JP5682333B2 - Projection type liquid crystal display device - Google Patents

Description

  The present invention relates to a projection type liquid crystal display device, and more particularly to a projection type liquid crystal display device capable of increasing the contrast of a display image.

  In recent years, there is an increasing demand for improvement in contrast performance of projection display devices. Various proposals have been made for both display elements and optical systems in order to improve contrast performance. In a projection display apparatus using a reflective liquid crystal display element, a wire grid type polarization beam splitter is used instead of a polarization beam splitter of a type in which a dielectric multilayer thin film that performs a polarization beam splitter function is provided between two glass prisms. Is advantageous for improving the contrast because of good polarization separation characteristics and low birefringence characteristics.

  In Patent Document 1, regarding a reflection type projection display device using a wire grid type polarization beam splitter (hereinafter referred to as WG-PBS), a C plate or A between a WG-PBS and a reflection type liquid crystal element is used. It has been proposed to provide a compensator comprising a plate or a biaxial film. This realizes high contrast by controlling the polarization of light modulated by the reflective liquid crystal display element by a compensator.

JP 2003-262831 A

  However, in order to further improve the contrast performance, there is a limit to only the polarization control between the WG-PBS and the reflective liquid crystal display element. Even if the compensation between the WG-PBS and the reflective liquid crystal display element is compensated, the WG -The light reflected from the PBS causes a mismatch in polarization with the analyzer disposed thereafter, which causes deterioration in contrast performance.

  The present invention has been made in view of such problems, and an object thereof is to provide a projection type liquid crystal display device capable of improving contrast in an optical system using a reflective liquid crystal display element and WG-PBS. .

  In order to solve the above-described problems of the prior art, the present invention provides a light source (1a), a wire grid type polarization beam splitter (9) that transmits and polarizes light from the light source, and the wire grid type polarization beam. A reflective liquid crystal display element (12) that reflects and modulates the polarized light emitted from the splitter and returns the modulated polarized light to the wire grid polarized beam splitter, and the modulated polarized light is reflected by the wire grid polarized beam splitter. And a compensator plate (13) having a retardation plate of 0.5λ to 0.6λ when the wavelength of the modulated polarized light is λ, and the light exit side of the compensator plate And a projection lens (16) for projecting light emitted from the analyzer. The liquid crystal display device is provided.

  In the above configuration, in a plane orthogonal to the optical axis in the optical path from the wire grid type polarization beam splitter to the analyzer, the direction is perpendicular to the direction of the wire grid of the wire grid type polarization beam splitter (9). In the case where the direction intersecting with the surface orthogonal to the optical axis when the surface of the wire grid type polarization beam splitter is extended is the y-axis, and the direction orthogonal to the y-axis is the x-axis, the compensation plate (13) The slow axis is preferably arranged in the direction perpendicular to the x-axis.

  The compensator (13) is disposed at an angle of 0 ° to + 12 ° with the x axis as a rotation axis, and the direction of the inclination is the surface of the wire grid type polarization beam splitter (9). It is preferable that a direction in which an acute angle formed by the surface of the compensation plate increases is a positive direction.

  According to the present invention, contrast can be improved in an optical system using a reflective liquid crystal display element and WG-PBS.

1 is a configuration diagram of a projection type liquid crystal display device according to a first embodiment of the present invention. 2 is a diagram showing a reflective liquid crystal display element 12. FIG. FIG. 4 is an explanatory diagram showing an optical path in which light transmitted through the WG-PBS 9 is transmitted through the compensator 11, reflected by the reflective liquid crystal display element 12, and further reflected by the WG-PBS 9 to reach the analyzer 14. The relationship between leakage light and the angle of the compensator when a half-wave plate is inserted as the compensator 13 is shown. The relationship between the leaked light and the angle of the compensator when a 0.6λ retardation plate is inserted as the compensator 13 is shown. FIG. 6 is a diagram for explaining the definition of the angle of conical light in the optical path from the reflective liquid crystal display element 12 to the analyzer 14. It is explanatory drawing which shows the case where the light of the polarization equivalent to a black screen is inject | emitted from the reflective liquid crystal display element. It is a figure which shows the result of having simulated the leaked light distribution in the position of the analyzer in the case of the conventional case without a compensator in front of the analyzer. FIG. 6 is a diagram in which a half-wave plate is installed as a compensator 13 between the WG-PBS 9 and the analyzer 14. 4 is a diagram for explaining a refractive index of a birefringent material 20. FIG. It is a figure which shows the birefringent material 21 when the direction of a refractive index is inclined at a predetermined angle with respect to the in-plane or thickness direction of the compensator.

