JP2008165066A - Projection type image projection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection type image projection device having a polarization separation means, in which light quantity loss in the polarization separation means can be reduced. <P>SOLUTION: The projection type image projection device 100 spatially modulates linearly polarized illumination light in a reflection type image display element 5 and projects the modulated light as reflection light exhibiting an image. The image projection device 100 includes: a polarization separation element 2 which transmits or reflects illumination light and reflection light reflected by a display surface 5a of the reflection type image display element 5 depending on the polarization direction; and a polarization direction rotating means 4 which is positioned between the polarization separation element 2 and the reflection type image display element 5 and rotates the polarization direction of reciprocally transmitted light by 90° around the optical axis, wherein the direction of bisecting an angle formed between the axial principal ray of the illumination light which is transmitted by a polarization separation surface 2a of the polarization separation element 2 and is made incident on the display surface 5a and the axial principal ray of reflection light reflected by the display surface 5a is caused to substantially match the direction of the optical axis of the polarization direction rotating means 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a projection type image projection apparatus.

Conventionally, in a projection type image projection apparatus using a reflective image display element, for example, a device such as a DMD (Digital Micromirror Device), illumination light having a large F number is incident on the reflective image display element at a shallow incident angle. Therefore, it is known that an optical path separating means for separating the optical path of illumination light and the optical path of reflected light from the reflective display element is disposed in the vicinity of the reflective display element.
For example, Patent Document 1 discloses, as such an optical path separation means, a polarization separation prism having a polarization separation surface for separating a light beam incident on the DMD and a light beam emitted from the DMD, and the polarization separation surface. An optical system for a projector provided with a polarization direction rotating means for rotating the polarization direction between the DMD and a projector apparatus (projection-type image projection apparatus) using the same is described.
JP 2004-101826 A

However, the conventional projection type image projection apparatus as described above has the following problems.
In the technique described in Patent Document 1, a polarization separation prism is used. For this reason, the polarization separation surface, for example, a dielectric multilayer film, uses one incident surface as a reference incident surface, transmits (reflects) the s-polarized component of this reference incident surface to the maximum, and reflects the p-polarized component to the maximum. Reflective transmittance characteristics are imparted (transmitted).
When incident light is incident on an incident surface that intersects with the reference incident surface, the s-polarized component and the p-polarized component are mixed, so that the polarization separation characteristic is deteriorated.
Further, when the light incident on such an incident surface is reflected by the polarization separation surface, the polarization direction of the light rotates around the optical axis of the light. When reflected by the DMD and transmitted through the polarization direction rotating means, it is further rotated by 90 ° around the optical axis with respect to the changed polarization direction.
For this reason, if the reflection direction of the light beam by the DMD is the same as the incident direction, the light is reflected by the polarization separation surface and rotated by 90 ° around the optical axis with respect to the polarization direction, and thus transmitted without loss of light amount. However, when the incident angle with respect to the reflection surface of the DMD is not 0 °, the polarization direction is different from the polarization direction that is efficiently transmitted at the re-incidence position of the polarization separation surface, and a light amount loss occurs.
Therefore, in the configuration of Patent Document 1, the optical path is efficiently separated by the polarization separation plane in the plane including the axial principal ray of the illumination light and the optical axis of the illumination light and the projection light. The light beam has a problem of causing a light amount loss when incident on and transmitted through the polarization separation surface.

  The present invention has been made in view of the above-described problems, and provides a projection type image projection apparatus capable of reducing a light amount loss in the polarization separation unit in the projection type image projection apparatus including the polarization separation unit. For the purpose.

In order to solve the above-described problems, a projection-type image projection apparatus according to the present invention is a projection-type projection apparatus configured to spatially modulate linearly polarized illumination light in a reflection-type image display element and project it as reflected light representing an image. An image projection apparatus, wherein the illumination light and the reflected light reflected by the display surface of the reflective image display element are transmitted or reflected on a polarization separation surface according to the polarization direction, A polarization direction rotating means that is positioned between the polarization separating means and the reflective image display element and that rotates the polarization direction of the reciprocating light 90 degrees around the optical axis, and the polarization separating surface of the polarization separating means The angle formed by the axial principal ray of the illumination light that is transmitted through and incident on the display surface of the reflective image display element and the axial principal ray of the reflected light reflected by the display surface is 2 etc. Dividing direction and the polarization direction A direction of the optical axis of the rolling means so as to substantially coincide, a configuration of arranging the polarization separating means and said polarization direction rotating means with respect to the reflection type image display device.
According to the present invention, linearly polarized illumination light is incident in accordance with the polarization separation direction of the polarization separation means. Then, the light is incident on the display surface of the reflective image display element via the polarization direction rotating means by being transmitted or reflected by the polarization separating means. The reflected light reflected by the display surface is incident again on the polarization direction rotating means and the polarization direction is rotated by 90 °, and thus is polarized and separated by the polarization separating means. At this time, the direction in which the angle formed by the axial principal ray of the illumination light incident on the display surface of the reflective image display element and the axial principal ray of the reflected light reflected by the display surface is equally divided into two, and the polarization direction Since the direction of the optical axis of the rotating means is substantially the same, the change of the polarization direction due to the oblique incidence of the illumination light to the polarization separation means and the change of the polarization direction due to the oblique incidence of the reflected light re-entering the polarization separation means Is substantially symmetric, so that it becomes possible to reduce or eliminate the change of the respective polarization directions by the polarization direction rotating means, and as a result, the light quantity loss is reduced.

  According to the projection type image projection apparatus of the present invention, even if the polarization separation unit is used, the influence of the rotation of the polarization direction due to the incident direction on the polarization separation unit can be reduced or eliminated. There is an effect that it can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In all the drawings, even if the embodiments are different, the same or corresponding members are denoted by the same reference numerals, and common description is omitted.

