JP3448266B2 - Position signal 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 position signal detecting device, and more particularly, to diffracting a guided light guided in a single mode plane type optical waveguide by a diffracting means and forming an image by the diffracted light on a predetermined image plane. The present invention relates to a position signal detecting device for a read-only storage medium for forming an image. 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 an optical information storage in the form of a portable memory card which is easy to carry like a magnetic card or an IC card. It can be used to read the medium.

[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 the minute irregularities diffract guided light in the direction normal to the waveguide layer to allow arbitrary wavefronts to exit the waveguide. The technique of taking out the optical waveguide is known as waveguide holography, and a desired image can be obtained on the image plane outside the waveguide by adjusting the number, size, and position of the minute irregularities. A set of minute irregularities formed so as to create a desired 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 laminated waveguide holograms are laminated can be used as a large-capacity optical memory because it can use a three-dimensional area as a recording area even though it is a thin-film holography. (JP-A-11-3454
No. 19, gazette of the invention, "reproduction-only multiplex hologram information storage medium").

The thin film holography is superior to the volume holography in that it has a large tolerance for the wavelength error of the light source, the thermal expansion of the storage medium, and the manufacturing error. This is because the Bragg condition, which is the diffraction condition of the volume holography, is not imposed on the thin-film holography, but only the Ramannas condition, which is much more gradual, is imposed. In other words, if there is an error in the wavelength used or the expansion / contraction of the storage medium, diffraction itself does not occur in volume holography, whereas in thin film holography, at least the diffraction occurs although the imaging position changes. To do.

Therefore, for example, as shown in FIG. 13, by providing a moving mechanism for causing the two-dimensional photodetector 132 for detecting the image formation pattern by the waveguide hologram 130 to follow the change of the image formation position, the oscillation wavelength can be adjusted individually. It is possible to use an inexpensive semiconductor laser, which has 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 requirements 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 centering on the three axes x, y and z is used.
A servo mechanism (not shown) for rotating 2 to control movement is provided, the initial state of the image formation pattern (reconstructed image) 134 by the waveguide hologram 130 is detected with mechanical accuracy, and the position of the detected image formation pattern 134 is detected. Two-dimensional photodetector for changes 1
By using 32 to track and perform pixel matching on the image plane, an inexpensive semiconductor laser with individual differences in oscillation wavelength is used, and a plastic material with a large thermal expansion coefficient but excellent mass productivity is stored. Medium (waveguide hologram)
Can be used as. These two requirements are essential requirements for a read-only storage medium that requires low cost. ◯ and ● of the image formation pattern 134 in FIG. 13 schematically show an example of distribution of minute unevenness.

Here, in order to make the two-dimensional photodetector follow the change of the imaging position, it is necessary to first detect the positional deviation between the imaging plane of the two-dimensional photodetector 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 the image forming surface has been adopted for detecting the position deviation. There is.

[0008]

However, with the above-mentioned conventional method, it is not possible to detect the positional deviation that accompanies the change in the distance between the hologram surface and the image plane. That is, there is a problem that it is not possible to detect the change in the focal length and the inclination of the hologram surface with respect to the two-dimensional photodetector surface. Also, although parallel movement in the image plane can be detected,
Since the detection is performed by the pattern recognition processing, an optical detector having a large number of pixels is required for detecting the positional deviation signal, and the pattern recognition processing requires complicated calculation, which makes cost reduction difficult, and There is a problem that the processing time becomes huge. Further, since it takes a long processing time, the response of feedback is poor, and focus servo in a vibrating environment is practically impossible.

An object of the present invention is to provide a position detecting device which can solve the above-mentioned problems with a simple structure and can detect a position with high accuracy. With this device, optical information is detected as a two-dimensional light intensity pattern, that is, by a two-dimensional photodetector as image information, and the positional deviation necessary for performing servo to correct the positional deviation between this optical detector and the optical information pattern. The signal can be detected.

