Abstract:
The present invention discloses a light modulation element, having a first optical surface and a second optical surface receiving an incident light, the light modulation element comprising: at least a transparent diffusion unit, for scattering the incident light, each being placed on the first optical surface; and at least a transparent collimation unit, for collimating the incident light, each being formed on top of the diffusion unit.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a light modulation element and the luminance control apparatus utilizing the same, and more particularly, to a light modulation element having at least a diffusion unit and at least a collimation unit formed on a surface thereof. 
   BACKGROUND OF THE INVENTION 
   Nowadays, it is commonly seen that backlight modules are used for electronic devices with flat panel displays, which includes devices as small as hand-held palm pilots and as large as big-screen TVs. A typical backlight consists of a light source, such as Cold Cathode Fluorescent (CCFL) or Light Emitting Diodes (LED), a light guide, a diff user, and a brightness enhancement film. The design challenge of a backlight module is to generate uniform illumination across the LCD surface and luminance that is high enough to produce good contrast in a day environment (so that you can see the display of a laptop computer or a handheld electronic device, for example, with the room lights on), by the cooperation of the diffuser and the brightness enhancement film. Although, Taiwan is now one of the three major production countries for Notebook PCs, the critical component, backlight modules, still has to be imported and there is a heavy reliance on foreign providers. Thus, it is imperative for Taiwan to establish the design and production technology. Moreover, a conventional backlight usually consists of a plurality of optical films, which is the cause of low luminous efficacy, high manufacture cost and low assembly yield, and so on. 
   Please refer to  FIG. 1 , which is a perspective view of a luminance control film assembly disclosed in U.S. Pat. No. 6,091,547, entitled “Luminance Control Film”. The luminance control film assembly of  FIG. 1  is the formation of stacking a luminance control film  12  on top of another luminance control film  10 , which can control and guide incident light to collimate for achieving the objects of improving on-axis luminance. However, the disclosed luminance control film is capable of collimating light effectively, it is disadvantageous by being able to diffuse incident light sufficiently enough to produce uniform illumination. 
   Please refer to  FIG. 2 , which is a cross-sectional view of a light-diffusing sheet disclosed in Japan. Pat. No. 2001324608, entitled “Light-Diffusing Sheet”. The light-diffusing sheet of  FIG. 2  is substantially a layer of resin  24  formed on a transparent substrate  20  with a plurality of resin particles  22  of different diameter dispersed therein, which enables incident light to be scattered and thus diffused, but is disadvantageous by the effect of reducing luminous efficiency caused by the light-scattering of the plural particles  22 . 
   Therefore, it is in great demand to have an improved light modulation element capable of overcoming the shortcomings of prior arts. 
   SUMMARY OF THE INVENTION 
   In view of the disadvantages of prior art, the primary object of the present invention is to provide a light modulation element with enhanced luminous efficiency, achieved by utilizing a plurality of microstructures with light collimation and diffusion capabilities formed thereon. 
   Another object of the invention is to provide a light modulation element and the luminance control apparatus utilizing the same, characterized in that the light modulation element is integrally manufactured by rolling a roller embossed with microstructures on an optical substrate for imprinting the microstructures thereon and thus the manufacturing cost of the light modulation element can be reduced. 
   To achieve the above objects, the present invention provides a light modulation element, having a first optical surface and a second optical surface for receiving an incident light, the light modulation element comprising:
     at least a transparent diffusion unit, for diffusing the incident light, each being formed on the first optical surface; and   at least a transparent collimation unit, for collimating the incident light, each being superposed on the diffusion unit.   

   In a preferred embodiment of the invention, the diffusion unit further comprises at least a semi-lenticular lens, characterized by a specific depth preferably in the range of 5 microns to 500 microns, moreover, the collimation unit further comprises at least a prism, characterized by a vertex angle preferably in the range of 30° to 140°, and a height preferably in the range of 0 micron to 500 microns. 
   In another preferred embodiment of the invention, the second optical surface can be an optical surface selected from the group consisting of a rugged surface and a smooth surface. 
   To achieve the above objects, the present invention further features a luminance control apparatus, comprising:
     a reflector;   a light guide plate, arranged over the reflector;   at least a light source, arranged at a side of the light guide plate for emitting an incident light; and   at least a light modulation element, arranged at a position over the light guide plate, each having a first optical surface and a second optical surface for receiving the incident light, each light modulation element further comprising:   at least a transparent diffusion unit, for diffusing the incident light, each being formed on the first optical surface; and   at least a transparent collimation unit, for collimating the incident light, each being superposed on the diffusion unit.   

