Higher order Stokes waves are easily generated in optical fibres through nonlinear stimulated Brillouin scattering. Since the Stokes waves have a linewidth limited by the narrow bandwidth of the Brillouin gain of ~20MHz, higher order Stokes waves are near multiples of the first Stokes shift of ~10GHz, generating a comb of frequencies. When Fourier transformed this comb can potentially lead to ultrashort pulse generation. Our investigations showed that short pulses of order 10ps can indeed be generated with a few Stokes waves, starting with a single CW pump. However, in longer cavities, these Stokes orders de-phase and lead to chaotic behaviour. Taming this source could lead to complex instruments being replaced by a simple optical fibre cavity.
|