JP2013250322A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image display device using a wire grid polarization separation element, capable of projecting an image which is bright and has a high contrast.SOLUTION: An image display device has a polarization separation element which separates first and second wavelength lights and guides them to respective reflection type optical modulation elements so as to synthesize first and second wavelength lights from the respective reflection type optical modulation elements. The polarization separation part includes first and second dielectric layers 3a, 3b and a metal one-dimensional lattice structure 3c provided between the dielectric layers. A reflectance ratio Rat the time when a first polarization component of the first wavelength light is injected from a first dielectric layer side to the polarization separation part, and a reflection ratio Rat the time when it is injected from a second dielectric layer side thereto satisfy a condition of R>R; and a reflectance ratio Rat the time when a first polarization component of the second wavelength light is injected from the first dielectric layer side to the polarization separation part, and a reflection ratio Rat the time when it is injected from a second dielectric layer side thereto satisfy a condition of R<R.

Description

  The present invention relates to an image display device such as a projector, and more particularly to an image display device that performs color separation and color composition using a wire grid polarization separation element including a wire grid and a dielectric layer.

  As an image display apparatus as described above, the light from the light source is separated into three color lights and led to light modulation elements such as three reflective liquid crystal panels, and the three color lights modulated by these light modulation elements are synthesized. Some display color images. In this image display device, there are cases where two of the three color lights are separated and combined by one polarization separation element depending on their polarization directions.

Patent Document 1 discloses an image display device that uses a SWS (Subwavelength Structure) which is a periodic structure having a period shorter than the wavelength of incident light (visible light) as a polarization separation element. ing. The apparatus disclosed in Patent Document 1 uses an SWS polarization separation element in which a plurality of dielectric one-dimensional gratings are stacked so that their periodic directions are orthogonal to each other. Specifically, the refractive index difference at the interface between the stacked gratings is different between the first linearly polarized light and the second linearly polarized light whose polarization directions are orthogonal to each other. On the other hand, Patent Document 2 discloses a polarization separation element using a wire grid in which one-dimensional gratings made of metal are arranged with a period shorter than the wavelength of incident light. It is disclosed. In the wire grid, linearly polarized light whose polarization direction is the periodic direction of the one-dimensional grating is transmitted, and linearly polarized light whose polarization direction is a direction orthogonal to the periodic direction (longitudinal direction of each grating) is reflected. Such a wire grid has better reflectance and transmittance angle characteristics than a polarization separation element having a dielectric film laminated thereon, and can secure good polarization separation characteristics for a wide incident angle.

  Furthermore, Patent Document 3 discloses a polarization separation element in which a wire grid is sandwiched between two transparent substrates and prisms, and an image display device using the polarization separation element.

JP 2009-151088 A Special table 2003-502708 gazette Special Table 2003-519818

  However, the SWS polarization separating element disclosed in Patent Document 1 needs to be manufactured by stacking one-dimensional gratings arranged with a period of 200 nm or less so that their periodic directions are orthogonal to each other, and is difficult to manufacture. is there. Moreover, in order to obtain sufficient contrast, the wire grid polarization separation element disclosed in Patent Document 2 and Patent Document 3 needs to increase the thickness of the metal grating, and 10% or more of the incident polarized light is 10% or more. It is absorbed by the metal grid part.

  The present invention provides an image display device using a wire grid polarization separation element that is easy to manufacture and can achieve both contrast and brightness because contrast can be ensured and absorption loss can be reduced by the wire grid.

