Abstract:
An electro-optical display backlight module for generating a light source of a single polarization state, which reduces the optical loss in light beam output, is suitable for mass production, and decreases manufacturing costs, is disclosed. The backlight module is easily integrated with conventional electro-optical display devices and achieves high-quality polarization splitting through suitable designs. The backlight module of the present invention comprises an under plate having a ridged lower surface and an upper surface; a phase retardation film of high reflectivity disposed on the lower surface of the under plate; a double-sided electroluminescent panel having a lower surface, substantially complementary to the upper surface and facing therewith, and an upper surface; a substrate having a lower surface, substantially complementary to the upper surface of the double-sided electroluminescent panel and facing therewith, and an upper surface; and a polarization splitting film disposed on the upper surface of the substrate, providing transmission of predetermined polarization state and reflection of predetermined polarization state of the light source.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to a backlight module of an electro-optical display device, and more particularly to a backlight module for generating a light source of a single polarization state.  
           [0003]    2. Description of the Prior Art  
           [0004]    With the advent of the information technology (IT) age, there is an increasing demand for high-quality liquid crystal displays (LCDs). Higher quality imaging requires the more efficient utilization of light sources. Conventionally, for obtaining singly-polarized light beam output from a LCD backlight module, a polarization plate is arranged near the light source to inhibit the passage of certain polarized light beams, whereby the polarized light beams which are not parallel are prevented from being transmitted. In practice, the resultant light beams of a single polarization state are less than half of those of the original light source in terms of illuminance.  
           [0005]    [0005]FIG. 1 illustrates a conventional liquid crystal display having a conventional single-sided electroluminescent panel (the conventional backlight module)  29  comprising a reflective film  291 , an insulating layer  292 , an illuminating layer  293  and a transparent electrode  294 . The illuminating layer  293  is a light source emitting light beams at its upper and lower surfaces. The light beams emitted from the upper surface of the illuminating layer  293  will pass through the upper transparent electrode  294 , whereas the light beams emitted from the lower surface of the illuminating layer  293  will transmit through the insulating layer  292  and thereafter be reflected by the reflective layer  291  so as to pass through the insulting layer  292  and illuminating layer  293  in sequence and finally pass through the transparent electrodes  294 . When a non-polarized light beam is emitted from single-sided electroluminescent panel  29 , it loses approximately 50% of its optical strength due to the screening effect in terms of polarization states by the polarization plate  14 . Moreover, reflective film  291  may cause further optical loss due to light absorption. In addition, the power consumption of the conventional backlight module is significant even as the display quality is adversely affected. Large scale liquid crystal displays utilizing such conventional backlight modules are also difficult to produce, particularly in large quantities. Conventional single-sided electroluminescent panels used for a backlight module of, for example, a cell phone, typically are utilized only in STN-LCDs (supertwist nematic LCD), rather than in the more technologically advanced TFT-LCDs (thin film transistor LCD).  
         SUMMARY OF THE INVENTION  
         [0006]    In view of the above problems, the principal object of the present invention is to provide a backlight module for generating a light source of a single polarization state, which reduces the optical loss in light beam output, is suitable for mass production, and decreases manufacturing costs.  
           [0007]    Another object of the present invention is to provide a backlight module for generating a light source of a single polarization state, which is easily integrated with conventional electro-optical display devices and achieves high-quality polarization splitting.  
           [0008]    To achieve these objects, the present invention provides a backlight module for generating a light source of single polarization state, comprising  
           [0009]    an under plate having a ridged lower surface and an upper surface;  
           [0010]    a phase retardation film of high reflectivity, disposed on the ridged lower surface of the under plate;  
           [0011]    a double-sided electroluminescent panel having a lower surface, substantially complementary to the upper surface of the under plate and facing therewith, and an upper surface;  
           [0012]    a substrate having a lower surface, substantially complementary to the upper surface of the double-sided electroluminescent panel and facing therewith, an upper surface and four side-surfaces; and  
           [0013]    a polarization splitting film disposed on the upper surface of the substrate, providing transmission of predetermined polarization state and reflection of predetermined polarization state of the light source.  
