JPH0830790B2 - Polarization conversion optical system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polarization conversion optical system capable of converting indefinite polarized light from a light source into linearly polarized light with high light utilization efficiency.

(Prior Art) In recent years, an image projection device has become popular as an example of a display device that can display a large area image on a screen by using a matrix type image display device using twisted nematic liquid crystal as a light valve. However, in this image projection apparatus, it is necessary to obtain a bright display screen by using linearly polarized light as light for image projection.

Further, not only the image projection device but also an optical computer, an image pickup device, various display devices other than the display device, etc. often require linearly polarized light having a bright performance.

The present applicant has previously proposed, as various means for obtaining a polarization conversion element capable of converting indefinitely polarized light into linearly polarized light with high light utilization efficiency and a display device using this means, in Japanese Patent Application No.
There is one as shown in FIG. 3 proposed in 316303.

For example, the polarization conversion element PCE shown in FIG. 3 which can convert indefinite polarized light into linearly polarized light includes a first polarization beam splitter PBS ₁ into which indefinite polarized light is incident and the first polarization beam splitter PBS. the second polarization beam splitter PBS ₂ to P-polarized light emitted from the ₁ enters, the P polarized light into S-polarized light the second P-polarized light emitted from the polarizing beam splitter PBS ₂ is incident A component used as an optical member that is converted and is incident on the second polarization beam splitter PBS ₂ , that is, the electrode Et and the light modulation material layer member.
It is composed of a PML, a reflecting mirror M (for example, a dielectric mirror), and a component portion including an electrode Er.

In the operation of the polarization conversion element PCE having the above configuration, the indefinite polarized light from the light source (not shown) incident on the first polarization beam splitter PBS ₁ is separated into S polarized light and P polarized light. That is, the polarization beam splitter PBS ₁ is
One of the hypotenuses of the two right-angle prisms is coated with a semi-transparent film made of a dielectric multilayer film or the like to join the hypotenuses together, and the incident indefinite polarized light can be separated into S-polarized light and P-polarized light. It is a thing. Here, the S-polarized light separated by the first polarization beam splitter PBS _{1 is referred} to as S _1- polarized light, and the P-polarized light is referred to as P _1- polarized light. The S ₁ polarized light is immediately emitted from the first polarization beam splitter PBS ₁ as shown.

Then, the P ₁ polarized light incident on the second polarized beam splitter PBS ₂ from the _first polarized beam splitter PBS ₁ is transmitted through the second polarized beam splitter PBS ₂ to generate the P polarized light (P ₁ polarized light). ) Is converted into S-polarized light and is incident on the electrode Et side of the optical member. This converted S-polarized light is hereinafter referred to as S ₂ -polarized light.

In the above optical member, a light modulation material layer member PML and a reflecting mirror M (for example, a dielectric mirror) are arranged between an electrode Et and an electrode Er, and an electric field from a power supply Vac is applied.
Here, the P ₁ polarized light incident on the electrode Et side is electrode Et → light modulation material layer member PML → reflecting mirror M → light modulation material layer member PML → electrode Et.
When reciprocating through the optical member and entering the _second polarizing beam splitter PBS ₂ again, an electric field is applied so that the P ₁ polarized light is converted into the S ₂ polarized light. . S _2-polarized light incident on the second polarizing beam splitter PBS ₂ is emitted from the second polarization beam splitter PBS ₂ is reflected by the second polarization beam splitter PBS _2. The S ₂ polarized light emitted from the second polarization beam splitter PBS ₂ is parallel linearly polarized light in the same traveling direction as the S ₁ polarized light emitted from the first polarization beam splitter PBS ₁ described above. is intended to be made, thus indefinite polarized light incident on the first polarization beam splitter PBS ₁ is different first, second polarization beam splitter PBS _1, respectively from PBS ₂ S ₁ polarized light,
It is emitted as S ₂ polarized light.

Further, the S ₁ polarized light and S ₂ polarized light emitted from the first and second polarization beam splitters PBS ₁ and PBS ₂ are made incident on the liquid crystal panel 101 serving as a light valve, and a projection lens (not shown),
The display device 100 is capable of magnifying and projecting using a screen. Then, a very bright image or the like can be obtained on the screen.

(Problems to be Solved by the Invention) In the polarization conversion element PCE and the display device 100 as an example of the previously proposed technique shown in FIG. 3, the indefinite polarized light can be converted into the linearly polarized light with high light utilization efficiency. The S ₁ polarized light emitted from the _first polarization beam splitter PBS ₁ and the S ₂ polarized light emitted from the second polarization beam splitter PBS ₂ have very different illuminance characteristics. The reason for this is
When S ₂ polarized light is produced, the light quantity is attenuated because it makes a round trip in the optical member. Therefore, the light flux incident on the liquid crystal panel 101 may be slightly different above and below the liquid crystal panel 101 in the figure, and a high quality image may not be obtained on a screen (not shown).

