JPH11326829A - Polarized light converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarized light converter preventing a polarizing beam splitter from being reduced in polarization degree by a light beam tilt angle. SOLUTION: Three pieces of polarizing beam splitters 1, 2, 3 are joined adjacently to each other in the transmitting and reflecting directions, and each polarizing beam splitting film 12, 22, 32 uses a medium exhibiting a high refractive index ratio for increasing s-polarized light in the reflecting strength and limits the number of reflection to about ten. The polarization degree is increased by making it possible to decrease a reflection degree of p-polarized light while gaining a sufficient reflection strength of the s-polarized light. An incident light beam is decreased in the tilt angle by incident light the refractive indices of the prisms 11, 13, 21, 23, 31, 33 of the polarizing beam splitters 1, 2, 3. Even under the existence of a light beam tilt angle, an image modulated by a liquid crystal light value is prevented from decreasing in the contrast ratio by suppressing the decrease in the polarization degree of the polarizing beam splitter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type display device using a liquid crystal light valve, and more particularly to a polarization conversion device for aligning the direction of polarization of randomly polarized light. The present invention relates to a polarization conversion device to be used.

[0002]

2. Description of the Related Art FIG.
In FIG. 7, a polarization illuminating device 100 includes a light source unit 200, a first lens plate 300, and a second lens, which are arranged along a system optical axis L. It comprises a plate 400 and an illumination area 500. Light emitted from the light source unit 200 is condensed in the second lens plate 400 by the first lens plate 300,
When passing through the lens plate 400, the randomly polarized light is converted into one type of polarized light having a uniform polarization direction, and the illumination area 5
00 is reached.

The light source unit 200 has a light source lamp 201 and a parabolic reflector 202. The light source optical axis R is inclined by a certain angle with respect to the system optical axis L.
The first lens plate 300 has a configuration in which minute condenser lenses 301 having a rectangular outline are arranged in a matrix.

[0004] The second lens plate 400 is a composite laminate having a condenser lens array 410, a polarization separation prism array 420, a λ / 2 retardation plate 430, and an exit lens 440. The condenser lens array 410 includes a condenser lens 301.
And the same number of rectangular condenser lenses 411 are arranged in a matrix. Polarization separation prism array 420
Is a pair of a polarization beam splitter 421 formed of a prismatic prism composite having a polarization separation film 423 therein and a reflection mirror 422 formed of a prismatic prism composite having a reflecting surface 424 therein. As a basic structural unit,
The plurality of pairs are arranged in a plane. One condensing lens 411 corresponds to a pair of basic structural units. The output surface of the polarization separation prism array 420 has λ /
Λ / 2 retardation plate 430 in which two retardation films 431 are selectively disposed only on the exit surface of polarization beam splitter 421
Is installed. Further, an emission-side lens 440 is provided so as to cover the λ / 2 phase difference plate 430.

Next, the operation will be described. Light source lamp 2
01 is emitted from the reflector 2
02 is reflected in one direction and becomes a substantially parallel light flux,
Is incident on the lens plate 300. First lens plate 300
Is incident by the condenser lens 301,
A condensed image serving as a secondary light source image is formed on the second lens plate 400 disposed in a plane perpendicular to the system optical axis L.

The randomly polarized light incident on the polarization separation prism array 420 is separated by a polarization beam splitter 421 into two types of polarized light, P-polarized light and S-polarized light having different polarization directions. The P-polarized light passes through the polarization beam splitter 421 without changing the traveling direction. The S-polarized light is supplied to the polarization splitting film 423 of the polarization beam splitter 421.
And the traveling direction is changed by 90 degrees, the traveling direction is changed again by the reflecting surface 424 of the adjacent reflecting mirror 422 and the traveling direction is changed again by 90 degrees, and finally, the light is separated from the polarization separation prism array 420 at an angle substantially parallel to the P-polarized light. Is emitted.

The P-polarized light emitted from the polarization beam splitter 421 is converted into S-polarized light by rotating the polarization plane when passing through the λ / 2 retardation film 431. Since the S-polarized light emitted from the reflection mirror 422 does not pass through the λ / 2 retardation film 431, the S-polarized light is not affected by the rotation of the polarization plane.
The s-polarized light passes through the λ / 2 retardation plate 430 as it is. In this manner, polarization separation prism array 420 and λ / 2
The phase difference plate 430 converts the randomly polarized light into one type of polarized light (in this case, S-polarized light).

