JP3292314B2 - Optical detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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 because 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 considered to be advantageous in that the data capacity can be increased as compared with the former, but in order to accurately reproduce information from a recording medium recorded by this method, information bits are required by the optical head part. Accuracy in reading the edge position of the image is required.

In recording 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 a mark is formed using reflected light from the light spot. 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 the recording medium by an objective lens, a minute spot is formed, and the change in the polarization state of the reflected light from this is converted into a change in the amount of light. This is done by converting and differentially detecting.

[0004] This information reproduction is described in, for example, Japanese Patent Application Laid-Open No. 3-26.
As shown in No. 8252, when a minute spot narrowed down to the diffraction limit is used, the behavior of the reflected light from the edge of the information bit is a phase type 0 / π edge or a phase type 0 / π edge.
Diffraction from the π lattice becomes dominant. Therefore, the behavior of the reflected light is significantly different from that of geometrical or geometrical optics, and the principle of detection is different from that of a conventional detection device using them, so that a more accurate new edge detection device can be realized.

[0005] As described above, Japanese Patent Application Laid-Open No. H10-110,087 discloses an example of obtaining a signal of higher quality when edge detection is performed by positively utilizing diffracted reflected light from the edge of an information bit.
No. 278702, Japanese Patent Application No. 2-27910, Japanese Patent Application No. 2-27910
As disclosed in Japanese Patent Application No. 307910 and Japanese Patent Application No. 2-310524, an apparatus using a spatially nonuniform optical filter or a split sensor has been proposed. In the new detection principle that actively utilizes these diffraction phenomena, the phase distribution of the diffracted wavefront has a particularly important meaning, and is clearly different in principle from the conventional example that can detect it ignoring it. .

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

The method disclosed in Japanese Patent Application Laid-Open No. 3-104401 is a special case where the diffraction phenomenon due to edges can be ignored and the elliptic effect (Kerr ellipticity) due to the Kerr effect can be ignored. In other words, the polarization state due to the Kerr effect in the domains on both sides of the edge (a state in which only a phase difference occurs between left and right circularly polarized light and only linearly polarized light is rotated) spatially bisects the far field geometrically as it is. This is a special case in which the rotation of the polarized light can be converted into a phase difference by a λ / 4 plate, and the polarization beam splitter is not performed by the magneto-optical domain on the optical disk but by the phase difference converted by the λ / 4 plate. The edge detection method in a special case where a difference in intensity occurs in the jitter direction in the far field due to the configuration using. This is a method that is different in principle from a new detection method that uses a diffracted wavefront from the edge of an information bit due to a diffraction-limited spot.

A detection principle similar to that of the conventional example is disclosed in Japanese Patent Application Laid-Open No. Sho 62-188047. The Kerr effect here is that normally incident linearly polarized light
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.
tilt _k . However, this conventional example is applied to a special case in which the reflected light from the non-recording portion remains incident linearly polarized light, and only the reflected light from the recording portion tilts as linearly polarized light. Further, the detection method is also a special method. By placing a λ / 4 plate in a parallel light beam and appropriately setting its direction, the inclination of the linearly polarized light reflected from the recording unit can be changed to λ / 4.
The plate is converted into a phase change (= π / 2) by a plate, and has a special configuration in which linearly polarized light having no inclination from a non-recording portion passes through an analyzer to cause interference. In addition to the interference using a special λ / 4 plate capable of giving a phase difference only to linearly polarized light having a slight inclination from the recording unit, the interference term of commonly known general light interferes with It is related to the phase difference between two interfering lights, and the phase difference is π
In the case of / 2, cosπ / 2 = 0, and the interference term disappears. However, the edge detection is performed by a special configuration in which a difference in light intensity occurs in the jitter direction on the parallel light flux. . Obviously, the new detection using the diffraction wavefront from the edge of the information bit due to the diffraction limited spot,
It is a different method in principle.

Further, according to the detection principle disclosed in JP-A-62-188047 and JP-A-3-104031, the rotation of polarized light generated on the disk surface is converted into a phase change later. Looking through the phase conversion, it can be considered that the detection principle is the same as that of the uneven pits described in Japanese Utility Model Application Laid-Open No. 56-90744. That is, the actual opening 56-9
As disclosed in Japanese Patent Application Laid-Open No. 0744, the intensity of the light reflected from the edge differs between the upper surface and the lower surface of the step at the edge portion, and the intensity of the light is geometrically and geometrically guided to the light detection surface. I will Here, this phenomenon is used.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 3-268252, a new detection principle using a diffracted wavefront from the edge of an information bit due to a diffraction-limited spot uses a point of each edge within the spot. It is impossible to make the reflected light of the optical field geometrically and geometrically correspond to each point of the far field, but light from all points in the spot overlaps at all points on the far field, and a new wavefront This is fundamentally different from the prior art in that the diffraction phenomenon of forming a diffraction wavefront can be used, and the amplitude distribution and phase distribution of the diffracted wavefront are efficiently detected.

The edge detection method disclosed in Japanese Patent Application Laid-Open No. 2-46544 is a method applicable to a recording mark having a width longer than the diameter of a light spot and having a wider width. 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 condensing position using the condensing lens.
In order to cope with the high density and high resolution of information, it is desirable to be able to detect the edge of a recording mark having a diameter equal to or less than the diameter of a light spot, 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 shape of the front and rear edges is 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 efficiently detecting edges by focusing on the amplitude distribution and phase distribution of the diffracted wavefront.

