Abstract:
An electromechanical conformal grating device including: at least two sets of elongated ribbon elements; a pair of end supports for supporting each elongated ribbon element at both ends over a substrate; a plurality of intermediate supports placed under each elongated ribbon element; and at least two inputs for selectively applying a force to the at least two sets of elongated ribbon elements; wherein the force causes selected elongated ribbon elements to deform between first and second operating states, wherein during the second operating state the elongated ribbon elements mechanically conform to the intermediate supports.

Description:
FIELD OF THE INVENTION 
     This invention relates to electromechanical grating devices for light modulation. More particularly, the invention relates to the formation of gray levels in a projection display system containing a linear array of electromechanical grating devices. 
     BACKGROUND OF THE INVENTION 
     Many projection display systems employ a spatial light modulator to convert electronic image information into an output image. At present in such systems, the light source is typically a white light lamp and the spatial light modulator is typically an area array containing liquid crystal devices or micromirror devices. Alternative display system architectures with one or more laser sources and spatial light modulators that are linear arrays of electromechanical grating devices show much promise for the future. To display high quality motion images, the individual devices of these different spatial light modulators must be capable of rapidly producing a large number of gray levels in the image. The limit on the number of possible gray levels is usually dictated either by the device dynamics or by the speed of electronic components within the display system. 
     Prior inventions have disclosed schemes for increasing the number of gray levels in the image without increasing the speed of the modulating elements or of the associated electronics. These schemes vary the illumination that is incident on the spatial light modulator during a frame. Specifically, according to U.S. Pat. No. 5,812,303, issued to Hewlett et al. on Sep. 22, 1998, entitled, “LIGHT AMPLITUDE MODULATION WITH NEUTRAL DENSITY FILTERS,” additional gray levels can be obtained with a micromirror device by using a variable neutral density filter to generate bright and dark gray levels. The dark gray scale is obtained by attenuating the illumination for some time during the display of a frame. The bright gray scale has no attenuation. In practice, the invention is implemented by rotating a filter wheel with a multi-segment neutral density filter in synchronization with the data stream. 
     An alternative approach employs a pulsating light source such as a pulsed laser to reduce speed requirements on the electronic components, as described in U.S. Pat. No. 5,668,611, issued to Ermstoff et al. on Sep. 16, 1997, entitled “FULL COLOR SEQUENTIAL IMAGE PROJECTION SYSTEM INCORPORATING PULSE RATE MODULATED ILLUMINATION.” The illumination on the spatial light modulator is adjusted by varying the pulse rate or pulse count. Moreover, the average brightness of the light source is determined by the number of pulses. A complementary method uses direct intensity modulation of the light source to obtain multiple levels of brightness, as disclosed in U.S. Pat. No. 5,903,323, issued to Ernstoff et al. on May 11, 1999, entitled “FULL COLOR SEQUENTIAL IMAGE PROJECTION SYSTEM INCORPORATING TIME MODULATED ILLUMINATION.” Both U.S. Pat. No. 5,668,611 and U.S. Pat. No. 5,903,323 address the specific problem of having a large enough time window for the electronic components to load new image data bits into the spatial modulator. 
     Each of the above described inventions trade light source efficiency for improved gray levels or reduced electronic component speed requirements. However, efficient use of the light source is needed for high-quality projection displays in order to maximize brightness and color saturation of the projected image. 
     Recently, an electromechanical conformal grating device consisting of ribbon elements suspended above a substrate by a periodic sequence of intermediate supports was disclosed by Kowarz in U.S. Pat. No. 6,307,663, entitled “SPATIAL LIGHT MODULATOR WITH CONFORMAL GRATING DEVICE” issued Oct. 23, 2001. The electromechanical conformal grating device is operated by electrostatic actuation, which causes the ribbon elements to conform around the support substructure, thereby producing a grating. The device of &#39;663 has more recently become known as the conformal GEMS device, with GEMS standing for grating electromechanical system. The conformal GEMS device possesses a number of attractive features. It provides high-speed digital light modulation with high contrast and good efficiency. In addition, in a linear array of conformal GEMS devices, the active region is relatively large and the grating period is oriented perpendicular to the array direction. This orientation of the grating period causes diffracted light beams to separate in close proximity to the linear array and to remain spatially separated thrughout most of an optical system and enables a simpler optical system design with smaller optical elements. Display systems based on a linear array of conformal GEMS devices were described by Kowarz et al. in U.S. Pat. No. 6,411,425, entitled “ELECTROMECHANICAL GRATING DISPLAY SYSTEM WITH SPATIALLY SEPARATED LIGHT BEAM”, issued Jun. 25, 2002 and by Kowarz et al. in U.S. Pat. No. 6,476,848, entitled “ELECTROMECHANICAL GRATING DISPLAY SYSTEM WITH SEGMENTED WAVEPLATE”, issued Nov. 5, 2002. 
