Optical: systems and elements – Holographic system or element – Having multiple object beam or diffuse object illumination
Reexamination Certificate
1997-03-25
2001-03-06
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Holographic system or element
Having multiple object beam or diffuse object illumination
C359S009000
Reexamination Certificate
active
06198555
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hologram manufacturing method for forming sharp interference fringes and a related exposure apparatus.
2. Related Art
Overhead projectors and slide projectors are commonly used for displaying images for numerous viewers gathering at the same place. These projectors mandatorily require screens. The screens preferably used for these projectors are generally the ones having the capability of displaying images brightly as well as reflecting particular light efficiently. To satisfy these requirements, some holographic screens have been proposed, for example, in Japanese Patent No. 5-85910, Unexamined Japanese Patent Application No. 5-333435, and Unexamined Japanese Patent Application No. 5-5953. According to these prior arts, a light diffusing member is recorded on a hologram by utilizing the selectivity of wavelength of the hologram.
FIG. 50
discloses a conventional exposure apparatus for Fresnel's hologram screens. A coherent (laser) beam
30
is emitted from a light source
91
and then separated into two beams by a half mirror
911
. One of the two beams, i.e., a beam reflected by the half mirror
911
, is converted into a reference beam
31
with an expanded width by a divergent lens
913
. The other of the two beams, i.e., a beam penetrating the half mirror
911
, is reflected by a reflection mirror
912
and then diverged by a divergent lens
914
. Then, the diverged beam passes through a diffusion member
92
and is converted into a scattered beam serving as an object beam
32
. Thus, interference fringes are formed on a photosensitive element
81
.
However, according to the arrangement of this conventional exposure apparatus, each beam advances a relatively long optical path after being separated by the half mirror
911
. This is disadvantageous in that there is a possibility of causing a significant phase difference between two beams
31
and
32
due to fluctuations of the intervening medium (i.e., air) residing along the optical paths. Such fluctuations of intervening medium possibly disturb the interference fringes formed on the photosensitive element
81
. As a result, the sharpness of interference fringes will be deteriorated, and the diffraction efficiency of the hologram is lowered.
FIG. 51
discloses another conventional exposure apparatus for Fresnel's hologram screens. This conventional exposure apparatus is characterized by the photosensitive element
81
and the diffusion member
92
connected hermetically with refractive-index-adjusting liquid, such as silicon oil, kept between them. The coherent beam
30
is not separated by using a separating means such as a half mirror. The reference beam
31
is first irradiated to the diffusion member
92
. Diffused beams are then introduced into the photosensitive element
81
. According to this arrangement, reference beam
31
and object beam
32
cannot be discriminated clearly. This is disadvantageous in that a resultant holographic screen cannot have an intended directionality, and the transparency of the hologram is not satisfactory. Furthermore, the interference fringes formed on the photosensitive element may be disturbed due to leak of the refractive-index-adjusting liquid.
Unexamined Japanese Patent Application No. 5-232854 discloses an exposure apparatus similar to
FIG. 51
but different in that the diffusion member
92
is replaced by a master hologram recording a diffusion member. In this case, there is a problem that, if noises are involved in the master hologram, the same noises are recorded in the holographic screen.
SUMMARY OF THE INVENTION
Accordingly, in view of the above-described problems encountered in the related art, a principal object of the present invention is to provide a hologram manufacturing method capable of preventing interference fringes formed on a photosensitive element from being disturbed by the fluctuations of intervening medium residing along the optical path, and efficiently forming holograms with sharp interference fringes, and a related exposure apparatus.
Another object of the present invention is to reduce the length of the separated optical paths after the beam is separated, to reduce the phase difference between the reference beam and the object beam, and to realize a holographic screen free from the fluctuation of intervening medium residing along the optical path.
Still another object of the present invention is to flexibly change the incident direction of the object beam advancing to the photosensitive element to adjust the view region of the holographic screen.
Yet another object of the present invention is to stabilize the formation of interference fringes during an exposure operation, and to increase the transparency of a resultant holographic screen.
Moreover, another object of the present invention is to form a holographic screen along an entire surface of a large-scale photosensitive element, and to form interference fringes at different local spots of the photosensitive element by a single exposure operation.
And further, another object of the present invention is to form the interference fringes successively along the photosensitive element to manufacture a large-scale holographic screen.
In order to accomplish the above and other related objects, a first aspect of the present invention provides a manufacturing method for Fresnel's holographic screens comprising the following steps. First, a coherent beam is converted into a light flux having an expanded width at a predetermined position to a photosensitive element. Next, part of the expanded light flux, as a reference beam, is irradiated directly on the photosensitive element. While, the remainder of the expanded light flux is diffused and its optical direction is changed, thereby converting the remainder of the expanded light flux not irradiated directly to the photosensitive element into a scattered beam advancing as an object beam toward the photosensitive element. Then, interference fringes are formed on the photosensitive element by using the reference beam and the object beam.
According to the features of preferred embodiments of the first aspect invention, the expanded light flux is irradiated through a prism disposed on an optical path of the expanded light flux. This prism has a first surface brought into contact with the photosensitive element, a second surface receiving the expanded light flux, and a third surface brought into contact with a reflecting member reflecting the expanded light flux. The expanded light flux passes a solid transparent member disposed on an optical path extending from a split point of the reference beam and the object beam to the photosensitive element. The interference fringes are formed at local spots on the photosensitive element by using a plurality of optical sets each consisting of a diffusing member and a directional-changing member. The interference fringes are formed successively by changing a positional relationship between the plurality of optical sets and the photosensitive element.
A second aspect of the present invention provides a manufacturing method for Fresnel's holographic screens comprising the following steps. A coherent beam is converted into a light flux having an expanded width at a predetermined position to a photosensitive element. Part of the expanded light flux is converted into a scattered beam which is directly irradiated on the photosensitive element as an object beam. The optical direction of the remainder of the expanded light flux is changed to convert the remainder of the expanded light flux into a reference beam advancing toward the photosensitive element. And, interference fringes are formed on the photosensitive element by using the reference beam and the object beam.
According to the features of preferred embodiments of the second aspect invention, the expanded light flux passes a solid transparent member disposed on an optical path extending from a split point of the reference beam and the object beam to the photosensitive elem
Ishizuka Atsuo
Kanda Tomoyuki
Kurokawa Kazumasa
Shiozawa Masahiro
Denso Corporation
Pillsbury Madison & Sutro LLP
Spyrou Cassandra
Treas Jared
LandOfFree
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