In the edge detection method disclosed in JP-A-3-120645, when a Kerr ellipticity is 0, when a light spot is detected by a two-part photodetector in a far field, a light projection system, In the case where a λ / 4 plate is inserted obliquely into the common optical path of the light receiving system to perform elliptically polarized light, and when the light is detected at the re-imaging position, the light is projected into the common optical path of the light receiving system. A case where a Brewster plate is inserted and detected by a two-segment photodetector matched to the edge shape, and
By combining a variable compensation phase plate whose phase compensation amount is unknown in the light receiving system and a matching filter, the transmitted light of the polarizing beam splitter /
Cases where a non-split photodetector for detecting reflected light and a λ / 2 plate for adjusting the light amounts of the two photodetectors are arranged are shown, respectively. In this conventional example, the spatial phase distribution seems to play an important role, but elliptically polarized light from an oblique λ / 4 plate is incident on a disk having a Kerr ellipticity of 0, and the reflected wave is further made elliptical. There is no description that the phase distribution in this case is particularly considered. Also, the operation of the total phase distribution and the polarization distribution by the variable compensation phase plate, the matching filter, the adjustable λ / 2 plate, and the polarization beam splitter whose compensation amount is unknown is similarly unknown. The detection principle is that the operation of detection on the re-imaging plane is the same. This is because, based on the new edge detection principle that efficiently detects edges by focusing on the amplitude distribution and phase distribution of the diffracted wavefront, the farfield surface and the re-imaging surface have completely different diffracted wavefronts. It is considered that the configuration is different because the principle is different.

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

[0014]

The edge detection does not use the amplitude distribution and the phase distribution of the diffracted wavefront. In the above-described conventional example, the phase distribution is not considered. No, of course,
In the new edge detection method typified by JP-A-52-52, the phase distribution due to diffraction has been considered only relatively so far, so that the degree of modulation of the light intensity distribution caused by multiplex 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 decreases.

[0015]

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

[0016]

Therefore, in the present invention,
In an optical detection device that irradiates a laser beam onto a phase object, guides reflected light / transmitted light from the phase object to a photodetector, and detects an attribute of the phase object, a diffracted wavefront from the phase object is referred to. A wavefront is combined and interfered, and the obtained interference intensity distribution is configured to be detected by the photodetector, and phase modulation due to the polarization characteristics of the phase object, spatial modulation by a diffracted wavefront from the phase object is performed. A phase compensator is provided to make the relative phase difference between the total phase obtained by the superposition of the phase modulations and the phase of the reference wavefront in the spatial partial region substantially an integral multiple of π.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a 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 polarizing beam splitter,
8 is a pickup lens, 9 is a magneto-optical disk which moves relatively in the direction A with respect to the pickup lens 8, 10
Is a beam splitter, 11 is a servo sensor lens having a cylindrical surface, 12 is a 4-split servo sensor, 13 is a phase compensator, 14 is a λ / 2 plate, 15 is a second polarization beam splitter, and 16 and 17 are 2-split RF. Sensor, 18a,
18b and 19 are differential amplifiers. The first polarization beam splitter 5 transmits 70% of the polarization component (P polarization) in the E direction and reflects 30%, and reflects 10% of the polarization component (S polarization) in the orthogonal direction. Further, the second polarization beam splitter 15 transmits 100% of the P-polarized light and transmits 1% of the S-polarized light.
Reflects 00%. 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 direction perpendicular to the track.

The light from the laser 1 is converted into a substantially circular parallel light beam by the collimator lens 3 and the beam shaping prism 4, and is transmitted through the first polarizing beam splitter 5 and the pickup lens 8 to magneto-optically. Disc 9
And is focused as a diffraction-limited spot. Then, part of the reflected light from the magneto-optical disk 9 is:
Again, the light reaches the first polarizing beam splitter 5 via the pickup lens 8, and thereby the P-polarized component 30.
%, And 100% of the S-polarized light component, and is guided to the detection optical system. Here, a part of the light split by the beam splitter 10 is guided to the four-split sensor 12 by the servo sensor lens 11. In this optical information recording / reproducing apparatus, the astigmatism method is used for autofocus, and the push bull method is used for auto tracking. The light transmitted through the beam splitter 10 is subjected to an optimal phase shift by the phase compensator 13.

FIG. 2 schematically illustrates a change in polarization due to a magnetic domain. That is, when the P-polarized light is made incident on the magneto-optical disk in FIG. 1, the polarization state of the reflected light is shown in FIG. 2A, in which the vertical direction of the recorded magnetic domain is shown. Is the rotation angle θk of the polarized light.
The sign of (car rotation angle) is reversed. The reflected light becomes elliptically polarized light, and the left and right directions are also reversed. (B) and (c) of FIG.
Represents the polarization state when the Kerr ellipticity of the Kerr effect is set to 0, that is, when only the rotation of linearly polarized light is considered, and the polarization state is divided into P and S components. Corresponding to FIGS. 2D and 2E show cases in which the Kerr ellipticity is considered. As is clear from the figure, the fact that the rotation of the polarization is inverted by ± θk depending on the direction of the magnetic domain means that
This corresponds to the fact that the phase of the S component shifts by π. Therefore, considering only the S 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, and the phase change is extremely large and a step-like steep change.

