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21 February 2011 Experimental study of phase locking of fiber collimators using internal beam-tail interference
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Experimental study of internal phase locking of a seven fiber collimator array is presented. As a metric for the feedback loop the periphery areas (tails) of beams outgoing from three adjacent fiber tips are used before the beams are clipped by the lens apertures. The "intercepted" tails of beams are redirected back into the collimator array forming an interference pattern located between adjacent collimators. Optical energy from one region of the pattern is selected by a pinhole, detected with a photo-diode and used as a metric signal for an SPGD controller to lock the phase of the three adjacent beam tails. The non-common phase difference of the outgoing wavefronts from these three collimators can be manipulated by altering the position of the pinhole in focal plane of the interference pattern and is removed (set to "zero" or 2π increments) by a displacement selected to produce the expected far field interference pattern. To phase lock the beams from seven collimators arranged in a hexagonal array, three pinholes, each of which receives some light from the center collimator are used. A sum of the signals from the three photo-diodes placed behind these pinholes is used to lock the phase of the six periphery beams to the central uncontrolled reference without beam splitters or a remote target-in-theloop metric.
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Leonid A. Beresnev, Mikhail A. Vorontsov, Thomas Weyrauch, Gary Carhart, Svetlana L. Lachinova, and Jiang Liu "Experimental study of phase locking of fiber collimators using internal beam-tail interference", Proc. SPIE 7914, Fiber Lasers VIII: Technology, Systems, and Applications, 79142Z (21 February 2011);

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