Abstract:
A lens module includes a lens barrel, at least one fixed focus lens fixed in the lens barrel, and at least two variable focus lenses fixed in the lens barrel. Each variable focus lens includes two electrodes and an electro-optical material between the electrodes. Each electrode is electrically connected to a voltage supply so as to be able to selectively apply a voltage to the electro-optical material and to thus selectively control the refractive index of that material. By changing the refractive index, a concordant change in the focus of a given variable focus lens is possible, without modifying the position and/or shape thereof.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to lens modules and, more particularly, to a lens module having a variable focus and to a camera module using the lens module. 
   2. Description of related art 
   With the development of wireless communication technologies, increasing numbers of mobile phones and PDAs now include digital cameras as a special feature. 
   Generally speaking, digital cameras are image-recording media capable of photographing images without using film. Such a digital camera typically uses an image pickup device, which is a kind of semiconductor device, such as a charged coupled device (CCD) or complementary metal oxide semiconductor (CMOS). In the digital camera, an object image formed on the image pickup device through a lens is converted into an electronic signal by the image pickup device, and the electrical signal is stored as a digital signal, for example, either in the camera unit or in a mobile phone or PDA in which the digital camera is mounted. 
   Since the digital camera is to be mounted in a small mobile phone or PDA, a fixed focus lens module is usually used to facilitate mounting thereof. However, images photographed by a digital camera module with a fixed focus lens module tend to be of poor quality. This poor quality is partly due to the fixed focus lens system, which is incapable of adjusting a distance between the lens(es) and the image pickup device and/or between the lenses themselves to make a clearer image when photographing objects at different distances from the camera. Thus, a focusing structure or a zoom structure is required to change the focus of the digital camera module. 
   A typical driving apparatus uses a gear or cam mechanism to realize the focusing or zoom function. This structure is relatively large and makes the camera structure fairly complicated. Furthermore, the operation of the mechanical structure consumes a substantial amount of energy, which is of concern given the limited battery capacity of the portable device with which it is associated. In addition, the precision of the mechanical transmission is not high. 
   Therefore, a new lens module is desired in order to overcome the above-described shortcomings. 
   SUMMARY OF THE INVENTION 
   In one embodiment thereof, a lens module is provided. The lens module includes a lens barrel, at least one fixed focus lens fixed in the lens barrel, and at least two variable focus lenses fixed in the lens barrel. Each variable focus lens includes two electrodes and an electro-optical material filled between the electrodes. Each electrode is electrically connected to a voltage supply so as to apply a voltage to the electro-optical material. 
   Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Many aspects of the lens module can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the lens module. Moreover, in the drawings like reference numerals designate corresponding parts throughout the several views. 
       FIG. 1  is a cut-away view of a first embodiment of a lens module; 
       FIG. 2  is a top view of a first embodiment of an electrode of the lens module in  FIG. 1 ; 
       FIG. 3  is a top-down view of a second embodiment of an electrode of the lens module in  FIG. 1 ; 
       FIG. 4  is a cut-away view of a second embodiment of a lens module; 
       FIG. 5  is a cut-away view of a third embodiment of a lens module; and 
       FIG. 6  shows a digital camera module, using the lens module shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , in a first preferred embodiment, a lens module  10  includes a barrel  11 , a fixed focus lens  12 , a front sealing cover  13 , a rear sealing cover  14 , and two variable focus lenses  15 . 
   The fixed focus lens  12  may be a spherical convex lens or a spherical concave lens and may be made of glass or plastic, with a fixed refractive index. The fixed focus lens  12  is received in the barrel  11 . 
   The front sealing cover  13  and the rear sealing cover  14  may be made, e.g., of glass or plastic and may be any optically-appropriate shape, such as a dome window or a planar plate. Advantageously, the front sealing cover  13  may be a protective window for the lens module  10 , and the rear sealing cover  14  may be an infrared-cut filter. The front sealing cover  13  is fixed in a first end of the barrel  11 , and the rear sealing cover  14  is fixed in a second end of the barrel  11 . Thus, a first sealed space may be defined between the front sealing cover  13  and the fixed focus lens  12 , and a second sealed space may be defined between the rear sealing cover  14  and the fixed focus lens  12 . 
   Each variable focus lens  15  includes a pair of transparent electrodes  151  and an electro-optical material  153  filled between the two transparent electrodes  151 . The electro-optical material  153  may, for example, be chosen from the group including lithium niobate, gallium arsenide, lithium tantalite, and liquid crystal material. A refractive index of the electro-optical material  153  may vary with a variable voltage applied by the electrodes  151 , and, thus, a focal length of the variable focus lens  15  may also vary with the variable voltage. 
