TWI387745B - Optical characteristic measurement system for liquid crystal unit and method thereof - Google Patents

Description

Optical characteristic measurement system of liquid crystal cell and method thereof

The present invention relates to an optical characteristic measuring system for a liquid crystal cell and a method thereof.

Among the components used in the liquid crystal panel, components having optical birefringence characteristics such as a liquid crystal layer and a compensation film, the optical properties of which determine the image quality of the liquid crystal display, and the optical properties of the components The characteristics can be measured by the system architecture of the Polarizer-Sample-Analyzer (PSA).

The PSA measurement of the optical axis angle or phase difference of the non-uniform substance is synchronously rotating or rotating the sample to be tested while the polarizing plate and the polarization axis of the analyzer are parallel or perpendicular, and is measured by the photodetector. The measured light intensity signal determines its maximum or minimum value, and the rotation angle at which the signal is maximum or minimum is its optical axis angle. However, the conventional method requires recording a large amount of data, and it is necessary to scan a sufficiently large angular range to avoid the error of the optical axis angle measurement produced by the heterodyne calculation. Therefore, it is doubtful whether this conventional method can cope with production demand on a production line that requires a higher measurement speed.

U.S. Patent No. 5,532,823 discloses the use of a PSA measurement architecture to measure a Twisted Nematic (TN) liquid crystal panel that sets the polarizer and the analyzer to a relative twist angle. After measuring the angle, then turn the LCD panel to the maximum penetration strength and measure. However, the method disclosed in this patent is the same as the above-described conventional method, and it is doubtful whether the production speed can be met in the measurement speed.

As described above, the prior art PSA system cannot accurately and quickly detect an element having optical birefringence characteristics, and in view of this, the present invention provides a solution for this.

An optical characteristic measuring system for a liquid crystal cell according to an embodiment of the present invention includes a light source, a light projecting probe, a light receiving probe, a spectrometer, and a signal analyzing unit. The light source emits an emitted light having a plurality of wavelengths. The light projecting probe has a first transmission axis and is used to convert the emitted light into a polarized light beam projected onto the device under test. The light-receiving probe has a second transmission axis and is configured to analyze a polarization state of the one-polarized beam after the polarized light beam penetrates the device to be tested, wherein the first transmission axis and the second transmission axis There is a relative angle between the two. The spectrometer is configured to acquire a spectral signal of the polarized light beam, wherein the light receiving probe is coupled to the spectrometer. The signal analysis unit is configured to calculate an optical axis azimuth angle and/or a phase difference distribution of the test object by using the plurality of spectral signals and a plurality of rotation angles corresponding to the spectral signals, wherein each of the spectral signals is The light-emitting probe and the light-receiving probe are rotated at the rotation angle and measured.

According to an optical characteristic measurement method of a liquid crystal cell according to an embodiment of the present invention, the method includes at least the following steps: setting a relative angle to a first penetration axis of a light-emitting probe and a second insertion of a light-receiving probe Rotating the light-emitting probe and the light-receiving probe a plurality of times, and recording one of the rotation angles and a spectral signal of the number of times; and calculating the light of the device to be tested according to the rotation angles and the spectral signals Axis bearing angle.

The above description is only an overview of the technical solution of the present invention, in order to be clearer The technical means of the present invention are understood and can be implemented according to the contents of the specification. Hereinafter, several embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The above and other objects, features, and advantages of the present invention will become more apparent and understood.

The technology disclosed by the invention completes the characteristic measurement of the birefringent sample, and obtains the optical axis angle of the sample by rotating the polarizing plate and the analyzer, and can effectively improve the measurement accuracy under a limited number of measurement times in the algorithm. The direct solution method does not require a large amount of measurement data and then fits the data to solve the optical axis angle. According to different applications, the phase difference information is obtained through mathematical theoretical calculation.

