JP2009186256A - Double refraction measuring method, double refraction measuring instrument and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure double refraction characteristics by a simple constitution without taking cost or the like. <P>SOLUTION: A double refraction measuring instrument 10 includes a light source 11, a polarizer 15, a phase element 16, a rotary analyzer 40, a receptor 18, and a controller 20. A phase difference film 19 is inserted in the gap between the phase element 16 and the rotary analyzer 40. The controller 20 allows the transmission axis azimuth θ of the rotary analyzer 40 to correspond to the intensity of the light received by the receptor 18 in the transmission axis azimuth to make light intensity data. The first light intensity data at the time when the transmission axis azimuth of the polarizer 15 is<SB>γ</SB>1 and the second light intensity data at the time when the transmission axis azimuth is γ<SB>2</SB>(γ<SB>2</SB>is an azimuth different from<SB>γ</SB>1) are stored in a light intensity data memory part 50. The main axis azimuth of the phase difference film 19 is calculated on the basis of the first or second light intensity data, and the retardation of the phase difference film 19 is calculated on the basis of its main axis azimuth, the first light intensity data and the second light intensity data. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a birefringence measuring method, apparatus, and program for measuring birefringence characteristics of an optical film such as a retardation film used in a liquid crystal display device.

  In recent years, many liquid crystal display devices (hereinafter referred to as “liquid crystal display devices”) are on the market. A liquid crystal cell in which a liquid crystal material is sealed is provided on a display panel of the liquid crystal display device. A backlight and a polarizing filter are provided on one side of the liquid crystal cell, and a phase difference film and a polarizing filter are provided on the other side.

  Since the liquid crystal cell has a wavelength dependency in which the transmittance changes according to the wavelength of light, when light passing through the backlight and the polarizing filter passes through the liquid crystal cell, a phase difference is generated in the transmitted light. The phase difference of the transmitted light is compensated with a phase difference film. Therefore, in order to reliably compensate for the phase difference of transmitted light, the birefringence characteristics such as the main axis direction (fast axis direction or slow axis direction) and phase difference (retardation) of the phase difference film must be measured with high accuracy. Is required.

  So far, various methods such as a rotational analyzer method, a phase modulator method, and a rotational phaser method have been proposed as methods for measuring birefringence characteristics (see Patent Documents 1 to 3). For example, in a birefringence measuring apparatus using the rotation analyzer method, a light source, a spectroscope, a polarizer, a rotation analyzer, and a light receiver are arranged in order along the optical axis of the light source, and between the polarizer and the rotation analyzer. A measurement object such as a phase difference film is put into the measurement, and the main axis direction and retardation of the measurement object are measured (see Patent Document 1).

  In the birefringence measuring apparatus of Patent Document 1, the principal axis direction and retardation of the phase difference film are obtained by the following procedure. First, the rotation analyzer is rotated at a constant angular velocity, and the light emitted from the rotation analyzer is detected by a light receiver. Then, the rotation angle of the rotation analyzer and the intensity of the received light detected by the light receiver at the rotation angle are stored in the memory in association with each other. And based on the rotation angle memorize | stored in memory and the intensity | strength of the received light in the case of the rotation angle, the main axis | shaft direction and retardation of a phase difference film are calculated | required.

In addition, in the birefringence measuring apparatus using the phase modulation method, a photoelastic modulator that periodically changes the phase of the light before entering the phase difference film is provided instead of the above-described birefringence measuring apparatus. (See Patent Document 2). Further, in the birefringence measuring apparatus using the rotational phaser method, the phaser fixed by the above-described birefringence measuring apparatus is rotated to perform measurement (see Patent Document 3).
JP-A-10-82697 JP 2006-511823 A JP 2004-20343 A

  However, the photoelastic modulator used in the birefringence measuring apparatus of Patent Document 2 is expensive, and this photoelastic modulator has a problem that it is easily affected by temperature. In addition, in Patent Document 2, the measurable retardation range is limited to “0 to λ / 2 (λ: wavelength of light source)”. In addition, the birefringence measuring apparatus of Patent Document 3 is provided with a retarder not only on the light source side but also on the light receiver side with respect to the measurement target, so that the configuration of the apparatus becomes complicated and the cost for measuring the birefringence characteristics is high. There is a problem that it takes.

  On the other hand, the birefringence measuring apparatus of Patent Document 1 can simply measure the birefringence characteristics without incurring costs compared to those of Patent Documents 2 and 3. There's a problem. In the birefringence measuring apparatus of Patent Document 1, the retardation of the retardation film is obtained based on a retardation calculation formula that is theoretically obtained in advance. The retardation calculation formula is an expression that expresses the relationship between the observation value obtained from the rotation angle of the rotation analyzer and the intensity of the received light at the rotation angle and the retardation with a cosine function. In the retardation calculation formula, the observed value is in the range of “−1” to “+1”, and when the observed value is “± 1” or “in the vicinity of ± 1”, the measurement of the retardation corresponding to the observed value is performed. There is a problem that the accuracy is extremely low.

  With respect to this problem, in Patent Document 1, when the observation value is “± 1” or “near ± 1”, the retardation is measured by inserting a phaser between the polarizer and the phase difference film. It prevented the loss of accuracy. However, since a device for inserting or removing the phase shifter is required separately, the cost increases. Moreover, since it is necessary to align the main axis of the phase shifter when inserting the phase shifter, the measurement takes time and effort.

  An object of the present invention is to provide a birefringence measurement method, apparatus, and program for accurately measuring birefringence characteristics such as principal axis orientation and retardation with a simple configuration without cost, labor, and time. .

  In order to achieve the above object, the present invention uses a light source, a polarizer, a phaser, a rotation analyzer whose transmission axis direction changes at a constant rotation angle, and a light receiver, and the phaser and the phaser In a birefringence measurement method for obtaining a retardation of the measurement object by inserting a measurement object between the rotation analyzer and the light from the light source in a state where the transmission axis of the polarizer is fixed in the first transmission axis direction. A first light detection step detected by the light receiver via the polarizer, the phaser, the measurement object, the rotation analyzer, and a transmission axis direction of the rotation analyzer after the first light detection step. And a first light intensity data creating step for creating first light intensity data by associating the light intensity detected by the light receiver with the transmission axis direction, and the transmission axis of the polarizer as the first transmission The direction different from the first transmission axis direction from the axis direction A second transmission light that performs the same step as the first light detection step in a state in which the transmission axis direction is changed to the second transmission axis direction and the transmission axis of the polarizer is fixed to the second transmission axis direction. After the detection step and the second light detection step, the same step as the first light intensity data creation step is performed to create second light intensity data, and the first or second light intensity data creation step. Based on the light intensity data, the main axis direction calculating step for obtaining the main axis direction of the measurement object, the main axis direction of the measurement object, the first light intensity data, and the second light intensity data, And a retardation calculating step for obtaining a retardation.

