JPWO2009139133A1 - Optical strain measurement device - Google Patents

Abstract

An object of the present invention is to provide a measuring instrument capable of collectively measuring optical distortion over a wide range. The present invention relates to an optical distortion measuring device including an optical system, a polarization measuring module, and an analyzing device. The optical system can emit circularly polarized light, elliptically polarized light, or linearly polarized light. The polarization measurement module includes a polarizer array and an area sensor. The polarizer array includes a plurality of unit units that are repeatedly arranged one-dimensionally or two-dimensionally. The polarizer array transmits light emitted from the optical system. The polarizer array transmits light emitted from the optical system and transmitted through the measurement sample. Each unit unit included in the polarizer array includes at least three types of polarizers having different transmission polarization axis directions. The area sensor can independently receive light that has passed through each polarizer of the polarizer array, and can measure the intensity of the received light. [Selection] Figure 1

Description

  The present invention relates to an apparatus for measuring a two-dimensional distribution of optical distortion.

  Polarimetry technology is indispensable for measuring retardation and optical axis caused by optical anisotropy. In particular, it is required to measure a large area at high speed for a sample such as a film or a substrate used in a liquid crystal panel. Retardation is represented by ΔnL where Δn is the birefringence of the object and L is the thickness.

  When measuring the retardation of a sample, the polarization state of a light beam incident on the sample and the polarization state of light after passing through the sample are measured. And a retardation and an optical axis can be calculated | required from the variation | change_quantity of a polarization state. The most common method for measuring the polarization is a method called a rotating polarizer method or a rotating phaser method. In this method, light intensity data is acquired while rotating a polarizer or a wave plate arranged in front of the light receiving element. When the wave plate is rotated, light is received through a fixed polarizer and the light intensity is measured. By analyzing the measured light intensity, the polarization information of the incident light can be obtained. Here, the polarization information of light is, for example, ellipticity and major axis orientation, or Stokes parameters. This method is simple. However, this method requires a driving device to rotate the polarizer or the wave plate, and cannot measure at high speed. Furthermore, when measuring the two-dimensional retardation distribution using this method, it is necessary to move the irradiation position of the light beam two-dimensionally. For this reason, it takes a lot of time to measure optical distortion such as a two-dimensional distribution of retardation using a conventional method. For this reason, the conventional method is not particularly suitable for measuring the optical distortion of a large-area sample.

  On the other hand, a camera capable of acquiring a two-dimensional distribution image of polarized light combining an area sensor composed of a CCD or CMOS and a fine polarizer array has been reported (Patent Document 1, Non-Patent Document 1). In this case, one micropolarizer having a different transmission polarization axis is arranged for each pixel of a CCD camera, and the polarization state is calculated from the output of each pixel. By using this sensor, the two-dimensional retardation distribution can be measured easily and at high speed. However, in order to measure a wide range of a sample at once, it is essential to use a wide-angle imaging lens. In such a case, the edge of the screen receives light obliquely transmitted through the sample, so that the obtained retardation has an error and it is difficult to measure accurately.

International Publication WO2004-068844 Pamphlet

Takashima Kawashima, Masanobu Sasaki, Yoshihiko Inoue, Hiroshi Honma, Nao Sato, Junichi Ota, Shojiro Kawakami, “Preparation and Application of Polarization Imaging Camera Using Photonic Crystals”, 32nd Optical Symposium, Lecture No. 3, pp. 7-8, July 5, 2007.

The problem to be solved by the present invention is to provide an optical distortion measuring apparatus capable of measuring a two-dimensional distribution of a wide range of retardation.

  A first aspect of the present invention relates to an optical distortion measuring device including an optical system, a polarization measuring module, and an analyzing device. The optical system can emit circularly polarized light, elliptically polarized light, or linearly polarized light. The polarization measurement module includes a polarizer array and an area sensor. The polarizer array includes a plurality of unit units that are repeatedly arranged one-dimensionally or two-dimensionally. The polarizer array transmits light emitted from the optical system. The polarizer array transmits light emitted from the optical system and transmitted through the measurement sample. Each unit unit included in the polarizer array includes at least three types of polarizers having different transmission polarization axis directions. The area sensor can independently receive light that has passed through each polarizer of the polarizer array, and can measure the intensity of the received light.

The analysis device can receive measurement information transmitted from the polarization measurement module. The analysis apparatus also includes a first polarization information calculation unit, a second polarization information calculation unit, a polarization change amount calculation unit, and an optical distortion calculation unit. Then, the first polarization information calculation means obtains information related to the polarization state of the light of the optical system from the information of the light of the optical system received from the polarization measurement module. The information on the light of the optical system is information regarding light emitted from the optical system and not transmitted through the measurement target. Examples of light information of the optical system are P ₁ , P ₂ , P ₃ , and P ₄ described below in this specification. Examples of information regarding the polarization state of light in the optical system are S ₁ and S ₂ .

