JPH05232408A - Polarized light illumination optical system - Google Patents

Abstract

PURPOSE:To provide the polarized light illumination optical system which supplies linearly polarized light to the liquid crystal light valve of a liquid crystal projector with high illumination efficiency. CONSTITUTION:An S-polarized light split by a polarized light splitting prism 1 is made incident on the polarized light splitting prism 1 again by a rectangular prism 2, a 1/2 wavelength plate 3 is provided between the polarized light splitting prism 1 and rectangular prism 2, and a deflecting prism which makes the direction of P-polarized light projected from the polarized light splitting prism 1 and the direction of P polarized light passed through the 1/2 wavelength plate 3 parallel to each other is provided adjacently to the polarized light splitting prism 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarized illumination optical system for converting an illumination light beam from a light source into a linearly polarized light beam and irradiating it on a liquid crystal light valve of a liquid crystal projector.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal light valve used in a liquid crystal projector has a TN type liquid crystal.
This TN type liquid crystal is, as shown in FIGS. 5 (a) and 5 (b),
The liquid crystal 150 in which the major axis direction of liquid crystal molecules is twisted by 90 ° is sandwiched between two glass plates 151 and 152 having electrodes.

The linearly polarized light passing through the liquid crystal 150 is 90
The twisted liquid crystal molecules rotate the polarization direction by 90 °. When a voltage is applied between the glass plates 151 and 152, the long axes of the liquid crystal molecules are oriented toward the electrodes, and the polarization direction of the linearly polarized light passing through the liquid crystal does not change. The liquid crystal light valve has the above-mentioned TN type liquid crystal sandwiched between two polarizing plates 153 and 154 whose polarization directions are orthogonal to each other. Therefore, when voltage is applied, as shown in FIG.
As shown in (a), the illumination light 110 passes through the first polarizing plate 153 to become linearly polarized light 111. The polarization direction of this linearly polarized light 111 is not changed by the TN type liquid crystals 150 to 152, so that it is blocked by the second polarizing plate 154. Then, when no voltage is applied to the TN type liquid crystal, as shown in FIG.
Passes through the first polarizing plate 153 to become linearly polarized light 111, and this linearly polarized light 111 is TN type liquid crystal 150-1.
The polarization direction is rotated 90 ° by 52 and passes through the second polarizing plate 154.

[0004]

As described above, since the liquid crystal light valve has the polarizing plate on the light source side thereof, when the light is illuminated with light whose polarization directions are not aligned, the polarizing plate on the light source side causes the polarizing plate to move. There has been a problem that polarized light other than polarized light parallel to the polarization direction is blocked and a loss of light amount occurs. Therefore, an object of the present invention is to provide a polarized illumination optical system that enables illumination under high illumination efficiency without causing a loss of light quantity.

[0005]

In order to achieve the above object, according to the present invention, for example, as shown in FIG. 1, an illumination light flux from a light source is converted into a linearly polarized light flux to be used in a liquid crystal light valve of a liquid crystal projector. In the polarized illumination optical system for irradiation, the illumination luminous flux (La, Lb) is converted into S-polarized light (LaS ₁ , LbS ₁ ) and P.
Polarization splitting prism (1) for splitting into polarized light (LaP ₁ , LbP ₁ ) and first reflections orthogonal to each other in order to re-enter S polarization (LaS ₁ , LbS ₁ ) into polarization splitting prism (1) A right-angle prism (2) having a surface (2a) and a second reflecting surface (2b), and
The S-polarized light (LbS ₁ ) traveling toward the polarization splitting prism (1) again through the reflection surface (2a) and the second reflection surface (2b) of P
The polarized light (LbP ₂ ) is converted into the S-polarized light (LaS) directed from the polarization splitting prism (1) to the second reflecting surface (2b).
A half-wave plate (3) for converting ₁ ) into P-polarized light (LaP ₂ ) is provided between the polarization separation prism (1) and the rectangular prism (2) and converted by the half-wave plate (3). The polarization separating prism (5) for making the emission directions of the P polarized light (LaP ₂ , LbP ₂ ) thus separated and the P polarized light (LaP ₁ , LbP ₁ ) separated by the polarization separating prism (1) mutually parallel It is configured to be provided adjacent to 1).

