Optical interferometers are normally used in Nuclear Fusion to measure the refractive index of the plasma, from which the line integrated electron density can be derived. Unfortunately, inteferometric measurements are inherently prone to be affected by fringe jumps, which is basically the erroneous phase difference determination, by multiples of 2π, between the reference and the measuring chords. On the other hand, the plasma density has become an essential piece of information for many real time control schemes, which can therefore be completely jeopardised by fringe jumps. Different algorithms have been developed at JET to correct the fringe jump events and to allow the use of the density measurements for real time purposes. The first category of methods adopted relies only on interferometric signals. The main developed solution is based on the second colour laser available for the lateral channels. Appropriate comparison of the phases of the two lasers allows identification of the fringe jumps and their correction in the vast majority of cases. Different approaches are being developed for the vertical lines of sight, for which the second colour is not available. One alternative is based on the comparison between geometrically similar vertical and lateral channels, with a proper correction taking into the account the plasma shape. A different approach consists of reconstructing the entire density profile with the available signals and of calculating the line integral of the chords affected by the fringe jumps. The second category of solutions tries to exploit other physical phenomena induced on electromagnetic radiation propagating in an optically active medium. The Faraday effect, on one hand, is proportional to the product of the density times the magnetic field parallel to the direction of propagation. Since the field at the edge of the plasma is known in a Tokamak by other diagnostics, this approach can be used to correct the most external interferometric chords. Another alternative is based on the Cotton-Mouton effect, proportional to the density times the magnetic field perpendicular to the direction of propagation, which can be used to correct the vertical lines of sight. The various solutions were tested and results compared in order to verify the most suitable for the various plasma configurations and operational scenarios. A "general purpose" version of the correction algorithm was implemented and is not normally running during JET operation.