JPS6312524B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to an apparatus for measuring the uneven shape of an information recording carrier, such as an optical video disk, on which information is recorded in an uneven shape.

[Technical background of the invention and its problems]

In so-called optical video disk devices and digital audio disk devices that read signals from an information recording carrier (hereinafter referred to as an optical disk) using a light beam such as a semiconductor laser, the information to be reproduced is read out on the optical disk. It is recorded as an uneven shape. These irregularities are called pits, and have a width of about 0.5 μm and a length of about 0.5 to 3 μm, and are formed in a spiral or concentric shape on the optical disk.

To read out this pit signal, a normal light beam is focused on a minute spot by an objective lens, and the optical disk is irradiated with this to trace the pit. At this time, the reflected or transmitted light of the light beam by the disk is diffracted by the pits. Therefore, by detecting this reflected or transmitted diffracted light with a photodetector, it is possible to obtain a reproduced signal corresponding to the uneven shape of the pit, that is, according to the recorded information.

As mentioned above, since information reproduction utilizes the diffraction phenomenon caused by pits, it is necessary to optimize the shape of the pits, such as the width, length, and depth. In particular, the degree of modulation of the reproduced signal depends on the depth of the pit, and the degree of modulation is maximum when the depth is λ/4n (λ: wavelength of the irradiation beam, n: refractive index of the optical disk). Therefore, in order to perform good reproduction, it is desirable to set the depth of the pit to the value of λ/4n. Therefore, when manufacturing an optical disk, it is necessary to measure the depth of the pit and confirm whether it matches the above-mentioned value.

Conventionally, as a method for measuring the uneven shape, there is a method of irradiating a laser beam onto an optical disc master or an optical disc copied from the master disc, and taking the ratio of the 0th-order diffracted light and the 1st-order diffracted light of the reflected or transmitted diffracted light.

FIG. 1 is a principle diagram for explaining this measurement method, and shows the case of transmission. The diameter of the irradiated light beam 21 is usually about 0.1 mm to 1 mm, and the light beam 21 is diffracted by a large number of pits 22 on the optical disk 20. As a result, there are first-order diffracted lights represented by I _T1 and -I _T1 in the track row direction (x direction) and in the signal row direction (y direction).
First-order diffracted light expressed as Is ₁ and -Is ₁ appears.
Note that I ₀ is the 0th order diffracted light, and represents transmitted diffracted light that is not refracted.

Here, if the wavelength of the pit is p, the track interval is g, the length of the pit is β, and the width of the pit is γ, the diffraction angles θ and φ of the first-order diffracted lights I _T1 and Is ₁ are gsinθ=m ₁ λ psinφ = m ₂ λ. However, m ₁ and m ₂ are the orders of diffraction, and in this case, m ₁ =m ₂ =1.
From the above formula, the diffraction angle φ of the first-order diffracted light Is ₁ in the signal train direction is
depends on the wavelength λ of the light beam and the wavelength p of the pit, and since the pit wavelength p generally changes depending on the recording signal, it is distributed over a fairly wide range. Therefore, the pit shape is measured by detecting _IT1 , which is the first-order diffracted light in the track row direction. The intensity It ₁ of I _T1 is calculated from diffraction theory as It ₁ = |A(e ⁱ -1)β/p・γ/g・sin(
πγ/q)/πγ/q｜ ² = 2A ² (1-cos) (β/P) ² (γ/
q) ² {sin(πγ/q)/πγ/q} ² ...(i) Here A ² is a constant corresponding to the intensity of the light beam 21. Further, as shown in FIG. 1b, with the pit 22 as a boundary, the refractive index on the incident side of the light beam 21 is n ₁ , that on the transmission side is n ₂ , and the depth of the pit is d. ) in the formula is expressed as =2π|n ₁ −n ₂ |d/λ (ii). Furthermore, the intensity I of the 0th order diffracted light I ₀ is I=A ² {1+2(1-cos)β/p・γ/q(β/
p・γ/q−1)}...(iii)

