JP3132499B2 - Color synthesis optical system and display optical system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color synthesizing optical system, and more particularly to a color synthesizing optical system for synthesizing and projecting different color information from a plurality of display panels. .

[0002]

2. Description of the Related Art Conventionally, in a color synthesizing optical system, a so-called multi-plate system has been often used for an image display element used as a display panel. The purpose of this is to perform color display in particular, and a dichroic mirror or a cross dichroic prism using surface reflection has been mainly used for color synthesis at that time.

However, in the configuration of the dichroic mirror using the surface reflection, since the reflection is performed directly on the dichroic film on the surface, the light from each image display element is reflected by the dichroic mirror or transmitted through the dichroic mirror. There is a difference in whether or not the light passes through the flat glass plate serving as the substrate, the optical path length to the projection plane is different, and the magnitude of the astigmatic difference occurs, which makes correction difficult. Image performance deteriorates.

In order to make the optical path length the same, recently, as a dichroic mirror, for example, Japanese Patent Laid-Open No.
As described in Japanese Patent Application Laid-Open No. 07501, a configuration in which flat glass is laminated is used. This is, as schematically shown in FIG. 6, two flat glass plates 41 and 4.
2 is provided with a bonding portion 43 by bonding. The joint 43 may have a slight air gap. Here, the two flat glass plates have the same thickness, and a dichroic coat is applied to one of the surfaces facing each other.

For example, in FIG. 1, the surface 41a of the flat glass 41 is a dichroic coated surface. Also,
The surface 42a of the flat glass 42 does not need to be coated in the case of the above-mentioned bonding, but is coated with an anti-reflection coating when a slight air gap is used instead of the joint 43. The surface 42a is a dichroic coat surface, and the surface 4a
1a may be provided with an anti-reflection coat. Further, the outer surfaces 41b and 42b of the flat glass plates 41 and 42, respectively,
It has an anti-reflection coated surface.

In such a dichroic mirror, both transmitted light and reflected light pass through two glass plates, so that they are completely optically equivalent. Further, the above-mentioned slight air gap specifically means 1 mm or less, and if it is larger than that, the holding member of the dichroic mirror becomes large, which is not preferable. As the dichroic mirror, the one having the configuration described above is mainly used.

FIG. 7 is a graph showing characteristics of a general dichroic film. That is, it shows how the characteristics change depending on the polarized light incident on the dichroic film. In the figure, the horizontal axis indicates the wavelength of the incident light (unit: nm), and the vertical axis indicates the transmittance. The figure shows the case where the dichroic mirror using reflection has an incident angle of 45 degrees on the surface. As shown in the figure, the transmission wavelength region (the region where the transmittance is around 1) is the P-polarized light indicated by the broken line. The S-polarized light indicated by the solid line is larger in the reflection wavelength region (region where the transmittance is near 0). Then, the two overlap each other at the portion where the transmittance rises, as indicated by the oblique lines. In addition, the reflection characteristics in the reflection wavelength region are flatter and better reflected by S-polarized light.

Therefore, in the color synthesis by the dichroic mirror, when at least the wavelength region of the reflected light and the wavelength region of the transmitted light are adjacent to each other, the boundary is set so as to have the wavelength within the above-mentioned hatched region. If the configuration is such that S-polarized light is reflected and P-polarized light is transmitted, it is advantageous in terms of efficiency and image performance. Incidentally, for a dichroic film having the characteristics shown in the same figure, for example, at the vicinity of 480 nm, B (blue) S-polarized light is reflected and G (green) P
What is necessary is just to make it the structure which transmits polarized light and colors these two colors.

At this time, R having a longer wavelength than these
Regarding the (red) light, it can be transmitted satisfactorily irrespective of the type of polarized light.
As a result, a total of three colors can be synthesized. If the two colors of G and R are to be synthesized before this, a configuration is used in which G P-polarized light is transmitted and R S-polarized light is reflected, and a dichroic film having characteristics suitable for it is used. What is necessary is just to use the dichroic mirror which has.

