Laser phase noise compensation in long-range OFDR by using an optical fiber delay loop

We propose and experimentally demonstrate a novel technique to compensate the laser phase noise in long-range OFDR by using an optical fiber delay loop, which mainly consists of a delay fiber and a frequency shifter. The delay fiber is used to shorten the optical path difference between two arms of the interferometer, and the frequency shifter works as a counter for taking the number of lightwave circulated in the loop. The preliminary experiment shows a successful compensation effect, and a 10 cm spatial resolution over 30 km measurement range is realized by using this method.