An image display device according to one aspect of the present invention includes a first reflective light modulation element and a second reflective light modulation element that modulate light, a first wavelength light from a light source, and the first wavelength, respectively. The second wavelength light having a wavelength longer than the light is separated and guided to the first reflection type light modulation element and the second reflection type light modulation element, respectively, and the first reflection type light modulation element and the second reflection And a polarization separation element that synthesizes and emits the first wavelength light and the second wavelength light from the type light modulation element. Each of the polarization separation portions of the polarization separation element includes a first dielectric layer and a second dielectric layer, each of which is configured by a single dielectric film or a plurality of dielectric films stacked and having different structures from each other, A one-dimensional lattice structure provided between the first and second dielectric layers and having a metal lattice formed at a period shorter than the wavelength of the first wavelength light. The first and second wavelength lights are transmitted to the polarization separation unit from the first dielectric layer side and the second dielectric layer side in the normal direction of the polarization separation unit and the periodic direction of the one-dimensional grating structure. In the case where the light enters from a direction forming 45 degrees with respect to the normal direction in a parallel plane, a polarization component having a polarization direction orthogonal to the normal direction and orthogonal to the periodic direction is defined as the first polarization component. When the first polarization component of the first wavelength light is incident on the polarization separation unit from the first dielectric layer side, the reflectance R ₁₁ of the polarization separation unit is incident on the second dielectric layer side. And the reflectance R ₁₂ of the polarized light separating part when
R ₁₁ > R ₁₂
Satisfying the conditions
When the first polarization component of the second wavelength light is incident on the polarization separation unit from the first dielectric layer side, the reflectance R ₂₁ of the polarization separation unit and the incident light from the second dielectric layer side The reflectance R ₂₂ of the polarization separation unit is
R ₂₁ <R ₂₂
It satisfies the following condition.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacture of a polarization separation part (polarization separation element) is easy, and the image display apparatus which can display a bright and high-contrast image is realizable.

1 is a cross-sectional view illustrating a configuration of an image display apparatus that is Embodiment 1 of the present invention. FIG. 3 is a cross-sectional view showing a polarization separation element and a reflective liquid crystal display element in the image display apparatus of Example 1. FIG. 3 is a cross-sectional view illustrating a structure of a polarization separation portion of the polarization separation element according to the first embodiment. FIG. 6 is a diagram illustrating reflectance characteristics with respect to s-polarized light of the polarization separation unit according to the first embodiment. FIG. 6 is a diagram illustrating an absorption characteristic for s-polarized light of the polarization separation unit in the first embodiment. Sectional drawing which shows the structure of the polarization separation part of the polarization separation element in Example 2 of this invention. FIG. 10 is a diagram illustrating reflectance characteristics with respect to s-polarized light of a polarization separation unit according to the second embodiment. FIG. 10 is a diagram illustrating an absorption characteristic for s-polarized light of a polarization separation unit according to the second embodiment. The figure which shows the reflectance characteristic with respect to s-polarized light of the polarization separation part of the comparative example 1. The figure which shows the reflectance characteristic with respect to s polarized light by grating | lattice thickness.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a configuration of a projector 100 as an image display apparatus that is Embodiment 1 of the present invention.

  The projector 100 includes a light source 20, a polarization conversion element 21, a dichroic mirror 22, and a wavelength selective phase difference plate 23. Further, the polarization separation elements 10a and 10c, the phase difference plates 24r, 24g, and 24b, the reflection type liquid crystal panels (reflection type light modulation elements) 25r, 25g, and 25b, the combining prism 26, and the projection lens (projection optical system). 30.

  The light emitted from the light source 20 is converted into a parallel light beam in a state including blue light (first wavelength light) 11b, green light (third wavelength light) 11g, and red light (second wavelength light) 11r. Incident on the element 21.

  In this embodiment, the wavelength of blue light is 420 nm or more and 500 nm or less, and the wavelength of red light is 570 nm or more and 680 nm. The wavelength of green light is longer than the wavelength of blue light and shorter than the wavelength of red light.

  Blue light 11b, green light 11g, and red light 11r as non-polarized light are all converted to p-polarized light by the polarization conversion element 21, and then enter the dichroic mirror 22. The p-polarized light is polarized light whose electric field oscillates in the incident plane, and the s-polarized light is polarized light whose electric field oscillates in a direction perpendicular to the incident plane. The direction in which the electric field vibrates is also referred to as the polarization direction.

  The dichroic mirror 22 has a characteristic of reflecting green light. Therefore, the green polarized light 12 g is reflected by the dichroic mirror 22, and the red polarized light 12 r and the blue polarized light 12 b are transmitted through the dichroic mirror 22. Thereby, the green polarized light 12g is color-separated from the red polarized light 12r and the blue p polarized light 12b.

  The green polarized light 12g passes through the polarization separation element 10a, then passes through the phase difference plate 24g, and enters the green reflective liquid crystal panel (third reflective light modulation element) 25g. On the other hand, the red polarized light 12 r and the blue polarized light 12 b are incident on the wavelength selective phase difference plate 23. The wavelength selective phase difference plate 23 has a characteristic of rotating only the polarization direction of the blue polarized light 12r by 90 °. As a result, the red polarized light 12r remains p-polarized, and the blue polarized light 12b is converted into s-polarized light by rotating the polarization direction by 90 ° and enters the polarization separation element 10c.

