Random distributed feedback Raman fiber lasers

In this chapter we briefly review the basic principles of Raman fiber lasers operating via random distributed feedback, including details of feedback mechanism, various cavity designs, and corresponding power and spectral characteristics, as well as their statistical properties. We also compare performances of the random Raman fiber lasers (RRFLs) with that for conventional Raman fiber lasers (RFLs) with linear cavity based on two reflectors. The performance analysis includes polarization management, optimization of conversion efficiency, cascaded generation of higher Stokes orders, opportunities for short-wavelength generation via direct pumping by high-power laser diodes, or frequency doubling of random Raman fiber laser radiation. Pulsed operation of random Raman fiber lasers via active or passive Q-switching is also analyzed. The analysis shows that the output characteristics of Raman fiber lasers with random distributed feedback reached to the moment already outperform in many aspects those for conventional Raman fiber lasers. The unique performance of random fiber lasers opens the door to their application in advanced technologies, such as long-distance amplifier-free transmission and remote sensing, low-coherence IR, and visible sources for bio-imaging and others.