Abstract:
A collimating lens includes at least two lens groups, each having an aspherical surface. The collimating lens also includes a flat diffraction lens disposed nearest to an image plane.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 14/929,221, filed on Oct. 30, 2015 and entitled COLLIMATING LENS, presently pending, the entire contents of which are hereby expressly incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
       [0002]    The present invention generally relates to a collimating lens, and more particularly to a collimating lens with a diffraction lens. 
       2. Description of Related Art 
       [0003]    A collimating lens is an optical device that aligns light beams in a specific direction to make collimated light or parallel rays. Accordingly, light does not disperse with distance, or at least, will disperse minimally. The collimating lens may be used with a light source such as a laser diode. 
         [0004]    A conventional collimating lens may consist of a mould-made curved lens composed of glass. As a result, cost is high and overall dimension is large. Moreover, the conventional collimating lens possesses at least one convex surface, which makes assembling the collimating lens difficult. 
         [0005]    For the foregoing reasons, a need has arisen to propose a novel collimating lens to eliminate drawbacks of the conventional collimating lens. 
       SUMMARY OF THE INVENTION 
       [0006]    In view of the foregoing, it is an object of the embodiment of the present invention to provide a collimating lens with compact dimension at low cost to facilitate the assembly of the collimating lens. 
         [0007]    According to one embodiment, a collimating lens includes at least two lens groups, each having an aspherical surface. The collimating lens includes a flat diffraction lens disposed nearest to an image plane. The collimating lens of one embodiment possesses no convex outer surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1A  shows a lens arrangement of a collimating lens according to a first embodiment of the present invention; 
           [0009]      FIG. 1B  shows an exemplary ray diagram of  FIG. 1A ; 
           [0010]      FIG. 2A  shows a lens arrangement of a collimating lens according to a second embodiment of the present invention; 
           [0011]      FIG. 2B  shows an exemplary ray diagram of  FIG. 2A ; 
           [0012]      FIG. 3A  shows a lens arrangement of a collimating lens according to a third embodiment of the present invention; and 
           [0013]      FIG. 3B  shows an exemplary ray diagram of  FIG. 3A . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]      FIG. 1A  shows a lens arrangement of a collimating lens  100  according to a first embodiment of the present invention, and  FIG. 1B  shows an exemplary ray diagram of  FIG. 1A . The collimating lens  100  of the first embodiment and collimating lenses of other embodiments as described in the specification may be preferably fabricated by wafer-level optics (WLO) technique. The collimating lens  100  of the first embodiment and collimating lenses of other embodiments as described in the specification may be composed of a transparent material such as glass or plastic. In the drawing, the left-hand side of the collimating lens  100  faces an object, and the right-hand side of the collimating lens  100  faces an image plane. 
         [0015]    In the first embodiment, the collimating lens  100  may include a first lens group  1 , a second lens group  2  and a third lens group  3  in the order from the object side to the image side. Specifically, the first lens group  1  may include, in the order from the object side to the image side, a negative-powered first lens  11  (that is, a lens with negative refractive power), a flat second lens  12  (that is, a lens with a planar object-side surface and a planar image-side surface), and a positive-powered third lens  13  (that is, a lens with positive refractive power). To be more specific, the negative-powered first lens  11  has an aspherical concave object-side surface s 1  (with a negative radius) and a planar image-side surface s 2 . The flat second lens  12  has a planar object-side surface s 2  and a planar image-side surface s 3 . The positive-powered third lens  13  has a planar object-side surface s 3  and an aspherical convex image-side surface s 4 . In the embodiment, the negative-powered first lens  11  is in substantially contact with the flat second lens  12 , which is further in substantially contact with the positive-powered third lens  13 . 
         [0016]    The second lens group  2  may include, in the order from the object side to the image side, a negative-powered fourth lens  14 , a flat fifth lens  15 , and a positive-powered sixth lens  16 . To be more specific, the negative-powered fourth lens  14  has an aspherical concave object-side surface s 5  (with a negative radius) and a planar image-side surface s 6 . The flat fifth lens  15  has a planar object-side surface s 6  and a planar image-side surface s 7 . The positive-powered sixth lens  16  has a planar object-side surface s 7  and an aspherical convex image-side surface s 8 . In the embodiment, the negative-powered fourth lens  14  is in substantially contact with the flat fifth lens  15 , which is further in substantially contact with the positive-powered sixth lens  16 . 
         [0017]    The third lens group  3  may include, in the order from the object side to the image side, a positive-powered seventh lens  17 , a flat eighth lens  18 , and a flat diffraction ninth lens  19 . To be more specific, the positive-powered seventh lens  17  has an aspherical convex object-side surface s 9  (with a positive radius) and a planar image-side surface s 10 . The flat eighth lens  18  has a planar object-side surface s 10  and a planar image-side surface s 11 . The flat diffraction ninth lens  19  has a planar object-side surface s 11  and a planar image-side surface s 12 . In the embodiment, the positive-powered seventh lens  17  is in substantially contact with the flat eighth lens  18 , which is further in substantially contact with the flat diffraction ninth lens  19 . 
         [0018]    Generally speaking, the collimating lens  100  of the embodiment has at least two aspherical surfaces, one of which has a positive radius and the other of which has a negative radius. For example, the collimating lens  100  has the aspherical concave object-side surface s 1  with a negative radius and the aspherical convex object-side surface s 9  with a positive radius. 
         [0019]    According to one aspect of the embodiment, the negative-powered first lens  11 , the positive-powered third lens  13 , the negative-powered fourth lens  14 , the positive-powered sixth lens  16 , the positive-powered seventh lens  17  and the flat diffraction ninth lens  19  have a refractive index ranging between 1.5 and 1.6, and have an Abbe number ranging between 31 and 48. 