[First Embodiment]
A projection type image projection apparatus according to a first embodiment of the present invention will be described.
FIG. 1A is a schematic front view showing a schematic configuration of a projection type image projection apparatus according to the first embodiment of the present invention. FIG.1 (b) is AA sectional drawing of Fig.1 (a). FIG. 2 is a perspective view showing a schematic configuration of polarization separation means used in the projection type image projection apparatus according to the first embodiment of the present invention.
For convenience, in order to refer to relative directions in each drawing, an XYZ orthogonal coordinate system corresponding to each positional relationship is shown. Hereinafter, unless there is a possibility of misunderstanding, the direction is referred to based on the coordinate axes (the same applies to the following drawings).
In this coordinate system, in FIG. 1A, the Z axis extends horizontally from the right to the left in the figure, the Y axis extends from the lower side to the upper side in the direction orthogonal to the Z axis, The X axis extends from the back side to the near side, and the paper surface is the YZ plane.

The projection type image projection apparatus 100 of the present embodiment can be suitably used as a projection type image projection apparatus such as a video projector or a projection television.
As shown in FIG. 1, the schematic configuration of the projection-type image projection apparatus 100 includes an illumination unit 1, a polarization separation element 2, a quarter wavelength plate 3, a polarization direction rotating unit 4, a reflection-type image display element 5, and projection optics. It consists of the system 6.
Reference numeral 7 in the drawing denotes a screen that displays a projection image of the projection type image projector 100. The screen 7 may be a transmissive screen or a reflective screen. When the screen 7 is a transmissive screen, it may be fixed to a housing (not shown) of the projection type image projection apparatus 100 and constitute a rear projection type image projection apparatus together with the projection type image projection apparatus 100. .

The illumination unit 1 emits, as illumination light, a light beam having a wavelength λ that has a substantially uniform light amount distribution and is linearly polarized.
Position of the illumination unit 1, as shown in FIG. 1 (a), FIG. 2, light L ₁ is an axial principal ray of the light beam emitted from the illumination unit 1, the XY plane, X-axis negative direction It is an arrangement position where the light advances obliquely from the side toward the Y-axis negative direction and enters the polarization separation element 2. The polarization direction of the light beam L ₁ is a direction parallel to the XY plane perpendicular to the optical axis as indicated by the double arrow in FIG. Angle light ray L ₁ intersects the Y axis, since it can be set as required, such as the convenience of the optical path layout, to reduce the incident angle to the reflection surface of the reflection type image display device 5, a shallow angle, e.g. A shallow angle of 15 ° or less is preferable.

The polarization separation element 2 reflects s-polarized light traveling on the axis P parallel to the Y-axis in the negative Y-axis direction, and reflects the axis Q parallel to the Z-axis approximately 100% in the negative Z-axis direction. This is a polarization separation prism having a polarization separation surface 2a made of a dielectric multilayer film that transmits substantially 100% of the p-polarized light going to step (b). In this embodiment, the outer shape is a rectangular parallelepiped.
Here, the plane formed by the axes P and Q constitutes a reference incident surface for defining the polarization separation characteristics by reflection and transmission on the polarization separation surface 2a. That is, in order to design the polarization separation plane with a dielectric multilayer film, the polarization directions of s-polarized light and p-polarized light that maximize the efficiency of polarization separation are defined. When the incident angle is constant, the light having the reference incident surface as the incident surface is polarized and separated with less light loss than the light having the surface intersecting the reference incident surface as the incident surface.

The first prism surface 2b between the polarization separation surface 2a and the illumination unit 1 constitutes an interface through which illumination light enters the polarization separation element 2, and in the present embodiment, the first prism surface 2b is a plane parallel to the ZX plane.
The second prism surface 2c between the polarization separation surface 2a and the quarter wavelength plate 3 constitutes an interface through which the light reflected by the polarization separation surface 2a is emitted from the polarization separation element 2, and in this embodiment, XY It consists of a plane parallel to the plane.
The third prism surface 2d, which is parallel to the second prism surface 2c and sandwiches the polarization separation surface 2a between the second prism surface 2c, projects light that passes through the polarization separation surface 2a from the Z-axis negative direction side. The interface which radiates | emits to is comprised.

In FIG. 2, broken lines P _s drawn on the first prism surface 2b and the second prism surface 2c are imaginary lines drawn for convenience to refer to the s-polarization direction of the reference incident surface of the polarization separation surface 2a. is there.
Note that the outer shape of the polarization separation element 2 is a rectangular parallelepiped, which is an example, and is not essential to the present invention. The first prism surface 2b, the second prism surface 2c, and the third prism surface 2d constituting the outer shape may be inclined at an appropriate angle as needed.
Further, in the following description, for simplification of description, refraction at the interfaces of the first prism surface 2b, the second prism surface 2c, the third prism surface 2d, etc. will be ignored.

The quarter-wave plate 3 is a quarter-wave plate with respect to the wavelength λ of the illumination light, and in the state where the direction of the main axis N is matched with the s-polarization direction of the polarization separation surface 2a, the Z-axis negative of the second prism surface 2c. It is arranged substantially parallel to the XY plane on the direction side.
The polarization direction rotating means 4 rotates the polarization direction of the reciprocating light by 90 ° around the optical axis, and is disposed substantially parallel to the negative side of the Z axis with respect to the quarter wavelength plate 3. That is, the optical axis of the polarization direction rotating means 4 is arranged parallel to the axis Q. As the polarization direction rotating means 4, for example, means such as an optical rotator using liquid crystal or the like can be adopted.

The reflective image display element 5 displays an image by spatially modulating the illumination light by controlling the reflection direction of a plurality of display elements arranged in a two-dimensional lattice pattern on the display surface 5a according to the display pixel. Is. In the present embodiment, a DMD (Digital) in which micromirrors (not shown) whose tilt angles are changed to two types of tilt angles, that is, an on state and an off state, are two-dimensionally arranged in a grid pattern as display elements. Micro mirror Device) is used.
In the present embodiment, the on-state micromirrors are aligned in the XY plane, and the off-state micromirrors are inclined with respect to the XY plane, so that the reflected light of the illumination light does not enter the projection optical system 6 described later. It is supposed to be reflected by the.
Further, the normal line of the reflecting surface of the micromirror in the on state is parallel to the reference incident surface of the polarization separation surface 2a. Therefore, the light beam incident on the on-state micromirror of the reflective image display element 5 is reflected in plane symmetry with respect to a plane parallel to the reference incident surface of the polarization separation surface 2a.

