Patent Publication Number: US-2009231877-A1

Title: Thin light bar and method of manufacturing

Description:
BACKGROUND 
     1. Field 
     The present invention relates to microelectromechanical systems (MEMS). 
     2. Description of the Related Art 
     Microelectromechanical systems (MEMS) include micro mechanical elements, actuators, and electronics. Micromechanical elements may be created using deposition, etching, and or other micromachining processes that etch away parts of substrates and/or deposited material layers or that add layers to form electrical and electromechanical devices. One type of MEMS device is called an interferometric modulator. As used herein, the term interferometric modulator or interferometric light modulator refers to a device that selectively absorbs and/or reflects light using the principles of optical interference. In certain embodiments, an interferometric modulator may comprise a pair of conductive plates, one or both of which may be transparent and/or reflective in whole or part and capable of relative motion upon application of an appropriate electrical signal. In a particular embodiment, one plate may comprise a stationary layer deposited on a substrate and the other plate may comprise a metallic membrane separated from the stationary layer by an air gap. As described herein in more detail, the position of one plate in relation to another can change the optical interference of light incident on the interferometric modulator. Such devices have a wide range of applications, and it would be beneficial in the art to utilize and/or modify the characteristics of these types of devices so that their features can be exploited in improving existing products and creating new products that have not yet been developed. 
     SUMMARY 
     In one embodiment, a display device comprises a light bar, having two or more distinct layers, that guides light along a length thereof, a turning microstructure disposed on at least one of a top and a bottom of the light bar, the turning microstructure configured to direct said light out a side of the light bar, a light guide panel disposed with respect to said side of the light bar such that said light from said light bar is coupled to said light guide panel, said light guide panel configured to direct said light coupled therein out of said light guide panel, and a plurality of light modulators disposed with respect to the light guide panel to receive said light directed out of said light guide panel. 
     In one embodiment, a display device comprises a first means for guiding light along a length thereof, means for turning said light guided in said first light guiding means and directing said light out a side of the first light guiding means, said light turning means disposed on at least one of a top and a bottom of the first light guiding means, a second means for guiding said light disposed with respect to said side of the first light guiding means such that said light from said first light guiding means is coupled therein, said second light guiding means configured to direct said light coupled therein out of said second light guiding means, and means for modulating said light disposed with respect to the second light guiding means to receive said light directed out of said second light guiding means. 
     In one embodiment, a method of manufacturing a display device comprises providing a light bar that guides light along a length thereof, said light bar having a turning microstructure disposed on a top or bottom thereof, the turning microstructure configured to direct said light out a side of the light bar, disposing a light guide panel with respect to the side of the light bar such that light from said light bar is coupled to said light guide panel, said light guide panel configured to direct said light coupled therein out of said light panel, and disposing a plurality of light modulators with respect to the light guide panel to receive said light directed out of said light guide panel. 
     In one embodiment, a light bar has a front surface in optical communication with a display device and the light bar is configured to guide light along a length thereof, wherein the light bar comprises a first film layer having a plurality of faceted features thereon, a second film layer having a plurality of faceted features thereon, and an optical coupling layer positioned between and coupling the first and second film layers, the optical coupling layer configured to propagate light, wherein the faceted features on the first and second film layers are configured to direct light out of the front surface of the light bar towards the display device. 
     In one embodiment, a method of manufacturing a light bar material for delivering light to a display device comprises embossing a first plurality of faceted features on a first film layer, embossing a second plurality of faceted features on a second film layer, coupling the first and second film layers to form a composite film, wherein the faceted features on the first and second film layers are configured to direct light out of the light bar material. 
     In one embodiment, an illumination apparatus comprises a light bar, having two or more distinct layers, that guides light along a length thereof, and a turning microstructure disposed on at least one of a top and a bottom of the light bar, the turning microstructure configured to direct said light out a side of the light bar. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view depicting a portion of one embodiment of an interferometric modulator display in which a movable reflective layer of a first interferometric modulator is in a relaxed position and a movable reflective layer of a second interferometric modulator is in an actuated position. 
         FIG. 2  is a system block diagram illustrating one embodiment of an electronic device incorporating a 3×3 interferometric modulator display. 
         FIG. 3  is a diagram of movable mirror position versus applied voltage for one exemplary embodiment of an interferometric modulator of  FIG. 1 . 
         FIG. 4  is an illustration of a set of row and column voltages that may be used to drive an interferometric modulator display. 
         FIGS. 5A and 5B  illustrate one exemplary timing diagram for row and column signals that may be used to write a frame of display data to the 3×3 interferometric modulator display of  FIG. 2 . 
         FIGS. 6A and 6B  are system block diagrams illustrating an embodiment of a visual display device comprising a plurality of interferometric modulators. 
         FIG. 7A  is a cross section of the device of  FIG. 1 . 
         FIG. 7B  is a cross section of an alternative embodiment of an interferometric modulator. 
         FIG. 7C  is a cross section of another alternative embodiment of an interferometric modulator. 
         FIG. 7D  is a cross section of yet another alternative embodiment of an interferometric modulator. 
         FIG. 7E  is a cross section of an additional alternative embodiment of an interferometric modulator. 
         FIG. 8  is an exploded perspective view of one embodiment of an illumination system disposed forward a spatial light modulator array. 
         FIG. 9  is a top view of an illumination apparatus comprising a light bar and a light guide panel. 
         FIGS. 10 and 11  are top views of embodiments of light bars comprising microstructures on a top and/or bottom surface of the light bars. 
         FIG. 12  is an elevated side view of the light bar of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS 
     The following detailed description is directed to certain specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. As will be apparent from the following description, the embodiments may be implemented in any device that is configured to display an image, whether in motion (e.g., video) or stationary (e.g., still image), and whether textual or pictorial. More particularly, it is contemplated that the embodiments may be implemented in or associated with a variety of electronic devices such as, but not limited to, mobile telephones, wireless devices, personal data assistants (PDAs), hand-held or portable computers, GPS receivers/navigators, cameras, MP3 players, camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, computer monitors, auto displays (e.g., odometer display, etc.), cockpit controls and/or displays, display of camera views (e.g., display of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, packaging, and aesthetic structures (e.g., display of images on a piece of jewelry). MEMS devices of similar structure to those described herein can also be used in non-display applications such as in electronic switching devices. 
