JP2013025293A - Image projecting apparatus, and image projecting apparatus having projective optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image projecting apparatus excelling in brightness while restraining decline in contrast.SOLUTION: In an image projecting apparatus, when a polarized light separating face that a polarized light separating element for green has is supposed to be a first polarized light separating face, a polarized light separating face that a polarized light converting element has is supposed to be a second polarized light separating face, a section parallel to the normal of the first polarized light separating face and to the normal of a reflection type light modulating element for green is supposed to be a first section, and a section parallel to the normal of the second polarized light separating face and to the normal of the polarized light converting element is supposed to be a second section, the first section and the second section are mutually orthogonal sections.

Description

  The present invention relates to an image projection apparatus that projects image light onto a projection surface, and more particularly to an image projection apparatus having a reflective light modulation element.

  In the conventional image projection apparatus, in order to improve the contrast of the projected image, the polarizing plate is disposed on the incident side or the emission side of the polarizing beam splitter. Concretely, it demonstrates using an example of the block diagram currently disclosed by patent document 1 (FIG. 11).

  The light from the light source 101 is reflected by the reflector 102 and emitted as substantially parallel light. Of the polarization components of the light reflected by the reflector 102, the S polarization component is absorbed by the polarizing plate 103, only the P polarization component is transmitted, and is emitted as P polarization. P-polarized light is transmitted through the polarization separation surface of the polarization beam splitter 104. Incident light is separated into a plurality of optical paths according to the wavelength bands by the color separation elements 105 and 106, and the separated light of each wavelength band illuminates the corresponding reflective image display elements 107, 108, and 109. To do. Then, the polarization state of the incident light is changed (modulated) by the image display elements 107, 108, and 109, the light is reflected, and is incident on the polarization beam splitter 104 again through the color separation elements 105 and 106. Of the light incident on the polarizing beam splitter 104, the S-polarized component is reflected by the polarizing beam splitter 104, enters the polarizing plate 110, and is guided to the projection lens 111. Then, the image is enlarged by the projection lens 111 and an image is projected onto the screen 112.

  When the image display elements 107, 108, and 109 change the incident light to a polarization state corresponding to the black image, a part of the incident light is incident on the image display element with P-polarized light, although the light should be incident with S-polarized light. The trapped light is reflected as P-polarized light. At this time, the P-polarized light is light that should pass through the polarization separation surface of the polarization beam splitter 104 and return to the light source 101 side, but part of the light is reflected by the polarization beam splitter 104 and guided to the projection lens 111. It will be scratched. This causes a decrease in the contrast of the projected image. Hereinafter, the light that causes the contrast to decrease is referred to as leakage light.

  In order to prevent this decrease in contrast, Patent Document 1 installs a polarizing plate 110 that transmits only S-polarized light on the exit side (projection lens side) of the polarizing beam splitter 104 and analyzes (blocks) P-polarized light that is leaking light. doing.

Japanese Patent Laid-Open No. 03-175437

  However, since the polarizing plate partially absorbs or reflects the light that should be transmitted (S-polarized light in FIG. 11), the polarizing plate that detects leakage light as in Patent Document 1 is used as the polarizing beam splitter exit side. Or if it arrange | positions at the incident side, there existed a subject that brightness fell.

