Ultra-long dual-sideband BOTDA with balanced detection

• A 200 km fiber-loop BOTDA with 100 km sensing range utilizing balanced detection is presented.
• A simple amplification regime (only bi-directional first-order Raman amplification) is used.
• We use one traditional FBG to separate two signal sidebands (only ~0.16 nm apart)
• We discuss the effect of the critical filter alignment on the sensing performance.

We experimentally study a dual-sideband Brillouin optical time-domain analyzer (BOTDA) with balanced detection. The amplification regime is simple (only bi-directional first-order Raman amplification); however, taking advantage of the balanced detection, 200 km fiber-loop sensing system is achieved (half of the whole length is used for sensing). Before the balanced detector, a FBG is used to separate the anti-Stokes and the Stokes components of the probe light, and the optical source׳s wavelength with regard to the given FBG׳s Bragg wavelength is shown to be highly relevant to the system׳s performance.