JP2002056552A - Positional signal detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect with high precision a relative positional error between an image forming surface of a hologram and a two-dimensional photodetector without detecting a positional deviation using complicated pattern matching. SOLUTION: A spot (bright spot) α is formed on the image forming surface 2 by light 6 diffracted from a disk shaped area 4 on the surface 1 of the hologram by waveguide light within a single mode plane type optical waveguide, and simultaneously a spot β is formed on the image forming surface 2 by light 7 diffracted from a disk shaped area 5 on the surface 1 of the hologram. Both spots are closely positioned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position signal detecting device, and more particularly, to diffracting guided light guided through a single-mode planar optical waveguide by a diffraction means, and forming an image based on the diffracted light on a predetermined image plane. The present invention relates to an apparatus for detecting a position signal of a read-only storage medium for imaging. INDUSTRIAL APPLICABILITY The position signal detecting device according to the present invention can be suitably used for a digital optical information storage medium and an optical information reproducing device, and is easily stored as a portable memory card such as a magnetic card or an IC card. It can be used for reading media.

[0002]

2. Description of the Related Art In a single-mode planar waveguide, minute irregularities are formed at the boundary between a core and a clad, and guided by the minute irregularities, a guided light is diffracted in the normal direction of the waveguide layer so that an arbitrary wavefront is formed outside the waveguide. The technique for extracting the light from the light source is known as waveguide holography, and a desired image can be obtained on an image forming surface outside the waveguide by adjusting the number, size, and position of minute irregularities. A collection of minute irregularities formed so as to form a target wavefront in the planar waveguide is called a waveguide hologram.

When holography is classified into volume holography and thin film holography, waveguide holography is classified into thin film holography. However, laminated waveguide holography, in which waveguides with waveguide holograms are laminated, can be used as a large-capacity optical memory because a three-dimensional area can be used as a recording area while being a thin-film holography. (JP-A-11-3454
No. 19, title of invention "reproduction-only hologram information storage medium").

[0004] Thin-film holography is superior to volume holography in that the tolerance for wavelength errors of light sources, thermal expansion of storage media, and fabrication errors is large. This is because the Bragg condition, which is a diffraction condition of the volume holography, is not imposed on the thin film holography, and only the Ramannas condition, which is much less severe, is imposed. In other words, if there is a wavelength error in use or expansion and contraction of the storage medium, diffraction itself does not occur in volume holography, but in thin film holography, the imaging position changes, but at least diffraction occurs. I do.

Accordingly, for example, as shown in FIG. 13, a two-dimensional optical detector 132 for detecting an image pattern formed by the waveguide hologram 130 is provided with a moving mechanism for following a change in the image forming position. It is possible to use an inexpensive semiconductor laser with a difference, and to use a plastic material having a large thermal expansion coefficient but excellent in mass productivity as a storage medium (waveguide hologram). These two requirements are essential for a read-only storage medium that is required to be inexpensive.

Therefore, as schematically shown in FIG. 13, a two-dimensional photodetector 13 such as a CCD is mounted around three axes x, y and z.
2 is provided with a servo mechanism (not shown) for controlling the movement by rotating 2, detecting the initial state of the imaging pattern (reproduced image) 134 formed by the waveguide hologram 130 with mechanical precision, and detecting the position of the detected imaging pattern 134. Two-dimensional light detector 1 for change
By following 32 and matching pixels on the image plane, an inexpensive semiconductor laser is used although there is an individual difference in oscillation wavelength, and a plastic material with a large coefficient of thermal expansion but excellent in mass productivity is stored. Medium (waveguide hologram)
It can be used as. These two requirements are essential for a read-only storage medium requiring low cost. In FIG. 13, に お け る and ● of the image forming pattern 134 schematically show examples of distribution of minute unevenness.

Here, in order for the two-dimensional optical detector to follow the change in the imaging position, it is necessary to first detect the positional deviation between the imaging plane of the two-dimensional optical detector and the imaging pattern. Conventionally, a method of embedding a position signal pattern in an image forming pattern and detecting how much the position signal pattern deviates from a predetermined position on an image forming plane has been adopted for this position shift detection. I have.

