Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
1999-08-10
2001-06-05
Malinowski, Walter J. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S005000
Reexamination Certificate
active
06243148
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a directly-visible transmissive type or projector type of liquid crystal display device.
2. Description of Related Art
A directly-visible transmissive type or projector type of liquid crystal display device is provided with a halogen lamp or the like as a light source. A lamp of this type is inferior from the utilization efficiency point of view, in that it generates a large amount of heat and it also emits a great deal of light outside the visible range. This utilization efficiency is degraded even further if the light is passed through a color filter to form a color display.
An image display device that uses laser beams of three colors (red, green, and blue) as a light source is disclosed in Japanese Patent Laying-Open No. 4-263244. Since a laser beam is colored light of a specific wavelength, the utilization efficiency is higher than that of a prior-art lamp.
However, the efficiency with which the light is utilized is also affected by the aperture ratio of the liquid crystal panel. In other words, not all of the light from the light source passes through the liquid crystal panel; some of it is blocked by dead areas such as the black matrix, signal lines, and transistors. To improve the ratio of light that passes through, it is necessary to reduce the size of dead areas, or increase the aperture ratio. However, since it is impossible to remove such dead areas, there is a limit to improvements in aperture ratio.
SUMMARY OF THE INVENTION
The invention was devised to solve the above described technical problems. An objective thereof is to provide a liquid crystal display device in which the ratio of light that passes therethrough is increased, thus increasing the efficiency with which the light is utilized.
The liquid crystal display device of the invention has a light source and comprises a two-dimensional light-emitting element array plate formed of a plurality of light-emitting elements arranged in a plane array, and a liquid crystal panel having a plurality of pixels. Each of the pixels corresponds to each of the light-emitting elements. A light-projecting portion of each of the light-emitting elements is disposed with n a light-transmitting region of the corresponding pixel.
In this aspect of the invention, a light-projecting portion that acts as a point light source is disposed within a light-transmitting region of the corresponding pixel, so that virtually no light is blocked, in comparison with a prior-art plane light source.
The light-emitting element could be a light-emitting diode, a semiconductor laser, or the like. Each of these components generates less heat than a prior-art halogen lamp or the like, and can also be limited to a specific wavelength, so that the utilization efficiency thereof is higher.
In particular, if a semiconductor laser is used as each light-emitting element, the polarization plane of the emitted light is aligned, making it possible to omit the conventional polarizer from the side of the liquid crystal panel on which light is incident.
The liquid crystal display device preferably comprises at least three pairs of the two-dimensional light-emitting element array plates and the liquid crystal panels. It is also preferable that an optical system combines light from all of the two-dimensional light-emitting element array plates. Light of different wavelengths is emitted from each of the two-dimensional light-emitting element array plates.
With the invention, at least three pairs of two-dimensional light-emitting element array plates and liquid crystal panels are used, and the light therefrom is combined to create a color display.
With the invention, it is preferable that each of the light-emitting elements is a semiconductor light-emitting element comprising at least three layers of light-emitting portions and four layers of reflective mirrors disposed in the depthwise direction. The first, second, and third light-emitting portions emit light of first, second, and third different wavelengths respectively that satisfy the relationships: first wavelength<second wavelength<third wavelength. The first reflective mirror, the first light-emitting portion, the second reflective mirror, the second light-emitting portion, the third reflective mirror, the third light-emitting portion, and the fourth reflective mirror form a multi-layer structure, in that sequence. The first reflective mirror has a reflectivity that is less than that of the fourth reflective mirror, to form the light-projecting portion. The second reflective mirror reflects light of the first wavelength but passes light of the second and third wavelengths. The third reflective mirror reflects light of the second wavelength but passes light of the third wavelength. The fourth reflective mirror reflects light of the third wavelength.
With this aspect of the invention, the first light-emitting portion is disposed between the first and second reflective mirrors. In this case, the second reflective mirror reflects light of the first wavelength, so that the light of the first wavelength oscillates between the first and second reflective mirrors and is thus amplified.
In a similar manner, the second light-emitting portion is disposed between the first and third reflective mirrors. In this case, the second reflective mirror passes light of the second wavelength and the third reflective mirror reflects light of the second wavelength. Therefore, light of the second wavelength oscillates between the first and third reflective mirrors and is thus amplified.
Furthermore, the third light-emitting portion is disposed between the first and fourth reflective mirrors. In this case, the second and third reflective mirrors pass light of the third wavelength and the fourth reflective mirror reflects light of the third wavelength. Therefore, light of the third wavelength oscillates between the first and fourth reflective mirrors and is thus amplified.
In this manner, each of three layers of light-emitting portions is interposed between a pair of reflective mirrors. Light of different wavelengths from each of the light-emitting portions can thus be emitted from a single light-projecting portion.
In addition, the following relationship are satisfied: first wavelength<second wavelength<third wavelength. The reason therefor is discussed below. Light of a short wavelength has a high energy level, whereas light of a long wavelength has a low energy level. The energy gap defined when a semiconductor emits light of a short wavelength is wider than that defined when a semiconductor emits light of a long wavelength. In addition, if the optical energy is greater than the energy gap of the semiconductor, a phenomenon in which the light is absorbed by the semiconductor occurs.
With this aspect of the invention, the first, second, and third light-emitting portions are arranged as layers in that sequence, in such a manner that the wavelength of the light emitted thereby increases sequentially as the energy gap decreases. Therefore, when light of the second wavelength passes through the first light-emitting portion, the optical energy thereof is less than the energy gap of the first light-emitting portion and thus the light is not absorbed. Similarly, when light of the third wavelength passes through the first and second light-emitting portions, the optical energy thereof is less than the energy gaps of the first and second light-emitting portions and thus the light is not absorbed.
Thus, Light from a plurality of light-emitting portions formed in the depthwise direction can all be emitted in the same direction.
This aspect of the invention makes it possible for a single pixel to display a plurality of colors. Thus the resolution of display can be greatly increased, in comparison with a liquid crystal display device in which a plurality of colors is obtained by combining a plurality of dots.
With the invention, it is also preferred that light of the first, second, and third wavelengths is emitted in a sequence at a predetermined period;
Kaneko Takeo
Nebashi Satoshi
Shimoda Tatsuya
Yokoyama Osamu
Malinowski Walter J.
Oliff & Berridg,e PLC
Seiko Epson Corporation
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