Birefringence measurements by an electro-optic modulator using a new heterodyne scheme

A new method for measuring changes in birefringence (or retardation) by modulating an electro-optic (EO) modulator in a sinewave signal is developed in a common-path interferometer (polarimeter). The standard heterodyne signal, therefore, can be formed with a new heterodyne scheme, and subsequently the phase shift regarding to changes in birefringence is demodulated by a lock-in amplifier or phase meter. As compared to the conventional techniques, this technique supplies an easier setup, wider modulated frequency, and therefore, a wider frequency response in a sensing system. Finally, the birefringence measurement based on an EO modulator and a new heterodyne scheme in a common-path interferometer is first demonstrated.