Abstract
The chapter demonstrates a detailed study of Raman fiber laser (RFL)-based amplification techniques and their applications in long-haul/unrepeatered coherent transmission systems. RFL-based amplification techniques are investigated from signal/noise power distributions, relative intensity noise (RIN), and fiber laser mode structures. RFL-based amplification techniques can be divided into two categories according to the fiber laser generation mechanism: cavity Raman fiber laser with two fiber Bragg gratings (FBGs) and random distributed feedback (DFB) Raman fiber laser using one FBG. In addition, in cavity fiber laser–based amplification, reducing the reflectivity near the input helps mitigate the signal RIN, thanks to the reduced efficiency of the Stokes shift from the secondorder pump. To evaluate the transmission performance, different RFL-based amplifiers were optimized in long-haul coherent transmission systems. Cavity fiber laser–based amplifier introduces >4.15 dB Q factor penalty, because the signal RIN is transferred from the second-order pump. However, random DFB fiber laser–based amplifier prevents the RIN transfer and therefore enables bidirectional second-order pumping, which gives the longest transmission distance up to 7915 km. In addition, using random DFB laserbased amplification achieves the distance of >350 km single mode fiber in unrepeatered DP-QPSK transmission.
Highlights
We focus on the novel Raman fiber laser (RFL)-based amplification techniques enabled by second-order pumping and fiber Bragg gratings (FBGs) at first-order pumping
When the distributed Raman amplification is evaluated in the long-haul transmission system, the optimum signal launch power depends on the best trade-off between the ASE noise and the nonlinearity
The cavity length of this fiber laser was not fixed due to the randomly distributed Rayleigh backscattering from the fiber [22]. These results show that with closed cavity with two FBGs, a random distributed feedback (DFB) fiber laser can be still achieved, which is different from the usual Fabry-Perot fiber laser with bidirectional pumping
Summary
We focus on the novel Raman fiber laser (RFL)-based amplification techniques enabled by second-order pumping and fiber Bragg gratings (FBGs) at first-order pumping. Random fiber laser– based amplification mitigates the signal relative intensity noise (RIN), reveals the benefit of the lower noise figure brought by FW-pumping, and effectively extends the maximum reach of the long-haul transmission system [5] Such random fiber laser–based amplification technique can be applied in unrepeatered transmission systems and achieve a record transmission distance of over 350 km standard single mode fiber (SSMF) using 22 × 100 Gbits DP-QPSK WDM transmitter [17]. RFL-based amplification techniques are characterized from different perspectives, including signal/noise power distributions, relative intensity noise (RIN), and the mode structures of fiber laser These results help give a better understanding of RFL-based amplification and support the long-haul and unrepeatered coherent transmission performances demonstrated in this chapter.
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