Optical interferometers are normally used in magnetically confined plasmas 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 are basically the erroneous phase difference determination, by multiples of 2p, 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.