Abstract
Modulation instability (MI) is a well-known limit for distributed fiber sensors. However, self-phase modulation (SPM) is rarely addressed as a standalone constraint in distributed acoustic sensing (DAS). This study demonstrates, through modeling and experiments, that SPM-induced spectral broadening causes significant backscattered signal losses and increased phase noise. These effects are particularly critical when using high-power, short Gaussian pulses commonly used to extend the sensing range. We highlight the predominant role of the detection bandwidth in these excess losses, proving that SPM is a limiting factor independent of MI for high-resolution nonlinear
ϕ
-OTDR measurements.