  The blue polarized light 12b as s-polarized light is reflected by the polarization separation element 10c, then passes through the phase difference plate 24b, and enters the blue reflective liquid crystal panel (first reflective light modulation element) 25b. The red polarized light 12r as p-polarized light is transmitted through the polarization separating element 10c, then transmitted through the phase difference plate 24r, and is incident on the red reflective liquid crystal panel (second reflective light modulation element) 25r. In this way, the blue polarized light 12b and the red polarized light 12r are color-separated by the polarization separating element 10c and guided to the blue and red reflective liquid crystal panels 25b and 25r.

  Each of the green, red, and green reflective liquid crystal panels 25b, 25r, and 25g modulates and reflects the incident light for each pixel in accordance with the image signal. Thereby, blue image light 13b, red image light 13r, and green image light 13g as reflected light are emitted from the green, red, and green reflective liquid crystal panels 25b, 25r, and 25g. Each phase difference plate (24b, 24r, 25b) corrects a phase shift of each color light generated in the polarization separation element and each reflection type liquid crystal panel to reduce so-called leakage light.

  The blue image light 13b and the red image light 13r are again transmitted through the phase difference plates 24b and 24r, and then enter the polarization separation element 10c again. The blue image light 13b is transmitted through the polarization separation element 10c, and the red image light 13r is reflected and emitted from the polarization separation element 10c, whereby the blue image light 13b and the red image light 13r are combined. The synthesized blue image light 13b and red image light 13r are incident on the synthesis prism 26 constituting the color synthesis system and pass through the dichroic film in the synthesis prism 26.

  The green image light 13g is again transmitted through the phase difference plate 24g, is incident again on the polarization separation element 10a, is reflected, and is incident on the combining prism 26. Then, it is reflected by the dichroic film in the synthesis prism 26. Thus, the green image light 13g, the red image light 13r, and the blue image light 13b are combined and projected onto a projection surface such as a screen (not shown) via the projection lens 30.

  FIG. 2 shows the relationship among the polarization separation element 10c, the phase difference plates 24b and 24r, and the reflective liquid crystal panels 25b and 25r. The polarization separating element 10c includes a first prism (first translucent member) 1, a second prism (second translucent member) 2, and the first and second prisms 1 and 2. It is comprised by the polarization separation part 3 arrange | positioned between.

  The blue reflective liquid crystal panel 25b is disposed on the first prism 1 side in the vicinity of the polarization separating element 10c, and the red reflective liquid crystal panel 25r is disposed on the second prism 2 side. In the polarization separation element 10 c of this embodiment, s-polarized light out of the light incident on the first prism 1 is reflected by the polarization separation unit 3, and p-polarized light is transmitted through the polarization separation unit 3.

  FIG. 3 shows the structure of the polarization separation unit 3. The polarization separation unit 3 includes a first dielectric layer 3a adjacent to the first prism 1, a second dielectric layer 3b adjacent to the second prism 2, and the first and second dielectric layers. It is comprised by the wire grid (one-dimensional structure part) 3c formed between 3a, 3b.

  The wire grid 3c has a period in which a grating (metal grating) made of a metal such as aluminum, silver, gold, nickel, chromium, copper, platinum, or tungsten is shorter than the wavelength of incident light (here, the wavelength of blue light). A metal one-dimensional lattice structure formed in a one-dimensional direction.

Each of the first and second dielectric layers 3a and 3b has a structure constituted by a single dielectric film or a structure in which a plurality of dielectric films are laminated. Furthermore, the first and second dielectric layers 3a and 3b have different structures. The different structures mentioned here include a difference in the number of dielectric films to be stacked, a difference in physical film thickness of the dielectric films, a difference in material (refractive index) of the dielectric films, and the like.
The wire grid 3c is formed so that the periodic direction C of the lattice is a horizontal direction parallel to the paper surface of FIG. 3 and the longitudinal direction D of each lattice is a direction perpendicular to the paper surface of FIG. . N in FIG. 3 indicates the normal direction of the polarization separation unit 3.