     Various embodiments disclosed herein comprise a display device comprising a plurality of spatial light modulators and an illumination apparatus. The illumination apparatus comprises a light bar that guides light along a length thereof and turning microstructure disposed on top or bottom of the light bar. The turning microstructure directs the light out a side of the light bar. The illumination apparatus further comprises a light guide panel disposed with respect to the side of the light bar such that the light from the light bar is coupled to the light guide panel. The light guide panel is configured to direct the light coupled therein out of the light guide panel. The plurality of light modulators disposed with respect to the light guide panel to receive the light directed out of the light guide panel. 
     In certain embodiments, the light modulators comprise reflective spatial light modulators. In some embodiments, the light modulators comprise MEMS devices. In various embodiments, the light modulators comprise interferometric modulators. 
     One interferometric modulator display embodiment comprising an interferometric MEMS display element is illustrated in  FIG. 1 . In these devices, the pixels are in either a bright or dark state. In the bright (“on” or “open”) state, the display element reflects a large portion of incident visible light to a user. When in the dark (“off” or “closed”) state, the display element reflects little incident visible light to the user. Depending on the embodiment, the light reflectance properties of the “on” and “off” states may be reversed. MEMS pixels can be configured to reflect predominantly at selected colors, allowing for a color display in addition to black and white. 
       FIG. 1  is an isometric view depicting two adjacent pixels in a series of pixels of a visual display, wherein each pixel comprises a MEMS interferometric modulator. In some embodiments, an interferometric modulator display comprises a row/column array of these interferometric modulators. Each interferometric modulator includes a pair of reflective layers positioned at a variable and controllable distance from each other to form a resonant optical cavity with at least one variable dimension. In one embodiment, one of the reflective layers may be moved between two positions. In the first position, referred to herein as the relaxed position, the movable reflective layer is positioned at a relatively large distance from a fixed partially reflective layer. In the second position, referred to herein as the actuated position, the movable reflective layer is positioned more closely adjacent to the partially reflective layer. Incident light that reflects from the two layers interferes constructively or destructively depending on the position of the movable reflective layer, producing either an overall reflective or non-reflective state for each pixel. 
     The depicted portion of the pixel array in  FIG. 1  includes two adjacent interferometric modulators  12   a  and  12   b . In the interferometric modulator  12   a  on the left, a movable reflective layer  14   a  is illustrated in a relaxed position at a predetermined distance from an optical stack  16   a , which includes a partially reflective layer. In the interferometric modulator  12   b  on the right, the movable reflective layer  14   b  is illustrated in an actuated position adjacent to the optical stack  16   b.    
     The optical stacks  16   a  and  16   b  (collectively referred to as optical stack  16 ), as referenced herein, typically comprise of several fused layers, which can include an electrode layer, such as indium tin oxide (ITO), a partially reflective layer, such as chromium, and a transparent dielectric. The optical stack  16  is thus electrically conductive, partially transparent and partially reflective, and may be fabricated, for example, by depositing one or more of the above layers onto a transparent substrate  20 . In some embodiments, the layers are patterned into parallel strips, and may form row electrodes in a display device as described further below. The movable reflective layers  14   a ,  14   b  may be formed as a series of parallel strips of a deposited metal layer or layers (orthogonal to the row electrodes of  16   a ,  16   b ) deposited on top of posts  18  and an intervening sacrificial material deposited between the posts  18 . When the sacrificial material is etched away, the movable reflective layers  14   a ,  14   b  are separated from the optical stacks  16   a ,  16   b  by a defined gap  19 . A highly conductive and reflective material such as aluminum may be used for the reflective layers  14 , and these strips may form column electrodes in a display device. 
     With no applied voltage, the cavity  19  remains between the movable reflective layer  14   a  and optical stack  16   a , with the movable reflective layer  14   a  in a mechanically relaxed state, as illustrated by the pixel  12   a  in  FIG. 1 . However, when a potential difference is applied to a selected row and column, the capacitor formed at the intersection of the row and column electrodes at the corresponding pixel becomes charged, and electrostatic forces pull the electrodes together. If the voltage is high enough, the movable reflective layer  14  is deformed and is forced against the optical stack  16 . A dielectric layer (not illustrated in this Figure) within the optical stack  16  may prevent shorting and control the separation distance between layers  14  and  16 , as illustrated by pixel  12   b  on the right in  FIG. 1 . The behavior is the same regardless of the polarity of the applied potential difference. In this way, row/column actuation that can control the reflective vs. non-reflective pixel states is analogous in many ways to that used in conventional LCD and other display technologies. 
       FIGS. 2 through 5  illustrate one exemplary process and system for using an array of interferometric modulators in a display application. 
       FIG. 2  is a system block diagram illustrating one embodiment of an electronic device that may incorporate aspects of the invention. In the exemplary embodiment, the electronic device includes a processor  21  which may be any general purpose single- or multi-chip microprocessor such as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®, Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any special purpose microprocessor such as a digital signal processor, microcontroller, or a programmable gate array. As is conventional in the art, the processor  21  may be configured to execute one or more software modules. In addition to executing an operating system, the processor may be configured to execute one or more software applications, including a web browser, a telephone application, an email program, or any other software application. 