The second polarization information calculation means obtains information on the polarization state of the light transmitted through the measurement sample from the information on the light transmitted through the measurement sample received from the polarization measurement module. The “information on the light of the measurement sample” is information relating to light emitted from the optical system and transmitted through the measurement object. Examples of information of light transmitted through the measurement sample are P ₁ ′, P ₂ ′, P ₃ ′, and P ₄ ′. Examples of “information on the polarization state of light transmitted through the measurement sample” are S ₁ ′ and S ₂ ′.

The polarization change amount calculation means obtains the polarization change amount for each unit of the polarization measurement module from the information on the polarization state of the light of the optical system and the information on the polarization state of the light transmitted through the measurement sample. . Examples of the “polarization change amount” for each unit are S ₁ ′ -S ₁ and S ₂ ′ -S ₂ .

  The optical distortion calculation means obtains information on the retardation of the measurement sample and the optical axis direction for each unit unit using the polarization change amount for each unit unit obtained by the polarization change amount calculation means. The retardation ρ and the optical axis direction θ can be obtained by performing a predetermined calculation using a “polarization change amount” for each unit unit as will be described later. The optical distortion calculation means is a means capable of performing the calculation.

  In a preferred embodiment of the optical strain measurement apparatus according to the first aspect, the polarizer array is made of a photonic crystal. As the photonic crystal, a self-cloning photonic crystal is particularly preferable. That is, by using the self-cloning photonic method, a polarizer array can be obtained as a single crystal using a substrate having a special shape.

A preferred embodiment of the optical distortion measuring apparatus according to the first aspect is that the analyzing apparatus described above further averages a polarization intensity that averages a signal related to the intensity of light that passes through a certain polarizer that is continuously photographed by the area sensor. Have averaging means. Then, information on the polarization state for each unit is obtained using the intensity averaged by the polarization intensity averaging means. For example, P ₁ is measured a plurality of times, and a value obtained by averaging this is used as P ₁ to perform a predetermined calculation. This aspect can be used in combination with any aspect of the apparatus described above.

In a preferred embodiment of the optical distortion measuring apparatus according to the first aspect, the analysis apparatus described above further includes polarization state averaging means for averaging information regarding the polarization state in adjacent units. And the information regarding a retardation and an optical axis direction is calculated | required using the information regarding the polarization state averaged by the polarization state averaging means. For example, summing the values of S ₁ in two units adjacent, the average is used as S _1, it performs a predetermined calculation. This aspect can be used in combination with any aspect of the apparatus described above.

In a preferred embodiment of the optical distortion measuring device according to the first aspect, the analysis device described above further includes amplitude ratio change storage means for storing the amplitude ratio change, and light polarization for correcting information relating to the polarization state of the light. State correction means. Here, the change in the amplitude ratio means a ratio at which the ratio of the x component and the y component of the electric field due to the light from the optical system changes through the measurement object. The amplitude ratio change is represented by “x” described later. For example, S ₁ is corrected using the value of “x”. Then, using the corrected S _1, it performs a predetermined calculation. This aspect can be used in combination with any aspect of the apparatus described above.

In a preferred embodiment of the optical strain measurement apparatus according to the first aspect, the analysis apparatus described above further includes incident angle correction means. In this aspect, the amplitude ratio change is expressed as a function of the incident angle and the refraction angle. For example, “x” to be described later is expressed as a function of an incident angle θ ₀ and a refraction angle θ ₁ in the sample. And the said incident angle (theta) ₀ is correct | amended using the information regarding the distance from the visual field center of a certain unit, the pixel count of all the visual fields, and a field angle. Then, the amplitude ratio change is corrected using information regarding the corrected incident angle θ ₀ . And the information regarding the polarization state of the light which permeate | transmitted the measurement sample is correct | amended using the correct | amended amplitude ratio change. Then, a predetermined calculation is performed using information regarding the polarization state of the corrected light. This aspect can be used in combination with any aspect of the apparatus described above.

  The second aspect of the present invention relates to an optical distortion measuring device including an optical system, a polarization measurement module, and an analysis device. The optical system can emit circularly polarized light, elliptically polarized light, or linearly polarized light. In addition, the polarization measuring module includes a wave plate array, a polarizer, and an area sensor in this order. That is, the light from the optical system passes through the wave plate array, then passes through the polarizer, and then received by the area sensor.

  The wave plate array has unit units that are repeatedly arranged one-dimensionally or two-dimensionally. The wave plate array transmits light emitted from the optical system. The wave plate array transmits light emitted from the optical system and transmitted through the measurement sample. The unit unit included in the wave plate array includes at least four types of wave plates having different fast axis directions. The polarizer has a unidirectional transmission polarization axis and transmits light transmitted through the wave plate array. The area sensor can independently receive light that has passed through each wave plate included in the wave plate array and has passed through the polarizer, and can measure the intensity of the received light.

  In the optical distortion measuring apparatus according to the second aspect of the present invention, the configuration and preferred mode of the analyzing apparatus are the same as those of the first aspect. For this reason, in order to avoid repetition, description is abbreviate | omitted as quoting description.

  The optical strain measuring apparatus of the present invention can collectively measure the retardation of a transparent and optically anisotropic sample or the two-dimensional distribution of the optical axis in a wide range. The optical strain measuring device of the present invention has a wide range of applications such as inspection processes for large-area optical components such as glass and films for liquid crystal panels. Therefore, the present invention can provide a new inspection technique.

