JP4055465B2 - projector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a projector, and more particularly to a projector that enlarges and projects an image of an electro-optical device using a reflective liquid crystal light valve.
[0002]
[Prior art]
A projection display device (liquid crystal projector) using a reflective liquid crystal light valve has attracted attention because it can display with high definition.
[0003]
The alignment mode generally used for liquid crystal light valves is a twisted nematic (non-voltage applied state) in which the major axis direction of the liquid crystal molecules is twisted along the direction substantially parallel to the substrate surface and perpendicular to the substrate surface. Twisted Nematic (hereinafter abbreviated as TN) mode and a vertical alignment mode in which liquid crystal molecules are aligned vertically.
[0004]
In the vertical alignment mode, the state in which the liquid crystal molecules are arranged substantially perpendicular to the substrate surface (the state in which there is no optical retardation viewed from the normal direction of the substrate) is used as the black display, so the quality of the black display is good. A high contrast ratio can be obtained. Further, in the vertical alignment type LCD having an excellent front contrast ratio, the viewing angle range in which a constant contrast ratio can be obtained is wider than that in the TN mode. From this point of view, the liquid crystal light valve in the vertical alignment mode has recently attracted attention for applications for video such as a rear projection TV. Japanese Patent Laid-Open No. 10-161127 is known as an example of a projector having a reflective liquid crystal light valve adopting a vertical alignment mode.
[0005]
By the way, in the liquid crystal light valve, if the pitch of the pixel electrodes is reduced in order to increase the resolution of the image, the influence of the lateral electric field generated between the adjacent pixel electrodes on the liquid crystal increases, especially when the vertical alignment mode is adopted. It is easy to be affected, and disclination occurs due to disorder of orientation. When disclination occurs, an abnormality occurs in the modulation operation of the liquid crystal in that region, causing a decrease in brightness of the projected image and display unevenness, resulting in deterioration of image quality.
[0006]
For this reason, measures are taken to prevent the occurrence of disclination by inclining liquid crystal molecules with respect to the normal of the substrate by processing the alignment film in advance to strengthen the alignment regulating force. In this specification, an angle formed between the normal line of the substrate surface in the state where no voltage is applied and the average major axis direction of liquid crystal molecules is defined as a “pretilt angle”.
[0007]
However, when the pretilt angle is increased, a relatively large retardation is generated in the liquid crystal molecules even when no voltage is applied. Ideally, the emitted light, which should be linearly polarized light, is converted into elliptically polarized light, so that even in the black display state. Light leaks out. As a result, the contrast is lowered and the characteristics of the vertical alignment mode cannot be used. In order to avoid this problem, Japanese Patent No. 3019813 discloses a method of converting elliptically polarized light emitted due to the pretilt angle again into substantially linearly polarized light using a quarter wave plate.
[0008]
In addition to this, in order to suppress degradation of image quality due to disclination, Japanese Patent Application Laid-Open No. 10-142605 sets the liquid crystal alignment direction to be substantially parallel or substantially orthogonal to the direction of the side of the pixel electrode. A method is disclosed.
[0009]
The configuration of the optical system of the projector using the reflective liquid crystal light valve is as follows. For each color, specifically, for each of the R (red), G (green), and B (blue) liquid crystal light valves. Is generally used, and the reflected light is emitted again vertically, that is, an “on-axis optical system” in which the optical paths of the incident light and the reflected light are coaxial. As examples of the on-axis optical system, Japanese Patent Laid-Open Nos. 63-39294 and 63-228887 are known.
[0010]
However, when an “on-axis optical system” is adopted, it is necessary to use a polarized beam splitter (hereinafter abbreviated as PBS) to separate incident light and reflected light, but PBS is expensive. Therefore, there has been a problem that the cost of the entire apparatus becomes high. Therefore, there has been proposed a projector that employs an “off-axis optical system” in which light is incident from an angle deviated from the vertical direction of the liquid crystal light valve and reflected light is emitted in a direction different from the incident direction. Since the off-axis optical system does not require PBS, the cost of the apparatus can be reduced. As an example of the off-axis optical system, JP-A-6-342141 is known.
[0011]
[Problems to be solved by the invention]
In a projector, light emitted in all directions from a light source having a finite size is collected and incident on a liquid crystal light valve. As a result, the incident azimuth and the incident angle of light incident on the liquid crystal light valve have a certain range. The wider this range, the brighter the projected image.
[0012]
In the contrast improving method using the quarter wavelength plate described above, the range of the light incident azimuth and the range of the light incident angle where the contrast improvement can be achieved are narrow and the light incident angle is limited to a small region. If you try to make it brighter, the contrast will not be improved sufficiently. Therefore, in order to realize high contrast, there is a problem that brightness must be sacrificed.
[0013]
Furthermore, when an off-axis optical system is used as the optical system, the optical axis of the light incident on the liquid crystal light valve is inclined with respect to the normal direction of the substrate, so that the light incident angle is increased and the contrast is further reduced. There was a problem.
[0014]
The present invention has been made to solve the above-described problems, and in a projector having a reflective light valve that employs a vertical alignment mode, a high contrast ratio can be obtained without sacrificing brightness. The purpose is to provide a simple configuration. Furthermore, it aims at providing the projector which consists of an off-axis optical system which can obtain a high contrast ratio.
[0015]
[Means for Solving the Problems]
In order to solve the above problems, a first projector according to the present invention has an illumination unit, a linear polarization unit that regulates a polarization direction of light emitted from the illumination unit, and a polarization direction regulated by the linear polarization unit. A projector having light modulating means for modulating light, light detecting means for detecting light modulated by the light modulating means, and projection means for projecting light detected by the light detecting means, The light modulation means includes a liquid crystal layer in a vertical alignment mode sandwiched between a pair of substrates, makes light from the illumination means enter from one of the pair of substrates and reflect it on the other substrate side. A reflective liquid crystal light valve that emits light from the one substrate; and at least one retardation plate on an outer surface side of the one substrate constituting the liquid crystal light valve, the first retardation plate Any of the main bending Characterized in that the rate orientation and arranged substantially parallel to the normal of the one substrate.
[0016]
The first retardation plate is a uniaxial retardation plate, and its optical axis is arranged substantially parallel to the normal line of the one substrate.
[0017]
The first retardation plate is a biaxial retardation plate.
[0018]
Further, when the main refraction included in the plane of the first retardation plate is n1 and n2, n1≈n2.
[0019]
Further, a light beam incident on the liquid crystal light valve from an orientation substantially orthogonal to or substantially parallel to the alignment direction of the liquid crystal layer in the vertical alignment mode has a birefringence action based on a pretilt angle given to the liquid crystal in the vertical alignment mode. The retardation in the thickness direction of the first retardation plate is set so that the elliptically polarized light generated as a result of the conversion is converted into polarized light closest to linearly polarized light.
[0020]
The in-plane retardation of the first retardation plate is approximately ¼ wavelength, and the retardation in the thickness direction of the first retardation plate is changed from the first retardation plate to the light detecting means. The major axis direction of the elliptically polarized light emitted toward the side is set so as to be converted in a direction substantially perpendicular to the polarization transmission axis of the light detecting means.
[0021]
When applying the reflective liquid crystal light valve in the vertical alignment mode to the projector, the present inventor sets one of the main refractive index directions on the outer surface side of the substrate on the light incident side of the liquid crystal light valve. It has been found that by arranging a phase difference plate arranged substantially parallel to the normal line, it is possible to effectively improve the contrast reduction caused by the pretilt angle in the vertical alignment mode, and as the phase difference plate, a uniaxial phase difference is obtained. The suitable optical performance conditions when using a plate and a biaxial retardation plate were found.
[0022]
Specific optical performance conditions of the retardation plate will be described in detail in the section of [Example], and in particular, the liquid crystal light valve from an orientation substantially orthogonal or substantially parallel to the alignment direction of the liquid crystal layer in the vertical alignment mode. The first polarized light is converted so that the elliptically polarized light resulting from the birefringence effect based on the pretilt angle imparted to the liquid crystal in the vertical alignment mode is converted into polarized light closest to linearly polarized light. When the retardation in the thickness direction of the retardation plate is set, it is possible to greatly improve the contrast of light incident from an oblique direction, and as a result, it is possible to obtain a high contrast in the off-axis optical system.
[0023]
Further, the first projector of the present invention further includes a second retardation plate on the outer surface side of the one substrate, the second retardation plate is a uniaxial retardation plate, and its slow axis is It is arranged in a plane substantially parallel to the one substrate.
[0024]
Further, the second retardation plate is a quarter wavelength plate.
[0025]
Further, the elliptical polarized light emitted due to the birefringence action based on the pretilt angle given to the liquid crystal in the vertical alignment mode is converted into polarized light closest to linearly polarized light, so that The thickness direction of the first retardation plate is set so that the slow axis direction is set and the major axis direction of the elliptically polarized light is converted into a direction substantially perpendicular to the polarization transmission axis of the light detecting means. It is characterized by setting a retardation.