In order to solve the above problems, the image projection apparatus of the present invention is
A reflective light modulation element for red on which light in the red wavelength band is incident;
A reflective light modulation element for green on which light in the green wavelength band is incident;
A reflective light modulation element for blue on which light in a blue wavelength band is incident;
A polarization conversion element having a plurality of polarization separation surfaces for converting light from the light source into linearly polarized light;
First, the light of the blue wavelength band is separated by reflecting the light of the blue wavelength band out of the light emitted from the polarization conversion element and transmitting the light of the green and red wavelength bands. A color separation element;
A second color that separates the light in the red wavelength band by reflecting the light in the red wavelength band out of the light in the green and red wavelength bands transmitted through the first color separation element; A separation element;
The image light reflected by the blue and green reflective light modulation elements is reflected, and the image light reflected by the red reflection light modulation element is transmitted to synthesize light of each wavelength band. A color composition element that leads to the projection optical system;
Light reflected in the blue wavelength band separated by the first color separation element is guided to the blue reflection-type light modulation element and modulated by the blue reflection-type light modulation element A polarization separation element for blue having a polarization separation surface that transmits image light and guides it to the color composition element,
Light reflected in the red wavelength band separated by the second color separation element is guided to the reflection light modulation element for red and modulated by the reflection light modulation element for red A polarization separation element for red having a polarization separation surface that transmits image light and guides it to the color composition element,
The green wavelength band light transmitted through the second color separation element is reflected to be guided to the green reflection type light modulation element, and the light modulated by the green reflection type light modulation element Among them, it has a polarization separation element for green having a polarization separation surface that transmits image light and guides it to the color composition element,
The polarization separation surface of the green polarization separation element is a first polarization separation surface,
The polarization separation surface of the polarization conversion element is a second polarization separation surface,
A cross section parallel to a normal line of the first polarization separation surface and a normal line of the reflective light modulation element for green is a first cross section,
When a cross section parallel to the normal line of the second polarization separation surface and the normal line of the polarization conversion element is a second cross section,
The first cross section and the second cross section are cross sections orthogonal to each other.

An image projection apparatus according to another aspect of the present invention,
A reflective light modulation element for red on which light in the red wavelength band is incident;
A reflective light modulation element for green on which light in the green wavelength band is incident;
A reflective light modulation element for blue on which light in a blue wavelength band is incident;
A polarization conversion element having a plurality of polarization separation surfaces for converting light from the light source into linearly polarized light;
A color separation element that reflects light in the blue and red wavelength bands out of the light emitted from the polarization conversion element and separates the light in the green wavelength band by transmitting the light in the green wavelength band; ,
Light of each wavelength band is synthesized by transmitting the image light reflected by the red and blue reflective light modulators and reflecting the image light reflected by the green reflective light modulator. A color composition element that leads to the projection optical system;
The light of the green wavelength band separated by the color separation element is reflected to be guided to the green reflection type light modulation element, and an image out of the light modulated by the green reflection type light modulation element A polarization separation element for green having a polarization separation surface that transmits light to the color composition element;
By reflecting one of the red and blue wavelength bands of light reflected by the color separation element and transmitting the other, the red reflective light modulation element and the blue reflective light are reflected. Red having a polarization separation surface that guides to each of the modulation elements, combines the image light modulated by the reflection light modulation element for red and the reflection light modulation element for blue, and guides the light to the color synthesis element, And a polarization separation element for blue,
A λ / 2 plate between the color separation element and the green polarization separation element;
The polarization separation surface of the green polarization separation element is a first polarization separation surface,
The polarization separation surface of the polarization conversion element is a second polarization separation surface,
A cross section parallel to a normal line of the first polarization separation surface and a normal line of the reflective light modulation element for green is a first cross section,
When a cross section parallel to the normal line of the second polarization separation surface and the normal line of the polarization conversion element is a second cross section,
The first cross section and the second cross section are cross sections orthogonal to each other.

  An image projection apparatus including a light modulation element that modulates light from the light source and provided with a projection optical system or detachably mounted also constitutes another aspect of the present invention.

  According to the present invention, it is possible to provide an image projection apparatus capable of projecting a bright image while obtaining a predetermined contrast.

1 is a first sectional view of an image projection apparatus according to a first embodiment of the present invention. Second sectional view of the image projection apparatus of Embodiment 1 of the present invention. The figure which shows the transmission characteristic with respect to the wavelength of a 1st color separation element The figure which shows the transmission characteristic with respect to the wavelength of a 2nd color separation element Cross section of polarization conversion element Diagram showing the incident angle characteristics of the polarization separation surface First sectional view of an image projection apparatus according to a second embodiment of the present invention. Second sectional view of the image projection apparatus according to the second embodiment of the present invention. The figure which shows the permeation | transmission characteristic of the color separation element of Embodiment 2 of this invention The figure which shows the permeation | transmission characteristic of the color composition element of Embodiment 2 of this invention Configuration diagram of conventional image projector

(Embodiment 1)
1 and 2 are sectional views of the configuration of the image projection apparatus according to the first embodiment. FIG. 1 is a configuration diagram of a cross section along the short side direction of an image display element (light modulation element). FIG. 2 is a configuration diagram of a cross section along the long side direction of the image display element.