In addition, the boundary surface between the first polarization beam splitter PBS ₁ and the second polarization beam splitter PBS ₂ becomes a shadow, and the emitted light flux appears to be split into two systems, and even on a screen not shown. In some cases, the image is projected in a state of being separated into an upper part and a lower part. That is, the emitted S ₁ -polarized light and S ₂ -polarized light are as if they were in one system, but are essentially two systems of light flux.

Further, since the two polarization beam splitters of the first polarization beam splitter PBS ₁ and the second polarization beam splitter PBS ₂ are used, the dielectric multilayer film formed on the oblique side of the polarization beam splitters PBS ₁ and PBS ₂ described above. The angle characteristics such as the above become a problem, and color shading (color unevenness) may occur in an image or the like on a screen (not shown).

An object of the present invention is to provide a polarization conversion optical system that solves the above problems.

(Means for Solving the Problems) The present invention has been made in view of the above problems, and an invention according to claim 1 is: two linearly polarized lights whose polarization directions are orthogonal to each other A polarization beam splitter that separates the light into S-polarized light and P-polarized light, a means that makes one of the separated S-polarized light and P-polarized light the same polarization plane as the other, and A polarized light mixing / combining means for mixing and combining the polarized light of the two systems through an optical path means for guiding the polarized light of the first system and the polarized light of the second system, which have the same polarization plane. The polarized light mixing / combining means reflects the polarized light of the first system in which a plurality of pairs of the polarized light of the first system and the polarized light of the second system are alternately arranged so as to be parallel to each other. Reflection surface and a second reflection surface that reflects the polarized light of the second system The invention according to claim 2 is characterized in that the angle formed by the first reflecting surface and the second reflecting surface is 120 degrees. The polarization conversion optical system according to claim 1 is provided.

(Example) An example of a polarization conversion optical system according to the present invention will be described in detail below with reference to FIGS. 1 and 2.

FIG. 1 is a longitudinal sectional view showing the construction of a polarization conversion optical system according to the present invention, and FIG. 2 is a partially enlarged view of the wavy mirror shown in FIG.

In FIG. 1, indefinite polarized light emitted from a light source such as a halogen lamp or a xenon lamp, which is not shown, passes through a condenser lens (not shown) to become an indefinite polarized light of a parallel light beam, and this indefinite polarized light is emitted from the polarization beam splitter 1. It is incident on the vertical surface 1a in the figure. The polarization beam splitter 1 is formed by joining two right-angle prisms 1A and 1B, that is, a half-layered structure made of a dielectric multilayer film or the like on either the hypotenuse 1e of the right-angle prism 1A or the hypotenuse 1f of the right-angle prism 1B. Means for separating incident indefinite polarized light into two linearly polarized lights, S-polarized light and P-polarized light, whose polarization directions are orthogonal to each other, by coating a film and joining hypotenuses 1e and 1f Is. Further, the surfaces 1a, 1b, 1c, 1d of the polarization beam splitter 1 are formed in, for example, a cubic shape (a square in a sectional view) by connecting them in a clockwise order in the above order and at right angles as shown in the drawing.

Here, the light fluxes of S-polarized light (hereinafter referred to as first S-polarized light) and P-polarized light (hereinafter referred to as first P-polarized light) separated by the polarization beam splitter 1 will be described later. The optical path system is divided into two systems and proceeds.

That is, the first S-polarized light is emitted from the surface 1b of the polarization beam splitter 1, and is directed to the 45 ° mirror 2 which is disposed above the surface 1b in the figure and is inclined 45 ° with respect to the surface 1b. The light is made incident, reflected there, and made incident on a 30 ° mirror 3 which is disposed facing the 45 ° mirror 2 at a distance and is inclined by 30 °. Furthermore, the first reflected by the 30 ° mirror 3
The S-polarized light is incident on a wavy mirror 4 which is arranged at a lower left portion of the 30 ° mirror 3 with a space therebetween and which is vertically arranged. As shown, the wavy mirror 4 is formed by a plurality of triangular mirror surfaces 4a. This mirror surface
4a is for a plurality of mirrors are connected, i.e. without the mirror surface 4a ₁ and the mirror surface 4a ₂ and are connected by symmetrical triangular shape and the mirror surface 4a ₁ and the mirror surface 4a ₂ alternating Are connected to each other.

