JP2003233124A - Projection optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact and efficient projection optical system which can obtain a high-contrast beautiful image although its basic arrangement is nearly the same as before, at a low cost. <P>SOLUTION: A first polarization beam splitter has ≤0.3% mean transmissivity to S-polarized light in the wavelength range of red light R and 0.3 to 2% mean transmissivity to S-polarized light in the wavelength range of blue light B. Or a second polarization beam splitter has ≤0.3%, preferably, ≤0.1% mean transmissivity to S-polarized light in the wavelength range of green light G and 0.1 to 10%, preferably, 0.3 to 10% mean transmissivity to S-polarized light in the wavelength range of the blue light B. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection optical system for projecting an image on a reflective liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, as such a projection optical system, as described in, for example, Japanese Unexamined Patent Publication No. 11-271683, a polarized light beam is formed by a dichroic mirror (color separation mirror) and a wavelength plate (phase plate). There is used a configuration in which color separation is performed into illumination light, which is color-combined by a reflective liquid crystal display element and a polarization beam splitter to produce projection light.

[0003]

However, in the conventional structure as described above, the red light R, the green light G,
Among the three color lights of the blue light B, a transmission optical path through which two color lights of two colors pass through one color separation mirror is formed. In the transmitted light path, a few percent of the reflected light is generated due to the characteristics of the color separation mirror. Therefore, the larger the number of color lights transmitted through the color separation mirror, the more disadvantageous. In particular, since the blue light B has a polarization plane different from that of the red light R and the green light G, a few percent of the reflected light is incident on a polarization beam splitter other than the predetermined polarization beam splitter, thereby lowering the image contrast. Will be made.

In view of the above problems, the present invention provides a projection optical system which has a basic structure similar to that of the conventional one but can obtain a beautiful image with higher contrast and is compact and efficient. The purpose is to provide at low cost.

[0005]

In order to achieve the above object, the present invention relates to a substantially polarized illumination light as a first
Of the light of the second wavelength range and the light of the third wavelength range and a first color separation mirror for separating one of the light of the third wavelength range by reflecting the other and transmitting the other, and A half-wave plate that transmits light and light in the second wavelength range or light in the third wavelength range and rotates the polarization direction; and reflects or transmits light in the first wavelength range, The light in the second wavelength range and the light in the third wavelength range are transmitted or reflected to combine the light in the first wavelength range and the light in the third wavelength range, and the second A second color separation mirror for separating light in the wavelength range, a first polarization beam splitter into which the light in the first wavelength range and the light in the third wavelength range are incident as illumination light, and the second wavelength A second polarization beam splitter on which light in a region is incident as illumination light, wherein the first polarization beam splitter is the first polarization beam splitter. And illuminating light in the third wavelength region, one of which is reflected and the other is transmitted to illuminate the first and third reflective liquid crystal display elements, respectively, and the second polarization beam splitter is configured to Of the second reflection type liquid crystal display element by reflecting or transmitting the illumination light in the wavelength region of the second reflection type liquid crystal display element and projecting light from the first and third reflection type liquid crystal display elements and the second reflection type liquid crystal display element. In a configuration including a combined polarization beam splitter that combines the projection light from the liquid crystal display device, the first polarization beam splitter is configured so that the illuminating light has a wavelength range S reflected by the first polarization beam splitter. The average transmittance of polarized light is 0.3% or less, and the average transmittance of S-polarized light is 0.3% to 2% with respect to the wavelength range in which the illumination light is transmitted through the first polarization beam splitter. Second polarized beam split Terpolymer, the second
The average transmittance of S-polarized light is 0.3% or less with respect to the light in the wavelength range of, and the average transmittance of S-polarized light is 0.1% to 10% with respect to the light in the first or third wavelength range. It is characterized by being.

Regarding the substantially polarized illumination light, one of the light of the first wavelength band, the light of the second wavelength band and the light of the third wavelength band is reflected and the other is transmitted to be separated. A first color separation mirror; a half-wave plate that transmits the light in the first wavelength band and the light in the second wavelength band or the light in the third wavelength band and rotates the polarization direction; The light in the first wavelength range is reflected or transmitted, the light in the second wavelength range and the light in the third wavelength range are transmitted or reflected, and the first
Second color separation mirror for combining the light of the second wavelength range and the light of the third wavelength range and separating the light of the second wavelength range, and the light of the first wavelength range and the third color separation mirror. A first polarization beam splitter on which light in a wavelength range is incident as illumination light;
A second polarization beam splitter into which light in the wavelength range of is incident as illumination light, wherein the first polarization beam splitter is one of the illumination light in the first and third wavelength ranges.
One is reflected and the other is transmitted, and
And illuminating the second reflective liquid crystal display element, wherein the second polarization beam splitter reflects or transmits the illumination light in the second wavelength range, and illuminates the second reflective liquid crystal display element. In a configuration including a combined polarization beam splitter that combines the projected light from the first and third reflective liquid crystal display elements and the projected light from the second reflective liquid crystal display element, A trimming filter for cutting light in the first or third wavelength range is arranged at a position immediately before the light enters the second polarization beam splitter.

Further, a trimming filter for cutting off light in the second wavelength region is arranged at a position immediately before the first or third reflective liquid crystal display element.

Further, each of the polarization beam splitters is
It is characterized in that it is adhered via a glass material.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing a basic configuration of a color separation / combination optical system according to the projection optical system of the present invention. In the figure, the solid arrow indicates P-polarized light, and the polarization direction is along the plane of the drawing. Also, the dashed arrow indicates S-polarized light, and the polarization direction is perpendicular to the paper surface. Furthermore, the dashed-dotted arrow is P
A mixture of polarized light and S-polarized light is shown.

First, light from a light source (not shown) is made into S-polarized light having a uniform intensity distribution by an integrator and a polarization conversion optical system, which will be described later. As shown in FIG. It is incident on the color separation mirror 1. The first color separation mirror 1 is a blue reflection mirror, which transmits red light R and green light G and reflects blue light B. The red light R and the green light G that have passed through the first color separation mirror 1 are reflected by the folding mirror 4 and then pass through the polarizing plate 5 to have their polarization directions perfectly aligned, and then the second color. It is incident on the separation mirror 2.