  White light emitted from the light source 1 is reflected by a parabolic reflector 2, and the reflected light is divided into a plurality of light beams by a first lens array 3 in which a plurality of lenses are two-dimensionally arranged. The light beam (divided light beam) divided by the first lens array 3 passes through the second lens array 4 and forms a plurality of light source images in the vicinity of the polarization conversion element 5.

  The polarization directions of the light beams from the plurality of light source images are aligned by the polarization conversion element 5 from non-polarized light to linearly polarized light. A plurality of split light beams whose polarization directions are aligned are superimposed on the image display elements 9, 14, and 18 by the condenser lens 6 to illuminate the image display element. In the first embodiment, the polarization conversion element 5 aligns the polarization direction of the incident light flux so that the polarization separation surfaces 8a, 13a, and 17a of the polarization beam splitters 8, 13, and 17 are S-polarized light.

  The image display elements 9, 14, and 18 are image display elements corresponding to light in the wavelength bands of green, red, and blue, respectively. The illumination optical system is from the light source 1 to the condenser lens 6.

  The light beam emitted from the illumination optical system is incident on a dichroic mirror 7 (first color separation element) having a function of separating an optical path according to a wavelength band. The transmission characteristics with respect to the wavelength of the dichroic mirror 7 are shown in FIG. The dichroic mirror 7 transmits light in the green and red wavelength bands and reflects light in the blue wavelength band.

  Next, the characteristics of the dichroic mirror 12 are shown in FIG. The dichroic mirror 12 (second color separation element) transmits light in the blue and green wavelength bands and reflects light in the red wavelength band. The dichroic mirror 12 may have a characteristic of reflecting light in the blue wavelength band.

  From the characteristics of the dichroic mirrors 7 and 12 shown in FIGS. 3 and 4, the light in the green wavelength band passes through the dichroic mirror 7 and the dichroic mirror 12. Then, since it is incident on the polarization separation surface 8a as S-polarized light, it is reflected by the polarization separation surface 8a and illuminates the image display element 9 (green reflection type light modulation element). The image display element 9 has a function of changing (modulating) the polarization state of incident light and reflecting it (the same applies to the image display elements 14 and 18). The image light (P-polarized component) modulated by the image display element 9 is transmitted through the polarization separation surface 8a and reflected by the color separation surface (dichroic surface) of the synthesis prism 10 (color synthesis device, optical path synthesis device). Then, it is guided to the projection lens 11 (projection optical system).

  And the image light of the green wavelength band reflected by the synthetic | combination prism 10 is expanded by the projection lens 11, and is projected on a screen (projection surface). Here, the image light is light that is guided to the projection lens when the polarization state is changed by the image display element. On the other hand, light in a polarization state that does not become image light is returned to the light source side.

  The light in the blue wavelength band reflected by the dichroic mirror 7 is further reflected by the reflection mirror 15 and reaches the polarization separation surface 17a via the relay lens 16. Then, the light is reflected by the polarization splitting surface 17a and illuminates the image display element 18 (blue reflection type light modulation element). Of the light whose polarization state has been changed by the image display element 18, the image light is transmitted through the polarization separation surface 17 a, reflected by the color separation surface of the combining prism 10, magnified by the projection lens 11, and projected onto the screen. Projected.

  The light in the red wavelength band that has passed through the dichroic mirror 7 is reflected by the dichroic mirror 12. Further, the light is reflected by the polarization separation surface 13a to illuminate the image display element 14 (red reflection type light modulation element). Of the light whose polarization state has been changed by the image display element 14, the image light passes through the polarization separation surface 13 a and the color separation surface of the combining prism 10, is enlarged by the projection lens 11, and is projected on the screen.

  An enlarged view of the polarization conversion element 5 is shown in FIG. As shown in FIG. 5, in the polarization conversion element, polarization separation surfaces 21 and reflection surfaces 22 are alternately arranged, and a λ / 2 plate 23 is attached to the surface on the exit side. The arrows in FIG. 5 indicate the traveling direction of light. The normal line of the polarization conversion element 5 is the z-axis direction of FIG.