On the other hand, the first P-polarized light separated by the polarization beam splitter 1 is emitted from the surface 1c of the polarization beam splitter 1 facing the surface 1a, and λ / is arranged in parallel to the surface 1c. 2 It is incident on the plate 5. Here, the first P-polarized light is transmitted through the λ / 2 plate 5 so that the S-polarized light (hereinafter referred to as the second P-polarized light).
(Hereinafter referred to as S-polarized light). That is, λ / 2
The plate 5 is means for making the polarization angle of either S-polarized light or P-polarized light separated by the polarization beam splitter the same as that of the other. Note that the above means λ
Without using the / 2 plate 5, for example, a mica plate, a Fresnel-Rom prism, a quartz wave plate, and the P described in the previously proposed technique.
An optical member or the like that converts polarized light into S-polarized light may be used instead, and is not limited.

The converted second S-polarized light is incident on a 45 ° mirror 6 which is arranged to face the surface 5a of the λ / 2 plate 5 with a space therebetween and which is inclined by 45 ° in the vertical direction. The second S-polarized light reflected by the 45 ° mirror 6 is incident on a 45 ° mirror 7 arranged below and facing the 45 ° mirror 6 in parallel at a distance. The second S-polarized light reflected by is incident on a 30 ° mirror 8 which is disposed facing the 45 ° mirror 7 with a space therebetween and is inclined by 30 °.
Then, the second S-polarized light reflected by the 30 ° mirror 8 is incident on the above-mentioned wavy mirror 4 which is arranged on the upper left side of the 30 ° mirror 8 with a space therebetween and which is vertically arranged. . The 30 ° mirror 8 is arranged vertically symmetrically with respect to the 30 ° mirror 3 described above with respect to the wavy mirror 4.

Then, when the first S-polarized light reflected by the mirror 3 and the second S-polarized light reflected by the 30 ° mirror 8 are incident on the wavy mirror 4, the mirror surface 4a of the wavy mirror 4 is formed.
Is reflected by. The light beam separated by the wavy mirror 4 into two optical path systems becomes a substantially one system light beam.

That is, the first S on the mirror surface 4a ₁ side of the mirror surface 4a
The polarized light is reflected, the second S-polarized light is reflected on the mirror surface 4a ₂ side, and the first S-polarized light and the second polarized light are mixed and synthesized as shown in the figure, and there is almost one system of parallel light fluxes. The linearly polarized light of the S-polarized light (hereinafter referred to as the third S-polarized light) is obtained. Since this third S-polarized light is mixed and synthesized, it becomes a substantially uniform linearly polarized light, and it is possible to apply the third S-polarized light to a display device or the like as shown in the conventional example by utilizing this third S-polarized light. Becomes

Further, in the above-mentioned structure, the 45 ° mirrors 2, 6, 7 and 30 ° mirrors 3, 8 used in the optical path respectively emit the light fluxes of the first S-polarized light and the second S-polarized light. It serves as an optical path means for carrying the light flux of two systems. Incidentally, the optical path means may be constituted by a prism without using the above-mentioned mirror, and is not limited.

The light flux incident on the wavy mirror 4 is reflected by the mirror surface 4a.
The angle condition of the wavy mirror 4 for being reflected by the mirror surfaces 4a ₁ and 4a ₂ to become a parallel light flux will be described with reference to FIG.

Further, as shown in the drawing, the reflected light beam from the mirror surface 4a of the wavy mirror 4 has a condition (first condition) for traveling horizontally to the right, that is, θ ₁ + θ ₂ = 90 ° θ ₃ + θ ₂ = 90 °, that is, θ ₁ = θ ₃ .

Further, the condition (second condition) that the wavy mirror 4 is uniformly incident on the mirror surface 4a is that the incident light flux is a slope (4a) of the mirror surface 4a.
Must be parallel to ₁ , 4a ₂ ).

That is, θ ₁ = θ ₄ .

Also, from 2θ ₃ + θ ₄ = 90 ° to 2θ ₃ + θ ₁ = 90 °.

Here, since θ ₁ = θ ₃ of the first condition, 2θ ₃ + θ ₃ = 90 °, and therefore θ ₃ = 30 °.

In the polarization conversion optical system configured as described above, λ / 2 arranged facing the surface 1c of the polarization beam splitter 1
By moving the plate 5 to the surface 1b side and disposing it so as to face the surface 1b, the S-polarized light emitted from the surface 1b of the polarization beam splitter 1 is converted into P-polarized light by the λ / 2 plate 5. At the same time, the P-polarized light is emitted from the surface 1c, and the light flux reflected from the mirror surface 4a of the wavy mirror 4 is a linearly polarized light of P-polarized light composed of parallel light fluxes that are mixed and combined. There is no problem with using the P-polarized light that is mixed and synthesized.

