such a magneto-optical recording medium, an inter-mark recording method and a mark length recording method (edge recording method) are known. The latter is advantageous in that the data capacity can be increased as compared with the former, but in order to accurately reproduce information from the recording medium recorded by this method, the edge of the information bit is required by the optical head. Accuracy in reading the position is required.

In recording information on a magneto-optical recording medium, light from a semiconductor laser as a light source is focused on a recording surface by an objective lens, formed into an image as a minute light spot, and a mark is formed using the light spot. It is performed by the long recording method. In reproducing information from a magneto-optical recording medium, light from a semiconductor laser is focused on a recording surface by an objective lens, formed as a small light spot, and the polarization state of reflected light from this light spot changes. Is converted into a change in the amount of light, and differential detection is performed.

As an optical head of such a rewritable magneto-optical information recording / reproducing apparatus, for example, a conventional example as shown in FIG. 22 is used. Here, a semiconductor laser 213 is used as a light source, and divergent light from the semiconductor laser 213 is converted into a parallel light beam through a collimator lens 214, and is provided to an objective lens 217 through a beam shaping prism 215 and a polarizing beam splitter 216. , Information recording medium 218
A light spot is formed on the magnetic layer. On the other hand, an external magnetic field is applied to the location by the magnetic head 219. Then, the reflected light from the information recording medium 218 returns to the polarization beam splitter 216 via the objective lens 217 again, where a part thereof is separated and supplied to the control optical system. In the control optical system, the separated light flux
The light is further separated by a separately prepared polarizing beam splitter 220, one of which is supplied to a reproducing optical system 21 to obtain an information signal, and the other is provided with a condenser lens 227 and a half prism 2.
The signal is supplied to the photodetector 229 via the control signal 28 and to the photodetector 231 via the knife edge 230 to obtain a control signal for the optical head.

[0005] The reproducing optical system 221 changes the polarization direction of the light beam to four.
A half-wave plate 222 for rotating by 5 degrees, a condenser lens 223 for condensing the light beam, a polarization beam splitter 224 for separating the light beam, and a light detection for detecting each of the light beams separated by the polarization beam splitter 224 Container 225
And 226. The reproduced signal is output from the photodetector 22.
5, 226 are obtained by differential detection of the signals.

In such a device, the magneto-optical signal is
It is obtained as follows. That is, in the information recording medium of magneto-optical recording, information is recorded by the difference in the direction of magnetization. When linearly polarized light is applied to this, the polarization direction of the linearly polarized light becomes clockwise or counterclockwise depending on the direction of magnetization. For example, as shown in FIG. 19, the polarization direction of the linearly polarized light incident on the information recording medium is _defined as the coordinate axis P, the reflected light for downward magnetization is R ₊ rotated by + θ _k, and the reflected light for upward magnetization is −θ _k. Assuming that R ₋ is rotated, the light transmitted through the analyzer is A for R _{+ and} B for R ₋ , and when this is detected by a photodetector, information can be obtained as a difference in light intensity. In the above-mentioned conventional example, the polarizing beam splitter 224 functions as an analyzer, and the one of the separated light beams is an analyzer in the direction of +45 degrees from the P axis and the other light beam is in the direction of -45 degrees from the P axis. Function. That is,
Since the signal components obtained by the photodetectors 225 and 226 have opposite phases, by performing differential detection of these signals, a reproduced signal with reduced noise can be obtained.

Now, when recording, when the recording sensitivity of the pits recorded on the information recording medium is steep due 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. Although pit edge recording becomes possible and the recording density can be increased, if the recording sensitivity of the pits recorded on the information recording medium is gentle, the pits vary in size. However, the center position of the pit does not change. Therefore, the recording of information on the information recording medium is performed by a pit position recording method in which the center position of the pit has the meaning of the information, and the reproduction of this pit edge is electrically set by a reproduction signal for the pit position recording of the device. It is determined as the position that crosses the slice level. However, at the stage where the density has been further increased, the size of the minimum pit is substantially equal to or smaller than the size of the light spot. In the signal detected by the optical means, the DC component fluctuates, and when an edge is detected at a constant slice level, an edge shift occurs.

In order to solve this problem, differential detection is performed optically by differential detection using a split photodetector having a split line in a direction perpendicular to the track to reduce fluctuations in the DC component. A method of detecting a pit edge in a state where the pit edge is detected has also been proposed. As can be seen from FIG. 19, S ₊ ,
S _- the two components of a component displaced by the same magnitude phase [pi. That is, focusing only on the S-polarized component, the magneto-optical pit can be regarded as a phase pit having a phase difference of π. Japanese Patent Application Laid-Open No. HEI 3-120645 discloses a method of realizing optical detection of a pit edge by detecting both an S-polarized light component and a polarized light component using a matching filter. However, here, the optical head is not optimally designed, has many parts, and has a drawback that it is structurally complicated. In Japanese Patent Publication No. 2-195546, FIG.
The light of R ₊ and R ₋ shown in FIG.
The light is converted into clockwise elliptically polarized light (a) and counterclockwise elliptically polarized light (b) as shown in FIG. 0, and this can be separated into clockwise and counterclockwise circularly polarized light as shown in FIG. It describes a method of separating and detecting two circularly polarized lights using a chromatic prism. However, it does not optically detect the edge of the magneto-optical pit.

For such reproduction, for example, as shown in Japanese Patent Application Laid-Open No. 3-268252, when a minute light spot narrowed to the diffraction limit is used, the reflected light from the edge of the information bit is used. Behaves as a phase type 0 / π
The diffraction from the edge / phase type 0 / π grating becomes dominant. This is in principle greatly different from the behavior of the reflected light geometrically or geometrically optically, and this new principle makes it possible to realize an accurate new edge detection device.

As described above, when edge detection is performed by using the diffracted and reflected light from the edge of the information bit, in order to obtain a signal of higher quality, Japanese Patent Application Nos. 2-278702 and 2-279710 are used. No., Japanese Patent Application No. 2-307910,
As disclosed in the specification of each patent application of Japanese Patent Application No. 2-310524, an apparatus using a spatially non-uniform optical filter (for example, a phase filter) and a split sensor has already been proposed. Further, an apparatus using a wavefront separation element such as a prism to guide the spatial light quantity non-uniformity of the diffraction pattern to the split sensor is disclosed in Japanese Patent Application No. 2-31068.
No. 2 is shown in the specification of the patent application.

In the edge detection method disclosed in Japanese Patent Application Laid-Open No. 3-104401, the diffraction phenomenon due to the edge as described above can be ignored, and the ellipse is formed by the Kerr effect (in this case, the positions of the P and S polarized lights are changed). In a special case where the phase difference can be neglected, the polarization state of the Kerr effect due to the domains on both sides of the edge (only the phase difference is added to the circularly polarized light, that is, only the rotation of the linearly polarized light) is used to directly describe the far field. In this case, the polarization operation can be performed by a λ / 4 plate, and the configuration using a polarization beam splitter as an analyzer has a characteristic that a difference in intensity occurs in the jitter direction in the far field.

