Pump RIN to Carrier Phase Noise Transfer in Distributed Fiber Raman System Evaluated through Carrier FM Noise Spectrum

Relative intensity noise (RIN) of pump lasers can be transferred to both RIN and phase noise of the optical signal in fiber systems with distributed Raman amplification (DRA). In coherent optical systems based on complex optical field modulation, transmission quality is most susceptible to the increase of carrier phase introduced by the pump RIN. In this paper we show that carrier FM-noise spectrum can be used to evaluate the impact of pump RIN to signal phase noise transfer. The FM-noise power spectral density (PSD) depends on the spectral shape of pump RIN, as well as the frequency dependency of pump RIN to signal phase noise transfer function. Carrier FM-noise PSD in DRA systems with FBG-stabilized pump laser and FP pump laser are compared. We also show that signal FM-noise can be increased by electrostriction nonlinearity in the fiber with the magnitude comparable to the pump RIN transfer.