Averaging-free vector Brillouin optical time domain analyzer assisted by reference probe lightwave

We propose and experimentally demonstrate a vector Brillouin optical time domain analyzer (BOTDA) system, which enables both distributed Brillouin gain spectrum (BGS) and Brillouin phase-shift spectrum (BPS) measurements without trace averaging. The proposed scheme generates and launches a reference light into the fiber under test (FUT), together with the Stokes probe light to indicate the phase noise and distortion in the probe. The commercial integrated coherent receiver at the detection end, using a local oscillator (LO) generated with single sideband (SSB) modulation, on the one hand, improves the signal-to-noise ratio (SNR) to avoid the need of trace averaging for the signal acquisition. On the other hand, by processing and analyzing the receiver outputs at specific intermediate frequencies (IF), the amplitude and phase signals carried by the Stokes probe and the reference light can be resolved at once. In this way, both Brillouin gain and Brillouin phase-shift signals can be obtained simultaneously. By scanning the the Stokes probe light frequency and recording the Brillouin response at each scanning frequency, both distributions of Brillouin gain spectrum and phase-shift spectrum have been acquired. The configuration is approved by experiments carried out over an 18.2 km FUT with the spatial resolution of 2 m.