JP2002062582A - Image display device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To significantly reduce speckle noise and enable high-quality image display. SOLUTION: The laser light source 4 is so set that the polarization directions of light incident on adjacent pixels of the spatial modulator 2 are orthogonal to each other.
After converting the spatial polarization distribution of the laser light emitted from the laser beam by the polarization distribution conversion means 5, the laser light having the spatial polarization distribution converted is incident on the spatial modulator 2, and Laser light modulated by the screen 3
And an image is displayed on the screen 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image display device for displaying an image using light modulated by a spatial modulator.

[0002]

2. Description of the Related Art Conventionally, as one form of an image display device, there has been proposed a projection display in which light modulated by a spatial modulator such as a liquid crystal panel is irradiated on a screen to project an image on the screen. I have. In such a projection display, a lamp such as a metal halide, halogen, or xenon has been used as a light source.

However, when such a lamp is used as a light source, there is a problem that the life of the light source is short and maintenance is complicated. Further, since the three primary colors of light are cut out from the white light from the lamp, the optical system becomes complicated, and further, there is a problem that the color reproduction area is limited and the light use efficiency is reduced.

[0004] In order to solve these problems, attempts have been made to use a laser light source such as a semiconductor laser as a light source for a projection display. A laser light source has a longer life than a lamp and can efficiently use light emitted with excellent directivity, so that the energy use efficiency is high. In addition, the laser light source can have a large color reproduction area due to its monochromaticity.

[0005]

However, when a laser light source is used as a light source of an image display device such as the above-mentioned projection display, there is a problem that speckle noise occurs and the image quality is deteriorated.

[0006] Speckle noise is generated by dispersing coherent light having a uniform phase from a laser light source by a random phase surface (object surface), and disturbing a wavefront from a region adjacent to the object surface on an observation surface. This is a phenomenon caused by interference, and appears on the observation surface as a granular intensity distribution.

[0007] In a projection display using a laser light source, such speckle noise is generated.
If it occurs between the screen, which is the object plane, and the eyes (retina) of the observer, which is the observation plane, the observer will recognize the deterioration of the image. Therefore, how to reduce such speckle noise is an important issue in realizing an image display device such as a projection display using a laser light source.

The present invention has been made in view of the above circumstances, and provides an image display apparatus capable of displaying high-quality images by greatly reducing speckle noise. It is an object.

[0009]

According to the present invention, there is provided an image display apparatus for displaying an image by light emitted from a light source and modulated by a spatial modulator. And a polarization distribution conversion unit that converts a spatial polarization distribution of light emitted from the light source so that polarization directions of light incident on the light source are orthogonal to each other.

According to this image display device, the light emitted from the light source has a spatial polarization distribution such that the polarization directions of the light incident on adjacent pixels of the spatial modulator are orthogonal to each other. The light converted by the conversion means is incident on the spatial modulator. Then, by irradiating the light modulated by the spatial modulator onto a display unit such as a screen, an image is displayed on the display unit.

At this time, since the orthogonal polarized lights do not interfere with each other, speckle noise does not occur in the image displayed on the display unit due to interference between regions corresponding to adjacent pixels of the spatial modulator. Furthermore, if there is a sufficient distance from the region corresponding to the adjacent pixel, the interference with the region can be ignored. Therefore, interference is a problem only in an area corresponding to one pixel of the spatial modulator.

Here, one pixel of the spatial modulator is usually set to a size close to the limit that can be visually recognized by an observer. Therefore, speckle noise generated by interference in a region corresponding to one pixel of the spatial modulator is minute enough to be hardly recognized by an observer.

As described above, in the image display device according to the present invention, since speckle noise is greatly reduced, a high-quality image can be displayed.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First, prior to a specific description of an image display device to which the present invention is applied, the principle of the present invention will be briefly described. The image display device according to the present invention converts the spatial polarization distribution of the light emitted from the light source by the polarization distribution conversion means so that the polarization directions of the light incident on the adjacent pixels of the spatial modulator are orthogonal to each other. After that, the light is made incident on the spatial modulator to greatly reduce speckle noise.

Assuming that the light emitted from the light source is p-polarized light, as shown in FIG. 1, this light is converted into a micro-wavelength plate in which minute half-wave plates and one-wave plates are alternately arranged. When incident on the array, this micro-wavelength plate array functions as a polarization distribution conversion means for converting a spatial polarization distribution of light emitted from the light source, and a spatially polarized light in which p-polarized light and s-polarized light are alternately arranged. Outgoing light having a distribution can be obtained. Here, each half-wave plate of the micro-wavelength plate array is configured to convert incident p-polarized light into s-polarized light that is orthogonal thereto and emit the converted light.

