JPH085939A - Display device - Google Patents

Abstract

PURPOSE:To provide the display device which is high in the utilization efficiency of light by providing a diffraction type projection efficiency varying means which is provided on the optical path and a lens which images the light projected from the projection efficiency varying means. CONSTITUTION:The light emitted by a light source 24 is converged by a condenser lens 28 including light reflected by a cold mirror 27. Only the red light is reflected by a dichroic mirror 29a to change its direction by 90 deg. and is made incident on the diffraction type projection efficiency varying means 25a. The diffraction type projection efficiency varying means 25a is switched, pixel by pixel, by a control circuit and the incident light is modulated by pixels to obtain pixels emitting light of 0th order and other pixels. The modulated red light has its optical path bent by a mirror 30a and is made incident on a coupling prism 31, and the light further has its optical path bent again and is multiplexed with other light to form an image on a screen through a projection lens 26. Similarly, the blue light and green light are also modulated and imaged by the projection lens 26.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type display device for moving images and still images.

[0002]

2. Description of the Related Art In recent years, display devices have tended to increase in size, and methods for projecting and enlarging images have been developed. Generally, there is a system in which an image formed on a liquid crystal panel is illuminated by a high-intensity light source, and light spatially modulated by reflection or transmission is formed on a screen by a projection lens. The conventional display device will be described below.

FIG. 5 shows the structure of a conventional display device. 5, 1 is a lamp, 2 is a reflecting mirror, 3 is an interference filter, 4a and 4b are dichroic mirrors, the dichroic mirror 4a selectively reflects only blue light, and the dichroic mirror 4b only green light. Selectively reflect. Reference numerals 5a, 5b and 5c are mirrors. 6a, 6b and 6c are liquid crystal panels, and 7 is a dichroic prism. Reference numeral 8 is a projection lens, and 9 is a screen.

The operation of the display device configured as described above will be described below. First, the light emitted from the lamp 1, including the light reflected by the reflecting mirror 2, becomes only visible light when passing through the interference filter 3. The dichroic mirror 4a reflects only blue light of visible light, changes its direction by 90 degrees, and transmits other light. The blue light is reflected by the mirror 5a and enters the liquid crystal panel 6a. In the liquid crystal panel 6a, only a blue signal of the color video signal is input by a control circuit (not shown), and the TFT (thin film transistor) provided for each pixel switches the pixel so that the incident blue light is emitted. Spatial modulation is performed by changing the plane of polarization.

The blue light spatially modulated and transmitted through the liquid crystal panel 6a is again reflected by the dichroic prism 7.
The direction is changed by 0 ° and the image is formed on the screen 9 by the projection lens 8 to form a blue image. Of the light transmitted through the dichroic mirror 4a, only the green light is reflected by the dichroic mirror 4b, the direction of the light is changed by 90 degrees, and after entering the liquid crystal panel 6b, a green image is formed on the screen 9 similarly to the blue light. . A red image is similarly formed on the screen 9 for the red light transmitted through the dichroic mirror 4b. Therefore, on the screen 9, blue,
The green and red images are combined to form a color image.

[0006]

However, the above-mentioned conventional configuration has a problem that the light utilization efficiency is poor because polarized light is used for spatial modulation of light and a TFT is used for each pixel. Hereinafter, this problem will be described in detail with reference to the drawings. FIG. 6 shows the structure of the liquid crystal panel.

In FIG. 6, 10 is incident light, 11 is a polarizing plate, 12a and 12b are glass substrates, 13 is a TFT, 14
Is a pixel electrode, 15 is a scanning line, 16 is a signal line, 17 is a liquid crystal, 18 is a common electrode, and 19 is a polarizing plate. The principle of spatial modulation by the liquid crystal panel is that when the incident light 10 enters the polarizing plate 11, only the polarized component in a specific direction passes through and the liquid crystal 17
After the plane of polarization is rotated while passing through, the light is amplitude-modulated due to the difference in the direction of the plane of polarization of the transmitted light and the direction of the plane of polarization of the polarizing plate 19 when passing through the polarizing plate 19 again. In the case of a lamp light source, since the incident light 10 is randomly polarized, the light transmitted through the polarizing plate 11 is 50% at most of the incident light 10, and the light utilization efficiency is low.