Further, the characteristics of the dichroic film have the property of shifting to a single wavelength side and a long wavelength side, respectively, according to the magnitude of the incident angle. Therefore, if the margin of the wavelength width indicated by the diagonal lines can be used, Since color unevenness to be described later can be reduced, this is also advantageous in this respect. That is, in the non-telecentric optical system, there is a difference in the incident angle of the principal ray between the on-axis ray and the off-axis ray, and even in the telecentric optical system, there is a spread of the ray due to the existence of the F-number, but these effects are reduced. Can do things. It should be noted that a countermeasure is separately taken by the present invention for the difference in the incident angle in the non-telecentric optical system, which will be described later.

Therefore, in the color synthesis by the dichroic mirror, a configuration in which S-polarized light is reflected and P-polarized light is transmitted has been mainly employed. Here, the S-polarized light has a vibration direction perpendicular to a plane including the light before and after the light reflected by the dichroic mirror, and the P-polarized light has a vibration parallel to the plane. Light that has a direction.

[0012]

However, a typical anti-reflection coating applied to a dichroic mirror is S
There is a problem that antireflection characteristics are poor for polarized light.
FIG. 8 is a graph showing an example of the characteristics of the ordinary antireflection film when the incident angle is 45 degrees. In the figure,
The horizontal axis represents the wavelength of the incident light (unit: nm), and the vertical axis represents the reflectance. As shown in the figure, in the P-polarized light indicated by ▲ and the broken line, the wavelength region of visible light (for example, 400 to 700 n) is used.
m), the reflectance is suppressed to approximately 1% or less,
Although the antireflection property is good, the S-polarized light indicated by the solid line
Nearly 2% reflection is observed in the visible light wavelength region, and the antireflection characteristics are poor.

At this time, in the above-described color synthesis using the dichroic mirror, if the configuration is such that the S-polarized light is reflected and the P-polarized light is transmitted, unnecessary light is generated due to poor antireflection characteristics. FIG. 9 is a diagram schematically illustrating a mechanism in which such unnecessary light rays are generated. In the figure, reference numerals 1 and 2 denote display panels, reference numerals 3 and 4 denote respective condenser lenses, and reference numeral 5 denotes a dichroic mirror. A dichroic film 6 is provided between the two flat glasses of the dichroic mirror 5.

A light beam indicated by an arrow A from the display panel 1 passes through the dichroic mirror 5 through the condenser lens 3, and a light beam indicated by an arrow B from the display panel 2 passes through the condenser lens 4. It is assumed that the light is reflected by the dichroic mirror 5 and is combined into a light beam indicated by an arrow C. At this time, as shown in FIG. 3A, even if an antireflection film is provided on the surface 5b where the light beam of arrow B is incident on the dichroic mirror 5, if the antireflection property is poor, the arrow B Are reflected and become unnecessary light rays as indicated by a broken-line arrow a.

Further, a part of the light beam indicated by the arrow B which is normally reflected by the dichroic film 6 is further reflected by the anti-reflection film, is again reflected by the dichroic film 6, and is unnecessary as shown by a broken arrow b. It becomes a ray. These unnecessary light rays create an unnecessary image near an image displayed by a regular light ray as shown by an arrow C, and deteriorate image performance.

As shown in FIG. 1B, an antireflection film is provided on a surface 5a on which the light beam indicated by the arrow A is incident on the dichroic mirror 5, and a light exit surface 5b (surface on which the light beam indicated by the arrow B is incident) is provided. ), Even if an anti-reflection film is provided, if these anti-reflection characteristics are poor, a part of the light beam of arrow A
Unnecessary light rays as shown by the broken arrow c. That is, a part of the light beam of the arrow A transmitted through the dichroic film 6
b Reflected by the anti-reflection film, transmitted again through the dichroic film 6, a part of which is further reflected by the surface 5a anti-reflection film,
Unnecessary light rays as shown by the broken arrow c.

Such an unnecessary light beam creates an unnecessary image near an image displayed by a regular light beam as shown by an arrow C, thereby deteriorating the image performance. However, FIG.
In the case of (1), the unnecessary light is secondary reflection by the two anti-reflection films, so that the intensity is lower than that in the case of FIG.
The effect is small. As described above, the antireflection film generally has poor antireflection characteristics with respect to S-polarized light and is favorable with respect to P-polarized light. However, unnecessary light rays as shown in FIG. 9 can be suppressed, but instead, the above-mentioned characteristics of the dichroic film cause disadvantages in image performance and cause color unevenness.