[0026]
When applying the vertical alignment mode reflective liquid crystal light valve to the projector, the present inventor sets one of the main refractive index directions on the outer surface side of the substrate on the light incident side of the liquid crystal light valve as described above. A phase difference plate arranged substantially parallel to the normal line of one substrate and a uniaxial phase difference plate having a slow axis arranged in a plane substantially parallel to the one substrate are arranged. It has been found that the contrast reduction caused by the pretilt angle in the vertical alignment mode can be effectively improved by arranging two retardation plates, and a quarter wavelength plate as a preferred example of the second retardation plate I found.
[0027]
In this configuration, as in the conventional example, elliptically polarized light generated due to the pretilt angle in the vertical alignment mode is converted into substantially linearly polarized light by the function of the quarter wavelength plate. However, the direction of this linearly polarized light varies depending on the incident direction and incident angle of the light beam to the liquid crystal light valve, so that the light cannot be sufficiently extinguished by the analyzer and high contrast cannot be obtained as it is. . Therefore, in the present invention, a retardation plate having a main refractive index azimuth arranged substantially parallel to the normal line of the one substrate is arranged. Such a retardation plate imparts a different retardation to the light beam depending on the incident direction and angle of incidence of the light beam. Therefore, by appropriately setting the retardation in the thickness direction of the retardation plate, the direction of the linearly polarized light is set. Can be made substantially the same and substantially perpendicular to the polarization transmission axis of the light detecting means. As a result, high contrast can be obtained.
[0028]
Specific optical performance conditions of the first retardation plate and slow axis orientation setting of the quarter wavelength plate will be described in detail in the section of [Example]. In addition, a function substantially equivalent to the contrast improving function using the quarter-wave plate and the retardation plate can be realized by appropriately setting the optical performance condition of one biaxial retardation plate. The details are also described in the section of [Example].
[0029]
In order to solve the above-described problem, a second projector according to the present invention includes an illumination unit, a linear polarization unit that regulates a polarization direction of light emitted from the illumination unit, and a polarization direction regulated by the linear polarization unit. A projector having light modulating means for modulating light, light detecting means for detecting light modulated by the light modulating means, and projection means for projecting light detected by the light detecting means, The light modulation unit includes a liquid crystal layer in a vertical alignment mode sandwiched between a pair of substrates, allows light from the illumination unit to enter from one substrate side of the pair of substrates, and reflect the light from the other substrate side. A reflection type liquid crystal light valve that emits light from the one substrate, a quarter wavelength plate on the outer surface side of the one substrate constituting the liquid crystal light valve, and a liquid crystal layer of the vertical alignment mode Nearly perpendicular to the orientation direction Alternatively, the elliptically polarized light generated as a result of the birefringence effect based on the pretilt angle imparted to the liquid crystal in the vertical alignment mode from the light incident on the liquid crystal light valve from a substantially parallel orientation is polarized light closest to linearly polarized light. It is characterized in that the direction of the slow axis of the quarter-wave plate is set so as to convert into
[0030]
According to this configuration, it is possible to significantly improve the contrast of light rays incident from an oblique direction, and as a result, high contrast can be obtained in the off-axis optical system. Specific azimuth setting of the quarter wavelength plate will be described in detail in the section of [Example].
[0031]
In the first and second projectors of the present invention, an optical axis of incident light from the illumination unit to the liquid crystal light valve and an optical axis of reflected light from the liquid crystal light valve to the projection unit are at a predetermined angle. The plane including the optical axis of the incident light and the optical axis of the reflected light is substantially orthogonal or substantially parallel to the alignment direction of the liquid crystal layer in the vertical alignment mode. It is characterized by being arranged in.
[0032]
The liquid crystal light valve including the retardation plate exhibits the highest contrast characteristics with respect to light incident from an orientation substantially parallel or substantially orthogonal to the alignment direction of the liquid crystal layer in the vertical alignment mode. On the other hand, in the off-axis optical system, the incident angle of the light beam that travels in the plane including the optical axis of the incident light and the optical axis of the reflected light and enters the liquid crystal light valve becomes the largest. Therefore, it is possible to obtain a high contrast characteristic in a projector that employs an off-axis optical system by matching the light incident direction with the direction having the highest contrast characteristic of the liquid crystal light valve.
[0033]
In the first and second projectors of the present invention, linear polarization means for regulating a polarization direction of the incident light is disposed in an optical path of incident light from the illumination means to the liquid crystal light valve, and the liquid crystal light valve is provided. A light detecting means having a polarization transmission axis orthogonal to the linearly polarizing means is disposed in the optical path of the reflected light from the light to the projecting means, and a third retardation plate is disposed on the light projecting means side of the light detecting means. The polarization direction of the linearly polarized light transmitted through the light detecting means is rotated by about 45 degrees by the third retardation plate. Furthermore, a fourth retardation plate is disposed on the liquid crystal light valve side of the linearly polarizing means, and the polarization direction of the linearly polarized light transmitted through the linearly polarizing means is rotated by 45 degrees by the retardation plate. To do.
[0034]
In the off-axis optical system, when the plane including the optical axis of the incident light and the optical axis of the reflected light is arranged in parallel with the short side of the liquid crystal light valve, the overall size of the optical system is the most compact. In order to obtain high contrast characteristics, it is necessary that the alignment direction of the liquid crystal layer in the vertical alignment mode and the polarization direction of the incident linearly polarized light form an angle of approximately 45 °.
[0035]
Therefore, the size of the entire optical system in the configuration in which the plane including the optical axis of the incident light and the optical axis of the reflected light is arranged substantially orthogonal or substantially parallel to the alignment direction of the liquid crystal layer in the vertical alignment mode. In order to make the most compact, the alignment direction of the liquid crystal layer must be parallel to the long side or the short side of the liquid crystal light valve, and the polarization direction of incident linearly polarized light is inevitably an angle of about 45 ° with them. It is necessary to make.
[0036]
On the other hand, a projector includes a dichroic optical element for decomposing white light emitted from a light source into three primary color components of R, G, and B, and conversely combining the three primary color components. The most preferable characteristic is exhibited when the polarization direction of linearly polarized light is parallel or orthogonal to the short side of the liquid crystal light valve.
[0037]
In the present invention, after passing through the analyzer, the linearly polarized light azimuth that forms an angle of 45 ° with the short side of the liquid crystal light valve is rotated by 45 ° by the third retardation plate and is incident on the dichroic optical element for color synthesis. Since the polarization direction of the linearly polarized light is converted into a direction parallel or orthogonal to the short side of the liquid crystal light valve, a projector having excellent color reproducibility can be realized. For the same reason, linearly polarized light that is parallel or orthogonal to the short side of the liquid crystal light valve having excellent color reproducibility among the light rays that have passed through the dichroic optical element for color separation is used by using the fourth retardation plate. It can be rotated to convert to the desired linear incident direction to the liquid crystal light valve.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of a projector according to the present invention will be explained below in detail with reference to the accompanying drawings.
[0039]
(Embodiment)
[Projector configuration]
FIG. 1 shows a schematic configuration diagram of projector 101 in the present embodiment. 1A is a top view of the projector, and FIG. 1B is a side view. Here, a schematic configuration of the projector 101 will be mainly described with reference to a side view of (b).
[0040]
The projector 101 includes an illumination unit 102, a color separation optical unit 103 that separates the light beam emitted from the illumination unit 102 into R, G, and B primary color components, a fourth retardation plate 104 that converts the polarization direction of the light beam, The polarizing plate 105 that regulates the polarization direction of the light beam, the retardation plate 106, the liquid crystal light valve 107 that modulates the polarization state of the incident light beam, the light detecting means 108 that detects the light beam modulated by the liquid crystal light valve 107, and the light detection A third phase difference plate 109 for converting the polarization direction of the linearly polarized light transmitted through the means 108, a color composition means 110 for synthesizing the three primary color components R, G, and B; and a screen (not shown) of the light beam synthesized by the color composition means A projection lens 111 for projecting to the projector. The illumination optical means 102 includes a white light source 112, an integrator lens 113 that uniformizes the intensity distribution of the light beam emitted from the white light source 112, and a polarization conversion element 114 that converts the light beam into a desired polarization state.
[0041]
In the entire optical system of the projector 101, the optical axis L1 of incident light incident on the liquid crystal light valve 107 from the illumination unit 102 and the optical axis L2 of reflected light emitted from the liquid crystal light valve 107 to the projection lens 111 form a predetermined angle. The off-axis optical system is arranged.
[0042]
The color separation means 103 and the color composition means 110 are constituted by a cross dichroic prism or a cross dichroic mirror. In addition, although the figure has shown the structural example which isolate | separated both means, both means may be comprised by one cross dichroic prism or the cross dichroic mirror.