1 shows a schematic diagram of an optical characteristic measurement system 100 for a liquid crystal cell according to an embodiment of the present invention. The optical characteristic measurement system 100 of the liquid crystal unit includes a light source 102 emitting a plurality of emitted light (for example, white light) having a plurality of wavelengths, a first transmission axis, and for converting the emitted light into a projection a light-emitting probe 106 of a polarized light beam of the measuring member 124, a light-receiving probe 110 having a second transmission axis and for generating a polarization state of one of the polarized light beams after the polarized light beam penetrates the test object, a spectrometer 112 for acquiring a spectral signal of the polarized beam, and a method for calculating an optical axis azimuth angle of the device under test 124 and/or using a plurality of the spectral signals and a plurality of rotation angles corresponding to the spectral signals The signal analysis unit 114 of the phase difference distribution. In the embodiment of the present invention, a relative angle between the polarizing plate 104 and the transmission axis of the analyzer 108 is set such that one of the two vertically polarized beams passes through the analyzer 108. Partial The diaphragm 104 is a 偏振-type polarizing plate or a sheet-type polarizing plate. In one embodiment, the analyzer 108 is a 稜鏡-type or sheet-type analyzer.

The light source 102 generates a broadband beam having a plurality of wavelengths, and uses a fiber bundle 116 to guide the light into a plurality of beams, and then is coupled to the light-emitting probe group 120 including the plurality of light-emitting probes 106 by the optical fiber 118. . The light projecting probe 106 further includes a collimating lens for collimating the beam, so that the light projecting probe 106 can project a linearly polarized parallel beam to the device under test 124.

The projection light of the device under test 124 that penetrates the birefringence characteristic changes its state of polarization to form two mutually perpendicular polarized beams due to the phase difference.

The light-receiving probe set 126 includes a plurality of light-receiving probes 110 that are disposed corresponding to the light-emitting probe set 120. The light receiving probe 110 further includes a focusing lens 128 for focusing the polarized light beam. The light collecting probe 110 can focusly couple the two mutually perpendicular polarized light beams into a fiber array 130 connected to the spectrometer 112 by rotation. In the embodiment of the present invention, the spectrometer 112 is a multi-channel spectrometer capable of simultaneously analyzing the spectral intensity information of a plurality of points to be measured, and the multi-channel spectrometer can simultaneously obtain two mutually perpendicular polarized beams and perform signal normalization processing.

The optical characteristic of the device under test 124 is analyzed and calculated by the signal analysis unit 114. The components in the system can be represented by Jones Matrix, and then the following equations for fitting the breakthrough spectral curve are obtained:

Where β ² = δ ² + ² and α is the angle of the polarizer, γ is the angle of the analyzer, Φ is the twist angle of the liquid crystal, Δn is the birefringence, d is the thickness of the sample, and λ is the wavelength of the light. Equation (1) can represent the optical birefringence characteristics of the non-uniform material, including the optical axis azimuth angle and phase difference information. When the device under test 124 is measured, the projection surface 202 of the optical axis azimuth angle of the device under test 124 is perpendicular to the direction of the incident optical axis, and the penetration axis (Transmission Axis) 204 of the polarizing plate 104 and the penetration of the analyzer 108 are penetrated. The axes 206 have a relative angle, and the angle between the polarizer 104 and the optical axis azimuth angle is α (as shown in Fig. 2). The measurement and calculation of the optical axis azimuth angle disclosed in the present invention may include the following two methods: (i) Method 1: For the test piece 124 having no torsion angle (Non-twisted) or a twist angle of 90 degrees, the equation ( 1) The equation can be simplified by the condition γ=α, and the dispersion characteristics are removed by the following formula:

In the equation (2), T _a is the penetration strength of the polarizing plate 104 at the initial angular position, at which time the optical axis azimuth angle of the test piece 124 is at an angle α with the transmission axis of the polarizing plate 104, and T _b is the polarizing plate 104 and The penetration spectrum intensity of the slice 108 after rotating the X angle. In equation (2), we can know that the unknown coefficient α is solved by known measurement conditions, which is the optical axis angular position of the test piece 124 or the liquid crystal alignment angle.

(ii) Method 2: This method correlates the relative position of the polarizing plate 104 and the analyzer 108 with the torsion angle, and equation (1) is at γ = α + Under the condition, the dispersion characteristic is removed from the equation by the following formula:

In the equation, T ₁ is the penetration strength of the polarizing plate 104 at the initial angular position. At this time, the liquid crystal alignment direction or the optical axis azimuth angle of the test piece 124 is unknown to the angle of the transmission axis of the polarizing plate 104 as α , T ₂ and T _{3 .} It represents the transmission spectrum intensity after the polarizing plate 104 and the analyzer 108 are rotated by the X ₁ angle, respectively, and after the X ₂ angle is rotated. At the beginning of the second method, a torsion angle is required to position the polarizing plate 104 and the analyzer 108 to a relative torsion angle position. This equation is also applicable to the sample to be tested 124 which is a non-torsion angle.