[0008]

However, in the above-mentioned conventional method, it is not possible to detect a positional shift accompanying a change in the distance between the hologram surface and the imaging surface. That is, there is a problem that it is not possible to detect a change in the focal length and a tilt of the hologram surface with respect to the two-dimensional light detector surface. In addition, although parallel movement on the image plane can be detected,
The detection by the pattern recognition processing requires a photodetector having a large number of pixels to detect the position shift signal, and the pattern recognition processing requires complicated calculations, making it difficult to reduce the cost, and There is a problem that the processing time becomes enormous. Further, since processing time is required, feedback responsiveness is poor, and focus servo in a vibration environment has not been practically possible.

An object of the present invention is to provide a position detecting device which can solve the above-mentioned problems with a simple configuration and can perform position detection with high accuracy. With this device, optical information is detected by a two-dimensional light detector as a two-dimensional light intensity pattern, that is, image information, and a positional shift required to perform a servo for correcting a positional shift between the optical detector and the optical information pattern. The signal can be detected.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for diffracting guided light guided in a single-mode planar optical waveguide by a diffraction means, and forming an image by the diffracted light into a predetermined image. In the position signal detecting device for a read-only storage medium for forming an image on an image plane, the diffracting means may be configured to diffract the diffracted light from a first area inside the image forming apparatus into another image whose relative position to the predetermined image forming plane is known. Incident on the surface at a predetermined incident angle to form a first spot at a predetermined position on the different imaging surface, and diffracts light from a second region including a region different from the first region into the predetermined incident surface. A second spot at a position near the first spot by being incident on the another imaging plane at an incident angle different from the angle, and forming the second spot at a position near the first spot. An optical detector for detecting a position; It was performed position signal detector arrangement that includes a detection means for detecting a position relative to the predetermined imaging plane of the further image plane according to the position of the second spot spare.

In the above configuration, the diffraction means is formed on the another image forming surface so as to form a plurality of the first and second spots. The light detector is a four-divided light detector. Detecting means for detecting the position in accordance with the amount of light received by the first and second spots in each of the detection areas; and moving the single-mode planar optical waveguide in a direction substantially perpendicular to the guiding direction of the guided light. A plurality of layers are stacked, and a line passing through a center position of the first region and a center position of the second region is on a line where a diffraction surface of the diffraction means and another surface are orthogonal to each other, and A line passing through the position of the center of gravity of the spot and the position of the center of gravity of the second spot may be substantially orthogonal to the another plane.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (One Embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. First, the operating principle of the device of the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram for explaining a method of creating a pattern sensitive to a change in the focal position using a hologram. Reference numeral 1 denotes a hologram in a single-mode planar optical waveguide (not shown), and reference numeral 2 denotes an imaging surface (imaging surface). The image plane 2 ideally coincides with the image plane of a two-dimensional photodetector such as a CCD image sensor.

FIG. 2 shows the relationship between the two-dimensional photodetector and the hologram. Hereinafter, the operation of the hologram 1 shown in FIG. 1 will be described using the vector representation in the three-dimensional coordinate system shown in FIG. Two-dimensional photo detector 2
0 is located on the yz plane and faces the hologram 1.

The light 6 diffracted from the disc-shaped region 4 on the hologram surface 1 by the guided light in the single-mode planar optical waveguide forms a bright spot α on the imaging surface 2 and at the same time. A hologram is formed by electron beam lithography or a stamper so that the light 7 diffracted from the disk-shaped region 5 on the hologram surface 1 forms a spot β on the imaging surface 2. For the sake of simplicity, the radius of the region 4 and the radius of the region 5 are R. A part of both regions overlap but mainly have different regions. Also, here, a single spot is condensed from both regions, but a hologram may be created so as to create a plurality of spots.

