JP2000056266A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the polarization conversion having high efficiency and the high uniformity of screen compatible. SOLUTION: The polarization conversion having high efficiency is performed by guiding a P-polarized light and an S-polarized light to different positions in the inlet part of a transparent rod 6 and providing a half-wave phase plate 8 which is arranged at a position conjugate with the inlet part of the transparent rod 6 in an image formation lens system and a position corresponding to one side of the P-polarized light and the S-polarized light and which rotates the linearly polarized light. Moreover, the uniformity of screen is obtained by forming the image of the outlet of the rod 6 in the vicinity of a spatial optical modulation element 9 with an image formation lens 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device used for, for example, a projector device.

[0002]

2. Description of the Related Art When configuring a projector device, when a signal having the same level over the entire screen is input to the device,
It is required that the screen luminance distribution on the screen is constant. The uniformity of the brightness on the screen is called high screen uniformity, and is one of the important items in achieving high quality image quality.

[0003] Generally, a light source has luminance unevenness in a light emitting portion. Here, as a configuration of the projector device, it is considered that light from a light source is formed on a spatial light modulator that inputs an image signal, and an image of the spatial light modulator is formed on a screen by a projection lens. When such an optical system is used, the uneven brightness of the light emitting portion of the light source is projected on the screen as it is, and a high screen uniformity cannot be obtained.

[0004] Therefore, an optical system from the light source to the spatial light modulator (referred to as an illumination optical system) needs a configuration capable of uniformly illuminating the spatial light modulator. An optical element generally called a light integrator is used for this. Two types of light integrators are generally used. One is called a multi-lens array or a fly-eye lens. A plurality of small lenses are spatially arranged, and light is uniformly illuminated by superimposing light on a spatial light modulator. Another is to use a transparent rod.

FIG. 12 shows an illumination optical system using a transparent rod. Consider a lamp as a light source. The light emitted from the light source 11 is guided to the transparent rod 14 using the concave reflecting mirror 12 and the condenser lens 13. Then, the spatial light modulator 16 is illuminated using the imaging lens 15. The illumination optical system forms an image of a light emitting portion from the exit portion of the transparent rod 14 on the spatial light modulator 16. FIG. 13 shows a transparent rod 14.
FIG. The transparent rod 14 has a cross section similar or similar to the spatial light modulator 16 (A: B is similar or similar to the spatial light modulator 16). It is made of a material having a high light transmittance, such as glass or plastic, and each surface is polished. The incident light is transmitted inside without loss by total internal reflection. Even if there is uneven brightness at the incident portion, the light is reflected inside and overlapped, so that the emitting portion of the transparent rod has a highly uniform light distribution. By forming an image of this emission part on the spatial light modulator 16 by the imaging lens 15, illumination with high uniformity becomes possible.

[0006]

By the way, as the spatial light modulation element 16, an element that modulates using the polarization of light is often used. A representative example is a spatial light modulator (hereinafter, referred to as a liquid crystal panel) using liquid crystal. When a liquid crystal panel is used, incident light is required to be linearly polarized light in a certain direction.

When a light source such as a discharge lamp is used, light emitted from the lamp is non-polarized. Even when a polarized light source such as a laser is used, the degree of polarization is reduced by an optical system in the middle. In the case where the liquid crystal panel is illuminated with light that is not linearly polarized as described above, the contrast on the screen deteriorates if light of a polarization component rotated by 90 degrees from the polarization required by the liquid crystal panel enters the liquid crystal panel. Therefore, it is necessary to separate unnecessary polarization components using a polarizing plate or a polarizing beam splitter (PBS).

