JPH0973128A - Liquid crystal projector device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce unevenness of color caused by polarized light generated by reflection at a reflection mirror. SOLUTION: Light from a light source 10 is condensed on a liquid crystal panel 22 by the reflection mirror 11, and the light modulated by the panel 22 is projected to a screen 26 by a projection lens 25 in the liquid crystal projector. A polarized light rotating means 27 rotating the polarization direction of incident light on a polarizing plate 23 arranged on the incident side of the panel 22 so that the intensity of the light transmitted through the polarizing plate 23 may be higher is arranged between the reflection mirror 11 and the polarizing plate 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal projector that uses a liquid crystal panel to project an image of the liquid crystal panel on a screen.

[0002]

2. Description of the Related Art In a conventional liquid crystal projector, a reflecting mirror having a parabolic or elliptical shape is used in order to efficiently collect light from a light source on a liquid crystal panel surface. This reflecting mirror is generally provided with a vapor deposition treatment of a dielectric multilayer film on the glass surface so that infrared rays and ultraviolet rays other than visible light can be transmitted.

It is generally known that when monochromatic light is obliquely incident on a smooth surface of glass or a dielectric, a reflected light beam is partially linearly polarized. The polarized light generated by reflection has a component (dominant component) that greatly oscillates in the direction perpendicular to the incident surface (the surface including the ray of light and the reflection surface), so it is generated by a parabolic or elliptical reflecting mirror. Polarized light has a dominant component in the concentric direction.

Further, the wavelength of the light whose polarization is generated by the reflection on the surface of the multilayer film is influenced by the spectral characteristic (cutoff wavelength) of the multilayer film.

[0005]

By the way, due to the reflection by the reflecting mirror having the shape of the paraboloid or the ellipsoid, any one of the light components of the three primary colors of red, green and blue is obtained. When polarized light is generated, this colored light component becomes polarized light having a dominant component in a concentric direction around the optical axis. A light ray whose direction of the dominant component is closer to the perpendicular to the transmission axis direction of the polarizer of the liquid crystal panel has a lower transmittance, and a light ray whose direction of the dominant component is closer to the parallel has a higher transmittance. Further, the hue of the dominant component and the hue of the component (recessive component) orthogonal to the dominant component are different depending on the polarization dependence of the spectral characteristic (cutoff wavelength) of the reflecting mirror.

As a result, with respect to the colored light component in which the polarized light is generated, a partial difference occurs in the amount of transmitted light and the hue when passing through the polarizer of the liquid crystal panel, so that there is a so-called color unevenness in which the hue is partially different in the projected image. appear.

The occurrence of the color unevenness will be described with reference to FIGS. 6 to 8. 6A and 6B are schematic diagrams showing how polarized light is generated by reflection, FIG. 6A shows the relationship between incident light and reflected light, and FIG. 6B shows the details.

As shown in FIG. 6, when a monochromatic incident ray 62 impinges obliquely on a smooth reflective surface 63 of a glass or other dielectric material 60, the reflected ray 66 is partially linear. It is polarized. In this case, the predominant vibration direction is perpendicular to the plane of incidence 61, ie the plane containing the ray 62 and the normal 64 of the reflecting surface 63. Where φ is the incident angle,
Let γ be the refraction angle and n be the refraction index. Considering the case where linearly polarized light is incident, the reflection coefficient when the direction of electric vibration is perpendicular to the incident side is ρ ₉₀ , and the reflection coefficient when parallel is ρ ₀ ,
Fresnel's equation is as follows.

[0009]

Mathematical Expression 1 ρ ₉₀ = sin ² (φ−γ) / sin ² (φ + γ) ρ ₀ = tan ² (φ−γ) / tan ² (φ + γ)

When φ = tan ² (φ + γ) = ∞, the reflection coefficient ρ ₀ becomes 0.

At this time, φ = tan ⁻¹ n, and the angle between the reflected light and the refracted light is 90 °. This special angle is called the polarization angle (Brewster angle). If the incident light rays are not biased, the degree of polarization V of the reflected light is as follows.

[0012]

[Equation 2] _{V = (ρ 90 -ρ 0)} / (ρ 90 + ρ 0)

This amount is 0 when φ = 0 ° or 90 °
Becomes Theoretically, the degree of polarization should be 1.0 when φ is equal to the polarization angle, but it is actually slightly smaller than 1.0 due to the presence of surface film, surface distortion, and the like.

