Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Reexamination Certificate
2001-07-25
2004-05-11
Dunn, Drew (Department: 2872)
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
C359S001000, C359S033000, C359S453000, C359S454000, C359S349000, C359S009000
Reexamination Certificate
active
06735001
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image display apparatus that utilizes a hologram element.
2. Description of the Related Art
An image display apparatus, that irradiates image light from various liquid projectors to a hologram screen formed by bonding a hologram element to light-transmissible films, reproduces images on the screen and offers the images to observers, is known.
Each light-transmissible film described above is pulled in a longitudinal direction V and in a transverse direction H during its production process as shown in
FIG. 3
that will be described later in more detail. A symbol RW represents a roll winding direction. This pulling operation orients the molecules of the light-transmissible film and the film becomes an anisotropic material. Therefore, birefringence occurs when rays of light are incident into the light-transmissible film from directions other than a specific direction.
When the rays of light are incident into a material that exhibits birefringence, the rays are divided into normal rays and abnormal rays depending on the direction of a vibration surface of the light, and travel inside the material.
Therefore, when image light
91
is irradiated to the hologram screen
2
as shown in
FIG. 12
, this image light
91
is divided into two rays of light
911
and
912
inside the light-transmissible film
21
that is the anisotropic material, and these rays enter, under such a state as described above, into the hologram element
20
. In consequence, these two rays of light
911
and
912
interfere with each other inside the hologram element
20
.
Due to this interference, an interference pattern
99
is displayed on the hologram screen
2
in superposition with the image
12
reproduced from the image light
91
, so that image quality of the image
12
is greatly deteriorated.
This problem manifests itself particularly in a large-scale hologram screen.
When the rays of light containing a mixture of S polarized light and P polarized light enter into a material that exhibits birefringence, the S polarized light component and the P polarized light component interfere with each other because the refractive index in the material varies depending on the direction of polarization.
Therefore, there develops a problem that, if the rays of light containing the mixture of S polarized light and P polarized light are incident when the image is displayed on the hologram screen
2
, the interference pattern appears in superposition with the image
12
on the hologram screen
2
. Incidentally, most of recent liquid crystal projectors are of a type that projects a mixture of S polarized light and P polarized light.
SUMMARY OF THE INVENTION
In view of the problems of the prior art described above, the present invention aims at providing an image display apparatus capable of offering high-quality images without superposition of an interference pattern with the images on a hologram screen.
According to the first aspect of the present invention, there is provided an image display apparatus including a hologram screen formed by bonding a hologram element to light-transmissible films and an illumination device for irradiating image light to the hologram screen and reproducing an image on the hologram screen, wherein: the light-transmissible film positioned on the irradiation side of the image light relative to the hologram element has an angle of deviation of not greater than 45 degrees between a direction of the light-transmissible film that gives the highest thermal shrinkage ratio and an axial direction in the hologram screen.
Here, the term “axial direction” is a direction parallel to a segment D obtained by rotating a segment B by 90° along an arc C with G
1
as the center when a segment connecting the center G
1
of the hologram screen and an irradiation center G
2
of the irradiation device is referred to as a segment A, a perpendicular at the center G
1
of the hologram screen is referred to as a perpendicular B, and an arc extending from the segment A to the segment B with a fan center at G
1
is referred to as the arc C.
It is most noteworthy, in the present invention, that the angle of deviation between a direction of the light-transmissible film on the irradiation side of the image light to the hologram device, which direction gives the highest thermal shrinkage ratio, and the axial direction in the hologram screen is within 45 degrees.
Incidentally, the term “within 45 degrees” represents the angle in either clockwise or counter-clockwise directions.
Next, the operation of the first embodiment of the present invention will be explained.
The light-transmissible film is pulled in both longitudinal and transverse directions during its production process as shown in FIG.
3
. This pulling operation orients the molecules of the light-transmissible film, and the film becomes an anisotropic material. The orientation condition of the molecules in the light-transmissible film varies depending on the thickness of the light-transmissible film, its production method, a manufacturing machine, and so forth, but generally has the tendency shown in FIG.
4
.
The thermal shrinkage ratio of the light-transmissible film made of the anisotropic material varies depending on direction. The thermal shrinkage ratio is large in the orientation direction of the molecules and is small in directions different from the molecular orientation direction.
When the orientation direction of the molecules is coincident with the axial direction of the hologram screen, the optical axis of the incident image light orthogonally crosses the plane on which a slice plane of a refractive index ellipse of the light-transmissible film describes a circle. Therefore, birefringence does not occur in the same way as in isotropic materials.
The first embodiment stipulates that the angle between the direction of the light-transmissible film giving the highest thermal shrinkage ratio and the axial direction of the hologram screen is not greater than 45 degrees. Therefore, the angle between the orientation direction of the molecules and the axial direction of the hologram screen is also within 45 degrees.
In the hologram screen according to the present invention, therefore, birefringence of the light-transmissible film does not easily occur so that almost no interference pattern occurs. Even when the interference pattern occurs, it is not very noticeable.
In this way, image quality is prevented from being deteriorated by the interference pattern.
When the angle between them is greater than 45°, a noticeable interference pattern is displayed in superposition with the image, and image quality of the image is greatly spoiled.
As described above, the first embodiment can provide an image display apparatus capable of offering high-quality images without superposition of an interference pattern with the image on a hologram screen.
The hologram screen according to the first embodiment can provide the effect described above when the direction of the light-transmissible film on the incidence side of the image light, that gives the highest thermal shrinkage ratio, is aligned with the axial direction of the hologram screen.
When the light-transmissible films are so disposed as to sandwich the hologram element, the direction of both light-transmissible films that gives the highest thermal shrinkage ratio can be aligned with the axial direction of the hologram screen.
In the hologram screen, it is possible to employ a construction in which the light-transmissible film having the direction giving the highest thermal shrinkage ratio and aligned with the axial direction of the hologram screen is disposed on the incidence side of the image light, and a transparent substrate made of a transparent isotropic material such as glass is disposed on the opposite side.
The light-transmissible film may be a colorless transparent film, or a thinly colored transparent film.
Further, a plurality of light-transmissible films may be bonded to the hologram element.
Various plastic films can be use
Assaf Fayez
Dunn Drew
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