Study on the generation and influence factors of the new wavelength components in backscattering light of Φ-OTDR

This paper investigates the new wavelength components in backscattering light of phase-sensitive optical time-domain reflectometry (ϕ-OTDR) fiber-optic vibration sensor based on quantitative spectrometric analysis. Experiments show that the new wavelength components are introduced into the optical spectrum as the optical pulse power increases. To explain this nonlinear phenomenon, different optical spectrum curves are obtained by changing the length of sensing fiber, pulse interval, and pulse width at different powers of Erbium-doped fiber amplifier (EDFA). Theoretical analysis and experimental results show that the nonlinear effect results from the four-wave mixing (FWM) effect. A comprehensive analysis of the influence factors is then proceeded, which guides us to avoid the nonlinear effect in advance and select appropriate parameters and optical devices for ϕ-OTDR system. This study suggests that the method of optical spectral analysis can also be applied to other fiber-optic sensors based on backscattering such as Brillouin scattering or Raman scattering.