JPH0694435A - Optical detection device - Google Patents

Abstract

PURPOSE:To enhance the degree of modulation of a detected signal in edge detection, and to improve the reliability of detection by bringing the diffraction wave surface from a phase body together with a reference wave surface so as to cause interference, and by detecting the obtained interference intensity distribution by means of a photodetector. CONSTITUTION:The beams emitted from a laser beam source 1 are converged on the recording surface of a photomagnetic disc 9 via a first polarized-beam splitter 5, and are imaged as a diffraction critical spot. A part of the reflected light from the disc 9 reaches again the beam splitter 5 where 30% of the P- polarized component and 100% of S-polarized component are reflected, and then is introduced into a detection optical system. After the phase difference distribution has been corrected by a phase compensation plate 13, the light passed through a beam splitter 10 maximizes the amplitude of an edge detection signal. Then, the asymmetry in the intensity distribution of the transmitted light/reflected light by means of a second beam splitter 15 is detected by two splitting sensors 16, 17, and when the difference has been detected by differential detectors 18a, 18b, the critical maximum amplitude of the signal can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection device for optically detecting an attribute of a phase object, and more particularly to an optical detection device optimal for edge reproduction of a magneto-optical disk.

[0002]

2. Description of the Related Art A recording medium used in an optical information recording / reproducing system is effectively used as an external storage means of a computer because of its large data recording capacity with respect to its size. Among them, the recording medium of the magneto-optical recording / reproducing system is extremely useful because the data can be rewritten. In order to record 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 said to be advantageous in that the data capacity can be increased compared to the former, but in order to accurately reproduce information from the recording medium recorded by this method, the information bit in the optical head part Accuracy in reading the edge position of is required.

To record information on a magnetic recording medium, a light beam from a semiconductor laser as a light source is condensed on a recording medium by an objective lens to form a minute spot, and reflected light from this light spot is used to make a mark. It can be performed by a long recording method. In reproducing information from a magneto-optical recording medium, a light beam from a semiconductor laser is focused on a recording medium by an objective lens to form a minute spot, and a change in the polarization state of reflected light from here is converted into a light amount change. This is done by converting and differentially detecting.

This information reproduction is performed, for example, in Japanese Patent Laid-Open No. 3-26.
As shown in No. 8252, the behavior of the reflected light from the edge of the information bit is 0 / π edge of phase type or 0 / π of phase type when a minute spot narrowed to the diffraction limit is used.
Diffraction from the π lattice becomes dominant. Therefore, the behavior of the reflected light is significantly different from the geometrical or geometrical optical behavior, and the detection principle is different from the conventional detection device using them, and a more accurate new edge detection device can be realized.

As described above, as an example of obtaining a higher quality signal when edge detection is performed by positively utilizing the diffracted and reflected light from the edge of the information bit, Japanese Patent Application No.
No. 278702, Japanese Patent Application No. 2-27910, Japanese Patent Application No. 2-
As shown in Japanese Patent Application No. 307910 and Japanese Patent Application No. 2-310524, a device using a spatially non-uniform optical filter or a split sensor has been proposed. In the new detection principle that positively utilizes these diffraction phenomena, the phase distribution of the diffracted wavefront has a particularly important meaning, which is clearly different from the conventional example that can be detected by ignoring it. .

For example, the device disclosed in Japanese Utility Model Laid-Open No. 56-90744 detects the light amount distribution of the reflected light from the concave and convex pits. Here, the light amount distribution of the reflected light from the stepped edge is The phenomenon of asymmetry is used. That is,
The light intensity distribution and the light intensity distribution are directly detected, and the phase distribution is an example of a detection method that can be completely ignored, and the polarization characteristic is also an example that can be ignored. Is distinctly different from the detection method that utilizes the wavefront diffracted from the edge of the information bit according to.

The method disclosed in Japanese Patent Application Laid-Open No. 3-104041 is a special case in which the diffraction phenomenon due to the edge can be ignored and the elliptic effect (Kerr ellipticity) due to the Kerr effect can be ignored. That is, the polarization states due to the Kerr effect in the domains on both sides of the edge (the state in which only the phase difference occurs in the left and right circularly polarized light and the linearly polarized light only rotates) spatially directly divide the far field geometrically into two. In a special case where the rotation of the polarized light can be converted into a phase difference with a λ / 4 plate, the polarization beam splitter is not based on the magneto-optical domain on the optical disk, but with the phase difference converted by the λ / 4 plate. An edge detection method in a special case in which a difference in intensity is generated in the jitter direction in the far field is shown by the configuration in which is the analyzer. This is a method that is different in principle from the new detection method that uses the diffraction wavefront from the edge of the information bit due to the diffraction limited spot.

Further, as a detection principle similar to this conventional example, there is one disclosed in Japanese Patent Laid-Open No. 188047/1987. The Kerr effect here is that normally incident linearly polarized light is
It is converted into left and right elliptically polarized light according to the direction of the domain, and the inclination of the major axis is ± θ with respect to the incident linearly polarized light.
_k tilt. However, this conventional example is applied to a special case in which the reflected light from the non-recording portion remains the incident linearly polarized light, and only the reflected light from the recording portion tilts as the linearly polarized light. Furthermore, the detection method is also a special method. By placing a λ / 4 plate in a parallel light beam and setting its orientation appropriately, the inclination of the linearly polarized light reflected from the recording unit is λ / 4.
This is a special configuration in which the plate is converted into a phase change (= π / 2) and linearly polarized light having no inclination from the non-recording portion is passed through the analyzer to cause interference. Not only interference using a special λ / 4 plate that can give a phase difference only to linearly polarized light with a slight inclination from the recording section, but also with commonly known general light interference, the interference term is It is related to the phase difference between two interfering lights, and the phase difference is π
When / 2, cosπ / 2 = 0, and the interference term disappears. However, the edge detection here is performed by a special configuration in which the light intensity difference appears in the jitter direction on the parallel light flux. . Apparently, the new detection using the wavefront diffracted from the edge of the information bit by the diffraction limited spot is
This is a different method in principle.

Further, in the detection principle disclosed in Japanese Patent Laid-Open Nos. 62-188047 and 3-104031, the rotation of polarized light generated on the disk surface is later converted into a phase change. From the viewpoint of phase conversion, it can be regarded as the same detection principle as the uneven pit of Japanese Utility Model Laid-Open No. 56-90744. That is, the actual exploitation 56-9
As described in Japanese Patent No. 0744, even in the edge portion, the intensity of the reflected light from the edge is different between the upper surface and the lower surface of the step, which leads to the light detection surface geometrically or geometrically and optically. Get burned. This phenomenon is used here.

On the other hand, as disclosed in Japanese Patent Laid-Open No. 3-268252, in the new detection principle utilizing the diffraction wavefront from the edge of the information bit by the diffraction limited spot, from each point of the edge in the spot. It is impossible to geometrically and optically correspond the reflected light of each point to each far field point, but the light from all the points in the spot overlaps at all the points on the far field, and a new wavefront is created. Is fundamentally different from the above-mentioned conventional example in that the diffraction phenomenon of forming a wave can be utilized and the amplitude distribution and phase distribution of the diffracted wavefront can be detected efficiently.

