Abstract:
Disclosed herein is a raster scanning-type display device using a diffractive optical modulator. The raster scanning-type display device includes an optical illumination unit, a diffractive optical modulator, and a projection unit. The optical illumination unit radiates light, which is emitted from a light source, in a spot beam form. The diffractive optical modulator causes an element to modulate the spot beam incident from the optical illumination unit, and generate diffracted light whose intensity is adjusted and which has a plurality of diffraction orders. The projection unit generates an image by projecting the diffracted light incident from the diffractive optical modulator onto a screen in a scanning spot beam form and performing raster scanning in which horizontal scanning and vertical scanning are alternated.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to a display device using a diffractive optical modulator and, more particularly, to a raster scanning-type display device using a diffractive optical modulator, which generates diffractive light whose intensity is adjusted by modulating a spot beam using one or more elements of a diffractive optical modulator, and then scans the generated diffractive light onto a screen in a scanning spot beam form and in a raster scanning fashion.  
         [0003]     2. Description of the Related Art  
         [0004]     With the development of micro technology, so-called micro Electro Mechanical Systems (MEMS) devices and small-sized equipment in which the MEMS devices are assembled have attracted significant attention.  
         [0005]     A MEMS device is a device in which an actuation body that is formed on a substrate, such as a silicon substrate or a glass substrate, in a micro-structure form and is configured to output a mechanical actuation force, is electrically and mechanically combined with a semiconductor Integrated Circuit (IC) that is configured to control the actuation body. The MEMS device is basically characterized in that the actuation body having a mechanical structure is part of the device, and the operation of the actuation body is electrically performed using Coulomb&#39;s force between electrodes.  
         [0006]     Recently, an optical modulator using the MEMS device has been developed. An example of such an optical modulator is the Grating Light Valve (GLV) disclosed in U.S. Pat. No. 5,311,360 by Bloom et al. In this patent, the GLV can be constructed to operate in reflecting and diffracting modes.  
         [0007]     Meanwhile, in order to use a GLV device, that is, an optical modulation device to which the above-described MEM device is applied, for a display application, the development of a corresponding display device is required.  
       SUMMARY OF THE INVENTION  
       [0008]     Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a raster scanning-type display device using a diffractive optical modulator, which generates diffractive light whose intensity is adjusted by modulating a spot beam using one or more elements of a diffractive optical modulator, and then scans the generated diffractive light onto a screen in a scanning spot beam form and in a raster scanning fashion.  
         [0009]     In order to accomplish the above object, the present invention provides a raster scanning-type display device using a diffractive optical modulator, including an optical illumination unit for radiating light, which is emitted from a light source, in a spot beam form; a diffractive optical modulator for causing an element to modulate the spot beam incident from the optical illumination unit, and generate diffracted light whose intensity is adjusted and which has a plurality of diffraction orders; and a projection unit for generating an image by projecting the diffracted light incident from the diffractive optical modulator onto a screen in a scanning spot beam form and performing raster scanning in which horizontal scanning and vertical scanning are alternated.  
         [0010]     In addition, the present invention provides a raster scanning-type display device using a diffractive optical modulator, including an optical illumination unit for radiating light, which is emitted from a light source in a spot beam form; a diffractive optical modulator for causing a plurality of elements to modulate the spot beam incident from the optical illumination unit, and generate diffracted light whose intensity is adjusted and which has a plurality of diffraction orders; and a projection unit for generating an image by projecting the diffracted light incident from the diffractive optical modulator onto a screen in a scanning spot beam form and performing raster scanning in which horizontal scanning and vertical scanning are alternated. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0012]      FIG. 1  is a block diagram showing the construction of a raster scanning-type display device using a diffractive optical modulator according to an embodiment of the present invention;  
         [0013]      FIG. 2A  is a perspective view of a recess and diffractive optical modulator used in the present invention, and  FIGS. 2B and 2C  are perspective views of open hole-based diffractive optical modulators used in the present invention,  
         [0014]      FIG. 3A  is a plan view showing the case where circular spot beams are illuminated on the upper micromirror of one element of the open hole-based diffractive optical modulator according to an embodiment of the present invention, and  FIG. 3B  is a plan view showing the case where circular spot beams are illuminated on the upper micromirrors of four elements of the open hole-based diffractive optical modulator according to an embodiment of the present invention; and  
         [0015]      FIG. 4  is a diagram showing the construction of the projection unit of  FIG. 1  in detail. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     A raster scanning-type display device using a diffractive optical modulator according to a preferred embodiment of the present invention will now be described with reference to the accompanying drawings.  