  Embodiments of a projection-type liquid crystal display device according to the present invention will be described below with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is a configuration diagram of a projection type liquid crystal display device according to a first embodiment of the present invention. The light source 1a is an ultra-high pressure mercury lamp and emits white light. The reflector 1b reflects light emitted from the light source. The direct light from the light source and the reflected light reflected by the reflector are made uniform in the luminance distribution of light by the first integrator 2a and the second integrator 2b, and then the polarization direction of the light is unified by the polarization conversion element 3. Aligned in the direction. The aligned polarized light is defined as P-polarized light.

  The P-polarized light emitted from the polarization conversion element 3 passes through the overlapping lens 4 and is separated into mixed light of red light and green light and blue light by the Y dichroic mirror 5a and the B dichroic mirror 5b. The optical path of the mixed light of red light and green light and blue light is bent by the mirrors 6a and 6b. The mixed light of red light and green light is separated into red light and green light by the G dichroic mirror 7, and the optical path of the green light is bent. Red light, green light, and blue light traveling through different optical paths respectively pass through the field lenses 10a, 10b, 10c, polarizers 8a, 8b, 8c, WG-PBSs 9a, 9b, 9c, and compensators 11a, 11b, 11c. After the transmission, red light is incident on the reflective liquid crystal display element 12a, green light is incident on the reflective liquid crystal display element 12b, and blue light is incident on the reflective liquid crystal display element 12c.

  The reflective liquid crystal display elements 12a, 12b, and 12c for each color reflect and modulate incident light of each color. The reflected and modulated red light and green light are transmitted again through the compensators 11a, 11b, and 11c, and the modulated S-polarized components are reflected by the WG-PBSs 9a, 9b, and 9c. S-polarized components of the reflected red light, green light, and blue light are transmitted through the compensators 13a, 13b, and 13c and the analyzers 14a, 14b, and 14c, and then synthesized by the cross dichroic prism 15 and projected by the projection lens 16. Is done.

  FIG. 2 is a diagram showing the reflective liquid crystal display element 12. The reflective liquid crystal display element 12 includes a transparent substrate having a transparent electrode formed on a surface thereof, and an active matrix substrate in which a reflective electrode and a driving circuit for each pixel are arranged in a matrix so that the transparent electrode and the reflective electrode face each other. Nematic liquid crystal having a negative dielectric anisotropy is sandwiched between the gaps arranged opposite to each other. The reflective liquid crystal element 12 has a cell gap of 1.3 μm and an aspect of 16: 9. Each surface on the liquid crystal layer side of the transparent substrate and the active matrix substrate is provided with an SiOx compound alignment film by a vapor deposition surface treatment method. The alignment direction of the pixel side (active matrix substrate side) liquid crystal by the alignment film of the SiOx compound and the incident side liquid crystal alignment direction (alignment direction of the transparent substrate side liquid crystal) by the alignment film of the SiOx compound are different by 120 degrees. An angle of 120 degrees is called a twist angle. The direction between the alignment direction of the pixel side liquid crystal and the incident side liquid crystal alignment direction, which is an angle that is equal to the alignment direction of the pixel side liquid crystal and the incident side liquid crystal alignment direction, is referred to as a reference axis. The reference axis is set to 45 degrees with the polarization direction of the incident light.

