JPH095725A - Transmission type display device - Google Patents

Abstract

PURPOSE: To form finer pixels by improving the light condensing efficiency of microlenses. CONSTITUTION: This transmission type display device 0 has a pair of transparent substrates 1, 2. These substrates are joined to each other via a prescribed spacing and have electrodes forming pixels B, R, G arranged at a specified pitch P. Electro-optical materials 4, such as liquid crystals, are held in the spacing and the transmittance of incident light 5 is modulated by each of the pixels B, R, G, by which the light is converted into exit light 6. The microlenses 7 condense the three primary color components of the incident light 5 previously separated from each other by having a prescribed angle difference (i) to the corresponding pixels B, R, G. The microlenses 7 are arranged in proximity by spacing to the incident light 5 side from the pixels B, R, G by the optical distance (t) determined by the arranging pitch (p) of the fined pixels B, R, G and the angular difference (i) of the three primary color components. The focal length of the microlenses 7 is shortened by setting the refractive index (n) in an optimum range according to the proximate optical distance) (t).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmissive display device incorporated in a projector or the like. More specifically, the present invention relates to a technique for improving light source light collection efficiency using a microlens.

[0002]

2. Description of the Related Art FIG. 8 shows a conventional single plate projector. A light source 102, a color liquid crystal panel 103, a projection lens 104, and a screen 105 are sequentially arranged along an optical axis 101. A single-plate type projector uses one color liquid crystal panel 103. The color liquid crystal panel 103 is, for example, an active matrix type, and color filters colored in three primary colors of R (red) G (green) B (blue) corresponding to individual pixels are integrally formed.
White light source light emitted from the light source 102 is transmitted through the color liquid crystal panel 103 and then enlarged and projected by the projection lens 104 to display a color image on the front screen 105. Since a single-panel type projector uses only one liquid crystal panel, the price can be reduced. However, the single-panel type uses a liquid crystal panel on which a color filter is formed, and thus has a drawback that it absorbs light and the image displayed on the screen 105 becomes dark.

FIG. 9 shows a conventional three-plate type projector. In the three-plate type, three monochrome liquid crystal panels 201 to 203 are used. No color filter is provided on each liquid crystal panel. Instead, the white light emitted from the light source 204 is divided into RGB three primary color components by using a dichroic mirror and a total reflection mirror, and the three primary color components are incident on the corresponding liquid crystal panel, and then the three primary color components are mixed again. Light source 2
The white light emitted from 04 is a dichroic mirror 205.
Thus, only the red component R is selectively reflected. This R component is transmitted through the total reflection mirror 206 to the corresponding liquid crystal panel 2
01 is transmitted. The transmitted R component is mixed with other color components by the dichroic mirrors 207 and 208, and enters the projection lens 209. On the other hand, dichroic mirror 2
The B component that has passed through 05 is separated from the G component by the dichroic mirror 210 and is transmitted through the corresponding liquid crystal panel 202. After this, the dichroic mirrors 207, 20
And mixed with other color components via 8. Finally, the G component transmitted through the dichroic mirror 210 irradiates the corresponding liquid crystal panel 203, and then is mixed with other color components via the total reflection mirror 211 and the dichroic mirror 208. The RGB three primary color components thus combined are enlarged and projected on the front screen 212 via the projection lens 209. In this way, in the three-plate system, white light source light is separated into RGB three primary color components by a combination of dichroic mirrors and made incident on the corresponding liquid crystal panels respectively, so that the image projected on the screen becomes bright without light loss.
Moreover, when a monochrome liquid crystal panel having the same number of pixels as the color liquid crystal panel used in the single plate type is used, the resolution is tripled by combining three panels. However, the cost is disadvantageous because three liquid crystal panels are used.