         [0017]      FIG. 1  is a block diagram showing the construction of a raster scanning-type display device using a diffractive optical modulator according to an embodiment of the present invention.  
         [0018]     Referring to  FIG. 1 , the raster scanning-type display device using the diffractive optical modulator according to the embodiment of the present invention includes an optical display system  102  and an electronic display system  104 . The optical display system  102  includes a laser  106 , an optical illumination unit  108  for generating a circular or elliptical spot beam in order to radiate light, which is emitted from the laser  106 , onto a diffractive optical modulator  110  in a circular or elliptical spot beam form, the diffractive optical modulator  110  for diffracting the spot beam illuminated from the optical illumination unit  108  and, thereby, generating diffracted light having desired diffraction orders, that is, diffracted light having a plurality of diffraction orders the intensity of which is adjusted, an optical filter unit  112  for separating the diffracted light, which has a plurality of diffraction orders and is emitted by the diffractive optical modulator  110 , according to order and passing diffracted light having desired orders therethrough, a projection unit  116  for scanning the diffracted light, which passes through the optical filter unit  112 , onto a display screen  118  in a scanning spot beam form and in a raster scanning fashion, and the display screen  118 .  
         [0019]     The electronic display system  104  is connected with the laser  106 , the diffractive optical modulator  110 , and the projection unit  116 .  
         [0020]     The electronic display system  104  provides power to the laser  106 . The laser  106  emits laser illumination. In this case, the section of the laser illumination is a circle, and the profile of the light intensity thereof is a Gaussian distribution. For example, the laser  106  (which actually includes Red (R), Green (G), and Blue (B) light sources) may sequentially emit R, G, and B light beams. The optical illumination unit  108  converts the laser illumination, which is emitted by the laser  106 , into a circular or elliptical spot beam, and focuses it on the diffractive optical modulator  110 . The optical illumination unit  108  may be constructed, for example, using a convex lens (not shown), or by a convex lens (not shown) and a collimating lens (not shown).  
         [0021]     Meanwhile, when the circular or elliptical spot beam is incident from the optical illumination unit  108 , the diffractive optical modulator  110  diffracts the spot beam light under the control of the electronic display system  104 , and thereby generates diffracted light having a plurality of diffraction orders. At this time, the intensity of the diffracted light having desired diffraction orders is appropriately adjusted.  
         [0022]     Examples of the diffractive optical modulator  110  are shown in  FIGS. 2A  to  2 C.  FIG. 2A  is a perspective view of a recess and diffractive optical modulator that uses piezoelectric material and is used in the present invention, and  FIGS. 2B and 2C  are perspective views of open hole-based diffractive optical modulators that use piezoelectric material and are used in the present invention.  
         [0023]     Referring to  FIG. 2A , the recess and diffractive optical modulator used in the present invention includes a silicon substrate  210  and a plurality of elements  212   a  to  212   n.    
         [0024]     In this case, the plurality of elements  212   a  to  212   n  may constitute a single-panel diffractive optical modulator by having uniform widths and being uniformly arranged. Furthermore, the plurality of elements  212   a  to  212   n  may constitute a single-panel diffractive optical modulator by having widths different from each other and being alternately arranged. Furthermore, the elements  212   a  to  212   n  may be spaced apart the same distance (almost the same distance as the widths of the elements  212   a  to  212   n ). In this case, a micromirror layer formed over the entire upper surface of the silicon substrate  210  reflects and diffracts incident light.  