After determining the optical axis angle, the phase difference distribution Δnd of the sample to be tested can be obtained by fitting (Fitting) or directly solving the equation, wherein Δn is a function of the wavelength, that is, a wavelength-dependent phase can be obtained. Difference distribution. We can also fit the phase difference distribution calculated by the Cauchy Dispersion Equation shown in equation (4), which can eliminate the error caused by system noise and obtain the phase of continuous distribution. The difference value.

Where A , B, and C are dispersion coefficients, all of the data solution curves can be fitted using the Least Square Method to find these three coefficients.

3 is a schematic view showing an optical characteristic measuring system 300 of a liquid crystal cell according to another embodiment of the present invention. The light collecting probe 304 included in the light receiving probe group 302 may also include a polarization beam splitter 306 and two light focusing lenses (308 and 310). The light-receiving probe 302 can simultaneously focus two mutually perpendicular polarized beams on the two light-receiving fiber arrays 130 and connect to the multi-channel image spectrometer 112 to simultaneously analyze the spectral intensity information of the multiple channels, and can be simultaneously obtained by the spectrometer. The two mutually perpendicular polarized beam signals are normalized for signal processing. In one embodiment, the polarization beam splitter 306 is a 偏振-type polarization beam splitter or a sheet-type polarization beam splitter.

4 is a flow chart showing a method of measuring optical characteristics of a liquid crystal cell according to an embodiment of the present invention. The flow chart of this disclosure applies Method 1 to a test piece having a twist angle or a twist angle of 90°. In step S402, the torsion angle of the device to be tested is given. In step S404, a relative angle is set between a first transmission axis of one of the light-emitting probes and a second transmission axis of a light-receiving probe, wherein the relative angle causes a transmitted polarized beam to have a maximum intensity. value. In this embodiment, the object to be tested has a non-twist angle or a twist angle of 90°, so the relative angle is 0° or 90°. In step S406, the light-emitting probe and the light-receiving probe are rotated a plurality of times ( T _a and T _b ), and one rotation angle ( X ) and one spectral signal of each of the times are recorded. In step S408, an optical axis azimuth angle of the one to be tested is calculated according to the rotation angles and the spectral signals. Using the T _a , T _b and X in the above steps, the angle α of the penetration axis in the formula (2) is calculated, and the angle α is the azimuth angle of the optical axis. In step S410, the light-emitting probe and the light-receiving probe are rotated to a measuring angle, wherein the angle between the measuring angle and the optical axis azimuth angle is 45° or -45°. In step S412, a normalized spectral signal is measured and calculated. In step S414, the phase difference distribution is calculated by using the optical axis azimuth angle and the normalized spectral signal, and the phase difference distribution can be obtained by fitting or directly calculating according to formula (1). In addition, the phase difference distribution can also be calculated by the equation (4) fitting.

FIG. 5 is a flow chart showing a method of measuring optical characteristics of a liquid crystal cell according to another embodiment of the present invention. This disclosed flow chart applies Method 2 to a device under test having a twist angle. In step S502, the torsion angle of the device to be tested is given ( ). In step S504, a relative angle is set between a first transmission axis of one of the light-emitting probes and a second transmission axis of one of the light-receiving probes, wherein the relative angle is a twist angle ( ) or angle ( +90°). In step S506, the light-emitting probe and the light-receiving probe are rotated a plurality of times ( T ₁ , T ₂ and T ₃ ), and one of the rotation angles ( X ₁ and X ₂ ) and a spectral signal are recorded. In step S508, an optical axis azimuth angle of the one to be tested is calculated according to the rotation angles and the spectral signals. Using the T ₁ , T ₂ and T ₃ and X ₁ , X ₂ in the above steps, the angle α of the penetration axis in the formula (3) is calculated, and the angle α is the azimuth angle of the optical axis. In step S510, the light-emitting probe and the light-receiving probe are rotated to a measuring angle, wherein the angle between the measuring angle and the optical axis azimuth angle is 45° or -45°. In step S512, a normalized spectral signal is measured and calculated. In step S514, the phase difference distribution is calculated by using the optical axis azimuth angle and the normalized spectral signal, and the phase difference distribution can be obtained by fitting or directly calculating according to formula (1). In addition, the phase difference distribution can also be calculated by the equation (4) fitting.