FIG. 3 schematically illustrates such a phase type edge and a diffracted wavefront from a phase type grating. In FIG. 3, the arrangement of the upward magnetic domains 21 and the downward magnetic domains 22 recorded on the magneto-optical film 20 is an array of minute 0 / π phase difference objects such as reference numeral 23 when the S component is considered as described above. Can be considered. When the diffracted wave from this edge is observed in the pupil plane of the pickup lens 8 or in the far field region 24, E in FIG.
With respect to the direction, that is, the P-polarized component, there is no object whose amplitude and phase are spatially modulated, so that the light amount distribution becomes a normal Gaussian as indicated by reference numeral 25.
On the other hand, the S-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. This is due to diffraction, which is the interaction between a minute object and light, and is different in principle from the case where the diffraction phenomenon as shown in the conventional example is negligibly small. For example, in the case of FIG. 3, the light quantity distribution is divided into two peaks, but these are not independent light beams, but are diffraction patterns formed in the interference far field by wavefronts from points in the diffraction-limited spot 5. That is, the reflected polarized light beam from the upward magnetic domain 21 and the reflected polarized light beam from the downward magnetic domain 22 are not arranged geometrically. And interfere and form one wavefront. This is, so to speak, a pattern resulting from a mixture of wavefronts from upward and downward magnetic domains.As shown in the conventional example, the polarization from each magnetic domain is considered geometrically and spatially separated. Is impossible to identify.

FIG. 4 shows a lens 4 for S-polarized light when the diffraction-limited spot 5 is scanned in the X direction in FIG.
Is obtained by calculation. In the figure, (a) to (g) show the difference in the spot position normalized by the spot diameter on the x coordinate. In the figure,
The solid line represents the amplitude distribution of the diffracted wavefront, and the dashed line represents the phase distribution. However, the phase is represented by a relative value for simplicity.
FIG. 4A shows a case where the spot 5 is projected only on the downward magnetic domain 22. The amplitude distribution is Gaussian, and the phase distribution is shifted by πrad indicated by reference numeral 23.
When the edge enters the spot, FIG.
As shown in (f), the amplitude distribution has a depression at the center, and in particular, in (d), where the optical axis coincides with the edge, the amplitude distribution is separated into two peaks. As described above, the phase distribution receives the modulation around πrad as shown in (b) and (c) due to the insertion of the edge, and jumps to the modulation around 0 rad in (d). Hereinafter, as the edge goes out of the light spot, the modulation becomes smaller and the phase becomes zero.
As shown in (g), the phase of the diffracted wavefront from the upward magnetic domain 21 of rad becomes 0 rad, and the amplitude distribution returns to Gaussian.

As can be seen from these results, in the reproduction utilizing the diffraction phenomenon of the present invention, each of the positions (b), (c), (e), and (f) where the edge is shifted from the optical axis is obtained. The superposition of the wavefronts from each point of the magnetic domain produces a diffraction pattern. In particular, since the phase distribution corresponds to the spatial polarization state distribution, reproduction using the phase asymmetry becomes possible. However, in this case, these (b), (c), (e),
It is impossible to describe the wavefront of (f) in the state of reflected polarization from a specific magnetic domain, and it is clear that the detection principle is different from that of the conventional example. 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, but this is different from the phase domain as in the present embodiment.

Next, 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 which is not modulated by the domain are combined and interfered with each other will be considered. Try. More specifically, in the embodiment of FIG.
Is rotated by 22.5 ° about the optical axis, and the two orthogonal polarizations are changed by the second polarization beam splitter 15 to ±
There is a case where the light is projected onto a 45 ° analyzer and multiplex interference is caused. Here, in order to clarify the principle difference between the conventional example and the present invention, first, the case where there is no phase compensation plate 13 and the Kerr ellipticity is 0 is considered. A case where the Kerr ellipticity is not 0 will be considered, and finally, the effect of improving the degree of modulation by the phase compensator 13 will be described.

FIG. 5 shows the spatial distribution of P-polarized light and S-polarized light when there is no phase compensator 13 and the Kerr ellipticity is zero. In the figure, (a) shows the amplitude distribution and phase distribution of the P-polarized light on the pupil plane, wherein the amplitude distribution is Gaussian and the phase distribution is 0 rad, which is constant. FIG.
(B) corresponds to (d) of FIG. 4 and shows the amplitude distribution (solid line) and phase distribution (solid line) on the pupil plane of S-polarized light when the magneto-optical domain edge is on the optical axis of the light spot. Broken line)
Represents Here, since the ovalization due to the Kerr effect is neglected, the phase of the S-polarized light is spatially divided into two regions of ± π / 2 rad around 0 rad. (C) to (i) of FIG. 5 show the coordinates ξ = ξ ₁ , ξ ₂ , ξ of the pupil plane.
₃ , 0, ξ ₄ , ξ ₅ , 表 わ す₆ represent the combined polarization state of P-polarized light and S-polarized light. Generally, P-polarized light and S-polarized light are E _P ,
E _S , the amplitudes are A _P and A _S , the angular frequency of light is ω,
Assuming that the wavelength is λ and the initial phase of each polarized light is φ _P1 and φ _S , 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 ,
Assuming φ _S , the combined polarized light is represented by elliptically polarized light clockwise when δ> 0 and counterclockwise when δ <0. When δ = 0, the light becomes linearly polarized light. When δ = ± π / 2 and A _P = A _S , the light is represented by clockwise or 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
₁ ) Since + π / 2> 0, 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, E _P (ξ ₆ ) = E _P (ξ ₁ ), and E _S
Since (ξ ₆ ) = E (ξ ₁ ), the light is elliptically polarized light having the same shape as that of FIG. 5C, but is left-handed elliptically polarized light. Since the difference between left and right rotation cannot be detected by an analyzer (second polarizing beam splitter) of ± 45 °, ξ = ξ ₁ ,
xi] = xi] of each point ₆ multiplexing interference intensity I (xi]) is equal.
That is, if the inclination angle of the analyzer from the 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) cos2 sin2 · cosδ (ξ), so α = ± 45 ° and A _{P
(Ξ 1) = A P (} ξ 6), A S (ξ 1) = A S (ξ 6)
Therefore, the following equation is obtained.