         [0025]     The silicon substrate  210  is provided with a recess to define an air space for elements  212   a  to  212   n , an insulation layer  211  is disposed on the silicon substrate  210 , and the end portions of the elements  212   a  to  212   n  are attached beside the recess.  
         [0026]     Each of the elements (although only a representative description of the element indicated by reference numeral  212   a  is made, the descriptions of the others  212   b  to  212   n  are the same) has a ribbon shape, and is provided with a lower support  213   a , the lower surfaces of both ends of which are attached beside the recess of the silicon substrate  210  such that the center portion of the element is spaced apart from the recess of the silicon substrate  210 , and a portion thereof located above the recess in the silicon substrate  210  is able to move upward and downward.  
         [0027]     Furthermore, the element  212   a  includes a lower electrode layer  214   a  disposed on the left end portion of the lower support  213   a  and configured to provide piezoelectric voltage, a piezoelectric material layer  215   a  disposed on the lower electrode layer  214   a  and configured to generate upward and downward driving force by contracting and expanding when voltage is applied to both sides thereof, and an upper electrode layer  216   a  disposed on the piezoelectric material layer  215   a  and configured to provide piezoelectric voltage to the piezoelectric material layer  215   a.    
         [0028]     Furthermore, the element  212   a  includes a lower electrode layer  214   a  disposed on the right end portion of the lower support  213   a  and configured to provide piezoelectric voltage, a piezoelectric material layer  215   a  disposed on the lower electrode layer  214   a  and configured to generate upward and downward driving force by contracting and expanding when voltage is applied to both sides thereof, and an upper electrode layer  216   a  disposed on the piezoelectric material layer  215   a  and configured to provide piezoelectric voltage to the piezoelectric material layer  215   a.    
         [0029]      FIG. 2B  is a perspective view of an open hole-based diffractive optical modulator used in the present invention. Referring to  FIG. 2B , the open hole-based diffractive optical modulator includes a silicon substrate  221 , an insulation layer  222 , a lower micromirror  223 , and a plurality of elements  230   a  to  230   n.    
         [0030]     In this case, the lower micromirror  223  is deposited on the upper portion of the silicon substrate  221 , and diffracts incident light by reflecting it. The lower micromirror  223  may be formed of a material such as metal (Al, Pt, Cr or Ag).  
         [0031]     Each of the elements (although only a representative description of the element indicated by reference numeral  230   a  is made, the others are the same) has a ribbon shape, and is provided with a lower support  231   a , the lower surfaces of the two ends of which are respectively attached on two sides beside the recess of the silicon substrate  221  such that the center portion of the element is spaced apart from the recess of the silicon substrate  221 .  
         [0032]     Piezoelectric layers  240   a  and  240   a ′ are formed on both sides of the lower support  231   a , and the driving force of the element  230   a  is provided to the lower support  231   a  by the contraction and expansion of the piezoelectric layers  240   a  and  240   a′.    
         [0033]     Furthermore, the left and right piezoelectric layers  240   a  and  240   a ′ include lower electrode layers  241   a  and  241   a ′ for providing piezoelectric voltage, piezoelectric material layers  242   a  and  242   a ′ disposed on the lower electrode layers  241   a  and  241   a ′ and configured to generate upward and downward driving force by contracting and expanding when voltage is applied to both sides thereof, and upper electrode layers  242   a  and  242   a ′ disposed on the piezoelectric material layers  242   a  and  242   a ′ and configured to provide piezoelectric voltage to the piezoelectric material layers  242   a  and  242   a ′. When voltage is applied to the upper electrode layers  243   a  and  243   a ′ and the lower electrode layers  241   a  and  241   a ′, the piezoelectric material layers  242   a  and  242   a ′ contract or expand, thus causing the lower support  231   a  to move upward or downward.  
