Phase tuning and phase stabilization of an interferometer

A method for phase tuning and phase stabilization of an interferometer, in particular an interferometer used for the measurement of energy-time entanglement, comprises:i) generation of an electronic modulation signal;ii) phase modulation of a laser beam by a phase modulator and the electronic modulation signal;iii) passing the modulated laser beam through the interferometer;iv) detection of the modulated laser beam by a detector;v) demodulation of the detected signal in order to generate an error signal;vi) tuning and/or stabilization of the interferometer by a feedback of the error signal to a movable element of the interferometer.According to the invention the electronic modulation signal in step i) comprises a carrier frequency ωc and a modulation frequency ωm, andthe modulation in step ii) generates frequency dependent sidebands, preferably ωc -sidebands corresponding to the carrier frequency ωe and ωm -sidebands corresponding to the modulation frequency ωm, andthe demodulation of the detected signal in step v) is realized by mixing the detected signal with a signal in phase and with the frequency of the modulation frequency ωm.