JPH0366737B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an apparatus for measuring the Mueller matrix of an optical element, and more particularly to an optical pickup apparatus for measuring the optical characteristics of a substrate for an optical disk. (Prior Art) Conventionally, an ellipsometer or a similar device has been used to measure the optical characteristics of a substrate of an optical disk. In these devices, the disk to be measured is irradiated with known polarized light of a parallel light beam, and the transmitted or reflected light is passed through, for example, a rotating analyzer to measure its polarization state. The optical properties of the measurement disk substrate were being 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 light incident on the substrate is not a parallel light beam but a focused light 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 the ellipsometer cannot be made as small as the width of the actual track formed on the disk, it has been difficult to determine the effect that changes in the optical properties of minute regions have on the actual reproduced signal. . In addition, the shape of the ellipsometer has become larger to improve the precision of the optical axis, and
The disadvantage was that it was difficult to make adjustments when the object to be measured was attached, and that it took time to make these adjustments. The object of the present invention is to provide an optical pickup device that solves these problems. (Means for Solving the Problem) In an optical pickup device, a means for irradiating an optical disk with focused laser irradiation light, and a polarization setting for selectively making the irradiation light polarized into four polarized lights by inputting a drive signal. control information detection means for detecting a tracking error and a focus error of the irradiation point of the laser irradiation light based on the reflected light from the optical disk; and polarization component division means for dividing the reflected light into four polarization components. and four light amount detection means for detecting the light amount of each of the polarized light components. (Function) By using the optical pickup device of the present invention having the above configuration, four types of polarized laser beams are irradiated to the same irradiation position on the optical disk while tracking control and focus control are applied. Total amount detected by the light amount detection means in 4.
It becomes possible to measure the Mueller matrix of an optical disk based on the 16 light intensity data. (Example) When measuring the Mueller matrix of an optical element to be measured, the characteristics of the optical element of the measurement system are expressed using the Mueller matrix, 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, the optical element to be measured is sequentially irradiated with four types of predetermined polarized light, and the Stokes parameters of each transmitted light or reflected light are measured. There is a way to do it. 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. Alternatively, it is necessary to detect the amount of reflected light using a photodetector. The principle will be explained below using FIG. 4. The linearly polarized laser beam emitted from the laser 1 is made into parallel light via the collimator lens 2, and is converted into circularly polarized light Pa by passing through the λ/4 plate 3.
becomes. 4 and 5 are a polarizer and a λ/4 plate that have predetermined rotation angles θ ₁ and θ ₂ with respect to a certain reference plane, and by appropriately selecting these rotation angles θ ₁ and θ ₂ , the passing circle can be adjusted. The optical element 6 to be measured is irradiated with the polarized light Pa as the irradiated 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, which have rotation angles θ ₃ and θ ₄ with respect to the reference plane, respectively, and then passes through a photodetector 9. The amount of light is detected as the 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. Let the Stokes parameters of the output light Pc and the incident light Pd be respectively, and the λ/4 plate 7 and the analyzer 8
If the Mueller matrices of are respectively 7 and 8, then =8・7・ ...(1). The amount of light detected by the photodetector 9 is the amount indicating the first component of the Stokes parameter of the incident light Pd, and the Stokes parameter of the incident light Pd under each condition shown below is 1, 2, 3, 4, Furthermore, these first components are Pd1, Pd2, Pd3,
Assuming Pd4, the rotation angles of λ/4 plate 7 and analyzer 8 are θ ₃ =0, θ ₄
= 0, equation (1) is 1=1/21 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 1 0 0-1 0 Pc ₁ +Pc ₂ Pc ₃ Pc ₄ =1/2Pc ₁ +Pc ₂ Pc ₁ +Pc ₂ 0 0
Then, Pd1 is Pd1=1/2 (Pc ₁ + Pc ₂ )...