  A plane parallel to the paper surface of FIG. 3 is a plane parallel to the normal direction N and the periodic direction C of the polarization separation unit 3. Further, the direction shown by the arrow I in FIG. 3 is a direction that is 45 ° with respect to the normal direction N in a plane parallel to the paper surface. The polarized light separation unit 3 receives blue s-polarized light and red p-polarized light that has passed through the first prism 1 and is not incident on the first dielectric layer 3a from the first dielectric layer 3a side. Incident in the angular range. Further, in the polarization separation unit 3, blue p-polarized light and red s-polarized light after color separation transmitted through the second prism 2 (after modulation by the liquid crystal panel) are viewed from the second dielectric layer 3b side in FIG. Incident light is incident in a predetermined incident angle range centered on a direction that forms 45 degrees with respect to the normal direction N in a plane parallel to the paper surface (not shown).

  An angle of 45 degrees with respect to the normal direction N in a plane parallel to the paper surface of FIG. 3 and a direction of 45 degrees with respect to the normal direction N within the plane parallel to the paper surface are respectively relative to the polarization separation unit 3. It can also be called a central incident angle and a central incident direction.

  When light is incident from the central incident direction, the s-polarized light corresponds to a first polarization component having a polarization direction orthogonal to the normal direction N and parallel to the direction orthogonal to the periodic direction C (longitudinal direction D), p The polarized light corresponds to a second polarization component having a polarization direction parallel to the normal direction N and the periodic direction C.

  In order for the wire grid 3c to have a polarization separation function with respect to the wavelength of visible light, the period of the wire grid 3c is desirably 200 nm or less. Furthermore, in order to prevent diffraction at a wide incident angle, it is desirable that it is 150 nm or less. Further, the first dielectric layer 3a and the second dielectric layer 3b have a characteristic of transmitting p-polarized light and reflecting s-polarized light. Thereby, when there is no dielectric layer 3a and dielectric layer 3b, a part of the light to be reflected by the wire grid 3a can be reflected by the dielectric layers 3a and 3b. Therefore, the wire grid 3a is used alone. Compared to the case, the wire grid 3a can be made thinner. As a result, both the reflectance with respect to s-polarized light and the transmittance with respect to p-polarized light in the wire grid 3a can be increased.

  In order for the first and second dielectric layers 3a and 3b to transmit p-polarized light and reflect s-polarized light, for example, dielectric films having different refractive indexes are laminated so as to satisfy the Brewster angle. There are methods for forming layers. At the Brewster angle, the p-polarized light is completely transmitted. For this reason, the H layer, which is a dielectric film having a high refractive index, and a dielectric having a lower refractive index are set so that a Brewster angle relationship is established when light enters the polarization separation unit 3 from the vicinity of the central incident angle direction. By laminating the L layer, which is a body membrane. It can transmit p-polarized light. On the other hand, the s-polarized light can be reflected by the difference in refractive index between the H layer and the L layer, and in order to further increase the reflectance, the film thickness of the H layer and the L layer is controlled, and each dielectric layer can be arbitrarily set. It can be made to function as a reflection-increasing layer that raises the reflectance of the wavelength.

  As described above, when the dielectric layer is made to function as an increased reflection layer by using thin film interference, it is difficult to simultaneously increase the reflectance in a wavelength band separated like red light and blue light. However, in the configuration shown in FIG. 1, blue light is reflected as s-polarized light when entering the polarization separation unit 3 from the first dielectric layer 3a side (first prism 1 side), and red light is converted into s-polarized light. The light is reflected when it enters the polarization separation unit 3 from the second dielectric layer 3b side (second prism 2 side). Therefore, both the reflectance of blue light and red light can be increased by using the first dielectric layer 3a as an increased reflection layer for blue light and the second dielectric layer 3b as an increased reflection layer for red light. Is possible. Thereby, the utilization efficiency of light can be improved and the brightness of the projected image can be improved.

  Furthermore, the amount of s-polarized light incident on the wire grid 3c can be reduced by using the first and second dielectric layers 3a and 3b as the high reflection layers. Thereby, the absorption loss of s-polarized light in the polarization separation unit 3 (wire grid 3c) is reduced, and generation of heat due to absorption can be suppressed. This is effective for reducing the influence of photoelasticity in the polarization beam splitter 10c.

  Hereinafter, with respect to the s-polarized light of each color light when blue light and red light are incident on the polarization splitting unit 3 from the first dielectric layer 3a side and the second dielectric layer 3b side from the central incident direction described above. The reflectance of the polarization separation unit 3 will be described.

