1. Field of the Invention
The present invention relates to a light modulating element array which is available as an optical exposure device and a panel display device and, more particularly, to a light modulating element array operative to modulate light traveling in a light guide by electromechanically deflecting a thin-film toward the light guide.
2. Description of the Related Art
There have been various panel display devices such as liquid crystal display devices and plasma display devices on the market. Such a liquid crystal display device has the problem that the utilization efficiency of light is low due to transmission of light from a backlight source through various optical elements including a polarizing plate, transparent electrodes and a color filter. On the other hand, because such a plasma display device needs to have an interstructure for discharge per pixel, there is the problem that it is difficult fort the plasma display device to provide a high luminance and a high efficiency when high definition is required and that the plasma display device needs a high drive voltage. This rises costs of the plasma display device.
In order to solve the problem, there have been proposed panel display devices equipped with electromechanically operated light modulating elements which modulate light from a light source for making an image display. One of such panel display devices is known from, for instance, a paper entitled xe2x80x9cWaveguide Panel Display Using Electromechanical Spatial Modulatorsxe2x80x9d published in SID International Symposium Digest of Technical Papers, 1998.
Before describing the present invention in detail, reference is made to FIGS. 14 and 15 showing the panel display device disclosed in that paper for the purpose of providing a brief background of electromechanical Light modulation that will enhance understanding of the light modulating element of the present invention.
As shown in FIG. 14, a panel display device 15 comprises a plurality of strip-shaped light guides 3 arranged in parallel to one another and a plurality of strip-shaped, electromechanically deflectable thin-films 11 arranged in parallel to one another and perpendicularly to the light guides 3. These light guides 3 and electromechanically deflectable thin-films 11 are disposed between a front transparent glass plate 1 and a rear transparent glass plate 13. The light guides are formed directly on the front transparent glass plate 1. However, each of the electromechanically deflectable thin-films 11 is partially connected to and supported by the rear transparent substrate 13 so as to be deflectable toward the light guide 3. An LED array 9 is optically coupled to the light guides 3 through a light guide member 7 equipped with micro-lenses 5. The LED array 9 comprises a straight row of a plurality of LEDs, one per light guide 3. The electromechanically deflectable thin-films 13 thus arranged are operative as optical switches.
As shown in FIG. 15, in operation of the panel display device 15, when selectively applying a drive voltage to electrodes of the electromechanically deflectable thin-films 11, the electromechanically deflectable thin-film 11 deflects and is brought close to the light guide 3 due to electrostatic force. On the other hand, the LEDs of the LED array 9 are energized with image signals in synchronisms with the application of drive voltages to the electrodes of the electromechanically deflectable thin-films 11 to emit light. The light emanating from the LED enters and travels in the light guide 3 repeating total reflection. When the light travels in the light guide 3 to a proximal contact point where the light guide 3 is contacted by the electromechanically deflectable thin-film 11, the light is reflected by a mirror 17 in the electromechanically deflectable thin-film 11 and enters the light guide 3 at a substantially right angle. As a result, the light passes though and comes out of the light guide 3 at the proximal contact point. On the other hand, when the drive voltage is removed, the electromechanically deflectable thin-film 11 is restored to its original state and provides a gap between the light guide 3 and the electromechanically deflectable thin-film 11, so that the light travels in the light guide 3 without coming out of the light guide 3 and entering the electromechanically deflectable thin-film 11.
The panel display device 15 employs the electromechanically deflectable thin-film 11 that can operate quickly responding to application of drive voltage. This makes the panel display device 15 operate with high responsiveness. Further, the panel display device 15 does not employ a number of layers through which light passes like the conventional liquid crystal display panels nor have the necessity of vacuum-sealing electrode arrays like the plasma display panels. This realizes manufacturing costs of the panel display device 15.
The conventional panel display device makes a two dimensional display by making a line display by applying drive voltage to one of the electromechanically deflectable thin-films and introducing light modulated according to image signals into the light guides in synchronism with the application of voltage to the electromechanically deflectable thin-film and shifting application of drive voltage to the electromechanically deflectable thin-films from one to another. In order for the conventional panel display device to make an animated color display in HDTV (high definition television) system which has 1080 scanning lines and a frame frequency of 60 Hz, it is essential to employ an LED array which is operative to modulate light at a high frequency less than 16 xcexcs. For this reason, it is one of drawbacks that the conventional panel display device can not employ a fluorescent lamp that is inexpensive and efficient. In addition, the conventional panel display device has the necessity to have the same number of LEDs as the light guides. Accordingly, when making a color display in HDTV system, the number of image signals is 1920 for a mono-color line display, and hence, 5760 for a color line display. This makes an image signaling circuit complex and the LED array expensive. In addition, this results in the necessity of precise positioning technique in order to optically couple the LED array to the light guides and provides a rise in manufacturing and assembling costs of the LED array and the light guides.
It is therefore an object of the present invention to provide a light modulating element array which does not need an array of light source elements nor has the necessity to modulate light at a high speed.
It is another object of the present invention to provide a light modulating element array simple in structure and unnecessary to use a precise positioning skill which results in a decrease in manufacturing and assembling costs of light source and the light guides.
It is still another object of the present invention to provide a panel display device equipped with a light modulating element array which is simple in structure and manufactured at low costs.