[0026]

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

[0027] in FIG. 5 (d), (h), respectively, the coordinates xi] = xi] _2, is a state of polarization at ξ = ξ _5, E _P =
E _S , δ = −π / 2, resulting in clockwise and counterclockwise circular polarization, respectively, and I (ξ ₂ ) = I (ξ ₅ ).
Further, (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 longitudinal axis coincides with P-polarized light is different only in a vertically long flat rotation direction, and I (ξ
₃₎ = a I (ξ _4). Further, FIG.
Since E _S = 0 in the polarization state at, the light becomes P-polarized light.

That is, the first thing to be understood from the above is that the diffraction effect of the Kerr component has not conventionally been neglected or taken into account, and thus the polarization distribution on the pupil plane becomes non-uniform. Was not known. Even if such a phenomenon occurs without being noticed, the light intensity distribution on the pupil plane caused by the combined interference does not become asymmetric in the conventional configuration of the detection principle. It is clear that no detection signal is obtained.

Next, a case where the Kerr ellipticity is not 0 will be described. FIG. 6 shows the polarization state on the pupil plane in that case. This corresponds to FIG. The difference from FIG.
The elliptic effect of the Kerr effect on S-polarized light, that is, δ _k
= Φ _kp −φ _ks . S in FIG. 6B
The amplitude distribution of the polarized light is the same as that in FIG. 5B, but the phase distribution is shifted by −δ ′ _k and is not rotationally symmetric with respect to the optical axis ξ = 0, that is, odd. Not a function. Each coordinate point xi] = xi] ₁ in this _{case, ξ 2, ξ 3, 0} , ξ 4, ξ
_5, a schematic diagram of the state of polarization at xi] ₆ is similar to FIG. 5,
6 (c), (d), (e), (f),
(G), (h), and (i). Here, due to the existence of the Kerr ellipticity δ _k , δ = φ _p −φ _s + δ _k becomes ±
It does not become π / 2. Therefore, the major axis and the minor axis of each elliptically polarized light do not coincide with the P direction and the S direction. FIG.
In the region of δ = −π / 2−δ ′ _k as shown in FIG. 6B, ξ <0, as shown in FIGS. 6C, 6D and 6E, the major axis of the elliptically polarized light Is right-handed elliptically polarized light inclined leftward with respect to the P direction, and δ = + π / 2−δ ′
_In the region of _R , ξ> 0, the light is left-handed elliptically polarized light with the long axis having the opposite inclination. 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 ), A _S (ξ ₅ ) = A _S (ξ ₂ ), the following equation is obtained, and the sign of the interference term is inverted around the optical axis ξ = 0.

[0030]

(Equation 2) In other words, it can be understood from this that the diffraction effect of the Kerr component alone does not show asymmetry in the interference intensity distribution on the pupil plane due to the edge as shown in FIG. And an edge detection signal can be obtained for the first time. Therefore, in the above-mentioned conventional example in which the diffraction effect of the Kerr ellipticity and the Kerr component is not used, no asymmetry occurs in the interference intensity distribution on the pupil plane. I couldn't get it.

Meanwhile, Japanese Patent Application Laid-Open No.
The edge detection signal obtained by a series of new edge detection methods typified by Japanese Patent No. 68252 includes 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, S It was clarified that the phase shift was caused by combining the phase shift caused by the polarization phase difference δ _o and the phase change due to diffraction. That is, if this is explained in FIG. 6B, if ξ <0,
−π / 2−δ ′ _R + δ _o , and when ξ> 0, + π / 2
−δ ′ _R + δ _o , and the difference in light intensity between the point + | ξ | and the point − | ξ | is the interference term A _P (ξ) A _S (ξ) si
n (δ ′ _R −δ _o ). Here, the phase difference distribution δ is not limited to the shift of δ ′ _R shown in FIG.
Is generalized to the following equation. δ = δ _d + δ _R + δ _o = φ _P −φ _S Here, δ _d is a phase difference caused by diffraction, δ _R is a phase difference caused by Kerr ellipticity, and δ _o is a position caused by other substrates or optical systems. It is a difference. Originally δ _d and δ _R
It is not necessary to divide them, but in order to facilitate the description of the case of the uniform domain and the case of the presence of the edge, they are considered in this way.

The Kramers-Kronig relationship is established between the Kerr rotation angle θ _k and the Kerr ellipticity δ _k , and they are not independent but of the same order. In general, θ _k is less than 1 degree and δ _k is also less than 1 degree. In the normal level detection, [delta] _o have been efforts made to reduce, the above-mentioned compensation plate therefor, example of using a phase shift of the reflection surface of the mirror or a beam splitter is known. That is, it is, in the conventional optical system, [delta] _k
It means that efforts are being made for + δ _o = 0. In the edge detection, it is an effort to eliminate the edge detection signal shown in FIG. Also, 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 of the amplitude (peak) of the edge detection signal.
= | A _P A _S sin (δ _k + δ _o ) |, and 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 difference distribution δ is corrected by the phase compensating plate 13 to maximize the amplitude of the edge detection signal.

