Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2000-04-19
2002-07-23
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S559000, C359S560000, C359S561000
Reexamination Certificate
active
06424449
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-110830, filed Apr. 19, 1999; and No. 11-322496, filed Nov. 12, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an optical information processing apparatus for carrying out image processing or image recognition using a reflection type spatial light modulator, for example, and more particularly to an optical information processing apparatus having a simplified and compact structure achieved by improving an optical system for use therein.
Further, the present invention relates to an optical information processing apparatus and more particularly, an optical information processing apparatus for optically carrying out image processing or image recognition using a reflection type spatial light modulator (hereinafter referred to as SLM) for filter display.
As well known, two-dimensional image Fourier transformation which requires a large amount of computation can be achieved rapidly by means of a single lens if optical means is used. Thus, since before, various researches on rapid optical information processing such as correlation, convolution, filtering and the like have been carried out.
FIG. 16
shows an example of general optical information processing apparatus optical system.
That is, as shown in
FIG. 16
, light emitted from a coherent light source
10
is condensed by a condensing lens
11
, is focused on a spatial filter
12
, and is filtered. Then the filtered light arrives to a collimator lens group
13
and is collimated. The collimated light arrives to a transmission type light modulator
14
T in which the input image
141
is displayed and is modulated. The modulated light arrives to a Fourier transformation lens group
15
, is Fourier transformed, and forms a Fourier transformation image
161
of the input image
141
on the rear focal plane (FB plane) of the Fourier transformation lens group
15
. A filter
16
is provided on the rear focal plane of the Fourier transformation lens group
15
to process optical information of the Fourier transformation image
161
of the input image
141
.
A Fourier inverse transformation lens group
17
is provided in a manner that a front focal plane (IEF) of the Fourier inverse transformation lens
17
locates on the filter
16
. The light that passes filter
16
arrives to the Fourier inverse transformation lens
17
and is Fourier inverse transformed. Finally, the Fourier inverse transformed light arrives at an images pickup device
18
placed on the rear focal plane (IFB) of the Fourier inverse transformation lens
17
. The processed result of image
181
is obtained by the image pickup device
18
. Thus, the input image
141
is Fourier transformed, filtered, Fourier inverse transformed, and picked up.
FIG. 16
shows an opening as the input image
141
and indicates an example of processing for carrying out bypass filtering for its Fourier transformation image
161
.
In this case, the Fourier transformation image
161
of the input image
141
is subjected to filtering by a filter
16
having a ring-like opening for extracting only high frequency components apart from the center thereof and consequently, the processing result image
181
whose boundary is emphasized is obtained on the image pickup device
18
.
FIGS. 17
,
18
show conventional cases where an input image is displayed on the reflection type spatial light modulator.
The optical information processing apparatus optical system shown in
FIG. 17
includes a reflection type spatial light modulator
14
R, a Fourier transformation lens group
15
, a filter
16
, a Fourier inverse transformation lens
17
, an image pickup device
18
. This optical information processing apparatus operates as the apparatus shown in FIG.
16
.
Its structure is different from that in
FIG. 16
in that a polarized beam splitter
19
is added to use the reflection type spatial light modulator
14
R as a spatial light modulator.
This polarized beam splitter
19
allows P-polarized light (light polarized in parallel to paper surface, indicated by both end arrows in
FIG. 17
) to pass and reflects S-polarized light (light polarized to a plane perpendicular to paper surface, indicated by a symbol indicating a perpendicular direction in FIG.
17
).
If collimated light just after it is emitted from the collimator lens group
13
is modulated to S-polarized light, it is reflected by a PBS plane
191
and then impinges upon the reflection type spatial light modulator
14
R.
The reflection type spatial light modulator
14
R expresses respective pixel values of an indicated input image
141
with an orientation direction of liquid crystal molecules in each pixel.
As a result, the entered collimator light is modulated so that its P-polarized light component is enlarged depending on the pixel value at the time of reflection.
That is, S-polarized light and P-polarized light are mixed in beam of light just after it is reflected by the reflection type spatial light modulator
14
R.
When light in which S-polarized light and P-polarized light are mixed reaches the plane
191
of the polarized beam splitter
19
, only the P-polarized light passes through. Consequently, the Fourier transformation image
161
of the input image
141
is generated on the FB plane at the rear focal plane of the Fourier transformation lens group
15
.
A structure after the filter
16
is the same as shown in
FIG. 16
, so that finally, the processing result image
181
is obtained on the FF plane.
A disposition shown in
FIG. 18
also produces the same function.
In this case, collimated light emitted from the collimator lens group
13
is modulated to P-polarized light and light for reading the input image
141
written in the reflection type spatial light modulator
14
R is modulated to S-polarized light.
Because the conventional optical information processing apparatus optical system shown in
FIGS. 17
,
18
has a structure redundant in the axial direction, if considering its practical performance, it is important to achieve as compact a structure as possible, and further a high performance Fourier transformation lens group is required to increase the capacity of the image.
For example, Jpn. Pat. Appln. KOKAI Publication No. 5-88079 has disclosed a design example of a Fourier transformation lens group comprised of three groups whose power is distributed to positive, negative and positive as shown in FIG.
19
.
A first group
151
is composed of cemented lens having positive power, a second group
152
is comprised of two meniscus lenses having negative power and a third group
153
is comprised of two meniscus lenses having positive power.
In this design example, by replacing the front main plane HF and rear main plane HB of the Fourier transformation lens group, a distance between the front focal plane FF and rear focal plane FB is 1.25f-less than 2f. In an optical information processing apparatus optical system using this, a length in the axial direction is short.
Although pixel size of the spatial light modulator has been decreased with a progress of technology, because the capacity of a handled image has increased, a display area size of a spatial light modulator having one million pixels, for example, is relatively large.
To illuminate this region with a uniform intensity, a lens having a high NA or a lens having a low NA but a long focal distance is required for the collimator lens group.
Because the focal distance is decreased if such a high NA collimator lens group is applied, apparently a distance in the axial direction required from the front focal plane up to a position in which a collimator light is obtained is thought to be decreased.
However, in this case, optical performance demanded for the collimator lens group becomes very high.
This results in increasing the number of the lens elements of the collimator lens group and the distance from the front focal plane CF of the colli
Epps Georgia
Olympus Optical Co,. Ltd.
Scully Scott Murphy & Presser
Spector David N.
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