  FIG. 3 shows an optical path in which light transmitted through the WG-PBS 9 is transmitted through the compensator 11, reflected by the reflective liquid crystal display element 12, and further reflected by the WG-PBS 9 to reach the compensator 13 and the analyzer 14. It is explanatory drawing. The compensator 11, the reflective liquid crystal display element 12, and the analyzer 14 are arranged such that their boundary surfaces are perpendicular to the optical axis. The WG-PBS 9 is a wire grid type polarization beam splitter in which a metal is formed in a grid shape on a glass substrate, and is provided with an inclination of 45 degrees with respect to the optical axis. That is, the angle formed by the normal vector of the WG-PBS 9 and the optical axis is 45 degrees. The direction orthogonal to the direction of the wire grid is the transmission axis direction that transmits the polarized light. The WG-PBS 9 serves as a polarizer that transmits polarized light from incident light and plays a role in detecting the modulated light modulated by the reflective liquid crystal display element 12. The light incident on the WG-PBS 9 has already been polarized to some extent by the polarization conversion element 3 and the polarizers (8a, 8b, 8c), but the WG-PBS 9 serves as a polarizer that transmits specific polarized light. There is no change in the responsibility.

  In the first embodiment, a half-wave plate is installed as the compensator 13 between the WG-PBS 9 and the analyzer 14. Here, the xy coordinate axes in the optical path from the WG-PBS 9 to the compensator 13 and the analyzer 14 are defined as shown in FIG. The xy plane is orthogonal to the optical axis of the optical path from the WG-PBS 9 to the compensator 13 and the analyzer 14. The x-axis is the direction of the wire grid of WG-PBS9. The y-axis is a direction orthogonal to the x-axis, that is, a direction perpendicular to the direction of the wire grid of the wire grid type polarization beam splitter, and is orthogonal to the optical axis when the surface of the wire grid type polarization beam splitter is extended. The direction that intersects the surface to be moved is the positive direction of the y-axis. The half-wave plate is a uniaxial material and has a refractive index of ne> no. At this time, the axial direction of ne having a high refractive index is called a slow layer axis, and no having a low refractive index is called a fast axis. At this time, the half-wave plate has the slow axis set in the y-axis direction. The half-wave plate has an x-axis direction (wire grid direction of the wire grid type polarization beam splitter) as a rotation axis with respect to a plane orthogonal to the optical axis of the optical system, and the wire grid type polarization beam splitter of the wire system. When the direction in which the acute angle formed by the surface and the surface of the compensation plate increases is defined as a positive direction, the surface is arranged with an inclination angle θ with respect to the y axis.

  FIG. 4 shows the relationship between the leakage light and the tilt angle (θ) of the compensator 13 when a half-wave plate is inserted as the compensator 13. The leakage light ratio is defined as the ratio of the total amount of light emitted from the analyzer 14 to the total incident light amount of the compensator. The case where the compensator 13 is not inserted is shown as 100%. When the compensator 13 is not tilted (θ = 0), the leakage light ratio is reduced by 2%. By tilting the compensator 13, the leakage light ratio changes. When the inclination angle is +5 degrees, the leakage light ratio is reduced by about 9%, and the contrast is improved most. When the tilt angle of the compensator 13 is +10 degrees, the leakage light ratio is reduced by 3%. On the other hand, when the compensator 13 is tilted in the negative direction, the leakage light ratio increases conversely. As described above, a contrast improving effect can be obtained by installing a half-wave plate as the compensator 13 between the WG-PBS 9 and the analyzer 14 and tilting it at a predetermined angle. The half-wave plate is also referred to as a 0.5λ retardation plate.

  Next, a case where a 0.6λ phase difference plate is provided between the WG-PBS 9 and the analyzer 14 as the compensator 13 will be described. The slow axis of the 0.6λ phase difference plate is set in the y-axis direction. FIG. 5 shows the relationship between the leakage light ratio and the tilt angle (θ) of the compensator 13 when a 0.6λ retardation plate is inserted as the compensator 13. When the 0.6λ phase difference plate is not tilted, the leakage light ratio is reduced by 2%. By tilting the retardation plate of 0.6λ, the leakage light ratio changes. When the inclination angle is +6 degrees, the leakage light ratio is reduced by about 12%, and the contrast is improved most. When the tilt angle of the compensator 13 is +13 degrees, the leakage light ratio is reduced by 2%. On the other hand, when the compensator 13 is set to a negative angle, the leakage light ratio increases conversely. As described above, a contrast improving effect is obtained by installing a 0.6λ phase difference plate as the compensator 13 between the WG-PBS 9 and the analyzer 14 and tilting it by a predetermined angle. It is most preferable that the slow axis of the half-wave plate or the 0.6λ phase difference plate is strictly aligned with the y-axis, but a certain amount of error can naturally be allowed.

