Optical: systems and elements – Holographic system or element – For reconstructing image
Reexamination Certificate
2000-01-04
2004-06-29
Chang, Audrey (Department: 2872)
Optical: systems and elements
Holographic system or element
For reconstructing image
C359S015000, C359S031000
Reexamination Certificate
active
06757087
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical display apparatus for displaying image information and character information.
BACKGROUND ART
In recent years, an optical display apparatus for displaying image information and character information has been used in various fields. An example of such an optical display apparatus is an electronic optical display apparatus widely used in a traffic information display board, a direction board or a billboard. Related techniques are disclosed in, for example, Japanese Laid-Open Publication Nos. 6-228921, 7-129108, 7-140912, 8-6513, 8-158322, 8-160894, etc. First, one of the most typical examples of such an optical display apparatus, an optical traffic sign incorporating a fluorescent lamp therein, will be described below with reference to the figures. However, various other conventional structures are known in the art, such as those incorporating an LED or an EL device for producing a self-luminous display, and those using an optical fiber or a light guide plate for guiding light from a light source.
FIG. 1A
is a side view illustrating a structure of a conventional optical traffic sign, and
FIG. 1B
is a front view illustrating the same. Specifically, reference numeral
156
denotes a sign display board,
157
a ring-shaped fluorescent tube,
158
a sign body, and
159
a sign pole.
The sign display board
156
includes a semi-transparent resin on which a sign pattern is printed. The sign can be recognized even at night by illuminating the pattern from the inside of the sign with light from the ring-shaped fluorescent tube
157
. The sign body
158
, supporting the ring-shaped fluorescent tube
157
and the sign display board
156
, is installed on a side wall beside a road or on a tunnel ceiling by being supported by the sign pole
159
.
However, the above-described conventional structure has the following problems.
First, since the sign pattern is either printed on the semi-transparent resin or is made of a color resin, a large portion of light emitted by the ring-shaped fluorescent tube
157
, as a light source, is absorbed by the resin, whereby the display is not sufficiently bright.
Second, since the display section, including the sign display board
156
and the fluorescent tube (light source)
157
, is supported by the sign body
158
, the portion including the display section is large and heavy. Moreover, since the sign pole
159
supporting the same must also be robust, the overall structure is even larger and heavier.
Third, the structure must be installed so that it substantially projects from the installation surface, i.e., a road side wall or a tunnel ceiling. Therefore, it may be hit for some reasons by a moving object such as a person, a car or a load, thereby damaging the display apparatus body while also damaging the moving object. To avoid such an accident requires a large installation space, which is not economical.
The above-described problems arise not only from the optical traffic sign incorporating a fluorescent lamp therein, illustrated in
FIGS. 1A and 1B
as a conventional example, but also from those of a self-luminous type such as an LED or those using an optical fiber or a light guide plate for guiding light from the light source. Moreover, the problems are not limited to the above-described traffic sign, but are common to a general class of optical display apparatuses where a pattern to be displayed is illuminated with light from a light source.
Those using a hologram are possible alternatives which may solve the above-described problems.
First, a principle of producing a hologram based on a commonly-employed conventional technique and a principle of displaying (reconstructing) image information using such a conventional hologram will be described below.
FIG. 2A
is a diagram schematically illustrating a typically-employed principle of producing a hologram.
In particular, an object O is illuminated with object illumination light IL emitted from a laser light source, thereby forming object light OL having information relating to the shape, etc., of the object O, and making the object light OL be incident upon a hologram dry plate H
1
. At the same time, reference light RL
1
, formed by splitting light emitted from the same laser light source as the object illumination light IL by means of a beam splitter, or the like, is directed to be incident upon the hologram dry plate H
1
from an inclined direction. Thus, interference fringes between the object light OL and the reference light RL
1
are recorded on the hologram dry plate H
1
. The hologram dry plate H
1
on which such interference fringes (having information of the object O) are recorded will hereinafter be referred to also as the “hologram plate H
1
”.
FIG. 2B
is a diagram schematically illustrating a principle of reconstructing the hologram plate H
1
which is provided according to FIG.
2
A.
In particular, the reconstruction illumination light RI
1
, which is light from the same laser light source as that used for producing the hologram plate H
1
, is directed to propagate through the same path as that for the reference light RL
1
(see
FIG. 2A
) so as to irradiate the hologram plate H
1
. Thus, light (reconstruction light) R
1
, having information of the object recorded on the hologram plate H
1
, is reconstructed, so that a reconstructed image I
1
is observed at a position where the object was originally located.
The above-described method, however, requires the use of a laser light source as a light source when producing and reconstructing the hologram plate H
1
, and thus has such problems that the cost cannot be reduced and the handling thereof is complicated.
On the other hand, in a reflection-type hologram to be described below, a hologram image can be reconstructed using white light.
To produce a reflection-type hologram, the hologram plate H
1
is first produced by the method as illustrated in
FIG. 2A
, and then irradiated with reconstruction illumination light (laser light) RI
21
, as illustrated in
FIG. 3A
, in a direction opposite to that of the reconstruction illumination light RI
1
illustrated in FIG.
2
B. Thus, reconstruction light R
21
, directed from the hologram plate H
1
to the position where the object was located, is reconstructed, thereby reconstructing a real image (reconstructed image) I
21
of the object at a position where the object was located. Then, a new hologram dry plate H
2
is placed at a position spaced apart from the reconstructed image I
21
of the object by a distance Z
0
, as illustrated in
FIG. 3B
, and reference light RL
2
is directed to be incident upon the hologram dry plate H
2
from an inclined direction opposite from the hologram plate H
1
. The reference light RL
2
is formed by splitting light emitted from the same laser light source as the reconstruction illumination light RI
21
by means of a beam splitter, or the like. Thus, interference fringes between the reconstruction illumination light RI
21
and the reference light RL
2
are recorded on the hologram dry plate H
2
. The hologram dry plate H
2
on which such interference fringes (having information of the object) are recorded as a reflection-type hologram will hereinafter be referred to also as the “reflection-type hologram plate H
2
”.
FIG. 3C
is a diagram schematically illustrating a principle of reconstructing the reflection-type hologram plate H
2
formed as described above.
In particular, the reflection-type hologram plate H
2
is irradiated with reconstruction illumination light RI
22
(white light from a point light source spaced apart from the reflection-type hologram plate H
2
by a certain distance) which propagates in a direction diametrically opposite to that of the reference light RL
2
illustrated in FIG.
3
B. Thus, reconstruction light R
22
having information of the object recorded on the reflection-type hologram plate H
2
is reconstructed so as to form a reconstructed image I
22
at a position where the object was originally located.
In a reflection-type hologram, a wavelength selectivity (color selec
Hayashi Zenrou
Kubota Toshihiro
Taketomi Yoshinao
Tanji Yoshihiko
Chang Audrey
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
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