     In one embodiment, the processor  21  is also configured to communicate with an array driver  22 . In one embodiment, the array driver  22  includes a row driver circuit  24  and a column driver circuit  26  that provide signals to a panel or display array (display)  30 . The cross section of the array illustrated in  FIG. 1  is shown by the lines  1 - 1  in  FIG. 2 . For MEMS interferometric modulators, the row/column actuation protocol may take advantage of a hysteresis property of these devices illustrated in  FIG. 3 . It may require, for example, a 10 volt potential difference to cause a movable layer to deform from the relaxed state to the actuated state. However, when the voltage is reduced from that value, the movable layer maintains its state as the voltage drops back below 10 volts. In the exemplary embodiment of  FIG. 3 , the movable layer does not relax completely until the voltage drops below 2 volts. There is thus a range of voltage, about 3 to 7 V in the example illustrated in  FIG. 3 , where there exists a window of applied voltage within which the device is stable in either the relaxed or actuated state. This is referred to herein as the “hysteresis window” or “stability window.” For a display array having the hysteresis characteristics of  FIG. 3 , the row/column actuation protocol can be designed such that during row strobing, pixels in the strobed row that are to be actuated are exposed to a voltage difference of about 10 volts, and pixels that are to be relaxed are exposed to a voltage difference of close to zero volts. After the strobe, the pixels are exposed to a steady state voltage difference of about 5 volts such that they remain in whatever state the row strobe put them in. After being written, each pixel sees a potential difference within the “stability window” of 3-7 volts in this example. This feature makes the pixel design illustrated in  FIG. 1  stable under the same applied voltage conditions in either an actuated or relaxed pre-existing state. Since each pixel of the interferometric modulator, whether in the actuated or relaxed-state, is essentially a capacitor formed by the fixed and moving reflective layers, this stable state can be held at a voltage within the hysteresis window with almost no power dissipation. Essentially no current flows into the pixel if the applied potential is fixed. 
     In typical applications, a display frame may be created by asserting the set of column electrodes in accordance with the desired set of actuated pixels in the first row. A row pulse is then applied to the row  1  electrode, actuating the pixels corresponding to the asserted column lines. The asserted set of column electrodes is then changed to correspond to the desired set of actuated pixels in the second row. A pulse is then applied to the row  2  electrode, actuating the appropriate pixels in row  2  in accordance with the asserted column electrodes. The row  1  pixels are unaffected by the row  2  pulse, and remain in the state they were set to during the row  1  pulse. This may be repeated for the entire series of rows in a sequential fashion to produce the frame. Generally, the frames are refreshed and/or updated with new display data by continually repeating this process at some desired number of frames per second. A wide variety of protocols for driving row and column electrodes of pixel arrays to produce display frames are also well known and may be used in conjunction with the present invention. 
       FIGS. 4 and 5  illustrate one possible actuation protocol for creating a display frame on the 3×3 array of  FIG. 2 .  FIG. 4  illustrates a possible set of column and row voltage levels that may be used for pixels exhibiting the hysteresis curves of  FIG. 3 . In the  FIG. 4  embodiment, actuating a pixel involves setting the appropriate column to −V bias , and the appropriate row to +ΔV, which may correspond to −5 volts and +5 volts respectively Relaxing the pixel is accomplished by setting the appropriate column to +V bias , and the appropriate row to the same +μV, producing a zero volt potential difference across the pixel. In those rows where the row voltage is held at zero volts, the pixels are stable in whatever state they were originally in, regardless of whether the column is at +V bias , or −V bias . As is also illustrated in  FIG. 4 , it will be appreciated that voltages of opposite polarity than those described above can be used, e.g., actuating a pixel can involve setting the appropriate column to +V bias , and the appropriate row to −μV. In this embodiment, releasing the pixel is accomplished by setting the appropriate column to −V bias , and the appropriate row to the same −ΔV, producing a zero volt potential difference across the pixel. 
       FIG. 5B  is a timing diagram showing a series of row and column signals applied to the 3×3 array of  FIG. 2  which will result in the display arrangement illustrated in  FIG. 5A , where actuated pixels are non-reflective. Prior to writing the frame illustrated in  FIG. 5A , the pixels can be in any state, and in this example, all the rows are at 0 volts, and all the columns are at +5 volts. With these applied voltages, all pixels are stable in their existing actuated or relaxed states. 
     In the  FIG. 5A  frame, pixels ( 1 , 1 ), ( 1 , 2 ), ( 2 , 2 ), ( 3 , 2 ) and ( 3 , 3 ) are actuated. To accomplish this, during a “line time” for row  1 , columns  1  and  2  are set to −5 volts, and column  3  is set to +5 volts. This does not change the state of any pixels, because all the pixels remain in the 3-7 volt stability window. Row  1  is then strobed with a pulse that goes from 0, up to 5 volts, and back to zero. This actuates the (1,1) and (1,2) pixels and relaxes the (1,3) pixel. No other pixels in the array are affected. To set row  2  as desired, column  2  is set to −5 volts, and columns  1  and  3  are set to +5 volts. The same strobe applied to row  2  will then actuate pixel ( 2 , 2 ) and relax pixels ( 2 , 1 ) and ( 2 , 3 ). Again, no other pixels of the array are affected. Row  3  is similarly set by setting columns  2  and  3  to −5 volts, and column  1  to +5 volts. The row  3  strobe sets the row  3  pixels as shown in  FIG. 5A . After writing the frame, the row potentials are zero, and the column potentials can remain at either +5 or −5 volts, and the display is then stable in the arrangement of  FIG. 5A . It will be appreciated that the same procedure can be employed for arrays of dozens or hundreds of rows and columns. It will also be appreciated that the timing, sequence, and levels of voltages used to perform row and column actuation can be varied widely within the general principles outlined above, and the above example is exemplary only, and any actuation voltage method can be used with the systems and methods described herein. 
       FIGS. 6A and 6B  are system block diagrams illustrating an embodiment of a display device  40 . The display device  40  can be, for example, a cellular or mobile telephone. However, the same components of display device  40  or slight variations thereof are also illustrative of various types of display devices such as televisions and portable media players. 
     The display device  40  includes a housing  41 , a display  30 , an antenna  43 , a speaker  45 , an input device  48 , and a microphone  46 . The housing  41  is generally formed from any of a variety of manufacturing processes as are well known to those of skill in the art, including injection molding, and vacuum forming. In addition, the housing  41  may be made from any of a variety of materials, including but not limited to plastic, metal, glass, rubber, and ceramic, or a combination thereof. In one embodiment the housing  41  includes removable portions (not shown) that may be interchanged with other removable portions of different color, or containing different logos, pictures, or symbols. 
