JP2014194472A - Microlens array, optical modulator, and projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microlens array capable of reducing speckle noise.SOLUTION: A microlens array is provided with a plurality of microlenses 201 that are two-dimensionally arrayed. The shape of one microlens 201, in a cross section including the optical axis of the one microlens 201 of the plurality of microlenses 201, comprises a curved portion 202a and a substantially linear portion 202b.

Description

  The present invention relates to a microlens array, a light modulation device, and a projector.

  2. Description of the Related Art Conventionally, a projector that illuminates a light modulation element with illumination light emitted from a light source and enlarges and projects the image light modulated and emitted by the light modulation element onto a screen by a projection optical system is widely known.

  As a light source of such a projector, a discharge lamp such as an ultrahigh pressure mercury lamp has been conventionally used. On the other hand, this type of discharge lamp has problems such as a relatively short life, difficult to light instantaneously, and ultraviolet rays emitted from the lamp deteriorate the liquid crystal light bulb.

  Therefore, a laser light source such as a semiconductor laser that can obtain light with high luminance and high output has attracted attention as a light source for a projector that can replace a discharge lamp. Compared with a conventional discharge lamp, the laser light source has advantages such as miniaturization, excellent color reproducibility, instant lighting, and long life.

  On the other hand, the laser light emitted from the laser light source is coherent (coherent) light, so when used as a light source for a projector, speckle patterns called speckles caused by interference are displayed on the screen, degrading display quality. Cause it.

  For this reason, in conventional projectors, for example, using a diffusing optical element, the spatial distribution of the light intensity on the exit pupil plane of the projection optical system is made uniform, thereby reducing the display quality due to the generation of speckles described above (so-called specs). (See, for example, Patent Document 1).

  On the other hand, in order to perform bright video display with excellent display quality in a projector, it is necessary to efficiently make illumination light incident on an image forming region in which a plurality of pixels of a light modulation element are arranged.

  However, in a conventional projector, illumination light is incident on an image forming area that does not contribute to image light formation, for example, between adjacent pixels or a light-shielding portion covered with a mask layer in the pixel. Become. Therefore, there is a problem that the use efficiency of the illumination light is deteriorated by the amount of illumination light incident on such a region.

  In view of this, illumination light is efficiently incident on each pixel in the image forming region using a microlens array in which a plurality of microlenses are two-dimensionally arranged (for example, see Patent Document 2). reference.).

  Specifically, this microlens array is attached on the surface of the image forming region so that a plurality of microlenses are positioned at positions corresponding to a plurality of pixels, respectively. Thereby, the illumination light condensed by each microlens can be made incident on each pixel in the image forming area.

JP 2011-180281 A JP 2008-281669 A

  By the way, the conventional microlens array is for making illumination light efficiently enter each pixel in the image forming region. Therefore, in order to reduce the speckle noise described above, it is necessary to separately provide an optical element for making the spatial distribution of the light intensity on the exit pupil plane of the projection optical system uniform. However, when such an optical element is added, not only the projector is reduced in size (light weight) but also in terms of cost.

  The present invention has been proposed in view of such conventional circumstances, a microlens array capable of reducing speckle noise, a light modulation device including such a microlens array, and Another object of the present invention is to provide a projector including such a light modulation device.

  To achieve the above object, a microlens array according to the present invention is a microlens array in which a plurality of microlenses are two-dimensionally arranged, and an optical axis of one microlens among the plurality of microlenses. In the cross section including the first microlens, the shape of the one microlens includes a curved portion and a substantially linear portion.

  According to the configuration of the microlens array, the spatial distribution of the light intensity on the exit pupil plane of the projection optical system can be made uniform, so that speckle generation can be suppressed.

  Further, it is preferable that the curved portion is provided between a top portion of the one microlens and the substantially linear portion.

  According to this configuration, since the spatial distribution of the light intensity on the exit pupil plane of the projection optical system can be made uniform, the generation of speckle can be suppressed.

    The inclination angle of the substantially linear portion with respect to the bottom surface of the one microlens is preferably 30 ° or more and 50 ° or less.

  According to this configuration, it is possible to increase the utilization efficiency of light collected by each microlens while suppressing generation of speckle.

  The microlens has a curved surface portion obtained by rotating the curved portion around the optical axis, and a slope portion obtained by rotating the substantially linear portion around the optical axis. It is preferable that the curved surface portion is continuous with the slope portion.