[0008] The light beam aligned to the S-polarized light is guided to the illumination area 500 by the exit lens 440, and is superposed and coupled on the illumination area 500.

The two lens plates 30 as described above are used.
Using 0,400, a plurality of condensing lenses 301 of the first lens plate 300 are used to form an array division number of light source images on the condensing lens array 410 of the second lens plate 400,
The first lens plate 300 is formed by the condenser lens array 410.
An optical system that forms a lens array image by the above on the illumination area 500 and superimposes it with a required accuracy is called an integrator optical system.

[0010]

In the above-described conventional polarization conversion illuminating device incorporated in an integrator optical system, a polarizing beam splitter is used in the optical path of a focused light beam or a divergent light beam in the integrator optical system.
The polarization splitting film of the polarization beam splitter is configured so that the sum of the refraction angles between two kinds of media having different refractive indexes becomes 90 degrees. Therefore, the refractive index of the two types of medium of the polarization separation film, the refractive index of the medium on the exit side of the polarization separation film, and the angle of incidence on the polarization beam splitter are obtained by summing the refraction angle between the two types of medium to 90 degrees. Subject to constraints to keep. The integrator optical system inherently has a light beam tilt angle, and there is a problem that the performance of the polarizing beam splitter is sharply reduced by exceeding the restriction range of the incident angle to the polarizing beam splitter.

FIG. 8 shows an example of the characteristics of a certain polarization beam splitter. In FIG. 8, the horizontal axis represents the incident angle and the vertical axis represents the reflection intensity.
─ × indicates the characteristics of S-polarized light and P-polarized light when the number of reflections is 20, respectively. A polarization beam splitter having such characteristics is disposed in an optical path having a light beam tilt angle, and the transmittance T of each of P-polarized light and S-polarized light when used as a polarization conversion illumination device.
p and Ts are defined as follows using the respective reflection intensities Rp and Rs. For example, the incident angle is 48 degrees and the number of reflections is 20.
The times are as follows. Tp = 0.5 {(1-Rp) + Rs} = 0.5 {(1-0.135) +0.9995} = 0.933 (Equation 1) Ts = 0.5 {(1-Rs) + Rp ｝ = 0.5 ｛(1-0.9995) +0.135｝ = 0.068 (Formula 2)

Light having a transmittance of Tp of the above formula 1 and Ts of the above formula 2 is incident on the liquid crystal light valve of the projection display device. In Equations 1 and 2, the reflection and transmission loss of the polarizing beam splitter is assumed to be zero. When a signal is applied to the liquid crystal light valve and polarization modulation is applied, assuming that the reflection loss and transmission loss of the liquid crystal light valve are zero, the liquid crystal light valve output becomes 0.932 when the signal intensity is maximum, and the signal intensity is 0.932. Is minimum, the liquid crystal light valve output is 0.068.

When the contrast ratio CR is defined as follows and specific numerical values of Tp and Ts in Expressions 1 and 2 are substituted, the following is obtained. CR = (Tp−Ts) ÷ Ts = (0.932−0.068) ÷ 0.068 = 12.7 (Equation 3)

Further, as the performance of the polarizing beam splitter alone, the following degree of polarization can be defined by using Equations 1 and 2. This degree of polarization is used as one performance index of the polarizing beam splitter. Degree of polarization [V] = (Tp−Ts) ÷ (Tp + Ts) (Equation 4)

Using the above equations 1, 2 and 3, FIG.
Table 1 below shows the characteristic results of the polarizing beam splitter shown in FIG.

[0016]

[Table 1]

Table 1 shows the characteristic of the deflection of the incident angle to the polarization separation film within a range of ± 5 degrees around 45 degrees, and forms an angle of 45 degrees with the polarization separation film that causes the deflection angle. Deflection angle of the incident angle at the polarizing beam splitter ()
Are shown as numerical values.

As can be seen from Table 1, when the polarizing beam splitter is arranged in an optical path having a light beam inclination and used as a polarization conversion illuminating device, the change in the maximum contrast ratio of the image formed by the liquid crystal light valve is shown in FIG. It is recognized as a problem that only a small value of the tilt angle is acceptable.