Therefore, there has been proposed a single plate type using one monochrome liquid crystal panel, which enables an image brightness equivalent to that of the three plate type, and is disclosed in, for example, Japanese Patent Laid-Open No. 4-60538. This system uses a monochrome liquid crystal panel without a color filter and is therefore called a "color filterless system". FIG. 10 schematically shows a color filterless projector. This projector includes a light source 301 along an optical axis, three dichroic mirrors 302 to 304 having different tilt angles, one monochrome liquid crystal panel 305, a projection lens 306, and a screen 307.
Are arranged in order. The light source 301 includes a reflecting mirror and a white lamp. The white light emitted from the lamp is separated into only the B component by the dichroic mirror 302 and enters the monochrome liquid crystal panel 305 at a predetermined incident angle. The R component is selectively reflected by the next dichroic mirror 303 and similarly enters the monochrome liquid crystal panel 305 at a predetermined incident angle. Similarly, the G component is selectively reflected by the last dichroic mirror 304 and enters the monochrome liquid crystal panel 305 at a predetermined incident angle. A relative angle difference is given between these three primary color components of RGB. On the other hand, the monochrome liquid crystal panel 305 includes three pixels corresponding to the three primary colors of RGB as one set, and a microlens corresponding to each set is provided. RGB incident with a certain angle difference
The components are condensed by the microlenses to the corresponding pixels. The RGB components transmitted through the corresponding pixels are combined via the projection lens 306, and the enlarged color image is projected on the screen 307 in the front.

[0005]

The above-described color filterless system is characterized in that the RGB three primary color components are given a relative angular difference in advance and each color component is condensed to the corresponding pixel by using a microlens. ing. Therefore, in order to increase the resolution, it is necessary to completely separate the three primary color components by the microlens and focus them on the corresponding pixels. However, since various aberrations are included in the microlens, it is impossible to completely separate the three primary color components from each other. Therefore, in order to actually increase the color resolution, it is necessary to increase the pixel size, which results in an increase in the size of the monochrome liquid crystal panel 305. As the size of the liquid crystal panel increases, the diameter of the projection lens 306 correspondingly increases, and the size of the dichroic mirror must be increased. Therefore, the price increases and the size of the projector body also increases.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, it is an object of the present invention to provide a small and high-definition transmissive display device that can be mounted on a color filterless type projector. The following measures were taken to achieve this purpose. That is, according to the first aspect of the present invention, the transmissive display device has, as a basic configuration, a pair of transparent substrates,
It comprises an electro-optic material and a microlens. The pair of transparent substrates are bonded to each other with a predetermined gap,
The electrodes are provided to form pixels arranged at a constant pitch. The electro-optical material is held in the gap and modulates the transmittance of incident light for each pixel to convert it into emitted light. The microlens collects the three primary color components of the incident light, which are separated from each other with a predetermined angle difference, in the corresponding pixels. Characteristically, the microlenses are arranged close to the incident light side from the pixels by an optical distance determined by the array pitch of the miniaturized pixels and the angular difference of the three primary color components, The focal length of the microlens is shortened by setting the refractive index in the optimum range according to the distance.
Specifically, the refractive index of the microlens is 1.60 to 1.60 corresponding to the arrangement pitch of pixels designed to be 20 μm or less.
Set to the optimum range of 1.70.

According to the second aspect of the present invention, the transmissive display device basically comprises a pair of transparent substrates, an electro-optical material, and optical means. The pair of transparent substrates are bonded to each other with a predetermined gap, and are provided with electrodes forming pixels arranged at a constant pitch. The electro-optical material is held in the gap and modulates the transmittance of incident light for each pixel to convert it into emitted light. The optical means collects the three primary color components of the incident light, which are separated from each other with a predetermined angle difference, in the corresponding pixels. Characteristically, the optical means is arranged in proximity to the incident light side from the pixel by an effective distance determined by the array pitch of the miniaturized pixels and the angular difference of the three primary color components, and the optical means is It has a plurality of microlenses that overlap each other in the optical axis direction, and has a synthetic focal length that is shortened according to the effective distance that is close to each other.

[0008]