On the other hand, the blue light B reflected by the first color separation mirror 1 is reflected by the folding mirror 3 and then halved.
Phase plate 6 that is a wave plate (single-layer or multi-layer phase plate for blue)
And then the polarization direction is rotated by 90 ° to become P-polarized light, which is then incident on the second color separation mirror 2. A polarizing plate that transmits P-polarized light may be arranged immediately before the second color separation mirror 2. The second color separation mirror 2 is a Red reflection mirror, which transmits blue light B and green light G and reflects red light R.

The red light R reflected by the second color separation mirror 2 and the blue light B transmitted through the second color separation mirror 2 are
It is incident on the first polarization beam splitter 9. here,
Since the red light R is S-polarized light, it is reflected by the first polarization beam splitter 9 and illuminates the first reflective liquid crystal display element 11. Since the blue light B is P-polarized light, it passes through the first polarization beam splitter 9 and illuminates the third reflective liquid crystal display element 13. On the other hand, the second color separation mirror 2
The green light G that has passed through is incident on the second polarization beam splitter 10. Since the green light G is S-polarized, it is reflected by the second polarization beam splitter 10 and illuminates the second reflective liquid crystal display element 12.

The red light R illuminating the first reflection type liquid crystal display element 11 is modulated here for each pixel. Then, the ON light that has been turned into P-polarized light by rotating the polarization direction by 90 ° is
After passing through the polarization beam splitter 9 of the above, the phase plate 7 (blue single-layer or multi-layer phase plate) which is a half-wave plate is rotated, and the polarization direction is rotated by 90 ° again, so that it is almost S-polarized (P
The polarized light is mixed, and then enters the combined polarized beam splitter 14.

As the phase plate 7, for example, in the case of a single layer type, a half wave plate whose slow axis forms 45 degrees with respect to the P or S polarization plane is used. In the two-layer type, a half-wave plate whose slow axis forms 22.5 degrees with respect to the P or S polarization plane, and 67.
A stack of half-wave plates forming 5 degrees is used. Further, in the three-layer type, in addition to the two-layer type, a one in which a half-wave plate whose slow axis forms 0 degree with respect to the P or S polarization plane is laminated is used. Alternatively, a half-wave plate whose slow axis forms 15 degrees with respect to the P or S polarization plane, a half-wave plate forming 75 degrees, and a half-wave plate forming 15 degrees are laminated. Is used.

The green light G illuminating the second reflective liquid crystal display element 12 is modulated here for each pixel. Then, the ON light whose polarization direction is rotated by 90 ° and becomes P-polarized light passes through the second polarization beam splitter 10,
After passing through the phase plate 8 (single-layer or multi-layer phase plate for green color) which is a half-wave plate, the polarization direction is rotated by 90 ° again to become S-polarized light, which is then incident on the composite polarization beam splitter 14.

Further, the blue light B illuminating the third reflective liquid crystal display element 13 is modulated here for each pixel. Then, the ON light that has been turned into the S-polarized light by rotating the polarization direction by 90 ° is reflected by the first polarization beam splitter 9,
After passing through the phase plate 7 (single-layer or multi-layer phase plate for blue as described above) which is a half-wave plate, the polarization direction is rotated by 90 ° again to become P-polarized light, which is then incident on the composite polarization beam splitter 14. To do.

Finally, the composite polarization beam splitter 14
Then, the red light R, the green light G, and the blue light B are combined and emitted to the projection optical system described later. The combined polarization beam splitter 14 transmits the P-polarized light to the blue light B and reflects the characteristics of the polarization beam splitter that reflects the S-polarized light, the green light G (S-polarized light), and the red light R (S-polarized light). )
It has the characteristic of a dichroic mirror that transmits light. Details will be described later. Therefore, the composite polarization beam splitter 14
In S, the red light R that is S-polarized light and the blue light B that is P-polarized light are transmitted, the green light G that is S-polarized light is reflected, and the three colors are combined.

By the way, as described above, the first polarization beam splitter 9 and the composite polarization beam splitter 14 are used.
A phase plate 7, which is a half-wave plate, is arranged between and. This is because the color light that is the illumination light on the side that passes through the first polarization beam splitter 9 (blue light B in this configuration)
Is a state in which not only ON light but also OFF light (P-polarized light) is completely mixed and the contrast is low at the stage of being reflected by the first polarization beam splitter 9 after passing through the third reflective liquid crystal display element 13. Has become. Therefore, the polarization direction of this color light is rotated by 90 ° through the ½ wavelength plate, and then the combined polarization beam splitter 14 is transmitted to cut off the OFF light, resulting in high contrast.

FIG. 2 is a diagram showing a first embodiment of the projection optical system of the present invention. The present embodiment is based on the basic configuration described above. In the figure, the light from the light source 15 is reflected and condensed by the reflector 16,
It enters the integrator and the polarization conversion optical system. The integrator and the polarization conversion optical system include the first lens array 1
7, bending mirror 18, second lens array 19, P
It comprises a BS array 20 and a superposing lens 22.
Phase plates 21 are arranged in stripes on the PBS array 20. These light source 15 and reflector 16
And an integrator and a polarization conversion optical system form an illumination optical system.

The light emitted through the integrator and the polarization conversion optical system passes through the color separation / synthesis optical system described above, and is projected onto a screen (not shown) via the projection optical system 28. In the present embodiment, the first polarizing plate 5 is provided immediately before the first polarizing plate 5.
The second condenser lens 24 is arranged immediately before the phase plate 6 and the second condenser lens 24 is arranged immediately before the phase plate 6.
This will be described later. Immediately before the reflective liquid crystal display elements 11, 12, and 13, quarter-wave plates 25, 26, and 27 for contrast correction and dedicated to each color are arranged.

