Optics: measuring and testing – By polarized light examination
Reexamination Certificate
2000-11-16
2003-03-25
Stafia, Michael P. (Department: 2877)
Optics: measuring and testing
By polarized light examination
Reexamination Certificate
active
06538738
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for evaluating optical modulation characteristics of a liquid crystal modulation element, a liquid crystal display device produced by applying the foregoing method, a device for evaluating optical modulation characteristics of the liquid crystal modulation element by the foregoing evaluating method, and a computer-readable storage medium storing a program for evaluating optical modulating characteristics of a liquid crystal modulation element by the foregoing evaluating method.
BACKGROUND OF THE INVENTION
A liquid crystal display (LCD) device is widely used as display device of an electronic apparatus, and the Jones matrix method is known as typical optical characteristic computing means. In this method, by expressing transmission of an electric field by light with a matrix with complex number elements in two rows and two columns (Jones matrix) and an input electric field of light with a complex vector with two rows and one column (Jones vector), and by operating the Jones matrix to the Jones vector, an electric field of the output light can be expressed and calculated in the same form of the Jones vector. This method is widely applied to optical designing of LCD elements since calculations conducted in the method are easy.
However, the foregoing designing method has two drawbacks shown below. First of all, (1) it is difficult to quickly understand a change in a polarization state with a phase difference, and (2) it is difficult to express a change in a polarization state of light in the case where a medium showing characteristics that may cause depolarization due to the scattering and the like is placed in a path of light.
The foregoing drawbacks can be solved by the Mueller matrix method that is another method of expression of polarization utilizing matrices. In this method, a polarization state is expressed with a Stokes's vector with real number elements in four rows and one column, and a change in a polarization state is expressed by a matrix with real number elements in four rows and four column (Mueller matrix). In the case where a polarized light is in a pure state (monochromatic light that does not require statistical averaging), particularly, such a polarization state can be expressed as a point on a spherical surface (Poincaré Sphere) with its radius being proportional to an intensity of the light. A change in the polarization state due to transmission with a normal phase difference is expressed by rotational transform on the surface of the Poincaré sphere. By so doing, the foregoing drawback (1) can be solved, with such quickly-understood expression. Further, this method is characterized in that expression of light in a mixed state (a monochromatic light that requires statistical averaging), which means that transmission characteristics of a medium that scrambles polarization (for instance, a scatterer with a strong scattering effect) can be expressed with the Mueller matrices.
Regarding these natures about polarization, details are described in “Polarized light: production and use”, William A. Shurcliff, Harvard University Press, 1962.
Conventionally, the aforementioned Jones calculating method has been used for predicting optical characteristics of liquid crystal display elements. This process is generally as follows. First, an optical configuration of a liquid crystal element or the like is set, and optical characteristics are calculated by calculating means such as the Jones matrix method, etc., then, the designer adjusts the optical configuration, considering the result of calculation and other design factors. Further, expressing design factors predicted by the designer beforehand as design parameters and adopting values of design parameters that optimize final characteristics is generally conducted. A reflection-type single-polarizing-plate LCD device in which a single polarizing plate is provided on the observer's side and a reflection plate is provided on the liquid crystal layer side, in particular, is disclosed in the Japanese Publication for Laid-Open Patent Application No. 236523/1990 (Tokukaihei 2-236523 [Date of Publication: Sep. 19, 1990]) (Japanese Patent No. 2616014) and the Japanese Publication for Laid-Open Patent Application No. 167708/1994 (Tokukaihei 6-167708 [Date of Publication: Jun. 14, 1994]).
According to conventional optical designs of liquid crystal modulation elements to which the foregoing designing method was applied, designing was conducted through the following flow. First, design parameters including characteristics and configurations of respective optical factors such as optical elements involved in display (polarizing elements such as a polarizing plate, a phase difference plate, a liquid crystal layer), control factors (voltages, etc.) for a liquid crystal layer, etc. are set to specific values intended by the designer. Then, transmittance (or reflectance) of light passing through the entirety of the optical element is calculated by means of Jones matrices or the like, and the result is judged by the designer. In the case where it is judged as inadequate, values of the design parameters are changed.
By the foregoing conventional designing method, however, even in the case where optimal solutions are obtained by correct calculations based on the optical principles in design parameter ranges assumed by the designer, a possibility that further better solution might be obtained in design parameter ranges outside the foregoing range cannot be denied. It follows that it is impossible to surely find the truly optimal setting.
Actually, as to the reflection-type signal-polarizing-plate liquid crystal display device disclosed, a range of the types of optical elements and a range of configurations thereof that the designer supposes are narrow.
More specifically, though calculations of polarization states are appropriately carried out in the foregoing Tokukaihei 2-236523, a guideline for designing a liquid crystal layer in cases including the case where a phase difference plate is used is not taught. Further, obtained in the publication is only an optimal solution in the case of an extremely restricted arrangement in which alignment (director) when a transmission axis (absorption axis) of a polarizing plate is parallel or orthogonal with respect to an alignment orientation of liquid crystal in an area of contact with a polarizing-plate-side substrate. Further, an optimal setting found in result is, in the case of liquid crystal alignment with twist, a setting in which the twist is 63° and a product &Dgr;nd of a thickness of a liquid crystal layer (d) and a refraction index difference (&Dgr;n) is 193 nm. Further, a case where circularly polarized light enters the liquid crystal layer is taken as an example in the disclosure of the foregoing publication, and the foregoing setting is regarded as optimal in this case as well.
Incidentally, in the disclosure of the foregoing publication, a liquid crystal alignment is limited to the following specific case: among the two types of liquid crystal alignment applied for bright display and for dark display, respectively, one is horizontal alignment with uniform twist, while the other is completely vertical alignment. This means that a combination of voltages applied to the liquid crystal layer is limited to the ideal of 0V and an infinite voltage, and this is far different from voltages actually applied to a liquid crystal modulation element.
Further, in the foregoing Tokukaihei 6-167708, the type and position of provision of the phase difference plate is restricted, and cases where a different type of a phase difference plate is used or cases where the phase difference plate is disposed at a different position are not considered. Moreover, though the device is appropriately designed by considering liquid crystal alignment under actual voltage application, the liquid crystal alignment is limited to alignment without twist, and other general alignment of liquid crystal is not considered.
To execute optimiz
Birch & Stewart Kolasch & Birch, LLP
Sharp Kabushiki Kaisha
Stafia Michael P.
LandOfFree
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