Modulation axis performs circular motion in a 45° dual-drive symmetric photoelastic modulator

A 45° dual-drive symmetric photoelastic modulator is demonstrated. Two piezoelectric actuators are connected to a symmetric photoelastic crystal at an angle of 45°. When the amplitudes of the stress standing waves induced by the two piezoelectric actuators are equal and the phase difference between the two stress standing waves is /π 2 , the modulation axis performs circular motion with a frequency of half of the photoelastic modulator's resonant frequency, while the retardation remains a constant that is determined at the driving voltage amplitudes. This reveals a new polarization modulation method. We have theoretically analyzed and experimentally observed the new polarization modulation, and the retardation calibration is also reported.