Further, in the figure, the normal required for image projection is
Light is represented by solid arrows and unwanted light is represented by dashed arrows.
It As shown in the figure, exit the light source and
Light that has passed through the polarization conversion optical system is mainly normal light.
Red light R, each of which is S-polarized _S, Green light G_S, Blue light B_S
And is partially P-polarized with unnecessary light.
Red light R_P, Green light G_P, Blue light B_PAre mixed. So
Then, when these are incident on the first color separation mirror 1, positive
Red light R that is the standard light_S, Green light G_S, And unnecessary light red
Color light R_P, Green light G_PIs transmitted through here and bent to mirror 4.
Towards blue light, which is regular light B_SAnd blue, which is unnecessary light
Color light B_PIs reflected here and goes to the bending mirror 3.
It will be.

FIG. 3 is an enlarged view of the main part of the color separation / combination optical system in this embodiment. As shown in the figure, of the light that has passed through the first condenser lens 23 from the bending mirror 4, the red light R _S and the green light G _S that are normal lights.
Passes through the polarizing plate 5. Then, the green light G _S passes through the second color separation mirror 2 and goes to the second polarization beam splitter 10. The red light R _S is reflected by the second color separation mirror 2 and goes to the first polarization beam splitter 9.

Further, the blue light B _S, which is the normal light, that has passed through the second condenser lens 24 from the folding mirror 3 is transmitted through the phase plate 6 and is polarized and converted into the blue light B _P. Then, the blue light B _P, which is the normal light, passes through the second color separation mirror 2 and goes toward the first polarization beam splitter 9. The blue light B _P is partially reflected by the second color separation mirror 2 and goes to the second polarization beam splitter 10 as unnecessary light.

In addition, when the red light R _S which is the normal light is reflected by the second color separation mirror 2, the polarization is slightly disturbed and the red light R _P which is the unnecessary light is generated. Further, when the green light G _S which is the normal light passes through the second color separation mirror 2, the polarization is slightly disturbed and the green light G _P which is the unnecessary light is generated. In order to substantially cut these unnecessary lights, a dichroic correction phase plate 29 is arranged immediately before the second polarization beam splitter 10, and a dichroic correction phase plate 30 is arranged immediately before the first polarization beam splitter 9. .

The red light R _S, which is the normal light and is incident on the first polarization beam splitter 9, is reflected here to form the first light.
Toward the reflective liquid crystal display element 11. In addition, the blue light B _P, which is the normal light and is incident on the first polarization beam splitter 9, is transmitted therethrough and the third reflective liquid crystal display element 1 is transmitted.
Head to 3. The blue light B _P is partially reflected by the first polarization beam splitter 9 and travels to the first reflective liquid crystal display element 11 as unnecessary light. On the other hand, the green light G that is the normal light and is incident on the second polarization beam splitter 10.
_S is reflected here, and is reflected by the second reflective liquid crystal display element 12
Head to.

The red light R _S which is the normal light and is incident on the first reflection type liquid crystal display element 11 is modulated here for each pixel, and the red light R _P (ON light) which is the normal light and unnecessary light are generated. A certain red light R _S (OFF light) is emitted to the first polarization beam splitter 9. The blue light B _P, which is unnecessary light and has entered the first reflective liquid crystal display element 11, is similarly emitted to the first polarization beam splitter 9.

Further, the blue light B _P which is the normal light and is incident on the third reflective liquid crystal display element 13 is modulated here for each pixel, and the blue light B _S (ON light) which is the normal light and unnecessary light. The blue light B _P (OFF light) that is light is emitted to the first polarization beam splitter 9. On the other hand, the green light G, which is the normal light, is incident on the second reflective liquid crystal display element 12.
_S is modulated here for each pixel, and is green light G _P that is normal light.
(ON light) and green light G _S (OFF light) that is unnecessary light are emitted to the second polarization beam splitter 10. The blue light B _P, which is unnecessary light and has entered the second reflective liquid crystal display element 12, is similarly emitted to the second polarization beam splitter 10.

Of the light incident on the first polarizing beam splitter 9 from the first reflective liquid crystal display element 11, the red light R _S which is unnecessary light is cut off here, and the red light R _P which is the normal light and Only the blue light B _P that is unnecessary light is transmitted through here,
Heading to the combined polarization beam splitter 14. Further, the blue light B _S that is the normal light and the blue light B _P that is the unnecessary light that have entered the first polarization beam splitter 9 from the third reflective liquid crystal display element 13 are reflected here and are combined into a polarized light beam. Head towards splitter 14. On the other hand, from the second reflective liquid crystal display element 12 to the second polarization beam splitter 1
Of the light incident on 0, the unnecessary green light G _S is cut off here, and only the green light G _P which is the normal light and the blue light B _P which is the unnecessary light are transmitted therethrough, and the combined polarization beam splitter Head to 14.

The red light R _P , the blue light B _S , which is the normal light, and the blue light B _P, which is the unnecessary light, from the first polarization beam splitter 9 are transmitted through the phase plate 7 and are polarized and converted. As the red light R _S , the blue light B _P , and the unnecessary blue light B _S, which are the light, the combined polarization beam splitter 14 is used.
Incident on. On the other hand, the second polarization beam splitter 10
The green light G _P, which is the normal light from, passes through the phase plate 8 and undergoes polarization conversion, and enters the combined polarization beam splitter 14 as the green light G _S that is the normal light. Finally, out of the light that has entered the combined polarization beam splitter 14, the blue light B _S that is unnecessary light is cut here, and the red light R _S and the blue light B _{P that} are normal lights pass through here, and the normal light The green light G _S is reflected here, these three colors are combined and emitted to the projection optical system 28.

By the way, in the present embodiment, the first polarization beam splitter 9 has
The average transmittance of S-polarized light is 0.3% or less, and the average transmittance of S-polarized light is 0.3% to 2% for the wavelength range of blue light B.
I am trying. Alternatively, the second polarization beam splitter 1
0 means that the average transmittance of S-polarized light is 0.3% or less, preferably 0.1% or less with respect to the wavelength range of green light G, and that of S-polarized light is with respect to the wavelength range of blue light B. Average transmittance of 0.1
% To 10%, preferably 0.3% to 10%.

