Spatial light modulator and picture-forming apparatus including same

A spatial light modulator is formed of a pair of transparent substrates, and a photoconductor layer, an optical modulation layer and a color filter layer disposed in lamination between the substrates. The photoconductor layer is designed to have a spectral sensitivity characteristic including an average sensitivity to blue light, an average sensitivity to green light and an average sensitivity to red light, of which a maximum and a minimum provide a ratio. S.sub.MAX /S.sub.MIN therebetween of at most 10, and a spectral transmittance characteristic including an average transmittance in a wavelength range of 420-480 nm, an average transmittance in a wavelength range of 520-560 nm and an average transmittance in a wavelength range of 600-660 nm, of which a maximum and a minimum provide a ratio T.sub.MAX /T.sub.MIN of at most 10. As a result, it becomes possible to provide a compact picture-forming and display apparatus of a see-through type by disposing a white writing light source and a white reading light source on a same side of the spatial light modulator.

FIELD OF THE INVENTION AND RELATED ART 
The present invention relates to a spatial light modulator (spatial light 
modulation device, hereinafter sometimes abbreviated as "SLM") for use in 
a display apparatus, a picture-forming apparatus, etc., and more 
particularly to a structure of such a spatial light modulator. 
A spatial light modulator proposed heretofore for use in a display 
apparatus, a picture-forming apparatus, etc., has a structure as shown in 
FIG. 23, including a liquid crystal layer 23 as an optical modulation 
layer and a photoconductor layer 24 as a photoelectric conversion layer 
between a pair of substrates 21 and 22. The spatial light modulator shown 
in FIG. 23 further includes transparent electrodes 25 and 26, alignment 
films 27 and 28, and a mirror layer 29. 
When a spatial light modulator 20 having such a structure is illuminated 
with picture data-carrying light (writing light) incident thereto from the 
lower substrate 22 side, the photoconductor layer 24 is caused to have a 
locally lowered resistivity depending on its light quantity. If the 
resistivity is lowered in such a manner, the photoconductor layer is 
provided with a resistivity distribution over its layer extension, so that 
locally different effective voltages are applied to the liquid crystal 
layer 23, wherein liquid crystal molecules are caused to have different 
orientations depending on the locally different effective voltages. 
As a result, the liquid crystal layer 23 forms a latent image due to its 
molecular orientation distribution, so that if the liquid crystal layer 
illuminated with reading light incident thereto from the upper substrate 
21 side, the reading light is modulated by the liquid crystal to provide 
reflected light carrying image data due to the function of the reflecting 
mirror layer 29. The mirror layer 29 may have a structure wherein 
dielectric layers having mutually different refractive indices are 
alternately disposed to form a laminate film so as to provide a good 
reflectance and a high resistance in a planar direction. 
On the other hand, FIG. 24 illustrates a sheet of SLM designed for optical 
modulation for color picture display, wherein a miller layer 29 is 
patterned in squares and color filter segments R, G and B are disposed 
corresponding thereto. The SLM further includes a transparent insulating 
film 30, a masking layer 31 and a spacer 32. 
In case of using a conventional reflecting-type SLM having no color filter 
(CF) as shown in FIG. 23, three sheets of SLM are required for R (red), B 
(blue) and G (green) display and three writing optical systems are 
required to effect a color synthesis, so that the entire apparatus is 
liable to be complicated and large-sized. Further, in the case of an 
electrophotographic image- or picture-forming apparatus, writing in the 
SLM has to be performed for the respective colors R, G and B, so that long 
step are included. Further, as the readout system requires a color 
separation--color synthesis system, a direct-see type display cannot be 
provided, but a special form of display such as a projection-type display 
for projecting onto a screen or a look-into reflection type display like a 
view finder, has to be constituted. 
On the other hand, in the case of a color picture display apparatus using a 
single-sheet reflection-type SLM as shown in FIG. 24, writing light has to 
be in the form of a spot beam incident to a position corresponding to a 
color filter segment, so that its control requires an extremely high 
degree of technique and a special writing optical system is required by 
nature, thus giving a difficulty in providing an inexpensive apparatus. 
Further, color filter segments and mirror segments have to be disposed in 
alignment with each other in the SLM device, so that the production 
thereof becomes difficult and expensive. 
Further, a reflection-type SLM is liable to be expensive because it 
includes a mirror. The mirror may be composed of a dielectric mirror or a 
separated metal mirror. The former-type mirror requires ten and several 
layers and also generally requires a vacuum production process. The 
latter-type mirror generally requires a mask structure so as to prevent 
the reading light from passing through a spacing between metals to 
incident to the photoconductor layer, thus resulting in a complicated 
structure. 