Japanese Patent Application Laid-Open No. 62-188047 discloses an apparatus employing the same principle of reproduction. Normally, the incident linearly polarized light is converted into left and right elliptically polarized light according to the direction of the domain by the Kerr effect, and the inclination of the major axis thereof is ±± with respect to the incident linearly polarized light.
Although the device tilts by θ _K , in the device disclosed herein, the light reflected from the non-recording portion tilts with the incident linearly polarized light, and only the light reflected from the recording portion tilts with the linearly polarized light. Then, the orientation of the λ / 4 plate is aligned on the far field, and the inclination of the linearly polarized light from the recording unit is converted into a phase change (= 90 °) by the λ / 4 plate. , The light interferes with the linearly polarized light from the non-recording portion. At this time, in ordinary general interference, the interference term = cos 90 ° =
0, and the interference term disappears. However, in the edge detection method using this special configuration, a difference in light intensity appears in the jitter direction on the far field. In these conventional examples, the domain on the medium is regarded as equivalent to the concave and convex pits, and it is shown that an intensity difference occurs in the jitter direction. However, in the above-described detection method using the diffraction phenomenon, the magnetic domain has a refractive index. Function as a phase-type domain in which the phase changes, and the edge is a phase-type 0 / π edge, so that the diffraction pattern intensity due to the edge on the far field is symmetric in the jitter direction, and no intensity difference occurs in the jitter direction. For this reason, it is impossible to detect an edge using the detection principle disclosed herein. Further, according to the method using the above-described diffraction phenomenon, even if a phase difference is given by the λ / 4 plate in the far field according to the rotation of the polarized light, as long as the phase difference is not a phase difference caused by the domain, the edge of the domain. However, there is a difference that even if a method such as interference is used, edge detection is impossible.

The above-mentioned Japanese Patent Application Laid-Open No. HEI 3-120645 discloses a method of placing a lens for reproducing a plane image of a medium on a divided sensor. However, here, it is shown that the operation of the re-imaging method is the same as that of the method of dividing the far field, even though the image of the medium is obtained by re-imaging. However, if a re-imaging lens is used in the method utilizing the above-described diffraction phenomenon, the pattern is converted by diffraction due to this, and the difference is that it is impossible to obtain the same operation as detection in the far field. Out.

[0014]

In the conventional example in which the diffraction phenomenon due to the edge as described above can be ignored and the ellipticity factor due to the Kerr effect can be ignored, the lens inserted into the far field is simply a lens. It has only the light condensing function, and the diffraction phenomenon is ignored in the behavior of various optical elements in the far field. Further, even in a conventional example in which re-imaging is performed and the same result is obtained as in the case of detection on the far field, pattern conversion using the diffraction function of the lens is ignored.

However, in a system in which the above-described diffraction phenomenon is dominant, when a change in the diffraction pattern in the far field based on a change in the relative position between the edge and the light spot is detected by the split sensor, the sensor size becomes large. This not only increases the cost, but also causes problems such as a decrease in the responsiveness of the sensor and the occurrence of jitter in edge detection due to uneven spatial sensitivity of the sensor. Therefore, in the far field by the lens, an image is formed again on the spot, for example, a Fourier transform diffraction pattern is used, and in order to solve the problem of the sensor size, considering the crosstalk between the divided sensors, the dividing line of the sensor is considered. Gap from several μm to 10
Since a thickness of about μm is required, there is a problem that spatial division of a minute re-imaging spot is impossible.

If the far field is spatially split by a wavefront splitting element such as a prism, a diffraction pattern by the optical element (for example, its Fourier transform diffraction image) appears at the position of the re-imaging spot. This causes a problem that the diffraction pattern from the original edge is different from the re-diffraction pattern.

Further, in the edge detection system using the diffraction phenomenon, the intensity due to combined interference of a Fresnel reflection component not subjected to diffraction by a domain, a polarization component orthogonal to the Fresnel reflection component, and a Kerr reflection component diffracted by a domain. Changes in the distribution are detected. However, since the phase difference (generated elliptically polarized light) received by the two and the amplitude and phase distribution spatially modulated by diffraction greatly affect the detection signal, the polarizer and the phase shifter are detected. The spatial distribution, insertion position, and the like have the same effect, and there is a problem that the signal quality is degraded by an easy operation. In other words, some of the conventional examples require a wave plate and an analyzer, but it is difficult to detect an edge using such an optical element in an edge detection method using diffraction.

[0018]

According to the present invention, a light spot narrowed to a diffraction limit by an objective lens is used, and the size of the diffracted light from a recording domain of about the size of the light spot or less. The part, through the objective lens, the polarizing element, the re-imaging lens, to a position substantially conjugate to the light spot, converted as a new diffraction pattern, having a wavefront splitting element, a multiple image element and a plurality of light receiving areas By performing photoelectric conversion and calculating the output by a sensor unit with an integrated photodetector, it is possible to obtain a good spatial difference signal, and it is possible to detect an edge of a recording domain smaller than the size of a light spot. You can do it.

According to the present invention, information is recorded on an information recording medium having a plurality of tracks and recording information pits based on the difference in the direction of magnetization by utilizing the interaction between light, heat and magnetism. And / or at the time of reproduction, in an optical information reproducing apparatus in which linearly polarized light is incident on an information recording medium and the boundary of information pits is optically detected from the reflected light flux, A wavefront splitting element and a circularly polarized light separating element, the reflected light is split into two light beams parallel to the track by the wavefront splitting element, and the clockwise and counterclockwise Then, the information is reproduced by detecting the boundary portion of the information pit from the change in the amount of light of these four light beams.

In a similar magneto-optical information recording / reproducing apparatus, the reflected light flux has a large influence on a half light flux.
A half-wave plate and a circularly polarized light separating element are arranged, and the boundary between the information pits is detected from the change in the amount of light of two clockwise and counterclockwise circularly polarized light beams that have passed therethrough.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 schematically shows an optical head of an optical information reproducing apparatus for reproducing a magneto-optical recording medium according to the present invention. In the figure, reference numeral 1 denotes a wavelength λ (λ
= 830 nm), a semiconductor laser that emits linearly polarized light (the direction of the electric field vector is indicated by E), 2 is a collimator lens that converts this light beam into a parallel light beam, and 3 transmits almost the polarized component (S polarized light) in the E direction. A first polarization beam splitter 4 that reflects 100% of a polarization component (P-polarized light) in a direction perpendicular to the first and second directions is an objective lens. By providing these components, a light projection optical system is configured. Reference numeral 5 denotes a light projection spot formed at the diffraction limit by the objective lens 4, 6 denotes one information track provided on the magneto-optical disk, and 7 denotes a guide groove provided for tracking the light projection spot 5. is there. The information track 6 extends in the direction E, and the detected information magnetic domain edge is in a direction orthogonal thereto. Reference numeral 8 denotes a second polarization beam splitter which originally transmits 100% of P-polarized light and transmits 100% of S-polarized light.
Although the light is reflected at%, it is arranged at an angle of 45 degrees with respect to the E direction in order to perform differential detection.
Reference numeral 9 denotes a sensor lens for connecting reflected light of the second polarizing beam splitter to a spot, and reference numeral 10 denotes a sensor lens for connecting transmitted light to a spot. This is a result of performing aberration correction similar to that of the lens 4. Reference numerals 11 and 12 denote prism-integrated split sensors described later, and each split line is directed in the direction X of the information domain edge.

The linearly polarized light beam (S-polarized light) emitted from the semiconductor laser 1 is converted into a parallel light beam by the collimator lens 2, passes through the first polarizing beam splitter 3, and is transmitted by the objective lens 4 to the transparent magneto-optical disk. After passing through a substrate (not shown), an image is formed as an optical spot 5 on an information track 6 formed on a magneto-optical recording film such as TbFeCo. Usually, after the collimator, a beam shaping prism for converting the elliptical light amount distribution of the laser 1 into a circle is generally provided, but this is omitted here.

The reflected light that has been subjected to the magnetic Kerr effect (rotation of the polarization direction) by the magneto-optical recording film also has a polarization component (P polarization) orthogonal to the E direction, and this polarization component is the first polarization component.
The polarization component (S-polarized light) in the E direction is partially reflected by the first polarization beam splitter 3 and travels toward the second polarization beam splitter 8. Note that a beam splitter is inserted between the first and second polarization beam splitters, and the reflected light flux is guided to various autofocus focus error detection optical systems and autotracking tracking error detection optical systems. The description is omitted.