           [0014]    For avoidance of the optical loss from the side-surfaces of the substrate, reflective films of high reflectivity may be provided on four side-surfaces of the substrate so as to confine the light beams therein. It should be noted that the substrate could be omitted so as to simplify the construction of the backlight module. In order to enhance optical performance, the ridge pitch of each of the ridged surfaces may be constant or not, and the ridge lines thereof are preferred not to be parallel to the polarizing direction of the light beam reflected by the polarization splitting film, thus allowing greater freedom of backlight module design. Further, an undulated film with, for example, cylindrical, spherical or non-spherical undulations can be disposed on the polarization splitting film for controlling the output angle and diffusion angle of the light beams.  
           [0015]    The present invention further provide a backlight module for generating a light source of single polarization state, comprising  
           [0016]    a double-sided electroluminescent panel having a lower surface and an upper surface;  
           [0017]    a scattering structure having an upper surface, substantially complementary to the lower surface of the double-sided electroluminescent panel and facing therewith, and a lower surface;  
           [0018]    a reflective film of high reflectivity disposed on the lower surface of the scattering structure; and  
           [0019]    a polarization splitting film disposed on the upper surface of the double-sided electroluminescent panel, providing transmission of predetermined polarization state and reflection of predetermined polarization state of the light source.  
           [0020]    In addition, the concept for increasing the efficiency of light beams output from a backlight module according to the present invention may be utilized with a single-sided electroluminescent panel, wherein the backlight module comprises  
           [0021]    a single-sided electroluminescent panel having an upper surface and a lower surface, comprising an illuminating layer, an insulating layer, a transparent electrode and a reflective layer;  
           [0022]    a scattering structure having a lower surface, substantially complementary to an upper surface of the single-sided electroluminescent panel and facing therewith, and an upper surface; and  
           [0023]    a polarization splitting film disposed on the upper surface of the scattering structure, providing transmission of predetermined polarization state and reflection of predetermined polarization state of the light source.  
           [0024]    To simplify such a construction, the scattering structure may be omitted if the insulating layer of the single-sided electroluminescent panel effects scattering for conversion of the polarization states of the light beams.  
           [0025]    Additional advantages, objects and features of the present invention will become more apparent from the drawings and description which follows. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0026]    The present invention will become more apparent from the detailed description given hereinbelow when read in conjunction with the accompanying drawings, which are given by means of illustration only and thus are not limitative of the present invention, in which:  
         [0027]    [0027]FIG. 1 is a schematic drawing showing a conventional backlight module comprising a single-sided electroluminescent panel for a liquid crystal display;  
         [0028]    [0028]FIG. 2 is a schematic drawing showing a double-sided electroluminescent panel according to the present invention;  
         [0029]    [0029]FIG. 3 is a sectional view showing a backlight module comprising a double-sided electroluminescent panel according to one embodiment of the present invention;  
         [0030]    [0030]FIG. 4 is a schematic drawing showing a two-layer stake of films forming a single interface according to U.S. Pat. No. 5,962,114;  
         [0031]    [0031]FIG. 5 is a schematic drawing, showing the reflection and transmission effect regarding light beams of two different polarization states according to U.S. Pat. No. 5,962,114;  
         [0032]    [0032]FIG. 6 is a schematic drawing showing the optical path in the backlight module according to the present invention;  
         [0033]    [0033]FIG. 7 is a perspective view showing the backlight module according to the present invention;  
         [0034]    [0034]FIG. 8 shows the relationship between the relative phase difference of P-S polarized components over different wavelengths of light beams reflected by a typical phase retardation film of high reflectivity;  
         [0035]    [0035]FIG. 9 shows the relationship between the reflectivity of P-S polarized components over different wavelengths of light beams reflected by a typical phase retardation film of high reflectivity.  