(2) becomes. Similarly, when θ ₃ =0 and θ ₄ =π/2, Pd2=1/2(Pc ₁ −Pc ₂ ) (3). Similarly, when θ ₃ =π/4 and θ ₄ =π/4, Pd3=1/2(Pc ₁ +Pc ₃ )...(4). Similarly, when θ ₃ =0 and θ ₄ =π/4, Pd4=1/2(Pc ₁ +Pc ₄ )...(5). Calculating Pc ₁ to Pc ₄ from equations (2) to (5) above, Pc ₁ = Pd1 + Pd2 Pc ₂ = Pd1-Pd2 Pc ₃ = 2Pd3- (Pd1 + Pd2) Pc ₄ = 2Pd4- (Pd1 + Pd2) ... (6 ) becomes. Therefore, the light emitted from the optical element 6 to be measured
To find the Stokes parameters of Pc,
It can be determined by setting the rotation angles of the λ/4 plate 7 and 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. Letting the Mueller matrix of the optical element 6 to be measured be 6 and the Stokes parameter of the irradiation light Pd, the following equation is obtained: =6·...(7). The irradiation light Pb has a desired Stokes parameter by appropriately selecting the rotation angles θ ₁ and θ ₂ of the polarizer 4 and the λ/4 plate 5 as shown below. If the Stokes parameters of the output light Pc obtained by irradiating the optical element 6 with these irradiation lights Pb are respectively 1, 2, 3, and 4, the above equation (7) becomes as follows. The rotation angles of the polarizer 4 and the λ/4 plate 5 are respectively θ ₁
= 0, θ ₂ = 0, the irradiated light Pb becomes horizontal linearly polarized light, and equation (7) is 1=Pc1 ₁ Pc1 ₂ Pc1 ₃ Pc1 ₄ =M6 ₁₁ M6 ₁₂ M6 ₁₃ M6 ₁₄ M6 ₂₁ M6 ₂₂ M6 ₂₃ M6 ₂₄ M6 ₃₁ M6 ₃₂ M6 ₃₃ M6 ₃₄ M6 ₄₁ M6 ₄₂ M6 ₄₃ M6 ₄₄ 1 1 0 0 = M6 ₁₁ +M6 ₁₂ M6 ₂₁ +M6 ₂₂ M6 ₃₁ +M6 ₃₂ M6 ₄₁ +M6 ₄₂ ...(8). Similarly, if θ ₁ = π/2 and θ ₂ = 0, the irradiation light
Pb becomes vertically linearly polarized light, and equation (7) is 2=Pc2 ₁ Pc2 ₂ Pc2 ₃ Pc2 ₄ = M6 ₁₁ M6 ₁₂ M6 ₁₃ M6 ₁₄ M6 21 M6 ₂₂ M6 ₂₃ M6 ₂₄ M6 ₃₁ M6 ₃₂ M6 ₃₃ M6 ₃₄ M6 _{41 M6 42} M6 ₄₃ M6 ₄₄ 1 −1 0 0=M6 ₁₁ −M6 ₁₂ M6 ₂₁ −M6 ₂₂ M6 ₃₁ −M6 ₃₂ M6 ₄₁ −M6 ₄₂ ...(9). Similarly, when θ ₁ = π/4 and θ ₂ = π/4, the irradiated light Pb becomes linearly polarized light of π/4, and equation (7) becomes 3=Pc3 ₁ Pc3 ₂ Pc3 ₃ Pc3 ₄ =M6 ₁₁ M6 ₁₂ M6 ₁₃ M6 ₁₄ M6 ₂₁ M6 ₂₂ M6 23 M6 24 M6 ₃₁ M6 ₃₂ M6 ₃₃ M6 ₃₄ M6 ₄₁ M6 ₄₂ M6 ₄₃ M6 ₄₄ 1 0 1 0=M6 ₁₁ +M6 ₁₃ M6 ₂₁ +M6 _{23 M6 31 + M6 33} M6 ₄₁ +M6 ₄₃ ...(10) becomes. Similarly, if θ ₁ = 0 and θ ₂ = π/4, the irradiation light
Pb becomes right-handed circularly polarized light, and equation (7) is 4=Pc4 ₁ Pc4 ₂ Pc4 ₃ Pc4 ₄ = M6 ₁₁ M6 ₁₂ M6 ₁₃ M6 ₁₄ M6 ₂₁ M6 ₂₂ M6 ₂₃ M6 ₂₄ M6 ₃₁ M6 ₃₂ M6 ₃₃ M6 ₃₄ M6 ₄₁ M6 ₄₂ M6 ₄₃ M6 ₄₄ 1 0 0 1=M6 ₁₁ +M6 ₁₄ M6 ₂₁ +M6 ₂₄ M6 ₃₁ +M6 ₃₄ M6 ₄₁ +M6 ₄₄ ...(11). From the above equations (8) to (11), becomes. In addition, each Stokes parameter of the output light in the above equation
Pc1 to Pc4 can be determined by the method described above. In this way, by sequentially irradiating the irradiation light Pb of four types of polarized light onto the optical element to be measured 6 and determining each Stokes parameter 1 to 4 of the output light Pc from the optical element to be measured, the Mueller of the optical element to be measured 6 can be calculated. It is possible to measure matrices. The optical pickup device of the present invention is used based on the above-mentioned principle, and one embodiment thereof will be described below in the first embodiment.