     The conformal Grating Electromechanical System (GEMS) devices disclosed in U.S. Pat. No. 6,307,663 are illustrated in FIGS. 1-3. FIG. 1 shows two side-by-side conformal GEMS devices  5   a  and  5   b  in an unactuated state. The conformal GEMS devices  5   a  and  5   b  are formed on top of a substrate  10  covered by a bottom conductive layer  12 , which acts as an electrode to actuate the devices  5   a ,  5   b . The bottom conductive layer  12  is covered by a dielectric protective layer  14  followed by a standoff layer  16  and a spacer layer  18 . On top of the spacer layer  18 , a ribbon layer  20  is formed which is covered by a reflective layer and conductive layer  22 . The reflective and conductive layer  22  provides electrodes for the actuation of the conformal GEMS devices  5   a  and  5   b . Accordingly, the reflective and conductive layer  22  is patterned to provide electrodes for the two conformal GEMS devices  5   a  and  5   b . The ribbon layer  20 , preferably, comprises a material with a sufficient tensile stress to provide a large restoring force. Each of the two conformal GEMS devices  5   a  and  5   b  has an associated elongated ribbon element  23   a  and  23   b , respectively, patterned from the reflective and conductive layer  22  and the ribbon layer  20 . The elongated ribbon elements  23   a  and  23   b  are supported by end supports  24   a  and  24   b , formed from the spacer layer  18 , and by one or more intermediate supports  27  that are uniformly separated in order to form equal-width channels  25 . The elongated ribbon elements  23   a  and  23   b  are secured to the end supports  24   a  and  24   b  and to the intermediate supports  27 . A plurality of standoffs  29  is patterned at the bottom of the channels  25  from the standoff layer  16 . These standoffs  29  reduce the possibility of the elongated ribbon elements  23   a  and  23   b  sticking when actuated. 
     A top view of a four-device linear array of conformal GEMS devices  5   a ,  5   b ,  5   c  and  5   d  is shown in FIG.  2 . The elongated ribbon elements  23   a ,  23   b ,  23   c , and  23   d  are depicted partially removed over the portion of the diagram below the line A—A in order to show the underlying structure in an active region  8 . For best optical performance and maximum contrast, the intermediate supports  27  should preferably be completely hidden below the elongated ribbon elements  23   a ,  23   b ,  23   c , and  23   d . Therefore, when viewed from the top, the intermediate supports  27  should not be visible in the gaps  28  between the conformal GEMS devices  5   a - 5   d . Here, each of the conformal GEMS devices  5   a - 5   d  has three intermediate supports  27  with four equal-width channels  25 . The center-to-center separation Λ of the intermediate supports  27  defines the period of the conformal GEMS devices in the actuated state. The elongated ribbon elements  23   a - 23   d  are mechanically and electrically isolated from one another, allowing independent operation of the four conformal GEMS devices  5   a - 5   d . The bottom conductive layer  12  of FIG. 1 can be common to all of the conformal GEMS devices  5   a - 5   d.    