FIG. 1 is a block diagram showing an example of the structure of an optical distortion measuring apparatus according to the present invention. FIG. 2 is a diagram showing a photonic crystal polarizer. FIG. 2A shows a substrate and FIG. 2B shows a photonic crystal polarizer. FIG. 3 is a diagram showing an example of a pattern of the polarizer array of the present invention. FIG. 4 is a diagram illustrating a configuration example of a wave plate array, a polarizer, and an area sensor. FIG. 5 is a graph showing the relationship between the incident angle and the error due to the oblique incidence. FIG. 6 is a graph in which the actually measured retardation and the relationship between the number N of pixels in the measurement unit and the number F of images are plotted. FIG. 7 is a diagram showing an optical distortion measuring apparatus according to an embodiment of the present invention. FIG. 8 is a photograph showing the retardation distribution. FIG. 8A is a photograph showing the retardation distribution before correction. FIG. 8B is a photograph showing the retardation distribution after correction.

  FIG. 1 is a block diagram showing an example of the structure of an optical distortion measuring apparatus according to the present invention. In the example of FIG. 1, a polarizer array 101 is bonded to a CCD area sensor 102 that is a light receiving element array. The area sensor is connected to the electronic circuit unit, and an output signal from the camera 103 is transmitted to an analysis device (not shown). The light emitted from the planar light source 104 is substantially circularly polarized through the circularly polarizing film 105 and passes through the sample 107. Light having circularly polarized light can be emitted by the optical system including the light source and the circularly polarizing film. The optical system can emit elliptically polarized light or linearly polarized light by changing the light source or the polarizing film. The light transmitted through the sample forms an image of the sample on the area sensor through the imaging lens 106. When no sample is present, the light from the optical system may be directly incident on the imaging lens.

  The polarizer array includes a plurality of unit units that are repeatedly arranged one-dimensionally or two-dimensionally. The polarizer array transmits light emitted from the optical system. The polarizer array transmits light emitted from the optical system and transmitted through the measurement sample. As the polarizer array, for example, a polarizer made of a photonic crystal described in Japanese Patent No. 3486334 can be used. For example, a method described in Japanese Patent No. 3325825 can be used as a method for producing the photonic crystal. FIG. 2 is a diagram showing a photonic crystal polarizer. FIG. 2A shows a substrate and FIG. 2B shows a photonic crystal polarizer. A transparent high-refractive index medium 202 and a low-refractive index medium 203 as shown in FIG. 2B are formed on the transparent material substrate 201 in which a periodic groove array as shown in FIG. 2A is formed. Laminate alternately while preserving. This figure shows a structure in which two regions whose groove directions are different by 90 ° are integrally formed. Here, by selecting the layer thickness of the mediums 202 and 203 and the period of the substrate, it can be operated as a polarizer at a specific wavelength. That is, polarized light parallel to the groove can be blocked and polarized light perpendicular to the groove can be transmitted. By forming the concave / convex pattern by changing the direction of the grooves in advance, it becomes possible to collectively form a polarizer array having different transmission axes.

  FIG. 3 is a diagram showing an example of a pattern of the polarizer array of the present invention. The arrow in the figure indicates the direction of the transmission polarization axis. In the example shown in FIG. 3, four types of polarizer arrays 301 are shown with transmission polarization axes of 0 degrees, 45 degrees, 90 degrees, and 135 degrees. Reference numeral 302 in the figure indicates an area sensor. In the example shown in FIG. 3, the size of the transmission polarization axis matches the size of the pixel of the area sensor. Such micro-polarizers are repeatedly arranged in the X and Y directions. These four micro-polarizers become one unit for polarization measurement. The following description will be made using the polarizer array 301, but the same polarization measurement is possible even when the following wave plate array is used.

  That is, as shown in Japanese Patent No. 3325825, it is possible to form a wave plate with a photonic crystal structure. A wave plate can be realized by appropriately selecting the period and film thickness of the groove array formed on the substrate (Japanese Patent Laid-Open No. 2001-51122). Therefore, by forming the concave / convex pattern by changing the direction of the groove row, it is possible to collectively form wave plate arrays having different optical axes. The wave plate array has unit units that are repeatedly arranged one-dimensionally or two-dimensionally. The wave plate array transmits light emitted from the optical system. The wave plate array transmits light emitted from the optical system and transmitted through the measurement sample. The position unit includes at least four types of wave plates having different fast axis directions. FIG. 4 is a diagram illustrating a configuration example of a wave plate array, a polarizer, and an area sensor. In the example shown in FIG. 4, the fast axis of the wave plate array 401 has four different directions as indicated by arrows. In the example shown in FIG. 4, a polarizer 402 having a uniform transmission polarization axis is disposed between the wave plate array and the area sensor 302. The axial direction of the wave plate array is set to, for example, ± 15 ° and ± 50 ° with respect to the transmission axis of the polarizer 402. Further, the phase difference of each wave plate is set to 130 °, for example.