The light incident on the second polarization beam splitter selects the same polarization direction as the case where the angle of the analyzer is set to ± 45 ° with respect to the E direction, and is divided into reflected light and transmitted light. As a result, the relative phases of the magneto-optical signals included in the reflected light and the transmitted light are shifted by 180 °, and signals having opposite phases are obtained. By differentially detecting this, it is possible to obtain a double magneto-optical signal in which the light source noise of the laser 1 having the same phase and the medium noise such as the fluctuation of the Fresnel reflectance of the medium are removed.

Next, the principle of edge detection using the diffraction phenomenon of the present invention will be described. FIG. 2 schematically shows a change in polarization due to a magnetic domain. In FIG. 1, the polarization state of the reflected light when the polarized light in the E direction (S-polarized light) is projected is shown in FIG. 2A, and the rotation angle θ of the polarized light depends on whether the recorded magnetic domain is upward or downward. The sign of _k is reversed. Strictly speaking, the polarization of the reflected light is clockwise and counterclockwise elliptically polarized light. However, for simplicity, first, a description will be given of a model of rotation of linearly polarized light in the long axis direction, and later, elliptically polarized light will be described. explain. In FIG. 2, (b) and (c) correspond to -θ
_The linearly polarized light rotated by _K and θ _K is decomposed into S and P components,
This is developed on the time axis (in the case of a strict elliptically polarized light model, the phase shift may be given to the P component, and the following description holds). As is apparent from this figure, the fact that the polarization rotation is inverted by ± θ _K depending on the direction of the magnetic domain corresponds to the fact that the phase of the P component is shifted by π in the system of FIG. Therefore, considering only the P component, the upward and downward arrangement of the magnetic domains is considered to be an arrangement of phase objects having a phase difference of 0 and π. It can be seen that the domain wall, that is, the edge portion, functions as a 0 / π phase edge, has a very large phase change, and is a step-like steep change.

FIG. 3 is a schematic diagram for explaining such a phase type edge and a diffracted wavefront from a phase type grating. In FIG. 3, the upward magnetic domain 21 recorded on the magneto-optical film 20 is shown.
As described above, the arrangement of the downward magnetic domains 22 can be considered as an arrangement of minute phase difference objects of 0 / π as indicated by the reference numeral 23 when considering the P component. When the diffracted wave from this edge is observed in the pupil plane of the objective lens 4 or the far field region 24, the component in the E direction in FIG. 1, that is, the S component, is particularly an object whose amplitude and phase are spatially modulated. Since it does not exist, the light amount distribution
Normal Gaussian such as 5. On the other hand, the P-polarized light component is diffracted from the phase edge of 0 / π, and becomes a light quantity distribution of two peaks split at the center. It is to be noted that this is due to diffraction, which is the interaction between a minute object and light, and is of course different in principle from the case where the diffraction phenomenon as shown in the conventional example is as small as possible. For example, in the case of FIG. 3, the light quantity distribution is divided into two peaks, but these are not independent light fluxes.
This is a diffraction pattern created in the far field by interference of wavefronts from each point in the diffraction-limited spot 5. In other words, the luminous flux of the reflected polarized light from the upward magnetic domain 21 and the luminous flux of the reflected polarized light from the downward magnetic domain 22 are not arranged side by side, but the wavefront from each point of each magnetic domain exists everywhere on the far field. Then, it is one wavefront formed by interference. In other words, it is a pattern generated as a result of the mixing of the wavefronts from the upward and downward magnetic domains, which is spatially separated by geometrically considering the polarization from each magnetic domain as shown in the conventional example. It is impossible to specify.

FIG. 4 shows the result of Fourier transform of the diffraction wavefront of P-polarized light on the pupil plane of the lens 4 when the diffraction-limited spot 5 is scanned in the X direction in FIG. Here, (a) to (g) show the difference in the X coordinate of the spot position normalized by the spot diameter. In the figure, the solid line represents the amplitude distribution of the diffracted wavefront, and the broken line represents the phase distribution. FIG. 4A shows a case where the spot 5 is projected only on the downward magnetic domain 22, the amplitude is Gaussian, and the phase is shifted by πrad indicated by reference numeral 23. When the edge enters the spot, (b) ~
As shown in (f), the amplitude distribution has a dent at the center, and in (d) where the optical axis and the edge coincide, the peak is separated into two peaks.
The phase distribution is expressed by (b), (c)
Modulation around πrad like
In (d), it jumps to the modulation centered on 0 rad. Below, as the edge goes out of the light spot,
The modulation becomes small, and the phase becomes 0 rad and the amplitude distribution returns to Gaussian on the diffracted wavefront from the upward magnetic domain 21 having the phase of 0 rad as shown in (g). As can be seen from this result, in the edge detection using the diffraction phenomenon of the present invention, the position (b) where the edge is shifted from the optical axis,
Also in (c), (e) and (f), a diffraction pattern is generated by superposition of wavefronts from each point of each magnetic domain,
In particular, it can be understood that the phase distribution corresponds to the spatial polarization state distribution, and that edge detection using the phase asymmetry can be performed. Here, it is impossible to describe the wavefronts of (b), (c), (e), and (f) geometrically and geometrically in the state of opposite polarization from a specific magnetic domain. The detection principle is different. Further, in the conventional example in which the magneto-optical domain acts as uneven pits, it is shown that asymmetry occurs in the amplitude distribution of the far field, which is different from the phase domain as in the present invention.

By the second polarization beam splitter, the P-polarized light whose wavefront has been modulated and the S-polarized light which has not been modulated by the magnetic domain are diffracted by the second polarization beam splitter. When the light is projected onto the polarization plane and multiplexed, the distribution of the S-polarized wavefront is similar to, for example, the amplitude distribution and the phase distribution shown in FIG. Actually, as shown in FIG. 2A, the polarization state immediately after reflection from the recording medium becomes elliptically polarized light due to the Kerr effect, and the phase difference of P-polarized light with respect to S-polarized light is not 0 but slightly shifted. However, the phase distribution of the S-polarized light is, for example,
There is no problem if the phase of the S-polarized light is considered to be slightly shifted as in the case of FIG. Then, the S-polarized light and each of the P-polarized lights shown in FIG. 4 are inclined at a polarization plane of ± 45 °, and synthesized at each point according to the respective spatial distributions, and the transmitted light of the second beam splitter is And it becomes reflected light. 4 (a),
In the case of a wavefront that is symmetric with respect to the optical axis as in (g), the synthesized wavefront is also symmetric, but an edge exists (b) to (b).
In the case of (f), the amplitude distribution is symmetric with respect to the optical axis, but the phase distribution is asymmetric, so that the distribution of the combined wavefront is asymmetric.

In the case of FIG. 4 (g), FIG. 2 (c)
If the slight phase difference of the S-polarized light is neglected, if the light is combined at an analyzer angle of + 45 °, the wavefronts are uniform and almost in-phase in the light beam, and therefore, they are mutually strengthened. In addition, when combined at an analyzer angle of -45 °, P
The slope of the wave amplitude is minus and the phase is exactly πrad
The phases are out of phase with each other and are mutually weakened in the light beam. Therefore, the total light amount (light intensity) on the + 45 ° side is S, P
The interference term of both polarizations is cos 0 = 1, where it is almost maximum, and the total light amount on the −45 ° side is cos π = −1
Which is almost the minimum. In FIG. 4A, that is, in FIG. 2B, it is reversed. In FIG. 4D,
On the left and right sides of the optical axis, the phase difference between the S and P polarized light is elliptically polarized.
That is, if the phase shift of the S-polarized wave is ignored, it is almost ± π
Cos ± π / 2 = 0 when considered in terms of light intensity, the gray levels are almost the same, and the total amount of light in the light flux also becomes the central value between the maximum and minimum values. That is, in the detection of the magneto-optical domain by the diffraction-limited spot as in the present invention,
As described above, in addition to the change in the polarization state due to the Kerr effect of the magnetic domain, the polarization state and the wavefront change due to diffraction.
Then, when the total light amount of the transmitted light and the reflected light of the second polarization beam splitter 8 is detected, the total light amount is modulated in the direction of the magnetic domain ((a) and (g) of FIG.
The minimum value appears, the edge ((d) in FIG. 4) has an intermediate value, and differential detection is possible between transmitted light and reflected light.

