JPS63103925A - Measuring method for optical characteristic of optical disk - Google Patents

Abstract

PURPOSE:To measure optical characteristics of an optical disk in an actual use state by irradiating the optical disk with converged laser irradiation light and performing tracking control, etc., over the irradiation light according to the reflected light. CONSTITUTION:Linearly polarized laser light from a laser 1 is made into parallel light 2, which passes through a lambda/4 plate 3 to become circular polarized light Pa. Then, the angles of rotation of a polarizer 4 and a lambda/4 plate 5 which have specific angles of rotation to a certain reference surface are selected to irradiate an optical element 6 to be measured with passing circular polarized light Pa as desired polarized irradiation light Pb. Then, projection light Pc which is transmitted or reflected by the element 6 is passed through the lambda/4 plate 7 and an analyzer 8 which have angles of rotation to the reference surface and then its quantity of light Pd incident on a photodetector 9 is detected. The Stokes' parameter of the projection light Pc from the element is found by setting the angles of rotation of the lambda/4 plate 7 and analyzer 8 to four conditions and measuring the quantity of the incident light Pd under the set conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for measuring optical properties such as the Mueller matrix of an optical disc, and more particularly to a method for measuring optical properties of a substrate for an optical disc.

(Prior art) Conventionally, an ellipsometer (ellipsometer) has been used to measure the optical characteristics of optical disk substrates, etc.
Or a similar device was used.

In these devices, the measured disk is irradiated with parallel light beams of known polarization, and the transmitted or reflected light is passed through, for example, a rotating analyzer to measure its polarization state. The optical characteristics of the substrate of the measurement disk were determined.

(Problems to be Solved by the Invention) However, in actual use when the disk to be measured is used as a recording medium, the incident light on the substrate is not a parallel beam but a focused beam. Therefore, it is extremely troublesome to determine the influence of the optical characteristics of the substrate on the actual reproduced signal from the measurement results using an ellipsometer.

Furthermore, since the parallel beam diameter of an ellipsometer cannot be made as small as the actual track width formed on the disk, it has been difficult to determine the effect that changes in optical properties in minute areas have on actual reproduced signals. . In addition, the ellipsometer has a disadvantage in that its shape has to be increased in order to improve the accuracy of the optical axis, and that it is difficult to make adjustments when mounting an object to be measured, and that it takes time to make these adjustments.

(Means for solving the problem) An optical disc is irradiated with focused laser irradiation light, tracking and focusing of the irradiation light is controlled based on the reflected light from the optical disc, and the optical disc is further controlled based on the reflected light. to measure the deflection characteristics of

(Example) When measuring the Mueller matrix of a d11 constant optical element,
The characteristics of the optical elements of the side chamber system are expressed using Mueller matrices, and the emitted or detected light is expressed using Stokes parameters. In this case, in order to measure the Mueller matrix of the optical element to be measured, a predetermined 4
There is a method in which the optical element to be measured is sequentially irradiated with different types of polarized light and the Stokes parameters of each transmitted light or reflected light are measured. Furthermore, in order to obtain this Stokes parameter, a polarizer and a λ/4 plate are placed on the optical path of the transmitted light or reflected light to the photodetector, and the transmitted light that passes through these under four types of arrangement conditions is calculated. It is necessary to detect the amount of light or reflected light using a photodetector.

The principle will be explained below using FIG. 4.

The linearly polarized laser light emitted from the laser 1 is made into parallel light via the collimator lens 2, and becomes circularly polarized light Pa by passing through the λ/4 plate 3. 4.5 is a polarizer and a λ/4 plate each having a predetermined rotation angle θ and C2 with respect to a certain reference plane, and by appropriately selecting these rotation angles O1 and C2, the circularly polarized light Pa that passes through one time can be The optical element 6 to be measured is irradiated with the irradiation light pb having a desired polarization. The output light Pc transmitted or reflected from the optical element 6 to be measured passes through a λ/4 plate 7 and an analyzer 8, each having a rotation angle of O1°04 with respect to the reference plane, and then is transmitted to a photodetector 9. The amount of light is detected as incident light Pd.

In the above configuration, first, a method for determining the Stokes parameter of the output light Pc from the optical element 6 to be measured will be explained.

