RIN transfer in copumped Raman amplifiers using polarization-combined diodes

Pump-to-signal relative-intensity-noise (RIN) transfer in a forward-pumped Raman amplifier using polarization-combined diodes is measured and analyzed. For the first time, by means of experiment and simulations, we call attention to the impact of the polarized nature of stimulated Raman scattering on RIN transfer. We show that measuring the RIN at the output of a depolarized Raman pump and inserting this figure in the commonly used RIN transfer equation is not sufficient for good signal RIN prediction. Although depolarizing the Raman pump enables polarization-independent signal gain, proper modeling of RIN transfer should include the polarization dependence of the Raman effect and the polarization mode dispersion of the fiber.