The foregoing objects are accomplished by providing a light modulating element array comprising a grid arrangement of stripe-shaped light guides, such as optical wave guides or light guide plates, for guiding light entering there so that the light travels in the light guide repeating total reflection at opposite interfaces of the light guide and strip-shaped electromechanically deflectable subsidiary thin-films disposed such as to face the light guides, respectively, at a specified regular distances from the interface of the respective light guides, and strip-shaped electromechanically deflectable main thin-films each of which extends in a direction in which the light travels in the light guide and is disposed such as to face the light guide before the subsidiary thin-film at a specified regular distance from the interface of the light guide. When the main thin-film is electromechanically deflected to be brought close to the interface of the light guide means, the light guide means changes a transmission rate of light traveling therein. On the other hand, when the subsidiary thin-film is electromechanically deflected to be brought into contact with the light guide means, the light traveling in the light guide means comes out of the light guide means and passes through the subsidiary thin-film at a point where the light guide means is contacted by the subsidiary thin-film. In the light modulating element array thus driven, the light that travels in the light guide means is changed in transmission rate by electromechanically deflecting the main thin-film while the light source remains turned on, so that the light traveling in the light guide means is modulated at a high speed. This avoids the necessity of modulating a light source and employment of an array of light source elements.
More specifically, the light modulating element array comprises a parallel arrangement of strip-shaped light guides and a parallel arrangement of strip-shaped electromechanically deflectable subsidiary thin-films which spatially intersect each other at a right angle and strip-shaped electromechanically deflectable main thin-films disposed such that one main thin-film spatially overlaps each light guide in front of the strip-shaped subsidiary thin-film. This arrangement of the light guides and the subsidiary thin-films provides an orthogonal matrix of light spots that are modulated by electromechanical action of the main thin-films. This avoids the necessity of providing the same number of light source elements as the light guides and controlling a large number of light source elements to independently and selectively turn on, as a result of which the driving circuit of the light modulating element array is simplified in structure In addition, this avoids the necessity of employing an array of light source elements, as a result of which there is no necessity of precisely positioning and optically coupling the parallel arrangement of light guides and the light source elements, respectively.
Each of these main thin-film, subsidiary thin-film and light guide may be provided with a transparent electrode. The electromechanical action of the main thin-film is caused by electrostatic force generated under application of a potential difference between the electrodes of the light guide and the main thin-film. Similarly, the electromechanical action of the subsidiary thin-film is caused by electrostatic force generated under application of a potential difference between the electrodes of the light guide and the subsidiary thin-film.
The main thin-film may contain light absorbing means for absorbing light entering the main thin-film. When the main thin-film is brought into contact with or close to the light guide, the main thin-film absorbs light entering from the light guide and prevents the light from coming out of the main thin-film, so that the transmission rate of light traveling in the light guide is certainly changed. Otherwise, the main thin-film may be accompanied by light reflective means for reflecting light entering the main thin-film so that the reflected light comes out of the main thin-film and enters the light guide at a right angle. When the main thin-film is brought into contact with or close to the light guide, the reflective means reflects light passing through the main thin-film back to the main thin-film The light enters again the main thin-film at a right angle and passes though the main thin-film. Then the light enters the light guide at a right angle and passes though the light guide. As a result, the transmission rate of light traveling in the light guide is certainly changed.
A plurality of the main thin-films may be arranged in a straight row per each light guide such as to be deflected independently from one another. This can increasingly change the amount of light coming out of the light guide and entering the main thin-films by increasing the number of main thin-films that are deflected, so that the transmission rate of light traveling in the light guide changes in steps.
The fluorescent means for producing different colors of fluorescence, namely red green and blue fluorescence, may be provided such as to be excited by light coming out of the subsidiary thin-film. The light modulating element array equipped with the fluorescent means can make any desired color display with a single mono color light source. Otherwise, different color filters for transmitting specific colors of light, respectively, may be disposed such as to selectively transmit the specific colors of light coming out of the subsidiary thin-film, respectively. The light modulating element array equipped with the color filters can make any desired color display with a single mono color light source such as a white light source.
The light modulating element array may further comprises main thin-film accompanied by light reflective means for reflecting back light entering the main thin-film and fluorescent means or color filters on one side of the light guide opposite to the side on which the main and subsidiary thin-films are disposed so that the reflected light comes out of the main thin-film and enters the light guide at a right angle. According to the light modulating element array, when the subsidiary thin-film is brought into contact with the light guide, light traveling in the light guide to a point where the subsidiary thin-film is in contact with the light guide comes out of the light guide and enters the subsidiary thin-film. Then the light is reflected back by the reflective means, enters the light guide at a right angle and passes through the light guide. The light coming out of the light guide excites the fluorescent means or passes through the color filter. The light modulating element array can make any desired color display with a single mono color light source and allows the fluorescent means or the color filters as an integral part of the light guide.
In the case where the light modulating element array is used as a panel display device, light source means is disposed in a specified positional relation to the light guide so that light emanating from the light source and entering the light guide impinges the interface of the light guide at an angle greater than the critical angle of total reflection. In order for the panel display device to make a color display, the light source means may comprises three primary colors of light sources arranged side by side or may be a single mono-color light source when the subsidiary thin-film is accompanied by the fluorescent means or the color filter.