  As shown in FIG. 5, the polarization conversion element 5 has a structure in which every other λ / 2 plate 23 is disposed between the polarization separation surface 21 and the reflection surface 22. Unpolarized light (thick solid line) incident on the polarization conversion element 5 is separated into P-polarized light (broken line) and S-polarized light (solid line) by the polarization separation surface 21, and S-polarized light is emitted from the adjacent reflecting surface 22. The light is reflected in the direction of the surface, passes through the λ / 2 plate 23, is converted into P-polarized light, and is emitted. Of the light incident on the polarization separation surface 21, the P-polarized light transmitted through the polarization separation surface 21 is emitted between the λ / 2 plate 23 and the λ / 2 plate 23. As described above, the non-polarized light incident on the polarization conversion element 5 is aligned with the P-polarized light. In the description here, P-polarized light and S-polarized light are defined based on the polarization separation surface of the polarization conversion element 5.

  FIG. 6 shows the polarization separation characteristics with respect to the wavelength of the polarization separation surface (polarization separation film) of the polarization conversion element 5. The horizontal axis is the wavelength [nm], the vertical axis is the polarization separation characteristic [%], and the solid line, broken line, and alternate long and short dash line in the graph are the incident angles to the polarization separation surface at 45 degrees, 42 degrees, and 39 degrees, respectively. It represents the polarization conversion efficiency. As shown in FIG. 6, as the incident angle on the polarization separation surface is away from 45 degrees, the polarization separation characteristic is degraded. This indicates that the more the incident angle with respect to the polarization separation surface is away from 45 degrees, in other words, the greater the spread of the incident angle of the light beam with respect to the polarization separation surface, the greater the leakage light.

  The polarization separation characteristics of the polarization separation surfaces 8a, 13a, and 17a of the polarization beam splitters 8, 13, and 17 in FIG. 1 are substantially the same as the characteristics shown in FIG.

  In FIG. 6, 45 degrees, 42 degrees, and 39 degrees represent angles formed with the normal line of the polarization separation plane in the incident plane (a plane including the normal line of the polarization separation plane and the incident light beam). Light having various angles is incident on the same point on the surface from oblique directions in the vertical and horizontal directions. For example, a light beam incident on the same point on the polarization separation surface has an isotropic angle distribution (predetermined solid angle) with respect to a light beam having an incident angle (for example, 45 °) at which an ideal polarization separation characteristic is obtained. Think if you are. In this case, the distribution of the incident light angle in the incident surface matches the distribution of the incident angle (the angle formed between the incident light beam and the normal of the polarization separation surface). On the other hand, in a plane that includes the normal line of the polarization separation plane and is perpendicular to the incident plane (hereinafter referred to as plane X), even if the spread of the angle distribution of incident rays is the same as that in the incidence plane, the polarization separation plane There is little deviation of the angle with respect to the normal. That is, on the surface X, the change in the incident angle is small, and there is almost no deviation from the angle at which an ideal polarization conversion efficiency is obtained.

  In the present invention, as shown in FIGS. 1 and 2, the polarization separation surface 21 (second polarization separation surface) of the polarization conversion element 5 and the polarization separation surface 8a (first polarization separation surface) of the polarization beam splitter 8 are used. Are arranged so that they are not in the same cross section. In other words, a cross section parallel to the normal line of the polarization separation surface 8a and the normal line of the image display element 9 is defined as the first cross section. A cross section including the optical axis 11A of the projection lens 11 and perpendicular to the first cross section is defined as a second cross section. At this time, the arrangement direction of the plurality of polarization separation surfaces 21 of the polarization conversion element 5 is configured to be a direction along the second cross section. In other words, the polarization separation surface of the green polarization separation element is the first polarization separation surface, and the polarization separation surface of the polarization conversion element is the second polarization separation surface. A cross section parallel to the normal line of the first polarization separation surface and the normal line of the green reflective light modulation element is a first cross section, the normal line of the second polarization separation surface and the polarization conversion element A cross section parallel to the normal is defined as a second cross section. At this time, the first cross section and the second cross section are cross sections orthogonal to each other.