  The polarization measurement module includes a polarizer array and an area sensor. The area sensor can independently receive light that has passed through each polarizer of the polarizer array, and can measure the intensity of the received light. When the optical distortion measuring device includes a wave plate array, the polarization measurement module includes a wave plate array, a polarizer, and an area sensor. Then, the area sensor can independently receive light that has passed through each wave plate and transmitted through the polarizer, and can measure the intensity of the received light. A CCD area sensor is an example of the area sensor.

  The analysis device receives measurement information transmitted from the polarization measurement module. The analysis apparatus includes first polarization information calculation means, second polarization information calculation means, polarization change amount calculation means, and optical distortion calculation means. The analysis device has an input / output unit, a control unit, a calculation unit, and a storage unit, and each element is connected by a bus or the like. The arithmetic unit is provided with a circuit for performing a predetermined arithmetic operation. In addition, a control program for performing a predetermined calculation may be stored in the storage unit. When predetermined information is input from the input unit, the control unit reads the control program. And according to the instruction | indication of a control program, the required information memorize | stored in the memory | storage part is read. Then, using the input information or the read information, the calculation unit performs a predetermined calculation in accordance with a command from the control program. The calculation performed by the calculation unit realizes, for example, the contents described later.

The first polarization information calculation means is means for obtaining information relating to the polarization state of the light of the optical system from the information of the light of the optical system received from the polarization measurement module. The polarization state of light is obtained from the light intensity of each polarizer or each wave plate. Specifically, the intensity (P ₁ , P ₂ , P ₃ , and P ₄ ) of light passing through a polarizer having different polarization axes is obtained. As information on the polarization state, Stokes parameters (S ₁ and S ₂ ) can be mentioned. What calculates | requires the polarization state for every unit from the image which averaged the some image acquired by the area sensor is preferable. That is, a plurality of signals related to the intensity passing through a certain polarizer are measured, and the average value is set as the intensity in a certain polarization state. Here, “information on light of the optical system” is information regarding light emitted from the optical system and not transmitted through the measurement target. The first polarization information calculation means temporarily stores information on the light of the optical system received from the polarization measurement module, and calculates information related to the polarization state of the light of the optical system based on a command of a predetermined control program Can be done.

The second polarization information calculation means is means for obtaining information on the polarization state of the light transmitted through the measurement sample from the information on the light transmitted through the measurement sample received from the polarization measurement module. Specifically, the intensity (P ₁ ′, P ₂ ′, P ₃ ′, and P ₄ ′) of light that passes through a polarizer having different polarization axes is obtained. As information on the polarization state, Stokes parameters (S ₁ ′ and S ₂ ′) can be mentioned. “Information on the light of the measurement sample” means information on light emitted from the optical system and transmitted through the measurement object. That is, the second polarization information calculation means temporarily stores information on the light transmitted through the measurement sample received from the polarization measurement module, and the polarization of the light transmitted through the measurement sample based on a command of a predetermined calculation program An operation for obtaining information on the state may be performed.

The polarization change amount calculation means is a means for obtaining the polarization change amount for each unit of the polarization measurement module from information relating to the polarization state of the light of the optical system and information relating to the polarization state of the light transmitted through the measurement sample. . The amount of change in polarization is expressed by, for example, S ₁ '-S ₁ and S ₂ ' -S ₂ . The polarization change amount calculation means reads information on the polarization state of the light of the optical system temporarily stored and information on the polarization state of the light transmitted through the measurement sample. Then, in response to a command from the control program, an operation for obtaining the amount of change in polarization may be performed. That is, the polarization change amount calculation means obtains the polarization change amount for each unit of the polarization measurement module from the information about the polarization state of the light of the optical system and the information about the polarization state of the light transmitted through the measurement sample.

  The optical distortion calculation means is means for obtaining information on the retardation and optical axis direction of the measurement sample for each unit unit using the polarization change amount for each unit unit obtained by the polarization change amount calculation means. The optical distortion calculation means reads the polarization change amount for each unit unit obtained by the polarization change amount calculation means temporarily stored in accordance with the instruction of the control program, and obtains information on the retardation and the optical axis direction. Can be done. That is, the optical distortion calculation means obtains information on the retardation of the measurement sample and the optical axis direction for each unit unit using the polarization change amount for each unit unit obtained by the polarization change amount calculation means.

  A preferred aspect of the analysis apparatus further includes a polarization calculation means for obtaining a polarization state for each unit from an image obtained by averaging a plurality of images acquired by the area sensor. Another preferred embodiment further includes a polarization calculation means for obtaining a polarization state obtained by averaging Stokes parameters calculated for a plurality of adjacent polarization measurement units. And this preferable analyzer calculates | requires a retardation and an optical axis direction using the information regarding the polarization state which the polarization calculating means calculated | required. The specific calculation contents are as described later.

  In another preferred embodiment of the analysis apparatus, the measurement sample is used in a flat plate shape. And when measuring the polarization state of the light that has passed through the flat measurement sample for each unit, the correction means for correcting the polarization dependence of the reflectance on the sample surface based on the incident angle with respect to the sample calculated for each unit Have The specific calculation contents are as described later.

