Abstract:
A waveguide includes a longitudinal structure having a first end opposite a second end. The waveguide further includes a grooved surface formed on the structure adjacent the first end. The geometric size of the longitudinal structure is substantially constant while the grooved surface reshapes a light input ray to decrease the divergence of the ray in the vertical direction and increase the divergence of the ray in the horizontal direction.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is directed to a light guide, and in particular to a groove-shaped waveguide for shaping light rays.  
         BACKGROUND OF THE INVENTION  
         [0002]    The prior art primarily uses light guides to transfer light as far as possible. In this regard, one method of guiding light energy is to use a dielectric waveguide that includes a solid rod made of transparent material. The light rays are reflected inward by the surface of the rod (e.g., total internal reflection). Another method of guiding light energy includes having light propagate mainly through air and periodically redirecting the light to keep it confined and traveling in the correct direction.  
           [0003]    Conventional waveguides typically include a circular cross-section having an optical lighting film, a back reflector and an outer shell. The back reflector is fitted tightly against a portion of the inner surface of the shell and the film is a continuous sheet that abuts the back reflector. Therefore, the back reflector is sandwiched between the outer shell and the optical lighting film.  
           [0004]    These light waveguides disclosed in the prior art are constructed with a variety of cross-sectional shapes using a variety of materials including transparent dielectric materials such as acrylic plastic or optically clear glass, or multiplayer optical films.  
           [0005]    In certain applications, however, instead of propagating the light as far as possible, the challenge is to reshape the light without increasing the geometrical size of the waveguide (e.g., shaping the light from a circular entrance beam to a required elliptical output). Thus, because current waveguide systems cannot significantly reshape the light without modifying the size of the system, it would be desirable to provide a waveguide capable of reshaping the light without increasing the size of the guide.  
         SUMMARY OF THE INVENTION  
         [0006]    It is an object of this invention to provide a waveguide including a longitudinal structure having a first end opposite a second end. A grooved surface is formed on the structure adjacent the first end.  
           [0007]    It is further an object of this invention to provide a waveguide including a longitudinal structure having a first end opposite a second end. The waveguide further includes a grooved surface formed on the structure adjacent the first end. The geometric size of the longitudinal structure is substantially constant while the grooved surface reshapes a light input ray to decrease the divergence of the ray in a first direction and increase the divergence of the ray in a second direction.  
           [0008]    It is yet another object of this invention to provide an illumination system to transmit an input light ray from a fiber optic source to a signboard display. The illumination system includes a collimating guide having a first end opposite a second end, and a longitudinal plank formed therebetween including a top surface and a bottom surface. A grooved surface is formed on the top surface and the bottom surface adjacent the first end. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    A preferred exemplary embodiment of the invention is illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which:  
         [0010]    [0010]FIG. 1A is a diagram illustrating an angular beam spread without the use of a lateral groove waveguide;  
         [0011]    [0011]FIG. 1B is a diagram illustrating the anisotropic angular beam spread with the use of a lateral groove waveguide according to the present invention;  
         [0012]    [0012]FIG. 2A is a diagram illustrating a collimating structure without a lateral groove waveguide;  
         [0013]    [0013]FIG. 2B is a diagram illustrating a collimating structure with a lateral groove waveguide according to the present invention;  
         [0014]    [0014]FIG. 3 is a elevated perspective view of a lateral groove waveguide according to the present invention;  
         [0015]    [0015]FIG. 4 is a top view of the lateral groove waveguide according to the present invention;  
         [0016]    [0016]FIG. 5 is an end view of the lateral groove waveguide according to the present invention;  
         [0017]    [0017]FIG. 6 is a top planar view of the lateral groove waveguide according to the present invention;  
         [0018]    [0018]FIG. 7 is a diagram of a ceiling display system according to the present invention;  
         [0019]    [0019]FIG. 8 is a partial view of the groove structure of the lateral groove waveguide according to the present invention;  
         [0020]    [0020]FIG. 9 is a diagram illustrating the reflection at the groove of the lateral groove waveguide according to the present invention;  
         [0021]    [0021]FIG. 10 is a diagram illustrating the reflection without the lateral groove waveguide;  
         [0022]    [0022]FIG. 11 is a diagram illustrating the reduction of the output angle using the lateral groove waveguide according to the present invention; and  
         [0023]    [0023]FIG. 12 is a perspective view of a rectangular bar with the lateral groove waveguide according to the present invention.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0024]    Light directionality and beam collimation are essential for light shaping and display progress, in both imaging and non-imaging optics. The latter is important for backlighting and other light-shaping applications because only non-imaging optics can achieve the theoretical limit of maximum light collimation and concentration. In this regard, the beam collimation always comes at the expense of cross-section increasing.  