If such a mirror layer is omitted, the reading light enters the 
photoconductor layer to disturb the written latent image, thus resulting 
in a picture with only a low S/N ratio. 
SUMMARY OF THE INVENTION 
In view of the above-mentioned problems of the prior art, an object of the 
present invention is to provide a spatial light modulator capable of 
writing and reading a color picture or image by using writing light and 
reading light incident thereto from an identical substrate side (or color 
filter side). 
Another object of the present invention is to provide a spatial light 
modulator requiring no reflection mirror. 
A further object of the present invention is to provide a spatial light 
modulator allowing a simple illumination system for writing light. 
According to the present invention, there is provided a spatial light 
modulator, comprising a pair of transparent substrates, and a 
photoconductor layer, an optical modulation layer and a color filter layer 
disposed in lamination between the substrates, wherein the photoconductor 
layer has 
a spectral sensitivity characteristic including an average sensitivity to 
blue light, an average sensitivity to green light and an average 
sensitivity to red light, of which a maximum and a minimum provide a ratio 
S.sub.MAX /S.sub.MIN therebetween of at most 10, and 
a spectral transmittance characteristic including an average transmittance 
in a wavelength range of 420-480 nm, an average transmittance in a 
wavelength range of 520-560 nm and an average transmittance in a 
wavelength range of 600-660 nm, of which a maximum and a minimum provide a 
ratio T.sub.MAX /T.sub.MIN of at most 10. 
According to the present invention, there is also provided a 
picture-forming apparatus including the spatial light modulator and a 
writing light source disposed in a position suitable for illuminating the 
photoconductor layer through the color filter layer of the spatial light 
modulator. The picture-forming apparatus may preferably further include a 
reading light source disposed in a position suitable for illuminating the 
optical modulation layer through the color filter layer of the spatial 
light modulator. 
As a result, it becomes possible to provide a compact picture-forming and 
display apparatus of a see-through type allowing writing and reading of 
color picture data by illuminating the spatial light modulator form a same 
side thereof. 
These and other objects, features and advantages of the present invention 
will become more apparent upon a consideration of the following 
description of the preferred embodiments of the present invention taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a sectional illustration of a spatial light modulator according 
to an embodiment of the present invention. Referring to FIG. 1, a spatial 
light modulator (SLM) 9 includes a pair of transparent substrates 101 and 
108, a color filter layer 102 including color filter segments of R, G and 
B and disposed on the substrate 101 on a side illuminated with writing 
light (hereinafter called "writing-side substrate"), transparent 
electrodes 103 and 107, a photoconductor layer (or photoelectric 
conversion layer) 104, a layer of optical modulation substance 
(hereinafter called an optical modulation layer) 105, and an alignment 
film 106. 
The writing-side substrate 101 and the reading-side substrate 108 may be 
composed of glass, quartz, alumina, resin, etc., and the color filter 
layer may comprise a well-known pigment dispersion-type color filter, a 
dyed filter, etc. 
The color filter layer 102 may optionally be provided with masking parts 
(not shown) between respective color filter segments of R, G and B or may 
be coated with a transparent layer (not shown) covering the color filter 
segments. The R, G and B color filter segments may be in the form of 
stripes or in a mosaic arrangement. FIG. 2 shows an example of 
relationship between transmittances and wavelengths for respective color 
filter segments of a color filter layer. 
The transparent electrodes 103 and 107 may comprise, e.g., SnO.sub.2 or ITO 
and may be formed in a layer thickness of 700-1500 .ANG.. The alignment 
film may suitably comprise a polyimide, etc., formed in a thickness of 
100-10,000 .ANG. and may suitably be subjected to a rubbing treatment The 
periphery of the substrates 101 and 108 may be sealed with a sealing 
agent, such as silicone or epoxy resin. 
The optical modulation substance may suitably comprise a liquid crystal, 
particularly a liquid crystal showing chiral smectic phase or chiral 
nematic phase, or a polymeric liquid crystal. A specific example of liquid 
crystal showing chiral smectic phase may be one comprising the following 
composition and showing a spontaneous polarization at 25.degree. C. of 26 
nC/cm.sup.2, a smectic layer inclination angle .delta. at 20.degree. C. of 
0 deg., and an apparent tilt angle of 27 deg. 