  Before the first light detection step, the same steps as the first light detection step and the first light intensity data creation step are performed in a state where the measurement object is excluded, and the first pre-measurement light intensity data is created. First pre-measurement light intensity data creation step, and first Stokes parameter calculation step for obtaining a first Stokes parameter indicating a polarization state of light before entering the measurement object based on the first pre-measurement light intensity data Before the second light detection step, the same steps as the second light detection step and the second light intensity data creation step are performed in a state where the measurement object is excluded, and the second pre-measurement light intensity data is obtained. A second pre-measurement light intensity data creation step to be created, and a second Stokes indicating the polarization state of the light before entering the measurement object based on the second pre-measurement light intensity data A second Stokes parameter calculation step for obtaining a parameter, and in the main axis direction calculation step, based on the first or second Stokes parameter, in addition to the first or second light intensity data, the main axis of the measurement object In the retardation calculating step, the retardation of the measurement target is calculated based on the first and second Stokes parameters in addition to the main axis direction of the measurement target, the first light intensity data, and the second light intensity data. Is preferably obtained.

  The calculation in the first pre-measurement light intensity data creation step, the first Stokes parameter calculation step, the second pre-measurement light intensity data creation step, and the second Stokes parameter calculation step is not limited to before the measurement. It is preferable to go in advance. By doing so, it becomes unnecessary to remove or set the measurement object during the measurement flow of the measurement object. At the same time, the first and second pre-measurement light intensity data creation steps and the first and second Stokes parameter calculation steps are unnecessary in the measurement flow, and the measurement time can be shortened.

  The retardation calculating step specifies a plurality of first retardation candidate values of the measurement target based on the first observed value obtained from the first Stokes parameter, the first light intensity data, and the main axis direction of the measurement target. The measurement target based on a second observation value obtained from a first retardation candidate value identification step, the second observation value obtained from the second Stokes parameter, the second light intensity data, and the principal axis direction of the measurement object The second retardation candidate value specifying step for specifying a plurality of second retardation candidate values, and among the plurality of first and second retardation candidate values, a retardation candidate value whose values match or substantially match is set as the measurement target retardation. It is preferable to include a retardation determining step for determining.

  The relationship between the first observed value and the first retardation candidate value and the relationship between the second observed value and the second retardation candidate value are expressed by a sine function, and the first observed value and the first retardation candidate value The sine curve obtained from the relationship is preferably separated from the sine curve obtained from the second observed value and the second retardation candidate value by a predetermined phase.

  The first or second observation value is not less than “−1” and not more than “1”, and the retardation determining step includes a plurality of the first and second retardation candidate values whose values match or substantially match with each other. A step of specifying a value, a step of determining whether or not an observation value corresponding to a retardation candidate value that matches or substantially matches the value is in a range other than “± 1” or “near ± 1”, and “± It is preferable to include a step of determining a retardation candidate value corresponding to an observed value in a range other than “1” or “near ± 1” as the retardation of the measurement target.

  In the transmission axis direction changing step, it is preferable that the transmission axis of the polarizer is changed to the second transmission axis direction symmetrical to the first transmission axis direction with respect to the main axis direction. The light that has passed through the polarizer and the phase shifter is preferably circularly polarized light, linearly polarized light, or elliptically polarized light. The measurement object is preferably a phase difference film.

  The birefringence measuring apparatus of the present invention includes a transmission axis direction changing unit that changes the transmission axis of the polarizer between a first transmission axis direction and a second transmission axis direction different from the first transmission axis direction, With the transmission axis of the polarizer fixed to the first transmission axis direction or the second transmission axis direction, the light from the light source is passed through the polarizer, the phaser, the measurement object, and the rotating analyzer. The transmission axis of the polarizer by associating the light detection unit to be detected by the light receiver, the transmission axis direction of the rotating analyzer and the intensity of the light detected by the light receiver at the transmission axis direction. A first light intensity data when the first transmission axis is in the first transmission axis direction and a second light intensity data when the transmission axis of the polarizer is in the second transmission axis; A main axis for obtaining the main axis direction of the measurement object based on the first or second light intensity data A position calculating section, the principal axis direction of the measurement target, the first light intensity data, and based on the second light intensity data, and having a retardation calculation section for obtaining the retardation of the measurement target.

  In the birefringence measurement program of the present invention, in the state where the transmission axis of the polarizer is fixed in the first transmission axis direction, the light from the light source is converted into the polarizer, the phaser, the measurement object, and the rotation analyzer. The procedure of detecting by the light receiver via the first light detecting step is associated with the transmission axis direction of the rotating analyzer and the intensity of the light detected by the light receiver at the transmission axis direction. The first light intensity data is generated, the transmission axis of the polarizer is changed from the first transmission axis direction to a second transmission axis direction different from the first transmission axis direction, and the polarizer. The procedure of performing the same step as the first light detection step in the state where the transmission axis is fixed to the second transmission axis direction, and the same as the first light intensity data creation step after the second light detection step Perform the steps to create the second light intensity data The main axis direction of the measurement object based on the first or second light intensity data, the main axis direction of the measurement object, the first light intensity data, and the second light intensity data. And causing the computer to execute a procedure for obtaining the retardation of the measurement target.

  According to the present invention, it is possible to accurately measure birefringence characteristics such as the principal axis direction and retardation with a simple configuration without cost, labor, and time.

  As shown in FIG. 1, the birefringence measuring apparatus 10 of the present invention includes a light source 11, a spectroscope 12, an optical fiber 13, a lens 14, a polarizer 15, a phaser 16, a light detector 17, and a light receiver 18. Yes. Here, the light source 11, the spectroscope 12, and the incident portion 25 of the optical fiber 13 are sequentially provided along the optical axis LL of the light source, and the lens 14, the polarizer 15, the phase shifter 16, the light detection portion 17, and the light receiving portion. The part 18 is provided in order along the optical axis L of the emitting part 27 of the optical fiber 13. The birefringence measurement apparatus 10 is provided with a controller 20 that performs various controls and calculations. The phase difference film 19 to be measured is inserted between the phase shifter 16 and the rotation analyzer 17. The spectroscope 12 may be provided along the optical axis L between the light detector 17 and the light receiver 18.

  The centers of the light emitting surface 27 of the optical fiber 13, the lens 14, the polarizer 15, the phase retarder 16, the phase difference film 19, the light detector 17, and the light receiver 18 are aligned with the optical axis L. Hereinafter, the direction of the optical axis L is the Z direction, and in the plane orthogonal to the optical axis L, the horizontal direction is the X direction and the vertical direction is the Y direction.