Assuming that the Stokes parameters of the output light Pc and the incident light Pd are Pc and Pd, respectively, and the Mueller matrices of the λ/4 plate 7 and the analyzer 8 are M7 and M8, respectively, the amount of light detected by the photodetector 9 is: This is the amount indicating the first component of the Stokes parameter Pd of the incident light Pd, and the Stokes parameter of the incident light Pd under each condition shown below is Pd
1, Pd2, Pd3, Pd4, and these first components are respectively Pdl, Pd2 . Assuming Pd3 and Pd4, the rotation angles of the λ/4 plate 7 and analyzer 8 are 03=0°θ4=0
In this case, equation (1) is P dl=(P cx + P ci) ”...(
2) It becomes.

Similarly, if θ, = 0, θ, = π/2, Pd2=
(PcmPC2)...=(3).

Similarly, if θ, = π/4, θ4 = π/4, Pd3
=-(Pc, +Pc,)-(4).

Similarly, when θ, =O1θ, =π/4.

P d4=(P ct + P C4) ”...= (
5) It becomes.

Pc1 to Pc4 are obtained from the above equations (2) to (5), respectively.

becomes. Therefore, in order to obtain the Stokes parameter Pc of the output light Pc from the optical element to be measured 6, the λ/4 plate 7.
It can be determined by setting each rotation angle of the analyzer 8 to the four conditions described above and measuring the amount of incident light Pd under each setting.

Next, a method for obtaining the Mueller matrix of the optical element 6 to be measured will be explained.

The Mueller matrix of the optical element to be measured 6 is M6, and the irradiation light pb is
If the Stokes parameter of is pb, then Pc=M6・P
b...(7)

The irradiation light pb becomes a desired Stokes parameter by appropriately selecting the rotation angles O, 02 of the polarizer 4 and the λ/4 plate 5 as shown below. The Stokes parameters of the output light Pc obtained by irradiating the optical element 6 with these irradiation lights pb are Pal, Pc2, and Pc3, respectively.
, Pc4, the above equation (7) becomes as follows.

The rotation angles of the polarizer 4 and the λ/4 plate 5 are each 01=O1.
When 02=0, the irradiated light pb becomes horizontally linearly polarized light, and equation (7) similarly becomes θ□=π/2. When θ, = 0, the irradiation light pb
becomes vertically linearly polarized light, and equation (7) similarly becomes 01=π/4
．． When 0□=π/4, the irradiation light pb becomes linearly polarized light of π/4, and equation (7) similarly becomes 0□=o, 02=π/4.
In this case, the irradiation light pb becomes right-handed circularly polarized light, and the equation (7) becomes from the above equations (8) to (11). Incidentally, each of the Stokes parameters Pcl to Pc4 of the emitted light in the above equation can be determined by the method described above.

In this way, by sequentially irradiating the optical element 6 with the four types of polarized irradiation light pb and determining the Stokes parameters PC1 to Pc4 of the output light Pc from the optical element 6, the Muller Matrix can be measured.

Furthermore, measurement becomes easier if the outline of the polarization characteristics of the optical element to be measured is known in advance or if the parameters to be measured are limited.

The principle will be explained below using FIG. 8.

The laser beam emitted from the laser 40 is collimated through the collimator lens 41 and then passed through the λ/4 plate 1. By passing through the optical element group 42 consisting of a polarizer etc.
The optical element to be measured 43 is irradiated as irradiation light Pe having desired polarization characteristics.

The output light Pf transmitted or reflected from the optical element to be measured 43 is separated by each spectroscopic mirror 44 and 44□, and after passing through optical element groups 451, 45□ and 45°, photodetectors 46 and 46□ , 46. The incident light Pgl, PH1,
PH1, and the respective light amounts are detected.

In the above configuration, the irradiation light Pe and the incident light pg1, P
Each Stokes parameter of H1 and PH1 is Pa
, Pgl, PH1, PH1, and the optical element to be measured 4
3 and optical element group 45□, 45. Letting the Mueller matrices of M, Ma, Mb, and Me respectively, the following is obtained.

The amount of light detected by each photodetector 461.46□, 4G is determined by each Stokes parameter Pg1. This is the amount indicating the first component of Pg2 and Pg3, and the first component is l
1g1Pg22g3□, each Mueller matrix Ma
, Mb, and Me are respectively [Mat Ma2M
a3 Ma4 ], CMbt MbZ Mb3 Mb
4 pieces, [MciMc2Mc1Mc4 pieces, the following equation holds true.

Here, assuming that the optical element 43 to be measured is a linear phase shifter, and its orientation θ is θ and 0, its Mueller matrix M' can be expressed as M'=. However, r is transmittance or reflectance,
Δ indicates retardation.

