JPH0556571B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an apparatus for measuring the groove shape of an optical disk. Conventional structure and its problems Optical disks, which are expected to be used for high-density, large-capacity information storage, have tracking grooves formed in advance on the recording surface of the optical disk to facilitate tracking during recording and playback. There is. The cross-sectional shape has a strong relationship with tracking signals and reproduction signals, and in order to obtain high-quality optical discs, it is desired to develop a method and apparatus for accurately measuring the groove shape of an optical disc. A conventional optical disk groove shape measuring device will be explained below. FIG. 1 is an explanatory diagram showing a laser irradiation section of a conventional optical disk groove shape measuring device. A light beam of wavelength λ emitted from a He-Ne laser is incident on the disk surface 3 with the directional component of the wavefront normal on the cross section perpendicular to the optical disk track groove forming an angle with the normal 2 of the optical disk recording surface. The reflected light is diffracted into zero-order light 4, first-order light 5, second-order light 6, etc. by the grooves on the recording surface. FIG. 2 is an explanatory diagram showing a laser light receiving section of a conventional optical disk groove shape measuring device. The parallel light enters the disk surface 7 at an incident angle on the cross section perpendicular to the track groove, passes through the base member 8 with a refractive index n, and then reaches the groove width a, groove depth d,
It is reflected by the optical disk recording surface 9 having grooves in the shape of a rectangular wave with the groove pitch b, and the reflected diffracted light passes through the base member 8 again and is emitted from the optical disk surface 7. Condenser lenses 10, 11, and 12 are arranged on the 0th-order, 1st-order, and 2nd-order diffraction optical axes, respectively, and photoelectric elements 13, 14, and 15 are arranged near the focal positions, respectively. The measurement principle of the conventional optical disk groove shape measuring device configured as described above will be explained below. As shown in FIG. 2, the intersection line between the track groove orthogonal cross section and the disk surface 7 is the u axis, and the intersection line between the track groove orthogonal cross section and the disk recording surface 9 is the x axis.
The axis. Amplitude distribution of the incident light before entering the disk surface g ₁ (u) = 〓 (u/c) e ^-j2 〓 ^/ 〓 Amplitude distribution of the incident light from immediately after ^usin incidence to the disk recording surface g ₂ (x) is given by the following equation. g ₂ (u)=〓(u/c)e ^-j2 〓 ^/ 〓 ^{usin /n} The amplitude distribution g ₃ (x) of the reflected light on the disk recording surface 9 is given by the following equation. g ₃ (x)＝〓(x/c)e ^-j2 〓 ^/ 〓 ^{xsin /n} [1/b{〓
(x/a)*〓(x/b)}+1/b{〓(x-b/2
/b-a) *〓(x/b)}e ^-j4 〓 ^nd/ 〓〕 The amplitude distribution g ₄ (u) of this reflected light immediately after exiting from the disk surface 7 is given by the following equation. g ₄ (u)＝〓(u/c)e ^-j2 〓 ^/ 〓 ^usin [1/b{〓(
u/a)*〓(u/b)}+1/b{〓(u-b/2/
b-a)*〓(u/b)}e ^{-j4〓nd /} 〓] The amplitude distribution G(f) in the Fraunhofer region of the reflected light after being emitted from the disk surface is given by the following equation. G(f)=K ₁ F [g ₄ (u)] _f=sio 〓 _/ 〓 ...(1) Here, K ₁ is the proportionality constant, F is the Fourier transform symbol,
θ is the viewing angle from the disk surface normal. formula