     FIG. 3 a  is a side view, through line  3 — 3  of FIG. 2, of two channels  25  of the conformal GEMS device  5   b  in an unactuated state. FIG. 3 b  shows the same view for an actuated state. For operation of the device, an attractive electrostatic force is produced by applying a voltage difference between the bottom conductive layer  12  and the reflective and conductive layer  22  of the elongated ribbon element  23   b . In the unactuated state (see FIG. 3 a ), with no voltage difference (V=0), the ribbon element  23   b  is suspended flat between the supports. In this state, an incident light beam  30  is primarily reflected into a 0th order light beam  32 , as in a simple planar mirror. To obtain the actuated state, a voltage is applied to the conformal GEMS device  5   b , which deforms the elongated ribbon element  23   b  and produces a partially conformal grating with period A. FIG. 3 b  shows the device  5   b  (as shown and described in FIGS. 1 and 2) in the fully actuated state with the applied voltage at V=V HIGH  and the elongated ribbon element  23   b  in contact with standoffs  29 . The height difference between the bottom of element  23   b  and the top of the standoffs  29  is chosen to be approximately ¼ of the wavelength λ of the incident light. The optimum height depends on the specific conformal shape of the actuated device. In the actuated state, the incident light beam  30  is primarily diffracted into the +1st conformal order  35   a  and −1st conformal order  35   b , with additional light diffracted into the +2nd conformal order  36   a  and −2nd conformal order  36   b . A small amount of light is diffracted into even higher conformal orders and some light remains in the 0th order. In general, one or more of the various beams can be collected and used by an optical system, depending on the application. When the applied voltage is removed, the forces due to tensile stress and bending restores the ribbon element  23   b  to its original unactuated state, as shown in FIG. 3 a.    
     FIG. 4 illustrates a display system containing a linear array  85  of conformal GEMS devices, as disclosed in U.S. Pat. No. 6,411,425. Light emitted from a source  70 , preferably a laser, is conditioned by a pair of lenses  72  and  74 , before hitting a turning mirror  82  and illuminating the linear array  85 . The display system forms an entire two-dimensional scene from a scan of a one-dimensional line image of the linear array  85  across the screen  90 . The conformal GEMS devices of the linear array  85  are capable of rapidly modulating incident light to produce multiple lines of pixels with gray levels. The controller  80  selectively activates the linear array  85  to obtain the desired pixel pattern for a given line of a two-dimensional scene. If a particular conformal GEMS device is not actuated, it reflects the incident light beam primarily into the 0th order light beam, which is directed back towards the source  70  by the turning mirror  82 . If a particular conformal GEMS device is actuated, it diffracts the incident light beams primarily into +2 nd , +1 st , −1 st  and −2 nd  conformal order beams. These diffracted light beams pass around the turning mirror  82  and are projected on the screen  90  by the projection lens system  75 . The scanning mirror  77  sweeps the line image across the screen  90  to form the two-dimensional image. Synchronization between the sweep of the scanning mirror  77  and the image data stream is provided by the controller  80 . 
     In order to form gray levels in an image, pulse-width-modulated (PWM) waveforms are applied to the conformal GEMS devices of the linear array  85 , as described by Kowarz et al., “Conformal Grating Electromechanical System (GEMS) for High-Speed Digital Light Modulation,” IEEE 15 th  International MEMS Conference Technical Digest, pgs. 568-573 (2002). FIG. 5 shows a conventional PWM waveform  45  with voltage V HIGH , together with the corresponding device&#39;s output (e.g., diffracted light intensity). To obtain a desired gray level, the controller  80  selects the voltage pulse width in each modulation window  54 , according to a data stream. When the PWM waveform  45  transitions from 0 V to V HIGH , the device (for example,  5   a  and  5   b  shown in FIG. 1) actuates and begins diffracting light. When the waveform transitions back to 0 V, the device stops diffracting light. This process is applied to each conformal GEMS device of the linear array  85 . For the display system of FIG. 4, the modulation window  54  corresponds to the time used to form a single line of the two-dimensional image. The gray level perceived in a pixel of the image is, therefore, the time-integrated light intensity  53  within the modulation window  54 . To minimize charging effects within the device, the applied voltage can be periodically switched between V HIGH  and −V HIGH  (see U.S. Pat. No. 6,144,481). Since the force on the ribbon elements  23   a - 23   d  is independent of polarity, the diffracted light intensity is polarity independent. 
     FIG. 6 shows an example of a gray scale generated using the conventional PWM approach of FIG.  5 . In this plot, relative gray levels are shown as a function of pulse width for a modulation window  54  of 20 μsec. When the pulse width is between 0.3 μsec and 20 μsec, the relationship between gray level and pulse width is approximately linear. A non-monotonic (and nonlinear) region  50  is present, however, for pulse widths between approximately 0.1 μsec and 0.3 μsec. This non-monotonic behavior occurs because of the resonant dynamics of the conformal GEMS device. The particular shape of the non-monotonic region  50  depends on a number of factors, including device geometry and driver slew rate. For pulse widths shorter than approximately 0.1 μsec, there is a monotonic, non-linear correspondence between pulse width and gray level. The dark (gray) levels in the non-monotonic region  50  can be difficult to use in practice because of the difficulty in determining the exact correspondence between a desired gray level and the pulse width required to generate that particular gray level. 