This will be explained using figures. Optical pickup device 3 of the present invention indicated by a broken line
A laser beam output from a laser 10 placed at a predetermined position within the laser beam 5 is collimated by a collimator lens 11, and then passes through a λ/4 plate 12 to become circularly polarized light Pa. This circularly polarized light Pa passes through a polarizer 13 and a λ/4 plate 14 held in an optical pickup device 35 such that their respective rotation angles θ ₅ and θ ₆ with respect to a reference plane are variable, and irradiates desired polarized light. After becoming light Pb, it further passes through spectroscopic mirrors 15 ₁ and 15 ₂ and reaches total reflection mirror 16 . The irradiated light reflected by the total reflection mirror 16 is made into a focused light by the objective lens 17, and then is irradiated as actual irradiated light Pb' onto the reflective surface ₂₅₁ of the optical disk 25 on which a track is formed. The objective lens 17 is driven by drive currents flowing through the tracking coil 23 and focusing coil 24 arranged near the optical disc 2.
The optical pickup device 35 is installed in an optical pickup device 35 so that the irradiation point on the optical pickup device 5 can be moved in the radial direction and the focus can be adjusted. The reflected light Pc reflected by the reflecting surface 25 ₁ passes through the objective lens 17 again and becomes parallel light, and then is reflected by the total reflection mirror 16 and reaches the spectroscopic mirror 15 ₂ . As shown in Fig. 3, the reflecting surface ₂₅₁ is covered with a substrate 253 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 ₂ is separated by the spectroscopic mirrors 15 ₃ , 15 ₄ , 15 ₅ , and the reflected light to be measured Pc ₁ , Pc ₂ , Pc ₃ , Pc ₄ is transmitted to the optical element groups 18a, 18b, respectively. Pass through 18c and 18d. These optical element groups each consist of a λ/4 plate and an analyzer, each set at a desired rotation angle with respect to the reference plane, and after optically processing the reflected light to be measured that passes therethrough, each photodetector 19a, 19b, 19c, 19d
The incident lights Pd ₁ , Pd ₂ , Pd ₃ , and Pd ₄ incident on the light source are emitted, respectively. On the other hand, the reflected light that passed through the spectroscopic mirror 15 ₂ is
After being reflected by the spectroscopic mirror 15 ₁ , the reflected light enters a control information detector 20 that detects tracking and focusing information of the irradiation point on the reflecting surface 25 ₁ from this reflected light. 21 and 22 are optical pickup devices 35, respectively.
A polarizer rotation drive device provided in the
In the _plate rotation drive device, the polarizer 13 and
The plates 14 are set at desired rotation angles θ ₅ and θ ₆ , respectively. Reference numeral 26 denotes a spindle motor, which rotates the optical disk 25 at a desired rotation speed by a drive means (not shown). The light amount signals detected by each of the photodetectors 19a to 19d are converted into digital signals by an A/D converter 32, and then input to a signal processing device 33, where various arithmetic processing is performed. . Further, this signal processing device 33 inputs the rotation information signal _S5 from the spindle motor 26 to detect the rotation information of the optical disk 25, and also detects the rotation information of the optical disk 25 .