  According to this configuration, since the spatial distribution of the light intensity on the exit pupil plane of the projection optical system can be made uniform, the generation of speckle can be suppressed.

  The light modulation device according to the present invention includes any one of the above-described microlens arrays and a light modulation element having an image forming region in which a plurality of pixels are arranged, and the microlens array includes the plurality of pixels. Among these, the one microlens is provided so as to correspond to one pixel.

  According to the configuration of the light modulation device, the spatial distribution of the light intensity on the exit pupil plane of the projection optical system can be made uniform. Therefore, generation of speckle can be suppressed and light condensed by each microlens can be efficiently incident on each pixel in the image forming area.

  A projector according to the present invention includes an illumination device that irradiates illumination light, a light modulation device that forms image light obtained by modulating the illumination light according to image information, a projection optical system that projects the image light, And the above-described light modulation device is used as the light modulation device.

  According to the configuration of the projector, bright display with excellent image quality can be performed.

  Moreover, the structure provided with the laser light source may be sufficient as the said illuminating device.

  According to this configuration, high luminance and high output light can be obtained, and the light source can be miniaturized.

  The laser light source may be an array light source in which a plurality of semiconductor lasers are arranged.

  According to this configuration, light with higher luminance and higher output can be obtained using an array light source in which a plurality of semiconductor lasers are arranged.

1 is a schematic diagram illustrating a schematic configuration of a projector according to an embodiment of the invention. It is a top view which shows schematic structure of the liquid crystal panel to which the micro lens array was attached. FIG. 3 is a cross-sectional view taken along line H-H ′ in FIG. 2. It is sectional drawing which expands and shows a micro lens. It is sectional drawing for demonstrating the manufacturing method of a micro lens. It is a graph which shows the relative relationship between the area (diameter) of the intensity image in the exit pupil of a microlens, and speckle contrast. It is a graph which shows the relative relationship between the uniformity of the intensity image in the exit pupil of a microlens, and speckle contrast. It is the graph which calculated | required the uniformity of the intensity image in the exit pupil with respect to inclination-angle (theta).

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.

(projector)
First, an example of the projector 10 shown in FIG. 1 will be described as an embodiment of the present invention. FIG. 1 is a schematic diagram showing a schematic configuration of the projector 10.

  As shown in FIG. 1, the projector 10 is a projection type image display device that displays a color video (image) on a screen (projection surface) SCR. Further, the projector 10 uses three liquid crystal light valves (liquid crystal panels) each corresponding to each color light of red light (R), green light (G), and blue light (B) as a light modulation device. . Further, the projector 10 uses a semiconductor laser (laser light source) that can obtain light with high luminance and high output as a light source of the illumination device.

  Specifically, the projector 10 includes a first illumination device 11R that emits red light (R) that is first color light, and a second illumination device that emits green light (G) that is second color light. 11G, the third illumination device 11B that emits the blue light (B) that is the third color light, and each color light R, G, B is modulated according to the image information and corresponds to each color light R, G, B From the light modulation device 12R, the light modulation device 12G, and the light modulation device 12B that form the image light respectively, the combining optical system 13 that combines the image light from each of the light modulation devices 12R, 12G, and 12B, and the combining optical system 13 Projection optical system 14 for projecting the image light toward the screen SCR.

  The first illuminating device 11R, the second illuminating device 11G, and the third illuminating device 11B include a laser light source 15R, a laser light source 15G, and a laser light source 15B that respectively emit laser light corresponding to the respective color lights R, G, and B. It has the same structure except having. Therefore, in the following description, the first lighting device 11R will be described, and descriptions of the second lighting device 11G and the third lighting device 11B will be omitted.

  The first illumination device 11R includes a laser light source 15R that emits laser light, a diffractive optical element 16 that receives laser light from the laser light source 15R, and a collimating lens 17 that receives diffracted light from the diffractive optical element 16. And have.

  The laser light source 15 </ b> R is made of, for example, a semiconductor laser, and emits laser light that is coherent light toward the diffractive optical element 16. The laser light source 15R is not limited to one having a single semiconductor laser, but may be an array light source in which a plurality of semiconductor lasers are arranged.

  The diffractive optical element 16 includes, for example, a computer generated hologram (CGH). The diffractive optical element 16 has a function of making the intensity distribution of the diffracted light incident on the image forming area of the light modulation device 12R uniform by diffracting the laser light from the laser light source 15R. In the present invention, the intensity distribution of illumination light may be made uniform by using an integrator optical system such as a multi-lens array or a rod lens instead of the diffractive optical element 16.