Incidentally, it is known that a polarizing plate made of a plastic film is inserted on the incident side of the liquid crystal light valve in order to prevent a decrease in the contrast ratio of an image produced by the liquid crystal light valve. Taking Table 1 as an example, P which is 0.784 in transmittance (incident angle: 50 degrees, number of reflections: 20)
When polarized light is incident on a polarizing plate made of plastic film, the transmittance is about 80%, 0.627, and the transmittance (incident angle: 50 degrees, number of reflections: 20 times).
When the S-polarized light of 216 is incident on a polarizing plate made of a plastic film, the transmittance is reduced to a value with almost no problem due to the extinction effect of the polarizing plate. As a result,
A decrease in contrast ratio can be prevented.

However, about 20% of the light is lost by the plastic film polarizing plate, and the loss of about 20% causes a rise in the temperature of the plastic film polarizing plate, resulting in a decrease in the degree of polarization due to aging. A new problem of promoting

As described above, in the conventional polarization conversion device arranged in the optical path having the light beam inclination, the degree of polarization of the polarization beam splitter is reduced, and as a result, the contrast ratio of the image formed by the liquid crystal light valve is reduced. Decrease. Also,
When a polarizing plate made of a plastic film is used to prevent the reduction of the contrast ratio, the luminous flux yield decreases, and the initial performance of the projection image surface illuminance and the projection image surface luminance decreases. There is a problem that the aging of the polarizing plate is promoted and the illuminance and the luminance of the projected image surface are changed over time.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a polarization conversion device capable of preventing a decrease in the degree of polarization of a polarization beam splitter due to a light beam tilt angle.

Another object of the present invention is to provide a polarization conversion device capable of preventing a decrease in contrast ratio of an image modulated by a liquid crystal light valve.

Still another object of the present invention is to provide a polarization conversion device capable of preventing a decrease in illuminance of an illumination area due to a difference in optical path length.

Still another object of the present invention is to provide a polarization conversion device which can be easily formed into an array structure.

Still another object of the present invention is to provide a polarization conversion device which can prevent incident light from an adjacent surface when the device has an array structure.

[0027]

The polarization converter of the present invention uses three polarization beam splitters. Each of the polarization beam splitters has a prism having a right-angled isosceles triangle cross section disposed on the incident side of the polarization separation film, a prism having a right-angled isosceles triangle cross section disposed on the emission side of the polarization separation film, and these two. It is composed of a polarization separation film disposed between the prisms, and has a cubic or rectangular parallelepiped shape as a whole. In each polarization beam splitter, the refractive index ratio of the two types of media constituting the polarization splitting film is made as large as possible. Further, the number of reflection surfaces, which is a boundary surface between the two types of media, is set to a predetermined number. In addition, the polarization separation film is arranged at 45 degrees with respect to the optical axis. Further, the medium refractive index of these two prisms is made as large as possible. The first polarized beam splitter, into which the randomly polarized light is incident and separates into the first polarized light and the second polarized light, is connected to the surface that transmits the first polarized light to form a second polarized light splitter. A polarizing beam splitter is arranged, and a third polarized beam splitter is arranged by connecting the reflected second polarized light to a surface from which the second polarized light is emitted. The second polarized light is arranged on a light emitting surface of the third polarized beam splitter. Is connected to a λ / 2 retardation plate for converting the light into the first polarized light.

According to the first aspect of the present invention, the polarization conversion device of the first invention has a configuration in which three polarization beam splitters are combined as described above. The first polarized light is separated into the first polarized light and the second polarized light, the separated first polarized light is emitted through the second polarized beam splitter, and the separated second polarized light is transmitted to the third polarized beam splitter. The random polarized light is converted into one type of polarized light (first polarized light) by being introduced, converting the second polarized light into the first polarized light by the λ / 2 retardation plate, and emitting the first polarized light. . According to the first aspect, even when the polarization beam splitter is disposed in an optical path having a light beam inclination, a decrease in the degree of polarization of the polarization beam splitter is reduced, and as a result, a decrease in the contrast ratio of an image modulated by the liquid crystal light valve is prevented.

According to a second aspect of the present invention, there is provided a polarization conversion device, wherein the first polarized light emitted from the second polarization beam splitter and the first polarized light emitted from the third polarization beam splitter are converted. A condensing lens for compensating for a difference in optical path length between the polarized light and the polarized light is provided on the long optical path length side (third polarization beam splitter side). According to the second aspect, the illuminance of the illumination area is prevented from being reduced due to the difference in the optical path length.