##STR1## 
According to our study regarding such a photoconductor layer 104, it has 
been found possible to write in color data through a color filter layer by 
using a white light source having a flat spectral characteristic if the 
photoconductor layer shows an average sensitivity to blue light Sb, an 
average sensitivity to green light Sg and an average sensitivity to red 
light Sr, of which a maximum Smax (i.e., the largest one among Sb, Sg and 
Sr) and a minimum Smin (i.e., the smallest one among Sb, Sg and Sr) 
provide a ratio Smax/Smin therebetween of at most 10 (.ltoreq.10). 
In case of Smax/Smin&gt;10, even when the maximum sensitivity color data is 
written to cause full inversion of a corresponding portion of liquid 
crystal, the corresponding portion of liquid crystal is not substantially 
inverted by the minimum sensitivity color data, so that it becomes 
difficult to reproduce full color even if the reading light source and 
color filter segment areas are optimized. In case where the Smax/Smin 
ratio .ltoreq.5.0, 1/3 or more of the corresponding portion can be 
inverted by the minimum sensitivity color data, so that full color 
reproduction becomes easier and a natural picture or human picture can be 
reproduced naturally through optimization of reading light, etc. 
Further, it has been found possible to read out a beautiful color picture 
having a good white balance if the photoconductor layer 104 shows a 
spectral transmittance characteristic such that the photoconductor layer 
shows an average transmittance Tb in a wavelength range of 420-480 nm, an 
average transmittance (Tg) in a wavelength range of 520-560 nm and an 
average transmittance Tr in a wavelength level of 600 nm 660 nm, of which 
a maximum Tmax (i.e., the largest one among Tb, Tg and Tr) and a minimum 
Tmin (i.e., the smallest one among Tb, Tg and Tr) provide a ratio 
Tmax/Tmin therebetween of at most 10 (.ltoreq.10). If the ratio exceeds 
10, it is difficult to take white balance by adjustment of reading light, 
thus being liable to fail in natural color reproduction. If the ratio is 
at most 3, the white balance adjustment becomes easier to allow natural 
reproduction of a human picture, etc. 
By using a photoconductor layer 104 satisfying the above-mentioned 
conditions, it becomes possible to write in color picture data through a 
color filter layer by using white illumination light (latent image 
formation) and also possible to read out a beautiful picture with white 
reading light incident to the photoconductor layer 104 from the writing 
side (visible image formation). Thus, by using a photoconductor layer 
showing appropriate levels of Smax, Smin, Tmax and Tmin, it is possible to 
constitute a transmission-type color SLM with good performances. 
In this embodiment, the photoconductor layer (or photoelectric conversion 
layer) 104 may preferably comprise an organic photoconductor, which is an 
organic semiconductor allowing a broad latitude in designing of spectral 
sensitivity and spectral transmittance. In this case, it is preferred that 
the photoconductor layer assumes a two layer-laminate structure including 
a charge transport layer and a charge generation layer. 
More specifically, known photoconductor materials include a- (i.e., 
(amorphous-)Si and organic photoconductors (OPC). Such a known 
photoconductor material has been used for constituting a photo-sensor, a 
solar cell, an electrophotographic photosensitive member, etc., wherein 
the spectral transmittance or transmittance in visible wavelength region 
thereof has not been thought much of. Moreover, when such a photoconductor 
material is used for color picture processing, a light source, such as an 
LED or a laser, emitting light having a prescribed peak wavelength has 
been used, and therefore it has not been practiced to effect writing in a 
single step. In the case of a photosensor, the sensitivity thereof, i.e., 
an ability of generating much charge in response to light absorbed 
thereby, has been questioned, and little attention has been paid to the 
color of the photosensor. 
Accordingly, SLM designers have adopted a-Si and OPC preferably used in 
photosensors and photosensitive members as they are for providing SLMs, 
and thus they have not made an approach taken by me. 
Now, a process for producing a spatial light modulator based on a specific 
example will be described with reference to FIGS. 3A-3D. 
As shown in FIG. 3A, first of all, a reading-side substrate 108 is 
surface-coated with a 700 .ANG.-thick transparent electrode film 107 by 
sputtering of ITO. Separately, as shown in FIG. 3B, a writing-side 
substrate 101 is provided with a color filter layer 102 including color 
filter segments of R, G and B according to pigment dispersion and then 
coated with a transparent electrode 103. 