Here, the unnecessary polarized component light can be separated and re-used by rotating the polarized light to a required polarization direction using a wave plate. This is called polarization conversion. For example, in an illumination optical system using a transparent rod 14, a polarizing beam splitter (PBS) 1 as shown in FIG.
7, a method of incorporating the triangular prism 18 and the λ / 2 retardation plate 19 into the transparent rod 14 and using it has been considered. As can be seen from FIG. 15A, the P-polarized light and the S-polarized light are separated by the PBS 17 and the reflected S-polarized light is
8, the light is guided to the λ / 2 retardation plate 19, and the S-polarized light is converted to λ / 2.
The light is converted into P-polarized light by the wave plate 19. Thus, the liquid crystal panel as the spatial light modulator 16 can be efficiently irradiated with P-polarized light.

However, this method cannot completely perform polarization conversion. For example, as shown in FIG.
This is because there is light that passes through the PBS 17 without passing through the polarization splitting surface.

When such a method is used, P
It is necessary to make the size of the BS 17 substantially equal to the size of the cross section of the transparent rod 14. In the optical system of FIG. 14, the divergence angle of light is relatively large inside the transparent rod 14. This is because it is necessary to focus light on a small area.
In the PBS 17, a light beam perpendicular to the incidence plane of the PBS 17 (incident angle of 45 degrees with respect to the polarization separation plane) can be efficiently separated into P-polarized light and S-polarized light. However, as the distance from the vertical increases, S-polarized light that should be reflected is transmitted and P-polarized light that should be transmitted is reflected. That is, the efficiency of the polarization conversion is reduced. Therefore, when the PBS 17 is used as a part of the polarization conversion optical element, it is more efficient to use the PBS 17 in a portion where the divergence angle of light is small.

For these reasons, there is a drawback that if the polarization conversion is performed using the portion of the transparent rod 14, the efficiency is low.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to achieve both efficient polarization conversion and high screen uniformity.

Therefore, as an optical device, a light source for outputting non-polarized light, a spatial light modulator for modulating light using polarized light, and a transparent rod having a uniform light intensity distribution at an exit portion by total reflection of light. A polarization separation unit that separates non-polarized light emitted from the light source into P-polarized light and S-polarized light; An imaging lens system that forms an image of the exit portion of the transparent rod in the vicinity of the spatial light modulator, and a position conjugate with the entrance portion of the transparent rod by the imaging lens system, and a P-polarized light and an S-polarized light. And a λ / 2 retardation plate that is disposed at a position corresponding to one of the two and rotates the linearly polarized light.

In this case, since the P-polarized light and the S-polarized light are positionally separated at the entrance of the transparent rod by the condensing optical system, if the position is conjugate with the entrance of the transparent rod, The P polarized light and the S polarized light are positionally separated. Therefore, by arranging a λ / 2 retardation plate on one of them, polarization conversion becomes possible. Then, at this time, the factor for lowering the conversion efficiency does not occur structurally. Of course, uniformity is also guaranteed by using a transparent rod.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical device according to an embodiment of the present invention will be described. FIG. 1 is a structural view of an optical device according to an embodiment of the present invention. This is an illumination optical system using a transparent rod as a light integrator, and can efficiently perform polarization conversion.

The light source 1 is formed by, for example, a discharge lamp. The unpolarized light emitted from the light source 1 is
The light is condensed by the concave reflecting mirror 2 and is polarized by the polarization beam splitter 3.
It is led to. Then, by the polarizing beam splitter 3, P
It is separated into polarized light and s-polarized light. That is, the S-polarized light is reflected by the polarization splitting film of the polarization beam splitter 3, and the P-polarized light passes through the polarization splitting film. The reflected S-polarized light is guided to the condenser lens system 5. The P-polarized light transmitted through the polarization splitting film is reflected by the reflection mirror 4.
And travels in the same direction as the S-polarized light separated by the polarizing beam splitter 3. Here, an optical path difference occurs between the P-polarized light and the S-polarized light due to the polarization beam splitter 3 and the reflecting mirror 4.