  Next, the procedure for obtaining the retardation and the optical axis direction together with the contents of each calculation will be described. As a pre-stage for measuring the retardation of the sample, an image is acquired without the sample. Then, the distribution of the polarization state of the light source is measured. Subsequently, a sample to be measured is installed, an image is acquired in the same manner, and the distribution of the polarization state is measured. From the two-dimensional distribution data of these two polarization states, the retardation in the sample and the optical axis direction are calculated.

For example, let S ₁ and S _{2 be} the initial polarization states of a unit, and S ₁ ′ and S ₂ ′ be the polarization states after the sample is placed. Then, the retardation ρ and the optical axis direction θ are expressed by the following equations. The relationship between the intensity actually measured by the CCD and the Stokes parameters (S ₁ , S ₂ , S ₁ ′ and S ₂ ′) is, for example, as follows. When the angles of the polarizers are 0 °, 45 °, 90 °, and 135 °, the intensities that are transmitted through and received by the polarizers are P ₁ , P ₂ , P ₃ , and P ₄ . In this case, S ₁ = (P ₁ −P ₃ ) / (P ₁ + P ₃ ) and S ₂ = (P ₂ −P ₄ ) / (P ₂ + P4) may be used. 'S ₁ ' and S ₂ 'can be obtained similarly. The following expression is an approximate expression when ρ is small.

In the above formula, S ₃ is a number satisfying the relationship of S ₁ ² + S ₂ ² + S ₃ ² = 1.

As represented by the above formula, the present invention relates to the retardation of the measurement sample and the optical axis direction for each unit using the amount of change in polarization for each unit (S ₁ '-S ₁ and S ₂ ' -S ₂ ). You can ask for information. Specifically, the variation of S ₁ obtains a value obtained by dividing the amount of change S _2, and stores. By using this stored value and referring to, for example, the tan2θ table, the optical axis direction θ can be obtained.

Next, by referring to the table relating to the Poincare sphere S ₃ determined. Alternatively, S ₁ ² and S ₂ ² may be obtained, then 1-S ₁ ² may be obtained by a difference circuit, 1-S ₁ ² -S ₂ ² may be obtained thereafter, and S ₃ may be obtained by referring to the square root table. . It may also seek S ₃ with the software for operation. By referring to the trigonometric function table, sin2θ is obtained from the value of tan2θ. Then, S ₃ sin2θ is obtained by a multiplication circuit. 1 / S ₃ sin 2θ is obtained from the reciprocal table. Thereafter, (S ₁ ′ −S ₁ ) / S ₃ sin 2θ is obtained by a multiplication circuit. The retardation ρ is obtained with reference to the trigonometric function table. In addition, you may perform the calculation which calculates | requires retardation (rho) using software. As described above, according to the present invention, the retardation ρ and the optical axis direction θ can be obtained, and thereby the optical distortion of the measurement object can be measured.

A preferred embodiment of the present invention collects a plurality of signals related to the intensity of light measured through a certain polarizer and averages them. Thereby, measurement accuracy can be improved. _P 1 _{to P} m a _{(P 1} '~P _m') measured n times for each unit, stores the measured value. And the measured value for n times is totaled, respectively. Divide the sum by n for the number of samples. In this way, averaged intensity information (that is, an image) can be obtained. For example, to observe 4 times in a row _{P 1.} Then, divided to the combined four P ₁ in 4 is the sample number. P _{2 to} P ₄ are similarly averaged. For example, the Stokes parameter can be obtained from the relationship between the Stokes parameter described above and the polarization intensity. In this way, the Stokes parameter for each unit can be obtained from an image obtained by averaging a plurality of images. Thus it is possible to increase the measurement accuracy of P ₁ to P ₄ by obtaining the polarization state using the averaged image a plurality of images. Thereby, the accuracy of the obtained Stokes parameter can be improved.

Further, the Stokes parameters calculated for a plurality of adjacent units are averaged. That is, P _{1 to} P ₄ (and P ₁ ′ to P ₄ ′) are obtained for each unit, and the Stokes parameters (S ₁ , S ₂ , S ₁ ′, and S ₂ ′) are determined for each unit based on this value. Is required. At this time, the Stokes parameters in the adjacent 2 to 16 units are averaged. The number of units to be averaged may be two, four, or eight. In this way, the accuracy of the Stokes parameter can be improved. For example, a case where Stokes parameters are averaged for two adjacent units will be described. First, as described above, a Stokes parameter for each unit is obtained. This is defined as (S ₁₁ , S ₂₁ , S ₁₁ ′ and S ₂₁ ′) and (S ₁₂ , S ₂₂ , S ₁₂ ′ and S ₂₂ ′). The averaged Stokes parameter is, for example, (S ₁₁ + S ₁₂ ) / 2.

  Using the Stokes parameters corrected in this way and obtaining the retardation and the optical axis direction from the above-described equations is a preferred aspect of the present invention.

  By the way, the size of the sample that can be measured is determined by the width of the visual field of the screen. The range of the field of view depends on the angle of view of the lens and the distance between the camera and the sample. The distance between the camera and the sample is about several tens of centimeters to 2 meters at most even when incorporated in a generally considered measuring apparatus or manufacturing process. On the other hand, the sample is as large as 2 to 3 m as the liquid crystal panel becomes larger. For this reason, it is inevitable to choose to widen the angle of view of the lens.