     The display  30  of exemplary display device  40  may be any of a variety of displays, including a bi-stable display, as described herein. In other embodiments, the display  30  includes a flat-panel display, such as plasma, EL, OLED, STN LCD, or TFT LCD as described above, or a non-flat-panel display, such as a CRT or other tube device, as is well known to those of skill in the art. However, for purposes of describing the present embodiment, the display  30  includes an interferometric modulator display, as described herein. 
     The components of one embodiment of exemplary display device  40  are schematically illustrated in  FIG. 6B . The illustrated exemplary display device  40  includes a housing  41  and can include additional components at least partially enclosed therein. For example, in one embodiment, the exemplary display device  40  includes a network interface  27  that includes an antenna  43  which is coupled to a transceiver  47 . The transceiver  47  is connected to the processor  21 , which is connected to conditioning hardware  52 . The conditioning hardware  52  may be configured to condition a signal (e.g. filter a signal). The conditioning hardware  52  is connected to a speaker  45  and a microphone  46 . The processor  21  is also connected to an input device  48  and a driver controller  29 . The driver controller  29  is coupled to a frame buffer  28  and to the array driver  22 , which in turn is coupled to a display array  30 . A power supply  50  provides power to all components as required by the particular exemplary display device  40  design. 
     The network interface  27  includes the antenna  43  and the transceiver  47  so that the exemplary display device  40  can communicate with one or more devices over a network. In one embodiment the network interface  27  may also have some processing capabilities to relieve requirements of the processor  21 . The antenna  43  is any antenna known to those of skill in the art for transmitting and receiving signals. In one embodiment, the antenna transmits and receives RF signals according to the IEEE 802.11 standard, including IEEE 802.11(a), (b), or (g). In another embodiment, the antenna transmits and receives RF signals according to the BLUETOOTH standard. In the case of a cellular telephone, the antenna is designed to receive CDMA, GSM, AMPS or other known signals that are used to communicate within a wireless cell phone network. The transceiver  47  pre-processes the signals received from the antenna  43  so that they may be received by and further manipulated by the processor  21 . The transceiver  47  also processes signals received from the processor  21  so that they may be transmitted from the exemplary display device  40  via the antenna  43 . 
     In an alternative embodiment, the transceiver  47  can be replaced by a receiver. In yet another alternative embodiment, network interface  27  can be replaced by an image source, which can store or generate image data to be sent to the processor  21 . For example, the image source can be a digital video disc (DVD) or a hard-disc drive that contains image data, or a software module that generates image data. 
     Processor  21  generally controls the overall operation of the exemplary display device  40 . The processor  21  receives data, such as compressed image data from the network interface  27  or an image source, and processes the data into raw image data or into a format that is readily processed into raw image data. The processor  21  then sends the processed data to the driver controller  29  or to frame buffer  28  for storage. Raw data typically refers to the information that identifies the image characteristics at each location within an image. For example, such image characteristics can include color, saturation, and gray-scale level. 
     In one embodiment, the processor  21  includes a microcontroller, CPU, or logic unit to control operation of the exemplary display device  40 . Conditioning hardware  52  generally includes amplifiers and filters for transmitting signals to the speaker  45 , and for receiving signals from the microphone  46 . Conditioning hardware  52  may be discrete components within the exemplary display device  40 , or may be incorporated within the processor  21  or other components. 
     The driver controller  29  takes the raw image data generated by the processor  21  either directly from the processor  21  or from the frame buffer  28  and reformats the raw image data appropriately for high speed transmission to the array driver  22 . Specifically, the driver controller  29  reformats the raw image data into a data flow having a raster-like format, such that it has a time order suitable for scanning across the display array  30 . Then the driver controller  29  sends the formatted information to the array driver  22 . Although a driver controller  29 , such as a LCD controller, is often associated with the system processor  21  as a stand-alone Integrated Circuit (IC), such controllers may be implemented in many ways. They may be embedded in the processor  21  as hardware, embedded in the processor  21  as software, or fully integrated in hardware with the array driver  22 . Typically, the array driver  22  receives the formatted information from the driver controller  29  and reformats the video data into a parallel set of waveforms that are applied many times per second to the hundreds and sometimes thousands of leads coming from the display&#39;s x-y matrix of pixels. 
     In one embodiment, the driver controller  29 , array driver  22 , and display array  30  are appropriate for any of the types of displays described herein. For example, in one embodiment, driver controller  29  is a conventional display controller or a bi-stable display controller (e.g., an interferometric modulator controller). In another embodiment, array driver  22  is a conventional driver or a bi-stable display driver (e.g., an interferometric modulator display). In one embodiment, a driver controller  29  is integrated with the array driver  22 . Such an embodiment is common in highly integrated systems such as cellular phones, watches, and other small area displays. In yet another embodiment, display array  30  is a typical display array or a bi-stable display array (e.g., a display including an array of interferometric modulators). 
     The input device  48  allows a user to control the operation of the exemplary display device  40 . In one embodiment, input device  48  includes a keypad, such as a QWERTY keyboard or a telephone keypad, a button, a switch, a touch-sensitive screen, a pressure- or heat-sensitive membrane. In one embodiment, the microphone  46  is an input device for the exemplary display device  40 . When the microphone  46  is used to input data to the device, voice commands may be provided by a user for controlling operations of the exemplary display device  40 . 
     Power supply  50  can include a variety of energy storage devices as are well known in the art. For example, in one embodiment, power supply  50  is a rechargeable battery, such as a nickel-cadmium battery or a lithium ion battery. In another embodiment, power supply  50  is a renewable energy source, a capacitor, or a solar cell, including a plastic solar cell, and solar-cell paint. In another embodiment, power supply  50  is configured to receive power from a wall outlet. 
