Measurement of a true Brillouin grating distribution generated at mated fiber connectors with optical low coherence reflectometry coupled with dispersive Fourier spectroscopy

We previously reported a reflectogram from mated fiber connectors that was measured at a spatial resolution of 100 μm with Brillouin-gating-based optical low coherence reflectometry, and that agreed with a theoretical curve calculated by assuming that there was a step-like Brillouin grating distribution [Electron. Lett.53, 423 (2017)]. The agreement meant that the reflectogram was determined by the coherence function of the low coherence light and did not mean that we could observe the Brillouin grating distribution generated around the fiber connector joint. In this paper, we focused on increasing the spatial resolution to reveal the actual distribution by broadening the low coherence light, removing the erbium-doped fiber amplifier from the probe port of the interferometer to reduce the dispersion and phase fluctuations, and introducing dispersive Fourier spectroscopy to numerically and completely eliminate the residual dispersion. Although the signal-to-noise ratio (S/N) of a reflectogram obtained by a single translation of the stage was only 4, we succeeded in increasing the S/N 15-fold by averaging 200 samples acquired with repetitive measurements while maintaining a spatial resolution of 30 μm. We were able to clearly observe 320 and 430 μm wide transitions in a Brillouin grating distribution generated around the joint.