Abstract:
The present invention relates generally to an apparatus for resetting the location of the reflective part of a diffractive optical modulator. More particularly, the present invention relates to an apparatus for resetting the location of the reflective part of a diffractive optical modulator, which resets the location of the reflective part of the diffractive optical modulator to an initial location thereof at a specific time point, thus increasing the ability to control the location of the reflective part.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2006-0082839, filed on Aug. 30, 2006, entitled “Resetting Apparatus of the Reflective Part in the Optical Diffractive Modulator”, which is hereby incorporated by reference in its entirety into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to an apparatus for resetting the location of the reflective part of a diffractive optical modulator. More particularly, the present invention relates to an apparatus for resetting the location of the reflective part of a diffractive optical modulator, which resets the location of the reflective part of the diffractive optical modulator to an initial location thereof at a specific time point, thus increasing the ability to control the location of the reflective part. 
         [0004]    2. Description of the Related Art 
         [0005]    With the development of micro-technology, micro-machine (Micro-Electro-Mechanical System: MEMS) devices and small-sized apparatuses in which MEMS devices are included are attracting attention. 
         [0006]    Recently, spatial optical modulators using such MEMS devices have been developed. An example of such spatial optical modulators is a diffractive optical modulator. 
         [0007]      FIG. 1  is a perspective view showing a conventional open hole-based diffractive optical modulator. 
         [0008]    Referring to  FIG. 1 , the open hole-based diffractive optical modulator includes a silicon substrate  121 , an insulating layer  122 , a lower reflective part  123 , and a plurality of actuating elements  130   a  to  130   n.    
         [0009]    The lower reflective part  123  is deposited on the silicon substrate  121  and is adapted to reflect incident light. Material used for the lower reflective part  123  may include a metal material, such as Al, Pt, Cr, or Ag. 
         [0010]    An actuating element (as a representative, the actuating element designated by reference numeral  130   a  is described, but the remaining actuating elements are constructed in the same way) is formed in a ribbon shape, and includes a lower support  131   a  the bottom surfaces of opposite ends of which are respectively attached to opposite locations on the silicon substrate  121  deviating from the recess part of the silicon substrate  121 , so that the center portion of the lower support  131   a  is arranged to be spaced apart from the recess part. 
         [0011]    Piezoelectric layers  140  and  140 ′ are provided on the opposite ends of the lower support  131   a  , and the actuating force of the actuating element  130   a  is provided by the contraction or expansion of the provided piezoelectric layers  140   a  and  140   a′.    
         [0012]    Each of the left and right piezoelectric layers  140   a  and  140   a ′ includes a lower electrode layer  141   a  or  141 ′ for supplying piezoelectric voltage, a piezoelectric material layer  142   a  or  142   a  stacked on the lower electrode layer  141   a  or  141   a ′ and adapted to contract or expand when voltage is applied to both surfaces of the piezoelectric material layer, thus generating a vertical actuating force, and an upper electrode layer  143   a  or  143   a ′ stacked on the piezoelectric material layer  142   a  or  142   a ′ and adapted to supply piezoelectric voltage to the piezoelectric material layer  142   a  or  142   a ′. When voltage is applied both to the upper electrode layer  143   a  or  143   a ′ and the lower electrode layer  141   a  or  141   a ′, the piezoelectric material layer  142   a  or  142   a ′ contracts or expands, thus causing vertical motion of the lower support  131   a.    
         [0013]    Meanwhile, the lower support  131   a  is provided with an upper reflective part  150   a  deposited on the center portion thereof, and is provided with a plurality of open holes  151   a   1  and  151   a   2  formed therein. 
         [0014]    Such open holes  151   a   1  and  151   a   2  allow light incident on the actuating element  130   a  to pass therethrough and to be incident on the lower reflective part  123  corresponding to the location at which the open hole  151   a   1  or  151   a   2  is formed, thus enabling light reflected from the lower reflective part  123  and light reflected from the upper reflective part  150   a  to form diffracted light. 
         [0015]    In this case, the light, which is incident on the actuating element  130   a  while passing through the open hole  151   a   1  or  151   a   2  of the upper reflective part  150   a , can be incident on the corresponding location of the lower reflective part  123 . In the case where the distance between the upper reflective part  150   a  and the lower reflective part  123  is a multiple of an odd number of λ/4 when the wavelength of incident light is λ, the most diffracted light is generated. 
