Optical: systems and elements – Holographic system or element
Patent
1992-06-23
1998-07-21
Epps, Georgia Y.
Optical: systems and elements
Holographic system or element
359 15, 359 19, 359483, 359485, 359487, 359488, 359495, G02B 532, G02B 2728
Patent
active
057841810
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an illumination device and its application to a display device. It is especially applicable to polarization splitting, to focusing and to spectral splitting of a light beam as well as enlargement of a beam by anamorphosis.
Especially, it finds one particular application in a display using a monochromatic and a trichromatic liquid-crystal screen.
2. Description of the Related Art
In order to generate large-size video images, the current tendency is to use liquid-crystal active matrices in projection devices.
The projection of colored images can be achieved either from 3 monochromatic valves or from a single valve fitted with colored filters.
These image-projection techniques, which are appealing for their compactness as compared to cathode-ray tubes, have the drawback of having a poor light yield on the order of a few percent. The principal limiting causes being the following: polarized light and leads to a loss of 50% of the light emitted by the source to which it is necessary to add the absorption of the polarizers. by the transistor and the control electrodes. This factor constitutes the principal limitation for devices using small-size and high-resolution cells (spacing of the pixels<100 .mu.m) which will be required for HDTV needs. implemented in particularly simple devices. On the other hand, they lead to a loss of luminosity by a factor of at least three for each of the three chromatic components, a loss imposed by the spatial distribution of the colored filters. Since the non-negligible absorption of these filters is incompatible with the use of intense light sources, projection devices having one valve are therefore currently limited to the projection of small-size colour images. light sources, leads to the search for architectures which include beam-anamorphosis functions.
SUMMARY OF THE INVENTION
The invention relates to an illumination device characterised in that it comprises a holographic polarization-splitting device illuminated by a non-polarized light source and a holographic focusing device receiving a polarized beam from the holographic polarization-splitting device and enabling this beam to be focused.
Such an illumination source is applicable to the display of a liquid-crystal device which requires a polarized light.
The invention therefore also relates to a display device characterised in that it comprises a liquid-crystal screen receiving the beam focused by the holographic focusing device.
The holographic components are obtained by interference and enable complex optical functions to be provided in thin films such as is described in the document: "L. Solymar, D. J. Cooke, Volume Holography and Volume Grating--Academic Press (1981).
The properties of these holographic components in terms of angular, spectral or polarization selectivity are described by way of the coupled-wave formalism in the document: H. Kogelnik, Bell Syst. Tech. J. 48, p. 2909 (1969).
Their importance for use with a white source of the type used in projection devices may be summarised as follows: =7.5.degree. (in air) and spectral .increment..lambda.=40 nm pass-bands are obtained in structures, of approximately 10 .mu.m thickness (d) and having an index variation .increment.n of approximately 0.03, operating in reflection mode (HR type) or operating in transmission mode (HT type). They are consequently compatible with trichromatic sources of the arc-lamp type (.increment..lambda..sub.i =10 nm; the typical diameter of the 3 mm sources collimated with the aid of a 30 mm focal-length condenser and opened to f/1 corresponds to an angular divergence .increment..THETA..sub.o =6.degree.). pass-band properties. the thickness) enable the chromatic dispersion to be limited (.delta..THETA..sub.80 .apprxeq.1 mrd
m).
BRIEF DESCRIPTION OF THE DRAWINGS
The various aims and characteristics of the invention will appear more clearly in the description which will follow, given by way of example, and in the attached figures which represent:
FIG.
REFERENCES:
patent: 3622220 (1971-11-01), Kogelnik
patent: 4497534 (1985-02-01), Sincerbox
patent: 4807978 (1989-02-01), Grinberg et al.
patent: 5009502 (1991-04-01), Shih et al.
patent: 5073830 (1991-12-01), Loucks
patent: 5124841 (1992-06-01), Oishi
patent: 5181054 (1993-01-01), Nicolas et al.
patent: 5206674 (1993-04-01), Puech et al.
Patent Abstracts of Japan, vol. 11, No. 121 (P-568) 16 Apr. 1987, & JP,A,61 267 946 (Fujitsu) 27 Nov. 1986.
IBM Technical Disclosure Bulletin, vol. 31, No. 3, Aug. 1988, (New York, US) "Three-beam optical detection for magneto-optical storage using holography", pp. 12-13.
Patent Abstracts of Japan, vol. 12, No. 303 (P-746) 18 Aug. 1988, & JP,A, 63 074 149 (Fujitsu) 4 Apr. 1988.
Huignard Jean-Pierre
Loiseaux Brigitte
Nicolas Christophe
Puech Claude
"Thomson-CSF"
Epps Georgia Y.
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