JPH07261004A - Fresnel optical element and projection type display device - Google Patents

Abstract

PURPOSE:To obtain a Fresnel optical element which can prevent a ghost image from being formed and is easily manufactured by forming plural beltlike prisms and making the beltlike prisms different in the tilt angle of step surfaces to a reference surface from one another. CONSTITUTION:The Fresnel lens 10 is constituted by forming annular lenses 11A-11E concentrically with one another and connecting the annular lenses 11A and 11B, 11B and 11C, 11C and 11D, and 11D and 11E by step surfaces 12A-12C and 12D. When the plane 13 of the Fresnel lens 10 is considered as the reference surface, the tilt angles theta-theta4 of the step surfaces 12A-12D to the reference surface are different from one another. Consequently, when a parallel light is made incident on the Fresnel lens as shown by an alternate long and short dash line, lights (unnecessary light) which do not contribute to the formation of a regular image travel in directions which are greatly different from one another as shown in the figure and a host image is prevented from being formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a Fresnel optical element which is a Fresnel lens or a Fresnel prism in which a plurality of belt-shaped prisms are formed and the belt-shaped prisms are connected by a stepped surface. The present invention relates to a projection display device.

[0002]

2. Description of the Related Art A Fresnel lens is thinly and lightly used in a large-sized projection display device because it is integrally molded with acrylic resin or the like and the ring-shaped lenses are connected by a stepped surface. FIG. 3 shows a partial cross section of a conventional Fresnel lens.
In the Fresnel lens 10A shown in FIG. 3A, the ring-shaped lenses 11A to 11C are concentric, and the stepped surfaces 12A and 12B are formed between the ring-shaped lenses 11A and 11B and between the ring-shaped lenses 11B and 11C, respectively. It is in a row. Considering the flat surface 13 of the Fresnel lens 10A as a reference surface, the inclination angles θ1 of the step surfaces 12A and 12B with respect to the reference surface are equal to each other.

When parallel light is made incident on the Fresnel lens 10A as shown by the alternate long and short dash line, the light rays incident on the annular lenses 11A and 11B are refracted in substantially the same direction, but the light rays incident on the step surface 12A. Is refracted in a direction significantly different from these. As shown in FIG. 3 (B), when the inclination angle θ2 is brought close to 90 °, the light beam incident on the step surface 12B side of the annular lens 11C is not reflected by the Fresnel lens 10
Within B, the traveling direction is significantly different from other light rays reflected by the step surface 12B and not reflected by the step surface 12B.

FIG. 4A shows a case where the Fresnel lens 10A shown in FIG. 3 is applied to a projection display device. The luminous flux emitted from the portion 21 of the display panel 20 is formed by the imaging optical system 2
2 and the Fresnel lens 10A to form an image on the screen 23. The Fresnel lens 10A includes an image forming optical system 2
It is for adjusting the image forming position and the enlargement magnification by 2.

On the screen 23, the Fresnel lens 1
A normal image 24 and a ghost image 25 are formed through the ring-shaped lens of 0 A and the step surface. FIG. 4 (B) shows
A normal image 24 and a ghost image 25 on the screen 23 are shown. Even if the Fresnel lens 10B shown in FIG. 3B is used instead of the Fresnel lens 10A, the ghost image 25 is similarly obtained.
Is formed.

In order to prevent the formation of the ghost image 25,
In FIG. 3, there has been proposed a configuration in which a light absorber is attached to the step surfaces 12A and 12B.

[0007]

However, it is not easy to form the light absorber on the step surface, and it is difficult to form the light absorber, especially in the case of the Fresnel lens. In view of such problems, it is an object of the present invention to provide a Fresnel optical element that can prevent the formation of a ghost image and is easy to manufacture, and a projection display device to which the Fresnel optical element is applied.

[0008]

In the first invention, as shown in FIG. 1, for example, a plurality of strip-shaped prisms 11A are provided.
11E are formed, and the Fresnel optical elements that are Fresnel lenses or Fresnel prisms in which the band-shaped prisms 11A to 11E are connected by the step surfaces 12A to 12D, the inclination angles θ1 to θ4 of the step surfaces 12A to 12D with respect to the reference surface 13. Have different things.

According to the first aspect of the present invention, since the inclination angles of the step surfaces with respect to the reference surface are different from each other, when parallel light as indicated by a chain line is made incident on the Fresnel optical element,
Lights that do not contribute to the formation of the regular image travel in different directions as shown in the figure, and the ghost image 25 as shown in FIG. 4 is hardly formed. Further, since it is not necessary to attach the light absorber to the step surface, the Fresnel optical element can be easily manufactured.

In the first aspect of the first invention, the strip prism 1
Reference numerals 1A to 11E are ring-shaped lenses that are concentric with each other. In the second aspect of the first invention, the strip prisms 11A to 11E.
Are parallel to each other. In the projection type display device of the second invention, for example, as shown in FIG. 2, the Fresnel lens is arranged in the optical path for forming an image on the screen 23.

