Methods to maintain and control the polarization state from 3c optical fiber

Abstract

Fiber laser amplification systems and methods are disclosed for use with a chirally coupled core (3C) optical fiber enabling the generation of a high-power output beam having a controlled stable polarization state. Vector modulation instabilities which typically induce undesirable sidebands in 3C fiber optics are greatly reduced even at high peak powers, enabling operation of the up to power levels limited mainly by stimulated Raman scattering (SRS). Polarization extinction ratios (PER) demonstrate long-term stability and minimal degradation due to changes in system temperature. Delays in reaching stable operation during start-up are also greatly reduced.

I claim: 
     
         1 . An apparatus, comprising:
 an optical fiber wound a number of turns in a single direction about a coiling axis between an input end and an output end of the optical fiber to form an optical fiber coil such that a number of twists in the optical fiber with the input end and output end extended to form a straight fiber configuration is smaller than the number of turns.   
     
     
         2 . The apparatus of  claim 1 , wherein the input end is situated to receive a beam with an input circular polarization state and the wound optical fiber is configured to amplify the beam to produce an amplified output beam with an output circular polarization state and to reduce a polarization state variability of the output circular polarization state based on the smaller number of twists and the input circular polarization state. 
     
     
         3 . The apparatus of  claim 1 , wherein the optical fiber includes an actively doped core configured to amplify an input beam propagating from the input to the output end. 
     
     
         4 . The apparatus of  claim 3 , further comprising a seed source optically coupled to the input end of the optical fiber and configured to generate a seed beam that becomes the amplified output beam. 
     
     
         5 . The apparatus of  claim 4 , further comprising a pump source optically coupled to the input end and/or the output end of the optical fiber and configured to optically pump the actively doped core of the optical fiber. 
     
     
         6 . The apparatus of  claim 5 , further comprising an input polarization converter including a half-wave plate situated to receive the seed beam and to adjust an angle of a linear polarization state of the seed beam and including a quarter-wave plate situated to receive the seed beam with the angled-adjusted linear polarization state and to change the linear adjusted polarization state to the input circular polarization state. 
     
     
         7 . The apparatus of  claim 6 , further comprising a polarization maintaining fiber situated to receive the seed beam from the seed source and to direct the seed beam to the input polarization converter. 
     
     
         8 . The apparatus of  claim 7 , wherein the input polarization converter is fiber spliced at an input end to the polarization maintaining fiber and at an output end to the input end of the optical fiber. 
     
     
         9 . The apparatus of  claim 6 , further comprising an output polarization converter including a quarter-wave plate situated receive the amplified output beam and to change the output circular polarization state of the amplified output beam to a linear polarization state and including a half-wave plate situated to receive the amplified output beam with the linear polarization state and to adjust an angle of the linear polarization state of the amplified output beam. 
     
     
         10 . The apparatus of  claim 1 , further comprising an optical fiber rotator coupled to at least one of the input end or the output end of the optical fiber and configured to rotate the corresponding input end or output end to selectively vary the number of twists. 
     
     
         11 . The apparatus of  claim 1 , wherein the optical fiber coil is a right-handed coil. 
     
     
         12 . The apparatus of  claim 1 , wherein the optical fiber coil is a left-handed coil. 
     
     
         13 . The apparatus of  claim 1 , wherein the optical fiber includes a reference marking on an exterior surface of the optical fiber between the input end and the output end to provide an indication of a twisting of the optical fiber. 
     
     
         14 . The apparatus of  claim 1 , wherein the number of turns is one or greater, and the number of twists is zero. 
     
     
         15 . The apparatus of  claim 1 , wherein a number of quasi-twists of the optical fiber in the 3C fiber coil is uniformly provided between the input end and output end. 
     
     
         16 . The apparatus of  claim 1 , wherein the polarization state variability corresponds to a time-dependent variation in polarization extinction ratio during an optical pulse and/or over multiple optical pulses. 
     
     
         17 . The apparatus of  claim 1 , further comprising a subsequent gain stage coupled to the amplified output beam and configured to amplify the amplified output beam and/or a non-linear optical element situated to receive the amplified output beam and to produce a non-linearly converted optical beam. 
     
     
         18 . The apparatus of  claim 1 , wherein the optical fiber is a 3C fiber. 
     
     
         19 . A method, comprising:
 winding an optical fiber a number of turns in a single direction about a coiling axis between an input end and an output end of the optical fiber to form an optical fiber coil such that a number of twists in the optical fiber with the input end and output end extended to form a straight fiber configuration is smaller than the number of turns.   
     
     
         20 . The method of  claim 19 , further comprising:
 optically coupling a seed source to the optical fiber so that the optical fiber is situated to receive an input beam having a circular polarization state and so that the optical fiber is configured to produce an amplified output beam with an output circular polarization state and having a reduced polarization state variability based on the smaller number of twists and the input circular polarization state.