  As described above, with respect to the change of the incident angle in the incident plane including the normal line of the polarization splitting surface 21 and the incident light, the change in the incident angle in the plane including the normal line and perpendicular to the incident plane. Is small. Therefore, even if light having a large divergence angle in the incident surface is incident on the polarization separation surface 21 of the polarization conversion element 5, the polarization separation surface 8 a of the polarization beam splitter 8 includes a normal line and is incident on the incidence surface. Incident light is incident in a vertical plane (in plane X). That is, light is incident at a substantially desired incident angle (for example, 45 °) in a plane perpendicular to the incident surface of the polarization separation surface 8a of the polarization beam splitter 8.

  Thereby, the polarization splitting surface 8a can detect incident light with the characteristics shown by the solid line in FIG. 6, and can reduce leakage light. That is, since a polarizing plate for cutting (absorbing or reflecting) leakage light is not required, a brighter image can be projected as compared with the case where a polarizing plate is inserted. Another advantage of the present invention is that it is possible to project a projected image having a high contrast because leakage light can be reduced.

  In general, the first lens array 3 is composed of a plurality of lens cells, and in order to increase the illumination efficiency of the image display element, an effective area (area where an image is actually displayed) of the lens cell and the image display element. The area to be used as is similar. The interval (pitch) at which the plurality of polarization separation surfaces 21 are arranged is proportional to the width of the lens cell in the y-axis direction.

  In the first embodiment, the cross section along the long side direction of the image display element and the cross section along the direction in which the polarization separation surface 21 of the polarization conversion element 5 is arranged are the same cross section (FIG. 2). Thereby, compared with the case where the cross section along the long side direction of the image display element and the cross section along the direction in which the polarization splitting surface 21 of the polarization conversion element 5 are arranged are orthogonal, the polarized light is polarized. The pitch of the polarization separation surface 21 of the conversion element 5 can be increased. If the pitch is large, the amount of light that is vignetted by the polarization conversion element 5 is reduced, so that a brighter image can be projected that can increase the polarization conversion efficiency of the polarization conversion element 5.

  In the first embodiment, the above effect can be obtained even if the polarization direction of the light incident on the polarization splitting surface 8a is P-polarized light. However, more preferably, the polarization direction of light incident on the polarization splitting surface 8a is S-polarized light. In general, the polarization separation surface has a higher extinction ratio with respect to S-polarized light than P-polarized light. Therefore, if S-polarized light is incident, a polarizing plate is generally disposed on the incident side of the polarizing beam splitter 8. is there. Therefore, if S-polarized light is incident, there is no need to dispose a polarizing plate on the exit side of the polarizing beam splitter 8. Furthermore, in the configuration of the present invention, as described above, since the polarizing beam splitter 8 can detect light at an incident angle with high light detection performance, it is necessary to dispose a polarizing plate on the incident side of the polarizing beam splitter 8 as well. There is no. That is, since it is not necessary to dispose the polarizing plate for the purpose of analyzing leaked light on the incident side and the outgoing side of the polarizing beam splitter 8, it is possible to obtain the effect of suppressing the decrease in brightness due to absorption or reflection of the polarizing plate. be able to. It can be said that the polarization beam splitter 8 used in the above description is an element for analyzing the modulated light of the image display element. Or it can be said that it is an element which has the polarization separation surface arrange | positioned between an image display element and a color composition element.

  In the above description, the polarization separation surface 8a of the polarization beam splitter 8 among the three polarization beam splitters in the first embodiment has been described as a representative example. The same explanation can be made for the optical paths in other wavelength bands, even if the polarizing beam splitter 8 is replaced with the polarizing beam splitters 13 and 17.

  In the first embodiment, the image display element 9 corresponds to an image display element corresponding to light in the green wavelength band, the image display element corresponding to light in the red wavelength band, and 18 corresponding to light in the blue wavelength band. However, the combinations may be different.

  Moreover, it is preferable that the transmittance | permeability with respect to P polarized light of a polarization separation surface is 1% or less.

  In the polarization conversion element 5 used in the first embodiment, the polarization separation films and the reflection films are alternately arranged, but a plurality of light shielding plates are provided on the incident side at every other pitch of the polarization separation surface. Even if it is a polarization conversion element comprised only by the polarization separation film of this, the effect of this invention can be acquired.

