Abstract:
The present invention relates, in general, to a light modulator having a variable blaze diffraction grating and, more particularly, to a light modulator having a variable blaze diffraction grating, in which a diffraction member rotates due to piezoelectric force so as to incline a reflective surface.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates, in general, to a light modulator having a variable blaze diffraction grating and, more particularly, to a light modulator having a variable blaze diffraction grating, in which a diffraction member rotates due to piezoelectric force so as to incline a reflective surface.  
         [0003]     2. Description of the Prior Art  
         [0004]     Generally, optical signal processing technology has advantages in that a great amount of data is quickly processed in a parallel manner unlike a conventional digital information processing technology in which it is impossible to process a large amount of data in real-time, and studies have been conducted on the design and production of a binary phase only filter, an optical logic gate, a light amplifier, an image processing technique, an optical device, and a light modulator using a spatial light modulation theory.  
         [0005]     Of them, the spatial light modulator is applied to optical memory, optical display, printer, optical interconnection, and hologram fields, and studies have been conducted to develop displays employing it.  
         [0006]     The spatial light modulator is embodied by a reflective deformable grating light modulator  10  as shown in  FIG. 1 . The modulator  10  is disclosed in U.S. Pat. No. 5,311,360 by Bloom et al. The modulator  10  includes a plurality of reflective deformable ribbons  18 , which have reflective surface parts, are suspended on an upper part of a substrate  16 , and are spaced apart from each other at regular intervals. An insulating layer  11  is deposited on the silicon substrate  16 . Subsequently, a sacrificial silicon dioxide film  12  and a silicon nitride film  14  are deposited.  
         [0007]     The nitride film  14  is patterned by the ribbons  18 , and a portion of the silicon dioxide film  12  is etched, thereby maintaining the ribbons  18  on an oxide spacer layer  12  using a nitride frame  20 .  
         [0008]     In order to modulate light having a single wavelength of λ o , the modulator is designed so that thicknesses of the ribbon  18  and oxide spacer  12  are each λ o /4.  
         [0009]     Limited by the vertical distance (d) between the reflective surface  22  of each ribbon  18  and the reflective surface of the substrate  16 , the grating amplitude of the modulator  10  is controlled by applying voltage between the ribbon  18  (the reflective surface  22  of the ribbon  18  acting as a first electrode) and the substrate  16  (a conductive layer  24  of a lower side of the substrate  16  acting as a second electrode). In its undeformed state, with no voltage applied, the grating amplitude is λ o /2 and the total round-trip path difference between light beams reflected from the ribbon and substrate is one wavelength λ o , and thus; the phase of the reflected light is reinforced.  
         [0010]     Accordingly, in its undeformed state, the modulator  10  acts as a plane mirror when it reflects light. In  FIG. 2 , reference numeral  20  denotes incident light and reflected light in its undeformed state.  
         [0011]     When a proper voltage is applied between the ribbon  18  and substrate  16 , the electrostatic force enables the ribbon  18  to be moved downward toward a surface of the substrate  16 . At this time, the grating amplitude is changed to λ o /4. The total round-trip path difference is a half of a wavelength, and light reflected from the deformed ribbon  18  and light reflected from the substrate  16  are subjected to destructive interference.  
         [0012]     The modulator diffracts incident light  26  resulting from the interference. In  FIG. 3 , reference numerals  28  and  30  denote light beams diffracted in a ± diffractive mode (D+1, D−1) in a deformed state.  
         [0013]     However, the Bloom&#39;s light modulator adopts an electrostatic method to control the position of the micromirror, which has disadvantages in that the operating voltage is relatively high (usually, 20 V or so) and the correlation between the applied voltage and the displacement is not linear, resulting in unreliable light control.  
         [0014]     Meanwhile, Silicon Light Machines Inc. has suggested a blaze light valve device, in which blaze diffraction is conducted to control the intensity of light, as disclosed in Korean Patent Laid-Open Publication No. 2004-32908.  
         [0015]      FIG. 4  shows a perspective view of a blaze grating light valve according to conventional technology. The blaze grating light valve  120  comprises a substrate  122 , elongate members  124 , first posts  126  (only one post is shown), and second posts  128  (only one post is shown).  
         [0016]     The substrate  122  includes a first conductor  130 . It is preferable that each of the elongate members  124  include reflective first and second surfaces  132 ,  134 . The first and second surfaces  132 ,  134  form a blaze profile  136  for the elongate member  124 . One of the first posts  126  and one of the second posts  128  function to connect each elongate member  124  to the substrate  122 . Furthermore, the elongate member  124  is connected to the substrate  122  at first and second ends thereof (not shown).  