Usually, a high-contrast polarizing beam splitter has a very low average transmittance of S-polarized light of 0.3% or less. However, as the transmittance of S-polarized light is reduced, the transmittance of P-polarized light is also reduced, and unnecessary reflection occurs. Specifically, considering the luminous flux spread by the F number, when the average transmittance of S-polarized light is set to 0.3% or less,
The transmittance of P-polarized light is about 80 to 90%.

In this embodiment, with respect to the blue light B, the polarization of the illumination light is adjusted to some extent by polarization conversion, and the blue light B is further transmitted through the first polarization beam splitter 9. It may be low, and it is better that the transmittance of P-polarized light is high. Furthermore, in the projection optical path, the first polarization beam splitter 9 reflects S-polarized light, and the combined polarization beam splitter 14 transmits P-polarized light, but when the first polarization beam splitter 9 reflects S-polarized light, To increase the contrast to some extent,
It is better to lower the reflectance of P-polarized light (that is, increase the transmittance).

Therefore, the first polarization beam splitter 9
Makes the transmittance of S-polarized light different for the respective wavelength ranges of the red light R and the blue light B. That is, for the wavelength range of the red light R, the average transmittance of S-polarized light has a normal high contrast PBS characteristic, and for the wavelength range of the blue light B, the transmittance of P-polarized light is high (that is, reflection In order to reduce the reflectance), the average transmittance of S-polarized light is set to 0.3% to 2%, which is higher than usual.

On the other hand, the second polarization beam splitter 10
In the above, only the green light G is passed as the normal light, but if a part of the blue light B _P having a different polarization direction is mixed, the contrast is lowered. Therefore, the blue light B is the second
In order not to reach the reflective liquid crystal display element 12 of
For the wavelength range of blue light B, the reflectance of P-polarized light is made low (that is, the transmittance of S-polarized light for blue light B is made low) so that the normal PBS characteristics of high contrast are obtained for green light G. There is.

FIG. 4 is a graph showing the characteristics of the first or second polarization beam splitter, where the horizontal axis represents wavelength (unit: nm) and the vertical axis represents transmittance. In the same figure, a curve a is a graph showing characteristics for P-polarized light incident at 45 °, and a curve b is a graph showing characteristics for P-polarized light incident at 40 °. The curve c is a graph showing the characteristics for S-polarized light incident at 45 °, and the curve d is 40.
7 is a graph showing the characteristics of S-polarized light incident at an angle of °. Further, the film constitution is shown in Table 1 below. In the table, the numbers in the left column are the numbers of the laminated films, Ni in the center is the refractive index of each film, and the numbers in the right column are the optical film thickness of each film (reference wavelength λ ₀
= 660 nm).

[0036]

[Table 1]

The polarization beam splitter of this structure has the same film structure as MacN as the normal polarization beam splitter.
Hi-Index and Lo-Index layers close to the eile condition are alternately stacked by a quarter wavelength thickness. Furthermore, a stack for the wavelength range of red light R or green light G having different reference wavelengths,
Two kinds of stacks for the wavelength range of blue light B are overlapped,
The number of layers of the stack for the wavelength range of the red light R or the green light G is 1.2 times or more the number of layers of the stack for the wavelength range of the blue light B.

Further, in this embodiment, the red light R is combined with the blue light B, and the green light G is separated from them and independently enters the second polarization beam splitter 10.
If the blue light B having a polarization direction different from that of the green light G is mixed therein, the contrast is lowered. Therefore, in order to cut this, a trimming filter for cutting the blue light B is arranged immediately before the second polarization beam splitter 10. This is the same position as the dichroic correction phase plate 29 shown in FIG. Or the second
The position may be immediately after the light is emitted from the polarization beam splitter 10. Note that such a configuration is performed instead of the above-described configuration in which the reflectance of P-polarized light with respect to the wavelength range of the blue light B is lowered in the second polarization beam splitter 10.

For the same reason as above, a polarizing plate for transmitting the polarized light of the green light G may be arranged immediately before the second polarization beam splitter 10. This may also be at the same position as the dichroic correction phase plate 29 shown in FIG.
Since the blue light B has a polarization direction different from that of the green light G, the blue light B can be cut by this polarizing plate so as not to be mixed with the green light G.

Further, in this embodiment, a trimming filter for cutting the green light G is inserted immediately before the first reflective liquid crystal display element 11. This is shown in FIG. 2 or FIG.
The position is the same as that of the quarter-wave plate 25 shown in FIG.
FIG. 5 is a graph showing the characteristics of the trimming filter, where the horizontal axis represents wavelength (unit: nm) and the vertical axis represents transmittance. In the figure, the solid line is a graph showing the characteristic for a single pass, and the broken line is a graph showing the characteristic for a double pass.

As shown in the figure, this trimming filter has a so-called sharp cut property and has a transmittance of 10%.
To 90% of the wavelength width is 25 nm or more. Since the normal trimming filter sharply cuts the wavelength, the wavelength width from the transmittance of 10% to 90% is 20 nm or less, but in the present embodiment, it is immediately before the first reflective liquid crystal display element 11. On the other hand, a trimming filter having a gentle sharp cut property is arranged where the red light R passes twice during illumination and during projection. As described above, by loosening the sharp cut property, an appropriate sharp cut property is obtained by two passes, and the loss when passing through this filter is reduced.

The film structure is shown in Table 2 below. In the table, the numbers in the left column indicate the numbers of laminated films, the Ni in the center indicates the refractive index of each film, and the numbers in the right column indicate the optical film thickness (reference wavelength λ ₀ = 490 nm) of each film. ing.