   The transparent electrodes  151  can, for example, be indium tin oxide conductive films and are respectively coated on two side surfaces of the fixed focus lens  12 , on an inside surface of the front cover  13 , and on an inside surface of the rear sealing cover  14 . Each pair of transparent electrodes is electrically connected to a variable voltage supply  17  controlled by a switch  18 . Thus, a variable voltage can be applied to the electro-optical material  153 . An adjustment of the voltage results in a change in the refractive index of the electro-optical material  153 , and, as such, the electro-optical material  153  is effectively able to operate as an adjustable/variable lens without having to undergo a position and/or shape change. 
   Referring to  FIG. 2 , each of the electrodes  151  can be designed as a configuration including a plurality of spaced annular rings  1511  with varying radiuses and/or widths. The annular rings  1511  are arranged to be concentric with each other. Beneficially, the widths of the rings  1511  decrease, respectively, as the radiuses of the rings  1511  decrease, and ring spaces between neighboring rings decreases as the center thereof is approached. The rings  1511  are connected with very thin spoke connections  1512 , which will not introduce any significant additional electrical field due to the widths of the spoke connections  1512  being thin enough. Alternatively, referring to  FIG. 3 , each of the electrodes  151  can instead be designed so that the widths of the rings  1511  increase as the radius of the rings  1511  decreases, and the ring spaces increase also, as the ring center is approached. 
   One of the variable focus lenses  15  is received in the first sealed space defined by the front sealing cover  13  and the fixed focus lens  12 , with two corresponding electrodes  151  being formed on a surface of the front sealing cover  13  and a surface of the fixed focus lens  12 . Another one of the variable focus lenses  15  is received in the second sealed space defined by the rear sealing cover  14  and the fixed focus lens  12 , with two corresponding electrodes  151  being formed on a surface of the rear sealing cover  14  and a surface of the fixed focus lens  12 . 
   When the voltage supply  17  applies a voltage to the electrodes  151  of one of the variable focus lenses  15 , an electric field may be formed between the electrodes  151  to change the focal length of the corresponding one of the variable focus lenses  15 . The electric field formed between electrodes  151  can be modified according to modifications of the ring spaces and ring widths. 
   It should be understood that the lens module  10  further includes a servo system (not shown in FIGS) for automatically controlling the switch  18 . Thus, a four-position auto focus of the lens module  10  can be achieved with each switch  18  being selectively switched on or off. The focal lengths of the lens modules  10  also can be continuously/selectively modified with continuous/selective change of the voltage applied to the electrodes  151  (i.e., a variance in the applied voltage will result in change in the effective focal length, in addition to a change in on/off status). 
   In a second embodiment, as shown in  FIG. 4 , a lens module  20  includes two fixed focus lenses  12  and three variable focus lenses  15  received in the barrel  11 . Thus, eight-position auto focus of the lens module  10  can be achieved with each switch  18  being selectively switched on or off. 
   In yet a third embodiment, as shown in  FIG. 5 , a lens module  30  includes three fixed focus lenses  12  and four variable focus lenses  15  received in the barrel  11 . Thus, sixteen-position auto focus of the lens module  10  can be achieved with each switch  18  being selectively switched on or off. 
   Referring to  FIG. 6 , a digital camera module  100  includes the lens module  10  and an image module  40 . The image module  40  includes a carrier member  41 , a image-receiving chip  42 , a printed circuit board  43 , and a plurality of connective wires  44 . 
   The carrier member  41  is made of a material such as a plastic, a ceramic, or a fibrous composite. The carrier member  41  has a base plate  410 . The base plate  410  has a plurality of top pads  411  formed on a top surface thereof and a plurality of bottom pads  412  formed on a bottom surface thereof. Each of the top pads  411  is electronically connected to a corresponding one of the bottom pads  412 . The image-receiving chip  42  is mounted on the base plate  410  and electronically connected to top pads  411  via the connective wires  44 . The printed circuit board  43  is disposed under the base plate  410  and electronically connected to bottom pads  412 , thereby allowing the image-receiving chip  42  being electronically linked to the printed circuit board  43 . 
   The lens module  10  is fixed to the carrier member  41  of the image module  40  such that a light signal formed by the lens module  10  can be received by the image-receiving chip  42 . The light signal may be converted into an electrical signal via the image-receiving chip  42 . The electrical signal is then processed by the printed circuit board  43  to obtain an image date. 
   It should be understood that the lens module  10  associated with the image module  40  can also instead be the lens module  20 , the lens module  30 , or other lens structures similar thereto, consistent with the scope of the present lens module. 
   A main advantage is that, due to the limitation of the refractive index change of the electro-optical material  153 , multiple variable focus lenses will achieve the desired range of focus and permit compensation of any potential image aberration. 
   It should be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.