FIG. 7 is a schematic diagram of the phase compensator 13. The phase compensator 13 is made of quartz, and has a laminated structure utilizing a difference in thickness so as to cancel optical rotation and use only birefringence. Here, the thickness of the phase compensator 13 is set so that the total phase difference between the fast axis F and the slow axis S is (π / 2) − (δk + δo). Further, the arrangement is such that the fast axis F is aligned with the P polarization direction and the orthogonal slow axis S is matched 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)
Since 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 compensator 13,
After passing through the phase compensator 13, they become 0 and π for P-polarized light.

FIG. 8 shows the polarization state after phase correction by the phase compensating plate 13, and corresponds to FIGS. 5 and 6. Here, as shown in FIG.
When the phase of the P-polarized light is set as a reference (Orad), the phase compensator 13 is operated so that the phase distribution of the S-polarized light becomes 0 and πrad. That is, in FIG. 5 and FIG.
<0 delays the phase that was -π / 2, -π / 2-δk 'to 0, and ξ> 0 delays the phase that was + π / 2, + π / 2-δk' 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 respectively shown in (c), (d), and (d) of FIG.
(E), (f), (g), (h), and (i). In this case, since the phase difference δ between the P-polarized light and the S-polarized light is 0 or π,
It is not elliptically polarized light but linearly polarized light. However, it can be seen that the rotation angle and the amplitude of the polarized light are unevenly distributed. As in the case described above, for 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 °. I do. Thereby, ± 45 with respect to the P polarization axis.
The combined interference intensity distribution by the analyzer set to °
The light is obtained as transmitted light and reflected light by the second polarization beam splitter 15 having a differential detection configuration for removing in-phase noise.

As can be seen from FIG. 8, the intensity distribution includes
A large asymmetry has occurred. This ξ = ξ _1, when compared with _{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 largest asymmetry. Therefore, the maximum modulation is obtained as the edge detection signal. Each other point pair (ξ ₂ ,
ξ _5), (ξ _3, also in the xi] _4), it has occurred a similar maximum asymmetry. That is, asymmetry of the intensity distribution is detected by the two-divided sensors 16 and 17, and the differential detector 1
8a and 18b, when the difference is detected, the amplitude of the signal is
It is proportional to 2 Ap As. In the prior art shown in FIG. 6, the amplitude is 2Ap As · sin (δk + δo), which is very small. However, the present invention has obtained the limit maximum amplitude.

From a different perspective, rectangles (side length 2A _P on the P-polarized side, side on the S-polarized side) in the PS plane of each of (c) to (i) in FIGS. It can be said that the shape of the elliptically polarized light inscribed within the length 2A _S ) is controlled and set to an optimum value. That is, the present invention is not limited to the configuration shown in FIG. 1, but includes a concept applicable to a polarization state caused by any optical phenomenon such as the Kerr effect, diffraction, and birefringence. For example, also in the optical head of the magneto-optical disk shown in FIG. 1, the medium configuration of the magneto-optical disk is such that the linear polarization distribution as shown in FIG.
It is also possible to set a multilayer structure. For example, δ _R including the phase shift due to multiple reflection in advance,
Phase change due to diffraction and phase change due to optical system in the middle δ _o
This also includes the concept of an edge recording / reproducing optical disk that has a phase distribution of an integral multiple of π after receiving it. Further, in consideration of the compatibility of the optical disk, the invention is also an invention capable of defining an ellipticity of the optical disk, an optical head defining the influence of diffraction and the phase change of the optical system. In addition,
It goes without saying that the phase compensation plate 13 is not limited to a quartz plate. Furthermore, even if the phase compensator 13 is not provided, if the target phase distribution can be obtained by a combination of the phase difference between the P-polarized light and the S-polarized light in the mirror or the beam splitter, the phase compensator 13 is not required. 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 a configuration of an optical head of a magneto-optical disk recording / reproducing apparatus according to the present invention. In the figure, the same components as those in the embodiment of FIG. 1 are represented by the same reference numerals. The embodiment of FIG. 10 has a configuration of re-imaging plane detection, whereas the embodiment of FIG. 1 is pupil plane detection. Here, reference numeral 30 denotes a phase compensator, 31 and 32 denote sensor lenses, 33 and 34 denote two-split RF sensors (the split lines extend in a direction perpendicular to the plane of the drawing and are orthogonal to the tracks on the magneto-optical disk 9) 35,3
6, 37 are differential amplifiers.

As in the previous embodiment, to clarify the principle difference between the conventional example and the present invention, first, the phase compensator 3
Consider a 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 on the magneto-optical disk 9.
Here, (a) to (g) show the difference in the spot position normalized 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 the P-polarized light is set to the reference value 0. From this, it is first understood that the change of the diffracted wavefront in the pupil plane of FIG. 4 is greatly different from the above-described conventional example in which the same operation is performed in the pupil plane detection and the re-imaging plane detection. You. When the edge is not within the spot, (a) and (g) basically have a Gaussian type amplitude distribution, and the phase is π or π depending on the direction of the domain at that time.
It will be 0. Further, here, the pupils of the sensor lenses 31 and 32 are made smaller than the pupils of the pickup lens 8 to reduce the influence of axis deviation due to tracking or the like. The phase difference between the annular zones is π. Now, when the edge enters the spot, the amplitude distribution becomes asymmetric as shown in (b) to (f), the valley having an amplitude of 0 moves, and the edge comes to the center of the spot. In FIG. 11D, the valley is at the center, and as a result, the amplitude distribution becomes symmetric. In addition, the phase distribution takes values of 0 and π when the edge enters the spot, and the values are replaced for each ring zone. In FIG. 11D, 0 / π occurs at the center. I have. Therefore, by causing multiplex interference with a P-polarized wavefront not affected by diffraction (similar to the case where the amplitude of (g) in FIG. 11 is amplified), asymmetry of the intensity distribution can be generated. At this time, since the values of the S-polarized light with respect to the P-polarized light are 0 and π, the image is re-imaged from the pupil plane of the sensor lens following the diffraction from the magneto-optical disk to the pupil plane of the pickup lens (corresponding to FIG. 4). Due to the two diffractions of the plane, the phase distribution on the re-imaging plane has the largest asymmetry, such as cos 0 = 1 and cos π = -1, and the maximum edge signal amplitude can be obtained. Become. However, in actuality, there exists a Kerr ellipticity δk, and a phase difference δo between P-polarized light and S-polarized light caused by reflection of a mirror or a beam splitter.
A decrease in the degree of modulation of cos (δk + δo) and cos (π + δk + δo) has occurred.

