JP2011107463A - Projection display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection display device that prevents color bleeding and decreases the occurrence of interference pattern. <P>SOLUTION: The projection display device includes: a polarization separation element with a polarized light separating surface that has curvature, transmits a P polarized light and guides it to a first crystal liquid display element and reflects a S polarized light and guides it to a second crystal liquid display element; and a projection optical system that projects images displayed by the first and second crystal liquid display elements on a projected surface. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a projection display device, and more particularly to a projection display device using a reflective liquid crystal display element.

  Projection-type display devices have been widely used for presentations and watching movies at home as devices capable of projecting images such as personal computers and videos onto a large screen. In particular, a projection display device using a reflective liquid crystal display element having features such as a high aperture ratio and high definition as compared with a transmissive liquid crystal display element has recently attracted attention.

  It is known that interference fringes are generated as a problem of a projection display device using a reflective liquid crystal display element. Specifically, a part of the light that should be totally transmitted through the polarization separation film of the polarization separation element is reflected by the polarization separation film, so that interference fringes are generated by the slightly reflected light and transmitted light. .

  Therefore, in Patent Documents 1 and 2, two liquid crystal display elements are arranged so that the distances from the polarization separation film are unequal, thereby reducing interference fringes. In these inventions, an image obtained by shifting the positions of the two liquid crystal display elements by applying axial chromatic aberration corresponding to the shift amount of the liquid crystal display elements to the projection lens (an image of one of the colors). To prevent blur.

JP 2006-047967 A JP 2006-343692

  However, in the inventions described in Patent Documents 1 and 2, interference fringes can be reduced. However, since axial chromatic aberration is imparted to the projection lens, color blur occurs within one light band.

  In order to solve the above-described problems, it is an object of the present invention to provide a color separation / synthesis system and a projection display device that suppress the generation of interference fringes and reduce color bleeding.

  In order to solve the above problems, the present invention provides a polarization separation element having a polarization separation surface that transmits P-polarized light and guides it to the first liquid crystal display element, reflects S-polarized light and guides it to the second liquid crystal display element, In the projection type display device having a projection optical system for projecting images displayed by the first and second liquid crystal display elements onto the projection surface, the polarization separation surface has a curvature.

  The effect of the present invention resides in that generation of interference fringes can be suppressed and color blurring can be reduced.

Configuration diagram of Embodiment 1 Axial chromatic aberration diagram of the projection lens of Embodiment 1 Second polarization separation prism and axial chromatic aberration diagram of embodiment 1 Second polarization separation prism and longitudinal chromatic aberration diagram of Embodiment 2 Second polarization separation prism and axial chromatic aberration diagram of Embodiment 3 Second polarization separation prism and axial chromatic aberration diagram of Embodiment 4 Comparative second polarization splitting prism and longitudinal chromatic aberration diagram

(Embodiment 1)
FIG. 1 is a configuration diagram of a projection display device according to the first embodiment. Reference numeral 1 denotes a light source, and a high-pressure mercury lamp is used in this embodiment. 2 is a paraboloid reflector, 3 is a first lens array, 4 is a second lens array, 5 is a polarization conversion element, and 6 is a condenser lens. Here, the lens array is an optical element in which a plurality of minute lenses are arranged. 7 is a dichroic mirror as a color separation element, 8 is a polarizing plate that cuts unnecessary polarized light, and 9 is a polarization beam splitter that transmits P-polarized light and reflects S-polarized light on the polarization separation surface.

  The polarization separation surface is formed by laminating a polarization separation film, 10 is a 1 / 4λ plate, and 11 is a G liquid crystal display element. Reference numeral 13 denotes a polarizing plate, and reference numeral 14 denotes a wavelength selective phase plate (polarization direction adjusting means) that acts only on the B light and rotates its polarization direction by 90 °. Reference numeral 15 denotes a polarization beam splitter that transmits P-polarized light and reflects S-polarized light, 16 is a λ plate, and 17 is a liquid crystal display element for B. Reference numeral 18 denotes a 1 / 4λ plate, and 19 denotes an R liquid crystal display element. 20 is a wavelength-selective phase plate that acts only on R light and rotates its polarization direction by 90 °, 12 is a polarization beam splitter that transmits P-polarized light and reflects S-polarized light on a polarization separation surface, and 21 is a projection lens. (Projection optical system). Hereinafter, the polarization beam splitter is PBS, the wavelength-selective phase plate is CS, and red, blue, and green color lights are R light, B light, and G light, respectively.