         [0020]    According to another aspect of the embodiment, the flat second lens  12 , the flat fifth lens  15  and the flat eighth lens  18  have a refractive index ranging between 1.5 and 1.6, and have an Abbe number ranging between 45 and 65. 
         [0021]      FIG. 2A  shows a lens arrangement of a collimating lens  200  according to a second embodiment of the present invention, and  FIG. 2B  shows an exemplary ray diagram of  FIG. 2A . 
         [0022]    In the second embodiment, the collimating lens  200  may include a first lens group  4  and a second lens group  5  in the order from the object side to the image side. Specifically, the first lens group  4  may include, in the order from the object side to the image side, a flat first lens  21  and a negative-powered second lens  22 . To be more specific, the flat first lens  21  has a planar object-side surface t 1  and a planar image-side surface t 2 . The negative-powered second lens  22  has a planar object-side surface t 2  and an aspherical concave image-side surface t 3  (with a negative radius). In the embodiment, the flat first lens  21  is in substantially contact with the negative-powered second lens  22 . 
         [0023]    The second lens group  5  may include, in the order from the object side to the image side, a positive-powered third lens  23 , a flat fourth lens  24 , and a flat diffraction fifth lens  25 . To be more specific, the positive-powered third lens  23  has an aspherical convex object-side surface t 4  (with a positive radius) and a planar image-side surface t 5 . The flat fourth lens  24  has a planar object-side surface t 5  and a planar image-side surface t 6 . The flat diffraction fifth lens  25  has a planar object-side surface t 6  and a planar image-side surface t 7 . In the embodiment, the positive-powered third lens  23  is in substantially contact with the flat fourth lens  24 , which is further in substantially contact with the flat diffraction fifth lens  25 . 
         [0024]    The collimating lens  200  of the second embodiment may further include a ring spacer  26 , which is disposed between and in contact with peripheries of the first lens group  4  and the second lens group  5 , such that the first lens group  4  may be coupled with the second lend group  5 . 
         [0025]    Generally speaking, the collimating lens  200  of the embodiment has at least two aspherical surfaces, one of which has a positive radius and the other of which has a negative radius. For example, the collimating lens  200  has the aspherical concave image-side surface t 3  with a negative radius and the aspherical convex object-side surface t 4  with a positive radius. 
         [0026]    According to one aspect of the embodiment, the negative-powered second lens  22 , the positive-powered third lens  23  and the flat diffraction fifth lens  25  have a refractive index ranging between 1.5 and 1.6, and have an Abbe number ranging between 31 and 48. 
         [0027]    According to another aspect of the embodiment, the flat first lens  21  and the flat fourth lens  24  have a refractive index ranging between 1.5 and 1.6, and have an Abbe number ranging between 45 and 65. 
         [0028]      FIG. 3A  shows a lens arrangement of a collimating lens  300  according to a third embodiment of the present invention, and  FIG. 3B  shows an exemplary ray diagram of  FIG. 3A . 
         [0029]    In the third embodiment, the collimating lens  300  may include a first lens group  6  and a second lens group  7  in the order from the object side to the image side. Specifically, the first lens group  6  may include, in the order from the object side to the image side, a flat first lens  31  and a positive-powered second lens  32 . To be more specific, the flat first lens  31  has a planar object-side surface m 1  and a planar image-side surface m 2 . The positive-powered second lens  32  has a planar object-side surface m 2  and an aspherical convex image-side surface m 3  (with a positive radius). In the embodiment, the flat first lens  31  is in substantially contact with the positive-powered second lens  32 . 
         [0030]    The second lens group  7  may include, in the order from the object side to the image side, a positive-powered third lens  33 , a flat fourth lens  34 , and a flat diffraction fifth lens  35 . To be more specific, the positive-powered third lens  33  has an aspherical convex object-side surface m 4  (with a positive radius) and a planar image-side surface m 5 . The flat fourth lens  34  has a planar object-side surface m 5  and a planar image-side surface m 6 . The flat diffraction fifth lens  35  has a planar object-side surface m 6  and a planar image-side surface m 7 . In the embodiment, the positive-powered third lens  33  is in substantially contact with the flat fourth lens  34 , which is in substantially contact with the flat diffraction fifth lens  35 . 
         [0031]    The collimating lens  300  of the third embodiment may further include a ring spacer  36 , which is disposed between and in contact with peripheries of the first lens group  6  and the second lens group  7 , such that the first lens group  6  may be coupled with the second lend group  7 . 
         [0032]    Generally speaking, the collimating lens  300  of the embodiment has at least two aspherical surfaces. For example, the collimating lens  300  has the aspherical convex image-side surface m 3  and the aspherical convex object-side surface m 4 . 
         [0033]    According to one aspect of the embodiment, the positive-powered second lens  32 , the positive-powered third lens  33  and the flat diffraction fifth lens  35  have a refractive index ranging between 1.5 and 1.6, and have an Abbe number ranging between 31 and 48. 
         [0034]    According to another aspect of the embodiment, the flat first lens  31  and the flat fourth lens  34  have a refractive index ranging between 1.5 and 1.6, and have an Abbe number ranging between 45 and 65. 
         [0035]    According to the embodiments discussed above, a collimating lens with reduced dimension may be made by wafer-level optics (WLO) technique at low cost. Moreover, the collimating lens of the embodiments possesses no convex outer surface, thereby facilitating the assembly of the collimating lens. 
         [0036]    Moreover, as the flat diffraction lens ( 19 ,  25  or  35 ) has a planar image-side surface (s 12 , t 7  or m 7 ), on which a diffractive optical elements (DOEs) pattern (not shown) may be directly formed, an additional glass plate as in the conventional art is thus not required and may be omitted, thereby reducing the thickness of the collimating lens. 
         [0037]    The aspheric surface (e.g., s 1 , s 4 , s 5 , s 8 , s 9 , t 3 , t 4 , m 3  or m 4 ) may be defined by the following equation: 
         [0000]    
       