  In the drawing, the display surface 5a of the reflective image display element 5 and the reflective surface of the micromirror in the on state are drawn in the same plane, but this is an example and the micromirror in the on state is illustrated. May be inclined with respect to the display surface 5a. What is essential is the relationship between the normal of the micromirror in the on state and the reference incident surface.

The projection optical system 6 is reflected by the on-state micromirror of the reflective image display element 5 out of the illumination light irradiated on the reflective image display element 5, and the polarization direction rotating means 4, quarter wavelength plate 3, It is an optical element or an optical element group that enlarges and projects an image by light sequentially transmitted through the polarization beam splitting element 2 toward the screen 7.
In this embodiment, the optical axis 50 of the projection optical system 6 corresponds to the reflected optical axis of the reflected light by the micromirrors aligned on the XY plane, and the Z-axis positive direction from the X-axis negative direction side in the ZX plane. It arrange | positions in the direction which inclines toward the side.

  In the present embodiment, the polarization separation element 2, the quarter wavelength plate 3, and the polarization direction rotating means 4 are provided between the illumination unit 1 and the reflection type image display element 5, and between the projection optical system 6 and the reflection type image display element 5. The polarization separating means 20 is configured to separate the optical path of the illumination light and the optical path of the reflected light reflected by the reflective image display element 5 according to the polarization direction.

Next, the operation of the projection type image projector 100 according to the present embodiment will be described along the optical path with the operation of the polarization separation means as the center. Each light ray in the following description represents an axial principal ray of an optical system constituting the projection type image projector 100 unless otherwise specified.
FIGS. 3A and 3B are perspective explanatory views for explaining the operation of the polarization separation means of the comparative example according to the prior art. FIG. 4A is a conceptual diagram of polarization direction change for explaining the operation of the quarter-wave plate according to the first embodiment of the present invention. FIG. 4B is a conceptual diagram of polarization direction change for explaining the combined action of the quarter-wave plate and the polarization direction rotating means according to the first embodiment of the present invention.

As shown in FIG. 2, the light beam L ₁ emitted from the illumination unit 1 is linearly polarized in a direction perpendicular to the optical axis and parallel to the XY plane, and is inclined at a shallow angle with respect to the axis P in the XY plane. From this direction, the light enters the first prism surface 2b and reaches the point a on the polarization separation surface 2a. At point a, the polarization direction of the light beam L ₁ can also correspond to the deflecting surface of the s-polarized light of the polarization separation surface 2a, light L ₁ is reflected substantially 100% by the polarization separating surface 2a, as ray L _2, a second prism The light travels to a point b on the surface 2c and is emitted toward the quarter-wave plate 3.
At this time, since the incident surface with respect to the polarization separation surface 2a including the light beams L ₁ and L ₂ is slightly inclined with respect to the reference incident surface, the polarization direction of the light beam L ₂ is changed according to the inclination angle. Rotates with respect to the s-polarization direction. For example, at the point b, it rotates by an angle φ (°) clockwise as viewed from the negative direction of the Z-axis.
Here, light polarization direction of L _2, since the inclined with respect to the XY plane, but different in a strict sense of the rotation angle φ of the optical axis of the rotation angle and the XY plane, in this embodiment, light rays since the inclination angle relative to the axis Q of L ₂ is small, it has almost the same angle.

The light beam L ₂ travels in the ZX plane from the X-axis negative direction side toward the Z-axis negative direction side with a shallow angle α with respect to the axis Q, and is transmitted through the quarter-wave plate 3 and the polarization direction rotating means 4. Then, the light enters the reflective image display element 5 and illuminates the display surface 5a of the reflective image display element 5 together with other light beams.
Assuming that light L ₂ is incident on the micromirrors in the ON state, and at an incident angle α in the point d, is reflected as beam L ₃ in the direction of the exit angle α in the ZX plane. Then, in the ZX plane, proceed from the X-axis negative direction side to the Z-axis positive direction side with a shallow angle α with respect to the axis Q, and pass through the polarization direction rotating means 4 and the quarter-wave plate 3. , And enters the point f on the second prism surface 2c.
That is, the light beam L ₃ reaching the point f has been transmitted through the quarter-wave plate 3 and the polarization direction rotating means 4 in a reciprocating manner.

Here, the operation of the quarter wavelength plate 3 and the polarization direction rotating means 4 will be described.
First, with reference to FIGS. 3A and 3B, a change in polarization direction in an example in the case where the quarter wavelength plate 3 is not provided will be described. In FIG. 3A, for the sake of easy viewing, each light beam is displayed while being shifted from the axes P and Q which are actual optical paths.
As shown in FIG. 3A, consider a case where a light beam L ₁₀ traveling on the axis P is incident on the polarization separation element 2 instead of the light beam L ₁ . The polarization direction of the light beam L ₁₀ is matched to the s-polarization direction of the reference incident surface is reflected substantially 100% by the polarization splitting surface 2a, emitted from the second prism surface 2c as light ray L _20, changing the polarization direction Instead, the light passes through the polarization direction rotating means 4, is reflected as the light beam 30 by the reflective image display element 5, passes through the polarization direction rotating means 4 again, and reenters the second prism surface 2c.
At this time, the light beam L ₃₀ is reciprocally transmitted through the polarization direction rotating means 4 so that the polarization direction is rotated by 90 ° around the optical axis, and is in a direction perpendicular to the reflected polarization direction. For this reason, the light beam L _{30 that} has reached the polarization separation surface 2 a is transmitted approximately 100%, and is emitted as the light beam L ₄₀ from the third prism surface 2 d.
Therefore, the optical path of the light beam 10 and the optical path of the light beam 40 are polarized and separated without causing a substantial light amount loss.