  In the case of using an imaging lens that can enter a wide field of view, the light that is received toward the end of the screen passes obliquely with respect to the sample. The problem at this time is that the transmittance of light transmitted through the transparent flat plate has polarization-dependent characteristics. That is, the reflectance of the P wave (polarized light parallel to the incident surface) is smaller than the reflectance of the S wave (polarized light perpendicular to the incident surface). For this reason, the transmittance of the P wave is larger. Since this polarization dependency is not caused by the retardation of the sample, an error occurs due to this phenomenon in order to calculate the retardation and the optical axis. FIG. 5 is a graph showing the relationship between the incident angle and the error due to the oblique incidence. Therefore, it can be said that it is preferable to correct this influence.

The polarization state measured after placing the sample includes polarization characteristics caused by the surface reflection of the sample. An incident angle from a medium having a refractive index n ₀ to a sample having a refractive index n ₁ is θ ₀ , and a refractive angle in the sample is θ ₁ . P-wave, and the amplitude transmittance of the S-wave, respectively and _{t p} and _{t s, t p} and _{t s} is represented by the following equation.

That is, the amplitude ratio regardless of the phase difference between the x and y directions is changed by _(t s _/ t _p). In practice, it is necessary to consider the reflection on both sides of the sample. Therefore, the amplitude ratio change x can be regarded as (t _s / t _p ) ² . When the ratio between the x component and the y component of the electric field is A, and the phase difference between the x component and the y component of the electric field is δ, the Stokes parameter representing a certain elliptical polarization state is expressed by the following equation.

When the incident angle is θ ₀ and the amplitude ratio is changed from A to Ax (x represents the amplitude ratio change described above), the Stokes parameters S ₁ and S ₂ change as follows.

When measuring the retardation of the sample, it can be said that it is preferable to use the values corrected in Equation 4 as S ₁ ′ and S ₂ ′ in Equation 1. That is, the information on the polarization state of the light transmitted through the measurement sample is corrected using the amplitude ratio change. Specifically, S ₁ amplitude ratio change and the obtained _{', S 2' S 1 '} , and S _2' may be corrected in accordance with Equation 4 above using. Note that “amplitude ratio change” means the ratio at which the ratio of the x component and the y component of the electric field due to light from the optical system changes through the measurement object.

The angle of view is determined when a specific lens is installed in the camera. If the distance from the center of the visual field is determined at a certain point in the screen, the incident angle θ ₀ with respect to the sample can be obtained. Accordingly, the correction value based on the incident angle can be obtained, and correction at each point can be performed.

  The case where the size of the micro-polarizer is matched with the pixel size of the area sensor has been described. However, the present invention is not limited to a one-to-one correspondence between the area sensor pixel size and the polarizer (or wavelength plate). In the case of one-to-one correspondence, for example, when an area sensor having a pixel period of 5 microns and an element number of 1360 × 1024 is used, the number of polarization measurement units is 680 × 512. However, the size of the micropolarizer does not necessarily need to match the size of the light receiving element. For example, the vertical and horizontal sizes can be set to integer multiples of the pixel size. In this case, the number of polarization measurement units is reduced, and the spatial resolution is reduced. Can do. That is, it is possible to suppress variations in measured values of the S parameter that is a polarization parameter. This is equivalent to suppressing variation in retardation. The same effect can be obtained by further averaging the polarization state values obtained from a plurality of polarization measuring units. Alternatively, a plurality of images may be taken repeatedly and the received light intensity of the same pixel may be averaged. It is not easy to statistically analyze the relationship between these various averaging conditions and the standard deviation σ (Re) of the measurement fluctuation of the obtained retardation Re because the situation is extremely complicated. The inventors repeated the actual measurement and inductively obtained the relationship of the following equation.

  Here, Q is the light receiving element average charge amount, λ is the wavelength of light, N is the number of pixels used as one unit, and F is the number of frames (number of frames) averaged over time. If λ = 540 nm and Q = 5000, Equation 5 becomes the following equation.

  For example, when N = 400 and F = 50, σ (Re) = 0.01 nm. This indicates that a value required when measuring the retardation of a glass for a liquid crystal panel having a small retardation can be realized.

  FIG. 6 is a graph in which the actually measured retardation and the relationship between the number N of pixels in the measurement unit and the number F of images are plotted. It can be seen that the graph shown in FIG. 6 agrees with the theoretical formula shown in Formula 6. That is, FIG. 6 shows that the retardation has reproducibility. It is possible to determine the optimum N and F from the standard deviation required by the measurement object, the measurement time, and the spatial resolution. That is, in the present invention, the number N of pixels used as one unit and the number of frames F to be temporally averaged can be obtained using information on the standard deviation of retardation, measurement time, and spatial decomposition.

  FIG. 7 is a diagram showing an optical distortion measuring apparatus according to an embodiment of the present invention. The area sensor 102 is a monochrome CCD sensor having 1000 × 1000 pixels. Reference numeral 101 denotes a polarizer array made of a photonic crystal, and the transmission axis of each polarizer is a unit of four types that differ by 45 °. Reference numeral 103 denotes a camera module. That is, the optical distortion measuring device of the present invention may be included in a camera.

