Abstract:
An apparatus for a liquid crystal display includes a polarizer film configured to receive light from a liquid crystal display and an optical polarizer screen configured to filter light for the liquid crystal display. The optical polarizer screen has multiple grooves. Each groove includes a first transflective material and a second transflective material that differs from the first transflective material.

Description:
FIELD 
     This invention relates generally to display systems. More particularly, embodiments relate to a high efficiency, low-leakage liquid crystal display (“LCD”) polarizer. 
     DESCRIPTION OF THE RELATED ART 
     A thin-film-transistor liquid crystal display (TFT/LCD), in general use for notebook computers, has a structure similar to that shown in  FIG. 7 . As shown in  FIG. 7 , the LCD  700  may include a backlight  705 , a thin-film-transistor (TFT) glass  710 , a color-filter glass  715 , and the two cross-polarizers  720 A,  720 B attached to the color-filter glass and the TFT glass. 
     The backlight  705  is the light source for an LCD system  700 . It typically consists of an acrylic light pipe with diffusive dots printed on its rear face, a lamp usually placed at one end of the light pipe, a reflective film on the rear face, and optical films on the front face to enhance the light output in the normal direction. Light from the lamp, which is conducted into the light pipe, travels longitudinally within the light pipe and is reflected by the diffusive dots and emitted out the front face of the pipe. The arrangement and density of the dots are controlled to achieve uniformity of light output throughout the front surface. 
     The TFT glass  710  has a matrix of transparent pixel electrodes with nonactive space between them. Each of the pixel electrodes corresponds to a color filter on the color-filter substrate. The nonactive area is coated with an absorptive material, which is called the black matrix. The aperture ratio is the proportion of the sum of all of the pixel electrode areas to the total area of the TFT glass  710 . 
     The color-filter glass  715  also has a matrix of pixels. A triplet of red, green, and blue pixels forms a unit that works as a screen pixel. Each pixel on the color-filter substrate is aligned to a corresponding pixel electrode on the TFT glass  710 . 
     An analysis of the LCD system  700  reveals that it is an optically very inefficient system. For example, in a 12.1-in. SVGA panel, currently in wide use for notebook computers, a mere 10% of the total light output from the backlight eventually reaches the viewer&#39;s eye; the rest is lost along the way. There are four major absorbers. The first is the polarizer  720   a  attached to the TFT glass  710 . As the unpolarized output from the backlight passes through the polarizer  720   a , its intensity is halved owing to complete absorption of one polarization component as well as some absorption of the other component. The second absorber is the black matrix on the TFT glass  710 , an absorptive substance coated on the non-pixel area of the TFT glass  710 . The amount of loss by the black matrix is proportionate to the non-pixel area, or the complement of the aperture ratio of the TFT glass  710 . Since the aperture ratios of 12.1-in. SVGA panels range around 70%, the loss is approximately 30%. The third absorber is the color filter  715 . Although various alternative filter schemes are being developed, the method currently in general use is pigment dispersion. Each pigment-dispersed pixel on the color filter transmits light in its specific wavelength range and absorbs the rest. The color-filter absorption is approximately 70%. The fourth absorber is polarizer  720   b , which absorbs the unpolarized light from the color-filter glass  715 . Finally, the combination of these four major factors yields the above-mentioned low figure of 10%. 
     Major efforts have naturally been directed toward eliminating the loss due to the dichroic polarizer because of the large loss associated with it. One solution is to pre-polarize light coming from the backlight without losing the second polarization component, so that the amount of loss by the cross polarizer is reduced proportionately as the rate of polarization increases. Several types of polarizers have been developed in this approach. They are implemented as an additional film placed on top of a conventional backlight to polarize the output. They typically have a reflective mechanism by which one polarization component is transmitted and the other is reflected. The reflected component is repeatedly reused by being depolarized and sent back into the film. These films are collectively classified as reflective polarizer films. 
       FIG. 8  illustrates a system  800  using reflective polarizer films. As shown in  FIG. 8 , the system  800  includes an LCD  805 , diffusers  810   a - b , a transflective film  815 , a light guide  820 , and a specular reflector  825 . 
     Light with polarity of P 1  and P 2  is emitted from the light guide  820  towards the LCD  805 . The light passes through the diffuser  810 A which disperses light in wider angles. The light then interacts with the transflective film  815 . More particularly, transflective film  815  allows light with P 1  polarization through the diffuser  810   b  and to the LCD  805  while reflecting light with P 2  polarization. The reflected P 2  light is then reflected back to the LCD  805  by the specular reflector  825 . The reflected light from the specular reflector  825  is scattered, i.e., having components of P 1  and P 2 . This type of polarization recycling is a lossy process, where there is substantial loss due to the absorption and scattering. 
     SUMMARY 
     An embodiment generally relates to an apparatus for a liquid crystal display. The apparatus includes a polarizer film configured to receive light from a liquid crystal display and an optical polarizer screen configured to filter light for the liquid crystal display. The optical polarizer screen has multiple grooves. Each groove includes a first transflective material and a second transflective material that differs from the first transflective material. 
