JPH063269A - Method for measuring phase difference - Google Patents

Abstract

PURPOSE:To calculate the phase difference of a transparent film by emitting a laser beam to the transparent film to be measured formed on the reflecting surface of a base through a polarizer, a modulator, and a first optical element, reflecting the reflected light emitted from the transparent film in different right-angled directions by first and second optical elements, respectively, and detecting the light through an analyzer by a light detector. CONSTITUTION:A transparent film 20 to be measured is formed on the reflecting surface 21a of a base 21. The output light of a laser 11 is emitted to the transparent film 20 through a polarizer, a photoelastic modulator 13, and a first half mirror prism 14. This light is reflected by the reflecting surface 21a, advanced in an optical path A1, and reflected to a right-angled optical path A2 by the reflecting surface 14b of the prism 14. This light is collided with the reflecting surface 15b of a second half mirror prism 15, and reflected in the direction right-angled to the optical paths A1, A2. Thereafter, the light is emitted to a light detector 17 through an analyzer 16. The intensity of the light passed through the analyzer 16 is measured by the light detector 17, the measurement value of the detector 17 is processed by an arithmetic device, and the phase difference of the transparent film 20 can be highly precisely measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retardation measuring method for measuring retardation of a transparent film having optical anisotropy.

[0002]

2. Description of the Related Art Generally, a laser is generally used to measure a phase difference (a phase difference between ordinary light and extraordinary light) of a transparent film having optical anisotropy such as an alignment film formed on a substrate surface of a liquid crystal display device. It depends on the method used.

The measurement of the phase difference by this laser is conventionally performed
As shown in FIG. 4A, the transparent film 10 to be measured is formed on the upper surface of the transparent glass substrate 11, and the light from the laser 1 is passed through the transparent film 10 via the polarizer 2 and the photoelastic modulator 3. Light which is transmitted through the transparent film 10 and is emitted to the lower surface side of the glass substrate 11 is detected by the photodetector 5 through the analyzer 4, and the transparent film is detected based on the change in the intensity of the detected light. The phase difference of 10 is calculated.

FIG. 4B shows the transmission axis 2a of the polarizer 2,
Refractive index vibration direction 3a of photoelastic modulator 3, transparent film 1 to be measured
A fast axis 10a of 0 and a transmission axis 4a of the analyzer 4 are shown. The photoelastic modulator 3 vibrates in the direction of the refractive index 3a at a cycle of ω. Therefore, the refractive index phase difference of the photoelastic modulator 3 is expressed as δ sin ωt. Where δ
Is δ such that J0 (δ) = 0. J0 (x) is a zero-order Bessel function. In such a case, the light intensity I detected by the photodetector 5 is: I = 1/2 + J1 (δ) sinΔ sinωt Δ; Refractive index phase difference J1 (x) of the transparent film 10 to be measured; function

And the lock-in amplifier causes sinωt
The coefficient Iω = J1 (δ) sinΔ of can be derived, and the phase difference of the transparent film to be measured 10 can be calculated from this by the following formula [1].

[0006]

[Equation 1]

[0007]

However, in such a conventional phase difference measuring method, the light detected by the photodetector 5 is the transparent film 10 to be measured and the substrate 11 on which the transparent film 10 is formed. Since the light is transmitted through both of them, there is a problem that the phase difference of the transparent film 10 cannot be accurately measured.

This is because the glass substrate 11 on which the transparent film 10 is formed also has optical anisotropy. Therefore, the measured phase difference shows the phase difference between both the transparent film 10 and the glass substrate 11. It will be the combined value.

Further, in the conventional phase difference measuring method, when the transparent film to be measured 10 is a transparent film having a small film thickness and a small phase difference such as an alignment film made of a monomolecular film, the intensity of the detection light is very small. Since it changes only slightly, there is also a problem that it is difficult to measure the retardation of a transparent film having a small retardation like the above-mentioned monomolecular film.

The present invention has been made paying attention to such a point, and an object thereof is to make it possible to measure a phase difference of a transparent film to be measured with high accuracy and to obtain a transparent film having a small phase difference. An object of the present invention is to provide a phase difference measuring method capable of measuring even the phase difference of.