         [0016]    A single upper reflective part  150   a  and a lower reflective part  123  corresponding thereto can form scanned diffracted light spots used to form the pixels of an image formed on a screen. Referring to  FIG. 2  to describe this operation in detail, a diffractive optical modulator includes n upper reflective parts  150   a  to  150   n,  corresponding to an ath pixel, a bth pixel, a cth pixel, a dth pixel, an eth pixel, . . . , an nth pixel, which form an image formed on the screen. The diffractive optical modulator is described with reference to a single upper reflective part designated by reference numeral  150   a . Light, reflected from the reflective surfaces  150   a   1 ,  150   a   2 , and  150   a   3  of the upper reflective part  150   a  and light, passed through the open holes  151   a   1 ,  151   a   2 , and  151   a   3  of the upper reflective part  150   a  (where  151   a   3  is the interval between the upper reflective part  150   a  and an upper reflective part  150   b  adjacent thereto) and reflected from the lower reflective part  123 , forms diffracted light. This diffracted light forms scanned diffracted light spots corresponding to the pixels of the image formed on the screen. 
         [0017]    That is, the upper reflective parts  150   a  to  150   n  respectively form scanned diffracted light spots corresponding to the pixels of the image formed on the screen, together with the reflective surface of the lower reflective part  123  corresponding to the upper reflective parts. The scanned diffracted light spots are aligned in a line, thus forming a scan line (in this case, a scan line is assumed to be composed of n scanned diffracted light spots corresponding to n pixels). 
         [0018]    Meanwhile, in the above-described open hole-based diffractive optical modulator, when piezoelectric voltage is applied to the left and right piezoelectric layers, the displacement of each upper reflective part, caused by the actuating force generated by the piezoelectric layer, exhibits hysteresis characteristics, as shown in  FIGS. 3A and 3B . Referring to  FIG. 3A , when the piezoelectric voltage to be applied to the left and right piezoelectric layers increases from 0V up to Vmax, the displacement of the upper reflective part is changed along line A. When the piezoelectric voltage decreases from Vmax down to 0V, the displacement of the upper reflective part exhibits hysteresis characteristics progressing along line B. Further, lines A and B are curved lines rather than straight lines, and thus exhibit non-linearity. 
         [0019]    The hysteresis characteristics of the diffractive optical modulator exhibit the displacement characteristics of  FIG. 3B  when the piezoelectric voltage to be applied increases up to the maximum voltage Vmax, at which the maximum displacement is reached, decreases from the maximum voltage Vmax down to a voltage less than Vmax, and increases again from that voltage up to the maximum voltage Vmax. 
         [0020]    That is, referring to  FIG. 3B , the displacement characteristics of line B 4  are exhibited when the application voltage increases from 0V up to the maximum voltage Vmax, at which the maximum displacement is reached, gradually decreases from Vmax down to voltage V 4 , and subsequently increases from V 4  up to the maximum voltage Vmax. 
         [0021]    Further, the displacement characteristics of line B 3  are exhibited when the application voltage gradually decreases from Vmax down to voltage V 3  and subsequently increases from V 3  up to the maximum voltage Vmax. 
         [0022]    Further, the displacement characteristics of line B 2  are exhibited when the application voltage gradually decreases from Vmax down to V 2  and subsequently increases from V 2  up to the maximum voltage Vmax. 
         [0023]    Further, the displacement characteristics of line B 1  are exhibited when the application voltage gradually decreases from Vmax down to V 1  and subsequently increases from V 1  to the maximum voltage Vmax. 
         [0024]    Meanwhile, the hysteresis characteristics of the diffractive optical modulator are also exhibited even when the application voltage increases from the minimum voltage up to an arbitrary voltage, at which desired displacement is reached, and then gradually decreases from the arbitrary voltage down to 0V. 
         [0025]    Such hysteresis characteristics of the diffractive optical modulator make it difficult to determine the voltage to be applied to move the upper reflective part to a desired location. 
         [0026]    Meanwhile, the above-described diffractive optical modulator exhibits a creep phenomenon in which, even if the same drive voltage is applied, the reflective part has different initial locations. 
         [0027]    Such hysteresis and creep phenomenon make it difficult to determine the voltage required to move the upper reflective part to a desired location, and a solution to overcome this difficulty is required. 
       SUMMARY OF THE INVENTION 
       [0028]    Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and the present invention is intended to provide an apparatus for resetting the location of the reflective part of a diffractive optical modulator, which resets the location of the reflective part of a diffractive optical modulator to an initial location at a specific time point, thus increasing the ability to control the location of the reflective part. 