The edge detection method disclosed in Japanese Patent Laid-Open No. 2-46544 is applicable to a recording mark having a width wider than the diameter of the light spot. Here, the recording on the recording surface is performed. The two-dimensional shape of the mark is different between the front edge and the rear edge of the recording mark,
The difference in the correlation value with the light spot is captured as the asymmetry of the light intensity distribution at the focusing position using the focusing lens.
In order to deal with high density and high resolution of information, it is desirable to be able to detect the edge of a recording mark having a diameter of the light spot or less, but this conventional example is difficult to apply. Further, in this conventional example, the recording mark by the magnetic field modulation recording cannot be used because the two-dimensional shapes of the front and rear edges are almost the same. Further, in this conventional example, since only the light amount of the orthogonal polarization component (Kerr component) of the incident linearly polarized light is detected, very weak light is detected, and a good SNR cannot be obtained. As described above, this conventional example also differs from the new edge detection principle of detecting edges efficiently by paying attention to the amplitude distribution and phase distribution of the diffracted wavefront.

In the edge detection method disclosed in Japanese Patent Laid-Open No. 3-120645, when a Kerr ellipticity is 0 and a light spot is detected by a two-division photodetector in the far field, a light projection system, In the case where the λ / 4 plate is placed in a tilted state in the common optical path of the light receiving system to make elliptically polarized light, in the common optical path of the light projecting system and the light receiving system when detecting at the re-imaging position. A case where a Brewster plate is inserted to detect with a two-part photodetector that matches the edge shape, and
By combining a variable compensation phase plate with unknown phase compensation amount and a matched filter in the light receiving system,
Cases in which an undivided photodetector that detects reflected light and a λ / 2 plate for adjusting the light amounts of the two photodetectors are arranged are shown. In this conventional example, it is considered that the spatial phase distribution plays an important role, but elliptically polarized light by an oblique λ / 4 plate is incident on a disk having a Kerr ellipticity of 0, and the reflected wave is further ellipticized. There is no description that the phase distribution in such a case is particularly taken into consideration. In addition, the variable compensation phase plate with unknown compensation amount, matched filter, adjustable λ / 2 plate, total phase distribution by polarization beam splitter, and polarization distribution operation are also unknown. The principle of detection is that the detection operation on the re-imaging plane is the same. This is because, based on the new edge detection principle that efficiently detects edges by paying attention to the amplitude distribution and phase distribution of the diffracted wavefront, the diffracted wavefronts of the far field surface and the re-imaging surface are completely different. It is considered that the structure is different because the principle is different.

Here, not only the Kerr ellipticity but also
A phase compensating plate for compensating a phase difference between a comprehensive Fresnel component and a Kerr component caused by phase shift due to multiple attributes or reflection in an optical element such as a disk, a mirror or a beam splitter is already known.

[0014]

The edge detection does not utilize the amplitude distribution and phase distribution of the diffracted wavefront. In the above-mentioned conventional example, the phase distribution is not taken into consideration. Of course, JP-A-3-2682
In the new edge detection method typified by Japanese Patent Laid-Open No. 52-52, the phase distribution due to diffraction has only been relatively taken into consideration so far, so that there is a problem that the modulation degree of the light intensity distribution caused by the combined interference is very low. there were. Here, since the degree of modulation is low, the SNR deteriorates, the error rate deteriorates, and the reliability of data reproduction becomes low.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an optical detection device which improves the degree of modulation of a detection signal in edge detection and improves the reliability of detection. Is.

[0016]

Therefore, in the present invention,
In an optical detection device for irradiating a phase object with laser light, guiding reflected light / transmitted light from the phase object to a photodetector, and detecting an attribute of the phase object, refer to a diffraction wavefront from the phase object. It is configured so that the interference intensity distribution is combined with the wavefront, and the obtained interference intensity distribution is detected by the photodetector, and phase modulation due to the polarization characteristics of the phase object, and the spatial modulation by the wavefront diffracted from the phase object. A phase compensating plate is provided for making the relative phase difference between the total phase by superposition of the phase modulation and the phase of the reference wavefront in a spatial partial region approximately an integral multiple of π.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an optical head of a magneto-optical disk recording / reproducing apparatus according to the present invention. In the figure,
1 is a semiconductor laser, 3 is a collimator lens, 4 is a beam shaping prism, 5 is a first polarization beam splitter,
8 is a pickup lens, 9 is a magneto-optical disk that moves relative to the pickup lens 8 in the A direction, 10
Is a beam splitter, 11 is a servo sensor lens having a cylindrical surface, 12 is a 4-division servo sensor, 13 is a phase compensation plate, 14 is a λ / 2 plate, 15 is a second polarization beam splitter, and 16 and 17 are 2-division RF. Sensor, 18a,
18b and 19 are differential amplifiers. The first polarization beam splitter 5 transmits 70% of the polarization component in the E direction (P polarization) and reflects 30% thereof, and reflects 10% of the polarization component in the orthogonal direction (S polarization). The second polarization beam splitter 15 transmits 100% of P-polarized light and 1% of S-polarized light.
00% reflection. The dividing lines of the two-divided RF sensors 16 and 17 extend in the direction perpendicular to the plane of the drawing, and divide the track on the magneto-optical disk 9 into two in the orthogonal direction.

The light from the laser 1 is converted by the collimator lens 3 and the beam shaping prism 4 into a substantially circular parallel light beam, and passes through the first polarization beam splitter 5 and the pickup lens 8 to generate a magneto-optical signal. Disk 9
It is focused on the recording surface of and is imaged as a diffraction limited spot. And a part of the reflected light from the magneto-optical disk 9 is
Again, it reaches the first polarization beam splitter 5 via the pickup lens 8 and thereby the P polarization component 30
%, 100% of the S-polarized component is reflected and guided to the detection optical system. Here, a part of the light split by the beam splitter 10 is guided to the 4-split sensor 12 by the servo sensor lens 11. In this optical information recording / reproducing apparatus, the astigmatism method is used for auto focus, and the push bull method is used for auto tracking. The light transmitted through the beam splitter 10 is subjected to an optimum phase shift by the phase compensating plate 13.

FIG. 2 schematically illustrates a change in polarization due to magnetic domains. That is, FIG. 2A shows the polarization state of the reflected light when P-polarized light is incident on the magneto-optical disk in FIG. 1, and here, the upward and downward directions of the recorded magnetic domain are shown. The polarization rotation angle θk
The sign of (Kerr rotation angle) is reversed. The reflected light becomes elliptically polarized light, and the left and right directions are also reversed. 2 (b) and (c)
Represents the state of polarization divided into P and S components when the Kerr ellipticity of the Kerr effect is set to 0, that is, when only the rotation of linearly polarized light is considered. Corresponding to. Further, (d) and (e) of FIG. 2 show the case where the Kerr ellipticity is taken into consideration. As is clear from the figure, the fact that the rotation of polarized light is reversed by ± θk depending on the direction of the magnetic domain means
This corresponds to the phase shift of the S component by π. Therefore, considering only the S component, the upward and downward arrangements of the magnetic domains are considered to be arrangements of phase objects having phase differences of 0 and π. It can be seen that the domain wall, that is, the edge portion functions as a 0 / π phase edge, and the phase change is extremely large and is a step-like steep change.

