A novel high-power all-fiberized flexible spectral filter for high power linearly-polarized Raman fiber laser

Power scaling of linearly polarized Raman fiber laser (LPRFL), which has wide application potentials, is mainly limited by the generation of high-order Stokes light. In this paper, we propose a novel flexible spectral filter with all-fiberized configuration and high-power handling. Combining with the polarization-dependence of Raman gain, the filter could be used to efficiently suppress high-order Stokes light in LPRFL and thus help further power scaling. The filter is fabricated by two 45° cross-splice of three pieces of polarization maintaining (PM) passive fibers. The bandwidth and central wavelength of transmission spectrum of the spectral filter could be flexibly tuned through changing the length and temperature of the cross-spliced fiber. The insertion loss of the filter fabricated in the lab is measured to be as low as 0.07 dB. The filter is employed in a LPRFL, and the maximum output power of the LPRFL is increased by 48.7%.