     In some implementations control programmability resides, as described above, in a driver controller which can be located in several places in the electronic display system. In some cases control programmability resides in the array driver  22 . Those of skill in the art will recognize that the above-described optimization may be implemented in any number of hardware and/or software components and in various configurations. The details of the structure of interferometric modulators that operate in accordance with the principles set forth above may vary widely. For example,  FIGS. 7A-7E  illustrate five different embodiments of the movable reflective layer  14  and its supporting structures.  FIG. 7A  is a cross section of the embodiment of  FIG. 1 , where a strip of metal material  14  is deposited on orthogonally extending supports  18 . In  FIG. 7B , the moveable reflective layer  14  is attached to supports at the corners only, on tethers  32 . In  FIG. 7C , the moveable reflective layer  14  is suspended from a deformable layer  34 , which may comprise a flexible metal. The deformable layer  34  connects, directly or indirectly, to the substrate  20  around the perimeter of the deformable layer  34 . These connections are herein referred to as support posts. The embodiment illustrated in  FIG. 7D  has support post plugs  42  upon which the deformable layer  34  rests. The movable reflective layer  14  remains suspended over the cavity, as in  FIGS. 7A-7C , but the deformable layer  34  does not form the support posts by filling holes between the deformable layer  34  and the optical stack  16 . Rather, the support posts are formed of a planarization material, which is used to form support post plugs  42 . The embodiment illustrated in  FIG. 7E  is based on the embodiment shown in  FIG. 7D , but may also be adapted to work with any of the embodiments illustrated in  FIGS. 7A-7C  as well as additional embodiments not shown. In the embodiment shown in  FIG. 7E , an extra layer of metal or other conductive material has been used to form a bus structure  44 . This allows signal routing along the back of the interferometric modulators, eliminating a number of electrodes that may otherwise have had to be formed on the substrate  20 . 
     In embodiments such as those shown in  FIG. 7 , the interferometric modulators function as direct-view devices, in which images are viewed from the front side of the transparent substrate  20 , the side opposite to that upon which the modulator is arranged. In these embodiments, the reflective layer  14  optically shields some portions of the interferometric modulator on the side of the reflective layer opposite the substrate  20 , including the deformable layer  34  and the bus structure  44 . This allows the shielded areas to be configured and operated upon without negatively affecting the image quality. This separable modulator architecture allows the structural design and materials used for the electromechanical aspects and the optical aspects of the modulator to be selected and to function independently of each other. Moreover, the embodiments shown in  FIGS. 7C-7E  have additional benefits deriving from the decoupling of the optical properties of the reflective layer  14  from its mechanical properties, which are carried out by the deformable layer  34 . This allows the structural design and materials used for the reflective layer  14  to be optimized with respect to the optical properties, and the structural design and materials used for the deformable layer  34  to be optimized with respect to desired mechanical properties. 
     As described above, light incident on an interferometric modulator is either reflected or absorbed via constructive or destructive interference according to an actuation state of one of the reflective surfaces. Such interferometric phenomena are highly dependent on both the wavelength and the angle of incidence of the incident light. This complicates the design of an illumination apparatus that provides artificial lighting to a display device comprising an interferometric modulator or array thereof. In various embodiments, however, the illumination apparatus may advantageously effectively illuminate the display during low lighting conditions. Moreover, in some embodiments an illumination system that is used with an interferometric display device is designed for the unique characteristics of the modulators in the display device. 
       FIG. 8  illustrates a perspective view of one embodiment of an illumination system  80  disposed forward a light modulating array  81  comprising a plurality of light modulating elements  81   a . In certain embodiments, the light modulating elements  81   a  are reflective display elements that reflect light incident thereon. The light modulating array  81  may, for example, comprise an array of interferometric modulators. In the embodiments shown in  FIG. 8 , the light modulating array  81  comprises rows and columns of light modulating elements (e.g., extending along x and y directions). At least part of the illumination system  80  is disposed forward of the light modulating array  81  (e.g., in the z direction) to provide front illumination thereof. 
     In the embodiment of  FIG. 8 , the illumination system comprises a light source  82 , a reflector  84 , a light bar  86 , and a light guide panel  88 . In  FIG. 8 , these components are illustrated in an exploded view. In general, lights rays are emitted from the light source  82  into the light bar  86  and are reflected within the light bar  86  due to total internal reflection (TIR). Thus, the light rays propagate through the light bar  86  until the rays are angled below the critical angle by turning features, which are discussed below, and are ejected from the light bar  86 . In an advantageous embodiment, the light that is ejected from a front side  86   f  of the light bar  86  is increased or maximized. 
     In the embodiment of  FIG. 8 , because some light rays will escape from the light bar from surfaces other than the front side  86   f , the illumination system additionally comprises the reflector  84  that is configured to encase at least a portion of the light bar  86  and possibly the light source  82 . Thus, in one embodiment the light emitting portion of the light source  82  is at least partially encased in end  84 A of the reflector  84  and a portion of the light bar  86  is surrounded by a portion  84 B of the reflector  84 . In one embodiment, the reflector  84  substantially surrounds all sides of the light bar  86  except for a front side  86   f  of the light bar  86  from which light may be ejected and an opening for the light source  82 , for example. By positioning the reflector  84  around the light bar  86  in such as way, light that escapes from the light bar  86  from the top, bottom, or rear side  86   r  might be reflected by the reflector  84  back into the light bar  86 , and eventually ejected from the front side  86   f  of the light bar  86 . 