FIG. 3 is a view for schematically explaining a wavefront diffracted from such a phase-type edge and phase-type grating. In FIG. 3, the arrangement of the upward magnetic domains 21 and the downward magnetic domains 22 recorded in the magneto-optical film 20 is an arrangement of minute 0 / π phase difference objects such as reference numeral 23 when considering the S component as described above. Can be considered. Observing the diffracted wave from this edge on the pupil plane of the pickup lens 8 or the far field region 24, E in FIG.
With respect to the direction, that is, the P-polarized component, there is no object in which the amplitude and the phase are spatially modulated, so that the light amount distribution becomes a normal Gaussian such as reference numeral 25.
On the other hand, the S-polarized component is diffracted from the phase edge of 0 / π and has a light amount distribution of two crests broken at the center. This is due to diffraction, which is an interaction between a minute object and light, and is theoretically different from the case where the diffraction phenomenon as shown in the conventional example is so small that it can be ignored. For example, in the case of FIG. 3, the light amount distribution is divided into two peaks, but these are not independent light fluxes but a diffraction pattern formed by the wavefront from each point in the diffraction limited spot 5 in the interference far field. That is, the reflected polarized light flux from the upward magnetic domain 21 and the reflected polarized light flux from the downward magnetic domain 22 are not arranged geometrically, but the wavefront from each point ξ of each magnetic domain exists everywhere on the far field. However, it is a wavefront formed by interfering with each other. This is, so to speak, a pattern generated as a result of the wavefronts from the upward and downward magnetic domains being mixed, and as shown in the conventional example, the polarization from each magnetic domain is geometrically considered and spatially separated. , Impossible to identify.

FIG. 4 shows the lens 4 for S-polarized light when the diffraction-limited spot 5 in FIG. 3 is scanned in the X direction.
It is the one obtained by calculation of the diffracted wavefront on the pupil plane. In the figure, (a) to (g) show the difference in spot positions normalized by the spot diameter at the x coordinate. In the figure,
The solid line represents the amplitude distribution of the diffracted wavefront, and the broken line represents the phase distribution. However, the phase is represented by a relative value for simplicity.
In FIG. 4A, when the spot 5 is projected only on the downward magnetic domain 22, the amplitude distribution is Gaussian and the phase distribution is shifted by π rad indicated by the reference numeral 23.
When the edge enters the spot, (b) of FIG.
As shown in (f), the amplitude distribution has a dent in the center, and in particular, in (d) where the optical axis and the edge coincide with each other, they are separated into two peaks. The phase distribution undergoes a modulation around πrad as in (b) and (c) due to the entry of edges as described above, and jumps to a modulation around 0rad in (d). Below, as the edge goes out of the light spot, the modulation becomes smaller and the phase 0
The diffracted wave front from the upward magnetic domain 21 of rad has a phase of 0 rad and the amplitude distribution returns to Gaussian as shown in (g).

As can be seen from these results, in the reproduction utilizing the diffraction phenomenon of the present invention, even at the positions (b), (c), (e) and (f) where the edges are deviated from the optical axis, the respective The superposition of the wavefronts from each point of the magnetic domain produces a diffraction pattern, and in particular, its phase distribution corresponds to the spatial distribution of polarization states, so that reproduction using the asymmetry of the phase is possible. However, in this case, geometrically or geometrically optically, these (b), (c), (e),
It is impossible to describe the wavefront of (f) by the polarization state reflected from a specific magnetic domain, and it is clear that the detection principle is different from the conventional example. Further, in the conventional example in which the magneto-optical domain acts as an uneven pit, it is shown that the amplitude distribution of the far field is asymmetrical, but this is different from the phase domain as in this example.

Next, consider the light intensity distribution when the S-polarized light whose wavefront is modulated by the diffraction by the magneto-optical domain and the P-polarized light that is not modulated by the domain are combined and interfered with each other. Try. Specifically, in the embodiment of FIG. 1, the λ / 2 plate 14 is used.
Is rotated about the optical axis by 22.5 °, and the second polarization beam splitter 15 separates two polarizations orthogonal to each other.
An example is a case in which the light is projected on a 45 ° analyzer to cause multiple wave interference. Here, in order to clarify the principle difference between the conventional example and the present invention, first, a case where there is no phase compensating plate 13 and the Kerr ellipticity is 0 is considered. Next, similarly, there is no phase compensating plate 13, Considering the case where the Kerr ellipticity is not 0, and finally, the effect of improving the modulation degree by the phase compensating plate 13 will be described.

FIG. 5 shows the spatial distribution of P-polarized light and S-polarized light when the Kerr ellipticity is 0 without the phase compensating plate 13. In the figure, (a) represents the amplitude distribution and the phase distribution on the pupil plane of the P-polarized light. The amplitude distribution is Gaussian and the phase distribution is 0 rad, which are constant. Figure 5
4B corresponds to FIG. 4D, and the amplitude distribution (solid line) and the phase distribution (solid line) and the phase distribution (in solid line) on the pupil plane of the S-polarized light when the magneto-optical domain edge is on the optical axis of the light spot. (Dashed line)
Represents Here, since the ellipticity due to the Kerr effect is ignored, the phase of S-polarized light is spatially divided into two regions of ± π / 2 rad centered on 0 rad. 5 (c) to (i) show the respective coordinates ξ = ξ ₁ , ξ ₂ , ξ of the pupil plane.
_It represents the combined polarization state of P-polarized light and S-polarized light at ₃ , 0, ξ ₄ , ξ ₅ , and ξ ₆ . Generally, P polarized light and S polarized light are E _P ,
_Let E _S be the amplitude, A _P and A _S , the angular frequency of light be ω,
If the wavelength is λ and the initial phase of each polarization is φ _P1 and φ _S , then E _P = A _P cos (τ + φ _P ) E _S = A _S cos (τ + φ _S ) (where τ = ωt-2π / λZ) Become. δ = φ _P ,
If φ _S , the combined polarized light is represented by elliptically polarized light of δ> 0 for right rotation and δ <0 for left rotation. Further, when δ = 0, it becomes a linearly polarized light, and when δ = ± π / 2 and A _P = A _S , it is represented by clockwise and counterclockwise circularly polarized light.