  In the first embodiment, the contrast can be further improved by providing a light shielding portion in the polarization conversion element 5 or in the vicinity of the polarization conversion element 5. The light shielding part may be attached in a bowl shape on the incident side of the polarization conversion element 5, or may be a stop that limits the diameter of the incident light beam to the polarization conversion element 5.

  The image display element of Embodiment 1 is a reflection type, but may be a transmission type image display element or an image display element such as a digital mirror device (DMD). When a transmissive image display element is used, incident light is color-separated using a wavelength-selective retardation plate and a polarizing beam splitter. In this embodiment, the first cross section is defined as a cross section parallel to the normal line of the polarization separation surface of the polarization beam splitter that performs color separation and the normal line of the image display element. A section including the optical axis of the projection lens and perpendicular to the first section is defined as a second section. At this time, the arrangement direction of the plurality of polarization separation surfaces of the polarization conversion element may be configured to be along the second cross section. If the light source emits light having a uniform polarization direction such as a laser, the wavelength-selective retardation plate may not be provided.

  Although the lens array of Embodiment 1 is two-dimensionally arranged, a lens array in which cylindrical lenses and toric lenses are arranged only in the one-dimensional direction may be used.

  FIG. 1 is a cross-sectional view taken along the short side direction of the image display element, but FIG. 1 shows the normal line of the polarization separation surface for detecting the light whose polarization state has been changed by the image display element. It can also be said that it is a configuration diagram in a section A parallel to the normal line of the image display element. Further, FIG. 2 can be said to be a configuration diagram in a section B including the optical axis of the illumination optical system and being a section perpendicular to the section A.

  FIG. 2 is a diagram in which the polarizing beam splitter 8 and the combining prism 10 of FIG. 1 are developed in one direction, but the polarizing beam splitter 8 may be replaced with the polarizing beam splitter 13 or 17.

(Embodiment 2)
7 and 8 are configuration diagrams of the image projection apparatus according to the second embodiment. 7 is a configuration diagram of a cross section along the short side direction of the image display element, similarly to FIG. 1, and FIG. 8 is a configuration diagram of a cross section along the long side direction of the image display element, similarly to FIG.

  The second embodiment differs from the first embodiment in that the parabolic reflector is an elliptical reflector, and in the first cross section (FIG. 7), the second lens array has a negative refractive power. . Furthermore, in the second cross section (FIG. 8), the first lens array has a negative refractive power, and two image displays for one polarization beam splitter (a polarization separation element for red and blue). The element is arranged. As a result, the contrast was further improved.

  White light emitted from the light source 31 is reflected by the elliptical reflector 32 and becomes a converged light beam. The converged light beam is divided into a plurality of light beams by the first lens array 33 in which the lens cell is decentered in the cross section of FIG. The divided light beams are condensed by the lens cells of the second lens array 34 whose lens cells are decentered in the cross section of FIG. 7, and a plurality of light source images are formed in the vicinity of the polarization conversion element 35. The light beam that has passed through the polarization conversion element 35 is aligned in a predetermined polarization direction, and then illuminates the image display elements 39, 46, and 47 via the condenser lens 36.

  The image display elements 39, 46, and 47 are image display elements corresponding to light in the wavelength bands of green, red, and blue, respectively. In order from the light source 31 toward the image display element, an elliptical reflector 32 (optical element) having a positive refractive power is provided between the light source 31 and the polarization conversion element 35 in the first cross section and the second cross section. Further, a first lens array 33 (optical element) having a negative refractive power in the second cross section (FIG. 8) and a second lens array 34 (optical) having a negative refractive power in the first cross section (FIG. 7). Element). The definitions of the first cross section and the second cross section are the same as those in the first embodiment.

  With this configuration, the convergent light beam is collimated and emitted by the first lens array 33 in the second cross section. In the first cross section, the convergent light beam is collimated by the second lens array 34 and emitted. The width of the collimated light beam is smaller in the first cross section than in the second cross section.