According to a third aspect of the present invention, there is provided a polarization conversion device in which, when a plurality of polarization conversion devices are combined to form an array structure, a light reflection coating is applied to an adjacent surface which is in contact with an adjacent polarization beam splitter. . In the third invention,
An array structure can be easily formed, and in the case of an array structure, incident light from an adjacent surface is prevented.

According to a fourth aspect of the present invention, there is provided a polarization conversion device, wherein a λ / 4 retardation plate is disposed on an adjacent surface of the third polarization beam splitter in the case of an array structure. The light reflecting surface is provided with a light reflecting coating.
According to the fourth aspect of the present invention, the array structure can be easily formed, and in the case of the array structure, incident light from the adjacent surface is prevented.

According to a fifth aspect of the present invention, there is provided a polarization conversion device in which a plurality of the above-described polarization conversion devices are arranged in an array. In the fifth invention, an array structure is easily realized.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments.

(Embodiment 1) FIG. 1 is a configuration diagram of a polarization conversion device according to Embodiment 1 of the present invention. The polarization converter shown in FIG. 1 includes a first polarization beam splitter 1 and a second polarization beam splitter.
The third polarization beam splitter 2 and the third polarization beam splitter 3 are optically coupled to each other. FIGS. 2A, 2B, and 2C are perspective views of the first, second, and third polarization beam splitters 1, 2, and 3, respectively.

The first polarizing beam splitter 1 has a structure shown in FIG.
As shown in FIG. 1A, the prism has a cubic shape in which two right-angled isosceles triangular prisms 11 and 13 are coupled therebetween via a polarization separation film 12, and has one square-shaped incident surface 14 and 2
And two square emission surfaces 15 and 16. Anti-reflection coatings 14a and 15a, 16a are applied to the entrance surface 14 and the exit surfaces 15, 16.

The second polarizing beam splitter 2 has a structure similar to that of FIG.
As shown in FIG. 2B, the prism has a cubic shape in which two right-angled isosceles triangular prisms 21 and 23 are coupled via a polarization separation film 22 therebetween, and has a square incident surface 24 and a parallel parallel surface. And a single exit surface 25 having a square shape. Anti-reflection coatings 24a and 25a are applied to the entrance surface 24 and the exit surface 25.

The third polarizing beam splitter 3 is provided in FIG.
As shown in FIG. 3C, the prism has a cubic shape in which two right-angled isosceles triangular prisms 31 and 33 are coupled therebetween via a polarization separating film 32, and has one square-shaped incident surface 34 and 1
And two square emission surfaces 35. Anti-reflection coatings 34a and 35a are provided on the entrance surface 34 and the exit surface 35, respectively.

The first, second, and third polarizing beam splitters 1, 2, and 3 having such a configuration are integrated as follows. As shown in FIG. 1, the exit surface 15 of the first polarization beam splitter 1 and the entrance surface 24 of the second polarization beam splitter 2 are brought into close contact with each other via an air layer or an adhesive, and The exit surface 16 of the beam splitter 1 and the entrance surface 3 of the third polarization beam splitter 3
4 is brought into close contact with an air layer or an adhesive.
A λ / 2 retardation plate 4 is adhesively bonded to the exit surface 35 of the third polarization beam splitter 3, and the λ / 2 retardation plate 4 has a λ / 2 retardation plate exit surface 41. .

Each of the polarization splitting films 12, 22, and 32 has 2
It is configured by laminating a plurality of layers of adjacent media. The refractive index ratio of these two media is set to about 1.7,
The number of layers is from several layers to at most about 10 layers in terms of the number of reflection surfaces. In addition, the angle of light rays incident on the polarization splitting films 12, 22, and 32 is 45 degrees at the optical axis position, and the sum of the refraction angles of the two types of media is 90 degrees to obtain the brutus angle in this case. The refractive indices of the right-angled isosceles triangular prisms 11, 13, 21, 23, 31, and 33 are determined so that they can be performed.