     Another embodiment generally pertains to a method of polarizing light. The method includes receiving unpolarized light at a groove having a first side and a second side and transmitting light of a first polarization from the first side of the groove. The method also includes transmitting light of a second polarization from the second side of the groove. 
     Yet another embodiment generally relates to an apparatus for improved light efficiency. The apparatus includes a polarizer film adapted to be in contact with a liquid crystal display and an optical polarizer screen adapted to filter light for the liquid crystal display. The optical polarizer screen includes a plurality of grooves, where each groove includes a first transflective material and a second transflective material that differs from the first transflective material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features of the embodiments can be more fully appreciated, as the same become better understood with reference to the following detailed description of the embodiments when considered in connection with the accompanying figures, in which: 
         FIG. 1  illustrates an exemplary system in accordance with an embodiment of the invention; 
         FIG. 2  illustrates a more detailed view of the optical polarizer screen in accordance with the another embodiment; 
         FIG. 3  depicts a more detailed view of a microgroove in accordance with yet another embodiment; 
         FIG. 4  illustrates a more detailed view of the system shown in  FIG. 1  in accordance with yet another embodiment; 
         FIG. 5  illustrates a more detailed view of the polarizer film; 
         FIG. 6  illustrates yet another embodiment; 
         FIG. 7  illustrates a conventional system; and 
         FIG. 8  illustrates another conventional system. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     For simplicity and illustrative purposes, the principles of the present invention are described by referring mainly to exemplary embodiments thereof. However, one of ordinary skill in the art would readily recognize that the same principles are equally applicable to, and can be implemented in, all types of liquid crystal display (“LCD”) systems, and that any such variations do not depart from the true spirit and scope of the present invention. Moreover, in the following detailed description, references are made to the accompanying figures, which illustrate specific embodiments. Electrical, mechanical, logical and structural changes may be made to the embodiments without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense and the scope of the present invention is defined by the appended claims and their equivalents. 
     Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein. For example, a range of “less than 10” can include any and all sub-ranges between (and including) the minimum value of zero and the maximum value of 10, that is, any and all sub-ranges having a minimum value of equal to or greater than zero and a maximum value of equal to or less than 10, e.g., 1 to 5. 
     Embodiments generally relate to a high efficiency low leakage LCD polarizer system. More particularly, the optical polarizer screen comprises of a clear material, e.g., acrylic, with a large number of prismatic microgrooves (or a prism array) formed on one side. Each prismatic microgroove may be configured to have one side transflective to polarizations P 1 -P 2  (transparent to P 1 , reflective to P 2 ) and the opposite side transflective to P 2 -P 1  (transparent to P 2 , reflective to P 1 ). The prismatic microgrooves may also be configured with a reflector embedded in the clear material between the transflective materials. As a result of this configuration, the optical polarizer screen may output regions of P 1  polarized light and regions of P 2  polarized light in an alternating pattern. 
     The optical polarizer screen may be in contact with an LCD. On the viewing side of the LCD, a polarizer film may be in contact with this side of the LCD. The polarizer film may be configured with polarized P 1  and P 2  strips (or regions) in an alternating pattern. The polarized P 1  strip may cover a corresponding P 2  output from the prismatic microgroove of the optical polarizer screen through the LCD. Similarly, the P 2  strip of the polarizer film may cover corresponding P 1  output from the prismatic microgroove of the optical polarizer screen through the LCD. It should be readily apparent to those skilled in the art that an LCD array may be disposed between the optical polarizer screen and the polarizer film. Moreover, the pixels in the LCD array may rotate light proportional to the amount of voltage applied to the pixels. 
       FIG. 1  illustrates a block diagram of an exemplary system  100  in a side view where an embodiment may be practiced. It should be readily apparent to those of ordinary skill in the art that the system  100  depicted in  FIG. 1  represents a generalized schematic illustration and that other components may be added or existing components may be removed or modified. 
     As shown in  FIG. 1 , system  100  may include an optical polarizer screen  105 , an LCD array  110 , and a polarizer film  115 . The optical polarizer screen  105  may be configured to improve the efficiency of polarization or light recycling through the use of microgrooves or a prismatic array. More particularly, the optical polarizer  105  may include on one side a series of microgrooves embedded with two types of transflective material. One side of the microgroove may be coated with a transflective material that is transparent to light with the polarization of P 1  and reflective to light with the polarization of P 2 . The second side of the microgroove may be coated with a second transflective material that is transparent to light with the polarization of P 2  and reflective to light with the polarization of P 1 . Each microgroove maintains the order of transflective materials such that alternating pattern of transflective material is formed across the one side of the optical polarizer screen  105 , which is illustrated with respect to  FIG. 2 . 
       FIG. 2  depicts an exemplary microgroove array  200  of the optical polarizer screen  105  (shown in  FIG. 1 ) in accordance with an embodiment of the invention. As shown in  FIG. 2 , the microgroove array  200  may include a substrate  205 , grooves  210 , and reflectors  215 . 