Even on the reflecting mirror surface where the dielectric multilayer film is vapor-deposited on the glass surface, the above-mentioned reflected polarized light is generated although the phenomenon is complicated.

7A and 7B show an example of the generation of reflected polarized light in a reflecting mirror. FIG. 7A is a side view and FIG. 7B is a front view seen from the light emitting side.

As shown in FIG. 7, light rays from the light source 70 are incident on the mirror surfaces 72 to 75 of the reflecting mirror 71 at incident angles θ _{1 to} θ ₄ , respectively. At this time, the degree of polarization of the reflected polarized light 78 at the peripheral portion of the reflecting mirror 71 increases due to the relationship of the incident angle. Further, in this case, since the dominant vibration direction is perpendicular to the incident surface, the dominant vibration direction (dominant component 76) of the reflected polarized light from each reflecting surface position of the reflecting mirror 71 is the concentric direction when the reflecting mirror 71 is viewed from the front. Matches And each dominant component 76
An inferior vibration direction (recessive component 77) appears in the direction orthogonal to. However, the light beam from the light source 70 is not monochromatic light,
Since the light of the wavelength component in the visible light region is included, the polarization degree of the reflected polarized light 78 differs for each color light component due to the relationship of the refractive index in the multilayer film.

Next, an example in which a light beam whose reflected polarized light is generated by the reflecting mirror enters a polarizer having a transmission axis direction at an angle of 45 ° will be described with reference to FIG.

As shown in FIG. 8, the area 8 on the polarizer 80 is
Most of the rays incident on the position 0a are in the area 7 of the reflecting mirror 71.
It is a ray from 1a. In addition, the area 80 on the polarizer 80
Most of the light rays incident on the positions b to 80e are light rays from the regions 71b to 71e of the reflecting mirror 71, respectively.

Therefore, the light beam incident on the position of the region 80a on the polarizing plate 80 is hardly biased with respect to the transmission axis direction 81 of the polarizer 80. In addition, the area 80 on the polarizer 80
Most of the rays incident on the positions of c and 80d are the polarizer 80.
Is a polarized light having a dominant component 76 in a direction close to the transmission axis direction 81 of. On the contrary, most of the light rays incident on the positions of the regions 80b and 80e on the polarizer 80 have a transmission axis direction 81 of the polarizer 80.
The polarized light has a dominant component 76 in a direction close to the vertical direction.

As a result, the light rays passing through the polarizer 80 are
Since the regions 80c and 80d on the polarizer 80 are rays close to the dominant component 76 of the reflected polarized light, the amount of transmitted light is large, and the regions 80b and 80e on the polarizer 80 are rays close to the inferior component 77 of the reflected polarized light. The amount of transmitted light decreases. Further, since the polarization degree of the reflected polarized light is different for each color light component, the color light component having a high degree of polarization is polarized, and the difference in the amount of transmitted light between the positions of the regions 80c and 80d and the regions 80b and 80e on the polarizer 80 is large. And color unevenness occurs.

The present invention has been made to solve the above-mentioned problems, and its object is to reduce color unevenness caused by polarized light generated by reflection by a reflecting mirror.

[0022]

The present invention relates to a liquid crystal projector in which light from a light source is condensed on a liquid crystal panel surface by a reflecting mirror, and light modulated by the liquid crystal panel is projected on a screen by a projection lens. A polarization rotation means for rotating the polarization direction of the incident light to the polarizer is provided between the reflection mirror and the polarizer so that the intensity of the light transmitted through the polarizer arranged on the incident side of is increased. It is characterized by being arranged.

The polarization direction rotating means can be composed of a half-wave plate or a half-wave film.

Further, in the present invention, it is preferable that a plurality of half-wave plates or half-wave films are arranged so that the directions of the slow axes (crystal axes) are different.

That is, according to the present invention, a retardation plate is partially or plurally provided between the reflecting mirror and the polarizer of the liquid crystal panel so that the amount of light transmitted through the polarizer of the liquid crystal panel is increased. Are arranged so that the directions of the slow axes (crystal axes) are different, thereby eliminating the difference in the polarization direction of the incident light ray with respect to the transmission axis direction of the polarizer.