  The collimating lens 17 is disposed on the light incident surface side of the light modulation device 12R and has a function of collimating diffracted light incident on the light modulation device 12R.

  Each of the three light modulation devices 12R, 12G, and 12B includes a transmissive liquid crystal light valve (liquid crystal panel). The three light modulators 12R, 12G, and 12B form image light obtained by modulating the color lights R, G, and B according to image information. A pair of polarizing plates (not shown) are arranged on the light incident side and light emission side of each of the light modulation devices 12R, 12G, and 12B, and allows only linearly polarized light in a specific direction to pass therethrough. It is a mechanism.

  The synthesizing optical system 13 is composed of a cross dichroic prism, synthesizes the image light incident from each of the light modulation devices 12R, 12G, and 12B, and emits the synthesized image light toward the projection optical system 14.

  The projection optical system 14 includes a projection lens, and enlarges and projects the image light combined by the combining optical system 13 toward the screen SCR. Thereby, an enlarged color video (image) is displayed on the screen SCR.

(Light modulation device)
By the way, for the light modulation devices 12R, 12G, and 12B, for example, a liquid crystal panel (light modulation element) 100 to which a microlens array 200 as shown in FIGS. 2 and 3 is attached is used. However, FIG. 3 does not show a surface layer 207 to be described later. 2 is a plan view showing a schematic configuration of the liquid crystal panel 100 to which the microlens array 200 is attached. FIG. 3 is a cross-sectional view taken along line HH ′ in FIG.

  The liquid crystal panel 100 generally includes an element substrate 101, a counter substrate 102 disposed to face the element substrate 101, and a liquid crystal layer 103 disposed between the element substrate 101 and the counter substrate 102.

  A light shielding layer 106 having a rectangular frame shape in plan view is formed on the surface of the counter substrate 102 facing the liquid crystal layer 103. Inside the light shielding layer 106 is an image forming area 107 in which a plurality of pixels G are arranged in a matrix. Further, a light shielding film 115 is provided for partitioning a region corresponding to each pixel G into a matrix. The region covered with the light shielding film 115 is a region that does not contribute to the formation of image light.

  A plurality of pixel electrodes 113 are provided corresponding to the respective pixels G on the side of the element substrate 101 facing the liquid crystal layer 50. Each pixel electrode 113 is connected to a switching element (not shown) such as a thin film transistor (TFT). The liquid crystal panel 100 has a configuration roughly described above.

(Micro lens array)
The microlens array 200 includes a lens substrate on which a plurality of microlenses 201 are two-dimensionally arranged, and is attached to a surface of the counter substrate 102 opposite to the liquid crystal layer 103. Further, the microlens array 200 is positioned on the surface of the image forming region 107 so that the plurality of microlenses 201 are positioned at positions corresponding to the plurality of pixels G, respectively. That is, the microlens array 200 is provided so that one microlens 201 corresponds to one pixel G.

FIG. 4 is an enlarged cross-sectional view showing one microlens 201.
In the cross section including the optical axis Z of the microlens 201, the shape of the microlens 201 includes a substantially linear portion 202b and a curved portion 202a. The curved portion 202a is provided between the apex AP of the microlens 201 and the substantially straight portion 202b.

  The microlens 201 has a curved surface portion 203a obtained by rotating the curved portion 202a around the optical axis Z and a slope obtained by rotating the substantially linear portion 202b around the optical axis Z. And a refracting surface 204 including a portion 203b. In the refracting surface 204, the curved surface portion is continuous with the slope portion.

  Next, a manufacturing method of the microlens 201 will be described with reference to FIG. FIG. 5 is a cross-sectional view of the lens substrate 205 including the axis Z ′ that is the optical axis Z of the microlens 201.

  First, a surface layer 207 having an etching rate higher than that of the lens substrate is formed on one surface of the lens substrate 205.

  Next, a mask layer 208 having pinholes 210 is formed on the surface layer 207. Then, the surface layer 207 and the lens substrate 205 are etched by wet etching through the pinhole 210. Since the etching rate of the surface layer 207 is higher than the etching rate of the lens substrate 205, the etching of the surface layer 207 proceeds faster in the direction parallel to the surface of the lens substrate 205 than the lens substrate 205.

  As a result, a concave portion 211 serving as a mold of the microlens 201 is formed on one surface of the lens substrate 205. After removing the mask 208, the microlens 201 can be formed by filling the recess 211 with a lens member 206 made of, for example, an ultraviolet curable resin.