[0025] (c), FIG. 5, a state of polarization at the coordinate _{ξ = ξ 1, E P (} ξ 1) < In _{E S (ξ 1) δ (} ξ
_{Since 1} ) = + π / 2> 0, a flat right-handed elliptically polarized light whose major axis is in the S direction as shown in the figure is obtained. In symmetrical positions xi] = xi] ₆ in the space, as shown in (i) of FIG. 5, in _{E P (ξ 6) <E} S (ξ 6), δ (ξ 6) = - π
/ 2 <0, in _{E P (ξ 6) = E} P (ξ 1), E S
Since (ξ ₆ ) = E (ξ ₁ ), the elliptically polarized light has the same shape as that in (c) of FIG. The difference between left and right rotation cannot be detected by an analyzer (second polarization beam splitter) of ± 45 °, so ξ = ξ ₁ ,
The combined interference intensity I (ξ) at each point of ξ = ξ ₆ becomes equal.
That is, when the tilt angle of the analyzer from P-polarized light is α, I (ξ) = (A _P (ξ) cos α) ² + (A _S (ξ) sin α) ² + 2A _P (ξ) A _S (ξ) Since it is expressed as cos2 sin2 · cosδ (ξ), α = ± 45 °, and A _{P
(Ξ 1) = A P (} ξ 6), A S (ξ 1) = A S (ξ 6)
Therefore, the following formula is obtained.

[0026]

[Equation 1] As long as the phase difference between P-polarized light and S-polarized light is δ = ± π / 2, the interference term becomes 0, and if the amplitudes are equal, the intensities are also equal. In the conventional example, λ / such that | δ | = π / 2
There was one in which four plates were arranged, but this is basically the phase difference at which the interference effect disappears.

5D and 5H show polarization states at coordinates ξ = ξ ₂ and ξ = ξ ₅ , respectively, where E _P =
E _S , δ = −π / 2, right-handed and left-handed circularly polarized light, respectively, and I (ξ ₂ ) = I (ξ ₅ ).
In addition, (e) and (g) of FIG.
₃ represents the polarization state at _{ξ = ξ 4, E P <} E S,
Since δ = ± π / 2, elliptically polarized light whose major axis coincides with P-polarized light and which is different only in a vertically elongated flat rotation direction becomes I (ξ
₃ ) = I (ξ ₄ ). Further, in FIG. 5F, ξ = 0
In the polarization state of E, since E _S = 0, P-polarized light is obtained.

That is, the first thing to understand from the above is that, in the past, the Kerr component diffraction effect was not neglected or taken into consideration, and thus the polarization distribution becomes non-uniform on the pupil plane. Was not known. Even if such a phenomenon occurs without being noticed, in the conventional detection principle configuration, the light intensity distribution on the pupil plane that is subjected to the multiplexing interference does not become asymmetrical. It is clear that no detection signal is obtained.

Next, the case where the Kerr ellipticity is not 0 will be described. FIG. 6 shows the polarization state in the pupil plane in that case. This corresponds to FIG. The difference from Fig. 5 is that
The effect of ellipticization due to the Kerr effect on S-polarized light, that is, δ _k
This is a point that includes = φ _kp −φ _ks . S in FIG. 6B
The amplitude distribution of the polarized light is the same as that in (b) of FIG. 5, but the phase distribution is shifted by −δ ′ _k and is not rotationally symmetric with respect to the optical axis ξ = 0. Not a function. Each coordinate point in this case ξ = ξ ₁ , ξ ₂ , ξ ₃ , 0, ξ ₄ , ξ
The schematic diagram of the polarization state at ₅ , ξ ₆ is
6 (c), (d), (e), (f),
(G), (h), (i). Here, due to the existence of the Kerr ellipticity δ _k , δ = φ _p −φ _s + δ _k is ±
It will never be π / 2. Therefore, the major axis and minor axis of each elliptically polarized light do not coincide with the P direction and the S direction. Figure 6
In the region of δ = −π / 2−δ ′ _k as shown in (b) of FIG. 6 and ξ <0, as shown in (c), (d) and (e) of FIG. Is right-handed elliptically polarized light that is tilted counterclockwise with respect to the P direction, and δ = + π / 2−δ ′
_In the region of _R , ξ> 0, left-handed elliptically-polarized light having the major axis with the opposite inclination is obtained. Therefore, the combined interference intensity at each point is no longer equal, and the interference intensity distribution becomes asymmetric. Coordinate point ξ ＝
Comparing ξ ₂ and ξ ₅ , A _P (ξ ₅ ) = A _P (ξ
₂ ) and A _S (ξ ₅ ) = A _S (ξ ₂ ), the following formula is obtained, and the sign of the interference term is inverted at the optical axis ξ = 0.

[0030]

[Equation 2] That is, it can be understood from the fact that the diffraction effect of the Kerr component alone does not show asymmetry in the interference intensity distribution of the pupil plane due to the edge as shown in FIG. Occurs, and the edge detection signal is obtained for the first time. Therefore, in the above-mentioned conventional example which does not utilize the diffraction effect of the Kerr ellipticity and the Kerr component, the asymmetry does not occur in the interference intensity distribution on the pupil plane, and as in the present invention, the edge detection signal is I couldn't get it.

By the way, Japanese Patent Application Laid-Open No. 3-2 by the same applicant
The edge detection signal obtained in the series of new edge detection methods represented by Japanese Patent No. 68252 is the elliptic effect δ _R due to the Kerr effect, the P-polarized light generated by the substrate and the optical system in the middle, and S described in FIG. It was clarified that it was obtained by combining the phase shift caused by the phase difference δ _o of polarized light and the phase change caused by diffraction. That is to say, with reference to FIG. 6B, if ξ <0,
−π / 2−δ ′ _R + δ _o , and when ξ> 0, + π / 2
In the state of −δ ′ _R + δ _o , the difference in light intensity between the + | ξ | and − | ξ | points is due to the interference term A _P (ξ) A _S (ξ) si
It is represented by n (δ ′ _R −δ _o ). Here, the phase difference distribution δ is not limited to the shift of δ ′ _R shown in FIG.
Is further generalized into the following equation. δ = δ _d + δ _R + δ _o = φ _P −φ _S where δ _d is the phase difference caused by diffraction, δ _R is the phase difference caused by Kerr ellipticity, and δ _o is the position caused by other substrates or optical systems. It is a phase difference. By nature, δ _d and δ _R
Although it is not necessary to divide them, it is considered separately in this way in order to facilitate the explanation of the case of the uniform domain and the case of having the edge.

The Kram rotation angle θ _k and the Kerr ellipticity δ _k have the Kramers-Kronig relationship, which is not independent but of the same order. Generally, θ _k is 1 degree or less, and δ _k is also 1 degree or less. Further, in normal level detection, efforts have been made to reduce δ _o , and there are known examples in which the above-described phase shift of the compensating plate, the mirror or the reflecting surface of the beam splitter is used for that purpose. That is, it is δ _k in conventional optics.
It means that efforts are being made for + δ _o = 0. In the first place, it is an effort to eliminate edge detection signals shown in FIG. 5 in edge detection. Further, even if δ _k + δ _o ≠ 0, and there is a residual phase difference, it is very small and | A _P A _S cos δ | corresponding to the modulation degree of the amplitude (peak) of the edge detection signal.
= | A _P A _S sin (δ _k + δ _o ) |, it is clear that only a very small signal can be obtained.

The present invention improves the modulation of the edge detection signal, improves the quality of the reproduced signal, and improves the reliability of data reproduction. That is, in the embodiment of FIG. 1, the phase compensation plate 13 corrects the phase difference distribution δ to maximize the amplitude of the edge detection signal.

