JPS62115120A - Color projector - Google Patents

Abstract

PURPOSE:To improve a color display characteristic by providing a grating- shaped mirror with which an optical system for projection and display reflects partially onto the front focal plane of a projecting lens and transmits the same. CONSTITUTION:Projection light 1 from a projecting light source 6 is condensed by a lens 7, is reflected by the grating-shaped mirror 2 and is conducted by the projecting lens 3 to a color image display element 4. A diffraction grating is contained in the element 4. Only 5a, 5a', 5a'', 5b which are zero order light and + or - 1st order light pass the mirror 2 and + or - 1st ordr diffracted light beams 5a', 5b are reflected by the lens 3 and 5a'', 5b' are shielded by the mirror 2 when the projection light beams 1a, 1b are made incident thereto. The wavelength distribution of the zero order diffracted light returning in the specular reflection direction depends on the depth (d) and the intensity eta of the zero order diffracted light of an optional wavelength lambda is expressed by the formula when the refractive index of the medium where the light advances is designated as (n). The intensity eta attains the max. value 1 when the depth (d) is d=mlambda/2n (m is integer) and min. value 0 when d=(2m+1)lambda/4n.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical system for a display that performs color projection display.

(Prior art) Conventionally, for color display using a liquid crystal display element, a method has been used in which color filters are used to separate the colors of the projected light and pixels are switched using the liquid crystal element. This method could not be used in high-brightness projection displays because the color filters made of pigments and dyes had insufficient light resistance and heat resistance. Therefore, JP-A-59-
134303 r Color Thermal Writing Liquid Crystal Light Valve", by using a display element that uses a diffraction grating as a color filter, the above-mentioned drawbacks of light resistance and heat resistance are solved, and the projection display is now possible. In the above document, a transparent substrate,
In a thermal writing liquid crystal light valve composed of a light absorption film, a light reflection film, a liquid crystal alignment film, a transparent electrode film, and a transparent substrate, a grating with different optical retardations between the above components is used. A periodically arranged diffraction grating is formed. The diffraction grating diffracts the projected light, and by controlling the pitch and phase of the diffraction grating, a specific wavelength range of light can be diffracted in any direction.

If this diffraction grating is configured inside a liquid crystal light valve instead of a color stripe, the diffraction grating does not absorb light, has no problems in light resistance and heat resistance, and can be colored in the same way as a color stripe. Brightness color display becomes possible. However, color filters using diffraction gratings use the principle of obtaining a specific color by using only light of a specific diffraction order, such as 0th order light, and blocking diffracted light of other orders. There were restrictions on the light source. In other words, in order not only to separate the incident light and the outgoing light but also to block unnecessary diffracted light, the light flux on the front focal plane of the projection lens must be made as narrow as possible, and a point light source projection light source must be used. there were.

(Problem to be Solved by the Invention) In order to manufacture a small, low-cost projection device, it is desirable to use a small, high-intensity lamp such as a halogen lamp, but since it is a filament light source and not a point light source, The light separation described above was insufficient, and colors with sufficient saturation could not be obtained. For this reason, a point light source such as a canon lamp or an arc lamp must be used as a light source, making the color projection device large and expensive. An object of the present invention is to solve this problem and provide a color projection device using an inexpensive filament light source such as a halogen lamp.

(Means for Solving Problems) The gist of the present invention is to provide a color projection device with sufficient saturation even if it is not a point light source by using a lattice-like mirror to remove unnecessary projection light. It is composed of an image display element using a color filter using a diffraction grating, and an optical system for projecting and displaying the image display element, and further, the optical system for projecting and displaying is partially positioned on the front focal plane of the projection lens. The structure is equipped with a lattice-shaped mirror that reflects and transmits light.

(Function) A lattice-shaped mirror is placed on the front focal plane of the projection lens, and the lattice mirror is transmitted or reflected so that the projection light passes through the projection lens and enters the image display element, and the diffracted light from the image display means is redirected. By configuring the diffracted light to be guided to the grating mirror through the projection lens, only specific diffracted light passes through the grating mirror, and other diffracted light is reflected by the grating mirror so that it does not appear on the display screen. Therefore, even if the projected light is not sufficiently focused on the front focal plane of the projection lens, color display with sufficient saturation using the diffraction grating is possible.

(Example) Hereinafter, a color projection apparatus according to the present invention will be explained with reference to an illustrated example. FIG. 1 is a diagram showing an embodiment of the present invention.

Projection light 1 from a projection light source 6 is focused by a lens 7, reflected by a grid mirror 2, and guided to a color image display element 4 by a projection lens 3. The image display element 4 has a built-in diffraction grating, and when the projected light beams 1a and lb enter, the θ-order light, ±
5a, 5a', 5a'' which are primary lights.

5b' and 5b'' are obtained. These lights pass through the projection lens 3 again and are guided to the grating mirror 2, but the zero-order light 5a
.

Only the 5b passes through the grating mirror 2, and the ±1st-order diffracted light 5a'
.

5b'' is cut off by the lens 3, and 5a'' and 5b' are shielded from light by a grating mirror. Conventionally, these diffracted lights 5a'' and 5b' were not blocked, so that sufficient color display could not be achieved.The wavelength distribution of the 0th order diffracted light returning in the direction of specular reflection depends on the depth ``d''. The intensity n of the 0th-order diffracted light at an arbitrary wavelength λ can be obtained by the following equation, where n is the refractive index of the medium through which the light travels.

rl = cos2(2rrnd/λ) (1) Equation (1) takes the maximum value 1 when the depth d of the grating satisfies the following equation.

d = mX/2n (m is an integer) (2) Moreover, the minimum value O is obtained when the depth d of the grating satisfies the following formula.

d = (2m+1)A/4n (m is an integer) (3) Third
In the figure, the refractive index of the liquid crystal is 1.5 as the refractive index n, and the value of the depth d of the diffraction grating is (a) 310 nm, (b) 260 nm,
(c) Shows the wavelength distribution of 0th order diffracted light at 210 nm. The colors obtained in each case are (a) cyan, (b) magenta, and (C) yellow.

FIG. 2 is a diagram showing the shape of the grating mirror 2 and the positional relationship with the image display element. Each figure (a) and (b) shows two types of lattice mirrors. The lattice mirror 2 has reflective mirror parts 2' and transmitting parts 2'' formed alternately in a lattice shape, and the image They are arranged at a pitch q in the diffraction direction of the diffraction grating of the display element.This grating mirror can be created by depositing an aluminum film on a glass substrate.The pitch q of this grating mirror is determined by the focal length of the projection lens 3 being f, and the color When the pitch of the diffraction grating of the image display element 4 is d, and the wavelength of the projected light 1 is λ, the following equation is given.

q-DJd (4) f=50mm
, when λ=550nm and d=4pm, q is about 7m
It is sufficient to create it so that it has the value of m.

(Effects of the Invention) As described above, by using the present invention, a projection device with improved color display characteristics than the conventional one can be obtained. It goes without saying that the present invention is effective when applied not only to liquid crystal display devices using color filters, but also to other display devices using color filters using diffraction gratings.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram explaining a grating mirror used in the present invention, and FIG. 3 is a diagram showing the wavelength distribution of O-order diffracted light. In the figure, 2 is a grating mirror, 3 and 7 are lenses, 4 is an image display element, and 6 is a projection light source.

Claims (1)

[Claims] In a projection display device comprising an image display element using a color filter using a diffraction grating, and an optical system for projecting and displaying the image display element, the optical system for projecting and displaying the image is partially positioned on the front focal plane of the projection lens. A color projection optical device characterized by comprising a grid mirror that reflects and transmits light.