JP2564835B2 - Optical diffraction angle of optical disc, position deviation, and warp detection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to measurement of optical discs and the like having diffraction grating properties, and more particularly to a method for measuring and detecting diffraction angle position deviation and warpage.

[Conventional technology]

Conventionally, this type of diffraction angle detection method uses a transmitted diffracted light to install a photomultiplier (hereinafter referred to as “photomul”) on a mechanism that moves on an arc, as shown in FIG. There has been a method of obtaining the diffraction angle and the peak intensity by obtaining the position showing the peak of the amount of received light of Photomul. In this case, as shown in FIG.
-2 and + 1st order diffracted light 5-3, 0th order diffracted light 5-4,-
Intensity and angle of each diffracted light of each diffracted light at the positions of 5-7, 5-8, 5-9 by moving Photomar on the arc according to the diffraction angle 5-6 (= Diffraction angle) was sought. There is also a method in which the photomultiplier having a large light-receiving surface is installed in advance at positions 5-7 to 5-9 because the photomultiplier needs to be moved, but in this method, the angular resolution of the angle θ in the diffraction direction is not good ( = Photomal size 5-10 P _D
If the distance from the diffraction point to photomultipliers and r _P), i.e. the resolution of θ was _{P O / r P (rad)} .

Next, FIG. 6 shows a system in which the photomultiplier is simply replaced by the one-dimensional or two-dimensional solid-state imaging device 6-1. -2nd order diffracted light 6-3, -1st order diffracted light 6-4, 0th order diffracted light 6-5, 1st order diffracted light 6
-6,2 if you try to light at a time-order diffracted light 6-7 H _e
-N _e laser 6-2, when 14 microns × 2048 pixels the length of the solid-state imaging device 6-1 when the CD disc 6-8, CD disc 6-
The distance l _D between 8 and the solid-state image sensor is only 7 mm. From this, the fluctuation Δl _{D of} l _D is the measurement error Δθ ₁ of θ ₁ (= first-order diffraction angle) with respect to the measured value of θ. Therefore, when l _D is small, the fluctuation of Δl _D has a large effect on the measurement.
The measurement of θ could not be put to practical use unless the fluctuation of l _D was suppressed. Further, the angular resolution of theta is _{r P (θ) = l D} tan P if the pixel size and P _D when _{(θ) D / (l D} tanθ) (rad) angle resolution and l _D is small because it is There was a drawback that it became worse. This has a great influence particularly on a two-dimensional solid-state imaging device having a small device size. For this reason, it is possible to increase the size of the light receiving part by arranging multiple light receiving elements.
Such a method of FIG. 7 to earn a l _D there is. Incidentally filter 7-1 to 7-5 of Figure 7 is a neutral density filter for adjusting the light amount of the laser, the one-dimensional image sensor 7-6～7-10, 7-11 H _e -N _{The e-} laser beam 7-12 is a CD disc.

[Problems to be solved by the invention]

The above-described conventional measurement method using the photomultiplier and the solid-state image sensor has drawbacks such as insufficient angular resolution, labor, and strict position conditions of the diffraction grating. Further, in the measurement of the optical disk, it is necessary to simultaneously measure the warp position blurring amount, the intensity measurement of the diffracted light, the transmittance and the reflectance by another sensor.

[Means for solving problems]

The diffraction angle, position deviation, and warp detection method of the present invention has a solid-state image sensor having a parallel light-receiving surface with a disc sandwiched in the middle, and a mechanism for irradiating the disc with laser light.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

1 (A) and 1 (B) are optical system block diagrams showing an embodiment of the present invention. FIG. 1 (A) is a front view and FIG. 1 (B).
Is a side view. H _e -N _e laser oscillator laser beam 1-1 outputted from the (not shown) is applied to the optical disk 1-2. At this time, the laser light 1-1 is applied perpendicularly to the surface of the optical disk 1-2 by the half mirror 1-3 formed by the rectangular prism. The laser light 1-1 is shown with the 0th-order diffracted light shifted in order to facilitate understanding. Here, the transmitted diffracted lights 1-4, 1-5, 1-6, 1-7, 1-8 are neutral density filters 1-9, 1-10, 1-11, 1-12 having an appropriate extinction ratio. , 1-13
And is received by the first solid-state imaging device 1-14.
At the same time, reflected diffracted light (-2nd order, -1st order, 1st order, 2nd order) 1-
15,1-16,1-17,1-18 are solid-state image pickup devices for transmitted diffracted light after passing through the neutral density filters 1-20,1-21,1-22,1-23 having an appropriate extinction ratio. It is received by 1-24. Further, the 0th-order reflected diffracted light 1-25 is received by the second solid-state imaging device 1-24 for the diffracted light after the diffracted reflected light by the half mirror 1-3 and the neutral density filter 1-26 having an appropriate dimming rate. To do.

