Abstract:
An exemplary camera module includes a barrel, a holder engaged with the barrel, a first lens received in the barrel, an image sensor received in the holder and a second lens received in the holder. The holder includes an inner chamber. The second lens is mounted on the holder proximate to the image sensor. The second lens is configured for preventing dust accessing into the inner chamber. The second lens includes a main body and an infrared cut film formed on and in contact with an outside surface of the main body or embedded within the main body.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to optical imaging devices and, particularly, to a camera module. 
     2. Discussion of Related Art 
     Currently, with the development of electronic devices having multiple functions, image pick-up apparatuses have been widely used in a variety of consumer electronic devices, such as cellular telephones, notebook computers, digital cameras, personal digital assistants (PDAs), etc. In the meantime, demand for improving image quality is increasing, which essentially depends on the quality of a camera module of the image pick-up apparatus. Accordingly, a camera module with high resolution and image quality is desired. 
     Referring to  FIG. 7 , a typical camera module  100  includes a holder  11 , a barrel  12 , a plurality of lenses  13  received in the barrel  12  and an image sensor  14  arranged in the holder  11 . Usually, the camera module  100  further includes an infrared cut filter  15  for preventing infrared light disturbing the image sensor  14  and a glass cover  16  for preventing dusts from falling on the image sensor  14 . However, the infrared cut filter  15  and the glass cover  16  will take up some space of the holder  11  which is not suitable for the camera module  100  to be compact. 
     Therefore, what is needed is a camera module capable of overcoming the described limitations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present camera module can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present camera module. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a schematic, cross-sectional view of a camera module in accordance with a first embodiment. 
         FIG. 2  is a schematic, cross-sectional view of a second lens in the camera module of  FIG. 1 . 
         FIG. 3  is a schematic, top view of a second lens in the camera module of  FIG. 1 . 
         FIG. 4  is a schematic, cross-sectional view of a camera module in accordance with a second embodiment. 
         FIG. 5  is a schematic, cross-sectional view of a second lens in the camera module of  FIG. 4 . 
         FIG. 6  is a schematic, cross-sectional view of a second lens in the camera module of  FIG. 4 . 
         FIG. 7  is a schematic, cross-sectional view of a typical camera module. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Reference will now be made to the drawings to describe in detail of the exemplary embodiment of the camera module. 
     Referring to  FIG. 1 , a camera module  200 , in accordance with the first embodiment, includes a barrel  21 , a holder  22  engaged with the barrel  21 , a first lens  23  received in the barrel  21 , an image sensor  24  received in the holder  22 , and a second lens  25  received in the holder  22 . 
     The barrel  21  is a hollow cylinder, including an inner wall and an outer wall  211 . The outer wall  211  has screw threads for mounting the barrel  21  to the holder  22 . The barrel  21  is configured for receiving optical elements, such as lenses, spacers or other optical elements. The barrel  21  may be made of plastic materials, such as polyethylene, polypropylene, polyvinyl chloride or polystyrene. 
     The holder  22  is a hollow cylinder with a top portion  221  and a bottom portion  223 . The top portion  221  is configured for engaging with the barrel  21 , and partly receiving the barrel  21 . The top portion  221  includes an inner surface  2211 . A plurality of screw threads is formed on the inner surface  2211  for fixing the barrel  21  to the holder  22 . It should be understood that the barrel  21  also can be fixed in the holder  22  by adhering. In the present embodiment, the cross-sectional shape of the top portion is round. The bottom portion  223  of the holder  22  has an inner chamber  226  for receiving the image sensor  24 . The cross-sectional shape of the bottom portion  223  is rectangular. It should be understood that the shape of the holder  22  can also be other shapes depending on the practical need. The holder  22  may be made of plastic materials, such as polyethylene, polypropylene, polyvinyl chloride and polystyrene. 
     The image sensor  24  is arranged in the bottom portion  223  of the holder  22  and is configured for receiving the light beams converged by the first and second lenses  23 ,  25  in the barrel  21 . 
     The second lens  25  is arranged in the bottom portion  223  of the holder  22  above the image sensor  24 . The second lens  25  includes a main body  251  and an infrared cut film  252 . The second lens  25  is provided for obviate the need of arranging a transparent plate in the holder  22  to prevent contamination of the image sensor  24 . The infrared cut film  252  can be formed on the main body  251  or embedded within the main body  251  (see  FIG. 2 ). The second lens  25  is adjoined to the image sensor  24 , which means no other optical elements exit between the second lens  25  and the image sensor  24 . 