     In one embodiment, the light source  82  is effectively a point source (e.g., an LED) that emits light into an end of the light bar  86 , such as end  86 A of the light bar  86 , while the light bar  86  itself is effectively a linear source. For example, the injected light from the light source  82  is guided along at least a portion of a length of the light bar  86 . As described above, the light rays are reflected from a surfaces of the light bar  86 , such as top, bottom, rear  86 R and front surfaces  86 F of the light bar  86  due to total internal reflection (TIR). The light rays are ejected across the length thereof from the front surface  86 F of light bar  86  after being reflected from one or more turning structures on the rear surface  86 R. Thus, the light bar  86  is configured to spread light in the indicated x direction (e.g., along a length of the light bar  86 ) and to turn the light in the y direction (e.g., out of the front surface  86 F towards the light guide panel  88 ). The light guide panel  88  then spreads the light in the y direction and turns the light towards the z direction so that the light is emitted towards one or more display elements therebelow. In one embodiment, the light guide panel  88  includes a turning film that directs light propagating through the light guide panel  88  towards the one or more display elements. This prismatic turning film may comprise a film having a plurality of grooves  89  disposed therein that reflect light downwards or rearward out of the rear of the light guide panel  88  and to the light modulating array  81 . The grooves  89  in the light guide panel  88  may operate based on total internal reflection in some embodiments. In other embodiments, other type of features may be included in the light guide panel  88  to reflect, scatter, or redirect light guided within the light guide panel to the light modulating elements  81   a.    
     For display devices comprising interferometric modulators, for example, the emission characteristics into the light guide panel  88  are important for the optimal performance of the interferometric modulators. For example, the light is uniformly distributed in both the x and y directions across the light guide panel  88  and the plurality of display elements. 
     Turning features in the light bar  86  can be used to distribute light into the light guide panel  88 . As discussed more fully below, control over the position and orientation of the turning features in the light bar  86  enables control over the distribution of light within the light guide panel  88  and the consequent illumination of the array of display elements (e.g., in the x direction). 
       FIG. 9  is a top view of an illumination apparatus comprising a light bar  90  and the light guide panel  88  showing in more detail the turning features that turn light propagating within the light bar into the light guide panel  88 . In the embodiment of  FIG. 9 , the light bar  90  has a first end  90 A for receiving light from a light source  92 . As noted above, the light source  92  may comprise a light emitting diode (LED) or any other suitable light source. In this embodiment, the light bar  90  comprises material that supports propagation of light along the length of the light bar  90 . 
     In the embodiment of  FIG. 9 , the light bar  90  also comprises turning microstructure on or adjacent to a rear surface  90 R, which is substantially opposite the front surface  90 F. In one embodiment, the turning microstructure is configured to turn at least a substantial portion of the light incident on the rear surface  90 R of the light bar  90  and to direct that portion of light out of the light bar  90  into the light guide panel  88 . The turning microstructure of the light bar  90  comprises a plurality of faceted features  91 . In one embodiment, the turning microstructure is integrated with the light bar  90 . For example, the light bar with turning microstructure can be formed by injection molding. In other embodiments, a turning film may be disposed on the rear side of the light bar  90 . Turning films may be formed by, e.g., embossing, and the film may be laminated on the rear side of the light bar  90 . 
     In one embodiment, reflectors  96 ,  97  may be disposed with respect to the light bar  90  to reflect light escaping therefrom back into the light bar. Such reflectors  96 ,  97  may have contoured shape, for example, matching the grooves  91  of the light bar  90 . The reflectors  96 ,  97  may also comprise retro-reflectors in some embodiments. 
     Additionally, in one embodiment an optical coupling element (not shown) may be disposed between the light bar  90  and the light guide panel  88 . This optical coupling element may comprises for example a collimator that at least partially collimates light ejected from the light bar  90  and directed into the light guide panel  88 . This optical coupling element may be tapered; for example, the optical coupling element may have a first side closer to the light bar that is larger and a second side closer to the light guide panel that is smaller. Such tapered geometry may provide increase collimation. In other embodiments, the optical coupling element is excluded and the light bar  90  is tapered. The rear side  90   r  of the light bar  90  farthest from the light guide panel  88  may be larger and the front side  90   f  closest to the light guide panel may be smaller. Light exiting the light bar  90  and entering the light guide panel  88  may thereby be collimated. In other embodiments, no optical coupling element is disposed between the light bar  90  and the light guide panel  88 . 
     An example ray of light is also illustrated in  FIG. 9 . The light ray emitted from the light source  92  propagates into the light bar  90 , where it undergoes total internal reflection (TIR) at a front surface  90 F that is adjacent air or some other medium. The light ray then reflects off the rear surface  90 R. In particular, the light ray reflects off a reflective surface portion parallel to the length of the light bar  90  and then off of a sloped surface portion forming a turning feature. The light ray is turned by one or more turning microstructures and directed out of the light bar  90 . The light ray shown is directed near normal to the length of the light bar. 
       FIGS. 10 ,  11 , and  12  show how the orientation, position, and configuration of the turning features can be adjusted to control the propagation of light from the light bar to the light guide panel  88 .  FIGS. 10 and 11  are top views of embodiments of light bars  100 , including light bars  100 A and  100 B, wherein each of the light bars  100  comprises microstructures on a top and/or bottom surface of the light bars  100 .  FIG. 12  is an elevated side view of the light bar  100 A of  FIG. 10 . In the embodiments of  FIGS. 10 ,  11 , and  12 , the light bars  100  comprise one or more turning features that are adapted to selectively turn light from the light bars  100  onto the light guide panel  88 . In one embodiment, the turning features comprise elongated structures that are angled with respect to the length and width of the light bar to control the injection of light into the light guide panel. 
     For example, in the embodiment of  FIGS. 10 ,  11 , and  12 , the turning features comprise one or more turning features  102  that are configured to redirect light rays towards the light guide panel  88 . In the embodiment of  FIGS. 10 ,  11 , and  12 , the faceted features  102  comprise V-shaped grooves in a top layer  104  ( FIG. 12 ) and/or bottom layer  106  ( FIG. 12 ) of the light bar  100 . The V-shaped grooves comprise sloping sidewalls or facets. The sloping sidewalls or facets have normals that are angled with respect to the length, width, and/or height of the light bar  100 . In other embodiments, the turning features may comprise any other structures that are suitable for turning light out of a light bar. For example, the grooves need not be in the shape of a V but can instead have one sloping sidewall and one straight sidewall. The sloping surface portions may be curved instead of straight. The elongate features need not extend continuously from the rear side to the front side of the light bar but may be interrupted. Additionally, the elongate features may vary in size, shape, or other property from the rear side to the front side of the light bar. Other variations are possible. 