  The light source 11 is composed of a monochromatic light source or a white light source. As the monochromatic light source, a He—Ne laser, a laser diode, an LED, or the like is used. A halogen lamp, an Xe lamp, or the like is used as the white light source. In order to efficiently guide the light from the light source 11 to the incident portion 25 of the optical fiber 13, a condensing means such as a lens or an elliptical mirror is attached along the optical axis LL before the incident portion 25 of the optical fiber 13. Also good.

  The spectroscope 12 includes a spectral filter and a diffraction grating, and extracts light having a center wavelength of 590 nm and a half width of 10 nm from the light from the light source 11. Note that although the center wavelength of the light extracted by the spectroscope is 590 nm, the present invention is not limited to this, and it is sufficient that the monochromality of the light from the light source can be improved by the spectroscope. For example, the center wavelengths are preferably 440 nm, 550 nm, 630 nm, and 750 nm. Further, although the half width is 10 nm, it is not necessary to be limited to this.

  The optical fiber 13 includes an incident portion 25 that takes in light from the spectroscope 12, a branch portion 26 that branches the incident light into three, and an emission portion 27 that emits each branched light. The emission unit 27 includes three emission units 27a to 27c. As described above, by branching the light from the light source 11 into the plurality of emitting portions 27a to 27c, a plurality of locations of the phase difference film 16 can be measured. In addition, although the output parts 27a-27c were set to three, two or four or more may be sufficient.

  As for the type of optical fiber, when the wavelength of the light from the spectroscope is light in the blue or infrared wavelength region, the optical fiber made of quartz glass is used rather than the plastic optical fiber in which the light attenuation is large. Fiber is preferred. Further, in order to increase the efficiency of the condensing action by the lens 14 with respect to the light from the emitting portion 27 of the optical fiber 13, the strand diameter of the optical fiber is preferably a small diameter, specifically, 50 to 800 μm is preferable. 200-400 micrometers is more preferable.

  The lens 14 is composed of a telecentric lens or the like, and makes light from each of the emitting portions 27 a to 27 c of the optical fiber 13 parallel to the optical axis L. The focal point of the lens 14 is adjusted to the emission surface of the emission part 27b of the optical fiber. Thereby, the light emitted from the lens 14 becomes light parallel to the optical axis L. When the strand diameter of the optical fiber 13 is used and the spot diameter of the light emitted from the lens 14 is several mm, the focal length of the lens is preferably 40 mm. The light emitted from the lens is preferably parallel light having a spot diameter of about 4 mm.

The polarizer 15 is composed of a linearly polarizing plate, and converts the light from the lens 14 into linearly polarized light. The polarizer 15 has an extinction ratio on the order of 10 ⁻⁶ to 10 ⁻⁵ . For example, a polymer type using iodine absorption or a prism type using optical crystals is used.

  The transmission axis direction of the transmission axis 15a of the polarizer 15 is represented by an angle γ with respect to the Y direction. When the transmission axis is in the + Y direction, the transmission axis direction γ is 0 °, and the transmission axis 15a is to the right with respect to the + Y direction. If the transmission axis is γ, the transmission axis direction γ is a positive direction, and if the transmission axis 15a is on the left semicircle side with respect to the + Y direction, the transmission axis direction γ is a negative direction. An azimuth changing unit 29 is attached to the polarizer 15, and the azimuth changing unit 29 rotates the polarizer 15 clockwise R1 or counterclockwise R2 according to an instruction from the controller 20 to change the transmission axis azimuth γ. To do. The changeable range of the transmission axis direction is set to −π / 2 to π / 2 (−90 ° to 90 °), but is not limited thereto.

  The phaser 16 is composed of a quarter wave plate and converts linearly polarized light from the polarizer 15 into elliptically polarized light. A combination of optical crystals such as quartz having birefringence is used for the phaser 16. The main axis 16a (fast axis) of the phaser 16 is set to a 45 ° azimuth from the + Y direction to the R1 direction. When the transmission axis direction γ of the polarizer 15 is other than 0 °, the phaser 16 converts linearly polarized light from the polarizer 15 into elliptically polarized light, and the transmission axis direction γ of the polarizer 15 is 0 °. In this case, the linearly polarized light from the polarizer 15 is converted into circularly polarized light.

  The polarization state immediately after exiting the phase shifter 16 is represented by Stokes parameters S0, S1, S2, and S3. The Stokes parameters obtained by standardizing these S1, S1, and S2 with S0 are hereinafter referred to as XP, YP, and ZP. The Stokes parameters XP, YP, and ZP are obtained in advance by calculation of the controller before measuring the birefringence characteristics of the phase difference film.

  The phase difference film 19 is an object to be measured, and the principal axis direction α and retardation δ (phase difference) of the phase difference film are obtained by calculation of the controller 20. The measurement target is not limited to the phase difference film, but may be other optical members.

  The principal axis direction α of the principal axis 19a (fast axis) of the phase difference film 19 is represented by an angle with respect to the Y direction. When the main axis 19a is in the + Y direction, the main axis direction α is 0 °. When the main axis 19a is on the right semicircle side with respect to the + Y direction, the main axis direction α is a positive direction and the main axis 19a is in the + Y direction. In the case of the left semicircle side, the main axis direction α is a negative direction.

  Further, an azimuth changing unit 31 is attached to the phase difference film 19, and the azimuth changing unit 31 rotates the phase difference film 19 in the R1 direction or the R2 direction to change the main axis azimuth α of the phase difference film 19. . The phase difference film 19 is provided with a shift unit 33. The shift unit 33 moves the phase difference film 19 in the XY plane so that a predetermined measurement position of the phase difference film 19 is moved to the optical axis L. At the same time, the phase difference film 19 is moved in the XY plane, and the phase difference film 19 is separated from the optical axis L.

  The light analyzing unit 17 includes a rotating analyzer 40, a rotating body 41, a rotation driving unit 42, and an encoder 43. The rotation analyzer 40 is composed of a linear polarizing plate, and converts the light emitted from the phase shifter 16 or the phase difference film 19 into linearly polarized light. The transmission axis azimuth θ of the transmission axis 40a of the rotary analyzer 40 is represented by an angle with respect to the Y direction. When the transmission axis 40a is in the + Y direction, the transmission axis azimuth θ is set to 0 °. The rotating body 41 is provided with a hollow portion, and the rotation analyzer 40 is fitted into the hollow portion.