     In the present embodiment, the infrared cut film  252  may be formed on the main body  251  either on a top surface of the main body  251  facing the barrel  21  or on a bottom surface of the main body  251  facing the image sensor  24 . Alternatively, the infrared filter film  252  can be formed embedded within the main body  251  by using an insert molding method. The shape of the main body  252  is rectangular which is cooperated with that of the bottom portion  223  of the holder  22  (see  FIG. 3 ). When the bottom portion  223  of the holder  22  is chosen as an annular shape, the main body  252  of the second lens  25  could be round in the shape. 
     The second lens  25  can be produced using injection molding method by the following steps. Firstly, the main body  251  of the second lens  25  is produced by injection molding machine; secondly, the infrared cut film  252  is coated on one surface of the main body  251  by evaporation coating device or sputter coating device. Then, the second lens  25  can be produced. 
     The second lens  25  is adhered to the inner surface  2231  of the bottom portion  223  of the holder  22 . In the present embodiment, the holder  22  includes a step  225 , and the second lens  25  is also adhered to the bottom surface  2251  of the step  225 . 
     To protect the second lens  25 , an annular protrusion  224  is formed on the inner surface  2211  of the top portion  221  of the barrel  22  between the second lens  25  and the barrel  21 . The annular protrusion  224  can prevent small fragments or dusts from falling down to the second lens  25  when the barrel  21  is threadedly coupled to the holder  22 , or prevent glue from falling down to the second lens  25  when the barrel  21  is fixed to the holder  22  via the glue. 
     The second lens  25  is arranged in the holder  22 , which can reduce the number of the lenses  23  in the barrel  21  and then reduce the height of the barrel  21 . The second lens  25  also can prevent the image sensor  23  from being polluted by dusts, replacing the glass cover  16  of the camera module  100  in the prior art. Furthermore, the second lens  25  includes an infrared cut film  252 , so an additional infrared cut filter can be removed. The second lens  25  has the function of an optical lens, an infrared cut filter and a glass cover, so the camera module  200  with the second lens  25  can be more compact. Moreover, because the infrared cut filter and the glass cover are removed, the assembly of the camera module  200  can be greatly simplified and the time and cost of assembly can be greatly reduced. 
     Referring to  FIG. 4 , a camera module  300 , in accordance with the second embodiment, includes a barrel  31 , a holder  32  engaged with the barrel  31 , a first lens  33  received in the barrel  31 , an image sensor  34  received in the holder  32 , and a second lens  35  received in the holder  32 . The camera module  300  is similar with the camera module  200  in the first embodiment except the structure of the second lens  35 . 
     Referring to  FIG. 5 , the second lens  35  includes a main body  351  and an infrared cut film  352 . The main body  351  includes a flat portion  3511  and two curving portions  3512 ,  3513 . The flat portion  3511  includes two opposite surfaces, and the two curving portions  3512 ,  3513  are respectively formed on the two surfaces of the flat portion  3511 . 
     The main body  351  can be produced using a nano-imprinting method. Firstly, the flat portion  3511  is provided. Secondly, the curving portion  3512  is formed on one surface of the flat portion  3511  using the nano-imprinting method. Thirdly, the flat portion  3511  is turned over and the curving portion  3513  is formed on an opposite surface of the flat portion  3511 . Lastly, the main body  351  is done. 
     To avoid total reflection at the interfaces of the flat portion  3511  and the two curving portions  3512 ,  3513 , the second lens  35  further includes two multi-layer films  3514 ,  3515  respectively sandwiched between the flat portion  3511  and the two curving portions  3512 ,  3513 . The multi-layer films  3514 ,  3515  have the same structure each of which includes a plurality of low refractive index layers and high refractive index layers when each low refractive index layer and each high refractive layer are alternately stacked one on another. Such that, the total reflection at the interfaces of the flat portion  3511  and the two curving portions  3512 ,  3513  can be reduced or eliminated. 
     The infrared cut film  352  is coated on one surface of the main body  351 . It may be coated after the main body  351  is produced. That is to say, a part of the infrared cut filter  352  is formed on an outer surface  40  of the curving portion  3512  and rest of the infrared cut filter  352  is formed on the peripheral portion  3516  of the flat portion  3511 . Alternatively, the infrared cut film  352  may be coated directly on one surface of the flat portion  3511  before the curving portion  3512  or the curving portion  3513  is formed on the surface (see  FIG. 6 ). It should be understood that, the infrared cut film  352  may be formed inside the flat portion  3511  of the main body  351  similar with the structure as shown in  FIG. 2 . 
     While the present invention has been described as having preferred or exemplary embodiments, the embodiments can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the embodiments using the general principles of the invention as claimed. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and which fall within the limits of the appended claims or equivalents thereof.