Low-noise high-order Raman fiber laser pumped by random lasing.

Raman fiber lasers (RFLs) have been widely utilized in long-haul optical transmission systems as pump sources for distributed Raman amplification (DRA) to increase transmission distance and capacity. However, RFLs with relatively large temporal intensity fluctuations would deteriorate signal quality due to the transfer of relative intensity noise (RIN). In this Letter, a low-noise high-order RFL common cavity pumped by an ytterbium-doped random fiber laser (YRFL) is proposed and demonstrated for the first time, to the best of our knowledge. Stable 4th-order random Raman lasing operating at 1365 nm is generated with 8.9 W of output power, without use of a multi-stage master oscillation power amplification system. Thanks to the YRFL common-cavity pumping where a wavelength division multiplexer (WDM)-assisted fiber-loop mirror is used to generate stable 1090 nm ytterbium-doped random lasing and cascaded random Raman lasing simultaneously, the RIN of the 1365 nm RFL is suppressed as low as 120 dB/Hz without any peak over a 0-100 MHz span. Furthermore, the output power and lasing wavelength of this RFL can be flexibly tuned by adjusting the laser diode pump power, high-reflectivity fiber Bragg grating center wavelength, and single-mode fiber length. Hence, such a low-noise high-order RFL paves a way for the development of novel tunable RFLs with stable temporal output, leading to potential replacement of conventional RFLs for DRA in long-haul optical transmission systems to achieve better performances. (C) 2020 Optical Society of America