In the present invention, the pixel array pitch is made fine in order to miniaturize the transmissive display device and to achieve high definition. Therefore, the optical distance between the microlens and the pixel is inevitably shortened. In this state, since the three primary color components of the incident light having the angle difference from each other are condensed on the corresponding pixels, the focal length of the microlens is shortened and the color resolution is improved. As a specific means for shortening the focal length, the refractive index of the optical material forming the microlens is set to be high. Alternatively, a plurality of microlenses are stacked along the optical axis direction,
Its combined focal length is shortened.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic partial sectional view showing a first embodiment of a transmissive display device according to the present invention. As shown, the transmissive display device is formed using a pair of transparent substrates 1 and 2. The transparent substrate 1 on the upper side and the transparent substrate 2 on the lower side are bonded to each other with a predetermined gap, and are provided with electrodes forming pixels arranged at a constant pitch.
For simplification of the drawing, only three pixels B, R, and G corresponding to the three primary color components are drawn. The individual pixels are separated from each other by the black matrix 3. The electrodes forming the individual pixels are not shown. An electro-optical material 4 such as liquid crystal is held in the gap between the pair of transparent substrates 1 and 2, and the transmittance of incident light 5 is modulated for each pixel and converted into emitted light 6. B, R, G1
Microlenses 7 are provided corresponding to the pixels of the set. In this example, the microlens 7 is incorporated in a laminated body that constitutes the transparent substrate 1. That is, the microlens 7 is interposed between the upper transparent layer 8 and the lower transparent layer 9. Each transparent layer is made of, for example, quartz glass.
The microlens 7 is formed by patterning a concave surface on the upper transparent layer 8 by etching and then filling it with an epoxy resin or the like having an optical refractive index n. This micro lens 7
Is the incident light 5 separated from each other with a predetermined angle difference i.
The three primary color components of are collected on the corresponding pixels. In the figure, only the incident light 5 of the B component is shown, and is condensed on the corresponding pixel B via the microlens 7. On the other hand, although not shown, the R component is incident substantially vertically and is condensed on the corresponding pixel R via the microlens 7. Therefore, B
The angular difference between the component and the R component is i. This angle difference i is set to 8 °, for example. The remaining G component is also incident with a predetermined angle difference and is condensed on the corresponding pixel G via the microlens 7.

The microlenses 7 are arranged close to the incident light side from the pixels by an optical distance t determined by the arrangement pitch p of the miniaturized pixels and the angle difference i of the RGB three primary color components. As a feature of the present invention, the refractive index n is set in the optimum range according to the optical distance t that is close to the optical distance t, and the focal length of the micro lens 7 is shortened. In particular,
The microlens 7 has a refractive index n of 1.60 to 1.70 corresponding to the pixel arrangement pitch p designed to be 20 μm or less.
Is set to the optimum range.

The optical distance t between the microlens and the pixel is determined by the angle difference i of the incident light and the pixel arrangement pitch p. The calculation method is shown in the following mathematical formula. n1 · sin i = n2 · sin r r = sin ⁻¹ (n1 · sin i / n2) t = p / tan r In the above formula, n1 represents the refractive index of air, and n2
Represents the refractive index of the transparent substrates 1 and 2 constituting the transmissive display device 0. i represents the incident angle of the incident light 5, and r also represents the refraction angle. p represents the arrangement pitch of the pixels, and t represents the optical distance between the microlens 7 and the pixels. As understood from the above formula, the refraction angle r is the refractive index n.
1, n2 and the incident angle (more precisely, the incident angle difference) i. The refractive index n2 is about 1.46 when the transparent substrates 1 and 2 are made of quartz glass. Next, as apparent from the geometrical relationship shown in FIG. 1, the optical distance t is determined by the refraction angle r and the pixel arrangement pitch p. For example, the incident angle difference i is 8 ° and the pixel arrangement pitch p is 20.
In the case of μm, the optical distance t is about 200 μm.

FIG. 2 shows pixels B, R and G and a microlens 7.
It is a schematic diagram which shows the planar relationship of. As shown in the figure, the microlens 7 corresponds to each set of pixels B, R, and G. Each pixel is divided into a central opening 10 and a light shielding portion 11 surrounding the opening 10. The light shielding portion 11 is covered with the black matrix 7 shown in FIG. In this example, the transmissive display device has an overall diagonal dimension of 1.35 inches,
The pixel arrangement pitch is set to 18.8 μm in the horizontal direction and 35 μm in the vertical direction. The size of the opening 10 is 15.3 × 2.
It is set to 0 μm.

FIG. 3 is a graph showing the relationship between the microlens / pixel distance t and the effective aperture ratio. It should be noted that the effective aperture ratio represents the ratio of light rays that have actually entered the microlens and passed through the pixel aperture. This graph simulates a case where an epoxy resin having a refractive index of 1.6 is used as the optical material of the microlens. As understood from the graph, the microlens / pixel distance t is set to 200 μm in accordance with the above calculation result.
When set to about m, an effective aperture ratio of about 60% can be obtained. When the microlens is arranged closer to the pixel than 200 μm, the effective aperture ratio deteriorates.

