shorter than the length of the fibre and other characteristic length scales such as the modulation instability length , fission will dominate. Modulation instability regime Modulation instability (MI), leads to the breakup of a continuous wave (CW) or quasi-continuous wave fields, which becomes a train of fundamental solitons. It is important to stress that the solitons generated in this regime are fundamental, as several papers on CW and quasi-CW supercontinuum formation have accredited short wavelength generation to soliton fission and dispersive wave generation as described above. In a similar manner to the soliton fission regime, the long wavelength side of the continuum is generated by the solitons undergoing intra-pulse Raman scattering and self-frequency shifting to longer wavelengths. As the MI process is noise driven, a distribution of solitons with different energies are created, resulting in different rates of self-frequency shifting. The net result is that MI driven soliton-Raman continua tends to be spectrally much smoother than those generated in the fission regime. Short wavelength generation is driven by four-wave mixing, especially for higher peak powers in the quasi-CW regime. In the pure CW regime, short wavelength generation has only recently been achieved at wavelengths shorter than those of a 1 μm pump source. In this case soliton trapping has been shown to play a role in short wavelength generation in the MI driven regime. A continuum will only occur in the MI regime if the fibre and field parameters are such that MI forms and dominates over other processes such as fission. In a similar fashion to the fission regime it is constructive to develop a characteristic length scale for MI, : where is the level of the background noise below the peak power level. Equation is essentially a measure of the length required for the MI gain to amplify the background quantum noise into solitons. Typically this shot noise is taken to be ~200 dB down. So provided then MI will dominate over soliton fission in the quasi-CW case and this condition may be expressed as: The middle term of the equation is simply the soliton equation. For MI to dominate we need the left hand side to be much less than the right hand side which implies that the soliton order must be much greater than 4. In practice this boundary has been established as being approximately . Therefore, we can see that it is predominantly ultra-short pulses