         [0036]    [0036]FIG. 10 is a perspective view of the backlight module according to the present invention, in which a film having cylindrical undulations thereon is disposed on the polarization splitting film;  
         [0037]    [0037]FIG. 11 is a perspective view of the backlight module according to the present invention, in which a film having square protuberances thereon is disposed on the polarization splitting film;  
         [0038]    [0038]FIG. 12 is a sectional view of the backlight module according to another embodiment of the present invention, comprising a scattering structure;  
         [0039]    [0039]FIG. 13 is a sectional view of the backlight module utilizing a single-sided electroluminescent panel according to another embodiment of the present invention, wherein a scattering structure is included therein; and  
         [0040]    [0040]FIG. 14 is a sectional view of the backlight module utilizing a single-sided electroluminescent panel according to another embodiment of the present invention, wherein the insulating layer of the single-sided electroluminescent panel has scattering effect. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]    With reference to FIG. 2, a double-sided electroluminescent panel  30  according to the present invention is shown. The double-sided electroluminescent panel  30  comprises two transparent electrodes  301 , one insulating layer  302  and one illuminating layer  303 . The illuminating layer  303  is a light source emitting light beams at its upper and lower surfaces. The light beams emitted from the upper surface of the illuminating layer  303  will pass through the upper transparent electrode  301 , whereas the light beams emitted from the lower surface of the illuminating layer  303  will transmit through the insulating layer  302  and thereafter pass through the lower transparent electrode  301 . The light beams out of the double-sided illuminator  30  are generally designated as I. Since a reflective layer  291  used in a conventional single-sided electroluminescent panel is omitted, the resultant illuminance according to the present invention can be greatly enhanced.  
         [0042]    With reference to FIG. 3, a section view of a backlight module according to one embodiment of the present invention is shown. The backlight module is a laminate configuration comprising an under plate  21 , a double-sided electroluminescent panel  30 , a substrate  22  and a polarization splitting film  31 . The under plate  21  has a ridged lower surface and a phase retardation film  61  is disposed thereon, which functions to convert the light beams incident thereto in terms of polarization states and reflect the converted light beams to the polarization splitting film  31 . In this embodiment, the ridge angle between any two neighboring ridges on the ridged lower surface of the under plate  21  is 90 degrees. However, any ridge angle suitable for reflection of the light beams thereto can be utilized. The polarization splitting film  31  is a film that permits light beams of specific polarization state to be transmitted through and others to be reflected. For example, the multilayer film disclosed in U.S. Pat. No. 5,962,114, which is incorporated herein for reference, can be utilized as a polarization splitting film according to the present invention. FIG. 4 shows a two-layer stake of films forming a single interface according to U.S. Pat. No. 5,962,114, in which two films are laminated along the z-direction. The refractivity of the films along the x-, y- and z-direction are (n1x,n1y,n1z)         (n2x,n2y,n2z) respectively. According to the teaching from U.S. Pat. No. 5,962,114, if (n1y-n2y) and (n1z-n2z) are of the same sign, the polarized light beam along the x-direction will be transmitted through the films and the polarized light beam along the y-direction will be reflected. Therefore, light beams of different polarization states can be splitted.  
         [0043]    [0043]FIG. 5 shows the reflection and transmission effect regarding light beams of two different polarization states according to the multilayer film of U.S. Pat. No. 5,962,114, which can be utilized in the present invention. The multilayer film shown in FIG. 5 is composed of PEN (2,6-polyethylene naphthalate) and coPEN (copolymer derived from ethyleneglycol, naphthalene dicarboxylic acid and some other acids such as terephthalate) and allows polarized light beams in specific direction to be transmitted and others in the direction perpendicular to the specific direction to be reflected.  