According to the present invention, the polarization rotating means for rotating the polarization direction, such as the half-wave plate, is used between the reflecting mirror and the polarizer to rotate the polarization direction at the portion where the amount of transmitted light decreases. As a result, the partial difference in the amount of transmitted light is reduced, and the color unevenness is reduced.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the concept of the present invention. As shown in FIG. 1, the light rays from the light source 10 enter the mirror surface of the reflecting mirror 11 at different incident angles, as described above. At this time, the degree of polarization of the reflected polarized light 15 at the peripheral portion of the reflecting mirror 11 becomes large due to the incident angle. Further, in this case, since the dominant vibration direction is perpendicular to the incident surface, the dominant vibration direction (dominant component 16) of the reflected polarized light from each reflecting surface position of the reflecting mirror 11 is the concentric direction when the reflecting mirror 11 is viewed from the front. Matches And each dominant component 16
An inferior vibration direction (recessive component 17) appears in the direction orthogonal to.

When the light beam generated by the reflected polarized light 15 by the reflecting mirror 11 is directly incident on the polarizer 12 having the transmission axis direction at an angle of 45 °, the light beam transmitted through the polarizer 12 is on the polarizer 12. A difference occurs depending on the position of. That is, the amount of transmitted light is large at a position where a light ray close to the dominant component 16 of reflected polarized light is transmitted, and the transmitted light amount is small at a position where a light ray close to the inferior component 17 of reflected polarized light is transmitted.

Therefore, in the present invention, as shown in FIG. 1, a half-wave plate or a 1 / wave plate is provided between the reflecting mirror 11 and the polarizer 12.
The polarization rotating means 13 for rotating the polarization direction, such as a two-wavelength film, is arranged at a place where the amount of transmitted light decreases. By using the arranged polarization rotating means 13 to rotate the polarization direction at the position where the transmitted light amount decreases, the partial difference in the transmitted light amount decreases and the color unevenness also decreases.

Next, an embodiment in which the present invention is applied to a single plate type color liquid crystal projector will be described. FIG. 2 is a schematic view showing an embodiment in which the present invention is applied to a single plate type color liquid crystal projector, and is an example in which a large amount of reflected polarized light is generated in the red light component due to the spectral characteristics of the reflecting mirror 11.

As shown in FIG. 2, the light from the light source 10 is condensed by the reflecting mirror 11 toward the liquid crystal panel 22. The polarizing plate 23 is on the light incident side of the liquid crystal panel 22, and the polarizing plate 2 is on the light emitting side.
4 are provided respectively, the polarizing plate 23, the liquid crystal panel 22,
Also, the color image light obtained by passing through the polarizing plate 24 is imaged on the screen 26 via the projection lens 25, and the color image is enlarged and projected on the screen 26.

When the light from the reflecting mirror 11 is directly applied to the light incident side polarization plate 23 of the liquid crystal panel 22, the polarized light having the dominant component in the concentric direction in the red component is generated by the reflection by the reflecting mirror 11. Therefore, the liquid crystal panel 22
Since the amount of transmitted light is large at the positions of the regions 23d and 23c on the incident side of the polarizing plate 23 and the amount of transmitted light is small at the positions of the regions 23b and 23e,
The bluish color unevenness at the position 6b is caused by the areas 26c and 26
Reddish color unevenness occurs at the position of d.

For this reason, in this embodiment, the polarization rotating means 27 in which a half-wave plate is partially arranged is provided between the reflecting mirror 11 and the incident side polarizing plate 23. By arranging this polarization rotating means 27, the regions 23b and 2 on the polarizing plate 23
The polarization direction incident on the position 3e is rotated, the difference in the amount of transmitted light is reduced, and color unevenness is improved.

FIG. 3 is a schematic view showing the polarization rotating means 27 in which the half-wave plate used in the above embodiment is partially arranged. As shown in FIG. 3, the polarization rotating means 27 is
A place where the amount of transmitted light of the polarizing plate 23 decreases (regions 23b, 2
The half-wavelength film 27b for rotating the polarization direction is provided in the slow axis (crystal axis) direction 27c at a diagonal position of the glass plate 27a corresponding to 3e).

Further, instead of the polarization rotating means 27 shown in FIG. 3, a plurality of half-wavelength films 37 as shown in FIG. 4 are used.
By using the polarization rotation means 37 in which a to 37h are arranged on the glass 36 so that the directions of the slow axes (crystal axes) are different, the difference in the direction of the dominant component of the polarization with respect to the transmission axis direction of the polarizing plate 23 is further reduced. The effect of improving color unevenness also increases.