[0006]

The light beam incident on the polarized illumination optical system according to the present invention is separated into P-polarized light and S-polarized light by the polarization separation prism. Then, the S separated by the half-wave plate
Convert all polarized light to P polarized light. Next, one of the P-polarized lights is deflected by the deflecting prism so that the direction of the converted P-polarized light and the direction of the P-polarized light separated by the polarization separation prism are parallel to each other. Therefore, all the light fluxes incident on the polarized illumination optical system become P-polarized light, and the illumination light fluxes can be effectively used.

Moreover, since the respective reflecting surfaces for deflecting light are totally reflected, in principle, there is no loss of light quantity due to the deflection of light. Further, as shown in FIG. 3, even if the illumination light obliquely enters the polarized illumination optical system, P-polarized light emerges with the same inclination as the incident angle, which is also advantageous for oblique incidence.

[0008]

EXAMPLES Examples of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic diagram showing a polarized illumination optical system according to the present invention, and FIG. 2 is a schematic diagram showing an example in which the polarized illumination optical system according to the present invention is applied to a liquid crystal projector. First, the configuration of a liquid crystal projector to which the polarized illumination optical system according to the present invention is applied will be described with reference to FIG.

In FIG. 2, for simplicity of explanation, the light flux passing through this optical system is represented by only the light rays passing through the optical axis. In FIG. 2, the light source unit 11 has a light source such as a halogen lamp and a reflecting mirror, and in the emission direction of the illumination light from the light source unit 11, a heat ray cut filter 12 that blocks infrared rays emitted from the light source unit 11 and a light source. Part 11
There is provided an illumination optical system 13 having an optical system for uniformizing the light intensity of the illuminating light beam from the optical system and an optical system for converting the light beam having a circular cross section into a rectangular cross section. Then, the illumination light from the light source unit 11 passes through the heat ray cut filter 12 and the illumination optical system 13, then, is reflected by the mirror M _1, reaches a dichroic mirror DM _1.

This dichroic mirror DM₁Is blue
The light of the red component and the green component while reflecting the light of the component
Has a function of transmitting light, and is a dichroic mirror.
DM ₁Light B in the illumination light that reached₁Is reflected. This
Blue light B₁Is a dichroic mirror DM₁How to reflect
Mirror M installed facing₂Reflected by the
It is incident on rhythm 15B.

On the other hand, in the transmission direction of the dichroic mirror DM ₁ , there is provided a dichroic mirror DM ₂ which reflects the red component light and transmits the green component light. The red light R ₁ transmitted through the dichroic mirror DM ₁ is reflected by the dichroic mirror DM ₂ and enters the linear polarization conversion prism 15R. Further, the green light G _{1 that} has passed through the dichroic mirror DM ₁ also passes through the dichroic mirror DM ₂ and the linear polarization conversion prism 15
It is incident on G.

Here, these linear polarization conversion prisms 1
Each of 5B, 15R, and 15G has a function of converting the incident illumination light into linearly polarized light having a uniform polarization direction, for example, linearly polarized light vibrating in the paper surface direction. Then, in the emission direction of the linear polarization conversion prisms 15B, 15R, 15G,
Liquid crystal light valves 16B, 16R, and 16G for providing image information based on video signals of three primary colors to light are provided.

The blue light B ₁ emitted from the linear polarization prism 15B becomes a linearly polarized light whose polarization directions are uniform, passes through the liquid crystal light valve 16B, and contains blue image light B containing blue image information by a blue image signal. Become ₂ . Further, the red light R ₁ emitted from the linear polarization prism 15R becomes a linearly polarized light having a uniform polarization direction, passes through the liquid crystal light valve 16R, and red image light R ₂ including red image information by a red image signal. become. Then, the linear polarization conversion prism 15G
The green light G ₁ emitted from becomes a linearly polarized light whose polarization directions are aligned and enters the liquid crystal light valve 16G.