The coordinates of the centers O ₁ and O ₂ of the regions 4 and 5 are respectively

[0016]

[Outside 1]

The spots α and β are located near each other, and are schematically shown here as circular. The spots α and β are at most a few μm in size, but the shapes need not be circular because the center of gravity of the light intensity distribution of the spots α and β may be detected. Diffracted light 6 on the focal plane (imaging plane) 2
The coordinates of the center of gravity on the focal plane 2 of the light intensity distribution of the spots α and β designed to focus

[0018]

[Outside 2]

However, the difference between the positions of the centers of gravity on the focal plane 2 is sufficiently smaller than the difference between the positions of the centers O ₁ and O ₂ on the hologram plane 1. That is,

[0020]

(Equation 1)

Assume that

Now, the position of the center of gravity of the diffracted light 6 forming the spot α is

[0023]

[Outside 3]

Therefore, assuming that these spots α and β are received at a position (distance f + δf) shifted by δf near the focal plane 2 at the designed focal distance f, the center of gravity of each spot α and β

[0025]

[Outside 4]

[0026]

(Equation 2)

[0027]

[Outside 5]

[0028]

(Equation 3)

Is given by However, the difference between the centers of gravity of the spots α and β on the focal plane 2 is sufficiently smaller than the difference between the coordinates of the centers O ₁ and O ₂ of the regions 4 and 5 on the hologram 1 plane.

[0030]

(Equation 4)

It is assumed that Therefore, if Expression (1) is satisfied and the two spots α and β are in a range where they do not overlap, from Expression (6), the relative displacement between the two spots α and β due to the focus error can be calculated as Displacement on the hologram surface 1 regardless of the position

[0032]

[Outside 6]

[0033]

[Outside 7]

That is, when the vector of the position shift on the focal plane 2 and the vector of the position shift on the hologram plane 1 are oriented in the same direction, or antiparallel, the vector of the position shift on the focal plane 2 and the hologram plane 1 If the top misalignment vector is pointing 180 degrees in the opposite direction,

[0035]

(Equation 5)

Is satisfied, the spot α and the spot β
There is no danger of getting confused. Therefore, spots α, β
By measuring the distance between the positions of the center of gravity, the defocus amount δ
By obtaining f, a focus error signal can be obtained as described later.

[0037]

[Outside 8]

It can be seen that, if is sufficiently larger than the spot size, the defocus amount can be calculated without mistaking the spots. Here, orthogonal is defined as hologram surface 1
Assuming a plane perpendicular to the hologram surface 1 (not shown), when both surfaces have a displacement vector on the hologram surface 1 on a line perpendicular to each other, the plane perpendicular to the hologram surface 1 This means that the displacement vectors are orthogonal.

The size of the spots α and β is about λf / R where λ is the wavelength of light, so that λ = 680 nm
in the case of,

[0040]

[Outside 9]

[0041]

[Outside 10]

The basic principle of operation in the case where a pair of spots are formed as servo marks only at one location on the light receiving surface has been described. In this case, it is only possible to observe the defocus in the vicinity where the spot pair forms an image. However, by disposing three or more similar spot pairs in the focal plane (a plurality of pairs other than the above one pair), , The position of the two-dimensional photodetector can be detected by judging the amount of movement in all six degrees of freedom. As shown in FIG. 2, the six degrees of freedom means three degrees of freedom for translation of the two-dimensional photodetector 20 in the x, y, and z axes, and rotation in the xy plane (θ) about the z axis as the center of rotation.
1 degree of freedom, rotation in the xz plane around the y axis (φ)
And one degree of freedom for rotation in the yz-plane rotation (ψ) about the x-axis as the center of rotation.

If the above-mentioned spot pairs are formed at three different positions facing the hologram surface and not on one straight line, and if the positional relationship between the plane determined by these three spot pairs and the focal plane is known, in principle, , All degrees of freedom (x, y, z, θ,
φ, ψ) can be determined. Hereinafter, a simple method of forming a four-spot pair and performing position detection using four quadrant photodetectors arranged at predetermined positions with respect to the focal plane will be described.

FIG. 3 shows, by way of example, a four-segment photodetector for position detection which is arranged substantially on the same plane as the image-forming plane, and which is projected onto the hologram plane. Hereinafter, description will be made with reference to this projection view and the projection view of FIG. 4. It is assumed that the four-segmented photodetector is substantially on the same plane as the imaging plane, and the distance from the hologram plane is substantially equal to the focal length f. About this,
It will not be mentioned further hereafter.