  FIG. 9 shows the transmittance characteristics with respect to the wavelength of the dichroic mirror 37 (color separation element). The characteristic of the dichroic mirror 37 is that light in the green wavelength band is transmitted and light in the red and blue wavelength bands is reflected. The light in the green wavelength band (P-polarized light) incident on the dichroic mirror 37 is converted by the λ / 2 plate 40 into a 90-degree polarization direction (becomes S-polarized light), and is polarized by the polarization separation surface 38a (first polarization separation surface). The reflected light illuminates the image display element 39. Thereafter, the image light converted by the image display element 39 is transmitted through the polarization separation surface 38a and is incident on the dichroic polarization prism 41 having the optical surface 41a having both the color separation effect and the polarization separation effect.

  The optical surface 41a has the characteristics shown in FIG. 10 and transmits both P-polarized light and S-polarized light with respect to light in the blue wavelength band. For light in the red wavelength band, it reflects S-polarized light and transmits P-polarized light. For light in the green wavelength band, both P-polarized light and S-polarized light are reflected.

  Therefore, the light in the green wavelength band is reflected by the optical surface 41a of the dichroic polarizing prism 41, enlarged via the projection lens 42, and projected onto the screen.

  The light in the red wavelength band is reflected by the dichroic mirror 37 and passes through the polarizing plate 43 and the wavelength selective phase plate 44 that rotates the polarization direction by 90 degrees only for the light in the red wavelength band, and becomes S-polarized light.

  The light in the red wavelength band is reflected by the polarization separation surface 45a and illuminates the image display element 46. Thereafter, image light out of the light whose polarization direction is changed by the image display element 46 passes through the polarization separation surface 45a. Then, the light passes through the optical surface 41a of the blue polarizing plate 48 and the dichroic polarizing prism 41, which acts as a polarizing plate only for the blue wavelength band, and is enlarged by the projection lens 42 and projected onto the screen.

  The light in the blue wavelength band is reflected by the dichroic mirror 37, passes through the polarizing plate 43, and passes through the wavelength selective phase plate 44. The light in the blue wavelength band is transmitted through the polarization separation surface 45a and illuminates the image display element 47. Thereafter, of the light whose polarization state has been changed by the image display element 47, the image light is reflected by the polarization separation surface 45a. Unnecessary polarized light is absorbed or reflected (analyzed) by the blue polarizing plate 48, passes through the optical surface 41a of the dichroic polarizing prism 41, is enlarged by the projection lens 42, and is projected onto the screen.

  The wavelength-selective retardation plate may be an element that rotates the polarization direction by 90 degrees only for light in the blue wavelength band. At this time, since the light in the blue wavelength band is converted to S-polarized light, it is reflected by the polarization separation surface 45a, and the light in the other red wavelength band remains P-polarized light, and thus passes through the polarization separation surface 45a.

  The image projection apparatus according to the second embodiment can obtain the same effects as the image projection apparatus according to the first embodiment.

  Another effect of the second embodiment is that the light beam width in the first cross section is made smaller than the light beam width in the second cross section, so that the light beam incident on the first cross section where the incident angle characteristic of the polarization beam splitter 38 is sensitive is obtained. Since the width can be reduced, leakage light can be further reduced.

  In the second embodiment, when the wavelength bands are separated by the dichroic mirror 37, the red and blue optical paths and the green optical path are separated, but other combinations are possible.

  The polarization beam splitter may be a wire grid.

  In the first and second embodiments, it is more preferable that a polarizing plate is not disposed between the color separation element and the image display element in the optical path of light in all wavelength bands. Even if the polarizing plate is not disposed only in the optical path, the effect of improving the brightness can be obtained. In particular, a brighter projected image can be projected by removing the polarizing plate in the optical path of the green wavelength band with high specific visibility.

DESCRIPTION OF SYMBOLS 5 Polarization conversion element 7 Color separation element 8, 13, 17 Polarization separation element 8a, 13a, 17a Polarization separation surface 9, 14, 18 Image display element 10 Synthetic prism

Claims (6)