The switching of the liquid crystal 17 is performed by the scanning line 15
This is done by applying a voltage between the transparent pixel electrode 14 and the transparent common electrode 18 by the TFT 13 selected by the signal line 16, but since the TFT portion is opaque, light is transmitted. This causes a decrease in light utilization efficiency. This means that in a high-definition TV liquid crystal panel or the like, the number of pixels increases and the area of each pixel decreases, so the area ratio of the TFT in each pixel increases, and the aperture ratio (= the area through which light actually transmits). / Pixel area) is 30%
Becomes a serious problem.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a display device having high light utilization efficiency.

[0010]

In order to achieve this object, a display device according to a first aspect of the present invention comprises a light source, a diffractive emission efficiency changing means provided in an optical path of light emitted from the light source, and the diffractive type. And a lens that forms an image of the light emitted from the emission efficiency varying means.

According to a second aspect of the invention, the diffractive type emission efficiency varying means is composed of a plurality of diffraction gratings, and the region where the phase difference between adjacent diffraction gratings is ½ of the incident light wavelength. Is provided.

A third aspect of the present invention has a structure in which the diffractive type emission efficiency varying means supports a plurality of beams in a hollow shape on a substrate, and the width of the supporting portion is smaller than the width of the movable portion. are doing.

[0013]

With respect to the diffractive output efficiency varying means, the O.D. S
olgaard et al., Optics Letters, Vol. 17, 9
Issue, pp. 688-690, 1992, and the principle is explained using figures. FIG. 7 is a perspective view of the diffractive type emission efficiency varying means, and in the figure, 20 is a silicon substrate. 21 is a spacer, 22 is a dielectric film,
It is held in the hollow by the spacer 21. The thicknesses of the spacer 21 and the dielectric film 22 are each 4 times the incident light wavelength.
It is set to one-half. 23 a to 23 e are slits provided in the dielectric film 22. On the surface of the silicon substrate 20 and the surface of the dielectric film 22, aluminum or silver is formed as a reflective film and an electrode.

FIG. 8 shows the operation of the diffractive type emission efficiency changing means. In FIG. 8, the same parts as those in FIG. 7 are designated by the same reference numerals and the description thereof will be omitted. FIG. 8A is a diagram showing a state in which no voltage is applied to the electrodes, and the step between the surface of the dielectric film 22 and the surface of the silicon substrate 20 is ½ of the wavelength of the incident light. At this time, the optical path difference between the light reflected on the surface of the dielectric film 22 and the light reflected on the surface of the silicon substrate 20 is 1 round trip.
Since the wavelengths and the phases are aligned, the diffractive emission efficiency changing means merely functions as a mirror.

Next, in the state where voltage is applied to the electrodes, FIG.
As shown in (b), since the dielectric film 22 contacts the silicon substrate 20 due to electrostatic force, the step between the surface of the dielectric film 22 and the surface of the silicon substrate 20 becomes 1/4 of the wavelength of the incident light, and Light reflected on the surface of the film 22 and the silicon substrate 20
Since the optical path difference of the light reflected on the surface is one-half wavelength in a round trip, the phases are offset by half a wavelength and cancel each other out, and the 0th-order diffracted light disappears. Instead, the 1st-order or higher-order diffracted light Will be emitted. Therefore, the diffractive emission efficiency varying means can modulate the 0th-order diffracted light.

Since this system utilizes only the phase of the incident light, the emission efficiency of the 0th-order diffracted light hardly depends on the polarization plane of the incident light, and any polarization plane can be used. Where 0
The emission efficiency of the second-order diffracted light is defined as the intensity ratio of the light reflected by the diffractive emission efficiency changing means and the incident light. Therefore, the light utilization efficiency of the light source is higher than that in the case where a polarization plane is used as in a liquid crystal panel. Further, by providing a switching element for applying a voltage to the electrode below the dielectric thin film, it is possible to obtain a wide light reflecting surface and increase the aperture ratio.

