JP2007010611A - Device for determining wedge angle measurement pair - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely measure a wedge angle, to enhance the number of pair acquisitions, and to make pair combination work efficient. <P>SOLUTION: This device for determining a wedge angle measurement pair is provided with a laser beam source 2, a polarization plate 3, a stage 1 mounted with a setting jig for a rutile polarization element 4, a calescence point plate 5 for reflecting a calescence point image of a laser beam transmitted through the rutile polarization element 4, a CCD camera 6 with a height variable from a reference face and for imaging laser calescence points 9, 10, and a wedge angle measuring means having a computer 7 and a program 8 for calculating the wedge angle based on positions of the laser calescence points 9, 10. The device is further provided with a pair determination means for selecting the pair of polarization elements within a set angle difference to form a group, and for determining the pair group not only to maximize the pair number but also to minimize an average value of the angle differences in the group where the pair number gets maximum. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wedge-shaped optical component measurement pair determination device, and more particularly to a wedge angle measurement pair determination device suitable for manufacturing a wedge-shaped polarizing element for an optical isolator.

  Conventionally, measurement of a wedge-shaped optical component used in an optical isolator or the like has been performed by a shape measuring device such as a three-dimensional measuring instrument. In general, to measure the angle between two surfaces such as an optical prism, a laser beam is irradiated on the surface to be measured, and the beam spot at the light receiving point depends on the angle changed by reflection or refraction at the interface. A method of measuring the position change to obtain the angle is often used for measuring the angle between the surfaces of the optical element (for example, Patent Document 1).

  By the way, for products such as polarization-independent optical isolators that use a pair of wedge-shaped polarizing elements, the combination of which is determined by polarizing elements with the same wedge angle with high precision, the human being based on the measured angle data. Repeated the process of selecting the pair and found the optimal combination.

JP-A-9-304036

  In the measurement by a shape measuring device such as a three-dimensional measuring instrument, the magnification is limited by the size of the polarizing element, and the inspection accuracy is affected. In addition, because of the general-purpose shape measuring device, the price of the measuring device itself is high. Furthermore, since the measuring operation is manual, it takes a long time to measure. Accordingly, an object of the present invention is to provide inspection accuracy that is not limited by the dimensions of the polarizing element, and an angle measurement technique that is inexpensive and has a short measurement time.

  Furthermore, in the case of polarizing elements that are used in pairs with well-aligned angles, if a person performs a combination based on the measured angle data, it takes a lot of time to determine the combination when the number of combinations increases. In order to minimize the residual rate (the ratio of the number of polarizing elements that cannot form a pair to the number of input elements) that has the smallest angle error and that cannot be combined, skilled skills are required. Even so, as an example, for 100 polarizing elements, 42 pairs (84) can be paired, but the remaining 16 pairs are formed within a predetermined angular difference. There was a situation where it was impossible. Therefore, another object of the present invention is to improve the number of acquired pairs and to make the pair combination work more efficient and simple.

  That is, an object of the present invention is to provide a wedge angle measurement pair determination device that can measure a wedge angle with high accuracy, and can improve the number of pair acquisitions and increase the efficiency of pair combination work.

  The present invention relates to a stage for setting a polarizing element to be measured, a laser light source for irradiating laser light, a polarizing plate, a plate on which a bright spot of refracted and transmitted laser light is reflected, and a CCD for imaging the plate Consists of a camera and a computer and program for automatically recognizing the position of the bright spot by image processing. The wedge angle processed on the polarizing element is calculated from the position of the bright spot by the program, and the measured angle Data is stored in a computer, and based on the data, a combination in which the angle error is minimized and the remaining rate that cannot be combined is minimized is automatically combined by a computer program.

  That is, the wedge angle measurement pair determination device of the present invention selects a wedge angle measurement unit for a wedge-shaped optical component, a unit for storing measurement data of the wedge angle, and a pair of polarizing elements within a set angle difference. Pair determining means for determining the group of pairs so as to minimize the average value of the angle difference for the group having the maximum number of pairs as well as forming the group and maximizing the number of pairs. Means for managing data of a group of pairs.