FIG. 2 shows a graph of axial chromatic aberration of the projection lens itself used in the first to fourth embodiments. The horizontal axis indicates the wavelengths of B light, G light, and R light. The vertical axis represents axial chromatic aberration (difference in image formation position of each color light). This indicates where the light of each wavelength forms an image with respect to the center wavelength (not shown) of the G light, and indicates that the image is formed at a position closer to the screen (projection surface) in the direction of the arrow. That is, the liquid crystal display elements for R and B are fixed at positions where the central wavelengths λ _R and λ _B of the respective wavelength bands intersect with the graph. In the case of FIG. 2, assuming that the geometric distance through which G light passes from the G liquid crystal display element to the screen is a reference value, the B liquid crystal display element is separated from the PBS 15 by + a (μm) with respect to the reference value. It is fixed at the position. Similarly, the liquid crystal display element for R is fixed at a position away from the PBS 15 by + b (μm). Let Δ _BR = | a−b | be the amount of longitudinal chromatic aberration, and this embodiment satisfies Δ _BR = | _ab− ≦ 20 μm.

  In this specification, in order to express the difference between the fixing positions of the liquid crystal display elements for B and R, the wavelength at the center of each band is used as the representative wavelength of each wavelength band (each color). Not necessarily.

  FIG. 3A is an enlarged view around the PBS 15. FIG. 3B is an axial chromatic aberration diagram when the PBS shown in FIG. 3A is used. 3A, reference numeral 31 denotes a first triangular prism (first prism) constituting the PBS 15, and reference numeral 32 denotes a second triangular prism (second prism). The first triangular prism 31 is disposed on the PBS 12 side (FIG. 1), and the second triangular prism 32 is disposed on the dichroic mirror 7 side (FIG. 1), and each is bonded by an adhesive. The polarization separation film of the PBS 15 is deposited on the first triangular prism 31 side, and the first triangular prism 31 has a concave gentle curvature. Preferably, r ≦ 20000 (mm) where r is the radius of curvature. This polarization separation film becomes the polarization separation surface of the PBS 15.

  In this embodiment, the polarization separation film is deposited on the first triangular prism 31 side, but may be deposited on the second triangular prism side. Hereinafter, the bonding surface is a surface of the prism and is a surface in contact with the adhesive or a surface on which the polarization separation film is deposited.

  The optical action due to the curvature of the polarization splitting surface of the PBS 15 will be described. The light beam emitted from the light source 1 is emitted as substantially parallel light by the parabolic reflector 2. This parallel light is divided and collected by the first fly-eye lens 3. Each divided light beam divided by the first fly-eye lens 3 is condensed near the second fly-eye lens 4 to form an image of the light source. The split luminous flux emitted from the second fly-eye lens 4 is aligned by the polarization conversion element 5 in the polarization direction from P-polarized light to S-polarized light, and is condensed by the condenser lens 6. The split luminous flux collected by the condenser lens 6 illuminates the liquid crystal display elements 11, 17, and 19 through a color separation / synthesis system composed of 7 to 20, and is projected and enlarged on the screen by the projection lens 21.

  Next, the optical action of the color separation / synthesis systems 7 to 20 will be described. The light condensed by the condenser lens 6 is separated by the dichroic mirror 7 into light in the first wavelength band and light in the second and third wavelength bands. In the present embodiment, light in the first wavelength band is G light, light in the second wavelength band is B light (blue band light, first color light), and light in the third wavelength band is R light (red). Band light, second color light).

  The G light is transmitted through the dichroic mirror 7, P-polarized light that is unnecessary light is cut by the polarizing plate 8, is reflected by the polarization separation film of the PBS 9, is transmitted through the ¼λ plate 10, and the G liquid crystal display element 11 is Illuminate. The liquid crystal display element 11 modulates the polarization state of the G light based on the image, and the modulated S polarization component is reflected by the polarization separation film of the PBS 9 and returned to the light source side. On the other hand, the P-polarized light component modulated by the liquid crystal display element 11 passes through the PBS 9 and enters the PBS 12. The G light incident on the PBS 12 passes through the polarization separation film and reaches the projection lens 21.

