We propose a novel method to increase sensing points of Brillouin optical correlation domain analysis (BOCDA) by utilizing degenerated four-wave-mixing (FWM) process. A sinusoidally frequency-modulated lightwave is used as the pump of FWM, and the generated idlers have a broadened frequency modulation span. The idlers produced by FWM are used in BOCDA system to increase the sensing points of BOCDA since the number is proportional to the frequency modulation span of the laser source. We experimentally demonstrate a modulation span of 74 GHz by using the firstorder idler produced by FWM process, which is the largest frequency modulation span achieved in BOCDA system, doubling the sensing points of BOCDA from 1936 to 3872. It provides a possibility to use this method in the state-of-art BOCDA system to achieve several millions of effective sensing points.
We demonstrate a novel method to compensate the optical source phase noise in long-range OFDR by using an optical fiber delay loop (OFDL). In this method, a 10 km OFDL is incorporated in the reference interferometer of the reflectometry. A frequency shifter is used to count the circulation rounds of the light traveling in OFDL. The preliminary “proof-of-concept” experiment shows a successful compensation effect and an 11 cm spatial resolution over 20 km measurement range is realized by this method.