Then, as shown in FIG. 3C, over the transparent electrode 103 on the 
writing-side substrate, a dispersion liquid containing a charge generation 
substance is applied by spin coating and dried at 80.degree. C. for 15 
min. to form a charge generation layer 104a, which is then spin-coated 
with a dispersion liquid containing a charge-transporting substance, 
followed by drying at 120.degree. C. for 60 min. to form a 0.70 
.mu.m-thick charge transport layer 104b. Thus, a laminate photoconductor 
layer 104 including the charge generation layer 104a and the charge 
transport layer 104b is completed. (On the other hand, it is also possible 
to use a single-layered photoconductor layer containing both a charge 
generation substance and a charge-transporting substance in mixture.) 
As a specific example, an OPC photoconductor layer 104 showing spectral 
transmittance and spectral sensitivity characteristics as shown in FIGS. 6 
and 7, respectively, may be provided as a laminate including a charge 
generation layer 104 containing a charge generation substance of the 
following formula: 
##STR2## 
and a charge transport layer 104b formed applying an 8:10 (by weight) 
mixture of a charge transfer material mixture (of F1 and P1 of the 
following formulae in 7:3 by weight) and a binder mixture (of 5 wt. % of 
siloxane-containing polycarbonate and 95 wt. % of polycarbonate): 
##STR3## 
Then, as shown in FIG. 4D, the reading-side substrate 108 provided with the 
transparent electrode 107 is further coated with a polyimide-precursor 
liquid, followed by baking at 220.degree. C. for 1 hour in an oven to form 
a 200 .ANG.-thick polyimide alignment film 106, which is then rubbed by a 
nylon cloth. Further, a dispersion of 20.0 .mu.m-dia. spacer beads in IPA 
(isopropyl alcohol) is applied by spin coating on the alignment film-side 
substrate 108 and dried at 110.degree. C. for 5 min. in an oven. 
Then, an epoxy resin-based sealing agent is applied (printed) along a 
periphery of the reading-side substrate 108, and after leveling, the 
writing-side substrate 101 is superposed thereon and applied thereon to 
form a superposed blank cell structure, which is then heated at 
150.degree. C. for 1 hour in an oven and then filled with a liquid crystal 
13. For the liquid crystal filling (injection), the blank cell structure 
may be retained at 95.degree. C. and then cooled at a rate of 1.degree. 
C./min. As a final treatment after the liquid crystal injection, the cell 
may be heated to 110.degree. C., gradually cooled at a rate of 0.1.degree. 
C./min down to 90.degree. C. and then cooled down to room temperature. 
After writing picture data in an SLM 9 prepared in the above-described 
manner in a manner as illustrated in FIG. 4, the SLM 9 is disposed between 
polarizers 109 and 110 arranged in cross nicols and illuminated with white 
reading light as shown in FIG. 5. In this instance, the respective parts 
may be provided with varying contrasts by changing the energy density of 
illumination light, and a positive-negative inversion may be effected by 
changing the direction of the polarizers 109 and 110 relative to the SLM 
9. 
At the time of writing picture data in the SLM 9, the writing light is 
incident to the photoconductor layer 104 through the color filter layer 
102, while a prescribed DC voltage is applied between the transparent 
electrodes 103 and 107. As the writing light is incident to the 
photoconductor layer 104, the resistivity of the photoconductor layer 104 
is lowered at portions thereof corresponding to the color filter segments 
of R, G and B in proportion to local illumination light quantity, where 
the optical modulation layer 105 is supplied with locally varying voltages 
(FIG. 4). 
When the applied voltage locally exceeds the inversion threshold voltage of 
the optical modulation substance, the optical state thereof is locally 
changed from "bright" to "dark" or "dark" to "bright". As the optical 
modulation substance used herein is a liquid crystal having a memory 
characteristic, the written picture data is retained even if the writing 
light illumination is terminated. In this way, as it is not necessary to 
keep the application of a voltage for retaining picture data, power 
consumption can be reduced. On the other hand, if a reverse polarity 
voltage is applied, the memorized picture data is cleared or reset. 
On the other hand, at the time of reading out picture data recorded or 
written in the optical modulation layer 105, a portion (pixel) of the 
optical modulation layer is illuminated through a corresponding color 
filter segment (R in FIG. 5). 
Next, a principle of color picture display by using the FLC will be 
described with reference to FIG. 4 (illustrating a writing operation) and 
FIG. 5 (illustrating a readout operation). 
Referring to FIG. 4, in the writing operation, when R-wavelength picture 
data-carrying light (R-writing light) is incident to a color filter layer 
102, the light flux is incident to not only an R-filter segment 102R but 
also a G-filter segment 102G and a B-filter segment 102B, but light flux 
incident to the G- and B-segments other than the R-segment 102R is 
absorbed by the G- and B-segments 102G and 102B, thus being prevented from 
reaching the photoconductor layer 104. 