[0043]

[Table 2]

Further, in the present embodiment, in the combined polarization beam splitter 14, the red light R is transmitted with respect to the S polarization and the dichroic characteristic that the green light G is reflected, and the P polarization with respect to the blue light B is transmitted. , S-polarized light has a PBS characteristic of perfect reflection. As a result, as described above, the red light R that is S-polarized light and the blue light B that is P-polarized light are transmitted through the composite polarization beam splitter 14,
The S-polarized green light G is reflected and the three colors are combined.

FIG. 6 shows the combined polarization beam splitter 1
4 is a graph showing characteristics of No. 4, where the horizontal axis represents wavelength (unit: nm)
Is taken and the vertical axis shows the transmittance. In the same figure, a curve a is a graph showing characteristics for 45 ° incident S-polarized light, and a curve b is a graph showing characteristics for 45 ° incident P-polarized light. Further, the film structure is shown in Table 3 below. In the table, the numbers in the left column indicate the numbers of laminated films, the Ni in the center indicates the refractive index of each film, and the numbers in the right column indicate the optical film thickness (reference wavelength λ ₀ = 649 nm) of each film. ing.

[0046]

[Table 3]

In a normal polarization beam splitter, layers of Hi-Index and Lo-Index close to MacNeile conditions are alternately stacked by a quarter wavelength thickness as a film structure, but in this embodiment, a dichroic characteristic is provided. , Several layers at both ends are 1
The structure is deviated from the / 4 wavelength thickness, and the thin layer includes the ⅛ wavelength, and the thick layer includes the layer exceeding ½ wavelength. In a normal polarization beam splitter, ripples are generated outside the band having the PBS characteristic (in this case, the red light R region), so flat and high S-polarized light transmittance cannot be obtained. There is.

In this embodiment, as shown in FIG. 2, the first color separation mirror 1 and the second color separation mirror 2 are used.
A first condenser lens 23 and a second condenser lens 24 are arranged in the optical path between and. With such a configuration, each condenser lens and the superposing lens 22 can be downsized. It should be noted that these condenser lenses are for illuminating the reflection type liquid crystal display element in a substantially telecentric manner.

If such a condenser lens is arranged at the entrance of each polarization beam splitter, in the optical path from the superposing lens to the condenser lens,
Since the first and second color separation mirrors are arranged, the optical path becomes long. At this time, the superposing lens and the first and second lens arrays become very large, which is not desirable. Also,
When the condenser lens is arranged in the optical path from the superposing lens to the first color separation mirror, there is an advantage that only one condenser lens is required because the three colors are mixed. Therefore, the distance between the reflective liquid crystal display elements becomes long and the condenser lens becomes very large, which is not desirable.

In addition, in this embodiment, all the polarization beam splitters are made of glass materials and are bonded to each other. FIG. 7 is a side view schematically showing the bonding configuration of the polarization beam splitter. Here, as shown in the figure, the first polarization beam splitter 9 or the second polarization beam splitter 10 and the composite polarization beam splitter 14 are combined.
The phase plate 7 or the phase plate 8 is attached to one of the surfaces where and face each other. Then, in a region of the polarization beam splitter through which the light flux does not pass, the both ends are supported by, for example, a square columnar glass block 32 (bridge shape), and combined with the first polarization beam splitter 9 or the second polarization beam splitter 10. Polarizing beam splitter 14
It is configured to bond and fix and.

Further, the first polarization beam splitter 9
When the reflective liquid crystal display element 11 is attached to, for example, the L-shaped angled bracket 33 provided on the first polarization beam splitter 9 side and the reflective liquid crystal display element 11 are attached.
The base plate 34 provided on the side is connected via a pin 35, and is bonded after positioning adjustment. this is,
The same applies when the reflective liquid crystal display element 12 is attached to the second polarization beam splitter 10. In this way, each polarization beam splitter and each reflection type liquid crystal display element are integrated.

Here, when a phase plate made of a resin film is arranged between the polarization beam splitters made of a glass material, for example, when glass-resin film-glass is directly adhered, a difference in linear expansion coefficient and heat dissipation are caused. Due to
It becomes less reliable. Therefore, by adopting the configuration as described above, it is possible to prevent a deviation in convergence after assembly,
The reliability can be increased. Further, by passing air through a gap between the polarization beam splitters with a fan or the like, it is possible to cool the phase plate, which is a resin film that is weak against heat. Note that FIG. 8 is a perspective view showing a part of the bonding structure of the polarization beam splitter.

FIG. 9 is a plan view showing the construction of the polarization beam splitter and its vicinity. As shown in the figure, in the present embodiment, the combined polarization beam splitter 14 is provided with a cut portion 14a that is formed by cutting the corners of the combined polarization beam splitter 14 that face the second color separation mirror 2. As a result, the second color separation mirror 2 can be easily held, and each polarization beam splitter can be made as small as possible to shorten the lens back.

In the present embodiment, the first polarization beam splitter 9 and the second polarization beam splitter 10 are also included.
As the glass, a glass having a photoelastic ratio of 1.0 × 10 ⁻¹² (1 / Pa) or less is used, and for the synthetic polarization beam splitter 14, a glass having a photoelastic ratio of 1.0 × 10 ⁻¹² (1 / Pa) or more is used. It is configured to be used.

First polarization beam splitter 9 and second polarization beam splitter 9
The polarization beam splitter 10 substantially cuts off the OFF light in the projected light of the red light R and the green light G, that is, the S-polarized unnecessary light, and the OFF light in the projected light of the blue light B, that is, the P-polarized unnecessary light. Has a function to cut the If a glass material with a high photoelasticity ratio is used as the glass material of these polarization beam splitters, the disturbance of the polarization occurs when the light flux passes through the glass, and unnecessary light leaks to the projection side. It is desirable to use a photoelastic glass material.

On the other hand, the composite polarization beam splitter 14
Has a role of cutting off the OFF light in the projection light of the blue light B leaked from the first polarization beam splitter 9, that is, the unnecessary light that has been changed from P polarization to S polarization by the phase plate 7. However, since the OFF light is substantially cut by the first polarization beam splitter 9 in advance, the contrast is not deteriorated even if some polarization disorder occurs in the combined polarization beam splitter 14. Therefore, the synthetic polarization beam splitter 1
As described above, it is desirable to use a glass material that does not have low photoelasticity for 4, so as to reduce the cost.