FIG. 3B shows an example in which only the quarter wavelength plate 3 is removed from the present embodiment. In this case, since the light L ₂ is emitted in the same manner as in the present embodiment, the polarization direction of the light L ₂ is inclined by an angle φ with respect to the s-polarization direction of the reference incident surface of the polarization separation surface 2a. ing. Therefore, light rays L ₂ is the polarization direction rotating means 4, the reflection type image display device 5, as rays L ₃₁ through the polarization direction rotating means 4, and reaches the second prism surface 2c, the polarization of the light beam L ₃₁ at point f The direction is rotated by 90 ° around the optical axis, and is inclined by (90 ° −φ) with respect to the reflected polarization direction of the polarization separation surface 2a. Further, with respect to the direction orthogonal to the reflected polarization direction, the rotation is clockwise by φ as viewed from the negative Z-axis direction.
However, since the light beams L ₂ and L ₃ are in a plane-symmetrical positional relationship with respect to the reference incident surface of the polarization separation surface 2a, the polarization direction most efficiently reflected by the polarization separation surface 2a and the most efficiently transmitted light. The polarization direction is also symmetrical with respect to the reference entrance plane. Therefore, the polarization component having the polarization direction rotated counterclockwise by φ as viewed from the negative Z-axis direction with respect to the s-polarization direction of the reference incident surface at the point f is approximately 100% at the point g of the polarization separation surface 2a. A polarization component having a polarization direction reflected and rotated by φ counterclockwise as viewed from the Z-axis negative direction with respect to the direction (X-axis direction) orthogonal to the s-polarized light of the reference incident plane in the XY plane is approximately 100% will be transmitted.
Therefore, the light beam L ₃₁ has a polarization direction shifted by 2 · φ clockwise as viewed from the negative Z-axis direction with respect to the polarization direction of polarization separation at such a point g. Therefore, as shown in FIG. 3B, at the point g, the transmitted light L _41T and the reflected light L _41R are polarized and separated. Since this reflected light L _41R does not reach the projection optical system 6, the light amount is lost.

On the other hand, in this embodiment, between the light beams L ₂ and L ₃ between the polarization separation element 2 and the polarization direction rotating means 4, the main axis is 1/4 of the same direction as the s-polarization direction of the reference incident surface. due to the arrangement a wavelength plate 3, the polarization direction of the light beam L ₃ is corrected in the polarization direction that is most efficiently transmitted through the polarization separation surface 2a.
The quarter wave plate 3 converts linearly polarized light into elliptically polarized light or circularly polarized light according to the angle formed with the principal axis N, or vice versa. Since it works equivalently to a half-wave plate, it has the effect of turning the polarization direction of linearly polarized light around the principal axis N. That is, in the present embodiment, considering the case where the polarization direction rotating means 4 is deleted, as shown in FIG. 4A, the polarization direction p _f ′ of the light beam L _{3 at} the point f is the light beam L _{2 at the} point b. for folding the polarization direction p _b to the main axis N, the main axis N, is the same as that rotate as viewed from the Z-axis negative direction counterclockwise by an angle phi. Further, since the main axis N coincides with the normal direction of the reference incident surface, the quarter wavelength plate 3 has a function of symmetrically converting the linearly polarized light transmitted and received through the reference incident surface.

If the polarization direction rotating means 4 is inserted between the quarter-wave plate 3 and the reflective image display element 5 as in the present embodiment, since this is not linearly polarized light, it will be conceptual only. 4 (b), the polarization direction p _b is rotated by 90 ° around the optical axis by the polarization direction rotating means 4 and folded back with respect to the main axis N, so that the polarization direction pf of the point _f is changed to the X axis. On the other hand, the polarization direction conversion action equivalent to the rotation of the angle φ counterclockwise when viewed from the negative direction of the Z-axis is shown.
That is, the quarter-wave plate 3 and the polarization direction rotating means 4 change the polarization direction of the light that is polarized and separated by the polarization separation surface 2a toward the reflective image display element 5, and symmetrically transform the reference incident surface and the optical axis. The polarization direction correcting unit corrects the light by a conversion corresponding to a combined conversion with the 90 ° rotation conversion.

Therefore, as shown in FIG. 2, in this embodiment, the polarization direction of the light beam L ₃ coincides with the polarization direction that transmits approximately 100% at the point g of the polarization separation surface 2a, and is approximately 100% as the light beam L _4. The light is transmitted and emitted from the third prism surface 2d.
As shown in FIG. 1, the light beam L ₄ travels along the optical axis 50 of the projection optical system 6 and is projected onto the screen 7 by the projection optical system 6.
As described above, in the projection type image projection apparatus 100, even if the illumination light is incident from the direction intersecting the reference incident surface of the polarization separation element 2, the axial principal ray hardly loses the light amount in the polarization separation element 2. Is polarized and separated. For this reason, for example, the light amount loss is reduced as compared with a configuration in which the quarter wavelength plate 3 as shown in FIG. 3B is not provided in the optical path between the polarization separation element 2 and the polarization direction rotating means 4. Can do.

Such an action is achieved by arranging the reflection surface normal of the reflective image display element 5 so as to be parallel to the reference incident surface of the polarization separation element 2, and thereby allowing polarization on the optical path of the axial principal ray. The fact that the inclination of the direction is plane-symmetric with respect to the reference incident surface is utilized.
When such a positional relationship is not realized, a light amount loss occurs according to the amount of deviation. However, if the light amount loss is in an allowable range, the normal line of the reflective surface of the reflective image display element 5 is defined as the reference incident surface. It may be a substantially parallel positional relationship slightly inclined.

