Polarization Dependent Gain Stability of Raman Amplification Single-Core Feedback Structure Based on Consistency of Long-Axis Azimuths Variation

The law of the polarization state of Raman fiber amplifier switch in single-core feedback structures is unknown. In this paper, two kinds of optical paths with single-core feedback structures are constructed, namely the Raman amplified Faraday rotating mirror single-core feedback structure (RFA-FRMOP) and the Raman amplified ordinary flat mirror single-core feedback structure (RFA-RMOP). In the process of optical signal amplification involving Raman fiber amplifiers, the polarization dependent gain (PDG) generated by Raman switches is affected by the polarization state, and RFA-FRMOP shows better stability. Surprisingly, polarization analysis of the RFA-FRMOP structure shows that both the ellipticity angle and the long-axis azimuth of the output feedback structure changed less than that of the signal entering the feedback structure. The consistency of the long-axis azimuth variation is the main characteristic of the RFA-FRMOP structure. It is found that the variation of the azimuth of the long axis of the RFA-FRMOP structure is obviously greater than that of the ellipticity. These conclusions provide a theoretical basis for the polarization dependent application of Raman fiber amplifiers in single-core feedback structures.