     The techniques described in the prior art for improving gray levels all lower the average optical power incident on the spatial light modulator for some period of time, thus generating multiple illumination levels corresponding to decreased intensity. Multiple illumination levels reduce the speed requirements of the spatial light modulator and its associated electronic components. However, a serious technical drawback to this approach is that it wastes optical power that is available from the light source during lower illumination intervals. Furthermore, for certain types of light sources, reducing the illumination level increases system complexity. The same drawbacks apply when these techniques are used in a display system based on electromechanical grating devices. There is a need, therefore, for a method for generating enhanced gray levels in an electromechanical grating display system that makes efficient use of available optical power and does not significantly increase system complexity. 
     SUMMARY OF THE INVENTION 
     The aforementioned need is met according to the present invention by providing an electromechanical conformal grating device that includes at least two sets of elongated ribbon elements; and a pair of end supports for supporting each elongated ribbon element at both ends over a substrate. Also included are a plurality of intermediate supports placed under each elongated ribbon element; and at least two inputs for selectively applying a force to the at least two sets of elongated ribbon elements; wherein the force causes selected elongated ribbon elements to deform between first and second operating states, wherein during the second operating state the elongated ribbon elements mechanically conform to the intermediate supports. 
     Another aspect of the present invention provides an array of electromechanical conformal grating devices for producing gray levels in an image by light modulation, each electromechanical conformal grating device including at least two sets of elongated ribbon elements; a pair of end supports for supporting each elongated ribbon element at both ends over a substrate; a plurality of intermediate supports placed under each elongated ribbon element and defining a diffraction grating period; and at least two inputs, each input receiving a different modulated waveform that causes selected ribbon elements to conform around the intermediate supports; wherein the different modulated waveforms are derived from an image data stream. 
     A third aspect of the present invention provides a method for producing gray levels in an image by light modulation with an array of electromechanical conformal grating devices; each electromechanical conformal grating device including at least two sets of elongated ribbon elements and at least two inputs, including the steps of: providing an image data stream; producing at least two modulated waveforms for each electromechanical conformal grating device from the image data stream; and applying the at least two modulated waveforms to the at least two inputs, wherein application of the at least two modulated waveform to the at least two inputs produces gray levels for an image. 
     A fourth aspect of the present invention provides a light modulation system for producing image gray levels. The light modulation system includes a data source for providing a data stream; and a serial-to-parallel converter for receiving the data stream and transmitting parallel data to parallel data channels. Each parallel data channel includes at least one pulse-width generator and at least two input drivers working in conjunction with the at least one pulse-width generators to produce at least two pulse-width-modulated waveforms. Also included in the light modulation system are a clock for controlling the timing of the at least one pulse-width generators; and an array of electromechanical conformal grating devices for modulating an incident light beam; each electromechanical conformal grating device including at least two sets of elongated ribbon elements and at least two inputs receiving the at least two pulse-width-modulated waveforms from the at least two input drivers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a prior art perspective, partially cut-away view of two conformal GEMS devices in a linear array; 
     FIG. 2 is a prior art top view of four conformal GEMS devices in a linear array; 
     FIGS. 3 a  and  3   b  are prior art cross-sectional views through line  3 — 3  in FIG. 2, showing the operation of a conformal GEMS device in an unactuated state with V=0 and a fully actuated state with V=V HIGH , respectively; 
     FIG. 4 is a prior art schematic illustrating a line-scanned display system incorporating a linear array of conformal GEMS devices; 
     FIG. 5 illustrates prior art formation of gray levels through pulse width modulation; 
     FIG. 6 is a plot showing a gray scale for a conformal GEMS device with gray levels obtained through pulse width modulation; 
     FIG. 7 is a top view of a linear array of dual-input conformal GEMS devices, illustrating the unactuated state; 
     FIG. 8 is a top view of a linear array of dual-input conformal GEMS devices, illustrating different states of actuation; 
     FIG. 9 is a plot showing the gray scale of the dual-input conformal GEMS device of FIGS. 7 and 8; 
     FIG. 10 is a top view of an alternate linear array of dual-input conformal GEMS devices, illustrating different states of actuation; 
     FIG. 11 is a plot showing the gray scale of the dual-input conformal GEMS device of FIG. 10; and 
     FIG. 12 shows a block diagram of the electronic architecture used to generate two pulse-width-modulated waveforms for driving a dual-input conformal GEMS device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the present invention, each conformal GEMS device of the linear array is constructed to have at least two inputs instead of a single input. The multiple inputs, in conjunction with appropriate modulated waveforms, are used to improve generation of gray levels in image-forming systems, such as projection displays and printers. 