In the above description, the operation of the quarter wave plate 3 by the axial principal ray has been described. However, in the illumination light other than the axial principal ray, the light incident from the direction intersecting the reference incident surface is also the same. The light quantity loss is reduced by the correction action of the quarter-wave plate 3.
In the above description, the case where the incident surface of the reflective image display element 5 is set in the ZX plane and is in a positional relationship orthogonal to the reference incident surface has been described. An oblique state in which the incident surface of the reflective image display element 5 is rotated around the normal line of the reflective surface of the micromirror, for example, a point a that is the incident position on the polarization separation surface 2a in FIG. In the light beam passing through the optical path where the point g is shifted to the Y axis negative direction side on the positive direction side, the rotation of the polarization direction is not symmetric with respect to the reference incidence plane, so the rotation of the polarization direction is completely Although not corrected, the degree of rotation is reduced. Therefore, the light amount loss is reduced as compared with the case where the polarization direction correcting means is not provided.

Next, a first modification of the present embodiment will be described.
FIG. 5 is a perspective view showing a schematic configuration of the polarization separation means used in the projection type image projection apparatus according to the first modification of the first embodiment of the present invention.

This modification includes a polarization separation element 2A having a polarization separation surface 2e whose reference polarization direction is the direction of transmitted light, instead of the polarization separation element 2 of the above embodiment, and the polarization direction of the illumination light is the reference incident surface. P-polarized light. Therefore, the main axis N of the quarter-wave plate 3 is rotated by 90 ° in the XY plane in accordance with the polarization direction of the light reflected by the polarization separation surface 2e and traveling toward the reflective image display element 5, and the Y-axis direction Arrange along.
In FIG. 5, in order to help understanding of the polarization direction of the light reflected by the polarization separation surface 2e and traveling toward the reflective image display element 5, the virtual plane along the polarization plane of p-polarization of such a reference incident surface is used as a reference. A line is shown on each optical path as a broken line P _p . Dashed P _p on the second prism surface 2c is, knowing that is parallel to the main axis N of 1/4-wave plate 3, the purpose of illustration is achieved.

According to this modification, the light beam L ₁₃ that is the axial principal ray of the illumination light from the illuminating unit 1 is shallow with the axis P in the YZ plane from the Z-axis positive direction side to the Y-axis negative direction side. And enters the first prism surface 2b and reaches the point h on the polarization separation surface 2e.
Since the light beam L ₁₃ is p-polarized light, it is reflected almost 100% by the polarization separation surface 2e and emitted as a light beam L ₂₃ from the point i on the second prism surface 2c. 4, and reaches the reflective image display element 5. Then, it is reflected as a light beam L ₃₃ by the micromirror on the reflective image display element 5, retransmits the polarization direction rotating means 4 and the quarter wavelength plate 3, and reaches a point n on the second prism surface 2 c. .
Here, since the polarization direction of the point i is the X-axis direction, it is the same direction as the main axis N of the quarter-wave plate 3, so that the polarization direction of the point n is around the optical axis only by the polarization direction rotating means 4. It is rotated 90 ° and becomes the X-axis direction.
Therefore, the light beam L ₃₃ is transmitted through the polarization splitting surface 2 e at the point q approximately 100%, enters the projection optical system 6 along the optical axis 50 as the light beam L ₄₃ from the third prism surface 2 d, and enters the screen 7. Projected.

  Thus, in the present embodiment, the axial principal ray is polarized and separated with almost no light loss in the polarization separation element 2A. At this time, since the axial principal ray travels in the reference incident plane, it is not subjected to the polarization direction correcting action by the quarter wavelength plate 3. However, in the illumination light other than the axial principal ray, the light incident from the direction intersecting the reference incident surface rotates in the polarization direction as in the above embodiment, but receives the correction action of the quarter wavelength plate 3. Thus, light loss is reduced. Therefore, as a whole illumination light, light loss is reduced by the action of the quarter-wave plate 3.

[Second Embodiment]
A projection type image projection apparatus according to the second embodiment of the present invention will be described.
FIG. 6A is a schematic front view showing a schematic configuration of a projection type image projection apparatus according to the second embodiment of the present invention. FIG.6 (b) is BB sectional drawing of Fig.6 (a). FIG. 7 is a perspective view showing a schematic configuration of the polarization separation means used in the projection type image projection apparatus according to the second embodiment of the present invention. FIG. 8 is a conceptual diagram of polarization direction change for explaining the operation of the quarter-wave plate according to the second embodiment of the present invention.

  As shown in FIGS. 6A and 6B, the projection-type image projection apparatus 110 according to the present embodiment deletes the quarter-wave plate 3 from the projection-type image projection apparatus 100 according to the first embodiment. A quarter wave plate 9 is provided instead of the polarization direction rotating means 4. The polarization separation element 2 and the quarter wavelength plate 9 constitute a polarization separation means 21. Hereinafter, a description will be given centering on differences from the first embodiment.

  The quarter-wave plate 9 is a quarter-wave plate with respect to the wavelength λ of the illumination light, and as shown in FIG. 7, the direction of the principal axis N is inclined by approximately 45 ° with respect to the s-polarization direction of the reference incident surface. In this state, the second prism surface 2c is disposed substantially parallel to the XY plane on the Z axis negative direction side.

According to the configuration of the present embodiment, when the light beams L ₂ and L ₃ pass through the quarter-wave plate 3 and the polarization direction rotating means 4 in the first embodiment, the quarter-wave plate is used in the present embodiment. 9 is reciprocally transmitted.
At that time, as shown in FIG. 8, the light beam L ₂ is incident on the quarter-wave plate 9 with a polarization direction p _b rotated clockwise by 45 ° with respect to the main axis N when viewed from the Z-axis negative direction side. since the ray L ₃ is corrected to the polarization direction p _f folded back against the direction of the main axis N. Therefore, the polarization direction _pf is the same as the direction rotated by an angle φ counterclockwise when viewed from the Z axis negative direction side from the direction orthogonal to the s polarization direction of the reference incident surface. Therefore, the light beam L ₃ is transmitted through the polarization splitting surface 2 a substantially 100% and enters the projection optical system 6 along the optical axis 50, as in the first embodiment.
That is, the quarter wavelength plate 9 changes the polarization direction of the light that is polarized and separated by the polarization separation surface 2a and travels toward the reflective image display element 5 with this arrangement, symmetrical conversion with respect to the reference incident surface, and around the optical axis. Polarization direction correction means for correcting by a conversion corresponding to a combined conversion with a 90 ° rotation conversion is configured.