  The rotation drive unit 42 includes a drive source 45 such as a brushless motor or a stepping motor, and a connection unit 46 such as a belt or a gear for connecting the drive source 45 and the rotating body 41. The rotational drive from the drive source 45 is transmitted to the rotator 41 via the connecting portion 46. Thereby, the rotating body 41 rotates in the R1 direction at a constant period T. In accordance with the rotation of the rotating body 41, the transmission axis direction θ of the rotating analyzer 40 is changed at a constant period T. The encoder 43 is attached to the rotating body 41, and transmits an encoder pulse signal to the controller 20 every time the rotating body 41 rotates at a constant rotation angle.

  The light receiver 18 converts the light emitted from the rotation analyzer 40 into an electrical signal. This electrical signal (hereinafter referred to as “light intensity signal”) is converted from analog to digital by an A / D converter and transmitted to the controller 20. For example, a photodiode, a photomultiplier tube (PMT (Photo Multiplier Tube)), or a CCD (Charge Coupled Device) is provided on the light receiving surface 18 a of the light receiver 18. In addition, it is preferable to provide a current / voltage converter for converting a current signal into a voltage and a sensitivity adjuster for making the light receiving sensitivity variable by the method of the light receiving surface 18a.

  The controller 20 includes a light intensity data storage unit 50, a ROM 51, and a RAM 52. Based on the encoder pulse signal from the encoder 43 and the light intensity signal from the light receiver 18, the controller 29 receives the received light detected by the light receiver 18 at the transmission axis direction θ of the rotation analyzer 40 and the transmission axis direction θ. The light intensity data is created in association with the intensity of the light. This light intensity data is stored in the light intensity data storage unit 50. The ROM 51 stores a program for performing processing for obtaining the Stokes parameters XP, YP, and ZP, and processing for obtaining the principal axis direction α and retardation δ of the phase difference film. The RAM 52 stores various data obtained by executing the above-described program.

  Next, the operation of the birefringence measuring apparatus will be described with reference to the flowchart of FIG. First, before setting the phase difference film 19 on the optical axis L, the azimuth changing unit 29 rotates the polarizer 15 in the R1 direction to change the transmission axis azimuth γ to a positive azimuth γ1. Then, light is emitted from the light source 11 in a state where the rotation analyzer 40 is rotated at a constant angular velocity (2π / T). The irradiated light is detected by the light receiver 18 through the spectroscope 12, the optical fiber 13, the lens 14, the polarizer 15, the phaser 16, and the rotation analyzer 40. The encoder 43 is used to detect the transmission axis azimuth θ of the rotary analyzer 40, and the detected transmission axis azimuth θ of the rotary analyzer 40 is associated with the intensity of the received light at the transmission axis azimuth θ. Intensity data SA1 (θ) is created. The light intensity data SA1 (θ) is stored in the light intensity data storage unit 50. Hereinafter, the steps from the irradiation of light from the light source to the creation of light intensity data are referred to as the light intensity data creation step. The transmission axis direction γ1 is preferably 8 °.

  Then, the Stokes parameters XP1, YP1, and ZP1 are obtained based on the light intensity data SA1 (θ) stored in the light intensity data storage unit 50. The obtained Stokes parameters XP1, YP1, ZP1 are stored in the RAM 52. A method for calculating the Stokes parameter will be described later.

  Next, the shift unit 33 is operated to set a predetermined measurement position of the phase difference film 19 on the optical axis L. When a predetermined measurement position of the phase difference film 19 is set on the optical axis L, a light intensity data creation step is performed, and light intensity data SB1 (θ) is created. The light intensity data SB1 (θ) is stored in the light intensity data storage unit 50.

［数１］式は予め理論的に導出される式であり、この式の導出方法については後述する。［数１］に示すように、光強度データＳＢ１（θ）及びストークスパラメータＸＰ１，ＸＰ２と主軸方位αとの関係は逆正接関数で表されるため、一つの光強度データＳＢ１（θ）及びストークスパラメータＸＰ１，ＸＰ２から主軸方位αが一意に決まる。主軸方位αが求まると、方位変更部３１を操作して、位相差フイルム１９をＲ１方向又はＲ２方向に回転させ、位相差フイルム１９の主軸方位αを０°に変更する。 Next, based on the light intensity data SB1 (θ) stored in the light intensity data storage unit 50 and the Stokes parameters XP1 and YP1 stored in the RAM 52, the main axis of the phase difference film 19 is expressed by the following [Equation 1]. Find the direction α.

[Expression 1] is an equation that is theoretically derived in advance, and a method for deriving this equation will be described later. As shown in [Equation 1], since the relationship between the light intensity data SB1 (θ) and the Stokes parameters XP1 and XP2 and the principal axis direction α is expressed by an arctangent function, one light intensity data SB1 (θ) and Stokes The principal axis direction α is uniquely determined from the parameters XP1 and XP2. When the principal axis azimuth α is obtained, the azimuth changing unit 31 is operated to rotate the phase difference film 19 in the R1 direction or the R2 direction, thereby changing the main axis azimuth α of the phase difference film 19 to 0 °.

［数２］式は予め理論的に算出される式であり、この式の算出方法については後述する。 Next, in addition to the light intensity data SB1 (θ) and the Stokes parameters XP1, YP1, ZP1, based on the principal axis direction α of the phase difference film, the retardation candidate value δ1j (j = 1, 2) according to the following [Equation 2]: ) Any one of these retardation candidate values is specified as the retardation δ of the phase difference film 19 by the process described later.

[Expression 2] is an expression that is theoretically calculated in advance, and the calculation method of this expression will be described later.

  The expression of the first term on the right side of [Formula 2] is an inverse sine function with respect to the light intensity data SB1 (θ), the Stokes parameters XP1, YP1, ZP1, and the main axis direction α. Here, the value of F1 (XP1, YP1, ZP1, SB1 (θ), α) in [Expression 2] is hereinafter referred to as “observed value”. Further, the expression of the second term on the right side of [Equation 2] is obtained by calculating an arctangent with respect to the light intensity data SB1 (θ), the Stokes parameters XP1, YP1, ZP1, and the main axis direction α, as shown in [Equation 21] described later. It is a function. Therefore, the value of the expression in the second term on the right side of [Equation 2] is uniquely determined from one light intensity data SB1 (θ), Stokes parameters XP1, YP1, ZP1, and principal axis direction α, whereas [Equation 2] The value of the expression in the first term on the right side of is not uniquely determined. Therefore, the retardation candidate value δ1j is not uniquely determined from the single light intensity data SB1 (θ), the Stokes parameters XP1, YP1, ZP1, and the principal axis direction α.