FIG. 7 is a schematic diagram of the phase compensation plate 13. The phase compensating plate 13 is made of quartz and has a laminated structure that utilizes the difference in thickness so as to cancel out the optical rotatory power and use only the birefringence. Here, the thickness of the phase compensating plate 13 is set so that the phase difference between the overall fast axis F and the slow axis S is (π / 2) − (δk + δo). Further, the fast axis F is aligned with the P polarization direction, and the orthogonal slow axis S is aligned with the S polarization direction. Therefore, when the domain edge is on the optical axis of the light spot, the phase distribution of S-polarized light on the pupil plane is-(π
/ 2) + (δk + δo) and (π / 2) + (δk + δo)
Although it has already been clarified that the phase distribution of the S-polarized light is delayed by (π / 2) − (δk + δo) with respect to the P-polarized light by the phase compensating plate 13 described above,
After passing through the phase compensation plate 13, it becomes 0 and π for P-polarized light.

FIG. 8 shows the polarization state after being subjected to the phase correction by the phase compensating plate 13, and corresponds to FIGS. 5 and 6. Here, as shown in FIG.
When the phase of P-polarized light is used as a reference (Orad), the phase compensation plate 13 operates so that the phase distribution of S-polarized light becomes 0 and πrad. That is, in FIG. 5 and FIG.
When <0, the phase that was −π / 2, −π / 2−δk ′ is delayed to 0, and when ξ> 0, the phase that is + π / 2, + π / 2−δk ′ is delayed to π. . By this operation, the polarization states at each point ξ = ξ ₁ , ξ ₂ , ξ ₃ , O, ξ ₄ , ξ ₅ , ξ ₆ are (c), (d), and FIG.
(E), (f), (g), (h), and (i). In this case, since the phase difference δ between P-polarized light and S-polarized light is 0 or π,
It is not elliptically polarized but linearly polarized. However, it can be seen that the rotation angle and the amplitude of the polarized light are non-uniformly distributed. As in the case described above, with respect to the polarization distribution in FIG. 8, the λ / 2 plate 14 rotates the slow axis by 22.5 ° with respect to the P polarization direction, thereby uniformly rotating each polarization state by 45 °. To do. This gives ± 45 with respect to the P polarization axis.
The combined interference intensity distribution by the analyzer set to °
The second polarization beam splitter 15 having a differential detection configuration that removes in-phase noise obtains transmitted light and reflected light.

As can be seen from FIG. 8, the intensity distribution is
There is a great deal of asymmetry. Comparing this with ξ = ξ ₁ and ξ ₆ , Ap (ξ ₁ ) = Ap (ξ ₆ ), and As
From (ξ ₁ ) = As (ξ ₆ ), the following equation is obtained.

[0037]

[Equation 3] That is, the obtained asymmetry has the maximum asymmetry. Therefore, the maximum modulation degree can be obtained as the edge detection signal. Each other point pair (ξ ₂ ,
The same maximum asymmetry occurs in ξ ₅ ) and (ξ ₃ , ξ ₄ ). That is, the two-divided sensors 16 and 17 detect the asymmetry of the intensity distribution, and the differential detector 1
When the difference is detected by 8a and 18b, the amplitude of the signal is
It is proportional to 2 Ap As. In the conventional case shown in FIG. 6, the amplitude is 2 Ap As.sin (δk + δo), which is very small, but the present invention provides the limit maximum amplitude.

From a different point of view, a rectangle in the PS plane of each of (c) to (i) in FIGS. 5, 6, and 8 (side length on the side of P polarization is 2A _P , side on the side of S polarization is It can be said that the shape of the elliptically polarized light inscribed within the length 2A _s ) of the is controlled and set to the optimum value. That is, the present invention is not limited to the configuration of FIG. 1 and includes a concept applicable to polarization states caused by any optical phenomenon such as Kerr effect, diffraction, and birefringence. For example, even in the optical head of the magneto-optical disk shown in FIG. 1, the medium structure of the magneto-optical disk has a linear polarization distribution as shown in FIG. 8 on the pupil plane.
It is also possible to set a multilayer film structure. For example, δ _R including the phase shift due to multiple reflection beforehand,
Phase change due to diffraction and phase change due to optical system in the middle δ _o
It also includes the concept of an edge recording / reproducing optical disk that has a phase distribution of an integral multiple of π after receiving. Further, in consideration of the compatibility of optical disks, the invention is capable of separation such as an optical head in which the ellipticity of the optical disk is specified and the influence of diffraction and the phase change of the optical system are specified. In addition,
It goes without saying that the phase compensating plate 13 is not limited to the crystal plate. Further, in particular, even if the phase compensating plate 13 is not provided, if the target phase distribution can be obtained by combining the phase difference between the P polarized light and the S polarized light in the mirror or the beam splitter, the phase compensating plate 13 may be omitted. However, it goes without saying that the present invention can be implemented.

Next, another embodiment of the present invention will be described. FIG. 10 shows the structure of the optical head of the magneto-optical disk recording / reproducing apparatus according to the present invention. In the figure, the same components as those of the embodiment of FIG. 1 are designated by the same reference numerals. The embodiment of FIG. 10 has a configuration of re-imaging plane detection, while the embodiment of FIG. 1 is pupil plane detection. Here, reference numeral 30 is a phase compensation plate, reference numerals 31 and 32 are sensor lenses, reference numerals 33 and 34 are two-divided RF sensors (division lines extend in a direction perpendicular to the paper surface, and are directions orthogonal to the tracks on the magneto-optical disk 9), 35,3
Reference numerals 6 and 37 are differential amplifiers.

Similar to the above-mentioned embodiment, in order to clarify the principle difference between the conventional example and the present invention, first, the phase compensation plate 3
Consider the case where there is no 0 and the Kerr ellipticity is 0. FIG. 11 shows the S-polarized wavefront of the spot on the re-imaging plane of the sensor lenses 31 and 32 when the diffraction-limited spot scans the magneto-optical disk 9.
Here, (a) to (g) show the difference in spot position standardized by the spot diameter, the solid line in the figure shows the amplitude distribution, and the broken line shows the phase distribution. However, the phase distribution is a relative value when the uniform phase distribution of P-polarized light is set to the reference value 0. From this, it is first understood that the difference from the change of the diffracted wavefront on the pupil plane in FIG. 4 is substantially different, and is basically different from the above-described conventional example in which the pupil plane detection and the re-imaging plane detection perform the same operation. It When the edge is not in the spot, (a) and (g) are basically Gaussian type amplitude distribution, and the phase is π or depending on the direction of the domain at that time.
It will be 0. Further, here, since the pupils of the sensor lenses 31 and 32 are made smaller than the pupil of the pickup lens 8 to reduce the influence of axis misalignment due to tracking or the like, the diffraction pattern of the ring zone becomes minute, The phase difference between the zones is π. Now, when the edge enters the spot, the amplitude distribution becomes asymmetric as shown in (b) to (f), the valley having the amplitude of 0 moves, and the edge comes to the center of the spot. In FIG. 11 (d), the valley becomes the center, and as a result, the amplitude distribution becomes symmetrical. In addition, the phase distribution takes values of 0 and π when the edge enters the spot, and the values are exchanged for each ring zone. In FIG. 11D, 0 / π occurs at the center. There is. Therefore, the asymmetry of the intensity distribution can be generated by causing the optical interference with the P-polarized wavefront that is not affected by the diffraction (the same as the amplified amplitude of (g) in FIG. 11). At this time, since the values of S polarization with respect to P polarization are 0 and π, diffraction from the magneto-optical disk to the pupil plane of the pickup lens (corresponding to FIG. 4) is followed by re-imaging from the pupil plane of the sensor lens. Due to the two diffractions to the surface, the phase distribution on the re-imaging surface has the largest asymmetry, such as cos 0 = 1 and cos π = -1, and the maximum edge signal amplitude is obtained. Become. However, in reality, there is a Kerr ellipticity δk and a phase difference δo of P-polarized light and S-polarized light caused by reflection of a mirror or a beam splitter.
There is a decrease in the degree of modulation of cos (δk + δo) and cos (π + δk + δo).