[0043]
The fourth retardation plate 104, the polarizing plate 105, the retardation plate 106, the liquid crystal light valve 107, the light detection means 108, and the third retardation film 109 are provided on the optical paths of the three primary color light beams separated by the color separation means 103. It is desirable to use the ones that are arranged respectively and have the performance optimized according to the wavelengths of the three primary color light beams. In the top view of (a), the symbols R, G, and B are added to the symbols. It is described. In the side view of (b), the symbols R, G, and B are not added for general description.
[0044]
The light analyzing means 108 is preferably a polarizing plate arranged in crossed Nicols with respect to the polarizing plate 105. By these actions, transmission and blocking of light modulated by the liquid crystal light valve 107 is selected, and bright display, darkness is selected. The display is switched.
[0045]
For the sake of explanation, the phase difference plate 106 is shown as a single piece in the figure, but it may be composed of a plurality of pieces, and the details thereof will be described in the section of the third embodiment.
[0046]
The fourth retardation plate 104 and the third retardation plate 109 are not necessarily installed, and details thereof will be described in the section of the fifth embodiment.
[0047]
In the present embodiment, the coordinate system is an xyz right-handed rectangular coordinate system, and the z-axis is parallel to the normal line of the liquid crystal light valve 107 and the projection lens as shown in FIG. The y-axis is arranged so as to be included in the plane formed by the optical axis L1 of incident light and the optical axis L2 of reflected light.
[0048]
Next, the definition of the traveling direction of the light beam in this embodiment will be described with reference to FIG. In this embodiment, the traveling direction of the light beam 201 is defined as the light beam traveling direction OR immediately after reflection by the liquid crystal light valve 107, and the direction is defined using the xyz orthogonal coordinate system described with reference to FIG. In FIG. 2A, the angle formed by the reflected light traveling direction OR and the z axis is defined as a polar angle θ. The line segment OA is an intersection of the plane OABC including the ray traveling direction OR and the xy plane, and the angle formed by this and the x axis is counterclockwise from the x axis as a base point. The azimuth angle φ is defined as positive.
[0049]
In the following description, various characteristics for each light traveling direction will be described with reference to a viewing angle characteristic diagram shown in FIG. The characteristic value or characteristic at the point K on this viewing angle characteristic diagram indicates the characteristic value or characteristic of the light beam, where the distance between the point K and the origin is θ, and the angle between the horizontal axis and the point K is φ. The angle φ formed by the horizontal axis and the K point is positive in the counterclockwise direction with the horizontal axis of the viewing angle characteristic diagram as a base point.
[0050]
[Configuration of liquid crystal light valve]
FIG. 3 shows a schematic configuration of the liquid crystal light valve in the present embodiment. 3A is a cross-sectional view of the liquid crystal light valve 107, and FIG. 3B is an enlarged plan view of the pixel configuration viewed from the light incident side. In the liquid crystal light valve 107, a silicon substrate 302 having a reflective pixel electrode 303 formed in a matrix on a surface thereof and a transparent substrate 305 having a transparent electrode 304 disposed opposite each other via a spacer 306, between which a liquid crystal 307 is enclosed. Yes. Note that a drive circuit (not shown) for driving the reflective pixel electrode 303 is also formed on the silicon substrate 302. Alignment films 308 and 309 for aligning the liquid crystal 307 in a predetermined direction are formed on the opposing surfaces of the two substrates 302 and 305, respectively.
[0051]
As shown in FIG. 3B, the individual pixel electrodes 303 are arranged in a matrix with sides substantially parallel to the x-axis or y-axis.
[0052]
FIG. 4A shows the alignment state of the liquid crystal molecules 401 in the vertical alignment mode when no voltage is applied. The liquid crystal molecules 401 have a long axis 402 with a predetermined small angle with respect to the normal line of the substrates 302 to 305. Are oriented substantially parallel to each other.
[0053]
The definition of the alignment state of the liquid crystal molecules 401 will be described with reference to FIG. Also in this definition, the xyz orthogonal coordinate system described in FIG. 1 is used. In the figure, the angle between the major axis 402 of the liquid crystal molecules and the z-axis is defined as the pretilt angle. A line segment OA is an intersection line of the plane OABC including the major axis 402 of the liquid crystal molecule and the xy plane, and the angle formed by the x axis is counterclockwise with the x axis as a base point. The orientation is defined as the orientation direction with the periphery being positive, and is described as φlc.
[0054]
[Configuration of retardation plate]
The configuration of the retardation plate 106 in this embodiment will be described in detail in the following examples. Prior to that, the function of the retardation plate 106 in this embodiment will be described with reference to FIG. 23 (a) and 23 (b) show how the liquid crystal light valve 107 changes the polarization state of the light beam when the liquid crystal light valve 107 is in the dark display state. FIG. 23 (a) shows the state when the retardation plate 106 is not provided. The state when the phase difference plate 106 is arranged is shown. The incident-side polarizing plate 2301 has its polarization transmission axis 2302 in the plane of the paper, so that the light beam that has passed through it becomes linearly polarized light 2303 that vibrates in the plane of the paper. Note that the orientation of the polarization transmission axis 2302 is set for convenience of this description, and the orientation of the polarization transmission axis in each embodiment will be described each time. When the liquid crystal light valve 107 is in dark display, only a small voltage is applied to the liquid crystal molecules, so that the liquid crystal molecules have a pretilt angle given in advance with respect to the normal line of the substrate 305 as shown in FIG. It is oriented and gives a phase difference to the incident polarized light by the birefringence action resulting from this pretilt angle. When the retardation plate 106 is not provided as shown in FIG. 23A, the linearly polarized light 2303 is given a phase difference by the liquid crystal molecules, and after being reflected by the liquid crystal light valve 107, becomes the elliptically polarized light 2304, and continues to transmit the polarized light. The light enters the exit-side polarizing plate (analyzing means) 2305 arranged in crossed Nicols so that the axis 2306 is substantially orthogonal to the polarization transmission axis 2302 of the incident-side polarizing plate.
[0055]
Since the elliptically polarized light 2304 has both a polarized light component parallel to the polarization transmission axis 2306 and a polarized light component orthogonal thereto, the former is transmitted through the output side polarizing plate 2305. As a result, the projected image becomes bright despite the liquid crystal light valve 107 being in the black display state, and the contrast characteristics of the projector are significantly reduced.
[0056]
On the other hand, the phase difference plate 106 in FIG. 23B has a function of imparting to the polarized light a phase difference that substantially cancels the phase difference imparted to the polarized light due to the birefringence action caused by the pretilt angle of the liquid crystal molecules. In the present invention, this function is referred to as a phase compensation function. This phase compensation function is manifested by the birefringence characteristics of the phase difference plate 106. The linearly polarized light 2303 incident on the phase difference plate 106 is given a phase difference by the phase difference plate 106 to become elliptically polarized light 2307. The elliptically polarized light 2307 is further given a phase difference by the birefringence action resulting from the pretilt angle of the liquid crystal molecules and becomes the elliptically polarized light 2308 after reflection, but as a result of being given the phase difference again by the phase difference plate 106, the linearly polarized light 2303 is obtained. Then, the light returns to the elliptically polarized light 2309 which is substantially equal to the light and enters the output-side polarizing plate 2305. Since the elliptically polarized light 2309 has very little polarization component parallel to the polarization transmission axis 2306, most of the light is absorbed by the output-side polarizing plate 2305, and the amount of light that leaks out is small. As a result, the contrast characteristics of the projector can be greatly improved as compared with the case where the phase difference plate 106 is not provided.
[0057]
Next, details of the polarization state of the elliptically polarized light 2309 which is substantially equal to the linearly polarized light 2303 will be described with reference to FIG. As shown in FIG. 24A, the linearly polarized light 2303 has an ellipticity of 0 and is substantially orthogonal to the polarization transmission axis 2306 of the output side polarizing plate 2305. Here, the ellipticity of elliptically polarized light is defined as the ratio expressed by S / L where S is the length of the minor axis of the ellipse and L is the length of the major axis.
[0058]
On the other hand, the elliptically polarized light 2304 without the retardation plate 106 has a large ellipticity as shown in FIG. 24B, and its major axis azimuth 2401 is deviated from the polarization absorption axis azimuth 2402 orthogonal to the polarization transmission axis 2306. ing. The polarization component leaking from the exit-side polarizing plate 2305 is a component parallel to the polarization transmission axis 2306 of the elliptically polarized light 2304. This increases as the ellipticity increases, and is formed by the major axis azimuth 2401 and the polarization absorption axis azimuth 2402. The bigger the corner, the bigger it becomes.