The incident surface 1 of the first polarizing beam splitter 1
4, the polarization splitting film 1
The angles of light rays incident on 2, 22, 32 deviate from 45 degrees. To reduce this angle deviation, right-angled isosceles triangular prisms 11, 13, 21, 23, 31, 31,.
The larger the refractive index of 33 is, the more preferable it is. The refractive index of the medium on the high refractive index side of the polarization separation films 12, 22, 32 is selected so that this refractive index can be made as large as possible.

Next, the operation will be described. The randomly polarized light incident on the incident surface 14 of the first polarizing beam splitter 1 is separated by the first polarizing beam splitter 1 into two types of polarized light, P-polarized light and S-polarized light having different polarization directions. You. The P-polarized light passes through the first polarizing beam splitter 1 as it is without changing its traveling direction, and its exit surface 15
The light enters the second polarization beam splitter 2 via the incident surface 24 from the light source, passes through the second polarization beam splitter 2 as it is, and is emitted from the emission surface 25 thereof.

On the other hand, the S-polarized light is reflected by the polarization splitting film 12 of the first polarization beam splitter 1, changes its traveling direction by 90 degrees, passes from its exit surface 16 to its entrance surface 34, and enters the third polarization beam splitter 3. Then, the light is further reflected by the polarization splitting film 32 of the third polarization beam splitter 3 and changes its traveling direction again by 90 degrees.
Out of the exit surface 35 of the polarization beam splitter 3. The emitted S-polarized light is converted into P-polarized light by the rotation of the polarization plane when passing through the λ / 2 retardation plate 4, and the converted P-polarized light is converted into the λ / 2 light. The light is emitted from the phase difference plate emission surface 41.

As described above, the incident random polarized light is converted into one kind of polarized light (P-polarized light in this example) by the polarization converter of the present invention. Then, the luminous flux aligned with the P-polarized light is guided to the illumination region 500 (see FIG. 7), and is superposed and coupled on the illumination region 500.

Table 2 below shows the results of calculating the characteristics of the polarization conversion device having such a configuration. Polarization separation film 1
The refractive index ratio of the two media 2, 22, and 32 is set to 1.7, the refractive index of each prism 11, 13, 21, 23, 31, 33 is set to 1.68, and the polarization separation films 12, 22, 32 are set. -Polarized light transmittance Tp, S at 10 times of reflection when the angle of incidence on light is changed from 40 degrees to 50 degrees in steps of 1 degree
Table 2 shows the calculated values of the polarization transmittance Ts and the contrast ratio. Also, as in Table 1, the deflection angle of the incident angle at the polarization beam splitter is shown as a numerical value in parentheses. In addition, in order to perform comparison at the same level as in Table 1, the reflection loss and the transmission loss at each polarization beam splitter were set to 0. Further, the P-polarized light transmittance Tp and the S-polarized light transmittance T
s is calculated by using the reflection intensities Rp and Rs,
Defined in. Note that the contrast ratio was defined by Equation 3 described above. Tp = 0.5 {(1-Rp) ² + Rs ² } (Equation 5) Ts = 0.5 {(1-Rs) ² + Rp ² } (Equation 6)

[0045]

[Table 2]

When the results in Table 2 are compared with the results in Table 1,
It is apparent that the polarization converter of the present invention can greatly improve the contrast ratio.

As described above, when the polarization conversion device of the present invention is installed in an optical path having a light beam tilt angle, a decrease in the degree of polarization is prevented, and as a result, the contrast ratio of the image formed by the liquid crystal light valve is reduced. I will not let you.

(Embodiment 2) In Embodiment 1, the second
And the optical path length from the exit surface 25 of the polarization beam splitter 2 to the illumination area, and λ / 2 of the third polarization beam splitter 3
A difference occurs in the optical path length from the phase plate exit surface 41 to the illumination area. Specifically, the λ / 2 retardation plate emission surface 41
The length of the optical path of the P-polarized light emitted from the light source is longer than the length of the optical path of the P-polarized light emitted from the emission surface 25 of the right-angled isosceles triangular prism 21 forming the second polarization beam splitter 2. It is substantially longer by the length of the isosceles. As a result, the illumination area is unnecessarily enlarged.

Embodiment 2 solves such a problem. FIG. 3 is a configuration diagram of the polarization conversion device according to the second embodiment of the present invention. As shown in FIG. 3, the condenser lens 5 is provided on the λ / 2 retardation plate emission surface 41 of the third polarization beam splitter 3. Condensing lens 5
Has a plano-convex lens shape, the plane-side condensing lens entrance surface 51 is joined to the λ / 2 retardation plate exit surface 41, and the curvature of the converging lens exit surface 52 on the curved surface side is The value is set to a value that compensates for the optical path difference described above.