  As described above, when a retardation plate of 0.5λ to 0.6λ is provided as the compensator 13 at a predetermined inclination angle between the WG-PBS 9 and the analyzer 14, the leakage light ratio is reduced and the contrast is increased. Will improve. The result can be reproduced even by repeated experiments. The reason why the leakage light ratio is reduced and the contrast is improved when a phase difference plate of 0.5λ to 0.6λ is provided between the WG-PBS 9 and the analyzer 14 as the compensator 13 at a predetermined inclination angle. Although not necessarily clear, the reason will be discussed below.

  Returning to FIG. 1, in the optical system shown in FIG. 1, the optical path between the field lens 10 and the cross dichroic prism 15 is designed in a telecentric region. That is, in the optical system region after the field lens 10, the optical axis of the optical system and the principal ray are designed in parallel. Further, because the light source 1a of the projection display device has a light emitting part of a finite size, the light rays incident on a place where the optical system is present have a finite angular distribution. In illumination optics, a light beam having a finite angular distribution is usually expressed as consisting of a large number of conical light beams centered on the principal light beam.

  FIG. 6 is a diagram for explaining the definition of the angle of the conical light in the optical path from the reflective liquid crystal element 12 to the analyzer 14. The optical path from the reflective liquid crystal element 12 to the analyzer 14 is a telecentric region as described above. In FIG. 6, the polar angle and azimuth angle of the conical light beam around the principal ray are defined for the light incident on the WG-PBS 9. The polar angle indicates how the light spreads, and indicates that conical light extending from the principal ray to the polar angle exists. The polar angle is also referred to as a cone angle.

  Returning to FIG. 1, the polarizer 8 is a polarizing plate, which increases the degree of polarization of light that is substantially linearly polarized (P-polarized) by the polarization conversion element 3, and changes the polarization direction of incident light to the transmission axis of the WG-PBS 9. It also has a role to match the direction. It is determined by transmitting the polarizer 8 what kind of polarization direction the “light having an angle defined by the polar angle and the azimuth angle” which is transmitted through the polarizer 8 and enters the WG-PBS 9 is determined. Has been. The efficiency of the WG-PBS 9 is determined by the positional relationship between the polarization direction of incident light and the transmission axis direction perpendicular to the wire grid. The light transmitted through the WG-PBS 9 enters the compensator 11 and the reflective liquid crystal element 12.

  FIG. 7 is an explanatory diagram showing a case where polarized light corresponding to a black screen is emitted from the reflective liquid crystal element 12. For convenience of explanation, FIG. 7 shows light 1 on the optical axis, light 2 with an azimuth angle of 0 degrees, and light 3 with an azimuth angle of 45 degrees out of the light emitted from the reflective liquid crystal element 12. . In the case of a black screen, the light that has passed through the WG-PBS 9 and entered the compensator 11 and the reflective liquid crystal element 12 is reflected without being modulated by the reflective liquid crystal element 12 and passes through the compensator 11 again. . And it injects into WG-PBS9.

  If the polarization direction of the light incident on the WG-PBS 9 coincides with the transmission axis direction of the WG-PBS 9, most of the incident light is transmitted through the WG-PBS 9 according to the polarization separation characteristics of the WG-PBS 9. The light reflected by the WG-PBS 9 enters the analyzer 14. Here, the transmission axis direction of the analyzer is orthogonal to the direction of the wire grid of the WG-PBS 9. Therefore, in the light beam 1, the angle θ1 formed by the polarization direction of the incident light to the analyzer 14 and the transmission axis direction of the analyzer 14 becomes 90 degrees and is blocked by the analyzer. On the other hand, the angles θ2 and θ3 of the light rays 2 and 3 with respect to the transmission axis of the analyzer 14 are shifted from 90 degrees. Therefore, the light rays 2 and 3 are not blocked by the analyzer 14 and are projected onto the screen as a result, resulting in a decrease in contrast.