[0010]

In order to achieve the above-mentioned object, the present invention diffracts guided light guided in a single mode planar optical waveguide by a diffracting means, and forms an image by the diffracted light in a predetermined manner. In the position signal detecting apparatus for the read-only storage medium for forming an image on the image plane, the diffracting means forms another image of the diffracted light from the first area inside the diffracting means whose relative position to the predetermined image forming surface is known. A first spot at a predetermined position on the other imaging surface by making the light incident on the surface at a predetermined incident angle, and diffracted light from a second region including a region different from the first region is incident on the predetermined spot. Is formed so as to form a second spot at a position in the vicinity of the first spot by being incident on the another image plane at an incident angle different from that of the first spot and the second spot. A photodetector for detecting a position, and the detected first detector 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 structure, the diffractive means is formed on the another image plane so as to form a plurality of the first and second spots, and the photodetector is a four-division photodetector and is divided. In addition, the detection means performs the position detection according to the amount of light received by the first and second spots in each detection region, and the single mode planar optical waveguide is placed in a direction substantially perpendicular to the waveguide direction of the guided light. A plurality of layers are laminated, and a line passing through the center position of the first region and the center position of the second region is on a line where the diffractive surface of the diffractive means and another surface are orthogonal to each other. 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 surface.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION (One Embodiment) One embodiment of the present invention will be described in detail below 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 forming a pattern that is sensitive to changes in the focal position by using a hologram. Reference numeral 1 denotes a hologram in a single mode planar optical waveguide (not shown), and 2 denotes an image plane (imaging plane). 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. The operation of the hologram 1 shown in FIG. 1 will be described below using the vector representation in the three-dimensional coordinate system shown in FIG. Two-dimensional photo detector 2
It is assumed that 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 spot (bright spot) α on the image plane 2 and at the same time. A hologram is created by electron beam drawing 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 image forming surface 2. For simplicity, the radius of each of the regions 4 and 5 is R. Part of both areas overlap, but have primarily different areas. Further, here, it is assumed that a single spot is condensed from both areas, but a hologram may be formed so as to form a plurality of spots.

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

[0016]

[Outer 1]

The spots α and β are located near each other, and are schematically shown here as circles. The spots α and β have a size of at most several μm, but the shape does not need to be circular because the position of the center of gravity of the light intensity distribution of the spots α and β can be detected. Diffracted light 6 on the focal plane (imaging plane) 2
The barycentric coordinates on the focal plane 2 of the light intensity distribution of the spots α and β designed to collect 7 are respectively

[0018]

[Outside 2]

However, the difference between the positions of both 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 surface 1. That is,

[0020]

[Equation 1]

Assume that

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

[0023]

[Outside 3]

Therefore, if these spots α and β are received at a position (distance f + δf) deviated by δf in the vicinity of the focal plane 2 at the designed focal length f, the barycentric position of each spot α and β is detected.

[0025]

[Outside 4]

[0026]

[Equation 2]

[0027]

[Outside 5]

[0028]

[Equation 3]

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

[0030]

[Equation 4]

It is assumed that Therefore, if the expression (1) is satisfied and the two spots α and β are in the range where they do not overlap, from the expression (6), the relative positional deviation of the two spots α and β due to the focus error is Position shift on hologram surface 1 regardless of

[0032]

[Outside 6]

[0033]

[Outside 7]

That is, when the vector of displacement on the focal plane 2 and the vector of displacement on the hologram surface 1 are oriented in the same direction, or antiparallel, the vector of displacement on the focal plane 2 and the hologram surface 1 are antiparallel. If the top misalignment vector points 180 degrees backwards,

[0035]

[Equation 5]

If is satisfied, spot α and spot β
There is no fear of mixing up. Therefore, the spots α, β
By measuring the distance between the center of gravity positions, the amount of defocus δ
It is possible to obtain f and obtain a focus error signal as described later.

[0037]

[Outside 8]

It is understood that if is larger than the spot size, the defocus amount can be calculated without confusing the spots with each other. Here, orthogonal means the hologram surface 1
When a plane (not shown) orthogonal to the hologram plane 1 is present on the line orthogonal to each other, and the vector of the positional deviation on the hologram plane 1 exists on the focal plane 2 with respect to the plane orthogonal to the hologram plane 1. It 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 λ = 680 nm.
in the case of,

[0040]

[Outside 9]

[0041]

[Outside 10]

The basic operation principle in the case of forming a pair of spots as servo marks only at one place on the light receiving surface has been described above. In this case, it is only possible to observe the defocus in the vicinity of the image formation of the spot pair, but by arranging three or more pairs (several pairs other than the above one pair) of similar spot pairs in the focal plane. , The position of the two-dimensional photodetector can be detected by determining the amount of movement in all six degrees of freedom. As shown in FIG. 2, 6 degrees of freedom means 3 degrees of freedom of translation of the two-dimensional photodetector 20 in the x, y, and z axial directions, and rotation in the xy plane (θ) about the z axis as a rotation center.
1 degree of freedom, rotation in the xz plane about the y-axis (φ)
And 1 degree of rotation of yz in-plane rotation (ψ) about the x-axis.