The operation of the first invention is to construct a display device by arranging the diffractive emission efficiency changing means two-dimensionally and using it as a spatial light modulator instead of the liquid crystal panel. . However,
O. In the report of Solgaard et al., Parallel light is used as incident light and the pitch of the slits 23a to 23e is 6 times or less of the wavelength. However, for use as a display device, light from a light source is collected by a lens. It is necessary to make the light incident on the diffractive emission efficiency varying means, and it is necessary to consider the incident angle dependency of the diffractive emission efficiency varying means.
We examined the relationship between the ratio of the incident wavelength λ to the pitch Λ of the slit and the emission efficiency of the 0th-order diffracted light, and found that the emission efficiency exceeded 90% when λ / Λ ≧ 6, and also λ / Λ ≧ 7
At that time, I found that the amount of light on the screen was uniform. Therefore, 7 or more is suitable as the value of λ / Λ.

Further, when the diffractive type emission efficiency changing means is two-dimensionally arranged, it is necessary to provide a region (black matrix) which does not reflect light due to separation of pixels.
When the diffraction type emission efficiency varying means such as Solgaard is two-dimensionally arranged as it is, a reflection band is formed between the pixels, and light is always reflected, so that the pixels are mixed with each other on the screen and the display performance is deteriorated. Becomes

The function of the second invention is to provide an area in which the phase difference is half the wavelength of the incident light between the pixels.
The light reflected between the pixels cancels each other to form a black matrix.

The operation of the third aspect of the invention is to make the support beam easier to deform by making the width of the beam supporting the movable portion of the diffraction type emission efficiency varying means narrower than the width of the movable portion. .

[0021]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the basic configuration of the first embodiment of the present invention, in which 24 is a light source, 25 is a diffractive emission efficiency changing means, and 26 is a projection lens.
FIG. 2 shows the structure of a display device according to the first embodiment of the present invention, in which the basic structure shown in FIG. 1 is provided for each of the three primary colors of light. The operation will be described below with reference to FIG.

In FIG. 2, the same parts as those in FIG. 1 are designated by the same reference numerals. A light source 24 is a white light source such as a metal halide lamp or a xenon lamp. Reference numerals 25a to 25c are diffraction type emission efficiency changing means, and 26 is a projection lens. Reference numeral 27 denotes a cold mirror that transmits heat rays and reflects visible light. 28 is a condenser lens. Reference numerals 29a to 29c are dichroic mirrors.
9a selectively reflects only red light, the dichroic mirror 29b selectively reflects only blue light, and the dichroic mirror 29c selectively reflects only green light. Three
Reference numerals 0a and 0b are mirrors. Reference numeral 31 is a coupling prism, which synthesizes light.

The operation of the display device configured as described above will be described below. First, the light emitted from the light source 24, including the light reflected by the cold mirror 27, is converged by the condenser lens 28. Only the red light is reflected by the dichroic mirror 29a,
The direction is changed by 0 ° and the diffractive type emission efficiency changing means 25a enters. The diffractive type emission efficiency varying means 25a is switched for each pixel by a control circuit (not shown), and the incident light is modulated for each pixel, and according to the principle described in the section of action, 0th-order light is emitted and is not emitted. Pixels are created. The modulated red light has its optical path bent by the mirror 30a, enters the coupling prism 31, is bent again, is combined with other light, and is imaged on a screen (not shown) by the projection lens 26. .

Of the green and blue light transmitted through the dichroic mirror 29a, the blue light is reflected by the dichroic mirror 29b, changes its direction by 90 degrees, and enters the diffraction type emission efficiency changing means 25b. Diffraction type emission efficiency changing means 25b
The blue light spatially modulated by the dichroic mirror 2
9c is transmitted, the direction is changed by 90 degrees by the mirror 30b,
It is combined with another color by the coupling prism 31 and is imaged by the projection lens 26.

