Cell optimisation for transmission with ultralong laser amplification

Relative intensity noise (RIN) transfer from the pump to the signal is one of the most limiting factors in the deployment of Raman distributed amplification in modern telecommunication systems [1]. Due to the unavailability of low-RIN, high-power semiconductor pumps, fibre lasers are typically used to efficiently pump ultralong cavity Raman fibre lasers (URFL) and random distributed feedback (rDFB) laser amplifiers. Such pump lasers exhibit high RIN transfer that counter balances the benefits of symmetric bidirectional amplification, where signal power variation is ideally distributed over the entire transmission length [2]. In recent work we showed how RIN transfer in 2nd order URFL can be mitigated by lowering the reflectivity of the front-end fibre Bragg grating (FBG) [3]. In this paper we extend the analysis and show the optimal pumping configurations for amplifiers of various lengths, providing a valuable help in Raman-based amplification system design for optimal transmission performance.