Method for reducing the Kerr effect in an interferometry measuring device, and interferometry measuring device configured to implement this method

A method for reducing the Kerr effect in an interferometric measuring device including

• a light signal generator configured to emit a periodic input light signal having at least two non-zero input power values, and
• a Sagnac interferometer comprising
• an optical loop,
• a splitter configured to couple the periodic input light signal to the optical loop in order to split the light signal into a first signal and a second signal which are mutually counter-propagating, which have each at least two power values, each power value corresponding to one of the non-zero input power values, and which propagate in opposite directions in the optical loop, and to combine said counter-propagating signals after their propagation in the loop so as to form a periodic output signal having at least two output power values, each output power value corresponding to one of the non-zero input power values,
• the method comprising a periodic modulation with at least two opposite states of the phase shift between the two counter-propagating signals and, over a same modulation period,
• a. performing a first series of measurements that comprises at least two output power measurements at points of the output signal that have first output power values corresponding to a first non-zero input power value and that correspond to opposite modulation states;
• b. determining a first phase-shift between the two counter-propagating signals each having a power value corresponding to the first non-zero input power value, and performing a cancellation of the first phase shift that comprises adjusting the modulation depending on the cancellation of a first calculated demodulation term that is function of said at least two output power measurements of the first series of measurements and that is representative of said phase shift, then
• c. performing a second series of measurements that comprises at least two measurements at points of the output signal that have second output power values corresponding to a second non-zero input power value and that correspond to opposite modulation states;
• d. determining a second phase-shift between the two counter-propagating signals each having a power value corresponding to the second input power value, and a cancellation of the second phase shift, depending on the cancellation of a second calculated demodulation term that is function of said at least two measurements of the second series of measurements and that is representative of the phase shift.