In the configuration using the above-mentioned cross dichroic prism, there is no problem in terms of imaging performance and unnecessary light rays. However, since the volume is generally large, a large glass block is required, and four rectangular prisms are bonded together. Since the dichroic film is coated on the surface sandwiching the right-angled side, very high precision is required for bonding, resulting in a very high cost.

The present invention has been made in view of the above problems, and has as its object to provide a color synthesis optical system which performs color synthesis using a mirror and has low cost and good imaging performance.

[0020]

In order to achieve the above object, the present invention provides at least two image display elements and a dichroic mirror for synthesizing image information of the image display elements. Is provided with a dichroic film on the back surface of the flat plate or in the vicinity of the back surface, is a color combining optical system that performs the combining using reflection and transmission of the dichroic mirror, and light combined using the reflection is In a color combining optical system in which an anti-reflection film is provided on an incident surface of the dichroic mirror where the S-polarized light is incident on the dichroic mirror, the anti-reflection film has a wavelength of the S-polarized light. The configuration is such that the antireflection effect is high for the region.

The wavelength region of light synthesized using the reflection and the wavelength region of light synthesized using the transmission are:
The light that is adjacent to the light and that is synthesized using the transmission is P-polarized light with respect to the dichroic mirror.

The image display device further includes three image display elements, and first and second dichroic mirrors for synthesizing image information of the image display elements, wherein the first dichroic mirror synthesizes the image information using the reflection. The transmitted light is red S-polarized light, the light combined using the transmission is green P-polarized light, and the light combined using the reflection in the second dichroic mirror is blue S-polarized light. Light that is polarized light and combined using the transmission is the red S-polarized light and the green P-polarized light, and is provided on the incident surface of the first dichroic mirror on which the red S-polarized light is incident. The anti-reflection film has a high anti-reflection effect on the red S-polarized light and the green P-polarized light, and is provided on the incident surface of the second dichroic mirror on which the blue S-polarized light is incident. An anti-reflection effect is higher configured for the red S polarized light and green P polarized light and blue S-polarized light.

Further, the antireflection film provided on the incident surface of the dichroic mirror, on which the light synthesized using the transmission is incident, prevents reflection in the polarization and wavelength region of the light synthesized using the transmission. The configuration is effective.

Further, the reflectivity to light incident on the antireflection film is 1% or less.

The color synthesizing optical system is a non-telecentric optical system, and changes the thickness of the dichroic film of the dichroic mirror at the incident position in accordance with the incident angle of the principal ray incident on the dichroic mirror. The dichroic film is configured to have substantially constant transmittance characteristics with respect to wavelength.

Further, a configuration having a dichroic mirror satisfying the following conditional expression is adopted. 8 <D / t <50, where t: the thickness of the flat glass on which the dichroic film is coated, D: the long side or the long diameter of the effective range in which the dichroic mirror is used.

[0027]

[0028]

Embodiments of the present invention will be described below with reference to the drawings. In the present invention, an antireflection film having good antireflection characteristics with respect to S-polarized light is used. The specific configuration of such an antireflection film is, for example, first, second, third, fourth,
In a five-layer antireflection film in which a fifth layer of thin film is laminated, the refractive indices and the thicknesses of the first, second, third, fourth, and fifth layers are n1, n2, n3, n4, n5, and n5. d1, d2, d
3, d4, d5, and when the design dominant wavelength is λ0, n2 or n3 is 1.56 or less, and n4 ≧ n2> n1 ≧ n5 n2> n30 0 <n1d1 ≦ 0.06λ0 0.03λ0 ≦ n2d2 ≦ 0.15λ0 0.02λ0 ≦ n3d3 ≦ 0.19λ0 0.09λ0 ≦ n4d4 ≦ 1.30λ0 0.24λ0 ≦ n5d5 ≦ 0.36λ0 or n4 ≧ n2> n1 ≧ n5 n2> n3 0.20 ≦ n1d1 ≦ 1.25λ0 0.03λ0 ≦ n2d2 ≦ 0.15λ0 0.02λ0 ≦ n3d3 ≦ 0.19λ0 0.09λ0 ≦ n4d4 ≦ 1.30λ0 0.24λ0 ≦ n5d5 ≦ 0.36λ0

Further, in the antireflection film having the above structure, when the refractive index of the substrate is ns, 1.50 ≦ ns ≦ 1.85 1.35 ≦ n1 ≦ 1.80 2.00 ≦ n2 ≦ 2. 60 1.35 ≦ n3 ≦ 1.80 2.00 ≦ n4 ≦ 2.60 1.38 ≦ n5 ≦ 1.48.