The technical and technical features of the present invention have been disclosed as above, and those skilled in the art can still make various substitutions and modifications without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be construed as not limited by the scope of the invention, and the invention is intended to be

100‧‧‧Optical characteristic measurement system

102‧‧‧Light source

104‧‧‧Polarizer

106‧‧‧Lighting probe

108‧‧‧Check film

110‧‧‧Lighting probe

112‧‧‧ Spectrometer

114‧‧‧Signal Analysis Unit

116‧‧‧Fiber bundle

118‧‧‧Fiber

120‧‧‧Lighting probe set

122‧‧‧Light collimating lens

124‧‧‧Deters to be tested

126‧‧‧Lighting probe set

128‧‧‧Light focusing lens

130‧‧‧Fiber Array

202‧‧‧Projection surface

204, 206‧‧‧ penetration axis

300‧‧‧Optical characteristic measurement system

302‧‧‧Lighting probe set

304‧‧‧Lighting probe

306‧‧‧ polarized beam splitter

308, 310‧‧‧Light focusing lens

S402~5416‧‧‧ Process steps

S502~S516‧‧‧ Process steps

1 is a schematic view showing an optical characteristic measuring system of a liquid crystal cell according to an embodiment of the present invention; and FIG. 2 is a schematic view showing a position of an optical axis azimuth angle and a polarization axis of a polarizing plate and a polarizing plate according to an embodiment of the present invention; FIG. 4 is a flow chart showing an optical characteristic measurement system of a liquid crystal cell according to another embodiment of the present invention; FIG. 4 is a flow chart showing a method for measuring optical characteristics of a liquid crystal cell according to an embodiment of the present invention; and FIG. 5 is a view showing another embodiment of the present invention. A flow chart of a method for measuring optical characteristics of a liquid crystal cell.

100‧‧‧Optical characteristic measurement system

102‧‧‧Light source

104‧‧‧Polarizer

106‧‧‧Lighting probe

108‧‧‧Check film

110‧‧‧Lighting probe

112‧‧‧ Spectrometer

114‧‧‧Signal Analysis Unit

116‧‧‧Fiber bundle

118‧‧‧Fiber

120‧‧‧Lighting probe set

122‧‧‧Light collimating lens

124‧‧‧Deters to be tested

126‧‧‧Lighting probe set

128‧‧‧Light focusing lens

130‧‧‧Fiber Array

Claims (23)