  The B and R light reflected by the dichroic mirror 7 is P-polarized light that is unnecessary light is cut by the polarizing plate 13, and the B-light that is S-polarized light is converted in its polarization direction by the CS 14 to become P-polarized light. Thereafter, the B light passes through the PBS 15 and the ¼λ plate 16 and illuminates the B liquid crystal display element 17. Of the B light whose polarization state is modulated by the liquid crystal display element 17 based on the image, the P-polarized light component passes through the PBS 15 and is returned to the light source side. The S-polarized component of the B light modulated by the liquid crystal display element 17 reflects the polarization separation film of the PBS 15, passes through the CS 20, is reflected by the polarization separation film of the PBS 12, and reaches the projection lens 21.

  The R light from which unnecessary light has been cut by the polarizing plate 13 passes through the CS 14, is reflected by the polarization separation film of the PBS 15, and passes through the ¼λ plate 18 to illuminate the R liquid crystal display element 19. The polarization state of the liquid crystal display element 19 for R is modulated based on the image. The modulated S-polarized light is reflected by the polarization separation film of the PBS 15 and returned to the light source side. The modulated P-polarized light component is transmitted through the PBS 15 and its polarization direction is converted into S-polarized light by the CS 20 acting only on the R light. Thereafter, the R light that is S-polarized light is reflected by the polarization separation film of the PBS 12 and reaches the projection lens 21. The PBS 12 (combining element) combines the R, G, and B lights and emits the combined light to the projection lens 21.

  The action and effect of the PBS 15 shown in FIG. 3A will be described in detail. As shown in FIG. 3A, the PBS 15 has a curvature on its polarization separation surface. The polarization separation surface is not a flat surface but is concave toward the liquid crystal display element for B. In other words, since the joint surface of the first triangular prism 31 is concave, the B light reflected from the B liquid crystal display element 17 reflects the convex surface, so that the space between the liquid crystal display element 17 and the screen is reduced. The combined focal length of the optical system is increased. Therefore, it is possible to dispose the liquid crystal display element 17 away from the screen as compared with the case where the polarization separation surface is flat.

  As can be seen from the axial chromatic aberration diagram of FIG. 3B, the difference between the center wavelength of the B light and the center wavelength of the R light, the value of | a−b | (axial chromatic aberration amount) is increased. Out of Michelson's interference conditions, the generation of interference fringes can be suppressed. Further, since the axial chromatic aberration of the projection lens is kept almost flat, it is possible to suppress the occurrence of color blur of the B light.

  Another advantage is that there is no need to insert a lens or filter in the optical path, thus providing a projection display device that can suppress the occurrence of interference fringes with short back focus without deteriorating brightness and color. This is a possible point.

  In the present embodiment, the shape of the joint surface of the first prism 31 is concave. However, the effect of the present invention can be obtained even if the shape is convex. In this case, the liquid crystal display element 17 for B is fixed at a position closer to the PBS 15 than the position shown in the axial chromatic aberration diagram of FIG.

  In the first embodiment, the form in which the polarization separation surface of the PBS 15 has a curvature has been described. However, in the second embodiment, the first triangular prism has a curvature, and the adhesive between the second triangular prism and the PBS is further refracted. A mode for suppressing the generation of interference fringes by providing a rate difference will be described.

(Embodiment 2)
FIG. 4A shows an enlarged view around the PBS 40 corresponding to the PBS 15 of the first embodiment. FIG. 4B shows axial chromatic aberration of the projection lens 21 when the PBS 40 shown in FIG. 4A is used. Since the same reference numerals are used for the same configurations as those in the first embodiment, only portions different from those in the first embodiment will be described.

