Relative intensity noise transfer reduction in raman-assisted BOTDA systems

Abstract

Raman-assistance (RA) has been identified as a promising technique to extend the measurement range of Brillouin optical time-domain analysis (BOTDA)-based distributed sensors. Unfortunately, Raman amplification introduces a great amount of relative intensity noise (RIN) to the detected low-frequency probe wave. This RIN transfer problem has been widely identified as a major limitation in RA-BOTDA. In vector BOTDA (VBOTDA), the detected signal is transferred to a high-frequency carrier where the Raman RIN transfer turns out to be much less harmful. In addition, a VBOTDA can also provide information about the phase-shift induced by the local stimulated Brillouin scattering gain curve, paving the way for dynamic measurements. In this letter, we demonstrate, for the first time to our knowledge, the RA in a VBOTDA obtaining gain and phase measurements. Our results show a significant reduction of the RIN transfer effect in RA-VBOTDA compared with standard RA-BOTDA, making this type of scheme particularly interesting for long-range and dynamic distributed sensing.