[0011]

In order to achieve such an object, the present invention forms a transparent film to be measured on a reflecting surface of a substrate made of a reflecting plate and modulates light from a laser with a polarizer and photoelastic modulation. The light which is incident on the transparent film through the container and the first optical element, is transmitted through the transparent film, is reflected by the reflecting surface of the substrate, and is emitted again through the transparent film.
Light is reflected at a right angle on the reflection surface of the optical element, the reflected light is incident on the reflection surface of the second optical element, and the incident light is reflected from the reflection surface of the second optical element to the first optical element. An optical path incident on the reflecting surface of the element and a light path emitted from the reflecting surface are reflected in a direction perpendicular to the surface, and the reflected light is detected by a photodetector via an analyzer. It is characterized in that the phase difference of the transparent film is calculated based on the change in the intensity of light detected by the detector.

[0012]

According to such a phase difference measuring method, the light incident on the transparent film to be measured does not pass through the substrate but only through the transparent film. Therefore, the light is detected by the photodetector via the analyzer. The light detected is only the light that has passed through the transparent film, and therefore the phase difference calculated based on the change in the intensity of the detected light is the phase difference of only the transparent film that does not include the phase difference of the substrate.

Further, in this phase difference measuring method, the light incident on the transparent film is transmitted through the transparent film, reflected by the reflecting surface of the substrate, and again emitted through the transparent film. The detected light is light that has been transmitted through the transparent film twice, and therefore the intensity of the detected light changes at a rate of twice the phase difference of the transparent film. Therefore, the phase difference of the transparent film having a small phase difference is measured. Will also be possible.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows the construction of an apparatus for measuring the phase difference. This apparatus comprises a laser 11, a polarizer 12, a photoelastic modulator 13, first and second half mirror prisms 14 as optical elements, 15, an analyzer 16, and a photodetector 17.

Although not shown, a laser oscillator for driving the laser 11 is connected to the laser 11, and the photoelastic modulator 1 is connected.
3 is connected to a photoelastic modulation oscillator for driving it,
Further, the photodetector 17 is connected to an arithmetic unit that calculates the phase difference of the transmitted light based on the change in the intensity of the detected light.

Reference numeral 20 shown in FIG. 1 is a transparent film to be measured, and this transparent film 20 is formed on a substrate 21.
The substrate 21 is a reflecting plate made of an aluminum plate having a mirror-finished surface or a glass plate having a reflecting film such as an aluminum film deposited on the surface. The transparent film 20 is formed on the reflecting surface 21 a of the substrate 21. There is.

The transparent film 20 to be measured is, for example, an alignment film, and this alignment film is formed by depositing a monomolecular film in which single molecules are arranged in one direction by the LB method on the substrate 21, or Apply an alignment material such as polyimide on top,
The film surface is formed by rubbing. The optical axis of this alignment film is the alignment direction thereof, that is, the alignment direction of the single molecules in the monomolecular film and the rubbing direction in the rubbing-treated film.

The polarizer 12, the photoelastic modulator 13 and the substrate 21 are arranged at right angles to the optical axis a of the light output from the laser 11. Then, the photoelastic modulator 13 and the substrate 2
The first half mirror prism 14 is located between 1 and
The first half-mirror prism 14 has a light incident surface 1
4a is arranged at a right angle to the optical axis a, and a light reflecting surface 1
4b is provided so as to be inclined at an angle of 45 ° with respect to the optical axis a.

The second half mirror prism 15 is
The first half mirror prism 1 is provided on the side facing the reflecting surface 14b of the first half mirror prism 14.
The light reflected by the fourth reflecting surface 14b is arranged so as to enter the light reflecting surface 15b of the second half mirror prism 15.

The light incident on the reflecting surface 15b of the second half-mirror prism 15 is incident on the reflecting surface 14b of the first half-mirror prism 14, and the light path A1 of the light is the first half-mirror prism. 14 reflective surface 14b
The reflection surface 1 of the second half mirror prism 15
The reflecting surface 15b faces in a direction perpendicular to the plane containing the optical path A2 of the light incident on 5b. The phase difference of the measured transparent film 20 is measured as follows. First, the output light from the laser 11 is applied to the polarizer 12, the photoelastic modulator 13, and the incident surface 14a of the first half prism 14.
Through the transparent film 20.