Reference numeral 41 denotes a first triangular prism constituting the PBS 40, and reference numeral 42 denotes a second triangular prism constituting the PBS 40. Reference numeral 43 denotes an adhesive for bonding the first and second triangular prisms. Reference numeral 44 denotes a joint surface between the first triangular prism 41 and the adhesive, and 45 denotes a joint surface between the second triangular prism 42 and the adhesive. Note that the polarization separation film (polarization separation surface) of the PBS 40 is deposited on the joint surface 44 of the first triangular prism 41, and the joint surface 44 has a concave gentle curvature. On the other hand, the joint surface 45 is a flat surface. The tropism of the first triangular prism 41 and _{N P,} has a refractive index of the adhesive 43 on the relationship _N S -N _P ≧ 0.1 When _{N S.}

The operation and effect of the PBS 40 having the shape shown in FIG. 4 will be described. When a concave curvature is given to the joint surface 44 of the first triangular prism 41, the B light reflected from the B liquid crystal display element 17 reflects the convex surface, and is between the liquid crystal display element 17 and the screen. The combined focal length of the optical system becomes longer. Therefore, it is possible to dispose the liquid crystal display element 17 away from the screen as compared with the case where the polarization separation surface is flat.
On the other hand, the B light reflected by the R liquid crystal display element passes through the adhesive 43 having a convex lens action. That is, the combined focal length of the optical system between the liquid crystal display element 19 and the screen is shortened, and the liquid crystal display element 19 can be arranged farther from the screen than when the polarization separation surface is flat.

  That is, as shown in FIG. 4B, the B liquid crystal display element 17 is fixed at a position away from the projection lens, and the R liquid crystal display element 19 is fixed at a position approaching the projection lens side. That is, when the value of | a−b | (axial chromatic aberration amount) is increased, the interference condition is not satisfied, and the generation of interference fringes can be suppressed. In addition, since the axial chromatic aberration in each wavelength band is almost flat, it is possible to reduce color blurring and maintain good image quality.

  As in the present embodiment, the first triangular prism 41 is given a curvature, and the refractive index of the adhesive and the refractive index of the prism are made different so that the position where the B and R liquid crystal display elements are fixed is fixed. It is possible to shift in the opposite direction.

  As another effect, by shifting the B and R liquid crystal display elements in the reverse direction, a sufficient effect can be obtained even with a gentle curvature radius of about 10,000 mm on the prism joint surface.

  In this embodiment, the curvature of the joint surface is concave, but a convex shape is also possible. In the third embodiment, an embodiment in which the cemented surface of the first triangular prism is convex will be described.

(Embodiment 3)
FIG. 5A shows an enlarged view around the PBS 50 corresponding to the PBS 15 of the first embodiment. FIG. 5B shows the axial chromatic aberration of the projection lens 21 when the PBS 50 shown in FIG. 5A is used. Since the same reference numerals are used for the same configurations as those in the first embodiment, only portions different from those in the first embodiment will be described.

Reference numeral 51 denotes a first triangular prism constituting the PBS 50, and 52 denotes a second triangular prism constituting the PBS 50. Reference numeral 53 denotes an adhesive for bonding the first and second triangular prisms. Reference numeral 54 denotes a joint surface of the first triangular prism, and reference numeral 55 denotes a joint surface of the second triangular prism. Note that the polarization separation film (polarization separation surface) of the PBS 50 is deposited on the joint surface 54 of the first triangular prism 51, and the joint surface has a gentle curvature convex with respect to the plane. The tropism of the first triangular prism 51 and _{N P,} has a refractive index of the adhesive 53 on the relationship _N S -N _P ≧ 0.1 When _{N S.}

  FIG. 5B is a longitudinal chromatic aberration diagram when the PBS 50 shown in FIG. 5A is used. When a convex curvature is given to the joint surface of the first triangular prism 51, the B light reflected by the B liquid crystal display element 17 is reflected by the concave surface, and therefore, is located between the liquid crystal display element 17 and the screen. The combined focal length of the optical system is shortened. Therefore, the liquid crystal display element 17 can be disposed closer to the screen than when the polarization separation surface is flat. On the other hand, the B light reflected by the R liquid crystal display element passes through the adhesive 53 having the effect of a concave lens. In other words, since the combined focal length of the optical system between the liquid crystal display element 19 and the screen becomes longer, the liquid crystal display element 19 can be arranged farther from the screen than when the polarization separation surface is flat. Become. For this reason, the value of | a−b | becomes large and deviates from the Michelson interference condition, and the generation of interference fringes can be suppressed. In addition, since the axial chromatic aberration in each wavelength band is almost flat, it is possible to reduce color blurring and maintain good image quality.

