Optical pulse transforms using tapered optical fibres

A common problem in optics is optical pulse transformation which can be done in either the spatial or the temporal domain. In the spatial domain, beam reshaping has many different solutions from holography and phase plates to using a simple lens. Similarly in the temporal domain different solutions such as fibre Bragg gratings can be used to alter the profile of a pulse, producing square or parabolic pulses from a sech-shaped input for example. A common feature of all these schemes is the linear nature of the transformation which means that no new frequency components are introduced and thus for a transformed limited input pulse the transformed pulse will always be longer. If pulse compression and reshaping is desired then nonlinear effects must be introduced and in this paper I look at how to design long fibre tapers in order to control the output pulse characteristics in the nonlinear regime.