Continuum band jointly generated by SFPM and SRS in a multimode fiber

Abstract

Stimulated four photon mixing (SFPM) and stimulated Raman scattering (SRS) are two third-order nonlinear effects with different mechanisms, occurring in intense light transmission process in fibers. Their common feature is that they are able to convert coherent pump light at a certain frequency into new coherent light at different frequencies. Since threshold power for SFPM and SRS in fibers is much lower than in bulk material, it is recognized that SFPM and SRS in fibers are effective approaches to the frequency tuning of laser radiation. Incomparison with SRS, the advantage of SFPM is that it is able to achieve frequency up- conversion as well as down-conversion, but the problem is that SFPM process requires a harsher phase matching condition. Therefore, it is rather difficult to generate a Stokes-anti -Stokes (S-AS) pair experimentally, and even more difficult to generate multiple pairs. So far as we know, only one or two, at most three S-AS line-pairs were reported to be observed simultaneously[ 1] . Recently, through many experiments, we have simultaneously recorded six S-AS line-pairs of SFPM for the first time. It is specially worth notice that the six Stokes lines of SFPM act as new "pump radiation" and initiate the multi-order Stokes lines of SRS. All these lines, overlapping the cascade Stokes lines of SRS directly generated by the initial pump radiation, form a continuum band in the spectral range of 540-640nm.