Apparatus, system, and method for active compensation of aberrations in an optical system

Abstract

Active compensation of aberrations in an optical system involves attaching first and second force bars to a mirror. The first force bar is bifurcated to form an opening near its longitudinal midpoint. This opening defines first and second opposed surfaces. A second force bar is substantially perpendicular to the first force bar and extends through the opening of the first force bar so that a medial portion of the second force bar is disposed in the opening of the first force bar. The second force bar is connected to the first surface by at least one actuator. Longitudinal movement of the actuator causes a displacement of the mirror. A support structure is used to support the weight of the force bars and actuator. The force bars are connected to the support structure by a plurality of flexures. A control module receives information from a sensing module and controls the actuator. Other embodiments use more than two force bars and are capable of more fully compensating for any aberrations in the optical system.

What is claimed is:  
     
         1 . An apparatus for active compensation of aberrations in an optical system, comprising: 
 a first force bar having at least two ends configured for attachment to a first and second portion of a mirror;    a second force bar having at least two ends configured for attachment to a third and forth portion of said mirror; and    at least one actuator, each of said actuators having a first end connected to said first force bar and a second end connected to said second force bar, such that longitudinal movement of said actuator between said first and second force bars applies a force to said mirror.    
     
     
         2 . The apparatus of  claim 1 , wherein said first and second force bars each have two ends and wherein said first force bar is substantially perpendicular to said second force bar.  
     
     
         3 . The apparatus of  claim 1 , wherein said first and second force bars each have three ends.  
     
     
         4 . The apparatus of  claim 2 , wherein said first force bar has an opening near its longitudinal midpoint, and wherein said second force bar partially resides in said opening.  
     
     
         5 . The apparatus of  claim 4 , wherein said first force bar is bifurcated to form said opening, and wherein said opening defines first and second opposed surfaces, said second force bar having a medial portion disposed within said opening and being connected to said first surface by at least one said actuator.  
     
     
         6 . The apparatus of  claim 5 , wherein said actuators are pneumatic bellows.  
     
     
         7 . The apparatus of  claim 6 , further comprising: 
 a support structure for supporting the weight of said first and second force bars; and    a plurality of flexures for connecting said first and second force bars to said support structure, each of said flexures having a first end connected to said support structure and a second end connected to an end of said first or said second force bar.    
     
     
         8 . The apparatus of  claim 7 , further comprising: 
 a third force bar having ends configured for attachment to a peripheral portion of a mirror;    a fourth force bar having ends configured for attachment to said peripheral portion of said mirror; and    at least one additional actuator, each of said additional actuators having a first end connected to said third force bar and a second end connected to said fourth force bar, such that longitudinal movement of said actuator between said third and fourth force bars applies a force to said peripheral portion of said mirror.    
     
     
         9 . The apparatus of  claim 8 , wherein said first and second force bars are aligned to compensate for Z 5  astigmatism, and wherein said third and fourth force bars are aligned to compensate for Z 6  astigmatism.  
     
     
         10 . The apparatus of  claim 9 , wherein each of said force bars are leaf springs.  
     
     
         11 . A system for active compensation of aberrations in an optical system, comprising: 
 a mirror having a concave first surface and a second surface;    a compensation module attached to said second surface of said mirror;    a sensing module; and    a control module in communication with said sensing module to control said compensation module to bend said mirror and compensate for an aberration in the optical system based on information received from said sensing module.    
     
     
         12 . The system of  claim 1 , further comprising: 
 a support structure for supporting the weight of said compensation module; and    a plurality of flexures for connecting said compensation module to said support structure, each of said flexures having a first end connected to said support structure and a second end connected to said compensation module.    
     
     
         13 . The system of  claim 12 , wherein said compensation module comprises pneumatic actuators.  
     
     
         14 . The system of  claim 13 , further comprising: 
 an air supply module in fluid communication with compensation module.    
     
     
         15 . The system of  claim 14 , wherein said pneumatic actuators are pneumatic bellows.  
     
     
         16 . The system of  claim 11 , wherein said compensation module corrects for both Z 5  and Z 6  astigmatism.  
     
     
         17 . The system of  claim 11 , wherein said sensing module measures temperature and pressure.  
     
     
         18 . The system of  claim 11 , wherein said sensing module measures electromagnetic energy exiting the optical system.  
     
     
         19 . The system of  claim 11 , wherein said control module comprises a central processing unit and a memory unit.  
     
     
         20 . A system for active compensation of aberrations in an optical system, comprising: 
 an mirror having a concave first surface and a second surface;    compensation means, attached to said second surface of said mirror, for bending said mirror;    sensor means for measuring a parameter related to an aberration in the optical system; and    a control means in communication with said sensor means for receiving data from said sensor means and for controlling said compensation means to compensate for the aberration in the optical system based on the data received from said sensor means.    
     
     
         21 . The system of  claim 20 , further comprising: 
 support means for supporting the weight of said compensation module.    
     
     
         22 . The system of  claim 21 , further comprising: 
 air supply means for supplying air to said compensation means.    
     
     
         23 . A method for active compensation of aberrations in an optical system, comprising the steps of: 
 (1) predicting the presence of an aberration in the optical system;    (2) generating a corrective signal related to the predicted aberration; and    (3) adjusting at least one actuator that controls a force applied to a mirror to compensate for the predicted aberration.    
     
     
         24 . The method of  claim 23 , further comprising the steps of: 
 (4) repeating steps (1) through (3) for additional correction of the predicted aberration.    
     
     
         25 . The method of  claim 24 , wherein step (1) comprises looking up a value in a lookup table stored in a memory unit.  
     
     
         26 . The method of  claim 24 , wherein step (1) comprises using an output of a sensing module and an algorithm to predict the presence of an aberration.