The four-divided photodetectors A, B, C, and D are arranged near the vertices of the hologram surface 2 on the projection view. The four light receiving sections of each quadrant detector are represented by lowercase letters a, b, c, and d, respectively. A, b, c, d are z
For example, the names of the light receiving sections of the four-segment photodetector B and the four-segment photodetector A, which are at the same position when the four-segment photodetector A is rotated 90 degrees counterclockwise around the axis 30 as the center of rotation, are matched. It is.
The names of the photodetectors of the quadrant photodetector C when rotated further by 90 degrees and the names of the photodetectors of the quadrant photodetector D when rotated further by 180 degrees correspond to the names.

In order to indicate a specific light receiving section of a specific quadrant detector, the main characters are indicated by the photo detector name and the subscripts are indicated by the light receiving section name, and the light receiving section m of the photo detector X is indicated.
If it referred to as X _m.

Each of the four-divided photodetectors A,
The spots focused on B, C, and D are diffracted from the four disc-shaped regions 35, 36, 37, and 38 on the hologram surface 2. This situation is shown in FIG. 4 focusing on the four-segment photodetector A.

The spots focused on the four-divided photodetector A are one pair diffracted from the area 37 and one spot diffracted from the area 37. However, when focusing, the area 35
Spotted 45 position its center of gravity at the boundary of the light receiving portion A _d and the light-receiving unit A _c from, the spot 44 from the region 37 the hologram so that the center of gravity at the boundary of the light receiving portion A _b and the light-receiving unit A _a is located Is designed. At this time, the center O of the region 37
Vector, spot 4 connecting the center O _{A C} and region 35
It is orthogonal to the vector connecting the centers of gravity of 4,45.

To other four-segment photodetectors B, C, and D
Is also condensed in the same manner as above, and the light receiving portion B_c
And light receiving section B_dThe spot whose center of gravity is located at the boundary of
Optical part B _aAnd light receiving section B_bSpot whose center of gravity is located at the boundary of
The photodetector B to the four-segment photodetector B_cAnd light receiving section
C_dSpot whose center of gravity is located at the boundary of_aWhen
Light receiving section C_bThe spot where the center of gravity is located at the boundary of is 4 minutes
The photodetector C and the photodetector D_cAnd light receiving section D_dBoundary
Where the center of gravity is located and the light receiving section D_aAnd light receiving section D_b
The spot whose center of gravity is located at the boundary of
The light is focused on each of the detectors D (not shown).

That is, in FIG. 3, from the region 35 to the four-divided photodetectors A and C, from the region 36 to the four-divided photodetectors B and D, from the region 37 to the four-divided photodetectors A and C, and from the region 38 to the four-divided photodetectors A and C. A hologram is designed so that light is diffracted (not shown) into the split photodetectors B and D, respectively.

FIGS. 5 to 8 show how spot positions change on the four-divided photodetectors when a positional shift such as a focus shift or an in-focus plane shift occurs. FIG.
6 shows a four-divided photodetector A, FIG. 6 shows a four-divided photodetector region B, FIG. 7 shows a four-divided photodetector C, and FIG.
Are shown according to the displacement modes (A) to (I).

As the modes of the positional deviation, in addition to those shown in (A) to (I), those obtained by combining the reverse shift of the x-axis, the reverse shift of the y-axis, and the shifts of both the x and y axes. is there. All of the above aspects occur independently for each photodetector.

For example, when there is no angular displacement (rotation about each axis of θ, φ, ψ), no in-plane shift (x, y), and only the focus position is far (only a shift in the z-axis direction occurs),
Since all the spots are shifted away from the center of the hologram, FIGS. 5B, 6B, 7B, and 8
The aspect of (B) does not occur simultaneously. In this case, for example, with the 4-split photodetector A alone, the light distribution (combination of FIGS. 5E and 5H) classified as being farther from the focus and shifted in the −x direction and the −y direction is obtained. To be observed.

[0054] Therefore, in order to separate and detect the six degrees of freedom, the signal intensity from the light receiving portion X _m described as P _{X m,} performs a calculation as shown below. This operation is only addition and subtraction of an analog amount, and can be performed by an addition circuit, a subtraction circuit (not shown) or the like without using a CPU. The load on these circuits is small, and the operation can be performed in a short time. There is.
Further, the apparatus can be configured at low cost.

