Optical: systems and elements – Projection screen
Reexamination Certificate
2002-05-15
2004-03-16
Mahoney, Christopher (Department: 2851)
Optical: systems and elements
Projection screen
C359S457000, C359S742000
Reexamination Certificate
active
06707605
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Fresnel lens sheet, and also to a transmission-type projection screen which utilizes the Fresnel lens sheet.
2. Description of the Related Art
A Fresnel lens sheet and a transmission-type projection screen are generally used in order that projection light incident on an incident surface is polarized and emitted from an light-emission surface at a desired angle.
However, a portion of the projected light is reflected at the light-emission surface and eventually emitted from a position which is slightly dislocated from the position where the light should be emitted, resulting in generation of a what is called double image.
FIGS. 11 and 12
are drawings which show an optical path of light which is incident on a conventional Fresnel lens sheet
100
or
101
.
Most of an incident light L
in
which is incident on the Fresnel lens sheet
100
of
FIG. 11
is emitted from a light-emission surface
100
b
as a normal emission light L
out
. However, a portion of the incident light L
in
is reflected back at the light-emission surface
100
b
, entirely reflected at an incident surface
100
a
and becomes a disoriented light L
out100
. Since the disoriented light L
out100
is emitted from a position which is distanced from the normal emission light L
out
, the resulting image is observed as a double image.
Further, an incident light LA
in
which is incident on the incident surface
101
a
of the Fresnel lens sheet
101
of
FIG. 12
is emitted from a light-emission surface
101
c
as a normal emission light LA
out101
. However, an incident light LB
in
which is incident on an ineffective surface
101
b
is reflected back at a light-emission surface
101
c
, subjected to inner surface reflection and becomes a disoriented light LB
out101
. Since the disoriented light LB
out101
is emitted from a position which is distanced from the normal emission light LA
out101
, the resulting image is observed as a double image.
Therefore, the Fresnel lens sheet
100
or
101
is conventionally made thin so that the length of the optical path of the light reflected back at the light-emission surface
100
b
or
101
c
is shortened, in order that the distance between the position where the emission light L
out
is emitted and the position where the disoriented light L
out100
is emitted, as well as the distance between the position where the emission light LA
out101
is emitted and the position where the disoriented light LB
out101
is emitted, are made closer. By such modification, the double image can be made less conspicuous as compared with the unmodified Fresnel lens sheet.
SUMMARY OF THE INVENTION
However, in the conventional Fresnel lens sheet as described above, as the thickness thereof is made thin, there arises a problem that the Fresnel lens sheet exhibits poor self-supporting property and cannot be held easily when the Fresnel lens sheet is used for a screen of large-size.
Examples of a method of holding a thin Fresnel lens sheet include a method of applying tension to a Fresnel lens sheet. However, this method has drawbacks in that the method requires provision of specific members for applying tension to a Fresnel lens sheet and that the size of the portion thereof other than the display of the back-projection-type screen increases, which results in an increase in the production cost.
Further, there also arises a problem that the holding frame for holding the Fresnel lens sheet must have a width of several tens of mm. In a multi-display device which effects multi-displaying faces or an enlarged displaying face by stacking up a plurality of transmission-type (or a back-projection-type in other word) projection screens, especially, there arises a problem that connection portions having a width of tens of mm, at which image cannot be displayed, are inevitably generated between the displays because the width of the holding frame cannot be reduced any further.
An object of the present invention is to provide a Fresnel lens sheet and a transmission-type projection screen which can be easily held and exhibits less conspicuous double image as compared with the conventional Fresnel lens sheet.
The present invention solves the above-mentioned problems by means for solution as described below. Although the embodiments of the present invention are described with corresponding reference numerals attached thereto, these reference numerals by no means restrict the present invention.
Specifically, a first aspect of the present invention provides a Fresnel lens sheet (
10
,
20
,
30
,
40
,
50
) for polarizing and emitting projection light, comprising: a lens layer (
11
,
21
,
31
,
41
,
51
) at which Fresnel lens configuration has been formed; a base material layer (
12
,
22
,
32
,
42
,
52
) provided further toward a light-incident or light-emission side than the lens layer; and a total reflection surface (
11
a
,
23
a
,
31
a
,
40
a
,
50
a
) for totally reflecting a portion of the projection light, wherein the total reflection surface is disposed between an incident surface (
12
a
,
22
a
,
32
a
,
41
a
,
51
a
) and a light-emission surface.
In the first aspect of the Fresnel lens sheet (
10
,
20
,
30
,
40
,
50
), a disoriented light originated from a part of the projection light incident on the incident surface which may be a surface of the base material layer or the lens layer is totally reflected by the total reflection surface (
11
a
,
23
a
,
31
a
,
40
a
,
50
a
), when the disoriented light proceeds in a direction from the lens layer side toward the base material side. That is, the disoriented light is originated when the projection light passes through or is reflected back by the surface with the Fresnel lens configuration of the lens layer, and proceeds in a direction from the lens layer side toward the base material side, and thus reaches the total reflection surface, at which the disoriented light is subjected to the total reflection.
In the first aspect, an optical path of the disoriented light in the Fresnel lens sheet is shortened, because the disoriented light is reflected back by the total reflection surface before it proceeds across an entire thickness of the Fresnel lens sheet. Accordingly, an extent of the double image can be reduced, even if thickness of the Fresnel lens sheet is made large to increase the self-standing property, thus providing a Fresnel lens sheet with a good self-standing and a reduced double image.
A first embodiment, which realizes the above-mentioned first aspect of the present invention, provides a Fresnel lens sheet (
10
,
20
,
30
) comprising: a base material layer (an incident layer) (
12
,
22
,
32
) provided as a layer having an incident surface; a lens layer (
11
,
21
,
31
) at which a Fresnel configuration has been formed; and a total reflection surface (
11
a
,
23
a
,
31
a
) for totally reflecting a portion of projection light reflected at a light-emission surface (
11
b
,
21
b
,
31
b
), wherein the total reflection surface is disposed between the incident surface (
12
a
,
22
a
,
32
a
) and the light-emission surface. According to the first embodiment of the present invention, generation of double image can be significantly suppressed, even when the base material is relatively thick. As a result, a Fresnel lens sheet which is easily held and in which double image is not so conspicuous can be obtained.
In the above-mentioned first embodiment, the Fresnel lens sheet (
10
,
20
,
30
) may comprise: a low refractive index layer (
12
,
24
,
33
) having a predetermined refractive index; and a high refractive index layer (
11
,
23
,
31
) having a refractive index higher than the refractive index of the low refractive index layer, the high refractive index layer being adjacent to the light-emission side of the low refractive index layer, wherein the total reflection surface (
11
a
,
23
a
,
31
a
) is a surface at which the low refractive index layer is in contact with the high refractive index layer. In this case, as the total reflection surf
Keefer Timothy J.
Mahoney Christopher
Wildman Harrold Allen & Dixon LLP
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