In the above-described antireflection film, the first
The layers are MgF ₂ , thiolite, SiO ₂ , Al ₂ O ₃ , MgO
And the second layer is made of TiO ₂ , Z
nS, ZrTiO ₄ , Ta ₂ O ₅ , as a main component, and the third layer is made of MgF ₂ , thiolite, SiO ₂ , A
l ₂ O _3, and one or more principal components of MgO, the fourth layer is _{TiO 2, ZnS, ZrTiO 4,} Ta 2 O 5, 1 or more of the main component, the fifth layer MgF _2, It is characterized by using one or more of thiolite and SiO ₂ as main components. The thin film of each of the above layers can be formed by a vacuum evaporation method or the like.

Alternatively, as another configuration, in a four-layered antireflection film in which first, second, third, and fourth thin films are laminated in order from the substrate side, the first, second, third, and The refractive index and film thickness of the fourth layer are n1, n2, n3, n4 and d1, d
2, d3, d4, and when the design dominant wavelength is λ0, n3>n2> n1 ≧ n4, 0 <n1d1 ≦ 0.75λ0, 0.20λ0 ≦ n2d2 ≦ 0.43λ0, 0.07λ0 ≦ n3d3 ≦ 1.10λ0, 0.28λ0 ≦ n4d4 ≦ 0.35λ0.

Further, in the antireflection film having the above structure, when the refractive index of the substrate is ns, 1.50 ≦ ns ≦ 1.85 1.35 ≦ n1 ≦ 1.48 1.47 ≦ n2 ≦ 1. 80 2.30 ≦ n3 ≦ 2.60 1.35 ≦ n4 ≦ 1.48.

In the above-described antireflection film having another configuration, the first layer is mainly composed of one or more of MgF ₂ , thiolite and SiO ₂ , and the second layer is composed of SiO ₂ , YF ₃ , Al
One or more of ₂ O ₃ , Y ₂ O ₃ and MgO as main components;
The third layer is characterized by containing one or more of TiO ₂ and ZnS as main components, and the fourth layer is mainly made of one or more of MgF ₂ , thiolite and SiO ₂ .

Alternatively, the first layer is characterized by containing MgF ₂ as a main component. Alternatively, the first layer is mainly composed of SiO ₂ , and the optical thickness n1d1 of the first layer is set in a range of 0.15λ0 ≦ n1d1 ≦ 0.75λ0. The thin film of each of the above layers can be formed by a vacuum evaporation method or the like.

FIG. 1 is a graph showing an example of such an anti-reflection film used in the color synthesizing optical system of the present invention when the incident angle is 45 degrees. In the figure, the horizontal axis indicates the wavelength of the incident light (unit: nm), and the vertical axis indicates the reflectance.

As shown in the figure, in the case of the S-polarized light indicated by the solid line, the B (blue) wavelength region (for example, 400 to 500) is used.
nm), the reflectance is sufficiently suppressed to 1% or less as an example, and the antireflection property is good. Also, in the R (red) wavelength region (for example, 600 to 700 nm), a certain degree of antireflection effect is seen, though insufficient. Further, for P-polarized light indicated by ▲ and a broken line, G (green)
The anti-reflection characteristics are good in the wavelength region (for example, 500 to 600 nm).

FIG. 2 is a graph showing another example of the antireflection film used in the color synthesizing optical system of the present invention when the incident angle is 45 degrees. Also in this figure, the horizontal axis indicates the wavelength of the incident light (unit: nm), and the vertical axis indicates the reflectance. As shown in the figure, in the case of the S-polarized light indicated by the solid line, the reflectance is sufficiently suppressed to, for example, 1% or less in the R (red) wavelength region (for example, 600 to 700 nm). is there. In the G (green) wavelength region (for example, 500 to 600 nm), the reflectance is generally suppressed to 1% or less.