Similarly, the green light transmitted through the dichroic mirror 29b is spatially modulated by the diffractive emission efficiency changing means 25c, the optical path is bent by the dichroic mirror 29c, and the green light is imaged through the same optical path as the blue light. Above, the three primary colors are mixed to obtain a color image.
In this configuration, as described in the section of action, when the ratio of the grating pitch Λ of the diffractive emission efficiency changing means to the center wavelength λ of the incident light is set to λ / Λ = 7, the diffraction emitting efficiency changing means produces it. Since the diffraction angle of the first-order diffracted light is 8.2 degrees, in order to prevent this first-order diffracted light from entering the entrance pupil of the projection lens 31, the F value (= focal length / effective aperture of the lens) of the projection lens is set. Must be 3.5 or higher. Therefore, the F value of the condenser lens needs to be 3.5 or more, and at this time, the amount of light on the screen becomes substantially uniform, as described in the section of the action.

As described above, according to the present embodiment, the light from the light source is separated into the three primary colors of red, green and blue, and the reflection type diffraction type emission efficiency varying means is provided for each color, and λ / Λ = 7. With this, it is possible to obtain a display device with high light utilization efficiency and less unevenness in light amount.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings. Since only the diffractive emission efficiency changing means is different from the first embodiment, parts other than the diffractive emission efficiency changing means are omitted. 3A and 3B are diagrams showing the configuration of one pixel of the diffractive emission efficiency varying means, FIG. 3A is a perspective view, and FIG. 3B is a sectional view taken along line AA.

In FIG. 3, reference numerals 32a to 32e denote beams, each of which has a thickness of ¼ of the wavelength of incident light and is formed by patterning a dielectric film such as silicon nitride. Beams 32a-e
Aluminum, silver, or the like is formed on the upper surface of the film as an electrode / reflection film. 33 is a spacer, and the thickness thereof is ¼ of the incident light wavelength. Reference numeral 34 denotes an electrode, which is provided on a substrate (not shown). Further, the electrode 34 reflects incident light.

As described in the section of action, the diffractive type emission efficiency varying means constructed as described above can modulate the 0th-order diffracted light, but the beam 32a provided on the spacer 33 is used.
And 32e do not bend even if electrostatic force is applied, so beam 32a
Or, the phase difference between the light reflected on the upper surface of 32e and the light reflected on the upper surface of the spacer 33 is always one-half wavelength in a round trip, and the same applies to the portions supported by the spacer 33 of the beams 32b, c, d. The phase difference is 1/2 wavelength.
Therefore, the phase difference between the pixels is halved.
Since the wavelength becomes the wavelength and the 0th-order diffracted light is not generated, the problem of pixel separation can be solved.

As described above, in the diffractive type emission efficiency varying means, by providing the region where the phase difference is ½ between the pixels, substantially the same effect as that of providing the black matrix can be obtained. To be

(Third Embodiment) A third embodiment of the present invention will be described below with reference to the drawings. Since only the diffractive emission efficiency changing means is different from the first embodiment, parts other than the diffractive emission efficiency changing means are omitted. FIG. 4 is a diagram showing the configuration of the diffractive type emission efficiency changing means.
(A) is a top view and (b) is the same AA sectional drawing.

In FIG. 4, reference numeral 35 denotes a dielectric film, the thickness of which is 1/4 of the wavelength of incident light, and aluminum, silver or the like is formed on the upper surface as an electrode / reflection film. 36a ~
36l is a slit formed by etching the dielectric film 35. Reference numeral 37 is a support beam, which is formed by etching the dielectric film 35. 38 is a spacer and 39 is an electrode. The electrode 39 also reflects light.

The operation of the diffractive emission efficiency changing means constructed as described above will be described below. Dielectric film 3
5 is hollowly supported by the support beam 37 and the spacer 38, but when a voltage is applied between the electrode provided on the upper surface of the dielectric film and the electrode 39, the dielectric film 35 causes the electrode 3 to move to the electrode 3 by electrostatic force.
The contact with 9 is the same as described in the operation section. Since the width of the supporting beam is narrower than the width of the dielectric film 35 in the movable portion, the supporting beam is easily deformed, the area in contact with the electrode 39 is increased, and as a result, the area for modulating the 0th-order diffracted light is increased. The aperture ratio is improved.