     In one embodiment, the top and/or bottom layers  104 ,  106  may comprise one or more thin films that are imprinted with the turning features, such as the faceted features  102 . In the illustrations of  FIGS. 10 and 11 , top surfaces of the light bars  100 A,  100 B are illustrated having faceted features  102  on the top surfaces. Each of the light bars  100 A,  100 B may further include a bottom surface that also comprises faceted features  102 . The turning films comprising thin films may be adhered together or one or more of the turning films may be adhered to a thin film carrier resulting in a stack of thin films having a reduced thickness in comparison with conventional light bars. Accordingly, the light bars  100  of  FIGS. 10 ,  11 , and  12  may advantageously have thicknesses that are less than other light bars, such as the light bar  90  of  FIG. 9 . Additionally, one or both of the thin turning films may be adhered to a carrier that has an optical function such as filters. For example, such an optical element  108  may be positioned in a central portion of the light bars  100  shown in  FIGS. 10 ,  11 , and  12 . 
     As described above, after light is injected into the light bars  100  from light source  92 , the light propagates inside the light bar by total internal reflection (TIR) and is redirected towards the light guide panel  88  when rays strike the faceted features  102 , which are embossed on the top or the bottom surfaces  104 ,  106  in the embodiment shown in  FIG. 12 . An angle φ, which represents the orientation of the elongate turning features, can be set according to how much turn is desired for incident light rays. (In  FIGS. 10 and 11 , the angle φ is the angle between a longitudinal direction of the elongate features  102  and the normal to the light bar, although other angles can be used to characterize the orientation of the elongate features on the top and bottom of the light bars  100 .) 
     In various preferred embodiments, the angle φ can be chosen to allow tuning of the orientation of the light distribution with respect to the light guide panel  88 . In one embodiment, the angle φ is set to 45° such that a 90° rotation of the light incident on the faceted features  102  occurs, thus directing the light rays toward the light guide panel  88 , such as along exemplary paths  93   a ,  93   b , and  93   c  of  FIGS. 10 and 11 . In the exemplary embodiment of  FIG. 10 , the angle φ is set to about 45°, while in the embodiment of  FIG. 11  the angle φ is set to about 60°. Thus, exemplary paths  93   a  and  93   b  indicate a rotation of about 90° due to reflection from the faceted features  102  of light bar  100 A ( FIG. 10 ) that are positioned such that φ is about 45°. As illustrated in these Figures, as the angle of φ increases, the angle at which the light rays are ejected from the light bar  100  (with respect to the normal of the input face  88 A or the centerline or width of the light guide panel  88 ) also increases. Thus, φ may be adjusted depending on the angular distribution of light from the light source  92  in order to optimize the angle of light ejected from the light bars  100 . Additionally, φ may be adjusted to achieve a desired light injection angle into the light guide panel  88 . This control can be used to produce the desired illumination on the array of display elements. For example, the turning features may be configured to produce increased uniformity within the light guide panel and on the array of display elements. Additionally, the turning features may be adjusted to provide optimal viewing of the light modulating array  81  at a desired viewing angle. 
     In one embodiment, the faceted features  102  may be spaced substantially evenly along a length of a light bar. In other embodiments, such as those of  FIGS. 10 ,  11 , and  12 , spacing between adjacent faceted features  102  decreases as the distance from the light source  92  increases. In this embodiment, the faceted features  102  are spaced more closely together in order to increase a proportion of the remaining light that is ejected from the light bar  100  in order to uniformly distribute light injected across the entire input face  88 A of the light guide panel  88 . In other embodiments, the depth of the facets may be increased to increase a proportion of light rays that are ejected from the facets. For example, in one embodiment a depth of the faceted features  102  may increase as the distance from the light source  92  increases. In other embodiments, the spacing and orientation of the faceted features  102  can vary along the length of the light bar in any other manner in order to obtain substantially equal, or other desired, light ejection across the entire length of the input face  88 A of the light guide panel  88 . 
     In the embodiment of  FIG. 12 , the light bar  100 C comprises a coupling layer  108  between the top and bottom layers  104 ,  106 . In one embodiment, the coupling layer  108  comprises an optical grade adhesive that bonds the layers  104 ,  106  together. In one embodiment, the layers  104 ,  106  are casted directly onto the coupling layer  108 . Depending on the embodiment, the coupling layer  108  may comprise one or more optical components, such as filters, for example. Adhesives may be used to adhere films, film stacks, and/or components together. Thus, the light bar  100 C may advantageously comprise a desired optical component, rather than positioning the desired optical component outside of the light bar  100 C. More or less layers may be used. As noted above, although the light bar  100 C is illustrated with both a top and bottom layers  104 ,  106  having faceted features  102 , in other embodiments a light bar may comprise only a single layer, such as either layer  104  or  106 , having facets on one or both of a top and bottom surface. 
     In one embodiment, the faceted features  102  can be fabricated by imprinting the surface relief geometry on a thin film substrate. For example, a roll-to-roll embossing (e.g., hot or UV) or casting process may be used to imprint the faceted features  102  on a film. In one embodiment, a method of forming a faceted light bar, such as light bar  100 , comprises embossing faceted features  102  on a film layer, cutting layers  104 ,  106  from the embossed film layer, and laminating layers  104 ,  106  together, optionally with a coupling layer therebetween. Depending on the embodiment, large sheets of a thin film may be embossed with faceted features and laminated together prior to cutting the laminated film layers to the appropriate sizes for use as light bars. In one embodiment, for example, the laminated thin films may be cut to lengths of from about 30-80 mm and widths from about 1-5 mm. In an exemplary embodiment, the laminated thin films are cut to create light bars having dimensions of about 40 mm×3 mm, with a thickness defined by the thickness of the embossed thin films. In embodiments where the layers  104 ,  106  are embossed with facets, the layers may be very thin, such as from 5-60 um, for example. In other embodiments, the film layers may have other thicknesses, such as from 25-350 um, for example. Accordingly, a light bar comprising two light bars of 10 um and a coupling layer of 10-30 um, for example, has a total thickness of less than 50 um. In contrast, a light bar having similar faceted features that is fabricated by injection molding typically has a thickness of 200 um or more. Accordingly, the footprint of faceted light bars formed by embossing may be smaller than the footprint of faceted light bars formed by other methods, such as injection molding. 
