Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2001-06-15
2004-09-28
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C362S035000
Reexamination Certificate
active
06798469
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical luminescent element that is used together with an excitation light source such as a fluorescent lamp, and, more particularly, to an optical display device equipped with the optical luminous element which provides fluorescent light with controlled excitation fight.
2. Description of the Related Art
In the prior art optical device operative to absorb excitation light and to admit fluorescent light to come out thereof, a filter operative to transmit ultra-violet light and reflects fluorescent light has not been incorporated in a fluorescent lamp that emits fluorescent light when a fluorescent substance is excited by ultra-violet excitation light or a general light source system which causes a fluorescence luminous element to absorb excitation light other than ultra-violet light and to emit fluorescent light. In consequence, the optical element that is made so as to absorb fluorescent light traveling toward an excitation light source raises a decline in the output efficiency of fluorescent light.
In order to improve the output efficiency of fluorescent light from the fluorescence luminous element there have been proposed optical display devices equipped with a filter function in, for example, Japanese Unexamined Patent Publications Nos. 63-172120 and 9-159994.
Before describing the present invention in detail, reference is made to
FIGS. 18 and 19
for the purpose of providing a brief background in connection with a prior art optical display device that will enhance understanding of the optical element and the optical display device equipped with the optical element of the present invention.
As schematically shown in
FIG. 18
, the optical display device
100
A described in Japanese Unexamined Patent Publication No. 63-172120 comprises an ultra-violet light source
110
a
, a liquid crystal shutter
102
, an interference filter
114
and fluorescence luminous elements
108
a
provided for three primary colors, red, green and blue, on the interference filter
114
, which are arranged in this order. The interference filter
114
comprises a multi-layer (more than 20 layers) dielectric thin film that has an alternate structure of high refractivity dielectric layers and low refractivity dielectric layers or a multi-layer thin film that has an alternate structure of metal layers and dielectric layers. Such an interference filter
114
transmits ultra-violet rays L as excitation light for exciting the fluorescence luminous elements
108
a
and absorbs fluorescent rays M emanating backward from the fluorescence luminous elements
108
a
The interference filter
114
improves the resolusion and contrast of the optical display device
100
A.
Further, as schematically shown in
FIG. 19
, the optical display device
100
B described in Japanese Unexamined Patent Publication No. 9-159994 comprises an ultra-violet light source
110
b
, deflection plates
120
and
124
disposed on opposite sides of a liquid crystal light modulator
123
, a reflection mirror
126
operative to reflect visible light M and fluorescence luminous elements
108
b
provided for three primary colors, red, green and blue, on the visible light reflection plate
126
, which are arranged in this order. The visible light reflection mirror
126
comprises a multi-layer dielectric thin film like the interference filter
114
of the optical display device shown in FIG.
18
and operates to transmit ultra-violet rays L and to reflect forward scattered fluorescent rays M from the fluorescence luminous elements
108
b.
These prior art optical display devices described above by way of example increase the utilization efficiency of fluorescent light by reflecting the scattered fluorescent rays M traveling backward from the fluorescence luminous elements
108
a
or
108
b
by a multi-layer dielectric thin film, namely the interference filter
114
or the visible light reflection mirror
126
. However, because the multi-layer dielectric thin film is formed by vacuum evaporation, in order for the multilayer dielectric thin-film to be capable of reflecting almost 100% of visible light incident thereupon, the multi-layer dielectric thin-film necessitates ordinarily consisting of several tens of layers. This results in high production costs of the optical display device.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical element that is used together with a fluorescent light source and an optical display device that makes a display.
It is another object of the present invention to provide an optical element which employs an inexpensive filter other than an optical filter consisting of a multi-layer dielectric thin-film which is expensive.
It is still another object of the present invention to provide an optical element having a high utilization efficiency of excitation energy.
The foregoing objects of the present invention are accomplished by an optical element comprises a fluorescence luminous element operative to emit fluorescent light when excited by excitation light and a cholesteric filter comprising a cholesteric liquid crystal layer. The cholesteric liquid crystal layer as the cholesteric filter is formed over the fluorescence luminous element at one side of the fluorescence luminous element at which the excitation rays enter the fluorescence luminous element so as to transmit at least partly the excitation rays and to reflect at least partly the fluorescent rays traveling to the cholesteric filter.
The optical element transmits either right- or left-handed circularly polarized component of excitation light that is coincident in twist direction with a spiral structure of the cholesteric liquid crystal layer as the cholesteric filter and reflects a circularly polarized component of scattered fluorescent rays traveling to the cholesteric liquid crystal layer that is coincident in twist direction with the spiral structure of the cholesteric liquid crystal layer. In consequence, the optical element integrates the scattered fluorescent rays traveling backward to the cholesteric liquid crystal layer with the fluorescent rays directly coming out of the fluorescence luminous element, so as thereby to provide an increase in the utilization efficiency of fluorescent light.
The cholesteric filter may comprise two cholesteric liquid crystal layers having spiral structures opposite in twist direction, respectively, which are formed one on top of the other. This cholesteric filter can reflect both right- and left-handed circularly polarized components of scattered fluorescent rays.
The cholesteric filter may comprise a half wave plate element and two cholesteric liquid crystal layers having the same directional spiral structure between which the half wave plate is disposed. Because the half wave plate element reverses a circularly polarize component of excitation rays, the cholesteric filter reflects both right- and left-handed circularly polarized components of scattered fluorescent rays.
The cholesteric filter may further comprise a plurality of cholesteric liquid crystal layers operative to reflect visible light having wavelengths different from one another, specifically red, green and blue light, that are formed one on top of another. The optical element equipped with this type of cholesteric filter can reflect the entire range of visible light.
The optical element may comprise such a fluorescence luminance element as to emit visible fluorescent light or infrared light when excited by ultra-violet excitation light. In the case where the fluorescence luminance element is of a type which emits red, green and blue fluorescent light when excited by ultra-violet excitation light, the cholesteric filter is adapted so as to admit the ultra-violet excitation light to pass through and to reflect red, green and blue fluorescent light.
When the optical element is used to make a fulfill color display, the fluorescence luminance element is of a type which emits red and/or green fluorescent light when excited b
Akkapeddi P. R.
Chowdhury Tarifur R.
Young & Thompson
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