The track position of the irradiation point is detected by inputting the position signal S ₆ of the potentiometer 36 which detects the movement position of the laser beam 5, and also the track jump command signal S ₃ ,
Polarizer 13 and λ/4 in optical pickup device 35
A rotation angle command signal S ₄ for setting each rotation angle θ ₅ and θ ₆ of the plate 14 is outputted. The pick-up control circuit 28 inputs the tracking and focusing information signals output from the control information detector 20, and outputs a tracking control signal S ₁ and a focus control signal S ₂ to perform these respective controls. The objective lens drive circuit 31 inputs the focus control signal S ₂ and the high frequency signal of the tracking control signal S ₁ selected by the filter 29, and uses each drive current based on these signals for focusing in the optical pickup device 35. The signal is output to the coil 24 and the tracking coil 23, respectively, to drive the objective lens 17. The pickup drive circuit 30 also inputs the low frequency signal of the tracking control signal _S1 selected by the filter 29, and drives a pickup drive means (not shown) based on this signal to pick up the radius of the optical disk of the entire optical pickup device 35 . Perform directional movement. Further, the pickup control circuit 28 outputs a tracking control signal _S1 based on the track jump command signal _S3 from the signal processing device 33, thereby enabling track jump movement of the irradiation point. These series of focus control, tracking control, and tracking jump control are known techniques, and detailed explanations thereof will be omitted. The operation of the above configuration will be explained. 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 reflection surface ₂₅₁ of the optical disk 25 and each optical element. The relationship between the measured reflected lights Pc ₁ to Pc ₄ , which are the incident lights of the groups 18a to 18d, differs in characteristics depending on the optical properties of the spectroscopic mirror, objective lens 17, and total reflection mirror 16 interposed therebetween. However, for ease of explanation, Pb=Pb′,
It is assumed that 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. Furthermore, by performing arithmetic processing that takes into account the difference in these characteristics, equivalent correction becomes possible, but a description of these correction methods will be omitted. The Stokes parameter of the reflected light Pc is determined using the above-mentioned equation (1). In this case, λ/ of each optical element group 18a to 18d
The Mueller matrices of the four plates and analyzer are 7 in the same equation,
Compatible with M8. And λ/ of the optical element group 18a
The rotation angles of the four plates and the analyzer are set to 0 and 0, respectively, those of the optical element group 18b are set to 0 and π/2, and those of the optical element group 18c are set to π/4 and π/4, respectively.
Similarly, by setting those of the optical element group 18d to 0 and π/4, respectively, the photodetectors 19a to 1
The amounts of the incident lights Pd ₁ to Pd ₄ detected at 9d correspond to Pd1 to Pd4 in the equations (2) to (5) described above. Therefore, the Stokes parameter 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 25 ₁ of the optical disk is determined by a method using the above-mentioned equation (7). In this case, the Mueller matrix at the irradiation position of the reflecting surface 25 ₁ corresponds to 6 in the equation. and polarizer 13,
The rotation angles θ ₅ and θ ₆ of the λ/4 plate 14 are (1) θ ₅ =0, θ ₆ =0 (2) θ ₅ =π/2, θ ₆ =0 (3) θ ₅ =λ/4 , θ ₆ =λ/4 (4) θ ₅ =0, θ ₆ =λ/4 are set in sequence. Reflected light Pc obtained by irradiating the same irradiation position on the reflective surface with each irradiation light Pb ₁ to Pb ₄ obtained when θ ₅ and θ ₆ are set to each of (1) to (4)
Assuming that each Stokes parameter of is 1 to 4,
These correspond to the respective Stokes parameters 1 to 4 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 25 , and one round of the track ₂₅₂ is shown in FIG. The signal processing device 33 inputs the rotation information signal S ₅ and the position signal S ₆ , respectively, and detects position information such as the track position and rotation angle of the irradiation point whose tracking is controlled along the track ₂₅₂ , When the beam reaches the irradiation position A ₀ , the rotation angle command signal S ₄ is output to set the rotation angles θ ₅ and θ ₆ of the polarizer 13 and the λ/4 plate 14 in the optical pickup device 35 to θ ₅ =0. , θ ₆ =0. Then, when the irradiation point reaches each irradiation position A ₁ 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. When reaching An, which is at the same rotation angle as the irradiation position _A0 , a track jump command signal _S3 is output to cause the irradiation point to jump one track and return to _A0 again. At the same time, a rotation angle command signal S ₄ is output to the polarizer 13 and the λ/4 plate 14 in the optical pickup device 35.
The rotation angles θ ₅ and θ ₆ are respectively θ ₅ =π/2 and θ ₆ =0.