As described above, by making the width of the support beam narrower than the width of the movable portion, the support beam is easily deformed,
The effect that the dead space that does not contribute to the modulation of the 0th-order diffracted light can be reduced can be obtained. It is needless to say that in the third embodiment, the same effect can be obtained even if each beam forming the diffraction type emission efficiency changing means is thinned only near the spacer 38.

[0035]

As described above, according to the first aspect of the invention, the light source, the diffractive emission efficiency changing means provided in the optical path of the light emitted from the light source, and the light emitted from the diffractive emission efficiency changing means are provided. By providing a lens for forming an image, a display device with high light utilization efficiency can be realized.
Further, by setting the ratio of the wavelength λ of the incident light to the grating pitch Λ of the diffractive emission efficiency changing means to 7 or more, even if the light from the light source is converged and made incident on the diffractive emission efficiency changing means, A display device with less unevenness can be obtained.

Further, according to the second aspect of the invention, the area on the screen is clearly defined by providing a region where the phase difference is ½ of the incident light between the pixels of the diffraction type emission efficiency varying means. Can be separated.

According to the third aspect of the invention, the movable portion of the diffraction type emission efficiency varying means is supported by the support beam having a width narrower than the width of the movable portion, whereby the aperture ratio is improved and the light is utilized. A highly efficient display device can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a display device according to the first embodiment of the present invention.

FIG. 3A is a perspective view of one pixel of the diffraction type emission efficiency varying means of the second embodiment of the present invention, and FIG. 3B is a perspective view of one diffraction type emission efficiency varying means of the second embodiment of the present invention. Cross section of pixel

FIG. 4A is a plan view of the diffractive emission efficiency changing means in the third embodiment of the present invention, and FIG. 4B is a sectional view of the diffractive emission efficiency changing means in the third embodiment of the present invention.

FIG. 5 is a configuration diagram of a conventional display device.

FIG. 6 is a configuration diagram of a liquid crystal panel

FIG. 7 is a perspective view of a diffractive type emission efficiency changing means.

FIG. 8A shows an operation in a state where no voltage is applied to the electrode of the diffraction type emission efficiency varying means, and FIG. 8B shows an operation in which a voltage is applied to the electrode of the diffraction type emitting efficiency varying means. Figure

[Explanation of symbols]

 24 Light source 25 Diffraction type emission efficiency changing means 26 Projection lens 27 Cold mirror 28 Condensing lens 29 Dichroic mirror 30 Mirror 31 Coupling prism 32 Beam 33 Spacer 34 Electrode 35 Dielectric film 36 Slit 37 Support beam 38 Spacer 39 Electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Yokoyama 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Shinichi Mizuguchi, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. A light source, a diffractive emission efficiency changing means provided in an optical path of light emitted from the light source, and a lens for focusing light emitted from the diffractive emission efficiency changing means. Display device. 2. The display device according to claim 1, wherein the diffractive type emission efficiency varying means is a reflective type. 3. The ratio of the diffraction grating pitch of the diffractive output efficiency varying means to the center wavelength of the wavelength range of the light incident on the diffractive output efficiency varying means is 7 or more. 1. The display device according to 1. 4. A light source, a diffractive emission efficiency changing means provided in an optical path of light emitted from the light source, and a lens for focusing light emitted from the diffractive emission efficiency changing means. The display, characterized in that the diffractive type emission efficiency varying means is composed of a plurality of diffraction gratings, and an area having a phase difference of ½ of the incident light wavelength is provided between the adjacent diffraction gratings. apparatus. 5. A light source, a diffractive emission efficiency changing means provided in an optical path of light emitted from the light source, and a lens for forming an image of light emitted from the diffractive emission efficiency changing means. A display device, wherein the diffractive type emission efficiency varying means has a structure in which a plurality of beams are movably supported in a hollow manner on a substrate, and a width of the supporting portion is smaller than a width of the movable portion. 6. A means for separating the light emitted from the light source into red light, green light and blue light, and diffractive type emission efficiency varying means is provided in the optical path of each light. 1. The display device according to 1.