ここで、Ｆ１はＦ１（ＸＰ１，ＹＰ１，ＺＰ１，ＳＢ１（θ），α）を、Ｋ１はＫ１（ＸＰ１，ＹＰ１，ＺＰ１，ＳＢ１（θ），α）を表している。図３は［数３］の式を２次元グラフ上で表した正弦曲線６０であり、この正弦曲線６０から、１つの観測値Ｆ１に対して２つのレタデーション候補値δ１１、δ１２が存在することが分かる。そして、観測値Ｆ１と、この観測値Ｆ１に対応するレタデーション候補値δ１１、δ１２とを関連付けてレタデーションデータを作成する。作成されたレタデーションデータはＲＡＭ５２に記憶される。 On the other hand, when the formula [2] is rewritten into a sine function for the retardation candidate value [delta] 1j, the following formula [3] is obtained.

Here, F1 represents F1 (XP1, YP1, ZP1, SB1 (θ), α), and K1 represents K1 (XP1, YP1, ZP1, SB1 (θ), α). FIG. 3 shows a sine curve 60 in which the equation of [Equation 3] is represented on a two-dimensional graph. From this sine curve 60, there are two retardation candidate values δ11 and δ12 for one observed value F1. I understand. Then, the observation value F1 and the retardation candidate values δ11 and δ12 corresponding to the observation value F1 are associated to create retardation data. The created retardation data is stored in the RAM 52.

  Next, the shift unit 33 is operated, and the phase difference film 19 is separated from the optical axis L. Then, the azimuth changing unit 29 rotates the polarizer 15 in the R2 direction to change the transmission axis azimuth γ from the positive azimuth γ1 to the negative azimuth γ2. The negative azimuth γ2 is symmetrical to the positive azimuth γ1 with respect to the + Y direction. When the transmission axis azimuth γ is changed to a negative azimuth γ2, a light intensity data creation step is performed, and light intensity data SA2 (θ) is created. The light intensity data SA2 (θ) is stored in the light intensity data storage unit 50. The transmission axis direction γ2 is preferably −8 °.

  Then, the Stokes parameters XP2, YP2, and ZP2 are obtained in the same manner as when the Stokes parameters XP1, YP1, and ZP1 are obtained based on the light intensity data SA2 (θ) stored in the light intensity data storage unit 50. Here, since the transmission axis direction γ2 of the polarizer is a negative direction that is symmetrical to the positive direction γ1, XP2 = XP1 between the Stokes parameters XP2, YP2, ZP2 and the Stokes parameters XP1, YP1, ZP1. , YP2 = −YP1, ZP2 = ZP1.

  Next, the shift unit 33 is operated to set the center of the phase difference film 19 on the optical axis L. When the phase difference film 19 is set on the optical axis L, a light intensity data creation step is performed, and light intensity data SB2 (θ) is created. The created light intensity data SB2 (θ) is stored in the light intensity data storage unit 50.

［数４］式は予め理論的に導出される式であり、この式の導出方法についても［数２］式の導出方法と合わせて後で説明する。 Next, based on the light intensity data SB2 (θ), the Stokes parameters XP2, YP2, ZP2, and the principal axis direction α of the phase difference film, the retardation value candidate value δ2j of the phase difference film is expressed by the following [Equation 4]. j = 1, 2).

[Equation 4] is an equation that is theoretically derived in advance, and the method of deriving this equation will be described later together with the method of deriving [Equation 2].

  The expression of the first term on the right side of [Expression 4] is an inverse sine function with respect to the light intensity data SB2 (θ), the Stokes parameters XP2, YP2, ZP2, and the main axis direction α. Here, the value of F2 (XP2, YP1, ZP1, SB2 (θ), α) in [Equation 4] is also referred to as “observed value” in the same manner as F1 described above. In addition, the expression of the second term on the right side of “Equation 4” is the inverse of the light intensity data SB2 (θ), the Stokes parameters XP2, YP2, ZP2, and the main axis direction α, as shown in [Equation 21] described later. Tangent function. Accordingly, the retardation candidate value δ2j is not uniquely determined from the single light intensity data SB2 (θ), the Stokes parameters XP2, YP2, ZP2, and the principal axis direction α, as in the equation (2).

ここで、Ｆ２はＦ２（ＸＰ２，ＹＰ２，ＺＰ２，ＳＢ２（θ），α）を、Ｋ２はＫ２（ＸＰ２，ＹＰ２，ＺＰ２，ＳＢ２（θ），α）を表している。図４は［数５］の式を２次元グラフ上で表した正弦曲線６１であり、この正弦曲線６１から、１つの観測値Ｆ２に対して２つのレタデーション候補値δ２１、δ２２が存在することが分かる。また、後述の［数２１］式に示すように、ＸＰ２＝ＸＰ１、ＹＰ２＝−ＹＰ１、ＺＰ２＝ＺＰ１のときにはＫ２＞Ｋ１となるため、正弦曲線６１は、正弦曲線６０を（Ｋ２―Ｋ１）だけＴ方向に平行移動させたものとなる。 On the other hand, when the formula [4] is rewritten into a sine function for the retardation candidate value [delta] 2j, the following formula [5] is obtained.

Here, F2 represents F2 (XP2, YP2, ZP2, SB2 (θ), α), and K2 represents K2 (XP2, YP2, ZP2, SB2 (θ), α). FIG. 4 shows a sine curve 61 in which the equation of [Equation 5] is represented on a two-dimensional graph. From this sine curve 61, there are two retardation candidate values δ21 and δ22 for one observed value F2. I understand. Further, as shown in [Expression 21], which will be described later, when XP2 = XP1, YP2 = −YP1, and ZP2 = ZP1, K2> K1, so the sine curve 61 represents the sine curve 60 by (K2−K1). It is the one translated in the T direction.

  Then, the observation value F2 and the retardation candidate values δ21 and δ22 corresponding to the observation value F2 are associated with each other to create retardation data. The created retardation data is stored in the RAM 52.

  Next, based on the retardation data stored in the RAM 52, the four candidate retardation values δ11, δ12, δ21, and δ22 that have the same or almost the same value are identified. Then, it is determined whether or not the observed value corresponding to the retardation candidate value that matches or substantially matches the value is within the measurement accuracy allowable range. The measurement accuracy tolerance range refers to an observation value range in which the accuracy of the retardation candidate value is ensured, and specifically, an observation value range in which the accuracy of the retardation candidate value becomes low, that is, “± 1” or “± 1”. A range other than the “near” range.

  As a result of the determination, when both of the observed values F1 and F2 are within the measurement accuracy allowable range, one of the retardation candidate values is determined as the retardation δ of the phase difference film. On the other hand, if only one of the observed values F1 and F2 is within the measurement accuracy tolerance, the retardation candidate value corresponding to the observation within the measurement accuracy tolerance is the retardation δ of the phase difference film. As determined.