When a change in the intensity distribution of the transmitted light / reflected light of the second polarizing beam splitter 8 is detected in a far field by a two-division sensor or the like, a region without an edge (FIG. 4A, FIG. In (g)), the difference signal becomes 0, and if there is an edge due to the phase difference of the elliptically polarized light, asymmetry appears in the light intensity distribution of the wave field of the interfered and combined far field, and the edge is on the optical axis ( As shown in FIG. 4D, since the difference signal takes the maximum value or the minimum value, edge detection becomes possible.

In the present invention, as shown in FIG.
The transmitted light / reflected light of the second polarizing beam splitter 8 is further connected to a light spot by sensor lenses 9 and 10.
Also in this case, a diffraction phenomenon occurs in the present invention, and it is not a mere light-collecting action as in the conventional example. Therefore, far-field detection and re-imaging detection are not the same.

In the following, the Fourier transform image of the distribution of orthogonal linearly polarized light after the projection of the P-polarized light and the Gaussian S-polarized light onto the ± 45 ° polarization plane in FIG.
Consider a model that is formed at the spot positions according to and. The wavefront obtained by combining P-polarized light having a uniform phase distribution and similar S-polarized light as shown in FIGS. 4A and 4G also has a uniform phase distribution and Gaussian amplitude distribution. Therefore, the Fourier transform image has a uniform phase distribution and Gaussian amplitude distribution, and its intensity distribution is Gaussian. As shown in FIGS. 4B to 4F, when the edge has an asymmetric phase distribution due to the edge, the distribution of the combined linearly polarized light is also asymmetric. For example, in the case of FIG. 4D, first, for simplicity, ovalization due to the Kerr effect is ignored, and only the polarization plane is rotated in FIGS. 2B and 2C.
Considering this model, the intensity of the combined light is at the gray level as described above. Regarding the wavefront incident on the second polarization beam splitter 8, reference may be made to FIGS. 5 (a) and 5 (b). These are the same as those representing the phase distribution shown in FIG. 4, and schematically show the phase distribution of the diffracted wavefront by the 0 / π edge and the π / 0 edge, respectively. FIGS. 5C and 5D disclose the polarization states of P-polarized light having such a phase distribution and S-polarized light having a uniform phase distribution (assumed to be 0 rad). The region 31 in which the phase of the P-polarized light in FIG. 5A is −π / 2 is represented by a waveform 36 in FIG. It becomes clockwise elliptically polarized light that matches the direction. Similarly, the P-polarized light in the region 32 has a waveform 38 shown in FIG. 5D and is combined with the S-polarized light 35 to have the same elliptical shape as in FIG. It becomes the surrounding elliptically polarized light 39. Similarly, in the case of the other edge, the polarization of the region 33 in FIG. 5B is represented by FIG. 5D, and the polarization of the region 34 is represented by FIG. 5C. Although the influence of the amplitude is not described in FIG. 5, as shown in FIG. 4D, the amplitude of the P-polarized light is 0 on the optical axis. As the distance from the distance to the periphery increases, the S-polarized light amplitude of the Gaussian distribution becomes smaller, and as shown in FIG. 4D, the P-polarized light amplitude becomes larger due to diffraction, so that FIG. 5C and FIG. The ellipticity of the elliptically polarized light changes. At the end of the pupil in the ξ direction, if the amplitude of the S-polarized light is sufficiently smaller than the amplitude of the P-polarized light, the polarization state is almost close to the P-polarized light.

In the above description, the ovalization by the Kerr effect is omitted for simplicity (FIG. 2B,
(C) model). In edge detection using diffraction, the polarization ellipse and the phase difference between the S and P polarizations in the Kerr effect have a significant meaning and cannot be ignored as in the conventional example. (E) and (f) of FIG.
This is shown in consideration of the effect that the phase of the P-polarized light is slightly shifted with respect to the S-polarized light due to the Kerr effect and becomes elliptically polarized light, and represents the oscillation of the polarized light corresponding to FIGS. 5C and 5D. Things. Here, as described above, a model in which the phase difference is given to the S-polarized light 40 equivalently is shown, but the elliptically polarized light 41 having different Kerr rotation angles and Kerr ellipticities with respect to the elliptically polarized lights 37 and 39 is shown. , 42 are obtained. 4 (b), (c),
In the intermediate state as shown in (e) and (f), the phase distribution and the amplitude distribution are more complicated, and thus the spatial distribution of the wavefront obtained by combining the P-polarized light and the S-polarized light is more complicated. Become. Therefore, it is impossible to consider the polarization state of the far field only by the Kerr effect of each magnetic domain (also only the rotation of linearly polarized light) as shown in the conventional example, and the Kerr rotation angle and the Kerr ellipticity are not considered. The polarization state is uniformly distributed.

That is, in the magnetic domain edge detection by the diffraction-limited spot according to the present invention, the polarization state is spatially non-uniform in the far-field region due to the Kerr effect and the diffraction effect. Unlike the principle, it has a distribution that cannot be described only by the Kerr effect of magnetic domains. Next, the wavefront after transmission and reflection of the second polarization prism 8 in such a polarization state will be considered. The linearly polarized light obtained by the projection onto the analyzer (± 45 °) has cos (±
45 °) and sin (± 45 °) to form a superimposed wave. For example, in the case of the polarized light 37 in FIG. 5C, the projected component a · sin ωt from the S-polarized light and the projected component b · sin ｛ω from the P-polarized light having a phase of −π / 2 rad.
t- (π / 2)｝ = − b · cos ωt
(A ² + b ² ) ⁻² · sin {ωt-tan (b / a)} Here, a and b are the amplitudes of the S and P polarizations projected on the analyzer, respectively, and ω is the angular frequency of the light. In the case of FIG. 5D, the projected component a · si from the S-polarized light 35
n ωt and the contribution b ｛sin ωt + (π
/ 2) synthesized wave with ・ = b · cos ωt (a ² + b ² ) ^-2 ·
sin {ωt-tan (b / a)}. In other words, the amplitude and phase of the synthesized wave are determined by the magnitude of the synthesized wave, and it can be seen that the phase is inverted in the region where the polarization state is represented by (c) and (d) in FIG. .

In a more general case, such as (b), (c), (e) and (f) in FIG.
sin ωt and a composite wave (a ² + 2ab ·) of a projected component b · sin (ωt + θ) of P-polarized light having an arbitrary phase shift θ
cos θ + b ² ) ^-2 sin [ωt-tan ^-1 ｛b · sin θ /
(A + b · cos θ)｝]. In other words, the amplitude and phase of the combined linearly polarized light at each point changes according to the amplitude and phase at each point of the two combined linearly polarized lights, and the linearly polarized light has a more complicated spatial amplitude promulgation and phase distribution. Form a wavefront. Therefore, the wavefront is essentially different from the wavefront imagined geometrically and geometrically as in the conventional example.