This Mueller matrix M' can be substituted into the above equation (16) and rearranged. However, C1C11=, ・Pe, +Ma2・Pe.

CL,=2(Ma,・Pem Ma,・Pe,)C,
,=2(Ma,Pe4+Ma4・P,e,)C□*=
(Ma, T P e3+ Ma4 ・P C4) C□
,=Ma, "Pe4-Ma*" Pe1I Similarly, C2□
〜C25, C3□〜C3, respectively replace Ma in the above formula with M
The formula is obtained by replacing b and Me. Therefore, by performing the calculations described above, the transmittance or reflectance r, the orientation θ, and the retardation Δ can be determined.

Furthermore, a method for simplifying the calculation for solving equation (16)' is shown, and for this purpose, for example, the following conditions are assumed.

C1z 't"OC12'F OC1aki OC1,4
0Cts40C2x ”rOCxz 'FOCzs 4
Q C24'FOC2SkiOC,, :IFOCa2 year 0
Caa 40 C34'FOC35'FO When calculated by substituting these into the above (16 trials), Pgl□=r (C
,,+Cxs ・sinΔ) ・(17)P
C2x = r (Cii + C23-θsinΔ)
-(18)Pg3. = r (Caz+C33・
osinΔ) (19). In addition, it may be set as an example that satisfies the above conditions. In this case, the above O
-O formula is Pgl, = r(1+sinΔ)
・(17) 'Pg2□=r(1-20sinΔ)
・(1g)'Pg31= r (1+2θsinΔ
) −(19)′, and these (17)′～(
19) When calculating the transmittance or reflectance r, orientation θ, and retardation Δ of the optical element 43 to be measured from the formula, r = (P gZt×P g3□)/2
”・(20) sinΔ=2Pgl, / (Pg2□+P
g3. ) −1−(21)0=(2g3□−P C2,
)/2(P gl□-Pg2.-2g3□)...(
22), which allows easy calculation.

As described above, assuming that the optical element 43 to be measured is a linear phase shifter, a predetermined irradiation light Pe is irradiated to this optical element to be measured, and the transmitted or reflected output light Pf is separated into three parts.
The transmittance of the optical element 43 to be measured is determined by detecting each scene by passing through optical element groups 45□, 45□, and 45° having different types of Mueller matrices Ma, Mb, and Me, and performing calculations based on this amount of light. Alternatively, the reflectance r, orientation θ, and retardation Δ can be determined.

Further, optical element groups 45, 45□, 45. By setting the first components of the Mueller matrices Ma, Mb, and Me and the Stokes parameter re of the irradiation light Pe to the conditions described above, the calculation becomes easy.

The present invention is based on the above-mentioned principle, and will first be described with reference to FIG. 1 as an example for determining the Mueller matrix of an optical disc.

Laser light output from a laser 10 placed at a predetermined position inside the pickup, indicated by a broken line, is collimated by a collimator lens 11 and then passed through a λ/4 plate 2 to become circularly polarized light Pa. Become.

This circularly polarized light Pa has each rotation angle θ6 with respect to the base plane.
．． 06 is variably held in the pickup, the polarizer 13 is made of one λ/4 plate, and the irradiation light pb of the desired polarization is passed through
After that, it further passes through the spectroscopic mirror 151.15□ and reaches the total reflection mirror 16.

The irradiated light reflected by the total reflection mirrors 1 and 6 is focused into light by the objective lens 17, and then is irradiated as actual irradiated light Pb' onto the reflective surface 251 of the optical disc 25 on which tracks are formed.

The objective lens 17 is installed in the pickup main body so as to be movable in the tracking direction and the focus direction by drive currents flowing through a tracking coil 23 and a focusing coil 24 arranged in the vicinity thereof.

The reflected light Pc reflected by the reflective surface 25□ passes through the objective lens 17 again and becomes parallel light, and then the total reflection mirror 1
6 and reaches the spectroscopic mirror 152. Reflective surface 25.
As shown in FIG. 3, the substrate 254 is covered with a substrate 254 made of polycarbonate or the like, and optical effects such as birefringence that occur when light is reflected mainly occur when it passes through this substrate.

The reflected light reflected by the spectroscopic mirror 15□ is 1 spectroscopic mirror 1
53.15 15. The reflected light to be measured P C
, , pass through optical element groups 18a, 18b, 18c, and 18d as PC2, PC3, and PC4, respectively.