As described above, the light emitted from the micro-wavelength plate array having a spatial polarization distribution in which p-polarized light and s-polarized light are alternately arranged is transmitted to a spatial modulator driven in accordance with image data to be displayed. Make it incident. At this time, light whose polarization directions are orthogonal to each other, that is, p-polarized light and s-polarized light are alternately incident on adjacent pixels of the spatial modulator. Then, by irradiating the display unit such as a screen with the light modulated by the spatial modulator, an image corresponding to the image data is displayed on the display unit.

In the image displayed on the display unit, the light emitted to the area corresponding to the adjacent pixel of the spatial modulator has the polarization directions orthogonal to each other. Since no interference occurs between light beams having orthogonal polarization directions, speckle noise due to interference between regions corresponding to adjacent pixels of the spatial modulator may occur in an image displayed on the display unit. Absent.

In the image displayed on the display unit, the regions corresponding to every other pixel of the spatial modulator have the same polarization direction of the irradiated light. If they are sufficiently far apart, the interference between these regions can be neglected. Therefore, speckle noise that causes deterioration of an image displayed on the display unit is only caused by interference in a region corresponding to one pixel of the spatial modulator.

Here, one pixel of the spatial modulator usually has a size close to a limit that can be visually recognized by an observer, and speckle noise caused by interference in a region corresponding to one pixel of the spatial modulator. Is so small that it is hardly recognized by an observer. Therefore, as described above, the light emitted from the light source is made incident on polarization distribution conversion means such as a microwavelength plate array to convert its spatial polarization distribution, and is incident on an adjacent pixel of the spatial modulator. If the polarization directions of the light are orthogonal to each other and the display unit is irradiated with the light modulated by the spatial modulator, the occurrence of speckle noise is significantly suppressed,
High-quality images can be displayed on the display unit.

FIG. 2 shows an example of the configuration of an image display device to which the present invention is applied. The image display device 1 shown in FIG. 2 projects a one-dimensional image from the spatial modulator 2 on a screen 3,
By scanning this one-dimensional image on the screen 3, a two-dimensional image is displayed on the screen 3. The image display apparatus 1 includes a laser light source 4 that emits a laser beam that is monochromatic and has high directivity and is coherent light. A polarization distribution conversion unit 5 is provided on the optical path of the laser beam emitted from the laser light source 4. Each optical element such as the optical modulator and the spatial modulator 2 is provided.

In the image display device 1, the laser light emitted from the laser light source 4 enters the polarization distribution conversion means 5 via the lens 6. Then, the polarization distribution converting means 5
The laser light whose spatial polarization distribution has been converted by the laser beam enters the spatial modulator 2 driven according to image data to be displayed via the imaging lens 7. As a result, the image of the polarization distribution conversion means 5 illuminated by the laser light source 4 is projected on the spatial modulator 2.

Here, the spatial distribution of the laser light incident on the spatial modulator 2 is converted by the polarization distribution converting means 5, and the polarization direction of the light incident on the adjacent pixel of the spatial modulator 2 is changed. They are orthogonal to each other. That is, light whose polarization directions are orthogonal to each other enters adjacent pixels of the spatial modulator 2.

As the spatial modulator 2, for example, any of a liquid crystal panel using a liquid crystal cell and a display using a digital micromirror device (DMD) can be applied. Also,
In recent years, a grating light valve (GL) using an active-driven grating by a micromachine has been developed.
A display called V) has been developed, and this GLV may be used as the spatial modulator 2. GLV
Is suitable as the spatial modulator 2 because it can display a clear and bright image seamlessly and can operate at high speed, and can be manufactured at low cost by using micromachine technology.

The laser light incident on the spatial modulator 2 is modulated by the spatial modulator 2 in accordance with image data to be displayed, and then emitted from the spatial modulator 2. The laser light emitted from the spatial modulator 2 is applied to a galvanomirror 9 via a relay lens 8. Then, the laser beam reflected by the galvanometer mirror 9 is
The light is emitted to the screen 3 via the projection lens 10.