FIG. 3 is a diagram schematically showing an example of a two-color color synthesizing optical system according to the present invention. In the figure, reference numerals 1 and 2 denote display panels, reference numerals 3 and 4 denote respective condenser lenses, and reference numeral 5 denotes a dichroic mirror. Dichroic mirror 5
A dichroic film 6 is provided between the two flat glass plates. As shown in the drawing, a light beam indicated by an arrow A from the display panel 1 passes through a dichroic mirror 5 via a condenser lens 3, and a light beam indicated by an arrow B from the display panel 2 is transmitted by a condenser lens 4. , Are reflected by the dichroic mirror 5, and are combined into light rays indicated by an arrow C.

Here, the light beam of the arrow A is G (green) P-polarized light having a wavelength region of, for example, 500 to 600 nm, and the light beam of the arrow B is R light having a wavelength region of, for example, 600 to 700 nm.
(Red) S-polarized light. At this time, the antireflection film provided on the surface 5a where the light beam of the arrow A is incident on the dichroic mirror 5 has a good antireflection property for the P-polarized light of G, and the light beam of the arrow B is incident on the dichroic mirror 5. The antireflection film provided on the surface 5b may be configured to have good antireflection characteristics with respect to R S-polarized light and G P-polarized light.

In this case, the anti-reflection film provided on the surface 5a may be, for example, a conventional anti-reflection film having characteristics as shown in FIG. 8 (of course, as shown in FIG. 1). An anti-reflection film provided on the surface 5b may be an anti-reflection film having the characteristics shown in FIG. A membrane is used.

Since the structure of such a color synthesizing optical system is mainly a non-telecentric optical system, in this case, as shown in FIG.
a and Ba) and off-axis rays (Ab, Ac and Bb, Bc)
And the incident angles of the respective principal rays with respect to the dichroic mirror 5 are different. At this time, as described in the above-mentioned conventional technique, the characteristics of the dichroic film are shifted to a single wavelength side and a long wavelength side in accordance with the magnitude of the incident angle, respectively. Color unevenness occurs with light rays.

This is because, when the film thickness is constant, the length of the light passing through the dichroic film varies depending on the incident angle, so that the apparent film thickness changes and the characteristics of the film change. Because. Therefore, the film thickness is changed according to the incident angle depending on the incident position, so that the characteristics of the film are uniform regardless of on-axis and off-axis.

For example, in this embodiment, the thickness of the portion where the off-axis light beam Ab is incident is made thinner and the thickness of the portion where the off-axis light beam Ac is incident is thicker than the on-axis light beam Aa. Also,
Compared with the on-axis light beam Ba, the film thickness of the portion where the off-axis light beam Bb is incident is made thinner, and the film thickness of the portion where the off-axis light beam Bc is incident is made thicker. This is not only for dichroic membranes,
The same treatment is applied to the antireflection film. Also,
The above-described treatment is similarly applied to the following three color synthesis optical system examples.

FIG. 4 is a diagram schematically showing a display optical system using an example of the three-color combining optical system of the present invention. In the figure, reference numerals 1 and 2 denote display panels, reference numerals 3 and 4 denote respective condenser lenses, and reference numeral 5 denotes a dichroic mirror. A dichroic film 6 is provided between the two flat glasses of the dichroic mirror 5. As shown in the figure,
The G light beam from the display panel 1 passes through the dichroic mirror 5 via the condenser lens 3, and the R light beam from the display panel 2 is reflected by the dichroic mirror 5 via the condenser lens 4, and The light rays are combined into R and G light rays.

Here, the light beam of G has a wavelength range of, for example, 50
The light ray of R is P-polarized light of 0 to 600 nm, and the light ray of R is S-polarized light having a wavelength region of, for example, 600 to 700 nm. At this time,
The antireflection film provided on the surface 5a on which the G light beam enters the dichroic mirror 5 has good antireflection characteristics for the P-polarized light.
The anti-reflection film provided on the surface 5b which is incident on the surface may have a good anti-reflection property with respect to R S-polarized light and G P-polarized light. The above configuration is the same as that shown in FIG.