  For example, as shown in FIG. 5, when the relationship between the retardation candidate value δ1j and the observed value is represented by the sine curve 63 and the relationship between the retardation candidate value δ2j and the observed value is represented by the sine curve 64, the values match. Alternatively, the retardation candidate values that substantially match are the retardation candidate values δ12 and δ22. Since both the observed value F1 corresponding to the retardation candidate value δ12 and the observed value F2 corresponding to the retardation candidate value δ22 are within the measurement accuracy allowable range, either one of the retardation candidate values δ12 or δ22 is the phase difference film 19. The retardation δ is determined.

  In addition, as shown in FIG. 6, when the relationship between the retardation candidate value δ1j and the observed value is represented by the sine curve 66 and the relationship between the retardation candidate value δ2j and the observed value is represented by the sine curve 67, the values match. Alternatively, the retardation candidate values that substantially match are the retardation candidate values δ12 and δ22. Since the observed value F1 corresponding to the retardation candidate value δ12 is within the measurement accuracy allowable range and the observed value F2 corresponding to the other retardation candidate value δ22 is outside the measurement accuracy allowable range, the retardation candidate value δ12 is ranked. The retardation δ of the phase difference film 19 is determined.

  In the conventional birefringence measuring apparatus, for example, in the birefringence measuring apparatus of Patent Document 1, the wavelength of light incident on the phase difference film to be measured is changed a plurality of times, and the retardation candidate value and the observation are observed every time the wavelength is changed. The relationship between values is being sought. On the other hand, in the birefringence measuring device of the present invention, the transmission axis direction of the polarizer is simply set a plurality of times (not described above) without providing a device for changing the wavelength of the light as in the conventional birefringence measuring device. In the embodiment, only by changing the two times, a plurality (two in the above embodiment) of the relationship between the retardation candidate value and the observed value can be obtained for each change of the transmission axis direction.

  Further, in the birefringence measuring apparatus of the present invention, by changing the transmission axis direction of the polarizer a plurality of times (twice in the above embodiment), a plurality of sinusoidal curves showing the relationship between the retardation candidate value and the observed value (the above-mentioned) In the embodiment, two) are obtained. For example, the sine curves are separated by a certain phase such that the sine curve 60 and the sine curve 61 shown in FIG. 4 are separated by a phase of (K2−K1). For this reason, even when the observed value of one sine curve is outside the allowable measurement accuracy range, at least the observed value of the other sine curve is within the allowable measurement accuracy range. A device for inserting or removing a phase shifter, like the birefringence measurement device of Patent Document 1, by specifying a retardation candidate value corresponding to an observed value within the measurement accuracy allowable range as a phase difference of a phase difference film. Even if it is not separately provided, a highly accurate retardation can be obtained.

  In addition, in each case of the birefringence measuring apparatus, in the case of the above-described embodiment, the spectroscope, the optical fiber, the lens, the polarizer, the phaser, the light detecting unit, the alignment error of the light receiving unit, the optical characteristics of the optical element, In the case of the above embodiment, the wavelength dependency of the phase shifter, the polarizer, the rotating polarizer, and the light receiver is included, and these alignment errors and wavelength dependency affect the accuracy of birefringence measurement. There is a problem that. In order to solve this problem, the birefringence measuring apparatus of the present invention obtains in advance Stokes parameters in consideration of alignment error and wavelength dependency before measuring the principal axis direction and retardation of the phase difference film. By using this Stokes parameter, it is possible to minimize the influence of alignment error and wavelength dependency and to measure the birefringence characteristics with high accuracy.

  Next, a method of deriving a calculation formula ([Formula 1]) and a retardation candidate value calculation formula ([Formula 2] and [Formula 4]) of the principal axis direction α of the phase difference film 19 and an actual measurement of the Stokes parameters The value calculation method will be described. In the following description, S represents the theoretical value of the light intensity of the received light obtained by the light receiver, and XP, YP, and ZP represent the theoretical values of the Stokes parameters.

この［数６］式は、回転検光子４０の透過軸方位θを変数とするフーリエ級数展開である。［数６］のＫは電気信号変換ゲインなどで決まる定数を示している。また、Ａはｃｏｓ２θ成分のフーリエ係数を、Ｂはｓｉｎ２θ成分のフーリエ係数を示している。フーリエ係数Ａ及びＢと、位相差フイルムの主軸方位α、レタデーションδ、及びストークスパラメータＸＰ，ＹＰ，ＺＰとの関係は、以下の［数７］及び「数８」で表される。

First, a method for deriving a calculation formula ([Formula 1]) of the principal axis direction α of the phase difference film 19 will be described. The intensity of the received light received by the light receiver 18 can be expressed theoretically, and the intensity S of the received light that can be expressed theoretically (hereinafter referred to as “theoretical light intensity”) is the Stokes parameters XP, YP, ZP. And the Mueller matrix representing the optical characteristics of the phase difference film and the rotation analyzer, and expressed by the following [Equation 6].

This [Equation 6] is a Fourier series expansion with the transmission axis direction θ of the rotating analyzer 40 as a variable. K in [Expression 6] indicates a constant determined by an electric signal conversion gain or the like. A represents the Fourier coefficient of the cos 2θ component, and B represents the Fourier coefficient of the sin 2θ component. The relationship between the Fourier coefficients A and B and the principal axis direction α, retardation δ, and Stokes parameters XP, YP, ZP of the phase difference film is expressed by the following [Equation 7] and “Equation 8”.

［数９］式のうち、ストークスパラメータＸＰはｃｏｓ２θ成分のフーリエ係数を、ストークスパラメータＹＰはｓｉｎ２θ成分のフーリエ係数を示している。 Further, the theoretical light intensity S when the phase difference film 19 is not set on the optical axis L is the theory when α = 0 and δ = 0 in the following [Equation 6] shown in the following [Equation 9]. It is expressed by a formula.

In the equation 9, the Stokes parameter XP indicates the Fourier coefficient of the cos 2θ component, and the Stokes parameter YP indicates the Fourier coefficient of the sin 2θ component.

  Next, Fourier transform is performed using the light intensity data SA1 (θ) and SA2 (θ) when the phase difference film 19 is separated from the optical axis L, and the Fourier coefficient of the formula [9], that is, the Stokes parameter XPi, YPi (i = 1, 2) are obtained. The Fourier transform is performed by filter processing using a Fourier transform algorithm such as discrete Fourier transform (DFT) or FFT (fast Fourier transform).

［数１０］式のＰは消光比および光検出器の非理想性による補正係数を示している。光検出器の非理想性とは、検出器から出力される信号の直流成分に対する交流成分の減衰を示している。偏光子１５及び回転検光子４０に非偏光成分が含まれる場合や、光検出器に非理想性が存在する場合にはＰは１未満となる。補正係数Ｐは、位相子１６を光軸Ｌ上から離脱させた状態で、偏光子１５の透過軸１５ａに対して、回転検光子４０の透過軸４０ａを平行にしたとき（パラレルニコル）の光強度と直交にしたとき（クロスニコル）の光強度とを用いて消光比を求めた後、回転検光子４０を回転させて光検出器の信号波形の直流成分と交流成分の振幅比(光検出器が理想的であれば１)から求めることが可能である。この方法については、公知文献(分光エリプソメトリー、藤原 祐之 著、丸善（株）)に詳しい。 Then, based on the Stokes parameters XPi and YPi, the Stokes parameter ZPi is obtained by the following [Equation 10].