FIG. 10 is a diagram schematically showing another basic configuration of the color separation / combination optical system according to the projection optical system of the present invention. The figure (a) has shown the whole structure and the figure (b) has shown the detailed structure of a color separation mirror. In this configuration, color separation is performed by one mirror. In the figure, a solid arrow indicates P-polarized light,
The polarization direction is along the plane of the paper. Also, the dashed arrow indicates S-polarized light, and the polarization direction is perpendicular to the paper surface. Furthermore, the dashed-dotted line arrow indicates the mixture of P-polarized light and S-polarized light.

First, the light from a light source (not shown) is made into S-polarized light having a uniform intensity distribution by an integrator and a polarization conversion optical system, which will be described later, and as shown in FIG. The light is transmitted through the plate 5, the polarization direction is perfectly aligned, and then the light enters the color separation mirror 40. Here, the color separation mirror 40 includes the Red reflection dichroic mirrors 40a, 1 in order from the surface as shown in FIG.
/ 4 wave plate 40b, Blue reflection dichroic mirror 40
c, a quarter wave plate 40d are laminated.

Here, the red light R is reflected by the Red reflection dichroic mirror 40a. Further, the blue light B is reflected by the Blue reflection dichroic mirror 40c. At this time, since the blue light B is transmitted through the quarter-wave plate 40b twice when it is incident and when it is reflected, it is equivalent to passing through the half-wave plate, and the S-polarized light has a polarization direction. Is rotated by 90 ° and converted into P-polarized light. On the other hand, the green light G passes through the color separation mirror 40. At this time, the green light G is transmitted through the quarter-wave plate 40b to rotate its polarization direction, which is canceled by the quarter-wave plate 40d.

The red light R and the blue light B reflected by the color separation mirror 40 enter the first polarization beam splitter 9. Here, since the red light R is S-polarized light, it is reflected by the first polarization beam splitter 9 and illuminates the first reflective liquid crystal display element 11. Since the blue light B is P-polarized light, it passes through the first polarization beam splitter 9 and illuminates the third reflective liquid crystal display element 13. On the other hand, the green light G transmitted through the color separation mirror 40 enters the second polarization beam splitter 10. Since the green light G is S-polarized, it is reflected by the second polarization beam splitter 10 and illuminates the second reflective liquid crystal display element 12. Hereinafter, the configuration is the same as that described with reference to FIG.

FIG. 11 is a diagram showing a second embodiment of the projection optical system of the present invention. The present embodiment is based on the other basic configuration described above. In the figure, the light from the light source 15 is reflected and condensed by the reflector 16 and is incident on the integrator and the polarization conversion optical system.
The integrator and the polarization conversion optical system include a first lens array 17, a second lens array 19, and a PBS array 2.
0 and the superposing lens 22. These light sources 1
5 and the reflector 16 and the integrator and the polarization conversion optical system form an illumination optical system.

The light emitted through the integrator and the polarization conversion optical system is reflected by the folding mirrors 3 and 4,
The projection optical system 28 passes through the color separation / synthesis optical system described above.
And then projected onto a screen (not shown). In this embodiment, the condenser lens 41 is provided immediately before the polarizing plate 5.
Are arranged. This is for the same reason as in the case of the first embodiment. Immediately before the reflective liquid crystal display elements 11, 12, and 13, quarter-wave plates 25, 26, and 27 for contrast correction and dedicated to each color are arranged.

Further, in the figure, the normal required for image projection is
Light is represented by solid arrows and unwanted light is represented by dashed arrows.
It As shown in the figure, exit the light source and
Light that has passed through the polarization conversion optical system is mainly normal light.
Red light R, each of which is S-polarized _S, Green light G_S, Blue light B_S
It is composed of. Then, these pass through the polarizing plate 5 and color
When entering the separation mirror 40, red light R_SAnd blue light B_S
Is reflected here, and further blue light B_SIs B_PWas converted to
Go to the first polarization beam splitter 9 and turn green
Light G_SPasses through here and the second polarization beam splitter
We are going to 10. Hereinafter, in the first embodiment described above
It is similar to the configuration described in FIG.

In each of the embodiments described above, the red light R
The blue light R may be replaced with the blue light R. In addition, a contrast correction phase plate (1/4 wavelength plate) arranged in front of each reflective liquid crystal display element is attached to a glass plate and rotated to correct the contrast. Basically, the slow axis is made to coincide with the P-polarized plane or the S-polarized plane, but the reduction in contrast due to an assembly error is corrected by this phase plate.

Further, when an ultra-high resolution reflective liquid crystal display element is used, color shift due to lateral chromatic aberration of each color of R, G and B in the projection lens becomes a problem. Therefore, by using a glass plate to which a contrast correction phase plate is attached as a loose lens having a little different power for R, G, and B, it is possible to reduce the chromatic aberration of magnification of each of R, G, and B colors. .

In the wide-angle projection lens, the chromatic aberration of magnification of the red light R and the blue light B is small, but the magnification of the red light R and the blue light B with respect to the green light G is large. Therefore,
A phase plate for inverting the polarization plane between the first polarization beam splitter and the synthetic polarization beam splitter, or a phase plate for inverting the polarization plane between the second polarization beam splitter and the synthetic polarization beam splitter or a polarizing plate is placed on the glass plate. It is also possible to correct the lateral chromatic aberration of the red light R and the blue light B with respect to the green light G by holding and holding the glass plate having a very gentle curvature.

Of course, the entrance / exit surface of the polarization beam splitter may be an extremely gentle curved surface. The radius of curvature for correcting the chromatic aberration of magnification is 1000 mm to tens of thousands of meters.
It is extremely loose on the order of m.