The P-polarized light and the S-polarized light are made incident on the transparent rod 6 by the condenser lens system 5. At this time, the P-polarized light and the S-polarized light are entered at the entrance (position) of the transparent rod 6 using the path difference between the two polarized lights. The condensing lens system 5 is designed so that polarized light is separated and incident on the transparent rod. The P-polarized light and S-polarized light separated and incident on the transparent rod 6 travel toward the exit by total reflection on the wall surface of the transparent rod 6. At the exit portion (position) of the transparent rod, a uniform light intensity distribution is obtained. Further, at the exit portion, both polarized lights are mixed to be in a non-polarized state.

An imaging lens system 7 is used to illuminate the exit portion of the transparent rod 6 onto a spatial light modulator 9 (position) formed by, for example, a liquid crystal panel. In addition, the distance λ between the imaging lens system 7 and the spatial light modulator 9 (position)
A / 2 phase difference plate 8 is provided.

The place (position) where the λ / 2 retardation plate 8 is disposed is near the position conjugate with the imaging lens system 7 at the entrance (position) of the transparent rod 6. In this position,
As shown in FIG. 3, rectangular [lambda] / 2 retardation plates having long sides are arranged at appropriate intervals and numbers. Λ / 2 at this position
The polarization conversion is performed by providing the phase difference plate. That is, in this example, the polarized light is separated before entering the transparent rod 6, and the P-polarized light and the S-polarized light are separated and incident on the incident surface of the transparent rod 6. At this time, if a λ / 2 retardation plate for performing polarization conversion is arranged at a position conjugate with the entrance of the transparent rod 6, polarization conversion can be performed with extremely high efficiency.

The principle will be described below. First, when the transparent rod 6 is used as a light integrator, how the light is made uniform will be considered. As shown in FIG. 4, inside the transparent rod 6, the number of reflections on the wall surface of the transparent rod 6 is determined by the angle of incidence of the light beam and the shape of the transparent rod 6. For example, the light beam L3 travels without being reflected by the wall surface, the light beam L2 is reflected once, and the light beam L1 is reflected twice. Here, the light ray L2 is reflected only once on the wall surface in the transparent rod 6, and this is considered that light comes from the position of Z2. That is, it can be considered that the image Z3 on the incident surface is at the position of the image Z2. Since the light is reflected once, it looks like an inverted image Z2. Next, it can be considered that the light ray L1 is reflected twice in the transparent rod 6, that is, the image Z3 is located at the position of the image Z1. Since the light is reflected even number of times, it has the same direction as the image L3.

That is, by passing through the transparent rod 6, the luminance distribution at the exit end is made uniform. This is because the image of the entrance end is virtually spread on the upper, lower, left and right sides of the incident portion, and is superimposed on the exit end. You can think that it is.

Next, the transparent rod 6 is formed by using the imaging lens 7.
A case is considered in which the exit portion is illuminated on the spatial light modulator 9 (liquid crystal panel). As shown in FIG. 5, an image Z12 of the exit end of the transparent rod 6 is formed as an image Z14 on a liquid crystal panel (position) by using an imaging lens 7. At this time, the virtually formed spread image Z11 formed at the incident end (position) of the transparent rod 6 can be positioned as the image Z13 by the imaging lens 7.

Here, when the images Z11 and Z13 in FIG. 5 are considered with P-polarized light and S-polarized light, the result is as shown in FIG. As described above, since the P-polarized light and the S-polarized light are separately incident on the incident surface of the transparent rod 6, the image Z11 is partially separated into P-polarized light and S-polarized light as shown in FIG. I have.
Therefore, the image Z13 generated by the imaging lens 7 is also partially separated into P-polarized light and S-polarized light as shown in the figure. From this, it is understood that by placing the λ / 2 phase difference plate 8 at the position shown in FIG. 6 in a required arrangement state, highly efficient polarization conversion becomes possible.