         [0029]    The present invention provides an apparatus for resetting a location of an upper reflective part of a diffractive optical modulator used in a display system for processing diffracted light, generated by the diffractive optical modulator, and generating continuous images, comprising a control unit for outputting a reset control signal when the diffracted light emitted from the diffractive optical modulator disposed in the display system is present in a first scan time section on a screen of the display system; and a reset driving circuit for initializing the diffractive optical modulator when a reset control signal is input from the control unit. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    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: 
           [0031]      FIG. 1  is a perspective view showing a conventional open hole-based diffractive optical modulator; 
           [0032]      FIG. 2  is a plan view showing a conventional open hole-based diffractive optical modulator; 
           [0033]      FIGS. 3A and 3B  are diagrams showing the hysteresis characteristics of a typical actuator using a piezoelectric material; 
           [0034]      FIG. 4A  is a diagram showing an apparatus for resetting the location of the reflective part of a diffractive optical modulator according to an embodiment of the present invention, and  FIG. 4B  is a diagram showing an apparatus for resetting the location of the reflective part of a diffractive optical modulator according to another embodiment of the present invention; 
           [0035]      FIG. 5  is a diagram showing an effective picture section and a blank time section on the screen used in the present invention; 
           [0036]      FIG. 6  is a timing diagram showing synchronization signals provided by the control unit of  FIGS. 4A and 4B  to an image data output unit, an optical modulator driving circuit, and a reset driving circuit; 
           [0037]      FIG. 7  is a diagram showing the displacement of an upper reflective part generated when a drive voltage corresponding to sample image data is applied to the diffractive optical modulator of  FIGS. 4A and 4B ; and 
           [0038]      FIG. 8  is a diagram showing the construction of an apparatus for resetting the location of the reflective part of a diffractive optical modulator according to a further embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0039]    Hereinafter, embodiments of an apparatus for resetting the location of the reflective part of a diffractive optical modulator according to the present invention will be described in detail with reference to  FIGS. 4A to 8 . 
         [0040]      FIG. 4A  is a diagram showing the construction of an apparatus for resetting the location of the reflective part of a diffractive optical modulator according to an embodiment of the present invention. 
         [0041]    Referring to  FIG. 4A , the apparatus for resetting the location of the reflective part of the diffractive optical modulator according to an embodiment of the present invention includes an image input unit  501 , an image pivoting unit  502 , memory  503 , a control unit  504 , an image data output unit  505 , an optical modulator driving circuit  506 , a reset driving circuit  507 , a photosensor  550 , and an element-based reset voltage calculation unit  560 . 
         [0042]    The image input unit  501  receives image data from an external device while receiving a vertical synchronization signal Vsync and a horizontal synchronization signal Hsync therefrom. 
         [0043]    The image pivoting unit  502  performs data transposition to convert laterally arranged image data into vertically arranged image data, thus converting laterally input image data into vertical image data and storing the vertical image data in the memory  503 . The reason for performing data transposition in the image pivoting unit  502  in this way is that the scan lines emitted from the diffractive optical modulator are adapted to laterally scan and display image data because scanned diffracted light spots corresponding to a plurality of pixels are vertically arranged. 
         [0044]    The memory  503  is adapted to store the image data transposed by the image pivoting unit  502 , and to store sample image data so as to perform a reset operation. The sample image data stored in the memory  503  may be arbitrary image data, which is used for a process of calculating element-based reset voltages, which will be described later. Further, the memory  503  is adapted to store element-based light intensities that are predicted to be measured for diffracted light emitted from respective elements when the drive voltage corresponding to the sample image data is applied to the diffractive optical modulator. Such predicted element-based light intensities are also used for the process of calculating element-based reset voltages, which will be described later. 
         [0045]    The image data output unit  505  sequentially reads and outputs the image data stored in the memory  503 . 
         [0046]    The optical modulator driving circuit  506  modulates incident light by driving the diffractive optical modulator according to the image data output from the image data output unit  505 , thus forming diffracted light having image information. 
         [0047]    Further, the photosensor  550  detects the intensities of element-based light, emitted from respective elements corresponding to pixels, from the diffracted light emitted from the diffractive optical modulator, and outputs the element-based light intensities. 
         [0048]    When the element-based light intensities measured by the photosensor  550  are input, the element-based reset voltage calculation unit  560  compares the element-based light intensities that are predicted to be output from respective elements when the drive voltage corresponding to sample image data is applied to the elements, with measured element-based light intensities input from the photosensor  550 , thus calculating an element reset voltage. 