Further, 7 is a display panel, 8 is a condenser lens thereof, 9 is a dummy glass made of flat glass for optically making the optical path of the B light ray equivalent to the optical paths of the R and G light rays, and 10 is a dummy glass. It is a dichroic mirror. A dichroic film 11 is provided between the two flat glasses of the dichroic mirror 10. As shown in the drawing, the B light beam emitted from the display panel 7 passes through the dummy glass 9 via the condenser lens 8 and is reflected by the dichroic mirror 10, and the R and G light beams pass through the dichroic mirror 10. Then, they are combined into R, G, B light rays.

Here, the B ray has a wavelength range of, for example, 40
S-polarized light of 0 to 500 nm. At this time, the anti-reflection film provided on the surface 9a where the B light beam enters the dummy glass 9 and the surface 9b where it exits has good anti-reflection characteristics with respect to the S-polarized light. The anti-reflection film provided on the surface 10a incident on the dichroic mirror 10 has good anti-reflection characteristics with respect to the S-polarized light of R and the P-polarized light of G, and the surface 10b (R , And G), the antireflection film provided on the (surface on which the G light beam is emitted) has good antireflection characteristics with respect to R S-polarized light, G P-polarized light, and B S-polarized light. As an anti-reflection film satisfying these conditions, for example, a film having characteristics as shown in FIG. 1 can be used.

The R, G, and B rays combined by the three color combining optical systems as described above are projected by the projection optical system 12.
It is guided to a projection plane (not shown) and forms an image. At this time, the R, G, and B rays are respectively passing through optically equivalent optical paths in the color combining optical system, and the same astigmatic difference is caused by the dichroic mirrors 5 and 10 or the dummy glass 9 respectively. It has occurred. To compensate for this,
In the projection optical system 12, a lens surface having a different power (toric) in a direction parallel to the plane of the drawing and a direction perpendicular thereto is provided so that the lens back does not extend. Examples of such a surface include a cylinder surface, a toric surface, and a free-form surface.

Incidentally, in the dichroic mirror, a configuration is adopted in which a dichroic film is coated on a flat glass. At this time, however, there is a problem that the flat glass is deformed by the stress of the dichroic film.
FIG. 5 schematically shows the state. As shown in FIG. 1A, when a dichroic film is coated on the reflection surface 13a of the ordinary flat glass 13, the flat glass 13 is deformed and warped as indicated by the arrow due to the stress. In addition, as shown in FIG.
When the dichroic film is coated on the reflecting surface 14a of No. 4, the flat glass 14 is greatly deformed by the stress as shown by the arrow, and becomes more warped than the normal flat glass 13.

As described above, when the deformation of the flat glass increases, the distortion of the reflection surface measured by the Newton ring cannot be tolerated. To prevent such deformation,
For example, as shown in FIG. 4C, when a dichroic film is coated on the reflection surface 15a of the flat glass 15 which has been deformed with a curvature in the opposite direction in advance, the flat glass 15 is distorted by the stress as shown by the arrow. Deforms in the direction to cancel each other out, resulting in a distortion-free dichroic mirror. However, since this method is inferior in productivity, a method is usually used in which the thickness of the flat glass is regulated to keep the distortion within an allowable range.

Specifically, the dimensions are set so as to satisfy the following conditional expressions. 8 <D / t <50, where t: the thickness of the flat glass on which the dichroic film is coated, D: the long side or the long diameter of the effective range in which the dichroic mirror is used. If the value exceeds the upper limit of the above conditional expression, the distortion becomes too large. Conversely, if the thickness is less than the lower limit, the thickness of the flat glass becomes too thick, resulting in high cost.

Further, the following conditional expression is satisfied:
When each dimension is set, it is more advantageous in terms of both distortion and cost. 8 <D / t <20 By the way, in the present embodiment, for example, one flat glass having a thickness of 3 mm and an effective range of 50 mm on the long side, that is, D
The one with /t=16.7 is used as a dichroic mirror.

[0053]

As described above, according to the present invention,
By performing color synthesis using a mirror, it is possible to provide a color synthesis optical system having low cost and good imaging performance.

In particular, according to the first, second, fourth, and fifth aspects, it is possible to prevent unnecessary light rays and obtain good image forming performance without color unevenness.

According to the third aspect of the present invention, in the three-color color synthesizing optical system, it is possible to prevent unnecessary light rays and obtain good imaging performance without color unevenness.

According to the sixth aspect, in the non-telecentric optical system, the characteristics of the dichroic film can be made uniform for the principal rays having different incident angles, and color unevenness can be eliminated.