In the present invention, this Kerr ellipticity and the phase distribution that integrates the phase change due to diffraction, the phase change due to the optical system, etc. are set to an integral multiple of π even with respect to the phase distribution of the reference wavefront. Since the modulation degree is improved by doing so, in this embodiment, the maximum amplitude is achieved by correcting the phase of δk + δo. Therefore, in FIG. 10, as the phase compensating plate 30, a compensating plate configuration in which the phase difference between the fast axis and the slow axis is δk + δo (or an integral multiple of π of addition) is used, and the fast axis is set to P By arranging so as to match the polarization direction, the phase distribution of the S-polarized wavefront on the re-imaging planes of the sensor lenses 31 and 32 is set to an integral multiple of π with respect to P-polarized light, as shown in FIG. be able to. As a result, the amplitude of the differential output by the differential amplifiers 35 and 36 can be maximized.

Next, another embodiment according to the present invention will be described. FIG. 11 shows the structure of the optical head of the optical disk recording / reproducing apparatus according to the present invention. In the figure,
The same parts as those in FIG. 1 are designated by the same reference numerals. In this embodiment, the present invention is applied to the case where the marks recorded on the optical disc are not the magneto-optical domain but the concave and convex pits, unlike the above-mentioned embodiments. Here, reference numeral 39 is a pickup lens, 40 is a first polarization beam splitter which transmits 50% of P-polarized light, reflects 50% and reflects 100% of S-polarized light, and 41 is mechanically integrated with the pickup lens 39. Λ / 4 plate half mirror, 42 is an optical disc on which concave and convex pits are recorded, and 43 is P-polarized light of 10
A third polarization beam splitter which transmits 0%, transmits 80% of S-polarized light and reflects 20%, 44 is a phase compensation plate, 45,
Reference numeral 46 is a two-divided RF sensor, and 47, 48 and 49 are differential amplifiers. Here, the pickup lens 39 irradiates the optical disc 42 with a diffraction-limited spot.
FIG. 2 is an enlarged schematic view of it. For the sake of explanation, the lens surface and each surface of the optical disk are omitted. The light emitted from the optical disc side surface 56 facing the pickup lens 39 is incident on the λ / 4 plate half mirror 41 and is 60%.
Is transmitted and 40% is reflected. In addition, the reflective multilayer film surface 5
The light that has passed through 0 passes through the λ / 4 substrate 51 and is converted into right-handed circularly polarized light.
It is tied up as a light spot 54. The light diffracted and reflected here becomes substantially left-handed circularly polarized light, passes through the λ / 4 substrate again, and is converted into substantially S-polarized light.
%, And returns to the pickup lens 39. On the other hand, the incident light reflected by the reflective multilayer film surface 50 forms a light spot 55 equivalent to the light spot 54 on the optical disc 42 at the apex on the optical axis of the pickup lens surface 56. Since the lens surface 56 on the optical disk side is a flat surface or a surface having a very large radius of curvature and the light spot is as small as about 1 μm, the light specularly reflected by the lens surface 56 returns to the λ / 4 plate half mirror again. , 40% is re-reflected and returns to the pickup lens. This light remains P-polarized and is used as a reference wavefront. It should be noted that the efficiency of light utilization can be improved by attaching the high reflection film 52 to the apex of the optical axis of the lens surface, which is several μmφ.

In FIG. 11, the S-polarized signal light and the P-polarized reference light are thus configured to have fixed substantially equal optical path lengths, whereby an actuator (which corresponds to the surface wobbling of the disk and the autofocus) ( Noise due to the movement of (not shown) can be removed. The P and S polarized lights that have been returned to the parallel light flux by the pickup lens 39 are reflected by the first polarization beam splitter 401 toward the detection system side. Also,
By the third polarization beam splitter 43, the S having the signal for auto-tracking and auto-focus of the disc
A part of the polarized light is reflected and guided to the servo optical system.
FIG. 13 shows the wavefront of S-polarized light that has passed through the third polarization beam splitter 43. Here, (a) to (g) show the edges of uneven pits when the diffraction-limited spot 54 is scanned, that is, the diffracted wavefronts from the step edges,
The difference due to the spot position normalized by the spot diameter is shown. The solid line in the figure represents the amplitude distribution of the diffracted wavefront, and the broken line represents the phase distribution. Unlike the phase edge as shown in FIG. 4, the diffracted wavefront in the case of the step edge becomes asymmetric in the amplitude distribution, and the phase distribution is also not an odd function. This is because the diffracted wave from the step portion differs depending on the left and right steps. The step shown here is vertical and the height is λ / 4, and ξ <0.
And the height is 0, and ξ> 0 and the height is λ / 4. It is natural that the diffracted wavefront changes depending on the height and the inclination of the step, but the asymmetric tendency changes. Since it is not available, this example will be described. The asymmetrical direction of the amplitude depends on the direction of the step, and even if the spot moves, the unbalanced direction of the amplitude distribution does not change. Further, the position of the dip with a small amplitude is shifted from the optical axis, and the shift amount hardly changes even if the spot moves. The center point of the curve of the phase distribution coincides with the dip position of the amplitude distribution, the spatial change is gentler than that of the phase edge, and even in the case of (d) in FIG. 5 in which the optical axis coincides with the edge center, + π / The change from 2 to + 3π / 2 is gradual.
Here, since the Kerr effect does not exist, a phase change δ _d due to diffraction occurs, and the reference wave and the phase 0 that cause the multiplexing interference are generated.
Similar to FIG. 4 and FIG. 5, the P-polarized light of rad causes only the non-uniformity of the light quantity due to the asymmetry of the amplitude distribution of the S-polarized light, the interference term is eliminated, and the amplitude of the edge detection signal is extremely small. It becomes very small. Further, as shown in FIG. 12, the optical path length difference between the P-polarized light and the S-polarized light is minute and fixed, but it is difficult to mechanically reduce the optical path length difference to 0 in the initial adjustment, and the thermal expansion There are differences in coefficients, temperature characteristics of the refractive index of the λ / 4 plate, residual autofocus offset, and changes over time. Further, since there is also a phase shift caused by each of the above-mentioned optical elements, if a value including the optical path length difference between the P-polarized light and the S-polarized light is set as δ _o again, the phase difference of δ = δ _d + δ _o is comprehensively expressed. Occurs. Therefore, this phase difference is corrected by the phase compensating plate 44 so that the portion where the phase difference between the P-polarized light and the S-polarized light becomes an integral multiple of π is increased, thereby increasing the amplitude of the edge detection signal. , The degree of modulation can be increased. In the case of FIG. 13, as can be seen from (d), the required amplitude is realized by giving a phase difference of 3π / 2−δ _o by the phase compensating plate 44. However, as is clear from (d), the phase distribution has a small number of constant parts and is curved slightly, and when the opposite edge comes, the wavefront and the phase distribution inverted around the ξ = 0 axis are obtained. Therefore, in that case, the amount of phase compensation given by the phase compensating plate 44 may be finely adjusted while monitoring the waveform of the edge detection signal so that the amplitude of the edge detection signal becomes maximum. Further, the phase compensation amount may be corrected so that an average stable signal amplitude is obtained in consideration of the above-mentioned error of each optical element, fluctuation, and temporal change. For that purpose, a method of slightly tilting the phase compensating plate 44 with respect to the optical axis, or rotating the fast axis slightly from the P-polarized direction as shown in FIG. 11 can be adopted.