         [0044]    With reference to FIG. 6, an optical path, regarding light beams generated from the double-sided electroluminescent panel  30 , between the under plate  21  and the polarization splitting film  31  is shown, wherein the solid arrow designates the direction which the light beams propagates, the hollow arrow designates the P-polarized component, and the circle with a black dot in designates the S-polarized component. It should be noted that the P-polarized component means the component which may pass through the polarization splitter film, whereas the S-polarized component is perpendicular to the P-polarized one and will be reflected back by the polarization splitter film. In this case, non-polarized light beams I travel upward to the polarization splitting film  31 , with the P-polarized components directly passing through the polarization splitting film  31  and the S-polarized components reflected by the polarization splitting film  31 . After the S-polarized components reflected by the polarization splitting film  31  and non-polarized light beams generated by the double-sided electroluminescent panel  30  travelling downward are continuously reflected at the ridged lower surfaces of the under plate  21 , they will be converted by the phase retardation film  61  to possess P- and S-polarized components partially. Similarly, the P-polarized components will pass through the polarization splitting film  31 , whereas the S-polarized components will be reflected and then be reflected and converted by the phase retardation film  61  again. Through a series of the above procedures, the non-polarized light beams are output as P-polarized light beams of a single polarization state. It is noted that in FIG. 6, the ridge pitch of the ridged lower surfaces of the under plate is a predetermined constant value.  
         [0045]    It should be noted that while the direction of the S-polarized components reflected by the polarization splitting film is not parallel to that of the ridge lines on the ridged lower surface of the under plate, any conventional reflection film may be advantageously utilized to achieve the effect by the phase retardation film disclosed in the present invention. Alternatively, while the direction of the S-polarized components is parallel to that of the ridge lines, the phase retardation effect and thereby the conversion of the polarization states cannot be achieved by the phase retardation film unless certain magnetic materials are adding therein. The phase retardation film may be a dry film formed by an optical-precision application process or be coated through evaporation onto the ridged lower surface of the under plate. In this embodiment, the ridge angle between any two neighboring ridges of the under plate is 90 degrees, so that continuous reflection or total reflection of the light beams can be achieved at the ridged lower surface of the under plate  21 .  
         [0046]    With reference to FIG. 7, another embodiment of backlight module in accordance with the present invention is disclosed. The ridge pitch of the ridges on the ridged lower surface of the under plate is variable, and the direction of the S-polarized components reflected by the polarization splitting film is not parallel to that of the ridge lines, so as to increase the freedom in designing the phase retardation film. It should be noted that any conventional reflection film may be advantageously utilized to achieve the effect by the phase retardation film disclosed in the present invention in this embodiment since the direction of the S-polarized components of the light beams reflected by the polarization splitting film is not parallel to that of the ridge lines.  
         [0047]    For clarifying the features of the present invention, the configuration and inventive principles of the present invention is in detail described below.  
         [0048]    In consideration of the production process, the substrate  22  may be made of any suitable optical material, for example, plastic material such as PMMA, PC or ARTON™ or any other glass material, depending on the specific process therefor. In designing a suitable optical coating thereof, it is fundamental to determine the refractivity of the substrate in advance. Table 1 shows the refractivity over different wavelength for ARTON™ at different absorption rate and temperature. With reference to FIG. 8 and FIG. 9, the relative phase difference and the reflectivity of P-S polarized components over different wavelength of light beams reflected by a typical phase retardation film of high reflectivity are shown respectively.  
         [0049]    It may be noted that in practical production, the phase retardation film is a dry film formed by an optical-precision application process or be coated through evaporation onto the ridged lower surface of the under plate so as to reflect the light beams incident thereto back to the substrate. For example, if the substrate is made of PMMA having optical coefficient 1.53 with the criteria that the ridge angle of the ridged lower surface of the under plate is 90 degrees and the wavelength of the incident light beam is 400 to 700 nm, the typical composition of the film may be MgF 2 , ZnS, CeF 3 , MgF 2 , ZnS, CeF 3  and MgF 2 , and the thickness thereof may be respectively 110.82, 20.13, 84.88, 141.93, 111.47, 84.88 and 25.38 nm. If the above conditions remain the same except for a substrate made of Norbornene (ARTON™), the composition of the film may be MgF 2 , ZnS, CeF 3 , MgF 2 , ZnS, CeF 3  and MgF 2 , and the thickness thereof may be respectively 110.14, 26.54, 84.88, 139.92, 117.22, 84.88 and 117.71 nm.  
         [0050]    For increasing the transmissivity of the light beams, films having undulations of any suitable profiles can be disposed on the polarization splitting film  31  such that the output light beam can be in parallel or at any suitable angle. FIG. 10 shows that a film having cylindrical undulations thereon is disposed on the polarization splitting film. FIG. 11 shows a film having square protuberances thereon is disposed on the polarization splitting film. In this way, the output angle as well as the diffusion angle of the polarized light beams may be controlled and determined, and thus the output illuminance over different angles of view may be predetermined.  