As for the strict Kerr effect as considered in FIGS. 5E and 5F, the elliptical effect is added to the phase θ of the generalized P-polarized projection component, and the S-polarized light is projected. Obviously, if the above phase shift is restored, the above explanation will hold. When the orthogonal linearly polarized wavefronts thus obtained are imaged again into spots by the lenses 9 and 10, the pattern is further changed by diffraction. For example, FIG. 5 corresponding to FIG.
Considering (a), (c), and (d), as in the above calculation, (a ² + b ² ) ⁻² sin
{Ωt-tan (b / a)} and (a ² + b ² ) ^-2 sin {ω
The far field wavefront has a wavefront distribution represented by t-tan ^-1 (b / a)｝. That is, the phase is ±
At tan ^-1 (b / a), since the Kerr effect is minute, b
Although the absolute value of the phase difference is small in ≪a, FIG.
As can be seen from the distribution of the amplitude a substantially represented and the distribution of the amplitude b substantially represented in FIG. 4D, the absolute value of the phase increases as the distance from the optical axis increases, and The sign is inverted around. The amplitude distribution is symmetric since it is the average of the sum of squares. The re-imaging plane pattern of the wavefront can be obtained by, for example, Fourier transform. Again, for simplicity, considering the scalar, the amplitude of the S and P polarization components on the far field is
Each of the analyzers undergoes spatially uniform attenuation in the analyzer and the Fourier transform images superimposed by the sensor lens are superimposed to form a model that becomes a diffraction pattern of each re-imaged spot.

FIG. 6 is a schematic diagram showing the state of the contribution from the P-polarized light to the re-imaging pattern, obtained from the P-polarized far-field pattern shown in FIG. In FIG. 6, the solid line represents the amplitude distribution, and the dashed line represents the phase distribution. It is clear from the figure that the pupil diameter (NA) of the pickup lens is finite when reproducing magneto-optical domains of the same size using the diffraction phenomenon in a diffraction-limited spot as in the present invention. Therefore, even if re-imaging,
The point and the amplitude and the phase of the magneto-optical domain on the disk are not reproduced. Further, as shown in FIGS. 6A and 6G, the Gaussian is not completely Gaussian, but has a diffraction pattern. Further, this is significantly different from the re-imaging detection described in JP-A-3-120645. That is, in the far field (FIG. 4) and the re-imaging plane (FIG. 6), the amplitude distribution and the phase distribution are completely different from those in the conventional example, so that the edge detection on the far field and the edge detection on the re-imaging plane are performed. It cannot be the same.

The re-imaging of the wavefront of the S-polarized light after passing through the analyzer is basically Gaussian, similar to FIG. 6 (g), and is superimposed on each distribution of FIG. , A re-imaging pattern is obtained.

As shown in FIG. 6D, when the edge is at the center of the spot, the amplitude distribution of the re-imaging of the wavefront after the P-polarized light is obliquely projected on the analyzer is symmetric with respect to the optical axis. Yes,
The phase becomes asymmetric and takes a value of 0, πrad. Speaking of a simple linear polarization rotation model ignoring the elliptical Kerr effect, the phase distribution of the contribution from S-polarized light is uniform at 0 rad, so the intensity distribution after multiplexing is enhanced with a phase difference of 0 rad. , Cos 0 = + 1, and the phase difference is weakened by πrad, and cos π = −1. The effect of the elliptically polarized light shifts the slight phase difference, changes the maximum value and the minimum value of the intensity distribution, and slightly degrades the degree of modulation.

FIG. 7 is a schematic diagram showing the configuration of the prism-integrated split sensors 11 and 12 of the embodiment of FIG. The prism-integrated split sensor 50 is a Si-P on Al frame.
An IN photodiode 52 is molded and packaged with an optically transparent polycarbonate resin. Note that the gaps between the two divided light receiving regions 53 are separated to such a level that optical, electrical and thermal crosstalk between the regions can be ignored. The shape of the mold 51 is prism-shaped, and by just combining two triangular prisms, the incident light flux 54 is split into two wavefronts,
The divided light flux is guided to each light receiving area 53. With such a configuration, the spatial difference detection of the re-imaging spot as described above can be performed. Regarding the crosstalk between the light receiving areas, the gap is several tens μm.
In the case of about m, electrical crosstalk due to diffusion of generated carriers is dominant, and there is also a reduction effect due to reverse bias or the like.
And the dark current increases.

As in the present invention, when a light beam is spatially divided by the optical wavefront dividing means and a signal obtained by photoelectric conversion in the light receiving region 52 with less crosstalk is obtained, the signal is converted from this signal by the differential amplifier. It is possible to obtain a differential signal with less crosstalk. In the present invention, the aberrations of the re-imaging lenses 9 and 10 are sufficiently corrected, and the re-imaging diffraction pattern is as small as several μm to several tens μm. As described above, in the conventional detection by the split sensor, since the practical gap of the sensor is 5 to 15 μm, most of the light amount enters, and it is impossible to obtain a good differential signal with small crosstalk. However, this is only possible with the present invention. There is another method of extending the focal length of the re-imaging lenses 9 and 10 and enlarging the re-imaging diffraction pattern.
In order to obtain a re-imaging diffraction pattern of about 100 μm with respect to 5 mm, it is necessary to set the focal length of the re-imaging lenses 9 and 10 to several hundred mm, which is not practical because the apparatus becomes large.

In the optical space division according to the present invention, it is desirable to place the wavefront division part of the prism 51 of the sensor 50 at the re-imaging position, that is, at the focal position of the re-imaging lenses 9 and 10. By doing so, the prism 51
In addition, it is possible to minimize the influence of new diffraction due to the dividing line, and to arrange the light receiving region 52 having a size that can sufficiently cover the spread of the pattern due to the diffraction at a relative position where the crosstalk is reduced. . That is, after the spatial division, it is sufficient to detect the entire light amount of each of the divided regions, and it is not necessary to detect the light amount distribution based on a diffraction pattern or the like therein. This is also a feature of the present invention. Therefore, in the vicinity of before and after the re-imaging position, the position of the dividing line of the prism 51 is set to the optical axis within a range where there is no pattern change that causes a large change in the difference detection signal waveform, such as inversion of the asymmetry of the re-imaging diffraction pattern. Can move in any direction. Further, in the present invention, since the prism 51 for dividing the light beam into a wavefront and the light receiving region 52 are integrated, the alignment adjustment becomes easy. Using a luminous flux having a symmetric light amount distribution, two sensor outputs are adjusted in the Y-axis direction within the focal plane of the entire sensor 50 so that the sum signal thereof is maximized, and two sensor outputs are adjusted in the X-axis direction. Are temporarily adjusted so that the difference becomes equal and the difference signal is minimized. Then, while reproducing the actual magneto-optical signal, fine adjustment including adjustment in the optical axis direction and the rotation direction about the division line may be performed.

FIGS. 7 to 13 show other embodiments according to the present invention. In the embodiment of FIG. 8, a prism portion for splitting the wavefront is provided on only one side. With such a configuration, the adjustment can be simplified. In the case of the embodiment of FIG. 7, the relative movement amount of the two divided light beams is large with respect to the movement of the sensor main body 50 in the x direction and the rotation around the division line, but in the case of FIG. Is small, the crosstalk of the movement of the two light receiving areas during the adjustment is small, and the adjustment is easy.

FIG. 9 shows a sensor 5 divided into four in the edge direction.
The present invention is also applicable to a case where a corrected edge signal is obtained by performing arithmetic processing on signals from each light-receiving region that has been multi-divided, instead of a mere difference based on spatial division into two. This indicates that the present invention is applicable (a wavefront splitting prism is formed by combining four triangular prisms so as to guide a light beam to each light receiving area).

In the embodiment shown in FIG. 10, the light beams split by the prism are crossed and guided to the light receiving region. When this is formed by a resin mold, since a mold is used, it is possible to select both the concave and convex prism shapes as shown in the figure according to the molding accuracy of the mold and the ease of release. In particular, in the present invention, since the dividing line, and those having high accuracy near the dividing line are required, glass sealing,
A method of processing and polishing the prism shape using other dielectrics, or a method of additionally processing and polishing the mold can be considered. Therefore, the degree of freedom in selecting the unevenness is important.

