The Second-Order Raman Stokes Stronger Than the First-Order Raman Stokes Due to Inverse Raman Scattering in a Single Mode Tellurite Fiber

The evolution Raman effect in a single-mode tellurite fiber (SMTF) was investigated by pumping a nanosecond laser operated at ~1545 nm. With the increase of the average pump power, inverse Raman scattering (IRS) effect was first observed in a 2.5-m-long SMTF, which induced a steadily growing second-order Raman Stokes that finally exceeded the first-order Raman Stokes. When the length of the SMTF was reduced to 0.5 m, no IRS effect was obtained due to the lower Raman gain.