     A top view of a linear array of dual-input conformal GEMS devices, in an unactuated state, is illustrated in FIG.  7 . Although only three dual-input conformal GEMS devices  40   a ,  40   b  and  40   c  are shown explicitly in FIG. 7, in practice, there could be a thousand or more devices on the linear array. Each device  40   a ,  40   b  and  40   c  has two inputs  41  and  42 . Each of these inputs is connected to a set of elongated ribbon elements. In the embodiment shown in FIG. 7, input  41  is connected electrically to two elongated ribbon elements  51  and input  42  to two elongated ribbon elements  52 . The ribbon elements are partially removed below line B—B to illustrate the structure underneath. This underlying structure is very similar to that of the prior art (single-input) conformal GEMS device shown in FIGS. 1-3, including end supports  24   a  and  24   b , channels  25 , standoffs  29 , and intermediate supports  27  within active region  8 . As before, to obtain maximum contrast, the intermediate supports  27  should be completely hidden below the elongated ribbon elements  51  and  52 . Therefore, when viewed from the top, the intermediate supports  27  should not be visible in the gaps  55 . 
     Although conformal GEMS devices with multiple ribbon elements were previously disclosed in U.S. Pat. No. 6,307,663, in that disclosure all of the ribbon elements were connected together electrically and addressed by a single input. In the present invention, the ribbon elements associated with a dual-input conformal GEMS device are grouped into two sets, with each set addressed by its own input. Multi-input conformal GEMS devices with more than two sets of elongated ribbon elements and more than two inputs are also possible. 
     FIG. 8 is a top view of the dual-input conformal GEMS devices  40   a ,  40   b  and  40   c  of FIG. 7, with a voltage applied to some of the inputs  41  and  42 . When any ribbon element is actuated by an applied voltage, the resulting electrostatic force causes it to conform partially around the intermediate supports  27  located underneath. In FIG. 8, the shading on the various ribbon elements represents their profile and state of actuation. Specifically, in device  40   a , both inputs  41  and  42  are in the off-state, i. e., there is no applied voltage. All of the elongated ribbon elements  51  and  52  associated with device  40   a  are, therefore, unactuated and suspended flat above the intermediate supports  27 . On the other hand, in device  40   b , both inputs  41  and  42  are in the on-state (voltage applied). The elongated ribbon elements  51  and  52  attached to those two inputs are actuated into contact with the standoffs  29 . Lastly, device  40   c  has its two inputs in opposites states, with input  42  in the on-state and the two associated ribbon elements  52  actuated, and input  41  in the off-state and the two associated ribbon elements  51  unactuated. 
     When illuminated by an incident light beam, preferably a line of laser light, the dual-input conformal GEMS devices  40   a ,  40   b  and  40   c  shown in FIGS. 7 and 8 function either as a mirror, a complete grating or a partial grating, depending on the state of the two inputs  41  and  42 . If both inputs  41  and  42  are in the off-state, a dual-input conformal GEMS device  40   a - 40   c  behaves like a simple planar mirror that reflects an incident light beam into the 0 th  order. If both inputs  41  and  42  are in the on-state, the device  40   a - 40   c  acts as a complete grating with period Λ and diffracts the majority of incident light into the +1 st  and −1 st  conformal orders. Additional light is diffracted into the +2 nd  and −2 nd  conformal orders and higher non-zero conformal orders. In a high-contrast display system, the optics would be designed to capture one or more of these non-zero conformal orders and block all other light. Several of the non-zero conformal orders could be captured if high efficiency is required. With inputs  41  and  42  in opposite states, i. e., one input in the on-state and one input in the off-state, a dual-input conformal GEMS device  40   a - 40   c  forms a partial grating with period Λ. The partial grating configuration, illustrated on device  40   c  of FIG. 8, has some of the elongated ribbon elements associated with a particular device actuated and others unactuated. 