In the embodiment shown in FIG. 11, for example,
The present invention is applied to edge detection using a four-divided sensor in a letter shape, which is referred to as "four-leaf clover detection" described in Japanese Patent No. 47789. In this embodiment, the prisms are formed for wavefront splitting so that the normal vectors of each of the four surfaces of the prism face different directions. The light is guided to each light receiving area 55.

In the embodiment shown in FIG. 12, in the optical system of the same optical head as that shown in FIG. 1, in particular, the second polarization beam splitter 8 and the split sensors 11 and 12 are integrated. In this case, only one re-imaging lens is required, and the light flux is made to enter the sensor unit 56. Also, as shown in the embodiment of FIG.
The configuration in which the polarization beam splitter 8 is rotated about the optical axis can be realized in this embodiment, but for the sake of simplicity, the polarization beam splitter 8 is led to the detection optical system by the first polarization beam splitter. A configuration is employed in which a λ / 2 plate is inserted into the light beam, the polarization is rotated by 45 °, and then guided to the sensor unit 56 by the re-imaging lens. Such a configuration will be described below. In FIG. 12A, a prism 57 also serves as a second polarization beam splitter and a wavefront splitting prism, and a polarization splitting surface 58 transmits polarized light in the plane of the paper and reflects polarized light in a direction perpendicular to the plane of the paper. I do. Here, the re-imaging diffraction pattern is incident on the polarization splitting surface 58 from the left of the drawing. The optical axis is aligned with the center of the sensor unit 56, that is, on the division line of the polarization division plane 58. The polarized light component in the direction perpendicular to the plane of the paper is spatially split into two by the polarization splitting surface 58, and the respective light beams are guided to the light receiving regions 59a and 59b. on the other hand,
The polarized light component in the direction parallel to the paper surface is transmitted through the polarization splitting surface 58 and guided to the light receiving regions 59c and 59d of the wavefront splitting prism 57 that are spatially split by another splitting surface. Then, by differentially amplifying the outputs of the light receiving regions 59a and 59c, a differential signal from which the in-phase component has been removed is obtained.
Similarly, a differential signal is obtained from the outputs of the light receiving regions 59b and 59d. Further, by taking a differential with these differential signals, a spatial differential signal can be obtained.

FIG. 12B shows a further simplified embodiment of the sensor unit 56 in which a divided light receiving area is realized by a divided photodiode on one Si substrate. Here, the light flux reflected and split by the polarization splitting surface 58 is guided to the light receiving areas 59a and 59d, and the transmitted light flux is wavefront split by the effect of the prism 57, and the light receiving area 5d.
9b and 59c. In the present embodiment, the angle of incidence on the polarization splitting surface 58 is different from that of a normal polarization beam splitter, and there is a problem in the refractive index difference from the resin mold, film formation thereon, and the like. May be inferior in the polarization separation characteristic, or the sensitivity may decrease due to an increase in the incident angle of the light beam on the light receiving regions 59a and 59d.

In the embodiment shown in FIG. 12, compared with the embodiment shown in FIG. 1, one re-imaging lens can be used, and the re-imaging lens 9 and the sensor 11 shown in FIG. There is an effect that the optical branch on the side becomes unnecessary, the configuration becomes in-plane, and the size as the optical head is significantly reduced.

The embodiment shown in FIG. 13 is also similar to the embodiment of FIG. 12 in that the optical system of the optical head shown in FIG.
, The polarization beam splitter 8 and the split sensors 11 and 12 are integrated, and only one re-imaging lens is required.
A configuration that does not require a / 2 plate is also possible. However, here, for simplicity of description, a case where a λ / 2 plate is inserted and the polarization plane is rotated by 45 ° is described. In this embodiment,
Instead of the second polarizing beam splitter 8, a double image element (Wollaston prism, Rochon prism, etc.) is used. In FIG. 13A, the sensor unit 60
Means Wollaston prism 61, wavefront splitting prism 6
2. It has an integral structure consisting of a mold section 63 and a divided light receiving area 64. The re-imaging luminous flux incident on the Wollaston prism is divided into two luminous fluxes along a normal ray and an extraordinary ray. When the re-imaging luminous flux exits the Wollaston prism, it is directed in the x direction, that is, in the direction parallel to the track. Separate into two orthogonally polarized light beams. Further, each light beam is spatially split into two by a wavefront splitting prism 62,
A total of four light beams are led to four light receiving regions 64 divided in the x direction.

Here, signals from the upper and lower two light receiving areas are obtained. However, if a differential is obtained within one set, a spatial difference signal is obtained. A differential edge signal from which components have been removed is obtained. Of course, first, the in-phase component is removed by the differential between the signals of the odd-numbered light receiving regions and the signals of the even-numbered light receiving regions in the x direction, and then, a differential signal is obtained by the differential between them. You may. In this embodiment, as compared with the embodiment of FIG. 12A, the light receiving area can be arranged on the same plane, so that it can be constituted by one divided Si-PIN photodiode, and the size is small. However, it should be noted that Wollaston prisms are more expensive than polarizing beam splitters.

FIG. 13B similarly includes a Wollaston prism 61, a wavefront splitting prism 65, a mold 66, and a photodiode having four light receiving regions 67. However, Wollaston prism
With respect to the direction x parallel to the track, the configuration is such that the axis is rotated by 90 degrees with respect to the case of FIG. 13A, so that the four luminous fluxes are separated into a cross-shaped area. . The light beam incident on the Wollaston prism is split into two polarized light beams orthogonal to the direction perpendicular to the x direction at the exit surface of the Wollaston prism. This polarized light flux
The wavefront dividing prism 65 spatially divides the light into two in the x direction.
Be guided. From the signals from the four light receiving regions 67, a differential detection signal for removing the in-phase component is obtained by differentially amplifying the upper and lower sides, and a differential detection signal is obtained by differentially amplifying the left and right sides. . This may be calculated first. This embodiment is advantageous in forming an integrated structure because the wavefront dividing line by the prism 65 may be one in comparison with the embodiment of FIG. Yes, not only in the x direction, but also in the orthogonal direction,
Accuracy and adjustment become severe.

In the above description of the embodiment, for convenience, it is assumed that there is only one edge in the light spot 5 on the recording medium. In the conventional examples other than the conventional example by humans, since edge detection is merely mere, in order to clarify the difference therefrom, detection of one edge in the light spot targeted by them is compared in detail. As described above, however, the present invention detects the interaction between the recorded domain and the spot by using the diffraction phenomenon, unlike the conventional examples in which the size of the light spot is the resolution limit. Therefore, the present invention can be applied to a case where a plurality of edges exist in a light spot.

In the above description, λ = 0.8
The description assumes 3 μm and NA = about 0.5, but of course,
Although the illustrated diffraction pattern changes due to the change in these parameters, spot size, and domain size, the present invention can cope with the change. In addition, here, for the sake of convenience, the description is made using the Fourier transform to explain the difference in the detection principle from the conventional example.However, it is a region that cannot be applied under Kirchhoff's boundary condition, and a stricter analysis than originally required There is a difference from the result obtained by numerical calculation such as the boundary element method using the Helmholtz wave equation, however, to explain the information reproducing apparatus of the present invention, there is no particular inconvenience .

