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Problem Addressed

It has been demonstrated that at high powers, substantial levels of Raman gain can be achieved with use of conventional silica fibers to produce significant spectral red-shifts through spontaneous cascaded Raman (CR) processes. However, spectral broadening and pulse distortions due to both spontaneous Raman emission and four-wave mixing (FWM) generally limit the efficiency of the Raman process. For instance, at high powers, anomalous dispersion and Kerr nonlinearities can give rise to modulation instabilities (MI), which result in a significant spectral broadening and pulse distortion. For this reason, normal dispersion fibers are more desirable for controlled and maximally efficient CR at the nanosecond time-scale. Unfortunately, silica fibers generally possess anomalous dispersion due to strong mid-IR absorption resonances.