As a result, a one-dimensional image from the spatial modulator 2 is formed into a relay image and projected on the screen 3. Then, the galvanomirror 9 is driven in synchronization with the spatial modulator 2, and the traveling direction of the laser beam reflected by the galvanomirror 9 changes, so that a one-dimensional image from the spatial modulator 2 is displayed on the screen 3. Scanning is performed, and a two-dimensional image is displayed on the screen 3.

The image displayed on the screen 3 is constituted as one image by a set of a plurality of regions corresponding to each pixel of the spatial modulator 2. Then, among the plurality of regions constituting the image, the regions corresponding to the adjacent pixels of the spatial modulator 2 are irradiated with light whose polarization directions are orthogonal to each other, and these regions interfere with each other. And speckle noise due to interference between these regions does not occur. Therefore, this image display device 1
Accordingly, it is possible to display a high-quality image in which the occurrence of speckle noise is significantly suppressed.

Here, the polarization distribution conversion for converting the spatial polarization distribution of the laser light emitted from the laser light source 4 so that the polarization directions of the light incident on the adjacent pixels of the spatial modulator 2 are orthogonal to each other. A specific configuration example of the means 5 will be described.

The polarization distribution converting means 5 can be realized, for example, by using a liquid crystal cell 20 as shown in FIG. In the liquid crystal cell 20 shown in FIG. 3, the polarization direction of the incident light is spatially controlled by using the optical alignment and the liquid crystal, and the transparent electrodes (ITO) 21a and 21b and the alignment film 22 are formed.
a and a pair of glass substrates 2 on which 22b are respectively formed.
3a and 23b are abutted via a spacer 24 so that the alignment films 22a and 22b are opposed to each other, and the liquid crystal 2 is inserted into a gap between the pair of glass substrates 23a and 23b.
5, and has a structure sealed with a sealing member 26.

The alignment films 22a and 22b of the liquid crystal cell 20
Has a plurality of alignment regions corresponding to each pixel of the spatial modulator 2 as shown in FIG.
And the region B are formed such that their orientation directions are different. Such alignment films 22a and 22b can be easily manufactured by a photo-alignment method of performing exposure using linearly polarized ultraviolet light. The linearly polarized ultraviolet light is applied to the alignment film 22a,
When irradiating 22b, the polymer on the surfaces of the alignment films 22a and 22b is oriented in a direction perpendicular to the polarization direction of the ultraviolet light. Therefore, by irradiating the regions A and B with ultraviolet rays having different polarization directions while controlling the polarization direction of the ultraviolet light, the alignment films 22 having different alignment directions between the region A and the region B are provided.
a, 22b can be easily manufactured.

When assembling the liquid crystal cell 20 having such alignment films 22a and 22b, it is required that the relative positioning of the pair of glass substrates 23a and 23b be accurately performed. Glass substrate 23a,
If, for example, a cross-shaped marker or the like is formed around the periphery of 23b, and the positioning is performed using this marker as a reference, accurate positioning of the pair of glass substrates 23a and 23b is appropriately and simply performed. be able to.

In the liquid crystal cell 20 having such alignment films 22a and 22b, when no electric field is applied, the molecules of the liquid crystal 25 between the alignment films 22a and 22b move along the alignment direction of the alignment films 22a and 22b. And arrange them.
That is, the liquid crystal molecules located between the regions A of the alignment films 22a and 22b and the liquid crystal molecules located between the regions B of the alignment films 22a and 22b are arranged in different directions. Here, since each alignment region of the alignment films 22a and 22b corresponds to one pixel of the spatial modulator 2 as described above, the molecules of the liquid crystal 5 between the alignment films 22a and 22b Are arranged in directions different from each other for each portion corresponding to adjacent pixels.

In the liquid crystal cell 20, when an electric field is applied between the transparent electrodes 21a and 21b, the orientation direction of the molecules of the liquid crystal 25 is continuously and gradually changed in a direction parallel to the direction in which the electric field is applied. And it will change. Therefore, when an appropriate electric field is applied between the transparent electrodes 21a and 21b, the alignment direction of the molecules of the liquid crystal 25 is changed to the alignment films 22a and 22b.
The liquid crystal 25 is appropriately controlled for each portion corresponding to each region of
, The spatial polarization distribution of the incident light can be converted.