[0055]

[6] _{F A = (P Ab + P} Ad) - (P Aa + P Ac) (7) F B = (P Bb + P Bd) - (P Ba + P Bc) (8) F C = (P Cb + P Cd _{) - (P Ca + P Cc} ) (9) F D = (P Db + P Dd) - (P Da + P Dc) (10) T A = (P Aa + P Ab) - (P Ac + P Ad) (11) T _{B = (P Ba + P Bb} ) - (P Bc + P Bd) (12) T C = (P Ca + P Cb) - (P Cc + P Cd) (13) T D = (P Da + P Db) - (P Dc _{+ P Dd) (14) R} A = (P Ab + P Ac) - (P Aa + P Ad) (15) R B = (P Bb + P Bc) - (P Ba + P Bd) (16) R C = (P Cb _{+ P Cc) - (P Ca} + P Cd) (17) R D = (P Db + P Dc) - (P Da + P Dd) (18) E θ = -T A -T B -T C -T D (19) _{E φ = (F B + F} C) - (F A + F D) (20) E ψ = (F A + F B) - (F C + F D) (21) _{z = F A + F B +} F C + F D (22) E x = (R B + R C) - (R A + R D) (23) E y = (R C + R D) - (R A + R B) (24 )

In the above calculation, the equations (7) to (10)
Represents a focus signal, equations (11) to (14) represent a tangential shift signal, and equations (15) to (18) represent a radial shift signal. Equations (19) to (19)
By calculating (24), it is possible to obtain an error signal that independently represents a positional shift of six degrees of freedom by using these equations.

In the coordinate system shown in FIG. 2, E _θ is a rotation error signal in the θ direction, and E _φ is a rotation error (tilt) in the φ direction.
Signal, the E _[psi is rotation error (tilt) signal [psi direction.
E _x translational position shift signal in the x-axis direction, E _y translational positional displacement signal y-axis direction, E _z is the z-axis direction of the translational position deviation signal,
That is, it is a focus error signal. The sign of the rotation direction is determined by a right-handed system with respect to each axis. For example, θ is the amount of rotation around the z-axis, but when the z-axis is viewed from the positive direction to the negative direction, the direction is counterclockwise. Is positive, and the clockwise rotation is negative.

Each of the position shift signals or error signals is shifted in the positive direction of each axis when the numerical value is large. Therefore, by using a servo mechanism (not shown) for controlling the movement of the two-dimensional photodetector 20 and applying a feedback servo to make the value of each signal 0 according to the above calculation result, the image forming surface of the two-dimensional photodetector 20 is formed. 2, real-time pixel matching can be performed.

(Modification) As shown in FIG. 9, a plurality of waveguide holograms formed so as to detect the above-described displacement signal or error signal can be stacked.

In FIG. 9, a reproduction-only multiplex hologram memory 90 has a laminated single mode having a periodic layer structure such as a cladding 91-1, a core 92-1, a cladding 91-2, a core 92-2,. The waveguide hologram is made in a planar waveguide. A reflection surface 93 is provided on the end face of the stacked planar waveguide, and forms an angle of 45 ° with a direction perpendicular to the waveguide plane. For example, a laser beam 95 is incident on a reflection surface 93 via a convex lens 94, and is reflected at a reflection point 96.
Propagates the guided light 97 from.

A spot pair is formed as a servo mark on each of the four-divided photodetectors 90A, 90B, 90C, and 90D by the diffracted light 99 diffracted at the uneven portion 98 formed at the boundary between the core layer and the clad layer.

The read-only multiplex hologram memory 90 has a core layer laminated thereon, and requires a finite time when light incident on the waveguide layer jumps between the waveguide layers. Therefore, when the safety against the vibration of the reproducing apparatus is not guaranteed within the time of the interlayer jump, the servo mark is superimposed on the image so that the two-dimensional displacement signal of the above embodiment can be obtained from each waveguide hologram. By doing so, it is possible to quickly recover from the displacement caused by the vibration.