In this way, the polarization of the pupil plane when the edge is on the optical axis is corrected, it is rotated by 45 ° by the λ / 2 plate, and the second polarization beam splitter and the two-division sensor 4 are used.
5, 46 is detected by the differential detection optical system, and the detected signals are differentiated by the differential amplifiers 47, 48. Further, the differential amplifier 49 takes the differential to remove common mode noise, thereby obtaining a good edge. A detection signal can be obtained.

FIG. 14 shows another embodiment according to the present invention.
In this embodiment, the present invention is applied to a position detecting device. Here, reference numeral 60 is a frequency-stabilized He-Ne laser, 61 is a beam expander, 62 is a non-polarizing beam splitter, 63 and 66 are pickup lenses, 65 is a phase compensation plate, 64 is an object, 67 is a mirror, and 68. Is λ /
Two plates, 69 is a polarization beam splitter, 70 and 71 are two-divided sensors, 72, 73 and 74 are differential amplifiers, and 75 is a phase compensation plate controller. A light beam from the laser 60 is expanded by a beam expander 61, split by a non-polarizing beam splitter 62, and further, is picked up by a pickup lens 63 on a target object 64 such as a silicon wafer or a reticle as a diffraction limited spot. It The spot is diffracted by the edges of the uneven structure of various shapes, and the diffracted wavefront is guided to the detection system via the pickup lens 63 and the non-polarization beam splitter 62. on the other hand,
The reference wavefront is returned by the pickup lens 66 and the mirror 67, and passes through the phase compensation plate 65 in a reciprocating manner. As a result, the phase shift δ _d due to the diffraction due to the step edge as shown in the embodiment of FIG. 11 (for example, see FIG. 13).
Then, the optical path length difference and the phase shift δ _o due to the optical element are corrected, and the phase correction is performed so that the partial phase difference between the diffracted wavefront from the object and the reference wavefront becomes an integral multiple of π. As a result, the edge detection signal has the maximum amplitude when the edge is on the optical axis of the spot. That is, the diffracted wavefront shown in FIG. 13 shows the S-polarized component of the circularly polarized light diffracted by the step edge of λ / 4, and the height of the step and the shape of the edge are not limited in the above embodiment. However, the uneven pits recorded as data on the optical disc as in the above embodiment have substantially the same step height and shape, and this is an example in which a phase compensating plate fixed accordingly can be used. . However, in the present embodiment of FIG. 14, the height and shape of the edge of the object 64 are not always constant. Therefore, in this embodiment, a position detecting device adapted to various heights and shapes of edges is provided by analyzing the detected edge detection signal and providing a phase compensating plate optimized for the edges. That is, by inputting the output of the differential detector 74 to the phase compensator controller 75,
The peak value of the amplitude of the edge detection signal is obtained. The peak value is compared with a preset value, and the error signal is fed back to the compensation amount of the phase compensator 65 to increase the peak value. At this time, in order to detect the direction of correction of the compensation amount, the phase compensation amount is wobbled at a frequency f _w, which is preferably 10 times or more the maximum frequency f _c of edge position detection, if possible, and is controlled in the f _w band. It is desirable to employ the wobbling method, which detects an error signal and controls the amount of phase compensation in the f _c band. In addition,
A method of tilting and rotating the compensating plate 65 is used for controlling the amount of compensation of the phase compensating plate 65, but the present invention is not limited to any means, and here, the electro-optical effect is used. Various means such as control of the refractive index used, variable thickness control, and control of the optical path length on the reference light side by piezo can be implemented.

As described above, even in the position detecting device, conventionally, since the phase shift δ _d due to diffraction has not been dealt with in the related art, a single height without an edge of the symmetrical object or a position between the phase regions is set. Considering only the phase difference, increasing the difference in interference intensity between the plurality of states, there was no choice but to detect the edge as an intermediate value of the difference, according to the present invention, the phase shift of the diffracted wave by the edge, The quality of the edge detection signal is dramatically improved by optimizing the intensity of the combined wave interference of the diffracted wave front by the edge by utilizing the phenomenon that the phase of those single regions is modulated positively and negatively. Therefore, high reliability of the position detection device can be realized.

FIG. 15 also shows still another embodiment according to the present invention. Here, the present invention is applied to an encoder using a holographic phase grating. In the figure, reference numerals 60 and 61 are the same lasers and expanders as those shown in the embodiment of FIG. 14, 80 is a λ / 2 plate for rotating polarization by 45 degrees, 81 is a polarization beam splitter, and 82 is a phase compensation plate. 83 and 84 are mirrors, 8
5, 87 is a pickup lens, 86 is a holographic phase grating, 88 is a beam splitter, and 89 is a polarized light.
Λ / 2 plate rotated by 0 degree, 90 and 91 are sensor lenses,
Reference numerals 92 and 93 are two-divided sensors, and 94, 95 and 96 are differential amplifiers. The S-polarized light reflected by the polarization beam splitter 81 passes through a mirror 84 and a pickup lens 85,
The light imaged as a spot on the phase grating 86, and the light diffracted by the edge of the phase grating 86 is guided to the beam splitter 88 by the pickup lens 87 and interferes with the reference wave. The P-polarized light transmitted through the polarization beam splitter 81 has a phase shift δ _d of the S-polarized light received by the diffraction of the phase grating 86, a phase shift caused by the optical path length difference from the S-polarized light, and a phase shift caused by the reflection of the optical element. total δ phase correcting of _o, the sensor 92 of the re-imaging plane of,
Phase compensation is performed by the phase compensation plate 82 so that the phase difference of the light from the S-polarized side on 93 is partially an integral multiple of π. Further, the reflected light transmitted through the polarization beam splitter 81 is converted into S-polarized light by the λ / 2 plate 89 via the mirror 83, and the beam splitter 88 combines and interferes with the S-polarized light which is the diffracted wave from the phase grating 86. To be done. In this case, the beam splitter 88 constitutes a film in which the S-polarized reflected light undergoes a phase shift of π rad with respect to the transmitted light at the time of reflection. , And the relative phase is a π-shifted combined interference wave, realizing a differential detection configuration. Sensors 92, 93
The wavefront of the re-imaging plane of the wavefront diffracted by the upper phase grating is shown in FIG.
0 and the phase shifted by π, which is also the case where the phase difference of the edge portion of the phase grating 86 is an integral multiple of π, as in the previous embodiment. As described above, the phase difference of the grating 86 does not prevent the application of the present invention. As described above, conventionally, when the grating pitch of the encoder is reduced and the resolution is increased, the signal quality deteriorates due to the diffraction phenomenon of light,
Although it has been impossible to achieve high resolution, the present invention enables a high resolution encoder by positively utilizing the edge diffraction phenomenon.