Calculate (1) and get G(f) = K ₁ [ac{sinc(of)〓(bf)}*sinc(cf) +c(ba-a)e ^-j4 〓 ^nd/ 〓{e ^-j 〓 ^bf sinc (b −a) f〓(bf)｝＊sinc(cf)〕 _f=sio 〓 _{+sio /} 〓 When c≫b, G(f) ≒K ₁ C [{〓(bf)＊sinc(cf)} {asinc(af) +(b-a)e ^-j(4 〓 ^nd/ 〓 ⁾⁺ 〓 ^bf) sinc(ba-a)f〕 _f=sio 〓 _{+sio /} 〓 For simplicity, ε=a/ b δ=2πnd/λ
far. When f=0, -1/b, -2/b, G(f) takes a peak value and gives amplitude values of 0th-order, 1st-order, and 2nd-order diffracted light, respectively. Letting the 0th, 1st, and 2nd order diffracted light intensities be I ₀ , I ₁ , and I ₂ , I ₀ =K ₂ |G(O)| ² =K ² ₁ K ₂ b ² c ² {ε ² +2ε
(1-ε) cos2δ+(1-ε) ² } I ₁ = K ₂ | G (1/b) | ² = K ^2/1 K ₂ 2b ² c ² /
π ² sin ² πε・(1−cos2δ) I ₂ = K ₂ | (G2/b) | ² = K ² ₁ K ₂ b ² /2π ²
sin ² 2πε・(1−cos2δ) Therefore I ₁ /I ₀ =2sin ² πε・(1−cos2δ)/π ² {1−2ε
(1-ε) (1-cos2δ)} ...(2) I ₂ /I ₁ = cos ² πε ...(3) Also, the angle θ0 between the disk surface normal and the wavefront normal of the 0th order diffracted light 4 is 0. = sin θ ₀ + sin/λ θ ₀ = −
It is. Therefore, if the angle between the wavefront normal of the 1st-order diffracted light 5 and the wavefront normal of the 0th-order diffracted light 4 is θ ₀₁ , -1/b=sin(+θ ₀₁ )+sin/λ. b=λ/sin (θ ₀₁ +) − sin ...(4) The power values of I ₀ , I ₁ , and I ₂ are determined by the photoelectric elements 13, 14,
I ₁ /I ₀ , I ₂ /I ₁ , θ ₀₁ , etc. can be measured by detecting with 15 and measuring the angle θ ₀₁ formed by the 1st-order diffracted light and the 0th-order diffracted light based on the positional relationship of the photoelectric elements 13 and 14. .
Therefore, by combining the relational expressions (2), (3), and (4), the groove width a, groove depth d, and groove pitch b can be measured.
However, with the above configuration, it is not possible to measure a trapezoidal groove including an inclined portion at the groove end, that is, a groove droop. Purpose of the invention The present invention solves the above-mentioned conventional problems.
It is an object of the present invention to provide an optical disk groove shape measuring device capable of measuring a trapezoidal groove shape including an inclination or sag at the groove end. Structure of the Invention The present invention provides a groove width a, a groove depth d, a groove pitch b, and a width e of an inclined portion at the groove end, which is covered with a base material having a refractive index n.
A parallel beam of wavelength λ is irradiated onto an optical disk recording surface having trapezoidal grooves, and the directional component of the wavefront normal of the parallel beam on a cross section orthogonal to the optical disk track groove forms an angle with the normal to the optical disk recording surface. , 0th order of parallel light, 1
A photoelectric element is disposed on the optical axis of the next, second, and mth-order reflected or diffracted light, and the respective light intensities I ₀ ,
I ₁ , I ₂ , I _n are detected, and 0 is determined by the positional relationship between the elements.
Detect the angle θ between the optical axes of the next and first-order reflected or transmitted diffracted lights, a/b=ε, (ba-a-2e)/b
=ε, 2πnd/λ=δ, b=λ/{sin(θ+)−sin} I ₁ /I ₀ = sin ² πε−2sinπεsinπ
εcos2δ＋sin ² πε／π ² (ε ² +2εεcos2δ＋ε ² I ₂ /I ₀ = sin ² 2πε＋2sin2πεsin2
πεcos2δ＋sin ² 2πε／4π ² (ε ² +2εεcos2δ＋ε ^{2
I _n /I ₀ = sin 2 mπε + 2 (-1) msi
nmπεsinmπεcos2δ＋sin 2 mπε／mπ 2 (ε 2 +2εεc
The groove shape can be measured by combining the following four equations: os2δ+ε 2 ). DESCRIPTION OF EMBODIMENTS FIG. 3 is an explanatory diagram showing a laser light receiving section of an optical disk groove shape measuring device in an embodiment of the present invention. The parallel light is incident on the disk surface 7 at an incident angle on the cross section orthogonal to the track groove, and the parallel light enters the disk surface 7 at a base material portion 8 with a refractive index n.