P in [Expression 10] represents a correction coefficient due to the extinction ratio and the non-ideality of the photodetector. The non-ideality of the photodetector indicates the attenuation of the AC component with respect to the DC component of the signal output from the detector. P is less than 1 when the polarizer 15 and the rotation analyzer 40 include a non-polarized component, or when non-ideality exists in the photodetector. The correction coefficient P is the light when the transmission axis 40a of the rotation analyzer 40 is parallel to the transmission axis 15a of the polarizer 15 (parallel Nicols) in a state where the phase shifter 16 is separated from the optical axis L. After obtaining the extinction ratio using the light intensity when orthogonal to the intensity (crossed nicols), the rotation analyzer 40 is rotated to detect the amplitude ratio between the direct current component and alternating current component of the signal waveform of the photodetector (light detection). If the vessel is ideal, it can be obtained from 1). About this method, it is detailed in well-known literature (spectral ellipsometry, Yuji Fujiwara, Maruzen Co., Ltd.).

  Next, Fourier transform is performed using the light intensity data SB1 (θ), SB2 (θ) when the phase difference film 19 is set on the optical axis L, and Fourier coefficients Ai, Bi (i = 1, 2).

Next, when the Stokes parameters XPi, YPi, ZPi and the Fourier coefficients Ai, Bi obtained by Fourier transform are substituted into the above [Equation 7] and [Equation 8], the following [Equation 11] and [Equation 12] are obtained. It becomes.

ただし、［数１３］式のＤは以下の［数１５］で、［数１４］式のＦｉは［数１６］で、［数１４］式のＫｉは［数１７］で表される。

Then, by simultaneously solving [Equation 11] and [Equation 12], the calculation formula ([Equation 13]) of the principal axis direction α of the phase difference film and the retardation candidate value δij (i = 1, 2) are calculated. The formula ([Equation 14]) is obtained.

However, D in [Expression 13] is expressed by [Expression 15] below, Fi in [Expression 14] is expressed by [Expression 16], and Ki in [Expression 14] is expressed by [Expression 17].

ここで、［数１８］式のεは位相子のレタデーションを示している。 In the above-described embodiment, the Stokes parameters are obtained without setting the phase difference film to be measured in the apparatus, and the principal axis direction and retardation of the phase difference film are calculated based on the Stokes parameters. The Stokes parameter may be theoretically obtained by an equation, and the principal axis direction and retardation of the retardation film may be calculated based on the theoretically obtained Stokes parameter.

Here, ε in the equation [18] indicates retardation of the phase shifter.

  In the above embodiment, the transmission axis direction of the polarizer is changed twice to different directions, the Stokes parameter and the retardation candidate value are calculated for each change, and the retardation of the phase difference film is calculated based on the Stokes parameter and the retardation candidate value. However, the present invention is not limited to this, and the retardation of the retardation film may be determined by the same method as described above by changing the transmission axis direction of the polarizer to a different direction several times (three times or more).

  In the example, first, the birefringence phase difference of the BSC compensator was measured as an object to be measured. The BSC compensator is a phaser whose birefringence phase difference changes continuously with respect to the micro screw feed amount. In the first verification, in order to verify that the measurement can be performed with high accuracy in the birefringence phase difference range of 0 ° to 360 °, the BSC phase difference is changed from 0 ° to 360 °, and the measurement absolute value and the measurement 100 are measured. The repeatability accuracy per round was confirmed. It can be determined that the higher the linearity of the measured birefringence phase difference with respect to the micro screw feed amount, the higher the measurement accuracy. Further, as shown in FIG. 7, the repeatability was set to 3σ (σ is a standard deviation). This measurement was performed at a measurement wavelength of 590 nm.

  FIG. 8 shows the result of the first verification. According to FIG. 7, the measured value (FIG. 7 “◯”) shows very high linearity with respect to the BSC micro screw feed amount, and the measurement accuracy of the birefringence phase difference according to the present invention is high. Show. At the same time, the birefringence phase difference has a high measurement reproducibility within 0.06 ° over the range of 0 ° to 360 °, and the birefringence phase difference measurement method according to the present invention provides a range of 0 ° to 360 °. It is possible to accurately measure the birefringence phase difference.

  Next, the wavelength dependence of the birefringence phase difference according to the present invention was verified using a λ / 8 phase shifter made of artificial quartz (second verification). In the second verification, the measurement wavelengths were 450 nm, 550 nm, 590 nm, 630 nm, and 750 nm. The theoretical value of the birefringence phase difference was calculated using the sellmeier's dispersion formula based on the ordinary light refractive index no and the extraordinary light refractive index ne known from the literature values of artificial quartz.

  FIG. 9 shows the result of the second verification. As shown in FIG. 9, the actual measurement value (FIG. 9 “□”) measured by the measurement method of the present invention is in good agreement with the theoretical value (FIG. 9 “◯”) over the entire measurement wavelength range. Thus, it can be seen that the wavelength dependence (dispersion) measurement of the birefringence phase difference according to the present invention can be realized with high accuracy.

It is the schematic which shows the birefringence measuring apparatus of this invention. It is a flowchart which shows the flow of the birefringence measuring method of this invention. It is the graph which represented the relationship between the retardation candidate value in case a transmission axis direction is (gamma) 1, and an observed value with a sine curve. It is the graph which represented the relationship between the retardation candidate value in case a transmission-axis direction is (gamma) 2, and an observed value with a sine curve. It is the graph which represented the relationship between the retardation candidate value in case a transmission axis direction exists in (gamma) 1 and (gamma) 2, and an observed value with a sine curve. It is the graph which represented the relationship between the retardation candidate value in case a transmission axis direction exists in (gamma) 1 and (gamma) 2, and an observed value with a sine curve. It is a graph which shows the relationship between a phase difference range and measurement reproducibility. It is a graph which shows the relationship between BSC feed amount and a phase difference measured value. It is a graph which shows the relationship between the measured value and theoretical value of (lambda) / 8 phase difference plate made from artificial quartz.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Birefringence measuring apparatus 11 Light source 15 Polarizer 16 Phaser 17 Light detection part 18 Light receiver 19 Phase difference film 20 Controller 40 Rotation analyzer

Claims (10)