By the way, even if the microlenses are arranged apart from the pixels by a predetermined optical distance t in accordance with the above-mentioned calculation result, a high effective aperture ratio cannot be obtained as it is. It is necessary to optimize the focal length of the microlens according to the microlens / pixel distance t. In particular, when the optical distance t is shortened with the miniaturization of the pixel array pitch, it is necessary to adjust the focal length of the microlens accordingly. FIG. 4 schematically shows a case where the focal length of the microlens is outside the optimum range. Since the incident light cannot be efficiently collected, the light spots 12 of the three primary color components are larger than the openings 10 of the corresponding pixels. Therefore, the amount of light blocked by the black matrix 3 increases, and the effective aperture ratio is poor. The size of each light spot 12 of the three primary color components is larger than the size of the opening 10 with respect to the surface of the black matrix 3. This deteriorates the effective aperture ratio. In addition to this, when the size of the opening 10 is miniaturized as the pixel becomes finer, the light spot 1 is generated by the diffraction of the light passing through the microlens 7.
As 2 spreads, this effect is also significant. Further, although a metal halide lamp or the like is usually used as a light source of the projector, since the arc is not a point light source but a finite length, the light rays incident on the display device are not perfectly parallel light. This also causes the size of the light spot 12 to be enlarged.

FIG. 5 shows a state in which the focal length of the microlens 7 is within the optimum range. As shown in the figure, the size of the light spots 12 of the three primary color components is reduced on the surface of the black matrix 3, and the entire light spots 12 are substantially aligned with the openings 10 of the corresponding pixels. Therefore, the effective aperture ratio can be significantly improved as compared with the state of FIG.

By the way, generally, the focal length of an optical lens is determined by the refractive index and the radius of curvature. However, in the case of a microlens, as shown in FIG. 2, its outer diameter is regulated by the pixel arrangement pitch, and there is no room for adjustment. That is, in order to improve the utilization efficiency of light incident on the display device, adjacent microlenses are arranged as shown in the pattern of FIG. 2 (Δ arrangement). Therefore, the radius of curvature of each microlens is uniquely determined by the pixel arrangement pitch.
Therefore, in the present invention, the lens focal length is optimized by adjusting the refractive index of the microlens (correctly, the difference between the refractive index of the microlens and the refractive index of the transparent substrate). FIG. 6 is a graph showing the relationship between the refractive index n of the microlens and the effective aperture ratio, which is a simulation result in the optical configuration shown in FIG. As is clear from this graph, an effective aperture ratio of 60% or more can be secured by setting the refractive index of the microlens in the range of 1.60 to 1.70. In the present invention, the refractive index of the microlens is made larger than 1.60 to shorten the focal length of the microlens so as to match the optical distance t described above. As a result, the effective aperture ratio is increased and the brightness of the projected image is increased. However, if the refractive index of the microlens is increased to more than 1.7, the focal length is shortened too much, and the effective aperture ratio deteriorates. The optimum condition is that the microlens has a refractive index of 1.
It can be seen that it is the time when about 65 optical materials are used. As a material that meets this condition, for example, Al ₂ O ₃ can be used. In this case, the effective aperture ratio reaches about 80%, the condensing effect of the microlens is remarkably exhibited, and the color resolution is significantly improved. In this way, by adjusting the refractive index of the microlens, the focal length can be optimized, and a compact and high-definition display device can be incorporated in a color filterless projector.

FIG. 7 is a schematic partial sectional view showing a second embodiment of the transmissive display device according to the present invention. This transmissive display device is an active matrix type and has a panel structure in which a counter substrate 50 and a drive substrate 51 are bonded to each other with a certain gap, and a liquid crystal 52 is held as an electro-optical substance in the gap. . A counter electrode 53 is formed on the entire inner surface of the counter substrate 50. On the other hand, drive substrate 5
Pixel electrodes 54 are arranged in a matrix on the inner surface of 1. Further, a thin film transistor 55 that drives each pixel electrode 54 is also integrated. A pixel is defined between the pixel electrode 54 and the counter electrode 53. Individual pixels are separated by a black matrix 56 formed on the counter substrate 50. The black matrix 56 is the drive substrate 5.
It may be formed on one side. Optical means is formed on the counter substrate 50, and the three primary color components of the incident light, which are separated from each other with a predetermined angle difference, are condensed on the corresponding pixels. This optical means is arranged close to the incident light side from the pixels by an effective distance determined by the array pitch of the miniaturized pixels and the angular difference of the three primary color components. Specifically, this optical means is composed of two microlenses 57 and 58 that are overlapped with each other in the optical axis direction, and has a synthetic focal length shortened in accordance with the effective distance in proximity. One microlens 57 has an upper transparent layer 59 and an intermediate transparent layer 60.
It is sandwiched between and, and its focal length is f2.
The other microlens 58 is sandwiched between an intermediate transparent layer 60 and a lower transparent layer 61, and its focal length is f.
It is one. The distance between the pair of microlenses 57 and 58 is d
Is set to That is, the thickness of the intermediate transparent layer 60 is d
It has become. In this way, the pair of microlenses 57,
With the structure in which 58 is stacked in two layers, the focal length of the microlens can be substantially shortened. That is, the first
The same effect as the method of increasing the refractive index of the microlens shown in the embodiment can be obtained. Here, the composite focal length of the microlens is given by f = f1 × f2 / (f1 + f2-d). For example, f1 is 200 μm and f2 is 25 μm.
When 0 μm and d are 85 μm, the combined focal length f becomes 137 μm, and focal lengths shorter than the focal lengths of the respective microlenses 57 and 58 are obtained. The same effect can be obtained by stacking three or more microlenses. Since the synthetic focal length f is shortened, the pixel arrangement pitch can be further miniaturized.