         
           
             z 
             = 
             
               
                 
                   cr 
                   2 
                 
                 
                   1 
                   + 
                   
                     
                       1 
                       - 
                       
                         
                           ( 
                           
                             1 
                             + 
                             k 
                           
                           ) 
                         
                          
                         
                           c 
                           2 
                         
                          
                         
                           r 
                           2 
                         
                       
                     
                   
                 
               
               + 
               
                 
                   α 
                   1 
                 
                  
                 
                   r 
                   2 
                 
               
               + 
               
                 
                   α 
                   2 
                 
                  
                 
                   r 
                   4 
                 
               
               + 
               
                 
                   α 
                   3 
                 
                  
                 
                   r 
                   6 
                 
               
               + 
               
                 
                   α 
                   4 
                 
                  
                 
                   r 
                   8 
                 
               
               + 
               
                 
                   α 
                   5 
                 
                  
                 
                   r 
                   10 
                 
               
               + 
               
                 
                   α 
                   6 
                 
                  
                 
                   r 
                   12 
                 
               
               + 
               
                 
                   α 
                   7 
                 
                  
                 
                   r 
                   14 
                 
               
               + 
               
                 
                   α 
                   8 
                 
                  
                 
                   r 
                   16 
                 
               
             
           
         
       
     
         [0000]    where z is a distance from a vertex of lens in an optical axis direction, r is a distance in the direction perpendicular to the optical axis, c is a reciprocal of radius of curvature on vertex of lens, k is a conic constant and α 1  to α 8  are aspheric coefficients. 
         [0038]    Although specific embodiments have been illustrated and described, it will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the present invention, which is intended to be limited solely by the appended claims.