Optical: systems and elements – Optical modulator – Light wave temporal modulation
Patent
1997-05-13
1998-10-13
Ben, Loha
Optical: systems and elements
Optical modulator
Light wave temporal modulation
359291, 359295, 359846, 348771, 348772, G02B 2600
Patent
active
058221107
DESCRIPTION:
BRIEF SUMMARY
This invention relates to projection display systems and to a light valve for use in such systems.
A well known class of projection displays based on electron beam addressed Oil-Film, such as the Eidophor and GE light valve, provide high quality projection systems at the top end of the market which is almost unrivalled by any other technology. However, they suffer from oil decomposition and cathode poisoning, short life, very high system complexity and high cost.
Another class of projection display system uses the so-called deformographic storage display tube (DSDT), as described in U.S. Pat. No. 3,676,588 which uses a deformable layer and a mirror to effect light valve projection display. This device has two vacuum chambers with a necessary thick mica membrane for isolating the two chambers. The membrane is difficult to handle and mount, and cannot be made thin enough for good resolution. This was followed by IBM's single chamber DSDT, U.S. Pat. No. 3,858,080, in which an electron beam deposits charge pattern on a dielectric mirror lying over an elastomer layer attached on the inside faceplate of the tube. The charge pattern deforms the mirror and effects light modulation. The disadvantages of this patent are: dielectric mirrors are difficult to make especially on a deformable layer, and cannot be made as thin as a metal layer. The mirror is stiff, leading to low sensitivity and low resolution. Therefore, there are serious conflicting requirements: on the one hand it is desirable to make all layers above the deformable layer thick enough for good deformable layer sealing and isolation from an electron beam but on the other hand the opposite requirement is desired for good sensitivity.
The required performance of light vales suitable for the reproduction of Television (TV) and High Definition Television (HDTV) pictures and images are very demanding. The present invention seeks to fulfill all or most of these requirements.
According to the invention, there is provided a light valve modulator of reflective operation which includes a multi-layer structure which is controlled electrostatically, comprising a transparent substrate supporting a first transparent deformable layer and a second insulating dielectric deformable layer, with a mirror layer sandwiched between, and a third, dielectric insulating layer on the outside of the second layer, at least one of the layers between the second layer and the substrate being electrically conductive, and the third dielectric layer being capable of receiving an electric charge pattern by means of one or more electron beams, whereby the mirror layer is locally deformed by electrostatic forces occurring between the third layer and the conductive layer.
Such a structure permits the use of deformable materials such as elastomers inside vacuum electron beam tubes, a task normally very problematic. The harmonisation between electron beam and deformable materials (elastomers is brought about because the third layer may simultaneously provide a number of desirable functions such as: electron beam bombardment protection, high resolution, sealing and sensitivity enhancement.
According to a further aspect, the invention proposes deformable light valve display tube comprising an envelope with a transparent faceplate facing one or more electron guns, wherein a light valve modulator as mentioned above is mounted within said faceplate. In particular, the faceplate may itself form the transparent substrate of the modulator.
A practical projection system e.g. for T.V. applications may then comprise a light source, a schlieren-type optical system, a screen and a deformable light valve display tube as mentioned above, wherein the latter is controlled by signals which cause the light valve modulator to modulate light received from the light source whereby the optical system projects a television-type picture on the screen. Such a system may project onto the front or back of the screen.
In order that the invention in its various aspects shall be clearly understood, various exemplary embodim
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E. T. Kozol, Technical Disclosure Bulletin, vol. 19, No. 1, Jun. 1976, pp. 102-103.
Sansom et al, Deformographic Storage Display Tube, Sep. 1971, pp. 324-329.
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