The operation of the present embodiment utilizing such a principle is shown in FIG. FIG. 2 schematically shows the state of the image at each position in FIG. At the position where the transparent rod 6 is incident, as shown in FIG.
Polarized light is incident with its position separated. At a position which is an emission portion of the transparent rod 6, P is set as shown in FIG.
The polarized light and the s-polarized light are mixed to be in a non-polarized state.

However, as a result of the incidence of the P-polarized light and the S-polarized light separated at the incident portion of the transparent rod 6, the conjugate position of the entrance portion of the transparent rod 6 by the imaging lens system 7 is shown in FIG. A spread image like this is created. In this example, a 5 × 5 spread image exists. The one at the center is not reflected inside the transparent rod 6. An image which is reflected an odd number of times in the left-right direction or the up-down direction has an inverted image, so that adjacent P and S images are adjacent to each other as shown in the figure. At this position, the P-polarized light and the S-polarized light are separated in this way, so that the λ / 2 phase difference plate 8 as shown in FIG. That is, λ / 2 corresponding to where P-polarized light exists at the position.
When the retardation plate 8 is provided, all images (FIG. 2D) formed at the position of the spatial light modulator 9 become S-polarized light. If a λ / 2 retardation plate is provided corresponding to the position where S-polarized light is present at the position, all images (FIG. 2D) formed at the position of the spatial light modulator 9 become P-polarized light. As described above, in this example, polarization conversion is realized, and in this case, there is no factor that hinders conversion efficiency, and polarization conversion can be performed only with a λ / 2 retardation plate because polarization separation is not performed in the conversion part. Therefore, highly efficient polarization conversion can be realized.

Further, as described above, at the exit portion of the transparent rod 6, the light overlaps and has a uniform spatial distribution. Since the spatial light modulator 9 forms an image of the emission portion of the transparent rod 6, it is possible to achieve both high uniformity illumination and polarization conversion.

The transparent rod 6 is not limited to a glass material but may be any transparent one. For example, a plastic material, quartz, or the like can be used.

Hereinafter, modified examples of the optical device according to the embodiment of the present invention will be described. In the example shown in FIG. 7, a concave lens 5b is added to the next stage of the convex lens 5a as the condenser lens system 5. By providing the concave lens 5b, the transparent rod 6
In contrast, the telecentric optical system, that is, the principal ray of the image can be made parallel to the optical axis. In this way, by adjusting the condensing lens system to the light source 1, the concave reflecting mirror 2, and the like, and determining the number of lenses and the lens shape, efficient condensing can be performed. For example, as shown in FIG.
(5c, 5d, 5e), the polarization beam splitter 3
It is conceivable to provide a lens 5e for condensing the light, or a lens 5d for only one of the two separated polarized lights. Further, as shown in FIG. 9, the condenser lens system 5 (5f, 5f,
As g), it is conceivable to dispose a lens 5g for condensing light on the polarization beam splitter 3 and a deflection prism 5f.

FIG. 10 shows a case where the condenser lens system 5 is an anamorphic optical system (an optical system having different curvatures between the X axis and the Y axis). In this case, the size of the focused spot at the entrance of the transparent rod 6 can be increased. This makes it possible to minimize the angle of light incident on the spatial light modulator 9.

FIG. 11 shows an example in which the polarizing beam splitter 3 and the reflecting mirror 4 are arranged close to each other. That is, the reflection mirror 4 is attached to the polarization beam splitter 3 as shown in the figure. As a method of forming the reflecting mirror 4, a method of forming the reflecting mirror 4 on the polarizing beam splitter 3 by vacuum deposition, sputtering, or the like, or a method of closely attaching a mirror to the outside of the polarizing beam splitter 3 are considered.

In order to obtain a high-efficiency and high-quality image as a projector device, it is common to use different liquid crystal panels for three colors of red, green and blue (called a three-panel system). Even when the present invention is adopted, a three-plate system can be realized by disposing a color separation mirror and the like between the rod integrator and the liquid crystal panel.