[0063]

(Embodiment 1) A description will be given of the result of forming a servo mark for confirming the operation principle of the present invention and detecting a spot displacement. As shown in FIG. 10, the parameters at the time of the experiment are f = 4 mm, and a spot pair having five spots as one unit by the diffracted light from the regions 100 and 105 on the hologram surface is used as a servo mark on the imaging surface. At this time, ftanθ is 0.5 μm and 0.83
It was set to 3.

The displacement Δd of the servo mark is

[0065]

Δd = (δf / f) × (0.833−0.5) = 0.08325δf (25)

And is proportional to δf.

At the time of focusing at δf = 0, a servo mark is detected by a position detecting photodetector (not shown) as shown in FIG. 11A (FIG. 10 schematically shows a detected image). Is). Here, a spot 110 by one area and a spot 11 by another area
1 are arranged in a straight line. As δf increases, the displacement between the spot 110 and the spot 111 increases (FIGS. 11 (B) → (C) → (D) and (E) →).
(F) → (G)), with a 120 μm defocus, equation (25)
About 10 with respect to the theoretical value Δd = 9.99 μm calculated by
μm could be detected.

(Embodiment 2) In order to implement the apparatus of the present invention, the relative positional relationship between the imaging surface (light receiving surface) and the photodetector for positional displacement signals needs to be accurately known as described above. is there. Therefore, in the present embodiment, as shown in FIG. 12, four-division photodetectors 120A, 120A are provided at diagonal portions in the data receiving portion 121 of the CMOS image sensor 120.
B, 120C, and 120D were implemented. Accordingly, the four-divided photodetectors are arranged in the plane of the light receiving unit 121, and the relative positions of the four-divided photodetectors can be easily known from the dimensions of the light receiving unit 121.

Here, the data light receiving section 121 has a pixel pitch of 5 μm and forms 1024 × 1024 square pixels. That is, the size of the data receiving unit 121 is
It is a square with a side of 5.12 mm. Four-division photodetectors 120A and 120
B, 120C and 120D are arranged, and the size is 7 μm.
× 7 μm. The division form is the same as described above.

The distance between the hologram surface 122 and the CMOS image sensor 120 is 5 mm, and the waveguide hologram 123
Was 5 mm × 5 mm. The wavelength of the light source is 680
nm. Radius on hologram surface 122
The waveguide hologram 123 is designed so that a spot pair having a size of about 3 μm is formed on each of the four divided photodetectors by diffracting from a 25 mm disc-shaped area (not shown), and the distance between the spot centroids is about 5 μm. did.

Using the above configuration, 10 mW light was coupled to the waveguide hologram 123 so that the light intensity of the spot on each of the four divided photodetectors was about 0.1 μW. The light intensity received by each pixel of the data light receiving unit 121 is about 100 pW. By condensing a spot having a significantly higher optical power on each of the four divided photodetectors, the detection signal can be obtained in a short time. Enabled sampling.

Accordingly, based on the detection signal thus obtained, the arithmetic unit 124 performs high-speed arithmetic operation according to the equations (7 to 24) as described above to calculate a position shift signal. By performing position control of the CMOS image sensor 120 with six degrees of freedom, it is possible to obtain a result substantially in accordance with the theory.

[0073]

As described above, according to the signal detection apparatus of the present invention, the relative position error between the hologram image plane and the two-dimensional photodetector can be eliminated without the necessity of performing position shift detection using complicated pattern matching. Can be detected with high accuracy. By applying this position shift detecting device to a holographic memory, it is possible to access a page of a predetermined hologram at high speed, and to improve a transfer speed, thereby enabling focus servo in a vibration environment. be able to. Further, since a position shift signal can be generated only by addition and subtraction, a low-cost device using a simple electric circuit can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a method for creating a pattern sensitive to a change in a focal position by the apparatus of the present invention.

FIG. 2 is a perspective view showing a coordinate system for explaining a relationship between a hologram surface and a two-dimensional photodetector surface in one embodiment of the position signal detection device according to the present invention.

FIG. 3 is a projection view showing an arrangement of a four-segment photodetector for measuring a positional shift of a two-dimensional photodetector with six degrees of freedom in the apparatus of the present invention.