  The lens 106 is a fixed focus lens having a focal length of 9 mm. The size of the CCD sensor is 1/2 inch, and the angle of view is 38 ° (corresponding to the end of the field of view). Therefore, the light passing through the sample is received at an angle of 19 ° at the edge of the visual field. A fluorescent lamp is used as the light source 104, and a diffusion plate is arranged to make the intensity distribution uniform. Further, a circularly polarizing film 105 is installed to constitute a substantially circularly polarized light source.

The camera is attached to the frame 501 and can move up and down. The camera can be moved according to the size of the sample 107, and the sample can be measured with an appropriate visual field size. Here, the size of the sample was 200 × 200 mm, and the distance between the camera and the sample was 580 mm. Assuming that the distance from the center of the field of a unit is p pixels, the number of pixels of the entire field of view is 2N, and the field angle is 2θg, the incident angle θ ₀ of light at the corresponding point on the sample can be obtained from the following equation.

From this, θ ₀ in each unit is obtained, and the retardation is calculated after correcting the Stokes parameters expressed by the mathematical expressions 2 to 4 described above. From Snell's law, there is a relationship of sin θ ₁ = (n ₀ / n ₁ ) sin θ ₀ . That is, a preferred embodiment of the present invention corrects the incident angle using information on the distance from the center of the field of view of the unit, the number of pixels in the entire field of view, and the field angle. Specifically, information on the distance from the center of the visual field of a certain unit is stored. Also, information regarding the number of pixels in the entire field of view is stored. Also, information regarding the angle of view is stored. Then, information on the number of pixels and information on the distance are read out, and the distance is divided by the number of pixels. On the other hand, tan θg is obtained from the angle of view. By multiplying these, tan θ ₀ is obtained. Using this value, a table is appropriately referred to and a value related to θ ₀ is obtained.

  FIG. 8 is a photograph showing the retardation distribution. FIG. 8A is a photograph showing the retardation distribution before correction. FIG. 8B is a photograph showing the retardation distribution after correction. It can be seen from FIG. 8A that the apparent retardation is superimposed on the edge of the field of view and increases. Further, from FIG. 8B, it is understood that the apparent retardation is removed and displayed at 0.2 nm or less, and the retardation inherent in the glass is measured. Here, the standard deviation of the retardation to be realized is 0.01 nm. This is because the retardation of the glass is as small as about 0.1 nm. The number of pixels N in one polarization measurement unit required to realize this standard deviation and the number of screens F to be averaged are NF = 5000 from Equation 6. The combination of N and F is arbitrary. For example, if the number of pixels N is 400 and the number of average frames is 50, the measurement time corresponds to about 7 seconds and the number of measurement points is 100 × 100 (= 10,000 pixels). Become. When the same sample was actually measured repeatedly, a standard deviation σ (Re) of 0.01 nm was obtained.

DESCRIPTION OF SYMBOLS 101 Polarizer array 102 Light receiving element array 103 Camera module 104 Light source 105 Circular polarizing film 106 Imaging lens 107 Measurement sample 201 The substrate 202 which formed the groove row 202 High refractive index material 203 Low refractive index material 301 Polarizer array 302 Area sensor 401 Wavelength Plate array 402 polarizer 501 frame with uniform transmission polarization axis

Claims (12)

An optical distortion measuring device comprising an optical system, a polarization measurement module, and an analysis device,

The optical system can emit circularly polarized light, elliptically polarized light, or linearly polarized light,

The polarization measurement module includes a polarizer array and an area sensor,
The polarizer array includes a plurality of unit units that are repeatedly arranged one-dimensionally or two-dimensionally, and transmits light emitted from the optical system or is emitted from the optical system and transmits a measurement sample. The transmitted light,
The unit unit includes at least three types of polarizers having different directions of transmission polarization axes,
The area sensor can independently receive light that has passed through each polarizer of the polarizer array, and can measure the intensity of the received light,

The analyzer can receive measurement information transmitted from the polarization measurement module,

The analysis device includes:
A first polarization information calculation unit; a second polarization information calculation unit; a polarization change amount calculation unit; and an optical distortion calculation unit.
The first polarization information calculation means is means for obtaining information related to the polarization state of the light of the optical system from the information of the light of the optical system received from the polarization measurement module,
The light information of the optical system is information about light emitted from the optical system that does not pass through the measurement target,

The second polarization information calculation means is means for obtaining information on a polarization state of light transmitted through the measurement sample from information on light transmitted through the measurement sample received from the polarization measurement module;
The information on the light of the measurement sample is information on light emitted from the optical system and transmitted through the measurement object,

The polarization change amount calculation means calculates the polarization change amount for each unit of the polarization measurement module from information related to the polarization state of light of the optical system and information related to the polarization state of light transmitted through the measurement sample. Is a means of seeking,

The optical distortion calculation means is means for obtaining information on the retardation of the measurement sample and the optical axis direction for each unit unit using the polarization change amount for each unit unit obtained by the polarization change amount calculation means.