         [0034]     Meanwhile, an upper micromirror  250   a  is deposited on the center portion of the lower support  231   a , and a plurality of open holes  251   a   1  to  251   a   4  is formed therein. In this case, although it is preferred that each of the open holes  251   a   1  to  251   a   4  be formed in a rectangular shape, they may be formed in any closed-curve shape, such as a circular shape or an elliptical shape. Furthermore, the open holes  251   a   1  to  251   a   4  are characteristically arranged in a direction perpendicular to the traverse direction of the silicon substrate  221 .  
         [0035]     The open holes  251   a   1  to  251   a   4  allow light incident on the element  230   a  to pass through the element  230   a  and be incident on the portions of the lower micromirror layer  223  corresponding to the open holes  251   a   1  to  251   a   4 , thus causing diffracted light, which is formed by the lower micromirror layer  223  and the upper micromirror layer  250   a , to form a single pixel.  
         [0036]     That is, for example, light reflected from portion (A) of the upper micromirror layer  250   a , through which the open holes  251   a   1  to  251   a   4  are formed, and light reflected from portion (B) of the lower micromirror layer  223  may form diffracted light corresponding to a single pixel.  
         [0037]     In this case, incident light, which has passed through the portion of the upper micromirror layer  250   a  through which the open holes  251   a   1  to  251   a   4  are formed, can be incident on the corresponding reflection surface of the lower micromirror layer  223 . When the interval between the upper micromirror layer  250   a  and the lower micromirror layer  223  is an odd multiple of λ/4, maximally diffracted light is generated.  
         [0038]     Meanwhile,  FIG. 2B  describes the open hole-based diffractive optical modulator characterized in that the open holes  251   a   1  to  251   a   4  are arranged in a direction perpendicular to the traverse direction of the silicon substrate  221 , and  FIG. 3  describes the open hole-based diffractive optical modulator provided with the open holes  251   a   1  to  251   a   4  arranged in the traverse direction of the silicon substrate  221 .  
         [0039]      FIG. 3A  illustrates a plan view showing the case where circular R, G and B light beams are sequentially incident on the upper micromirror  310   a  of one element of the open hole-based diffractive optical modulator according to an embodiment of the present invention.  
         [0040]     Referring to  FIG. 3A , circular R, G and B light beams are sequentially incident on some  310   a - 1  and  310   a - 2  of all of the reflection surfaces  310   a - 1  to  310   a - 3  of the upper micromirror  310   a , and all of the holes  311   a - 1  and  311   a - 2  of the upper micromirror  310   a.    
         [0041]     As described above, when a circular spot beam is incident on the reflection surfaces  310   a - 1  and  310   a - 2  of the upper micromirror  310   a  and the holes  311   a - 1  and  311   a - 2  of the upper micromirror  310   a,  the incident circular spot beam is diffracted due to the step difference that exists due to the reflection surfaces (not shown) of a lower micromirror (not shown) corresponding to the reflection surfaces  310   a - 1  and  310   a - 2  and holes  311   a - 1  and  311   a - 2  of the upper micromirror  310   a  and, thereby, diffracted light having a plurality of diffraction orders is generated.  
         [0042]     In this case, when the step difference between the reflection surfaces  310   a - 1  and  310   a - 2  of the upper micromirror  310   a  and the corresponding reflection surfaces of the lower micromirror is varied by moving the upper micromirror  310   a  upward and downward, the intensity of the diffracted light varies, so that a two-dimensional image can be generated while raster scanning onto a screen (not shown) is performed.  
         [0043]     In this case, although a description of the case where circular spot beams are incident on the upper micromirror  310   a  of the element was made above, the same description applies in the case where elliptical spot beams are incident on the upper micromirror  310   a.    