The light incident on the transparent film 20 strikes the reflecting surface 21a of the substrate 21 perpendicularly and is reflected in the same optical path A1 as the incident light, and the reflected light strikes the reflecting surface 14b of the first half mirror prism 14 to form a right angle. Reflected by the optical path A2 of the second half mirror prism 15
Head towards.

Then, this light strikes the reflecting surface 15b of the second half mirror prism 15 and is reflected by this reflecting surface 15b. The direction of this reflection is the optical path A1 from the substrate 21 to the reflecting surface 14b of the first half mirror prism 14,
The direction is at right angles to the plane including the optical path A2 from the reflecting surface 14b of the first half mirror prism 14 to the reflecting surface 15b of the second half mirror prism 15.

The light reflected by the reflecting surface 15b of the second half mirror prism 15 passes through the analyzer 16 and enters the photodetector 17, and the intensity of the light passing through the analyzer 16 is determined by the photodetector 17. It is measured and the value is calculated via a computing device.

Here, the first half mirror prism 14
It is conceivable that the light reflected by the reflecting surface 14b of the above is directly incident on the analyzer 16 and the intensity of the light is measured by the photodetector 17.

In this case, however, the polarization state changes when the light is reflected by the reflecting surface 14b of the first half mirror prism 14 and the light bends at a right angle. The state of the reflection is shown in FIG. 3, and in the light incident on the reflecting surface 14b of the half mirror prism 14, the intensity of the component 1a vibrating at right angles to the paper surface of the figure is AH, and the intensity of the component 1b vibrating in parallel is Intensity is AL, in the light reflected at the reflecting surface 14b of the half mirror prism 14 and bent at a right angle, the intensity of the component 2a that vibrates at a right angle to the paper surface of the drawing is BH, and the intensity of the component 2b that vibrates in a parallel direction is BL. Then, AH = BH AL = γBL γ; the reflection coefficient of the component that oscillates parallel to the paper surface, and the polarization ratio before and after reflection differs as shown in the following [Equation 2].

[0027]

[Equation 2] This makes accurate measurement impossible.

Therefore, in the present invention, the light reflected by the reflecting surface 14b of the first half mirror prism 14 is reflected by the reflecting surface 15b of the second half mirror prism 15.
To the reflecting surface 15b of the first half-mirror prism 14 and the optical path A1
And a light path A2 from the reflection surface 14b of the first half mirror prism 14 to the reflection surface 15b of the second half mirror prism 15 from the reflection surface 14b of the first half mirror prism 14 to the reflection surface 15b of the second half mirror prism 15. Reflected in the direction,
This light is made incident on the photodetector 17 through the analyzer 16,
The photodetector 17 measures the intensity of the light passing through the analyzer 16.

As in the conventional case, the photoelastic modulator 13 oscillates in the direction of constant refractive index with a cycle of ω. Therefore, the refractive index phase difference of the photoelastic modulator 3 is expressed as δ sin ωt. Here, δ is δ such that J0 (δ) = 0.
J0 (x) is a zero-order Bessel function. In such a case, the light intensity I detected by the photodetector 17 is

The equation of [Equation 4], which is the coefficient of sin ωt, can be derived from the equation of [Equation 3], which is obtained by the equation of [Equation 3]. A phase difference of 20 can be calculated.

[0031]

[Equation 3]

[0032]

[Equation 4]

[0033]

[Equation 5]

In this case, as shown in FIG. 2, the reflecting surface 14a of the first half mirror prism 14 is shown.
Of the component 1a that vibrates in the x-axis direction and has the intensity of A1 and the component 1b that vibrates in the y-axis direction.
Is B1, the intensity of component 2a that vibrates in the x-axis direction is A2, and the intensity of component 2b that vibrates in the z-axis direction is light that is reflected by the reflecting surface 14b of the first half mirror prism 14 and travels along the optical path L2. Is B2, the intensity of the component 12b that vibrates in the y-axis direction is A3, and the intensity of the component 12b that vibrates in the z-axis direction is B3, which is the light reflected on the reflecting surface 15b of the second half mirror prism 15 and traveling along the optical path L3. Then, A1 = A2 = γA3 B1 = γB2 = γB3, and therefore the polarization ratio until the reflected light from the transparent film 20 to be measured reaches the analyzer 16 is (A1 / B1) = (A3 / B3). Therefore, there is no change in the polarization ratio, and accurate measurement can be performed.