FIG. 14 shows an embodiment in which the present invention is applied to a reproducing optical system of an optical head of a magneto-optical information reproducing apparatus.
In FIG. 14, reference numeral 101 denotes an optical rotatory prism as a circularly polarized light separating element. This optically rotating prism 101
Since the right-handed circularly polarized light and the left-handed circularly polarized light have different refractive indices, when the reflected light flux from the magneto-optical recording medium passes,
The right-handed circularly polarized light and the left-handed circularly polarized light are emitted at different refraction angles. Reference numeral 102 denotes a wavefront splitting element that splits a light beam in a direction parallel to the track (the direction of arrow T). Further, reference numeral 103 denotes a condenser lens, and reference numeral 104 denotes a quadrant photodetector. That is, of the two light beams split in the direction parallel to the track, for example, the left-handed circularly polarized light component of the right-handed light beam is incident on the light receiving surface 104-1 of the detector, and the right-handed circularly polarized light component is also the same. -2. Also,
The left-handed circularly polarized light component of the light beam on the left enters the light receiving surface 104-3, and the right-handed circularly polarized light component enters the light receiving surface 104-4.

The detection signals obtained from the respective light receiving surfaces are converted into signals (104-1), (104-2), (104-
3), (104-4), the differential amplifiers 105, 1
06, the ｛signal (104-2) −the signal (1
04-1)｝, ｛signal (104-4) -signal (104-)
3) Obtain the value of｝. Then, the signal {104 (14-1) + signal (104-4)} −
{Signal (104-2) + Signal (104-3)}], and an edge detection signal 108 is obtained.

Next, the detection principle will be described in more detail with reference to FIG. In FIG. 15, (a) shows the reproduction position of the light spot by the objective lens. Here, [I] indicates the state in which the downward magnetization is being reproduced, and [I]
[I] shows the state of reproducing the upward magnetization, [III]
Indicates the state of downward magnetization on the left side at the edge of the pit, and further, [IV] indicates the state of upward magnetization on the left side at the edge of the pit. In the figure, T
Indicates the scanning direction of the light spot in the direction parallel to the track.

(B) is a reflected light beam in each of the states [I] to [IV], showing the distribution of the light beam immediately after the light beam exits the magneto-optical recording medium. (C) similarly shows the distribution on the far field plane. Here, the incident light is linearly polarized light (P-polarized light) polarized in the P-axis direction as shown in FIG. (B-1) and (c-1) are P-polarized light amplitude distributions, (b-2) and (c-2) are S-polarized light distributions (ignoring their magnitudes), and (b-3) and (c-3). ) Indicates the phase distribution of S-polarized light with reference to P-polarized light, (b-4) and (c-4).
Indicates the polarization state on the left side of the light beam, and (b-5) and (c-5) indicate the polarization state on the right side of the light beam.

[I] In the case of downward magnetization, the amplitude distribution of the P-polarized light and the S-polarized light at the point (b) exiting the magneto-optical recording medium is as follows:
It has the same symmetrical shape. The polarization distribution is the same for the left and right, but is assumed to be clockwise rotated linearly polarized light (R +) as shown in FIG. At this time, the phase difference between the P-polarized light and the S-polarized light is set to 0. Even in the far field plane (c), the P-polarized light and the S-polarized light are bilaterally symmetric,
The phase of the polarized light remains unchanged at 0, and the left and right polarization states remain unchanged.

In the case of [II] upward magnetization, the amplitude distributions of P-polarized light and S-polarized light at the point (b) exiting the magneto-optical recording medium are bilaterally symmetric as in [I]. However, the phase of the S-polarized light is different from [I] by π, and the polarization state of both the left and right sides is the linearly polarized light (R−) rotated counterclockwise, opposite to [I]. Also on the far-field surface (c), the amplitude distributions of the P-polarized light and the S-polarized light are bilaterally symmetric, the phase of the S-polarized light is π, and the left and right polarization states are linearly polarized light rotated counterclockwise.

In the case of [III], when the left side of the pit edge is magnetized downward, the P at the point (b) where the magneto-optical recording medium exits is shown.
The amplitude distribution of polarized light is bilaterally symmetric as in [I] and [II], but the amplitude distribution of S-polarized light is divided into two, and its phase distribution is 0 on the left and π on the right. The polarization state at this time is linearly polarized light (R +) rotated clockwise on the left side and linearly polarized light rotated leftward on the right side. In the far field plane (c), the amplitude distribution of the P-polarized light is symmetrical, the amplitude distribution of the S-polarized light remains divided into two, and the phase distribution of the S-polarized light changes. / 2 and + π / 2 on the right. That is, the polarization state is, for example, clockwise elliptical polarization on the left side and counterclockwise elliptical polarization on the right side. The ellipticity and magnitude of each elliptically polarized light are the same, and their major axes are in the P polarization direction.

In the case of [IV], when the left side of the pit edge is magnetized upward, the left and right sides are in a state opposite to that in the case of [III].

In FIG. 14, the rotatory prism 1 is arranged on the far field surface shown in FIG. When the polarization state is linear polarization ([I],
In the case of [II]), the linearly polarized light is obtained by combining the right-handed circularly polarized light and the left-handed circularly polarized light having the same magnitude with the signal (10).
4-1), the signal (104-2), and the signal (104)
-3) and the output signal of the signal (104-4) have the same magnitude, and the edge detection signal 108 becomes 0. On the other hand, when the polarization state is elliptically polarized light (in the case of [III], [IV]), each elliptically polarized light is shown in FIGS.
As shown by 1, the right-handed circularly polarized light and the left-handed circularly polarized light having different sizes are combined. In the case of [III],
{Signal (104-2) -signal (104-1)} <0,
{Signal (104-4)-(Signal 104-3)}> 0, and as the edge detection signal 108, [{Signal (104
-1) + signal (104-4)｝-｛signal (104-2)
+ Signal (104-3)}]> 0.
On the other hand, in the case of [IV], the signal {104-2) −
Signal (104-1)}, {signal (104-4) −signal (104-3)} <0, and as the edge detection signal 108, [{signal (104-1) + signal (104−
4)｝ − ｛signal (104-2) + signal (104−)
3) A negative signal of｝] <0 is obtained.

FIG. 16 shows an edge detection signal when a magneto-optical pit recorded by the magnetic field modulation method is detected by the reproducing system of FIG. Here, (a) shows a state in which a magneto-optical pit row is recorded on a magneto-optical medium by a pit edge recording method. Here, the shaded portion is assumed to be upward magnetization. An arrow T indicates a moving direction of the light spot in a direction parallel to the track. Then, the edge detection signal shown in (b) is obtained by the reproduction optical system of FIG.

FIG. 17 shows another reproducing optical system of the optical head used in the magneto-optical information recording / reproducing apparatus of the present invention. FIG.
In the same manner as described above, reference numeral 201 denotes an optical rotatory prism,
203 is a condenser lens. Reference numeral 209 denotes a half-wave plate that affects approximately half of the light beam in a direction parallel to the track (the direction of arrow T). Here, 1/2
The fast axis or slow axis of the wave plate 209 is placed in the direction of the incident linearly polarized light. After passing through the half-wave plate 209, the state of the light beam is converted from FIG. 15C to FIG. 18D. Here, １ ／ wavelength plate 209
, The phase of the S-polarized light with respect to the P-polarized light of the right-hand light beam is advanced by π. As a result, [I],
[II] The left and right polarization states at the time of downward and upward magnetization are converted from linearly polarized light in the same direction to linearly polarized light in different directions.
The light amounts of right-handed and left-handed circularly polarized light separated by 01 are the same. On the other hand, [III], [IV]
Are converted from elliptically polarized light having different rotation directions to elliptically polarized light having the same rotation direction. In the case of [III], right and left elliptically polarized light becomes right and left, and after passing through the optical rotatory prism 201, the amount of clockwise circularly polarized light increases. Conversely, in the case of [IV], left and right are left-handed elliptically polarized light, and after passing through the optical rotatory prism 201, the amount of left-handed circularly polarized light increases. Symbol 210
Is a two-segmented detector. Assume that left-handed circularly polarized light separated by the optical rotation positive prism 201 is detected by the light receiving surface 210-1, and right-handed circularly polarized light is detected by the light receiving surface 210-2. 210-1) and the signal (210-2), the pit edge detection signal 212 obtained by the differential amplifier 211 is the ｛signal (210-2) −the signal (210).
-1)}, and becomes 0 in the states of [I] and [II], a positive signal in the state of [III], and a positive signal in the state of [IV].
A negative signal is obtained, which is equivalent to the edge detection signal in FIG.

