Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-03-28
2003-09-23
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S005000, C349S117000
Reexamination Certificate
active
06624862
ABSTRACT:
This application is based on applications No. H11-086204 filed in Japan on Mar. 29, 1999 and No.11-133782 filed in Japan on May 14, 1999, the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display optical apparatus using a display panel, and a projector display apparatus using the display apparatus.
2. Description of the Prior Art
Conventionally, as a reflective liquid crystal display device used as a display panel, TN (twisted nematic) liquid crystal, homogeneous liquid crystal and DAP (deformation of aligned phases) liquid crystal have been used. These all perform light modulation by use of the birefringent property of liquid crystal. Of these, the TN liquid crystal has a structure in which the liquid crystal molecules are aligned, from the obverse surface to the rear surface of the display panel, horizontally to the surface of the display panel so as to be twisted at a predetermined angle. To cause the TN liquid crystal to act as a reflective display, the above-mentioned birefringent property is used. While the optical rotatory power is used when the TN liquid crystal is used as a transmissive display device, the present invention is not directed thereto.
The birefringent property is a property to cause a phase difference in the incident light by a polarization plane to thereby modulate the polarization condition. In the TN liquid crystal, at each pixel of the liquid crystal, when no voltage is applied, because of the horizontal alignment, a birefringent effect acts on the incident light to cause the modulation, and when a voltage is applied, the liquid crystal molecules are aligned in a direction vertical to the surface of the display panel, so that no birefringent effect acts on the incident light, particularly on the light vertically incident on the surface and consequently, no modulation is caused.
The homogeneous liquid crystal has a structure in which the liquid crystal molecules are aligned horizontally to the surface of the display panel in a predetermined direction. Like the above-described TN liquid crystal, when no voltage is applied, because of the horizontal alignment, a birefringent effect acts on the incident light to cause the modulation, and when a voltage is applied, the liquid crystal molecules are aligned in a direction vertical to the surface of the display panel, so that no birefringent effect acts on the light vertically incident on the surface and consequently, no modulation is caused.
The DAP liquid crystal has a structure in which the liquid crystal molecules are aligned vertically to the surface of the display panel conversely to the homogeneous liquid crystal. When no voltage is applied, because of the vertical alignment, no birefringent effect acts on the light vertically incident on the surface, so that no modulation is caused. When a voltage is applied, the liquid crystal molecules are aligned in a direction horizontal to the surface of the display panel, so that the birefringent effect acts on the incident light to cause the modulation.
In all of these types of liquid crystal, the display of each pixel is turned on and off according to whether the birefringent effect acts on the incident light or not. That is, when the birefringent effect acts on incident light of a specific polarization condition, the incident light is reflected under a condition where it is modulated to a different polarization condition, and when no birefringent effect acts as incident light, the incident light is reflected under a condition where it is not modulated. To obtain a high-contrast image with a display optical apparatus employing a display panel using such a reflective liquid crystal display device particularly when a projector display apparatus is structured, what is important is the level of black display that is, how completely black is displayed, in other words, how much light can be intercepted at the black portion of the displayed image.
Examples of liquid crystals other than the above-described types include ferroelectric liquid crystal (FLC). In this liquid crystal, unlike the above-described types of liquid crystals, the birefringent effect always acts on the incident light, and the modulation is caused by changing the axial direction of birefringence. Compared to the above-described types of liquid crystals, the ferroelectric liquid crystal has characteristics such as a wide viewing angle, memory capability and fast response.
FIG. 15
schematically shows the ferroelectric liquid crystal viewed from the front side of the panel.
Assume that, is shown in &agr; of the figure, the direction of alignment of the liquid crystal molecules m viewed from a direction toward the surface of the display panel p, that is, viewed from the front side is inclined leftward by &thgr; with respect to the broken line
1
representing the reference direction of the figure, for example, when there is no electric field. When an electric field is applied under this condition, as shown in &bgr; of the figure, the direction of alignment of the liquid crystal molecules m is inclined rightward by &thgr; with respect to the broken line
1
. In the ferroelectric liquid crystal, the modulation is caused by changing the axial direction of birefringence between these two conditions. Antiferroelectric liquid crystal exhibits substantially similar characteristics optically.
An example of the conventional display optical apparatus is one in which a polarizing plate is disposed immediately in front of a display panel. In this apparatus, when incident light having a specific polarization axis and having passed through the polarizing plate is modulated by the display panel, the incident light is reflected with its polarization axis being rotated 90 degrees and returns to the polarization plate. At the polarizing plate, the incident light is intercepted, thereby providing black display. When the incident light is not modulated by the display panel, the incident light is reflected with its polarization axis being as it is and passes through the polarization plate, thereby providing white display or, in the case of the so-called multi-panel type, display of the color of the display panel.
Another conventional example is one in which a PBS(polarization beam splitter) is disposed immediately in front of a display panel. In this apparatus, of the illuminating light illuminating the display panel, for example, only s-polarized light is reflected at the PBS and the reflected s-polarized light is made incident on the display panel. When the s-polarized light is not modulated at the display panel, it is reflected as it is and returns to the PBS. At this time, the s-polarized light is not transmitted by the PBS (but is reflected toward the side of the illuminating light from which it originates), thereby providing black display. When the incident light is modulated by the display panel, it is converted into p-polarized light and reflected, and the p-polarized light is transmitted by the PBS, thereby providing white display or, in the case of the so-called multi-panel type, display of the color of the display panel. Such modulation is generally called cross nicol modulation.
Yet another conventional example is one in which a quarter-wave plate having an axis of phase retardation or an axis of phase advancement forming an angle of 45 degrees with respect to the axis of polarization of a polarizing plate disposed immediately in front of a display panel is disposed between the display panel and the polarizing plate. In this apparatus, when incident light having a specific polarization axis and having passed through the polarizing plate is not modulated by the display panel, the incident light passes through the quarter-wave plate twice in opposite directions to undergo the working of a half-wave plate, so that the polarization axis rotates 90 degrees. Then, the incident light returns to the polarizing plate and is intercepted at the polarizing plate, thereby providing black display.
When the incident l
Hayashi Kohtaro
Kobayashi Nobuyuki
Konno Kenji
Nagata Hideki
Nishiguchi Kenji
Minolta Co. , Ltd.
Parker Kenneth
Sidley Austin Brown & Wood LLP
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