Here, a dichroic mirror DM ₃ which transmits light of a blue component and reflects light of a red component is provided in the emission direction of the liquid crystal light valve 16B, and the dichroic mirror DM ₃ is transmitted in the transmission direction. Is provided with a dichroic mirror DM ₄ which transmits light of blue component and red component and reflects light of green component.

Therefore, the blue image light B ₂ emitted from the liquid crystal light valve 16B is dichroic mirror DM ₃
To reach the dichroic mirror DM ₄ . In addition, the red image light R emitted from the liquid crystal light valve 16R
₂ is reflected by the dichroic mirror DM _3, and reaches the dichroic mirror DM _4. On the other hand, the green image light G ₂ emitted from the liquid crystal light valve 16G and including the green image information based on the green image signal is reflected by the mirror M ₃ provided in the emission direction of the liquid crystal light valve 16G, and then the dichroic mirror DM ₄ is emitted. Reach

The dichroic The blue image light B ₂ and the red image light R ₂ reaching the dichroic mirror DM _4, transmitted through the dichroic mirror DM _4, On the other hand, the dichroic mirror DM ₄
The green image light G _{2 that} has reached the level is the dichroic mirror DM.
_The light is reflected by ₄ and enters the projection lens 17. Then, the blue image light B ₂ , the red image light R ₂ , and the green image light G ₂ incident on the projection lens 17 are projected toward a screen (not shown).

Next, the linear polarization conversion prism used in the above liquid crystal projector will be described in detail with reference to FIG. Each linear polarization conversion prism 15B, 15
R and 15G are, as shown in FIG. 1, a polarization splitting prism 1 having a polarization splitting surface 1a for splitting an incident light beam into P polarization and S polarization, and a side of the polarization splitting prism 1 on which S polarization exits. It has a right-angle prism 2 having a reflecting surface 2a and a reflecting surface 2b, and a deflecting prism 5 having a total reflecting surface 5a on the side from which P-polarized light exits. Then, the polarization separation prism 1
Between the right-angled prism 2 and the right-angled prism 2 are half-wave plates 3 and 1 having an optical axis inclined by 45 ° with respect to the polarization direction of S-polarized light.
A half-wave plate and a glass plate 4 having the same thickness are provided.

The polarization separating prism 1 is formed by laminating two right-angle prisms, and the laminating surface has
A polarization splitting surface 1a, which is a thin film that transmits the P-polarized component and reflects the S-polarized component, is deposited. In addition,
As shown in FIG. 2, the linear polarization conversion prism 15B provided in the liquid crystal projector in this embodiment,
Since 15G and 15R are provided for the three color-separated blue light, green light, and red light, respectively, the polarization splitting surface 1a has a center wavelength (reference wavelength) of the color light of each color. It is desirable that the configuration is such that the effect of separating P-polarized light and S-polarized light is maximized. Then, the half-wave plate 3 in the linear polarization conversion prisms 15B, 15G and 15R is
It is desirable that the action of rotating the polarization direction of the linearly polarized light by 90 ° is maximized with respect to the center wavelength of the color light of each color.

The illumination lights La and Lb incident on the linearly polarized light conversion prism having the above-mentioned configuration are P-polarized LaP ₁ and LbP ₁ and S-polarized L on the polarization splitting surface 1a of the polarization splitting prism 1.
It is separated into aS ₁ and LbS ₁ . The P-polarized light LaP ₁ and LbP ₁ are emitted from the polarization splitting prism 1, and the S-polarized light LaS ₁ and LbS _{1 are} emitted.
Faces the right-angled prism 2. One S-polarized light LaS ₁ reflected by the polarization splitting surface 1a enters the half-wave plate 3 and
It is converted to P-polarized LaP ₂ . After that, the P-polarized light LaP ₂ converted by the ½ wavelength plate is totally reflected by the second reflection surface 2b and the first reflection surface 2a of the right-angle prism 2, and the polarization separation prism is formed through the glass plate 4. Pass 1.