Such an action is achieved by arranging the reflection surface normal of the reflective image display element 5 so as to be parallel to the reference incident surface of the polarization separation element 2, and thereby allowing polarization on the optical path of the axial principal ray. The fact that the inclination of the direction is plane-symmetric with respect to the reference incident surface is utilized.
When such a positional relationship is not realized, the polarization direction of the incident light and the principal axis N are changed as in the case of using a quarter wave plate for polarization direction conversion in which the polarization direction is rotated by 90 ° around the optical axis by reciprocal transmission. If only 45 ° crosses, the polarization direction of the light beam L ₃ is rotated by 90 ° around the optical axis, and at the position where it is obliquely incident on the polarization separation surface 2a, it does not coincide with the polarization direction that is most efficiently polarized and separated. It is.
However, as long as the light loss can be tolerated, a substantially parallel positional relationship in which the normal line of the reflective surface of the reflective image display element 5 is slightly inclined with respect to the reference incident surface may be used.

  As described above, in the projection type image projection apparatus 110, for example, on the optical path between the polarization separation element 2 and the reflection type image display element 5 as shown in FIG. In addition, the light amount loss can be reduced as compared with the configuration having only the polarization direction rotating means 4.

[Third Embodiment]
A projection type image projection apparatus according to a third embodiment of the present invention will be described.
FIG. 9A is a schematic front view showing a schematic configuration of a projection type image projection apparatus according to the third embodiment of the present invention. FIG. 9B is a cross-sectional view taken along the line C-C in FIG. FIG.9 (c) is DD sectional drawing of Fig.9 (a). FIG. 10 is a perspective view showing a schematic configuration of the polarization separation means used in the projection type image projection apparatus according to the third embodiment of the present invention.

As shown in FIGS. 9A, 9 </ b> B, and 9 </ b> C, the projection type image projection apparatus 120 of the present embodiment is replaced with the polarization separation element 2 of the projection type image projection apparatus 100 of the first embodiment. In addition, a wire grid polarizer (hereinafter referred to as WGP) 8 is provided, and the quarter wavelength plate 3 is omitted. Hereinafter, a description will be given centering on differences from the first embodiment.
In the present embodiment, the illumination unit 1, the projection optical system 6, and the screen 7 are arranged in the same manner as in the first embodiment. However, since the illumination light from the illumination unit 1 guides the transmitted light of the WGP 8 to the reflection type image display element 5, the polarization direction rotating means 4 and the reflection type image display element 5 are arranged in parallel to the ZX plane. Has been.

As shown in FIG. 10, the WGP 8 arranges a plurality of metal wires 8A, which are thin metal wires, in parallel at a fine pitch on a substrate 8B made of an insulator, and the electric vector of light is orthogonal to the extending direction of the metal wires 8A. The TM polarization component is transmitted through approximately 100%, and the TE polarization component whose light electric vector is orthogonal to the TM polarization component is reflected by approximately 100%. The arrangement pitch of the metal wires 8A is appropriately set according to the wavelength λ of the illumination light of the illumination unit 1 so that the polarization separation efficiency is good.
Hereinafter, an incident surface that is parallel to the extending direction of the metal wire 8A and orthogonal to the substrate 8B is referred to as a reference incident surface of the WGP 8.
In the present embodiment, the substrate 8B is disposed so as to be orthogonal to the YZ plane and inclined to the ZX plane and the XY plane, respectively, and the normal V of the reflection surface of the reflective image display element 5 is parallel to the reference incident surface. Is arranged. That is, when TE polarized light passing through the axis V is reflected by the WGP 8, it travels along the axis U parallel to the Z axis.

  In the present embodiment, the WGP 8 and the polarization direction rotating means 4 are provided between the illumination unit 1 and the reflective image display element 5 and between the projection optical system 6 and the reflective image display element 5, and the optical path and reflection of the illumination light. The polarization separating means 22 is configured to separate the optical path of the reflected light reflected by the type image display element 5 in accordance with the polarization direction.

According to the projection-type image projecting apparatus 120, as shown in FIG. 10, light L ₁ is an axial principal ray of the illumination light from the illumination portion 1 which is linearly polarized in the X-axis direction, the XY plane X-axis negative From the direction side toward the Y-axis negative direction side, the vehicle proceeds while being inclined with respect to the reference incident surface.
Since the light beam L ₁ is TM polarized light with respect to the WGP 8, the light beam L ₁ is transmitted approximately 100% to the polarization direction rotating means 4 side as the light beam L ₂₄ . Since the polarization direction of the light beam L ₂₄ after transmission is the direction of the metal wire 8A of the WGP 8, TM polarization is maintained. This is because only the direction in which the metal wire 8A extends determines the polarization direction of the transmitted light and does not depend on the angle of the incident surface with respect to the metal wire 8A with respect to the reference incident surface.
Then, the light beam L ₂₄ passes through the polarization direction rotating unit 4, is reflected by the reflection surface in the ON state of the reflective image display element 5, and reenters the polarization direction rotating unit 4 as the light beam L ₃₄ .
The light beam L _{34 that} has passed through the polarization direction rotating unit 4 has its polarization direction rotated by 90 ° around the optical axis, and enters the polarization direction rotating unit 4 as TE polarized light. Therefore, the light beam L _{34 that} has become TE-polarized light is substantially 100% reflected by the WGP 8 and travels along the optical axis 50 as the light beam L ₄₄ . The light beam L ₄₄ enters the projection optical system 6 and is projected onto the screen 7. In this way, the light reflected by the reflective surface of the reflective image display element 5 in the illumination light from the illumination unit 1 is incident on the projection optical system 6 with almost no light loss caused by the WGP 8. Then, it is projected on the screen 7.

