Abstract

Differential pulse-width-pair BOTDA technique is combined with bi-directional Raman amplification and Simplex coding to achieve sub-meter spatial resolution over very long sensing distances. Numerical simulations are used to optimize the power levels of the Raman pumps, avoiding nonlinear effects and pump depletion. Distortions in the Brillouin gain spectrum due to acoustic-wave pre-excitation are also avoided by numerical optimization of the pulse width and duty cycle of return-to-zero Simplex coding, providing significant SNR enhancement. We demonstrate 50 cm spatial resolution over 93 km of standard SMF with a strain/ temperature accuracy of 34 mu epsilon/1.7 degrees C, respectively.