The reflected diffracted light is reflected by the optical disc recording surface 9' having a trapezoidal groove with a groove width a, a groove depth d, a groove pitch b, and a width e of the inclined part at the groove end, and the reflected diffracted light returns to the base material part 8. The light is then emitted from the optical disk surface 7. Condensing lenses 10, 11, 12, 11' are arranged on the 0th, 1st, 2nd and m-th diffraction optical axes, respectively,
Photoelectric elements 13 and 1 are located near the focal point, respectively.
Install 4, 15, 14'. The measurement principle of the optical disk groove shape measuring apparatus of this embodiment configured as described above will be explained below. As shown in FIG. 3, the line of intersection between the cross-section perpendicular to the track groove and the disk surface 7 is defined as the u-axis, and the line of intersection between the cross-section perpendicular to the track groove and the disk recording surface 9' is defined as the x-axis.
Amplitude distribution of incident light before entering the disk surface q ₁
(u), the amplitude distribution g ₂ (x) of the incident light from immediately after incidence to the disk recording surface is as described above. The amplitude component g' ₃ (x) of the reflected light on the disk recording surface 9' is given by the following equation. g ₃ (x)＝〓(x/c)e -j2 〓 / 〓 xsin /n [1/b{〓
(x/a)*〓(x/b)}+1/b{〓(x-b/2
/ba-a-2e) e j2 〓 / 〓 n(xtan2a-2d) }*〓(x/b)〕 The amplitude distribution g ₄ ′(u) of this reflected light immediately after exiting from the disk surface 7 is given by the following equation. It will be done. g ₄ ′(u)＝〓(u/c)e -j2 〓 / 〓 usin [1/b{〓
(u/a)*〓(u/b)}+1/b{〓(n-b/2
/b-a-ze) e -j2 〓 / 〓 n(utan2a-2d) }*〓(u/b) The amplitude distribution G(f) in the Fraunhofer region of the reflected light after exiting from the disk surface is given by the following formula. Given. G′(f)=K ₁ F[g′ ₄ (u)] ……(5) Calculate equation (5), G(f) = K ₁ [ac{sinc(af)〓(bf)}＊ sinc(cf) +c(b-a-2e)e -j4 〓 nd/ 〓{e -j 〓 bf sinc(b-a-ze)f〓(bf)} *sinc(cf)〕 _f=sio 〓 _{+ sio /} 〓 However, when f ₀ = nsin2d λ c≫b, G′(f) ≒K ₁ C [{〓(bf)＊sinc(cf)}{asinc(af) +(b-a-2e)e - j(4 〓 nd/ 〓 )+ 〓 bf) sinc(b−a −2e)(f−f ₀ )f〕 _f=sio 〓 _{+sio /} 〓 For simplicity, ε=a/bε=(b− a-
2e)/b, δ=2πnd/λ. When f=0, -1/b, -2/b, m/b, G(f) takes a peak value and gives the amplitude values of the 0th-order, 1st-order, and 2nd-order diffracted light, respectively. 0
The diffracted light intensities of order, first order, second order and m order are I ₀ , I ₁ ,
When I ₂ and I _n , I ₀ , I ₁ , I ₂ , and I _n are given by the following equation. I ₀ = |G′(O)| 2 =K 21 K ₂ b 2 c 2 {ε 2 +2εcos2δ+ 2 } I ₁ = |G′(−1/b)| 2 =K 2/1 K ₂ 2b 2 c 2 /π 2 (sin 2 πε−2sinπεsinπεcos2δ+sin 2 πε) I ₂ = |G′(−2/b| 2 = K 2 ₁ K ₂ b 2 c 2 /4π 2 (sin 2 2πε+2sin2πεsin2πcos2δ + sin 2 2π) I _n = | G ′ ( ₋ n _/ b | _
sin 2 mπ) Therefore, the following equations (6), (7), and (8) are based. I ₁ /I ₀ = sin 2 πε−2sinπεsinπεcos2δ
+sin 2 πε/π 2 (ε 2 +2εεcos2δ+ε 2 )……(6) I ₂ /I ₀ = sin 2 2πε+2sin2πεsin2πεcos2
δ＋sin 2 2πε／4π 2 (ε 2 +2εεcos2δ＋ε 2 )……(7
) I _n /I ₀ = sin 2 mπε+2(-1) m sinmπεsi
n2πεcos2δ＋sin 2 mπε／m 2 π 2 (ε 2 +2εεcos2δ＋
ε 2 )...(8) Further, the groove width b is given by the above-mentioned equation (4) using the angle θ ₀₁ formed by the normal to the wavefront of the 0th-order and 1st-order diffracted light. The power values of I ₀ , I ₁ , I ₂ , and I _n are determined by the photoelectric elements 13 and 1.