         [0049]    Meanwhile, the reset driving circuit  507  is attached to a lower reflective part  123  and an upper reflective part  150   a  (in the case of, for example, a single element  130   a ). 
         [0050]    When a reset control signal is input, the reset driving circuit  507  reads a reset voltage value stored in the memory  503  and applies the read reset voltage value to the upper reflective part  150   a  (in the case of, for example, a single element  130   a ) and the lower reflective part  123  of the diffractive optical modulator in a period during which the optical modulator driving circuit  506  is turned off, thus performing the reset operation corresponding to the applied voltage. This reset voltage value output from the reset driving circuit  507  is the value required to initialize the upper reflective parts  150   a  to  150   n  of the diffractive optical modulator, and is not to be understood to be a value of ‘0’. 
         [0051]    The control unit  504  operates the diffractive optical modulator by controlling the optical modulator driving circuit  506 , and resets the diffractive optical modulator by controlling the reset driving circuit  507 . 
         [0052]    In a display device using the diffractive optical modulator, the control unit  504  of the apparatus for resetting the location of the reflective part of the diffractive optical modulator having the above construction causes image data to be output from the image data output unit  505  to the optical modulator driving circuit  506  in the period during which diffracted light is projected from the diffractive optical modulator onto the effective picture section of the screen ( 520  of  FIG. 5 ), and turns off the optical modulator driving circuit  506  and outputs a reset control signal to the reset driving circuit  507  in the blank time section of the screen ( 510  or  530  of  FIG. 5 ). 
         [0053]    Referring to  FIG. 5 , the effective picture section  520 , the first blank time section  510 , and the second blank time section  530  are shown clearly. That is, referring to  FIG. 5 , a single frame image is composed of the effective picture section  520 , during which image information desired to be shown to the user is output, and the first and second blank time sections  510  and  530  formed on opposite sides of the effective picture section  530  before and after the output of the effective picture section  520 . The control unit  504  outputs the reset control signal to the reset driving circuit  507  so that a predetermined reset voltage is applied to the diffractive optical modulator in the first or second blank time section  510  or  530 . 
         [0054]    In this case, the first or second blank time section  510  or  530  may correspond to a period during which a single pixel is scanned in a horizontal direction or during which a plurality of pixels is scanned, and may be adjusted according to the application. 
         [0055]    This operation is described with reference to the timing diagram of  FIG. 6 . The control unit  504  provides an ON data synchronization signal both to the image data output unit  505  and to the optical modulator driving circuit  506  in the effective picture section  520 , thus causing the image data to be output from the image data output unit  505  to the optical modulator driving circuit  506 . Further, in the blank time section  510  or  530 , the control unit  504  provides an OFF data synchronization signal both to the image data output unit  505  and to the optical modulator driving circuit  506 , thus preventing the image data from being output from the image data output unit  505  to the optical modulator driving circuit  506 , and also provides both an ON reset synchronization signal and a reset control signal to the reset driving circuit  507 . 
         [0056]    Meanwhile, when the reset control signal is input, the reset driving circuit  507  reads the reset voltage value stored in the memory  503  and applies the reset voltage value to the upper reflective part ( 150   a  in the case of, for example, a single element  130   a ) and the lower reflective part  123  of the diffractive optical modulator in the blank time section  510  or  530 , during which the optical modulator driving circuit  506  is turned off, thus performing the reset operation corresponding to the applied reset voltage. In this case, the reset voltage value, output from the reset driving circuit  507 , is the value required to initialize the upper reflective parts  150   a  to  150   n  of the diffractive optical modulator, and is not to be understood to be a value of ‘0’. 
         [0057]    If the diffractive optical modulator is reset by the reset driving circuit  507  in this way, an application voltage versus displacement curve starts again at the initialized value, as shown in  FIG. 3A , so that control is started at the location that does not greatly deviate from a predicted displacement curve in the effective picture section. Accordingly, a voltage value very close to the application voltage value required to obtain desired displacement can be obtained. As a result, in the diffractive optical modulator, the ability to control the location of the upper reflective part can be increased. 
         [0058]    Meanwhile, the reset voltage value stored in the memory  503  may be preset to a certain value and may be stored, but may be calculated in such a way that, after the drive voltage corresponding to sample image data, stored in the memory  503 , is provided to the diffractive optical modulator using the optical modulator driving circuit  506 , the intensity of diffracted light emitted from the diffractive optical modulator is measured by the photosensor  550 , and thus the element-based reset voltage calculation unit  560  can calculate reset voltages for respective elements. 
