Spectral gain control using shaped pump pulses in a counter-pumped cascaded fiber Raman amplifier

We investigate the Raman gain spectra produced from pulse-pumping a highly nonlinear fiber with shaped optical pulses delivered from a Yb-doped fiber MOPA pump source. Cascaded Raman wavelength shifting up to seven Stokes orders is demonstrated and the counter-propagating gain is measured across all seven Stokes orders. Step-shaped optical pulses with varying instantaneous powers are then used to pump the highly nonlinear fiber, generating a controllable gain spectrum across multiple Stokes orders. Furthermore, we extend this work by using multiple pump wavelengths along with step-shaped pulses to increase the bandwidth of the Raman gain spectrum.