Using a light source, a polarizer, a phaser, a rotation analyzer whose transmission axis direction changes at a constant rotation angle, and a light receiver, a measurement object is inserted between the phaser and the rotation analyzer. In the birefringence measurement method for obtaining the retardation of the measurement object,
With the transmission axis of the polarizer fixed in the first transmission axis direction, the light from the light source is detected by the light receiver via the polarizer, the phaser, the measurement object, and the rotating analyzer. A first light detection step to:
After the first light detection step, a first light intensity data is created by associating the transmission axis direction of the rotating analyzer with the intensity of light detected by the light receiver at the transmission axis direction. A data creation step;
A transmission axis direction changing step of changing the transmission axis of the polarizer from the first transmission axis direction to a second transmission axis direction different from the first transmission axis direction;
A second light detection step for performing the same steps as the first light detection step in a state where the transmission axis of the polarizer is fixed in the second transmission axis direction;
After the second light detection step, the same step as the first light intensity data creation step is performed, and a second light intensity data creation step for creating second light intensity data;
A main axis direction calculating step for determining a main axis direction of the measurement object based on the first or second light intensity data;
A birefringence measurement method, comprising: a retardation calculation step for obtaining a retardation of the measurement object based on the principal axis direction of the measurement object, the first light intensity data, and the second light intensity data. Before the first light detection step, the same steps as the first light detection step and the first light intensity data creation step are performed in a state where the measurement object is excluded, and the first pre-measurement light intensity data is created. A first pre-measurement light intensity data creation step;
A first Stokes parameter calculation step for obtaining a first Stokes parameter indicating a polarization state of light before entering the measurement object based on the first pre-measurement light intensity data;
Before the second light detection step, the same steps as the second light detection step and the second light intensity data creation step are performed in a state where the measurement object is excluded, and second light intensity data before measurement is created. A second pre-measurement light intensity data creation step;
A second Stokes parameter calculation step for obtaining a second Stokes parameter indicating a polarization state of light before entering the measurement object based on the second pre-measurement light intensity data;
In the main axis direction calculating step, in addition to the first or second light intensity data, the main axis direction of the measurement object is obtained based on the first or second Stokes parameter,
In the retardation calculating step, the retardation of the measurement object is obtained based on the first and second Stokes parameters in addition to the main axis direction of the measurement object, the first light intensity data, and the second light intensity data. The birefringence measuring method according to claim 1, wherein: The retardation calculating step includes:
First retardation candidate value specification that specifies a plurality of first retardation candidate values of the measurement target based on the first observation value obtained from the first Stokes parameter, the first light intensity data, and the main axis direction of the measurement target Steps,
A plurality of second retardation candidate values for the measurement target are specified based on the second observation value obtained from the second observation value obtained from the second Stokes parameter, the second light intensity data, and the main axis direction of the measurement target. A second retardation candidate value identification step,
The retardation determination step of determining a retardation candidate value whose values match or substantially match among the plurality of first and second retardation candidate values as a retardation of the measurement object. Refraction measurement method.   The relationship between the first observed value and the first retardation candidate value and the relationship between the second observed value and the second retardation candidate value are expressed by a sine function, and the first observed value and the first retardation candidate value 4. The birefringence measurement method according to claim 3, wherein the sine curve obtained from the relationship is separated from the sine curve obtained from the second observed value and the second retardation candidate value by a predetermined phase. The first or second observation value is “−1” or more and “1” or less,
The retardation determining step includes:
Identifying a candidate retardation value whose values match or substantially match among the plurality of first and second retardation candidate values;
Determining whether the observed value corresponding to the retardation candidate value with which the values match or substantially match is in a range other than “± 1” or “in the vicinity of ± 1”;
The birefringence measurement according to claim 4, further comprising: determining a retardation candidate value corresponding to an observation value in a range other than “± 1” or “near ± 1” as the retardation of the measurement object. Method.   6. The transmission axis direction changing step, wherein the transmission axis of the polarizer is changed to the second transmission axis direction symmetrical to the first transmission axis direction with respect to the main axis direction. 2. The birefringence measuring method according to item 1.   The birefringence measuring method according to claim 1, wherein the light passing through the polarizer and the phase shifter is circularly polarized light, linearly polarized light, or elliptically polarized light.   The birefringence measuring method according to claim 1, wherein the object to be measured is a phase difference film. Using a light source, a polarizer, a phaser, a rotation analyzer whose transmission axis direction changes at a constant rotation angle, and a light receiver, a measurement object is inserted between the phaser and the rotation analyzer. In the birefringence measuring device for obtaining the retardation of the measurement object,
A transmission axis direction changing unit that changes the transmission axis of the polarizer between a first transmission axis direction and a second transmission axis direction different from the first transmission axis direction;
With the transmission axis of the polarizer fixed to the first transmission axis direction or the second transmission axis direction, the light from the light source is changed to the polarizer, the phaser, the measurement object, and the rotation analyzer. A light detection unit that detects with the light receiver,
The transmission axis direction of the rotating analyzer is associated with the intensity of the light detected by the light receiver when the transmission axis direction is the first direction when the transmission axis of the polarizer is in the first transmission axis direction. A light intensity data creating unit that creates light intensity data and second light intensity data when the transmission axis of the polarizer is on the second transmission axis;
Based on the first or second light intensity data, a main axis direction calculation unit for determining a main axis direction of the measurement object;
A birefringence measurement apparatus comprising: a retardation calculation unit that obtains a retardation of the measurement object based on the principal axis direction of the measurement object, the first light intensity data, and the second light intensity data. Using a light source, a polarizer, a phaser, a rotation analyzer whose transmission axis direction changes at a constant rotation angle, and a light receiver, a measurement object is inserted between the phaser and the rotation analyzer. In the birefringence measurement program for obtaining the retardation of the measurement object,
With the transmission axis of the polarizer fixed in the first transmission axis direction, the light from the light source is detected by the light receiver via the polarizer, the phaser, the measurement object, and the rotating analyzer. And the steps to
After the first light detection step, a procedure for creating first light intensity data by associating the transmission axis direction of the rotating analyzer with the light intensity detected by the light receiver at the transmission axis direction;
Changing the transmission axis of the polarizer from the first transmission axis direction to a second transmission axis direction different from the first transmission axis direction;
A procedure of performing the same steps as the first light detection step in a state where the transmission axis of the polarizer is fixed in the second transmission axis direction;
After the second light detection step, the same step as the first light intensity data creation step is performed to create second light intensity data;
A procedure for obtaining a principal axis orientation of the measurement object based on the first or second light intensity data;
A birefringence measurement program for causing a computer to execute a procedure for obtaining a retardation of the measurement object based on the principal axis direction of the measurement object, the first light intensity data, and the second light intensity data.

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