         [0044]      FIG. 3B  illustrates a plan view showing the case where circular R, G and B light beams are sequentially incident on the upper micromirrors  310   a ′ to  310   d ′ of four elements of the open hole-based diffractive optical modulator according to an embodiment of the present invention.  
         [0045]     Referring to  FIG. 3B , it can be seen that in the first upper micromirror  310   a ′, which belongs to the upper micromirrors  310   a ′ to  310   d ′ of the four elements, the circular spot beams are incident on some  310   a ′- 2  and  310   a ′- 3  of all of the reflection surfaces  310   a ′- 1  to  310   a ′- 4  and some  311   a ′- 2  of all of the holes  311   a ′- 1  to  311   a ′- 3 . Furthermore, it can be seen that in the second upper micromirror  311   b,  the circular spot beams are incident on all of the reflection surfaces  310   b ′- 1  to  310   b ′- 4  and all of the holes  311   b ′- 1  to  311   b ′- 3 . Furthermore, it can be seen that in the third upper micromirror  310   c ′, the circular spot beams are incident on all of the reflection surfaces  310   c ′- 1  to  310   c ′ 4  and all of the holes  311   c ′- 1  to  311   c ′- 3 . Furthermore it can be seen that in the fourth upper micromirror  310   d ′, the circular spot beams are incident on some  310   d ′- 2  and  310   d ′- 3  of all of the reflection surfaces  310   d ′- 1  to  310   d ′- 4  and some  311   d ′- 2  of all of the holes  311   d ′- 1  to  311   d ′- 3 . In this case, although, in the upper micromirrors  310   a ′ to  310   d ′ of the four elements, the circular spot beams are sequentially incident on the some of the reflection surfaces and the some of the holes, the incident area may be widened in the case where elliptical or square spot beams, rather than circular spot beams, are used, according to the application, and the circular spot beams may be incident on all of the reflection surfaces and all of the holes.  
         [0046]     As described above, when circular spot beams are incident on the some of the reflection surfaces and the some of the holes in the upper micromirrors  310   a ′ to  310   d ′, the incident circular spot beams are diffracted due to the step difference that exists due to some of the reflection surfaces (not shown) of a lower micromirror (not shown), corresponding to the some of the reflective surfaces of the upper micromirror  310   a ′ to  310   d ′ and the holes of the upper micromirror  310   a ′ to  310   d ′ and, thereby, diffracted light having a plurality of diffraction orders is generated.  
         [0047]     In this case, when the step difference between the reflection surfaces of the upper micromirror  310   a ′ to  310   d ′ and the corresponding reflection surfaces of the lower micromirror is varied by moving the one or more upper micromirrors  310   a ′ to  310   d ′ upward and downward, the intensity of the diffracted light varies, so that a two-dimensional image can be generated while raster scanning onto a screen (not shown) is performed.  
         [0048]     As describe above, when the diffracted light is generated using the plurality of elements, diffracted light having relatively wide light intensity selectivity can be generated, in contrast to when diffracted light is generated using a single element. For example, when diffracted light is generated using four elements, it is possible to cause only a single element, two elements, three elements or four elements to generate diffracted light Accordingly, when creating diffracted light, four diffracted light beams having different intensities can be acquired in the above-described manner, so that light intensity selectivity can be improved.  
         [0049]     In this case, although a description of the case where circular spot beams are incident on the upper micromirrors  310   a ′ to  310   d ′ of the elements was made above, the same description applies in the case where elliptical spot beams are incident on the upper micromirrors  310   a ′ to  310   d′.    