Each of these optical element groups consists of J, (a λ/4 plate set at a desired rotation angle with respect to the mold surface and an analyzer,
After optically processing the passing reflected light to be measured, each photodetector 1
Incident light Pd□ incident on 9a, 19b, 19c, 19d
, Pd2, Pd, , Pd, respectively.

On the other hand, the reflected light that has passed through the spectroscopic mirror 15□ is reflected by the spectroscopic mirror 151, and then from this reflected light to the reflective surface 251
The light enters a control information detector 20 that detects tracking and focusing information of the upper irradiation point.

Reference numerals 21 and 22 denote a polarizer rotation drive device and a λ/4 plate rotation drive device provided in the pickup, respectively, and drive output from the rotation drive circuit 27 based on the rotation angle command signal S4 from the signal processing device 33. Polarizer 13 according to the signal,
and one λ/4 plate 4 are set to desired rotation angles θ and θ6.

Reference numeral 26 denotes a spindle motor which rotates the optical disk λ at a desired rotational speed by means of a driving means (not shown).

The light amount signals detected by each photodetector 19a to 19d are A
After being converted into a digital signal by the /D converter 32, the signal is input to a signal processing device 33, where various arithmetic operations are performed. Further, this signal processing device 33 inputs a rotation information signal S from the spindle motor 26 and detects rotation information equivalent to that of an optical disk.
The track position of the irradiation point is detected by inputting the position signal SG of the potentiometer 36 which detects the movement position of the pickup 5, and also the track jump command signal Sj, the polarizer 13 inside the pickup and the λ/4 plate 4 Rotation angle command signals S4 for setting rotation angles θ9 and θ6 are output, respectively.

The pickup control circuit 28 receives tracking and focusing information signals output from the control information detector 20, and outputs a tracking control signal S and a focus control signal S2 to perform these controls.

The objective lens drive circuit 31 inputs the focus control signal S2 and the high frequency signal of the tracking control signal S1 selected by the filter 29, and picks up each drive current based on these signals.
Each signal is output to the tracking coil 23 to drive the objective lens 17. The pickup drive circuit 30 also inputs the low frequency number 42 of the tracking control signal S□ selected by the filter 29, and drives a pickup drive means (not shown) based on this signal to once move the entire pickup in the track direction. Let's do it.

Furthermore, the pickup control circuit 28 includes a signal processing device 33
A tracking control signal S1 based on a track jump command signal S3 from the irradiation point is outputted to enable track jump movement of the irradiation point.

These series of focus control, tracking control, and track jump control are known techniques, and detailed explanations thereof will be omitted.

The operation of the apparatus of the present invention having the above configuration will be explained.

In addition, the relationship between the irradiation light pb, which is the output light of the λ/4 plate 14, and the actual irradiation light Pb', which is the output light of the objective lens 17, and the reflected light Pc from the reflective surface 25□, which is similar to an optical disk, and each optical element group. Measured reflected light Pc which is the incident light of 18a to 18d
The relationship of Pc4 varies depending on the optical characteristics of the spectroscopic mirror, objective lens 17, and total reflection mirror 16 interposed therebetween, but for the sake of simplicity, pb=
pb', Pc=Pc1=Pc2=Pc3=Pc4.

These setting conditions can be achieved by inserting an optical element having appropriate optical characteristics at a predetermined position in the optical path for correction. Further, by performing arithmetic processing that takes into consideration the difference in these characteristics, it becomes possible to perform correction in one equivalent manner, but a description of these correction methods will be omitted.

The Stokes parameter Pc of the reflected light Pc is as described above (
1) Calculate using the formula.

In this case, each Mueller matrix of the λ/4 plate and analyzer of each optical element group 18a to 18d corresponds to A and M8 in the same equation. Then, the rotation angles of the λ/4 plate and the analyzer of the optical element group 18a are each set to 0.0, those of the optical element group 18b are set to O5π/2, and those of the optical element group 18c are set to π/4.
, π/4, and that of the optical element group 18d to 0, π/4.
4, the photodetectors 19a to 1
The amounts of the incident lights Pd1 to Pd4 detected at 9d correspond to Pd1 to Pd4 in the equations (2) to (5) described above.

Therefore, the Stokes parameter Pc of the reflected light Pc can be obtained by calculating the above equation (6).

On the other hand, the Mueller matrix of the reflective surface 251 of the optical disc is
This is carried out by a method using the above-mentioned equation (7).