As described above, in the second embodiment, by providing the condenser lens 5 on the exit side of the third polarizing beam splitter 3, it is possible to prevent the illumination area from being unnecessarily enlarged, and to reduce the illumination area. Compensate for reduced illumination.

(Embodiment 3) Embodiments 1 and 2 described above
In 2, the case where the first, second, and third polarization beam splitters 1, 2, and 3 are used is described.
It is also possible to arrange a plurality of these to form a polarizing beam splitter array. In the case of such an array, it is necessary to prevent light from entering from adjacent surfaces.
The third embodiment is designed to prevent such intrusion light.

FIGS. 4A and 4B are perspective views of the first polarizing beam splitter 1 and the third polarizing beam splitter 3 according to the third embodiment.

As shown in FIG. 4A, a plane parallel to the emission surface 16 of the first polarization beam splitter 1 is an adjacent surface 17 that is joined to the adjacent third polarization beam splitter 3. The adjacent surface 17 is provided with a reflective coating 17b. Further, as shown in FIG. 4B, a plane parallel to the incident plane 34 of the third polarizing beam splitter 3 is an adjacent plane 36 which is joined to the adjacent first polarizing beam splitter 1.
The adjacent surface 36 is provided with a reflective coating 36b.

As described above, in the third embodiment, the reflection coatings 17a and 36a are applied to the adjacent surfaces 17 and 36 of the first and third polarizing beam splitters 1 and 3 in the case of an array, so that the adjacent surfaces are provided. Light incident from the surfaces 17 and 36 can be prevented.

(Embodiment 4) FIG. 5 is a perspective view of a third polarizing beam splitter 3 according to Embodiment 4. As shown in FIG. 5, an anti-reflection coating 36a is applied to the adjacent surface 36 of the third polarizing beam splitter 3, and
The / 4 retardation plate 6 is joined, and a reflection coating 6b is applied to the emission surface of the λ / phase retardation plate 6.

As described above, in the fourth embodiment, the P-polarized light to be emitted from the adjacent surface 36 of the third polarizing beam splitter 3 is converted to the S-polarized light by reciprocating through the λ / 4 phase plate 6. Then, since the converted S-polarized light can be surely reflected by the polarization separation film 32 and returned to the light source side, intrusion of light into the adjacent surface 36 can be almost completely prevented.

(Embodiment 5) Each of the first, second, and third polarizing beam splitters 1, 2, and 3 has a rectangular parallelepiped shape.
Embodiment 5 is an example of realizing an array structure. FIG. 6 is a configuration diagram of a polarization conversion device according to the fifth embodiment of the present invention. As shown in FIG. 6, each of the first, second, and third polarizing beam splitters 1, 2, and 3 has a vertically long rectangular parallelepiped shape, and has respective incident surfaces 14, 24, 34, and exit surfaces 15,.
16, 25, 35 and adjacent surfaces 17, 36 are divided into n sections. Also, corresponding to this classification, the λ / 2 retardation plate 4,
The condenser lens 5 is also divided into n pieces. That is, the first polarizing beam splitter 1 is configured to have the n-sectioned incident surface 14-.
, 14-n, adjacent surfaces 17-1, 17-
, 17-n, etc., and the third polarizing beam splitter 3 includes n divided adjacent surfaces 36-1, 36-2,.
36-n, λ / 2 phase difference plates 4-1, 4-2,..., 4-
, 5-n, condenser lenses 5-1, 5-2,..., 5-n, condenser lens emission surfaces 52-1, 52-2,. The interval between such divisions may be set in accordance with a desired pitch of the array.

As described above, in the fifth embodiment, since the first, second, and third polarizing beam splitters 1, 2, and 3 having a rectangular parallelepiped shape that can be divided into a cubic shape are joined, an array-like shape is provided. The configuration can be realized very easily.

