Optical pulses of this type can be generated by mode-locked lasers.For different pulse shapes, the minimum duration-bandwidth product is different.A bandwidth-limited pulse can only be kept together if the dispersion of the medium the wave is travelling through is zero; otherwise dispersion management is needed to revert the effects of unwanted spectral phase changes.For example, when an ultrashort pulse passes through a block of glass, the glass medium broadens the pulse due to group velocity dispersion.Keeping pulses bandwidth-limited is necessary to compress information in time or to achieve high field densities, as with ultrashort pulses in modelocked lasers.
The duration-bandwidth product depends on the shape of the power spectrum of the pulse.