  The curved portion 202a can be approximated as an arc centered on the open end 209 of the mask layer 208 in the cross-sectional view shown in FIG. In that case, the substantially straight portion 202b can be approximated to be a tangent at the end of the curved portion 202a. Note that a region 212 of the recess 211 corresponding to the opening of the mask layer 208 is a flat portion. Therefore, a flat portion is formed at the top AP of the microlens 201.

Further, when the microlens 201 is formed by wet etching, the width w and height t of the microlens 201 and the diameter AD of the pinhole 210 have a relationship represented by the following expression.
W = 2 × (AD / 2 + t / sin θ)

  The curved surface portion 203a is a portion that functions as a convex lens in the central portion of the microlens 201 in plan view, and light incident on the curved surface portion 203a contributes to the formation of an effective area of the pixel G (image light formation while being condensed). It is injected toward the area.

  On the other hand, the inclined surface portion 203b is a portion that functions as a prism lens in the peripheral portion of the microlens 201 in plan view. The light incident on the slope portion 203b is refracted by the slope portion 203b and emitted toward the effective region of the pixel G (region contributing to the formation of image light).

Here, a graph showing the relative relationship between the area (diameter) of the light source image at the exit pupil of the projection optical system 14 and the speckle contrast is shown in FIG.
As shown in FIG. 6, the speckle contrast decreases as the area (diameter) of the light source image increases. A decrease in speckle contrast means that speckle noise is not easily recognized by an observer. This is because the larger the light source image at the exit pupil of the projection optical system 14, the wider the angular distribution of the intensity of light incident on the screen.

FIG. 7 is a graph showing the relative relationship between the uniformity of the light intensity distribution at the exit pupil of the projection optical system 14 and the speckle contrast.
As shown in FIG. 7, the higher the uniformity of the light intensity distribution at the exit pupil, the lower the speckle contrast. In order to reduce the speckle contrast, it is preferable to make the light intensity distribution uniform over the entire exit pupil.

  FIG. 8 shows the uniformity of the light intensity distribution at the exit pupil of the projection optical system 14 and the inclination angle θ for the microlenses ML1 to microlens ML6 having different inclination angles θ of the substantially linear portion 202b with respect to the bottom surface of the microlens. It is a figure which shows the relationship. The uniformity of the light intensity distribution at the exit pupil can be determined by the angular distribution of the intensity of light emitted from the light modulation device.

  The wider and more uniform the angular distribution of the intensity of light emitted from the light modulation device, the higher the uniformity of the light intensity distribution at the exit pupil. The uniformity of the light intensity distribution shown in FIG. 8 is a value obtained by normalizing the value obtained from the angle distribution of the intensity of the emitted light obtained by computer simulation with the maximum value.

  The curved portion 202a is approximated as an arc centered on the opening end 209 of the mask layer 208 in the cross-sectional view shown in FIG. 5, and the substantially straight portion 202b is a tangent at the end of the curved portion 202a. A computer simulation was performed with the approximation.

  Table 1 shows the tilt angle θ, the height t, the distance z from the bottom surface 203c to the liquid crystal layer 103, and the width W of the microlens ML1 to the microlens ML6.

  As shown in FIG. 8, in the case of the microlens ML4 having the inclination angle θ of 45 °, the uniformity of the light intensity distribution is the highest. On the other hand, in the case of the micro lens ML6 having the inclination angle θ of 55 °, the uniformity of the light intensity distribution is the lowest among the micro lenses ML1 to ML6.

  Table 2 shows the difficulty in recognizing speckle noise when each of the microlenses ML1 to microlens ML6 is used. In Table 2, the difficulty in recognizing speckle noise is represented by the number of +, and the greater the number of +, the more difficult it is to recognize the speckle noise.

  When the microlens ML4 is used, speckle noise is hardly recognized. When the microlens ML6 is used, the effect of reducing speckle noise is the lowest among the microlenses ML1 to microlens ML6. The effect of reducing speckle noise when the microlens ML6 is used is a level between the microlens ML5 and the microlens ML6.

  Note that the microlens according to the prior art does not include a substantially linear portion, which corresponds to a case where the inclination angle θ is 90 °. When the inclination angle θ is 90 °, the effect of reducing speckle noise is extremely low (denoted as − in Table 2).