Further, the specific embodiments described above include inventions having the following configurations. (1) Regarding the substantially polarized illumination light, first of the light in the first wavelength range, the light in the second wavelength range, and the light in the third wavelength range is reflected and the other is transmitted to be separated. A color separation mirror, a half-wave plate that transmits the light in the first wavelength band and the light in the second wavelength band, or the light in the third wavelength band and rotates the polarization direction; Light in the first wavelength range is reflected or transmitted, light in the second wavelength range and light in the third wavelength range is transmitted or reflected, and light in the first wavelength range and third wavelength Second color separation mirror for combining light in the wavelength range and separating light in the second wavelength range, and the light in the first wavelength range and the light in the third wavelength range are incident as illumination light. A first polarization beam splitter, and a second polarization beam splitter on which the light in the second wavelength range enters as illumination light,
The first polarization beam splitter reflects one of the illumination lights of the first and third wavelength ranges and transmits the other of the illumination light, and the first and third reflection type liquid crystal display elements, respectively. Illuminating the second polarizing beam splitter,
The illumination light in the second wavelength range is reflected or transmitted,
A projection optical system for illuminating the reflective liquid crystal display element, wherein the projection light from the first and third reflective liquid crystal display elements and the projection light from the second reflective liquid crystal display element are combined. In the projection optical system including a polarization beam splitter, the first polarization beam splitter has an average transmittance of S-polarized light of 0.3% with respect to a wavelength range in which illumination light is reflected by the first polarization beam splitter. Hereinafter, the average transmittance of S-polarized light for the wavelength range in which the illumination light has passed through the first polarization beam splitter is 0.
3% to 2%, or the second polarization beam splitter has an average transmittance of S-polarized light of 0.3% or less for the light in the second wavelength range, and the first or the third polarization beam splitter. A projection optical system having an average transmittance of S-polarized light of 0.1% to 10% with respect to light in a wavelength range. (2) Regarding the substantially polarized illumination light, first of the light of the first wavelength band, the light of the second wavelength band, and the light of the third wavelength band is reflected and the other is transmitted to be separated. A color separation mirror, a half-wave plate that transmits the light in the first wavelength band and the light in the second wavelength band, or the light in the third wavelength band and rotates the polarization direction; Light in the first wavelength range is reflected or transmitted, light in the second wavelength range and light in the third wavelength range is transmitted or reflected, and light in the first wavelength range and third wavelength Second color separation mirror for combining light in the wavelength range and separating light in the second wavelength range, and the light in the first wavelength range and the light in the third wavelength range are incident as illumination light. A first polarization beam splitter, and a second polarization beam splitter on which the light in the second wavelength range enters as illumination light,
The first polarization beam splitter reflects one of the illumination lights of the first and third wavelength ranges and transmits the other of the illumination light, and the first and third reflection type liquid crystal display elements, respectively. Illuminating the second polarizing beam splitter,
The illumination light in the second wavelength range is reflected or transmitted,
A projection optical system for illuminating the reflective liquid crystal display element, wherein the projection light from the first and third reflective liquid crystal display elements and the projection light from the second reflective liquid crystal display element are combined. In a projection optical system including a polarization beam splitter, trimming for cutting light in the first or third wavelength band at a position immediately before the light in the second wavelength band enters the second polarization beam splitter. A projection optical system characterized by arranging a filter. (3) The trimming filter for cutting the light in the second wavelength region is arranged immediately in front of the first or third reflective liquid crystal display element, (1) or (2). The projection optical system described in. (4) The above-mentioned (1) to (1) characterized in that each of the polarization beam splitters is configured to be bonded via a glass material.
The projection optical system according to any one of (3). (5) A polarizing plate that transmits polarized light in the second wavelength range is arranged at a position immediately before the light in the second wavelength range is incident on the second polarization beam splitter. The projection optical system according to any one of 1) to (4). (6) The synthetic polarization beam splitter has a dichroic characteristic of transmitting the light in the first wavelength range and reflecting the light in the second wavelength range, and a P-polarized light with respect to the light in the third wavelength range. The projection optical system according to any one of the above (1) to (5), characterized in that it has a PBS characteristic that allows the light to pass therethrough and completely reflects the S polarized light. (7) A condenser lens for illuminating the reflective liquid crystal display element in a substantially telecentric manner is arranged in an optical path between the first color separation mirror and the second color separation mirror. The projection optical system according to any one of (1) to (6). (8) The above-mentioned (1) to (1), characterized in that the composite polarization beam splitter is provided with a cut portion which is a corner portion of the composite polarization beam splitter, the cut portion being opposed to the second color separation mirror.
The projection optical system according to any one of (7). (9) In the first and second polarization beam splitters,
A glass material having a photoelasticity ratio of 1.0 × 10 ^-12 (1 / Pa) or less is used, and a glass material having a photoelasticity ratio of 1.0 × 10 ^-12 (1 / Pa) or more is used for the synthetic polarization beam splitter. The projection optical system according to any one of (1) to (8) above. (10) Regarding the substantially polarized illumination light, one of the light of the first wavelength band and the light of the third wavelength band and the light of the second wavelength band is reflected and the other is transmitted, and separated. The light in the first wavelength range and the light in the second wavelength range, or the third wavelength range.
A color separation mirror that rotates the polarization direction of light in the wavelength range of
A first polarization beam splitter into which the light in the first wavelength range and the light in the third wavelength range enter as illumination light, and a second polarization beam splitter into which the light in the second wavelength range enters as illumination light. The first polarization beam splitter reflects one of the illumination lights of the first and third wavelength ranges and transmits the other of the illumination light of the first and third wavelength bands, and the first and third reflection type liquid crystals, respectively. A projection optical system for illuminating a display element, wherein the second polarization beam splitter reflects or transmits the illumination light in the second wavelength range and illuminates a second reflective liquid crystal display element, the projection optical system comprising: A projection optical system comprising a combined polarization beam splitter for combining the projection light from the first and third reflection type liquid crystal display elements and the projection light from the second reflection type liquid crystal display element.

The light in the first wavelength range, the light in the second wavelength range, and the light in the third wavelength range referred to in the claims are red light R, green light G, and light in the embodiment, respectively. It corresponds to blue light B.