On the other hand, R-wavelength light having passed through the R-filter 
segment 102R is absorbed by the photoconductor layer 104 to generate a 
charge in the charge generation layer 104a to be transported through the 
charge transport layer 104b, thus allowing an electric field applied 
between the transparent electrodes 101 and 108 to be applied by voltage 
division across the optical modulation layer 105 for driving the liquid 
crystal. 
As a result, within an area illuminated by the R-wavelength writing light, 
portions of the liquid crystal corresponding to only R-filter segments 
102R are caused to change an alignment state. By using G-wavelength 
writing light and B-wavelength light similarly, portions corresponding to 
G-filter segments 102G and B-filter segments 102B, respectively, are 
written with corresponding data. 
On the other hand, in the readout operation, the cross nicol polarizers 109 
and 110 are disposed to sandwich the SLM 9, e.g., in such a position that 
portions of the optical modulation layer 105 provide a bright state and 
the other portions provide a dark state, and white reading light is 
incident to the SLM from its writing side. The white light passes through 
the first polarizer 109 and the color filter layer 102 to form light 
fluxes of RGB, which are partially absorbed by the photoconductor layer 
104 and are locally selectively subjected to optical rotation by the 
optical modulation layer 105 to enter the second polarizer 110. As the 
white reading light is caused to illuminate the SLM 9 from the side 
identical to the writing side, it is preferred that the optical modulation 
layer 105 exhibits an optical rotation power which is predominant over its 
birefringence power. 
When the spatial light modulator 9 written in the manner illustrated in 
FIG. 4 by illumination with R-writing light is subjected to illumination 
with white-reading light, only a portion of reading light having passed 
through the R-filter segment 102R and the corresponding portion of the 
optical modulation layer 105 is allowed to pass through the second 
polarizer 110, and the remainder portion is absorbed by the second 
polarizer 110, so that the written data can be read out as an R-light 
image. 
As described above, writing light is caused to enter the photoconductor 
layer 104 after passing through the color filter layer 102. On the other 
hand, reading light need not enter a photoconductor layer after passing 
through a color filter layer. Accordingly, in addition to the layer 
arrangement order shown in FIG. 4, it is possible to adopt an arrangement 
as shown in FIG. 25 wherein a color filter layer 102, an optical 
modulation layer and a photoconductor layer 104 are disposed in this 
order, or an arrangement as shown in FIG. 26 wherein an optical modulation 
layer 105, a color filter layer 102 and a photoconductor layer 104 are 
disposed in this order. A pair of transparent electrodes 103 and 107 may 
be disposed in any positions as far as they sandwich an optical modulation 
layer and a photoconductor layer. 
FIGS. 6, 8 and 10 are graphs each showing a spectral transmittance 
characteristic of a photoconductor layer used in the present invention, 
and FIGS. 7, 9 and 11 are graphs each showing a spectral sensitivity 
characteristic of such a photoconductor layer corresponding thereto. These 
graphs are based on experimental results for photoconductor layers 
obtained by using different combinations of a mixing ratio between a 
charge transport substance and a charge generation substance and a 
photoconductor layer thickness. 
More specifically, FIG. 6 shows a spectral transmittance characteristic of 
a photoconductor layer which shows an average transmittance Tb of 0.6 in 
B-region having a wavelength range of 420-480 nm, an average transmittance 
Tg of 0.2 in G-region having a wavelength range of 520-560 nm and an 
average transmittance Tr of 0.7 in R-region having a wavelength range of 
600-660 nm. Among the average transmittances Tb, Tg and Tr, a maximum one 
(Tr=0.7) and a minimum one (Tg=0.2) provide a ratio Tr/Tg=3.5&lt;10. 
On the other hand, FIG. 7 shows a spectral sensitivity characteristic of 
the photoconductor layer which shows an average sensitivity Sb of 0.4 to 
blue light in a wavelength range of 400-500 nm, an average sensitivity Sg 
of 0.92 to green light in a wavelength range of 500-600 nm and an average 
sensitivity Sr of 0.5 to red light in a range of 600-700 nm. Among the 
average sensitivities, a maximum one (Sg=0.92) and a minimum one (Sb=0.4) 
provide a ratio Sg/Sb=2.3&lt;10. 