Next, an embodiment in which the present invention is applied to a three-plate type color liquid crystal projector will be described. FIG. 5 is a schematic diagram showing an embodiment in which the present invention is applied to a three-plate color liquid crystal projector, and in this embodiment too, a large amount of reflected polarized light is generated in the red light component due to the spectral characteristics of the reflecting mirror 11. Here is an example.

As shown in FIG. 5, the white light emitted from the light source is condensed by the reflecting mirror 11 toward the dichroic mirror 41. The light from the reflecting mirror 11 is split by the two dichroic mirrors 41 and 42 into three optical paths for red, green and blue. Liquid crystal panel units 43, 44, and 45 are provided on the respective optical paths. Each of the liquid crystal panel units 43, 44, 45 is composed of a light incident side polarization plate, a liquid crystal panel, and a light emission side polarization plate. In this embodiment, the liquid crystal panel unit 43 is used for red, the liquid crystal panel unit 44 is used for green, and the liquid crystal panel unit 45 is used for blue. Each liquid crystal panel 4
The red, green, and blue image lights obtained by passing light on the images formed on 3, 44, and 45 are two mirrors 46,
47 and two dichroic mirrors 48 and 49 collect them on one outgoing optical path and superimpose the red image, the green image, and the blue image. Then, the color image formed by this superposition is projected on the screen 26 through the projection lens 25.

As described above, in this embodiment, a large amount of reflected polarized light is generated in the red light component due to the spectral characteristics of the reflecting mirror 11, so that there is a polarization between the reflecting mirror 11 and the liquid crystal panel unit 43 for red. The rotating means 27 is arranged so as to eliminate the difference in the amount of transmitted light. In this embodiment, the polarization rotation means 27 is provided between the dichroic mirror 41 and the reflection mirror 47. The polarization rotating means 27 of this embodiment can also use the polarization rotating means shown in FIGS.

[0039]

As described above, according to the present invention, in the liquid crystal projector, the light use efficiency at the spot where color unevenness occurs is improved without reducing the light use efficiency, and the difference in the amount of transmitted light is eliminated. As a result, it is possible to reduce color unevenness depending on the reflected polarized light generated by the reflecting mirror.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the concept of the present invention.

FIG. 2 is a schematic view showing an embodiment in which the present invention is applied to a single plate type color liquid crystal projector.

FIG. 3 is a schematic view showing a polarization rotating means in which a half-wave plate used in the present invention is partially arranged.

FIG. 4 is a schematic view showing a polarization rotating means in which a half-wave plate used in the present invention is partially arranged.

FIG. 5 is a schematic view showing an embodiment in which the present invention is applied to a three-plate type color liquid crystal projector.

6A and 6B are schematic views showing how polarized light is generated by reflection, where FIG. 6A shows the relationship between incident light and reflected light, and FIG. 6B shows the details.

FIG. 7 shows an example of generation of reflected polarized light in a reflecting mirror,
(A) is a side view, (b) is a front view seen from the exit side.

FIG. 8 is a schematic diagram showing an example in which a light beam having reflected polarized light is incident on a polarizer having a transmission axis direction at an angle of 45 °.

[Explanation of symbols]

 10 Light Source 11 Reflector 12 Polarizer 13 Polarization Rotating Means 22 Liquid Crystal Panel 23 Polarizing Plate 24 Polarizing Plate 25 Projection Lens 26 Screen 27 Polarizing Rotating Means

Claims (3)

[Claims] 1. A liquid crystal projector in which light from a light source is condensed on a liquid crystal panel surface by a reflecting mirror, and light modulated by the liquid crystal panel is projected on a screen by a projection lens, and a polarized light arranged on an incident side of the liquid crystal panel. A liquid crystal characterized in that a polarization rotating means for rotating the polarization direction of the incident light to the polarizer is arranged between the reflecting mirror and the polarizer so that the intensity of the light transmitted through the child is increased. Projector device. 2. The liquid crystal projector device according to claim 1, wherein the polarization direction rotating means is a half-wave plate. 3. The liquid crystal projector device according to claim 2, wherein a plurality of half-wave plates are arranged such that the directions of the slow axes are different.