  The wedge angle measuring means includes a laser light source, a polarizing plate, a stage on which a jig for setting a wedge-shaped optical component is mounted, and a bright spot plate for projecting a bright spot image of laser light transmitted through the wedge-shaped optical component; The camera may be provided with a camera that captures the bright spot image with a variable height from a reference plane, and a processing device that calculates a wedge angle from the position of the bright spot image.

  In the wedge angle measuring means, the wedge angle may be obtained by a bisection method from the position coordinates of the bright spot on the bright spot plate and the distance between the wedge-shaped optical component and the bright spot plate.

  The pair determination means calculates a pair of measurement values within a predetermined angle difference for the k (1 ≦ k ≦ n) measurement values with respect to the measurement values of n (natural number) wedge angles. The first step of each permutation is the step of creating a sequence of numbers in order from the smallest of n, creating a total of n sequences for all k, and all the n factorial permutations possible for n measurements. Starting from a certain measured value up to the nth in order, repeat the selection of the pair with the smallest angle difference except for the measurement values already selected as a pair, and the permutation giving the maximum number of pairs among all permutations When there are a plurality of permutations that determine the maximum number of pairs, it is preferable to include a step of determining a permutation that minimizes the average value of the angular differences between the pairs.

  The pair determination means may include means for selecting a pair between lots for a wedge-shaped optical component in which a pair is not formed in one lot as well as determining a group of pairs for each lot.

  In the present invention, the polarizing element to be measured is directly irradiated with laser light, and the wedge angle is calculated from the position of the bright spot. By increasing the distance between the polarizing element and the bright spot, the measurement accuracy can be increased. It does not depend on the dimensions of the polarizing element. The time required for the measurement can be completed in about 0.1 seconds or less after the polarizing element is set on the stage. Therefore, it is possible to perform highly accurate angle measurement at low speed and at high speed as compared with a general-purpose shape measuring apparatus.

  Also, since the combination processing is automatically performed by the computer program, it is possible to perform the combination processing at high speed without requiring specialized skills, and to improve the production efficiency.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a wedge angle measuring device for a rutile polarizing element according to an embodiment of the present invention, FIG. 1 (a) is a schematic diagram showing the overall configuration, and FIG. 1 (b) is a bright spot on a bright spot plate. FIG. This apparatus is refracted by passing through a stage 1 on which the XYZΘ axis can be finely adjusted for setting a polarizing element, a laser light source 2 for irradiating the polarizing element with laser light, a polarizing plate 3, and a rutile polarizing element 4. A luminescent spot plate 5 for capturing the luminescent spot of the laser beam, a CCD camera 6 for imaging the luminescent spot plate, a computer 7 for performing image processing and calculation, and a program 8 are included.

  The laser light emitted from the laser light source 2 is refracted by the rutile polarizing element 4 set on the stage 1 and projected onto the bright spot plate 5. At this time, two bright spots are generated by birefringence of rutile, and the polarizing plate 3 is adjusted so that the two bright spots are uniformly reflected. The laser luminescent spots 9 and 10 projected on the luminescent spot plate 5 are imaged by the CCD camera 6, image processing is performed by a program in the computer, and the wedge angle of the rutile polarizing element is calculated from the position of the luminescent spot on the image. Is. For the laser bright spots 9 and 10, the wedge angle may be calculated using only one coordinate, and the measurement accuracy may be increased by using both coordinates.

[Angle Measurement Principle] FIG. 2 shows an angle measurement principle according to an embodiment of the present invention, FIG. 2 (a) is a perspective view showing a rutile polarizing element, and FIG. 2 (b) passes through the rutile polarizing element. It is an optical diagram which shows the luminescent point position of a laser beam. FIG. 2B shows a case for a birefringent medium, but a case where Snell's law is established for both ordinary light and extraordinary light. By using this relational expression, the wedge angle θ _x can be obtained by back calculation from the coordinates (X, Y) of the laser bright spot projected by refraction when the laser is incident on the rutile polarizing element having the wedge angle θ _x. .

