Narrow band laser speckle suppression

Abstract

A method and apparatus for reducing points of zero intensity, i.e. speckle pattern, emerging from a multimode fiber. The apparatus comprises a beam deflector for rotating an input beam in a conical shape around a launch lens for projecting the beam into the fiber. The rotation of the beam further incorporates the use of two tilting mirrors being 90° out of phase to ensure a conical rotation. The conical rotation of the beam deflector ensures that the lens aberrations, which are rotationally symmetric, do not play a factor in beam alignment into the fiber aperture.

We claim:  
     
       1. A method for suppressing laser pulse at an output of a short multimode optical fiber, comprising the steps of: 
       projecting a laser beam into a multimode fiber by means of a plurality of lenses; and changing a launch angle of the laser beam.  
     
     
       2. The method of  claim 1 , wherein said launch angle change being at least one divergence in time. 
     
     
       3. The method of  claim 2 , wherein said launch angle change being by means of a standard beam deflector device. 
     
     
       4. The method of  claim 2 , wherein said launch angle changing method further includes: 
       incorporating two tilting mirrors for rotation of the beam entering the fiber.  
     
     
       5. The method of  claim 4 , wherein said mirrors being 90° out of phase. 
     
     
       6. The method of  claim 3 , wherein said beam deflector rotates said beam in a conical motion. 
     
     
       7. An apparatus for reducing points of zero intensity emerging from a multimode fiber, comprising: 
       an input laser beam;  
       an input lens;  
       a launch lens;  
       a multimode fiber; and  
       a means for deflecting the input beam.  
     
     
       8. The apparatus of  claim 7 , wherein said deflecting means being an electro-optic beam deflector. 
     
     
       9. The apparatus of  claim 8 , wherein said electro-optic beam deflector rotating said laser beam from about 0 to about 10 GHz. 
     
     
       10. The apparatus of  claim 7 , wherein said deflecting means being an acousto-optic beam deflector. 
     
     
       11. The apparatus of  claim 10 , wherein said acousto-optic beam deflector rotating said beam from about 0 to about 10 MHz. 
     
     
       12. The apparatus of  claim 7 , wherein said deflecting means being a mechanical beam deflector. 
     
     
       13. The apparatus of  claim 12 , wherein said mechanical beam deflector rotating said beam from about 0 to about 10 kHz. 
     
     
       14. The apparatus of  claim 7 , further comprising two tilting mirrors for effecting rotation of beam entering said fiber. 
     
     
       15. The apparatus of  claim 14 , wherein said mirrors being 90° out of phase. 
     
     
       16. The apparatus of  claim 15 , wherein said means for deflecting the input beam effectively rotating said beam in a conical motion.