**6. Conclusions**

In this paper the state of the art of fiber Raman amplifier and fiber Raman laser is described. Today, Raman amplifiers are widely commercialized devices. Almost every long-haul (typically defined 300 to 800 km) or ultralong-haul (typically defined above 800 km) fiber-optic transmission system uses Raman amplification. On the other hand, nowadays, commercially available fiber-based Raman lasers can deliver output powers in the range of a few tens of Watts in continuous-wave operation. In addition, due to their tunability, compactness, and capability for multi-wavelength operation, FRLs have great commercial potential in a variety of applications.

**Author Contributions:** L.S. and M.A.F.; writing—original draft preparation, review and editing. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.

## **References**


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