[0070]

As described above, according to the present invention,
Although the basic configuration is the same as the conventional one, it is possible to provide a high-contrast and beautiful image, and to provide a compact and efficient projection optical system at low cost.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a basic configuration of a color separation / combination optical system according to a projection optical system of the present invention.

FIG. 2 is a diagram showing a first embodiment of a projection optical system of the present invention.

FIG. 3 is an enlarged view of a main part of a color separation / synthesis optical system according to this embodiment.

FIG. 4 is a graph showing characteristics of the first or second polarization beam splitter.

FIG. 5 is a graph showing characteristics of a trimming filter.

FIG. 6 is a graph showing characteristics of a composite polarization beam splitter.

FIG. 7 is a side view schematically showing an adhesive structure of a polarization beam splitter.

FIG. 8 is a perspective view showing a part of the bonding configuration of the polarization beam splitter.

FIG. 9 is a plan view showing a configuration of a polarization beam splitter and its vicinity.

FIG. 10 is a diagram schematically showing another basic configuration of the color separation / synthesis optical system according to the projection optical system of the present invention.

FIG. 11 is a diagram showing a second embodiment of the projection optical system of the present invention.

[Explanation of symbols]

1 First color separation mirror 2 Second color separation mirror 3,4 folding mirror 5 Polarizer 6,7,8 Phase plate 9 First polarization beam splitter 10 Second polarization beam splitter 11 First reflective liquid crystal display element 12 Second reflective liquid crystal display element 13 Third reflective liquid crystal display element 14 Composite polarization beam splitter 15 light source 16 reflector 17 First lens array 18 folding mirror 19 Second lens array 20 PBS array 21 Phase plate 22 Superimposing lens 23 1st condenser lens 24 Second condenser lens 25, 26, 27 1/4 wave plate 28 Projection optical system 29 Dichroic correction phase plate 30 dichroic correction phase plate 32 glass blocks 33 bracket 34 Base plate 35 pin 40 color separation mirror 41 Condenser lens

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomokazu Taguchi             2-3-3 Azuchi-cho, Chuo-ku, Osaka             Kokusai Building Minolta Co., Ltd. F-term (reference) 2H088 EA14 EA15 EA16 HA13 HA15                       HA18 HA20 HA21 HA28 MA02                 2H091 FA01X FA10X FA11X FA14X                       FA15X FA41X FD06 FD14                       LA11 LA12 LA17

Claims (4)

[Claims] 1. About substantially polarized illumination light, one of the light in the first wavelength range, the light in the second wavelength range, and the light in the third wavelength range is reflected and the other is transmitted to be separated. A first color separation mirror; a half-wave plate that transmits the light in the first wavelength range and the light in the second wavelength range or the light in the third wavelength range and rotates the polarization direction; The light in the first wavelength range is reflected or transmitted, the light in the second wavelength range and the light in the third wavelength range is transmitted or reflected, and the light in the first wavelength range and the third light are transmitted. A second color separation mirror for combining light in the wavelength range of 1) and separating light in the second wavelength range, and the light in the first wavelength range and the light in the third wavelength range as illumination light. A first polarization beam splitter that is incident, and a second polarization beam splitter that is incident as illumination light with the light in the second wavelength range. The first polarization beam splitter reflects one of the illumination light in the first and third wavelength ranges and transmits the other, and illuminates the first and third reflective liquid crystal display elements, respectively. The second polarization beam splitter is a projection optical system that reflects or transmits the illumination light in the second wavelength range to illuminate the second reflective liquid crystal display element, and the first and third reflective beam splitters. In a projection optical system including a combined polarization beam splitter that combines the projection light from the liquid crystal display device of the second type and the projection light from the second reflection type liquid crystal display device, the first polarization beam splitter is First
Average transmittance of S-polarized light is 0.3% or less with respect to the wavelength range reflected by the polarization beam splitter, and average transmittance of S-polarized light is the wavelength range in which the illumination light is transmitted through the first polarization beam splitter. Is 0.3% to 2%, or the second polarization beam splitter has an average transmittance of S-polarized light of 0.3% with respect to the light in the second wavelength range.
Hereinafter, the projection optical system is characterized in that the S-polarized light has an average transmittance of 0.1% to 10% with respect to the light in the first or third wavelength range. 2. With respect to the substantially polarized illumination light, one of the light of the first wavelength band, the light of the second wavelength band and the light of the third wavelength band is reflected and the other is transmitted to be separated. A first color separation mirror; a half-wave plate that transmits the light in the first wavelength range and the light in the second wavelength range or the light in the third wavelength range and rotates the polarization direction; The light in the first wavelength range is reflected or transmitted, the light in the second wavelength range and the light in the third wavelength range is transmitted or reflected, and the light in the first wavelength range and the third light are transmitted. A second color separation mirror for combining light in the wavelength range of 1) and separating light in the second wavelength range, and the light in the first wavelength range and the light in the third wavelength range as illumination light. A first polarization beam splitter that is incident, and a second polarization beam splitter that is incident as illumination light with the light in the second wavelength range. The first polarization beam splitter reflects one of the illumination light in the first and third wavelength ranges and transmits the other, and illuminates the first and third reflective liquid crystal display elements, respectively. The second polarization beam splitter is a projection optical system that reflects or transmits the illumination light in the second wavelength range to illuminate the second reflective liquid crystal display element, and the first and third reflective beam splitters. In a projection optical system provided with a synthetic polarization beam splitter for synthesizing the projection light from the liquid crystal display element of the second type and the projection light from the second reflection type liquid crystal display element, the light in the second wavelength range is A projection optical system characterized in that a trimming filter for cutting the light in the first or third wavelength region is arranged at a position immediately before entering the polarization beam splitter. 3. A trimming filter for cutting light in the second wavelength region is arranged at a position immediately before the first or third reflective liquid crystal display element. The projection optical system according to item 2. 4. The projection optical system according to claim 1, wherein each of the polarization beam splitters is configured to be bonded via a glass material.