  By using the microlens 201 according to the present invention, the uniformity of the light intensity distribution at the exit pupil of the projection optical system 14 can be improved. That is, light can be incident over a wide range of the exit pupil plane. Further, it is possible to reduce the concentration of incident light in a specific region of the exit pupil plane, for example, the center of the exit pupil plane. Thereby, the angular distribution of the intensity of light incident on the screen can be widened. Therefore, according to the present invention, speckle noise can be reduced.

  The inclination angle θ of the substantially linear portion 202b is preferably 30 ° or more and 50 ° or less with respect to the bottom surface (surface facing the counter substrate 102) 203c of the microlens 201. Thereby, speckle noise can be greatly reduced.

  The diameter of the microlens 201 (corresponding to the height t of the microlens 201) is preferably 90% or more of the diagonal length of the pixel G. Thereby, the light which does not pass the microlens 201 among the light which passes the pixel G can be reduced.

  In the liquid crystal panel 100 to which the microlens array 200 as described above is attached, the angular distribution of the intensity of light emitted from the liquid crystal panel 100 is widened and the uniformity is improved. Therefore, speckle noise in the image formed by the liquid crystal panel 100 is greatly reduced. Further, the light condensed by each microlens 201 can be efficiently incident on each pixel G in the image forming region 107. Therefore, in the projector 10 including the liquid crystal panel 100 to which such a microlens array 200 is attached, speckle noise is greatly reduced and bright display with excellent image quality can be performed.

  In addition, this invention is not necessarily limited to the thing of the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.

  In the present embodiment, the curved portion 202a has a substantially arc shape, but the curved portion 202a may have an aspherical shape or a free-form surface. Moreover, although the shape of the substantially linear part 202b is linear in this embodiment, the shape of the substantially linear part 202b may be bent. Further, the configuration is not limited to the configuration in which the substantially straight portion 202b is a tangent to the end portion of the curved portion 202a.

  In the above-described embodiment, the projector 10 including the three light modulation devices 12R, 12G, and 12B is exemplified. However, the projector 10 can be applied to a projector that displays a color image (image) with one light modulation device. Further, the light modulation device is not limited to the above-described liquid crystal panel, and for example, a digital mirror device (DMD: registered trademark of Texas Instruments Inc., USA) can be used.

DESCRIPTION OF SYMBOLS 10 ... Projector 11R ... 1st illumination device 11G ... 2nd illumination device 11B ... 3rd illumination device 12R, 12G, 12B ... Light modulation device (liquid crystal light valve) 13 ... Synthesis optical system 14 ... Projection optical system 15R, 15G, 15B ... Laser light source 16 ... Diffraction optical element 17 ... Parallelizing lens SCR ... Screen 100 ... Liquid crystal panel (light modulation element) 101 ... Element substrate 102 ... Counter substrate 103 ... Liquid crystal layer 107 ... Pixel formation region 113 ... Pixel electrode G ... Pixel 200 ... Microlens array 201 ... Microlens 202a ... Curved part 202b ... Substantially linear part 203a ... Curved surface part 203b ... Slope part 203c ... Bottom

Claims (8)

A microlens array in which a plurality of microlenses are two-dimensionally arranged,
In the cross section including the optical axis of one microlens among the plurality of microlenses, the shape of the one microlens includes a curved portion and a substantially linear portion.   2. The microlens array according to claim 1, wherein the curved portion is provided between a top portion of the one microlens and the substantially linear portion.   The microlens array according to claim 1 or 2, wherein an inclination angle of the substantially linear portion with respect to a bottom surface of the one microlens is 30 ° or more and 50 ° or less. The microlens is a curved surface portion obtained by rotating the curved portion around the optical axis, and a slope portion obtained by rotating the substantially linear portion around the optical axis, A refracting surface including
The microlens array according to claim 1, wherein the curved surface portion is continuous with the slope portion. The microlens array according to any one of claims 1 to 4,
A light modulation element having an image forming region in which a plurality of pixels are arranged,
The light modulation device, wherein the microlens array is provided so that the one microlens corresponds to one pixel of the plurality of pixels. An illumination device that emits illumination light;
A light modulation device for forming image light obtained by modulating the illumination light according to image information;
A projection optical system for projecting the image light,
A projector using the light modulation device according to claim 5 as the light modulation device.   The projector according to claim 6, wherein the illumination device includes a laser light source.   The projector according to claim 7, wherein the laser light source is an array light source in which a plurality of semiconductor lasers are arranged.

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