Optics: measuring and testing – Material strain analysis – With polarized light
Reexamination Certificate
1998-12-03
2001-04-10
Rosenberger, Richard A. (Department: 2877)
Optics: measuring and testing
Material strain analysis
With polarized light
C356S445000, C356S369000
Reexamination Certificate
active
06215549
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an apparatus of measuring the optical characteristics of the boundary area of a given medium to be inspected.
2. Related Background Art
The following conventional methods are known, which measure various optical characteristics by using total internal reflection of light.
(1) TIR Method (a total internal reflection method, J. Z, Xue, N. A. Clark, and M. R. Meadows, Appl. Phys. Lett. 53, p. 2397 (1988)).
(2) Calibration Curve Method (JP-A-6-82239)
As an example of an optical-characteristic measuring apparatus that utilizes each of the above methods, an optical anisotropy measuring apparatus for measuring a pre-tilt angle of liquid crystal will be described.
(1)-1 Optical anisotropy measuring apparatus utilizing the TIR method (Prior Art 1)
FIG. 1
is a schematic diagram showing an example of the structure of an optical anisotropy measuring apparatus utilizing the TIR method and illustrating an optical anisotropy measuring method. This optical anisotropy measuring apparatus
1
has a glass member of a semispherical shape (hereinafter called a “semispherical glass”). As shown in detail in
FIG. 2
, this semispherical glass
2
has a flat part
2
a
and a spherical part
2
b
. A glass substrate
3
is disposed facing the flat part
2
a
. On the surfaces of the glass substrate
3
and flat part
2
a
, transparent electrodes
5
and orientation films
6
are formed. The glass substrate
3
and flat part
2
a
are bonded together by a sealing member
7
. Liquid crystal
9
as a medium to be inspected is filled in a space between the glass substrate
3
and flat part
2
a.
The semispherical glass
2
is supported by an unrepresented rotation mechanism to rotate the spherical glass
2
about a rotary axis C normal to the flat part
2
a
. The refractive index of the semispherical glass
2
is set larger than that of the polarization film
6
and liquid crystals
9
. The film thickness of the orientation film
6
is made smaller than the wavelength of an applied light beam A
1
(the details will be given later).
An He—Ne laser source
10
is disposed on one side (lower left in
FIG. 1
) of the semispherical glass
2
and applies the light beam A
1
to the semispherical glass
2
along a downward oblique direction relative to the flat part
2
a
(the light beam A
1
applied to the liquid crystal
9
from the He—Ne laser source
10
is called hereinafter an “incidence light beam A
1
”). A photodetector
11
is disposed on the other side (lower right in
FIG. 1
) of the semispherical glass
2
and detects a light beam B
1
totally reflected from the interface to the liquid crystal
9
(the light beam B
1
totally reflected is hereinafter called a “reflection light beam B
1
”).
A polarizer
12
is disposed between the semispherical glass
2
and He-Ne laser source
10
and linearly polarizes the incidence light beam A
1
from the He-Ne laser source
10
. An analyzer
13
is disposed between the semispherical glass
2
and photodetector
11
and has a polarization direction perpendicular to the polarizer
12
.
Next, an optical anisotropy measuring method (a pre-tilt angle measuring method) using the above-described optical anisotropy measuring apparatus will be described.
The incidence light beam A
1
output from the He—Ne laser source
10
is linearly polarized by the polarizer
12
into p-polarization relative to the incidence plane of total internal reflection, and applied to the semispherical glass
2
. This incidence light beam A
1
is totally reflected by an interface between the transparent electrode
5
and orientation film
6
. Evanescent light, generated when the total reflection occurs, enters once the liquid crystal and then is reflected. This evanescent light changes its polarization state in accordance with the optical anisotropy of liquid crystal near at the interface to the orientation film
6
.
Of the reflection light beam B
1
output from the semispherical glass
2
, only the components (s-polarization components) having a polarization direction perpendicular to the polarizer
12
pass through the analyzer
11
.
As the semispherical glass
2
together with the glass substrate
3
and the like is rotated about the rotary axis C, the direction of a director, which is a unit vector representative of the direction of a liquid crystal molecule of the liquid crystal
9
, changes with the direction of an electric field of the incidence light beam A
1
. Therefore, the polarization state of the reflection light beam B
1
output from the semispherical glass
2
changes with the rotational angle of the semispherical glass
2
. By plotting an output of the photodetector
11
relative to the rotational angle of the semispherical glass
2
, a characteristic curve representative of the optical anisotropy of the liquid crystal, such as shown in
FIG. 3
, can be obtained. The pre-tilt angle can be calculated from a ratio of Imax/Imin, where Imax is a maximum extreme intensity and Imin is a minimum extreme intensity. The larger the pre-tilt angle, the smaller the ratio of Imax/Imin becomes, whereas the smaller the pre-tilt angle, the larger the ratio of Imax/Imin becomes.
With the optical anisotropy measuring apparatus
1
described above, the optical anisotropy or pre-tilt angle of the liquid crystal
9
is calculated in accordance with a change in the polarization state of the reflection light beam B
1
to be caused by the interaction between the liquid crystal molecules and the evanescent light generated when the total reflection occurs.
The measurement area (an ellipsoid having a minor axis of about 0.6 mm and a major axis of about 3 mm) of the optical anisotropy measuring apparatus
1
is larger than the size (a square of 30 to 50 &mgr;m) of one pixel of a liquid crystal device used with a display or the like. Therefore, the orientation state of each unit pixel cannot be measured so that the orientation states of pixels cannot be compared. It is also difficult to detect a variation in orientation directions of one pixel. It is also impossible to detect a fine defect smaller than, for example, 8 &mgr;m and it is difficult to compare the orientation state of a defect area with that of another area. From the above reasons, the orientation state of the liquid crystal
9
cannot be detected correctly and it is difficult to elucidate the mechanism of defect formation.
(1)-2 Optical anisotropy measuring apparatus utilizing the TIR method (Prior Art 2).
To solve the above problems, an apparatus
20
shown in
FIG. 4
has been proposed (JP-A-9-105704) which has an input side optical system
31
disposed between an He—Ne laser source
10
and a semispherical glass
2
to converge an incidence light beam A
1
and make the measurement area small (a major axis of about 10 to 30 &mgr;m). In
FIG. 4
, reference numeral
22
represents a liquid crystal device, and reference symbol A
2
represents an incidence light beam converged by the input side optical system
31
. The major axis of the measurement area of this apparatus
20
is about 8 &mgr;m.
(1)-3 An optical anisotropy measuring apparatus utilizing the TIR method (Prior Art 3).
In the Prior Art 1, the orientation film
6
is formed directly on the side of the semispherical glass
2
. However, it is very difficult to form good medium samples by subjecting the orientation film
6
to a rubbing process.
To form a good medium, an apparatus has been proposed (JP-A-9-105704) that uses a discrete liquid crystal device and a discrete semispherical glass
2
. With this apparatus, since the liquid crystal device is movable relative to the semispherical glass
2
, a variation of pre-tilt angles can be measured (refer to Technical Digest, the Fifth Microoptics Conference (MOC' 95 Hiroshima), G10, p. 144, by Y. Ohsaki and T. Suzuki).
(1)-4 An optical anisotropy measuring apparatus utilizing the TIR method (Prior Art 4).
The major axis of the measurement area of Prior Art 2 is about 8 &mgr;m. An optical anisotropy measuring apparatus
30
, such as shown in
F
Ohsaki Yoshinori
Suzuki Takashi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Rosenberger Richard A.
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