     The substrate  205  may be a clear material such as acrylic, polycarbonate, thin glass, or other similar transparent material. Formed on the substrate may be the microgrooves  210 . For example, microgroove  210 A may be a V-shaped groove with an angle within the range of 30 to 70 degrees. 
     One side of the microgrooves  210  may be in contact with a P 1 -P 2  transflector polarizer filter  220 , i.e., transparent to P 1  and reflective to P 2 . The other side of the microgrooves  210  may also be in contact with a P 2 -P 1  transflector polarizer filter  225 , transparent to P 2  and reflective to P 1 . These transflector polarizer filters may be deposited onto the microgrooves  210  using deposition techniques or embedded onto the microgrooves  210  through a machine press or other similar technique. 
     The optical polarizer screen  200  may also include reflectors  215 . The reflectors  215  may be configured to reflect all light. In some embodiments where high-index of refraction materials are used, the reflector may be a thin cut (slit, groove, etc.) in the substrate  205 . In yet other embodiments, the reflectors  215  may be implemented using silver or other types of mirroring materials. The reflectors  215  may be positioned between the microgrooves  210 . In some embodiments, the reflectors  215  are aligned along the joint or seam line between two microgrooves. 
       FIG. 3  illustrates the path for non-polarized light as it travels through a microgroove  200  shown in  FIG. 2 . As shown in  FIG. 3 , non-polarized light may enter the microgroove  210 . For the light incident to the P 1 -P 2  transflector filter  220 , P 1  polarized light may pass through the P 1 -P 2  transflector filter while reflecting the P 2  polarized light to the other side of the microgroove  210 . The P 1  polarized light may reflect off the reflector  215  towards an LCD array (e.g., the LCD array  110  shown in  FIG. 1 ) The reflected P 2  polarized light may pass through the P 2 -P 1  transflector filter  225  and subsequently be reflected toward an LCD array (e.g., LCD array  110  shown in  FIG. 1 ) by the reflector  215 . Accordingly, the optical polarizer screen  105  may improve the efficiency of the backlighting by directing the incident light toward the appropriate filter with a minimum number of reflectors and refractors. 
     Similarly, for light incident to the P 2 -P 1  transflector filter  225 , P 2  polarized light passes through the P 2 -P 1  transflector filter while P 1  polarized light is reflected toward the P 1 -P 2  transflector filter  220 . The polarized P 2  light is reflected toward an LCD array (e.g., LCD array  110  shown in  FIG. 1 ). The reflected P 1  polarized light passes through the P 1 -P 2  transflector filter  220 , reflected off the reflector  215  towards an LCD array (e.g., LCD array  110  shown in  FIG. 1 ). 
       FIG. 4  depicts the output of the microgroove array  200  in accordance with another embodiment. As shown in  FIG. 4 , the light output from a microgroove  210  may be divided into P 1  polarized output  405  and a P 2  polarized output  410 . More particularly, the side of the microgroove with the P 1 -P 2  transflector filter  220  may output P 1  polarized light and the side of the microgroove with the P 2 -P 1  transflector filter  220  may output P 2  polarized light. 
     Returning to  FIG. 1 , the LCD array  110  may be implemented by conventional LCD arrays or LCD arrays designed to accommodate alternate cross-polarizers. The LCD arrays are well known to those skilled in the art. The system  100  also includes a polarizer film  115 , which is depicted in  FIG. 5  in a frontal view. As shown in  FIG. 5 , the polarizer film  115  may be comprised of alternating strips of P 1  polarizing film  505  and P 2  polarizing film  510 . The width of the P 1  polarizing film  505  may be equivalent to the width of the P 2  output of a microgroove from the optical polarizer screen  105 . Similarly, the width of the P 2  polarizing film  510  may be substantially equivalent to the width of the P 1  output of a microgroove from the optical polarizer screen  105 . In some embodiments, the width may be substantially equivalent to one pixel of an accompanying LCD array. 
     The polarizer film  115  may be positioned so that the P 2  polarizing film strips  510  covers the P 1  output from the prismatic microgroove of the optical polarizer screen  105  through the LCD array  110 . Similarly, the P 1  polarizing film strips  505  may cover corresponding P 2  output from the prismatic microgroove of the optical polarizer screen  105  through the LCD array  110 . 
       FIG. 6  illustrates another embodiment. As shown in  FIG. 6 , the system  600  includes the microgroove array  200  (as previously described with respect to  FIG. 2 ). The system  600  may also include a high-index film  605 . The high-index film  605  may be deposited over the microgrooves (or prismatic array)  200 . The high-index film  605  may be implemented with a high-index of refraction material such as boro-silicon or other similar materials. The high-index film  605  may be configured to refract light to become more perpendicular to the microgrooves of the microgroove array  200 . 
     While the invention has been described with reference to the exemplary embodiments thereof, those skilled in the art will be able to make various modifications to the described embodiments without departing from the true spirit and scope. The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. In particular, although the method has been described by examples, the steps of the method may be performed in a different order than illustrated or simultaneously. Those skilled in the art will recognize that these and other variations are possible within the spirit and scope as defined in the following claims and their equivalents.