In this case, the Mueller matrix at the irradiation position of one reflecting surface 251 corresponds to M6 in the equation. And each rotation angle θ5 of the polarizer 13 and the λ/4 plate 14. θ6 is 1) θ, = 0, θ6 = O1 2) 0. =π/2. θ,=O1 3) θ,=λ/4, θ6=λ/4. 4) Sequentially set each state of θ, = 0, θ6 = λ/4. If the Stokes parameters of the reflected light Pc obtained by irradiating the same irradiation position on the reflective surface with the respective irradiation lights Pb1 to Pb4 obtained when O6 is set to each of 1) to 4) are Pc1=Pc4, These correspond to the Stokes parameters Pcl to Pc4 in equations (8) to (11) described above.

Next, an actual measurement example will be explained.

A spiral track 252 is formed in a predetermined area of the reflective surface 251 of the optical disk, and FIG. 2 shows the circumference of the spiral track 252.

The signal processing device 33 outputs a rotation information signal Ss, a position (i.
6 respectively to track 25. When the irradiation point reaches the irradiation position A, a rotation angle command signal S4 is output and the polarized light in the pickup 35 is detected. Each rotation angle θ of the child 13 and the λ/4 plate 14 is set to θ=0.06=0. When the irradiation point reaches each irradiation position A to An-1 corresponding to a preset rotation angle, the incident light amount data of the photodetectors 19a to 19d detected at each of these positions is It is sequentially stored along with the information in the memory within the signal processing device. And irradiation position A. When reaching An at the same rotation angle as the track jump command signal S
, to make the irradiation point jump by one track and return to A again. At the same time, a one-rotation angle command signal S4 is output, and the polarizer 13 and the λ/4 plate 1 in the pickup 35 are output.
4, each rotation angle θ6, O6 is θ5=π/2.0G.
= 0. Then, when the irradiation point reaches each irradiation position A, to An-1 again, the incident light amount data of the photodetectors 19a to 19d detected at those positions is stored together with the position information. Similarly, the rotation angles θ8 and O6 of the polarizer and the λ/4 plate are set to O6=π/4 and θ6=π, respectively.
The incident light amount data at each of the irradiation positions A to An-1 when set to the states θ5=0 and θ6=π/4 are stored together with position information.

After performing the above measurements, the signal processing device 33 further performs arithmetic processing on the stored incident light amount data.
The Mueller matrix of each irradiation position A to An-1 on the optical disc is calculated.

For example, the Mueller matrix at the irradiation position A1 is calculated as follows.

The signal processing device 33 retrieves the incident light quantity data of the incident lights Pd1 to Pd4 from the memory when the rotation angles θ5.06 of the polarizer 13 and the λ/4 plate 14 are set to the conditions of 1) above, and ) is calculated to obtain the Stokes parameter PCI of the reflected light Pc.

Similarly, the above rotation angles θ9 and θ6 are set to 2) to 4).
Each incident light amount data when set to each state is sequentially retrieved from the memory, and each Stokes parameter Pc2, Pc3, and Pc4 of the reflected light Pc at that time is determined. Next, based on each of these Stokes parameters, the above (
12) Calculate the equation to calculate the Mueller matrix M□ of the irradiation position A.
seek.

In the same way, the incident light amount data corresponding to each irradiation position A2 to An-1 is sequentially pulled out from the memory, and the above (6), (
12) The Mueller matrices M2 to Mn (at these positions) are obtained by calculating the equation.

34 is a display that displays these measurement results.
For example, track position can be displayed as a display method.

There are various possible methods, such as a method of digitally displaying these measurement results together with the rotation angle information, or a graphic display that displays the color divisions of the optical disk surface based on the position information and measurement results, but detailed explanations of these are omitted. do.

Next, assuming that the optical characteristic of the optical disc is a linear phase shifter, an example in which the reflectance, orientation, and retardation are determined will be described with reference to FIG.

A laser beam outputted from a laser 50 placed at a predetermined position within a pickup 69 shown by a broken line is collimated by a collimator lens 51, and then passed through an optical element group 52 consisting of a λ/4 plate, a polarizer, etc. It passes through and becomes irradiated light Pe having desired polarization characteristics. Furthermore, this irradiation light Pe passes through the spectroscopic mirrors 531.53□ and reaches the total reflection mirror 54. The irradiated light reflected by the total reflection mirror 54 is focused by the objective lens 55 and then irradiated as actual irradiated light Pe' onto the reflective surface 61° of the optical disk 61 on which tracks are formed.

The objective lens 55 is installed inside the pickup so that it can be moved in the tracking direction and the focus direction of the optical disc by each current flowing through a tracking coil 59 and a focusing coil 60 arranged in the vicinity thereof.