[0059]
As shown in FIG. 24C, the elliptically polarized light 2309 subjected to the phase compensation action by the phase difference plate 106 has a reduced ellipticity as compared to the elliptically polarized light 2304, as shown in FIG. 24D or FIG. In this state, the angle formed by the major axis azimuth 2401 and the polarization absorption axis azimuth 2402 becomes smaller, or both of them are provided. As a result, the polarization component leaking from the exit-side polarizing plate 2305 is reduced, and the contrast characteristics of the projector can be greatly improved.
[0060]
In all the embodiments described below, the F number of the optical system is F3.5, and the angle between the optical axis L1 of incident light and the normal line of the liquid crystal light valve 107 is 13 °. As a liquid crystal material,
Liquid crystal elastic constant k11: 1.3e-11 k22: 4.875e-12 k33: 1.95e-11
Liquid crystal relative permittivity ε (parallel): 3.5 ε (vertical): 7.4
Liquid crystal refractive index no: 1.475 ne: 1.556
An example in which a liquid crystal light valve cell thickness is set to 3 μm is used.
[0061]
Of course, the characteristics of the retardation plate 106 are the main points of the respective embodiments even when the optical system F number other than those described here, the angle between the optical axis L1 and the normal line of the liquid crystal light valve, the liquid crystal material and the cell configuration are used. By optimizing appropriately so as to follow, effects equivalent to the effects described in the respective embodiments can be obtained.
[0062]
Example 1
The present embodiment is an example in which the phase difference plate 106 is constituted by one phase difference plate in which any of the main refractive index directions is arranged in parallel to the normal line of the liquid crystal light valve 107.
[0063]
In general, the optical properties of the retardation plate are expressed by three main refractive indexes n1, n2, and n3 which are refractive indexes in directions orthogonal to each other. When attention is paid to the relationship between the magnitudes of these three main refractive indexes, for example, when the two main refractive indexes are equal such that n1 = n2 ≠ n3, the retardation plate is a uniaxial retardation plate, and n1 If they are not equal, such as ≠ n2 ≠ n3, it is a biaxial retardation plate.
[0064]
Here, in order to simplify the description, first, the description will be made taking a uniaxial retardation plate as an example. This retardation plate is arranged so that the orientation of the main refractive index n3 is parallel to the normal line of the liquid crystal light valve 107. Further, it is assumed that the three main refractive indexes have a relationship of n1 = n2 ≠ n3. In such a phase difference plate, the optical axis coincides with the direction of the main refractive index n3.
[0065]
In general, when a light beam is incident on the retardation plate, a polarization component (abnormal light component) that vibrates in the plane formed by the optical axis of the retardation plate and the incident light beam and a polarization component (ordinary light component) that oscillates perpendicularly to the polarization component. A phase difference occurs between them, and the polarization state changes.
[0066]
FIG. 5 shows the relationship between the vibration plane orientation of the extraordinary light component and the azimuth angle φ of the light beam with respect to the retardation plate of the present embodiment. In this embodiment, since the optical axis of the phase difference plate is arranged parallel to the normal line of the liquid crystal light valve 107, for example, the vibration surface of the extraordinary light component of the light beam with the azimuth angle of 60 ° is as indicated by 501. It faces the direction of azimuth 60 °. The vibration surface of the ordinary light component is orthogonal to the vibration surface. Similarly, the vibration plane orientations of the extraordinary light components of the light beams having the azimuth angles of 90 ° and 120 ° are directed to the azimuth angles of 90 ° and 120 ° as indicated by 502 and 503, respectively.
[0067]
Next, consider the case where the liquid crystal alignment direction φlc601 is set to 180 ° as shown in FIG. This orientation is a direction parallel to the long side of the pixel electrode 303 of the liquid crystal light valve, and as described in the section of the prior art, is a liquid crystal orientation orientation that is effective in suppressing image quality degradation due to disclination. . In this case, the polarization transmission axis direction of the incident side polarizing plate 105 is set to an azimuth angle of 135 ° as indicated by 602. Accordingly, the linearly polarized light azimuth of the light incident on the phase difference plate 106 is almost directed to an azimuth angle of 135 ° as indicated by 603 in any azimuth light. In the following description, the linear polarization direction of incident light is described as φpol. Further, the linearly polarized light azimuth 603 in FIG. 6A is shown only for the light beam having the maximum polar angle θ for the sake of simplification, but the same applies to the light beam having a smaller polar angle θ.
[0068]
Therefore, a light beam with an azimuth angle φ of 135 ° has only an extraordinary light component 604 with respect to the phase difference plate 106 because the azimuth angle φ and the linearly polarized light azimuth φpol coincide. Therefore, the polarization state of the light beam having this azimuth angle φ is not changed by the phase difference plate 106. Similarly, since the light beam with the azimuth angle of 45 ° has only the ordinary light component 605, the polarization state is not changed by the phase difference plate 106. The other light beams having the azimuth angle φ have both an extraordinary light component and an ordinary light component, and the polarization state is changed by the phase difference plate 106. This is schematically shown in FIG. In the drawing, hatched areas 606 to 609 indicate light beam angle areas that are susceptible to a change in polarization state by the phase difference plate 106.
[0069]
The regions 606 to 609 that are susceptible to changes in the polarization state are regions in which elliptically polarized light generated as a result of the birefringence action based on the pretilt angle of the liquid crystal is likely to be linearly polarized by the phase compensation function of the phase difference plate 106. This is an area where the contrast performance can be enhanced. As is apparent from the figure, these regions 606 to 609 are present around the liquid crystal orientation azimuth φlc 601 that is substantially parallel or substantially orthogonal. For the retardation plate 106 having one characteristic, the contrast performance is not improved in all of the regions 606 to 609, but the contrast performance of any one region is selectively improved. When the characteristics of the phase difference plate 106 are changed, the region where the contrast performance is improved changes accordingly. Details will be described later.
[0070]
In the configuration of the optical system of the present embodiment (F number is F3.5, the angle formed by the optical axis L1 of incident light and the normal line of the liquid crystal light valve 107 is 13 °), the region where the light beam angle of the illumination light beam is distributed is roughly. A region 701 indicated by hatching in FIG. In general, this region has a light beam azimuth angle φ ranging from 60 ° to 120 ° and a polar angle θ ranging from 5 ° to 20 °, and exists in a direction substantially perpendicular to the azimuth angle 180 °, which is the liquid crystal alignment direction. Therefore, the region where the contrast region can be improved by the retardation plate 106 is almost the same. Therefore, it is possible to improve the contrast characteristics of the projector by appropriately adjusting the phase difference generated in the phase difference plate 106 to an amount necessary for the phase compensation of light in this region.
[0071]
In addition, when the liquid crystal orientation azimuth φlc is set to 270 °, the angle region 701 in which light rays are distributed exists in an azimuth substantially parallel to the liquid crystal orientation azimuth φlc, so that the contrast characteristics can be improved in this case as well. It becomes possible.
[0072]
In order to perform phase compensation throughout the light beam in the region 701, the phase difference generated in the phase difference plate 106 is adjusted to an amount necessary for phase compensation of the optical axis light beam in the approximate center of the region 701. Is desirable.
[0073]
In the above description, the uniaxial retardation plate has been described as an example. However, even when a biaxial retardation plate having a relationship of n1 ≠ n2 ≠ n3 is used as the retardation plate 106, the above function is realized. As long as it can be considered that n1≈n2, the same explanation holds.
[0074]
Next, the configuration of the phase difference plate 106 will be described. Here, in order to give a more general description, a biaxial retardation plate will be described as an example, but the uniaxial retardation plate may be understood as an example that satisfies the special conditions. The optical property of the biaxial retardation plate is expressed by three main refractive indexes n1, n2, and n3 which are refractive indexes in directions orthogonal to each other. In the present embodiment, the thickness direction of the retardation film 106 and the direction of the main refractive index n3 are configured to substantially coincide. As a result, n1 and n2 become the main refractive index in the plane of the phase difference plate 106, and the directions are determined so as to satisfy the relationship of n1 ≧ n2. Moreover, in order to define the phase difference which generate | occur | produces in the phase difference plate 106, in-plane retardation Rf and thickness direction retardation Rp are defined according to the following formula | equation.
Rf = (n1-n2) * d
Rp = [(n1 + n2) / 2−n3] × d
Here, d is the thickness of the retardation film 106.