When incident from the first dielectric layer 3a side, the reflectance of blue light (which may be the shortest wavelength in the blue wavelength region) with respect to s-polarized light is R _ba (reflectance R ₁₁ ), and red light (red wavelength region) Let R _ra (reflectance R ₂₁ ) be the reflectance for s-polarized light.

When incident from the second dielectric layer 3b side, the reflectance of blue light (which may be the shortest wavelength in the blue wavelength region) with respect to s-polarized light is R _bb (reflectance R ₁₂ ), and red light (red wavelength region) Let R _rb (reflectance R ₂₂ ) be the reflectance for the s-polarized light.

At this time, the polarization separation unit 3
R _ba > R _bb (R ₁₁ > R ₁₂ )
R _ra <R _rb (R ₂₁ <R ₂₂ )
Satisfy both conditions.

Although not necessarily satisfied, in order to obtain a brighter projected image, the reflectances R _ba , R _bb , R _ra , and R _rb are
_{R ba -R bb> 3% (} R 11 -R 12> 3%)
R _rb -R _ra > 3% (R ₂₂ -R ₂₁ > 3%)
It is desirable to satisfy at least one of the following conditions.

  In this embodiment, the first wavelength is the blue band, the second wavelength is the red band, and the third wavelength is the green band. The first to third wavelengths can be freely selected from the blue band, the red band, and the green band. You can choose. However, when p-polarized light is transmitted through the polarization separation element 10c, the absorption on the short wavelength side tends to be larger than that on the long wavelength side. For this reason, as in the configuration of the present embodiment, it is generated at 10c that light on the short wavelength side is incident on the polarization separation element 10c as s-polarized light and light on the long wavelength side is incident on the polarization separation element 10c as p-polarized light. Less absorption is preferable.

  In this embodiment, the phase difference plates 24b, 24g, and 24r are used to correct the phase shift. However, the phase difference plate is not always necessary.

  Furthermore, in this embodiment, the wavelength-selective phase difference plate 23 is used. For example, a light source that divides the light source into a plurality of colors and controls the polarization for each color or uses only a single linearly polarized light is used. The wavelength selective phase difference plate is not always necessary.

As described above, in the present embodiment, the first dielectric layer 3a mainly functions as a reflection enhancement layer for blue light, and the second dielectric layer 3b mainly increases the reflection layer for red light. Acts as Therefore, the average physical thickness d _A of the first dielectric layer 3a, the average physical thickness d _B of the second dielectric layer 3b is
d _A <d _B
It is desirable to satisfy the following conditions. Here, the average physical film thickness is an average value of physical film thicknesses of one or more dielectric films constituting each dielectric layer (3a, 3b).

  In the above embodiment, the reflective liquid crystal projector including the color separation / synthesis optical system has been described. However, a projector using a DMD (digital micromirror device), which is a reflective light modulation element other than the liquid crystal panel, is also included in the image display apparatus as another embodiment of the present invention.

Hereinafter, specific numerical examples of the polarization separation element 10c described above will be described.
[Numerical example 1]
FIG. 3 shows a polarization separation element of Numerical Example 1. The refractive indexes of the first and second prisms 1 and 2 are n = 1.6. The wire grid 3c is made of aluminum, and the space between the lattices is air or vacuum. The first and second dielectric layers 3a and 3b are formed by laminating an L layer with a refractive index of 1.46 and an H layer with 2.12 in the order of LHL from the prism side adjacent to each dielectric layer. With a structure. Table 1 shows the thickness of each dielectric film in order from the first prism 1 side. The filling factor (grating width / period) of the wire grid 3c is 0.55, the grating thickness is 50 nm, and the grating period is 100 nm.

  The wavelength characteristics of the reflectance of s-polarized light and the absorption loss are shown in FIGS. 4 and 5, respectively. In these drawings, when s-polarized light is incident in the above-described central incidence direction from the first dielectric layer 3a side (first prism 1 side) (hereinafter referred to as the first dielectric layer 3a side incidence). The characteristics are shown by a solid line. Further, the characteristics when s-polarized light is incident in the central incident direction from the second dielectric layer 3c side (second prism 2 side) (hereinafter referred to as incident upon the second dielectric layer 3b side) are indicated by broken lines. ing.

The shortest wavelength of blue light is 420 nm, and the longest wavelength of red light is 670 nm. At this time, from FIG. 4, the reflectance R _ba when the first dielectric layer 3 a is incident on the shortest wavelength of blue light and the reflectance R _bb when the second dielectric layer 3 b is incident are
R _ba > R _bb
Satisfied.

