Beat Noise Reduction by Fast Optical Switching in Brillouin Grating-Based FMCW Reflectometry

We demonstrated an optical switching method for deriving a Brillouin reflectogram from a 1-m-long optical fiber without the use of a polarization diversity technique or a least-squares procedure in coherent frequency-modulated continuous wave reflectometry. We reduced the intrinsic beat noise by blocking one pump light from entering the balanced mixer for 120 μs with an acousto-optic modulator while sweeping the laser wavelength at a rate of 0.5 nm/s. The variations in the derived reflectograms at the center of the Brillouin spectrum were within ±14 %, and these were governed mainly by the multiplicative noise.