Forward Raman scattering spectral properties

Forward and backward Raman scattering in fibers hold significant application value in numerous fields, including optical communications, optical sensing, chemical detection, and bio-medicine. In distributed optical sensing, although temperature-sensitive backward Raman scattering technology is relatively mature, research on forward Raman scattering remains comparatively limited. This study focused on the spectra of spontaneous forward Raman scattering in optical sensing. We theoretically analyzed the transmission process of spontaneous forward Raman scattering light in optical fibers and derived analytical expressions for it in the time domain. Subsequently, through numerical simulations and experimental validation, we elucidated the spectral power distribution characteristics of both forward and backward Raman scattering. The results demonstrated that the disparity in the effective sensing fiber length—where the spontaneous forward Raman scattering light integrated signals over the entire fiber, while the spontaneous backward Raman scattering light was the superposition within the much shorter spatial scale corresponding to a single optical pulse width—directly resulted in the forward scattering light being more easily collected than backward scattering light. This research sheds light on the spectral properties of forward and backward Raman scattering, providing a theoretical foundation for the advancement of optical sensing technologies.