         [0017]      FIG. 5  is a perspective view of one of the elongate members  124  and a portion of the substrate  122 . Each elongate member  124  includes the reflective first and second surfaces  132 ,  134 . The first and second surfaces  132 ,  134  form the blaze profile  136 .  
         [0018]     The elongate member  124  is connected through the first and second posts  126 ,  128  to the substrate at the first and second ends thereof (not shown). Preferably, the elongate members  124 , the first posts  126 , and the second posts  128  are made of an elastic material. It is preferable that the elastic material include silicon nitride.  
         [0019]     Preferably, the first and second surfaces  132 ,  134  each include a reflector. It is preferable that the reflector include an aluminum layer. Alternatively, the reflector is made of another metal. Selectively, the reflector is a multilayer dielectric reflector. The substrate  122  includes the first conductor  130 . Preferably, the substrate  122  includes silicone, and a first conductive layer is doped polysilicone. If a visible spectrum is used, the portion of the elongate member  124  between the first post  126  and the second post  128  has a length of about 200 μm and a width of about 4.25 μm.  
         [0020]      FIG. 6  illustrates a second blaze grating light valve according to conventional technology. In the second blaze grating light valve  120 B, a second elongate member  124 C is used instead of the elongate member  124  of the blaze grating light valve  120 . In the second elongate member  124 C, a step profile  150  of the elongate member  124  is substituted by a flat surface  226  inclined at a blaze angle (γ).  
         [0021]     Meanwhile, U.S. Pat. No. 5,311,360 discloses a conventional blaze diffraction grating, which diffracts light by inclining a reflective surface using electrostatic force, as described in an example ( FIG. 7 ) thereof. However, the conventional blaze diffraction grating (disclosed in the patent application of Silicon Light Machines Inc. as well as U.S. Pat. No. 5,311,360) is problematic in that the generation force per unit volume is insufficient because of the use of electrostatic force, thus rotation displacement efficiency per unit input is poor.  
       SUMMARY OF THE INVENTION  
       [0022]     Therefore, the present invention has been made keeping in mind the above disadvantages occurring in the prior arts, and an object of the present invention is to provide a light modulator having a variable blaze diffraction grating, which has excellent rotation displacement efficiency per unit input.  
         [0023]     The above object can be accomplished by providing a light modulator having a variable blaze diffraction grating. The light modulator comprises a substrate; a pair of supporting members, which are provided on the substrate and spaced apart from each other; a plurality of diffraction members, which are connected to the supporting members at both ends thereof so as to be suspended on the substrate, which are arranged parallel to each other, and which are transversely bent; a plurality of reflective plates having reflective surfaces on upper sides thereof, which are attached to upper sides of the plurality of diffraction members, the adjacent reflective surfaces of which are parallel to each other; and a plurality of driving units, which moves the diffraction members upward or downward so that the reflective surfaces of the adjacent diffraction members are situated at a first position, in which the reflective surfaces form a flat mirror, or at a second position, in which the reflective surfaces diffract the incident light, thereby causing outwardly bent portions of the diffraction members to be rotated more than inwardly bent portions of the diffraction members due to rotational force using piezoelectric material. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0025]      FIG. 1  illustrates an electrostatic-type grating light modulator according to conventional technology;  
         [0026]      FIG. 2  illustrates reflection of incident light by the electrostatic-type grating light modulator in an undeformed state according to conventional technology;  
         [0027]      FIG. 3  illustrates diffraction of incident light by the grating light modulator in a deformed state due to electrostatic force, according to conventional technology;  
         [0028]      FIG. 4  is a perspective view of a blaze grating light valve (GLV) according to conventional technology;  
         [0029]      FIG. 5  is a perspective view of one elongate member and a lower substrate of the blaze grating light valve according to conventional technology;  
         [0030]      FIG. 6  illustrates a second grating light valve according to conventional technology;  
         [0031]      FIG. 7A  is a perspective view of a light modulator having a variable blaze diffraction grating according to the present invention,  FIG. 7B  is a plane view of the light modulator having the variable blaze diffraction grating according to the present invention, and  FIG. 7C  is a front view of the light modulator having the variable blaze diffraction grating according to the present invention;  
         [0032]      FIG. 8  is a perspective view of a diffraction member of  FIG. 7A ; and  
         [0033]      FIG. 9  illustrates diffraction of the variable blaze diffraction grating according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]     Hereinafter, a detailed description will be given of the present invention, with reference to  FIGS. 7A  to  9 .  