     In one embodiment, a faceted light bar comprises only a single film layer. Such a light bar may be fabricated, for example, by embossing both a top and a bottom layer of a film with facets. For example, the top side of the film may initially be embossed, the film may then be nipped, and the bottom side can then be embossed. Alternatively, both sides may be embossed concurrently. Depending on the embodiment, the film that is embossed by any of the methods described herein may be pre-sized for a single light bar, e.g., cut to the size of layers  104 ,  106 , or a larger film layer may be embossed and then cut to the size needed for individual light bars, e.g., the size of layers  104 ,  106 . Alternatively, two large film layers may be embossed and coupled together, such as via an optical coupling layer, and then cut into the appropriate sizes for use in individual light bars. 
     In one embodiment, the film has a thickness in the range of between about 10 μm to 300 μm. In other embodiments, the film has a thickness in the range of between about 50 μm to 60 μm. In other embodiments, other thicknesses of film may also be used. As noted above, in one embodiment, large sheets of film are imprinted with the surface relief geometry defining the faceted features  102 , such as by an embossing process, for example, and the film is subsequently cut to the desired sizes. After cutting the film, two pieces of the film may be used as top and bottom layers, such as layers  104 ,  106  of  FIG. 3 , of a light bar. 
     In one embodiment, the coupling layer  108  comprises an optical quality adhesive material that is index-matched to the top and/or bottom layers  104 ,  106  in order to reduce Fresnel reflections between the coupling layer and the top and bottom layers  104 ,  106 , for example. In some embodiments it is acceptable for the index of refraction of the coupling layer  108  to be less than or equal to that of the top and bottom layers  104 ,  106 , but preferably not larger than any one of the refractive indices of the layers  104 ,  106 . Such an embodiment may reduce any loss of ejection efficiency. In other embodiments, however, such as when the coupling layer  108  is substantially lossless, the refractive index of the coupling layer  108  may be larger than the refractive indices of the layers  104 ,  106 . In other embodiments, the coupling layer may comprise other materials, such as filters, in addition to, or as a replacement of, one or more adhesive materials. For example, the coupling layer  108  may comprise an optical component that is coated with optical adhesive in order to adhere to one or more film layers  104 ,  106  having faceted features  102 . In various embodiments, depending partially on the optical component or components that are included in the coupling layer  108 , the thickness of the coupling layer  108  may range from 10 μm to 100&#39;s of μm or more, for example. 
     In one embodiment, the faceted features  102  of the top and bottom film layers  104 ,  106  are spatially offset so that the corresponding facets do not directly overlap. For example, in the embodiment of  FIG. 12  the faceted features  102  on the top and bottom film layers  104 ,  106  are horizontally aligned. However, in one embodiment the faceted features  102  on one of the surfaces may be offset so that the faceted features  102  on the top film are not horizontally aligned with corresponding faceted features  102  on the bottom layer  106 . In one embodiment, offsetting the facets on the top and bottom film layers  104 ,  106  may advantageously control the efficiency of ejecting light rays from the light bar  100 . 
     Due to the possible large scale fabrication of film with facets, such as according to the above-described processes, light bars comprising such faceted films may be manufactured at a high volume and possibly at reduced costs when compared with conventional injection molded light bars. 
     As described above, in one embodiment reflectors  96 ,  97  may be disposed with respect to the light bar  100  to reflect light escaping therefrom back into the light bar. Such reflectors  96 ,  97  may have contoured shape, for example, matching the grooves  102  of the light bar  100 . The reflectors  96 ,  97  may also comprise retro-reflectors in some embodiments. 
     Additionally, in one embodiment an optical coupling element (not shown) may be disposed between the light bar  100  and the light guide panel  88 . This optical coupling element may comprises for example a collimator that at least partially collimates light ejected from the light bar  100  and directed into the light guide panel  88 . This optical coupling element may be tapered; for example, the optical coupling element may have a first side closer to the light bar that is larger and a second side closer to the light guide panel that is smaller. Such tapered geometry may provide increase collimation. In other embodiments, the optical coupling element is excluded and the light bar  100  is tapered. The side of the light bar  100  farthest from the light guide panel  88  may be larger and the side closest to the light guide panel may be smaller. Light exiting the light bar  100  and entering the light guide panel  88  may thereby be collimated. In other embodiments, no optical coupling element is disposed between the light bar  100  and the light guide panel  88 . 
     A wide variety of other variations are also possible. Films, layers, components, and/or elements may be added, removed, or rearranged. Additionally, processing steps may be added, removed, or reordered. Also, although the terms film and layer have been used herein, such terms as used herein include film stacks and multilayers. Such film stacks and multilayers may be adhered to other structures using adhesive or may be formed on other structures using deposition or in other manners. 
     Furthermore, as those of skill in the art will appreciate, as front lights and backlights that are used in electronic devices become thinner, it becomes harder to efficiently inject light into the thinner light guide panels with injection molded light bars. More particularly, because currently available light bars are typically injection molded, physical and process limitations of injection molding can limit the minimum thickness of such light bars. Accordingly, because the light bars described herein, such as light bars  100 , may be fabricated using one or more thin films, a thickness of the light bars may be reduced when compared to injection molded light bars. Thus, the thin film light bars advantageously allow efficient ejection of light in a reduced thickness package. 
     The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention can be practiced in many ways. As is also stated above, it should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to including any specific characteristics of the features or aspects of the invention with which that terminology is associated. The scope of the invention should therefore be construed in accordance with the appended claims and any equivalents thereof.