         [0050]     Meanwhile, the optical filter unit  112  separates diffracted light having desired orders therefrom when diffracted light having a plurality of diffraction orders is incident thereon. As an example, the optical filter unit is composed of a Fourier lens (not shown) and a Fourier filter (not shown), and selectively passes 0-order diffracted light or ±1-order diffracted light, among entering diffracted light beams, therethrough. Although the optical filter unit  112 , as shown in  FIG. 1 , is located behind the diffractive optical modulator  110 , the optical filter unit  112  is not limited thereto and may be located behind the projection unit  116 . Furthermore, in the case where the optical filter unit  112  is located behind the projection unit  116 , the diffracted light having a plurality of diffraction orders travels sufficiently and a predetermined distance between the diffraction orders is ensured, so that a separate Fourier lens for ensuring sufficient distance between the diffraction orders is not necessary, and the optical filter unit  112  may be implemented using a Fourier filter alone.  
         [0051]     Furthermore, the projection unit  116 , as shown in  FIG. 4 , is composed of a condenser lens  116   a , a scanning mirror  116   b,  and a projection lens  116   c,  and projects entering diffracted light onto the screen  118 . That is, the projection unit  116  plays the role of focusing diffracted light, entering through the Fourier filter (not shown), onto the screen  118  and generating a spot.  
         [0052]     In this case, the condenser lens  116   a  condenses the diffracted light such that the diffracted light beams, which have passed through the Fourier filter (not shown), can be focused on the screen  118 . A concave lens (not shown) may be further provided downstream of the condenser lens  116   a , so that the diffracted light that has passed through the filter  112   b  may be condensed, converted into parallel light, and then projected onto the scanning mirror  116   b.    
         [0053]     The scanning mirror  116   b  is composed of an X scanning mirror  116   ba  and a Y scanning mirror  116   bb.  The X scanning mirror  116   ba  scans an incident spot on the screen  118  leftward and rightward under the control of the electronic display system  104 , and the Y scanning mirror  116   ba  scans an incident spot onto the screen  118  upward and downward under the control of the electronic display system  104 . The scanning mirror  116   b  may be constructed using an X-Y scanning mirror (not shown) that can perform both X-axis scanning and Y-axis scanning, rather than a combination of the X scanning mirror  116   ba  and the Y scanning mirror  116   bb.    
         [0054]     A description of the raster scanning is made in detail. As shown in  FIG. 4 , left-right scanning is first performed from the left to the right by the X scanning mirror  116   ba  and then up-down scanning to a subsequent line is performed by the Y scanning mirror  116   bb.  Thereafter, right-left scanning is performed from the right to the left by the X scanning mirror  116   ba  and then up-down scanning to a subsequent line is performed again by the Y scanning mirror  116   bb.  The above-described operation of the X scanning mirror  116   ba , which is repeated, is referred to as raster scanning. As another example of raster scanning, a series of operations, in which scanning is performed from the left to the right, up-down scanning to the right side of a subsequent line is performed, scanning is performed from the right to the left, the line is changed, and then scanning is performed from the left to the right, may be repeated.  
         [0055]     The electronic display system  104  operates the scanning mirror  116   b  of the projection unit  116 . In order to form a two-dimensional image on the display screen  118 , the projection unit  116  projects the scanning spot beam onto the display screen  118  and scans the scanning spot beam over the display screen  118  in a raster scanning fashion.  
         [0056]     Meanwhile, in FIGS.  1  to  4 , although a two-dimensional image is generated using a single scanning spot beam that takes chare of a single pixel, it is possible to generate a two-dimensional image using scanning spot beams that take charge of a small number of pixels and correspond to the number of the pixels.  
         [0057]     Furthermore, in FIGS.  1  to  4 , although a color image is generated using a single diffractive optical modulator, it may be possible to generate a color image using three diffractive optical modulators. In this case, two additional diffractive optical modulators are necessary for implementation of the color image.  
         [0058]     In accordance with the present invention described above, a line beam shaper that is necessary for a one-dimensional illumination system, that is, an accurate optical system that converts circular light to linear light, is no longer necessary.  
         [0059]     Furthermore, in accordance with the present invention, one or a small number of scanning spot beams that take charge of one or a small number of pixels are used, so that the optical system can be simplified.  
         [0060]     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.