Interest in the fabrication of devices compatible with optical fibres has been stimulated by the possibility of introducing non-linear organic materials in and around waveguides. In this paper, the application of electric fields on cylindrical devices with a view to performing all-optical non-linear interactions is examined theoretically. It is shown how a static field in the core of the fibre based device can be enhanced by a suitable choice of surrounding material. We also propose the use of pure liquids, solutions and doped polymeric materials as cores of optical fibres as an alternative to the crystal cored fibre, in order to perform all-optical nonlinear interactions. The isotropy of the such guides can be used to advantage in device design. These waveguides can then exploit third-order processes, to make devices such as, all optical modulators and logic gates. As an example of a parametric process, phase-matched second-harmonic generation in a nitrobenzene waveguide, by modulating the third-order nonlinearity is considered. It is shown that conversion efficiencies in SI units, as high as 0.06P(w fundaTptal) can be expected for a 30 mm optimised device. An order of magnitude increase in x (3) nitrobenzene is all that is required to make such devices competitive with x (2) devices. This should be possible with currently available materials.