Optical distortion measuring device.   The optical strain measurement apparatus according to claim 1, wherein the polarizer array includes a polarizer made of a photonic crystal. The analysis device includes:
Furthermore, it has a polarization intensity averaging means that averages a signal related to the intensity of light that passes through a certain polarizer taken continuously by the area sensor,
Using the intensity averaged by the polarization intensity averaging means, information on the polarization state of each unit is obtained.
The optical distortion measuring device according to claim 2. The analysis device includes:
Furthermore, it has polarization state averaging means for averaging signals relating to polarization states in adjacent units,
Using information on the polarization state averaged by the polarization state averaging means, information on retardation and the optical axis direction is obtained.
The optical distortion measuring device according to claim 2 or 3. The analysis apparatus further includes an amplitude ratio change storage unit that stores an amplitude ratio change, and a light polarization state correction unit that corrects information related to the polarization state of the light,
Here, the change in the amplitude ratio means the ratio at which the ratio of the x component and the y component of the electric field due to the light from the optical system changes through the measurement object,

The light polarization state correction means includes:
The optical distortion measuring apparatus according to claim 4, wherein information on a polarization state of light transmitted through the measurement sample is corrected using the amplitude ratio change. The analysis apparatus further includes incident angle correction means,

The amplitude ratio change is expressed as a function of incident angle and refraction angle,
Using the information about the distance from the center of the visual field of the certain unit, the number of pixels of the entire visual field, and the angle of view, the incident angle is corrected, and the amplitude ratio change is corrected using the information about the corrected incident angle. The optical distortion measuring apparatus according to claim 5, wherein information relating to a polarization state of light transmitted through the measurement sample is corrected using the corrected amplitude ratio change. An optical distortion measuring device including an optical system, a polarization measurement module, and an analysis device,

The optical system can emit circularly polarized light, elliptically polarized light, or linearly polarized light,

The polarization measurement module has a wave plate array, a polarizer, and an area sensor in this order,
The wave plate array has unit units that are repeatedly arranged one-dimensionally or two-dimensionally, and transmits light emitted from the optical system or is emitted from the optical system and passes through the measurement sample. Transmitting light,
The unit unit includes at least four types of wave plates having different fast axis directions,
The polarizer has a transmission polarization axis in one direction, and transmits light transmitted through the wave plate array.
The area sensor is light that has passed through each wave plate included in the wave plate array, and has received the light that has passed through the polarizer, and can measure the intensity of the received light.

The analyzer can receive measurement information transmitted from the polarization measurement module,

The analysis device includes:
A first polarization information calculation unit; a second polarization information calculation unit; a polarization change amount calculation unit; and an optical distortion calculation unit.
The first polarization information calculation means is means for obtaining information related to the polarization state of the light of the optical system from the information of the light of the optical system received from the polarization measurement module,
The light information of the optical system is information about light emitted from the optical system that does not pass through the measurement target,

The second polarization information calculation means is means for obtaining information on a polarization state of light transmitted through the measurement sample from information on light transmitted through the measurement sample received from the polarization measurement module;
The information on the light of the measurement sample is information on light emitted from the optical system and transmitted through the measurement object,
The polarization change amount calculation means calculates the polarization change amount for each unit of the polarization measurement module from information related to the polarization state of light of the optical system and information related to the polarization state of light transmitted through the measurement sample. Is a means of seeking,
The optical distortion calculation means is means for obtaining information on the retardation of the measurement sample and the optical axis direction for each unit unit using the polarization change amount for each unit unit obtained by the polarization change amount calculation means.
Optical distortion measuring device.   The optical distortion measuring apparatus according to claim 7, wherein the wave plate array includes a wave plate made of a photonic crystal. The analysis device includes:
Furthermore, it has a polarization intensity averaging means for averaging a signal related to the intensity of light that passes through a certain wavelength plate continuously photographed by the area sensor,
Using the intensity averaged by the polarization intensity averaging means, information on the polarization state of each unit is obtained.
The optical distortion measuring device according to claim 8. The analysis device includes:
Furthermore, it has polarization state averaging means for averaging signals relating to polarization states in adjacent units,
Using information on the polarization state averaged by the polarization state averaging means, information on retardation and the optical axis direction is obtained.
The optical distortion measuring device according to claim 9. The analysis device includes:
Furthermore, it has an amplitude ratio change storage means for storing the amplitude ratio change, and a light polarization state correction means for correcting information relating to the polarization state of the light,

The light polarization state correction means includes:
The optical distortion measuring apparatus according to claim 10, wherein information relating to a polarization state of light transmitted through the measurement sample is corrected using the amplitude ratio change. The analysis device includes:
Furthermore, it has an incident angle correction means,

The amplitude ratio change is expressed as a function of incident angle and refraction angle,
Using the information about the distance from the center of the visual field of the certain unit, the number of pixels of the entire visual field, and the angle of view, the incident angle is corrected, and the amplitude ratio change is corrected using the information about the corrected incident angle. The optical distortion measuring apparatus according to claim 11, wherein information regarding a polarization state of light transmitted through the measurement sample is corrected using the corrected change in amplitude ratio.

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