More specifically, the liquid crystal 25 located between the regions A of the alignment films 22a and 22b functions as a half-wave plate, and the liquid crystal 2 located between the regions B of the alignment films 22a and 22b.
5 functions as a one-wavelength plate or the alignment film 22
The transparent electrodes 21a, 22b are arranged such that the liquid crystal 25 located between the regions A of the a and 22b functions as a one-wavelength plate and the liquid crystal 25 located between the regions B of the alignment films 22a, 22b functions as a half-wave plate. If an appropriate electric field is applied between the liquid crystal cells 21b, the liquid crystal cell 20 functions as the above-mentioned polarization distribution conversion means 5, and the polarization directions of light incident on adjacent pixels of the spatial modulator 2 are orthogonal to each other. Thus, the spatial polarization distribution of the laser light emitted from the laser light source 4 can be converted. When the above-described image display device 1 is configured using such a liquid crystal cell 20, a high-quality image in which the occurrence of speckle noise is significantly suppressed can be displayed.

When a liquid crystal panel is used as the spatial modulator 2, the liquid crystal panel is connected to the liquid crystal cell 20 described above.
With the configuration similar to that described above, the spatial modulator 2 itself can have a function as the polarization distribution converting means 5. The basic configuration and principle of the liquid crystal cell 20 described above are disclosed in Japanese Patent Application Laid-Open No. 2000-122062.

The polarization distribution conversion means 5 includes, for example, a beam expander array 30 for converting a beam diameter using microlens arrays 31 and 32, as shown in FIG.
And the birefringent optical crystal 33.

The beam expander array 30 is a combination of a first microlens array 31 having a focal length of 2 s and a second microlens array 32 having a focal length of s. The light incident on the microlens array 31 is emitted from the second microlens array 32 after the beam diameter is converted to about １ ／.

The birefringent optical crystal 3 is placed on the optical path of the light whose beam diameter has been converted by the beam expander array 30.
When the light having the converted beam diameter is incident on the birefringent optical crystal 33, the birefringent optical crystal 3
Due to the birefringence of 3, the mutually orthogonal polarization components of the incident light are spatially separated. Then, the light transmitted through the birefringent optical crystal 33 is emitted from the birefringent optical crystal 33 in a state where the lights having the orthogonal polarization directions are adjacent to each other. That is, light sequentially transmitted through the beam expander array 30 and the birefringent optical crystal 33 has a spatial polarization distribution such that the polarization directions of adjacent regions are orthogonal to each other.

Therefore, the beam expander array 3
The optical design of the first microlens array 31 and the second microlens array 32 constituting the optical fiber 0 and the birefringent optical crystal 33 is appropriately performed, and each of the light emitted from the birefringent optical crystal 33 is one by one. If one region corresponds to each pixel of the spatial modulator 2, the beam expander array 30 and the birefringent optical crystal 33 function as the above-described polarization distribution conversion means 5, and The spatial polarization distribution of the laser light emitted from the laser light source 4 can be converted so that the polarization directions of the light incident on the adjacent pixels are orthogonal to each other. If the above-described image display device 1 is configured using the beam expander array 30 and the birefringent optical crystal 33, it is possible to display a high-quality image in which the occurrence of speckle noise is significantly suppressed. Can be.

As described in detail above, the image display apparatus 1 to which the present invention is applied emits light from the laser light source 4 so that the polarization directions of the light entering adjacent pixels of the spatial modulator 2 are orthogonal to each other. After the spatial polarization distribution of the laser beam thus converted is converted by the polarization distribution conversion means 5, the laser light having the converted spatial polarization distribution is incident on the spatial modulator 2, and modulated by the spatial modulator 2. The image is displayed on the screen 3 by irradiating the screen 3 with the selected laser beam, so that the generation of speckle noise can be significantly suppressed, and a high-quality image can be displayed on the screen 3. .

In the above, only the optical system using one laser light source 4 has been illustrated for easy understanding of the features of the present invention, but the laser corresponding to each of R, G, and B colors has been described. Each of the light sources is used, and the spatial polarization distribution of the laser light from each of these laser light sources is converted by the polarization distribution conversion means. By modulating and irradiating the screen, a high-quality color image can be displayed on the screen.