The reflectance R _rb during the second reflectance during the dielectric layer 3b side incident R _ra and second dielectric layer 3b side entrance at the longest wavelength of the red light,
R _ra <R _rb
Satisfied.

Further, the reflectances R _ra and R _rb at the longest wavelength of red light are
R _rb -R _ra > 3%
Satisfied.

From FIG. 5, the absorption loss of blue light is smaller than the absorption loss of red light when incident on the first dielectric layer 3a side. Moreover, the absorption loss over a wide wavelength band is as low as 4% or less when incident on the second dielectric layer 3b side. Therefore, by using this polarization separation element as the polarization separation element 10c in FIG. 1, it is possible to realize a projector that can obtain a bright and high-contrast projection image.
[Numerical example 2]
FIG. 6 shows a polarization separation element of Numerical Example 2. The refractive indexes of the first and second prisms 1 and 2 are n = 1.6. The wire grid 3c is made of aluminum, and the space between the lattices is filled with a dielectric having a refractive index of 1.46.

  The first and second dielectric layers 3a and 3b are formed by laminating an L layer with a refractive index of 1.46 and an H layer with 2.12 in the order of LHL from the prism side adjacent to each dielectric layer. With a structure. By using the same dielectric as the L layer adjacent to the wire grid 3c between the lattices, the structure can be manufactured more easily than in the first embodiment. Table 2 shows the thickness of each dielectric film in order from the first prism 1 side. The filling factor of the wire grid 3c is 0.4, the grating thickness is 40 nm, and the grating period is 100 nm.

  The wavelength characteristics of the reflectance and absorption loss of s-polarized light are shown in FIGS. 7 and 8, respectively. Also in these drawings, the characteristics at the time of incidence on the first dielectric layer 3a side (when entering from the central incidence direction) are indicated by solid lines, and the characteristics at the time of incidence on the second dielectric layer 3c side (when entering from the central incidence direction) are shown. The characteristic is indicated by a broken line.

The shortest wavelength of blue light is 420 nm, and the longest wavelength of red light is 670 nm. At this time, from FIG. 4, the reflectance R _ba when the first dielectric layer 3 a is incident on the shortest wavelength of blue light and the reflectance R _bb when the second dielectric layer 3 b is incident are
R _ba > R _bb
Satisfied.

The reflectance R _rb during the second reflectance during the dielectric layer 3b side incident R _ra and second dielectric layer 3b side entrance at the longest wavelength of the red light,
R _ra <R _rb
Satisfied.

Further, the reflectances R _ba and R _bb at the shortest wavelength of blue light are
_{Rba- Rbb} > 3%
And the reflectances R _ra and R _rb at the longest wavelength of red light are
R _rb -R _ra > 3%
Satisfied.

Further, from FIG. 8, the absorption loss of blue light is smaller than the absorption loss of red light when incident on the first dielectric layer 3a side. Moreover, the absorption loss of red light is smaller than the absorption loss of blue light when incident on the second dielectric layer 3b side. Therefore, by using this polarization separation element as the polarization separation element 10c in FIG. 1, it is possible to realize a projector that can obtain a bright and high-contrast projection image.
[Comparative Example 1]
In FIG. 9, the wavelength characteristic of the reflectance with respect to s-polarized light of the polarization beam splitting element as the comparative example 1 is shown. In this comparative example, the polarization separation unit is configured only by a wire grid. The wire grid is made of aluminum, and the space between the grids is air or vacuum. The filling factor is 0.4, the grating thickness is 100 nm, and the grating period is 100 nm.

Also in FIG. 9, the characteristics when incident from the prism 1 side in the above-described central incident direction (corresponding to the first dielectric layer side incident in the embodiment) are indicated by solid lines, and from the prism 2 side in the above-described central incident direction. The characteristics when incident (corresponding to the incident on the second dielectric layer side of the embodiment) are indicated by broken lines. However, in the configuration of this comparative example, the characteristics when the light is incident from the prism 1 side and the light incident from the prism 2 side are the same, and therefore the solid line and the broken line appear to overlap in FIG. In this comparative example, the reflectance with respect to s-polarized light is about 90%, as compared with the examples (numerical examples 1 and 2) in which the first and second dielectric layers 3a and 3b and the wire grid 3c are combined. It can be seen that the reflectance is low.