Further, according to the polarization conversion optical system of the present invention configured as described above, the indefinite polarized light from the light source can be converted into a single polarization beam splitter without using a plurality of polarization beam splitters as shown in the above proposed technique. 1, linearly polarized light of S-polarized light or P-polarized light that is mixed and composed of parallel light beams is obtained.

Therefore, the mixed and combined linearly polarized light of S-polarized light or P-polarized light does not have different illuminance characteristics as shown in the above-mentioned proposed technique, and bright illuminance characteristics with high light utilization efficiency can be obtained.

Further, since the linearly polarized light of the S-polarized light or the P-polarized light is mixed and synthesized, the light flux of the finally-polarized linearly-polarized light as shown in the above proposed technique is separated into two systems. This is not the case, and a substantially uniform luminous flux of one system is obtained, and when applied to, for example, a display device, good performance quality can be obtained. If the two linearly polarized light paths are different from each other, or if they are not perfectly parallel light,
The intensity of the light beam reflected by the mirror 4 _a1 of the wavy mirror and that of the light beam reflected by the mirror 4 _a2 may be slightly different, or the light beam may spread, which may cause uneven illumination in the linearly polarized light. The unevenness of illuminance can be reduced by narrowing the pitch. For example, when the pitch is set to about 0.2 mm, it is possible to obtain good linearly polarized light in which uneven illuminance is not noticeable.

Further, by using the single polarization beam splitter 1, the angle characteristic of the dielectric multilayer film or the like attached to the hypotenuses of the plurality of polarization beam splitters as shown in the above-mentioned proposed technique is relaxed as compared with the case of using two. The mixed and combined linearly polarized light of S-polarized light or P-polarized light becomes a substantially uniform light flux and also reduces color shading. Therefore, when applied to, for example, a display device or the like, a good performance quality is obtained. Obtainable.

(Effect of the Invention) As described in detail above, according to the polarization conversion optical system of the present invention, in the first aspect, the indefinite polarized light from the light source is a plurality of polarized light beams as shown in the above-mentioned proposed technique. By using a single polarization beam splitter without using a beam splitter, mixed and combined linearly polarized light of S-polarized light or P-polarized light can be obtained.

Therefore, the mixed and combined linearly polarized light of S-polarized light or P-polarized light does not have different illuminance characteristics as shown in the above-mentioned proposed technique, and bright illuminance characteristics with high light utilization efficiency can be obtained.

Further, since the linearly polarized light of the S-polarized light or the P-polarized light is mixed and synthesized, the light flux of the finally-polarized linearly-polarized light as shown in the above proposed technique is separated into two systems. This is not the case, and a substantially uniform luminous flux of one system is obtained, and when applied to, for example, a display device, good performance quality can be obtained.

Furthermore, by using a single polarization beam splitter, the angular characteristics of a dielectric multilayer film or the like attached to the hypotenuses of a plurality of polarization beam splitters as shown in the above-mentioned proposed technique are alleviated more than when two are used. Since the mixed and combined linearly polarized light of S-polarized light or P-polarized light becomes a substantially uniform luminous flux and the color shading is reduced, a good performance quality can be obtained when it is applied to, for example, a display device as in the above. be able to.

Further, according to the second aspect, by using the wavy mirror, it is possible to obtain the linearly polarized light which is the S-polarized light or the P-polarized light that is mixed and composed of parallel light beams.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing the construction of a polarization conversion optical system according to the present invention, FIG. 2 is a partially enlarged view of the wavy mirror shown in FIG. 1, and FIG. 3 is a conventional example. It is the figure which showed the structure of the polarization conversion element and the display apparatus to which the polarization conversion element is applied. 1 ... Polarizing beam splitter, 3 ... 30 ° mirror, 4 ...
… Wavy mirror, 5 …… λ / 2 plate, 8 …… 30 ° mirror.

Claims (2)

[Claims] 1. A polarization beam splitter that separates indefinite polarized light from a light source into two linearly polarized lights, S polarized light and P polarized light, whose polarization directions are orthogonal to each other, and the separated S polarized light. And a means for making one of the P-polarized light polarization planes the same as the other, and a first series of polarized light and a second polarization light having the same polarization plane as each other.
And polarized light mixing / combining means for mixing and combining the polarized light of the two systems via an optical path means for guiding the polarized light of the system of the first system. Light and second
A first reflecting surface for reflecting the polarized light of the first system and a second reflecting surface for reflecting the polarized light of the second system, which are alternately arranged so as to be parallel to the polarized light of the system A polarization conversion optical system characterized in that 2. The polarization conversion optical system according to claim 1, wherein the angle formed by the first reflecting surface and the second reflecting surface is 120 degrees.