  As described above, according to the projection type image projector 120 of the present embodiment, the axial principal ray hardly loses light amount in the WGP 8 even when the illumination light is incident from the direction intersecting the reference incident surface of the WGP 8. Is polarized and separated. For this reason, for example, the light quantity loss can be reduced as compared with the configuration in which the polarization separation unit as shown in FIG. 3B is composed of only the polarization separation element 2 and the polarization direction rotation unit 4.

Further, when the WGP 8 is used as a polarization separation element as in this embodiment, the polarization direction of the reflected and transmitted light that is polarized and separated is the reference of the incident surface as in the case where the dielectric multilayer film is used as the polarization separation surface. Since the tilt angle with respect to the incident surface and the incident angle of the light beam do not matter, the degree of freedom in setting the optical path is improved.
For example, in the description of the present embodiment, as in the first and second embodiments, the normal line of the reflective surface in the ON state of the reflective image display element 5 is parallel to the reference incident surface of the WGP 8. As described in the example of the case, in the present embodiment, such a positional relationship is not essential, and can be modified into various positional relationships as necessary.

Next, a first modification of the present embodiment will be described.
FIG. 11A is a schematic side view of the polarized light separating means of the first modification of the third embodiment of the present invention. FIG. 11B is a schematic side view of the polarization separation means of the third exemplary embodiment of the present invention for comparison with FIG. FIG. 12 is a schematic graph for explaining the polarization separation efficiency of the third embodiment of the present invention and the first modification thereof. The horizontal axis represents the incident angle θ with respect to the metal grating polarization separation element, and the vertical axis represents the polarization separation efficiency (the same applies to FIG. 14). FIG. 13: is a typical side view which shows the other optical path of the polarization separation means of the 1st modification of the 3rd Embodiment of this invention. FIG. 14 is a schematic graph for explaining the polarization separation efficiency in the optical path arrangement of FIG.

In this modification, as shown in FIG. 11A, the extending direction of the metal wire 8A of the WGP 8 of the third embodiment is rotated 90 ° on the substrate 8B. That is, in the third embodiment, the incident surface of the light beam L ₁ that is the illumination light incident on the WGP 8 and the incident surface of the light beam L ₃₄ that is the reflected light reflected by the reflective image display element 5 on the WGP 8. Crossing, and the angle of intersection of these incident surfaces is equally divided into two, and with respect to an intermediate plane (a plane stretched by the axes U and V in FIG. 10) including the normal line of the reflective surface of the reflective image display element 5, Although the metal wire 8A is extended in parallel, in this modification, the metal wire 8A is disposed in the normal direction of the intermediate plane. When the incident surface of the illumination light and the incident surface of the projection light are on the same plane, they are arranged in the normal direction of the common incident surface.

For this reason, the illumination light incident on the WGP 8 is incident with the light beam L ₁₅ whose polarization direction is rotated by 90 ° around the optical axis in the third embodiment. The light beam L ₁₅ passes through the polarization direction rotating means 4 and is reflected by the reflective image display element 5, and enters the WGP 8 as a light beam L ₂₅ whose polarization direction is rotated by 90 ° around the optical axis, and becomes a light beam L _35. Reflected.

In this case, although polarization separation is performed in the same manner as in the third embodiment, the polarization separation efficiency can be further improved as compared with the third embodiment. Here, the polarization separation efficiency means the ratio between the amount of illumination light incident on the polarization separation unit and the amount of reflected light emitted from the polarization separation unit and reflected from the reflective image display element that contributes to projection.
Assuming that the incident angle of the illumination light with respect to the WGP 8 is θ, the relationship between the incident angle θ and the polarization separation efficiency is substantially flat as the incident angle θ increases from 0 ° to 70 ° as shown by a curve 200 in FIG. It shows a close, mountain-like change.
On the other hand, when the metal wire 8A is arranged in the same direction as in the third embodiment as shown in FIG. 11B, the angle of incidence θ is 0 as shown by the curve 201 in FIG. The polarization separation efficiency deteriorates at 60 ° or more after a substantially flat change while increasing from 55 ° to 55 °. Therefore, when the incident angle with respect to WGP8 is large, it is preferable to provide the metal wire 8A in the direction of this modification.

In this modification, an optical path as shown in FIG. 13 can also be employed. That is, between the WGP 8 and the reflective image display element 5, the optical path of the light beam L ₁₅ that is illumination light and the optical path of the light beam L ₃₅ that is reflected and separated by the WGP 8 intersect.
In this case, since the optical paths intersect, a compact layout can be achieved. However, as shown by a curve 202 in FIG. 14, the polarization separation efficiency is generally inferior compared to the case where the optical paths of the light beams L ₁₅ and L ₃₅ do not intersect as shown in FIG. Therefore, in order to further increase the polarization separation efficiency, it is preferable that the light rays L ₁₅ and L ₃₅ have a positional relationship that does not intersect.

  In the description of the first and second embodiments, an example in which the illumination light is reflected by the polarization separation unit and incident on the image display element will be described. In the description of the third embodiment, the illumination light is used. However, since the polarization separation action does not change even if each optical path is reversed, all the optical paths related to the polarization separation means are traveling. All configurations with the direction reversed can also be adopted.

  Further, in the above description, for the sake of simplicity, an example in which each optical path is along the XY, YZ, ZX plane, and the like has been described. However, these are examples, and within the scope of the technical idea of the present invention. By appropriately setting the arrangement angles of the polarization separation surface and the reflection surface, the present invention can be implemented in various optical paths that are not limited to these positional relationships.

  In the description of the third embodiment, the example in which the polarization direction rotating unit 4 is used as the polarization direction rotating unit has been described. However, a quarter wavelength plate whose principal axis is 45 ° with respect to the reference incident surface is used. May be. In this case, unlike the second embodiment, there is an advantage that almost no light loss occurs in the WGP 8 even if the normal line of the reflective surface of the reflective image display element 5 is not parallel to the reference incident surface.