         [0035]      FIG. 7A  is a perspective view of a light modulator having a variable blaze diffraction grating according to the present invention,  FIG. 7B  is a plane view of the light modulator having the variable blaze diffraction grating according to the present invention, and  FIG. 7C  is a front view of the light modulator having the variable blaze diffraction grating according to the present invention.  
         [0036]     Referring to  FIGS. 7A  to  7 C, the light modulator having the variable blaze diffraction grating according to the present invention comprises a substrate  410 , a first supporting member  420 , a second supporting member  420 ′, diffraction members  430   a - 430   d , first piezoelectric units  440   a - 440   d , and second piezoelectric units  440   a ′- 440   d′.    
         [0037]     The first supporting member  420  and the second supporting member  420 ′ have a rectangular section, are attached to the substrate  410 , and are opposite to and parallel to each other (refer to  FIG. 7B ). The diffraction members  430   a - 430   d  are attached to the supporting members at both ends thereof so that the diffraction members  430   a - 430   d  are suspended on the substrate  410 .  
         [0038]     The diffraction members  430   a - 430   d  include central parts  431   a - 431   d , first external parts  432   a - 432   d , and second external parts  432   a ′- 432   d ′. Material for the diffraction members  430   a - 430   d  may be exemplified by Si oxides (e.g. SiO 2 ), Si nitrides (e.g. Si 3 N 4 ), ceramic substrates (Si, ZrO 2 , Al 2 O 3 ), or Si carbides.  
         [0039]     Reflective plates  450   a - 450   d  are provided on upper sides of the central parts  431   a - 431   d  to reflect incident light. Additionally, first ends of the first external parts  432   a - 432   d  are attached to the first supporting member  420 , and second ends of the first external parts are inclinedly integrated with the central parts  431   a - 431   d . Furthermore, second ends of the second external parts  432   a ′- 432   d ′ are attached to the second supporting member  420 ′, and first ends of the second external parts are inclinedly integrated with the central parts  431   a - 431   d.    
         [0040]     Each of the first piezoelectric units  440   a - 440   d  is layered on an upper side of each first external part  432   a - 432   d , and is provided on the first supporting member  420  at an end thereof and on the second end of the first external part  432   a - 432   d  at the other end thereof. Each of the second piezoelectric units  440   a ′- 440   d ′ is layered on an upper side of each second external part  432   a ′- 432   d ′, and is provided on the second supporting member  420 ′ at an end thereof and on the first end of the second external part  432   a ′- 432   d ′ at the other end thereof.  
         [0041]     With reference to  FIGS. 7A  to  7 C, the first piezoelectric units  440   a - 440   d  include lower electrode layers  441   a - 441   d , piezoelectric material layers  442   a - 442   d , and upper electrode layers  443   a - 443   d . The piezoelectric material layers  442   a - 442   d  are shrunken or expanded when voltage is applied to the lower electrode layers  441   a - 441   d  and the upper electrode layers  443   a - 443   d , thereby generating upward or downward driving force.  
         [0042]     Furthermore, referring to  FIGS. 7A  to  7 C, the second piezoelectric units  440   a ′- 440   d ′ include lower electrode layers  441   a ′- 441   d ′, piezoelectric material layers  442   a ′- 442   d ′, and upper electrode layers  443   a ′- 443   d ′. The piezoelectric material layers  442   a ′- 442   d ′ are shrunken or expanded when voltage is applied to the lower electrode layers  441   a ′- 441   d ′ and the upper electrode layers  443   a ′- 443   d ′, thereby generating upward or downward driving force.  
         [0043]     With respect to this, electrode material for the lower electrode layers  441   a - 441   d ,  441   a ′- 441   d ′ may be exemplified by Pt, Ta/Pt, Ni, Au, Al, or RuO 2 . Any of upper and lower piezoelectric materials and left and right piezoelectric materials may be used as the piezoelectric material layers  442   a - 442   d ,  442   a ′- 442   d ′. The piezoelectric material for the piezoelectric material layers  442   a - 442   d ,  442   a ′- 442   d ′ may be exemplified by PZT, PNN—PT, PLZT, AIN, or ZnO, and piezoelectric electrolytic material containing at least one of Pb, Zr, Zn, or titanium may be used.  
         [0044]     Electrode material for the upper electrode layers  443   a - 443   d ,  443   a ′- 443   d ′ may be exemplified by Pt, Ta/Pt, Au, Al, Ti/Pt, IrO 2 , or RuO 2 .  
         [0045]     Meanwhile, a description will be given of movement and diffraction of the light modulator having the variable blaze diffraction grating according to the present invention, referring to  FIGS. 7A  to  7 C and  9 .  