Conventionally, the measurement of unevenness has been carried out at one point in the track row direction.
This was done by detecting the intensities of I _T1 , which is the order diffracted light, and _I0 , which is the zeroth order diffracted light, and finding their ratio. The ratio between the intensity It ₁ of the 1st-order diffracted light I _T1 and the intensity I of the 0th-order diffracted light I ₀ is calculated from equations (i) and (iii) as follows: It ₁ /I=2(1-cos)(β/p) ²・(γ/q) ²
{sin(πγ/q)/πγ/q} ² /1+2(1-cos
)β/p・γ/q(β/p・γ/q−1)……(iv) From equation (iv), It ₁ /I has three variables: pit depth d (see equation (ii)), pit duty ratio (β/p), and the ratio of track interval q to pit width γ. have. Therefore, in order to determine the value of the uneven shape, for example the depth d of a pit, from the value of It ₁ /I, it is necessary to determine the values of the other two variables β/p and γ/q by other measurement methods. must not. However, it is difficult to accurately determine the values of q/p and γ/q, and it is impossible to accurately determine the value of pit depth d using this conventional method. One possible method of determining the value of the depth d of the pit is to directly measure it using an interference microscope, but the resolution is not good and it has been impossible to determine the value of d even with this method.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an uneven shape measuring device that can determine the value of the pit depth d, which was not possible with the above-mentioned conventional uneven shape measuring device.

[Summary of the invention]

The present invention irradiates two light beams with different wavelengths onto the same spot on an optical disk master or an optical disk copied from the master, and receives and detects the first-order diffracted light of each light beam. Provided is an unevenness shape measuring device that calculates the ratio of intensities and measures the depth d of a pit based on this value.

〔Effect of the invention〕

According to the present invention, the value of the pit depth d, which must be known because it affects the playback characteristics of an optical disc, can be determined by the track spacing q and the pit width γ.
It is not necessary to know the values of the ratio of .beta./p and the pit duty ratio .beta./p, and they can be uniquely determined.

[Example of the present invention]

First, the measurement principle of the uneven shape measuring device of the present invention will be explained.

Now, two light beams with different wavelengths are I _L1 ,
I _L2 and the respective wavelengths are λ ₁ and λ ₂ (λ ₁ ≠ λ ₂ ). Furthermore, the light intensities of the beams I _L1 and I _L2 are respectively Il ₁ and Il ₂ , and when both beams are irradiated onto the same spot on the optical disk, the intensities of the first-order diffracted light in the track row direction are I ₁ and Il 2 , respectively. Let it be I ₂ .

In the present invention, each of the light beams I _L1 and I _L2 is
The next order diffraction light is detected and the ratio of the light intensity I ₁ /I ₂ is detected. From the above equation (i), the value of I ₁ /I ₂ is calculated as I ₁ /I ₂ = A ₁ ² (1 −cos ₁ )/A ₂ ² (1−cos ₂ )……
(v) becomes. Here, A ₁ ² and A ₂ ² are equal to the intensities Il ₁ and Il ₂ of the two irradiated light beams, respectively, and A ₁ ² = Il ₁ and A ₂ ² = Il ₂ . Further, ₁ and ₂ are expressed as 〓 ₁ =2π|n ₁ −n ₂ |d/λ _{1 2} =2π|n ₁ −n ₂ |d/λ ₂ (vi) from equation (ii). Therefore, I ₁ /I ₂ is I ₁ /I ₂ = Il ₁ /Il ₂・1−cos(2π|n ₁ −n ₂ |/λ ₁ d)
/1−cos(2π|n ₁ −n ₂ |/λ ₂ d)…(vii). Transforming equation (vii), I ₁ /I ₂ ×Il ₂ /Il ₁ =1−cos(2π|n ₁ −n ₂ |/λ ₁ d)
/1−cos(2π|n ₁ −n ₂ |/λd)...(viii) is found. The right side of equation (viii) has the refractive index n ₁ ,
n ₂ , the wavelengths λ ₁ , λ ₂ of the light beam, and the depth d of the pit, but the refractive index n ₁ , n ₂ and the wavelength λ ₁ ,
The exact value of λ ₂ can be easily known and can be treated as a constant. Therefore, I ₁ /I ₂ ×Il ₂ /Il ₁ expressed by equation (viii) is a function only of the pit depth d.

Therefore, the ratio of the first-order diffraction intensities of the two light beams is
By finding I ₁ /I ₂ , detecting the ratio of the light intensities of the light beams I _L1 and I _L2 themselves, Il ₂ /Il ₁ , and knowing the value by multiplying the two, the depth d of the pit can be uniquely determined. It becomes possible to measure.