The reflected light Pf reflected by this reflective surface 61□ passes through the objective lens 55 again and becomes parallel light, and then passes through the total reflection mirror 55.
4 and reaches the spectroscopic mirror 532. Reflective surface 61□
As shown in FIG. 7, a substrate 61. is made of polycarbonate or the like. The optical effects such as birefringence that occur when light is reflected mainly occur when it passes through this substrate.

The reflected light reflected by the spectroscopic mirror 53□ is further transmitted to the spectroscopic mirror 53. ．． 534, the reflected light to be measured PfL,
Optical element groups 56a and 56 as Pf, , Pf, respectively
b, passing through 56c. Each of these optical element groups consists of a λ/4 plate, an analyzer, etc., and after optically processing the reflected light to be measured, detects the incident light Pg□, Pgz, and Pgz that enters each photodetector 57a, 57b, and 57c, respectively. Idemitsu.

On the other hand, the reflected light that has passed through the spectroscopic mirror 53□ is reflected by the spectroscopic mirror 53□, and then from this reflected light to the reflective surface 61□.
The light enters a control information detector 58 that detects tracking and focusing information of the upper irradiation point.

Reference numeral 62 denotes a spindle motor that rotates the optical disk at a desired rotation speed by a drive means (not shown).

The light amount signals detected by each of the photodetectors 57a, 57b, and 57c are converted into digital signals by an A/D converter 67, and then input to a signal processing device 68, which performs various arithmetic processing. will be carried out. This signal processing device 68 also receives a rotation information signal S from the spindle motor 62.
g is input to detect the rotation information of the optical disc holder. At the same time, the position signal Sii of the potentiometer 70 which detects the moving position of the pickup holder is inputted to detect the track position of the irradiation point, and furthermore, a track jump command is issued. Outputs signal S1°.

The pickup control circuit 63 receives tracking and focusing information signals outputted from the control information detector 58, and outputs a tracking control signal S1 and a focus control signal S to perform these controls.

The objective lens drive circuit 66 inputs the focus control signal S and the high frequency signal of the tracking control signal S7 selected by the filter 64, and picks up each drive current based on these signals to the focusing coil 60 in the burner,
The signals are output to the tracking coils 59 to drive the objective lens 55. The pickup drive circuit 65 also inputs the low frequency signal of the tracking control signal S selected by the filter 64, and drives a pickup drive means (not shown) based on this signal to move the entire pickup 69 in the track direction.

Furthermore, the pickup control circuit 63 includes a signal processing device 68.
A tracking control signal S7 based on the track jump command signal s1o from the irradiation point is outputted to enable track jump movement of the irradiation point.

These series of focus control, tracking control, and track jump control are known techniques, and detailed explanations thereof will be omitted.

The operation of the apparatus of the present invention having the above configuration will be explained.

The relationship between the irradiation light Pg, which is the output light of the optical element group 52, and the actual irradiation light Pe', which is the output light of the objective lens 55, and the relationship between the reflected light Pf from the reflective surface 611 of the optical disc j1 and each optical element group 56a, What is the relationship between the measured reflected lights Pf, ~Pf, which are the incident lights of 56b and 56c?

Although the characteristics differ depending on the optical characteristics of each spectroscopic mirror, objective lens 55, and total reflection mirror 54 interposed therebetween, for the sake of easy explanation, Pe=Pe', Pf=
It is assumed that Pf,=Pf2=Pf.

These setting conditions can be achieved by inserting an optical element having appropriate optical characteristics at a predetermined position in the optical path for correction. Further, by performing arithmetic processing that takes into consideration the difference in these characteristics, equivalent correction becomes possible, but a description of these correction methods will be omitted.

A measurement example will be described in which the reflectance r, azimuth θ, and retardation Δ of the irradiation position on the reflective surface 61□ of the optical disc are determined using the above-mentioned equation (16) under the above setting conditions.

However, the irradiation position of the optical disc and each optical processor 56a,
The Mueller matrices of 56b and 56c are M, Ma, respectively.
Mb and Me, and the first components of these Mueller matrices are [MaiMa2Ma3Ma4] and CMblMbz, respectively.
N1bi Mbn], [Me, Me, Me.

Mc4].

Furthermore, the amounts of incident light detected by each photodetector 57a, 57b, and 57c are P gll, Pg2□, and P g
31, and the Mueller matrix when the reflective surface 611 of the optical disc is assumed to be a linear phase shifter is M'.