         [0025]    [0025]FIG. 1A illustrates an angular beam spread from NA′ to NA for the regular symmetrical waveguide. As illustrated in FIG. 1B, however, the beam can also spread anisotropically using a lateral groove waveguide structure resulting in anamorphic collimation to increase the beam directionality in the horizontal direction at the expense of the vertical direction (e.g., from a circle to an ellipse).  
         [0026]    A collimating system  10  without a lateral groove waveguide is illustrated in FIG. 2A corresponding to the beam spread in FIG. 1A. A collimating system  12  with a grooved surface  14  corresponds to the horizontal beam spread illustrated in FIG. 1B.  
         [0027]    As illustrated in FIG. 3, in the preferred embodiment of the present invention, a rectangular waveguide  14  includes a first end  16 , a second end  18 , a top surface  20 , a bottom surface  22 , and a groove portion  24  disposed adjacent first end  16 . Guide  14  is generally decreasingly tapered in width from first end  16  to second end  18 , for increasing horizontal divergence together with the groove structure. First end  16  is parallel to second end  18 . Groove portion  24  is preferably formed on both top surface  20  and bottom surface  22 .  
         [0028]    As illustrated in FIG. 5, groove portion  24  includes a series of generally triangular protrusions  26  (e.g., three protrusions on each surface  20  and  22 ) forming a series of grooves  28 . In the present invention, the height of protrusions  26  is approximately 0.3 mm, the thickness of waveguide  14  is approximately 2 mm and the length of first end  16  is approximately 4 mm. As illustrated in FIG. 6, the length of second end  18  is approximately 2.5 mm, and the length of waveguide  14  from first end  16  to second end  18  is approximately 50 mm.  
         [0029]    Waveguide  14  is formed from optically clear acrylic and input grooves  28  improve coupling efficiency and reduce output divergency in a vertical direction. Grooves  28  are placed at the entrance of waveguide  14  at first end  16  and therefore affect only high divergence input rays. The reflection at the inclined grooves&#39; surface decreases the vertical divergence and increases the horizontal divergence of these rays. The taper provides a specific increasing light output divergence in the horizontal direction.  
         [0030]    Waveguide  14  provides a means to input light energy from fiber optic sources for the purpose of delivering that light energy to a display. In the preferred embodiment of the present invention, waveguide  14  delivers light energy to a signboard display. In the alternative, waveguide  14  can deliver light energy to a variety of other displays including highway information displays (emergency announcements, traffic conditions, better signage for complex and dangerous intersections) and roadside advertising (electronic billboards).  
         [0031]    Waveguide  14  may also be used in special illumination systems for theaters, convention/trade show areas, department stores, automobile showrooms and other public/semipublic areas that are enhanced by ceiling lighting that can be varied from high brightness in one area to low-level illumination in another area.  
         [0032]    Turning to FIG. 7, a display system  30  is a ceiling display to deliver information and advertising to visitors in large halls, lobbies, and other facilities. System  30  includes waveguides  14  coupled to numerous delivery fibers  32  on the ceiling of a hall. A visitor  34  at a floor level  36  observes information from display system  30 . To preserve the output brightness, light has to be concentrated in an observation sector  38 , ±α through the lobby passway. In the preferred embodiment, the approximate value of α is ±50° and divergence in the orthogonal direction is ±20°.  
