Impact of self phase modulation on the performance of Brillouin distributed fibre sensors

Abstract

The spectral broadening of the pump pulse through self phase modulation in a time domain distributed Brillouin sensor is demonstrated to have a non-negligible detrimental effect, leading to a doubling of the effective gain linewidth after some 20 km in standard conditions. The theoretical modeling is fully confirmed by experimental results.

Optimization of long-range BOTDA sensors with high resolution using first-order bi-directional Raman amplification

“…If meter-scale spatial resolution is required by a specific application, it is possible to extend the sensing distance by using higher pump power levels; however, the onset of nonlinear effects limits the maximum pump power allowed into the sensing fiber. Actually, nonlinearities such as modulation instability (MI) and self-phase modulation (SPM) have been identified to have a detrimental impact on the sensing performance of long-range BOTDA sensors [8,9], due to the spectral broadening induced in the BGS.…”

“…In particular, the input optical power levels of the Brillouin pump, probe signal and Raman pumps need to be carefully optimized to avoid nonlinear effects [8,9] (such as MI and SPM) as well as depletion of the Brillouin pump during propagation along the sensing fiber [10,11]. Moreover, several sources of noise, potentially affecting the probe electrical SNR in DRAs, must be kept under control; among them the most important issues are related to polarization-dependent gain, double Rayleigh scattering, amplified spontaneous emission, and RIN transfer from pumps to signals [14][15][16][17].…”

“…In fact, although distributed Raman amplification can be used for enhancing the performance of distributed fiber sensors based on stimulated or spontaneous Brillouin scattering [3][4][5][6], a great care must be taken in their practical implementation. Actually, three main sources of distortions have been observed or can be expected in Ramanassisted BOTDA sensors, potentially affecting their performance to a great extent: RIN transfer from the Raman pumps to the continuous-wave (CW) Brillouin probe [3,7], fiber nonlinear effects [8,9] and nonlocal effects induced by pump depletion [10,11]. In order to fully exploit the Raman amplification benefit, it is then necessary to minimize such arising penalties by employing suitable techniques and devising effective solutions.…”

“…The optimization has been performed considering the optical signal-to-noise ratio (OSNR) of the probe signal, the minimum power difference between Brillouin pump and probe (to avoid pump depletion [10,11]) and the maximum Brillouin pump power along the sensing fiber (to avoid nonlinear effects [8,9]). We theoretically show and experimentally verify that, when employing Raman pumps in co-propagating direction with respect to the CW-probe, low relative intensity-noise (RIN) lasers are crucial in avoiding strong noise transfer effect and the consequent strong induced penalties.…”

BOTDA sensor with 2-m spatial resolution over 120 km distance using bi-directional distributed Raman amplification

“…In fact, although distributed Raman amplification has already been used also for enhancing the performance of WDM optical communications systems [3] and in distributed fiber sensors based on spontaneous Brillouin scattering [4], we show here that great care must be taken when employing it for BOTDA systems. Three main sources of distortions have been in fact identified in Raman-assisted BOTDA sensors, potentially seriously affecting their performance: RIN transfer from the Raman pumps to the CW Brillouin probe [5], fiber nonlinear effects [6] and nonlocal effects induced by pump depletion [7].…”