Spatial optical modulating device

Details Spatial optical modulating device Spatial optical modulating device

2002-03-15

2003-05-06

Ben, Loha (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

C359S290000, C359S291000, C359S618000, C359S619000, C349S025000, C349S005000, C349S007000, C349S020000, C348S757000, C348S383000, C348S751000, C353S031000, C353S034000, C353S030000, C353S037000

Reexamination Certificate

active

06560001

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a spatial light modulating device which uses a spatial light modulator, which is an element for attaining a particular modulation in a cross-section of a light beam.
BACKGROUND ART
A spatial light modulating device is used for optical information processing and for computer-generated holograms (CGH). Especially, a spatial light modulating device of a type that prepares signal images according to electric addresses is very useful because this type of spatial light modulating device can easily prepare those signal images. A device that can efficiently perform phase modulation is required for the above-described usage.
A device that employs a transmission type liquid crystal element can be considered as an example of this type of spatial light modulating device. Such a device has a merit of being purchasable at a relatively low price. However, such a device generally employs twisted-nematic liquid crystal, and therefore is unable to attain a phaseonly modulation. Diffraction occurs due to the pixel structure of the transmission type liquid crystal element, and deteriorates the light using efficiency. The diffracted light becomes undesirable stray light.
As an example of another device that is capable of being electrically addressed, there is a spatial light modulating device that employs an optically-addressed type spatial light modulator and that employs an electrically-addressed type element to generate write light that will fall incident on the optically-addressed type spatial light modulator. In such a device, a small-sized cathode ray tube (CRT) or the transmission-type liquid crystal element can be used as the electrically-addressed element. The transmission-type liquid crystal element can be effectively used because it causes no image distortions and has high contrast characteristics. There is also known a spatial light modulating device that employs a transmission type liquid crystal element as an input device for inputting optical information for being processed and that employs an optically-addressed type parallel-aligned nematic-liquid-crystal spatial light modulator (PAL-SLM). The optically-addressed type PAL-SLM is a spatial light modulator of a type that employs parallel-aligned nematic-liquid-crystal as light modulation material. In this device, an imaging lens is disposed between the transmission type liquid crystal element and the optically-addressed type parallel-aligned nematic-liquid-crystal spatial light modulator. Write light from the transmission type liquid crystal element passes through the imaging lens to reach the optically-addressed type PAL-SLM. It is possible to attain phase modulation of 2&pgr; or greater by using the optically-addressed type SLM that employs the parallel-aligned nematic-liquid-crystal. Because phase-only modulation can be attained, it is also possible to attain high diffraction efficiency.
In this type of spatial light modulating device that employs the PAL-SLM, however, the lens is used as a device for transmitting an output image from the electrically-addressed element to the optically-addressed spatial light modulator. Because the lens generally has a long distance between an object plane and an image plane, the entire spatial light modulating device becomes large.
In order to solve this problem, as disclosed in Japanese unexamined patent application publication No.7-72503, for example, the size of the spatial light modulating device is made small by using a fiber optic plate (FOP) to transmit images.
The spatial light modulating device of this publication No.7-72503 will be described below with reference to the accompanying drawings.
FIG. 1
schematically shows the configuration of the spatial light modulating device that uses a fiber optic plate (FOP) to transmit images. In this spatial light modulating device, glass substrates
3
a
-
3
d
are used as substrates of an electrically-addressed element
1
a
and an optically-addressed spatial light modulator
2
a.
The electrically-addressed element
1
a
has an image display portion
4
between its glass substrates
3
a
and
3
b.
The optically-addressed spatial light modulator
2
a
has a thin film material portion
5
between its glass substrates
3
c
and
3
d.
The electrically-addressed element
1
a
and the optically-addressed spatial light modulator
2
a
are coupled together by using a fiber optic plate (FOP)
6
a.
This spatial light modulating device, however, has a problem that an image becomes blurred when the image is transmitted through the glass substrates
3
b
and
3
c.
It is conceivable to irradiate a parallel light beam onto the spatial light modulating device in order to solve this problem. This method can decrease the degree how the image is degraded while the image is transmitted through the glass substrate
3
b.
However, light which has passed through the fiber optic plate (FOP)
6
a
and outputted from the fiber optic plate (FOP)
6
a
is not a parallel light beam. Accordingly, the image borne on the light will be greatly degraded while the light is transmitted through the glass substrate
3
c.
In order to solve this problem, the publication proposes another spatial light modulating device as shown in FIG.
2
.
In this spatial light modulating device in
FIG. 2
, the fiber optic plate (FOP) is also used for transmitting images. In this spatial light modulating device, a fiber optic plate (FOP)
6
b
is used as a substrate of the electrically-adressed element
1
b
that faces the optically-addressed spatial light modulator
2
b,
while another fiber optic plate (FOP)
6
c
is used as a substrate of the optically-addressed spatial light modulator
2
b
that faces the electrically-adressed element
1
b.
With this structure, it is possible to greatly reduce the image degradation. It is possible to effectively use the spatial light modulating device as an optical amplifier in a projection device or the like.
In order to use such a spatial light modulating device to an optical information processing or a hologram, the output image from the spatial light modulating device is frequently subjected to Fourier transform operation using a lens or the like. However, the spatial light modulating device of
FIG. 2
attains a high image transmission characteristic between the electrically-addressed element
1
b
and the optically-addressed spatial light modulator
2
b.
Accordingly, the image of the pixel structure of the electrically-addressed element
1
b
is accurately transmitted to the optically-addressed spatial light modulator
2
b.
If the output image from the spatial light modulating device is subjected to the Fourier transformation, diffraction phenomenon occurs due to the image of the pixel structure. As a result, the light using efficiency decreases. The diffraction phenomenon produces undesirable stray light.
DISCLOSURE OF THE INVENTION
The present invention is attained to solve the above-described described problems. It is an objective of the present invention to provide a spatial light modulating device that has a small size and that can greatly suppress the diffraction phenomenon that occurs due to the pixel structure.
In order to overcome the above-described problem, the present invention provides a spatial light modulating device, comprising: an electrically-addressed type element for being addressed by electric signals representing information to be written, the electrically-addressed type element including an image display portion having a pixel structure, the electrically-addressed type element being inputted with write light; an optically-addressed type spatial light modulator including a thin film material portion and a pair of substrates, the thin film material portion being provided between the pair of substrates, the thin film material portion having an optical addressing layer and a light modulation layer, the optically-addressed type spatial light modulator being inputted with read light, one of the pair of substrates that faces the electrically-addressed type element being constructed fro

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