Athermalized plastic lens

Abstract

A plastic lens includes refractive and diffractive optical apparatus configured to produce optothermal changes substantially canceling each other over a predetermined working temperature range to render the plastic lens substantially athermalized over the range.

What is claimed is:  
     
         1 . A plastic lens, comprising: 
 refractive and diffractive optical apparatus configured to produce optothermal changes substantially canceling each other over a predetermined working temperature range to render the plastic lens substantially athermalized over the range.    
     
     
         2 . The lens of  claim 1 , comprising 
 a refractive surface and a diffractive optical element, wherein optothermal changes due to the refractive surface counter optothermal changes due to the diffractive optical element.    
     
     
         3 . The lens of  claim 1 , wherein the optothermal changes canceling each other include changes affecting the focal length of the lens.  
     
     
         4 . The lens of  claim 1 , comprising polycarbonate.  
     
     
         5 . The lens of  claim 1 , comprising acrylic.  
     
     
         6 . The lens of  claim 1 , wherein the lens has a net positive power.  
     
     
         7 . The lens of  claim 1 , wherein an optothermal expansion coefficient of the refractive optical apparatus is higher than an optothermal expansion coefficient of the diffractive optical apparatus.  
     
     
         8 . The lens of  claim 1 , comprising a diffractive optical element that is substantially smaller than the lens.  
     
     
         9 . The lens of  claim 1 , wherein a first surface of the lens provides substantially all of the negative power of the lens, and a second surface of the lens provides substantially all of the positive power of the lens.  
     
     
         10 . The lens of  claim 1 , wherein a surface of the lens provides substantially all of the negative power of the lens and substantially all of the positive power of the lens.  
     
     
         11 . The lens of  claim 1 , wherein the diffractive optical apparatus includes a diffractive optical element that is substantially spherical in average.  
     
     
         12 . The lens of  claim 1 , wherein a surface of the lens is substantially flat.  
     
     
         13 . The lens of  claim 1 , wherein the refractive optical apparatus is divided unevenly between first and second surfaces of the lens.  
     
     
         14 . The lens of  claim 1 , wherein substantially all of the diffractive optical apparatus is disposed on one surface of the lens.  
     
     
         15 . The lens of  claim 1 , wherein the diffractive optical apparatus is divided substantially evenly between first and second surfaces of the lens.  
     
     
         16 . The lens of  claim 1 , wherein the lens includes an axicon.  
     
     
         17 . The lens of  claim 16 , wherein the axicon includes a polymer.  
     
     
         18 . The lens of  claim 16 , wherein the axicon is disposed at a substantially spherical surface of the lens.  
     
     
         19 . The lens of  claim 16 , wherein a diffractive optical element and the axicon are disposed at different surfaces of the lens.  
     
     
         20 . The lens of  claim 16 , comprising a diffractive optical element that includes at least eight phase levels.  
     
     
         21 . The lens of  claim 16 , comprising a diffractive optical element that includes fewer than nine phase levels.  
     
     
         22 . The lens of  claim 16 , wherein the axicon is affixed to a surface of the lens.  
     
     
         23 . The lens of  claim 16 , wherein the lens has an aspherical surface having the optical properties of a combination of a spherical surface with the axicon.  
     
     
         24 . The lens of  claim 16 , wherein the lens includes a doublet.  
     
     
         25 . The lens of  claim 16 , wherein the lens includes a Cook triplet anastigmat.  
     
     
         26 . The lens of  claim 16 , wherein the lens includes a symmetric double Gaussian.  
     
     
         27 . The lens of  claim 16 , wherein the MTF of the lens is higher with the axicon than without the axicon for bar code symbols having spatial wavelengths of 10-20 mils, inclusive.  
     
     
         28 . The lens of  claim 16 , wherein the MTF of the lens is at least 0.2 for a 10 mil bar code symbol that is from about 4 to about 16 inches away from the lens.