[0066]

As described above, the present invention uses a diffraction-limited spot and transfers a part of the diffracted light from the minute recording domain to a conjugate position with the spot by using an objective lens, a polarizing element, and a re-imaging lens. To obtain a good spatial difference detection signal by converting it into a new diffraction pattern, photoelectrically converting it by an integrated photodetector having a wavefront splitting element, a multiple image element, and a plurality of light receiving areas. Therefore, edge detection with less jitter can be performed, and information can be reproduced when there are a plurality of edges in a spot.
Therefore, there is an effect that a large capacity memory can be realized by increasing the density of the storage medium, and a compact and highly reliable information reproducing apparatus can be realized.

Further, a wavefront splitting element and a circularly polarized light separating element are arranged in the reflected light beam from the magneto-optical medium, and a change in the amount of light of the four separated light beams passing therethrough is detected. A half-wave plate and a circularly-polarized light separating element which affect the half light flux are disposed therein, and by detecting a change in the amount of light of the two separated light fluxes passing through them, the optical magnetic pits are formed. Edge parts can be detected,
The effect is obtained that a reproduced signal with little change in the linear component is obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical head showing an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a change in polarization due to the Kerr effect.

FIG. 3 is an explanatory diagram of a reproduction principle of the present invention.

FIG. 4 is a schematic diagram showing a change in a far field pattern in the present invention.

FIG. 5 is a schematic diagram for explaining a polarization distribution in the present invention.

FIG. 6 is a schematic diagram showing a change in a re-imaging diffraction pattern in the present invention.

FIG. 7 is a schematic view of a sensor unit showing another embodiment according to the present invention.

FIG. 8 is a schematic view of a sensor unit showing another embodiment according to the present invention.

FIG. 9 is a schematic view of a sensor unit showing another embodiment according to the present invention.

FIG. 10 is a schematic view of a sensor unit showing another embodiment according to the present invention.

FIG. 11 is a schematic view of a sensor unit showing another embodiment according to the present invention.

FIG. 12 is a schematic view of a sensor unit showing another embodiment according to the present invention.

FIG. 13 is a schematic view of a sensor unit showing another embodiment according to the present invention.

FIG. 14 shows a reproducing optical system of an optical head used in the magneto-optical information recording / reproducing apparatus of the present invention.

FIG. 15 is a view for explaining the principle of reproduction of the reproduction optical system shown in FIG. 14;

FIG. 16 is a waveform diagram of an edge detection signal.

FIG. 17 shows another reproducing optical system.

18 is a diagram illustrating the principle of reproduction of the reproduction optical system of FIG.

FIG. 19 is a diagram illustrating the principle of reproduction.

FIG. 20 is a diagram illustrating the relationship between elliptically polarized light and circularly polarized light.

FIG. 21 is a diagram illustrating the relationship between elliptically polarized light and circularly polarized light.

FIG. 22 is a configuration diagram of an optical system of a conventional example.

[Explanation of symbols]

Reference Signs 4 Objective lens 5 Light spot 9, 10 Reimaging lens 11, 12, 50, 54, 56, 60 Sensor unit 101 Optical rotation positive prism 102 Wavefront splitting element 103 Condensing lens 104 Photodetector 109 1/2 wavelength plate 110 Photo detector

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Matsumura 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 11/105

Claims (8)

(57) [Claims] 1. A laser beam is focused on an information recording surface via an objective lens to form an image as a light spot, and reflected light from the information recording surface is transmitted through the objective lens and a re-imaging lens. In an optical information reproducing apparatus that guides a light detector disposed at a position optically conjugate with a light spot and reproduces information recorded on the information recording surface, the light spot is narrowed to a diffraction limit, A part of the diffracted light from the information recording domain equal to or smaller than the spot size, the objective lens,
By the polarizing element and the re-imaging lens, the light is converted into a diffraction pattern, and further, by the wavefront splitting means, the diffraction pattern is spatially separated into a plurality, and each of the separated light intensities is divided into a plurality of respective light in the photodetector. An optical information reproducing apparatus, wherein the information is guided to a light receiving area for detection. 2. An optical information reproducing apparatus according to claim 1, wherein said wavefront dividing means is constituted by a combination of a plurality of prisms having different deflection angles, and is integrated with said light receiving area. apparatus. 3. A method according to claim 1, wherein a difference signal is obtained from signals of the plurality of light receiving regions having a spatial difference relationship among the plurality of light receiving regions by an electrical operation process, and an edge of the information recording domain is detected. The optical information reproducing apparatus according to claim 1, wherein the optical information reproducing apparatus is configured. 4. A light from a laser is focused on an information recording surface via an objective lens to form an image as a light spot, and reflected light from the information recording surface is passed through the objective lens and a re-imaging lens. In an optical information reproducing apparatus that guides a light detector disposed at a position optically conjugate with a light spot and reproduces information recorded on the information recording surface, the light spot is narrowed to a diffraction limit, A part of the diffracted light from the information recording domain equal to or smaller than the spot size, the objective lens,
The light is converted into a diffraction pattern by the polarizing element and the re-imaging lens, and further, the diffraction pattern is spatially separated into a plurality by the double image element and the wavefront splitting element. An optical information reproducing apparatus, wherein the optical information reproducing apparatus guides the light to each of the plurality of light receiving areas for detection. 5. The double image element is a Wollaston prism or a Rochon prism, and the wavefront dividing means is constituted by a combination of a plurality of prisms having different deflection angles,
5. The optical information reproducing apparatus according to claim 4, wherein the optical information reproducing apparatus has an integrated structure with the light receiving area. 6. A method according to claim 1, wherein a difference signal is obtained from signals of a plurality of light receiving regions having a spatial difference relationship among the plurality of light receiving regions by an electrical operation process to detect an edge of the information recording domain. 5. The optical information reproducing apparatus according to claim 4, wherein: 7. A method for recording and / or reproducing information on an information recording medium having a plurality of tracks and recording information pits based on a difference in magnetization direction by utilizing an interaction between light, heat and magnetism. , Linearly polarized light is incident on the information recording medium,
In the optical information reproducing apparatus configured to optically detect the boundary of the information pit from the reflected light flux, a wavefront splitting element and a circularly polarized light separating element are arranged in the path of the reflected light, and the wavefront splitting element is used. Separating the reflected light into two light beams parallel to the track, and separating the reflected light into clockwise and counterclockwise circularly polarized light beams by the circularly polarized light separating element;
An optical information reproducing apparatus characterized in that a boundary portion between information pits is detected from these four light flux changes and information is reproduced. 8. When information is recorded and / or reproduced on an information recording medium having a plurality of tracks and recording information pits based on a difference in magnetization direction by utilizing an interaction between light, heat and magnetism. , Linearly polarized light is incident on the information recording medium,
In an optical information reproducing apparatus which optically detects a boundary portion of an information pit from the reflected light beam, a half-wave plate and a circularly-polarized light separation which generally affect a half light beam are provided in the path of the reflected light. An optical device characterized by arranging elements and detecting a boundary of an information pit based on a change in the amount of light of two right-handed and left-handed circularly polarized light beams passing therethrough to reproduce information. Information reproducing device.