Abstract

Since the observation of the soliton self-frequency shift,^1,2it has been known that the Raman effect has a profound impact on soliton propagation for solitons with durations less than a picosecond. According to the theory developed by Gordon,²under the condition that the soliton duration τ_pis much longer than the period of molecular oscillations ${\text{T}}_{\text{R}}=2\pi {\Omega }_{\text{R}}^{-1}$ a soliton experiences a self-frequency shift, which is proportional to ${\tau }_{\text{p}}^{-4}$. On the other hand, recently, in a number of experiments on soliton transmission and amplification in doped fibers,³solitons with durations as short as 20 fs were observed. Since the characteristic period of molecular oscillations in silica glass is about T_r≃ 80 fs (corresponding to the Stokes frequency shift of Ω_R≃ 440 cm^-1), in these experiments the condition τ_p< T_Ris fulfilled. This implies a qualitatively new regime of stimulated Raman scattering (SRS) in which the spectrum of the initial pulse contains already both Stokes and anti-Stokes spectral components.⁴In this situation, the conditions for the validity of the theoretical model developed in Ref. 2are not fulfilled, and an adequate analysis is required.

© 1994 IEEE