  In the first to third embodiments, the first triangular prism constituting the PBS has a concave surface or a convex surface. However, the present invention is not limited to this. In the fourth embodiment, a mode in which the first triangular prism and the second triangular prism have curvature will be described.

(Embodiment 4)
FIG. 6 shows an enlarged view around the PBS used in the fourth embodiment. 60 is a PBS corresponding to the PBS 15 of the first embodiment, 61 is a first triangular prism constituting the PBS 60, and 62 is a second triangular prism constituting the PBS 60. 63 is an adhesive for bonding the first and second triangular prisms. Reference numeral 64 is a joint surface between the first triangular prism and the adhesive, and 65 is a joint surface between the second triangular prism and the adhesive. Note that the polarization separation film is deposited on the joint surface of the first triangular prism 61. The joint surfaces of the first and second triangular prisms each have a concave and gentle curvature with respect to the plane. Further, assuming that the refractive index of the triangular prism is Np and the refractive index of the adhesive 63 is Ns, the relationship is N _S −N _P ≧ 0.1.

  If a concave curvature is given to the joint surfaces of the first and second triangular prisms 61 and 62, the light reflected by the B liquid crystal display element 17 and reflected by the adhesive 64 will reflect the convex surface. The combined focal length of the optical system between the liquid crystal display element 17 and the screen becomes longer. Therefore, it is possible to dispose the liquid crystal display element 17 away from the screen as compared with the case where the polarization separation surface is flat. On the other hand, the composite focal length of the optical system between the liquid crystal display element 19 and the screen is shortened by the adhesive 64 having a convex lens action. Therefore, the liquid crystal display element 19 is fixed at a position closer to the screen than in the second embodiment. For this reason, the value of | a−b | becomes large and deviates from the Michelson interference condition, so that no interference fringes are generated. In addition, since the axial chromatic aberration in each wavelength band is almost flat, it is possible to maintain good image quality without occurrence of flare.

  In this embodiment, the curvature of the joint surface of the first and second triangular prisms is concave, but a convex surface is also possible. In this case, the B liquid crystal display element 17 is fixed at a position approaching the projection lens, while the R liquid crystal display element 19 is fixed at a position away from the projection lens.

  In the above first to fourth embodiments, examples in which the wavelength selective phase plate is used as the polarization direction adjusting unit have been described, but a phase plate may be used. When the phase plate is used, the color light corresponding to the first liquid crystal display element and the color light corresponding to the second liquid crystal display element are separated by the color separation element. Then, after inserting a phase plate so that each may become P polarized light and S polarized light, each color light may be synthesize | combined and it may inject into a polarization beam splitter. It is good also as a structure. In this case, the light from the light source is separated into R, G, and B optical paths. For example, the R light passes through the phase plate and is incident from the surface of the polarization separation element and reflected. The B light is incident and transmitted from the back surface of the polarization separation surface without passing through the phase plate. As a result, two colored lights having different polarization directions are combined, so that the same effect as in the first to fourth embodiments can be obtained by making this incident on a polarization separation element whose polarization separation surface has a curvature.

  The light source is not limited to a high-pressure mercury lamp, and a laser light source may be used.

(Comparison form)
In order to make the present invention easier to understand, a conventional form is shown in FIG. 7 as a comparative form.

  FIG. 7A is an enlarged view of the vicinity of a polarizing beam splitter that separates and combines two colors of light. Conventionally, no curvature is provided on the polarization separation surface of the polarization separation prism. 15a is a polarization separation prism, 31a is a first triangular prism constituting the polarization separation prism, 32a is a second triangular prism, 33a is a polarization separation surface, 17a is a liquid crystal display element for B, and 19a is a liquid crystal display element for R. is there. The solid arrow is incident on the polarization separation prism 15a, passes through the polarization separation surface 33a, and then enters the liquid crystal display element 17a. The dotted arrow indicates p-polarized light reflected by the polarization separation surface 33a. Indicates.