  [Wedge angle calculation method] Although the Newton method and bisection method can be used for the wedge angle measurement algorithm as in this device, the angle measurement in this embodiment is more stable than the Newton method. A characteristic dichotomy is used. Hereinafter, a specific process of the wedge angle measuring method will be described.

  FIG. 2B shows the rutile polarizing element as viewed from the A position shown in FIG. This will be described with reference to this figure.

The distance between the upper end and the X-axis origin of the camera field of view X ₀ is by performing the calibration of the measurement system by using a reference workpiece (angle known rutile polarizing element), and are made known. Here, the coordinate value X ₁ is obtained by the image processing, and the emission angle θ _y2 is obtained from X ₁ .

θ _y2 = tan ⁻¹ (X ₀ + X ₁ ) / L

Snell's law is n ₀ · sin θ _x = n ₁ · sin θ _y1 and n ₀ = 1, so the following relational expression holds.

sin θ _y2 = n ₁ · sin (θ _x −θ _y1 ) (1)
sin θ _y1 = (sin θ _x ) / n ₁ (2)

Applying the addition theorem to the right side of equation (1),
sin θ _y2 = n ₁ (sin θ _x · cos θ _y1 −cos θ _x · sin θ _y1 )
= N ₁ {sin θ _x · (1-sin ² θ _y1 ) ^1/2 −cos θ _x · sin θ _y1 }
= N ₁ [sin θ _x · (1-sin ² θ _y1 ) ^1/2 − (1-sin ² θ _x ) ^1/2 · sin θ _y1 ]
Substituting equation (2)
sin θ _y2 = n ₁ [sin θ _x · {1-((sin θ _x ) / n ₁ ) ² } ^1/2 − (1-sin ² θ _x ) ^1/2 (sin θ _x ) / n ₁ }
_{= N 1 · sinθ x [{} 1 - ((sinθ x) / n 1) 2} 1/2 - (1-sin 2 θ x) 1/2 / n 1]
= N ₁ · sin θ _x {(n ₁ ² −sin ² θ _x ) ^1/2 / n ₁ − (1-sin ² θ _x ) ^1/2 / n ₁ }
= Sin θ _x {(n ₁ ² −sin ² θ _x ) ^1/2 − (1−sin ² θ _x ) ^1/2 } (3)
It becomes. here,
x = sin θ _x (4)
y = sin θ _y2 (5)
Then, equation (3) is
y = x {(n ₁ ² −x ² ) ^1/2 − (1−x ² ) ^1/2 }. Substituting both sides and subtracting y from both sides yields x {(n ₁ ² −x ² ) ^1/2 − (1−x ² ) ^1/2 } −y = 0,
Here, f (x) = x {(n ₁ ² −x ² ) ^1/2 − (1−x ² ) ^1/2 } −y,
By _obtaining a solution x _ans of f (x) = 0, the wedge angle θ _x is obtained from the equation (4). At that time, a _bisection method is used to obtain a solution x _ans of f (x) = 0.

[Dichotomy] The dichotomy is described below. A method of gradually narrowing the width of the section (a, b) in which the solution of f (x) = 0 is considered, while checking the sign of f (x) is called a section reduction method. There are various ways to reduce the section width, but the simplest method is to reduce the width by half, which is the bisection method.

In the bisection method, when the function f (x) is a continuous function, if f (a) <0 and f (b)> 0, the solution x _{ans in} which f (x _ans ) = 0 is obtained in the interval (a , B) is used.

The procedure for finding the solution is as follows.
(1) A search interval (a, b) is given. Here, the range in which the solution exists was set as a = 0 and b = 1 / (2 ^1/2 ).
(2) Search interval width d = | b−a |.
(3) x ₀ = b.
(4) Calculate x ₁ = f (x ₀ ).
(5) When x ₁ > 0, x ₀ = x ₀ −d / 2 and d = d / 2.
When x ₁ <0, x ₀ = x ₀ + d / 2 and d = d / 2.
(6) If the convergence _conditions: | _x 1 | if <x 0/1000000, the solution _{x ans} = x _0, if not, return to (4). Incidentally, the error including a convergence condition _x 0/1000000 corresponds to 0.162 "(0.162 seconds).