[0075]
A light beam having a light wavelength of 550 [nm] and a linear polarization direction φpol of 135 ° is incident on a liquid crystal light valve having a liquid crystal pretilt angle of 5 ° and a liquid crystal alignment direction φlc of 180 °, and Rf≈0 [ FIG. 8 (a) shows the contrast viewing angle characteristics when the ones having the characteristics of [nm] and Rp = 180 [nm] are used. The curve shown in the figure is an iso-contrast curve, a dark curve is an iso-contrast curve with a contrast of 3000, and a thin curve is an iso-contrast curve with a contrast of 1000. A region surrounded by the same type of isocontrast curve is a region having a contrast characteristic equal to or higher than the contrast value indicated by the curve. FIG. 8B is a diagram showing the relationship between the contrast viewing angle characteristics of FIG. 8A and the ray angle distribution region 701 of the illumination light beam in the optical configuration of the present embodiment. The high contrast region and the ray angle of the illumination light beam are shown in FIG. It can be seen that the distribution regions are in good agreement. In this case, 1950 was obtained as the contrast characteristic value of the projector.
[0076]
In the present embodiment, a contrast viewing angle characteristic diagram having a wavelength of 550 [nm] is shown. However, by appropriately adjusting the optical characteristics of the phase difference plate, substantially the same viewing angle characteristics can be obtained at other wavelengths. Needless to say. This situation is the same in the following embodiments.
[0077]
FIG. 9 shows changes in contrast characteristics of the projection display device when the pretilt angle of the liquid crystal is set to three levels of 1 °, 5 °, and 7.5 ° and the Rp value of the phase difference plate 106 is changed. FIG. 9 is a graph in which the vertical axis represents the contrast value and the horizontal axis represents the Rp value of the phase difference plate 106. The unit of the Rp value is displayed in units of λ, which is the ratio to the used wavelength. In any Rp value, Rf≈0 [nm] is set.
[0078]
Further, at a pretilt of 1 °, the data at Rp <0.41 is a value obtained under the conditions of the liquid crystal orientation azimuth φlc = 180 ° and the linear polarization orientation φpol = 135 °, and the data at Rp ≧ 0.41 is the liquid crystal orientation azimuth φlc. = 270 ° and linear polarization direction φpol = 225 °. Similarly, data at Rp ≦ 0.41 at pretilts of 5 ° and 7.5 ° are values obtained under the conditions of liquid crystal alignment direction φlc = 180 ° and linear polarization direction φpol = 135 °, and data at Rp> 0.41. It is a value obtained under the conditions of the liquid crystal alignment azimuth φlc = 270 ° and the linear polarization azimuth φpol = 225 °.
[0079]
This is because when the Rp value is changed, the region where the contrast performance is improved moves 90 ° in a direction parallel to the liquid crystal alignment direction φlc from a certain Rp value. This is because it is necessary to rotate φlc and φpol by 90 ° in accordance with the light angle distribution region 701.
[0080]
As can be seen from FIG. 9, by using the retardation film 106 of the present embodiment, high contrast characteristics of 1000 or more can be obtained over a wide range of Rp values even if the pretilt angle is changed.
[0081]
A preferred example of such a retardation plate is a VAC film manufactured by Sumitomo Chemical Co., Ltd. The VAC film is a biaxial retardation plate having a small in-plane retardation Rf and an in-plane average refractive index larger than the refractive index in the thickness direction, and the thickness direction retardation Rp can be arbitrarily set. Specific retardation values of some products are shown below.
VAC-C30 Rf = 6 [nm], Rp = 87.5 [nm]
VAC-C60 Rf = 6 [nm], Rp = 133.9 [nm]
VAC-C90 Rf = 6 [nm], Rp = 178.7 [nm]
VAC-C190 Rf = 6 [nm], Rp = 330.2 [nm]
All of these products have characteristics applicable to this embodiment.
[0082]
(Example 2)
In this embodiment, the retardation plate 106 is formed of a ¼ wavelength plate, and the slow axis direction thereof is arranged in a specific direction, thereby realizing a contrast viewing angle characteristic substantially equivalent to that of the first embodiment.
[0083]
The relationship between the slow axis direction of the quarter-wave plate and the contrast viewing angle characteristic will be described with reference to FIG. Now, assuming that the pretilt angle of the liquid crystal is 5 °, the liquid crystal alignment direction φlc 1001 is set to 135 °, and the incident linear polarization direction φpol 1002 is set to 90 ° as shown in FIG. By setting the axis azimuth φqw 1003 in the vicinity of 89.5 °, the contrast characteristics of the region 1004 shown by hatching in FIG. 10B can be greatly improved. This region 1001 extends linearly in the directions of azimuth angles of 0 °, 90 °, 180 °, and 270 °, and the region where the ray angle distribution region 701 of the illumination light beam shown in FIG. 7 overlaps is narrow.
[0084]
FIG. 11 is a diagram for explaining a change in contrast viewing angle characteristics when the slow axis direction of the quarter-wave plate is changed. FIG. 11A shows the contrast viewing angle characteristic when φqw is set in the vicinity of 89.5 ° as in FIG. 10B. When φqw is set larger than 89.5 °, as shown in FIG. 11B, the high-contrast regions 1102 and 1103 are directions of azimuth angles 45 ° and 225 °, which are directions substantially orthogonal to the liquid crystal alignment direction φlc. The range of the polar angle θ gradually increases. On the other hand, when φqw is set to be smaller than 89.5 °, as shown in FIG. 11C, the high contrast regions 1104 and 1105 have azimuth angles 315 ° and 135 ° which are directions substantially parallel to the liquid crystal alignment direction φlc. And the range of the polar angle θ gradually increases. This is because, as the slow axis direction of the quarter wave plate is changed, the phase difference imparted to the light beam by the quarter wave plate changes, and as a result, the ray angle distribution region that is best phase compensated changes. Because.
[0085]
Since all of the high contrast regions 1102 to 1105 are grouped in a specific range as compared with 1004, the overlap region is made wider by matching these with the ray angle distribution region 701 of the illumination light beam. As a result, it is possible to improve the contrast characteristics of the projector using the off-axis optical system.
[0086]
For example, in order to align the high contrast region 1102 with the light beam angle distribution region 701 of the illumination light beam, the liquid crystal alignment directions φlc and φpol may be arranged by being rotated by + 45 ° with respect to the arrangement of FIG. Similarly, in order to align the high contrast region 1105 with the ray angle distribution region 701 of the illumination light beam, the liquid crystal alignment directions φlc and φpol may be arranged by being rotated by −45 ° with respect to the arrangement shown in FIG.
[0087]
In order to perform phase compensation over the entire light beam in the region 701, the slow axis direction of the quarter-wave plate is set so as to best compensate the optical axis light beam at the approximate center of the region 701. It is desirable.
[0088]
A light flux with a light wavelength of 550 [nm] and φpol 135 ° is incident on a liquid crystal light valve set with a liquid crystal pretilt angle of 5 ° and φlc180 °, and the slow axis direction φqw of the quarter-wave plate is set to 135.5 °. The contrast viewing angle characteristics in this case are shown in FIG. In this example, the high-contrast region 1102 in FIG. 11B is rotated by + 45 ° to fit the light angle distribution region 701.
[0089]
In addition, a light beam having a light wavelength of 550 [nm] and φpol 225 ° is incident on a liquid crystal light valve set to a liquid crystal pretilt angle of 5 ° and φlc270 °, and the slow axis direction φqw of the quarter-wave plate is set to 223.5 °. FIG. 12B shows the contrast viewing angle characteristics when set. In this example, the high-contrast region 1104 in FIG. 11C is rotated by + 135 ° to fit the light angle distribution region 701.
[0090]
In any viewing angle characteristic, it can be seen that the high contrast region and the ray angle distribution region 701 of the illumination light beam in FIG. In this case, the contrast characteristic value of the projector was 1760 in the case of FIG. 12A and 1860 in the case of FIG. 12B.
[0091]
FIG. 13 shows the contrast characteristic values of the projector when the slow axis azimuth φqw of the quarter wavelength plate is changed. The vertical axis of this graph represents the contrast value of the projector, and the horizontal axis represents the difference between the quarter-wave plate slow axis directions φqw and φpol (φqw−φpol). The liquid crystal pretilt angle was set at two levels of 5 ° and 10 °. In addition, when the pretilt is 5 °, the data when (φqw−φpol) ≧ −0.5 ° is a value obtained under the condition of the liquid crystal alignment direction φlc = 180 ° and the linear polarization direction φpol = 135 °, (φqw−φpol) < The data at −0.5 ° is a value obtained under the conditions of the liquid crystal orientation azimuth φlc = 270 ° and the linear polarization azimuth φpol = 225 °. Similarly, the data at (φqw−φpol) ≧ −2 ° at a pretilt of 10 ° is a value obtained under the conditions of the liquid crystal alignment direction φlc = 180 ° and the linear polarization direction φpol = 135 °, (φqw−φpol) <− 2 ° The data in are the values obtained under the conditions of the liquid crystal orientation azimuth φlc = 270 ° and the linear polarization azimuth φpol = 225 °.
[0092]
When the pretilt angle is 5 °, the highest contrast characteristics are obtained when the slow axis direction of the quarter-wave plate is set to −1.5 ° and + 0.5 °, and when the pretilt angle is 10 °, 1 is obtained. When the slow axis direction of the / 4 wavelength plate is set to -3 ° and -1.5 °, the highest contrast characteristics are obtained.