     The partial grating configuration is designed to diffract a small portion of incident light into the (non-zero) conformal orders. Specifically, the relative diffraction efficiency into the conformal orders depends on the fill-factor squared of the light-reflecting surface that is in the actuated state. Therefore, for the dual-input conformal GEMS devices  40   a - 40   c  of FIGS. 7 and 8, the partial grating configuration has approximately a quarter of the light intensity in conformal orders compared to the complete grating configuration, since only half of the ribbon elements are activated. Light that is not diffracted into the conformal orders is either reflected into the 0 th  order or diffracted into other directions (not shown) blocked by the optical system. 
     Several different embodiments of dual-input conformal GEMS devices are possible. For example, the two inputs could have different numbers of elongated ribbon elements or the ribbons could have different widths. By proper selection of the ribbon number and ribbon width for each of the two inputs, it is possible to obtain any desired diffraction efficiency ratio between the complete grating and partial grating configurations. 
     FIG. 10 illustrates an alternate embodiment in which the light intensity of the conformal orders for the partial grating configuration is approximately one-ninth of that for the complete grating configuration. Four dual-input conformal GEMS devices  60   a - 60   d  are shown, each having two inputs  61  and  62 . Input  61  is connected to two elongated ribbon elements  51 , whereas input  62  is connected to a single elongated ribbon element  52 . As depicted in FIG. 10, devices  60   a  and  60   b  behave like a mirror, because both inputs  61  and  62  are in the off-state; device  60   c  functions as a complete grating, because both inputs  61  and  62  are in the on-state; and device  60   d  functions as a partial grating, because input  61  is in the off-state and input  62  is in the on-state. It should be noted that an alternate partial grating configuration with a different relative efficiency (four-ninths) can also be produced with this embodiment if input  61  is in the on-state and input  62  is in the off-state. 
     As mentioned earlier, by applying appropriate waveforms to dual-input conformal GEMS devices, it is possible to improve gray scale generation. FIGS. 9 and 11 show examples of gray scale formation for the dual-input conformal GEMS devices of FIGS. 8 and 10, respectively. As for single-input conformal GEMS devices, pulse-width-modulated waveforms similar to FIG. 6 are used to generate gray levels. The gray levels then correspond to the time-integrated light intensity of the conformal orders. In FIGS. 9 and 11, gray levels are formed either by applying the same pulse width to both inputs, activating the complete grating configuration, or by applying a pulse to a single input, keeping the other input in the off-state and activating the partial grating configuration. Bright levels in an image are, therefore, generated with both inputs turned on, whereas dark levels are generated with a single input turned on. As is desirable for good images, for a fixed pulse width increment, the spacing between relative gray levels is finer for dark levels than for bright levels. A transition region (not shown), where the gray levels can be formed either with both inputs on or with a single input on, could be used to provide headroom for calibration between the two gray level curves to produce a smooth gray scale. Furthermore, the impact of the non-monotonic region  50  of FIG. 6 can be reduced by activating a single input with the appropriate pulse width to generate the dark levels of interest. 
     Additional improvements in the gray scale can be obtained by simultaneously applying different pulse widths to the two inputs of a dual-input conformal GEMS device. Unlike the approach of FIGS. 9 and 11, this approach allows the fine gray level spacing to extend from dark levels to bright levels at the expense of greater electronic architecture complexity. 