By repeating the above procedure, a solution x _ans = x ₀ is obtained. Therefore, when the solution x _ans obtained from the _bisection method is substituted into the equation (4), the wedge angle θ _x can be obtained as θ _x = sin ⁻¹ x _ans .

  Next, how the angle data of the polarizing elements measured by the above-described angle measuring method is combined to form a pair group will be described. Data measured by the measurer is stored as a measurement result file in the computer in the order of measurement. With respect to the measurement values of n (natural number) wedge angles based on the file, for the k (1 ≦ k ≦ n) -th measurement values, paired measurement values within a predetermined angle difference are small in angle difference. Create a sequence of numbers in order and create a total of n sequences for all k, and the first of each permutation for all n factorial permutations possible for n measurements. Starting from a certain measured value up to the nth in order, except for the measurement values already selected as pairs, the angle difference is minimized and the selection of pairs within a predetermined angular difference range is repeated; Of these, the permutation that gives the maximum number of pairs is determined, and when there are multiple permutations that give the maximum number of pairs, the group of pairs is determined through the step of determining the permutation that minimizes the average angle difference between the pairs. To do.

Specifically, for example, by performing the combination forming process shown in the flow of FIG. 3, the program automatically determines the combination of the wedge angles and generates a combination list result file. In FIG. 3, in a combination list generation step 31, a list of counterparts that can be combined is generated in ascending order of combination angle difference (combination angle error) from 1 to n of workpieces (polarization elements). For example, in the case of ₁₀₀ workpieces, there may be a maximum of ₁₀₀ C ₂ (4950) pairs. In step 32 for determining a combination pattern, the pattern having the largest number of combinations and the smallest combination angle difference average value is set.

  In the combination list result file, the measurement number to be combined and the measurement number to be combined are automatically displayed. Therefore, the measurer only needs to perform the combination work mechanically according to the numbers displayed in the angle combination list result file. That is, the measurer does not need time to determine the combination, and can efficiently work according to the display. The important point here is the combination formation processing flow shown in FIG. 3, and by this, a device for selecting the combination so that the combination having the maximum number of combinations and the minimum combination angle difference average value is selected. Therefore, it is possible to keep the residual rate that cannot be combined low.

  Next, details of the results obtained in the present embodiment will be described. In the wedge angle measurement pair determination device (this device) according to the present invention and the conventional device, the same operator resets a known polarizing element with a wedge angle of 5 ° 7.5 ′ (5 ° 7.5 minutes). The repeatability when measured 10 times was confirmed.

  Tables 1 and 2 show the repeatability of the present apparatus and the repeatability of the conventional apparatus at that time, respectively.

  From the table above, when the same polarizing element is reset in this apparatus, the variation in the wedge angle is 3σ, and in the case of this apparatus, 0.13 ′ (= 7.8 ″ (7.8 seconds)) On the other hand, in the case of the conventional apparatus, it is 0.29 ′ (= 17.4 ″). Therefore, it was found that this apparatus has improved repeatability compared with the conventional apparatus.

[Comparison of remaining rate in wedge angle combination selection processing] The following table shows that this device and the conventional device when the same operator performs angle measurement with the conventional device and this device and then performs the combination selection processing. Table 3 and Table 4 show the remaining ratio of the polarizing elements after the combination selection process in (3). FIG. 4 shows a comparison of the remaining rate between the present apparatus and the conventional apparatus.

  Further, Table 5 shows a comparison of working time required for the operator to measure the angle and select a combination between the conventional apparatus and the present apparatus.