In the present invention, the Kerr ellipticity and a phase distribution obtained by integrating a phase change due to diffraction, a phase change due to an optical system, and the like are partially integer-multiplied by π with respect to the phase distribution of the reference wavefront. By doing so, the degree of modulation is improved, and in this embodiment, the maximum amplitude is achieved by correcting the phase of δk + δo. Therefore, in FIG. 10, the phase compensating plate 30 has 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). By making the arrangement coincide with the polarization direction, the phase distribution of the S-polarized wavefront on the re-imaging plane of the sensor lenses 31 and 32 is made an integral multiple of π with respect to the P-polarized light as shown in FIG. be able to. Thereby, the amplitude of the differential output by the differential amplifiers 35 and 36 can be maximized.

Next, still another embodiment according to the present invention will be described. FIG. 11 shows a configuration of an optical head of an optical disk recording / reproducing apparatus according to the present invention. In the figure,
1 are given the same reference numerals. In this embodiment, the present invention is applied to a case where marks recorded on an optical disk are not pits in the magneto-optical domain but are concave and convex pits. Here, reference numeral 39 denotes a pickup lens, 40 denotes a first polarizing beam splitter that 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 disk on which uneven pits are recorded, 43 is P-polarized light
A third polarizing beam splitter transmitting 0%, transmitting 80% of S-polarized light, and reflecting 20%, 44 is a phase compensator, 45,
46 is a two-division RF sensor, and 47, 48 and 49 are differential amplifiers. Here, the optical disc 42 is irradiated with a diffraction-limited spot by the pickup lens 39.
FIG. 2 is an enlarged schematic view of the same. For the sake of explanation, the lens surface and each surface of the optical disk are omitted. The light exiting the optical disk-side surface 56 facing the pickup lens 39 enters the λ / 4 plate half mirror 41 and
Is transmitted and 40% is reflected. Also, the reflective multilayer surface 5
0 passes through the λ / 4 substrate 51 and is converted into clockwise circularly polarized light.
Above is connected 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, is converted into substantially S-polarized light,
%, And returns to the pickup lens 39. On the other hand, the incident light reflected on the reflective multilayer film surface 50 connects a light spot 55 equivalent to the light spot 54 on the optical disc 42 to the vertex 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 with a very large radius of curvature, and the light spot is as small as about 1 μm, the light specularly reflected on the lens surface 56 returns to the λ / 4 plate half mirror again. , 40% are reflected back to the pickup lens. This light is used as a reference wavefront, while remaining P-polarized. It is to be noted that the use efficiency of light can be improved by attaching the high reflection film 52 to the vertex of the optical axis of the lens surface, a few μmφ.

In FIG. 11, by making the S-polarized signal light and the P-polarized reference light into a fixed and substantially equal optical path length in this manner, an actuator ( Noise (not shown) can be removed. The P and S polarized lights returned to the parallel light flux again by the pickup lens 39 are reflected by the first polarizing beam splitter 401 toward the detection system. Also,
The third polarization beam splitter 43 has an S signal having a signal for auto-tracking and auto-focusing of the disc.
Part of the polarized light is reflected and guided to the servo optical system.
FIG. 13 shows the wavefront of the S-polarized light transmitted through the third polarization beam splitter 43. Here, (a) to (g) show the edges of the concave and convex pits when the diffraction-limited spot 54 is scanned, that is, the diffracted wavefront from the step edge,
The difference depending on 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 a phase edge as shown in FIG. 4, the diffraction wave front in the case of a step edge has an asymmetric amplitude distribution and a non-odd phase distribution. This is because the diffracted waves from the steps differ depending on the left and right steps. The steps shown here are vertical and have a height of λ / 4, and ξ <0.
Is 0, and ξ> 0 and the height is λ / 4. Naturally, the diffraction wavefront changes depending on the height and the inclination of the step, but the asymmetric tendency does not change. Since there is no such description, this example will be described. The asymmetry direction of the amplitude depends on the direction of the step, and even if the spot moves, the unbalance direction of the magnitude of the amplitude distribution does not change. The position of the dip having 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 curvature of the phase distribution coincides with the dip position of the amplitude distribution, the spatial change is slower than the phase edge, and even in the case of FIG. 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 has occurred, and the reference wave to be multiplexed, the phase 0
In the case of the P-polarized light of rad, as in FIGS. 4 and 5, only the non-uniformity of the light amount occurs 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 large. Will be smaller. Although the optical path length difference between the P-polarized light and the S-polarized light is small and fixed as shown in FIG. 12, it is difficult to mechanically reduce the optical path length difference to zero in the initial adjustment, and the thermal expansion There are differences in coefficients, temperature characteristics of the refractive index of the λ / 4 plate, offsets of residual autofocus, changes over time thereof, and the like. Moreover, because some phase shift caused by the optical elements described above, it P-polarized light, a value including the optical path length difference between the S-polarized light, when put anew [delta] _o, Overall, the phase difference δ = δ _d + δ _o Occurs. Accordingly, the phase difference is corrected by the phase compensator 44 so that the portion where the phase difference between the P-polarized light and the S-polarized light is an integral multiple of π is increased, thereby increasing the amplitude of the edge detection signal. , The degree of modulation can be increased. For Figure 13, as seen from (d), the providing the phase difference of 3π / 2-δ _o by a phase compensator 44, to achieve the required amplitude. However, as is apparent from (d), the phase distribution has a small number of fixed portions and is slightly curved, and when the opposite edge comes, the wavefront and the phase distribution inverted around the ξ = 0 axis become Therefore, in this case, the phase compensation amount provided by the phase compensating plate 44 may be finely adjusted while monitoring the edge detection signal waveform so that the edge detection signal amplitude becomes maximum. In addition, the phase compensation amount may be corrected so as to obtain an averagely stable signal amplitude in consideration of the error, fluctuation, and aging of each optical element described above. For this purpose, a method of tilting the phase compensating plate 44 by a small amount with respect to the optical axis as shown in FIG. 11, or rotating the fast axis by a small amount from the P-polarized direction can be adopted.