[0093]
Thus, a projector having high contrast characteristics can be realized by appropriately setting the slow axis direction of the quarter-wave plate according to the pretilt angle of the liquid crystal light valve to be used.
[0094]
(Example 3)
This embodiment is an example in which the retardation plate 106 is composed of two pieces of a retardation plate and a quarter-wave plate whose main refractive index azimuth is arranged parallel to the normal line of the liquid crystal light valve 107. is there. The schematic configuration is shown in FIG. A phase difference plate 1401 and a quarter wavelength plate 1402 are disposed on the light incident surface side of the liquid crystal light valve 107. The main refractive index azimuth 1403 of any one of the retardation plates 1401 is disposed substantially parallel to the normal line 1404 of the liquid crystal light valve, and the slow axis 1405 of the quarter-wave plate 1402 is disposed substantially in the plane. . Further, as shown in FIG. 14B, when the quarter-wave plate 1402 is viewed from the positive direction of the z-axis, the slow axis 1408 is disposed with a predetermined angle φqw with respect to the x-axis.
[0095]
In FIG. 14, for convenience of explanation, the retardation plate 1401 and the quarter-wave plate 1402 are drawn separately, but both are integrated using an optical adhesive or the like to reduce light energy loss due to surface reflection. can do. Furthermore, by integrating the retardation plate 106 so integrated with the transparent substrate 305 of the liquid crystal light valve, it becomes possible to further reduce the light energy loss.
[0096]
Further, in FIG. 14, a configuration in which the retardation plate 1401 and the quarter wavelength plate 1402 are arranged in this order from the liquid crystal light valve 107 toward the light source is illustrated, but the order may be reversed.
[0097]
Next, the phase compensation function of the retardation plate of this embodiment will be described. The phase compensation function of the retardation plate of the present embodiment can be understood as a single phase compensation function of the quarter-wave plate 1402 and a cooperative action of that of the retardation plate 1401.
[0098]
First, the single phase compensation function of the quarter wavelength plate 1402 will be described. As described with reference to FIG. 10 in the second embodiment, when the pretilt angle of the liquid crystal is set to 5 °, φlc is set to 135 °, and φpol is set to 90 °, the azimuth φqw of the slow axis of the quarter-wave plate 1402 is set. By setting the angle in the vicinity of 89.5 °, the contrast characteristics of the region 1004 shown by hatching can be greatly improved. On the other hand, the contrast characteristics in other regions are not improved so much. The reason for this will be described with reference to FIG.
[0099]
FIG. 15 is a diagram showing, for each azimuth angle, the polarization state of the light beam after reciprocating through the quarter-wave plate in the configuration shown in FIG. These rays all have the same polar angle θ. The display state of the polarization state in FIG. 15 will be described taking the case of a light beam of φ30 ° as an example. The polarization state of the 30 ° light beam is indicated by elliptically polarized light 1501. A straight line 1502 indicates the absorption axis direction of the output-side polarizing plate. The major axis direction of the elliptically polarized light 1501 is indicated by a straight line 1503. The polarization state is shown in the same form at other azimuth angles. Note that the polarization state of the light beam shown in FIG. 15 is drawn exaggerating the ellipticity of the elliptically polarized light 1501 and the orientation of the major axis 1503 for convenience of explanation. Actually, the ellipticity of elliptically polarized light 1501 is smaller and almost close to linearly polarized light. Further, the angle formed by the major axis 1503 and the absorption axis direction 1502 of the output side polarizing plate is very small.
[0100]
Looking at the polarization states of the light beams of φ0 °, 90 °, 180 °, and 270 °, the major axis direction of the elliptically polarized light and the absorption axis of the exit-side polarizing plate are almost the same. On the other hand, it can be seen that light beams with other orientations form an angle with the major axis orientation of elliptically polarized light and the absorption axis of the exit-side polarizing plate. If the ellipticity of the elliptically polarized light is substantially the same, the greater the angle between the major axis direction of the elliptically polarized light and the absorption axis of the exit side polarizing plate, the more light leaks from the exit side polarizing plate. Therefore, compared to the light beams of φ0 °, 90 °, 180 °, and 270 °, the light beams with other azimuths have more light beams leaking from the output side polarizing plate, and the contrast characteristics are relatively deteriorated. This is the reason why the contrast characteristic distribution as shown in FIG. 10B is produced when the quarter wavelength plate is used alone.
[0101]
FIG. 16 is a diagram for more quantitatively explaining the above contents. FIG. 16 shows an angle (azimuth angle) formed by the azimuth angle φ on the horizontal axis and the long axis azimuth 1503 of the elliptical polarized light 1501 on the vertical axis of FIG. Difference). Note that this angle is positive in the counterclockwise direction with the absorption axis orientation of the output side polarizing plate as a base point. Further, the azimuth angle φ is shown up to 165 ° for the sake of simplicity of explanation, but the same tendency is shown at angles beyond this. The dotted curve in FIG. 16 shows the angle difference when the ¼ wavelength plate is used alone. As described with reference to FIG. 15, the azimuth angle is 0 °, and 90 ° is 0 °. In the azimuth angle, the angle difference becomes large.
[0102]
Next, the function of a single retardation plate in which any of the main refractive index directions is arranged in parallel to the normal line of the liquid crystal light valve 107 will be described. With respect to this, as already described with reference to FIGS. 5 to 6 in the first embodiment, the phase with respect to a light ray incident from a range centered on a direction substantially orthogonal or substantially parallel to the alignment direction φlc of the liquid crystal. Express compensation function. When this is applied to the present embodiment, the liquid crystal orientation azimuth φlc is set to 135 ° in this embodiment, so that the incident light is incident from an azimuth centered at an azimuth angle of 45 ° or an azimuth angle of 135 °. Therefore, the phase compensation function is expressed with respect to the light beam. Referring to FIG. 16, when the ¼ wavelength plate is used alone, the light beams having the azimuth angle of 45 ° and the azimuth angle of 135 ° have the largest angle difference as shown by the dotted lines. Accordingly, the contrast characteristic of the projector can be improved by adjusting the retardation value in the thickness direction of the retardation plate as appropriate so that the elliptical major axis direction of the light beams of these azimuth angles is close to the absorption axis direction of the exit side polarizing plate. it can.
[0103]
The absorption axis of the output side polarizing plate when the slow axis direction of the quarter-wave plate 1002 is set to 89.5 °, the thickness direction retardation Rp of the retardation plate 1401 is set to 135 nm, and the in-plane retardation Rf is set to about 0 nm. The angle difference between the azimuth and the major axis of elliptically polarized light is shown by a solid line in FIG. As can be seen from the figure, the angle difference is extremely reduced by adding the phase difference plate 1401. FIG. 17 shows the contrast viewing angle characteristics in this case. As a contrast characteristic value of the projector, 6500 was obtained.
[0104]
FIG. 18 shows the contrast characteristic value of the projector when the Rp value of the retardation film 1401 is changed. In the figure, the horizontal axis indicates the Rp value and the vertical axis indicates the contrast characteristic value. A high contrast characteristic is obtained in a wide range of Rp values. The unit of the Rp value is displayed with λ, which is the ratio to the used wavelength, as a unit. Further, Rf≈0 [nm] is set for any Rp value.
[0105]
FIG. 19 shows contrast characteristic values when the Rp value of the retardation film 1401 is set to about 0.25λ and the liquid crystal pretilt angle is changed. In the figure, the horizontal axis indicates the liquid crystal pretilt angle and the vertical axis indicates the contrast characteristic value. Even when the pretilt angle is increased, high contrast characteristics are obtained.
[0106]
A preferred example of the retardation film 1401 is the VAC film manufactured by Sumitomo Chemical Co., Ltd. described in Example 1.
[0107]
In this embodiment, an example using an off-axis optical system as the optical system of the projector has been described. However, when the retardation plate of this embodiment is used, the contrast viewing angle characteristic is a high contrast region as shown in FIG. It is needless to say that high contrast characteristics can be obtained even in a projector using an on-axis optical system as an optical system. Further, the case where the liquid crystal orientation azimuth φlc is 135 ° has been described, but it goes without saying that high contrast characteristics can be obtained even if this is set to another orientation for the same reason.
[0108]
Example 4
The present embodiment is an example in which the phase compensation function by the cooperative action of the retardation plate 1401 and the quarter-wave plate 1402 described in the third embodiment is realized by a single biaxial retardation plate.