  The problem of interference fringes tends to occur mainly for light incident on the polarization splitting prism as p-polarized light. The polarization separation prism is generally configured such that a polarization separation surface 33a, which is a dielectric multilayer film, is sandwiched between two triangular prisms 31a and 32a. The dielectric multilayer film 33a is set so that the film material satisfies the so-called Brewster condition where the reflectivity is 0 for p-polarized light, and the film thickness is set so that each interface reflected light is strengthened for s-polarized light. As a result, p-polarized light is transmitted and s-polarized light is reflected. However, due to the nature of using such a principle, reflection occurs in the p-polarized light as the incident angle of the film deviates from the Brewster angle, and the polarization separation characteristic is not perfect. Since the illumination light beam of the projector generally has a finite angular distribution, reflected light is generated not a little, especially p-polarized light. Accordingly, as shown in FIG. 7A, the light incident on the polarization splitting prism as p-polarized light is partially reflected on the polarization splitting surface 33a, and the reflected light path light (dotted line) and the transmitted light path light (solid line) are generated. This is the same relationship as a so-called Michelson interferometer. As a result, if the difference between the two optical paths is within the coherence distance of the light source, interference fringes are generated. In particular, interference fringes are conspicuous in a low-brightness projection image in which the amount of light in the transmitted light path and the amount of light in the reflected light path are comparable, and the image quality is greatly reduced.

  Therefore, conventionally, by applying axial chromatic aberration as shown in FIG. 7B to the projection lens in advance, the B liquid crystal display element 17a is fixed at a position farther than the projection lens. Is possible. With this configuration, since the optical path lengths of the light reflected by the polarization separation surface and the transmitted light are different from each other, it is out of Michelson's conditional expression, and the generation of interference fringes can be suppressed.

  However, if a large axial chromatic aberration as shown in FIG. 7B is applied to the projection lens, the axial chromatic aberration in the band of B light becomes large, and the color blur of the B light occurs. Resulting in.

  On the other hand, the present invention can change the fixing position of the liquid crystal display element while maintaining the axial chromatic aberration in a nearly flat state, so that interference fringes can be suppressed (reduced) while suppressing the occurrence of color bleeding. it can.

7 Dichroic mirror 14, 20 Wavelength selective phase plate 11, 17, 18 Liquid crystal display element 9, 12, 15 Polarization beam splitter

Claims (9)

A polarization separation element having a polarization separation surface that transmits P-polarized light and guides it to the first liquid crystal display element, and reflects S-polarized light and guides it to the second liquid crystal display element;
In a projection type display device having a projection optical system for projecting an image displayed by the first and second liquid crystal display elements onto a projection surface,
The projection display device, wherein the polarization separation surface has a curvature.   The curvature of the polarization separation surface is an image of reflected light reflected by the first liquid crystal display element and reflected by the polarization separation surface and transmitted light reflected by the second liquid crystal display element and transmitted through the polarization separation surface. The projection display device according to claim 1, wherein the positions are provided so as to be separated from each other.   3. The projection display device according to claim 1, wherein a curvature of the polarization separation surface is a convex surface toward the first liquid crystal display element. 4.   3. The projection display device according to claim 1, wherein a curvature of the polarization separation surface is a concave surface toward the first liquid crystal display element. 4. The polarization separation element has a first prism and a second prism,
The first prism and the second prism are bonded with an adhesive,
5. The projection display device according to claim 1, wherein the polarization separation surface is deposited on a first prism having a curvature. The refractive index N _P of the first and second _prism, and the refractive index of the adhesive and N _S,
N _S -N _P ≧ 0.1
The projection display device according to claim 5, wherein   7. The projection type display device according to claim 1, wherein the color light reflected by the first liquid crystal display element and reflected by the polarization separation surface is light in a blue band. When the representative wavelength of light in the blue band is λ _B and the representative wavelength of light in the red band is λ _R ,
When the axial chromatic aberration amount between the blue band and the red band of the projection optical system is Δ _BR = | λ _B −λ _R |
Δ _BR ≦ 20μm
The projection display device according to claim 1, wherein the following condition is satisfied. When the light incident on the first liquid crystal display element and the second liquid crystal display element is a first color light and a second color light, respectively,
The polarization direction adjusting means for adjusting the polarization direction so that the polarization directions of the first color light and the second color light are P-polarized light and S-polarized light, or S-polarized light and P-polarized light. The projection display device according to any one of 1 to 8.

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