Abstract:
This invention relates to a variable focal length lens system including a deformable lens and a piezoelectric device surrounding the deformable lens. The piezoelectric device is configured for exerting a radial inward or outward force to the deformable lens so as to deform the deformable lens, thereby changing a focal length thereof.

Description:
FIELD OF THE INVENTION 
   This invention relates generally to optical lens assemblies, more particularly, to a variable focal length lens system. 
   DESCRIPTION OF RELATED ART 
   Generally, a variable focal length lens system includes a plurality of lenses, and an effective focal length thereof can be adjusted by varying the relative spacing between the lenses along an optical axis. Referring to  FIG. 2 , a conventional variable focal length lens system  100  includes a first lens  102 , and a second lens  104 . The first lens  102  and the second lens  104  are aligned with along a common optical axis. The first lens  102  is received inside a movable barrel  106 , and the second lens  104  is received inside a stationary barrel  108 . The movable barrel  106  is adjustably movable relative to the stationary barrel  108 . The relative spacing between the first lens  102  and the second lens  104  can be adjusted by moving the movable barrel  106  forward and backward along the optical axis, thereby an effective focal length of the variable focal length lens system is adjusted. However, the conventional variable focal length lens system needs more space available for movements of the lenses, which makes the variable focal length lens system awkwardly and bulky. 
   What is needed, therefore, is to provide an improved variable focal length lens system. 
   SUMMARY OF INVENTION 
   A preferred embodiment provides a variable focal length lens system including a deformable lens and a piezoelectric device surrounding the deformable lens. The piezoelectric device is configured for exerting a radial inward or outward force so as to deform the deformable lens, thereby changing a focal length thereof. 
   Compared with the conventional variable focal length lens system, the variable focal length lens system in accordance with a preferred embodiment performs a zoom function by varying the focal length of the deformable lens thereof, which makes the variable focal length lens system be compact. 
   Other advantages and novel features will become more apparent from the following detailed description of embodiments when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     Many aspects of the variable focal length lens system 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 variable focal length lens system. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
       FIG. 1  is a schematic, cross-sectional view of a variable focal length lens system in accordance with a preferred embodiment; and 
       FIG. 2  is a schematic, cross-sectional view of a conventional variable focal length lens system. 
   

   The exemplifications set out herein illustrate at least one preferred embodiment of the variable focal length lens system, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
   DETAILED DESCRIPTION 
   Reference will now be made to the drawing figures to describe the present variable focal length lens system in detail. 
   Referring to  FIG. 1 , a variable focal length lens system  10  in accordance with a preferred embodiment is shown. The variable focal length lens system  10  includes a deformable lens  12 , a number of piezoelectric devices  13 , and a barrel  14 . The barrel  14  has an inner space receiving the lens  12  and the piezoelectric devices  13  therein. Upon being applied with a voltage, the piezoelectric devices  13  can exert a radial inward or outward force onto the deformable lens  12 . The deformable lens  12  is thus deformed. This deformation of the deformable lens  12  results in a change in the focal length thereof. Accordingly, an effective focal length of the variable focal length lens system  10  is adjusted. 
   In the illustrated embodiment, the deformable lens  12  is a composite lens. The composite lens includes a base lens  122  having a first lens surface and an opposite second lens surface, and two plastic lenses  124 ,  126 . The base lens can be a glass lens. The plastic lens  124  is attached on the first lens surface of a base lens  122  by means of a hot embossing process, and surrounded by one piezoelectric device  13 . The other plastic lens  126  is attached on the second lens surface of the base lens, and is surrounded by another piezoelectric device  13 . The plastic lens  124 ,  126  can be made of optically plastic materials, such as polycarbonate (PC), polystyrene (PS), polymethylmethacrylate (PMMA), polydimethylsiloxane (PDMS), etc. 
   The base lens  122  typically includes two opposite protruding portions  1222  projecting from two sides thereof. The barrel  14  defines two grooves  142  corresponding to the protruding portions  1222 . Thus, the base lens  122  is secured in the barrel  14  with the protruding portions  1222  being engaged in the grooves of the barrel. 
   It is understood that, the composite lens may have a base lens  122  and only one plastic lens integrally formed on one surface of the base lens  122 . In addition, the plastic lens can be attached on the base lens  122  using a glue; and the base lens could also be a plastic lens. 
   Each of the piezoelectric devices  13  typically includes a ring-shaped piezoelectric member  133 , and two ring-shaped electrodes  132  attached to opposite sides of the piezoelectric member  133 . The piezoelectric member  133  can be made of lead zirconate titanate (PZT), or any other piezoelectric materials. Each of the ring-shaped electrodes  132  is connected to a voltage source, therefore, voltages can be applied to the piezoelectric layer  133 . The electrodes  132  can be made of an electrically conductive material, such as silver (Ag), gold (Au), etc. The piezoelectric devices  13  can be bonded to the plastic lenses  124 ,  126  with an adhesive, such as thermally cured epoxy. The piezoelectric devices  13  are disposed between an inner wall of the barrel  14  and an outer surface of the plastic lenses  124 ,  126  respectively. 
   It is well known to those skilled in that art that a piezoelectric material is one of electrostrictive materials, and can convert electrical energy into mechanical energy and vice versa. As such, when a voltage is applied to the piezoelectric device  13 , the piezoelectric members  133  of the piezoelectric device  13  will expand or contract along a radial direction thereof. The expansion or contraction of the piezoelectric members  133  results in the radial inward or outward force, which is, in turn, applied to the plastic lenses  124 ,  126 . Thereby, the plastic lenses  124 ,  126  are deformed. The deformation of the plastic lenses  124 ,  126  results in the change in the focal length of the plastic lenses  124 ,  126 . Thus, the effective focal length of the variable focal length lens system  10  is adjusted, accordingly. If the voltage is shut off, the variable focal length lens system  10  will recover the original normal effective focal length thereof. 
   It could be understood by those skilled in the art that, the deformation degree of the plastic lens  124  is proportional to the voltages applied to the piezoelectric device  13 , and the adjusting range of the effective focal length of the variable focal length lens system  10  is proportional to the voltages accordingly. That is, the effective focal length of the variable focal length lens  10  can be adjusted continuously. 
   Alternatively, the deformable lens  12  may be a simple plastic lens, and is surrounded by the piezoelectric device  13 . 
   It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.