         [0051]    For further increasing the efficiency of the output of the polarized light beams, reflective films can be applied on the four side-surfaces of the substrate  22  so as to confine the light beams reflected therein from emitting therethrough. Accordingly, the optical loss of the backlight module may be further decreased. The reflective films can be coated through evaporation, and the composition and the thickness thereof respectively can be looked up from Table 2.  
         [0052]    With reference to FIG. 12, a backlight module according to another embodiment of the present invention is shown, wherein the lower surface of the under plate  21  is of unspecific profile and a scattering structure  70  is provided thereon. A reflective film of high reflectivity  63  is provided on the lower surface of the scattering structure  70 . Thus, the conversion of the polarization states of light beams according to the previous embodiments of the present invention may be achieved based on the scattering effect by the scattering structure  70 . It should be noted that the scattering structure may be formed by a painting process or formed of materials of different optical coefficients. Moreover, the scattering effect by the scattering structure can be achieved through the rough surface thereof. In addition, for constructing another complete backlight module based on above embodiment, the scattering structure  70  can be directly attached onto the double-sided electroluminescent panel  30  with the under plate  21  being omitted.  
         [0053]    With reference to FIG. 13, a backlight module utilizing a single-sided electroluminescent panel according to another embodiment of the present invention is shown. In this case, a scattering structure  70  is disposed between the upper surface of the single-sided electroluminescent panel  29  and the substrate  22 , with the under plate being omitted. Similarly, the conversion of the polarization states of light beams may be achieved based on the scattering effect by the scattering structure  70 . In addition, the substrate  22  can be further omitted to simplify the construction of the backlight module.  
         [0054]    With reference FIG. 14, another backlight module utilizing a single-sided electroluminescent panel according to another embodiment of the present invention is shown, wherein the insulating layer of the single-sided electroluminescent panel  29  has a high scattering coefficient. Since the conversion of the polarization states of light beams can be achieved by the insulating layer of the single-sided electroluminescent panel  29 , neither a under plate nor a scattering structure is necessary in this embodiment. In addition, attaching the polarization splitting film  31  with the single-sided electroluminescent panel  29  directly with the substrate  22  being further omitted can simplify the construction of the backlight module.  
         [0055]    Although the preferred embodiment of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modification, additions and substitutions are possible, without departing from the scope and spirit of the present invention as recited in the accompanying claims.  
                                                                             TABLE 1                           ARTON FX26       Main Chain: NORBORNENE       Branch Chain: polyester function group                Measured wavelength                794.76 nm   656 nm   588 nm   486 nm   436 nm                        Absorption                           rate(%)        0.01   1.5161   1.5198   1.5227   1.5298   1.5354        0.25   1.5163   1.5200   1.5230   1.5300   1.5357       temperature       (° C.)       30   1.515   1.519   1.521   1.528   1.534       40   1.514   1.518   1.520   1.527   1.533                  
 
         [0056]    [0056]                     TABLE 2                       Typical composition and thickness of anti-reflection layer       (unit: nm)                                ZnS 38.59           MgF 2  66.30           ZnS 41.01           MgF 2  70.47           ZnS       43.59           MgF 2  74.89           ZnS 46.33           MgF 2  79.60           ZnS 49.24                  MgF 2  84.60           ZnS 52.33           MgF 2  89.91           ZnS 55.62           MgF 2         95.56           ZnS 59.11           MgF 2  101.56           ZnS 62.83           MgF 2  107.93                  ZnS 66.77           MgF 2  114.73           ZnS 70.96           MgF 2  121.92           ZnS       75.41           MgF 2  129.58           ZnS 80.15           MgF 2  137.72           ZnS 85.18                  MgF 2  146.38           ZnS 90.54           MgF 2  155.56           ZnS 96.23           MgF 2         165.34           ZnS 102.27           MgF 2  175.72           ZnS 108.70