Here, the glass plate 4 has a half-wave plate 3 between the polarization separation prism 1 and the rectangular prism 2 so that the linear polarization conversion prism does not have a discontinuous surface such as a step.
It is provided with the same thickness as. If between the two prisms,
If there is a discontinuous surface such as a step, light rays may be diffusely reflected by the discontinuous surface, and the light intensity of the light flux passing therethrough may become uneven. Therefore, the glass plate 4 has a function of preventing this problem. Have

The other S-polarized light LbS ₁ reflected by the polarization splitting surface 1a, after passing through the glass plate 4, is totally reflected by the second reflecting surface 2b and the first reflecting surface 2a of the rectangular prism 2. Then, the light enters the half-wave plate 3 and is converted into P-polarized light LbP ₂ . Then, the P-polarized light LbP ₂ passes through the polarization separation prism 1. P-polarized LaP that has passed through the polarization splitting surface 1a
₂ and P-polarized light LbP ₂ are emitted from the polarization separation prism 1 and are incident on the deflection prism 5. And P-polarized LaP ₂
And the P-polarized light LbP ₂ travel at 90 ° on the total reflection surface 5a.
It is bent and emitted from the deflection prism 5.

By the linear polarization conversion prism described above, a parallel light beam having a uniform polarization direction is supplied to the liquid crystal light valve of the liquid crystal projector. Then, the linear polarization conversion prism according to the present embodiment emits a light flux in the same direction as the traveling direction of the illumination light flux even if the illumination light flux is obliquely incident. Therefore, for example, as shown in FIG. 4, even if the linear polarization conversion prism 16 is obliquely attached to the liquid crystal light valve 15, the direction of the emitted light beam is the same as the direction of the incident light beam. Therefore, the tolerance of the parallelism between the liquid crystal light valve 15 and the linear polarization conversion prism 16 becomes loose.

[0023]

According to the present invention, it is possible to realize a polarized illumination optical system capable of illuminating a polarized light beam having a uniform polarization direction with a small loss of the light amount of the illumination light source and a high illumination efficiency. Moreover, in the polarized illumination optical system of the present invention, since the direction of the incident light beam and the direction of the emitted light beam are parallel to each other, it is not necessary for the parallel light beam from the light source to strictly enter the polarized illumination optical system vertically. Therefore, the tolerance of the parallelism between the liquid crystal bulb of the liquid crystal projector and the polarized illumination optical system can be relaxed at the time of assembly, which facilitates manufacturing.

[Brief description of drawings]

FIG. 1 is a plan view of a linear polarization conversion prism of the present invention.

FIG. 2 is a plan view showing an example in which a polarized illumination optical system of the present invention is provided in a liquid crystal projector.

FIG. 3 is a plan view illustrating a state when a light beam obliquely enters the linear polarization conversion prism of the present invention.

FIG. 4 is a diagram illustrating a state in which the linear polarization conversion prism of the present invention is obliquely attached to a liquid crystal projector.

FIG. 5 is a diagram illustrating the principle of TN liquid crystal.

[Explanation of symbols for main parts]

1 ‥‥ polarization separating prism 2 ‥‥ rectangular prism 3 ‥‥ 1/2 wave plate 4 ‥‥ glass plate 5 ‥‥ deflecting prism La, Lb ‥‥ illumination beams LaS _1, LbS ₁ ‥‥ S polarized light LaP _1, LaP ₂ , LbP ₁ , LbP ₂ ... P polarized light

Claims (1)

[Claims] 1. A polarization separation optical system for converting an illumination light beam from a light source into a linearly polarized light beam and irradiating the liquid crystal light valve of a liquid crystal projector with the polarization beam splitting prism for separating the illumination light beam into S-polarized light and P-polarized light. And a right-angled prism having a first reflective surface and a second reflective surface orthogonal to each other for re-incident the S-polarized light on the polarized light separating prism. Reflective surface and the second
Half-wave plate for converting S-polarized light, which is directed toward the polarization splitting prism again through the reflection surface of P to P-polarized light, and for converting S-polarized light, which is directed from the polarization splitting prism to the second reflective surface, to P-polarized light. Is provided between the polarization splitting prism and the right-angled prism, and makes the emission directions of the P-polarized light converted by the half-wave plate and the P-polarized light split by the polarization splitting prism parallel to each other. Is provided adjacent to the polarization separation prism.