According to the second aspect of the invention, since the ghost image is hardly formed, the display quality is improved.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1A shows a partial cross section of a Fresnel lens 10. The Fresnel lens 10 is an annular lens 1.
1A to 11B are concentric with each other, and an annular lens 11A
And 11B, between the annular lenses 11B and 11C,
Between the annular lenses 11C and 11D and the annular lens 1
Step surfaces 12A and 12 are provided between 1D and 11E, respectively.
B, 12C and 12D are connected. Considering the plane 13 of the Fresnel lens 10 as a reference plane, the inclination angles θ1 to θ4 of the step surfaces 12A to 12D with respect to the reference plane are different from each other. When parallel light as indicated by the alternate long and short dash line is made incident on the Fresnel lens 10, the light (unnecessary light) that does not contribute to the formation of the regular image travels in directions greatly different from each other as shown in the figure.

When this Fresnel lens 10 is used in place of the Fresnel lens 10A of FIG. 4A as shown in FIG. 1B, unnecessary light is projected at random on the screen 23. The ghost image 25 as shown in FIG. According to the first embodiment, it is not necessary to cover the step surface with the light absorber, and hence the Fresnel lens can be easily manufactured.

[Second Embodiment] FIG. 2 shows a projection type multi-screen display device according to a second embodiment. This display device employs Fresnel concave lenses 101 and 102 and a Fresnel convex lens 103 whose step surfaces are formed as in the first embodiment. The display device is housed in the housing 30. On the bottom surface side of the housing 30, a plurality of liquid crystal light valves 31 and 32 are arranged in a matrix in order to form one large screen as a whole. A driver IC is arranged around each of the liquid crystal light valves 31 and 32, and thus is a non-display portion. Liquid crystal light valve 31
The backlight 3 is provided between the housings 32 and 32 and the bottom surface of the housing 30.
3 are arranged. In front of the liquid crystal light valve 31, a Fresnel concave lens 101 is arranged via an imaging lens 34, and similarly, in front of the liquid crystal light valve 32, a Fresnel concave lens 102 is arranged via an imaging lens 35. A screen 23 is arranged in front of the Fresnel concave lenses 101 and 102 with a Fresnel convex lens 103 interposed therebetween. The imaging lens 34 is composed of an optical fiber bundle and forms an erect image of equal magnification. Imaging lenses 34 and 35
By arranging Fresnel concave lenses 101 and 102 in front of, respectively, the light passing through the liquid crystal light valves 31, 32 and the imaging lens 34 from the backlight 33 is expanded as shown by the one-dot chain line, and then Fresnel. The convex lens 103 collimates the light and forms an image on the screen 23. On the screen 23, the portion corresponding to the gap between the liquid crystal light valves 31 and 32 disappears, and an image in which adjacent portions are continuous can be obtained.

According to this display device, for the above reason,
Since the ghost image is not formed, the display quality is improved.
In addition, the present invention includes various modifications. For example, various methods are conceivable for setting the inclination angle of the step surface of the Fresnel lens. For example, with respect to the Fresnel lens 10 having a radius of 3d, the inclination angles of the step surfaces are different from each other in the ranges of 0 to d, d to 2d, and 2d to 3d, and the permutations of the inclination angles are the same in each range. It may be.

Further, the present invention is applied to a Fresnel cylindrical lens in which band-shaped lenses are connected in a shape-slope, a Fresnel prism in which band-shaped prisms parallel to each other are connected in a shape-slope, and the like, the Fresnel lens of the first embodiment. The same effect as in case of is obtained.

[0017]

As described above, in the Fresnel optical element which is the Fresnel lens or the Fresnel prism according to the first aspect of the present invention, the stepped surfaces connecting a plurality of band-shaped prisms have different inclination angles with respect to the reference surface. , The light that does not contribute to the formation of the regular image travels in different directions, the ghost image is hardly formed, and it is not necessary to attach the light absorber to the step surface, so that the Fresnel optical element can be easily manufactured. It has a great effect that it contributes to the provision of an inexpensive Fresnel optical element of good quality.

In the projection type display device according to the second aspect of the present invention, since the Fresnel lens is arranged in the optical path for forming an image on the screen, a ghost image is hardly formed, which contributes to improvement of display quality. large.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a Fresnel lens according to a first embodiment of the present invention and its operation explanatory view.

FIG. 2 is a sectional configuration diagram of a projection type multi-screen display device of a second embodiment to which the Fresnel lens of the first embodiment is applied.

FIG. 3 is a partial sectional view of a conventional Fresnel lens.

FIG. 4 is a diagram illustrating a problem of a conventional Fresnel lens.

[Explanation of symbols]

 10, 10A, 10B Fresnel lens 101, 102 Fresnel concave lens 103 Fresnel convex lens 11A-11E Ring-shaped lens 12A-12D Step surface 13 Plane 20 Display panel 22 Imaging optical system 23 Screen 24 Regular image 25 Ghost image 31, 32 Liquid crystal light valve 33 Back light 34, 35 Imaging lens

Claims (4)

[Claims] 1. A plurality of strip prisms (11A to 11E)
Is formed, and a step surface (12A to 12A) is formed between the strip-shaped prisms.
In the Fresnel optical element, which is a Fresnel lens or Fresnel prism connected in series in D), the inclination angles (θ1 to θ) of the step surface with respect to the reference surface (13).
Fresnel optical element characterized in that 4) are different from each other. 2. The Fresnel lens according to claim 1, wherein the belt-shaped prisms (11A to 11E) are annular belt lenses that are concentric with each other. 3. The Fresnel prism according to claim 1, wherein the strip prisms (11A to 11E) are parallel to each other. 4. A projection display device, characterized in that the Fresnel lens according to claim 2 is arranged in the optical path for forming an image on a screen (23).