As shown in the above embodiment of FIGS. 6 and 7, it may be convenient to 
use wavelength ranges of 400-500 nm, 500-600 nm and 600-700 nm or 
evaluating average sensitivities to blue, green and red light, 
respectively, whereas wavelength ranges of 420-480 nm, 520-560 nm and 
600-660 nm for evaluating average transmittances for blue, green and red 
light, respectively. This is because an average sensitivity characteristic 
is principally questioned during writing wherein an entire wavelength 
range including ranges between peak wavelengths is utilized, whereas an 
transmittance characteristic is principally questioned during reading 
wherein limited wavelengths in proximity to peak wavelengths of a back 
light and thought much of for providing a good color separation 
characteristic. 
FIG. 8 shows a spectral transmittance characteristic of another 
photoconductor layer used in the present invention which shows an average 
transmittance Tb of 0.92 in B-region having a wavelength range of 420-480 
nm, an average transmittance Tg of 0.72 in G-region having a wavelength 
range of 520-560 nm, and an average transmittance Tr of 0.92 in R-region 
having a wavelength range of 600-660 nm. Among the average transmittances 
Tb, Tg and Tr, a maximum one (Tb, Tr=0.92) and a minimum one (Tg=0.72) 
provide a ratio Tb/Tg=1.3&lt;10. 
FIG. 9 shows a spectral sensitivity characteristic of the above 
photoconductor layer which shows an average sensitivity Sb of 0.26 to blue 
light in a wavelength range of 400-500 nm, an average sensitivity Sg of 
0.92 to green light in a wavelength range of 500-600 nm and an average 
sensitivity Sr of 0.42 to red light in a wavelength range of 600-700 nm. 
Among the average sensitivities Sb, Sg and Sr, a maximum one (Sg=0.92) to 
a minimum one (Sb=0.26) provide a ratio Sg/Sb of 3.69&lt;10. 
FIG. 10 shows a spectral transmittance characteristic of another 
photoconductor layer used in the present invention which shows an average 
transmittance Tb of 0.31 in B-region having a wavelength range of 420-480 
nm, an average transmittance Tg of 0.04 in G-region having a wavelength 
range of 520-560 nm, and an average transmittance Tr of 0.37 in R-region 
having a wavelength range of 600-660 nm. Among the average transmittances 
Tb, Tg and Tr, a maximum one (Tr=0.37) and a minimum one (Tg=0.04) provide 
a ratio Tb/Tg=9.25&lt;10. 
FIG. 11 shows a spectral sensitivity characteristic of the above 
photoconductor layer which shows an average sensitivity Sb of 0.53 to blue 
light in a wavelength range of 400-500 nm, an average sensitivity Sg of 
0.94 to green light in a wavelength range of 500-600 nm and an average 
sensitivity Sr of 0.61 to red light in a wavelength range of 600-700 nm. 
Among the average sensitivities Sb, Sg and Sr, a maximum one (Sg=0.94) to 
a minimum one (Sb=0.53) provide a ratio Sg/Sb of 1.8&lt;10. 
On the other hand, FIG. 12 shows a spectral transmittance characteristic of 
a conventional OPC for SLM which shows an average transmittance Tb of 0.78 
in B-region having a wavelength range of 420-480 nm, an average 
transmittance Tg of 0.95 in G-region having a wavelength range of 520-560 
nm, and an average transmittance Tr of 0.82 in R-region having a 
wavelength range of 600-660 nm. Among the average transmittances Tb, Tg 
and Tr, a maximum one (Tg=0.95) and a minimum one (Tg=0.78) provide a 
ratio Tb/Tg=1.2&lt;10. 
FIG. 13 shows a spectral sensitivity characteristic of the conventional OPC 
for SLM which shows an average sensitivity Sb of 0.04 to blue light in a 
wavelength range of 400-500 nm, an average sensitivity Sg of 0.38 to green 
light in a wavelength range of 500-600 nm and an average sensitivity Sr of 
0.88 to red light in a wavelength range of 600-700 nm. Among the average 
sensitivities Sb, Sg and Sr, a maximum one (Sr=0.88) to a minimum one 
(Sb=0.04) provide a ratio Sr/Sb of 22&lt;10. 
Further, FIG. 14 shows a spectral transmittance characteristic of a 
conventional a-Si for SLM which shows an average transmittance Tb of 10 in 
B-region having a wavelength range of 420-480 nm, an average transmittance 
Tg of 0 in G-region having a wavelength range of 520-560 nm, and an 
average transmittance Tr of 0.17 in R-region having a wavelength range of 
600-660 nm. Among the average transmittances Tb, Tg and Tr, a maximum one 
(Tr=0.17) and a minimum one (Tg=0) provide a an infinitely large ratio 
(i.e., &gt;10). 
