Strong Cancellation of RIN Transfer in a Raman-Assisted BOTDA Using Balanced Detection

Raman assistance is one of the most interesting routes toward extending the range of Brillouin optical time-domain analysis (BOTDA) systems. Unfortunately, the use of Raman amplification normally entails an important relative intensity noise (RIN) transfer toward the probe wave, which severely limits this approach. In this letter, we show that the RIN transfer problem can be effectively avoided using a slightly modified scheme comprising a dual-sideband modulated probe and balanced detection. Our measurements clearly indicate a nearly complete cancellation of the RIN noise in the detected trace signal. The use of balanced detection in our Raman-assisted BOTDA setup implies a fivefold increase in figure of merit compared with the same setup using conventional detection.