[0059]

As described above, in the polarization converter of the first invention, the first polarized light obtained by transmitting the incident light as it is and the incident light are reflected by combining the three polarizing beam splitters. And the second polarized light obtained through the λ / 2 phase difference plate are arranged to be the same kind of polarized light (first polarized light). In addition, the polarizing beam splitter can prevent a decrease in the degree of polarization, which is the performance of a polarizing beam splitter, and as an effect, a polarizing plate made of a plastic film for removing unnecessary polarized light without reducing the contrast ratio of an image formed by a liquid crystal light valve. It is not necessary to use a plate, so that unnecessary reduction in luminous flux yield can be prevented, and deterioration of illuminance and brightness of the projected image surface can be prevented from aging as in the case of using a polarizing plate made of a plastic film. That.

In the polarization converter according to the second aspect of the present invention, the difference in optical path length between the first polarized light obtained by directly transmitting the incident light and the first polarized light converted after reflecting the incident light is compensated. Since the condensing lens is provided on the long optical path length side, it is possible to prevent the illuminance of the illumination area from being reduced due to the difference in the optical path length.

In the polarization converter of the third invention, the first, third
Reflective coating was applied to the adjacent surface of the polarizing beam splitter to prevent light incident from the adjacent surface,
An array structure can be easily realized.

In the polarization converter of the fourth invention, an anti-reflection coating is applied to the surface adjacent to the third polarization beam splitter, and a λ / 4 phase difference plate is further disposed, and the light is reflected on the emission surface of the λ / 4 phase difference plate. Since the coating is applied, an array structure can be easily formed, and in the case of an array structure, incident light from an adjacent surface can be prevented.

In the polarization converter of the fifth invention, the structure of the three polarization beam splitters is a rectangular parallelepiped which can be divided into a plurality of cubes, so that an array structure can be easily realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a polarization conversion device of the present invention.

FIG. 2 is a perspective view of a polarization beam splitter in the polarization conversion device of the present invention.

FIG. 3 is a configuration diagram of another polarization conversion device of the present invention.

FIG. 4 is a perspective view of another polarization beam splitter in the polarization conversion device of the present invention.

FIG. 5 is a perspective view of yet another polarization beam splitter in the polarization conversion device of the present invention.

FIG. 6 is a configuration diagram of still another polarization conversion device of the present invention.

FIG. 7 is a configuration diagram of a conventional polarization conversion optical system.

FIG. 8 is a graph showing a characteristic example of a polarization beam splitter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 First polarizing beam splitter, 2 Second polarizing beam splitter, 3 Third polarizing beam splitter, 4
λ / 2 retardation plate, 5 condenser lens, 6 λ / 4 retardation plate, 11, 13, 21, 23, 31, 33 prism,
12, 22, 32 polarization splitting film, 14, 24, 34 entrance plane, 15, 16, 25, 35 exit plane, 14a, 15
a, 16a, 24a, 25a, 34a, 35a, 36a
Anti-reflective coating, 6b, 17b, 36b Reflective coating, 17, 36 Adjacent surface.

Claims (5)

[Claims] 1. A structure in which a polarized light separating film is interposed between the maximum side surfaces of a pair of triangular prisms, the incident random polarized light is separated into a first polarized light and a second polarized light, and the first polarized light is separated from the first polarized light.
A first polarizing beam splitter having a first light emitting surface for emitting the polarized light and a second light emitting surface for emitting the second polarized light, and a polarization separating film interposed between the largest side surfaces of the pair of triangular prisms. And a second polarization beam splitter having a light incident surface joined to the first light exit surface of the first polarization beam splitter, and a polarization separation film interposed between the largest side surfaces of the pair of triangular prisms. And the first
A third polarizing beam splitter having the light incident surface joined to the second light emitting surface of the polarizing beam splitter, and a λ / light beam splitter provided on the light emitting surface of the third polarizing beam splitter.
A polarization converter comprising: a two-phase retarder. 2. The polarization conversion device according to claim 1, further comprising a condenser lens provided on a light exit surface of the λ / 2 retardation plate. 3. A light reflecting coating is applied to a surface of the first polarization beam splitter facing the second light exit surface and a surface of the third polarization beam splitter facing the light incidence surface. The polarization conversion device according to claim 1. 4. The λ / 4 phase difference plate further provided on a surface of the third polarization beam splitter facing the light incident surface, and a light reflection coating is provided on a light exit surface of the λ / 4 phase difference plate. 3. The polarization conversion device according to claim 1, wherein 5. A polarization converter having a configuration in which a plurality of the polarization converters according to claim 1 are arranged.