A reflective light modulation element for red on which light in the red wavelength band is incident;
A reflective light modulation element for green on which light in the green wavelength band is incident;
A reflective light modulation element for blue on which light in a blue wavelength band is incident;
A polarization conversion element having a plurality of polarization separation surfaces for converting light from the light source into linearly polarized light;
First, the light of the blue wavelength band is separated by reflecting the light of the blue wavelength band out of the light emitted from the polarization conversion element and transmitting the light of the green and red wavelength bands. A color separation element;
A second color that separates the light in the red wavelength band by reflecting the light in the red wavelength band out of the light in the green and red wavelength bands transmitted through the first color separation element; A separation element;
The image light reflected by the blue and green reflective light modulation elements is reflected, and the image light reflected by the red reflection light modulation element is transmitted to synthesize light of each wavelength band. A color composition element that leads to the projection optical system;
Light reflected in the blue wavelength band separated by the first color separation element is guided to the blue reflection-type light modulation element and modulated by the blue reflection-type light modulation element A polarization separation element for blue having a polarization separation surface that transmits image light and guides it to the color composition element,
Light reflected in the red wavelength band separated by the second color separation element is guided to the reflection light modulation element for red and modulated by the reflection light modulation element for red A polarization separation element for red having a polarization separation surface that transmits image light and guides it to the color composition element,
The green wavelength band light transmitted through the second color separation element is reflected to be guided to the green reflection type light modulation element, and the light modulated by the green reflection type light modulation element Among them, it has a polarization separation element for green having a polarization separation surface that transmits image light and guides it to the color composition element,
The polarization separation surface of the green polarization separation element is a first polarization separation surface,
The polarization separation surface of the polarization conversion element is a second polarization separation surface,
A cross section parallel to a normal line of the first polarization separation surface and a normal line of the reflective light modulation element for green is a first cross section,
When a cross section parallel to the normal line of the second polarization separation surface and the normal line of the polarization conversion element is a second cross section,
The image projection apparatus according to claim 1, wherein the first cross section and the second cross section are cross sections orthogonal to each other. A reflective light modulation element for red on which light in the red wavelength band is incident;
A reflective light modulation element for green on which light in the green wavelength band is incident;
A reflective light modulation element for blue on which light in a blue wavelength band is incident;
A polarization conversion element having a plurality of polarization separation surfaces for converting light from the light source into linearly polarized light;
A color separation element that reflects light in the blue and red wavelength bands out of the light emitted from the polarization conversion element and separates the light in the green wavelength band by transmitting the light in the green wavelength band; ,
Light of each wavelength band is synthesized by transmitting the image light reflected by the red and blue reflective light modulators and reflecting the image light reflected by the green reflective light modulator. A color composition element that leads to the projection optical system;
The light of the green wavelength band separated by the color separation element is reflected to be guided to the green reflection type light modulation element, and an image out of the light modulated by the green reflection type light modulation element A polarization separation element for green having a polarization separation surface that transmits light to the color composition element;
By reflecting one of the red and blue wavelength bands of light reflected by the color separation element and transmitting the other, the red reflective light modulation element and the blue reflective light are reflected. Red having a polarization separation surface that guides to each of the modulation elements, combines the image light modulated by the reflection light modulation element for red and the reflection light modulation element for blue, and guides the light to the color synthesis element, And a polarization separation element for blue,
A λ / 2 plate between the color separation element and the green polarization separation element;
The polarization separation surface of the green polarization separation element is a first polarization separation surface,
The polarization separation surface of the polarization conversion element is a second polarization separation surface,
A cross section parallel to a normal line of the first polarization separation surface and a normal line of the reflective light modulation element for green is a first cross section,
When a cross section parallel to the normal line of the second polarization separation surface and the normal line of the polarization conversion element is a second cross section,
The image projection apparatus according to claim 1, wherein the first cross section and the second cross section are cross sections orthogonal to each other.   The long side direction of the reflection type light modulation elements for red, green, and blue and the direction in which the polarization separation surfaces of the polarization conversion elements are arranged are the same direction. Image projection device. Between the light source and the first color separation element, in order from the light source side,
An optical element having positive refractive power in the first cross section and the second cross section;
An optical element having negative refractive power in the first cross section;
The image projection apparatus according to claim 1, further comprising an optical element having negative refractive power in the second section. Between the light source and the color separation element, in order from the light source side,
An optical element having positive refractive power in the first cross section and the second cross section;
An optical element having negative refractive power in the first cross section;
The image projection apparatus according to claim 2, further comprising an optical element having negative refractive power in the second cross section. An image projection apparatus according to any one of claims 1 to 5,
An image projection apparatus comprising: a projection optical system that projects light synthesized by the color synthesis element onto a projection surface.

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