In the measurement of such a phase difference, the light incident on the transparent film 20 to be measured is transferred to the transparent film 20.
But not through the substrate 21, and the light detected by the photodetector 17 through the analyzer 16 is only the light that has passed through the transparent film 20. The phase difference calculated based on the change in intensity is
The phase difference of only the transparent film 20 does not include the phase difference of 1. Therefore, the phase difference of the transparent film 20 can be measured with high accuracy.

In this phase difference measuring method, light incident on the transparent film 20 passes through the transparent film 20, is reflected by the reflecting surface 21a of the substrate 21, and is again transparent film 20.
Therefore, the light detected by the photodetector 17 becomes light that has passed through the transparent film 20 twice, and thus the intensity of the detected light changes at a rate of twice the phase difference of the transparent film 20. However, for this reason, even if the transparent film 20 having a small phase difference, such as an alignment film made of a monomolecular film, the phase difference can be measured.

However, in this phase difference measuring method, the transparent film 2
Since the light detector 17 detects light that has transmitted 0 twice, the value of the phase difference calculated based on the change in the intensity of the detected light is twice the phase difference of the transparent film 20. Value 1
/ 2 is the true phase difference of the transparent film 20.

Although the first and second optical elements are half mirror prisms in the above embodiment, for example, the first optical element is a normal prism and the second optical element is a normal plane mirror. It is also possible to do so. Further, the phase difference measuring method of the present invention is not limited to the alignment film,
It can be applied to the measurement of retardation of various transparent films having optical anisotropy.

[0039]

As described above, according to the present invention, the transparent film to be measured is formed on the reflecting surface of the substrate composed of the reflecting plate, and the light from the laser is applied to the polarizer, the photoelastic modulator and the first optical element. The light incident on the transparent film through the element, transmitted through the transparent film, reflected by the reflective surface of the substrate, and emitted again through the transparent film is reflected by the reflective surface of the first optical element. The light is reflected at a right angle, the reflected light is incident on the reflection surface of the second optical element, and the incident light is incident on the reflection surface of the first optical element from the reflection surface of the second optical element. The reflected light is reflected in a direction at a right angle to the surface including the optical path and the optical path emitted from the reflecting surface, the reflected light is detected by a photodetector through an analyzer, and the light detected by the detector is detected. Since the phase difference of the transparent film is calculated based on the change in intensity, It can measure the phase difference film with high precision, yet can be advantageously be a small transparent film having a phase difference measuring the phase difference.

[Brief description of drawings]

FIG. 1 is a diagram showing a phase difference measuring method according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the action of light reflected by a first half mirror prism and a second half mirror prism in the phase difference measuring method.

FIG. 3 is a diagram for explaining an action of light reflected by a first half mirror prism in the phase difference measuring method.

FIG. 4 is a diagram showing a conventional phase difference measuring method.

[Explanation of symbols]

 11 ... Laser 12 ... Polarizer 13 ... Photoelastic modulator 14 ... First half-mirror prism 15 ... Second half-mirror prism 16 ... Analyzer 17 ... Photodetector 20 ... Transparent film 21 ... Substrate

Claims (1)

[Claims] 1. A method for measuring a phase difference of a transparent film having optical anisotropy, wherein a transparent film to be measured is formed on a reflecting surface of a substrate composed of a reflecting plate,
The light from the laser is made incident on the transparent film through the polarizer, the photoelastic modulator, and the first optical element, and the light is transmitted through the transparent film and reflected by the reflection surface of the substrate to make the transparent film again. The light emitted via the first optical element is reflected at a right angle on the reflection surface of the first optical element, the reflected light is incident on the reflection surface of the second optical element, and the incident light is incident on the second optical element. From the reflection surface of the first optical element, the light is incident on the reflection surface of the first optical element and is reflected in a direction at a right angle to the surface including the light path emitted from the reflection surface, and the reflected light is analyzed by an analyzer. A phase difference measuring method, characterized in that the phase difference of the transparent film is calculated based on a change in the intensity of light detected by the photodetector through the photodetector.