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

FIG. 3 shows, as an example, a four-division photodetector for position detection, which is arranged substantially on the same plane as the image plane and projected on the hologram plane. The following description will be given with reference to this projection view and the projection view of FIG. 4, but it is assumed that the four-division photodetector is substantially on the same plane as the image plane and the distance from the hologram plane is substantially equal to the focal length f. About this
I will not make any further mentions thereafter.

Now, four-divided photodetectors A, B, C and D are arranged near each vertex of the hologram surface 2 on the projection view. The four light receiving parts of each four-division detector are represented by small letters a, b, c, d, respectively. This a, b, c, d is z
For example, the names of the light receiving portions of the four-divided photodetector B and the four-divided photodetector A, which are in the same position when the four-divided photodetector A is rotated 90 degrees in the counterclockwise direction with the shaft 30 as the center of rotation, are attached so that the names thereof match. There is.
The names are attached so that when they are further rotated by 90 degrees, the respective light receiving portions of the four-divided photodetector C and the respective light receiving portions of the four-divided photodetector D are further rotated when rotated by 180 degrees.

In order to indicate a specific light receiving portion of a specific four-divided detector, the photodetector name is used as the main character and the light receiving portion name is used as the subscript, and the light receiving portion m of the photodetector X is indicated.
If so, it is written as X _m .

Each four-division photodetector A in FIG.
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 state is shown in FIG. 4 focusing on the 4-division photodetector A.

The spots focused on the four-divided photodetector A are a pair of spots diffracted by the area 37 and spots diffracted by the area 37. However, when focusing, the area 35
The spot 45 from the hologram has its center of gravity located at the boundary between the light receiving parts A _c and A _d , and the spot 44 from the region 37 has its center of gravity located at the boundary between the light receiving parts A _a and A _b. Is designed. At this time, the center O of the region 37
_The vector connecting _C and the center O _{A of the} area 35 is the spot 4
It is orthogonal to the vector connecting the centers of gravity of 4,45.

To other 4-division photo detectors B, C, D
Spots are also collected in the same manner as above, and the light receiving portion B_c
And the light receiving part B_dThe spot where the center of gravity is located
Light part B _aAnd the light receiving part B_bThe spot whose center of gravity is located at the boundary of
To the 4-division photodetector B and the light receiving part C_cAnd light receiver
C_dThe spot where the center of gravity is located at the boundary of_aWhen
Light receiving part C_bThe spot where the center of gravity is located at the boundary of 4 minutes
The photodetector C and the light receiving part D_cAnd the light receiving part D_dBoundaries of
At the spot where the center of gravity is located and the light receiving part D_aAnd the light receiving part D_b
The spot whose center of gravity is located at the boundary of the
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 four. Holograms are designed so that the split photodetectors B and D respectively diffract light (not shown).

FIGS. 5 to 8 show how the position of the spot changes on each of the four-divided photodetectors when a position shift occurs such as a focus shift or a focal plane shift. Figure 5
Is for a 4-part photodetector A, FIG. 6 is for a 4-part photodetector region B, FIG. 7 is for a 4-part photodetector C, and FIG. 8 is for a 4-part photodetector D.
Is shown according to the mode (A) to (I) of the positional deviation.

In addition to the modes shown in (A) to (I), the position shift mode includes a reverse shift of the x axis, a reverse shift of the y axis, and a combination of these shifts in 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 deviation (rotation about the axes of θ, φ, and ψ), there is no in-plane shift (x, y), and only the focus position is far (only the z-axis direction shift occurs),
Since all the spots are displaced from the center of the hologram in the direction away from each other, the spots shown in FIGS. 5 (B), 6 (B), 7 (B) and 8
The aspect (B) does not occur simultaneously. In this case, for example, the light distribution (combining FIG. 5E and FIG. 5H) that is classified as far from the focal point and shifted in the −x direction and the −y direction by the 4-division photodetector A alone 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 calculation is only addition and subtraction of analog amounts, and can be performed by an adder circuit, a subtracter circuit (not shown), etc. without using a CPU, and the load on these circuits can be small, and the calculation can be performed in a short time. There is.
Further, the device can be constructed at low cost.