  FIG. 8 is a diagram showing the result of simulating the leakage light distribution at the position of the analyzer in the conventional case where there is no compensation plate before the analyzer 14. That is, it is a diagram showing the distribution of light at the position of the analyzer when polarized light corresponding to a black screen is emitted from the reflective liquid crystal element 12. The xy axis in FIG. 8 of the black screen corresponds to the xy axis when the polar angle and azimuth angle of the conical light beam around the principal ray are defined for the light incident on the WG-PBS 9 in FIG. The light beam 1 on the optical axis corresponds to the origin of the xy coordinates in FIG. The ray with the maximum polar angle corresponds to a point on the circumference of FIG. “Ray ray 2 with an azimuth angle of 0 °” corresponds to the intersection of the x-axis (positive) and the circle. “Ray 3 with an azimuth angle of 45 degrees” corresponds to the intersection of y = x and a circle in the first quadrant. Further, the numerical values in FIG. 8 indicate the amount of leaked light (arbitrary scale), and the solid line indicates the contour of the amount of leaked light.

  As described with reference to FIG. 7, the polarization direction of the leaked light on the y-axis is parallel to the y-axis from FIG. On the other hand, the polarization direction of the light emitted from the position shifted from the y-axis, such as the light 2 and the light 3, is not parallel to the y-axis. Here, a compensation plate for controlling the polarization is installed between the WG-PBS 9 and the analyzer 14, and the polarization direction of all leaked light is aligned in parallel with the y-axis. If the transmission axis of 14 is in a relationship of 90 degrees, the light beam passing through the analyzer 14 is suppressed, and the contrast of the projection screen can be improved. Since θ2 and θ3 have different angles, the correction angles required at each location on the analyzer 14 are different. That is, the polarization direction on the y-axis is not changed, and it is necessary to change the polarization direction corresponding to the distance from the y-axis for light other than on the y-axis.

  FIG. 9 is a diagram in which a half-wave plate is installed as the compensator 13 between the WG-PBS 9 and the analyzer 14. First, the half-wave plate is arranged perpendicular to the optical axis of the illumination / imaging system, and the slow axis of the half-wave plate is set in the y-axis direction. When the angle between the polarization vector of the incident polarized light and the slow axis of the half-wave plate is θ, the outgoing light rotates by 2θ. Accordingly, in FIG. 9, polarized light that is inclined by θ from the x-axis is inclined by −θ when transmitted through the half-wave plate. Therefore, according to the above simulation, there is almost no improvement effect when the half-wave plate is arranged perpendicular to the optical axis of the illumination / imaging system.

  The above consideration is the knowledge obtained by simulating the optical path from the reflective liquid crystal element to the analyzer in consideration of the angular distribution of the illumination light without considering the characteristics of the WG-PBS 9. It is close to the actual measurement value (+ 2% improvement) when the tilt angle is set to 0 degree. However, it is not clear to the details why the leakage light ratio changes when the inclination angle of the compensator 13 is changed. Probably, it is considered that leakage light is reduced when the compensator 13 is tilted about the x-axis in association with some characteristic of the WG-PBS 9 that is disposed with an inclination of 45 degrees with respect to the optical axis.

  Further, the above experimental results are valid even when various characteristics of the reflective liquid crystal display element 9 are changed. The compensator 11 compensates for the characteristics of the reflective liquid crystal display element, and the compensator 13 compensates for the time when the angled light beam is reflected by the WG-PBS 9 and travels toward the analyzer 14. It is thought that some kind of characteristic is compensated. Therefore, it is considered that the same characteristics are obtained regardless of the type of the reflective liquid crystal element.

  Next, a general description of the compensator will be given. FIG. 10 is a diagram for explaining the refractive index of the optical material 20. The optical material can have up to three principal refractive indices nx, ny, nz. An isotropic medium such as glass has a single refractive index. Two materials having the same principal refractive index are called uniaxial materials. Two equal refractive indices of a uniaxial material are called normal refractive indices (no). nx = nz = no. Different refractive indices of uniaxial materials are called extraordinary refractive indices (ne). ny = ne. In an optical material, when the values of the refractive indexes no and ne are different, an axis having a high refractive index is called a slow axis and an axis having a low refractive index is called a fast axis. When the refractive index is high, the light traveling speed is slow, and when the refractive index is low, the light traveling speed is fast. Therefore, the axis in the direction where the refractive index is high is called the slow axis. Examples of the material of the compensator 13 include a polymer material, a crystal material such as quartz, and a liquid crystal polymer.