In the above, a two-dimensional image is projected on the screen 3 by projecting a one-dimensional image from the spatial modulator 2 on the screen 3 and scanning the one-dimensional image on the screen 3. Image display device 1 to be displayed
However, a two-dimensional image from the spatial modulator may be projected on the screen to display a two-dimensional image on the screen. In this case, the spatial polarization distribution of the laser light emitted from the laser light source is such that the polarization components orthogonal to each other are alternately arranged in the vertical direction and the horizontal direction by the polarization distribution conversion means, and the distribution becomes a checkered pattern as a whole. Will be converted to

In the above description, the case where the spatial polarization distribution of linearly polarized light (p-polarized light, s-polarized light) is converted has been described as an example, but the present invention converts the spatially polarized light distribution of circularly polarized light. By doing so, a similar effect can be obtained. In this case, the spatial polarization distribution of the light emitted from the light source is converted by the polarization distribution converting means such that clockwise circularly polarized light and counterclockwise circularly polarized light are alternately arranged.

In the above, the image display device 1 for displaying an image on the screen 3 by projecting the light modulated by the spatial modulator 2 on the screen 3 has been described. The present invention is not limited to the above example, and can be effectively applied to any image display device that displays an image using a spatial modulator. Further, for example, not only a device mainly for displaying an image such as a projection display using a laser light source, but also a displayed image such as a laser printer or a recording device for recording data on a recording medium such as a movie film. The present invention can also be effectively applied to an apparatus mainly for recording the information.

In the above, the image display device 1 using the laser light source 4 for emitting laser light as a light source has been described as an example. However, the present invention is not limited to the above-described example, and the present invention is not limited thereto. The present invention can be effectively applied to any image display device having a light source that emits light.

[0046]

According to the image display device of the present invention, the spatial polarization distribution of the light emitted from the light source is polarized so that the polarization directions of the light incident on adjacent pixels of the spatial modulator are orthogonal to each other. After converted by the distribution conversion means, this light is incident on the spatial modulator, and the image is displayed using the light modulated by this spatial modulator, so the occurrence of speckle noise is greatly suppressed. Thus, a high-quality image can be displayed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the principle of the present invention.

FIG. 2 is a schematic diagram illustrating a configuration example of an optical system of an image display device to which the present invention has been applied.

FIG. 3 is a sectional view of a liquid crystal cell used as a polarization distribution conversion means.

FIG. 4 is a plan view of an alignment film provided in the liquid crystal cell.

FIG. 5 is a schematic diagram showing a state in which a beam expander array and a birefringent optical crystal function as polarization distribution conversion means.

[Explanation of symbols]

Reference Signs List 1 image display device, 2 spatial modulator, 3 screen, 4 laser light source, 5 polarization distribution conversion means, 2
0 liquid crystal cell, 21a, 21b transparent electrode, 22a,
22b orientation plate, 23a, 23b glass substrate, 2
5 liquid crystal, 30 beam expander array, 33
Birefringent optical crystal

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H04N 5/74 G02F 1/1335 530 F-term (Reference) 2H049 BA05 BA42 BA46 BB05 BC22 2H091 FA10Z FA29Z FA46Z LA16 LA30 MA07 5C058 AA06 BA23 BA33 EA05 EA12 EA26 5G435 BB12 BB17 FF05 FF11 GG23 GG28 LL15

Claims (4)

[Claims] 1. An image display device for displaying an image by light emitted from a light source and modulated by a spatial modulator, wherein polarization directions of light incident on adjacent pixels of the spatial modulator are orthogonal to each other. An image display device comprising: a polarization distribution conversion unit that converts a spatial polarization distribution of light emitted from the light source. 2. The liquid crystal display device according to claim 1, wherein the polarization distribution converting unit includes a liquid crystal cell in which liquid crystal is sandwiched between a pair of alignment films having a plurality of alignment regions corresponding to each pixel of the spatial modulator and a pair of transparent electrodes. The alignment directions of the adjacent alignment regions of the pair of alignment films are different from each other, and a predetermined electric field is applied between the pair of transparent electrodes, so that the light enters the adjacent pixels of the spatial modulator. 2. The image display device according to claim 1, wherein the spatial polarization distribution of the light emitted from the light source is converted so that the polarization directions of the light beams are orthogonal to each other. 3. The polarization distribution conversion means includes a beam expander array that converts a beam diameter using a microlens array, and a birefringent optical crystal, and the beam diameter is reduced to about half by the beam expander array. By making the plurality of beams incident on the birefringent optical crystal, by separating the mutually orthogonal polarization components of each of the incident beams by the birefringence of the birefringent optical crystal,
2. The image according to claim 1, wherein a spatial polarization distribution of light emitted from the light source is converted so that polarization directions of light incident on adjacent pixels of the spatial modulator are orthogonal to each other. Display device. 4. The image display device according to claim 1, wherein said light source emits a laser beam.