High-Power Random Raman Fiber Laser With an Ultrashort Random Fiber Grating

We propose and demonstrate the power scalability in a novel random Raman fiber laser (RRFL) with localized random feedback provided by an ultrashort low-reflection random fiber grating (RFG). The RFG is composed of a randomly distributed sub-grating array, and is directly written by a femtosecond laser with point-by-point inscription approach. The fabricated RFG has a total length of only 1.86 mm and thus has relatively broad reflection peaks. A narrow-band high-reflection fiber Bragg grating at the end of the Fabry-Perot cavity can easily implement spectral filtering to ensure that the RRFL only lases at the wavelength of the highest reflection peak of the RFG due to the large wavelength separation between adjacent reflection peaks in RFG. The RRFL has a low threshold of 2.16W and a high slope efficiency of 91.56%, and the optical signal-to-noise ratio is 55 dB. Moreover, the spectral broadening of this RRFL is proved to be turbulence-induced square-root broadening.