In this way, the polarization of the pupil plane when the edge is on the optical axis is corrected, and the pupil plane is rotated 45 degrees by the λ / 2 plate, and the second polarization beam splitter and the split sensor 4 are rotated.
The differential signal is detected by the differential detection optical system by the differential amplifiers 5 and 46, the detected signals are differentiated by the differential amplifiers 47 and 48, the differential signal is obtained by the differential amplifier 49, and the common-mode noise is removed to obtain 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 denotes a frequency-stabilized He-Ne laser, 61 denotes a beam expander, 62 denotes a non-polarization beam splitter, 63 and 66 denote pickup lenses, 65 denotes a phase compensator, 64 denotes an object, 67 denotes a mirror, and 68 Is λ /
Two plates, 69 is a polarization beam splitter, 70 and 71 are two-split sensors, 72, 73 and 74 are differential amplifiers, and 75 is a phase compensator controller. The light beam from the laser 60 is expanded by a beam expander 61, split by a non-polarizing beam splitter 62, and further focused by a pickup lens 63 on a target 64 such as a silicon wafer or a reticle as a diffraction-limited spot. You. The spot is diffracted by edges of various shapes of the concavo-convex structure, and the diffracted wavefront is guided to the detection system via the pickup lens 63 and the non-polarizing beam splitter 62. on the other hand,
The reference wavefront is returned by the pickup lens 66 and the mirror 67, and transmits through the phase compensator 65 in a reciprocating manner. Accordingly, 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)
If, to correct the phase shift [delta] _o due to the optical path length difference and the optical element provides a diffractive wavefront from the object, a partial phase difference between the reference wavefront π phase correction as an integral multiple. Thus, when the edge is on the optical axis of the spot, the edge detection signal has the maximum amplitude. In other words, 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 embodiment is not limited to the height of the step and the edge shape. However, the uneven pits recorded as data on the optical disc, as in the above-described embodiment, are almost constant in step height and shape, and can be dealt with by a phase compensator fixed in accordance therewith. . However, in the present embodiment of FIG. 14, the height and shape of the edge of the object 64 are not always constant. Thus, in the present embodiment, a position detecting device adapted to various edge heights and shapes is provided by analyzing a detected edge detection signal and providing a phase compensator optimized for the edge. 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. This peak value is compared with a preset value, and the amount of compensation of the phase compensator 65 is fed back based on the error signal, thereby performing control to increase the peak value. At that time, in order to detect the direction of the compensation amount of the correction, the maximum frequency f _c of the edge position detection, with 10 times the frequency f _w hopefully small amount the phase compensation amount, wobbling control a band of f _w detecting an error signal, where for controlling the phase compensation amount in the band of f _c, it is desirable to employ the wobbling method. In addition,
To control the amount of compensation of the phase compensator 65, a method based on the tilt and rotation of the compensator 65 is used. However, the present invention is not limited to any means. Various means, such as the used refractive index control, 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 it does not correspond to the phase shift δ _d due to diffraction, a single height without an edge of a symmetric object or a position between phase regions is used. Considering only the phase difference, increasing the difference in the interference intensity between the plurality of states, and only had 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, By utilizing the phenomenon of positive and negative modulation around the phase of the single region, the quality of the edge detection signal is dramatically improved by optimizing the intensity of the combined interference of the diffracted wavefront by the edge. As a result, high reliability of the position detecting device can be realized.

