Analytical Study of RIN Transfer in Pulse-Pumped Raman Amplifiers

Abstract

Relative intensity noise (RIN) is one of the most significant artifacts that ultimately limits the use of broadband Raman amplifier applications in optical communications systems. Recently, as a way to alleviate some of the detrimental features of continuously pumped Raman amplifiers, pulsed pumping was introduced. In this paper, we study the RIN transfer in pulse-pumped fiber Raman amplifiers. An analytical expression describing RIN transfer from a pump with an arbitrary pulse shape has been derived for co- and counter-pumping configurations. The dependence of RIN transfer on pump modulation frequency, depth of modulation, and duty cycle in a typical 80-km fiber span has been analyzed for pumps with sinusoidal and rectangular profiles. We show that in the case of rectangular pulsing of pump, RIN transfer in counter-pumping regime is substantially enhanced compared with that of continuous wave (CW) pumping due to the presence of resonant peaks at the pump intensity harmonics. In the co-propagation regime, RIN transfer for pulsed pumping does not exhibit resonant peaks and is generally lower than that for CW pumping. These features are reflected on the Q-penalty and may have detrimental effects on the system performance.

© 2009 IEEE