FIG. 15 shows a spectral sensitivity characteristic of the conventional 
a-Si for SLM which shows an average sensitivity Sb of 0.83 to blue light 
in a wavelength range of 400-500 nm, an average sensitivity Sg of 0.98 to 
green light in a wavelength range of 500-600 nm and an average sensitivity 
Sr of 0.78 to red light in a wavelength range of 600-700 nm. Among the 
average sensitivities Sb, Sg and Sr, a maximum one (Sg=0.98) to a minimum 
one (Sr=0.78) provide a ratio Sg/Sr of 1.3&lt;10. 
FIG. 16 shows a spectral transmittance characteristic of another 
conventional a-Si for SLM which shows an average transmittance Tb of 0.92 
in B-region having a wavelength range of 420-480 nm, an average 
transmittance Tg of 0.91 in G-region having a wavelength range of 520-560 
nm, and an average transmittance Tr of 1.0 in R-region having a wavelength 
range of 600-660 nm. Among the average transmittances Tb, Tg and Tr, a 
maximum one (Tr=1.0) and a minimum one (Tg=0.11) provide a ratio 
Tb/Tg=9.1&lt;10. 
FIG. 17 shows a spectral sensitivity characteristic of the above a-Si for 
SLM which shows an average sensitivity Sb of 0.9 to blue light in a 
wavelength range of 400-500 nm, an average sensitivity Sg of 0.24 to green 
light in a wavelength range of 500-600 nm and an average sensitivity Sr of 
0 to red light in a wavelength range of 600-700 nm. Among the average 
sensitivities Sb, Sg and Sr, a maximum one (Sb=0.9) to a minimum one 
(Sr=0) provide an infinitely large ratio (i.e., &gt;10). 
FIGS. 18 and 19 illustrate a picture-forming apparatus or picture display 
apparatus using a spatial light modulator of the present invention. FIG. 
18 is a schematic illustration of such a picture display apparatus, 
wherein an already developed IX 240 film (hereinafter called D-cart.) 2 as 
a negative film is loaded in a picture display apparatus 1, whereby 
photographed pictures are displayed as high-resolution images after 
negative-positive inversion. 
FIG. 19 is a sectional view of the picture display apparatus, wherein a 
developed negative film 3 carrying a photographed picture is pulled out of 
D-cart. 2 and set in position frame by frame by a known film advance 
mechanism (not shown). Below the film 3 is disposed a strobe device 5, and 
a milky white diffusion plate 4 is disposed between the negative film 3 
and the strobe device 5 so that emitted light from the strobe device 5 is 
uniformly diffused to illuminate the negative film 3. The strobe device 5 
may be one used for a camera, etc., and may comprise a Xe (xenone) lamp, a 
reflection shade, a luminescent circuit, etc., so as to cause light 
emission in response to a known microprocessor (not shown). 
Above the film 3, an orange base-removal filter 6 is disposed for removing 
an orange tint from the negative image and comprises an optical film of 
blue that is complementary color of the orange. A projection lens 7 is 
disposed thereabove so as to enlarge a negative picture on the negative 
film 3 at a prescribed magnification and project the enlarged image onto a 
photoconductor layer in SLM 9 via a reflection mirror 8. The SLM 9 is 
illuminated by a linear tube type illumination device 12, frequently used 
as a backlight in a flat display, etc. 
FIGS. 20 and 21 illustrate the organization and function of an SLM 9 during 
picture writing and picture viewing, respectively. Referring to these 
figures, the SLM 9 includes a color filter layer 9a composed of RGB color 
filter segments which may preferably comprise one of a fine 
resolution-type as used in a CCD image sensor for a video camera, etc., as 
it allows observation of a silver salt picture without deterioration, for 
the picture display apparatus 1. 
The SLM 9 further includes a pair of polarizers 9b and 9h as a polarization 
device sandwiching a liquid crystal layer 9e. The polarizer 9b has a 
polarization direction perpendicular to the drawing paper and the 
polarizer 9h has a lateral polarization direction parallel to the drawing 
paper, thus assuming a so-called cross nicol arrangement. The liquid 
crystal layer 9e is disposed between transparent conductor films 9c and 
9f, which are ordinarily composed of ITO (indium tin oxide), etc., and 
driven by a drive circuit (detail not shown) as schematically represented 
by a power supply 10 and a switch 11 so as to generate opposite polarities 
of potentials at the ITO films 9c and 9f. 