         [0046]     In the drawings, if piezoelectric voltage is applied to the first piezoelectric units  440   a - 440   d , the piezoelectric units  440   c ,  440   d  (refer to  FIG. 9 ) are shrunken by the occurrence of piezoelectric force, thus upward forces are generated at both ends of the piezoelectric units. At this time, the first ends of the piezoelectric units  440   c ,  440   d  are attached to the supporting member  420 , thus the upward forces are applied to the supporting member  420 . However, since the supporting member  420  is fixed, it is unmovable. The second ends of the piezoelectric units  440   c ,  440   d  are attached to the second ends of the first external parts  432   c ,  432   d  of the diffraction members  430   c ,  430   d , thus upward forces are applied to the second ends of the first external parts  432   c ,  432   d . Hence, the second ends of the first external parts  432   c ,  432   d  are lifted.  
         [0047]     However, since the first external parts  432   c ,  432   d  are inclinedly integrated with the central parts  431   c ,  431   d , the upward forces of the first external parts  432   c ,  432   d  cause rotation of the central parts  431   c ,  431   d . In other words, since the diffraction members  430   a - 430   d  are bent, outwardly bent portions of the diffraction members are more deformed than inwardly bent portions of the diffraction members, thus the central parts  431   c ,  431   d  are inclined.  
         [0048]     Meanwhile, if piezoelectric voltage is applied to the second piezoelectric units  440   a ′- 440   d ′, the piezoelectric units  440   c ′,  440   d ′ (refer to  FIG. 9 ) are shrunken by the occurrence of piezoelectric force, thus upward forces are generated at both ends of the piezoelectric units. At this time, the second ends of the piezoelectric units  440   c ′,  440   d ′ are attached to the supporting member  420 ′, thus the upward forces are applied to the supporting member  420 ′. However, since the supporting member  420 ′ is fixed, it is unmovable. The first ends of the piezoelectric units  440   c ′,  440   d ′ are attached to first ends of the second external parts  432   c ′,  432   d ′ of the diffraction members  430   c ,  430   d , thus upward forces are applied to the first ends of the second external parts  432   c ′,  432   d ′. Hence, the first ends of the second external parts  432   c ′,  432   d ′ are lifted.  
         [0049]     However, since the second external parts  432   c ′,  432   d ′ are inclinedly integrated with the central parts  431   c ,  431   d , the upward forces of the second external parts  432   c ′,  432   d ′ cause rotation of the central parts  431   c ,  431   d . In other words, since the diffraction members  430   c ,  430   d  are bent, outwardly bent portions of the diffraction members  430   c ,  430   d  are deformed more than inwardly bent portions of the diffraction members, thus the central parts  431   c ,  431   d  are inclined.  
         [0050]     As described above, when the voltage is applied to both the first and second piezoelectric units  440   a - 440   d ,  440   a ′- 440   d ′, the diffraction members  430   a - 430   d  rotate by the resultant force of two piezoelectric forces, thus reflective surfaces are inclined.  
         [0051]     As shown in  FIG. 9 , the reflective surfaces  450   c ,  450   d  of the inclined and adjacent diffraction members  430   c ,  430   d  are parallel to each other while being inclined. Furthermore, if the distance between upper sides of the inclined reflective surfaces is multiples of λ/4 when a wavelength of incident light is λ, diffraction occurs.  
         [0052]     In  FIG. 9 , diffracted light beams  3 ,  3 ′ are generated because the distance between the upper sides of the inclined reflective surfaces  450   c ,  450   d  is multiples of λ/4 when the wavelength of incident light  1  is λ. However, since the distance between upper sides of the reflective surfaces  450   a ,  450   b  is not multiples of λ/4, reflected light  2  is generated.  
         [0053]     Meanwhile,  FIG. 8  is a perspective view of a diffraction member, in which a first external part is inclinedly integrated with a central part and a second external part is inclinedly integrated with the central part. However, the diffraction member may have an arc shape.  
         [0054]     A conventional blaze diffraction grating, which causes electrostatic-type distortion displacement, is problematic in that it is not useful to produce a small light modulator having high resolution and generating sufficient rotation force, because it has limited electrostatic driving force.  
         [0055]     According to the present invention, since a variable micro blaze diffraction grating is driven using a piezoelectric device, such as PZT, the generation force per unit volume is great. Therefore, it is possible to develop a light modulator having small-sized multipixels, that is, high resolution.  
         [0056]     Although a light modulator having a variable blaze diffraction grating according to the present invention has 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.