Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Reexamination Certificate
2003-01-03
2004-11-09
Boutsikaris, Leo (Department: 2872)
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
C359S272000, C349S201000, C349S202000
Reexamination Certificate
active
06816290
ABSTRACT:
TECHNICAL FIELD
This invention relates to an image display device and an image display apparatus employing a reflection type spatial light modulator and, more particularly, to such image display device and image display apparatus in which the apparatus may be reduced in weight and lowered in production costs while the image displayed may be improved in contrast.
BACKGROUND ART
So far, a variety of image display devices and image display apparatus produced using these display devices have been proposed.
[1] Spatial Light Modulator
The spatial light modulator (SLM) is such a device in which, as image signals are incident thereon, the incident light is modulated, from one pixel to another, based on image data corresponding to the image signals. The spatial light modulator (SLM) may be classified into a transmission type in which the light transmitted through the spatial light modulator is modulated, and a reflection type in which the light reflected by the spatial light modulator is modulated.
The reflection type spatial light modulator is constructed by e.g., a liquid crystal or a digital micro-mirror. In particular, the device formed using the liquid crystal is termed a liquid crystal type spatial light modulator.
The liquid crystal may be classified into an optical rotatory (polarization light guide) mode type, a birefringence mode type, a light scattering mode type and a light absorption mode type. The liquid crystal used in general may be enumerated by a TN liquid crystal, employing the optical rotatory (polarization light guide) mode type twisted nematic (TN) operational mode, an STN liquid crystal employing a birefringence operational mode type super-twisted nematic (STN) operational mode and an FLC type liquid crystal employing the ferroelectric liquid crystal (FLC) mode.
These reflection type spatial light modulator, modulating the state of polarization, may be enumerated by a liquid crystal spatial light modulator of perpendicular orientation, employing the TN crystal, an anti-ferroelectric liquid crystal spatial light modulator and a birefringence mode spatial light modulator employing the TN liquid crystal, in addition to the ferroelectric liquid crystal spatial light modulator.
[2] Reflection Type FLC Spatial Light Modulator
The structure and the operating principle of the reflection type FLC spatial light modulator, in the reflection type spatial light modulator modulating the state of polarization, is explained.
Referring to
FIGS. 1A
to
1
C, the reflection type FLC spatial light modulator is made up of a pair of electrodes and a liquid crystal material
105
inserted therebetween. An electrode part shown on an upper part of
FIG. 1
includes a glass substrate
101
A, a transparent electrode material
102
A on an inner side (a lower side) thereof, and an film of orientation (a film the liquid crystal molecules of which have been aligned in one direction such as by rubbing)
103
A on a further inner side (a further lower side) thereof. The other electrode part, shown on the lower side, is made up of a silicon substrate
101
B, an aluminum electrode
102
B, shown on an inner side (an upper side) thereof, and a film of orientation
103
B, shown on a further inner side (further upper side) thereof. The aluminum electrode
102
B also operates as a reflection film. On an outer (upper) side of the glass substrate
101
A of the upper electrode part is arranged a polarizer
104
.
FIG. 1A
shows the state of the first voltage direction in which the voltage of a first direction is applied to the transparent electrode material
102
A and to the aluminum electrode
102
B.
FIG. 1B
shows the state of the second voltage direction in which the voltage of a second direction opposite to the first direction is applied to the transparent electrode material
102
A and to the aluminum electrode
102
B.
Referring to
FIG. 1C
, the liquid crystal material
105
exhibits no birefringence effect with respect to the incident polarized light in the state of the first voltage direction, however, in the state of the second voltage direction, it exhibits a birefringence effect with respect to the incident polarized light.
Since a beam of polarized light
107
A, incident via polarizer
104
, is transmitted through the liquid crystal material
105
, under the condition of the first voltage direction, shown in
FIG. 1A
, and reaches the aluminum electrode
102
B without changing the state of the wave polarization, since the liquid crystal material
105
exhibits no birefringence effect under this condition. A polarized light beam
107
B, reflected by the aluminum electrode (reflecting film)
102
B, is again transmitted through the liquid crystal material
105
to reach the polarizer
104
without changing the state of the wave polarization. That is, the light of the same state of wave polarization as that of the incident light is returned to the polarizer
104
. Consequently, the light reflected by the aluminum electrode (reflecting film)
102
B is obtained via polarizer
104
as the outgoing light.
On the other hand, under the condition of the second voltage direction, shown in
FIG. 1B
, the polarized light beam
107
A, incident via polarizer
104
, is transmitted through the liquid crystal material
105
and thereby subjected to birefringence effects so as to be changed from the state of linear polarization to that of circular polarization to generate a circular polarized light beam
107
B. This circular polarized light beam
107
B is reflected by the aluminum electrode (reflecting film)
102
B and has its direction of rotation of the polarized light reversed by this reflection. The circular polarized light beam
107
B, having the direction of rotation reversed, is re-transmitted through the liquid crystal material
105
so as to be subjected to the birefringence effect and so as to be thereby turned into a linear polarized light beam. This linear polarized light beam is perpendicular to the direction of polarization of the polarizer
104
and hence is not transmitted through the polarizer
104
.
That is, in this reflection type FLC spatial light modulator, ‘white display’ and ‘black display’ dominate in a portion of the state of the first voltage direction and in a portion of the state of the second voltage direction, respectively.
[3] Projection Type Image Display Device Employing Reflection Type Spatial Light Modulator
In a routine reflection type spatial light modulator, for example, a projection type image display apparatus including e.g., a reflection type TN liquid crystal panel, the illuminating light projected from a lamp light source
201
falls on an illuminating optical system
202
having the functions of correcting the cross-sectional profile of a light beam, uniforming the intensity and controlling the angle of divergence, as shown in FIG.
2
. This illuminating optical system
202
may be provided with a P-S polarization converter, not shown. This P-S polarization converter is an optical block for aligning the illuminating light in the non-polarized state into the P-polarized light or into the S-polarized light at an efficiency of 50% or higher.
In an embodiment, shown here, the illuminating light, transmitted through the illuminating optical system
202
, is in a state of polarization in which the electrical vector is oscillated along a direction perpendicular to the drawing sheet, that is, in a state of S-polarized light with respect to the reflecting surface of a dichroic mirror reflecting the red light. That is, the illuminating light, emitted by the illuminating optical system
202
, has only its red light component deflected 90° in its proceeding direction, by the dichroic mirror
203
reflecting the red light. This red light component then is reflected by a mirror
204
to fall on a polarizing beam splitter (PBS) for red light
210
.
The red light beam, incident on the PBS
210
, has only its S-polarized component reflected by a dielectric film
210
a
of the PBS
210
to fall as incident polarized light on a reflection type TN liquid crys
Boutsikaris Leo
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
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