FIG. 4 is a projection view for explaining a method of condensing light on one quadrant photodetector.

FIG. 5 is an explanatory diagram illustrating an example of a change in a spot position in a four-segment photodetector due to a displacement of a two-dimensional photodetector.

FIG. 6 is an explanatory diagram showing another example of a change in a spot position in another four-segmented photodetector due to a displacement of a two-dimensional photodetector.

FIG. 7 is an explanatory diagram showing another example of a change in spot position in another four-segmented photodetector due to a displacement of the two-dimensional photodetector.

FIG. 8 is an explanatory diagram showing another example of a change in a spot position in another four-segmented photodetector due to a displacement of the two-dimensional photodetector.

FIG. 9 is a diagram showing another embodiment of the position signal detecting device according to the present invention.

FIG. 10 is an explanatory diagram illustrating servo mark experimental conditions for confirming the operation principle of the present invention.

FIG. 11 is a diagram schematically showing a servo mark experiment result.

FIG. 12 is a diagram schematically showing an embodiment of a position signal detecting device according to the present invention.

FIG. 13 is an explanatory diagram illustrating an example of a conventional technique.

[Explanation of symbols]

Reference Signs List 1 hologram 2 imaging plane 4, 5, 35, 36, 37, 38, 100, 105 disk-shaped area 6, 7 diffracted light 90 reproduction-only multiplex hologram memory 90A, 90B, 90C, 90D, 120A, 120
B, 120C, 120D, A, B, C, D Quadrant photodetector α, β, 110, 111 Spot 120 CMOS image sensor 121 Light receiving unit 122 Hologram surface 123 Waveguide hologram 124 Operation unit 125 Servo mechanism

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Yoshiaki Kurokawa, Inventor 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Takaya Tanabe 2-3-3, Otemachi, Chiyoda-ku, Tokyo No. 1 Inside Nippon Telegraph and Telephone Corporation (72) Akiyuki Tate 2-3-0 Otemachi, Chiyoda-ku, Tokyo F-term within Nippon Telegraph and Telephone Corporation (reference) 2H049 CA01 CA04 CA05 CA08 CA15 CA17 CA20 CA22 CA28 5D090 AA03 BB02 CC04 CC16 DD03 FF02 GG22 HH01 LL05 5D118 AA06 BA06 BB01 BF02 CC06 CC15 CD03 CF06 5D119 AA28 AA38 BA02 DA05 EA02 KA02 KA03 KA08 KA19 KA24

Claims (5)

[Claims] 1. A position signal detecting device for a read-only storage medium for diffracting guided light guided in a single-mode planar optical waveguide by a diffraction means and forming an image based on the diffracted light on a predetermined image plane. The diffracting means causes diffracted light from a first area inside the diffracted light to enter a different imaging plane whose relative position to the predetermined imaging plane is known at a predetermined incident angle, and A first spot is formed at a predetermined position, and diffracted light from a second region including a region different from the first region is incident on the another imaging plane at an incident angle different from the predetermined incident angle. An optical detector configured to form a second spot at a position near the first spot, an optical detector for detecting the positions of the first spot and the second spot, and the detected first and second spots. 2 according to the position of the spot. A position signal detection device comprising: a detection unit configured to detect a position with respect to the predetermined imaging plane. 2. The position signal detecting device according to claim 1, wherein said diffracting means is formed on said another image forming plane so as to further form a plurality of said first and second spots. Position signal detecting device. 3. The position signal detection device according to claim 1, wherein the light detector is a four-divided light detector, and the light detector is configured to receive the first and second spots in each of the divided detection areas. A position signal detection device, wherein a detection unit performs the position detection. 4. The position signal detecting device according to claim 1, wherein a plurality of said single-mode planar optical waveguides are stacked in a direction substantially perpendicular to a guiding direction of said guided light. apparatus. 5. The position signal detection device according to claim 1, wherein a line passing through a center position of the first region and a center position of the second region is different from a diffraction surface of the diffraction unit. A position signal detection device, wherein a line on a line orthogonal to each other and passing through the barycentric position of the first spot and the barycentric position of the second spot is substantially orthogonal to the another surface.