FIG. 15 shows still another embodiment of the present invention. Here, the present invention is applied to an encoder using a holographic phase grating. 14, reference numerals 60 and 61 denote the same laser and expander as those shown in the embodiment of FIG. 14, 80 denotes a λ / 2 plate for rotating polarization by 45 degrees, 81 denotes a polarization beam splitter, 82 denotes a phase compensator, 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 polarized light.
Λ / 2 plate rotated by 0 degree, 90 and 91 are sensor lenses,
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 diffracted by the edge of the phase grating 86 is guided to the beam splitter 88 by the pickup lens 87, and multiplexes 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 due to diffraction of the phase grating 86, a phase shift caused by an optical path length difference from the S-polarized light, and a phase shift caused by reflection of an optical element. total δ phase correcting of _o, the sensor 92 of the re-imaging plane of,
Phase compensation is performed by the phase compensating plate 82 so that the phase difference of the light from the S-polarized light side on 93 becomes partially an integral multiple of π. The reflected light transmitted through the polarization beam splitter 81 is converted into S-polarized light by a λ / 2 plate 89 via a mirror 83, and is combined with S-polarized light, which is a diffracted wave from a phase grating 86, by a beam splitter 88. Is done. In this case, the beam splitter 88 has a film in which the reflected light of the S-polarized light causes a phase shift of πrad with respect to the transmitted light when reflected, so that the two emitted lights of the beam splitter 88 are , The combined interference waves are shifted in relative phase by π, and a differential detection configuration is realized. Sensors 92 and 93
The wavefront of the re-imaging plane of the diffracted wavefront by the above phase grating is shown in FIG.
0 and the phase shifted by π. This is also the case where the phase difference at the edge of the phase grating 86 is an integral multiple of π, as in the previous embodiment. As described above, the application of the present invention is not impossible due to the phase difference of the grating 86. As described above, conventionally, when the grating pitch of the encoder is reduced and the resolution is increased, the signal quality is deteriorated due to the light diffraction phenomenon,
Although high resolution cannot be achieved, according to the present invention, a high resolution encoder can be realized by positively utilizing the edge diffraction phenomenon.

Next, the processing of the edge detection signal waveform obtained according to the present invention will be described. FIG. 16 is a schematic block diagram for explaining signal processing. Here, reference numeral 10
Reference numeral 6 denotes an input terminal of an edge detection signal obtained in the above-described plurality of embodiments, 100 denotes a differentiating circuit, 101 and 102 denote window circuits I and II of an upward waveform, and 103 and 104 denote windows of respective window circuits. The corresponding comparators I, II, and 105 are multiplexing circuits that perform an operation by ORing the pulse trains. FIG. 17 is a schematic diagram of the waveform in each case.

FIG. 17A shows an edge detection signal.
An upward pulse and a downward pulse are generated at the edge portion. If the edge interval is large, the pulse becomes an isolated pulse. If the edge interval is small, the pulse becomes a sinusoidal connection pulse. Undergoes deformation such as becoming smaller. From the edge detection signal, window waveforms (b) and (c) corresponding to an upward pulse and a downward pulse are obtained by window circuits 101 and 102 whose thresholds are set to positive and negative, respectively. The window width becomes smaller as the edges become denser than in the case of an isolated pulse. On the other hand, a differentiating waveform (d) is obtained by the differentiating circuit 100, and an S-shaped pattern that crosses zero at each edge is obtained. Using the upward and downward window waveforms (b) and (c), the comparators 103 and 104 detect the zero cross point of the edge from the differential waveform (d), and a one-shot pulse train ( e) and (f) are obtained. This pulse train is synthesized again by the multiplexing circuit 105, and for example,
As shown in (g) of FIG.
A waveform in which H is inverted is obtained, and the edge position is detected.

In the above embodiments, the present invention has been described for the case where the present invention is applied to an apparatus for a different purpose. However, as described above, the edge receiving diffraction depends on the difference in the refractive index. Even if the phase difference is not 0, and the phase difference is not 0, the diffracted wavefront is modulated and the phase distribution changes.
In principle, detection according to the invention is possible. Therefore, it goes without saying that, for example, the grating of the embodiment in FIG. Examples of the information represented by such a phase edge include digital data in an optical memory and position data in an encoder. However, the present invention is not particularly limited to this, and analog data, two-dimensional image data, and the like are not limited thereto. The present invention can be applied to detection. For example, in the embodiment shown in FIG. 11, it is possible to target image data by performing two-dimensional 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. However, the place where the change of the diffracted wavefront is captured is not limited to these two points. However, the present invention can be implemented even in a convergent or divergent light beam. Naturally, this is not a concept of the present invention that the sensor is a two-part sensor, but corrects the phase distribution including diffraction, emphasizes the non-uniformity of the interference intensity distribution, and detects the non-uniformity. As the simplest means, an example in which asymmetry is detected by a difference between two-divided sensors has been described. Therefore, it is also possible to employ an optimal space division method for detecting non-uniformity, and in a detection method for calculating an output from a sensor unit having 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-segment sensor, and the interference fringe intensity distribution and the imaged spot are captured as a two-dimensional image, and the change in the intensity distribution is captured by combining various image processing, edge position, depth, etc. Can be obtained.

[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 the 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 the 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 diagram of a phase compensator.

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

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

FIG. 10 is also an explanatory view of a diffraction pattern.

FIG. 11 is also an embodiment of an optical disk recording / reproducing apparatus.

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

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

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

FIG. 15 is an embodiment 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 compensator 9 magneto-optical disk 42 optical disk 64 silicon wafer 86 holographic grating

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Matsumura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-6-96448 (JP, A) JP-A-6 -111406 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01B 11/00

Claims (3)

(57) [Claims] 1. An optical detection device for irradiating a laser beam onto a phase object, guiding reflected light / transmitted light from the phase object to a photodetector, and detecting an attribute of the phase object. The diffracted wavefront is multiplexed and interfered with the reference wavefront, and the obtained interference intensity distribution is configured to be detected by the photodetector.Phase modulation due to the polarization characteristics of the phase object, Having a phase compensator for making the relative phase difference between the total phase by superposition of the spatial phase modulation by the diffracted wavefront and the phase of the reference wavefront, in a spatial partial region, an integral multiple of substantially π. An optical detection device characterized by: 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 overall phase is a Kerr component phase, and the reference wavefront is a Fresnel component.