[0055]

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, equations (7) to (10)
Is a focus signal, formulas (11) to (14) are tangential shift signals, and formulas (15) to (18) are radial shift signals. Equation (19)-
By calculating (24), it is possible to obtain an error signal that independently represents the positional deviation of 6 degrees of freedom by 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.
The signal, E _ψ, is the rotation error (tilt) signal in the ψ direction.
E _x is a translational displacement signal in the x-axis direction, E _y is a translational displacement signal in the y-axis direction, E _z is a translational displacement signal in the z-axis direction,
That is, it is a focus error signal. Positive or negative of the rotation direction is determined by the right-handed system with respect to each axis. For example, θ is the rotation amount with the z axis as the center of rotation, but when the z axis is viewed from the positive direction to the negative direction, the counterclockwise direction Rotation is positive, and rotation in the clockwise direction is negative.

If the numerical values of the positional deviation signals or the error signals are large, the positional deviation signals or the error signals are deviated in the positive direction of each axis. Therefore, a servo mechanism (not shown) for controlling the movement of the two-dimensional photodetector 20 is used, and feedback servo is performed so as to set the value of each signal to 0 according to the above calculation result. You can do real-time pixel matching on the 2.

(Modification) A plurality of waveguide holograms can be laminated as shown in FIG. 9 so as to detect the above-mentioned position shift signal or error signal.

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

Spot pairs are formed as servo marks on the four-divided photodetectors 90A, 90B, 90C, and 90D by the diffracted light 99 diffracted by the uneven portion 98 formed on the boundary between the core layer and the clad layer.

In this reproduction-only multiplex hologram memory 90, core layers are laminated, and it takes a finite time when the light incident on the waveguide layer jumps between the waveguide layers. Therefore, when the safety against vibration of the reproducing device is not guaranteed within the time of the interlayer jump, the servo mark is superimposed on the image so that the two-dimensional position shift signal of the above embodiment can be obtained from each waveguide hologram. By doing so, it is possible to quickly recover from the displacement due to vibration.

[0063]

(Embodiment 1) A result of detecting a positional deviation of a spot by forming a servo mark for confirming the operation principle of the present invention will be described. The parameter at the time of the experiment is f = 4 mm as shown in FIG. 10, and spot pairs each having 5 spots as 1 unit by the diffracted light from the regions 100 and 105 on the hologram surface are used as servo marks on the image plane. And ftan θ is 0.5 μm and 0.83.
It was set to 3.

The positional deviation Δd of this servo mark is

[0065]

[Equation 7]     Δd = (δf / f) × (0.833−0.5)         = 0.08325δf (25)

It is expressed as follows and is proportional to δf.

At the time of focusing at δf = 0, a servo mark was detected by a position detector photodetector (not shown) as shown in FIG. 11A (FIG. 10 schematically shows the detected image. Is). Here, the spot 110 formed by one area and the spot 11 formed by another area
1s are arranged in a straight line. The positional deviation between the spot 110 and the spot 111 increases as δf increases (FIG. 11 (B) → (C) → (D), and the same (E) →
(F) → (G)), with a focus deviation of 120 μm, equation (25)
Is approximately 10 for the theoretical value Δd = 9.99 μm calculated by
It was possible to detect μm.

(Embodiment 2) In order to carry out the device of the present invention, as described above, it is necessary to accurately know the relative positional relationship between the image forming surface (light receiving surface) and the photodetector for the positional deviation signal. is there. Therefore, in this embodiment, as shown in FIG. 12, four-divided photodetectors 120A and 120 are provided at diagonal portions in the data light receiving portion 121 of the CMOS image sensor 120.
The position signal detection device incorporating B, 120C and 120D was implemented. Therefore, the four-division photo detectors are arranged in the plane of the light receiving portion 121, and the relative position of each four-division photo detector can be easily known from the size of the light receiving portion 121.

Here, the data light receiving section 121 has a pixel pitch of 5 μm, and makes 1024 × 1024 square pixels. That is, the size of the data light receiving unit 121 is
It is a square with one side of 5.12 mm. On the extension of the diagonal line of this square, the four-division photo detectors 120A, 120
B, 120C, 120D are placed, 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 is used.
The size was 5 mm × 5 mm. Wavelength 680 for light source
The thing of nm was used. Radius on hologram surface 122 1.
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 region (not shown), and the distance between the centers of gravity of the spots is set to about 5 μm. did.