From the above, the intensities of all the diffracted lights of the optical disc and their positions can be understood as shown in FIG. 2 as the peak level and peak position of the solid-state image pickup device. That is, 2-1,2-2,2-3,
2-4 and 2-5 are peak values of the −2nd order, −1st order, 0th order, 1st order, and 2nd order reflected diffracted light, and their positions. Also, 2 at the same time
−6,2−7,2−8,2−9,2−10 is −2nd, −1st, 0th, 1st, 2
It is the peak value of the next transmitted diffracted light and its position. In this state, if the extinction ratio for each diffracted light is δ _ij (the combined extinction ratio with the half mirror for the 0th-order reflected diffracted light), or its peak level is P _ij or its pixel is d _ij.
ij . Here, i is the diffracted light order, j is the difference between the reflected diffracted light and the transmitted diffracted light (0: reflection, 1: transmission). Also, l _D0 , l
_As shown in FIG. 3, _D1 is an optical disk 3-3, a first solid-state image sensor 3-1 for receiving reflected diffracted light, a second solid-state image sensor 3-2 for receiving transmitted diffracted light, and an optical disk 3.
-3 and the distance. In this case, the i-th order diffraction angle θi is calculated by using the pixel size D _P , l _D0 + l _D1 = 2l _D (= -constant value)
n ^-1 ({| d _i0 −d ₀₀ | ＋ | d _i1 −d ₀₁ |} ・ D _P / 2l _D ) ＝ θ _i Position blurring amount Δl _D is Can be obtained with.

Further, if the symmetry is satisfied, that is, if the laser irradiation direction is perpendicular to the light receiving surface of the image sensor, the i-th order diffraction angle θ _i with higher accuracy can be obtained by the following equation.

Further, when the laser irradiation direction and the light receiving surface of the image sensor are not perpendicular, the correction of the inclination Θ ′ can be performed with higher accuracy than the conventional one because the effective _ID is doubled. That is, {| d _i0 −d ₀₀ | ＋ | d _i1 −
Using d ₀₁ |} / {| d _-i0 −d ₀₀ | + | d _i1 −d ₀₁ |}, we can also obtain Θ ′ by using the fact that the 0th-order light is an angle bisector. .

Further, the diffracted light intensity Powerij is obliquely incident as shown in FIG. Can be obtained with. (It is necessary to multiply by the correction filter effectively) Note that the effective extinction ratio is δ _ij / Sin θi. The warp can be similarly measured by using a two-dimensional fixed body image pickup device.

It should be noted that the light attenuating filter for adjusting the light amount can be coated with a light absorbing substance on the side surface of the filter to improve the degree of separation of diffracted light of each order.

〔The invention's effect〕

As described above, according to the present invention, by disposing the disk between the solid-state image pickup devices whose light-receiving surfaces are parallel and face each other, the arrangement distance l _D of the image pickup device for measurement is effectively 2
There is an effect that the double displacement can be obtained, and the positional deviation of the disk can be completely compensated when the diffraction angle is calculated, and at the same time, the positional deviation amount can be obtained by proportional distribution. Furthermore, if the peak intensity of the pixel (= used for calculating the diffraction angle) where the output of the solid-state image sensor shows a peak is corrected from the oblique light receiving (= diffraction angle) angle, the transmittance of the dark filter, etc. Is determined by the transmitted and reflected diffracted light. At the same time, the transmittance of the disk can be obtained from the intensity of the transmitted diffracted light and the reflected diffracted light. Furthermore, if a two-dimensional solid-state image pickup device is used, there is an effect that the influence of the warp of the disk can be measured at the same time.

[Brief description of drawings]

1 (A) and 1 (B) are optical system block diagrams showing an embodiment of the present invention, FIG. 2 is a schematic diagram of diffracted light and a light receiving portion, and FIG. 3 is a positional relationship between an optical disc and an image sensor. FIG. 4 and FIG. 4 are explanatory diagrams of the angle correction of the peak value. FIG. 5 is a schematic diagram of a method of using a conventional photomultiplier, FIG. 6 is a schematic diagram of a method of using a conventional image sensor, and FIG. 7 is a diagram showing an example of improving measurement accuracy in FIG. is there. 1-1 ... He- _Ne laser light, 1-2 ... Optical disc, 1
-3 ... Half mirror, 1-4 to 1-8 ... Transmitted diffracted light,
1-9 to 1-13 ... neutral density filter, 1-14 ... first solid-state image sensor, 1-15 to 1-18 ... reflected diffracted light, 1-20 to
1-23, 26 ... neutral density filter, 1-24 ... second solid-state image sensor, 1-25 ... 0th-order reflected diffracted light.

Claims (6)

(57) [Claims] 1. An optical disk is arranged in the middle of a one-dimensional or two-dimensional first and second solid-state image pickup device having light-receiving surfaces parallel to each other and opposed to each other, and perpendicular to the surface of the optical disk. A method for detecting the optical diffraction angle and position deviation of an optical disc, wherein the transmitted diffraction light and the reflected diffraction light from the optical disc are measured by irradiating a laser beam on the optical disc. 2. A method for detecting a light diffraction angle, a position deviation, and a warp of an optical disk according to claim 1, wherein a right-angle prism is used as the laser light irradiation method. 3. An attenuating filter for adjusting a light amount according to reflected diffracted light (-2nd order, −1st order, 0th order, 1st order, 2nd order −) of laser diffracted light on the light receiving surface side of the image pickup device. The method for detecting the diffraction angle, position deviation, and warpage according to claim 1, which is arranged. 4. A neutral density filter for adjusting the amount of light according to the transmitted diffracted light of the laser diffracted light (--2nd order, -1st order, 0th order, 1st order, 2nd order ...) On the light receiving surface side of the image pickup device The diffraction angle, the position deviation, and the warp detection method according to claim 1. 5. A method for detecting a diffraction angle, a position deviation, and a warp according to claim 3, wherein the neutral density filter has a side surface coated with a light absorbing substance. 6. A known transmittance of the neutral density filter,
The diffraction angle, position deviation, and warp detection method according to claim 3, wherein the intensity of diffracted light of each order is also measured at the same time.