Piston phase error due to bending of delivery fiber

Delivering coherently in phase high power laser beams by fiber optics to transmitter telescopes is desirable to Fourier Telescopy (FT) Imaging technique. One of the requirements to such delivery fibers is to maintain its optical path length while being bent over 150 degrees. We have designed an apparatus and assessed the piston phase error versus both the radius of bending curvature and total bending angle of an optical fiber. The bending apparatus we built can evaluate delivery fiber, and the result of bending a single-mode fiber indicates that bending induced piston phase error can be neglected in the range of fiber optic diameter and radius of bending curvature that we are interested.