[0109]
Since the orientations of the main refractive indexes n1, n2, and n3 in the biaxial retardation plate of the present embodiment are the same as those described in the first embodiment, description thereof is omitted here. In the biaxial retardation plate of this example, the in-plane retardation Rf is set to approximately λ / 4, and the orientation of the in-plane main refractive index n1 is set at a predetermined azimuth angle. These configurations are almost the same as the configuration of the quarter-wave plate 1402 in the third embodiment. The retardation Rp in the thickness direction is appropriately adjusted so as to exhibit substantially the same function as the retardation plate 1401 of the third embodiment. In the biaxial retardation plate of the present embodiment, since the in-plane retardation retardation Rf has a large value, the retardation Rp in the thickness direction for expressing a function substantially equivalent to that of the retardation plate 1401 is implemented. This value is inevitably different from the Rp value of the phase difference plate 1401 described in Example 3.
[0110]
As an example of specific numerical values, when the liquid crystal azimuth angle φlc is 135 °, the liquid crystal pretilt angle is 5 °, and the incident polarization axis direction is φpol 90 °, the main refractive index of the biaxial retardation plate is n1 = 1.50074, n2 = 1.499122, n3 = 1.495696, the azimuth angle of n1 was set to 89.5 °, and the thickness was set to d = 85 μm. In this configuration, the in-plane retardation Rf of the biaxial retardation plate with respect to the wavelength of 550 nm is about λ / 4, and the thickness direction retardation Rp is about 0.65λ. The contrast viewing angle characteristics of this configuration are shown in FIG. In this case, 6400 was obtained as the contrast characteristic value of the projector.
[0111]
FIG. 21 shows the contrast characteristic values of the projector when the biaxial retardation plate Rp value is changed. In the figure, the horizontal axis indicates the Rp value and the vertical axis indicates the contrast characteristic value. A high contrast characteristic is obtained in a wide range of Rp values. The unit of the Rp value is displayed with λ, which is the ratio to the used wavelength, as a unit. Further, Rf≈λ / 4 is set for any Rp value.
[0112]
FIG. 22 shows contrast characteristic values when the liquid crystal pretilt angle is changed when the Rp value of the biaxial retardation plate is set to about 0.65λ. In the figure, the horizontal axis indicates the liquid crystal pretilt angle and the vertical axis indicates the contrast characteristic value. Even when the pretilt angle is increased, high contrast characteristics are obtained.
[0113]
In this embodiment, the example using the off-axis optical system as the optical system of the projector has been described. However, the contrast viewing angle characteristics when the biaxial retardation plate of this embodiment is used are as shown in FIG. It goes without saying that high contrast characteristics can be obtained even in a projector using an on-axis optical system as an optical system because the high contrast region extends in a wide direction.
[0114]
(Example 5)
In the configuration in which the liquid crystal alignment direction φlc is set to 180 ° as described in the first and second embodiments, the incident polarization axis direction φpol needs to be set to 135 °. Therefore, the polarization transmission axis direction of the output side polarizing plate 108 is required. Is set to 45 ° orthogonal to it.
[0115]
By the way, in order to reduce the size of the projector, it is desirable to arrange the normal line of the dichroic surface of the color synthesizing unit 110 configured by a cross dichroic prism, a cross dichroic mirror, or the like in parallel to the xz plane. In this arrangement, the color synthesizing means 110 exhibits the most excellent color synthesizing function for linearly polarized light having a linear polarization direction of 0 ° or 90 °. Accordingly, when the polarization transmission axis direction of the exit side polarizing plate 108 is arranged at 45 °, it is difficult to obtain sufficiently excellent color synthesis characteristics, and the image quality of the projector is deteriorated.
[0116]
In the present embodiment, in order to avoid this problem, a third retardation plate 109 is provided between the emission-side polarizing plate 108 and the color composition unit 110. The third retardation plate 109 rotates the polarization axis of linearly polarized light having a 45 ° linearly polarized light transmitted through the output-side polarizing plate 108 by + 45 ° or −45 °, so that the linearly polarized light entering the color synthesizing means is incident. It has a function of converting the polarization axis direction to 0 ° or 90 °. As such a phase difference plate, a ½ wavelength plate whose slow axis direction is set to 22.5 ° or 67.5 ° is a preferable example.
[0117]
The above situation also holds for the color separation means 103. The color separation means 103 exhibits the most excellent color separation function for linearly polarized light having a linear polarization direction of 0 ° or 90 °. Therefore, the linearly polarized light having such a polarization direction has a polarization transmission axis direction of 135. A fourth retardation plate 104 is provided between the color separation means 103 and the incident-side polarizing plate 105 so as to pass through the incident-side polarizing plate 105 set at an angle. A preferred example of the fourth retardation plate is a half-wave plate with a slow axis orientation appropriately set.
[0118]
When the liquid crystal alignment azimuth φlc is set to 45 °, 135 °, 225 °, or 315 °, the incident polarization axis azimuth φpol and the linear polarization axis azimuth transmitted through the output side polarizing plate 108 are 0 ° or 90 °. The third retardation plate 109 and the fourth retardation plate 104 are not necessarily required and may be omitted.
[0119]
【The invention's effect】
As described above, according to the present invention, in a projector including a reflective liquid crystal light valve having a liquid crystal layer in a vertical alignment mode, any one of the main refractive index directions is substantially parallel to the normal line of the liquid crystal light valve. The contrast characteristics of a light beam with a large incident angle can be improved by adjusting the retardation in the thickness direction of the retardation plate as appropriate. The contrast characteristics of the projector can be improved. A similar effect can be realized by using a quarter wave plate as a retardation plate and appropriately setting the slow axis direction thereof.
[0120]
Further, a retardation plate in which any of the main refractive index directions is arranged substantially parallel to the normal line of the liquid crystal light valve and a quarter wave plate are used in combination, and the retardation in the thickness direction of the retardation plate is reduced to ¼. By appropriately setting the slow axis orientation of the wave plate, the contrast characteristics of the projector can be further improved. The same effect can also be realized by a biaxial retardation plate in which in-plane retardation is approximately ¼ wavelength and retardation in the thickness direction is appropriately set.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an optical system of a projector according to a first embodiment of the invention.
FIG. 2 is a diagram illustrating a definition of a light beam traveling direction and a view angle characteristic diagram according to the embodiment of the present invention.
FIG. 3 is a schematic configuration diagram of a reflective liquid crystal light valve.
FIG. 4 is an explanatory diagram of a liquid crystal molecule alignment state in a vertical alignment mode when no voltage is applied.
FIG. 5 is a diagram showing the relationship between the vibration plane orientation of the extraordinary light component and the light beam azimuth angle in the first embodiment.
6 is a relationship diagram between linearly polarized light azimuth and light beam azimuth in Example 1. FIG.
FIG. 7 is an explanatory diagram of a ray angle distribution region of an illumination light beam in an example.
FIG. 8 is a contrast characteristic viewing angle characteristic diagram according to the first exemplary embodiment.
FIG. 9 is a graph showing the relationship between Rp of the phase difference plate and contrast characteristics of the projector in the first embodiment.
FIG. 10 is a contrast characteristic viewing angle characteristic diagram using a quarter-wave plate.
FIG. 11 is a contrast characteristic viewing angle characteristic diagram when the slow axis of the quarter-wave plate is changed.
12 is a contrast characteristic viewing angle characteristic diagram in Embodiment 2. FIG.
FIG. 13 is a diagram showing the relationship between the slow axis direction of a quarter-wave plate and the contrast characteristics of a projector in Example 2.
14 is a schematic configuration diagram of a phase difference plate in Embodiment 3. FIG.
FIG. 15 is a diagram showing the relationship between the polarization state after passing through the quarter-wave plate and the light beam azimuth angle.
FIG. 16 is a diagram showing the relationship between the major axis direction of the elliptically polarized light after passing through the phase difference plate and the light beam azimuth angle.
FIG. 17 is a contrast characteristic viewing angle characteristic diagram according to the third embodiment.
FIG. 18 is a diagram showing the relationship between Rp of the retardation plate and contrast characteristics of the projector in Example 3.
FIG. 19 is a graph showing the relationship between the liquid crystal pretilt angle and the contrast characteristics of the projector in Example 3.
20 is a contrast viewing angle characteristic diagram according to Embodiment 4. FIG.
FIG. 21 is a graph showing the relationship between Rp of a retardation plate and contrast characteristics of a projector in Example 4.
22 is a graph showing the relationship between the liquid crystal pretilt angle and the contrast characteristics of the projector in Embodiment 4. FIG.
FIG. 23 is an explanatory diagram of functions of a retardation plate.
FIG. 24 is an explanatory diagram of details of a polarization state.