Reflective surface 61 on the optical disc. A spiral track 61 . is formed, a part of which is shown in FIG.

The signal processing device 68 outputs a position signal S□□1 rotation information signal S
, respectively, and position information such as the track position and rotation angle of the irradiation point that is tracked and controlled along the track 61□ is detected. When starting the measurement, a track jump command signal S is outputted to a desired irradiation position on the reflective surface 611, for example, irradiation position B in FIG. Move this to start measuring. Each irradiation position 8 corresponds to a rotation angle where the irradiation point is set in advance.
1 to Bn, the incident light amount data of the photodetectors 57a to 57c detected at each of these positions is sequentially stored in the memory in the signal processing device 68 together with the position information.

After performing the above measurements, the signal processing device 68 further performs arithmetic processing based on the stored incident light amount data, and determines each irradiation position B on the optical disc.

~Calculate the reflectance r, orientation θ, and retardation Δ of Bn.

For example, when determining the reflectance r, azimuth θ, and retardation Δ of irradiation position B, the corresponding incident light amount data is retrieved from the memory and the equation (16) is solved. However, as described above, each optical element group 5
The first component of the Mueller matrix of 6a, 56b, 56c,
It can be easily determined by setting the Stokes parameters of the irradiation light Pa respectively.

Similarly, the incident light amount data corresponding to each of the irradiation positions B1 to Bn is sequentially retrieved from the memory, and
2) Calculate the reflectance r at these positions by calculating the formula
Find the orientation θ and retardation Δ.

Reference numeral 71 denotes a display for displaying these calculation results.1 Display methods include a method of digitally displaying these measurement results together with positional information of the optical disk such as track position and rotation angle, and a method of displaying these measurement results digitally together with positional information of the optical disk such as track position and rotation angle; Various methods are conceivable, such as a graphic display that displays the disc surface in different colors, but a detailed explanation of these will be omitted.

Next, FIG. 9 shows another embodiment.

This is the optical element group 18a to 18d having a λ/4 plate and an analyzer set to each of the conditions described above in FIG.
, spectroscopic mirror 15. ~15. Instead, the respective rotation angles 07, θ with respect to the reference plane. This is an example in which a λ/4 plate 75 and an analyzer 76 which are variably held in a pickup are used.

Portions common to those in FIG. 1 are given the same symbols and their explanations will be omitted.

77 and 78 are λ provided in the pickup, respectively.
/4 plate rotation drive device and analyzer rotation drive device, the drive signal output from the rotation drive circuit 79 based on the rotation angle command signal S□ from the signal processing device 33' causes the rotation angle of λ/4.
The plate 75 and the analyzer 76 are rotated at the desired rotation angle θ7.08.
Set to .

Therefore, when determining the Stokes parameter of the reflected light Pc, these rotation angles (θ7, θ8) are sequentially (0, O), (
0, π/2), (π/4, π/4), (0, π/4
). And the light of the incident light Pd at each setting -ff
The Stokes parameter of the reflected light Pc can be determined by sequentially detecting iPdl-Pd4 with the photodetector 19 and calculating the above equation (6) based on these light amount data.

However, in the case of this embodiment, in order to capture the above-mentioned light amount data, it is necessary to perform light amount detection at the same irradiation position four times under the same irradiation light source. Therefore, the measurement time required is at least four times that of the embodiment shown in FIG. 1 described above.

Similarly, in the embodiment shown in FIG. 5, instead of the optical element groups 56a to 56c1 and the spectral mirrors 537 and 534, λ/4 plates held in the pickup so that their rotational angles relative to the reference plane can be varied are used. It is clear that similar measurements can be made using a device using an analyzer.

In the embodiment shown in FIG. 1, the sub-chamber method of the Mueller matrix at each irradiation position for one round of the track was shown, but the measurement order is not limited to this. By irradiating the same irradiation position on the track with irradiation light having the four types of polarization characteristics described above and determining the amount of light detected by each photodetector at that time, it is possible to calculate the Mueller matrix. Of course, various methods can be considered for obtaining the light amount data.

In addition, a polarizer 1 rotatably held within the pickup
3 is not limited to this, for example, λ/4
Various embodiments are conceivable, such as a Faraday element whose polarization plane is rotated by voltage may be used instead of the plate 12 and the polarizer 13.

(Effects of the Invention) According to the present invention, it is possible to completely measure the optical characteristics of a disk such as a substrate while the optical disk is actually used as a recording medium. Therefore, by analyzing the measurement results, it is possible to contribute to the investigation of various causes of errors that occur during recording and reproduction using optical discs. It can also be used for various inspections, such as checking the performance of substrates and checking whether optical discs are good or bad.