   In a preferred embodiment of the invention, the diffusion unit further comprises at least a semi-lenticular lens, characterized by a specific depth preferably in the range of 5 microns to 500 microns, moreover, the collimation unit further comprises at least a prism, characterized by a vertex angle preferably in the range of 30° to 140°, and a height preferably in the range of 0 micron to 500 microns. 
   In another preferred embodiment of the invention, the second optical surface can be an optical surface selected from the group consisting of a rugged surface and a smooth surface. 
   Yet, preferably, the luminance control apparatus of the invention can comprises two light modulation elements, wherein the orientation of one of the two light modulation elements is rotated by an angle range between 0° and 90° to be placed overlapping another light modulation element. 
   Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of examples about the principles of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a luminance control film assembly disclosed in U.S. Pat. No. 6,280,063. 
       FIG. 2  is a cross-sectional view of a light-diffusing sheet disclosed in Japan. Pat. No. 2001324608. 
       FIG. 3A  is a schematic diagram depicting the optical characteristics of a prism shaped lens. 
       FIG. 3B  is a schematic diagram depicting the optical characteristics of a semi-lenticular lens shaped lens. 
       FIG. 4  is cross-sectional view of a light modulation element according to the present invention. 
       FIG. 5  is a schematic diagram showing a rolling process for manufacturing a light modulation element of the invention. 
       FIG. 6  is a cross-sectional view of a light modulation element according to a preferred embodiment of the invention. 
       FIG. 7  is a cross-sectional view of a luminance control apparatus utilizing the light modulation element according to a preferred embodiment of the present invention. 
       FIG. 8  is a cross-sectional view of a luminance control apparatus utilizing the light modulation element of another preferred embodiment of the present invention. 
       FIG. 9  is cross-sectional view of stacked light modulation elements according to the present invention. 
       FIG. 10  is cross-sectional view of a light modulation element according to another preferred embodiment of the present invention. 
       FIG. 11  is cross-sectional view of a light modulation element according to yet another preferred embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   For your esteemed members of reviewing committee to further understand and recognize the fulfilled functions and structural characteristics of the invention, several preferable embodiments cooperating with detailed description are presented as the follows. 
   According to Snell&#39;s Law, it is noted that a prism shaped lens can be used to collimate light effectively as seen in  FIG. 3A , that is, it can reduce the divergent angle of an incident light. In  FIG. 3A , when an incident light  32  traveling in the prism  30  is traveling across an interface from the prism  30  to the external environment by an angle of θ, i.e. from a media with higher refractive index to another media with lower refractive index, at the condition that the incident angle θ is larger than the critical angle of total internal reflection, then the light is totally reflected off the interface following the dotted arrow of  FIG. 3A , on the other hand, when the incident angle θ is smaller than the critical angle of total internal reflection, the exiting light, shown as the solid arrow of  FIG. 3A , will bend away from the normal of the interface (i.e. the dotted line of  FIG. 3A ). 
   Please refer to  FIG. 3B , which is a schematic diagram depicting the optical characteristics of a semi-lenticular lens shaped lens. It is noted that a semi-column shaped lens can be used to controllably diffuse light within a specific range. As seen in  FIG. 3B , as four incident light  36   a ,  36   b ,  36   c  and  36   d , each incident to the lens  34  by different angles, is traveling across an interface from the lens  34  to the external environment, all the exiting light corresponding respectively to the four incident light will converge in the convergence area  38  and then dissipate. Accordingly, the exiting angle of the light with large incident angle can be controlled to converge so as to enable all the incident light to be uniformly and controllably diffused. 
   Thus, by forming microstructures with the two abovementioned geometric characteristics on a surface of a light modulation element, the light modulation element is enabled to collimate as well as diffuse light. Hence, by a superposed formation of the prisms and the semi-lenticular lens, the light modulation element is equipped with light collimation and diffusion capabilities. 
   Please refer to  FIG. 4 , which is cross-sectional view of a light modulation element according to the present invention. The light modulation element  40  of the present invention has a first optical surface  42  and a second optical surface  44 , wherein at least a semi-lenticular lens  48  is formed on the first surface  42  while forming at least a prism  46  on top of each semi-lenticular lens  48 . The function of each prism  46  is to collimate light and thus is addressed as the collimation unit while the function of each semi-lenticular lens  48  is to scatter light and thus is addressed as the diffusion unit. Since each prism  46  is characterized by a vertex angle a and a height h, and the semi-lenticular lens is characterized by a specific depth b, the light collimation and diffusion capability of the light modulation element  40  can be controlled by the proper selection of the vertex angle a, the height h, the specific depth b, and the material of the light modulation element  40  (i.e. the refractive index of the light modulation element  40 ). 
     FIG. 5  depicts a process for manufacturing the light modulation element of the invention. The process for manufacturing the light modulation element of the invention comprises the steps of:
     coating a layer of an UV curable material  52  on a flexible substrate  50 ;   rolling a roller  56  embossed with microstructures  54  on the layer of UV curable material  52  for patterning the UV curable material  52 ; and   curing the layer of UV curable material  52 .   
   In a preferred embodiment of the invention, the collimation unit of the invention can comprise more than one prism  46 , which is similar to the diffusion unit. As seen in  FIG. 6 , a basic optical unit  60  of the light modulation element of the invention can comprises two prisms and one semi-lenticular lens, and so on. 
   Please refer to  FIG. 7 , which is a cross-sectional view of a luminance control apparatus utilizing the light modulation element of a preferred embodiment of the present invention. The luminance control apparatus  7  of the invention comprises a light source  70 , a reflector  72 , a light guide plate  74 , and a light modulation element  76 ; wherein the light source  70  is arranged at a side of the light guide plate  74  for emitting an incident light  700  thereto; the light guide plate  74  is arranged over the reflector  72 ; and the light modulation element  76  is arranged at a position over the light guide plate  74 ; thereby the optical performance of the luminance control apparatus  7  is enhanced since the light modulation element  76  is capable of diffusing and collimating the incident light  700  simultaneously in a specific direction (i.e. a display utilizing the luminance control apparatus can either has a better vertical viewing angle or a better horizontal viewing angle). 
   Please refer to  FIG. 8 , which is a cross-sectional view of a luminance control apparatus utilizing the light modulation element of another preferred embodiment of the present invention. The luminance control apparatus  8  of the invention comprises a light source  80 , a reflector  82 , a light guide plate  84 , and two light modulation elements  86 ,  88 ; wherein the light source  80  is arranged at a side of the light guide plate  84  for emitting an incident light  800  thereto; the light guide plate  84  is arranged over the reflector  82 ; and the orientation of the light modulation element  88  are being rotate by an angle α (as seen in  FIG. 9 ) to be placed over the light modulation element  86  while the two stacked light modulation elements  86 ,  88  are arranged at a position over the light guide plate  84 ; thereby the optical performance of the luminance control apparatus  8  is enhanced since the light modulation element  86 ,  88  is capable of diffusing and collimating the incident light  800  simultaneously in two specific directions (i.e. the vertical viewing angle and the horizontal viewing angle of a display utilizing the luminance control apparatus can both be increased simultaneously). 
   In a preferred embodiment of the invention, the a semi-lenticular lens is characterized by a specific depth preferably in the range of 5 microns to 500 microns, and a prism is characterized by a vertex angle, preferably in the range of 30° to 140°, and a height, preferably in the range of 0 micron to 500 microns. Moreover, as seen respectively in  FIG. 11  and  FIG. 10 , the second optical surface can be an optical surface selected from the group consisting of a rugged surface and a smooth surface. When the second optical surface is designed as a rugged surface, the rugged surface either can be integrally formed while manufacturing the light modulation element, or can be formed by coating a layer of resin with particles  440  dispersed therein. Furthermore, in another preferred embodiment of the invention, when the luminance control apparatus of the invention comprises two light modulation elements, the orientation of one of the two light modulation elements is being rotated by an angle in the range of 0° to 90° to be placed overlapping another light modulation element. 
   From the above description, it is noted that the light modulation element of the invention is equipped with functions of light collimation and diffusion simultaneously, which can be used as the replacement for a conventional brightness enhancement film and a diffuser. Moreover, as the light modulation element of the invention is being applied in a luminance control apparatus like a backlight module, not only the luminous efficacy of the backlight module is enhanced, but also the manufacturing cost of the backlight module is reduced because of the structure of the same is simplified. 
   While the preferred embodiment of the invention has been set forth for the purpose of disclosure, modifications of the disclosed embodiment of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.