Patent ID: 7692420

Claim:
A method for measuring a current comprising the steps of sending left and right circularly polarized light waves at least once along a sensing fiber extending around said current, passing said right and left circularly polarized light waves through an optical retarder for generating two orthogonally linearly polarized returning light waves, sending a first part of said returning light waves to a first detector, a second part of said returning light waves to a second detector, characterized by the step of sending a third part of said returning light waves to a third detector, wherein said first part of said returning light is passed through a first circular analyzer before impinging on said first detector, wherein said second part of said returning light waves is passed through a second circular analyzer before impinging on said second detector and having a polarization opposite to said first circular analyzer, and wherein said third part of said returning light waves is passed through a linear analyzer before impinging on said third detector, wherein said first detector generates a signal I + and said second detector generates a signal I − and said third detector generates a signal I L , and knowledge of the three signals I + , I − , I L allows to obtain the current even if the values for fringe visibility V and arriving optical power I 0 are not known in advance.