[0018]

As described above, according to the present invention, for example, in a small and high-definition display device in which the pixel arrangement pitch is 20 μm or less, the refractive index of the microlens is 1.60 to 1.60.
By designing in the range of 1.70, a microlens with a short focal length is realized, and the efficiency of collecting incident light divided into three primary color components is improved. Alternatively, by stacking microlenses in multiple layers, a function equivalent to that of a microlens having a short focal length is realized. By using a display device having such a configuration in a projector, the size of the entire projector can be reduced, which can contribute to cost reduction.

[Brief description of drawings]

FIG. 1 is a schematic partial sectional view showing a first embodiment of a transmissive display device according to the present invention.

FIG. 2 is a schematic diagram showing a planar shape of the first embodiment.

FIG. 3 is a graph showing the relationship between the effective aperture ratio and the microlens / pixel distance.

FIG. 4 is a plan view showing how incident light is condensed by a microlens.

FIG. 5 is a schematic diagram showing a condensed state of incident light by a microlens.

FIG. 6 is a graph showing the relationship between the effective aperture ratio and the refractive index of microlenses.

FIG. 7 is a schematic partial sectional view showing a second embodiment of the transmissive display device according to the present invention.

FIG. 8 is a schematic view showing a conventional single plate projector.

FIG. 9 is a schematic diagram showing a conventional three-plate type projector.

FIG. 10 is a schematic view showing a projector adopting a conventional color filterless system.

[Explanation of symbols]

 0 transmissive display device 1 transparent substrate 2 transparent substrate 3 black matrix 4 electro-optical material 5 incident light 6 emitted light 7 microlens 10 opening 11 light shielding part

Claims (3)

[Claims] 1. A pair of transparent substrates, which are bonded to each other through a predetermined gap and have electrodes forming pixels arranged at a constant pitch, and a transmittance of incident light held in the gap for each pixel. A transmissive display device having an electro-optical substance that is modulated into light and converted into emitted light, and a microlens that condenses the three primary color components of incident light, which are separated from each other with a predetermined angle difference, to corresponding pixels. The microlenses are arranged close to each other on the incident light side from the pixels by an optical distance determined by the array pitch of the miniaturized pixels and the angular difference of the three primary color components, and the optical distances are close to each other. Accordingly, the transmission type display device is characterized in that the refractive index is set in the optimum range to shorten the focal length of the microlens. 2. The refractive index of the microlens is 1.60 corresponding to the arrangement pitch of pixels designed to be 20 μm or less.
2. The transmissive display device according to claim 1, wherein the transmissive display device is set to an optimum range of 1.70. 3. A pair of transparent substrates, which are joined to each other through a predetermined gap and have electrodes forming pixels arranged at a constant pitch, and a transmittance of incident light held in the gap for each pixel. A transmissive display device having an electro-optical material that is modulated into light and converted into emitted light, and an optical means that condenses the three primary color components of the incident light, which are separated from each other with a predetermined angle difference, to corresponding pixels. The optical means is disposed close to the incident light side from the pixel by an effective distance determined by the array pitch of the miniaturized pixels and the angular difference of the three primary color components, and the optical means are arranged close to each other. A transmissive display device comprising a plurality of microlenses overlapping in the optical axis direction, and having a synthetic focal length shortened according to the effective distance of proximity.