I ₁ /I _{0 ,} I ₂ /I ₀ , I _n /I ₀ ,
θ ₀₁ etc. can be measured. Therefore, by combining the relational expressions (2), (3), (4), and (6), we can calculate the trapezoidal groove dimensions: groove width a, groove depth d, groove pitch b, and slope of the groove end. Width e can be measured. As described above, according to this embodiment, the 0th order, the 1st order,
By arranging photoelectric elements on the optical axes of the second-order and m-order reflected diffraction lights, and measuring the respective light intensities, and detecting the angle formed by the optical axes of the zero-order and first-order diffraction lights, the light can be detected. Disc recording surface groove width, groove depth, groove pitch,
Also, it is possible to measure the width of the sloped portion of the groove end. In the above embodiments, a measurement method by detecting reflected diffracted light was explained, but similar measurement is also possible by detecting transmitted diffracted light. Furthermore, even if the parallel light irradiating the disk is incident on the cross section of the track groove at an angle, there is no change in the calculation formula for measuring the groove shape. Effects of the Invention The optical disc groove shape measuring device of the present invention has zero-order,
A photoelectric element is placed on the axes of the 1st, 2nd, and m-order reflected or transmitted diffracted lights to measure the respective light intensities and detect the angle formed by the optical axes of the 0th- and 1st-order diffracted lights. By doing so, it is possible to measure the groove width, groove depth, groove pitch, and width of the sloped portion of the groove end on the recording surface of an optical disk having a trapezoidal groove shape, and its practical effects are great.}

[Brief explanation of drawings]

FIG. 1 is a diagram showing a laser irradiation part of a conventional optical disc groove shape measuring device, FIG. 2 is a diagram showing a laser receiving part of a conventional optical disc groove shape measuring device, and FIG. 3 is a diagram showing a laser receiving part of a conventional optical disc groove shape measuring device. FIG. 3 is a diagram showing a laser light receiving section of the optical disk groove shape measuring device. 7... Optical disk surface, 8... Base material part, 9,
9'... Recording surface, 10, 11, 11', 12... Condensing lens, 13, 14, 14', 15... Photoelectric element.

Claims (1)

[Claims] 1. A recording surface of an optical disk having a trapezoidal groove with a groove width a, a groove depth d, a groove pitch b, and a width e of an inclined portion at the groove end, covered with a base material having a refractive index n. λ parallel light is irradiated, and the directional component of the wavefront normal of the parallel light on the cross section orthogonal to the optical disc track groove forms an angle with the normal to the optical disc recording surface, and the 0th order of the parallel light,
A photoelectric element is placed on the optical axis of the 1st, 2nd, and m-order reflected or diffracted lights to adjust the light intensity of each.
I ₀ , I ₁ , I ₂ , _{and In} are detected, and the angle θ formed by the optical axes of the 0th and 1st order reflected or transmitted diffracted lights is detected based on the positional relationship between the elements, and a/b=ε , (b-
a−2e)/b=, 2πnd/λ=δ, b=λ/{sin(θ+)−sin} I ₁ /I ₀ = sin ² πε−2sinπεsinπεcos
2δ＋sin ² π／π ² (ε ² +2εεcos2δ＋ε ² I ₂ /I ₀ = sin ² 2πε＋2sin2πεsin2πε
cos2δ＋sin ² 2πε／4π ² (ε ² +2εεcos2δ＋ε ² I _n /I ₀ = sin ² mπε+2(-1) ^m sinmπ
εsinmπεcos2δ＋sin ² mπε／m ² π ² (ε ² +2εεcos2
An optical disk groove shape measuring device characterized in that the groove shape is measured by simultaneously using four equations: δ+ε ² ).