An optical characteristic measuring system for measuring a liquid crystal cell for measuring an optical characteristic of a device to be tested, the optical characteristic measuring system comprising: a light source emitting a plurality of emitted light having a plurality of wavelengths; and a light emitting probe having a first a transmission axis for converting the emitted light into a polarized beam that is projected onto the device to be tested; a light-receiving probe having a second transmission axis for analyzing the penetration of the device to be tested from the polarized beam And generating a polarization state of the polarized light beam, wherein the first transmission axis and the second transmission axis have a relative angle; a spectrometer for acquiring a spectral signal of the polarized light beam, wherein the light receiving probe The signal is coupled to the spectrometer; and a signal analysis unit is configured to calculate an optical axis azimuth angle and/or a phase difference of the one of the test elements by using the plurality of spectral signals and a plurality of rotation angles corresponding to the spectral signals. The distribution, wherein each of the spectral signals is measured by rotating the light-emitting probe and the light-receiving probe at the rotation angle. According to the optical characteristic measuring system of claim 1, wherein the calculation of the optical axis azimuth angle is based on the following formula: Wherein, α is an angle between the first transmission axis and the optical axis azimuth angle of the device to be tested; and T ₁ is the spectral signal obtained when the angle is α ; T ₂ and T ₃ are respectively The spectral signal obtained by the light projection probe and the light receiving probe after the rotation angles X ₁ and X ₂ . According to the optical characteristic measuring system of claim 1, wherein the calculation of the optical axis azimuth angle is based on the following formula: Wherein, α is an angle between the first transmission axis and the optical axis azimuth angle of the device to be tested; and T ₁ is the spectral signal obtained when the angle is α ; T ₂ and T ₃ are respectively The spectral signal obtained by the light projection probe and the light receiving probe after the rotation angles X ₁ and X ₂ . The optical characteristic measuring system according to claim 1, wherein the relative angle is a twist angle of the one to be tested Or another angle +90°. The optical characteristic measuring system of claim 1, wherein the relative angle is 0° or 90°. According to the optical characteristic measuring system of claim 1, wherein the calculation of the optical axis azimuth angle is based on the following formula: Wherein, α is an angle between the first transmission axis and the optical axis azimuth angle of the device to be tested; T _a is the spectral signal obtained when the angle is α ; T _{b is} the light projection probe The spectral signal obtained after the angle X of the light receiving probe is rotated. The optical characteristic measuring system of claim 1, wherein the light projecting probe comprises a polarizing plate and a light collimating lens. The optical property measuring system according to claim 7, wherein the polarizing plate is a polarizing plate or a sheet-type polarizing plate. The optical characteristic measuring system of claim 1, wherein the light receiving probe comprises a polarizer and a light focusing lens. The optical characteristic measuring system according to claim 9, wherein the analyzer is a cymbal or a sheet-type analyzer. The optical characteristic measuring system of claim 1, wherein the light receiving probe comprises a polarization beam splitter and a light focusing lens. The optical characteristic measuring system according to claim 11, wherein the polarization beam splitter is a 偏振-type polarization beam splitter or a sheet-type polarization beam splitter. The optical characteristic measuring system of claim 1, wherein the spectrometer is a multi-channel image spectrometer. The optical characteristic measurement system according to claim 1, wherein the calculation of the phase difference distribution is a penetration spectral curve fitting solution. The optical characteristic measurement system according to claim 1, wherein the calculation of the phase difference distribution is based on a Cauchy dispersion fitting solution. A method for measuring an optical characteristic of a liquid crystal cell, comprising the steps of: setting a relative angle between a first transmission axis of a light-emitting probe and a second penetration axis of a light-receiving probe; rotating the light-emitting probe and the receiving The optical probe is plural times, and records one rotation angle and one spectral signal of each of the times; and calculates an optical axis azimuth angle of the device to be tested according to the rotation angles and the spectral signals. According to the optical characteristic measurement method of claim 16, wherein the calculation of the optical axis azimuth angle is based on the following formula: Wherein, α is an angle between the first transmission axis and the optical axis azimuth angle of the device to be tested; and T ₁ is the spectral signal obtained when the angle is α ; T ₂ and T ₃ are respectively The spectral signal obtained after the light projection probe and the light receiving probe rotate the angles X ₁ and X ₂ . The optical characteristic measuring system of claim 16, wherein the calculation of the optical axis azimuth angle is based on the following formula: Wherein, α is an angle between the first transmission axis and the optical axis azimuth angle of the device to be tested; and T ₁ is the spectral signal obtained when the angle is α ; T ₂ and T ₃ are respectively The spectral signal obtained by the light projection probe and the light receiving probe after the rotation angles X ₁ and X ₂ . According to the optical characteristic measuring method of claim 16, wherein the relative angle is a twist angle of the one to be tested Or another angle +90°. The optical property measuring method according to claim 16, wherein the relative angle is 0° or 90°. According to the optical characteristic measurement method of claim 16, wherein the calculation of the optical axis azimuth angle is based on the following formula: Wherein, α is an angle between the first transmission axis and the optical axis azimuth angle of the device to be tested; T _a is the spectral signal obtained when the angle is α ; T _{b is} the light projection probe The spectral signal obtained after rotating the angle X with the light-receiving probe. The optical characteristic measuring method of claim 16, further comprising the steps of: rotating the light projecting probe and the light receiving probe to a measuring angle, wherein the measuring angle is at an angle of 45° with respect to the optical axis azimuth angle or -45°; measuring a normalized spectral signal; and utilizing the optical axis azimuth angle and the normalized spectral signal, wherein the machine of the phase difference distribution is based on a penetration spectral curve fitting solution. The optical characteristic measuring method of claim 16, further comprising the steps of: rotating the light projecting probe and the light receiving probe to a measuring angle, wherein the measuring angle is at an angle of 45° with respect to the optical axis azimuth angle or -45°; measuring one of the measured angles to normalize the spectral signal; and using the normalized spectral signal, the calculation of the phase difference distribution is based on the Cauchy dispersion fitting solution.