Set to . Then, when the irradiation point reaches each of the irradiation positions A ₁ to An-1 again, the incident light amount data of the photodetectors 19a to 19d detected at those positions are stored together with the position information. Similarly,
The rotation angles θ ₅ and θ ₆ of the polarizer and the λ/4 plate are respectively θ ₅
= π/4, θ ₆ = π/4, and θ ₅ =0, θ ₆ = π/
Each irradiation position A ₁ ~ An− when set to each state of 4.
The incident light amount data at step 1 is stored together with position information. By performing the above measurements, the memory in the signal processing device 33 stores the polarizer 13, the λ/4 plate 14,
Incident light amount data at each of the irradiation positions A ₁ to An-1 when the rotation angles θ ₅ and θ ₆ are set to the conditions (1) to (4) above are stored together with position information. After performing the above measurements, the signal processing device 33
Furthermore, calculation processing is performed based on these stored incident light amount data, and each irradiation position A ₁ to An of the optical disk is
Calculate the Mueller matrix of −1. For example, the Mueller matrix at the irradiation position _A1 is calculated as follows. The signal processing device 33 includes a polarizer 13 and a λ/4 plate 1.
When the rotation angles θ ₅ and θ ₆ of 4 are set to the conditions of (1) above, the incident light amount data of the incident light Pd ₁ to _{Pd 4} is retrieved from the memory, and the calculation of the above equation (6) is performed to calculate the reflected light. light
Find the Stokes parameter 1 of Pc. Similarly, each incident light amount data when the rotation angles θ ₅ and θ ₆ are set to each of the states (2) to (4) above is sequentially retrieved from the memory, and each Stokes parameter of the reflected light Pc at that time is obtained. Find 2, 3, and 4 respectively. Next, Equation (12) is calculated based on these Stokes parameters to obtain the Mueller matrix ₁ at the irradiation position _A1 . Similarly, the incident light amount data corresponding to each irradiation position A ₂ to An-1 is sequentially retrieved from the memory, and the calculations of equations (6) and (12) are performed to calculate the Mueller matrices ₂ to -1 at these positions. demand. 34 is a display for displaying these measurement results, and display methods include, for example, track position,
Various methods can be considered, such as a method of digitally displaying these measurement results together with the rotation angle information, and a graphic display of color-coded display of the optical disk surface based on the position information and measurement results, but detailed explanations of these methods will be omitted. In the above embodiment, the method of measuring the Mueller matrix at each irradiation position for one track round 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. Further, the polarizer 13 rotatably held in the optical pickup device 35 is not limited to this, but for example, instead of the λ/4 plate 12 or the polarizer 13, a Faraday device whose polarization plane is rotated by voltage is used. Various aspects are possible, such as using an element. (Effects of the Invention) By using the optical pickup device of the present invention, it is possible to completely measure the optical characteristics of a disk such as a substrate under the conditions in which 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 disks. We also check the performance of the substrate, the quality of the optical disk, and the condition of the optical disk.
It can be used for various tests.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention. Second
3 and 4 respectively show diagrams for explaining the present invention. 10... Laser, 11... Collimator lens, 12, 14... λ/4 plate, 13... Polarizer,
15 ₁ to 15 ₅ ... Spectroscopic mirror, 16 ... Total reflection mirror, 17 ... Objective lens, 18a to 18d ...
Optical element group, 19a to 19d...photodetector, 20
... Control information detector, 21 ... Polarizer rotation drive device, 22 ... λ/4 plate rotation drive device, 25 ... Optical disk, 26 ... Spindle motor, 27 ...
Rotation drive circuit, 28...Pickup control circuit,
29...Filter, 30...Pickup drive circuit, 31...Objective lens drive circuit, 32...A/
D converter, 33...signal processing device, 34...display, 35 ...optical pickup device, 36...
...potentiometer.

Claims (1)

[Scope of Claims] 1. An optical pickup device for measuring the Mueller matrix of an optical disk, comprising means for irradiating the optical disk with focused laser irradiation light, and selectively polarizing the irradiation light into four types of polarization. polarization setting means; control information detection means for detecting a tracking error and a focusing error of the irradiation point of the laser irradiation light based on the reflected light from the optical disk; and a polarization component that divides the reflected light into four polarization components. An optical pickup device having a dividing means.