Between the ITO films 9c and 9f, a photoconductor layer 9d of an OPC 
(organic photoconductor) and the liquid crystal layer 9e are disposed in 
contact with each other. The liquid crystal layer 9e may be composed of 
FLC and disposed between and in contact with the photoconductor layer 9d 
and the ITO film 9f. At least one side of the SLM 9 may be provided with a 
glass sheet 9g for providing a rigidity and protecting the other layers. 
During the picture writing, a negative picture schematically illustrated 
as a sheet image 9j is incident to the SLM as a result of projection from 
the above-mentioned negative film 3 via the projection lens 7. 
Now, the operation of the picture display apparatus 1 will be described 
with reference to a flow chart in FIG. 22. 
Referring to FIG. 22, when a D-cart. 2 is loaded in the picture display 
apparatus 1 so as to view pictures recorded therein (S501), the display 
apparatus 1 performs a loading operation including a thrusting operation 
for sending out a negative film 3 out of the D-cart. 2 and setting a first 
frame of the D-cart. 2 in position as shown in FIG. 19 (i.e., at an 
aperture (not shown) of the display apparatus 1) to stop the film supply 
(S502). In this state, the display apparatus 1 is placed in a waiting mode 
for waiting signals from respective switches (not shown) (S503). 
In this state, when a frame-setting command for advancing a prescribed 
frame for viewing is inputted (S504), a frame-setting operation is started 
to set the prescribed frame at the aperture of the display apparatus 1 
(S505), and the apparatus waits for a command as to whether the frame is 
displayed or not (S506). 
When a display command is received from the user in this state (S507), the 
picture of a previously displayed frame is cleared by turning on the 
switch 11 to form a voltage application state (S508), turning on the 
illumination device (S509) and applying an electric field from the power 
supply 10 in a direction reverse to that applied at the time of writing 
(S510). 
As a result of the reverse electric field application, molecules of FLC 9e 
are entirely reset in a state of lateral extension (as locally illustrated 
in FIG. 20) (S511). The resetting electric field application is performed 
for a time sufficient to place all the pixels in the reset state. In this 
state, the switch 11 may be turned off (made open) (S512) and the 
illumination device may be turned off (S513). 
Then, a fresh picture writing operation may be started. 
Now, if it is assumed that the picture display apparatus 1 placed on an 
office desk or on a wall at home and under illumination at several hundred 
lux, such environmental light is reduced to about a half after passing 
through the polarizer 9b to be incident to the photoconductor layer 9d. In 
this state, however, the switch 11 is open (as shown in FIG. 21) so that 
the FLC 9e is not supplied with an electric field and does not cause any 
reaction. 
In this state, the switch 11 is turned on (S514) to apply a forward 
electric field for picture writing between the ITO films 9c and 9f (S515), 
and the strobe device 5 is turned on to project image light through the 
negative film 3 onto the SLM 9. 
The writing operation is performed while the environmental light is also 
incident to the SLM 9 and, accordingly, it should be performed quickly so 
that the projection light has a prescribed S/N ratio or above relative to 
the environmental light. As the strobe light emission is completed within 
a time of ca. 500 .mu.sec., the switch 11 is turned on for a period 
comparable to and in synchronism with the strobe light emission 
(S514-S517). 
A picture thus recorded in the SLM 9 is illuminated by turning on the 
illumination device 12 to be observed as transmitted light image to the 
user (S518). Then, the display apparatus 1 is placed in the waiting mode 
for awaiting a subsequent command (S503), and the picture is continually 
displayed on the display apparatus. 
As described above, since it is possible to write in the SLM by supplying 
an electric field to the photoconductor layer 9d for a short period in 
synchronism with the lighting of the strobe device 5, it becomes possible 
to unnecessitate a shading cover for screening the SLM 9 from the 
environmental light, so that a high-resolution picture-forming apparatus 
can be formed in a smaller size. The written picture in a memory state 
after termination of the electric field application can be illuminated for 
viewing by a small power consumption light source, such as a fluorescent 
lamp, different from the writing light source. 
The polarizer 9b may be disposed in such a movable form that it is inserted 
between the spatial light modulator 9 and the light source 12 at the time 
of viewing and retreated from the position at the time of writing. 
As described above, according to the present invention, there is provided a 
picture forming and display apparatus including a spatial light modulator 
that can be written in with color picture data and can be read therefrom 
as visible color picture data by illuminating white light having a flat 
spectral distribution through a color filter in a same direction both for 
writing and reading, so that a complicated optical system including a 
reflection mirror and a screen as required in a reflection-type apparatus. 
As a result, such a picture forming and display apparatus can be produced 
through a simple process and at a lower production cost.