[0032]

As described above, according to the present invention, the P-polarized light and the S-polarized light are guided to different positions at the entrance of the transparent rod, and the P-polarized light and the S-polarized light are conjugated with the entrance of the transparent rod by the imaging lens system. , Which is arranged at a position corresponding to one of P-polarized light and S-polarized light and rotates linearly polarized light.
Since it has a / 2 phase difference plate, highly efficient polarization conversion is realized. In addition, since the image of the exit portion of the transparent rod is formed near the spatial light modulator by the imaging lens system, high screen uniformity can be obtained. That is, in the case where a projector device is configured using a spatial light modulation element using polarization, it is possible to achieve both efficient polarization conversion and high screen uniformity by using the optical device of the present invention. Image quality, high efficiency, and high luminance can be realized. Further, in the present invention, since only one polarization separation unit is required, for example, only one polarization beam splitter is sufficient, and there is no cost burden. By making it even more efficient, the power of the light source can be reduced,
Heat generation can be suppressed. This leads to an advantage of simplifying measures against heat generation in devices such as a projector device. Further, it is possible to reduce the energy used.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a structure of an optical device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an image state at each position of the optical device according to the embodiment.

FIG. 3 is an explanatory diagram of a λ / 2 wavelength plate used in the optical device according to the embodiment.

FIG. 4 is an explanatory diagram of reflection on a transparent rod according to the embodiment.

FIG. 5 is an explanatory diagram of a polarization conversion principle of the embodiment.

FIG. 6 is an explanatory diagram of the polarization conversion principle of the embodiment.

FIG. 7 is an explanatory diagram of a modified example of the optical device of the embodiment.

FIG. 8 is an explanatory diagram of a modification of the optical device of the embodiment.

FIG. 9 is an explanatory diagram of a modification of the optical device of the embodiment.

FIG. 10 is an explanatory diagram of a modification of the optical device of the embodiment.

FIG. 11 is an explanatory diagram of a modified example of the optical device of the embodiment.

FIG. 12 is an explanatory diagram of a conventional illumination optical system.

FIG. 13 is an explanatory diagram of a transparent rod.

FIG. 14 is an explanatory diagram of an illumination optical system incorporating a polarization conversion element.

FIG. 15 is an explanatory diagram of the operation of the polarization conversion element.

[Explanation of symbols]

1 light source, 2 concave reflecting mirror, 3 polarizing beam splitter, 4 reflecting mirror, 5 condenser lens system, 6 transparent rod,
7 imaging lens system, 8 λ / 2 wavelength plate, 9 spatial light modulator

Claims (4)

[Claims] A light source that outputs unpolarized light; a spatial light modulator that modulates light using polarized light; a transparent rod that has a uniform light intensity distribution at an exit portion by total reflection of light; A polarization separation unit that separates non-polarized light emitted from the light into P-polarized light and S-polarized light; and a condensing optic that guides the P-polarized light and the S-polarized light separated by the polarization separation unit to different positions at the entrance of the transparent rod A system, an imaging lens system that forms an image of an exit portion of the transparent rod in the vicinity of the spatial light modulator, and a position conjugate with an entrance portion of the transparent rod by the imaging lens system, and Λ / is arranged at a position corresponding to one of P-polarized light and S-polarized light and rotates linearly polarized light.
An optical device comprising: a two-phase retarder; 2. The optical device according to claim 1, wherein the transparent rod has a cross section similar to or similar to the shape of the spatial modulation portion of the spatial light modulator. 3. The light-collecting optical system is provided with a reflecting mirror that reflects P-polarized light transmitted through the polarized light separating unit so as to be closer to the optical axis direction of S-polarized light reflected by the polarized light separating unit. The optical device according to claim 1, wherein: 4. The optical device according to claim 1, wherein the λ / 2 phase difference plate has a shape corresponding to a plurality of separated condensed images that can be formed at a position where the λ / 2 phase difference plate is arranged.