         [0059]    That is, the control unit  504  transmits a sample voltage output control signal so that the drive voltage corresponding to the sample image data is output to the optical modulator driving circuit  506  at the time point at which the first or second blank time section  510  or  530  starts. 
         [0060]    Then, the optical modulator driving circuit  506  reads the sample image data stored in the memory  503  and applies the drive voltage corresponding to the sample image data to the diffractive optical modulator. 
         [0061]    Further, the photosensor  550  detects the intensities of element-based diffracted light, emitted from respective elements corresponding to pixels, and outputs the element-based light intensities to the element-based reset voltage calculation unit  560 . 
         [0062]    In this case, the memory  503  stores therein light intensities that are predicted to be measured when the drive voltage corresponding to the sample image data is applied to the diffractive optical modulator. The element-based reset voltage calculation unit  560  compares the element-based light intensities that are predicted to be output from respective elements when the drive voltage corresponding to the sample image data is applied and that are stored in the memory  503 , with measured element-based light intensities, thus calculating an element reset voltage and storing the element reset voltage in the memory  503 . 
         [0063]    That is, referring to  FIG. 7 , when a specific reference voltage is applied, displacement corresponding thereto is generated. In the case of an element having an upper reflective part  150   a , when the drive voltage corresponding to sample image data is applied, location  150   a ′ is predicted to be reached, but, in practice, location  150 ″ may be reached. In this case, if the difference la between the heights of the upper reflective part  150   a  and the lower reflective part  123  is assumed to be k/ 4  when the wavelength of incident light is X, the intensity of diffracted light determined according to such displacement becomes less than predicted light intensity. Therefore, in order to move the upper reflective part, which was moved to the location designated by reference numeral  150   a ″, to the location designated by reference numeral  150   a , a reverse voltage, greater than that of the case where such displacement does not exist, must be applied both to the upper reflective part  150   a  and to the lower reflective part  123 . 
         [0064]    Of course, referring to  FIG. 7 , in the case of an element having an upper reflective part  150   b , when the drive voltage corresponding to sample image data is applied, location  150   b ″ is predicted to be reached, but, even when the element  150   a  is moved to a location lower than predicted location  150   b ″, as in the case where the actual location  150   b ′ is reached, the same description can be made. In this case, if the difference 1 b between the heights of the upper reflective part  150   b  and the lower reflective part  123  is assumed to be λ/4 when the wavelength of incident light is λ, the intensity of the diffracted light determined according to such displacement becomes greater than predicted light intensity. Therefore, in order to move the upper reflective part  150   b , which was moved to the location designated by reference numeral  150   b ′, to the location designated by reference numeral  150   b , reverse voltage less than that of the case where such displacement does not exist must be applied both to the upper reflective part  150   b  and the lower reflective part  123 . 
         [0065]    As described above, the element-based reset voltage calculation unit  560  calculates an element reset voltage by comparing the predicted element-based light intensities, which are stored in the memory  503  and are predicted to be output from respective elements when drive voltage corresponding to the sample image data is applied to the elements, with measured element-based light intensities, and stores the element reset voltage in the memory  503 . 
         [0066]    In this embodiment, abnormal displacement has been measured using diffracted light emitted from the diffractive optical modulator, but can also be determined by measuring the capacitances charged in the upper reflective part and the lower reflective part. 
         [0067]      FIG. 4B  is a diagram showing the construction of an apparatus for resetting the location of the reflective part of the diffractive optical modulator according to another embodiment of the present invention. Compared to that of  FIG. 4A , this embodiment is characterized in that a lower reflective part  123  is not used as a reference electrode for moving an upper reflective part  150   a , but a separate reference electrode part  570 , which is disposed over the upper reflective part  150   a  and is provided with terminals connected to a reset driving circuit  507 , is provided. Such a reference electrode part  570  can be formed of a transparent element (Indium-Tin-Oxide: ITO), etc. The apparatus for resetting the location of the reflective part of the diffractive optical modulator according to another embodiment of the present invention is different from the reset apparatus of  FIG. 4A  in that it applies a reset voltage to the upper reflective part  150   a  and to the reference electrode part  570 , rather than the upper reflective part  150   a  and the lower reflective part  123 , and the remaining construction and operation thereof are the same as those of the reset apparatus of  FIG. 4A . 