  In the above description, the illumination light from the illumination unit has been described as having a wavelength λ. However, for example, a plurality of illumination units that emit red (R), green (G), and blue (B) wavelength light are provided. Provided according to each wavelength light, the polarization separation means and the image display element are arranged, the optical paths are synthesized by the optical path synthesis means such as a dichroic prism for synthesizing each wavelength light, and then incident on the projection optical system. Thus, a full-color projection type image projection apparatus may be used. In this case, when a polarization separation means that can be used in common at each wavelength can be used, an optical path synthesis means for synthesizing a plurality of illumination lights into one optical path is provided, and the polarization separation means and the image display element are arranged at each wavelength. You may make the structure shared by light.

  In addition, the constituent elements described in the above embodiments can be implemented in appropriate combination within the scope of the technical idea of the present invention, if technically possible.

1 is a schematic front view showing a schematic configuration of a projection type image projector according to a first embodiment of the present invention, and an AA cross-sectional view thereof. It is a perspective view which shows schematic structure of the polarization separation means used for the projection type image projector which concerns on the 1st Embodiment of this invention. It is perspective explanatory drawing for demonstrating the effect | action of the polarization separation means of the comparative example which concerns on a prior art. The conceptual diagram of the polarization direction change explaining the effect | action of the quarter wavelength plate which concerns on the 1st Embodiment of this invention, and the composite of the quarter wavelength plate and polarization direction rotation means which concern on the 1st Embodiment of this invention It is a conceptual diagram of the polarization direction change explaining a typical operation. It is a perspective view which shows schematic structure of the polarization separation means used for the projection type image projector which concerns on the 1st modification of the 1st Embodiment of this invention. It is the typical front view which shows schematic structure of the projection type image projector which concerns on the 2nd Embodiment of this invention, and its BB sectional drawing. It is a perspective view which shows schematic structure of the polarization separation means used for the projection type image projector which concerns on the 2nd Embodiment of this invention. It is a conceptual diagram of the polarization direction change explaining the effect | action of the quarter wavelength plate which concerns on the 2nd Embodiment of this invention. It is the typical front view which shows schematic structure of the projection type image projector which concerns on the 3rd Embodiment of this invention, its CC sectional drawing, and DD sectional drawing. It is a perspective view which shows schematic structure of the polarization separation means used for the projection type image projector which concerns on the 3rd Embodiment of this invention. It is a typical side view of the polarization separation means of the 1st modification of the 3rd Embodiment of this invention, and a typical side view of the polarization separation means of the 3rd Embodiment of this invention for comparison with it. . It is a typical graph explaining the polarization splitting efficiency of the 3rd Embodiment of this invention and its 1st modification. It is a typical side view which shows the other optical path of the polarization separation means of the 1st modification of the 3rd Embodiment of this invention. It is a typical graph explaining the polarization splitting efficiency in the case of the optical path arrangement | positioning of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Illumination part 2 Polarization separation element 2a Polarization separation surface 3 1/4 wavelength plate 4 Polarization direction rotation means 5 Reflective image display element 6 Projection optical system 7 Screen 8 WGP (metal grating polarization separation element)
8A Metal wire 8B Substrate 9 1/4 wavelength plate (polarization rotating means)
20, 21, 22 Polarization separation means 100, 110, 120 Projection type image projection apparatus

Claims (7)

A projection-type image projection device adapted to spatially modulate linearly polarized illumination light in a reflective image display element and project it as reflected light representing an image,
Polarization separation means for transmitting or reflecting the illumination light and the reflected light reflected by the display surface of the reflective image display element on the polarization separation surface according to the polarization direction;
A polarization direction rotating means that is positioned between the polarization separating means and the reflective image display element, and that rotates the polarization direction of light reciprocally transmitted by 90 ° around the optical axis;
An axial principal ray of the illumination light that passes through the polarization separation surface of the polarization separation means and is incident on the display surface of the reflective image display element, and an axis of the reflected light that is reflected by the display surface The polarization separation means and the polarization direction rotating means are arranged in the reflective image display element so that the direction of the angle formed by the principal ray is equally divided into the direction of the optical axis of the polarization direction rotating means. A projection-type image projector characterized by being arranged with respect to the above. The polarization separation means includes
The projection type image projection apparatus according to claim 1, wherein the projection type image projection apparatus is a polarization separation element that is formed of a dielectric multilayer film and separates s-polarized light and p-polarized light on the polarization separation surface. The polarization separation means includes
The projection type image projection device according to claim 1, wherein the projection type image projection device comprises a metal grating polarization separation element in which a plurality of fine metal wires are arranged in parallel at a fine pitch on an insulator toward the reflective image display element side. . The wiring direction of the thin metal wire of the metal grating polarization separation element is such that the incident surface of the axial principal ray of the illumination light in the metal grating polarization separation element and the axial principal ray of the reflected light in the metal grating polarization separation element are 4. The projection according to claim 3, wherein the crossing angle of the incident surface is equally divided into two and is a normal direction of an intermediate plane including a normal line of the reflection surface that reflects the reflected light toward the projection direction. Type image projector. The optical path length of the axial principal ray of the illumination light from the transmission through the metal grating polarization separating element to the display surface of the reflective image display element reflects the display surface of the reflective image display element. The metal grating polarization separating element and the reflective image display element are arranged so that the length of the reflected light is shorter than the optical path length of the axial principal ray of the reflected light until reaching the metal grating polarization separating element. The projection type image projector according to claim 3 or 4. Of the two polarization directions positioned between the polarization separation means and the polarization direction rotation means and separated by the polarization separation surface, the polarization direction of light that is polarized and separated toward the reflective image display element side The projection-type image projector according to claim 1, further comprising: a quarter-wave plate having a principal axis substantially in the same direction as the projection. The polarization direction rotating means is
Of the two polarization directions separated by the polarization separation surface, the light is polarized approximately 45 ° in a plane perpendicular to the optical axis with respect to the polarization direction of the light that is polarized and separated toward the reflective image display element. 6. The projection type image projection apparatus according to claim 1, wherein the projection type image projection apparatus comprises a quarter wavelength plate having a main axis.

Images