  Here, since the reflectance and transmittance of the wire grid depend on the lattice thickness, when the lattice thickness of the wire grid of this comparative example is changed, the center wavelength of blue light is 460 nm and the center wavelength of red light is 620 nm. The reflectance with respect to s-polarized light is shown in FIG. From this figure, the reflectance of s-polarized light increases by increasing the grating thickness until the grating thickness is about 100 nm. However, the reflectance is about 90% even if the grating thickness is increased further. It turns out that it becomes constant regardless. Therefore, it is difficult to realize a high s-polarized light reflectance as in the embodiment with the configuration of only the wire grid.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

  An image display device such as a projector that can display a bright and high-contrast image can be provided.

3 Polarization Separator 3a First Dielectric Layer 3b Second Dielectric Layer 3c Wire Grid 10c Polarization Separation Elements 25b, 25b, 25r Reflective Liquid Crystal Panel 100 Liquid Crystal Projector

Claims (6)

A first reflective light modulation element and a second reflective light modulation element that respectively modulate light;
The first wavelength light from the light source and the second wavelength light having a longer wavelength than the first wavelength light are separated into the first reflective light modulation element and the second reflective light modulation element, respectively. A polarization separation element that synthesizes and emits the first wavelength light and the second wavelength light from the first reflection type light modulation element and the second reflection type light modulation element,
The polarization separation portion of the polarization separation element is
A first dielectric layer and a second dielectric layer each composed of a single dielectric film or a plurality of dielectric films laminated and having different structures;
A one-dimensional lattice structure provided between the first and second dielectric layers, wherein a metal lattice is formed with a period shorter than the wavelength of the first wavelength light,
The first and second wavelength lights are transmitted to the polarization separation unit from the first dielectric layer side and the second dielectric layer side, and the normal direction of the polarization separation unit and the one-dimensional grating structure. In the case of incidence from a direction forming 45 degrees with respect to the normal direction in a plane parallel to the periodic direction of
When a polarization component having a polarization direction perpendicular to the normal direction and perpendicular to the periodic direction is a first polarization component,
Said first of said second dielectric layer side and the reflectance R ₁₁ of the polarizing separation unit when said first polarization component of the wavelength light is incident from the first dielectric layer side to said polarization separation section And the reflectivity R ₁₂ of the polarization separation part when entering from
R ₁₁ > R ₁₂
Satisfying the conditions
The second dielectric layer side and the reflectance R ₂₁ of the polarizing separation unit when said first polarization component of the second wavelength is incident on the first dielectric layer side to said polarization separation section And the reflectance R ₂₂ of the polarized light separating portion when entering from
R ₂₁ <R ₂₂
An image display device satisfying the following conditions:   The image display device according to claim 1, wherein the period of the one-dimensional lattice structure is 200 nm or less. The wavelength of the first wavelength light is 420 nm or more and 500 nm or less, and the wavelength of the second wavelength light is 570 nm or more and 680 nm,
When a polarization component having a polarization direction orthogonal to the polarization direction of the first polarization component is a second polarization component as a second polarization component,
The polarization separation element is
Of the first wavelength light, the first polarization component is reflected and guided to the first reflection type light modulation element, and the second polarization component from the first reflection type light modulation element is transmitted. And then
Of the second wavelength light, the second polarization component is transmitted and guided to the second reflective light modulation element, and the first polarization component from the second reflection light modulation element is reflected. The image display apparatus according to claim 1, wherein the image display apparatus is ejected. The reflectances R ₁₁ , R ₁₂ , R ₂₁ and R ₂₂ are:
R ₁₁ -R ₁₂ > 3%
R ₂₂ -R ₂₁ > 3%
The image display apparatus according to claim 1, wherein at least one of the following conditions is satisfied. The average physical film thickness d _{A of} the one or more dielectric films constituting the first dielectric layer, and the one or more dielectric films constituting the second dielectric layer. the average physical thickness _{d B} is,
d _A <d _B
The image display apparatus according to claim 3, wherein the following condition is satisfied. A third reflective light modulation element that modulates third wavelength light having a wavelength longer than the first wavelength light and shorter than the second wavelength light;
A dichroic mirror,
A color composition system,
The dichroic mirror separates the third wavelength light from the light source from the first and second wavelength lights,
The color synthesis system synthesizes the first and second wavelength light from the first and second reflective light modulation elements and the third wavelength light from the third reflective light modulation element. The image display device according to claim 1, wherein the image display device emits the image.