Optical mask for all-optical extended depth-of-field for imaging systems under incoherent illumination

Abstract

A mask for enhancing the depth of focus of an optical imaging system is designed by optimizing an optical property (transmittance or reflectance) of the mask relative to the intensity distribution in the system's image plane. Preferably, a desired PSF intensity is selected, a desired misfocus parameter range is selected, and the optical property is adjusted to minimize a measure of the departure of the system's PSF intensity, as computed from the mask's optical property, from the desired PSF intensity, over the entire misfocus parameter range. Most preferably, the desired PSF intensity is selected as the inverse Fourier transform of a desired OTF. Preferably, the mask is fabricated as a DOE.

1 . A method of making a mask for an optical imaging system, comprising the steps of: 
 (a) optimizing an optical property of the mask relative to an intensity distribution incident on an image plane of the optical imaging system; and    (b) fabricating the mask in accordance with said optical property.    
   
   
       2 . The method of  claim 1 , wherein the mask overcomes misfocus degradation in the optical imaging system.  
   
   
       3 . The method of  claim 1 , wherein said optical property is a transmittance of the mask.  
   
   
       4 . The method of  claim 1 , wherein said optical property is a reflectance of the mask.  
   
   
       5 . The method of  claim 1 , wherein said optimizing is effected by steps including: 
 (i) selecting a desired point spread function intensity;    (ii) selecting a desired misfocus parameter range; and    (iii) adjusting said optical property to minimize a measure of a departure of a system point spread function intensity from said desired point spread function intensity over substantially all of said misfocus parameter range, said system point spread function intensity being computed from said optical property.    
   
   
       6 . The method of  claim 5 , wherein said measure is a minimum mean square error measure.  
   
   
       7 . The method of  claim 5 , wherein said desired point spread function intensity is selected by steps including selecting a desired optical transfer function, said desired point spread function intensity then being an inverse Fourier transform of said desired optical transfer function.  
   
   
       8 . The method of  claim 7 , wherein said desired optical transfer function lacks phase differences between spatial frequency components thereof in a pre-selected band of spatial frequencies.  
   
   
       9 . The method of  claim 1 , wherein said optimizing is effected by steps including simulated annealing.  
   
   
       10 . A mask made according to the method of  claim 1 .  
   
   
       11 . The mask of  claim 10 , wherein the mask is one-dimensional  
   
   
       12 . The mask of  claim 1   1 , wherein a phase of said mask is antisymmetric.  
   
   
       13 . The mask of  claim 10 , wherein the mask is two-dimensional.  
   
   
       14 . The mask of  claim 13 , wherein the mask is a separable mask.  
   
   
       15 . The mask of  claim 13 , wherein the mask is a radial mask.  
   
   
       16 . The mask of  claim 10 , wherein the mask is real.  
   
   
       17 . The mask of  claim 10 , wherein the mask is a phase-only mask.  
   
   
       18 . The mask of  claim 10 , wherein the mask is fabricated as a diffractive optic element.  
   
   
       19 . The mask of  claim 18 , wherein said diffractive optical element is fabricated by a method selected from the group consisting of etching, injection molding, deposition and overlay casting.  
   
   
       20 . An optical element comprising the mask of  claim 10 .  
   
   
       21 . The optical element of  claim 20 , selected from the group consisting of lenses, filters, windows and prisms.  
   
   
       22 . An optical imaging system comprising the mask of  claim 10 .  
   
   
       23 . The optical imaging system of  claim 22 , selected from the group consisting of general-purpose lenses, computer vision systems, automatic vision systems, barcode readers, cameras and surveillance security imaging systems.  
   
   
       24 . The optical imaging system of  claim 23 , wherein said cameras are selected from the group consisting of mobile phone cameras and PC-mounted cameras.