  As shown in Tables 3 and 4 above and FIG. 4, it can be confirmed that the remaining rate after the combination selection processing in the conventional apparatus and the present apparatus has decreased from 16.4% to 3.3%. This can be said to be due to the fact that this apparatus has automatically performed a combination selection process using a computer. This is because, in the past, when the measurer determines the combination, the combination that maximizes the number of combinations is not substantially considered. This is because the combination angle difference average value is considered as the condition for determining the combination. Moreover, it can be confirmed from Table 5 that the work time is shortened to one third.

  As described above, according to the angle measuring apparatus of the present invention, it is possible to improve measurement accuracy by automatically performing angle measurement using image processing. Furthermore, in the angle combination selection process, the use of a computer does not require time for the operator to select a combination as before, and skill is not required for measurement, thus reducing the work time. . Therefore, the present invention has made it possible to improve the efficiency and simplification of the angle measurement combination work.

  By the way, if a pair cannot be formed in one lot and the remaining polarizing elements are collected and a pair is formed by the same method as selecting a pair in one lot, the pair can be further used. The number of pairs can be increased.

  In the above embodiment, a pair of rutile polarizing elements, which are birefringent materials, is determined. However, a prism made of an isotropic transparent material, etc., is used by forming a pair of prism angles with high accuracy and equality. The combination apparatus for angle measurement and pair determination according to the present invention can be used for applications to be performed.

1 shows a wedge angle measuring device for a rutile polarizing element according to an embodiment of the present invention, FIG. 1 (a) is a schematic diagram showing an overall configuration, and FIG. 1 (b) is a front view showing a bright spot on a bright spot plate. . FIG. 2A is a perspective view illustrating a rutile polarizing element, and FIG. 2B is an optical diagram illustrating a bright spot position of laser light that has passed through the rutile polarizing element. Figure. The combination formation processing flowchart. Comparison chart of survival rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stage 2 Laser light source 3 Polarizing plate 4 Rutile polarizing element 5 Bright spot plate 6 CCD camera 7 Computer 8 Program 9, 10 Laser bright spot 31, 32 steps

Claims (5)

  Simply select the wedge angle measuring means of the wedge-shaped optical component, the means for storing the measurement data of the wedge angle, and the pair of polarizing elements within the set angle difference to form a group and maximize the number of pairs A pair deciding means for deciding the group of pairs so that the average value of the angle difference is minimized for the group having the largest number of pairs, and means for managing data of the decided group of pairs Wedge angle measurement pair determination device characterized by   The wedge angle measuring means includes a laser light source, a polarizing plate, a stage on which a jig for setting a wedge-shaped optical component is mounted, and a bright spot plate for projecting a bright spot image of laser light transmitted through the wedge-shaped optical component; 2. The wedge angle measurement according to claim 1, further comprising: a camera that is variable in height from a reference plane and that captures the bright spot image; and a processing device that calculates a wedge angle from the position of the bright spot image. Pair determination device.   The wedge angle measuring means obtains a wedge angle by a bisection method from a position coordinate of a bright spot on the bright spot plate and a distance between the wedge-shaped optical component and the bright spot plate. 2. A wedge angle measurement pair determination device according to 2.   The pair determining means calculates a pair of measurement values within a predetermined angle difference for the k (1 ≦ k ≦ n) measurement values with respect to the measurement values of n (natural number) wedge angles. The first step of each permutation is the step of creating a sequence of numbers in ascending order of n, creating a total of n sequences for all k, and all the n factorial permutations possible for n measurements. Starting from a certain measured value up to the nth in order, repeat the selection of the pair with the smallest angle difference except for the measurement values already selected as a pair, and the permutation giving the maximum number of pairs among all the permutations And a step of determining a permutation that minimizes the average value of the angular differences between the pairs when there are a plurality of permutations that determine and provide the maximum number of pairs. Wedge angle measurement as described in Pair determining device.   The pair determining means includes means for selecting a pair between lots for a wedge-shaped optical component in which a pair is not formed in one lot as well as a group of pairs for each lot. The wedge angle measurement pair determination apparatus according to any one of claims 1 to 4.

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