[Brief explanation of the drawing]

FIG. 1, FIG. 5, and FIG. 9 are configuration diagrams showing one embodiment of the present invention. FIG. 2, FIG. 3, FIG. 4, FIG. 6, FIG. 7, and FIG. 8 each show a diagram for explaining the present invention. 10.50... Laser, 11.51... Collimator lens, 12.14... λ/4 plate, 13... Polarizer, 15□~15i53□~534... Spectroscopic mirror,
16.54... Total reflection mirror, 17.55... Objective lens, 18a-l 8d, 52.56 a-56 c
- Optical element group, 19a to 19d, 57a to 57c
- Photodetector, 20.58... Control information detector, 21.
... Polarizer rotation type ia device, 22.77 ... λ/4 plate rotation drive device, 11.61 ... Optical disk, 26.6
2...Spindle motor, 27.79...Rotation drive circuit, 28.63...Pickup control circuit, 29.
64...Filter, 30.65...Pickup drive circuit, 31.66...Objective lens drive circuit 232.
67... A/D converter, 33.68... Signal processing bag C, 34, 71... Display, 35.69...
Pickup, 36.70... Potentiometer, 7
5...λ/4 plate, 76...Analyzer, 78...Analyzer rotation drive device Figure 1 Figure 4 Procedural amendment (voluntary) February 18, 1988 1, Incident display 3 , Relationship with the case of the person making the amendment Patent applicant address 1-153 Suzuki-cho, Kodaira-shi, Tokyo 187
(0423) 45-3353 Ming Im,
Column for detailed description of the invention. 5. Contents of the amendment (1) In the 13th line of page 12 of the specification, the statement ``By calculating as described above'' has been changed to ``Calculating to obtain the unknowns r, θ, and Δ from equation (16)' respectively. By doing so, it is corrected to ``. (2) Amend the statement "The above O-O formula is" on page 13, line 10 of the Memorandum to "the above formulas (17) to (19) are" 6(3) Section 15 of the specification The description of "movement in the track direction and focus direction" in lines 13 to 14 of the same page is corrected to "movement of the irradiation point on the reflective surface 251 in the radial direction and focus adjustment." (4) r Substrate 25 on page 15, line 20 of the specification. The description of J is corrected to "Substrate 25." (5) The statement "and the entire optical disc A is moved in the track direction" on page 18, line 16 of the specification is corrected to "the entire optical disc 11 is moved in the radial direction of the optical disc A." (6) “Various methods?” on page 24, line 8 of the specification.
amend the statement to "various methods...". (7) The description “moves in the optical disc focus direction” on page 25, line 6 to line 7 of the same page has been changed to “reflective surface 6
The radial movement of the irradiation point on 1□ and the focus adjustment are corrected to ``. (8) In the 19th line of page 27 of the book M, the statement ``and the entire disk is moved in the track direction'' is corrected to ``the entire disk is moved in the radial direction of the optical disk.'' (9) The statement "using the above-mentioned formula (16)" on page 29, line 4 to line 5 of the same page of the specification is deleted. (10) In the fourth line of page 31 of the specification, [the description of irradiation light PaJ is amended to ``irradiation light PeJ. Written amendment (voluntary) 1. Indication of the case 1985 Inter-Patent No. 250331 2. Title of Invention Method for Measuring Optical Characteristics of Optical Discs 3, Relationship to the Case of Person Who Makes Amendment Patent Applicant Address 1-153 Suzuki-cho, Kodaira-shi, Tokyo 187
(0423)45-33534, Claims column and Detailed description of the invention column of the specification subject to amendment. (2) The description of "polarization characteristics" on page 3, line 6 of the specification is corrected to "polarization characteristics." 6. Attachment stating the scope of claims after amendment to the list of attached documents 1 general paper Claims: An optical disc is irradiated with focused laser irradiation light, and the irradiation light is calculated based on the reflected light from the optical disc. A method for measuring optical characteristics of an optical disc, comprising controlling tracking and focusing, and further measuring polarization characteristics of the optical disc based on the reflected light.

Claims (1)

[Claims] irradiating an optical disc with focused laser irradiation light, controlling tracking and focus of the irradiation light based on reflected light from the optical disc, and further measuring deflection characteristics of the optical disc based on the reflected light. A method for measuring optical characteristics of an optical disc, characterized by: