Patent Publication Number: US-2005141837-A1

Title: Bendable light guide

Description:
DESCRIPTION OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates in general to a light guide device and, more particularly, to a flexible light guide device in a liquid crystal display.  
      2. Background of the Invention  
      A light guide assembly for a liquid crystal display (“LCD”) typically includes a light source and a wedge-shaped light guide device. The light guide device functions to transform a linear form of light provided by the light source into a planar one. In general, the light guide device in the art is made of acrylic or plastic materials, and does not afford to be bendable because an optical path determined in the structure will be distorted. In addition, it may be difficult to downsize the light guide device due to the nature of the materials.  
      There is thus a general need in the art for a light guide device and method overcoming at least the aforementioned shortcomings in the art. A particular need exists for a flexible light guide that overcomes optical distortion problems in the art.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention is directed to a light guide device and a method of manufacturing the light guide device that obviate one or more of the problems due to limitations and disadvantages of the related art.  
      To achieve these and other advantages, and in accordance with the purpose of the invention as embodied and broadly described, there is provided a light guide device having light propagating therein that comprises a first film of a first index of refraction including a surface, a second film of a second index of refraction different from the first index of refraction formed in the first film in a waveform, a plurality of first parts of the second film formed parallel to each other, and a plurality of second parts of the second film corresponding to the first parts formed parallel to each other, wherein a part of the light is reflected toward the surface of the first film when the propagating light is incident upon one of the first parts of the second film.  
      In one aspect, the first parts of the second film form an angle of generally 45 degrees with respect to the surface of the first film.  
      In another aspect, a part of the light is reflected in a direction normal to the surface of the first film when the propagating light is incident upon one of the first parts of the second film.  
      Also in accordance with the present invention, there is provided a light guide device having light propagating therein that comprises a pair of first transparent films of a first index of refraction, a base of each of the first transparent films, the base of one first transparent film facing the base of the other first transparent film, a plurality of protrusions of each of the first transparent films being separated from each other on the base of a corresponding first transparent film, the protrusions of one first transparent film being interleaved with the protrusions of the other first transparent film, a space defined between the interleaved protrusions, and a second transparent film of a second index of refraction different from the first index of refraction formed in the space including a plurality of first parts and a plurality of second parts interleaved with the first parts, wherein a part of the light is reflected toward the base of one of the first transparent films when the propagating light is incident upon one of the first parts of the second transparent film.  
      In one aspect, each of the protrusions further comprises a first side, a second side, and a tapered end connecting the first and second sides.  
      In another aspect, the first sides of the protrusion are generally perpendicular to the base associated with the protrusions.  
      Still in accordance with the present invention, there is provided a method of manufacturing a light guide device that comprises preparing a pair of first transparent films of a first index of refraction, providing each of the first transparent films with a base, providing each of the first transparent films with a plurality of protrusions separated from each other on the base of a corresponding first transparent film, each of the protrusions including a tapered end, interleaving the protrusions of one first transparent film with the protrusions of the other first transparent film to define a space between the interleaved protrusions, and filling the defined space with a second transparent film of a second index of refraction different from the first index of refraction.  
      In one aspect, the method further comprises the step of using an optical glue to serve as the first transparent films and the second transparent film.  
      In another aspect, the method further comprises the step of engaging the tapered ends of the protrusions of one first transparent film to the base of the other first transparent film.  
      Yet still in accordance with the present invention, there is provided a method of operating a light guide device that comprises providing a light guide device including a first film of a first index of refraction including a surface, a second film of a second index of refraction different from the first index of refraction formed in the first film in a waveform, a plurality of first parts of the second film formed parallel to each other, and a plurality of second parts of the second film corresponding to the first parts formed parallel to each other, providing a light source that provides light to the light guide device, and reflecting a part of light propagating in the light guide device toward the surface of the first film in a predetermined direction each time when the light is incident upon one of the first parts of the second film.  
      In one aspect, the method further comprises the step of reflecting the light from the light source at one end of the light guide device and at a different surface of the first film.  
      In another aspect, the method further comprises the step of converging the light provided by the light source before providing the light to the light guide device.  
      Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.  
      The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic diagram of a light guide device in accordance with one embodiment of the present invention;  
       FIG. 2  is a schematic diagram illustrating a flexible light guide device  10  in accordance with one embodiment of the present invention;  
       FIGS. 3A, 3B  and  3 C are schematic diagrams of a light assembly in accordance with one embodiment of the present invention; and  
       FIGS. 4A and 4B  are diagrams illustrating a method of manufacturing a light guide device in accordance with one embodiment of the present invention. 
    
    
     DESCRIPTION OF THE EMBODIMENTS  
      Reference will now be made in detail to the present embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
       FIG. 1  is a schematic diagram of a light guide device  10  in accordance with one embodiment of the present invention. Light guide device  10  includes a first film  12  of a first index of refraction and a second film  14  of a second index of refraction different from the first index of refraction. First film  12  and second film  14  include a transparent, optical film. In one embodiment according to the invention, first film  12  and second film  14  include an optical glue. In another embodiment, first film  12  and second film  14  are flexible. First film  12  includes a surface  12 - 2 . Second film  14  is formed in first film  12  in a waveform, and includes a plurality of first parts  14 - 2  formed parallel to each other and a plurality of second parts  14 - 4  corresponding to first parts  14 - 2  also formed in parallel to each other.  
      In operation, light  16  propagating in light guide device  10  is incident upon a leading first part  14 - 2  of second film  14 . At the boundary between first film  12  and second film  14 , a part of light  16  is reflected by the first part  14 - 2  toward surface  12 - 2  and another part of light  16  transmits into second film  14 . The reflection rate R and the transmission rate T of incident light  16  at the boundary are defined by Fresnel&#39;s Law as follows. 
 
 R =[( n   1  cos θ 1   −n   2  cos θ 2 )/( n   1  cos θ 1   +n   2  cos θ 2 )] 2 ; and 
 
 T= 1− R  
          wherein n 1  and n 2  are respectively the first index of refraction of first film  12  and the second index of refraction of second film  14 , and θ 1  and θ 2  are respectively the incident angle and refracted angle in accordance with Snell&#39;s Law.        

      First parts  14 - 2  of second film  14  form an acute angle with respect to surface  12 - 2  of first film  12 . Second parts  14 - 4  of second film  14  are disposed in such a manner that light  16  departing from first parts  14 - 2  transmits into second parts  14 - 4  without refraction. That is, light  16  departing from first parts  14 - 2  propagates in a direction normal to second parts  14 - 4 . In an embodiment according to the invention, first parts  14 - 2  of second film  14  form an angle of approximately 45° with respect to surface  12 - 2  of first film  12 . As a result, the part of light  16  reflected by first parts  14 - 2  transmits in a direction normal to surface  12 - 2 , and second parts  14 - 4  of second film  14  are disposed substantially perpendicular to surface  12 - 2  of first film  12 .  
      Due to differences in the refraction index, an offset is generated between an optical path light  16  is incident on one of first parts  14 - 2  and a different optical path light  16  departs from the one of first parts  14 - 2 . The offset becomes greater as the difference between the first and second indices of refraction becomes greater. To avoid a large offset, the first index of refraction of first film  12  is selected to be close to the second index of refraction of second film  14 . In one embodiment according to the invention, the first index of refraction is approximately 1.5.  
       FIG. 2  is a diagram illustrating a flexible light guide device  10  in accordance with one embodiment of the present invention. When first parts  14 - 2  of second film  14  form an angle of 45° with respect to surface  12 - 2  of first film  12 , light  16  propagating in flexible light guide device  10  is reflected by first parts  14 - 2  of second film  14  in a direction normal to surface  12 - 2  of first film  12  over the entire length of flexible light guide device  10 .  
       FIGS. 3A, 3B  and  3 C are schematic diagrams of a light assembly  30  in accordance with one embodiment of the present invention. Referring to  FIG. 3A , light assembly  30  includes a light guide device  32  and a light source  34 . Light guide device  32  includes a similar structure to light guide device  10  shown in  FIG. 1 . Light guide device  32  functions to direct light  40  from light source  34  toward a first surface  32 - 6  of light guide device  32 , and transforms a form of linear light provided by light source  34  into a planar one. Light source  34  includes a lamp  34 - 2  and a reflector  34 - 4  surrounding lamp  34 - 2 . Light guide device  32  includes an end  32 - 2  coupled to light source  34 .  
      Referring to  FIG. 3B , light assembly  30  may further include a light collector  36  disposed between light guide device  32  and light source  34 . Light collector  36  converges the light  40  provided by light source  34 .  
      Referring to  FIG. 3C , light assembly  30  may further include a first reflector  38 - 2  and a second reflector  38 - 4 . First reflector  38 - 2  is disposed at another end  32 - 4  of light guide device  32 . Second reflector  38 - 4  is attached to a second surface  32 - 8  of light guide device  32 . First reflector  38 - 2  and second reflector  38 - 4  function to reflect light  40  traveling to end  324  toward first surface  32 - 6  of light guide device  32 .  
       FIGS. 4A and 4B  are diagrams illustrating a method of manufacturing a light guide device  60  in accordance with one embodiment of the present invention. Referring to  FIG. 4A , a pair of first transparent films  62  and  64  of a first index of refraction is prepared. Each of first transparent films  62  and  64  is then respectively provided with a base  72  and  74 , and a plurality of protrusions  82  and  84 . Protrusions  82  are separated from each other on base  72 . Similarly, protrusions  84  are separated from each other on base  74 . Each of protrusions  82  and  84  respectively includes a tapered end  82 - 2  and  84 - 2 .  
      Referring to  FIG. 4B , protrusions  82  of one first transparent film  62  are interleaved with protrusions  84  of the other first transparent film  64  to define a space (not numbered) between the interleaved protrusions  82  and  84 . The interleaving of protrusions  82  and  84  is implemented by engaging tapered ends  82 - 2  of one first transparent film  62  to base  74  of the other first transparent film  64 , and tapered ends  84 - 2  of the other first transparent film  64  to base  72  of the one first transparent film  62 . A second transparent film  66  of a second index of refraction different from the first index of refraction is then filled in the space.  
      In one embodiment according to the invention, an optical glue is used to serve as first transparent films  62  and  64  and second transparent film  66 . The first index of refraction is selected to be close to the second index of refraction. In another embodiment, first and second transparent films  62  and  64  are flexible.  
      Each of protrusions  82  is respectively further provided with a first side  82 - 4  and a second side  82 - 6  connected to first side  82 - 4  via tapered end  82 - 2 . Similarly, each of protrusions  84  is respectively further provided with a first side  84 - 4  and a second side  84 - 6  connected to first side  84 - 4  via tapered end  84 - 2 . In one embodiment according to the invention, first sides  82 - 4  of protrusions  82  are formed at approximately a right angle with respect to base  72 , and second sides  82 - 6  of protrusions  82  are formed at an acute angle with respect to base  72 . Likewise, first sides  84 - 4  of protrusions  84  are formed at approximately a right angle with respect to base  74 , and second sides  84 - 6  of protrusions  84  are formed at an acute angle with respect to base  74 . In one embodiment according to the invention, second sides  82 - 6  and  84 - 6  form an angle of approximately 45° with respect to bases  72  and  74 , respectively.  
      The present invention also provides a method of operating a light guide device  10 . Light guide device  10  is provided with a first film  12  of a first index of refraction and a second film  14  of a second index of refraction different from the first index of refraction. First film  12  includes a surface  12 - 2 . Second film  14  is formed in first film  12  in a waveform, and includes a plurality of first parts  14 - 2  formed parallel to each other and a plurality of second parts  14 - 4  formed parallel to each other. A light source  34  is then provided to provide light to light guide device  10 . A part of light propagating in light guide device  10  is reflected toward surface  12 - 2  of first film  12  in a predetermined direction each time when the light is incident upon one of first parts  14 - 2  of second film  14 .  
      In one embodiment according to the invention, the method further comprises the step of reflecting the light provided by a light source toward surface  12 - 2  of first film  12  at one end of light guide device  10  and at a different surface of first film  12 . In another embodiment, the method further comprises the step of converging light provided by a light source before providing the light to light guide device  10 .  
      Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.