FIG. 2 shows the method based on the new measurement principle described above.
FIG. 1 is a block diagram showing an embodiment of the unevenness shape measuring device of the present invention. The first laser light source 11 emits a light beam I _L1 with a wavelength λ ₁ and the second laser light source 12 emits a light beam I _L2 with a wavelength λ ₂ . Both light beams I _L1 , I _L2
are half mirrors 1 each having the same transmittance.
After passing 10 and 112, dichroic mirror 1
3, and the same location on the optical disk 14 is irradiated. The light beams I _L1 and I _L2 irradiated onto the optical disk 14 are diffracted and transmitted diffracted lights I' _L1 and I' _L2
occurs. Since the light beams I _L1 and I _L2 have different wavelengths, their diffraction angles also differ, and the transmitted diffracted lights I _L ′ ₁ and I _L ′ ₂ travel straight in different directions. Photodetectors 15 and 16 are provided in each straight direction, and the photodetector 15 receives the diffracted light I _L ' ₁ , and the photodetector 16 receives the diffracted light I _{L' 2,} respectively. Photodetectors 15 and 16 receive light
Electric signals corresponding to the light intensities I _{1 and} I 2 of I _L ′ ₁ and I _{L ′ 2} are emitted. They are amplified to predetermined values by passing through amplifiers 17 and 18, respectively, and then guided together to a divider 19. The divider 19 performs division between the supplied signals and calculates the ratio I ₁ /I ₂ of the transmitted diffraction light intensities I ₁ and I ₂ .

Now, when the light beams I _L1 and I _L2 pass through the half mirrors 110 and 112, respectively, a portion is reflected. The reflected light of the light beam I _L1 is transmitted to the photodetector 111, and the reflected light of the light beam I _L2 is transmitted to the photodetector 11.
3, the light is received by each of them. The photodetector 111 generates an electrical signal according to the intensity Il ₁ of the light beam I _L1 ,
The photodetector 113 generates electrical signals depending on the intensity Il ₂ of the light beam I _L2 , and these are respectively connected to the amplifier 11.
After passing through 4,115, it is directed to a divider 116.
The divider 116 functions similarly to the divider 19 described above, performs division between the supplied signals, and calculates the ratio Il ₂ /Il ₁ of the light intensities Il ₁ and Il ₂ . The value of I ₁ /I ₂ which is the output of the divider 19 and the value of Il ₂ /I which is the output of the divider 116
Both l ₁ values are directed to multiplier 117. The multiplier 117 multiplies the supplied I ₁ /I ₂ and Il ₂ /Il ₁ to calculate I ₁ /I ₂ ×Il ₂ /Il ₁ and outputs it to the terminal 118. In this way, from the terminal 118, I ₁ /I ₂ ×Il ₂ expressed by equation (viii)
/Il ₁ is obtained, and from this value the value of the depth d of the pit can be known.

[Other embodiments of the invention]

In the above embodiment, transmitted diffracted light was used as an example of the diffracted light received by the photodetectors 15 and 16, but similar measurements can be made by detecting reflected diffracted light. In this case, the value shown in equation (ii) can be treated as =4πn ₁ d/λ.

Also, we have explained the case where two laser light sources are prepared to obtain beams of different wavelengths, but as a laser light source, it is better to use a single laser device that emits light of different wavelengths, such as an Ar laser device. Good too. In this case, it is sufficient to provide one photodetector that receives the light beam itself emitted from a single laser light source, and it is sufficient to provide only one half mirror in front of the photodetector. However, the light intensity
Similarly, the ratio of Il ₁ and Il ₂ must be calculated, so the light intensity detected by a single photodetector
It is necessary to provide a means for holding one of the values of Il ₁ and Il ₂ , such as a storage circuit or a delay circuit, in a stage before the divider 116, and to guide the light intensities Il ₁ and Il ₂ in parallel to the divider 116. be done.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram for explaining the principle of the unevenness measuring method, and FIG. 2 is a block diagram showing an embodiment of the unevenness measuring apparatus of the present invention. 11, 12... Laser light source, 14... Optical disk, 15, 16, 111, 113... Photo detector,
19,116...divider, 117...multiplier,
I _L1 , I _L2 ... light beam, I _L ′ ₁ , I _L ′ ₂ ... first-order diffracted light.

Claims (1)

[Scope of Claims] 1. In an uneven shape measuring device for measuring the size of the uneven shape of an information recording carrier on which information is recorded in an uneven shape, the information recording carrier is obtained by irradiating the information recording carrier with a first light beam. a first photodetector for detecting first-order diffracted light; and a second light detector for detecting first-order diffracted light obtained by irradiating the information recording carrier with a second light beam having a different wavelength from the first light beam. a detector, the first and second
a first divider that takes a ratio of electrical signals proportional to the intensity of the first-order diffracted light obtained from the photodetector; a third photodetector that receives the first light beam; and a third photodetector that receives the first light beam; a fourth photodetector that receives light; and the first and second photodetectors obtained from the third and fourth photodetectors.
The second takes the ratio of the electrical signal proportional to the intensity of the ray of light.
and a multiplier that multiplies the outputs of the first and second dividers, and the depth of the uneven shape is detected from the multiplication result of the multiplier. measuring device.