[Explanation of symbols]
101 projector
102 Illumination means
103 Color separation optical means
104 Fourth retardation plate
105 Polarizing plate
106, 106R, 106G, 106B retardation plate
107, 107R, 107G, 107B Reflective liquid crystal light valve
108, 108R, 108G, 108B Photometric means
109, 109R, 109G, 109B Third retardation plate
110 color composition means
111 Projection lens
112 White light source
113 Integrator lens
114 Polarization conversion element
201 rays
302 Silicon substrate
303 Reflective pixel electrode
304 Transparent electrode
305 Transparent substrate
306 Spacer
307 liquid crystal
308 Alignment film
309 Alignment film
401 Liquid crystal molecules
402 Long axis of liquid crystal molecules
501 Vibration surface of extraordinary light component
502 Vibration surface of abnormal light component
503 Vibration surface of extraordinary light component
601 Liquid crystal orientation
602 Polarization transmission axis direction
603 Linear polarization direction
604 Abnormal light component
605 Ordinary light component
606 Area subject to change in polarization state
607 Area subject to change in polarization state
608 Area subject to change in polarization state
609 Area subject to change in polarization state
701 Ray angle distribution area of illumination luminous flux
1001 Liquid crystal orientation
1002 Incident linear polarization direction
1003 Slow axis orientation of quarter wave plate
1004 Area where contrast characteristics are improved
1102 High contrast area
1103 High contrast area
1104 High contrast area
1105 High contrast area
1401 phase difference plate
1402 1/4 wave plate
1403 Main refractive index direction
1404 Liquid crystal light valve normal
1405 Slow axis
1406 Incident ray
1407 Emission rays
1408 Slow axis
1501 Elliptical polarization
1502 Absorption axis orientation of output side polarizing plate
1503 Long axis of elliptically polarized light
2301 Incident-side polarizing plate
2302 Polarization transmission axis
2303 Linearly polarized light
2304 Elliptical polarization
2305 Output side polarizing plate
2306 Polarization transmission axis
2307 Elliptical polarization
2308 Elliptical polarization
2309 Elliptical polarization
2401 Long axis of elliptically polarized light
2402 Polarization absorption axis direction
2403 Elliptical polarization
2404 Elliptical polarization

Claims (12)

Lighting means;
A plurality of light modulation means for modulating the light emitted from the illumination means ;
A polarization unit that regulates a polarization direction of light incident on the light modulation unit, and detects light modulated by the light modulation unit;
A color synthesizing unit having a dichroic surface and synthesizing the light analyzed by the polarizing unit;
Projection means for projecting the light synthesized by the color synthesis means ;
A projector having
The light modulation means includes a liquid crystal layer in a vertical alignment mode sandwiched between a pair of substrates, makes light from the illumination means enter from one of the pair of substrates and reflect it on the other substrate side. A reflective liquid crystal light valve that emits light from the one substrate,
A first retardation plate is provided between the one substrate constituting the liquid crystal light valve and the polarizing means, and a main refractive index direction of any one of the first retardation plates is defined as a normal line of the one substrate. substantially parallel disposed,
A third retardation plate is further disposed between the polarizing means and the color synthesizing means, and the polarization direction of the linearly polarized light emitted from the polarizing means is changed by the third retardation plate to the normal line of the dichroic surface. And a projector that is parallel or perpendicular to a plane defined by the normal line of the one substrate .   Lighting means;
  Color separation means for separating light emitted from the illumination means into a plurality of color lights;
  A plurality of light modulation means for modulating a plurality of color lights emitted from the color separation means;
  A polarization unit that regulates a polarization direction of light that is separated by the color separation unit and is incident on the light modulation unit, and that detects light modulated by the light modulation unit;
  A color synthesizing unit having a dichroic surface and synthesizing the light analyzed by the polarizing unit;
  Projection means for projecting the light synthesized by the color synthesis means;
  A projector having
  The light modulation means includes a liquid crystal layer in a vertical alignment mode sandwiched between a pair of substrates, makes light from the illumination means enter from one of the pair of substrates and reflect it on the other substrate side. A reflective liquid crystal light valve that emits light from the one substrate,
  A first retardation plate is provided between the one substrate constituting the liquid crystal light valve and the polarizing means, and a main refractive index direction of any one of the first retardation plates is defined as a normal line of the one substrate. Placed almost parallel to
  The illuminating means has polarization conversion means for converting light into desired linearly polarized light,
  A fourth retardation plate is further arranged between the color separation means and the polarization means, and the polarization direction of the linearly polarized light emitted from the color separation means is emitted from the polarization means by the fourth retardation plate. A projector having a polarization direction that is incident on the liquid crystal light valve. 3. The projector according to claim 1, wherein the first retardation plate is a uniaxial retardation plate, and an optical axis thereof is arranged substantially parallel to a normal line of the one substrate. The projector according to claim 1 or 2, wherein the first retardation plate is a biaxial retardation film. 5. The projector according to claim 4 , wherein n <b> 1 ≈ n <b> 2 when main refraction included in the plane of the first retardation plate is n <b> 1 and n <b> 2. A light beam incident on the liquid crystal light valve from an orientation substantially perpendicular or substantially parallel to the orientation orientation of the liquid crystal layer in the vertical alignment mode is subjected to a birefringence action based on a pretilt angle given to the liquid crystal in the vertical orientation mode. the resulting elliptically polarized light, to convert the polarization closest to linearly polarized light, according to any one of claims 1 to 5, characterized in that is set in the thickness direction retardation of the first retardation plate Projector. A second retardation plate is further provided on the outer surface side of the one substrate, the second retardation plate is a uniaxial retardation plate, and its slow axis is in a plane substantially parallel to the one substrate. the projector according to any one of claims 1 to 5, characterized in that it is arranged.   The projector according to claim 7, wherein the second retardation plate is a ¼ wavelength plate. Lighting means;
A plurality of light modulation means for modulating the light emitted from the illumination means ;
A polarization unit that regulates a polarization direction of light incident on the light modulation unit, and detects light modulated by the light modulation unit;
A color synthesizing unit having a dichroic surface and synthesizing the light analyzed by the polarizing unit;
Projection means for projecting the light synthesized by the color synthesis means ;
A projector having
The light modulation means includes a liquid crystal layer in a vertical alignment mode sandwiched between a pair of substrates, makes light from the illumination means enter from one of the pair of substrates and reflect it on the other substrate side. A reflective liquid crystal light valve that emits light from the one substrate,
A ¼ wavelength plate is provided between the one substrate constituting the liquid crystal light valve and the polarizing means, and the liquid crystal light valve is viewed from an orientation substantially orthogonal or substantially parallel to the alignment direction of the liquid crystal layer in the vertical alignment mode. In order to convert the elliptically polarized light resulting from the birefringence effect based on the pretilt angle imparted to the liquid crystal in the vertical alignment mode into the polarized light closest to the linearly polarized light, Set the direction of the slow axis of the plate ,
A third retardation plate is further disposed between the polarizing means and the color synthesizing means, and the polarization direction of the linearly polarized light emitted from the polarizing means is changed by the third retardation plate to the normal line of the dichroic surface. And a projector that is parallel or perpendicular to a plane defined by the normal line of the one substrate .   Lighting means;
  Color separation means for separating light emitted from the illumination means into a plurality of color lights;
  A plurality of light modulation means for modulating a plurality of color lights emitted from the color separation means;
  A polarization unit that regulates a polarization direction of light that is separated by the color separation unit and is incident on the light modulation unit, and that detects light modulated by the light modulation unit;
  A color synthesizing unit having a dichroic surface and synthesizing the light analyzed by the polarizing unit;
  Projection means for projecting the light synthesized by the color synthesis means;
  A projector having
  The light modulation means includes a liquid crystal layer in a vertical alignment mode sandwiched between a pair of substrates, makes light from the illumination means enter from one of the pair of substrates and reflect it on the other substrate side. A reflective liquid crystal light valve that emits light from the one substrate,
  A ¼ wavelength plate is provided between the one substrate constituting the liquid crystal light valve and the polarizing means, and the liquid crystal light valve is viewed from an orientation substantially orthogonal or substantially parallel to the alignment direction of the liquid crystal layer in the vertical alignment mode. In order to convert the elliptically polarized light resulting from the birefringence effect based on the pretilt angle imparted to the liquid crystal in the vertical alignment mode into the polarized light closest to the linearly polarized light, Set the direction of the slow axis of the plate,
  The illuminating means has polarization conversion means for converting light into desired linearly polarized light,
  A fourth retardation plate is further arranged between the color separation means and the polarization means, and the polarization direction of the linearly polarized light emitted from the color separation means is emitted from the polarization means by the fourth retardation plate. A projector having a polarization direction that is incident on the liquid crystal light valve.   An off-axis optical system in which an optical axis of incident light from the illumination unit to the liquid crystal light valve and an optical axis of reflected light from the liquid crystal light valve to the projection unit form a predetermined angle is provided. The projector according to claim 1.   12. The surface including the optical axis of the incident light and the optical axis of the reflected light is disposed substantially orthogonal or substantially parallel to the alignment direction of the liquid crystal layer in the vertical alignment mode. projector.

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