         [0068]      FIG. 8  is a diagram showing the construction of an apparatus for resetting the location of the reflective part of a diffractive optical modulator according to a further embodiment of the present invention. 
         [0069]    Referring to  FIG. 8 , the apparatus for resetting the location of the reflective part of the diffractive optical modulator according to a further embodiment of the present invention includes an image input unit  501 , an image pivoting unit  502 , memory  503 , a control unit  504 , an image data output unit  505 , an optical modulator driving circuit  506 , and a reset driving circuit  507 ′. 
         [0070]    The image input unit  501  receives image data from an external device while receiving a vertical synchronization signal Vsync and a horizontal synchronization signal Hsync therefrom. 
         [0071]    Further, the image pivoting unit  502  performs data transposition to convert laterally arranged image data into vertically arranged image data, thus converting laterally input image data into vertical image data and storing the vertical image data in the memory  503 . 
         [0072]    The memory  503  is adapted to store the image data, transposed by the image pivoting unit  502 , and a reset voltage. 
         [0073]    The image data output unit  505  sequentially reads and output the image data stored in the memory  503 . 
         [0074]    The optical modulator driving circuit  506  modulates incident light by driving the diffractive optical modulator according to the image data output from the image data output unit  505 , thus forming diffracted light having image information. 
         [0075]    Further, the image data output unit  505  sequentially reads the image data, which is transposed by the image pivoting unit  502  and is stored in the memory  503 , from the first column to the last column and outputs the read image data during a scanning period. 
         [0076]    Meanwhile, in the display device using the diffractive optical modulator, the control unit  504  causes image data to be output from the image data output unit  505  to the optical modulator driving circuit  506  in the period during which diffracted light is projected from the diffractive optical modulator onto the effective picture section of the screen ( 520  of  FIG. 5 ), and turns off the optical modulator driving circuit  506  and outputs a reset control signal to the reset driving circuit  507 ′ in the blank time section ( 510  or  530  of  FIG. 5 ) of the screen. 
         [0077]    Referring to the timing diagram of  FIG. 6 , the control unit  504  provides an ON data synchronization signal both to the image data output unit  505  and to the optical modulator driving circuit  506  in the effective picture section  520 , thus causing the image data to be output from the image data output unit  505  to the optical modulator driving circuit  506 . Further, in the blank time section  510  or  530 , the control unit  504  provides an OFF data synchronization signal both to the image data output unit  505  and to the optical modulator driving circuit  506 , thus preventing the image data from being output from the image data output unit  505  to the optical modulator driving circuit  506 , and also provides both an ON reset synchronization signal and a reset control signal to the reset driving circuit  507 ′, thus causing the reset driving circuit  507 ′ to reset the diffractive optical modulator. 
         [0078]    In this case, the reset driving circuit  507 ′ applies a reset voltage both to the upper electrode layer ( 143   a  and  143   a ′ in the case of a single element  130   a ) and to the lower electrode layer  141   a  and  141   a ′ of the diffractive optical modulator in the blank time section  510  or  530 , during which the optical modulator driving circuit  506  is turned off, thus performing a reset operation. In this case, the reset voltage output from the reset driving circuit  507 ′ denotes the minimum voltage at which lines A and B are coincident with each other in the hysteresis curve of the diffractive optical modulator of  FIG. 3A , and is not to be understood to be a value of ‘0’. 
         [0079]    If the diffractive optical modulator is reset by the reset driving circuit  507 ′ in this way, an application voltage versus displacement curve starts again at the initialized value, as shown in  FIG. 3A , so that control is started at the location that does not greatly deviate from a predicted displacement curve in the effective picture section. Accordingly, a voltage value very close to the application voltage value required to obtain desired displacement can be obtained. As a result, in the diffractive optical modulator, the ability to control the location of the upper reflective part can be increased. 
         [0080]    Accordingly, the present invention is advantageous in that the location of an upper reflective part can be initialized using a convenient method, thus suppressing abnormal operation caused by the hysteresis characteristics of the diffractive optical modulator. 
         [0081]    Further, the present invention is advantageous in that the location of an upper reflective part is initialized, thus preventing abnormal operation caused by the creep phenomenon of the diffractive optical modulator. 
         [0082]    Further, the present invention is advantageous in that the location of an upper reflective part is initialized, so that the possibility of predicting the location corresponding to subsequently applied voltage can be increased, and thus the ability to control the location of the upper reflective part can be increased. 
         [0083]    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.