Next, processing of the edge detection signal waveform obtained by the present invention will be described. FIG. 16 is a schematic block diagram for explaining the signal processing. Here, reference numeral 10
Reference numeral 6 is an input terminal for an edge detection signal obtained in the above-described embodiments, 100 is a differentiating circuit, 101 and 102 are window circuits I having an upward waveform and window circuits II having downward waveforms, and 103 and 104 are window circuits. Corresponding comparators I, II and 105 are multiplexing circuits that take the OR of the pulse trains to perform the operation. Further, FIG. 17 is a schematic diagram of waveforms in each.

FIG. 17A shows an edge detection signal,
An upward pulse and a downward pulse are generated at the edge part. If the edge interval is large, it becomes an isolated pulse, if it is small, it becomes a sinusoidal concatenated pulse, and if the edge interval becomes small, pulse height increases due to intersymbol interference. Undergoes deformation such as becoming smaller. From the edge detection signal, window waveforms (b) and (c) corresponding to the upward pulse and the downward pulse are obtained by the window circuits 101 and 102 whose thresholds are set to positive and negative, respectively. The window width becomes narrower when the edges are denser than when the isolated pulse is used. On the other hand, the differentiating circuit 100 obtains a differentiated waveform (d), and an S-shaped pattern with zero crossing at each edge portion is obtained. Using the window waveforms (b) and (c) facing upward and downward, the comparators 103 and 104 detect the zero crossing point of the edge from the differential waveform (d), and the one-shot pulse train indicating the edge position ( e) and (f) are obtained. This pulse train is synthesized again by the multiplexing circuit 105, and for example,
Depending on the edge position, as shown in FIG.
A waveform in which H is inverted is obtained, and the edge position is detected.

In the above-mentioned plural embodiments, the case where the present invention is applied to the devices for different purposes is explained. However, as described above, the edge to be diffracted depends on the difference in the refractive index. Whether it is a stepped type or a stepped type, unless the phase difference is 0, the diffracted wavefront is modulated and the phase distribution changes.
In principle, the detection according to the invention is possible. Therefore, it goes without saying that, for example, the grating of the embodiment shown in FIG. Further, as the information represented by such a phase edge, an example of digital data in the optical memory and position data in the encoder is shown, but the information is not particularly limited to this, and analog data, two-dimensional image data, etc. It can also be applied to detection. For example, in the embodiment of FIG. 11, image data can be targeted by two-dimensionally scanning.

Further, an example has been described in which the two-divided sensor is always placed on the pupil plane or the re-imaging plane, but of course the place where the change in the diffracted wavefront can be detected is not limited to these two points. Instead, it can be implemented even in a convergent or divergent light beam. Of course, this is not the idea of the present invention that it is a two-divided sensor, but the phase distribution including diffraction is corrected to emphasize the nonuniformity of the interference intensity distribution and detect the nonuniformity. As the simplest means, an example in which the asymmetry is detected by the difference between the two-divided sensors has been described. Therefore, it is also possible to adopt an optimal space division method for detecting nonuniformity, and for example, in the detection method of calculating the output from the sensor unit of three or more divisions, for example, in the embodiment of FIG. 14 or FIG. A two-dimensional CCD camera is placed at the position of the two-divided sensor, the interference fringe intensity distribution and the image spot are captured as a two-dimensional image, and changes in the intensity distribution are captured by combining various image processing, such as edge position and depth. It is also possible to obtain the three-dimensional information of.

[0052]

As described above, the present invention corrects the phase of the diffracted wavefront from various edges and the phase change caused by other optical elements, and optimizes the phase difference from the reference wavefront. By increasing the non-uniformity of the interference intensity distribution and improving the modulation degree of the detection signal, there is an effect of improving the reliability of the detection accuracy.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical head in which the present invention is applied to a magneto-optical disk recording / reproducing apparatus.

FIG. 2 is an explanatory diagram of a Kerr effect.

FIG. 3 is an explanatory diagram of diffraction from a magneto-optical domain edge.

FIG. 4 is an explanatory diagram of a diffraction pattern.

FIG. 5 is an explanatory diagram of a polarization state.

FIG. 6 is an explanatory diagram of a polarization state.

FIG. 7 is a schematic view of a phase compensation plate.

FIG. 8 is an explanatory diagram of a polarization state.

FIG. 9 is a second embodiment of the present invention.

FIG. 10 is likewise an explanatory diagram of a diffraction pattern.

FIG. 11 is likewise an embodiment of an optical disc recording / reproducing apparatus.

FIG. 12 is a schematic diagram of an optical head.

FIG. 13 is likewise an explanatory diagram of a diffraction pattern.

FIG. 14 is likewise an embodiment of a position detecting device.

FIG. 15 is an example of an optical encoder.

FIG. 16 is a block diagram of a processing circuit.

FIG. 17 is a schematic diagram of a signal waveform.

[Explanation of symbols]

 1,60 Laser 13,30,44,68,82 Phase compensation plate 9 Magneto-optical disk 42 Optical disk 64 Silicon wafer 86 Holographic grating

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Susumu Matsumura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (3)

[Claims] 1. An optical detection device for irradiating a phase object with laser light, guiding reflected light / transmitted light from the phase object to a photodetector, and detecting an attribute of the phase object, comprising: The diffracted wave front is combined with the reference wave front, and the obtained interference intensity distribution is detected by the photodetector, and phase modulation due to the polarization characteristics of the phase object, It has a phase compensator for making the relative phase difference between the total phase by the superposition of spatial phase modulation by the diffracted wavefront and the phase of the reference wavefront in a spatial partial region approximately an integer multiple of π. Characteristic optical detection device. 2. The optical detection device according to claim 1, wherein the total phase includes a phase modulation received by an optical element in an optical path from the phase object to the photodetector. 3. The phase object is a magneto-optical domain,
The optical detection device according to claim 1, wherein the attribute of the phase object is a domain wall of a magneto-optical domain, the total phase is a Kerr component phase, and the reference wavefront is a Fresnel component.