175-km Repeaterless BOTDA With Hybrid High-Order Random Fiber Laser Amplification

High-order random fiber laser amplification (RFLA) is an effective way for realization of ultralong optical transmission and sensing. However, potential issues such as modulation instability (MI) and relative intensity noise transfer would largely decrease the system performance unless the amplifying schemes and pump power are cautiously designed. In this paper, through simulations and optimizations, a 175 km repeaterless Brillouin optical time-domain analysis (BOTDA) with uncertainty of ±2.06 MHz and spatial resolution of 8 m is demonstrated based on the hybrid of forward 2nd-order RFLA and backward 3rd-order RFLA. The figure of merit (FoM) of the system is >200,000. As far as we know, this is the longest distance and highest FoM for repeaterless BOTDA reported so far.