The half-wave plate uses a polymer material, a crystal material such as quartz, a liquid crystal polymer, and the like, and sets the phase difference between the slow axis and the fast axis to a half wavelength. That is, when the phase difference (δ) (unit: radians), the thickness of the material is d, and the wavelength of light is λ,
δ = 2π (ne−no) d / λ
A half-wave plate is one in which the phase difference (δ) given by is π (radian) which is half of one wavelength (2π). The 0.6λ phase difference plate means a phase difference (δ) of 1.2π (radian) which is 0.6 times one wavelength (2π).

  Normally, as shown in FIG. 10, the directions of the refractive indexes nx, ny, and nz are parallel to the in-plane direction and the thickness direction of the compensator. In that case, the compensator is inclined and installed as described above. If the main refractive index (n1, n2, n3) as shown in FIG. 11 is present in any direction in the plane, the same effect can be obtained without tilting the compensator itself from the direction orthogonal to the optical axis. Is obtained.

  In the first and second embodiments, the integrator illumination optical system is used as the illumination optical system. However, an illumination optical system different from this, for example, an illumination optical system using a rod integrator may be used. Further, the three-plate optical system using three reflective liquid crystal elements has been described, but the present invention can be similarly applied to a single-plate optical system using one reflective liquid crystal element.

1a light source lamp, 1b reflector 2a first integrator, 2b second integrator,
3 Polarization Conversion Element 4 Superposition Lens 5a Y Dichroic Mirror, 5b B Dichroic Mirror 6a, 6b Mirror 7 G Dichroic Mirror 8a Red Polarizer, 8b Green Polarizer, 8c Blue Polarizer,
9a WG-PBS for red, 9b WG-PBS for green,
9c Blue WG-PBS,
10a Red field lens, 10b Green field lens,
10c Blue field lens,
11a Red compensator, 11b Green compensator,
11c Blue compensator,
12a Red reflective liquid crystal element, 12b Green reflective liquid crystal element,
12c Blue reflective liquid crystal element,
12 reflective liquid crystal elements,
13a Red compensator, 13b Green compensator, 13c Blue compensator 13 Compensator 14 Analyzer, 14a Red analyzer, 14b Green analyzer,
14c Blue analyzer,
15 Cross dichroic prism,
16 Projection lens 20 Birefringent material

Claims (3)

A light source;
A wire grid type polarization beam splitter that transmits and polarizes light from the light source;
A reflective liquid crystal display element that reflects and modulates the polarized light emitted from the wire grid type polarization beam splitter and returns it to the wire grid type polarization beam splitter;
A phase difference plate of 0.5λ to 0.6λ when the modulated polarized light is disposed in an optical path that travels after being reflected by the wire grid type polarization beam splitter, and the wavelength of the modulated polarized light is λ. A compensator having
An analyzer provided on the light exit side of the compensation plate;
A projection lens for projecting light emitted from the analyzer;
A liquid crystal display device comprising: The wire grid type polarization beam splitter is in a direction perpendicular to the direction of the wire grid of the wire grid type polarization beam splitter in a plane perpendicular to the optical axis in the optical path from the wire grid type polarization beam splitter to the analyzer. In the case where the direction intersecting with the surface perpendicular to the optical axis when the surface is extended is the y-axis, and the direction perpendicular to the y-axis is the x-axis,
The liquid crystal display device according to claim 1, wherein the compensation plate has a slow axis arranged in a direction perpendicular to the x axis. The compensator is disposed at an angle of 0 to +12 degrees with the x axis as a rotation axis, and the tilted direction is formed by the surface of the wire grid type polarization beam splitter and the surface of the compensator. 3. The liquid crystal display device according to claim 2 , wherein a direction in which an acute angle increases is a positive direction.

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