     It is instructive to compare the speed requirements of the electronics for a dual-input conformal GEMS device with those for an ordinary (single-input) conformal GEMS device. The system is taken to be a high-quality projection display based on a linear array of devices, with a gray scale formed by pulse width modulation (PWM). Specifically, the system has HDTV resolution with 1,920 scanned lines (1,080 by 1,920 pixels), a frame rate of 60 Hz and a gray scale capability of 13 linear bits per color per flame (8,192 gray levels). For an ordinary conformal GEMS device, the pulse width increment must be somewhat less than 1/(1,920*60*8,192) seconds ˜1 nanoseconds to allow for some overhead for scanning the line to form a two-dimensional image. The digital electronics in the controller, therefore, need to generate an effective PWM clock of approximately 1 GHz. This effective clock frequency can be reduced substantially with a dual-input conformal GEMS device, while maintaining the same final system specifications. For example, for the embodiment depicted in FIG. 10, the effective PWM clock frequency can be reduced by a factor of 9 to approximately 111 MHz. 
     FIG. 12 shows a block diagram of an electronic architecture that could be used to drive a dual-input conformal GEMS device with pulse-width-modulated waveforms. This particular architecture enables two different pulse widths to be simultaneously applied to the two inputs in order to generate fine gray levels throughout the gray scale. It will be evident to those skilled in the art that this architecture can be simplified if the pulse widths applied to the two inputs are not independent, as in the case of FIGS. 9 and 11. A data source  100  provides a (serial) data stream  105  that has been appropriately preprocessed for generating an image from a linear array of devices. Since each dual-input conformal GEMS device  120  of the linear array requires its own parallel data channel  115 , a serial-to-parallel converter  102  is first needed to demultiplex the data stream  105  into parallel data to feed the parallel data channels  115 . For example, in the HDTV system mentioned above, there would be 1080 parallel data channels  115  in order to address 1080 dual-input conformal GEMS devices  120 , although only one of these parallel data channels  115  is shown in FIG.  12 . Each parallel data channel consists of an input pulse-width selector  103 , a pair of pulse-width generators  106  and  107  synchronized with clock  104 , and a pair of input drivers  108  and  109 . The pulse-width selector  103  determines the two pulse widths that need to be applied to the two inputs  110  and  111  of the dual-input conformal GEMS device  120  in order to obtain a desired gray level. These two pulse widths are produced by a pair of high-voltage input drivers  108  and  109  that are controlled digitally by pulse-width generators  106  and  107  and synchronized with clock  104 . If ribbon charging is a problem, the pulse-width selector  103  could also be used to select polarity of the pulses applied to the two inputs  110  and  111 , in order to generate pulse-width-modulated waveforms that are DC-free. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
       5   a  conformal GEMS device 
       5   b  conformal GEMS device 
       5   c  conformal GEMS device 
       5   d  conformal GEMS device 
       8  active region 
       10  substrate 
       12  bottom conductive layer 
       14  dielectric protective layer 
       16  standoff layer 
       18  spacerlayer 
       20  ribbon layer 
       22  reflective and conductive layer 
       23   a  elongated ribbon element 
       23   b  elongated ribbon element 
       23   c  elongated ribbon element 
       23   d  elongated ribbon element 
       24   a  end support 
       24   b  end support 
       25  channels 
       27  intermediate supports 
       28  gaps 
       29  standoffs 
       30  incident light beam 
       32  0 th  order light beam 
       35   a  +1 st  conformal order 
       35   b  −1 st  conformal order 
       36   a  +2 nd  conformal order 
       36   b  −2 nd  conformal order 
       40   a  dual-input conformal GEMS device 
       40   b  dual-input conformal GEMS device 
       40   c  dual-input conformal GEMS device 
       41  inputs 
       42  inputs 
       45  conventional PWM waveform 
       50  non-monotonic region 
       51  elongated ribbon elements 
       52  elongated ribbon elements 
       53  time-integrated light intensity 
       54  modulation window 
       55  gaps 
       60   a  dual-input conformal GEMS device 
       60   b  dual-input conformal GEMS device 
       60   c  dual-input conformal GEMS device 
       60   d  dual-input conformal GEMS device 
       61  inputs 
       62  inputs 
       70  source 
       72  spherical lens 
       74  cylindrical lens 
       75  projection lens system 
       77  scanning mirror 
       80  controller 
       82  turning mirror 
       85  linear array 
       90  screen 
       100  data source 
       102  serial-to-parallel converter 
       103  input pulse-width selector 
       104  clock 
       105  data stream 
       106  pulse-width generator 
       107  pulse-width generator 
       108  input driver 
       109  input driver 
       110  input 
       111  input 
       115  parallel data channels 
       120  dual-input conformal GEMS device