Using the above structure, 10 mW of light was coupled to the waveguide hologram 123 so that the light intensity of the spot on each of the four-divided photodetectors would be about 0.1 μW. The light intensity received by each pixel of the data light receiving unit 121 is about 100 pW, and a detection signal can be obtained in a short time by converging a spot of light power significantly higher than this value on each of the four-division photodetectors. I was able to sample.

Therefore, 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 the positional deviation signal, and the servo mechanism 125 operates in accordance with this signal. By performing position control of the CMOS image sensor 120 with 6 degrees of freedom, it is possible to obtain a result which is almost theoretical.

[0073]

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

[Brief description of drawings]

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

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

FIG. 3 is a projection view showing an arrangement of four-division photodetectors for measuring displacement of a two-dimensional photodetector in six degrees of freedom in the device of the present invention.

FIG. 4 is a projection diagram for explaining a light focusing method on one 4-division photodetector.

FIG. 5 is an explanatory diagram showing an example of changes in spot positions on a four-divided photodetector due to displacement of a two-dimensional photodetector.

FIG. 6 is an explanatory diagram showing another example of changes in spot positions in another four-division photodetector due to displacement of the two-dimensional photodetector.

FIG. 7 is an explanatory diagram showing another example of changes in spot positions in another 4-division photodetector due to displacement of the two-dimensional photodetector.

FIG. 8 is an explanatory diagram showing another example of changes in spot positions in another four-division photodetector due to 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 for explaining servo mark experimental conditions for confirming the operation principle of the present invention.

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

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 Codes] 1 Hologram 2 Image plane 4, 5, 35, 36, 37, 38, 100, 105 Disc-shaped regions 6, 7 Diffracted light 90 Reproduction-only multiplex hologram memory 90A, 90B, 90C, 90D, 120A, 120
B, 120C, 120D, A, B, C, D 4-division photodetector α, β, 110, 111 Spot 120 CMOS image sensor 121 Light receiving part 122 Hologram surface 123 Waveguide hologram 124 Arithmetic part 125 Servo mechanism

─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Takaya Tanabe 2-3-1, Otemachi, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (72) Inventor Akinoyuki 2-3-3, Otemachi, Chiyoda-ku, Tokyo No. 1 within Nippon Telegraph and Telephone Corporation (56) References JP-A-11-345419 (JP, A) JP-A-2000-47557 (JP, A) JP-A-11-337756 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G11B ^7/ 09-7/22 G11B 7/0065 G02B 5/32

Claims (5)

(57) [Claims] 1. A position signal detecting apparatus for a read-only storage medium, wherein a guided light guided in a single-mode planar optical waveguide is diffracted by a diffracting means, and an image of the diffracted light is formed on a predetermined image plane. The diffracting means causes the diffracted light from the first region inside the diffracting means to be incident on another image forming surface whose relative position with respect to the predetermined image forming surface 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 image plane at an incident angle different from the predetermined incident angle. A photodetector which is formed so as to form a second spot in the vicinity of the first spot, and which detects the positions of the first spot and the second spot; and the detected first and second spots. According to the position of the two spots, A position signal detecting device comprising: a detecting unit that detects a position with respect to the predetermined image plane. 2. The position signal detecting device according to claim 1, wherein the diffracting means is formed on the another image plane so as to further form a plurality of the first and second spots. Position signal detector. 3. The position signal detection device according to claim 1, wherein the photodetector is a four-division photodetector, and the photodetector is divided into four detection regions in accordance with the received light amounts of the first and second spots. A position signal detecting device characterized in that the detecting means detects the position. 4. The position signal detecting device according to claim 1, wherein a plurality of the single mode planar optical waveguides are stacked in a direction substantially perpendicular to a guiding direction of the guided light. apparatus. 5. The position signal detecting device according to claim 1, wherein the line passing through the center position of the first area and the center position of the second area is a surface different from the diffraction surface of the diffractive unit. A position signal detecting apparatus, which is on lines orthogonal to each other, and a line passing through the barycentric position of the first spot and the barycentric position of the second spot is substantially orthogonal to the another surface.