According to the seventh aspect, the distortion of the dichroic mirror can be reduced, and the influence on the imaging performance can be kept within an allowable range.

[0058]

[Brief description of the drawings]

FIG. 1 is a graph showing characteristics of an antireflection film used in a color combining optical system of the present invention.

FIG. 2 is a graph showing characteristics of an antireflection film used in the color combining optical system of the present invention.

FIG. 3 is a view schematically showing an example of a two-color color synthesizing optical system according to the present invention.

FIG. 4 is a diagram showing a display optical system using an example of a three-color color synthesizing optical system of the present invention.

FIG. 5 is a view showing a state in which a flat glass is deformed by a dichroic film.

FIG. 6 is an explanatory view schematically showing a configuration of a dichroic mirror.

FIG. 7 is a graph showing characteristics of a general dichroic film.

FIG. 8 is a graph showing an example of a characteristic of a normal antireflection film.

FIG. 9 is a diagram schematically showing a mechanism of generating unnecessary light rays.

[Explanation of symbols]

 1,2,7 Display panel 3,4,8 Condenser lens 5,10 Dichroic mirror 6,11 Dichroic film 9 Dummy glass 12 Projection optical system

Continuation of the front page (56) References JP-A-5-107501 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 27/18 G02F 1/1335 G02B 1/10 G03B 21 / 00 G03B 33/12

Claims (8)

(57) [Claims] At least two image display elements, and a dichroic mirror for synthesizing image information of the image display element, wherein the dichroic mirror has a dichroic film on or near a back surface of a flat plate. A color combining optical system for performing the combining using reflection and transmission of the dichroic mirror, wherein light combined using the reflection is S-polarized light with respect to the dichroic mirror, and the S-polarized light is incident on the dichroic mirror; In a color combining optical system in which an antireflection film is provided on an incident surface of the dichroic mirror, the antireflection film has a high antireflection effect in a wavelength region of the S-polarized light. Optical system. 2. A wavelength region of light synthesized using the reflection and a wavelength region of light synthesized using the transmission are adjacent to each other.
2. The color combining optical system according to claim 1, wherein the light combined using the transmission is P-polarized light with respect to the dichroic mirror. 3. An image display device comprising: three image display elements; and first and second dichroic mirrors for synthesizing image information of the image display elements, wherein the first dichroic mirror synthesizes using the reflection. The transmitted light is red S-polarized light, and the light synthesized using the transmission is green P-polarized light.
In the dichroic mirror, the light synthesized using the reflection is blue S-polarized light, and the light synthesized using the transmission is the red S-polarized light and the green P-polarized light. The antireflection film provided on the incident surface of the first dichroic mirror on which polarized light is incident has a high antireflection effect on the red S-polarized light and the green P-polarized light, and the blue S-polarized light enters. 2. The anti-reflection film provided on the incident surface of the second dichroic mirror has a high anti-reflection effect on the red S-polarized light, the green P-polarized light, and the blue S-polarized light. Alternatively, the color combining optical system according to claim 2. 4. An anti-reflection film provided on an incident surface of the dichroic mirror, on which light combined using the transmission is incident, prevents reflection in a polarization and wavelength region of the light combined using the transmission. 2. The effect is high.
The color combining optical system according to claim 3. 5. The color synthesizing optical system according to claim 1, wherein a reflectance of the light incident on the anti-reflection film is 1% or less. 6. The color synthesizing optical system is a non-telecentric optical system, and changes a thickness of a dichroic film of the dichroic mirror at an incident position corresponding to an incident angle of a principal ray incident on the dichroic mirror. 6. The color synthesizing optical system according to claim 1, wherein a characteristic of a transmittance of the dichroic film with respect to a wavelength is made substantially constant. 7. A color synthesizing optical system according to claim 1, further comprising a dichroic mirror satisfying the following conditional expression: 8 <D / t <50, where t: dichroic film is coated. The thickness D of the flat glass is the long side or the long diameter of the effective range in which the dichroic mirror is used. 8. An anti-reflection film having a dichroic film on or near the rear surface of the flat plate, wherein the anti-reflection film has a higher anti-reflection effect on S-polarized light than on P-polarized light in light reflected by the dichroic film. A dichroic mirror that features