         [0033]    Without the use of lateral groove waveguide  14  in system  30 , the original divergence from the plastic fiber is ±30°. In order to increase the divergence up to ±50° in observation sector  38 , the output size of waveguide  14  has to be reduced in this direction. In this regard, output size in that direction has to be increased in order to reduce divergence to ±20°. Unfortunately, there are limitations (e.g., packaging problems) that prevent an increase in the geometric size of waveguide  14 .  
         [0034]    Therefore, in order to reduce the divergence, grooves  26  are molded at the lateral size of waveguide  14 . Grooves  26  thereby reshape the light without increasing the geometrical size of the waveguide  14 .  
         [0035]    In particular, FIG. 8 illustrates the effect of grooves  26  on the shape of the light. When light is incident to grooves  28 , the angle between reflected ray, {overscore (N)}, and the axis, Y, increases. Hence, the outgoing divergence angle, γ 1 , decreases. FIG. 9 illustrates this reflection of the incident ray at point A in greater detail.  
         [0036]    Angle α is the angle between the axis, Y, and incident ray, {overscore (N)}. Angle β is the angle of the normal to the groove surface and axis Y in plane ZAY. Without the grooves, the angle β in FIG. 9 is 0. If {overscore (x)}, {overscore (y)}, {overscore (z)} are the eigen vectors of the axes,  
           {overscore (r)}={overscore (x)} (sin α)+ {overscore (y)} (cos α)+ {overscore (z)} (0), and  {overscore (N)}={overscore (x)} (0)+ {overscore (y)} (−cos β)+ {overscore (z)} (sin β).  (1-1)  
         [0037]    The reflection law is  
           {overscore (r′)}={overscore (r)}+{overscore (N)} (−2 {overscore (Nr)} ).  (1-3)  
         [0038]    The scalar product of Nr is (−cos αcos β).  
         [0039]    Hence,  
           {overscore (r′)}={overscore (x)} (sin α)+ {overscore (y)} (cos α−2 cos 2 β cos α)+ {overscore (z)} (2 sin β cos β cos α),  (1-4)  
         [0040]    or  
           {overscore (r′)}={overscore (x)} (sin α)+ {overscore (y)} (1−2 cos 2 β)cos α+ {overscore (z)}  cos+Z cos α·sin 2β).  (1-5)  
         [0041]    If β=0, or reflection takes place without the grooves, the reflected ray {overscore (r′)} is  
           {overscore (r′)}={overscore (x)} (sin α)+ {overscore (y)} (−cos α).  (1-6)  
         [0042]    This is illustrated in FIG. 10 (reflection without lateral groove waveguide  14 ).  
         [0043]    In the case of using lateral groove waveguide  14 , however, the direct cosine of {overscore (r′)} with axis y is reduced to (1−2 cos 2 )cos α, and the angle, γ, in FIG. 8 and FIG. 11 is  
         γ= a  cos[−(1−2 cos 2  β)cos α].  (1-7)  
         [0044]    Hence,  
         γ&gt;α.  (1-8)  
         [0045]    The output angle, γ′, in FIG. 8 is reduced as illustrated in FIG. 11.  
         [0046]    [0046]FIG. 12 illustrates a rectangular acrylic bar  40  including lateral groove waveguide  14 . For the optimal tradeoff between outgoing angles γ′ and δ′, the specific shape and geometry of grooves  28  may vary. In this regard, the geometry of grooves  28  is determined by angle β in FIG. 9. The shape of grooves  28  slightly increases the angle of divergence, δ′.  
         [0047]    The scope of the application is not to be limited by the description of the preferred embodiments described above, but is to be limited solely by the scope of the claims that follow.